1. A laser system with self-injection locking, the laser system comprising:
(a) a single frequency laser having a laser output for delivering laser light at a frequency \u03c9o;
(b) a modulator coupled to the output of the laser for generating two sidebands, the modulator being driven by a RF signal at a frequency \u03c9m;
(c) a filter coupled to an output of the modulator for suppressing or passing one of the two sidebands; and
(d) an optical path coupling an output of the filter to the laser for injection locking.
2. The laser system with self-injection locking of claim 1 wherein the modulator is coupled to the laser via an optical coupler whereby the modulator receives a portion of the laser’s output.
3. The laser system with self-injection locking of claim 2 wherein the modulator is a Mach-Zehnder modulator.
4. The laser system with self-injection locking of claim 2 wherein the modulator is an accousto-optic modulator.
5. The laser system with self-injection locking of claim 2 wherein the modulator is an electro-optic modulator.
6. The laser system with self-injection locking of claim 1 wherein the filter suppresses one of the two sidebands and leaves the other sideband substantially unattenuated.
7. The laser system with self-injection locking of claim 1 wherein the laser is a distributed feedback laser.
8. The laser system with self-injection locking of claim 1 wherein the modulator produces carrier suppressed sidebands.
9. The laser system with self-injection locking of claim 1 wherein the filter suppresses any carrier produced by the modulator.
10. The laser system with self-injection locking of claim 1 wherein the filter is a Bragg Fiber Grating.
11. A method of enhancing the modulation bandwidth of a distributed feedback laser, the distributed feedback laser having a operating frequency and having an output and an input, the method comprising the steps of:
(a) tapping the output from the distributed feedback laser to thereby define a tapped optical signal;
(b) shifting the frequency of the tapped optical signal to thereby define a shifted optical signal;
(c) feeding the shifted optical signal back into the input of the distributed feedback laser.
12. The method of claim 11 wherein a Surface Acoustic Wave (SAW) device is used to shift the frequency of the tapped optical signal.
13. The method of claim 11 wherein an optical modulator device is used to shift the frequency of the tapped optical signal.
14. The method of claim 13 wherein the modulator is a Mach-Zehnder modulator.
15. The method of claim 13 wherein the shifting step includes suppressing unwanted frequencies.
16. The method of claim 15 wherein a Bragg Fiber Grating filter is used to suppress the unwanted frequencies further.
17. The method of claim 11 wherein the step of feeding the shifted optical signal back into the input includes suppressing unwanted frequencies.
18. The method of claim 17 wherein a Bragg Fiber Grating is used to suppress the unwanted frequencies.
19. A laser system with self-injection locking, the laser system including:
(a) a laser having a laser output at a frequency \u03c9o;
(b) an optical port providing a portion of said laser output at said port;
(c) a modulator coupled to the port, the modulator generating two sidebands, the modulator being driven by a RF signal at a frequency \u03c9m;
(d) a filter coupled to an output of the modulator for suppressing one of the two sidebands and leaving the other sideband essentially unattenuated; and
(e) an optical path coupling an output of the filter to the laser for injection locking.
20. The laser system with self-injection locking of claim 19 wherein the modulator generates two carrier-suppressed sidebands.
21. The laser system with self-injection locking of claim 19 wherein the filter is a Bragg Fiber Grating.
22. The laser system with self-injection locking of claim 19 wherein the optical port is provided by an optical coupler connected to receive the laser output.
23. A laser system with self-injection locking, the system including a laser having a laser output at a frequency \u03c9o; an optical port providing a portion of the laser output at the port; a modulator, coupled to the port, driven by a RF signal at a frequency \u03c9m to generate two sidebands at \u03c9o\xb1\u03c9m; a filter coupled to the modulator for passing or suppressing one of the two sidebands of the signal \u03c9o\xb1\u03c9m; and an optical path for coupling an output of the filter to the laser for injection locking the laser.
24. The laser system of claim 23 wherein the modulator produces the signal \u03c9o\xb1\u03c9m as a carrier suppressed signal.
25. The laser system of claim 23 wherein the modulator produces the signal \u03c9o\xb1\u03c9m as a signal with a carrier and said two side bands and wherein said filter suppresses said carrier and one of said two sidebands.
