In this paper we propose a novel design of prism-based device as a Fabry-Perot resonance mode sensor. In this setup, liquid or gaseous sample to be probed acts as a core of the F-P device, in which supporting oscillating field, rather than evanescent field. Owing to the strong concentration of the electromagnetic field in the sensing medium, which is about an order of magnitude higher than that in typical evanescent field sensors using SPR, the proposed device exhibits unusual optical properties. It is shown that the fundamental limitation of device sensitivity is set by beam divergence of the laser.
A new technique for achieving efficient Cerenkov-type second-harmonic generation (SHG) in a nonlinear-optical (NLO) polymer waveguide is presented. The configuration, which can prevent the losses of light caused by relatively long-distance propagation and the multiple reflections that appear in the conventional Cerenkov technique, exhibits ease of fabrication and compactness. We experimentally observed a conversion efficiency of 1.6% W(-1) cm(-1), which to our knowledge is the highest value reported for Cerenkov SHG in polymer, by tuning both the thickness and the refractive index of the polymer film close to phase matching between a guided fundamental wave and a guided harmonic wave. The experimental results agreed well with the theoretical prediction.
In this paper, the lateral beam shift in a prism-waveguide coupling system at wavelengths ranging from visible to near infrared is theoretically examined. A simple theoretical formula is derived to analyze the behavior of the beam shift. We demonstrate that large positive and negative lateral optical beam shifts can be obtained when guided modes are excited. It is also found that the magnitude of the beam shift is closely related to the intrinsic and radiative damping. When the intrinsic damping is larger than the radiative damping, negative lateral beam shift occurs. Numerical calculations confirm the theoretical analysis and show that a beam shift of the order of millimeters is possible.
The giant Goos–Hänchen shift on a long-range surface plasmon (LRSP) configuration is examined theoretically. This lateral shift at the resonance of the LRSP can be two orders of magnitude greater than a wavelength. The analytical formulas of the radiative damping and the intrinsic damping of the LRSP are derived. It is found that the thicknesses of the second medium and the metal film determine the radiative damping and the intrinsic damping is illuminated by the imaginary part of the dielectric constant of the metal. Negative lateral beam shift occurs when the intrinsic damping is larger than the radiative damping. The theoretical results show good agreement with the predictions of the formulas.
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.
A fast speed electro-optic polymer variable optical attenuator (VOA) is fabricated by utilizing cascaded attenuated-total-reflection technique. The proposed VOA demonstrates high dynamic range and low driving voltage. An ∼200ns response time of the device is obtained, and other measured parameters include a dynamic range up to 24.1dB, a driving voltage of 39.6V, and an insertion loss of 1.02dB.
A new method which bases on the attenuated total reflection (ATR) technique is developed to determine the electro-optic coefficient of a poled-polymer film. The proposed ATR arrangement consists of a coupling prism, and four film layers deposited directly onto the base of the prism in sequence. The four film layers are metal film (which serves as a top electrode), poled polymer film, buffer and base electrode, respectively. A convergent light beam covering a suitable angular range is incident onto the prism base to excite a guided wave mode and the reflected light beam is imaged by a CCD array. Then resonance angle of the guided wave mode can be determined from the position of the reflectance minimum. It is demonstrated that the applying electrical field will cause a minute change in the refractive index of a poled- polymer film, due to the Pockles effect, which will result in a shift of the resonance angle. In order to make the measurement more successful, computer image processing method and optical image spatial filter technology are used in our measurement.
We extend the analytical transfer matrix method (ATMM) to study the bound-state spectra for hydrogenic donors in GaAs–(Ga, Al)As quantum dots. Comparison of the energy eigenvalues from ATMM with those from the wavefunction method reveals wavefunction results show large deviation from the exact ones when the radius of quantum dots r0 become large, whereas ATMM is better accuracy.
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