Single-mode Fiber Coil Research Articles

Optical injection locking assisted all-optical microwave oscillator

This paper reports an optical injection locking (OIL) assisted all-optical microwave oscillator (AOMO) scheme for the photonic generation of a microwave (MW) signal and demonstrates a 40th harmonic single-mode signal generation with an external low-frequency radio-frequency (RF) signal. In this all-optical single-loop oscillator that only depends on optical devices, the stimulated Brillouin scattering (SBS) effect of a coil of single-mode fiber (SMF) and a semiconductor optical amplifier (SOA) are used to select the oscillation frequency and modulate the optical feedback signal, respectively. The OIL effect in a distributed feedback (DFB) laser multiplies the frequency of the external RF signal. Thanks to the OIL module, it only requires an optical loop to acquire a single-mode oscillation and the oscillation signal is phase-related to the low-frequency RF source. The experiment demonstrates the generation of a single-mode MW signal of 10.71 GHz with an external RF signal of 267.8 MHz, with a frequency multiplication factor of 40. Mode-hopping is not evident in the output signal, and a moderately low-quality OIL signal is acceptable since unwanted harmonics and the phase noise floor of the OIL signal have little impact on the generated MW signal.

Software compensation for the coupling error of a single-mode fiber coil under time-varying temperature and magnetic field

Previous studies have shown that there exists a large nonreciprocal phase error in the single-mode fiber coil of a depolarized interference fiber optic gyroscope (De-IFOG) under time-varying temperature and magnetic field, which evidently weakens its environmental adaptability. A real-time software compensation method considering the coupling effect of time-varying temperature and magnetic field is first proposed and verified experimentally. After compensation, the error of De-IFOG decreases from 50 deg / h to 6 deg / h when the magnitude of the magnetic field is 10 G and temperature uniformly increases from 10°C to 60°C with time-varying rate of 36 ° C / h. The compensation method is of great significance in De-IFOG engineering applications.

Elimination of polarization effect in a fiber-optic gyro by using polarization elements

This paper proposes the theoretical design of a polarized interferometric fiber-optic gyroscope (IFOG). The polarized IFOG utilizes a coherent light source and polarization elements (Faraday rotators and polarizing beam splitter) to obtain maximum visibility of an interference signal and to compensate for the birefringent effect of a single-mode fiber coil in an IFOG.

Coupling Effect of a Single-Mode Fiber Coil Under Time-Varying Temperature and Magnetic Field

A coupling effect in the single-mode fiber coil (SMFC) of a depolarized interference fiber optic gyroscope (De-IFOG) under time-varying temperature and magnetic field, which can cause a serious nonreciprocal phase error, is revealed. In this paper, the mechanism of the coupling effect is thoroughly studied and the related theory is derived in detail. Simulations and experiments are carried out to verify the validity. The experiments show a peak-to-peak value error of about 50 °/h in the SMFC when the magnitude of magnetic field is 10 Gauss and the temperature uniformly increases from 10 to 60 °C at the rate of 36 °C/h, which cannot be neglected in the applications of De-IFOGs.

Thermal phase noise in giant interferometric fiber optic gyroscopes.

The thermal phase noise in giant interferometric fiber optic gyroscopes (fiber length L > 10 km) and its impact on the detection sensitivity are theoretically derived and experimentally verified. It is confirmed that thermal phase noise cannot be overlooked for the giant IFOGs. Utilizing high order eigen frequency modulation can effectively suppress the walk-off component of thermal phase noise, but the residual part contributes to high-frequency range thus limits the detection bandwidth of giant IFOGs. The self-noise is experimentally demonstrated as 3.5 nrad/s/Hz at low frequencies and 5.2 nrad/s/Hz at 100 Hz in the IFOG with a 30-km single mode fiber coil. Discussions about the fiber characteristics on thermal phase noise are presented, which paves the way to the design of giant IFOGs.

Excess relative intensity noise suppression in depolarized interferometric fiber optic gyroscopes

Excess relative intensity noise (excess RIN) is one of the major factors that degrade the short-term performance of interferometric fiber optic gyroscopes (IFOGs). We theoretically and experimentally investigate the correlation of excess RIN between interferometric and reference signals in depolarized IFOGs in which single-mode fiber coils are adopted to make them cost-effective. The Lyot depolarizers decrease the correlation coefficient to about 81%, giving a lower limit that excess RIN can be suppressed to 59%. Then, an excess RIN suppression method by co-processing interferometric and reference signals electronically is proposed that works well with the open-loop demodulation. Experimental results show the proposed method compensates the excess RIN to 60.4% compared to original, almost achieve the noise limit of the depolarized configuration.

Compensation of thermal strain induced polarization nonreciprocity in dual-polarization fiber optic gyroscope.

