JPH08122705A - Optical system device for optical communication - Google Patents

Abstract

PURPOSE: To keep the light quantity of monitor light of transmission light from a beam splitter constant for the dispersion of wavelength of the transmission light or its change by setting the incident angle of a laser beam to a beam splitter part at a value within a specific one. CONSTITUTION: The transmission light emitted from a semiconductor laser 101 is changed to parallel rays by a collimator lens 102, and their directions are controlled by a steering mirror 104, and made incident on the beam splitter 105. In such a case, an output laser beam is made incident so as to set the incident angle at the one between 30-60 deg. for the beam splitter 105 consisting of a dichroic mirror, for example, 45 deg., and to form its polarization plane at an angle between 1-30 deg. for the S polarization plane of the beam splitter. The beam splitter 105 is provided with polarization spectral transmission characteristic in which P polarization permeability goes to nearly 100% and S polarization permeability to nearly 0% at the wavelength position of the output laser beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system device for optical communication used for optical communication using laser light, and more specifically, it separates transmitted and received light from each other by using a beam splitter and also monitors transmitted light. The present invention relates to an optical system device for optical communication that monitors the output content of transmitted light using this monitor light.

[0002]

2. Description of the Related Art In recent years, an optical communication optical system device for performing optical communication between artificial satellites and between an artificial satellite and the ground using laser light is known.

In such an optical communication optical system device, a beam splitter splits a transmitted light transmitted toward a communication object through a telescope and a received light incident from the communication object through the telescope, and separates from the beam splitter. What detects the received light in the photodetector, detects the monitor light obtained by separating a part of the transmitted light by the beam splitter by the detector, and monitors the content of the transmitted light in the transmission mode. Are known.

FIG. 4 is a schematic view showing an example of a conventional optical communication optical system device. The direction of the laser light output from the laser light source unit 403 including the semiconductor laser 401 and the collimator lens 402 is controlled by the steering mirror 404, most of it is reflected by the beam splitter 405, and the beam diameter is expanded by the telescope 406. Then, it is sent out in the direction of the target device (not shown) that is going to perform the optical communication.

On the other hand, the received light beam transmitted from the target device has its beam diameter reduced by the telescope 406, passes through the beam splitter 405, and is condensed by a condenser lens 407 on a detector 408. The detector 408 photoelectrically converts the intensity of the received light as a received signal and the detected position as a direction signal of the target device, and outputs the signal.

A part of the transmission light transmitted through the beam splitter 405 is reflected by the retroreflector 409, reflected by the beam splitter 405, and collected by the condenser lens 407 as monitor light on the detector 408. Be illuminated. As a result, the detector 408 outputs a signal in the transmission direction corresponding to the direction signal of the target device output at the time of reception.

When the distance to the target device is long, particularly when communication is performed with a target device at a very long distance such as communication between artificial satellites arranged in outer space, the beam direction of the transmitted light is strict. Must face the target device. Therefore, the transmission direction signal is made to match the direction signal of the target device by controlling the steering mirror 404 or by using a device (not shown) capable of controlling the direction of the entire device.

[0008]

In such an optical system device for optical communication, the efficiency of utilizing the light emitted from the laser light source is improved by using different wavelengths for the transmission light and the reception light. If the wavelength difference between the two is increased, the chromatic aberration of the telescope 406 increases, the wavefront accuracy of the transmitted light deteriorates, and the amount of transmitted light reaching the target device decreases. On the contrary, if the wavelength difference is made small, the beam splitter 405 cannot efficiently separate the transmitted light and the received light.

Therefore, in the conventional optical system for optical communication, for example, the laser wavelength of the received light is 820 nm, the laser wavelength of the transmitted light is 850 nm, and the beam splitter 405 has a dichroic transmittance as shown in FIG. Mirror (light other than transmitted light can be almost reflected light)
Is used to efficiently transmit the received light and reflect the transmitted light.

However, the spectral transmittance of the beam splitter 405 in the vicinity of 850 nm of the laser wavelength of transmitted light is
As shown in FIG. 6 (a part of FIG. 5 is enlarged), the change due to the wavelength is large, and the laser wavelength itself also has a variation of about ± 5 nm due to the variation of the manufacturing of the light source 401. It was difficult to make the amount of transmitted light (monitor light) that transmitted through the 405 constant. further,
Since the wavelength of the semiconductor laser has a temperature characteristic of about 0.3 nm / ° C, there is a problem that the amount of transmitted light changes due to a change in temperature.

