JPS63148726A - Wavelength-division multiplex bidirectional optical communication equipment - Google Patents

Abstract

PURPOSE:To simplify a light source, and also, to miniaturize an external form by providing a transmission power source being capable of wavelength modulation, for sending out successively the wavelength corresponding to each channel by time division. CONSTITUTION:A station side 40 uses a semiconductor laser 11 of a single transmission source having a comparatively wide variable wavelength range, selects a wavelength corresponding to each channel and sends it out successively by a time division by a multiplexing circuit 9, and an optical signal being equivalent to wavelength diviation multiplexing is sent out to a subscriber side 41 from an optical fiber transmission line 14 by a single light source. In the subscriber side 41, the optical signal is demultiplexed to each wavelength by an optical demultiplexer 15, photodetected by photodetecting parts 25, 26 and 27, a part of the light beam received by an optical modulator 33 is remodulated and sent back to the station side 40, at this remodulated light beam is received, the station side 40, and bidirectional communication is executed. In such a way, many light sources are not required, and the transmission equipment is miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical communication device, and more particularly to a wavelength division multiplexing bidirectional optical communication device.

[Conventional technology]

2. Description of the Related Art Optical fiber communication systems are rapidly becoming popular as semiconductor lasers, photodetectors, optical fibers, and the like become more sophisticated. In this optical fiber communication system, in order to increase the utilization efficiency of optical communication lines and reduce communication costs, it is necessary to increase the signal transmission speed and use devices such as wavelength division multiplexing to transmit and receive multiple signals on one line. is valid.

An example of the latter is the bidirectional wavelength division multiplexing system described by Ishiya et al. in IEICE Technical Report, C378-28, May 24, 1978. In this system, as shown in FIG. 7, the wavelengths in the transmission device 70 are λ1 to λ, respectively.

The output lights of the first to third light sources 71 to 73 are sent to an optical multiplexer 74.
This is a system in which the wavelengths are multiplexed, coupled into one optical fiber 76, propagated, split into wavelengths by the optical demultiplexer 75 of the transmission device 70' on the receiving side, and received separately.

[Problem that the invention seeks to solve]

By the way, when using such a conventional system, it is necessary to prepare a light source with a different wavelength for each signal channel, but when building a system with a large number of channels, a light source with a desired wavelength is used on the transmitting side and on the receiving side. It is not necessarily easy to provide a large number of light sources on both sides, and the use of a large number of light sources poses problems such as the transmission device becoming larger. Therefore, it has been difficult to realize a wavelength division multiplexing communication device with a large number of channels.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks, provide a wavelength division multiplexing bidirectional optical communication device that does not require a large number of light sources with different wavelengths, and can be made compact.

[Means for solving problems]

The wavelength division multiplexing bidirectional optical communication device of the present invention includes a plurality of first
a first transmitting section comprising a multiplexing circuit for time-division multiplexing the signals of , and a light source capable of wavelength modulation according to the time-division multiplexed signal obtained by the multiplexing circuit; An optical transmission line that slowly transmits output light via a branch circuit, a first demultiplexer that demultiplexes the light propagated through the optical transmission line into individual wavelengths, and an output end of the first demultiplexer. a first optical receiver provided on the side, which receives a part of each of the demultiplexed output lights, and re-modulates the other part of each of the demultiplexed output lights with a second signal; a plurality of second transmitting units that propagate the re-modulated outputs through the optical transmission line and transmit them to the first transmitting unit side; and the plurality of re-modulated outputs are branched by the branch circuit and separated into wavelengths. It is characterized by having a second demultiplexing means that transmits a wave, and a plurality of second receiving sections connected to the output end of the second demultiplexing means.

[Effect]

The present invention uses a single transmitting light source with a relatively wide variable wavelength range on the transmitting side, selects wavelengths corresponding to each channel, and sequentially transmits them in a time-division manner, thereby achieving wavelength division multiplexing using a single light source. The receiving side detects the received light, re-modulates a small portion of the received light with another signal, and sends it back to the transmitting side.
The transmitting side performs bidirectional communication by receiving this remodulated light. This makes it possible to provide a wavelength division multiplexing bidirectional communication device that does not require a large number of light sources and has a small transmission device.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a wavelength division multiplexing bidirectional optical communication device obtained by the present invention, and FIG. 2 is a diagram showing signal waveforms of each part thereof.

