Spectral behavior of a low-cost all-fiber component based onuntapered multifiber unions

Untapered multifiber unions are reported to show a spectral behavior similar to the tapered ones. Their oscillatory behavior does not depend on the biconical regions. This suggests a novel way to make low-cost all-fiber devices with applications as passive components such as optical filters and wavelength multiplexers/demultiplexers. Two types of multimode fibers have been studied and information about the index profile influence has been obtained. Polarization insensitivity and temperature stability have been observed     

Interrogation of wavelength multiplexed fiber Bragg gratings using spectral filtering and amplitude-to-phase optical conversion

A technique for interrogating multiplexed FBG sensors using all-fiber low-cost devices is demonstrated. It is based on spectral filtering employing a fused biconical wavelength-division multiplexer and on amplitude-to-phase optical conversion to perform power referencing. Four FBG sensors are wavelength multiplexed in the network, and a 3-nm-wide tunable optical filter is employed at the detection block for sensor demultiplexing. With this technique an operation range of more than 2 nm is demonstrated for the sensors with achievable wavelength static resolution ranging from 1.9 to 13.4 pm/Hz/sup 1/2/ with no observable hysteresis. As for power referencing, the system is proven to be unaffected by power variations as high as 75% of the total power launched by the source. Finally, output-phase variations due to crosstalk are shown to be under 1% of the total output phase range, with more than 29-dB optical isolation between channels.     

Depressed-index waveguides (DIW's) in integrated optics

A general theoretical consideration of depressed-index waveguides (DIWs) is undertaken. Two-mode interference structures are studied utilizing this model. Emphasis is placed on the use of the model as a wavelength demultiplexer in order to provide the theoretical basis of a recently proposed device based on a symmetric three-modal waveguide     

Single and double distributed optical amplifier fiber bus networkswith wavelength division multiplexing for photonic sensors

This paper presents numerical simulations of single and dual fiber bus networks with distributed amplification, which are used for the wavelength division multiplexing of photonic sensors. The model upon which the simulations are based has been compared to a previously published experimental result and good agreement has been obtained. A novel technique for allocating the signal wavelength to the sensor position in order to equalize the received signal power is also discussed     

Multiplexing of fibre optic intensity sensors using fused biconicalwavelength selective couplers

Fused biconical wavelength division multiplexers have been used to replace standard couplers in an intensity-sensor multiplexing network. The wavelength-selective power splitting and the low insertion losses of these devices (<0.2 dB) improve the power budget, while providing network overall optical isolations >30 dB. With this isolation, crosstalk effects in the network are proven to be negligible     

Multiwavelength fiber laser sources with Bragg-grating sensormultiplexing capability

Two erbium-doped fiber ring lasers (EDFRLs) wvith simultaneous emission at four different wavelengths are demonstrated. Both systems employ fiber Bragg gratings (FBGs) to select the operation wavelengths within the ring. The sensing capability of the FBGs has been taken advantage of, allowing for the sources to be used as sensor multiplexing schemes. The first system employs four FBGs in a tree filter topology, achieving four output channels with -5 dBm power each. The second system comprises an in-line filtering topology with active fiber segments within the filter. This second source yields 2-dBm output signals and allows for a higher number of lines to be easily added to the system. A comparison between both topologies is carried out, and their capability for sensor multiplexing is demonstrated     

Stability comparison of two quadruple-wavelength switchable erbium-doped fiber lasers

An experimental stability comparison between two different switchable Erbium-doped fiber lasers (EDFL) is carried out. Both topologies use fiber Bragg grating reflectors in order to select the emission wavelengths and two 2 × 4 optical switches. By adjusting the switches combinations, the lasers can be switched among the sixteen different wavelength lasing configurations. An output power and wavelength instability analysis with time for both topologies was performed. The experimental results confirm that the topology based on a serial configuration offers a better stability, efficiency and higher optical signal-to-noise ratios (OSNR) than the one based on a parallel configuration.     

Double Raman Amplified Bus Networks for Wavelength-Division Multiplexing of Fiber-Optic Sensors

In this paper, three different double Raman fiber bus networks are compared and demonstrated experimentally for the first time as a means of gathering information from wavelength- division-multiplexed optical sensors: the double-bus scheme, the improved double-bus configuration, and the hybrid topology. We report how these structures reduce the received amplified- spontaneous-scattering noise generated. This low-noise configuration yields signal-to-noise ratios over 43 dB and increases the number of sensors that could be multiplexed in a single structure. Furthermore, the last one enables the reutilization of the gratings' wavelengths.     

Optimization of the frequency-modulated continuous wave technique for referencing and multiplexing intensity-based fiber optic sensors

In this paper, we demonstrate the interrogation of fiber optic intensity sensors by using the combination of the frequency-modulated continuous wave concept with the spectral selective reflectivity of fiber Bragg gratings. Thus, we multiplex these kinds of sensors with this technique having simultaneously a referenced system. The basis of this dual functionality is described and results are presented for the case of interrogation of two multiplexed intensity sensors. Their evaluation permits to establish the conditions to address a sensor network of this type. Also, it is proposed a strategy to implement this sensing approach without the requirement of using optical fiber delay lines in the sensor heads.