| 摘要 |
An optical circuit comprises a bistable optical waveguide (34) having a first and a second transmission state. The waveguide is more transmissive to light of a given wavelength in the second state than in the first state. A first light source (11) and a second light source (21) emit light of a first and second wavelength respectively and are coupled to the waveguide at one end. Selective transmission of a sufficient amount of light of the first wavelength through the waveguide "sets" the waveguide, causing it to switch from the first into the second state, whereas transmission of a sufficient amount of light of the second wavelength "resets" the waveguide causing it to switch back from the second into the first state. A sensing or reading ("test") light source (36) is arranged at the other end of the waveguide to transmit a sensing light signal through the waveguide (34) in the opposite propagation direction to that of light of the first and second wavelengths. This sensing light source can be an external light source or an "internal" source provided by spontaneous emission in the waveguide. A sensor (38) is arranged to detect the amount of the sensing light signal transmitted through the waveguide (34). In this way the waveguide can be set into a given transmission state, which can be determined at a later time by measuring the amount of the sensing light signal transmitted. The optical circuit therefore exhibits a memory effect and may be used to produce an all-optical bistable logic circuit such as an optical latch or an optical flip-flip. Typically, the waveguide (34) is a doped optical fibre, such as an Erbium-Ytterbium (Er-Yb) doped fibre. Light of the first (set)/second (reset) wavelengths excites or de-excites respectively the dopant ions in the fibre thus tuning its transmission.
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