Carrier-suppressed Return-to-zero Differential Phase-shift Keying Research Articles

Performance evaluation of optical carrier suppressed RZ‐DPSK signal in WDM networks employing OFC

AbstractA new arrangement of optical frequency comb and its deployment in a wavelength division multiplexed optical network is proposed and demonstrated. The generated optical carriers are separated by a frequency spacing of 10GHz and the overall spectra comprise 63 individual optical carriers. These carriers are identified and separated by utilizing rectangle optical filters, and 10Gbps data is modulated on each carrier frequency. The data is modulated using carrier suppressed return to zero differential phase‐shift keying (CSRZ‐DPSK) modulation technique. Furthermore, the performance analysis of DPSK and CSRZ‐DPSK (presuppressed RZ‐DPSK, postsuppressed RZ‐DPSK, and suppression of multiplexed DPSK signal) are studied in details. In our analysis, it is observed that the three suppression techniques produce almost the same level of suppression, however, the bit error rate and Q factor differ. It has been observed that the postsuppressed DPSK modulation scheme offers more tolerance towards chromatic dispersion and other fiber impairments and nonlinearities such as self‐phase modulation and offers better overall performance. The results are analyzed in terms of BER performance, Q‐factor, and eye‐opening penalty.

Investigation of Different Modulation Formats for Extended Reach NG-PON2 using RSOA

Global market forecasts predicted that by 2020, more than 26 billion internet devices and connections universally interconnected will require nearly 3 times the data traffic generated when compared to the year 2015. The increase in data traffic, demands for enormous bandwidth capacity. The potential to deliver 10 Gbps of huge data to individual businesses and households will be of paramount importance and a challenging issue for the present day service providers. An intensive study is carried out for the Fiber-To-The-Home Passive Optical Network (FTTH PON) for their use in the optical communication, due to their high data rates and more bandwidth. The current evolution of Next Generation-Passive Optical Networks Stage 2 (NG-PON2) network is the primary key technology for the growing demands of higher bandwidth and transmission of the data to the subscribers present in the access network from the service providers. Time Wavelength Division Multiplexing PON (TWDM-PON) architecture is the viable essential solution for NG-PON2 which provides more bandwidth for bidirectional transmission. This article proposes a design for extended reach TWDM-PON based on reflective semiconductor optical amplifier (RSOA). The exclusive feature of the RSOA is the wavelength conversion, which replaces the transmitters in the subscriber end. The Quality of Service (QoS) performance is critically analyzed for different optical modulation formats in proposed extended reach TWDM-PON using RSOA. The TWDM-PON using RSOA is simulated and investigated for different photodetectors. The analysis is also carried for various distance and data rates. The results exhibited that APD receivers have better performance of minimum bit error rate obtained is 10-11 and minimum Q factor is 6.2 when compared with PiN receivers. The comparative analysis of different modulation formats shows that the Carrier Suppressed Return to Zero- Differential Phase Shift Keying (CSRZ-DPSK) gives the best performance for longer distance and large data rates and Return to Zero(RZ) gives the least performance.

All-optical logic XOR gate for high-speed CSRZ-DPSK signals based on cSFG/DFG in PPLN waveguide

A report is presented on all-optical logic XOR operation for high-speed carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) signals based on cascaded sum- and difference-frequency generation (cSFG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. The linear relationship of complex amplitudes between the converted idler and input signals enables a CSRZ-DPSK logic XOR gate with the converted idler carrying the RZ-DPSK format. An all-optical logic XOR gate for 40 Gbit/s CSRZ-DPSK signals is demonstrated in the experiment. Dual-channel-output and wavelength variable-in variable-out operations are also shown for the PPLN-based CSRZ-DPSK logic XOR gate.

Phase-erased wavelength/format conversion and demodulation of 40 Gbit/s DPSK assisted by periodically poled lithium niobate

We report a novel phase-erased demodulation of differential phase-shift keying (DPSK) by exploiting cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. Analytical solutions are derived to clearly describe the operation principle. The binary optical phase information carried by the conventional DPSK demodulation outputs is removed thanks to the cSHG/DFG in a PPLN waveguide. PPLN-assisted phase-erased wavelength conversion and demodulation of 40 Gbit/s non-return-to-zero DPSK (NRZ-DPSK), return-to-zero DPSK (RZ-DPSK), and carrier-suppressed return-to-zero DPSK (CSRZ-DPSK) are demonstrated in the experiment. Moreover, the accompanying all-optical format conversions from optical duobinary (ODB) to NRZ and from ODB/alternate-mark inversion (AMI) to RZ are also substantiated in the experiment. In addition, the calculated theoretical results including optical spectra, temporal waveforms, and phase diagrams also confirm the successful implementation of PPLN-assisted 40 Gbit/s NRZ-DPSK/RZ-DPSK/CSRZ-DPSK phase-erased wavelength conversion, demodulation, and ODB-to-NRZ and ODB/AMI-to-RZ format conversions.

