JP2013124865A - Spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make resolution improvement compatible with reduction in size by acquiring data of required bands.SOLUTION: A spectrometer comprises a drive mirror 12, an immersion grating 15, a PD 17, and a DMD 16. The drive mirror 12 is wavelength sweep means which deflects incident light and sweeps a wavelength of a desired band. The immersion grating 15 is a dispersion element which diffracts light deflected by the drive mirror 12 in a different direction for each wavelength. The PD 17 is a photodetector. The DMD 16 is a deflection element array which makes only light of a specific wavelength, in the light diffracted by the immersion grating 15, incident to the PD 17.

Description

  The present invention relates to a spectrometer.

  A spectroscopic optical system that splits incident light in different directions for each wavelength is used as a spectroscope. In optical communication, a signal conduction state can be confirmed by being incorporated in a network device, so that it is used as a monitor. The characteristic required at that time is that it can acquire data of a necessary band (for example, L band) and has high resolution and small size.

  An example of a general small spectroscope is shown in FIG. 8 (see, for example, Non-Patent Document 1). The lens 2 converts the light emitted from the optical fiber 1 into parallel light. The deflection element 3 deflects the light that has passed through the lens 2. The dispersion element 4 such as a diffraction grating separates the reflected light from the deflection element 3 for each wavelength. The lens 5 collects the light dispersed by the dispersive element 4. The slit 6 allows only light having a single wavelength out of the light collected by the lens 5 to pass through. The PD (photodiode) 7 receives light passing through the slit 6 and converts it into an electric signal. In this spectroscope, the wavelength of light received by the PD 7 can be changed by rotating the deflection element 3. A MEMS (Microelectro-Mechanical Systems) mirror may be used as the deflecting element 3 that sweeps the wavelength in order to realize miniaturization. In such a spectroscope, the equation indicating the resolution is as follows.

Here, Δλ is the resolution, λ is the wavelength of light, ω is the beam radius, that is, the minimum radius of the dispersion element 4, dθ / dλ is the dispersion capability of the dispersion element 4, and k is a constant. In order to achieve high resolution of the spectroscope (that is, Δλ is reduced), it is necessary to increase the size of the dispersive element 4 (that is, increase ω) or to increase the dispersibility dθ / dλ of the dispersive element 4. is there. In order to achieve both high resolution and downsizing, it is important to increase the dispersion capability of the dispersion element 4.
However, in order to acquire spectral data of a necessary band, the maximum rotation angle of the mirror increases in proportion to the dispersion capability of the dispersion element 4. On the other hand, a MEMS mirror generally has only a minute change in angle, so that there is a problem that the rotation angle cannot be increased and the bandwidth of spectral data becomes narrow.

Takanori Saitoh, et al., “Optical Spectrum Analyzer Utilizing MEMS Scanning Mirror”, Photo.Tech.let., Vol.18, no.6, 2006

  As described above, the conventional spectrometer has a trade-off relationship with the data acquisition band, resolution, and size, and there is a problem that it is difficult to improve the performance of all of them.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spectrometer that can acquire data of a necessary band and can achieve both high resolution and downsizing.

The spectroscope of the present invention includes a wavelength sweep unit that deflects incident light and wavelength-sweeps a desired band, a dispersion element that splits light deflected by the wavelength sweep unit in different directions for each wavelength, and receives light. And a deflecting element array that causes only light having a specific wavelength out of the light dispersed by the dispersion element to enter the light receiving element.
Also, one configuration example of the spectroscope of the present invention is characterized in that a light receiving element array that receives light dispersed by the dispersion element is provided instead of the light receiving element and the deflection element array. .
In addition, one configuration example of the spectroscope of the present invention further uses storage means for storing in advance characteristic data of the optical system representing the intensity overlap between adjacent wavelengths of light, and using the characteristic data of the optical system, And data processing means for processing the output signal of the light receiving element to obtain the light intensity for each wavelength.

