Two-section DBR laser transmitters with accurate channel spacing and fast arbitrary-sequence tuning for optical FDMA networks

The N-frequency two-section distributed-Bragg-reflector (DBR) Iaser is a promising candidate for use in optical frequency-division multiple-access (FDMA) networks.1 The present design has an active gain section, a Bragg section, and an integrated photodetector in an AT&T ASTROTEC package with a high-efficiency microlens, a built-in thermoelectric cooler, and a solid-state temperature sensor. The laser operates in a single longitudinal rnode with excellent side-mode suppression (>35 dB), offering more than 1 mW of fiber-coupled power with typical bias currents of 50 mA. Figure 1(a) shows the optical frequency as a function of the Bragg current, demonstrating 23 frequency channels spaced equally by approximately 49.8 GHz. The tuning hysteresis effect is small. The channel frequency spacing is inversely proportional to the laser Fabry-Perot cavity length, with a length ≈800 µm for 50-GHz spacing. Thus precise cleaving allows for a matching of the laser channel spacing to a desired value with the same fractional accuracy as the cleave length. We have achieved ±0.5% channel-spacing accuracy for the 50-GHz range. The laser temperature is adjusted ( − 12 GHz/°C) for alignment of the laser modes to standard optical frequency-division-multiplexing (FDM) channel frequencies. Figure 1 (b) shows the frequency offset from channel center. Each mode spans a frequency band ~4-6 GHz wide.