Showing papers on "Mode scrambler published in 2007"

Implications of higher-order mode content in large mode area fibers with good beam quality.

Abstract: The impact of Higher-Order Mode content on beam quality in large mode area fibers supporting several guided modes is carefully investigated. It is shown that even excellent beam quality (M2 < 1.1) in LMA fibers does not guarantee low HOM content, and that the presence of HOMs can lead to significant uncontrollable changes in beam quality, peak intensity, and pointing uncertainty that depend on the uncontrollable relative phase of the modes in the fiber.

Characterization of mid-infrared single mode fibers as modal filters.

Abstract: We present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Q(sub f) as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Q(sub f) for this fiber at 10.5 micron wavelength is 1000 +/- 300. The absorption and scattering losses in the fundamental mode are approximately 8 dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428 +/- 0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Q(sub f).

Integrated lateral mode converter

Abstract: The invention describes method and apparatus for a mode converter enabling an adiabatic transfer of a higher order mode into a lower order optical mode within a photonic integrated circuit exploiting integrated semiconductor ridge waveguide techniques. As disclosed by the invention, such a mode conversion is achievable by using an asymmetric coupler methodology. In an exemplary embodiment of the invention, the invention is used to provide a low insertion loss optical connection between laterally-coupled DFB laser operating in first order mode and passive waveguide operating in the zero order optical mode. The integrated arrangement fabricated by using one-step epitaxial growth allows for a launch of the laser's light into the waveguide circuitry operating in the zero order lateral mode or efficiently coupling it to single-mode fiber, an otherwise high loss interface due to the difference in laser and optical fiber modes.

Mode Coupling in Plastic Optical Fiber Enables 40-Gb/s Performance

Abstract: We report 40-Gb/s capability of 50-mum core plastic optical fiber using differential modal delay measurements and power penalty due to intersymbol interference computations. The results are explained via a comprehensive multimode fiber model that includes mode coupling (MC) and differential modal attenuation (DMA). We show that strong MC can enable 40-Gb/s transmission for reach in excess of 100 m even in the presence of irregularities in the refractive index profile that prevent 10-Gb/s performance without MC. Furthermore, we show that DMA effects are negligible and that the mode power distributions are not a good indicator of bandwidth.

Dual acceleration sensor system

Abstract: Provided is a dual acceleration sensor system usable for detecting impact, when strong impact works on a mobile device, and recording a history of applied impact, and workable with a low power consumption. It contains low range and high range acceleration sensors, a signal processing circuit, and/or an operation mode controller for switching signal between the two sensors and an operation mode of the signal processing circuit. The operation mode controller switches between a low range mode in which a signal from the low range acceleration sensor is processed at a low range operation rate and a high range mode in which a signal from the high range acceleration sensor is processed at a high range operation rate. It is judged whether data processed in the low range mode exceeds a first threshold or not, and if not, the low range mode continues, while the mode switches to the high range mode if it does. In the high range mode, when a state that the data is less than a second threshold continues for a predetermined period of time, the mode returns to the low range mode, and if not, the high range mode remains.

Multi-mode fiber, optical fiber transmission system with offset-launch, single-mode, long-wavelength, vertical cavity surface emitting laser transmitter

Abstract: A multimode fiber optical fiber transmission system includes an improved configuration for launching a single mode long wavelength transmission signal into existing multimode optical fiber networks. More specifically, the invention utilizes new single mode long wavelength VCSEL devices to realize a novel transmitter/transceiver for multimode fiber links where offset launch with controlled mode conditioning is achieved without the use of a mode conditioning patchcord, and in some embodiments, without the use of any collecting or focusing elements.

Higher order mode dispersion compensating fiber and mode converter for higher order fiber

Abstract: A higher order mode dispersion compensating fiber includes an optical fiber and a first loss layer which is provided within the fiber and which attenuates a lower order mode propagating through the optical fiber while not attenuating a higher order mode which is higher than the lower order mode. A dispersion compensating fiber mode converter for a higher order fiber includes a single mode fiber; a higher order mode dispersion compensating fiber; and a fused and extended portion which has been formed by fusing and extending the single mode fiber and the higher order mode fiber. The fused and extended portion converts between the LP01 mode of the single mode fiber and the LP02 mode of the higher order mode dispersion compensating fiber.

