Km Of Standard Single-mode Fiber Research Articles

Beyond 200G Direct Detection Transmission With Nyquist Asymmetric Twin-SSB Signal at C-Band

For short reach and metro applications, single sideband (SSB) is a promising scheme due to its high spectral efficiency and tolerance to chromatic dispersion. In this study, we propose a novel asymmetric twin-SSB scheme based on Nyquist pulse shaping. Without joint equalization, the two sidebands can be separately detected with a small guard band. We experimentally demonstrate 224-Gb/s 16-ary quadrature amplitude modulation (16-QAM) asymmetric twin-SSB transmission with direct detection. After 240-km standard single mode fiber (SSMF) transmission, the bit error rates (BERs) of the right-sideband (RSB) and the left-sideband (LSB) are 3.2 × 10−3 and 2.8 × 10−3, respectively, which are below the 7% hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10−3. The net bitrate is 203.7 Gb/s with consideration of both frame redundancy and HD-FEC overhead. To our best knowledge, we report the longest transmission distance for 200G single wavelength and single polarization direct detection systems. The advantages of the asymmetric twin-SSB scheme over the symmetric scheme are discussed through simulating the crosstalk resistance of both two schemes. We also demonstrate 300-Gb/s 32-QAM transmission over 80-km SSMF. The BERs of RSB and LSB are 1.50 × 10−2 and 1.61 × 10−2, respectively, which are below the 15% soft-decision forward error correction (SD-FEC) threshold of 1.8 × 10−2. The net bitrate is 254.3 Gb/s with consideration of both frame redundancy and SD-FEC overhead. To our best knowledge, it is the maximum bitrate ever reported for C-band 80-km single wavelength and single polarization direct detection transmission. The proposed scheme provides a useful and low-cost solution for high speed datacenter interconnection and metro-scale transmission.

High-speed low-chirp PAM-4 transmission based on push-pull silicon photonic microring modulators.

We report a silicon photonic modulator based on the use of dual parallel microring modulators (MRMs) inserted in a Mach-Zehnder interferometer (MZI). It is operated in a push-pull configuration for low-chirp transmission at approximately 1550 nm. The chirp parameters of the device are measured using 10 Gb/s on-off keying (OOK) transmission over 20 km of standard single mode fiber (SSMF), and they are less than 0.01, showing the low-chirp characteristic of the modulator. We further demonstrate four-level pulse amplitude modulation (PAM-4) transmission at 92 Gb/s over 1 km of SSMF and at 40 Gb/s over 20 km of SSMF. The measured bit error rates (BERs) are below the hard-decision (HD) forward error correction (FEC) threshold of 3.8 × 10-3.

Photonic Integrated Gain Switched Optical Frequency Comb for Spectrally Efficient Optical Transmission Systems

We demonstrate the performance of a novel integrated gain switched optical frequency comb source (GS-OFCS) in two different optical transmission systems. The device generates a 6.25-GHz frequency spaced comb that comprises eight spectral tones in a 3-dB spectral power ripple. The GS-OFCS presents good noise properties, which include relative intensity noise of ${\sim -}$ 125 dB/Hz and linewidth of 1.5 MHz. We then employ the device in two transmission systems that use advanced modulation formats. First, it is employed in a four-level pulse amplitude modulation format system operating at 3.125-GBaud per channel and over 3 km of standard single mode fiber (SSMF), where all the channels performed below the 7% FEC limit and the receiver sensitivity achieved was $-$ 21 dBm. Then, the GS-OFCS is used in a Nyquist quadrature phase-shift keying (QPSK) system at 5-Gbaud per channel and over 50 km of SSMF, where all the channels exhibited a similar performance well below the 7% FEC limit. These results, in conjunction with the compactness and cost efficiency of the integrated device, denote the quality and relevancy of the resultant comb source for future optical transmission systems.

Evaluation of selective control information detection scheme in orthogonal frequency division multiplexing-based radio-over-fiber and visible light communication links

Block-level detection is required to decode what may be classified as selective control information (SCI) such as control format indicator in 4G-long-term evolution systems. Using optical orthogonal frequency division multiplexing over radio-over-fiber (RoF) links, we report the experimental evaluation of an SCI detection scheme based on a time-domain correlation (TDC) technique in comparison with the conventional maximum likelihood (ML) approach. When compared with the ML method, it is shown that the TDC method improves detection performance over both 20 and 40 km of standard single mode fiber (SSMF) links. We also report a performance analysis of the TDC scheme in noisy visible light communication channel models after propagation through 40 km of SSMF. Experimental and simulation results confirm that the TDC method is attractive for practical orthogonal frequency division multiplexing-based RoF and fiber-wireless systems. Unlike the ML method, another key benefit of the TDC is that it requires no channel estimation.

