JP2001160783A - Spatial light transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spatial light transmission device which can stably obtain satisfactory calibration. SOLUTION: In the spatial light transmission device, PBS 24 dividing an incident transmission beam in accordance with a polarization direction is installed, communication is executed by using an S polarized beam among polarized beams divided by a polarized beam division means and an offset angle being an axial angle between the transmission beam and a reception beam in an initial state is calculated by using a P polarized beam. At least a wavelength board switch 1 rotating the polarization direction of the transmission beam by 90 deg. only when the transmission beam which is made incident on PBS 24 is the S polarized beam and the offset angle is calculated is disposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spatial light transmission device used for optical communication, and more particularly to a spatial light transmission device used for inter-satellite optical communication.

[0002]

2. Description of the Related Art In the case of a spatial optical transmission device capable of bidirectional optical communication, for example, in a case where a communication partner is extremely distant, as in the case of inter-satellite optical communication in space, the directivity of the transmission optical axis is highly accurate. Therefore, it is common practice to emit the transmission beam along the optical axis direction of the reception beam while tracking the optical axis of the reception beam.

As an example of a spatial light transmission device capable of directing the transmission optical axis with high precision, a reception optical axis angle detector for controlling the tracking of the reception light, and a transmission light for directing control of the transmission optical axis. There is an apparatus which includes a shaft angle detector and corrects an offset angle between these detectors. In this spatial light transmission device, usually, a part of the transmission beam is made incident on the reception optical axis angle detector, and the difference between the detection angles of the transmission optical axis angle detector and the reception optical axis angle detector at that time is the offset angle. Is required.

FIG. 11 shows a schematic configuration of a conventional spatial light transmission device. A polarizer (POL) 21, a long-wavelength pass filter (LPF) 22, a λ / 2 plate 3, a transmission beam deflector 12,
Beam splitters (BS) 23 are sequentially arranged, and BS2
3, a polarization beam splitter (PBS) 24, an optical blocker 15, a λ / 4 plate 2 in the traveling direction of one of the beams divided at 3.
5. A corner cube reflector (CCR) 26 is sequentially arranged, and the transmission optical axis angle detector 13 is arranged in the traveling direction of the other beam split by the BS 23. BS
A transmission / reception beam deflector 16 is disposed in a traveling direction of a beam in which a beam incident from 23 is reflected by the PBS 24,
A short-wavelength pass filter (SPF) 27 and a receiving optical axis angle detector 14 are arranged in the traveling direction of the beam, which is reflected by the PBS 24 when the beam enters through the optical blocker 15. Outputs of the transmission optical axis angle detector 13 and the reception optical axis angle detector 14 are input to an offset angle calculation unit 28, respectively.

[0005] The optical transmitter 11 includes an LD (laser diode) as a light source, and a beam emitted from the LD is shaped into a circular shape, collimated in parallel, and output as a transmission beam. The transmission beam output from the optical transmitter 11 is linearly polarized light, and the beam contains a spontaneous emission component in addition to the laser beam component. FIG. 2 shows a spectrum of a transmission beam composed of a laser beam component and a spontaneous emission component of the LD. The spontaneous emission component is a non-polarized component, and its wavelength range extends over both the short wavelength side and the long wavelength side of the wavelength of the laser light component as shown in FIG.
Normally, in inter-satellite optical communication, the transmission light wavelength region and the reception light wavelength region are different, so that the natural light emission component on the short wavelength side also occurs in the reception light wavelength region as shown in FIG.

The POL 21 transmits a single polarization component, and its polarization direction is the same as the polarization direction of the laser beam component of the transmission beam output from the optical transmitter 11.
Here, since the beam itself emitted from the LD of the optical transmitter 11 is biased to the S-polarized component, the polarization direction of the POL 21 is S-polarized. The LPF 22 blocks components on the short wavelength side of the natural light emission components of the transmission beam. FIG. 3 shows the spectral characteristics of the LPF 22. The transmittance for wavelengths on the shorter wavelength side than the transmission light wavelength range is low.

