Polarization Sagnac Interferometer Research Articles

Degenerate polarization entangled photon source based on a single Ti-diffusion lithium niobate waveguide in a polarization Sagnac interferometer

Combining a Ti-diffusion periodically poled lithium niobate (PPLN) waveguide with a Sagnac interferometer, two opposite directions type-II spontaneous parametric down conversions (SPDC) occur coherently and yield a high brightness, high stability polarization entanglement source. The source produces degenerate photon pairs at 1540.4 nm with a brightness of B = (1.36 ± 0.03) × 106 pairs/(s⋅nm⋅mW). We perform quantum state tomography to reconstruct the density matrix of the output state and obtain a fidelity of F = 0.983 ± 0.001. The high brightness and phase stability of our waveguide source enable a wide range of quantum information experiments operating at a low pump power as well as hold the advantage in mass production which can promote the practical applications of quantum technologies.

White-light channeled imaging polarimeter using Savart plates and a polarization Sagnac interferometer.

A Stokes white-light channeled imaging polarimeter using Savart plates and a polarization Sagnac interferometer (IPSPPSI) is presented, which provides an effective solution to the problem of channel aliasing in broadband polarimeters. The expression for the light intensity distribution and a method to reconstruct polarization information are derived, and an example design for an IPSPPSI is given. The results reveal that a complete measurement of the Stokes parameters in broad band can be achieved with a snapshot on a single detector. The use of dispersive elements like gratings suppresses broadband carrier frequency dispersion so the channels in the frequency domain do not affect each other, ensuring the integrity of information coupled across the channels. Furthermore, the IPSPPSI has a compact structure and does not employ moving parts or require image registration. It shows great application potential in remote sensing, biological detection, and other fields.

Elementary tripartite quantum communication photonic network at the telecom wavelength

An elementary tripartite quantum communication network for discrete variables is proposed. In this network three nodes are quantum wired with quantum channel created by a pair of Greenberger–Horne–Zeilinger (GHZ) triplet. We show that in this network by local operations and classical communication an arbitrary two-qubit state can be deterministically teleported from any node to any other node. In this network tripartite teleportation of two-qubit state is achieved by first splitting the qubit into fragments and then at the destination, qubit is re-constructed from the fragments. A high flux source for generation of fully inseparable GHZ photonic quantum channel required for developing an ideal tripartite quantum network is presented. This GHZ source employ a group velocity matched periodically poled potassium titanyl phosphate crystal in pulsed polarization Sagnac interferometer configuration and is based on selecting a three-photon entangled state from the product state of an entangled photon pair and a weak coherent state. This GHZ source generates tripartite entangled photons at telecom wavelength (1584 nm). Genuine entanglement in the generated GHZ state is detected with a witness (W) operator. Complete detail of the experimental apparatus required for developing an ideal tripartite quantum communication photonic network, which employ fully inseparable quantum channel, is presented. This quantum network fully operates at wavelength 1584 nm, which occurs in the L-band of the technologically important third telecom window. Success probability for teleportation of two-qubit photonic state within the tripartite quantum network is determined. We show that such quantum network is experimentally feasible. Experimental procedure to unambiguously verify the teleportation of an arbitrary two-qubit photonic state within the network is discussed. It is shown that our scheme can be implemented in a programmed teleportation system and it paves the way towards a large-scale quantum network.

Dispersion-compensated polarization Sagnac interferometer with high imaging quality

Multistage diffraction of a dispersion-compensated polarization Sagnac interferometer (DCPSI) reduces the fringe visibility of interference fringes generated in a focal plane array, thereby leading to the poor quality of the reconstructed polarization images. In this paper, a double total reflection prism between the DCPSI and imaging lens is added to limit the effect of multistage diffraction and improve the imaging quality. First, the influence of multistage diffraction on the interference fringes and the ratio of fringe amplitude to the background was analyzed. Second, the range of angles of the two right angle prisms was calculated. Simulation and experiment were carried out to prove the superiority of the proposed method. Result shows that the ratio of fringe amplitude to the background increases from 1/5 to 1/3 and from 1/10 to 1/6 in simulation and experiment when a double total reflection prism structure is added respectively. This method can reduce the influence of multistage diffraction on interference fringes and improve the image quality of DCPSI effectively.

