45 research outputs found
Highly tunable repetition-rate multiplication of mode-locked lasers using all-fibre harmonic injection locking
Higher repetition-rate optical pulse trains have been desired for various
applications such as high-bit-rate optical communication, photonic
analogue-to-digital conversion, and multi- photon imaging. Generation of multi
GHz and higher repetition-rate optical pulse trains directly from mode-locked
oscillators is often challenging. As an alternative, harmonic injection locking
can be applied for extra-cavity repetition-rate multiplication (RRM). Here we
have investigated the operation conditions and achievable performances of
all-fibre, highly tunable harmonic injection locking-based pulse RRM. We show
that, with slight tuning of slave laser length, highly tunable RRM is possible
from a multiplication factor of 2 to >100. The resulting maximum SMSR is 41 dB
when multiplied by a factor of two. We further characterize the noise
properties of the multiplied signal in terms of phase noise and relative
intensity noise. The resulting absolute rms timing jitter of the multiplied
signal is in the range of 20 fs to 60 fs (10 kHz - 1 MHz) for different
multiplication factors. With its high tunability, simple and robust all-fibre
implementation, and low excess noise, the demonstrated RRM system may find
diverse applications in microwave photonics, optical communications, photonic
analogue-to-digital conversion, and clock distribution networks.Comment: 25 pages, 9 figure
Long-term Stabilization of Fiber Laser Using Phase-locking Technique with Ultra-low Phase Noise and Phase Drift
We review the conventional phase-locking technique in the long-term
stabilization of the mode-locked fiber laser and investigate the phase noise
limitation of the conventional technique. To break the limitation, we propose
an improved phase-locking technique with an optic-microwave phase detector in
achieving the ultra-low phase noise and phase drift. The mechanism and the
theoretical model of the novel phase-locking technique are also discussed. The
long-term stabilization experiments demonstrate that the improved technique can
achieve the long-term stabilization for the MLFL with ultra-low phase noise and
phase drift. The excellent locking performance of the improved phase-locking
technique implies that this technique can be used to stabilize the mode-locked
fiber laser with the highly stable H-master or optical clock without stability
loss
Microresonator Soliton Frequency Combs in the Zero-Dispersion Regime
Chip-scale optical frequency combs have attracted significant research
interest and can be used in applications ranging from precision spectroscopy to
telecom channel generators and lidar systems. In the time domain,
microresonator based frequency combs correspond to self-stabilized soliton
pulses. In two distinct regimes, microresonators have shown to emit either
bright solitons in the anomalous dispersion regime or dark solitons (a short
time of darkness in a bright background signal) in the normal dispersion
regime. Here, we investigate the dynamics of continuous-wave-laser-driven
soliton generation in the zero-group-velocity-dispersion (GVD) regime, as well
as the generation of solitons that are spectrally crossing different dispersion
regimes. In the measurements we observe zero-dispersion solitons with doublet
structures (soliton molecules) that can be deterministically accessed with a
predictable spectral envelope. Numerical simulations agree well with the
observed soliton structures. These results could be of interest for chip-based
pump-probe schemes, optical telecom systems, gas sensing and precision
metrology
Room-Temperature Sputtered Ultralow-loss Silicon Nitride for Hybrid Photonic Integration
Silicon-nitride-on-insulator photonic circuits have seen tremendous advances
in many applications, such as on-chip frequency combs, Lidar,
telecommunications, and spectroscopy. So far, the best film quality has been
achieved with low pressure chemical vapor deposition (LPCVD) and
high-temperature annealing (1200 {\deg}C). However, high processing temperature
poses challenges to the cointegration of Si3N4 with pre-processed silicon
electronic and photonic devices, lithium niobate on insulator (LNOI), and
Ge-on-Si photodiodes. This limits LPCVD as a front-end-of-line process. Here,
we demonstrate ultralow-loss Silicon nitride photonics based on
room-temperature reactive sputtering. Propagation losses as low as 5.4 dB/m
after 400 {\deg}C annealing and 3.5 dB/m after 800 {\deg}C annealing are
achieved, enabling ring resonators with more than 10 million optical quality
factors. To the best of our knowledge, these are the lowest propagation losses
achieved with low temperature silicon nitride. This ultralow loss enables
threshold powers for optical parametric oscillations to 1.1 mW and enables the
generation of bright soliton frequency combs at 1.3 and 1.5 {\mu}m. Our work
features a full complementary metal oxide semiconductor (CMOS) compatibility
with front-end silicon electronics and photonics, and has the potential for
hybrid 3D monolithic integration with III-V-on-Si integrated lasers, and LNOI
