Polarization-maintaining Optical Fiber Research Articles

Suspension of the fiber mode-cleaner launcher and measurement of the high extinction-ratio (10−9) ellipsometer for the Q & A experiment

The Q & A experiment, first proposed and started in 1994, provides a feasible way of exploring the quantum vacuum through the detection of vacuum birefringence effect generated by QED loop diagram and the detection of the polarization rotation effect generated by photon-interacting (pseudo-)scalar particles. Three main parts of the experiment are: (1) Optics System (including associated Electronic System) based on a suspended 3.5-m high finesse Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio polarizer and analyzer, and (3) Magnetic Field Modulation System for generating the birefringence and the polarization rotation effect. In 2002, the Q & A experiment achieved the Phase I sensitivity goal. During Phase II, we set (i) to improve the control system of the cavity mirrors for suppressing the relative motion noise, (ii) to enhance the birefringence signal by setting-up a 60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to reduce geometrical noise by inserting a suspended polarization-maintaining optical fiber (PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio (10−9) polarizer and analyzer for ellipsometry. Here we report on (iii) & (iv); specifically, we present the properties of the PM-fiber modecleaner, the transfer function of its suspension system, and the result of our measurement of high extinction-ratio polarizer and analyzer.

Stress birefringence analysis of polarization maintaining optical fibers

Thermal stress characteristics for polarization-maintaining optical fibers (PMFs) with panda shape, bow-tie shape, elliptical shape, and “pseudo-rectangle” shape are analyzed by finite element method. Stress birefringence is calculated by principle of the stress-photoelastic coupling effect. Stress distribution contours and the stress birefringence distributions are presented. At the same time, the stress birefringence is studied in different stress regions with different structure parameters, and compared with that obtained from the classical thermal stress theory. The numerical results demonstrate that a higher degree of birefringence can be obtained by increasing area of stress applying region, decreasing the distance of the stress region from the core, as well as changing stress region shape, etc. The “pseudo-rectangle” shape fiber can produce a larger and more uniform stress birefringence than the panda fiber, the elliptical fiber and the bow-tie fiber. The elliptical core bow-tie fiber has also bigger stress birefringence, which is induced by the thermal stress and as well as geometrical shape.

Pulsed X-ray and /spl gamma/ rays irradiation effects on polarization-maintaining optical fibers

We studied the sensitivities at 1.55 /spl mu/m of three polarization-maintaining (PM) and three unstressed single-mode (SM) optical fibers under pulsed X-ray (/spl sim/1 MeV) and steady-state /spl gamma/-ray (/spl sim/1 MeV) radiation. Our results showed no differential radiation-induced attenuation (RIA) between the two orthogonal polarization axes of PM fibers for times ranging from 10/sup -6/ s to 100 s after ionization pulse (dose 1MGy/s). The two inner cladding phosphorus-codoped PM fibers and their corresponding SM fibers exhibited the same RIA levels and kinetics after both irradiation types. Their radiation responses could be explained by their compositions and by the properties of the absorbing phosphorus-related defects generated in the light guiding region (core and inner cladding). The inner cladding fluorine-codoped PM fiber showed radiation-tolerant properties compared with its SM counterpart. We assumed, therefore, that the outer stress applying region dopants could have an impact on the fiber radiation sensitivity under both irradiation types. More particularly, we showed that the cladding phosphorus-codoping far from the light guiding region reduces the RIA related to the germanium defects in the fiber core. This effect could be due to the donor nature of the double phosphorus-oxygen bond and could be exploited to design radiation-hardened polarization-maintaining and single-mode optical fibers.

Observation of polarization property in near-field optical imaging by a polarization-maintaining fiber probe.

