Qingjiang Chang

Simultaneous generation of independent wired and 60-GHz wireless signals in an integrated WDM-PON-RoF system based on frequency-sextupling and OCS-DPSK modulation

We propose a simple and cost-effective scheme to integrate a wavelength division multiplexed-passive optical network (WDM-PON) with a 60-GHz radio-over-fiber (RoF) system. In optical line terminal/central station (OLT/CS), 10-GHz electronic devices and single-drive Mach-Zehnder modulators (MZMs) are used to generate 60-GHz wireless signals based on frequency-sextupling and optical carrier suppression-differential phase shift keying (OCS-DPSK) modulation. By designing a new architecture, only N + 1 single-drive MZMs are required for an N-channel WDM-PON-RoF converged system. The proposed scheme is experimentally demonstrated with 1.25-Gb/s independent wired, wireless and upstream data. Error-free performances are achieved for all these signals after transmission of 25-km single mode fiber (SMF).

Generation and transmission of multiband and multi-gigabit 60-GHz MMW signals in an RoF system with frequency quintupling technique.

We propose and experimentally demonstrate a cost-effective radio-over-fiber (RoF) system to simultaneously generate and transmit multiband and multi-gigabit 60-GHz millimeter wave (MMW) signals using frequency quintupling technique. Multiband signals at 56-GHz and 60-GHz are realized with two cascaded single-drive Mach-Zehnder modulators (MZMs), where phase control is not required. Furthermore, only low-frequency (≤12GHz) optical and electrical devices are used in the central station (CS), which enable a cost-effective system. At the user-terminal, two-stage down-conversions are employed by envelope detection (ED) and intermediate frequency (IF) mixing, eliminating expensive high-speed synthesizer and critical phase control components. Error-free performances are achieved for the multiband MMW signals after 50-km single-mode fiber (SMF) and 10-ft wireless link transmissions.

Generation of Multiband Signals in a Bidirectional Wireless Over Fiber System With High Scalability Using Heterodyne Mixing Technique

We propose and experimentally demonstrate a bidirectional radio over fiber system to simultaneously generate and transmit downstream multiband signals and upstream data. To the best of our knowledge, this is the first time that the multiband signals, including baseband, 24-GHz microwave (MW), and 42- and 60-GHz millimeter-wave (MMW) signals, are realized through multicarrier generation and heterodyne mixing techniques. The frequencies of the MW and MMW signals are continuously tunable, thus high scalability can be achieved. In the base station, part of the continuous wave light is used as an optical carrier for upstream data, which is transmitted back to the central station though the same fiber. Error-free performances are achieved for all the signals after 25-km single-mode fiber and 5 ft air link transmission for wireless data.

Power margin improvement for OFDMA-PON using hierarchical modulation.

We propose and experimentally demonstrate a hierarchical modulation scheme to improve power margin for orthogonal frequency division multiple access-passive optical networks (OFDMA-PONs). In a PON system, under the same launched optical power, optical network units (ONUs) have different power margins due to unequal distribution fiber lengths. The power margin of the PON system is determined by the ONU with the lowest power margin. In our proposed scheme, ONUs with long and short distribution fibers are grouped together, and downstream signals for the paired ONUs are mapped onto the same OFDM subcarriers using hierarchical modulation. In a pair of ONUs, part of the power margin of the ONU with short distribution fiber is re-allocated to the ONU with long distribution fiber. Therefore, the power margin of the ONU with the longest distribution fiber can be increased, leading to the power margin improvement of the PON system. Experimental results show that the hierarchical modulation scheme improves the power margin by 2.7 dB for an OFDMA-PON system, which can be used to support more users or extend transmission distance.

A DSP-assisted symbol-cascade mobile fronthaul solution with large capacity and neat RRHs

A mobile fronthaul approach that can facilitate 96 channels of 20MHz 64QAM LTE formatted signals over 20km fibre has been demonstrated for the first time, due to centralized pre-compensation for downlink and post-compensation for uplink in BBU, RRH sustains neat.

