Kerry J. Vahala

California Institute of Technology, Pasadena, California, United States

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Publications (407)1356.04 Total impact

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    Preview · Article · Jan 2016 · Nature Communications
  • Xu Yi · Qi-Fan Yang · Ki Youl Yang · Myoung-Gyun Suh · Kerry Vahala
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    ABSTRACT: Frequency combs are having a broad impact on science and technology because they provide a way to coherently link radio/microwave-rate electrical signals with optical-rate signals derived from lasers and atomic transitions. Integrating these systems on a photonic chip would revolutionize instrumentation, time keeping, spectroscopy, navigation, and potentially create new mass-market applications. A key element of such a system-on-a-chip will be a mode-locked comb that can be self-referenced. The recent demonstration of soliton mode locking in crystalline and silicon nitride microresonators has provided a way to both mode lock and generate femtosecond time-scale pulses. Here, soliton mode locking is demonstrated in high-
    No preview · Article · Dec 2015 · Optica
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    ABSTRACT: The counting and control of optical cycles of light has become common with modelocked laser frequency combs. But even with advances in laser technology, modelocked laser combs remain bulk-component devices that are hand-assembled. In contrast, a frequency comb based on the Kerr-nonlinearity in a dielectric microresonator will enable frequency comb functionality in a micro-fabricated and chip-integrated package suitable for use in a wide-range of environments. Such an advance will significantly impact fields ranging from spectroscopy and trace gas sensing, to astronomy, communications, atomic time keeping and photonic data processing. Yet in spite of the remarkable progress shown over the past years, microresonator frequency combs ("microcombs") have still been without the key function of direct f-2f self-referencing and phase-coherent frequency control that will be critical for enabling their full potential. Here we realize these missing elements using a low-noise 16.4 GHz silicon chip microcomb that is coherently broadened from its initial 1550 nm wavelength and subsequently f-2f self-referenced and phase-stabilized to an atomic clock. With this advance, we not only realize the highest repetition rate octave-span frequency comb ever achieved, but we highlight the low-noise microcomb properties that support highest atomic clock limited frequency stability.
    Full-text · Article · Nov 2015
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    Xu Yi · Qi-Fan Yang · Ki Youl Yang · Myoung-Gyun Suh · Kerry Vahala
    [Show abstract] [Hide abstract]
    ABSTRACT: Because they coherently link radio/microwave-rate electrical signals with optical-rate signals derived from lasers and atomic transitions, frequency combs are having a remarkably broad impact on science and technology. Integrating these systems on a photonic chip would revolutionize instrumentation, time keeping, spectroscopy, navigation and potentially create new mass-market applications. A key element of such a system-on-a-chip will be a mode-locked comb that can be self-referenced. The recent demonstration of soliton pulses from a microresonator has placed this goal within reach. However, to provide the requisite link between microwave and optical rate signals soliton generation must occur within the bandwidth of electronic devices. So far this is possible in crytalline devices, but not chip-based devices. Here, a monolithic comb that generates electronic-rate soliton pulses is demonstrated.
    Preview · Article · Aug 2015
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    ABSTRACT: Control of dispersion in fibre optical waveguides is of critical importance to optical fibre communications systems and more recently for continuum generation from the ultraviolet to the mid-infrared. The wavelength at which the group velocity dispersion crosses zero can be set by varying fibre core diameter or index step. Moreover, sophisticated methods to manipulate higher-order dispersion so as shape and even flatten dispersion over wide bandwidths are possible using multi-cladding fibre. Here we introduce design and fabrication techniques that allow analogous dispersion control in chip-integrated optical microresonators, and thereby demonstrate higher-order, wide-bandwidth dispersion control over an octave of spectrum. Importantly, the fabrication method we employ for dispersion control simultaneously permits optical Q factors above 100 million, which is critical for efficient operation of nonlinear optical oscillators. Dispersion control in high Q systems has taken on greater importance in recent years with increased interest in chip-integrable optical frequency combs.
    Full-text · Article · Jun 2015
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    ABSTRACT: We demonstrate a Brillouin microcavity laser based on a microrod resonator exhibiting a frequency noise of 140 Hz/√Hz at 10 Hz offset. The corresponding laser linewidth is measured to be below 400 Hz.
    No preview · Article · May 2015
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    ABSTRACT: We describe a successful effort to produce a laser comb around 1.55 $\mu$m in the astronomical H band using a method based on a line-referenced, electro-optical-modulation frequency comb. We discuss the experimental setup, laboratory results, and proof of concept demonstrations at the NASA Infrared Telescope Facility (IRTF) and the Keck-II telescope. The laser comb has a demonstrated stability of $<$ 200 kHz, corresponding to a Doppler precision of ~0.3 m/s. This technology, when coupled with a high spectral resolution spectrograph, offers the promise of $<$1 m/s radial velocity precision suitable for the detection of Earth-sized planets in the habitable zones of cool M-type stars.
    Full-text · Article · Jan 2015
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    ABSTRACT: We demonstrate the combination of a tunable Brillouin microcavity laser and a second reference microcavity that together provide a compact 1550 nm laser source with fractional noise < 7.8×10-14 1/√Hz at 10 Hz offset.