Flexible Multiband OFDM Ultra-Wideband Services Based on Optical Frequency Combs

In the paper, a flexible multiband orthogonal frequency-division multiplexing (OFDM) ultra-wideband service based on optical frequency combs is proposed and experimentally demonstrated for 5G wireless communications. By using optical frequency comb technology, the flexibility and capacity of wavelength-division multiplexing passive optical networks (WDM-PONs) can be improved. Meanwhile, the different sub-bands of multiband OFDM ultra-wideband signals are modulated with different modulation formats to ensure the data rate needs of different users. An adaptively modulated 128-/64-/32-ary-quadrature-amplitude-modulation-encoded multiband OFDM ultra-wideband signal is generated. In addition, a joint channel estimation method with training sequences and pilot symbols is applied to improve system performance. After 50-km standard single-mode fiber transmission, the experimental results show that the proposed system can provide bandwidth resources for 15 end users with an average access rate of 1.781  Gb/s per user and a high data rate of 5.343  Gb/s.

High-Speed Ultralow-Power Hybrid Optical Transmitter Module With InP I/Q-SEMZM and BiCMOS Drivers With 4-b Integrated DAC

A hybrid optical transmitter module comprising a 15-segment InP in-phase/quadrature-phase segmented Mach–Zehnder modulator and two SiGe:C BiCMOS drivers featuring integrated 4-b digital-to-analog converter functionality is described. The drivers, fabricated in the 0.13- $\mu \text{m}$ process of IHP, deliver a differential output voltage of $2.5~V_{\mathrm{ pp}}$ across all the 15 segments while dissipating less than 1 W of power each, at the maximum. Clear electrical eye diagrams up to 40-Gb/s from every output are reported. The module allows a wide range of modulation formats, among which up to eight-pulse amplitude modulation and polarization-division-multiplexed (PDM) 64-quadrature amplitude modulation (QAM) back-to-back error-free electro-optical transmission at a record speed of 32 GBd are demonstrated. The 32-GBd PDM 64-QAM signal was transmitted error-free over 80 km of standard single-mode fiber, featuring 7.8-pJ/b energy consumption. The devised hybrid arrangement proves the suitability of SiGe HBT drivers for achieving higher speeds over their CMOS counterparts, with comparable low power dissipation, for advanced optical transceivers.

A 100-Gbps, time-, frequency- and wavelength-division-multiplexed OFDMA passive optical network upstream scheme

This paper introduces a 100-Gbps, time-, frequency- and wavelength-division-multiplexed passive optical network upstream scheme based on the employment of orthogonal frequency-division-multiplexing access and scalable transmitter frontend technique. The feasibility of the proposed scheme is experimentally demonstrated over 50-km standard single-mode fiber using 32-QAM mapping.

Effects of Electrical and Optical Equalizations in 28-Gb/s RSOA-Based WDM PON

We experimentally investigate the roles of electrical and optical equalizers in the 28-Gb/s wavelength-division-multiplexed passive optical network implemented by using reflective semiconductor optical amplifiers (RSOAs) and direct-detection receivers. For the generation of 28-Gb/s signal, we directly modulate an RSOA in the polar return-to-zero (RZ) ${N}$ -ary pulse-amplitude-modulation (PAM) format. The results show that the optical equalization is capable of compensating the waveform distortions caused by both the bandwidth-limitation of RSOA and fiber’s chromatic dispersion without deteriorating the signal-to-noise ratio (SNR). On the other hand, the electrical equalization is effective for the compensation of the bandwidth-limitation of RSOA only at the cost of SNR. The results also show that the electrical equalization is helpful to compensate for the remaining waveform distortions after the optical equalization. By using both equalizers, we demonstrate the transmission of the 28-Gb/s signals in polar RZ-PAM- ${N}$ formats ( ${N} =2$ , 3, and 4) over 20 km of standard single-mode fiber.

