- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Vacuum-enhanced optical nonlinearities with disordered molecular photoswitches
摘要： It is well known that nonlinear optical signals such as cross-phase modulation can be coherently enhanced in multilevel atomic gases under conditions of electromagnetically induced transparency, but analogous results in solids are challenging to obtain due to natural energetic disorder. We propose a solid-state cavity QED scheme to enable cross-phase modulation between two arbitrarily weak classical fields in the optical domain, using a highly disordered intracavity medium composed of organic molecular photoswitches. Even in the presence of strong energetic and orientational disorder, the unique spectral properties of organic photoswitches can be used to enhance the desired nonlinearity under conditions of vacuum-induced transparency, enabling cross-phase modulation signals that surpass the detection limit imposed by absorption losses. Possible applications of the scheme include integrated all-optical switching with low photon numbers.
关键词： organic photoswitches,cavity QED,vacuum-induced transparency,cross-phase modulation,disorder
更新于2025-09-23 15:23:52
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Analogue Wireless Beamforming Exploiting the Fiber-Nonlinearity of Radio Over Fiber Based C-RANs
摘要： As a key technique of supporting the fixed backbone network, radio over fiber (RoF) systems transmit the radio frequency signals over optical fiber in order to take advantage of their large available bandwidth. In this context, optical fiber aided phased antenna array (PAA) based beamforming techniques have attracted substantial research interest with the goal of improving the cell-edge coverage of cellular base stations. In this paper, we conceive a novel optical fiber aided beamforming technique based on the fiber's nonlinearity to be applied in cloud radio access network (C-RAN). In our proposed technique, the PAA elements are fed by the phase-shifted signals introduced by our highly nonlinear fiber (HNLF) aided phase-shifting solution, which results in an angular beamsteering range of around 90°. This can be exploited by sectorization in cellular networks to reduce the cochannel interference imposed. Furthermore, we exploit the proposed RoF-aided phase shifting technique in C-RAN, where our proposed system takes advantage of the centralized signal processing capability of the RoF system to conceive an all-optical processing based tunable beamforming system. While our flexible HNLF-aided phase-shifting process is confined to the central office of the C-RAN, the end users in the C-RAN cellular networks are capable of flexibly choosing the serving remote radio heads (RRHs) and employing diverse wireless transmission techniques. Through integrating our HNLF-aided phase-shifting design into the proposed C-RAN, we impose as little as 0.1 dB signal-to-noise Ratio (SNR) degradation compared to its traditional electronic counterpart, which requires extra phase-shifters.
关键词： phase-shifter,self-phase modulation,phased array antenna beamforming,C-RAN,cross-phase modulation,highly nonlinear fiber,Optical fiber,optical nonlinearity
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - Chennai (2018.3.22-2018.3.24)] 2018 International Conference on Wireless Communications, Signal Processing and Networking (WiSPNET) - An Efficient Photonic-based Millimeter Wavelength Switching Techniques Towards 5G
摘要： Millimeter Waves (MMWs) operating at 30–300 GHz band, is very encouraging to the next-generation 5G wireless communication systems, supporting data rates of multiple Gbps per user. By using the Four Wave Mixing (FWM), Self-Phase Modulation (SPM) and Cross Phase Modulation (XPM) effects in the Semiconductor Optical Amplifier (SOA) and Erbium Doped Fiber Amplifier (EDFA), the photonic millimeter switching is realized. These effects can reduce the switching crosstalk since the Optical Single Sideband (OSSB) signal occupies the least optical bandwidth. The best operating conditions improve the Sideband Suppression Ratio (SSR) and at the same time reduce the intensity of unintended sideband signal. This leads to a dispersion-free transmission in the optical fiber and improves the data rate as required in 5G communication. In this paper, the wavelength switching of a 9 Gbps QPSK signal carried on the 30 GHz over a spacing of 1.6 nm as a function of probe wavelength of 1548.515 nm and pump wavelength of 1550.115 nm is achieved.
