АДАПТИВНЫЕ ЛИНЗЫ НА ОСНОВЕ ЖИДКИХ КРИСТАЛЛОВ
ÎÏÒÈ×ÅÑÊÎÅ ÏÐÈÁÎÐÎÑÒÐÎÅÍÈÅ È ÒÅÕÍÎËÎÃÈß
ÓÄÊ 771.36
ÀÄÀÏÒÈÂÍÛÅ ËÈÍÇÛ ÍÀ ÎÑÍÎÂÅ ÆÈÄÊÈÕ ÊÐÈÑÒÀËËÎÂ*
© 2008 ã.
Ã. Å. Íåâñêàÿ*, äîêòîð òåõí. íàóê; Ì. Ã. Òîìèëèí**, äîêòîð òåõí. íàóê
** Ñàíêò-Ïåòåðáóðãñêèé ãîñóäàðñòâåííûé ìîðñêîé òåõíè÷åñêèé óíèâåðñèòåò, Ñàíêò-Ïåòåðáóðã
** Ñàíêò-Ïåòåðáóðãñêèé ãîñóäàðñòâåííûé óíèâåðñèòåò èíôîðìàöèîííûõ òåõíîëîãèé, ** ìåõàíèêè è îïòèêè, Ñàíêò-Ïåòåðáóðã
Ðàññìîòðåíû ïðèíöèïû è òåîðåòè÷åñêèå îñíîâû ïîñòðîåíèÿ ðàçëè÷íûõ òèïîâ àäàïòèâíûõ ëèíç íà îñíîâå æèäêèõ êðèñòàëëîâ. Ïîêàçàíî èõ ðàçâèòèå îò ëèíç, ðàáîòàþùèõ â ïîëÿðèçîâàííîì ñâåòå ñ áîëüøèìè âðåìåíàìè ôîêóñèðîâêè, äî ëèíç, ðàáîòàþùèõ â íåïîëÿðèçîâàííîì ñâåòå, ñ óâåëè÷åííîé àïåðòóðîé, áûñòðîäåéñòâèåì è óëó÷øåííûì êà÷åñòâîì èçîáðàæåíèÿ. Îáñóæäåíû âîçìîæíîñòè èõ ïðèìåíåíèÿ â îïòè÷åñêèõ ñèñòåìàõ.
Êîäû OCIS: 160.3710.
Ïîñòóïèëà â ðåäàêöèþ 28.01.2008.
Ââåäåíèå
Àäàïòèâíàÿ îïòèêà – ýòî ñîâðåìåííîå, èíòåíñèâíî ðàçâèâàþùååñÿ íàó÷íîå íàïðàâëåíèå, â êîòîðîì ïåðñïåêòèâíî èñïîëüçîâàíèå ýëåìåíòîâ è óñòðîéñòâ íà îñíîâå æèäêèõ êðèñòàëëîâ (ÆÊ). Îáëàñòè ïðèìåíåíèÿ ÆÊ-ýëåìåíòîâ îïðåäåëÿþòñÿ âîçìîæíîñòÿìè ïëàâíîãî èëè äèñêðåòíîãî èçìåíåíèÿ â øèðîêèõ ïðåäåëàõ îïòè÷åñêèõ ñâîéñòâ òîíêîãî ñëîÿ ìàòåðèàëà ïðè ìàëûõ óïðàâëÿþùèõ íàïðÿæåíèÿõ (U) ýëåêòðè÷åñêîãî ïîëÿ (Å-ïîëÿ). Îíè îñíîâàíû íà êîíòðîëèðóåìîé äåôîðìàöèè ñëîÿ ÆÊ, îñóùåñòâëÿåìîé ëèáî ëîêàëüíî, ëèáî ïî âñåìó ïîëþ çðåíèÿ. Ýòè ñâîéñòâà óæå òðè äåñÿòèëåòèÿ ïðèâëåêàþò âíèìàíèå ðàçðàáîò÷èêîâ ëèíç ñ ïåðåìåííûì ôîêóñíûì ðàññòîÿíèåì èëè àäàïòèâíûõ ëèíç (ÀË).
 ÀË èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ îñóùåñòâëÿåòñÿ íå çà ñ÷åò ìåõàíè÷åñêîãî ïåðåìåùåíèÿ êîìïîíåíòîâ îáúåêòèâà, à â ïëîñêîé ÿ÷åéêå áåç ïåðåìåùàþùèõñÿ äåòàëåé ïðè ïåðåîðèåíòàöèè ìîëåêóë ÆÊ. Ïðèíöèï ðàáîòû ÀË ñîñòîèò â ôîðìèðîâàíèè óïðàâëÿåìîé ôàçîâîé çàäåðæêè ñëîåì ÆÊ ñ íåîáõîäèìûì ïðîñòðàíñòâåííûì ðàñïðåäåëåíèåì ïîä äåéñòâèåì Å-ïîëÿ. Èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ ÀË ìîæåò áûòü äèñêðåòíûì èëè ïëàâíûì è îñóùåñòâëÿåòñÿ èçìåíåíèåì àìïëèòóäû U è åãî ÷àñòîòû.
* Îáçîð ñîñòàâëåí ïî ìàòåðèàëàì äîêëàäà Ã.Å. Íåâñêîé è Ì.Ã. Òîìèëèíà “Àíàëèç ðàçâèòèÿ àäàïòèâíûõ ëèíç íà æèäêèõ êðèñòàëëàõ”, ñäåëàííîãî íà VII ìåæäóíàðîäíîé êîíôåðåíöèè “Ïðèêëàäíàÿ îïòèêà-2006”, ÑÏá. 16–18.10.2006.
Ïèîíåðñêèå èññëåäîâàíèÿ ïî ñîçäàíèþ ÀË îòíîñÿòñÿ ê 1970-ì ãîäàì è ñâÿçàíû ñ ðàáîòàìè Áåððèìàíà [1] è Ñàòî [2] ñ ñîòðóäíèêàìè. Ïåðâûå ÀË ïðåäñòàâëÿëè ñîáîé ÆÊ-ÿ÷åéêó, îäíà èç ïîäëîæåê êîòîðîé áûëà âûïîëíåíà â âèäå ëèíçû, íàõîäÿùåéñÿ â êîíòàêòå ñî ñëîåì ÆÊ. Èõ íåäîñòàòêîì ÿâëÿëîñü íèçêîå áûñòðîäåéñòâèå, âûçâàííîå áîëüøîé òîëùèíîé ñëîÿ ÆÊ â öåíòðå èëè íà ïåðèôåðèè. Êðîìå òîãî, âîçíèêëà ïðîáëåìà â îäíîðîäíîé îðèåíòàöèè ÆÊ â îòíîñèòåëüíî òîëñòîì ñëîå è íà íåïëîñêîé ïîâåðõíîñòè. Ïîýòîìó îíè íå íàøëè äàëüíåéøåãî ðàçâèòèÿ.
Öèëèíäðè÷åñêèå ÆÊ-ëèíçû, ñîäåðæàùèå ñîâîêóïíîñòü ýëåêòðîäîâ ñ èíäèâèäóàëüíîé àäðåñàöèåé áûëè ðàçðàáîòàíû â 1981 ã. ãðóïïîé èç Ñèðàêóçñêîãî óíèâåðñèòåòà (ÑØÀ) [3]. Ýëåêòðîäû ñ èíäèâèäóàëüíîé àäðåñàöèåé áûëè èñïîëüçîâàíû äëÿ ñîçäàíèÿ ñôåðè÷åñêèõ ÆÊ-ëèíç [4, 5]. Âïåðâûå ÆÊ ìèêðîëèíçû áûëè ïðåäëîæåíû â ðàáîòàõ Ñàòî [6, 7]. Ëèíçû Ôðåíåëÿ íà îñíîâå ÆÊ âïåðâûå îïèñàíû â [8]; èõ ìîäèôèêàöèè ïðîàíàëèçèðîâàíû â îáçîðå [9].
Èñïîëüçîâàíèå ÀË ìîæåò äàòü ðÿä èíòåðåñíûõ ïðèìåíåíèé â öèôðîâûõ ôîòîêàìåðàõ ñ ïåðåìåííûì ôîêóñíûì ðàññòîÿíèåì, ñêàííåðàõ îáúåìíûõ äèñïëååâ, êîððåêòîðàõ àñòèãìàòèçìà ïîëóïðîâîäíèêîâûõ ëàçåðîâ è óñòðîéñòâàõ ñ àâòîìàòè÷åñêîé ôîêóñèðîâêîé. ÀË ðàññìàòðèâàþòñÿ êàê ïåðñïåêòèâíûå îïòè÷åñêèå ïåðåêëþ÷àòåëè â îäíîìîäîâûõ âîëîêîííîîïòè÷åñêèõ ýëåìåíòàõ ïðèìåíèòåëüíî ê ýíäîñêîïèè. Ïîæèëûì ëþäÿì, ñòðàäàþùèì äàëüíîçîðêîñòüþ, ïðè íàáëþäåíèè áëèçêî ðàñïîëîæåííûõ îáúåêòîâ, íàõîäÿùèõñÿ íà ðàçíîì ðàññòîÿíèè îò íàáëþäàòåëÿ,
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
35
òðåáóåòñÿ íåñêîëüêî ïàð î÷êîâ. Áîëüíûå êàòàðàêòîé ïðè óäàëåíèè õðóñòàëèêà òàêæå èñïîëüçóþò íåñêîëüêî ïàð î÷êîâ, ÷òî íåóäîáíî â ïîâñåäíåâíîé æèçíè. Ëåãêèå è ìèíèàòþðíûå ÀË, óïðàâëÿåìûå îò ìàëîìîùíûõ èñòî÷íèêîâ, ìîãóò óñòðàíèòü ýòè ïðîáëåìû.
 îáçîðå ðàññìàòðèâàþòñÿ ïðèíöèïû è îñíîâû òåîðèè ïîñòðîåíèÿ ÀË, à òàêæå òåíäåíöèè èõ ðàçâèòèÿ: óâåëè÷åíèå àïåðòóðû, áûñòðîäåéñòâèÿ è ïîâûøåíèå êà÷åñòâà èçîáðàæåíèÿ. Îáñóæäåíû âîçìîæíîñòè ïðèìåíåíèÿ ÀË â îïòè÷åñêèõ ñèñòåìàõ.
Òåîðåòè÷åñêèå îñíîâû ðàáîòû àäàïòèâíûõ ëèíç
Ðàññìîòðèì äâà ýòàïà ñîçäàíèÿ óïðàâëÿåìîé ôàçîâîé çàäåðæêè: ôîðìèðîâàíèå íåîáõîäèìîé êîíôèãóðàöèè Å-ïîëÿ è âûçâàííóþ èì äåôîðìàöèþ ñëîÿ ÆÊ. Îáóñëîâëåííàÿ ýòîé äåôîðìàöèåé ôàçîâàÿ çàäåðæêà îáåñïå÷èâàåò ôîêóñèðóþùèå ñâîéñòâà ëèíçû. Èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ ÀË îñóùåñòâëÿåòñÿ èçìåíåíèåì àìïëèòóäû è ÷àñòîòû Å-ïîëÿ.
Ñïîñîáû ñîçäàíèÿ ïðîñòðàíñòâåííî íåîäíîðîäíûõ ïîëåé è èõ ðàñ÷åò
Ýëåêòðè÷åñêîå ïîëå â ìèêðîëèíçàõ
Êîíôèãóðàöèÿ Å-ïîëÿ â ìèêðîëèíçàõ (ÌË) çàäàåòñÿ ãåîìåòðèåé ýëåêòðîäîâ.  ñôåðè÷åñêîé ÌË äëÿ ïîëó÷åíèÿ àêñèàëüíî-ñèììåòðè÷íîãî Å-ïîëÿ â ýëåêòðîäàõ ñîçäàþòñÿ êðóãëûå îòâåðñòèÿ äèàìåòðîì L. Ðàçëè÷àþò íåñèììåòðè÷íûå ÌË – îòâåðñòèÿ èìåþòñÿ â îäíîì èç ýëåêòðîäîâ, è ñèììåòðè÷íûå – ñîâìåùåííûå îòâåðñòèÿ èìåþòñÿ â îáîèõ ýëåêòðîäàõ.  öèëèíäðè÷åñêîé ÌË â ýëåêòðîäàõ âûïîëíåíà ùåëü.
Ðàñ÷åò ðàñïðåäåëåíèÿ íàïðÿæåííîñòè â àêñèàëüíî-ñèììåòðè÷íîì ïîëå íåñèììåòðè÷íîé ÌË ïðîâåäåí â ðàáîòàõ [10, 11], ñèììåòðè÷íîé – â ðàáîòàõ [12–14].  ðàáîòå [10], â ÷àñòíîñòè, ó÷òåíî âëèÿíèå äèýëåêòðè÷åñêèõ ñâîéñòâ ïîäëîæêè íà ðàñïðåäåëåíèå Å-ïîëÿ. Íà ðèñ. 1 ïðèâåäåíà ñõåìà íåñèììåòðè÷íîé ÌË. Âåðõíèé ýëåêòðîä èç õðîìà èìååò îòâåðñòèå, íèæíèé ýëåêòðîä – ñïëîøíîé. Çàçîð ìåæäó íèìè òîëùèíîé d çàïîëíÿåòñÿ ÆÊ. Óðàâíåíèÿ, îïèñûâàþùèå Å-ïîëå, èìåþò âèä:
divD = 0, E = gradu,
ãäå D – âåêòîð ýëåêòðè÷åñêîãî ñìåùåíèÿ, u – ïîòåíöèàë Å-ïîëÿ.
Òàê êàê ïîëå ïîòåíöèàëà u(r, z) â ÌË ñôåðè÷åñêè ñèììåòðè÷íî, óðàâíåíèå äëÿ ïîòåíöèàëà â öèëèíäðè÷åñêèõ êîîðäèíàòàõ èìååò âèä:
L d
Cr In2O3
Ðèñ. 1. Ñõåìà íåñèììåòðè÷íîé ìèêðîëèíçû. L – àïåðòóðà ìèêðîëèíçû, d – òîëùèíà ñëîÿ ÆÊ
d, ìêì 20
10
0 20 40 R, ìêì
Ðèñ. 2. Ýêâèïîòåíöèàëüíûå ïîâåðõíîñòè äëÿ ìèêðîëèíçû ñ L = 70 ìêì, d = 20 ìêì, ÆÊ Å-7 (ôèðìû Merk). R – ðàññòîÿíèå îò öåíòðà ëèíçû äî ðàññìàòðèâàåìîé òî÷êè àïåðòóðû.
ε⊥
⎛ ⎜ ⎝
∂2u ∂r 2
+
1 r
∂u ∂r
⎞ ⎟ ⎠
+
ε&
∂2u ∂z 2
=
0,
(1)
ãäå ε⊥ è ε|| – äèýëåêòðè÷åñêàÿ ïðîíèöàåìîñòü â ïåðïåíäèêóëÿðíîì è ïàðàëëåëüíîì äèðåêòîðó íàïðàâëåíèÿõ.
Äàëåå ôîðìóëèðóþòñÿ ãðàíè÷íûå óñëîâèÿ äëÿ ýëåêòðè÷åñêîãî ïîòåíöèàëà â îêðåñòíîñòè îòâåðñòèÿ è óðàâíåíèå (1) ðåøàþò ÷èñëåííûìè ìåòîäàìè. Ðåçóëüòàòû ðàñ÷åòà â âèäå ýêâèïîòåíöèàëüíûõ ïîâåðõíîñòåé äëÿ ÌË ñ L = 70 ìêì, d = 20 ìêì, ÆÊ Å-7 ôèðìû Merk ïðèâåäåíû íà ðèñ. 2. Âáëèçè êðàÿ îòâåðñòèÿ Å-ïîëå íàèáîëåå íåîäíîðîäíî. Ñ óâåëè÷åíèåì L íåîäíîðîäíîñòü óìåíüøàåòñÿ, è ýòî ïðèâîäèò ê èñ÷åçíîâåíèþ ôîêóñèðóþùèõ ñâîéñòâ.
Ýëåêòðè÷åñêîå ïîëå â àäàïòèâíûõ ìîäàëüíûõ ÆÊ-ëèíçàõ
Ñîçäàíèå ÀË ñ áîëüøîé àïåðòóðîé îñíîâàíî íà èíîì ôîðìèðîâàíèè Å-ïîëÿ [15-17]. Èçâåñòíû äâà ïîäõîäà: çîíàëüíûé (Å-ïîëå ñîçäàåòñÿ ñ ïîìîùüþ ñîâîêóïíîñòè èíäèâèäóàëüíî àäðåñóåìûõ ýëåêòðîäîâ) è ìîäàëüíûé (ïðè èõ îãðàíè÷åííîì êîëè÷åñòâå). Ìîäàëüíûå ëèíçû (ÌË) â îòëè÷èå îò çîíàëüíûõ îáåñïå÷èâàþò ïëàâíîå, íåïðåðûâíîå èçìåíåíèå ôàçîâîãî ïðîôèëÿ.  ÌË îäèí èç ýëåêòðîäîâ
36 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ÿâëÿåòñÿ âûñîêîîìíûì óïðàâëÿþùèì ýëåêòðîäîì (ÓÝ), ïî ïåðèôåðèè êîòîðîãî íàíîñÿòñÿ íèçêîîìíûå êîíòàêòû. Âîçíèêàþùàÿ ñèñòåìà ñ ðàñïðåäåëåííûì ñîïðîòèâëåíèåì (ÓÝ) è åìêîñòüþ (ñëîé ÆÊ) èìååò ðåàêòèâíûé õàðàêòåð è óïðàâëÿåò ïàðàìåòðàìè ÀË ïðè èçìåíåíèè àìïëèòóäû è ÷àñòîòû U.
Ðàçðàáîòàíû ñôåðè÷åñêèå è öèëèíäðè÷åñêèå ÀË. Õàðàêòåð âîëíîâîãî ôðîíòà îïðåäåëÿåòñÿ ãåîìåòðèåé êîíòàêòîâ: äëÿ ñôåðè÷åñêîé ëèíçû – êîëüöåâîé êîíòàêò, öèëèíäðè÷åñêîé – äâà ïàðàëëåëüíûõ ïîëîñêîâûõ êîíòàêòà. Ñëîé ÆÊ ïîìåùåí ìåæäó äâóìÿ ñòåêëÿííûìè ïîäëîæêàìè ñ ýëåêòðîäàìè. Ïîâåðõíîñòíîå ñîïðîòèâëåíèå ÓÝ (1–10 ÌÎì/ ) ìíîãî áîëüøå ñîïðîòèâëåíèÿ ñïëîøíîãî (çàçåìëåííîãî) ýëåêòðîäà (50–200 Îì/ ). U ïðèêëàäûâàåòñÿ ê êîíòàêòàì, ðàñïîëîæåííûì íà ïåðèôåðèè ÓÝ. Åñëè ê êîíòàêòàì ïðèëîæèòü ñèíóñîèäàëüíîå íàïðÿæåíèå, òî èç-çà ðåçèñòèâíî-åìêîñòíîãî õàðàêòåðà ñèñòåìû èçìåíåíèå U â öåíòðå áóäåò ìåíüøå èçìåíåíèÿ U íà êîíòàêòíûõ ýëåêòðîäàõ. Ñ óâåëè÷åíèåì ÷àñòîòû ðàçëè÷èå ðàñòåò, ïðèâîäÿ ê óìåíüøåíèþ ñðåäíåêâàäðàòè÷íîãî çíà÷åíèÿ U â öåíòðå àïåðòóðû.  óñòàíîâèâøåìñÿ ðåæèìå ðåàëèçóåòñÿ ðàñïðåäåëåíèå ñðåäíåêâàäðàòè÷íîãî çíà÷åíèÿ U â ñëîå ÆÊ, è â äîñòàòî÷íî øèðîêîé îáëàñòè èçìåíåíèÿ ïàðàìåòðîâ óïðàâëÿþùåãî U ýòî ðàñïðåäåëåíèå áóäåò êâàçèïàðàáîëè÷åñêèì. Óðàâíåíèå, îïèñûâàþùåå ðàñïðåäåëåíèå U ïî àïåðòóðå U(x, y), èìååò âèä [16]:
∇2U
=
ρsc
∂U ∂t
+ ρs gU ,
(2)
ãäå g – ïðîâîäèìîñòü ñëîÿ ÆÊ íà åäèíèöó ïëîùàäè, ρs – ïîâåðõíîñòíîå ñîïðîòèâëåíèå ÓÝ, ñ – åìêîñòü íà åäèíèöó ïëîùàäè ÓÝ.
Óðàâíåíèå (2) ïðè ñèíóñîèäàëüíîì óïðàâëÿþùåì íàïðÿæåíèè èìååò âèä:
∇2U = χ2U,
(2à)
ãäå χ2 = ρs(g – iωc). Óðàâíåíèå (2à) ïðèìåíåíî äëÿ ðàñ÷åòà ïîëÿ öè-
ëèíäðè÷åñêîé ÀË:
∂2U ∂x2
= χ2U.
(3)
Èç ðåøåíèÿ ýòîãî óðàâíåíèÿ ñ ó÷åòîì ãðàíè÷íûõ óñëîâèé ñëåäóåò, ÷òî ïðè |χ|l 0 (5ÑÂ).
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
39
(à) (á)
(â) (ã)
(ä) (å)
Ðèñ. 8. Èíòåðôåðåíöèîííûå êàðòèíû ïëàíàðíîé ìèêðîëèíçû, ïîêàçûâàþùèå âîçíèêíîâåíèå äèñêëèíàöèè (à, á) è åå èñ÷åçíîâåíèå (â, ã, ä, å) ñ òå÷åíèåì âðåìåíè ïðè íàëè÷èè ìóëüòèäîìåííîé ñòðóêòóðû: â – ÷åðåç 1 ñ, ã – 10 ñ, ä – 20 ñ, å – 40 ñ.