This example shows the case of bidirectional communication with 4 uplink channels and 4 downlink channels between transmitter and receiver. Even in bidirectional communication with such a number of channels, one Only a light source is required, and no light source is used on the receiving side (subscriber side).

As shown in FIG. 1, the station side 40 includes a multiplexing circuit 9 to which a plurality of signals, in the case of the present embodiment, first to fourth channel signals 5 to 8 are supplied through respective channel terminals 1 to 4. ,
Waveform conversion circuit 10, semiconductor laser 11, and branch circuit 3
0 and to which the upstream signal sent from the subscriber side 41 to the station side 40 is supplied via the branch circuit 30, and the station side receiving circuits 37 to 39.28. We are prepared.

The subscriber side 41 includes an optical demultiplexer 15 connected to the branch circuit 30 of the central office side 40 by an optical fiber transmission line 14, and an optical demultiplexer 15 connected to the subscriber side optical fibers 16 to 19, respectively. Individual sections 101 to 104 and optical receiving sections 24 to 2
It has 7.

As shown in FIG. 1, the individual section 101 includes a branch circuit 31,
32 and an optical modulator 33, to which an up channel signal 34 from the subscriber side is applied. The other individual sections 102 to 104 also have the same configuration as the individual section 101, respectively.

The multiplexing circuit 9 on the station side 40 is a circuit that time-division multiplexes the first to fourth channel signals 5 to 8, and the semiconductor laser 11 multiplexes the time-division multiplexed signals obtained by this multiplexing circuit 9. This constitutes a light source that can be wavelength modulated according to the wavelength. These multiplexing circuits 9 and the semiconductor laser 11 constitute a first transmitter.

The output light 13 from such a transmitter is transmitted to a subscriber side 41 via an optical fiber transmission line 14 as an optical transmission line after passing through a branch circuit 30.

The optical demultiplexer 15 on the subscriber side 41 connects the optical fiber transmission line 14
It is a demultiplexer that demultiplexes the light propagated into each wavelength.
Further, each of the optical receivers 24 to 27 is connected to the output end of such a demultiplexer, and receives a part of each of the branched demultiplexed output lights 20 to 23.

Furthermore, the optical modulator 33 in each individual section 101 to 104 is a modulator that re-modulates at least another part of each demultiplexed output light with an upstream channel signal from the subscriber side. In this way, each modulator re-modulates a part of each demultiplexed output light 20 to 23 with an uplink channel signal, and propagates the re-modulated output to the station side 40 via the optical fiber transmission line 14. It constitutes a second transmitting section that transmits data to the first transmitting section described above.

The remodulated output of the second transmitting section of each subscriber side 41 is branched by the branch circuit 30 of the station side 40, and then sent to the optical demultiplexer 3.
6. This optical demultiplexer 36 is a demultiplexer that demultiplexes the supplied upstream channel signal into each wavelength, and each station side receiving circuit 37 to 39.28 is connected to the output end of this optical demultiplexer 36. There is. These station side receiving circuits 37 to 39.28 constitute a second receiving section.

As described above, the device of this embodiment has a multiplexing circuit 9 that time-division multiplexes the first to fourth channel signals 5 to 8 as a plurality of first signals, and A first transmitting section including at least a semiconductor laser 11 as a light source capable of wavelength modulation according to a multiplexed signal, and an optical transmission line for transmitting output light 13 from this transmitting section after passing through a branch circuit 30. An optical fiber transmission line 14, an optical demultiplexer 15 as a first demultiplexer that demultiplexes the light propagated through this optical transmission line into each wavelength, and a connection to the output end of this first demultiplexer. optical receivers 24 to 27 that receive a part of each branched output light, and re-modulate the other part of each branched output light with an upstream channel signal as a second signal;
A plurality of second transmitting units transmit the re-modulated outputs to the first transmitting unit side by propagating the above-mentioned optical transmission line, and a plurality of re-modulated outputs are branched by a branching circuit 30 and then demultiplexed for each wavelength. It has an optical demultiplexer 36 as a second demultiplexer circuit, and a plurality of local receiving circuits 37 to 39, 28 as second receivers connected to the output end of the second demultiplexer circuit.

