Side-polished Optical Fiber Research Articles

Side-coupled fibre semiconductor laser

A novel composite fibre-semiconductor laser that can greatly alleviate the alignment complexities associated with the conventional pigtailed laser diode modules is presented. The laser has a threshold current density of 3 kA/cm 2 , emits evanescently into a singlemode side-polished optical fibre at 854 nm, and operates singlemode without any additional gratings.

Characterization of evanescent wave coupling in side-polished hollow optical fiber and its application as a broadband coupler

We have investigated side-polished fiber coupler made of a hollow optical fiber (HOF) with a ring core. It is theoretically shown that the large mode size and the weakly guiding property of the HOF makes it easy to excite the evanescent field by the side-polishing technique. Analytic equation to calculate the remaining cladding thickness of the side-polished HOF is presented and a novel technique to couple the conventional single mode fiber is also experimentally demonstrated.

Light coupling and propagation in a fiber–dielectric-slab composite with a conductor cladding

A theoretical presentation of evanescent coupling is offered, with consideration of the refractive indices, between a side-polished optical fiber and an infinite planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and coated with a perfect conductor on the far side. The behavior of the distributed coupler is examined using a coupled mode model, which takes account of the two dimensions of the waveguide configuration. The coupling and propagation of light were found to depend on both the relation between the refractive indices of the materials and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of the PWGCC is described in terms of a simple geometrical interpretation of the synchronization condition that is in agreement with a previous investigation of the problem based on the coupled mode theory. The power of the light propagated in the fiber decreases exponentially along the fiber axis as power is transferred to the PWGCC, where it is carried away. Then a 3-D finite-difference beam propagation method was applied to the fiber-PWG composite; results of the simulation by this means presented.

Effect of a Conductor Cladding on a Dielectric Slab for Coupling with a Side-polished Fiber

A theoretical presentation by using a three-dimensional finite difference beam propagating method (3-D FD-BPM) for the evanescent coupling is offered with respect to the refractive indexes between a side-polished optical fiber and an infinitely planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and attached with a perfect conductor (PEC) on one side. The coupling and propagation of light are found to depend on both the relationship between the refractive index values of two structures and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of a PWGCC is presented with the distribution of electric fields in xy - plane and the absolute amplitude of electric fields along the x and y axis. The power of the light propagation in a fiber decreases exponentially along the fiber axis as it is transferred to the PWGCC, where it is carried away.

MEMS Device for Controlling Evanescent Field on Side-Polished Optical Fiber

Application of micro-electro-mechanical system (MEMS) technology for controlling the evanescent field is attractive because the dimension of the evanescent field is of the same order as that of the movement distance of the MEMS device. Two different types of MEMS-based devices are proposed and developed for controlling the evanescent field generated at the surface of the side-polished optical fiber. The first one is a hybrid type and the other is a monolithic type. Both devices have merit and demerit from the aspects of process ease and alignment. The hybrid-type of device has a problem of close contact of the diaphragm with the side-polished optical fiber. The monolithic-type of device is a pre-aligned structure but has a difficulty in terms of polishing depth control on the single mode fiber. A change in the transmission spectrum due to device operation (movement of diaphragm with respect to polished optical fiber surface) has been noticed. However, the extent of change in transmission has to be improved. Fine control of polishing depth and parallel alignment of side-polished fiber with a diaphragm are the critical factors for effective interaction of the diaphragm with an evanescent field.

The Analysis of tight Coupling and Propagation for a Composite Fiber-Dielectric Slab with a Conductor Cladding

A theoretical presentation of evanescent coupling is offered with respect to the refractive indexes between a side-polished optical fiber and an infinitely planar waveguide with a conductor cladding (PWGCC). The PWG is suspended at a constant distance from an unclad fiber core and attached with the perfect conductor (PEC) on one side. The behavior of the distributed couple. is examined using a coupled mode model, which takes account of the two dimensions of the waveguide configuration. The coupling and propagation of light were found to depend on both the relationship between the refractive index values of each structure and the configuration of the side-polished fiber used in the PWGCC. The spreading of light in the unconfined direction of the PWGCC is described in terms of a simple geometrical interpretation of the synchronization condition that is in agreement with a previous investigation of the problem based on the coupled-mode theory (CMT). The power of the light propagation in the fiber decreased exponentially along the fiber axis as it was transferred to the PWGCC, where it was carried away.

Analysis of nanostructured porous films by measurement of adsorption isotherms with optical fiber and ellipsometry.

An optical method to determine the nanostructure and the morphology of porous thin films is presented. This procedure is based on the response of a side-polished optical fiber with the film under study, when an adsorption-desorption cycle is carried out. Spectroscopic ellipsometry provides additional information about the optical properties and adsorption behavior of the film. Pore size distribution, anisotropy, and inhomogeneity of films can be determined by use of these two complementary techniques. To check the performances and suitability of the optical method, we have characterized a typical porous material: a TiO2 film deposited by evaporation. Water vapor has been used for the adsorption cycles. The well-known columnar structure of the evaporated TiO2 has been evidenced, and the relation between the nanostructure and the optical properties of the film is showed.

