InP-based semiconductor lasers with novel sampled Bragg gratings and applications

Semiconductor diode lasers have a wide variety of applications in optical communications, spectroscopy and imaging. This thesis reports on work to produce novel semiconductor diode lasers, and expand their application areas. Semiconductor lasers designed and fabricated in this work are based on quantum well structures operating at 1550 nm. Three main findings are reported in this thesis. The first finding is about distributed feedback semiconductor lasers and laser arrays based on novel sampled Bragg grating structures. These semiconductor lasers have enhanced effective coupling coefficients compared to distributed feedback lasers based on the conventional sampled Bragg grating structure. The effective coupling coefficient of the conventional sampled Bragg grating is only about 0.32 times of a uniform Bragg grating. However, based on novel sampled Bragg grating structures, the effective coupling coefficients can be up to 0.9 times of a uniform Bragg grating. An eight-wavelength distributed feedback semiconductor laser array is reported, which has a precise wavelength separation of 100 GHz at 1550 nm. 10 mW of output optical power was achieved by a single diode laser. The second finding regards a novel dual-mode semiconductor diode laser based on a single cavity. The dual wavelengths of this laser are lasing stably with a wavelength separation of 4.45 nm. Based on this dual-mode diode laser, a THz frequency of 560 GHz is generated based on the photomixing technique. The third finding of this thesis is about THz repetition frequency mode-locked semiconductor lasers. The mode-locked semiconductor lasers are based on novel sampled grating distributed Bragg reflector structures. Compared to the mode-locked laser based on the conventional sampled grating distributed Bragg reflector structure, the effective coupling coefficient is increased by more than a factor of three in the new mode-locked laser. Optical pulses at repetition frequencies of 620 GHz and 1 THz are generated based on the mode-locked diode laser. Design, fabrication and characterisation of these semiconductor lasers are introduced in detail in this thesis