Method and device for optical power limiter
An optical power limiter, a method of fabricating the optical power limiter, a method of limiting optical power, a method of upper bounding information leakage in quantum cryptography, and a quantum cryptography system. The optical power limiter comprises 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 limiting how much of the light beam reaches the output port.
1 . A quantum cryptography system including 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
the diaphragm is disposed in a path of the light beam for limiting how much of the light beam reaches the output port; and
the optical power limiter is configured for upper bounding information leakage.
2 . The quantum cryptography system of claim 1 , wherein the diaphragm is tunable for adjusting a limit of how much of the light beam reaches the output port.
3 . The quantum cryptography system of claim 1 , wherein the effective medium has a negative thermo-optic coefficient for diverging the light beam as a result of the refractive index gradient.
4 . The quantum cryptography system of claim 1 , wherein the input port comprises a collimator for forming the light beam from an input light signal.
5 . The quantum cryptography system of claim 1 , wherein the input port is configured for coupling to free space, to an input fiber, or to an input waveguide.
6 . The quantum cryptography system of claim 1 , wherein the output port comprises a collimator for focusing the light beam after the diaphragm.
7 . 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.
8 . The method of claim 7 , comprising adjusting a limit of how much of the light beam reaches the output port.
9 . The method of claim 7 , comprising diverging the light beam as a result of the refractive index gradient.
10 . The method of claim 7 , comprising collimating and input light signal into the light beam.
11 . The method of claim 7 , comprising input coupling the light beam from free space, from an input fiber, or from an input waveguide.
12 . The method of claim 7 , comprising collimating the light beam for focusing after the limiting.
13 . 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.
14 . The method of claim 13 , wherein the diaphragm is tunable for adjusting a limit of how much of the light beam reaches the output port.
15 . The method of claim 13 , wherein the effective medium has a negative thermo-optic coefficient for diverging the light beam as a result of the refractive index gradient.
16 . The method of claim 13 , wherein the input port comprises a collimator for forming the light beam from an input light signal.
17 . The method of claim 13 , wherein the input port is configured for coupling to free space, to an input fiber, or to an input waveguide.
18 . The method of claim 13 , wherein the output port comprises a collimator for focusing the light beam after the diaphragm.