JP2005030933A - Spectral device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a spectral device capable of attaining the reduction of polarization dependence without enlarging the area of a photodetector placed in a light detector. <P>SOLUTION: This invention adds an improvement to a spectral device, in which a first polarization resolution plate separates a light beam to be measured and the separated first and second separated beams are emitted in different angles for each wavelength by a diffraction grating. The device provides a second polarization resolution plate for separating each of the first and the second separated beams from the diffraction grating, and a light detector for detecting one of the first separated beam separated by the second polarization resolution plate and one of the second separated beam separated by the second polarization resolution plate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spectroscopic device that separates measured light by a first depolarizing plate and separates the separated first and second separated lights by a diffraction grating at different angles for each wavelength. The present invention relates to a spectroscopic device that reduces polarization dependence without increasing the area of a light receiving element provided in a photodetector.

  The spectroscopic device emits light to be measured by a diffraction grating at different angles for each wavelength and separates the light, and the light to be measured dispersed by the diffraction grating is received and detected by a photodetector. Such an apparatus is used, for example, for measuring the signal level, wavelength, etc. of each optical signal of the light under measurement in which a plurality of optical signals are wavelength division multiplexed. And in order to measure accurately, the polarization dependence in a diffraction grating is reduced using the depolarizing plate (for example, refer patent document 1).

  This depolarizing plate consists of two quartz plates. The thickness of the first crystal plate is continuously converted in a direction of 45 ° with respect to the optical axis (first optical axis) of the crystal plate. Further, the thickness of the second crystal plate is continuously converted in a direction of 45 ° with respect to the optical axis (second optical axis) of the crystal plate. The first crystal plate and the second crystal plate are bonded to each other so that the first optical axis and the second optical axis are orthogonal to each other. Furthermore, instead of the quartz plate, a birefringent crystal may be used (for example, see Patent Document 2).

  FIG. 6 is a block diagram showing a conventional example of such a spectroscopic device. In FIG. 6, an optical fiber 1 is a transmission path having an exit opening that emits light under measurement 100. The collimating lens 2 is installed to face the exit of the optical fiber 1 and emits the measured light 100 emitted from the optical fiber 1 as parallel light.

  The diffraction grating 3 is tilted with respect to the collimating lens 2 in order to diffract light emitted from the collimating lens 2 to a desired angle. The diffraction grating 3 emits the light to be measured 100 at different angles for each wavelength and separates the light.

  The focusing lens 4 is installed on the optical path of the outgoing light from the diffraction grating 3 and converges the outgoing light to form an image.

  The photodetector 5 is, for example, a photodiode array having a plurality of light receiving elements, and is installed at a position where the measured light 100 converges and forms an image. The light receiving elements are arranged along the direction in which the diffraction grating separates the light to be measured 100, and wavelengths are assigned in advance.

  The depolarization plate (first depolarization plate) 6 has the above-described configuration, and is provided between the collimating lens 2 and the diffraction grating 3, and in particular the diffraction grating 3 when the light to be measured 100 is transmitted. It is possible to remove the polarization dependence at the. Specifically, the depolarizing plate 6 has an optical axis at 45 ° with respect to the direction along the groove of the diffraction grating 3, and the direction of the inclined surface of the depolarizing plate is the direction along the groove of the diffraction grating. Become parallel. Therefore, the direction in which the light is separated by the depolarization plate 6 is the direction along the groove of the diffraction grating 3 (that is, the direction perpendicular to the spectral direction of the diffraction grating, and the direction perpendicular to the paper surface in FIG. 6). Become.

The operation of such an apparatus will be described.
The light to be measured 100 emitted from the optical fiber 1 is converted into parallel light by the collimating lens 2. The light to be measured 100 that has passed through the collimating lens 2 is incident on the depolarization plate 6.

  Refraction occurs at the inclined surface of the depolarizing plate 6, and the measured light 100 is separated in a direction along the grooves of the diffraction grating. That is, the depolarizing plate 6 separates one side in the direction perpendicular to the paper surface and the other in the lower direction.

