1. An optical amplifier comprising:
a substrate having disposed thereon an optical waveguide, the optical waveguide having an active region,
a pump source arranged to irradiate the optical waveguide with electromagnetic radiation, and
a suitable shaped reflective element for concentrating a signal into the active region of the optical waveguide, wherein the irradiation of the optical waveguide is orthogonal to the plane of propagation of the signal,
wherein the suitable shaped reflective element is arranged such that the signal under goes total internal reflection off said element.
2. An amplifier as claimed in claim 1, wherein the reflective element is formed by etching a step into the waveguide.
3. An amplifier as claimed in claim 1, wherein the step is coated with a reflective material.
4. An amplifier as claimed in claim 1, wherein the suitable shaped reflective element is an elliptical mirror.
5. An amplifier as claimed in claim 1, wherein the suitable shaped reflective element is a pair of parabolic mirrors.
6. An optical amplifier as claimed in claim 1, wherein the active region comprises silicon nanocluster erbium doped silica.
7. An amplifier as claimed in claim 1, wherein the pump source is an array of light emitting diodes.
8. An amplifier as claimed in claim 7, wherein the light emitting diode emits electromagnetic radiation in the region of 400\u2013500 nanometers.
9. An amplifier as claimed in claim 8, wherein the light emitting diode emits electromagnetic radiation at 470 nanometers.
10. An amplifier as claimed in claim 1, further comprising an input optical waveguide and an output optical waveguide arranged to optically connect the amplifier with the signal from a communications network.
11. An amplifier as claimed in claim 10, wherein the input andor the output waveguides are tapered.
12. An amplifier as claimed in claim 1, further comprising a diffuser disposed between the light source and the waveguide.
13. An optical amplifier comprising:
a substrate having disposed thereon an optical waveguide, the optical waveguide having an active region,
a pump source arranged to irradiate the optical waveguide with electromagnetic radiation, and
a suitable shaped reflective element for concentrating a signal into the active region of the optical waveguide, wherein the suitable shaped reflective element is an elliptical mirror, and wherein the irradiation of the optical waveguide is orthogonal to the plane of propagation of the signal.
14. An optical amplifier comprising:
a substrate having disposed thereon an optical waveguide, the optical waveguide having an active region,
a pump source arranged to irradiate the optical waveguide with electromagnetic radiation, and
a suitable shaped reflective element for concentrating a signal into the active region of the optical waveguide, wherein the suitable shaped reflective element is a pair of parabolic mirrors, and wherein the irradiation of the optical waveguide is orthogonal to the plane of propagation of the signal.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A vehicle-mounted synthetic aperture system comprising:
a ping transmitter configured to transmit a series of pings;
an array of receiving elements configured to receive a ping return for each transmitted ping;
a plurality of acquisition circuits, each connected to one of the receiving elements and configured to produce digital sampled data at a plurality of points in time;
a processing unit configured to receive the sampled data; and
the processing unit being configured to receive real-time navigation state data and configured to form a plurality of stave sums, each stave sum being the sum of sampled data corresponding to a contiguous subset of the receiving elements;
the processing unit being configured to select the contiguous subset, based on the navigation state data, to form a phase center for a ping at substantially the same point as a phase center for a previous ping.
2. The synthetic aperture system of claim 1, wherein the processing unit includes a first-in first-out circuit (FIFO) configured to store the digital sampled data.
3. The synthetic aperture system of claim 2, wherein the processing unit includes a summation circuit connected to the FIFO, the summation circuit configured to form a plurality of stave sums from digital sampled data received from the FIFO.
4. The synthetic aperture system of claim 1, wherein the processing unit includes a plurality of FIFOs, each FIFO configured to store digital sampled data from a respective subset of the acquisition circuits.
5. The synthetic aperture system of claim 4, wherein the processing unit includes a plurality of first summation circuits, each first summation circuit configured to sum data received from a respective FIFO.
6. The synthetic aperture system of claim 5, wherein the processing unit includes a second summation circuit, the second summation circuit configured to sum data received from the first summation circuits.
7. The synthetic aperture system of claim 1, wherein the processing unit is configured to receive vehicle velocity data from a navigation calculator, and to estimate the distance the vehicle moved between the ping and the previous ping.
8. The synthetic aperture system of claim 7, wherein the processing unit is configured to select the contiguous subset based on the estimated distance moved.
