Liquid Crystal - Meadowlark Optics
Contents
1. eb Cc 2 ae Switching Time 10 to 90 at 50 us a c 40 C ke th N 0 4 Transmitted Wavefront lt N 5 e Distortion at 632 8 nm j ao 2 0 2 Surface Quality 60 40 scratch and dig f keJ S Reflectance per surface lt 0 5 at normal incidence al 400 500 900 1100 1300 1500 Recommended Safe 1 W cm2 CW Time us Operating Limit 300 mJ cm2 10 ns visible Fig 4 21 Swift LC Response Time Plot Glass Thickness 0 48 0 52 inches ORDERING INFORMATION Polarization Direction Vertical on input face horizontal on output face Operating temperature 10 C to 60 C Clear Thickness Part Di D in Aperture CA romeren OLR i in t in Number 58 meadouslark optics www meadowlark com e 303 833 4333 e mlo meadowlark com Basic Liquid Crystal Controller Key Benefits e Convenient stand alone bench top operation e Versatile compatible with all standard Meadowlark Optics LC devices and other nematic liquid crystal devices with compatible listed specifications e System memory retains voltage and frequency settings at power down Bright green digital LED voltage and frequency readouts SMA and BNC outputs with no adapters required Voltage and frequency save and restore function Out of the box functionality Sets up in minutes Safe low voltage operation Fuse protected Intuitive operation Compact Easy to use ROHS and CE compliant Low DC bias protects liquid crystal Model D4010 com2. Variable retarder b Typical temporal response for half wave operation at 632 8 nm 21 C c Improved temporal response using Transient Nematic Effect Fig 4 7 Temporal response of LC Variable Retarder The applied voltage is a 2 kHz square wave Excessive DC voltage will damage the liquid crystal Retardance waves 10 15 Voltage volts rms Retardance waves 10 Voltage volts rms Fig 4 8 Liquid Crystal Variable Retarder performance versus applied voltage at 632 8 nm 21 C a without compensator and b with compensator mlo meadowlark com 303 833 4333 www meadowlark com Response Time Liquid Crystal Variable Retarder response time depends on several parameters including layer thickness viscosity temperature variations in drive voltage and surface treatment Liquid crystal response time is proportional to the square of the layer thickness and therefore the square of the total retardance Response time also depends upon direction of the retardance change If the retardance increases response time is determined solely by mechanical relaxation of the molecules If retardance decreases in value response time is much faster due to the increased electric field across the liquid crystal layer Typical response time for our standard visible Liquid Crystal Variable Retarder is shown in figure 4 7b It takes about 5 ms to switch from one half to zero waves low to high voltage
3. Dimensions L x W x H 9 50 x 6 25 x 1 50 in went is ADVANCED PACKAGE ONLY external modulation input 0 5 V sinusoidal triangle square sawtooth transient nematic effect Modulation Waveforms Temperature Control one channel Active heating passive only cooling to within 1 C of nominal set point Sync Output TTL 1 us pulse user specified phase Minimum System Requirements PC with Pentium II class processor 32 MB RAM CD ROM drive 20 MB hard drive space USB or RS232 COM Port Windows 98 ME 2000 XP Vista Use of LabVIEW Instrument Library requires LabVIEW version 6 1 or higher ORDERING INFORMATION SMA to SMB Cables SMA SMB Two year and three year extended warranty options available please contact your Meadowlark Optics sales engineer mlo meadowlark com 303 833 4333 www meadowlark com Basic package includes e D3040 Controller Unit e User Manual e USB and RS232 cables e Power supply and power cable e CellIDRIVE 3000 Basic Software e National Instruments LabVIEW virtual instruments driver Advanced package includes e D3050 Controller Unit with external input and sync output front panel connectors e User Manual e USB and RS232 cables e Temperature control cable e LC Controller interface cable e Power supply and power cable e Temperature monitoring and control e CellIDRIVE 3100 Advanced Software e National Instruments LabVIEW virtual instruments driver NOT
4. QO o p Controllers 60 Four Channel Digital Interface The Four Channel Digital Interface is designed for high precision computer control of up to four Meadowlark Optics nematic liquid crystal devices at one time and is available in either Basic or Advanced Package options The D3040 Basic comes with CellDRIVE 3000 Basic software to allow independent control of the amplitude of the 2 kHz square wave drive for four separate nematic liquid crystal cells meadowlark optics CELLDRIVE 3000 Basic QUAD CELL NEMATIC LC DIGITAL INTERFACE LUSA Manua Controler 1 interface Port Test Update Mode Exil Readout Voltage Set Voltage Voltage Update Update 1 000 2 500 O87 3 141 Fig 5 2 Basic D3040 operation enables computer control for up to four Liquid Crystal Variable Retarders meadowlark optics Key Benefits USB or RS232 interface C code examples including dll libraries Compact and simple to use Microsoft HyperTerminal configuration file included Independent control of voltage levels on four channels to 1 mV resolution e Includes National Instruments LabVIEW Virtual Instrument drivers to interface with custom software The D3050 Advanced Package includes all the functionality of the Basic Package plus the added features of the CellIDRIVE 3100 Advanced software and capability for temperature monitoring and control on one channel The Advanced Package allows the amplitude of
