光磁気の基礎 - Katsuaki Sato`s Homepage 佐藤勝昭の

Recent Advances in
Magneto-Optics
Katsuaki Sato
Department of Applied Physics
Tokyo University of Agriculture & Technology
ICFM2001 Crimia October 1-5, 2001
CONTENTS
1.
2.
3.
Introduction
Fundamentals of Magneto-Optics
Magneto-Optical Spectra
•
4.
Recent Advances in Magneto-Optics
•
•
•
5.
Magneto-optics in nano-structures
Nonlinear magneto-optical effect
Scanning near-field magneto-optical microscope
Current Status in Magneto-Optical Devices
•
•
•
6.
Experiments and theory
Magneto-optical disk storages
Magneto-optical isolators for optical communication
Other applications
Summary
ICFM2001 Crimia October 1-5, 2001
1. Introduction
• Magneto-Optical Effect：Discovered by Faraday on 1845
• Phenomenon：Change of Linear Polarization to Elliptically
Polarized Light Accompanied by Rotation of Principal Axis
• Cause：Difference of Optical Response between LCP and
RCP
• Application：
–
–
–
–
Magneto-Optical Disk
Optical Isolator
Current Sensors
Observation Technique
ICFM2001 Crimia October 1-5, 2001
2.Fundamentals of Magneto-Optics
• MO Effect in Wide Meaning
Any change of optical response induced by
magnetization
• MO Effect in Narrow Meaning
Change of intensity or polarization induced by
magentization
– Faraday effect
– MOKE(Magneto-optical Kerr effect)
– Cotton-Mouton effect
ICFM2001 Crimia October 1-5, 2001
2.1 Faraday Effect
• (a) Faraday Configuration:
– Magnetization // Light Vector
• (b)Voigt Configuration:
– Magnetization  Light Vector
ICFM2001 Crimia October 1-5, 2001
Faraday Effect
• MO effect for optical transmission
– Magnetic rotation（Faraday rotation）F
– Magnetic Circular Dichroism（Faraday Ellipticity） F
• Comparison to Natural Optical Rotation
– Faraday Effect is Nonreciprocal (Double rotation for round
trip)
– Natural rotation is Reciprocal (Zero for round trip)
• Verdet Constant
– F=VlH (For paramagnetic and diamagnetic materials）
ICFM2001 Crimia October 1-5, 2001
Illustration of Faraday Effect
Rotation of
Principal axis
For linearly polarized light
incidence,
Elliptically
Polarized light
Linearly polarized
light
• Elliptically polarized light
goes out (MCD)
• With the principal axis
rotated (Magnetic rotation)
ICFM2001 Crimia October 1-5, 2001
Faraday rotation of magnetic materials
Materials
wavelength
(nm)
578
temperature
(K)
RT
Mag. field
(T)
2.4
Fe
rotation
(deg)
3.825･105
Co
1.88･105
546
〃
2
Ni
1.3･105
826
120 K
0.27
Y3Fe5O12
250
1150
100 K
Gd2BiFe5O12
1.01･104
800
RT
MnSb
2.8･105
500
〃
MnBi
5.0･105
633
〃
YFeO3
4.9･103
633
〃
NdFeO3
4.72･104
633
〃
CrBr3
1.3･105
500
1.5K
EuO
5･105
104
660
4.2 K
2.08
CdCr2S4
3.8･103
35(80K)
1000
4K
0.6
figure of
merit(deg/dB)
44
1.43
ICFM2001 Crimia October 1-5, 2001
2.2 Magneto-Optical Kerr Effect
• Three kinds of MO Kerr effects
– Polar Kerr（Magnetization is oriented
perpendicular to the suraface）
– Longitudinal Kerr（Magnetization is in plane
and is parallel to the plane of incidence）
– Transverse Kerr （Magnetization is in plane
and is perpendicular to the plane of incidence）
ICFM2001 Crimia October 1-5, 2001
Magneto-optical Kerr effect
M
Polar
M
Longitudinal
ICFM2001 Crimia October 1-5, 2001
M
Transverse
MO Kerr rotation of magnetic materials
rotation
Photon
energy
temperature
field
(deg)
(eV)
(K)
(T)
Fe
0.87
0.75
RT
Co
0.85
0.62
〃
Ni
0.19
3.1
〃
Gd
0.16
4.3
〃
Fe3O4
0.32
1
〃
MnBi
0.7
1.9
〃
PtMnSb
2.0
1.75
〃
1.7
CoS2
1.1
0.8
4.2
0.4
CrBr3
3.5
2.9
4.2
EuO
6
2.1
12
USb0.8Te
9.0
0.8
10
0.2 S
CoCr
2 4
4.5
0.7
80
a-GdCo
*
CeSb
0.3
1.9
RT
Materials
90
2
ICFM2001 Crimia October 1-5, 2001
4.0
2.3 Electromagnetism and
Magnetooptics
• Light is the electromagnetic wave.
• Transmission of EM wave：Maxwell equation
• Medium is regareded as continuum→dielectric
permeability tensor
– Effect of Magnetic field→mainly to off-diagonal element
• Eigenequation
• →Complex refractive index：two eigenvalues
eigenfunctions：right and left circularpolarization
– Phase difference between RCP and LCP→rotation
– Amplitude difference →circular dichroism
ICFM2001 Crimia October 1-5, 2001
Dielectric tensor
~ E
D ε
0
  xx

