Mode-locked laser diodes for the 750 – 770 nm spectral region

Abstract

Ultrashort pulse lasers are widely used in research, industry, medicine, and communications, because of their characteristics of narrow pulse width, high repetition frequency, broad spectrum and high peak power. They are influencing and changing our world. Mode-locking is an effective way to generate ultrashort pulses. Semiconductor mode-locked lasers are excellent candidates for ultrashort pulse generation due to their advantages in compactness, weight, energy efficiency and cost. In this dissertation, we present the first demonstration of semiconductor mode-locked laser diodes in two wavebands – 750 nm and 760 nm. Both chips were based on an AlGaAs multi-quantum-well structure, with slight differences depending on the target spectral band.
At the 760 nm waveband, the laser diodes were passively mode-locked and generated pulses at around 766 nm, with pulse durations down to approximate 4 ps. They are designed with different laser cavity lengths of 1.815 mm and 1.515 mm, leading to the pulse repetition rates of 19.4 GHz or 23.2 GHz respectively.
Deep-red semiconductor monolithic mode-locked lasers are demonstrated, in the waveband of 750 nm. These lasers enable the generation of picosecond optical pulses at 752 nm, at pulse repetition rates of 19.37 GHz and 23.1 GHz, corresponding to 1.815 mm and 1.515 mm cavity lengths respectively. An investigation of the dependence of the pulse duration as a function of reverse bias revealed a predominantly exponential decay trend of the pulse duration, varying from 10.5 ps down to 3.4 ps. A 30-MHz-tunability of the pulse repetition rate with bias conditions is also achieved.
We checked the influence of the bias conditions on the mode-locking characteristics for these new lasers. It was also found that the front facet reflectivity played a quite important role in the possibility of mode-locking.
The demonstration of these compact, efficient and versatile ultrafast lasers in this spectral region paves the way for its deployment in a wide range of applications such as bio-imaging, pulsed terahertz generation, microwave generation and millimeter-wave generation, with further impact on sensing, imaging and optical communications.

Date of Award	2015
Original language	English
Awarding Institution	University of Dundee
Supervisor	Maria Cataluna (Supervisor) & Ying Ding (Supervisor)