Showing papers on "Polarization-maintaining optical fiber published in 1984"

Fiber Optic Communications

Abstract: Preface. 1. Fiber Optic Communications Systems. 2. Optics Review. 3. Lightwave Fundamentals. 4. Integrated Optic Waveguides. 5. Optic Fiber Waveguides. 6. Optical Sources and Amplifiers. 7. Light Detectors. 8. Couplers and Connectors. 9. Distribution Networks and Fiber Components. 10. Modulation. 11. Noise and Detection. 12. System Design. Bibliography. Answers. Index.

Bending effects in optical fibers

Abstract: Mode coupling at bends in optical fibers supporting one or only a few guided modes is analyzed by considering the local normal modes for the corresponding straight waveguide. Matrix elements giving the strength of coupling between guided modes at a corner bend, and for coupling between guided modes and radiation modes, are calculated as a function of guiding strength for this "geometrical" effect. The correction to these matrix elements due to the longitudinal strain in a bent fiber is also determined. The increase in propagation constant for the fundamental mode of a fiber wrapped in a coil of constant radius is calculated from information on the coupling strengths and mode propagation constants. The phase shift and attenuation of the fundamental mode caused by a spatially periodic microbending of the fiber axis are also considered. Finally, potential applications of these effects in fiber-optic devices such as mode converters, phase shifters, switches, and sensors are discussed.

Two-mode fiber modal coupler.

Abstract: When a single-mode fiber is used at a wavelength below the cutoff wavelength, the fiber guides second-order modes, which travel at different phase velocities from the fundamental mode. Periodically stressing this two-mode fiber once per beat length can cause coherent coupling between the modes. Such a modal coupler has been developed and is described here. Coupling to one of the second-order modes has been achieved, leaving less than -40-dB residual power in the fundamental mode. Two couplers have been mounted on a single strand of fiber to construct a Mach-Zehnder interferometer with better than a 30-dB on/off ratio. The coupler is polarization sensitive and can be used as an in-line polarizer. A 36-dB extinction ratio between polarizations has been observed.

Generation and measurement of optical pulses as short as 16 fs

Abstract: We describe measurements of pulses consisting of only eight optical periods. The pulses were produced by compression with a short optical fiber and a grating pair. Measurement was by autocorrelation using noncollinear second harmonic generation in a thin crystal of potassium dihydrogen phosphate.

Analytical method for calculation of stresses and material birefringence in polarization-maintaining optical fiber

Abstract: An analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber. The method is based on the thermoelastic displacement c potential in which the principle of superposition applies. The method is applicable to any fiber structure. Its application to fibers with isolated stress-producing regions and a variety of core shapes is demonstrated. The optimum fiber parameters required to achieve maximum material birefringence for fibers with circular or bow-tie shaped stress regions are given. It is also shown that the thermal stresses tend to make the bow-tie fiber more crack-resistant than the fiber with circular stress lobes.

Acousto-optic frequency shifting in birefringent fiber

Abstract: Single-sideband frequency shifting has been accomplished using traveling acoustic waves to couple the orthogonal polarizations of birefringent fiber. The light coupled from one polarization to the other is shifted in frequency by the frequency of the acoustic wave. An upper sideband is produced in one polarization, a lower sideband in the other. Both surface and bulk acoustic waves have been used. Sideband suppression of better than 30 dB and carriersuppression of better than 20 dB below the desired sideband have been achieved.

In-line fiber-polarization-rocking rotator and filter.

Abstract: An in-line polarization rotator has been built into a single-mode birefringent fiber. The rotator utilizes periodic twists of the fiber’s principal axes, which were formed by rocking the preform as the fiber was drawn. The polarization conversion between the principal axes is wavelength dependent, with a bandwidth inversely proportional to the number of twist periods. The bandwidth of the present rotator was 4.8 nm for 100% conversion in a fiber length of 170 cm.

High power laser energy delivery system

Abstract: A low-divergence 1.06 micrometer wavelength beam from a total-internal-reflection, face-pumped laser (TIR-FPL) is focused onto the end of a quartz optical fiber to a spot having a size smaller than the fiber diameter and with a beam cone angle less than twice the numerical aperture of the fiber. The fiber transmits the energy to emerge at the other end where it is collimated and focused onto material to be processed. A laser average output power level greater than 400 watts can be transmitted through an optical fiber having a diameter less than 600 micrometers.

