1500-km SSMF Transmission of Mixed 40-Gb/s CS-RZ Duobinary and 100-Gb/s CS-RZ DQPSK Signals

We demonstrated transmission of eight channelsof 200-GHz channel spacing and 100-Gb/s carrier-suppressed return-to-zero (CS-RZ) differential quadrature phase-shift keying (DQPSK) signals together with eight channels of 40-Gb/s CS-RZ duobinary (DRZ) signals also with 200-GHz channel spacing in order to improve the optical spectral efficiency of the wavelength-division-multiplexing system. Each DRZ channel is inserted in the middle of two adjacent CS-RZ DQPSK channels. A bit-error rate (BER) of less than 5E-4 is achieved for the 40-Gb/s DRZ channel after 1500-km SSMF transmission while a BER of 1E-3 is achieved for the 100-Gb/s CS-RZ DQPSK signals.      

Impact of Channel Plan and Dispersion Map on Hybrid DWDM Transmission of 42.7-Gb/s DQPSK and 10.7-Gb/s OOK on 50-GHz Grid

We investigate experimentally the performance of 42.7-Gb/s return-to-zero (RZ) differential quadrature phase-shift-keyed (DQPSK) channels in a dense wavelength-division-multiplexed transmission system having 10.7-Gb/s nonreturn-to-zero (NRZ) on-off keyed (OOK) channels. Cross-phase modulation (XPM) from the OOK channels is found to be a dominating nonlinear penalty source for copropagating DQPSK channels in a dispersion-managed transmission link with multiple standard single-mode fiber spans. It is also found that the XPM penalty strongly depends on channel occupancy and residual dispersion per span (RDPS). Large RDPS effectively mitigates XPM even for the worst-case occupancy where a 42.7-Gb/s RZ-DQPSK channel is amidst several 10.7-Gb/s NRZ-OOK channels on a 50-GHz channel grid.     

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.     

A novel mode-splitting detection scheme in 43-Gb/s CS- and DCS-RZ signal transmission

Sophistication of the transmission format for 40-Gb/s/ch WDM networks is indispensable. In long-haul transmission applications, the selection of transmission format should be a principal issue. Recently, we have proposed several transmission formats including carrier-suppressed return-to-zero (CS-RZ) and duo-binary-carrier-suppressed (DCS-RZ), in so doing addressing the issue of superior performance versus fiber nonlinearity and spectral efficiency. The special spectrum structure of these formats enables a novel mode-splitting detection scheme. The scheme realizes a variety of applications in 40-Gb/s/ch transmission; including expansion of dispersion tolerance, automatic dispersion compensation, and BER improvement. We achieved 1.6 times. expansion of dispersion tolerance of 43-Gb/s DCS-RZ signals by introducing mode-splitting in the receiver. By applying the mode-splitting scheme for CS-RZ signals, we also demonstrated precise chromatic dispersion measurement with its sign detection without the need for any dithering operation and its application to automatic dispersion compensation at 43-Gb/s CS-RZ transmission.     

Terabit Transmission at 42.7-Gb/s on 50-GHz Grid Using Hybrid RZ-DQPSK and NRZ-DBPSK Formats Over 16 × 80 km SSMF Spans and 4 Bandwidth-Managed ROADMs

We demonstrate for the first time the use of asymmetric-bandwidth interleaver-based reconfigurable optical add-drop multiplexer (ROADM) to transmit 42.7-Gb/s channels on a 50-GHz grid. Differential binary phase shift keyed (DBPSK) format was used on the wide passband side and differential quadrature phase shift keyed (DQPSK) format was used on the narrow passband side of the ROADM. 25 channels with an aggregate capacity of 1-Tb/s were transported over 1280-km of standard single-mode fiber (SSMF) including 4 ROADMs.     

