Polished Optical Fiber Research Articles

All-fiber self-calibrating polarization synthesizer.

As the component technology for optical telecommunication systems advances, more and more mechanisms that influence the performance are discovered. After the problems of modal and chromatic dispersion were solved, polarization effects became to play an important role. Due to the polarization transmission properties of optical devices the magnitude and phase of the lightwave's electric-field components are changed depending on the state of polarization of the lightwave. Fiber-optic polarimetric sensors make constructive use of these polarization effects to measure physical quantities like temperature, strain, pressure and electric currents. In other cases, like long-haul telecommunication systems, polarization effects will result in shorter transmission distances. Both, the positive and negative effects of polarization, require measurement techniques to analyze the component's polarization properties. In this paper, a fiber-optic polarization synthesizer which is able to generate any desired state of polarization is described. Using a novel self-calibration procedure, this setup is completely self-supporting. The construction of the polarization synthesizer will be explained in detail and it will be shown, how this setup allows a simple measurement of the polarization properties of optical devices.

Fiber-Optic Polarizer Using Resonant Tunneling through a Multilayer Overlay

We demonstrate an in-line fiber-optic polarizer using resonant tunneling through a leaky multilayer overlay for the first time. Polarization extinction ratio (PER)≃27 dB with an insertion loss (IL)≃3 dB has been demonstrated experimentally with scope of further improvement. A simple planar waveguide model is developed to analyze the device whose predictions match very well with the experimental results. It is further shown that by properly selecting the device parameters one can achieve PER≃68 dB with IL≃0.2 dB for λ=0.6328 μm and PER≃80 dB with IL≃1.2 dB for λ=1.3 μm.

High-performance optical fiber polarizers based on long-period gratings in birefringent optical fibers

We have demonstrated the feasibility of achieving high-performance fiber polarizers (insertion loss 30 dB), based on polarization mode dispersion in a long-period grating. Chirped operation with 100-nm bandwidth has also been achieved, showing the possibility of a broad-band device.

PH sensor using Langmuir–Blodgett overlays on polished optical fibers

Evanescent coupling between a side-polished single-mode optical fiber and a single-mode, pH-sensitive Langmuir-Blodgett overlay is used to demonstrate an intrinsic fiber-optic pH sensor. The sensor shows a wavelength sensitivity of 18.8 +/- 0.8 nm/pH and a transmission sensitivity of 9.7 +/- 0.8 dB/pH when operating at 750 nm.

Electric-field thermally poled optical fibers for quasi-phase-matched second-harmonic generation

We report on quasi-phase-matched frequency doubling to the blue in electric-held poled optical fibers. An increase of a factor of /spl sim/10 in the conversion efficiency in comparison with the previous results is obtained. Our experiments show that the structure of the induced nonlinear grating is not uniform, both longitudinally and transversely. For this reason the value of the effective nonlinear coefficient is still far from the optimum expected from the measured value, through Maker's oscillation, for a uniformly poled fiber.

Evaluation of a fiber optic immunosensor for quantitating cocaine in coca leaf extracts

A fiber optic evanescent fluoroimmunosensor was used to rapidly detect and quantitate coaca alkaloids as cocaine equivalents in leaf extracts of five Erythroxylum species. A monoclonal antibody (mAb) made against benzoylecgonine (BE), a major metabolite of cocaine, was immobilized covalently on quartz fibers and used as the biological sensing element in the portable fluorometer. Benzoylecgonine-fluorescein (BE-FL) was used as the optical signal generator when it bound to the fiber. If present, cocaine competed for the mAb and interfered with the binding of BE-FL, thereby reducing the fluorescence transmitted by the fiber. Calibration curves were prepared by measuring (over 30 s) the rates of fluorescence increase in the absence, or presence of cocaine. Ethanol or acid extracts of dry coca leaves were assayed by this fiber optic biosensor, gas chromatography and fluorescent polarization immune assay. Biosensor values of cocaine content of leaves from five Erythroxylum species were not significantly different from gas chromatography values, but had higher variance. The biosensor assay was rapid and did not require cleanup of the crude leaf extracts. Cocaine in acid extracts was reduced significantly after 4 weeks at 23°C and after 3 weeks at 37°C. Fibers (mAb-coated), stored at 37°C in phosphate-buffered solution (0.02% NaN 3), gave stable responses for 14 days.

Glass fiber poling and applications

Recent developments in the application of poled optical fibers to second harmonic generation and electrooptic light modulation are reviewed.

Elastic polishing plate method and conditions for forming angled convex surface on ferrule endface

This paper describes an apparatus for forming an angled convex surface at the ferrule endface by polishing the ferrule endface utilizing an elastic polishing plate performing orbital and rotational motion. When the diameter of the ferrule tip was greater than approximately 0.4 mm and when the Shore hardness of the elastic plate was approximately softer than 95, the formed convex radius on the ferrule endface was found to be an unique function of both the deformed depth of the elastic polishing plate and the diameter of the ferrule tip. The backreflection of the light beam from the polished optical fiber endface was as low as less than -64 dB for all tested samples when singlemode optical fibers were polished at a slanted angle of 8 degrees.

Measurement of normalization factor of n_2 for random polarization in optical fibers

The 8/9 normalization coefficient for the nonlinear refractive index in nonpolarization-maintaining optical fibers is confirmed directly by measurement of the ratio of the self- and cross-phase modulation coefficients for two orthogonal polarizations. The nonlinear phase shift is accurately measured with a dual-frequency beat signal as a pump source.

