JP2006518880A - Liquid crystal variable optical attenuator - Google Patents

Abstract

A twisted nematic liquid crystal variable optical attenuator (100) is provided with one substrate containing an integrated subwavelength nanostructured polarizer (111). The device can incorporate an integrated isolator, and the liquid crystal sandwich substrate is formed from a doped garnet substrate including a Faraday rotator etched into a polarization grating of sub-wavelength optical nanostructures. And the substrate functions as an isolator. The liquid crystal variable optical attenuator is a deposited metal gasket moisture-proof layer (106) that joins both the top and bottom substrates opposite to each other, each having a spacer layer in order to accurately control the cell gap thickness. )including. The liquid crystal variable optical attenuator (100) also includes an integrated thermal sensor and heated evaporation layer (108) sandwiched between at least one or both of the substrates facing each other and deposited on at least one of them.

Description

  The present invention relates generally to optical liquid crystal devices. The present invention particularly relates to a liquid crystal variable optical attenuator shaped by a nanostructured grating substrate that has been etched at sub-wavelengths.

  This application is a continuation of the priority claim assigned with the name “Liquid Crystal Cell Platform” of application number 10 / 371,235 filed on February 21, 2003. The present application also includes the following pending US patent applications: “Method of manufacturing a liquid crystal cell” of application number 10/371976, filed on February 21, 2003, and application filed on February 21, 2003. No. 10 / 371,983 “Liquid Crystal Cell Thermal Control System”, which are incorporated herein by reference.

  Since the advent of optical fibers, fiber optic communication infrastructure has become more diverse and sophisticated. Optical fiber applications range from low-speed local area networks to high-speed long-distance telecommunications systems. In recent years, the demand for wider bandwidth and lower network costs has resulted in increased component integration and optical devices that provide multiple functions in a single package. For example, an optical cross-connect switch designed to be incorporated into a variable optical attenuator provides power equalization across all channels. Optical integrated circuits route, tune and monitor all DWDM wavelengths in one package. The popularity of such integrated devices is mainly based on the cost savings and performance advantages they offer on individually implemented components. Such an integrated instrument also simplifies coupling and alignment challenges in the optical system and provides a lower insertion loss across their individually packaged counterparts.

  Optical isolators are used in today's fiber optic networks to prevent reflected signals from reaching the laser source or LED, and optical isolators are used in front of variable optical attenuators in next generation transceiver modules. Or is expected to be placed behind. The optical isolator typically comprises a sandwich first polarizer, a Faraday rotator, and a second polarizer, and laser polarization parallel to the optical axis of the first polarizer passes through the first polarizer, Prior to passing through the second polarizer having an optical axis with a 45 degree deviation from the first polarizer, it is rotated 45 degrees by a Faraday rotator so that the light beam passes through the second polarizer. In the optical isolator, the reflected light from the second polarizer is further rotated 45 degrees by the Faraday rotator and absorbed by the first polarizer.

  As previously mentioned, transceiver modules often include a variable optical attenuator connected to the output of the optical isolator to control the laser output signal strength. There are mechanical and non-mechanical types of variable optical attenuators (VOAS). A conventional mechanical VOAS includes a movable lens that defocuses output light, a beam manipulation mirror that operates to shift the center of the spot light from the output collimator, a cantilever arm that asserts bending in the fiber, and a shutter that blocks the light transmission path. Including a mechanism based on These methods adjust the coupling between the two fibers, thereby controlling attenuation across the optical path, but are known to suffer from reliability issues such as mechanical wear and failure. . In order to overcome these problems, non-mechanical VOAS has been introduced in the last few years, including VOAS based on liquid crystal technology.

  Liquid crystal is a promising non-mechanical VOAS technology with no moving parts. A liquid crystal optical attenuator is generally a twisted nematic type consisting of two right-angled polarizers (outside of a transparent conductive glass plate with a sandwich structure each fixed with a right-angled structural layer). TN). Liquid crystal molecules that are homeotropically sealed between the glass plates align with the perpendicular anchor layer and follow a helical twist in the center of the liquid crystal sandwich structure. The voltage applied across the liquid crystal plate variably attenuates the light source at the output polarizer by untwisting and realigning the liquid crystal molecules to controllably rotate the polarized light passing through the cell. However, liquid crystal cells are susceptible to changes in temperature and humidity, and optical performance is degraded by changes in high humidity and high temperature, resulting in high insertion loss and low attenuation in two important measures of liquid crystal cell performance. It is generally known to occur.

  The result of recent advances in nanoimprint lithography is the ability to cost-effectively etch substrates with subwavelength optical grating nanostructures, which are sub-wavelengths of incident light It is known to exhibit unique optical properties as a result of having characteristic sizes from hundred nanometers to tens of nanometers. For example, etching has recently been performed to form a subwavelength optical nanostructured diffraction grating on its surface so that the glass substrate functions as a polarizing filter. Furthermore, a similar sub-wavelength optical nanostructure diffraction grating was formed on the Faraday rotator substrate by etching to form an integrated isolator.

  Taking into account the cost and performance advantages of integration, the claim that liquid crystal technology has the potential to produce a liquid crystal substrate that is highly compatible with imprint lithography and capable of providing optical functions of polarization and separation There is a strong need for a liquid crystal with variable light attenuation, which integrates individual polarizers and isolators to solve the above-mentioned problems associated with liquid crystal technology.

  The present invention includes several features that are configured independently or in combination with other features of the present invention, depending on the application and mode of operation. The description of such features is not intended to limit the scope of the invention, but merely to outline certain specific functions associated with the invention.

  The present invention provides a liquid crystal variable optical attenuator that can be formed from glass etched with sub-wavelength optical features.

  The present invention provides a liquid crystal variable optical attenuator that can incorporate an integrated isolator.

  The present invention provides a first substrate etched with a sub-wavelength optical nanostructure that functions as a polarizer and a second Faraday rotator providing an isolation function. A liquid crystal variable optical attenuator capable of incorporating an integrated isolator including a substrate is provided.

