JPH0435240A - Video transmitter - Google Patents

Abstract

PURPOSE:To obtain a video image transmitter with high quality and economy in which a modulation form of an information source is transparent by applying frequency division multiplexing to a received signal separately in a 1st modulation section applying frequency division multiplexing to an amplitude modulation video signal and a 2nd modulation section applying frequency division multiplexing to a frequency modulation video signal. CONSTITUTION:A 1st drive means 15 of an optical transmitter 3 drives an output signal of a 1st modulation section 8, and a single longitudinal mode semiconductor laser 10 outputs an optical signal modulated based on the output signal. Then a 2nd drive means 13 drives an output signal of a 2nd modulation section 9, and a multiaxis oscillation semiconductor laser 11 outputs an optical signal modulated based on the output signal. Moreover, an optical multiplexer 12 multiplexes the output optical signals of both the lasers 10, 11 and sends the result to an optical fiber 4. Thus, the video image transmitter with high quality and economy is realized, in which a modulation form of an information source is transparent.

Description

[Detailed description of the invention] [Industrial application field] INDUSTRIAL APPLICATION This invention is utilized for the video transmission apparatus of FDM video communication.

In particular, the present invention relates to a video transmission device that optically transmits FDM video signals.

[Conventional technology]

FIG. 3 is a block diagram of a conventional video transmission device. Figure 4 shows the average optical received power vs. evaluated SNR of the video transmission equipment.
FIG. 3 is a diagram showing characteristics. FIG. 5 is a diagram showing the optical modulation degree per channel versus average optical reception power characteristic of the video transmission apparatus. Table 1 is a table comparing the characteristics of AM-FDM and FM-FDM video transmission devices. Table 2 is a table showing parameters used to calculate the characteristics of the video transmission device. Fourth
The figure shows a case where the wavelength is 1.55 μm and the optical modulation degree is 6%. FIG. 5 shows a case where the photodetector is an APD, the wavelength is 1.55 μm, the total optical modulation degree M=0.5, and M2=N−m2. Also, in Table 2, ■. - dark current component that is not multiplied Idm - dark current component that is multiplied.

(Hereinafter referred to as the margin of this page) Conventionally, video transmission devices are SCM (Subcarrier).
r Mu-Itiplexed) system,
In recent years, it has been introduced mainly in the United States (
Literature: IEICE Microwave Study Group Proceedings, 199
0.2.16 Etsugo Yoneda, “Trends in Microwave Subcarrier Technology in Optical Fiber Transmission J). Figure 3 shows the basic configuration of the SCM system, and Table 1 shows the AM-FDM signal and FM-FDM signal. An example of the system characteristics when optically transmitted is shown below.As shown in Table 1, AM-FDM system and FM-
The requirements for system characteristics are significantly different from that of the FDM system. In particular, the following two points should be noted.

■ [Relationship between video signal evaluation SNR and CNR] AM-F
DM system: Evaluation SNR=CN R-0,3 (dB) CV S
B-A M broadcasting parameters] FM-FDM system: Evaluation 5NR=CNR↓35.5 (dB) CBS broadcasting parameters] The conditions required for optical transmission based on the above calculation formula are shown in Figure 4 and Table 2. .

Here, RIN is relative intensity noise generated by a semiconductor laser.
e), and in a multi-axis oscillation type single conductor laser such as FP (Fabry-Perot cavity), -120 dB/Hz, DF
B (Distributed Feedback Type, Distributed Fee
dback) and DBR (distributed Bragg reflection type, Dist
-150 to 16
There is a commonly achieved value of 0 dB/Hz.

FIG. 5 shows the relationship between the evaluation SNR and the optical modulation degree m per channel. The parameters in Table 2 were used except for the conditions in FIG.

In FIGS. 4 and 5, it is assumed that the multiplication factor is optimally controlled when an APD photodiode (APD) is used.

■Beat interference DUR) AM-FDM system: DUR > 55 dB [Performance standard recommended by Radio Technology Association Cable Television Technical Investigation Committee] FM-FDM system: D U R > 31 dB C IEICE Technical Report, 89 , NO, 304, P 7-P12.1
989, Maeda et al.: Problems to be solved by the two inventions However, in such conventional video transmission devices, AM-
When attempting to transmit FDM and FM-FDM systems simultaneously, the performance that the optical transmission system must satisfy for both tone signals is so different that the equipment performance is limited by the AMFDM system. This method has the disadvantage that a separate optical transmission device is required for each modulation format.

