Hodeok Jang

Performance evaluation for UWB signal transmission with different modulation schemes in multi-cell environment distributed using ROF technology

We describe a radio-over-fiber (ROF) based ultra-wideband (UWB) transmission system. In a multi-cell environment using ROF technology, the performance of UWB signal transmission with different modulation schemes is evaluated in a realistic channel model based on a modified /spl Delta/-K model. Then, we investigate the effects of multipath interference and delay time at the overlapped area on the performance of UWB in terms of link margin and bit error rates. The performance of a RAKE receiver with maximal-ratio combining is also studied using the optical and wireless link analysis simulator, Photonics CAD.

Transmission performance of 10-Gb/s 1550-nm transmitters using semiconductor optical amplifiers as booster amplifiers

We have demonstrated the transmission performance of 10-Gb/s transmitters based on LiNbO/sub 3/ modulator using semiconductor optical amplifiers (SOAs) as booster amplifiers. Utilizing the negative chirp converted in SOAs and self-phase modulation induced by high optical power, we can successfully transmit 10-Gb/s optical signals over 80 km through the standard single-mode fiber with the transmitter using SOAs as booster amplifiers. SOAs can be used for booster amplifiers with a careful adjustment of the operating conditions. In order to further understand an SOAs characteristics as a booster amplifier, we model SOAs and other subsystems to verify the experimental results. Based on the good agreement between the experimental and simulation results, we can find the appropriate parameters of input signals for SOAs, such as extinction ratio, rising/falling time, and chirp parameter to maximize output dynamic range and available maximum output power (P/sub o,max/).

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.

Chromatic dispersion tolerance of new duobinary transmitters based on two intensity modulators without using electrical low-pass filters

This paper describes an investigation of the effect of the extinction ratio and the chirp parameter of the first intensity modulator on the transmission performance of a proposed duobinary transmitter based on two intensity modulators without using electrical low-pass filters. This modulation scheme can generate duobinary signals using only two-level electrical signals without the conversion process to three-level electrical signals using electrical low-pass filters. The simulation results suggest that the appropriate chirp and extinction ratio of the first intensity modulator provide larger dispersion tolerance, compared with the conventional duobinary transmitter. The duobinary transmitter based on two intensity modulators can increase the dispersion tolerance without using electrical low-pass filters.

Theoretical Investigation of First-order and Second-order Polarization-mode Dispersion Tolerance on Various Modulation Formats in 40 Gb/s Transmission Systems with FEC Coding

We investigated the polarization-mode dispersion (PMD) tolerance for 40Gb/s non-return to zero (NRZ), duobinary NRZ, return to zero (RZ), carrier-suppressed RZ (CS-RZ), and duobinary-carrier-suppressed RZ (DCS-RZ) modulation formats with a forward error correction (FEC) coding. The power penalty has been calculated as a measure of the system performance due to PMD. After comparison of the PMD tolerance of various modulation formats, our results suggest that RZ signals have the best tolerance against the effect of first-order PMD only. The duobinary NRZ modulation format is most resilient to PMD when both first- and second-order PMD are considered. However, the duobinary NRZ modulation format is the most sensitive to the incident angle of the input signal to a fiber axis in the presence of first- and second-order PMD, leading to incident angle-dependent power penalty. The coding gain by FEC can cope with the power penalties induced by first- and second-order PMD up to a DGD value of 16ps.

Comparison of Transmission Performance of 40-Gb/s Optical Duobinary and DCS-RZ Signals Using 10- and 40-Gb/s

We investigated a cost-effective method using 10-Gb/s LiNbO3 Mach-Zehnder modulators (MZMs) for transmitting 40-Gb/s duobinary nonreturn-to-zero (NRZ) and duobinary carrier-suppressed return-to-zero (DCS-RZ) signals. The transmission performance of the signals was investigated. The optimum bandwidths of low-pass filters in transmitters using 10- and 40-Gb/s LiNbO3 MZMs were also investigated. The calculated transmission performance of the transmitter using 10-Gb/s LiNbO3 MZMs was compared to that using 40-Gb/s LiNbO3 MZMs. The effect of the bias offset in the transmitters was investigated. Compared to duobinary-NRZ and DCS-RZ signals generated by a transmitter using 40-Gb/s LiNbO3 MZMs, those generated by using 10-Gb/s LiNbO3 MZMs can be transmitted with 1-dB power penalty over 480-km transmission

\hbox{LiNbO}_{3}

Forward-error correction (FEC) coding is theoretically investigated to improve bit-error-rate (BER) performance in a 10-Gb/s optical transmission system using randomly irregular low-density parity-check (LDPC) codes, regular LDPC codes, and the Reed-Solomon (RS) (255,239) code as a comparison. The irregular LDPC codes has different row-weight variances of a parity-check matrix from 10.9 to 18.8 and a row-weight mean of 60. Simulation is carried out under various conditions including the impairment factors such as dispersion, polarization-mode dispersion (PMD), and fiber nonlinearities. Results suggest that the irregular LDPC code with a low row-weight variance (=10.9) generally has better performance for the most impairment factors except for the factor of dispersion. On the other hand, for the factor of dispersion the irregular LDPC code performs better with a high row-weight variance (=18.8). A specific LDPC code can overcome the impairment limits in a deployed link.

Mach–Zehnder Modulators

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.

BER performance due to irregularity of row-weight distribution of the parity-check matrix in irregular LDPC codes for 10-gb/s optical signals

We investigated how the polarization-mode dispersion (PMD) tolerance was degraded by semiconductor optical amplifier (SOA)-induced chirp for the 10 Gb/s nonreturn-to-zero (NRZ), duobinary NRZ, return-to-zero (RZ), and carrier-suppressed RZ (CS-RZ) modulation formats. The power penalty was calculated as a measure of the system performance due to PMD for a given SOA-induced chirp. Considering only first-order PMD, all modulation formats have a similar PMD tolerance regardless of SOA-induced chirp. On the other hand, when both first- and second-order PMD are considered, the PMD tolerance of all modulation formats with the exception of the CS-RZ modulation format are degraded by SOA-induced chirp. Among all modulation formats considered here, the NRZ modulation format has the PMD tolerance with the highest sensitivity to SOA-induced chirp. When the peak-to-peak chirp induced by SOAs is