  Then, measured light (first separated light, second separated light) 100 separated by the depolarization plate 6 enters the diffraction grating 3. Further, the light to be measured 100 is emitted and split by the diffraction grating 3 at different angles for each wavelength. Then, the light to be measured 100 dispersed by the diffraction grating 3 is converged by each of the light receiving elements of the photodetector 5 by the focusing lens 4 to form an image.

  For example, the light receiving elements located at “FP01”, “FP02”, and “FP03” in FIG. Then, an output detection unit (not shown) obtains the wavelength of the light to be measured and the optical signal level based on the light intensity output from each light receiving element of the photodetector 5 and the assigned wavelength, and outputs from the photodetector 5. Is output to an external device.

  Here, FIG. 7 is a view of the photodetector 5 as viewed from the incident side of the light to be measured 100, and shows, for example, the light receiving element 5a of the photodetector 5 in the vicinity of FP02. In FIG. 7, a first separated light 101 and a second separated light in which the depolarization plate 6 separates the measured light 100 in a direction orthogonal to the arrangement direction of the light receiving elements 5 a (up and down direction in FIG. 7). 102 forms an image.

Next, the description of the light intensity detected by the photodetector 5 will be made in detail.
The depolarizing plate 6 separates the measured light 100 into a light component whose polarization plane is parallel to the optical axis and a light component perpendicular to the optical axis, and these light components are incident on the grooves of the diffraction grating 3 at an angle of 45 ° to the left and right. To do.

  Here, when viewed from the traveling direction of the light 100 to be measured, the right 45 ° polarization component and the left 45 ° polarization component are referred to with respect to the direction along the groove of the diffraction grating 3. Further, the measured light 100 is separated in a direction along the groove. For example, the separated light 101 has a right 45 ° polarization component, and the separated light 102 has a left 45 ° component. Therefore, regardless of the polarization state of the light to be measured 100 emitted from the optical fiber 1, the light to be measured 100 incident on the diffraction grating 3 has a ratio between a component perpendicular to the groove and a component parallel to the groove. Are equal.

  The diffraction efficiency of the diffraction grating 3 with respect to polarized light perpendicular to the groove (that is, the spectral direction of the diffraction grating and in the horizontal direction in FIG. 6) is ηp, and parallel to the groove (in FIG. 6, the vertical direction of the paper surface). When the diffraction efficiency of the diffraction grating 3 for a polarized light is ηs, it is difficult to set ηp = ηs, and usually ηp ≠ ηs. When the depolarization plate 6 is not used, the efficiency of the measured light 100 to be diffracted varies depending on the polarization state of the measured light 100.

  However, in the apparatus shown in FIG. 6, the light is separated into the right 45 ° polarized component separated light 101 and the left 45 ° polarized component separated light 102 by the depolarizer 6 and then incident on the diffraction grating 3 and diffracted. Both the 45 ° polarization component and the left 45 ° polarization component have a light intensity of (ηp + ηs) / 2 times. The ratio of the right 45 ° polarization component and the left 45 ° polarization component varies depending on the polarization state of the light 100 to be measured, but the total diffraction efficiency of the total light becomes (ηp + ηs) / 2. Therefore, regardless of the polarization state of the measured light 100 emitted from the optical fiber 1, the light intensity of the measured light 100 emitted from the optical fiber 1 and the light intensity diffracted by the diffraction grating 3 and detected by the photodetector 5. Therefore, the light intensity of the measured light 100 from the optical fiber 1 can be measured.

Japanese Patent Laid-Open No. 9-229771 (paragraph numbers 0005 to 0014, FIGS. 1 to 4) Japanese Patent No. 2995985 (paragraph numbers 0012 to 006, FIG. 1)

  Thus, the polarization dependence of the diffraction grating 3 is reduced by the depolarization plate 6. Then, the device under test 100 is separated into separated lights 101 and 102 and detected on the detector 5 in two points.