In addition, coaxial CATV systems are limited by the loss-frequency characteristics of coaxial cables, so satellite broadcasting channels (
When transmitting FM-FDM system (intermediate frequency 1 to 1, 8 GHz), it is first demodulated to baseband and then AM modulated and converted to UHF band, resulting in quality deterioration and the need for a modulator/demodulator. There were drawbacks such as.

When making a video transmission device multi-channel, especially M-
In the case of the FDM system, it is difficult to ensure beat disturbance DUR. In a system that transmits 40 channels on a single radar, a method is used in which channels that do not cause problems with beat interference DUR are picked up as appropriate in the desired frequency arrangement of coaxial CATV (out of 60 channels, channels that do not cause problems with beat interference DUR) are used. In order to secure the beat disturbance DUR, it is difficult to create a system in which AM-FDM and FM-FDM systems coexist or to create multiple channels.

The present invention solves the above-mentioned drawbacks and improves the performance of the device.
It is an object of the present invention to provide a video transmission device that is not limited by the M-FDM system, is high quality, economical, and transparent to the modulation format of the information source.

5 Means for Solving the Problems The present invention provides modulation means for frequency division multiplexing video signals subjected to amplitude modulation and frequency modulation, and converts the output electric signal of this modulation means into an optical signal and sends it to an optical fiber. In the video transmission device, the modulation means includes a first variable R section that frequency division multiplexes the amplitude modulated video signal and a second modulation section that frequency division multiplexes the frequency modulated video signal. The optical transmitting device is provided separately, and includes a first driving means for driving the output signal of the first modulating section, and a single vertical drive means for outputting an optical signal modulated based on the output signal of the first driving means. a mode type semiconductor laser, a second driving means for driving the output signal of the second modulation section, and a multi-axis oscillation type semiconductor laser for outputting an optical signal modulated based on the output signal of the second driving means. , and an optical multiplexer that combines the output optical signals of both lasers and sends the combined signal to the optical fiber.

Further, the present invention provides the second driving means such that the degree of optical modulation per channel of the frequency modulated signal by this means is smaller than the degree of optical modulation per channel of the amplitude modulated signal by the first driving means. It can include means for adjusting.

Furthermore, the present invention includes modulation means for frequency-division multiplexing the amplitude-modulated and frequency-modulated video signals, and an optical transmitter for converting the output electrical signal of the modulation means into an optical signal and transmitting the optical signal to an optical fiber. In the video transmission device, the modulation means separately includes a first modulation section that frequency-division multiplexes the amplitude-modulated video signal and a second modulation section that frequency-division-multiplexes the frequency-modulated video signal. an optical modulation degree adjusting circuit connected to the output of the modulation section and adjusting the optical modulation degree per channel of the frequency modulation signal to be smaller than the optical modulation degree per channel of the amplitude modulation signal; and an output electrical signal of the first modulation section. and an electric mixer that mixes the output electric signal of the optical modulation degree adjustment circuit, and the optical transmitter includes a third drive means that drives the output electric signal of the electric mixer, and a third drive means that drives the output electric signal of the electric mixer; and a single longitudinal moat type semiconductor laser that sends an optical signal modulated based on the output signal of the driving means to the optical fiber.

[Effect]

The modulating means is separately integrated into a first modulating section that frequency-division multiplexes the amplitude-modulated video signal and a second modulating section that frequency-division-multiplexes the frequency-modulated video signal, and performs frequency-division multiplexing, respectively.

The first driving means of the optical transmitter drives the output signal of the first modulation section, and the single longitudinal mode semiconductor laser outputs an optical signal modulated based on this output signal. The second driving means drives the eight-power signal of the second modulation section, and the multi-axis oscillation type semiconductor laser outputs an optical signal modulated based on this output signal. The optical combiner combines the output optical signals of both lasers and sends it to an optical fiber.

Further, the second driving means is adjusted so that the degree of optical modulation per channel of the frequency modulation signal by this means is smaller than the degree of optical modulation per channel of the amplitude modulation signal by the first driving means.

As described above, the performance of the device is not limited by the AM-FDM system, and is high quality, economical, and transparent to the modulation format of the information source.

