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2 August 2004 Tilted cavity laser (Critical Review Lecture)
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Tilted Cavity Laser (TCL) is developed that combines advantages of a high power operation of an edge-emitting semiconductor diode laser and wavelength-stabilized operation of a surface emitting laser. A TCL emits laser light in a tilted optical mode that propagates effectively at a certain tilt angle to the p-n junction. Designed TCL comprises a high-finesse cavity into which an active region is placed and at least one multilayer interference reflector (MIR). The cavity and the MIR are designed such that the spectral position of the reflectivity dip of the cavity and the position of the stopband reflectivity maximum of the MIR coincides at one tilt angle of a tilted optical mode, and draw apart as the angle deviates from the optimum value. As a result, the leakage loss of the optical modes to the substrate is minimum at the optimum wavelength and increases dramatically as the wavelength deviates from the optimum one. This ensures the stabilization of the wavelength of the emitted laser light. Both quantum well (QW) and quantum dot (QD) TCLs have been fabricated on the basis of GaAs/GaAlAs waveguides. QW TCL using InGaAs QW as the active region and operating at 1000-1100 nm reveals the temperature shift of the lasing wavelength 0.2 nm/K. QW TCL operates up to and above 210°C with the differential efficiency 20%. QD TCL using InAs QD overgrown by InGaAs alloy as the active region and operating at 1100-1200 nm reveals the temperature shift of the lasing wavelength 0.165 nm/K. These shifts are significantly slower than the shift for a conventional edge-emitting semiconductor diode laser. The QD TCL shows an output power 2W in a pulsed mode. Characteristic temperature of the threshold current measured at and below room temperature (T0) is 150 K.
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