Comparison between NRZ and duobinary Modulation at 43 gb/s for MLSI-based and DCF-based transmission systems

In this paper, the performance of midlink spectral inversion (MLSI) is compared with the performance of "conventional" dispersion compensation fiber (DCF)-based transmission for two data formats: 43-Gb/s ON-OFF keying nonreturn-to-zero (OOK-NRZ) and 43-Gb/s duobinary. In the MLSI-based system, a polarization-diverse subsystem was used for spectral inversion employing magnesium-oxide-doped periodically poled lithium niobate (PPLN) waveguide technology. The transmission link consists of 8 /spl times/ 100 km standard single-mode fiber (SSMF) using erbium-doped fiber amplifiers (EDFAs) for amplification. Compared to the DCF-based system, it is seen that the MLSI-based configuration enhances the dispersion tolerance for both the NRZ and the duobinary modulation formats. It is concluded that the combination of the MLSI and the duobinary modulation format yields a highly dispersion-tolerant stable 43-Gb/s transmission system.     

Optimization of Single-Sideband DCS-RZ Format for Long-Haul 43-Gb/s/channel Ultradense WDM Systems

The optimization of the single-sideband (SSB) duobinary carrier-suppressed (DCS) return-to-zero (RZ) format for long-haul ultradense wavelength-division multiplexing (UDWDM) systems with a 43-Gb/s/channel and a channel spacing of 50 GHz is investigated numerically. It is shown that the optimized SSB-DCS-RZ format with an electrical transmitter bandwidth of 0.35 of the bit rate has about 1 dB of Q-factor improvement relative to the conventional SSB-DCS-RZ format (an electrical transmitter bandwidth of 0.25 of the bit rate) due to the reduction of noise bandwidth, smaller linear crosstalk, and better tolerance to the intra-channel fiber nonlinear effects. No substantially different UDWDM system performance is observed when varying the duty cycle of the DCS-RZ signal with optimized SSB filters settings. The UDWDM transmission performance of SSB-DCS-RZ formats is compared with the bandwidth-limited (BL)-duobinary formats. It is shown that generally, the SSB-DCS-RZ formats have poorer Q-factor and tolerance to the total residual dispersion but much higher tolerance to the in-line dispersion compensation and intra-channel nonlinear effects than the BL-duobinary formats     

Alternative modulation formats in N×40 Gb/s WDM standardfiber RZ-transmission systems

A comparison of carrier-suppressed return-to-zero (CSRZ) and single sideband return-to-zero (SSB-RZ) formats is made in an attempt to find the optimum modulation format for high bit rate optical transmission systems. Our results show that CSRZ is superior to return-to-zero (RZ) and SSB-RZ with respect to signal degradation due to Kerr nonlinearities and chromatic dispersion in wavelength division multiplexing (WDM) as well as in single-channel 40-Gb/s systems over standard single-mode fibers (SSMF). It is shown that CSRZ enables a maximum spectral efficiency of approximately 0.7 (b/s)/Hz in a N×40 Gb/s WDM system with equally polarized channels. Furthermore, the CSRZ format in N×40 Gb/s WDM systems shows no further signal degradation compared to single-channel transmission     

Highly Spectrally Efficient DWDM Transmission at 7.0 b/s/Hz Using 8 65.1-Gb/s Coherent PDM-OFDM

In this paper, we discuss the realization of wavelength-division multiplexing (WDM) transmission at high spectral efficiency. For this experiment, coherent polarization-division multiplexing--orthogonal frequency-division multiplexing (PDM-OFDM) is used as a modulation format. PDM-OFDM uses training symbols for channel estimation. This makes OFDM easily scalable to higher level modulation formats as channel estimation is realized with training symbols that are independent of the constellation size. Furthermore, because of its well-defined spectrum OFDM requires only a small guard band between WDM channels. The dependence of the number of OFDM subcarriers is investigated with respect to the interchannel linear crosstalk. At a constant data rate the number of OFDM subcarriers is estimated to achieve lower linear crosstalk in order to achieve higher spectral efficiency. We then experimentally demonstrate dense WDM (DWDM) transmission with 7.0-b/s/Hz net spectral efficiency using 8 $,times,$65.1-Gb/s coherent PDM-OFDM signals with 8-GHz WDM channel spacing utilizing 32-quadrature-amplitude-modulation subcarrier modulation. Successful transmission is achieved over 240 km standard single-mode fiber (SSMF) spans with hybrid erbium-doped fiber amplifiers/Raman amplification.      