Single-polarization operation in highly birefringent optical fibers.

Abstract: Single-polarization characteristics in highly birefringent fibers have been investigated by considering the photoelastic effect in the entire cross section of the fiber. It has been shown by stress analysis that the stress-induced birefringence between the two orthogonal polarization modes in the cladding is much smaller than that in the core and the vicinity of the core–cladding interface, which causes differential bending loss for the two polarization modes. A bending loss formula, which takes into account the photoelastic effect, has been derived for each polarization mode. Differential attenuation characteristics and extinction ratios have been investigated for several bending radii using the bending loss formula.

High-birefringence optical fibers by preform deformation

Abstract: High-birefringence optical fibers have been fabricated using a preform deformation technique in which an initially round preform is locally heated and squeezed from two sides. This technique has been used to make both polarization-preserving and single-polarization fibers. A novel feature of these new fibers is their rectangular shape which facilitates location of the principal axes and increases resistance to polarization breakdown from external perturbations. These fibers have circular cores, low loss, and excellent polarization holding.

Polarizer requirements for fiber gyroscopes with high-birefringence fiber and broad-band sources

Abstract: Polarizer requirements for fiber-optic gyroscopes with high-birefringence fiber and broad-band sources are investigated theoretically by employing a model with a single coupling center between polarization modes. The phase bias offset due to a finite polarizer extinction ratio is greatly reduced by incoherent effects, and may be further reduced by using a depolarized source or by appropriate orientation of the polarizer transmission axis. Some experimental data is presented which supports the theoretical model.

The search for very low loss fiber-optic materials

Abstract: Today's fiber-optic communications systems are fused-silica-based fibers for which signals require reamplification every 30 kilometers. Repeaterless long-haul (transcontinental and transoceanic) links can only be envisaged if a new fiber material with intrinsic power losses significantly lower than those of silica can be identified and developed. This article reviews the development of silica-based systems, details the physical mechanisms which produce signal attenuation in fiber materials in general, and identifies that class of materials from which ultralow loss glasses are most likely to be developed in the future.

Active transmission line: light amplification by backward-stimulated Raman scattering in polarization-maintaining optical fiber

Abstract: The possibility of an active transmission line with a polarization-maintaining optical fiber has been investigated by means of backward-stimulated Raman gain. The fourth Stokes line of the stimulated Raman scattering is placed near 1.3 μm with pumping light of 1.06-μm wavelength, in which Raman gain at 1.30 μm is produced in terms of a strong pump that is due to the third Stokes line at 1.24 μm. A laser diode (InGaAsP/InP) operating at 1.30 μm is used as signal light to meet the Raman gain. As a result, a Raman gain as high as 20 dB and a gain coefficient of 2.0 × 10−12 cm/W have been obtained. It is shown experimentally that it is important to meet exactly the polarization directions between the pump and the signal pulses to obtain a large Raman gain.

Optical fiber having in-line polarization filter

Abstract: A device using a birefringent optical fiber having periodic integral perturbations with the period equal to the birefringence beat length being useful as, for example, a polarization rotator and an optical filter.

Measurements of polarization mode couplings along polarization-maintaining single-mode optical fibers

Abstract: A new technique for measuring the polarization mode coupling along a polarization-maintaining optical fiber is demonstrated Additional analyses of optical time-domain reflectometry signals are used Using a 134-μm Nd3+:YAG laser as a light source and an acousto-optical light switch to reduce the Fresnel reflection at the input end of the fiber, we have examined characteristics of the polarization mode couplings for four fibers with different extinction ratios The extinction ratios evaluated by the present method are in good agreement with those obtained by a conventional technique within ±05 dB

Fiber optic interferometer transducer

Abstract: A sensor or transducer having a dual path optical fiber, such as a single mode, two polarization state, waveguide fiber, utilizes the relative change in propagation constant of the paths to sense and transduce an applied force to an interference variation and ultimately an electrical signal. In this arrangement, in-phase light is introduced to both polarized states or paths in the fiber and transmitted therealong past a stress area of birefringement inducing force and ultimately combined, thereby producing in the combined beam a variation in interference which is related to the applied force. Specific structures are provided for converting isotropic forces such as pressure and temperature to anisotropic forces on the fiber to thereby produce birefringement and to also magnify the latter effect.

