JPH07245587A - Space optical communication equipment - Google Patents

Abstract

PURPOSE:To suppress a reduction rate of transmission light intensity due to atmospheric absorption to be low by adopting light emitting elements for plural semiconductor lasers with different wavelengths and emitting a transmission beam including plural signal lights modulated by a same signal to an opposite equipment. CONSTITUTION:An output of a signal modulation section 1 is given to two light emitting sections 3a, 3b employing a semiconductor laser whose oscillating wavelengths (lambdaa, lambdab) differ via two drive circuits 2a, 2b, and a projection optical system 4 is arranged in front of the light emitting sections 3a, 3b. Then a signal S modulated by a signal modulation section 1 is fed to the two drive circuits 2a, 2b and then sent to the light emitting sections 3a, 3b and projected from the projection optical system 4 as a signal light (L=La+Lb) including the same signal. In this case, since the oscillating wavelengths (lambdaa, lambdab) of the light emitting sections 3a, 3b differ from each other, they are not coincident with a same atmospheric absorption spectrum at a same temperature. Thus, the probability of the two signal lights LA, Lb receiving the attenuation due to atmospheric absorption simultaneously is less and the reduction rate of the transmission light intensity is suppressed low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial optical communication device for transmitting and receiving optical signals using space as a transmission medium.

[0002]

2. Description of the Related Art Conventionally, in spatial optical communication in which an optical signal is transmitted using a space as a transmission medium, a device for emitting a signal light including this signal from a single light projecting portion is generally used. The following phenomena occur in the space optical communication used in the atmosphere of the earth.

(1) Attenuation of transmitted light intensity occurs due to absorption and scattering by the atmosphere. This is due to absorption due to various factors, as shown by the spectral characteristics of sunlight in FIG. That is, in the visible region, Rayleigh scattering and absorption and scattering by aerosols are considered to be the main causes of attenuation, and in the near infrared region, absorption due to water vapor and oxygen, among gas components in the atmosphere, is considered to be the main cause of attenuation. . Since the emission wavelength of the light emitting element used in the conventional spatial optical communication is generally in the near infrared region, it is considered that the attenuation of the transmitted light intensity is mainly due to the absorption by the gas component in the atmosphere.

Also, looking at the result of measuring the attenuation of the propagation light of 150 m in the room at the wavelength of 800 to 850 nm by the halogen light source as shown in FIG. 18, the spectrum width is 0. It can be seen that the very narrow absorption spectrum of about 06 nm is dense. Further, it has been found that the absorption spectrum of water vapor changes its intensity depending on the amount of water vapor contained in the atmosphere.

(2) Further, a semiconductor laser used as a light source for long-distance communication generally has a very narrow oscillation spectrum width of 0.01 nm or less in single longitudinal mode oscillation, and as shown in FIG. When the case temperature, that is, the element temperature changes, so-called mode hopping occurs, and the oscillation wavelength changes discontinuously.

FIG. 19 shows a conventional spatial optical communication device.
Single longitudinal mode oscillation used as a light emitting device,
The temperature dependence characteristics of the oscillation wavelength of the semiconductor laser near 30 nm are shown, and at the same time, the absorption spectrum position of the atmosphere is also shown. When the element temperature of the semiconductor laser changes in accordance with the change in environmental temperature, the oscillation spectrum of the semiconductor laser coincides with the absorption spectrum of the atmosphere at the points A and B in FIG.

[0007]

Therefore, the following problems occur in the conventional spatial optical communication device.

(A) As described in (1) above, the transmission light propagating in the space is attenuated due to the absorption and scattering of gas components such as water vapor and oxygen in the atmosphere, and the light intensity is reduced.

(B) Further, as described in (2) above, the device temperature of the semiconductor laser changes depending on the ambient temperature to cause mode hopping, which is absorbed by the atmosphere during long-distance propagation and communication is interrupted.

The first object of the present invention is the above-mentioned problem (a).
It is an object of the present invention to provide a spatial optical communication device that solves the above problem and suppresses the attenuation of transmitted light intensity due to absorption of the atmosphere.

