Jesús Subías

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.

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.

Measurement of the effective area of non-linear power transfer in single-mode fibers due to stimulated Raman scattering

Abstract A method to measure the non-linear effective area in single-mode fibers is described. It is based on a Raman non-linear effect characterization set-up that uses a continuous-wave double beam arrangement in counter-propagating configuration. Non-linear effective areas are theoretically evaluated and experimentally determined for various types of fibers (standard single-mode fiber, dispersion-shifted fiber and large effective area dispersion-shifted fiber) and a correction factor that relates these effective areas with the mode field diameters of the fibers is introduced for taking into account the departures of the power distributions from the Gaussian shape.

Analysis of the modal solutions of rib antiresonant reflecting optical waveguides

The modal behavior of rib antiresonant reflecting optical waveguides (ARROWs) is theoretically analyzed in this work. Two numerical analysis methods have been used for the analysis of an open rib structure: the spectral index method and a vectorial mode matching method, where the real and the imaginary part of the modal solutions of several structures have been studied. A nearly polarization independent open rib structure and a embedded rib structure have also been studied using the mode matching method. Obtained numerical results will be also compared with experimental data in order to point some observed discrepancies.

Wavelength selective optical fiber couplers based on longitudinal Fabry-Perot structures

A new approach for the development of wavelength selective optical fiber couplers is proposed. It is based on a standard polished fiber coupler in which an intermediate planar multilayer structure, which acts as a transversal optical filter, is included between the two fibers. The simplest multilayer structure, with interesting potential applications, is constituted by high refractive index single-layer Fabry-Perot filters. Experimental results for several single-layer Fabry-Perot filters, as well as a phenomenological model that provides accurate predictions about the wavelength selective coupling ratio, are presented. >

Novel in-band OSNR monitoring system based on a polarization interferometer

In this communication we propose a OSNR measurement system capable of perform in-band measures of optical noise in OOK/PSK channels. Our design takes advantage of the noise polarization insensibility, using a polarization interferometer to discriminate it from the signals.

In-Band DGD Monitoring Based on Polarization Controlled Stimulated Brillouin Scattering

In this letter, we present a new all-optical method for the measurement of the wavelength-resolved state-of-polarization vector across the bandwidth of multiple in-service channels. Taking advantage of the narrow spectral selectivity of stimulated Brillouin scattering and its dependence with the relative polarization alignment between the pump and the stimulus, polarization selective spectral measurements are performed on the signal under test. Obtaining the spectra for three pairs of orthogonal polarization states of the pump, the three Stokes parameters are retrieved for each spectral component. Differential group delay is then calculated from the spectral evolution of the polarization state.

Analysis of the polarization dependence of non-linear effects using high-resolution spectrally-resolved polarimetry

In this work a full characterization in the Stokes space is presented of diverse polarization issues associated with non-linear effects such as Cross Phase Modulation (XPM) and Four Wave Mixing (FWM). A high resolution spectral polarimetry technique has been applied that allows simultaneous visualization of the polarization parameters in the full spectral range of interest. The state of polarization of all the spectral components is obtained without filtering or isolating each component individually. The measurement technique that has been used is based on the polarization properties of Stimulated Brillouin Scattering (SBS), and is achieved by analyzing the polarization dependence of the spectral contribution of the SBS generated in the interaction of a given signal with a tunable optical pump. This allows a high resolution characterization of the polarization properties of the generated spectral components generated by non-linear effects. Without prior knowledge or alignment, all the polarization related impairments can be monitored. The source of the polarization related impairment can be arranged as a linear effect (Polarization Mode Dispersion) or non-linear effect (XPM). The complete information of the polarization states allows also full quantification of the non-linear interaction in the XPM and thus obtaining a value of the non-linear coefficient, n2.

Novel method for the measurement of the wavelength-resolved high-resolution polarization state of optical signals and application to the monitoring of communication signals

We present a method for the characterization of the polarization state of the optical spectrum components of an optical signal with high resolution (80 fm). Polarization dependence of stimulated Brillouin scattering is used to obtain the projections of the high-resolution optical spectrum to a state determined by controlling the polarization state of the pump signal. Combining data from different polarizations we extract the wavelength-resolved optical polarization state of the signals. Applications of this measurement to the study of polarization effects in communication signals are also presented.

In-band optical signal-to-noise ratio monitoring method based on high-resolution polarization analysis and induced differential group delay

We report on an in-band optical signal-to-noise ratio monitoring technique for wavelength division multiplexed channels. Our proposal relies on the different degree of polarization between the signal (highly polarized) and the noise (not polarized). Using this principle, we divide the signal under test into two orthogonal polarization components and induce a differential group delay via a controlled birefringence apparatus that produces a wavelength-dependent shift of the polarization state of the signal. After a linear polarizing filter, high-resolution spectral analysis allows measurement of the amplified spontaneous emission noise level. The method is tested by experimental measurements of a 40 Gbit/s differential phase-shift keying channel showing very good performance.