Research On Monolithic Integrated Dual-wavelength Semiconductor Laser Chip

Due to their small size,high integration,high frequency modulation,and long service life,semiconductor lasers have become important components in modern optical communication networks and photonic integrated circuits.Ultilizing dual-wavelength laser to generate microwave signals has attracted much research interest since optical fiber has the characteristics of large bandwidth and extremely low loss.In addition,the lidar system made of dual-wavelength semiconductor lasers can be used for high-precision speed and distance measurement.These factors make dual-wavelength semiconductor lasers have high application value.For dual-wavelength semiconductors,reducing its manufacturing difficulty,production cost,and improving its performance have become the key to research.In this paper,a dual-wavelength laser based on reconstruction-equivalent chirp technology is poposed,fabricated and experimentally demonstrated in this thesis.The difficulty of the grating manufacturing process is reduced to the sub-micron level based on reconstruction-equivalent chirp technique.At the same time,a grating structure based on equivalent apodization is also introduced in this thesis,which is used to obtain dual-wavelength lasing and can operate on each channel of the sampled grating.In addition,in the last chapter of this thesis,a high-performance laser based on Moire gratings and a method for equivalent apodization with interlaced sampling gratings are briefly described.The main content of this thesis include the following,(a)Based on the reconstruction-equivalent chirp technology,two equivalent phase shifts are designed and introduced in the cavity to realize dual-wavelength lasing in the±1^st channel.And on this basis,the equivalent chirp is realized in the±1^st channel by linearly adjusting the sampling grating period.Therefore the photon distribution of the two lasing modes in the cavity is separated,thereby suppressing the mode competition effect.The effects of different cavity lengths,different refractive index modulation depths and different chirp rates on dual-mode lasing are studied.The pattern size of the entire grating structure is in the micron level,which greatly reduces the difficulty of production.The sampled grating lithography and secondary epitaxial lithography are designed and handed over to the company's foundry.The fabricated chip is experimentally demonstrated,and the results showed that the wavelength spacing of the laser under this structure remained unchanged at 0.82 nm at 14°C-40°C.When the injection current was 60m A-120m A,the side mode suppression ratio remained above 35d B.At room temperature,the parameters of the laser remained stable for one hour of continuous testing.(b)An equivalent apodized grating structure for dual-wavelength lasing is proposed and calculated.The duty cycle of the sampled grating is changed to achieve equivalent apodization.The distribution of the grating coupling coefficient in the cavity is modulated into an anti-Gaussian curve,thereby amplifying the side lobes on both sides of the stopband of the transmission spectrum,where the dual-wavelength lasing obtained.The effects of different cavity lengths,different refractive index modulation depths and different distribution curves on dual-wavelength lasing are studied.Its frequency spacing design range can be from 38GHz to 660GHz at the 1550 nm band.At the same time,the yield of the structure under different coating conditions is calculated.Compared with the uniform sampling structure and the equivalent phase shift structure,the equivalent apodization structure is not affected by arbitrary phase in the case of AR coating(reflection coefficient less than 0.1).The yield rates of the uniform sampling structure and the dual phase-shifts structure under this condition are 55%and 70%,respectively.(c)An extremely narrow wavelength difference dual-wavelength laser based on a sampled Mohr grating is designed to locking to Cs-133 Atomic transitions.The wavelength spacing of the laser under this structure is only 0.0245nm.Besides,a staggered sampled grating structure is proposed,which reduces the size of the grating pattern of equivalent apodization to the micron level,thereby greatly reduces the difficulty of fabrication process.