[Embodiments] Examples of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram of a video transmission device according to an embodiment of the present invention. In FIG. 1, the video transmission device includes modulation means for frequency division multiplexing video signals subjected to amplitude modulation and frequency modulation, and converts the output electrical signal of this modulation means into an optical signal and sends it to a single mode optical fiber 4. An optical transmitter 3 is provided.

Here, the feature of the present invention is that the modulation means includes:
AM including an FDM channel unit 1 and an electric mixer 2 as a first modulation unit that frequency division multiplexes an amplitude modulated video signal
- The FDM modulation unit 8 and the second modulation unit for frequency division multiplexing the frequency modulated video signal are divided into the FM-FDM submodulation 89 including the FDM channel unit 1 and the electric mixer 2, and the optical transmitter 3 is a laser drive circuit 1 as a first drive means for driving an output signal of the AM-FDM modulation section 8;
5, a single longitudinal moat type semiconductor laser 10 that outputs an optical signal modulated based on the output signal of the laser drive circuit 15,
A laser drive circuit 13 with an optical modulation degree adjustment function serves as a second driving means for driving the output signal of the FM-FDM modulation section 9, and an optical signal modulated based on the output signal of the laser drive circuit 13 with an optical modulation degree adjustment function. The optical multiplexer 12 combines the output optical signals of both lasers and sends them to the single mode optical fiber 4.

Further, the optical multiplexer 12 is composed of a wavelength multiplexing multiplexer, a polarization combiner, or a directional coupler.

Furthermore, the laser drive circuit with optical modulation degree adjustment function 13 is a means for adjusting the optical modulation degree per channel of the frequency modulation signal by this means to be smaller than the optical modulation degree per channel of the amplitude modulation signal by the laser drive circuit 15. including.

The operation of the video transmission device having such a configuration will be explained. In FIG. 1, an FDM channel section 1 consisting of an information source and an FDM modulation section has AM and FDM channels for each modulation format.
- The FDM modulation section 8 and the FM-FDM modulation section 9 are caught together.

The single longitudinal mode semiconductor laser 10 receives the AM-FDM signal group output from the AM-FDM modulator 8 via the laser drive circuit 15 and converts the electrical signal into an optical signal. The multi-axis oscillation type semiconductor laser 11 manually converts the FM-FDM signal group output from the FMFDM modulation section 9 through a laser drive circuit 13 with an optical modulation degree adjustment function, and converts the electric signal into an optical signal. The laser drive circuit 13 with a light modulation degree adjustment function performs adjustment to lower the light modulation degree compared to the laser drive circuit 15.

An optical multiplexer 12 composed of one of a wavelength multiplexer, a polarization combiner, or a directional optical coupler combines the optical signals output from each laser and connects them to the single-mode optical fiber 4. Send.

The optical receiver 5 converts the optical signal of the single mode optical fiber 4 into an electrical signal and supplies it to each demodulator 7 via an electrical branching device 6, and each demodulator 7 demodulates the input electrical signal. The optical receiver 5 includes a wavelength selection element when the optical multiplexer 12 is of a wavelength multiplexing type.

As mentioned above, the FM-FDM signal is generated by a multi-axis oscillation type semiconductor laser 11 with a poor RIN characteristic and a frequency of about 120 dB/Hz.
Since the AM-FDM signal is optically modulated by a single longitudinal mode semiconductor laser 10 with good RIN characteristics and a frequency of about 150 dB/Hz, transmission with high SNR quality is possible as shown in Fig. 4. can.

Furthermore, since the FM-FDM signal can be adjusted to have a smaller optical modulation degree per channel than the AM-FDM signal by the laser drive circuit 13 with optical modulation adjustment function, the same average value can be obtained as shown in FIG. AM-F in optical reception power value
The difference in SNR quality between the DM system and the FM-FDM system can be reduced, and the number of transmission channels can be increased.

When the optical multiplexer 12 is configured with a wavelength multiplexing multiplexer,
By using the emission center wavelength of the multi-axis oscillation type semiconductor laser 11 and matching it with the zero dispersion wavelength of the optical fiber, high-quality transmission is possible, and the channel frequency arrangement of the AM-FDM system and the FM-FDM system can be made independent. Since the required transmission band can be narrowed, the coaxial CATV IC can be used for other purposes.