[0007] The λ / 2 plate 3 has optical rotation and is configured to slightly rotate the polarization direction of the transmission beam. With this configuration, most of the polarization component of the transmission beam that has passed through the λ / 2 plate 3 is S-polarized light, but slightly includes P-polarized light. S-polarized light is used for transmission, and P-polarized light is used for calibration between a transmission optical axis and a reception optical axis.

The transmission beam deflector 12 controls the direction of the optical axis of the transmission beam with respect to the direction of the optical axis of the reception beam. The BS 23 splits a part of the transmission beam, and is configured so that one of the split beams enters the PBS 24 and the other enters the transmission optical axis angle detector 13. The transmission optical axis angle detector 13 detects the optical axis angle of the incident transmission beam. The result detected by the transmission optical axis angle detector 13 is the transmission beam deflector 1
2 and is used for controlling the direction of the optical axis of the transmission beam.

The PBS 24 reflects S-polarized light and transmits P-polarized light in the transmission light wavelength range (including the wavelength range of the laser beam component of the transmission beam), and transmits S-polarized light on the shorter wavelength side than the transmission light wavelength range. Both the polarized light and the P-polarized light are transmitted, and the S-polarized light and the P-polarized light are both reflected on the longer wavelength side than the transmission light wavelength range. FIG. 4 shows the spectral characteristics of the PBS 24.
Shown in

The optical circuit breaker 15 is configured to block light when transmitting a transmission beam to the outside of the apparatus, and to pass light when performing calibration between the transmission optical axis and the reception optical axis in the apparatus. ing. The λ / 4 plate 25 converts the transmission beam (linearly polarized light) incident from the PBS 24 into circularly polarized light,
The transmission beam (circularly polarized light) incident from R26 is converted into linearly polarized light. The CCR 26 is λ
The transmission beam incident through the / 4 plate 25 is reflected while maintaining the optical axis direction and the property of circular polarization. SPF
Numeral 27 is configured to transmit light in the wavelength range of the received light and below, and to reflect light on the longer wavelength side than the wavelength range of the received light. The spectral characteristics of this SPF 27 are shown in FIG.
Shown in

The transmission / reception beam deflector 16 transmits the transmission beam to the outside of the apparatus and controls the optical axis direction of the reception beam so that the reception beam enters the center of the reception optical axis angle detector 14. The receiving optical axis angle detector 14
It detects the optical axis angle of the incident receiving beam. The result detected by the reception optical axis angle detector 14 is fed back to the transmission / reception beam deflector 16 and used for controlling the direction of the optical axis of the reception beam.

Next, the operation of the spatial light transmission device will be described in detail.

(1) When Calibration is Performed When the direction of the optical axis of the transmission beam is controlled with respect to the direction of the optical axis of the reception beam, the distance between the transmission optical axis angle detector 13 and the reception optical axis angle detector 14 is controlled. It is necessary to obtain the offset angle in advance and correct it. In this spatial light transmission device, the offset angle is obtained as follows and calibration is performed.

The transmission beam output from the optical transmitter 11 sequentially passes through the POL 21, the LPF 22, and the λ / 2 plate 3. In the LPF 22, the components of the transmission beam on the shorter wavelength side than the transmission light wavelength range are removed to some extent (not completely removed) according to the spectral characteristics shown in FIG. 3, and the polarization direction of the transmission beam is changed in the λ / 2 plate 3. Rotate slightly. Therefore, the transmission beam at the time of passing through the λ / 2 plate 3 includes the S-polarized light and the P-polarized light obtained by slightly rotating the polarization direction. P-polarized light of these S and P-polarized lights is used for calibration.

The transmission beam passing through the λ / 2 plate 3 passes through the transmission beam deflector 12 and is divided into two directions by the BS 23, one of which is incident on the PBS 24 and the other is transmitted to the transmission optical axis angle detector 13. Incident. BS23 to PBS2
Most of the transmission beam incident on the reflection surface 4 is incident on the reflection surface of the PBS 24 as S-polarized light, and only the component whose polarization direction is slightly rotated by the λ / 2 plate 3 is incident as P-polarized light. In the incident light component, the P-polarized light passes through the PBS 24 for the spontaneous emission component on the longer wavelength side than the wavelength region of the laser light component, and the S and P polarizations pass through the PBS 24 for the spontaneous emission component on the shorter wavelength side.

