Needs for sensor miniaturization, versatile sensing solutions, and improved measurements’ performances in difficult operating environments have recently driven considerable research in optical fiber sensor for multiparameter measurements. Multiparameter sensors not only enable new sensors’ functionalities, but can also improve achievable measurement performances for some frequently measured parameters considerably. This study provides a review of work in the field of miniature fiber-optic sensors that allows independent and simultaneous measurements of two or more different physical or chemical parameters. Sensor designs and corresponding signal processing schemes are reviewed and compared.
A combination of focused ion beam milling and chemical etching is proposed for the creation of Fabry-Pérot cavities in microwires. Both simple cavities and cantilevers are created on 15 μm-diameter microwires and characterized in temperature. The cantilever structure shows sensitivity to vibration and is capable of measuring frequencies in the range 1 Hz – 40 kHz.
This paper presents a highly effective micromachining process that can reform a section of an optical fiber into an allfiber,
complex photonic microstructure. The proposed process utilizes specially designed structure forming fibers that are
reformed into various complex shapes through selective etching. The control over the etching rate of the structureforming
fiber sections is achieved by the introduction of dopants, particularly phosphorus pentoxide, into silica glass
through the standard fiber manufacturing technology. Doping with appropriate dopants and dopant concentrations can be
used to create highly-preferential etchable areas within a fiber cross-section that can be selectively removed upon
exposing the fiber to the etching medium. The doped areas in the fiber cross-section can thus serve as sacrificial layers,
similar to those in the case of silicon MEMS production. Thus, the shaping of fiber devices can be achieved through the
design and fabrication of structure-forming fibers.
This paper presents the design, fabrication process, and experimental evaluation of a high-sensitivity, all-silica, all-fiber,
micro machined Fabry-Perot strain-sensor. This sensor has a short Fabry-Perot cavity and thus allows for the application
of low-resolution spectral interrogation systems; in our case the commercial white light signal interrogator was used. The
fabrication process includes the design and production of special sensor-forming optical-fiber. This fiber includes a
central titanium-doped region, a phosphorus doped-ring surrounding a titanium doped region, and pure silica cladding in
order to produce the proposed sensor, two sections of sensor forming fiber are cleaved and etched in a HF/IPA solution.
The phosphorus-doped region etches at a considerably higher rate than the other fiber-sections, and thus creates a deep
gutter on the cleaved fibers frontal surface. The titanium-doped region etches at a rate that is, to some extent, higher than
the etching-rate of pure silica, and thus creates a slightly retracted surface relative to the pure silica fiber-cladding. The
etched fibers are then re-spliced to create an all-silica strain sensor in "double configuration", which has a section of
etched sensor-forming fiber on both sides. Thus this sensor has a long active length, whilst the length of the Fabry-Perot
cavity can be adjusted by a titanium-doping level. The central titanium-doped region also creates a waveguide structure
that is used to deliver light to the cavity through one of the fibers. The proposed fabrication process is cost-effective and
suitable for high-volume production. The greatest achievement of the depicted in-line strain sensor is the extension of its
active sensor length, which is more than 50 times greater than the sensor-cavity's length, and is thus approximately 50
times more sensitive to strain. This sensor also exhibits low-intrinsic temperature sensitivity.