US 5,398,008 AGranted

Circuit arrangement for amplitude-modulating the drive signal of a laser

AssigneeAlcatel

InventorsDieter Nissler, Norbert Kaiser, Werner Manz

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Abstract

The universally-applicable circuit arrangement of the invention makes possible an adjustment procedure for holding emitted optical power of a laser constant independent of temperature and aging. This circuit arrangement may be carried out as a three-stage cascade circuit supplied with operating voltages greater than 5 V. In accordance with the purpose of the invention, a circuit arrangement is provided which is universally applicable in a temperature range T=-40.degree. C. to 100.degree. C. for commercially available lasers and can be supplied by a standard 5 V source. In order to accomplish this as per the invention, differential amplifiers acting as current switches are arranged in a first cascade stage and the current sources feeding the differential amplifiers arranged in a second cascade stage. A data signal (D) serving to control the modulating current (I.sub.mod) is logically combined with a pilot signal (P) serving to control the pilot currents (I.sub.P1, I.sub.P2) in at least one cascade stage.

Claims9

Dependent claims

T3, T4;
T5, T6) are connected to a combinatorial logical circuit (L) controlled by a data signal (D) and a pilot signal (P) and that the differential amplifiers (T1, T2;
T3, T4;
T5, T6) are each connected to a second pole of the operating voltage source (V.sub.EE) via a voltage-controlled current source (I.sub.P1, I.sub.P2, I.sub.mod), wherein the voltage-controlled current sources (I.sub.P1, I.sub.P2, I.sub.mod) are jointly connected at their control inputs to an output of a control circuit, and wherein the differential amplifiers (T1, T2;
T3, T4;
T5, T6) each comprise a first transistor (T1, T3, T5) and a second transistor (T2, T4, T6), respectively, wherein the collector-emitter path of a third transistor T11, T33) is connected in parallel respectively to the collector-emitter path of the first transistor (T1) of the first differential amplifier (T1, T2) and to the collector-emitter path of the first transistor (T3) of the second differential amplifier (T3, T4) and wherein the base terminals of the transistors of the differential amplifiers are connected as follows:
the base of the third transistor (T11) of the first differential amplifier and the base of the first transistor (T5) of the third differential amplifier to the data signal (D), the base of the first transistor (T1) of the first differential amplifier to a negated pilot signal (P), the base of the second transistor (T2) of the first differential amplifier and the base of the second transistor (T4) of the second differential amplifier to a constant reference signal (PR), the base of the third transistor (T33) of the second differential amplifier to a negated data signal (D), the base of the first transistor (T3) of the second differential amplifier to the pilot signal (P) and the base of the second transistor (T6) of the third differnetial amplifier to a reference signal (D.sub.R) and wherein the voltage-controlled current sources (I.sub.P1, I.sub.P2, I.sub.mod) each comprise a series circuit of a transistor (T7, T8, T9) and an emitter resistor (R.sub.E7, R.sub.E8, R.sub.E9) and wherein the base terminals of these transistors are jointly kept at a control voltage (U.sub.S).

4 more elements

A circuit arrangement for amplitude-modulating a drive signal of a laser (LD), comprising a cascade of differential amplifiers and current sources which amplitude-modulates a modulating current (I.sub.mod) of the laser (LD) with two pilot currents (I.sub.P1, I.sub.P2), wherein a first (T12, T42) and a second (T22, T32) differential amplifier are arranged in a first cascade stage and wherein the inputs of the first and second differential amplifiers are connected to each other and wherein the outputs of the first and second differential amplifiers are cross-connected such that at a first connecting point a first output of the first differential amplifier (T12, T42) is connected to a second output of the second differential amplifier (T22, T32) and at a second connecting point a second output of the first differential amplifier (T12, T42) is connected to a first output of the second differential amplifier (T22, T32), and wherein the first connecting point is connected via the laser (LD) with a first pole of an operating voltage source, and the second connecting point is connected with the first pole of the operating voltage source, and wherein inputs of the differential amplifiers (T12, T42;

T22, T32) are connected to a combinatorial logical circuit (L) controlled by a data signal (D) and a pilot signal (P) and wherein the differential amplifiers (T12, T42;
T22, T32) are connected to a second pole of the operating voltage source via a first, a second and a third voltage controlled current source, the second and the third voltage-controlled current source are arranged in a second cascade stage and jointly controlled by means of a control voltage (U.sub.B), wherein the first voltage-controlled current source for feeding the modulating current (I.sub.mod) and the third voltage-controlled current source for feeding a second pilot current (I.sub.P2) are connected to the first differential amplifier (T12, T42), wherein the second voltage-controlled current source for feeding a first pilot current (I.sub.P1) is connected to the second differential amplifier (T22, T32) and wherein the second and third voltage-controlled current sources respectively are each alternately activated via a transistor stage (T82, T92) contingent upon the pilot signal (P, P).

Dependencies are inferred from the claim text.