Sivakumar Lanka

System performance optimization in SCM-WDM passive optical networks in the presence of XPM and GVD

The authors investigate semi-analytically the optimized system performance limitation in an SCM-WDM passive optical network (PON) in the presence of cross phase modulation (XPM) and group velocity dispersion (GVD). A general expression for electrical average crosstalk noise power due to XPM and GVD was derived to measure the system performance for increasing number of WDM channels. Using the expression, we show that XPM and GVD causes crosstalk in the system and imposes a power penalty as the WDM channels increases for a given channel spacing and modulating frequency. These results are extended to show that the system can be optimized to achieve a minimum BER of 10-9 by controlling the channel spacing and modulating frequency as the number of WDM channels increases.

Optical performance monitoring using a poled lithium niobate (PP-LNO3)

Optical second harmonic generation in dense wavelength division multiplexing were used to monitor the performance of each channel in all optical networks. A poled Lithium-Niobate (PP-LNO3) device is used to convert C and L- Band optical WDM channels into half wavelength channels where silicon arrayed detectors and CMOS electronics were used to perform advanced digital signal processing to predict optical channel presence, channel power, signal to noise ratio and the quality (Q) factor parameter. With further processing, the bit error rate per channel can be estimated from the Q factor. The technique is realized on a system-on-a-chip CMOS technology which can potentially improve all optical networking architectures.

4-ary PAM Signaling for increasing the Capacity of Metro Light-wave Systems

We investigated both experimentally and by simulation, non-return-to-zero (NRZ) and return-to-zero (RZ) 4-ary PAM operating at 20 Gb/s. A simple scheme to realize the quadratic signal leveling by suitably driving a MZ modulator is proposed, which provides greater than 6 dB improvement in receiver sensitivity as compared to equal level spacing. We experimentally demonstrated NRZ and RZ 10 Gbaud/s 4-ARY PAM transmissions over an 80 km standard single mode fiber (SSMF) link as a proof of concept and more detailed experimental results over longer reach will follow. Numerical simulations for the 4-ary PAM performance over longer distances (>200 km) are also presented.

Effect of optical beat interference on channel spacing in DWDM optical systems

The information capacity of dense wavelength division multiplexing (DWDM) optical systems is reviewed. The effect of optical beat interference of closely spaced optical carriers sets the limit on the allowed channel spacing even in the absence of nonlinear effects. Present DWDM networks operating at 10.7 Gb/s in the C and L bands region have channel spacing no less than 25 GHz. We show that this limit is a constraint and smaller spacing may not be allowed without further optical and electrical pulse shaping.

Mode polarization partition noise in multimode short-wavelength VCSELs

Vertical cavity surface emitting lasers (VCSELs) designed for 10 G Ethernet over 300 m graded index multimode fiber in general have optical aperture diameters of 7 to 10 μm; cavities of these sizes support multiple transverse modes. The circularly symmetric structures are assumed to have no polarization selection, however, we show that orthogonally polarized lasing modes are often present and cause polarization partition noise which degrades the link bit error rate (BER). When a polarization selector was used in the link to allow only one polarization, the BER improved by two-order of magnitude even with the loss of more than 32 percent of the VCSEL average emitted power.

Resonant second harmonic generation using holey fiber for optical performance monitoring in DWDM networks

Optical second harmonic generation in dense wavelength division multiplexing (DWDM) was used to monitor the performance of each channel in all optical DWDM networks. A highly nonlinear photonic crystal fiber is used to convert C and L bands optical channels into half wavelength channels where silicon arrayed detectors and CMOS electronics were used to perform advanced digital signal processing to predict the optical channel presence, channel power, signal to noise ratio and the quality factor (Q) parameter. With further processing, the bit error rate per channel can be estimated from the Q factor.

Effect of the spectral width on mode partition noise in multimode VCSELs

The dependence of the mode partition noise (MPN) and the power penalty associated with it can be measured from the source spectral width. Our findings show that there is strong dependence of the carrier lifetime on the bit error rate degradation caused by MPN on the spectral width of the vertical cavity surface emitting laser (VCSEL). VCSELs with smaller spectral width (shorter carrier lifetime) exhibited smaller MPN induced power penalty. We found that the theoretical calculation of the power penalties caused by MPN from the carrier lifetime and the spectral width is in good agreement with the measured system penalties.

Resonant Second Harmonic Generation for Optical Performance Monitoring in DWDM Networks

SHG in DWDM systems was used for optical performance monitoring. A poled Lithium-Niobate device is used to convert C/L band channels to 1/2 wavelenghts where Si detectors/CMOS were used to predict performance monitoring parameters.