JPH0457533A - Rf signal wavelength division multiplex optical transmitter - Google Patents

Abstract

PURPOSE:To relax a limit of a transmission available channel number due to a noise characteristic and a distortion characteristic of a semiconductor laser and to attain multi-channel transmission at a low cost by providing plural optical transmitters, an optical multiplexer, an optical fiber, an optical demultiplexer and plural receivers to the title transmitter. CONSTITUTION:The transmitter is provided with plural optical transmitters 1, 2 making an AM-FDM signal subject to analog frequency multiplex as to a TV signal of each group into a signal light with light sources with a different wavelength, an optical multiplexer 3 multiplexing signal lights from the plural optical transmitters 1, 2 and an optical fiber 4 through which a multiplexed signal light from the optical multiplexer 3 and also with an optical demultiplexer 5 demultiplexing the multiplexed signal light sent through the optical fiber 4 into signal lights for each wavelength and plural receivers 61, 62 receiving the signal lights with each wavelength demultiplexed and outputted from the optical demultiplexer 5. Since number of channels shared by one semiconductor laser is reduced, noise and distortion characteristic required for the semiconductor laser is relaxed, the cost of the transmitter is reduced and multi-channel transmission is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical transmission device that directly modulates the light intensity of a light source using an analog signal and transmits the light, and more specifically, the present invention relates to an optical transmission device that directly modulates the light intensity of a light source using an analog signal and transmits light. Naru AM-FD
The present invention relates to an RF signal wavelength division multiplexing optical transmission device that optically transmits M signals by wavelength division multiplexing.

2. Description of the Related Art When a plurality of TV signals are analog frequency multiplexed and optically transmitted using a semiconductor laser, the semiconductor laser is required to have low noise and low distortion characteristics, and both characteristics limit the number of channels that can be transmitted.

It is known that when a semiconductor laser is subjected to analog modulation, the manner in which noise is generated and the amount of harmonic distortion of the signal vary depending on the degree of modulation, and overmodulation significantly deteriorates the distortion characteristics. It is also known that when a portion of the laser output light is reflected and returns to the semiconductor laser, noise and distortion characteristics are significantly degraded.

Therefore, the modulation degree per channel has been determined according to the number of TV signals to be transmitted so that the total modulation degree does not become overmodulated. In addition, in order to prevent reflected light from re-inputting, AM-
It was optically transmitting FD'M signals. The number of channels that can be transmitted is limited by the noise and distortion characteristics of the semiconductor laser, but by selecting and using an excellent semiconductor laser, it is currently possible to transmit about 40 channels over 10 km.

Problems to be Solved by the Invention However, semiconductor lasers with excellent characteristics are expensive, leading to an increase in the cost of the device. Also,
Even if an attempt is made to increase the number of transmission channels, it may be difficult to obtain a semiconductor laser having the characteristics necessary to transmit this number of channels, and this imposes significant restrictions on the design of the transmission device.

In view of the above circumstances, it is an object of the present invention to provide an RF signal wavelength division multiplexing optical transmission device that can alleviate the limitations on the number of channels that can be transmitted due to the noise characteristics and distortion characteristics of semiconductor lasers, and can perform multi-channel transmission at low cost. purpose.

Means for Solving the Problems An RF signal wavelength division multiplexing optical transmission apparatus according to the invention of claim 1 divides a plurality of TV signals into a plurality of groups, and performs analog frequency multiplexing on each group of TV signals.
A plurality of optical transmitters that convert FDM signals into signal lights using light sources with different wavelengths, an optical multiplexer that multiplexes the signal lights from the plurality of optical transmitters, and a combined signal light from the optical multiplexer. an optical fiber for transmitting a signal, an optical demultiplexer for demultiplexing the multiplexed signal light transmitted through the optical fiber into signal light for each wavelength, and a demultiplexer for demultiplexing each wavelength output from the optical demultiplexer. It is characterized by comprising a plurality of receivers that receive signal light.