Gratings in dispersion-compensated polarization Sagnac interferometer

A dispersion-compensated polarization Sagnac interferometer (DCPSI) can obtain interference fringes, and then be applied to many fields. Using two identical blazed gratings in DCPSI, and the grating period of blazed gratings should be considerably larger than the wavelength, which means that the grating period has its limitations and the different grating period will affect the quality of interference fringes. Aside from the grating period, the influence of other parameters on the interference fringe is also considered, such as substrate thickness and blaze angle. Kudenov theory is recalculated from the grating equation without any approximation to reveal the limitation of the grating period. Substrate thickness and the blaze angle of the grating are then investigated. The influence of the grating parameters on interference fringes is finally confirmed through simulation and experiment. The results of this study are important for guiding researchers in choosing gratings to obtain clear interference fringes.

Quantum interferometric generation of polarization entangled photons

Quantum interference, like Hong-Ou-Mandel interference, has played an important role to test fundamental concepts in quantum physics. We experimentally show that the multiple quantum interference effects enable the generation of high-performance polarization entangled photons. These photons have a high-emission rate, are degenerate, have a broadband distribution, and are postselection free. A quantum interferometric scheme, based on a round-trip configuration of a double-pass polarization Sagnac interferometer, makes it possible to use the large generation efficiency of polarization entangled photons in the process of parametric down-conversion and to separate degenerate photon pairs into different optical modes with no requirement of postselection. We demonstrate experimentally that multiple quantum interference is not only an interesting fundamental quantum optical phenomenon but can be used for novel photonic quantum information technologies.

Polarization Sagnac interferometer with reflective grating for white-light channeled imaging polarimeter

The white-light channeled modulated snapshot polarization imaging technique can simultaneously obtain targets with multiple Stokes parameters, it need not require image registration and has a simple structure. Hence, it attracts lots of attention in recent years. The theoretical analysis and experimental structure of a white-light channeled modulated snapshot polarization imaging technique are presented in this study. The core part of the instrument is only composed of three components with low cost, portable size and easy adjustment. Results has shown that the RMS between the measured and the theoretical value of normalized Stokes parameter is 0.0276. The outdoor experiment shows that the model can obtain S0, S2 and S3 in the target Stokes parameters in white-light.

Relationship between the difference of the two arms and spectral width of a dispersion-compensated polarization Sagnac interferometer

The difference of the two arms of a dispersion-compensated polarization Sagnac interferometer (DCPSI) may introduce additional shear distance in the shear distance generated by the equiangular DCPSI that will reduce the spectral width of DCPSI. The effects of interference fringes produced by DCPSI under different wavelengths were analyzed according to the relationship between fringe contrast and the period of interference fringes. The relationship of the difference of the two arms of the DCPSI and the width of the wavelength is presented. Under the condition that the DCPSI can generate interference patterns, this relationship only depends on the difference of the two arms but not the length of the arm. For our experimental structure, we have established the difference of the two arms that should be less than 60 μm and within the 400–700 nm range. This finding is consistent with the calculation results.

Spin-orbit beams for optical chirality measurement

Accurate measurement of chirality is essential for the advancement of natural and pharmaceutical sciences. We report here a method to measure chirality using non-separable states of light with geometric phase-gradient in the circular polarization basis, which we refer to as spin-orbit beams. A modified polarization Sagnac interferometer is used to generate spin-orbit beams wherein the spin and orbital angular momentum of the input Gaussian beam are coupled. The out-of-phase interference between counter-propagating Gaussian beams with orthogonal spin states and lateral-shear or/and linear-phase difference between them results in spin-orbit beams with linear and azimuthal phase gradient. The spin-orbit beams interact efficiently with the chiral medium, inducing a measurable change in the center-of-mass of the beam, using the polarization rotation angle and hence the chirality of the medium are accurately calculated. Tunable dynamic range of measurement and flexibility to introduce large values of orbital angular momentum for the spin-orbit beam, to improve the measurement sensitivity, highlight the techniques' versatility.