Dual-polarization interferometric fiber optic gyroscope (IFOG) is a novel scheme in which the polarization nonreciprocal (PN) phase error of the two orthogonal polarizations can be optically compensated. In this work, we investigate the effective of PN phase error compensation under varying temperature. It is proved that, the thermally induced strain deforms the fiber, and results in perturbations on the birefringence and polarization cross coupling which degrades the IFOG's stability. A wave propagation model and analytical expressions of PN phase error are derived by using coupled-wave equation and Jones matrix. We theoretically and experimentally verify that, although the single-mode (SM) and polarization-maintaining (PM) fiber coils behave different owing to their intrinsic properties of wave propagation, the thermal strain induced PN phase error can still be compensated under slow and adiabatic temperature variations. This could be a promising feature to overcome the temperature fragility of IFOG.

A Simple, Full-Dynamic-Range Optical Heterodyne Single-Mode Fiber Gyroscope

In this study, a theoretical design of a simple fiber-optic gyroscope is proposed. This fiber-optic gyroscope not only realizes the full-dynamic-range of Sagnac-phase measurement, but also eliminates the excess phase affected by the elliptical birefringence of a single-mode fiber coil. Under the conditions that the fiber coil has 1100 turns and the fiber length is 242.9 m, the bias stability of this gyroscope is theoretically evaluated as 9.44 °/h. In this study, we also discuss the error signal that arises from the intensity stability, as well as the polarization nonreciprocity. We generate 1000 random values to simulate the possible distribution of a bias drift, and the result shows that the drift of the Sagnac phase is less than 10 $^{-3{\circ}}$ . In addition, we deduce the influence of the error signal induced by polarization nonreciprocity. The result indicates that the maximum error arises if the reciprocal phase of the SMF is $\varphi = 2m\pi $ ( $m = 0, \pm 1, \pm 2, \pm 3,\ldots$ ) and the optical rotation angle is $\theta = 45^{\circ}$ .

Microwave photonic filter with two independently tunable passbands based on paralleled fiber Mach–Zehnder interferometers and dispersive medium

In this article, we propose and experimentally demonstrate a novel microwave photonics filter (MPF) with two independently tunable passbands. The MPF is based on a sliced broadband optical source and a dispersive medium, and two paralleled fiber Mach–Zehnder interferometers (FMZIs) have been employed as the optical spectrum slicer. A coil of single-mode fiber has been used as a dispersion medium, which introduces time delay for each tap. A stable dual-passband MPF has been obtained, and the experimental results show that each passband of the MPF can be tuned freewill by adjusting the variable optical delay line (VODL) in each of the FMZIs.

A Selectable Multiband Bandpass Microwave Photonic Filter

A multiband bandpass microwave photonic filter (MPF) whose passband number and position can be selected is theoretically analyzed and experimentally demonstrated. The proposed MPF is based on a wide-band optical source (WBOS) and a two-order high-birefringence fiber loop mirror (HB-FLM), which serves as a slicing filter. Two segments of high-birefringence fiber (HBF) with the lengths of 3 m and 6 m are used in the HB-FLM, and three typical spectral periods or their combinations can be independently achieved by simply adjusting the polarization controllers (PCs) in the HB-FLM. Subsequently, the light source is sliced with uniform or mixing wavelength spacing. A coil of single-mode fiber (SMF) is then used to act as a dispersive medium to introduce time delay between taps. Thus, a single or multiband bandpass response is obtained at the output of a high-speed photodetector (PD). In addition, the passband centered at dc frequency is removed due to the use of phase modulation. All of the radio frequency (RF) characteristics of the proposed MPF show good agreement with the theoretical prediction. It has the merits of good flexibility, high spectrum efficiency, and great potential of extension.

Nonreciprocity in single-mode fiber coil induced by orthogonal magnetic field

We investigated the nonreciprocity induced by an orthogonal magnetic field (OMF) in a single-mode fiber coil and expressions for the propagation constant of light waves in the bent fiber are deduced. Coils with different radiuses are put into depolarized interferometric fiber optic gyroscopes (D-IFOGs) for experimental verification. Theories, simulations and experimental results show that the OMF induced nonreciprocal phase error is closely related to the bending radius and the generated magnetic drift in D-IFOGs is linear to the amplitude of the OMF.

Multiwavelength L-Band Brillouin–Erbium Comb Fiber Laser Utilizing Nonlinear Amplifying Loop Mirror

In this paper, we demonstrate a novel multiwavelength L-band Brillouin-erbium fiber laser utilizing nonlinear amplifying loop mirror. The erbium-doped fiber section in the fiber loop mirror provides efficient amplification of Brillouin pump (BP) to generate the stimulated Brillouin scattering in the single-mode fiber coil. The laser structure can achieve symmetry breaking of the loop without requirements to an asymmetric coupler or polarization controller. The proposed fiber laser has a low threshold power of about 10 mW to create the first Brillouin-Stokes signal. The maximum number of 27 Stokes signals with a spacing of 0.089 nm is achieved by setting the BP wavelength at 1604 nm and its BP power is set at 2.2 mW.