All-optical 40 Gbit/s CSRZ-DPSK logic XOR gate and format conversion using four-wave mixing

We report simultaneous logic XOR gate for carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) and format conversion from CSRZ-DPSK to return-to-zero differential phase-shift keying (RZ-DPSK) by exploiting non-degenerate four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). We derive analytical solutions to complex amplitudes under non-depletion approximation to show the principle of operation and verify the CSRZ-DPSK logic XOR gate and format conversion by theoretical analyses. Three converted idlers are obtained by three non-degenerate FWM processes. All-optical 40 Gbit/s simultaneous multicasting CSRZ-DPSK logic XOR gate and CSRZ-DPSK to RZ-DPSK format conversion are successfully demonstrated in the experiment.

All-Optical Format Conversions Using Periodically Poled Lithium Niobate Waveguides

We investigate all-optical format conversions by using cascaded second-order nonlinearities in periodically poled lithium niobate (PPLN) waveguides. Analytical solutions under non-depletion approximation with clear physical insights are derived, showing operation principles of various PPLN-based format conversions. We propose and theoretically demonstrate all-optical 40 Gb/s nonreturn-to-zero (NRZ) to carrier-suppressed return-to-zero (CSRZ), nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) to return-to-zero differential phase-shift keying (RZ-DPSK), and NRZ-DPSK to carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) format conversions based on cascaded sum- and difference-frequency generation (cSFG/DFG). Tunable all-optical 20 Gb/s NRZ to return-to-zero (RZ) format conversion based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) is successfully confirmed in the experiment by setting NRZ signal at SHG quasi-phase matching (QPM) wavelength. Moreover, we experimentally report for the first time, PPLN-based all-optical 40 Gb/s NRZ-to-CSRZ, NRZ-to-RZ, and NRZ-DPSK-to-RZ-DPSK format conversions.

Performance Comparison of SSMF and UltraWave Fibers for Ultra-Long-Haul 40-Gb/s WDM Transmission

We experimentally compare the performance of standard single-mode fiber (SSMF) and UltraWave fiber (UWF) for ultra-long-haul (ULH) 40-Gb/s wavelength-division-multiplexing transmissions. We used the carrier-suppressed return-to-zero amplitude-shift-keying (CSRZ-ASK) and the carrier-suppressed return-to-zero differential-phase-shift-keying (CSRZ-DPSK) formats, which are particularly well-adapted to 40-Gb/s pulse-overlapped propagation. We demonstrate that transmission distance well beyond 2000 km can be reached on UWF with both the CSRZ-ASK and CSRZ-DPSK formats, or on SSMF with the CSRZ-DPSK format only, thus indicating that SSMF-based infrastructure of incumbent carriers can be upgraded at 40-Gb/s channel rates to ULH distances.

DWDM 40G Transmission Over Trans-Pacific Distance (10 000 km) Using CSRZ-DPSK, Enhanced FEC, and All-Raman-Amplified 100-km UltraWave Fiber Spans

We demonstrate error-free dense-wavelength-division multiplexing (DWDM) transmission of 40 40-Gb/s channels with 100-GHz spacing over 10 000 km dispersion-managed fiber using carrier-suppressed return-to-zero differential-phase-shift keying (CSRZ-DPSK), enhanced foward-error correction, and all-Raman-amplified spans with 100-km terrestrial length.

70-GHz-Spaced 40>tex<$,times,$>/tex<42.7 Gb/s Transpacific Transmission Over 9400 km Using Prefiltered CSRZ-DPSK Signals, All-Raman Repeaters, and Symmetrically Dispersion-Managed Fiber Spans

70-GHz-spaced 40/spl times/42.7 Gb/s prefiltered carrier-suppressed return-to-zero differential phase-shift keying (CSRZ-DPSK) signals have been transmitted over transpacific distances for the first time, using all-Raman repeaters with two pump-wavelengths, dispersion-managed fiber commercially available in volume, and an ETDM receiver. In this paper, first, in order to enhance the spectral efficiency, the impact of bandlimitation to a CSRZ-DPSK signal was experimentally investigated in comparison to a conventional CSRZ-on-off-keying (OOK) signal, and we found that the bandlimitation tolerance of CSRZ-DPSK signal was smaller than that of CSRZ-OOK signal in back-to-back condition. We also confirmed that the prefiltering CSRZ-DPSK signal with up to 65 GHz bandlimitation potentially had better transmission performance than the prefiltered CSRZ-OOK signal. In addition, we found that, although the nonlinear transmission penalty was increased by bandlimitation, this penalty for CSRZ-DPSK signal was smaller than that for CSRZ-OOK signal. Through this study, long-term stability of the transmission performance was also evaluated with low-speed signal polarization scrambling without using any polarization mode dispersion (PMD) compensation.