Improved Single-Mode Property of DFB Semiconductor Laser Based on Sampling Technique Using Chirp Compensation

Abstract

A DFB semiconductor laser with a bent waveguide and an equivalent chirp compensation based on the sampled grating technique is proposed to improve the single longitudinal mode (SLM) performance for the first time. In such a structure, the bent waveguide is used to form the basically chirped grating so that the zeroth-order resonance is greatly suppressed. However, for the $-$ first-order resonance, the equivalent chirp by designing the sampling pattern is used to compensate the chirp in the $-$ first subgrating caused by bent waveguide. As a result, the $-$ first-order resonance is enhanced, whereas the zeroth resonance is well suppressed. Since the wavelength spacing between the zeroth and $-$ first subgrating can be reduced by adopting this method, the sampling period can be increased. Therefore, the corresponding line in photomask can be enlarged as well to ease the fabrication, and the lasing wavelength accuracy can be further improved according to the theoretical analysis. Because the lasing wavelength can be controlled by changing the sampling period, the performances of the multiwavelength DFB laser array can also be improved using this method.