JPS63110828A - Wavelength divided multiplex optical communication equipment - Google Patents

Abstract

PURPOSE:To transmit an optical signal equivalent to wavelength subjected to division and multiplex by employing a single transmission light source with a relatively wide range of variable wavelength and selecting a wavelength corresponding to a channel. CONSTITUTION:After signals 5-8 inputted to channels 1-4 are multiplexed 9 in terms of time division, they are waveformconverted 10 into a laser 11 and a drive waveform 12(i1-i4). The waveform 12 is designed so that where the channel signals 5-8 stand at '1', the laser 11 oscillates by corresponding wavelengths lambda1-lambda4 and so that where the signals 5-8 stand at '0', the laser 11 oscillates by lambda5. By linking to an optical fiber transmission line 14, the output beam 13 of the laser is propagated and made incident on an optical demultiplexer 15. A diffraction grating demultiplexes the beam on a waveform basis and makes the demultiplexed beam 20-23 incident on respective reception parts 24-27 through optical fibers 16-19 on a reception side, thereby demodulating the signals 5-8 for the channels 1-4 on a transmission side. Since one laser 11 can function as a light source for four channels, advanced IC techniques allow a small-sized device even if a multiplex circuit 9 and a waveform conversion circuit 10 are added to it, and its cost is substantially slashed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention pertains to optical fiber communication devices, particularly wavelength multiplexed optical fiber communication devices.

(Prior art and its problems) 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 Ishio et al. in IEICE Technical Report, C378-28, May 24, 1978. As shown in FIG. 7, this system combines the output lights of first to third light sources 71 to 73 with wavelengths of 1 to λ3, respectively, in a transmission device 70 using an optical multiplexer 74. This is a system in which the signals are coupled and propagated within a main optical fiber 76, separated into wavelengths by an optical demultiplexer 75 on the receiving side, and received separately. By the way, in this system, a light source with a different wavelength must be prepared for each signal channel, but when building a system with a large number of channels, it is not always easy to prepare a light source with the desired wavelength, and it is necessary to prepare a light source with a different wavelength for each signal channel. There were problems such as the size of the transmission equipment needed to be used. Therefore, it has been difficult to realize a wavelength division multiplexing communication device with a large number of channels.

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

(Structure of the Invention) According to the present invention, a transmission light source capable of modulating the wavelength of output light, an optical fiber transmission line for transmitting the output light, and first to
a demultiplexer that has an n-th (n is a positive integer of 2 or more) passing wavelength range and wavelength-demultiplexes the output light propagated through the optical fiber transmission line; an optical receiver connected to each output end corresponding to a passing wavelength range of the splitter, and performs multi-value frequency modulation of the transmitting light source with a wavelength corresponding to the first to nth passing wavelength ranges of the demultiplexer. A wavelength division multiplexing optical communication device is obtained.

(Principle of the Invention) The present invention uses a single transmitting light source with a relatively wide variable wavelength range to select wavelengths corresponding to each channel and sequentially transmit them in a time-division manner. This is a device that sends out optical signals equivalent to division multiplexing. This makes it possible to provide a wavelength division multiplexing optical communication device that does not require a large number of light sources and has a small transmission device.

(Example 1) Next, the present invention will be explained in detail using the drawings. FIG. 1 is a block diagram showing a first embodiment of a wavelength division multiplexing optical communication device obtained by the present invention, and FIG. 2 is a diagram showing signal waveforms of each part. 1st to 4th channel terminals 1 to 4
Each signal input to (first to fourth channel signals 5 to 8)
The waveforms shown in FIG. 2(a) are time-division multiplexed by the multiplexing circuit 9 into the signal waveforms shown in FIG.
It is converted to 2.

The drive waveform 12 includes first to fourth channel signals 5 to 8.
When is a mark (or 1), the wavelength of the semiconductor laser 11 oscillates at the corresponding wavelength λ1 to A4, and when it is a space (or 0), the semiconductor laser 11 oscillates at the wavelength λ5. The waveform is as shown in (C). The semiconductor laser 11 operated by this driving waveform 12 emits an output light 13 having a wavelength as shown in FIG. The light enters the vessel 15. This sufficient wave splitter 15 is constituted by a diffraction grating, and separates the output light 13 into wavelengths and couples them to the first to fourth receiving optical fibers 16 to 19 corresponding to each wavelength. The first to fourth demultiplexed output lights 20 to 23 (FIG. 2(e)) propagated through the first to fourth receiving side optical fibers 16 to 19 are transmitted to the first to fourth optical receivers 24 to 23, respectively. 27, and each of the first to fourth channel signals 5 to 8 on the transmitting side is input to the corresponding first to fourth channel signals 5 to 8.
The optical receivers 24 to 27 demodulate the signal.

As the semiconductor laser 11, a semiconductor laser having a distributed reflection structure as shown in FIG. 3 was used. Regarding the operating principle and structure of this type of semiconductor laser, Japanese Patent Application No. 58-241
267 (filed on October 21, 1982), so a detailed explanation will be omitted, but this semiconductor laser 11 has an active layer region of InGaAsP formed on an InP substrate 30 by a liquid phase growth method. 31, a direct current 3 is applied to the diffraction grating region 32 and the active layer region 31 which act as distributed reflectors.
The first electrode 33 injects a signal current 35 corresponding to the drive waveform 12 into the diffraction grating region 32, and the second electrode 36 injects a signal current 35 corresponding to the drive waveform 12 into the diffraction grating region 32. The dependence of the output wavelength of the semiconductor laser 11 on the signal current 35 is shown in FIG. It can be seen that the output wavelength takes discrete values depending on the magnitude of the signal current 35. In this embodiment, as shown in FIG.
~λ5 is used, and the magnitude of the signal current 35 is determined so as to oscillate this wavelength.

