163 research outputs found
Ultrafast electrooptic dual-comb interferometry
The femtosecond laser frequency comb has enabled the 21st century revolution
in optical synthesis and metrology. A particularly compelling technique that
relies on the broadband coherence of two laser frequency combs is dual-comb
interferometry. This method is rapidly advancing the field of optical
spectroscopy and empowering new applications, from nonlinear microscopy to
laser ranging. Up to now, most dual-comb interferometers were based on
modelocked lasers, whose repetition rates have restricted the measurement speed
to ~ kHz. Here we demonstrate a novel dual-comb interferometer that is based on
electrooptic frequency comb technology and measures consecutive complex spectra
at a record-high refresh rate of 25 MHz. These results pave the way for novel
scientific and metrology applications of frequency comb generators beyond the
realm of molecular spectroscopy, where the measurement of ultrabroadband
waveforms is of paramount relevance
Electro optic combs rise above the noise
Electro-optic modulation of light can have a precision equivalent to one optical-field cycl
Electro-optic dual-comb interferometry over 40-nm bandwidth
Dual-comb interferometry is a measurement technique that uses two laser
frequency combs to retrieve complex spectra in a line-by-line basis. This
technique can be implemented with electro-optic frequency combs, offering
intrinsic mutual coherence, high acquisition speed and flexible repetition-rate
operation. A challenge with the operation of this kind of frequency comb in
dual-comb interferometry is its limited optical bandwidth. Here, we use
coherent spectral broadening and demonstrate electro-optic dual-comb
interferometry over the entire telecommunications C band (200 lines covering ~
40 nm, measured within 10 microseconds at 100 signal-to-noise ratio per
spectral line). These results offer new prospects for electro-optic dual-comb
interferometry as a suitable technology for high-speed broadband metrology, for
example in optical coherence tomography or coherent Raman microscopy
Optical Frequency Comb Noise Characterization Using Machine Learning
A novel tool, based on Bayesian filtering framework and expectation
maximization algorithm, is numerically and experimentally demonstrated for
accurate frequency comb noise characterization. The tool is statistically
optimum in a mean-square-error-sense, works at wide range of SNRs and offers
more accurate noise estimation compared to conventional methods
Shaping the ultrafast temporal correlations of thermal-like photons
We show that the temporal correlations between two light beams arising from a broadband thermal-like source can be controlled in the femtosecond regime. Specifically, by introducing spectral phase-only masks in the path of one of the beams, we show that the timing and strength of the photon correlations can
be programmed on demand. This example demonstrates that the interbeam second-order coherence function propagates as a phase-sensitive ultrafast wave packet in the path towards the detectors, and is
thus, susceptible to be modified by acting on just one of the beams. For quite some time, it has been thought that this could only happen with sources showing time-energy entanglement. Our work shows that such a property is due to the existence of a certain type of correlation, but not necessarily the entanglementPeer ReviewedPostprint (published version
Performance tradeoffs in low-loss Si3N4 waveguides for linear and nonlinear applications
We experimentally analyze tradeoffs in terms of waveguide losses, dispersion engineering and single-mode behaviour for different waveguide geometries. Our results suggests that photonic integrated circuits relying on nonlinear waveguides benefit from including a dedicated waveguide geometry via multi-layer integration to yield a seven-fold improvement in terms of loss
Thermal noise reduction in soliton microcombs via laser self-cooling
Thermal noise usually dominates the low-frequency region of the optical phase noise of soliton microcombs, which leads to decoherence that limits many aspects of applications. In this work, we demonstrate a simple and reliable way to mitigate this noise by laser cooling with a pump laser. The key is rendering the pump laser to simultaneously excite two neighboring cavity modes from different families that are respectively red and blue detuned, one for soliton generation and the other for laser cooling
A unified approach to describe optical pulse generation by propagation of periodically phase-modulated CW laser light
The analysis of optical pulse generation by phase modulation of narrowband
continuous-wave light, and subsequent propagation through a
group-delay-dispersion circuit, is usually performed in terms of the so-called
bunching parameter. This heuristic approach does not provide theoretical
support for the electrooptic flat-top-pulse generation reported recently. Here,
we perform a waveform synthesis in terms of the Fresnel images of the
periodically phase-modulated input light. In particular, we demonstrate
flat-top-pulse generation with a duty ratio of 50% at a quarter of the Talbot
condition for the sinusoidal phase modulation. Finally, we propose a binary
modulation format to generate a well-defined square-wave-type optical bit
pattern.Comment: 10 pages, 5 figures. Submitted to Optics Expres
Optical bandgap engineering in nonlinear silicon nitride waveguides
Silicon nitride is awell-established material for photonic devices and
integrated circuits. It displays a broad transparency window spanning from the
visible to the mid-IR and waveguides can be manufactured with low losses. An
absence of nonlinear multi-photon absorption in the erbium lightwave
communications band has enabled various nonlinear optic applications in the
past decade. Silicon nitride is a dielectric material whose optical and
mechanical properties strongly depend on the deposition conditions. In
particular, the optical bandgap can be modified with the gas flow ratio during
low-pressure chemical vapor deposition (LPCVD). Here we show that this
parameter can be controlled in a highly reproducible manner, providing an
approach to synthesize the nonlinear Kerr coefficient of the material. This
holistic empirical study provides relevant guidelines to optimize the
properties of LPCVD silicon nitride waveguides for nonlinear optics
applications that rely on the Kerr effect
High-Q Si3N4 microresonators based on a subtractive processing for Kerr nonlinear optics
Microresonator frequency combs (microcombs) are enabling new applications in frequency synthesis and metrology – from high-speed laser ranging to coherent optical communications. One critical parameter that dictates the performance of the microcomb is the optical quality factor (Q) of the microresonator. Microresonators fabricated in planar structures such as silicon nitride (Si3N4) allow for dispersion engineering and the possibility to monolithically integrate the microcomb with other photonic devices. However, the relatively large refractive index contrast and the tight optical confinement required for dispersion engineering make it challenging to attain Si3N4 microresonators with Qs > 107 using standard subtractive processing methods – i.e. photonic devices are patterned directly on the as-deposited Si3N4 film. In this work, we achieve ultra-smooth Si3N4 microresonators featuring mean intrinsic Qs around 11 million. The cross-section geometry can be precisely engineered in the telecommunications band to achieve either normal or anomalous dispersion, and we demonstrate the generation of mode-locked dark-pulse Kerr combs as well as soliton microcombs. Such high-Qs allow us to generate 100 GHz soliton microcombs, demonstrated here for the first time in Si3N4 microresonators fabricated using a subtractive processing method. These results enhance the possibilities for co-integration of microcombs with high-performance photonic devices, such as narrow-linewidth external-cavity diode lasers, ultra-narrow filters and demultiplexers
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