B. Konrad

Alternative modulation formats in N/spl times/40 Gb/s WDM standard fiber RZ-transmission systems

A comparison of carrier-suppressed return-to-zero (CSRZ) and single sideband return-to-zero (SSB-RZ) formats is made in an attempt to find the optimum modulation format for high bit rate optical transmission systems. Our results show that CSRZ is superior to return-to-zero (RZ) and SSB-RZ with respect to signal degradation due to Kerr nonlinearities and chromatic dispersion in wavelength division multiplexing (WDM) as well as in single-channel 40-Gb/s systems over standard single-mode fibers (SSMF). It is shown that CSRZ enables a maximum spectral efficiency of approximately 0.7 (b/s)/Hz in a N/spl times/40 Gb/s WDM system with equally polarized channels. Furthermore, the CSRZ format in N/spl times/40 Gb/s WDM systems shows no further signal degradation compared to single-channel transmission.

Impact of fiber chromatic dispersion in high-speed TDM transmission systems

General guidelines for high-speed time-division multiplexing (TDM) data-rate transmission are essential for the increase of the overall transmission capacity. In this paper, general theoretical investigations concerning fiber chromatic dispersion in optical TDM systems are performed. Recent experiments that confirm the theoretical predictions are presented. Nonzero dispersion-shifted fiber and standard single-mode fiber are recommended for 40 and 160 Gb/s, respectively, independent of the chromatic dispersion compensation scheme.

Improvement of system performance in N x 40-Gb/s WDM transmission using alternate polarizations

We show that the alternate polarization of adjacent bits and channels in N/spl times/40-Gb/s wavelength-division-multiplexing (WDM) transmission system causes significant improvement of system performance through suppression of nonlinear effects. The suppression of nonlinear effects results in an improvement of the spectral efficiency in N/spl times/40-Gb/s WDM systems.

Optimized filtering for 40-gb/s/ch-based DWDM transmission systems over standard single-mode fiber

We show that the optimized optical filtering at the transmitter and receiver side is the key technology for the achievement of higher spectral efficiencies in 40-Gb/s-based dense wavelength-division-multiplexing (DWDM) systems. Through the improved filtering, the spectral efficiency of 0.8 b/s/Hz can be realized in DWDM systems independently on the used modulation format.

Optimum fiber dispersion in high-speed TDM systems

Single-channel transmission at 40 Gb/s and above is investigated by numerical simulations with respect to optimal fiber dispersion. Since optimum dispersion depends on the bit rate nonzero dispersion shifted fiber is recommended for 40-Gb/s transmission and standard single-mode fiber for 160-Gb/s transmission.

Prechirp in NRZ-based 40-Gb/s single-channel and WDM transmission systems

We investigate the impact of the prechirp on nonreturn-to-zero (NRZ)-based single-channel and 40-Gb/s/ch wavelength-division-multiplexing systems over standard single-mode fibers by means of numerical simulations. It was shown that prechirping of NRZ pulses improve the total transmission length and make the NRZ pulses more robust to Kerr-nonlinearities.

Dispersion compensation schemes for 160 Gb/s TDM-transmission over SSMF and NZDSF

Various dispersion compensation schemes have been investigated by numerical simulations for standard single-mode fiber (SSMF) and nonzero dispersion-shifted fiber (NZDSF) in 160 Gb/s optical TDM-systems. SSMF yields the better performance.

Novel modulation format for N/spl times/40 Gbit/s WDM transmission with 50 GHz channel spacing

N/spl times/40 Gbit/s WDM transmission is analysed using a novel chirped RZ (nCRZ) modulation format over standard single mode fiber based transmission line. A spectral efficiency of 0.8 bit/s/Hz has been achieved with equally polarised channels.

Strategies for spectrally efficient optical fiber communication systems with direct detection

In order to use the available optical bandwidth efficiently, efforts are under way to achieve spectral efficiencies of at least 0.8 bits/s/Hz. For such spectrally efficient systems (considering copolarized WDM-channels), we discuss the importance of filtering for different modulation formats, different channel bitrates from 10-160 Gbit/s and different dispersion map designs. It turns out that the optimisation strategy for spectrally efficient WDM systems shows considerable differences to that of single channel systems. The specific modulation format and the chosen channel bitrate turn out to be of minor importance, thus enabling simple analytic expressions for the achievable system performance.

Improvement of NRZ based 40 Gbit/s single channel and WDM transmission using pre-chirp

Chirped NRZ (nCRZ) modulation format has been presented for single channel and WDM 40 Gbit/s transmission. The transmission properties of cNRZ are compared with conventional NRZ and RZ signals and analysed by means of numerical simulations. It was shown that an appropriate pre-chirping through phase modulation can improve the nonlinear characteristics and maximum transmission length in NRZ based transmission systems over standard single mode fiber (SSMF). The results confirmed that the use of a cNRZ form reduces the self phase modulation-group velocity dispersion (SPM-GVD) impairments in SSMF compared to NRZ and RZ signal forms.