OPTOELECTRONICS OPTICAL STORAGE-Н ТАНИЛЦУУЛГА

◦Optical storage гэдэг нь бичигдсэн мэдээллийг гэрлийг ашиглан хадгалах юм. ◦Record density is determined by the spot size of the light beam, which is limited by the wavelength of the light and the NA (numerical aperture) of lens. ◦There are three categories of optical storage, i.e., read-only type, write-once type and rewritable type. ◦Different physical phenomena are used for recording of the signal on optical disks.

Spot size at the focal point ◦Numerical aperture of lens ◦ NA = nsin α ◦ d=0.6λ/NA CD-ROM: NA=0.6 λ=780nm→d=780nm DVD: λ=650nm→d=650nm BD: NA=0.85 λ=405nm→d=285nm HD-DVD: NA=0.6 λ=405nm→d=405nm spot size d α

Optical storages-н ангилал ◦Optical disk ◦Read only type /З ө вх ө н уншдаг т ө рлийн/ ◦CD, CD-ROM, DVD-ROM ◦Recordable type /Бичлэг хийх т ө рлийн/ ◦Direct read after write (Write once type) /Бичсэнийхээ дараа уншдаг (З ө вх ө н бичдэг т ө рлийн)/ ◦CD-R, DVD-R ◦Rewritable (recording and erasing) /Дахин бичдэг (бичээд м ө н устгадаг)/ ◦Phase change CD-RW, DVD-RAM, DVD-RW, DVD+RW, BD, HD-DVD ◦Magneto-optical: MO, GIGAMO, MD, Hi-MD, AS-MO, iD-Photo ◦Holographic memory, Hole-burning memory

Оptical disk-н технологид физикийн ү зэгдлийг хэрэглэх нь ◦CD-ROM, DVD-ROM: ◦pit formation / хонхортой байх/ ◦CD-R, DVD-R: ◦Chemical decomposition of organic dye / Органик будгаар химийн задралд оруулсан / ◦CD-RW, DVD-RAM, DVD-RW, DVD+RW : ◦Phase change between ordered and disordered states /Бичигдсэн ба бичигдээг ү й мужийн хооронд фаз шилждэг/ ◦MO, MD, GIGAMO, iD-Photo, HD-MD: ◦Magnetic phase change between ferromagnetic and paramagnetic states ◦Holographic memory ： Photorefractive effect ◦Hole-burning memory : Local structure change /Байршил дахь б ү тэц нь өө рчл ө гдд ө г /

Optical disk-н шинж чанар ◦Removable /Салгагддаг/ ◦Large capacity, high density /Их багтаамж, их нягттай/ ◦10Gb/in 2 (HD(100 Gb/in 2 –с бага байна) ) ◦Aiming at 100 Gb/in 2 using near-field technique ◦Random accessibility ◦Cassette  MD, VTR  DVD ◦Shorter access than magnetic tape ◦Longer seek time than HD ◦High reliability ◦Higher head clearance than HD

Increase of Areal Density in Optical Disks T. Suzuki:113th Topical Meeting of Magn. Soc. Jpn. (2000.1) p.11 Hard disk Optical disk MO

Different Disks

CD-ROM ◦Polycarbonate substrates ： n=1.55 ◦λ=780nm →λ’=503nm (wavelength in the substrate) ◦Pit depth:110nm ~ ¼wavelength ◦Phase difference in reflectionπ ： Destructive addition of reflected beams

CD-ROM Drive ◦Focusing servo ◦Tracking servo ◦Optical pickup Optical detector Cylindrical lens Polarization Beam Splitter Collimating lens Quarter wave-plate Objective lens Tracking Servo Focusing Servo Grating

CD-RW ◦Phase change ◦Crystalline and amorphous Substrate Protective layers UV coat Land Recording layer Reflection layer Printed surface

Phase change recording ◦Phase change between different phases ◦Rewritable: As grown amorphous state is initialized to crystalline state by annealing. Recording is performed by heating above the melting point T m (600  C) followed by quenching to amorphous state. Erasing is done by heating to T cr (400  C) to crystallize. ◦High level ： Heating above T m →rapid cool→amorphous ◦Low level ： Heating above T cr →slow cool→crystalline DVD-RAM: GeSbTe based alloy DVD±RW: Ag-InSbTe based alloy

