Showing papers on "Mode scrambler published in 2000"

Optical bend sensor based on measurement of resonance mode splitting of long-period fiber grating

Abstract: We report an effective new method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating. The bending induced mode splitting exhibits a near-linear response and the bending sensitivity achieved by this method is nearly four times higher than the previously reported wavelength shift detection method. The evolution of the transmission loss under bending appears dependent on the initial mode coupling strength.

Single mode optical fiber coupling systems

Abstract: Coupling devices (90, 140) for coupling a lens (8, 30, 72, 96) to a single mode optical fiber (4, 104, 144, 184) are disclosed. The lens assembly is the coupling device and includes a single mode optical fiber (4, 104, 144, 184), a lens (8, 30, 72, 96), and a locating tube (6, 114, 182).

Multi-amplifier, high power mode locked laser

Abstract: A mode locked semiconductor laser that can generate relatively high-power output pulses. The semiconductor mode locked laser is formed from an array of optical amplifiers that are coupled to a common resonant cavity by way of an optical channelizer or wavelength division multiplexer (WDM). By utilizing an array of optical amplifiers, the output pulses will have a relatively higher power than known mode locked lasers. As such, the mode locked semiconductor laser in accordance with the present invention does not depend on the power handling capability of the individual optical amplifiers and allows the average output power to be scaled, for example, up to the kilowatt range using semiconductor optical amplifiers. A mode locked laser in accordance with the present invention can be implemented with active mode locking, passive mode locking or a hybrid of the two. In embodiments utilizing active mode locking, the output pulse shape can be tailored by the amplifier drive current distribution.

High order spatial mode optical fiber

Abstract: The invention relates to method and apparatus for transmitting an optical signal having optical energy substantially in a high order spatial mode. The optical waveguide, in one embodiment, includes a few mode fiber designed to have specific transmission characteristics for supporting the single high order spatial mode, and the few mode fiber transmits the single high order spatial mode. The optical waveguide, in one embodiment, has a dispersion and a dispersion slope for a given transmission bandwidth. Another aspect of the invention includes a method for transmitting an optical signal having optical energy substantially in a single high order spatial mode. The method includes the steps of providing a few mode fiber, which supports optical energy in the single high order spatial mode. In one embodiment, the single high order spatial mode is the LP 02 spatial mode In another embodiment, the few mode fiber supports an optical signal having optical energy having less than twenty spatial modes.

Dispersion compensating module and mode converter, coupler and dispersion compensating optical waveguide therein

Abstract: A dispersion compensating module, mode converter, coupler and dispersion compensated optical fiber therein. The dispersion compensating fiber has a plurality of core segments, the refractive index profile being selected to exhibit properties such that an LP02 mode at 1550 nm may be propagated a distance (generally 0.5-3.0 km), upon conversion to LP02, to compensate for dispersion of a length of transmission waveguide preferably greater than 25 km propagating in an LP01 mode. In another embodiment, the dispersion compensating module has a mode converter having a reflective fiber grating for converting a first to a second mode interconnected to a dispersion compensated fiber propagating in the second mode. The mode converter has a coupler adapted to operatively couple light propagating in a first mode from a first fiber into a second, and a reflective fiber grating operatively coupled to the second fiber; the grating being capable of converting light from the first into the second mode. According to another embodiment, an optical fiber coupler is provided having a first fiber with a first propagation constant in a first mode, and a second fiber within the coupler having a second propagation constant, the second fiber including a necked-down portion which is formed prior to fusion of the fibers, the necked-down portion being formed such that the local propagation constant of the second fiber substantially matches the first propagation constant thereby enhancing first mode coupling.

High performance fused-type mode selective coupler for two-mode fiber devices

Abstract: We demonstrate a high performance fused-type mode selective coupler that couples the LP11 mode of a two-mode fiber and the LP01 mode of a matching single-mode fiber, the phase-matching condition was satisfied by etching and pre-pulling of a two-mode fiber, the excess loss and the maximum coupling ratio of 0.15 dB and 92%, respectively, are achieved.

