| Starting with sparing in dense wavelength division multiplexing (DWDM) fiber-opticscommunication systems, tunable lasers is expected to find increased use in systems andnetworks. Among all kinds of tunable lasers, the external cavity tunable laser (ECTL)consisting of gain chip and separated bulky optical filters, due to its narrow linewidth andwide tuning range, has received extensive concerns.This dissertation systematically analyzed the theory, design and manufacturing ofECTL based on microelectromechanical systems (MEMS) technology. The research resultsof this dissertation can be helpful to the design and manufacturing of commercial ECTL.The main innovations of the dissertation are summarized as follows:A compact and narrow linewidth tunable laser with an external cavity based on adiffraction grating and a simple single-axis-MEMS mirror is presented. A fused silica etalonwith50GHz free spectral range (FSR) helps the laser’s output wavelength match thestandard ITU-T grid, and it also acts as a filter to suppress the neighboring lasing modes.The combination of the diffraction grating, MEMS mirror and the etalon filter, can selectdifferent ITU-T channels and make this ECTL tune over C-band with50GHz grid. TheMEMS-based ECTL features simpler mechanical structure and lower cost as well as highreliability, while keeping all the merits of conventional external cavity lasers.A novel and hybrid analysis method is applied to design, analyze and optimize theECTL: for the passive external cavity without considering resonating behavior, ZEMAXand Gaussian beam propagation method are implemented to calculate the impact of thespecifications of collimating lens, etalon charicterstic and MEMS mirror on the passiveexternal cavity characteristics such as TOF bandwidth and cavity loss. Then we useimproved time domain traveling wave (TDTW) method to demonstrate the relationshipbetween wavelength accuracy and etalon specifications as well as the tuning characteristicsof the ECTL. The spectral linewidth of the ECTL is also theoretically discussed. Thishybrid method is also suitable for analyzing all kinds of external cavity lasers.The fabricating and packaging methods for the MEMS ECTL are discussed, thecompact electrical circuit with low noise is researched and developed successfully, theoptical aligning, packaging and testing platforms for the MEMS ECTL are also constructed. An integrated tunable laser assembly (ITLA) based on the MEMS ECTL is successfullyresearched and developed. This module can fully comply with OIF-MSA-ITLA-01.2. Ahigh output power of more than20mW, a wide wavelength tuning range about40nm inC-band with a narrow linewidth of less than50kHz and a high wavelength accuracy of±1GHz over the entire tuning range can be obtained.Several experiments in coherent fiber-optic communication systems under differentconditions are also conducted to test the performance of the MEMS ITLA: First, an112Gbit/s PM-QPSK back-to-back system is constructed to verify the ITLA’s performance.This ITLA is then used as transmitter laser source in a coherent optical OFDM (CO-OFDM)system with4–QAM modulation format, and its performance is further evaluated underdifferent FFT sizes. This device shows a slightly-improved performance in112Gbit/sPM-QPSK system compared with commercial narrow linewidth ITLA, and reveals anexcellent performance in CO-OFDM systems especially when the FFT size is larger than256. This MEMS ITLA can fully meet the requirement of commercial PM-QPSK coherentsystem and has the potential in the application of higher rate (400Gbit/s and1Tbit/s)coherent systems with higher-order modulation formats. |
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