Further, one configuration example of the spectrometer of the present invention includes a deflection control unit that adjusts a voltage applied to the dispersion element or a temperature of the dispersion element instead of the wavelength sweeping unit, and the dispersion element includes a voltage or A diffraction grating composed of a transmissive member whose refractive index changes according to temperature, and controls the light emission angle from the dispersion element by adjusting the voltage applied to the dispersion element or the temperature of the dispersion element. It is what.
In addition, one configuration example of the spectroscope of the present invention further includes a Fabry-Perot etalon disposed in the optical path before the dispersive element.
In addition, one configuration example of the spectroscope of the present invention further includes a cylindrical lens disposed in an optical path before the Fabry-Perot etalon, and the wavelength sweeping unit is a drive mirror that can be rotated about two axes. It is characterized by being.

  According to the present invention, it is possible to extract light of a desired wavelength within a band with high resolution by fine adjustment by the wavelength sweeping means while acquiring light of the entire band necessary by the deflection element array. Data can be acquired, and both high resolution and downsizing can be achieved.

It is a block diagram which shows the structure of the spectrometer which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the control apparatus of the spectrometer which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the control apparatus of the spectrometer which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the spectrometer which concerns on the 3rd Embodiment of this invention. It is a figure which shows the change of the output angle with respect to the temperature of an immersion grating. It is a block diagram which shows the structure of the spectrometer which concerns on the 4th Embodiment of this invention. It is a block diagram which shows the structure of the spectrometer which concerns on the 5th Embodiment of this invention. It is a block diagram which shows the structure of the conventional spectrometer.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the spectrometer according to the first embodiment of the present invention.
The spectroscope according to the present embodiment includes a fiber collimator 11, a drive mirror 12, a lens 13, a concave mirror 14, an immersion grating 15, a DMD (Digital Micromirror Device) 16, and a PD 17. Is done. The DMD 16 is formed on a silicon substrate as described in, for example, the literature “PETER F. VAN KESSEL, et al.,“ A MEMS-Based Projection Display ”, PROCEEDINGS OF THE IEEE, VOL. 86, NO. 8, 1998”. A plurality of MEMS mirrors are formed in an array so that the deflection angle of the mirrors can be controlled by electrostatic attraction.

  The drive mirror 12 that is a wavelength sweeping unit reflects the light emitted from the fiber collimator 11. At this time, the drive mirror 12 rotates around a rotation axis 18 (rotation axis perpendicular to the paper surface of FIG. 1) perpendicular to the mirror arrangement direction (up and down direction in FIG. 1) of the DMD 16. It is possible. The lens 13 collects the reflected light from the drive mirror 12. The concave mirror 14 reflects the light collected by the lens 13 and makes it incident on an immersion grating 15 which is a dispersive element. The immersion grating 15 separates the reflected light from the concave mirror 14 for each wavelength. The concave mirror 14 reflects the light dispersed by the immersion grating 15 and makes it incident on the DMD 16 used as a variable filter.

  By irradiating the DMD 16 with the light split by the immersion grating 15 in this way, each mirror arranged in an array on the light receiving surface of the DMD 16 is irradiated with light having a different wavelength. Therefore, by controlling the DMD 16 by a control device (not shown) so that the light reflected by the specific mirror of the DMD 16 is incident on the PD 17, it is possible to acquire only light of a specific wavelength. Since 1000 or more mirrors of the DMD 16 are arranged in the major axis direction, it is possible to realize a high resolution spectrometer of 3.5 pm obtained by dividing the band 35 nm of the C band (communication wavelength 1530-1565 nm) into 1000.

  The power of the light received by the PD 17 has a Gaussian distribution with respect to the wavelength axis, and the center wavelength of the Gaussian distribution can be finely adjusted by the rotation of the drive mirror 12. It is possible to simply increase the number of acquisition and sampling points. In the present embodiment, since the silicon immersion grating 15 is used as the dispersive element, a dispersive power several times that of a normal diffraction grating can be obtained, and the spectrometer can be miniaturized. .

