JP2009246621A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and small-sized optical receiver having at least either high-overload resistance and high distribution compensation capability. <P>SOLUTION: The invention relates to the optical receiver internally including: a diffraction grating 7 for reflecting and diffracting an optical signal made incident through an optical fiber 1; a diaphragm 12 for passing a part of the optical signal reflected and diffracted by the diffraction grating 7; an angle adjusting element for adjusting an angle of the diffraction grating 7 with respect to the incident optical signal to pass through the diaphragm 12 only one of optical signal reflected by the diffraction grating 7 and a plurality of optical signals diffracted by the diffraction grating 7 and to adjust the quantity of light in the optical signal that passes through the diaphragm 12; and a photo-detector 8 on which the optical signal passed through the diaphragm 12 is made incident. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiver for optical fiber communication.

  Conventionally, in order to improve the performance of an optical receiver, a method of adding performance improvement parts for each performance item has been employed. For example, in order to improve overload tolerance, the configuration shown in FIG. 7A is adopted, and in order to extend the communication distance, the configuration shown in FIG. 7B is adopted. In FIG. 7, reference numeral 101 denotes a variable optical attenuator, 102 denotes an optical receiver, and 103 denotes an optical dispersion compensator.

  Specifically, when a very strong optical signal is input to the optical receiver 102 and there is a possibility that the code error rate may decrease or components inside the optical receiver 102 may be damaged, FIG. As shown in (a), a variable optical attenuator 101 is disposed in front of the optical receiver 102, and a mechanism for reducing the light intensity to an appropriate signal level is used.

  If the transmission distance by the optical fiber is very long (approximately 80 km or more in a system using a single mode optical fiber), some dispersion compensation is used. In FIG. 7B, an optical dispersion compensator 103 is arranged in front of the optical receiver 102, and a device for extending the transmission distance by compensating for the dispersion generated in the optical fiber is devised.

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However, the use of the variable optical attenuator and the optical dispersion compensator other than the optical receiver has the following drawbacks.
(1) Increase in cost due to an increase in the number of parts and increase in cost due to the connection work between these parts.
(2) Increase in size of the entire device.
(3) Increased vulnerability of optical transmission lines and optical fibers due to connection between components.

  The present invention has been made in view of the above problems, and an object thereof is to provide an inexpensive and small-sized optical receiver having at least one of high overload resistance and high dispersion compensation capability.

An optical receiver according to a first invention for solving the above-described problems is
A diffraction grating that reflects and diffracts an optical signal incident via an optical fiber;
A light receiving element on which a part of the optical signal reflected and diffracted by the diffraction grating is incident;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is incident on the light receiving element from the optical signal reflected by the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of the optical signal incident on the light receiving element.

An optical receiver according to a second invention for solving the above-mentioned problems is as follows.
A diffraction grating that reflects and diffracts an optical signal incident via an optical fiber;
A diaphragm for passing a part of the optical signal reflected and diffracted by the diffraction grating;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is allowed to pass through the diaphragm from among the optical signal reflected by the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of light signal passing through the diaphragm,
A light receiving element into which an optical signal having passed through the diaphragm is incident is provided inside.

An optical receiver according to a third invention for solving the above-mentioned problem is as follows.
In the optical receiver according to the first or second invention,
The light receiving element or the stop and the light receiving element are arranged so that the reflection angle of the optical signal reflected by the diffraction grating is other than a right angle.

An optical receiver according to a fourth invention for solving the above-mentioned problem is as follows.
A diffraction grating that transmits and diffracts an optical signal incident via an optical fiber;
A light receiving element on which a part of the optical signal transmitted and diffracted by the diffraction grating is incident;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is incident on the light receiving element from the optical signal transmitted through the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of the optical signal incident on the light receiving element.

An optical receiver according to a fifth invention for solving the above-mentioned problem is as follows.
A diffraction grating that transmits and diffracts an optical signal incident via an optical fiber;
A diaphragm that transmits a part of the optical signal transmitted and diffracted by the diffraction grating;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is allowed to pass through the diaphragm from among the optical signal transmitted through the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of light signal passing through the diaphragm,
A light receiving element into which an optical signal having passed through the diaphragm is incident is provided inside.

