Showing papers on "Polarization mode dispersion published in 2010"
TL;DR: In this article, the authors compare single carrier (SC) versus orthogonal frequency-division multiplexing (OFDM) for polarization-multiplexed transmission and show that at realistic data rates and transmission distances, polarization mode dispersion does not significantly degrade the performance of digital backpropagation and can be mitigated by a post-BP linear equalizer.
Abstract: Digital backpropagation (BP) is a universal method for jointly compensating dispersion and nonlinear impairments in optical fiber and is applicable to signals of any modulation format. In this paper, we compare single carrier (SC) versus orthogonal frequency-division multiplexing (OFDM) for polarization-multiplexed transmission. We show that at realistic data rates and transmission distances, polarization mode dispersion does not significantly degrade the performance of BP and can be mitigated by a post-BP linear equalizer. Dispersion unmanaged transmission can significantly reduce nonlinearity, and in this transmission regime, SC and OFDM have similar nonlinear tolerance. Multichannel BP is effective at mitigating interchannel nonlinearity for point-to-point links.
267 citations
TL;DR: This work proposes low-pass filtering the compensation signal (the intensity waveform used to calculate the nonlinearity compensation) in each backpropagation step and optimizing the position of the non linear section in each step, which improves system performance and reduces the oversampling for a given system performance.
Abstract: Backpropagation has been shown to be the most effective method for compensating intra-channel fiber nonlinearity in long-haul optical communications systems. However, effective compensation is computationally expensive, as it requires numerous steps and possibly increased sampling rates compared with the baud rate. This makes backpropagation difficult to implement in real-time. We propose: (i) low-pass filtering the compensation signal (the intensity waveform used to calculate the nonlinearity compensation) in each backpropagation step and (ii) optimizing the position of the nonlinear section in each step. With numerical simulations, we show that these modifications to backpropagation improve system performance, reducing the number of backpropagation steps and reducing the oversampling for a given system performance. Using our ‘filtered backpropagation’, with four backpropagation steps operating at the same sampling rate as that required for linear equalizers, the Q at the optimal launch power was improved by 2 dB and 1.6 dB for single wavelength CO-OFDM and CO-QPSK systems, respectively, in a 3200 km (40 × 80km) single-mode fiber link, with no optical dispersion compensation. With previously proposed backpropagation methods, 40 steps were required to achieve an equivalent performance. A doubling in the sampling rate of the OFDM system was also required. We estimate this is a reduction in computational complexity by a factor of around ten.
265 citations
TL;DR: In this paper, a unified multiblock nonlinear model for the joint compensation of the impairments in fiber transmission is presented, and it is shown that commonly used techniques for overcoming different impairments are often based on the same principles such as feedback and feedforward control, and time-versus-frequency-domain representations.
Abstract: Next-generation optical fiber systems will employ coherent detection to improve power and spectral efficiency, and to facilitate flexible impairment compensation using digital signal processors (DSPs). In a fully digital coherent system, the electric fields at the input and the output of the channel are available to DSPs at the transmitter and the receiver, enabling the use of arbitrary impairment precompensation and postcompensation algorithms. Linear time-invariant (LTI) impairments such as chromatic dispersion and polarization-mode dispersion can be compensated by adaptive linear equalizers. Non-LTI impairments, such as laser phase noise and Kerr nonlinearity, can be compensated by channel inversion. All existing impairment compensation techniques ultimately approximate channel inversion for a subset of the channel effects. We provide a unified multiblock nonlinear model for the joint compensation of the impairments in fiber transmission. We show that commonly used techniques for overcoming different impairments, despite their different appearance, are often based on the same principles such as feedback and feedforward control, and time-versus-frequency-domain representations. We highlight equivalences between techniques, and show that the choice of algorithm depends on making tradeoffs.
207 citations
TL;DR: Few-mode fibers (FMFs) are demonstrated as a good compromise since they are sufficiently resistant to mode coupling compared to standard multimode fibers but they still can have large core diameters compared to single-mode fiber.