The transmission beam transmitted through the PBS 24 enters the CCR 26 via the optical circuit breaker 15 and the λ / 4 plate 25, is reflected by the CCR 26 in the same direction as the incident optical axis, and is again transmitted to the λ / 4 plate 25. The light reenters the PBS 24 via the circuit breaker 15. The λ / 4 plate 25 converts the transmission beam incident from the PBS 24 from linearly polarized light to circularly polarized light,
The transmitted beam reflected at 26 and re-entered is converted from circularly polarized light to linearly polarized light. Here, the CCR 26 is a hollow type or a prism type having a reflective surface coated with a reflective coating, and the circularly polarized light reflected by the CCR 26 is opposite to the circularly polarized light when incident. For this reason,
The polarization direction of the transmission beam reflected by the CCR 26 and passed through the λ / 4 plate 25 again is changed from the PBS 24 to the λ / 4 plate 2.
5 rotates by 90 ° with respect to the polarization direction of the transmission beam. Therefore, most of the transmission beam re-entering the PBS 24 becomes S-polarized light. PBS24
According to the spectral characteristics shown in FIG. 4, the laser beam component of the transmission beam re-entering the PBS 24 via the λ / 4 plate 25 is almost reflected, and the natural light emission component on the shorter wavelength side than the transmission light wavelength region. Is transmitted, and the spontaneous emission component on the long wavelength side is reflected similarly to the laser light component.

The transmission beam (S) reflected by the PBS 24
The polarized light enters the reception optical axis angle detector 14 via the SPF 27. In the SPF 27, according to the spectral characteristics shown in FIG. 5, a part of the laser beam component of the transmission beam is cut off, and a spontaneous emission component on the long wavelength side is completely cut off.
Part of the laser light component that has passed through the PF 27 enters the reception optical axis angle detector 14. The transmission beam deflector 12 adjusts the optical axis direction of the transmission beam so that the laser beam component of the transmission beam incident on the reception optical axis angle detector 14 enters the center of the detector. Shaft angle detector 13
The transmission optical axis angle detected at is obtained as an offset angle required for calibration.

By performing calibration between the transmission optical axis angle detector 13 and the reception optical axis angle detector 14 based on the offset angle obtained as described above, the optical axis direction of the reception beam in the initial state is obtained. And the optical axis of the transmission beam.

(2) In the case of performing spatial light transmission In the spatial light transmission, after performing the above-described calibration, while tracking the optical axis of the reception beam, the optical axis of the transmission beam with respect to the optical axis direction of the reception beam. The direction is controlled as follows.

As described above, the transmission beam that has passed through the λ / 2 plate 3 passes through the transmission beam deflector 12 and then passes through the BS 23
Incident on. Then, the light beam is divided into two directions by the BS 23, one of which is incident on the PBS 24, and the other is incident on the transmission optical axis angle detector 13. Since most of the transmission beam incident on the PBS 24 is S-polarized, most of the transmission beam is reflected by the PBS 24, and the reflected transmission beam (S-polarized light) is output to the outside of the apparatus via the transmission / reception beam deflector 16. The output transmission beam is received by the satellite that is the communication partner.

The adjustment of the transmission beam optical axis direction with respect to the reception beam optical axis direction is performed by the transmission optical axis angle, the reception optical axis angle, and the transmission optical axis angle detected by the transmission optical axis angle detector 13 and the reception optical axis angle detector 14, respectively. This is performed based on the offset angle described above.

On the other hand, the reception beam enters the reception optical axis angle detector 14 via the transmission / reception beam deflector 16, the PBS 24, and the SPF 27. The result detected by the reception optical axis angle detector 14 is fed back to the transmission / reception beam deflector 16 and used for tracking in the direction of the reception beam optical axis.

[0023]

However, the above-mentioned conventional spatial light transmission device has the following problems.
A conventional spatial light transmission device has a λ / 2 in the optical path of a transmission beam.
The plate 3 is always inserted, and the offset angle at the time of calibration is obtained using a small amount of P-polarized light (laser light component) obtained when the transmission beam passes through the λ / 2 plate 3. . Therefore, the light intensity level of the laser beam component of the LD incident on the reception optical axis angle detector 14 is small, and the structure is easily affected by noise (natural light emission component of the LD).