Next-Generation Optical Fronthaul Systems Using Multicore Fiber Media

This paper proposes and investigates the use of multicore fiber (MCF) media performing space-division multiplexed transmission for next-generation optical fronthaul systems. We report the experimental demonstration of combined radio-over-fiber (RoF) transmission of full-standard LTE-Advanced (LTE-A) and WiMAX signals providing fronthaul connectivity in 150 m of 4-core fiber (4CF), transmitting simultaneously fully independent wireless services. Operating in linear and nonlinear optical power regimes, the experimental evaluation verifies that the error vector magnitude (EVM) is not degraded when intercore and intracore Kerr nonlinearities are excited in MCF with high input power levels. As a result, nonlinear regime is proposed as a key factor to reduce the temporal EVM fluctuation induced by the random nature of the intercore crosstalk in MCF. In addition, MCF fronthaul applied to converged fiber-wireless polarization multiplexed passive optical networks is demonstrated to transmit LTE-A and WiMAX signals over two orthogonal optical polarizations. The polarization-multiplexed signal is transmitted in RoF over 25.2 km of standard single-mode fiber and then demultiplexed and injected in different cores of the 4CF to provide fronthaul connectivity. Finally, the extension of multicore optical fronthaul capacity is proposed using MIMO LTE-A signals. The tolerance of the MIMO LTE-A RoF transmissions to in-band crosstalk is reported and compared to single-input single-output (SISO) configuration. The experimental results indicate that MIMO configuration is more tolerant than SISO to in-band crosstalk considering both internal and external interferences. MIMO and SISO configurations are compared when transmitted in RoF over a 4CF operating in linear and nonlinear regimes and core interleaving nonlinear stimulation is proposed to reduce the temporal and spectral EVM fluctuation when the same wireless standard is propagated in each core.

Demonstration of 4 128-Gb/s DFT-S OFDM Signal Transmission over 320-km SMF With IM/DD

Intensity modulation and direct detection (IM/DD) is a promising solution for short-reach links. In this paper, we experimentally demonstrate transmission of 128-Gb/s discrete Fourier transform (DFT)-spread 16-ary quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) signals in an IM/DD optical system. Vestigial sideband (VSB) modulation with 20-dB suppression ratio enabled by a cost-effective interleave or a tunable optical filter (TOF) is employed to eliminate chromatic dispersion (CD) induced power fading. Meanwhile, a combination of advanced digital signal processing (DSP) algorithms, such as pre-equalization, nonlinearity equalization (NE), and decision-directed least mean square (DDLMS), are utilized to mitigate the system distortions and improve system performance. By using this scheme, the 32-GBd DFT-spread OFDM signals can be successfully transmitted over 320-km standard single mode fiber (SSMF) with the measured bit error ratio (BER) under the soft-decision forward-error-correction (SD-FEC) threshold of $2\times 10^{-2}$ . We also achieved 144-Gb/s for 80-km SSMF transmission. Additionally, 4 $\times$ 128-Gb/s wavelength division multiplexing (WDM) DFT-S OFDM signals transmission over 320-km SSMF is experimentally investigated. To the best of our knowledge, this work reports the longest transmission distance for beyond 100-Gb/s IM/DD system.

Low-cost coherent UDWDM-PON by hybrid DBPSK/ASK-2 modulation

The coherent ultra-dense wavelength division multiplexed passive optical network (UDWDM-PON) has been widely studied recently, in which the envelop detection based coherent reception of on-off keying (OOK) signal has been shown to possess both high receiver sensitivity and tolerance against laser linewidth/chirp. In order to increase the spectral efficiency (SE) to 2bit/s/Hz, researchers formulated a hybrid DBPSK/ASK-2 modulation using the silicon Mach–Zehnder modulator (MZM), where both amplitude and phase modulation are employed. The experimental result shows that the proposed DBPSK/ASK-2 modulation is of better performance than PAM-4 at the same SE of 2bit/s/Hz. When the low-cost silicon MZM and DFB laser of 4-MHz linewidth are employed, the receiver sensitivity of DBPSK/ASK-2 exceeds that of the PAM-4 by about 5.7dB. This work can achieve about −46dBm receiver sensitivity at 2.5GBaud after transmission over 80-km standard single mode fiber (SSMF). The proposed DBPSK/ASK-2 modulation using low-cost silicon MZM and DFB laser is considered as a practical and reliable method for the future UDWDM-PON at the SE of 2bit/s/Hz.

A Cost-Effective Distributed Acoustic Sensor Using a Commercial Off-the-Shelf DFB Laser and Direct Detection Phase-OTDR

We propose and experimentally demonstrate the use of cyclic pulse coding for enhanced performance in distributed acoustic sensing based on a phase-sensitive optical time-domain reflectometry ( $\phi$ -OTDR) using direct detection. First, we present a theoretical analysis showing that to make cyclic pulse coding effective in $\phi$ -OTDR, the laser linewidth and stability must be optimized to simultaneously guarantee intrapulse coherence and interpulse incoherence. We then confirm that commercial off-the-shelf distributed feedback (DFB) lasers can satisfy these conditions, providing coding gain consistent with theoretical predictions. By externally modulating such lasers with cyclic pulse coding, we demonstrate a distributed acoustic sensor capable of measuring vibrations of up to 500 Hz over 5 km of standard single-mode fiber with 5-m spatial resolution with ∼9-dB signal-to-noise ratio (SNR) improvement compared with the single-pulse equivalent. We also show that the proposed solution offers sensing performances that are comparable to similar sensors employing highly coherent and stabilized external cavity lasers and a single-pulse $\phi$ -OTDR.

