Birefringent Plate Research Articles

Ultra-compact Fourier transform imaging spectrometer using a focal plane birefringent interferometer.

A new Fourier transform imaging spectrometer based on a focal plane birefringent interferometer (FPBI) is presented. The FPBI, located in front of the detector, is capable of performing spectral imaging measurements. It mainly consists of a birefringent plate and a birefringent wedge. The ordinary and extraordinary rays-with an optical path difference-are split by the FPBI and interfere on the focal plane. The spectral image of the target can be acquired via scene scanning and spectral recovery. The principle of interferometric imaging of the FPBI is investigated, and verification experiments are then performed. The experiments indicate that the FPBI not only provides effective spectral imaging measurements, but also presents the advantages of being ultra-compact and lightweight. As a result, it can be effectively applied in situations such as outdoor surveillance and airborne remote sensing.

Line-tunable Er:GGAG laser.

In this Letter, for the first time, to the best of our knowledge, a pulse and CW laser based on an Er-doped Gd3Ga2.7Al2.3O12 (Er:GGAG) active medium emitting laser radiation at 2.8μm are presented. With the longitudinal diode pumping, the maximal output energy of 4.9mJ and slope efficiency of 13.5% in the pulse regime were reached. Using the birefringent MgF2 plate, the line tunability of Er:GGAG at several spectral bands of 2800-2822nm, 2829-2891nm, and 2917-2942nm were obtained.

Core-pumped mode-locked ytterbium-doped fiber laser operating around 980 nm

In this letter, we first demonstrate a core-pumped passively mode-locked all-normal-dispersion ytterbium-doped fiber oscillator based on nonlinear polarization evolution operating around 980 nm. The dissipative soliton fiber laser pulse can be compressed down to 250 fs with 1 nJ pulse energy, and the slope efficiency of the oscillator can be as high as 19%. To improve the dissipative soliton laser output spectrum smoothness, we replace the birefringent plate based intracavity filter with a diffraction-grating based filter. The output pulse duration can then be further compressed down to 180 fs with improved spectral-smoothness. These schemes have potential applications in seeding cryogenic Yb:YLF amplifiers and underwater exploration of marine resources.

3‐3: Distinguished Student Paper: Resolution Enhanced Light Field Near‐to‐Eye Display Using E‐shifting Method with Birefringent Plate

Light field near‐to‐eye display (LFNED) achieves lightweight device and solves accommodation‐convergence conflict. However, low spatial resolution of LFNED brings users bad immersive experience. In this paper, the new method proposed using birefringent plate to enhance image resolution. In results, our method apparently improves resolution in LFNED.

Dual-wavelength operation of a diode-pumped Nd:YVO4 laser at the 1064.1 & 1073.1 nm and 1064.1 & 1085.3 nm wavelength pairs

Two dual-wavelength operation regimes of a diode-pumped Nd:YVO4 laser were demonstrated at 1064.1 & 1073.1 and 1064.1 & 1085.3 nm with two intracavity birefringent plates. The output power ratio of the dual-wavelength output could be freely adjusted. The highest total output power was 1.44 W under the dual-wavelength condition with 1:1 power ratio for both wavelength pairs. The slope efficiency was more than 16% and optical-to-optical efficiency more than 13% with respect to the absorbed pump power.

Resolution enhanced light field near eye display using e‐shifting method with birefringent plate

AbstractLight field near eye displays (LFNED) can produce lightweight devices and address the accommodation–convergence conflict. However, low spatial resolution creates a poor immersive experience in LFNED. In addition, although many e‐shifting devices have been proposed to enhance resolution in projection system, yet those devices are too bulky to be applied in an LFNED to keep it lightweight. In this paper, a compact e‐shifting component is proposed to enhance image resolution in an LFNED by using a birefringent plate and twisted nematic switch cell. The proposed e‐shifting device is a flat and thin component with only 2.6 mm of thickness, which could be placed in the gap of an LFNED without increasing the thickness. The results show that the proposed components could be easily integrated in an LFNED with the result of resolution enhancement.

