LCoS box thickness measuring method and device

Abstract

The invention discloses an LCoS box thickness measuring method and equipment. The device comprises a light source, a fiber optic spectrometer, a communication module and a calculation module. The measuring method comprises the following steps: 1, acquiring an environment dark spectrum and a spectrum of a light source by a fiber optic spectrometer; 2, light of each wavelength enters each pixel point of the LCoS device, forms two beams of coherent reflected light on the surfaces of the upper substrate and the lower substrate respectively, and enters the optical fiber spectrometer; 3, the communication module automatically obtains the model and serial port information corresponding to the spectrograph; 4, the communication module transmits the spectral data back to the data calculation module, filters the input data and compares the filtered data with a background spectrum to obtain an interference spectrum; and 5, automatically identifying the interference spectrum waveform by a calculation module, and calculating to obtain the box thickness and the box thickness uniformity of the LCoS device. The LCoS box thickness measuring equipment is simple in composition and convenient to use, the measuring method is high in automation degree, the LCoS box thickness measuring efficiency and precision can be remarkably improved, and the practical engineering significance is achieved.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a method and device for measuring the thickness of an LCoS cell. Background Technology

[0002] LCoS (Liquid Crystal on Silicon) devices feature high integration and high reconfigurability. Using micron-scale pixel arrays fabricated with CMOS technology, they can flexibly display liquid crystal images to achieve the required functions and have wide applications in projection, spatial light modulation, and other fields.

[0003] The vertical structure of an LCoS device can be divided into three parts: upper, middle, and lower, consisting of a liquid crystal layer and upper and lower substrates. The upper substrate serves as the incident and emitting substrate for light, using transparent glass as the base, on which transparent ITO electrode layers and alignment layers are sequentially fabricated. The lower substrate is the LCoS phase modulator substrate fabricated using CMOS technology, divided into PAD areas, pixel areas, and driving circuit areas. An alignment layer is also fabricated on the CMOS substrate, working together with the alignment layer on the upper substrate to provide alignment for the liquid crystal layer. Spacers are used to support the upper and lower substrates, providing a defined thickness and filling space for the liquid crystal layer. After the liquid crystal layer is filled, a complete LCoS phase modulation device is formed.

[0004] When the liquid crystal molecules are aligned in ECB mode, the light incident on the liquid crystal layer is decomposed into o-rays and e-rays due to birefringence. Since the o-ray and e-ray correspond to different refractive indices n... o and n e The refractive index of o-ray incident with a polarization direction perpendicular to the optical axis is n. o The refractive index of the e-ray incident along the parallel optical axis changes due to the change in the direction of the liquid crystal molecules' orientation under the influence of the electrical signal. The corresponding effective refractive index n is related to this direction. eff Since LCoS is a reflective device, the liquid crystal molecules are modulated twice by the liquid crystal layer.

[0005] Considering practical realities, the pointing vectors of liquid crystal molecules are not strictly uniform and exhibit slight variations. In this case, integration calculations can be performed on the liquid crystal layer in the vertical direction. The magnitude of the phase retardation of the o-ray and e-ray caused by the liquid crystal molecules is affected by factors such as the LCoS cell thickness and driving voltage. Phase modulation is the most important performance characteristic of LCoS devices, and the thickness of the liquid crystal layer plays a decisive role in the magnitude of phase modulation. The uniformity of the liquid crystal layer determines the uniformity of phase modulation; therefore, characterizing the cell thickness of the device is extremely crucial. Devices with uniform cell thickness have a uniform liquid crystal layer, resulting in smaller errors in modulation between different regions and better modulation capabilities compared to devices with non-uniform cell thickness. Therefore, to improve the modulation capabilities of LCoS devices, it is necessary to design appropriate measurement equipment and methods for LCoS cell thickness. Summary of the Invention

[0006] This invention provides an LCoS cell thickness measurement method and device for measuring the liquid crystal cell thickness and cell thickness uniformity of LCoS devices. The LCoS cell thickness measurement device proposed in this invention is simple in composition and easy to use. The measurement method is highly automated, fast, and accurate, which can significantly improve the efficiency and accuracy of LCoS cell thickness measurement and has practical engineering significance.