ôåðåíöèîííûå êàðòèíû ïðè ðàçëè÷íûõ U. Ïðè óâåëè÷åíèè U íà êðàþ âîçíèêàåò èçëîì ôàçîâîãî ïðîôèëÿ (ðèñ. 8à). Ñ ðîñòîì U îáëàñòü èçëîìà ðàñòåò, ïîêà íå ïîÿâèòñÿ äèñêëèíàöèÿ (ðèñ. 8á). Ñïîñîáû åå óñòðàíåíèÿ îïèñàíû â ðÿäå ðàáîò. Íàïðèìåð, â ðàáîòå [25] íà ãðàíèöå ìèêðîëèíçû, ãäå ôîðìèðóåòñÿ äèñêëèíàöèÿ, ñîçäàåòñÿ êëèíîîáðàçíàÿ îáëàñòü ñ ãèáðèäíîé îðèåíòàöèåé. Ýòà îáëàñòü ìåíÿåò õàðàêòåð ïåðåîðèåíòàöèè ìîëåêóë ÆÊ â ÌË, â ðåçóëüòàòå ÷åãî äèñêëèíàöèÿ óõîäèò èç îáëàñòè îòâåðñòèÿ (ðèñ. 8â, ã, ä, å).
Èññëåäîâàíèå çàâèñèìîñòè ÷èñëîâîé àïåðòóðû è ðàçðåøàþùåé ñïîñîáíîñòè ÌË ñ ïëàíàðíîé îðèåíòàöèåé [24] îò U äëÿ ðàçíûõ îòíîøåíèé L/d ïîêàçàëî, ÷òî íàèëó÷øèå îïòè÷åñêèå ñâîéñòâà íàáëþäàþòñÿ íà íèñïàäàþùåé âåòâè çàâèñèìîñòè ôîêóñíîãî ðàññòîÿíèÿ îò U è â îáëàñòè ìèíèìóìà ýòîé çàâèñèìîñòè. Ñîîáùàåòñÿ, ÷òî äîñòèãíóòî óìåíüøåíèå óïðàâëÿþùåãî íàïðÿæåíèÿ äî 6,5–7  ïðè ÷àñòîòå 10 êÃö è èñïîëüçîâàíèè ÆÊ ñ Δε = 2 ïðè òîëùèíå ñëîÿ 50 ìêì [26].
êèõ – ðàññåèâàþùåé, î ÷åì ñâèäåòåëüñòâóåò ñòðóêòóðà ôàçîâûõ ïðîôèëåé. Çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò U äëÿ ãèáðèäíîé ÌË â ôîêóñèðóþùåì ðåæèìå àíàëîãè÷íà ñîîòâåòñòâóþùåé çàâèñèìîñòè äëÿ ïëàíàðíîé ÌË (ðèñ. 7á). Èçìåðåíèÿ âðåìåí îòêëèêà è âîññòàíîâëåíèÿ îðèåíòàöèè ïîêàçàëè, ÷òî äëÿ ÌË ñ Δε > 0 îíè ñîñòàâëÿþò íåñêîëüêî ñåêóíä. Ïðè Δε < 0 â ôîêóñèðóþùåì ðåæèìå íóæíû áîëåå âûñîêèå U, è âðåìÿ îòêëèêà ìîæåò áûòü óìåíüøåíî äî íåñêîëüêèõ ìèëëèñåêóíä.  îòëè÷èå îò ïëàíàðíîé ÌË, â ãèáðèäíîé íå âîçíèêàåò äèñêëèíàöèè. Íåäîñòàòêîì ýòîãî òèïà ÌË ÿâëÿåòñÿ ñäâèã öåíòðà ôàçîâîãî ïðîôèëÿ îòíîñèòåëüíî öåíòðà îòâåðñòèÿ.
Ãîìåîòðîïíûå ÌË
Ðåçóëüòàòû èññëåäîâàíèÿ îïòè÷åñêèõ ñâîéñòâ ÌË ñ ãîìåîòðîïíî îðèåíòèðîâàííûì ÆÊ ïðåäñòàâëåíû â ðàáîòàõ [11, 20, 30].  ýòîì ñëó÷àå ïðè ïðèëîæåíèè U ôîðìèðóåòñÿ àêñèàëüíî-ñèììåòðè÷íîå ðàñïðåäåëåíèå ïîêàçàòåëÿ ïðåëîìëåíèÿ äëÿ e-âîëíû ñ ìèíèìóìîì â öåíòðå (êàê íà ðèñ. 5â), ò. å. ãîìåîòðîïíàÿ ëèíçà äîëæíà èìåòü ñâîéñòâà ðàññåèâàþùåé ëèíçû. Èññëåäîâàíû èíòåðôåðåíöèîííûå êàðòèíû (ðèñ. 9) è ôàçîâûå ïðîôèëè ýòèõ ÌË ïðè ðàçëè÷íûõ U. Íàáëþäàåòñÿ äåôîêóñèðóþùèé ðåæèì, ïðè÷åì ïðè îïðåäåëåííîì íàïðÿæåíèè Up ïðîôèëü ôàçîâîé çàäåðæêè ñòàíîâèòñÿ êâàäðàòè÷íûì è ÌË òàêæå ñòàíîâèòñÿ ñôåðè÷åñêîé. Up ïîâûøàåòñÿ ñ óâåëè÷åíèåì ðàçìåðà ëèíçû. Ïðè äàëüíåéøåì óâåëè÷åíèè U ïðîôèëü ôàçîâîé çàäåðæêè ñòàíîâèòñÿ áëèçêèì ê ëèíåéíîìó. Ðåæèì ïåðåñòðàèâàåìîé ëèíçû íàèáîëåå âûðàæåí ó ÌË ñ îòíîøåíèåì L/d = 3,5. Ïðè ìàëûõ U ÌË îáëàäàþò äâóìÿ ôîêóñàìè, ïðè÷åì îäèí èç íèõ ÿâëÿåòñÿ êîëüöåâûì, äðóãîé – òî÷å÷íûì. Òî÷å÷íîìó ôîêóñó ñîîòâåòñòâóþò áîëüøèå çíà÷åíèÿ ôîêóñíîãî ðàññòîÿíèÿ. Êîãäà íàïðÿæåíèå ñòàíîâèòñÿ ðàâíûì Up, òî÷å÷íûé è êîëüöåâîé ôîêóñ ñëèâàþòñÿ.
ÌË ñ ãîìåîïëàíàðíîé (ãèáðèäíîé) îðèåíòàöèåé
Ìîëåêóëû ÆÊ â ãèáðèäíîé ÌË èìåþò ðàçëè÷íóþ èñõîäíóþ îðèåíòàöèþ âáëèçè ðàçíûõ ïîäëîæåê: ãîìåîòðîïíóþ íà îäíîé è ïëàíàðíóþ íà äðóãîé. Ðåçóëüòàòû èññëåäîâàíèé ïðèâåäåíû â ðàáîòàõ [23, 24, 27–29].  ñëó÷àå ÆÊ ñ Δε < 0 ïðè íèçêèõ U ÌË èìååò äåôîêóñèðóþùèå ñâîéñòâà. Ïðè âûñîêèõ U (îêîëî 80 Â) ÌË ñòàíîâèòñÿ ñîáèðàþùåé è èìååò õîðîøèå îïòè÷åñêèå ñâîéñòâà, îäíàêî åå ôîêóñíîå ðàññòîÿíèå ñëàáî çàâèñèò îò U. Ïðè èñïîëüçîâàíèè ÆÊ ñ Δε > 0 íàáëþäàåòñÿ îáðàòíàÿ ñèòóàöèÿ: ïðè ìàëûõ U ÌË ÿâëÿåòñÿ ñîáèðàþùåé, ïðè âûñî-
40
(à) (á)
Ðèñ. 9. Èíòåðôåðåíöèîííûå êàðòèíû ãîìåîòðîïíîé ÌË. L = 600 ìêì, à – U = 6, á – 14 Â.
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
×èñëîâàÿ àïåðòóðà ÌË çàâèñèò îò îòíîøåíèÿ L/d. Ìàêñèìàëüíàÿ ÷èñëîâàÿ àïåðòóðà ïðè Up íàáëþäàåòñÿ ó ÌË ñ îòíîøåíèåì L/d = 3,5, îíà äîñòèãàåò çíà÷åíèÿ 0,11. Ðàçðåøàþùàÿ ñïîñîáíîñòü ãîìåîòðîïíûõ ÌË óâåëè÷èâàåòñÿ ñ óìåíüøåíèåì ïàðàìåòðà L/d è äîñòèãàåò çíà÷åíèÿ ïðèìåðíî 200 ëèí/ìì, ÷òî ÿâëÿåòñÿ âûñîêîé âåëè÷èíîé äëÿ ÀË.
 ðàáîòå [11] èññëåäîâàíà ÌË ñ ÆÊ ñ Δε > 0, îáëàäàþùàÿ äåôîêóñèðóþùèìè ñâîéñòâàìè. Îäíàêî åå ôîêóñíûå ðàññòîÿíèÿ íà ïîðÿäîê ìåíüøå, ÷åì ó àíàëîãè÷íûõ ÌË ñ Δε < 0. Òåìè æå àâòîðàìè ïðèâåäåíû âåëè÷èíû ñôåðè÷åñêèõ àáåððàöèé ýòèõ ëèíç ïðè íàïðÿæåíèè 6,5  è ÷àñòîòå 10 êÃö, ñâèäåòåëüñòâóþùèå îá îòíîñèòåëüíî âûñîêîì îïòè÷åñêîì êà÷åñòâå.
Ñèììåòðè÷íûå ÌË
Ñèììåòðè÷íàÿ ÌË èìååò îòâåðñòèÿ îäèíàêîâîãî äèàìåòðà â îáîèõ ýëåêòðîäàõ, ïîìåùåííûå îäíî íàä äðóãèì. Ðåçóëüòàòû èññëåäîâàíèé ïðåäñòàâëåíû â ðàáîòàõ [31–35]. Ïåðåõîä ê òàêèì ÌË èìåë öåëüþ óñòðàíèòü äèñêëèíàöèè è ñäâèã öåíòðà èíòåðôåðåíöèîííîé êàðòèíû ó íåñèììåòðè÷íûõ ïëàíàðíûõ è ãèáðèäíûõ ÌË.  ñèììåòðè÷íûõ ÌË íå íàáëþäàåòñÿ ñäâèãà öåíòðà èíòåðôåðåíöèîííîé êàðòèíû îòíîñèòåëüíî öåíòðà îòâåðñòèé, îäíàêî ïðè ïîâûøåíèè U âáëèçè êðàÿ îòâåðñòèÿ âîçíèêàþò äâå íåáîëüøèå äèñêëèíàöèè. E-ïîëå â ñèììåòðè÷íîé ÌË îòëè÷àåòñÿ ñèëüíîé íåîäíîðîäíîñòüþ – íàïðÿæåííîñòü ïîëÿ â öåíòðå çíà÷èòåëüíî íèæå, ÷åì ïðè íåñèììåòðè÷íûõ ýëåêòðîäàõ, à ðàáî÷èå U ïî ñðàâíåíèþ ñ íåñèììåòðè÷íîé ÌË ïîâûøàþòñÿ. Ïðè ìàëûõ U èìåþòñÿ äâà ôîêóñà. Ïðè ïîâûøåíèè U ôîêóñíîå ðàññòîÿíèå ñíà÷àëà óáûâàåò, äîñòèãàåò ìèíèìàëüíîãî çíà÷åíèÿ, à çàòåì ðàñòåò. Ïðè íåêîòîðîì U ôîêóñû ìèêðîëèíçû ñëèâàþòñÿ è íàáëþäàþòñÿ íàèëó÷øèå îïòè÷åñêèå ñâîéñòâà. Êà÷åñòâî èçîáðàæåíèÿ ñèììåòðè÷íûõ ëèíç õàðàêòåðèçóåòñÿ ïîëóøèðèíîé êðèâîé ôóíêöèè ðàññåÿíèÿ òî÷êè íà óðîâíå ïîëóìàêñèìóìà (FWHM), ðàâíîé äëÿ ñôåðè÷åñêîé ëèíçû 2,5 ìêì [13], à äëÿ öèëèíäðè÷åñêîé 2,2–2,3 ìêì [36].
 ðàáîòàõ [34, 35] èññëåäîâàíà çàâèñèìîñòü ïàðàìåòðîâ ÌË îò ñâîéñòâ ÆÊ-ìàòåðèàëà. Ìàêñèìàëüíîå çíà÷åíèå ÷èñëîâîé àïåðòóðû ëèíåéíî óâåëè÷èâàåòñÿ ñ ðîñòîì îïòè÷åñêîé àíèçîòðîïèè Δn è ïðèâåäåííîé äèýëåêòðè÷åñêîé àíèçîòðîïèè Δε/ε, à U, ïðè êîòîðîì íàáëþäàåòñÿ ìàêñèìóì, óáûâàåò ñ ðîñòîì äèýëåêòðè÷åñêîé àíèçîòðîïèè.  ðàáîòå [35] ïðîàíàëèçèðîâàíà ðîëü óïðóãèõ ñâîéñòâ íåìàòèêà â ôîðìèðîâàíèè àñòèãìàòèçìà ÌË è ïîêàçàíî, ÷òî ÷åì áîëüøå àíèçîòðîïèÿ óïðóãèõ ñâîéñòâ, òåì ñèëüíåå àñòèãìàòèçì.
Óñîâåðøåíñòâîâàíèå ñèììåòðè÷íûõ ÌË îïèñàíî â ðàáîòàõ [37, 38]. Ýëåêòðîäû èìåþò îòâåðñòèÿ è ðàçäåëåíû óçêèìè ùåëÿìè íà äâà (÷åòûðå) ñåêòîðà; íà ýòè ñåêòîðû ìîãóò ïîäàâàòüñÿ ðàçíûå U. Âñëåäñòâèå ðàçëè÷èÿ äåôîðìàöèè íåìàòèêà â ðàçíûõ ÷àñòÿõ ÌË âîçíèêàåò ëèíåéíàÿ äîáàâêà â ôàçîâûé ïðîôèëü, âûçûâàþùàÿ ñäâèã ëó÷à â ïîïåðå÷íîì íàïðàâëåíèè. Ïðè íåáîëüøîé ðàçíèöå U îïòè÷åñêèå ñâîéñòâà îñòàþòñÿ õîðîøèìè, è ïîÿâëÿåòñÿ âîçìîæíîñòü óïðàâëÿåìîãî ñìåùåíèÿ òî÷êè ôîêóñèðîâêè ïåðïåíäèêóëÿðíî ê îïòè÷åñêîé îñè.  ðàáîòå [37] ñîîáùàåòñÿ, ÷òî ýòî ñìåùåíèå ïðè ñîõðàíåíèè ïàðàáîëè÷åñêîãî ôàçîâîãî ïðîôèëÿ ñîñòàâëÿåò 10 ìêì (ïðè L/d = 3).
 ðàáîòàõ [36, 39] ïðåäëîæåí äðóãîé âàðèàíò ÌË: ïîìèìî îáû÷íûõ óïðàâëÿþùèõ ýëåêòðîäîâ èìåþòñÿ ÷åòûðå äîïîëíèòåëüíûõ, ê êîòîðûì ïîäâîäÿòñÿ ðàçëè÷íûå U. Ïðè îïðåäåëåííûõ óñëîâèÿõ óïðàâëåíèÿ óäàåòñÿ èçáåæàòü ïîÿâëåíèÿ äèñêëèíàöèè â îáëàñòè îòâåðñòèÿ è ðàñøèðèòü äèàïàçîí U íàáëþäåíèÿ ôîêóñèðóþùèõ ñâîéñòâ. Óëó÷øåíèå îïòè÷åñêèõ ñâîéñòâ ÌË áûëî äîñòèãíóòî ïðè èñïîëüçîâàíèè 4 ýëåêòðîäîâ, ðàñïîëîæåííûõ äðóã íàä äðóãîì [14, 40]. Äâà èç íèõ èìåëè êðóãëûå îòâåðñòèÿ (ëèíçîâûå ýëåêòðîäû), äâà äðóãèõ ÿâëÿëèñü ñïëîøíûìè, íàíåñåííûìè íà ñòåêëÿííûå ïîäëîæêè è ðàñïîëîæåííûìè âûøå è íèæå îáû÷íûõ ëèíçîâûõ ýëåêòðîäîâ.  ðàáîòå [40] èññëåäîâàíà ÷èñëîâàÿ àïåðòóðà (NA) ÌË ïðè ñëîæåíèè è âû÷èòàíèè Å-ïîëåé, ñîçäàííûõ ïàðàìè ýëåêòðîäîâ â ñëîå ÆÊ. Ïîêàçàíî, ÷òî NAmax íà 40% âûøå ïðè âû÷èòàíèè Å-ïîëåé, ÷åì â ñëó÷àå èõ ñëîæåíèÿ, à òàêæå ÷åì â ñëó÷àå îáû÷íîé ÌË.  ðàáîòå [14] òåîðåòè÷åñêè è ýêñïåðèìåíòàëüíî ïîêàçàíà âîçìîæíîñòü óìåíüøåíèÿ ñôåðè÷åñêîé àáåððàöèè è àñòèãìàòèçìà ïðè ïîäáîðå U íà ýëåêòðîäàõ.
Ðàññìîòðåâ èçâåñòíûå òèïû ÌË íà íåìàòèêàõ, ìîæíî êîíñòàòèðîâàòü, ÷òî ïðè ìàëûõ U ÌË ñ ïëàíàðíîé è ãèáðèäíîé îðèåíòàöèåé îáëàäàþò ôîêóñèðóþùèìè ñâîéñòâàìè, à ñ ãîìåîòðîïíîé – äåôîêóñèðóþùèìè. Ñðàâíåíèå îïòè÷åñêèõ ñâîéñòâ ÌË ïðîâåäåíî â ðàáîòå [29]. Çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò U ñõîæà äëÿ âñåõ òèïîâ ÌË: ïðè ïîâûøåíèè U îíî ñíà÷àëà óìåíüøàåòñÿ, äîñòèãàÿ ìèíèìóìà ïðè íåêîòîðîì Um, à çàòåì âîçðàñòàåò. Ïðè äàëüíåéøåì óâåëè÷åíèè U ïðîèñõîäèò èíâåðñèÿ îïòè÷åñêèõ ñâîéñòâ ÌË: ó ãèáðèäíîé è ïëàíàðíîé ÌË íàáëþäàþòñÿ äåôîêóñèðóþùèå ñâîéñòâà. Ìàêñèìàëüíàÿ ÷èñëîâàÿ àïåðòóðà äëÿ âñåõ ÌË ÿâëÿåòñÿ íàèáîëüøåé â ñëó÷àå, åñëè îòíîøåíèå L/d = 3. Ñðàâíåíèå NAmax ó ðàçëè÷íûõ ÌË ïîêàçûâàåò, ÷òî íàèáîëüøàÿ ôîêóñèðóþùàÿ ñïîñîáíîñòü äîñòèãàåòñÿ ïðè ïëàíàðíîé îðèåíòàöèè (NAmax = 0,21), à äåôîêóñèðóþùàÿ – ïðè ãîìåîòðîïíîé (NAmax = 0,22). Äèàïàçîí U, â êîòîðîì ìîæíî óï-
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
41
ðàâëÿòü ôîêóñíûì ðàññòîÿíèåì, çàâèñèò îò òèïà ÌË è îò âåëè÷èíû ïàðàìåòðà L/d. Áîëåå øèðîêèì îí áóäåò ó ãîìåîòðîïíûõ ìèêðîëèíç. Ìàêñèìàëüíàÿ ðàçðåøàþùàÿ ñïîñîáíîñòü ïëàíàðíûõ è ãèáðèäíûõ ÌË íàáëþäàåòñÿ ïðè Um, ïðè÷åì îíà âûøå ó ïëàíàðíûõ.  äåôîêóñèðóþùåì ðåæèìå íàèáîëüøàÿ ðàçðåøàþùàÿ ñïîñîáíîñòü ó ãîìåîòðîïíîé ÌË.
Îïòè÷åñêèå ñâîéñòâà ñèììåòðè÷íîé è íåñèììåòðè÷íîé ÌË ñ ïëàíàðíîé îðèåíòàöèåé ñõîæè. Ñîçäàíèå ñèììåòðè÷íûõ ÌË ñâÿçàíî ñ áîëüøèìè òåõíîëîãè÷åñêèìè òðóäíîñòÿìè. Íàáëþäàåìàÿ â íåñèììåòðè÷íûõ ïëàíàðíûõ ÌË äèñêëèíàöèÿ âîçíèêàåò ïðè U â ïîëòîðà ðàçà ïðåâûøàþùèõ íàïðÿæåíèÿ ìàêñèìóìà ÷èñëîâîé àïåðòóðû Um, è ïîòîìó â ðàáî÷åì äèàïàçîíå U ìàëî âëèÿåò íà îïòè÷åñêèå ñâîéñòâà ÌË.
