JPH0817347B2 - RF multiple signal optical transmitter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF multiple signal optical transmitter that optically transmits an RF multiple signal by a light source such as a semiconductor laser.

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

In FIG. 2, 34 ... Is a modulator for amplitude-modulating each television signal, and 35 is an RF obtained by being modulated by the modulator 34.
A mixer for mixing signals into an RF multiplex signal, 30 an amplifier for amplifying the RF multiplex signal, 32 a semiconductor laser to be brightness-modulated by the amplified RF multiplex signal, 31 a semiconductor laser 32 A semiconductor laser bias circuit for applying a necessary bias for driving the
It is an optical fiber that transmits the optical signal emitted from the optical fiber.

Therefore, in the above RF multiple signal optical transmitter, the input multi-channel television signals are directly transmitted to the modulator 34.
, And becomes an RF multiplex signal through the mixer 35, and the amplifier
DC current (bias current) from the semiconductor laser bias circuit 31 after being amplified to an amplitude that can obtain the required modulation degree at 30
Is superimposed on The semiconductor laser 32 is brightness-modulated by the superimposed signal current, and the semiconductor laser 32 is driven.
The output optical signal from the optical fiber is propagated to the receiving side through the optical fiber 33 as a transmission path.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described conventional configuration, in the input signals, due to the overlap of the effective screen signal period in one TV signal and the horizontal synchronization signal period in another TV signal, The phenomenon that the signal current becomes lower than the threshold value of the semiconductor laser 32 due to the increase in the amplitude of the RF multiplex signal occurs, resulting in an overmodulation state. In this overmodulation state, the output light waveform is largely distorted, and this distortion becomes beat noise, which causes deterioration of the image quality on the effective screen after transmission.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an RF multiplex signal optical transmitter capable of reducing deterioration of image quality after transmission.

An RF multiplex signal optical transmitter according to the invention of claim 1 is an optical device for directly brightness-modulating an RF signal obtained by amplitude-modulating a television signal by multi-channel frequency multiplexing. The transmitter is characterized by having means for making the generation timings coincide with each other so that the horizontal synchronizing signal periods of all television signals overlap each other.

An RF multiplex signal optical transmitter according to the invention of claim 3 is an optical transmitter for directly luminance-modulating a light source by multi-channel frequency-multiplexing an RF signal obtained by amplitude-modulating a television signal, and at least an effective screen signal. It is characterized in that it has means for making the generation timings different from each other so that the other horizontal synchronization signal periods do not overlap each other during the period.

According to the configuration of the invention of claim 1, the horizontal synchronizing signal periods of all television signals overlap each other, and overmodulation occurs in this period, but this period is directly related to the image quality. Since it is included in the blanking period, the image quality does not deteriorate on the effective screen.

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

That is, when the horizontal synchronization signal period in one television signal overlaps with the effective screen signal period in another television signal, overmodulation does not occur in the effective screen signal period, and the horizontal synchronization signal periods in the two television signals are mutually Overlapping, and when this overlapping portion overlaps with the effective screen signal period in another TV signal, overmodulation occurs in the effective screen signal period, which may deteriorate the effective screen.
In this case, according to the present configuration, the horizontal sync signal periods of the television signal are displaced from each other and do not overlap each other at least on the effective screen signal period, so that the effective screen is prevented from being deteriorated.

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

FIG. 1 is a block diagram showing an RF multiple signal optical transmitter. In the figure, 14 is a sync signal detection circuit for detecting the sync signal of each television signal, and 15 is a delay for inputting the detection results from the sync signal detection circuit 14 and setting delay amounts for the television signals respectively. Amount setting circuit, 16 ... 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, and 17 ... A modulator for amplitude-modulating each television signal. is there.

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

18 is a mixer that mixes the RF signals obtained by being modulated by the modulator 17 into an RF multiplex signal, 10 is an amplifier for amplifying the RF multiplex signal, 12 is brightness-modulated by the amplified RF multiplex signal A semiconductor laser to be obtained, 11 is a semiconductor laser bias circuit for applying a necessary bias for driving the semiconductor laser, and 13 is an optical fiber for transmitting an optical signal emitted from the conductor laser 12.

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

The horizontal sync signal in the TV signal of each channel is
Each is detected by the synchronization signal detection circuit 14. The delay amount setting circuit 16 sets the delay amounts of the variable delay circuits 16 based on the detection timings obtained by the respective sync signal detection circuits 14 so that the horizontal sync signal periods of all television signals overlap each other.