Polarization-Insensitive Single-Balanced Photodiode Coherent Receiver for Long-Reach WDM-PONs

In an access network based on a passive optical network architecture, coherent detection is attractive since it allows for high receiver sensitivity coupled with inherent frequency selectivity. Nevertheless, solutions employed in core networks are prohibitively complex and costly, requiring the optical complexity of the coherent receivers to be reduced to make them feasible for access networks. For monolithic integration, a key challenge is posed by the polarization beam splitter (PBS). If, however, the PBS is removed, the receiver needs to be redesigned to be insensitive to the incoming polarization state of the received signal. In this paper, we experimentally demonstrate a polarization-insensitive (i.e., polarization-independent) coherent receiver for the optical network unit in passive optical networks (PONs). The receiver consists of only a 3-dB coupler and a single-balanced photodiode such that the complexity is comparable to a direct detection receiver. The proposed cost-effective coherent receiver is implemented by using the Alamouti polarization-time block coding scheme combined with heterodyne detection. To verify the technique, the Alamouti-coded orthogonal frequency division multiplexing (OFDM) signal is rotated over the full Poincare sphere. Compared to the dual-polarization-OFDM signal operating at a net bit rate of 10 Gb/s per polarization (a gross bit rate of 10.7 Gb/s including a 7% FEC overhead), only a 0.6 dB sensitivity degradation is observed. The sensitivity at the FEC threshold, assumed to be $4\times 10^{-3}$ , is measured to be $-$ 41.5 dBm (56 photons-per-bit) on a 25-GHz grid. Following this, different channel spacings are investigated and the signal is transmitted over 80 km of standard single-mode fiber in a long-reach wavelength division multiplexed PON system. The loss budgets are found to be 43.0 and 42.8 dB for 50- and 25-GHz grids, respectively.

Impact of Optical Power in the Guard-Band Reduction of an Optimized DDO-OFDM System

A multiobjective optimization on the parameters of direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems in short-range links is proposed. Based on genetic algorithms, the optimization process takes into account the influence of optical power in the guard-band reduction of such multicarrier systems with 4- and 16-quadratic-amplitude modulation (QAM) subcarrier mapping and for propagation in $40$ km of standard single-mode fiber (SSMF). Simulation results show that the parameters optimization is responsible for a gain of approximately $2.5$ dB [ $\approx 1.8$ dB] in the required optical power for bit-error-rate ${\le }10^{-3}$ , for DDO-OFDM system transmission over $40$ km of uncompensated SSMF, with a guard band $B_G$ equals to $50\%$ of the signal bandwidth $B_w$ and 16-QAM [4-QAM] subcarrier mapping. For an extremely reduced guard band of only $1\%$ of $B_w$ , the gain reduced to $\approx 0.5$ dB and $\approx 1.5$ dB for 16- and 4-QAM mapping, respectively. The optimization process is experimentally validated under the transmission of the optimized DDO-OFDM systems in optical back-to-back (B2B) configuration and $40$ km of uncompensated SSMF. A fair performance comparison is discussed in the experimental results considering $B_G/B_w=0.5$ and $B_G/B_w=0.01$ in the range of the optimized optical powers. It is shown that a maximum optical power penalty of approximately $2$ dBm is registered according to a guard-band reduction from $50\%$ to $1\%$ of the useful bandwidth, for transmission over the 40 km of SSMF, considering 16-QAM subcarrier mapping.