Äëÿ óâåëè÷åíèÿ àïåðòóðû ïðåäëîæåíî ðàñïîëîæèòü óïðàâëÿþùèé ýëåêòðîä íà âíåøíåé ïîâåðõíîñòè îäíîé èç ñòåêëÿííûõ ïîäëîæåê.  ýòîì ñëó÷àå ôîêóñèðóþùèå ñâîéñòâà ðåàëèçóþòñÿ äëÿ îòâåðñòèé áîëüøåãî äèàìåòðà (5–7 ìì) [41]. Ýòî ïðèâîäèò ê óâåëè÷åíèþ ðàáî÷åãî U äî 40–100 Â, ÷òî ñíèæàåò ïðèâëåêàòåëüíîñòü òàêèõ ëèíç.  öèëèíäðè÷åñêèõ ëèíçàõ ñ øèðèíîé ùåëè 2 ìì àíàëîãè÷íîå ðåøåíèå óâåëè÷èëî U äî 120–180  [42].  ðàáîòå [43] â ýòó ëèíçó íàä âåðõíåé ïîäëîæêîé áûë äîáàâëåí åùå îäèí ñëîé ÆÊ (óïðàâëÿþùèé ýëåêòðîä îäèí è íàõîäèòñÿ â öåíòðå). Ðàññìîòðåíû äâà ñëó÷àÿ âçàèìíîé îðèåíòàöèè ìîëåêóë ÆÊ: îïòè÷åñêèå îñè ïàðàëëåëüíû è îðòîãîíàëüíû. Îïòè÷åñêàÿ ñèëà ëèíç â ýòèõ ñëó÷àÿõ ìàëî îòëè÷àåòñÿ (îêîëî 6 ì–1 ïðè U = 100 Â), íî îíà ñóùåñòâåííî âûøå, ÷åì ó ëèíçû ñ îäíèì ñëîåì (îêîëî 4 ì–1 ïðè U = 100 Â). Äèàïàçîí ðàáî÷èõ íàïðÿæåíèé äëÿ ëèíç ñ äâóìÿ ñëîÿìè 90–120 Â, ÷òî âûøå, ÷åì äëÿ ëèíç ñ îäíèì ñëîåì ÆÊ.
Îáùèì íåäîñòàòêîì ÀË íà íåìàòèêàõ ÿâëÿåòñÿ áîëüøîå âðåìÿ èõ ôîêóñèðîâêè, ñîñòàâëÿþùåå íåñêîëüêî ñåêóíä.  ðàáîòå [44] ïðåäëîæåíî èñïîëüçîâàòü íåìàòèê ñ äâóõ÷àñòîòíûì ðåæèìîì óïðàâëåíèÿ, ÷òî ïîçâîëÿåò óìåíüøèòü âðåìåíà ôîêóñèðîâêè ïî÷òè íà ïîðÿäîê.
Ìèêðîëèíçû íà îñíîâå ñåãíåòîýëåêòðè÷åñêèõ ñìåêòèêîâ (Ñ*ÆÊ)
Íåäîñòàòêîì ÌË íà îñíîâå íåìàòèêîâ ÿâëÿåòñÿ èõ íèçêîå áûñòðîäåéñòâèå. Ïîâûøåíèå áûñòðîäåéñòâèÿ îñóùåñòâëÿåòñÿ èñïîëüçîâàíèåì Ñ*ÆÊ [45]. Äèïîëüíûå ìîìåíòû ìîëåêóë â Ñ*ÆÊ ïåðïåíäèêóëÿðíû äèðåêòîðó è ëåæàò â ïëîñêîñòè ñìåêòè÷åñêîãî ñëîÿ.  Å-ïîëå âñå äèïîëè âûñòðàèâàþòñÿ ïî íàïðàâëåíèþ ïîëÿ. Ïîëå ïðîòèâîïîëîæíîãî çíàêà ïåðåîðèåíòèðóåò äèïîëè, à âìåñòå ñ íèì è äèðåêòîð, êîòîðûé ïîâîðà÷èâàåòñÿ ïî îáðàçóþùåé êîíóñà â ïëîñêîñòè ñëîÿ íà óãîë 2θ, ãäå θ – óãîë íàêëîíà
(à) (á)
11 2
4
35
3
4 6
7 8
Âêëþ÷åíî (ôîêóñèðîâêà)
Âûêëþ÷åíî (ðàñôîêóñèðîâêà)
Ðèñ. 11. Ôîêóñèðóþùèé (à) è äåôîêóñèðóþùèé (á) ðåæèìû ðàáîòû ÌË íà îñíîâå Ñ*ÆÊ. 1 – íàïðàâëåíèå íàòèðàíèÿ, 2 – ïîëÿðèçîâàííûé ñâåò, 3 – íàïðàâëåíèå ýëåêòðè÷åñêîãî ïîëÿ, 4 – îðèåíòèðóþùèé ñëîé, 5 – ñëîé Ñ*ÆÊ, 6 – ôîòîïîëèìåð, 7 – ïðîçðà÷íûé ýëåêòðîä, 8 – ñòåêëî.
ìîëåêóë îòíîñèòåëüíî îñè ñïèðàëè. Ýëåêòðîîïòè÷åñêèé îòêëèê çàâèñèò îò ïîëÿðíîñòè ïðèëîæåííîãî U, ïðè÷åì âðåìÿ îòêëèêà ñóùåñòâåííî ìåíüøå, ÷åì äëÿ íåïîëÿðíûõ ÆÊ.  ðàáîòå [45] äëÿ ñîçäàíèÿ ìàññèâà Ñ*ÆÊ-ÌË íà îäíîé èç ïîâåðõíîñòåé ôîðìèðóåòñÿ ïåðèîäè÷åñêàÿ ñòðóêòóðà èç îòâåðñòèé ãëóáèíîé 9 ìêì è ðàäèóñîì 200 ìêì. Äëÿ ýòîãî íà ïîâåðõíîñòü íàíîñèòñÿ ôîòîïîëèìåð è ÷åðåç ôîòîìàñêó ïîäâåðãàåòñÿ âîçäåéñòâèþ óëüòðàôèîëåòîâîãî (ÓÔ) èçëó÷åíèÿ. Ñ*ÆÊ ââåäåí â ÿ÷åéêó êàïèëëÿðíûì ìåòîäîì è èìååò ïëàíàðíóþ îðèåíòàöèþ. Ïðèíöèï ðàáîòû ÌË ïîêàçàí íà ðèñ. 10.  çàâèñèìîñòè îò íàïðàâëåíèÿ Å-ïîëÿ ðåàëèçóåòñÿ êàê ôîêóñèðóþùèé (ðèñ. 10à), òàê è äåôîêóñèðóþùèé (ðèñ. 10á) ðåæèìû. Èññëåäîâàíà çàâèñèìîñòü âðåìåíè îòêëèêà îò âåëè÷èíû Å-ïîëÿ. Âðåìÿ ïåðåêëþ÷åíèÿ èç îäíîãî ðåæèìà â äðóãîé ñîñòàâëÿåò 100– 200 ìêñ. Ñ óâåëè÷åíèåì íàïðÿæåííîñòè ïîëÿ âðåìÿ îòêëèêà óìåíüøàåòñÿ.
Îïòè÷åñêèå õàðàêòåðèñòèêè àäàïòèâíûõ ëèíç
Ìîäàëüíûå ëèíçû
 ðàçäåëå “Ýëåêòðè÷åñêîå ïîëå â àäàïòèâíûõ ìîäàëüíûõ ÆÊ-ëèíçàõ” îïèñàí ñïîñîá ôîðìèðîâàíèÿ Å-ïîëÿ è ïðèâåäåíû óðàâíåíèÿ, îïèñûâàþ-
42 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ùèå ðàñïðåäåëåíèå íàïðÿæåíèÿ ïî àïåðòóðå ëèíçû. ×èñëåííûé ðàñ÷åò ïîçâîëÿåò íàõîäèòü îïòèìàëüíûå çíà÷åíèÿ ÷àñòîòû è àìïëèòóäû óïðàâëÿþùåãî U äëÿ ïîëó÷åíèÿ ïàðàáîëè÷åñêîé çàâèñèìîñòè ôàçîâîé çàäåðæêè ïî àïåðòóðå ëèíçû [15–17, 46–50]. Îäíàêî äàæå ïðè èçâåñòíûõ ïàðàìåòðàõ ÆÊ è ìîäàëüíûõ (ÀË) âû÷èñëåííûå îïòèìàëüíûå ñîîòíîøåíèÿ àìïëèòóäà-÷àñòîòà íå âñåãäà ïðèåìëåìû äëÿ ðåàëüíîé ëèíçû. Ýòî ñâÿçàíî ñ òåõíîëîãè÷åñêèìè îñîáåííîñòÿìè èõ ñáîðêè: êàëèáðîâî÷íûå ïàðàìåòðû äëÿ êàæäîé ëèíçû èíäèâèäóàëüíû. Îñíîâíûå ïàðàìåòðû ýêñïåðèìåíòàëüíûõ îáðàçöîâ ÌÀË ñëåäóþùèå: ôîêóñíûå ðàññòîÿíèÿ ñôåðè÷åñêèõ è öèëèíäðè÷åñêèõ ëèíç èçìåíÿëèñü îò 0,5 ì äî áåñêîíå÷íîñòè; äèàìåòð àïåðòóðû ñôåðè÷åñêîé ëèíçû ñîñòàâëÿë 5 ìì, ðàçìåðû àïåðòóðû öèëèíäðè÷åñêîé ëèíçû áûëè ðàâíû 5×15 ìì. Èñïîëüçîâàëñÿ ïëàíàðíî îðèåíòèðîâàííûé íåìàòèê ôèðìû “Merck” c Δn = 0,26. Âûñîêîîìíûé ýëåêòðîä áûë ñîçäàí íàïûëåíèåì ïðîçðà÷íîãî ðåçèñòèâíîãî ïîêðûòèÿ ñ ñîïðîòèâëåíèåì îêîëî 9 ÌÎì/ . Óïðàâëÿþùåå íàïðÿæåíèå íå ïðåâûøàëî 10 Â, ÷àñòîòà – 17 êÃö.
 ðàáîòàõ [18, 49, 51] ñîîáùàåòñÿ îá ÀË ñ îïòè÷åñêèì óïðàâëåíèåì. Îíè ñî÷åòàþò â ñåáå âñå ïðåèìóùåñòâà ýëåêòðè÷åñêè óïðàâëÿåìûõ àäàïòèâíûõ ëèíç, íî èìåþò äîïîëíèòåëüíóþ îñîáåííîñòü – çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò èíòåíñèâíîñòè ïàäàþùåãî íà ëèíçó èçëó÷åíèÿ. Îíè ïðåäñòàâëÿþò ñîáîé ìíîãîñëîéíóþ ñòðóêòóðó. Âíåøíèìè ñëîÿìè ÿâëÿþòñÿ ñòåêëÿííûå ïîäëîæêè ñ íàíåñåííûìè íà íèõ ýëåêòðîäàìè. Íà îäíîé èç íèõ ýëåêòðîä èìååò êðóãëîå îòâåðñòèå äëÿ ñëó÷àÿ ñôåðè÷åñêîé ëèíçû èëè ïðåäñòàâëÿåò ñîáîé äâà ïîëîñêîâûõ êîíòàêòà äëÿ öèëèíäðè÷åñêîé ëèíçû. Îáëàñòü áåç ýëåêòðîäîâ èãðàåò ðîëü àïåðòóðû ëèíçû. Íà ýòó ïîäëîæêó íàíîñèòñÿ ñëîé ôîòî÷óâñòâèòåëüíîãî ïîëóïðîâîäíèêà. Ïîâåðõíîñòíîå ñîïðîòèâëåíèå ýòîãî ñëîÿ ìíîãî áîëüøå ñîïðîòèâëåíèÿ ñïëîøíîãî íèçêîîìíîãî ýëåêòðîäà ïðè ëþáîé èíòåíñèâíîñòè ïàäàþùåãî èçëó÷åíèÿ. Èñïîëüçóåòñÿ ïëàíàðíî îðèåíòèðîâàííûé íåìàòèê. Êîíñòðóêöèÿ ïîçâîëÿåò ñîçäàâàòü â îáëàñòè àïåðòóðû åìêîñòíî-ðåçèñòèâíûé äåëèòåëü U. Óïðàâëÿòü â òàêîé ñèñòåìå ðàñïðåäåëåíèåì U ìîæíî íå òîëüêî ñ ïîìîùüþ àìïëèòóäû è ÷àñòîòû ïðèëîæåííîãî U, íî è èçìåíåíèåì èíòåíñèâíîñòè èçëó÷åíèÿ. Òåîðåòè÷åñêèå è ýêñïåðèìåíòàëüíûå èññëåäîâàíèÿ ïîêàçàëè, ÷òî ïðîôèëü ôàçîâîé çàäåðæêè äëÿ ïó÷êà ñâåòà ñ îäíîðîäíûì è ãàóññîâûì ðàñïðåäåëåíèåì èíòåíñèâíîñòè áëèçîê ê ïàðàáîëè÷åñêîìó. Ôîêóñíîå ðàññòîÿíèå ìîíîòîííî âîçðàñòàåò ñ óâåëè÷åíèåì ìîùíîñòè èçëó÷åíèÿ. Ïðèâåäåíû ïðèìåðû ïðîñòûõ àäàïòèâíûõ ñèñòåì ýòîãî òèïà.
Ëèíçû íà îñíîâå ñòðóêòóð ïîëèìåð-äèñïåðãèðîâàííûõ ÆÊ
 ýëåêòðè÷åñêè óïðàâëÿåìûõ ëèíçàõ íà îñíîâå ïîëèìåð-äèñïåðãèðîâàííûõ ÆÊ (ÏÄÆÊ) ãðàäèåíò ïîêàçàòåëÿ ïðåëîìëåíèÿ ñîçäàåòñÿ ïðè èçìåíåíèè ðàçìåðîâ ìèêðîêàïåëü [52, 53]. Äëÿ ýòîãî íà ñìåñü ÆÊ-ìîíîìåð âîçäåéñòâóþò ÓÔ èçëó÷åíèåì ÷åðåç ôîòîìàñêó. Âîçäåéñòâèå ñëàáîãî ÓÔ èçëó÷åíèÿ äàåò êàïëè áîëåå êðóïíîãî ðàçìåðà è íàîáîðîò – ÷åì ñèëüíåå îáëó÷åíèå, òåì ìåíüøå ðàçìåð êàïåëü. Îáëàñòè ñ êàïëÿìè ìåíüøåãî ðàçìåðà èìåþò áîëüøóþ êîíöåíòðàöèþ ïîëèìåðà, è ïîòîìó ïîêàçàòåëü ïðåëîìëåíèÿ ýòîé îáëàñòè áóäåò ìåíüøå, ÷åì îáëàñòü ñ áîëüøèìè êàïëÿìè. Ïðè âîçäåéñòâèè Å-ïîëÿ ïåðåîðèåíòàöèÿ ìîëåêóë íåìàòèêà íà÷èíàåòñÿ ïðè êðèòè÷åñêîì íàïðÿæåíèè Ud. Çàâèñèìîñòü Ud îò ðàçìåðà êàïëè (D) âûãëÿäèò ñëåäóþùèì îáðàçîì: U = C/ D, ãäå C – const. ×åì áîëüøå ðàçìåð êàïëè, òåì ìåíüøå óïðàâëÿþùåå U. Äëÿ ñîçäàíèÿ ñîáèðàþùåé è ðàññåèâàþùåé ëèíç èñïîëüçóþòñÿ ôîòîìàñêè ñ êðóãîâûì ãðàäèåíòîì ïðîïóñêàíèÿ. Íà ðèñ. 11 ïîêàçàíû ôîòîìàñêè è ïðîôèëè ïîêàçàòåëåé ïðåëîìëåíèÿ äëÿ ñîáèðàþùåé (à) è ðàññåèâàþùåé ëèíç. Íåäîñòàòêîì ÏÄÆÊ-ëèíç – âûñîêîå óïðàâëÿþùåå U (áîëåå 100 Â). Äëÿ óìåíüøåíèÿ óïðàâëÿþùåãî U àâòîðû ïðåäëîæèëè èñïîëüçîâàòü ÆÊ ñ ïîëèìåðíîé ñåòêîé ñ ãðàäèåíòîì ïðîôèëÿ ïîêàçàòåëÿ ïðåëîìëåíèÿ. Êîíöåíòðàöèÿ ÆÊ â ýòîé ñìåñè – 95%, ïîýòîìó U ñíèæàåòñÿ äî 10 Â. Ôîêóñíîå ðàññòîÿíèå ýòîé ëèíçû ïðèìåðíî 310 ì, è äëÿ ðàáîòû ëèíçà äîëæíà èñïîëüçîâàòü ñêðåùåííûå ïîëÿðîèäû. Ëèíçà ñ òàêèì áîëüøèì ôîêóñíûì ðàññòîÿíèåì
V=0
V=0
V=∞
V=∞
n
V=0 V1
V=∞
n V=∞
V=0 V1
xx
(à) (á)
Ðèñ. 11. Àäàïòèâíûå ëèíçû íà ÏÄÆÊ äëÿ ôîêóñèðóþùåãî (à) è ðàñôîêóñèðóþùåãî (á) ðåæèìîâ.
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
43
ïðåäñòàâëÿåò èíòåðåñ äëÿ öåëåé àñòðîíîìèè è ñïóòíèêîâîé àïïàðàòóðû. Äëÿ ðàáîòû â íåïîëÿðèçîâàííîì ñâåòå ïðåäëîæåíî èñïîëüçîâàòü äâà îðòîãîíàëüíî îðèåíòèðîâàííûõ ãîìîãåííûõ ñëîÿ ÆÊ [53].
 ðàáîòàõ [54, 55] îïèñàíû ëèíçû, â êîòîðûõ ôîêóñèðóþùèå ñâîéñòâà çàäàþòñÿ èñõîäíûì ïðîôèëåì ïîâåðõíîñòè ïîäëîæêè, âûïîëíåííûì â âèäå ñôåðè÷åñêèõ óãëóáëåíèé äèàìåòðîì 450–500 ìêì. Íàíåñåííûå íà íèõ ýëåêòðîäû ôîðìèðóþò íåîäíîðîäíûå Å-ïîëÿ. Ïðè óâåëè÷åíèè U äî 200  ôîêóñíîå ðàññòîÿíèå èçìåíÿåòñÿ îò 3,3 äî 3,5 ñì, âðåìÿ ôîêóñèðîâêè – 200 ìêñ [54].
 ðàáîòå [56] ïðåäëîæåíû ÀË, èñïîëüçóþùèå íîâûé ïðèíöèï ôîðìèðîâàíèÿ ãðàäèåíòà ïîêàçàòåëÿ ïðåëîìëåíèÿ â êîìïîçèöèè ÆÊ/ìîíîìåð.  îòñóòñòâèå Å-ïîëÿ ÆÊ è ìîíîìåð â ñìåñè ðàñïðåäåëåíû ðàâíîìåðíî. Ïðè ïðèëîæåíèè íåîäíîðîäíîãî Å-ïîëÿ ìîëåêóëû ÆÊ ïåðåìåùàþòñÿ â îáëàñòü áîëåå ñèëüíîãî ïîëÿ. Ñ äðóãîé ñòîðîíû, íàáëþäàåòñÿ èõ äèôôóçèÿ â îáðàòíîì íàïðàâëåíèè, âûçâàííàÿ ðàçëè÷èåì êîíöåíòðàöèè.  èòîãå âîçíèêàåò ãðàäèåíò êîíöåíòðàöèè ÆÊ, ÷òî ïðèâîäèò ê ãðàäèåíòó ïîêàçàòåëÿ ïðåëîìëåíèÿ. Èçìåíåíèå âåëè÷èíû óïðàâëÿþùåãî íàïðÿæåíèÿ ïîçâîëÿåò èçìåíÿòü ðàñïðåäåëåíèå ïîêàçàòåëÿ ïðåëîìëåíèÿ è, ñëåäîâàòåëüíî, ôîêóñíîãî ðàññòîÿíèÿ ëèíç. Àâòîðû ñ÷èòàþò äîñòîèíñòâîì òàêèõ ÀË ìàëûå âåëè÷èíû àñòèãìàòèçìà è ñâåòîðàññåÿíèÿ. Íåäîñòàòêàìè ÿâëÿþòñÿ âûñîêèå âåëè÷èíû óïðàâëÿþùèõ íàïðÿæåíèé (äî 180 Â) è äëèòåëüíûå âðåìåíà ôîêóñèðîâêè (3 ìèí ïðè ñâåòîâîì äèàìåòðå 9 ìì, 1 ñ ïðè äèàìåòðå 50 ìêì). Äàííûé ïðèíöèï ðåêîìåíäîâàí äëÿ ñîçäàíèÿ îïòè÷åñêèõ ìèêðîýëåìåíòîâ: ìèêðîëèíç, ìèêðîïðèçì, ëèíç Ôðåíåëÿ.
Èíòåðåñíî ïðåäëîæåíèå èñïîëüçîâàòü ÀË äëÿ ôîðìèðîâàíèÿ ñòðàíèö òåêñòà â îïòè÷åñêèõ ñèñòåìàõ ïàìÿòè [57].
