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(a) Schematic structure of the device, and illustration of its operating principles. [(b)–(e)] Microscope images of the devices (top view). For all devices, the period of the PC is . Small regions in two corners of each device are introduced for wire bonding. (b) Standard PC, the hole radius is ; (d) the same structure as (b) with a -shift; [(c) and (e)] graded PC structures with optimized -factors, with and without phase shift, respectively. The radii of the holes are in the range .
Electro-optical characteristics of the lasers. (a) characteristics voltage-light-current density (LJV) of devices with and without -shift, and with and without -factor optimization. The measurements were performed at 78 K, using a Peltier-cooled far-IR DTGS detector. The devices were operated at a 20 kHz repetition rate, with 300 ns wide pulses. (b) Temperature dependence of for the four devices; (c) Typical laser spectra of the devices. The devices without optimization lase on a water vapor absorption line, which could partially explain the lower measured output power.
Far-field emission patterns of the lasers. The central inset defines the angles of scanning. A Golay cell detector was used for the measurement. [(a) and (b)] correspond to the measured far-field patterns of the optimized structures, without and with the -shift phase-delay, respectively [Figs. 2(c) and 2(e)]. [(c) and (d)] Show the corresponding predicted far-fields, respectively.
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