In the conventional optical system for optical communication, a corner cube is used as the retroreflector 409. However, since the transmitted light passing through the beam splitter 405 is polarized, the corner cube is used. Since the reflected transmitted light is a light flux with six different polarization states in its cross section, the reflectance of the beam splitter 405 differs depending on the polarization state, and is condensed on the detector 408 by the condenser lens 407. At times, the image formation state deteriorates, which causes the accuracy of the detection position to decrease.

The present invention has been made in view of such circumstances, and even if the transmitted light and the received light having a relatively small wavelength difference are used, the transmitted light due to the variation of the wavelength of the transmitted light or the change of the temperature. It is an object of the present invention to provide an optical system device for optical communication capable of keeping the amount of monitor light of the transmitted light from the beam splitter constant with respect to the change of the wavelength of the.

Further, when the monitor light of the transmission light transmitted through the beam splitter and reflected by the monitor light retroreflecting device is focused on the photodetector to form an image, the deterioration of the image formation state is prevented. It is another object of the present invention to provide an optical system device for optical communication capable of preventing a decrease in the accuracy of the detection position.

[0014]

In order to achieve the above object, the optical system device for optical communication according to the present invention according to claim 1 is
The output laser light is transmitted at a predetermined ratio to serve as monitor light, and the rest is reflected as transmission light to the communication target, and further includes a beam splitter unit that transmits the input laser light from the communication target. The polarization spectral transmission characteristics of P-polarized light decrease from about 100% to about 0% in the direction of increasing wavelength at a wavelength value slightly larger than the wavelength of the transmitted light, and for S-polarized light, the wavelength of the transmitted light decreases. And a wavelength value located between the wavelength of the received light smaller than the wavelength of the transmitted light and the wavelength value located between
% To about 0%, the incident angle of the output laser light on the transmission / reflection surface of the beam splitter is set to 30 ° or more and 60 ° or less, and the light is incident on the transmission / reflection surface. It is characterized in that the polarization plane of the output laser light is set to 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section.

In the present invention according to claim 2, the output laser light is reflected at a predetermined ratio to be monitor light, and the rest is transmitted as transmission light to the communication target, and further the input laser light from the communication target is transmitted. It is equipped with a beam splitter part that reflects the
In S-polarized light, a wavelength value slightly smaller than the wavelength of the transmitted light is used as a boundary, and the wavelength increases from approximately 100% to approximately 0.
%, And in the case of P-polarized light, the wavelength value located between the wavelength of the transmitted light and the wavelength of the received light smaller than the wavelength of the transmitted light serves as a boundary, and increases from approximately 100% to approximately 0. %, The incident angle of the output laser light on the transmission / reflection surface of the beam splitter section is set to 30%.
The angle of rotation is set to 0 ° or more and 60 ° or less, and the polarization plane of the output laser light incident on the transmission / reflection surface is set to 1 ° or more and 30 ° or less with respect to the P polarization plane of the beam splitter section. It is characterized by becoming.

According to a third aspect of the present invention, the wavelength of the transmitted light is set to a value smaller than the wavelength of the received light, and
In the P-polarized light, the light transmission characteristic of the beam splitter section increases from approximately 0% to approximately 100% in the wavelength increasing direction with a wavelength value slightly smaller than the wavelength of the transmission light as a boundary.
The polarization is configured to increase from approximately 0% to approximately 100% in the wavelength increasing direction with the wavelength value located between the wavelength of the transmitted light and the wavelength of the received light as a boundary. This is different from the present invention according to claim 1.

Further, in the present invention according to claim 4, the wavelength of the transmitted light is set to a value larger than the wavelength of the received light, and the light transmission characteristic of the beam splitter section is greater than the wavelength of the transmitted light for S-polarized light. The wavelength value increases from approximately 0% to approximately 100% in the direction of increasing wavelength with a slightly large wavelength value as a boundary, and in P-polarized light, a wavelength value positioned between the wavelength of the transmitted light and the wavelength of the received light is the boundary. As the wavelength increases in the direction of 0
The present invention differs from the present invention according to claim 2 in that it is configured to increase from 100% to about 100%.

Further, in the optical system device for optical communication of the present invention according to claim 5, a ½ wavelength plate is arranged between the laser light source part and the beam splitter part, and the ½ wavelength plate has an optical axis. Is adjusted so that the polarization plane of the laser light incident on the beam splitter section is 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section.

