Mode Dispersion Compensation Research Articles

Photonic generation and transmission of dual-band double-TBWP chirped microwave waveforms with frequency multiplication and immunity to dispersion-induced power fading

A novel photonic approach for generating and transmitting dual-band double-time bandwidth product (TBWP) chirped microwave waveforms with frequency multiplication and immunity to dispersion-induced power fading is proposed. Utilizing an integrated dual-drive dual-parallel Mach-Zehnder modulator (DD-DPMZM), single-sideband modulation of the RF input and suppression of odd-order optical sidebands are achieved. By adjusting the RF input's centre frequency and the DD-DPMZM's bias voltages, dual-band waveforms with frequency multiplication are realized, enabling transmission through optical fibres without dispersion-induced power fading. Experimental validation demonstrates successful transmission over dispersion compensation modules equivalent to 60 km or 20 km of single-mode fibre. The proposed system features a simplified architecture, reconfigurability, and robust anti-dispersion capabilities, making it highly suitable for distributed multi-band radar networks over optical fibre links.

Strategy for Attacking the Key Parameters of Electro-Optic Self-Feedback Phase Encryption System

In this paper, we propose a method for cracking the key parameters of an electro-optic self-feedback temporal optical phase encryption system and experimentally demonstrate the feasibility of the scheme. By scanning a tunable dispersion compensation (TDC) module at the receiver, the time delay signature (TDS) of an encrypted signal can be exposed, making it possible to extract other key parameters of the system and reconstruct a decryption setup. The TDS characteristics for three typical modulation formats are investigated, revealing that while such an encryption system is secure against power detection attack, there is a risk of TDS leakage. The findings can guide the design of advanced optical encryption schemes with TDS suppression for security enhancement.

Cost-Effective C-Band 50-Gb/s PON Implemented by Using a 2-Bit DAC and Linear Electrical Equalizer

We propose and demonstrate a cost-effective C-band 50-Gb/s downstream 4-ary pulse amplitude modulation passive optical network system implementable by using a 2-bit digital-to-analog converter and a linear electrical equalizer. The waveform distortions induced by band-limitation of opto-electronic devices and fiber chromatic dispersion are compensated by using an electrical and optical pre-equalizers realized by a high-pass filter (HPF) and a dispersion-compensation module (DCM), respectively. To facilitate easy operation and management of the system, the amounts of pre-equalization are all fixed regardless of transmission distance up to 20 km. At the receiver, a linear feed-forward equalizer is employed to compensate for the remaining waveform distortions adaptively to transmission distance. Also, a semiconductor optical amplifier (SOA) is used as an optical pre-amplifier to increase the power budget. We determine the system parameters through experiment to maximize the power budget of the system. The experimental results show that the proposed system is capable of securing the power budget of 29.2 dB.

Design and performance investigation of Gaussian apodized FBG as hybrid dispersion compensation module for long-haul optical link

Abstract A hybrid dispersion compensation module design, using Gaussian apodized fiber Bragg grating and 11 km long dispersion compensation fiber, is proposed for a 111 km long optical link. The proposed module is examined successively with four different chirping techniques. Further, the design is investigated thoroughly in pre-, post- and symmetrical-compensation modes. The performance characteristics of the optimized links are evaluated orderly by quality-factor (Q-factor) values, Eye-diagram and pulse width reduction percentage (PWRP). To further enhance the Q-factor value, optimal parameters of FBG are determined comprehensively by varying the effective refractive index and grating length values. The results show that the proposed dispersion compensation module using Gaussian apodized fiber Bragg grating works well for the quadratic chirping technique. The Q-factor values attained in pre-, post- and symmetrical-compensation modes are 40.5, 49 and 50, respectively, far higher than the values proposed in the literature to date. Thus the proposed technique is best suited for symmetrical and post-compensation modes. The workability of the proposed system is verified using OptiSystem software.

