Showing papers on "Polarization mode dispersion published in 2014"
TL;DR: In this paper, the authors designed and built a new type of spatial mode multiplexer based on MPLC, with very low intrinsic loss and high mode selectivity, and demonstrated its performance for the first 6 eigenmodes of a few-mode fiber.
Abstract: We designed and built a new type of spatial mode multiplexer, based on Multi-Plane Light Conversion (MPLC), with very low intrinsic loss and high mode selectivity. In this first demonstration we show that a typical 3-mode multiplexer achieves a mode selectivity better than −23 dB and a total insertion efficiency of −4.1 dB (optical coating improvements could increase efficiency to −2.4 dB), across the full C-band. Moreover this multiplexer is able to perform any mode conversion, and we demonstrate its performance for the first 6 eigenmodes of a few-mode fiber: LP01, LP11a, LP11b, LP02, LP21a and LP21b.
264 citations
TL;DR: The performance of digital backpropagation (DBP) equalization when applied over multiple channels to compensate for the nonlinear impairments in optical fiber transmission systems is investigated and the effectiveness of the algorithm is evaluated.
Abstract: The performance of digital backpropagation (DBP) equalization when applied over multiple channels to compensate for the nonlinear impairments in optical fiber transmission systems is investigated. The impact of a suboptimal multichannel DBP operation is evaluated, where implementation complexity is reduced by varying parameters such as the number of nonlinear steps per span and sampling rate. Results have been obtained for a reference system consisting of a 5×32 Gbaud PDM-16QAM superchannel with 33 GHz subchannel spacing and Nyquist pulse shaping under long-haul transmission. The reduction in the effectiveness of the algorithm is evaluated and compared with the ideal gain expected from the cancellation of the nonlinear signal distortion. The detrimental effects of polarization mode dispersion (PMD) with varying DBP bandwidth are also studied. Key parameters which ensure the effectiveness of multichannel DBP are identified.
125 citations
TL;DR: It is shown experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.
Abstract: In this work we experimentally investigate the improved intra-channel fiber nonlinearity tolerance of digital subcarrier multiplexed (SCM) signals in a single-channel coherent optical transmission system. The digital signal processing (DSP) for the generation and reception of the SCM signals is described. We show experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold of 3.8 × 10−3 and by 8% in a 24 GBaud DP-16-QAM transmission with a BER threshold of 2 × 10−2. Moreover, we show by simulations that the improved performance of SCM signals is observed over a wide range of baud rates, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.
124 citations
TL;DR: Strong modal coupling between the TE00 and TM00 modes in Si3N4 ring resonators revealed by avoided crossings of the corresponding resonances leads to an effective dispersion that is one order of magnitude larger than the intrinsic dispersion and creates broad windows of anomalous dispersion.
Abstract: We observe strong modal coupling between the TE00 and TM00 modes in Si3N4 ring resonators revealed by avoided crossings of the corresponding resonances. Such couplings result in significant shifts of the resonance frequencies over a wide range around the crossing points. This leads to an effective dispersion that is one order of magnitude larger than the intrinsic dispersion and creates broad windows of anomalous dispersion. We also observe the changes to frequency comb spectra generated in Si3N4 microresonators due to polarization mode and higher-order mode crossings and suggest approaches to avoid these effects. Alternatively, such polarization mode crossings can be used as a tool for dispersion engineering in microresonators.
100 citations
TL;DR: A polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity and has negligible sensitivity to the polarization states of the neighboring WDM channels is demonstrated.
Abstract: We demonstrate a polarization-managed 8-dimensional modulation format that is time domain coded to reduce inter-channel nonlinearity. Simulation results show a 2.3 dB improvement in maximum net system margin (NSM) relative to polarization multiplexed (PM)-BPSK, and a 1.0 dB improvement relative to time interleaved return-to-zero (RZ)-PM-BPSK, for five WDM channels propagating over 1600 km ELEAF with 90% inline optical dispersion compensation. In contrast to the other modulations considered, the new 8-dimensional format has negligible sensitivity to the polarization states of the neighboring WDM channels. High-density WDM (HD-WDM) measurements on a 5000 km dispersion-managed link show a 1.0 dB improvement in net system margin relative to PM-BPSK.
96 citations
TL;DR: In this article, a residual dispersion compensating octagonal photonic crystal fiber (OPCF) with an elliptical array of circular air-holes in the fiber core region is proposed.