Polarization-orthogonal filament array induced by birefringent crystals in air

We demonstrate the generation of filament array with orthogonal polarizations in air by using specifically designed wedge-type birefringent quartz plates. Experimental results show that the number of the generated filaments can be expressed as N = 2n wherenis the number of quartz plates inserted in the laser propagation path. By manipulating the optic axis of the quartz plates with respect to the polarization direction of the input laser pulse, the generated filaments can be separated into two parts with the polarization directions perpendicular with each other. The separation distance between the adjacent filaments is found to be linearly dependent on the focal length of external focusing lens. Our results provide a simple and efficient way to generate regular and reproductive femtosecond filament array in air.

Highly efficient birefringent quarter-wave plate based on all-dielectric metasurface and graphene

All-dielectric metasurfaces offer remarkable properties including high efficiency and flexible control of the optical response. However, extreme, narrow bandwidth is a limitation that lowers applicability of these structures in photonic sensing applications. In this work, we numerically design and propose a switchable quarter-wave plate by hybridizing an all-dielectric metasurface with graphene. By using a single layer of graphene between a highly refractive index silicon and a silica substrate, the transmissive resonance is enhanced and broadened. Additionally, integrating graphene with silicon effectively modulates the Q-factor and the trapped magnetic modes in the silicon. A stable birefringence output is obtained and manipulated through the structure dimensions and the Fermi energy of graphene. A 95% polarization conversion ratio is achieved through converting linearly polarized light into circularly polarized light, and a 96% ellipticity ratio is obtained at the resonance wavelength. The structure is compact and has an ultrathin design thickness of 0.1λ, in the telecommunication region. The above properties are essential for integration into photonic sensing devices and the structure has potential for compatibility with the CMOS devices.

Improved common-path spectral interferometer for single-shot terahertz detection

To seek high signal-to-noise ratio (SNR) is critical but challenging for single-shot intense terahertz (THz) coherent detection. This paper presents an improved common-path spectral interferometer for single-shot THz detection with a single chirped pulse as the probe for THz electro-optic (EO) sampling. Here, the spectral interference occurs between the two orthogonal polarization components with a required relative time delay generated with only a birefringent plate after the EO sensor. Our experiments show that this interferometer can effectively suppress the noise usually suffered in a non-common-path interferometer. The measured single-shot SNR is up to 88.85, and the measured THz waveforms are independent of the orientation of the used ZnTe EO sensor, so it is easy to operate and the results are more reliable. These features mean that the interferometer is quite qualified for applications where strong THz pulses, usually with single-shot or low repetition rate, are indispensable.

Compact birefringent interferometer for Fourier transform hyperspectral imaging.

A compact birefringent interferometer (CBI) for Fourier transform hyperspectral imaging is presented. The CBI employs only two birefringent crystal plates: a shearing plate (SP) and a compensation plate (CP). The SP generates the optical path difference (OPD) associated with the field of view for broadband interference. The CP compensates the constant term and square term OPDs of the SP to adjust the position of the zero-order fringe pattern and suppress inconsistent total OPDs and other nonlinear OPDs. This paper details the theoretically deduced OPDs and then presents simulation analyses and verification experiments conducted to investigate the OPD distribution characteristics. To verify the CBI performance, experimental spectral measurements and hyperspectral imaging were performed. The experimental results demonstrate that the CBI can suppress inconsistent total OPDs and other nonlinear OPDs with only two birefringent crystal plates, and therefore offers much promise for miniature and high-precision Fourier transform hyperspectral imaging.

Simple Method for Measuring Small Retardance

Small retardances are encountered in many experimental works. Internal stresses, weakly birefringent materials, optical windows and formation of contaminating surface layers are sources of small retardances. Most known methods for retardance measurements fail to determine accurately their values which are sometimes essential in the evaluation of experimental results. In this work, we present a method for accurate measurement of a small retardance. Our study aims to find the retardance error in a birefringent full-wave plate which, if perfect, is considered as of zero retardance. Our treatment will make use of a previously presented model for simultaneous calibration of two phase plates.

