121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM bands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10$,times,$ 121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.      

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 transmission using orthogonal frequency-division multiplexing

The possibility of 100-Gb/s transmission over 25-GHz bandwidth using orthogonal frequency-division multiplexing (OFDM) is demonstrated. It is shown that 100-Gb/s transmission over 3840 km can be achieved using single-sideband quadrature-phase-shift keying OFDM transmission and low-density parity-check codes.     

High-Performance and Low-Cost 40-Gb/s CWDM Optical Modules

High-performance and low-cost 40-Gb/s optical modules using four different wavelength uncooled 10-Gb/s distributed-feedback (DFB) lasers are proposed and demonstrated. The 40-Gb/s optical module was integrated with coarse wavelength division multiplexing (CWDM) thin-film filters which enabled four 10-Gb/s transmission channels output through a single fiber. The 10-Gb/s DFB laser was packaged by commercialized low-cost coaxial TO-Can technology. The results of the 40-Gb/s optical module showed that the output optical power was above ${-}1$ dBm per channel and the system power budget was 12 dB. The transmission distance with a single-mode fiber reached more than 30 km at a bit-error-rate of $10^{{-}9}$. Compared with conventional 40-Gb/s optical modules, the module is easy to fabricate and is low cost. This proposed high-performance 40-Gb/s CWDM optical module demonstrates not only the feasibility of a 30 km transmission, but also shows the low-cost possibility of ensuring the application of WDM-passive optical network fiber-to-the-home systems.      

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.      

19-Gb/s adaptively modulated optical OFDM transmission by separated I/Q baseband delivery using 1 GHz RSOAs

19-Gb/s transmission over 23-km SMF is demonstrated based on 1-GHz bandwidth limited RSOAs with adaptively modulated optical OFDM. A novel baseband transmission technique is applied to halve the sampling speed requirements compared to traditional OFDM transmission techniques using Hermitian Symmetric. Selective bit loading with pre-emphasis and compensation is used to optimize the transmission performance.     

10-Gb/s AlGaInAs Colorless Remote Amplified Modulator by Selective Area Growth for Wavelength Agnostic Networks

We developed a 10-Gb/s AlGaInAs colorless remote amplified modulator with a gain peak detuned semiconductor optical amplifier using a selective epitaxy and semi-insulating buried heterostructure. The device provides up to 10-dB insertion gain and lossless operation together with static extinction ratio larger than 20 dB over a 50-nm range. Using this device, we achieved 10-Gb/s remote modulation over 80-nm spectral range in a back-to-back transmission. The device operates also in a single-mode fiber bidirectional link without penalty at 20 $^{circ}$ C.      

Performance Comparison of Duobinary Formats for 40-Gb/s and Mixed 10/40-Gb/s Long-Haul WDM Transmission on SSMF and LEAF Fibers

Duobinary formats are today considered as being one of the most promising cost-effective solutions for the deployment of 40-Gb/s technology on existing 10-Gb/s WDM long-haul transmission infrastructures. Various methods for generating duobinary formats have been developed in the past few years but to our knowledge their respective performances for 40-Gb/s WDM transmission have never been really compared. In this paper, we made an extensive numerical evaluation of the robustness of these different types of duobinary transmitter to accumulation of ASE noise, chromatic dispersion, PMD but also to single-channel and WDM 40-Gb/s transmission impairments on standard single-mode fiber. A numerical evaluation of the ability of duobinary format for mixed 10/40-Gb/s WDM long-haul transmission with 50-GHz channel spacing is also led, on both standard single-mode and LEAF fibers, and compared to DQPSK format. In order to clearly identify the limiting transmission effects on each of these two fiber types, the assessment of the performance of a 50-GHz spaced WDM 40-Gb/s long-haul transmission using either duobinary or DQPSK channels only is implemented at last.      

Beyond 240 Gb/s per Wavelength Optical Transmission Using Coded Hybrid Subcarrier/Amplitude/Phase/Polarization Modulation

In this letter, we propose a low-density parity-check coded hybrid subcarrier/amplitude/phase/polarization (H-SAPP) modulation scheme suitable to achieve a 240-Gb/s single-channel transmission rate over optical channels. The proposed scheme doubles the aggregate transmission rate achievable by eight-quadrature amplitude modulation while providing 2-dB optical signal-to-noise ratio performance improvement at a bit-error-ratio (BER) of $10^{-6}$ . Moreover, H-SAPP can increase the aggregate rate of the hybrid amplitude/phase/polarization scheme while maintaining the BER performance intact.      

