Query: Laser soliton microcombs heterogeneously integrated on silicon

Candidate papers:

abstract: Chip based frequency combs The realization of optical frequency combs, light sources with precisely spaced frequencies across a broad spectrum of wavelengths, in dielectric microresonators has affected a range of applications from imaging and ranging to precision time keeping and metrology. Xiang et al. demonstrate that the entire system, the laser pumping system and the comb generating microresonators, can be combined into an integrated silicon based platform. Compatibility with foundry fabrication methods will enable this innovation to have a major impact on coherent communications, optical interconnects, and low noise microwave generation. Science, abh2076, this issue p. 99 Optical microresonator frequency combs are realized in an integrated Si based platform. Silicon photonics enables wafer scale integration of optical functionalities on chip. Silicon based laser frequency combs can provide integrated sources of mutually coherent laser lines for terabit per second transceivers, parallel coherent light detection and ranging, or photonics assisted signal processing. We report heterogeneously integrated laser soliton microcombs combining both indium phospide/silicon (InP/Si) semiconductor lasers and ultralow loss silicon nitride (Si3N4) microresonators on a monolithic silicon substrate. Thousands of devices can be produced from a single wafer by using complementary metal oxide semiconductor compatible techniques. With on chip electrical control of the laser microresonator relative optical phase, these devices can output single soliton microcombs with a 100 gigahertz repetition rate. Furthermore, we observe laser frequency noise reduction due to self injection locking of the InP/Si laser to the Si3N4 microresonator. Our approach provides a route for large volume, low cost manufacturing of narrow linewidth, chip based frequency combs for next generation high capacity transceivers, data centers, space and mobile platforms.
author_names: Chao Xiang

Junqiu Liu

Joel Guo

Lin Chang

Wenle Weng

Jonathan Peters

Weiqiang Xie

Zeyu Zhang

Johann Riemensberger

Jennifer Selvidge

Tobias J Kippenberg

John E Bowers
title: Laser soliton microcombs heterogeneously integrated on silicon
venue: Science
year: 2021

abstract: A monolithic ultra high Q silica resonator featuring an integrated silicon nitride waveguide is described. The resonator can be configured for either high coherence Brillouin laser action or stable microwave rate mode locking over C band at low pumping power.
author_names: Kerry J Vahala

K -Y Yang

Dong Yoon Oh

Shing Lee

Q -F Yang

Boqiang Shen

H Wang
title: Silicon Chip Based Brillouin Lasers and Soliton Microcombs using an Integrated Ultra High Q Silica Resonator
venue: 2019 Optical Fiber Communications Conference and Exhibition (OFC)
year: 2019

abstract: Microcombs provide a path to broad bandwidth integrated frequency combs with low power consumption, which are compatible with wafer scale fabrication. Yet, electrically driven, photonic chip based microcombs are inhibited by the required high threshold power and the frequency agility of the laser for soliton initiation. Here we demonstrate an electrically driven soliton microcomb by coupling a III V material based (indium phosphide) multiple longitudinal mode laser diode chip to a high Q silicon nitride microresonator fabricated using the photonic Damascene process. The laser diode is self injection locked to the microresonator, which is accompanied by the narrowing of the laser linewidth, and the simultaneous formation of dissipative Kerr solitons. By tuning the laser diode current, we observe transitions from modulation instability, breather solitons, to single soliton states. The system operating at an electronically detectable sub 100 GHz mode spacing requires less than 1 Watt of electrical power, can fit in a volume of ca. 1 cm3, and does not require on chip filters and heaters, thus simplifying the integrated microcomb.Chip based frequency combs promise many applications, but full integration requires the electrical pump source and the microresonator to be on the same chip. Here, the authors show such integration of a microcomb with 100 GHz mode spacing without additional filtering cavities or on chip heaters.
author_names: Arslan S Raja

