JPS6243231A - Multiplex transmitting method for optical heterodyne/ homodyne detection wavelength - Google Patents

Abstract

PURPOSE:To set the wavelength of each local oscillation light so that the appropriate correspondence is secured between channels at the transmitter and receiver sides, by attaining the identification of each channel. CONSTITUTION:The channel identifying signal 5 is inserted every bit after a frame cycle pulse 9 within a single frame and the same code is repeated every 10 frames. The code strings of the signal 5 are formed in different constitutions for each channel. The 1st channel signal light 7 undergoes the wavelength multiplexing with the 2nd-10th channel signal light 52-60 through a multiplexing circuit 10 and travels into an optical fiber transmission line 40. The multiplexed light 11 passed through the line 40 is divided equally by an optical distributor 12 and sent to the 1st-10th channel reception parts in the form of the 1st-10th distribution light 71-80 respectively. A channel identifying circuit 21 performs its function by reading out the pulse 9 at first and then the pulses following the pulse 9 by a step successively through gates. Then the channel numbers are detected out of the code strings.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical fiber communication method, and particularly to an optical heterodyne/homodyne detection communication method.

(Description of Prior Art) Optical heterodyne/homodyne detection communication methods can significantly improve optical reception sensitivity and enable high-density wavelength multiplexing communication compared to conventional optical direct detection methods that detect only the intensity of light. Therefore, it is expected to be a method to enable long-distance, high-capacity communication in the future (Okoshi, “Study of the possibilities and problems of optical heterodyne or optical homodyne type frequency division multiplexed optical fiber communication,” IEICE Technology Research report, 0QE78
-139. p61゜1978).

In particular, in wavelength division multiplexing communication, for example, a wavelength of 1°311
In fact, it is possible to allocate more than 10,000 channels between m and 1.5 pm, and communication capacity can be dramatically increased.

In the optical heterodyne detection method, local oscillation light with a slightly different wavelength from that of the signal light is prepared in the receiving section, multiplexed with the signal light, and a beat signal corresponding to the difference frequency between the two is obtained by a photodetector. This is a method of demodulating a signal from a beat signal (intermediate frequency signal).

Therefore, when wavelength multiplexing communication is performed, wavelength-controlled local oscillation light must be prepared on the receiving side for each of a large number of signal lights arranged at short wavelength intervals. But 1
In optical heterodyne/homodyne detection wavelength division multiplexing communication methods where several channels are lined up within one person, it is difficult to accurately detect the absolute value of the carrier wavelength of each channel, so the wavelength of the locally oscillated light cannot be set. Conventionally, there has been no method for transmitting and receiving each channel on the transmitting side and each channel on the receiving side in a 1=1 or appropriate correspondence.

(Object of the Invention) The object of the present invention is to solve these problems, to enable each channel to be identified, and to ensure that each channel on the transmitting side and each channel on the receiving side correspond 1:1 or appropriately. An object of the present invention is to provide an optical heterodyne/homodyne detection wavelength multiplexing transmission method that allows wavelength setting of each locally oscillated light.

(Structure of the Invention) According to the present invention, on the transmitting side, signal lights from a plurality of channel transmitting units having different carrier wavelengths are wavelength-multiplexed and transmitted, while in the receiving system, the wavelengths are multiplexed for each channel receiving unit. Optical heterodyne/homodyne detection is performed by combining appropriately controlled local oscillation light source output light with signal light to extract the signal of the desired channel.
In the homodyne detection wavelength division multiplexing transmission method, on the transmitting side, a signal light in which a channel identification signal is superimposed on the main signal is transmitted for each channel transmitter, while on the receiving side,
An optical heterodyne/homodyne system characterized in that each channel receiving section connects to a desired channel transmitting section by controlling the wavelength of each local oscillation light source so that the channel receiving section receives a channel identification signal from the desired channel transmitting section. A detection wavelength multiplexing transmission system is obtained.

(Principle of the Invention) This invention inserts an identification code of the channel into the transmission signal of each channel transmitter in advance and transmits it, and the receiving side reads the channel identification signal from the demodulated signal to obtain the correct channel signal. This is to determine whether or not it is being received. If it is found that a signal on the wrong channel is being received, the wavelength of the local oscillation light source is changed, and when a beat signal with the correct channel is obtained, the wavelength of the local oscillation light source is fixed.

As a result, according to the present invention, each channel can be identified, and the wavelength of each local oscillation light can be set so that each channel on the transmitting side and each channel on the receiving side correspond 1=1 or appropriately. - A homodyne detection wavelength multiplexing transmission method can be provided.

