27 research outputs found
A universal frequency engineering tool for microcavity nonlinear optics: multiple selective mode splitting of whispering-gallery resonances
Whispering-gallery microcavities have been used to realize a variety of
efficient parametric nonlinear optical processes through the enhanced
light-matter interaction brought about by supporting multiple high quality
factor and small modal volume resonances. Critical to such studies is the
ability to control the relative frequencies of the cavity modes, so that
frequency matching is achieved to satisfy energy conservation. Typically this
is done by tailoring the resonator cross-section. Doing so modifies the
frequencies of all of the cavity modes, that is, the global dispersion profile,
which may be undesired, for example, in introducing competing nonlinear
processes.Here, we demonstrate a frequency engineering tool, termed multiple
selective mode splitting (MSMS), that is independent of the global dispersion
and instead allows targeted and independent control of the frequencies of
multiple cavity modes. In particular, we show controllable frequency shifts up
to 0.8 nm, independent control of the splitting of up to five cavity modes with
optical quality factors , and strongly suppressed frequency
shifts for untargeted modes. The MSMS technique can be broadly applied to a
wide variety of nonlinear optical processes across different material
platforms, and can be used to both selectively enhance processes of interestand
suppress competing unwanted processes.Comment: 13 pages, 8 figure
Sub-Doppler spectroscopy of quantum systems through nanophotonic spectral translation of electro-optic light
An outstanding challenge for deployable quantum technologies is the
availability of high-resolution laser spectroscopy at the specific wavelengths
of ultranarrow transitions in atomic and solid-state quantum systems. Here, we
demonstrate a powerful spectroscopic tool that synergistically combines high
resolution with flexible wavelength access, by showing that nonlinear
nanophotonics can be readily pumped with electro-optic frequency combs to
enable highly coherent spectral translation with essentially no efficiency
loss. Third-order (\c{hi}(3)) optical parametric oscillation in a silicon
nitride microring enables nearly a million optical frequency comb pump teeth to
be translated onto signal and idler beams; while the comb tooth spacing and
bandwidth are adjustable through electro-optic control, the signal and idler
carrier frequencies are widely tuneable through dispersion engineering. We then
demonstrate the application of these devices to quantum systems, by performing
sub-Doppler spectroscopy of the hyperfine transitions of a Cs atomic vapor with
our electro-optically-driven Kerr nonlinear light source. The generality,
robustness, and agility of this approach as well as its compatibility with
photonic integration are expected to lead to its widespread applications in
areas such as quantum sensing, telecommunications, and atomic clocks.Comment: 17 pages, 5 figure
Stably accessing octave-spanning microresonator frequency combs in the soliton regime
Microresonator frequency combs can be an enabling technology for optical
frequency synthesis and timekeeping in low size, weight, and power
architectures. Such systems require comb operation in low-noise, phase-coherent
states such as solitons, with broad spectral bandwidths (e.g., octave-spanning)
for self-referencing to detect the carrier-envelope offset frequency. However,
stably accessing such states is complicated by thermo-optic dispersion. For
example, in the Si3N4 platform, precisely dispersion-engineered structures can
support broadband operation, but microsecond thermal time constants have
necessitated fast pump power or frequency control to stabilize the solitons. In
contrast, here we consider how broadband soliton states can be accessed with
simple pump laser frequency tuning, at a rate much slower than the thermal
dynamics. We demonstrate octave-spanning soliton frequency combs in Si3N4
microresonators, including the generation of a multi-soliton state with a pump
power near 40 mW and a single-soliton state with a pump power near 120 mW. We
also develop a simplified two-step analysis to explain how these states are
accessed in a thermally stable way without fast control of the pump laser, and
outline the required thermal properties for such operation. Our model agrees
with experimental results as well as numerical simulations based on a
Lugiato-Lefever equation that incorporates thermo-optic dispersion. Moreover,
it also explains an experimental observation that a member of an adjacent mode
family on the red-detuned side of the pump mode can mitigate the thermal
requirements for accessing soliton states
Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy
Infrared spectroscopy is a powerful tool for basic and applied science. The
molecular spectral fingerprints in the 3 um to 20 um region provide a means to
uniquely identify molecular structure for fundamental spectroscopy, atmospheric
chemistry, trace and hazardous gas detection, and biological microscopy. Driven
by such applications, the development of low-noise, coherent laser sources with
broad, tunable coverage is a topic of great interest. Laser frequency combs
possess a unique combination of precisely defined spectral lines and broad
bandwidth that can enable the above-mentioned applications. Here, we leverage
robust fabrication and geometrical dispersion engineering of silicon
nanophotonic waveguides for coherent frequency comb generation spanning 70 THz
in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides
significant spectral broadening and engineered spectra targeted at specific
mid-infrared bands. We use this coherent light source for dual-comb
spectroscopy at 5 um.Comment: 26 pages, 5 figure
A Kerr-microresonator optical clockwork
Kerr microresonators generate interesting and useful fundamental states of
electromagnetic radiation through nonlinear interactions of continuous-wave
(CW) laser light. Using photonic-integration techniques, functional devices
with low noise, small size, low-power consumption, scalable fabrication, and
heterogeneous combinations of photonics and electronics can be realized. Kerr
solitons, which stably circulate in a Kerr microresonator, have emerged as a
source of coherent, ultrafast pulse trains and ultra-broadband
optical-frequency combs. Using the f-2f technique, Kerr combs support
carrier-envelope-offset phase stabilization for optical synthesis and
metrology. In this paper, we introduce a Kerr-microresonator optical clockwork
based on optical-frequency division (OFD), which is a powerful technique to
transfer the fractional-frequency stability of an optical clock to a lower
frequency electronic clock signal. The clockwork presented here is based on a
silicon-nitride (SiN) microresonator that supports an optical-frequency
comb composed of soliton pulses at 1 THz repetition rate. By electro-optic
phase modulation of the entire SiN comb, we arbitrarily generate
additional CW modes between the SiN comb modes; operationally, this
reduces the pulse train repetition frequency and can be used to implement OFD
to the microwave domain. Our experiments characterize the residual frequency
noise of this Kerr-microresonator clockwork to one part in , which
opens the possibility of using Kerr combs with high performance optical clocks.
In addition, the photonic integration and 1 THz resolution of the SiN
frequency comb makes it appealing for broadband, low-resolution liquid-phase
absorption spectroscopy, which we demonstrate with near infrared measurements
of water, lipids, and organic solvents