[0007] The specific technical solutions provided by the embodiments of the present invention are as follows:

[0008] In a first aspect, a silicon-based liquid crystal (LCoS) cell thickness measurement device includes: a light source, a fiber optic spectrometer, a communication module, and a computing module; the light source is in the range of 490-710nm, and the spectrometer is a visible light band spectrometer.

[0009] The communication module mainly includes:

[0010] Spectrometer connection, wavelength reading, light intensity reading, spectrometer shutdown;

[0011] The spectrometer connection section is mainly responsible for establishing a link between the computer and the spectrometer, and obtaining the spectrometer's model information and serial port speed for further communication.

[0012] After establishing the connection, the wavelength information of the spectrometer is queried through the wavelength reading section, and the wavelength corresponding to the data collected by the spectrometer is obtained through serial communication, which serves as a reference for subsequent calculations.

[0013] The system sends a read command to the spectrometer via serial port. The spectrometer reads the light intensity data. The number of bytes read is determined by the USB communication rate specified in the connection section. In high-speed mode, the data is in units of 512 bytes, and in low-speed mode, it is in units of 64 bytes. Finally, the read byte information is converted into the corresponding spectral data for use by the calculation module.

[0014] After the box thickness measurement is completed, the connection between the computer and the spectrometer is terminated by closing the spectrometer.

[0015] The calculation module is mainly used for:

[0016] The spectral data returned by the communication module is filtered to remove high-frequency noise and dark-state noise, and the interference spectrum at the corresponding wavelength is obtained.

[0017] The peaks and troughs of the waveform are automatically obtained from the interference spectrum, and the cell thickness is calculated according to the formula.

[0018] Secondly, a method for measuring the cell thickness of a silicon-based liquid crystal (LCoS) includes the following main steps:

[0019] 1. The LCoS cell thickness measurement equipment collects the ambient dark spectrum and the spectrum of the light source itself as the basis for subsequent identification of the interference spectrum;

[0020] 2. Light of different wavelengths is incident on each pixel of the LCoS device, forming two coherent reflected beams on the surfaces of the upper and lower substrates of the LCoS device, respectively, and then incident on a fiber optic spectrometer.

[0021] III. The communication module of the box thickness measurement equipment automatically obtains the model information and serial port speed of the spectrometer for further communication.

[0022] IV. The spectral data is transmitted back to the data calculation module via the communication module. The data calculation module automatically filters the input data to reduce the interference of high-frequency noise on the calculation and compares it with the background spectrum.

[0023] 5. The calculation module automatically identifies the peaks and troughs of the interference spectrum waveform. Based on the relationship between the cell thickness and the wavelengths corresponding to the peaks and troughs, and using the five-point measurement method, it calculates the cell thickness and cell thickness uniformity of the LCoS device. The five-point measurement method involves taking the pixel at the midpoint of the diagonal of the LCoS device as the center sampling point, and then selecting four pixels equidistant from the center sampling point on the diagonal as sampling points. The cell thickness at each of the five points is measured, averaged, and the cell thickness uniformity is calculated.

[0024] Therefore, the method provided in this invention can accurately measure the cell thickness of LCoS devices and calculate the cell thickness uniformity. This method eliminates the need for manual reading of the wavelengths corresponding to the maximum and minimum intensity values ​​of the reflected light spectrum to determine the LCoS device cell thickness, thus avoiding errors caused by human intervention. The light source spectrum used is in the 490-710nm band, comprehensively covering the visible light spectrum, which helps improve the accuracy of cell thickness measurement and calculation. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the vertical structure of the LCoS device in an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of an LCoS cell thickness measuring device disclosed in this invention.

[0027] Figure 3 This is a schematic diagram of an LCoS cell thickness measurement method disclosed in this invention.