Measurement of the temporal coherence in broadband sources using the radio-frequency transfer function of a dispersive system

We present a noninterferometric method for direct and complete characterization of the degree of first-order temporal coherence γ(τ) of low-coherence broadband sources both in amplitude and phase. The method is based on measuring the radio-frequency transfer function HRF(f) of amplitude-modulated partially coherent guided waves in a system with first-order dispersion. Experimental data for sources based on amplitude-modulated amplified spontaneous emission in the 1.55 μm band having spectral widths up to 30 nm and subsequently dispersed in a 12.77 km standard single-mode fiber coil provide complete characterization of the temporal coherence with 6.5 fs resolution and a dynamic range exceeding 20 dB.

Compact integrated depolarizer for interferometric fiber optic gyroscopes

We propose an integrated waveguide depolarizer for use in interferometric fiber optic gyroscopes (IFOGs) with single-mode fiber coils. The integrated waveguide depolarizer is based on a Mach-Zender interferometer with polarizing beamsplitters. A waveguide polarizing beamsplitter is designed using multiple air trench structures oriented at the Brewster angle. We also analyze the effect of component imperfections on the degree of polarization achievable with an integrated waveguide depolarizer.

Differential all-birefringent-fiber frequency-modulated continuous-wave Sagnac gyroscope

Disclosed is a differential birefringent fiber frequency-modulated continuous-wave (FMCW) Sagnac gyroscope for measuring rotation velocity. The gyroscope uses a 90°-twisted single-mode birefringent fiber coil as a double unbalanced fiber-optic FMCW Sagnac interferometer, and uses the phase difference between the two beat signals from the fiber coil to determine the rotation velocity. This gyroscope can eliminate the nonreciprocal phase drift and provide a doubled resolution.

All-fiber single-mode fiber frequency-modulated continuous-wave Sagnac gyroscope

An all-fiber single-mode fiber unbalanced Sagnac gyroscope is described. The gyroscope is based on optical frequency-modulated continuous-wave interference and consists primarily of four Y-type single-mode fiber directional couplers and a single-mode fiber coil. The rotational velocity of the fiber coil is determined simultaneously by detection of the phase shift of the beat signal. The advantages and limitations of the gyroscope are discussed.

Fiber optic temperature sensor with duplex Michleson interferometric technique

An interferometric fiber optic temperature sensing system employing a light emitting diode (LED) as the broadband optical source and a single mode fiber coil, which was fabricated in definite length as the sensor head, is described. The fiber transmitting line back and forth along the same path is used, so the changing caused by the environmental temperature fluctuation of the fiber path can automatically be compensated. The sensitivity of the sensing system can be easily improved by using the long length of the sensing fiber. The experimental result of the sensing gauge length vs. the sensitivity is given. A typical wavelength 1300-nm LED source is used in the experiments. The experimental curve of the resolution characteristic of the system related with the length of sensing fiber coil is also discussed.

Low Cost Fiber-Optic Gyroscope for Industrial Application.

Middle and high grade Fiber-Optic Gyroscopes (FOG) have been developed aiming for industrial applications such as Auto-guided-vehicle, Angular rate stabilizer etc. Those FOGs are based on the minimum reciprocal configuration with single mode fiber coil which reduces the production cost. This paper describes the low cost configuration of FOG and its applications.

A reciprocal-compensated fiber-optic electric current sensor

A novel reciprocal-compensated structure is proposed and demonstrated for intensity-modulated intrinsic fiber-optic current sensors. Both the component losses and birefringence influences can be partly compensated using this configuration, and the sensor is sensitive only to nonreciprocal Faraday rotation. The dependence of the signal on circular birefringence drift can be reduced by a factor better than 10 for low birefringence fibers. The property of total reciprocity reduces the sensitivity of the current sensor to temperature changes and vibrations. The experimental results agree well with the theoretical predictions for the sensor, fabricated using a coil of low birefringence single-mode fiber. >

Annealing of linear birefringence in single-mode fiber coils: application to optical fiber current sensors

Annealing procedures that greatly reduce linear birefringence in single-mode fiber coils are described. These procedures have been successfully applied to coils ranging from 5 mm to 10 cm in diameter and up to 200 or more turns. They involve temperature cycles that last 3-4 days and reach maximum temperatures of about 850 degrees C. The residual birefringence and induced loss, are minimized by proper selection of fiber. The primary application of these coils is optical fiber current sensors, where they yield small sensors that are more stable than those achieved by other techniques. A current sensor with a temperature stability of +8.4*10/sup -5//K over the range from -75 to +145 degrees C has been demonstrated. This is approximately 20% greater than the temperature dependence of the Verdet constant. Packaging degrades the stability, but a packaged sensor coil with a temperature stability of about +1.6+10/sup -4//K over the range from -20 to +120 degrees C has also been demonstrated. >