of 7
Article
https://doi.org/10.103
8/s41467-023-42289-0
Visible-to-mid-IR tunable frequency comb in
nanophotonics
Arkadev Roy
1,3
, Luis Ledezma
1,2,3
,LuisCosta
1
,RobertGray
1
,RyotoSekine
1
,
Qiushi Guo
1
, Mingchen Liu
1
,RyanM.Briggs
2
&AlirezaMarandi
1
Optical frequency comb is an enabling technology for a multitude of appli-
cations from metrology to ranging an
d communications. The tremendous
progress in sources of optical frequency combs has mostly been centered
around the near-infrared spectral re
gion, while many applications demand
sources in the visible and mid-infrared, which have so far been challenging to
achieve, especially in nanophotonics
. Here, we report widely tunable fre-
quency comb generation us
ing optical parametric osci
llators in lithium nio-
bate nanophotonics. We demonstrat
e sub-picosecond frequency combs
tunable beyond an octave extending from 1.5 up to 3.3
μ
m with femtojoule-
level thresholds on a single chip. We utilize the up-conversion of the infrared
combs to generate visible frequency combs reaching 620 nm on the same
chip. The ultra-broadband tunability and
visible-to-mid-infrared spectral cov-
erage of our source highlight a practical and universal path for the realization
of ef
fi
cient frequency comb so
urces in nanophotonics, overcoming their
spectral sparsity.
Optical frequency combs consisting of several spectral lines with
accurate frequencies are at the core of a plethora of modern-day
applications
1
,
2
, including spectroscopy
3
, optical communication
4
,
optical computing
5
, atomic clocks
6
,ranging
7
,
8
and imaging
9
. Many of
these applications demand optical frequency combs in the technolo-
gically important mid-infrared
10
,
11
and visible
12
,
13
spectral regimes.
Accessing optical frequency comb sources in integrated photonic
platforms is of paramount importance for the translation of many of
these technologies to real-world applications and devices
14
.Despite
outstanding progress in that direction in the near-infrared, there is a
dearth of widely tunable frequency comb sources, especially in the
highly desired mid-infrared and visible spectral regimes.
Notable efforts on miniaturized mid-IR comb sources typically
rely on supercontinuum generation and/or intra-pulse difference fre-
quency generation
15
,
16
. Not only do these nonlinear processes usually
require a femtosecond pump as an input (which has its own challenges
for ef
fi
cient on-chip manifestation), but their power is also distributed
over a wide frequency range, including undesired spectral bands.
While the broad instantaneous spectral bandwidth may be suitable for
certain applications, others may require the existence of more con-
centrated spectral power to enhance the signal-to-noise ratio. Engi-
neered semiconductor devices like quantum cascade lasers have
successfully been demonstrated as mid-infrared frequency comb
sources
17
, however, they are not tunable over a broad wavelength
range and are still dif
fi
cult to operate in the ultrashort pulse regime
18
,
19
.
The situation is exacerbated by the lack of a suitable laser gain medium
that is amenable to room temperature operation in the mid-IR. Kerr
nonlinearity can lead to tunable broadband radiation
20
22
but is con-
tingent on satisfying demanding resonator quality factor requirements
and typically relies on a mid-IR pump, to begin with, for subsequent
mid-infrared frequency comb generation. Similar challenges exist for
Raman-based mid-IR frequency comb generation
23
.
On the other hand, optical parametric oscillators (OPOs) based on
quadratic nonlinearity have been the predominant way of accessing
tunable coherent radiation in the mid-IR spectral region enjoying
broadband tunability through appropriate phase matching of the
three-wave mixing
11
. However, their impressive generation of tunable
frequency combs in the mid-infrared has been limited to bulky free-
Received: 19 April 2023
Accepted: 5 October 2023
Check for updates
1
Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
2
Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California 91109, USA.
3
These authors contributed equally: Arkadev Roy, Luis Ledezma.
e-mail:
marandi@caltech.edu
Nature Communications
| (2023) 14:6549
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