Fiber Bragg grating-based thermometer for drill bit temperature monitoring.

The temperature measurement of a drill bit during an implantology drilling process is proposed by using a fiber Bragg grating fitted inside the drill bit. Due to the rotational nature of the drilling process, a free-space fiber-optic rotary joint is used for interrogating the fiber Bragg grating. Due to mechanical clearances and interferometric noise induced at this rotary joint, signal integrity is strongly deteriorated and is not workable without adequate measures.

Interferometric measurements beyond the coherence length of the laser source.

Interferometric measurements beyond the coherence length of the laser are investigated theoretically and experimentally in this paper. Thanks to a high-bandwidth detection, high-speed digitizers and a fast digital signal processing, we have demonstrated that the limit of the coherence length can be overcome. Theoretically, the maximal measurable displacement is infinite provided that the sampling rate is sufficiently short to prevent any phase unwrapping error.

Liquid-air based Fabry-Pérot cavity on fiber tip sensor.

This paper presents a Fabry-Perot fiber tip sensor based on an air-liquid filled cavity. The cavity is sealed off by a thin gold coated membrane of parylene C, between 300 and 350 nm, creating a particularly flexible diaphragm. In order to retrieve and track the cavity of interest from other cavities formed within the sensor tip, a signal processing of the feedback signal is performed by inverse fast Fourier transform.

Superheterodyne configuration for two-wavelength interferometry applied to absolute distance measurement.

We present a new superheterodyne technique for long-distance measurements by two-wavelength interferometry (TWI). While conventional systems use two acousto-optic modulators to generate two different heterodyne frequencies, here the two frequencies result from synchronized sweeps of optical and radio frequencies. A distributed feedback laser source is injected in an intensity modulator that is driven at the half-wave voltage mode.

Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry.

We present a new technique applied to the variable optical synthetic wavelength generation in optical interferometry. It consists of a chain of optical injection locking among three lasers: first a distributed-feedback laser is used as a master to injection lock an intensity-modulated laser that is directly modulated around 15 GHz by a radio frequency generator on a sideband. A second distributed-feedback laser is injection locked on another sideband of the intensity-modulated laser.

High-accuracy absolute distance measurement using frequency comb referenced multiwavelength source.

We propose a new approach to multiple-wavelength interferometry, targeted to high bandwidth absolute distance measurement, with nanometer accuracy over long distances. Two cw lasers are stabilized over a wide range of frequency intervals defined by an optical frequency comb, thus offering an unprecedented large choice of synthetic wavelengths. By applying a superheterodyne detection technique, we demonstrated experimentally an accuracy of 8 nm over 800 mm for target velocities up to 50 mm/s.

Air-dispersion measurement by second-harmonic heterodyne interferometry.

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers.

Frequency-comb-referenced two-wavelength source for absolute distance measurement.

We propose a new tunable laser source concept for multiple-wavelength interferometry, offering an unprecedented large choice of synthetic wavelengths with a relative uncertainty better than 10(-11) in vacuum. Two lasers are frequency stabilized over a wide range of frequency intervals defined by the frequency comb generated by a mode-locked fiber laser. In addition, we present experimental results demonstrating the generation of a 90 mum synthetic wavelength calibrated with an accuracy better than 0.