  Note that, as the depolarization plate 6 increases the angle (separation angle) for separating the light to be measured 100, the polarization state is better separated and the polarization dependency of the diffraction grating 3 can be reduced.

  Of course, since both the separated lights 101 and 102 are detected by the photodetector 5, it is necessary to increase the area of the light receiving element 5a of the detector 5 with respect to the separation direction as the separation angle increases.

  However, when the light receiving element 5a is enlarged, the photodetector 5 itself is also enlarged. In addition, when the area of the light receiving element 5a is increased, the manufacturing yield is generally deteriorated. Furthermore, problems such as a decrease in responsiveness (rapid response) to the light under measurement 100 occur.

  SUMMARY OF THE INVENTION An object of the present invention is to realize a spectroscopic device that reduces polarization dependence without increasing the area of a light receiving element provided in a photodetector.

The invention described in claim 1
In the spectroscopic device in which the first depolarizing plate separates the measured light, and the diffraction grating emits the separated first and second separated light at different angles for each wavelength,
A second depolarizing plate for separating each of the first and second separated lights from the diffraction grating;
A photodetector for detecting one of the first separated light separated by the second depolarizing plate and one of the second separated light separated by the second depolarizing plate is provided. To do.

The invention according to claim 2 is the invention according to claim 1,
The first depolarizing plate and the second depolarizing plate are separated in a direction perpendicular to the spectral direction of the diffraction grating.

The invention according to claim 3 is the invention according to claim 1 or 2,
Provided between the first depolarizing plate and the second depolarizing plate, each of the first and second separated lights is orthogonal to the plane of the direction in which the diffraction grating separates or the spectral direction. It is characterized in that a polarizer for providing a plane polarization state is provided.

The invention according to claim 4 is the invention according to claim 3,
The polarizer is integrated with the diffraction grating.

The invention according to claim 5 is the invention according to claim 4,
The polarizer is a multilayer film provided on the diffraction surface of the diffraction grating.

The invention according to claim 5 is the invention according to claim 4,
The polarizer is characterized in that long stretched metals are arranged in one direction in the diffraction grating.

The invention according to claim 7 is the invention according to any one of claims 1 to 6,
The diffraction grating is characterized in that the first and second separated light beams are emitted in a polarization state of a plane in the direction of splitting or a plane perpendicular to the spectral direction, depending on the groove shape or groove interval. .

The invention according to claim 8 is the invention according to any one of claims 1 to 7,
The first depolarizing plate and the second depolarizing plate are common.

The invention according to claim 9 is the invention according to any one of claims 1 to 8,
Reflecting means for reflecting the diffracted light from the diffraction grating and making the reflected light incident on the diffraction grating again is provided.

The invention according to claim 10 is the invention according to any one of claims 1 to 9,
The photodetector is composed of a plurality of light receiving elements.

The invention according to claim 11 is the invention according to any one of claims 1 to 9,
The diffraction grating is rotated in the spectroscopic direction, and driving means for selecting light to be measured incident on the photodetector is provided.

The present invention has the following effects.
According to the first to eleventh aspects, each of the first and second separated lights from the diffraction grating is separated by the second depolarizing plate, and one of the first separated lights and one of the second separated lights are separated from each other. Are detected at substantially the same position of the photodetector, and the other of the first separated light and the other of the second separated light are imaged out of the photodetector, so that the first and second depolarizing plates The separation angle can be increased. As a result, the polarization dependence can be reduced without increasing the area of the light receiving element provided in the photodetector. Therefore, the photodetector itself can be reduced in size, and the manufacturing yield is not deteriorated. Furthermore, the response (speed response) to the light to be measured can be improved.

  According to the fourth to sixth aspects, since the polarizer is integrated with the diffraction grating, the apparatus can be miniaturized.

  According to the seventh aspect, since the polarization state of the diffracted light is changed depending on the groove shape or groove interval of the diffraction grating, it is not necessary to provide a polarizer. As a result, the apparatus can be miniaturized and the cost can be reduced.