Since the output of the laser beam component of the LD is generally elliptical, the optical transmitter 11 usually shapes the laser beam into a circle using an anamorphic prism pair. Since the wavelength range of the natural light-emitting component is widened as shown in FIG. 2, when the natural light-emitting component passes through such a prism pair, the natural light-emitting component spreads out with respect to the laser light component and is output. become. For this reason, the angle of the transmission beam output from the optical transmitter 11 (the incident angle to the receiving optical axis angle detector) differs between the laser light component and the spontaneous emission component, and the light intensity level of the spontaneous emission component If the value of becomes a level that cannot be ignored as compared with the laser light component, the calibration performance of the apparatus will be degraded. In the configuration shown in FIG. 11, the reception optical axis angle detector 1
Immediately before step 4, the SPF having a steep cut-off characteristic with respect to the transmission light wavelength region as shown in FIG. 5 so as to transmit the reception light but suppress the crosstalk component of the transmission beam as much as possible.
Since the transmission beam 27 is provided, the transmission beam after passing through the calibration optical path until the transmission beam output from the optical transmitter 11 enters the reception optical axis angle detector 14 is shown in FIG.
And the spontaneous emission component of the LD in the same wavelength band as the received light (natural emission component on the short wavelength side)
Is the same light intensity level as the laser light component of the LD. Therefore, in the conventional spatial light transmission device, the spontaneous light emission component on the short wavelength side becomes noise, and the reception optical axis angle detector 1
4, the S / N ratio at the time of detecting the laser light component of the LD decreases, and the calibration performance decreases due to the influence of the natural light emission component of the LD.

In addition, in the conventional spatial light transmission device, as described above, since the light intensity level of the laser beam component of the LD used for calibration is small, a wavelength flatness compensation filter is provided in the optical path of the transmission beam. Can not. Therefore, the spectral characteristic of the laser light component in the wavelength band of the calibration optical path does not become flat, and if the wavelength of the light source fluctuates even during calibration, the light receiving level of the receiving optical axis angle detector 14 becomes unstable. And good calibration cannot be stably obtained.

An object of the present invention is to solve the above-mentioned problems and to provide a spatial light transmission device capable of stably obtaining good calibration. Furthermore, SPF
It is an object of the present invention to provide a spatial light transmission device having a level margin capable of compensating the spectral characteristics of the optical signal.

[0027]

In order to achieve the above object, a spatial light transmission apparatus according to the present invention has a polarization beam splitting means for splitting an incoming transmission beam in accordance with a polarization direction. The communication is performed using the first polarized beam among the polarized beams split by the means, and the optical axis angle between the transmitting beam and the receiving beam in the initial state is initialized using the second polarized beam. In the spatial light transmission device in which the offset angle that is the shift is calculated, the transmission beam incident on the polarization beam splitting means is the first polarization, and only when the offset angle is calculated, the polarization direction of the transmission beam. Characterized in that it has at least a polarization direction rotating means for rotating 90 °.

In the above invention, a wavelength flattening compensation filter may be further provided in the optical path of the second polarized light beam split by the polarizing beam splitting means.

(Operation) In the present invention as described above, at the time of calibration, the polarization direction of the transmission beam is rotated by 90 °, so that most of the transmission beam incident on the polarization beam splitting means is the second beam. Is output as a polarized light beam. Therefore, most of the transmission beam can be used for calculating the offset angle at the time of calibration.

In the present invention having a wavelength flattening compensation filter, the spectral characteristic of the calibration light path can be made flat, so that even if the wavelength of the light source fluctuates during calibration, The transmission light level at the time of calibration does not become unstable unlike the related art.

[0031]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of a spatial light transmission device according to a first embodiment of the present invention. In this spatial light transmission device, in the configuration shown in FIG. 11 described above, a wavelength plate switch 1 as a polarization direction rotating means is provided instead of the λ / 2 plate 3, and the spectral characteristic of the calibration optical path is made flat. The configuration is almost the same except that a wavelength flattening compensation filter (FCF) 2 is provided. In FIG. 1, FIG.
The same components as those shown in FIG. 1 are denoted by the same reference numerals, and a detailed description of those components is omitted here.