Transmission Performance of 448 Gb/s Single-Carrier and 1.2 Tb/s Three-Carrier Superchannel Using Dual-Polarization 16-QAM With Fixed LUT Based MAP Detection

Transmission of single-carrier 448 Gb/s dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) electrical time-division multiplexed (ETDM) signal and a 1.206 Tb/s three-carrier superchannel ETDM signal using DP 16-QAM is demonstrated by applying a fixed look-up table (LUT) based on maximum-a-posteriori (MAP) detection. The MAP detector is used to mitigate the effect of pattern dependent distortion in the transmitted signal arising from the high symbol rates. Different decision rules for the MAP detector are considered based on multiple observations of the same symbol as the detection window advances through the received symbol sequence. The back-to-back optical signal-to-noise ratios for a bit error ratio of $\mathbf {10^{-3}}$ are 26.9 and 26.4 dB for the 448 Gb/s signal (12% overhead with 7% for forward error correction (FEC) coding overhead) and 1.206 Tb/s superchannel signal (20% overhead with 15% for FEC coding overhead), respectively. Compared to conventional MAP detection, a seven-symbol minimum distance MAP detector reduces the required OSNR by about 0.8 and 1 dB at the FEC thresholds of $\mathbf {3.8\times 10^{-3}}$ and $\mathbf {1.9\times 10^{-2}}$ for the 448 Gb/s signal and 1.206 Tb/s superchannel signal, respectively. Transmission over 1200 and 1500 km of standard single-mode fiber with EDFA amplification is achieved for the 448 Gb/s signal and 1.206 Tb/s superchannel signal, respectively.

Silicon Photonic Segmented Modulator-Based Electro-Optic DAC for 100 Gb/s PAM-4 Generation

We report on the design and characterization of a silicon-on-insulator traveling-wave multi-electrode Mach–Zehnder modulator (MZM). The 2-bit electro-optic (EO) digital-to-analog converter is formed by dividing a series push–pull MZM into two segments, one for each bit. The EO bandwidth of the longer segment of the MZM is measured to be 48 GHz at 0 V reverse bias. We operate the device at speeds up to 50 GBd to create a four-level pulse amplitude modulation signal, and thus generating 100 Gb/s on a single wavelength without signal processing at the transmitter or the receiver. The pre-forward error correction (FEC) bit error rate is estimated to be lower than the hard-decision FEC threshold of $3.8 \,\, \times \,\, 10^{-3}$ over 1 km of standard single-mode fiber, and thus leading to error-free transmission at 100 Gb/s.

Coherent Nyquist UDWDM-PON With Digital Signal Processing in Real Time

Nyquist shaping UDWDM-PON combined with digital coherent optical systems has been recently proposed as a promising technology for future optical access networks. In this paper, we report real-time transmitter and receiver for a future coherent PON with high spectral efficiency and low-cost DSP implementation. Using field-programmable gate array (FPGA)-based 8-bit DSP, we experimentally demonstrate a high performance system based on 16 × 2.5 Gb/s QPSK signals in terms of receiver sensitivity and fiber transmission. An optimal transmitted power of –7 dBm per channel is achieved for 50-km standard single-mode fiber in a 2.5-GHz grid. The experimental results show the feasibility of coherent PON scenarios based on DSP supported by FPGAs.

Experimental Assessment of the Adaptive Stokes Space-Based Polarization Demultiplexing for Optical Metro and Access Networks

We experimentally analyze an adaptive polarization-demultiplexing (PolDemux) technique based on the representation of the state of polarization of the signal in the Stokes space. The performance and convergence speed of the Stokes PolDemux are compared with the constant modulus algorithm, for dual polarization QPSK and 16QAM modulation formats in a system with a maximum polarization rotation of 6 kHz. Moreover, the applicability of the adaptive Stokes algorithm is tested in an ultradense wavelength-division multiplexing scenario over 80 km of standard single-mode fiber. The BER results show a very small power penalty confirming the suitability of the adaptive Stokes method in systems where the accumulated chromatic and polarization-mode dispersion are small, such as high capacity optical metro and access networks scenarios.

Single-section quantum well mode-locked laser for 400 Gb/s SSB-OFDM transmission.

Successful use of a single-section quantum well (QW) passively mode-locked laser (MLL) as a comb source for optical interconnects is demonstrated for the first time. Sixteen comb lines spaced by 37.6 GHz are modulated using 25 Gb/s compatible single sideband orthogonal frequency division multiplexed (SSB-OFDM) signals and transmitted over 50 km of standard single-mode fiber with bit error ratio below the 7% forward error correction limit. The system performance, analyzed on the basis of the relative intensity noise of the device, reveal the suitability of single-section QW MLLs as inexpensive comb sources for inter- and intra-data center communication scenarios.

Offset Manchester coding for Rayleigh noise suppression in carrier-distributed WDM-PONs

We propose a novel offset Manchester coding in upstream to simultaneously realize Rayleigh noise suppression and differential detection in a carrier-distributed wavelength division multiplexed passive optical network. Error-free transmission of 2.5-Gb/s upstream signals over 50-km standard single mode fiber is experimentally demonstrated, with a 7-dB enhanced tolerance to Rayleigh noise.