Polarization Eigenmodes Research Articles

Turning four-wave mixing on and off in elliptically birefringent fibers via narrow frequency detuning

Controlling four-wave mixing (FWM) is vital for several applications, including fiber optical communication, optical signal processing, optical amplification, and frequency generation. This paper presents a novel, to our knowledge, approach to control unidirectional FWM in elliptically birefringent fibers. By leveraging the frequency-dependent polarization eigenmodes of these fibers and detuning the optical frequency of one of the pump fields by a few megahertz, we can turn the FWM interaction on and off, thus controlling the generation of signal and idler fields. Moreover, this approach allows us to turn off the FWM interaction at any desired frequency, enabling all-optical switching and narrowband filtering applications.

Distributed and polarimetric pressure sensitivity in spun highly birefringent optical fibers.

We examine experimentally the influence of the fiber inelastic twist on polarimetric sensitivity to hydrostatic pressure and pressure sensitivity in a Rayleigh-scattering-based optical frequency-domain reflectometer (OFDR) for highly birefringent side-hole fibers. The fibers were drawn from the same preform with different spin pitches varying from 5 mm to 200 mm. We also demonstrate that the sensitivities of spun fiber can be estimated analytically based on its spin pitch, measured birefringence, and the sensitivity of the corresponding non-twisted fiber, showing good agreement with the experimental results. We proved that polarimetric sensitivity to pressure decreases with the shorter spin pitches, while distributed pressure sensitivity decreases for the one polarization eigenmode and increases for the second polarization eigenmode. Therefore, the spun-fibers can operate well as the polarimetric sensors of other physical parameters inducing circular birefringence even under varying pressure. Moreover, they can be used to obtain the desired difference between sensitivities for both polarization eigenmodes.

Tunable birefringence and elliptical polarization eigenmodes in a biplate of two quarter-wave plates.

Birefringence of elliptical polarization eigenmodes can be conceptualized as a composite system comprising two distinct media: one with linear polarization eigenmodes and the other with circular polarization eigenmodes. However, the practical realization of such a system often involves the combination of two birefringent quarter-wave plates (QWPs). In this study, our objective is to characterize the variable retardation and variable elliptical polarization eigenmodes exhibited by a biplate consisting of two quarter-wave plates. Additionally, we aim to analyze the geometric properties of the transformation of one state of polarization on the Poincaré sphere, employing the emerging state's curve. This curve corresponds to the intersection between the Poincaré sphere and a cone. The outcomes of our study are presented as a function of the angle between the fast axes of the two QWPs. The findings have the potential to contribute to the configuration of q-plates and facilitate the development of quantum communication protocols.

Linear polarization emission of Yb:YAG laser via polarization mode frequency locking

Direct linear polarization emission from a diode-pumped Yb:YAG laser is realized by changing the intracavity loss anisotropy which is controlled by finely adjusting the resonator. A theoretical model describing the relationship between loss and phase anisotropy on the frequency difference of polarization eigenmode has been established. The frequency difference of the polarization eigenmodes is investigated by recording the beat-note with a radio-frequency spectrum analyzer. By slightly tilting the output coupler, the beat-note frequency varied with the polarization state of the Yb:YAG laser. When the beat-note frequency disappeared, the laser was highly linearly polarized. The analysis of the beam profile of the linearly polarized output shows that the output originated from the coherent combination between two orthogonal polarization eigenmodes. The experimental results are in good agreement with the calculated results. Our research results confirm that the linearly polarized output in the isotropic laser can be realized by polarization eigenmode frequency locking.

Nd:YAG linearly polarized laser based on polarization eigenmodes

Nd:YAG linearly polarized laser based on polarization eigenmodes

Temperature-independent multi-parameter sensor based on polarization maintaining fiber Bragg grating

