Showing papers on "Mode scrambler published in 2006"

An Ultracompact Optical Mode Order Converter

Abstract: We describe the design and fabrication of an ultracompact optical mode order converter employing submicron waveguides. The mode converter can realize optical mode conversion between zeroth- and first-order optical modes with a device footprint less than 18 mum by 3 mum. The optical mode converter could be employed in various types of photonic integrated circuits where optical mode order conversion is needed

Selective excitation of the LP11 mode in step index fiber using a phase mask

Abstract: We present a novel mode selective coupling technique for step index fiber. This technique utilizes phase matching for excitation of higher-order modes while suppressing the fundamental mode. Using this technique, a phase element is fabricated and tested to demonstrate the high coupling efficiency to the LP11 mode. In addition, we derive an analytical expression of the coupling efficiency of the LP11 using a single

Antiresonant reflecting optical waveguide microstructured fibers revisited: a new analysis based on leaky mode coupling

Abstract: Using two different modal methods, the multipole method and the more recent fast Fourier factorization method, we exhibit and explain a core mode transition induced by avoided crossing between a core localized leaky mode and an high-index cylinder leaky mode in anti-resonant reflecting optical waveguide microstructured optical fibers (ARROW MOFs). Due to its wavelength selectivity and to the leaky nature of the involved modes, this transition doesn't seem to have already been described in detail and analyzed as done in this work in spite of several already published studies on core mode dispersion properties. The main properties of this transition are also described. We also revisite the already mentionned cut-off phenomena limiting the transmission band in ARROW MOFs in terms of mode coupling between the core mode and one or several high- index cylinder modes.

Fiber acousto-optic mode coupling between the higher-order modes with adjacent azimuthal numbers

Abstract: It is pointed out theoretically that fiber acousto-optic mode coupling can occur between the higher-order modes with adjacent azimuthal numbers. Selective fiber mode conversion from LP01 to LP11, and then to LP21 or LP02 is demonstrated experimentally in a few-mode fiber by using a method of cascaded acousto-optic mode coupling.

High-order modes suppression in large mode area active fibers by controlling the radial distribution of the rare earth dopant

Abstract: Many high power fiber laser applications require doped fibers having large mode area but still working in the single mode regime. The most common techniques to keep a large mode area fiber in the single mode regime are to reduce the core numerical aperture, to strip the high order modes by coiling the fiber, to launch only a single transverse mode, or to use photonic crystal fibers. All these methods have limits and disadvantages. In this paper we demonstrate by simulation the effectiveness of another method to suppress the high order modes in large mode area active fibers by optimizing the rare earth dopant concentration across the core while keeping the step index structure of the core of the fiber. This method was not previously employed because the traditional doped fiber manufacturing technologies do not have the required capability to radially control the dopant concentration. However, Direct Nanoparticle Deposition (DND) can be used to manufacture large mode area fibers having any radial distribution of active element concentration and any refractive index profile. Thus, DND fibers can be designed to benefit from this high order mode suppression technique. The simulation results presented in this paper have been obtained using Liekki Application Designer v3.1, a software simulator for fiber lasers and amplifiers.

Variable Optical Mode Generator in a Multimode Waveguide

Abstract: A variable optical mode generator in an integrated-optic multimode waveguide is proposed and fabricated. It consists of a power divider, controllable parallel phase retarders, and a mode combiner. In this device, a desired output mode is generated by controlling the relative phase differences among the arms. The operation of device has been confirmed by observation of the output mode patterns at a wavelength of 1.55 mum

Determination of the differential mode delay of a multimode fiber using Fourierdomain intermodal interference analysis.

Abstract: We present a novel differential mode delay (DMD) measurement method for a multimode optical fiber (MMF) based on Fourier-domain lowcoherence interferometry (fLCI) for the first time. An optical spectrum analyzer and a mode scrambler are used to obtain the intermodal interference signal in spectral domain after light passes an MMF. The MMF is used as a common path interferometer by itself without using any reference arm in an interferometer. Instead of using an offset launching technique, we present an effective method to obtain all available intermodal interference signals at a single shot by using a mode scrambler. The measured results using the proposed method are compared with those obtained using a conventional time-domain DMD measurement method.

