SU1501257A1 - Device for converting electric signals into optical signals - Google Patents

Abstract

The invention relates to electrical engineering. The purpose of the invention is to increase the stability of operation in a wide range of temperature variations. The device contains a laser diode 1, a feedback photodiode 2, an operational amplifier 3, a regulating transistor (T) 4, resistors 5 and 7, T 6, a thermo-dependent voltage source 8, made on T 10 and 11, a resistive voltage divider made resistors 12 and 13. With continuous overload, the device operates in the stabilization mode of the current of the laser diode 1 due to an electric negative feedback circuit: T 6 - T 10 and 11 - resistor 12. At the same time, the resistance value of resistor 12 is chosen such that communication did not exceed one us The goal is achieved by protecting the laser diode 1 from beatings over a wide temperature range. 3 il.

Description

SP

0 / L.

JV

(jjue.i

315P

The invention relates to electrical engineering and can be used in electronic circuits of transmitting modules of fiber-optical communication lines.

The purpose of the invention is to increase the stability of operation over a wide range of temperature variations.

Figure 1 is a circuit diagram of a device for converting electrical signals into optical signals; Fig. 2 illustrates the principle of an electrical circuit of one of the implementations of a thermodependent voltage source; FIG. 3 shows a watt-ampere characteristic of a laser diode.

A device for converting electrical signals into optical signals comprises an input laser diode 1, a feedback photodiode 2, an operational amplifier 3, a control transistor 4, a resistor 5, an additional resistor 7, a thermo-dependent voltage source 8, a current reflector 9 made on transistors 10, 11 , resistive voltage divider, made on resistors 12, 13.

A device for converting electrical signals to optical works as follows.

In normal operation, polo. The operating point on the watt-ampere characteristic of the laser diode (Fig. 3) will be determined by the conversion ratio of the current of the laser diode 1 to the current of the photodiode 2, the resistance of the resistors 12 and 13 and the voltage on the non-inverting input of the operational amplifier 3, and condition.

1, (T)

+ V

ev (o

, I - working voltage and A A,

laser diode current 1,

respectively; R is the resistance of the additional resistor 7 V (T) is the voltage of the thermal-dependent voltage source 8

- emitter voltage - base of additional transistor 6.

In this mode, the entire current regupire of the transistor 4 flows through the laser diode 1, while the transistor 6

closed, and the transistors 10 and 11 of the current reflector 9 are not involved in the operation of the circuit. When the laser diode 1 reaches the maximum permissible value that corresponds to the maximum permissible optical power, condition (1) stops expiration, while transistors 6 and 10 open and the further current increase through laser diode 1 is limited. With a long overload, the circuit operates in the mode of stabilization of the current of the laser diode 1 for

negative negative feedback circuit circuit: additional transistor 6 - transistor: tori 10 and 11 current reflector 9 - resistor 12, while the resistance value

resistor 12 is chosen such that the depth of the electrical feedback does not exceed unity.

Let us define the requirements for a thermodependent voltage source 8. Fig. 3 shows the watt-ampere characteristic of a laser diode at two temperatures.

The threshold current of the laser diode can be represented as:

In (-),

 -about

 П9

(Z)

where T is the working temperature; 1p5, T - constants,

35 and Tr lies in the range from 80 to 120 K

T T + M,

(3)

where Tp is the initial temperature,

BT is the increment of the operating temperature over the control time. Substituting (3) into (2) and decomposition in the power series, we have:

  In.exp () (-) exp (| -) - 1 „exp (| -). (4) oo

,,. | 1. f f) ....

L 0, i

Expression (4) can be converted to

mind:

55

H ino ui, (t)

I T fft-I-l () G% o T 2) 4 /

(five)

T

MO

T (-, -) - the value of gyu o

horn current at the starting temperature T,

It is assumed that the differential efficiency of the laser diode h

id does not depend on temperature.

 dP / dl

that for real devices is performed with a sufficient degree of accuracy, we can assume that the equality is:

CP (T) UI (T),

MQKC

Where

Ui ...)

temperature drift of the maximum allowable operating current in a given temperature range.

Based on the expression (5), taking into account (6), the law of voltage variation as a function of the temperature of the thermo-dependent voltage source 8 should be:

V (T) V + & V (T)

 about

RI

no

U.T

T

- +

J (t)

2 T

about

 Max

where Vo is a constant component, uV (T) is the temperature drift of the thermal-dependent voltage source 8;

R is the resistance of the additional resistor 7;

maximum permissible operating current at temperature T

The complexity of the circuit implementation of the thermodependent voltage source depends on the magnitude of the operating temperature UT. ADDITION in expressions (5) and (7) can be neglected by members of the highest order, and the law of change of the thermal-dependent source will be linear

. max about

RI

by

18)

The scheme of the simplest thermodependent voltage source with a linear law of variation of the voltage of the form (8) is shown in Fig.2. The temperature drift of the voltage UV (T) in the circuit (Fig. 2) is determined by the temperature drift of the series-connected pn-junctions (2 mV / C: - for each transition), the constant component

0 voltage source V, with

from a particular source voltage can vary up to the opposite sign

:

ten

15

20

25

type of laser, voltage V to change,

With a circuit implementation of a thermodependent voltage source 8, it will be more complicated and depends on the accuracy of the protection circuit.

It should be noted that the temperature drifts of the laser diode 1 and the voltage of the emitter — the base of the additional transistor 6 included in the expression (1) are the same in sign and are approximately large in magnitude and therefore compensate each other.

Thus, the proposed technical solution allows one to achieve the goal by protecting the laser diode 1 from breakdown in a wide temperature range.

Claims (1)

Formula invented 0 five A device for converting electrical signals into optical signals, comprising an output laser diode, the anode of which is connected to the positive power supply bus and the cathode of the feedback photodiode, the anode of which is connected to the inverting input of the operational amplifier, the regulating transistor whose base is connected to the output of the operational amplifier, the emitter The resisor is connected to the common bus by a common bus, which is connected with the fact that, in order to test work stability in a wide range of temperature variations, additional ranzistor having a regulating-transistor structure, current reflector, thermo-dependent voltage source, additional resistor, resistive1, p {voltage divider connected between common bus and inverting input of operational amplifier, non-inverting input of which is an input of device for converting electrical signals, the cathode of the input laser diode is connected through an additional resistor to the collector of the control transistor and the emitter of the additional transistor, whose collector is connected with five 0 five I ioi: -,; 8 tixoAOM current reflector, power output is connected to the base of additional which is connected to a positive power source, to a power supply point through a thermally dependent source, for example, the traysistor, and the output of the current reflector is connected by a tap of a resistive voltage divider. P1 () 1 / I (r} I JfTO TaTfOttoT 2) fig.Z