The wavelength plate switch 1 has a λ / 2 having a crystal axis of 45 ° with respect to the polarization direction of the incident transmission beam.
The λ / 2 plate is inserted into the optical path of the transmission beam at the time of calibration, and the transmitted transmission beam is passed as it is at the time of optical transmission. Since the polarization direction of the laser beam output from the optical transmitter 11 is biased toward S-polarized light, when the λ / 2 plate is inserted into the optical path of the transmission beam by the wavelength plate switch 1 during calibration, λ Most of the polarization component of the transmission beam after passing through the / 2 plate becomes P-polarized light. Therefore, most of the transmission beam reflected by the BS 23 and incident on the PBS 24 during the calibration is incident on the reflection surface of the PBS 24 as P-polarized light. As a result, the light intensity level of the laser beam component of the transmission beam detected by the reception optical axis angle detector 14 at the time of calibration is approximately 100 times larger than that of the configuration shown in FIG.

The FCF 2 is provided between the λ / 4 plate 25 and the CCR 26. The spectral characteristic in the calibration optical path from the transmitter 11 to the reception optical axis angle detector 14 shows a steep characteristic in the transmission light wavelength region as shown in FIG. 6 except for the FCF2. No. The cause is, as explained in the above-mentioned problem, the SPF disposed immediately before the reception optical axis angle detector 14.
27 has a steep spectral characteristic as shown in FIG. The FCF 2 makes the spectral characteristics shown in FIG. 6 flat, and the spectral characteristics as shown in FIG. 7, that is, the transmittance is constant in the wavelength band exceeding the transmission light wavelength range, and is equal to or less than the transmission light wavelength range. In the wavelength band, it has a spectral characteristic such that the transmittance decreases at a constant inclination. As shown in FIG. 8, the spectral characteristic in the calibration optical path in which the FCF 2 is inserted becomes flat in the transmission light wavelength region. In the present embodiment, the above-described wavelength plate switch 1 allows the reception optical axis angle detector 14 to be used during calibration.
Since the light intensity level of the laser beam component of the transmission beam detected in step (1) is about 100 times as large as that of the conventional one, the transmission beam loss caused by the FCF 2 does not matter.

Next, the operation of the spatial light transmission device will be described in detail.

(1) Case of Performing Calibration Here, the calibration is performed by obtaining the offset angle between the transmission optical axis angle detector 13 and the reception optical axis angle detector 14 as follows.

The transmission beam output from the optical transmitter 11 after being shaped into a circle and collimated in parallel is limited in its polarization direction when passing through the POL 21. Here, LD
Since the laser beam component has the same polarization direction (S-polarized light) as POL21, it passes through with almost no loss,
As for the spontaneous light emission component of the LD, only the same polarization component (here, S-polarized light) as the laser light component among the non-polarization components is POL2.
1 is transmitted.

The transmission beam (S-polarized light) transmitted through the POL 21 sequentially passes through the LPF 22 and the wavelength plate switch 1.
In the LPF 22, components on the short wavelength side of the transmission light wavelength range of the transmission beam are removed to some extent according to the spectral characteristics shown in FIG. In the wavelength plate switch 1, a λ / 2 plate is inserted in the optical path of the transmission beam.
The polarization direction of both the laser beam component (S-polarized light) and the spontaneous emission component (S-polarized light) of the transmission beam is rotated by 90 ° by the plate. Most of the polarization component of the transmission beam that has passed through the wavelength plate switch 1 becomes P-polarized light.

The transmission beam that has passed through the wavelength plate switch 1 is
After passing through the transmission beam deflector 12, it is split into two directions by the BS 23, one of which is incident on the PBS 24, and the other is incident on the transmission optical axis angle detector 13. PB from BS23
Most of the transmission beam incident on S24 enters both the laser beam component and the spontaneous emission component on the reflection surface of the PBS 24 as P-polarized light, and most of the incident light component passes through the PBS 24 without loss.

