JPH0334633A - Optical transmission device - Google Patents

Abstract

PURPOSE:To reduce the cost by detecting an output level of a light emitting element of each optical channel by an optical receiving part of the destination to which an optical transmission is executed, executing the transmission of receiving level information in the lump by electricity or light from the optical receiving part to an optical transmitting part, and correcting the output level of the light emitting element of each optical channel of the optical transmitting part. CONSTITUTION:The respective receiving levels of an optical channel are detected by optical receiving parts 401-404, and receiving level information of each optical channel by detecting the receiving level is multiplexed and transferred by light or electricity to optical transmitting parts 201-204 from the optical receiving parts 401-404. Subsequently, in the optical transmitting parts 201-204, the multiplexed receiving level information is restored, and also, by the receiving level information, a transmitting level of each optical channel is corrected. Accordingly, it is unnecessary to provide an optical output level monitor of a light emitting element of each optical channel on the optical transmitting parts 201-204, and in the optical receiving parts 401-404, in order to observe an actual optical receiving level, an optimum optical transmitting level can be set directly. In such a way, the cost of an automatic optical output controller per an optical channel is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical information transmission device, and particularly to an optical transmission device in which a plurality of optical channels exist in parallel.

(Prior art) Optical transmission equipment, especially optical fiber communication equipment, has characteristics such as non-inductive communication paths and non-ground loop noise due to road communication, in addition to high speed. It is also possible to overcome the technical difficulties of electrical transmission devices in the field. In this way, optical transmission equipment exhibits its usefulness even in relatively low-speed areas, but in the case of parallel transmission, the cost per communication line decreases less when the degree of parallelism is increased than in the case of electricity. However, there were problems in terms of versatility and low cost. Additionally, there is a problem in that the original performance has to be sacrificed, such as removing the compensation function of the optical transmission equipment to lower the price, which is an obstacle to the widespread use of general-purpose optical transmission equipment. was. The conventional technology will be explained below using the drawings.

FIG. 6 is a configuration diagram showing the configuration of a conventional optical transmission device,
One optical channel is shown. Reference numeral 1 denotes a drive circuit, which drives a light emitting element such as a semiconductor laser according to an input signal and a control signal from a comparison circuit. 2 is a light emitting element, which uses a semiconductor laser or a light emitting diode. A light output monitor 20 monitors the average light output level using a photodiode or the like. A comparison circuit 21 compares the signal from the photodiode 20 with a preset reference level and generates a control signal for output level correction in accordance with the difference. 3 is an optical transmission medium, which uses an optical fiber, a leading waveguide, or the like.

Reference numeral 4 denotes a light-receiving element, which electrically converts a light-receiving signal using a PIN photodiode, an avalanche photodiode, or the like. Reference numeral 5' denotes an amplifier circuit which reproduces the level of the electrical signal, including supplying bias voltage to the light receiving element 4. The operation of this prior art device is such that the drive circuit 1 drives the light emitting element 2 in response to an input signal from the signal input terminal A.
The light output level of the light emitting element 2 is detected by the light output monitor 20. The comparison circuit compares the optical output levels, generates a correction signal for the optical output level, and sends it to the drive circuit.

The drive circuit further corrects the drive level of the light emitting element 2 according to the correction signal to ensure a pre-designed and set optical output level. On the other hand, the optical signal from the light emitting element 2 is sent to the light receiving element 4 through the optical fiber 3, electrically converted by the light receiving element, signal level regenerated by the amplifier circuit 5'', and outputted to the signal output terminal B. This conventional technology is characterized in that it is possible to monitor the optical output level within the transmitting side, and that it is possible to independently correct characteristic fluctuations of the light emitting element and monitor the timing of deterioration.

However, in such conventional techniques, the output level to be monitored is the pre-output level of the light emitting element, and not the optical transmission level introduced into the actual optical fiber, guide waveguide, etc.

Therefore, it is not possible to compensate for changes in the radiation pattern of the light emitting element caused by changes in driving conditions or environmental conditions (temperature, etc.), and it is not possible to compensate for changes in the radiation pattern of the light emitting element caused by changes in driving conditions or environmental conditions (temperature, etc.). There was a problem that it was impossible to respond.

