Simultaneous TDM/FDM Using Rapidly-tunable Transmitters And Receivers For Multi-access Optical Networks

Abstract

Optical networks using frequency division multiplexed (FDM) signals can be segmented by frequency and therefore allow the scalability of frequency re-use. When each frequency channel can be time-shared by many optical terminals such networks have the potential for greater network efficiency, scalability, and flexibility for multiple low-rate users than either FDM or TDM can provide alone [ 11. Optical terminals using rapidly-tunable components can maintain multiple logical connections by time-sharing the optical frequencies with other terminals. Fast-tuning transmitters using discretely-tuned distributed Bragg reflector (DBR) lasers offer excellent performance for such applications. Optical heterodyne receivers using rapidly-tunable DBR local oscillators are well-suited to such transmission. A heterodyne receiver can be more selective 121 and faster than conventional optomechanical devices such as piezo-driven Fabry-Perot filters. In this work, 1.248 Gbps signals transmitted by a DBR laser on up to 20 optical frequencies visited i n random sequence are transmitted into an erbium-amplified optical network. The frequency-hopped signals are detected by a polarization-diversity heterodyne receiver with a wavelength-tunable local-oscillator (LO) laser. The signals, multiplexed both in time and optical frequency, are transmitted into time “slots” 2 p long with random-access frequency-switching times under 128 ns.