Method and device for optical power limiter

A method of upper bounding information leakage in quantum cryptography using a method of limiting optical power comprising the steps of:

• directing a light beam into an effective medium disposed via an input port;
• subjecting the light beam to a refractive index gradient in the effective medium in a direction perpendicular to a propagation direction in the effective medium as a result of absorption;
• and
• upper bounding the information leakage by limiting how much of the light beam reaches an output port along the propagation direction.

A method of upper bounding information leakage in quantum cryptography using an optical power limiter comprising:

• an optical input port;
• an optical output port;
• an effective medium disposed between the input port and the output port;
• and
• a diaphragm disposed between the effective medium and the output port;
• wherein the effective medium has a thermo-optic coefficient such that a light beam entering the effective medium from the direction of the input port experiences a refractive index gradient in a direction perpendicular to a propagation direction in the effective medium as a result of absorption;
• and
• wherein the diaphragm is disposed in a path of the light beam for upper bounding the information leakage by limiting how much of the light beam reaches the output port.