Showing papers on "Equilibrium mode distribution published in 1994"

Optical waveguide including singlemode waveguide channels coupled to a multimode fiber

Abstract: An intrusion-alarmed optical fiber communication system, where light from two or more sources are launched with a planar channel waveguide launcher into two or more modes of a multimode graded-index transmission fiber, is disclosed. Input fibers containing the source light waves and the output fibers are in direct contact with the waveguide channels. Waveguide channels redistribute the light from input channels to output channels by rerouting, crossing, merging, or splitting channels. Waveguide launcher precisely launches data light into the fundamental mode and intrusion monitor light into high order modes of a multimode graded-index fiber. Fiber intrusion attenuates light in high order modes, but much less of the data in the fundamental mode, thereby forming a basis for the intrusion-alarmed system. Waveguide launcher permits light from a plurality of sources to be launched selectively into several types of fibers: singlemode fibers, multimode fibers, multicore fibers, multimode fibers having high refractive-index ring profile within the fiber core boundary. Waveguide channel configuration permit other versatile functions to be performed; these include optical time domain reflectometry, channel feedback stabilization of the diodes, launching light from more than one light source into the fundamental mode of a multimode graded-index fiber, and other functions. Means for launching and propagating the fundamental mode in multimode graded-index fiber in order to increase bandwidth capacity of said fiber are disclosed. Optical-electronic intrusion-alarmed systems with synchronous phase sensitive detection of intrusion are described, including reference recovery means. In order to decrease false alarm rates, information on transmitter light source variations are transmitted to the receiver via digital bit stream. A precise fiber optic sensor system based on the waveguide launcher is disclosed.

Optical waveguide intensity modulator using electro-optic polymer

Abstract: An optical waveguide intensity modulator of a polymer waveguide utilizes and electro-optic effect and optical birefringence induced from a poling process of a nonlinear polymer thin-film. The optical waveguide intensity modulator is constructed by a series combination of a TE/TM mode selector, a TE or TM mode converter and another TE or TM mode selector. In the polymer waveguide, the mode selectors and mode converter can be easily obtained by making the direction of a poling field to be horizontal (or vertical) and approximately 45° direction. According to the present invention, the optical waveguide intensity modulator is formed by integrating the TE or TM mode selectors and the TE or TM mode converter onto a single substrate. Further, because no element, is required which results in optical loses for example an optical isolator, an optical coupler or a curved portion of the waveguide, the efficiency of the device can be improved.

Mode selective loss penalties in VCSEL optical fiber transmission links

Abstract: The system performance with respect to modal noise of both single mode and multi-transverse mode vertical cavity surface emitting lasers is reported. A bit error ratio floor is observed with only 1 dB of mode selective loss for the single mode device but no such floor is observed using the multimode device with up to 7.8 dB of mode selective loss. The modal noise penalty for the single mode device is attributed to its higher coherence and spectral fluctuations during modulation. >

Distributed coupling between a single-mode fiber and a planar waveguide

Abstract: Light transfer between a curved single-mode fiber and a two-mode planar waveguide is investigated experimentally with respect to its dependence on the refractive index and the thickness of the planar waveguide and for different polishing depths. The behavior of this distributed coupler is treated theoretically with a coupled-mode model, which takes into account the two dimensions of the waveguide configuration, as well as the even or the odd symmetry of the planar waveguide mode field. Coupling of a fiber to a multimode planar waveguide is also considered.

Modal characteristics of bent dual mode planar optical waveguides

Abstract: Modal characteristics of bent dual-mode planar optical waveguides are obtained. The bending-induced changes in the modal power distribution is found to be quite different for the two modes. Surprisingly, unlike the fundamental mode, bending causes the fractional modal power for the second mode to increase in the inner core-half and to decrease in the outer core-half of the waveguide. Interestingly, this leads to a decrease in effective index of the second mode due to bending at sufficiently high V-values. >

Mode splitter and a magneto-optical disk pick-up device having the mode splitter

Abstract: A mode splitter and the magneto-optical pick-up device including the mode splitter are provided. The mode splitter includes a tapered waveguide portion whose thickness gradually becomes thin so that a light of at least one mode can be cut off. An emission position of a light wave can be varied depending on its mode. In this mode splitter, the emission position of the light wave of each mode can be adjusted by changing a thickness of the tapered waveguide, thereby improving the degree of freedom in designing the device.

