Engineering of cylindrical vector fields with a twisted nematic spatial light modulator

Generation of vectorial optical fields with complex spatial distribution in the cross section is of great interest in areas where exotic optical fields are desired, including particle manipulation, optical nanofabrication, beam shaping and optical imaging. In this work, a vectorial optical field generator capable of creating arbitrarily complex beam cross section is designed, built and tested. Based on two reflective phase-only liquid crystal spatial light modulators, this generator is capable of controlling all the parameters of the spatial distributions of an optical field, including the phase, amplitude and polarization (ellipticity and orientation) on a pixel-by-pixel basis. Various optical fields containing phase, amplitude and/or polarization modulations are successfully generated and tested using Stokes parameter measurement to demonstrate the capability and versatility of this optical field generator.

Vectorial optical fields: recent advances and future prospects

Compact vectorial optical field generator based on a 10-megapixel resolution liquid crystal spatial light modulator

We experimentally demonstrate a vectorial optical field generator (VOF-Gen) with an adaptive close loop control. The close loop control capability is illustrated with the calibration of polarization modulation of the system. To calibrate the polarization ratio modulation, we generate 45° linearly polarized beam and make it propagate through a linear analyzer whose transmission axis is orthogonal to the incident beam. For the retardation calibration, circularly polarized beam is employed and a circular polarization analyzer with the opposite chirality is placed in front of the CCD as the detector. In both cases, the close loop control automatically changes the value of the corresponding calibration parameters in the pre-set ranges to generate the phase patterns applied to the spatial light modulators and records the intensity distribution of the output beam by the CCD camera. The optimized calibration parameters are determined corresponding to the minimum total intensity in each case. Several typical kinds of vectorial optical beams are created with and without the obtained calibration parameters, and the full Stokes parameter measurements are carried out to quantitatively analyze the polarization distribution of the generated beams. The comparisons among these results clearly show that the obtained calibration parameters could remarkably improve the accuracy of the polarization modulation of the VOF-Gen, especially for generating elliptically polarized beam with large ellipticity, indicating the significance of the presented close loop in enhancing the performance of the VOF-Gen.

In this paper, we propose an optical comb filter based on polarization-diversified-loop (PDL) configuration that offers switching operation between dual transmission spectra with different channel spacings by controlling the state of polarization (SOP) of input light with orthogonal relation. As shown in Fig. 1(a), the PDL-based filter consists of a four-port polarization beam splitter, combination of three half-wave plates (HWPs), one Faraday rotator (FR), and two bow-tie polarization-maintaining fiber (PMF) segments with different lengths (L and 2L) and equal birefringence (B). By controlling an input polarizer located before port 1 of the PBS, ASE light is linearly polarized such as linear horizontal polarization (LHP) and linear vertical polarization (LVP) components which propagate along clockwise (CW) and counterclockwise (CCW) directions in the PDL loop, respectively [1]. Fig. 1(b) represents principal optical paths (CW and CCW paths) divided by orthogonal SOPs of input light. Generally, when PMF segments are utilized as birefringence elements, channel spacings (Δλ) of output transmission spectra are determined by the product of their effective length (L eff ) and birefringence expressed as the equation Δλ=λ2/B-L eff where λ is wavelength in vacuum. In the proposed filter, the effective length of the two PMF segments can be the sum of or difference between their two lengths according to their angular combination of the orientation angles of the three HWPs for orthogonal input SOPs. That is, by properly adjusting angle sets of the three HWPs, the proposed filter can create two sinusoidal transmittance functions with different channel spacings determined by LB and 3LB for orthogonal input SOPs of LHP and LVP, and vice versa. According to theoretical analysis, the resulting filter transmittance is the algebraic sum of two sub transmittances along the CW and CCW paths calculated by Jones matrix formulation, given by (1-a)t CW + at CCW where a is a splitting ratio of optical power coupled to x- and y-axes at the PBS and ranges from 0 to 1 for LHP and LVP input components, respectively. Fig. 1(c) shows the switching operation between dual transmission spectra with different channel spacings for orthogonal input signals at different angle set of three HWPs, measured in a wavelength range from 1548 nm to 1552 nm. In the upper figure of Fig. 1(c), two measured transmission spectra with channel spacings of ∼0.75 nm and ∼0.25 nm were obtained for LHP and LVP input SOPs, indicated as blue solid and red dotted lines, respectively. In a similar manner, two transmission spectra with channel spacings of ∼0.25 nm and ∼0.75 nm were achieved for LHP and LVP input SOPs, indicated as blue solid and red dotted lines in the lower figure of Fig. 1(c), respectively. Consequently, the fabricated filter could demonstrate the input polarization-controlled switching operation between two transmission spectra with different channel spacings of −0.25 nm and −0.75 nm without modifying the filter structure.

Polarisation rotators are used to set defined launch polarisation states in systems designed to measure the polarisation properties of optical fibre and optical fibre components. In order to predictably set polarisation states the properties of the control elements must be well known. This paper describes the calibration of a polarisation rotator based on three rotating optical elements: a linear polariser, a quarter wave plate and a half wave plate. The calibrated polarisation rotator was used to reliably set polarisation states.