Andrey S Voloshin

Hairun Guo

Sofya E Agafonova

Junqiu Liu

Alexander S Gorodnitskiy

Maxim Karpov

Nikolay G Pavlov

Erwan Lucas

Ramzil R Galiev

Artem E Shitikov

John D Jost

Michael L Gorodetsky

Tobias J Kippenberg
title: Electrically pumped photonic integrated soliton microcomb
venue: Nature Communications
year: 2019

abstract: Soliton microcombs constitute miniaturized optical frequency combs and have already been used for coherent telecommunications, astronomical spectrometer calibration and ultrafast ranging. The majority of these applications have utilized silicon nitride (Si$_3$N$_4$ a space and CMOS compatible material platform featuring ultralow optical losses, suitable for integration with on chip lasers. However, soliton microcombs in Si$_3$N$_4$ at microwave repetition rates have not been achieved, which enable e.g. photonics based microwave oscillators and dense WDM channels for coherent communication, and can significantly reduce the system complexity of recently demonstrated photonic integrated frequency synthesizers and atomic clocks. Here, using the photonic Damascene reflow process, we fabricate integrated Si$_3$N$_4$ microresonators with quality factor exceeding 22 million, and demonstrate a 19.6 GHz, K band single soliton microcomb at an ultralow input power of 35 mW, without requiring a complex soliton initiation technique. This power level is on a par with silica and crystalline resonators, and compatible with integrated lasers. We utilize the device to create low noise K band microwave oscillators, with phase noise levels at 65 dBc/Hz at 1 kHz and 115 dBc/Hz at 100 kHz offset frequency, and study the phase noise performance limitations. Equally important, we demonstrate a single soliton at X band repetition rate of only 9.77 GHz. Our results establish integrated Si$_3$N$_4$ soliton microcombs as photonic microwave oscillators, that may form central elements for future microwave photonics systems.
author_names: Junqiu Liu

Erwan Lucas

Jijun He

Arslan S Raja

Rui Wang

Maxim Karpov

Hairun Guo

Romain Bouchand

Tobias J Kippenberg
title: Photonic microwave oscillators based on integrated soliton microcombs
year: 2019

abstract: Soliton microcmb [1] devices based on integrated waveguides are miniaturized optical frequency combs, which are ideal for portable applications for timing, spectroscopy and metrology. Chip based soliton microcomb devices have already been employed for coherent telecommunications, dual comb spectroscopy, ultrafast ranging, astrophysical spectrometer calibration, and for creating integrated frequency synthesizers and atomic clocks. A particularly promising application is to build soliton microcomb based photonic integrated microwave oscillators, whose center frequency can be freely designed and actively tuned by users. Yet, so far, soliton microcombs at microwave repetition rate have not been reported on integrated material platform, such as silicon nitride (Si3N4) [2] mainly due to high optical loss in waveguides caused by the fabrication process. Therefore, sufficient power assisted by power amplifiers for soliton formation is required, which however is incompatible with current integrated lasers. Here, through improving the photonic Damascene reflow process [3, 4] to fabricate integrated Si3N4 microresonators with quality factor exceeding 22 x 106 [5] we demonstrate, not only for the first time but also with an ultralow power of 35 mW, the single soliton formation at 19.6 GHz repetition rate, at microwave K band. We further characterize the phase noise of the soliton repetition rate, and reveal the main issue limiting the phase noise performance, i.e. the chip device input coupling, which causes significant power fluctuation. Our results pave way to build low noise, cost effective, small footprint, soliton microcomb based integrated microwave oscillator using low loss Si3N4 waveguides, promising for chip based telecommunication, high frequency arbitrary waveform generation, frequency synthesis and spectroscopy.
author_names: Junqiu Liu

Jijun He

Erwan Lucas

Arslan S Raja

Rui Wang

Maxim Karpov

Hairun Guo

Romain Bouchand

Tobias J Kippenberg
title: Photonic Integrated Microwave Oscillator Based on Silicon Nitride Soliton Microcomb
venue: 2019 Conference on Lasers and Electro Optics Europe European Quantum Electronics Conference (CLEO/Europe EQEC)
year: 2019

