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Transmission performance analysis of 8/spl times/10 Gb/s WDM signals using cascaded SOAs due to signal wavelength displacement

We have analyzed the transmission performance of 8/spl times/10 Gb/s wavelength division multiplexing (WDM) signals due to crosstalk in cascaded conventional semiconductor optical amplifiers (SOAs). Using two different methods, the crosstalk over the whole gain bandwidth in SOAs is calculated to be 2-5 dB lower for the positive detuning. Then, transmission performance of 8/spl times/10 Gb/s WDM signals up to 6/spl times/40 km span in terms of receiver sensitivity is estimated over various transmission distances using cascaded SOAs for the positive signal wavelength displacement of 30, 40, and 50 nm. Especially for 50 nm detuning, transmission performances with and without using a reservoir channel are similar to each other. Our results suggest that SOAs can be used as an optical amplifier for displacement larger than 50 nm without using the reservoir channel.

Performance analysis of signal vias using virtual islands with shorting vias in multilayer PCBs

The mitigation method of parallel-plate waveguide (PPW) noises excited from signal vias due to the mode conversion of desired propagation modes into parasitic PPW modes in multilayer printed circuit boards (PCBs) has been proposed. The mitigation of PPW noises has been achieved using virtual islands with shorting vias. The shorting vias are used to provide the return current path with low impedances and the virtual islands are used to block the propagation of the PPW noises through PCBs. The transmission and coupling responses of signal vias applied to the virtual islands with shorting vias are calculated using the finite-difference time-domain method to show effectiveness of the proposed mitigation method of PPW noises. The PPW noises propagating through PPWs are dramatically suppressed and the electrical performances of signal vias in multilayer PCBs are improved using the proposed method. The effectiveness of the proposed mitigation method of PPW noises is also verified by measurements of S-parameters of signal vias in simple test boards applied to the virtual islands with shorting vias. The effects of geometrical parameters of the virtual islands on performances of signal vias are also investigated. The performances of signal vias applied to the virtual islands with shorting vias can be improved up to higher frequency by reducing the size of virtual islands. The effect of the gapwidth of slots can be neglected. The effective number of shorting vias of the proposed mitigation method is four. Since several signal vias can be located at a virtual island, the needed number of shorting vias to obtain good transmission and coupling responses using the proposed mitigation method is less than half of that to obtain similar performance using only shorting vias.

Theoretical investigation of optical wavelength conversion techniques for DPSK Modulation formats using FWM in SOAs and frequency comb in 10 gb/s transmission systems

We have investigated the wavelength conversion techniques for differential phase-shift keying (DPSK) modulation formats in 10 Gb/s transmission systems, compared with the non-return-to-zero (NRZ) modulation format. For the wavelength conversion of DPSK modulation formats, we employed the wavelength converters based on the four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) and the frequency comb generated by phase modulation. The power penalty at 10/sup -9/ bit error rate was used as a measure of the system performance degraded by the wavelength conversion. Our simulation results show that the DPSK modulation formats have a smaller power penalty than the NRZ modulation format for the wavelength conversion using the FWM effect in an SOA due to a much lower pattern effect. However, as the wavelength conversion uses the frequency comb generated by phase modulation, it has a similar power penalty compared with the NRZ modulation format. It is also shown that the DPSK modulation formats are possible to obtain the power penalty less than 0.4 dB for both wavelength conversion techniques.

Performance Evaluation of Electroabsorption Modulators as Optical Transceivers in Radio-Over-Fiber Systems By FDTD Method

In this paper, the limitations of the performance of electroabsorption modulators (EAMs) as optical transceivers in passive picocell systems by using the finite-difference time-domain (FDTD) method are theoretically investigated. EAMs with no bias voltage are modeled by the FDTD method with consideration of the interaction between electromagnetic fields and optical powers in optical waveguides. Transmission and responsivity of EAMs according to various optical input powers and chip lengths are calculated. Then, power margins of the downlink and uplink paths are estimated to define the service ranges of the passive picocell systems. In addition, EAMs with biased voltage are characterized for comparison. The results suggest that the service range of the passive picocell system using a no-biased EAM can be extended up to 20 m with a chip length of 400 mum and an optical input power larger than 10 dBm

Performance Evaluation for UWB Signal Transmissions in the Distributed Multi-Cell Environment Using ROF Technology

We estimate the performance of ultra-wideband (UWB) signal transmissions for a multi-cell environment combined with a large virtual cell using radio-over-fiber (ROF) technologies. For a large virtual cell, UWB signal transmissions have been evaluated in the overlapped area between cells using a realistic channel model based on a modified Δ – k model. The effects of multipath interference and delay time at the overlapped area have been evaluated in terms of link margins and bit error rates using Rake receivers. Our simulation results suggest that the delay time of about 125ps significantly affects the link margin for PPM. The optimum peak-to-peak voltage (Vp-p) of Mach-Zehnder modulators (MZM) has been obtained to be 2.4V for the best link margin. Considering link margins, bite error rates (BER), and packet error rates (PER), the BPM modulation format has better performance than the PPM modulation format.