    No preview · Article · Oct 2014
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    ABSTRACT: Ultralow noise, yet tunable lasers are a revolutionary tool in precision spectroscopy, displacement measurements at the standard quantum limit, and the development of advanced optical atomic clocks. Further applications include LIDAR, coherent communications, frequency synthesis, and precision sensors of strain, motion, and temperature. While all applications benefit from lower frequency noise, many also require a laser that is robust and compact. Here, we introduce a dual-microcavity laser that leverages one chip-integrable silica microresonator to generate tunable 1550 nm laser light via stimulated Brillouin scattering (SBS) and a second microresonator for frequency stabilization of the SBS light. This configuration reduces the fractional frequency noise to $7.8\times10^{-14} 1/\sqrt{Hz}$ at 10 Hz offset, which is a new regime of noise performance for a microresonator-based laser. Our system also features terahertz tunability and the potential for chip-level integration. We demonstrate the utility of our dual-microcavity laser by performing optical spectroscopy with hertz-level resolution.
    Preview · Article · Oct 2014 · Optica
  • Jiang Li · Xu Yi · Hansuek Lee · Scott A Diddams · Kerry J Vahala
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    ABSTRACT: Optical frequency division by using frequency combs has revolutionized time keeping and the generation of stable microwave signals. We demonstrate optical frequency division and microwave generation by using a tunable electrical oscillator to create dual combs through phase modulation of two optical signals that have a stable difference frequency. Phase-locked control of the electrical oscillator by means of optical frequency division produces stable microwaves. Our approach transposes the oscillator and frequency reference of a conventional microwave frequency synthesizer. In this way, the oscillator experiences large phase noise reduction relative to the frequency reference. The electro-optical approach additionally relaxes the need for highly linear photodetection of the comb mode spacing. As well as simplicity, the technique is also tunable and scalable to higher division ratios.
    No preview · Article · Jul 2014 · Science
  • Jiang Li · Scott Diddams · Kerry J Vahala
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    ABSTRACT: As thermo-optic locking is widely used to establish a stable frequency detuning between an external laser and a high Q microcavity, it is important to understand how this method affects microcavity temperature and frequency fluctuations. A theoretical analysis of the laser-microcavity frequency fluctuations is presented and used to find the spectral dependence of the suppression of laser-microcavity, relative frequency noise caused by thermo-optic locking. The response function is that of a high-pass filter with a bandwidth and low-frequency suppression that increase with input power. The results are verified using an external-cavity diode laser and a silica disk resonator. The locking of relative frequency fluctuations causes temperature fluctuations within the microcavity that transfer pump frequency noise onto the microcavity modes over the thermal locking bandwidth. This transfer is verified experimentally. These results are important to investigations of noise properties in many nonlinear microcavity experiments in which low-frequency, optical-pump frequency noise must be considered.
    No preview · Article · Jun 2014 · Optics Express
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    ABSTRACT: A low-loss silica spiral waveguide is used for demonstrating on-chip supercontinuum generation. The broadest measured spectrum spans an octave (936 - 1888 nm) at -50 dB from peak when 2.17 nJ pulses are launched.
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: We demonstrate an optical clock based on stabilization of a microcomb to rubidium optical transitions. The clock’s output is the 33 GHz microcomb line spacing, which is a coherent, integer sub-division of the rubidium reference.
    No preview · Conference Paper · Jun 2014
  • Tong Chen · Hansuek Lee · Kerry J Vahala
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    ABSTRACT: Whispering gallery delay lines have demonstrated record propagation length on a silicon chip and can provide a way to transfer certain applications of optical fiber to wafer-based systems. Their design and fabrication requires careful control of waveguide curvature and etching conditions to minimize connection losses between elements of the delay line. Moreover, loss characterization based on optical backscatter requires normalization to account for the impact of curvature on backscatter rate. In this paper we provide details on design of Archimedean whispering-gallery spiral waveguides, their coupling into cascaded structures, as well as optical loss characterization by optical backscatter reflectometry.
    No preview · Article · Mar 2014 · Optics Express
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    ABSTRACT: Supercontinuum generation is demonstrated in an on-chip silica spiral waveguide by launching 180 fs pulses from an optical parametric oscillator at the center wavelength of 1330 nm. With a coupled pulse energy of 2.17 nJ, the broadest spectrum in the fundamental TM mode extends from 936 to 1888 nm (162 THz) at -50 dB from peak. There is a good agreement between the measured spectrum and a simulation using a generalized nonlinear Schrödinger equation.
    Full-text · Article · Feb 2014 · Optics Letters
  • Jiang Li · Hansuek Lee · Kerry J Vahala
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    ABSTRACT: We demonstrate narrow-linewidth-stimulated Brillouin lasers at 1064 nm from ultra-high-Q silica wedge disk resonators on silicon. Fundamental Schawlow-Townes frequency noise of the laser is on the order of 0.1 Hz<sup>2</sup>/Hz. The technical noise spectrum of the on-chip Brillouin laser is close to the thermodynamic noise limit of the resonator (thermorefractive noise) and is comparable to that of ultra-narrow-linewidth Nd:YAG lasers. The relative intensity noise of the Brillouin laser also is reduced by using an intensity-stabilized pump laser. Finally, low-noise microwave synthesis up to 32 GHz is demonstrated by heterodyne of first and third Brillouin Stokes lines from a single resonator.
