Residual Dispersion Research Articles

Independent and continuous third-order dispersion compensation using a pair of prisms

Abstract The dispersion of a pair of prisms is analyzed by means of a ray-tracing method operating at other than tip-to-tip propagation of the prisms, taking into consideration the limited spectral bandwidth. The variations of the group delay dispersion and the third-order dispersion for a pair of prisms are calculated with respect to the incident position and the separation between the prisms. The pair of prisms can provide a wide range of independent and continuous third-order dispersion compensation. The effect of residual third-order dispersion on the pulse contrast ratio and pulse duration is also calculated. The residual third-order dispersion not only worsens the pulse contrast ratio, but also increases the pulse duration to the hundreds of femtosecond range for a tens of femtosecond pulse, even when the residual third-order dispersion is small. These phenomena are helpful in compensating for the residual high-order dispersion and in understanding its effect on pulse contrast ratios and pulse durations in ultrashort laser systems.

분산 제어와 Mid-Span Spectral Inversion이 적용된 광전송 링크에서 반 전송 구획의 잉여 분산이 전체 잉여 분산에 미치는 영향

분산 제어와 Mid-Span Spectral Inversion이 적용된 광전송 링크에서 반 전송 구획의 잉여 분산이 전체 잉여 분산에 미치는 영향

An Elliptical-Shaped Core Residual Dispersion Compensating Octagonal Photonic Crystal Fiber

A residual dispersion compensating photonic crystal fiber (PCF) is proposed having elliptical-shaped core and octagonal structure with isosceles triangular-latticed cladding. The finite element method with circular perfectly matched layer is used to investigate the guiding properties. It is demonstrated that it is possible to obtain average dispersion of -544.7 ps/(nm.km) in a wavelength range of 1.46-1.70 μm with ultrahigh birefringence of 2.2 × 10 -2 and nonlinear coefficient of 52.7 W -1 km -1 at a 1.55-μm wavelength. Besides, the proposed PCF shows confinement losses <;42.4 and 0.012 dB/km for five and eight rings, respectively.

Design and Characterization of Highly Birefringent Residual Dispersion Compensating Photonic Crystal Fiber

A residual dispersion compensating octagonal photonic crystal fiber (OPCF), with an elliptical array of circular air-holes in the fiber core region, is proposed. The full-vector finite-element method with perfectly matched layer boundary is used as the analysis tool. It is demonstrated that it is possible to obtain large average negative dispersion of -562.52 ps/(nm · km) over 240 nm and -369.10 ps/(nm · km) over 630 nm wavelength bands for the fast and the slow axis, respectively. In addition to large negative dispersion, ultra-high birefringence, high nonlinearity, and zero-dispersion wavelengths with low confinement loss are also warranted. The proposed OPCFs would be a promising candidate for residual dispersion compensation, supercontinuum generation, and other applications.

Signed chromatic dispersion monitoring of OOK signal by evaluating the distance ratio of delay tap sampling

We analyze the residual chromatic dispersion (CD) monitoring of non-return-to-zero on–off keying (NRZ-OOK) signals using delay-tap asynchronous sampling. By evaluating the distance ratio of delay-tap plots and using a 0.5-bit optical delay interferometer (ODI), signed residual CD can be monitored accurately via numerical simulations. This CD monitoring method is independent of optical signal-to-noise ratio (OSNR) and polarization-mode dispersion (PMD). The measuring range was around ±900ps/nm for 10-Gbit/s NRZ-OOK link and ±60ps/nm for 40G link, the monitoring error is smaller than 2ps/nm.

Proposal for highly residual dispersion compensating defected core decagonal photonic crystal fiber over S+C+L+U wavelength bands

A defected core decagonal photonic crystal fiber is designed and numerically optimized to obtain its residual chromatic dispersion compensation in the wavelength range of 1460 to 1675 nm i.e., over S+C+L+U wavelength bands having an average dispersion of about −390 ps/(nm km) with a dispersion variation of 7 ps/(nm km). The designed fiber, with a flattened dispersion profile, has four rings of holes in the cladding region, which results in low confinement loss and small effective mode area at wavelength 1550 nm. For residual chromatic dispersion compensation, the proposed fiber can be used in wavelength division multiplexing optical fiber data communication systems.

