Using Quantum Photonics to
Create Optical Frequency combs
Tobias J. Kippenberg
The problem of the “whispering gallery”: observation
of Lord Rayleigh in St. Paul Cathedral (London)*
*L. Rayleigh
Acoustic Whispering Gallery
Mode
diameter of a human hair
~100 µm
A photon storage time of 1 micro-second implies that the
Light can travel up to 1 km inside a glass torus!
𝜏𝑃ℎ𝑜𝑡𝑜𝑛 > 1𝜇𝑠𝑒𝑐𝑜𝑛𝑑
Coupling light into a microresonator
Just like a Guitar string has several vibrational
modes, an optical microresonator has many
optical modes
1/R
40 m
Pin
taper-microcavity junction exhibits
extremely high ideality (coupling losses
<0.3%)
Coupling both to-and-from a 80m
microtoroid on a chip
Using Quantum Photonics to creat frequency combs
The Nobel Prize in Physics 1981
Nicolaas Bloembergen
Nonlinear Optics
Prism
Pump laser
At high intensities the interaction
becomes nonlinear leading to «twin»
photon generation
𝜔𝑝 + 𝜔𝑝 → 𝜔𝐼 + 𝜔𝑆
Energy conservation requires
𝜔𝐼 = 𝜔𝑝 + Δ
𝜔𝑆 = 𝜔𝑝 − Δ
Silica Resonator (1
Generating a frequency comb from a microresonator
Optical microresonator
A frequency
comb
Optical fiber
Pump laser
Comb generation mechanism
Twin Photon generation
wp1
ws
wp2
wi
Comb Generation Mechanism
Twin photon generation
wp
ws
wp
wi
Der Entstehungsprozess: Zwillingphotonen
Twin photon generation
Generating a frequency comb in an optical microresonator
𝜔𝑝 − 3Δ
Δ
Δ
Δ
𝜔𝑝 − 2Δ
𝜔𝑝 − Δ
Δ
Δ
𝜔𝑝
𝜔𝑝 + Δ
Optical frequency comb
The perfectly equidistant
arrangement is called on optical
frequency comb
Δ
𝜔𝑝 + 2Δ
𝜔𝑝 + 3Δ
Microresonotor frequency comb
An octave spanning optical spectrum
is generated from a single laser
frequency
Optical frequency combs
Hz
With an optical frequency combs
an unknown optical frequency can
be determined accurately
measured
𝜔𝑜𝑝𝑡𝑖𝑞𝑢𝑒 ≈ 1015 𝐻𝑧
𝑇𝑝𝑒𝑟𝑖𝑜𝑑 ≈ 10−14 𝑠𝑒𝑐.
Nobel Prize Physics 2005: “for their contributions to the development of
laser-based precision spectroscopy, including the optical frequency comb
technique"
Why are frequency combs interesting?
Frequency combs allow to create
very accurate optical atomic
clocks. Clocks that loose less
than 1 second in the age of the
universe of 14 Billion years…
Mode locked lasers for frequency comb generation
Ronald Holtzwarth, TWH
October 2005
Frequency combs on a chip
MgF2
More than 1000 comb lines that are perfectly
equidistant generated from a single laser…
T. Herr et al. Nature Photonics 2012 (July)
Advantages of microresonator frequency combs
Vorteile:
-Very compact compact comb
generator
- The distance between comb
teeth is very large
Microresonator frequency combs as channel generators
Fiber optical communication uses
several wavelength that travel down
on optical fiber spaced in frequency
by ca. >40 GHz
Applications of Frequency combs in Telecommunication
Today: picture of 4 laser
modules to generate 4
channels…
Future: A single
microresonator can generate >
1000 channels from a single
Astrophysical spectrometer: searches for exoplanets
Microresonator frequency
combs can assist to calibrate
astrophysical spectrometers
Frequency
comb assisted
spectrometer
First spectrometer
calibration
with a calibration
Microcavity
ESO‘s Very Large Telescope (VLT) in Chile
X-Shooter spectrometer (in
X-Shooter Telescope
Munich)
(ESO)
Microcavity comb spectrum (83 GHz mode spacing) on echelle grating based
spectrometer
20
Microresonator frequency combs…
Applying them in
astrophysical planets
searches as calibratoin tool..
…applying them in space
optical clocks…
… enable them to become
sources of mid IR radiation
used in chemistry or
pharmaceutical minitoring..
.. Linking RF to optical on a
chip…