5. aB 2 gt m Ww San QO ke pn Liquid Crystal Controllers 52 Liquid Crystal Variable Attenuators A Liquid Crystal Variable Attenuator can be configured with high efficiency calcite or beamsplitting polarizers to maximize light transmittance and increase damage threshold With a linearly polarized input beam and a calcite polarizer transmittance values exceed 90 at most wavelengths Very high contrast ratios in excess of 5000 1 can be achieved with custom double attenuators In this design two Liquid Crystal Variable Retarders are combined with three polarizers Custom devices for near infrared applications utilizing appropriate dichroic polarizers can also be manufactured Please see the section on Polarizers for a selection of available polarizers Our Basic Controller and Four Channel Interface described on pages 59 61 offer the precision waveforms necessary to obtain accurate and repeatable intensity control for your application Contrast Ratio Wavelength nm Fig 4 14 Typical Contrast Ratio of a Liquid Crystal Variable Attenuator optimized at 550 nm meadowlark optics SPECIFICATIONS Retarder Material Nematic liquid crystal with Birefringent polymer Polarizer Material Dichroic polymer Substrate Material Optical quality synthetic fused silica Wavelength Range Visible Near Infared 1 Near Infared 2 450 700 nm 700 900 nm 900 1550 nm Contrast Ra
6. and about 20 ms to switch from zero to one half wave high to low voltage Response time improves by using custom materials with high birefringence and a thinner liquid crystal layer At higher temperature material viscosity decreases also contributing to a faster response For speed critical applications see page 56 for Swift LC devices Another technique involves the Transient Nematic Effect TNE to improve response times With this drive method a high voltage spike is applied to accelerate the molecular alignment parallel to the applied field Voltage is then reduced to achieve the desired retardance When switching from low to high retardance all voltage is momentarily removed to allow the liquid crystal molecules to undergo natural relaxation Response time achieved with the transient nematic effect is also shown in figure 4 7c Our Four Channel Digital Interface described on pages 60 61 conveniently provides the necessary TNE voltage profiles Our standard Liquid Crystal Variable Retarders provide a minimum retardance range of 30 nm to at least half wave at the specified wavelength With an attached compensator retardance is guaranteed to range from zero to at least half wave at the specified wavelength Custom retardance ranges up to a few waves and custom compensators are available Contact our Sales Department to discuss your requirements Each Liquid Crystal Variable Retarder is supplied with retardance versus voltage per
7. and or wavelength Ko Q La lt Wi w g D U SPECIFICATIONS Liquid crystal design space Switching Speed 50 us to several seconds 9 7 J 2 Wavelength Range 350 nm 2 2 microns S oO o lt fan or Extinction Ratio Up to 50 000 1 for linear gv O i ips O polarized monochromatic light a Clear Aperture 1 mm to 100 mm 1510 1520 1530 1540 1550 1560 15 0 1580 159 o Normally White o Normally Black Contrast Contrast Fig 4 4 Contrast ratio for a twisted nematic liquid crystal cell mlo meadowlark com e 303 833 4333 e www meadowlark com meadowlark optics 47 N amp so N lt S O a Mounting Hardware f Retarders 74 ab 2 gt aP m wn San QO aS ke pn Liquid Crystal Controllers 48 Liquid Crystal Variable Retarders These products all use nematic liquid crystal materials to electrically control polarization Meadowlark Optics standard liquid crystal products provide tunable retardation by changing the effective birefringence of the material with applied voltage thus altering the input polarized light to any chosen elliptical linear or circular polarization Our precision Liquid Crystal Variable Retarders require unique fabrication and assembly steps We construct these retarders using optically flat fused silica windows coated with our transparent conductive Indium Tin Oxide QTO Our ITO coating is specia
8. closed Transmitted Wavefront i lt h 2 Distortion at 632 8 nm Surface Quality 60 40 scratch and dig Reflectance per surface lt 0 5 at normal incidence Beam Deviation lt 5 arcmin Recommended Safe 1W 2 CW Operating Limit a Glass Thickness 0 48 0 52 inches Vertical on input face horizontal on output face 20 C to 80 C 0 C to 50 C Polarization Direction Storage temperature Operating temperature mlo meadowlark com 303 833 4333 www meadowlark com Key Benefits High Contrast No mechanical motion Computer control capability No vibration This liquid crystal shutter is a vibration free alternative to mechanical shutter that is especially convenient for use in polarized light beams The liquid crystal switches between a state that rotates the input polarization by 90 with no voltage applied and a state that makes no change in the input polarization with 8 to 10 volts applied The applied voltage is 2 kHz AC as supplied by our 4010 3040 or 3050 liquid crystal drivers The liquid crystal configuration is twisted nematic The shutter is supplied with integral dichroic visible polarizers that function over the wavelength range of 450 nm to 700 to provide an average contrast ratio of better than 1 000 1 over this wavelength range Shutters with larger aperture sizes and with wavelength coverage to 2 1 microns are available on a custom basis Please call with your special
9. k 0 275 8 32 TAP 8 32 TAP Model LVR 100 k t gt _ 0 500 p Mounting Hardware l Retarders Polarizers a Fig 4 9 Model LVR 100 dimensions Fig 4 10 Models LVR 200 and LVR 300 dimensions All dimensions in inches All dimensions in inches SPECIFICATIONS ORDERING INFORMATION Retarder Material Nematic liquid crystal Diameter Clear Thickness Part Number Aperture CA Substrate Material Optical quality synthetic D in lin t in f ili eaa Without Attached Compensator 30 nm to 2 Wavelength Range 450 1800 nm specify Retardance Range Without compensator 30 nm to A 2 74 aB 2 gt e3 m 74 n San QO aS o p T y D D custom ranges are available With Attached Compensator 0 nm to d 2 lt SS bistortion at 632 8 nm s LRC 100 Distortion at 632 8 nm SNA i i a m ozs irc 200 keJ S Surface Quality 40 20 scratch and dig 200 on oe ee at 100 tRc 300_ i a We offer standard liquid crystal variable retarders to cover Reflectance per surface lt 0 5 at normal incidence four spectral regions Temperature Range 0 C to 50 C IR2 900 1250nm IR 3 1200 1700 nm Recommended Safe 500 W cm CW Please specify spectral region when placing your order Operating Limit 300 mJ cm 10 ns visible For temperature control option append TSC to part number 50 meadowlark optics www meadowlark com e 303 833 4333 e mlo meadowlark com Liquid
