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In optical fibre communication system, improved modulation schemes have been proposed to increase capability and high bit rate transmission. One such technique is optical duobinary modulation, which can able to broadcast high‐speed optical signals over bandwidth‐limited channels. The conventional modulation schemes employ the non‐return‐to‐zero modulation and return‐to‐zero modulation technique. These schemes decrease spectrum width and increase the dispersion tolerance. However, the effect of inter‐symbol inference presents between the pulses. These techniques give a reduced performance for high bit rate transmissions and transmission over long distances. Hence in this work, the implementation of duobinary modulation improves the performance of optical communication along with the provision of enhanced security through bio‐inspired chaos masking scheme. The bio‐inspired chaos‐masking scheme generates the security key using the spider security pattern generator to provide improved security. The parameters of the proposed technique are analysed for different transmission rates and the performance improvement is validated. [ABSTRACT FROM AUTHOR]

A frequency-tunable terahertz (THz) wave generation scheme based on an optically injected semiconductor laser is proposed for radar and communication applications. The THz generator has a very simple structure, and it is demonstrated to have a broad tuning range of 0.1–3.257 THz, which is realised by adjusting the detuning frequency and injection strength of the semiconductor laser. Feasibility of the proposed THz generator is verified by a THz wireless communication experiment, in which error-free transmission of 150 Mbit/s on–off keying pseudorandom bit sequence signals with a 115-GHz carrier is achieved over a 1-meter free-space link.

In this study, a performance comparison of fibre non‐linearity mitigation is performed in the context of 10 and 20 Gb/s coherent optical orthogonal frequency‐division multiplexing and wavelength division multiplexing (CO‐OFDM‐WDM). The authors compare two regression methods based on the third‐order Volterra series and least mean square algorithm in terms of the bit error rate (BER) for different transmission distances and modulation formats. They also evaluate the BER as a function of the number of OFDM subcarriers for the Volterra‐based non‐linear equaliser (VNLE). In addition, by increasing the order of the VNLE from third‐order to fifth‐order series, a significant increase of performance is obtained for 100 Gb/s CO‐OFDM‐WDM system. Likewise, a comparison study of 16‐QAM 40 Gb/s CO‐OFDM system is performed as a function of Q‐factor for support vector machine, Volterra equaliser and linear equaliser, respectively. [ABSTRACT FROM AUTHOR]

In this study, the statistical distribution of the received signal in a coherent optical orthogonal frequency‐division multiplexing (CO‐OFDM) system with quadrature‐phase shift keying modulation in the orthogonal frequency‐division multiplexing (OFDM) subcarriers is investigated, and the accuracy and correctness of the Gaussian probability density function (pdf) assumption is analysed. The well‐known Anderson–Darling test is utilised to measure the deviation extent of the statistical distribution of the received signal from the Gaussian pdf. Finally, the Johnson SU ‐distribution is suggested as a more exact distribution for the statistical modelling of the received signal. After non‐linear propagation, its accuracy is assessed through comparison with Monte‐Carlo simulations, based on the time‐domain split‐step Fourier method. [ABSTRACT FROM AUTHOR]

A frequency-tunable terahertz (THz) wave generation scheme based on an optically injected semiconductor laser is proposed for radar and communication applications. The THz generator has a very simple structure, and it is demonstrated to have a broad tuning range of 0.1–3.257 THz, which is realised by adjusting the detuning frequency and injection strength of the semiconductor laser. Feasibility of the proposed THz generator is verified by a THz wireless communication experiment, in which error-free transmission of 150 Mbit/s on–off keying pseudorandom bit sequence signals with a 115-GHz carrier is achieved over a 1-meter free-space link. [ABSTRACT FROM AUTHOR]

The authors present an expanded porous polytetrafluoroethylene terahertz fibre transmission link using resonant tunnelling diodes integrated with photonic‐crystal waveguides as a transmitter and a receiver. The measured coupling efficiency between the terahertz fibre and the photonic‐crystal waveguide integrated with a silicon tapered coupler is ∼30% with a 3 dB bandwidth of 50 GHz at the 0.3 THz band. Error‐free 10 Gbit/s transmission and uncompressed 4 K high‐definition video transmission have been successfully demonstrated using 1 m‐long terahertz fibre. [ABSTRACT FROM AUTHOR]

Transmission characteristics of an optical signal, which is converted from a high‐speed terahertz‐wave signal with high spectral efficiency, are investigated and reported. A Nyquist time division multiplexing 40 Gbit/s on–off keying signal in the terahertz band is generated with high‐speed photo‐mixing. The generated terahertz‐wave signal is again converted into an optical signal with heterodyne detection, optical intensity modulation, and optical filtering. Then the chromatic dispersion tolerance of the converted optical signal is investigated in order to obtain knowledge for realising the connection between the fibre‐optic and the wireless links. After briefly explaining the conversion method, some related experimental results are reported. The results include evaluation of chromatic dispersion tolerance with regard to the optical signal at the final stage. As a sequel to bit error rate measurement, the optical signal can be transmitted to a 9 km‐long single‐mode fibre without chromatic dispersion compensation. [ABSTRACT FROM AUTHOR]

