Birefringent Single-mode Fiber Research Articles

Depolarization compensation in spun highly birefringent fiber with built-in half waveplate

Nowadays, the spun highly birefringent single-mode optical fiber is increasingly being considered for current-sensing applications. However, when a broadband polarized light is launched into the fiber, apparent depolarization will occur with its propagation. This leads to a decrease in the polarization sensibility. In this paper, we propose a kind of method to compensate for the depolarization in spun highly birefringent fibers. An all-fiber half waveplate made of the helically wound spun highly birefringent fiber is placed at the center of the whole fiber. To obtain this half waveplate, the torsion of the helix should be equal to the inherent polarization rotation of the spun highly birefringent fiber. The advantages of the proposed method are simple, effective and without breaking the fiber. Simulations and experiments have demonstrated the excellent performance of the proposed method.

Figure of merit for optimizing nonlinear transmission in fiber ring lasers

Passive mode-locking based on nonlinear polarization evolution as a saturable absorber is a powerful technique which has been performed in many optical configurations. The saturable absorption effect results from the intensity discrimination due to the interplay of the optical Kerr nonlinearity of the fiber, wave plates, and polarizers. This paper highlights the nonlinear transmission of a single-mode birefringent fiber exhibiting an optical Kerr nonlinearity placed between two polarizers and a set of several phase plates. Optical Kerr effect involves self-phase and cross-phase modulation terms and eventually four-wave mixing term. Different optical configurations are investigated involving various number of phase plates at both fiber ends. A figure of merit is defined which provides a universal way of comparison between different optical configurations. It demonstrates that the nonlinear transmission has a minimal sensitivity to both the exact optical configuration and the exact considered nonlinear terms. Consequently, the simplest model based on a single-mode birefringent fiber, exhibiting self-phase and cross-phase modulation, placed between two half-wave plates can be used without loss of generality.

Heralded spectroscopy with a fiber photon-pair source

The correlations between photons generated by nonlinear optical processes offer advantages for many quantum technology applications, including spectroscopy, imaging, and metrology. Here, we use spontaneous four-wave mixing in a birefringent single-mode fiber pumped by a tunable pulsed laser as a broadly tunable source of phase-matched non-degenerate photon pairs for spectroscopy. The pairs are tunable such that the idler beam measures the transmittance spectrum of a sample in the near infrared, while the visible signal beam independently reports correlation information. By the time-resolved counting of both signal and idler photons, we use photon-number correlations to remove uncorrelated noise from the probe beam. Here, we have used heralded spectroscopy to measure the absorption spectrum of gallium arsenide near its band edge, despite the idler photon spectrum being dominated by a large background from spontaneous Raman scattering.

CURRENT STATE OF METHODS AND MEANS OF REGISTRATION OF HIGH TEMPERATURES AND MECHANICAL STRESSES IN STRUCTURES

An analytical review of physically possible methods and available achievements in registering hydrostatic pressure or mechanical stresses using fiber optic fibers and sensors based on them based on published works that can be used in harsh environmental conditions is carried out. The results of the review show that fully distributed or quasidistributed fiber-optic systems for recording hydrostatic pressure or mechanical stress can be implemented on the following physical principles and apparatus with measures to compensate or suppress the influence of temperature: polarizing sensors on birefringent single- mode light guides and OTDR equipment; micro-flexible sensors with OTDR equipment on conventional multimode fibers; measuring systems on fiber Bragg gratings; on discrete sensors, in particular, on sealed fiber Fabry–Perot interferometers; Brillouin distributed sensors on single-mode fibers that are not sensitive to temperature changes. It is shown that single-mode birefringent fibers with hollow holes in the shell and fiber Bragg gratings written in the core have a good linear sensitivity to hydrostatic pressure and a weak dependence on temperature. Lattices in phosphorous-containing single-mode light guides have increased high-temperature properties up to ~500 C and higher. A number of discrete fiber sensors’ structures and pressure recorders are investigated. Various structures of sensitive elements of pressure sensors on sealed fiber Fabry–Perot interferometers and fiber gratings in spherical and cylindrical small-sized cases are investigated. Sensors based on Fabry–Perot fiber interferometers soldered into a glass capillary and protected from water by external high-temperature hermetic coatings showed good linearity in the pressure range of 0…540 ATM at temperatures up to ~200 C. The sensors are efficient at temperatures up to 600 °C and are promising for use in severe and special external conditions. The possibility of compensating the temperature sensitivity by selecting external coatings is shown. Pressure sensors were tested on local areas with microbends and it was shown that they can measure pressures up to ~24 МPа at temperatures up to ~450 C, but to compensate for the dependence of the readings on temperature, it must be measured by an independent sensor. The possibility of independent and simultaneous measurement of hydrostatic pressure and temperature along a single fiber using spontaneous Brillouin scattering is shown. Pressure is measured by the frequency shift of Brillouin scattering, and temperature by its intensity. The operation of the Brillouin recorder in the pressure range 0…34 MРа is demonstrated. The pressure resolution was ~0,2 МРа. New methods are proposed for detecting Brillouin scattering – a heterodyne signal with a high signal-to-noise ratio and based on frequency modulation of a semiconductor single-frequency distributed feedback laser. The measurement range has been increased by more than 10 km and the coordinate resolution has been increased. The Brillouin scattering method is promising for creating distributed systems for measuring hydrostatic pressure or mechanical stress for severe physical conditions, including temperatures of ≥3000 C.

