JPH0437225A - Optical transmitter and optical receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to video signals, audio signals,
The present invention relates to an optical transmitter and an optical receiver used to transmit various signals such as data by optical wavelength multiplexing.

Conventional technology In recent years, optical transmission systems using optical fibers have been making remarkable progress with the reduction of loss in optical fibers and advancements in optical devices, and the transmission of large amounts of digital data has also become possible due to faster transmission speeds. Steady progress is being made. Optical wavelength multiplexing techniques such as optical WDM and optical FDM are attracting particular attention as transmission systems for this large-capacity digital data, which enable multiplex transmission of multiple signals through a single optical fiber. Using this method, PCM audio,
Transmission experiments of video, etc. are also being conducted (for example, Nishioka et al., r.
HDTV wavelength division multiplexing optical transmission system” 1989989 1
(See TV Jiran report on October 26th) (For example, Shibuya et al.
[Coherent optical CATV...10 channel FDM transmission experiment...] IEICE Technical Report 0QE88-7
(see 0).

Furthermore, in video transmission service networks such as urban CATV, there is a shift from transmission using conventional coaxial cables to optical fiber transmission, which has characteristics such as broadband, low loss, and non-induction. In this CATV optical fiber transmission,
In order to reduce costs and to ensure compatibility with existing coaxial cable transmission, the light source (DFB-LD) is configured to be directly intensity-modulated and transmitted using an analog signal that is multiplexed with dozens of channels of video signals using FDM. (For example, Nakata et al., “rCATV Optical Fiber Backbone” 1989
Refer to the Technical Report of the Television Society of Japan, October 26, 2016].

In CATV, the addition of transmission service channels and the addition of new services must be done while ensuring consistency with the existing system. In CATV using optical fibers, by using the optical wavelength division multiplexing transmission described above, it is possible to add high-quality services while maintaining system matching.

An example of an optical transmitter and an optical receiver using conventional optical wavelength multiplexing will be described below with reference to the drawings. FIG. 6 shows a configuration of an optical wavelength multiplexing section and an optical wavelength demultiplexing section of a conventional optical transmitter and optical receiver. In the same figure,
600 is an optical coupler, and 601 is an optical demultiplexer. In the optical transmitter, the lights with wavelengths λ1 to λ4 have different wavelengths as shown in FIG. transmitted to. In the optical receiver, light of each wavelength is demultiplexed by an optical demultiplexer 601 (for example, the diffraction grating type optical demultiplexer in the above-mentioned document "HDTV wavelength division multiplexing optical transmission system") having the characteristics shown in FIG. 7 (0)). Ru.

In this transmission system, multiple channels of signals can be transmitted through a single optical fiber by modulating light of each wavelength with multiple signals and transmitting the modulated signals.

Problems to be Solved by the Invention However, in the above configuration, crosstalk between channels occurs when multiplexing at narrow wavelength intervals, and therefore CA
In systems that transmit analog signals, such as TVs, RB often causes interference between channels. As shown in Figure 7, since the laser light from the semiconductor LD has wide side lobes, multiplexing at narrow wavelength intervals causes crosstalk between signal lights, making it unsuitable for transmitting analog signals by direct intensity modulation, etc. It disappears. Furthermore, if multiplexing is performed at wideband intervals to avoid crosstalk between channels, the number of multiplexes cannot be obtained, resulting in low scalability.

In view of the above problems, the present invention provides an optical transmitter and an optical receiver that enable multi-channel optical wavelength division multiplex transmission of digital signals while suppressing crosstalk to analog signals.

Means for Solving the Problems In order to solve the above problems, the optical transmitting device of the present invention multiplexes digital signals of a plurality of channels using narrowband optical wavelength multiplexing means, and directly multiplexes the digital signals with the wideband optical wavelength multiplexing means. It has a configuration in which intensity-modulated analog signals are multiplexed.

Further, the optical receiving device of the present invention separates the digital signals of multiple channels from the directly intensity-modulated analog signals by the broadband optical wavelength separation means, and separates the digital signals of the multiple channels by the narrowband optical wavelength separation means. It has the following configuration.