Further, in the optical system device for optical communication of the present invention according to claim 6, the retroreflecting section for returning the monitor light outputted from the beam splitter section to the beam splitter section is a polarization-preserving corner cube. A quarter-wave plate is arranged between the corner cube and the beam splitter section.

[0020]

According to the optical system device for optical communication of the present invention according to claim 1, the incident angle of the output laser light incident on the beam splitter portion is set to 30 ° or more and 60 ° or less, whereby the beam splitter portion is formed. As shown in FIG. 2, the spectral transmittance of P can increase the wavelength difference between the P-polarized light and S-polarized light transmittance changing positions.

Further, in this apparatus, the polarization plane of the output laser light incident on the beam splitter section is set to 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section.

That is, if the plane of polarization of the laser light is set to 1 ° or more and 30 ° or less with respect to the S-polarized plane of the beam splitter section, most of the S-polarized light and P-polarized light of the light incident on this beam splitter section will be described. Will be transmitted by the polarization effect of the beam splitter section. However, in the vicinity of the wavelength position of the output laser light, due to the action of the dichroic mirror film provided on the transmission / reflection surface of the beam splitter section, the S-polarized transmission component becomes approximately 0% as shown in FIG. Is approximately 100%, so the final transmitted light from the beam splitter is
Only P-polarized light having a light amount of a predetermined ratio (a predetermined value close to 0% to about 25%, for example, about several%) with respect to the original output laser light is provided.

Moreover, as shown in FIG. 2, the transmittance of P-polarized light is substantially constant in the wavelength region near the wavelength position of the output laser light, and as described above, the output laser light is transmitted to the beam splitter section. By setting the incident angle to a value within a predetermined range, the wavelength range in which the transmittance of the P-polarized light is about 100% and the transmittance of the S-polarized light is about 0% is widened. The P-polarized light is constant in a wide range around the wavelength of the output laser light. As a result, even if the transmitted light and the received light with a relatively small wavelength difference are used, the output transmitted through the beam splitter section against the change in the wavelength of the transmitted light due to the variation in the wavelength of the transmitted light or the change in temperature. It is possible to make the amount of laser light constant.

Also, in the device of the present invention according to claims 2 to 4, substantially the same operational effects as those of the device of the present invention according to claim 1 can be obtained.

Next, according to the optical system device for optical communication of the present invention according to claim 5, a half wavelength plate is disposed between the laser light source part and the beam splitter part, and the half wavelength plate is provided. By adjusting the direction of the optical axis of the plate, it is possible to easily set the polarization plane of the laser light incident on the beam splitter section to 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section. It is possible to set the angle to be a desired angle, and it is possible to set the transmittance of the monitor light of the output laser light in the beam splitter section to a desired value.

Further, according to the optical system device for optical communication of the present invention according to claim 6, the retroreflecting portion is a polarization-preserving type corner cube so that the beam is transmitted through the beam splitter portion and the polarization-preserving portion is preserved. The monitor light of the output laser light reflected by the mold corner cube can have the same polarization state in its cross section. As a result, the reflectivity of the beam splitter section becomes constant in the cross section of this monitor light, and when it is condensed on the detector by the condenser lens, the image formation state deteriorates and the accuracy of the detection position decreases. Such a situation can be prevented. When such a polarization-preserving corner cube is used, the polarization-preserving corner
When the quarter wavelength plate is not arranged between the cube and the beam splitter section, the monitor light of the output laser light transmitted through the beam splitter section is almost P-polarized,
Since its polarization state does not change when it is reflected by the polarization-preserving corner cube, it is not reflected when it returns to the beam splitter section, and most of the light amount is transmitted, and the condenser lens Is not reflected in the direction of. However, in the device of the present invention, since the quarter-wave plate is arranged between the polarization-preserving corner cube and the beam splitter unit, when the monitor light of the output laser light returns to the beam splitter unit, the S-polarized component is also included. As a result, the beam splitter section can reflect the monitor light in the direction of the condenser lens with an appropriate reflectance.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a functional configuration in an embodiment of the present invention. In FIG. 1, a laser light source unit 103 is composed of a semiconductor laser 101 and a collimator lens 102. The transmitted light emitted from the semiconductor laser 101 is collimated by the collimator lens 102 and its direction is controlled by a steering mirror 104. , Enters the beam splitter 105.

Since the characteristics of the beam splitter 105 differ depending on the polarization direction, and the semiconductor laser 101 outputs polarized laser light, the semiconductor laser 101 must be mounted with its polarization direction adjusted.
However, since the semiconductor laser 101 is small in size, it is not easy to adjust it.
It is preferable to dispose the 2λ plate 110 in front of the beam splitter 105 and adjust the polarization direction of the laser beam incident on the beam splitter 105 by rotating and adjusting the 1 / 2λ plate 110.

