Photonic-Crystal Single-Mode Waveguide
Photonic-Crystal Single-Mode Waveguide Photonic-Crystal Single-Mode Waveguide Masaya Notomi
https://www.rd.ntt/e/brl/result/activities/file/report01/E/report20.html
Spot-Size Converter of Photonic Crystal Waveguide
Spot-Size Converter of Photonic Crystal Waveguide Spot-Size Converter of Photonic Crystal
https://www.rd.ntt/e/brl/result/activities/file/report02/E/report20.html
Enhanced Optical Nonlinearity in a Silicon Photonic Crystal Slow-Light Waveguide
Enhanced Optical Nonlinearity in a Silicon Photonic Crystal Slow-Light Waveguide Enhanced Optical
https://www.rd.ntt/e/brl/result/activities/file/report11/report24.html
List of Invited Talks at International Conferences (2005)
Nonlinear Control of Resonator-Waveguide Coupled System in Photonic Crystal Slabs", CIPS Annual Meeting 2005
https://www.rd.ntt/e/brl/result/activities/file/report05/data12.html
国際会議招待講演一覧 (2005)
. Notomi, "Dynamic Nonlinear Control of Resonator-Waveguide Coupled System in Photonic Crystal Slabs", CIPS
https://www.rd.ntt/brl/result/activities/file/report05/data11.html
Demonstration of ultrafast and energy-efficient all-optical switching with graphene and plasmonic waveguides|NTT Basic Research Laboratories | NTT R&D Website
switching with graphene and plasmonic waveguides - Progress toward photonic integrated circuits for
https://www.rd.ntt/e/brl/latesttopics/2019/11/latest_topics_201911261120.html
InGaAs Photodetectors Based on Photonic Crystal Waveguide Including Ultrasmall Buried Heterostructure
InGaAs Photodetectors Based on Photonic Crystal Waveguide Including Ultrasmall Buried
https://www.rd.ntt/e/brl/result/activities/file/report13/report28E.html
On-Chip Generation and Demultiplexing of Quantum Correlated Photons Using Si-Silica Monolithic Waveguide Platform
Waveguide Platform On-Chip Generation and Demultiplexing of Quantum Correlated Photons Using Si-Silica
https://www.rd.ntt/e/brl/result/activities/file/report14/report21E.html
Demonstration of Efficient Mode Conversion for Deep-subwavelength Plasmonic Waveguides
waveguides enable us to utilize light-propagating modes much smaller than a wavelength dimension in photonic
https://www.rd.ntt/e/brl/result/activities/file/report16/report26E.html
no_32_e.pdf
Si waveguide ・Ultra-compact filter ・Spot-size converter ・PIN attenuator, modulator ・Ge photo-detector
https://www.rd.ntt/brl/event/splaza2009/poster/EN/no_32_e.pdf
Programmable linear optical circuit realized on a chip|NTT Basic Research Laboratories | NTT R&D Website
of experiments using single photons. The photonic waveguide circuit can be re-programmed by
https://www.rd.ntt/e/brl/latesttopics/2015/08/latest_topics_201508171025.html
Ultra-small and low energy consumption optical bit memory developed|NTT Basic Research Laboratories | NTT R&D Website
consumption optical bit memory developed - Long memory holding time of 150 nsec achieved in photonic crystal
https://www.rd.ntt/e/brl/latesttopics/2008/04/latest_topics_200804240001.html
Nanostructured Device Research Group|Device Technology Laboratories|NTT R&D Website
, overwhelmingly low cost, miniaturization, and low power consumption to next-generation photonic devices. ・Ultra
https://www.rd.ntt/e/dtl/technology/nanostructured_device_research_group_ntt_device_technology_laboratories_ntt_rd_website.html
An on-chip quantum buffer realized|NTT Basic Research Laboratories | NTT R&D Website
/11/13 An on-chip quantum buffer realized - A key component for a photonic quantum computer on a chip
https://www.rd.ntt/e/brl/latesttopics/2013/11/latest_topics_201311130702.html
国際会議招待講演一覧(2008)
generation using silicon photonic wire waveguide", The IEEE Nanotechnology Materials and Device Conference
https://www.rd.ntt/brl/result/activities/file/report08/data11.html
