Dar-Zu Hsu

Cost-effective 33-Gbps intensity modulation direct detection multi-band OFDM LR-PON system employing a 10-GHz-based transceiver

We develop a dynamic multi-band OFDM subcarrier allocation scheme to fully utilize the available bandwidth under the restriction of dispersion- and chirp-related power fading. The experimental results successfully demonstrate an intensity-modulation-direct-detection 34.78-Gbps OFDM signal transmissions over 100-km long-reach (LR) passive-optical networks (PONs) based on a cost-effective 10-GHz EAM and a 10-GHz PIN. Considering 0-100-km transmission bandwidth of a 10-GHz EAM, the narrowest bandwidth is theoretically evaluated to occur at ~40 km, instead of 100 km. Consequently, the performances of 20-100-km PONs are experimentally investigated, and at least 33-Gbps capacity is achieved to support LR-PONs of all possible 20-100-km radii.

21 Gb/s after 100 km OFDM long-reach PON transmission using a cost-effective electro-absorption modulator.

We experimentally demonstrate a superior performance of 2.1-Tb/s·km OFDM signal transmission over 100-km long-reach PONs. While the bandwidth of a 100-km SMF transmission system is limited to 4.3 GHz due to positive chirp, we successfully achieve spectrally-efficient 21-Gb/s signaling by using a cost-effective and low-chirp EAM, and adopting the 128-QAM format and adaptive subcarrier pre-emphasis.

A High-Performance OFDMA PON System Architecture and Medium Access Control

Orthogonal frequency-division multiplexing (OFDM) passive optical network (PON) has been considered to be a promising next-generation broadband wired access solution. However, based on the current tree-based architecture, existing OFDM PON systems face severe challenges when increasing the scalability and data-rate performance. In this paper, we propose a high-performance virtual-tree orthogonal frequency-division multiple access PON system (VTOPS). With the virtual-tree architecture and coupled with the use of inexpensive direct modulation, VTOPS features high reliability, scalability, spectrum efficiency, and cost effectiveness all at once. For governing the flexible/fair access and dynamic allocation of bandwidth, VTOPS incorporates a rate-based medium access control (MAC) scheme. The MAC scheme performs dynamic rate adjustment using a neural-fuzzy system. By adjusting the system parameters, the MAC scheme can achieve a wide range of delay and fairness performance under a variety of traffic patterns. Finally, we show both theoretical and experimental results to demonstrate that, by applying the power pre-emphasis algorithm and adaptive subchannel modulation, VTOPS achieves 40 Gb/s downlink and 40 Gb/s uplink transmissions, using low-cost 10 GHz directly modulated lasers.

A 40-Gb/s OFDM PON System Based on 10-GHz EAM and 10-GHz Direct-Detection PIN

This letter demonstrates a 40-Gb/s optical double-sideband (ODSB) orthogonal frequency-division multiplexing passive optical network (OFDM-PON) system using a cost-effective 10-GHz-bandwidth electroabsorption modulator (EAM). By employing a subcarrier-adaptive modulation format and pre-emphasis, we successfully achieve 20-km EAM-based single-mode-fiber (SMF) transmission.

SSII cancellation in an EAM-based OFDM-IMDD transmission system employing a novel dynamic chirp model

We develop a novel subcarrier-to-subcarrier intermixing interference (SSII) cancellation technique to estimate and eliminate SSII. For the first time, the SSII cancellation technique is experimentally demonstrated in an electro-absorption modulator- (EAM-) based intensity-modulation-direct-detection (IMDD) multi-band OFDM transmission system. Since the characteristics of SSII are seriously affected by the chirp parameter, a simple constant chirp model, we found, cannot effectively remove the SSII. Therefore, assuming that the chirp parameter linearly depends on the optical power, a novel dynamic chirp model is developed to obtain better estimation and cancellation of SSII. Compared with 23.6% SSII cancellation by the constant chirp model, our experimental results show that incorporating the dynamic chirp model into the SSII cancellation technique can achieve up to 74.4% SSII cancellation and 2.8-dB sensitivity improvement in a 32.25-Gbps OFDM system over 100-km uncompensated standard single-mode fiber.

An Energy and Cost Efficient WDM/OFDMA PON System: Design and Demonstration

In this paper, we propose an energy and cost efficient WDM/OFDMA PON system, referred to as NEWOPS. Based on a new two-tiered semi-tree architecture, NEWOPS allows a large number of ONUs to be connected to OLT using only a handful of colorless transceivers. Due to the architecture, NEWOPS not only facilitates high spectral efficiency and flexible sub-channel bandwidth allocation, but also reduces the Rayleigh backscattering (RB) problem and achieves high energy and cost efficiency. Experimental results demonstrate that, taking only 5-GHz bandwidth for each wavelength, NEWOPS successfully achieves 20-Gb/s downstream and 10-Gb/s upstream OFDM-xQAM transmissions via the same fiber trunk. We depict that, to support 40 ONUs for example, NEWOPS achieves energy efficiency that is three to six times higher than that of a typical 10-Gb/s WDM/OFDM PON.

20-Gbps WDM-PON transmissions employing weak-resonant-cavity FPLD with OFDM and SC-FDE modulation formats

We experimentally demonstrate a superior performance of 20-Gbps OFDM/SC-FDE transmission over 20-km WDM-PONs, using a channelized weak-resonant-cavity FPLD with a modulation bandwidth of only 1.25 GHz by using injection-locking, direct detection and adopting the power-loading algorithm.

74.4% SSII cancellation in an EAM-based OFDM-IMDD transmission system

We develop a novel SSII cancellation technique and experimentally demonstrated that 74.4% SSII cancellation and 2.8-dB sensitivity improvement can be achieved in a 32-Gbps EAM-based IMDD OFDM transmission system over 100-km uncompensated SSMF.

Cost-Effective OFDM Transmission Technologies for Long-Reach PONs

As the development of broadband services, such as IPTV, HDTV, blue ray disk, telepresence, 3D HDTV, and super HDTV, increases, so is people’s demand for high bandwidth and a high quality entertainment experience. So far, we have many access network solutions to support the broadband services, such as Fiber to the x (FTTx), WiMAX, LTE, and so on. Among these, FTTx is the most expensive, due to costly fiber deployment. However, optical fiber can provide huge bandwidth, ultra-low power loss of transmission, and is not necessary to be upgraded for many years, thus it is a long-term solution. Therefore, many operators have invested in a lot of budget to deploy the FTTx infrastructures.

106-fJ/(bit·km) 2-km OFDM OM4 MMF transmissions for energy efficient optical interconnects

Employing high-performance 850-nm VCSELs with oxide-relief and Zn-diffusion structures, we demonstrate 17.8-Gbps 2-km OM4 fiber transmissions. Meanwhile, ultra-low EDDR of 106 fJ/(bit·km) with bias current as low as 1.9 mA is achieved.