A transfer function of the thermal FM response of laser diodes is theoretically derived that is in excellent agreement with the experimentally measured FM response and agrees in general with an empirical expression reported earlier in the literature. The characteristic dip in the overall sinewave FM response and the time-domain stepresponse of the laser diode are analysed theoretically as a function of a thermal cutoff frequency and the ratio of thermal FM at d.c. to the carrier FM at d.c. From the step response analysis, the lower bound on the bit rate for penalty-free Alternate Mark Inversion FSK (AMI-FSK) transmission is derived which tallies well with the experimental observations. A first-order equalization network to correct the drooping nature of the FSK output pulse response is analysed theoretically.
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