NTT Research and Development 2008 Review of Activities

High-speed wavelength-tunable lasers will be key devices in future photonic networks, where they will provide functions such as dynamic wavelength management in high-traffic WDM^*1 networks and packet-by-packet wavelength-routing switching in photonic packet routers. We recently developed a compact and simple widely tunable laser monolithically integrated with a semiconductor double-ring resonator. This laser is capable of high-speed wide-band tuning and has a low tuning current.

The laser consists of a gain section, a phase control section, and two micro-ring resonators with ring radii of around 10 µm. The device has a small footprint of 1.0 x 0.3 mm², and can be monolithically integrated with other photonic devices such as SOAs^*2 and AWGs^*3 without any additional fabrication process. The lasing wavelength can be tuned with a fast switching time (several nsec) by injecting currents into the ring resonators. The tuning range of up to 50.0 nm, which can cover the full C-band^*4 (1530-1565 nm), is achieved with injection currents of less than 5.2 mA.

The low tuning current operation makes the laser very promising for use as a high-speed tunable light source in photonic integrated circuits, because thermal wavelength drift due to current injection, which prevents a tunable laser from fast and accurate wavelength tuning, can be effectively suppressed. Future plans include fabrication of photonic integrated circuits such as wavelength converters and large-scale optical switches, and its application to photonic networks.

• *1 WDM: Wavelength Division Multiplexing
• *2 SOA: Semiconductor Optical Amplifier
• *3 AWG: Arrayed-Waveguide Grating
• *4 C-band: Conventional band