Study On Linewidth Narrowing And Polarization Control Of Vertical-cavity Surface-emitting Lasers

In contrast to edge-emitting lasers,vertical-cavity surface-emitting lasers(VCSELs)has the advantages of on-wafer testing,single-longitudinal mode lasing,circularly symmetric beam profile,low threshold,high-speed modulation,and two-dimensional array integration,enabling VCSELs to be widely used in optical communication,microwave photonics,precision measurement.However,due to the length of laser cavity is micron scale,the linewidth of VCSELs is usually on the order of MHz or above,and the isotropy gain medium and circular symmetrical resonator lead to the random switching of the polarization of VCSELs with the change of bias current or operating temperature,increasing of the system background noise.To realize the polarization controllable narrow linewidth VCSEL,the linewidth narrowing and polarization control of the VCSEL based on the resonant feedback from a whispering gallery mode microcavity(WGM)are studied in this dissertation.The main contents of this dissertation are as follows:(1)The unique self-injection locking property of the WGM microcavity is integrated into the theory framework of laser external cavity feedback.The laser dynamic equation based on the resonant feedback of the WGM microcavity is established.The principles of laser frequency locking,linewidth narrowing and polarization control under the resonant feedback of the WGM microcavity are analyzed.The impacts of the quality factor of the WGM microcavity,and the detuning between the VCSEL wavelength and the resonance wavelength of WGM microcavity on VCSEL linewidth narrowing and polarization control are studied.It provides theoretical guidance for the selection of the WGM microcavity and the experimental study of VCSEL linewidth narrowing and polarization control.(2)A narrow linewidth VCSEL based on resonant feedback from a WGM microcavity is proposed and constructed.The linewidth of VCSEL is narrowed using the resonant feedback which is generated by tuning the wavelength of the VCSEL to match the resonance wavelength of the WGM microcavity with quality factor of 1.36 million.The experimental results show that when the effective feedback intensity of the WGM microcavity is-24.77 d B,the linewidth of the VCSEL can be narrowed from 2.1 MHz to32.6 k Hz using the resonant feedback from the WGM microcavity,which is the same order of magnitude(15 k Hz)as the linewidth calculated from the frequency noise spectrum.In addition,using the thermal self-locking effect of the resonant feedback from the WGM microcavity,the frequency noise of VCSEL is reduced by 60 d B and 50 d B at10 Hz and 10 k Hz respectively,which provides an effective method for realizing narrow linewidth VCSEL.(3)A polarization controllable VCSEL based on resonant feedback from a WGM microcavity is proposed and constructed.Due to the two orthogonal polarization states of VCSEL have a wavelength interval of about 100 pm and the narrow bandwidth of high-quality factor WGM microcavity,the polarization control of VCSEL is realized by using the resonant feedback of WGM microcavity.The experimental results show that when the lasing wavelength of the two orthogonal polarization modes of VCSEL are locked to the resonant wavelength of WGM microcavity with a quality factor of 10~6,the two orthogonal polarization modes of VCSEL can be arbitrarily switched to the main polarization mode lasing under different bias currents,and the linewidth of VCSEL can be maintained at tens of k Hz,which provides an effective method for realizing polarization controllable VCSEL.(4)Narrow linewidth dual-wavelength VCSEL based on resonant feedback from a WGM microcavity is proposed and constructed.By locking dual-wavelength VCSEL with wavelength interval of 0.8 nm to different order resonant modes of WGM microcavity,the linewidths of dual-wavelength VCSEL are simultaneously narrowed.The experimental results show that the linewidths of two VCSELs can be narrowed from3.5 MHz and 5 MHz to 20.9 k Hz and 24.1 k Hz respectively by a single WGM microcavity with a quality factor of 10~6,the level of the linewidth narrowing is equivalent to that of narrowing a single VCSEL by resonant feedback of WGM microcavity,which provides a reference for realizing two-dimensional integrated narrow linewidth multi-wavelength VCSEL array.