  According to the eighth aspect, since the depolarization plate is used in common, the apparatus can be reduced in size and the cost can be reduced.

  According to the ninth aspect, since the reflecting means reflects the light to be measured (diffracted light) dispersed by the diffraction grating, and the diffraction grating again separates the reflected light from the reflecting means, the wavelength resolution can be improved. it can.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 is a block diagram showing a first embodiment of the present invention. Here, the same components as those in FIG. FIG. 2 is a view of the photodetector 5 as seen from the incident side of the light to be measured 100, and shows the light receiving element 5a of the photodetector 5 in the vicinity of FP02. In FIG. 1, a second depolarizing plate 7 is newly provided between the diffraction grating 3 and the focusing lens 4. The second depolarization plate 7 is the same as the first depolarization plate 6, and the first and second separated light beams 101 and 102 from the diffraction grating 3 are converted into the diffraction grating 3 in the same manner as the depolarization plate 6. (I.e., the direction perpendicular to the spectral direction of the diffraction grating and perpendicular to the paper surface in FIG. 1).

  The polarizer 8 is provided between the diffraction grating 3 and the depolarizing plate 7, and the first and second separated light beams 101 and 102 split by the diffraction grating 3 are incident thereon. Then, each of the separated lights 101 and 102 is set to a polarization state of a plane in a direction in which the diffraction grating 3 splits and is emitted to the depolarization plate 7. The polarizer 8 has various polarization states as described in Applied Optical Electronics Handbook Editorial Committee, “Applied Optoelectronics Handbook”, first edition, Shosodo Co., Ltd., April 1989, p173. An element that separates and selects light in a specific polarization state from light, such as a prism using a crystal, a glass plate using a dielectric multilayer film, and a device using a polyvinyl alcohol film.

The operation of such an apparatus will be described.
The polarizer 8 sets the polarization state of the separated light beams 101 and 102 from the diffraction grating 3 as a plane in the direction in which the diffraction grating 3 separates the light, and emits it to the second depolarization plate 7. Then, by the second depolarization plate 7, the separated light 101 is further separated into separated lights 101a and 101b, and the separated light 102 is separated into separated lights 102a and 102b. The separated lights 101a and 102a are separated in the same direction as the separated light 101 (upper side in the direction perpendicular to the paper surface in FIG. 1), and the separated lights 101b and 102b are separated in the same direction as the separated light 102 (in FIG. 1). , Down in the direction perpendicular to the paper surface).

  The separated lights 101a, 101b, 102a, and 102b are converged by the focusing lens 4, but the separated light (one of the first separated lights 101) 101b and the separated light (one of the second separated lights 102) 102a are combined. Then, an image is formed and detected by the light receiving element 5a of the photodetector 5. Further, the separated light (the other of the first separated lights 101) 101 a and the separated light (the other of the second separated lights 101) 102 b are imaged outside the photodetector 5.

  For example, in the light receiving elements located at “FP01”, “FP02”, and “FP03” in FIG. 1, light of different wavelengths is converged and imaged. Then, an output detection unit (not shown) obtains the wavelength of the light to be measured and the optical signal level based on the light intensity output from each light receiving element of the photodetector 5 and the assigned wavelength, and outputs from the photodetector 5. Is output to an external device.

  The operation until the light to be measured 100 enters the diffraction grating 3 and the diffraction grating 3 is diffracted is the same as that of the apparatus shown in FIG.

Next, the description of the light intensity detected by the photodetector 5 will be made in detail.
The light intensity diffracted by the diffraction grating 3 is 45 ° right polarized component (separated light 101) and 45 ° left polarized component (separated light) with respect to the measured light 100 as in the conventional example of the apparatus shown in FIG. 102) is also (ηp + ηs) / 2 times, but since it passes through the polarizer 8, the relative intensity of the separated light beams 101 and 102 that have been polarized at 45 ° to the left and right after passing through the polarizer 8 is ηp / 2.