Cloud-based indoor wireless access and fronthaul solution for high capacity MIMO services using fixed network architecture of economical LAN cables and fiber

We proposed and experimentally demonstrated an in-building mobile communication of 200× 20MHz MIMO LTE-A signals over sequential wireless-interface, economical twisted copper lines and fiber between UEs and centralized BBUs in the uplink direction.

Ultra-broadband semiconductor optical amplifier for long-reach optical access networks

In recent years, semiconductor optical amplifiers (SOAs) have shown great promise for use in evolving optical communication networks, especially long-reach passive optical networks (LR-PONs). These networks can be beneficial in reducing the number of required optical line termination sites (i.e., to a few major central offices).1, 2 However, few LR-PONs that include optical fiber amplifiers, such as erbium-doped fiber amplifiers (EDFAs), have actually been experimentally demonstrated. This is because the operation region of EDFAs is limited to the C (1524–1544nm) and L (1565–1625nm) bands.3, 4 It has been shown that linear SOAs are a more promising technology for use in LR-PONs.5, 6 This is because these devices can counteract the weakness of the EDFA operation region. Linear SOAs offer an ultra-broad wavelength window (about 1280–1650nm), a constant moderate gain (about 15dB) over a large range of input power levels (typically up to 0dBm), a large gain bandwidth (about 60–100nm), and a moderate noise figure (about 7–8dB).7 In addition, the Full Service Access Network and the International Telecommunication Union’s Telecommunication Standardization Sector have recently defined the next-generation passive optical network (NGPON) wavelength window. Within this window, an initial future time and wavelength division multiplexed passive optical network (TWDMPON) has been identified. The upstream (US) wavelength is thus in the C-band and the downstream (DS) wavelength range is within the L+ band (1596–1603nm).8 By contrast, in the wavelength division multiplexed passive optical network (WDMPON), the full spectrum across both the C and L bands (i.e., 1524–1625nm) is adopted.8 It is therefore necessary for SOAs to Figure 1. Dual-active-layer (DAL) design of the proposed semiconductor optical amplifier (SOA) structure. The shallow-etched ridge waveguide has a length (L) of 1.5mm and a width (W) of 5 m. US: Upstream wavelength. DS: Downstream wavelength. GaAs: Gallium arsenide. AlGaAs: Aluminum gallium arsenide. GaInNAs: Gallium indium nitride arsenide. QD: Quantum dot. QW: Quantum well. P: Ptype semiconductor. N: N-type semiconductor.

An upstream burst-mode equalization scheme for 40 Gb/s TWDM PON based on optimized SOA cascade

We present a novel upstream burst-mode equalization scheme based on optimized SOA cascade for 40 Gb/s TWDMPON. The power equalizer is placed at the OLT which consists of two SOAs, two circulators, an optical NOT gate, and a variable optical attenuator. The first SOA operates in the linear region which acts as a pre-amplifier to let the second SOA operate in the saturation region. The upstream burst signals are equalized through the second SOA via nonlinear amplification. From theoretical analysis, this scheme gives sufficient dynamic range suppression up to 16.7 dB without any dynamic control or signal degradation. In addition, a total power budget extension of 9.3 dB for loud packets and 26 dB for soft packets has been achieved to allow longer transmission distance and increased splitting ratio.

Demonstration of quantum dot SOA-based colorless ONU transmitter for symmetric 40 Gb/s TWDM PON

Detailed numerical investigation of self-seeded colorless ONU transmitter using quantum dot (QD) SOA as the intensity modulator for symmetric 40 Gb/s TWDM-PON has been developed. It is shown that the QD SOA-based intensity modulator is able to support 10 Gb/s OOK upstream signal transmission with an optical extinction ratio of over 10 dB. Chromatic dispersion compensation free of 20 km passive transmission has been achieved for error free reception. Moreover, the system performance and power budget have been analyzed and discussed for different transmission distance and split ratio.

A symmetric 100Gb/s TWDM-PON with RSOA-based 12.5Gb/s colorless ONU and duplex optical equalization

We propose and validate a bandwidth-limited RSOA based 100Gb/s symmetric TWDM-PON system with centralized wavelength generation technique and a single delay interferometer for simultaneous optical equalization of 8 pairs of duplex 12.5Gb/s NRZ signals.