JPH0239743A - Spatial optical transmitter - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of a delaying time to about 1/1000 of the conventional value and to prevent the disturbance of a transmitting signal due to the temperature change by using a delay line composed of an optical fiber for a light sending device. CONSTITUTION:A light sending device 31 provides an optical fiber delay line 33 and for this reason, an electrical/optical converter 32 is provided at the rear step of a parallel serial converter 8 and between an optical fiber delay line 33 and a light emitting element driving circuit 10, an optical/electrical converter 34 is provided. The fluctuation width of the delaying time at action temperature of -10-+50 deg.C when the optical fiber delaying line 33 is used is + or -0.037ns. For this, the fluctuation width of the delaying time due to the temperature change of an electrical delaying circuit 9 is 10ns. Consequently, a stable spatial optical transmitting system without generating the disturbance of a video and audio signal due to the temperature change can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a spatial optical transmission device for transmitting optical signals from a stationary light transmitter to a mobile light receiver, and particularly to a spatial optical transmission device that extends the signal transmission coverage area of the device. Regarding suppression of signal fluctuations in cases.

[Prior art] As this type of technology, for example, Utility Model Application No. 62-188835
The method disclosed in the publication is proposed.

FIGS. 3 and 4 are a block diagram showing a schematic configuration of devices constituting a conventional spatial optical transmission system and a layout diagram showing a schematic positional relationship of devices constituting the spatial optical transmission system, respectively.

In Fig. 3, (1) is a light transmitter, and the signal that has passed through a video input terminal (2), a video amplifier (4), and an AD converter (5) is transmitted to an audio input terminal (2), an audio amplifier (6), and an audio amplifier (6). ), A.D.
The signal passed through the converter (7) and the parallel/serial converter (
8), and is emitted as an optical signal via an electrical delay circuit (9), a light emitting element drive circuit (10), and a light emitting element (11), and sent out from a transmission lens (12).

(13) is a light receiver, which captures the optical signal with a receiving lens (14), a photodetector (15), and a preamplifier (
16), serial-parallel converter (17), DA
A video signal is taken out from a video output terminal (20) via a converter (18) and a video amplifier (19). On the other hand, the audio signal passes through a DA converter (21) and an audio amplifier (22).
It is taken out from the audio output terminal (23).

Figure 4 shows the installation status of these devices, (25), (
26) and (27) are three light transmitters fixedly installed near the trajectory A, and a light receiver (2,4) installed on the moving body (2, 4).
28), the signal distributed by the distributor (30) is sent to the luminous flux (2
9).

Next, the operation will be explained. In Fig. 3, the video signal and the audio signal are respectively connected to the video input terminal (
2) is input to the audio input terminal (3). The video signal is amplified by a video amplifier (4) and digitally modulated by an AD converter (5).

Also, the audio signal is amplified by an audio amplifier (6)
It is digitally modulated by a D converter (7). These digitally modulated video and audio signals are multiplexed by a parallel-to-serial converter (8) and input to a light emitting element drive circuit (10) via an electrical delay circuit (9). Light whose brightness is modulated based on the multiplexed digital signal is emitted from the light emitting element (11). This light is converted into a luminous flux having a predetermined angular spread by a transmission lens (12) and sent out into space.

A part of this luminous flux is transmitted through the receiving lens (14) of the light receiver (13).
The light beam enters the photodetector (15) and is converted into a convergent beam by this lens. Here, the optical signal is converted into an electrical signal. This electrical signal is a multiplexed video signal and audio signal, which is passed through the preamplifier (16).
After being amplified by a serial-to-parallel converter (17
) are separated into digitally modulated video and audio signals. Among these, the digitally modulated video signal is returned to the original video signal by the DA converter (18), and is amplified by the video amplifier (19) and then the video output terminal (2
0) is output.

In addition, the audio signal that has been converted into a digital converter is also transferred to a DA converter (2
1) returns the original audio signal to the audio amplifier (22)
The signal is amplified by and output from the audio output terminal (23).

FIG. 4 shows a plurality of the light transmitters (1) and the light receiver (13).
) is used to communicate with a mobile object.

In the figure, A is the trajectory of the moving body (24), (2
5), (26), and (27) are light transmitters fixedly installed near this trajectory A. (28) is a light receiver installed on the moving body (24), and arrow P represents the traveling direction of the moving body (22). In addition, (29) is the luminous flux emitted from the light transmitter (25), and (30) is a distributor that distributes the video and audio signals to the light transmitters (25), (26), and (27) and sends them out. be.

