Design of a photonic crystal fiber polarization beam splitter with simple structure and ultra-wide bandwidth

A novel polarization beam splitter(PBS)based on dual-core photonic crystal fiber(DC-PCF)is proposed in this work.The proposed DC-PCF PBS contains two kinds of lattices and three kinds of air holes to form the asymmetrical elliptic dual-core structure.By using the full-vector finite element method,the propagation characteristics of the proposed DC-PCF PBS are investigated.The simulation results show that the bandwidth of the proposed DC-PCF PBS can reach to 340 nm,which covers the S+C+L+U communication bands,the shortest splitting length is 1.97 mm,and the maximum extinction ratio appears near wavelength 1550 nm.Moreover,the insertion loss of the proposed DC-PCF PBS is very low.It is believed that the proposed DC-PCF PBS has important applications in the field of all-optical communication and network.

An Ultra-Compact Broadband Polarizing Beam Splitter Utilizing Hybrid Plasmonic Waveguide

Polarizing beam splitter has rather significant applications in polarization diversity circuits and polarization multiplexing systems.In this paper,we present an asymmetric polarizing beam splitter utilizing hybrid plasmonic waveguide.The special hybrid structure with a hybrid waveguide and a dielectric waveguide can limit the energy of TE and TM modes to a different layer.Therefore,we can achieve beam splitting by adjusting the corresponding parameters of the two waveguides.First,we studied the influences of different structure parameters on the real part of the effective mode refractive index of the two waveguides,and obtained a set of parameters that satisfy the condition of strong coupling of TM mode and weak coupling of TE mode.Then,the performance of our proposed polarizing beam splitter is evaluated numerically.The length of the coupling section is only 4.1μm,and the propagation loss of TM and TE modes is 0.0025 d B/μm and 0.0031 d B/μm respectively.Additionally,the extinction ratios of TM and TE modes are 10.62 d B and 12.55 d B,respectively.Particularly,the proposed device has excellent wavelength insensitivity.Over the entire C-band,the fluctuation of the whole normalized output power is less than 0.03.In short,our proposed asymmetric polarizing beam splitter features ultra-compactness,low propagation loss,and broad bandwidth,which would provide promising applications in polarization multiplexing system and polarization diversity circuits relevant to optical interconnection.

Novel Even Beam Splitters Based on Subwavelength Binary Simple Periodic Rectangular Structure

In this paper, a novel method of a subwavelength binary simple periodic rectangular structure is presented to realize even beam splitting by combining the rigorous couple-wave analysis with the genetic algorithm. Several even splitters in the terahertz region were designed and one of the silicon-based beam splitters designed to separate one incident beam into four emergent beams has total efficiency up to 92.23 %. Zero-order diffraction efficiency was reduced to less than 0.192 % and the error of uniformity decreased to 6.51 9 10-6. These results break the limitation of even beam splitting based on the traditional scalar theory. In addition, the effects of the incident angle, wavelength, as well as the polarizing angle on the diffraction efficiency and uniformity were also investigated.

Optimal design of sub-wavelength metal rectangular gratings for polarizing beam splitter based on effective medium theory

A novel optimal design of sub-wavelength metal rectangular gratings for the polarizing beam splitter （PBS） is proposed. The method is based on effective medium theory and the method of designing single layer antireflection coating. The polarization performance of PBS is discussed by rigorous couple-wave analysis （RCWA） method at a wavelength of 1550 nm. The result shows that sub-wavelength metal rectangular grating is characterized by a high reflectivity, like metal films for TE polarization, and high transmissivity, like dielectric films for TM polarization. The optimal design accords well with the results simulated by RCWA method.

Performance measurement of broadband, wide-angle polarizing beam splitter

Polarizing beam splitter (PBS) is a critical optical component in projection display system because PBS performance greatly influences the contrast and brightness of the system. PBS performance is usually measured by spectrophotometer after coating and cementing, but the measured result cannot represent the actual performance in practice because people usually change the incident angle in one plane (horizontal plane) and do not consider the other plane (vertical plane). Geometrical polarization rotation occurring at reduced F-number influences the measuring precision of s-polarization transmittance (Ts) and p-polarization reflectance (Rp). A more accurate and practical way to measure the performance of broadband, wide-angle PBS is presented in this paper.

Designing of a polarization beam splitter for the wavelength of 1310 nm on dual-core photonic crystal fiber with high birefringence and double-zero dispersion

We have proposed a novel kind of photonic crystal fiber which contains two asymmetric cores. The bireti＇ingence and the dispersion are numerically analyzed based on finite element method when the size of the air holes and the pitch of two adjacent air holes are changed. It is shown that the proposed photonic crystal fiber has high birefringence up to the order of 10-2 and double-zero dispersion points are at the wavelengths of 1310 nm and 800 rim, simultaneously. At the same time, the normalized power and the extinction ratios of the proposed photonic crystal fiber have been simulated. It is demonstrated that, at the wavelength of 1310 rim, the x-polarized mode and the y-polarized mode are separated when the propagation distance is 2.481 ram.

Demonstration of a cold atom beam splitter on atom chip

We report an experimental demonstration of a new scheme to split cold atoms on an atom chip. The atom chip consists of a U-wire and a Z-wire. The cold atom cloud is initially loaded and prepared in the Z-trap, which is split into two separate parts by switching on the current of the U-wire. The two separate atom clouds have a distance more than one millimeter apart from each other and show almost symmetrical profiles, corresponding to about a 50/50 splitting ratio.

Security of quantum key distribution using two-mode squeezed states against optimal beam splitter attack

For the beam splitter attack strategy against quantum key distribution using two-mode squeezed states, the analytical expression of the optimal beam splitter parameter is provided in this paper by applying the Shannon information theory. The theoretical secret information rate after error correction and privacy amplification is given in terms of the squeezed parameter and channel parameters. The results show that the two-mode squeezed state quantum key distribution is secure against an optimal beam splitter attack.

Maximal entanglement from photon-added nonlinear coherent states via unitary beam splitters

In this paper, we construct photon-added f-deformed coherent states （PAf-DCSs） for nonlinear bosonic fields by discussing Klauder＇s minimal set of conditions required to obtain coherent states. Using this set of nonlinear states, we propose a very useful scheme for generating the maximal amount of entanglement via unitary beam splitters for different strength regimes of the input field α, deformation q and excitation number m. Therefore, the possibility to create highly entangled states and to control the entanglement is proposed. Moreover, the condition for a maximal and separable output beam state is obtained. Finally, we examine the statistical properties of the PAf-DCSs through the Mandel parameter and exploit a connection between this quantity and the behavior variation of the output state entanglement. Our result may open new perspectives in different tasks of quantum information processing.

Broadband non-polarizing beam splitter based on guided mode resonance effect

A broadband non-polarizing beam splitter （NPBS） operating in the telecommunication C＋L band is designed by using the guided mode resonance effect of periodic silicon-on-insulator （SOI） elements. It is shown that this double layer SOI structure can provide ~50/50 beam ratio with the maximum divergences between reflection and transmission being less than 8% over the spectrum of 1.4μm-l.7 μm and i% in the telecommunication band for both TE and TM polarizations. The physical basis of this broadband non-polarizing property is on the simultaneous excitation of the TE and TM strong modulation waveguide modes near the designed spectrum band. Meanwhile, the electric field distributions for both TE and TM polarizations verify the resonant origin of spectrum in the periodic SOI structure. Furthermore, it is demonstrated with our calculations that the beam splitter proposed here is tolerant to the deviations of incident angle and structure parameters, which make it very easy to be fabricated with current IC technology.

A novel optical beam splitter based on photonic crystal with hybrid lattices

A novel optical beam splitter constructed on the basis of photonic crystal（PC） with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process

Dual-function beam splitter of high contrast gratings

we preset the design and rabrication of a novel auai-iunction hign contrast gratings that can De usea as a polarizationselective beam splitter with transverse magnetic polarization,which performs two independent functions,i.e.,reflection focusing and power equalization at a wavelength of 1550 nm.This dual-function grating profile is optimized by the rigorous coupled-wave analysis and the finite-element method.Simple analytical expressions of phase and modal guideline for the beam splitter design are given.The beam splitter based on the grating structure is experimentally studied at a distance of 160 μm from the reflection plane,the results are consistent with the theoretical results basically.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

Designing analysis of the polarization beam splitter in two communication bands based on a gold-filled dual-core photonic crystal fiber

We design a novel kind of polarization beam splitter based on a gold-filled dual-core photonic crystal fiber （DC-PCF）. Owing to filling with two gold wires in this DC-PCF, its coupling characteristics can be changed greatly by the second-order surface plasmon polariton （SPP） and the resonant coupling between the surface plasmon modes and the fiber-core guided modes can enhance the directional power transfer in the two fiber-cores. Numerical results by using the finite element method show the extinction ratio at the wavethlengths of 1.327 μm and 1.55 μm can reach -58 dB and -60 dB and the bandwidths as the extinction ratio better than -12 dB are about 54 nm and 47 nm, respectively. Compared with the gold-unfilled DC-PCF, a 1.746-mm-long gold-filled DC-PCF is better applied to the polarization beam splitter in the two communication bands of λ = 1.327 μm and 1.55 μm.

Second-order temporal interference of two independent light beams at an asymmetrical beam splitter

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman＇s path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.

A Kind of Three-Mode Entangled States of Continuum Variables Generated by Beam Splitter and Parametric Down-Conversion Amplifier

In 3-mode Fock space we find a new tripartite entangled state |α,γ 】 λ,which make up a new quantum mechanical representation. The state |α,γ 】 λ, can be generated byusing the setup composing of a beam splitter and a parametric down-conversion amplifier. Applicationof the state is briefly discussed.

Ultra-thin anisotropic transmitting metasurface for polarization beam splitter application

We report a polarization beam splitter based on phase gradient metasurface for microwave frequency region.The metasurface is constructed by anisotropic cells with independent phase response for differently-polarized waves.Through putting different gradient phases for orthogonally-polarized waves on a focusing metasurface,the anisotropic sample has the ability to enhance gain and split orthogonally-polarized waves.The simulation results indicate that the incident spherical waves are converted into plane waves and split into an x-polarized wave with a refraction angle of-24° and a ypolarized wave with a refraction angle of 37.6° in the y direction.For verification,a metasurface sample with a size of 102.5 mm x 102.5 mm is fabricated and measured.The consistence between numerical and experimental results validates the improved gain of 10.5-dB against the feed source and the splitting effect.Moreover,the thickness of the proposed metasurface is 3 mm which is ultra-thin against the wavelength at 15 GHz.The proposed prescription opens a new route to the applications of anisotropic metasurface in microwave band.

Terahertz Wave Polarization Beam Splitter Using Asymmetrical Coupler

This study has proposed and numerically demonstrated a compact terahertz wave polarization beam splitter. The splitter is built by using a asymmetrical directional coupler consisting of a bend waveguide and a slot bend waveguides and achieves a high extinction ratio of 24.88 dB and 16.55 dB for cross and through ports. The optimal coupling region length is found to be 26 ttm. By using such a polarization beam splitter, the size of the terahertz wave system could he reduced significantly. The simulation results show that the designed polarization beam splitter can split TE- and TM-polarized terahertz wave into different propagation directions with high efficiency over the terahertz wave frequency range from 9.40 THz to 9.65 THz. The device obtained is readily used for a polarization diversity terahertz wave integrated circuit field, particularly for platforms with slot waveguide.

Attacking a high-dimensional quantum key distribution system with wavelength-dependent beam splitter

The unconditional security of quantum key distribution(QKD) can be guaranteed by the nature of quantum physics.Compared with the traditional two-dimensional BB84 QKD protocol, high-dimensional quantum key distribution(HDQKD) can be applied to generate much more secret key.Nonetheless, practical imperfections in realistic systems can be exploited by the third party to eavesdrop the secret key.The practical beam splitter has a correlation with wavelength,where different wavelengths have different coupling ratios.Using this property, we propose a wavelength-dependent attack towards time-bin high-dimensional QKD system.What is more, we demonstrate that this attacking protocol can be applied to arbitrary d-dimensional QKD system, and higher-dimensional QKD system is more vulnerable to this attacking strategy.

Single-Photon Interaction with Beam Splitters

The production of maxima and minima by the superposition of two or more light signals provides fundamental support for the wave nature of light. This result is based on the study of wave interference phenomena which remains the only approach to explain the production of those maxima and minima. In a system that is prepared to work with only one photon at a time, any detector can signal only one or zero. In 1986, a rigorously controlled experiment was designed by Grangier, G. Roger, and A. Aspect, [Europhys Lett. 1(4), p. 173, 1986] that guaranteed a single-photon beam. The explanation of the experimental results implied the interference of the wave function of a single-photon with itself. Thus, the explanation of interference that is accepted for an ensemble of photons was assumed to be valid for a single photon. In this study, we prepare a Mach-Zehnder interferometer using the same type of beam splitters used by Grangier et al. to test the assumption mentioned above. Our results allow us to explain the results of Grangier et al. because of the interaction between light and the beam splitters. Our results also verify that their wave interpretation of the results is not valid. Here, we present the essential findings of the extensive experimental evidence that supports our ideas.