Changjian Guo

Elimination of Multiple Access Interference in Ultrashort Pulse OCDMA Through Nonlinear Polarization Rotation

A multiple access interference elimination scheme based on nonlinear polarization rotation (NPR) is proposed for ultrashort pulse optical code-division multiple access (OCDMA). This scheme is experimentally investigated in a four-user and 2.5-Gb/s coherent OCDMA system encoded/decoded by 127-chip superstructured fiber Bragg gratings. The measured bit-error-rate results of the NPR-based thresholder are also compared with those of a conventional supercontinuum-based thresholder in both the back-to-back and 20-km transmission cases. Our proposed scheme has the advantage of colorless operation over C-band.

A Novel Architecture for Peer-to-Peer Interconnect in Millimeter-Wave Radio-Over-Fiber Access Networks

A novel peer-to-peer (P2P) interconnection architecture in a 60-GHz millimeter-wave (mm-wave) radio-over-flber (RoF) access network is proposed for the flrst time. In this scheme, the beating of the lightwaves for downlink and P2P transmissions at the photodiode (PD) can provide signal up-conversion for both signals. Phase noise and frequency instability between the two independent lightwaves can be eliminated by a self-heterodyned radio frequency (RF) receiver (envelope detector) located on the user terminal, which can also down- convert simultaneously the two mm-wave signals to their associated intermediate frequencies. No high-frequency clock sources or other high bandwidth devices are required for signal up/down-conversions. A proof-of-concept experimental demonstration has also been carried out. Error-free transmission of the 1-Gb/ signals is achieved over 50- km flber (downlink) or 25-km flber (P2P) plus 4-m air link.

Demonstration of 1 Gb/s

The downlink transmission of a 1 Gb/s × 15-user code-division multiplexing (CDM) over wavelength-division-multiplexing passive optical network (WDM-PON) based on electrical spatial coding and subcarrier multiplexing is experimentally demonstrated. Two wavelengths with 100-GHz spacing are used to carry the 15 spatial encoded subcarriers generated by an arbitrary waveform generator. Our results show that error-free operation can be achieved after 20-km standard single-mode fiber (SSMF) transmission when 15 simultaneous users are present assuming that forward-error correction coding is used.

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It is shown that a ring topology is better than a star topology for an optical-code-division multiple access (OCDMA) network as an optical metropolitan or local area network in terms of security and capacity. Each node in an OCDMA ring network requires an OCDMA add/drop multiplexer. We present what we believe to be a novel OCDMA add/drop multiplexer that can simultaneously add and drop multiple code channels, and a proof-of-feasibility experiment is demonstrated. An OCDMA ring may also adapt code channels for time domain multiplexing and other digital signal transmission systems. An experiment for the synchronized digital hierarchy (SDH) signal over a OCDMA link is demonstrated.

15-User CDM Over WDM-PON Using Electrical Spatial Coding and Subcarrier Multiplexing

We propose and demonstrate an OCDMA-PON scheme with optical network unit (ONU) internetworking capability, which utilizes low-cost gain-switched Fabry-Pérot (GS-FP) lasers with external dual-wavelength injection as the pulse sources on the ONU side. The injection-generated optical pulses in two wavelengths from the same GS-FP laser are used separately for the PON uplink transmission and ONU internetworking. Experimental results based on a two-user OCDMA system confirm the feasibility of the proposed scheme. With OCDMA technologies, separate ONU-internetworking groups can be established using different optical codes. We also give experiment results to analyze the performance of the ONU-ONU transmission at different power of interference signals when two ONU-internetworking groups are present in the OCDMA-PON.

Add/drop multiplexing and TDM signal transmission in an optical CDMA ring network

In this paper, we consider the design and analysis of a coherent optical OFDM (CO-OFDM) transmitter using an optical in-phase/quadrature (I/Q) modulator with limited extinction ratio (ER) under four modulation formats. The transmitter-side digital signal processing (DSP), including hard clipping and predistortion, is introduced to combat the penalty induced by the limited ER of the modulator and the quantization noise of the digital-to-analog converter (DAC). The DAC resolution needed for transmitters using modulators with various ER values are examined. The peak-to-peak driving voltage (Vpp) and the clipping ratio (CR) of the transmitted signals are also optimized with respect to minimizing the Q-factor penalty for the modulator with different ER values. The simulation results show that, unlike previous work using modulators with an infinite ER, the optimum Vpp and CR values vary with different ERs and modulation levels.

OCDMA PON supporting ONU inter-networking based on gain-switched Fabry–Pérot lasers with external dual-wavelength injection

A picosecond flat-top pulse shaper using an abrupt taper interferometer is proposed and experimentally demonstrated. A theoretical model based on coupled mode equations is also derived to simulate the propagation of picosecond pulses through the abrupt taper interferometer. Through properly designing the abrupt taper interferometer, a 3.8-ps flat-top pulse with less than 4% ripple is successfully generated from a 2.2-ps Gaussian pulse. The proposed technique can also be used in the sub-picosecond regime.

Design and Analysis of a CO-OFDM Transmitter With Limited Modulator Extinction Ratio

We propose and demonstrate a simple and low-cost uplink transmission scheme for coherent optical code-division multiple access (OCDMA) passive optical networks (PONs), using gain-switched Fabry-Perot (GS-FP) lasers with external injection as local light sources at optical network units. Experimental results based on the two-user 1.25-Gb/s OCDMA system confirm the feasibility of this scheme. The system performance is compared with that of the OCDMA system using a conventional mode-locked laser (MLL). The auto-correlation peak to the maximum wing level (P/W) ratio is also given as the central wavelength of the GS-FP laser varies. The present low-cost scheme is highly preferable for OCDMA PON applications.

Picosecond and Sub-Picosecond Flat-Top Pulse Shaping Using Abrupt Taper Interferometers

A novel upstream data remodulation scheme with downstream ASK-DPSK modulation format is proposed for WDMPONs in this letter. And this kind of scheme is also experimentally demonstrated on one particular wavelength channel. Both the 2.5-Gb/s downstream optical DPSK signal and the 2.5-Gb/s downstream optical ASK signal are demodulated respectively at the receiving side, while part of the downstream carrier is directly remodulated by an optical intensity modulator for upstream transmission of 2.5-Gb/s data. System performance under different amplitude ratios of downstream optical ASK signal is investigated. It is shown that effective reception and robust performance can be achieved after having been transmitted for 25-km.

Demonstration of Low-Cost Uplink Transmission in a Coherent OCDMA PON Using Gain-Switched Fabry–Pérot Lasers With External Injection

With Manchester coding induced spectral shaping, high-speed optical VPN service channels can be added in a low-speed legacy TDM-PON. The VPN service upgrade can be selective and causes no disruption to the remaining service users.