Ki Youl Yang
California Institute of Technology
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Featured researches published by Ki Youl Yang.
Optica | 2015
Xu Yi; Qi-Fan Yang; Ki Youl Yang; Myoung-Gyun Suh; Kerry J. Vahala
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-Q silica resonators. The resonators produce low-phase-noise soliton pulse trains at readily detectable pulse rates—two essential properties for the operation of frequency combs. A method for the long-term stabilization of the solitons is also demonstrated, and is used to test the theoretical dependence of the comb power, efficiency, and soliton existence power on the pulse width. The influence of the Raman process on the soliton existence power and efficiency is also observed. The resonators are microfabricated on silicon chips and feature reproducible modal properties required for soliton formation. A low-noise and detectable pulse rate soliton frequency comb on a chip is a significant step towards a fully integrated frequency comb system.
Optics Letters | 2016
Xu Yi; Qi-Fan Yang; Ki Youl Yang; Kerry J. Vahala
Soliton mode locking and femtosecond pulse generation have recently been demonstrated in high-Q optical microcavities and provide a new way to miniaturize frequency comb systems, as well as create integrated comb systems on a chip. However, triggering the mode-locking process is complicated by a well-known thermal hysteresis that can destabilize the solitons. Moreover, on a longer time scale, thermal drifting of the cavity resonant frequency relative to the pumping frequency causes loss of mode locking. In this Letter, an active feedback method is used both to capture specific soliton states and to stabilize the states indefinitely. The capture and stabilization method provides a reliable way to overcome thermal effects during soliton formation and to excite a desired number of circulating cavity solitons. It is also used to demonstrate a low pumping power of 22 mW for generation of microwave-repetition-rate solitons on a chip.
Nature Physics | 2016
Qi-Fan Yang; Xu Yi; Ki Youl Yang; Kerry J. Vahala
A soliton is reported that regenerates by optimizing its Raman interaction with another soliton within a shared optical potential well. The soliton is observed in a high-Q silica optical microcavity.
Optics Express | 2012
Jiang Li; Hansuek Lee; Ki Youl Yang; Kerry J. Vahala
The measurement of dispersion and its control have become important considerations in nonlinear devices based on microcavities. A sideband technique is applied here to accurately measure dispersion in a microcavity resulting from both geometrical and material contributions. Moreover, by combining the method with finite element simulations, we show that mapping of spectral lines to their corresponding transverse mode families is possible. The method is applicable for high-Q, micro-cavities having microwave rate free spectral range and has a relative precision of 5.5 × 10(-6) for a 2 mm disk cavity with FSR of 32.9382 GHz and Q of 150 milllion.
Optics Letters | 2014
Dong Yoon Oh; David Sell; Hansuek Lee; Ki Youl Yang; Scott A. Diddams; Kerry J. Vahala
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.
Nature Photonics | 2016
Ki Youl Yang; Katja Beha; Daniel C. Cole; Xu Yi; Pascal Del'Haye; Hansuek Lee; Jiang Li; Dong Yoon Oh; Scott A. Diddams; Scott B. Papp; Kerry J. Vahala
The 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 the fibre core diameter or index step. Moreover, sophisticated methods to manipulate higher-order dispersion so as to shape and even flatten the dispersion over wide bandwidths are possible using multi-cladding fibres. 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 the efficient operation of nonlinear optical oscillators. Dispersion control in high-Q systems has become of great importance in recent years with increased interest in chip-integrable optical frequency combs.