Ïðèìåíåíèå àäàïòèâíûõ ëèíç â îïòè÷åñêèõ ñèñòåìàõ
Óñòðîéñòâî çàïèñè èíôîðìàöèè íà îïòè÷åñêèå äèñêè
Áèôîêàëüíûå ÀË (ñ äâóìÿ ôèêñèðîâàííûìè çíà÷åíèÿìè ôîêóñíîãî ðàññòîÿíèÿ) èñïîëüçîâàíû äëÿ çàïèñè èíôîðìàöèè íà îïòè÷åñêèå äèñêè [58]. Íîâûå ðàçðàáîòêè íàïðàâëåíû íà óâåëè÷åíèå îáúåìà ïàìÿòè íîñèòåëåé. Äëÿ ýòîãî â òîëùå äèñêà ïîìåùåí äîïîëíèòåëüíûé ðåãèñòðèðóþùèé ñëîé. Äëÿ çàïèñè è ñ÷èòûâàíèÿ èíôîðìàöèè ïðè èñïîëüçîâàíèè äâóõ ñëîåâ óäîáíà áèôîêàëüíàÿ îïòè÷åñêàÿ ñèñòåìà. Çàäà÷à ðåøåíà ñ ïîìîùüþ ÀË, âûïîëíåííîé â âèäå òâèñòîâîé ÆÊ ÿ÷åéêè (ÒÆÊß) è îñóùåñòâ-
L1 L2 1 2 P 3 S 4 λ/4 RHC 5
SP S OFF
LHC 6
L1 L2 1 2 P 3 P 4 λ/4 LHC 5
SS S ON
RHC 6
Ðèñ. 12. Ñõåìà áèôîêàëüíîé ÀË, âûïîëíåííîé â âèäå ÒÆÊß. 1 – èçëó÷åíèå ëàçåðà, 2 – äåëèòåëü ïó÷êà, 3 – ÒÆÊß, 4 – ÀË, 5 – îáúåêòèâ, 6 – äèñê. S, P – îðòîãîíàëüíûå íàïðàâëåíèÿ ïîëÿðèçàöèè ñâåòà; OFF, ON – ðåæèìû “âûêëþ÷åíî” è “âêëþ÷åíî”; LHC, RHC – ëåâî- è ïðàâîöèðêóëÿðíûé ñâåò; L1, L2 – ðåãèñòðèðóþùèå ñëîè â îáúåìå äèñêà.
ëÿþùåé ïåðåêëþ÷åíèå ìåæäó ðàçëè÷íûìè ìîäàìè ïîëÿðèçàöèè (ðèñ. 12).  ïîëîæåíèè “âûêëþ÷åíî” ÒÆÊß çà ñ÷åò çàêðó÷åííîé ñòðóêòóðû ÆÊ ïîâîðà÷èâàåò ëèíåéíî ïîëÿðèçîâàííûé ñâåò íà 90°.  ðåçóëüòàòå ñâåò âçàèìîäåéñòâóåò ñ ÆÊ ñ ïîêàçàòåëåì ïðåëîìëåíèÿ nî è ôîêóñèðóåòñÿ â òî÷êå íà áîëüøîì ôîêóñíîì ðàññòîÿíèè (âåðõíÿÿ ÷àñòü ðèñ. 12).  ïîëîæåíèè “âêëþ÷åíî” îïòè÷åñêàÿ àêòèâíîñòü ñëîÿ ÆÊ èñ÷åçàåò, è ïëîñêîñòü ïîëÿðèçàöèè ñâåòà íå èçìåíÿåòñÿ ïðè åãî ïðîõîæäåíèè ÷åðåç ñëîé ÆÊ ñ ïîêàçàòåëåì ïðåëîìëåíèÿ ne. Ïðè ýòîì ñâåò ôîêóñèðóåòñÿ â òî÷êå ñ ìàëûì ôîêóñíûì ðàññòîÿíèåì (íèæíÿÿ ÷àñòü ðèñ. 12), è ÒÆÊß ðàáîòàåò êàê áèôîêàëüíàÿ ïåðåêëþ÷àåìàÿ ëèíçà.
Ôèðìîé Philips (Íèäåðëàíäû) áûëè èçãîòîâëåíû îáðàçöû áèôîêàëüíûõ ÀË [58]. Ìàòåðèàëîì ñëóæèë ïîëèìåðèçóþùèéñÿ ÆÊ ôèðìû “Merck” íà îñíîâå öèàíîáèôåíèëîâ ñ äîáàâêîé, óâåëè÷èâàþùåé äèýëåêòðè÷åñêóþ àíèçîòðîïèþ. ÀË ñôåðè÷åñêîé êîíôèãóðàöèè ñ ðàäèóñîì 49 ìì è äèàìåòðîì 3,44 ìì èçãîòîâëÿëèñü ôîðìîâêîé ñ ïîñëåäóþùåé ôîòîïîëèìåðèçàöèåé. Ðàçíèöà â ôîêàëüíîì ðàññòîÿíèè äëÿ äâóõ ïîëÿðèçàöèé ñîñòàâèëà 19 ìì.
Îïòîâîëîêîííûé ïåðåêëþ÷àòåëü
Ñåìåéñòâî ÌË ïðåäëîæåíî èñïîëüçîâàòü â êà÷åñòâå îïòè÷åñêèõ ïåðåêëþ÷àòåëåé äëÿ âîëîêîííîîïòè÷åñêèõ ýëåìåíòîâ [22, 59]. Îñîáåííîñòüþ ýòî-
44 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ãî íàïðàâëåíèÿ ÿâëÿåòñÿ ïðèìåíåíèå íå ñòîëüêî ôîêóñèðóþùèõ ñâîéñòâ ÌË, ñêîëüêî ôîðìèðîâàíèå àïåðòóðû âûõîäíîãî ñâåòîâîãî ñèãíàëà, êîòîðóþ ñîãëàñóþò ñ âõîäíîé àïåðòóðîé îïòè÷åñêîãî âîëîêíà. Ñëîé ÆÊ â ÌË èìåë òîëùèíó 50 ìêì è ðàçìåùàëñÿ íà ðàññòîÿíèè 7 ìì îò òîðöà îïòè÷åñêîãî âîëîêíà (NA = 0,1) ñ ñåðäöåâèíîé äèàìåòðîì 10 ìêì. Ñ ïîìîùüþ ÏÇÑ-ìàòðèöû èçìåðÿëîñü èçìåíåíèå èíòåíñèâíîñòè ïðîõîäÿùåãî ÷åðåç ÌË è îïòè÷åñêîå âîëîêíî ñâåòîâîãî ñèãíàëà îò He–Neëàçåðà ñ äèàìåòðîì ïó÷êà 2 ìì ïðè ïîäà÷å U îò 0 äî 4 Â. Èññëåäîâàëèñü èçìåíåíèÿ èíòåíñèâíîñòè èçëó÷åíèÿ íà âûõîäå îïòè÷åñêîãî âîëîêíà ïðè èçìåíåíèè U, âðåìåíà îòêëèêà ïðè ðàçëè÷íûõ óñëîâèÿõ îðèåíòàöèè ÆÊ è çíà÷åíèÿõ äèýëåêòðè÷åñêîé àíèçîòðîïèè. Ýêñïåðèìåíòû ïîêàçàëè, ÷òî èíòåíñèâíîñòü èçëó÷åíèÿ íà âûõîäå îïòè÷åñêîãî âîëîêíà âîçðîñëà ïðè îïòèìàëüíîé ôîêóñèðîâêå â 210 ðàç ïðè U = 1 Â. Âðåìÿ îòêëèêà ïðè äâóõ÷àñòîòíîì ðåæèìå óïðàâëåíèÿ ÌË ñîñòàâèëî 5 ñ.
 ðàáîòàõ [60, 61] ÌË èñïîëüçîâàíà äëÿ óïðàâëåíèÿ ñâåòîâûì ïîòîêîì â îäíîìîäîâîì îïòè÷åñêîì âîëîêíå äëÿ ýíäîñêîïîâ. Áëàãîäàðÿ ôîêóñèðóþùåìó äåéñòâèþ ÌË èíòåíñèâíîñòü ïðîõîäÿùåãî ñèãíàëà (λ = 458 íì) ÷åðåç îïòè÷åñêîå âîëîêíî ñ äèàìåòðîì æèëû 3,2 ìêì óâåëè÷èëîñü áîëåå ÷åì â 1100 ðàç ïðè U = 1  è ðàññòîÿíèè äî îïòè÷åñêîãî âîëîêíà 1 ñì. Ïðè òîëùèíå ñëîÿ ÆÊ 27 ìêì âðåìÿ îòêëèêà ÌË ñîñòàâèëî íåñêîëüêî äåñÿòêîâ ñåêóíä. Äëÿ øèðîêîãî ïðèìåíåíèÿ íåîáõîäèìî ïîâûøåíèå áûñòðîäåéñòâèÿ, ÷òî ïîçâîëÿþò Ñ*ÆÊ.
Ñèñòåìû îïòè÷åñêîãî îãðàíè÷åíèÿ
Ìàññèâ íåñèììåòðè÷íûõ ÌË áûë èñïîëüçîâàí äëÿ îãðàíè÷åíèÿ èíòåíñèâíîñòè ñâåòîâîãî ïîòîêà, ïðîõîäÿùåãî ÷åðåç êþâåòó, çàïîëíåííóþ íåëèíåéíî ïîãëîùàþùåé ñðåäîé – ðàñòâîðîì ôóëëåðåíà Ñ70 â òîëóîëå ïðè êîíöåíòðàöèè 2,3×10–3 Ì [62, 63]. Òîëùèíà êþâåòû ïîäáèðàëàñü òàê, ÷òîáû ïîãëîùàþùàÿ ñðåäà îêàçàëàñü â ôîêàëüíîé ïëîñêîñòè ÌË. Èñòî÷íèêîì èçëó÷åíèÿ ñëóæèë ìíîãîèìïóëüñíûé Nd:YAG ëàçåð (λ = 532 íì) ñ äëèòåëüíîñòüþ èìïóëüñà 1 íñ. Äëÿ ðåãèñòðàöèè îñëàáëåíèÿ èíòåíñèâíîñòè ñâåòîâîãî ïîòîêà èñïîëüçîâàëñÿ êàëèáðîâàííûé äèîä ÔÄ-23 è êàëîðèìåòð ÈÝÊ-1. Èçìåðåíèÿ ïðîèçâîäèëèñü ïðè ïàðàëëåëüíîé è ïåðïåíäèêóëÿðíîé îðèåíòàöèè ïîëÿðèçàöèè èçëó÷åíèÿ ïî îòíîøåíèþ ê îðèåíòàöèè äèðåêòîðà ÆÊ. Ðåçóëüòàòû, ïîëó÷åííûå äëÿ èçëó÷åíèÿ âûøå ïîðîãà â 3 ìÄæ ñ ïàðàëëåëüíîé îðèåíòàöèåé ïîëÿðèçàöèè, ïîäòâåðäèëè âîçìîæíîñòü èñïîëüçîâàíèÿ ÌË äëÿ îïòè÷åñêîãî îãðàíè÷åíèÿ.
Äåôëåêòîð íà îñíîâå ÀË ñ ðàçäåëåííûìè ýëåêòðîäàìè Îñîáåííîñòü êîíñòðóêöèè òàêèõ ÀË ñîñòîèò â òîì, ÷òî ñèñòåìà ñèììåòðè÷íîé ëèíçû èìååò íà âåðõíåé è íèæíåé ïîäëîæêå ïî äâà íåçàâèñèìî óïðàâëÿåìûõ ðàçäåëåííûõ ýëåêòðîäà, ïàðàëëåëüíûõ äðóã äðóãó [32, 37]. Èññëåäîâàíèÿ ïðîâîäèëèñü ñ ÀË, ñîäåðæàùåé îòâåðñòèÿ äèàìåòðîì 300 ìêì, ïðè òîëùèíå ñëîÿ ÆÊ 40 ìêì. Èçìåðèòåëüíàÿ óñòàíîâêà ñîäåðæàëà He–Neëàçåð è CCD-êàìåðó, ñâÿçàííóþ ñ ïîëÿðèçàöèîííûì ìèêðîñêîïîì. Ïðè ïîäà÷å U = 16  íà îäíó ïàðó ýëåêòðîäîâ è 14,5  íà äðóãóþ ïàðó íàáëþäàëñÿ ñäâèã ñôîêóñèðîâàííîãî ïó÷êà íà 2,7 ìêì â ïëîñêîñòè ôîêóñèðîâêè. Ýòîò ýôôåêò ìîæíî èñïîëüçîâàòü â îïòè÷åñêèõ ñèñòåìàõ ñâÿçè.
Àäàïòèâíàÿ êîíòàêòíàÿ ëèíçà Ïðè èñïîëüçîâàíèè î÷êîâ ðàçðåøàþùóþ ñïîñîáíîñòü ìîæíî ïîâûñèòü óñòðàíåíèåì àáåððàöèé ëèíç. Êîìïåíñàöèÿ àáåððàöèé âûñøåãî ïîðÿäêà âîçìîæíà, åñëè êîððåêòèðóþùèé ýëåìåíò îïòè÷åñêè ñîïðÿæåí ñ î÷êîâîé ëèíçîé.  ðàáîòàõ [64–68] ïðåäëîæåíî èñïîëüçîâàòü ÆÊ-êîððåêòîð â âèäå àäàïòèâíîé êîíòàêòíîé ëèíçû, èìïëàíòèðîâàííîé â ãëàç. Ýòî ðåøàåò ïðîáëåìó îïòè÷åñêîãî ñîïðÿæåíèÿ è ïîçâîëÿåò êîìïåíñèðîâàòü àáåððàöèè íåïîñðåäñòâåííî â ãëàçó. Ðàññìîòðåíû èíäóêòèâíûé (ðèñ. 13) è ýëåêòðîñòàòè÷åñêèé âàðèàíòû áåñïðîâîëî÷íîãî óïðàâëåíèÿ èìïëàíòàíòîì. Ïðè èñïîëüçîâàíèè êîíòàêòíîé ëèíçû äèàìåòðîì 5 ìì ïîêàçàíà âîçìîæíîñòü ýëåêòðîñòàòè÷åñêîãî óïðàâëåíèÿ ïðè èçìåíåíèè ãëóáèíû àêêîìîäàöèè îò áåñêîíå÷íîñòè äî 30 ñì, ÷òî îòêðûâàåò ïåðñïåêòèâû äèíàìè÷åñêîé êîððåêöèè àáåððàöèé âûñøåãî ïîðÿäêà ÷åëîâå÷åñêîãî ãëàçà.
ÆÊ-ëèíçû äëÿ áèôîêàëüíûõ î÷êîâ Åñëè àäàïòèâíàÿ êîíòàêòíàÿ ëèíçà íàõîäèòñÿ íà ñòàäèè ðàçðàáîòîê, òî ÆÊË äëÿ áèôîêàëüíûõ î÷êîâ – íà ñòàäèè ïðîèçâîäñòâà ôèðìîé Pixel Optics
Ðèñ. 13. Àäàïòèâíàÿ ÆÊ-ëèíçà ñ áåñïðîâîëî÷íûì óïðàâëåíèåì.
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Ðèñ. 14. Ïðîòîòèï áèôîêàëüíûõ î÷êîâ ðàçðàáîòêè ôèðìû Pixel Optic.
Ñ*ÆÊ ïîçâîëèëî ïîëó÷èòü áûñòðîäåéñòâèå ïîðÿäêà 100–200 ìêñ (ïðè êîìíàòíîé òåìïåðàòóðå). Ïåðñïåêòèâíûì äëÿ ïîâûøåíèÿ îïòè÷åñêîãî êà÷åñòâà ÀË ÿâëÿåòñÿ ïðèìåíåíèÿ ñòðóêòóð íà îñíîâå ÆÊ, äèñïåðãèðîâàííûõ â ïîëèìåðíóþ ìàòðèöó.
Ñëåäóåò ïðèçíàòü, ÷òî ìíîãèå ýêñïëóàòàöèîííûå ïàðàìåòðû, òàêèå êàê îòíîñèòåëüíî íèçêîå áûñòðîäåéñòâèå, áîëüøîå ñâåòîðàññåÿíèå è íåâûñîêîå îïòè÷åñêîå êà÷åñòâî, åùå íóæäàþòñÿ â óëó÷øåíèè. Òåì íå ìåíåå, äîñòèãíóòûå ýêñïëóàòàöèîííûå ñâîéñòâà ÀË îòêðûâàþò èíòåðåñíûå âîçìîæíîñòè èõ ïðèìåíåíèÿ â óñòðîéñòâàõ ôîòîíèêè: èíôîðìàöèîííûõ äèñïëåÿõ, îïòè÷åñêèõ ìîäóëÿòîðàõ, ñèñòåìàõ îïòè÷åñêîé ôîêóñèðîâêè, óñòðîéñòâàõ êîððåêöèè çðåíèÿ, îïòè÷åñêèõ ïèíöåòàõ è ëîâóøêàõ.
(ðèñ. 14) [69, 70]. Î÷êè ïðåäíàçíà÷åíû äëÿ êîìïåíñàöèè äàëüíîçîðêîñòè, îò êîòîðîé ñòðàäàåò 93% íàñåëåíèÿ ñòàðøå 45 ëåò. Ïðè îòñóòñòâèè íàïðÿæåíèÿ î÷êè èñïîëüçóþòñÿ äëÿ ðàññìàòðèâàíèÿ áëèçêî ðàñïîëîæåííûõ îáúåêòîâ, ïðè ïîäà÷å íàïðÿæåíèÿ – äëÿ íàáëþäåíèÿ óäàëåííûõ îáúåêòîâ. Äëÿ óïðàâëåíèÿ ñëîåì ÆÊ òîëùèíîé 5 ìêì ïðè äèñêðåòíîì èçìåíåíèè ôîêóñèðîâêè òðåáóåòñÿ íàïðÿæåíèå 1,8 Â.
ÀË ìîæíî èñïîëüçîâàòü è äëÿ èçìåíåíèÿ ïðåëîìëÿþùåé ñïîñîáíîñòè ãëàçà. Ë. Òèáîñ è À. Áðýäëè èç Êàëèôîðíèè ñîçäàëè ïðîñòðàíñòâåííûé ìîäóëÿòîð ñâåòà, ñîäåðæàùèé 127 ÆÊ-ÿ÷ååê è ðàñïîëîæåííûé âî âõîäíîì çðà÷êå ãëàçà. Ýòè ÿ÷åéêè ïîçâîëÿþò ïî ïðîãðàììå îñóùåñòâëÿòü èçìåíåíèÿ ïðåëîìëåíèÿ ïðèçìàòè÷åñêîãî (0,8 äèîïòð.), ñôåðè÷åñêîãî (1,5 äèîïòð.) õàðàêòåðà è àñòèãìàòèçìà â ñå÷åíèè çðà÷êà äèàìåòðîì 3 ìì. Ñóáäèñêðåòèçàöèÿ ìîæåò áûòü ôàêòîðîì, îãðàíè÷èâàþùèì äèàïàçîí èçìåíåíèÿ ïðåëîìëåíèÿ.
Ïðèìåíåíèå ÀË â îïòè÷åñêèõ ñèñòåìàõ íå îãðàíè÷èâàåòñÿ ïðèâåäåííûìè ïðèìåðàìè. Íîâûì ÿâëÿåòñÿ èõ èñïîëüçîâàíèå â êà÷åñòâå îïòè÷åñêèõ ïèíöåòîâ è ëîâóøåê ïðè ðàáîòå ñ ìàëûìè îáúåêòàìè â îáúåìíûõ ñðåäàõ [71].
Çàêëþ÷åíèå
 îáçîðå ïðîâåäåí àíàëèç òåíäåíöèé ðàçâèòèÿ àäàïòèâíûõ ëèíç íà ÆÊ: óâåëè÷åíèå àïåðòóðû, áûñòðîäåéñòâèÿ è óëó÷øåíèå êà÷åñòâà èçîáðàæåíèÿ. ÀË ïðåäñòàâëÿþò ñîáîé ïëîñêèå ýëåìåíòû áåç ïåðåìåùàþùèõñÿ äåòàëåé, ïîçâîëÿþùèå îñóùåñòâëÿòü èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ â øèðîêèõ ïðåäåëàõ. Ðàçëè÷àþò ìèêðîëèíçû è ëèíçû ñ óâåëè÷åííîé àïåðòóðîé. Áîëüøèíñòâî ÀË ðàáîòàþò ïðè ìàëûõ óïðàâëÿþùèõ íàïðÿæåíèÿõ. Èñïîëüçîâàíèå
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46. Naumov A.F., Love G.D., Loktev M.Yu, Vladimirov F.L. Control optimization of spherical modal liquid crystal lenses // Opt. Exp. 1999. V. 4. ¹ 9. P. 344–352.
47. Loktev M.Yu., Belopukhov V.N., Vladimirov F. L., Vdovin G.V., Love G.D., Naumov A.F. Wave front control systems based on modal liquid crystal lenses // Rev. of Scientific Instr. 2000. V. 71. ¹ 9. P. 3290–3297.
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49. Ãóðàëüíèê È.Ð., Ñàìàãèí Ñ.À. Ñôåðè÷åñêàÿ æèäêîêðèñòàëëè÷åñêàÿ ëèíçà ñ îïòè÷åñêèì óïðàâëåíèåì. Òåîðèÿ è ýêñïåðèìåíò // Êâàíò. ýëåêòðîí. 2003. Ò. 33. Ñ. 430–434.
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55. Ren H., Fan Y.-H., Lin Y.-H., Wu S.-T. Tunable-focus microlens arrays using nanosize PDLC droplets // Opt. Commun. 2005. V. 247. P. 101–106.
56. Ren H., Lin Y.-H, Wu S.-T. Adaptive lenses using liquid crystal concentration redistribution // Appl. Phys. Lett. 2006. V. 88. 1911116–1-6.
57. Brinkley P.F, Kowel S.T. Liquid crystal adaptive lens: operation and aberration // Proc. SPIE. 1993. V. 1773. P. 449–458.
58. Stapert H.R., Verstegen E.J.K., del Valle S., van der Zande B.M.I., Lub. J., Stallinga S. Photoreplicated anisotropic liquid crystalline lenses for aberration control and dual layer read out of optical disks // Philips Research Information. 2002. P. 1.
59. Nose T., Sato S. Application of LC microlens to an optical fiber switch // Electronics and communications in Japan. 1992. Part 2. V. 75. ¹ 11. P. 1–10.
60. Smith P.J., Taylor C.M., McCabe E.M., Selviah D.R., Day S.E., Commander L.G. Switchable fiber coupling using variable-focal-length microlenses // Review of scientific instruments. 2001. V. 72. ¹ 7. P. 3132–3134.