Abstract: 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.
57 citations
TL;DR: In this paper, a spiral photonic crystal fiber (PCF) with flat and low dispersion over a wide wavelength range has been proposed, which adopts an elliptical slot core.
Abstract: We propose a new type of highly nonlinear spiral photonic crystal fiber (PCF) with flat and low dispersion over a wide wavelength range. The new PCF structure adopts an elliptical slot core. The simulation results show that the nonlinear coefficients in our proposed PCF are (quasi-TE mode) and 226 W-1 m-1 (quasi-TM mode) at the wavelength of 1.55 μm and the nonlinear coefficient increases with the wavelength increasing. It is also demonstrated that ultraflattened dispersion of 0.91 ps/(nm·km) (quasi-TE mode) and 1.33 ps/(nm·km) (quasi-TM mode) can be achieved over a 150-nm wavelength range, and two near-zero dispersion slopes of -1.25×10-3 ps/(nm2·km) (quasi-TE mode) and -4.82×10-3 ps/(nm2·km) (quasi-TM mode) at 1.55 μm can also be obtained. Owing to its high nonlinear coefficient and flattened dispersion, the proposed slotted spiral PCF will have great potential for all-optical signal processing applications.
53 citations
TL;DR: In this article, a highly birefringent dispersion compensating hybrid photonic crystal fiber is presented, which successfully compensates the chromatic dispersion of standard single mode fiber over E-to-L communication bands.
Abstract: A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm −1 at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10 −2 at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.
46 citations
24 Nov 2014
TL;DR: In this article, an alternative derivation of analytical expressions for the coefficients of the perturbative nonlinear precompensation algorithm in dispersion-unmanaged regime for arbitrary pulse shapes is presented.
Abstract: We present an alternative derivation of analytical expressions for the coefficients of the perturbative nonlinear pre-compensation algorithm in dispersion-unmanaged regime for arbitrary pulse shapes. We specialize to Nyquist pulse-shapes and show the usefuleness of new formulae through simulations and experiments.
45 citations
TL;DR: In this article, a single mode circular photonic crystal fiber (C-PCF) was proposed for broadband dispersion compensation covering 1400 to 1610nm wavelength band over the telecommunication windows.
42 citations
TL;DR: In this article, a fast, accurate and simple field coupling model is presented which is capable of describing mode coupling effects due to bends and splices in multimode fibers with parabolic index profile as well as the coupling losses induced by this process.
Abstract: A fast, accurate and simple field coupling model is presented which is capable of describing mode coupling effects due to bends and splices in multimode fibers with parabolic index profile as well as the coupling losses induced by this process. This model is validated numerically by comparing the results to the well-known coupled amplitude theory model yielding the same relative bandwidth increase behavior as long as the coupling losses are the same. It is shown, that the number of discrete segments used in this model can be reduced considerably as long as the coupling losses are kept constant. The effect of mode coupling on the differential group delay, mode dependent loss, bandwidth gain and impulse response width reduction are analyzed. It is shown that the relative bandwidth gain induced in MMF links induced by the coupling process is independent of fiber parameters or number of guided modes; it can be fully characterized by coupling induced losses. The model is compared to well-known results given by power coupling models and a good agreement is observed for high steady state loss values.
TL;DR: The experimental results are the first demonstration of using MSSI for nonlinearity compensation in any dual polarization coherent system, and an overall transmission distance increase of more than 70% is expected using M SSI.
Abstract: We experimentally demonstrate fiber nonlinearity compensation in dual polarization coherent optical OFDM (DP CO-OFDM) systems using mid-span spectral inversion (MSSI). We use third-order nonlinearity between a pump and the signal in a highly nonlinear fiber (HNLF) for MSSI. Maximum launch powers at FEC threshold for two 10 × 80-km 16-QAM OFDM systems were increased by 6.4 dB at a 121-Gb/s data rate and 2.8 dB at 1.2 Tb/s. The experimental results are the first demonstration of using MSSI for nonlinearity compensation in any dual polarization coherent system. Simulations show that these increases could support a 22% increase in total transmission distance at 1.2-Tb/s system without increasing the number of inline amplifiers, by extending the fiber spans from 90 to 110 km. When spans of 80 km are used, simulations reveal that MSSI system performance shows less degradation with increasing transmission distance, and an overall transmission distance increase of more than 70% is expected using MSSI.