  This embodiment is a spectroscope including a fiber collimator 11, a dispersion optical system including a drive mirror 12 as a deflection element, and an immersion grating 15 as a dispersion element, a DMD 16 as a deflection element array, and a PD. Thus, the light emitted from the fiber collimator 11 can be dispersed by the dispersion optical system, only a specific wavelength can be received by the DMD 16 and the PD 17, and the incident position of the light on the DMD 16 can be shifted by the drive mirror 12.

In the present embodiment, a wavelength section selection function for performing rough adjustment by controlling the rotation angle of each mirror of the DMD 16 so that only light in a desired wavelength section enters the PD 17, and the center wavelength of the light incident on the PD 17 And a wavelength selection function for performing detailed adjustment by controlling the rotation angle of the drive mirror 12 so that the value becomes a desired value. In addition, when acquiring power with high precision, it is better to have a lens that forms an image on the PD 17, but the function is satisfied without a lens.
With the above configuration, in the present embodiment, data of a necessary band can be acquired, and both high resolution and downsizing can be achieved.

  Although the fiber collimator 11 is used in the present embodiment, an optical fiber and a collimator lens may be used instead of the fiber collimator 11. Further, as another deflection element array in place of the DMD 16, for example, LCOS (liquid-crystal-on-silicon) or liquid crystal may be used. LCOS is disclosed in, for example, the document “Douglas J. McKnight, et al.,“ 256 × 256 liquid-crystal-on-silicon spatial light modulator ”, APPLIED OPTICS, Vol. 33, No. 14, 1994”. . A PD array may be used instead of the DMD 16 and the PD 17. When a PD array is used, light in different wavelength sections is incident on each PD of the PD array.

Further, a MEMS mirror may be used as the drive mirror 12 that deflects the light emitted from the fiber collimator 11 and sweeps a desired band. Further, instead of the driving mirror 12 that sweeps the wavelength by rotating, an optical element made of KTa _1-x Nb _x O ₃ (KTN) that deflects light by utilizing the change in refractive index depending on the voltage is used. It doesn't matter. Regarding KTN, for example, the literature “Koichiro Nakamura, et al.,“ Wide-angle, low-voltage electro-optic beam deflection based on space-charge-controlled mode of electrical conduction in KTa _1-x Nb _x O ₃ ”, APPLIED. PHYSICS LETTERS 89, 131115, 2006 ".

[Second Embodiment]
Next, a second embodiment of the present invention will be described. Also in this embodiment, the configuration of the spectrometer is the same as that of the first embodiment, and therefore, description will be made using the reference numerals in FIG. In the first embodiment, the number of sampling points of the wavelength can be increased by rotating the drive mirror 12, but data having different center wavelengths are not completely separated because of overlapping in the wavelength region. . Therefore, the light intensity of a specific wavelength can be separated by converting the measurement light intensity using the characteristic data of the optical system representing the degree of overlap of the light intensity of each wavelength.

  FIG. 2 is a block diagram showing the configuration of the spectroscopic control device of the present embodiment, and FIG. 3 is a flowchart showing the operation of the control device. The control device 20 includes a wavelength section selection control unit 21, a wavelength selection control unit 22, a data acquisition unit 23, a storage unit 24, and a data processing unit 25.

The wavelength section selection control unit 21 controls the rotation angle of each mirror of the DMD 16 so that only light in a desired wavelength section enters the PD 17 (step S1 in FIG. 3).
The wavelength selection control unit 22 controls the rotation angle of the drive mirror 12 so that the center wavelength of the light incident on the PD 17 becomes a desired value (step S2).

The PD 17 photoelectrically converts incident light and outputs an electrical signal. The data acquisition unit 23 receives the output signal of the PD 17 (step S3).
The data processing unit 25 acquires characteristic data of the optical system stored in advance in the storage unit 24 (step S4), and processes the output signal of the PD 17 using this characteristic data to obtain the light intensity for each wavelength. Obtained (step S5).

  Here, consider four consecutive wavelengths of light that are applied to an arbitrary mirror in the DMD 16. Assume that light other than these four wavelengths is being filtered by another mirror of DMD 16. Assume that the light intensities of these four different wavelengths are y1, y2, y3, and y4. When expressed as a vector, the following equation is obtained.

