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Tenth International Conference on Information Optics and Photonics

Optical parametric loop mirror with adjustable reflectivity by using tunable optical attenuators

Nannan Liu, Zhipeng Kong, Zhenming Dou, Kun Yang

Published Dec 15, 2022• 0 citations
Publisher

Abstract

We propose an optical parametric loop mirror whose reflectivity is adjustable by setting two tunable optical attenuators in Sagnac loop. The scheme of the optical parametric loop mirror is consisted of a nonlinear four wave mixing medium, a dispersive element, two optical attenuators, and a beam splitter. The generated four wave mixing wave can be totally separated from signal and pumps no matter how the beam splitter ratio is. When the beam splitter ratio is more than 0.5, we can separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the first attenuator, and when the beam splitter ratio is less than 0.5, we can also separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the second attenuator. Our research can help to generate and separate frequency degenerate twin beams in experiment.

DOI
10.1117/12.2654616

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We propose an optical parametric loop mirror whose reflectivity is adjustable by setting two tunable optical attenuators in Sagnac loop. The scheme of the optical parametric loop mirror is consisted of a nonlinear four wave mixing medium, a dispersive element, two optical attenuators, and a beam splitter. The generated four wave mixing wave can be totally separated from signal and pumps no matter how the beam splitter ratio is. When the beam splitter ratio is more than 0.5, we can separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the first attenuator, and when the beam splitter ratio is less than 0.5, we can also separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the second attenuator. Our research can help to generate and separate frequency degenerate twin beams in experiment.
Using a Sagnac fiber loop functions as a deterministic splitter of photon pairs produced by the frequency degenerate four wave mixing, we show that the background noise of the degenerate photon pairs is contributed by both Raman scattering and frequency non-degenerate four wave mixing. To improve the purity of photon pairs in the high gain regime, in addition to suppressing the noise photons by cooling the nonlinear fiber and by optimizing the detuning between the frequencies of the pump and photon pairs, the walk-off effect of the two pulsed pump fields should be mitigated by managing the dispersion of the fiber. Our investigation is not only the first step towards the generation of multi-mode squeezed vacuum in fiber optical parametric amplifiers pumped with pulsed lights, but also contributes to improving the purity of the fiber sources of degenerate photon pairs.
Degenerate correlated photon pairs (DCPPs) have been widely used in quantum information science,especially in the areas of quantum computation,quantum state control and precision measurement,which are typically generated in a (2) nonlinear crystal through the spontaneous parametric down-conversion.However,such a source is not compatible with optical fiber as large coupling losses occur when the pairs are launched into it,which restricts its direct application to quantum information processing system.More recently,DCPP generation from spontaneous four-wave mixing in (3) optical fiber has aroused strong interest,due to its advantages of compatibility with existing fiber networks and free of alignment.The process of generating DCPP in fiber can be described as follows:two pump photons at different frequencies p1 and p2 scatter through the (3) nonlinearity to create a pair of identical photons at the mean frequency c,such that p1+p2=2c.Because the collinear tensor component xxxx(3) in a Kerr nonlinear medium is 3 times as large as the tensor component xyxy(3),the co-polarized four-wave mixing is preferred,which means the two pump photons and new-born twin photons are both co-polarized.Therefore,it is very challenging to deterministically separate the fiber-based DCPP,since the twin photons share the same properties in all degrees of freedom:frequency,polarization and spatial.Sagnac fiber loop (SFL),composed of a piece of nonlinear fiber and 50/50 coupler,is presented as the splitter for DCPP based on the reversed Hong-Ou-Mandel quantum interference of counter-propagating DCPPs.The SFL can be configured as a total reflector,total transmitter or equally transmissive and reflective state,which sets the differential phases of counter-propagating DCPPs meeting at 50/50 coupler to be ,0 and -,respectively.In order to satisfy the differential phase requirement for completely splitting the DCPP,the SFL is always set to be equally transmissive and reflective state,however,the polarization-mode matching of counter-propagating DCPPs is not easily achieved due to the disturbance of fiber birefringence.According to the Jones matrix derivation of DCPP propagating in the SFL,the polarization mode of counter-propagating DCPPs when interference at 50/50 coupler is automatically matched,if the SFL is set as a total reflector or total transmitter.In experimental scheme,utilizing the SFL as a total reflector,the 1.1 nm bandwidth and 1544.53 nm central wavelength DCPPs are generated by two pulsed light beams pumping the 300 m dispersion-shifted fiber in the SFL.Using the two pieces of single mode fiber connecting the 300 m dispersion-shifted fiber and 50/50 coupler,whose length difference is fixed at 3.3 m,the differential phase of counter-propagating DCPPs highly dependent on the dispersion properties of single mode fiber is managed at 2 for fully distributing DCPPs into which degrades the fidelity of DCPP source.The measured ratio of coincidence to accidental-coincidence of DCPPs from one port is approximately 1.8:1,which indicates that the coincidence counts mainly originate from accidental coincidence counts and extra coincidence counts from photon bunching and there are not any DCPPs outputting from one port.Meanwhile,the ratio of best measured coincidence to accidental-coincidence of DCPPs from two ports reaches 47:1,when the average power of two pumps is fixed at 0.026 mW.The experimental results demonstrate that the high purity and fully spatial separation DCPPs are successfully prepared in optical fibers,which is a very useful tool for realizing various quantum information systems.How the spatial state of outputting DCPPs depends on the length difference between single-mode fiber and detuning wavelength is also discussed in detail.
In order to improve the phase sensitivity of nonlinear Sagnac interferometer, a nonlinear Sagnac fiber optic interferometer based on feedback control is designed to improve the phase sensitivity by introducing a feedback control loop into the nonlinear Sagnac interferometer. This design adopts the composite feedback control structure of Nonlinear Beam Splitter (NBS) and Linear Beam Splitter (BS). By adjusting the reflectivity of the Linear Beam Splitter, the intensity of the feedback signal can be effectively changed to regulate the phase sensitivity of the interferometer. The feedback amplified signal light passes through the Sagnac fiber optic ring before being processed by a second NBS for quantum enhancement to further improve the phase sensitivity of the interferometer. The simulation results show that the phase sensitivity of the interferometer with certain feedback strength is better than that without feedback. Especially when the phase difference is π, the phase sensitivity of the interferometer with low and medium feedback strengths is improved by 33.3% and 28.9% respectively; In addition, the gain coefficient of the NBS is a key parameter affecting the performance of the interferometer, and a suitable gain coefficient can further optimize the phase sensitivity of the interferometer.
A passive phase conjugate mirror based on four-wave mixing in an optical ring cavity is described. Unlike previously demonstrated passive phase conjugate mirrors it generates only one of its pumping beams by nonlinear optical interactions, the other being provided by feedback of the probe after transmission through the nonlinear medium. The results of a theory yielding phase conjugate reflectivity and oscillation thresholds are presented together with an experimental demonstration of phase conjugation in barium titanate and strontium barium niobate. The device is self-starting by four-wave mixing, and has an oscillation threshold lower than that of other previously demonstrated passive phase conjugate mirrors with similar ease of alignment. The operation of a device which generates nonconjugate oscillation beams is also reported.
Four wave mixing, a third-order optical parametric process, is the nonlinear optical process in which four waves interact with each other through the third-order optical nonlinearity. In this process, three waves form a nonlinear polarization at the frequency of the fourth wave. An important application of degenerate four wave mixing is the generation of phase conjugate wave or simply the phase conjugation. The phase conjugate wave has the same wavefront as the incident wave; however, it propagates backward. The phase conjugation is equivalent to the time reversal. Straightforward application of the time reversal is the correction of phase aberration. Suppose that, the incident wave propagates in the nonuniform medium, such as a laser amplifier, where the temperature is fluctuated by intense pumping. Then, the incident wave suffers severe phase aberration during the propagation and the transmitted wave is then reflected by the phase conjugate mirror and goes back into the same nonuniform medium.