Abstract
The study of a single short length Bragg grating for sensing applications is presented. The dependences of the central wavelength, reflected optical power and spectral width of a 250 mu m length grating on strain and temperature are analyzed. The obtained results indicate the feasibility of this novel sensing head for simultaneous measurement of strain and temperature.

Abstract
Integrated optics (IO) technology has been primarily used in optical communication applications but it is expanding fast into the field of optical sensing. In this work we report the fabrication of integrated devices using hybrid sol-gel technology and in particular its application in the fabrication of a refractive index integrated sensor based in a Mach-Zehnder interferometric configuration. In one of the interferometer arms, a analysis chamber is created by exposing the waveguide through the removal of the device cladding. On the same arm, two Bragg gratings with the same period are fabricated: one in the unprotected waveguide area and another in close proximity (cladded area); because of the different effective index in the two grating regions, two peaks are observed in reflection if the device is tested with a broadband source. Any change of the refractive index of the material filling the analysis chamber can be detected in two ways: by measuring the intensity of the interferometric output (at a wavelength different from the Bragg wavelength of the two gratings) or by measuring the spectrum of the reflected signal. The high sensitivity is obtained by measuring the interferometric output, while the high dynamic range can be achieved by measuring the reflected signal from the grating structures.

Abstract
The major achievements in the field of optical sensors in the past two decades have remained mostly limited to the laboratory demonstrations. There are very few examples of optical sensors, which have been reduced to practice, and have established themselves in major markets. The main bottleneck in this field is the issue of manufacturability. In this paper we present optical sensors based on slotted multimode interference waveguides. We show that the sensitivity increases proportionally to the number of slots. The sensor can be tuned to highest sensitivity in the refractive index ranges necessary to detect protein-based molecules or other water-soluble chemical or biological materials. The material of choice is a sol-gel (ORMOCER) matrix that after completion of the process becomes mostly glass and it is highly stable. Sensors made with this technology are suited to high volume manufacturing.

Abstract
Fiber Bragg Gratings (FBG) are widely used in various fields, including optical fiber sensors. In this work, the temperature and strain response of C-band FBG in pure silica four-leaf clover shaped suspended-core fibers was analyzed. These FBGs were fabricated by femtosecond laser exposure, which enabled the refractive index modulation of the pure-silica-core of the fibers. We compared the Bragg wavelength variation with strain and temperature for two different suspended-core fibers (256b2 and 256b5). The 256b2 fiber has a core diameter of 4,9 µm and a hollow hole inside the core with 1,4 µm; the 256b5 fiber has a solid silica core with a 7,2 µm diameter. For strain and temperature characterization, the sensing head was attached to a translation stage with a resolution of 1 µm and was placed in a tubular oven, which permits a temperature reading to be set with an error smaller than 0,1 °C. Both have shown the same sensitivity to strain (1,2 pm/µe) but different sensitivity to temperature variation (8,4 pm/°C and 10 pm/°C respectively). The relative difference between the thermal coefficients of the two selected Bragg signatures is 16%. The results obtained indicate that these gratings can be used in optical fiber sensing, for example in the context of the important problem of simultaneous strain and temperature measurement. © 2009 SPIE.

Abstract
We report the use of the electric arc technique to apodise Fibre Bragg Gratings (FBG). Electric arc discharges applied at the ends of the grating produce a smoothing of the refractive index modulation profile which reduces the side lobes at longer wavelengths. Using this technique, a FBG was apodised with a side lobe reduction of 17 dB.

Abstract