Further explanation will be given below with reference to FIGS. 2 to 4.

On the station side 40, the first to fourth channel terminals 1 to 4
When each channel signal 5 to 8 is input to the , the supplied first to fourth channel signals 5 to 8 (each waveform is shown in Fig. 2 (
al) is time-division multiplexed by the multiplexing circuit 9 into the signal waveform shown in FIG.
It is converted into a drive output 12 of the semiconductor laser 11 by .

This drive output 12 corresponds to each of the first to fourth channel signals 5.
When ~8 is a mark (or l), the wavelength of the semiconductor laser 11 oscillates at the corresponding wavelength λ1 to λ4, and when it is a space (or 0), the semiconductor laser 11 oscillates at the wavelength λ. The waveform is as shown in Figure 2 fc).

Here, the semiconductor laser 11 will be explained. In this embodiment, a semiconductor laser having a distributed reflection structure as shown in FIG. 3 is used as the semiconductor laser 11. Regarding the operating principle and structure of this type of semiconductor laser, the patent application
8-241267 (filed on October 21, 1982), so detailed explanation will be omitted.
This semiconductor laser 11 includes an InGaAsP active layer region 61 formed by liquid phase growth on an InP substrate 60, a diffraction grating region 62 serving as a distributed reflector, and an active layer region 61.
It consists of a first electrode 63 for injecting a direct current 64 into the diffraction grating region 62, a second electrode 66 for injecting a signal current 65 corresponding to the drive waveform 12 into the diffraction grating region 62, and the like. The dependence of the output wavelength of this semiconductor laser 11 on the signal current 65 is shown in FIG. It can be seen that the output wavelength takes discrete values depending on the magnitude of the signal current 65. In this embodiment, as shown in FIG. 4, a portion of λ1 to λ is used, and the magnitude of the signal current 65 is determined so as to oscillate at this wavelength.

Now, when the drive output 12 of the waveform conversion circuit 10 is applied to the semiconductor laser 11, the semiconductor laser 11 operated by the drive output 12 emits an output light 13 having a wavelength change as shown in FIG. 2(d). This output light 13 is coupled to the optical fiber transmission line 14 via the first optical branching circuit 30, propagates, and enters the first optical demultiplexer 15 on the subscriber side 41. The first optical demultiplexer 15 is composed of a diffraction grating, and demultiplexes the output light 13 into wavelengths, and connects the output light 13 to the first to fourth subscriber-side optical fibers 16 to 16 corresponding to each wavelength.
19. First to fourth subscriber side optical fibers 1
The first to fourth demultiplexed output lights 20 to 23 propagated through 6 to 19
(Fig. 2(e)) are respectively 2. Third branch circuit 31
．． 32, the signals enter the first to fourth optical receivers 24 to 27 on the subscriber side 41, and the first to fourth channel signals 5 to 8 on the transmitting side are transmitted to the corresponding first to fourth optical receivers 24 to 27 on the subscriber side 41, respectively. It is demodulated by the optical receivers 24 to 27 of No. 4.

Next, a method for transmitting uplink signals from the subscriber side 41 to the station side 40 will be described. Since all of the first to fourth channels have the same configuration, only the first channel will be described here.

A part of the first demultiplexed output light 20 is branched in the third branch circuit 32 and is incident on a subscriber-side optical modulator 33 made of niobium oxide. This subscriber side optical modulator 33 is
It operates with an upstream channel signal 34 whose transmission rate is approximately 1720 times higher than the transmission rate of the first channel signal 5, and transmits the upstream channel signal light 35 (FIG. 2(f)) to the second branch circuit 31. It is sent out into the optical fiber transmission line 14 via the first optical demultiplexer 15. The upstream channel signal light 35 propagated through the optical fiber transmission line 14 returns to the station side 40, is branched by the first optical branching circuit 30, and enters the second branching filter 36.

The second optical demultiplexer 36 has almost the same wavelength demultiplexing characteristics as the first optical demultiplexer 15, and the upstream channel signal light 3
5 is demultiplexed into each channel and outputted, and inputted into the first to fourth station-side receiving circuits 37 to 39.28. After the first station-side receiving circuit 37 detects the upstream channel signal light 35,
By using an appropriate attenuation filter, for example, Fig. 2 (
A demodulated waveform 29 as shown in g) is obtained.