Next, the conventional technology in the case of arraying will be described. 7th
The figure is a diagram showing the configuration of a parallel optical transmission device having a plurality of optical channels, and here a four-channel optical transmission device is taken as an example. Here, A1-A4 are input terminals, 101-1
04 is a drive circuit, 201 to 204 are light emitting elements, 2001
~2004 is a monitor photodiode, 2101~21
04 is a comparison circuit, aOt~304 is an optical fiber, 401
~404 is a light receiving element, 50F~504° is an amplifier circuit, B
1-84 is an output terminal. As can be seen from the figure, in the prior art device, each channel independently has the same configuration as in FIG. 6, and there is no particular advantage of arraying other than collective connection and the same packaging. Therefore, even when the number of channels is increased by increasing the number of arrays, the configuration of each channel remains unchanged, and therefore there are few benefits other than simultaneous production and cost reduction due to arraying. This is the main reason why electrical transmission is inferior when the number of channels is increased as described above.

Furthermore, in the past, the pursuit of low cost has led to a demand for devices that do not include a light emitting element comparison circuit or a monitor photodiode in order to reduce the cost per communication line, and as a result, light emitting elements are limited to light emitting diodes. There was a problem. This has made it difficult to achieve high-speed transmission, which is one of the characteristics of optical transmission, and has prevented the widespread use of optical transmission devices using semiconductor lasers capable of high-speed transmission.

(Problems to be Solved by the Invention) The present invention has been made in consideration of the problems of the prior art,
The object of the present invention is to provide an optical transmission device that can reduce the cost per communication line in parallel optical transmission while fully utilizing the inherent qualities of optical transmission.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a device that performs optical parallel transmission using a plurality of destination channels, and detects the light emitting element output level of each optical channel by detecting the light emitting element output level of each optical channel. This is performed in the receiving section, and the reception level of each optical channel is used as the detection result. Then, reception level information is collectively transmitted from the optical receiver to the optical transmitter by electricity or light, and the light emitting element output level of each optical channel of the optical transmitter is corrected.

That is, in an optical transmission device that transmits signals through a plurality of optical channels, the present invention detects the received level of each of the optical channels in an optical receiving section, and transmits the received level detection from the optical receiving section to the optical transmitting section. The received level information of each optical channel is multiplexed and transmitted optically or electrically (7. The optical transmitter restores the multiplexed received level information and corrects the transmitted level of each optical channel using the received level information. This is an optical transmission device characterized by the following.

(Function) According to the present invention, it is not necessary to provide an optical output level monitor of the light emitting element of each optical channel in the optical transmitting section, and in addition, since the actual optical reception level can be observed in the optical receiving section, the optimum optical It has the feature of being able to set the transmission level. Furthermore, since the optical reception level can be determined by detecting the average optical power, information transmission is relatively slow, and reception level information of a plurality of optical channels can be sent using one transmission line.

Therefore, according to the present invention, it is possible to control the optical output of a plurality of optical channels using one reception level information line, and the cost of an automatic optical output controller for each optical channel can be significantly reduced compared to the conventional technology. .

In addition, the cost reduction increases as the number of optical channels to be transmitted increases, and the effect of optical transmission using multiple optical channels such as arraying increases. As an application of this other invention, the advantage is that by checking the transmission information of each optical channel (for example, parity check, etc.) and sending it back to the optical transmission side, it is possible to correct the condition of the communication line and generate a signal line alarm. have.

(Embodiment) FIG. 1 is a configuration block diagram showing the contents of a first embodiment of the apparatus of the present invention. Here, we will show an example of 4-channel parallel transmission similar to the conventional example, but this basically allows the same configuration in most cases where parallel transmission is performed using multiple channels, and the number of Nayanels can be changed at any time. It is something.

