A pressure or touch sensor is proposed by using a tapered optical fiber and polydimethylsiloxane ( PDMS) curved films. Under pressure, the light in the tapered optical fiber is partially leaked into the films by the evanescent field properties. The optical attenuation of the tapered optical fiber is directly related to the pressure change and sensitive to the profile of the film. By monitoring the change of the transmitted optical power of the tapered optical fiber, the change of pressure is measured.

The polymer polydimethylsiloxane (PDMS), which is used as a cladding layer in waveguide-based optical components, is sensitive to the organic compounds. In this work, a compact organic compound optical sensor with a simple fabrication is proposed by using a taped optical fiber with PDMS coating. The sensing mechanism is based on the reaction of sensing material PDMS with chemical molecules to result in the changes of PDMS cladding layer which cause the transmitted optical power of the taped optical fiber.

In this work, a ridge waveguide Bragg grating pressure or touch sensor is proposed. The sensor consists of an open top ridge waveguide Bragg grating with a pressure sensing film: polydimethylsiloxane (PDMS) on the waveguide surface. Under pressure, the guided mode of the waveguide accesses the film by coupling of the evanescent field. A large shift of the Bragg wavelength occurs when the effective index of the waveguide is changed by stress-indued variations in the film refractive index that are caused by increases in pressure. By monitoring the shifts of Bragg wavelengths in TE and TM modes, respectively, the external pressure change and the internal strain change in the film are measured. The sensitivities of the sensor with different waveguide structures are investigated.

A technique for creating a temperature-insensitive refractometer that utilizes transverse electric (TE) and transverse magnetic (TM) modes in an open-top ridge waveguide design is presented. By using the TE mode resonance as a temperature reference, the relative shift of the TM mode can be monitored in order to measure the refractive index of liquids under test. Specifically, the device fabricated here produces a resonance shift of 1 pm for every 1 x 10(-4) of measured index change, with a temperature sensitivity less than 0.5 pm degrees C-1. To increase the sensitivity of these devices, a theoretical model is developed to investigate the performance of some potential waveguide structures. Relationships between the waveguide core size, refractive index distribution, as well as the relative evanescent sensitivity of TE and TM modes are examined.

In our previous work, a highly sensitive waveguide Bragg grating (WBG) sensor for measuring small changes in the refractive index of a surrounding liquid was developed [1]. We proposed a technique for creating a temperature insensitive refractometer that utilizes core and cladding modes in an open-top ridge waveguide architecture in order to discriminate between Bragg wavelength changes in temperature and refractive index [2]. In this work, a technique for creating a temperature insensitive refractometer that utilizes TE and TM modes in an open-top ridge waveguide design is presented. By using the TE mode resonance as a temperature reference, the relative shift of the TM mode can be monitored in order to measure the refractive index of liquids under test. Specifically, the device fabricated here produces a relative resonance shift of 1 pm for every 1×10-4 of measured index change, with a temperature sensitivity less than 0.2 pm/°C.

A highly sensitive waveguide Bragg grating (WBG) sensor for measuring small changes of the refractive index of the surrounding liquid is presented. By using an open top ridge waveguide with a small core, the evanescent field interaction of the guided mode with the liquid analyte on the top of the waveguide is enhanced. The sensitivity measured via a shift in the resonance wavelength of the Bragg grating as high as 1 pm of wavelength shift for a change of 4 x 10(-5) in the refractive index around 1.402 is realized. With a polarization insensitive Bragg grating, the polarization dependence of the sensor is improved. A theoretical analysis for the sensitivity of ridge waveguide sensors is given. The experimental results are in good agreement with the theoretical analysis.

Experimentally, in the open-top ridge waveguides, the sensitivities of core and cladding resonances to the surrounding medium's refractive index are different while the temperature sensitivities are similar. Based on these characteristics, a temperature insensitive refractometer has been proposed. To increase the sensitivity of these devices, a theoretical model is developed to investigate the performance of some potential waveguide and Bragg grating structures. Relationships between the waveguide core size, refractive index distribution, tilt angle of the Bragg gratings as well as the relative evanescent sensitivity of the core and cladding modes are examined. As a result, we find that sensitivity can be enhanced by decreasing the waveguide core size, making the effective index of the waveguide close to the expected refractive index of the analyte, and incorporating tilt in the Bragg grating structures. Furthermore, the inclusion of tilt also appears to reduce the grating's birefringence for the waveguide structure examined.