DBR‐free semiconductor disc laser on SiC heatspreader emitting 10.1 W at 1007 nm

We report a distributed Bragg reflector-free semiconductor disc laser which emits 10 W continuous wave output power at a wavelength of 1007 nm when pumped with 40 W at 808 nm, focused into a 230 μm diameter spot on the gain chip. By introducing a birefringent filter plate in the laser cavity the wavelength could be tuned from 995 to 1020 nm. The laser consisted of a gain chip located at the beam waist of a linear concentric resonator with an output coupling of 2.15%. The gain chip consists of a 1.574-μm-thick resonant periodic gain structure, with ten In 0.13 Ga 0.87 As quantum wells embedded in strain-compensating GaAs 0.94 P 0.06 barrier layers, van der Waals bonded to a silicon carbide intra-cavity heat spreader.

Common-path spectral interferometry for single-shot terahertz electro-optics detection.

We propose a common-path spectral interferometer for single-shot terahertz (THz) electro-optics (EO) detection, where a probe pulse pair with orthogonal polarizations and a relative time delay are generated by simply using a birefringent plate. One of them, as the object, transmits through a THz EO crystal with THz phase modulation, while the other goes through the crystal without any phase imposed by target the THz field as the reference. The co-axial propagation of the pulse pair can effectively reduce the noises due to mechanical vibrations, air turbulences, and temperature fluctuations in the traditional non-common-path spectral interferometers. Our experiments show that, for a given target THz pulse field, the measured THz signals in a single-shot mode have a signal-to-noise ratio (SNR) of 41.2 with our THz common-path spectral interferometer, but 7.91 with a THz Mach-Zehnder spectral interferometer; thus, our design improves the SNR of the THz signal by about 5.2 times.

Detecting Casimir torque with an optically levitated nanorod

The linear momentum and angular momentum of virtual photons of quantum vacuum fluctuations can induce the Casimir force and the Casimir torque, respectively. While the Casimir force has been measured extensively, the Casimir torque has not been observed experimentally though it was predicted over forty years ago. Here we propose to detect the Casimir torque with an optically levitated nanorod near a birefringent plate in vacuum. The axis of the nanorod tends to align with the polarization direction of the linearly polarized optical tweezer. When its axis is not parallel or perpendicular to the optical axis of the birefringent crystal, it will experience a Casimir torque that shifts its orientation slightly. We calculate the Casimir torque and Casimir force acting on a levitated nanorod near a birefringent crystal. We also investigate the effects of thermal noise and photon recoils on the torque and force detection. We prove that a levitated nanorod in vacuum will be capable of detecting the Casimir torque under realistic conditions.

Off-surface optic axis birefringent filters for smooth tuning of broadband lasers.

Transition metal-doped gain media, such as Ce:LiCAF, Ti:sapphire, Cr:ZnSe, and Fe:ZnSe, possess wide gain bandwidths that could provide ultra broadly tunable laser output with the usage of adequate intracavity tuning elements. Birefringent filters (BRFs) are a low-cost and easy to use solution for tuning. However, for ultrabroad gain media, regular on-surface optic axis BRFs could not provide smooth tuning of laser wavelength in the whole emission range. Basically, regular BRFs could not accommodate a large enough free spectral range with acceptable modulation depth variation while tuning, due to their slow tuning rates. Motivated by this, in this study, we have numerically investigated the effect of optic axis orientation on filter parameters for magnesium fluoride birefringent tuning plates. We have shown that a magnesium fluoride BRF with an optic axis diving by 30° into the plate could provide smooth tuning of ultra-broad laser gain media. A similar analysis has shown that for broadband tuning applications, the optimum optic axis diving angle lies around 25° for crystal quartz BRFs. The proposed filters have the potential to be useful in tuning of broadband lasers in continuous-wave, long-pulsed, and femtosecond operation regimes.