abstract: The generation of dissipative Kerr solitons in optical microresonators has provided a route to compact frequency combs of high repetition rate, which have already been employed for optical frequency synthesizers, ultrafast ranging, coherent telecommunication, and dual comb spectroscopy. Silicon nitride (Si3N4) microresonators are promising for photonic integrated soliton microcombs. Yet to date, soliton formation in Si3N4 microresonators at electronically detectable repetition rates, typically less than 100 GHz, is hindered by the requirement of external power amplifiers, due to the low quality (Q) factors, as well as by thermal effects that necessitate the use of frequency agile lasers to access the soliton state. These requirements complicate future photonic integration, heterogeneous or hybrid, of soliton microcomb devices based on Si3N4 microresonators with other active or passive components. Here, using the photonic Damascene reflow process, we demonstrate ultralow power single soliton formation in high Q(Q0>15x106)Si3N4 microresonators with 9.8 mW input power (6.2 mW in the waveguide) for devices of electronically detectable, 99 GHz repetition rate. We show that solitons can be accessed via simple, slow laser piezo tuning, in many resonances in the same sample. These power levels are compatible with current silicon photonics based lasers for full photonic integration of soliton microcombs, at repetition rates suitable for applications such as ultrafast ranging and coherent communication. Our results show the technological readiness of Si3N4 optical waveguides for future all on chip soliton microcomb devices.
author_names: Junqiu Liu

Arslan S Raja

Maxim Karpov

Bahareh Ghadiani

Martin Hubert Peter Pfeiffer

Nils J Engelsen

Hairun Guo

Michael Zervas

Tobias J Kippenberg
title: Ultralow power chip based soliton microcombs for photonic integration
year: 2018

abstract: We present the detailed characterization of the phase dynamics of a telecom hybrid III V on silicon passively mode locked laser with a ring cavity. We explore the various regimes of operation as a function of gain current and saturable absorber bias voltage. We use a steppedheterodyne measurement to quantify the spectral chirp and reconstruct the pulse envelope. With this technique, we are able to identify regimes of near transform limited operation, and we assess the degradation of mode locking in the comb phase relationship when saturable absorber bias voltage is changed. Finally, we present a preliminary study of the phase locking in hybrid mode locked operation and demonstrate transform limited pulses. (c) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Passive Mode Locking (PML) is a well known technique that uses a saturable absorber (SA) inside a laser cavity to generate a pulsed laser output with a broad optical frequency comb. This technique has been employed in a variety of laser devices and for a large number of applications including high resolution imaging [1] optical signal processing [2] and time resolved measurements [3] Nowadays, extensive work is dedicated to the generation of Optical Frequency Combs (OFCs) with integrated semiconductor laser technologies to satisfy the requirements for low energy consumption, small footprint and reproducibility. Integrated OFCs can also be obtained with injected Kerr microresonators which usually rely on power consuming pumping lasers [4] even if battery operated devices [5] and turnkey soliton microcomb operation [6] are now available. A challenge for integrated PML lasers technologies is to offer the possibility to reach low Free Spectral Range (FSR) values for optical cavities. Such a property is for example required for spectroscopic applications [7] where a ultra dense set of comb lines allows to obtain a high resolution in the spectral analysis of gas. Former monolithic integrated technologies showed large bandwidth OFC emission but the FSR could not reach values lower than 10 GHz due to the losses imposed by the III V material [8] This limitation has been recently bypassed by the use of hybrid laser technologies, where the optical cavity is made of a silicon waveguide and light is evanescently coupled from the III V active region to the underneath passive Si layer [9,10] The low loss Si waveguide enables the propagation of light in the cavity over several centimeters. OFC lasing in PML hybrid lasers has been demonstrated with multiple cavity geometries and laser designs [11,12] and a record 1 GHz FSR has been achieved, providing a ultra dense comb spectrum containing more than 1400 lines [13] The FSR of extended cavity PMLs could be even further reduced by using ultra low loss waveguide cavities based on for example the III V on silicon nitride technology [14] The hybrid III V on Si laser technology has proved mature enough for spectroscopic applications [15] and better understanding of the noise performance and pulse quality of these lasers is required. In PML semiconductor lasers, the overall performances are strongly affected by the SA properties, hence the ability to measure the influence of the SA during lasing is essential to control the laser operation. #412039 https:/doi.org/10.1364/OSAC.412039 Journal (c) 2021 Received 8 Oct 2020; revised 11 Dec 2020; accepted 14 Dec 2020; published 8 Jan 2021 Research Article Vol. 4, No. 1 15 January 2021 OSA Continuum 130 Fig. 1. Layout of the hybrid 8 GHz ring frequency comb laser. Semiconductor Optical Amplifier (SOA) and Saturable Absorber (SA) are integrated within the active Indium Phosphide (InP) material. The long spiral waveguide is etched in the underlying Si membrane that is bonded to InP. Light is evanescently coupled between active and passive
author_names: V A

