Abstract

Extremely high-repetition-rate (over 100 GHz) optical pulse generation is possible with mode-locked semiconductor laser diodes (MLLDs) where the saturable absorber (SA) section is monolithically integrated.¹-³ MLLDs are expected to become compact terahertz-rate optical pulse sources in the near future. A terahertz optical source is useful for coherent excitation of lattice, molecular, and charge vibrations in gaseous and solid media⁴ and semiconductor heterostructures.⁵ A straightforward method of increasing repetition rate in a MLLD is to decrease the cavity length. Chen et al.¹ demonstrated 350 GHz pulse generation from a 250-pm-long symmetric collidingpulse mode-locked (SCPM) LD where the SA section was at the center of the cavity. To generate a pulse train with a repetition rate over a terahertz, the cavity length of a SCPM-LD should be less than 90 pm. It is difficult to precisely fabricate the cavity at this cavity length. Moreover, it may also be difficult to obtain an enough gain for laser oscillation. This paper demonstrates an asymmetric colliding-pulse mode-locked (ACPM) LD where the SA section is at a submultiple position of the cavity length.

© 1995 IEEE