anyan Li

High channel count and high precision channel spacing multi-wavelength laser array for future PICs

Multi-wavelength semiconductor laser arrays (MLAs) have wide applications in wavelength multiplexing division (WDM) networks. In spite of their tremendous potential, adoption of the MLA has been hampered by a number of issues, particularly wavelength precision and fabrication cost. In this paper, we report high channel count MLAs in which the wavelengths of each channel can be determined precisely through low-cost standard μm-level photolithography/holographic lithography and the reconstruction-equivalent-chirp (REC) technique. 60-wavelength MLAs with good wavelength spacing uniformity have been demonstrated experimentally, in which nearly 83% lasers are within a wavelength deviation of ±0.20 nm, corresponding to a tolerance of ±0.032 nm in the period pitch. As a result of employing the equivalent phase shift technique, the single longitudinal mode (SLM) yield is nearly 100%, while the theoretical yield of standard DFB lasers is only around 33.3%.

Study of the Multiwavelength DFB Semiconductor Laser Array Based on the Reconstruction-Equivalent-Chirp Technique

A detailed theoretical analysis of the lasing wavelength precision of the DFB laser array based on a reconstruction-equivalent-chirp (REC) technique is presented. Experimental results of the eight-wavelength DFB laser array with equivalent π phase shift (π-EPS) and four-wavelength DFB laser array with equivalent three shifts are also given. High lasing wavelength precision was obtained. This paper demonstrates that the REC technique is a promising way for fabricating the multiwavelength DFB laser array with low cost and high yield.

Reflectionless Tilted Grating Couplers With Improved Coupling Efficiency Based on a Silicon Overlay

Grating couplers are important photonic devices on a complementary metal-oxide-semiconductor compatible silicon-on-insulator platform to couple light between optical waveguides and free space optical components or fibers. In this letter, we report the combination of a tilted grating coupler design, which strongly suppresses the back-reflection for light incident on the grating coupler from a waveguide, and a silicon overlay locally deposited on top of the grating region, which enhances the coupling efficiency of the grating coupler, by means of simulation and experiment. The fabricated tilted focusing grating couplers with silicon overlay show a coupling efficiency of -2.2 dB in combination with a back-reflection of around -40 dB when excited from the silicon waveguide. The tilted design also provides an alternative approach to enhance the transmission of a grating coupler when the thickness of the Si overlay is not optimized.

Dual Wavelength Semiconductor Laser Based on Reconstruction-Equivalent-Chirp Technique

A novel dual wavelength semiconductor laser is proposed and experimentally demonstrated. Stable dual wavelength lasing is established by the grating structure consisting of two asymmetric phase-shifts, which are distributed along the phase-arranging regions in the sampling pattern. The wavelength spacing between the two modes is about 0.51 nm at room temperature. A microwave signal at about 64 GHz can be generated by beating the two wavelengths. Based on the reconstruction-equivalent-chirp technique, the laser is fabricated by a low-cost manufacturing method.

Experimental demonstration of a low-cost tunable semiconductor DFB laser for access networks

A low-cost tunable semiconductor distributed feedback (DFB) laser design in access networks is proposed and experimentally demonstrated. It covers 9 nm continuous tuning range by changing the temperature. The side mode suppression ratios are above 42 dB over the tuning range. The current and temperature coefficients of wavelength tuning are 0.0124 nm mA−1 and 0.0875 nm °C, respectively. The results indicate that the reconstruction-equivalent-chirp (REC) technique is promising to fabricate low-cost tunable DFB lasers meeting the requirement of wavelength-division-multiplexing passive optical networks (WDM-PONs). It should be also noted that the tuning range can be easily extended by using more sections.

Experimental demonstration of DFB semiconductor lasers with varying longitudinal parameters

The distributed-coupling-coefficient and distributed-coupling-coefficient corrugation-pitch-modulated DFB lasers are experimentally demonstrated. The proposed lasers maintain good side mode suppression ratio over 50dBfrom 2.5 times to 12.5 times threshold current. The grating profiles of varying longitudinal parameters are equivalently obtained by specially designed sampled Bragg gratings and fabricated by conventional holographic exposure and μm-level photolithography.

Demonstration of a discretely tunable III-V-on-silicon sampled grating DFB laser

We demonstrate discrete wavelength tuning with a heterogeneously integrated III-V-on-silicon sampled grating distributed feedback laser. With only two injection currents, the laser is tunable over a wavelength range larger than 55 nm in wavelength steps of 5 nm. A maximum waveguide-coupled output power of 15 dBm is obtained as well as a high side mode suppression of more than 33 dB for all wavelength channels.

A Matrix-Grating Equivalent Phase Shifted Laser Array With 25-nm Wavelength Tuning Range

A matrix-grating equivalent phase shifted (MG-EPS) eight-wavelength distributed-feedback (DFB) semiconductor laser array is experimentally demonstrated. This device contains eight index-coupled DFB semiconductor laser diodes with a V-junction combiner, which have wavelength channel spacing of ~3.37 nm, with quarter-wave EPS structures. 25-nm continuous wavelength tuning range is achieved by changing the temperature, with side mode suppression ratios >42 dB within the entire tuning range. Meanwhile, because of the quarter-wave equivalent phase shift structures, no mode-hopping problems have been observed and good single-longitudinal mode operation is achieved. This device is promising for cost-effective applications of wavelength division multiplexing systems.

Improved Single-Mode Property of DFB Semiconductor Laser Based on Sampling Technique Using Chirp Compensation

A DFB semiconductor laser with a bent waveguide and an equivalent chirp compensation based on the sampled grating technique is proposed to improve the single longitudinal mode (SLM) performance for the first time. In such a structure, the bent waveguide is used to form the basically chirped grating so that the zeroth-order resonance is greatly suppressed. However, for the -first-order resonance, the equivalent chirp by designing the sampling pattern is used to compensate the chirp in the -first subgrating caused by bent waveguide. As a result, the -first-order resonance is enhanced, whereas the zeroth resonance is well suppressed. Since the wavelength spacing between the zeroth and -first subgrating can be reduced by adopting this method, the sampling period can be increased. Therefore, the corresponding line in photomask can be enlarged as well to ease the fabrication, and the lasing wavelength accuracy can be further improved according to the theoretical analysis. Because the lasing wavelength can be controlled by changing the sampling period, the performances of the multiwavelength DFB laser array can also be improved using this method.

An Equivalent-Asymmetric Coupling Coefficient DFB Laser With High Output Efficiency and Stable Single Longitudinal Mode Operation

An equivalent-asymmetric coupling coefficient (EACC) distributed feedback laser (DFB) semiconductor laser with equivalent-half apodization grating (EHAG) structure is proposed and experimentally demonstrated for the first time; the EHAG profile is equivalently realized by linearly changing the duty cycle of a sampled Bragg grating along the one half cavity, while that of the other half cavity is kept uniform. Compared with the equivalent-symmetric coupling coefficient DFB laser, the simulated intensity distribution of the EACC DFB laser shows that the light power is concentrated not only on near the phase-shift region and that the power at the front end is enlarged. Therefore, the longitudinal spatial hole burning may be reduced; the output efficiency and the single-mode stability may be improved. The experimental results show that the output power ratio between the front and rear facets is about 2.17 and the side-mode suppression ratios are over 50 dB when the injection current is in the range from 60 to 200 mA.