229 research outputs found
Vernier spectrometer using counter-propagating soliton microcombs
Acquisition of laser frequency with high resolution under continuous and
abrupt tuning conditions is important for sensing, spectroscopy and
communications. Here, a single microresonator provides rapid and broad-band
measurement of frequencies across the optical C-band with a relative frequency
precision comparable to conventional dual frequency comb systems. Dual-locked
counter-propagating solitons having slightly different repetition rates are
used to implement a Vernier spectrometer. Laser tuning rates as high as 10
THz/s, broadly step-tuned lasers, multi-line laser spectra and also molecular
absorption lines are characterized using the device. Besides providing a
considerable technical simplification through the dual-locked solitons and
enhanced capability for measurement of arbitrarily tuned sources, this work
reveals possibilities for chip-scale spectrometers that greatly exceed the
performance of table-top grating and interferometer-based devices
Data class-specific all-optical transformations and encryption
Diffractive optical networks provide rich opportunities for visual computing
tasks since the spatial information of a scene can be directly accessed by a
diffractive processor without requiring any digital pre-processing steps. Here
we present data class-specific transformations all-optically performed between
the input and output fields-of-view (FOVs) of a diffractive network. The visual
information of the objects is encoded into the amplitude (A), phase (P), or
intensity (I) of the optical field at the input, which is all-optically
processed by a data class-specific diffractive network. At the output, an image
sensor-array directly measures the transformed patterns, all-optically
encrypted using the transformation matrices pre-assigned to different data
classes, i.e., a separate matrix for each data class. The original input images
can be recovered by applying the correct decryption key (the inverse
transformation) corresponding to the matching data class, while applying any
other key will lead to loss of information. The class-specificity of these
all-optical diffractive transformations creates opportunities where different
keys can be distributed to different users; each user can only decode the
acquired images of only one data class, serving multiple users in an
all-optically encrypted manner. We numerically demonstrated all-optical
class-specific transformations covering A-->A, I-->I, and P-->I transformations
using various image datasets. We also experimentally validated the feasibility
of this framework by fabricating a class-specific I-->I transformation
diffractive network using two-photon polymerization and successfully tested it
at 1550 nm wavelength. Data class-specific all-optical transformations provide
a fast and energy-efficient method for image and data encryption, enhancing
data security and privacy.Comment: 27 Pages, 9 Figures, 1 Tabl
Chaos-assisted two-octave-spanning microcombs
Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated through χ^((2)) and χ^((3)) nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging
SpatialCodec: Neural Spatial Speech Coding
In this work, we address the challenge of encoding speech captured by a
microphone array using deep learning techniques with the aim of preserving and
accurately reconstructing crucial spatial cues embedded in multi-channel
recordings. We propose a neural spatial audio coding framework that achieves a
high compression ratio, leveraging single-channel neural sub-band codec and
SpatialCodec. Our approach encompasses two phases: (i) a neural sub-band codec
is designed to encode the reference channel with low bit rates, and (ii), a
SpatialCodec captures relative spatial information for accurate multi-channel
reconstruction at the decoder end. In addition, we also propose novel
evaluation metrics to assess the spatial cue preservation: (i) spatial
similarity, which calculates cosine similarity on a spatially intuitive
beamspace, and (ii), beamformed audio quality. Our system shows superior
spatial performance compared with high bitrate baselines and black-box neural
architecture. Demos are available at https://xzwy.github.io/SpatialCodecDemo.
Codes and models are available at https://github.com/XZWY/SpatialCodec.Comment: Paper in Submissio
Quantum diffusion of microcavity solitons
Coherently pumped (Kerr) solitons in an ideal optical microcavity are expected to undergo random quantum motion that determines fundamental performance limits in applications of the soliton microcombs. Here this random walk and its impact on Kerr soliton timing jitter are studied experimentally. The quantum limit is discerned by measuring the relative position of counter-propagating solitons. Their relative motion features weak interactions and also presents common-mode suppression of technical noise, which typically hides the quantum fluctuations. This is in contrast to co-propagating solitons, which are found to have relative timing jitter well below the quantum limit of a single soliton on account of strong correlation of their mutual motion. Good agreement is found between theory and experiment. The results establish the fundamental limits to timing jitter in soliton microcombs and provide new insights on multisoliton physics
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