Conventional Multimode Fiber Research Articles

A simple reflection-type two-dimensional refractive index profile measurement technique for optical waveguides

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode at 650nm wavelength instead of a laser diode or He–Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and a curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 800nm and an index precision of 2×10−4. To verify the system’s capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

Reflection-type Optical Waveguide Index Profiling Technique

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode (LED) at 650 nm wavelength instead of a laser diode (LD) or He-Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 700 nm and an index precision of $2\times10^{-4}$ . To verify the system's capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

Optical chemsensor based on etched tilted Bragg grating structures in multimode fiber

We present a simple optical chemsensor device based on tilted Bragg grating structures ultraviolet-inscribed in conventional multimode fiber and sensitized by a hydrofluoric (HF)-etching treatment. The transition behaviors of fiber Bragg gratings (FBGs) from normal to tilted structures and their spectral evolution under HF-etching have been studied. The etched devices have been used to measure the concentrations of sugar solution, showing a potential capability of detecting concentration changes as small as <0.5%, which is an order of magnitude lower than that of previously reported FBG sensors in single-mode fiber.

Optical fiber hydrogen sensor for concentrations below the lower explosive limit

We report a simple and inexpensive optical fiber hydrogen sensor which consists of a palladium-coated cladded multimode tapered fiber. The working mechanism of such a sensor is based on the absorption changes of the evanescent waves. With a conventional multimode fiber, a low-power LED operating at 850 nm, and a simple detection scheme we demonstrate some sensors. It was found that the sensor's performance can be adjusted with the taper diameter. The sensor is suitable for monitoring concentrations of hydrogen below 4% (the lower explosive limit) with fast response.

High-Peak-Power Ultrashort Pulse Generation Using All-Fiber Chirped Pulse Amplification System with Small Core Multimode Fiber

We present an all-fiber chirped pulse amplification system based on a normally dispersive single mode Er-doped fiber and a multimode fiber of 25 µm core diameter. The 260 fs sech2 transform-limited pulses generated in a passively mode-locked Er-doped fiber laser are stretched to 1 ps and amplified in an Er-doped fiber amplifier. Then the subsequent multimode fiber in which the pulses propagate only in the fundamental mode compresses the pulses to 80 fs. The pulse compression using the conventional multimode fiber as a large-core single-mode fiber is demonstrated for the first time. The peak power of the output pulses is increased to 44 kW.

High-Speed Polymer Optical Fiber Network

The status of the polymer optical fiber (POF) for high-speed data communication is reviewed. Recently, the low-loss and high-bandwidth perfluorinated GI POF which has no serious absorption loss from visible to near infrared region was successfully prepared at Keio University. Since the core diameter (300–1000 μm) of the GI POF is much larger than that of the multimode silica fiber (62.5 μm), the serious modal noise in the conventional multimode silica fiber was virtually eliminated, resulting in stable giga bit order data transmission with inexpensive couplers and connectors.

A novel optical fiber-based strain sensor

This communication reports on a novel intensity-based optical fiber strain sensor. A conventional multimode fiber was drawn-down to give a reduced cross section that resembled a symmetrical taper. The sensors were embedded into glass fiber reinforced epoxy composites and the light transmission characteristics through the profiled optical fiber were measured as a function of applied stress. A linear response was observed.

Cross-sectional transformers for the signal enhancement of intensity-based evanescent-field sensors

A cross-sectional transformer (CST) that allows efficient interconnection between a conventional multimode optical fibre and a broad shallow waveguide, designed for strong interaction of guided modes with sensing materials in the evanescent field, is described. A ray approach is used to determine a simple theoretical relationship between the geometrical configuration of the transformer and the enhancement in sensitivity to absorption. Thinly clad rectangular optical fibres have been drawn from a composite preform, and a CST has been fabricated using a suitably formed bundle of these fibres. An enhancement of 3.9±0.6 dB of the power collected from a broad slab waveguide compared with that collected directly by a multimode fibre is measured. The attenuation of the rectangular fibres that comprise the CST is 0.1±10.07 dB cm −1 at 550 nm.

