JPS60263540A - Monitor system of ld bias current - Google Patents

Abstract

PURPOSE:To attain an easy remote monitor for the LD bias current information by driving a laser diode LD with the modulation of amplitude given to a pre- modulated pulse train by the output of a VCO having its frequency changed by the bias current signal of the LD. CONSTITUTION:The input data signal is converted into a pulse train PFM having a repetitive frequency proportional to the amplitude of the input data signal through a PFM modulation circuit 12 and supplied to an amplitude modulation circuit 13. The circuit 13 gives the modulation of amplitude to the pulse train supplied from the circuit 12 with the signal given from a VCO17 whose frequency is varied by an LD bias current 16 supplied to an LD module 15. The output signal of this modulation drives the module 15 via an LD driving circuit 14. Thus the electrical signal is converted into the optical signal and sent to an optical fiber 20. A light reception part 30 converts 31 the input optical signal into the electrical signal and supplied to a limiter circuit 33 and an envelope curve detection circuit 35 after amplification 32. The signal underwent the fixed amplitude receives PFM demodulation 34 through the circuit 33 and the data signal is delivered. The circuit 35 detects the frequency of the VCO17 and converts 36 it into the voltage to obtain the LD bias current information.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention includes two light emitting elements including a semiconductor laser diode (hereinafter referred to as
In an optical transmission device using a LD (abbreviated as LD), Guiasmi flow information of the LD used in the opposing, distant optical transmitter is transmitted to a monitoring station on the optical receiver side, and the bias current information is transmitted to the monitoring station on the optical receiver side. Concerning how to monitor remotely.

Generally, in an optical transmission device that uses LDs as two light emitting elements, the optical output power is controlled to be constant by increasing or decreasing the bias current value of the LDs. for example.

When the light output power decreases due to deterioration of the LD, the bias current is increased to control the light output to a constant level. Therefore, by monitoring the LD bias current value, the operating state of the LD can be grasped.

[Conventional technology]

Conventionally, as a method for transmitting this LD bias current information to a monitoring station on the optical receiver side, there are two methods: (1) transmitting an LD bias alarm to the monitoring station when the LD bias current value reaches a predetermined limit value;

■The LD bias current value is controlled by a voltage controlled oscillator (hereinafter referred to as

A method is known in which the oscillation frequency is converted into an oscillation frequency proportional to the bias current value (abbreviated as VCQ) and transmitted to a monitoring station. In both methods (1) and (2), the LD bias current information is transmitted using an intervening pair within the optical fiber cable transmission line or a metallic transmission line attached to the optical fiber transmission line.

[Problem that the invention seeks to solve]

Therefore, in the conventional LD bias current information transmission method as described above, in the case of an optical fiber cable transmission line without an intervening pair, or when there is no parallel metallic line, the L
There is a drawback that D bias current information cannot be transmitted. Also,
Even with the above-mentioned intervening pairs and metallic lines, long-distance transmission is impossible. Additionally, it is easy to consider a method of transmitting LD bias current information using a light source and optical fiber transmission line separate from those used for transmitting data information, but this method would be uneconomical. There is a drawback.

[Failure to solve the problem]

In the LD bias current monitoring method according to the present invention, the input data signal is a pulse 'train premodulated on the time axis of ie pulses.
In an optical transmission device that transmits data information by driving D, on the optical transmitter side.

A VCO that converts an LD bias current value (voltage) into an oscillation frequency proportional to the voltage, and an amplitude modulation circuit that amplitude modulates the premodulation pulse train using an output signal of the VCO, and an output signal of the amplitude modulation circuit. By driving the LD with fi, the LD bias current information is multiplexed with the data information and transmitted to the optical receiver side (monitoring station side)-N.

In addition, on the optical receiving unit side (monitoring station side), the pulse train received via the optical fiber cable transmission line is envelope-detected and further converted into stain pressure information by a demodulator (frequency-voltage conversion circuit). Then, the LD bias current value at a far location (on the optical transmitter side) can be monitored in real time.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to two drawings.

