DRIVE CURRENT AND DESIGN CONSIDERATION OF AN ULTRA-LOW THRESHOLD CURRENT LASER FOR OPTICAL PARALLEL DATA COMMUNICATION

Drive current of a directly modulated semiconductor laser for optical parallel data communication was investigated by taking into account of both the threshold current and the differential quantum efficiency wh ich are defined from the cavity length and the mirror reflectivities, Then the drive current required for an error free data communication ( bit error rate: BER < 10(-9)) with the bit rate of 1 Gb/s was shown as a function of the threshold current with parameters of the cavity len gth and the mirror reflectivities. As the results, it was found that t he laser cavity design which yields the minimum drive current is almos t the same condition to achieve the minimum threshold current operatio n when the total system loss is low (< 10 dB), whereas the cavity desi gn for higher differential quantum efficiency is required when the tot al system loss is much higher, When the cavity length is 100 mu m and the rear mirror reflectivity R-r is 0.99 for an example, the front mir ror reflectivity R-f which gives the minimum drive current was obtaine d to be 0.94, 0.91, and 0.8 for the total system loss of 6, 10, and 20 dB, respectively.