An optical receiver according to a sixth invention for solving the above-mentioned problems is as follows.
In the optical receiver according to any one of the first to fifth inventions,
The angle adjusting element is a micromachine or a piezoelectric element.

An optical receiver according to a seventh invention for solving the above-mentioned problems is as follows.
In the optical receiver according to any one of the first to sixth inventions,
The diffraction grating is a blazed diffraction grating.

An optical receiver according to an eighth invention for solving the above-described problems is
In the optical receiver according to any one of the first to seventh inventions,
A light intensity detecting means for detecting the light intensity of the optical signal incident on the light receiving element from the direct current component of the photocurrent flowing through the light receiving element is provided.
The angle of the diffraction grating is controlled by the angle adjusting element so that the light intensity detected by the light intensity detecting means falls within a predetermined range.

  According to the present invention, an optical signal is dispersed using a diffraction grating, a diaphragm, and an angle adjusting element, and only one optical signal is incident on the light receiving element from a plurality of dispersed optical signals, and the incident intensity is adjusted. Therefore, it is possible to perform variable attenuation of the optical signal incident on the light receiving element, and as a result, it is possible to increase overload resistance. In addition, when only one diffracted optical signal (for example, first-order diffracted light) is incident on the light receiving element among the plurality of dispersed optical signals, and the incident intensity is adjusted, the optical signal incident on the light receiving element. In addition, the optical spectrum slice can suppress the dispersion of the optical signal. As a result, the overload resistance can be enhanced and the dispersion compensation capability can be enhanced.

  In particular, when adjusting the incident intensity of one diffracted optical signal (for example, first-order diffracted light) to the light receiving element, high overload resistance and high dispersion compensation capability can be simultaneously provided to the optical receiver. Both a long transmission distance and a short transmission distance can be covered with one type of optical receiver. As a result, in optical fiber communication using wavelength division multiplexing, the design of a network, a node, and a link becomes easy, and it is an effective means even in an optical fiber communication network that does not use wavelength division multiplexing.

  In addition, according to the present invention, the diffraction grating, the diaphragm, and the angle adjusting element are provided inside the optical receiver so as to have high overload resistance and high dispersion compensation capability. It can be made smaller. Further, since connection with other external parts is not required, the cost can be reduced and the cost can be reduced, and the vulnerability due to the connection does not increase.

  Hereinafter, embodiments of an optical receiver according to the present invention will be described with reference to the drawings.

  An example of an embodiment of an optical receiver according to the present invention will be described with reference to FIGS. 1 is a schematic configuration diagram of the optical receiver of the present embodiment, FIG. 2 is a signal flow diagram in the optical receiver of the present embodiment, and FIG. 3 is a diagram of the optical receiver of the present embodiment. FIG. 4 is an explanatory diagram showing the angle of the diffraction grating and the light receiving pattern at the photodiode, and FIG. 4 is a graph showing the amount of attenuation and the eye opening improvement with respect to the angle of the diffraction grating in the optical receiver of this example.

  As shown in FIG. 1, the optical receiver of this embodiment includes an optical fiber 1 that serves as an optical interface for inputting an optical signal into the optical receiver, and a lens 4 that collects the optical signal from the optical fiber 1. The optical signal collected by the lens 4 is reflected and diffracted by the diffraction grating 7 that reflects and diffracts, the angle adjustment element 6 that adjusts the angle of the diffraction grating 7 with respect to the incident optical signal, and the diffraction grating 7. A diaphragm 12 that passes a part of the optical signal, a photodiode (hereinafter abbreviated as PD) 8 that photoelectrically converts the incident optical signal into an electrical signal, and an output from the PD 8 A transimpedance amplifier (hereinafter abbreviated as TIA) 9 for amplifying the generated electric signal, and a thermistor 10 serving as a temperature sensor for measuring the ambient temperature, and includes a lens 4, a diffraction grating 7, an angle adjusting element 6, Aperture 1 , PD8, TIA9, those having a thermistor 10 or the like in the housing 5.