FIG. 1 shows the present invention using pulse frequency modulation (hereinafter referred to as "pulse frequency modulation").

An example of the application to the PFM (abbreviated as PFM) method is shown in a block diagram.
A specific waveform example of part 0 is shown.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2.

The input data signal input from the data input terminal 11 to the optical transmitter 1o is processed by the PFM modulator 12 into a pulse train having a repetition frequency proportional to the amplitude of the input data signal, as shown in FIG. (below.

(abbreviated as PFM pulse train). The amplitude modulation circuit 13, as shown in FIG. The output signal ■ is used to drive the LD module 15, and the electrical signal is converted into an optical signal.

Here, the LD module 15 has a built-in monitor for monitoring optical output, and an LD bias current control circuit 161'i.
, monitors the monitor and increases/decreases the LD bias current value so that the optical output of the LD module 5 becomes constant. VCO17
is the L output from the LD bias current control circuit 16
A DZ Iasumi current value (voltage) is input, and an oscillation frequency proportional to this voltage is supplied to the amplitude modulation circuit 13. Therefore, the optical signal output from the optical transmitter 10 has the LD bias current information multiplexed with the data information.

The optical signal output from the optical transmitter 10 is transmitted through the optical fiber cable transmission line 20 and is sent to the optical receiver (monitoring station).
Received at 30.

In the monitoring station 30, first, an optical-to-electrical conversion element (for example, an avalanche photodiode (hereinafter abbreviated as APD)) is installed.
) 31, the optical signal is converted into an electrical signal, and the electrical signal is amplified by an amplifier 32 to produce the same signal waveform as the output signal (■) of the amplitude modulation circuit 13, as shown in FIG. 2 (■). is obtained.

The output signal (■) of the amplifier 32 is made constant in amplitude by the limiter circuit 33, as shown in FIG.
The demodulation circuit 34 obtains an output data signal that is the same as the original input data signal, and outputs it from the data output terminal 37. On the other hand, the envelope detection circuit 35 reproduces the amplitude modulation component of the output signal of the amplifier 32, as shown in FIG. The output signal (■) of the line detection circuit 35 is sent to the LD bias current control circuit 1 by the two-frequency/voltage conversion circuit 36.
6 is converted into the same voltage as the bias current value (voltage) outputted from LD bias current information output terminal 38 .

〔Effect of the invention〕

As explained above, according to the present invention, the opposing LD bias current information is multiplexed into a PFM pulse train and transmitted without using intervening lines or metallic lines, so that it can be easily and economically transmitted over long distances. This has the effect of allowing monitoring.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the LD bias current monitoring method according to the present invention, and FIG. 2 is a waveform diagram showing examples of signal waveforms at various parts in FIG. 10... Optical transmitter, 11... Data input terminal, 12
... PFM modulation circuit, 13 ... amplitude modulation circuit, 14
...LD drive circuit, 15...LD module, 16.
...LD bias current control circuit, 17. ... Voltage controlled oscillator (VCO), 20... Optical fiber cable transmission line. 30... Optical receiving unit (monitoring station), 31... Optical/electric conversion device (APD), 32... Amplifier, 33...
limiter circuit. 34...PFM demodulation circuit, 35...Envelope detection circuit. 36... Frequency/voltage conversion circuit, 37... Data output terminal, 38... LD pieanu current information output terminal.

Claims (1)

[Claims] 1. In the Noculus premodulation optical transmission system in which data information is transmitted by driving a semiconductor laser diode with a somewhat pulse train in which the input data signal is premodulated on the time axis of Noculus, a voltage controlled oscillator whose oscillation frequency is changed by a bias current signal of the semiconductor laser diode;
an amplitude modulation circuit that amplitude modulates the pre-modulated pulse train with the output of the voltage controlled oscillator, and drives the semiconductor laser diode with the output of the amplitude modulation circuit;
An LD bias current monitoring method characterized in that bias current information of the semiconductor laser diode is multiplexed with the data information and transmitted. Below margin