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62. Ãðÿçíîâà Ì.Â., Äàíèëîâ Â.Â., Êóçíåöîâ Þ.À., Ðûëüêîâ Â.Â., Øàõâåðäîâ Ï.À., Õðåáòîâ À.È. Æèäêîêðèñòàëëè÷åñêèå ëèíçû â ñèñòåìå îïòè÷åñêîãî îãðàíè÷åíèÿ // Ïèñüìà â ÆÒÔ. 2001. Ò. 27. Â. 2. Ñ. 24–29.
63. Gryaznova M.V., Danilov V.V., Belyaeva M.A., Shakhverdov P.A., Chistyakova O.V., Khrebtov A.I. Optical limiters based on LC microlens // Optics and Spectroscopy. 2002. V. 92. ¹ 4. P. 614–618.
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65. Vdovin G., Loktev M., Zhang X. Adaptive Optics for
WIndourksstrhyopanMdu..Mnsetedri,ciGneerm// aPnryo.c2.0o0f3.thOec4t.thP.
International 19–24.
66. Kotova S.P., Kvashnin M.Yu., Rakhmatulin M.A., Zayakin O.A., Guralnik I.R., Klimov N.A., Klark P., Love G.D., Naumov A.F., Saunter C.D., Loktev M. Modal LC front correcror // Opt. Expr. 2002. V. 10 ¹ 22. P. 1258–1272.
67. Simonov A.N., Vdovin G., and Loktev M. Liquid-Crystal intraocular adaptive lens with wireless control // Opt. Expr. 2007. 15. P. 7468–7478.
68. Naumov A.F., Love G.D. Control optimization of spherical modal liquid crystal lenses // Opt. Expr. 1999. 4. P. 344–352.
69. Peyghambarian N., Li. G., Mathine D., Valley P., Schwiegerling J., Honkanen S., Ayras P., Haddock J.N., Malalahalli G., Kippelen B. Electro-optic Adaptive Lens as a New Eyewear // Mol. Cryst. and Liq. Cryst. 2007. V. 454. P. 157–166.
70. Hain M., Glokner R., Bhattacharya S., Dias D., Stankovic S., Tschudi S. Fast switching LC lenses for dual focus digital versatile disk pickup // Opt. commun. 2001. V. 188. ¹ 5. P. 291–299.
71. Hands P.J. W., Tatarkova S.A., Kirby A.K., Love G.D. Modal LC devices in optical tweezing 3D control and oscillating potential wells // Opt. Expr. 2006. V. 14. ¹ 10. P. 4525–4537.
48 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ÓÄÊ 771.36
ÀÄÀÏÒÈÂÍÛÅ ËÈÍÇÛ ÍÀ ÎÑÍÎÂÅ ÆÈÄÊÈÕ ÊÐÈÑÒÀËËÎÂ*
© 2008 ã.
Ã. Å. Íåâñêàÿ*, äîêòîð òåõí. íàóê; Ì. Ã. Òîìèëèí**, äîêòîð òåõí. íàóê
** Ñàíêò-Ïåòåðáóðãñêèé ãîñóäàðñòâåííûé ìîðñêîé òåõíè÷åñêèé óíèâåðñèòåò, Ñàíêò-Ïåòåðáóðã
** Ñàíêò-Ïåòåðáóðãñêèé ãîñóäàðñòâåííûé óíèâåðñèòåò èíôîðìàöèîííûõ òåõíîëîãèé, ** ìåõàíèêè è îïòèêè, Ñàíêò-Ïåòåðáóðã
Ðàññìîòðåíû ïðèíöèïû è òåîðåòè÷åñêèå îñíîâû ïîñòðîåíèÿ ðàçëè÷íûõ òèïîâ àäàïòèâíûõ ëèíç íà îñíîâå æèäêèõ êðèñòàëëîâ. Ïîêàçàíî èõ ðàçâèòèå îò ëèíç, ðàáîòàþùèõ â ïîëÿðèçîâàííîì ñâåòå ñ áîëüøèìè âðåìåíàìè ôîêóñèðîâêè, äî ëèíç, ðàáîòàþùèõ â íåïîëÿðèçîâàííîì ñâåòå, ñ óâåëè÷åííîé àïåðòóðîé, áûñòðîäåéñòâèåì è óëó÷øåííûì êà÷åñòâîì èçîáðàæåíèÿ. Îáñóæäåíû âîçìîæíîñòè èõ ïðèìåíåíèÿ â îïòè÷åñêèõ ñèñòåìàõ.
Êîäû OCIS: 160.3710.
Ïîñòóïèëà â ðåäàêöèþ 28.01.2008.
Ââåäåíèå
Àäàïòèâíàÿ îïòèêà – ýòî ñîâðåìåííîå, èíòåíñèâíî ðàçâèâàþùååñÿ íàó÷íîå íàïðàâëåíèå, â êîòîðîì ïåðñïåêòèâíî èñïîëüçîâàíèå ýëåìåíòîâ è óñòðîéñòâ íà îñíîâå æèäêèõ êðèñòàëëîâ (ÆÊ). Îáëàñòè ïðèìåíåíèÿ ÆÊ-ýëåìåíòîâ îïðåäåëÿþòñÿ âîçìîæíîñòÿìè ïëàâíîãî èëè äèñêðåòíîãî èçìåíåíèÿ â øèðîêèõ ïðåäåëàõ îïòè÷åñêèõ ñâîéñòâ òîíêîãî ñëîÿ ìàòåðèàëà ïðè ìàëûõ óïðàâëÿþùèõ íàïðÿæåíèÿõ (U) ýëåêòðè÷åñêîãî ïîëÿ (Å-ïîëÿ). Îíè îñíîâàíû íà êîíòðîëèðóåìîé äåôîðìàöèè ñëîÿ ÆÊ, îñóùåñòâëÿåìîé ëèáî ëîêàëüíî, ëèáî ïî âñåìó ïîëþ çðåíèÿ. Ýòè ñâîéñòâà óæå òðè äåñÿòèëåòèÿ ïðèâëåêàþò âíèìàíèå ðàçðàáîò÷èêîâ ëèíç ñ ïåðåìåííûì ôîêóñíûì ðàññòîÿíèåì èëè àäàïòèâíûõ ëèíç (ÀË).
 ÀË èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ îñóùåñòâëÿåòñÿ íå çà ñ÷åò ìåõàíè÷åñêîãî ïåðåìåùåíèÿ êîìïîíåíòîâ îáúåêòèâà, à â ïëîñêîé ÿ÷åéêå áåç ïåðåìåùàþùèõñÿ äåòàëåé ïðè ïåðåîðèåíòàöèè ìîëåêóë ÆÊ. Ïðèíöèï ðàáîòû ÀË ñîñòîèò â ôîðìèðîâàíèè óïðàâëÿåìîé ôàçîâîé çàäåðæêè ñëîåì ÆÊ ñ íåîáõîäèìûì ïðîñòðàíñòâåííûì ðàñïðåäåëåíèåì ïîä äåéñòâèåì Å-ïîëÿ. Èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ ÀË ìîæåò áûòü äèñêðåòíûì èëè ïëàâíûì è îñóùåñòâëÿåòñÿ èçìåíåíèåì àìïëèòóäû U è åãî ÷àñòîòû.
* Îáçîð ñîñòàâëåí ïî ìàòåðèàëàì äîêëàäà Ã.Å. Íåâñêîé è Ì.Ã. Òîìèëèíà “Àíàëèç ðàçâèòèÿ àäàïòèâíûõ ëèíç íà æèäêèõ êðèñòàëëàõ”, ñäåëàííîãî íà VII ìåæäóíàðîäíîé êîíôåðåíöèè “Ïðèêëàäíàÿ îïòèêà-2006”, ÑÏá. 16–18.10.2006.
Ïèîíåðñêèå èññëåäîâàíèÿ ïî ñîçäàíèþ ÀË îòíîñÿòñÿ ê 1970-ì ãîäàì è ñâÿçàíû ñ ðàáîòàìè Áåððèìàíà [1] è Ñàòî [2] ñ ñîòðóäíèêàìè. Ïåðâûå ÀË ïðåäñòàâëÿëè ñîáîé ÆÊ-ÿ÷åéêó, îäíà èç ïîäëîæåê êîòîðîé áûëà âûïîëíåíà â âèäå ëèíçû, íàõîäÿùåéñÿ â êîíòàêòå ñî ñëîåì ÆÊ. Èõ íåäîñòàòêîì ÿâëÿëîñü íèçêîå áûñòðîäåéñòâèå, âûçâàííîå áîëüøîé òîëùèíîé ñëîÿ ÆÊ â öåíòðå èëè íà ïåðèôåðèè. Êðîìå òîãî, âîçíèêëà ïðîáëåìà â îäíîðîäíîé îðèåíòàöèè ÆÊ â îòíîñèòåëüíî òîëñòîì ñëîå è íà íåïëîñêîé ïîâåðõíîñòè. Ïîýòîìó îíè íå íàøëè äàëüíåéøåãî ðàçâèòèÿ.
Öèëèíäðè÷åñêèå ÆÊ-ëèíçû, ñîäåðæàùèå ñîâîêóïíîñòü ýëåêòðîäîâ ñ èíäèâèäóàëüíîé àäðåñàöèåé áûëè ðàçðàáîòàíû â 1981 ã. ãðóïïîé èç Ñèðàêóçñêîãî óíèâåðñèòåòà (ÑØÀ) [3]. Ýëåêòðîäû ñ èíäèâèäóàëüíîé àäðåñàöèåé áûëè èñïîëüçîâàíû äëÿ ñîçäàíèÿ ñôåðè÷åñêèõ ÆÊ-ëèíç [4, 5]. Âïåðâûå ÆÊ ìèêðîëèíçû áûëè ïðåäëîæåíû â ðàáîòàõ Ñàòî [6, 7]. Ëèíçû Ôðåíåëÿ íà îñíîâå ÆÊ âïåðâûå îïèñàíû â [8]; èõ ìîäèôèêàöèè ïðîàíàëèçèðîâàíû â îáçîðå [9].
Èñïîëüçîâàíèå ÀË ìîæåò äàòü ðÿä èíòåðåñíûõ ïðèìåíåíèé â öèôðîâûõ ôîòîêàìåðàõ ñ ïåðåìåííûì ôîêóñíûì ðàññòîÿíèåì, ñêàííåðàõ îáúåìíûõ äèñïëååâ, êîððåêòîðàõ àñòèãìàòèçìà ïîëóïðîâîäíèêîâûõ ëàçåðîâ è óñòðîéñòâàõ ñ àâòîìàòè÷åñêîé ôîêóñèðîâêîé. ÀË ðàññìàòðèâàþòñÿ êàê ïåðñïåêòèâíûå îïòè÷åñêèå ïåðåêëþ÷àòåëè â îäíîìîäîâûõ âîëîêîííîîïòè÷åñêèõ ýëåìåíòàõ ïðèìåíèòåëüíî ê ýíäîñêîïèè. Ïîæèëûì ëþäÿì, ñòðàäàþùèì äàëüíîçîðêîñòüþ, ïðè íàáëþäåíèè áëèçêî ðàñïîëîæåííûõ îáúåêòîâ, íàõîäÿùèõñÿ íà ðàçíîì ðàññòîÿíèè îò íàáëþäàòåëÿ,
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òðåáóåòñÿ íåñêîëüêî ïàð î÷êîâ. Áîëüíûå êàòàðàêòîé ïðè óäàëåíèè õðóñòàëèêà òàêæå èñïîëüçóþò íåñêîëüêî ïàð î÷êîâ, ÷òî íåóäîáíî â ïîâñåäíåâíîé æèçíè. Ëåãêèå è ìèíèàòþðíûå ÀË, óïðàâëÿåìûå îò ìàëîìîùíûõ èñòî÷íèêîâ, ìîãóò óñòðàíèòü ýòè ïðîáëåìû.
 îáçîðå ðàññìàòðèâàþòñÿ ïðèíöèïû è îñíîâû òåîðèè ïîñòðîåíèÿ ÀË, à òàêæå òåíäåíöèè èõ ðàçâèòèÿ: óâåëè÷åíèå àïåðòóðû, áûñòðîäåéñòâèÿ è ïîâûøåíèå êà÷åñòâà èçîáðàæåíèÿ. Îáñóæäåíû âîçìîæíîñòè ïðèìåíåíèÿ ÀË â îïòè÷åñêèõ ñèñòåìàõ.
Òåîðåòè÷åñêèå îñíîâû ðàáîòû àäàïòèâíûõ ëèíç
Ðàññìîòðèì äâà ýòàïà ñîçäàíèÿ óïðàâëÿåìîé ôàçîâîé çàäåðæêè: ôîðìèðîâàíèå íåîáõîäèìîé êîíôèãóðàöèè Å-ïîëÿ è âûçâàííóþ èì äåôîðìàöèþ ñëîÿ ÆÊ. Îáóñëîâëåííàÿ ýòîé äåôîðìàöèåé ôàçîâàÿ çàäåðæêà îáåñïå÷èâàåò ôîêóñèðóþùèå ñâîéñòâà ëèíçû. Èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ ÀË îñóùåñòâëÿåòñÿ èçìåíåíèåì àìïëèòóäû è ÷àñòîòû Å-ïîëÿ.
Ñïîñîáû ñîçäàíèÿ ïðîñòðàíñòâåííî íåîäíîðîäíûõ ïîëåé è èõ ðàñ÷åò
Ýëåêòðè÷åñêîå ïîëå â ìèêðîëèíçàõ
Êîíôèãóðàöèÿ Å-ïîëÿ â ìèêðîëèíçàõ (ÌË) çàäàåòñÿ ãåîìåòðèåé ýëåêòðîäîâ.  ñôåðè÷åñêîé ÌË äëÿ ïîëó÷åíèÿ àêñèàëüíî-ñèììåòðè÷íîãî Å-ïîëÿ â ýëåêòðîäàõ ñîçäàþòñÿ êðóãëûå îòâåðñòèÿ äèàìåòðîì L. Ðàçëè÷àþò íåñèììåòðè÷íûå ÌË – îòâåðñòèÿ èìåþòñÿ â îäíîì èç ýëåêòðîäîâ, è ñèììåòðè÷íûå – ñîâìåùåííûå îòâåðñòèÿ èìåþòñÿ â îáîèõ ýëåêòðîäàõ.  öèëèíäðè÷åñêîé ÌË â ýëåêòðîäàõ âûïîëíåíà ùåëü.
Ðàñ÷åò ðàñïðåäåëåíèÿ íàïðÿæåííîñòè â àêñèàëüíî-ñèììåòðè÷íîì ïîëå íåñèììåòðè÷íîé ÌË ïðîâåäåí â ðàáîòàõ [10, 11], ñèììåòðè÷íîé – â ðàáîòàõ [12–14].  ðàáîòå [10], â ÷àñòíîñòè, ó÷òåíî âëèÿíèå äèýëåêòðè÷åñêèõ ñâîéñòâ ïîäëîæêè íà ðàñïðåäåëåíèå Å-ïîëÿ. Íà ðèñ. 1 ïðèâåäåíà ñõåìà íåñèììåòðè÷íîé ÌË. Âåðõíèé ýëåêòðîä èç õðîìà èìååò îòâåðñòèå, íèæíèé ýëåêòðîä – ñïëîøíîé. Çàçîð ìåæäó íèìè òîëùèíîé d çàïîëíÿåòñÿ ÆÊ. Óðàâíåíèÿ, îïèñûâàþùèå Å-ïîëå, èìåþò âèä:
divD = 0, E = gradu,
ãäå D – âåêòîð ýëåêòðè÷åñêîãî ñìåùåíèÿ, u – ïîòåíöèàë Å-ïîëÿ.
Òàê êàê ïîëå ïîòåíöèàëà u(r, z) â ÌË ñôåðè÷åñêè ñèììåòðè÷íî, óðàâíåíèå äëÿ ïîòåíöèàëà â öèëèíäðè÷åñêèõ êîîðäèíàòàõ èìååò âèä:
L d
Cr In2O3
Ðèñ. 1. Ñõåìà íåñèììåòðè÷íîé ìèêðîëèíçû. L – àïåðòóðà ìèêðîëèíçû, d – òîëùèíà ñëîÿ ÆÊ
d, ìêì 20
10
0 20 40 R, ìêì
Ðèñ. 2. Ýêâèïîòåíöèàëüíûå ïîâåðõíîñòè äëÿ ìèêðîëèíçû ñ L = 70 ìêì, d = 20 ìêì, ÆÊ Å-7 (ôèðìû Merk). R – ðàññòîÿíèå îò öåíòðà ëèíçû äî ðàññìàòðèâàåìîé òî÷êè àïåðòóðû.
ε⊥
⎛ ⎜ ⎝
∂2u ∂r 2
+
1 r
∂u ∂r
⎞ ⎟ ⎠
+
ε&
∂2u ∂z 2
=
0,
(1)
ãäå ε⊥ è ε|| – äèýëåêòðè÷åñêàÿ ïðîíèöàåìîñòü â ïåðïåíäèêóëÿðíîì è ïàðàëëåëüíîì äèðåêòîðó íàïðàâëåíèÿõ.
Äàëåå ôîðìóëèðóþòñÿ ãðàíè÷íûå óñëîâèÿ äëÿ ýëåêòðè÷åñêîãî ïîòåíöèàëà â îêðåñòíîñòè îòâåðñòèÿ è óðàâíåíèå (1) ðåøàþò ÷èñëåííûìè ìåòîäàìè. Ðåçóëüòàòû ðàñ÷åòà â âèäå ýêâèïîòåíöèàëüíûõ ïîâåðõíîñòåé äëÿ ÌË ñ L = 70 ìêì, d = 20 ìêì, ÆÊ Å-7 ôèðìû Merk ïðèâåäåíû íà ðèñ. 2. Âáëèçè êðàÿ îòâåðñòèÿ Å-ïîëå íàèáîëåå íåîäíîðîäíî. Ñ óâåëè÷åíèåì L íåîäíîðîäíîñòü óìåíüøàåòñÿ, è ýòî ïðèâîäèò ê èñ÷åçíîâåíèþ ôîêóñèðóþùèõ ñâîéñòâ.
Ýëåêòðè÷åñêîå ïîëå â àäàïòèâíûõ ìîäàëüíûõ ÆÊ-ëèíçàõ
Ñîçäàíèå ÀË ñ áîëüøîé àïåðòóðîé îñíîâàíî íà èíîì ôîðìèðîâàíèè Å-ïîëÿ [15-17]. Èçâåñòíû äâà ïîäõîäà: çîíàëüíûé (Å-ïîëå ñîçäàåòñÿ ñ ïîìîùüþ ñîâîêóïíîñòè èíäèâèäóàëüíî àäðåñóåìûõ ýëåêòðîäîâ) è ìîäàëüíûé (ïðè èõ îãðàíè÷åííîì êîëè÷åñòâå). Ìîäàëüíûå ëèíçû (ÌË) â îòëè÷èå îò çîíàëüíûõ îáåñïå÷èâàþò ïëàâíîå, íåïðåðûâíîå èçìåíåíèå ôàçîâîãî ïðîôèëÿ.  ÌË îäèí èç ýëåêòðîäîâ
36 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ÿâëÿåòñÿ âûñîêîîìíûì óïðàâëÿþùèì ýëåêòðîäîì (ÓÝ), ïî ïåðèôåðèè êîòîðîãî íàíîñÿòñÿ íèçêîîìíûå êîíòàêòû. Âîçíèêàþùàÿ ñèñòåìà ñ ðàñïðåäåëåííûì ñîïðîòèâëåíèåì (ÓÝ) è åìêîñòüþ (ñëîé ÆÊ) èìååò ðåàêòèâíûé õàðàêòåð è óïðàâëÿåò ïàðàìåòðàìè ÀË ïðè èçìåíåíèè àìïëèòóäû è ÷àñòîòû U.
Ðàçðàáîòàíû ñôåðè÷åñêèå è öèëèíäðè÷åñêèå ÀË. Õàðàêòåð âîëíîâîãî ôðîíòà îïðåäåëÿåòñÿ ãåîìåòðèåé êîíòàêòîâ: äëÿ ñôåðè÷åñêîé ëèíçû – êîëüöåâîé êîíòàêò, öèëèíäðè÷åñêîé – äâà ïàðàëëåëüíûõ ïîëîñêîâûõ êîíòàêòà. Ñëîé ÆÊ ïîìåùåí ìåæäó äâóìÿ ñòåêëÿííûìè ïîäëîæêàìè ñ ýëåêòðîäàìè. Ïîâåðõíîñòíîå ñîïðîòèâëåíèå ÓÝ (1–10 ÌÎì/ ) ìíîãî áîëüøå ñîïðîòèâëåíèÿ ñïëîøíîãî (çàçåìëåííîãî) ýëåêòðîäà (50–200 Îì/ ). U ïðèêëàäûâàåòñÿ ê êîíòàêòàì, ðàñïîëîæåííûì íà ïåðèôåðèè ÓÝ. Åñëè ê êîíòàêòàì ïðèëîæèòü ñèíóñîèäàëüíîå íàïðÿæåíèå, òî èç-çà ðåçèñòèâíî-åìêîñòíîãî õàðàêòåðà ñèñòåìû èçìåíåíèå U â öåíòðå áóäåò ìåíüøå èçìåíåíèÿ U íà êîíòàêòíûõ ýëåêòðîäàõ. Ñ óâåëè÷åíèåì ÷àñòîòû ðàçëè÷èå ðàñòåò, ïðèâîäÿ ê óìåíüøåíèþ ñðåäíåêâàäðàòè÷íîãî çíà÷åíèÿ U â öåíòðå àïåðòóðû.  óñòàíîâèâøåìñÿ ðåæèìå ðåàëèçóåòñÿ ðàñïðåäåëåíèå ñðåäíåêâàäðàòè÷íîãî çíà÷åíèÿ U â ñëîå ÆÊ, è â äîñòàòî÷íî øèðîêîé îáëàñòè èçìåíåíèÿ ïàðàìåòðîâ óïðàâëÿþùåãî U ýòî ðàñïðåäåëåíèå áóäåò êâàçèïàðàáîëè÷åñêèì. Óðàâíåíèå, îïèñûâàþùåå ðàñïðåäåëåíèå U ïî àïåðòóðå U(x, y), èìååò âèä [16]:
∇2U
=
ρsc
∂U ∂t
+ ρs gU ,
(2)
ãäå g – ïðîâîäèìîñòü ñëîÿ ÆÊ íà åäèíèöó ïëîùàäè, ρs – ïîâåðõíîñòíîå ñîïðîòèâëåíèå ÓÝ, ñ – åìêîñòü íà åäèíèöó ïëîùàäè ÓÝ.