Low-Chirp 85-Gb/s Duobinary Modulator in InP Using Electroabsorption Modulators

In 2005, Griffin showed that an InP phase-shift-keying/duobinary Mach–Zehnder interferometer (MZI) modulator could achieve good transmission performance at 10 Gb/s, despite modest residual amplitude modulation in the phase modulators in the MZI (ratio of real to imaginary part of index change was $sim$0.1). Here we show that even strong amplitude modulation in the “phase” modulators (ratio of real to imaginary part of index change is $sim$ 1.0) gives good transmission performance. Allowing for strong amplitude modulation allows a significant increase in modulator bandwidth. We demonstrate low-chirp 85.4-Gb/s optical duobinary generation in a fully packaged InP photonic integrated circuit.      

Multidimensional LDPC-Coded Modulation for Beyond 400 Gb/s per Wavelength Transmission

In this letter, we propose a multidimensional low-density parity-check-coded modulation scheme suitable for use in up to 400 Gb/s per wavelength transmission, using currently available commercial components operating at 40 gigasymbols/s. We show that we can achieve multiples of the current transmission speed with negligible penalty. At the same time, using this scheme, the transmission and signal processing are done at 40 gigasymbols/s, where dealing with all the nonlinear effects is more convenient and the polarization-mode dispersion is more manageable. In addition, we show that using the proposed technique, we can achieve an improvement ranging from 3 dB over 8-quadrature-amplitude modulation (QAM) to 14 dB over 256-QAM, and an improvement of up to 9.75 dB over the 256-3D-constellation at bit-error ratio (BER) of $10^{- 9}$. We also show that we can reach the 400-Gb/s aggregate rate with a coding gain of 10.75 dB at BER of $10^{- 12}$.      

Photonic Impulse-Radio Wireless Link at $W$-Band Using a Near-Ballistic Uni-Traveling-Carrier Photodiode-Based Photonic Transmitter-Mixer

A $W$-band photonic transmitter-mixer, constructed by integrating a planar quasi-yagi radiator for feeding the WR-10 waveguide-based horn antenna and a near-ballistic uni-traveling-carrier photodiode, is used with a mode-locked fiber laser to obtain 2.5-Gb/s impulse-radio (IR) wireless data transmission at around a center frequency of 100 GHz. The bias-modulation technique provides less jitter and a longer maximum transmission distance compared with the technique of modulating the optical pulse train using an electrooptics modulator. Using the bias-modulation technique, we achieve a 2.5-Gb/s IR wireless data transmission.      

System Outage Probability Due to PMD in High-Speed Optical OFDM Transmission

In this paper, closed-form analytical bounds on PMD-induced symbol error rate and outage probability in high-speed long-haul optical orthogonal frequency division multiplexed (OFDM) systems are derived, evaluated, and verified experimentally in order to assess the PMD tolerance of this modulation format. To obtain the analytical results, the PMD channel is modeled as a linear time-invariant system, whose end-to-end transfer function is used to upper-bound symbol error and outage probabilities in IM/DD optical OFDM transmission. The symbol error rate bounds predicted by the general analytical model are verified experimentally on a 10-Gb/s OFDM system with instantaneous DGD ranging between $Deltatau = 0$ and 120 ps . The outage probability bounds indicate that, if no RF guard bands are required, OFDM enables high-speed transmission with at least twice the PMD tolerance provided by an equivalent uncompensated OOK-based system at system outage probabilities $P_{{rm out, sys}}≪10^{-5}$ . If RF guard bands are required to mitigate effects of other distortions, it is shown that a penalty in the system PMD tolerance proportional to the intermediate RF subcarrier frequency, $f_{{rm RF}}$, is exerted. Consequently, a tolerance tradeoff exists in IM/DD OFDM systems, wherein $f_{rm RF}$ as well as baseband constellation size may be viewed as design parameters that can be optimized depending on specific system requirements.      

60-GHz Photonic Millimeter-Wave Link for Short- to Medium-Range Wireless Transmission Up to 12.5 Gb/s

In this paper, a 60-GHz photonic millimeter-wave link system for short- to medium-range broadband wireless data transmission is investigated. The system employs advanced mm-wave photonic components and radio-over-fiber (RoF) techniques for the generation of a DSB-SC optical mm-wave carrier and its subsequent on-off-keying modulation and transmission. For short-range applications, we have constructed a compact wireless RoF transmitter consisting of a high-frequency photodiode and a mm-wave antenna only. This system achieved error-free ($hbox {BER}=10^{-9}$, $2^{31}-1$ PRBS, NRZ) in-door transmission of 12.5-Gb/s signals over wireless distances up to 3.1 m with a receiver sensitivity as low as $-$ 45.4 dBm . For fixed wireless access (FWA) requiring a bit error rate of $10^{-4}$, the maximum transmission distance for 12.5 Gb/s is increased up to 5.8 m. For medium-range broadband wireless transmission an electrical radio-frequency (RF) amplifier was employed in the RoF transmitter. Here we achieved 7.5-Gb/s error-free transmission in out-door line-of-sight experiments over wireless distances of up to 36 m. Based upon the experimental results, we expect that the maximum wireless distance the system could accommodate for 12.5 Gb/s is in the kilometer range when using high-gain antennas and an RF transmitter amplifier with a sufficient bandwidth.      