We fabricated an original near-field scanning optical microscopy (NSOM) fiber probe made of polarization-maintaining and attenuation-reducing (PANDA)-type polarization-maintaining optical fiber, and observed the polarization property of propagation light in a polymer optical waveguide. The distribution of the transmission coefficient in polarization angles through this NSOM probe showed that the linear polarization is maintained in the two crossing directions: the fast and slow axes. The polarization degree parallel to the slow axis decreases from 1000:1 to 2:1 by bending the fiber probe and the decrease is independent of the bending direction. Using this PANDA-type NSOM probe, we investigated the polarization property of periodic intensity modulation. It was found that the intensity modulation was observed clearly with the electric vector parallel to the radius direction of the waveguide, but was observed vaguely with the electric vector perpendicular to the radius direction.

Using GRENOUILLE to characterize asymmetric femtosecond pulses undergoing self- and cross-phase modulation in a polarization-maintaining optical fiber

Self- and Cross-phase modulation of asymmetric femtosecond pulses (~ 810 nm) propagating through a birefringent single-mode optical fiber (~ 6.9 cm) is studied both experimentally (using GRENOUILLE) and numerically (by solving a set of coupled nonlinear Schrödinger equations or CNLSEs). An optical spectrogram representation is derived from the electric field of the pulses and is linearly juxtaposed with the corresponding optical spectrum and optical time-trace. The simulations are shown to be in good qualitative agreement with the experiments. Measured input pulse asymmetry, when incorporated into the simulations, is found to be the dominant cause of output spectral asymmetry. The results indicate that it is possible to modulate short pulses both temporally and spectrally by passage through polarization maintaining optical fibers with specified orientation and length.

Method for the rotational alignment of polarization-maintaining optical fibers and waveguides

A novel method has been developed for measuring the rota- tional angle of a fiber's or a waveguide's polarization axis with respect to a reference angle. The reference angle is the polarization axis of the measuring device. The method also gives the true polarization extinction ratio of the measured fiber or waveguide. The method is suitable for the characterization and rotational alignment of polarization-maintaining waveguides and fibers. In particular, the method can be used to rotation- ally align the fiber-waveguide interconnections during waveguide char- acterization. The measuring device is either a linear polarizer or a polar- ization splitter that is accurately rotated with respect to the device under test. According to the experiments with a polarization-maintaining fiber, the method is very easy and inexpensive to implement, and the angular accuracy can be better than 0.2 deg. © 2003 Society of Photo-Optical Instrumen- tation Engineers. (DOI: 10.1117/1.1600730)

Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber

A novel wavelength modulation-based fiber-optic surface plasmon resonance (SPR) sensor is reported which utilizes both polarization separation and broad band radiation depolarization in polarization-maintaining fibers to enhance sensor stability. Theoretical analysis of the sensing structure with ideally separated polarizations based on the mode of expansion and propagation method is presented. The effect of polarization cross-coupling was also analyzed in the approximation of an equivalent bulk optic structure. A laboratory prototype of the fiber-optic SPR sensor was characterized in terms of sensitivity and resolution. Experimental results indicate that this fiber-optic SPR sensor is able to resolve refractive index changes as low as 4×10 −6 under moderate fiber deformations.

Towards atomic force microscopy up to 100 MHz

An atomic force microscope for nanocantilevers measuring from a few 100 nm to a few μm in length was implemented. The natural frequencies of the nanocantilevers lie in the range of 1 MHz to 1 GHz, and optical detection schemes adapted to their size and frequency range was selected. A helium neon laser with a beat frequency of 890 MHz was used as the laser source. The beat was shifted to 1090 MHz by an acousto-optical-modulator, and used as the carrier for heterodyne laser Doppler measurement. This enabled velocity measurement up to around 100 MHz. The probe beam of the Doppler interferometer was guided to the nanocantilever by a single mode polarization-maintaining optical fiber terminated by a collimating lens, a quarter wave plate, and a focusing lens. Reflected light was collected by the same optics and mixed with the reference beam. Self-excitation of the nanocantilever at its lowest natural frequency was implemented for an amplitude of 1 nmp-p at 36 MHz. The Q factor of the cantilever was 8000. Noise effective amplitude of the Doppler interferometer was smaller than 10 pmp-p above 10 MHz. Frequency detection was possible for a nanowire measuring 100 nm in width.