10. never cease working on polarization solutions for our customers We hope the information below will provide our customers with new ideas that will challenge us to create new exciting solutions for polarization control Twisted Nematic Liquid Crystal Cell One is often only interested in producing two orthogonal linear polarization states of an optical system or in the case of a digital optical switch only two states are frequently required If you desire to switch the polarization state between only two angles for example 0 and 90 a twisted nematic device is an excellent solution A big advantage of the twisted nematic device over an LCVR is the simplicity of the driving scheme High voltage above 10 V gives 0 rotation and low voltage below 1 V gives 90 rotation so you need not concern yourself with exact voltages or tight tolerances Also the field of view is wide when compared to an LCVR because the cell is being used in a situation where the optical axis of the liquid crystal molecules is not at an arbitrary angle to the light but is either parallel or perpendicular to it meadowlark optics A twisted nematic liquid crystal cell is constructed in the same manner as a standard LCVR except the alignment of the liquid crystal molecules is twisted 90 As in an LCVR high voltage 10 V aligns the molecules with the field and removes the birefringence and therefore does not affect the light At low voltage however the t
11. surfaces for the liquid crystal material This allows for alignment surface effects throughout the bulk of the cell Figure 4 17 b The addition of a polymer stabilizing material in the bulk essentially decouples the cell gap from the switching speed The challenge to this type of device is now there are no means for uniform liquid crystal alignment in the bulk such that after infiltration of polymer material the liquid crystal is aligned in random fashion with no particular fast axis for functional retarder devices For liquid crystal alignment to occur Meadowlark Optics performs a mechanical shearing process on the devices that aligns the bulk liquid crystal material Figure 4 17 c Once this step is performed the cell is locked into place and sealed This assembly process ensures excellent uniformity in alignment of the liquid crystal molecules and gives a retardance uniformity across the clear aperture of less than 20nm Meadowlark Optics Swift liquid crystal technologies can be used throughout the visible and near infrared region While these devices like all liquid crystal devices are affected by temperature and wavelength changes they can be calibrated to accommodate those differences Each Swift liquid crystal variable retarder is supplied with retardance versus voltage performance data for your specified wavelength while our shutter devices are provided with temporal performance data A coaxial cable with mating connector
12. Crystal Variable Attenuators Linear Polarized Unpolarized Input Compensated Polarizer Liquid Crystal Entrance Variable Polarizer Retarder Fig 4 11 Standard Liquid Crystal Variable Attenuator design uses crossed linear polarizers 00 O ab T E 52 F EN a SE oe ow Q Voltage volts rms Fig 4 12 Normalized transmittance of Liquid Crystal Variable Attenuator with crossed linear polarizers at a single wavelength Key Benefits e High contrast ratio e Computer control capability e Continuous control of light intensity Meadowlark Optics Liquid Crystal LC Variable Attenuator offers real time continuous control of light intensity Our attenuator consists of an LC Variable Retarder with attached compensator operating between crossed linear polarizers With crossed polarizers light transmission is maximized by applying the correct voltage to achieve half wave retardance from the LC cell as shown in figure 4 11 Half wave operation rotates the incoming polarization direction by 90 so that light is passed by the second polarizer Minimum transmission is obtained with the retarder operating at zero or a whole number of waves Transmission decreases as the applied AC voltage amplitude increases half to zero waves retardance The relationship between transmittance T and retardance 0 in degrees for crossed polarizer configuration is given by TQ 1 2 1 c
13. ES 1 D3040 Controllers may be upgraded to D3050 specifications This upgrade also includes CellIDRIVE 3100 Please contact a Sales Engineer for more information 2 Previous generations of Meadowlark LC devices with TSC option may not be compatible with the TSC option in the D3050 3 Previous generations of Meadowlark LC Controllers used BNC to SMB cables Adapters and replacement cables are available Please contact a Sales Engineer for assistance 4 Temperature monitoring and control is only available on the D3050 and requires a liquid crystal device with the temperature sensing and control TSC option meadowlark optics sre jeysAu pn JIEMPJeH SUQUNO W SJOPIEOY l S19Zz11e Od p 19 012U0Z Q Q O a i lt N et 61 Two Channel High Voltage Interface Key Benefits USB or RS232 interface C code examples all required libraries included Compact and simple to use Microsoft HyperTerminal configuration file included e Independent control of voltage levels on two channels to 10 mV resolution e includes National Instruments LabVIEW Virtual Instrument drivers to interface with custom software meadoulark ptics SPECIFICATIONS Fundamental Drive Waveform 13 kHz ac square wave Modulation Amplitude 0 100 V rms The Two Channel High Voltage Digital Interface is designed for Modulation Resolution 10mVv high precision computer control of up to two Meadowlark Pa a using LabVIEW Optics Sw
