3. Measurement of Optical Frequencies
A NIST - oriented objective to my program
Optical Signals cannot be measured directly because they are
of extremely high frequency
4. Frequency Combs
Present a way to measure optical frequencies by creating an “optical
ruler”, a precise spectrum of light
𝑓0 Offset Frequency
𝑓𝑟 Interval between
adjacent frequencies
𝑣 𝑛 Arbitrary wave in
a frequency comb
5. Optical Microresonators
Optical microresonators are micrometer scale devices capable
of confining light to the scale of a cubic wavelength
They can be used to create frequency combs if a resonant
wavelength is used.
6. Resonance
In small containers, light
can only exist if the
container’s length is an
integer multiple of the
light’s wavelength.
The container is a
“resonator” and can only
contain very specific
wavelengths of light.
7. Optical Microresonators
Optical microresonators are micrometer scale devices capable
of confining light to the scale of a cubic wavelength
They can be used to create frequency combs if a resonant
wavelength is used.
8. Resonance in Microresonators
If light exists within the ring,
the ring’s circumference
must be evenly divisible
by the light’s wavelength.
We are using ring-resonators
If the above condition is
met, light forms a closed
loop within the ring
If not, the light bypasses
the ring altogether.
9. Finding Resonance
1. Use a laser to test a specific wavelength on a resonator
2. If the wavelength is not in resonance, it cannot exist within the
resonator, and the photodetector signal will be full strength
3. If the wavelength is in resonance, light will enter the resonator,
and the photodetector signal will drop
10. Finding Resonance With Computers
1. A Data Acquisition (DAQ) Card sends a signal to the laser forcing it
to a specific wavelength.
2. The DAQ Card reads the photodetector signal and displays a graph
11. Objectives of Final Application
1. Conduct sweeps over broad wavelength ranges (tens
of nanometers)
2. Allow researcher to manually adjust laser position into
resonance
3. Conduct fine sweeps in the neighborhood of the
resonance (tens of picometers)
13. Current Methods: LabVIEW
A visual programming
language
Designed for scientific
experiments by
National Instruments
Required to use
interface of controls
given by LabVIEW
14. Benefits of Using Python
A text-based programming language that is more familiar to the
researchers
Allows direct interfacing with laser motor, is more versatile
Fully customizable interface
Continually updatable and open-source
15. Components of Experiment
Tunable DC Motor Laser
Internal DC motor must be directly
programmable using voltage signals
Photodetector
Sends voltage signals to DAQ Card
Data Acquisition Card (DAQ Card)
Device to send and receive voltage
signals
16. DAQ CARD Abilities
Change voltage of output pins with following parameters
Array of points to send
Rate to move from point to point
Sample voltage on input pins and save data into an array
Array must be passed as a parameter
Rate of sampling must be specified
17. DAQ Card Limitations
DAQ Card cannot synchronize sending and receiving signals to
the same clock
Poses a challenge that must be solved by the program
18. Algorithm
This is a graph of the outgoing voltage signal as given by the
LOOPBACK CHANNEL
19. Algorithm
The DAQ Card will be listening to the photodetector signal in
between the green lines
20. Algorithm
The orange line is the photodetector signal. The two dips represent
resonances (one time passing it forward, one time backwards)
21. Algorithm
Using the loopback
channel, we
determine the start
of the sweep by
checking the
difference between
two consecutive
outgoing values.
Then we pair it with
the corresponding
point in the
photodetector
signal
22. Algorithm
The orange line is the photodetector signal. The two dips represent
resonances (one time passing it forward, one time backwards)
25. Conclusions
All initial objectives have been met
1. Conduct sweeps over broad wavelength ranges (tens of
nanometers)
2. Allow researcher to manually adjust laser position into
resonance
3. Conduct fine sweeps in the neighborhood of the resonance
(tens of picometers)
Also able to save data in csv files
26. Future Work
Resonance shifts to the
right when working with
high intensity light
Very difficult to land on
backside of resonance
Must experiment with
different wavelength
approach speeds and
patterns to stop on
backside of resonance