Based on the Fraunhofer diffraction theory and the properties of dove prism, the coordinate relationships among the four spatial light modulator (SLM) sections in a vectorial optical field generator (VOF-Gen) are derived and experimentally verified. Taking the coordinate system of the first SLM section as reference, the coordinate displacements between the first SLM section and the subsequent ones are measured through employing the specially designed four-quadrant patterns with varying shifts of the corresponding cross point. Complex optical field could be accurately generated by combining the derived coordinate relationships and pre-compensation of the measured coordinate displacements. A typical complex optical field is generated and the experimental results demonstrate the validity of the proposed transverse alignment method for the VOF-Gen.

We describe a polarization-sensitive fiber optic based confocal microscope. Polarization maintaining single mode fibers are used to illuminate a specimen with linearly polarized light. The orientation of the incident linearly polarized light is continuously variable using a Se´narmont polarization rotator. A polarization-sensitive light detector enables the microscope to record the intensity and polarization orientation of the reflected light. The microscope can thus function as a conventional confocal microscope as well as detect rotations of the polarization orientation of the incident light by a birefringent specimen. Lateral scanning of the microscope focal volume is achieved by moving the fiber tip in a reciprocal layout. Confocal operation of the system is demonstrated both theoretically and experimentally. The theoretical and measured responses of the microscope to a dielectric mirror, glass slide, quarter wave plate, linear polarizer, and calcite crystal are considered. Images of a birefringent specimen are presented.

In this paper, a high-efficiency and broadband reflective linear polarization rotator based on anisotropic metamaterial is proposed, which is verified by simulation and experiment. Simulated results indicate that our design can achieve 90° polarization rotation from 5.7 to 10.3 GHz with the relative bandwidth of 57.5 %, which is agreement well with experiment. The further simulated results indicate that our design can achieve linear polarization conversion or rotation by 90° under oblique incident angles with large range for both transverse electric and transverse magnetic waves. Finally, the amplitude and phase of reflective coefficients with different polarization, and surface current distribution of the unit cell structure are simulated to explain the physics mechanism of the high-efficiency and broadband polarization rotation. Our design will provide an important reference for the practical applications of the metamaterial in polarization manipulation.

Systems using optical elements such as linear polarizers, retarders, and mirrors can be represented by Mueller matrices. Some polarimeters include elements with time-varying polarization properties, multiple light beams, light detectors, and signal processing equipment. Standard Mueller matrix forms describing time-varying retarders, and beam splitters are presented, as well as non-Mueller matrices which describe detection and signal processing. These matrices provide a compact and intuitive mathematical description of polarimeter response which can aid in the refining of instrument designs.

An experimental all-optical 2*1 free-space switching node that was implemented with semiconductor laser diodes, beam splitters, retardation plates, lenses, mirrors, dichroic filters and binary phase gratings is demonstrated. Two symmetric self-electrooptic effect device arrays used as optical logic elements were cascaded. Two electronically controlled optical signals were used to determine the switch routing. The 2*1 node transmitted at a data rate of 5 kb/s. >

The four sets of two optimum rotation angles for a polarimeter consisting of a quarter-wave plate in conjunction with a linear polarizer, both of which are free to rotate, are determined. These angles are obtained by maximizing the determinant of the system measurement matrix. The determinant for this system is approximately twice the value of the determinant when only the quarter-wave plate is free to rotate. In addition, the condition numbers of the measurement matrix decrease with the additional consideration of a rotatable linear polarizer.

An optical isolator with a (CeY)3Fe5O12 guiding layer employing TE–TM mode conversion was investigated. The optical isolator consisted of a nonreciprocal polarization rotator and a reciprocal polarization rotator. The reciprocal polarization rotator was realized by inserting a polyimide half-wave plate into a groove in the magnetooptic waveguide. Propagation distances required for the nonreciprocal polarization rotator were calculated at a wavelength of 1.55 µm. Diffraction loss due to the insertion of the half-wave plate was also calculated. The reciprocal polarization rotator integrated with a spot-size converter was proposed for suppressing the diffraction loss. By introducing the spot-size converter for an input facet and an output facet of the half-wave plate, a calculated total insertion loss was reduced to 0.22 dB.

Optical single sideband modulation with tunable optical carrier-to-sideband ratio using DP-BPSK modulator

A Thomson scattering light source can produce polarization-controllable x rays with quasi-monochromaticity and high brightness, making it an excellent probe for x-ray imaging and nuclear physics research. In this paper, a clear physical picture of the polarization transfer process from a laser to x rays is given based on a dipole radiation model. For arbitrary interaction geometries between a laser and relativistic electrons, the electric field relation between the scattered x rays and the laser is derived analytically. The result shows that the polarization characteristics of the laser can be completely transferred into x rays, regardless of the interaction geometry. Meanwhile, the polarization of scattered x rays is dependent on the collecting angle. As the collecting angle increases, both the degree of polarization (DOP) and the bandwidth of scattered x rays will be degraded. A collecting angle confining scattered x rays of 5% rms bandwidth can guarantee a DOP higher than 97% for both linear and circular polarizations. A method for any polarization control of scattered x rays is demonstrated by using wave plates for the laser. Both the rotation of linear polarization and the switch of polarization state from linear polarization to circular polarization and from left-handed polarization to right-handed polarization can be easily realized.