Studies on strain and temperature characteristics of a slanted multimode fiber Bragg grating and its application in multiwavelength fiber Raman ring laser

Abstract: Detailed strain and temperature characteristics of a 2/spl deg/ slanted multimode fiber Bragg grating (MFBG) are developed theoretically and observed experimentally. Results show that the strain and temperature sensitivities are almost the same for different transmission dips of the 2/spl deg/ slanted MFBG. Utilizing two characteristics of the 2/spl deg/ slanted MFBG, namely 1) resonant wavelength intensities strongly affected by excited mode propagating before the grating and 2) uniform strain sensitivities of different resonant wavelengths, a switchable and tunable multiwavelength fiber Raman ring laser is realized. The configuration is simple and multipurpose. Results show that the laser can generate single-, dual-, three-, four-, and five-wavelength lasing by switching between each operation if a mode scrambler (MS) that is inserted in front of the slanted MFBG is adjusted; furthermore, a 4.2-nm continuous wavelength-tuning range is achieved by straining the slanted MFBG when the MS is fixed.

Intrusion detection system for a multimode optical fiber using a bulk optical wavelength division multiplexer for maintaining modal power distribution

Abstract: Intrusion detection of one section only of a multimode fiber uses a light signal launched into the fiber at a location spaced from the source through a single mode fiber to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the fiber. A small portion of the higher order signal modes at the a second location also spaced from the destination is sampled by a tap coupler and monitored for transient changes in the mode field power distribution which are characteristic of intrusion to activate an alarm. A fiber being used for data transmission can be monitored for intrusion by introducing a monitor wavelength different from that of the data signal. Central to this invention is the use of a bulk optic (commonly referred to as a pass/reflect) wavelength division multiplexer, one which maintains the modal distribution within the fiber.

Fourier-domain low-coherence interferometry for differential mode delay analysis of an optical fiber.

Abstract: We propose a novel mode analysis and differential mode delay measurement method for an optical fiber using Fourier-domain low-coherence interferometry. A spectral interferometer based on a Mach-Zehnder interferometer setup was used with a broadband source and an optical spectrum analyzer to detect relative temporal delays between the guided modes of a few-mode optical fiber by analyzing spectral interference signals. We have shown that experimental results of the proposed method agree well with those results obtained by using a conventional time-domain measurement method. We have demonstrated that this new mode analysis technique has high sensitivity (<60 dB) and very good resolution (<1 ps/m).

Analysis of the effects of mode coupling on the bandwidth characteristics of step‐index plastic optical fiber

Abstract: The mode coupling of SI-POF is analyzed by observing the far-field radiation patterns. The results show that no obvious mode coupling occurs at a transmission distance of 5 m. While a transmission distance of 10–30 m occurs, strong mode coupling and the equilibrium mode distribution is established after 30 m. In order to clarify the mode-coupling effect on the bandwidth of step-index plastic optical fiber (SI-POF), the bandwidths of SI-POF samples were measured under different launch conditions and compared with theoretical values that neglect mode coupling. It is found that although mode coupling contributes to enhancing the bandwidth of the fiber as it averages out the total propagation delays, the energy transfer between the neighboring modes will excite high-order modes during the propagation, which functions to increase the effective numerical aperture (NA) of the incident light and will decrease the bandwidth of the fiber. The net effect of mode coupling on the bandwidths of SI-POFs at different launch conditions indicates the competition between the two effects. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 432–435, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21372

Apparatus for measuring differential mode delay of multimode optical fiber

Abstract: Disclosed herein is an apparatus for measuring the differential mode delay of multimode optical fiber. The apparatus includes a tunable laser source, an interferometer, a data collecting device, and a computer. The tunable laser source outputs light, frequencies of which vary linearly. The interferometer generates multimode light and single mode light by separating light, which is output from the tunable laser source, transmitting the multimode light and the single mode light to the multimode optical fiber, which is a measurement target, and a single mode path, which is a reference, and generating a beating signal by causing the multimode light and the single mode light to interfere with each other. The data collecting device collects the beating signal from the interferometer. The computer converts the frequency components of the beating signal into components in a time domain, and calculating the mode delay of the multimode light.

Mode splitter based on triple-core waveguide.

Abstract: The mode index and mode field of a triple-core waveguide are simulated by the compact supercell method and the FEM method. The coupling property of LP(11) mode is analyzed, for the first time to our knowledge, which is similar to that of LP(01) mode except the different coupling length. Both LP(01) and LP(11) modes can be separated based on their different coupling lengths in the waveguide. When both modes are put into the central port, they will come out on different ports by optimizing the coupler length, and the mode extinction ratio can approach 30dB.

Bend resistance of large-mode-area higher-order-mode fibers

Abstract: Higher-order-mode fibers with very large mode area are shown to be naturally resistant to bend induced mode distortion, an important limitation on amplifier fibers. Simulations and measurements display resistance of these fibers to bending.