Abstract: Using multimode fibers for long-haul transmission is proposed and demonstrated experimentally. In particular few-mode fibers (FMFs) are demonstrated as a good compromise since they are sufficiently resistant to mode coupling compared to standard multimode fibers but they still can have large core diameters compared to single-mode fibers. As a result these fibers can have significantly less nonlinearity and at the same time they can have the same performance as single-mode fibers in terms of dispersion and loss. In the absence of mode coupling it is possible to use these fibers in the single-mode operation where all the data is carried in only one of the spatial modes throughout the fiber. It is shown experimentally that the single-mode operation is achieved simply by splicing single-mode fibers to both ends of a 35-km-long dual-mode fiber at 1310 nm. After 35 km of transmission, no modal dispersion or excess loss was observed. Finally the same fiber is placed in a recirculating loop and 3 WDM channels each carrying 6 Gb/s BPSK data were transmitted through 1050 km of the few-mode fiber without modal dispersion.
174 citations
TL;DR: A technique is demonstrated for polarization demultiplexing of arbitrary complex-modulated signals using data in Stokes space to find the best fit plane and the normal to it which contains the origin.
Abstract: A technique is demonstrated for polarization demultiplexing of arbitrary complex-modulated signals. The technique is based entirely on the observation of samples in Stokes space, does not involve demodulation and is modulation format independent. The data in Stokes space is used to find the best fit plane and the normal to it which contains the origin. This normal identifies the two orthogonal polarization states of transmission and the desired polarization alignment transformation matrix. The technique is verified experimentally and is compared with the constant modulus algorithm.
169 citations
TL;DR: This work demonstrates optical performance monitoring of in-band optical signal to noise ratio (OSNR) and residual dispersion, using slow-light enhanced optical third harmonic generation (THG) in a compact 2D silicon photonic crystal waveguide, and opens the door for slow light to play a key role in ultra-high bandwidth telecommunications systems.
Abstract: We demonstrate optical performance monitoring of in-band optical signal to noise ratio (OSNR) and residual dispersion, at bit rates of 40Gb/s, 160Gb/s and 640Gb/s, using slow-light enhanced optical third harmonic generation (THG) in a compact (80µm) dispersion engineered 2D silicon photonic crystal waveguide. We show that there is no intrinsic degradation in the enhancement of the signal processing at 640Gb/s relative to that at 40Gb/s, and that this device should operate well above 1Tb/s. This work represents a record 16-fold increase in processing speed for a silicon device, and opens the door for slow light to play a key role in ultra-high bandwidth telecommunications systems.
156 citations
TL;DR: In this paper, the authors reported the frequency and polarization characteristics of correlated photon pairs generated in a Si wire waveguide (SWW) and confirmed that the bandwidth for correlated photon-pair generation was at least 2.8 THz.
Abstract: We report the frequency and polarization characteristics of correlated photon pairs generated in a Si wire waveguide (SWW). We confirmed that the bandwidth for correlated photon-pair generation was at least >2.8 THz. Moreover, we carried out a classical four-wave mixing experiment using strong pump and idler lights to estimate the bandwidth for correlated photon-pair generation. The results indicated that it is possible to generate photon pairs over a bandwidth as large as ~12 THz. We also showed that the generation efficiencies of the signal and idler photons for the horizontal polarization mode were much higher than those for the vertical polarization mode. This is probably caused by the large efficiencies in the group indexes and the effective cross-sectional areas for the two polarization modes. Furthermore, the bandwidth for the correlated photon-pair generation in the vertical polarization mode was ~±1 THz, and this was much narrower than that for the horizontal polarization mode. The difference between the bandwidths of the two polarization modes indicates that the SWW dispersion for the vertical polarization mode is significantly larger than that for the horizontal polarization mode. We then confirmed that the noise photons generated by spontaneous Raman scattering in an SWW were suppressed to below the detection limit of our setup.
103 citations
TL;DR: The orthogonal frequency division multiplexing (OFDM) technique in long-haul next generation optical communication links is analyzed and compared with the well-established single-carrier (SC) data transmission using high-level modulation formats and coherent detection.