10 Gbps WDM transmission performance limits using in-line SOAs and an optical phase conjugator based on four-wave mixing in SOAs as a mid-span spectral inversion technique

We have theoretically investigated the transmission performance limits of all semiconductor optical amplifiers (SOA)-based 10 Gb/s wavelength division multiplexing (WDM) systems using in-line SOAs and an optical phase conjugator (OPC) based on four-wave mixing in SOAs as a mid-span spectral inversion technique. With a verified numerical model of SOAs, we have found that the crosstalk from SOAs in OPC is a dominant factor to limit the number of channels in WDM systems. In order to increase the available number of channels, we optimize the input optical power and the injection current to SOAs in OPC with using a reservoir channel in in-line SOAs. All SOA-based 10 Gb/s WDM systems using the OPC can transmit 16 channel signals up to 240 km distance with a 3 dB power penalty.

Investigation of transmission performance of 40-gb/s conventional DCS-RZ signals and DCS-RZ signals generated from phase-modulated duobinary signals

A 40-Gb/s duobinary carrier-suppressed return-to-zero (DCS-RZ) signal format generated from phase-modulated (PM) duobinary signals by using a phase modulator and an external intensity modulator is proposed. The transmission performance of the proposed DCS-RZ format is theoretically investigated. The proposed DCS-RZ format can produce a signal bandwidth similar to that produced by the conventional DCS-RZ format generated from conventional duobinary signals using low-pass filters. However, the receiver sensitivities of the proposed DCS-RZ format can be improved by about 2 dB more than those of the conventional DCS-RZ format due to high extinction ratio and nonlinear tolerance. Due to a short pulse of the proposed DCS-RZ format, the tolerance of the first-order polarization mode dispersion (PMD) for the format can be improved by about 1 dB up to the differential-group-delay (DGD) value of 16 ps

Investigation on transmission characteristics of 10Gb/s phase-modulated duobinary in optical networks

This paper describes the transmission performance of the 10Gb/s phase-modulated (PM) duobinary modulation format, compared with the conventional duobinary modulation format using a low-pass filter (LPF) in cascaded optical networks. We theoretically investigate the transmission characteristics of both modulation formats with considering the effect of narrowing bandwidth of multiplexers (MUX) and demultiplexers (DEMUX) at cascaded nodes with different fiber launching powers (FLP). Its shown that PM duobinary signals, at the FLP of 9dBm, can be transmitted over 3 nodes (up to a distance of 1,200km) with only 1.25dB power penalty.

Performance Margins of Passive Pico-Cell Systems with an Electroabsorption Modulator Using Radio-Over-Fiber Techniques

We investigate the performance limits of a passive pico-cell system with an electroabsorption modulator (EAM) using the radio-over-fiber technique in a 2.4 GHz wireless local area network (WLAN) environment. WLAN signals from a wireless router can not be detected properly at the WLAN card even in a service range of 1 m for the zero bias voltage to the EAM. To overcome and understand the performance limits, we apply bias voltage to the EAM and vary the optical modulation index (OMI) of the transmitter. Power margins in the links are found to estimate a possible service range, and packet loss rates in the pico-cell system are measured to evaluate the transmission performance. The service range can be extended up to 3 m by applying bias voltage to the EAM or adjusting the OMI of the transmitter.

Theoretical investigation of 8 /spl times/ 10-Gb/s WDM signal transmission performance based on gain-equalized SOAs using backward Raman pumping at DCF

We have theoretically investigated 8 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) signal transmission characteristics based on semiconductor optical amplifiers (SOAs) with equalized gain using discrete Raman amplification (DRA). Gain equalization and low noise figures have been obtained by adjusting the backward Raman pumping power and wavelength at a dispersion compensating fiber (DCF) for each span. Bit-error-rate characteristics were calculated for 8 /spl times/ 10-Gb/s WDM signal transmission over 6 /spl times/ 40-km single-mode fiber (SMF) + DCF links with gain-equalized SOAs using DRAs at DCF. Approximately a 2.5-dB improvement of the receiver sensitivity was achieved by using SOAs and DRAs with optimized Raman pumping. One can easily upgrade the transmission length of a link based on SOAs with an appropriate backward pump laser at each DCF.