Characteristic evaluation method, device and program of single mode optical fiber

Abstract: PROBLEM TO BE SOLVED: To provide a characteristic evaluation device of a single mode optical fiber capable of evaluating nondestructively and highly accurately a distribution characteristic in the longitudinal direction between connected optical fibers, in an optical fiber transmission path constituted of a plurality of single mode optical fibers. SOLUTION: This device has a back-scattering light intensity measuring device 11 for measuring back-scattering light intensity S (λ, z) on a position z of the single mode optical fiber 13 on both ends, when pulse light having the wavelength λ is allowed to enter the single mode optical fiber 13 having an optional length L; and a back-scattering light intensity waveform analyzer 12 for operating a specific refractive index difference Δ(z) on an optional position z of the single mode optical fiber 13 by using a normalization structure inconsistency loss component In (λ, z) on the position z of the single mode optical fiber 13 operated from the back-scattering light intensity S (λ, z), and a mode field diameter 2W (λ, z 0 ) and the specific refractive index difference Δ(z 0 ) at its optional reference point z 0 . COPYRIGHT: (C)2008,JPO&INPIT

Periodic microbending-induced mode coupling in microstructured optical fiber

Abstract: Microstructured optical fiber (MOF) is a new class of optical fiber that has emerged in recent years. It is formed by an array of air holes running along the fiber length. They are fascinating because of various novel properties, including endlessly single-mode operation, scalable dispersion and nonlinearity, and the surprising phenomenon of a short wavelength bend loss edge, etc. These optical characteristics make possible wide-ranging applications in optical communication. In this paper, we investigate the mode coupling characteristics induced by periodic microbending in MOF. Coupling between various modes in normal single mode fiber (SMF) and polarization maintaining fiber (PMF) have already been investigated theoretically as well as experimentally. Periodic microbending created by a corrugated fixture on a SMF is known to induce the mode coupling between a codirectional propagating core (LP01) and cladding mode (LP11). In our experiment, a core-cladding mode coupler was built and tested based on a section of endlessly single mode MOF (fabricated with the stack-and-draw process). The fiber was bended between a pair of identical grooved plates with 250μm periodicity, thus this can be treated as a mechanical-stress-induced long period grating (LPG). The effect of microbending is controlled using stress gauge. The coupling strength is compared between single mode fiber and MOF under the same stress gage condition. The modal coupling coefficient enhancement is observed in MOF because of the complex index distribution.

Evanescent Wave Coupling Between Optical Fiber and Planar Optical Waveguide

Abstract: Transverse coupling between single mode fiber and single mode planar waveguide is analyzed for the first time-to the authors' knowledge - by an Improved Coupled Mode Theory (ICMT). The coupling is established via the evanescent part of the modal field propagating in the fiber which penetrates the slab waveguide. The main parameters that characterize the coupling process are calculated. A comparison between the results of the ICMT and those obtained by the usual coupled mode theory reveals an improvement in the accuracy by almost twenty percent.

Modular interference characteristic of two-mode fiber

Abstract: The modular interference characteristics of circular-core and elliptical-core two-mode fibers are investigated in theory. The intensity distribution and figure of two-lobe mode patterns are evaluated and simulated quantitatively for different phase difference change between LP01 and LP11^(even) mode. The interference mode patterns of elliptical-core and circular-core two-mode fibers are compared, the result shows that the two-lobe interference patterns of the two-mode fibers generate energy exchange and oscillation, and the difference is that the interference mode patterns of circular-core two-mode fiber are almost elliptical, while the interference mode pattern of elliptical-core two-mode fiber is approximately circular on condition that proper selection of the ellipticity. Their two-dimensional (2D) profile determines the choice of the core shape of the information pick-up fiber.

Static and tunable dispersion management with higher order mode fibers

Abstract: Few mode fibers have recently attracted a lot of attention, because of the prospect of enhanced design flexibility, unique modal properties, and the existence of several simultaneous light-paths in them. After the pioneering experiments by Craig Poole from Bell Labs in 1993, an application that faded away but saw a re-emergence in 2000-2003 was higher order mode dispersion compensation. In this scheme, mode converters are used to selectively propagate the signal in a higher order mode of a few-mode fiber.

Large mode area fibers by using conversion to higher order modes

Abstract: The specification describes an optical fiber device wherein a lower order mode (LOM) i.e. LP 01 is converted to a higher order mode (HOM) i.e. LP 02 prior to entering the gain section. The gain section is a few mode fiber that supports the HOM. The output from the gain section, i.e. the HOM, may be utilized as is, or converted back to the LOM. With suitable design of the few mode fiber in the gain section of the device, the effective area, Aeff, may be greater than 1600 μm 2 The large mode separation in the gain section reduces mode coupling, allowing greater design freedom and reducing the bend sensitivity of the optical fiber. The fiber designs suitable for the gain section of the devices comprise a core, inner cladding and a trench (down doped region). The inner cladding and the trench regions govern the properties of the higher order mode (LP 02 ).

