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Tunable side‐polished optical fiber filter using the thermo‐sensitive characteristics of the polymer dispersed liquid crystal
Abstract
The tunable property of a side-polished optical fiber filter developed using a polymer dispersed liquid crystal (PDLC) is investigated. The thermo-sensitive characteristic of the PDLC provides the new type of tunable side-polished optical fiber filter with a desirable free spectral range (FSR) and eliminates the influence of the high refractive index of indium tin oxide (ITO). As a result, the resonance wavelength of the side-polished fiber filter is tuned at a rate of −0.015 nm/mW. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1229–1230, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21662
... Because the evanescent field of guided light wave in SPF could leak beyond the polished surface, SPF is very sensitive to the refractive index change of overlaid materials on its side polished surface [21,22]. SPFs overlaid with liquid crystal have been made into optical polarizer [23], modulator [24] and filter [25] et al. SPF overlaid with hybrid photoresponsive liquid crystal has also been demonstrated as light sensors [26][27][28][29]. ...
... A crucial point of these studies is that light must be coupled into and out of the cavity efficiently. Using prism coupling [19] or a side-polished optical fiber [20] as excitation sources is feasible but not flexible or efficiently. ...
Planar Microtoroid cavities with ultrahigh quality factor have very
strong confined function to the electromagnetic wave coupled into them
due to their novel ring-like structures. Therefore, they have very good
applications in high sensitivity sensors and other micro optics
components. In this paper, the Planar Microtoroid cavity and its
coupling system constructed together with the tapered fiber are
introduced. Then, micro sensors based on the above coupling system are
designed. These sensors measure environmental parameters by means of
monitoring the changes in the transmission spectrum of the high finesse
Planar Microtoroid cavities, obtaining fine resolution and high accuracy
due to their ultrahigh quality factor (Q) performance. The sensitive
mechanism and the feasibility are demonstrated through optical and
mechanical software simulation. With software BeamPROP, the evident
resonance and strengthened phenomenon to the electromagnetic wave
coupled into the micro-cavity are shown, which have a big relation with
the light frequency. The results indicate that, Planar Microtoroid
cavity is very promising in designing new micro sensors.
The orientation change of nematic liquid crystal (NLC) can be used in biosensor. The sensing characteristics of side-polished fiber (SPF) for measurement of NLC orientation are investigated. The relationship between the theoretical formula of liquid crystal refractive index and the optical transmission power in SPF is derived by empirical approach. The mechanical rotating method is designed to change the orientation of NLC on the polished surface. Experimental results show that the orientation variation of liquid crystal can indeed be used to monitor the output optical power transmitted through the SPF. With mechanical rotation method, when the rotation angle increases from 0° to 90°, the output optical power increases by 28.10 dB. With in the angle range from 0° to 30°, the response is almost linear. The average response slope is about 0.359 dB/(°), which indicates relatively high sensitivity. Experiments indicate that SPF can be used to measure the orientation variation of NLC, and the variation range is also obtained. The work provides a reference for a new fiber optical biosensor based on the SPF and NLC.
The orientation of nematic liquid crystal (NLC) can be used in biosensor. The sensing characteristics of side-polished fiber (SPF) for determination of azimuthal orientation of NLC have been investigated. The relationship between the azimuthal angle of NLC director and the optical transmission power in SPF was derived by empirical approach. Experimental results showed that the azimuthal transition of liquid crystal affected the optical transmission power in SPF. While the azimuthal angle increased from 0° to 90°, the optical transmission power increased by 28.10dB, which is similar to the variation tendency of the empirical analysis. When it changes from 0° to 30°, the azimuthal angle is linear to the change of optical transmission power. The respondence of azimuthal angle for optical sensing is averagely 0.359dB/°. Experiments indicate that SPF can be used in determination of the azimuzal transition of NLC. It would be used for a new fiber optical biosensor based on the SPF and NLC.
In this paper, a novel all-fiber electric field sensor based on tapered fiber-slab waveguide coupler was proposed for the first time. Experiments were implemented for investigating the dependences of TFSC transmission features on their geometries parameters. On the base of that a TFSC based sensor with optimal construction parameters and sharper coupling spectra were fabricated. The nearly linear relationship between the changes of sensor outputs and the external applied electric field are demonstrated by experiments. The minimal detectable of electric field has also been demonstrated experimentally to be ~50V/cm.
A method for obtaining the mode characteristics of a tunable filter by a polymer-dispersed liquid crystal (TSFP) is presented, where the optical characteristics are analyzed using the coupled-mode theory. The TSFP is modeled as a fiber-to-planar waveguide (PWG) coupler with 4 layers, including a fiber cladding layer, a polymer-dispersed liquid crystal (PDLC) as a buffer layer, a PWG layer, and overlay layer. When applied to a 3-layer waveguide without a buffer layer, the proposed model gave more exact solutions for the TSFP. The coupling is easily tuned by using the heat of the electrode, and more occurred for the buffer layer with a higher index of refraction.
Refractometric sensor elements were studied consisting of a side-polished single-mode
optical fibre covered by a pulsed laser deposited ZnO thin film. A measurement scheme was
used for in situ control of the film thickness during the deposition process. Highly sensitive
sensors were produced based on the interaction with the zero- and first-order modes of the
ZnO planar waveguide. The sensors' applicability to the two spectral regions for
communications, namely 800–1000 nm and 1300–1600 nm, was demonstrated. A high
sensitivity of the order of 3000–6700 nm per refractive index unit change was
obtained for sensor elements utilizing the interaction of the fibre mode with the
TE0 or
TM0
mode of the ZnO thin-film waveguide.
A tapered fiber-slab waveguide coupler (TFSC) is proposed in this paper. Both the numerical analysis based on the beam propagation method and experiments are used for investigating the dependencies of TFSC transmission features on their geometric parameters. From the simulations and experimental results, the rules for fabricating a TFSC with low transmission loss and sharp resonant spectra by optimizing the configuration parameters are presented. The conclusions derived from our work may provide helpful references for optimally designing and fabricating TFSC-based devices, such as sensors, wavelength filters, and intensity modulators.
A first thermo-optical characterisation of a new type of polymer dispersed liquid crystal is presented. An experimental study on the transmittivity as a function of the temperature shows a temperature switch based on an optically bistable device. Our results suggest the possibility of employing such a material to realise all-optical temperature sensors.
A number of in-line components utilizing the evanescent coupling between a side-polished fiber and a high-index slab overlay have recently been demonstrated. The wavelength response of the structure shows a series of resonances, the position of which must be precisely controlled for practical applications. We present experimental and theoretical results for the tuning of the resonance position through variation of the superstrate parameters.
A tunable in-line fibre optic channel dropping filter is reported
using evanescent coupling from a single-mode fibre to a thin waveguiding
layer of nematic liquid crystal material. The large electro-optic
coefficient of the liquid crystal allows low drive voltages. A tuning
range of 40 nm for 10 V has been demonstrated