Design of form-birefringent multilayer nonpolarizing beam splitter

Nonpolarizing beam splitters, which are based on the form birefringence of subwavelength multilayer binary gratings, have been proposed. The design is based on effective-medium theory and thin-film theory. Rigorous coupled-wave analysis is used to optimize the design of this nonpolarizing beam splitter. The simulation shows that the structure can eliminate polarization effect and provide high reflectivity.     

Photonic crystal beam splitters

In this work, the beam splitter with two input ports and two output ports in two-dimensional photonic crystals is studied through the finite-difference time-domain method. The beam splitter consists of two orthogonally cross line defects. The diameter of the two diagonal air holes at the intersection of the two line defects was modified. The input light can be identically divided into the two output ports. The beam splitters can be applied in the photonic crystal Mach-Zehnder interferometers or photonic crystal optical switches.     

Achromatization of Wollaston polarizing beam splitters

We describe the achromatization of Wollaston prisms to reduce the angular dispersion in the splitting angle. Analytical theory and ray-tracing modeling is presented. In an example application, a sixfold reduction in dispersion is achieved for wavelengths in the region 400 nm to 1.7 μm. Experimental proof of concept is demonstrated, and in an example application, the spectral dispersion of extended images recorded through cascaded Wollaston prisms is shown to be reduced by an order of magnitude.     

Designs of infrared non-polarizing beam splitters

When used at oblique angles of incidence, the reflectance and transmittance of thin films exhibit strong polarization effects (PEs), particularly for the films inside a glass cube, which result from the fact that the tangential components of the electric and magnetic fields are continuous across each layer interface. However, for many applications, the PEs are undesirable and should be reduced. Therefore, the concept of non-polarizing beam splitter (NPBS) is proposed. Up till now, however, most of the reports of NPBSs are suitable for visible light. Therefore, it is necessary to find out some methods to reduce the PEs for infrared applications. A design method of the infrared NPBS in a cube is proposed, the theoretical analysis is given, designs for different substrates are demonstrated and the simulations of their optical properties are presented in this paper.     

Four-photon interference with asymmetric beam splitters

Two experiments of four-photon interference are performed with two pairs of photons from parametric downconversion with the help of asymmetric beam splitters. The first experiment is a generalization of the Hong-Ou-Mandel interference effect to two pairs of photons while the second one utilizes this effect to demonstrate a four-photon de Broglie wavelength of lambda/4 by projection measurement.     

Quantum-enhanced interferometry with asymmetric beam splitters

In this paper,we investigate the phase sensitivities in two-path optical interferometry with asymmetric beam splitters.Here,we present the optimal conditions for the transmission ratio and the phase of the beam splitter to gain the highest sensitivities for a general class of non-classical states with parity symmetry.Additionally,we address the controversial question of whether the scheme with a combination of coherent state and photon-added or photon-subtracted squeezed vacuum state is better or worse than the most celebrated one using a combination of coherent state and squeezed vacuum state.     

Polarization beam splitters using polarization diffraction gratings

We report a polarization beam splitter that uses polarization gratings written onto a zero-twist nematic liquid-crystal display. We show three configurations. The first two separate the diffracted light into two orthogonally polarized orders that are either linearly or circularly polarized. In the third configuration, we demonstrate a novel case for which the output is separated into two nonorthonormal polarization states. One component is linearly polarized and the second is circularly polarized.     

偏光分束棱镜透射光强特性分析

偏光分束棱镜两出射光束的光强透射比会随入射角的改变而发生不同的变化,同时这种变化也会受设计角一定的影响。本文对它们的关系进行了分析。     

Polarization-independent self-collimating bends and beam splitters in photonic crystals

Polarization independent bends and beam splitters for transverse electric (TE) and transverse magnetic (TM) polarizations have been demonstrated in two-dimensional (2D) photonic crystals (PhCs). In virtuel of equi-frequency contour analysis and finite-difference time-domain calculations, self-collimation behaviors for TE- and TM-polarizations are achieved at the same frequency. Simulation results show a 90-degree bend with 90% efficiency and beam splitters with about 96% total efficiency for both TE- and TMpolarizations, where the light is self-guided by the self-collimation effect. Such bends and beam splitters are expected to play important roles in optical devices where polarization insensitivity is needed.     

近红外单光子探测器

该单光子探测器在实验中使用半导体制冷器制冷，雪崩二极管工作于盖革模式下，使用交流耦合方式提供门脉冲信号，通过延迟补偿和采样门控消除尖脉冲干扰，采用反馈门控减小后脉冲影响，优化电路参数减小暗计数.经实验测试与分析，温度在-62.5℃，门脉冲宽度为50ns，采样门控为10ns的条件下，最佳工作点的暗计数率小于4×10^-6ns^-1，量子效率约18%，噪声等效功率为2.4×10^-19W/Hz^1/2.     

金属-电介质复合结构实现荧光远场增强

本文提出一种大尺度的金属-电介质复合微纳结构(银-硅结构),用于提高荧光生物检测的灵敏度及解决荧光物质距离结构远场范围时荧光增强的近场局限。这种大尺度的金属-电介质复合微纳结构与之前的金属-电介质复合微纳结构不同,其通过光的散射和干涉实现了荧光物质距离结构远场范围时的荧光增强。在本文中,通过采用时域有限差分法,主要从荧光激发和荧光发射两个过程研究银-硅结构。结果表明,在激发过程中,银-硅结构的荧光强度高于玻璃结构且位于银-硅结构两柱之间的狭缝中的电场分布比金属结构(银结构)更均匀,因此在银-硅结构中可以实现荧光增强,而且分子运动行为的检测更准确。在发射过程中,当荧光纳米粒子距离结构远场范围内时,与玻璃相比,银-硅结构可以实现更好的荧光增强效果。利用银-硅结构实现荧光增强的机理是光的散射和干涉,荧光被银膜向上散射,同时,结构两侧的银/硅柱也散射一部分荧光,荧光相互干涉传播至远场实现荧光增强。此外,银-硅结构易于制备和集成。因此,其可以很好地应用于生物传感领域。     

Binary diffractive beam splitters with arbitrary diffraction angles

Diffractive optical beam splitters designed with iterative Fourier transform type algorithms can produce only certain diffraction angles given by the spatial frequencies used for the computations, which are multiples of a certain base spatial frequency. We have developed a design algorithm that overcomes this limitation and can be used to compute binary diffractive elements with arbitrary diffraction angles. The simulated and experimentally measured properties of optical elements producing beam arrays in circular arrangements are presented and discussed.     

红外探测装置中光谱分光镜的设计与制备

在红外探测装置中,光谱分光镜是用来把3 μm～5 μm和8 μm～12 μm 2个波段的光谱分开的零件.介绍了一种在通用镀膜机上制备光谱分光镜的新工艺.在该膜系的设计过程中,把Willey公式引入到对其平均透过率最高值进行估算的过程中,同时针对国产镀膜机控制精度不高的特点,尽量使用规整膜层进行设计.为了进一步提高8 μm～12 μm波段的透过率,在膜系的最外侧引进了一层自行配制的低折射率氟化物材料,制备出了符合技术指标的红外光谱分光镜.     

Planck spectroscopy and quantum noise of microwave beam splitters

We use a correlation function analysis of the field quadratures to characterize both the blackbody radiation emitted by a 50 Ω load resistor and the quantum properties of two types of beam splitters in the microwave regime. To this end, we first study vacuum fluctuations as a function of frequency in a Planck spectroscopy experiment and then measure the covariance matrix of weak thermal states. Our results provide direct experimental evidence that vacuum fluctuations represent the fundamental minimum quantum noise added by a beam splitter to any given input signal.     

基于耦合波理论设计偏振分束光栅

亚波长周期结构光栅具有传统光栅所不具有的特殊性质。针对通信中常用的1.55μm光波,采用严格耦合波理论分析了亚波长光栅的偏振分光特性,设计了对应的偏振分束光栅。所设计的光栅在入射角为56°时,透射消光比和反射消光比都大于9000,且在1.27μm~1.67μm全光波段内,入射角在51°~57°之间时,透射消光比和反射消光比都大于100,达到了宽带宽、宽角度以及透射消光比和反射消光比都较高的要求。     

New designs and characteristics analysis of non-polarizing beam splitters

When used at oblique angles of incidence, the reflectance and transmittance of thin films exhibit strong polarization effects, particularly for the films inside a glass cube, which results from the fact that the tangential components of the electric and magnetic fields are continuous across each layer interface. However, for many applications, the polarization effects are undesirable and should be reduced. In the present paper, a method for designing a non-polarizing beam splitter (NPBS) in a cube is introduced, based on the Brewster condition. Applied examples of the NPBSs designed employing this method are also researched within specified wavelength ranges. Moreover, the effects of some important parameters, including the incident angle and the material indices, on the NPBS are investigated. Optical property simulations are presented.     

Atom interferometry with up to 24-photon-momentum-transfer beam splitters

We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Bordé (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel.     

Fabrication of pellicle beam splitters for optical bus application

The optical bus architecture for on-board applications requires a number of optical splitters with precise split ratios to route part of the input signal. Since hollow metal waveguide provides well collimated beams with very small gap loss, it opens the possibility of inserting discrete optical beam splitters (taps). The optical tap requires low excess loss, polarization insensitivity, temperature stability, minimized walk-off of the propagating beam, and cost effective manufacturing. By benefiting from the mature interference coating technology for polarization insensitivity and temperature stability, we design a pellicle beam splitter based on a static microelec tro-mechanical system (MEMS) and develop processes to fabricate pellicle splitters using wafer level bonding of silicon and glass substrates, with subsequent thinning to 20 μm. With the approaches described in this paper, we have demonstrated optical beam splitters with excess loss of less than 0.17 dB that operate at a data rate of 10 Gb/s showing a clean eye diagram while providing controlled split ratio and polarization insensitivity. We have demonstrated a high yielding MEMS based silicon processing platform which has the potential to provide a cost effective manufacturing solution for optical beam splitters.     

Photoresist Bragg gratings as beam splitters and beam reflectors for integrated optical systems

Based on the theory of coupled waves the diffraction efficiency (DE) of Bragg reflectors on planar glass waveguides is described for the case of obliquely incident waves. The coupling coefficients of the different types of mode conversion are determined both by a perturbational analysis and by fitting of the theoretical DE curves to the experimental data. Results on the fabrication and use of photoresist gratings on monomode glass waveguides as beam splitters and beam reflectors are given.