(Embodiment) FIG. 1 is a block diagram of a first embodiment of an optical communication device obtained based on the present invention, and FIG. 2 is a diagram showing the structure of a channel identification signal in the same embodiment. In this example, the wavelength interval is 0.5 people (approximately 6G) in the 1.511m wavelength band.
This is a device that transmits wavelength multiplexed signals of 10 channels at 10 channels (Hz). The modulation and demodulation method is a frequency shift keying (FSX) method, and the code transmission rate of each channel is 4000 Mb/s. FIG. 1 mainly shows the first channel.

The first channel transmitter 1 includes an optical output section 2 composed of a semiconductor laser (Kunimitsu), a drive circuit 3 that drives the semiconductor laser, a code conversion circuit 6 that adds a channel identification signal 5 to the first channel transmit signal 4, etc. It consists of The semiconductor laser is binary frequency shift modulated by direct modulation using an applied current from the drive circuit 3. The amount of frequency deviation is 6
00MHz.

As shown in FIG. 2a), the channel identification signal 5 is inserted one bit after the frame periodic pulse 9 within one frame, and repeats the same code every 10 frames.

The code string of this channel identification signal 5 is preset in a different configuration for each channel, as shown in FIG. 2b).

The first channel signal light 7 is transferred to the second channel by the multiplexing circuit 10.
- It is wavelength-multiplexed with the tenth channel signal light 52 . . . 60 and propagates through the optical fiber transmission line 40 . These multiplexed lights 11 propagated through the optical fiber transmission line 40 are divided into equal parts by the optical splitter 12 and then sent to the first to tenth channel receivers as first to tenth distributed lights 71 to 80, respectively.

In the first channel receiving section 61, the first distributed light 71 is first multiplexed with the local oscillation light 14 by the received light multiplexer 513, enters the photodetector 15, and enters the electrical signal (intermediate frequency signal 16).
) is converted to The wavelength of the local oscillation light 14 does not necessarily match the wavelength of the first channel signal light 7 at the start of the receiving operation, and the wavelength of the local oscillation light 14 does not necessarily match the wavelength of the first channel signal light 7.
, 52, . . . , 60, the intermediate frequency signal 16 is obtained by adjusting its own wavelength to the wavelength of one of the channels.

(Such operations are performed by microprocessor 20, which will be described later). The obtained intermediate frequency signal 16 is sent to the amplifier circuit 1
7, the demodulated signal 19 is then amplified by the demodulation circuit 18.
is converted to A part of the demodulated signal 19 is sent to a channel identification circuit 21, which detects the channel identification signal 5 and can recognize which channel the demodulated signal 19 belongs to. The recognition result is processed by microprocessor 2.
However, if the demodulated signal 19 is not the first channel transmission signal 4, a control signal 24 is sent to the frequency control circuit 23 of the local oscillation light source 22, and the wavelength of the local oscillation light 14 is read as the first channel transmission signal. Move it to the wavelength of 4. It should be noted that the frequency control circuit 23 controls the wavelength by changing the magnitude of the current applied to the semiconductor laser (without a loop) that constitutes the local oscillation light source 22. After the first channel transmission signal 4 is correctly received, the error signal 26 from the frequency discrimination circuit 25 that detects the frequency of the intermediate frequency signal 16 is mainly used to determine that the intermediate frequency is a predetermined value (IGHz in this embodiment). The frequency control circuit 23 is operated so that.

In the second to tenth receiving channel units (without any gagging), the respective channel identification codes are read by the same operation, and control can be performed so that the corresponding channels are correctly connected.

Identification in the channel identification circuit 21 is performed in the order of first reading out the frame periodic pulse 9, then sequentially reading out the pulse after one of the frame periodic pulses 9 using a gate, and detecting the channel number from the code string. ing. Such an identification operation can be easily performed using techniques commonly used in digital communications, so a detailed description thereof will be omitted. Furthermore, since the detailed content of the control method in the microprocessor 20 can be implemented using conventional technology, the explanation will be omitted. In addition, the multiplexing circuit 10, optical distribution 512, and receiving optical multiplexer 1 shown in this embodiment
All of the 3rd prize were obtained by heating, fusing, and drawing optical fibers together.

FIG. 3 is a block diagram for explaining a second embodiment of the present invention. In the second embodiment, the transmitted signal light intensity of each channel is minutely modulated by a slow constant frequency sine wave, and by changing the minute modulation frequency for each channel, the receiving side can identify the channel. This is a characteristic. This embodiment is an example of a device that transmits wavelength multiplexed signals of 15 channels with a wavelength interval of 0.6 (approximately 10 GHz) in the 1.3 um wavelength band. The modulation and demodulation method is phase shift keying (PSK), and the transmission rate is 280 Mb/s for each channel. FIG. 3 mainly shows the first channel.