Highly birefringent broadband-dispersion-compensating photonic crystal fibre over the E + S + C + L + U wavelength bands

The key features of this manuscript include a hybrid design of a square-core octagonal-lattice photonic crystal fibre with only circular air holes that exhibits high birefringence and broadband dispersion compensation covering the E, S, C, L, and U communication bands (1360–1675nm) and a statistical comparison of the proposed design with some other recently proposed designs. A numerical simulation showed a negative dispersion coefficient in the range of approximately −134 to −385ps/(nmkm) over E and U bands with a relative dispersion slope (RDS), which is equal to that of a single-mode fibre (SMF, approximately 0.0036nm−1) and a birefringence in the order of 2.13×10−2 at the operating wavelength of 1.55μm. Because sensing applications require a highly birefringent fibre, statistical correlations between the birefringence and different parameters were investigated. Moreover, the effective area, residual dispersion, effective dispersion, and confinement loss associated with the proposed design are also reported.

Low overhead and nonlinear-tolerant adaptive zero-guard-interval CO-OFDM.

We propose an adaptive channel estimation (CE) method for zero-guard-interval (ZGI) coherent optical (CO)-OFDM systems, and demonstrate its performance in a single channel 28 Gbaud polarization-division multiplexed ZGI CO-OFDM experiment with only 1% OFDM processing overhead. We systematically investigate its robustness against various transmission impairments including residual chromatic dispersion, polarization-mode dispersion, state of polarization rotation, sampling frequency offset and fiber nonlinearity. Both experimental and numerical results show that the adaptive CE-aided ZGI CO-OFDM is highly robust against these transmission impairments in fiber optical transmission systems.

Dispersion Managed Optical Transmission Links with an Artificial Distribution of the SMF Length and Residual Dispersion per Span

Dispersion management (DM), optical phase conjugation (OPC), and the combination of DM and OPC are promising techniques to compensate for optical signal distortion due to group velocity dispersion and nonlinear Kerr effects. The system performance improvement in DM links combined with OPC has been reported; however, the fixed residual dispersion per span (RDPS) usually used in these links restricts the flexibility of link configuration. Thus, in this paper, a flexible optical link configuration with artificially distributed single-mode fiber (SMF) lengths and RDPS in the combination of DM and OPC is proposed. Simulation results show that the best artificial distribution pattern is the gradually descending distribution of SMF lengths and the gradually ascending distribution of RDPS, as the number of fiber spans is increased, regardless of the average RDPS, the optimal net residual dispersion, and the dispersion coefficient of the dispersion compensating fiber.

Wavelength assignment using a hybrid evolutionary computation to reduce cross-phase modulation

In this paper, we propose a hybrid methodology based on Graph-Coloring and Genetic Algorithm (GA) to solve the Wavelength Assignment (WA) problem in optical networks, impaired by physical layer effects. Our proposal was developed for a static scenario where the physical topology and traffic matrix are known a priori. First, we used fixed shortest-path routing to attend demand requests over the physical topology and the graph-coloring algorithm to minimize the number of necessary wavelengths. Then, we applied the genetic algorithm to solve WA. The GA finds the wavelength activation order on the wavelengths grid with the aim of reducing the Cross-Phase Modulation (XPM) effect; the variance due to the XPM was used as a function of fitness to evaluate the feasibility of the selected WA solution. Its performance is compared with the First-Fit algorithm in two different scenarios, and has shown a reduction in blocking probability up to 37.14% when considered both XPM and residual dispersion effects and up to 71.42% when only considered XPM effect. Moreover, it was possible to reduce by 57.14% the number of wavelengths.

Compensation Characteristics of the Distorted WDM Signals Depending on the Variation Degree of RDPS Random Variables in the Optical Links with Dispersion Management and Optical Phase Conjugation

The effects of the variation degree of residual dispersion per span (RDPS) random variables on the compensation characteristics of the distorted signals in optical links with the dispersion management (DM) and the mid-way optical phase conjugator (OPC) are investigated in this paper. In order to obtain this goal, the effective launch power range and the effective net residual dispersion (NRD) range are induced as a function of the variation degree of RDPS random variables. We confirm that it is needed to select the RDPS random variables of the narrow deviation in each fiber spans for implementing the flexible optical links transmitting the relative higher launch power. Also, we confirmed that it is more advantageous to use postcompensation rather than precompensation for expanding the effective NRD range.

Residual dispersion compensation over the S + C + L + U wavelength bands using highly birefringent octagonal photonic crystal fiber.

