System and method for beam alignment
A method of aligning a quantum laser beam with a receiver, the method including: generating a quantum laser beam and a first classical, non-quantum, laser beam at a transmitter, the quantum laser beam and the first classical laser beam being substantially aligned in direction; transmitting the quantum laser beam and the first classical laser beam; and directing the quantum laser beam and first classical laser beam to a receiver; measuring the photon reception rate through the quantum laser beam at the receiver, and reporting the photon reception rate to the transmitter; at the transmitter, making a series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam, and monitoring the reported photon reception rate; wherein, each of the series of adjustments is based, at least in part, on the effect of the preceding adjustment on the reported photon detection rate.
1 . A method of aligning a quantum laser beam with a receiver, the method comprising:
generating a quantum laser beam and a first classical, non-quantum, laser beam at a transmitter, the quantum laser beam and the first classical laser beam being substantially aligned in direction;
transmitting the quantum laser beam and the first classical laser beam; and
directing the quantum laser beam and first classical laser beam to a receiver;
measuring the photon reception rate from the quantum laser beam at the receiver, and reporting the photon reception rate to the transmitter;
at the transmitter, making a series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam, and monitoring the reported photon reception rate;
wherein, each of the series of adjustments is based, at least in part, on the effect of the preceding adjustment on the reported photon detection rate.
2 . The method of claim 1 , in which:
if one of the series of adjustments results in a reduction in the reported photon reception rate, reversing that adjustment; and
if one of the series of adjustments results in an increase in the reported photon reception rate, retaining that adjustment.
3 . The method of claim 1 , in which the series of adjustments begins with a plurality of predetermined adjustments, and the method further comprises:
using the effects of the plurality of predetermined adjustments on the reported photon detection rate to determine a gradient of the photon detection rate relative to the adjusted direction of the transmitted quantum laser beam; and
basing subsequent adjustments, at least in part, on the determined gradient.
4 . The method of claim 1 , in which directing the quantum laser beam and first classical laser beam to the receiver is carried out using a coarse pointing system, and the series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam are carried out using a separate fine pointing system.
5 . The method of claim 1 , and further comprising transmitting a second classical, non-quantum, laser beam from the receiver to the transmitter.
6 . The method of claim 1 , in which the first classical laser beam is used as a communication link from the transmitter to the receiver.
7 . The method of claim 5 , in which the transmitter and receiver cooperate to direct the first classical laser beam to the receiver using a first closed loop control method which uses the second classical laser beam as a beacon, and to direct the second classical laser beam to the transmitter using a first closed loop control method which uses the second classical laser beam as a beacon.
8 . The method of claim 1 , in which the monitoring the reported photon reception rate comprises measuring the photon reception rate for a period of time after each of the series of adjustments, the period of time is a configurable time period determined at the transmitter, and the first classical laser beam is used as a communication link to communicate the configurable time period from the transmitter to the receiver.
9 . The method of claim 1 , in which the transmitter is a satellite and the receiver is a ground station.
10 . The method of claim 1 , in which the transmitter is a ground station and the receiver is a satellite.
11 . The method of claim 10 , in which the ground station comprises an optical ground receiver (OGR).
12 . A system for aligning a quantum laser beam with a receiver, the system comprising:
a transmitter arranged to:
generate a quantum laser beam and a first classical, non-quantum, laser beam, the quantum laser beam and the first classical laser beam being substantially aligned in direction;
transmit the quantum laser beam and the first classical laser beam; and
direct the quantum laser beam and first classical laser beam to a receiver; and
a receiver arranged to:
measure the photon reception rate from the quantum laser beam;
and report the photon reception rate to the transmitter;
wherein the transmitter is further arranged to make a series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam, and monitor the reported photon reception rate; and
wherein, each of the series of adjustments is based, at least in part, on the effect of the preceding adjustment on the reported photon detection rate.
13 . The system of claim 12 , in which the transmitter is arranged to:
if one of the series of adjustments results in a reduction in the reported photon reception rate, reverse that adjustment; and
if one of the series of adjustments results in an increase in the reported photon reception rate, retain that adjustment.
14 . The system of claim 12 , in which the series of adjustments begins with a plurality of predetermined adjustments, and the transmitter is further arranged to:
use the effects of the plurality of predetermined adjustments on the reported photon detection rate to determine a gradient of the photon detection rate relative to the adjusted direction of the transmitted quantum laser beam; and
base subsequent adjustments, at least in part, on the determined gradient.
15 . The system of claim 12 , in which the transmitter comprises a course pointing system arranged to direct the quantum laser beam and first classical laser beam to the receiver, and comprises a separate fine pointing system arranged to carry out the series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam.
16 . The system of claim 12 , wherein the receiver is further arranged to transmit a second classical, non-quantum, laser beam to the transmitter.
17 . The system of claim 12 , in which the monitoring the reported photon reception rate comprises measuring the photon reception rate for a period of time after each of the series of adjustments, the period of time is a configurable time period, wherein the transmitter is arranged to determine the configurable period of time, and to use the first classical laser beam as a communication link to communicate the configurable time period to the receiver.
18 . The system of claim 12 , in which the transmitter is a satellite and the receiver is a ground station.
19 . The system of claim 12 , in which the transmitter is ground station and the receiver is a satellite.
20 . A method of aligning a quantum laser beam with a receiver, the method comprising:
generating a quantum laser beam and a first classical, non-quantum, laser beam at a transmitter, the quantum laser beam and the first classical laser beam being substantially aligned in direction;
transmitting the quantum laser beam and the first classical laser beam; and
directing the quantum laser beam and first classical laser beam to a receiver;
making a series of adjustments to the direction of the transmitted quantum laser beam and the first classical laser beam; and
receiving reports of the photon reception rate from the receiver;
wherein, each of the series of adjustments is based, at least in part, on the effect of the preceding adjustment on the reported photon detection rate.