A second object of the present invention is to solve the above-mentioned problem (b) and to provide a spatial optical communication device which avoids communication interruption due to environmental temperature during long-distance communication.

[0012]

A spatial optical communication device according to a first aspect of the present invention for achieving the above object is to provide a plurality of light emitting parts having different emission wavelengths and a light projecting device for projecting a light beam from the plurality of light emitting parts. An optical system is provided, and the plurality of light emitting units project a signal light modulated by the same signal by using a semiconductor laser as a light emitting element.

The spatial optical communication device according to the second invention is
A plurality of light emitting units having different emission wavelengths, and a light projecting optical system for projecting a light flux from the plurality of light emitting units, and a photopolymerization unit for matching a plurality of transmission optical axes from the plurality of light emitting units,
It is characterized in that a light receiving means having a light receiving optical system and a light receiving part, a light separating means for aligning a transmission optical axis and a reception optical axis, and a beam expander are provided to enable bidirectional communication.

[0014]

In the spatial optical communication device according to the first aspect of the present invention having the above-described structure, the plurality of light emitting portions using the semiconductor laser as the light emitting element emit the signal light having different oscillation wavelengths, and the plurality of signal light are the same. It is modulated with a signal and radiated to a partner device as a transmission beam via a projection optical system.

The spatial optical communication device according to the second invention is
The transmission optical axis and the reception optical axis of a plurality of signal lights modulated by the same signal are made to coincide with each other, and a beam expander adjusts to an optimum transmission beam diameter at an arbitrary communication distance so that almost the same range can be irradiated.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 shows a first embodiment, which is composed of two sets of light emitting units and drive circuits and one projecting optical system. That is, the output of the signal modulator 1 is connected via the two drive circuits 2a and 2b to the two light emitting units 3a and 3b using semiconductor lasers having different oscillation wavelengths, respectively. Projection optical system 4 in front
Are arranged.

The signal S modulated by the signal modulator 1 is sent to the two drive circuits 2a and 2b, and then to the light emitters 3a and 3b which emit light of different oscillation wavelengths λa and λb, respectively, and the same. The signal light L including a signal is emitted from the light projecting optical system 4 as L = La + Lb. In this case, the two light emitting units 3
Since the oscillation wavelengths λa and λb of a and 3b are different from each other, they do not coincide with the same atmospheric absorption spectrum at the same temperature. Therefore, the probability that the two signal lights La and Lb are simultaneously attenuated by the absorption of the atmosphere is very small, and the reduction rate of the transmitted light intensity can be suppressed to a low level.

In the present embodiment, an example in which the two light emitting portions 3a and 3b are arranged adjacent to each other has been shown, but three or more light emitting portions may be adjacent to each other in a plane perpendicular to the optical axis, and one element emits a plurality of light. A multi-beam semiconductor having a portion may be used as a light source.

FIG. 2 shows a second embodiment, which comprises a signal modulator 1, two sets of drive circuits 2a and 2b, and light emitters 3a and 3b, as well as a photopolymerization means and a projection optical system 4. ing. That is,
Similar to the first embodiment, the output of the signal modulation section 1 is connected to the two light emitting sections 3a and 3b via the two drive circuits 2a and 2b. The two light emitting parts 3a and 3b intersect their optical axes, and the dichroic prism 5 is arranged at the intersecting part so that the emitted light La from the light emitting part 3a is transmitted and the light emitting part 3a is transmitted.
The bonding surface of the prism 5 is provided with a coating that reflects the light Lb emitted from the lens b. The projection optical system 4 is arranged in front of the dichroic prism 5.

Similar to the first embodiment, the signal S from the signal modulator 1 is transmitted through the two drive circuits 2a and 2b to the light emitting unit 3.
The light flux La transmitted to a and 3b and emitted from the light emitting unit 3a passes through the dichroic prism 5, and the light beam Lb emitted from the light emitting unit 3b is reflected by the dichroic prism 5 and enters the projection optical system 4. Other operations are the same as those in the first embodiment.

A dichroic mirror may be used in place of the dichroic prism 5 shown in FIG. 2, and a light emitting portion may be formed by using a three-color separation prism or a four-color separation prism used in a television camera or the like. By increasing, even if the oscillation wavelength from one light emitting portion matches the absorption spectrum of the atmosphere, the rate of decrease in the intensity of the entire signal light can be suppressed.