High sensitivity temperature sensor based on side-polished optical fiber

Side-polished optical fiber has long been used to build fiber sensors and other devices. In this work, we present a particular application leading to temperature sensors operating in the 10 to 70/spl deg/C temperature range. Although the temperature-induced modulation yields variations of the output optical power amplitude, high sensitivity in the order of 0.5 dB/spl deg/C/sup -1/ can be obtained (insertion loss being around 2 dB). The sensor principle combines the extreme sensitivity of polished fibers to external refractive indices, especially for those values close to the core index and the variation of the refractive index with temperature as in the case of reference liquids such as vegetable oils.

High-sensitivity temperature sensor based on overlay on side-polished fibers

A temperature sensor based on overlay on side-polished fibers is presented. It works on the basis of the evanescent field coupling between a single-mode side-polished optical fiber and a dielectric waveguide overlay. The spectrum of a white light beam transmitted through the former system exhibit sharp and deep regularly spaced resonances whose central wavelenths are linearly shifted with temperature. It has a wavelength sensitivity of /spl sim/1 nm//spl deg/C, which is one order of magnitude better than that obtained with fiber Bragg sensors.

Imaging local index variations in an optical waveguide using a tapping-mode near-field scanning optical microscope

Imaging local index variations by using a form of modulated near-field scanning optical microscopy is suggested. To test these ideas, we have probed two different optical structures, one a well-characterized BK-7 glass prism in the total internal reflection configuration, and the other a side-polished optical fiber waveguide with a step index of refraction of 4.5×10−3. Using a recently developed tapping-mode tuning-fork near-field scanning optical microscope, we have obtained images showing distinct local index variations. This method may have applicability to the characterization of a wide variety of optical waveguide structures.

Voltage-Controlled Optical Fiber Coupler Using a Layer of Low-Refractive-Index Liquid Crystal with Positive Dielectric Anisotropy

A variable fiber directional coupler is made using liquid crystal as the intermediate cladding layer between two side-polished optical fibers. A nematic liquid crystal with low refractive index and positive dielectric anisotropy is used. An ac electric field is applied to the liquid crystal by applying a voltage across two parallel electrode stripes on the two sides of the fibers. The electric field rotates the molecular orientations and changes the refractive index of the liquid crystal. The coupling ratio between the two fibers is then controlled by the applied voltage. The dependence of the coupling ratio on the applied voltage is studied for various light wavelengths, including a continuous variable range between 1.272 µ m and 1.310 µ m.

Thin Films of Ferroelectrics Made by Pulsed Laser Deposition for Optoelectronic Applications

ABSTRACTWe have deposited ferroelectric thin films by pulsed laser deposition to be used as an inline optoelectronic modulator utilizing evanescent field coupling to a side-polished optical fiber. In order to satisfy waveguiding conditions, amorphous quartz substrates (n= 1.447) were necessary. Ferroelectric films of (Pb0.91La0.90)(Zr0.65,Ti0.35)O3, Pb0.80La0.20TiO3 (PLZT), and Sr0.5Ba0.5TiO3 were deposited on quartz substrates and thin Bi4Ti3O12 buffer layers were explored as a chemical barrier and to improve crystallographic texturing. The morphology of thick films (˜3 µm) of PLZT was not acceptable for optical applications, whereas the Sr0.5Ba0.5TiO3 films were very smooth, but had some cracking. The Sr0.5Ba0.5TiO3 films were optically determined to be uniform and of sufficient quality for use in fabricating in-line fiber optic modulators.

In-line fiber-optic components using Langmuir–Blodgett films

Langmuir-Blodgett (LB) films of omega-tricosenoic acid are deposited onto side-polished optical fibers, resulting in wavelength-selective elements. The wavelength response is shown to be strongly dependent on film thickness, giving a shift in central wavelength with film thickness of Deltalambda(0)/Deltad = 2.4, in agreement with a simple phasematching model. It is demonstrated that an alternative polishing technique, requiring no substrates or epoxy, allows more repeatable LB deposition and produces devices with similar characteristics. This is the only technique that will allow deposition of more complex electro-optic LB film-forming molecules.

In-line fibre optic channel dropping filter using Langmuir-Blodgett films

A low loss in-fibre channel dropping filter is demonstrated by exploiting the evanescent coupling between a side polished monomode optical fibre and a singlemode Langmuir-Blodgett (LB) film. The LB technique is shown to provide precise film thickness control ( approximately 3 nm) for the tight fabrication tolerances demanded for this device. >

Analysis of two-dimensional fibre grating

Theoretical analysis of an array of miniature dielectric spheres on a side polished optical fibre is presented. The array of spheres acts as a fibre grating with resonances occurring at different wavelengths for different diameter and different arrangements of spheres in the array.