In the first embodiment, one semiconductor laser 11 functions as a light source for four channels. Compared to the conventional method, new electrical circuit systems such as the multiplex circuit 9 and the waveform conversion circuit 10 are required, but these circuits can be easily realized using high-speed circuit technology such as GaAs-IC, and the conventional method cannot Compared to the case where four drive circuits and four light sources with different wavelengths were required, the degree of improvement in terms of size and cost is significant. Furthermore, this device has a new advantage in that it does not require a multiplexer 74 for optical multiplexing as seen in the conventional example shown in FIG.

Note that in a system to which the device of the first embodiment is applied, the optical fiber transmission line 14 is several kilometers to 10 kilometers.

Receiving side optical fibers 16 to 19 are several hundred meters to several kilometers long
A certain subscriber communication system is “effective.
~The fourth channel signals 5 to 8 each have a transmission rate of 1
Signals of up to 00 Mb/s or more could be easily transmitted.

(Embodiment 2) FIG. 5 is a block diagram showing a second embodiment of the present invention. The second embodiment is essentially the first embodiment multilayered, and the basic device used is the same as the first embodiment, so a detailed explanation will be omitted. The first to fourth transmitting units 40 to 43 are transmitting units that wavelength-multiplex and transmit signals for five channels, and each transmitting unit includes a first transmitter.
As in the embodiment, a multiplexing circuit, a waveform conversion circuit, and a semiconductor laser are used. The wavelength difference between each channel is 2, and the wavelength difference between each transmitter 40 to 43 is 10n.
It has been selected as m. The first to fourth output lights 44 to 47 from the first to fourth transmitters 40 to 43 propagate through first to fourth transmitter side optical fibers 48 to 51, respectively, and then become light beams composed of diffraction gratings. The signals are multiplexed by the multiplex circuit 52 and propagated through the optical fiber transmission line 14. In the first branching circuit 53 in the middle of this optical fiber transmission line 14, the first output light 44 is
In the branching circuit 54, the second output light 45 is branched, and in the third branching circuit 55, the third and fourth output lights 46,47 are branched, respectively, to the first to fourth receiving ends 56 to 47. 59. Each of the receiving ends 56 to 59 includes a sufficient frequency transmitter and an optical receiving section similar to those in the first embodiment, and each of them is designed to demodulate transmission signals for five channels.

The second embodiment is a device that transmits wavelength division multiplexed signals for 20 channels in total, but transmission is possible using four light sources.

(Modifications) Various modifications of the present invention are possible in addition to the above-described embodiments. First, as a method of modulating the semiconductor laser 11, in the first embodiment, the mark is λ1~1 and the space is λ1.
Although the semiconductor laser was modulated so that the number of wavelengths is 5, it is not limited to this. Two examples are shown in Figure 6, and Figure 6(a)
is the mark (1) at the center wavelength of λ1~, and the space (0
) is set at an intermediate wavelength between adjacent channels, that is, at the cutoff wavelength range of the sufficient wavelength filter 15. Also, Figure 6 (
b) is a method of setting mark wavelengths and space wavelengths on the long wavelength side or short wavelength side, centering on each of the wavelengths λ1 to X4. Note that in the latter method, each optical receiver 24 to 2
In step 7, it is necessary to use an optical discriminator or an optical heterodyne detection circuit to discriminate the wavelength difference between marks and spaces.

Although the semiconductor laser 11 having a distributed reflection structure is used as the light source, any other light source may be used as long as it is easy to modulate and provides a sufficient wavelength shift.

In addition, the number of wavelengths multiplexed in one semiconductor laser 11 is 4.
Although an example of ~5 channels has been shown, multiplexing of 10 or more channels is also possible if the signal transmission rate of each channel is about several MHz to several tens of MHz.

(Effects of the Invention) As described in detail above, according to the present invention, there is no need to use a large number of light sources with different wavelengths, and therefore, there is no need for these light source modules, drive circuit sections, and even optical multiplex circuit sections, so that the transmission device Accordingly, it is possible to obtain a wavelength division multiplexing optical communication device that can be downsized and cost reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
This figure similarly shows signal waveforms at various parts, and FIGS. 3 and 4 are diagrams showing the structure of the light source used in the first embodiment and the wavelength characteristics of output light, respectively. Also, FIG. 5 is a block diagram showing the second embodiment, FIG. 6 is a modified example, and FIG.
The figure shows a conventional example. In the figure, 1 to 4: channel terminal 11: semiconductor laser 14: optical fiber transmission line. Representative Patent Attorney Susumu Uchihara, 2.
``Fig. 2 5' Time 05 every 8 days j[l['' Fig. 6 λ1 λ2 λ3 λ4 λ1 χ2 λ3 λ4

Claims (1)

[Claims] A transmitting section including at least a multiplexing circuit that time-division multiplexes a plurality of signals and a light source capable of wavelength modulation according to the time-division multiplexed signal obtained by the multiplexing circuit; At least a receiver including an optical transmission line for transmitting data, a demultiplexer that demultiplexes the light propagated through the optical transmission line into each wavelength, and an optical receiver connected to each output end of the demultiplexer. A wavelength division multiplexing optical communication device characterized by: