Quarter-wave Retarder Research Articles

Polarisation tunable terahertz generation with optical rectification

Terahertz (THz) polarisation manipulation is critical to obtaining circularly polarised THz, vector and vortex THz for spectroscopy, polarisation-sensitive time-domain spectroscopy, polarisation-sensitive imaging, etc. Thus, THz with tunable polarisation is widely desirable. For example, THz with tunable polarisation can be converted into elliptically polarised THz with arbitrary ellipticity with a quarter-wave Fresnel retarder. Two-colour plasma is an example source radiating THz with tunable polarisation. However, varying the polarisation of THz from two-colour plasma usually suffers side effects, such as variations in the efficiency of THz yield and THz ellipticity. Hereby, we present how to generate THz with tunable polarisation through optical rectification in 111-cut ZnTe crystal. Unlike the two-colour plasma source, the variation of THz polarisation does not alter the generation efficiency by changing the orientation angle of the 111-cut ZnTe crystal. The generation mechanism is theoretically described and experimentally verified.

Highly circularly polarized monochromatic high harmonic pulses via a reflective phase retarder at 27.9eV.

A circularly polarized (CP) single-order high harmonic pulse light source, operating at a photon energy of 27.9 eV, is developed. The production of CP harmonic pulses with a degree of polarization exceeding 99% is achieved by utilizing a high-throughput phase retarder composed of SiC mirrors. Notably, our phase retarder exhibits minimal deviation from quarter-wave phase retardation, with a precision of less than ±λ/50 across a 3.1 eV bandwidth. This wide bandwidth enables effective polarization conversion of attosecond pulses preserved. By implementing the phase retarder, we converted the linear polarization to circular with an ellipticity of 0.93.

Tunable broadband polarization retarders.

We theoretically propose a type of tunable polarization retarder, which is composed of sequences of half-wave and quarter-wave polarization retarders, allowing operation at broad spectral bandwidth. The constituent retarders are composed of stacked standard half-wave retarders and quarter-wave retarders rotated at designated angles relative to their fast polarization axes. The proposed composite retarder (CR) can be tuned to an arbitrary value of the retardance by varying the middle retarder alone while maintaining its broadband spectral bandwidth intact.

Continuously wavelength‐tuneable general transmittance function in first‐order fibre multiwavelength filter based on composite combination of wave retarders

AbstractThe wavelength tunability of a general transmittance function (GTF) is investigated in a first‐order fibre multiwavelength filter based on a polarisation‐diversified fibre loop, which utilised a composite combination of wave retarders. The filter consists of a polarisation beam splitter, two equal‐length high birefringence fibre (HBF) segments, and two different sets of wave retarders with each set positioned before each HBF segment. Specifically, a combination of a set of dual quarter‐wave retarders (QWRs) and another set of a QWR and a half‐wave retarder is focused upon. By considering the effect of the four wave retarders and two HBF segments on the output polarisation state (OPS) of each element in the filter, the four wave retarder angles (WRAs) are identified that caused all polarisation states on the OPS trace of the second HBF move in the direction of wavelength decrease, resulting in a redshift of the GTF. 360 WRA sets are derived that enabled tuning the GTF by one free spectral range SR. For eight sets chosen from the WRA sets, inducing a wavelength shift of SR/8 for each set order, wavelength‐shifted spectra are calculated. Finally, this theoretical prediction is experimentally verified, confirming the wavelength tunability of the GTF of the filter.

Single-shot characterization of special multi-soliton and noise-like pulse emissions in a mode-locked fiber laser

Single-shot characterization of three categories of multi-pulse emissions in a passively mode-locked fiber laser based on nonlinear polarization rotation is experimentally reported. The mechanism to control the intracavity polarization state relies on a polarizer beam splitter cube together with a half-wave and a quarter-wave retarders. With a precise adjustment of the retarders, the fiber laser can reach different mode locking regimes involving noise-like pulses (NLP) and solitons. These regimes include (i) NLP emission exhibiting broad-bandwidth supercontinuum spectrum, (ii) multiple soliton emission in the form of soliton bunches with rectangular-shaped envelope, and (iii) NLP emission with complex pulse patterns, such as the one obtained from the breakup of a rectangular NLP, or the harmonic mode locking regime exhibiting multiple, uniformly spaced NLP wave packets. The experimental results presented in this work provide useful information for a better understanding of different types of multi-pulse emission from the same fiber laser system, complementing the studies focused on the nature and physical mechanisms underlying NLP emission.

