Optic axis determination accuracy for fiber-based polarization-sensitive optical coherence tomography

We present a generalized analysis of fiber-based polarization-sensitive optical coherence tomography with an emphasis on determination of sample optic axis orientation. The polarization properties of a fiber-based system can cause an overall rotation in a Poincaré sphere representation such that the plane of possible measured sample optic axes for linear birefringence and diattenuation no longer lies in the QU-plane. The optic axis orientation can be recovered as an angle on this rotated plane, subject to an offset and overall indeterminacy in sign such that only the magnitude, but not the direction, of a change in orientation can be determined. We discuss the accuracy of optic axis determination due to a fundamental limit on the accuracy with which a polarization state can be determined as a function of signal-to-noise ratio.     

拉曼效应对低双折射光纤偏振特性的影响

在低双折射光纤中,利用线偏振光满足的包含拉曼效应的非线性耦合模传输方程,通过引入斯托克斯参量,导出了斯托克斯参量所满足的耦合模传输方程.利用庞加莱球图示法,描述了拉曼增益效应作用下光波偏振态的演化,研究分析了拉曼效应对低双折射光纤中光波偏振态演化规律的影响.结果表明,当输入功率与运动常量满足一定关系时,拉曼增益效应改变了光波传输时其偏振态演化周期和偏振态的椭圆率.     

Polarization mode dispersion probability distribution for arbitrary distances

The probability distribution of the differential group delay (DGD) at any fiber length is determined by use of a physically reasonable model of the fiber birefringence. We show that if the fiber correlation length is of the same order as or larger than the beat length, the DGD distribution approaches a Maxwellian in roughly 30 fiber correlation lengths, corresponding to a couple of kilometers in realistic cases. We also find that the probability distribution function of the polarization dispersion vector at the output of the fiber depends on the angle between it and the local birefringence vector on the Poincaré sphere, showing that the DGD remains correlated with the orientation of the local birefringence axes over arbitrarily long distances.     

Tuning the polarization states of optical spots at the nanoscale on the Poincaré sphere using a plasmonic nanoantenna

It is shown that the polarization states of optical spots at the nanoscale can be manipulated to various points on the Poincaré sphere using a plasmonic nanoantenna. Linearly, circularly, and elliptically polarized near-field optical spots at the nanoscale are achieved with various polarization states on the Poincaré sphere using a plasmonic nanoantenna. A novel plasmonic nanoantenna is illuminated with diffraction-limited linearly polarized light. It is demonstrated that the plasmonic resonances of perpendicular and longitudinal components of the nanoantenna and the angle of incident polarization can be tuned to obtain optical spots beyond the diffraction limit with a desired polarization and handedness.     

Polarization orthogonalization properties of optical systems

We investigate the conditions under which an optical system (or device) may transform polarization states at its input into orthogonal states at its output. We find that such polarization orthogonalization is possible if the Jones matrix of the optical system satisfies a specific inequality. One, two, or an infinite number of input polarization states may be orthogonalized. In the latter case, the locus of input states is a circle in the complex plane (and on the Poincaré sphere) of polarization. Several examples are given for illustration.     

Mimicking optical activity for generating radially polarized light

We propose a new scheme for generating radially polarized light by mimicking optical activity using linear birefringence. It involves a birefringent spirally varying retarder sandwiched between two orthogonally oriented quarter-wave plates. Using Poincaré sphere representation, we show that the polarization transformation of such a scheme is equivalent to that of a spirally varying optical activity and is capable of generating radially polarized light. We demonstrate the proof-of-concept using y-cut crystalline quartz.     

Highly repeatable all-solid-state polarization-state generator

We report an all solid-state polarization-state generator that uses magneto-optic polarization rotators. The device can generate either five or six distinctive polarization states uniformly across a Poincaré sphere with repeatability better than 0.1 degrees. It is ideal for polarization analysis, swept-wavelength measurement, and monitoring of polarization-related parameters and signal-to-noise ratios of optical networks.     