14. Polarization Control with Liquid Crystals Liquid Crystal Variable Retarders are solid state real time continuously tunable waveplates Nematic liquid crystals are birefringent materials whose effective birefringence can be changed by varying an applied voltage Meadowlark Optics Liquid Crystal Retarders are constructed using precision polished optically flat fused silica windows spaced a few microns apart The cavity is filled with nematic liquid crystal material and sealed This assembly ensures excellent transmitted wavefront quality and low beam deviation required for many demanding applications The long axis of the liquid crystal molecules defines the extraordinary or slow index With no voltage present the molecules lie parallel to the windows and maximum retardance is obtained When voltage is applied across the liquid crystal layer the molecules tip toward the direction of the applied electric field As voltage increases the effective birefringence decreases causing a reduction in retardance See Figure 4 6 Voltage Retardance Output State Vn 5 1 2 2 4 lt lt 2 4 0 lt lt 4 U QO 0 Fig 4 1 Output polarization forms for different retardance values of a compensated variable retarder with horizontal linearly polarized input Retardances greater than half wave can be achieved by using high birefringent materials and or increased liquid crystal layer thickness Birefringence of liqu
15. Sync Output tiii me puke user oD T e User Manual specified phase SS e USB and RS232 cables Oo Minimum System Requirements ie e Temperature control cable PC with Pentium II class processor 9 e LC Controller interface cable 32 MB RAM e Power supply and power cable CD ROM drive e Temperature monitoring and control 20 MB hard drive space e CelIDRIVE 3100 HV Software USB or RS232 COM Port Windows 98 ME 2000 XP Vista Use of LabVIEW Instrument Library requires LabVIEW version 6 1 or higher e National Instruments LabVIEW virtual instruments driver ORDERING INFORMATION High Voltage Controller D3060HV High Voltage Cable Swift LC Cable 62 meadouslark optics www meadowlark com e 303 833 4333 e mlo meadowlark com
16. e Internal Frequency modulation 0 5 150 Hz specifications listed Digital LED voltage and frequency readouts 50 duty cycle provide added convenience Now frequency and voltage settings External Frequency modulation DC 500 Hz variable duty can be easily stored by simply pressing the adjustment knob cycle allowable Also system memory retains voltage and frequency settings at power down External Dimensions W x D x H 7 0 x 5 0 x 3 0 in With a Liquid Crystal Variable Retarder manual adjustment of the CE Compliance voltage amplitude controls the device retardance Figure 4 8 on page 49 illustrates the relationship between voltage and retardance Basic Liquid Crystal Controller Model D4010 sadiAag je3sAi9 pinbiy 19 01 U0Z JeysA1D pinbiy ORDERING INFORMATION Independent voltage settings allow easy and repeatable selection of two retardance values Often it is desirable to modulate between the two states For example switching between quarter wave and half wave retardance changes linearly polarized light to either left or right circular A manual toggle allows easy switching between two states Two year and three year extended warranty options available please contact your Meadowlark Optics sales engineer mlo meadowlark com 303 833 4333 www meadowlark com meadouslark optics 59 Polarizers Retarders Liquid Crystal Devices Mounting Hardware i 4 Ww pa
17. es equipped with its own internal modulation control The Internal Frequency knob adjusts periodic switching between the two voltage settings An external input allows modulation to run synchronously with other equipment meadoulark optics COLLATERALS REVERE Each Meadowlark Optics Liquid Crystal Variable Retarder is Internal Frequency Voltage 1 Voltage 1 gt 000 supplied with a plot of its actual retardance versus voltage Using i amp your Model D4010 Controller and this retardance plot ensures Output Voltage 1 Frequency B Internal m 1 500 External accurate retardance to voltage correlation Voltage 2 D O Q 2 N e W a e P Q o a gt _ W p lt G ef va am Q Q o SPECIFICATIONS Output Voltage O to 20 V rms maximum Voltage Resolution 1 mV for lt 10 V output 10 mV for 10 V output Fundamental Drive Waveform 2 kHz ac square wave Fig 5 1 Model D4010 Basic Liquid Controller front panel External Modulation input TTL compatible layout 5 V maximum Meadowlark Optics is excited to announce the release of the Model D4010 our new Basic Liquid Crystal Controller This Power Requirements 100 240 V ac liquid crystal LO driver is designed to integrate with any single 47 63 Hz standard Meadowlark Optics LC device currently offered as calle well as any nematic Liquid Crystal device compatible with th
18. formance data for your specified wavelength A coaxial cable with mating connector is provided for easy attachment to one of our electronic controllers QUESTION The temporal response of a liquid crystal device seems very complicated Where can I find some clarification ANSWER See our Application Note on temporal response of liquid crystal devices at www meadowlark com meadowlark optics vIEMpPJeH SUQUNO W SJOPIEOY S19Zz11e Od B Q a lt WV P UO g U 0S oc gt a on T M a 49 Liquid Crystal Variable Retarders Liquid crystal devices should be electrically driven with Key Benefits an AC waveform with no DC component to prevent ionic buildup which can damage the liquid crystal layer We require a 2 kHz square wave of adjustable amplitude for controlling our Liquid Crystal Variable Retarders LCVR Our Basic Controller and Four Channel Interface described on pages 59 61 ensure these drive requirements are met A temperature sensing and control option can be added to our LCVRs for accurate controlling of the operating temperature The sensor is attached directly to the LCVR substrate outside its clear aperture Without this option retardance decreases by approximately 0 2 to 0 3 per C increase in temperature Computer control capability Temperature control options Usable from 450 to 1800 nm Precision non mechanical retardation control SMB connector Er
