JPH0437329A - Fm multiplex signal optical transmitter - Google Patents

Abstract

PURPOSE:To decrease the deterioration in the picture quality after transmission by making the generating timing of all television signals coincident with each other so that the horizontal synchronizing signal periods of all the television signals are overlapped with each other in an optical transmitter modulating the television signal. CONSTITUTION:A horizontal synchronizing signal in a television signal of each channel is detected respectively by a synchronizing signal detection circuit 14. A delay time of a delay quantity setting circuit 16 is set respectively based on a detection timing obtained from each synchronizing signal detection circuit 14 so that the horizontal synchronizing signal periods of all television signals are overlapped with each other. A television signal of each channel delayed by the variable delay circuit 16 is amplitude-modulated by an amplitude modulator 17 into an RF signal and the signal is frequency-multiplexed by a mixer 18. After the obtained RF multiplex signal is amplified by an amplifier 10, the resulting signal drives a semiconductor laser 12. An output light from the semiconductor laser 12 is sent to a receiver side by using an optical fiber 13 as a medium.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an RF multiplex signal optical transmitter that optically transmits an RF multiplex signal using a light source such as a semiconductor laser.

2. Description of the Related Art As a conventional RF multiplex signal optical transmitter, for example, an optical transmitter shown in a block diagram as shown in FIG. 2 is known.

In FIG. 2, 34... is a modulator for amplitude modulating each television signal, 35 is a mixer that mixes the RF multiplied signals modulated by the modulator 34... to produce an RF multiplexed signal; 30 is an amplifier for amplifying the RF multiplexed signal; 32
31 is a semiconductor laser whose brightness is modulated by the amplified RF multiplexed signal; 31 is a semiconductor laser bias circuit that applies the necessary bias to drive the semiconductor laser 32; and 33 is the light emitted from the semiconductor laser 32. An optical fiber that transmits signals.

Therefore, in the above-mentioned RF multiplexed signal optical transmitter, each input multi-channel television signal is sent directly to the modulator 3.
4... and mixer 35 to become an RF multiplexed signal,
After being amplified by the amplifier 30 to an amplitude that allows the required degree of modulation, the DC current from the semiconductor laser bias circuit 31 (
bias current). The semiconductor laser 32 is driven by brightness modulation by this superimposed signal current, and the output optical signal from the semiconductor laser 32 is transmitted to the optical fiber 33.
is propagated to the receiving side using the transmission path.

Problems to be Solved by the Invention However, in the above-mentioned conventional configuration, due to the fact that the effective screen signal period of one television signal and the horizontal synchronization signal period of another television signal overlap among the input signals, etc. A phenomenon occurs in which the amplitude of the RF multiplexed signal increases and the signal current falls below the dark value of the semiconductor laser 32, resulting in an overmodulation state. When this overmodulation occurs, the output light waveform is greatly distorted, and this distortion becomes beat noise, which causes deterioration of the image quality on the effective screen after transfer.

In view of the above circumstances, it is an object of the present invention to provide an RF multiplexed signal optical transmitter that can reduce image quality deterioration after transmission.

Means for Solving the Problems The RF multiplexed signal optical transmitter according to the invention of claim 1 is an RF multiplexed signal obtained by amplitude modulating a television signal, multi-channel frequency multiplexed, and a light source directly brightness modulated. The transmitter is characterized in that it has means for matching the generation timings of all the television signals so that the horizontal synchronization signal periods of all the television signals overlap with each other.

The RF multiplexed signal optical transmitter according to the invention of claim 3 is an optical transmitter that performs multi-channel frequency multiplexing of an RF multiplexed signal obtained by amplitude modulating a television signal and directly brightness modulates a light source. The present invention is characterized in that it includes means for differentiating the generation timings of other horizontal synchronizing signal periods so that they do not overlap each other.

According to the configuration of the invention as claimed in claim 1, the horizontal synchronizing signal periods of all television signals overlap with each other, and overmodulation occurs in this period, but this period has no direct relation to image quality. Since this is included in the blank blanking period, no deterioration in image quality occurs on the effective screen.

According to the configuration of the third aspect of the invention, the horizontal synchronization signal periods of the television signals do not overlap with each other, so deterioration of image quality is suppressed.

That is, if the horizontal synchronization signal period of one television signal overlaps with the effective screen signal period of another television signal, overmodulation will not occur on the effective screen signal period, and the horizontal synchronization signal period of the two television signals will overlap. overlap each other,
In addition, if this overlapping portion overlaps with the effective screen signal period of another television signal, overmodulation may occur on the effective screen signal period, deteriorating the effective screen, but in this case, according to this configuration, Since the horizontal synchronizing signal periods in the television signal are shifted from each other and do not overlap at least on the effective screen signal period, deterioration of the effective screen 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 an RF multiplex signal optical transmitter. In the same figure, 14... is a sync signal detection circuit that detects the sync signal of each TV signal, and 15 is a sync signal detection circuit that inputs the detection results from the sync signal detection circuit 14... and sets the amount of delay for the TV signal. 16 is a variable delay circuit that delays the generation timing of the horizontal synchronizing signal of the television signal based on the setting signal from the delay amount setting circuit 15; 17 is a variable delay circuit for delaying each television signal; This is a modulator for amplitude modulation.

The synchronization signal detection circuit 14, the variable delay circuit 16, and the modulator 17 are provided for the number of television signals (the number of channels).