Multimode optical fiber having function to remove higher order mode

Abstract: PROBLEM TO BE SOLVED: To obtain an optical fiber having a large effective core area, low loss, small absolute value of dispersion and small bending loss susceptibility by controlling the difference in the propagation constant between the lowest mode and the second-order mode to be twice or more of the difference in the propagation constant between adjacent modes of higher-order modes. SOLUTION: The distribution structure of the refractive index is designed in such a manner that when light signal enters, three or more modes of linearly polarized waves are present as the propagation modes. In this state, the difference in the propagation constant between LP01 mode and LP11 mode is specified to be twice or more, preferably three times or more, of the difference in the propagation constant of the LP11 mode or higher-order mode and the adjacent higher mode. As a result, this structure enables such an arrangement of modes that only the LP11 mode or higher-order modes are coupled to the crack mode and that only the LP01 mode substantially propagates after the light propagates at a proper distance. If the difference is less than twice, proper attenuation for only the higher-order modes is impossible and a single mode transmission is made difficult.

Optical transmitter having optically pumped vertical external cavity surface emitting laser

Abstract: An optical fiber transmitter comprises an optically pumped single mode MQW VECSEL for emitting an information-carrying laser beam and has an external cavity length defining a comb of optical modes, each mode corresponding to a channel wavelength of an optical telecommunications system having plural optical channels. A semiconductor structure of the VECSEL has an optical-pump-excited multiple quantum well (MQW) homogeneously broadened gain region active over a band which is less than mode-to-mode spacing, the gain region being tunable to hop from a first mode to an adjacent second mode. A tuning arrangement tunes the VECSEL from mode to mode thereby to select each one of the plural optical channels. An optical modulator adds modulation to a beam emitting from the laser to provide the information-carrying laser beam, and a coupler couples the information-carrying laser beam into an optical fiber of the optical telecommunications system. A calibration method based on detecting inter-mode optical transitions (mode hopping) is described.

Single transverse mode selectively oxidized vertical cavity lasers

Abstract: Vertical cavity surface emitting lasers (VCSELs) which operate in multiple transverse optical modes have been rapidly adopted into present data communication applications which rely on multi-mode optical fiber. However, operation only in the fundamental mode is required for free space interconnects and numerous other emerging VCSEL applications. Two device design strategies for obtaining single mode lasing in VCSELs based on mode selective loss or mode selective gain are reviewed and compared. Mode discrimination is attained with the use of a thick tapered oxide aperture positioned at a longitudinal field null. Mode selective gain is achieved by defining a gain aperture within the VCSEL active region to preferentially support the fundamental mode. VCSELs which exhibit greater than 3 mW of single mode output power at 850 nm with mode suppression ratio greater than 30 dB are reported.

High order spatial mode transmission system

Abstract: The invention relates to methods and apparatus for transmitting an optical signal having optical energy. The system, in one embodiment, includes at least one transmission span including an optical waveguide. The transmission span transmits substantially all of the optical energy in a single high order spatial mode. The optical waveguide, in one embodiment, has a dispersion and a dispersion slope for a given transmission bandwidth. In another embodiment, the invention further relates to an optical transmission system which includes a spatial mode transformer positioned to receive an optical signal. The spatial mode transformer transform the optical energy of the optical signal from a low order spatial mode to a high order spatial mode. The system further includes an optical transmission waveguide in optical communication with a spatial mode transformer, and the optical transmission waveguide transmits substantially all of the optical energy in the high order spatial mode. Another aspect of the invention relates to a method for transmitting an optical signal having optical energy substantially in a single high order spatial mode. The method includes the steps of receiving the optical signal having optical energy in the single high order spatial mode, and transmitting the optical signal having optical energy in the single high order spatial mode through a transmission span. The transmission span includes an optical waveguide.