  The diffraction grating 7 is attached to the angle adjustment element 6, and the angle adjustment element 6 can adjust the angle of the diffraction grating 7 with respect to the incident optical signal as described above. By adjusting the angle of the diffraction grating 7 with respect to the incident optical signal, only one optical signal is allowed to pass through the stop 12 from the optical signal reflected by the diffraction grating 7 and the plurality of diffracted optical signals. The light quantity of the optical signal passing through the diaphragm 12 is adjusted. For example, the diaphragm 12 may be an aperture that is opened like a pinhole. In this embodiment, the case of using a stop is described. However, when the opening of the PD itself performs the stop operation, it is not necessary to use the stop. For example, the diameter of the PD is approximately proportional to the -1/2 power of the bit rate. However, when the diameter is close to the diameter of the diaphragm used in the present invention, it is not necessary to separately provide the diaphragm itself.

  In this embodiment, a micromachine (MEMS) formed on a silicon (Si) substrate is used as the angle adjusting element 6. If MEMS is used, it is possible to adjust the angle of the diffraction grating 7, that is, the angle of the optical signal reflected and diffracted by the diffraction grating 7 with a voltage of about 10V. The angle adjusting element 6 is preferably one that can electrically adjust the angle of the diffraction grating 7, and a piezoelectric element or the like can also be used. Both MEMS and the piezoelectric element can give a sufficient angular displacement to the optical signal reflected and diffracted by the diffraction grating 7 at about 10V.

  The lens 4 collects an optical signal emitted from the optical fiber 1 and forms an image on the PD 8. The lens 8 has one end of the optical fiber 1 attached to the fiber sleeve 2 and the PD 8 with a magnification of about 1: 3 are optically coupled by the imaging optical system. Since the core diameter of a general single mode optical fiber is about 10 μm and the light receiving diameter of a general 10 Gb / s class PD is about 30 μm, the optical fiber 1 and the PD 8 can be efficiently connected when the lens 4 has this magnification. It can be optically coupled.

The optical receiver of this embodiment is assembled in the following procedure. The connection relationship and the signal flow will be described in detail in FIG.
(1) An electronic circuit portion for receiving an optical signal, that is, PD8, TIA9 and thermistor 10 are mounted on the sub-board 11, and necessary wiring is performed.
(2) The sub-board 11 is attached to the inside of the housing 5. The attachment may be silver paste or soldering.
(3) The diffraction grating 7 is attached to the angle adjustment element 6, and then the angle adjustment element 6 is fixed inside the housing 5.
(4) The lens housing 3 in which the lens 4 is housed is fixed to the housing 5 by welding with a YAG laser.
(5) The fiber sleeve 2 to which one end of the optical fiber 1 is attached is fixed to the lens housing 3 by welding with a YAG laser. At this time, laser light of 1.55 μm band is input from the other end side of the optical fiber 1 and the photocurrent flowing through the PD 8 is monitored, thereby adjusting the positions of the fiber sleeve 2 and the PD 8 and maximizing the photocurrent. By the way, laser welding was performed.
(6) Finally, the diaphragm 12 is fixed inside the housing 5.

  Next, the signal flow in the optical receiver of the present embodiment will be described with reference to FIG. In FIG. 2, a solid line indicates an optical signal, and a broken line indicates an electrical signal.

  An optical signal received and photoelectrically converted by the optical receiver of this embodiment is incident on the inside of the optical receiver through the optical fiber 1. High-speed optical signals can be used in the optical receiver of this embodiment. The optical signal incident on the inside is incident on the PD 8 through the lens 4, the diffraction grating 7, and the stop 12. At this time, the optical signal is reflected or diffracted by the diffraction grating 7, but they have different optical characteristics, and only one light among them is arranged between the diffraction grating 7 and the PD 8. 12 is selected to enter the PD 8. Since the angle of the diffraction grating 7 with respect to the incident optical signal is determined by the angle adjustment element 6, the selection of the optical signal incident on the PD 8 is also determined by the angle adjustment element 6. The selection of the optical signal will be described in detail with reference to FIGS.

  And the optical signal input into PD8 is converted into an electric signal. In this embodiment, an avalanche photodiode (hereinafter abbreviated as APD) having a high speed and high gain characteristic is used as the PD 8. In the APD, the temperature dependency and the applied voltage dependency of the gain are remarkable. Therefore, the temperature dependency and the applied voltage dependency of the gain are controlled by controlling the applied voltage to the APD by the signal of the thermistor 10. . The electrical signal photoelectrically converted in this way is amplified by the TIA 10 and output to the outside of the optical receiver.