Abstract: We analyze the orthogonal frequency division multiplexing (OFDM) technique in long-haul next generation optical communication links and compare it with the well-established single-carrier (SC) data transmission using high-level modulation formats and coherent detection. The analysis of the two alternative solutions is carried out in the 100 Gbps scenario, which is commonly considered to be the next upgrade of existing optical links, with special emphasis on quaternary phase-shift keying (QPSK) modulations. The comparison between OFDM and SC takes into account the main linear and nonlinear impairments of the optical channel, e.g., group velocity dispersion (GVD), polarization mode dispersion (PMD), self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM), as well as the phase noise due to transmit and receive lasers, their relative frequency offset, other synchronization aspects, the overall complexity, the power and spectral efficiency, and the technological constraints.
90 citations
TL;DR: Dispersion characteristics for the low-loss waveguide modes, the linearly-polarized HE(11) mode and the TE(01) mode are obtained, and the experimental results to the metallic waveguide dispersion are compared.
Abstract: Thin dielectric layers deposited on the inner surface of hollow cylindrical metallic waveguides for Terahertz (THz) waves reduce transmission losses below 1 dB/m. Impact of the dielectric layer on the waveguide dispersion is experimentally investigated by near-field mapping of guided short THz pulses at the input and the output of the waveguide. We obtain dispersion characteristics for the low-loss waveguide modes, the linearly-polarized HE11 mode and the TE01 mode, and compare the experimental results to the metallic waveguide dispersion. The additional dispersion due to the dielectric layer is found to be small for the HE11 mode and the phase velocity is primarily determined by the waveguide radius.
79 citations
TL;DR: In this paper, the optimal design of coherent coherent optical receivers for polarization-multiplexed optical signals, in the absence of polarization mode dispersion (PMD), has been investigated, and it is shown that simultaneous joint estimation of the symbols, over the two received states of polarization, yields optimal performance.
Abstract: Spectrally-efficient optical communications systems employ polarization division multiplexing (PDM) as a practical solution, in order to double the capacity of a fiber link. Polarization demultiplexing can be performed electronically, using polarization-diversity coherent optical receivers. The primary goal of this paper is the optimal design, using the maximum-likelihood criterion, of polarization-diversity coherent optical receivers for polarization-multiplexed optical signals, in the absence of polarization mode dispersion (PMD). It is shown that simultaneous joint estimation of the symbols, over the two received states of polarization, yields optimal performance, in the absence of phase noise and intermediate frequency offset. In contrast, the commonly used zero-forcing polarization demultiplexer, followed by individual demodulation of the polarization-multiplexed tributaries, exhibits inferior performance, and becomes optimal only if the channel transfer matrix is unitary, e.g., in the absence of polarization dependent loss (PDL), and if the noise components at the polarization diversity branches have equal variances. In this special case, the zero-forcing polarization demultiplexer can be implemented by a 2 ? 2 lattice adaptive filter, which is controlled by only two independent real parameters. These parameters can be computed recursively using the constant modulus algorithm (CMA). We evaluate, by simulation, the performance of the aforementioned zero-forcing polarization demultiplexer in coherent optical communication systems using PDM quadrature phase shift keying (QPSK) signals. We show that it is, by far, superior, in terms of convergence accuracy and speed, compared to conventional CMA-based polarization demultiplexers. Finally, we experimentally test the robustness of the proposed constrained CMA polarization demultiplexer to realistic imperfections of polarization-diversity coherent optical receivers. The PMD and PDL tolerance of the proposed demultiplexer can be used as a benchmark in order to compare the performance of more sophisticated adaptive electronic PMD/PDL equalizers.
51 citations
TL;DR: The technique is based on optically processing an optical double sideband signal using stimulated Brillouin scattering effect and an unwanted sideband suppression over 40 dB in a broadband range from 50 MHz to 20 GHz is experimentally demonstrated.
