Study of photonic crystal nanobeam lasers and their applications

Abstract

Photonic crystals are studied intensively as an attractive optical material for controlling and manipulating light in a wavelength-scale cavity. Recently, a one-dimensional photonic crystal, called a nanobeam, received attention for its small feature size while maintaining high Q/V. This thesis presents study of nanobeam lasers and their applications: tunable photonic crystal lasers and photonic crystal refractive index sensors. Nanobeams showed high-performance as a device in the application areas introduced in the thesis. In Chapter 1, study on the photonic crystal nanobeam bandedge laser is introduced. One dimensional photonic bandedge lasers with three InGaAsP quantum wells inside are demonstrated at room temperature from the lowest dielectric band of photonic crystal waveguides. The incident optical power at threshold measured was 0.6 mW. To confirm the lasing from the dielectric bandedge mode, the polarization and the photoluminescent spectra are measured from nanobeams of varying lattice constants. The observed shift of the lasing wavelength agrees well with the computational prediction. In the following two chapters, two application areas of a nanobeam are introduced. In Chapter 2, a low-voltage-tunable laser by placing one-dimensional nanobeam cavity between lateral electrodes is reported. Spec-tral tuning of the resonant wavelength is achieved by controlling the molecular alignment of the directors in the surrounding liquid crystals. The one-dimensional photonic crystal nanobeam structure is transfer-printed in the middle of the micron-scale gap. The total tuning range of 8.0 nm is obtained with a low DC bias of 5V. The spectral tuning rate of 2.1 nm/ 1.0V, which is the largest value ever reported to our knowledge, is measured. In Chapter 3, highly sensitive high-Q photonic crystal refractive index (RI) sensors using higher energy mode are demonstrated. $4^{th}$ bandedge mode from the lowest energy band is studied for its high quality factor and hi...