Jiří Čtyroký

Novel spectral fiber optic sensor based on surface plasmon resonance

Abstract A novel fiber optic surface plasmon resonance (SPR) sensing device based on spectral interrogation of SPR in a miniature fiber optic sensing element using depolarized light is reported. Optimization analysis of the sensor based on the equivalent planar waveguide approach and the mode expansion and propagation method is presented. A laboratory prototype of the sensor has been proved to be able to measure refractive index variations as small as 5×10−7. Suitability of the sensor for biosensing has been demonstrated by detecting IgG via respective monoclonal antibodies immobilized on the SPR sensor surface.

Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber

Abstract A novel wavelength modulation-based fiber-optic surface plasmon resonance (SPR) sensor is reported which utilizes both polarization separation and broad band radiation depolarization in polarization-maintaining fibers to enhance sensor stability. Theoretical analysis of the sensing structure with ideally separated polarizations based on the mode of expansion and propagation method is presented. The effect of polarization cross-coupling was also analyzed in the approximation of an equivalent bulk optic structure. A laboratory prototype of the fiber-optic SPR sensor was characterized in terms of sensitivity and resolution. Experimental results indicate that this fiber-optic SPR sensor is able to resolve refractive index changes as low as 4×10−6 under moderate fiber deformations.

Single-mode optical fiber surface plasmon resonance sensor

Abstract A fiber optic surface plasmon resonance (SPR) sensor utilizing the resonant interaction between a guided mode of a single-mode optical fiber and a surface plasma wave supported by a thin metal film is described. Theoretical analysis of the SPR sensing structure based on the equivalent planar waveguide approach and the mode expansion and propagation method is presented. A detailed analysis of the effect of the major parameters of the SPR sensing structure on the sensor performance is carried out. Experimental results obtained with fabricated laboratory prototypes of the SPR sensing device for measurement of the refractive index of analyte are reported. It has been demonstrated that the fiber optic SPR sensing device may be used as a spectral as well as an amplitude sensor.

Miniaturization of fiber optic surface plasmon resonance sensor

Abstract A novel design of surface plasmon resonance (SPR) sensor is reported which leads to a highly miniaturized optical fiber sensing element with high sensitivity. A surface plasmon wave is excited on a thin metal film on a side-polished single-mode optical fiber and variations in the refractive index of analyte are detected by measuring changes in the intensity of the light back-reflected from a mirrored end face of the fiber. The operation range of the sensor is tuned toward aqueous media by using a thin tantalum pentoxide overlayer. It is demonstrated that the sensor is capable of detecting changes in the refractive index below 4×10 −5 .

A surface plasmon resonance based integrated optical sensor

Abstract An integrated optical sensor based on the resonant coupling between a surface plasmon wave and a guided mode of an integrated optical waveguide is reported. Detailed theoretical analysis of the proposed sensor based upon the modal approach and upon the mode expansion and propagation method is presented. The performance of a realized sample of the waveguide sensor is investigated. It is demonstrated that by measuring the optical power transmitted through the sensing element, variations in the refractive index of the analyte as small as 2×10 −5 may be resolved.

Waveguide structures with antisymmetric gain/loss profile

Waveguide structures with an antisymmetric gain/loss profile were studied more than a decade ago as benchmark tests for beam propagation methods. These structures attracted renewed interest, recently e.g. as photonic analogues of quantum mechanical structures with parity-time symmetry breaking. In this paper, properties of both weakly and strongly guiding two-mode waveguides and directional couplers with balanced loss and gain are described. Rather unusual power transmission in such structures is demonstrated by using numerical methods. We found that the interface between media with balanced loss and gain supports propagation of confined unattenuated TM polarized surface wave and we have shown that its properties are consistent with the prediction of a simple analytical model.

Modelling of the surface plasmon resonance waveguide sensor with Bragg grating

The operation of a novel device – a waveguide surface plasmon resonance sensor with a UV-written Bragg grating – is theoretically analysed using two methods. In the simple perturbation approach, the metal/dielectric layer system supporting the resonance excitation of the surface plasma wave is considered to be a perturbation of the original dielectric waveguide with Bragg grating that is analysed using a coupled-mode theory. The second approach consists of the rigorous method of bi-directional mode expansion and propagation using the Floquet mode formalism developed recently for the analysis of waveguide grating structures. The results of both approaches are mutually compared, and the operation characteristics of this novel sensing device are briefly described.

Interaction between fiber modes and surface plasmon waves: spectral properties.

The interaction between a guided mode of a single-mode optical fiber and a surface plasmon wave supported by a thin metal overlayer is studied. A theoretical description is given of this phenomenon based on the mode expansion and propagation method. It is demonstrated that the interaction can take place only within a narrow wavelength range therefore is manifested by a dip in the spectrum of the transmitted optical power. One can control the wavelength position of the dip by varying the refractive index of the superstate. Experimental study of the realized structure, consisting of a single-mode optical fiber with locally removed cladding and a thin gold overlayer, shows that the 2x10(-3) change in the refractive index of the superstrate shifts the dip by ~10 nm.

Photonic bandgap structures in planar waveguides

If a one-dimensional (1D) or two-dimensional (2D) photonic bandgap (PBG) structure is incorporated into a planar optical waveguide, the refractive-index nonuniformity in the direction perpendicular to the waveguide plane responsible for waveguiding may affect its behavior detrimentally. Such influence is demonstrated in the paper by numerical modeling of a deeply etched first-order waveguide Bragg grating. On the basis of physical considerations, a simple condition for the design of 1D and 2D waveguide PBG structures free of this degradation is formulated; it is, in fact the separability condition for the wave equation. Its positive effect is verified by numerical modeling of a modified waveguide Bragg grating that fulfills the separability condition.

Guided and semileaky modes in anisotropic optical waveguides of the LiNbO3 type

Abstract Light propagation in anisotropic optical waveguides formed by an isotropic or a uniaxial layer onto a uniaxial substrate is studied theoretically. Special attention is paid to semileaky modes which are lossy due to the radiation of energy into the substrate. Both their propagation constants and loss coefficients are calculated numerically for waveguide parameters close to As-S glass layer onto LiNbO 3 substrate and to LiNbO 3 out-diffused and in-diffused waveguides.