Papers - Tanabe, Takasumi

Field Demonstration of Multi-Wavelength Optical Transmission with Microresonator Frequency Combs

Tanikawa K., Fujii S., Kogure S., Tanaka S., Tasaka S., Wada K., Kumazaki H., Kawanishi S., Tanabe T.

2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023  2023

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Data traffic has been increasing with the spread of the internet. Therefore, a network that connects data centers and metropolitan areas requires a high-capacity, low-latency, and low-power-consumption optical communication system [1]. Since microresonator-based optical frequency combs (i.e., microcombs) have many longitudinal modes, they are expected to be applied to wavelength division multiplexing (WDM) communications [2,3]. We describe a field demonstration of a multi-wavelength optical transmission with a soliton microcomb. We employed intensity modulation and direct detection (IM-DD) for a simple and low-latency communication system [3]. We also used a magnesium fluoride (MgF2) microresonator because it has a small free spectral range (FSR) for efficient bandwidth use. Although sophisticated experiments have already been reported in the laboratory, we believe that our demonstration using a commercially installed optical fiber in a metropolitan area is a significant step towards the practical use of a microresonator system.

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Field Demonstration of Low-Latency Massively Parallel Communication with Microresonator Frequency Comb

Tanikawa K., Fujii S., Tanaka S., Tasaka S., Wada K., Kogure S., Kumazaki H., Kawanishi S., Tanabe T.

CLEO: Science and Innovations, CLEO:S and I 2023  2023

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We demonstrated low-latency optical transmission with a microresonator frequency comb using a 9-km optical fiber in a metropolitan area. The delay time of the entire system, excluding the transmission fiber, was only 3.1 μs.

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Field Demonstration of Low-Latency Massively Parallel Communication with Microresonator Frequency Comb

Tanikawa K., Fujii S., Tanaka S., Tasaka S., Wada K., Kogure S., Kumazaki H., Kawanishi S., Tanabe T.

2023 Conference on Lasers and Electro-Optics, CLEO 2023  2023

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We demonstrated low-latency optical transmission with a microresonator frequency comb using a 9-km optical fiber in a metropolitan area. The delay time of the entire system, excluding the transmission fiber, was only 3.1 us.

Assessment of the Feasibility of Employing Chaos Synchronization in Two Cascaded Microresonators for Secure Data Transmission

Lemcke D., Moreno D., Fujii S., Nakashima A., Uchida A., Tanabe T.

2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023  2023

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As the limits of computational power continue to increase, concern has arisen regarding insufficient security along with a demand for improvements in encryption methods for data transmission, which might be achieved by chaos synchronization [1, 2]. Using modified Lugiato-Levefer equations (LLEs), we numerically explore two cascaded microresonator frequency combs [3]. To obtain a chaotic state, both cavities are pumped by continuous-wave lasers until modulation instability (MI) combs are generated. By injecting the output of the first resonator into the second resonator, both chaotic fields in the cavities are synchronized. In this work, we investigate to what extent the chaos is synchronized and how this phenomenon may be implemented in existing data transmission systems over a chaotic channel to enable secure communication.

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A small spectrometer with extremely high resolution (0.07 nm) realized with an improved reconstruction algorithm

Tanabe T., Kokubu J., Sugano R.

International Conference on Metamaterials, Photonic Crystals and Plasmonics    291 - 292 2023

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We successfully reconstruct the spectrum of a multi-wavelength input by using the inverse matrix method for data obtained with a random chirped photonic crystal waveguide.

Passive mode-locking without a saturable absorber using a coupled microresonator

Imamura R., Fujii S., Nakashima A., Tanabe T.

2023 Conference on Lasers and Electro-Optics, CLEO 2023  2023

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Mode-locking usually requires saturable absorption or active modulation to trigger and build short pulses. We show through calculations that self-starting mode-locking may be achieved simply by coupling active and passive microresonators without a saturable absorber.

Synchronization of microresonator frequency combs in chaotic regime

Moreno D., Fujii S., Nakashima A., Uchida A., Sanchis P., Tanabe T.