Widely flexible and finely adjustable nonlocal dispersion cancellation with wavelength tuning.

In fiber-based quantum information processing with energy-time entangled photon pairs, optimized dispersion compensation is vital to preserve the strong temporal correlation of the photon pairs. We propose and experimentally verify that, by simply tuning the wavelength of the entangled photon pairs, nonlocal dispersion cancellation (NDC) can provide a widely flexible and finely adjustable solution for optimizing the dispersion compensation, which cannot be reached with the traditional local dispersion cancellation (LDC) instead. By way of example, when a 50 km-long single-mode fiber (SMF) is dispersion compensated by a 6.2-km-long commercial dispersion compensating fiber (DCF) based on the LDC configuration, it will lead to an almost invariant over-compensation in the wavelength range of 1500-1600 nm which restricts the observed temporal coincidence width of the self-developed energy-time entangled photon-pairs source to a minimum of ∼110 ps. While in the NDC configuration, the dispersion compensation can be readily optimized by tuning the signal wavelength to 1565.7 nm and a minimum coincidence width of 86.1 ± 0.7 ps is observed, which is mainly limited by the jitter of the single-photon detection system. Furthermore, such optimized dispersion compensation can also be achieved as the fiber length varies from 48 km to 60 km demonstrating the wide flexibility of NDC. Thanks to these capabilities, elaborate dispersion compensation modules are no longer required, which makes NDC a more versatile tool in fiber-based quantum information and metrology applications.

Nonlinear Coherent Optical Systems in the Presence of Equalization Enhanced Phase Noise

Equalization enhanced phase noise (EEPN) occurs due to the interplay between laser phase noise and electronic dispersion compensation (EDC) module. It degrades significantly the performance of uncompensated long-haul coherent optical fiber communication systems. In this work, a general expression accounting for EEPN is presented based on Gaussian noise model to evaluate the performance of multi-channel optical communication systems using EDC and digital nonlinearity compensation (NLC). The nonlinear interaction between the signal and the EEPN is analyzed. Numerical simulations are carried out in nonlinear Nyquist-spaced wavelength division multiplexing (WDM) coherent transmission systems. Significant performance degradation due to EEPN in the cases of EDC and NLC are observed, with and without the consideration of transceiver (TRx) noise. The validation of the analytical approach has been done via split-step Fourier simulations. The maximum transmission distance and the laser linewidth tolerance are also estimated to provide important insights into the impact of EEPN.

Performance of different hybrid dispersion compensation modules (DCMs) in long reach ultra dense WDM passive optical networks

Abstract Long reach Passive optical network (LR-PON) is an attractive solution to fulfill the ever-increasing bandwidth requirements due to propelling internet applications and competent to serve distant optical network units (ONUs). Wavelength division multiplexed (WDM) PON systems experience distance and performance limiting constraint termed as Dispersion. In order to compensate dispersion effects, Fiber bragg gratings (FBGs) and Dispersion compensation fibers (DCFs) are incorporated extensively in PONs. Performance of DCF is better than FBG in terms of dispersion compensation, but it comes at the cost of 3 $/m (very expensive). Therefore, long reach ultra dense WDM-PON systems are needed with incorporation of economical and high performance DCMs. Three newly constructed hybrid DCMs are investigated such as FBG-DCF (module 1), OPC-DCF (module 2), and FBG-DCF-OPC (module 3) in WDM-PON to get optimal DCM in terms of dispersion compensation efficiency (DCE) and economical operation. As per author’s best knowledge, DCE calculations and performance enhancement with cost reduction using hybrid DCMs in ultra dense WDM-PON, is not reported so far. WDM-PON consists of 32 channels at 25 GHz channel spacing is analyzed for 300 km link distance at 10 Gbps/channel using different hybrid DCMs. It is perceived that highest DCE of 70% is given by module 3 with maximum cost reduction of 19.84%. DCE performance of three modules is as follows: Module 3 (DCE 70%), Module 1 (DCE 55%), Module 2 (DCE 45%) and cost reduction/increase from conventional module by 19.84% reduction (Module 3), 19.05% reduction (Module 1), and increase 10.5% (Module 2). Hence, Module 3 is preferred for long reach WDM-PON to get high performance with lesser cost.