Óðàâíåíèå (2) ïðè ñèíóñîèäàëüíîì óïðàâëÿþùåì íàïðÿæåíèè èìååò âèä:
∇2U = χ2U,
(2à)
ãäå χ2 = ρs(g – iωc). Óðàâíåíèå (2à) ïðèìåíåíî äëÿ ðàñ÷åòà ïîëÿ öè-
ëèíäðè÷åñêîé ÀË:
∂2U ∂x2
= χ2U.
(3)
Èç ðåøåíèÿ ýòîãî óðàâíåíèÿ ñ ó÷åòîì ãðàíè÷íûõ óñëîâèé ñëåäóåò, ÷òî ïðè |χ|l 0 (5ÑÂ).
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
39
(à) (á)
(â) (ã)
(ä) (å)
Ðèñ. 8. Èíòåðôåðåíöèîííûå êàðòèíû ïëàíàðíîé ìèêðîëèíçû, ïîêàçûâàþùèå âîçíèêíîâåíèå äèñêëèíàöèè (à, á) è åå èñ÷åçíîâåíèå (â, ã, ä, å) ñ òå÷åíèåì âðåìåíè ïðè íàëè÷èè ìóëüòèäîìåííîé ñòðóêòóðû: â – ÷åðåç 1 ñ, ã – 10 ñ, ä – 20 ñ, å – 40 ñ.
ôåðåíöèîííûå êàðòèíû ïðè ðàçëè÷íûõ U. Ïðè óâåëè÷åíèè U íà êðàþ âîçíèêàåò èçëîì ôàçîâîãî ïðîôèëÿ (ðèñ. 8à). Ñ ðîñòîì U îáëàñòü èçëîìà ðàñòåò, ïîêà íå ïîÿâèòñÿ äèñêëèíàöèÿ (ðèñ. 8á). Ñïîñîáû åå óñòðàíåíèÿ îïèñàíû â ðÿäå ðàáîò. Íàïðèìåð, â ðàáîòå [25] íà ãðàíèöå ìèêðîëèíçû, ãäå ôîðìèðóåòñÿ äèñêëèíàöèÿ, ñîçäàåòñÿ êëèíîîáðàçíàÿ îáëàñòü ñ ãèáðèäíîé îðèåíòàöèåé. Ýòà îáëàñòü ìåíÿåò õàðàêòåð ïåðåîðèåíòàöèè ìîëåêóë ÆÊ â ÌË, â ðåçóëüòàòå ÷åãî äèñêëèíàöèÿ óõîäèò èç îáëàñòè îòâåðñòèÿ (ðèñ. 8â, ã, ä, å).
Èññëåäîâàíèå çàâèñèìîñòè ÷èñëîâîé àïåðòóðû è ðàçðåøàþùåé ñïîñîáíîñòè ÌË ñ ïëàíàðíîé îðèåíòàöèåé [24] îò U äëÿ ðàçíûõ îòíîøåíèé L/d ïîêàçàëî, ÷òî íàèëó÷øèå îïòè÷åñêèå ñâîéñòâà íàáëþäàþòñÿ íà íèñïàäàþùåé âåòâè çàâèñèìîñòè ôîêóñíîãî ðàññòîÿíèÿ îò U è â îáëàñòè ìèíèìóìà ýòîé çàâèñèìîñòè. Ñîîáùàåòñÿ, ÷òî äîñòèãíóòî óìåíüøåíèå óïðàâëÿþùåãî íàïðÿæåíèÿ äî 6,5–7  ïðè ÷àñòîòå 10 êÃö è èñïîëüçîâàíèè ÆÊ ñ Δε = 2 ïðè òîëùèíå ñëîÿ 50 ìêì [26].
êèõ – ðàññåèâàþùåé, î ÷åì ñâèäåòåëüñòâóåò ñòðóêòóðà ôàçîâûõ ïðîôèëåé. Çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò U äëÿ ãèáðèäíîé ÌË â ôîêóñèðóþùåì ðåæèìå àíàëîãè÷íà ñîîòâåòñòâóþùåé çàâèñèìîñòè äëÿ ïëàíàðíîé ÌË (ðèñ. 7á). Èçìåðåíèÿ âðåìåí îòêëèêà è âîññòàíîâëåíèÿ îðèåíòàöèè ïîêàçàëè, ÷òî äëÿ ÌË ñ Δε > 0 îíè ñîñòàâëÿþò íåñêîëüêî ñåêóíä. Ïðè Δε < 0 â ôîêóñèðóþùåì ðåæèìå íóæíû áîëåå âûñîêèå U, è âðåìÿ îòêëèêà ìîæåò áûòü óìåíüøåíî äî íåñêîëüêèõ ìèëëèñåêóíä.  îòëè÷èå îò ïëàíàðíîé ÌË, â ãèáðèäíîé íå âîçíèêàåò äèñêëèíàöèè. Íåäîñòàòêîì ýòîãî òèïà ÌË ÿâëÿåòñÿ ñäâèã öåíòðà ôàçîâîãî ïðîôèëÿ îòíîñèòåëüíî öåíòðà îòâåðñòèÿ.
Ãîìåîòðîïíûå ÌË
Ðåçóëüòàòû èññëåäîâàíèÿ îïòè÷åñêèõ ñâîéñòâ ÌË ñ ãîìåîòðîïíî îðèåíòèðîâàííûì ÆÊ ïðåäñòàâëåíû â ðàáîòàõ [11, 20, 30].  ýòîì ñëó÷àå ïðè ïðèëîæåíèè U ôîðìèðóåòñÿ àêñèàëüíî-ñèììåòðè÷íîå ðàñïðåäåëåíèå ïîêàçàòåëÿ ïðåëîìëåíèÿ äëÿ e-âîëíû ñ ìèíèìóìîì â öåíòðå (êàê íà ðèñ. 5â), ò. å. ãîìåîòðîïíàÿ ëèíçà äîëæíà èìåòü ñâîéñòâà ðàññåèâàþùåé ëèíçû. Èññëåäîâàíû èíòåðôåðåíöèîííûå êàðòèíû (ðèñ. 9) è ôàçîâûå ïðîôèëè ýòèõ ÌË ïðè ðàçëè÷íûõ U. Íàáëþäàåòñÿ äåôîêóñèðóþùèé ðåæèì, ïðè÷åì ïðè îïðåäåëåííîì íàïðÿæåíèè Up ïðîôèëü ôàçîâîé çàäåðæêè ñòàíîâèòñÿ êâàäðàòè÷íûì è ÌË òàêæå ñòàíîâèòñÿ ñôåðè÷åñêîé. Up ïîâûøàåòñÿ ñ óâåëè÷åíèåì ðàçìåðà ëèíçû. Ïðè äàëüíåéøåì óâåëè÷åíèè U ïðîôèëü ôàçîâîé çàäåðæêè ñòàíîâèòñÿ áëèçêèì ê ëèíåéíîìó. Ðåæèì ïåðåñòðàèâàåìîé ëèíçû íàèáîëåå âûðàæåí ó ÌË ñ îòíîøåíèåì L/d = 3,5. Ïðè ìàëûõ U ÌË îáëàäàþò äâóìÿ ôîêóñàìè, ïðè÷åì îäèí èç íèõ ÿâëÿåòñÿ êîëüöåâûì, äðóãîé – òî÷å÷íûì. Òî÷å÷íîìó ôîêóñó ñîîòâåòñòâóþò áîëüøèå çíà÷åíèÿ ôîêóñíîãî ðàññòîÿíèÿ. Êîãäà íàïðÿæåíèå ñòàíîâèòñÿ ðàâíûì Up, òî÷å÷íûé è êîëüöåâîé ôîêóñ ñëèâàþòñÿ.
ÌË ñ ãîìåîïëàíàðíîé (ãèáðèäíîé) îðèåíòàöèåé
Ìîëåêóëû ÆÊ â ãèáðèäíîé ÌË èìåþò ðàçëè÷íóþ èñõîäíóþ îðèåíòàöèþ âáëèçè ðàçíûõ ïîäëîæåê: ãîìåîòðîïíóþ íà îäíîé è ïëàíàðíóþ íà äðóãîé. Ðåçóëüòàòû èññëåäîâàíèé ïðèâåäåíû â ðàáîòàõ [23, 24, 27–29].  ñëó÷àå ÆÊ ñ Δε < 0 ïðè íèçêèõ U ÌË èìååò äåôîêóñèðóþùèå ñâîéñòâà. Ïðè âûñîêèõ U (îêîëî 80 Â) ÌË ñòàíîâèòñÿ ñîáèðàþùåé è èìååò õîðîøèå îïòè÷åñêèå ñâîéñòâà, îäíàêî åå ôîêóñíîå ðàññòîÿíèå ñëàáî çàâèñèò îò U. Ïðè èñïîëüçîâàíèè ÆÊ ñ Δε > 0 íàáëþäàåòñÿ îáðàòíàÿ ñèòóàöèÿ: ïðè ìàëûõ U ÌË ÿâëÿåòñÿ ñîáèðàþùåé, ïðè âûñî-
40
(à) (á)
Ðèñ. 9. Èíòåðôåðåíöèîííûå êàðòèíû ãîìåîòðîïíîé ÌË. L = 600 ìêì, à – U = 6, á – 14 Â.
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
×èñëîâàÿ àïåðòóðà ÌË çàâèñèò îò îòíîøåíèÿ L/d. Ìàêñèìàëüíàÿ ÷èñëîâàÿ àïåðòóðà ïðè Up íàáëþäàåòñÿ ó ÌË ñ îòíîøåíèåì L/d = 3,5, îíà äîñòèãàåò çíà÷åíèÿ 0,11. Ðàçðåøàþùàÿ ñïîñîáíîñòü ãîìåîòðîïíûõ ÌË óâåëè÷èâàåòñÿ ñ óìåíüøåíèåì ïàðàìåòðà L/d è äîñòèãàåò çíà÷åíèÿ ïðèìåðíî 200 ëèí/ìì, ÷òî ÿâëÿåòñÿ âûñîêîé âåëè÷èíîé äëÿ ÀË.
 ðàáîòå [11] èññëåäîâàíà ÌË ñ ÆÊ ñ Δε > 0, îáëàäàþùàÿ äåôîêóñèðóþùèìè ñâîéñòâàìè. Îäíàêî åå ôîêóñíûå ðàññòîÿíèÿ íà ïîðÿäîê ìåíüøå, ÷åì ó àíàëîãè÷íûõ ÌË ñ Δε < 0. Òåìè æå àâòîðàìè ïðèâåäåíû âåëè÷èíû ñôåðè÷åñêèõ àáåððàöèé ýòèõ ëèíç ïðè íàïðÿæåíèè 6,5  è ÷àñòîòå 10 êÃö, ñâèäåòåëüñòâóþùèå îá îòíîñèòåëüíî âûñîêîì îïòè÷åñêîì êà÷åñòâå.
Ñèììåòðè÷íûå ÌË
Ñèììåòðè÷íàÿ ÌË èìååò îòâåðñòèÿ îäèíàêîâîãî äèàìåòðà â îáîèõ ýëåêòðîäàõ, ïîìåùåííûå îäíî íàä äðóãèì. Ðåçóëüòàòû èññëåäîâàíèé ïðåäñòàâëåíû â ðàáîòàõ [31–35]. Ïåðåõîä ê òàêèì ÌË èìåë öåëüþ óñòðàíèòü äèñêëèíàöèè è ñäâèã öåíòðà èíòåðôåðåíöèîííîé êàðòèíû ó íåñèììåòðè÷íûõ ïëàíàðíûõ è ãèáðèäíûõ ÌË.  ñèììåòðè÷íûõ ÌË íå íàáëþäàåòñÿ ñäâèãà öåíòðà èíòåðôåðåíöèîííîé êàðòèíû îòíîñèòåëüíî öåíòðà îòâåðñòèé, îäíàêî ïðè ïîâûøåíèè U âáëèçè êðàÿ îòâåðñòèÿ âîçíèêàþò äâå íåáîëüøèå äèñêëèíàöèè. E-ïîëå â ñèììåòðè÷íîé ÌË îòëè÷àåòñÿ ñèëüíîé íåîäíîðîäíîñòüþ – íàïðÿæåííîñòü ïîëÿ â öåíòðå çíà÷èòåëüíî íèæå, ÷åì ïðè íåñèììåòðè÷íûõ ýëåêòðîäàõ, à ðàáî÷èå U ïî ñðàâíåíèþ ñ íåñèììåòðè÷íîé ÌË ïîâûøàþòñÿ. Ïðè ìàëûõ U èìåþòñÿ äâà ôîêóñà. Ïðè ïîâûøåíèè U ôîêóñíîå ðàññòîÿíèå ñíà÷àëà óáûâàåò, äîñòèãàåò ìèíèìàëüíîãî çíà÷åíèÿ, à çàòåì ðàñòåò. Ïðè íåêîòîðîì U ôîêóñû ìèêðîëèíçû ñëèâàþòñÿ è íàáëþäàþòñÿ íàèëó÷øèå îïòè÷åñêèå ñâîéñòâà. Êà÷åñòâî èçîáðàæåíèÿ ñèììåòðè÷íûõ ëèíç õàðàêòåðèçóåòñÿ ïîëóøèðèíîé êðèâîé ôóíêöèè ðàññåÿíèÿ òî÷êè íà óðîâíå ïîëóìàêñèìóìà (FWHM), ðàâíîé äëÿ ñôåðè÷åñêîé ëèíçû 2,5 ìêì [13], à äëÿ öèëèíäðè÷åñêîé 2,2–2,3 ìêì [36].
 ðàáîòàõ [34, 35] èññëåäîâàíà çàâèñèìîñòü ïàðàìåòðîâ ÌË îò ñâîéñòâ ÆÊ-ìàòåðèàëà. Ìàêñèìàëüíîå çíà÷åíèå ÷èñëîâîé àïåðòóðû ëèíåéíî óâåëè÷èâàåòñÿ ñ ðîñòîì îïòè÷åñêîé àíèçîòðîïèè Δn è ïðèâåäåííîé äèýëåêòðè÷åñêîé àíèçîòðîïèè Δε/ε, à U, ïðè êîòîðîì íàáëþäàåòñÿ ìàêñèìóì, óáûâàåò ñ ðîñòîì äèýëåêòðè÷åñêîé àíèçîòðîïèè.  ðàáîòå [35] ïðîàíàëèçèðîâàíà ðîëü óïðóãèõ ñâîéñòâ íåìàòèêà â ôîðìèðîâàíèè àñòèãìàòèçìà ÌË è ïîêàçàíî, ÷òî ÷åì áîëüøå àíèçîòðîïèÿ óïðóãèõ ñâîéñòâ, òåì ñèëüíåå àñòèãìàòèçì.
Óñîâåðøåíñòâîâàíèå ñèììåòðè÷íûõ ÌË îïèñàíî â ðàáîòàõ [37, 38]. Ýëåêòðîäû èìåþò îòâåðñòèÿ è ðàçäåëåíû óçêèìè ùåëÿìè íà äâà (÷åòûðå) ñåêòîðà; íà ýòè ñåêòîðû ìîãóò ïîäàâàòüñÿ ðàçíûå U. Âñëåäñòâèå ðàçëè÷èÿ äåôîðìàöèè íåìàòèêà â ðàçíûõ ÷àñòÿõ ÌË âîçíèêàåò ëèíåéíàÿ äîáàâêà â ôàçîâûé ïðîôèëü, âûçûâàþùàÿ ñäâèã ëó÷à â ïîïåðå÷íîì íàïðàâëåíèè. Ïðè íåáîëüøîé ðàçíèöå U îïòè÷åñêèå ñâîéñòâà îñòàþòñÿ õîðîøèìè, è ïîÿâëÿåòñÿ âîçìîæíîñòü óïðàâëÿåìîãî ñìåùåíèÿ òî÷êè ôîêóñèðîâêè ïåðïåíäèêóëÿðíî ê îïòè÷åñêîé îñè.  ðàáîòå [37] ñîîáùàåòñÿ, ÷òî ýòî ñìåùåíèå ïðè ñîõðàíåíèè ïàðàáîëè÷åñêîãî ôàçîâîãî ïðîôèëÿ ñîñòàâëÿåò 10 ìêì (ïðè L/d = 3).
 ðàáîòàõ [36, 39] ïðåäëîæåí äðóãîé âàðèàíò ÌË: ïîìèìî îáû÷íûõ óïðàâëÿþùèõ ýëåêòðîäîâ èìåþòñÿ ÷åòûðå äîïîëíèòåëüíûõ, ê êîòîðûì ïîäâîäÿòñÿ ðàçëè÷íûå U. Ïðè îïðåäåëåííûõ óñëîâèÿõ óïðàâëåíèÿ óäàåòñÿ èçáåæàòü ïîÿâëåíèÿ äèñêëèíàöèè â îáëàñòè îòâåðñòèÿ è ðàñøèðèòü äèàïàçîí U íàáëþäåíèÿ ôîêóñèðóþùèõ ñâîéñòâ. Óëó÷øåíèå îïòè÷åñêèõ ñâîéñòâ ÌË áûëî äîñòèãíóòî ïðè èñïîëüçîâàíèè 4 ýëåêòðîäîâ, ðàñïîëîæåííûõ äðóã íàä äðóãîì [14, 40]. Äâà èç íèõ èìåëè êðóãëûå îòâåðñòèÿ (ëèíçîâûå ýëåêòðîäû), äâà äðóãèõ ÿâëÿëèñü ñïëîøíûìè, íàíåñåííûìè íà ñòåêëÿííûå ïîäëîæêè è ðàñïîëîæåííûìè âûøå è íèæå îáû÷íûõ ëèíçîâûõ ýëåêòðîäîâ.  ðàáîòå [40] èññëåäîâàíà ÷èñëîâàÿ àïåðòóðà (NA) ÌË ïðè ñëîæåíèè è âû÷èòàíèè Å-ïîëåé, ñîçäàííûõ ïàðàìè ýëåêòðîäîâ â ñëîå ÆÊ. Ïîêàçàíî, ÷òî NAmax íà 40% âûøå ïðè âû÷èòàíèè Å-ïîëåé, ÷åì â ñëó÷àå èõ ñëîæåíèÿ, à òàêæå ÷åì â ñëó÷àå îáû÷íîé ÌË.  ðàáîòå [14] òåîðåòè÷åñêè è ýêñïåðèìåíòàëüíî ïîêàçàíà âîçìîæíîñòü óìåíüøåíèÿ ñôåðè÷åñêîé àáåððàöèè è àñòèãìàòèçìà ïðè ïîäáîðå U íà ýëåêòðîäàõ.
Ðàññìîòðåâ èçâåñòíûå òèïû ÌË íà íåìàòèêàõ, ìîæíî êîíñòàòèðîâàòü, ÷òî ïðè ìàëûõ U ÌË ñ ïëàíàðíîé è ãèáðèäíîé îðèåíòàöèåé îáëàäàþò ôîêóñèðóþùèìè ñâîéñòâàìè, à ñ ãîìåîòðîïíîé – äåôîêóñèðóþùèìè. Ñðàâíåíèå îïòè÷åñêèõ ñâîéñòâ ÌË ïðîâåäåíî â ðàáîòå [29]. Çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò U ñõîæà äëÿ âñåõ òèïîâ ÌË: ïðè ïîâûøåíèè U îíî ñíà÷àëà óìåíüøàåòñÿ, äîñòèãàÿ ìèíèìóìà ïðè íåêîòîðîì Um, à çàòåì âîçðàñòàåò. Ïðè äàëüíåéøåì óâåëè÷åíèè U ïðîèñõîäèò èíâåðñèÿ îïòè÷åñêèõ ñâîéñòâ ÌË: ó ãèáðèäíîé è ïëàíàðíîé ÌË íàáëþäàþòñÿ äåôîêóñèðóþùèå ñâîéñòâà. Ìàêñèìàëüíàÿ ÷èñëîâàÿ àïåðòóðà äëÿ âñåõ ÌË ÿâëÿåòñÿ íàèáîëüøåé â ñëó÷àå, åñëè îòíîøåíèå L/d = 3. Ñðàâíåíèå NAmax ó ðàçëè÷íûõ ÌË ïîêàçûâàåò, ÷òî íàèáîëüøàÿ ôîêóñèðóþùàÿ ñïîñîáíîñòü äîñòèãàåòñÿ ïðè ïëàíàðíîé îðèåíòàöèè (NAmax = 0,21), à äåôîêóñèðóþùàÿ – ïðè ãîìåîòðîïíîé (NAmax = 0,22). Äèàïàçîí U, â êîòîðîì ìîæíî óï-
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
41
ðàâëÿòü ôîêóñíûì ðàññòîÿíèåì, çàâèñèò îò òèïà ÌË è îò âåëè÷èíû ïàðàìåòðà L/d. Áîëåå øèðîêèì îí áóäåò ó ãîìåîòðîïíûõ ìèêðîëèíç. Ìàêñèìàëüíàÿ ðàçðåøàþùàÿ ñïîñîáíîñòü ïëàíàðíûõ è ãèáðèäíûõ ÌË íàáëþäàåòñÿ ïðè Um, ïðè÷åì îíà âûøå ó ïëàíàðíûõ.  äåôîêóñèðóþùåì ðåæèìå íàèáîëüøàÿ ðàçðåøàþùàÿ ñïîñîáíîñòü ó ãîìåîòðîïíîé ÌË.