Dynamic multi-parameter detection is of great significance in predicting fatigue damage to structures such as tunnels, bridges, and pipelines. Developing a high-sensitivity, environmentally friendly, low-cost, and easy-to-operate multi-parameter dynamic detection technology has always been the goal of the industry. The polarization-maintaining fiber Bragg grating (PM-FBG) has a special grating structure composed of fiber Bragg grating (FBG) directly written into high birefringence and polarization-maintaining fiber, and it supports two distinct polarization eigenmodes with two effective refractive indices. The PM-FBG couples the light beams polarized along the two principal axes corresponding to slow axis and fast axis at two different Bragg wavelengths. The two peaks of PM-FBG have different responses to external changes, which may be used to solve the cross-sensitivity problem of FBG sensor and realize the simultaneous multi-parameter measurement of the temperature, longitudinal strain, transverse strain, or twist. In order to solve the problems of complex structure and principle and high production cost of FBG-based multi-parameter sensors, a novel multi-parameter fiber-optic sensor with high sensitivity and temperature independence is designed based on PM-FBG in this work. The PM-FBG sensor proposed can simultaneously measure the changes of displacement and twist in two vertical directions at a certain point and has the function of temperature self-compensation. The external structure of the sensor is fabricated by using three-dimensional printing technology through the fused deposition method and the raw material for creating different components through using polylactic acid. Experimental results show that the fast axis and slow axis of the sensor have different temperature responses, with linear sensitivities of 11.4 pm/℃ and 10.6 pm/℃, respectively, and the temperature compensation coefficient and average torsional sensitivity of the PM-FBG sensor are 0.8 pm/℃ and 0.20 dB/(°), respectively. The fast axis and slow axis of the PM-FBG sensor have the same response to displacement, with a sensitivity of 31.5 pm/mm and an adjustable range of 0–20 mm. The sensitivity to displacement, torsion, and temperature sensitivities of the sensor are all superior over those of commercial FBG sensors. By changing the temperature field around the sensor, its displacement- and torsion-sensing performances are not affected, thereby realizing the temperature self-compensation. Consequently, the proposed sensor has potential applications in the multi-parameter dynamic detection due to its simple structure, high sensitivity, good mechanical strength, and low cost.

Polarization and longitudinal modes of Möbius fiber ring lasers

Möbius optical cavities have attracted great interest for their unique topological properties. Here, the polarization and longitudinal modes of two types of Möbius fiber ring lasers are investigated. A theoretical model is established with Jones matrix to solve the polarization eigenmodes and longitudinal modes of a twisted polarization-maintaining fiber ring cavity. It is found that twisting the fiber axis causes polarization hybridization and a geometry-dependent phase, which induces a frequency shift to the longitudinal modes. The Möbius cases (180° and 90° splicing) are analyzed in detail, in which the 90° case leads to peculiar polarization and longitudinal mode properties. We believe the presented fiber ring laser provides a convenient platform to study lasers with a Möbius structure, and could enable further fiber laser applications.

Sub-megahertz spectral dip in a resonator-free twisted gain medium

Ultra-narrow optical spectral features resulting from highly dispersive light–matter interactions are essential for a broad range of applications such as spectroscopy, slow-light and high-precision sensing. Features approaching sub-megahertz or, equivalently, Q-factors up to one billion and beyond, are challenging to obtain in solid-state systems, ultimately limited by loss. We present a novel approach to achieve tunable sub-megahertz spectral features at room temperature without resonators. We exploit gain-enhanced polarization pulling in a twisted birefringent medium where polarization eigenmodes are frequency-dependent. Using Brillouin gain in a commercial spun fibre, we experimentally achieve a 0.72 MHz spectral dip, the narrowest backward Brillouin scattering feature ever reported. Further optimization can potentially reduce the linewidth to <0.1 MHz. Our approach is simple and broadly applicable, offering on-demand tunability and high sensitivity, with a wide range of applications such as microwave photonic filters, slow and fast light, and optical sensing. Tunable sub-megahertz spectral features are demonstrated without resonators. The approach, which exploits gain-enhanced polarization pulling in a twisted birefringent medium, may be useful in applications such as microwave photonic filters, slow and fast light, and optical sensing.

Fiber optic temperature sensor utilizing thin PMF based Sagnac loop

A fiber optic temperature sensor utilizing a thin polarization maintaining fiber (PMF) based Sagnac loop is proposed and experimentally demonstrated. A Sagnac loop consisting of a thin PMF has a large fringe visibility of up to 46.16 dB. Except polarization eigen modes, cladding modes are excited owing to fiber mismatch to enhance the temperature sensitivity. The resonant dips of the wavelength spectrum are utilized to investigate the temperature characteristics. Experimental results show that the excited cladding modes in the thin PMF can improve the sensitivity. The temperature sensitivity of the sensor is enhanced by exciting more cladding modes, and it reaches as high as -1.55 nm/°C and the corresponding linearity is 99.96%. The sensor is anticipated to has promising prospects in temperature measurement for harsh environment.

