Correction circuit, drive circuit, light emitting device, and method of correcting current pulse waveform

A drive circuit comprising:

• a surface-emitting semiconductor laser,
• a current source operative for driving the surface-emitting semiconductor laser in a pulsed manner and having a current source output terminal for outputting a rectangular current pulse;
• and
• a correction circuit having output terminal connected to the current source output terminal and including a RC time constant circuit operative for outputting an assist current pulse having an initial peak value that attenuates over time, and using the RC time constant circuit to correct a waveform of the rectangular current pulse outputted from the current source,
• wherein the correction circuit adds the assist current pulse to the rectangular current pulse to form a resultant corrected current pulse so that a pulse waveform of light output of the semiconductor laser is approximately a rectangle,
• wherein both the rectangular current pulse and the assist current pulse commence at least substantially simultaneously at a time T1 and terminate at least substantially simultaneously at a later time T2,
• wherein the waveform of the rectangular current pulse is corrected so that a resultant initial peak value of the resultant corrected current pulse is attenuated with time in accordance with an RC time constant of the RC time constant circuit, the time being a period of time equal to time T2 minus time T1,
• wherein the RC time constant circuit includes a plurality of first time constant circuits attenuating the initial peak value of the current pulse with time,
• the first time constant circuits have RC time constants different from one another,
• at least one second time constant circuit of the plurality of first time constant circuits has an RC time constant having a value within a range of 20 nsec to 50 nsec both inclusive, and
• one or multiple third time constant circuits other than the second time constant circuit of the plurality of first time constant circuits have an RC time constant having a value of more than 50 nsec,
• wherein the semiconductor laser has a vertical resonator structure including an active layer sandwiched by a pair of multilayer reflectors and
• wherein the correction circuit corrects the waveform of the rectangular current pulse so that the initial peak value of the rectangular current pulse varies in correspondence to variation in temperature of the active layer.

A light emitting device comprising:

• one or multiple surface-emitting semiconductor lasers;
• a current source operative for driving the surface-emitting semiconductor laser in a pulsed manner and having a current source output terminal for outputting a rectangular current pulse;
• and
• a correction circuit having a correction circuit output terminal connected to the current source output terminal and including a RC time constant circuit operative for outputting an assist current pulse having an initial peak value that attenuates over time to correct a waveform of the rectangular current pulse outputted from the current source,
• wherein the correction circuit adds the assist current pulse to the rectangular current pulse to form a resultant corrected current pulse so that a pulse waveform of light output of the semiconductor laser is approximately a rectangle,
• wherein both the rectangular current pulse and the assist current pulse commence at least substantially simultaneously at a time T1 and terminate at least substantially simultaneously at a later time T2,
• wherein the waveform of the rectangular current pulse is corrected so that a resultant initial peak value of the resultant corrected current pulse is attenuated with time in accordance with an RC time constant of the RC time constant circuit, the time being a period of time equal to time T2 minus time T1,
• wherein the RC time constant circuit includes a plurality of first time constant circuits attenuating the initial peak value of the current pulse with time,
• the first time constant circuits have RC time constants different from one another,
• at least one second time constant circuit of the plurality of first time constant circuits has an RC time constant having a value within a range of 20 nsec to 50 nsec both inclusive, and
• one or multiple third time constant circuits other than the second time constant circuit of the plurality of first time constant circuits have an RC time constant having a value of more than 50 nsec,
• wherein the one or each one of multiple semiconductor lasers has a vertical resonator structure including an active layer sandwiched by a pair of multilayer reflectors and
• wherein the correction circuit corrects the waveform of the rectangular current pulse so that the initial peak value of the rectangular current pulse varies in correspondence to variation in temperature of the active layer of the one or each one of multiple semiconductor lasers.

A method of correcting a current pulse waveform, comprising the steps of:

• providing the surface-emitting semiconductor laser;
• and
• using a correction circuit including an RC time constant circuit for outputting an assist current pulse having an initial peak value that attenuates over time, the correction circuit being used to correct a waveform of a rectangular current pulse outputted from a current source, the current source operative for driving the surface-emitting semiconductor laser in a pulsed manner, so that a pulse waveform of light output of the semiconductor laser is approximately a rectangle by adding the assist current pulse to the rectangular current pulse to form a resultant corrected current pulse,
• wherein both the rectangular current pulse and the assist current pulse commence at least substantially simultaneously at a time T1 and terminate at least substantially simultaneously at a later time T2,
• wherein the waveform of the rectangular current pulse is corrected so that a resultant initial peak value of the resultant corrected current pulse is attenuated with time in accordance with an RC time constant of the RC time constant circuit, the time being a period of time equal to time T2 minus time T1,
• wherein the RC time constant circuit includes a plurality of first time constant circuits attenuating the initial peak value of the current pulse with time,
• the first time constant circuits have RC time constants different from one another,
• at least one second time constant circuit of the plurality of first time constant circuits has an RC time constant having a value within a range of 20 nsec to 50 nsec both inclusive, and
• one or multiple third time constant circuits other than the second time constant circuit of the plurality of first time constant circuits have an RC time constant having a value of more than 50 nsec,
• wherein the semiconductor laser has a vertical resonator structure including an active layer sandwiched by a pair of multilayer reflectors and
• wherein the correction circuit corrects the waveform of the rectangular current pulse so that the initial peak value of the rectangular current pulse varies in correspondence to variation in temperature of the active layer.