Measurement of spontaneous emission factor for injection lasers

Accurate numerical simulation of the dynamic behavior of injection lasers requires accurate values for the parameters used in physical models. One such parameter which has been difficult to measure accurately in the past is the spontaneous emission factor or degree of coupling of spontaneous emission into the lasing modes. A numerical value for this spontaneous emission factor is obtained by distortion analysis of the optical output of a biased laser modulated by a small audio frequency sine wave. This technique can be used on either single or multimode lasers, and accounts for the different behavior of the different modes. Detailed studies were done on two different multimode devices, under varying thermal and modulation conditions. The values obtained by this technique for the spontaneous emission factor were of the order of 0.00001 and showed good agreement with the results using more conventional methods. Values of the spontaneous emission factor for different modes of the same device typically agree to within 10 percent. This is significantly better than other techniques whose results are typically good to within no better than a factor of two.