  Further, it is assumed that the light intensities of four different wavelengths acquired by the PD 17 of the spectroscope are x1, x2, x3, and x4, respectively. When the vector is displayed, the following formula is obtained.

  Here, if the four lights can be completely separated by the spectroscope, x = y holds, but it is assumed that the wavelength interval is so narrow that separation is impossible. At that time, the light intensity of the adjacent wavelength is added to obtain the light intensity. For example, 75% light is added to the measurement wavelength light from light having a wavelength adjacent to the desired measurement wavelength light, and 50% light is added to the measurement wavelength light from light having a wavelength two away from the measurement wavelength light. And At that time, the light intensity x measured by the PD 17 is as follows.

  By obtaining the inverse matrix B of this matrix A, the following equation is obtained.

The light intensity y = (y1, y2, y3, y4) of each wavelength can be obtained from equation (5). Since the matrix A varies depending on the optical system of the spectroscope, it is desirable to obtain it in advance. Then, the inverse matrix B of the matrix A may be registered in advance in the storage unit 24 as the optical system characteristic data. The data processing unit 25 uses the inverse matrix B acquired from the storage unit 24 to convert the light intensity x represented by the output signal of the PD 17 by the equation (5), so that the light intensity y = (y1, y2) for each wavelength. , Y3, y4) can be calculated (step S5).
With the above configuration, a higher-resolution spectrometer can be realized in the present embodiment.

  The configuration of this embodiment can also be used in the conventional spectrometer shown in FIG. 8, but when the number of sampling points is increased in the acquisition wavelength band, the maximum rotation angle of the deflecting element 3 is increased. Alternatively, it is not practical because the rotational angle resolution of the deflecting element 3 needs to be made fine. On the other hand, this embodiment has the advantage that the performance of the maximum rotation angle and the rotation angle resolution of the mirror does not have to be so good since only a few sampling points are required in the band corresponding to the mirror of the DMD 16.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 4 is a block diagram showing a configuration of a spectrometer according to the third embodiment of the present invention.
The spectroscope of the present embodiment includes a fiber collimator 61, a concave mirror 62, a silicon immersion grating 63, a DMD 64, a PD 65, and a temperature adjusting unit 66 which is a deflection control means.

  The concave mirror 62 reflects the light emitted from the fiber collimator 61 and makes it incident on an immersion grating 63 which is a dispersive element. The immersion grating 63 splits the reflected light from the concave mirror 62 for each wavelength. Further, the concave mirror 62 reflects the light dispersed by the immersion grating 63 and makes it incident on the DMD 64 used as a variable filter. By irradiating the DMD 64 with the light split by the immersion grating 63 in this manner, each mirror arranged in an array on the light receiving surface of the DMD 64 is irradiated with light having a different wavelength. Therefore, only light of a specific wavelength can be acquired by controlling the DMD 64 by a control device (not shown) so that the light reflected by the specific mirror of the DMD 64 enters the PD 65.

  The immersion grating 63 made of silicon has a property that the refractive index changes as the temperature changes. Therefore, by adjusting the temperature of the immersion grating 63 by the temperature adjusting unit 66, the light emission angle from the immersion grating 63 changes, so that the center wavelength of the light incident on the specific mirror of the DMD 64 can be changed.

  FIG. 5 shows a change in the emission angle with respect to the temperature of the immersion grating 63. The horizontal axis in FIG. 5 is the temperature of the immersion grating 63, and the vertical axis is the light emission angle. In FIG. 5, 50 indicates characteristics when the wavelength of light is 1530 μm, 51 indicates characteristics when the wavelength is 1547 μm, and 52 indicates characteristics when the wavelength is 1565 μm. As can be seen from FIG. 5, by changing the temperature of the immersion grating 63 by 300 ° C., the light emission angle can be changed by 2 °.

  As described above, in this embodiment, by adjusting the temperature of the immersion grating 63, a wavelength selection function equivalent to that of the first embodiment can be realized without a driving mirror. The system can be simplified and a more compact spectroscope can be realized.