100-Gb/s DQPSK Transmission Experiment Without OTDM for 100G Ethernet Transport

In order to realize a future 100-Gb Ethernet (100 GbE) transport, 100-Gb/s transmission without 100-GHz-class electronics and optical time-division-multiplexing technique was demonstrated. By using a differential quadrature phase-shift-keying (DQPSK) modulation format and commercially available electronics, 2- and 50-km transmissions of 100-Gb/s signal were successfully achieved over a standard single mode fiber. The receiver sensitivity, chromatic dispersion, and differential group delay tolerances of 100-Gb/s DQPSK signal were also evaluated. Through these evaluations, the possibility of DQPSK modulation for future 100-GbE transport is verified     

Combining DPSK and duobinary for the downstream in 40-Gb/s long-reach WDM-PONs

We propose and demonstrate combining differential phase-shift keying (DPSK) and duobinary transmission for the downstream in 40-Gb/s long-reach wavelength division multiplexed-passive optical networks (WDM-PONs) in order to provide robust transmission performance in the backhaul section and simple detection at the ONUs. DPSK is deployed in the trunk span as it provides stronger robustness to fiber nonlinearity. Duobinary is used in the access span where its higher chromatic dispersion tolerance relieves the need for dispersion compensation. All-optical multichannel modulation format conversion from DPSK to duobinary is realized in the local exchange in a single delay interferometer to reduce system cost. Single and multi-channel 80-km long-reach DPSK transmission and up to 5-km duobinary access transmission are experimentally demonstrated at 40 Gb/s. The proposed approach shows great potential for future high data rate optical access networks.     

Experimental Demonstration and Numerical Simulation of 107-Gb/s High Spectral Efficiency Coherent Optical OFDM

Orthogonal frequency-division multiplexing (OFDM) is a multicarrier modulation format in which the data are transmitted with a set of orthogonal subcarriers. Recently, this modulation format has been actively explored in the field of optical communications to take advantages of its high spectral efficiency and resilience to chromatic and polarization dispersion. However, to realize the optical OFDM at 100 Gb/s and beyond requires extremely high electronic bandwidth for the electronic signal processing elements. In this paper, we investigate orthogonal-band-multiplexed OFDM (OBM-OFDM) as a suitable modulation and multiplexing scheme for achieving bandwidth scalable and spectral efficient long-haul transmission systems. The OBM-OFDM signal can be implemented in either RF domain, or optical domain, or a combination of both domains. Using the scheme of OBM-OFDM, we show the successful transmission of 107 Gb/s data rate over 1000-km standard single-mode fiber (SSMF) without optical dispersion compensation and without Raman amplification. The demonstrated OBM-OFDM system is realized in optical domain which employs 2 $times$ 2 MIMO-OFDM signal processing and achieves high optical spectral efficiency of 3.3 bit/s/Hz using 4-QAM encoding. Additionally, we perform numerical simulation of 107-Gb/s CO-OFDM transmission for both single-channel and wavelength-division-multiplexed (WDM) systems. We find that the $Q$ -factor of OBM-OFDM measured using uniform filling of OFDM subbands is in fact more conservative, in particular, is 1.2 dB and 0.4 dB lower than using random filling for single-channel and WDM systems, respectively.      

NRZ versus RZ in 10-40-Gb/s dispersion-managed WDM transmissionsystems

We compare nonreturn-to-zero (NRZ) with return-to-zero (RZ) modulation format for wavelength-division-multiplexed systems operating at data rates up to 40 Gb/s. We find that in 10-40-Gb/s dispersion-managed systems (single-mode fiber alternating with dispersion compensating fiber), NRZ is more adversely affected by nonlinearities, whereas RZ is more affected by dispersion. In this dispersion map, 10- and 20-Gb/s systems operate better using RZ modulation format because nonlinearity dominates. However, 40-Gb/s systems favor the usage of NRZ because dispersion becomes the key limiting factor at 40 Gb/s     

132.2-Gb/s PDM-8QAM-OFDM Transmission at 4-b/s/Hz Spectral Efficiency

In this letter, we investigate 132.2-Gb/s polarization- division-multiplexed orthogonal frequency-division-multiplexing (PDM-OFDM) transmission at 25-GHz channel spacing. We show that the nonlinear tolerance is dependent on the OFDM symbol length. By using 14.4-ns-long OFDM symbols, 7 $, times ,$132.2-Gb/s transmission of PDM-OFDM at 4-b/s/Hz spectral efficiency is reported over 1300-km standard single-mode fiber.      