Abstract: We propose a technique for the generation of broadband optical single sideband modulated signals The technique is based on optically processing an optical double sideband signal using stimulated Brillouin scattering effect An unwanted sideband suppression over 40 dB in a broadband range from 50 MHz to 20 GHz is experimentally demonstrated In addition, we apply the generated optical single sideband signal for the spectral characterization of polarization dependent parameters of optical components The experimental characterization of the polarization dependent loss and the differential group delay of a phase-shifted fiber Bragg grating is performed in order to demonstrate the feasibility of the technique
TL;DR: In this paper, the performance and limitation of real WPT-OFDM systems were investigated, and the Haar wavelet was used as an alternative approach to the conventional optical OFDM systems.
Abstract: Wavelet packet transform-based optical OFDM (WPT-OFDM) systems can be used as an alternative approach to the conventional optical OFDM systems. In this paper, we investigate the performance and limitation of real WPT-OFDM systems. Its double-sideband characteristic makes it sensitive to spectrally non-symmetric dispersion such as polarization-mode dispersion (PMD). Simulations of dual-polarization WPT-OFDM transmission are carried out in the presence of PMD, and compared with conventional Fourier transform-based optical OFDM (FT-OFDM). The results show that WPT-OFDM is very sensitive to PMD, incurring 1-dB penalty at 5-11 ps DGD for 112-Gb/s dual-polarization transmission. PAPR and nonlinearity performance of WPT-OFDM are also analyzed in this work. We show that the Haar wavelet has 0.9-dB improvement in nonlinear launch power limit compared with FT-OFDM (CP=1/8) in a conventional transmission dispersion configuration where inline dispersion is fully compensated by a dispersion-compensation-fiber (DCF).
TL;DR: In this paper, an optical performance monitoring technique for simultaneous monitoring of optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion, using an artificial neural network trained with asynchronous amplitude histograms (AAHs), was proposed.
Abstract: We propose an optical performance monitoring technique for simultaneous monitoring of optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) using an artificial neural network trained with asynchronous amplitude histograms (AAHs). Simulations are conducted to demonstrate the technique for both 40-Gb/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) and 40-Gb/s noneturn-to-zero 16 quadrature amplitude modulation (16-QAM) systems. The OSNR, CD, and PMD monitoring range and root-mean-square (rms) errors are 10-30 and 0.43 dB, 0-400 and 9.82 ps/nm, and 0-10 and 0.92 ps, respectively, for RZ-DQPSK systems. For 16-QAM system, the monitoring range and rms errors are 10-30 and 0.2 dB, 0-400 and 9.66 ps/nm, and 0-30 and 0.65 ps for OSNR, CD, and PMD, respectively. As the generation of AAH does not require any clock or timing recovery, the proposed technique can serve as a low-cost option to realize in-service multiparameter monitoring for the next-generation transparent optical networks.
TL;DR: This work proposes and demonstrates the parametric optimization of Digital Backward Propagation algorithm for mitigating fiber transmission impairments and investigates the optimization of iterative and non-iterative symmetric split-step Fourier method for solving the inverse non-linear Schrödinger equation (NLSE).
Abstract: The parametric optimization of Digital Backward Propagation (DBP) algorithm for mitigating fiber transmission impairments is proposed and numerically demonstrated for phase modulated signals in mixed-optical fiber transmission link. The optimization of parameters i.e. dispersion (D) and non-linear coefficient (γ) offer improved eye-opening (EO). We investigate the optimization of iterative and non-iterative symmetric split-step Fourier method (S-SSFM) for solving the inverse non-linear Schrodinger equation (NLSE). Optimized DBP algorithm, with step-size equal to fiber module length i.e. one calculation step per fiber span for obtaining higher computational efficiency, is implemented at the receiver as a digital signal processing (DSP) module. The system performance is evaluated by EO-improvement for diverse in-line compensation schemes. Using computationally efficient non-iterative symmetric split-step Fourier method (NIS-SSFM) upto 3.6dB referenced EO-improvement can be obtained at 6dBm signal launch power by optimizing and modifying DBP algorithm parameters, based on the characterization of the individual fiber types, in mixed-optical fiber transmission link.
