JP2005031007A - Spectroscope using liquid crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spectroscope using liquid crystal, light in weight, light in transmission light, capable of obtaining high spectrum precision, and moreover is capable of being manufactured easily. <P>SOLUTION: The spectroscope is constituted, such that for an interferometer 10 for light separation with the Fourier transform spectrometer which uses a liquid crystal panel 10A, in which one or multiple liquid crystal cells 12 are held between a pair of polarizers 11 and 13, with the light 1 incident on the liquid crystal panel is divided into two components of normal light 1A and abnormal light 1B; and by varying the cell voltage of the liquid crystal cells, the optical path difference δ between the two components is generated, and the resultant interference light 2 is emitted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spectroscopic device using a liquid crystal, and more particularly to a spectroscopic device using a liquid crystal that performs spectroscopy by Fourier transform spectroscopy.

  As a spectroscopic device using liquid crystal, a plurality of optical uniaxial crystals sandwiched between parallel polarizers (the optical axis phase difference between the polarizer and the uniaxial crystal is 45 °) are laminated (the thickness of the uniaxial crystal is incident light). In the rio filter formed by d, 2d, and 4d from the side (Non-Patent Document 1: This does not use liquid crystal), it is a kind of liquid crystal cell instead of a stack of optical uniaxial crystals. A band-pass filter using a stack of ECB cells (electrically controlled birefringent cells) (cell thickness is the same for all cells d) has been proposed (Non-patent Document 2). In the bandpass filter of Non-Patent Document 2, one of a plurality of ECB cells is sandwiched between orthogonal polarizers in order to suppress transmission of unnecessary wavelength light within the visible wavelength. According to this, the wavelength range (or wave number range) showing a narrow transmission spectrum can be changed by changing the voltage applied to the liquid crystal layer, that is, the cell voltage, so that a plurality of types of narrow transmission spectra can be obtained without replacing the filter. There is an advantage that it can be obtained. However, in order to satisfy the optical conditions of the rio filter, the cell voltage must be changed for each cell, and thus a complicated voltage control circuit is required.

  In order to eliminate this disadvantage, the orientation of the liquid crystal in the cell obtained by analyzing the electro-optical properties of the liquid crystal layer based on the elastic continuum theory (Non-patent Document 3) Based on the knowledge that there is no relation to the cell thickness, the cell thickness of the ECB cell to be stacked is a combination that satisfies the optical conditions of the Rio filter, ie, d, 2d, 1.5 d from the incident side, and an electrically adjustable color A filter has been proposed (Non-Patent Document 3).

  According to this, since the cell voltage is the same in any cell and a plurality of types of narrow transmission spectra can be obtained simply by controlling the voltage of a single power supply that supplies the cell voltage, the voltage control circuit is very simple. . In Non-Patent Document 3, in order to improve responsiveness, the cell thickness was reduced while maintaining the thickness ratio, and a retardation film (1: 2: 1.5 which is the same as the cell) was attached to each cell. In place of the ECB cell and the ECB cell, an OCB cell (optically compensated bend cells) (Non-Patent Documents 4 to 11) excellent in viewing angle and response has been proposed.

  On the other hand, there is a Fourier Transform Infrared Spectroscopy (FT-IR) as a spectroscopic device that is not used for liquid crystal but is referred to in making the present invention. In this method, the interference light obtained by the interferometer is converted into a digital signal and spectrally dispersed by Fourier transforming it with a computer. Specifically, the light emitted from the light source is passed through the interferometer to produce interference light, which is The sample is irradiated through the sample chamber, the light (reflected light, scattered light, or transmitted light) emitted from the sample chamber is captured by a detector, and the output signal of the detector is digitized by an AD (analog-digital) converter. Thereafter, the data is transmitted to a computer, and the computer performs a Fourier transform on the transmitted data, and the obtained spectrum waveform is displayed on a display.

  An interferometer is an optical element that has a structure that causes interference by dividing incoming light into multiple optical paths, creating optical path differences between them, and synthesizing them again. It was created for the purpose of measuring faint light with high sensitivity and precise measurement of the surface accuracy of optical lenses and mirrors. Various things have been devised since the 19th century, but FT-IR uses a Michelson interferometer. Most commonly used.

  The Michelson interferometer is composed of one semi-transparent mirror and two plane mirrors (one of which is a moving mirror and the other is a fixed mirror). The light incident on the semi-transparent mirror is divided into two beams of reflected light that are reflected in a direction perpendicular to the transmitted light that is transmitted in the straight direction. Both luminous fluxes are folded back by a plane mirror and synthesized again by a semi-transparent mirror. By moving the moving mirror, an optical path difference between the two light beams is created.