40-Gb/s WDM transmission with virtually imaged phased array (VIPA) variable dispersion compensators

We have demonstrated variable dispersion compensation by using a virtually imaged phased array (VIPA) to overcome the small dispersion tolerance in 40-Gb/s dense wavelength-division multiplexing (WDM) transmission systems. By utilizing the periodical characteristics of VIPA compensators, we performed simultaneous dispersion compensation in a 1.28-Tb/s (40-Gb/s/spl times/32 ch; C band) short-haul transmission and confirmed that only two VIPA compensators and one fixed dispersion-compensating fiber are required for a large transmission range of 80 km. This performance can greatly reduce the cost, size, and number of compensator menus in a 40-Gb/s WDM short-haul transmission system. In addition, we achieved 3.5-Tb/s (43-Gb/s/spl times/88 ch; C and L bands) transmission over a 600-km nonzero dispersion-shifted fiber by using VIPA compensators. Although channel-by-channel dispersion compensation is required due to the larger residual dispersion slope in long-haul transmission, the periodical characteristics of the VIPA compensators offer the advantage of considerably reducing the number of different modules required to cover the whole C (or L) band. An adequate optical signal-to-noise ratio, which was the same for all channels, was-obtained by using distributed Raman amplification, a gain equalizer, and a preemphasis technique. We achieved a Q-factor of more than 11.8 dB; (BER<10/sup -17/ with forward-error correction) for all 88 channels.     

20-Gb/s PolDM Duobinary Transmission Over 350-km SSMF Supported by a Polarization Stabilizer and an Optical Dispersion Compensator

A 20-Gb/s transmission over 350-km standard single-mode fiber exploiting duobinary dispersion robustness and polarization-division multiplexing has been demonstrated. The system performance is evaluated employing an automatic endless polarization stabilizer and a suitably designed transmitter-side optical dispersion compensator.     

111-Gb/s Transmission Over 1040-km Field-Deployed Fiber With 10G/40G Neighbors

We demonstrate transmission of a 111-Gb/s coherent polarization-multiplexed return-to-zero differential quadrature phase-shift keying signal over 1040-km field-deployed fiber together with different types of neighboring channels, and with a cascade of 50-GHz reconfigerable optical add-drop multiplexers. Our transmission experiment proves the feasibility of transmitting a 111-Gb/s phase-modulated channel with 10 times 10.7-Gb/s on-off keying neighboring channels on a 50-GHz grid, despite the presence of strong cross-phase modulation.     

Prechirp in NRZ-based 40-Gb/s single-channel and WDM transmissionsystems

We investigate the impact of the prechirp on nonreturn-to-zero (NRZ)-based single-channel and 40-Gb/s/ch wavelength-division-multiplexing systems over standard single-mode fibers by means of numerical simulations. It was shown that prechirping of NRZ pulses improve the total transmission length and make the NRZ pulses more robust to Kerr-nonlinearities     

10-Gb/s, 4-channel wavelength division multiplexing fibertransmission using semiconductor optical amplifier modules

A dense wavelength-division-multiplexing (WDM) transmission system with very-high-speed channels was investigated experimentally. A 10-Gb/s four-channel WDM optical transmission (total capacity of 40 Gb/s) over a 40-km dispersion-shifted fiber was achieved by using hybrid-integrated DFB-LD/driver modules for transmitters and two cascaded semiconductor optical amplifier (SOA) modules for receivers. The experiment confirmed that the SOA is applicable for WDM transmission systems with high bit rates because of its inherent wide bandwidth. The transmission capacity of 40 Gb/s, achieved using an intensity modulation/direct detection (IM/DD) scheme, is the highest ever reported. This technology will make possible ultralarge capacity (up to several-hundred gigabits per second) and long-haul transmission systems in the future     

Surface Mountable 10-Gb/s InP Mach–Zehnder Modulator Module for SFF Transponder

We have developed a small, surface mountable InP-based Mach-Zehnder modulator module. New designs for the electrical ports enable the modulator to be directly mounted on a printed circuit board. We demonstrated a 100-km transmission through single-mode fiber with a 10-Gb/s nonreturn-to-zero signal and a 220-km transmission with a 10-Gb/s optical duobinary signal to confirm the applicability of this device as an ultralong-haul small form factor transponder.