List of Invited Talks at International Conferences (2008)
. Tokura, and S. I. Itabashi, "Entangled photon-pair generation using silicon photonic wire waveguide", The
https://www.rd.ntt/e/brl/result/activities/file/report08/data12.html
Research Activities in NTT Basic Research Laboratories Vol. 24 (2013)
Si Photonic Crystal InGaAs Photodetectors Based on Photonic Crystal Waveguide Including Ultrasmall
https://www.rd.ntt/e/brl/result/activities/file/report13/2013_E.html
List of Invited Talks at International Conferences (Fiscal 2002) IV. Quantum Optics & Optical Materials
, K. Yamada, C. Takahashi and J. Takahashi, “Highly dispersive nature of photonic-band-gap waveguide
https://www.rd.ntt/e/brl/result/activities/file/report02/E/data15.html
国際会議招待講演一覧 (2002年度) IV.量子光学・光物性関連
, “Highly dispersive nature of photonic-band-gap waveguide”, CLEO/QELS 2002, Long Beach, USA (May 2002). (4
https://www.rd.ntt/brl/result/activities/file/report02/J/data15.html
Overview of Quantum Optics and Optical Materials Research
photonic crystal optical circuits (ultra-low loss waveguide, resonator, filter) (2) Interaction between
https://www.rd.ntt/e/brl/result/activities/file/report03/E/report15.html
Fabrication and Physics of Low-Loss Photonic Crystal Slab Waveguides
photonic crystal waveguides [2]. Another aim of our research is to reveal the physics of PCS waveguide loss
https://www.rd.ntt/e/brl/result/activities/file/report04/report31.html
D02-e.pdf
. Achieving this requires high-precision photonic devices, enabled using advanced microfabrication
https://www.rd.ntt/forum/2025/doc/D02-e.pdf
Ultra High-Q Photonic Crystal Nanocavities Based on Compound Semiconductors
Ultra High-Q Photonic Crystal Nanocavities Based on Compound Semiconductors Ultra High-Q Photonic
https://www.rd.ntt/e/brl/result/activities/file/report07/report29.html
Ultrahigh-Q Photonic Crystal Nanocavity Realized with Locally Modulated Line Defect
Ultrahigh-Q Photonic Crystal Nanocavity Realized with Locally Modulated Line Defect (a) Schematic
https://www.rd.ntt/e/brl/result/activities/file/report05/k04.html
Publication
photonic-crystal waveguide," APL Photonics 2, 056105 (2017). [abstract] M. Takiguchi, A. Yokoo, K. Nozaki
https://www.rd.ntt/npc/group/ryouna-g/publication-j.html
Publication
photonic-crystal waveguide," APL Photonics 2, 056105 (2017). [abstract] M. Takiguchi, A. Yokoo, K. Nozaki
https://www.rd.ntt/npc/group/ryouna-g/publication.html
Lambda-Scale Embedded Active-Region Photonic-Crystal (LEAP) Lasers
Lambda-Scale Embedded Active-Region Photonic-Crystal (LEAP) Lasers Scanning electron microscope
https://www.rd.ntt/e/brl/result/activities/file/report12/k04e.html
Lambda-Scale Embedded Active-Region Photonic-Crystal (LEAP) Lasers
Lambda-Scale Embedded Active-Region Photonic-Crystal (LEAP) Lasers Lambda-Scale Embedded Active
https://www.rd.ntt/e/brl/result/activities/file/report12/report30e.html
Publications
. Notomi, "Slow light enhanced waveguide nonlinearity in ultrahigh-Q photonic crystal coupled resonator
https://www.rd.ntt/brl/people/htakesue/papers.html
2DPCslab
2DPCslab SOI Photonic Crystal Slab Having 2D PBG SOI (Silicon-On-Insulator) substrate PBG
https://www.rd.ntt/brl/group_introduction/butsuna-g/project2/
2DPCslab
2DPCslab SOI Photonic Crystal Slab Having 2D PBG SOI (Silicon-On-Insulator) substrate PBG
https://www.rd.ntt/brl/group_introduction/butsuna-g/project2/index-j.html
2DPCslab
2DPCslab SOI Photonic Crystal Slab Having 2D PBG SOI (Silicon-On-Insulator) substrate PBG
https://www.rd.ntt/npc/group/ryouna-g/project2/index-j.html
2DPCslab
2DPCslab SOI Photonic Crystal Slab Having 2D PBG SOI (Silicon-On-Insulator) substrate PBG
https://www.rd.ntt/npc/group/ryouna-g/project2/
Overview of Research in Laboratories