  Then, each of the separated light beams 101 and 102 in the polarization state in the direction in which the diffraction grating 3 splits is again separated into the right 45 ° polarization component and the left 45 ° polarization component by the second depolarization plate 7. However, since the polarized light is polarized only in the spectral direction by the polarizer 8, ½ is separated (upper and lower sides in the direction perpendicular to the paper surface in FIG. 1 and up and down in the paper surface in FIG. 2). If the ratio of the separation angle between the depolarization plate 6 and the depolarization plate 7 is the same as the ratio of the focal lengths of the lens 2 and the lens 4, the depolarization plate 6 separates the upper side in the vertical direction of the paper and the depolarization plate 7 lowers the vertical direction The separated light 101b separated to the side and the separated light 102a separated to the lower side in the direction perpendicular to the paper surface by the depolarization plate 6 and separated to the upper side by the depolarization plate 7 are symmetric with respect to the plane to be dispersed. 4 forms an image at the same position on the photodetector 5.

  The light intensity of the imaged separated lights 101b and 102a is (ηp / 4) times the measured light 100 emitted from the optical fiber 1, and the light intensity and light of the measured light 100 from the optical fiber 1 are increased. The ratio of the light intensity detected by the detector 5 becomes constant, and the light intensity of the light under measurement 100 from the optical fiber 1 can be measured.

  The other demultiplexed light 101a separated by the depolarization plate 6 in the vertical direction on the paper surface and separated by the depolarization plate 7 in the vertical direction on the paper surface, and the depolarization plate separated by the depolarization plate 6 in the lower side in the vertical direction of the paper surface. The separated light 102b separated downward in 2 is imaged outside the photodetector 5 by taking a sufficiently large separation angle of the depolarizers 6 and 7 (that is, improving the separation of the polarization state). So there is no effect on the measurement.

  In this way, the first and second separated lights 101 and 102 from the diffraction grating 3 are separated by the second depolarization plate 7, and only the separated separated lights 101b and 102a are substantially the same as those of the photodetector 5a. Since the separated lights 101a and 102b are detected at the positions and imaged outside the photodetector 5, the separation angle of the depolarizers 6 and 7 can be increased. As a result, the polarization dependence can be reduced without increasing the area of the light receiving element provided in the photodetector. Therefore, the photodetector 5 itself can be reduced in size, and the yield at the time of manufacture is not deteriorated. Furthermore, the responsiveness (rapid response) to the light under measurement 100 can be improved.

[Second Embodiment]
FIG. 3 is a block diagram showing a second embodiment of the present invention. Here, the same components as those in FIG. Further, only the optical path for one wavelength (the optical path that forms an image on FP02) is illustrated. In FIG. 3, a mirror 9 is newly provided as reflecting means for reflecting the diffracted light from the diffraction grating 3 and making the reflected light incident on the diffraction grating 3 again.

The operation of such an apparatus will be described.
Such an apparatus is substantially the same as the operation of the apparatus shown in FIG. 1 except that the mirror 9 reflects the diffracted light from the diffraction grating 3 and makes this reflected light incident on the diffraction grating 3 again. . Then, the diffraction grating 3 emits the reflected light from the mirror 9 at different angles for each wavelength, separates it, and emits it to the polarizer 8.

  In this way, the mirror 9 reflects the diffracted light from the diffraction grating 3, and the diffraction grating 3 splits the reflected light again and emits it to the polarizer 8, so that the wavelength resolution can be improved.

[Third embodiment]
FIG. 3 is a block diagram showing a third embodiment of the present invention. Here, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted and illustration is omitted. Further, only the optical path for one wavelength (the optical path that forms an image on FP02) is illustrated.

  In FIG. 4, a lens 10 is provided instead of the lens 2, and the lens 2 and the lens 4 are shared. The depolarizing plate 11 is provided in place of the depolarizing plate 6, and the depolarizing plate 6 and the depolarizing plate 7 are used in common. The mirror 12 which is a reflection means is newly provided, reflects the outgoing light from the polarizer 8, transmits the polarizer 8 again, and makes it incident on the diffraction grating 3. In FIG. 4, the mirror 12 is slightly tilted downward in the direction perpendicular to the paper surface. The photodetector 5 is provided at a position where the measured light 100 is imaged by the lens 10.