Variable weight optical code division multiple access system (VW‐OCDMA) is developed to provide service differentiation in optical metro networks where different applications demand for different quality of services. In VW‐OCDMA, different number of wavelengths carries the data for different services. Hence, the fibre impairment effects vary for different services. In this study, the performance of a VW‐OCDMA is analysed under the impact of fibre impairments including chromatic dispersion, self‐phase modulation, four wave mixing and stimulated Brillouin scattering. It is shown that how higher weights which are supposed to deliver higher quality are more affected by fibre impairments. At last, the experimental results of three users with different weights are demonstrated. [ABSTRACT FROM AUTHOR]

The authors propose a transmitter digital filter for joint optimisation of signal pulse shaping and chromatic dispersion pre‐compensation, providing a detailed analysis of the architecture complexity. Experimental transmission of 40 × 50G channels (28 Gbaud four‐level pulse amplitude modulation) over up to 110 km uncompensated standard single mode fibre with low‐bandwidth hardware is demonstrated. [ABSTRACT FROM AUTHOR]

The continual increase in demand for extremely high data‐rate systems spans the full range of network systems from local area networks to long‐haul systems. While coherent optical systems dominate the long‐haul market, there is significant interest in using simpler direct detection systems for application areas, where simplicity and lower‐cost is a key driver. Pulse‐amplitude modulation (PAM) is appropriate to consider as it enables the reduction of the channel symbol rate for a given data rate, without unduly increasing the complexity of the system. A route to the design of optimum post‐detection filter for PAM systems is presented that offers significantly improved robustness to timing jitter, which is an impairment of increasing import as symbol rates are increased. [ABSTRACT FROM AUTHOR]

The authors compare transmission reach of 100 Gb/s four‐level pulse amplitude modulated signals over single‐span systems constructed with three optical fibre types. They demonstrate reach up to 160 km with fibres having ultra‐low attenuation, one with a large effective area. [ABSTRACT FROM AUTHOR]

A novel scheme for optical millimetre-wave (mm-wave) generation based on tandem sub-carrier multiplexing in hybrid communication systems is suggested. The method is analysed mathematically for optimum settings. The tandem single side-band (TSSB) method is tolerant to fibre chromatic dispersion. However, the TSSB technique is prone to critical interference of unwanted harmonics which may result in poor data transmission bit error rate (BER). Based on the proposed mathematical derivation for TSSB modulation, a framework is provided to enhance the mm-wave generation system performance. Up to 2 Gb/s data transmission over multiple 60 GHz sub-bands is considered. The model includes a single-mode fibre with chromatic dispersion factor of 16 ps/(nm km). Two cascaded dual electrode Mach–Zehnder modulators are used to generate TSSB 60 GHz sub-bands. Three oscillators are required to generate two tandem mm-wave signals. A proper selection of these three frequencies is vital to guarantee a successful data transmission. Mathematical analysis is carried out to verify the proposed scheme and a summary of appropriate frequency sets is presented and discussed. The BER curves are obtained. The results verify that the TSSB-based mm-wave generation framework proposed in this study guarantees data transmission with an acceptable BER.

A 100‐Gbit/s PAM‐4 (pulse amplitude modulation) transmission over 4‐km standard single‐mode fibre (SSMF) and a C‐band 4 × 80‐Gbit/s PAM‐4 transmission over 8‐km standard SSMF experimentally demonstrated. A digital Wiener filter (WF) at the receiver side is utilised to compensate the impairments introduced by the transmission link. Bit error rate below 7% forward error correction threshold (3.8 × 10−3) is achieved with received optical power of 0 dBm for the single lane 100‐Gbit/s transmission and around −4 dBm for the four channels after 8‐km transmission with WF, which is over one order of magnitude better than that without equalisation. The results indicate that WF is a good enough option for practical application in short reach optical interconnect. [ABSTRACT FROM AUTHOR]

This Letter presents a novel CMOS transceiver for short‐reach multigigabit communication over step‐index plastic optical fibre (SI‐POF), a very interesting transmission medium for industrial and home‐end applications due to its low cost, ease of handling and inherent immunity to electromagnetic interference. The transceiver uses amplitude duobinary modulation, which is added to continuous‐time equalisation. For that purpose, a duobinary precoder and a duobinary decoder have been fabricated in a standard 0.18‐µm CMOS technology, consuming only 28.4 mW. The system enables a 50‐m SI‐POF channel bandlimited to 100 MHz to operate at a data bit rate of 3.125 Gbit/s. [ABSTRACT FROM AUTHOR]

