Spectrally stabilized laser

Claim 2

In combination: a semiconductor laser having a preferred operating mode; means for measuring the output powers in a pair of side modes of said laser located adjacent to said preferred mode; means for comparing said output powers and forming an error signal; and means, responsive to said error signal, for controlling the operating temperature of said laser.

Claim 3

The combination according to claim 1 wherein: said laser has longitudinal cavity modes at wavelengths λ 2 , λ 1 , λ 0 , λ 1 ', λ 2 '; said laser has a gain curve whose peak gain occurs at a wavelength which varies as a function of temperature; and wherein said operating temperature is adjusted such that said peak gain coincides with said cavity mode at λ 0 .

Claim 4

The combination according to claim 2 wherein: said side modes are at wavelengths λ 1 and λ 1 ', where λ 1 <λ 0 <λ 1 '; said means for measuring is a pair of photodetectors whose output signals V a and V b are proportional to the power in the laser output signal at wavelengths λ 1 and λ 1 ', respectively; and wherein the error signal is proportional to V a -V b .

Claim 5

The combination according to claim 2 wherein said means for measuring comprises: means, including a first beam splitter and a first wavelength filter, for deriving a first optical signal tuned to λ 1 ; and a first photodetector, responsive to said first optical signal, for producing an output signal V a ; means, including a second beam splitter and a second wavelength filter, for deriving a second optical signal tuned to λ 1 '; and a second photodetector, responsive to said second optical signal, for producing an output signal V b ; and wherein said means for comparing comprises a differential amplifier whose output error signal is proportional to V a -V b .

Claim 6

The combination according to claim 2 wherein said means for measuring comprises: a beam splitter for extracting a portion of the output signal from said laser and for directing said portion of signal onto a dual wavelength photodetector having dual diodes; the output from one of said dual diodes including a signal component V a at wavelength λ 1 , and a signal component V oa at wavelength λ 0 ; the output from the other of said dual diodes including a signal component V b at wavelength λ 1 ', and a signal component V ob at wavelength λ 0 ; a first amplifier having a gain g 1 for coupling said one diode to said comparing means; a second amplifier having a gain g 2 for coupling said other diode to said comparing means; where said gains g 1 and g 2 are such that g.sub.1 V.sub.oa =g.sub.2 V.sub.ob.

Claim 7

The combination according to claim 1 including: means for measuring the output power from said laser; and means, responsive to said measurement, to vary the bias applied to said laser.