4$,times,$25 Gb/s Frequency-Modulated DBR Laser Array for 100-GbE 40-km Reach Application

A monolithically integrated 100-Gb/s throughput (4 $,times,$25 Gb/s) laser array has been developed that employs frequency-modulated distributed Bragg reflector lasers. An optical filter converts a frequency-modulated signal to an amplitude-modulated signal with a high contrast ratio in addition to reducing the lasing spectrum bandwidth. A clear eye opening after 40-km transmission was observed with a 25-Gb/s nonreturn-to-zero signal in the 1550-nm region.      

Advanced components and sub-system solutions for 40 Gb/s transmission

With the commissioning of the latest 10-Gb/s systems, vendors are now in the process of developing architectures for their next-generation products. 40-Gb/s components and subsystems are currently in development to address the necessities of these next-generation systems. The top three challenges associated with 40-Gb/s transmission are optical signal-to-noise ratio, dispersion, and high-speed components. In order to realize 40-Gb/s transmission, new component and subsystem developments are crucial. This paper reviews the latest transmission technologies and dispersion compensation techniques developed to fulfill 40-Gb/s transmission system requirements.     

40-Gb/s Time-Division-Multiplexed Passive Optical Networks Using Downstream OOK and Upstream OFDM Modulations

In this investigation, we first propose and investigate a 40-Gb/s time-division-multiplexed passive optical network (TDM-PON) using four wavelength-multiplexed signals in both downstream and upstream traffic. Here, each downstream signal uses 10-Gb/s on–off keying (OOK) format encoded by a Mach–Zehnder modulator (MZM) in 1.5-$mu{hbox {m}}$ band. And each upstream channel utilizes the highly spectral efficient 10-Gb/s orthogonal frequency-division-multiplexing quadrature amplitude modulation (OFDM-QAM) generated by directly modulating a 1.3-$mu{hbox {m}}$ laser. Based on the proposed scheme, 40-Gb/s data traffic in a TDM-PON can be obtained easily by using four wavelength-multiplexed channels. In addition, the performance of the proposed PON architecture has also been discussed.      

Theoretical and Experimental Investigations of Direct-Detected RF-Tone-Assisted Optical OFDM Systems

In this paper, we propose and experimentally demonstrate a radio frequency (RF)-tone-assisted optical orthogonal frequency-division multiplexing (OFDM) transmission. By inserting an RF tone at the edge of the signal band and biasing the Mach–Zehnder modulator (MZM) at the null point, the proposed system has a better sensitivity and chromatic dispersion (CD) tolerance compared to the previous intensity-modulated single-sideband OFDM (SSB-OFDM). We show analytically that the majority of the linear channel impairments, such as the transmitter, CD, optical filtering, and receiver, can be compensated for by a simple zero-forcing equalizer. Besides, the optimum value of the important parameter, carrier-to-signal-power ratio (CSPR), is analytically obtained and supported via the experimental results. We also observe that the relatively worse sensitivity of the previous SSB-OFDM can be attributed to the limited CSPR. We experimentally demonstrate a 10-Gb/s, 8 quadrature-amplitude modulation (QAM) RF-tone-assisted OFDM transmission, and show that our system has a ${sim}$5-dB better sensitivity compared to the previous intensity-modulated SSB-OFDM and exhibits a negligible transmission penalty after 260-km uncompensated standard single-mode fiber (SSMF).      

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.     

A $W$ -Band Photonic Transmitter-Mixer Based on High-Power Near-Ballistic Uni-Traveling-Carrier Photodiodes for BPSK and QPSK Data Transmission Under Bias Modulation

In this study, we demonstrate wireless binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) data transmission at the $W$-band by use of bias modulation on photonic transmitters-mixers, which are composed of near-ballistic uni-traveling-carrier photodiodes and quasi-Yagi antennas without the integration of an Si-lens. By use of such a device and a novel optical millimeter-wave source with octupling optical frequency, we can successfully achieve 1.25-Gb/s BPSK and 0.625-Gb/s QPSK data-transmission at 105 GHz with 5-GHz intermediate-frequency signals.