By using a Mach-Zehnder intensity modulator (MZM)-based Q-factor enhanced 40-GHz optoelectronic oscillator (OEO) loop, a self-starting pulsed encoder is demonstrated to generate 40-Gbit/s return-to-zero on-off-keying (RZ-OOK) data-stream. By nonlinearly driving the MZM with an OEO circuitry via a proper setting on the intra-loop delay, both the RF and optical output of the OEO at 40 GHz can be extracted to deliver the clock with a Q-factor of up to 2×108, and trigger the synthesizer-free 40-Gbit/s RZ-OOK data-stream. The maximal output power and the carrier-to-noise ratio of the RF output from the OEO are 20 dBm and 62 dB, respectively. Moreover, the single side-band phase noise is suppressed to -120 dBc/Hz at 100-kHz offset frequency by lengthening the single-mode fiber in the OEO loop up to 900 m. In addition, the pulsed RZ carrier with a pulsewidth of 10.5 ps provides a jitter as low as 120 fs and an on/off extinction ratio of 7.7 dB, which is particularly suitable for the RZ-OOK transmission at 40 Gbit/s. The back-to-back transmitted synthesizer-free 40-Gbit/s RZ-OOK data with a pattern length of 223-1 reveals a receiving power sensitivity of -15.2 dBm at the requested bit error rate of 10-9. [ABSTRACT FROM AUTHOR]

In this letter, the fiber-optic communication channel with a quadrature amplitude modulation (QAM) input constellation is treated. Using probabilistic shaping, we show that high-order QAM constellations can achieve and slightly exceed the lower bound on the channel capacity, set by ring constellations. We then propose a mapping function for turbo-coded bit-interleaved coded modulation based on optimization of the mutual information between the channel input and output. Using this mapping, spectral efficiency as high as 6.5 bits/s/Hz/polarization is achieved on a simulated single channel long-haul fiber-optical link excluding the pilot overhead, used for synchronization, and taking into account frequency and phase mismatch impairments, as well as laser phase noise and analog-to-digital conversion quantization impairments. The simulations suggest that major improvements can be expected in the achievable rates of optical networks with high-order QAM. [ABSTRACT FROM PUBLISHER]

A simple chromatic dispersion (CD) compensation scheme for a certain frequency is first proposed by utilizing a phase modulator in conjunction with a polarizer. Properly adjusting the input polarization states, the frequency response of the dispersive link can be controlled. Experimental results show that the dispersion-induced power fading (PF) occurred at 14 and 10.8 GHz over 40- and 65-km transmission is fully maximized or compensated. Furthermore, the spurious-free dynamic range of the proposed analog photonic link is improved to 96 dB·Hz2/3 for the 40-km fiber transmission, which is 12 dB higher than that of the phase modulation-based link. On the other hand, an improved scheme for CD compensation is further demonstrated, where a polarization beam combiner is employed instead of a polarizer. Such an approach achieves the broadband CD compensation since it can be equivalent to the sum of two first schemes. In this case, the PF is greatly mitigated for the RF signal with a bandwidth up to 15 GHz. Meanwhile, the error vector magnitude reduces to ~5% with the fluctuation of only 0.7%. [ABSTRACT FROM PUBLISHER]

With the ever-increasing bandwidth demand of the end-customers, the 100-Gb/s access solution has attracted more and more attention. In this letter, we propose a symmetric 100-Gb/s digital signal processing-enhanced time wavelength division multiplexed passive optical networ (TWDM-PON) architecture with four pairs of wavelengths. A 4 × 25 -Gb/s TWDM-PON is experimentally demonstrated over a 26.7-km fiber using double sideband (DSB) orthogonal frequency division multiplexing (OFDM) modulation. The reflective semiconductor optical amplifier is deployed in the optical network unit (ONU) to enhance the receiver sensitivity of downstream OFDM signals, and DSB single-carrier frequency domain equalization modulation is used for upstream transmission to reduce the complexity and cost of the ONU. [ABSTRACT FROM PUBLISHER]

We report a high-gain, low-noise-figure, and high-linearity analog photonic link. The link combines a high-power and low-noise fiber laser, a Mach-Zehnder modulator, a high-gain erbium-doped fiber amplifier (EDFA), and a high-performance charge-compensated modified unitraveling-carrier photodiode. The critical characteristics of the photodiode include 16-GHz bandwidth, 200-mA saturation current, and >35 dBm third-order intercept point. In the link, low biasing is utilized to reduce the noise and maximize the signal-to-noise ratio, and an EDFA is used to provide sufficient optical input to the MUTC photodiode to ensure that the link can achieve high gain and high output RF power. The combination of high-power low-noise fiber laser and high-bandwidth high-power photodiode, we have enabled high gain (27.8 dB at 6 GHz and 24.5 dB at 12 GHz), low noise figure (4.7 dB at 6 GHz and 6.9 dB at 12 GHz), and high spur free dynamic range (>120 dB · Hz2/3) in the frequency range 6-12 GHz. [ABSTRACT FROM PUBLISHER]