Possibility of Using the Spiral Single Mode Optical Fiber for Dispersion Compensation

This research show the possibility of using the Anisotropy of spiral single mode optical fiber for compensation the main three types (material,waveguide,and polarized) of dispersion.it is also study the effect of energies mutual transformation of optical pulsed signals that carried by orthogonal waves (HEe11) and (HEo11) on the generation the chromatic and polarized dispersions and inter symbol distortions of signals.an example of polarized modal dispersion compensation is gives.

Experimental Investigation of Intensity Modulator/Direct Detection (IM/DD) Optical OFDM System with Fiber Bragg Grating (FBG)

AbstractTo improve the performance of optical fiber transmission and to compensate the fiber chromatic dispersion (CD), we propose to use fiber Bragg grating (FBG) in intensity modulator/direct detection IM/DD optical orthogonal frequency division multiplexing (OOFDM) system, and experimentally demonstrate 2.5-Gbit/s QPSK-OFDM transmission over 200 km SMF-28. FBG used before the detection as a chromatic dispersion compensation module, reducing the beating noise between ASE noise and OFDM signal. By using the FBG in IM/DD OOFDM system, our experimental results show that the receiver sensitivity was improved about 2 dB at a bit error rate (BER) of $1 \times {10^{ - 3}}$ for 2.5 Gbit/s QPSK-OFDM signals after 200 km SMF-transmission compared to regular system without FBG.

Statistical Evaluation of PAM4 Data Center Interconnect System With Slope-Compensating Fiber Bragg Grating Tunable Dispersion Compensation Module

Data center interconnect (DCI) links with high data-rate direct-detection require strict chromatic dispersion compensation. One such solution which has been widely deployed is based on four-level pulse amplitude modulation (PAM4). With this application in mind, we describe in detail a 50-GHz channelized fiber Bragg grating (FBG) tunable dispersion compensation module (TDCM) which can compensate chromatic dispersion slope over the full C-band (4.8 THz) and is thus suitable for dense wavelength division multiplexing (DWDM) PAM4 DCI systems. We then present a comprehensive set of system performance results comprising 1,120 unique link measurements, to characterize the combined effect of statistical variations in component characteristics and link impairments, and show that a statistical approach to link budgeting is advantageous in this type of system. We also analyze the group delay ripple characteristics of the FBG-TDCM device and the corresponding impact on the PAM4 system. Instead of the conventional phase ripple standard deviation, we introduce a novel metric to quantify high-frequency phase ripple, which is better correlated with the impact on the PAM4 system.

Performance analysis of an improved modal dispersion compensation receiver for low-frequency and long-range shallow water communication experiment

Low-frequency acoustic signal will suffer from dispersion effect when propagating in long-range shallow water waveguide, which leads to multi-mode and waveform expanding. Longer transmission range and shallower waveguide will result in more serious dispersion effect. In this paper, we propose an improved modal dispersion compensation receiver, and evaluate its performance for a shallow water acoustic communication experiment. The receiver not only exploits time-frequency analysis approach to compensate the waveform expanding effect of each mode simultaneously, but also combines the modified multi-mode energy to enhance symbol estimation accuracy. The experiment is conducted by a differential-binary-phase-shift-keying modulated direct-sequence-spread-spectrum communication system, which is suitable for long-range transmission. With this receiver, we obtain no error demodulation results without coding in the experiment. The experimental data analysis also shows that the proposed receiver can obtain about 3 dB gain than the conventional one, which is of significant importance for long-range communications.

Modal dispersion compensation receiver for the long range shallow water acoustic communications.