TL;DR: 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.
TL;DR: The designs proposed in this paper have bright prospects for applications in all-optical format conversion, supercontinuum generation, optical wavelength conversion, and many other fields.
Abstract: A novel (to our knowledge) type of photonic crystal fiber (PCF) with high nonlinearity and flattened dispersion is proposed. The propagation characteristics of chromatic dispersion, effective area, and nonlinearity are studied numerically by using the full-vector finite element method. Several PCF designs with high nonlinearity and nearly zero flattened dispersion or broadband flattened, and even ultraflattened, dispersion over different wavelength bands are obtained by optimizing the structural parameters. One optimized PCF has a nearly zero ultraflattened dispersion of 2.3 ps/(nm·km) with a dispersion variation of 0.2 ps/(nm·km) over the C+L+U wavelength bands. In addition, the dispersion slope and nonlinear coefficient at 1.55 μm can be up to 2.2×10−3 ps/nm2·km and 33.2 W−1·km−1, respectively. The designs proposed in this paper have bright prospects for applications in all-optical format conversion, supercontinuum generation, optical wavelength conversion, and many other fields.
TL;DR: A source based on spontaneous parametric downconversion is presented, which allows one to control spectral correlations within the entangled photon pair without spectral filtering by changing the pump-pulse duration or the characteristics of the coupled spatial modes.
Abstract: Spectrally correlated photon pairs can be used to improve the performance of long-range fiber-based quantum communication protocols. We present a source based on spontaneous parametric downconversion, which allows one to control spectral correlations within the entangled photon pair without spectral filtering by changing the pump-pulse duration or the characteristics of the coupled spatial modes. The spectral correlations and polarization entanglement are characterized. We find that the generated photon pairs can feature both positive spectral correlations, decorrelation, or negative correlations at the same time as polarization entanglement with a high fidelity of 0.97 (no background subtraction) with the expected Bell state.
TL;DR: It is theoretically proved that Nyquist pulses with a spectrum of 5 flat comb lines can be generated using a single DPMZM, which is also verified with simulation and the tunability of repetition rate is verified.
Abstract: The generation of Nyquist pulses with a dual parallel Mach-Zehnder modulator (DPMZM) driven by a single RF signal is demonstrated theoretically and experimentally. A complete theoretical analysis is developed and the limitation of the proposed scheme is also discussed. It is theoretically proved that Nyquist pulses with a spectrum of 5 flat comb lines can be generated using a single DPMZM, which is also verified with simulation. 7 flat comb lines in frequency domain can also be obtained if a large RF driving voltage is applied to DPMZM but the generated waveforms won’t present a sinc-shape. This scheme is further investigated experimentally. 40 GHz Nyquist pulses with full-width-at-half-maximum (FWHM) less than 4.65 ps, signal-to-noise ratio (SNR) better than 29.5 dB, and normalized root-mean-square error (NRMSE) less than 2.4% are generated. It is found that a tradeoff exists between the insertion loss of the DPMZM and the deviation of generated pulses. The tunability of repetition rate is experimentally verified by generation of 1 GHz to 40 GHz Nyquist pulses with SNR better than 28.4 dB and NRMSE less than 6.15%.
TL;DR: A polarization-independent 2 × 2 switch based on silicon-wire waveguides has been realized with a compact size of 600 × 500 μm², achieved with a polarization-diversity technique which implements polarization splitters, TE-TM intersections, and Mach-Zehnder switches.
Abstract: A polarization-independent 2 × 2 switch based on silicon-wire waveguides has been realized with a compact size of 600 × 500 μm². Polarization-independent operation was achieved with a polarization-diversity technique which implements polarization splitters, TE-TM intersections, and Mach-Zehnder switches. The extinction ratios of the 2 × 2 switch for TE, TM, and a mixed polarization at a wavelength of 1550 nm were measured to be larger than 30 dB, 25 dB, and 30 dB, respectively. The measured switching powers for the TE and TM polarizations were 25 and 55 mW, respectively. The measured polarization-dependent loss was lower than 1 dB. The differential group delay (DGD) between the TE and TM modes was also evaluated using the Mueller matrix method, which was in good agreement with the values estimated from the path lengths for each mode. A path-length-compensated switch was fabricated, whose DGDs for all paths were indeed as small as ~2 ps, mainly from the access waveguides. The switch could provide an important route to develop ultra-compact polarization-independent integrated circuits based on silicon-wire waveguides.