  When the incident light is monochromatic light having a wavelength λ (wave number ν = 1 / λ), both light beams are weakened in opposite phases when the optical path difference is a multiple of λ / 2, and the optical path difference is 0 or a multiple of λ. By the way, it becomes the same phase and strengthens each other. Therefore, when the output light from the interferometer is observed by continuously moving the movable mirror, the light and dark are periodically repeated. When this is graphed with the optical path difference as the horizontal axis, the result is a cosine wave according to the wavelength of the incident light. When the incident light is two monochromatic lights having different wavelengths, each monochromatic light is modulated according to the wavelength by continuous scanning of the moving mirror, and the output light from the interferometer is observed as a sum of two cosine waves. Even if light with more wavelengths is introduced, a composite wave modulated for each wavelength component is output, and the intensity of the light from an actual light source having continuous wavelengths increases as the optical path difference increases. A decreasing output waveform is observed. This waveform is called an interferogram. By analyzing the signal intensity of each frequency included in the interferogram, the intensity of light of each wavelength (wave number) can be obtained.

  When the optical path difference is δ, the interferogram F (δ) is expressed by an integral function shown in Formula 1.

B (ν) is a so-called spectrum representing the intensity of light for each wave number. Equation 1 corresponds to an equation of Fourier transform, and a spectrum is obtained by performing this calculation (Fourier transform of the interferogram). In FT-IR, the computer performs this calculation.
B.Lyot: Comptes Rendus 197,1593 (1933) K. Sato, N. Kato, Y. Hanazawa and T. Uchida: proc. Japan Display, 392 (1989); proc. SID 32, 183 (1991) P.Sheng: RCA Laboratories, Princeton, NJ08540 S. Araki, H. Chiba, M. Suzuki, T. Miyashita, T. Uchida: Proc. Eurodisplay '99 19th Int. Display Research Conf. P. 133-136 (1999) Y. Yamaguchhu, T. Miyashita and T. Uchida: SID Symp. Digest, p. 277 (1993) T.Miyashita, P. Vetter, M. Suzuki, Y. Yamaguchi and T. Uchida: Eurodisplay Conf. Proc., P. 149 (1993); J. SID, 3, p. 29 (1995) CL. Kuo, T. Miyashita, M. Suzuki and T. Uchida: SID Symp. Digest, p. 927 (1994); Japan. J. Appl. Phys., 34 (1995) L1362; Appl. Phys. Lett., 68.p.1461 (1996) T.Miyashita and T.Uchida: IEICE Trans.Electronics, E79E-Cp1076 (1996) T. Miyashita and T. Uchida: Digest of Technical Paper, AM-LCD, p.181 (1996) T. Uchida, K. Saitoh, T. Miyashita and M. Suzuki: Conf. Record of The International Display Research Conf., P. 37 (1997) K. Saitoh, T. Miyashita, M. Suzuki and T. Uchida: Proc. International Display Workshops, p. 179 (1997)

  In the prior art described above, a rio filter type spectroscopic device using liquid crystal is a liquid crystal cell or a laminate of two sheets of this and a retardation film sandwiched between a pair of polarizers (this is The liquid crystal panel is required to be configured by stacking at least three sheets (polarizers can be shared between adjacent liquid crystal panels). Moreover, the cell thickness cannot be made thinner than the lower limit determined by the Rio filter conditions. Therefore, there is a problem that the weight is heavy and it is inconvenient to carry, and the transmitted light becomes dark and difficult to observe, and because there are many different layers to overlap, it is difficult to manufacture with high accuracy. There is also a problem that there is a limit.

  An object of the present invention is to solve these problems, and to provide a spectroscopic device using liquid crystal that is light in weight, bright in transmitted light, high in spectral accuracy, and easy to manufacture.

  The present invention is as follows.

  (1) Using one liquid crystal panel in which one or a plurality of liquid crystal cells are sandwiched between a pair of polarizers, the light incident on the liquid crystal panel is divided into two components of ordinary light and extraordinary light. An interferometer configured to emit an interference light obtained by combining the two components of light by changing the cell voltage to add an optical path difference, and two-dimensionally detecting the interference light emitted from the interferometer A photodetector that converts the signal into an electrical signal and outputs it, a converter for inputting the output of the photodetector to a computer, a signal output from the converter, the received signal, and the A spectroscopic device using liquid crystal, comprising: a computer that calculates a spectrum of visible light by Fourier transform from an optical path difference.

