Transmission control techniques in quantum cryptographic communication system
AssigneeNEC Corporation
InventorHiroshi Imai
Life of this patent
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Abstract
An illustrative transmitter can achieve improvement in SN ratio and stability of the signal output under control at the transmission side, even in the case of an optical transmission line having the propagation characteristics susceptible to environmental changes. The transmitter includes: an optical transmission section configured to generate weak signal light and reference light from a transmission light pulse, and transmit the signal light and the reference light to the optical transmission line; and a controller configured to modulate pulse intensity and pulse width of the transmission light pulse according to a transmission line state of probe light having propagated through the optical transmission line.
Claims17
A transmitter that is optically connected to a receiver through an optical transmission line with propagation characteristics of light changing due to changes of environment in a quantum cryptographic communication system, the transmitter comprising:
- an optical transmission section configured to generate signal light and reference light from a transmission light pulse of coherent light, and transmit the signal light and the reference light to the optical transmission line, wherein the signal light is weak light having quantum states and the reference light is light having no quantum states;
- and
- a controller configured to modulate pulse intensity and pulse width of the transmission light pulse according to a transmission line state detected based on probe light of predetermined intensity,
- wherein the probe light is transmitted from one of the transmitter and the receiver to the other through the optical transmission line, and
- wherein the transmission line state is calculated at one of the transmitter and the receiver based on the probe light.
A transmission control method in a transmitter that is optically connected to a receiver through an optical transmission line with propagation characteristics of light changing due to changes of environment in a quantum cryptographic communication system, the method comprising:
- by an optical transmission section:
- a) generating signal light and reference light from a transmission light pulse of coherent light;
- and
- b) transmitting the signal light and the reference light to the optical transmission line, wherein the signal light is weak light having quantum states and the reference light is light having no quantum states;
- and
- by a controller:
- c) modulating pulse intensity and pulse width of the transmission light pulse according to a transmission line state detected based on probe light of predetermined intensity,
- wherein the probe light is transmitted from one of the transmitter and the receiver to the other through the optical transmission line, and
- wherein the transmission line state is calculated at one of the transmitter and the receiver based on the probe light.
A quantum cryptographic communication system comprising a transmitter and a receiver, wherein the transmitter and the receiver are optically connected to each other through an optical transmission line with propagation characteristics of light changing due to changes of environment,
- wherein the transmitter includes:
- an optical transmission section configured to generate signal light and reference light from a transmission light pulse of coherent light, and transmit the signal light and the reference light to the optical transmission line, wherein the signal light is weak light having quantum states and the reference light is light having no quantum states;
- and
- a controller configured to modulate pulse intensity and pulse width of the transmission light pulse,
- wherein the receiver includes:
- an optical reception section configured to receive received signal light and received reference light arriving from the transmitter through the optical transmission line;
- and
- a signal detector configured to generate a signal output by interfering the received reference light with the received signal light,
- wherein either the transmitter or the receiver further includes a calculator that calculates a transmission line state detected based on probe light of the predetermined intensity, the probe light having propagated through the optical transmission line, and
- wherein the controller is configured to modulate the pulse intensity and the pulse width of the transmission light pulse according to the transmission line state.
Dependencies are inferred from the claim text.