TL;DR: The results obtained demonstrate that the use of digital nonlinear backpropagation increases the optimum launch power from -4 dBm to -1 dBm with a consequent increase in maximum reach from 1440 km to 2400 km, which is a record transmission distance for QAM-16 reported to date for an SMF link with EDFAs only.
Abstract: In this paper long-haul, single channel, polarization multiplexed 16-state quadrature amplitude modulation (PDM-QAM-16) transmission at 112 Gbit/s is investigated. Novel digital signal processing techniques are used to perform carrier phase estimation and symbol estimation, in combination with nonlinear digital backpropagation. The results obtained demonstrate that the use of digital nonlinear backpropagation increases the optimum launch power from -4 dBm to -1 dBm with a consequent increase in maximum reach from 1440 km to 2400 km, which is a record transmission distance for QAM-16 reported to date for an SMF link with EDFAs only. Furthermore, experimental measurements are supported by simulations, based on the link used in the experiment.
22 Nov 2010
TL;DR: A siliconWaveguide based TE mode converter was designed for the mode conversion between a horizontal waveguide and vertical waveguide in the two-layer structure waveguide based polarization diversity circuit and its performance was studied.
Abstract: A silicon waveguide based TE mode converter was designed for the mode conversion between a horizontal waveguide and vertical waveguide in the two-layer structure waveguide based polarization diversity circuit. The TE mode converter's performance was studied. The polarization mode converter with minimum length of 5μm was demonstrated to provide the TE mode conversion while maintaining the polarization status. The insertion loss at the transition region was less than 3dB.
TL;DR: In this article, the supercontinuum process in optical fibers was studied numerically for a variety of dispersion profiles to investigate how a specific dispersion profile controls the emission of dispersive waves.
TL;DR: A widely tunable synchronously pumped coherent source based on the process of narrowband parametric amplification in a dispersion-shifted fiber that yields oscillations at 1970 to 2140 nm-the longest reported wavelength for a fiber parametric oscillator.
Abstract: We describe a widely tunable synchronously pumped coherent source based on the process of narrowband parametric amplification in a dispersion-shifted fiber. Using an experimental fiber with a zero-dispersion wavelength of 1590nm and pump wavelengths of 1530 to 1570nm yields oscillations at 1970 to 2140nm—the longest reported wavelength for a fiber parametric oscillator. The long-wavelength oscillations are accompanied by simultaneous short-wavelength oscillations at 1200 to 1290nm. The parametric gain is coupled to stimulated Raman scattering. For parametric oscillations close to the Raman gain peak, the two gain processes must be discriminated from each other. We devised two configurations that achieve this discrimination: one is based on the exploitation of the difference in group delay between the wavelengths where Raman and parametric gain peak, and the other uses intracavity polarization tuning.
TL;DR: In this paper, a new structure of polarization splitter based on a dual-elliptical core photonic crystal fiber was proposed, and the vector boundary element method was used to investigate the propagation characteristics of the device under various conditions.
Abstract: We propose a new structure of polarization splitter based on a dual-elliptical-core photonic crystal fiber. The polarization splitter has a simple and symmetric directional coupler configuration. The vector boundary element method is used to investigate the propagation characteristics of the device under various conditions. Results of the numerical calculation relevant to the design conditions are presented. A 0.3-mm-long splitter with an extinction ratio of 23 dB is obtained.
TL;DR: The results show that the nonlinear phase noise induced by FWM is significantly larger than that induced by SPM and XPM, which is in contrast to traditional WDM systems where ASE-FWM interaction is negligible in quasi-linear systems.
Abstract: We derive an analytical formula to estimate the variance of nonlinear phase noise caused by the interaction of amplified spontaneous emission (ASE) noise with fiber nonlinearity such as self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in coherent orthogonal frequency division multiplexing (OFDM) systems The analytical results agree very well with numerical simulations, enabling the study of the nonlinear penalties in long-haul coherent OFDM systems without extensive numerical simulation Our results show that the nonlinear phase noise induced by FWM is significantly larger than that induced by SPM and XPM, which is in contrast to traditional WDM systems where ASE-FWM interaction is negligible in quasi-linear systems We also found that fiber chromatic dispersion can reduce the nonlinear phase noise The variance of the total phase noise increases linearly with the bit rate, and does not depend significantly on the number of subcarriers for systems with moderate fiber chromatic dispersion
TL;DR: Two polarization-independent Michelson fiber interferometers were used to measure the in-band OSNR of an optical signal from 5 to 30 dB within an accuracy of 0.5 dB using an expansion of the amplitude autocorrelation function of the signal around zero delay.
