Method and apparatus for an oscillation frequency separation among a plurality of laser devices

Claim 1

A method for stabilizing oscillation frequency seperation among a plurality of laser devices comprising, sweeping the oscillation frequency of a reference semiconductor laser device to which an external signal is applied to radiate a light output whose oscillation frequency varies over a range of frequencies, driving a plurality of semiconductor laser devices to radiate light outputs each at an oscillation frequency in the frequency range of said oscillation frequency sweep of light output from said reference semiconductor laser, combining the frequency swept light output from said reference semiconductor laser and said light outputs from said plurality of semiconductor laser devices to produce combined light signals which are then converted to electric signals, a low frequency component of said electric signals being filtered to produce a train of beat pulses corresponding to said oscillation frequencies of said plurality of laser devices, passing a part of the frequency swept light output from said reference semiconductor laser through an optical resonator having periodic frequencies to produce reference light outputs at said periodic resonant frequencies which are then converted to electric reference pulses, the interval between said periodic resonant frequencies being equal to a predetermined oscillation frequency seperation among said plurality of semiconductor laser devices, comparing occurence times of said beat pulses and those of said reference to produce error signals corresponding to the time differences therebetween, and controlling the oscillation frequencies of said plurality of semiconductor laser devices such that said error signals are approximately equal to a predetermined value.

Claim 2

A method for stabilizing oscillation frequency seperation among a plurality of laser devices comprising, sweeping the oscillation frequency of a reference semiconductor laser device to which an external signal is applied to radiate a light output whose oscillation frequency varies over a range of frequencies, driving a plurality of semiconductor laser devices to radiate light outputs each at an oscillation frequency in the frequency range of said oscillation frequency sweep of light output from said reference semiconductor laser, combining the frequency swept light output from said reference semiconductor laser and said light outputs from said plurality of semiconductor laser devices to produce combined light signals which are then converted to electric signals, a low frequency component of said electric signals being filtered to produce a train of beat pulses corresponding to said oscillation frequencies of said plurality of laser devices, passing a part of the frequency swept light output from said reference semiconductor laser through an optical resonator having periodic frequencies to produce reference light outputs at said periodic resonant frequencies which are then converted to electric reference pulses, the interval between said periodic resonant frequencies being equal to a predetermined oscillation frequency seperation among said plurality of semiconductor laser devices, comparing occurence times of said beat pulses and those of said reference to produce error signals corresponding to the time differences therebetween, and controlling the oscillation frequencies of said plurality of semiconductor laser devices such that said error signals are approximately equal to a predetermined value.

Claim 7

An apparatus for stabilizing oscillation frequency seperation among a plurality of laser devices comprising, a reference semiconductor laser device to which an oscillation frequency sweep signal is applied over a frequency range which includes the oscillation frequencies of a plurality of laser devices to be controlled, an optical divider for dividing the light output of said reference semiconductor laser device into at least two light outputs, a first optical coupler for combining light outputs from said plurality of laser devices, a second optical coupler for combining one of said at least two light outputs and the light outputs combined in said first optical coupler, an optical resonator through which the other one of said at least two light outputs is passed to produce transmission light outputs whose intensity levels correspond to said so that reference light outputs are the transmissivity of the optical resonator which varies with frequency to electric reference pulses, means for converting the combined output light obtained in said second optical coupler to an electric signal, a low-pass filter through which a low frequency component of said electric signal is passed to produce beat pulses corresponding to said oscillation frequencies of said plurality of laser devices, means for producing error signals in accordance with the difference of the occurrence times between said reference pulsed and said beat pulses, and means for controlling said plurality of laser devices to be driven in accordance with said error signals such that said error signals become a predetermined value.

Claim 8

An apparatus for stabilizing oscillation frequency seperation among a plurality of laser devices comprising, a reference semiconductor laser device to which an oscillation frequency sweep signal is applied over a frequency range which includes the oscillation frequencies of a plurality of laser devices to be controlled, an optical divider for dividing the light output of said reference semiconductor laser device into at least two light outputs, a first optical coupler for combining light outputs from said plurality of laser devices, a second optical coupler for combining one of said at least two light outputs and the light outputs combined in said first optical coupler, an optical resonator through which the other one of said at least two light outputs is passed to produce transmission light outputs whose intensity levels correspond to said so that reference light outputs are the transmissivity of the optical resonator which varies with frequency to electric reference pulses, means for converting the combined output light obtained in said second optical coupler to an electric signal, a low-pass filter through which a low frequency component of said electric signal is passed to produce beat pulses corresponding to said oscillation frequencies of said plurality of laser devices, means for producing error signals in accordance with the difference of the occurrence times between said reference pulsed and said beat pulses, and means for controlling said plurality of laser devices to be driven in accordance with said error signals such that said error signals become a predetermined value.