  Further, in the case where a transmissive material capable of modulating the refractive index by the electro-optic effect by applying a voltage is used for the immersion grating 63, a voltage adjusting unit capable of adjusting the voltage applied to the material of the immersion grating 63. If this is provided, the same effect as that obtained when the temperature adjusting unit 66 adjusts the temperature of the immersion grating 63 can be obtained.

  Also in this embodiment, a high-resolution spectrometer can be realized by applying the second embodiment. However, in the case of the present embodiment, since there is no drive mirror, the wavelength selection control unit 22 is unnecessary.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 6A is a block diagram showing a configuration of a spectrometer according to the fourth embodiment of the present invention. FIG. 6B is a side view of the spectroscope viewed from the right side of FIG.
The spectroscope according to the present embodiment includes a fiber 71, a drive mirror 72, a Fabry-Perot etalon 73, a lens 74, a dispersion element 75 such as a transmission type diffraction grating, a lens 76, and a PD array 77. Is done.

  The drive mirror 72 reflects the light emitted from the fiber 71 and makes it incident on the Fabry-Perot etalon 73. At this time, the drive mirror 72 can be rotated about a rotation shaft 78 parallel to a plane (xz plane in FIG. 6A) in which the light of the dispersive element 75 is dispersed. The drive mirror 72 implements the same wavelength selection function as in the first embodiment. The lens 74 condenses the light that has passed through the Fabry-Perot etalon 73. The dispersive element 75 separates the light collected by the lens 74 for each wavelength. The light split by the dispersive element 75 enters the PD array 77 through the lens 76. The dispersive element 75 and the PD array 77 realize a wavelength section selection function similar to that of the first embodiment.

  Here, the transmission spectrum of the Fabry-Perot etalon 73 is designed such that a peak appears in a cycle shorter than the entire measurement band and has sufficiently higher resolution than that cycle. Since the Fabry-Perot etalon 73 transmits light having a specific wavelength period, the light of each wavelength transmitted through the Fabry-Perot etalon 73 is dispersed by the dispersive element 75 and received by each PD of the PD array 77. As shown in FIG. 6B, the transmission spectrum of the Fabry-Perot etalon 73 can be shifted on the frequency axis by rotating the drive mirror 72 to change the incident angle of the light to the Fabry-Perot etalon 73. The light intensity at a desired wavelength can be acquired.

In the present embodiment, the light emitted from the fiber 71 is converted into light having a periodic and steep wavelength by the Fabry-Perot etalon 73, the wavelength is selected by the drive mirror 72, and the light dispersed by the dispersive element 75 is PD array 77. Receive light at. For this reason, the resolution of the spectroscope depends on the Fabry-Perot etalon 73, and the band is determined by the section where the light is divided by the dispersive element 75 and the PD array 77. Therefore, by designing the Fabry-Perot etalon so as to have a high resolution, it is possible to realize a higher resolution than in the first embodiment, and to achieve both high resolution and downsizing.
Instead of the PD array 77, the same DMD and PD as in the first embodiment may be used, LCOS and PD may be used, and liquid crystal and PD may be used.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. FIG. 7A is a block diagram showing a configuration of a spectrometer according to the fifth embodiment of the present invention. FIG. 7B is a side view of the spectroscope viewed from the right side of FIG.
The spectroscope according to the present embodiment includes a fiber 81, a biaxial drive mirror 82, a cylindrical lens 83, a Fabry-Perot etalon 84, a lens 85, a dispersive element 86, a lens 87, and a PD 88. .

  The biaxial drive mirror 82 reflects the light emitted from the fiber 81 and makes it incident on the cylindrical lens 83. At this time, the biaxial drive mirror 82 can rotate around a first rotation axis 89 parallel to a plane (xz plane in FIG. 7A) in which the light of the dispersive element 86 disperses. It is also possible to rotate about the second rotation axis 90 perpendicular to the plane in which the light of the dispersive element 86 disperses. A wavelength selection function similar to that of the first embodiment can be realized by turning the biaxial drive mirror 82 around the first turning shaft 89, and by turning around the second turning shaft 90. The same wavelength section selection function as in the first embodiment can be realized.

