Birefringent Plate Research Articles

Super achromatic wide-angle quarter-wave plates using multi-twist retarders.

The achromaticity and wide-angle property of quarter-wave plates (QWPs) are crucial for the color uniformity and image resolution of the future displays such as virtual reality (VR) pancake lens and augmented reality (AR) waveguide/focusing systems. However, most reported achromatic wide-angle QWPs designs composed by stacks of different birefringent plates are too complicated with limited achromaticity and wide-angle performance. The multi-twist retarders (MTR) QWPs presented in previous work already showed its potential to achieve high achromaticity in RGB using one monolithic film in normal incidence, but the incompetent polarization control in blue-violet limits its application in LED-based polarization-sensitive AR/VR headsets. In this work, we theoretically investigate a new type of MTR QWPs achieving super achromaticity from violet to red with average ellipticity 43° and simultaneously maintaining wide-viewing angle up to ±45°, which enables a precise polarization control within the field-of-view (FOV) of current AV/VR headset. The new proposed MTR QWP is also reported to obtain average reflection luminance leakage 0.15~% and maximum leakage 0.23~%, making it a promising element to reduce polarization leakage and enhance image resolution in the next-generation displays.

Pre-chirp managed divided-pulse amplification using composite birefringent plates for pulse division and recombination: en route toward GW peak power.

Pre-chirp managed amplification (PCMA) allows the generation of optical pulses with a duration well below 100 fs. However, the pulse peak power is limited to <50 MW due to poor energy scalability. In this paper, we combine PCMA and divided pulse amplification to overcome this bottleneck. The resulting pre-chirp managed divided-pulse amplification (PCM-DPA) employs birefringent plates as the pulse divider/recombiner thanks to the picosecond pulse duration in the amplifier. Our numerical analysis shows that the group-delay dispersion (GDD) difference among pulse replicas results in reduced combining efficiency with increased replica numbers. We propose using composite birefringent plates to construct the divider/recombiner that features negligible GDD-difference. An Yb-fiber PCM-DPA system incorporating such composite-plate based divider/recombiner for 64 replicas can produce 121-µJ, 44-fs pulses with 2.3-GW peak power. To have a compact system, we further propose a hybrid design which can deliver 61-µJ, 48-fs pulses with 1.13-GW peak power. These results represent >30 times improvement in both pulse energy and peak power compared with current Yb-fiber PCMA systems.

Phase-stable optical activity measurement by common-path spectral interferometry.

A robust optical activity (OA) spectrometer covering the visible and near-infrared regimes was designed and built via a combination of a linear polarizer and a birefringent plate. The OA spectrometer relies on common-path spectral interferometry, where the two interfering fields travel common optical paths, and ensures signal reproducibility over several hours. By detecting OA without polarization switching, the data acquisition time is shortened to 1 s, enabling real-time monitoring of the chiral complex formation. The present configuration also allows OA measurement with broadband pulses, which is promising for probing ultrafast circular dichroism and optical rotatory dispersion.

Carving out configurable ultrafast pulses from a continuous wave source via the optical Kerr effect.

Wavelength-tunable, time-locked pairs of ultrafast pulses are crucial in modern-day time-resolved measurements. We demonstrate a simple means of generating configurable optical pulse sequences: sub-picosecond pulses are carved out from a continuous wave laser via pump-induced optical Kerr switching in 10 cm of a commercial single-mode fiber. By introducing dispersion to the pump, the near transform-limited switched pulse duration is tuned between 305-570 fs. Two- and four-pulse signal trains are also generated by adding birefringent α-BBO plates in the pump beam. These results highlight an ultrafast light source with intrinsic timing stability and pulse-to-pulse phase coherence, where pulse generation could be adapted to wavelengths ranging from ultraviolet to infrared.

Nonastigmatic alexandrite ring laser design with wavelength-tunable single-longitudinal-mode operation

This work presents a study of a fully nonastigmatic design of a single-longitudinal-mode, wavelength-tunable, unidirectional alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A “displaced mode” nonastigmatic laser cavity design eliminating astigmatic cavity elements is developed around an alexandrite crystal end-pumped by a low-brightness, high-power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power of 700 mW with an excellent T E M 00 mode ( M 2 &lt; 1.1 ) across a wide pump power range. Wavelength tuning from 748–773 nm is produced using a birefringent filter plate. The nonastigmatic alexandrite laser design achieves better spatial quality and resilience to maintain T E M 00 operation across wide variation in pump-induced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional alexandrite ring system in a fully nonastigmatic cavity regime.

