Hiromasa Tanobe

Bio: Hiromasa Tanobe is an academic researcher from Nippon Telegraph and Telephone. The author has contributed to research in topics: Waveguide (optics) & Signal. The author has an hindex of 15, co-authored 91 publications receiving 722 citations.

Over 67 GHz Bandwidth and 1.5 V Vπ InP-Based Optical IQ Modulator With n-i-p-n Heterostructure

Abstract: We report novel high-bandwidth InP-based Mach–Zehnder modulator and in-phase/quadrature (IQ) modulators that we realized by combining an n-i-p-n heterostructure and a capacitively loaded traveling wave electrode. The extremely low electrical and optical loss structure enhances the 3-dB electro-optic bandwidth of over 67 GHz without degrading other properties such as driving voltage and optical loss. The modulator also exhibits a static extinction ratio of over 24 dB with a V π of less than 1.5 V for the entire C-band. Furthermore, we demonstrate the first 120-Gbaud rate IQ modulation without optical pre equalization, and 100-Gb/s non-return-to-zero on-off keying modulation with a dynamic extinction ratio of over 10 dB.

Directly modulated membrane lasers with 108 GHz bandwidth on a high-thermal-conductivity silicon carbide substrate

Abstract: Increasing the modulation speed of semiconductor lasers has attracted much attention from the viewpoint of both physics and the applications of lasers. Here we propose a membrane distributed reflector laser on a low-refractive-index and high-thermal-conductivity silicon carbide substrate that overcomes the modulation bandwidth limit. The laser features a high modulation efficiency because of its large optical confinement in the active region and small differential gain reduction at a high injection current density. We achieve a 42 GHz relaxation oscillation frequency by using a laser with a 50-μm-long active region. The cavity, designed to have a short photon lifetime, suppresses the damping effect while keeping the threshold carrier density low, resulting in a 60 GHz intrinsic 3 dB bandwidth (f3dB). By employing the photon–photon resonance at 95 GHz due to optical feedback from an integrated output waveguide, we achieve an f3dB of 108 GHz and demonstrate 256 Gbit s−1 four-level pulse-amplitude modulations with a 475 fJ bit−1 energy cost of the direct-current electrical input. Directly modulated membrane distributed reflector lasers are fabricated on a silicon carbide platform. The 3 dB bandwidth, four-level pulse-amplitude modulation speed and operating energy for transmitting one bit are 108 GHz, 256 Gbit s−1 and 475 fJ, respectively.

Optical communication network system

Abstract: A fiber optic communication system includes a device of switching and setting wavelength of optical signals used in communication by network-node equipments, which sets the mapping of the wavelength of the optical signal used in communication by the network node equipments, and the input/output ports of an array waveguide grating (AWG), so as to construct a predetermined logical network topology by a plurality of network node equipments which are connected via optical fibers to the array waveguide grating that outputs optical signals inputted to optical input ports, to predetermined optical output ports in accordance with the wavelength thereof. As well as enabling a simple construction, it is easy to realize flexible network design, construction, and operation, and different network groups can also be easily connected to each other. Moreover, a fiber optic communication system having robust security and which can be stably operated even at the time of failure is realized at low cost.

80-GHz Bandwidth and 1.5-V V π InP-Based IQ Modulator

Abstract: We report a promising IQ optical modulator for beyond 100-GBd transmitter. By introducing both a new n-i-p-n heterostructure and an optimized capacitance-loaded traveling-wave electrode (CL-TWE), high-frequency electrical losses of the modulator can be drastically reduced. As a result, we extended an electro-optic (EO) bandwidth without degrading other properties, such as half-wave voltage (Vπ) and optical losses. The 3-dB EO bandwidth of the 1.5-V Vπ modulator reaches 80 GHz. Furthermore, we demonstrated up to 128-GBd IQ modulations by co-assembling with an ultra-broadband InP-based driver IC.

A temperature insensitive InGaAsP-InP optical filter

Abstract: A temperature insensitive optical filter (TIOF) with InGaAsP-InP material system is proposed. Less than 0.1 /spl Aring///spl deg/C temperature dependence is achieved for the first time even though we used the InGaAsP-InP material system. By changing the optimum structure of the TIOF, blue-shift temperature characteristics are also obtained. These two novel phenomena are in good agreement with the TIOF design principle.

Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages

Abstract: Electro-optic modulators translate high-speed electronic signals into the optical domain and are critical components in modern telecommunication networks1,2 and microwave-photonic systems3,4. They are also expected to be building blocks for emerging applications such as quantum photonics5,6 and non-reciprocal optics7,8. All of these applications require chip-scale electro-optic modulators that operate at voltages compatible with complementary metal–oxide–semiconductor (CMOS) technology, have ultra-high electro-optic bandwidths and feature very low optical losses. Integrated modulator platforms based on materials such as silicon, indium phosphide or polymers have not yet been able to meet these requirements simultaneously because of the intrinsic limitations of the materials used. On the other hand, lithium niobate electro-optic modulators, the workhorse of the optoelectronic industry for decades9, have been challenging to integrate on-chip because of difficulties in microstructuring lithium niobate. The current generation of lithium niobate modulators are bulky, expensive, limited in bandwidth and require high drive voltages, and thus are unable to reach the full potential of the material. Here we overcome these limitations and demonstrate monolithically integrated lithium niobate electro-optic modulators that feature a CMOS-compatible drive voltage, support data rates up to 210 gigabits per second and show an on-chip optical loss of less than 0.5 decibels. We achieve this by engineering the microwave and photonic circuits to achieve high electro-optical efficiencies, ultra-low optical losses and group-velocity matching simultaneously. Our scalable modulator devices could provide cost-effective, low-power and ultra-high-speed solutions for next-generation optical communication networks and microwave photonic systems. Furthermore, our approach could lead to large-scale ultra-low-loss photonic circuits that are reconfigurable on a picosecond timescale, enabling a wide range of quantum and classical applications5,10,11 including feed-forward photonic quantum computation. Chip-scale lithium niobate electro-optic modulators that rapidly convert electrical to optical signals and use CMOS-compatible voltages could prove useful in optical communication networks, microwave photonic systems and photonic computation.