Elimination of error induced by a beam splitter substrate for a dispersion-compensated polarization Sagnac interferometer.

A wire grating beam splitter (WGBS) substrate in a dispersion-compensated polarization Sagnac interferometer (DCPSI) may introduce an additional shear distance in the shear distance generated by the DCPSI, thereby causing poor adaptability of the DCPSI to white light. This work applies a compensation scheme of an optical flat with the same material and thickness as the WGBS and parallel to the WGBS introduced in the other arm of the DCPSI. Theoretically, this method can decrease the additional shear distance approaching 0. The ideal shear distance in the simulation experiment is 5.86mm, and the shear distance before and after compensation is 5.40 and 5.86mm, respectively. The theoretical value of the additional shear distance in this experiment is -0.6625 mm, and the average compensation value is 0.66mm. Overall, experiment and simulation results indicate that the above method can effectively eliminate the additional shear distance.

Non-coaxial superposition of vector vortex beams.

Vector vortex beams are classified into four types depending upon spatial variation in their polarization vector. We have generated all four of these types of vector vortex beams by using a modified polarization Sagnac interferometer with a vortex lens. Further, we have studied the non-coaxial superposition of two vector vortex beams. It is observed that the superposition of two vector vortex beams with same polarization singularity leads to a beam with another kind of polarization singularity in their interaction region. The results may be of importance in ultrahigh security of the polarization-encrypted data that utilizes vector vortex beams and multiple optical trapping with non-coaxial superposition of vector vortex beams. We verified our experimental results with theory.

Determination of surface roughness of plane optical components using quasimonochromatic light source and phase shifting interferometry

A differential interferometric technique for the measurement of surface roughness of plane optical surfaces is proposed. A polarization Sagnac interferometer, placed in the image space of a reflection microscope system with linearly polarized, spatially coherent, quasimonochromatic incident beam illumination, splits the image-forming beam from a plane test surface (TS) into laterally sheared (LS) linear orthogonal components. The LS components interfere when brought to the same state of polarization. The optical path difference (OPD) variation along the direction of lateral shear is a measure of the slope variation on the TS. Polarization phase shifting interferometry has been applied to extract the OPD variation and thus the slope distribution, slope errors, and, subsequently, height errors. System error contribution is eliminated by combining height error data obtained for parallel sections of the TS that lie along a section of the image field parallel to the direction of lateral shear, as the TS is shifted in a direction normal to the lateral shear direction between the data capture. Results obtained for an aluminized plane polished TS are presented.

Fabrication of elliptic microfibers with CO2 laser for high-sensitivity refractive index sensing.

We propose a convenient method for achieving highly birefringent (HiBi) elliptic microfibers by use of the CO2-laser machining and the flame-brushing techniques. With optimization of fabrication process, a high birefringence of up to 2.10×10(-2) is experimentally obtained. Especially, within a polarization Sagnac interferometer acting as a refractive index (RI) sensor, both positive and abnormal negative sensitivity is measured, dependent on the geometrical variables of the HiBi microfiber. The maximum RI sensitivity is ∼195,348 nm/RI-unit around RI=1.35887, which is the highest among the microfiber devices as reported, to our knowledge.

Determination of the surface form error of a spherical mirror with phase shifting Sagnac interferometer.

A polarization Sagnac interferometer (SI) is used to produce two laterally separated, identical, convergent emergent beams with linear orthogonal polarizations. The emergent p-polarized and s-polarized beams converge toward their respective focal points. The test and reference spherical mirrors are placed at confocal positions with respect to the s and p focal points so as to normally reflect back the test and reference beams through the SI that recombines the test and reference waves. Polarization phase shifting interferometry is applied to obtain the surface form error of the test surface with respect to the reference surface. A two-step measurement procedure eliminates the system aberrations. Results obtained for a concave spherical test surface with respect to a convex spherical reference surface are presented. The optical configuration is relatively less susceptible to external mechanical vibration.