Recording and erasing ◦Rapid cooling ： amorphous →low reflectivity ◦Slow cooling below Tm crystalline →high reflectivity sj/j/cdrw/rw_phase.html melting point crystalli- zation point crystalline amorphous Energy low reflectivity high reflectivity activation energy temperature Rapid cool Slow cool time melting point crystalli- zation point

Crystalline and amorphous Initial ： crystalline recorded: amorphous R: high R: low Record Erase laser spot recorded mark

What is amorphous? ◦Amorphous ◦non crystalline (disordered) state ◦without LRO (long range order) but with SRO (short range order) ◦Atomic arrangement of liquid is frozen ◦Metastable state introduced by rapid cooling of liquid ◦Random metallic alloy, chalcogenide glass, tetrahedral system, oxide glass ◦DRPHS (dense random packing of hard spheres) can explain RDF (radial distribution function)

Radial distribution function (RDF) ◦G(r): Probability to find a neighboring atom at a distance of r. experiment Calculated

CD-R ◦Organic dye is used ◦Thermal decomposition ◦Deformation of substrate by heat ◦Work as a pit laser beam deformation of substrate protective layer PC substrate Dye layer PC substrate Organic dye layer Protective layer Reflecting layer Pre-groove Recorded mark CD-R CD Protective layer Reflecting layer PC substrate Pit

DVD Family DVD-ROMDVD-RDVD-RAMDVD-RWDVD+RW capacity (GB) 4.7 / 層 / / 9.4 Formdisk cartridgedisk Mark formation/ Material/ reflectivity pit formation 1L R= L R=18-30 thermal deform organic dye R=45-85% phase change GeSbTe alloy R=18-30% phase change AgInSbTe alloy R=18-30% phase change AgInSbTe alloy R=18-30% wavelength nm lens NA 650/ / / shortest mark size １層 :0.4 2 層： track width Wobbled Land pre-bit 0.74 Wobbled L/G 0.74 Wobbled Land pre-bit 0.74 HF Wobbled groove Cyclability －－

MO （ magneto-optical ） Recording ◦Recording ： Thermomagnetic (Curie point ） recording ◦Heat-assisted magnetic recording ◦Playback ： Magneto-optical effect ◦Rotation of linear polarization is converted to the electrical signal ◦Employed in MO, MD disks ◦Compatibility ◦High repeatability ： 10,000,000 times ◦Complicated optical head (Polarization detection ） ◦Novel inventions such as MSR, MAMMOS, DWDD are realized as commercial products

Magneto-optical (MO) Recording ◦Recording : Thermomagnetic recording ◦Magnetic recording using laser irradiation ◦Reading out : Magneto-optical effect ◦Magnetically induced polarization state ◦MO disk, MD(Minidisk) ◦High rewritability ： more than 10 7 times ◦Complex polarization optics ◦New magnetic concepts: MSR, MAMMOS and DWDD

History of MO recording ◦1962 Conger,Tomlinson Proposal for MO memory ◦1967 Mee Fan Proposal of beam-addressable MO recording ◦1971 Argard (Honeywel)MO disk using MnBi films ◦1972 Suits(IBM)MO disk using EuO films ◦1973 Chaudhari(IBM)Compensation point recording to a-GdCo film ◦1976 Sakurai(Osaka U)Curie point recording on a-TbFe films ◦1980 Imamura(KDD)Code-file MO memory using a-TbFe films ◦1981 Togami(NHK)TV picture recording using a-GdCo MO disk ◦1988 Commercial appearance of 5”MO disk (650MB) ◦1889 Commercial appearance of 3.5 ”MO disk(128MB) ◦1991 Aratani(Sony)MSR ◦1992 SonyMD ◦1997 SanyoASMO(5” 6GB ： L/G, MFM/MSR) standard ◦1998 FujitsuGIGAMO(3.5” 1.3GB) ◦2000 Sanyo, Maxell iD-Photo(5cmφ730MB) ◦2004 SonyHi-MD