TL;DR: In this article, a systematic analysis of the dispersion characteristics of a selectively liquid-filled dual-core PCF by varying different geometrical parameters towards achieving ultra negative dispersion values around a desired wavelength has been carried out.
TL;DR: This paper presents for the first time the numerical analysis and experimental demonstration of single-carrier SV-DD, a novel detection scheme that is resilient to both chromatic dispersion and signal-to-signal beat noise and does not require polarization tracking or narrow band optical filtering for carrier extraction.
Abstract: We propose a novel detection scheme called Stokes vector direct detection (SV-DD) to realize high electrical spectral efficiency and cost-effective optical communication for short and medium reach. With SV-DD, the signal is modulated in only one polarization and combined with the carrier in the orthogonal polarization for fiber transmission. At reception, the combined signal is detected in Stokes space by three or four photo-detectors. Compared with conventional DD technique, SV-DD is resilient to both chromatic dispersion and signal-to-signal beat noise. Furthermore, SV-DD does not require polarization tracking or narrow band optical filtering for carrier extraction. In this paper, we present for the first time the numerical analysis and experimental demonstration of single-carrier SV-DD. We report 62.5-Gb/s data rate single-carrier SV-DD transmission over 160-km SSMF using 12.5-Gbaud 32-QAM modulation.
TL;DR: The experimental results show that there is no correlation between the programmed frequency offset between a subcarrier and nearest comb line, and the received signal quality, so subcarriers could be inserted into unused portions of an optical transmission system's spectrum without restriction on their particular center frequencies.
Abstract: We investigate the underlying mechanism that allows OFDM subcarriers in an all-optical OFDM system to be assigned to any optical frequency using an optical filter, even if that frequency is not generated by the comb-line source feeding the filters. We confirm our analysis using simulations, and present experimental results from a 252-subcarrier system that uses a mode-locked laser (MLL) as the comb source and a wavelength selective switch. The experimental results show that there is no correlation between the programmed frequency offset between a subcarrier and nearest comb line, and the received signal quality. Thus, subcarriers could be inserted into unused portions of an optical transmission system's spectrum without restriction on their particular center frequencies. Any percentage of cyclic prefix can be added to the OFDM symbol simply by reprogramming the optical filter to give wider subcarrier frequency spacing than the comb line spacing, which is useful for tailoring the CP to the dispersion of various optical transmission paths, to maximize the spectral efficiency. Finally, the MLL's center frequency need not be locked to a system reference.
TL;DR: In this article, the channel equalizer (CE) based on independent component analysis (ICA) for optical OFDM systems without using training symbols (TSs) is studied. And the authors propose a channel matrix initialization method to solve the permutation indeterminacy and complex uncertain scaling problems in ICA.
Abstract: We study the channel equalizer (CE) based on independent component analysis (ICA) for optical orthogonal-frequency-division-multiplexing (OFDM) systems without using training symbols (TSs). We begin by studying mathematical ICA models of optical OFDM systems and considering both the direct-detection optical OFDM (DDO-OFDM) and polarization division multiplexing coherent-detection optical OFDM (PDM-CO-OFDM) systems. One purpose of this paper is to provide a comprehensive study of ICA-based CE in both DDO-OFDM and CO-OFDM systems. Next, we propose a channel matrix initialization method to solve the permutation indeterminacy and complex uncertain scaling problems in ICA for both DDO-OFDM and PDM-CO-OFDM systems. Several algorithms are then investigated for ICA-based CEs including maximization of negentropy (MN), maximum likelihood (ML), minimization of mutual information (MMI), and fast ICA. It is found that the ICA-based CEs using MN, ML, and MMI can successfully recover the OFDM signal. Through both simulation and experiment, we show that in comparison to conventional TSs-based CEs with and without inter-symbol frequency-domain averaging (ISFA) and adaptive decision-directed CE, ICA-based CEs can provide slightly better or similar performances for both SP and DP optical OFDM systems with QPSK and 16-QAM modulations. Specifically, apart from higher spectral efficiency, the ICA-based CEs show significant better chromatic dispersion and polarization mode dispersion (PMD) tolerances than TSs-based CEs with ISFA in PDM-CO-OFDM systems over long-haul transmission.