The transmission beam transmitted through the PBS 24 passes through the optical circuit breaker 15, the λ / 4 plate 25, and the FCF 2 sequentially, and
6, the light is reflected by the CCR 26 in the coaxial direction with the incident optical axis, and is returned to the FCF 2, the λ / 4 plate 25, and the optical circuit breaker 15 again.
Are sequentially incident on the PBS 24 again. In the λ / 4 plate 25, the transmission beam incident from the PBS 24 is converted from linearly polarized light into circularly polarized light, and the transmission beam reflected by the CCR 26 and re-entered is converted from circularly polarized light into linearly polarized light.
Here, the CCR 26 is a hollow type or a prism type having a reflective surface coated with a reflective coating.
The circularly polarized light reflected by the CR 26 is opposite to the circularly polarized light when it is incident. Therefore, the polarization direction of the transmission beam reflected by the CCR 26 and passed through the λ / 4 plate 25 again is rotated by 90 ° with respect to the polarization direction of the transmission beam incident on the λ / 4 plate 25 from the PBS 24. Therefore, most of the transmission beam re-entering the PBS 24 becomes S-polarized light. In the PBS 24, according to the spectral characteristics shown in FIG. 4, of the transmission beam that re-enters the PBS 24 via the λ / 4 plate 25, the laser light component is almost reflected, and the natural light emission on the shorter wavelength side than the transmission light wavelength region. The component is transmitted, and the spontaneous emission component on the long wavelength side is reflected similarly to the laser beam component.

The transmission beam (S) reflected by the PBS 24
The polarized light enters the reception optical axis angle detector 14 via the SPF 27. In the SPF 27, according to the spectral characteristics shown in FIG. 5, a part of the laser beam component of the transmission beam is cut off, and the natural light emission component on the long wavelength side is completely cut off.
Part of the laser light component that has passed through the PF 27 enters the reception optical axis angle detector 14. The transmission beam deflector 12 adjusts the optical axis direction of the transmission beam so that the laser beam component of the transmission beam incident on the reception optical axis angle detector 14 enters the center of the detector. Shaft angle detector 13
The transmission optical axis angle detected at is obtained as an offset angle required for calibration.

By performing calibration between the transmission optical axis angle detector 13 and the reception optical axis angle detector 14 based on the offset angle obtained as described above, the optical axis direction of the reception beam in the initial state is obtained. And the optical axis of the transmission beam.

In this embodiment, the FCF 2 is provided between the λ / 4 plate 25 and the CCR 26, and thereby, the spectral characteristic of the calibration optical path from the optical transmitter 11 to the receiving optical axis angle detector 14 is obtained. , The flatness in the transmission light wavelength range is compensated (see FIG. 7). Therefore, even if the oscillation wavelength of the LD light source of the optical transmitter 11 fluctuates slightly, the light receiving level of the reception optical axis angle detector 14 does not fluctuate greatly, and the detection performance of the reception optical axis angle detector 14 is stabilized. Can be secured. Therefore, calibration can be stably maintained.

As shown in FIG. 7 and FIG.
With CF2, the spontaneous light emission component (noise component) of the LD on the short wavelength side can be largely removed, so that the calibration performance is further improved. FIG. 9 shows the LD spectrum characteristics after passing through the calibration optical path from the optical transmitter 11 to the receiving optical axis angle detector 14.
As can be seen from FIG. 9, in the present embodiment, a natural light-emitting component other than the laser light component, which becomes noise, particularly a natural light-emitting component on the short wavelength side is sufficiently removed.

(2) In the case of performing spatial light transmission In spatial light transmission, after performing the above-described calibration, while tracking the optical axis of the reception beam, the optical axis of the transmission beam with respect to the optical axis direction of the reception beam. The direction is controlled as follows.

The transmission beam (S-polarized light) output from the optical transmitter 11 and transmitted through the POL 21 sequentially passes through the LPF 22 and the wavelength plate switch 1. At this time, in the wavelength plate switch 1, the λ / 2 plate is not inserted in the optical path of the transmission beam, and the incident transmission beam passes through the wavelength plate switch 1 as it is. The transmission beam that has passed through the wavelength plate switch 1 passes through the transmission beam deflector 12 and then passes through the BS 23
Incident on. Then, the light beam is divided into two directions by the BS 23, one of which is incident on the PBS 24, and the other is incident on the transmission optical axis angle detector 13. Since most of the transmission beam incident on the PBS 24 is S-polarized, most of the transmission beam is reflected by the PBS 24, and the reflected transmission beam (S-polarized light) is output to the outside of the apparatus via the transmission / reception beam deflector 16. The output transmission beam is received by the satellite that is the communication partner.