The light beam (29) emitted by the light transmitter (25) propagates through space and crosses the trajectory A. A light receiver (
2S), a line is established with the light transmitter (25). Due to limitations such as orbit curvature and receiving field of view, the transmitter
In some cases, it may not be possible to secure the required transmission coverage. In this case, a method is used to connect the coverage areas using a plurality of light transmitters to ensure the required coverage area.

That is, in FIG. 4, the area covered by the light transmitter (25) and the area covered by the light transmitter (26) partially overlap, and the area covered by the light transmitter (26) partially overlaps.
) and the area covered by the light transmitter (27) partially overlap to ensure the required coverage area as a whole.

By the way, in the area where these light beams overlap, the light receiver (28)
Because it simultaneously receives optical signals from two light transmitters, the phase difference between the signals becomes a problem. In particular, if a phase difference of more than half the period occurs between the signals at the point where the levels of the optical signals from the two light transmitters are equal, the bit error rate of the digital signal will increase, making it impossible to reproduce the video and audio signals. This problem occurs. Therefore, the electrical delay circuit (9) is adjusted so that the phase difference between the signals becomes zero at this point.

Here, as a specific example, a case where the interval 1 between two adjacent light transmitters is 100 m and a digital signal is transmitted at a transmission rate of 50 Mbps will be described.

The delay time caused by the difference in propagation distance is calculated by converting 1 to the speed of light C (=
3X10”rn/s) divided by 1/C-333n
It becomes s. This delay time is compensated by an electrical delay circuit (9). Normally, the electrical delay circuit (9) fluctuates by an amount corresponding to ±3% of the compensation delay time at an operating temperature of -10 to +50°C. Therefore, 333nsX (±3
/100) fluctuates by γ±10ns.

On the other hand, one period for a transmission speed of 50 Mbps is 20n
s, and in order to ensure a code error rate of 10-9 or less, it is necessary to suppress the phase difference between signals to π or less. In other words, the allowable delay time is 20n/sX(π/2π)=
It is 10ns.

Thus, from the comparison of the two numerical values, it can be seen that there is no margin for the delay time. Also, 50 Mbps
It can be seen that at higher transmission speeds, disturbances occur in the video and audio signals due to temperature changes.

[Problems to be Solved by the Invention] Conventional spatial optical transmission devices have the above-described configuration, and therefore have the problem of large fluctuations in compensation delay time due to temperature changes, making it impossible to achieve stable optical transmission. Ta.

The present invention has been made to solve this problem, and an object of the present invention is to provide a blank optical transmission device in which the range of variation in compensation delay time within the operating temperature range is suppressed.

[Means for Solving the Problems] A spatial optical transmission device according to the present invention is a spatial optical transmission device that transmits optical signals from a plurality of light transmitters installed near an orbit to a light receiver moving on an orbit. In the apparatus, the light transmitter has a delay line using an optical fiber so that optical signals from adjacent light transmitters have the same phase at a light receiving point.

[Operation] According to the present invention, instead of the pneumatic delay circuit of the light transmitter,
By converting the electrical signal into an optical signal, delaying it using an optical fiber, and converting the optical signal back into an electrical signal before emitting the optical signal from the light emitting element, the variation in delay time has been reduced to approximately 171,000 times compared to the conventional method. and is suppressed by three digits.

As a result, a spatial optical transmission device is provided in which video and audio signals are not disturbed by temperature changes.

[Embodiment] Next, the present invention will be explained in more detail based on an embodiment of the present invention shown in FIGS. 1 and 2.

In the figure, the same reference numerals as in FIGS. 3 and 4 indicate the same or corresponding parts.

The light transmitter (31) according to the present invention shown in FIG. 1 is provided with an optical fiber delay line (33), so that an electrical-to-optical converter [
An optical-to-electrical converter (hereinafter referred to as φ/E converter) is connected between the optical fiber delay line (33) and the light emitting element drive circuit (10). ] (34
) is provided.

Compared to the conventional example, the light transmitter (31) according to the present invention replaces the electrical delay circuit (9) of the light transmitter (1) with an E/φ converter (32) and an optical fiber delay line (33). , φ/E converter (34). Therefore, in the light transmitter (1), a parallel-to-serial converter (
8) ,! physical delay circuit (9), light emitting element drive circuit (
10), the video/audio signals transmitted via the parallel/serial converter (8) and the E/φ converter (32)
, optical fiber delay line (33), φ/E converter (34),
The light is transmitted via the light emitting element driving circuit (10).

Here, the function of the optical fiber delay line (33) will be explained.

As shown in FIG. 4, consider a case where a plurality of light transmitters are installed, the interval 1 between two adjacent light transmitters is 1° Om, and a digital signal is transmitted at a transmission rate of 50 Mbps.