TL;DR: In this article, a data-aided in-band optical-signal-to-noise ratio (OSNR) monitoring method was proposed, which employs the periodic property of a specially de-signed short training sequence to differentiate the signal power from noise and is proved to be insensitive to the first-order polarization mode dispersion (PMD).
Abstract: We propose and demonstrate a new data-aided in-band optical-signal-to-noise ratio (OSNR) monitoring method, which employs the periodic property of a specially de- signed short training sequence to differentiate the signal power from noise and is proved to be insensitive to the first-order polarization mode dispersion (PMD). This method is verified in a typical 112-Gb/s polarization multiplexed-quadrature phase shift keying and a 224-Gb/s polarization multiplexed-16 quadrature amplitude modulation coherent optical transmission system. The results show that the method is highly accurate, with the moni- toring error less than 1 dB in the OSNR range of 7-30 dB under different linewidths and has good robustness to a large amount of residual accumulated CD and first-order PMD.
TL;DR: The vector PSA is experimentally shown to be sensitive to the pump states of polarization due to polarization mode dispersion in the fiber, but the scheme performance agrees well with theory under specific pump SOPs and the scheme achieves an on-off gain over 10 dB with a small deviation from the theoretically expected results.
Abstract: We comprehensively investigate a degenerate vector phase-sensitive amplifier (PSA). We determine the gain dependence on the relative phase and polarization angle between the pumps and the degenerate signal wave. The vector PSA is experimentally shown to be sensitive to the pump states of polarization (SOP) due to polarization mode dispersion in the fiber. However, the scheme performance agrees well with theory under specific pump SOPs and we achieve an on-off gain over 10 dB with a small deviation from the theoretically expected results. In comparison to the scalar scheme, the proposed vector scheme has larger tolerance for pump depletion due to four-wave mixing between pumps and generation of higher-order idlers.
TL;DR: This method of PDL monitoring and compensation in Stokes space is applied for each subcarrier in the frequency domain after SS-PDM and can match the performance of channel estimation based on training symbols (TSs).
Abstract: We have recently demonstrated polarization demultiplexing in Stokes space (SS-PDM), which is susceptible to polarization-dependent loss (PDL). In this paper, we apply the method of PDL monitoring and compensation in Stokes space to enhance SS-PDM. It is applied for each subcarrier in the frequency domain after SS-PDM. Because each subcarrier has a much lower speed and narrower bandwidth, the polarization effects that it experiences can be treated as flat. This method can work for different modulation formats on orthogonal frequency-division multiplexing (OFDM) subcarriers and only needs a small number of samples for convergence. In simulation, when the PDL is less than 3.5 dB, it significantly improves the performance of SS-PDM and is comparable with the conventional channel estimation based on training symbols (TSs). We also conduct the experiments of 66.6-Gb/s coherent optical PDM-OFDM with 4QAM subcarrier modulation over 5440-km SSMF and 133.3-Gb/s coherent optical PDM-OFDM with 16QAM subcarrier modulation over 960-km SSMF, respectively. The experimental results show that this method improves the performance of SS-PDM significantly and can match the performance of channel estimation based on TSs. To the best of our knowledge, this is the first experimental validation of PDL monitoring and compensation in Stokes space.
TL;DR: A novel update algorithm for the filter coefficients of the adaptive digital equalizer in coherent receivers, which is based on error signals evaluated in Stokes space and is insensitive to both phase-noise and frequency-offset is described.
Abstract: In this paper, we describe a novel update algorithm for the filter coefficients of the adaptive digital equalizer in coherent receivers, which is based on error signals evaluated in Stokes space and is insensitive to both phase-noise and frequency-offset. We also introduce an optimized decision rule in the Stokes space, which takes into account the exact statistics of noise and yields a performance improvement with respect to the minimum distance decision criterion. We compare the performance of the new algorithm to the standard constant-modulus algorithm (CMA) for polarization-multiplexed 16QAM modulation, achieving similar performance in the absence of phase noise, with comparable complexity. Differently from CMA, the proposed Stokes-space algorithm allows us to remove the phase offset between polarizations, thus enabling the use of a joint carrier-phase estimation algorithm on both polarizations, which in turns yields a nearly doubled phase noise tolerance.
24 Nov 2014
TL;DR: In this article, each principal mode of a few-mode fiber is generated and characterised for the first time, exhibiting more than an order of magnitude less modal dispersion than the idealised LP mode basis.