The beam splitter 105 has an incident angle of 45.
Since the values are in degrees, the spectral transmittances of P and S polarized light are as shown in FIG. 2, for example. The beam splitter 105 is
Since it is a dichroic mirror in which transparent films having different refractive indexes are alternately laminated and coated on a transparent substrate such as glass, light that does not pass through is almost reflected. Therefore, if the wavelength of the received light is 810 nm, the received light entering the beam splitter 105 from the telescope 106 has a high transmittance of 90% or more in any polarization state, as shown in FIG. The transmitted light transmitted through the beam splitter 105 can be reflected or transmitted at a desired reflectance by adjusting the polarization state.

Here, if the incident angle is larger than 60 °, the beam splitter 105 needs to be large and the size of the entire apparatus is also large, which is not preferable, and if the incident angle is less than 30 °, for example, as shown in FIG. At the angle of 22.5 ° used in the prior art shown in FIG.
The wavelength difference at the position where the transmittance of polarized light changes becomes small as shown in FIG. 3, and the received light and the transmitted light cannot be effectively separated, which is not preferable.

The transmission light reflected by the beam splitter 105 is transmitted with the beam diameter enlarged by the telescope 106, while the received light is transmitted by the beam splitter 105 after the beam diameter is reduced by the telescope 106. Then, the light is focused on the detector 108 by the condenser lens 107.

Of the transmitted light, the monitor light transmitted through the beam splitter 105 is retroreflected by the retroreflector 109, further reflected by the beam splitter 105, and condensed by the condenser lens 107 on the detector 108. However, when a commonly used corner cube prism is used as the retroreflecting device 109, since this reflecting surface utilizes the total reflection effect of glass, the retroreflected light beam becomes light beams of six different polarization states, Since the reflectance when reflected by the beam splitter 105 differs depending on its polarization state, when the light enters the condenser lens 107, the cross sections of the light flux have different intensities, and when the light is condensed on the detector 108, the result becomes different. The image state deteriorates and the accuracy of the detection position decreases.

In this embodiment, since the retroreflecting device 109 is a polarization preserving type in which the reflecting surface of the corner cube prism is coated with silver, for example, the polarization state does not change and the beam is not changed. Splitter 10
The intensity distribution in the luminous flux of the transmitted light reflected by 5 and condensed on the detector 108 by the condenser lens 107 becomes uniform, and the accuracy of the detection position does not decrease.

However, when a polarization preserving type is used as the retroreflecting device 109, the beam splitter 105 is used.
Since the direction of polarization of the transmitted light retroreflected by P is P-polarized light and the reflectance of P-polarized light of the beam splitter 105 is low, the amount of transmitted light reflected in the direction of the condenser lens 107 is small. There is a problem that becomes. Therefore, in this embodiment, a 1/4 λ plate 111 is arranged between the beam splitter 105 and the retroreflector 109, and the polarization plane is appropriately rotated to transmit the light reflected in the direction of the condenser lens 107. The amount of light is set to be appropriate.

The optical system device for optical communication of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made.

For example, in the above embodiment, when the transmission light is separated by the beam splitter 105, a part of it is transmitted as monitor light, and the rest is reflected toward the telescope 106 and sent out. As shown in FIG. 7, a part of the transmitted light may be reflected by the beam splitter 105a toward the quarter-wave plate 111a and the retroreflecting portion 109a to be monitor light, and the rest may be transmitted toward the telescope 106a.

In this case, the polarization plane of the transmission light incident on the transmission / reflection surface of the beam splitter 105 is set to 1 ° or more and 30 ° or less with respect to the P polarization plane of the beam splitter 105, so that It is necessary to obtain a stable small amount of reflected monitor light even if there are wavelength fluctuations and wavelength variations.

Although the wavelength of the transmitted light is set to a value larger than the wavelength of the received light in the above embodiment, the wavelength of the received light may be set to a value larger than the wavelength of the transmitted light. However, in this case, the beam splitter 105
As shown in FIG. 8, the polarized light spectral transmission characteristics of the polarized light are increased from approximately 0% to approximately 100% with respect to a predetermined wavelength position in the wavelength increasing direction. It must be characteristic.

Also in this case, when the transmission light is separated by the beam splitter 105, a part of the transmission light may be reflected to be monitor light, and the rest may be transmitted to the telescope 106. .