  Here, the angle of the diffraction grating 7 and the light receiving pattern at the PD 8 will be described with reference to FIG. 3A illustrates the spectrum of + 1st order diffracted light when θ = 45 °, FIG. 3B illustrates the case of θ> 45 °, and FIG. 3C illustrates the spectrum of the + 1st order diffracted light when θ> 45 °. It is. Here, θ is an angle formed by the center of the optical signal that has passed through the lens 4 and the diffraction grating 7 (incident angle to the diffraction grating 7).

  As shown in FIG. 3, when the optical signal is reflected by the diffraction grating 7, it is divided into reflected light (0th order light) and a plurality of diffracted lights (± nth order light, n is an integer). The reflected light and the diffracted light have different intensity ratios and the presence or absence of dispersion compensation. Since the diaphragm 12 is provided between the diffraction grating 7 and the PD 8, only one of the reflected light and the plurality of diffracted lights enters the PD 8.

  When θ = 45 °, as shown in FIG. 3A, only the reflected light passes through the diaphragm 12 and enters the PD 8. On the other hand, when the angle of the diffraction grating 7 is changed to θ> 45 °, for example, θ = [45 ° + (n-order diffraction angle)], only + n-order diffracted light passes through the diaphragm 12. Is incident on PD8. As an example, when θ = [45 ° + (first order diffraction angle)], as shown in FIG. 3B, only the + 1st order diffracted light passes through the stop 12 and enters the PD 8.

  FIG. 3C shows an outline of the principle by which an optical spectrum slice is generated by this configuration and dispersion suppression can be realized. Here, NRZ (Non Return Zero) intensity shift keying is taken as an example of the optical modulation method.

  Since the diffraction angle in the diffraction grating is approximately inversely proportional to the wavelength, if the modulated light is incident on the diffraction grating, the short wavelength side is closer to the 0th order light (reflected light), and the long wavelength side is Diffracted to the far side from 0th order light (reflected light). In general, light propagated through a single mode optical fiber undergoes different phase changes on the short wavelength side and the long wavelength side due to the chromatic dispersion of the optical fiber. The information existing on the short wavelength side and the long wavelength side is essentially the same in the opposite phase, but if the phase difference is disturbed by chromatic dispersion, the original NRZ waveform cannot be reproduced on the receiving side.

  As a technique for improving such a problem, there is an optical spectrum slice. This is a technique in which only one of the sidebands generated on both sides of the center wavelength by modulation is allowed to pass and received by square detection. In FIG. 3C, the diaphragm 12 is omitted. However, if the diaphragm 12 is arranged so that only one of the widened sidebands passes, more specifically, only the + 1st-order diffracted light blocks the diaphragm 12. If the angle of the diffraction grating 7 is adjusted so as to pass, the optical spectrum slice can suppress the dispersion to some extent, and the optical fiber transmission distance can be extended.

  FIG. 4 shows the attenuation amount and the eye opening improvement amount with respect to the angle θ of the diffraction grating 7. In FIG. 4, the upper graph is the attenuation amount (logarithmic scale), and the lower graph is the eye opening improvement amount (arbitrary unit). In addition, as the diffraction grating 7, what was manufactured so that the pitch may become equal intervals was used.

  As can be seen from FIG. 4, when θ is increased from 45 °, the 0th-order reflected light is incident on the PD 8, but a part of the light beam cannot enter the PD 8 at the stop 12. growing. In this part, the optical receiver is provided with a function as an optical variable attenuator, but the eye opening is not improved.

  When θ is further increased, the + 1st order diffracted light passes through the stop 12 and enters the PD 8. As a result, the amount of attenuation once decreases and then increases again. During this time, the spectrum slicing effect acts on the optical signal, and both functions of optical variable attenuation and dispersion suppression work. The degree of eye opening improvement measured at that time is as shown in FIG. As θ, the eye opening was maximized when only one sideband was incident on PD8. Since the sidebands on both sides basically have the same information, the same effect can be obtained regardless of which sideband is incident on the PD 8. That is, the improvement of the eye opening shows bimodality.