9. A method for processing digital sampled data from a plurality of receiving elements in a vehicle-mounted synthetic aperture system, the digital sampled data corresponding to a current ping, the method comprising:
selecting contiguous subsets of the digital sampled data, each contiguous subset corresponding to a contiguous set of receiving elements, and
forming the sum of each of the selected contiguous subsets of the digital sampled data,
wherein a first contiguous subset, corresponding to a first contiguous set of receiving elements, is selected so that, for the current ping, a phase center of the first contiguous set of receiving elements is located at substantially the same point as a phase center, for a preceding ping, for a second contiguous set of receiving elements.
10. The method of claim 9, further comprising:
receiving vehicle velocity data; and
integrating the velocity data to estimate the change in the position of the vehicle between the current ping and the preceding ping.
11. The method of claim 10, wherein the integrating of the velocity data comprises converting the velocity data from north, east, down, (NED) format, into orthogonal coordinates aligned with axes of the vehicle.
12. The method of claim 9, wherein the selecting of contiguous subsets of the digital sampled data comprises:
estimating the distance traveled by the vehicle;
computing the shift for a contiguous subset of the digital sampled data, relative to a null shift, as a distance; and
converting the shift calculated as a distance to a shift calculated as a number of receiving elements.
13. The method of claim 12, wherein the computing of the shift for a contiguous subset of the digital sampled data, relative to a null shift, as a distance, comprises evaluating:
shift
\ue89e
\ue89e
2
\u2261
R
\ue89e
\ue89e
2
\u2032
–
R
\ue89e
\ue89e
2
shift
\ue89e
\ue89e
1
\u2261
R
\ue89e
\ue89e
1
\u2032
–
R
\ue89e
\ue89e
1
PC
\ue89e
\ue89e
1
\u2032
\u2261
T
\ue89e
\ue89e
1
+
R
\ue89e
\ue89e
1
\u2032
2
PC
\ue89e
\ue89e
2
\u2032
\u2261
T
\ue89e
\ue89e
2
+
R
\ue89e
\ue89e
2
\u2032
2
PC
\ue89e
\ue89e
2
\u2032
\u2261
PC
\ue89e
\ue89e
1
\u2032
+
n
\ue89e
\ue89e
pcSpacing
T
\ue89e
\ue89e
2
+
R
\ue89e
\ue89e
2
+
shift
\ue89e
\ue89e
2
=
T
\ue89e
\ue89e
1
+
R
\ue89e
\ue89e
1
+
shift
\ue89e
\ue89e
1
+
2
\ue89e
n
\ue89e
\ue89e
pcSpacing
shift
\ue89e
\ue89e
2
=
–
(
T
\ue89e
\ue89e
2
–
T
\ue89e
\ue89e
1
)
–
(
R
\ue89e
\ue89e
2
–
R
\ue89e
\ue89e
1
)
+
shift
\ue89e
\ue89e
1
+
2
\ue89e
n
\ue89e
\ue89e
pcSpacing
,
\ue89e
and
shift
\ue89e
\ue89e
2
=
2
\ue89e
n
\ue89e
\ue89e
pcSpacing
–
2
\ue89e
distAdv
+
shift
\ue89e
\ue89e
1
,
wherein:
R1 and R2 are the receiver positions of a stave on the preceding ping and the current ping, respectively,
R1\u2032 and R2\u2032 are the shifted receiver positions of the stave on the preceding ping and the current ping, respectively,
T1 and T2 are the transmitter positions on the preceding ping and the current ping, respectively,
PC1\u2032 and PC2\u2032 are the shifted positions of the phase centers of the stave on the preceding ping and the current ping, respectively,
shift2 is the shift, as a distance, to be used on the current ping,
shift1 is the shift, as a distance, used on the previous ping,
distAdv is the distance advanced by the vehicle between the previous ping and the current ping, and
pcSpacing is the phase center spacing across the aperture, and
n is an integer.
14. The method of claim 13, wherein n is chosen to minimize the magnitude of shift2.
15. The method of claim 13, comprising calculating a non-integer value corresponding to n, according to
n
fractional
=
1
pcSpacing
\ue89e
(
distAdv
–
shift
\ue89e
\ue89e
1
2
)
.
16. The method of claim 15, comprising calculating n according to the equation
n=round(nfractional).
17. The method of claim 16, comprising calculating the shift as a number of receiving array elements according to the equation:
elementShift
=
round
\ue8a0
(
shift
\ue89e
\ue89e
2
elementSpacing
)
.