Polarization-bistable VCSELs and their applications for all-optical signal processing

In this paper, we overview recent status of polarization-bistable VCSELs and their applications for all-optical signal processing. All-optical flip-flop operation was achieved at a record low bias current of 0.85 mA using 980-nm polarization-bistable VCSELs with an oxidation confinement structure. Using four 1.55-μm polarization-bistable VCSELs, a 4-bit optical buffer memory was constructed. Here, two sets of shift-register memory were connected in parallel. Successful memorization of an arbitrary one bit of 20-Gb/s RZ and 40-Gb/s NRZ signals was also demonstrated. These are the fastest operations of optical bistable flip-flop memories. An optical header processing system was demonstrated using a 1.55-μm polarization-bistable VCSEL that operated as an all-optical AND gate and a holding element. Depending on the state of one bit in a 4-bit header, the VCSEL held one of two orthogonal polarization states. The output light of the VCSEL through a polarizer switched and held the output state of an optical switch. This enabled a payload to be sent to the destination determined by the header.