The television signal of each channel delayed by the variable delay circuit 16 by a required time is amplitude-modulated by the amplitude modulator 17 into an RF signal, and then frequency-multiplexed by the mixer 18. The RF multiplexed signal obtained by this multiplexing is amplified by the amplifier 10 to an amplitude capable of obtaining a required modulation degree, and then superimposed on the direct 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 through the optical fiber 13 as a medium.

According to the above configuration, the overlap between the effective screen signal in one TV signal and the horizontal synchronizing signal of the other TV signal is prevented, and, for example, in the RF multiplex signal, the maximum value of the amplitude in the effective screen signal period is the synchronizing signal. It can be reduced to about 70% or less of the maximum amplitude of the period. This prevents the semiconductor laser 12 from being overmodulated.

On the other hand, the amplitude of the horizontal sync signal period is maximum, so RF
In the multiplex signal, if the synchronization signal periods of all channels are synchronized, the amplitude of the RF multiplex signal also becomes maximum in this horizontal synchronization signal period. Therefore, in this synchronizing signal period, overmodulation often occurs, but since it is a retrace line period, it has little influence on the image quality of the visible effective screen.

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

In the first embodiment, the generation timings of the horizontal synchronizing signals of all television signals are made to coincide with each other, but in the present embodiment, other horizontal synchronizing signal periods do not overlap each other at least on the effective screen signal period. The generation timings are different from each other. In this case, the horizontal sync signal period is provided based on the detection timing obtained by the sync signal detection circuit 14 ... As a delay amount setting circuit, including the sync signal detection circuit 14 ... And the variable delay circuit 16 ... The delay amounts may be set so that the occurrence timings of the delay times are different from each other.

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

That is, when the horizontal synchronizing signal period in one TV signal overlaps with the effective good screen signal period in another TV signal, overmodulation does not occur in the effective screen signal period, and 2
When the horizontal sync signal periods in one television signal overlap each other and the overlapping portion overlaps with the valid screen signal period in another television signal, overmodulation may occur in the valid screen signal period to deteriorate the valid screen. But
In this case, according to this configuration, the horizontal synchronization signal periods in the television signal are displaced from each other and do not overlap each other at least in the effective screen signal period, so that overmodulation does not occur and deterioration of the effective screen is prevented. Will be.

In the above embodiments, a baseband television signal is input as an input signal and is modulated into an RF signal after adding a predetermined delay.However, an amplitude-modulated RF signal is input as an input signal, and a subsequent amplitude is input. The modulator may be omitted.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to prevent the amplitude of the multiplexed signal from exceeding a specified value during the effective screen period, and thus it is possible to prevent the deterioration of the image quality after transmission. Play.

[Brief description of drawings]

FIG. 1 shows the present invention, a block diagram of an RF multiple signal optical transmitter, and FIG. 2 shows a conventional example.
It is a block diagram of an RF multiple signal optical transmitter. 10 ... Amplifier, 11 ... Semiconductor laser bias circuit, 12 ...
… Semiconductor laser, 13 …… Optical fiber, 14 …… Sync signal detection circuit, 15 …… Delay amount setting circuit, 16 …… Variable delay circuit,
17 …… Amplitude modulator, 18 …… Mixer.

Claims (4)

[Claims] 1. An optical transmitter for directly luminance-modulating a light source by multi-frequency-multiplexing an RF signal obtained by amplitude-modulating a television signal, and generating the horizontal synchronizing signal periods of all television signals so that they overlap each other. An RF multiplex signal optical transmitter having means for matching timings with each other. 2. The matching means includes a sync signal detecting means for detecting a horizontal synchronizing signal of each television signal, a delay amount setting means for setting a delay amount of each horizontal synchronizing signal from the detection result, and this setting. 2. The RF multiple signal optical transmitter according to claim 1, further comprising variable delay means for delaying each horizontal synchronizing signal based on the delay amount set by the means. 3. An optical transmitter for directly luminance-modulating a light source by multi-channel frequency-multiplexing an RF signal obtained by amplitude-modulating a television signal, wherein other horizontal synchronizing signal periods are mutually mutually at least on an effective screen signal period. An RF multiplex signal optical transmitter having means for making generation timings different from each other so that they do not overlap. 4. The differentiating means is a sync signal detecting means for detecting a horizontal synchronizing signal of each television signal, a delay amount setting means for setting a delay amount of each horizontal synchronizing signal from the detection result, and this setting. 4. The RF multiple signal optical transmitter according to claim 3, comprising variable delay means for delaying each horizontal synchronizing signal based on the delay amount set by the means.