~   
yx

  zx
 xy
 yy
 zy
 xz 

 yz 

 zz 
  yy

~   C 1~ C    
4
4
xy

   zy
ij  ij  ij
Isotromic media；M//z
Invariant C4 for 90°rotation
around z-axis
 xz
 xx
 zx
  yz 

 xz 

 zz 
 xx   yy
 yx   xy
  yz   zx   zy  0
  xx
~    
 xy
 0

ICFM2001 Crimia October 1-5, 2001
  yx
 xy
 xx
0
0 

0 
 zz 
MO Equations (1)
Maxwell Equation
Eigenequation
Eigenvalue
~
   2
rotrotE  2
E 0
2
c t
 Nˆ 2   xx

  xy

0

  xy
Nˆ 2   xx
0
0  E x 
 
0  E y   0

  zz  E z 
Nˆ 2   xx  i xy
Eigenfunction：LCP and RCP
Without off-diagonal terms：No difference between LCP & RCP
No magnetooptical effect
ICFM2001 Crimia October 1-5, 2001
MO Equations (2)
Nˆ  Nˆ   Nˆ    x x  i x y   x x  i x y  i
xy
 xx
Nˆ 
i  x y
F  




 xx
 (xy1) M
i



 (xx0)  12  (xx2) M 2
Both diagonal and off-diagonal terms contribute to
Magneto-optical effect
ICFM2001 Crimia October 1-5, 2001
Phenomenology of MO effect
Linearly polarized light can be
decomposed to LCP and RCP
Difference in phase causes rotation of
the direction of Linear polarization
Difference in amplitudes makes
Elliptically polarized light
In general, elliptically polarized light
With the principal axis rotated
ICFM2001 Crimia October 1-5, 2001
2.4 Electronic theory of MagnetoOptics
• Magnetization→Splitting of spin-states
– No direct cause of difference of optical response
between LCP and RCP
• Spin-orbit interaction→Splitting of orbital states
– Absorption of circular polarization→Induction of circular
motion of electrons
• Condition for large magneto-optical response
– Presence of strong (allowed) transitions
– Involving elements with large spin-orbit interaction
– Not directly related with Magnetization
ICFM2001 Crimia October 1-5, 2001
Dielectric functions derived from
Kubo formula
 f x mn
Nq 2
 xx    1 
  n   m 
m 0 n
  i 2   n20
 mn  f mn
Nq 2
 xy    i
  n   m 
2
2m 0 n
   i 2   mn

where
n 

exp(  n / kT )
exp(  n / kT )

Tr exp(  H 0 / kT )  exp(  n / kT )
n
f xj  2 m j 0 j x 0
2


 f mn  f mn
 f mn
ICFM2001 Crimia October 1-5, 2001


f jo

m j 0 0 x  j

2
Microscopic concepts of
electronic polarization
E
+
+
-
Wavefunction
perturbed by
electric field
Unperturbed
wavefunction
+
-
=
+ ・・
+
+
S-like
P-like
Expansion by unperturbed
orbitals
ICFM2001 Crimia October 1-5, 2001
Orbital angular momentum-selection
rules and circular dichroism
py-orbital
px-orbital
Lz=+1
p+=px+ipy
Lz=-1
p-=px-ipy
Lz=0
ICFM2001 Crimia October 1-5, 2001
s-like
Role of Spin-Orbit Interaction
Jz=-3/2
Jz=-1/2
L=1
LZ=+1,0,-1
L=0
Without
magnetization
LZ=0
Exchange
splitting
Jz=+1/2
Jz=+3/2
Jz=-1/2
Jz=+1/2
Exchange
+spin-orbit
ICFM2001 Crimia October 1-5, 2001
MO lineshapes (1)
1.Diamagnetic lineshape
Excited state
”xy
’xy
Lz=-1