26. The laser system of claim 23 wherein the optical path includes at least one fiber optic cable.
27. The laser system of claim 23 wherein the filter is a Bragg Fiber Grating.
28. The laser system of claim 23 wherein the optical path includes a portion of free-space.
29. The laser system of claim 23 wherein the modulator is a surface acoustic wave (SAW) device.
30. A laser system with self-injection locking, the laser system comprising:
(a) a single frequency laser having a laser output for delivering laser light at a frequency \u03c9o;
(b) an optical modulator coupled to the output of said laser for generating two optical sidebands, the modulator being driven by a RF signal at a frequency \u03c9m;
(c) an optical filter coupled to an output of the modulator for suppressing one of the two sidebands; and
(e) an optical path coupling an output of the filter to the laser for injection locking.
31. The laser system with self-injection locking of claim 1 further including an optical isolator disposed at the laser output for inhibiting reflective laser output from feeding back into the laser.
32. The laser system with self-injection locking of claim 19 further including an optical isolator disposed at the laser output for inhibiting reflective laser output from feeding back into the laser.
33. The laser system with self-injection locking of claim 23 further including an optical isolator disposed at the laser output for inhibiting reflective laser output from feeding back into the laser.
34. The laser system with self-injection locking of claim 30 further including an optical isolator disposed at the laser output for inhibiting reflective laser output from feeding back into the laser.
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 method of estimating carrier frequency offset introduced on an RF multicarrier signal received via a transmission channel on a direct downconversion analog receiver, comprising:
a) generating a preamble comprising multiple sets of training symbols,
b) transmitting the preamble via the channel and receiving it on the receiver,
c) introducing a predetermined artificial carrier frequency offset on at least one of the sets of training symbols,
d) determining a carrier frequency offset estimate from each set of training symbols of the received preamble by an estimation method which has a higher precision for a first range of carrier frequency offset values and a lower precision for a second range of carrier frequency offset values, wherein each of the carrier frequency offset estimates is determined by a direct algebraic relationship between a number of the training symbols of the considered set, the direct algebraic relationship cancelling out IQ imbalance; and
e) exploiting the direct algebraic relationship to take noise into account in determining an overall carrier frequency offset estimate from the carrier frequency offset estimates;
wherein the predetermined artificial carrier frequency offset is chosen for shifting the carrier frequency offset of that set of training symbols of the generated preamble to the first range of carrier frequency offset values, wherein the carrier frequency offset is modelled as a phase rotation and that the determining of a carrier frequency offset estimate comprises determining a phase rotation for each received set of training symbols by the direct algebraic relationship, wherein the direct algebraic relationship for determining the phase rotation for each received set of training symbols is based at least in part on the following equation:
y
\u2061
(
k
)
+
y
\u2061
(
k
+
2
\u2062
l
)
y
\u2061
(
k
+
l
)
=
2
\u2062
cos
\u2062
\u2062
\u03c6
wherein y(k), y(k+l) and y(k+2l) are three equal training symbols of the respective set of the received preamble, spaced by a delay l in time, and wherein \u03c6 is the phase rotation between these training symbols.
2. The method according to claim 1, wherein each of the multiple sets of training symbols comprises at least three equal training symbols at the same delay from each other.
3. The method according to claim 1, wherein noise is taken into account by taking a weighted average of the multiple estimates, by introducing weights which are chosen inversely proportional with a variance of the estimations into the direct algebraic relationship, thereby obtaining the overall carrier frequency offset estimate.
4. The method according to claim 1, wherein the average carrier frequency offset estimate is determined based at least in part on by the following equation, which forms the direct algebraic relationship including the weights:
cos
\u2062
\u2062
\u03c6
=
\u2062
\u2062
\u2211
k
=
1
l
\u2062
y
\u2061
(
k
)
\u2062
y
*
\u2061
(
k
+
l
)
+
y
\u2061
(
k
+
2
\u2062
l
)
\u2062
y
*
\u2061
(
k
+
l
)
2
\u2062
\u2211
k
=
1
l
\u2062
\uf603
y
\u2061
(
k
+
l
)
\uf604
2
wherein
cos \u03c6 is the overall carrier frequency offset estimate.
5. The method according to claim 1, wherein the preamble generated comprises a first and a second set of training symbols, the training symbols of the first set being substantially the same as those of the second set, and that the introducing of a predetermined artificial carrier frequency offset comprises introducing a first predetermined artificial carrier frequency offset on the first set and a second predetermined artificial carrier frequency offset on the second set, the first and second predetermined artificial carrier frequency offsets differing from each other in such a way that the carrier frequency offset of at least one of the first and second sets of training symbols of the preamble received is shifted to the first range.