  The present invention includes a transceiver, a dynamic gain equalizer, a tunable laser, a reconfigurable optical add / drop multiplexer, a variable optical attenuator array, and an optical add / drop multiplexer that can be adjusted with or without optical power monitoring. The present invention provides a liquid crystal variable optical attenuator that can be incorporated in various applications as well as telecommunications applications.

  The present invention provides a liquid crystal variable optical attenuator that can be constructed from a material that is substantially impermeable to moisture.

  The present invention provides a liquid crystal variable optical attenuator that can be constructed from a material that is substantially impermeable to moisture and can include an integral isolator.

The present invention provides a liquid crystal variable optical attenuator that can include a heater and a temperature sensor integrated therein as a single material element, providing accurate heating control and accurate temperature sensing.

  The present invention provides a liquid crystal variable optical attenuator that can integrally include an isolator, a heater, and a temperature sensor.

The present invention provides a novel method of operating a liquid crystal variable optical attenuator over a range of temperatures without the need for a look-up table commonly used to compensate for real-time temperature changes.

  The present invention provides a liquid crystal variable optical attenuator that passes strict telecommunications guidelines as outlined in Telcordia GR1221, without the need for a sealed housing.

  The present invention provides an optically flat liquid crystal variable optical attenuator that is less likely to warp during manufacturing.

  The present invention provides an optically flat liquid crystal variable optical attenuator that is less prone to warping when exposed to various thermal and humidity atmospheres.

  The present invention provides a liquid crystal variable optical attenuator whose thickness can be controlled with nanometer resolution.

  The present invention provides a liquid crystal variable optical attenuator whose thickness can be controlled with nanometer resolution and which can include an integrated isolator.

  The present invention provides a novel method for manufacturing a liquid crystal variable optical attenuator with some or all of the features described above.

  The present invention provides a liquid crystal variable optical attenuator that can be formed in an N × M array of a plurality of liquid crystal variable optical attenuators.

  The present invention provides a liquid crystal variable optical attenuator that can be formed in an N × M array of liquid crystal variable optical attenuators, each of which can include an isolator.

  The disadvantages of the prior art can be overcome by a twisted nematic liquid crystal variable optical attenuator comprising at least one substrate comprising an integrated subwavelength nanostructured polarizer. In one form, the device can be formed from a doped garnet substrate that includes a Faraday rotator etched into a polarization grating of sub-wavelength optical nanostructures, the substrate acting as an isolator. The liquid crystal variable optical attenuator includes a deposited metal gasket moisture-proof layer that joins both the top and bottom substrates facing each other, both substrates each having a spacer layer to accurately control the cell gap thickness. . The liquid crystal variable optical attenuator also includes an integrated thermal sensor and a thermal evaporation layer sandwiched between at least one or both of the substrates facing each other.

  Another disadvantage of the prior art is that the liquid crystal is variable using a time-division scheme that multiplexes the temperature sensing and heating functions across the integrated active thermal element so that the cell is held at a nearly constant temperature. It is eliminated by the optical attenuator control system. A calibration process is included to characterize the profile of the cell and generates a polynomial regression equation that provides drive voltage output for temperature and cell state input. The control system stores the state of the liquid crystal cell and the regression equation, reads the temperature of the liquid crystal cell to calculate and execute a drive voltage for temperature compensation.

  In this application, like reference numerals are used to refer to like elements throughout. The integral polarizer is referenced by the same index throughout the embodiments as described and supported in the specification, but is adjusted by different optical axes. In addition, those support elements and features of the present invention that are distributed over each substrate and later joined together are reference numbers for specific substrates A, B, or for the purpose of simplicity. Referenced with a shared reference sign.

  A first embodiment of the present invention is illustrated in FIG. 1A, which shows a liquid crystal variable optical attenuating platform 100 having a first substrate 110A opposite a second substrate 110B, said first substrate. Includes a polarizer structure 111 on one side of the substrate, a transparent conductive electrode layer 104A, a first liquid crystal alignment layer 109A, a metal gasket layer 106A and a spacer layer 107A on the other side, and a second The substrate 110B includes a transparent conductive electrode layer 104B, a second liquid crystal alignment layer 109B fixed to the first liquid crystal alignment layer 109A at a friction angle perpendicular to the first liquid crystal alignment layer 109A, and a spacer layer 107B. FIG. 1b shows a free-space variable optical attenuator 100 and a light source 5 that generates polarized light 10, which is input to the instrument and is subject to rotation control as it passes through a twisted nematic liquid crystal arrangement. . When no voltage is applied to the electrode layer, the instrument causes the polarization 10 to rotate by approximately 90 degrees and approximately all of the light passes through the polarizing grating structure having an optical axis perpendicular to the light. The limiting voltage applied to the electrodes gives the liquid crystal molecules a tendency to revert or align along the electric field, resulting in partial rotation of the input light 10 and partial light 10 through the polarizer structure 111. Delay. The reference voltage applied to the electrodes 104A and 104B results in the molecular arrangement almost completely following the electric field, and does not substantially rotate the light 10 passing through the device. This defines the maximum attenuation or extinction state of the liquid crystal variable attenuator.

  The second embodiment of the present invention includes all the features of the first embodiment, and further includes a polarizer structure 112 on the outer surface of the substrate 110B, as shown in FIG. The polarizer structure 112 provides a reference polarizer surface for incident light and is formed with the same deflection as that of the light 10, but has an optical axis that is perpendicular to the polarization of the polarization structure 111 of the substrate 110A. .