Angular alignment of a polarization-maintaining optical fiber

We describe a simple, fast, and accurate technique for the angular alignment of a polarization-maintaining monomode optical fiber. The method uses simple mechanical supports and is based on the de- tection of the ellipticity of the light polarization at the fiber output, with the help of a simple rotating polarizer, a photodetector, and an oscilloscope. © 2001 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1383992)

New fractal coding scheme using reference images

We describe a simple, fast, and accurate technique for the angular alignment of a polarization-maintaining monomode optical fiber. The method uses simple mechanical supports and is based on the detection of the ellipticity of the light polarization at the fiber output, with the help of a simple rotating polarizer, a photodetector, and an oscilloscope.

Low-amplitude-noise laser for AURIGA detector optical readout

We implemented a laser system to be used in an optical transduction chain for the gravitational-wave bar detector AURIGA (Antenna Ultracriogenica Risonante per l'Indagine Gravitazionale Astronomica; Ultracryogenic Resonant Antenna for Astronomical Gravitational Investigation). This system is based on a Nd:YAG laser and includes quantum-limited power stabilization in the acoustic range, deep phase modulation and near-quantum-limited rf detection for locking onto optical cavities, and coupling to a single-mode polarization-maintaining optical fiber without deterioration of performance. Such a system has wide applications in optical metrology.

Beat-length measurement of high-birefringence polarization-maintaining optical fiber using the dc Faraday magneto-optic effect

The polarization-maintaining (PM) capability of a high- birefringence (hi-bi) optical fiber can be described in terms of its modal birefringence or beat length. In the hi-bi (PM) fiber the beat length can be measured by changing the state of polarization of the light through an external means. One such technique is based on the Faraday magnetooptic effect. The technique is nondestructive, relatively simple, and efficient, and beat lengths of 2 mm and less have been measured accurately with it, thus fulfilling the measurement requirements for many of the currently available PM fibers. Utilizing optical sources with wavelengths of 633 and 814 nm, the beat lengths in a total of four hi-bi fibers have been successfully measured using the dc Faraday magneto-optic effect. The experimental results are comprehensive and very promising, and it has been demonstrated that this nondestructive technique has significant advantages over many others in simplicity, versatility, productivity, practicality, and accuracy.

A fiber optic sensor for transverse strain measurement

A fiber optic sensor capable of measuring two independent components of transverse strain is described. The sensor consists of a single Bragg grating written into high-birefringent, polarization-maintaining optical fiber. When light from a broadband source is used to illuminate the sensor, the spectra of light reflected from the Bragg grating contain two peaks corresponding to the two orthogonal polarization modes of the fiber. Two independent components of transverse strain in the core of the fiber can be computed from the changes in wavelength of the two peaks if axial strain and temperature changes in the fiber are zero or known. Experiments were performed to determine the response of the sensor by loading an uncoated sensor in diametral compression over a range of fiber orientations relative to the loading. The results of these experiments were used with a finite element model to determine a calibration matrix relating the transverse strain in the sensor to the wavelength shifts of the Bragg peaks. The performance of the sensor was then verified by measuring the transverse strains produced by loading the fiber in a V-groove fixture.

An optical fiber flow speed sensor of increased sensitivity

A simple-structured speed sensor in which a polarization-maintaining optical fiber is used as a Karman vortex generator and also as a vortex frequency sensor had earlier been proposed. For measuring ocean current velocity, a double-fin-type sensor mount was designed and investigated in detail experimentally. Although the experimental results showed its essential effectiveness, several problems were found. A conduit-type sensor mount has newly been proposed for solving these problems. A sensor for this mount has been constructed by using a circular pipe 16 mm in diameter. Experimental studies of the sensor show a wide range of agreement between detected frequencies versus measured flow speeds and the frequencies expected from the Roshko equation. The minimum detectable flow speed is 0.27 m/s. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 1–8, 1998

A novel fibre optic strain sensor

A novel strain sensor based on polarisation-maintaining optical fibre and FMCW laser diode technology is described. The sensor consists of a l00m length of fibre, a frequency-modulated laser diode light source and a PIN photodiode detector. The principle of operation relies on that facts that the optical frequency of the laser light is modulated by approximately 1GHz during a current modulated cycle of 1ms, and that the fibre has a twist inserted to induce coupling between the eigenmodes HEx 11 or HEy 11 due to circular birefringence. By selectively launching the modulated laser light into one of the eigenmodes and retaining the other for detection of coupled modes, the length of fibre from the launch end to the twist was rendered insensitive to changes in environmental conditions such as temperature. The system was shown to have a sensitivity of approximately 2πrad per 1000 microstrain with a resolution of 2 microstrain within a dynamic range of 5000 microstrain.