Hamilton’s theory of turns and a new geometrical representation for polarization optics

Hamilton’s theory of turns for the group SU(2) is exploited to develop a new geometrical representation for polarization optics. While pure polarization states are represented by points on the Poincaré sphere, linear intensity preserving optical systems are represented by great circle arcs on another sphere. Composition of systems, and their action on polarization states, are both reduced to geometrical operations. Several synthesis problems, especially in relation to the Pancharatnam-Berry-Aharonov-Anandan geometrical phase, are clarified with the new representation. The general relation between the geometrical phase, and the solid angle on the Poincaré sphere, is established.     

Scattered light measurement of the circular birefringence in a twisted single mode fiber

This paper reports the measurements of the twist induced circular birefringence in a single mode fiber by direct observation of the scattered light. The results agree well with earlier theoretical prediction. In addition, an analysis of the evolution of the polarization in a linearly birefringent twisted medium (applicable to weakly guiding single mode (fibers) is given using the coupled mode theory and Poincaré sphere representation.     

Polarization locked vector solitons and axis instability in optical fiber

We experimentally observe polarization-locked vector solitons in optical fiber. Polarization locked-vector solitons use nonlinearity to preserve their polarization state despite the presence of birefringence. To achieve conditions where the delicate balance between nonlinearity and birefringence can survive, we studied the polarization evolution of the pulses circulating in a laser constructed entirely of optical fiber. We observe two distinct states with fixed polarization. This first state occurs for very small values birefringence and is elliptically polarized. We measure the relative phase between orthogonal components along the two principal axes to be +/-pi/2. The relative amplitude varies linearly with the magnitude of the birefringence. This state is a polarization locked vector soliton. The second, linearly polarized, state occurs for larger values of birefringence. The second state is due to the fast axis instability. We provide complete characterization of these states, and present a physical explanation of both of these states and the stability of the polarization locked vector solitons. (c) 2000 American Institute of Physics.     

基于Metasurface的柱矢量光束的产生

本文提出了一种基于Metasurface产生任意柱矢量光束的方法.采用的Metasurface是在熔融石英上刻蚀空间变化的非周期光栅构成.非周期光栅会形成空变的有效双折射,从而对光场的偏振态空间分布进行调制.通过琼斯矩阵的方法分析得出这样的Metasurface可以将入射线偏振光转换为柱矢量光束,并且只需要改变入射线偏振光的偏振方向即可获得高阶庞加莱球赤道上任意一点的柱矢量光束.最后,用Metasurface搭建了一套简单、高效的柱矢量光束产生系统,实验结果与理论分析一致.     

Poincaré-sphere equivalent for light beams containing orbital angular momentum

The polarization state of a light beam is related to its spin angular momentum and can be represented on the Poincaré sphere. We propose a sphere for light beams in analogous orbital angular momentum states. Using the Poincaré-sphere equivalent, we interpret the rotational frequency shift for light beams with orbital angular momentum [Phys. Rev. Lett. 80, 3217 (1998)] as a dynamically evolving geometric phase.     

Use of the poincare sphere in polarization optics and classical and quantum mechanics. Review

The method of the Poincaré sphere, which was proposed by Henri Poincaré in 1891–1892, is a convenient approach to represent polarized light. This method is graphical: each point on the sphere corresponds to a certain polarization state. Apart from the obvious representation of polarized light, the method of the Poincaré sphere permits efficient solution of problems that result from the use of a set of phase plates or a combination of phase plates and ideally homogeneous polarizers. Recently, to calculate the geometric phase (which is often called the Berry phase) in polarization optics and quantum and classical mechanics, the method of the Poincaré sphere has drawn much attention, since it allows us to carry out these calculations very efficiently and intuitively using the solid angle resting, on a closed curve on the Poincaré sphere that corresponds to the change in the state of light polarization or in the state of spin of an elementary particle or its orientation in space from the viewpoint of systems in classical mechanics. The review considers papers on the above problems. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 265–307, March. 1997.     