The received low frequency signals in the long range shallow water will suffer severe attenuation and modal dispersion effect, which will distort the signal and deteriorate the communication performance. In this letter, a modal dispersion compensation receiver is proposed, which exploits the de-dispersion transform to compensate intra-mode dispersion and the rake combination to combine the multi-mode components. With the proposed receiver, the waveform expansion of high order modes is compensated, and thus more modes can be distinguished from the noise and the rake combination gain is improved, which leads to high communication accuracy. Simulation results show that the proposed receiver can achieve about 3 dB gain for the 40 km range and signal with a center frequency 400 Hz.

Modified Manchester modulation format for high‐speed optical transmission systems

A novel advanced modulation format based on Manchester signalling is proposed and assessed for high-speed optical communication systems. The new advanced modulation format known as modified Manchester derived from the combination of Manchester and vestigial sideband (VSB) techniques. Its performance assessed and compared in terms of spectral efficiency, chromatic dispersion tolerance and receiver sensitivity against conventional Manchester, return-to-zero (RZ) and non-RZ (NRZ) (with the same spectral width). The optimisation of the optical filter that performed the VSB filtering on the Manchester signal and its detuning frequency results in the compression of the spectral width of the Manchester signal and thereby enhanced the spectral efficiency of the modified Manchester to about 31.3%. This results in the improvement of dispersion tolerance to ∼140 ps/nm. In comparison with conventional modulation formats, the proposed system can improve the dispersion tolerance by three times more than conventional Manchester, which is 44 ps/nm, and twice more than NRZ, which is 51.8 ps/nm and has a better dispersion tolerance of 31 ps/nm than RZ with dispersion tolerance of 109 ps/nm at a bit-error-rate of 10−9. The improvement in the proposed modulation performance achieved without utilisation of any dispersion compensation module or electronic equalisation.

Incorporating SDC Module for ISI Compensation for a Long-Haul Co-OFDM System

Abstract With the increase in demand of bandwidth hungry applications, it is recommended to develop a high data rate system for long-haul coherent optical orthogonal frequency division multiplexing (CO-OFDM). At a very high data rate, CO-OFDM signal experiences deterioration. At 50 Gbps, the signal experiences ISI effect and in order to overcome this ISI effect, a prolonged system has been developed to reach optimal ISI compensation technique. One of the prominent and competent techniques to enhance system performance is (SDCM) symmetrical dispersion compensation module. In order to make system more bandwidth efficient 4-QAM (Quadrature Amplitude Modulation) with gray coding is applied and manual adjustments are done at receiver phase to decrease error vector magnitude (EVM). OFDM data stream is successfully transmitted over a distance of 4,000 km to compete the demand of long-haul CO-OFDM system. With different launch powers and laser linewidths, the performance of the system is enhanced in terms of Q-factor, SNR and EVM.

4 × 10 Gbps WDM repeaterless transmission system using asymmetrical dispersion compensation for rural area applications

We demonstrate experimentally 4 × 10 Gbps wavelength division multiplexing repeaterless transmission system using non-return-to-zero differential phase-shift keying modulation format over 300-km standard single-mode fiber. The channels used were 1546.9, 1547.7, 1548.51 and 1549.2 nm with 100 GHz spacing. In this system design, a dispersion compensation module is used; multi-channel-chirped fiber Bragg grating was deployed with asymmetrical configuration with different compositions of dispersion values at the transmitting and the receiving sides. The transmission system was pumped bidirectionally with 1445 and 1455 nm wavelength in a forward direction, and three pump wavelengths of 1430, 1440 and 1450 nm are deployed for the backward direction. The total on–off Raman gain is 47 dB from total pump power of 1.862 W. The result for dispersion pre-compensation of − 2006.0 and − 2338.3 ps/nm has minimal effect on nonlinearity showing the best performance for 300-km repeaterless transmission system.

