F.P. Payne

Single-mode optical fibre surface plasma wave chemical sensor

Abstract We describe a new design of optical fibre surface plasma wave chemical sensor. The basic sensor consists of a tapered single-mode optical fibre with a thin layer of silver evaporated onto the tapered section. The gradually changing diameter of the fibre along the taper and the variation in silver depth around the taper result in a distributed coupling between the guided mode of the fibre and the surface plasma wave. As a result, the coupling to the surface plasma wave occurs over an enlarged spectral range. The device shows good sensitivity to refractive index with refractive index changes of 5 × 10 −4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.

The single mode tapered optical fibre loop immunosensor

A novel single mode tapered optical fibre loop biochemical sensor based on fluorescence spectroscopy has been developed. The fundamental fibre mode propagates through the tapered portion of an optical fibre and generates an evanescent field which penetrates into the aqueous environment surrounding the fibre where the bio-recognition event occurs. A two-step assay was used, in which the analyte was labelled secondarily with a fluorescent dye, fluorescein isothiocyanate or tetramethyl rhodamine. When excited by the input argon ion laser light from the near end of the taper, generated fluorescence is coupled into the guided mode of the fibre and collected at the far end of the taper. Methods of making the sensor chemically reusable were investigated. The high sensitivity (75 pg/ml) of the single mode tapered loop device, combined with a simple immobilization protocol, provides a powerful tool for performing immunoassays.

Single-mode tapered optical fiber loop immunosensor II: assay of anti-cholera toxin immunoglobulins

An evanescent wave immunoassay for cholera antitoxin immunoglobulins was performed using a single mode tapered optical fiber loop sensor. The transducer was silanized with 3- glycidoxypropyltrimethoxysilane and chemically modified to link covalently either cholera toxin B subunit or a synthetic peptide derived from it, CTP3. The sensor was exposed to seral fluids, obtained from human volunteers having been exposed to live virulent Vibrio cholerae 01 and shown to produce rice-water stools. Other toxins of interest, such as Clostridium botulinum toxin A, have been tested on similar systems. The bound unlabelled immunoglobulins were then exposed to a mixture of FITC-anti-IgG and TRITC-anti-IgA, without requirement for a separation step. The emanating fluorescent emissions of fluorescein and rhodamine, excited by the input laser light, were coupled back into the guided mode of the tapered fiber, and used to determine the concentrations of the complementary antigens.

Single-mode tapered optical fiber immunosensor I: characterization with model analytes

A novel single mode tapered optical fiber loop biochemical sensor based on fluorescence spectroscopy has been developed. The fundamental fiber mode propagating through the tapered portion of the waveguide has evanescent fields which penetrate into the aqueous environment where the biochemical recognition event occurs. The model measurands were conjugated with a fluorescent dye, fluorescein isothiocyanate. When excited by the input laser light from the near end of the taper, generated fluorescence is coupled into the guided mode of the fiber and collected at the far end of the taper. Several radioactive and fluorescent quantification methods have been explored to determine the density of available binding sites immobilized on the fiber, and thus the ultimate sensitivity of the device. A generic avidin- biotin system has been tested as a model immunological diagnostic system. The high sensitivity of a single mode tapered loop device combined with a simple immobilization method provides a powerful tool for performing immunoassays.

Switching properties of generalized Mach-Zehnder photonic switches

Mach-Zehnder photonics switches have the desirable attributes of good power balance and the absence of external crossovers. In this paper, the switching capabilities of this type of structure are examined.

Optical switches based on the generalized Mach-Zehnder interferometer

A brief outline of the switching capabilities of the generalized Mach-Zehnder interferometer has been given. This study has led to the design of a novel 4/spl times/4 switch. This type of switch has good loss uniformity and requires only a relatively small number of phase-shifting or switching elements.

Generalized Mach-Zehnder optical switches

Compact integrated optical circuits for signal routing and signal processing are currently the subjects of much active research. Multimode interference (MMI) couplers are widely used as splitters and combiners since they possess the desirable attributes of small size, low excess loss, well- defined slitting, dimensional tolerance and ease of fabrication. Recently there has been renewed interest in employing MMI devices within Mach-Zehnder structures to achieve splitting and switching functions. However, the extent of the switching capabilities achieved so far has been quite limited. This paper highlights how the switching capabilities of these Mach-Zehnder switches can be extended and presents design techniques for this type of photonic switch.

Novel applications of monomode fiber tapers

Adiabatically tapered single-mode fibers provide a novel and effective method of gaining access to the optical field inside an optical fiber. The fabrication of low-loss tapered fibers with waist diameters of less than one micron is described. By surrounding a tapered fiber with laser-dye solution, compact very efficient amplifiers, saturable absorbers, and super- fluorescent sources have been demonstrated.

Broadband single-mode optical fiber surface plasma wave chemical sensor

We describe a new design of optical fiber surface plasma wave chemical sensor. The sensor consists of a tapered single mode optical fiber with a thin layer of silver evaporated on to the tapered section. The gradually changing diameter of the fiber along the taper results in a distributed coupling between the guided mode of the fiber and the surface plasma wave. As a result, and in contrast to conventional plasma wave sensors, coupling to the surface plasma wave occurs over a broad spectral range, typically several hundred nm. The device shows good sensitivity to changes in the refractive index of the external environment, with refractive index changes of 10-4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.