[0028] Figure 4 This is a schematic diagram of the five-point measurement method in an embodiment of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are merely preferred embodiments of the present invention, and not all embodiments. For example, the light source in this application can refer to a broadband light source of any wavelength range. In the preferred embodiment shown in this invention, to illustrate the reliability of LCoS cell thickness measurement in the visible light band, a light source of 490-710 nm is selected, and a visible light band spectrometer is selected as the fiber optic spectrometer.

[0030] This invention provides a method and apparatus for measuring the cell thickness of an LCoS device, used to measure the cell thickness and cell thickness uniformity of the LCoS device. The method and apparatus are based on the same inventive concept. Since the principles by which the method and apparatus solve the problem are similar, their implementations can be referred to interchangeably, and repeated details will not be elaborated further.

[0031] The specific structure of LCoS devices will be introduced below, such as... Figure 1 As shown, the vertical structure of an LCoS device can be divided into three parts: upper, middle, and lower, consisting of a liquid crystal layer and upper and lower substrates. The upper substrate serves as the incident and emitting substrate for light, using transparent glass as the base, on which transparent ITO electrode layers and alignment layers are sequentially fabricated. The lower substrate is the LCoS phase modulator substrate fabricated using CMOS technology, divided into PAD areas, pixel areas, and driving circuit areas. An alignment layer is also fabricated on the CMOS substrate, which, together with the alignment layer on the upper substrate, provides alignment for the liquid crystal layer. Spacers are used to support the upper and lower substrates, providing a defined thickness and filling space for the liquid crystal layer. After the liquid crystal layer is filled, a complete LCoS phase modulation device is formed.

[0032] When the liquid crystal molecules are aligned in ECB mode, the light incident on the liquid crystal layer is decomposed into o-rays and e-rays due to birefringence. Since the o-ray and e-ray correspond to different refractive indices n... o and n e The refractive index of o-ray incident with a polarization direction perpendicular to the optical axis is n. oThe refractive index of the e-ray incident along the parallel optical axis changes due to the change in the direction of the liquid crystal molecules' orientation under the influence of the electrical signal. The corresponding effective refractive index n is related to this direction. eff Since LCoS is a reflective device, the liquid crystal molecules are modulated twice by the liquid crystal layer.

[0033] Considering the actual situation, the pointing vectors of liquid crystal molecules are not strictly consistent and exhibit slight variations. In this case, the phase retardation of the o-ray and e-ray caused by the liquid crystal molecules can be calculated by integrating the liquid crystal layer in the vertical direction. The magnitude of this phase retardation can be expressed as:

[0034]

[0035] θ z The angle between the liquid crystal director and the incident light varies with the vertical height; d represents the LCoS liquid crystal cell thickness. Phase modulation is the most important performance characteristic of LCoS devices. The thickness of the liquid crystal layer plays a decisive role in the magnitude of phase modulation, while the uniformity of the liquid crystal layer determines the uniformity of phase modulation. Therefore, characterizing the cell thickness of the device is extremely crucial. Devices with uniform cell thickness have a uniform liquid crystal layer, resulting in smaller errors in modulation between different regions and better modulation capabilities compared to devices with non-uniform cell thickness. Therefore, to improve the modulation capabilities of LCoS devices, it is necessary to design corresponding measurement equipment and methods for LCoS cell thickness.

[0036] The interferometric method for measuring cell thickness is simple to operate, provides intuitive observations, and is suitable for measuring reflective devices. When polychromatic incident light is incident on an LCoS device, two reflected beams are formed on the glass substrate surface and the LCoS chip surface, respectively. The optical path difference between the two beams is twice the cell thickness *d*. By measuring the interference spectrum at a specific point in space, the cell thickness can be calculated based on the condition of destructive and constructive interference. Ideally, the air refractive index between the substrates is 1, so the optical path difference between the two beams is 2d. At a point P in space, the conditions for interference maxima and minima are as follows:

[0037] 2d=kλ (k=0, ±1, ±2...)

[0038]

[0039] Let λ1 be the wavelength at which interference maxima occur at P, and λ2 be the adjacent minimum wavelength. Eliminating k from both equations, we get:

[0040]

[0041] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. (See attached drawings) Figure 2 As shown, an embodiment of the present invention provides an LCoS cell thickness measuring device, the device comprising:

[0042] The system includes a light source, a fiber optic spectrometer, a communication module, and a computing module; the light source is in the range of 490-710nm, and the spectrometer is a visible light spectrum analyzer.