[0040]

As described above, according to the present invention, even if the transmitted light and the received light having a relatively small wavelength difference are used, the monitor light of the output laser light varies due to the wavelength variation or the temperature change of the monitor light. It is possible to make the light amount of the monitor light focused on the detector constant with respect to the change of the light wavelength.

Further, the polarization plane of the output laser light incident on the beam splitter section can be easily set to a desired angle of 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section. The transmittance or reflectance of the output laser light at the beam splitter section can be set to a desired value.

Furthermore, the monitor light of the output laser light which is transmitted through the beam splitter portion and reflected by the polarization-preserving corner cube can be made to have the same polarization state in its cross section. As a result, the reflectivity of the beam splitter portion becomes constant in the cross section of the monitor light, and when the monitor light is focused on the detector by the condenser lens, the image formation state deteriorates and the accuracy of the detection position decreases. Such a situation is prevented. The beam splitter section can reflect the monitor light toward the condenser lens with an appropriate reflectance.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical system device for optical communication according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing polarization spectral transmittance of the beam splitter shown in FIG.

FIG. 3 is a characteristic diagram showing polarization spectral transmittance of a beam splitter according to a conventional technique.

FIG. 4 is a block diagram showing a configuration of an optical system device for optical communication according to a conventional technique.

5 is a characteristic diagram showing the spectral transmittance of the beam splitter shown in FIG.

FIG. 6 is an enlarged view showing a part of the characteristic diagram of FIG.

FIG. 7 is a block diagram showing the configuration of an optical system device for optical communication according to another embodiment of the present invention.

FIG. 8 is a characteristic diagram showing polarization spectral transmittance of a beam splitter used in a device of still another embodiment of the present invention.

[Explanation of reference symbols] 101, 401 Semiconductor laser 102, 402 Collimator lens 103, 403 Laser light source 104, 404 Steering mirror 105, 105a, 405 Beam splitter 106, 106a, 406 Telescope 107, 407 Condenser lens 108, 408 Light detection Vessel 109, 109a, 409 Retroreflector 110, 110a 1 / 2λ plate 111, 111a 1 / 4λ plate

Claims (6)