An octagonal photonic crystal fiber (PCF) with an elliptical shape in the center core is numerically investigated for residual dispersion compensation in the wavelength range 1460-1675 nm. The designed fiber exhibits flattened negative dispersion over the S + C + L + U wavelength bands and an average dispersion of -465.5 ps/(nm·km) with an absolute dispersion variation of 10.5 ps/(nm·km). In addition, the proposed PCF shows a high birefringence of 2.68×10(-2) at the operating wavelength 1550 nm, which meets the requirement of high birefringence. Moreover, the variation of two air holes in the first ring up to 5% ensures an average dispersion of -491.5 ps/(nm·km) with a dispersion variation of 13 ps/(nm·km), and birefringence reaches up to 3×10(-2). Furthermore, to evaluate the sensitivity of the fiber dispersion properties, ±5% variation in the optimum parameters is studied.

SMF 길이와 RDPS의 분포 패턴에 따른 왜곡된 WDM 신호의 보상 특성

고품질 초고속 광 신호 전송을 위해서는 그룹 속도 분산과 비선형 현상에 의한 왜곡을 억제하거나 줄여주는 기술이 필요하다. 가장 대표적인 기술로 분산 제어 (DM; dispersion management), 광 위상 공액 기술과 이 둘을 결합한 기술이 있다. 하지만 이러한 기술들에서 현재 사용되고 있는 단일 모드 광섬유의 고정 길이와 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)의 고정값은 유연한 링크 구성을 제한하고 있다. 본 연구의 목적은 광전송 링크를 구성하는 모든 중계 구간의 SMF 길이와 RDPS의 인위적 분포와 랜덤 분포를 통한 초고속 장거리 광전송 시스템의 유연한 구성 가능성을 살펴보는 것이다. 전송 링크 전체의 평균 RDPS와 입사 전력과 같은 링크 파라미터에 의존하지만 제안한 링크 구조들이 유연한 광전송 시스템 구성에 유용하다는 것을 확인하였다. For transmitting the ultra-high speed optical signals with better performance, the techniques to suppress or mitigate the signal distortion due to group velocity dispersion and optical Kerr effects are required. Dispersion management (DM), optical phase conjugation, and the combination of these two are promising techniques to compensate for the signal distortion. However, the fixed length of single mode fiber (SMF) and the fixed residual dispersion per span (RDPS) usually used in these optical links restricts flexible link configuration. The goal of this paper is to investigate the possibility of the flexible configurations of the ultra-high and long-haul optical transmission systems by using the artificial and the random distribution of SMF length and RDPS of each fiber spans consisted of the optical link. It is confirmed that the proposed link configurations should be one of the methods suitable for implementing the flexible optical transmission systems, however which depend on other link parameters, such as the averaged RDPS, and the launch power.

A single mode ultra flat high negative residual dispersion compensating photonic crystal fiber

In this paper, a single mode photonic crystal fiber based on hexagonal architecture is numerically demonstrated for the purpose of residual dispersion compensation in the wavelength range of 980–1580nm. The designed fiber offers ultraflattened negative dispersion in the near-infrared to most widely used S to L wavelength bands and average dispersion of about −138ps/(nmkm) with an absolute dispersion variation of 12ps/(nmkm). Besides, the proposed fiber successfully operates as a single mode in the entire band of interest. Moreover, to check the dispersion accuracy, sensitivity of the fiber dispersion properties to a ±1–5% variation in the optimum parameters is studied for practical conditions.

Broadband Impairment Compensation in Hybrid Fiber-Wireless OFDM Long-Reach PONs

This paper proposes and demonstrates experimentally the broadband transmission impairment compensation in optical and electrical domain, enabling the provision of a bundle of simultaneous services using orthogonal frequency division multiplexing (OFDM) modulation in hybrid wireless-optic networks. The combination of electrical pre-compensation and fixed optical dispersion compensation is assessed in long-reach passive optical networks (LR-PONs): i) An electrical pre-compensation technique using extra RF-pilots located in the free spectrum of a bundle of OFDM-based services is proposed to evaluate the response of the transmission channel. The impact of the number of extra RF-pilots and the digital signal processing algorithm used for channel estimation is analyzed experimentally for different configurations. Using the proposed electrical pre-compensation technique, an error vector magnitude (EVM) improvement of 5.2 dB in the higher frequency OFDM signal is achieved. The electrical compensation enables the long-reach transmission at 100 km of simultaneous long term evolution (LTE), worldwide interoperability for microwave access (WiMAX) and ultra wideband (UWB) signals and an I/Q OFDM signal providing GbE connectivity. ii) Fixed optical dispersion compensation is used to overcome partly the dispersion-induced impairments of the long-reach transmission. With the combination of electrical and optical impairment compensation approaches, we demonstrate that the electrical compensation technique is able to counterbalance the residual dispersion of the optical access network. An EVM fluctuation below 1 dB is obtained for residual dispersion values ranging from -425 to 425 ps/nm. The EVM of the highest frequency UWB signal centered at 4.49 GHz is improved by 8.8 dB when using the combination of electrical and optical compensation, enabling the simultaneous transmission of the bundle of OFDM-based signals in a 125 km LR-PON.