Îïòè÷åñêèå ñâîéñòâà ñèììåòðè÷íîé è íåñèììåòðè÷íîé ÌË ñ ïëàíàðíîé îðèåíòàöèåé ñõîæè. Ñîçäàíèå ñèììåòðè÷íûõ ÌË ñâÿçàíî ñ áîëüøèìè òåõíîëîãè÷åñêèìè òðóäíîñòÿìè. Íàáëþäàåìàÿ â íåñèììåòðè÷íûõ ïëàíàðíûõ ÌË äèñêëèíàöèÿ âîçíèêàåò ïðè U â ïîëòîðà ðàçà ïðåâûøàþùèõ íàïðÿæåíèÿ ìàêñèìóìà ÷èñëîâîé àïåðòóðû Um, è ïîòîìó â ðàáî÷åì äèàïàçîíå U ìàëî âëèÿåò íà îïòè÷åñêèå ñâîéñòâà ÌË.
Äëÿ óâåëè÷åíèÿ àïåðòóðû ïðåäëîæåíî ðàñïîëîæèòü óïðàâëÿþùèé ýëåêòðîä íà âíåøíåé ïîâåðõíîñòè îäíîé èç ñòåêëÿííûõ ïîäëîæåê.  ýòîì ñëó÷àå ôîêóñèðóþùèå ñâîéñòâà ðåàëèçóþòñÿ äëÿ îòâåðñòèé áîëüøåãî äèàìåòðà (5–7 ìì) [41]. Ýòî ïðèâîäèò ê óâåëè÷åíèþ ðàáî÷åãî U äî 40–100 Â, ÷òî ñíèæàåò ïðèâëåêàòåëüíîñòü òàêèõ ëèíç.  öèëèíäðè÷åñêèõ ëèíçàõ ñ øèðèíîé ùåëè 2 ìì àíàëîãè÷íîå ðåøåíèå óâåëè÷èëî U äî 120–180  [42].  ðàáîòå [43] â ýòó ëèíçó íàä âåðõíåé ïîäëîæêîé áûë äîáàâëåí åùå îäèí ñëîé ÆÊ (óïðàâëÿþùèé ýëåêòðîä îäèí è íàõîäèòñÿ â öåíòðå). Ðàññìîòðåíû äâà ñëó÷àÿ âçàèìíîé îðèåíòàöèè ìîëåêóë ÆÊ: îïòè÷åñêèå îñè ïàðàëëåëüíû è îðòîãîíàëüíû. Îïòè÷åñêàÿ ñèëà ëèíç â ýòèõ ñëó÷àÿõ ìàëî îòëè÷àåòñÿ (îêîëî 6 ì–1 ïðè U = 100 Â), íî îíà ñóùåñòâåííî âûøå, ÷åì ó ëèíçû ñ îäíèì ñëîåì (îêîëî 4 ì–1 ïðè U = 100 Â). Äèàïàçîí ðàáî÷èõ íàïðÿæåíèé äëÿ ëèíç ñ äâóìÿ ñëîÿìè 90–120 Â, ÷òî âûøå, ÷åì äëÿ ëèíç ñ îäíèì ñëîåì ÆÊ.
Îáùèì íåäîñòàòêîì ÀË íà íåìàòèêàõ ÿâëÿåòñÿ áîëüøîå âðåìÿ èõ ôîêóñèðîâêè, ñîñòàâëÿþùåå íåñêîëüêî ñåêóíä.  ðàáîòå [44] ïðåäëîæåíî èñïîëüçîâàòü íåìàòèê ñ äâóõ÷àñòîòíûì ðåæèìîì óïðàâëåíèÿ, ÷òî ïîçâîëÿåò óìåíüøèòü âðåìåíà ôîêóñèðîâêè ïî÷òè íà ïîðÿäîê.
Ìèêðîëèíçû íà îñíîâå ñåãíåòîýëåêòðè÷åñêèõ ñìåêòèêîâ (Ñ*ÆÊ)
Íåäîñòàòêîì ÌË íà îñíîâå íåìàòèêîâ ÿâëÿåòñÿ èõ íèçêîå áûñòðîäåéñòâèå. Ïîâûøåíèå áûñòðîäåéñòâèÿ îñóùåñòâëÿåòñÿ èñïîëüçîâàíèåì Ñ*ÆÊ [45]. Äèïîëüíûå ìîìåíòû ìîëåêóë â Ñ*ÆÊ ïåðïåíäèêóëÿðíû äèðåêòîðó è ëåæàò â ïëîñêîñòè ñìåêòè÷åñêîãî ñëîÿ.  Å-ïîëå âñå äèïîëè âûñòðàèâàþòñÿ ïî íàïðàâëåíèþ ïîëÿ. Ïîëå ïðîòèâîïîëîæíîãî çíàêà ïåðåîðèåíòèðóåò äèïîëè, à âìåñòå ñ íèì è äèðåêòîð, êîòîðûé ïîâîðà÷èâàåòñÿ ïî îáðàçóþùåé êîíóñà â ïëîñêîñòè ñëîÿ íà óãîë 2θ, ãäå θ – óãîë íàêëîíà
(à) (á)
11 2
4
35
3
4 6
7 8
Âêëþ÷åíî (ôîêóñèðîâêà)
Âûêëþ÷åíî (ðàñôîêóñèðîâêà)
Ðèñ. 11. Ôîêóñèðóþùèé (à) è äåôîêóñèðóþùèé (á) ðåæèìû ðàáîòû ÌË íà îñíîâå Ñ*ÆÊ. 1 – íàïðàâëåíèå íàòèðàíèÿ, 2 – ïîëÿðèçîâàííûé ñâåò, 3 – íàïðàâëåíèå ýëåêòðè÷åñêîãî ïîëÿ, 4 – îðèåíòèðóþùèé ñëîé, 5 – ñëîé Ñ*ÆÊ, 6 – ôîòîïîëèìåð, 7 – ïðîçðà÷íûé ýëåêòðîä, 8 – ñòåêëî.
ìîëåêóë îòíîñèòåëüíî îñè ñïèðàëè. Ýëåêòðîîïòè÷åñêèé îòêëèê çàâèñèò îò ïîëÿðíîñòè ïðèëîæåííîãî U, ïðè÷åì âðåìÿ îòêëèêà ñóùåñòâåííî ìåíüøå, ÷åì äëÿ íåïîëÿðíûõ ÆÊ.  ðàáîòå [45] äëÿ ñîçäàíèÿ ìàññèâà Ñ*ÆÊ-ÌË íà îäíîé èç ïîâåðõíîñòåé ôîðìèðóåòñÿ ïåðèîäè÷åñêàÿ ñòðóêòóðà èç îòâåðñòèé ãëóáèíîé 9 ìêì è ðàäèóñîì 200 ìêì. Äëÿ ýòîãî íà ïîâåðõíîñòü íàíîñèòñÿ ôîòîïîëèìåð è ÷åðåç ôîòîìàñêó ïîäâåðãàåòñÿ âîçäåéñòâèþ óëüòðàôèîëåòîâîãî (ÓÔ) èçëó÷åíèÿ. Ñ*ÆÊ ââåäåí â ÿ÷åéêó êàïèëëÿðíûì ìåòîäîì è èìååò ïëàíàðíóþ îðèåíòàöèþ. Ïðèíöèï ðàáîòû ÌË ïîêàçàí íà ðèñ. 10.  çàâèñèìîñòè îò íàïðàâëåíèÿ Å-ïîëÿ ðåàëèçóåòñÿ êàê ôîêóñèðóþùèé (ðèñ. 10à), òàê è äåôîêóñèðóþùèé (ðèñ. 10á) ðåæèìû. Èññëåäîâàíà çàâèñèìîñòü âðåìåíè îòêëèêà îò âåëè÷èíû Å-ïîëÿ. Âðåìÿ ïåðåêëþ÷åíèÿ èç îäíîãî ðåæèìà â äðóãîé ñîñòàâëÿåò 100– 200 ìêñ. Ñ óâåëè÷åíèåì íàïðÿæåííîñòè ïîëÿ âðåìÿ îòêëèêà óìåíüøàåòñÿ.
Îïòè÷åñêèå õàðàêòåðèñòèêè àäàïòèâíûõ ëèíç
Ìîäàëüíûå ëèíçû
 ðàçäåëå “Ýëåêòðè÷åñêîå ïîëå â àäàïòèâíûõ ìîäàëüíûõ ÆÊ-ëèíçàõ” îïèñàí ñïîñîá ôîðìèðîâàíèÿ Å-ïîëÿ è ïðèâåäåíû óðàâíåíèÿ, îïèñûâàþ-
42 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ùèå ðàñïðåäåëåíèå íàïðÿæåíèÿ ïî àïåðòóðå ëèíçû. ×èñëåííûé ðàñ÷åò ïîçâîëÿåò íàõîäèòü îïòèìàëüíûå çíà÷åíèÿ ÷àñòîòû è àìïëèòóäû óïðàâëÿþùåãî U äëÿ ïîëó÷åíèÿ ïàðàáîëè÷åñêîé çàâèñèìîñòè ôàçîâîé çàäåðæêè ïî àïåðòóðå ëèíçû [15–17, 46–50]. Îäíàêî äàæå ïðè èçâåñòíûõ ïàðàìåòðàõ ÆÊ è ìîäàëüíûõ (ÀË) âû÷èñëåííûå îïòèìàëüíûå ñîîòíîøåíèÿ àìïëèòóäà-÷àñòîòà íå âñåãäà ïðèåìëåìû äëÿ ðåàëüíîé ëèíçû. Ýòî ñâÿçàíî ñ òåõíîëîãè÷åñêèìè îñîáåííîñòÿìè èõ ñáîðêè: êàëèáðîâî÷íûå ïàðàìåòðû äëÿ êàæäîé ëèíçû èíäèâèäóàëüíû. Îñíîâíûå ïàðàìåòðû ýêñïåðèìåíòàëüíûõ îáðàçöîâ ÌÀË ñëåäóþùèå: ôîêóñíûå ðàññòîÿíèÿ ñôåðè÷åñêèõ è öèëèíäðè÷åñêèõ ëèíç èçìåíÿëèñü îò 0,5 ì äî áåñêîíå÷íîñòè; äèàìåòð àïåðòóðû ñôåðè÷åñêîé ëèíçû ñîñòàâëÿë 5 ìì, ðàçìåðû àïåðòóðû öèëèíäðè÷åñêîé ëèíçû áûëè ðàâíû 5×15 ìì. Èñïîëüçîâàëñÿ ïëàíàðíî îðèåíòèðîâàííûé íåìàòèê ôèðìû “Merck” c Δn = 0,26. Âûñîêîîìíûé ýëåêòðîä áûë ñîçäàí íàïûëåíèåì ïðîçðà÷íîãî ðåçèñòèâíîãî ïîêðûòèÿ ñ ñîïðîòèâëåíèåì îêîëî 9 ÌÎì/ . Óïðàâëÿþùåå íàïðÿæåíèå íå ïðåâûøàëî 10 Â, ÷àñòîòà – 17 êÃö.
 ðàáîòàõ [18, 49, 51] ñîîáùàåòñÿ îá ÀË ñ îïòè÷åñêèì óïðàâëåíèåì. Îíè ñî÷åòàþò â ñåáå âñå ïðåèìóùåñòâà ýëåêòðè÷åñêè óïðàâëÿåìûõ àäàïòèâíûõ ëèíç, íî èìåþò äîïîëíèòåëüíóþ îñîáåííîñòü – çàâèñèìîñòü ôîêóñíîãî ðàññòîÿíèÿ îò èíòåíñèâíîñòè ïàäàþùåãî íà ëèíçó èçëó÷åíèÿ. Îíè ïðåäñòàâëÿþò ñîáîé ìíîãîñëîéíóþ ñòðóêòóðó. Âíåøíèìè ñëîÿìè ÿâëÿþòñÿ ñòåêëÿííûå ïîäëîæêè ñ íàíåñåííûìè íà íèõ ýëåêòðîäàìè. Íà îäíîé èç íèõ ýëåêòðîä èìååò êðóãëîå îòâåðñòèå äëÿ ñëó÷àÿ ñôåðè÷åñêîé ëèíçû èëè ïðåäñòàâëÿåò ñîáîé äâà ïîëîñêîâûõ êîíòàêòà äëÿ öèëèíäðè÷åñêîé ëèíçû. Îáëàñòü áåç ýëåêòðîäîâ èãðàåò ðîëü àïåðòóðû ëèíçû. Íà ýòó ïîäëîæêó íàíîñèòñÿ ñëîé ôîòî÷óâñòâèòåëüíîãî ïîëóïðîâîäíèêà. Ïîâåðõíîñòíîå ñîïðîòèâëåíèå ýòîãî ñëîÿ ìíîãî áîëüøå ñîïðîòèâëåíèÿ ñïëîøíîãî íèçêîîìíîãî ýëåêòðîäà ïðè ëþáîé èíòåíñèâíîñòè ïàäàþùåãî èçëó÷åíèÿ. Èñïîëüçóåòñÿ ïëàíàðíî îðèåíòèðîâàííûé íåìàòèê. Êîíñòðóêöèÿ ïîçâîëÿåò ñîçäàâàòü â îáëàñòè àïåðòóðû åìêîñòíî-ðåçèñòèâíûé äåëèòåëü U. Óïðàâëÿòü â òàêîé ñèñòåìå ðàñïðåäåëåíèåì U ìîæíî íå òîëüêî ñ ïîìîùüþ àìïëèòóäû è ÷àñòîòû ïðèëîæåííîãî U, íî è èçìåíåíèåì èíòåíñèâíîñòè èçëó÷åíèÿ. Òåîðåòè÷åñêèå è ýêñïåðèìåíòàëüíûå èññëåäîâàíèÿ ïîêàçàëè, ÷òî ïðîôèëü ôàçîâîé çàäåðæêè äëÿ ïó÷êà ñâåòà ñ îäíîðîäíûì è ãàóññîâûì ðàñïðåäåëåíèåì èíòåíñèâíîñòè áëèçîê ê ïàðàáîëè÷åñêîìó. Ôîêóñíîå ðàññòîÿíèå ìîíîòîííî âîçðàñòàåò ñ óâåëè÷åíèåì ìîùíîñòè èçëó÷åíèÿ. Ïðèâåäåíû ïðèìåðû ïðîñòûõ àäàïòèâíûõ ñèñòåì ýòîãî òèïà.
Ëèíçû íà îñíîâå ñòðóêòóð ïîëèìåð-äèñïåðãèðîâàííûõ ÆÊ
 ýëåêòðè÷åñêè óïðàâëÿåìûõ ëèíçàõ íà îñíîâå ïîëèìåð-äèñïåðãèðîâàííûõ ÆÊ (ÏÄÆÊ) ãðàäèåíò ïîêàçàòåëÿ ïðåëîìëåíèÿ ñîçäàåòñÿ ïðè èçìåíåíèè ðàçìåðîâ ìèêðîêàïåëü [52, 53]. Äëÿ ýòîãî íà ñìåñü ÆÊ-ìîíîìåð âîçäåéñòâóþò ÓÔ èçëó÷åíèåì ÷åðåç ôîòîìàñêó. Âîçäåéñòâèå ñëàáîãî ÓÔ èçëó÷åíèÿ äàåò êàïëè áîëåå êðóïíîãî ðàçìåðà è íàîáîðîò – ÷åì ñèëüíåå îáëó÷åíèå, òåì ìåíüøå ðàçìåð êàïåëü. Îáëàñòè ñ êàïëÿìè ìåíüøåãî ðàçìåðà èìåþò áîëüøóþ êîíöåíòðàöèþ ïîëèìåðà, è ïîòîìó ïîêàçàòåëü ïðåëîìëåíèÿ ýòîé îáëàñòè áóäåò ìåíüøå, ÷åì îáëàñòü ñ áîëüøèìè êàïëÿìè. Ïðè âîçäåéñòâèè Å-ïîëÿ ïåðåîðèåíòàöèÿ ìîëåêóë íåìàòèêà íà÷èíàåòñÿ ïðè êðèòè÷åñêîì íàïðÿæåíèè Ud. Çàâèñèìîñòü Ud îò ðàçìåðà êàïëè (D) âûãëÿäèò ñëåäóþùèì îáðàçîì: U = C/ D, ãäå C – const. ×åì áîëüøå ðàçìåð êàïëè, òåì ìåíüøå óïðàâëÿþùåå U. Äëÿ ñîçäàíèÿ ñîáèðàþùåé è ðàññåèâàþùåé ëèíç èñïîëüçóþòñÿ ôîòîìàñêè ñ êðóãîâûì ãðàäèåíòîì ïðîïóñêàíèÿ. Íà ðèñ. 11 ïîêàçàíû ôîòîìàñêè è ïðîôèëè ïîêàçàòåëåé ïðåëîìëåíèÿ äëÿ ñîáèðàþùåé (à) è ðàññåèâàþùåé ëèíç. Íåäîñòàòêîì ÏÄÆÊ-ëèíç – âûñîêîå óïðàâëÿþùåå U (áîëåå 100 Â). Äëÿ óìåíüøåíèÿ óïðàâëÿþùåãî U àâòîðû ïðåäëîæèëè èñïîëüçîâàòü ÆÊ ñ ïîëèìåðíîé ñåòêîé ñ ãðàäèåíòîì ïðîôèëÿ ïîêàçàòåëÿ ïðåëîìëåíèÿ. Êîíöåíòðàöèÿ ÆÊ â ýòîé ñìåñè – 95%, ïîýòîìó U ñíèæàåòñÿ äî 10 Â. Ôîêóñíîå ðàññòîÿíèå ýòîé ëèíçû ïðèìåðíî 310 ì, è äëÿ ðàáîòû ëèíçà äîëæíà èñïîëüçîâàòü ñêðåùåííûå ïîëÿðîèäû. Ëèíçà ñ òàêèì áîëüøèì ôîêóñíûì ðàññòîÿíèåì
V=0
V=0
V=∞
V=∞
n
V=0 V1
V=∞
n V=∞
V=0 V1
xx
(à) (á)
Ðèñ. 11. Àäàïòèâíûå ëèíçû íà ÏÄÆÊ äëÿ ôîêóñèðóþùåãî (à) è ðàñôîêóñèðóþùåãî (á) ðåæèìîâ.
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
43
ïðåäñòàâëÿåò èíòåðåñ äëÿ öåëåé àñòðîíîìèè è ñïóòíèêîâîé àïïàðàòóðû. Äëÿ ðàáîòû â íåïîëÿðèçîâàííîì ñâåòå ïðåäëîæåíî èñïîëüçîâàòü äâà îðòîãîíàëüíî îðèåíòèðîâàííûõ ãîìîãåííûõ ñëîÿ ÆÊ [53].
 ðàáîòàõ [54, 55] îïèñàíû ëèíçû, â êîòîðûõ ôîêóñèðóþùèå ñâîéñòâà çàäàþòñÿ èñõîäíûì ïðîôèëåì ïîâåðõíîñòè ïîäëîæêè, âûïîëíåííûì â âèäå ñôåðè÷åñêèõ óãëóáëåíèé äèàìåòðîì 450–500 ìêì. Íàíåñåííûå íà íèõ ýëåêòðîäû ôîðìèðóþò íåîäíîðîäíûå Å-ïîëÿ. Ïðè óâåëè÷åíèè U äî 200  ôîêóñíîå ðàññòîÿíèå èçìåíÿåòñÿ îò 3,3 äî 3,5 ñì, âðåìÿ ôîêóñèðîâêè – 200 ìêñ [54].
 ðàáîòå [56] ïðåäëîæåíû ÀË, èñïîëüçóþùèå íîâûé ïðèíöèï ôîðìèðîâàíèÿ ãðàäèåíòà ïîêàçàòåëÿ ïðåëîìëåíèÿ â êîìïîçèöèè ÆÊ/ìîíîìåð.  îòñóòñòâèå Å-ïîëÿ ÆÊ è ìîíîìåð â ñìåñè ðàñïðåäåëåíû ðàâíîìåðíî. Ïðè ïðèëîæåíèè íåîäíîðîäíîãî Å-ïîëÿ ìîëåêóëû ÆÊ ïåðåìåùàþòñÿ â îáëàñòü áîëåå ñèëüíîãî ïîëÿ. Ñ äðóãîé ñòîðîíû, íàáëþäàåòñÿ èõ äèôôóçèÿ â îáðàòíîì íàïðàâëåíèè, âûçâàííàÿ ðàçëè÷èåì êîíöåíòðàöèè.  èòîãå âîçíèêàåò ãðàäèåíò êîíöåíòðàöèè ÆÊ, ÷òî ïðèâîäèò ê ãðàäèåíòó ïîêàçàòåëÿ ïðåëîìëåíèÿ. Èçìåíåíèå âåëè÷èíû óïðàâëÿþùåãî íàïðÿæåíèÿ ïîçâîëÿåò èçìåíÿòü ðàñïðåäåëåíèå ïîêàçàòåëÿ ïðåëîìëåíèÿ è, ñëåäîâàòåëüíî, ôîêóñíîãî ðàññòîÿíèÿ ëèíç. Àâòîðû ñ÷èòàþò äîñòîèíñòâîì òàêèõ ÀË ìàëûå âåëè÷èíû àñòèãìàòèçìà è ñâåòîðàññåÿíèÿ. Íåäîñòàòêàìè ÿâëÿþòñÿ âûñîêèå âåëè÷èíû óïðàâëÿþùèõ íàïðÿæåíèé (äî 180 Â) è äëèòåëüíûå âðåìåíà ôîêóñèðîâêè (3 ìèí ïðè ñâåòîâîì äèàìåòðå 9 ìì, 1 ñ ïðè äèàìåòðå 50 ìêì). Äàííûé ïðèíöèï ðåêîìåíäîâàí äëÿ ñîçäàíèÿ îïòè÷åñêèõ ìèêðîýëåìåíòîâ: ìèêðîëèíç, ìèêðîïðèçì, ëèíç Ôðåíåëÿ.
