The integration of optical and wireless systems is considered to be one of the most promising solutions for increasing the existing capacity and mobility as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for hybrid optical-wireless access networks are described, including optical millimeter-wave (mm-wave) generation, upconversion, and transmission in a downlink direction, and full-duplex operation based on wavelength reuse by using a centralized light source in an uplink direction. By employing these enabling technologies, we design and experimentally demonstrate an optical-wireless testbed that is simultaneously delivering wired and wireless services in the integrated optical-wireless and wavelength-division-multiplexing passive-optical-network access networks. The actual applications consisting of 270-Mb/s uncompressed standard-definition TV signal and 2.5-Gb/s data channels for downstream are successfully transmitted over a 25-km fiber and a 10.2-m indoor wireless link with less than a 1.5-dB power penalty. The results show that this integrated system is a practical solution to deliver superbroadband information services to both stationary and mobile users.

Key Enabling Technologies for Optical–Wireless Networks: Optical Millimeter-Wave Generation, Wavelength Reuse, and Architecture

The broadband penetration and continuing growth of Internet traffic among residential and business customers are driving the migration of today's end user's network access from cable to optical fiber and superbroadband wireless systems The integration of optical and wireless systems operating at much higher carrier frequencies in the millimeter-wave (mm-wave) range is considered to be one of the most promising solutions for increasing the existing capacity and mobility, as well as decreasing the costs in next-generation optical access networks. In this paper, several key enabling technologies for very high throughput wireless-over-fiber networks are reviewed, including photonic mm-wave generation based on external modulation or nonlinear effects, spectrum-efficient multicarrier orthogonal frequency-division multiplexing and single-carrier multilevel signal modulation. We also demonstrated some applications in wireless-over-fiber trials using these enabling techniques. The results show that the integrated systems are practical solutions to offer very high throughput wireless to end users in optically enabled wireless access networks.

Cost-Effective Optical Millimeter Technologies and Field Demonstrations for Very High Throughput Wireless-Over-Fiber Access Systems

We propose and experimentally demonstrate simultaneous generation and transmission of downstream multiband signals and upstream data in a bidirectional radio-over-fiber system. The scheme is based on a dual-parallel Mach-Zehnder modulator and a following single-drive Mach-Zehnder modulator. Multiband data including baseband, frequency-doubled, and frequency-quadrupled signals are generated through optical carrier suppression and frequency-shifting techniques. Upstream data transmission is realized by remodulation of the downstream differential phase-shift-keying signal without the need of additional light source and wavelength management at the base station.

Simultaneous Generation and Transmission of Downstream Multiband Signals and Upstream Data in a Bidirectional Radio-Over-Fiber System

By using a nully biased MZM to modulate an incoming single-mode light into a double sideband (CCA-DSB or CCS-DSB) master with preserved or suppressed central carrier, the directly OFDM encoded dual-mode colorless laser diode is performed for a successful fusion between wired and wireless links to establish a 5G-based MMWoF system. The dual-mode L-band optical carrier successfully delivers a 36-Gb/s OFDM data with a BER of $3.2 \times 10^{-3}$ , while the stabilized 39-GHz mm-wave carrier can provide wireless 4-Gb/s 16-QAM OFDM data with 16.6-dB SNR. The in-situ 39-GHz mm-wave carrier can be synthesized by optically heterodyne mixing the dual-mode carrier at remote node. When injection-locking with the CCS-DSB master, the dual-mode slave colorless laser diode improves its central carrier suppression ratio and RIN to 38 dB and −104 dBc/Hz, respectively. In comparison, the dual-DFBLD master injection-locking mixed mm-wave carrier is relatively unstable due to the individual DFBLDs at free-running condition. With the CCS-DSB master, the mm-wave carrier self-beat from the dual-mode optical carrier exhibits a narrow linewidth of <3 kHz with high purity and stability. Such a dual-mode colorless laser diode-based MMWoF link is capable of fusing the fiber wired and the 5G wireless links demanded in the near future.

39-GHz Millimeter-Wave Carrier Generation in Dual-Mode Colorless Laser Diode for OFDM-MMWoF Transmission

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Robust optical transmission systems : modulation and equalization

We propose a novel radio-over-fiber system to provide full-duplex services by using optical differential phase-shift keying modulation format at the central station for downstream and on-off keying remodulation of the downlink carrier at the base station (BS) for upstream. The optical carrier suppression modulation scheme is employed to simultaneously generate and up-convert 40-GHz optical millimeter wave. As the same optical carrier is used for both uplink and downlink, no additional light source is required at the BS, which greatly reduces the cost and simplifies the overall system. Simulations and experimental results show that the bidirectional 2.5-Gb/s data is successfully transmitted over 40-km single-mode fiber (SMF-28) with less than 2-dB power penalty

Bidirectional ROF Links Using Optically Up-Converted DPSK for Downstream and Remodulated OOK for Upstream

We propose and demonstrate a novel full-duplex radio-over-fiber system using OOK re-modulation of up-converted downstream DPSK signal for upstream connection. The bi-directional 2.5 Gbits/s data is successfully transmitted over 40 km SMF-28 with <2 dB power penalty

A Bi-directional Radio-over-Fiber System with All-optical Up-converted DPSK for Downstream and Re-modulated OOK for Upstream

We have experimentally demonstrated 8 times 10 Gbit/s modified duo-binary RZ (MD-RZ) signal repeaterless transmission over a record length of 240 km standard fibre (SMF-28). A Raman amplifier was used to enhance the OSNR and extend the repeaterless transmission distance with low receiver penalty.

8×10 Gbit/s WDM repeaterless transmission over 240km SMF using modified duobinary RZ signals

We present experimental and simulation results for RZ/NRZ DQPSK decoder free spectral range optimization for high bit rates in the presence of strong optical filtering and show that filtering degradations can be relieved by higher FSR.

Impact of Free Spectral Range Optimization on RZ/NRZ DQPSK Modulation Format with Strong Optical Filtering for Ultra-High Data Rate Systems

Phase jitter is the major impairment of long-haul phase-shift keying systems. In this letter, we propose and investigate a novel experimental method to estimate the optical phase variance of return-to-zero differential phase-shift-keyed (RZ-DPSK) systems. The means and variances of the power detected before and after DPSK demodulation are the only physical parameters needed to determine the optical phase variance. This can be easily measured with the histogram function of a fast oscilloscope. Numerical simulations confirm a posteriori the accuracy of the method which can be considered as a useful and simple tool to characterize a DPSK transmission

M. Haris

Papers

Bidirectional ROF Links Using Optically Up-Converted DPSK for Downstream and Remodulated OOK for Upstream

A Bi-directional Radio-over-Fiber System with All-optical Up-converted DPSK for Downstream and Re-modulated OOK for Upstream

8×10 Gbit/s WDM repeaterless transmission over 240km SMF using modified duobinary RZ signals

Impact of Free Spectral Range Optimization on RZ/NRZ DQPSK Modulation Format with Strong Optical Filtering for Ultra-High Data Rate Systems

Experimental Measurement of Optical Phase Variance in RZ-DPSK Systems Using Direct Detection After Demodulation by an MZDI