Proceedings of SPIE - The International Society for Optical Engineering 12407 2023

ISSN  0277786X

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We numerically study the chaotic synchronization of microresonator frequency combs. The chaotic state of microresonators could be a key factor in optical communications because the modulation instability state (chaotic) has a larger output than the soliton state (stable), which may enable us to realize a higher signal-to-noise ratio. In addition, it will allow secure communication. We show that two microresonator frequency combs in a leader-follower configuration can be synchronized in chaotic regimes. Interestingly, the follower comb synchronizes even when some longitudinal modes of the leader comb are absent. We also show that the Turing pattern comb in the follower ring becomes chaotic and synchronizes when we inject the leader's modulation instability comb.

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Small Spectrometer with Extremely High-resolution (0.07 nm) Realized with an Improved Reconstruction Algorithm

Kokubu J., Sugano R., Ohtsuka M., Yokoyama N., Okano M., Tanabe T.

CLEO: Science and Innovations, CLEO:S and I 2023  2023

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Spectra are reconstructed by capturing wavelength-specific patterns of localized light in a photonic-crystal-waveguide. We show that real-time reconstruction at a wavelength resolution of 0.07 nm is possible by using low-rank approximation with singular-value-decomposition and regularized-least-squares.

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Small Spectrometer with Extremely High-resolution (0.07 nm) Realized with an Improved Reconstruction Algorithm

Kokubu J., Sugano R., Ohtsuka M., Yokoyama N., Okano M., Tanabe T.

2023 Conference on Lasers and Electro-Optics, CLEO 2023  2023

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Spectra are reconstructed by capturing wavelength-specific patterns of localized light in a photonic-crystal-waveguide. We show that real-time reconstruction at a wavelength resolution of 0.07 nm is possible by using low-rank approximation with singular-value-decomposition and regularized-least-squares.

Passive mode-locking without a saturable absorber using a coupled microresonator

Imamura R., Fujii S., Nakashima A., Tanabe T.

CLEO: Fundamental Science, CLEO:FS 2023  2023

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Mode-locking usually requires saturable absorption or active modulation to trigger and build short pulses. We show through calculations that self-starting mode-locking may be achieved simply by coupling active and passive microresonators without a saturable absorber.

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Passive mode-locking without a saturable absorber using a coupled microresonator

Imamura R., Fujii S., Nakashima A., Tanabe T.

CLEO: Applications and Technology, CLEO:A and T 2023  2023

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Mode-locking usually requires saturable absorption or active modulation to trigger and build short pulses. We show through calculations that self-starting mode-locking may be achieved simply by coupling active and passive microresonators without a saturable absorber.

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Passive mode-locking without a saturable absorber using a coupled microresonator

Imamura R., Fujii S., Nakashima A., Tanabe T.

CLEO: Science and Innovations, CLEO:S and I 2023  2023

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Mode-locking usually requires saturable absorption or active modulation to trigger and build short pulses. We show through calculations that self-starting mode-locking may be achieved simply by coupling active and passive microresonators without a saturable absorber.

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Carbon Nanotubes Coupled with Silica Toroid Microcavities as Emitters for Silicon-Integrated Photonics

Tokunaga R., Kinoshita K., Imamura R., Nagashima K., Imafuku R., Nakagawa K., Tanabe T., Maki H.

ACS Applied Nano Materials 5 ( 10 ) 14328 - 14335 2022.10

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A light source based on single-walled carbon nanotubes (SWNTs) is one of the promising candidates for a microsized light source on a silicon chip at telecommunication wavelengths in optical communications and optical interconnects. However, SWNT-based light emitters possess the disadvantage of having a very broad emission spectrum. Here, we present an ultranarrow-linewidth photoluminescence (PL) emitter based on a silica toroid resonator, along with SWNTs, on a silicon chip. We simultaneously managed both excitation and emission lights at telecommunication wavelengths on a silicon chip by employing a very simple in-line configuration consisting of a toroid resonator and a tapered fiber for light input and output. Owing to the extremely high Q factor of our silica toroid resonator, we obtained an ultrahigh Q factor (∼2.1 × 104) of C-band PL emission. We also demonstrated strong PL emission under laterally polarized excitation conditions owing to the strong coupling to the toroid resonator, and laterally polarized PL emission can be selectively generated independently of the excitation polarization direction. This SWNT-based PL emitter based on a simple system with a silica toroid resonator can open routes to highly integrated photonics and optoelectronics on silicon-based platforms.

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Deterministic generation of a perfect soliton crystal microcomb with a saturable absorber

Nakashima A., Fujii S., Imamura R., Nagashima K., Tanabe T.