The RF signal wavelength division multiplexing optical transmission apparatus according to the invention of claim 2 divides a plurality of TV signals into a plurality of groups, and performs analog frequency multiplexing on the TV signals of each group.
A plurality of optical transmitters that convert FDM signals into signal lights using light sources with different wavelengths, an optical multiplexer that multiplexes the signal lights from the plurality of optical transmitters, and a combined signal light from the optical multiplexer. and an optical receiver that receives the multiplexed signal light transmitted through the optical fiber, and the frequency bands of the AM-FDM signals of each group are different from each other. It is said that

According to the configuration of the invention as claimed in claim 1, the number of channels of TV signals that are borne by one light source is reduced, so that the requirements for the noise and distortion characteristics of the light source are relaxed. In addition, even if a part of the emitted light enters another light source due to crosstalk in the optical multiplexer/demultiplexer, there will be no interference because light sources with different wavelengths are used, and the characteristics of the light source will deteriorate. can be avoided.

According to the configuration of the invention as claimed in claim 2, only one optical receiver is required on the receiving side, and no optical demultiplexer or other optical receiver is provided, so that the cost is reduced accordingly.

In this case, the first AM-FDM signal and the second
Since the frequency bands of M-FDM signals are different from each other, even if received by one optical receiver, the received TV
Mutual interference between signals is prevented.

Example 1 An example of the invention according to claim 1 will be described below with reference to FIG.

FIG. 1 is a block diagram showing the configuration of an RF signal wavelength division multiplexing optical transmission apparatus. In Fig. 1, 1 is a first laser beam using a distributed feedback semiconductor laser (DFB-LD) with a built-in optical isolator of wavelength λ1 (for example, 1.3 μm band) as a light source.
The optical transmitter 2 is a distributed feedback semiconductor laser (DFB-
3 is a dielectric multilayer filter type optical multiplexer, 4 is a single mode optical fiber, 5 is a dielectric multilayer filter type optical demultiplexer, and 61 is a dielectric multilayer filter type optical demultiplexer.
The optical receiver 2 for 3 μm μm light is an optical receiver for 1.5 μm μm light.

AM-FDM signals obtained by frequency-multiplexing M TV signals from first channel to first channel are input to the first optical transmitter 1 . Further, an AM-F DM signal obtained by frequency multiplexing N TV signals from the M+1 channel to the M+N channel is input to the second optical transmitter 2 . That is, the TV signal is frequency-multiplexed into one of two frequency bands (the frequency band from the first channel to the Mth channel, and the frequency band from the M+1th channel to the M+Nth channel) and then transmitted. be done.

In each optical transmitter 1.2, the semiconductor laser is directly intensity-modulated by the input AM-FDM signal. The signal light emitted from the semiconductor laser is sent to an optical multiplexer 3 and multiplexed, and then transmitted through a single mode optical fiber 4. The signal light transmitted by the single mode optical fiber 4 is separated into a 1.3 μm band signal light and a 1.3 μm band signal light by an optical demultiplexer 5.
It is demultiplexed into signal light in the 5 μm band. Demultiplexed 1.3μm
The signal light in the 1.3 μm band is input to an optical receiver 61 for the 1.3 μm band and converted into an electrical signal, while the demultiplexed signal light in the 1.5 μm band is input to the optical receiver 62 for the 1.5 μm band. It is input and similarly converted into an electrical signal.

A semiconductor laser has a built-in optical isolator. This optical isolator functions to attenuate light re-entering the semiconductor laser by external reflection.

The dielectric multilayer filter type optical multiplexer 3 and optical demultiplexer 5 have small loss upon incidence, excellent wavelength selectivity, and large crosstalk attenuation, and are therefore suitable for wavelength division multiplexing of AMFDM signals.

According to the above configuration, when the total number of transmission channels is M10N as described above, the optical transmitter 1 has M transmission channels, and the optical transmitter 2 has N transmission channels. Each will share their share. That is, the number of transmission channels covered by one optical transmitter is halved, harmonic distortion is reduced, and the distortion characteristics required of the semiconductor laser are significantly relaxed.

Considering the performance of current semiconductor lasers, those with the characteristics necessary for transmission of about 20 channels can be obtained at a relatively low price, and it is possible to increase the total number of transmission channels to 40 or more while reducing costs. I can do it.

Note that the plurality of TV signals are divided into two groups and are frequency-multiplexed and transmitted in different frequency bands, thereby preventing mutual interference between the received TV signals and obtaining good image quality. However, in the present invention, even if the frequency f of the first channel and the frequency fH+1 of the M+1th channel are the same, the frequency f2 of the second channel and the frequency fM of the M+2th channel. 2 are the same,
From now on, even if the frequencies are the same, these two
The TV signals divided into two groups are optical signals with different wavelengths λ1 and λ2, and are split by the optical demultiplexer 5 and received by the respective optical receivers, so it is not always possible to separate the TV signals into two groups. It is not necessary to frequency-multiplex the signal into any one of the divided frequency bands and transmit it.

