84 research outputs found
An Integrated-Photonics Optical-Frequency Synthesizer
Integrated-photonics microchips now enable a range of advanced
functionalities for high-coherence applications such as data transmission,
highly optimized physical sensors, and harnessing quantum states, but with
cost, efficiency, and portability much beyond tabletop experiments. Through
high-volume semiconductor processing built around advanced materials there
exists an opportunity for integrated devices to impact applications cutting
across disciplines of basic science and technology. Here we show how to
synthesize the absolute frequency of a lightwave signal, using integrated
photonics to implement lasers, system interconnects, and nonlinear frequency
comb generation. The laser frequency output of our synthesizer is programmed by
a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and
traceability to the SI second. This is accomplished with a heterogeneously
integrated III/V-Si tunable laser, which is guided by dual
dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through
out-of-loop measurements of the phase-coherent, microwave-to-optical link, we
verify that the fractional-frequency instability of the integrated photonics
synthesizer matches the reference-clock instability for a 1
second acquisition, and constrain any synthesis error to while
stepping the synthesizer across the telecommunication C band. Any application
of an optical frequency source would be enabled by the precision optical
synthesis presented here. Building on the ubiquitous capability in the
microwave domain, our results demonstrate a first path to synthesis with
integrated photonics, leveraging low-cost, low-power, and compact features that
will be critical for its widespread use.Comment: 10 pages, 6 figure
Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators
Recent advances in nonlinear optics have revolutionized integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as SiâNâ and SiOâ. While semiconductor materials feature much higher nonlinear coefficients and convenience in active integration, they have suffered from high waveguide losses that prevent the realization of efficient nonlinear processes on-chip. Here, we challenge this status quo and demonstrate a low loss AlGaAs-on-insulator platform with anomalous dispersion and quality (Q) factors beyond 1.5âĂâ10â¶. Such a high quality factor, combined with high nonlinear coefficient and small mode volume, enabled us to demonstrate a Kerr frequency comb threshold of only âŒ36â”W in a resonator with a 1âTHz free spectral range, âŒ100 times lower compared to that in previous semiconductor platforms. Moreover, combs with broad spans (>250ânm) have been generated with a pump power of âŒ300â”W, which is lower than the threshold power of state-of the-art dielectric micro combs. A soliton-step transition has also been observed for the first time in an AlGaAs resonator
Microresonator-referenced soliton microcombs with zeptosecond-level timing noise
Optical frequency division relies on optical frequency combs to coherently
translate ultra-stable optical frequency references to the microwave domain.
This technology has enabled microwave synthesis with ultralow timing noise, but
the required instruments are too bulky for real-world applications. Here, we
develop a compact optical frequency division system using microresonator-based
frequency references and comb generators. The soliton microcomb formed in an
integrated SiN microresonator is stabilized to two lasers referenced to
an ultrahigh- MgF microresonator. Photodetection of the soliton pulse
train produces 25 GHz microwaves with absolute phase noise of -141 dBc/Hz (547
zs Hz) at 10 kHz offset frequency. The synthesized microwaves are
tested as local oscillators in jammed communication channels, resulting in
improved fidelity compared with those derived from electronic oscillators. Our
work demonstrates unprecedented coherence in miniature microwave oscillators,
providing key building blocks for next-generation timekeeping, navigation, and
satellite communication systems.Comment: 8 pages, 7 figures and table
Integrated turnkey soliton microcombs operated at CMOS frequencies
While soliton microcombs offer the potential for integration of powerful
frequency metrology and precision spectroscopy systems, their operation
requires complex startup and feedback protocols that necessitate
difficult-to-integrate optical and electrical components. Moreover, CMOS-rate
microcombs, required in nearly all comb systems, have resisted integration
because of their power requirements. Here, a regime for turnkey operation of
soliton microcombs co-integrated with a pump laser is demonstrated and
theoretically explained. Significantly, a new operating point is shown to
appear from which solitons are generated through binary turn-on and turn-off of
the pump laser, thereby eliminating all photonic/electronic control circuitry.
These features are combined with high-Q resonators to fully integrate
into a butterfly package microcombs with CMOS frequencies as low as 15 GHz,
offering compelling advantages for high-volume production.Comment: Boqiang Shen, Lin Chang, Junqiu Liu, Heming Wang and Qi-Fan Yang
contributed equally to this wor
Stability of laser cavity-solitons for metrological applications
Laser cavity-solitons can appear in systems comprised of a nonlinear microcavity nested within an amplifying fiber loop. These states are robust and self-emergent and constitute an attractive class of solitons that are highly suitable for microcomb generation. Here, we present a detailed study of the free-running stability properties of the carrier frequency and repetition rate of single solitons, which are the most suitable states for developing robust ultrafast and high repetition rate comb sources. We achieve free-running fractional stability on both optical carrier and repetition rate (i.e., 48.9 GHz) frequencies on the order of 10^-9 for a 1 s gate time. The repetition rate results compare well with the performance of state-of-the-art (externally driven) microcomb sources, and the carrier frequency stability is in the range of performance typical of modern free-running fiber lasers. Finally, we show that these quantities can be controlled by modulating the laser pump current and the cavity length, providing a path for active locking and long-term stabilization
Electrically empowered microcomb laser
Optical frequency comb underpins a wide range of applications from
communication, metrology, to sensing. Its development on a chip-scale platform
-- so called soliton microcomb -- provides a promising path towards system
miniaturization and functionality integration via photonic integrated circuit
(PIC) technology. Although extensively explored in recent years, challenges
remain in key aspects of microcomb such as complex soliton initialization, high
threshold, low power efficiency, and limited comb reconfigurability. Here we
present an on-chip laser that directly outputs microcomb and resolves all these
challenges, with a distinctive mechanism created from synergetic interaction
among resonant electro-optic effect, optical Kerr effect, and optical gain
inside the laser cavity. Realized with integration between a III-V gain chip
and a thin-film lithium niobate (TFLN) PIC, the laser is able to directly emit
mode-locked microcomb on demand with robust turnkey operation inherently built
in, with individual comb linewidth down to 600 Hz, whole-comb frequency tuning
rate exceeding Hz/s, and 100% utilization of optical
power fully contributing to comb generation. The demonstrated approach unifies
architecture and operation simplicity, high-speed reconfigurability, and
multifunctional capability enabled by TFLN PIC, opening up a great avenue
towards on-demand generation of mode-locked microcomb that is expected to have
profound impact on broad applications
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