Characterization of normal dispersion mode-locked Yb-doped fiber laser with birefringent spectral filter

We present an investigation into the characteristics of a normal dispersion mode-locked Yb-doped fiber laser using a birefringent plate as a spectral filter. Before implementing mode locking using a birefringent plate, the transmission characteristics of the birefringent plate were analyzed. It was observed that the center wavelength and the full width at half maximum (FWHM) of the transmitted light varied according to the azimuthal angle and optical axis of the birefringent plate. The total dispersion value of the laser cavity was 0.04673 ps2 at a center wavelength of 1.03 μm. The mode locking was therefore achieved in the normal-dispersion region. The total cavity length of the Yb-doped fiber laser was about 1.9 m including free space, and the repetition rate of the mode-locked pulse was ∼104.2 MHz. The FWHM of the optical spectrum was ∼18.09 nm, and the pulse width measured by an autocorrelator was ∼1.71 ps assuming a Gaussian pulse shape. To obtain the transform limited pulse, a pulse was compressed using a pair of diffraction gratings outside the cavity. We achieved a compressed pulse of ∼148 fs assuming a Gaussian pulse shape. The output characteristics of the mode-locked Yb-doped fiber laser were observed while rotating the optical axis of the birefringent plate in the laser cavity. It was found that the center wavelength and FWHM of the optical spectrum could be varied by rotating the optical axis of the birefringent plate. The center wavelength changed by about 18.7 nm from 1026.9 to 1045.6 nm during rotation of the optical axis of the birefringent plate.

In-line balanced detection stimulated Raman scattering microscopy

We introduce a novel configuration for stimulated Raman scattering (SRS) microscopy, called In-line Balanced Detection (IBD), which employs a birefringent plate to generate a time-delayed polarization-multiplexed collinear replica of the probe, acting as a reference. Probe and reference cross the sample at the same position, thus maintaining their balance during image acquisition. IBD can be implemented in any conventional SRS setup, by adding a few simple elements, bringing its sensitivity close to the shot-noise limit even with a noisy laser. We tested IBD with a fiber-format laser system and observed signal-to-noise ratio improvement by up to 30 dB.

Characterization of a pulsed injection-locked Ti:sapphire laser and its application to high resolution resonance ionization spectroscopy of copper

A high repetition rate pulsed Ti:sapphire laser injection-locked to a continuous wave seed source is presented. A spectral linewidth of 20 MHz at an average output power of 4 W is demonstrated. An enhanced tuning range from 710–920 nm with a single broadband mirror set is realized by the inclusion of a single thin birefringent quartz plate for suppression of unseeded emission. The spectral properties have been analyzed using both a scanning Fabry–Pérot interferometer as well as crossed beam resonance ionization spectroscopy of the hyperfine levels of natural copper. Delayed ionization of the long-lived excited state is demonstrated for increased resolution. For the excited state hyperfine coupling constant of the 244 nm 4s 2S 4s4p4P° ground-state transition in Cu, a factor of ten reduction in error compared to previous literature was achieved. The described laser system has been in operation at several radioactive ion beam facilities.

Growth and lasing performance of a Tm,Y:CaF_2 crystal

A Tm3+ ion and Y3+ ion co-doped CaF2 crystal was grown and characterized, in which spectral and lasing performance was presented for the first time, to the best of our knowledge. Under diode end-pumping, in a continuous-wave regime, maximum output power of 453 mW was delivered under an absorption pump power of 2.5 W, corresponding to an optical-to-optical conversion efficiency of 17.9% and a slope efficiency of 21%. With a birefringent quartz plate, wavelength-tunable operation with a tunable range of more than 190 nm was realized. The results show that Tm,Y:CaF2 is a promising laser crystal operating in a spectral region ranging from 1850 nm to 2050 nm.

Vector optical field generation based on birefringent phase plate.

Vector optical field has recently gained interest in a variety of application fields due to its novel characteristics. Conventional approaches of generating vector optical fields have difficulties in forming highly continuous polarization and suffer from the issue of high energy utilization rates. In order to address these issues, in this study a single optical path was proposed to generate vector optical fields where the birefringent phase plate modulated a linear polarized light into a vector optical field, which was then demodulated to a non-uniform linear polarization distribution of the vector optical field by the polarization demodulation module. Both a theoretical model and numerical simulations of the vector optical field generator were developed, illustrating the relationship between the polarization distribution of the target vector optical field and the depth distribution of the birefringent phase plate. Furthermore, the birefringent phase plate with predefined surface distributions was fabricated by grayscale exposure and ion etching. The generated vector optical field was experimentally characterized, capable of producing continuous polarization with high light energy utilization ratio, consistent with simulations. This new approach may have the potential of being widely used in future studies of generating well-controlled vector optical fields.