The adjustment of the transmission beam optical axis direction with respect to the reception beam optical axis direction is performed by the transmission optical axis angle, the reception optical axis angle detected by the transmission optical axis angle detector 13 and the reception optical axis angle detector 14, respectively. This is performed based on the offset angle described above.

On the other hand, the reception beam enters the reception optical axis angle detector 14 via the transmission / reception beam deflector 16, PBS 24, and SPF 27. The result detected by the reception optical axis angle detector 14 is fed back to the transmission / reception beam deflector 16 and used for tracking in the direction of the reception beam optical axis.

As described above, the wavelength plate (λ / 2 plate) switch for rotating the direction of the linearly polarized light of the transmission beam using the LD as the light source by 90 ° is provided between the optical transmitter and the transmission beam deflector. By switching the wavelength plate between when transmitting a transmission beam and when performing calibration between the transmission optical axis and the reception optical axis in the device, spontaneous emission different from the laser light component of the LD during calibration is performed. The amount of components returning to the receiving optical axis angle detector can be greatly reduced. Thereby, the calibration performance of the device can be improved.

(Other Embodiments) In the above-described embodiment, the wavelength plate switch 1 is provided as the polarization direction rotating means. Instead of the wavelength plate switch 1, two optical transmitters are used. The same operation can be realized by using.

FIG. 10 is a block diagram showing a spatial light transmission device according to a second embodiment of the present invention. This spatial light transmission device uses a polarization direction rotating means instead of a wave plate switch as a 2
1 except that two optical transmitters 11a and 11b were provided.
Are almost the same as those shown in FIG. In FIG. 10, FIG.
The same reference numerals are given to the same components as those shown in (1), and the detailed description of those components is omitted here.

The two optical transmitters 11a and 11b are configured so that the polarization directions of the output transmission beams are orthogonal to each other, so that these optical transmitters can be switched between when communicating and when calculating the offset angle. It has become. Here, an S-polarized transmission beam is output from the optical transmitter 11a during communication, and a P-polarized transmission beam is output from the optical transmitter 11b during calibration. The POL 21 is composed of a polarization beam splitter, and includes optical transmitters 11a and 11a.
b has the function of multiplexing the transmission beams respectively output from b and the function as a polarizer.

In the spatial light transmission device of the present embodiment, the optical transmitter 11b is driven when performing calibration, and the optical transmitter 11a is driven when performing spatial light transmission. Thereby, substantially the same effects as those shown in FIG. 1 can be obtained.

The spatial light transmission apparatus of each of the embodiments described above is bidirectional and coaxial with the optical axis of the transmission / reception beam, and is adapted when the wavelength of the transmission beam is longer than the wavelength of the reception beam. Conversely, the configuration may be such that the wavelength of the transmission beam is shorter than the wavelength of the reception beam.
Further, the interval between the wavelengths of the transmitting and receiving beams may be set as long as it does not affect the optical transmission. However, considering the branching characteristics of a device provided in the optical path of the transmitting beam, 1
It is desirable to set the distance close to 0 to several tens nm.

In each embodiment, sufficient calibration performance can be ensured even if the POL 21 and the LPF 22 are omitted. The reason is that even if the spontaneous emission component on the short wavelength side becomes slightly larger than the laser beam component of the LD, sufficient S
/ N can be secured.

Further, the spatial light transmission apparatus of each of the above-described embodiments can be directed to a very long distance spatial optical communication, for example, an inter-satellite optical communication, because it can direct an extremely sharp transmission beam with high accuracy. .