  The third embodiment of the present invention includes an integral isolator. For this example, the substrate material must be selected to make the substrate 110A function as a Faraday rotator. Such materials can include those based on single crystal technology of thick films of rare earth iron garnet substituted with Bi. The substrate 110B can be made of glass. In this embodiment, sub-wavelength optical polarizer elements 111 and 101 are formed by etching on both the upper and lower surfaces of the Faraday substrate 110A, respectively. The period and size of the grating polarizer elements are selected such that their optical axes are spaced 45 degrees as in a typical isolator, as can be designed by those skilled in the art. It is desirable that the diffraction grating polarizing element 101 disposed adjacent to the liquid crystal alignment layer 104A has an optical axis perpendicular to the polarized light 10. FIG. 3b shows a free space variable optical attenuator 100 with an integrated isolator. The light source 5 generates a controllable rotating polarization 10 that is input to the instrument and passes through a twisted nematic liquid crystal arrangement. When no voltage is applied to the electrode layer, the instrument causes the polarized light 10 to rotate by approximately 90 degrees, and substantially all of the light is transferred to the first polarizer 101, the Faraday rotator substrate 110A, and the second. The light is input to an optical isolator formed in a sandwich structure by the polarizer 111 and allowed to pass therethrough. When no voltage is applied, the output light 10 from the liquid crystal is substantially parallel to the optical axis of the first polarizer 101 and therefore passes through the first polarizer and is further rotated by the Faraday rotator. Prior to passing through a second polarizer having an optical axis offset by 45 degrees from the first polarizer allowing light to pass through, it is rotated 45 degrees by a Faraday rotator. In this embodiment, any return of reflected light that has passed through the second polarizer 111 is further rotated 45 degrees by the Faraday rotator substrate 110 </ b> A and absorbed by the first polarizer 101. The limiting voltage applied to the electrodes 104A and 104B tends to cause the liquid crystal molecules to twist back or align along the electric field, resulting in partial rotation of the input light 10 and the first polarizer. The light 10 is partially delayed through 101A. The reference voltage applied to the electrodes 104A and 104B results in the molecular arrangement almost completely following the electric field, and does not substantially rotate the light 10 passing through the device. This defines the maximum attenuation or extinction state of the liquid crystal variable attenuator.

  The fourth embodiment of the present invention also includes an isolator and is shown in FIG. 4a. In this embodiment, the isolator is arranged to receive the light at the input end of the device. The choice of substrate material for this example must allow the substrate 110B to function as a Faraday rotator. Such materials include those based on thick-film single crystal technology of Bi-substituted rare earth iron garnet. The substrate 110A can be made of glass. In this embodiment, sub-wavelength optical polarizer elements 111 and 101 are formed by etching on both the upper surface and the lower surface of the Faraday substrate 110B, respectively. The period and size of the grating polarizer elements are selected such that their optical axes are spaced 45 degrees as in a typical isolator, as can be designed by those skilled in the art. The diffraction grating polarization element 101 preferably has an optical axis equal to the optical axis of the polarized light 10. FIG. 4b shows a free space variable optical attenuator 100 with an integrated isolator. The light source 5 generates a polarized light 10 received by the first polarizing nanostructure 101 and rotated through a Faraday rotator substrate 110B by a constant angle of 45 degrees, and the polarized light is screwed through the second polarizing nanostructure 111. It is possible to continue passing through the liquid crystal arrangement of the nematic produced. When no voltage is applied to the electrode layers 104A and 104B, the liquid crystal device causes the polarized light 10 to rotate by approximately 90 degrees, and all of the light whose optical axis is offset by 135 degrees from the polarization of the light source polarized light 10 is the polarizer. It is possible to input to 112 and pass through the polarizer. The optical axis of the polarizer 112 is selected to be 135 degrees to accommodate both a 90 degree rotation through the liquid crystal as well as an initial 45 degree rotation through the isolator. The limiting voltage applied to the electrodes 104A and 104B tends to cause the liquid crystal molecules to twist back or align along the electric field, resulting in partial rotation of the input light 10 and output polarization nanostructures. Resulting in a partial delay of light 10 through 112. The reference voltage applied to the electrodes 104A and 104B results in the molecular alignment almost completely following the electric field, and does not substantially rotate the light 10 passing through the liquid crystal. In this state, the output nanostructure polarizer 112 blocks light that has passed through. This state defines the maximum attenuation or extinction state of the liquid crystal variable optical attenuator. In all states, any return of reflected light that has passed through the second polarizer 111 is further rotated 45 degrees through the Faraday rotator substrate 110A and finally absorbed by the first polarizer 101.

  FIG. 4 c shows an example of a liquid crystal cell platform incorporating an integrated heater / temperature sensor 108. The heater / temperature sensor 108 is an optional selection mechanism that can be set in all embodiments of the present invention not only to read the temperature of the liquid crystal device but also to apply thermal energy to the liquid crystal variable optical attenuator. It is. This feature will be explained in the subsequent processing steps and electronics control section.

  FIG. 5 shows an example of an assembly process for creating the liquid crystal cell platform 100. Depending on the implementation of the configuration to be formed, various additional steps can be eliminated.

  For FIG. 5, the first step involves incorporating a subwavelength nanostructured grating element into the substrate. In the first embodiment, this step includes integrating the sub-wavelength polarization diffraction grating 111 exclusively on the glass substrate 110A. In the second embodiment, this step includes integrating the sub-wavelength polarization diffraction grating 111 on the glass substrate 110A and the sub-wavelength diffraction polarizer 112 on the glass substrate 110B. In the third embodiment, this step includes integrating the sub-wavelength polarization diffraction grating 111 on the top surface of the Faraday rotator substrate 110A and the sub-wavelength polarization diffraction grating 101 on the bottom surface of the Faraday rotator substrate 110A. . In the fourth embodiment, this step includes the subwavelength polarization diffraction grating 112 of the fourth embodiment on the substrate 110A, the subwavelength polarization diffraction grating 111 of the fourth embodiment on the top surface of the Faraday rotator substrate 110B, and the Faraday. This includes integrating the sub-wavelength polarization diffraction grating 101 of the fourth embodiment on the bottom surface of the rotor substrate 110B. A substrate with the above-described feature structure integrated is available from “NanoOpto Corporation” located in New Jersey. However, the diffraction grating configuration also allows the surface relief photoresist pattern to be diffracted into the reference photoresist to create a surface relief pattern on the substrate that is etched to form a grating structure in the nanometer range. Nanoimprint lithography known in the field of imprinting grating masks or similar methods can be used to incorporate into substrates 110A and 110B. It will be apparent to those skilled in the art of modeling nanostructured diffraction gratings that the appropriate period and diffraction grating size can be chosen to form the optical axis of each polarizer. Alternatively, a polarizer can be incorporated into the substrate by selection of the substrate material. For example, the substrate may be a polarizing glass made by “Corning, Inc.”.

