Search

Fast optical switches have the potential of lowering the cost, power, and latency of today’s data-center networks. The on-off switching of DFB lasers in arrays is poised to provide extremely fast switching because the on-off time of a DFB laser is the level of sub-nanosecond. However, the key of the DFB laser array based tunable laser lies in the high precision control of the lasing wavelength. In this letter, we proposed and experimentally demonstrated a tunable laser by integrating 16 DFB lasers based on the reconstruction-equivalent-chirp (REC) technique. Without using the conventional e-beam lithography, an equivalent $\lambda $ /4 phase-shift is fabricated in each DFB laser to ensure the single-longitudinal-mode (SLM) yield. Moreover, high precise wavelength spacing is realized. Wavelength deviations of 89.3% DFB lasers are within ±0.2 nm. The output power of all the channels is above 7 mW, and the relative intensity noise is below −130 dB/Hz. By on-off switching the lasers, sixteen channels with 2.4-nm spacing can be fast switched. The switching time between any two channels is less than 50 ns. In addition, a wide-band continuous wavelength tuning range of 38.4 nm can be obtained with a small temperature variation of 18 °C. Owing to the REC technique, the tunable laser via high-density integration of DFB lasers is demonstrated with simple fabrication, high SLM yield, and high wavelength precision, which opens up a path for wide-band and especially fast tunable lasers. [ABSTRACT FROM AUTHOR]

Multi-wavelength distributed feedback laser array (DFB-MLA) based tunable semiconductor lasers have been widely used owing to the high mode stability and simple wavelength tuning scheme. In this paper, we proposed and experimentally demonstrated a matrix-grating tunable DFB laser array. And the reconstruction-equivalent-chirp (REC) technique is utilized to simplify grating fabrication and realize precise control of the grating phase. Traditionally, the laser is tuned by thermal-electric cooler (TEC), with large power consumption, slow wavelength tuning capability, and added device. To improve the wavelength tuning speed of laser, we varied laser’s injection current instead of adjusting TEC’s temperature. In addition, we analyzed the thermal influence of submount on the laser and then chose the SiO2 as the submount material for its low thermal conductivity and poor heat dissipation, resulting in wide wavelength tuning range via injection current. The DFB-MLA chip achieves a better tunable effect as the lasers can be tuned at 3.5–3.7 nm per channel from 50 to 120 mA with stable output power of over 3 mw as contrasted with the laser on the AlN submount being tuned at 1.4–1.5 nm per channel. And the chip has a side-mode suppressing ratio (SMSR) of over 35 dB and strong stability of wavelength in the repeated experiments. The proposed method may give a new way to realize the wide tuning range tunable DFB laser with a simple wavelength tuning mechanism in the future, especially for the applications of uncooled low-cost tunable lasers. [ABSTRACT FROM AUTHOR]

Multi-wavelength distributed feedback laser array based tunable semiconductor lasers have been widely used owing to their high mode stability and simple tuning scheme. Comparing with the in-parallel laser array, the in-series one can avoid a large power loss caused by the optical combiner. However, the single-mode stability of an in-series laser array is vulnerable to the reflections of other lasers. Here we experimentally demonstrated a tunable in-series laser array with high single-mode stability and high uniformity of wavelength spacing. To reduce the impact of such reflections, the Bragg gratings in different lasers were designed in phase, and the grating phase error was reduced by utilizing the reconstruction-equivalent-chirp technique. Besides, a three-section laser structure was applied in each laser to increase the priority of the dominant lasing mode. Four lasers with small wavelength-spacings of 2.5 nm were integrated in the in-series laser array. According to the measurement results of 40 in-series laser arrays (160 lasers), wavelength deviations of 90.6% lasers were within ±0.2 nm, average wavelength spacings of 97.5% of the measured laser arrays were deviated from the design within ±0.2 nm, and SMSRs of 96.3% lasers were above 45 dB. The output power was above 25 mW and the relative intensity noise was below −130 dB/Hz. Like the in-parallel laser array, the proposed laser array can be applied in either continuous wavelength tuning or fast channel switching. For the continuous wavelength tuning applications, the 10-nm tuning range was obtained with a temperature tuning range of less than 20 °C. For the fast channel switching applications, four channels with 2.5-nm spacing are available, and the switching time between two channels was less than 300 ns. [ABSTRACT FROM AUTHOR]

A four-channel wavelength-selectable in-series DFB laser array with good single-longitudinal-mode (SLM) property is proposed and theoretically analyzed. To realize good SLM property, a linearly chirped Bragg grating with multiple π phase shifts are implemented in the laser cavity. In addition, two reflector sections with chirped Bragg grating are specially designed for reflection compensation at both ends. In our simulation, the split-step time-domain model with coupled-wave equations and carrier rate equations are used. Based on the simulation results, all the channels work with low threshold currents and the SLM properties are considerably enhanced compared with the conventional in-series laser array. Notably a high precision control of grating phase is required in the practical fabrication due to the ultra-small variation of grating period. Therefore, the reconstruction-equivalent-chirp technique is discussed to provide the fabrication of high-precision grating. In addition, the complex heterogeneous integration or butt-joint technique is not required during the whole fabrication process, which simplifies the fabrication and reduces the cost. The proposed wavelength-selectable in-series laser array is deemed to be applied in the dense wavelength division multiplexing technology, especially when fast wavelength switching is needed, such as in the application of NG-PON2. [ABSTRACT FROM AUTHOR]