Study of a novel amplitude-phase modulation IRZ-MSK in high-speed optical fiber transmission system

In this paper, a novel amplitude-phase modulation format, inverse-return-to-zero minimum shift keying (IRZ-MSK), is proposed. A scheme to realize the IRZ-MSK is introduced, and especially a method of demodulating the phase branch is presented. The influence of different duty cycles on the performance of the IRZ-MSK is discussed. Numerical simulations and analysis are performed, and the comparison between the 70% IRZ-MSK and the NRZ-MSK is made. The phase branches of 70% IRZ-MSK and the NRZ-MSK almost have the same dispersion tolerance, and the amplitude branch of 70% IRZ-MSK has a better dispersion tolerance than that of the NRZ-MSK when the residual dispersion is larger than 1.9ps/nm/km. For the nonlinear tolerance, the EOP of the IRZ-MSK phase branch and amplitude branch reduces 0.5dB and 3.8dB than those of the NRZ-MSK respectively, when the launch power is 4mW and dispersion is completely compensated. Meanwhile, the BER curves of the NRZ-MSK and IRZ-MSK are also made. The results show that, our proposed IRZ-MSK can not only improve the spectral efficiency, but also greatly mitigate the dispersion and nonlinear effects.

Simultaneous global coupling and vertical dispersion correction in RHIC

Residual vertical dispersion in the order of +/−0.2m (peak to peak) has been measured at store energies for both polarized proton and heavy ion beams in RHIC. The hypothesis is that this may have impact on the polarization transmission efficiency during the energy ramp, the polarization lifetime at store and, for heavy ions, the dynamic aperture. An algorithm to correct global coupling and vertical dispersion simultaneously using existing skew quadrupoles was developed. Measured coupling and vertical dispersion functions acquired before and after correction are presented.

Visualization of high-order dispersion for compression of few-cycle pulses

We present a visually intuitive method for higher-order dispersion compensation based on multi-photon interpulse interference pulse scans. The dispersion values obtained from these scans are fed back as a correction to an acousto-optical programmable dispersive filter to compensate residual higher-order dispersions up to fifth order. This method is applied to the dispersion management of a non-collinear optical parametric chirped-pulse amplifier. A grism-pair stretcher is designed based on a global dispersion balance which provides a large stretching factor and supports a spectral bandwidth of up to 320 nm. It is implemented in a two-stage three-pass non-collinear optical parametric chirped-pulse amplifier and stretches 6-fs seed pulses to about 80 ps from 700 to 1,000 nm. The amplified pulses are compressed by material dispersion. Pulses of less than 10-fs duration with a pulse energy of 125 μJ are obtained at 20-kHz repetition rate.

Collimation effects on large CPA compressors

Modelling and analysis have been performed to show a link between laser collimation tolerances and dispersion effects in chirped pulse amplification (CPA) compressors. These show that an un-collimated beam can present itself as residual dispersion in a CPA system which uncorrected will have adverse effects on laser power and intensity. The techniques of shearing interferometry and beam propagation over large distances for setting beam collimation have been assessed for their limitations in measuring wavefront radii. An analysis of the sensitivity of CPA systems to non-collimated beams has been studied. This effect has been practically demonstrated for a high-power Nd:glass laser and the best techniques for alignment are discussed.

Dispersion Managed Optical Links with Optical Phase Conjugator Placed at the Various Positions

The needs of ultra-high optical backbone systems are currently increased to transmit the high-quality multimedia services. For transmitting the ultra-high speed optical signals with better performance, the techniques to suppress or mitigate the optical signal distortion due to group velocity dispersion and optical Kerr effects are required. Dispersion management (DM), optical phase conjugation, and the combination of these two are promising techniques to compensate for the signal distortion. The goal of this paper is to investigate the possibility of the flexible configurations of the ultra-high and long-haul optical backbone systems using optical links with the random distribution of residual dispersion per span (RDPS) and optical phase conjugator (OPC) placed at the various positions. We confirm that the proposed link configurations should be one of the methods suitable for implementing the flexible optical backbone systems, also, the possibility is more available to longer backbone.