0
Lz=+1
1
2
1+2
Ground state
Lz=0
Without
magnetization
With
magnetization
Photon energy
ICFM2001 Crimia October 1-5, 2001
Photon energy
MO lineshapes (2)
2.Paramagnetic lineshape
excited state
0
f+
f-
dielectric constant
 f=f+ - f’xy
”xy
ground state
without magnetic
field
with magnetic
field
photon energy
(b)
(a)
ICFM2001 Crimia October 1-5, 2001
3. Magneto-Optical Spectra
•
•
•
•
•
•
•
Measurement technique
Magnetic garnets
Metallic ferromagnet：Fe, Co, Ni
Intermetallic compounds and alloys：PtMnSb etc.
Magnetic semiconductor：CdMnTe etc.
Superlattices：Pt/Co, Fe/Au etc.
Amorphous：TbFeCo, GdFeCo etc.
ICFM2001 Crimia October 1-5, 2001
Measurement of magneto-optical spectra
using retardation modulation technique
i
Light source
monochro
mator
filter
/4
B
chopper
ellipsoidal mirror
polarizer
j
eletromagnet
sample
sample
P
D
PEM
quartz
A
Isotropic
medium
analyzer
detector
fused silica
CaF2
Ge etc.
Retardation
=(2/)nl sin pt
=0sin pt
computer
l
ICFM2001 Crimia October 1-5, 2001
Magnetic garnets
• One of the most intensively investigated
magneto-optical materials
• Three different cation sites; octahedral,
tetrahedral and dodecahedral sites
• Ferrimagnetic
• Large magneto-optical effect due to strong
charge-transfer transition
• Enhancement of magneto-optical effect by Bisubstitution at the dodecahedral site
ICFM2001 Crimia October 1-5, 2001
Electronic level diagram of
Fe3+ in magnetic garnets
Jz=
Jz=
J=7/2
6P (6T
6
2, T1g)
5/2
-
3/2
7/2
-3/2
-7/2
3/2
-3/2
3/2
-3/2
J=5/2
-3/2
J=3/2
P+
P+
P-
P-
6 S (6 A , 6 A )
1
1g
without
perturbation
spin-orbit
interaction
-5/2
5/2
tetrahedral
crystal field
(Td)
ICFM2001 Crimia October 1-5, 2001
octahedral
crystal field
(Oh)
Experimental and calculated
magneto-optical spectra of Y3Fe5O12
Faraday rotation (arb. unit)
0.8
experiment
+2
0
0.4
-2
calculation
0
-0.4
300
400
500
Wavelength (nm)
ICFM2001 Crimia October 1-5, 2001
600
Faraday rotation (deg/cm)
x104
Electronic states and optical transitions
of Co2+ and Co3+ in Y3Fe5O12
(a)
(b)
ICFM2001 Crimia October 1-5, 2001
Theoretical and experimental magnetooptical spectra of Co-doped Y3Fe5O12
ICFM2001 Crimia October 1-5, 2001
Theoretical and experimental
MO spectra of bcc Fe
Krinchik
Katayama
theory
ICFM2001 Crimia October 1-5, 2001
MO spectra of PtMnSb
Magneto-optical
Kerr rotation θK
and ellipticity ηK
(a)
K 
 xy
 xx 1   xx 
Diagonal dielectric
functions
(b)
ICFM2001 Crimia October 1-5, 2001
Off-diagonal
Dielectric function
(c)
Comparison of
theoretical and
experimental spectra
of half-metallic PtMnSb
(a)
(b)
(c)
After Oppeneer
(d)
ICFM2001 Crimia October 1-5, 2001
Magneto-optical spectra of
CdMnTe
Photon
Energy1-5,
(eV)
ICFM2001
Crimia October
2001
Pt/Co superlattices
Pt(10)/Co(5)
Pt(18)/Co(5)
simulation
experiment
Pt(40)/Co(20)
Photon energy
(eV)
Kerr rotation and
ellipticity(min)
Kerr rotation and
ellipticity(min)
PtCo alloy
rotation
elliptoicity
Photon energy
(eV)
ICFM2001 Crimia October 1-5, 2001
MO spectra in RE-TM (1)
Polar Kerr rotation (min)
Wavelength (nm)
ICFM2001 Crimia October 1-5, 2001
MO spectra in R-Co
Wavelength (nm)
300
400
500
600
700
Polar Kerr rotation (deg)
0
-0.2
-0.4
-0.6
5
4
3