  The second step includes adding an appropriate ITO (indium tin oxide) pattern to the first and second glass substrates to form the liquid crystal electrode. For the process flow 202 of FIG. 5, a standard PECVD process may be used to apply an ITO film about 100 angstroms thick. FIGS. 6A and 6B show example ITO masks used to pattern the substrates 110A and 110B, respectively.

  The third step includes adding a polyimide alignment layer to the first and second glass substrates. For the process flow 203 of FIG. 5, a standard spin coat step process at room temperature can be used to form a polyimide layer about 600 angstroms thick on each substrate.

  The fourth step includes patterning the polyimide layer. For process 204, a photoresist is first applied to the substrate and masked using conventional photolithography techniques, or laser etching can be used to pattern the substrate. Thereafter, wet or dry etching is performed to form a polyimide pattern.

  The fifth step includes fixing the liquid crystal alignment layer. For process step 205, one conventional method is to rub the polyimide on each substrate to form the alignment layer. In the twisted nematic form, the friction direction of the first substrate is perpendicular to the friction direction of the second substrate. In an electronically conductive birefringence (ECB) configuration, the friction direction of the first substrate is parallel to the friction direction of the second substrate. A friction angle other than 0 degree or 90 degrees can be obtained by various fixing plans. Another method for forming the alignment layer is to use an imprint lithography technique, in which the reference mask is later etched to form a highly accurate alignment groove with nanoscale tolerance. It is pressed onto the deposited photoresist layer to create a surface relief pattern of the receiving photoresist.

  An additional sixth step includes forming an integral heater and temperature sensor that are active thermal elements. FIGS. 7A and 7B show examples of masks used with respect to process step 206 of FIG. 5, in which a chromium seed adhesion layer is first deposited on the substrate at a thickness of about 200 Å, followed by PECVD. A 2000 Angstrom thick thin film platinum resistance layer is deposited, which forms the upper and lower portions of the integral heater / temperature sensor. The upper and lower parts of the integrated device applied to the substrates 110A and 110B are separated by about 9.6 microns by an air gap, and are formed by the metal deposition step described in the subsequent eighth step. Are mutually connected by vias (VIAS). The gap thickness is described as an example and will vary depending on the required application. The platinum thin film resistor is not limited to an arch, a curve, a circle, a zigzag, or a band, depending on the form, like the meander pattern of FIGS. 7A and 7B, but can be patterned into various shapes including these. Can do. Thin film platinum is given a resistivity of approximately 10.6 × 10E-8 ohm meters, resulting in a resistance of about 500 to 2000 ohms at room temperature, depending on the volume of the film, for example.

  The seventh step involves the formation of spacer elements 107. The spacer element 107 controls the gap thickness of the liquid crystal cell. Although it is not necessary to distribute the spacer elements equally and evenly on each substrate, the thickness of the spacer elements 107 can be defined so that half the desired gap thickness of the completed cell is deposited on each substrate. preferable. The gap thickness of the combined cell 100 is thus shaped to an acceptable range based on the deposition process. While silicon dioxide is the preferred material from which the spacer element is made, other materials that are compatible with substantially uncompressed thin film deposition processes such as aluminum oxide, silicon nitride, silicon monoxide are selected liquid crystal substrate materials Can be used as an alternative to silicon dioxide. FIGS. 8A and 8B show example masks used to perform process step 207 of FIG. 5 with a 5 micron thick patterned silicon dioxide layer deposited on each substrate.

  The eighth step includes forming the metal gasket element 106. The metal gasket element 108 can be formed from a variety of metals such as, but not limited to, indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium, and lead. However, it is desirable to use indium because of its flexibility and relatively low melting temperature. FIGS. A9 and 9B show example masks used to perform process step 208 of FIG. 5, and for the continuation example, indium is a layer approximately 7-9 microns thick, equally for each substrate. Deposited on top. It is generally desirable that the metal gasket layer of this processing step be deposited thicker than the previous spacer element due to leakage that occurs during the additional processing step. As shown in FIGS. 9A and 9B, the metal gasket mask forms associated vias (VIAS) 300 that allow electrical interconnection between materials deposited on either substrate 110A or 110B. Configured to do. A plurality of vias (VIAS) 300 are also formed to simplify the handling of external contact pads on the temperature sensor and the heating element. For example, the via (VIAS) 300 of this embodiment is disposed so as to overlap the heater / temperature sensor platinum layer defined in the sixth step. They are also arranged to overlap the ITO layer so as to define a contact pad for driving the two electrodes of the liquid crystal cell.

  The ninth step includes aligning and pressing wafer 110A to wafer 110B. It is known to form a visible alignment reference mark on the underlying wafer by etching, or to use physical features of the glass plate such as edges or alignment holes for wafer alignment. However, a high yield method is described herein that accurately performs the relative alignment of the two glass substrates without the use of an expensive high precision array device, thereby joining and pressing each substrate. In order to prevent relative movement of the glass sheets, complementary geometric interlocking structures formed on each substrate are coupled to each other. Such a connection structure mitigates any non-uniformity in the bonding process and assumes that the typical gap between the two glass plates of the liquid crystal cell is less than 20 micrometers, a thin film formation or screening process. Can be used to form precisely controlled and repeatable geometric structures. For process step 209 of FIG. 5, the substrates 110A and 110B are under room temperature pressure to mold a chemically bonded metal gasket with a gap distance defined by a sandwich spacer element formed from both substrates. Aligned and joined.

  The tenth step includes wafer dicing. Process step 210 of FIG. 5 can be performed using a dicing saw or via etching technique.