Adjustable and robust methods for polarization-dependent focusing

We present two methods for the precise independent focusing of orthogonal linear polarizations of light at arbitrary relative locations. Our first scheme uses a displaced lens in a polarization Sagnac interferometer to provide adjustable longitudinal and lateral focal displacements via simple geometry; the second uses uniaxial crystals to achieve the same effect in a compact collinear setup. We develop the theoretical applications and limitations of our schemes, and provide experimental confirmation of our calculations.

White-light Sagnac interferometer for snapshot multispectral imaging

The theoretical and experimental demonstration of a multispectral Sagnac interferometer (MSI) is presented. The MSI was created by including two multiple-order blazed diffraction gratings in both arms of a standard polarization Sagnac interferometer (PSI). By introducing these high-order diffractive structures, unique spectral passbands can be amplitude modulated onto coincident carrier frequencies. Extraction of the modulated multispectral images, corresponding to each passband, is accomplished within the Fourier domain. This yields a unique multispectral sensor capable of imaging all the passbands in a single snapshot. First, the theoretical operating principles of a PSI are discussed to provide a context for the MSI. This is followed by the theoretical and experimental development of the MSI, which is an extension of a dispersion-compensated PSI. Indoor and outdoor testing and validation of the MSI are performed by observing vegetation, demonstrating the ability of our experimental setup to detect four distinct spectral passbands.

White light Sagnac interferometer for snapshot linear polarimetric imaging

The theoretical and experimental demonstration of a dispersion-compensated polarization Sagnac interferometer (DCPSI) is presented. An application of the system is demonstrated by substituting the uniaxial crystal-based Savart plate (SP) in K. Oka's original snapshot polarimeter implementation with a DCPSI. The DCPSI enables the generation of an achromatic fringe field in white-light, yielding significantly more radiative throughput than the original quasi-monochromatic SP polarimeter. Additionally, this interferometric approach offers an alternative to the crystal SP, enabling the use of standard reflective or transmissive materials. Advantages are anticipated to be greatest in the thermal infrared, where uniaxial crystals are rare and the at-sensor radiance is often low when compared to the visible spectrum. First, the theoretical operating principles of the Savart plate polarimeter and a standard polarization Sagnac interferometer polarimeter are provided. This is followed by the theoretical and experimental development of the DCPSI, created through the use of two blazed diffraction gratings. Outdoor testing of the DCPSI is also performed, demonstrating the ability to detect either the S(2) and S(3), or the S(1) and S(2) Stokes parameters in white-light.

Experimental test of nonlocal realism using a fiber-based source of polarization-entangled photon pairs

We describe an experimental test of local realistic and nonlocal realistic theories using polarization-entangled two-photon singlet states created using a fiber-based polarization Sagnac interferometer. We show a violation of Bell's inequality in the Clauser-Horne-Shimony-Holt form by 15 standard deviations, thus excluding local hidden-variable theories, and a violation of a Leggett-type nonlocal hidden-variable inequality by more than three standard deviations, thus excluding a class of nonlocal hidden-variable theories.

High-visibility interferometric measurement of the diffraction phase

We obtain the absolute phase in Fresnel diffraction for Gaussian beams by using a modified polarization Sagnac interferometer in which counterpropagating paths are spatially separated and labeled according to polarization. By erasing the polarization "which-path" information with an analyzing polarizer situated after the modified interferometer, we are able to regain interference and to precisely control the relative intensities of the diffracted and the reference beams. The resulting optimized visibility allows for a precise phase determination. This setup is very stable, requiring no active elements.

A wavelength-tunable fiber-coupled source of narrowband entangled photons

We demonstrate a wavelength-tunable, fiber-coupled source of polarization- entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs (s mW nm)(-1), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T = 0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular geometry of the setup, the signal and idler wavelengths can be tuned over a wide range without loss of entanglement.