We propose here a monolithically integrated dual RF access electroabsorption-modulated laser called D-EML for the generation of optical single-sideband signal for both nonreturn to zero and orthogonal frequency division multiplexing formats. The benefits of optical single-sideband over double sideband in terms of resilience against chromatic dispersion effects are presented for high-bit rate intensity modulation/direct detection transmissions over standard single mode fiber in the C-band. Both simulation and experimentation exhibit transmission distance enhancement in the case of dual modulation of the D-EML, i.e., in optical single-sideband configuration, making this optical source an interesting solution because of its low-cost, low-size, and reasonable-power consumption. [ABSTRACT FROM PUBLISHER]

We demonstrate an integrated transmitter that can generate two 100-Gb/s optical channels with simple nonreturn-to-zero-ON-OFF keying format. The transmitter is based on the combination of an ultrafast electro-optic polymer platform for the photonic integration and the optical modulation with ultrafast InP-double heterojunction bipolar transistor electronics for the multiplexing and the amplification of the 100-Gb/s driving signals. Through error-free transmission of 2 × 80-Gb/s signals over 1 km of SMF and transmission of 2 × 100-Gb/s signals over 500 m of single-mode fiber with error performance way below the forward error correction limit, we reveal the potential of the approach for parallel 100-GbE optical interfaces in small footprint transceivers for intradata center networks. [ABSTRACT FROM PUBLISHER]

Effects of fiber dispersion on the radio-over-fiber (RoF) transmission of a microwave signal are experimentally demonstrated when deep optical modulation is employed. In a previous paper (J. Lightwave Technol., vol. 30, pp. 2625-2632, Aug. 2012), the authors analytically predicted that harmonics of sidebands generated by the nonlinear response of optical modulators would contribute to the cyclic variation of the signal amplitude other than by dispersion-induced fading. To confirm this prediction, we set up an RoF link that transmitted a 16-quadrature amplitude modulation microwave signal, and we observed changes in the constellation map. Experiments were conducted both for optical double-sideband (ODSB) signals and optical single-sideband plus carrier (OSSB+C) signals. In the ODSB case, outer symbols in the constellation map moved slightly outwards as the signal propagated down the fiber. If we eliminated the harmonic sidebands by using an optical filter, the movement was reversed; this was probably due to the residual chirp in the LN modulator. In the OSSB+C case, we observed a similar movement but also a slight phase rotation that depended on the amplitude of the symbol. These observations qualitatively agree with our predictions. [ABSTRACT FROM PUBLISHER]

The polarization reversal techniques of ferroelectric optical crystals enable us to construct new high-speed microwave signal processing devices with advanced functions; wireless microwave signal discrimination for space-division-multiplexing systems, pre-equalization for signal distortion caused by fiber dispersion in long haul optical fiber communications, and so on. In this paper, potential of these new functional devices for microwave photonic systems is discussed. [ABSTRACT FROM PUBLISHER]

System performance of optical steganography is theoretically analyzed and experimentally demonstrated. The optical stealth channel is carried by amplified spontaneous emission noise, which hides the stealth data in both the time and frequency domain. Meanwhile, because the stealth channel uses noise as the signal carrier, the relation between signal-to-noise ratio (SNR) and carrier power is fundamentally different from the traditional optical channels carried by modulating lasers. To transmit and hide the stealth signal in the existing public network, the degradation principle of SNR of the stealth channel is studied. Such principle can guide the design of the stealth transmission system and optimize the carrier power of the stealth channel. [ABSTRACT FROM PUBLISHER]

A blind and adaptive decision-feedback channel estimation method is proposed for optical intensity-modulated direct detection discrete multitone transmissions. Due to the channel state variation nature of the fiber, periodic channel estimation update is required. In previous works, periodic preambles are transmitted to acquire and track the channel state information at the receiver. In the proposed method, instead of using periodic preambles, the estimated channel is updated adaptively after decoding a sequence of orthogonal frequency-division multiplexing symbols using least-squares and minimum mean-square error criteria. The simulation results corroborate that the proposed method increases data-rate by 10%, and at the same time provides 0.24-dB Q-factor gains that can be converted into extra 2% data-rate increase, algorithm simplicity, or cost reduction. [ABSTRACT FROM PUBLISHER]

Self-phase locked loop (SPLL) through long optical delay lines is investigated for improving the phase noise of the optoelectronic oscillator (OEO) and the voltage-controlled oscillator (VCO). This paper features analytical modeling of close-in to carrier phase noise of oscillators employing SPLL technique using single and multiple delay loops. Experimental results are also provided to verify the analytical modeling and explore critical circuit design parameters to achieve substantial phase noise reduction. Performance comparison is presented for SPLL using electrical phase shifter, Mach-Zehnder modulator (MZM)-based phase shifting, and electrical VCO. Phase noise reduction of 65 dB at 1-kHz offset is achieved for an electrical VCO employing a dual-loop SPLL with 3- and 5-km optical fiber delay lines, whereas the phase locking based on MZM and electrical phase shifter provided 20- and 38-dB reductions at 1-kHz offset for an OEO, respectively. [ABSTRACT FROM PUBLISHER]