  The eleventh step includes removing a part of the protective glass from the liquid crystal cell. FIG. 10A shows a top perspective view of the various layers bonded through the substrates between the substrates in a completed embodiment of the invention. For process 211 of FIG. 5, substrate 110B is scored using a diamond dicing saw to cut a groove about 90% of the thickness of the substrate to form separation line 119 of FIG. 10A. A portion of substrate 110B provides access surface 113 of FIG. 10B allowing access to liquid crystal injection hole 115, underlying liquid crystal electrode contact pads 500 and 500 'and underlying liquid crystal heater / temperature sensor element electrical contact pads 502 and 502'. To define, they are separated along a separation line 119.

  The twelfth step includes filling the liquid crystal device with liquid crystal molecules (process 212 of FIG. 5). This step can be performed using conventional methods to fill the liquid crystal cell, where the cell is placed in a vacuum, a liquid crystal material of droplet size is placed in the injection hole 115, and the equilibrium pressure due to the release of the vacuum is adjusted to the liquid crystal. A substance is pushed into the injection hole 115 and the injection hole is plugged. In order to close the injection hole, in addition to the UV curable epoxy resin, various techniques for covering the injection hole can be used.

Electronics Control System A block diagram of components directed to a liquid crystal cell system and its host controller are shown in FIG. 11 along with the liquid crystal thermal management and voltage control subsystem of the present invention and will be described in further detail below.

  In one embodiment, the host computer 400 is configured to communicate with the microcontroller 402 over a full-duplex data interface so that the host computer can function and send commands and retrieve data from the microcontroller 402. Is possible. The microcontroller is configured to hold software control routines. The software control routine functions to adjust the drive voltage supplied to the liquid crystal cell in accordance with temperature fluctuations.

  The microcontroller utilizes a time division multiplexing scheme that multiplexes temperature sensing and heating functions with an integrated sensor / heater device such that the cell is held at a substantially constant temperature. The calibration process characterizes the cell profile and generates a polynomial regression equation that provides the optimal drive voltage output for a given temperature and cell state input. The microcontroller 402 stores the state of the liquid crystal cell and the regression equation, reads the temperature of the liquid crystal cell to calculate and assert a drive voltage that compensates for the temperature.

FIG. 11 shows the calibration process used to perform the method of the present invention, where the thermal operating characteristic profile of the liquid crystal cell is used to adjust the drive voltage applied to the cell as a function of temperature and cell state. Has been converted to deterministic coefficients incorporated into the stored regression equation.

  The first step in determining the coefficient values in the cell temperature and voltage compensation profile is to draw the driving characteristics of the liquid crystal cell over a range of temperatures. In the profile processing step 601, the light source passing through the cell and its attenuation are tested with a combination of a predetermined voltage and temperature. The operable liquid crystal cell is placed in a hot chamber programmed to change the operating temperature over a desired temperature range at predetermined intervals. At every temperature change interval, a voltage value in a certain range is applied to the liquid crystal cell while operating characteristics such as attenuation are measured. The voltage is scanned until the reference decay level is achieved, and the current voltage, decay and temperature levels are recorded as a grid point representation in the cell profile definition table. Liquid crystal cell performance is recorded at grid point attenuation and multiple temperature levels, resulting in a multi-dimensional lookup table that provides attenuation level output at any temperature and voltage input, which is displayed as three-dimensional Is done.

  The second step requires look-up table processing to smooth the temperature-related voltage profile at the predetermined attenuation level recorded in the previous stage. A statistical program capable of performing regression analysis, such as Mathematica & commat, can be used to perform process step 602. The regression software comprises the look-up table generated in the first step and the appropriate coefficients a, b, c, d, and e representing the cell's voltage versus temperature profile at each attenuation level, expressed as: 4th order regression curve fitting process is executed.

v = a + bT + cT ² + dT ³ + eT ⁴
v ₁ = a ₁ + b ₁ T + c ₁ T ² + d ₁ T ³ + e ₁ T4
v ₂ = a ₂ + b ₂ T + c ₂ T ² + d ₂ T ³ + e ₂ T ⁴
・
・
・
v _n = a _n + b _n T + c _n T ² + d _n T ³ + e _n T ⁴

Here, V is a voltage, T is a liquid crystal cell temperature, a, b, c, d and e are coefficients that fit the curve, and n is an attenuation level.

Assuming that a smooth curve is due to the previous step of defining the optimum drive voltage level for a given temperature at a recorded grid point attenuation level, the third step is the orthogonal axis of the three-dimensional surface. The result is a smooth curve regression equation fitted across, so that the smooth curve fits on the coarse attenuation grid points recorded in the first step. In this processing step 603, the five coefficients of the previous step are solved by quadratic regression, respectively. In particular, Mathematica & commat or a suitable program has 5 coefficients a, b, c, d and e, respectively, over the order of the regression equation v ″ = an + bT + cT ² + d ″ T ³ + e ″ T ⁴ The smooth surface profile thus defines the optimal voltage compensation level given the input decay state and temperature by the following formula:

V = a + bT + cT ² + dT ³ + eT ⁴ , where
a = (X + Yθ + Zθ ² )
b = (X ₁ + Y ₁ θ + Z ₁ θ ² )
c = (X ₂ + Y ₂ θ + Z ₂ θ ² )
d = (X ₃ + Y ₃ θ + Z ₃ θ ² )
e = (X ₄ + Y ₄ θ + Z ₄ θ ² )

θ is the liquid crystal attenuation level
X, Y, Z are the solutions of the zeroth order coefficient,
X ₁ , Y _l , Z _l are the solutions of the first-order coefficients
X ₂ , Y ₂ , Z ₂ are the solutions of the quadratic coefficients
X ₃ , Y ₃ , Z ₃ are the solutions of the third order coefficient
X ₄ , Y ₄ , Z ₄ are the solutions of the fourth-order coefficient

15 coefficients solutions (Xn, Yn, Zn, where n is from 0 to 4), by Masumateka (Mathematica), appropriate (data, {l, x, x ^2, and ..., x ^n}, x ) Can be generated using a function or other suitable software package capable of performing curve fitting regression.