Effect of the Invention With the above-described configuration, the present invention makes it possible to perform optical wavelength division multiplex transmission of an analog signal by separating the wavelength from a digital signal to the extent that crosstalk does not occur, and at the same time,
Since digital signals can be multiplexed in a narrow band, a sufficient number of multiplexed channels can be secured.

Embodiment Hereinafter, an optical transmitter and an optical receiver according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an optical transmission device and an optical reception device in a first embodiment of the present invention. In Figure 1, 1
00 is a frequency axis multiplexing circuit, 101° 103 is an encoding circuit, 102 is a time axis multiplexing circuit, 104 to 108 are light sources, 1
Reference numeral 09 is a diffraction grating type optical multiplexer, 110 is an interference film type optical multiplexer, and 111 is a basic transmitter, and the above constitutes an optical transmitter.

In addition, in the same figure, 120 is a frequency axis separation circuit;
1.123 is a decoding circuit, 122 is a time axis separation circuit, 1
24 to 128 are light receiving circuits, 120 is a diffraction grating type optical demultiplexer, 130 is an interference film type optical demultiplexer, and 131 is a basic receiving section, and the above constitutes an optical receiving device.

Regarding the optical transmitter and optical receiver configured as described above, the optical spectrum characteristic diagram shown in Fig. 2, Fig. 3,
This will be explained using the configuration diagram of the optical multiplexer/demultiplexer shown in FIG. 3 and 4 respectively show the configurations of an interference film type optical multiplexer 110, an interference film type demultiplexer 130, a diffraction grating type optical multiplexer 109, and a diffraction grating type demultiplexer 129 (for example, See Sanki, "Optical multiplexing and demultiplexing circuit," 1978, Conference of the Four Electrical Engineers of Japan, 125, and Miyazaki et al., "Optical demultiplexer - for four-wave wavelength multiplexing and two-way communication," IEICE Technical Report C378-46). The interference film type optical multiplexer/demultiplexer has a relatively wide wavelength interval that can be multiplexed/demultiplexed as shown in Figure 2 (b), but it has the characteristics of being easy to implement and can be made at low cost. Although the structure is complicated, the light source 10 is used in an optical transmitter that has the characteristic of being able to multiplex and demultiplex at narrow wavelength intervals as shown in FIG. 2(C).
The light of wavelength λ1 output from 4 has N T S C:
An analog signal obtained by frequency axis multiplexing of the video signals 1 to 3 is directly intensity-modulated, and the wavelength λ1 . The light beams are intensity-modulated by time-axis multiplexed digital signals after NTSC4-7 video signals are encoded, and the light beams with wavelengths λLt-λL4 output from light #106-108 have respective wavelengths λLt-λL4. , the intensity is modulated by the encoded digital signals of HDTV 1 to 3 (here, "direct intensity modulation" refers to the light source (semiconductor LD
"Intensity modulation" refers to analog modulation that takes advantage of the linearity between the input electrical signal level and the output optical brightness level (e.g.), and "intensity modulation" refers to discrete optical modulation for transmitting digital signals. ), at this time, as shown in Figure 2(a), the analog signal is
5. The digital signal is placed in a long wavelength band (e.g. 1
．． 55 μm band) from λLl to λ4. The wavelength band width is approximately 100 nm or less with narrow wavelength intervals of several tens of nanometers or less. Wavelength λ1 arranged in a narrow band section. The digital signals of wavelengths λ3, . The optical signal is multiplexed with the analog signal and transmitted to the optical receiver.

The optical spectrum at this time is the diffraction grating type optical multiplexer 10.
9 and the interference film type optical multiplexer 110, crosstalk due to side lobes of optical signals of each wavelength is reduced, as shown by the dotted line in Fig. No crosstalk occurs between the two.

In the optical receiver, since the wavelength interval is sufficiently wide, the interference film type optical demultiplexer 130 is used to separate short wavelength bands λ3. analog signals are separated without crosstalk. therefore,
NTSCI-3 video signals can be reproduced with high quality by subjecting the analog signal converted to an electrical signal by the light receiving circuit 124 to frequency separation processing in accordance with the processing by the optical transmitter.