Optical fiber polarizer

Abstract: A fiber-optic polarizer comprises an optical fiber (25) having a core (26) and cladding (27) with different refractive indices and forming a single-mode guiding region, the core (26) having a non-circular cross-section defining two transverse orthogonal axes which, in combination with the different refractive indices, permit the de-coupiing of waves polarized along the axes. The guiding region is located close to the surface (29) of the fiber (25), and the outer surface (29) of the fiber (25) has a non-circular cross-section so that the location of the guiding region and the orientation of the axes can be ascertained from the geometry of the outer surface (29). A polymeric film (40) is coupled to the fiber surface (29) that is closest to the core, the film (40) having different indices of refraction along axes aligned with the transverse orthogonal axes of the core (26), one of the indices of refraction of the film (40) being less than the effective index of refraction of a desired wave in the guiding region of the fiber (25), and the other index of refraction of the film (40) being greater than the effective index of refraction of an unwanted wave in the guiding region of the fiber (25).

Fiber optic structure and method for making.

Abstract: A fiber optic structure comprising an optical fiber having a body of material deposited upon the exterior surface such that the body of material is sufficiently strong and rigid to permit processing of the fiber for various fiber optics applications. The process for forming the fiber optic structure involves the electroplating of a body of material upon the exterior surface of the optical fiber which is to be processed. A built-up body on fiber allows coupling structures to be created. The built-up body enables the fiber to be used as liquid level sensors and other types of mode strippers.

Review of All-Fiber Phase and Polarization Modulators

Abstract: For at least ten years now workers have been contributing techniques for modulating light signals in optical fibers1'2'3'4. These techniques have been of the phase, polarization and frequency variety. However, whereas the phase and polarization modulation techniques can be accomplished in a very efficient manner in what is referred to as the "all-fiber" approach (i.e., an unbroken or unspliced fiber), frequency modulation schemes have not been very efficient (under 2%) using an all-fiber techniques '6. To date, practical frequency modulation is limited to accomplishment in bulk Bragg Cell media external to the fiber. Hence discussion of frequency modulation within an optical fiber is premature at this time. This paper therefore will survey those signal modulation techniques which apply to demonstrated in situ optical fiber modulation techniques, i.e., all-fiber phase and polarization modulation.

Fiber Faraday rotator.

Abstract: A single-mode fiber Faraday rotator is proposed and fabricated by using a paramagnetic glass with a high Verdet constant. The Faraday rotator is a W-fiber with three layers, namely, core, inner cladding, and outer cladding. To make the fiber FR-5 is used as the starting material. The Verdet constant of the rotator is −0.25 min/Oe·cm at a 0.633-μm wavelength. The rotator can be used in a fiber isolator.

Fiber optic polarizer with error signal feedback

Abstract: This invention provides apparatus and methods for converting a lightwave of an arbitrary polarization propagating in a single mode optical fiber into a wave having a single linear polarization state. A polarization couples light of an undesired polarization out of the fiber, and a photodetector produces an error signal responsive to light coupled from the fiber. Control circuitry processes the error signal to produce control signals which are input to a polarization of light input to the polarizer to null the error signal. With the error signal maintained at a minimum value the light input to the polarizer and, hence, the light output therefrom is a wave having only the desired linear polarization.

Method of aligning a polarization-preserving optical fiber with a semiconductor laser for attachment of the fiber to the laser

Abstract: A method of aligning the polarization-preserving axis of a receiving end of a polarization-preserving optical fiber with the linearly-polarized output of a semiconductor laser in which the fiber optic end is placed substantially adjacent the laser rather than being separated from the laser by a polarizing optical system.

