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Research On Wavelength Tunable Semiconductor Lasers Based On Novel Micro-nano Structures

Posted on:2016-12-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:J L ZhaoFull Text:PDF
GTID:1108330467996684Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Wavelength tunable semiconductor lasers can be used in a variety of applications, including optical communication systems and sensors, where lasers exhibiting wide wavelength tuning range, large output power, high sidemode suppression ratio (SMSR) and fast wavelength switching speed are required. They can be used in wavelength division multiplexing (WDM) systems for spare inventory reduction. They can also be used for dynamic wavelength provisioning and wavelength routing in next generation reconfigurable optical networks. When tunable lasers are used in coherent optical communication systems as transmitters and local oscillator lasers of coherent receivers, their phase noise characteristics are of crucial importantce to system performances. In this thesis, starting from the grating design theory, theoretical simulation model and experimental demonstration, tunable semiconductor lasers based on novel micro-nano structures are investigated and explored in detail. The main contains are organized as follows:(1) Based on the Bragg grating theory, the sampled grating structure, multiple phase shifts and reflection spectrum concatenation technologies are studied. And a novel wide-band, high channel-count comb filter structure based on digital concatenated grating with multiple phase shifts (MPSDCG) is proposed and simulated.(2) Two theoretical simulation models for analyzing the wavelength tunable semiconductor lasers are developed, including the frequency-domain transmission-line laser model and the time-domain traveling-wave model. These two models can be used for the simulation of static characteristics such as lasing wavelength, threshold current, output power, sidemode suppression ratio and output spectrum, as well as dynamic modulation response and wavelength switching characteristics.(3) The nanoimprint lithography technology for fabrication of digital concatenated grating is studied. By introducing a second soft-mold nanoimprint process and by optimizing the temperature and pressure during the nanoimprint process, the grating patterns are uniformly transfered from the mold to the polymer material on the substrate. A simple device is developed for the alignment of grating patterns on the mold and the substrate. Finally, the digital concatenated grating with sharp side-well is fabricated by optimizing the parameters of the inductively coupled plasma (ICP) etching process. (4) By testing the fabricated DCG-DBR laser, a wavelength tuning range of30nm has been achieved with a sidemode suppression ratio larger than30dB. To improve the performances of the DCG-DBR laser and relieve the fabrication accuracy for grating periods, the MPSDCG-DBR laser is proposed and simulated.(5) Based on the frequency-domain transmission-line laser model, the Langevin rate equations for the photon number and optical-field phase in SG-DBR laser cavity are derived. The SG-DBR laser phase noise characteristics are analyzed with the derived rate equations. Contributions from different noise sources to laser FM-noise spectrum are simulated, including the spontaneous emission white noise in active section and the carrier shot noises in passive tuning sections. The variation of linewidth broadening values due to different nosie sources with the passive section tuning currents are calculated and explained. The simulated linewidth trends are found to be in agreement with our experiment measurements. Finally, the impacts of the laser structure parameters such as phase section length and grating coupling coefficient on laser linewidth values are discussed.(6) A novel three-section slotted Fabry-Perot laser (SFP) with two shallow slots etched on the surface of the ridge waveguide is investigated theoretically by using the time-domain traveling-wave model. The slot structure is characterized by using the boundary conditions of the optical fields which propagate throught the slot facets. Laser characteristics including wavelength, sidemode suppression ratio, output spectrum and dynamic wavelength switching events are simulated based on the established model. By calculating the variations of carrier and photon densities along the laser cavity under different injected currents, the Vernier tuning mechanism of the three-section SFP laser is demonstrated. Furthermore, virtual digital infinite-impluse response (IIR) bandpass filters with different central wavelengths are developed to examine the mode power of different wavelength channels during wavelength switching events. Compared with the Fourier transform method, the IIR filter method is simpler and has a higher wavelength resolution.
Keywords/Search Tags:Wavelength tunable semiconductor laser, Multiple phase shifts, Reflection spectrum concatenation, Transmission-line model, Time-domain traveling-wave model, Nanoimprint lithography, Digital concatenated grating, Phase noise, Fabry-Perot laser
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