In this study, the 1.3 μm wavelength range super structure grating (SSG-) distributed Bragg reflector (DBR) laser was experimentally demonstrated for the first time. The use of 1.3 μm wavelength range tunable DBR lasers has been barely reported because of their small refractive index change compared with that of the 1.55-μm wavelength range, although 1.3 μm is a major wavelength range for optical communication. One reason is that increasing the carrier concentration in the InGaAsP core layer in the DBR sections is difficult. This is because the bandgap energy of the core layer for 1.3-μm wavelength range lasers should be relatively large compared with that of 1.55-μm wavelength range lasers, and it reduces the band offset between core and InP claddings. To efficiently trap the carrier inside the core layer, we introduced InAlAs carrier confinement layers (CCLs) to both boundaries between the core layer and cladding layers. As a result, the 1.3 μm wavelength range SSG-DBR laser was successfully demonstrated with a 4.9-nm quasi-continuous wavelength tuning range by using the single SSG-modes. Furthermore, the total wavelength tuning range of 31 nm and stable single mode operation for the entire tuning range were achieved. The introduced CCLs significantly enhanced the refractive index change due to the carrier-plasma effect and thus we can successfully demonstrate wide range tuning of the 1.3-μm wavelength range SSG-DBR laser.
An InGaAs based distributed Bragg reflector (DBR) laser operating at 2 μm was fabricated and evaluated as a light source for real-time gas sensing for which mode-hop free operation throughout its lifetime is essential. We therefore performed an aging test to confirm mode-hop free operation. Current was injected into the active/SOA region and/or the DBR/phase control (PC) region at 85 °C. The changes in threshold current and wavelength were not significant after 5000 h of aging. As the wavelength shifts for DBR and PC current after aging are comparable, we confirmed mode-hop free operation of the laser throughout its lifetime as a gas-sensing light source.
Electro-absorption modulator (EAM) integrated distributed feedback (EADFB) laser are widely used for 10-, 40- and over 40-km optical communications. In a certain power dissipation condition, there is intrinsic difficulty in increasing the modulated light output power of EADFB lasers, because large insertion loss of the EAM deteriorates the power conversion efficiency. In this study, we investigated an SOA integrated with a EADFB laser to improve the power conversion efficiency of the EADFB laser. The device is called an SOA assisted extended reach EADFB laser, or AXEL for short. For a transmission with a 1.3-μm wavelength, the transmission distance was limited to 40 km because of the large fiber loss of 0.3 dB/km. To overcome this kind of transmission distance limit, we demonstrated a 1.3-μm AXEL with significantly increased power conversion efficiency. In addition, a 25-Gbit/s 80-km transmission by using AXEL and APD-ROSA was firstly achieved beyond the limitation of transmission distance. In contrast, with respect to an L-band wavelength range, a large chromatic dispersion severely limits the transmission distance. Then, we also investigated the AXEL with 1.57 μm wavelength range, and found that the SOA can operate as both optical booster and chirp compensator. Furthermore, the extension of 10-Gbit/s transmission to 80-km and enhancement of modulated light output power to 9.0 dBm were simultaneously achieved by taking advantages of its chirp compensation effect and high power conversion efficiency. The presented results indicate that the AXEL is an attractive candidate for a high-efficiency modulated light source with any wavelength range.
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