Period doubling eigenstates in a fiber laser mode-locked by nonlinear polarization rotation.

Due to the weak birefringence of single mode fibers, solitons generated in fiber lasers are indeed vector pulses and exhibit periodic parameter change including polarization evolution even when there is a polarizer inside the cavity. Period doubling eigenstates of solitons generated in a fiber laser mode-locked by the nonlinear polarization rotation, i.e., period doubling of polarization components of the soliton, are numerically explored in detail. We found that, apart from the synchronous evolution between the two polarization components, there exists asynchronous development depending on the detailed operation conditions. In addition, period doubling of one polarization component together with period-one of another polarization component can be achieved. When the period tripling window is obtained, much complexed dynamics on the two polarization components could be observed.

Polarizing Grating-Based Ultrasensitive All-Fiber Angular Displacement Sensor

We have proposed and experimentally demonstrated an ultrasensitive all-fiber angular displacement sensor based on in-fiber polarizing gratings and half waveplate (IFHWP), in which the polarizing gratings are based on 45°-tilted fiber gratings (45°-TFGs) and the IFHWP is constructed by bending-induced birefringence in single mode fiber (SMF). Compared with the existing angular displacement sensors, the structure of our proposed sensor is more desirable to bring the prominent advantages of all-fiber structure, low transmission loss and high sensitivity. The experimental results show that the proposed angular displacement sensor has a sensitivity and a resolution up to 20.477 dB/rad and $2.8\times 10^{-3\circ }$ , respectively, within a large measurement range of about 25°. In addition, such sensor also has very low temperature sensitivity around $2.1\times 10^{-4}$ dB/°C.

Microwave photonic notch filter based on polarisation multiplexing and cross gain modulation in a semiconductor optical amplifier

A coherent interference-free tunable microwave photonic notch filter with a pair of negative and positive coefficients generated by employing polarisation multiplexing and cross gain modulation in a semiconductor optical amplifier is proposed and demonstrated through simulation results. The negative and positive coefficients of the notch filter are realised through two orthogonal polarisation states of a single continuous wave laser diode. The free spectral range of microwave photonic filter is tuned by varying the differential group delay of a birefringent single-mode fibre. The proposed filter shows good tunability, easy implementation and is cost-effective.

Lyot Filter With Femtosecond Laser-Induced High Birefringence Single-Mode Fiber for Torsion, Transverse Load and Temperature Sensing

We propose and experimentally demonstrate an all-fiber Lyot filter with femtosecond laser-induced high birefringence single-mode fiber (SMF) for torsion, transverse load and temperature sensing. With the femtosecond-laser processing technique, the SMF with the birefringence of 2.81 × 10 -4 is manufactured by directly writing a straight cladding stress track parallel with fiber core and employed to form an all-fiber Lyot filter for sensing application. The sensitivities of the all-fiber Lyot filter with respect to torsion, transverse load and temperature are found to be -4265.669 nm/(rad/mm), -321.004 nm/(N/mm), and 0.271 nm/°C, respectively. The experimental results are powerful proof of the excellent performance of the femtosecond laser-induced high birefringence SMF based all-fiber Lyot filter for sensing application, which not only adds significantly new and important results to the fields of optical sensing, but also develops the application fields of femtosecond-laser processing technique and all-fiber Lyot filter.