Azimuthal far-field analysis for the measurement of the effective cutoff wavelength in single-mode fibers/spl minus/effects of curvature, length, and index profile

Abstract: The spectral analysis of the optical power transmitted through a bow tie slit rotating in the far-field pattern of a single-mode fiber provides an easy and accurate mean of determining the effective cutoff wavelength of the fiber. The principle of this technique is described. Theoretical considerations show that the ratio between the optical powers carried by the LP/sub 11/ mode and the fundamental mode, respectively, is directly related to the amplitude of two particular lines in the spectrum. The degree of coherence of the analyzed field is shown to be related to the amplitude of a third line. Owing to the sensitivity of the method, the detectable amount of the total power which is contained in the LP/sub 11/ mode is as small as 0.5%. The effects of length and curvature on the effective cutoff wavelength are measured over wide ranges for different kinds of single-mode fibers. The behavior of a quadruple-clad flattened dispersion fiber is shown to be somewhat different from that of a typical depressed cladding fiber. >

A quasi-single mode optical fiber for long-haul transmission in severe bending environments

Abstract: We investigated the feasibility of a quasi-single mode optical fiber for low bending losses in long-haul transmission at 1550 nm The advantage of a quasi-single mode fiber is that for comparable bending losses the relative index difference, /spl Delta/, can be smaller than the /spl Delta/ in a single-mode fiber We demonstrated that a quasi-single mode fiber with /spl Delta/=072% and single-mode cutoff wavelength /spl lambda//sub c/ equal to 1630 mn exhibits bending losses as low as the losses in a single-mode fiber with P=093% and /spl lambda//sub c/=1259 nm Modal noise and modal dispersion effects in the quasi-single mode fiber also were tested and found to be minimal This letter describes the matched-clad, quasi-single mode fiber and presents the test results >

Waveguide type wavelength measuring apparatus

Abstract: A waveguide type wavelength measuring apparatus is provided with a single mode channel type optical waveguide formed on a waveguide substrate, in which the light to be measured is inputted, a double mode waveguide connected to the single mode channel type optical waveguide, waveguide branches for branching the light output from the double mode waveguide, and photodetectors for detecting independently the light branched by the waveguide branches. The wavelength of the inputted light is measured on the basis of the output signals from the photodetectors. Hence it is possible to perform precise real-time measurement of the wavelength of the incident light with a compact and extremely miniaturized structure.

Modal Mode Characteristics of Bent Dual Planar Optical Waveguides

Abstract: Modal characteristics of bent dual-mode planar optical waveguides are obtained. The bending-induced changes in the modal power distribution is found to be quite different for the two modes. Surprisingly, unlike the fundamental mode, bending causes the fractional modal power for the second mode to increase in the inner core-half and to decrease in the outer core- half of the waveguide. Interestingly, this leads to a decrease in effective index of the second mode due to bending at sufficiently high V-values.

Design of rectangular waveguides for integrated optics with mode matching techniques

Abstract: Rectangular core waveguides for integrated optics have been designed by the mode matching (transverse resonance) method. To achieve good coupling between the waveguides and an optical fiber, the core cross section of the waveguide at the fiber/waveguide interface has been optimized with regard to minimum coupling loss. In calculating the overlap integral between the fundamental mode of the waveguide and the fiber a very accurate fiber model has been used. Calculations of the effective index and the field distribution of the fundamental fiber mode with this model have been compared with analytic results for circular step-index-fibers. The convergence behavior and accuracy of overlap integral calculations with the mode matching method has been investigated. The calculations show that losses as low as 0.16 dB can be reached for waveguides with refractive index contrasts in the whole range 0.5 to 2%.

Low coupling loss between quantum well electron transfer waveguide modulator and single mode fiber

Abstract: We demonstrate low fiber-waveguide coupling loss in quantum well electron transfer modulators with a large optical mode structure. Electro-optic efficiency and propagation loss are comparable to those measured in a conventional waveguide structure with the same active material.

Field power distribution in variable core radius of optical fiber for optimal coupling with photodiode

Abstract: Many possibilities are offered to analyze the field in tapered fibers. We have used in this work the bpm method and the coupled-mode theory for a conical fiber. In the second case, it is shown by a length-scale criterion that some geometries should provide a good efficiency. The comparison between the quasi 3D numerical simulation and the local mode method is also performed. The complete resolution procedure is then dependent on certain essential approximations and simplifying hypothesis.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.