6. The method according to claim 5, wherein the first and second predetermined artificial carrier frequency offsets are respectively chosen such that they cause the respective phase rotations between training symbols in the first and second set to be \u03c61 and \u03c62 =\u03c61+\u03c02 +a multiple of 2\u03c0respectively.
7. The method according to claim 6, wherein the overall carrier frequency offset estimate is determined using the following equations:
cos
\u2062
\u2062
\u03c6
=
\u2062
\u2062
\u2211
k
=
1
l
\u2062
y
1
\u2061
(
k
)
\u2062
y
2
*
\u2061
(
k
)
+
y
3
\u2061
(
k
)
\u2062
y
2
*
\u2061
(
k
)
2
\u2062
\u2211
k
=
1
l
\u2062
\uf603
y
2
\u2061
(
k
)
\uf604
2
sin
\u2062
\u2062
\u03c6
=
–
\u2062
\u2062
\u2211
k
=
1
l
\u2062
z
1
\u2062
\u2062
(
k
)
\u2062
z
2
*
\u2061
(
k
)
+
z
3
\u2061
(
k
)
\u2062
z
2
*
\u2061
(
k
)
2
\u2062
\u2211
k
=
1
l
\u2062
\uf603
z
2
\u2061
(
k
)
\uf604
2
wherein
yx(k) for x=1, 2, 3 and k=1:l are the training symbols of the first set of the received preamble;
zx(k) for x=1, 2, 3 and k=1:l, are the training symbols of the second set of the received preamble;
l is the regular delay between two successive equal training symbols upon generation of the preamble;
\u03c6 is the phase rotation between the training symbols.
8. The method according to claim 7, wherein the carrier frequency offset estimate is determined as follows:
for
\u2062
\u2062
cos
\u2062
\u2062
\u03c6
\u2265
0
,
CFO
=
f
s
2
\u2062
\u03c0
\u2062
\u2062
l
\u2062
tan
–
1
\u2061
(
sin
\u2062
\u2062
\u03c6
cos
\u2062
\u2062
\u03c6
)
for
\u2062
\u2062
cos
\u2062
\u2062
\u03c6
<
0
,
CFO
=
f
s
2
\u2062
\u03c0
\u2062
\u2062
l
\u2061
tan
–
1
\u2061
(
sin
\u2062
\u2062
\u03c6
cos
\u2062
\u2062
\u03c6
)
+
sign
\u2062
\u2062
(
sin
\u2062
\u2062
\u03c6
)
\u2062
\u03c0
wherein
CFO is the carrier frequency offset estimate and
\u0192s is the frequency of the training symbols in the preamble.
9. The method according to claim 1, further comprising:
determining a noise power of the received preamble; and
determining an overall carrier frequency offset estimate using a maximum likelihood carrier frequency offset estimation method if the noise power is below a given threshold instead of performing the process described above in (d) and (e).
10. The method according to claim 1, wherein the introducing of a predetermined artificial carrier frequency offset is performed upon the generating of the preamble.
11. The method according to claim 1, wherein the introducing of a predetermined artificial carrier frequency offset is performed after the receiving of the preamble.
12. A method of compensating carrier frequency offset introduced on an RF multicarrier signal received via a transmission channel on a direct conversion analog receiver, comprising:
estimating the carrier frequency offset by a method, the method comprising:
a) generating a preamble comprising multiple sets of training symbols,
b) transmitting the preamble via the channel and receiving it on the receiver,
c) introducing a predetermined artificial carrier frequency offset on at least one of the sets of training symbols,
d) determining a carrier frequency offset estimate from each set of training symbols of the received preamble by an estimation method which has a higher precision for a first range of carrier frequency offset values and a lower precision for a second range of carrier frequency offset values, wherein each of the carrier frequency offset estimates is determined by a direct algebraic relationship between a number of the training symbols of the considered set, the direct algebraic relationship cancelling out IQ imbalance; and
e) exploiting the direct algebraic relationship to take noise into account in determining an overall carrier frequency offset estimate from the carrier frequency offset estimates;
wherein the predetermined artificial carrier frequency offset is chosen for shifting the carrier frequency offset of that set of training symbols of the generated preamble to the first range of carrier frequency offset values, wherein the carrier frequency offset is modelled as a phase rotation and that the determining of a carrier frequency offset estimate comprises determining a phase rotation for each received set of training symbols by the direct algebraic relationship, wherein the direct algebraic relationship for determining the phase rotation for each received set of training symbols is based at least in part on the following equation:
y
\u2061
(
k
)
+
y
\u2061
(
k
+
2
\u2062
l
)
y
\u2061
(
k
+
l
)
=
2
\u2062
cos
\u2062
\u2062
\u03c6
wherein y(k), y(k+l) and y(k+2l) are three equal training symbols of the respective set of the received preamble, spaced by a delay l in time, and wherein \u03c6 is the phase rotation between these training symbols; and
compensating the received RF signal for carrier frequency offset by the estimated carrier frequency offset.
