speed is faster for co-pumping than that for counter-pumping. We can achieve a relatively high PCE when input-signal power is low for co-pumping and high for counter-pumping. REFERENCES 1. L.D. Garrett, M. Eiselt, R.W. Tkach, V. Dominic, R. Waarts, D. Giltner, and D. Mehuys, Field demonstration of distributed Raman amplification with 3.8-dB Q-improvement for 5 ϫ 120-km transmission, IEEE

Limitations to a novel opto-electronic method of determining the ac response of fast photo-detectors (frequency range > GHz) in the 850 nm spectral region, based on a broadband, spectrally resolved separation of optical relative intensity and shot noise, are investigated. In common with a number of related techniques developed over the years, the method relies on the whiteness of quantum shot noise, which has the fundamental property of presenting a constant power level across all frequencies, to reveal the ac detector response over a potential large spectral range. The present work is, however, believed to be the first to exploit in this context a classic method of separating shot noise from other noise spectra for detector response determination, even in situations where non-white noise light sources are used. The method demands a minimum of extra equipment and could be appropriate for field measurements in optical communication and optical sensor systems. On the other hand, the new method has larger measurement uncertainties (several dB) than other methods of determining photo-detector ac response.

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A novel technique is presented of narrowing the spectral linewidth of microwave signals generated by heterodyning pairs of VCSELs which form an extended optically coupled cavity. We experimentally demonstrate a linewidth reduction by as much as a factor of 104 -to less than 10 kHz. IntroductionVertical cavity surface emitting semiconductor lasers (VCSEL) are attractive in several applications, such as optical communication owing to their ease of manufacture and good optical beam and power efficiency. However in applications where more exacting demands are placed on high spectral purity, such as precise frequency metrology, environmental spectroscopy sensors and microwave photonics, the large intrinsic spectral linewidth (circa 100 MHz) of VCSELs associated with the small laser gain volume presents a serious limitation [1].

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