Technique for measuring modal power distribution between an optical source and a multimode fiber

Abstract: A technique for measuring the modal power distribution of an optical source (for example, a laser) launching pulses into a multimode fiber involves a characterization of the multimode fiber itself in terms of its differential modal delay. A reverse differential mode delay measurement is then performed to characterize the interaction of the optical source with the multimode fiber. By knowing these characteristics, the modal power distribution of the source into the fiber can then be determined by using a reconstruction algorithm.

Multimode optical fiber with a higher order mode removing function

Abstract: The present invention's multimode optical fiber is characterized in that the propagating modes include a mode the lowest and second or higher order modes; and the difference between the propagation constants of the lowest order mode and the second order mode is 2-fold or more than the difference between the propagation constants of adjacent modes that are second order or higher order modes. Due to this design, single mode propagation becomes possible once the modes have propagated over a specific distance. As a result, it is possible to relax the conventional single mode conditions, enabling the fiber parameters to be set relatively freely.

Multimode optical fiber with high-order mode removing function

Abstract: A multimode optical fiber in which three or more linear polarization modes can exist as propagation modes when an optical signal is inputted. The multimodal optical fiber with high-order mode removing function is characterized in that the propagation modes include the lowest-order mode and high-order modes including the second-order mode, and the difference in propagation constant between the lowest-order mode and the second-order mode is twice or more those between the adjacent modes of the high-order modes. Thereby, since a single mode is possible the optical signal is propagated over a prescribed distance, conventional conditions for single mode are eased, and fiber parameters can be set comparatively arbitrarily. As a result, the dispersion is lowered in the wavelength band used. Moreover, the effective sectional area of the core can be larger. The connection loss, bend loss and nonlinear effects are decreased.

Mode scrambler for polymer optical fibers

Abstract: This paper covers the design and operation of a new mode scrambler for polymer optical fibers. This scrambler enables the rapid achievement of the equilibrium mode distribution without incurring significant insertion loss. Its main other features are small size and a costeffective design, making it very easy to build, configure, and operate. A numerical model based on geometrical optics is developed to understand the behavior of the scrambler, assess its overall performance, and help optimize its configuration. Results obtained through numerical simulation are then validated through experiments.

Thermo-electric cooler circuit and method for DWDM/TDM mode selection

Abstract: An optical transceiver and method therefore provides a cooled laser diode configured to run in either a low power mode or a standard mode. A method for a thermo-electric cooler includes coupling the thermo-electric cooler to a laser diode, operating the thermo-electric cooler in one of a low power mode and a standard mode, and switching between the low power mode and the standard mode. The laser diode is configured to transmit signals in the low power mode and the standard mode. The low power mode maintains the laser diode at a temperature within a predetermined range of temperatures. The standard mode maintains the laser diode at a temperature that corresponds to a predetermined wavelength of light output from the laser diode. In one embodiment, the low power mode is a Time Division Multiplexing (TDM) mode and the standard mode is a Dense Wavelength Divison Multipexing (DWDM) mode. The optical transceiver includes a temperature circuit, a thermo-electric cooler coupled to the temperature circuit, and a laser diode coupled to the thermo-electric cooler. The thermo-electric cooler is responsive to inputs from the temperature circuit, the inputs identifying one of at least a first mode and a second mode, wherein a choice of mode is a function of a performance requirement. The optical transceiver includes a temperature circuit that includes a switch configured to alter the thermo-electric cooler between the first mode and the second mode.

Ultra-short optical pulse laser, especially a mode-coupled laser pulse source used in telecommunications, has an optical guide element for restricting amplified light to the fundamental mode of a multi mode fiber

Abstract: An ultra-short optical pulse laser comprises a multi mode fiber (13), a mode coupler (35) and an optical guide (15) positioned on a resonator axis (23), the guide restricting amplified light to the fundamental mode of the fiber. A laser, for generating ultra-short optical pulses, comprises a laser resonator (11) through which light energy repeatedly passes along the resonator axis (23), an optical multi mode fiber portion (13) doped with an amplification material and positioned along the resonator axis, a pump system (51) for exciting the amplification material, a mode coupler (35) positioned on the resonator axis and an optical guide element (15) which is positioned on the resonator axis and which restricts light, amplified by the fiber, to the fundamental mode of the fiber. Independent claims are also included for the following: (i) a method of generating ultra-short pulses using the above laser; and (ii) a mode-coupled laser for generating high power ultra-short optical pulses.