We propose a graphene-based modulator integrated into currently used communication fibers. The graphene is directly built into the core of the fiber to ensure the coupling efficiency. The fiber is deliberately side-polished to enhance the light-graphene interaction. The two-dimensional model analysis method and three-dimensional finite difference time domain method are used to rigorously disclose the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Based on such a structure, a phase modulator with an arm length of 127 μm is numerically demonstrated with enhanced modulation efficiency. A quasi-linear relation between the phase change and chemical potential of graphene is found theoretically for the first time, providing a large linear dynamic range to control the phase of optical modulation. [ABSTRACT FROM PUBLISHER]

In this paper, we model and analyze the end-to-end energy consumption of 100-Gbps coherent long-haul transmission systems. In particular, we investigate the impact of forward error correction (FEC) on the end-to-end energy consumption. We compare the energy efficiency of commonly used modulation formats in 100-Gbps transmission, namely dual polarization-quadrature phase-shift-keying (DP-QPSK) and dual polarization-16-quadrature amplitude modulation (DP-16-QAM), for different transmission distance and input bit error rate. Our energy model includes consumption of transmitter, booster, link amplifier as well as receiver. Compared with previous digital signal processing models, we provide a very detailed model that not only includes all the significant functional blocks (such as timing and carrier recovery, chromatic and polarization mode dispersion compensation, and FEC), but also takes into account impact of the number of samples processed every clock cycle and of operations other than multiplications. We have found that receiver energy consumption dominates in transmission systems that use electronic dispersion compensation over long transmission distances. Our results show that for short transmission distances where hard-decision decoding is adequate for both modulation formats, DP-16-QAM is more energy efficient than DP-QPSK. However, as the transmission distance increases, the energy saving due to the low symbol rate of DP-16-QAM is offset by the energy consumption of soft-decision decoding. In this case, the two modulation formats have approximately similar energy consumption. [ABSTRACT FROM PUBLISHER]

We present an experimental demonstration of multilevel coded modulation (MLCM) for 16-ary constellations. Performance of MLCM coding is compared for two 16 QAM constellations: 1) a phase noise optimized and 2) a square constellation. We quantify experimentally the phase noise regimes where the optimized constellation outperforms square 16 QAM. While MLCM coding is designed for one linewidth at a given symbol time, for the same overhead we show it outperforms uniform rate coding over a wide range of linewidths. The MLCM coding strategy minimizes block error rate under some simplifying assumptions. We show that under realistic conditions, the MLCM also gives good post forward error correction and quantify the advantage over uniform rate coding experimentally. [ABSTRACT FROM PUBLISHER]

A new scheme for a flexible modulation and bit rate independent, polarization-insensitive optical wavelength converter (WC) based on four-wave mixing in a highly nonlinear fiber is demonstrated and characterized for different modulation formats and data rates. Its robustness is demonstrated in a data transmission experiment in which the WC is incorporated at the mid-point of a transmission line based on installed fiber. In addition, an optical feedback system designed to prevent slow polarization drift of the pumps, and consequently, to ensure the long-term stability of the system is implemented and characterized. The WC is tested with the feedback system in place enabling turn-key operation. [ABSTRACT FROM PUBLISHER]

We report on the first experimental demonstration of superposition coded modulation (SCM) for polarization-multiplexed coherent-detection optical fiber links. The proposed coded modulation scheme is combined with phase-shifted bit-to-symbol mapping (PSM) in order to achieve geometric and passive shaping of the signal's waveform. The output constellations in SCM-PSM exhibit nonbijective quasi-Gaussian statistical distributions that asymptotically reach the Shannon capacity limit, showing up to 0.7 dB sensitivity improvement for 256-ary SCM-PSM with respect to 256-ary quadrature amplitude modulation (QAM). The characteristic wave formation based on superposition of antipodal symbols and the lack of need for additional encoders for signal shaping, greatly reduces the transmitter and receiver processing complexity in comparison to conventional alternatives. Single-level coding strategy (SL-SCM) is employed in the framework of bit-interleaved coded modulation with iterative decoding (BICM-ID) for forward error correction. The fiber transmission system is characterized in terms of signal-to-noise ratio for back-to-back case and correlated with simulated results for ideal transmission over additive white Gaussian noise channel. Thereafter, successful demodulation and decoding after dispersion-unmanaged transmission over 240-km standard single mode fiber of dual-polarization 6-Gbaud 16-, 32- and 64-ary SCM-PSM is experimentally demonstrated. [ABSTRACT FROM PUBLISHER]