  The fourth step is a process 606, which is the final step in the calibration process of FIG. 11, and stores the coefficients of the liquid crystal control system being described.

  The coefficients describing the liquid crystal properties can be stored in the microcontroller memory by flashing the microcontroller 402 memory (FIG. 12) with the appropriate 15 coefficient values.

  The thermal compensation system of the present invention operates by reading the temperature of the liquid crystal cell and adjusting the cell drive voltage based on the cell state. Cell states can generally be operated off, on, or in variable mode. The cell state is stored in the microcontroller 402 and formed via the host computer 400.

  A microcontroller can be configured with a PIC microchip that has an analog-to-digital converter and operates with the clock of a 10 Mhz crystal oscillator 404. The microcontroller is connected to a digital to analog converter (DAC) configured to provide an output voltage level in response to the form of a pulse stream from the microcontroller at a serial interface. The output terminal of the DAC is connected to the input terminal of an analog switch 414 that is clocked by the microcontroller's port pin at about 1.2 kHz. The data passed to the DAC defines the AM transmission amplitude of the carrier above 1.2 kHz, which produces a differential drive voltage to the liquid crystal cell electrodes 500 and 500 ′ (FIG. 10B).

The temperature sensor reading is provided by an internal heater / temperature sensor internal from an external device. One of the heater / temperature sensor electrodes 502 and 502 ′ of the liquid crystal cell 100 is grounded, and the other is connected to the switch 407. Switch 407 is operatively associated with an integral heater / temperature sensor element 108 in a sensing or heating mode.
More particularly, switch 407 is configured to connect an ungrounded heater / temperature electrode to an ADC coupled through an instrumentation amplifier 406 to a microcontroller that reads the temperature of the liquid crystal cell and is on. Off, the power amplifier FET 410 is controlled by a pulse train from the microcontroller 402 and is connected to the power amplifier FET 410 that applies a potential difference to operate the device 108 as a heater.

  In the operation of a feedback closed loop for temperature sensing (referred to as the loop included in process steps 607 to 609 in FIG. 11), the microcontroller reads the temperature of the liquid crystal cell, and senses the temperature T and the liquid crystal cell. The driving voltage is calculated on the basis of the current state θ. The 15 coefficients are re-inserted into a quartic regression equation that establishes a smooth surface profile that describes the optimum voltage to supply to the liquid crystal cell for a given temperature and cell attenuation level.

v = (X + Yθ + Zθ ² ) +
(X _l + Y ₁ θ + Z ₁ θ ² ) T +
(X ₂ + Y ₂ θ + Z ₂ θ ² ) T ² +
(X ₃ + Y ₃ θ + Z ₃ θ ² ) T ³ +
(X ₄ + Y ₄ θ + Z ₄ θ ² ) T ⁴

  A new voltage value V is calculated and sent to a DAC 412 that supplies a DC voltage of the appropriate magnitude to the timed analog switch 414 to generate an AM drive voltage that is temperature compensated for the liquid crystal cell.

  The liquid crystal cell is also maintained at approximately the reference temperature. Process step 609 with respect to FIG. 11 includes heating to maintain the temperature of the liquid crystal cell at approximately the reference temperature. The reference temperature may exceed ambient room temperature or exceed the temperature of all carrier devices coupled to the LC (liquid crystal) cell. If a reference temperature is selected that exceeds the ambient temperature, after applying rapid heating, the LC will eventually be cooled to encounter the ambient temperature. Thus, a counter thermal bias is generated to support temperature stability with respect to the reference temperature.

  The memory of the microcontroller can store a reference temperature, a current temperature value, a temperature history, and a history of the heating level applied to the LC. In all cases, the sensed temperature T value is compared to a reference temperature to determine the amount of heat applied to the liquid crystal cell. Since the 8-bit analog-to-digital converter provides a temperature sensing resolution of approximately 1/3 degrees over the desired temperature range, in this embodiment, the temperature within 1/3 degrees Celsius for the reference temperature. May provide stability. In all examples of process step 609, when the sensed temperature of the liquid crystal cell falls below the desired operating reference temperature, the threshold detector routine stored in the microcontroller ROM triggers a control function. The control function determines how much heat is supplied to the liquid crystal cell. The control function utilizes a routine that minimizes errors, which tracks temperature changes throughout a number of examples of process step 609. The error correction routine can store the previous temperature reading TO together with the previous heat quantity HO applied to the liquid crystal cell. The temperature reading and all subsequent temperature readings Tl are compared to the TO to determine the amount of temperature change due to previous heating of the liquid crystal cell. As described above, heat is applied to the liquid crystal cell via the FET power driver. The heater is driven at a constant or variable duty cycle and is controlled by frequency modulation or amplitude modulation.

  While the invention has been fully described by the specification and the accompanying drawings, various changes and modifications will become apparent to those skilled in the art. For example, various patterns can be used to mold spacer elements, metal gaskets and integrated heater / temperature sensor elements in a basic cell platform. External temperature sensors and heaters can be used in part or in whole for the temperature compensation method and regression of the present invention. The metal gasket can be adjusted to provide a heating function in addition to the function as a moisture-proof support film. Epoxy resin gaskets can be used partially or entirely in combination with a metal gasket element, which can include one solder cap. The alignment and fixation of the liquid crystal material in the cell can also be performed using the photoalignment material, Staralign by Vantio, Switzerland, or other known alignment methods including laser etching can be used. . Fixing the liquid crystal material in the cell (fifth step) can be performed before the polyimide patterning (fourth step). The processing steps for closed loop temperature feedback can be recombined so that the heating process is performed prior to applying the drive voltage. The order of fitting the voltage to each dimension of the 3D surface is reversible, including, but not limited to, one dimension that fits the fourth order polynomial and other dimensions that fit the second order polynomial. These three-dimensional surfaces can be used. Amplitude modulation or frequency modulation can be used to drive the liquid crystal cell. The fourth embodiment of the present invention can be set by the integrated temperature sensor / heating element of the third embodiment of the present invention. The liquid crystal cell is not limited to a single pixel. A liquid crystal cell may consist of a number of pixels. The liquid crystal cell array can be formed to include an array of cells having one or more pixels. Accordingly, various changes and modifications from those abstractions defined herein are to be construed as included in the claims without departing from the scope of the invention.