Full-color optical combiner with good imaging quality and a wide angle of incident light acceptance.

This work demonstrates a full-color optical image combiner for augmented reality head-up displays. In this device, the angle of the incident light of the computer-generated image reflected by it can vary over a large range. It achieves improved performance by using a combination of polarization interference filters (PIFs), quarter-wave retarders (QWRs), and polarization volume holograms (PVHs). The details for an example design and its performance are presented.

Broadband composite nonreciprocal polarization wave plates and optical isolators

We theoretically study a technique for a broadband nonreciprocal wave retarder whose quarter-wave plate phase retardation is the same in forward and backward directions. The system is built using a number of sequential nonreciprocal wave plates. The proposed device can also be utilized to create a broadband optical diode, which consists of two achromatic quarter-wave plates, one reciprocal and the other non-reciprocal, that are sandwiched between two polarizers aligned in parallel.

Achromatic terahertz quarter-wave Fresnel rhomb retarder

Achromatic terahertz (THz) quarter-wave retarder is widely desired to manipulate the polarization states of broadband THz beams, which are essential for spectroscopic applications, such as circular dichroism spectroscopy and steering THz vortex beams. A retarder based on Fresnel reflection exhibits the potential for designing an achromatic THz quarter-wave retarder. However, special care should be taken to make a Fresnel retarder capable of manipulating the beam ellipticity by simply rotating its fast axis without affecting its propagation path. Hereby, we design a 4-bounce achromatic quarter-wave Fresnel rhomb retarder free of affecting beam propagation, which can easily change the input beam's ellipticity by simply rotating the retarder's fast axis.

13‐3: A full‐color optical combiner with good imaging quality and a wide angle of incident light acceptance

This work demonstrates a full‐color optical image combiner for AR and heads‐up displays. The novel feature of the device is that the angle of incident light of the computer‐generated image reflected by it, can vary over a large range. It achieves improved performance by using a combination of polarization interference filters (PIF), quarter wave retarders (QWR), and polarization volume holograms (PVH). Details of an example design and its performance are presented.

광섬유 빗살 필터의 사분파장 지연기 연속 조합을 이용한 협대역 다파장 스펙트럼의 연속 주파수 조정에 관한 연구

We propose an optical fiber comb filter based on a polarization-diversity loop structure, which can continuously adjust the narrowband multiwavelength spectrum. The proposed comb filter consists of a polarization beam splitter(PBS), a successive combination of quarter-wave retarders(QWRs), a set of a half-wave retarder and a QWR, and two polarization-maintaining fiber(PMF) segments of equal length. For the convenient adjustment of the narrowband multiwavelength spectrum, the successive combination of QWRs was located between the PBS and the first PMF segment. The transmittance function of the proposed filter was theoretically derived using the Jones calculus. Based on the filter transmittance, we theoretically predicted the orientation angle sets of four wave retarders, which allow the extra phase difference φ of the transmittance function to vary from 0˚ to 315˚ with increments of 45˚. Then, the proposed filter successfully demonstrated the predicted results by obtaining ∼0.0915 ㎚ average wavelength shift and a high linearity of 0.99878.

Efficient acquisition of Mueller matrix via spatially modulated polarimetry at low light field.

Mueller polarimetry performed in low light field with high speed and accuracy is important for the diagnosis of living biological tissues. However, efficient acquisition of the Mueller matrix at low light field is challenging owing to the interference of background-noise. In this study, a spatially modulated Mueller polarimeter (SMMP) induced by a zero-order vortex quarter wave retarder is first presented to acquire the Mueller matrix rapidly using only four camera shots rather than 16 shots, as in the state of the art technique. In addition, a momentum gradient ascent algorithm is proposed to accelerate the reconstruction of the Mueller matrix. Subsequently, a novel adaptive hard thresholding filter combined with the spatial distribution characteristics of photons at different low light levels, in addition to a low-pass fast-Fourier-transform filter, is utilized to remove redundant background noise from raw-low intensity distributions. The experimental results illustrate that the proposed method is more robust to noise perturbation, and its precision is almost an order of magnitude higher than that of the classical dual-rotating retarder Mueller polarimetry at low light field.

