Laser diode driver

Abstract

There is provided a laser diode driver including a DC current source supplying DC current to a laser diode, and a plurality of high frequency current sources alternately superposing onto the DC current high frequency current of the same polarity as the DC current and high frequency current of an opposite polarity to the DC current. The high frequency current of the opposite polarity is smaller than the high frequency current of the same polarity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit block diagram showing a laser diode driver according to a first embodiment of the present invention;

FIG. 2 is a detailed circuit diagram showing the laser diode driver according to the first embodiment of the present invention;

FIG. 3 is a view to describe the operation of the laser diode driver according to the first embodiment of the present invention;

FIG. 4 is a circuit block diagram showing a laser diode driver according to a second embodiment of the present invention;

FIG. 5 is a detailed circuit diagram showing the laser diode driver according to the second embodiment of the present invention;

FIG. 6 is a view to describe the operation of the laser diode driver according to the second embodiment of the present invention;

FIG. 7 is a view to describe the drive current of a laser diode;

FIG. 8 is a view to describe the drive current of a laser diode onto which high frequency current is superposed;

FIG. 9 is a circuit diagram (substantial part) showing a laser diode driver according to a related art;

FIG. 10 is a view to describe the operation of a laser diode driver according to a related art;

FIG. 11 is a view to describe the relationship between the drive current of a laser diode and light output;

FIG. 12 is a circuit diagram showing another laser diode driver according to a related art; and

FIG. 13 is a view to describe the operation of another laser diode driver according to a related art.

Claims

1. A laser diode driver comprising: a DC current source supplying DC current to a laser diode; anda plurality of high frequency current sources alternately superposing onto the DC current high frequency current of the same polarity as the DC current and high frequency current of an opposite polarity to the DC current,wherein the high frequency current of the opposite polarity is smaller than the high frequency current of the same polarity.

2. The laser diode driver according to claim 1, wherein the plurality of high frequency current sources include: a source-side high frequency current source connected between a node between the DC current source and the laser diode, and a power supply voltage; and a sink-side high frequency current source connected between the node between the DC current source and the laser diode, and a ground voltage, andthe laser diode driver further comprises an additional current source connected in parallel with the source-side high frequency current source.

3. The laser diode driver according to claim 2, wherein the source-side high frequency current source and the additional current source simultaneously turn ON and OFF by a common switching element.

4. The laser diode driver according to claim 1, wherein current of the sink-side high frequency current source is smaller than current of the source-side high frequency current source.

5. The laser diode driver according to claim 1, wherein the plurality of high frequency current sources include: a source-side high frequency current source connected between a node between the DC current source and the laser diode, and a power supply voltage; and a sink-side high frequency current source connected between the node between the DC current source and the laser diode, and a ground voltage, andthe laser diode driver further comprises a current setting circuit capable of setting current of the source-side high frequency current source and current of the sink-side high frequency current source to a different value from each other.

6. The laser diode driver according to claim 5, wherein current of the sink-side high frequency current source is smaller than current of the source-side high frequency current source.

7. A laser diode driver comprising: a DC current source supplying DC current to a laser diode;a first high frequency current source generating high frequency current of the same polarity as the DC current; anda second high frequency current source generating high frequency current of an opposite polarity to the DC current and being smaller than the high frequency current of the same polarity.

8. The laser diode driver according to claim 7, wherein the first and the second high frequency current sources alternately superpose onto the DC current the high frequency current of the same polarity and the high frequency current of the opposite polarity.

9. A laser diode driver comprising: a first superposition path outputting high frequency current of a first polarity; anda second superposition path outputting high frequency current of a second polarity,wherein the high frequency current of the first polarity from the first superposition path and the high frequency current of the second polarity from the second superposition path are alternately superposed onto DC current of the first polarity from a DC current source,an absolute value of the high frequency current of the second polarity is smaller than an absolute value of the high frequency current of the first polarity, andno current flows from the first superposition path to the second superposition path during the superposition.

10. The laser diode driver according to claim 9, further comprising: a source-side high frequency current source;a sink-side high frequency current source; andan additional current source,wherein high frequency current from the source-side high frequency current source and additional current from the additional current source are supplied to the first superposition path,high frequency current from the sink-side high frequency current source is supplied to the second superposition path, andan absolute value of the high frequency current from the source-side high frequency current source and an absolute value of the high frequency current from the sink-side high frequency current source are equal.

11. The laser diode driver according to claim 9, further comprising: a source-side high frequency current source; anda sink-side high frequency current source,wherein high frequency current from the source-side high frequency current source is supplied to the first superposition path,high frequency current from the sink-side high frequency current source is supplied to the second superposition path, andan absolute value of the high frequency current from the sink-side high frequency current source is smaller than an absolute value of the high frequency current from the source-side high frequency current source.

12. The laser diode driver according to claim 10, wherein the first superposition path is composed of a first switching element,the second superposition path is composed of a second switching element, andthe first switching element and the second switching element alternately turn ON and OFF during the superposition.