In FIG. 1, Al-A4 is an input terminal of each signal channel, 101 to 104 are drive circuits for light emitting elements, and 201 to 2 are
04 is a light emitting element (e.g. semiconductor laser), 301-3
04 is an optical transmission medium (optical fiber, guiding waveguide, etc.), 401
~404 is a light receiving element (for example, PIN photodiode)
, 501-504 are amplifier circuits, B1-84 are output terminals of each signal channel, 6 is a multiplex signal generator for average received level information, 7 is a coaxial line for feedback, 8 is a multiplex signal restorer, and 8 is a multiplex signal restorer for driving. The circuits 10 (~104) have a function of correcting the drive level of the light emitting elements 201~204 (for example, bias current correction of a semiconductor laser) according to the feedback signal of the light receiving element 4.
Each of them has a function of generating a level monitor output (for example, an averaged output after passing through a low-pass filter) of the signals received at 01 to 404. These drive circuits 201 to 204
The configuration examples of the amplifier circuits 501 to 504 are shown in FIGS. 2 and 3.
As shown in the figure. In FIG. 2, 1 represents one of the elements 10i to 104 in FIG. 1, and 2 represents a light emitting element (corresponding to 201 to 204 in FIG. 1), which is a semiconductor laser (for example, an oscillation wavelength of 1.
3. czm Ga InAsP/I nP semiconductor laser). For each terminal, A is the signal input terminal (
(corresponding to A1 to A4 in Figure 1), Vcc is a power supply terminal, D is a light emitting element output correction signal input terminal, and the bias level correction of the semiconductor laser (e.g. threshold fluctuation correction )It can be performed. Further, 5 in FIG. 3 indicates one of 501 to 504 in FIG. 1,
4 is a light-receiving element, and here it is a photodiode (for example, a GalnAs/InP photodiode).
) shall be used.

For each terminal, B is the signal output terminal (corresponds to B1-84 in Figure 1)
, Vcc is the power supply terminal, C is the light receiving element reception level monitor output terminal, and the received signal via Q5 is connected to the C terminal as Rr.
, , Cr low-pass filter receives the average signal and outputs it as a novel.

Such a drive circuit 1 (FIG. 1 101-104),
It is possible to perform the above-mentioned functional operation by the amplifier circuit 5 (501 to 504 in FIG. 1).
/s digital data transmission is performed on each channel shown in FIG. At that time, the repetition period of the data signal is at least 2.5n.
However, fluctuations in the optical transmission level and optical reception level due to fluctuations in ambient conditions (e.g. temperature, etc.) are long temporal changes of several ms or more, and a feedback signal response of several hundred μs is sufficient. It is.

Therefore, for example, the product (time constant) of Rr and Cr in Figure 3 is 20
0 μs, and the level monitor output of each channel is sequentially sampled every 10 μs in 6 multiplexed signal generators to perform A/D conversion and time division multiplexing. In this case, the data transmission on the feedback line is 100 kb.
/s, and sufficient transmission can be achieved using the transmission capacity of the coaxial line. Further, the feedback cycle of each channel in this case is equivalently 40 μs for an average level output of 200 μs, and a sufficient response speed can be obtained for the response of the average level output. Multiplexed signal restorer 8
Then, it is sufficient to separate the multiplexed signal sent from 6 into signals of each channel, perform signal D/A conversion every 40 μs, peak hold, and feed back to the drive circuits 101-104, respectively. Furthermore, in a normal coaxial line, lO
Transmission of Mb/s or more is sufficiently possible, and if the averaging time of the level monitor output is 200 μs as described above and the feedback line capacity is 10Mb/s (sampling period 1oans), 2000 optical channels can be controlled simultaneously. is possible. Therefore, the limit on the number of optical channels of the device of the present invention can be practically ignored,
The cost per channel of multi-channel parallelization can be significantly lower than that of the prior art. Furthermore,
As mentioned above, in the present invention, since the reception level is directly fed back, it is possible to set the optimum transmission level of the optical transmitter, and it is also possible to suppress excessive output of the optical transmitter and contribute to lower power consumption. .

Next, a second embodiment of the present invention will be described. FIG. 4 is a block diagram of the configuration of an embodiment of the present invention, which differs from the embodiment in FIG. 1 in that it also includes a feedback path. In FIG. 4, since the feedback path is optical transmission, a signal multiplexing optical transmitter 9 incorporating a multiplexing signal generator 6, a single-channel optical transmitter 1-, a multiplexing signal restorer 8, and a single-channel optical receiver are installed. A multiplexed signal restoring optical receiver 13 incorporating a receiver 5' is used. Here, since the transmission capacity of the feedback path is relatively small, an LED without optical output level monitoring can be used as the light emitting element 10. LED
In an optical transmission system using this, transmission of about 100 Mb/s is possible, and as in the embodiment of FIG. 1, the limit on the number of optical channels can be practically ignored.

The major difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. has been achieved. In addition, by using a semiconductor laser as the feedback light emitting element 10 and using one transmission channel for the output monitor, it is possible to perform very high-speed feedback.In addition to feedback for optical transmission level correction, each optical channel It also becomes possible to feed back signal checks. In this case, the signal check includes a parity check of the digital data, and the presence or absence of a data transmission error can be sent back to the transmitting side, making it possible to increase the reliability of data transmission by retransmitting the transmitted data. As described above, the embodiment of FIG. 4 has features such as non-grounded loop noise and high data transmission reliability while preserving the features of the embodiment of FIG. 1.