In this way, bidirectional communication of four uplink channels and four downlink channels can be performed.

In such bidirectional communication, in this first embodiment, one semiconductor laser 11 has four channels,
This means that a total of eight light sources, going up and down, functioned. Compared to the conventional example, new electrical circuit systems such as a multiplexing circuit 9 and a waveform conversion circuit 10 are required, but these circuits can be easily realized using high-speed electrical circuit technology such as GaAs-IC. Regarding the transmitting side, in the case of 4 channels, compared to the conventional method which requires four drive circuits and four light sources with different wavelengths, the degree of improvement in terms of size and cost is large. Furthermore, on the receiving side, there is no longer a need for four individual light sources with different wavelengths, resulting in significant improvements in terms of cost and maintenance. In addition, as a system to which the first embodiment is applied, the optical fiber transmission line 14 is several km to 1Q km, and the receiving side optical fiber 1 is
As 6 to 19, a subscriber communication system of several 100 m to several In+ is effective. Furthermore, the first to fourth channel signals 5 to 8 each have a transmission rate of 100 Mb/
It was possible to easily transmit signals up to 1000 s or more.

FIG. 5 is a block diagram showing a second embodiment of the present invention, and FIG.
The figure is a diagram showing signal waveforms, etc. of each part.

The second embodiment is characterized in that it is bidirectional communication with two uplink channels and two downlink channels, and can communicate at almost the same transmission speed for both uplink and downlink.

On the station side 40, the first . Second channel terminal 1.2
The first down line entered in second channel signal 5,6
(Each waveform is shown in FIG. 6(a)) is time-division multiplexed by the multiplexing circuit 9 into the signal waveform shown in FIG.
The waveform conversion circuit 10 converts the signal into a drive output 12 of the semiconductor laser 11 . In addition, at this time, the first uphill. This embodiment differs from the first embodiment in that the focus points for the second channel signals 50, 51 are inserted with all marks (all marks) as shown in FIG.

That is, in this way, as will be described later, the output light 13 of the semiconductor laser 11 is supplied with the first . All mark codes are included for the second channel signal light 52, 53, thereby making it possible to modulate the upstream channel up to the same transmission speed as the downstream channel. .

The modulation of the semiconductor laser 11 by the driving output 12 is the same as in the first embodiment, and the driving waveform as shown in FIG. 6(C) and the output light 13 as shown in FIG. 6(dl) are obtained.

This output light 13 is coupled to the optical fiber transmission line 14 via the optical branch circuit 30 and propagated, and at the subscriber side 41,
1st. Third. In the fourth optical demultiplexer 15.54.55, the sixth
As shown in Figure (e), each wavelength is separated.

In this case, 1. The third demultiplexed output lights 20 and 22 are respectively the first and second demultiplexed output lights 20 and 22. The light enters the second optical receiver 24.25 and is transmitted to the station side 40.
No. 1. The second channel signal 5.6 is demodulated.

On the other hand, the second. The fourth demultiplexed output light 21.23 is modulated by the 1st and 2nd subscriber-side optical modulators 56 and 57, and the upstream 1.degree. As the second channel signal light 52.53, the optical fiber transmission line 14 is passed through the second and third branch circuits 31.32.
The inside is transmitted toward the station side 40. Subscriber side optical modulator 5
6.57 uses a semiconductor optical amplifier, and the injection current of this optical amplifier is turned on by the upstream channel signals 50 and 51.
By turning it off, it operated as a light intensity modulator.

1st. The second upstream channel signal light 52,53
The first branch circuit 30 branches the branch circuit 30 and inputs the second branching filter 36 . The signals are received and demodulated by the second station-side receiving circuit.

In this second embodiment, one semiconductor laser 11 functions as a light source for a total of four light sources with two channels, one upward and two downward channels. Since the output light 13 includes all mark codes for the upstream 1st and 2nd channel signal lights 52 and 53, if this is modulated on the subscriber side 41, the maximum transmission speed is the same as that of the downstream channel. It is possible to modulate up to the speed.