Optics Letters 47 ( 6 ) 1458 - 1461 2022.03

ISSN  01469592

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We numerically investigate the deterministic generation of a perfect soliton crystal (PSC) in an optical microresonator functionalized with a saturable absorber (SA). The SAallows the direct formation of a PSC from an initial, periodic Turing roll. It prevents passage through a chaotic state, which induces a stochastic nature with regard to the number of generated dissipativeKerr solitons.We showthat PSCs form deterministically, and the number is controlled by adjusting the input power and SA parameter. Our work provides a simple approach for obtaining a stable PSC that offers an ultrahigh repetition rate and a high comb output power.

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Dissipative Kerr soliton microcombs for FEC-free optical communications over 100 channels

Fujii S., Tanaka S., Ohtsuka T., Kogure S., Wada K., Kumazaki H., Tasaka S., Hashimoto Y., Kobayashi Y., Araki T., Furusawa K., Sekine N., Kawanishi S., Tanabe T.

Optics Express 30 ( 2 ) 1351 - 1364 2022.01

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The demand for high-speed and highly efficient optical communication techniques has been rapidly growing due to the ever-increasing volume of data traffic. As well as the digital coherent communication used for core and metro networks, intensity modulation and direct detection (IM-DD) are still promising schemes in intra/inter data centers thanks to their low latency, high reliability, and good cost performance. In this work, we study a microresonator-based frequency comb as a potential light source for future IM-DD optical systems where applications may include replacing individual stabilized lasers with a continuous laser driven microresonator. Regarding comb line powers and spectral intervals, we compare a modulation instability comb and a soliton microcomb and provide a quantitative analysis with regard to telecom applications. Our experimental demonstration achieved a forward error correction (FEC) free operation of bit-error rate (BER) <10−9 with a 1.45 Tbps capacity using a total of 145 lines over the entire C-band and revealed the possibility of soliton microcomb-based ultra-dense wavelength division multiplexing (WDM) with a simple, cost-effective IM-DD scheme, with a view to future practical use in data centers.

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Theoretical approach on the critical depth of cut of single crystal MgF<inf>2</inf> and application to a microcavity

Hayama Y., Fujii S., Tanabe T., Kakinuma Y.

Precision Engineering 73   234 - 243 2022.01

ISSN  01416359

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Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF2, which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF2, MgF2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF2 plane. Unlike CaF2, MgF2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance.

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Active Thermal Tuning of a Soliton Frequency Comb in a Crystalline Optical Microresonator

Fujii S., Wada K., Kogure S., Kumazaki H., Tanabe T.

2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings  2022

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We report the thermal tuning of a Kerr soliton frequency comb in an ultrahigh-Q magnesium fluoride crystalline microresonator yielding broad pump frequency tuning of up to ~ 50 GHz and a repetition rate of ~ 6 MHz.

Multi-wavelength reconstruction in a compact (&lt; mm) high-resolution (&lt; 0.1 nm) random photonic crystal spectrometer

Kodama T., Sugano R., Hofs J., Ohtsuka M., Seki M., Yokoyama N., Okano M., Tanabe T.

Optics InfoBase Conference Papers  2022

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We experimentally demonstrate the reconstruction of multiple wavelength light with an ultra-compact spectrometer. The spectrometer is based on a random photonic crystal and operates with a spectral resolution beyond the fabrication error.

Multi-wavelength reconstruction in a compact (&lt; mm) high-resolution (&lt; 0.1 nm) random photonic crystal spectrometer

Kodama T., Sugano R., Hofs J., Ohtsuka M., Seki M., Yokoyama N., Okano M., Tanabe T.

2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings  2022

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We experimentally demonstrate the reconstruction of multiple wavelength light with an ultra-compact spectrometer. The spectrometer is based on a random photonic crystal and operates with a spectral resolution beyond the fabrication error.

Mode-locked Operation in a Coupled Microresonator System with Gain and Nonlinear Loss

Imamura R., Tate Y., Nakashima A., Nagashima K., Fujii S., Tanabe T.

Optics InfoBase Conference Papers  2022

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We numerically study the mode-locking behavior in a system in which an erbium-doped resonator (gain) is coupled to a carbon-nanotube functionalized resonator (nonlinear loss). We find that mode-locking is possible even with a small gain and relatively low Q by adjusting the coupling between two cavities.

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