Photon Energy (eV)
ICFM2001 Crimia October 1-5, 2001
2
MO spectra of Fe/Au superlattice
ICFM2001 Crimia October 1-5, 2001
Calculated MO spectra of Fe/Au
superlattice
By M.Yamaguchi et al.
ICFM2001 Crimia October 1-5, 2001
Au/Fe/Au sandwich
structure
By Y.Suzuki et al.
ICFM2001 Crimia October 1-5, 2001
4. Recent Advances in
Magneto-Optics
• Nonlinear magneto-optics
• Scanning near-field magneto-optical
microscope (MO-SNOM)
• X-ray magneto-optical Imaging
ICFM2001 Crimia October 1-5, 2001
NOMOKE
（Nonlinear magneto-optical Kerr
effect）
• Why SHG is sensitive to surfaces?
• Large nonlinear magneto-optical effect
• Experimental results on Fe/Au
superlattice
• Theoretical analysis
• Future perspective
ICFM2001 Crimia October 1-5, 2001
MSHG Measurement System
LD pump
SHG laser
Electromagnet
=810nm
Pulse=150fs
=532nm Ti: sapphire P=600mW Mirror
rep80MHz
laser
Filter
Stage
controller
Berek
compensator
Mirror
Sample
Analyzer
Lens
Filter
PMT
Chopper
lens
polarizer
Photon counting
Photon counter
Computer
ICFM2001 Crimia October 1-5, 2001
Sample
試料回転
 810nm)
Sample stage
45°
Rotating
analyzer
Filter
2 405nm)
 810nm)
Analyzer
Optical
arrangements
ICFM2001 Crimia October 1-5, 2001
Azimuthal dependence of
90
100
80
60
40
20
0
20
40
60
80
100
120
60
150
30
180
0
210
330
240
270
300
(a) Linear (810nm)
SHG intensity (counts/10sec.)
SHG intensity (counts/10sec.)
・ Linear optical response (=810nm)
The isotropic response for the azimuthal angle
・ Nonlinear optical response (=405nm)
The 4-fold symmetry pattern
Azimuthal pattern show 45-rotation by reversing the magnetic field
90
300
250
200
150
100
50
0
50
100
150
200
250
300
120
45
60
150
30
180
0
210
330
240
270
300
(b) SHG (405nm)
[Fe(3.75ML)/Au(3.75ML)] 超格子の
）配置の線形および非線形の方位角依存性
in Pout
ICFM2001（P
Crimia
October
1-5, 2001
Calculated and experimental patterns :x=3.5
SHG intensity (counts/10sec.)
SHG intensity (counts/10sec.)
(a) Pin-Pout
103
2000
1500
1000
500
0
500
1000
1500
2000
120
90
103
60
120
30
180
0
210
330
270
150
100
50
0
50
100
150
90
60
150
30
180
0
210
300
330
240
270
300
APP=1310, B=26, C=-88
APS=-300, B=26, C=-88
(c) Sin-Pout
(d) Sin-Sout
103
120
300
200
100
0
100
200
300
(b) Pin-Sout
150
240
Dots：exp.
Solid curve：calc.
90
103
60
150
30
180
0
210
330
240
270
300
40
30
20
10
0
10
20
30
40
120
90
60
150
30
180
0
210
330
240
270
300
ASP=460, B=26, C=ASS=100, B=26, C=ICFM2001 Crimia October 1-5, 2001
88
88
Nonlinear Kerr Effect
100000
90000
f = 31.1°
80000
70000
Rotating
60000
Analyzer
50000
Analyzer
40000
Filter
30000
2 (405nm)
20000
10000
0
-20 0 20 40 60 80 100 120 140 160 180 200
Electromagnet
S-polarized light
ω(810nm)
45°
The curves show a shift for two
opposite directions of magnetic field
Fe(1.75ML)/Au(1.75ML) Sin
ICFM2001 Crimia October 1-5, 2001
Nonlinear Magneto-optical
Microscope
Sample
P
Objective lens
L
F1
F2
A
CCD
Schematic diagram
50m
Linear and nonlinear magneto-optical
images of domains in CoNi film
ICFM2001 Crimia October 1-5, 2001
MO-SNOM
(Scanning near-field magneto-optical
microscope)
•
•
•
•
•
Near-field optics
Optical fiber probe
Optical retardation modulation technique
Stokes parameter of fiber probe