In this letter, we apply a nonequalization orthogonal frequency-division multiplexing (NE-OFDM) technique in optical turbulence channel for coherent free-space optical (FSO) systems, utilizing multilevel differential phase-shift keying (MDPSK). We adopt the modified Rician distribution as the optical turbulence channel for coherent FSO systems, where both amplitude fading and phase distortion are taken into consideration. The differential encoding process of MDPSK-based NE-OFDM can be performed either in the frequency domain (FD) or in the time domain (TD). Our simulation results show that NE-OFDM using FD-MDPSK achieves nearly the same bit-error-rate (BER) performance as that using TD-MDPSK, but with a relatively lower hardware complexity and a higher spectral efficiency. It is also revealed that FD-MDPSK-based NE-OFDM attains a comparable BER performance with the conventional OFDM with pilot tones or training sequences assisted channel estimation and equalization. Hence, FD-MDPSK-based NE-OFDM is promising for coherent FSO communication. [ABSTRACT FROM PUBLISHER]

In this study, the authors numerically analyse the electrical and the optical properties of a silicon microring phase modulator using reverse‐biased pn junction configuration. The performance of the device is examined in terms of frequency chirp, switching time and intensity dip. They also evaluate the data transmission performance by varying the propagation distances at a bit rate of 10 Gbit/s. The simulation results show that the generated differential‐phase‐shift‐keying data at a drive signal with rise and fall times of 10 ps can achieve error‐free transmission for propagation distances up to 55.6 km, whereas the one at a drive signal with rise and fall times of 50 ps needs a 4.13 dB power penalty in a 17.5 km fibre transmission without dispersion compensation. [ABSTRACT FROM AUTHOR]

A novel polarization splitter based on dual-core silica glass photonic crystal fiber with a liquid crystal modulation core is studied by the finite-element method. The mode birefringence is enlarged greatly with the infilling of nematic liquid crystal of E7. The simulation results demonstrate that the polarization splitter has an ultrabroad bandwidth of 250 nm, covering the E S C L optical communication bands, with the extinction ratio better than -20 dB. The separate length is 0.175 mm, and the extinction ratio is -80.7 dB at the communication wavelength of 1550 nm. The polarization splitter exhibits satisfactory splitter performance as the fabrication deviation reaches to 1%. The extinction ratio maintains better than -20 dB, at the C L optical communication bands, as the temperature increases from 15 °C to 50 °C. [ABSTRACT FROM PUBLISHER]

We experimentally demonstrate a 429.96-Gb/s signal transmission over a 400-km standard single-mode fiber within the 50-GHz grid and successfully achieve spectral efficiency as high as 8.63 bit/s/Hz. Orthogonal frequency-division multiplexing/offset quadrature amplitude modulation with 64-quadrature amplitude modulation is selected as the modulation format to provide a “perfect” rectangular spectrum that efficiently reduces the channel crosstalk. No timing or frequency alignment is required for the subbands to form the superchannel. [ABSTRACT FROM PUBLISHER]

There is a growing interest in applying carrierless amplitude-phase (CAP) modulation in intensity modulated optical links. CAP as a multilevel modulation scheme can reach high spectral efficiency and be generated at low cost. An interesting feature of CAP is that its signal basis can be extended to three or more dimensions (D). This paper aims to complete the knowledge on 3-D CAP. Discussed are design of transceiver filters, spectral efficiency, and digital equalization in 3-D. Several problems accompanying 3-D CAP transmission are identified. The most significant are the peak to average power ratio, which is higher than in one or two dimensions and noise correlation at the output of a 3-D equalizer. It is found that the latter problem severely degrades bit error rates achieved but can be efficiently mitigated using noise whitening equalization. Finally, 1-D, 2-D, and 3-D CAP are compared experimentally in a step-index polymer optical fiber link. [ABSTRACT FROM PUBLISHER]

Wavelength division multiplexing (WDM) is a promising solution for upgrading the capacity of polymer optical fiber (POF)-based telecommunication networks. In this letter, we report on the successful realization of a four-channel highspeed WDM transmission system for 1-mm diameter step-index POF (SI-POF). For combining the optical signals coming from 405-, 450-, 515-, and 639-nm laser diodes onto 1-mm SI-POF, a 4 × 1 coupler with low insertion loss (IL) has been developed. To spatially separate different wavelength channels, a fourchannel demultiplexer with low IL (<;5.7 dB) and high (non)adjacent channel isolation (>30 dB) has been realized in bulk optics. The 14.77-Gb/s data transmission based on the offline-processed discrete multitone modulation technique has been demonstrated over 50-m SI-POF at a bit-error rate of 10-3. [ABSTRACT FROM PUBLISHER]