Fiber-optic polarizer using birefringent crystal as a cladding

A new type of fiber-optic polarizer has been developed in which the birefringent material is formed around the core fiber as a cladding. A NaNO(3) single crystal is used as the birefringent material. The extinction ratios for the polarized light are measured for fibers with cores of various radii and claddings of various lengths. The extinction ratios obtained are typically 31.2 dB for a core diameter of 6 µm and a cladding length of 6 mm.

光ファイバ中の捩れによる偏光方向の回転

光ファイバ中の捩れによる偏光方向の回転

Anisotropic diffusion of the state of polarization in optical fibers with randomly varying birefringence

Polarization diffusion in communication fibers is studied. Diffusion of the states of polarization in an optical fiber is found to be anisotropic on the surface of the Poincaré sphere. The predicted anisotropy has significant implications for nonlinear evolution in long-distance communication systems.

In-line optical fiber polarizer and modulator coated with Langmuir-Blodgett films

In-line optical fiber polarizer and modulator were fabricated by depositing Langmuir-Blodgett (LB) films on polished fiber surface with gold layer. The thickness of LB film was adjusted by changing the number of monolayers, which then optimized the performance of the fiber polarizer. Good agreement was observed between the theoretically predicted conditions for efficient coupling and the experimentally determined conditions for high TM/TE extinction ratio of the optical field. By applying an electric field between the LB film, the polarization state of the lightwave in the optical fiber can be modulated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modulation of the polarization state in an optical fiber coated with Langmuir–Blodgett films

The optical fiber is bent in a slot and polished until one side of the fiber coating is only several micrometers thick. The hemicyanine Langmuir–Blodgett (LB) film is then deposited on the polished optical fiber surface. By applying an electric field between the LB film, the polarization state in the optical fiber has been modulated. The preparation details of the in-line optical fiber modulator and the measurement setup are described.

Application of a fiber Fourier transform spectrometer to the detection of wavelength-encoded signals from Bragg grating sensors

We describe an all-fiber Fourier transform spectrometer for decoding the wavelength shifts from a series of Bragg grating sensors. The system described uses an optical fiber Michelson interferometer with one arm wrapped on a piezoelectric driven stretcher capable of inducing a /spl sim/10 cm fiber length change. Passive polarization compensation is utilized which eliminates the possibility of random polarization fading in the interferometer causing apodization of the interferogram. This permits an all-fiber design without the need for speciality optical fiber or external polarization adjustments. A reference Nd:YAG laser is used to stabilize the interferometric scan in a phase-locked loop configuration by way of slow and fast feedback correction elements. A spectral resolution of <0.07 cm/sup -1/ was obtained, which corresponds to a Bragg wavelength shift of /spl sim/0.015 nm in the 1.55 /spl mu/m region. The simultaneous wavelength determination capacity of the device also permits it to be used in a variety of other applications for analysis of optical spectra.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In-line fiber optic polarimeter with a 99% coupler

A polarization transformer in combination with a polarization analyzer is well suited for the generation of any wanted polarization state. We describe the setup, calibration, and applications of an in-line fiber optic polarization detector (IPD) built with a fiber optic coupler of 99% coupling ratio. At the low power output port we use standard beamsplitters and polarizers to generate four different polarization dependent signals. For calibration, the polarization is measured at the high-power output port with an oft-line polarimeter (OPD). This enables the determination of the system matrix, which represents the relation between the polarization at the high-power port and the four signals at the low-power port. With this system matrix, a continuous and accurate determination of the polarization at the high-power output port is possible.

Blue-light generation by quasi-phase-matched frequency doubling in thermally poled optical fibers

Periodically patterned second-order nonlinearities are created in optical fibers by thermal poling in vacuo. Cw quasi-phase-matched frequency conversion to the blue is demonstrated. The measured bandwidth, 0.78 nm cm, is close to the theoretical prediction.

Optical fiber polarizer based on highly birefringent single-mode fiber

An in-line fiber polarizer is proposed and demonstrated. The attenuation of a single-mode fiber experiencing an axial periodic perturbation shows peaks at certain wavelengths, resulting from the power coupling between the guided mode and the cladding modes. When the fiber has significant linear birefringence, each of these peaks is split into two peaks. The fiber thus exhibits polarization-selective attenuation characteristics. An example of such a polarizer is demonstrated based on a highly birefringent fiber with a beat length of 1.3 mm. A 25-dB polarization extinction ratio is obtained, with an attenuation of 1.3 dB at an operating wavelength of 1177 nm.

Measurement of linear electro-optic effect intemperature/electric-field poled optical fibres

An electro-optic coefficient of r = 0.05 ± 0.02 pm/V is reported for a temperature/electric field poled Ge:SiO2 fibre. The fibre was a commercial, polarisation maintaining, singlemode (633 nm) fibre with a core composition of 18 wt% Ge and a fused silica cladding. Piezoelectric effects are seen at low frequency. Comparison with the r33 coefficient of bulk poled silica suggests that overlap between the nonlinear material and the guiding regions can be further optimised.

Dynamics of solitonlike pulse propagation in birefringent optical fibers.

Integrated Stokes parameters are used to describe solitonlike pulse propagation and its state of polarization in birefringent optical fibers. A qualitative analysis on the Poincar\'e sphere is developed to describe the evolution of the state of polarization of the soliton as a whole. Simple analytic equations describing the pulse evolution are derived in the approximation of the average profile. It is shown that two qualitatively different regimes of propagation are possible, depending on the material parameters and on the initial conditions. The approach takes into account the radiation processes. The results of the analytical approach are compared with exact numerical calculations.