Attitude metrology based on the field-of-view effect of birefringence using high-speed polarimetry.

A novel, to the best of our knowledge, optical method using a high-speed polarimetry is proposed for real-time attitude tracking in an ultra-large measurement range. The attitude metrology utilizes the field-of-view effect in birefringent crystals, which is known as the birefringence deviates with the field-of-view angle of polarized light. The basic principle of the metrology is presented via theoretical derivation and has been verified in the static retardance measurement experiments. With a resolution test, a temporal resolution of 0.4 ms per attitude measurement and an angular resolution up to 0.0025°are achieved. With the help of a bubble level, the attitude angles of an object attached with a birefringent wave plate are obtained in the dynamic experiments, which have achieved an accuracy better than 0.02°. Additionally, the angular velocity and acceleration of the real-time measured roll angle can be extracted simultaneously. The experimental results demonstrate that the proposed metrology has great potential and advantages in the real-time attitude sensing.

Numeric Study of Novel Compact Polarimeter for Full-Stokes Polarization Imaging Without Micro-Polarizer Array

This paper proposed a novel polarimeter for full-Stokes polarization imaging without using any kind of micro-polarizer array. The key components of the polarimeter are two grooved birefringent crystal plates with deviate fast axis, which are called Binary Birefringent Crystals (BBCs) in this paper. Mounting the jointed BBCs in the focal plane of an imaging detector, we manage to obtain the four components of Stokes vector simultaneously through the method proposed in this paper. We demonstrate the basic principle of the proposed polarimeter and verify it through numerical analysis. And one of the best-optimized configurations for the polarimeter is also presented. The proposed polarimeter is simultaneous, compact, easier in fabrication and capable of full-stokes polarization imaging. It is expected to be of potential use in a variety of applications.

Super-achromatic Quarter-wave Phase Retarder for Visible, Near Infrared and Short Wave Infrared Region Applications-=SUP=-*-=/SUP=-

Phase retarders are essential components in optical system design as they can control the phase shifts associated with the vector components of incoming light waves and hence, decide the state of polarization. Different optical systems are designed to work at different wavelength spectrums. Most of these developments focus on the different wavelength regions between visible to infrared, of which the near infrared and short-wave infrared ranges are popular domains for defense and remote sensing applications. In this present communication, a super achromatic quarter-wave phase retarder consisting of four birefringent plates of different materials, i. e. KDP, crystalline quartz, ADP and ZnS has been proposed, to cover the visible, near infrared and short wave infrared regions from 400-2100 nm. As circularly polarized light is less affected by atmospheric conditions the use of an achromatic broadband quarter-wave phase retarder as proposed is quite useful. The proposed system shows acceptable performance over the intended range of wavelengths. Keywords: Wave plates, Super achromatic, Retarder, SWIR.

An Achromatic Quarter-Wave and Half Wave Phase Retarder Combination Operating in Near Infrared (NIR) Region

Optical phase retarders are major components in design of different optical systems. Normally these retarders exhibit retardance which varies with wavelength. But achromatic phase retardation is necessary in optical system design. These achromatic phase retarders can be designed using different waveplates, sub-wavelength grating (SWG), liquid crystals, and polymers etc in different wavelength ranges. Present communication focus on designing of quarter-wave phase retarder in the near infrared range (NIR) with waveplates of different birefringent materials having different thicknesses. This system in NIR range shows comparable performance with those developed with SWGs and it also removes some drawbacks. The proposed system deals with an achromatic combination of four birefringent plates in 800–2000 nm range using Sapphire, CdSe, Calcite, and Rutile crystals having good transmittance in the NIR range. This system can also be used as a half wave phase retarder in NIR.

A new twist on the quantum vacuum

A subtle macroscopic effect in the space between two birefringent plates produces a measurable Casimir torque.

Interference-free and single exposure to generate continuous cycloidal alignment for large-area liquid crystal devices.