by using a coupled resonator optical waveguide based on silicon photonic crystal cavities. We
https://www.rd.ntt/e/brl/result/activities/file/report13/report00E.html
Publication
-absorption modulator consisting of InGaAsP-embedded photonic-crystal waveguide," APL Photonics 2, 056105
https://www.rd.ntt/brl/group_introduction/butsuna-g/publication.html
Publication
-absorption modulator consisting of InGaAsP-embedded photonic-crystal waveguide," APL Photonics 2, 056105
https://www.rd.ntt/brl/group_introduction/butsuna-g/publication-j.html
List of Visitor’s Talks (Fiscal 2004)
. Tikhodeev General Physics Institute, Russia “Waveguide-plasmon polaritons in photonic crystal slabs with
https://www.rd.ntt/e/brl/result/activities/file/report04/data08.html
来訪者による講演一覧
Quantum Dots」 8月19日 Mr. Aaron Danner The University of Illinois, USA 「Photonic Crystal VCSEL (Vertical
https://www.rd.ntt/brl/result/activities/file/report04/data08.html
An On-Chip Single Photon Buffer Based on Coupled Resonator Optical Waveguide
buffer experiment using a coupled resonator optical waveguide (CROW) based on silicon photonic crystal
https://www.rd.ntt/e/brl/result/activities/file/report13/report21E.html
Successful Fabrication of 2D Photonic Crystals
Successful Fabrication of 2D Photonic Crystals Successful Fabrication of 2D Photonic Crystals
https://www.rd.ntt/e/brl/result/activities/file/report00/E/report10_e.html
Successful Fabrication of 2D Photonic Crystals
Successful Fabrication of 2D Photonic Crystals Successful Fabrication of 2D Photonic Crystals
https://www.rd.ntt/e/brl/result/activities/file/report00/E/k04_report_e.html
Slow Light Propagation in Large-scale Photonic Crystal Coupled Resonator Waveguides
Slow Light Propagation in Large-scale Photonic Crystal Coupled Resonator Waveguides Slow Light
https://www.rd.ntt/e/brl/result/activities/file/report07/report31.html
First demonstration of nanowire lasers at telecom wavelengths and high-speed signal modulation|NTT Basic Research Laboratories | NTT R&D Website
). Future Plans Next, we aim for integrating this nanowire laser coupled to a photonic crystal waveguide in
https://www.rd.ntt/e/brl/latesttopics/2017/04/latest_topics_201704031636.html
Development of Membrane Optical Modulators for IOWN | NTT R&D Website
) shows a schematic of a photonic-integrated circuit using an MZ modulator consisting of a Si MZ
https://www.rd.ntt/e/research/JN202206_18502.html
Short Pulse Generation by Adiabatic Wavelength Shifting
spectrograms of the output light at a waveguide after it had been trapped in the photonic crystal nanocavity
https://www.rd.ntt/e/brl/result/activities/file/report08/k04.html
Photonic Nano-Structure Research Group | NTT Basic Research Laboratories | NTT R&D Website
photonic-crystal waveguide APL Phontonics 2 (5), 056105 (2017). S. Sergent, M. Takiguchi, T. Tsuchizawa, A
https://www.rd.ntt/e/brl/group_introduction/group_011.html
Demonstration of a high performance optical logic gate for ultralow-latency data processing|NTT Basic Research Laboratories | NTT R&D Website
photodetectors achieved by putting the absorber in photonic crystal waveguide whose structure is periodically
https://www.rd.ntt/e/brl/latesttopics/2020/03/latest_topics_202003061859.html
フォトニックナノ構造研究グループ|NTT物性科学基礎研究所|NTT R&D Website
photonic-crystal waveguide APL Phontonics 2 (5), 056105 (2017). S. Sergent, M. Takiguchi, T. Tsuchizawa, A
https://www.rd.ntt/brl/group_introduction/group_011.html
Dynamic High-Q Cavity Formation and Photon Pinning by Index Modulation
(typically, several nm shift of the air hole position) line-defect waveguides in two-dimensional photonic
https://www.rd.ntt/e/brl/result/activities/file/report08/report33.html
Efficient Light-to-voltage Conversion by Ultralow-capacitanceNano-photodetector
heterostructure to embed the compact InGaAs absorber in the photonic crystal (PhC) waveguide [Fig. 1(a)] [1], we