Abstract: Each principal mode of a few-mode fibre is generated and characterised for the first time, exhibiting more than an order of magnitude less modal dispersion than the idealised LP mode basis.
TL;DR: The proposed compact in-line modal interferometer is polarization-dependent and the adjacent interference fringes according to different components of LP(11) mode show greatly discrimination in sensitivities of temperature and strain, making it a good candidate for multiple physics parameters measurements.
Abstract: A compact in-line modal interferometer based on a long period grating (LPG) inscribed in water-filled photonic crystal fiber (PCF) is proposed and demonstrated. The interferometer works from the interference between fundamental core mode and different vector components of LP11 core mode. The LPG is especially inscribed to realize the energy exchange between the fundamental core mode and different vector components of LP11 core mode in the PCF. We build a complete theoretical model and systematically analyze the multi-component-intermodal-interference mechanism of the interferometer based on coupled-mode theory. Due to the asymmetric index distribution over the cross section of the PCF caused by CO2-laser side illumination, the dispersion curves and temperature sensitivities referring to different vector components of LP11 core mode are quite different. Thus the interferometer is polarization-dependent and the adjacent interference fringes according to different components of LP11 mode show greatly discrimination in sensitivities of temperature and strain, making it a good candidate for multiple physics parameters measurements.
TL;DR: A time domain structure of channel estimation for coherent optical communication systems, which employs training sequence based equalizer and is transparent to arbitrary quadrature amplitude modulation (QAM) formats is proposed.
Abstract: We propose a time domain structure of channel estimation for coherent optical communication systems, which employs training sequence based equalizer and is transparent to arbitrary quadrature amplitude modulation (QAM) formats. Enabled with this methodology, 1.02Tb/s polarization division multiplexed 32QAM Nyquist pulse shaping signal with a net spectral efficiency of 7.46b/s/Hz is transmitted over standard single-mode fiber link with Erbium-doped fiber amplifier only amplification. After 1190km transmission, the average bit-error rate is lower than the 20% hard-decision forward error correction threshold of 1.5 × 10−2. The transmission distance can be extended to 1428km by employing intra-subchannel nonlinear compensation with the digital back-propagation method.
01 Jan 2014
TL;DR: In this article, the shift of the zero dispersion wavelength (ZDW) is made by varying the refractive index profile of a USMF, then the designed profile is optimized for low dispersion and splice loss.
Abstract: Loss and dispersion are two crucial parameters to be determined as low as possible while designing optical fibers as optical transmission lines. In designing dispersion shifted fibers, one has to reduce the core diameter to smaller than unshifted single mode fiber (USMF) at 1550 nm wavelength region. This issue causes the nonlinear phenomenon of four wave mixing (FWM) to appear at 1550 nm. One of the approaches to reduce the effectiveness of the FWM is to shift the zero dispersion wavelength (ZDW) to some other wavelength in the third window of optical fiber communication. Dispersion compensating fibers (DCFs) with high negative dispersion are used in wavelength division multiplexing systems for neutralization of pulse spread in transmission fibers for higher system capacity. One of the approaches of securing a high negative dispersion is to change the refractive index profile of DCFs. In this paper, by using Optifiber software, the shifting of the ZDW is made by varying the refractive index profile of a USMF, then the designed profile is optimized for low dispersion and splice loss. The obtained results show that in designed profile the effective mode field diameter is reduced, which can effectively reduce the splice loss. In another attempt, the parameters of different DCF profiles are optimized to enhance negative dispersion of about -710 ps/nm.km, which is 5 times higher than the reported experimental results.
TL;DR: An SOI based polarization diversity scheme consisting of two 2D grating couplers and a micro ring resonator is proposed and fabricate and all-optical polarization insensitive clock recovery has been demonstrated successfully.
Abstract: We fabricate and demonstrate a compact polarization insensitive filter for all-optical clock recovery (CR) based on silicon-on-insulator (SOI), which consists of a microring resonator (MRR) and two modified two-dimensional (2D) grating couplers. The distributed Bragg reflectors (DBRs) are introduced to improve the coupling efficiency of the 2D grating coupler. The MRR works as a comb filter for CR, while the 2D grating couplers serve as the polarization diversity unit to achieve a polarization insensitive operation. A subsequent semiconductor optical amplifier (SOA) performs the amplitude equalization. Based on this scheme, a good clock signal with 970 fs timing jitter can be achieved at 44 Gb/s from input signals with arbitrary polarization states.