  Thus, in the optical receiver of this embodiment, the function as an optical variable attenuator and the function of dispersion suppression are added by adjusting the angle adjusting element 6, that is, adjusting the angle of the diffraction grating 7. Taking advantage of these features, when used as an optical receiver in a long-distance optical fiber network, it was confirmed that it operates as an optical receiver with a very low bit error rate in both short-distance and long-distance relays. It was. The reception wavelength was covered from 1.3 μm to 1.55 μm, and was sufficiently wide band.

  In the optical receiver of this embodiment, the example in which the + 1st order diffracted light from the diffraction grating 7 is incident on the PD 8 through the diaphragm 12 has been described. However, the reflected light (0th order light) from the diffraction grating 7 is used as the diaphragm. The light may be incident on the PD 8 via 12. In this case, it functions only as an optical variable attenuator. Further, the second-order diffracted light after the diffraction grating 7 may be incident on the PD 8 through the diaphragm 12. In this case, the assembly accuracy can be afforded more than in the case of reflected light (0th order light) and 1st order diffracted light.

  In the optical receiver of this embodiment, a reflection type diffraction grating is used as the diffraction grating 7, but the same effect can be obtained even if a transmission type diffraction grating or the like is used.

  In this embodiment, a blazed diffraction grating is used as the diffraction grating in the optical receiver of the first embodiment (see FIG. 1). Other configurations are the same as those of the optical receiver according to the first embodiment, and therefore, redundant description is omitted here.

  The blazed diffraction grating can set higher-order light intensity stronger than zero-order light. For example, if the diffraction efficiency of the + 1st order light is made highest, the attenuation amount of the 0th order light can be made larger than that of the + 1st order diffracted light. Therefore, by using such a blazed diffraction grating in the optical receiver described in the first embodiment, the optical signal intensity can be sufficiently attenuated even when used in a short-distance optical fiber network. This blazed diffraction grating can also be applied to Examples 3 and 4 described later.

  In the optical receiver according to the first embodiment, the configuration in which the optical signal is reflected substantially at right angles by the diffraction grating is shown. In this case, it is ideal to use a diffraction grating having no polarization dependency. However, it is very difficult and expensive to manufacture a diffraction grating having no polarization dependency. In order to eliminate the influence of polarization dependence, it is effective to shift the reflection direction of the optical signal from a right angle as much as possible.

  Therefore, in this embodiment, the reflection direction of the optical signal by the diffraction grating is not perpendicular. FIG. 5 is a schematic configuration diagram showing the optical receiver of the present embodiment. The optical receiver of this embodiment may have the same configuration as that of the optical receiver shown in the first embodiment except that the reflection angle of the optical signal is different. Therefore, in FIG. The same reference numerals as those in FIG. 1 are given, and the redundant description is omitted here.

  As shown in FIG. 5, in the optical receiver of this embodiment, the diaphragm 12 and the PD 8 are arranged at a position where the reflection angle of the optical signal reflected by the diffraction grating 7 is other than a right angle. Specifically, also in this embodiment, the PD 8, the TIA 9, and the thermistor 10 are mounted on the sub-substrate 11, and the sub-reflection angle of the optical signal reflected by the diffraction grating 7 is, for example, an acute angle. The PD 8 on the substrate 11 is arranged, and the diaphragm 12 is arranged on the optical path between the diffraction grating 7 and the PD 8.

  By adopting such a configuration, the manufacturing cost of the diffraction grating 7 itself can be reduced, and an optical receiver having good optical receiving characteristics as in the first embodiment can be manufactured at a lower cost than the first embodiment. it can.

  In this embodiment, a feedback control circuit for optimally controlling the angle of the diffraction grating is added to the optical receivers shown in the first to third embodiments based on the amount of optical attenuation.

  In a general optical receiver, the bit error rate is minimized when the optical intensity of the optical signal is in the range of −5 dBm to −10 dBm. Therefore, when the light intensity of the optical signal is less than −5 dBm, the attenuation is set to the minimum, and when it is −5 dBm or more, feedback is performed so that the light intensity incident on the PD 8 is in the range of −5 dBm to −10 dBm. For example, the optical receiver itself automatically controls the minimum bit error rate.