https://www.rd.ntt/e/brl/result/activities/file/report16/report28E.html
All-optical Bit Memory Based on Photonic Crystal Nanocavity
All-optical Bit Memory Based on Photonic Crystal Nanocavity All-optical Bit Memory Based on
https://www.rd.ntt/e/brl/result/activities/file/report07/report30.html
Publications | NTT Basic Research Laboratories | NTT R&D Website
consisting of InGaAsP-embedded photonic-crystal waveguide" APL Phontonics 2 (5), 056105 (2017). R. Ohta, H
https://www.rd.ntt/e/brl/result/publications/paper_2017.html
論文|NTT物性科学基礎研究所|NTT R&D Website
InGaAsP-embedded photonic-crystal waveguide APL Phontonics 2 (5), 056105 (2017). R. Ohta, H. Okamoto, and
https://www.rd.ntt/brl/result/publications/paper_2017.html
国際会議招待講演一覧(2011年)
(Jan. 2011). (2) M. Notomi, "Bi-layer Photonic Crystals for Optomechanics", SPIE Photonics West 2011
https://www.rd.ntt/brl/result/activities/file/report11/data06.html
List of Invited Talks at International Conferences (2011)
(Jan. 2011). (2) M. Notomi, "Bi-layer Photonic Crystals for Optomechanics", SPIE Photonics West 2011
https://www.rd.ntt/e/brl/result/activities/file/report11/data06.html
List of Award Winners
. Kuramochi M. Notomi Sub-fF-capacitance photonic-crystal photodetector towards fJ/bit on-chip receiver July 6
https://www.rd.ntt/e/brl/result/activities/file/report16/data04E.html
Coupled Resonator Waveguides Formed by Ultrahigh-Q Si Photonic Crystal Nano-resonators
Coupled Resonator Waveguides Formed by Ultrahigh-Q Si Photonic Crystal Nano-resonators Coupled
https://www.rd.ntt/e/brl/result/activities/file/report06/report32.html
国際会議招待講演一覧 (2006)
. Taniyama, and S. Mitsugi, "Dynamic Control of Light by Photonic-Crystal Resonator-Waveguide-Coupled System
https://www.rd.ntt/brl/result/activities/file/report06/data10.html
List of Invited Talks at International Conferences (2006)
. Mitsugi, "Dynamic Control of Light by Photonic-Crystal Resonator-Waveguide-Coupled System", Conference on
https://www.rd.ntt/e/brl/result/activities/file/report06/data11.html
List of Research Papers Published in International Journals
filter using mode gap of width-tuned photonic-crystal waveguide", Opt. Express 13 (11), 4202-4209 (2005
https://www.rd.ntt/e/brl/result/activities/file/report05/data15.html
Publications
Semiconductor Nanowires on a Si Photonic Crystal Platform", M. D. Birowosuto, A. Yokoo, G. Zhang, K. Tateno, E
https://www.rd.ntt/brl/people/taniyama.hideaki/publication.html
Contents
Semiconductor Micro/Nanomechanical Devices Spot-Size Converters for Photonic Crystal Waveguides Preface Member
https://www.rd.ntt/e/brl/result/activities/file/report02/E/2002_e.html
World's first large-scale coupling of optical nanocavities generating slow light|NTT Basic Research Laboratories | NTT R&D Website
an optical signal. The structure uses a photonic crystal, which is an artificial periodic structure
https://www.rd.ntt/e/brl/latesttopics/2008/11/latest_topics_200811280001.html
Contents
Time Resolved Measurement of Photonic Crystal Optical Nanocavity Coupled Resonator Waveguide Formed by
https://www.rd.ntt/e/brl/result/activities/file/report06/2006_E.html
Contents
-Scale Embedded Active-Region Photonic-Crystal (LEAP) Lasers Message from the Director NTT Basic Research
https://www.rd.ntt/e/brl/result/activities/file/report12/2012_E.html
Contents
-confinement Effect Ultralarge Optomechanical Coupling in a Bi-layer Photonic Crystal Message from the Director
https://www.rd.ntt/e/brl/result/activities/file/report09/2009_E.html
Ultrahigh-Q Photonic Crystal Nanocavity Realized with Locally Modulated Line Defect
Ultrahigh-Q Photonic Crystal Nanocavity Realized with Locally Modulated Line Defect Ultrahigh-Q
https://www.rd.ntt/e/brl/result/activities/file/report05/report32.html