Description of parts common to the first embodiment will be omitted.

The first channel transmitter 1 includes an optical output section 2 and an optical modulator 30.
, a drive circuit 3, a sine wave oscillation 531 for adding a channel identification signal 5, and the like. The optical modulator 30 is constituted by a waveguide type modulator made of lithium niobate, and performs binary phase shift modulation on the output light 32 from the optical output section 2.

The oscillation frequency of the oscillator 31 is 1.0 kHz, and by superimposing this signal on the current applied to the semiconductor laser in the optical output section 2, the output light 32 is slightly intensity-modulated (
modulation degree of approximately 1%). The oscillation frequency of oscillation '631 is changed by 200Hz for each channel. The third channel has a frequency of 1.2 kHz and 1.4 kHz, respectively, and the fifteenth channel has a frequency of 3.8 kHz.

On the other hand, in the one-channel receiving section 61, the channel number of the demodulated signal 19 is detected by detecting the above-mentioned intensity modulation frequency component from the intermediate frequency signal 16 using the channel identification circuit 21. microprocessor 2
The operation for selecting the correct channel using 0 is the same as in the first embodiment, so the explanation will be omitted.

(Modifications) In the present invention, many modifications can be made in addition to the above-described embodiments. Examples of methods for inserting the channel identification signal 5 include inserting it into a pulse train and inserting it as a minute modulation frequency of the signal light intensity, but there are other ways to insert the channel identification signal 5, such as by slightly changing the signal light wavelength or the signal light phase. It is also possible to insert the channel identification signal 5 into the changing frequency or the like.

In addition, an example of inserting one bit after frame period pulse 9 was shown as a method of inserting it into the pulse train, but where to insert it,
The number of bits etc. may be designed arbitrarily. Further, the frame period pulse 9 itself may be changed for each channel and may be used as a channel identification signal, or may be included in a stuff pulse or the like. Furthermore, a pilot signal may be inserted outside the signal band, and a channel identification code may be inserted into the pilot signal.

Note that it is not necessary to insert the channel identification signal 5 into each channel, and it is also possible to determine the signal light wavelength of the corresponding channel from the wavelength of the signal light of the reference channel having the identification signal.

Examples of signal modulation/demodulation methods are FSK and PSk, but there are also intensity modulation (ASK),
Generally, optical heterodyne, multi-value FSK, multi-value PSK method, etc.
It is applicable to all known optical homodyne detection methods. Furthermore, in this embodiment, an example was shown in which the channel transmitting section and the channel receiving section correspond to 1=1, but it is also possible to make them correspond to 1:n (n is an integer of 2 or more), or the channel receiving section corresponds to 1:n. It is also possible to receive signal light from an arbitrary channel transmitter as needed.

(Effects of the Invention) As described in detail above, in the present invention, each channel can be identified, and the local oscillation of each receiving channel can be performed so that each channel on the transmitting side and the receiving side corresponds 1:1 or appropriately. We have achieved an optical heterodyne/homodyne detection wavelength division multiplexing transmission system that allows the wavelength of light to be set.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a diagram showing a configuration example of a channel identification signal in the first embodiment, and FIG. 3 is a block diagram of a second embodiment. . Here, 1...first channel transmitting section 2...optical output section 4.
・・First channel transmission signal 5・・Channel identification signal 10・・Multiplex circuit 12・・Optical splitter 1
4... Local oscillation light 15... Photodetector 16
...Intermediate frequency signal 18...Demodulation circuit 20.
... Microprocessor 21 ... Channel identification circuit 22 ... Local oscillation light source 23 ... Frequency control circuit 40 ... Transmission line 5
2 to 60... 2nd to 10th channel signal light 61...
・This is the first channel reception rhyme.

Claims (1)

[Claims] On the transmitting side, the transmitted light from multiple channel transmitters with different carrier wavelengths is wavelength-multiplexed and transmitted, while on the receiving side, the output light from a local oscillation light source is outputted from a local oscillation light source with the wavelength appropriately controlled for each of the multiple channel receivers. An optical heterodyne/homodyne detection wavelength division multiplexing transmission method for multiplexing the signal light with the signal light and performing optical heterodyne/homodyne detection to extract a signal from the desired channel transmitting section, the transmitting side comprising: Each unit transmits the signal light in which a channel identification signal is superimposed on the main signal, while the receiving side transmits the signal light so that the channel identification signal in the received signal becomes the channel identification signal from the desired channel transmitting unit. An optical heterodyne/homodyne detection wavelength division multiplexing transmission method, characterized in that the signal light from the desired channel transmitter is received by controlling the wavelength of each local oscillation light source.