An approach for generating cycloidal pattern of liquid crystal (LC) molecules based on interference-free and single exposure is illustrated. The spatial manipulation of polarization state is achieved using birefringent prism and wave plates. And then, the spatially variant polarization of exposure beam is transferred to LC molecules by azo-dye photo-sensitive layer. Consequently, the LC samples fabricated shows periodically cycloidal texture and diffraction efficiency more than 99%. The measured period Λ and diffraction angle are in good consistency with theoretical results. Thus, this exposure method provides an effective and robust way for fabricating large-area LC elements, therefore paving the way for widespread applications of high-performance diffractive LC devices.

Wide field-of-view angle linear retarder with an ultra-flat retardance response.

We propose a universal method for optimal design of a wide field-of-view (FOV) angle linear retarder with an ultra-flat retardance response based on paired positive/negative birefringent plates. The mechanism and rules for the FOV effect compensation are revealed to determine the structure of the proposed retarder by introducing the partial derivative of refractive index with respect to the incident angle. A concrete example based on quartz/sapphire plates is designed and manufactured as a proof-of-concept of the proposed method. The maximum deviation in the retardance of the optimally designed quartz/sapphire wide FOV angle retarder over the concerned FOV angles (incidence: -20°-20°; azimuth: 0°-360°) is only 0.08°, which has been reduced by 3 orders of magnitude compared with the common quartz retarder.

High beam quality narrow linewidth microsecond pulse Ti:sapphire laser operating at 819.710 nm

A sub-pm linewidth high beam quality microsecond (μs) Ti:sapphire laser was reported, which was end-pumped by a frequency-doubled 1064 nm Nd:YAG laser. By inserting three birefringent plates tuner and one etalon into the cavity of the Ti:sapphire laser, a ∼ 0.8 pm linewidth at 819.710 nm was achieved with a maximum output power of 3 W operating at a high repetition rate of 500 Hz with pulse width of ∼25 μs. The beam quality factor M2 was measured to be ∼1.14. The wavelength could be finely tuned from 819.699 to 819.718 nm with tuning resolution of 0.76 pm. To the best of our knowledge, this is the first demonstration on the μs pulse Ti:sapphire laser at 819.710 nm with narrow linewidth and high beam quality simultaneously. Such μs 819.710 nm laser could be used to efficiently generate a polychromatic laser guide star together with a 589 nm laser for the tip-tilt correction of ground-based telescopes.

Embossing Reactive Mesogens: A Facile Approach to Polarization‐Independent Liquid Crystal Devices

AbstractReactive mesogens (RMs) are used in a wide variety of applications, from retardation plates for organic light‐emitting display screens, liquid crystal phase stabilization, optical or electrically active elastomers to novel optic components. They can be processed as standard liquid crystals and subsequently polymerized to stabilize both shape and anisotropic properties. However, creating complex shapes while maintaining good alignment of the RM optical axis can be a challenge. In the present work, embossing is used to replicate a wide variety of RM structures in several electro‐optic devices. A novel device geometry is proposed where a polarization‐independent lens is formed by opposing birefringent Fresnel zone plates embossed in aligned RM. The RM forms the optical elements and alignment layers for an index‐matched liquid crystal, arranged to produce the twisted nematic configuration. Low voltages switch the device between nonfocusing and focusing states. After characterizing lens efficiency and beam properties, the method is used to fabricate a switchable multilevel Fresnel zone plate with optical efficiencies beyond 50%, and theoretically able to produce polarization‐independent lenses with efficiencies approaching 100% from a single structure. Finally, manufactured polarization‐independent gratings and microlens arrays are presented using the method to illustrate the wide range of applicability.

Unidirectional single-frequency operation of a continuous-wave Alexandrite ring laser with wavelength tunability.

High resolution spectroscopy, metrology and quantum technologies (e.g. trapping and cooling) require precision laser sources with narrow linewidth and wavelength tunability. The widespread use of these lasers will be promoted if they are cost-effective, compact and efficient. Alexandrite lasers with a broad tuning band pumped efficiently by low-cost red diodes are a potential candidate, but full performance as a precision light source has not been fully achieved. We present in this work the first continuous-wave (CW) and single-frequency operation of a unidirectional diode-end-pumped Alexandrite ring laser with wavelength tunability. An ultra-compact bow-tie ring cavity is developed with astigmatic compensation and a novel 'displaced mode' design producing CW output power > 1 W in excellent TEM00 mode (M2 < 1.2) when using a low brightness pump (M2 ≥ 30). Wavelength tuning from 727 - 792 nm is demonstrated using a birefringent filter plate. This successful operation opens the prospects of precision light source applications.

