A coherent optical RF channelizer has been constructed and characterized. The optical channelizer is based on a free-space optical diffraction grating, and utilizes coherent optical heterodyne detection to translate all of the frequency channels to a common intermediate frequency (IF). The designed optical channelizer has a 1-GHz channel spacing, and a nominal 5-GHz IF, and can offer an instantaneous bandwidth greater than 100 GHz. The channelizing receiver has been characterized for its frequency response, crosstalk, and spur-free dynamic range, and the results are in a good agreement with the theoretical values.
CW injection locking of mode-locked semiconductor lasers has been experimentally demonstrated. The phases of the mode-locked frequency comb are shown to be coherent with that of the master CW laser. The pulsewidth of the mode-locked laser remains almost unchanged (<2 ps) for a broad range of injection power (028 to 012 dBm). Pulling of the entire modelocked frequency comb by 400 MHz has been demonstrated. The coherent multifrequency source can be used as a local oscillator comb for coherent optical channelizers for ultrawide-band RF signals.
We experimentally demonstrate a 240-fold increase in the efficiency of an AlGaAs/ALAs surface-emitting second-harmonic generation device by embedding the waveguide core in a monolithic vertical resonant cavity. Calculations indicate that conversion efficiencies of several percent per watt for second-harmonic generation of green or blue light may be expected in an optimized semiconductor resonant vertical-cavity surface emitter.
Coherent photonic systems promise novel functionality and/or improved performance compared to direct detection photonic systems, but have the disadvantage of being sensitive to optical phase noise. The most common approach to this problem is to force one laser to track the phase of the other with a phase locked loop (PLL), so that the phase noise of the lasers cancelsout of the RF heterodyne beat note. Although the PLL approach has been implemented for semiconductor lasers, the large linewidth of these lasers and the resulting large PLL loop bandwidth severely constrain the design and limit performance. This disadvantage of the PLL approach is particularly relevant for many applications, since semiconductor lasers are preferred for system insertion.An alternative approach for establishing coherence between two lasers is optical injection locking. Standard theory indicates that injection locking can act in the same way as a first order PLL with a bandwidth as high as several GHz, which is large enough to achieve state of the art noise levels (e.g. -130 dBcIHz @ 1 MHz offset) with semiconductor lasers. We present phase noise measurements on the beat note of two injection locked semiconductor lasers. Our results (phase noise @ 1 MHz offset as low as -125 dBcIHz) indicate that state of the art phase noise performance from injection locked lasers should be obtainable in practice. We found that it is necessary to length match the two paths in the experiment (master -> detector and master -> slave -> detector) to avoid excess noise due to delay decorrelation of the master, and also that environmental noise seems dominant at offsets < 20 kHz.
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