Research On The Fabrication And Characterization Of InP-based Chirped Quantum Well Superluminescent Diodes

In recent years,high accuracy sensing system has already been urgently-needed in various fields.As one of the key optoelectronic component of high-accuracy optical fiber sensing system,the Super Luminescent Diode(SLD)directly determines the accuracy and stability of the system.Holding the characteristics of broad spectrum,high power and weak temporal coherence,SLD has shown very promising application prospects in Fiber-Optic Gyroscope(FOG)and Optical Coherence Tomography(OCT).As it well-known,quantum well(QW)devices have easily-controlled growth conditions,good stability and sufficient output power.Moreover,by introducing the chirped structure into the QW active region,each period of the QWs will emit different wavelength,which can effectively enlarge the spectrum width of the photoemission devices.Therefore,SLDs with chirped QWs active region can simultaneously satisfy the requirements of high power,broad spectrum and high reliability.The fabrication of SLDs with chirped QWs is vital for the development of native high-accuracy sensing technology.The goal of this thesis is to prepare the 1.3 ?m InP-based SLD with high power and broad spectrum.We intended to expand the spectrum under the condition of high output power through introducing the InGaAsP chirped MQW structure which was alternately tensile/compressive strained.Meanwhile,the design and fabrication of the waveguide structure were systematically carried out to restrain the lasing of the device.In addition,the post process of SLD was optimized to improve the yield of SLD devices in the laboratory.The main research contents and achievements are listed as follows:1.The alternately tensile/compressive strained InGaAsP chirped MQW was designed and adopted as the active region of SLD.Corresponding MOCVD growth was completed by the cooperative institution.The PL measurements showed that the emission wavelength of the active region was located at 1.3 ?m band.The full width at half maximum(FWHM)value of the PL spectrum was about 150 nm,which can meet the requirement of broad spectrum.2.According to the requirement of the cooperative control of the device spectrum and output power,we optimized the whole process flow of the devices(including photolithography,chemical etching,deposition of SiO2 insulating layer,magnetron sputtering metal electrode,thinning,polishing and etc.).We focused on optimizing the wet-etching process of the ridge waveguide.The etching solution of H3PO4:H2O2:H2O and HCl:HBr were used alternately.The etchant ratio,etching time and the etching temperature were strictly controlled.As a result,the lateral undercut which was serious in the etching process was alleviated to the acceptable extend.3.InP-based InGaAsP chirped MQW SLD in 1.3 ?m band was successfully fabricated.Neither coating the anti-reflection film on the cavity facet nor welding the thermal sink,superluminescent operation was realized under the pulse current injection at room temperature(22?).The cycle of pulse current was 0.2 ms,the pulse duty ratio was 10%,and the central wavelength of the spectrum was 1340 nm.The diode with single-bend waveguide(10° bending angle),10 ?m ridge width and 3 mm cavity length achieved the superluminescence at room temperature.When the current is 530 mA,the output power is 4.91 mW and the FWHM is 94.8 nm.When the current increases to 620 mA,the output power ramps up to 10.53 mW and the FWHM is significantly decreased to 27.1 nm.4.According to the above results,we further optimized the SLD devices by adjusting the shape of the bend waveguide as well as the cavity length.The results are listed as follows:(1).The shape of the waveguide was adjusted to double-bend waveguide structure(3mm cavity length,mm bending length,10°bending angle).When the current is 740 mA,the output power reaches 2.96 mW and the FWHM is 83.4 nm.When the current increases to 980 mA,the output power is increased to 8.59 mW and the FWHM is slightly decreased to 56.2 nm.With the increasing of injection current,the narrowing effect of the FWHM is alleviated to a certain degree.The results show that the diode with double-bend waveguide structure has a better performance in restraining lasing.(2).The cavity length was reduced to 2 mm(single-bend waveguide,1 mm bending length,10° bending angle).When the current is 530 mA,the output power reaches 8.92 mW and the FWHM is 82.5 nm.When the current further increases to 620 mA,the output power is up to 19.99 mW and the FWHM is 22.5 nm.Compared with the 3mm-cavity-length diode,the shorter cavity SLD device can generate higher output power under the same injection current.