Optical Phase Conjugation Research Articles

랜덤하게 분포하는 RDPS의 분산 제어 광전송 링크에서의 시스템 성능 특성

Optical phase conjugation combining with dispersion management (DM) is promising technique to compensate for signal distortion due to group velocity dispersion (GVD) and nonlinear Kerr effects in optical communication systems. However the fixed residual dispersion per span (RDPS) usually used in the optical links with OPC and DM restricts the flexible link configuration. In this paper, OPC links combining DM of the randomly distributed RDPS is proposed for implementing the flexible optical transmission network. It is confirmed that the excellent compensation in the optical links with the randomly distributed RDPS is obtained, limiting the launch power of WDM channels to the relatively low. It is also confirmed that the relatively high launch power WDM channels are effectively transmitted through the optical links with the randomly distributed RDPS of averaged 50 - 100 ps/nm.

Study of optical phase conjugation in amorphous Znx–Sy–Se100−x−y chalcogenide thin films using degenerate four-wave mixing

Degenerate four-wave mixing (DFWM) experiment is performed to obtain light wavefront inversion (phase conjugation) in semiconducting chalcogenide thin films. Third order nonlinearity of amorphous Znx–Sy–Se100−x−y chalcogenide thin films using DFWM technique is studied at second harmonic of Nd:YAG laser. Influence of total input irradiance on phase conjugate signal is deliberated using log–log plot that has a slope of three and hence implies third order nonlinearity. The dependence of phase conjugate signal on forward beam and backward beam is also studied. The period of the grating formed by interference of forward and probe beam is determined. As the temporal overlapping and sample thickness conditions are satisfied, the third order nonlinear susceptibility, figure of merit and nonlinear refractive index of amorphous films are estimated. The nonlinear behavior is analyzed in terms of decrease in band gap with increasing Zinc and decreasing Sulfur content.

Study of Optical Limiting and Optical Phase Conjugation in DASPB Dye-doped Polymer Films

Study of Optical Limiting and Optical Phase Conjugation in DASPB Dye-doped Polymer Films

RDPS가 랜덤하게 분포하는 분산 제어 광전송 링크에서 전체 전송 거리에 따른 유효 전체 잉여 분산

분산 제어 (DM; dispersion management)와 광 위상 공액 (optical phase conjugation)이 적용된 파장 다중 (WDM; wavelength division multiplexing) 시스템의 유연한 구성을 위하여 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)이 랜덤하게 분포하는 전송 링크에서 전체 전송 거리에 따른 설계 기준을 도출하였다. 설계기준 분석에 사용된 DM 파라미터는 유효 전체 잉여 분산 (NRD; net residual dispersion)과 유효 입사 전력이다. 단일 모드 광섬유 (SMF; single mode fiber) 기준 전체 전송 거리가 1,000 km 이하인 링크에 랜덤 분포의 RDPS가 적용되는 경우 일정 분포에 비해 시스템 성능이 크게 차이나지 않아 유연한 네트워크 구성이 가능하고, 넓은 범위에 걸쳐 있는 WDM 채널에 대해 하나의 값이 아닌 폭넓은 NRD를 링크에 적용할 수 있다는 것을 확인하였다. The design rule depending on total transmission length is induced in the optical links with residual dispersion per span (RDPS) of the random distribution, which is adopted for implementing the flexible systems of wavelength division multiplexing (WDM) transmission with dispersion management (DM) and optical phase conjugation. DM parameters used for the analysis of the design rule are the effective net residual dispersion (NRD) and the effective launch power. It is confirmed that the flexible optical network configuration with the total transmission length lower than 1,000 km is possible, because the system performance difference between the randomly distribution and the uniform distribution of RDPS is small. And, in the optical links with the randomly distributed RDPS, the wide NRD can be applied for transmitting WDM channels of the relatively wide launch power.

Digital optical phase conjugation for delivering two-dimensional images through turbid media

Optical transmission through complex media such as biological tissue is fundamentally limited by multiple light scattering. Precise control of the optical wavefield potentially holds the key to advancing a broad range of light-based techniques and applications for imaging or optical delivery. We present a simple and robust digital optical phase conjugation (DOPC) implementation for suppressing multiple light scattering. Utilizing wavefront shaping via a spatial light modulator (SLM), we demonstrate its turbidity-suppression capability by reconstructing the image of a complex two-dimensional wide-field target through a highly scattering medium. Employing an interferometer with a Sagnac-like ring design, we successfully overcome the challenging alignment and wavefront-matching constraints in DOPC, reflecting the requirement that the forward- and reverse-propagation paths through the turbid medium be identical. By measuring the output response to digital distortion of the SLM write pattern, we validate the sub-wavelength sensitivity of the system.

