Xianping Wang

High-sensitivity temperature sensor using the ultrahigh order mode-enhanced Goos-Hänchen effect

A high-sensitivity temperature sensor based on the enhanced Goos-Hänchen effect in a symmetrical metal-cladding waveguide is theoretically proposed and experimentally demonstrated. Owing to the high sensitivity of the ultrahigh-order modes, any minute variation of the refractive index and thickness in the guiding layer induced by the thermo-optic and thermal expansion effects will easily give rise to a dramatic change in the position of the reflected light. In our experiment, a series of Goos-Hänchen shifts are measured at temperatures varying from 50.0 °C to 51.2 °C with a step of 0.2 °C. The sensor exhibits a good linearity and a high resolution of approximately 5×10(-3) °C. Moreover, there is no need to employ any complicated optical equipment and servo techniques, since our transduction scheme is irrelevant to the light source fluctuation.

Determination of trace chromium (VI) using a hollow-core metal-cladding optical waveguide sensor

A biosensor capable of highly sensitive detection of trace chromium (VI) with a simple hollow-core metal-cladding waveguide (HCMW) structure is theoretically modeled and experimentally demonstrated. Owing to the high sensitivity of the excited ultrahigh-order modes in the waveguide, a tiny variation of the extinction coefficients in the waveguide guiding layer where the chromate ions reacts with the diphenylcarbazide (DPC) can lead to a significant change of light intensity in the reflection spectrum. The experimental results indicate that using the proposed method, the chromium (VI) sensitivity detection limit can be as low as 1.2 nM, which represents a 16-fold improvement compared to the surface plasmon field-enhanced resonance light scattering (SP-RLS) method, and a 4-fold improvement compared to the flame atomic absorption spectrometry and fluorimetry spectroscopy, respectively.

Observation of magneto-optical effect in extremely dilute ferrofluids under weak magnetic field

We propose a novel liquid-core waveguide using water-based ferrofluids as the guiding layer in a symmetrical metal-cladding waveguide structure to investigate the magneto-optical effect of extremely dilute ferrofluids. Owing to the high sensitivity of the ultra-high-order modes, the reflection intensity can be effectively tuned even by a weak magnetic field and the modulated reflectivity exhibits no threshold behavior. Furthermore, by properly adjusting the transmission axes of the polarizer, the detected laser intensity can be magnetic-field independent because the refractive indices for ordinary and extraordinary rays vary oppositely under the external field.

Optical transduction of E. Coli O157:H7 concentration by using the enhanced Goos-Hanchen shift

Within the symmetrical metal-cladding waveguide structure, the optical transduction of the E. coli O157:H7 concentration by using the enhanced Goos-Hanchen (GH) shift is demonstrated to be an advantageous alternative over those evanescent wave-based biosensors. The experimental results indicate that the interaction between the analyte and the excited ultrahigh order modes (in the form of the oscillating wave) is the dominant reason leading to ultrahigh sensitivity. On the condition that the intrinsic damping is well-matched with the radiative damping, the giant GH shift (hundreds of micrometers) offers a higher sensitivity than the regular measurement of reflected light intensity. The transduction limit of E. Coli O157:H7 concentration about 100 cfu ml−1 is achieved.

Reflection-type space-division optical switch based on the electrically tuned Goos–Hänchen effect

A reflection-type space-division optical switch is theoretically proposed and experimentally demonstrated based on the electrically tuned Goos?H?nchen effect in a symmetrical metal-cladding waveguide which employs the PMN?PT ceramics as the guiding layer. Owing to the high sensitivity of the ultrahigh-order modes, the variation of refractive index and thickness induced by the exertion of the controlled voltage on the PMN?PT ceramics will easily give rise to a change in the position of the reflected light. In the experiment, a three-pinhole array is put in the reflected light path and a one-to-three optical switch is achieved. The switching time for 10%?90% light intensity change and the optical crosstalk are measured to be lower than 1.63??s and ?29?dB, respectively. Since the Goos?H?nchen shift can reach approximately 1?mm, the number of output ports can be further increased on condition that the utilized incident light has a smaller spot diameter.

Simultaneous measurement of electro-optical and converse-piezoelectric coefficients of PMN-PT ceramics

A new scheme is proposed to measure the electro-optical (EO) and converse-piezoelectric (CPE) coefficients of the PMN-PT ceramics simultaneously, in which the PMN-PT ceramics acts as the guiding layer of a symmetrical metal-cladding waveguide. As the applied electric field exerts on the waveguide, the effective refractive index (RI) (or synchronous angle) can be effectively tuned from a selected mode to another adjacent mode owing to the high sensitivity and the small spacing of the ultra-high order modes. Subsequently, a correlation between EO and CPE coefficients is established. With this correlation and the measurement of the effective RI change to the applied voltage, the quadratic EO and CPE coefficients of PMN-PT ceramics are obtained simultaneously. The obtained results are further checked by fitting the variations of effective RI to a quadratic function. Our measurement method can be extended to a wide range of other materials.

Ultrahigh-order mode-assisted determination of enantiomeric excess in chiral liquids.

A chiral liquid, whose constituent molecules lack mirror symmetry, exhibits a minor differential refractive index (RI) between the two circular polarization components. Theoretical analysis shows that the ultrahigh-order modes excited in a symmetrical metal-cladding waveguide (SMCW) are polarization-independent and have a highly sensitive response to the RI variation. We report the observation of circular differential reflectivity in a chiral liquid-filled SMCW and propose an alternative simple technique capable of determining enantiomeric excess with high sensitivity.

Goos–Hänchen Shift

This chapter introduces the readers to the related issues of the non-specular reflection effects and in particular of the Goos–Hanchen (GH) shift. We first briefly review two causality paradoxes in the optical reflection and their corresponding solutions with the consideration of GH time. Then, we elaborately describe the current work on the theoretical explanation and the experimental enhancement of the GH shift. Finally, we give a unified theory for all non-specular reflection effects.

All-optically tunable Goos-Hänchen shift owing to the microstructure transition of ferrofluid in a symmetrical metal-cladding waveguide

We report on the observation of all-optically tunable Goos-Hanchen (GH) shift in a symmetrical metal-cladding waveguide, whose guiding layer is filled with the water-based ferrofluid. The strong dependence of the GH shift and its switching time on the control beam power is suggested to be arising from the light-induced periodic-like microstructure transitions of ferrofluid in virtue of the competition between the optical trapping effect and the Soret effect. The indirect evidence of our qualitative hypothesis is given. The presented tunability of GH shift may have potential applications in optical switching and sensing.

Optical Devices Based on the Attenuated Total Reflection

This chapter introduces several basic optical devices based on the attenuated total reflection, including tunable filter, optical sensors, and electro-optical devices. We mainly focus on the description of optical sensors performance. It is found that the bigger the portion of power that propagates in the sample, the higher the sensitivity will be. Moreover, the sensors based on the GH shift are immune to the power fluctuation in the light source since the GH shift is position encoded. Finally, our experiments to explore the magneto-optical modulation and all-optical modulation in the ferrofluid-filled SMCW are given. The results are contributed to the competition between the optical trapping effect and the Soret effect.