关键词： Millimeter Waves,Four Wave Mixing,Self Phase Modulation,Cross Phase Modulation,Erbium Doped Fiber Amplifier
更新于2025-09-23 15:22:29
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Nonlinear Fiber Optics || Introduction
摘要： This introductory chapter is intended to provide an overview of the fiber characteristics that are important for understanding the nonlinear effects discussed in later chapters. Section 1.1 provides a historical perspective on the progress in the field of fiber optics. Section 1.2 discusses various fiber properties such as optical loss, chromatic dispersion, and birefringence. Particular attention is paid to chromatic dispersion because of its importance in the study of nonlinear effects probed by using ultrashort optical pulses. Section 1.3 introduces various nonlinear effects resulting from the intensity dependence of the refractive index and stimulated inelastic scattering. Among the nonlinear effects that have been studied extensively using optical fibers as a nonlinear medium are self-phase modulation, cross-phase modulation, four-wave mixing, stimulated Raman scattering, and stimulated Brillouin scattering. Each of these effects is considered in detail in separate chapters. Section 1.4 gives an overview of how this book is organized for discussing such a wide variety of nonlinear effects in optical fibers.
关键词： fiber optics,stimulated Raman scattering,four-wave mixing,stimulated Brillouin scattering,chromatic dispersion,nonlinear effects,self-phase modulation,cross-phase modulation,birefringence
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Polarization effects
摘要： A major simplification was made in Section 2.3 while deriving the nonlinear Schr?dinger (NLS) equation. It consisted of assuming that the polarization state of the incident light is preserved during its propagating inside an optical fiber. This is not really the case in practice. In this chapter we focus on the polarization effects and consider the coupling between the two orthogonally polarized components of an optical field induced by the nonlinear phenomenon known as cross-phase modulation (XPM). The XPM is always accompanied with self-phase modulation (SPM) and can also occur between two optical fields of different wavelengths, a situation covered in Chapter 7.
关键词： optical fibers,nonlinear Schr?dinger equation,polarization effects,self-phase modulation,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Stimulated Raman scattering
摘要： Stimulated Raman scattering (SRS) is an important nonlinear process that can turn optical fibers into broadband Raman amplifiers and tunable Raman lasers. It can also severely limit the performance of multichannel lightwave systems by transferring energy from one channel to the neighboring channels. This chapter is devoted to a thorough study of SRS phenomenon in optical fibers. Section 8.1 presents the basic theory behind SRS with emphasis on the pump power required to reach the Raman threshold. SRS under continuous-wave (CW) and quasi-CW conditions is considered in Section 8.2, where we also discuss the performance of fiber-based Raman lasers and amplifiers. Ultrafast SRS occurring for pulses of 100-ps width or less is considered in Sections 8.3 and 8.4 for normal and anomalous group-velocity dispersion (GVD), respectively. In both cases, attention is paid to the walk-off effects together with those resulting from self-phase modulation (SPM) and cross-phase modulation (XPM). Section 8.5 focuses on the polarization effects.
关键词： Raman amplifiers,optical fibers,Stimulated Raman scattering,nonlinear processes,group-velocity dispersion,Raman lasers,polarization effects,self-phase modulation,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Highly nonlinear fibers
摘要： As seen in the preceding chapters of this book, three major nonlinear effects occurring inside optical fibers—self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM)—are governed by a single nonlinear parameter γ, defined in Eq. (2.3.30). For conventional optical fibers γ has values of ～1 W?1/km. It was realized during the 1990s that this value is too small for optical fibers to be useful as a nonlinear medium for applications requiring short lengths. To solve this problem, several new kinds of fibers with γ > 10 W?1/km were developed; they are collectively referred to as highly nonlinear fibers (HNLFs). This chapter deals with the properties of such fibers. The techniques used to measure the nonlinear parameter are described first in Section 11.1. The following four sections then focus on the four kinds of HNLFs that have been developed to enhance the nonlinear effects. In each case, dispersive properties of the fibers are also described because they play an important role whenever HNLFs are used for practical applications. It will be seen in Chapters 12 and 13 that the combination of unusual dispersive properties and a high value of γ makes HNLFs useful for a variety of novel nonlinear effects. Section 11.6 shows how the design of some HNLFs modifies the effective value of the nonlinear parameter in the case of narrow-core fibers.
关键词： four-wave mixing,highly nonlinear fibers,optical fibers,nonlinear parameter,self-phase modulation,dispersion,cross-phase modulation
更新于2025-09-12 10:27:22
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Nonlinear Fiber Optics || Cross-phase modulation
摘要： So far we have focused on optical pulses whose spectrum is centered at a single wavelength. When two or more pulses, launched at different wavelengths, propagate simultaneously inside a fiber, they interact with each other through the fiber’s nonlinearity. In general, such an interaction can generate new waves under appropriate conditions through a variety of nonlinear phenomena such as stimulated Raman or Brillouin scattering and four-wave mixing; these are discussed in Chapters 8 to 10. The nonlinearity can also couple two optical fields through cross-phase modulation (XPM), without inducing any energy transfer between them [1]. The XPM phenomenon is discussed in this chapter. A set of two coupled nonlinear Schr?dinger (NLS) equations is derived in Section 7.1, assuming that each wave maintains its state of polarization. These equations are used in Section 7.2 to discuss how the XPM affects the phenomenon of modulation instability. Section 7.3 focuses on the soliton pairs whose members support each other through their XPM-mediated nonlinear interaction. The effects of XPM on the shape and the spectrum of ultrashort pulses are described in Section 7.4 by solving the coupled NLS equations. Several applications of XPM are discussed in Section 7.5. A vector theory of XPM is developed in Section 7.6 to account for the polarization effects. In Section 7.7 we extend this theory to the case of birefringent fibers. The case of two counterpropagating waves is discussed in Section 7.8.