Nature | 2018
Daryl T. Spencer; Tara E. Drake; Travis C. Briles; Jordan R. Stone; Laura C. Sinclair; Connor Fredrick; Qing Li; Daron A. Westly; B. Robert Ilic; Aaron Bluestone; Nicolas Volet; Tin Komljenovic; Lin Chang; Seung Hoon Lee; Dong Yoon Oh; Myoung-Gyun Suh; Ki Youl Yang; Martin H. P. Pfeiffer; Tobias J. Kippenberg; Erik J. Norberg; Luke Theogarajan; Kerry J. Vahala; Nathan R. Newbury; Kartik Srinivasan; John E. Bowers; Scott A. Diddams; Scott B. Papp
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 7.0x10^(−13) reference-clock instability for a 1 second acquisition, and constrain any synthesis error to 7.7x10^(−15) 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.Optical-frequency synthesizers, which generate frequency-stable light from a single microwave-frequency reference, are revolutionizing ultrafast science and metrology, but their size, power requirement and cost need to be reduced if they are to be more widely used. Integrated-photonics microchips can be used in high-coherence applications, such as data transmission1, highly optimized physical sensors2 and harnessing quantum states3, to lower cost and increase efficiency and portability. Here we describe a method for synthesizing the absolute frequency of a lightwave signal, using integrated photonics to create a phase-coherent microwave-to-optical link. We use a heterogeneously integrated III–V/silicon tunable laser, which is guided by nonlinear frequency combs fabricated on separate silicon chips and pumped by off-chip lasers. The laser frequency output of our optical-frequency synthesizer can be programmed by a microwave clock across 4 terahertz near 1,550 nanometres (the telecommunications C-band) with 1 hertz resolution. Our measurements verify that the output of the synthesizer is exceptionally stable across this region (synthesis error of 7.7 × 10−15 or below). Any application of an optical-frequency source could benefit from the high-precision optical synthesis presented here. Leveraging high-volume semiconductor processing built around advanced materials could allow such low-cost, low-power and compact integrated-photonics devices to be widely used.An optical-frequency synthesizer based on stabilized frequency combs has been developed utilizing chip-scale devices as key components, in a move towards using integrated photonics technology for ultrafast science and metrology.
Nature Communications | 2017
Dong Yoon Oh; Ki Youl Yang; Connor Fredrick; Gabriel Ycas; Scott A. Diddams; Kerry J. Vahala
Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip. Unlike fibre broadeners, the arrays provide a wide range of emission wavelength choices on a single, compact chip. This new capability is used to simplify offset frequency measurements of a mode-locked frequency comb. The arrays can also enable mode-locked lasers to attain unprecedented tunable spectral reach for spectroscopy, bioimaging, tomography and metrology.
Optics Letters | 2016
Xu Yi; Qi-Fan Yang; Ki Youl Yang; Kerry J. Vahala
Dissipative Kerr cavity solitons experience a so-called self-frequency shift (SFS) as a result of Raman interactions. The frequency shift has been observed in several microcavity systems. The Raman process has also been shown numerically to influence the soliton pumping efficiency. Here, a perturbed Lagrangian approach is used to derive simple analytical expressions for the SFS and the soliton efficiency. The predicted dependences of these quantities on soliton pulse width are compared with measurements in a high-Q silica microcavity. The Raman time constant in silica is also inferred. Analytical expressions for the Raman SFS and soliton efficiency greatly simplify the prediction of soliton behavior over a wide range of microcavity platforms.
arXiv: Optics | 2016
Qi-Fan Yang; Xu Yi; Ki Youl Yang; Kerry J. Vahala
The nonlinear propagation of optical pulses in dielectric waveguides and resonators provides a laboratory to investigate a wide range of remarkable interactions. Many of the resulting phenomena find applications in optical systems. One example is dispersive wave generation, the optical analog of Cherenkov radiation. These waves have an essential role in fiber spectral broadeners that are routinely used in spectrocopy and metrology. Dispersive waves form when a soliton pulse begins to radiate power as a result of higher-order dispersion. Recently, dispersive wave generation in microcavities has been reported by phase matching the waves to dissipative Kerr cavity (DKC) solitons. Here, it is shown that spatial mode interactions within a microcavity can also be used to induce dispersive waves. These interactions are normally avoided altogether in DKC soliton generation. The soliton self frequency shift is also shown to induce fine tuning control of the dispersive wave frequency. Both this mechanism and spatial mode interactions provide a new method to spectrally control these important waves.