Abstract
By extending the net-gain modulation phasor approach to account for the discrete distribution of the gain and saturable absorber sections in the cavity, a convenient model is derived and experimentally verified for the cavity design of two-section passively mode-locked quantum dash (QDash) lasers. The new set of equations can be used to predict functional device layouts using the measured modal gain and loss characteristics as input. It is shown to be a valuable tool for realizing the cavity design of monolithic long-wavelength InAs/InP QDash passively mode-locked lasers.
Highlights
Monolithic mode-locked lasers (MLLs) are promising candidates for inter-chip/intra-chip clock distribution as well as high bit-rate optical time division multiplexing, electro-optic sampling, and arbitrary waveform generation due to their compact size, low power consumption, and direct electrical pumping [1,2]
We have extended Lau and Paslaski’s model to a two-section MLL device geometry that includes a gain section of length Lg and an absorber section of length La, and have accounted for the internal loss, αi, in the optical waveguide
According to the model from the previous section, we examined InAs quantum dash (QDash) passive MLLs with a total cavity length of 2.3-mm, 3.5-mm, and 4-mm, respectively
Summary
Monolithic mode-locked lasers (MLLs) are promising candidates for inter-chip/intra-chip clock distribution as well as high bit-rate optical time division multiplexing, electro-optic sampling, and arbitrary waveform generation due to their compact size, low power consumption, and direct electrical pumping [1,2]. QD and quantum dash (QDash) MLLs made on InP substrates in the 1.55-μm range have been vigorously pursued, achieving mode-locking in two-section devices using these materials has been more challenging [7,8]. It is believed that this is caused by the higher threshold current density and waveguide internal loss in InP-based QDs and QDashes compared to the more mature InAs/GaAs QD material system [9,10]. To further improve the development of 1.55-μm passive QD/QDash MLLs, a simple analytical model is needed to provide cavity geometry guidelines that can improve the mode locking performance in two-section devices. Mode locking is achieved as predicted, and a repetition rate as high as 18.4 GHz is realized
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