Jhih-Heng Yan

An experimental demonstration for carrier reused bidirectional PON system with adaptive modulation DDO-OFDM downstream and QPSK upstream signals

A light source centralized bidirectional passive optical network (PON) system based on multiband direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) downstream and quadrature phase-shift keying (QPSK) upstream is experimentally demonstrated. By introducing a simple optical single-side band (SSB) filter at the optical network unit (ONU), all the desired signal bands will be immune from the deleterious signal-signal beating interference (SSBI) noise with only single-end direct-detection scheme. An adaptive modulation configuration is employed to enhance the entire downstream throughput which results in a 150-Gbps downstream data rate with a single optical carrier. In the upstream direction, by recycling the clean downstream optical carrier, a 12.5 Gb/s QPSK format with coherent receiving mechanism in central office is adopted for better receiving sensitivity and dispersion tolerance. With the power enhancement by the long-reach PON architecture, the downstream splitting ratio can achieve as high as 1:1024.

Fiber Bragg Grating-Based Three-Dimensional Multipoint Ring-Mesh Sensing System With Robust Self-Healing Function

By utilizing the cyclic filtering and free spectral range characteristics of an arrayed waveguide grating (AWG), we propose and experimentally demonstrate a novel 3-D ring-mesh sensing system with comprehensive self-healing function. The Bragg wavelengths of the employed fiber Bragg grating-based optical sensors are periodically assigned, with respect to the AWG. The proposed ring-mesh topology is constructed by 2 × 2 optical switches to link the ring-based subnets in a meshed architecture. Moreover, a simple and cost-effective signal sensing processor, provided by the AWG, is employed for classifying the sensing signals and monitoring the sensing elements. With the same constructional building block, the proposed sensing system can be easily scaled up which provides more self-healing paths in a self-reproduced manner. In addition, we also bring up a routing algorithm to seek for an optimal sensing path that has the least accumulated power loss to deal with any possible sensing point outage when the sensing system is scaling up.

Bidirectional fiber-wireless access technology for 5G mobile spectral aggregation and cell densification

Empowered by spectral aggregation and cell densification, future 5G mobile data networks pose a huge challenge to building next-generation mobile fronthaul systems with higher capacity, scalability, and energy efficiency. Under this circumstance, traditional solutions based on the Common Public Radio Interface or channel aggregation with digital signal processing (DSP) are not sufficient to support heterogeneous ubiquitous wireless access. In this paper, we demonstrate a point-to-multipoint bidirectional mobile fronthaul system. Wavelength division multiplexing plus frequency division multiplexing is applied to support independent asynchronous small cells. Intensity-modulation and direct-detection downlink (DL) as well as field-modulation and heterodyne-detection uplink (UL) are proposed. Combined with efficient virtual tone-based DSP for phase recovery and carrier-frequency-offset estimation, signal degradations from beating among incoherent asynchronous UL signals are mitigated. Proof-of-concept experiments are demonstrated where 20 and 16 80-MHz component carriers are transmitted over 25-km standard single-mode fiber for DL and UL, respectively. Less than 6% error vector magnitudes with 64-, 16-, and 4-ary quadrature amplitude modulation are obtained.

Over 210 Gb/s PDM multiband DDO-OFDM LR-PON downstream with simple self-polarization diversity

A simple polarization division multiplexed (PDM) multiband direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) long reach passive optical network (LR-PON) with net data rate over 210 Gb/s on single wavelength channel is proposed and experimentally demonstrated with self-polarization diversity technique. The proposed self-polarization diversity function is realized at a powered remote node with all passive components to achieve cost-effectiveness and simultaneously double both the channel capacity and subscriber numbers. Meanwhile, this architecture retains the simplicity of direct-detection single receiver-end without any hardware or software modification at the optical network units. The measured power penalty of the proposed PDM multiband DDO-OFDM LR-PON is 0.8 dB over 100 km transmission with respect to that of the ordinary single polarization scheme at a specified forward error correction threshold.