    No preview · Article · Jan 2014 · Optics Letters
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    ABSTRACT: Frequency references are indispensable to radio, microwave and time keeping systems, with far reaching applications in navigation, communication, remote sensing and basic science. Over the past decade, there has been an optical revolution in time keeping and microwave generation that promises to ultimately impact all of these areas. Indeed, the most precise clocks and lowest noise microwave signals are now based on a laser with short-term stability derived from a reference cavity. In spite of the tremendous progress, these systems remain essentially laboratory devices and there is interest in their miniaturization, even towards on-chip systems. Here we describe a chip-based optical reference cavity that uses spatial averaging of thermorefractive noise to enhance resonator stability. Stabilized fibre lasers exhibit relative Allan deviation of 3.9x10^-13 at 400 microµs averaging time and an effective linewidth <100 Hz by achieving over 26 dB of phase-noise reduction.
    Preview · Article · Sep 2013 · Nature Communications
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    ABSTRACT: Optical-frequency combs enable measurement precision at the 20th digit, and accuracy entirely commensurate with their reference oscillator. A new direction in experiments is the creation of ultracompact frequency combs by way of nonlinear parametric optics in microresonators. We refer to these as microcombs, and here we report a silicon-chip-based microcomb optical clock that phase-coherently converts an optical-frequency reference to a microwave signal. A low-noise comb spectrum with 25 THz span is generated with a 2 mm diameter silica disk and broadening in nonlinear fiber. This spectrum is stabilized to rubidium frequency references separated by 3.5 THz by controlling two teeth 108 modes apart. The optical clocks output is the electronically countable 33 GHz microcomb line spacing, which features an absolute stability better than the rubidium transitions by the expected factor of 108. Our work demonstrates the comprehensive set of tools needed for interfacing microcombs to state-of-the-art optical clocks.
    Preview · Article · Sep 2013 · Optica
  • Kerry Vahala · Hansuek Lee · Jiang Li · Tong Chen
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    ABSTRACT: form only given. High-Q performance in microcavities relies upon use of low absorption dielectrics and creation of smooth dielectric interfaces. For chip-compatible devices, silica has the lowest intrinsic material loss [1]. Microtoroid resonators combine this low material loss with a reflow technique in which surface tension is used to smooth lithographic and etch-related blemishes [2]. At the same time, reflow smoothing makes it very challenging to fabricate larger diameter UHQ resonators and likewise to leverage the full range of integration tools and devices available on silicon. The devices reported here attain Q factors as high as 875 million using only conventional semiconductor processing methods [3]. Moreover, the best Q performance occurs for diameters greater than 500 microns, a size range that is difficult to access using microtoroids on account of the limitations of the reflow process. Fabrication control of the free-spectral range to 1:20,000 is also demonstrated, opening the possibility of precision repetition rate control in microcombs [4] or precision spectral placement of modes in certain nonlinear oscillators [3,5,6]. As an application, the use of these devices in microcombs [5] and also for microwave generation by stimulated Brillouin scattering will be described [6]. For the latter, a microwave synthesizer with performance comparable to mid-range commercial systems is demonstrated. Finally, the resonator micro-fabrication process also lends itself to creation of record low loss waveguides on chip. Delay lines as long as 27 meters will be described in which waveguide loss is less than 0.1 dB/m [7].
    No preview · Conference Paper · Sep 2013
  • Jiang Li · Hansuek Lee · Kerry J Vahala
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    ABSTRACT: Low-phase-noise microwave oscillators are important to a wide range of subjects, including communications, radar and metrology. Photonic-based microwave-wave sources now provide record, close-to-carrier phase-noise performance, and compact sources using microcavities are available commercially. Photonics-based solutions address a challenging scaling problem in electronics, increasing attenuation with frequency. A second scaling challenge, however, is to maintain low phase noise in reduced form factor and even integrated systems. On this second front, there has been remarkable progress in the area of microcavity devices with large storage time (high optical quality factor). Here we report generation of highly coherent microwaves using a chip-based device that derives stability from high optical quality factor. The device has a record low electronic white-phase-noise floor for a microcavity-based oscillator and is used as the optical, voltage-controlled oscillator in the first demonstration of a photonic-based, microwave frequency synthesizer. The synthesizer performance is comparable to mid-range commercial devices.
    No preview · Article · Jun 2013 · Nature Communications

Publication Stats

19k Citations
1,356.04 Total Impact Points

Institutions

  • 1983-2015
    • California Institute of Technology
      • Department of Applied Physics
      Pasadena, California, United States
  • 2011
    • University of Victoria
      • Department of Electrical and Computer Engineering (ECE)
      Victoria, British Columbia, Canada
  • 2009
    • Max Planck Institute of Quantum Optics
      • Division of Laser Spectroscopy
      Arching, Bavaria, Germany
  • 1987
    • Pasadena City College
      Pasadena, Texas, United States