[0043] The communication module mainly includes:

[0044] Spectrometer connection, wavelength reading, light intensity reading, spectrometer shutdown;

[0045] The spectrometer connection section is mainly responsible for establishing a link between the computer and the spectrometer, and obtaining the spectrometer's model information and serial port speed for further communication.

[0046] After establishing the connection, the wavelength information of the spectrometer is queried through the wavelength reading section, and the wavelength corresponding to the data collected by the spectrometer is obtained through serial communication, which serves as a reference for subsequent calculations.

[0047] The system sends a read command to the spectrometer via serial port. The spectrometer reads the light intensity data. The number of bytes read is determined by the USB communication rate specified in the connection section. In high-speed mode, the data is in units of 512 bytes, and in low-speed mode, it is in units of 64 bytes. Finally, the read byte information is converted into the corresponding spectral data for use by the calculation module.

[0048] After the box thickness measurement is completed, the connection between the computer and the spectrometer is terminated by closing the spectrometer.

[0049] The calculation module is mainly used for:

[0050] The spectral data returned by the communication module is filtered to remove high-frequency noise and dark-state noise, and the interference spectrum at the corresponding wavelength is obtained.

[0051] The peaks and troughs of the waveform are automatically obtained based on the interference spectrum, and the cell thickness and cell thickness uniformity are calculated according to the formula.

[0052] like Figure 3 As shown, this embodiment of the invention provides a method for measuring the thickness of an LCoS cell. The implementation process of this embodiment is described in detail below with reference to a specific example. The method includes:

[0053] Step S01: The LCoS cell thickness measurement device collects the ambient dark spectrum and the spectrum of the light source itself as the basis for subsequent identification of the interference spectrum.

[0054] Step S02: Light of each wavelength is incident on each pixel of the LCoS device, forming two coherent reflected beams on the surfaces of the upper and lower substrates of the LCoS device, respectively, and then incident on the fiber optic spectrometer.

[0055] Optionally, the incident light wavelength can be selected from the visible light band. For example, light with a wavelength of 490-710nm is incident on each pixel of the LCoS device to obtain the reflected light interference intensity corresponding to each wavelength, and thus obtain the reflection spectrum data.

[0056] Optionally, the incident pixels can be selected as needed. For example, the pixel at the midpoint of the diagonal of the LCoS device can be taken as the center sampling point, and four pixels equidistant from the center sampling point can be selected on the diagonal as sampling points. Figure 4 As shown.

[0057] Step S03: The communication module of the box thickness measurement equipment automatically obtains the model information and serial port speed of the spectrometer for further communication. Since the wavelength information is fixed for a single spectrometer, only a single query is required.

[0058] Step S04: The spectral data is transmitted back to the data calculation module via the communication module. The data calculation module automatically filters the input data to reduce the interference of high-frequency noise on the calculation and compares it with the background spectrum. Using the filtered spectrum as the basis for calculation, dark noise is removed and compared with the background spectrum measured in step S01 to obtain the interference spectrum at the corresponding wavelength.

[0059] Step S05: The calculation module automatically identifies the peaks and troughs of the interference spectrum waveform. Based on the relationship between the cell thickness and the wavelengths corresponding to the peaks and troughs, and the five-point measurement method, it calculates the cell thickness and cell thickness uniformity of the LCoS device. The calculation module automatically identifies the wavelength data corresponding to the peaks and troughs, and the automatically detected peaks and troughs are marked with green straight lines on the program display panel. The five-point measurement method involves taking the pixel at the midpoint of the diagonal of the LCoS device as the center sampling point, and then selecting four pixels on the diagonal equidistant from the center sampling point as sampling points. The cell thickness of the device is measured at each of the five points, and the average is taken to obtain the LCoS device cell thickness. In this embodiment, the measured LCoS cell thickness is 3049.94nm, which is consistent with the 3μm cell thickness of the reference device, with an error of only 1.67%, indicating high accuracy. The measured cell thickness at the five points is then substituted into the following uniformity formula:

[0060]

[0061] Where V is the cell thickness uniformity of the LCoS device, n is the number of sampling points, and d i For the LCoS cell thickness at a certain sampling point, This represents the average box thickness.