V K

K B

G M

H G

M M
title: Analysis of the phase locking dynamics of a III V on silicon frequency comb laser
year: 2021

abstract: Soliton microcombs constitute chip scale optical frequency combs, and have the potential to impact a myriad of applications from frequency synthesis and telecommunications to astronomy. The demonstration of soliton formation via self injection locking of the pump laser to the microresonator has significantly relaxed the requirement on the external driving lasers. Yet to date, the nonlinear dynamics of this process has not been fully understood. Here, we develop an original theoretical model of the laser self injection locking to a nonlinear microresonator, i.e. nonlinear self injection locking, and construct state of the art hybrid integrated soliton microcombs with electronically detectable repetition rate of 30 GHz and 35 GHz, consisting of a DFB laser butt coupled to a silicon nitride microresonator chip. We reveal that the microresonator's Kerr nonlinearity significantly modifies the laser diode behavior and the locking dynamics, forcing laser emission frequency to be red detuned. A novel technique to study the soliton formation dynamics as well as the repetition rate evolution in real time uncover non trivial features of the soliton self injection locking, including soliton generation at both directions of the diode current sweep. Our findings provide the guidelines to build electrically driven integrated microcomb devices that employ full control of the rich dynamics of laser self injection locking, key for future deployment of microcombs for system applications. Self injection locking of the pump laser for a soliton microcomb has significantly relaxed the requirements for laser drives. Here the authors study self injection locking in experiment and theory and reveal that the soliton formation is feasible with detunings unreachable according to previous theories.
author_names: Andrey S Voloshin

Nikita M Kondratiev

Grigory V Lihachev

Junqiu Liu

Valery E Lobanov

Nikita Yu Dmitriev

Wenle Weng

Tobias J Kippenberg

Igor A Bilenko
title: Dynamics of soliton self injection locking in optical microresonators
venue: Nature communications
year: 2021

abstract: Thermal noise is ubiquitous in microscopic systems and in high precision measurements. Controlling thermal noise, especially using laser light to apply dissipation, substantially affects science in revealing the quantum regime of gases, in searching for fundamental physics, and in realizing practical applications. Recently, nonlinear light matter interactions in microresonators have opened up new classes of microscopic devices. A key example is Kerr microresonator frequency combs; so called soliton microcombs not only explore nonlinear science but also enable integrated photonics devices, such as optical synthesizers, optical clocks, and data communications systems. Here, we explore how thermal noise leads to fundamental decoherence of soliton microcombs. We show that a particle like soliton exists in a state of thermal equilibrium with its silicon chip based resonator. Therefore the soliton microcomb's modal linewidth is thermally broadened. Our experiments utilize record sensitivity in carrier envelope offset frequency detection in order to uncover this regime of strong thermal noise correlations. Furthermore, we have discovered that passive laser cooling of the soliton reduces thermal decoherence to far below the ambient temperature limit. We implement laser cooling by microresonator photothermal forcing, and we observe cooling of the frequency comb light to an effective temperature of 84 K. Our work illuminates inherent connections between nonlinear photonics, microscopic physical fluctuations, and precision metrology that could be harnessed for innovative devices and methods to manipulate light.
author_names: Tara E Drake

Jordan R Stone

Travis C Briles

Scott B Papp
title: Thermal decoherence and laser cooling of Kerr microresonator solitons (Conference Presentation)
year: 2019

abstract: 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.
author_names: Daryl T Spencer

Tara E Drake

Travis C Briles

Jordan R Stone

Laura C Sinclair

Connor Fredrick

Qing Li

Daron 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 Hubert Peter 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
title: An Integrated Photonics Optical Frequency Synthesizer
year: 2017