We experimentally investigate the performance of a 256-Gb/s polarization-division-multiplexed 16-ary quadrature-amplitude-modulation (PDM-16QAM) transmission system in dispersion uncompensated TeraWave SLA+ fiber spans using erbium-doped-fiber amplifiers (EDFAs), hybrid EDFA/Raman amplifiers, and all backward-pumped Raman amplifiers. The effects of 37.5- and 50-GHz channel spacings and cascaded optical add/drop multiplexers (ROADMs) on the system performance are studied. We find that when there are no ROADMs, hybrid EDFA/Raman amplifiers and all-backward-pumped Raman amplifiers can increase the reach by about 70% and 100%, respectively, compared to EDFA-only amplifiers, from 2000 to about 3500 and 4200 km, respectively, assuming 20% soft-decision forward-error-correction (SD-FEC) for the system with both 37.5- and 50-GHz channel spacings. We show that cascaded ROADMs have a small impact on the system with 50-GHz channel spacing, but can severely degrade the performance of the system with 37.5-GHz channel spacing and virtually eliminate the reach gain from Raman amplifiers in such systems due to large penalties and higher error floors induced by ROADM filtering effects. We also show that for the same number of channels, the system with 37.5- and 50-GHz channel spacings has similar performance when there are no ROADMs. [ABSTRACT FROM PUBLISHER]

Although the pump relative intensity noise transfer phenomenon in traditional Raman amplified amplitude-shift keying fiber communication systems has been investigated intensively, the stochastic intensity fluctuation of Raman pump laser will interplay with fiber nonlinearity and leads to additional phase noise of signal in the multilevel modulated coherent optical communication system. Such phase noise is defined as relative phase noise (RPN). In this paper, we present comprehensive analysis regarding the characteristics and impairments of RPN through both theoretical derivation and Monte Carlo simulation. We derive the analytical expressions of phase error variance for M-ary PSK and 16QAM modulation formats in consideration of RPN using decision-aided maximum-likelihood phase estimation algorithm. The analysis can be used to predict RPN induced impairment theoretically. Bit error rate (BER) performance is evaluated and compared for QPSK, 8PSK, 16PSK, and 16QAM modulation formats, and the result shows that in the context of RPN 16QAM signal outperforms 16PSK which has the same spectral efficiency. Finally, we extend the analytical result obtained in pump nondepletion regime to depletion regime via numerical analysis. It is observed by comparison that Q-factor penalty will increase in depletion regime. [ABSTRACT FROM PUBLISHER]

We analyze a family of modulation formats based on multidimensional position modulation (MDPM) with multiple pulses per frame (K-over-L-MDPM) in combination with quadrature phase shift keying (QPSK), polarization multiplexed QPSK (PM-QPSK) and polarization-switched QPSK (PS-QPSK) for coherent communication systems. MDPM is a generalization of pulse position modulation where different pulse slots can be realized by time slots, polarization states, frequencies, modes of multimode fibers, cores in multicore fibers or a combination of these. We show that by using K-over-L-MDPM with QPSK, it is possible to simultaneously increase both the spectral efficiency and the asymptotic power efficiency over QPSK. We also identify K-ary inverse-MDPM (KiMDPM-QPSK) as the special case of K-over-(K - 1)-MDPM and show that 4iMDPM-QPSK has a 1.25 dB increased asymptotic power efficiency over QPSK with a maintained spectral efficiency. [ABSTRACT FROM PUBLISHER]

Coherent optical communication has been well established as the technology of choice for long haul and high bit rate communication systems since a decade ago. Recent technology advances and ongoing price erosion further open the window of opportunity for the application of coherent optical transmission technology in other domains. This paper describes in detail the capabilities, design and implementation of a coherent ultra dense WDM technology for optical metro and access networks. Its capabilities enable a number of attractive options, such as variable downstream bit rates from 150 Mbit/s up to 10 Gbit/s per user, embedded OTDR and the coexistence with legacy systems such as GPON, EPON, XGPON or RF-Video in optical distribution networks. Due to its flexibility and capacity, it is also suitable for deployments in metropolitan networks, as well as for mobile front-haul and back-haul applications. [ABSTRACT FROM PUBLISHER]

We propose a modular architecture for long-haul optical networks supporting flexible-bandwidth superchannels. Colorless transceivers can be designed to modulate/detect up to M = 4 subcarriers, each at a symbol rate of 12.5 Gbaud, achieving a maximum bit rate of 200 Gbit/s, assuming polarization-multiplexed quadrature phase-shift keying (PM-QPSK). A set of N synchronized transceivers can cooperate to modulate/detect a superchannel comprising N·M subcarriers using no-guard-interval orthogonal frequency-division multiplexing, enabling transmission at bit rates beyond 1 Tbit/s. We analyze and simulate the performance of the proposed architecture in the presence of linear fiber impairments and synchronization errors and establish design requirements for practical deployment of the architecture. Simulation results are shown for transmission of a superchannel comprising 24 subcarriers, which conveys approximately 1.1 Tbit/s with a spectral efficiency of 3.5 bits/s/Hz using PM-QPSK. [ABSTRACT FROM PUBLISHER]