Depolarization by aerosols: Entropy of the Amsterdam light scattering database

In this paper we apply an entropy analysis to measured scattering matrices from the Amsterdam light scattering database. We select examples of mineral aerosols from the database and use them to demonstrate differences in polarization behavior between the particle clouds using a new coherency matrix formulation. These differences are further investigated by analyzing the polarized component of the matrices via two new eigenvector parameters, which can be mapped conveniently onto the surface of a sphere, analogous to the Poincaré sphere used for wave states. We conclude by considering the potential for discriminating different aerosols on the basis of their entropy/eigenvector signatures by solving the contrast optimization problem for clouds with different scattering matrices by using a novel generalized coherency eigenvalue formulation.     

Thomas rotation and polarized light: A non-abelian geometric phase in optics

We describe anon-abelian Berry phase in polarization optics, suggested by an analogy due to Nityananda between boosts in special relativity and the effect of elliptic dichroism on polarized light. The analogy permits a simple optical realization of the non-abelian gauge field describing Thomas rotation. We also show how Thomas rotation can be understood geometrically on the Poincaré sphere in terms of the Pancharatnam phase.     

Universal method for the synthesis of arbitrary polarization states radiated by a nanoantenna

Optical nanoantennas efficiently convert confined optical energy into free‐space radiation. The polarization of the emitted radiation depends mainly on nanoantenna shape, so it becomes extremely difficult to manipulate it unless the nanostructure is physically altered. Here, a simple way is demonstrated to synthetize the polarization of the radiation emitted by a single nanoantenna so that every point on the Poincaré sphere becomes attainable. The nanoantenna consists of a single scatterer created on a dielectric waveguide and fed from its both sides so that the polarization of the emitted optical radiation is controlled by the amplitude and phase of the feeding signals. The nanoantenna is created on a silicon chip using standard top‐down nanofabrication tools, but the method is universal and can be applied to other materials, wavelengths and technologies. This work will open the way towards the synthesis and control of arbitrary polarization states in nano‐optics.     

Two-dimensional depth-resolved Mueller matrix of biological tissue measured with double-beam polarization-sensitive optical coherence tomography

A double-beam polarization-sensitive system based on optical coherence tomography was built to measure the Mueller matrix of scattering biological tissue with high spatial resolution. The Jones matrix of a sample can be determined with a single scan and subsequently converted into an equivalent nondepolarizing Mueller matrix. As a result, the system can be used to measure the Mueller matrix of an unstable sample, such as soft tissue. The polarization parameters of a porcine tendon, including magnitude and orientation of birefringence and diattenuation, were extracted by decomposition of the measured Mueller matrix.     

Influence of the order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex turbid media such as biological tissues

The influence of the multiplication order of the constituent basis matrices on the Mueller matrix decomposition-derived polarization parameters in complex tissue-like turbid media exhibiting simultaneous scattering and polarization effects are investigated. A polarization sensitive Monte Carlo (MC) simulation model was used to generate Mueller matrices from turbid media exhibiting simultaneous linear birefringence, optical activity and multiple scattering effects. Mueller matrix decomposition was performed with different selected multiplication orders of the constituent basis matrices, which were further analyzed to derive quantitative individual polarization medium properties. The results show that for turbid medium having weak diattenuation (differential attenuation of two orthogonal polarization states), the decomposition-derived polarization parameters are independent of the multiplication order. Importantly, the values for the extracted polarization parameters were found to be in excellent agreement with the controlled inputs, showing self-consistency in inverse decomposition analysis and successful decoupling of the individual polarization effects. These results were corroborated further by selected experimental results from phantoms having optical (scattering and polarization) properties similar to those used in the MC model. Results from tissue polarimetry confirm that the magnitude of diattenuation is generally lower compared to other polarization effects, so that the demonstrated self-consistency of the decomposition formalism with respect to the potential ambiguity of ordering of the constituent matrices should hold in biological applications.     

Fiber Bragg grating as an optical filter tuned by a magnetic field

We describe a novel tunable optical filter for use in optical-frequency-domain multiplexed communication systems. The shift in the Bragg condition of a fiber Bragg grating as a result of magnetically induced circular birefringence is calculated with coupled-mode theory on the basis of circular states of polarization, and the values obtained for silica and terbium-doped optical fibers are compared.