Optical Packet and Burst Switching Technologies for the Future Photonic Internet

Abstract: This paper reviews advanced optical burst switching (OBS) and optical packet switching (OPS) technologies and discusses their roles in the future photonic Internet. Discussions include optoelectronic and optical systems technologies as well as systems integration into viable network elements (OBS and OPS routers). Optical label switching (OLS) offers a unified multiple-service platform with effective and agile utilization of the available optical bandwidth in support of voice, data, and multimedia services on the Internet Protocol. In particular, OLS routers with wavelength routing switching fabrics and parallel optical labeling allow forwarding of asynchronously arriving variable-length packets, bursts, and circuits. By exploiting contention resolution in wavelength, time, and space domains, the OLS routers can achieve high throughput without resorting to a store-and-forward method associated with large buffer requirements. Testbed demonstrations employing OLS edge routers show high-performance networking in support of multimedia and data communications applications over the photonic Internet with optical packets and bursts switched directly at the optical layer

High-performance coherent optical modulators based on thin-film lithium niobate platform

Abstract: The coherent transmission technology using digital signal processing and advanced modulation formats, is bringing networks closer to the theoretical capacity limit of optical fibres, the Shannon limit. The in-phase/quadrature electro-optic modulator that encodes information on both the amplitude and the phase of light, is one of the underpinning devices for the coherent transmission technology. Ideally, such modulator should feature a low loss, low drive voltage, large bandwidth, low chirp and compact footprint. However, these requirements have been only met on separate occasions. Here, we demonstrate integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil these requirements simultaneously. The presented devices exhibit greatly improved overall performance (half-wave voltage, bandwidth and optical loss) over traditional lithium niobate counterparts, and support modulation data rate up to 320 Gbit s−1. Our devices pave new routes for future high-speed, energy-efficient, and cost-effective communication networks. In-phase/quadrature (IQ) electro-optic modulators are underpinning devices for coherent transmission technology. Here the authors present IQ modulators in the lithium-niobate-on-insulator platform, which provide improved overall performance and advanced modulation formats for future coherent transmission systems.

Monolithic Silicon Photonic Integrated Circuits for Compact 100 $^{+}$ Gb/s Coherent Optical Receivers and Transmitters

Abstract: We present silicon photonic integrated circuits (PICs) based coherent optical transmitters and receivers for high-speed long-distance fiber optical transmission. High-degree photonic integration is achieved by monolithically integrating silicon electro-optic modulators, germanium photo detectors, silicon nitride-assisted on-chip polarization rotators, thermal phase shifters, and various passive silicon optical devices on a single wafer platform. We demonstrate the use of these PICs for modulating and detecting 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK) and 224-Gb/s PDM 16-ary quadrature amplitude modulation (PDM-16-QAM) signals. Transmission and coherent detection of a 112-Gb/s PDM-QPSK signal over 2560-km standard single-mode fiber is also demonstrated. The high-degree photonic integration for silicon PICs promises small-form-factor and low-power-consumption transceivers for future coherent systems that demand high cost efficiency and energy efficiency.

Integrated lithium niobate photonics

Abstract: Abstract Lithium niobate (LiNbO3) on insulator (LNOI) is a promising material platform for integrated photonics due to single crystal LiNbO3 film’s wide transparent window, high refractive index, and high second-order nonlinearity. Based on LNOI, the fast-developing ridge-waveguide fabrication techniques enabled various structures, devices, systems, and applications. We review the basic structures including waveguides, cavities, periodically poled LiNbO3, and couplers, along with their fabrication methods and optical properties. Treating those basic structures as building blocks, we review several integrated devices including electro-optic modulators, nonlinear optical devices, and optical frequency combs with each device’s operating mechanism, design principle and methodology, and performance metrics. Starting from these integrated devices, we review how integrated LNOI devices boost the performance of LiNbO3’s traditional applications in optical communications and data center, integrated microwave photonics, and quantum optics. Beyond those traditional applications, we also review integrated LNOI devices’ novel applications in metrology including ranging system and frequency comb spectroscopy. Finally, we envision integrated LNOI photonics’ potential in revolutionizing nonlinear and quantum optics, optical computing and signal processing, and devices in ultraviolet, visible, and mid-infrared regimes. Beyond this outlook, we discuss the challenges in integrated LNOI photonics and the potential solutions.