关键词： modulation instability,soliton pairs,counterpropagating waves,birefringent fibers,polarization effects,ultrashort pulses,nonlinear Schr?dinger equations,cross-phase modulation
更新于2025-09-12 10:27:22
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Vectorial dispersive shock waves in optical fibers
摘要： Dispersive shock waves are a universal phenomenon encountered in many fields of science, ranging from fluid dynamics, Bose-Einstein condensates and geophysics. It has been established that light behaves as a perfect fluid when propagating in an optical medium exhibiting a weakly self-defocusing nonlinearity. Consequently, this analogy has become attractive for the exploration of dispersive shock wave phenomena. Here, we observe of a novel class of vectorial dispersive shock waves in nonlinear fiber optics. Analogous to blast-waves, identified in inviscid perfect fluids, vectorial dispersive shock waves are triggered by a non-uniform double piston imprinted on a continuous-wave probe via nonlinear cross-phase modulation, produced by an orthogonally-polarized pump pulse. The nonlinear phase potential imparted on the probe results in the formation of an expanding zone of zero intensity surrounded by two repulsive oscillating fronts, which move away from each other with opposite velocities.
关键词： Dispersive shock waves,nonlinear fiber optics,cross-phase modulation,optical fluids
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Avoidance of Cross-Phase Modulation in Femtosecond Stimulated Raman Scattering
摘要： Raman scattering has become a powerful method in analytic spectroscopy and label-free imaging to study the chemical composition of a sample. Especially coherent Raman scattering (CRS) techniques such as stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) are developed further and show a great potential, due to their amplified signal in comparison to spontaneous Raman scattering. In CRS the interaction of light pulses with molecular vibrations are investigated, typically resulting in a characteristic molecular spectrum. However, especially CARS spectra are effected by the non-resonant contribution to the Raman scattering signal, resulting in a non-specific background and a distortion of the lineshape. SRS is free of a non-resonant background but is affected by two-photon absorption, cross-phase modulation (XPM) [1], and thermal scattering (temperature-induced refractive index change) [2]. The resulting artefacts in SRS become relevant for high pulses energies and ultra-short pulses. One example, where high pulse energies and ultra-short pulses are needed, is the field of spatial resolution enhancement in CRS. All techniques to overcome the diffraction limit by Abbe are based on depleting one of the scattering resources, as for example the pump or probe photons [3]. High pulse energies in the order of up to 200-300 nJ are needed, leading to also unwanted spectral distortions through XPM [4]. In this paper, we present the avoidance of spectral XPM artefacts in femtosecond stimulated Raman scattering, based on a systematic study varying the pump pulse duration in the high pulse energy regime. To study the effects of different pump pulse durations on the FSRS spectra a setup as shown in Fig. 1 (a) was realized, which consists of a folded Fourier filter, to freely choose the pump pulse duration, and a supercontinuum generation in a gadolinium vanadate crystal (GdVO4) working as broadband probe pulse source. After combining the two beams at the dichroic mirror (DM) measurements with different peak powers of the pump pulse, time delays between pump and probe and varying pump pulse durations were performed. For pump pulses with a duration between 2 ps and 3 ps the Raman spectra are nearly unaffected by XPM, whereas pulses shorter than 1 ps show a significant XPM induced distortion of the stimulated Raman lineshape and a reduction of the Raman resonance maximum, becoming visible as a negative stimulated Raman loss (SRL) signal on the high wavenumber side of the Raman resonances. Thus, it is favourable to choose pump pulses with a longer pulse duration in the regime of high peak power to reduce the impact of cross-phase modulation in stimulated Raman scattering.
关键词： stimulated Raman scattering,Raman scattering,femtosecond pulses,spectral distortions,cross-phase modulation
更新于2025-09-12 10:27:22