Simultaneous single mode and multi-mode propagation of signals in a double clad optical fiber

Abstract: An optical amplifier having a suitable length of Er/Yb co-doped double clad optical fiber is used to amplify an input optical signal. The inner clad of the double clad optical fiber supports the propagation of a multi mode signal used to excite Er/Yb co-dopants in the double clad optical fiber. Simultaneously, a single mode signal launched from a single mode laser pump co-propagates with the input optical signal in the core of the optical fiber. In this model, single mode light travels in the single mode core region and the multi mode pump light is mainly in the clad region. The interaction between the two laser pumps is negligible.

Integrated circuit devices having mode selection circuits that generate a mode signal based on the magnitude of a mode control signal when a power supply signal transitions from a first state to a second state

Abstract: Integrated circuit devices having improved test capabilities may include a mode selection circuit that generates a mode signal that designates an operational mode based on the magnitude of a mode control signal when a power supply signal transitions from a first state to a second state. A preferred embodiment of the mode selection circuit generates a mode signal that designates a first mode of the integrated circuit device when the power supply signal transitions from a first state to a second state while a magnitude of the mode control signal exceeds a potential threshold. Moreover, the mode selection circuit may also prevent subsequent changes in the magnitude of the mode control signal from disabling the first mode. The mode signal may be generated without the need for additional dummy pads and/or input pins, which may necessitate an increase in chip size and/or more complex test equipment to test an integrated circuit device.

Coupled mode optical sensor

Abstract: A sensor system for use in surface plasmon sensing which is capable of coupling a single propagating optical waveguide mode to a surface plasmon polariton mode mediated by an integrated optical grating positioned between the modes. The system provides optical coupling at a single wavelength and angle whilst simultaneously providing a wide range of excitation conditions to be monitored in real time.

C.w. optical parametric oscillators: single mode or multimode?

Abstract: This paper details the conditions for which a c.w. OPO pumped by a single mode field is working in a single or multimode regime. It shows that c.w. OPOs are intrinsically single mode systems in the steady state regime, both for the longitudinal and transverse modes, unless special conditions of mode degeneracy or mode coupling are met. Complex optical patterns may appear in such cicumstances, that we have recently observed. Furthermore, if one adds a linear coupling between the signal and idler modes, these two modes can phase-lock on each other: one then obtains a perfect degenerate single mode operation for the c.w. OPO.

Analysis of High Power Millimeter Wave Waveguide Mode Converters with Input Mode Mixture

Abstract: Based on the coupled mode theory, this paper presents the study on the influence of input mode mixture in circular oversized waveguide mode converters. Three kinds of commonly used waveguide mode converters, including the waveguide mode converters with varying wall radius or small axis perturbations, and the waveguide mode converters with bent structures, are taken as the examples. The results show that the spurious input modes do not simply superimpose onto the output modes, and in some cases they may deteriorate the conversion efficiency for the main output mode. Methods for transforming such spurious input mode mixture simultaneously into the main output mode are also presented in this paper.

A new type of low loss mode converter based on adiabatically tapered hollow silica optical fiber

Abstract: A new type of mode converter using a tapered hollow silica optical fiber is proposed and experimentally demonstrated. Three segments of single mode, hollow, and multimode fibers were concatenated serially to convert the fundamental mode to a ring shape mode. The proposed scheme could be applied to convert the fundamental LP 0 1 mode to TE 0 1 , TM 0 1 and LP 0 2 modes. Evolution of mode filed along the taper and the insertion loss were measured.