KEYWORDS: Signal generators, Digital signal processing, Eye, Receivers, Modulation, Signal detection, Multiplexers, Oscilloscopes, Modulators, Binary data
With the popularization of data center and other bandwidth hungry inter-connect applications, the desired capacity of short reach optical network has exponentially increased. In order to realize high-speed transmission, a few modulation formats or schemes, such as PAM4 and DMT are proposed and experimentally demonstrated. However, these modulation formats need expensive DAC and ADC as well as DSP procession. OOK modulation has simple architecture and high receiver sensitivity. Duo-binary signal is a special OOK signal. Here we experimentally demonstrate a record bit rate of 160-Gb/s OOK electrical signal generation, and realize a duobinary optical signal at a bit rate of 160Gb/s transmission and detection.
KEYWORDS: Laser sintering, Receivers, Modulation, Digital signal processing, Signal processing, Telecommunications, Data communications, Signal detection, Absorbance, Active optics
The intensity modulation and direct detection (IM/DD) systems have been widely investigated and demonstrated to fulfil the requirement of short reach data communication links with simple implementation. DMLs are a low cost solution for IM/DD systems due to their low power dissipation, small footprint and high output optical power. However, for DMLs, the driving current can influence the optical density at its active region, hence the intrinsic chirp affects the generated optical carrier and results in distortions of the signals, which reduces transmission rates and signals decision accuracy. We propose a machine learning-based decision technique to mitigate nonlinear distortions of the DMLs without using any nonlinear processing, and demonstrate a 60-Gb/s PAM-8 IM/DD system using a DML. About 0.6-dB receiver sensitivity improvement is achieved after 2km transmission.
Millimeter wave (mm-wave) and microwave frequency has become a hot research topic in recent years. Comparing to traditional wireless communication frequency, microwave possesses larger available bandwidth, which is up to tens of gigahertz, so that it can support advanced digital services with ultra-high bit rate. To support the transmission rate over 100Gbit/s in an optical wireless system, forward error correction (FEC) is adopted in real-time communication systems to correct bit errors. Polar code is a kind of FEC which can theoretically achieve channel capacity as the code length tends to infinity. In this paper, we experimentally demonstrate a photonics-aided microwave communication system at K-band. With polar coding, 20-Gbit/s signal is transmitted over 20m wireless link. Our experimental results show that BER performance of such optical wireless system can be improved largely after we employ polar coding.
We experimentally demonstrate a photonics-based radio-over-fiber orthogonal-frequency-division-multiplexing (ROFOFDM) system located within the terahertz-wave (THz-wave) frequency range from 350GHz to 510GHz. In our demonstrated system, 4.46-GHz-bandwidth OFDM quadrature-phases-shift-keying (OFDM-QPSK) THz-wave signal within the frequency range from 350GHz to 510GHz, can be generated and delivered over 2.5-inch wireless transmission distance, with a bit-error ratio (BER) under the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3. In our demonstrated system, 4.46-GHz-bandwidth OFDM-QPSK THz-wave signal at 450GHz is delivered over up to 35-km fiber transmission distance and 2.5-inch wireless transmission distance, with a BER of 3.8×10-3.
KEYWORDS: Modulation, Radio over Fiber, Orthogonal frequency division multiplexing, Frequency division multiplexing, Optical amplifiers, Digital signal processing, Lithium, Fiber amplifiers, Optical engineering, Antennas
DFT-S-orthogonal frequency division multiplexing (OFDM) and single-carrier (SC) modulation are two typical modulation formats in radio-over-fiber (RoF) systems. They may have respective advantages and disadvantages in different scenarios. Therefore, bit error ratio comparison results of these two modulation formats will be useful for designing and optimizing the practical RoF system. We experimentally compare these two modulation formats in a long wireless distance RoF system at W-band. It can be concluded that DFT-S-OFDM and SC modulation have similar performances in a RoF system with transmission distance over 80-km fiber and 224-m wireless link.
The nonlinear compensation algorithm based on Volterra series has been proved effective in low order modulation OFDM system, such as QPSK/16QAM. In this paper, we demonstrate a 64QAM/ 128QAM DFT-S-OFDM signal generation with DML with some advanced algorithms such as DD-LMS, ISFA, DFT-S and nonlinear compensation to improve the signal performance. For the first time we demonstrate that the nonlinear compensation algorithm based on Volterra series can improve the performance of the high-order modulation DFT-S-OFDM signal such as 64QAM and 128QAM. In this experiment we have realized 19.1/11.2Gb/s 64/128QAM signal transmission over 15km fiber at 1307nm. For 64QAM case, the receiver sensitivity can be improved about 1dB when all the algorithms mentioned in this paper are adopted. And the BER can be improved from 4.7x10-3 to 2.8x10-3 at 7.0dBm for 128QAM signal, which reaches the HD-FEC threshold of 3.8x10-3.
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