An optical fiber flow speed sensor of increased sensitivity

A simple-structured speed sensor in which a polarization-maintaining optical fiber is used as a Karman vortex generator and also as a vortex frequency sensor had earlier been proposed. For measuring ocean current velocity, a double-fin-type sensor mount was designed and investigated in detail experimentally. Although the experimental results showed its essential effectiveness, several problems were found. A conduit-type sensor mount has newly been proposed for solving these problems. A sensor for this mount has been constructed by using a circular pipe 16 mm in diameter. Experimental studies of the sensor show a wide range of agreement between detected frequencies versus measured flow speeds and the frequencies expected from the Roshko equation. The minimum detectable flow speed is 0.27 m/s. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 1–8, 1998

A spot reflection alignment system for fabrication of polarization-maintaining optical fiber couplers

A fiber orientation system that uses a spot reflection alignment technique for fast and simple fabrication of polarization-maintaining (PM) mechanical polished fiber optical couplers is presented. An extinction ratio higher than 27 dB (between the orthogonal polarized states) and a low insertion loss (0.2 dB) have been achieved at output ports for a 0.85 μm device, as well as good thermal and mechanical stability. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 75–77, 1998.

Detecting Damage in Composites

Research shows that polarimetric optical-fiber sensors embedded in composite laminates can monitor structural integrity and detect damage while the structure remains in service. An experimental arrangement can be created to monitor strain in composite specimens. Light from a linearly polarized helium-neon laser is converted into circularly polarized light using a quarter-wave plate, and is coupled into a polarization-maintaining optical fiber with a microscope objective lens and three-axis positioner. In order to ensure that the intensity modulation was a maximum, the input beam was polarized at 45 degrees to the axes of the fiber. Although this study used polarization-maintaining fibers, similar results also have been seen for standard single-mode fibers.

Optical Fiber-Based Wave Mixing as a Convenient and Sensitive Laser Analytical Tool for Condensed-Phase Analytes

A fiber-optic degenerate four-wave mixing (D4WM) probe for the measurement of small absorptions in liquid-phase samples is described. Laser D4WM is a nonlinear laser spectroscopic technique that has proven to be highly sensitive for the detection of trace analytes in condensed-phase media. A significant improvement in the forward-scattering optical arrangement of D4WM is demonstrated by using optical fibers for both laser light input and output. There is considerable flexibility inherent in the design since the system may be used in three configurations: (1) the simplest case of transmitting the signal radiation by optical fiber to the detection electronics, (2) the case of guiding the excitation beams to the analyte by polarization-maintaining optical fibers, and (3) the combination of both. The optical fiber-based D4WM system is shown to be an effective and sensitive laser analytical spectroscopic method for trace analysis, offering advantages such as detection in very small probe volumes, remote and in situ analysis, and convenient and efficient optical alignment enhancements obtained by the use of optical fibers.

Polarization model for a helically wound optical fiber

A polarization model for a helically wound optical fiber is presented. The model is based on a Mueller-matrix formalism that includes the effects of the winding configuration of the optical fiber on the polarization properties. A comparison between experimental polarimetric data for short lengths of polarization-maintaining optical fiber wound in a helical configuration upon the surface of a shell and the polarization model is presented. The effects of static radial displacements of a cylindrical shell are considered. Finally, the model is used to predict the effects of a range of displacements on the polarization properties of the transmitted light, hence demonstrating its use as a design tool for polarimetric sensors utilizing nontrivial geometric configurations.