Furthermore, since lasers are provided individually for the AM-FDM system and the FM-FDM system, it is easy to ensure beat disturbance DUR even in the case of multi-channel system.

Furthermore, if the optical modulation degree of the AM-FDM system and the FM-FDM system is not changed, FIV>F
Since the DM system allows high-quality transmission, it can also support transmission of MUSE signals and the like.

FIG. 2 is a block diagram of a video transmission device according to an unexplored embodiment. The basic concept of this embodiment is the same as that in Fig. 1, but SB-AM in airwave or coaxial CATV is
Similar to the VAR (video/audio ratio, -14 dB) of the transmission system, the optical modulation degree per channel of the AM-FDM system and the FMFDM system can be designed to be optimal in terms of system design.

J Effects of the Invention] As explained above, the Hofu Ri has the following excellent effects.

■ It is possible to create multiple channels by using a multi-axis oscillation semiconductor laser, which is more than an order of magnitude cheaper than a single longitudinal mode semiconductor laser, is transparent to the modulation format of the information source, satisfies the beat disturbance DUR, and is economical. Can be done.

■ Even when a single laser is used, it is transparent to the modulation format of the information source.

◎ If applied to an optical CATV system, it is highly economical and can be used as a satellite broadcasting tuner and a coaxial CATV tuner, allowing for diversification of services.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video transmission device according to an embodiment of the present invention. FIG. 2 is a block diagram of a video transmission device according to an embodiment of the present invention. FIG. 3 is a block diagram of a conventional video transmission device. FIG. 4 is a diagram showing average optical reception power versus evaluated SNR characteristics of the video transmission device. FIG. 5 is a diagram showing per-channel optical modulation degree versus average optical reception power characteristics of the video transmission device. DESCRIPTION OF SYMBOLS 1... FDM channel part, 2... Electric mixer, 3...
...Optical transmitter, 4...Single mode optical fiber
5... Optical receiver, 6... Electric branching device, 7... Demodulator, 8... AM-FDM modulation section, 9... FM-
F, DM modulation section, 10... single longitudinal mode semiconductor laser, 11... multi-axis oscillation semiconductor laser, 12...
Optical multiplexer, 13... Laser drive circuit with optical modulation degree adjustment function, 14... Optical modulation degree adjustment circuit, 15... Laser drive circuit. Patent 8 applicant: Nippon Telegraph and Telephone Co., Ltd. Agent, patent attorney Nao Takashi Ide + Burning light received power (dam) Average light received power pair is calculated as SNR 兇 4 ro

Claims (1)

[Claims] 1. A modulation means for frequency division multiplexing video signals subjected to amplitude modulation and frequency modulation, and an optical transmission device for converting the output electric signal of the modulation means into an optical signal and transmitting it to an optical fiber. In the video transmission device, the modulation means separately includes a first modulation section that frequency-division multiplexes the amplitude-modulated video signal and a second modulation section that frequency-division-multiplexes the frequency-modulated video signal. The transmitting device is
a first driving means for driving the output signal of the first modulation section; a single longitudinal mode semiconductor laser for outputting an optical signal modulated based on the output signal of the first driving means; A second driving means that drives the output signal of the modulation section, a multi-axis oscillation semiconductor laser that outputs an optical signal modulated based on the output signal of the second driving means, and the output optical signals of both lasers are combined. and an optical multiplexer that transmits the image to the optical fiber. 2. The second driving means includes means for adjusting the degree of optical modulation per channel of the frequency modulation signal by this means to be smaller than the degree of optical modulation per channel of the amplitude modulation signal by the first driving means. The video transmission device according to claim 1. 3. A video transmission device comprising modulation means for frequency-division multiplexing of amplitude-modulated and frequency-modulated video signals, and an optical transmission device for converting the output electrical signal of the modulation means into an optical signal and transmitting it to an optical fiber. In the above, the modulation means separately provides a first modulation section that frequency division multiplexes the amplitude modulated video signal and a second modulation section that frequency division multiplexes the frequency modulation video signal, and adjusts the output of the second modulation section. a light intensity adjustment circuit that is connected to and adjusts the optical modulation degree per channel of the frequency modulation signal to be smaller than the optical modulation degree per channel of the amplitude modulation signal; an electric mixer that mixes the output electric signal of the circuit; and a single longitudinal mode semiconductor laser that transmits an optical signal modulated based on the optical fiber to the optical fiber.