Direct-detection Optical Transmission Research Articles

Real-time optical spectrum monitoring in filterless optical metro networks

Filterless optical networks (FONs) have been proposed as a feasible solution for optical metro networks. In addition, as a result of the shorter distance compared to core optical networks, direct detection optical transmission systems can be used in metro FONs, which reduces costs, as compared to coherent detection systems. In this work, we present two optical signal tracking approaches for FONs that allow to detect small frequency laser drift problems and enable safely reducing channel spacing. Additionally, we study the most proper resolution for optical spectrum analyzers continuously scanning the whole C-band. Proposed approaches are: (1) feature-based tracking and (2) residual-based tracking. Experiments are carried out to compare the performance of the approaches for both direct detection and coherent detection systems, in the case of a single optical signal with no neighboring signals nearby in the spectrum, as well as in the case of a group of optical signals closely allocated in the spectrum. The results show that the residual-based approach enriched with contextual information enables to better track and correct the wavelength drifts before they reach their limits (e.g., ± 2.5 GHz), leading to the guard band reduction for what concerns wavelength drifts.

IMDD Transmission at Net Data Rate of 333 Gb/s Using Over-100-GHz-Bandwidth Analog Multiplexer and Mach–Zehnder Modulator

We demonstrate intensity-modulated direct-detection optical transmission at a record-high data rate with single wavelength and single polarization. The high data rate is achieved with simple optics by using electronic and electrooptic devices with large operation bandwidths. We use a digital-preprocessed analog-multiplexed digital-to-analog converter with a >100-GHz analog multiplexer (AMUX) to drive an 80-GHz Mach–Zehnder optical modulator (MZM). The AMUX is based on 0.25-μm-emitter-width InP heterojunction bipolar transistor technology, and the MZM has InP n-i-p-n heterostructure optical waveguides with capacitance-loaded travelling-wave electrodes. We employ discrete multi-tone modulation controlled by a margin-adaptive bit-loading algorithm. In the experiment, the signal was transmitted over a 20-km dispersion-compensated single-mode fiber link and received by a single photodiode followed by a digital signal processor including a nonlinear equalizer. At a gross bit rate of 400 Gb/s, the bit error rate of the received signal was below the threshold of 20% overhead soft-decision forward error correction code. This result corresponds to a net data rate of 333 Gb/s.

Digital chromatic dispersion pre-management for SSB modulation direct-detection optical transmission systems

Recently, single-side-band (SSB) modulation direct detection (DD) based optical transmission systems have attracted great interest due to their capability of electronic chromatic dispersion (CD) compensation. In this paper, we investigate the digital chromatic dispersion pre-management for optical SSB signals which are generated by radio frequency (RF) tone based on I/Q modulator and optical carrier based dual-drive Mach–Zehnder modulator (DDMZM) with DD at the C-band via numerical simulations. The impact of CD, self-phase modulation (SPM) and phase-to-amplitude noise on such a SSB DD optical transmission system with I/Q modulator based virtual carrier assisted, and the DDMZM based optical carrier are investigated. The simulation results have successfully demonstrated the transmission of a 224-Gb/s Nyquist 16-ary quadrature amplitude modulation (16QAM) signal over 75-km standard single mode fiber (SSMF) with bit error rate (BER) less than 3.8 × 10−3 in a SSB-DD system by using digital CD pre-management. It is shown that the SPM induced impairment can be optically mitigated by the residual positive CD of the SSMF link.

Improved BER Performance of Real-Time DDO-OFDM Systems Using Interleaved Reed–Solomon Codes

In this letter, we have experimentally demonstrated a Reed–Solomon (RS) coded and multiple symbol interleaved real-time orthogonal frequency-division multiplexing (OFDM) signals transmission over a single mode fiber (SMF)-based direct-detection optical system. To the best of our knowledge, this is the first time to realize the forward error correction (FEC) in real-time optical OFDM systems. The bit error rate (BER) performances of RS-coded OFDM signals are investigated in a low-cost directly modulated laser-based direct-detection optical transmission system. The experimental results show that after 25.26-km SMF-28 transmission of the real-time RS-coded and symbol interleaved optical OFDM signals, a post-FEC BER less than $1\times 10^{-8}$ is successfully achieved by using RS code with 7% overhead for a pre-FEC BER of $1\times 10^{-3}$ .

