C. W. Chow

Optimized OFDM modulation format for white-light LED optical wireless communication with pre-equalization

We demonstrate a simple orthogonal-frequency-division-multiplexing (OFDM) light-emitting-diode (LED) optical wireless communication system using power pre-equalization to enhance the transmission performance. Error free operation using 5Mbps at a distance of 2m is achieved.

High-speed phosphor-LED wireless communication system utilizing no blue filter

In this paper, we propose and investigate an adaptively 84.44 to 190 Mb/s phosphor-LED visible light communication (VLC) system at a practical transmission distance. Here, we utilize the orthogonal-frequency-division-multiplexing quadrature-amplitude-modulation (OFDM-QAM) modulation with power/bit-loading algorithm in proposed VLC system. In the experiment, the optimal analogy pre-equalization design is also performed at LED-Tx side and no blue filter is used at the Rx side for extending the modulation bandwidth from 1 MHz to 30 MHz. In addition, the corresponding free space transmission lengths are between 75 cm and 2 m under various data rates of proposed VLC. And the measured bit error rates (BERs) of < 3.8×10-3 [forward error correction (FEC) limit] at different transmission lengths and measured data rates can be also obtained. Finally, we believe that our proposed scheme could be another alternative VLC implementation in practical distance, supporting < 100 Mb/s, using commercially available LED and PD (without optical blue filtering) and compact size.

Advances in access networks - from long-reach (LR) to short-reach (SR), and from TDM/WDM to OFDM

We discuss the progress and advances in access network, which is considered as the “last-mile” connection between the end-user and the network. Different challenges and possible solutions of access network will be discussed, including the long-reach (LR) passive-optical-network (PON) and the short-reach (SR) wireless fiber-to-the-antenna (FTTA) system. Moreover, orthogonal-frequency-division-multiplexing (OFDM) can provide one more degree of freedom besides the time-division-multiplexing (TDM) and wavelength-division-multiplexing (WDM) for network capacity sharing. And the applications of OFDM in access network will be discussed.

Employing four-band OFDM signals for 40-Gb/s PON with 128 ONUs in single-Wavelength in 10-GHz bandwidth

In this work, we propose a novel modulation of four-band OFDM channels within 10-GHz bandwidth in 40-Gb/s PON with 128 ONUs. Here, we first propose using multi-band OFDM modulation format applying in -0.7 chirp parameter Mach-Zehnder modulator (MZM) to improve and compensate the fiber dispersion and RF fading effects. Moreover, -0.37 dB power penalty at FEC level (BER of 3.8×10-3) is also observed after 20 km fiber transmission.

Time division duplex for preventing reflection interference in visible light communication

In this work, an experimental time division duplex system is presented to prevent interference in visible light communication. The 40-LED array and a single LED were used for downlink and uplink respectively. The interference of signal reflection on mirrors was discussed and removed using time division duplex. At the distance of 2 m, the data rate achieved is above 1Mbps with bit error rate below 2×10-5 in each of the direction.

Equalization of PAM-4 Signal Generated by Silicon Microring Modulator for 64-Gbit/s Transmission

We propose and demonstrate a 64-Gbit/s four-level pulse-amplitude-modulation transmission by using a limited modulation bandwidth silicon microring modulator (SiMRM) and the Volterra equalization scheme. Severe intersymbol interference caused by both the chromatic dispersion of the optical fiber and the bandwidth limitation of components can be compensated. Besides, several equalization schemes are compared and analyzed in terms of performance and complexity. In addition, the design and characteristics of the SiMRM used in the experiment are also discussed.

Utilizing new erbium-doped fiber laser scheme for long-distance fiber Bragg grating (FBG) sensor system

We propose and demonstrate a new erbium-doped fiber (EDF) ring laser structure for 10 km long fiber sensor application. Here, we utilize ten fiber Bragg gratings (FBGs) as fiber sensors for sensing strain change. In the experiment, we can tune the passband of tunable bandpass filter (TBF) inside a fiber ring cavity to match the Bragg wavelength of each FBG to lase corresponding wavelength. Hence, the temperature-induced shift in Bragg wavelength could be monitored. In addition, 10 km long distance single-mode fiber (SMF) can be achieved by using the proposed EDF ring laser scheme for FGB-based remote sensor system.

Wavelength-tunable erbium-doped fiber laser using silicon-on-insulator (SOI) based micro-ring with narrow laser linewidth

We propose and demonstrate a wavelength-tunable and narrow-linewidth erbium-doped fiber (EDF) laser using siliconon- insulator (SOI) based micro-ring. We discuss the wavelength selection and wavelength-tunable operation of the proposed fiber laser. The SOI based micro-ring is fabricated on a SOI wafer with a 0.22 um thick top silicon layer and a 2 um thick burial oxide (BOX) layer. In order to enhance the coupling efficiency between the SOI based micro-ring and the EDF, a pair of uniform period grating couplers are used. In the experiment, the lasing wavelengths can be tuned in the wavelengths range from 1532 nm to 1567.2 nm with a tuning step of 2 nm. The wavelength range and the tuning step are determined by the EDFA gain-bandwidth and the FSR of the SOI based micro-ring respectively. The OSNR of each lasing wavelength is > 42 dB. By using a double-ring configuration, a narrow laser linewidth of 50 kHz can be achieved.

Low bending loss square-core optical fiber for optical communication

In this work, we propose and demonstrate a single-mode square-core optical fiber for optical communications. In the proposed square-core single-mode-fiber (SC-SMF), high bandwidth-distance product and low bending loss can be achieved. In this paper, first of all, we discuss the single mode condition of the SC-SMF theoretically and numerically. Then, we discuss the fabrication of the SC-SMF. We also characterize the performances of the proposed SC-SMF, such as the bending loss, and compare it with the standard single mode fiber (SSMF). A 10 Gb/s transmission experiment using 200 m, 500 m and 1 km SC-SMFs are performed. Negligible power penalty is observed.

Using injection-locked Fabry-Perot laser diode with 10% frond-facet reflectivity for 10 Gbps upstream PON access

We demonstrate a 10-Gbit/s upstream 16-QAM OFDM signal transmission using injection-locked Fabry-Perot laser diode with 10% frond-facet reflectivity for the long-reach PON access. Moreover, the relationship of BER and injection power is also analyzed.