Observation of recorded bits on MO disk
ICFM2001 Crimia October 1-5, 2001
Near-field
Propagating
wave
Medium 1
Evanescent
wave
Evanescent
field
ic
Medium 2
ic
d
Critical
angle
c
Total reflection and near
field
Scattered
wave
Scattered wave by a small sphere placed
in the evanescent field produced by
another sphere
ICFM2001 Crimia October 1-5, 2001
Levitation control methods
Quartz oscillator
Fiber probe
bimorph
Sample surface
Piezoelectricallydriven xyz-stage
Shear force type
Piezoelectricallydriven xyz-stage
Canti-lever type
ICFM2001 Crimia October 1-5, 2001
Collection mode(a) and
illumination mode(b)
ICFM2001 Crimia October 1-5, 2001
SNOM/AFM System
Photodiode
LD
Compensator
Polarizer
Bimorph
Sample
PEM
Optical fiber probe
Filter
Lock-in
Amplifier
XYZ
Bent fiber probe
Analyzer
Ar ion
laser
Signal
generator
Photomultiplier
scanner
Controller
(SPI3800 3800)
MO-SNOM system using PEM
ICFM2001 Crimia October 1-5, 2001
Computer
Recorded marks on MO disk
observed by MO-SNOM
topography
MO image
ICFM2001 Crimia October 1-5, 2001
MO-SNOM image of 0.2m recorded marks on Pt/Co
MO disk
Resolution ↓
Topographic
image
MO image
ICFM2001 Crimia October 1-5, 2001
Line profile
Reflection type SNOM
P. Fumagalli, A. Rosenberger, G.
Eggers, A. Münnemann, N. Held,
G. Güntherodt: Appl. Phys. Lett. 72,
2803 (1998)
ICFM2001 Crimia October 1-5, 2001
ＸMCD
(X-ray magnetic circular dichroism)
Occupation of minority 3d band
(b)
(a)
md
+2
+1
0
(1)
-1
(a)
(14)
(6)
(2)
mj +3/2
+1/2
mj +1/2
3d
(3)
(6)
(12)
-2
(6)
(3)
(3)
-1/2
-3/2
-1/2
(b)
Simulated
XMCD
spectra
corresponding to transitions (a) and
(b) in the left diagram
2p3/2
2p1/2
ICFM2001 Crimia October 1-5, 2001
Magnetic circular dichroism of L-edge
(b)
ICFM2001 Crimia October 1-5, 2001
Domain image of MO media observed
using XMCD of Fe L3-edge
SiN(70nm)/ TbFeCo(50nm)/SiN(20nm)/
Al(30nm)/SiN(20nm) MO 媒体
N. Takagi, H. Ishida, A. Yamaguchi, H.
Noguchi, M. Kume, S. Tsunashima, M.
Kumazawa, and P. Fischer: Digest Joint
MORIS/APDSC2000, Nagoya, October
30-November 2, 2000, WeG-05, p.114.
ICFM2001 Crimia October 1-5, 2001
Spin dynamics in nanoscale region
GaAs high speed
optical switch
Th. Gerrits, H. van den Berg, O. Gielkens, K.J.
Veenstra and Th. Rasing: Digest Joint
MORIS/APDSC2000, Nagoya, October 30ICFM2001November
Crimia October
2001
2, 1-5,
2000,
TuC-05, p.24.
Further Prospects
－For wider range of researches－
• Time (t)：Ultra-short pulse→Spectroscopy using ps, fslasers, Pump-probe technique
• Frequency ()：Broad band width, Synchrotron radiation
• Wavevector (k)：Diffraction, scattering, magneto-optical
diffraction
• Length (x)：Observation of nanoscale magetism,
Appertureless SNOM, Spin-polarized STM, Xray
microscope
• Phase ()：Sagnac interferrometer
ICFM2001 Crimia October 1-5, 2001
5. Magneto-optical Application
• Magneto-optical disk for high density storage
• Optical isolators for optical communication
• Other applications
ICFM2001 Crimia October 1-5, 2001
Magneto-optical (MO) Recording
• Recording:Thermomagnetic recording
– Magnetic recording using laser irradiation
• Reading out: Magneto-optical effect
– Magnetically induced polarization state