[Claims] 1. A laser light source section for generating linearly polarized laser light having a first wavelength, a light output direction control section for controlling an output direction of the generated laser light, and the output direction. A beam diameter converter for expanding the beam diameter of the controlled output laser beam and reducing the beam diameter of the input laser beam having a second wavelength slightly smaller than the first wavelength, which is input from the communication target. And the output laser light from the light output direction control unit is transmitted at a predetermined ratio to be monitor light, and the rest is reflected in the direction of the light flux diameter conversion unit, and further input laser light from the light flux diameter conversion unit. A beam splitter portion that transmits the beam splitter portion, a retroreflector that returns the monitor light that has passed through the beam splitter portion to the beam splitter portion, an input laser beam that has passed through the beam splitter portion, and the retroreflector And a photodetector for detecting the intensity and / or position of the monitor light reflected by the beam splitter unit, and the polarization spectral transmission characteristic of the beam splitter unit is the first wavelength in P-polarized light. The third wavelength value is slightly larger than the third wavelength value, and decreases from approximately 100% to approximately 0% in the wavelength increasing direction, and in S-polarized light, the position is between the first wavelength and the second wavelength. With the fourth wavelength value as a boundary, it is configured to decrease from approximately 100% to approximately 0% in the wavelength increasing direction, and the incident angle of the output laser light on the transmission / reflection surface of the beam splitter is 30%. Set from 0 ° to 60 ° and the transmission /
An optical system device for optical communication, characterized in that the polarization plane of the output laser light incident on the reflecting surface is set to 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section. . 2. A laser light source unit for generating linearly polarized laser light having a first wavelength, a light output direction control unit for controlling an output direction of the generated laser light, and an output direction A beam diameter conversion unit for expanding the beam diameter of the controlled output laser beam and reducing the beam diameter of the input laser beam having a second wavelength slightly larger than the first wavelength, which is input from the communication target. And the output laser light from the light output direction control unit is reflected at a predetermined ratio to become monitor light, and the rest is transmitted in the direction of the light flux diameter conversion unit, and further input laser light from the light flux diameter conversion unit. A beam splitter section that reflects the reflected light, a retroreflecting section that causes the monitor light reflected by the beam splitter section to return to the beam splitter section, an input laser beam reflected by the beam splitter section, and a front laser beam. A photodetector that detects the intensity and / or the position of the monitor light that has returned from the retroreflective portion and has passed through the beam splitter portion is provided, and the polarization spectral transmission characteristic of the beam splitter portion is the first for the S-polarized light. The wavelength decreases from about 100% to about 0% in the direction of increasing wavelength with a third wavelength value that is slightly smaller than the wavelength of, as a boundary, and in the case of P-polarized light, between the first wavelength and the second wavelength. The fourth wavelength value located at the boundary is configured to decrease from approximately 100% to approximately 0% in the wavelength increasing direction, and the incident angle of the output laser light on the transmission / reflection surface of the beam splitter section. Is set to 30 ° or more and 60 ° or less, and the transmission /
An optical system device for optical communication, characterized in that the polarization plane of the output laser light incident on the reflecting surface is set to 1 ° or more and 30 ° or less with respect to the P polarization plane of the beam splitter section. . 3. A laser light source section for generating linearly polarized laser light having a first wavelength, a light output direction control section for controlling an output direction of the generated laser light, and the output direction. A beam diameter conversion unit for expanding the beam diameter of the controlled output laser beam and reducing the beam diameter of the input laser beam having a second wavelength slightly larger than the first wavelength, which is input from the communication target. And the output laser light from the light output direction control unit is transmitted at a predetermined ratio to be monitor light, and the rest is reflected in the direction of the light flux diameter conversion unit, and further input laser light from the light flux diameter conversion unit. A beam splitter portion that transmits the beam splitter portion, a retroreflector that returns the monitor light that has passed through the beam splitter portion to the beam splitter portion, an input laser beam that has passed through the beam splitter portion, and the retroreflector And a photodetector for detecting the intensity and / or position of the monitor light reflected by the beam splitter unit, and the polarization spectral transmission characteristic of the beam splitter unit is the first wavelength in P-polarized light. From the third wavelength value, which is slightly smaller than the third wavelength, in the direction of increasing wavelength from approximately 0% to approximately 10
For S-polarized light, it increases from 0% to about 100% in the increasing direction of the wavelength with the fourth wavelength value located between the first wavelength and the second wavelength as a boundary. The incident angle of the output laser light on the transmission / reflection surface of the beam splitter unit is set to 30 ° or more and 60 ° or less, and
An optical system device for optical communication, characterized in that the polarization plane of the output laser light incident on the reflecting surface is set to 1 ° or more and 30 ° or less with respect to the S polarization plane of the beam splitter section. . 4. A laser light source section for generating a linearly polarized laser beam having a first wavelength, a light output direction control section for controlling an output direction of the generated laser beam, and the output direction. A beam diameter converter for expanding the beam diameter of the controlled output laser beam and reducing the beam diameter of the input laser beam having a second wavelength slightly smaller than the first wavelength, which is input from the communication target. And the output laser light from the light output direction control unit is reflected at a predetermined ratio to become monitor light, and the rest is transmitted in the direction of the light flux diameter conversion unit, and further input laser light from the light flux diameter conversion unit. A beam splitter section that reflects the beam, a retroreflecting section that returns the monitor light reflected by the beam splitter section to the beam splitter section, an input laser beam reflected by the beam splitter section, and A photodetector that detects the intensity and / or the position of the monitor light that has returned from the retroreflector and transmitted through the beam splitter section is provided, and the polarization spectral transmission characteristic of the beam splitter section is From the third wavelength value, which is slightly larger than the first wavelength, as a boundary, the wavelength increases from approximately 0% to approximately 10
For P-polarized light, it increases from 0% to about 100% in the increasing direction of the wavelength with the fourth wavelength value located between the first wavelength and the second wavelength as a boundary. The incident angle of the output laser light on the transmission / reflection surface of the beam splitter unit is set to 30 ° or more and 60 ° or less, and
An optical system device for optical communication, characterized in that the polarization plane of the output laser light incident on the reflecting surface is set to 1 ° or more and 30 ° or less with respect to the P polarization plane of the beam splitter section. . 5. The operation of setting the angle of the polarization plane of the output laser light incident on the transmission / reflection surface is performed by a half-wave plate disposed between the laser light source section and the beam splitter section. The optical system device for optical communication according to any one of claims 1 to 4, which is performed by adjusting a direction of an optical axis. 6. The polarization-preserving corner of the retroreflective portion
It is composed of a cube, and has a quarter between the retroreflective part and the beam splitter part.
A wavelength plate is provided, and the wavelength plate is provided.
The optical system device for optical communication according to any one of the above.