All single-mode fiber-based polarization-sensitive spectral domain optical coherence tomography system

We reported an all single-mode fiber (SMF)-based polarization sensitive spectral domain optical coherence tomography (PS-SDOCT) system with single input polarization state (IPS). In our design, polarization state was modulated only by four polarization controllers (PC) and a polarization beam splitter. To extract the phase retardance and optical axis orientation of sample, the Mueller matrix of the fiber system and sample is transferred to a new retardar by employing PCs with the advantage that the effects of fiber birefringence of SMFs and SMF components are corrected. The contribution of the multi-backscattering in tissues to the orthogonal polarization interference signals is readily suppressed by subtracting the unpolarized component of the scattered light. To demonstrate the capabilities of our system, the crossing-sectional images were presented of phase retardance and optical axis orientation of several tissues. The experiment results showed that the imaging depth, the image contrast of tissues and signal-to-noise ratio have been further increased.

Design and numerical analysis of highly birefringent single mode fiber in THz regime

Abstract A novel kind of porous core microstructure optical fiber is proposed in this paper. In order to create flexibility of the fiber only ring air hole is used for the cladding region. Finite Element Method (FEM) based Comsol v4.2 software is used to investigate the guiding characteristics of the proposed fiber. The optimum design parameter shows an ultrahigh birefringence of 0.051, low effective material loss of 0.07 cm−1 and low bending loss of 1.13 × 10−13 dB/cm at 1.2 THz. Moreover, the proposed fiber offers very low dispersion of 1.2 ± 0.32 ps/THz/cm over a wide range of frequency from 1.1 THz to 1.9 THz. Other important guiding characteristics such as confinement loss, effective area and single mode propagation are also discussed in detail. This structure may be a good choice in different remarkable terahertz applications.

Acousto-optic tunable bandpass filter based on acoustic-flexural-wave-induced fiber birefringence.

An acousto-optic tunable bandpass filter was proposed and fabricated based on acoustic-flexural-wave-induced single-mode fiber birefringence via coupling the core mode to a single-cladding vector mode. In the experiment, the resonant wavelength and insertion loss could be electrically tuned with a span of nearly 100nm and a lowest insertion loss of -1.7 dB. The structure gains advantages of a large tuning range, fast speed, easy fabrication, low insertion loss, and zero frequency shift.

Highly sensitive torsion sensor with femtosecond laser-induced low birefringence single-mode fiber based Sagnac interferometer.

A highly sensitive optical fiber torsion sensor with femtosecond laser-induced low birefringence SMF-based Sagnac interferometer (SI) is proposed and experimentally demonstrated in this paper. A straight-line waveguide positioned horizontally with respect to the fiber core is inscribed by the femtosecond laser in the cladding of the SMF, which leads to the asymmetry stress distribution in the SMF, and then gives rise to the low birefringence in the SMF. Compared with most of the previous reported SI based torsion sensors, there is no splicing joint in the femtosecond laser-induced low birefringence SMF-based SI, which lowers the transmission loss and makes the SI based torsion sensor more robust simultaneously. The experiment result shows that the proposed torsion sensor exhibits a torsion sensitivity of up to 3.2562 nm/degree, with the high torsion resolution of 0.003 degree. In contrast, the temperature cross-sensitivity and strain cross-sensitivity of the proposed torsion sensor are low, to -0.000055 degree/°C and 0.000013 degree/με, respectively, thus overcoming the cross-sensitivity problem resulting from temperature and strain. Moreover, theoretical analysis are carried out to compare with the experimental results to demonstrate the feasibility and good consistency.

Polarization dependent Brillouin frequency shift fluctuation induced by low birefringence in single mode fiber.

The polarization dependent fluctuation of Brillouin frequency shift (BFS) of stimulated Brillouin scattering (SBS) in practical single mode fibers (SMFs) is reported. The phenomenon is actually caused by the interference of the low birefringence in SMF with the SBS spectral polarization spreading of the signal light. The performance of the polarization dependent BFS fluctuation is studied by simulation and confirmed with agreeable experimental results.

Polarization dynamics in twisted fiber amplifiers: a non-Hermitian nonlinear dimer model.

