Chirp Characteristics Of Tunable V-Cavity Semiconductor Laser

Communication plays an increasingly important role in people’s work, life and learning. Semiconductor lasers with simple manufacturing technology and modulating format, tunable wavelength and good transmission performance are the essential devices in optical communication networks in the future.Direct amplitude modulation is the simplest and least expensive modulation format compared to those based on external modulators such as electro-absorption modulator (EAM) and Mach-Zehnder modulator. However, direct amplitude modulation of semiconductor laser is usually accompanied with unwanted positive frequency chirp. The positive frequency chirp causes the signal pulses to spread as they propagate through a standard single mode fiber that has positive chromatic dispersion at 1550nm. This is a serious limitation for transmission bit rate and distance in optical fiber communication systems. It is desirable that transmitters employed in dense wavelength division multiplexing metro-area networks possess both wavelength tunability and negative chirp characteristics.In this thesis, directly modulated tunable V-cavity laser with multi-electrode structure is studied. Negative frequency chirp of directly modulated tunable semiconductor laser is firstly discovered and confirmed. The change of carrier density in active region and output optical power in the V-cavity laser is opposite in the process of modulation. Therefore, output light signal with negative chirp is obtained, which is highly desirable.In this thesis, the dynamic change of the relationship between carrier density and output optical power in the V-cavity laser was first analyzed by using the time domain traveling wave model. The mechanism of the negative chirp is theoretically explained. Secondly, the time-resolved chirp of V-cavity laser was measured by using bandpass filter method. The experimental result of the negative chirp is consistent with that of the simulation analysis. Finally, partial dispersion compensation using negatively chirped signal light emitted by the V-cavity laser for propagation through G.652 standard single-mode fiber is analyzed based on the measurements. The results further confirm the negative chirp characteristics of the V-cavity laser.With advantages of fabrication simplicity, compact structure, wide tuning range and negatively chirped direct modulation, the V-cavity laser has great potential for broad applications in optical communication networks.