Mode control in multimode optical fibre and its applications

Abstract: This thesis describes an investigation into methods for controlling the mode distribution in multimode optical fibres. The major contributions presented in this thesis are summarised below. Emerging standards for Gigabit Ethernet transmission over multimode optical fibre have led to a resurgence of interest in the precise control, and specification, of modal launch conditions. In particular, commercial LED and OTDR test equipment does not, in general, comply with these standards. There is therefore a need for mode control devices, which can ensure compliance with the standards. A novel device consisting of a point-load mode-scrambler in tandem with a mode-filter is described in this thesis. The device, which has been patented, may be tuned to achieve a wide range of mode distributions and has been implemented in a ruggedised package for field use. Various other techniques for mode control have been described in this work, including the use of Long Period Gratings and air-gap mode-filters. Some of the methods have been applied to other applications, such as speckle suppression and in sensor technology. A novel, self-referencing, sensor comprising two modal groups in the Mode Power Distribution has been designed and tested. The feasibility of a two-channel Mode Group Diversity Multiplexed system has been demonstrated over 985m. A test apparatus for measuring mode distribution has been designed and constructed. The apparatus consists of a purpose-built video microscope, and comprehensive control and analysis software written in Visual Basic. The system may be fitted with a Silicon camera or an InGaAs camera, for measurement in the 850nm and 130nm transmission windows respectively. A limitation of the measurement method, when applied to well-filled fibres, has been identified and an improvement to the method has been proposed, based on modelled Laguerre Gauss field solutions.

Automatic mode determination for an input device

Abstract: Automatic mode determination for an input device is disclosed. Depending on conditions of the input device, the input device can transition from a first mode to a transition mode and/or a second mode.

Influence of modal filtering on the bandwidth of multimode optical fibers

Abstract: The multimode (MM) optical fiber maximum operational range is defined by the fiber bandwidth (related to the intermodal dispersion) rather than by the fiber attenuation. The relationship between the modal bandwidth of the fiber, the launching condition and mode coupling is fairly complicated. There is presented a theoretical study on the modal bandwidth of the multimode fiber. The theory is based on a numerical solution of the coupled mode diffusion equation that allows the bandwidth of the MM optical fiber to be calculated. It is shown that appropriate modal filtering at the receiver side of the fiber link increases the link bandwidth.

Single mode operation of photonic crystal fiber using a full vectorial finite element method

Abstract: Finite element-based rigorous full-vectorial modal solution approach has been developed to calculate the effective index of the fundamental space filling mode, cutoff condition of the fundamental and the second guided modes to identify the single mode operation ranges for the photonic crystal fiber. The single mode operation regime for a Terahertz photonic crystal fiber has also been discussed.

High-order mode based dispersion compensating modules using spatial mode conversion

Abstract: High-Order Mode Dispersion Compensating Modules (HOM-DCM) using spatial optical transformations for mode conversion are reviewed. It is shown that mode transformers using this technology can be designed to transform the LP01 mode of SMF fibers to the LP02 mode of specially designed dispersion compensating High-Order Mode Fiber (HOMF), with typical insertion loss of ∼1 dB, and typical extinction ratio to other modes less than -20 dB. The HOMF itself can provide high negative dispersion [typically in the range of 400-600 ps/(nm km)], and high negative dispersion slope, allowing efficient compensation of all types of transmission fiber. Combining two mode transformers with HOMF and possibly trim fiber for fine-tuning, results, for example, in a HOM-DCM that compensates 100 km LEAF® fiber, with Insertion loss < 3.5 dB, and Multi-Path Interference (MPI) < -36 dB. MPI phenomena in HOM-DCMs is characterized, and shown to comprise both coherent and incoherent parts, and to result from both the mode transformers and fiber coupling within the HOMF. MPI values of < -36 dB have been shown to allow error free transmission of 10 Gb/s signals over up to 6000 km. Finally, a number of applications well suited to the properties of HOM-DCMs are reviewed.

Transient fields in the input coupling region of optical single-mode waveguides

Abstract: We investigate numerically the optical field in the region immediately behind the input facets of dielectric step-index single-mode slab and fiber waveguides. Visualization of the intensity distributions gives insight into the formation of the fundamental mode and of radiation modes. For a more quantitative characterization we determine the amount of optical power and mode purity of the field in core vicinity as a function of propagation distance. The investigation assists in designing and optimizing waveguides being employed as modal filters, e.g. for astronomical interferometers.

Noise propagation path identification of variable speed drive in time domain via common mode test mode

Abstract: Electromagnetic Compatibility (EMC) debugging of power electronics systems depends heavily on the experience of specialists due to the complex mechanisms of electromagnetic noise. In this paper, the time domain approach is used instead of the conventional frequency domain method to identify noise propagation path. The proposed test mode switches the upper or lower transistors of the converter legs simultaneously on and off at a 50% fixed duty ratio. It is called common mode test mode. Because there is no significant functional current flowing, the differential mode noise is minimized and the remaining common mode noise and mixed mode noise are maximized. Therefore, the common mode noise in this test method gives its upper boundary of Electromagnetic Interference (EMI) level when the system is normal operated. A motor drive system is measured to show how this test mode works.