4 × 25-Gb/s NRZ-OOK Signals Transmission Over a 160-km Single-Mode Fiber Using 10G-Class DML and Photodiode

In this paper, we have experimentally demonstrated the C-band 4 × 25-Gb/s non-return-to-zero on - off -keying (NRZ-OOK) signals over a 160-km single-mode fiber transmission based on 10G-class directly-modulated lasers and photodiodes. The excessive negative dispersion at the receiver side is used to equalize the frequency response of bandwidth-limited directly-modulated signal, therefore enables 25-Gb/s NRZ-OOK transmission based on 10G-class optical devices. By employing a multichannel chromatic dispersion compensation module in the receiver, a single optical device can be used to equalize the frequency response of multiple channels realizing low-cost and high-capacity signal transmission. The results shown in this paper reveal that our proposed scheme would be a promising candidate for a low-cost transition to 100 Gb/s (4 × 25 Gb/s) for the point-to-point metro network applications.

Transmission of 20 Gb/s PAM-4 signal over 20 km optical fiber using a directly modulated tunable DBR laser

We report 20 Gb/s transmission of four-level pulse amplitude modulation (PAM) signal using a directly modulated tunable distributed Bragg reflector (DBR) laser. Transmission distance over 20 km was achieved without using optical amplifiers and optical dispersion compensation modules. A wavelength tuning range of 11.5 nm and a 3 dB bandwidth greater than 10 GHz over the entire wavelength tuning range were obtained.

A novel structure of photonic crystal fibre for dispersion compensation over broadband range

This paper studies a novel structure of photonic crystal fibre (PCF) for dispersion compensation at broadband wavelengths. The application of broadband is investigated using a design model based on combination of modal properties and dispersion compensation. The newly designed PCF with defect introduced is recorded over transmission spectrum range 146.7–256.98 THz, i.e., 1.16–2.04 µm. The modal characteristics and dispersion compensation of 2D PCF with circular air holes defect introduced are investigated and compared to those of conventional hexagonal 2D PCF. Changes in bandwidth behaviour are also observed by changing refractive index and geometric parameter of PCF.

Efficient generation and characterization of spectrally factorable biphotons.

Spectrally unentangled biphotons with high single-spatiotemporal-mode purity are highly desirable for many quantum information processing tasks. We generate biphotons with an inferred heralded-state spectral purity of 99%, the highest to date without any spectral filtering, by pulsed spontaneous parametric downconversion in a custom-fabricated periodically-poled KTiOPO4 crystal under extended Gaussian phase-matching conditions. To efficiently characterize the joint spectral intensity of the generated biphotons at high spectral resolution, we employ a commercially available dispersion compensation module (DCM) with a dispersion equivalent to 100 km of standard optical fiber and with an insertion loss of only 2.8 dB. Compared with the typical method of using two temperature-stabilized equal-length fibers that incurs an insertion loss of 20 dB per fiber, the DCM approach achieves high spectral resolution in a much shorter measurement time. Because the dispersion amount and center wavelengths of DCMs can be easily customized, spectral characterization in a wide range of quantum photonic applications should benefit significantly from this technique.

Transmission of 28-Gb/s Duobinary and PAM-4 Signals Using DML for Optical Access Network

We explore the possibility of utilizing 1.55- $\mu \text{m}$ directly modulated lasers (DMLs) for optical access networks operating at 28 Gb/s per wavelength. For this purpose, we attempt to maximize the power budgets of 28-Gb/s duobinary and four-level pulse amplitude modulation (PAM-4) signals generated from a DML without using optical amplifiers or optical dispersion compensation modules. For experimental investigation, we set the bias current of the DML far above the threshold current, optimize the extinction ratio of the signals, and utilize the electrical equalization at the receiver. The experimental results show that we can secure power margins of 9.6 and 10 dB after transmission over 40-km long standard single-mode fiber for the duobinary and PAM-4 signals, respectively.