Picosecond pulse generation in monolithic GaN-based multi-section laser diodes

Abstract

We develop a monolithic picosecond laser pulse generator, based on the classical design of a group-III-nitride Fabry-Pérot laser diode with electrically separated ridge sections. We use two different multi-section design variants, with the absorber section placed either in the center or at the end of the ridge. Profiting from the very low lateral conductivity in the p-type GaN top contact layer, we implement the multi-section concept just by etching off small sections of the top metalization on the ridge. The physical mechanism underlying short pulse generation within such system, operating in the 400 - 435nm wavelength range, strongly depends both on the reverse bias applied to the absorber and the forward current in the gain section. Varying the applied reverse bias affects both the absorption and the carrier lifetime in the absorber section through changes in the QW internal field. In consequence we can distinguish between different modes of operation. For moderately long carrier lifetimes the absorber stabilizes relaxation oscillations in the GHz frequency range and self-pulsation occurs, of relatively long duration. With increasing reverse bias, and thus decreasing carrier lifetime, we observe a transition to self-Q-switching. Finally, at large enough negative bias, the carrier life time in the absorber is so short that the laser diode operates in a passive self-mode-locking regime with a repetition rate of 87 GHz and pulse duration of 2 ps for a cavity length of 540 µm

Implementation and investigation of mode locking in GaN‐based laser diodes in external cavity configuration

“…A more detailed description on structures and processing can be found in Refs. . We employed different epitaxial structures with varying lasing wavelengths from 405 to 436 nm.…”

Repetition frequency variation of a 2 μm GaSb-based passively mode-locked laser （Invited）

“…Key words: Mode-locked semiconductor lasers; Repetition frequency; GaSb-based material system; 2 μm wavelength band 0 引言 高重复频率的超短光脉冲序列在光通信/存 储，传感，激光雷达，时钟信号和种子光产生等 领域都有着广泛的应用 [1][2][3][4][5][6] 下一步，我们将 Ig 设定在了 190 mA 保持不 变，这个电流远高于 20，40，和 60 °C 时激光器 激射的阈值。如图 6 所示，在每个温度下重复频 率随 Va 的变化趋势保持一致：在比较小的反偏 时上升，然后保持平稳，最后缓慢下降。其他的 课题组也报导了这个上升的过程 [7] ，而另一些课 题组则观察到了下降的过程 [3,11]…”