Laser frequency aging compensation

A semiconductor laser diode mounted to a heat sink body has a thermally resistive layer located between the two in order to provide a specified thermal impedance that balances the contrary responses to laser aging and changes in drive current. The required thermal impedance is determined by experimental trial on a plurality of identically mounted test structures differing only in their thermally resistive layer impedances, which are then operated to cause laser aging. The optical mode frequency output from the laser diodes in the test devices are measured under normal operating conditions at least before and after the laser aging, and the thermal impedance value that would result in a substantially zero change in laser output is calculated from these measurements. The resistive layer's thickness and/or doping level may be used to select the desired thermal impedance. As a result, the mounted laser device with this layer is characterized by an effective refractive index of the laser diode that remains substantially constant as the laser ages with constant operating conditions, and thus the device has an age-stable output frequency.