Single mode optical fiber polarimetric stress sensor having optical common mode rejection

Abstract: An instrument for measuring stress is arranged to be insensitive to stresses caused by conditions other than that of the phenomenon to be measured. The instrument employs two equal lengths of optical fibers of the kind exhibiting birefringence when stressed. Polarized light is directed into one of the optical fibers along its longitudinal axis. The two optical fibers are arranged in series with respect to the longitudinal transmission of the polarized light through those fibers. A polarization rotator is situated in the light path between the two optical fibers. The polarized light transmitted through the polarization rotator is rotated by an amount causing stresses imposed equally on the two optical fibers to have equal and opposite effects of the transmitted polarized light. The invention may be embodied to permit the measurement of acceleration, pressure, fluid flow rate, magnetic field gradient, magnetic field strength, electric field strength, electric field gradient, or any other phenomena that can be made to produce stress on an optical fiber. The invention is especially useful in differential measurement because the device measures the difference in stress imposed on the two optical fibers.

Coiled-birefringent-fiber polarizers

Abstract: Experimental results are presented that illustrate the excellent reproducibility and thermal stability of fiber polarizers made by coiling highly birefringent bow-tie fibers. The effective extinction ratio of the polarizer when used in a fiber-optic gyroscope is shown to be 62 dB.

Nuclear and pressure sensitive line/perimeter detection system

Abstract: A system for simultaneously detecting nuclear radiation and pressure combines light signals from a radiation sensitive scintillating optical fiber with light signals from a pressure sensitive optical fiber. The scintillating fiber is coupled to a light transmitting optical fiber for long distance light transmission to a detector unit such as a photomultiplier tube. The concurrent detection of radiation and pressure of radiation and pressure is used to trigger an alarm signal.

Switching fiber optic amplifier

Abstract: A fiber optic amplifier utilizes a crystal fiber of laser material to bidirectionally amplify light signals This amplifier permits the application of both pumping illumination and the signal to be amplified to the end of the crystal fiber to avoid the disadvantages inherent in side pumping this fiber End pumping is accomplished by taking advantage of the slow spontaneous fluorescence of the laser crystal to sequentially apply the pumping illumination and then the signal to be amplified to the crystal This sequential application of signals is made possible through the use of a switchable coupler which allows light to be selectively coupled from either of a pair of input optical fibers to a single output optical fiber which is coupled to the crystal fiber The pumping illumination is initially supplied to the crystal fiber to invert the ions within the crystal Once these ions are inverted, the coupler is switched to permit the application of the signal to be amplified to the crystal, and the application of pumping illumination is temporarily discontinued The signal to be amplified propagates through the crystal to stimulate emission of coherent light from the laser material resulting in amplification of the signal When this amplification process is complete, pumping illumination is again applied through the switch to the crystal fiber

All-fiber gyroscope with polarization-holding fiber

Abstract: An all-fiber gyroscope is reported that is constructed entirely of polarization-holding fiber. The random-drift coefficient was 5 x 10(-3) deg/ radicalh. Gyro bias drift is shown to be stable over periods of hundreds of hours. Device construction details and some thermal dependence of components are given.

Digital transmission of TV signals with a fiber-optic heterodyne transmission system

Abstract: A heterodyne-type fiber-optic television transmission is reported. The setup consists of a semiconductor transmission laser, a polarization maintaining fiber, and a heterodyne receiver with a local laser, fiber coupler, and an avalanche photodiode. Further, an interference experiment between two coherent optical channels was performed.

Design and performance of tuned fiber coil isolators

Abstract: Optical isolators using coiled single-mode fibers with controlled birefringence have been thoroughly analyzed and tested experimentally. Isolation ratios as high as 44.5 dB with insertion losses (excluding coupling and polarizer losses) of 0.3 to 0.4 dB have been obtained at 633 nm. Analysis indicates that these devices will have >20-dB isolation over a spectral range of 2.5 nm or a temperature range of 36°C.

Optical fiber mode scrambler

Abstract: The present invention relates to a mode scrambling arrangement for a multimode or graded-index optical fiber and, more particularly, to an optical fiber mode scrambler achieved by forming a deformation as, for example, a groove or notch on one side of the multimode or graded-index optical fiber orthogonal to the longitudinal axis thereof. The groove or notch can be produced by any suitable etching or machining process to extend through the cladding layer and at least very slightly into the outer surface of the core of the multimode or graded-index optical fiber. The depth of the groove or notch into the core can be controlled by monitoring the mode pattern in the multimode fiber during the etching or machining process to provide maximum mode scrambling with minimal loss.