In order to overcome the well-known limitation of temperature instability in Bragg grating waveguide sensors, a temperature insensitive open-top ridge waveguide refractometer is developed by using a cladding mode resonance as a temperature reference. The relative shift of the core mode resonance to cladding mode resonance is used to measure the refractive index of substances under test. Specifically, the device fabricated here produces a relative resonance shift of 1 pm for every 5 times10 -4 of measured index change, with a temperature sensitivity ~ 0.5 pm/degC.

Optical Bragg grating sensors based on side polished or etched waveguides have been demonstrated for the measurement of refractive index [1, 2, 3, 4]. However, these devices typically exhibit polarization dependent behavior for index values around 1.3. In this report, a ridge waveguide Bragg grating (WBG) sensor with high sensitivity, for refractive index measurement in liquids is presented. The device is based on a small core size silica open top cladding ridge waveguide and polarization independent Bragg gratings (PIBG) written and optimized using UV light [5,6,7]. The WBG is surrounded by a liquid analyte and is accessed via evanescent field interaction of the guided waveguide mode with the liquid layer. In the theoretical analysis, enhancement of sensitivity by optimizing waveguide structures is proposed. In the experiment, Bragg grating is induced in the open top cladding ridge waveguide using a phase mask and excimer laser radiation at 193 nm. A series of refractive index matching liquids are used to test the device. Results indicate the sensitivity is as high as 50 pm of wavelength shift for a change of the index 3×10-4. This technology can offer many advantages over previously proposed waveguide sensors, including enhanced sensitivity, and dynamic measurement range, better polarization stability, and a simpler fabrication processes.

A method for rapid compensation of high intrinsic birefringence in plasma-enhanced chemical vapor deposition (PECVD) based planar waveguides is presented. The intrinsic waveguide birefringence is compensated by a large UV induced opposite birefringence generated with polarized UV ArF excimer laser irradiation (oriented normal to the waveguide axis) and enhanced further through hydrogen loading. The fabrication of polarization insensitive Bragg gratings in PECVD planar waveguides with a large intrinsic birefringence of 6.3×10−4 is demonstrated by trimming it to zero birefringence with a low fluence blanket UV polarized exposure. After annealing for removal of the hydrogen, the polarization insensitive nature of the Bragg grating is unchanged.

A method of Bragg gratings written in silica-on-silicon planar waveguides to be used to monitor the overall uniformity of the waveguides and grating processing is presented. By measuring the shift of Bragg wavelength with UV exposure time, the initial effective index n(0eff) and birefringence B-0 of the planar waveguides are measured accurately. With one phase mask, Bragg gratings induced on different waveguides with widths that vary from 4.6 to 8.8 mum, result in variations of N-0eff and beta(0) of 1.5 x 10(-3)/mum and 1 x 10(-4)/mum, respectively. The result is used as a way of improving control over the waveguide dimensions obtained from the photolithographic and RIE processes, and optimizing the design of ridge waveguide structures to compensate the waveguide birefringence. This will improve the quality of the PLCs that include symmetric Bragg grating structures: MZI-OADM etc. By writing Bragg gratings on the linear taper planar waveguide, a chirped grating response is realized.

A simple numerical method is developed to analyze changes in intrinsic birefringence of ridge waveguides with waveguide dimensions and UV irradiation. Experimentally, Bragg gratings were written on different core size ridge waveguides using the phase mask technique and ArF laser irradiation. By monitoring the shifts in Bragg wavelength with UV irradiation, the variation of the waveguide birefringence with waveguide dimension and UV processing is observed and quantified. The mechanism of the waveguide birefringence controlled with UV irradiation is verified both in the theoretical analysis and experiment.