Signal interogator
All-optical, thermo-optical path length modulation based on the vanadium-doped fibers

This paper presents an all-fiber, fully-optically controlled, optical-path length modulator based on highly absorbing optical fiber. The modulator utilizes a high-power 980 nm pump diode and a short section of vanadium-co-doped single mode fiber that is heated through absorption and a non-radiative relaxation process. The achievable path length modulation range primarily depends on the pumps power and the convective heat-transfer coefficient of the surrounding gas, while the time response primarily depends on the heated fibers diameter. An absolute optical length change in excess of 500 m and a time-constant as short as 11 ms, were demonstrated experimentally. The all-fiber design allows for an electrically-passive and remote operation of the modulator. The presented modulator could find use within various fiber-optics systems that require optical (remote) path length control or modulation.

Rapid and broad wavelength sweeping of standard telecommunication distributed feedback laser diode

This Letter presents a method for the fast and broad wavelength sweeping of a standard setup of a diodes active region and its immediate vicinity, which contain the diodes optical feedback system. The selective and rapid heating of the active region is possible due to the confinement of the voltage drop to the active diodes region that has submicrometer thickness. Using the presented method and an off-the-shelf telecommunication distributed feedback laser diode, we demonstrate wavelength sweeps in excess of 10 nm that were completed in about 200 ns, while generating average optical power in excess of 50 mW. In spite of high-amplitude current-drive pulses, 6000 h continuous operation of the diode within such an operational regime did not show any significant degradation of the diodes performance.

High-resolution spectrally-resolved fiber optic sensor interrogation system based on a standard DWDM laser module

This paper presents a spectrally-resolved integration system suitable for the reading of Bragg grating, all-fiber Fabry-Perot, and similar spectrally-resolved fiber-optic sensors. This system is based on a standard telecommunication dense wavelength division multiplexing transmission module that contains a distributed feedback laser diode and a wavelength locker. Besides the transmission module, only a few additional opto- electronic components were needed to build an experimental interrogation system that demonstrated over a 2 nm wide wavelength interrogation range, and a 1 pm wavelength resolution. When the system was combined with a typical Bragg grating sensor, a strain resolution of 1 ?? and temperature resolution of 0.1 C were demonstrated experimentally. The proposed interrogation system relies entirely on Telecordia standard compliant photonic components and can thus be straightforwardly qualified for use within the range of demanding applications.

An all-fiber scanning interferometer with a largeoptical path length difference

This paper describes the design of an all-fiber scanning interferometer. The main component of the system is a thermoelectric cooler that can rapidly heat or cool several meters of optical fiber. Over 4 cm variation of optical path length is achieved with a scanning speed exceeding 12 mm/s. The system does not include any moving parts and has low insertion loss.

High-speed interrogation of low-finesse Fabry-Perot sensors using a Telecom DFB laser diode.

This paper presents a high-speed high-resolution low-finesse Fabry-Perot sensor interrogation system. The system utilizes a standard telecommunication distributed-feedback laser diode and an all-digital high-speed signal processing based on field-programmable-gate-array. The system can resolve multiple Fabry-Perot Interferometers (FPI) simultaneously, which might include multiple sensors, multiparameter sensors, or combinations of sensor(s) and reference FPIs. This opens up possibilities for adopting different measurement system configurations and compensation schemes. The system exhibits white-noise characteristics for a system bandwidth above 100 Hz, with spectral density of about 2 pm/?Hz when interrogating about 1 mm long low-finesse FPI. At an output sampling rate of 10 Hz, a sensor measurement length resolution of less than 50 pm was demonstrated for about a 600 ?m long sensing cavity (corresponding to a strain resolution of about 70 n?). Proper use of simple all-fiber reference also provided low long-term drift. The system provides an up to 40 KHz sampling rate and was used to demonstrate dynamic measurement of strain variation on a piezo-electric stack and for interrogation of in-cylinder pressure variations within a high-rotation-rate miniature diesel engine. Fabry-Perot sensors with typical lengths between a few hundred and a few mm can be read-out with the current version of the proposed interrogator. The proposed system was built out of a small number of highly cost-efficient optoelectronics and electronics components (all used in FTTH) and thus, opens-up potential for new applications where the cost of interrogation is presently limiting.

Interrogation of FBGs and FBGs arrays using standard telecom DFB diode

An efficient fiber Bragg grating (FBG) sensor integration system, which utilizes a small number of standard Telecom opto-electronics components, is presented in this paper. Wavelength-swept optical pulses were generated by driving a standard telecom DFB laser diode by high amplitude (>3 A) and short duration (300 ns) current pulses. A total laser diode's wavelength sweep in excess of 10 nm was achieved, which allows for simultaneous interrogation of several FBGs within similar wavelengths. The application of short duration wavelength-swept optical pulses also allows for time division multiplexing of small FBG arrays containing FBGs with overlapping characteristic wavelengths. When a short, wavelength-swept optical pulse is launched into the fiber containing single or multiple FBGs along its length, fractions of the launched pulse are back-reflected towards the detector. Since the launched pulse wavelength changes over the time, the reflections from the FBGs occur in the time moments that depend on the FBGs' characteristic wavelengths. Measurement of the time delay among back-reflected optical pulses is then used to determine the FBGs characteristic wavelengths. The experimental system demonstrated FBG wavelength readout resolution, which exceeded 3 pm at 1 KHz sampling rate, maximum sampling rate of over 40 KHz, and capability to readout/demultiplex over 30 FBGs located down a single optical fiber.