Broad-band tunable electroabsorption modulated laser for WDM application

Abstract

Design and fabrication of the first 1.55-/spl mu/m wavelength tunable electroabsorption modulated laser integrated with a bent waveguide distributed-feedback (DFB) laser is reported. A low-threshold high-efficiency and stable single-longitudinal-mode operation is obtained when the electrodes of the bent DFB waveguide were uniformly pumped. In a normal configuration where the modulator part is used as an intensity modulator (i.e., AR coating on the modulator side and HR coating on the DFB side), stable single longitudinal mode output power close to 40 mW in free space is obtained with a 0-V bias to the modulator and an extinction ratio of up to 15 dB at 2.5 V. This single mode stability is due to the continuously distributed phase shift implemented in the structure thus reducing the photon pile-up inside the laser cavity as compared to an abruptly quarter-wave phase shifted DFB laser. With a nonuniform injection in the multiple electrodes, it was possible to select one particular single longitudinal mode out of the three neighboring modes inside the broad reflection band of the reflector. A wavelength tuning range of about 3.5 nm was obtained while maintaining an optical output power of more than 2 dBm from each mode. The device has a very low chirp (0.01-nm peak-to-peak) when modulated with a 2.5 Gb/s pseudorandom binary sequence (PRES) data stream and an error-free transmission over 200 km of non-DSF fiber has been demonstrated for all four wavelength channels separated by 100-GHz spacing. Also, when the modulator part of the structure is used as a phase tuning element (i.e., antireflective (AR) coating on the DFB side and HR coating on the modulator side), we have successfully demonstrated high-speed optical packet switching with a fast and wide tunable wavelength range. The optical packets can be modulated at 2.5 Gb/s and may be switched among four wavelength channels in less than one bit period.