  The light that has passed through the cylindrical lens 83 enters the Fabry-Perot etalon 84. The lens 85 condenses the light that has passed through the Fabry-Perot etalon 84. The dispersive element 86 separates the light collected by the lens 85 for each wavelength. Of the light dispersed by the dispersive element 86, light having a specific wavelength enters the PD 88 via the lens 87.

  Compared with the fourth embodiment, the present embodiment employs a biaxial drive mirror 82 instead of the drive mirror 72, inserts one cylindrical lens 83, and replaces the single array instead of the PD array 77. The optical system adopts PD. The cylindrical lens 83 has a refractive power on the plane where the light of the dispersive element 86 disperses, and serves to converge the light from the biaxial drive mirror 82 onto the dispersive element 86, while the light of the dispersive element 86 is dispersed. On the plane orthogonal to the plane (yz plane in FIG. 6B), they are arranged so as not to have refractive power. In the present embodiment, only light in one wavelength section of the periodic transmission spectrum of Fabry-Perot etalon 84 is received by PD 88. By rotating the biaxial drive mirror 82 around the second rotation axis 90, light in a desired wavelength section can be incident on the PD 88.

  In the present embodiment, the light emitted from the fiber 81 is converted into light having a periodic and steep wavelength by the Fabry-Perot etalon 84, and a part of the periodic wavelength dispersed by the biaxial drive mirror 82 and the dispersion optical system is converted. Light is received by PD88. As described above, in this embodiment, it is possible to acquire data of a necessary band by separating the wavelength section selection axis and the wavelength selection axis, and to achieve both high resolution and downsizing.

  The present invention can be applied to a technique for splitting light.

  DESCRIPTION OF SYMBOLS 11, 61 ... Fiber collimator, 12, 72, 82 ... Drive mirror, 13, 74, 76, 85, 87 ... Lens, 14, 62 ... Concave mirror, 15, 63 ... Immersion grating, 16, 64 ... DMD, 17, 65, 88 ... PD, 18, 78 ... rotating shaft, 20 ... control device, 21 ... wavelength section selection control unit, 22 ... wavelength selection control unit, 23 ... data acquisition unit, 24 ... storage unit, 25 ... data processing unit , 66 ... temperature control unit, 71, 81 ... fiber, 73, 84 ... Fabry-Perot etalon, 75, 86 ... dispersion element, 77 ... PD array, 83 ... cylindrical lens.

Claims (6)

Wavelength sweeping means for deflecting incident light and wavelength sweeping a desired band;
A dispersion element that splits the light deflected by the wavelength sweeping means into different directions for each wavelength;
A light receiving element for receiving light;
A spectroscope comprising: a deflecting element array that causes only light having a specific wavelength to be incident on the light receiving element among light dispersed by the dispersive element. The spectrometer of claim 1, wherein
A spectroscope comprising a light receiving element array that receives light dispersed by the dispersion element instead of the light receiving element and the deflection element array. The spectrometer according to claim 1 or 2,
Furthermore, storage means for storing in advance optical system characteristic data representing the degree of intensity overlap between adjacent wavelengths of light;
A spectrometer comprising: data processing means for processing the output signal of the light receiving element using the characteristic data of the optical system to obtain the light intensity for each wavelength. The spectrometer according to any one of claims 1 to 3,
In place of the wavelength sweeping means, a deflection control means for adjusting the voltage applied to the dispersion element or the temperature of the dispersion element,
The dispersive element is a diffraction grating composed of a transmissive member whose refractive index changes with voltage or temperature,
A spectroscope characterized by controlling an emission angle of light from the dispersion element by adjusting a voltage applied to the dispersion element or a temperature of the dispersion element. The spectrometer according to any one of claims 1 to 3,
The spectroscope further comprising a Fabry-Perot etalon disposed in the optical path before the dispersive element. The spectrometer according to claim 5, wherein
Furthermore, a cylindrical lens arranged in the optical path before the Fabry-Perot etalon,
The spectroscope characterized in that the wavelength sweeping means is a drive mirror that can rotate about two axes.

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