A Multiband DDO-OFDM System With Spectral Efficient Iterative SSBI Reduction DSP

A multiband direct-detected optical orthogonal frequency-division multiplexing (DDO-OFDM) system effectively enhance data capacity without high-end electrical devices. However, signals are optical-to-electrically converted with only one photodetector in a direct detecting scheme, signal-signal beating interference (SSBI) is meanwhile introduced. Traditionally, a large guard band can be applied to evade SSBI, however, it seriously restricts the precious spectral efficiency (SE). In this letter, we propose an iterative digital signal processing (DSP) in the receiving end of a multiband DDO-OFDM system to cope with the SSBI. With this iterative DSP, the corresponding SE theoretically approach to that of single polarization coherent optical OFDM systems. A total 65.4-Gb/s data rate is experimentally demonstrated with a three-band DDO-OFDM signal in 16-QAM format, and the SSBI reduction DSP saturates within two iterations. Various bandgaps and carrier-to-signal power ratios settings are also evaluated to investigate the feasibility of the proposed iterative DSP.

Polarization-Insensitive Remote Access Unit for Radio-Over-Fiber Mobile Fronthaul System by Reusing Polarization Orthogonal Light Waves

To reduce the complexity and cost of remote access units (RAUs), colorless transport architecture is preferred in a wavelength-division multiplexing (WDM) system. The wavelength-reuse technique is commonly adopted to realize colorless RAUs. However, in traditional approaches, RAUs employ crystal-based Mach-Zehnder modulators (MZMs) to modulate the distributed carriers. Hence, polarization tracking systems are necessary to align the polarization state of the distributed carriers with the MZM principal axis. This increases the cost of the RAUs. In this paper, a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) access architecture employing polarization-insensitive RAUs is proposed. In our proposed RAUs, the upstream signals are generated using polarization-orthogonal lights, and the performance of the upstream signals is independent of the polarization state of the MZM input lights. The proposed system is mathematically formulated and experimentally demonstrated. The 1.2-Gb/s quadrature phase-shift keying (QPSK) orthogonal frequency-division multiplexing (OFDM) downstream signal at the 60-GHz band and 5-Gb/s on-off keying (OOK) polarization-insensitive upstream signal over a 15-km standard single-mode fiber (SSMF) are demonstrated. In our results, a polarization-insensitive RAU is successfully obtained. The power penalty resulting from the interference of downstream signal is about 0.4 and 0.6 dB with a bit error rate (BER) of 10-9 in back-to-back and 15-km fiber transmission, respectively.

A 1∶128 high splitting ratio long reach PON based on a simple receiving design for ONU with 120-Gb/s double-sided multiband DDO-OFDM signal

A 120-Gb/s double-sided multiband DDO-OFDM based LR-PON architecture is proposed and experimentally demonstrated. With a simple receiver design, the implementation complexity can be reduced and the splitting ratio can be as high as 1:128.

Improving Spectral Efficiency and Receiving Sensitivity in a Direct-Detected OFDM System

In this paper, we’ll review some latest results in improving the spectral efficiency and receiving sensitivity in both the electronic and optical domains of a direct-detected optical OFDM signal.

A novel double-sided multiband direct-detection optical OFDM system with single laser source

We proposed and experimentally demonstrated a double-sided multiband DDO-OFDM system requiring only half of the total signal bandwidth in the receiver. The experimental results match the simulations well for all the signal bands.

Polarization-Tracking-Free IFoF Mobile Fronthaul With Adaptively Modulated PDM Multiband DDO-OFDM

This letter proposes a polarization-tracking-free polarization division multiplexing (PDM) in an intermediate frequency over fiber mobile fronthaul system based on multiband direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) with adaptive modulation. The use of two orthogonally polarized optical carriers with a simple optical filter at each radio access unit is sufficient to perform passive demultiplexing of the corresponding multiband signals in PDM schemes without transmission efficiency loss in training signal, which is commonly found in conventional PDM demultiplexing schemes. We experimentally achieved a multiband OFDM signal with adaptive modulation, which maximizes signal capacity, in a PDM scheme with the data rate of 49.64 Gb/s, which doubles that of corresponding single polarization schemes, over a 25-km single mode fiber. We also achieved a 6-dB power margin which is sufficient for the wireless transmission part.