The operation of such an apparatus will be described.
The measured light 100 emitted from the optical fiber 1 is converted into parallel light by the lens 10. The light to be measured 100 that has passed through the lens 10 enters the depolarization plate 11.

  Refraction occurs at the inclined surface of the depolarizing plate 11, and the light under measurement 100 is separated in a direction along the groove of the diffraction grating. That is, one is separated into the upper side in the direction perpendicular to the paper surface and the other is separated into the lower side.

  Then, measured light (first separated light, second separated light) 100 separated by the depolarization plate 11 enters the diffraction grating 3. Further, the separated light of the light to be measured 100 is emitted and dispersed by the diffraction grating 3 at different angles for each wavelength.

  Further, the polarizer 8 sets the polarization state of each of the separated separated light beams 101 and 102 as a plane in the direction in which the diffraction grating 3 separates the light and emits the light to the mirror 12. Then, the mirror 12 reflects the separated lights 101 and 102, and the reflected light that has been reflected again passes through the polarizer 8 and enters the diffraction grating 3. Further, the diffraction grating 3 emits the separated light beams 101 and 102 again at different angles for each wavelength and separates them, and outputs them to the depolarization plate 11.

  Then, the depolarizing plate 11 further separates the separated light 101 into separated lights 101a and 101b, and the separated light 102 is separated into separated lights 102a and 102b. The separated lights 101a and 102a are separated in the same direction as the separated light 101, and the separated lights 101b and 102b are separated in the same direction as the separated light 102.

  The separated lights 101a, 101b, 102a, and 102b are converged by the lens 10, but the separated light (one of the first separated lights 101) 101b and the separated light (one of the second separated lights 102) 102a are An image is formed and detected by the light receiving element 5a of the photodetector 5. Since the mirror 12 is slightly tilted downward in the direction perpendicular to the paper surface in FIG. 4, the imaging position FP02 also forms an image below the optical fiber 1 in the direction perpendicular to the paper surface.

  Then, an output detection unit (not shown) obtains the wavelength of the light to be measured and the optical signal level based on the light intensity output from each light receiving element of the photodetector 5 and the assigned wavelength, and outputs from the photodetector 5. Is output to an external device.

  The light intensity detected by the photodetector 5 (the ratio of the light intensity of the measured light 100 from the optical fiber 1 to the light intensity detected by the photodetector 5 is constant) is the same as that of the apparatus shown in FIG. Therefore, explanation is omitted.

  In this manner, the first and second separated lights 101 and 102 from the diffraction grating 3 are separated by the depolarization plate 11, and only the separated separated lights 101b and 102a are detected at substantially the same position of the photodetector 5a. In addition, since the separated lights 101a and 102b are imaged outside the photodetector 5, the separation angle of the depolarizing plate 11 can be increased. Thereby, the polarization dependence can be reduced without increasing the area of the light receiving element provided in the photodetector 5. Therefore, the photodetector 5 itself can be reduced in size, and the yield at the time of manufacture is not deteriorated. Furthermore, the responsiveness (rapid response) to the light under measurement 100 can be improved.

  Further, since the mirror 12 reflects the light emitted from the polarizer 8, and the diffraction grating 3 splits the reflected light again and emits it to the depolarization plate 11, the wavelength resolution can be improved.

  Furthermore, since each of the lens 10 and the depolarizing plate 11 is made one, the apparatus can be miniaturized and the cost can be suppressed.