Multichannel transmission of intensity- and phase-modulated signals by optical phase conjugation using a quantum-dot semiconductor optical amplifier

We report the demonstration of optical phase conjugation using a quantum-dot semiconductor optical amplifier. The transmission performance of wavelength-multiplexed 10-Gbit/s intensity- and phase-modulated signals is investigated for different channel alignments. In a 100-km transmission, we have successfully achieved high transmission performance with low power penalties for all the transmitted signals.

Controllable optical negative refraction and phase conjugation in graphite thin films

Optical metamaterials have demonstrated remarkable physical properties, including cloaking, optical magnetism and negative refraction1,2,3. The last of these has attracted particular interest, mainly because of its promise for super-resolution imaging4,5,6. However, the widespread use of negative refraction at optical frequencies is challenged by high losses and strong dispersion effects, which typically limit operation to narrow frequency bands7. Here we use degenerate four-wave mixing to demonstrate controllable negative refraction at a graphite thin film, which acts as a highly efficient phase-conjugating surface. The scheme has very low loss because of the negligible thickness of the nonlinear material and it ensures broadband operation due to the linear band structure of graphene.

분산 제어 광전송 링크에서 중계 구간의 RDPS 기울기에 따른 WDM 신호의 보상 특성

분산 제어 (DM; dispersion management)와 광 위상 공액 (optical phase conjugation)이 적용된 광전송 링크에서 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span) 기울기 (slope)에 따른 파장 분할 다중 전송 (WDM; wavelength division multiplexed) 채널의 보상 특성을 분석하여 최적의 RDPS 기울기를 도출하였다. RDPS 기울기가 증가할수록 WDM 채널의 유효 입사 전력 범위를 더욱 증가시키고 채널 간 성능 차이를 더욱 감소시키는 것을 확인하였다. 아울러 RDPS 기울기가 증가할수록 유효 전체 잉여 분산 (NRD; net residual dispersion) 범위도 증가하여 큰 RDPS 기울기가 유연한 광전송 링크 구성에 더욱 유리하다는 것을 확인하였다. The optimal residual dispersion per span (RDPS) slope is induced through the analyses of the compensation characteristics of the wavelength division multiplexed (WDM) channels depending on RDPS slope in the optical links with a dispersion management (DM) and an optical phase conjugation. The simulation results show that the effective launch power of WDM is more increased and the performance difference between the channels is more decreased as RDPS slope is more increased. The simulation results also show that the effective net residual dispersion (NRD) range is more increased as RDPS slope is more increased, and consequently, it is more advantageous to use the large RDPS slope for implementing the flexible optical links.

Optical phase conjugation in Nd:YVO_4 for acousto-optic detection in scattering media

Acousto-optic imaging is a technique that maps the optical properties of a thick scattering sample with millimetric resolution. The detection of the acousto-optic signal represents a challenge, because it is very weak among a strong parasitic signal. Various methods based on holography in photorefractive crystals or digital holography have been studied. Here dynamic holography is obtained with the gain medium Nd:YVO(4). We study the experimental feasibility of a detection system based on holography in a gain medium and show acousto-optic results obtained in a 5 mm slice of chicken breast.

Optimizing experimental parameters on OPC in PMMA polymer doped azo dye

In this paper, the optical phase conjugation (OPC) using degenerate four wave mixing (DFWM) technique in a nonlinear DR1 chromophore doped in polymer PMMA thin films (by 8% W/W) is experimentally investigated. A CW Nd:YAG laser (532nm) with 50mW incident power has been used for (DFWM) technique to produce optical phase conjugation beam. The optimized reflectivity (R) relates to signal, forward and backward pump intensity titled with parameters M=IsignalIFP and q=IFPIBP. Furthermore, we have discussed temporal behavior and the maximum of phase conjugation reflectivity. The photo-induced reorientation of the DR1 by trans–cis–trans photoisomerization is the dominant mechanism for the OPC wave generation.