19. hearing process used for alignment of bulk liquid crystals with polymer stabilization gt SV S S S S S SDS S S S S S D gt V S S S S S S S S S S S D S OD S O S S O O DD O gt S Fig 4 17 a Typical bulk liquid crystal device showing both regions of fast and slow electro optical response b A polymer stabilized liquid crystal device showing random alignment in the bulk of the material c A Swift Liquid Crystal device after alignment process meadowlark optics Typical bulk liquid crystal devices such as Meadowlarks LCVR have response times that are governed by the bulk of the liquid crystal and are a function of cell gap As cell gap increases switching times increase as the square of the thickness This effect is due to molecular properties of the bulk liquid crystal material and the alignment layer of the cell See Figure 4 6 The actual temporal electro optical response of the cell has two components 1 a very fast surface layer effect that occurs very close to the alignment layer and is on the order of microseconds and 2 a relatively slow response that occurs in the bulk of the material on the order of milliseconds This second response dominates in a typical bulk liquid crystal device Figure 4 17 a defines these two regions for a standard liquid crystal variable retarder cell To overcome this effect the introduction of small amounts of polymer material into the bulk allow for a multitude of alignment
20. i S19Zz11e Od B TE 7 SS s a Ko a O a i lt 79 ot a UO 4 lt e fa 74 S1 01 U0 JeysA9 pinbiy 45 Mounting Hardware j Retarders f Polarizers E 74 ab gt cD m fa 7a n San QO 9 pn Liquid Crystal Controllers 46 Custom Liquid Crystal Capabilities Liquid Crystal Variable Retarders A basic building block of Meadowlark Optics line of liquid crystal products is the Liquid Crystal Variable Retarder LCVR Just one of these devices can replace an entire series of polymer and standard crystalline retarders They are electronically adjustable from nearly zero waves or less than with an optional compensator to over half wave in the order of 10 milliseconds With our new Swift LC technology the switching speeds are symmetric and approximately 150 microseconds An advanced use of LCVRs is described in the application note Stokes Polarimetry Using Liquid Crystal Retarders which is available on our website at www meadowlark com While we typically list our standard products as the Liquid Crystal Variable Retarder Attenuator and Polarization Rotator we also have the ability to utilize Liquid Crystals in other ways that are extremely useful The Twisted Nematic Liquid Crystal Device TN provides our customers with potential for custom applications where a standard LCVR might not be appropriate At Meadowlark Optics we
21. icroseconds to close The switching times are less than 50 microseconds if the shutter is heated to 40 C The D3060HV controller provides this temperature control capability These shutters show some haziness in the liquid crystal layer in the blue and green wave lengths The light loss from this haze is about 1 at 700 nm but increases monotonically to about 10 loss at 450 nm Scatter at wavelengths above 700 nm is negligible The shutter is supplied with integral dichroic visible polarizers that function over the 85 wavelength range of 450 nm to 700 nm to provide an average contrast ratio of better than 200 1 Shutters with larger aperture sizes and with wavelength coverage to 2 1 microns are available 19 on a custom basis Please call with your special requirements 70 65 60 55 50 80 SPECIFICATIONS Retarder Material Polymer stabilized nematic liquid crystals Mounting Hardware j Retarders f Polarizers Polarized Transmission Substrate Material Optical quality synthetic fused Wavelength nm Polarizer Material Dichroic Polymer Fig 4 20 Polarized transmission of the Swift Optical Shutter Wavelength Range 450 700 nm in the open state Contrast Ratio average 200 1 Angular Field of View 5 incidence angle Switching Time 10 to 90 at room temperature Closed to open 150 us Open to closed 150 us 74 ab p gt cD m 4 Ww Son QO So pn
22. id crystal materials decreases at longer wavelengths requiring proper evaluation and design for optimum performance Meadowlark Optics Liquid Crystal Variable Retarders are used throughout the visible and near infrared region While these liquid crystal retarders are affected by temperature and wavelength changes they can be calibrated to accommodate those differences The resulting Variable Retarder is versatile across a considerable thermal environment and significant wavelength range mlo meadowlark com e 303 833 4333 e www meadowlark com Liquid crystal retarders can offer outstanding performance over large incidence angles Material type cavity thickness and especially operating voltage play a large role in determining the acceptable input angle Phase control or modulation is possible for light linearly polarized 45 to the fast axis Electrical control of the effective extraordinary index allows precision tuning of an optical phase delay in the propagating beam Liquid Crystal Variable Retarders Meadowlark Optics Liquid Crystal Variable Retarders provide precise solid state retardance tunability These true zero order devices are precision engineered offering excellent performance in the visible to near infrared wavelength ranges When combined with other optical components our Liquid Crystal Variable Retarders produce electrically controllable attenuation linear polarization rotation or phase modulation Continuous t
23. ift LC liquid crystal devices at one time subroutines The D30G60HV Package includes all the functionality of the USB or RS232 D3050 plus the high voltage circuitry necessary for Swift LC LC cell to Controller LEMO RF cable devices CellDRIVE 3100 HV software includes all the features 2 m length of the CelIDRIVE 3100 Advanced software but is optimized for the high speed Swift LC devices Also included is capability for Power Requirements oe temperature monitoring and control on one channel The 25A Advanced Package allows the amplitude of the 13 kHz square Safety Feature Keyed Interlock Switch wave output to be driven either by an external signal supplied to a front panel connector or specific CellDRIVE generated Dimensions L x W x H 10 50 x 7 25 x 4 0 in transient nematic effect waveforms Additional functions Modulation Waveforms external modulation input include the capability to output a sync pulse on a front panel 0 5 V connector at desired points in the CellDRIVE generated Sinusoidal waveforms and the ability to save restore all CellDRIVE settings Triangle to from a file Square Sawtooth transient nematic effect i Crystal Devices f Mounting Hardware j Retarders f Polarizers Temperature Control one channel Active heating passive Package includes only cooling to within 1 C of _ e D3060HV Controller Unit with external input and sync nominal set point P vn output front panel connectors