  (2) The spectroscopic device using the liquid crystal according to (1), wherein the liquid crystal cell is a uniaxial liquid crystal cell, and the optical axis of the liquid crystal cell and the transmission axis of the polarizer are obliquely crossed. .

  (3) Instead of detecting the interference light emitted from the interferometer, the light detector detects light emitted from an object irradiated with the interference light emitted from the interferometer. A spectroscopic device using the liquid crystal according to (1) or (2).

  (4) Spectroscopy using the liquid crystal according to any one of (1) to (3), which has at least one retardation film inserted between one and the other of the pair of polarizers apparatus.

  (5) The spectroscopic device using liquid crystal according to (4), wherein the liquid crystal cell is an OCB cell.

  (6) The spectroscopic device using the liquid crystal according to any one of (1) to (5), further including a cut filter that removes a predetermined wavelength component from the light before being detected by the photodetector.

  According to the present invention, a single liquid crystal panel is used as an interferometer to perform spectroscopy by Fourier transform spectroscopy, so that the weight is light, the transmitted light is bright, high spectral accuracy is obtained, and manufacturing is easy. A spectroscopic device is realized.

  For example, as shown in FIG. 1, the spectroscopic device of the present invention includes an interferometer 10 that emits interference light 2 that is obtained by combining an incident light 1 with an optical path difference between two components of ordinary light and abnormal light, and an interferometer 10. Detector 20 that detects the interference light 2 emitted from the laser beam two-dimensionally, converts it into an electrical signal 3 and outputs it, and converts the signal 3 output from the photodetector 20 into a signal 4 that can be input to a computer. And a computer 40 that receives the signal 4 output from the converter 30 and calculates the spectrum of visible light by Fourier transform from the received signal 4 and the optical path difference. The incident light 1 may be light from a natural light source or light from an artificial light source.

  In the present invention, as the interferometer 10, for example, as shown in FIGS. 3 and 4, one liquid crystal cell 12 (cell thickness d is assumed to be d) is sandwiched between a pair of polarizers 11 and 13. By using the liquid crystal panel 10A, the incident light 1 incident on the liquid crystal panel 10A is divided into two components of ordinary light 1A and extraordinary light 1B, and the cell voltage of the liquid crystal cell 12 is changed by using the cell voltage setting device 50 or the like. An optical path difference δ is added to 1A and extraordinary light 1B so as to emit interfering light 2 that is synthesized is used. Although the liquid crystal cell 12 illustrated in FIGS. 3 and 4 is a uniaxial one, it can also be used as a biaxial one or a TN (twisted nematic) liquid crystal cell. In the case of uniaxiality, the optical axis 15 of the liquid crystal cell 12 and the transmission axes 14 and 16 of the polarizers 11 and 13 need to be obliquely crossed (obliquely crossed). The crossing angles θ1, θ2 are preferably θ1 = θ2 = 45 °.

  The cell voltage is commanded from the computer 40 to the cell voltage setter 50 of the interferometer 10 via the transmission path 6. Note that the cell voltage may be set by the cell voltage setting unit 50 by itself instead of instructing from the computer 40, and the set value may be transmitted to the computer 40. Alternatively, the confirmation signal indicating that the interferometer 10 has surely received the command from the computer 40 may be transmitted to the computer 40. Further, the operation timing may be instructed from the computer 40 to the photodetector 20 and the converter 30 via the transmission paths 7 and 8.

  The photodetector 20 is configured by two-dimensionally arranging a plurality of light receiving elements such as CCDs, and signals from each light receiving element are converted into signals that can be input to the computer 40 by the AD converter 30.

  The phase relationship between the transmission axes 14 and 16 of the polarizers 11 and 13 of the liquid crystal panel 10A may be either orthogonal (cross Nicol; see FIG. 3) or parallel (parallel Nicol; see FIG. 4). The exit side polarizer 13 is distinguished from the entrance side polarizer 11 and is referred to as an analyzer.

In the interferometer 10 composed of the above-described liquid crystal panel 10A, when θ1 = θ2 = 45 °, the intensity of the ordinary light 1A and the extraordinary light 1B generated by dividing the incident light 1 having the wave number ν (= 1 / λ) is equal. It will, when it is referred to as I _i, the intensity I _t of the interference light 2 which has passed through the analyzer 13 are combined is given by the following equation.