Broadband Continuous-wave Optical Quadrature Squeezer for Ultra-fast Optical Quantum Computers | NTT R&D Website
optical quadrature squeezer by using a periodically poled lithium niobate (PPLN) waveguide. The squeezer
https://www.rd.ntt/e/research/JN202206_18572.html
英文論文一覧
filter using mode gap of width-tuned photonic-crystal waveguide", Opt. Express 13 (11), 4202-4209 (2005
https://www.rd.ntt/brl/result/activities/file/report05/data14.html
Toshikazu Hashimoto | NTT R&D Website
; Hashimoto, Toshikazu, "Scalable reservoir computing on coherent linear photonic processor," Communications
https://www.rd.ntt/e/organization/researcher/superior/s_028.html
World premier: Success in realizing all-optical RAM|NTT Basic Research Laboratories | NTT R&D Website
) Schematic diagram of the device. A tiny InGaAsP region is buried in the InP photonic crystal waveguide and
https://www.rd.ntt/e/brl/latesttopics/2012/02/latest_topics_201202270100.html
High-Q One-Dimensional Photonic Crystal Nanocavity in a Silicon/SOI Platform
High-Q One-Dimensional Photonic Crystal Nanocavity in a Silicon/SOI Platform High-Q One
https://www.rd.ntt/e/brl/result/activities/file/report10/report30.html
Optical Circuit Technologies for Next-generation Computing Using Light | NTT R&D Website
from one optical waveguide to the other. By separating the optical waveguide at half the length of the
https://www.rd.ntt/e/research/JN202206_18579.html
List of Research Papers Published in International Journals
a semiconductor photonic crystal nanocavity side coupled to a waveguide," Phys. Rev. B 70 (19
https://www.rd.ntt/e/brl/result/activities/file/report04/data15.html
Masaya Notomi | NTT R&D Website
waveguide," Optica 3, pp. 999-1005 (2016). K. Takata, and M. Notomi, "Photonic Topological Insulating Phase
https://www.rd.ntt/e/organization/researcher/fellow/f_010.html
22-Gbit/s × 16-ch WDM Receiver Based on a Si-Ge-silica Monolithic Photonic Platform
22-Gbit/s × 16-ch WDM Receiver Based on a Si-Ge-silica Monolithic Photonic Platform 22-Gbit/s × 16
https://www.rd.ntt/e/brl/result/activities/file/report12/report31e.html
橋本 俊和 | NTT R&D Website
, Toshikazu, "Scalable reservoir computing on coherent linear photonic processor," Communications Physics Vol
https://www.rd.ntt/organization/researcher/superior/s_028.html
英文論文一覧
, and M. Notomi, "Coupling of small, low-loss hexapole mode with photonic crystal slab waveguide mode
https://www.rd.ntt/brl/result/activities/file/report04/data15.html
Control of Elastic Waves Using Phonon Waveguides and Phononic Crystals | NTT R&D Website
platforms, such as planar lightwave circuits and photonic crystals, improved the photon-control technology
https://www.rd.ntt/e/research/JN202202_17213.html
Hirofumi Sasaki | NTT R&D Website
-electronics converged wireless transmission, THz, photonic waveguide, High-capacity wireless transmission
https://www.rd.ntt/e/organization/researcher/special/s_092.html
List of Award Winners
InGaAs photodetectors based on photonic crystal waveguide including ultrasmall buried heterostructure Dec
https://www.rd.ntt/e/brl/result/activities/file/report14/data04E.html
Overview of Research in Laboratories
, and very small optical integrated circuits using two-dimensional photonic crystals, based on the
https://www.rd.ntt/e/brl/result/activities/file/report08/report01.html
Overview of Research in Laboratories
semiconductor nanowires, and a coupled resonator waveguide formed by ultrahigh-Q photonic crystal nano
https://www.rd.ntt/e/brl/result/activities/file/report07/report01.html
Time Resolved Measurement of Photonic Crystal Optical Nanocavity
Time Resolved Measurement of Photonic Crystal Optical Nanocavity Time Resolved Measurement of
https://www.rd.ntt/e/brl/result/activities/file/report06/report31.html
