High-capacity multiwavelength optical fiber communication systems

This paper deals with the implementation of multichannel wavelength-division-multiplexing (WDM) to more fully utilize the enormous fiber bandwidth for high-speed data transmission. The main research activities described in this paper relate to the all-optical network. The fundamental systems assumptions include: i) all-optical processes can potentially avoid an optoelectronic speed bottleneck, and ii) wavelength shifting of an incoming optical channel will be required in a reconfigurable WDM network in which there are fewer wavelengths than total users. The two main projects are: i) simultaneous all-optical packet-header replacement and wavelength shifting, and ii) all-optical TDM-to-WDM data format conversion. Project 1: We experimentally demonstrate a method simultaneous all-optical header replacement and wavelength shifting. These functions, important in a dynamically-reconfigurable WDM network, are realized by using cross-gain compression in semiconductor optical amplifier and by using three-level modulation of a probe laser only when the header bits require changing. We simultaneously replace the 8-bit modulation of a probe laser only when the header bits require changing. We simultaneously replace the 8-bit header of a 1-Gbit/s packet and wavelength-shift the entire packet by 19 nm. A receiver sensitivity of -27 dBm at 10-9 BER is measured when using a 416-bit NRZ data packet. Our approach requires no guard bits and allows both the header and data to be at the same bit rate and wavelength. Project 2: We demonstrate both single-stage and two-stage all-optical TDM-to- WDM data format converters based on cross gain compression in an SOA. Our method simultaneously time demultiplexes and wavelength shifts each channel's data within a TDM packet. We convert a 2-Gbit/s 4-channel TDM data stream at 1552 nm into four 500-Mb/s WDM channels at 1535, 1537, 1540, and 1571 nm. Moreover, we extend this single-stage approach by demonstrating a two-stage TDM-to-WDM converter that selectively time demultiplexes and wavelength shifts a 2-Gbit/s TDM input data stream into two 500-Mb/s WDM channels after the second stage. We find that low power penalties (< 2 dB can be achieved by using this scheme for both the single- and two-stage cases. This conversion scheme may be quite useful in WDM switching nodes. This work is performed in the context of a three-investigator multidisciplinary research program sponsored by the NSF initiative on all-optical networks.