In optics

Optics

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...

, optical bistability is an attribute of certain optical devices where two resonant transmissions states are possible and stable, dependent on the input. Optical devices with a feedback mechanism, e.g. a laser

Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

, provide two methods of achieving bistability

Bistability

Bistability is a fundamental phenomenon in nature. Something that is bistable can be resting in either of two states. These rest states need not be symmetric with respect to stored energy...

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• Absorptive bistability utilizes an absorber to block light inversely dependent on the intensity of the source light. The first bistable state resides at a given intensity where no absorber is used. The second state resides at the point where the light intensity overcomes the absorber's ability to block light.

• Refractive bistability utilizes an optical mechanism that changes its refractive index inversely dependent on the intensity of the source light. The first bistable state resides at a given intensity where no optical mechanism is used. The second state resides at the point where a certain light intensity causes the light to resonate to the corresponding refractive index.

This effect is caused by two factors

• Nonlinear atom-field interaction
• Feedback effect of mirror

Important cases that might be regarded are:

• Atomic detuning
• Cooperating factor
• Cavity mistuning

Applications of this phenomenon include its use in optical transmitters, memory elements and pulse shapers.