FIG. 3 shows a third embodiment, in which one set of the light emitting section 3 and the projecting optical system 4 is used as a unit, and n projecting means are used. Each signal light L is La, Lb, Lc, ...
Ln are arranged in this order, and the wavelength λ of each signal light is set to λa <λb <λ
When arranging so that c <... <λn,
Each dichroic mirror 6 used as a photopolymerization means
The cutoff wavelengths b, 6c, ..., 6n are shifted so that the short wavelength region is transmitted and the long wavelength region is reflected, such as the spectral characteristics αb, αc, ..., αn shown in FIG. If the short wavelength bandpass filter described above is used, the signal light L is La + Lb
It is efficiently combined as + Lc + ... + Ln.

Further, in FIG. 3, each signal light L is denoted by Ln, ..., L
Place c, Lb, and La in this order, and set the wavelength λ of each signal light to λa> λb
>Λc>...> λn, the dichroic mirrors 6b, 6c, ...
6n are spectral characteristics βa, βb, βc, ...
.., .beta.n, the signal lights L are similarly efficiently combined by using a long wavelength band pass filter having a cutoff wavelength shifted so as to reflect a short wavelength band and transmit a long wavelength band. From the viewpoint of effective use of the device space,
Each of the light projecting means including the dichroic mirrors 6b, 6c, ..., 6n may be rotated around the common optical axis.

Further, in FIG. 3, the drive circuit 1 and the light emitting section 2
By configuring the projection optical system 3 and the dichroic mirror 6 into one unit that can be inserted and removed, it is possible to add a small number of units for short-distance communication and add a unit according to the communication distance. A device with a degree can be assembled.

FIG. 6 shows a fourth embodiment which is a modification of the embodiment shown in FIG. 3, and has a structure in which the optical path lengths of the respective light projections on the transmission side are made equal by using mirrors 7c, ..., 7n. By doing so, the receiving side that receives a plurality of the same signals can receive them as higher quality signals. The dichroic mirrors 6b, 6c, ..., 6n used here are also
A short wavelength band pass filter or a long wavelength band pass filter exhibiting the spectral characteristics as shown in FIG. 4 or 5 may be used.

As described above, the semiconductor lasers having different oscillation wavelengths are used to irradiate the other device with the transmission beam including a plurality of signal lights modulated by the same signal, so that the reduction rate of the transmitted light intensity due to atmospheric absorption can be reduced. It can be kept low.

FIG. 7 shows a fifth embodiment, which includes a signal modulator 1, two sets of drive circuits 2a and 2b, a light emitter 3a and 3a.
b, the projection optical systems 4a and 4b, and the polarization beam splitter 8 as a photopolymerization means are provided to project two signal lights including the same signal.

Similar to the second embodiment, the output of the signal modulator 1 is connected via the drive circuits 2a and 2b to the light emitters 3a and 3b each having a semiconductor laser emitting linearly polarized light orthogonal to each other as a light source. ing. Projecting optical systems 4a and 4b are arranged on the front surfaces of the light emitting units 3a and 3b, respectively, and a polarization beam splitter 8 is provided at a front intersection of them.

The signal S modulated by the signal modulator 1 is sent to the two drive circuits 2a and 2b, and then sent to the light emitters 3a and 3b respectively to emit the signal lights La and Lb. The signal light La from the light emitting portion 3a is made into a substantially parallel light flux by the light projecting optical system 4a, almost passes through the polarization beam splitter 8, and is projected from the device to the transmission space. Further, the signal light Lb from the light emitting section 3b is made into a substantially parallel light beam by the light projecting optical system 4b, and is almost reflected by the polarization splitting surface of the polarization beam splitter 8 so that the optical axis is the same as that of the signal light La and the transmission space is transmitted from the device. Is projected to. Therefore, the emitted light L from the device is such that the signal lights La and Lb containing the same signal illuminate the same range in the transmission space.