13. The method according to claim 12, further comprising determining IQ imbalance parameters from the received preamble.
14. The method according to claim 13, further comprising compensating the received RF signal for IQ imbalance by the IQ imbalance parameters.
15. A system configured to estimate carrier frequency offset introduced on an RF multicarrier signal received via a transmission channel on a direct downconversion analog receiver, comprising:
means for generating a preamble comprising multiple sets of training symbols, means for transmitting the preamble via the channel and receiving it on the receiver,
means for introducing a predetermined artificial carrier frequency offset on at least one of the sets of training symbols,
means for determining a carrier frequency offset estimate from each set of training symbols of the received preamble by an estimation method which has a higher precision for a first range of carrier frequency offset values and a lower precision for a second range of carrier frequency offset values, wherein each of the carrier frequency offset estimates is determined by a direct algebraic relationship between a number of the training symbols of the considered set, the direct algebraic relationship cancelling out IQ imbalance; and
means for exploiting the direct algebraic relationship to take noise into account in determining an overall carrier frequency offset estimate from the carrier frequency offset estimates;
wherein the predetermined artificial carrier frequency offset is chosen for shifting the carrier frequency offset of that set of training symbols of the generated preamble to the first range of carrier frequency offset values, wherein the carrier frequency offset is modelled as a phase rotation and that the determining of a carrier frequency offset estimate comprises determining a phase rotation for each received set of training symbols by the direct algebraic relationship, wherein the direct algebraic relationship for determining the phase rotation for each received set of training symbols is based at least in part on the following equation:
y
\u2061
(
k
)
+
y
\u2061
(
k
+
2
\u2062
l
)
y
\u2061
(
k
+
l
)
=
2
\u2062
cos
\u2062
\u2062
\u03c6
wherein y(k), y(k+l) and y(k+2l) are three equal training symbols of the respective set of the received preamble, spaced by a delay l in time, and wherein \u03c6 is the phase rotation between these training symbols.
16. A system configured to estimate carrier frequency offset introduced on an RF multicarrier signal received via a transmission channel on a direct downconversion analog receiver, comprising:
a generating module configured to generate a preamble comprising multiple sets of training symbols,
a transmitting module configured to transmit the preamble via the channel and receiving it on the receiver,
an introducing module configured to introduce a predetermined artificial carrier frequency offset on at least one of the sets of training symbols,
a determining module configured to determine a carrier frequency offset estimate from each set of training symbols of the received preamble by an estimation method which has a higher precision for a first range of carrier frequency offset values and a lower precision for a second range of carrier frequency offset values, wherein each of the carrier frequency offset estimates is determined by a direct algebraic relationship between a number of the training symbols of the considered set, the direct algebraic relationship cancelling out IQ imbalance; and
an exploiting module configured to exploit the direct algebraic relationship to take noise into account in determining an overall carrier frequency offset estimate from the carrier frequency offset estimates;
wherein the predetermined artificial carrier frequency offset is chosen for shifting the carrier frequency offset of that set of training symbols of the generated preamble to the first range of carrier frequency offset values, wherein the carrier frequency offset is modelled as a phase rotation and that the determining of a carrier frequency offset estimate comprises determining a phase rotation for each received set of training symbols by the direct algebraic relationship, wherein the direct algebraic relationship for determining the phase rotation for each received set of training symbols is based at least in part on the following equation:
y
\u2061
(
k
)
+
y
\u2061
(
k
+
2
\u2062
l
)
y
\u2061
(
k
+
l
)
=
2
\u2062
cos
\u2062
\u2062
\u03c6
wherein y(k), y(k+l) and y(k+2l) are three equal training symbols of the respective set of the received preamble, spaced by a delay l in time, and wherein \u03c6 is the phase rotation between these training symbols.