The digital signals in the long wavelength band λ, -1 to λL4 are separated by an interference film type optical demultiplexer 130, and then further separated into wavelengths λLl to λL4 by a diffraction grating type optical demultiplexer 129, respectively. Light of each wavelength is transmitted through light receiving circuits 125 to 12.
NTSC 4 to 7 and H
Video signals of DTVs 1 to 3 are obtained.

As described above, according to this embodiment, an interference film type optical multiplexer/demultiplexer is used as the wideband wavelength multiplexing/demultiplexing means, and a diffraction grating type optical multiplexer/demultiplexer is used as the narrowband wavelength multiplexing/demultiplexing means. Modulating the light at narrow wavelength intervals in the wavelength band and multiplexing and demultiplexing it using the above-mentioned diffraction grating type optical multiplexer/demultiplexer, and converting the short wavelength band analog signal and the narrow wavelength multiplexed long wavelength band digital signal, By multiplexing and demultiplexing using an interference film type optical multiplexer/demultiplexer, it becomes possible to secure a sufficient number of digital channels and perform wavelength multiplex transmission without crosstalk to analog signals.

Furthermore, the basic transmitter 111 and the basic receiver 1 in FIG.
When expanding the existing transmission system consisting of It is possible to ensure interchangeability with the configured optical receiving device.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 shows the configuration of an optical transmitter and an optical receiver in a second embodiment of the present invention. In Figure 5, 5
00 is a frequency axis multiplexing circuit, 501 is an encoding circuit, 502
is a light source, 503 to 505 are coherent light sources, 506 is an optical coupler, and 507 is an interference film type optical multiplexer, and the above constitutes an optical transmitter. Further, in the figure, 510 is a selection circuit, 511 is a decoding circuit, 512 is a band pass filter, 513 and 514 are light receiving circuits, 515 is an optical mixer,
516 is a coherent light source, and 517 is a wavelength control circuit.

The operation of the optical transmitter and optical receiver configured as described above will be described below.

In FIG. 5, in the optical transmitter, analog signals consisting of NTSCI to 3 video signals are directly intensity-modulated to light of short wavelengths λ and I, as in the first embodiment. light source 5
Reference numerals 03 to 505 are light sources capable of emitting light with a narrow line spectrum width, and the multiplex interval can be made narrow to about several GHz, and the number of multiplexes can be several hundred times that of the first embodiment. This light source is HD
TV 1 to 1 changed by encoded digital signals from 1 to m
ll (e.g. frequency modulation, phase modulation, etc.), and the wavelength λ
It outputs light of L1 to λL. Interference film type optical multiplexer 507
The lights with wavelengths λ,1 and λL1 are multiplexed at the optical coupler 5.
At step 06, the remaining light is multiplexed and branched and transmitted to the optical receiver.

In the optical receiver, light with a short wavelength λ1 is separated by an interference film type optical demultiplexer 518, converted into an electric signal in a light receiving circuit 513, and then converted into an NT signal in a selection circuit 510.
One of the signals of SCI~3 is frequency selected and output. At this time, as in the first embodiment, a video signal without crosstalk from the digital signal can be reproduced. Wavelength λ5. ~λL, is mixed with light from a coherent light source 516 in an optical mixer 515, and then sent to a light receiving circuit 514.
is converted into an electrical signal by At this time, based on the principle of heterogain detection, an electrical signal having a frequency represented by the difference between the frequency of the light from the coherent light source 516 and the frequency of the transmitted light of wavelength λ, ~λ, is obtained. Therefore, a desired video signal HDTV M is reproduced by controlling the frequency of the coherent light -a 516 by a wavelength control circuit 517, separating the bands by a bandpass filter, and decoding by a decoding circuit 51.1.