[0062] In this embodiment, the thickness uniformity of the LCoS cell was measured to be 90%, which is good, and the measurement operation is simple.

[0063] In summary, the method provided by the embodiments of the present invention can measure the cell thickness and cell thickness uniformity of LCoS devices. Furthermore, the method provided by the embodiments of the present invention is applicable to the cell thickness measurement of all LCoS phase modulation devices, is simple to operate and has small error, and can accurately measure the cell thickness and cell thickness uniformity of LCoS devices.

[0064] It should be noted that the module division in the embodiments of this invention is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods. Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated modules described above can be implemented in hardware or as software functional modules.

[0065] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] Therefore, although the present invention has been shown above with reference to preferred embodiments, these preferred embodiments are not intended to limit the present invention. Those skilled in the art can still modify the technical solutions described in the foregoing embodiments. Any modifications, refinements, and equivalent substitutions made without departing from the spirit and scope of the present invention should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention is determined by the scope defined in the claims.

Claims

1. A silicon-based liquid crystal (LCoS) cell thickness measuring apparatus, characterized by, It comprises: a light source, a fiber-optic spectrometer, a communication module, and a calculation module; the wavelength of the light source is in the range of 490-710 nm; the spectrometer is a visible light band spectrometer; the communication module mainly includes: spectrometer connection, wavelength reading, light intensity reading, and spectrometer shutdown; the spectrometer connection part is mainly responsible for establishing a link between the computer and the spectrometer, obtaining the model information and serial port speed of the spectrometer for further communication; after establishing the link, the wavelength information of the spectrometer is queried through the wavelength reading part, and the wavelength corresponding to the data collected by the spectrometer is obtained through serial communication as a reference for subsequent calculation; read instructions are sent to the spectrometer through the serial port, the spectrometer reads the light intensity data, and the number of read bytes is determined by the USB communication rate determined by the connection part, which is 512 bytes in high-speed cases and 64 bytes in low-speed cases, and finally the read byte information is converted into corresponding spectral data for the calculation module; after the box thickness measurement is completed, the spectrometer shutdown part is used to end the connection between the computer and the spectrometer; the calculation module is mainly used for: filtering the spectral data returned by the communication module to remove high-frequency noise and dark-state noise and obtain the interference spectrum under the corresponding wavelength; automatically obtaining the wave peak and wave trough of the waveform according to the interference spectrum and calculating the box thickness according to the formula.

2. A method for measuring the cell thickness of a silicon-based liquid crystal (LCoS), characterized in that, It includes the following five main steps:

1. The LCoS box thickness measurement device collects the ambient dark spectrum and the spectrum of the light source itself as the basis for subsequent identification of the interference spectrum; 2. Each wavelength of light is incident on each pixel point of the LCoS device, forming two coherent reflected lights on the surface of the LCoS device substrate and the lower substrate, and the incident light is collected by the fiber-optic spectrometer; 3. The communication module of the box thickness measurement device automatically obtains the model information and serial port speed of the spectrometer for further communication; 4. The spectral data is returned to the data calculation module through the communication module, and the data calculation module automatically filters the input data to reduce the interference caused by high-frequency noise and compare it with the background spectrum; 5. The calculation module automatically identifies the wave peak and wave trough of the interference spectrum waveform, calculates the box thickness and box thickness uniformity of the LCoS device according to the relationship between the box thickness and the corresponding wavelength of the wave peak and wave trough, and the five-point measurement method. The five-point measurement method is to take the pixel point at the midpoint of the diagonal line of the LCoS device as the center sampling point, and select four pixel points with equal distance from the center sampling point on the diagonal line as sampling points; measure the device box thickness at the five points, take the average to obtain the LCoS device box thickness and calculate the box thickness uniformity.

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