1 shows a first embodiment of a liquid crystal attenuator having an integrated polarizer substrate. 1 shows a first embodiment of a liquid crystal attenuator having an integrated polarizer substrate. 2 shows a second embodiment of a liquid crystal attenuator having an integrated first polarizer substrate having an optical axis perpendicular to the optical axis of the integrated second polarizer substrate. 2 shows a second embodiment of a liquid crystal attenuator having an integrated first polarizer substrate having an optical axis perpendicular to the optical axis of the integrated second polarizer substrate. 3 shows a third embodiment of a liquid crystal attenuator having an integrated isolator substrate. 3 shows a third embodiment of a liquid crystal attenuator having an integrated isolator substrate. 4 shows a fourth embodiment of a liquid crystal attenuator having an integrated first isolator substrate and second polarizer substrate. 4 shows a fourth embodiment of a liquid crystal attenuator having an integrated first isolator substrate and second polarizer substrate. An arrangement example of an integrated heater / temperature sensor structure, which is an addition of the present invention, is shown. The processing flow for assembling the liquid crystal attenuator of this invention is shown. The example of the mask for electrode formation of this invention is shown. The example of the mask for electrode formation of this invention is shown. 2 shows an example of an integral active temperature element forming mask of the present invention. 2 shows an example of an integral active temperature element forming mask of the present invention. The example of the mask for spacer element formation of this invention is shown. The example of the mask for spacer element formation of this invention is shown. 2 shows an example of a mask for forming the metal gasket element layer of the present invention. 2 shows an example of a mask for forming the metal gasket element layer of the present invention. FIG. 3 shows an example of a plan view of an integrated perspective view showing the relationship between the various layers of the present invention. FIG. 5 is an isometric view showing the liquid crystal attenuator at the end of the assembly process. The flow of the thermal calibration of the liquid crystal attenuator and the feedback loop method is shown. 1 shows a block system diagram for an electronic control and temperature management system of the present invention. FIG.

Explanation of symbols

100 Liquid crystal variable optical attenuator 104A First electrode layer 104B Second electrode layer 106A, 106B Metal gasket layer 107A, 107B Spacer layer 108A, 108B Heater / temperature sensor element (active thermal element)
109A First liquid crystal alignment layer 109B Second liquid crystal alignment layer 110A First substrate 110B Second substrate 111, 112 Sub-wavelength nanostructure diffraction grating polarizer

Claims (52)

