J. Pelayo

Very high resolution optical spectrometry by stimulated Brillouin scattering

In this letter, we demonstrate very high-resolution optical spectrometry based on stimulated Brillouin scattering between a swept-tuned laser and a test optical signal. Measurement principles are presented along with spectral measurements of unmodulated and modulated optical sources showing 0.08-pm resolution and 80-dB dynamic range.

New in-line optical-fibre sensor based on surface plasmon excitation

Abstract A new ‘in-line’ fibre-optic sensor based on the excitation of surface plasmons in a thin metal film deposited in the polished cladding of the fibre is presented. Optical-power transmission characteristics of the device, for TM-polar- ized light, have been both experimentally and theoretically investigated. The obtained results show the feasibility of practical designs with in-line fibre-optic configuration for a large range of optical sensor applications.

Single-mode, optical-fiber sensors and tunable wavelength filters based on the resonant excitation of metal-clad modes

The resonant excitation of metal-clad modes, including fundamental and higher-order modes, in a multilayer structure deposited on the polished cladding of a single-mode optical fiber is theoretically analyzed and experimentally demonstrated. The excitation of metal-clad modes is shown as a resonant power transfer from the fiber to the metal-clad mode that takes place for an external refractive-index value such that the effective index of the metal-clad mode reaches the cladding level. The observed attenuation on the TM polarization provides a suitable transducing mechanism for refractive-index sensor devices as well as the principle for developing tunable wavelength-polarized filters with a wide range of optical performance characteristics.

High resolution light intensity spectrum analyzer (LISA) based on Brillouin optical filter

A high-resolution light intensity spectrum analyzer technique to derive the RF modulation spectrum of optical signals is presented and experimentally confirmed. It uses the XPM nonlinear effect in a dispersion shifted fiber to obtain the light intensity spectrum, and a Brillouin optical filtering method to implement the high resolution spectrometric analysis. Measured RF spectra of PRBS modulated optical signals at 2.5 Gb/s and 10 Gb/s are presented and compared with their corresponding ones obtained in the electrical detection domain to confirm the capabilities of the method.Influence of fiber electrostriction effect is measured and analyzed.

All in fiber optical frequency metrology by selective Brillouin amplification of single peak in an optical comb.

Suitable use of stimulated Brillouin amplification (SBA) effect for selective single peak amplification in an optical frequency comb is demonstrated to provide high accuracy in optical frequency metrology. A pump wave generated by a tunable laser source (TLS) is used to stimulate SBA of such optical comb along an optical fiber and selectively amplify only one single peak of the comb. Nature of SBA preserves both linewidth and absolute wavelength position of the selected comb peak. All of these features result in a simple, robust and compact all in fiber system. Relative optical frequency accuracy in the order of Hz is confirmed.

Brillouin induced self-heterodyne technique for narrow line width measurement

A novel technique is introduced for jitter-insensitive sub-KHz resolution linewidth characterization technique in ultra-narrow lasers for optical communication applications. The technique is based on self-heterodyne detection induced by Stimulated Brillouin Scattering (SBS). Non linear SBS drives the heterodyne mixing through optical frequency locking of a narrow tunable laser source and the signal under test, which is modulated in the low frequency range. Due to SBS nature, jitter variations in the optical frequency do not affect the correlation spectra measured with resolution figures up to 300 Hz, without the need for optical delay line as in conventional homodyne correlation techniques.

Subpicometer wavelength accuracy with gain-switched laser diode in high-resolution optical spectrometry

We present a method to generate an optical reference comb signal with subpicometer wavelength accuracy. XPM nonlinear effect in a fiber is used to get an optical frequency comb signal, free of frequency chirp and wavelength instabilities, from a pulsed gain-switched laser diode. Principles of such comb generation are presented as well as the application of this comb as a ruler to measure frequency differences in high resolution optical spectrum measurements. To confirm this method, Brillouin filtering optical spectrometric technique is used to characterize a modulated optical source. Typical resolution of this technique allows 0.08 pm wavelength accuracy.

Electrostriction-free n 2 measurement in single-mode optical fibers based on nonlinear-polarization evolution

An electrostriction-free continuous-wave measurement technique for the nonlinear index in telecommunication fibers, based on nonlinear-polarization evolution, is presented. Nonlinear birefringence induced in a fiber by cross-phase modulation from a pump beam determines the polarization-state evolution in a probe beam coming from the same source. Determination of the n2 refractive index from the nonlinear-polarization evolution allows an electrostriction-free n2 measurement, while the use of the same source for pump and probe beams avoids averaging effects caused by chromatic and polarization dispersion in long fibers.

Chromatic dispersion characterization in short single-mode fibers by spectral scanning of phase difference in a Michelson interferometer

Chromatic dispersion characteristics around zero-dispersion wavelength have been measured in short samples of single-mode fibers by a spectral scanning of the interference signal in a Michelson interferometer. The propagative refractive index is directly obtained from the phase-difference variations with the wavelength between a light beam propagated through the fiber and a reference beam. The optimum operative conditions of the interferometer for obtaining the unequivocal analysis of experimental signals are discussed. The accuracy of the results obtained shows the reliability of the method for a complete dispersion characterization. >

Direct measurement of frequency and polarization dependences of cross-phase modulation in fibers from high-resolution optical spectra

We present the results of an experiment for frequency and polarization dependence characterization of non-linear cross-phase-modulation (XPM) effects in optical fibers. The measurement technique is based on the direct analysis of high-resolution optical spectra of a signal wave that is phase modulated by an intensity-modulated pump wave. Measurement results provide experimental confirmation of the scalar character, over the whole resonant frequency range, of the electrostrictive contribution to the nonlinear refractive index. Also, the results confirm experimentally the relation describing the polarization dependence of the Kerr contribution to XPM in non-polarization-maintaining fibers.