FIG. 5 is a block diagram showing another embodiment of the device of the present invention. In the embodiment shown in FIG. 5, optical FDM (Pre
guency Dlvlslon Multlplex
, hereinafter referred to as FDM) technology. That is, each optical channel is transmitted using light of a different frequency with a narrow linewidth, and each channel is received by selecting the frequency by optical heterodyne detection or optical homodyne detection on the receiving side. In addition, in this example, only the feedback path uses an LED or a normal semiconductor laser, and only the feedback path uses WDM.
(WavelengthDfvlsion Multi
plex) technology. That is, since normal semiconductor lasers and LEDs have a wide emission half-width, the WDM method is used in which only the feedback path allows a wide emission line width. Reference numerals 201' to 204' in FIG. 5 are wavelength-controlled semiconductor lasers in which the oscillation amplitude and frequency (wavelength) of laser oscillation are controlled, and optical transmission is performed at wavelengths (frequencies) of λ1 to λ4, respectively. These lights are then combined into one fiber and introduced into the optical fiber 3 through the wavelength selective beam splitter 15.

Then, on the receiving side, each coherent receiver 401' to 404 passes through another wavelength-selective beam splitter 16.
° will be distributed and introduced. coherent receiver 401'40
4" each has a wavelength controlled semiconductor laser as a local oscillator, and selectively receives light of λ1 to λ4. Also, the WDM method of the feedback path is λ1.
The wavelength of λ0, which is relatively distant from the wavelength of λ1 to λ4, is reflected by the wavelength selective beam splitter 16 and 5 (90" direction change) to separate it from λ1 to λ4. Here, λ1
~ An example of setting λ4 and λ0 is λ. is the wavelength of about L3μm, and 5G1 is the wavelength of λ1 to λ4 and 1.55μm band.
The frequency difference may be set to about 1z (wavelength difference of about 0.5λ). Therefore, wavelength selective beam splitter 15.1B
For this purpose, a long wavelength pass filter type beam splitter having a boundary wavelength of approximately 1.4 μm may be used.

Note that when a wavelength-controlled semiconductor laser is used in the feedback path, it is also possible to use the FDM method entirely without providing a beam splitter. The features of this embodiment in FIG. 5 are, of course, the features of the embodiment in FIG. 4, but since the transmission path is one fiber, the transmission line cost is low.
It is possible to switch reception channels, that is, exchange transmission channels, on the receiving side. This can easily be done by changing the local oscillator frequency for each receiving channel, and it is also possible to simultaneously receive one channel signal with multiple receivers. In other words, the embodiment of FIG. 5 also has the major feature of the variable nature of the transmission line. Furthermore, this can be done not only by changing the frequency of the local oscillator on the receiving side but also by changing the frequency on the transmitting side, and has the feature that transmission such as time-division switching of transmission channels is also possible.

[Effects of the Invention] According to the present invention, it is possible to control the optical output of a plurality of optical channels using one reception level information line, and the cost of an automatic optical output controller for each optical channel can be significantly reduced compared to the conventional technology. can.

Furthermore, the cost reduction increases as the number of optical channels to be transmitted increases, and the effect of optical transmission using multiple optical channels such as arraying increases.

[Brief explanation of drawings]

FIGS. 1 to 5 are block diagrams of the configuration of the embodiment of the present invention, and FIGS. 6 and 7 are block diagrams of the configuration of the prior art. 1001-104)...Drive circuit 2 (201-204), 10...Light emitting element 3 (3
01-304), 11...Optical fiber 4 (4
01-404), 12... Light receiving element 5 (501-5
05)... Amplifier circuit 6... Multiplexed signal generator 7... Coaxial line 8... Multiplexed signal restorer

Claims (1)

[Claims] (1) Consisting of an optical transmission device that transmits signals through a plurality of optical channels, it includes a plurality of optical receivers that detect each optical reception level of the plurality of optical channels, and multiplexes optical reception bell information of the plurality of optical channels. an optical reception level information transmission means for transmitting the optical reception level information to the optical transmission side of the plurality of optical channels by light or electricity; and a transmission level of the plurality of optical channels according to the optical reception level information transmitted to the optical transmission side. 1. An optical transmission device comprising: a transmission level control section for controlling.