A first substrate comprising a top surface formed by etching a sub-wavelength diffraction grating polarizer and a bottom surface having an electrode and an alignment layer;
A second substrate having a bottom surface on which an optical diffraction grating polarizer having a second sub-wavelength is formed by etching and a top surface having a second electrode and an alignment layer, wherein the second polarizer is the first substrate. A second substrate having an optical axis perpendicular to the polarizer on the substrate, wherein the top surface of the second substrate is disposed to face the bottom surface of the first substrate;
A liquid crystal coupled between the first and second substrates,
An optical polarization signal having the same optical axis as the second polarizer is rotated by the second polarizer as it passes through the liquid crystal, and variably in response to application of a voltage across the electrode layer. Attenuable variable optical attenuator.   The variable optical attenuator of claim 1, further comprising a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.   The variable optical attenuator of claim 2, further comprising an active thermal element disposed between the first and second substrates.   The variable optical attenuator of claim 2, wherein the spacer layer comprises one or more materials selected from the group of silicon dioxide, aluminum oxide, silicon nitride, and silicon monoxide.   The variable optical attenuator of claim 2, wherein the metal gasket layer comprises one or more materials selected from the group of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium, and lead.   3. The variable optical attenuator of claim 2, wherein both substrates are glass products.   The variable optical attenuator of claim 2, wherein the spacer and metal gasket layer are deposited thin films.   4. The variable optical attenuator of claim 3, wherein the active thermal element is deposited on the first and second substrates.   4. The variable optical attenuator of claim 3, wherein the active thermal element is disposed substantially surrounding the liquid crystal cell.   4. The variable optical attenuator of claim 3, wherein the active thermal elements are arranged in a serpentine pattern.   The variable optical attenuator of claim 3, wherein the active thermal element comprises heating and temperature sensing capabilities.   The variable optical attenuator of claim 3, wherein the active thermal element comprises chromium-platinum.   4. The variable optical attenuator of claim 3, further comprising at least one via formed between the metal spacer layer and the first or second electrode.   The variable optical attenuator of claim 3, further comprising at least one via formed between the active thermal element and the metal spacer layer.   4. The variable optical attenuator of claim 3, wherein the active thermal element includes an electrode that provides a resistance value used to determine the temperature of the variable optical attenuator.   The switch further includes a microcontroller and a switch, the switch controlling the resistance value from the active thermal element to the microcontroller and the routing of voltage signals from the microcontroller to the active thermal element. The variable optical attenuator of claim 15 connected to the active thermal element.   The variable optical attenuator of claim 16, wherein a via formed by a layer of metal gasket material is coupled to the thermal element between the first and second substrates. A first substrate comprising a top surface formed by etching a sub-wavelength diffraction grating polarizer and a bottom surface having a first electrode layer and a first alignment layer;
A second substrate including a top surface having a second electrode layer and a second alignment layer fixed in a direction perpendicular to the first alignment layer, and facing the bottom surface of the first substrate. A second substrate arranged
A liquid crystal coupled between the first and second substrates;
A spacer layer coupled between the first and second substrates;
A metal gasket layer bonded to the first and second substrates,
An optical signal passing through the second substrate rotates its polarization as it passes through the liquid crystal, and can be variably attenuated by the polarizer on the first substrate in response to voltage application. Variable optical attenuator. A first substrate made of a material suitable for functioning as a Faraday rotator, having a top surface and a bottom surface formed by etching a sub-wavelength diffraction grating polarizer, thereby allowing the substrate to function as an isolator Therefore, the top polarizer has an offset angle of 45 degrees from the bottom polarizer, and the first substrate includes a first electrode layer and a first alignment layer on the bottom. A substrate,
A second substrate including a top surface having a second electrode layer and a second alignment layer fixed in a direction perpendicular to the first alignment layer, the second substrate facing the bottom surface of the first substrate. A second substrate arranged
A liquid crystal coupled between the first and second substrates,
An optical signal passing through the second substrate rotates its polarization as it passes through the liquid crystal, and is variably attenuated by the polarizer on the first substrate in response to application of the voltage of the electrode layer. A variable optical attenuator that is possible and is separated by the isolator formed from the first substrate.   20. The variable optical attenuator of claim 19, further comprising a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.   21. The variable optical attenuator of claim 20, further comprising an active thermal element disposed between the first and second substrates.   21. The variable optical attenuator of claim 20, wherein the spacer layer comprises one or more materials selected from the group of silicon dioxide, aluminum oxide, silicon nitride, and silicon monoxide.   21. The variable optical attenuator of claim 20, wherein the metal gasket layer comprises one or more materials selected from the group of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium, and lead.   21. The variable optical attenuator of claim 20, wherein both substrates are glass products.   21. The variable optical attenuator of claim 20, wherein the spacer layer and the metal gasket layer are deposited thin films.   The variable optical attenuator of claim 21, wherein the active thermal element is deposited on the first and second substrates.   The variable optical attenuator of claim 21, wherein the active thermal element is disposed substantially surrounding the liquid crystal cell.   The variable optical attenuator of claim 21, wherein the active thermal elements are arranged in a serpentine pattern.   The variable optical attenuator of claim 21, wherein the active thermal element provides heating and temperature sensing capabilities.   The variable optical attenuator of claim 21, wherein the active thermal element comprises chromium-platinum.   The variable optical attenuator of claim 21, further comprising at least one via formed between the metal spacer layer and the first or second electrode.   The variable optical attenuator of claim 21, further comprising at least one via formed between the active thermal element and the metal spacer layer.   The variable optical attenuator of claim 21, wherein the active thermal element includes an electrode that provides a resistance value used to determine the temperature of the variable optical attenuator. The switch further includes a microcontroller and a switch, the switch controlling the resistance value from the active thermal element to the microcontroller and the routing of voltage signals from the microcontroller to the active thermal element. The variable optical attenuator of claim 33 connected to the active thermal element.   35. The variable optical attenuator of claim 34, wherein a via formed by a metal gasket material layer is coupled to the thermal element between the first and second substrates. A first substrate having a sub-wavelength diffraction grating polarizer formed by etching and having a first electrode layer and a first alignment layer;
A second substrate made of a material suitable for functioning as a Faraday rotator and having a top surface and a bottom surface formed by etching a sub-wavelength diffraction grating polarizer, thereby allowing the substrate to function as an isolator. Accordingly, the top polarizer has an offset angle of 45 degrees from the bottom polarizer, and the second substrate further includes a second electrode layer and a second alignment layer on the top surface. The second alignment layer is fixed in a direction perpendicular to the first alignment layer on the first substrate, and the top surface of the second substrate is disposed to face the bottom surface of the first substrate. A second substrate,
A liquid crystal coupled between the first and second substrates,
An optical signal that passes through the second substrate is separated by the second substrate, rotates its polarization as it passes through the liquid crystal, and the first substrate in response to application of a voltage on the electrode layer. A variable optical attenuator that can be variably attenuated by the polarizer.   The variable optical attenuator of claim 36, further comprising a spacer layer coupled between the first and second substrates and a metal gasket layer bonded to the first and second substrates.   38. The variable optical attenuator of claim 37, further comprising an active thermal element disposed between the first and second substrates.   38. The variable optical attenuator of claim 37, wherein the spacer layer comprises one or more materials selected from the group of silicon dioxide, aluminum oxide, silicon nitride, and silicon monoxide.   38. The variable optical attenuator of claim 37, wherein the metal gasket layer comprises one or more materials selected from the group of indium, gold, nickel, tin, chromium, platinum, tungsten, silver, bismuth, germanium, and lead.   38. The variable optical attenuator of claim 37, wherein both substrates are glass products.   38. The variable optical attenuator of claim 37, wherein the spacer layer and the metal gasket layer are deposited thin films.   38. The variable optical attenuator of claim 37, wherein the active thermal element is deposited on the first and second substrates.   40. The variable optical attenuator of claim 38, wherein the active thermal element is disposed substantially surrounding the liquid crystal cell.   40. The variable optical attenuator of claim 38, wherein the active thermal elements are arranged in a serpentine pattern.   40. The variable optical attenuator of claim 38, wherein the active thermal element provides heating and temperature sensing capabilities.   40. The variable optical attenuator of claim 38, wherein the active thermal element comprises chromium-platinum.   40. The variable optical attenuator of claim 38, further comprising at least one via formed between the spacer layer and the first or second electrode.   40. The variable optical attenuator of claim 38, further comprising at least one via formed between the active thermal element and a metal spacer layer.   39. The variable optical attenuator of claim 38, wherein the active thermal element provides a resistance value used to determine the temperature of the variable optical attenuator.   The switch further includes a microcontroller and a switch, the switch controlling the resistance value from the active thermal element to the microcontroller and the routing of voltage signals from the microcontroller to the active thermal element. 52. The variable optical attenuator of claim 50 connected to the active thermal element.   52. The variable optical attenuator of claim 51, wherein a via formed by a metal gasket material layer is coupled to the thermal element between the first and second substrates.

Images