Ultrasensitive, high-dynamic-range and broadband strain sensing by time-of-flight detection with femtosecond-laser frequency combs
Ultrahigh-resolution optical strain sensors provide powerful tools in various
scientific and engineering fields, ranging from long-baseline interferometers
to civil and aerospace industries. Here we demonstrate an ultrahigh-resolution
fibre strain sensing method by directly detecting the time-of-flight (TOF)
change of the optical pulse train generated from a free-running passively
mode-locked laser (MLL) frequency comb. We achieved a local strain resolution
of 18 p{\epsilon}/Hz1/2 and 1.9 p{\epsilon}/Hz1/2 at 1 Hz and 3 kHz,
respectively, with largedynamic range of >154 dB at 3 kHz. For remote-point
sensing at 1-km distance, 80 p{\epsilon}/Hz1/2 (at 1 Hz) and 2.2
p{\epsilon}/Hz1/2 (at 3 kHz) resolution is demonstrated. While attaining both
ultrahigh resolution and large dynamic range, the demonstrated method can be
readily extended for multiple-point sensing as well by taking advantage of the
broad optical comb spectra. These advantages may allow various applications of
this sensor in geophysical science, structural health monitoring, and
underwater science.Comment: 20 pages, 4 figure
Interplay of Polarization and Time-Reversal Symmetry Breaking in Synchronously Pumped Ring Resonators
Optically induced breaking of symmetries plays an important role in nonlinear
photonics, with applications ranging from optical switching in integrated
photonic circuits to soliton generation in ring lasers. In this work we study
for the first time the interplay of two types of spontaneous symmetry breaking
that can occur simultaneously in optical ring resonators. Specifically we
investigate a ring resonator (e.g. a fiber loop resonator or whispering gallery
microresonator) that is synchronously pumped with short pulses of light. In
this system we numerically study the interplay and transition between regimes
of temporal symmetry breaking (in which pulses in the resonator either run
ahead or behind the seed pulses) and polarization symmetry breaking (in which
the resonator spontaneously generates elliptically polarized light out of
linearly polarized seed pulses). We find ranges of pump parameters for which
each symmetry breaking can be independently observed, but also a regime in
which a dynamical interplay takes place. Besides the fundamentally interesting
physics of the interplay of different types of symmetry breaking, our work
contributes to a better understanding of the nonlinear dynamics of optical ring
cavities which are of interest for future applications including all-optical
logic gates, synchronously pumped optical frequency comb generation, and
resonator-based sensor technologies
Real-time imaging of standing-wave patterns in microresonators
Real-time characterization of microresonator dynamics is important for many
applications. In particular it is critical for near-field sensing and
understanding light-matter interactions. Here, we report camera-facilitated
imaging and analysis of standing wave patterns in optical ring resonators. The
standing wave pattern is generated through bi-directional pumping of a
microresonator and the scattered light from the microresonator is collected by
a short-wave infrared (SWIR) camera. The recorded scattering patterns are
wavelength dependent, and the scattered intensity exhibits a linear relation
with the circulating power within the microresonator. By modulating the
relative phase between the two pump waves, we can control the generated
standing waves movements and characterize the resonator with the SWIR camera.
The visualized standing wave enables subwavelength distance measurements of
scattering targets with nanometer-level accuracy. This work opens new avenues
for applications in on-chip near-field (bio-)sensing, real time
characterization of photonic integrated circuits and backscattering control in
telecom systems
Spectral extension and synchronization of microcombs in a single microresonator
Abstract
Broadband optical frequency combs are extremely versatile tools for precision spectroscopy, ultrafast ranging, as channel generators for telecom networks, and for many other metrology applications. Here, we demonstrate that the optical spectrum of a soliton microcomb generated in a microresonator can be extended by bichromatic pumping: one laser with a wavelength in the anomalous dispersion regime of the microresonator generates a bright soliton microcomb while another laser in the normal dispersion regime both compensates the thermal effect of the microresonator and generates a repetition-rate-synchronized second frequency comb. Numerical simulations agree well with experimental results and reveal that a bright optical pulse from the second pump is passively formed in the normal dispersion regime and trapped by the primary soliton. In addition, we demonstrate that a dispersive wave can be generated and influenced by cross-phase-modulation-mediated repetition-rate synchronization of the two combs. The demonstrated technique provides an alternative way to generate broadband microcombs and enables the selective enhancement of optical power in specific parts of a comb spectrum