24. is provided for easy attachment to one of our new high voltage power supply sources www meadowlark com e 303 833 4333 mlo meadowlark com NEW Swift Liquid Crystal Variable Retarders Key Benefits Sub millisecond response times Computer control capability Temperature control options Performance from 450 to 1800 nm The next generation of liquid crystal variable retarders utilizes a new bulk stabilized polymer liquid crystal formulation With switching speeds of less than a 150 microseconds in both directions the Swift Liquid Crystal Variable Retarder SLCVR is perfect for applications where response time is critical The SLCVRs require a high voltage lt 100 Vrms 13 kHz square wave of adjustable amplitude that is provided by our D3060HV High Voltage Interface see page 62 A temperature sensing and control option can be added to our SLCVRs for accurate controlling of the operating temperature The thermal sensor is attached directly to the SLCVR substrate outside the clear aperture Custom SLCVRs are available for a variety of applications SPECIFICATIONS Retarder Material Polymer stabilized nematic liquid crystals Substrate Material Optical quality synthetic fused silica Response Time 10 90 lt 175 us zero to half wave lt 175 us half wave to zero JIEMpPJeH SUQUNO W SJOPIEOY i S19Zz11e Od B Contrast Ratio 150 1 minimum Retardance Range Normalized Response saaiaag V pinby Wi
25. lly designed for maximum transmission from 450 1800 nm see Figure 4 5 A thin dielectric layer is applied over the ITO and gently rubbed to provide for liquid crystal molecular alignment Two windows are then carefully aligned and spaced a few microns apart The cavity is filled with birefringent nematic liquid crystal material Electrical contacts are attached and the device is environmentally sealed We carefully place the Liquid Crystal Variable Retarder in an anodized aluminum housing such that the fast and slow axes are both at 45 relative to a convenient mounting hole Percent Transmission 800 Wavelength nm 1200 1600 Fig 4 5 Typical transmission through an uncoated liquid crystal device meadowlark optics Anisotropic nematic liquid crystal molecules form uniaxial birefringent layers in the liquid crystal cell An essential feature of nematic material is that on average molecules are aligned with their long axes parallel but with their centers randomly distributed as shown in figure 4 6 a With no voltage applied the liquid crystal molecules lie parallel to the glass substrates and maximum retardation is achieved When voltage is applied liquid crystal molecules begin to tip perpendicular to the fused silica windows as shown in figure 4 6 b As voltage increases molecules tip further causing a reduction in the effective birefringence and hence retardance Molecules at the surface however are unable to rota
26. n Small rotations have longer response times Key Benefits High power capability High polarization purity Computer control capability 180 degree polarization rotation Continuous rotation of linearly polarized light Polarization purity is defined as the ratio of the rotated linear component to the orthogonal component A selected rotation is very sensitive to applied voltage and operating temperature On average polarization purity or contrast ratio is better than 150 1 We provide test data including the required voltages corresponding to polarization orientations from approximately 40 to approximately 140 rotation in 10 increments These measurements are taken at room temperature for your specified wavelength Standard Liquid Crystal Polarization Rotators are supplied without an input polarizer Input polarization direction must be precisely aligned for optimum performance Please call if you require an input polarizer vIEMpPJeH SUQUNO W SJOPIEOY S19Zz11e Od B f f Q lt WV UO g D U Input Rotated Polarization Output on Polarization o S O Compensated Retarder Front LC Variable 2 Retarder Housing Plate Fig 4 15 Operation of Liquid Crystal Polarization Rotator showing complete rotation of a linearly polarized input beam meadowlark optics 53 mlo meadowlark com 303 833 4333 www meadowlark com Liquid Crystal Polarization Rotator
27. os Tmax where Tmax is the maximum transmittance when retardance is exactly one half wave or 180 Figure 4 12 shows transmittance as a function of applied voltage Maximum transmission is dependent upon properties of the LC Variable Retarder as well as the polarizers used in your system Figure 4 13 shows the transmission of an LC Variable Attenuator optimized for use at 550 nm with crossed polarizers An unpolarized light source is used for illumination Contrast ratio is defined as the maximum transmission obtained with the LC cell at half wave operation divided by the minimum transmission obtained with the LC cell at zero waves Values exceeding 1000 1 see figure 4 14 can be obtained for a single wavelength by optimizing the applied voltage levels for minimum and maximum transmission We guarantee a minimum contrast ratio of 500 1 at your specified wavelength o O Z T p N C L pa D O Soe D a l l l l l i 500 600 700 Wavelength nm Fig 4 13 Unpolarized Transmittance as a function of wavelength for LC Variable Attenuator optimized for 550 nm with polarizers and unpolarized input mlo meadowlark com e 303 833 4333 e www meadowlark com meadouslark optics JIEMpPJeH SUQUNOW SJOPIEOY S19Zz11e Od p Ko Q lt Wi P w g U oE o gt a oOo T e a 51 Mounting Hardware i Retarders Polarizers a 74