47.1: Green Technology of Photoalignment Layer Coating from H2O solution for Achromatic Polymerizable Liquid Crystal Retarder

Combination of several films from polymerizable liquid crystal (PLC) into single device system with complex properties faces a fabrication issue due to chemical compatibility and mutual alignment effect of the neighbouring layers. Eco-friendly green technology of high anchoring azo-dye photoalignment layer coating from water solvent provides efficient solution to hinder interlayer interaction of bottom PLC layer avoiding its chemical damage and providing unique photoalignment pattern for top PLC retarder. The advanced possibilities of green technology of photoalignment layers coated from H2O solution are demonstrated through fabrication of achromatic quarter-wave retarder system comprising formation of polimerizable liquid crystal layers on top of one another with arbitrary azimuthal photoalignment direction. The merge of photoaligned PLC retarders into single multi-layer anisotropic structure opens new approach to fabrication of thin-film phase devices with complex optical properties.

Vortex Dynamics and Structured Darkness of Laguerre-Gaussian Beams Transmitted Through Q-Plates Under Weak Axial-Asymmetric Incidence

We describe the rich vortex dynamics at normal and near-normal or off-centered Laguerre-Gaussian beam transmission through the q-plate – a waveplate capable of generating vortex beams from circularly polarized incident beams. First, we explore the basics of the spin-to-orbit angular momentum conversion and show the vortex constellations under normal incidence for the case of quarter-wave retardation. Second, we analyze the optical Gaussian and vortex beam profile transformations accompanying the giant beam shifts under axial-asymmetric incidence. Namely, we consider the near-normal (for the Fourier-space q-plate) and off-centered (for the real-space q-plate) incidence, when the incident angle becomes comparable with beam angular divergence and off-center distance becomes comparable with beam width, respectively. In this regime, one can control the positions of the single-charge vortices with the specified polarization components of the beam, including those residing in its structured darkness. All mentioned effects arise due to the extreme spin-orbit coupling. The results obtained form a novel platform for a plethora of optical vortex transformation and structured light phenomena.

Dual vortex retarder Mueller matrix ellipsometry

We propose a dual vortex retarder Mueller matrix ellipsometry (DVRMME) that can extract 16 Mueller matrix elements by analyzing a single intensity image. Two customized vortex quarter wave retarders (VQWRs) with different orders are employed to realize the spatial modulation in the polarization state generation (PSG) and polarization state analyzing (PSA) arms. Due to the spatial polarization modulation by VQWRs, a pattern with regularly varying intensity along the azimuth direction is formed, and the sample's Mueller matrix can be obtained by processing the modulated intensity image. The ellipsometry's working principle has been elaborated by the Stokes-Mueller formalism, and its main error sources are presented and analyzed, and then a modulation vector calibration method is proposed to reduce the measurement error. To verify the validity of the scheme, the DVRMME has been constructed and demonstrated in experiment. The Mueller matrices of air, polarizer and retarder were measured, and their RMS errors of 16 Mueller matrix elements were respectively less than 0.0110, 0.0094 and 0.0180, and their maximum absolute errors were respectively less than 0.0196, 0.0230 and 0.0352.

Elimination of ambient light reflection color in automotive organic light emitting diode displays

A simple method for eliminating reflective color differences that depend on the viewing angle in automotive organic light emitting diode display panels is reported. A two-domain quarter-wave retarder is employed as one layer of the circular polarizer to compensate for the retardation resulting from the incident angles. The reflective color differences of the panel between normal and oblique directions can be completely eliminated in an ambient light environment because of the effects of the multidomain retarder. Additionally, the two-domain quarter-wave retarder induces a symmetric reflectance distribution on the viewing angles, resulting in outstanding reflective properties.

