Enhanced frequency modulation in cleaved-coupled-cavity semiconductor lasers with reduced spurious intensity modulation

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Abstract
We have observed enhanced analog frequency modulation in a cleaved‐coupled‐cavity (C3) laser. One diode is dc biased above threshold to produce the desired output power and the other diode, the modulator, is biased below threshold with a dc current and a small modulating current superimposed to achieve analog frequency modulation of the output beam. Comparing with direct analog frequency modulation of a conventional semiconductor laser, the C3 laser has allowed us to obtain significantly larger frequency deviation with negligible spurious intensity modulation. Further, the present frequency modulation response is also much more uniform with respect to modulation frequency. In addition, this scheme is applicable to C3 lasers formed from all laser structures.