JPH05252518A - Catv light transmitter - Google Patents

Abstract

PURPOSE:To hold a stable picture quality by providing a circuit separating a CATV signal from an automatic light output control signal on a photodiode, detecting the extracted CATV signal, converting it into a control signal, and performing an automatic modulation control. CONSTITUTION:An APC (automatic light output control) signal and the CATV signal are outputted from a PD(photodiode) 31 integrated in the same casing of an LD module 5 with an LD (laser) 6. Then, the signals are separated to a signal processing circuit 32 and an APC circuit 8 by a signal separator circuit 30 to be connected. The CATV signal is amplified, detected, and the level is adjusted by the signal processing circuit 32, and an electronic variable attenuation circuit 34 is controlled by the detection signal so that the input level of the LD can be controlled. On the other hand, the signal for the APC is controlled by the APC circuit 8 so that the light output of the LD can be fixed. Thus, not only the fluctuation of the level of the CATV signal inputted to a transmission part, but also the modulation of the LD including the fluctuation of the LD or the like can be controlled.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a multi-channel CATV.
CA that converts signal to electric / optical and transmits by optical fiber
The present invention relates to a TV optical transmission device.

[0002]

2. Description of the Related Art In recent years, a large-scale urban CATV system, which is remarkably popular throughout the country, is planned for high-definition television broadcasting and the like. Has been. To cope with such a situation, in order to improve maintainability and improve image quality during long-distance transmission, long distances such as trunk lines between centers and sub-centers, or between receiving points and centers, etc. An optical transmission device is used in the transmission section, and is adjusted and set to the best operation on the transmission line in the field.

A conventional CATV optical transmission device will be described below with reference to the drawings. As shown in FIG. 3, the conventional CATV optical transmission device includes an optical transmitter 50 and an optical receiver 5.
1 is an image transmission system in which 1 is connected by an optical fiber cable 14. Then, from the headend 1 to the optical transmitter 50
The multi-channel CATV signal is sent to the. Further, the CATV signal from the head end 1 is set to an arbitrary level by the variable attenuator 2, amplified by the amplifier 3, and then, in the laser (hereinafter referred to as LD) drive circuit 4, impedance matching to the CATV signal and automatic optical output control (hereinafter The current drive of the LD 6 is performed by the circuit 8 called APC. L
The D module 5 includes an LD 6, a photodiode (hereinafter P
D) 7, a thermistor 9 and a Peltier element 10 are built in and connected to an automatic temperature control (ATC) circuit 11, and the temperature inside the LD module 5 is controlled to be constant.
The output from the PD 7 is input to the APC circuit 8, and the optical output from the LD 6 passes through the optical fiber 12 which is optically coupled and is output to the optical fiber cable 14 via the optical connector 13. In the receiver 51, an optical connector 21 connected to the optical fiber cable 14, a PD 22 for converting an optical CATV signal into an electric signal, a bias / matching circuit 23, an amplifier 2
4, a variable attenuator 25, a signal distribution circuit 26, and C
The signal is output from the transmission terminal 27 to the ATV main line. The signal monitor terminal 28 is an output terminal for monitoring.

With respect to the CATV optical transmission device having the above components, the relationship and operation of the components will be described below. First, the CATV signal (including the data signal) sent from the headend 1 is directly brightness-modulated by the variable attenuator 2 of the optical transmitter 50 by the variable attenuator 2 so that the signal level of the signal passes through the subsequent amplifier 3 and LD drive circuit 4. Is set to an appropriate level. The CATV optical signal converted from light to light by the LD 6 is connected to the optical connector 13 by the optical fiber 12 coupled to the LD 6 to form an optical transmitter. The operation up to this point is the optical transmission unit 50 that constitutes the transmission side. The optical fiber cable 14 is connected to the optical connector 13 of the optical transmitter, and the optical CATV signal is received by the receiver 51 at a remote place.
Be transmitted to. In the receiving side portion 51, the optical fiber cable 14 is connected to the optical connector 21 of the receiving portion, is optically / electrically converted by the PD 22, is efficiently input to the amplifier 24 through the bias / matching circuit 23, and its output is appropriate by the variable attenuator 25. The signal distribution circuit 26 distributes the signal to one of the trunk-system sending terminals 27 and the other to the receiving section monitor terminal 28. And LD
Degree of modulation for direct intensity modulation of 6 and transmitted CATV
The received image quality of the signal is evaluated by connecting the monitor terminal 28 to a television receiver or a television receiver via a CATV converter.

[0005]

However, in the above-described conventional configuration, in the optical transmission device installed in the field situation, the adjustment is performed by inputting the CATV signal into the optical transmission unit and converting the optical fiber into E / O in the optical transmission unit. The image quality is evaluated by O / E conversion in the optical receiver which is transmitted to the receiving side by the cable. Depending on the image state, the modulation degree of the LD forming the optical transmitter,
That is, the level of the CATV signal input to the LD is adjusted, and the image is set to have the best image in terms of C / N and distortion (CSO, CTB, XM). However, environmental changes and CATV signal transmission equipment (headend)
The level of the CATV signal may fluctuate depending on the stability of the signal. However, when the level of the CATV signal input to the transmitter, that is, the LD, changes, the modulation degree of the LD changes, and the image quality changes and deteriorates. Ie C /
Degradation of N, beat interference due to distortion, intermodulation interference and the like occur. Therefore, the modulation degree of the LD is set small in advance so that the change in the modulation degree of the LD does not significantly deteriorate the image quality. As a result, the C / N is sacrificed, the performance of the LD cannot be fully utilized by the conventional method, and the change in the modulation factor due to the long-term fluctuation of the LD is not taken into consideration. Had.