28. requirements Wavelength Fig 4 16 Transmission for Polarized Light ORDERING INFORMATION Clear SASE Aperture CA D in in Thickness Part t in Number meadouulark optics JIEMpPJeH SUQUNO W SJOPIeOY i S19Zz11e Od oF ofc 2 oO g e 55 Mounting Hardware Retarders i Polarizers E 74 od gt ab m F fer 7a gt Sun UO Ss Liquid Crystal Controllers 56 Swift Liquid Crystal Principles Meadowlark Optics next generation liquid crystal variable devices utilizes a new bulk stabilized polymer liquid crystal formulation With switching speeds of less than a 150 microseconds in both directions our new Swift Liquid Crystal devices are perfect for applications where response time is critical Swift Liquid Crystal Technology Liquid crystal polymer composite materials have been studied extensively is the past decades because of their intriguing physics and their potential application in robust fast switching liquid crystal devices Meadowlark Optics has developed a novel fabrication process in which a polymer network is utilized to enhance the electro optical performance of our liquid crystal devices Low Speed Bulk ms response T SGS lS S SDS S gt gt S SDS SVS S S Z gt 27 gt 74 64 ZINA 2727 72 1 Polymer material used for alignment layers in the bulk material ae 7 gt 744 44 Eee S
29. s SPECIFICATIONS ORDERING INFORMATION Retarder Material si aula ee ae with Diameter Meu ca Thickness Part SANT PTY D in in t in Number Substrate Material Optical quality synthetic sic ee LPR 200 IPR 300 Polarization Purity 130 ered Please specify operating wavelength in nanometers when Custom sizes are available Please contact our Sales Department Transmitted Wavefront lt h 4 P Distortion at 632 8 nm fe EES Cn CEO Surface Quality 40 20 scratch and dig Reflectance per surface lt 0 5 at normal incidence Diameter Tolerance 0 005 in Temperature Range 0 C to 50 C Recommended Safe Operating Limit 500 W cm CW 300 mJ cm 10 ns visible Mounting Hardware l Retarders Polarizers a 74 ab 2 gt bo m 74 n San QO aS gt e pn Liquid Crystal Controllers 54 meadowlark optics www meadowlark com e 303 833 4333 e mlo meadowlark com NEW High Contrast Optical Shutter SPECIFICATIONS Liquid crystal configuration Twisted nematic Optical quality synthetic fused silica Substrate Material Dichroic Polymer 450 700 nm 1 000 1 Polarizer Material Wavelength Range Contrast Ratio average 25 incidence angle with some reduction above 10 Angular Field of View eS c 2 D 2 D C H O N amp O A Switching Time 10 to 90 at room temperature 5 milliseconds 0 4 milliseconds Closed to open Open to
30. sk given the achromaticity of thicker cells why use the first minimum The simple answer is speed The switching speed of an LC is a strong function of the cell thickness generally speed drops quadratically with the thickness Thus while a cell operating at a particular wavelength in the first minimum condition might switch in 10 to 50 ms one designed to operate achromatically for example to transmit lt 1 between parallel polarizers over the entire visible range can take several seconds to switch from Meadowlark Optics Swift Liquid Crystal Variable Retarders see page 56 www meadowlark com e 303 833 4333 mlo meadowlark com Custom Liquid Crystal Capabilities Figure 4 4 shows the high contrasts of several thousands to one which can be achieved in practice with twisted nematic cells The curve termed Normally Black Contrast was taken between parallel polarizers where low voltage gives a dark state and high voltage yields a bright state The curve termed Normally White Contrast was taken between perpendicular polarizers where the dark state occurs at high voltage Custom sizes are available Please contact your Meadowlark Op tics sales engineer for assistance Transmission JIEMpPJeH SUQUNO W SJOPIEOY i SJOZIIEJOd B Cell Thickness arb units Fig 4 2 Transmission of a twisted nematic cell between Fig 4 3 Liquid crystal cell thickness changes parallel polarizers as a function of thickness
31. te freely because they are pinned at the alignment layer This surface pinning causes a residual retardance of 30 nm even at high voltage 20 volts Fused Silica ITO Alignment Layer Spacer LC Molecules TIN LC Molecules applied voltage NN Ses b Minimum Retardance V gt gt 0 Fig 4 6 Liquid Crystal Variable Retarder construction showing molecular alignment a without and b with applied voltage We achieve zero or any custom retardance with a subtractive fixed polymer retarder called a compensator attached to the liquid crystal cell Negative retardance values are sometimes preferred for example when converting between right and left circularly polarized states Figure 4 8 illustrates retardance as a function of voltage for a typical Liquid Crystal Variable Retarder with and without an attached compensator Placing a compensated Liquid Crystal Variable Retarder between two high extinction polarizers creates an excellent optical attenuator with convenient electronic control As with any anisotropic material retardance is dependent upon thickness and birefringence Liquid crystal material birefringence depends on operating wavelength drive voltage and temperature The overall retardance of a liquid crystal cell decreases with increasing temperature approximately 0 4 per C www meadowlark com e 303 833 4333 mlo meadowlark com Liquid Crystal Variable Retarders a Applied voltage to LC
32. the 2 kHz square wave output to be driven either by an external DC analog signal supplied to a front panel con nector or specific CellDRIVE generated waveforms including sinusoidal square triangle sawtooth and transient nematic effect waveforms Additional functions include the capability to output a sync pulse on a front panel connector at desired points in the CellDRIVE generated waveforms and the ability to save restore all CellDRIVE settings to from a file CELLDRIVE 3100 Adeauced QUAD CELL LIQUID CRYSTAL DIGITAL INTERFACE meadouslark optics USB Paused 3 A ierace Por Test Runs fs Period Phase Duty 3 wa Waveform 0 10V 0 10 V se c deg Cycle I o o EOE E 46000 20 aoe Se a Me smsa 84 000 feo o Ao l E E E sawiocth 42 00 4 000 Do a i 6 000 AAA 5 776 0 x y External SE Out nput 4 h Numeric 4 Plot 2 Plots 3 Plots 4 Plots Set Temp Temp Update Current Temp 10 c 2 9 Fc Fig 5 3 Advanced D3050 operation can accommodate an external modulation signal via a convenient front panel connection www meadowlark com e 303 833 4333 mlo meadowlark com Four Channel Digital Interface SPECIFICATIONS Fundamental Drive Waveform 2 kHz ac square wave Modulation Amplitude 0 10 V rms Modulation Resolution 1 mV 0 155 mV using LabVIEW subroutines LC Cell to Controller Connections SMA SMB 2 m cable length 100 240 V ac 47 63 Hz 500 mA Power Requirements