Photoluminescence property and widely tunable, efficient 2μm laser in Tm:Ca1−xGdxF2+x single crystals

3at.%Tm3+:Ca1−xGdxF2+x (x=0, 0.005, 0.01, 0.02) single crystals were grown by the vertical Bridgman method, where Gd3+ ions play the role of manipulating ions for local structure to form a disordered lattice site. Spectral properties of these crystals were investigated. Compared to 3at.%Tm3+:CaF2, the spectral parameters of 3at.%Tm3+:Ca1−xGdxF2+x were drastically enhanced in a large scale. LD pumped lasers have been demonstrated in the crystals for the first time. For CW operation, the slope efficiency up to 49.7% was achieved with output power of 1.927 W at 1970 nm. With a birefringent quartz plate, wavelength-tunable laser operation with a tuning range of more than 176 nm was realized.

Wavelength beam combining by spectrally selective polarization transformation

Efficient wavelength beam combining is demonstrated using spectrally selective polarization transformation in carefully designed stacks of birefringent plates combined with polarization-selective beam splitters. This beam-combining scheme is shown to enable a high-throughput power and intensity scaling of blue-diode-laser arrays. The wavelengths of individual diode lasers in the laser array are shifted with respect to each other by a few nanometers, by fine temperature adjustment, for the highest overall output radiance, limited by etendue conservation.

Flexible double-cladding ytterbium fibre based 9 W mode-locked laser with 102 fs compressible pulse duration

We report on a high power mode-locked femtosecond fiber laser oscillator with flexible double-cladding (DC) ytterbium-doped fiber (Yb-fiber) as gain medium and a fused fiber combiner as a pump coupling scheme, based on the nonlinear polarization evolution effect in a ring cavity configuration with a dual-stage birefringent plate as the spectral filter. Laser pulses with a pulse energy as high as 122 nJ and compressible pulse duration as short as 102 fs at 1041 nm center wavelength could been obtained. The experimentally recorded power fluctuations were better than 0.42% RMS and 0.40% RMS in 3 h under 5 W and 9 W output power, respectively. The measured beam quality factors M2 were 1.3 in both the horizontal and perpendicular directions. To the best of our knowledge, this is the highest output power generated from a flexible DC Yb-fiber-based ultrashort pulse mode-locking fiber laser oscillator pumped with a fusion spliced combiner.

Interferometric and Uhlmann phases of mixed polarization states

In our investigation into the effects of the degree of polarization in modulation of partially polarized light we assume general settings of the interferometry of partially polarized lightwaves and perform theoretical analysis of the Uhlmann and the interferometric phases. We introduce the relative Uhlmann phase determined by the Uhlmann holonomies of interfering beams and show that the interferometric phase generalized to the case of nonunitary evolution can, similar to the Uhlmann phase, be cast into the holonomy defined form. By using the technique based on a two-arm Mach-Zehnder interferometer, two different dynamical regimes of light modulation are experimentally studied: (a) modulation of the input light by the rotating quarter-wave plate (QWP); and (b) modulation of the testing beam by a birefringent plate with electrically controlled anisotropy represented by the deformed-helix ferroelectric liquid crystal (DHFLC) cell. In the setup with the rotating QWP, the interferometric phase is found to be equal to the relative Uhlmann phase. Experimental and theoretical results being in excellent agreement both show that this phase is an oscillating function of the QWP angle and increases with the degree of polarization. For modulation by the DHFLC cell, the data derived from our electro-optic measurements are fitted using the theory of the orientational Kerr effect in FLCs. This theory in combination with the results of fitting is used to evaluate electric field dependencies of the interferometric and the Uhlmann phases.

Elliptically polarized exciton-polariton condensate in a semiconductor microcavity with a chiral photonic crystal slab

We demonstrate a method for controling polarization of exciton-polariton condensate emission in a planar semiconductor microcavity based on modification of the electromagnetic mode structure in the microcavity. The modification is realized by fabrication of a chiral photonic crystal slab with partial etching of the upper Bragg mirror lowering the microcavity symmetry to C4. A degree of circular polarization as high as 70% has been demonstrated experimentally in the structure with optimized parameters without the use of a static magnetic field or birefringent wave plates.