Embodiment 2 FIG. 2 is a process diagram showing the configuration of an RF signal wavelength division multiplexing optical transmission apparatus according to the second aspect of the invention. In addition,
Members having the same functions as those in the first embodiment are given the same reference numerals and their explanations are omitted.

In FIG. 2, reference numeral 63 denotes an optical receiver whose reception sensitivity is constant for wavelengths in the 1.3 to 1.5 μm band.

Only one optical receiver 63 is provided, and the first optical receiver 63 is
Compared to the embodiment, the number of optical demultiplexers and one optical receiver are reduced, and the cost is reduced accordingly.

On the other hand, as in the first embodiment, the optical transmitter is provided with two optical transmitters 1 and 2, and as described above, M TV signals are frequency-multiplexed from the first channel to the first channel. The AM-FDM signal is input to the first optical transmitter l, and the AM-FDM signal is frequency-multiplexed from the M+1th channel to the M+Nth channel by N TV signals.
The signal is input to the second optical transmitter 2.

The optical receiver 63 uses an InGaAs light receiving element, and the efficiency of converting a received optical signal into an electrical signal is constant at wavelengths in the 1.3 to 1.5 μm band.

Therefore, the combined optical signals of the 1.3 μm and 1.5 μm bands transmitted through the single mode optical fiber 4 are converted into electrical signals all at once.

Even when the optical signals are converted into electrical signals all at once, the first AM-FDM signal and the second AM-
Since the FDM signals have different frequency bands, mutual interference between the received TV signals is prevented even if they are received by one optical receiver. Here, as a method of dividing the frequency bands, in addition to the method described above, there is a method of combining several frequency bands that avoid harmonic distortion components that occur when frequency multiplexing and transmitting them using the optical transmitter 1 or the optical transmitter 2. According to this method, better image quality can be obtained.

Effects of the Invention According to the present invention, the number of channels borne by one semiconductor laser is reduced, so that the noise and distortion characteristics required of the semiconductor laser are relaxed. Therefore, it is not necessary to select a particularly excellent semiconductor laser, and the cost of the transmission device can be reduced. Furthermore, it is possible to flexibly respond to an increase in the number of transmission channels in the existing transmission system, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the invention of claim 1, and is a block diagram showing the configuration of an RF signal wavelength division multiplexing optical transmission apparatus, and FIG. 2 shows an embodiment of the invention of claim 2. 1 is a block diagram illustrating the configuration of an RF signal wavelength division multiplexing optical transmission apparatus, showing one embodiment. FIG. 1... First optical transmitter, 2... Second optical transmitter, 3
... Dielectric multilayer filter type optical multiplexer, 4... Single mode optical fiber, 5... Dielectric multilayer filter type optical demultiplexer, 61... Optical receiver for 1.3 μm μm light 2.
...1.5 μm μm light optical receiver 3...1.3-1.
This is an optical receiver whose receiving sensitivity is constant for wavelengths in the 5 μm band.

Claims (2)

[Claims] (1) AM-F that divides multiple TV signals into multiple groups and performs analog frequency multiplexing on each group of TV signals.
a plurality of optical transmitters that convert DM signals into signal lights using light sources with different wavelengths; an optical multiplexer that combines the signal lights from the plurality of optical transmitters; and a combined signal light from the optical multiplexer. an optical fiber that transmits a signal, an optical demultiplexer that demultiplexes the multiplexed signal light transmitted through this optical fiber into signal light of each wavelength, and a An RF signal wavelength division multiplexing optical transmission apparatus comprising: a plurality of receivers that receive signal light; (2) AM-F that divides multiple TV signals into multiple groups and performs analog frequency multiplexing on each group of TV signals.
a plurality of optical transmitters that convert DM signals into signal lights using light sources with different wavelengths; an optical multiplexer that combines the signal lights from the plurality of optical transmitters; and a combined signal light from the optical multiplexer. AM-FDM of each group, comprising an optical fiber for transmitting
An RF signal wavelength division multiplexing optical transmission device characterized in that signals have different frequency bands.