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MO disk, MD(Minidisk)
High rewritability：more than 107 times
Complex polarization optics
New magnetic concepts: MSR, MAMMOS
ICFM2001 Crimia October 1-5, 2001
History of MO recording
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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 films1980
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 Sony
MD
1997 Sanyo
ASMO(5” 6GB：L/G, MFM/MSR) standard
1998 Fujitsu
GIGAMO(3.5” 1.3GB)
2000 Sanyo, Maxell
iD-Photo(5cmφ730MB)
ICFM2001 Crimia October 1-5, 2001
Structure of MO disk media
• MO disk structure
Al reflection
layer
Groove
Land
Polycarbonate
substrate
SiNx layer for
protection and
MO-enhancement
MO-recording layer
(amorphous TbFeCo)
Resin
ICFM2001 Crimia October 1-5, 2001
MO recording How to record(1)
• Temperature increase by focused laser beam
• Magnetization is reduced when T exceeds Tc
• Record bits by external field when cooling
M
Tc
Temp
Tc
Coil
External field
MO media
ICFM2001 Crimia October 1-5, 2001
Laser
spot
MO recording How to record(2)
• Use of compensation point Hc
writing
• Amorphous TbFeCo:
Ferrimagnet with Tcomp M
• HC takes maximum at Tcomp
– Stability of small recorded marks
Fe,Co
Tb
FeCo
Mtotal
Tb
RT
ICFM2001 Crimia October 1-5, 2001
Tcomp Tc T
アモルファスTbFeCo薄膜
TM
R
(Fe,Co) (Tb)
TM
(Fe,Co)
R
(Tb)
ICFM2001 Crimia October 1-5, 2001
Two recording modes
• Light intensity modulation
(LIM)： present MO
– Laser light is modulated by
electrical signal
– Constant magnetic field
– Elliptical marks
• Magnetic field modulation
(MFM)：MD, ASMO
– Field modulation by electrical
signal
– Constant laser intensity
– Crescent-shaped marks
Constant
laser beam
Modulated
laser beam
Constant field
Modulated field
(a)ICFM2001
LIM Crimia October 1-5,(b)
2001MFM
Magnetic head
Shape of Recorded Marks
(a) LIM
(b) MFM
ICFM2001 Crimia October 1-5, 2001
MO recording How to read
• Magneto-optical conversion of magnetic
signal to electric signal
D1
LD
+
D2
N
S
S
N
N
S
Differential
detection
Polarized
Beam
Splitter
ICFM2001 Crimia October 1-5, 2001
Structure of MO Head
Bias field coil
Recorded marks
Track pitch
Focusing lens
MO film
Rotation of
polarization
Beam splitter
mirror
lens
PBS
(polarizing beam splitter)
Laser diode
Half
wave-plate
Photo-detector
ICFM2001 Crimia October 1-5, 2001
Advances in MO recording
1. Super resolution
1. MSR
2. MAMMOS/DWDD
2. Use of Blue Lasers
3. Near field
1. SIL
2. Super-RENS (AgOx)
ICFM2001 Crimia October 1-5, 2001
MSR
(Magnetically induced super-resolution)
• Resolution is determined by diffraction limit
– d=0.6λ/NA, where NA=n sin α
– Marks smaller than wavelength cannot
α
be resolved
d
• Separation of recording and reading layers
• Light intensity distribution is utilized
– Magnetization is transferred only at the heated region
ICFM2001 Crimia October 1-5, 2001
Illustration of 3 kinds of MSR
ICFM2001 Crimia October 1-5, 2001
AS-MO standard
LD wavelength
NA
Disk diameter
Thickness
Track pitch
Recording method
Modulation
Signal processing
Velocity control
Code
650 nm
0.6
120 mm
0.6 mm
0.6 μm Land/Groove
MO & CAD-MSR
Laser pumped MFM
PRML
bit density 0.235μm) PR(1,1) or PR(1,2,1)