An object of the present invention is to solve the above-mentioned conventional problems, and an object thereof is to provide a CATV optical transmission device which maintains stable image quality even when the level of a CATV signal changes and the LD changes.

[0007]

In order to achieve the above object, a CATV optical transmission apparatus of the present invention is provided with a circuit for separating an APC signal and a CATV signal in a PD incorporated in an LD module to extract the CATV signal, It has a configuration in which this is detected and converted into a control signal for automatic modulation degree control.

[0008]

According to the present invention, it is possible to prevent the deterioration of the image quality due to the change of the modulation degree due to the change of the level of the CATV signal and the change of the LD in the above-mentioned structure, and it is possible to maintain the stable image quality.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, in the optical transmitter of the CATV optical transmission apparatus of this embodiment, the same components as those of the conventional example shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, from the PD 31 incorporated in the same housing of the LD module 5 together with the LD 6 to the AP
It outputs a C signal and a CATV signal. The signal separation circuit 30 connected to the PD 31 is separately connected to the signal processing circuit 32 and the APC circuit 8, and the signal processing circuit 32 is connected to the electronic variable attenuation circuit 34.

Next, the configurations of the signal separation circuit 30 and the signal processing circuit 32 will be described in more detail with reference to FIG. P
The capacitor 35, the coil 36, and the capacitor 37 connected to D31 form the signal separation circuit 30 of the low-pass filter, and the coil 36 is connected to the APC circuit 8. The signal processing circuit 32 is composed of an amplifier 38, a bandpass filter (abbreviated as BPF) circuit 39, a detection circuit 40, and a level setter 41, and its output is an electronic variable attenuation circuit 34.
It is connected to the.

With respect to the transmitting section of the CATV optical transmission apparatus having the above components, the relationship and operation of each component will be described below with reference to FIGS. First, as shown in FIG. 1, the CATV signal transmitted from the head end 1 is input to the amplifier 3 via the electronic variable attenuation circuit 34. Amplifier 3
The CATV signal amplified by is input to the LD drive circuit 4. The CATV signal input to the LD drive circuit 4 is L
Since it is superimposed with the D bias current, the light emission of the LD 6 is CAT.
Intensity modulation is directly performed by the V signal, and electrical / optical conversion is performed. The optical signal of the LD6 directly brightness-modulated by the CATV signal is introduced into the optical fiber 12 and the PD 31, respectively,
Optical fiber cable 14 relayed by optical connector 13
Is sent to the receiving side. The above operation is the same as that of the conventional example shown in FIG. 3, but the low-pass filter of the capacitors 35 and 37 and the coil 36, which is optically / electrically converted by the newly provided PD31 and connected to the PD31 as shown in FIG. The signal separation circuit 30 composed of
The V signal is input to the amplifier 38, amplified to an appropriate level, detected by the detection circuit 40 through the bandpass circuit 39, adjusted in level by the level setter 41, and led out to the electronic variable attenuation circuit 34. While coil 3
The signal for APC passing through 6 is input to the APC circuit 8 and controlled so that the optical output of the LD becomes constant.

As described above, according to the present embodiment, the CATV signal and the APC are sent to the PD 31 built in the LD module 5.
By providing the circuit for separating the signals, the CATV signal can be detected from the LD module 5 without affecting the optical output of the LD 6.

[0015]

As is apparent from the above embodiments, according to the present invention, a circuit for separating the CATV signal and the APC signal and outputting the separated signals is connected to the PD incorporated in the LD module in the transmitting section of the CATV optical transmission device. Established, CAT from this PD
The CAT input to the transmission unit in order to extract the V signal and the APC signal, detect the CATV signal, and control the electronic variable attenuation circuit by the detected signal to control the input level of the LD.
It is possible to realize an excellent CATV optical transmission device capable of maintaining stable image quality, because not only the fluctuation of the level of the V signal but also the modulation degree of the LD including the fluctuation of the LD is controlled. Is.

[Brief description of drawings]

FIG. 1 is a block diagram of a CATV optical transmission device according to an embodiment of the present invention.

FIG. 2 is a detailed block diagram of a signal separation circuit and a signal processing circuit in the device.

FIG. 3 is a block diagram of a conventional CATV optical transmission device.

[Explanation of symbols]

 4 LD drive circuit 5 LD module 6 LD (laser diode) 8 APC (automatic optical output control) circuit 30 signal separation circuit 31 PD (photodiode) 32 signal processing circuit

Claims (1)

[Claims] 1. A laser module in which a laser diode directly brightness-modulated by a CATV signal and a photodiode for automatic light output control are incorporated in the same housing, and a CATV signal and automatic light output control are provided to the photodiode. A circuit for separating and outputting the signal to be performed and a driving circuit for controlling the modulation degree of the laser diode are connected and provided, and a CATV signal and an automatic optical output signal are extracted from the photodiode, and the CATV signal modulates the laser diode. A CATV optical transmission device arranged so as to control a drive circuit for power control.