[Fourth embodiment]
FIG. 5 is a block diagram showing a fourth embodiment of the present invention. Here, the same components as those in FIG. In FIG. 5, the diffraction grating 13 is provided in place of the diffraction grating 3 and the mirror 12, and splits the measured light 100 (separated light 101, 102) emitted from the depolarization plate 11, and the split measured light 100 is again emitted to the depolarization plate 11. The polarizer 14 is provided between the depolarization plate 11 and the diffraction grating 13 instead of the polarizer 8, and emits the polarization state of the separated lights 101 and 102 in a plane in the direction in which the diffraction grating 3 splits. .

The operation of such an apparatus will be described.
Such an apparatus is almost the same as the operation of the apparatus shown in FIG. 4 except that the diffraction grating 13 splits the measured light 100 and the split measured light 100 to the depolarization plate 11. Exit. Further, the polarizer 14 emits the polarization state of the measured light 100 from the depolarization plate 11 and the measured light 100 dispersed by the diffraction grating 13 in a plane in the direction in which the diffraction grating 3 splits. Note that the diffraction grating 3 may be slightly tilted downward in the direction perpendicular to the paper surface in FIG. 5 so that the imaging position FP02 is imaged below the optical fiber 1 in the direction perpendicular to the paper surface.

  In this way, since the diffraction grating 3 emits the light obtained by splitting the light to be measured 100 to the depolarization plate 11, the mirror 12 becomes unnecessary, and the apparatus can be miniaturized and the cost can be reduced.

In addition, this invention is not limited to this, The following may be sufficient.
In the apparatus shown in FIGS. 1 and 3 to 5, the configuration in which the polarizers 8 and 14 and the diffraction gratings 3 and 13 are separately provided is shown. However, the polarizers 8 and 14 are integrated with the diffraction gratings 3 and 13. May be. For example, a dielectric multilayer film is vapor-deposited on the diffraction surface of the diffraction grating 3 to have polarization characteristics. Alternatively, in the apparatus shown in FIGS. 1, 3, and 4, the diffraction grating 3 is a transmissive type instead of a reflective type, and is elongated long as described in JP-A-2002-51479 (for example, silver). Are arranged in one direction in the glass itself to provide polarization characteristics. Thus, since the polarizer is integrated with the diffraction gratings 3 and 13, the apparatus can be miniaturized.

  Moreover, although the polarizers 8 and 14 have been shown to have a configuration in which the polarization state is a plane in the direction in which the diffraction grating 3 splits, it may be a plane orthogonal to the direction in which the light is split. In this case, the relative intensity after passing through the polarizers 8 and 14 is ηs / 2. Further, the light intensity of the separated light beams 101 b and 102 a imaged by the photodetector 5 is (ηs / 4) times that of the measured light 100 emitted from the optical fiber 1.

  The diffraction efficiencies of the diffraction gratings 3 and 13 are ηs ≠ ηp, but the diffraction efficiencies ηs and ηp are changed to ηs >> ηp (or ηs << ηp), for example, ηs: ηp = About 10: 1, the polarizer 8 may not be provided. In general, the groove shape of the diffraction gratings 3 and 13 is a triangular saw shape, but it is preferable to change the diffraction efficiency ηs and ηp by changing the apex angle, smoothing the apex portion, or making a quadrangular uneven shape. . In particular, in FIGS. 3 and 4 in which the diffraction grating 3 is passed twice, the ratio of the diffraction efficiencies ηs and ηp can be set to 100: 1 (about 0.04 [dBpp] in polarization dependence). no problem.

  Further, although the separation light 101 has a right 45 ° polarization component and the separation light 102 has a left 45 ° polarization component, the direction of the optical axis with respect to the groove of the diffraction grating 6 of the depolarization plate 6 is rotated by 90 °. The separated light 101 may be a left 45 ° polarized component, and the separated light 102 may be a right 45 ° polarized component. The same applies to the depolarization plates 7 and 11.

  Moreover, although the structure which detects the optical intensity of the to-be-measured light 100 containing the signal of 3 wavelengths was shown, how many wavelengths may be contained.

  Moreover, although the configuration of the transmission optical system using the lenses 2, 4, and 10 has been shown, a parabolic mirror may be provided to form a reflection optical system.