We study continuous-wave light propagation through a twisted birefringent single-mode fiber amplifier with saturable nonlinearity. The corresponding coupled-mode system is isomorphic to a non-Hermitian nonlinear dimer and gives rise to analytic polarization-mode dynamics. It provides an optical simulation of the semi-classical non-Hermitian Bose-Hubbard model and suggests its use for the design of polarization circulators and filters, as well as sources of polarized light.

Visualization of fiber Bragg gratings of type II induced by radiation of an ArF excimer laser in an anisotropic single-mode optical fiber with an elliptical stress cladding

results in visualization of fiber Bragg gratings of type II recorded in birefringent single-mode optical fibers with an elliptical stress cladding with a high concentration of germanium dioxide are shown. Periodic structures of the induced refractive index are inscribed by a single pulse of an excimer laser with a working- gas mixture of ArF using the phase mask. Fiber Bragg gratings into anisotropic optical fiber were investigated by optical and scanning-probe microscopes. It is shown that single-pulse recording by ArF excimer laser creates in the fiber, both inside and on the surface of the quartz cladding, periodic structures, the spatial period of which corresponds to the period of the phase mask, optimized for the +1/–1 diffraction order.

Harmful intrusion detection algorithm of optical fiber pre-warning system based on correlation of orthogonal polarization signals

At present, advanced researches of optical fiber intrusion measurement are based on the constant false alarm rate (CFAR) algorithm. Although these conventional methods overcome the interference of non-stationary random signals, there are still a large number of false alarms in practical applications. This is because there is no specific study on orthogonal polarization signals of false alarm and intrusion. In order to further reduce false alarms, we analyze the correlation of optical fiber signals using birefringence of single-mode fiber. This paper proposes the harmful intrusion detection algorithm based on the correlation of two orthogonal polarization signals. The proposed method uses correlation coefficient to distinguish false alarms and intrusions, which can decrease false alarms. Experiments on real data, which are collected from the practical environment, demonstrate that the difference in correlation is a robust feature. Furthermore, the results show that the proposed algorithm can reduce the false alarms and ensure the detection performance when it is used in optical fiber pre-warning system (OFPS).

Modulation instabilities in randomly birefringent two-mode optical fibers**Project supported by the Natural Science Foundation of Jiangsu Provincial Universities (Grant No. 14KJB140009), the National Natural Science Foundation of China (Grant No. 11447113), and the Startup Foundation for Introducing Talent of NUIST (Grant No. 2241131301064).

Modulation instabilities in the randomly birefringent two-mode optical fibers (RB-TMFs) are analyzed in detail by accounting the effects of the differential mode group delay (DMGD) and group velocity dispersion (GVD) ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers (RB-SMFs). New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD, no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by Pcr, which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power (Pcr), which increases (decreases) distinctly with the increment of DMGD (GVD ratio of the two modes) but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than Pcr, and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The MI analysis in this paper is verified by numerical simulation.

Nonplanar fiber-optic sensing head for the compensation of bending-induced birefringence in Faraday current sensors.

We demonstrate the compensation of bending-induced linear birefringence in single-mode fibers coiled in a nonplanar path by alternating orthogonal bending planes. This effect can be applied for the construction of birefringence-free fiber coils in Faraday sensor heads (e.g., in current sensors) to improve their sensitivity. Validation experiments are presented.

Curvature sensor based on a pressure-induced birefringence single mode fiber loop mirror

An optical fiber curvature sensor based on a pressure-induced birefringence singlemode fiber loop mirror is presented. The birefringer SMF is made by applying a transverse force against a short length of singlemode fiber. The length of the sensing element for the curvature sensing is about 150mm. The sensitivity of the curvature measurement experimentally is 0.0263m−1/pm. And the temperature effect of the proposed sensor is also analyzed. Comparing with the sensor of photonic crystal fiber, it is more convenient and simply.

Extended Mueller–Stokes description of polarization-mode transformation in linearly birefringent single-mode optical fibers

We derive a more general version of the commonly known quasi-monochromatic Mueller matrix of a linearly birefringent single-mode optical fiber. In the matrix, the complex degree of self-coherence of the illuminating field is replaced by the normalized cross-correlation of a pair of any jointly stationary light disturbances associated with the eigenpolarization modes, where both modulus and phase of the cross correlation are included. This allows one to write polychromatic Mueller-Stokes equations of multisection systems transmitting any uniformly polarized stationary field. A way for handling arbitrary phase birefringence dispersion is also suggested.