Sub-MHz linewidth of 633 nm diode lasers with internal surface DBR gratings
Proc. SPIE, vol. 8640, Photonics West, San Francisco, USA, Feb. 02-07, 86400A (2013).
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Red-emitting diode lasers having a large coherence length with a tunable wavelength and a narrow spectral linewidth with an emission power in the 10 mW range are sought for a variety of techniques in applications such as spectroscopy, interferometry and holography. Currently, helium-neon lasers or diode lasers with external wavelength stabilization are widely used for these applications. By integrating a wavelength selective element into the ridge waveguide (RW) of the diode laser chip itself a high degree of miniaturization and stability can be reached. To this end, we have developed RW lasers with deeply etched surface distributed Bragg reflector (DBR) gratings in order to achieve a high-yield, singleepitaxy manufacturing process. These DBR lasers consist of a 1.5 mm RW gain section and a 500 µm grating section, which has a reflectivity of about 60%. The facets of the lasers were coated to achieve a reflectivity of 30% at the front and smaller than 0.1% at the rear facet. The diode lasers achieve an optical output power of 20 mW at an injection current of 150 mA and a heat-sink temperature of 15°C at a wavelength of 633 nm. The DBR enables single longitudinal mode operation over a wide range of operation conditions. Self-delayed heterodyne measurements were performed to measure the emission linewidth of these lasers using a 1 km long fiber, which gives a spectral resolution of about 100 kHz. A linewidth of less than 1 MHz was obtained. In reliability tests at 14 mW a lifetime of more than 1,700 h could be demonstrated, dedicating these devices to the above mentioned applications.
a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
b eagleyard Photonics GmbH, Rudower Chaussee 29, 12489 Berlin, Germany
633 nm, diode laser, red-emitting, narrow linewidth, single mode, long coherence length.