  In addition, the configuration in which the photodiode array including the plurality of light receiving elements 5a is used for the photodetector 5 is shown, but the number of the light receiving elements 5a may be one. In this case, driving means for rotating the diffraction gratings 3 and 13 forward and backward in the direction in which the light to be measured 100 is dispersed is scanned, the wavelength of the light to be measured 00 is scanned, and the light to be measured 100 incident on the photodetector 5 is scanned. select.

  In the apparatus shown in FIGS. 1 and 3, the configuration in which the polarizer 8 is provided between the diffraction grating 3 and the depolarization plate 7 is shown. However, the polarizer 8 is provided between the depolarization plate 6 and the depolarization plate 7. May be.

  In the apparatus shown in FIG. 4, the configuration in which the polarizer 8 is provided between the diffraction grating 3 and the mirror 12 is shown, but the polarizer 8 may be provided anywhere between the depolarization plate 11 and the mirror 12.

  In the apparatus shown in FIGS. 4 and 5, the configuration in which the mirror 12 or the diffraction grating 13 is slightly tilted downward in the direction perpendicular to the paper surface is shown, but the configuration in which the mirror 12 or the diffraction grating 13 is tilted upward may be used. In this case, the photodetector 5 is provided above the optical fiber 1 in the direction perpendicular to the paper surface.

It is the block diagram which showed the 1st Example of this invention. FIG. 6 is a diagram showing an imaging relationship in the vicinity of a light receiving element 5a of a photodetector 5. It is the block diagram which showed the 2nd Example of this invention. It is the block diagram which showed the 3rd Example of this invention. It is the block diagram which showed the 4th Example of this invention. It is a block diagram of the conventional spectroscopic device. It is the figure which showed the imaging relationship on the light receiving element 5a of the photodetector 5. FIG.

Explanation of symbols

5 Photodetector 5a Light receiving element 6, 7, 11 Depolarization plate 8, 14 Polarizer 9, 12 Mirror 3, 13 Diffraction grating

Claims (11)

In the spectroscopic device in which the first depolarizing plate separates the measured light, and the diffraction grating emits the separated first and second separated light at different angles for each wavelength,
A second depolarizing plate for separating each of the first and second separated lights from the diffraction grating;
A photodetector for detecting one of the first separated light separated by the second depolarizing plate and one of the second separated light separated by the second depolarizing plate is provided. Spectroscopic device.   The spectroscopic apparatus according to claim 1, wherein the first depolarizing plate and the second depolarizing plate are separated in a direction orthogonal to a spectral direction of the diffraction grating.   Provided between the first depolarizing plate and the second depolarizing plate, each of the first and second separated lights is orthogonal to the plane of the direction in which the diffraction grating separates or the spectral direction. 3. The spectroscopic device according to claim 1, further comprising a polarizer for making the plane polarized.   The spectroscopic device according to claim 3, wherein a polarizer is integrated with the diffraction grating.   The spectroscopic device according to claim 4, wherein the polarizer is a multilayer film provided on a diffraction surface of the diffraction grating.   5. The spectroscopic apparatus according to claim 4, wherein the polarizer has a long stretched metal arranged in one direction in the diffraction grating.   2. The diffraction grating emits each of the first and second separated lights in a polarization state of a plane in the direction of splitting or a plane perpendicular to the spectroscopic direction, depending on a groove shape or a groove interval. The spectroscopic device according to any one of -6.   The spectroscopic device according to claim 1, wherein the first depolarizing plate and the second depolarizing plate are common.   The spectroscopic apparatus according to claim 1, further comprising a reflection unit configured to reflect diffracted light from the diffraction grating and to make the reflected light enter the diffraction grating again.   The spectroscopic device according to claim 1, wherein the photodetector includes a plurality of light receiving elements. The spectroscopic apparatus according to claim 1, further comprising a driving unit that rotates the diffraction grating in a spectroscopic direction and selects light to be measured incident on a photodetector.

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