Limitations of a threshold-sensing scheme for lasers at high bit rates

Results for a threshold-sensing method for lasers operating in the gigabit-per-second (GB/s) range are reported. Laser threshold sensing is accomplished by applying a low-frequency (1-20 kHz) dither current at low amplitude (1-2 mA) to the off-state of a laser that is being modulated at normal transmission rate. It is found that acceptable discrimination of the lasing threshold condition is possible for bit rates up to about 2 Gb/s. Loss in threshold discrimination at higher bit rates is attributed to the increased contribution of lasing delay time to the sensing signal when the bias is below threshold.<
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