Simple method for the characterization of birefringence of single-mode optical fibers

Over the past few decades, various laboratories have worked on non-destructive methods for the evaluation of residual birefringence of single-mode optical fibers. Among them, polarimetric methods allowing the measurement of polarization eigenmodes represent the best option when it is necessary either to understand or to control the evolution of the state of polarization of light along the fiber. In this work, we present a polarimetric technique based on the use of Mueller calculus and the Poincaré sphere. This is a simple, precise, and non-destructive method allowing the measurement of the azimuth and ellipticity angles of the polarization eigenmode, as well as the total retardation angle modulus-π.

Linear Transformation of Polarization Modes in Coiled Optical Spun Fibers. III. Approximate Analytic Presentation

We have obtained approximate analytical dependences of the integrated values of effective elliptic birefringence of eigenpolarization modes on the length of coiled spun optical fibers by using approximations of numerical simulation. The dependence of the integrated elliptic birefringence of the polarization eigenmodes on the length of these optical fibers very quickly reaches its limiting value. This dependence also has a complex periodic structure including two substantially different spatial periods. The shape of the considered dependences is determined by the lengths of the polarization beats of the initial linear birefringence of the spun fiber, unperturbed by coiling, and circular birefringence due to torsion of the spun fiber.

Exact Solutions for the Local Parameters of Polarization Modes in Coiled Optical Spun Fibers with Strong Unperturbed Linear Birefringence. I. Nonresonant Linear Transformation

The propagation of monochromatic radiation in coiled spun optical fibers is considered. The local parameters of the elliptical polarization eigenmodes, elliptic birefringence, and the ellipticity angle are the sum of the constant and variable components, with the latter being measured almost according to the harmonic law depending on the length of the fiber. The magnitudes of the constant components are significantly higher than the amplitudes of the variable components. The dependence of the local azimuth of the major axis of the ellipse of the polarization eigenmodes increases almost linearly.

Passive stabilization scheme for polarization mode interferometers using a polarization beam splitter

A passive stabilization scheme for polarization mode interferometers (PMIs) using a polarization beam splitter (PBS) is proposed and experimentally demonstrated. Polarization eigenmodes in a highly birefringent fiber are modulated by external signals. Quadrature signals utilized in demodulation algorithm are acquired from the square roots of the photo-voltages, which are detected from the transmission lights of the PBS. Experimental results show that the scheme has a large dynamic range (100.8 dB), good linearity (99.937%) and is capable of high sensitivity (10−7 rad detectability above 150 Hz). Furthermore, it is immune to intensity noise of lasers so that the system instability and complexity are obviously reduced.

Helmholtz decomposition analysis of electron energy loss: differentiating resonances on polarization and radiation eigenmodes

Helmholtz decomposition is a powerful mathematical tool for investigation and analysis of vector fields, particularly in electrodynamic systems. In this paper, we apply it to electron energy loss spectroscopy of magnetically inactive structures to get insight into field composition of energy losses. The obtained results show that losses are incurred through two pathways—excitation of transverse/longitudinal fields by solenoidal/conservative currents. Separation of these processes gives us important information about the fields and the type of eigenmodes (polarization or radiation) being in resonance with the electron beam. Capabilities of such analysis are demonstrated in the study case of metal nanofilms and nanodiscs, where we perform differentiation of the resonances that have occurred on plasmons (polarization eigenmodes) and plasmon polaritons (radiation eigenmodes).

Real-time acceleration sensing with an arctan algorithm based on a modal interferometer.

This study proposes a fiber-optic accelerometer for low-frequency vibration signal detection. The phase velocities of the polarization eigenmodes are affected differently by signals, leading to a polarization rotation of the transmitted lights. The orthogonal square roots of the photovoltages are utilized for an arctan demodulation scheme. Experimental results show that it provides a flat response of 75.04 mrad/g, an average resolution of 13.44 μg/√Hz, and a dynamic range of 111.62 dB below 180 Hz. The environmental instability and sensor complexity are significantly reduced, so that the sensor can be further used in the warning of coal and gas outburst.

Passive optical gyroscope with double homodyne readout.