Since the spectral transmittance of the polarization beam splitter 8 is sensitive to changes in the incident angle of the light beam, it is desirable that the light beams are parallel light beams whose incident angles are as uniform as possible. Further, in this embodiment, the projection optical systems 4a and 4b are moved in conjunction with each other along the optical axis so that the same range can be irradiated with the optimum transmission beam diameter at any reception point.

FIG. 8 shows a sixth embodiment. In addition to the two light projecting means shown in FIG. 7, n light projecting means and photopolymerization for making the respective light projecting axes coincide with each other. A plurality of polarization beam splitters 8b, 8d, ..., 8n and dichroic mirrors 6d ,. When arranging each signal light L in the order of La and Lb, Lc and Ld, ..., The wavelength λ of each signal light is λa <λb <λc <λd <...
・ Be sure to have a relationship of <λn. In this case, the dichroic mirrors 6d, ..., 6n shift the cutoff wavelengths that transmit the short wavelength region and reflect the long wavelength region, respectively, as shown by the spectral characteristics γb, γd, ..., γn in FIG. Use a short wavelength band pass filter.

Further, in FIG. 8, each signal light L is ..., Ld and L
c, Lb, and La are arranged in this order, and the wavelength λ of each signal light is
, Λa>λb>λc>λd>...> λn, the dichroic mirrors 6d ,.
., 6n are the spectral characteristics .delta.b, .delta.d, ... Of FIG.
........................................ use use.

Also in the case of this embodiment, the drive circuit 2, the light emitting section 3, the light projecting optical system 4, the dichroic mirror 6, and the polarization beam splitter 8 are constructed as one unit so that they can be inserted and removed. A small number of units can be lightly equipped at the time of distance communication, and a device having a degree of freedom that allows addition of units according to the communication distance can be assembled.

As described above, a plurality of signal lights containing the same signal are projected along the same optical axis by using the semiconductor lasers having different oscillation wavelengths as the light source, so that the reduction rate of the transmitted light intensity due to the atmospheric absorption can be suppressed to a low level. be able to.

In the case of using a semiconductor laser light-emitting element in which the oscillation wavelength is a single longitudinal mode oscillation having a temperature-dependent characteristic as shown in FIG. 19 and the oscillation wavelength band overlaps the dense band of the atmospheric absorption spectrum, Even if two elements are used, the oscillation wavelength at the same temperature is the same, and the oscillation wavelength is very unlikely to match the atmospheric absorption spectrum. Therefore, even if the oscillation wavelength of the semiconductor laser used as the light emitting element is within the dense band of the atmospheric absorption spectrum, by using the transmitting means according to the present embodiment, communication interruption due to atmospheric absorption at the time of long distance communication can be prevented. be able to.

Further, FIG. 11 shows a seventh embodiment, and FIG.
By making the optical path lengths of the respective light projections of the transmitting device equal to each other, a high-quality signal can be received on the receiving side as in the case of FIG. The dichroic mirror used here has the characteristics shown in FIGS. 9 and 10.

FIG. 12 shows an eighth embodiment, and similarly to FIG. 3, the signal modulating section 1, two sets of drive circuits 2a and 2b, and the light emitting section 3 are provided.
a, 3b, the transmission means having the projection optical system 4a, 4b,
A light receiving unit having a light receiving optical system 10 and a light receiving unit 11, a signal demodulating unit 12, and two dichroic mirrors 6 and 6'as light separating units for matching the transmitting optical axis and the receiving optical axis are provided, and the transmitting and receiving A bidirectional spatial optical communication device capable of performing the above is configured.

Similar to the dichroic mirror 6b shown in FIG. 3, the dichroic mirror 6'has the spectral characteristics shown by αb in FIG. 4, and the transmitted lights La and Lb having wavelengths λa and λb.
Of the wavelengths λc and λd and reflects the received lights Lc and Ld. Therefore, when two-way communication is performed by disposing them facing each other, the wavelengths of the light emitting elements used in the two devices are different from each other, and the wavelength λ of each signal light is λa <λb <λc.
<The relationship is λd.

In FIG. 12, the positions of the transmitting means and the receiving means are exchanged, and the dichroic mirror 6'is set to βa.
Even if the dichroic mirror having wavelength selectivity shown in FIG.