Doubling direct-detection data rate by polarization multiplexing of 16-QAM without active polarization control

We introduce and simulate a technique enabling to utilize the polarization dimension in direct-detection optical transmission, supporting polarization multiplexing (POL-MUX) over direct-detection (DD) methods previously demonstrated for a single polarization such as direct-detection OFDM. POL-MUX is currently precluded in self-coherent DD with remotely transmitted pilot, as signal x pilot components may randomly fade out. We propose POL-MUX transmission of advanced modulation formats, such as 16-QAM and higher, by means of a novel low-complexity photonic integrated optical front-end and adaptive 3x2 MIMO DSP. The principle of operation is as follows: an additional X x Y cross-polarizations signal is generated, providing three projections onto an over-complete frame of three dependent vectors. This enables to resiliently reconstruct the received state of polarization even when the remotely transmitted pilot fades along one of the received polarization axes.

Performance Comparison of Long-Haul Direct Detection Optical Transmission Systems Adopting Dispersion Management with Pre-Compensation

This article reports a numerical investigation on the performance of return-to-zero intensity-modulated direct detection, return-to-zero differential phase shifting key, and return-to-zero differential quadrature phase shifting key systems operating in G.652 links adopting dispersion management. Also illustrated are the role and benefits of pre-compensation. For such an aim, the influence of the non-linear Kerr impairments on the in-phase and quadrature components of the signal are studied, along with the consequent degradations in terms of the Q-factor for the different modulation formats. Such an investigation is applied to evaluate the maximum propagation distances for 40- and 80-Gb/s capacities.

Significant reach enhancement for dispersion limited direct detection systems using offset carrier and linear electrical equalizers

Abstract A scheme utilizing an offset optical carrier transmission and adaptive linear equalizer in electrical domain is proposed to enhance the transmission reach of a direct detection optical transmission system. In the proposed scheme, the detection process becomes linear and thereby, a simple linear equalizer in electrical domain can undo the distortion due to linear dispersive effects.

Compensation of optical fibre dispersion in theelectrical domain for transmissionsystems with direct detection

In direct detection optical transmission systems the fibre dispersion may be compensated for in the electrical domain, provided the modulation index is small, and the signal is carried as a combined phase and amplitude modulation. Limitations and design guidelines for transmission systems based on these principles are presented, with emphasis on directly modulated diode laser transmitters.

Polarization modulated direct detection optical transmission systems

A novel polarization modulated direct detection (PM-DD) system suitable both for binary and multilevel transmission is presented. At the transmitter the optical field is polarization modulated by a standard modulator. The receiver is based on the estimation of the Stokes parameters of the received optical field by means of a direct-detection optical front end and baseband electrical processing. The Poincare sphere rotation induced by the fiber is compensated by means of a purely electronic algorithm and the decision is performed in the Stokes space. The system performance is evaluated by an analytical model when the only relevant noise source is the receiver thermal noise and when erbium-doped optical amplifiers introduce amplified spontaneous emission (ASE) noise. The system is completely compatible with a direct-detection-based optical network, and it is possible to implement efficient multilevel modulation formats. >

High performance 10 Gbit/s pin -FET optical receiver

An optical receiver suitable for a 10 Gbit/s direct detection optical transmission system is described. It uses a pin diode, commercial GaAs MESFETs and hybrid construction techniques on a coplanar substrate. The measured sensitivity of the receiver is –20.4 dBm, which is the best reported sensitivity at 10 Gbit/s for a pin-FET optical receiver to date.

180 photons/bit in 140 Mbit/s, 305 km direct-detection optical transmission experiment

A sensitivity of −54.9 dBm or 180 photons/bit was achieved in a direct-detection optical system operating at 140 Mbit/s at a wavelength of 1554 nm after transmission through 305 km of standard single-mode fibre. The result was obtained using novel linecoding and commercially available components.

Simplified model of an FSK-to-ASK direct-detection system using a Fabry-Perot demodulator

Design guidelines are presented for a direct-detection optical transmission system in which an FSK (frequency-shift-keyed) signal is converted to ASK (amplitude-shift-keyed format) by a tunable Fabry-Perot filter demodulator/demultiplexer. The analysis gives an estimated set of conditions for the proper Fabry-Periot (FP) bandwidth and tone frequency deviation that reduces the system power penalities. This is accomplished by calculating the tonal power transmitted through the FP; this simplifying assumption neglects pattern dependences but provides a simple, useful expression for predicting regions of rapidly increasing power penalties. The generated curves agree well with experimental results for three different systems. >