The delay time caused by the difference in propagation distance is calculated by dividing 1 by the speed of light C (
=3X 108m1s) divided by f/C-333ns
It is. This delay time is compensated by an optical fiber.

Assuming that the length of the optical fiber required for compensation is n and the refractive index of the core of the L1 optical fiber is n, the delay time is given by n L / C.

Therefore, when nL/C=333ns, the refractive index of the core n
-'L, 5, substituting the speed of light C-3X108i/s, L
=67m is obtained.

Further, the amount of variation Δt in the delay time due to temperature change is given by Equation (1) n, where α is the linear expansion coefficient of the optical fiber, the temperature coefficient of the refractive index of αL1 is α, and the amount of temperature change is ΔT.

... (1) Here, the linear expansion coefficient αl of quartz, which is the main component of the core of the optical fiber, and the temperature coefficient α of the refractive index. are 0.35 each
X 10'/deg, -8, lx 10-6/deg
g, so if normal temperature is 20°C, the operating temperature is m degrees -
Variation amount Δt of delay time at 10'C and +50°C
is determined from equation (1) as follows.

(I) At 50°C Δt −-0,037n
s(I[) -10°C Δt -0,037
ns Therefore, when the optical fiber delay line (33) is used, the variation width of the delay time at an operating temperature of -10 to +50'C is ±0.037ns.

On the other hand, the variation width of the delay time due to temperature change in the electrical delay circuit (9) was 10 ns.

Comparing the above two numerical values, it can be seen that there is a three-digit difference in the fluctuation width and that it is sufficiently suppressed. Also, the transmission speed is 50M
The allowable delay time of 10 ns for bps is also satisfied with a sufficient margin. Therefore, a stable spatial optical transmission system can be obtained in which video and audio signals are not disturbed by temperature changes.

FIG. 2 shows another embodiment of the invention.

In the figure, the optical fiber delay line (33) is connected to the optical transmitter (31).
M) and forms part of the signal transmission path. In this case, the light transmitter (31M) is a φ/E converter (34)
, light emitting element drive circuit (10), light emitting element (11),
Consists of a transmission lens (12), the distributor (30M) includes AD converters (5), (7), serial/parallel converter (8), φ/E converter (32), and optical distributor (35). It has a built-in configuration. In this embodiment, since an optical fiber is used as a signal transmission path, the device is not only economical but also has the effect of being resistant to electromagnetic induction noise coming from around the transmission path.

In the above embodiment, the case where a digital signal is transmitted has been described, but the same effect can be provided when an analog signal is transmitted.

[Effects of the Invention] As explained above, by using a delay line made of optical fiber in the light transmitter, this invention suppresses the variation in delay time to about -1000 times compared to the conventional method, and reduces the fluctuation of the transmitted signal due to temperature changes. The effect of providing a stable spatial optical transmission device without disturbance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a light transmitter according to an embodiment of the present invention, FIG. 2 is a block diagram showing a distributor and a light transmitter according to another embodiment of the present invention, and FIG. 3 is a block diagram showing a light transmitter according to the prior art. FIG. 4 is a block diagram of the light transmitter and the light receiver. FIG. 4 is a layout diagram showing the positional relationship between the light transmitter and the light receiver. In the figure, (10) is a light emitting element drive circuit, (11) is a light emitting element, (31) is a light transmitter, (32) is an electro-optical converter, (33) is an optical fiber delay line, and (34) is a The optical-to-electrical converter (35) is an optical splitter. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Patent attorney Masuo Oiwa (and 2 others) Layout diagram of light transmitter and light receiver Figure 4 Procedural amendment 1 Sagi (voluntary) 5. Scope of claims of the specification to be amended and details of the invention Description field. 6. Contents of the amendment 2. Name space of the invention Optical transmission device 3. Relationship with the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Representative of Mitsubishi Electric Corporation Moriya Yoshiki 4, Agent Address: 2-2-3 Marunouchi, Chiyoda-ku, Tokyo, Japan Claims: A system for transmitting optical signals from a plurality of light transmitters installed near the orbit to a receiver moving on an orbit. In the spatial optical transmission device, the light transmitter is characterized in that the light transmitter is equipped with a delay line using an optical fiber so that the optical signals from adjacent light transmitters have the same phase at a point where the levels are equal. Spatial optical transmission device.

Claims (1)

[Claims] In a spatial optical transmission device that transmits optical signals from a plurality of light transmitters installed near the orbit to a light receiver moving on an orbit, the light transmitter receives optical signals from adjacent light transmitters. 1. A spatial optical transmission device comprising a delay line using an optical fiber so that the phases are the same at each point.