2.1.1 Laterally coupled distributed-feedback

A proposed method for DFB fabrication which was recently demonstrated by the Jet Propulsion Laboratory (JPL) [18], makes use of Bragg gratings etched alongside a ridge waveguide to form a laterally coupled distributed-feedback (LC-DFB) as shown in Figure 2 This approach enables fabrication of single-longitudinalmode laser following a single epitaxial growth process.

Characteristics of the LC-DFB laser are as follows; at a heat sink temperature of 10°C they demonstrate a single mode emission in the 2054 nm region with an SMSR > 30 dB and ex-facet power exceeding 80 mW. This is the highest reported power from a DFB laser at 2 μm. The wavelength shift with current and temperature is reported to be 5.39 <sup>10</sup><sup>3</sup> nm/mA and 0.2 nm/<sup>o</sup> C [19]. They also demonstrated LC-DFB laser linewidths of 1.4 MHz and 900 kHz for 500 and 10 ms observation times, respectively. The linewidths were derived from the frequencynoise power-spectral density measured using a Fabry-Perot interferometer.
