EDFA-enhanced sensitivity of RF magneto-optical probe

Abstract

EDFA-bsredsensilivit?. enhancement of MO field probe has been invortigated experimentally and theoretically. It was found out that optical pre-nmplifrration provider > 45 dB MO signal amplification and ASE-relaled noise reduction is P key issue. INTRODUCTIONOptical techniques for RF field measurement bared either on the eiectrodpti~ (EO) or magneto-optic (MO) effect have attracted considerable attention recently. This trend has been brought about not only by the advanced EO sampling techniques well developed so far but also by their anractive applications demonstrated for high speed electronic circuits evaluation^ and diagnosis [1]-[5]. In those measuremcnf techniques. their high speed and high spatial resolufion nature arc advantageous while their noninvasivene~s is also noteworthy. However, i t has been highly demanded to improve their sensitivity for many kinds of performance improvements and realization of funher useful and practical applications. Regarding the MO probe scheme, for example. higher spatial resolution, higher response speed. and real time imaging functionalily, etc. are expected to be brought about by sensitivity improvement in the optical detectionSimilar situaiion has been provided also for the EO probe scheme except for the issue of response speed improvement.One should note that preferable enhancement methods for the optical detection sensitivity depend on schsmes of optical measurement sysfcms. Generally, optical measurement schemer can be classified into two. One is the optical sampling and the other is the real wave measurement. A slow pholodetector (PD) is enough for the former while a fast photo-diode is necessary for the latter. An for the rampiing scheme. the input optical pulse energy is an impadant parameter and its improvement is principal ais pointed out in reference IO. On the other hand, an appropriate sensitivity enhancement method should be addressed to lhe Iattec measurement scheme accordingly to lhe esscntid features of fast photo-diodes.However. this important issue has been scarcely dealt with hitheno. In this paper, as described in the followings, we repon on our investigation rewits regarding EDFA-based enhancement of RF MO prove sensitivity.It was confirmed that the signal-to-noire-ratio (SNR) improvement is achievable by a me of an optical amplifier in prior to the PD stage, that is an optical pre-amplifier [ i l l , to&ether with the optimization of optical bias for lhe MO modulation. Funhemore, lhe details of the improvement mechanism have been investigated and it war figured out that an MO signal enhancement of 45 dB or higher is available by a standard Er-doped fiber amplifier (EDFA) and dominant RF noise components are given by amplified spontaneour emission (ASE) of EDFAs. Possibility of funher improvement was also examined on the basis of precise system modeling. 11. EXPERIMENTSHere, we explain experiments performed in order to clarify the optimum condition for lhe available best ~en~itivily of our system and the effectiveness of optical pre-amplification. Figu...

Electro-optic probing of microwave fields using a wavelength-tunable modulation depth

“…In the non-resonant configurations, the quarter waveplate/analyzer polarization components would be required, and typically 50% of the input probe light delivered to the detector, about five times more than for the resonant probe. While a non-resonant system can be operated with power levels reduced from this 50% level [14][15][16], a greater benefit in signal-to-noise ratio can be realized with the steeper modulation slopes of the resonant techniques. Moreover, in non-resonant, conventional systems, the index mismatch between the fiber/ferrule glasses and the crystal causes detrimental spectral modulation.…”