Abstract: Two polarization-independent Michelson fiber interferometers with different optical delays were used to measure the in-band OSNR of an optical signal from 5 to 30dB within an accuracy of 0.5dB. Using an expansion of the amplitude autocorrelation function of the signal around zero delay, it was possible to perform measurements without any prior knowledge of the signal. The system is shown to be immune to the effects of modulation frequency (up to 10G), partially and fully polarized noise, chromatic dispersion and poorly biased modulators.
TL;DR: A configuration for real-time measurement of unique, space-variant, polarizations is presented and results reveal that the full state of polarization at each location within the beam can be accurately obtained every 10 msec, limited only by the camera frame rate.
Abstract: A configuration for real-time measurement of unique, space-variant, polarizations is presented. The experimental results reveal that the full state of polarization at each location within the beam can be accurately obtained every 10 msec, limited only by the camera frame rate. We also present a more compact configuration which can be modified to determine the real-time wavelength variant polarization measurements.
TL;DR: In this article, it was shown that the nonlinear depolarization induced by cross-polarization modulation leads to crosstalk between the polarization-division multiplex (PolDM) subchannels during their demultiplexing.
Abstract: We show theoretically and with the aid of computer simulations that the nonlinear depolarization induced by cross-polarization modulation leads to crosstalk between the polarization-division multiplex (PolDM) subchannels during their demultiplexing. This additive crosstalk can be approximated as additive Gaussian noise, and we derive expressions to estimate its variance. It can lead to significant penalties of up to several decibels for PolDM transmission and must be properly accounted for. We also show why time-interleaving both subchannels can significantly reduce these penalties.
TL;DR: In this paper, the feasibility of non-local compensating for polarization mode dispersion (PMD) when polarization entangled photons are distributed in fiber-optic channels was studied, taking into account the possibility that entanglement is generated through the use of a pulsed optical pump signal.
Abstract: We study the feasibility of nonlocally compensating for polarization mode dispersion (PMD), when polarization entangled photons are distributed in fiber-optic channels.We quantify the effectiveness of nonlocal compensation while taking into account the possibility that entanglement is generated through the use of a pulsed optical pump signal.
21 Mar 2010
TL;DR: In this paper, a two-stage constant-modulus-algorithm (CMA) equalizer for polarization-demultiplexing in a polarization-division-multiplexed coherent receiver is demonstrated.
Abstract: A two-stage constant-modulus-algorithm (CMA) equalizer for polarization-demultiplexing in a polarization-division-multiplexed coherent receiver is demonstrated. The equalizer eliminates the singularity problem of CMA equalizers and provides an effective way to monitor polarization-mode dispersion and polarization-dependent loss.
TL;DR: A novel system for the accurate measurement of all polarization related parameters, including polarization mode dispersion and polarization dependent loss, using binary magneto-optic polarization rotators, which achieves unprecedented DGD, SOPMD, and PDL accuracies.
Abstract: We report a novel system for the accurate measurement of all polarization related parameters, including polarization mode dispersion and polarization dependent loss, using binary magneto-optic polarization rotators. By taking advantage of the binary nature of the rotators, we achieved unprecedented DGD, SOPMD, and PDL accuracies of 2.6 fs, 1.39ps2, and 0.06 dB respectively; repeatabilities of 0.022 fs, 0.28 ps2, and 0.034dB respectively; and resolutions of 1 fs, 0.005 ps2 and 0.01dB respectively, from 1480 to 1620 nm.
TL;DR: In this paper, a white-light interferometric technique for a broad spectral range measurement (e.g. 500-1600 nm) of chromatic dispersion of polarization modes in short-length optical fibres was presented.