For cross _{nicol: I t = (1/2) I} i {1-cos (2πδν)}
In the case of parallel Nicol: I _t = (1/2) I _i {1 + cos (2πδν)}
Here, the optical path difference δ is given by δ = Δn (V) d. Δn (V) is a difference in refractive index between ordinary light and extraordinary light, which is given as a function of the cell voltage V. That is, the interferometer 10 configured using the liquid crystal panel 10A can obtain the interference light 2 by changing the cell voltage V to change the optical path difference δ. In the case of using the liquid crystal cell than when or uniaxial not θ1 = θ2 = 45 °, to produce a difference in intensity of ordinary and extraordinary light, calculation of the interference light intensity I _t becomes somewhat complicated However, it is possible to obtain interference light by changing the optical path difference δ in the same manner.

  When the incident light 1 has a continuous spectral distribution, assuming that the intensity of the light for each wave number of the incident light is B (ν), each light receiving element of the photodetector detects the upper side of the equation 1 according to the optical path difference δ. Since analog signals corresponding to the interferogram F (δ) expressed by the equation are output, they are converted into digital signals by a converter, and the Fourier transform equation of F (δ), that is, The two-dimensional spectrum of visible light can be measured by calculating the equation on the side with a computer.

  In the present invention, a conventional spectroscopic device using liquid crystal is a rio filter using at least three liquid crystal panels, whereas an interferometer is configured using one liquid crystal panel, and Fourier transform spectroscopy is used. Since spectroscopy is performed, the weight is lighter than the conventional one, the transmitted light is bright, and high spectral accuracy is obtained. Moreover, manufacture is also easy.

  Compared to the conventional Michelson interferometer, the structure is simple because it does not have a moving part like a moving mirror. In addition, since the conventional interferometer splits the slit light, the spectral distribution in the two-dimensional image of the object used as the sample could not be measured at a time. However, in the present invention, the entire object or an arbitrary part thereof is measured. Since a photodetector that can be photographed in the field of view is used, the spectral distribution in the two-dimensional image of the object can be measured at a time.

  The example shown in FIG. 1 is an apparatus of a type in which light emitted from an object is incident on the interferometer. However, the present invention is not limited to this, and for example, as shown in FIG. An object 100 as a sample is placed between the detectors 20, the sample 100 is irradiated with the interference light 2 emitted from the interferometer 10, and the light emitted from the sample 100 (any of reflected light, transmitted light, and scattered light may be used). ) A device that receives 2A by the photodetector 20 may be used. This method can be suitably employed when the sample is broken when irradiated with strong light.

  In the present invention, the number of liquid crystal cells in the liquid crystal panel 10A is not limited to one, but may be a plurality. When a plurality of liquid crystal cells are used in an overlapping manner, a liquid crystal cell having a small cell gap can be used, which is advantageous in terms of response speed. When there are a plurality of liquid crystal cells, for example, as shown in FIG. 5 where there are three liquid crystal cells, the same cell voltage may be applied to the liquid crystal cells 12a, 12b and 12c. In this case, the optical path difference δ is given by the total value of each liquid crystal cell.

  In the present invention, a retardation film may be inserted between the polarizer 11 and the analyzer 13. When the liquid crystal cell and the retardation film are used in combination, the amount of retardation can be increased or decreased, which is advantageous when it is desired to change the voltage range to be applied and the necessary retardation range. The number of retardation films may be one or more. Further, the positions where the retardation film 17 is inserted are, for example, as shown in FIG. 6, between the polarizer 11 and the liquid crystal cell 12 (FIG. 6A), and between the liquid crystal cell 12 and the analyzer 13 (FIG. 6B). )), Or when there are a plurality of liquid crystal cells, it may be between a certain liquid crystal cell 12a and the adjacent liquid crystal cell 12b (FIG. 6C).

  Moreover, in this invention, when using a liquid crystal cell and a retardation film together, as a liquid crystal cell, an OCB cell (refer nonpatent literature 4-11) is used by the point that it is excellent in the response characteristic and the wide viewing angle characteristic. Is preferred.

  Further, in the present invention, for example, as shown in FIG. 7, the interference light 2 (see FIG. 7A) before entering the photodetector 20, or the light 2A emitted from the object 100 irradiated with the interference light 2 Therefore, it is preferable to have a cut filter 18 that removes a predetermined wavelength component. Examples of such a cut filter include an infrared cut filter and an ultraviolet cut filter. By providing such a cut filter, the light 2B from which the predetermined wavelength component is removed from the interference light 2 or the light 2A emitted from the object 100 irradiated with the interference light 2 enters the photodetector 20. The aliasing noise caused by the introduction of wavelength components that are not subject to spectroscopy, such as infrared rays or ultraviolet rays, is eliminated, and a higher resolution device can be obtained.