33. thout compensator 50 nm to A 2 With compensator Oto A 2 custom ranges are available Transmitted Wavefront f i lt A 2 Distortion at 632 8 nm Fig 4 18 Swift Liquid Crystal Response Time Plot Surface Quality 40 20 scratch and dig Beam Deviation lt 2 arc min Reflectance per surface lt 0 5 at normal incidence Diameter Tolerance 0 005 in Storage Temperature 20 C to 80 C 300 350 400 450 500 900 1000 1100 1200 1300 1400 1500 Time us n Operating Temperature 0 C to 55 C Q O E Wavelength Range VIS 450 700 nm 33 pa IR 1 650 950 nm SO o IR 2 900 1250 nm Z c IR 3 1200 1700 nm 0G p o ORDERING INFORMATION Clear SSS l Thickness Part Diameter D in ane a e CA t in Number 40 60 Voltage V Without Attached Compensator 50 nm to d 2 With Attached Compensator 0 nm to 2 Please specify spectral region when placing your order Fig 4 19 Swift Liquid Crystal Retardance vs Voltage mlo meadowlark com 303 833 4333 www meadowlark com meadowlark optics 57 Swift Optical Shutters Key Benefits No mechanical motion Computer control capability Noiseless High speed This liquid crystal shutter is a vibration free alternative to me chanical shutters for use in high speed shutter applications It uses a Swift LC cell between crossed polarizers to provide sub millisecond switching for both opening and closing Switching time is 125 microseconds to open and 125 m
34. tio 500 1 at single wavelength at 632 8 nm lt 0 5 at normal incidence Diameter Tolerance 0 005 in Temperature Range 0 C to 50 C Recommended Safe Operating Limit 1 W cm CW with dichroic polarizers ORDERING INFORMATION Clear D Thick P lameter Aperture CA ICKNESS art D in lin t in Number a va 300 Please specify operating wavelength in nanometers when placing your order Custom sizes are available www meadowlark com e 303 833 4333 mlo meadowlark com Liquid Crystal Polarization Rotators Our Liquid Crystal Polarization Rotator continuously rotates the polarization direction of a monochromatic linearly polarized input beam Our design consists of a Liquid Crystal Variable Retarder combined with a zero order polymer quarter wave retarder The fast axis of the liquid crystal variable retarder is oriented at 45 to the slow axis of the quarter wave retarder Linearly polarized input must be parallel to the quarter wave retarder slow axis Polarization rotation is achieved by electri cally controlling the retardance of the Liquid Crystal Variable Retarder eliminating any mechanical motion A quarter wave retarder converts elliptical polarization formed by the Liquid Crystal Variable Retarder to linear polarization The rotation angle is equal to one half the retardance change from the Liquid Crystal Variable Retarder Response time depends upon the desired amount of rotatio
35. uning of retarders over a broad wavelength range is required for many applications This added versatility makes real time polarization conversion possible with a single Liquid Crystal Variable Retarder and electronic controller Figure 4 1 shows a variety of output polarization forms achieved with a single device Pure phase modulation is accomplished by aligning the optic axis of the liquid crystal retarder parallel to a linearly polarized input beam Variable attenuators with no mechanical rotation are configured by placing a Liquid Crystal Variable Retarder between crossed polarizers Full 180 linear polarization rotation can easily be achieved by combining the Liquid Crystal Variable Retarder with a fixed quarter waveplate Spatial Light Modulators consist of individually controllable pixels These devices are used in a variety of intensity and or phase control applications where spatial variation is required Please refer to the Spatial Light Modulator section for details and specifications on these innovative products A Liquid Crystal Variable Retarder is the fundamental component used in the following devices and systems Variable Attenuators and Rotators Variable Beamsplitters Spatial Light Modulators Non Mechanical Shutters Beam Steerers Optical Compensators Polarimeters Tunable Filters QE from Meadowlark Optics Swift Liquid Crystal Variable Retarders see page 56 meadouulark optics JIEMPJeH SUQUNO W SJOPIEOY
36. wist does affect the light causing rotation of the polarization If the twist is gentle when compared to the wavelength of the light the polarization will simply follow the twist of the liquid crystal molecules Such a cell is said to be operating in the Mauguin limit and its rotation is quite achromatic The polarization rotation angle is equal to the twist angle for all wavelengths which are short enough for the twist to be viewed as sufficiently gentle When this is not the case the cell will no longer act as a pure rotator The result of inputting linearly polarized light is no longer an output of rotated linearly polarized light but rotated elliptically polarized light However for certain discrete wavelengths depending on the birefringence of the liquid crystal and the thickness of the cell the pure rotation characteristic is retained This concept is illustrated in figure 4 2 which shows the transmission normalized to 1 of a 90 twisted nematic cell between parallel polarizers to be a function of the variable U 2dQb A where d is the thickness of the cell b is the birefringence and is the wavelength Where the curve first goes to zero is termed the first minimum and this position is typically used The next highest transmission minimum is called the second minimum and so on In this plot moving along the horizontal axis can be viewed as increasing thickness or decreasing wavelength One might a
Download Pdf Manuals
Related Search