117 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
Broadband quantum-dot frequency-modulated comb laser
Frequency-modulated (FM) laser combs, which offer a periodic
quasi-continuous-wave output and a flat-topped optical spectrum, are emerging
as a promising solution for wavelength-division multiplexing applications,
precision metrology, and ultrafast optical ranging. The generation of FM combs
relies on spatial hole burning, group velocity dispersion (GVD), Kerr
nonlinearity, and four-wave mixing (FWM). While FM combs have been widely
observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a
low-dispersion FP cavity can be a challenge in platforms where the waveguide
dispersion is mainly determined by the material. Here we report a 60 GHz
quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM)
and the FM comb can be generated independently. The high FWM efficiency of -5
dB allows the QD laser to generate an FM comb efficiently. We also demonstrate
that the Kerr nonlinearity can be practically engineered to improve the FM comb
bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that
our QD platform can deliver is as large as 2.2 THz. This study gives novel
insights into the improvement of FM combs and paves the way for
small-footprint, electrically-pumped, and energy-efficient frequency combs for
silicon photonic integrated circuits (PICs)
Unveiling the dynamical diversity of quantum dot lasers subject to optoelectronic feedback
This paper investigates experimentally and numerically the nonlinear dynamics
of an epitaxial quantum dot laser on silicon subjected to optoelectronic
feedback. Experimental results showcase a diverse range of dynamics,
encompassing square wave patterns, quasi-chaotic states, and mixed waveforms
exhibiting fast and slow oscillations. These measurements unequivocally
demonstrate that quantum dot lasers on silicon readily and stably generate a
more extensive repertoire of nonlinear dynamics compared to quantum well
lasers. This pronounced sensitivity of quantum dot lasers to optoelectronic
feedback represents a notable departure from their inherent insensitivity to
optical feedback arising from reflections. Moreover, based on the Ikeda-like
model, our simulations illustrate that the inherent characteristics of quantum
dot lasers on silicon enable rapid and diverse dynamic transformations in
response to optoelectronic feedback. The emergence of these exotic dynamics
paves the way for further applications like integrated optical clocks, optical
logic, and optical computing
Soliton pulse pairs at multiple colors in normal dispersion microresonators
Soliton microcombs are helping to advance the miniaturization of a range of
comb systems. These combs mode lock through the formation of short temporal
pulses in anomalous dispersion resonators. Here, a new microcomb is
demonstrated that mode locks through the formation of pulse pairs in
normal-dispersion coupled-ring resonators. Unlike conventional microcombs,
pulses in this system cannot exist alone, and instead must phase lock in pairs
to form a bright soliton comb. Also, the pulses can form at recurring spectral
windows and the pulses in each pair feature different optical spectra. This
pairwise mode-locking modality extends to higher dimensions and we demonstrate
3-ring systems in which 3 pulses mode lock through alternating pairwise pulse
coupling. The results are demonstrated using the new CMOS-foundry platform that
has not previously produced bright solitons on account of its inherent normal
dispersion. The ability to generate multi-color pulse pairs over multiple rings
is an important new feature for microcombs. It can extend the concept of
all-optical soliton buffers and memories to multiple storage rings that
multiplex pulses with respect to soliton color and that are spatially
addressable. The results also suggest a new platform for the study of quantum
combs and topological photonics
Hertz-linewidth semiconductor lasers using CMOS-ready ultra-high- microresonators
Driven by narrow-linewidth bench-top lasers, coherent optical systems
spanning optical communications, metrology and sensing provide unrivalled
performance. To transfer these capabilities from the laboratory to the real
world, a key missing ingredient is a mass-produced integrated laser with
superior coherence. Here, we bridge conventional semiconductor lasers and
coherent optical systems using CMOS-foundry-fabricated microresonators with
record high factor over 260 million and finesse over 42,000. Five
orders-of-magnitude noise reduction in the pump laser is demonstrated, and for
the first time, fundamental noise below 1 Hz Hz is achieved in an
electrically-pumped integrated laser. Moreover, the same configuration is shown
to relieve dispersion requirements for microcomb generation that have
handicapped certain nonlinear platforms. The simultaneous realization of
record-high factor, highly coherent lasers and frequency combs using
foundry-based technologies paves the way for volume manufacturing of a wide
range of coherent optical systems.Comment: 19 pages, 11 figure
Probing material absorption and optical nonlinearity of integrated photonic materials
Optical microresonators with high quality () factors are essential to a
wide range of integrated photonic devices. Steady efforts have been directed
towards increasing microresonator factors across a variety of platforms.
With success in reducing microfabrication process-related optical loss as a
limitation of , the ultimate attainable , as determined solely by the
constituent microresonator material absorption, has come into focus. Here, we
report measurements of the material-limited factors in several photonic
material platforms. High- microresonators are fabricated from thin films of
SiO, SiN, AlGaAs and TaO. By using
cavity-enhanced photothermal spectroscopy, the material-limited is
determined. The method simultaneously measures the Kerr nonlinearity in each
material and reveals how material nonlinearity and ultimate vary in a
complementary fashion across photonic materials. Besides guiding microresonator
design and material development in four material platforms, the results help
establish performance limits in future photonic integrated systems.Comment: Maodong Gao, Qi-Fan Yang and Qing-Xin Ji contributed equally to this
work. 9 pages, 4 figures, 1 tabl
Engineered zero-dispersion microcombs using CMOS-ready photonics
Normal group velocity dispersion (GVD) microcombs offer high comb line power
and high pumping efficiency compared to bright pulse microcombs. The recent
demonstration of normal GVD microcombs using CMOS-foundry-produced
microresonators is an important step towards scalable production. However, the
chromatic dispersion of CMOS devices is large and impairs generation of
broadband microcombs. Here, we report the development of a microresonator in
which GVD is reduced due to a couple-ring resonator configuration. Operating in
the turnkey self-injection-locking mode, the resonator is hybridly integrated
with a semiconductor laser pump to produce high-power-efficiency combs spanning
a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb
lines. Fast, linear optical sampling of the comb waveform is used to observe
the rich set of near-zero GVD comb behaviors, including soliton molecules,
switching waves (platicons) and their hybrids. Tuning of the 20 GHz repetition
rate by electrical actuation enables servo locking to a microwave reference,
which simultaneously stabilizes the comb repetition rate, offset frequency and
temporal waveform. This hybridly integrated system could be used in coherent
communications or for ultra-stable microwave signal generation by two-point
optical frequency division.Comment: 8 pages, 4 figure
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