  A spectroscopic device having the configuration shown in FIG. The liquid crystal panel was configured as shown in FIG. An OCB cell (liquid crystal: TD-6004XX manufactured by Chisso Petrochemical Co., Ltd., cell thickness d = 10 μm) was used as the liquid crystal cell. The crossing angles θ1, θ2 between the optical axis of the liquid crystal cell and the transmission axes of the polarizer and analyzer (made cross Nicol) were set to 45 °. A retardation film made of polycarbonate having a retardation amount of 100 nm (thickness: 200 μm) was used as the retardation film, and ME-41 manufactured by Elmo Co., Ltd. was used as the photodetector. The Fourier transform formula is a software that allows the input of monochromatic light and discrete multi-color light with known intensities, changes the cell voltage, investigates the relationship between the optical path difference δ and the intensity of the interference light, and can perform computer calculations based on the results. It was in the form of wear. According to this apparatus, an interferogram F (δ) having a waveform as shown in FIG. 8, for example, is obtained from the observation data of incident light, and a Fourier transform thereof is executed by the computer, as shown in FIG. A spectral distribution B (λ) for a specific wavelength λ or a spectral distribution B (ν) for a wave number ν (= 1 / λ) (not shown) is obtained.

  The present invention can be used in various fields such as astronomical observation (star spectrum analysis), medical treatment (cell analysis, etc.), food (sugar content measurement, etc.).

It is a schematic diagram which shows an example of this invention. It is a schematic diagram which shows an example of this invention. It is a schematic diagram which shows an example of the interferometer used by this invention. It is a schematic diagram which shows an example of the interferometer used by this invention. It is a schematic diagram which shows an example of the interferometer used by this invention. It is a schematic diagram which shows an example of the interferometer used by this invention. It is a schematic diagram which shows an example of this invention. It is a wave form diagram which shows an example of interferogram F ((delta)) obtained by this invention, and spectrum distribution B ((lambda)) obtained by Fourier-transforming this.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Incident light 1A Ordinary light 1B Abnormal light 2 Interference light 2A Light emitted from the object irradiated with interference light 3 Signal (example: analog signal)
4 signals (example: digital signals)
5 Spectrum 6, 7, 8 Transmission path
10 Interferometer
10A LCD panel
11 Polarizer
12, 12a, 12b, 12c Liquid crystal cell
13 Polarizer (analyzer)
14 Transmission axis
15 optical axis
16 Transmission axis
17 Retardation film
18 Cut filter
20 photodetector
30 transmitter
40 computers
50 cell voltage setter
100 object (sample)

Claims (6)

  Using one liquid crystal panel with one or more liquid crystal cells sandwiched between a pair of polarizers, the light incident on the liquid crystal panel is divided into two components, ordinary light and abnormal light, and the cell voltage of the liquid crystal cell is An interferometer configured to emit an interference light obtained by adding an optical path difference to the light of the two components by changing and emitting the interference light, and detecting the interference light emitted from the interferometer in two dimensions. A photodetector that converts and outputs the signal to the computer, a converter for inputting the output of the photodetector to a computer, a signal output from the converter, and a signal received from the received signal and the optical path difference A spectroscopic device using liquid crystal, comprising: a computer that calculates a spectrum of visible light by Fourier transform.   2. The spectroscopic device using liquid crystal according to claim 1, wherein the liquid crystal cell is a uniaxial liquid crystal cell, and an optical axis of the liquid crystal cell and a transmission axis of the polarizer are obliquely crossed.   The light detector is configured to detect light emitted from an object irradiated with interference light emitted from the interferometer, instead of detecting the interference light emitted from the interferometer. A spectroscopic device using the liquid crystal according to claim 1.   The spectroscopic device using a liquid crystal according to any one of claims 1 to 3, further comprising at least one retardation film inserted between one and the other of the pair of polarizers.   5. The spectroscopic device using liquid crystal according to claim 4, wherein the liquid crystal cell is an OCB cell.   The spectroscopic device using a liquid crystal according to claim 1, further comprising a cut filter that removes a predetermined wavelength component from the light before being detected by the photodetector.

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