JPH0465931A - Optical catv transmitter - Google Patents

Abstract

PURPOSE:To confirm and adjust picture quality based on modulation of an LD module by monitoring and evaluating a CATV signal extracted through a photodiode at a sender side. CONSTITUTION:Part of an optical output of an LD 6 subjected to intensity modulation with a CATV signal directly inputted to an LD drive circuit 4 is sent to a receiver side through a fiber cable 14, the other output is subjected to photoelectric conversion by a PD 37 and the signal is inputted to an amplifier by a filter connecting to the PD 37. Then the signal is amplified to a proper level and the level is adjusted by an attenuator via a matching circuit and outputted from a monitor terminal 40. On the other hand, an APC signal for automatic light output control through a coil is inputted to an APC circuit 8, in which the signal is controlled so that the optical output of the LD 6 is made constant. Thus, the CATV signal is detected from an LD module 5 by connecting a circuit separating and outputting the CATV and an APC signal to the PD 37.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical transmission device for a CATV system that electrically/optically exchanges multi-channel CATV signals and transmits them through optical fibers.

Conventional technology In recent years, the urban CAT system (which has become popular nationwide) is being planned for large-scale, even higher-quality television broadcasting, and gradually multi-channel broadcasting and simultaneous (long-distance) In order to cope with this situation, there is a need for a center-sub-center system that is easy to maintain and improves image quality during long-distance transmission. In response, the long-distance transmission section of the trunk line between Tun and the center (this optical CATV transmission equipment is used,
at the site (adjusted and set to the best operation suitable for the transmission path with z).

Without referring to the drawings below, the above-mentioned conventional optical CATV
An example of a transmission device will be described. Figure 3 shows a configuration diagram of an optical CATV transmission device in a conventional CTV system, in which the optical transmitting part and the pre-receiving part are connected with an optical fiber cable, and each main part that transmits images is divided into blocks. It is.

In FIG. 3, reference numeral 1 denotes a front end, which sends a multi-channel CATV signal to the forwarding section. 2 is a variable attenuator to set the CATVI signal from Radend 1 to an arbitrary level. 3 is an amplifier, and 4 is a LDIIK operating circuit that performs impedance matching for CATV signals and automatic optical output control (hereinafter referred to as APC). A current drive of a laser diode (hereinafter referred to as LD) 6 is performed by a circuit 8 (hereinafter referred to as LD).

5 is an LD module; LD 6. Photodiode (hereinafter referred to as PD)7. Thermistor9. A Bertier element 10 is built in, and the output of the PD 7 is input to an APC circuit 8. 1
1 is an automatic temperature control 1t (ATC) circuit, and thermistor 9
The temperature of the Bertier element 10 is controlled by the output signal. 1
An optical fiber 2 is optically coupled to the LD 6 and is connected to an optical fiber cable 14 via an optical connector 13.

21 is an optical connector connected to the optical fiber cable 14 on the receiving side; 22 is a PD that converts an optical CATV signal into an electrical signal; 23 is a bias/matching circuit; 24 is an amplifier;
5 is a variable attenuator, and 26 is a signal distributor, which are connected in this order.

27 is a sending terminal to the CATV main line, and 28 is a signal monitor terminal.

The operation of the optical CATV transmission apparatus configured as described above will be described below.

First, CATV signals (including data signals) sent from the head end 1 are transmitted through the variable attenuator 2 of the optical transmission section.
The signal level passing through the subsequent amplifier 3 and LD driving circuit 4 is set to a level suitable for direct brightness modulation of the LD 6. The optical CATV signal electrically/optically converted by the LD 6 is connected to the optical connector 13 through the fiber 12 coupled to the LD 6 to form an optical transmitter. This is the optical transmitter that constitutes the transmitter side. An optical fiber cable 14 is connected to the optical connector 13 of the optical transmitter, and the optical CATV signal is transmitted to a remote receiver.

In the receiving section, the optical fiber cable 14 is connected to the optical connector 21 of the receiver, undergoes optical/electrical conversion by the PD 22, and is efficiently connected to the amplifier 24 through the bias matching circuit 23.
The output is set to an appropriate level by a variable attenuator 25, and a signal is distributed by a signal distributor 26, one to the transmission terminal 27 of the trunk system and the other to the monitor terminal 28 of the receiving section. The degree of modulation for modulating the brightness of the LD 6 and the received image quality of the transmitted CATV signal are evaluated by connecting the monitor terminal 28 to a TV set or via a CATV converter.

Invention or problem to be solvedHowever, optical CATV installed in the above-mentioned field situation
In a transmission device, the image quality is evaluated on the receiving side, and depending on the condition, the transmitting side adjusts the modulation degree of the LD, that is, the input level of the CATV signal using a variable attenuator. On the receiving side, it is difficult to make detailed judgments, and both the transmitting and receiving sides require at least 2 Å or more, and the adjustment is troublesome and time-consuming.