High-energy broadband single-pass fibre Raman laser pumped by a cavity-taper output Nd?YAG laser

High-energy (0.68 mJ or 55 kW) broadband (0.38 to 2.22 μm) nonlinear optical conversion has been obtained in a conventional multimode optical fibre using a Nd: YAG pump laser with a direct optical fibre taper output and a taper-to-fibre coupling scheme. A taper-to-fibre launching efficiency exceeding 75% has been determined analytically and is compared with the experimental results.

Fiber-optic subscriber loop systems for integrated services--The strategy for introducing fibers into the subscriber network

Two approaches to fiber-optic subscriber loop system development in Japan are described. In the first. Approach I, NTT aims at introducing inexpensive fiber-optic subscriber loop systems using conventional LED's, multimode fiber, and analog transmission techniques in the near future. In the second, Approach II, fiber-optic subscriber loop systems will be made highly functional by evolving from analog to digital transmission. This paper presents system fabrication examples for each approach and the results obtained in the tests.

Optical-fiber fanout connector for 10-fiber ribbon cable termination

This paper proposes a novel type of ribbon-to-single-fiber fanout connector applied to high-density high-count optical cables composed of fiber ribbons. The fanout connector provides individual access to fibers in the 10-fiber ribbon. Construction of the connector is made by assembling newly developed multifiber and single-fiber connectors: the former is a small plastic 10-fiber ribbon connector, and the latter is a push-on type single-fiber connector allowing easy push-pull reconnections. The fabricated fanout connector has shown an average insertion loss of 0.5 dB and a return loss of larger than 30 dB for the conventional graded-index multimode fibers. Mechanical and reconnectability test results have been entirely satisfactory for the practical use of the connector.

Fibre-optic laser Doppler anemometer with Bragg frequency shift utilising polarisation-preserving single-mode fibre

A fibre-optic laser Doppler anemometer (LDA) utilising a single-mode polarisation-preserving fibre as a (transmitting) link is discussed. Since these fibres are bimodal in the sense that they can sustain two modes with orthogonal polarisations, they can be used to transmit the two beams of a normal LDA in which one beam is frequency shifted. By rotating the polarisation of one beam 90 degrees before coupling it to the fibre, the two beams propagate independently through the fibre and can be separated again at the fibre exit. The performance of this type of fibre in a laser Doppler set-up is investigated and experimental results are given. A miniature optical measuring head using this principle and operating in backscatter is described. The backscattered light is collected by a conventional multi-mode fibre.

Arc-fusion splicing of single-mode fibers 1: Optimum splice conditions

The optimum conditions for arc-fusion splicing of single-mode fibers with core eccentricity of a few microns are investigated in detail. A narrow, quick fusion method, where the fiber-fused region is restricted by the narrowing of the electrode gap and the arc-discharge time is short compared with the conventional multi-mode fiber splice, is presented that will reduce the surface tension effect. The optimum values of electrode gap, prefusion time, and discharge duration are found to be 0.7 mm, 0.2 sec, and 1 sec, respectively, when the discharge current is 18 mA. The optimum pressing stroke of a fiber after the fiber end faces contact each other is determined to be 20 microm. Splice loss <0.1 dB is achieved in the present conditions for fibers with 2-microm core eccentricity and +/-3-microm o.d. discrepancy.

The light acceptance angle of a graded index fibre

The acceptance angle of a graded index fibre, which corresponds to the numerical aperture, is presented. A geometrical technique is used to obtain the exact ray trajectory of the beam propagating along the fibre. The acceptance angle in a conventional multimode fibre is not influenced by the position in the fibre cross-sectional area, especially for the meridional rays. However in a graded index fibre, it is a function of position on the cross section of the fibre and of the incident angle of the beam. As the position moves into the fibre periphery, the acceptance angle decreases monotonically and approaches zero.