Wavelength locker
An apparatus and method for calculating the frequency of the light.
1. A method comprising:
splitting a portion of light produced by a laser to a periodic wavelength filter;
measuring the phase in a period of the wavelength filter of the portion of the light;
calculating the frequency of the light using the measured phase;
comparing the wavelength of the light to a desired wavelength;
if the wavelength of the light does not match the desired wavelength, tuning the laser to match the desired wavelength;
wherein the measuring of the phase of the portion of light using the wavelength filter includes:
sending the portion of the light into a length imbalanced Mach-Zehnder interferometer with an optical 90-degree hybrid connected to two pairs of photodetectors; and
receiving from the two pairs of photodetectors an I signal and a Q signal in response to the light; and
wherein the measuring of the phase of the portion of light using the wavelength filter further includes:
calculating a wavelength of the light using according to the equation of:
f
=
c
0
n
(
f
)
Δ
L
(
m
+
1
2
π
tan
-
1
Q
I
)
;
where c 0 is the speed of light in a vacuum, n(f) is the refractive index in the MZI as a function of frequency f, ΔL is the path-length difference in the MZI, and m is an integer.
2. The method of claim 1 wherein the tuning of the laser includes changing the cavity length of the laser.
3. The method of claim 1 wherein the tuning of the laser includes changing the temperature of a heater near the laser.
4. An integrated wavelength locker fabricated on a silicon chip, the integrated wavelength locker comprising:
a length-imbalanced Mach-Zehnder interferometer coupled to an optical 90-degree hybrid; wherein the 90-degree hybrid has four outputs; wherein two of each of the outputs are coupled to a pair of photodiodes; wherein the photodiodes are coupled via electronics to analog-to-digital converters, wherein the input to the Mach-Zehnder interferometer is optically coupled to a laser via a waveguide; wherein the analog-to-digital converters provide input to a processor to calculate a wavelength of light of the laser; wherein the processor uses the equation
f
=
c
0
n
(
f
)
Δ
L
(
m
+
1
2
π
tan
-
1
Q
I
)
to calculate the wavelength of light; where c 0 is the speed of light in a vacuum, n(f) is the refractive index in the MZI as a function of frequency f, ΔL is the path-length difference in the MZI, and m is an integer; wherein I and Q are outputs of the 90-degree hybrid.
5. The apparatus of claim 4 further comprising a comparator to compare the determined wavelength of light to a desired wavelength of light and if the determined wavelength of light does not match the desired wavelength of light adjusting the wavelength of the light.
6. A system comprising:
a length-imbalanced Mach-Zehnder interferometer coupled to a 90-degree hybrid; wherein the 90-degree hybrid has four outputs; wherein two of each of the outputs are coupled to a pair of photodiodes; wherein the photodiodes are coupled via electronics to analog-to-digital converters;
a processor; and
logic; wherein the processor is enabled to execute the logic to perform:
determining a wavelength of light introduced to the length-imbalanced Mach-Zehnder interferometer; wherein the processor uses the equation:
f
=
c
0
n
(
f
)
Δ
L
(
m
+
1
2
π
tan
-
1
Q
I
)
to determine the wavelength of the light; where c 0 is the speed of light in a vacuum, n(f) is the refractive index in the MZI as a function of frequency f, ΔL is the path-length difference in the MZI, and m is an integer; wherein I and Q are outputs of the 90-degree hybrid.
7. The system of claim 6 wherein the processor is further enabled to execute the logic to perform:
changing the wavelength of the light of the last to match a desired wavelength.
8. The system of claim 6 wherein the changing the wavelength of light includes changing the cavity length in the laser.
9. The system of claim 8 wherein the changing the wavelength of light includes changing the temperature of a heater near the laser.