[0057]

As described above, according to the present invention,
Since most of the transmission beams can be used for calculating the offset angle at the time of calibration, the transmission light level at the time of calibration can be increased.
For this reason, the S / N for the spontaneous emission component of the LD can be significantly improved, and the calibration performance between the transmission optical axis and the reception optical axis in the device can be improved, and good calibration can be stably performed. Can be obtained. Further, it is possible to obtain a level margin capable of compensating the spectral characteristics of the SPF.

Further, according to the present invention, the spectral characteristic of the calibration optical path can be flattened by the wavelength flattening compensation filter, so that the receiving optical axis angle detector is stable even if the wavelength of the light source slightly changes. The light receiving level can be secured, and the calibration performance of the device can be more stably maintained. Therefore, the spontaneous light emission component of the LD can be further attenuated, and the S
/ N can be further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a spatial light transmission device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of an emission spectrum of an LD.

FIG. 3 is a diagram showing spectral characteristics of an LPF.

FIG. 4 is a diagram illustrating spectral characteristics of a PBS.

FIG. 5 is a diagram illustrating spectral characteristics of an SPF.

FIG. 6 is a diagram illustrating spectral characteristics in a calibration optical path in a state where an FCF is removed.

FIG. 7 is a diagram illustrating spectral characteristics of an FCF.

FIG. 8 is a diagram illustrating spectral characteristics in a calibration optical path in a state where an FCF is inserted.

FIG. 9 is a diagram illustrating a spectral characteristic of a transmission beam detected by a reception optical axis angle detector.

FIG. 10 is a block diagram illustrating a schematic configuration of a spatial light transmission device according to a second embodiment of the present invention.

FIG. 11 is a block diagram showing a schematic configuration of a conventional spatial light transmission device.

12 is a diagram illustrating a spectral characteristic of a transmission beam after passing through a calibration optical path in the spatial light transmission device illustrated in FIG. 11;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 wavelength plate switch 2 FCF 3 λ / 2 plate 11, 11a, 11b transmitter 12 transmission beam deflector 13 transmission optical axis angle detector 14 reception optical axis angle detector 15 optical blocker 16 transmission and reception beam deflector 21 POL 22 LPF 23 BS 24 PBS 25 λ / 4 plate 26 CCR 27 SPF

Claims (6)

[Claims] 1. A polarization beam splitter for splitting an incoming transmission beam in accordance with a polarization direction, and communication is performed using a first polarization beam of the polarization beams split by the polarization beam splitter. The spatial light transmission device in which an offset angle, which is a deviation of an optical axis angle between the transmission beam and the reception beam in an initial state, is calculated using a second polarization beam when the polarization beam splitting is performed. A transmission beam incident on the transmission light is a first polarization, and at least polarization direction rotating means for rotating the polarization direction of the transmission beam by 90 ° only when the offset angle is calculated. apparatus. 2. The spatial light transmission apparatus according to claim 1, wherein the polarization direction rotating unit has a λ / 2 plate that rotates the polarization direction of the transmission beam by 90 °, and calculates an offset angle. The spatial light transmission device is configured to insert the λ / 2 plate only in the optical path of the transmission beam. 3. The spatial light transmission device according to claim 1, wherein the polarization direction rotating means has two laser light sources whose polarization directions of output transmission beams are orthogonal to each other, and these light sources are used for communication. A spatial light transmission device that is configured to be switched when calculating an offset angle. 4. The spatial light transmission device according to claim 3, wherein the transmission beams output from the two laser light sources are multiplexed, and a laser beam component of each of the transmission beams output from each laser light source is adjusted. A spatial light transmission device comprising: a polarizer that limits a polarization direction so that a polarization component in the same direction as the polarization direction is output. 5. The spatial light transmission device according to claim 1, wherein a receiving optical axis angle detecting unit that detects an optical axis angle of the receiving beam; and an optical axis angle of the transmitting beam. Further comprising a transmitting optical axis angle detecting means for detecting, wherein the offset angle is a deviation of an optical axis angle between the receiving optical axis angle detecting means and the transmitting optical axis angle detecting means in an initial state. Characteristic spatial light transmission device. 6. The spatial light transmission device according to claim 1, further comprising a wavelength flatness compensation filter in an optical path of the second polarization beam split by the polarization beam splitting unit. A spatial light transmission device characterized by the above-mentioned.