Èíòåðåñíî ïðåäëîæåíèå èñïîëüçîâàòü ÀË äëÿ ôîðìèðîâàíèÿ ñòðàíèö òåêñòà â îïòè÷åñêèõ ñèñòåìàõ ïàìÿòè [57].
Ïðèìåíåíèå àäàïòèâíûõ ëèíç â îïòè÷åñêèõ ñèñòåìàõ
Óñòðîéñòâî çàïèñè èíôîðìàöèè íà îïòè÷åñêèå äèñêè
Áèôîêàëüíûå ÀË (ñ äâóìÿ ôèêñèðîâàííûìè çíà÷åíèÿìè ôîêóñíîãî ðàññòîÿíèÿ) èñïîëüçîâàíû äëÿ çàïèñè èíôîðìàöèè íà îïòè÷åñêèå äèñêè [58]. Íîâûå ðàçðàáîòêè íàïðàâëåíû íà óâåëè÷åíèå îáúåìà ïàìÿòè íîñèòåëåé. Äëÿ ýòîãî â òîëùå äèñêà ïîìåùåí äîïîëíèòåëüíûé ðåãèñòðèðóþùèé ñëîé. Äëÿ çàïèñè è ñ÷èòûâàíèÿ èíôîðìàöèè ïðè èñïîëüçîâàíèè äâóõ ñëîåâ óäîáíà áèôîêàëüíàÿ îïòè÷åñêàÿ ñèñòåìà. Çàäà÷à ðåøåíà ñ ïîìîùüþ ÀË, âûïîëíåííîé â âèäå òâèñòîâîé ÆÊ ÿ÷åéêè (ÒÆÊß) è îñóùåñòâ-
L1 L2 1 2 P 3 S 4 λ/4 RHC 5
SP S OFF
LHC 6
L1 L2 1 2 P 3 P 4 λ/4 LHC 5
SS S ON
RHC 6
Ðèñ. 12. Ñõåìà áèôîêàëüíîé ÀË, âûïîëíåííîé â âèäå ÒÆÊß. 1 – èçëó÷åíèå ëàçåðà, 2 – äåëèòåëü ïó÷êà, 3 – ÒÆÊß, 4 – ÀË, 5 – îáúåêòèâ, 6 – äèñê. S, P – îðòîãîíàëüíûå íàïðàâëåíèÿ ïîëÿðèçàöèè ñâåòà; OFF, ON – ðåæèìû “âûêëþ÷åíî” è “âêëþ÷åíî”; LHC, RHC – ëåâî- è ïðàâîöèðêóëÿðíûé ñâåò; L1, L2 – ðåãèñòðèðóþùèå ñëîè â îáúåìå äèñêà.
ëÿþùåé ïåðåêëþ÷åíèå ìåæäó ðàçëè÷íûìè ìîäàìè ïîëÿðèçàöèè (ðèñ. 12).  ïîëîæåíèè “âûêëþ÷åíî” ÒÆÊß çà ñ÷åò çàêðó÷åííîé ñòðóêòóðû ÆÊ ïîâîðà÷èâàåò ëèíåéíî ïîëÿðèçîâàííûé ñâåò íà 90°.  ðåçóëüòàòå ñâåò âçàèìîäåéñòâóåò ñ ÆÊ ñ ïîêàçàòåëåì ïðåëîìëåíèÿ nî è ôîêóñèðóåòñÿ â òî÷êå íà áîëüøîì ôîêóñíîì ðàññòîÿíèè (âåðõíÿÿ ÷àñòü ðèñ. 12).  ïîëîæåíèè “âêëþ÷åíî” îïòè÷åñêàÿ àêòèâíîñòü ñëîÿ ÆÊ èñ÷åçàåò, è ïëîñêîñòü ïîëÿðèçàöèè ñâåòà íå èçìåíÿåòñÿ ïðè åãî ïðîõîæäåíèè ÷åðåç ñëîé ÆÊ ñ ïîêàçàòåëåì ïðåëîìëåíèÿ ne. Ïðè ýòîì ñâåò ôîêóñèðóåòñÿ â òî÷êå ñ ìàëûì ôîêóñíûì ðàññòîÿíèåì (íèæíÿÿ ÷àñòü ðèñ. 12), è ÒÆÊß ðàáîòàåò êàê áèôîêàëüíàÿ ïåðåêëþ÷àåìàÿ ëèíçà.
Ôèðìîé Philips (Íèäåðëàíäû) áûëè èçãîòîâëåíû îáðàçöû áèôîêàëüíûõ ÀË [58]. Ìàòåðèàëîì ñëóæèë ïîëèìåðèçóþùèéñÿ ÆÊ ôèðìû “Merck” íà îñíîâå öèàíîáèôåíèëîâ ñ äîáàâêîé, óâåëè÷èâàþùåé äèýëåêòðè÷åñêóþ àíèçîòðîïèþ. ÀË ñôåðè÷åñêîé êîíôèãóðàöèè ñ ðàäèóñîì 49 ìì è äèàìåòðîì 3,44 ìì èçãîòîâëÿëèñü ôîðìîâêîé ñ ïîñëåäóþùåé ôîòîïîëèìåðèçàöèåé. Ðàçíèöà â ôîêàëüíîì ðàññòîÿíèè äëÿ äâóõ ïîëÿðèçàöèé ñîñòàâèëà 19 ìì.
Îïòîâîëîêîííûé ïåðåêëþ÷àòåëü
Ñåìåéñòâî ÌË ïðåäëîæåíî èñïîëüçîâàòü â êà÷åñòâå îïòè÷åñêèõ ïåðåêëþ÷àòåëåé äëÿ âîëîêîííîîïòè÷åñêèõ ýëåìåíòîâ [22, 59]. Îñîáåííîñòüþ ýòî-
44 “Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
ãî íàïðàâëåíèÿ ÿâëÿåòñÿ ïðèìåíåíèå íå ñòîëüêî ôîêóñèðóþùèõ ñâîéñòâ ÌË, ñêîëüêî ôîðìèðîâàíèå àïåðòóðû âûõîäíîãî ñâåòîâîãî ñèãíàëà, êîòîðóþ ñîãëàñóþò ñ âõîäíîé àïåðòóðîé îïòè÷åñêîãî âîëîêíà. Ñëîé ÆÊ â ÌË èìåë òîëùèíó 50 ìêì è ðàçìåùàëñÿ íà ðàññòîÿíèè 7 ìì îò òîðöà îïòè÷åñêîãî âîëîêíà (NA = 0,1) ñ ñåðäöåâèíîé äèàìåòðîì 10 ìêì. Ñ ïîìîùüþ ÏÇÑ-ìàòðèöû èçìåðÿëîñü èçìåíåíèå èíòåíñèâíîñòè ïðîõîäÿùåãî ÷åðåç ÌË è îïòè÷åñêîå âîëîêíî ñâåòîâîãî ñèãíàëà îò He–Neëàçåðà ñ äèàìåòðîì ïó÷êà 2 ìì ïðè ïîäà÷å U îò 0 äî 4 Â. Èññëåäîâàëèñü èçìåíåíèÿ èíòåíñèâíîñòè èçëó÷åíèÿ íà âûõîäå îïòè÷åñêîãî âîëîêíà ïðè èçìåíåíèè U, âðåìåíà îòêëèêà ïðè ðàçëè÷íûõ óñëîâèÿõ îðèåíòàöèè ÆÊ è çíà÷åíèÿõ äèýëåêòðè÷åñêîé àíèçîòðîïèè. Ýêñïåðèìåíòû ïîêàçàëè, ÷òî èíòåíñèâíîñòü èçëó÷åíèÿ íà âûõîäå îïòè÷åñêîãî âîëîêíà âîçðîñëà ïðè îïòèìàëüíîé ôîêóñèðîâêå â 210 ðàç ïðè U = 1 Â. Âðåìÿ îòêëèêà ïðè äâóõ÷àñòîòíîì ðåæèìå óïðàâëåíèÿ ÌË ñîñòàâèëî 5 ñ.
 ðàáîòàõ [60, 61] ÌË èñïîëüçîâàíà äëÿ óïðàâëåíèÿ ñâåòîâûì ïîòîêîì â îäíîìîäîâîì îïòè÷åñêîì âîëîêíå äëÿ ýíäîñêîïîâ. Áëàãîäàðÿ ôîêóñèðóþùåìó äåéñòâèþ ÌË èíòåíñèâíîñòü ïðîõîäÿùåãî ñèãíàëà (λ = 458 íì) ÷åðåç îïòè÷åñêîå âîëîêíî ñ äèàìåòðîì æèëû 3,2 ìêì óâåëè÷èëîñü áîëåå ÷åì â 1100 ðàç ïðè U = 1  è ðàññòîÿíèè äî îïòè÷åñêîãî âîëîêíà 1 ñì. Ïðè òîëùèíå ñëîÿ ÆÊ 27 ìêì âðåìÿ îòêëèêà ÌË ñîñòàâèëî íåñêîëüêî äåñÿòêîâ ñåêóíä. Äëÿ øèðîêîãî ïðèìåíåíèÿ íåîáõîäèìî ïîâûøåíèå áûñòðîäåéñòâèÿ, ÷òî ïîçâîëÿþò Ñ*ÆÊ.
Ñèñòåìû îïòè÷åñêîãî îãðàíè÷åíèÿ
Ìàññèâ íåñèììåòðè÷íûõ ÌË áûë èñïîëüçîâàí äëÿ îãðàíè÷åíèÿ èíòåíñèâíîñòè ñâåòîâîãî ïîòîêà, ïðîõîäÿùåãî ÷åðåç êþâåòó, çàïîëíåííóþ íåëèíåéíî ïîãëîùàþùåé ñðåäîé – ðàñòâîðîì ôóëëåðåíà Ñ70 â òîëóîëå ïðè êîíöåíòðàöèè 2,3×10–3 Ì [62, 63]. Òîëùèíà êþâåòû ïîäáèðàëàñü òàê, ÷òîáû ïîãëîùàþùàÿ ñðåäà îêàçàëàñü â ôîêàëüíîé ïëîñêîñòè ÌË. Èñòî÷íèêîì èçëó÷åíèÿ ñëóæèë ìíîãîèìïóëüñíûé Nd:YAG ëàçåð (λ = 532 íì) ñ äëèòåëüíîñòüþ èìïóëüñà 1 íñ. Äëÿ ðåãèñòðàöèè îñëàáëåíèÿ èíòåíñèâíîñòè ñâåòîâîãî ïîòîêà èñïîëüçîâàëñÿ êàëèáðîâàííûé äèîä ÔÄ-23 è êàëîðèìåòð ÈÝÊ-1. Èçìåðåíèÿ ïðîèçâîäèëèñü ïðè ïàðàëëåëüíîé è ïåðïåíäèêóëÿðíîé îðèåíòàöèè ïîëÿðèçàöèè èçëó÷åíèÿ ïî îòíîøåíèþ ê îðèåíòàöèè äèðåêòîðà ÆÊ. Ðåçóëüòàòû, ïîëó÷åííûå äëÿ èçëó÷åíèÿ âûøå ïîðîãà â 3 ìÄæ ñ ïàðàëëåëüíîé îðèåíòàöèåé ïîëÿðèçàöèè, ïîäòâåðäèëè âîçìîæíîñòü èñïîëüçîâàíèÿ ÌË äëÿ îïòè÷åñêîãî îãðàíè÷åíèÿ.
Äåôëåêòîð íà îñíîâå ÀË ñ ðàçäåëåííûìè ýëåêòðîäàìè Îñîáåííîñòü êîíñòðóêöèè òàêèõ ÀË ñîñòîèò â òîì, ÷òî ñèñòåìà ñèììåòðè÷íîé ëèíçû èìååò íà âåðõíåé è íèæíåé ïîäëîæêå ïî äâà íåçàâèñèìî óïðàâëÿåìûõ ðàçäåëåííûõ ýëåêòðîäà, ïàðàëëåëüíûõ äðóã äðóãó [32, 37]. Èññëåäîâàíèÿ ïðîâîäèëèñü ñ ÀË, ñîäåðæàùåé îòâåðñòèÿ äèàìåòðîì 300 ìêì, ïðè òîëùèíå ñëîÿ ÆÊ 40 ìêì. Èçìåðèòåëüíàÿ óñòàíîâêà ñîäåðæàëà He–Neëàçåð è CCD-êàìåðó, ñâÿçàííóþ ñ ïîëÿðèçàöèîííûì ìèêðîñêîïîì. Ïðè ïîäà÷å U = 16  íà îäíó ïàðó ýëåêòðîäîâ è 14,5  íà äðóãóþ ïàðó íàáëþäàëñÿ ñäâèã ñôîêóñèðîâàííîãî ïó÷êà íà 2,7 ìêì â ïëîñêîñòè ôîêóñèðîâêè. Ýòîò ýôôåêò ìîæíî èñïîëüçîâàòü â îïòè÷åñêèõ ñèñòåìàõ ñâÿçè.
Àäàïòèâíàÿ êîíòàêòíàÿ ëèíçà Ïðè èñïîëüçîâàíèè î÷êîâ ðàçðåøàþùóþ ñïîñîáíîñòü ìîæíî ïîâûñèòü óñòðàíåíèåì àáåððàöèé ëèíç. Êîìïåíñàöèÿ àáåððàöèé âûñøåãî ïîðÿäêà âîçìîæíà, åñëè êîððåêòèðóþùèé ýëåìåíò îïòè÷åñêè ñîïðÿæåí ñ î÷êîâîé ëèíçîé.  ðàáîòàõ [64–68] ïðåäëîæåíî èñïîëüçîâàòü ÆÊ-êîððåêòîð â âèäå àäàïòèâíîé êîíòàêòíîé ëèíçû, èìïëàíòèðîâàííîé â ãëàç. Ýòî ðåøàåò ïðîáëåìó îïòè÷åñêîãî ñîïðÿæåíèÿ è ïîçâîëÿåò êîìïåíñèðîâàòü àáåððàöèè íåïîñðåäñòâåííî â ãëàçó. Ðàññìîòðåíû èíäóêòèâíûé (ðèñ. 13) è ýëåêòðîñòàòè÷åñêèé âàðèàíòû áåñïðîâîëî÷íîãî óïðàâëåíèÿ èìïëàíòàíòîì. Ïðè èñïîëüçîâàíèè êîíòàêòíîé ëèíçû äèàìåòðîì 5 ìì ïîêàçàíà âîçìîæíîñòü ýëåêòðîñòàòè÷åñêîãî óïðàâëåíèÿ ïðè èçìåíåíèè ãëóáèíû àêêîìîäàöèè îò áåñêîíå÷íîñòè äî 30 ñì, ÷òî îòêðûâàåò ïåðñïåêòèâû äèíàìè÷åñêîé êîððåêöèè àáåððàöèé âûñøåãî ïîðÿäêà ÷åëîâå÷åñêîãî ãëàçà.
ÆÊ-ëèíçû äëÿ áèôîêàëüíûõ î÷êîâ Åñëè àäàïòèâíàÿ êîíòàêòíàÿ ëèíçà íàõîäèòñÿ íà ñòàäèè ðàçðàáîòîê, òî ÆÊË äëÿ áèôîêàëüíûõ î÷êîâ – íà ñòàäèè ïðîèçâîäñòâà ôèðìîé Pixel Optics
Ðèñ. 13. Àäàïòèâíàÿ ÆÊ-ëèíçà ñ áåñïðîâîëî÷íûì óïðàâëåíèåì.
“Îïòè÷åñêèé æóðíàë”, òîì 75, ¹ 9, 2008
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Ðèñ. 14. Ïðîòîòèï áèôîêàëüíûõ î÷êîâ ðàçðàáîòêè ôèðìû Pixel Optic.
Ñ*ÆÊ ïîçâîëèëî ïîëó÷èòü áûñòðîäåéñòâèå ïîðÿäêà 100–200 ìêñ (ïðè êîìíàòíîé òåìïåðàòóðå). Ïåðñïåêòèâíûì äëÿ ïîâûøåíèÿ îïòè÷åñêîãî êà÷åñòâà ÀË ÿâëÿåòñÿ ïðèìåíåíèÿ ñòðóêòóð íà îñíîâå ÆÊ, äèñïåðãèðîâàííûõ â ïîëèìåðíóþ ìàòðèöó.
Ñëåäóåò ïðèçíàòü, ÷òî ìíîãèå ýêñïëóàòàöèîííûå ïàðàìåòðû, òàêèå êàê îòíîñèòåëüíî íèçêîå áûñòðîäåéñòâèå, áîëüøîå ñâåòîðàññåÿíèå è íåâûñîêîå îïòè÷åñêîå êà÷åñòâî, åùå íóæäàþòñÿ â óëó÷øåíèè. Òåì íå ìåíåå, äîñòèãíóòûå ýêñïëóàòàöèîííûå ñâîéñòâà ÀË îòêðûâàþò èíòåðåñíûå âîçìîæíîñòè èõ ïðèìåíåíèÿ â óñòðîéñòâàõ ôîòîíèêè: èíôîðìàöèîííûõ äèñïëåÿõ, îïòè÷åñêèõ ìîäóëÿòîðàõ, ñèñòåìàõ îïòè÷åñêîé ôîêóñèðîâêè, óñòðîéñòâàõ êîððåêöèè çðåíèÿ, îïòè÷åñêèõ ïèíöåòàõ è ëîâóøêàõ.
(ðèñ. 14) [69, 70]. Î÷êè ïðåäíàçíà÷åíû äëÿ êîìïåíñàöèè äàëüíîçîðêîñòè, îò êîòîðîé ñòðàäàåò 93% íàñåëåíèÿ ñòàðøå 45 ëåò. Ïðè îòñóòñòâèè íàïðÿæåíèÿ î÷êè èñïîëüçóþòñÿ äëÿ ðàññìàòðèâàíèÿ áëèçêî ðàñïîëîæåííûõ îáúåêòîâ, ïðè ïîäà÷å íàïðÿæåíèÿ – äëÿ íàáëþäåíèÿ óäàëåííûõ îáúåêòîâ. Äëÿ óïðàâëåíèÿ ñëîåì ÆÊ òîëùèíîé 5 ìêì ïðè äèñêðåòíîì èçìåíåíèè ôîêóñèðîâêè òðåáóåòñÿ íàïðÿæåíèå 1,8 Â.
ÀË ìîæíî èñïîëüçîâàòü è äëÿ èçìåíåíèÿ ïðåëîìëÿþùåé ñïîñîáíîñòè ãëàçà. Ë. Òèáîñ è À. Áðýäëè èç Êàëèôîðíèè ñîçäàëè ïðîñòðàíñòâåííûé ìîäóëÿòîð ñâåòà, ñîäåðæàùèé 127 ÆÊ-ÿ÷ååê è ðàñïîëîæåííûé âî âõîäíîì çðà÷êå ãëàçà. Ýòè ÿ÷åéêè ïîçâîëÿþò ïî ïðîãðàììå îñóùåñòâëÿòü èçìåíåíèÿ ïðåëîìëåíèÿ ïðèçìàòè÷åñêîãî (0,8 äèîïòð.), ñôåðè÷åñêîãî (1,5 äèîïòð.) õàðàêòåðà è àñòèãìàòèçìà â ñå÷åíèè çðà÷êà äèàìåòðîì 3 ìì. Ñóáäèñêðåòèçàöèÿ ìîæåò áûòü ôàêòîðîì, îãðàíè÷èâàþùèì äèàïàçîí èçìåíåíèÿ ïðåëîìëåíèÿ.
Ïðèìåíåíèå ÀË â îïòè÷åñêèõ ñèñòåìàõ íå îãðàíè÷èâàåòñÿ ïðèâåäåííûìè ïðèìåðàìè. Íîâûì ÿâëÿåòñÿ èõ èñïîëüçîâàíèå â êà÷åñòâå îïòè÷åñêèõ ïèíöåòîâ è ëîâóøåê ïðè ðàáîòå ñ ìàëûìè îáúåêòàìè â îáúåìíûõ ñðåäàõ [71].
Çàêëþ÷åíèå
 îáçîðå ïðîâåäåí àíàëèç òåíäåíöèé ðàçâèòèÿ àäàïòèâíûõ ëèíç íà ÆÊ: óâåëè÷åíèå àïåðòóðû, áûñòðîäåéñòâèÿ è óëó÷øåíèå êà÷åñòâà èçîáðàæåíèÿ. ÀË ïðåäñòàâëÿþò ñîáîé ïëîñêèå ýëåìåíòû áåç ïåðåìåùàþùèõñÿ äåòàëåé, ïîçâîëÿþùèå îñóùåñòâëÿòü èçìåíåíèå ôîêóñíîãî ðàññòîÿíèÿ â øèðîêèõ ïðåäåëàõ. Ðàçëè÷àþò ìèêðîëèíçû è ëèíçû ñ óâåëè÷åííîé àïåðòóðîé. Áîëüøèíñòâî ÀË ðàáîòàþò ïðè ìàëûõ óïðàâëÿþùèõ íàïðÿæåíèÿõ. Èñïîëüçîâàíèå
ËÈÒÅÐÀÒÓÐÀ
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