Efficient Carrier Envelope Offset Locking for a Frequency Comb by Modifying a Collinear f-to-2f Interferometer
10-GHz repetition rate in order to resolve each mode of the frequency comb with an arrayed-waveguide
https://www.rd.ntt/e/brl/result/activities/file/report08/report28.html
Demonstration of a CEO-locked Frequency Comb at Telecommunications Wavelengths with Low Pulse Energy
. Our new method employs a tellurite photonic crystal fiber (PCF) for supercontinuum (SC) generation
https://www.rd.ntt/e/brl/result/activities/file/report07/report28.html
Overview of Research in Laboratories
optical integrated circuits using two-dimensional photonic crystals, based on the optical properties of
https://www.rd.ntt/e/brl/result/activities/file/report11/report01.html
Research Activities in NTT Basic Research Laboratories Vol. 25 (2014)
Monolithic Waveguide Platform Loss-Tolerant Quantum Cryptography with Imperfect Sources The Design of a
https://www.rd.ntt/e/brl/result/activities/file/report14/2014_E.html
NTTBrl__E_h1
Photonic crystal waveguide and the optical modulation by applying the signal voltage Quantum network T he
https://www.rd.ntt/e/brl/result/activities/file/annual_report/Annual_report_2017_E.pdf
Contents
Soft X-Ray Pulse Shape Quantum Gate Operation of Quantum Dot Exciton Qubit Photonic-Crystal Single-Mode
https://www.rd.ntt/e/brl/result/activities/file/report01/E/2001_e.html
Research
the construction of DOPOs using a PPLN waveguide-based PSA [5], and further increase of the DOPO
https://www.rd.ntt/brl/people/htakesue/research.html
Over-100-bit Integrated Optical RAM Chip
using a high-Q photonic crystal nanocavity [1]. However, the highly dense integration of many o-RAMs is
https://www.rd.ntt/e/brl/result/activities/file/report14/report27E.html
Leading the World in Optical Devices and Photonics-electronics Convergence Devices While Promoting Our Technology and Increasing the Number of Like-minded Researchers | NTT R&D Website
) shows a schematic of a photonic integrated circuit we fabricated, which integrates an MZ modulator
https://www.rd.ntt/e/research/JN202405_26186.html
Optoelectronics Integration Research Group|Device Technology Laboratories|NTT R&D Website
sciences. ・Optical metasurfaces and imaging applications ・Optical circuit technology for photonic computing
https://www.rd.ntt/e/dtl/technology/optoelectronics_integration_research_group_ntt_device_technology_laboratories_ntt_rd_website.html
Ultralow-Power All-Optical RAM Chip Based on Nanocavities
shown in Fig. 1(a), where an ultra-compact InGaAsP is buried in an InP-PhC waveguide [2]. This structure
https://www.rd.ntt/e/brl/result/activities/file/report11/report29.html
Observation of Exceptional Point Degeneracy with Current-injected Photonic Crystal Lasers | NTT R&D Website
Observation of Exceptional Point Degeneracy with Current-injected Photonic Crystal Lasers | NTT R
https://www.rd.ntt/e/research/JN202206_18514.html
Exploring New Fields and the World | NTT R&D Website
advancing research on photonic crystal devices that operate with the world's lowest energy consumption
https://www.rd.ntt/e/research/JN202006_2201.html
納富 雅也 | NTT R&D Website
「ナノテクノロジーハンドブック」(章を執筆))オーム社 2003年 "Roadmap on Photonic Crystals, edited by S. Noda and T. Baba, Kluwer
https://www.rd.ntt/organization/researcher/fellow/f_010.html
Over-100-bit Integrated Optical Memories Realized|NTT Basic Research Laboratories | NTT R&D Website
optical random access memory (RAM) *1 by integrating ultrasmall optical memories based on photonic crystal
https://www.rd.ntt/e/brl/latesttopics/2014/05/latest_topics_201405260900.html
学術論文出版一覧
, and T. Tanabe, "Fast Calculation of the Quality Factor for Two-Dimensional Photonic Crystal Slab
https://www.rd.ntt/brl/result/activities/file/report14/data09J.html