Abstract: We report on a white-light interferometric technique for a broad spectral range measurement (e.g. 500–1600 nm) of chromatic dispersion of polarization modes in short-length optical fibres. The technique utilizes an unbalanced Mach–Zehnder interferometer with a fibre under test of known length inserted in one of the interferometer arms and the other arm with adjustable path length. We record a series of spectral interferograms by VIS–NIR and NIR fibre-optic spectrometers to measure the equalization wavelength as a function of the path length difference, or equivalently the differential group index dispersion of one polarization mode. The differential group dispersion of the other polarization mode is obtained from measurement of the group modal birefringence dispersion. We verify the applicability of the method by measuring the chromatic dispersion of polarization modes in a birefringent holey fibre. We apply a five-term power series fit to the measured data and confirm by its differentiation that the chromatic dispersion agrees well with that specified by the manufacturer. We also measure by this technique the chromatic dispersion of polarization modes in an elliptical-core fibre.
TL;DR: In this paper, the authors report all optical clock recovery based on a monolithic integrated four-section amplified feedback semiconductor laser (AFL), with the different sections integrated based on the quantum well intermixing (QWI) technique.
Abstract: We report all optical clock recovery based on a monolithic integrated four-section amplified feedback semiconductor laser (AFL), with the different sections integrated based on the quantum well intermixing (QWI) technique. The beat frequency of an AFL is continuously tunable in the range of 19.8-26.3 GHz with an extinction ratio above 8 dB, and the 3-dB linewidth is close to 3 MHz. All- optical clock recovery for 20 Gb/s was demonstrated experimentally using the AFL, with a time jitter of 123.9 fs. Degraded signal clock recovery was also successfully demonstrated using both the dispersion and polarization mode dispersion (PMD) degraded signals separately.
TL;DR: In this paper, the design of a polarization de-multiplexer and a polarization mode dispersion compensator for direct-detect polarization division multiplexed (PDM) return-to-zero differential quadrature phase shift keying (RZ-DQPSK) systems are studied in detail.
Abstract: The design of a polarization de-multiplexer and a polarization mode dispersion compensator (PMDC) for direct-detect polarization division multiplexed (PDM) return-to-zero differential quadrature phase shift keying (RZ-DQPSK) systems are studied in detail. The impact of polarization dependent loss is studied in polarization de-multiplexers with different error detection configurations for both bit-aligned and bit-interleaved PDM systems. The level of the clock frequency of the combined pulse train of the two polarizations is proposed as the error signal for the PMDC. It enables the PMDC to work in the cancellation mode. Two separate control loops are proposed for the polarization de-multiplexer and the PMDC to allow them to work independently. The DGD tolerances for the one-stage and two-stage PMDC are measured and discussed. Finally the glitch problem in the polarization tuning algorithm is studied. An advanced dithering algorithm and the corresponding architecture of the polarization controller are proposed to solve the glitch problem.
TL;DR: The first experimental demonstration of compatible single-sideband (compatible-SSB) modulated OFDM optical system at 11.1Gb/s data rate for long distance transmission over 675 km uncompensated standard single-mode fiber and it is shown that optimum modulation index value decreases with increasing transmission distance.
Abstract: We present the first experimental demonstration of compatible single-sideband (compatible-SSB) modulated OFDM optical system at 11.1Gb/s data rate for long distance transmission over 675 km uncompensated standard single-mode fiber. Compatible-SSB modulation employing a simple dual-drive Mach-Zehnder modulator (MZM) in the transmitter and direct-detection at the receiver provides an OFDM system implementation with reduced complexity. It does not require a guard-band between the carrier and the OFDM sideband and so makes full use of available digital-to-analog converter (DAC) bandwidth. We demonstrate digital pre-compensation applied in the transmitter to correct MZM nonlinear transfer function and to improve the system transmission performance. We show that optimum modulation index value decreases with increasing transmission distance. We have also investigated the impact of self-phase modulation (SPM) on the system performance, and show that a compatible-SSB modulated system is less vulnerable to SPM in comparison to the conventional offset-SSB modulation at the same data rate.