  Therefore, in order to realize the above control, in the optical receiver of this embodiment, as shown in FIG. 6, a direct current monitor 13 (light intensity detecting means) is provided as a feedback control circuit. The direct current monitor 13 detects the light intensity of the incident optical signal from the direct current component of the photocurrent flowing through the PD 8, and outputs an output signal such that the detected light intensity is in the range of −5 dBm to −10 dBm. The angle of the diffraction grating 7 is controlled by feeding back to the angle control element 6. The DC current monitor 13 is configured to be provided on the sub-substrate 11 together with the PD 8 and the like, for example, with reference to FIG.

  By adopting such a configuration, the optical receiver of this embodiment can always perform photoelectric conversion at the minimum bit error rate without using an external circuit.

  The present invention provides a novel optical receiver provided with a variable optical attenuator and an optical spectrum slicing function (dispersion compensation function), and has a higher overload resistance than a conventional optical receiver. Since it has a high dispersion compensation capability and can cover both long distances and short distances with a single type of optical receiver, it is easy to design networks, nodes, and links.

It is a block diagram which shows an example (Example 1) of embodiment of the optical receiver which concerns on this invention. FIG. 2 is a signal flow diagram in the optical receiver shown in FIG. 1. It is a figure explaining the angle in the optical receiver shown in FIG. 1, and the light reception pattern in a photodiode. FIG. 3 is a graph showing attenuation with respect to angle and an eye opening improvement amount in the optical receiver shown in FIG. 1. FIG. It is a block diagram which shows another example (Example 3) of embodiment of the optical receiver which concerns on this invention. It is a block diagram which shows another example (Example 4) of embodiment of the optical receiver which concerns on this invention. It is a figure which shows the conventional optical receiver.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Fiber sleeve 3 Lens housing 4 Lens 5 Housing 6 Angle adjustment element 7 Diffraction grating 8 Photodiode (PD)
9 Transimpedance amplifier (TIA)
DESCRIPTION OF SYMBOLS 10 Thermistor 11 Sub-board 12 Diaphragm 13 DC current monitor 101 Variable optical attenuator 102 Optical receiver 103 Optical dispersion compensator

Claims (8)

A diffraction grating that reflects and diffracts an optical signal incident via an optical fiber;
A light receiving element on which a part of the optical signal reflected and diffracted by the diffraction grating is incident;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is incident on the light receiving element from the optical signal reflected by the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of the optical signal incident on the light receiving element. A diffraction grating that reflects and diffracts an optical signal incident via an optical fiber;
A diaphragm for passing a part of the optical signal reflected and diffracted by the diffraction grating;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is allowed to pass through the diaphragm from among the optical signal reflected by the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of light signal passing through the diaphragm,
An optical receiver comprising a light receiving element into which an optical signal having passed through the diaphragm is incident. The optical receiver according to claim 1 or 2,
An optical receiver, wherein the light receiving element or the diaphragm and the light receiving element are arranged so that a reflection angle of an optical signal reflected by the diffraction grating is other than a right angle. A diffraction grating that transmits and diffracts an optical signal incident via an optical fiber;
A light receiving element on which a part of the optical signal transmitted and diffracted by the diffraction grating is incident;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is incident on the light receiving element from the optical signal transmitted through the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of the optical signal incident on the light receiving element. A diffraction grating that transmits and diffracts an optical signal incident via an optical fiber;
A diaphragm that transmits a part of the optical signal transmitted and diffracted by the diffraction grating;
By adjusting the angle of the diffraction grating with respect to the incident optical signal, only one optical signal is allowed to pass through the diaphragm from among the optical signal transmitted through the diffraction grating and a plurality of diffracted optical signals. And an angle adjusting element for adjusting the amount of light signal passing through the diaphragm,
An optical receiver comprising a light receiving element into which an optical signal that has passed through the diaphragm is incident. The optical receiver according to any one of claims 1 to 5,
An optical receiver characterized in that the angle adjusting element is a micromachine or a piezoelectric element. The optical receiver according to any one of claims 1 to 6,
An optical receiver characterized in that the diffraction grating is a blazed diffraction grating. The optical receiver according to any one of claims 1 to 7,
A light intensity detecting means for detecting the light intensity of the optical signal incident on the light receiving element from the direct current component of the photocurrent flowing through the light receiving element is provided.
An optical receiver characterized in that the angle of the diffraction grating is controlled by the angle adjusting element so that the light intensity detected by the light intensity detecting means falls within a predetermined range.

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