Further, FIG. 13 shows a ninth embodiment, and FIG.
A light receiving unit having a light receiving optical system 10 and a light receiving unit 11, a signal demodulation unit 12, a polarization beam splitter 8, and a dichroic mirror 6 ″ are provided in a transmitting unit similar to
Bidirectional transmission and reception is possible as in the eighth embodiment.

Similar to the dichroic mirror 6d shown in FIG. 8, the dichroic mirror 6 "has the spectral characteristic shown by .gamma.b in FIG. 9, transmits the transmission lights La and Lb, and receives the reception lights Lc and Ld.
To reflect. Therefore, when two-way communication is performed by disposing them facing each other, the emission wavelengths of the light emitting elements used in the two devices are different from each other, and the wavelengths of the respective signal lights are λa <λb.
<Λc <λd.

Also in this case, the same effect can be obtained by exchanging the positions of the transmitting means and the receiving means and replacing the dichroic mirror 6 ″ with the dichroic mirror having the wavelength selectivity shown by δb.

FIG. 14 shows a tenth embodiment, which, as shown in FIG. 12 or FIG. 13, comprises a transmitting means having two light projecting means, a light receiving means, and a dichroic mirror as a light separating means. The bidirectional spatial optical communication device 15 has a beam expander 18 including a lens group 16 having a positive power and a lens group 17 having a negative power, thereby further increasing the amount of received light.

FIG. 15 shows an eleventh embodiment. In this embodiment, as shown in FIGS. 3, 6, 8 and 11, transmission means having a greater number of combinations of projection optical means is provided. In the bidirectional spatial optical communication device 20, the divergence angle of the transmitted light, that is, the transmitted beam diameter can be changed by a simple operation without changing the light receiving state of the received light. In this case, instead of the beam expander 18, a primary mirror 21 and a secondary mirror 22 are provided.
Is provided with a dichroic coat that transmits the transmission light L1 and reflects the reception light L2 reflected from the main mirror 21. A transmission light divergence angle variable optical system 23 is provided in front of the secondary mirror 22 in the transmission direction. The transmission light divergence angle variable optical system 23 includes a positive dichroic-coated optical member 24 and a positive optical member 24. Lens group 25 having power
And a lens group 26 having a negative power, by moving the lens group 25 along the optical axis, the transmission beam diameter can be changed to the optimum beam diameter according to the transmission distance.

Therefore, when two-way communication is performed by arranging them to face each other, the wavelengths of the transmission light L1 and the reception light L2 are different from each other. In FIG. 15, the lens group 25 having positive power is moved to make the transmission beam diameter variable, but a part of the lens group 25 or the lens group 26 having negative power is used.
Alternatively, the same effect can be obtained by moving a part of the beam to change the transmission beam diameter.

FIG. 16 shows a twelfth embodiment in which two devices having the same specifications for the combination of light emitting elements used for transmission and reception and having the same structure are arranged so as to be able to perform bidirectional communication. There is. In FIG. 15, instead of the secondary mirror 22, a secondary mirror 30 having a peripheral portion coated with a mirror coat having a high reflectance in the entire wavelength range of use is provided, and the primary mirror 21 and a plurality of light emitting means are provided. Between the means 31 and the beam splitter 32, a peripheral portion of which is provided with a mirror coat having a high reflectance in all wavelength regions is arranged. Then, in the reflection direction of the mirror coat of the beam splitter 32, the light receiving optical system 1
0, a light receiving unit 11, and a signal demodulating unit 12 are provided.

The transmitting light L1 emitted from the transmitting means 31 having a light projecting means, after passing through the beam splitter 32 and the secondary mirror 30, is the same as in FIG.
After passing through 3, the light is projected to the transmission space. On the other hand, the received light L2 is reflected by the primary mirror 21 and secondary mirror 30, and is reflected by the beam splitter 3
2 is reflected by the mirror coat around the beam splitter 32, and is guided to the light receiving section 1 via the light receiving optical system 10.
The light is condensed at 1, converted into a reception signal and transmitted to the signal demodulation unit 12.