We present a passive, resonant, single-frequency gyroscope design that utilizes polarization modes of an optical cavity to readout rotation and generate a laser frequency discriminant. This design is notable for its simplicity, requiring no modulation electronics or frequency counters. We extract both the cavity length signal and rotation signal from two copropagating beams with orthogonal polarizations. This readout scheme can be applied to an optical cavity whose polarization eigenmodes experience different phase shifts such as fiber rings, whispering gallery mode resonators, and folded free-space cavities. We apply this technique to the passive free-space gyroscope and achieve a bias stability of 0.03°/h and a sensitivity of 5×10-8 rad/s/Hz above 1Hz, with a cavity of area 400 cm2 and finesse of 104.

Точные решения для локальных параметров поляризационных мод в намотанных на катушку spun-световодах с сильным невозмущенным линейным двулучепреломлением. I. Нерезонансная линейная трансформация

The propagation of monochromatic radiation is considered in coiled spun-light guides. It is shown that the local parameters of the elliptic polarization modes, the elliptical birefringence and the angle of ellipticity, are the sum of the constant and variable components. The latter varying in accordance with the harmonic law of the fiber length and the magnitudes of the constant components are substantially larger than the amplitudes of the variable components. It is also shown that the dependence of the local azimuth of the ellipse major axis of eigenpolarization modes increases almost linearly.

Measurement of birefringence and ellipticity of polarization eigenmodes in spun highly birefringent fibers using spectral interferometry and lateral point-force method

We show that the spectral interferometry method and the lateral point-force method used up to now to measure spectral dependence of the group and the phase modal birefringence in highly birefringent fibers with linearly polarized eigenmodes, can be after some modifications extended for the class of spun highly birefringent fibers with elliptically polarized modes. By combining the two methods, it is possible to determine spectral dependence of the group and phase elliptical birefringence in spun highly birefringent fibers. Moreover, if the fiber spin pitch is independently measured, the spectral dependence of ellipticity angle of polarization eigenmodes as well as the built-in linear phase and group birefringence, can be also obtained using the analytical relations between the parameters of spun and non-spun fibers. We demonstrate the effectiveness of the proposed approach in spectral measurements (700-1600 nm) of the spun side-hole and microstructured highly birefringent fibers with different birefringence dispersion and spin pitches ranging from 4.1 to 200 mm.

Dual-wavelength fiber Fabry-Perot cavities with engineered birefringence.

We present a method to engineer the frequency splitting of polarization eigenmodes in fiber Fabry-Perot (FFP) cavities. Using specific patterns of multiple CO2 laser pulses, we machine paraboloidal micromirrors with controlled elliptical shape in a large range of radii of curvature. This method is versatile and can be used to produce cavities with maximized or near-zero polarization mode splitting. In addition, we realize dual-wavelength FFP cavities with finesse exceeding 40 000 at 780 nm and at 1559 nm in the telecom range. We provide direct evidence that the birefringent frequency splitting in FFP cavities is governed only by the geometrical shape of the mirrors, and that the astigmatism of the cavity modes needs to be taken into account for specific cavities.

Measuring the quantum geometric tensor in two-dimensional photonic and exciton-polariton systems

We first consider a generic two-band model which can be mapped to a pseudospin on a Bloch sphere. We establish the link between the pseudospin orientation and the components of the quantum geometric tensor (QGT): the metric tensor and the Berry curvature. We show how the k-dependent pseudospin orientation can be measured in photonic systems with radiative modes. We consider the specific example: a 2D planar cavity with two polarization eigenmodes, where the pseudospin measurement can be performed via polarization-resolved photoluminescence. We also consider the s-band of a staggered honeycomb lattice for polarization-degenerate modes (scalar photons). The sublattice pseudospin can be measured by performing spatially resolved interferometric measurements. In the second part, we consider a more complicated four-band model, which can be mapped to two entangled pseudospins. We show how the QGT components can be obtained by measuring six angles. The specific four-band system we considered is the s-band of a honeycomb lattice for polarized (spinor) photons. We show that all six angles can indeed be measured in this system. We simulate realistic experimental situations in all cases. We find the photon eigenstates by solving Schrodinger equation including pumping and finite lifetime, and then simulate the measurement of the relevant angles to finally extract realistic mappings of the k-dependent QGT components.