Abstract

We demonstrate the first all-optical sequential circuit by looping the output from a soliton dragging logic gate¹ back to its input. Previously we demonstrated an ultrafast soliton dragging NOR-gate with logic level restoration at the output, fan-out of six, and switching energy of 5.8 pJ. To prove the cascadability and fan-out of the logic gate, we implement a ring oscillator by connecting the NOR-gate as an inverter and adding a feedback loop. The logic gate consists of a 325 m long biréfringent optical fiber surrounded by two polarizing beam splitters. The fiber is carefully laid in a 1 m diameter track and enclosed in an insulating box for thermal stability. A passively mode-locked color center laser supplies the clock pulses (τ = 500 fs, λ = 1.685µm, 54-pJ energy in the fiber) that are coupled along the fast axis of the fiber. We place a 50:50 beam splitter at the output and send half of the output through a delay line and half wave plate to the orthogonally polarized input. The other half of the output is combined with a reference pulse and sent to a cross-correlator. With the feedback blocked the output is a string of l's. When the feedback is added, the output becomes an alternating train of l's and 0's whose period is twice the fiber latency (1.75µs). More complicated functionalities are possible by encoding the clock pulses at the input and decoding at the output.

© 1990 Optical Society of America