In the twelfth embodiment, the beam splitter 32 having the mirror coat on the periphery is used, but the beam splitter having the mirror coat on the central portion is used, and the transmitting means 31 and the receiving means are further provided. The same effect can be obtained by replacing.

[0049]

As described above, the spatial optical communication device according to the first invention uses a plurality of semiconductor lasers having different wavelengths as light emitting elements, and uses a transmission beam including a plurality of signal lights modulated by the same signal. By making it possible to irradiate the device, the rate of decrease in transmitted light intensity due to atmospheric absorption can be suppressed to a low level, and especially in long-distance communication, a small and lightweight structure can be achieved, enabling more reliable communication. Becomes

The spatial optical communication device according to the second invention is
Mode hopping that occurs in the transmission means using a single light source prevents the disadvantage that the absorption spectrum of the atmosphere and the transmission light spectrum match and communication is interrupted, and it is possible to perform accurate two-way communication. Especially, in the long distance communication, the structure is small and lightweight, and the communication with higher reliability can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is a configuration diagram of a second embodiment.

FIG. 3 is a configuration diagram of a third embodiment.

FIG. 4 is a graph showing spectral characteristics of a short wavelength band pass filter.

FIG. 5 is a graph showing spectral characteristics of a long wavelength band pass filter.

FIG. 6 is a configuration diagram of a fourth embodiment.

FIG. 7 is a configuration diagram of a fifth embodiment.

FIG. 8 is a configuration diagram of a sixth embodiment.

FIG. 9 is a graph showing spectral characteristics of a short wavelength band pass filter.

FIG. 10 is a graph showing spectral characteristics of a long wavelength band pass filter.

FIG. 11 is a configuration diagram of a seventh embodiment.

FIG. 12 is a configuration diagram of an eighth embodiment.

FIG. 13 is a configuration diagram of a ninth embodiment.

FIG. 14 is a configuration diagram of a tenth embodiment.

FIG. 15 is a configuration diagram of an eleventh embodiment.

FIG. 16 is a configuration diagram of a twelfth embodiment.

FIG. 17 is a graph showing the spectral characteristics of sunlight.

FIG. 18 is a graph showing an absorption spectrum of the atmosphere.

FIG. 19 is a graph showing the temperature dependence of the oscillation wavelength of the semiconductor laser.

[Description of Reference Signs] 1 signal demodulator 2 drive circuit 3 light emitting unit 4 light projecting optical system 6 dichroic mirror 8, 32 polarization beam splitter 10 light receiving optical system 11 light receiving unit 12 signal demodulating unit 15, 20 bidirectional spatial optical communication device 18 Beam expander 23 Transmitted light divergence angle variable optical system 31 Transmitting means

Claims (6)

[Claims] 1. A plurality of light emitting parts having different emission wavelengths and a light projecting optical system for projecting a light beam from the plurality of light emitting parts are provided, and the plurality of light emitting parts use a semiconductor laser as a light emitting element to output the same signal. A spatial optical communication device characterized by projecting a signal light modulated by. 2. The spatial optical communication device according to claim 1, further comprising a photopolymerization unit that matches a plurality of transmission optical axes from the plurality of light emitting units. 3. The spatial optical communication device according to claim 2, wherein the photopolymerization means is a dichroic mirror or a dichroic prism having wavelength selectivity. 4. The spatial optical communication device according to claim 2, wherein the photopolymerization means is a polarization beam splitter in which polarization directions of projected light beams are orthogonal to each other on a polarization separation surface. 5. Light which comprises a plurality of light emitting portions having different emission wavelengths and a light projecting optical system for projecting a light flux from the plurality of light emitting portions, and which makes a plurality of transmission optical axes from the plurality of light emitting portions coincide with each other. A superimposing means, a light receiving means having a light receiving optical system and a light receiving part, and a light separating means for aligning the transmission optical axis and the reception optical axis,
A spatial optical communication device comprising a beam expander for bidirectional communication. 6. The beam expander includes a main mirror, a sub-mirror that transmits the transmitted light and reflects the received light reflected by the main mirror, and a part of an optical system in front of the sub-mirror. 6. The spatial optical communication device according to claim 5, further comprising a transmission light divergence angle varying means that is movable along.