대역 평탄화된 빗살 스펙트럼의 간단한 연속 파장 조정을 위한 이종 파장 지연기 조합 기반 광섬유 1차 빗살 필터에 관한 연구

In this paper, we propose an optical fiber first-order comb filter based on a polarization-diversity loop structure(PDLS), whose passband-flattened comb spectrum can be continuously wavelength-tuned in a convenient way through heterogeneous wave retarder combination. The proposed filter consists of a polarization beam splitter, two equal-length polarization-maintaining fiber(PMF) segments, three quarter-wave retarders(QWRs) and one half-wave retarder(HWR). For convenient wavelength control, we inserted a set of a QWR and an HWR between two PMF segments. Using the filter transmittance theoretically derived with Jones calculus, we found the azimuth angle(AA) sets of four wave retarders, which enable the additional phase difference ø to change from 0° to 360° On the basis of these AA sets, we theoretically calculated passband-flattened transmittance spectra spaced with a wavelength interval of 0.1nm. Then, we experimentally demonstrated theoretical results.

Continuously wavelength‐tunable passband‐flattened fibre multiwavelength filter based on heterogeneous combination of wave retarders

By incorporating the heterogeneous combination of wave retarders, the authors demonstrated a continuously wavelength-tunable passband-flattened fibre multiwavelength filter comprised of a four-port polarization beam splitter (PBS), two equal-length polarization-maintaining fibre (PMF) segments, one wave retarder combination (WRC) of dual quarter-wave retarders (QWRs), and another WRC of a half-wave retarder (HWR) and a QWR. The former WRC lies before the first PMF segment, and the latter one is located between the two PMF segments. From the theoretically derived filter transmittance, the authors found the orientation angle (OA) sets of the four wave retarders where the additional phase ϕ of the transmittance function could be continuously modified from 0° to 360°. For eight OA sets allowing ϕ to increase from 0° to 315° by 45°, the authors calculated the passband-flattened transmission spectrum of the filter and confirmed its redshift by 0.1 nm per set. Then, this theoretical prediction was verified by the experimental implementation of the filter, which clearly indicates the continuous wavelength tuning capability of the proposed filter.

사분파장 편광 변환을 이용한 협대역 다파장 스펙트럼의 연속 파장 조정에 관한 연구

To continuously adjust the wavelength of the narrow band transmission spectrum in a multiwavelength filter based on polarization-diversity loop configuration(PDLC), we harnessed quarter-wave polarization transformation, which was implemented by a combination of four wave retarders. The PDLC-based multiwavelength filter consists of a polarization beam splitter(PBS), two polarization-maintaining fiber(PMF) segments of the same length, one half-wave retarder(HWR), and three quarter-wave retarders(QWRs). By utilizing the filter transmittance derived through the Jones calculus, we found a combination of orientation angles of the four wave retarders, which could induce an extra phase difference φ from 0° to 360° in the narrow band transmittance function. Then the calculated transmission spectrum was obtained from the eight sets of orientation angles combination of the wave retarders, which were selected to make φ vary from 0° to 315° at intervals of 45°. Theoretical prediction results on the continuous wavelength adjustment of narrow band multiwavelength spectrum using quarter-wave polarization transformation were also experimentally validated.

사분파장 편광 변환을 이용하여 파장 조정을 구현한 통과 대역 평탄화된 다파장 필터에 관한 연구

By harnessing quarter-wave polarization transformation, we propose a multiwavelength filter based on polarization-diversity loop configuration, which can continuously adjust the wavelength of the pass-band-flattened transmission spectrum. The proposed filter consists of a polarization beam splitter, two polarization-maintaining fiber segments of the same length, one half-wave retarder, and three quarter-wave retarders. We found a combination of the orientation angles of the four wave retarders, which could induce an extra phase difference φ from 0° to 360° in the pass-band-flattened transmittance function derived using Jones formulation. Then, we implemented the wavelength adjustment of the pass-band-flattened transmission spectrum at a wavelength interval of 0.1nm through the theoretical calculation of transmission spectra. As a result, we experimentally demonstrated the theoretically predicted results by controlling the azimuth angles of the wavelength retarders within the filter.

Generation of periodic and quasi-periodic two-dimensional non-diffractive beams with inhomogeneous polarization

In this work, two-dimensional periodic and quasi-periodic non-diffractive spatial inhomogeneous polarization optical fields are generated, numerically and experimentally, by the superposition of multiple plane waves with different polarizations. For the experimental implementation of the fields, synthetic phase holograms are employed in conjunction with half-wave and quarter-wave retarder films as polarization modulators. The obtained spatially inhomogeneous polarization optical fields show good quality and are in good agreement with numerical results. The proposed method is highly efficient for the generation of these types of optical fields.