Optical phase conjugation (OPC)-assisted isotropic focusing

Isotropic optical focusing - the focusing of light with axial confinement that matches its lateral confinement, is important for a broad range of applications. Conventionally, such focusing is achieved by overlapping the focused beams from a pair of opposite-facing microscope objective lenses. However the exacting requirements for the alignment of the objective lenses and the method's relative intolerance to sample turbidity have significantly limited its utility. In this paper, we present an optical phase conjugation (OPC)-assisted isotropic focusing method that can address both challenges. We exploit the time-reversal nature of OPC playback to naturally guarantee the overlap of the two focused beams even when the objective lenses are significantly misaligned (up to 140 microns transversely and 80 microns axially demonstrated). The scattering correction capability of OPC also enabled us to accomplish isotropic focusing through thick scattering samples (demonstrated with samples of ~7 scattering mean free paths). This method can potentially improve 4Pi microscopy and 3D microstructure patterning.

Dispersion Management and Optical Phase Conjugation in Optical Transmission Links with a Randomly Distributed Single-Mode Fiber Length

Suppressing or mitigating signal distortion due to group velocity dispersion and optical Kerr effects is necessary in ultra-high speed and long-haul wavelength division multiplexing (WDM) transmission systems. Dispersion management (DM), optical phase conjugation (OPC), and the combination of these two are promising techniques to compensate for signal distortion. In this paper, to implement a flexible optical WDM network, a new optical link configuration with a randomly distributed single-mode fiber (SMF) length and fixed residual dispersion per span in the combination of DM and OPC is proposed and investigated. The simulation results show that the best net residual dispersion (NRD) in the proposed optical links is +10 ps/nm, which is independent of pre- and postcompensation. The effective launch power of the WDM channel is increased more in the optical links with NRD = +10 ps/nm controlled by only precompensation. Furthermore, the system performance difference between the proposed optical link configuration with the best NRD and the conventional optical link with uniform distribution of the SMF length had little significance. Consequently, it is confirmed that the proposed optical link configuration with the best NRD is effective and useful for implementing a reconfigurable long-haul WDM network.

Optical Back Propagation With Optimal Step Size for Fiber Optic Transmission Systems

An optical back propagation scheme consisting of an optical phase conjugator, fiber Bragg gratings (FBGs), and highly nonlinear fibers (HNLFs) is investigated. Transmission fiber dispersion is compensated by the FBGs and the nonlinearity is compensated by HNLFs. Several sections of FBGs and HNLFs are concatenated in a way analogous to the split-step Fourier scheme used for solving the nonlinear Schrödinger equation. The optimum accumulated dispersion of each section of the FBG and the optimum nonlinear phase shift of the each section of the HNLF are calculated by minimizing the mismatch between the area under the exponentially increasing nonlinearity profile and its stepwise approximation. The method of Lagrange multipliers is used for optimization. The proposed optimization technique leads to significant performance improvement and/or reach enhancement as compared to uniformly spaced sections, for the given number of sections.

Improving performance of optical phase conjugation by splitting the nonlinear element

We show that optical phase conjugation (OPC) based on third order nonlinear effects for mid-span spectral inversion (MSSI) can be improved by splitting the nonlinear element into two parts and adding an optical filter between them. This band-stop filter suppresses the cross-phase-modulation products that are generated around the pump, which, if not removed, will be shifted to fall around the output OPC signal band. Numerical simulations show that this method reduces the fundamental limitations introduced by OPC by 3 dB, which results in improvement of the maximum signal quality, Qmax, by 1 dB in a 10 × 80-km 4-QAM 224-Gb/s CO-OFDM system with MSSI.

3D display based on complete digital optical phase conjugation

Digital optical wavefront reconstruction for 3D display at tens or hundreds centimeters scale with viewing angle over 100° calls for resolutions at sub-wavelength scale. However the pixel pitches of spatial light modulators (SLM) are at micrometer or tens of micrometer scale. When people generated 3D images by digital holography using SLMs they had to make the interference patterns very sparse, resulting in small image size or narrow viewing angle. The paper employed an adiabatic waveguide taper made of quantities of single-mode waveguides to decompose complicated light fields into simpler forms so that complete digital optical phase conjugation (CDOPC) could be performed using low resolution SLMs. Then the paper introduced an optical transforming unit to project the reconstructed small wavefronts over a large volume while maintaining large viewing angle. The paper shows both theoretically and experimentally that 3D display systems based on CDOPC could create large size 3D images with large viewing angle and diffraction limited image quality. Besides, CDOPC might also be widely used for 3D measurement, optical tweezers, high energy laser beam forming, etc.

Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance

We develop a theoretical expression to predict the ultimate back-to-back performance of coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems that rely on four-wave mixing to achieve phase conjugation for mid-span spectral inversion. Our analysis shows that two different two-stage nonlinear processes produce strong noise-like products in the conjugated signal band. We verify our theoretical results with simulations and experiments; these both show excellent agreement with the analytical theory. We identify the optimal design parameters and predict that optical phase conjugation of 10 THz wide orthogonal frequency-division multiplexing signals could be possible, given appropriate dispersion management of the nonlinear element. We also experimentally demonstrate the benefit of MSSI in an 800 km transmission of CO-OFDM.

Estimation and mitigation of FWM penalties in dispersion managed 32 channel long haul DWDM soliton link

In this paper, FWM power has been estimated and mitigated by using Optical Phase Conjugator (OPC) in the middle of the optical fiber span which strongly suppresses the FWM power by introducing destructive interference between the first and second halves of the fiber optic link. −20dBm FWM power has been suppressed by using OPC which is in close agreement with the calculated FWM power of −21.74dBm. Further, symmetrical dispersion compensation has been employed to negate the accumulated chromatic dispersion in a considered 32 channel, Terabit capacity, long haul DWDM soliton link.

Phase conjugation and slow light in dye-doped chiral nematics

Optical phase conjugation and slow light are obtained in dye-doped chiral nematics via degenerate four-wave mixing. The creation of the light-induced dynamical grating is described and the amplitude of the phase-conjugate wave is shown to follow the changes of the input signal, hence providing efficient distortion correction. Associated to these capabilities, slowing down of light pulses is obtained thanks to the dispersive properties of the wave mixing occurring in the cholesteric liquid crystals, opening the way to applications in interferometry and imaging through highly scattering media.

인위적인 단일 모드 광섬유 길이와 RDPS 분포를 갖는 분산 제어 광전송 링크에서 선치 보상과 후치 보상을 통한 WDM 신호의 성능 개선

단일 모드 광섬유의 그룹 속도 분산과 자기 위상 변조에 의해 왜곡된 파장 분할 다중 신호의 효율적인 보상을 위한 새로운 광전송 링크 기술을 제안하였다. 제안된 전송 링크는 WDM 송신이나 수신단 근처에 광 위상 공액기(OPC; optical phase conjugator)가 위치하고 각 중계 구간의 SMF 길이와 RDPS(residual dispersion per span)가 인위적으로 분포하는 구조이다. 시스템 성능을 개선하여 유효 입사 전력 범위와 유효 전체 잉여 분산 (NRD; net residual dispersion)을 늘릴 수 있는 최적의 링크 구조는 OPC가 WDM 수신단에 가깝게 위치하고 후치 보상(postcompensation)에 의해 NRD를 결정하고 중계 구간이 증가할수록 SMF 길이와 RDPS를 점진적으로 감소시키는 링크라는 것을 확인하였다. New optical transmission links technique for compensating of the distorted wavelength division multiplexed (WDM) signals due to group velocity dispersion (GVD) and self phase modulation (SPM) in single mode fiber (SMF) are proposed. The proposed optical links have optical phase conjugator (OPC) placed at nearby WDM transmitter or receiver and repeater spans with artificial distribution of SMF length and residual dispersion per span (RDPS). It is confirmed that optimal link configuration expanding effective launching power range and effective net residual dispersion (NRD) by improving system performance is that having OPC closely placed at WDM receiver and the gradually descended distribution of SMF length and RDPS of each repeater spans, related with the gradually increased optical link length. And, it is also confirmed that NRD is controlled by postcompensation in optimal optical link with OPC closely placed at WDM receiver.

Optical phase conjugation in azo-dye doped chiral liquid crystal

We report on optical phase conjugation phenomenon observed in chiral nematic liquid crystal showing band gap type Bragg reflection. The phase conjugate to the signal beam is observable only in the small temperature interval when the Bragg condition is fulfilled and only for circularly polarized light. The optical phase conjugation signals were observed at low cw laser light intensities (<100 mW/cm2, λ = 532 nm). Estimated value of third order optical susceptibility χ(3) = 2.8 × 10−17 m2/V2 is attributed to enhancement due to photoisomerisation of azo-dye (disperse red 1) inducing molecular reorientation process of liquid crystal molecules.