As described above, in this embodiment, by using optical heterogain detection as the narrowband optical wavelength separation means, transmission with a further increased number of multiplexing becomes possible. In addition, by multiplexing one digital signal in the long wavelength band and one analog signal in the short wavelength band using an interference film multiplexer, and then multiplexing all the optical signals with an optical coupler, multi-branched optical signals can be created. Transmission becomes possible.

In addition, 1. In the second embodiment, analog signals are placed in the short wavelength band and digital signals are placed in the long wavelength band, but the reverse placement method is also possible. It is also possible to provide multiple wavelengths for transmitting analog signals.

Furthermore, in the second embodiment, it is also possible to use optical homodyne detection instead of optical heterodyne detection as the narrowband wavelength separation means.

Effects of the Invention As described above, the present invention has a configuration in which a plurality of digital signals are multiplexed and separated by narrowband optical wavelength multiplexing and demultiplexing means, and a digital signal and an analog signal are multiplexed and separated by wideband wavelength multiplexing and demultiplexing means. By providing this, it becomes possible to secure a sufficient number of channels for digital signals and perform wavelength division multiplexing transmission without crosstalk to analog signals.

Further, according to the present invention, the transmission system in operation (CAT
Service channels can be easily added and expanded in V, etc.), and replaceability can be maintained by simply adding a low-resolution, low-cost duplexer to existing optical receivers.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical transmitter and an optical receiver in the first embodiment of the present invention, FIG. 2 is an optical spectrum characteristic diagram showing the processing process in FIG. 1, and FIG. 3 is an interference film type optical FIG. 4 is a configuration diagram of a diffraction grating type optical multiplexer/demultiplexer, FIG. 5 is a configuration diagram of an optical transmitter and an optical receiver in the second embodiment of the present invention, and FIG. 6 is a configuration diagram of a demultiplexer. 7 is a configuration diagram of a conventional optical transmitter and an optical receiver, and FIG. 7 is an optical spectrum characteristic diagram showing the processing process in FIG. 6. 104-108,502...Light source, 109...
...Diffraction grating type optical multiplexer, 110.507...
...Interference film type optical multiplexer, 124-128, 513, 51
4... Light receiving circuit, 129... Diffraction grating type optical demultiplexer, 130.518... Interference film type optical demultiplexer, 503-505 516... ... Coherent light source, 506 ... Optical cobra, 515 ...
... Optical mixer, 512 ... Bandpass filter,
517...Wavelength control circuit. Name of agent: Patent attorney Shigetaka Awano (1 person, 1 figure, 2 figures) λ1□□↑ Husband (words and deeds! (b) 5.B#F″jY rise, l (b no ke 1

Claims (7)

[Claims] (1) A plurality of channels of digital signals are multiplexed by a narrowband optical wavelength multiplexing means, and the digital signal and the directly intensity-modulated analog signal are multiplexed by a wideband optical wavelength multiplexing means at least in the wavelength band of the narrowband optical wavelength multiplexing means. An optical transmitter characterized by multiplexing at wavelength intervals wider than width. (2) The digital signals of multiple channels and the directly intensity-modulated analog signal are separated by the broadband optical wavelength demultiplexing means at least at a wavelength interval wider than the wavelength bandwidth of the narrowband optical wavelength multiplexing means, and the narrowband optical wavelength demultiplexing means An optical receiving device characterized in that it separates digital signals of multiple channels. (3) The optical transmitter according to claim (1), comprising a diffraction grating type optical multiplexer as the narrowband optical wavelength multiplexing means and an interference film type optical multiplexer as the broadband optical wavelength multiplexing means. . (4) An optical coupler is provided as the narrowband optical wavelength multiplexing means, and an interference film type optical multiplexer is provided as the broadband optical wavelength multiplexing means, and the output of the interference film type optical multiplexer is connected to the input of the optical coupler. An optical transmitter according to claim (1). (5) The optical receiving device according to claim (2), further comprising an interference film type optical multiplexer as the broadband wavelength separation means. (6) The optical receiving device according to claim (2), further comprising a diffraction grating type optical multiplexer as the narrowband wavelength separation means. (7) The optical receiving device according to claim (2), further comprising an optical mixer as the narrowband wavelength separation means.