Showing papers on "Mode scrambler published in 1997"

Reflective-mode conversion with UV-induced phase gratings in two-mode fiber

Abstract: In future fiber communications systems, efficient mode conversion has the potential to enable improved devices for dispersion compensation and wavelength routing. Previous reports of symmetric-asymmetric mode conversion in circular, multimode optical fibers have shown nonideal spectral characteristics due to polarization dependence and/or mode splitting of nearly degenerate components of the higher order LP/sub 11/ mode. This work avoids these problems through use of nominally polarization-independent UV-induced phase gratings while exploiting a reflective phase-matching condition that is much less sensitive to the mode splitting of the LP/sub 11/ mode than prior work.

Intermodal phase difference controller for beam angle modulation in index guided semiconductor devices

Abstract: A novel device and method of beam steering for semiconductor lasers or optical amplifiers is disclosed. The method of the present invention achieves high signal extinction ratios, high speed, low chirp modulation by biasing a multi-lateral mode beam steering section. The device of the present invention comprises an active single vertical and lateral mode optical waveguide, a multi-lateral mode waveguide, and a mode converter. The mode converter efficiently couples output from an active single mode waveguide to two or more modes of a multi-lateral mode waveguide. Two guided modes arrive at a device facet with a particular intermodal phase difference based on initial mode phasing, multi-lateral mode waveguide length and modal dispersion properties, and facet angle. Beam steering is achieved through carrier antiguiding effect by injecting current into the multi-lateral mode waveguide from the mode converter thus changing the intermodal dispersion. Changing the intermodal phase difference changes the direction of beam propagation relative to the device facet, providing enhanced beam steering.

An etched two-mode fiber modal coupling element

Abstract: When a fiber with topological structures built directly on the cladding is compressed longitudinally, lateral bends are induced. The lateral bends lead to mode coupling. We have built several etched two-mode fiber modal coupling elements to take advantage of this effect of bending. The resulting modal coupling elements are compact. More importantly, the percentage of power converting from one mode to another is variable by varying the axial compression. In this paper, we present a theoretical model describing the mode conversion in the etched fiber elements. Also discussed are the fabrication and testing of the modal coupling elements and the experimental confirmation of the theoretical model.

Rational harmonic mode-locking fiber laser

Abstract: Optical pulse sources with repetition rate approaching terahertz are very important for many photonics applications including ultra-high speed optical communication and generation of sub-mm waves. Both active and passive mode locked fiber lasers are the appropriate choice for this purpose because of the availability of erbium doped fiber amplifier. In general, the mode locking occurs with a repetition rate of nf0, where n is an integer and f0 is the longitudinal mode frequency spacing. This is called harmonic mode locking. In the case of rational harmonic mode locking, the repetition rate is (np plus 1) f0 where p is also another integer. For the case of active mode locking, this is obtained when the modulation frequency to the amplitude or phase modulator used for mode locking is given by (n plus 1/p) f0. For the case of passive mode-locking, the rational harmonic mode-locking occurs when the saturable absorber in a ring laser is offset by a fraction p/L: from the center where L is the length of the cavity. We have developed a theory of the rational mode locked fiber laser. The results of the theory are compared with experimental results obtained from a 1.5 (mu) fiber laser actively mode-locked with a LiNbO3 electro-optic phase modulator.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Selective modal sensing of vibrating beams using piezoelectric films

Abstract: The application of the principle of orthogonality of the vibration mode shapes of a structure to the design of shaped modal sensors, which detect the vibrational response of the structure for the mode for which they are designed, is presented. The principle was applied in the design of shaped polyvinylidene fluoride (PVDF) modal sensors for detecting the first and second modes of the bending vibration of a simply-supported beam. These sensors, which are designed as the mode 1 and the mode 2 sensors, respectively, were bonded to the same surface of a simply-supported steel beam. The beam was subjected to random vibration by an electromagnetic exciter connected to the opposite surface of the beam. The vibrational responses of the beam measured by the distributed mode 1 and mode 2 PVDF shaped sensors are compared with the vibrational responses measured using an accelerometer. It is shown that the distributed sensors produce maximum voltage output for modes 1 and 2, respectively, for which they were designed. Furthermore, is shown that by dividing the mode 1 and mode 2 sensors into two separate halves and adding or subtracting the output signals of these halves, the mode 1 sensor can be used to detect the second mode of vibration of the beam while the mode 2 sensor can be used to detect the first mode of vibration of the beam.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Application of modal domain distributed fiber optic sensors to smart materials and structures

Abstract: Modal domain distributed fiber optic sensors by using a birefringent single mode fiber can be applied for measurement of mode coupling distribution along a fiber attached to a structure. The mode couplings are caused by strain, stress, temperature, etc. In the present paper, some fundamental experiments were conducted to understand relations between the mode coupling and the external force. The relations between mode couplings in x and y polarized modes and the stress distribution at the cross section of a fiber subjected to a transverse load were derived theoretically by using a coupled mode equation. The stress distribution was calculated by two dimensional finite element method (FEM). Experiments were conducted to measure the mode couplings of a coated or uncoated fiber subjected to a transverse load at one point. Experimental results showed relation between a mode coupling and an external load was almost linear on a logarithmic graph. It was found that an uncoated fiber measured load more quantitatively than a coated fiber. A fiber optic load sensor module for a serial multiplexed sensor system was developed for future application of the present study. The above load identification technique can be combined with the OCDR (optical coherence domain reflectometry) technique developed by K. Hotate et al. to quantify the applied loads along a fiber on structures.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method for driving a wavelength changeable light source apparatus, such a wavelength changeable light source apparatus and an optical communication system using the same

Abstract: A light source apparatus includes a light source, a mode selecting unit, a light source control unit and a mode selection control unit. An oscillation mode of the light source is switchable between a first mode under a first stimulated condition and a second mode under a second stimulated condition, and an oscillation wavelength of the light source is changeable. The mode selecting unit selects between oscillation light in the first mode and oscillation light in the second mode emitted from the light source, and the mode selecting unit can change the mode to be selected between the first mode and the second mode. The light source control unit modulates the oscillation mode of the light source between the first mode and the second mode in accordance with a modulation signal and changes the oscillation wavelength of the light in the unselected mode to set this wavelength to a desired value, in response to an instruction from equipment connected to the light source apparatus, while repressing fluctuation of the oscillation wavelength of the light in the selected mode. The mode selection control unit controls the mode selecting unit to switch the mode to be selected by the mode selecting unit to the mode of the light whose oscillation wavelength has been set to the desired value by the light source control unit.

Displacement sensing by spatial mode conversion between single mode to multi-mode fiber

Abstract: Summary form only given. There have been many displacement sensing methods based on optical fibers such as using mode scrambling of multi-mode fibers or intensity change of single mode fibers due to coupling mismatch. In this work, we used as displacement sensing the mode excitation change caused by spatial variation of input beam. A single mode fiber is used as a point-like input beam source for a multi-mode fiber. Since the core size of the multi-mode fiber is about 10 times larger than that of the single mode fiber, if two fibers are closely located and the multi-mode fiber is sufficiently long, the input beam from the single mode fiber excites many modes of the multi-mode fiber without power loss.