The performance improvement of 10 Gbit/s single-sideband orthogonal frequency division multiplexing intensity-modulated direct-detection systems achieved by reducing the signal peak-to-average power ratio (PAPR) with a symbol precoding technique based on the raised-cosine pulse, without and with bandwidth expansion, is evaluated experimentally. The impact of pre-emphasis (PE), necessary to mitigate the setup frequency limitations, on the PAPR reduction achieved by symbol precoding is investigated. At the input of the optical modulator, PAPR reductions of ~ 3 dB with PE and without PE are achieved using the precoding technique without band excess; with precoding with band excess of 25%, PAPR reductions of ~ 4 dB with PE and 4.5 dB without PE are obtained. Due to precoding, a bit error ratio (BER) improvement of almost two orders of magnitude is shown along 150 km standard single mode fiber transmission, for BERs around 10 -4 . In addition, it is also shown that precoding enables similar BER improvement with 75 km fiber propagation when nonlinear fiber effects are moderate. [ABSTRACT FROM PUBLISHER]

In this letter, we demonstrate a novel monolithically integrated photonic multiwavelength transmitter that was realized by integrating an arrayed waveguide grating-based laser with selective distributed Bragg reflector mirrors and Mach-Zehnder modulators. The integrated circuit was designed according to a generic integration model, by utilizing standardized photonic building blocks, and was fabricated on an InP-based platform in a multiproject wafer run. The device delivers above 1 mW of optical power into the fiber with a side mode suppression ratio better than 40 dB. The linewidth of the generated signals is 275 kHz. We achieved error free 50-km transmission at the modulation data rate of 10 Gb/s per channel, for a received power of -26.5 dBm. [ABSTRACT FROM PUBLISHER]

In this paper, a post digital linearization technique is proposed and demonstrated for a conventional intensity-modulation direct-detection analog photonic link. Instead of precisely emulating the transfer function of the whole nonlinear system in the digital domain, the key distortion information is directly acquired from hardware. By low biasing the Mach-Zehnder modulator, linearization can be achieved through simply multiplying the distorted signal by the coreceived low-pass band. Theory analysis shows that only the bias angle should be known by the algorithm, whereas the simulation shows adequate tolerance. The low bias angle also results in an improved link gain. The experiment shows a well-suppressed third-order intermodulation distortion (IMD3). With the optical down conversion, we demonstrate a spurious-free dynamic range increasing from 103.2 to 123.3 dB in a 1-Hz bandwidth. [ABSTRACT FROM PUBLISHER]

Simultaneous amplitude and phase noise reduction of multiple signal states using a nonlinear amplifying loop mirror with integrated directional phase-sensitive amplifier are presented for the star-eight quadrature amplitude modulation transmission format as an example. The performance of this combined regenerator scheme is compared with that of a cascade of separate phase and amplitude regenerators. It could be shown that an improvement in the error vector magnitude of 4 dB for the high-power states with simultaneous improvement of 5 dB for the low-power states is possible in both cases. Transmission improvement by regeneration is considered for two noise types: 1) amplified spontaneous emission and 2) nonlinear phase noise. Both schemes can either improve the bit error rate by an order of magnitude or enable an increase of the fiber launch power by 3 dB. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a new optical spectrally efficient frequency division multiplexing (O-SEFDM) system, where non-orthogonal and overlapping sub-carriers are employed to provide higher spectral efficiency relative to optical-orthogonal frequency division multiplexing (O-OFDM). The O-SEFDM technique can increase spectral efficiency in both the electrical and optical domains. It is experimentally shown that for bandwidth saving up to 25%, we can achieve the same performance as O-OFDM. This is the first experimental verification of 25% optical faster than the Nyquist rate. Furthermore, for approximately the same spectral efficiency, 4QAM O-SEFDM outperforms standard 8QAM by 1.6 dB. It is experimentally shown that a lower-order modulation format can achieve a better performance by replacing a higher one. [ABSTRACT FROM PUBLISHER]

We demonstrate high speed optical transmission systems using digital coherent detection at all-electronically multiplexed symbol rates of 80 and 107 Gbaud. At 107 Gbaud, we demonstrate a single-carrier polarization division multiplexed quadrature phase shift keyed (PDM-QPSK) line rate of 428 Gb/s. At 80 Gbaud, we achieve a single-carrier line rate of 640 Gb/s using PDM 16-ary quadrature amplitude modulation (16-QAM). Using two optical subcarriers, we demonstrate a 1-Tb/s optical interface and conduct long-haul wavelength-division multiplexed (WDM) transmission on a 200-GHz grid over 3200 km of ultra-large effective area fiber. [ABSTRACT FROM PUBLISHER]