High energy fiber optics laser delivery system with improved scrambling capabilities

Abstract: The methods and apparatus of the present invention provide advantages for remote laser delivery systems that conduct high levels of light energy through a fiber optic cable to a target surface. Helical fiber optic mode scramblers in accordance with the present invention are an integral portion of a fiber optic cable having a spiral curvature predetermined to advantageously influence the intermodal dispersion characteristics of the fiber optic cable. Various embodiments of helical fiber optic mode scramblers in accordance with the present invention enable delivery of light energy at rates that can exceed continuous deliver of 30 Joules per millimeter squared of cross sectional area of a fiber optics cable. Particular embodiments of a fiber optic mode scrambler in accordance with the present invention include a support structure and a cylindrical sleeve that provide limited longitudinal flexibility maximizing the range of positions in which the fiber optics cable can be dynamically arranged.

A Mode Converter with Multi-waveguide Output from the TE 01 Circular Waveguide Mode to the TE 10 Rectangular Mode for Millimeter Wave Gyro-device Applications

Abstract: A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE01 circular waveguide mode into the TE10 rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.

Design guidelines and characteristics of a four-layer large flattened mode fiber

Abstract: A refractive index profile design, which can enable us to obtain a flat-top fundamental mode field around the center, is presented. The theoretical method to analyze the four-layer large flattened mode (LFM) fibers is given. The properties of the fiber, including the fundamental and higher order modal fields, effective area, and bending loss, are discussed. The reasons forming the different modal fields are explained. By discussion, the larger effective area of the LFM fiber compared with conventional step-index fiber is proven and the feasibility to suppress the higher order modes via bending is given.

LP 01 to TE 01 , fibre mode convertor

Abstract: Mode convertors couple light from one fibre mode to another. They have applications in dispersion compensation, nonlinear optics and atom guiding for example. We demonstrate coupling from the fundamental LP01 mode to the circularly symmetric TE01 mode, which has applications for atom guidance.

Resistance of higher order modes to bend-induced mode coupling and distortion

Abstract: Signal amplification in higher order modes with large mode area has been proposed to overcome power limitations in fiber amplifiers. Simulations and measurements demonstrate resistance of these modes to bend-induced distortion and coupling, respectively.

A Novel Mode Converter using Tapered Fiber for Dual Mode Transmission

Abstract: We propose and design a novel mode converter using a tapered fiber. The fabricated device can convert the LP11 mode to the LP01 mode in a dual mode transmission.

Simple method for differential mode delay of a multimode optical fiber using Fourier-domain intermodal interference analysis

Abstract: We present a novel differential mode delay (DMD) measurement method for a multimode optical fiber (MMF) based on Fourier-domain low-coherence interferometry (fLCI) for the first time. An optical spectrum analyzer and a mode scrambler were used to obtain intermodal interference signal in spectral-domain after light pass an MMF. The MMF was used as a common path interferometer by itself without using any reference arm in an interferometer. Our proposed method can measure a short or long optical multimode fiber simply, accurately, and rapidly.

Study the application of polarization scrambler in the multi-wavelength fiber laser

Abstract: In this paper, the Multi-wavelength fiber laser's polarization sensitivity is investigated in the experiment research, through adopting the polarization scrambler eliminate polarization sensitivity, Stabilizing output eight wavelengths with the 0.8nm or 1.6nm wavelength interval have been achieved.

Experimental Demonstration of Gain Guided Lasing in an Index Anti-Guiding Large Mode Area Fiber

Abstract: Recent observations of apparently single mode gain-guided lasing in Nd3+ fibers with 100 µm diameter index anti-guided cores demonstrate the potential of gain guiding for single mode fiber lasers with very large mode areas.

Transmission power controller

Abstract: A transmission apparatus has two modes of power amplifier operation, in which mode 1 is inherently accurate, mode 2 is inherently less accurate, and measurement of a power amplifier output from mode 1 is used to correct a power amplifier output in mode 2 . Mode 1 may be a compressed mode and mode 2 may be a non-compressed mode. The apparatus may include a power controller that provides overlapping scaling factor sets for modes 1 and 2 and controls transmission power using the scaling factor sets. Upon a mode transition, the controller uses the overlapping scaling factors and changes the scaling factor set for the mode of a destination of the transition based on actual measurement representative of transmission power, for example, by carrying out power alignment loop operations. A cellular mobile device may include such transmission apparatus. A polar modulation transmitter is also disclosed.

Mode signal generation for use in computer system involves producing mode signal indicating current operating mode of computer system and changes in mode signal in one of components of computer system

Abstract: The method involves generating a mode signal (N150) indicating the current operating mode of a computer system and the changes in the mode signal in one of the components (N100) of the computer system. The changes in the mode signal and the mode signal itself are provided outside the component of the computer system. The computer system comprises of several components including at least two execution units and a switching unit. The switching unit is provided for switching the operation mode of the computer system between comparison mode and performance mode. Independent claims are also included for the following: (A) Mode signal generator; (B) System component with mode signal generator; and (C) Computer system including the mode signal generator.

Characterization of the Single mode operation of PCF using Finite Element Method

Abstract: Finite element based full vectorial modal solution approach has been developed to determine effective index of space filling mode, cutoff of fundamental and second order guided modes, identifying single mode operation of photonic crystal fibers.