Raman Amplification in Multi Mode Fiber: A Method to Reduce Inter-symbol Interference via Mode Selective Gain

Abstract: We present theoretical and experimental results showing Raman gain in multimode fiber comparable to standard single mode fiber and mode selective amplification that reduces inter-symbol interference. Improvement in MMF link for high-speed data transmission is demonstrated.

Multimode fibers with integrated optical mode field adapters for 40Gbit/s optical ethernet systems

Abstract: In this paper we present the fabrication of optical mode field adaptors at the end of single mode and multimode optical fibers, which act as a micro lens, for fiber optical communications devices, capable up to 40Gbit/s data. The mode field adaptors were used to focus the optical output field (1550nm wavelength) of the fiber to receiver and transmitter OEICs. Based on the measurement of a singlemode fiber in accordance with ITU Recommendation G.652 the optical mode fields are measured in a new set-up, which is demonstrated and discussed in comparison to conventional methods. The work was performed in cooperation with the Heinrich-Hertz-Institute in Berlin.

Integrated Optical Mode Field Adapters for Optical Ethernet Systems

Abstract: In this paper we present the fabrication of optical mode field adaptors at the end of single mode and multimode optical fibers, which act as a micro lens, for fiber optical communications devices, capable up to 40Gbit/s data. The mode field adaptors were used to focus the optical output field (1550nm wavelength) of the fiber to receiver and transmitter OEICs. Based on the measurement of a single mode fiber in accordance with ITU Recommendation G.652 the optical mode fields are measured in a new set-up, which is demonstrated and discussed in comparison to conventional methods. The work was performed in cooperation with the Heinrich-Hertz-Institute in Berlin.

Asymmetric GRIN Lensed Single Mode Fiber-to-Waveguide Coupler

Abstract: 0.6 dB coupling loss was observed for a lensed, asymmetric graded-index mode converter. The mode converter is used to couple light at 1550 nm from a single mode optical fiber to an on-chip waveguide with n=1.7

Integrated optical mode field adapters for multimode 40-Gbit/s optical ethernet systems

Abstract: In this paper we present the fabrication of optical mode field adaptors at the end of single mode and multimode optical fibers, which act as a micro lens, for fiber optical communications devices, capable up to 40Gbit/s data. The mode field adaptors were used to focus the optical output field (1550nm wavelength) of the fiber to receiver and transmitter OEICs. Based on the measurement of a singlemode fiber in accordance with ITU Recommendation G.652 the optical mode fields are measured in a new set-up, which is demonstrated and discussed in comparison to conventional methods. The work was performed in cooperation with the Heinrich-Hertz-Institute in Berlin.

Recording and playback apparatus and optical head including a variable optical coupling efficiency device

Abstract: The light intensity of a light beam emitted from a light source is appropriately controlled when the light beam is transmitted through a variable optical coupling efficiency device in an optical head. During a read mode, the light beam from the light source is incident on an optical disk at an intensity relatively weaker than that of the light source. By switching the optical coupling efficiency of the variable optical coupling efficiency device between a write mode and a read mode, the light intensity directed to an optical recording medium is substantially varied from the write mode to the read mode. This arrangement eliminates the need for substantially increasing the optical output power ratio of the light source of write power to read power.

Large effective mode area fibers for high power lasers and amplifiers

Abstract: New progress for novel design for achieving large effective mode area fibers while maintaining single mode operation for fiber lasers and fibre amplifiers is addressed in the presentation.

Method for implementing circular light ring strength uniformization and optical fiber mode disturbing apparatus

Abstract: The present invention discloses a method for implementing circular optical ring intensity uniformization in differential absorption spectrometer and fiber-optic mode scrambler. It is characterized by that it makes one part of optical fibre between telescope of differential absorption spectrometer and spectrometer be passed through a workpiece with concave-convex surface and squeezed so as to mix high-order mode in the optical fibre and make the outputted light spot with uniformly-distributed intensity be fed into monochrometer. The fibre-optic mode scrambler is characterized by that a part of optical fibre is clamped between two clamping plates which have concave-convex surfaces and mutually coincided. According to the fibre-optic mode-scrambling effect in the fibre-optic mode scrambler the high-order mode in the optical fibre can be mixed so as to output light spot with uniformly-distributed intensity.