18 is a mixer that mixes the RF multiplied signals obtained by modulation by the modulator 17 to produce an RF multiplexed signal, 10 is an amplifier for amplifying the RF multiplexed signal, and 12 is used to adjust the brightness by the amplified RF multiplexed signal. a semiconductor laser to be modulated;
11 is a semiconductor laser bias circuit for applying a necessary bias to drive the semiconductor laser; 13 is an optical fiber for transmitting the optical signal emitted from the conductor laser 12;

The operation of the RF multiplexed signal optical transmitter configured as described above will be described below.

A horizontal synchronization signal in the television signal of each channel is detected by a synchronization signal detection circuit 14, respectively. The delay amount setting circuit 16 sets the delay amount of the variable delay circuit 16 based on the detection timing obtained by each synchronization signal detection circuit 14 so that the horizontal synchronization signal periods of all the television signals overlap with each other.

The television signal of each channel, which has been delayed by the necessary time by the variable delay circuit 16, is amplitude-modulated by the amplitude modulator 17, converted into an RF multiplied signal, and then frequency-multiplexed by the mixer 18. The RF multiplexed signal obtained by this multiplexing is amplified by an amplifier 1o to an amplitude that can obtain the required modulation degree, and then
It is superimposed on the DC current from the semiconductor laser bias circuit 11 to become a signal current, which drives the semiconductor laser 12. The output light of the semiconductor laser 12 is transmitted to the receiver side using the optical fiber 13 as a medium.

According to the above configuration, the effective screen signal of one television signal and the horizontal synchronization signal of another television signal are prevented from overlapping. For example, in an RF multiplex signal, the maximum amplitude value during the effective screen signal period is the synchronization signal. It can be reduced to about 70% or less of the maximum amplitude of the period. This prevents the semiconductor laser 12 from becoming overmodulated.

On the other hand, since the amplitude during the horizontal synchronization signal period is maximum, the RF
In a multiplex signal, if the synchronization signal periods of all channels are the same, the amplitude of the RF multiplex signal also becomes maximum during this horizontal synchronization signal period.

Therefore, overmodulation often occurs during this synchronization signal period, but since it is a retrace period, it hardly affects the image quality of the visible effective screen.

Example 2 An embodiment of the invention according to claim 3 will be described below.

In the first embodiment, the generation timings of the horizontal synchronization signals of all television signals were made to coincide, but in this embodiment, at least on the effective screen signal period, other horizontal synchronization signal periods do not overlap with each other. The timings of their occurrence are made to differ from each other. In this case, the aforementioned synchronization signal detection circuit 14... and the variable delay circuit 16...
and, as a delay amount setting circuit, each sets the delay amount so as to make the generation timing of the horizontal synchronization signal period different from each other based on the detection timing obtained by the synchronization signal detection circuit 14. You can use

According to this configuration, since the horizontal synchronization signal periods of the television signals are shifted from each other, deterioration in image quality is suppressed.

In other words, if the horizontal synchronization signal period of one television signal overlaps with the effective screen signal period of another television signal, overmodulation will not occur on the effective screen signal period, and the horizontal synchronization signal periods of the two television signals will overlap with each other. overlap,
In addition, if this overlapping portion overlaps with the effective screen signal period of another television signal, overmodulation may occur on the effective screen signal period and deteriorate the effective screen, but in this case, according to this configuration, At least on the effective screen signal period, the horizontal synchronizing signal periods in the television signal are shifted from each other and do not overlap, so overmodulation does not occur and deterioration of the effective screen is prevented by 4 degrees.

Note that in the above embodiments, a baseband television signal is input as an input signal, and after a predetermined delay is added, the RF signal is modulated.
It is also possible to input a double signal and omit the subsequent amplitude modulator.

As described in detail, according to the present invention, it is possible to prevent the amplitude of multiplexed signals from exceeding a specified value during the effective screen period, thereby preventing deterioration of image quality after transmission. play.

[Brief explanation of the drawing]

FIG. 1 shows the present invention and is a block diagram of an RF multiplexed signal optical transmitter, and FIG. 2 shows a conventional example and is a block diagram of an RF multiplexed signal optical transmitter. 16...Variable delay circuit, mixer.

Claims (4)

[Claims] (1) In an optical transmitter that modulates the brightness of a light source directly by multichannel frequency multiplexing an RF signal obtained by amplitude modulating a television signal, the generation timing is set so that the horizontal synchronization signal periods of all television signals overlap with each other. An RF multiple signal optical transmitter, characterized in that it has means for matching each other. (2) The above matching means includes a synchronization signal detection means for detecting the horizontal synchronization signal of each television signal, a delay amount setting means for setting the delay amount of each horizontal synchronization signal from this detection result, and this setting means. 2. The RF multiplexed signal optical transmitter according to claim 1, further comprising variable delay means for delaying each horizontal synchronization signal based on a set delay amount. (3) In an optical transmitter that directly modulates the brightness of a light source by multichannel frequency multiplexing an RF signal obtained by amplitude modulating a television signal, other horizontal synchronization signal periods do not overlap with each other at least in the effective screen signal period. 1. An RF multiplexed signal optical transmitter comprising means for making the generation timings different from each other. (4) The above-mentioned differentiating means includes a synchronizing signal detecting means for detecting the horizontal synchronizing signal of each television signal, a delay amount setting means for setting the delay amount of each horizontal synchronizing signal from the detection result, and this setting means. 4. The RF multiplexed signal optical transmitter according to claim 3, further comprising variable delay means for delaying each horizontal synchronization signal based on a set delay amount.