A fiber optic sensor for high sensitivity refractive index and temperature measurement able to withstand temperature up to 450 °C is reported. Two identical LPG gratings were fabricated, whereas one was coated with a high refractive index (~1.78) sol-gel thin film in order to increase its sensitivity to the external refractive index. The two sensors were characterized and compared in refractive index and temperature. Sensitivities of 1063 nm/RIU (1.338 – 1.348) and 260 pm/°C were achieved for refractive index and temperature, respectively.
Integrated optics is a mature technology with standard applications to telecommunications. Since the pioneering work of
Berger et al. 1999 beam combiners for optical interferometry have been built using this technology. Classical integrated
optics device production is very expensive and time consuming. The rapid production of devices using hybrid sol-gel
materials in conjunction with UV laser direct writing techniques allows overcoming these limitations. In this paper this
technology is tested for astronomical applications. We report on the design, fabrication and characterization of multiaxial
two beam combiners and a coaxial beam combiner for astronomical interferometry. Different multiaxial two beam combiner designs were tested and high contrast (better than 90%) was obtained with a 1.3 μm laser diode and with an
SLD ( λ0 = 1.26 μm, FWHM of 60 nm). High contrast fringes were produced with 1.3 μm laser diode using the coaxial two beam combiner. These results show that hybrid sol-gel techniques produce devices with high quality, allowing the
rapid prototyping of new designs and concepts for astronomy.
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.
Symmetric buried channel waveguides fabricated on silicon substrates by the organic-inorganic hybrid sol-gel process are reported. The buffer/cladding layer material is composed of methyl-modified silanes and presents high network flexibility and low refractive index, at low cost. Film thickness above 10 mm is possible without cracks, even after thermally baking the films at 150°C, and the refractive index is 1.468 at 632.8 nm. The influence of the methylsiloxane species on the material absorption loss was investigated, in particular at 1.55 mm. For channel waveguide core definition, a photopatternable layer was polymerised by 248 nm laser radiation through an amplitude mask, and the unexposed material was simply removed by an organic solvent. The transmission spectrum of the waveguides is presented and reveals an acceptable loss level of 0.3dB/cm at 1300 nm, but larger loss in the 1550 nm region. The procedure developed is compatible with optoelectronic integration in silicon.
The hybrid sol-gel process is recognized to be an alternative route for production of low cost silica-based integrated optic devices, since it allows the elaboration of ridge waveguides without recourse to high cost processing, like ion etching. However, the high absorption of these materials in the NIR region (1300 and 1550 nm) has limited so far their use.
The main objective of this article is to describe the major factors that lead to high losses in the final material and to give solutions to overcome this drawback. The choice of hybrid precursors and the influence of the experimental conditions of gel preparation are of paramount importance. Appropriate synthesis conditions allow a significant decrease of the gel losses (to 0,5 dB/cm) while keeping good wetability and UV-patternability. Each step of the waveguides elaboration was studied separately (UV-irradiation, etching, overcladding, storage) regarding the losses of the material. Post-baking of the waveguides is a way to significantly decrease the losses at 1550 nm. Under appropriate conditions, the losses measured in the waveguides can be kept below 1 dB/cm.
Definition of channel waveguides on hybrid sol-gel material was demonstrated using a 248 nm UV excimer laser, without mixing organic photoinitiators in the solution preparation step. Thin films fabricated by hydrolysis and polycondensation of methacryloxypropyltrimethoxysilane (MAPTMS) doped with zirconium oxide were deposited by spin-coating on soda-lime glass substrates (n = 1.514). Channel waveguides were defined by microlithography and then covered by a protective layer composed of a combination of MAPTMS and tetramethoxysilane (TMOS). Finally, after cutting and polishing, the waveguides were optically characterized.
Fibre Bragg grating has become the most attractive intrisic fibre sensor in recent years for various reasons [1-4]. One of the major advantage of this type of sensor is attributed to wavelength encoded information provided by the Bragg grating when affected by the mensurand. Since the wavelength is an absolute parameter, signal from a Bragg grating may be processed such that its information remain immune from power fluctuations along the optical path