Note that the present invention can be modified in various ways in addition to the above-described embodiments. First, as a method of modulating the semiconductor laser 11, the semiconductor laser 11 is modulated so that the mark is λ, to λ4, and the space is λ, but the method is not limited to this. For example, it is also possible to set the mark (1) to the center wavelength of λ, to λ4, and the space (0) to the intermediate wavelength between adjacent channels, that is, the cutoff wavelength range of the first optical demultiplexer 15. . It is also possible to set mark wavelengths and space wavelengths on the long wavelength side or short wavelength side from each of the center wavelengths λ1 to λ4, respectively, to obtain the so-called binary frequency shift keying output light 13. In this case, it is desirable to use an optical discriminator or an optical heterogain type detection circuit in each optical receiving section to discriminate the wavelength difference between marks and spaces.

Furthermore, as the subscriber side optical modulator 33, 56, 57, we have shown examples of a modulator made of niobium oxide and a semiconductor optical amplifier, but any other optical switch such as an absorption type semiconductor switch can also be used. Applicable. Further, although the system of the embodiment is an example in which simultaneous two-way communication is possible, time-division two-way communication may be used. In this case, station side 4 when not transmitting
It is desirable that the 0 output light 13 be sent out with all marks.

Further, as a light source, a semiconductor laser 11 with a distributed reflection structure is used.
An example of this is shown, but other types can be easily modulated,
Moreover, it can be used as long as a sufficient wavelength shift can be obtained. Furthermore, although the number of wavelength multiplexed channels is about four channels, it is of course possible to increase or decrease the number of channels depending on the signal transmission speed, transmission distance, etc.

〔Effect of the invention〕

As described above, according to the present invention, it is not necessary to use a large number of light sources with different wavelengths, and therefore, these light sources, light source modules, drive circuit units, etc. are not required, so that the cost of the transmission device can be reduced. A wavelength division multiplexing bidirectional optical communication device that can be miniaturized can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing signal waveforms of each part in FIG. 1, and FIG. 3 is a structural diagram showing an example of a light source used in the present invention. , FIG. 4 is a diagram showing the wavelength characteristics of the output light, FIG. 5 is a block diagram showing the second embodiment of the present invention, FIG. 6 is a diagram showing signal waveforms etc. of each part of FIG. 2, and FIG. The figure shows the configuration of a conventional example. 1 to 4... Channel terminals 5 to 8... Channel signal 9... Multiplexing circuit 10... Waveform conversion circuit 11... Semiconductor laser 12... Drive output 13... Output light 14. ...Optical fiber transmission line 15, 36.54.55...Optical demultiplexer 16-19...
・Subscriber-side optical fibers 20-23...Demultiplexed output lights 24-27...Optical receivers 28, 37-39...Office-side receiving circuits 30-32...Branch circuits 33, 56.57 . . . subscriber side optical modulators 34, 50 .
51...Uplink channel signal 35, 52.53...
Up channel signal light 60...InP substrate 61...Active layer region 62...Diffraction grating regions 63, 66...Electrode 64...DC current 65...Signal current 101 to 104...Individual Department Representative Patent Attorney Yoshiyuki Iwasa 1) Shu
岨

Claims (1)

[Claims] (1) A first transmitting unit including a multiplexing circuit that time-division multiplexes a plurality of first signals and a light source capable of wavelength modulation according to the time-division multiplexed signal obtained by the multiplexing circuit; an optical transmission line that transmits the output light from the first transmitting section after passing through a branch circuit; a first demultiplexing means that demultiplexes the light propagated through the optical transmission line for each wavelength; a first optical receiver, which is provided on the output end side of the demultiplexing means, and receives a part of each demultiplexed output light, and a second optical receiver which receives the other part of each demultiplexed output light; a plurality of second transmitting units that re-modulate the signal and transmit the re-modulated output to the first transmitting unit by propagating the re-modulated output through the optical transmission line; and branching the plurality of re-modulated outputs at the branch circuit. A bidirectional wavelength division multiplexing method characterized by having a second demultiplexing means that demultiplexes each wavelength after demultiplexing, and a plurality of second receiving sections connected to the output end of the second demultiplexing means. Communication device.