In view of the above-mentioned problems, the present invention provides an optical cATV that can easily set the modulation degree of LD accurately and without wasting time.
The purpose is to provide a transmission device.

Means for Solving the Problems In order to solve the above problems, the optical CATV transmission device of the present invention has an AP on the photodiode built in the LD module.
Connect the circuit that separates and outputs the C signal and CATV signal,
It is designed to extract CATV signals.

Operation With the above configuration, by monitoring and evaluating the CATV signal extracted through the photodiode on the transmitting side,
Image quality can be checked and adjusted at the same time based on the modulation degree of the LD module.

Embodiment Hereinafter, an optical CATV transmission apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram showing an optical transmission section of an optical CATV apparatus in an embodiment of the present invention, and parts having the same functions as those in FIG. 3 are given the same reference numerals, and detailed explanations are omitted. In FIG. 1, 37 is a PD built into the same housing of the LD module 5 together with the LD 6, and outputs an APC signal and a CATV signal. 30 is a modulation signal monitor circuit connected to the PD 37 and also connected to the APC circuit 8. 40 is an output terminal of the modulation signal monitor circuit 30;
Mo.

Outputs the CATV signal from Neil 5.

FIG. 2 is a block diagram showing the configuration of the modulated signal monitor circuit 30 of FIG. 1. 31 is a capacitor connected to the PD 37, 32.33 is a coil and a capacitor further connected in series to the PD 37, and the capacitor 31, the coil 32. The capacitor 33 constitutes a filter,
Coil 32 is connected to APC circuit 8. 34 is an amplifier, 35 is a matching circuit, and 36 is a variable attenuator, which are connected in series to the capacitor 31, and whose output is connected to the monitor terminal 40.

The operation of the transmitting section of the optical CATV transmission apparatus configured as described above will be explained below with reference to FIGS. 1 and 2. First, a CATV signal sent out from a head end 1 is input to an amplifier 3 via a variable attenuator 2. The CATV signal output from the amplifier 3 is input to the LD drive circuit 4. The operation up to this point is the same as the conventional example shown in FIG. L
Since the CATV signal input to the D drive circuit 4 is superimposed on the LD bias current, the luminance of the light emitted from the LD 6 is directly modulated by the CATV signal, and electrical/optical conversion is performed. CA
The optical output of the LD 6, which has been directly luminance-modulated with the TV signal, is guided to the fiber 12 and the PD 37, the former is relayed through the connector 13, and sent out to the receiving side through the fiber cable 14. The latter is optically/electrically converted by the PD 37, and is connected to the capacitor 31. coil 32
．． The filter made up of the capacitor 33 allows the CAT
The V signal is input to the amplifier 34, amplified to an appropriate level, passed through the matching circuit 35, level-adjusted by the attenuator 36, and output from the monitor terminal 40. On the other hand, coil 32
An APC signal for automatically controlling the light output passing through the LD 6 is input to the APC circuit 8, and is controlled so that the light output of the LD 6 is constant.

As described above, according to this embodiment, the PD 37 built in the LD module 5 separates the CATV signal and the APC signal.
By connecting the output circuit, CAT can be transmitted from the LD module 5 without affecting the optical output of the LD 6.
V signal can be detected.

Results of the first invention As described above, according to the present invention, a circuit for separating and outputting a CATV signal and an APC signal is provided on the device side of an optical CATV transmission device and is connected to a PD built in an LD module.
Since the CATV signal and APC signal are extracted from this PD, the state of the optical CATV signal output from the LD can be directly monitored and evaluated on the transmitting side, making it easy to set the variable attenuator that adjusts the modulation degree of the LD. This eliminates the need to monitor and adjust the status of the receiving side at a remote location, as was the case in the past, and allows for accurate installation in a short time.

[Brief explanation of drawings]

North Fig. 1 is a block diagram of an optical transmitter of a CATV transmission device according to an embodiment of the present invention, Fig. 2 is a block diagram of a modulated signal monitor circuit in the same optical transmitter, and Fig. 3 explains the operation of a conventional example. FIG. 2 is a configuration diagram of an optical CATV transmission device of a CATV system. l...Head end, 2...Variable attenuator, 4...
LD drive circuit, 5...LD module, 6...LD
, 8...APC circuit, 30...Modulation signal monitor circuit, 37...PD0 representative Morimoto
Yoshihiro 5... LD side one rule - LD B - APC circuit 30 -... Memoir of the Sergeant's Detective Monitor, 37... P-p Fig. f

Claims (1)

[Claims] 1. Photodiode and CATV for automatic light output control
Optical C having a laser module in which a laser diode whose brightness is directly modulated by a signal is built into the same housing.
An ATV transmission device, wherein the photodiode is provided with a CA
An optical CATV transmission device configured to connect and provide a circuit for separating and outputting a TV signal and a signal for automatic optical output control, and to extract an automatic optical output control signal and a CATV signal from the photodiode.