A 1542-nm planar-waveguide external cavity laser (PW-ECL) is shown to have a sufficiently low level of noise to be suitable for precision measurement applications. Its frequency noise and intensity noise was comparable or better than the non-planar ring oscillator (NPRO) and fiber laser between 0.1 mHz to 100 kHz. Controllability of the PW-ECL was demonstrated by stabilizing its frequency to acetylene ((13)C(2)H(2)) at 10(-13) level of Allan deviation. The PW-ECL also has the advantage of the compactness of a standard butterfly package, low cost, and a simple design consisting of a semiconductor gain media coupled to a planar-waveguide Bragg reflector.

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A 1550 nm DWDM planar external cavity laser (ECL) is demonstrated to provide low phase/frequency noise, narrow linewidth, and low RIN. The cavity includes a semiconductor gain chip and a planar lightwave circuit waveguide with Bragg grating, packaged in a 14-pin butterfly package. This planar ECL laser is designed to operate under vibration and in harsh environmental conditions. The laser shows linewidth ≤ 2.6 kHz, phase/frequency noise comparable with that of long cavity fiber lasers, RIN ≤ -147dB/Hz at 1kHz, and power ≥ 10mW. Performance is suitable for various high performance fiber optic sensing systems, including interferometric sensing in Oil and Gas, military/security and other applications, currently served mostly by costly and less reliable laser sources.Keywords: planar external cavity laser, phase noise, linewidth, relative intensity noise, fiber optic sensing, butterfly package, seismic exploration, remote interferometric sensing. IntroductionHigh performance, fiber optic distributed interferometric technology was developed over the past 15 years for obtaining high quality dynamic measurements, but it has only recently moved into the deployment stage. Due to the technology's historically high cost, applications fall mostly into military surveillance or remote sensing in severe environments (sub-sea or subsurface for the oil and gas industry). These applications are now moving toward cost/performance optimization as the technology matures. Other more cost sensitive applications, which include distributed structural monitoring, large area and perimeter surveillance, seismic monitoring, and communications systems security, are now gaining the benefits of this optimization, and these applications are much larger in terms of market size.

We describe the characteristics of the planar-waveguide external cavity diode laser (PW-ECL). To the best of our knowledge, it is the first butterfly-packaged 1064 nm semiconductor laser that is stable enough to be locked to an external frequency reference. We evaluated its performance from the viewpoint of precision experiments. Using a hyperfine absorption line of iodine, we suppressed its frequency noise by a factor of up to 10(4) at 10 mHz. The PW-ECL's compactness and low cost make it a candidate to replace traditional Nd:YAG nonplanar ring oscillators and fiber lasers in applications that require a single longitudinal mode.

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