Controllable optical lens

Abstract

A controllable optical lens system, comprises a chamber housing first and second fluids, the interface between the fluids defining a lens surface. An electrode arrangement controls the shape of the lens surface and has first and second electrodes. A parameter is determined by the system dependent on the electrical resistance through at least one of the lens fluids between the first and second electrodes. Thus, the series resistance through a lens fluid is used as a measure of meniscus position.

1 . A controllable optical lens system, comprising:
 a chamber housing first ( 10 ) and second ( 12 ) fluids, the interface between the fluids defining a lens surface;   an electrode arrangement for electrically controlling the shape of the lens surface, the electrode arrangement comprising first ( 14 ) and second ( 16 ) electrodes; and   means ( 40 ,  42 ,  44 ,  46 ) for determining a parameter dependent on the electrical resistance (R EW ) through at least one of the lens fluids ( 10 ) between the first and second electrodes.   
     
     
         2 . A system as claimed in  claim 1 , wherein the means for determining is for determining an electrical resistance (R EW ) and capacitance (C EW ) between the first and second electrodes. 
     
     
         3 . A system as claimed in  claim 1 , wherein the means for determining comprises:
 an ac power source ( 40 );   means ( 42 , 44 ) for analysing the current supplied by the ac power source.   
     
     
         4 . A system as claimed in  claim 3 , wherein the means for determining further comprises a first resistor (R m ) in series between the power source and one of the first and second electrodes, and wherein the means ( 42 , 44 ) for analysing the current supplied by the ac power source analyses the voltage drop across the first resistor. 
     
     
         5 . A system as claimed in  claim 4 , wherein the means for analysing is for determining a time constant for the response of the system. 
     
     
         6 . A system as claimed in  claim 4 , further comprising a second series resistor (R s ) which is selectively switched into circuit with the first resistor (R m ). 
     
     
         7 . A system as claimed in  claim 6 , wherein the means for analysing is for determining first and second time constants for the response of the system with and without the second series resistor. 
     
     
         8 . A system as claimed in  claim 7 , wherein the time constants are obtained by a best fit analysis. 
     
     
         9 . A system as claimed in  claim 3 , wherein the ac power source signal used for determining is superposed onto the dc power source signal used for driving the lens. 
     
     
         10 . A system as claimed in  claim 1 , wherein the electrode arrangement comprises:
 a drive electrode arrangement comprising a base electrode ( 14 ) and a side wall electrode ( 16 ).   
     
     
         11 . A system as claimed in  claim 10 , wherein the side wall electrode ( 16 ) comprises an annular electrode which surrounds the chamber. 
     
     
         12 . A system as claimed in  claim 10 , wherein the area of overlap of one of the fluids ( 10 ) with respect to the side wall electrode ( 16 ) varies in dependence on the lens surface position, and the side wall electrode ( 16 ) is formed from a material having a higher resistance than said one of the fluids. 
     
     
         13 . A system as claimed in  claim 12 , wherein the side wall electrode ( 16 ) is formed from a non-metal. 
     
     
         14 . A system as claimed in  claim 1 , wherein the first liquid ( 10 ) comprises a polar or conductive liquid and the second liquid ( 12 ) comprises a nonconductive liquid. 
     
     
         15 . A method of sensing the lens position of a controllable optical lens, the lens comprising a chamber housing first and second liquids ( 10 , 12 ), the interface between the liquids defining a lens surface and an electrode arrangement ( 14 , 16 ) for electrically controlling the shape of the lens surface, the electrode arrangement comprising first and second electrodes ( 14 , 16 ), wherein the method comprises:
 determining a parameter dependent on the electrical resistance (R EW ) through at least one of the lens liquids between the first and second electrodes; and   using the parameter to determine the lens surface position.   
     
     
         16 . A method as claimed in  claim 15 , further comprising determining an electrical capacitance (C EW ) between the first and second electrodes. 
     
     
         17 . A method as claimed in  claim 15 , wherein determining a parameter comprises determining a charging time constant for the lens 
     
     
         18 . A method as claimed in  claim 17 , wherein determining a parameter comprises determining two charging time constants for the lens, one with and without an additional known resistance (R s ), and further determining the lens capacitance (C EW ) and resistance (R EW ) from the two time constant measurements. 
     
     
         19 . A method as claimed in  claim 17 , wherein determining a charging time constant comprises driving the lens with an AC voltage. 
     
     
         20 . A method as claimed in  claim 17 , wherein determining a charging time constant comprises driving the lens with the superposition of a DC voltage and a lower voltage square wave AC voltage. 
     
     
         21 . A method as claimed in  claim 17 , wherein determining a charging time constant comprises driving the lens with the superposition of a DC voltage and a lower voltage sinusoidal wave AC voltage and measuring the phase relation between the voltage and the induced current through the lens. 
     
     
         22 . A method as claimed in  claim 17 , wherein the time constant is obtained by a best fit analysis. 
     
     
         23 . A method as claimed in  claim 17 , wherein the time constant is obtained using a look up table.