ZCAV/ZCLV
NRZI+ (DC supressed)
ICFM2001 Crimia October 1-5, 2001
iD-Photo specification
Memory Capacity
Surface memory density
LD wavelength
NA
Disk diameter
Thickness
Track pitch
Recording method
Modulation
bit density
Signal processing, PRML
Velocity control
Code
730 MB
4.6Gbit/in2
650 nm
0.6
50.8 mm
0.6 mm
0.6 μm Land/Groove
MO & CAD-MSR
Pulsed laser strobe MFM
0.235μm
PR(1,1) +Viterbi
ZCAV
NRZI+
ICFM2001 Crimia October 1-5, 2001
MAMMOS
(magnetic amplification MO system)
ICFM2001 Crimia October 1-5, 2001
Super-RENS
super-resolution near-field system
• AgOx film：decomposition
and precipitation of Ag
– Scattering center→near field
– Ag plasmon→enhancement
– reversible
• Applicable to both phasechange and MO recording
高温スポット
近接場散乱
ICFM2001 Crimia October 1-5, 2001
To shorter wavelengths
• DVD-ROM: Using 405nm laser, successful play back of
marks was attained with track pitch =0.26m、mark length
=213m (capacity 25GB) using NA=0.85 lens [i]。
[i] M. Katsumura, et al.: Digest ISOM2000, Sept. 5-9, 2000, Chitose, p. 18.
• DVD-RW: Using 405nm laser, read / write of recorded
marks of track pitch=0.34m and mark length=0.29m in
35m two-layered disk(capacity:27GB) was succeeded
using NA=0.65 lens, achieving 33Mbps transfer rate [ii] 。
[ii] T. Akiyama, M. Uno, H. Kitaura, K. Narumi, K. Nishiuchi and N. Yamada:
Digest ISOM2000, Sept. 5-9, 2000, Chitose, p. 116.
ICFM2001 Crimia October 1-5, 2001
Read/Write using Blue-violet LD
and SIL (solid immersion lens)
NA=1.5
405nm
80nm mark
40GB
ＳＩＬhead
405nm LD
I. Ichimura et. al.
(Sony),
ISOM2000
FrM01
ICFM2001 Crimia October 1-5, 2001
SIL (solid immersion lens)
ICFM2001 Crimia October 1-5, 2001
Optical recording using SIL
ICFM2001 Crimia October 1-5, 2001
Hybrid Recording
405nm
LD
Recording
head
(SIL)
Readout
MR head
Achieved 60Gbit/in2
H. Saga et al. Digest
MORIS/APDSC2000,
TuE-05, p.92.
TbFeCo
disk
ICFM2001 Crimia October 1-5, 2001
Optical elements for fiber
communication
• Necessity of optical isolators
• Principles of optical isolators
• Structure of optical isolators
– Polarization-independent type
– Polarization-dependent type
• Optical multiplexing and needs of optical
isolators
ICFM2001 Crimia October 1-5, 2001
Optical circuit elements proposed by
Dillon
(a) Rotator
(b) Isolator
(c) Circulator
(e) Latching switch
(d) Modulator
ICFM2001 Crimia October 1-5, 2001
Optical isolator for Laser diode
module
Optical isolator
for LD module
Optical fiber
Signal source
Laser diode
module
ICFM2001 Crimia October 1-5, 2001
Optical fiber amplifier and optical
isolator
isolators
EDFA
output
input
Band pass filter
mixer
Pumping laser
ICFM2001 Crimia October 1-5, 2001
Optical Circulator
B
A
C
D
ICFM2001 Crimia October 1-5, 2001
Optical add-drop and circulator
circulator
Fiber grating
circulator
ICFM2001 Crimia October 1-5, 2001
Polarization dependent isolator
analyzer
mag.field
reflected beam
polarizer
Faraday
rotator
input
ICFM2001 Crimia October 1-5, 2001
Polarization independent
isolator
Faraday rotator F
½ waveplate C
Birefringent plate B1
Birefringent plate B2
Fiber 1
Fiber 2
Forward direction
×
Fiber 1
B1
F
C
B2
Fiber 2
×
Reverse direction
ICFM2001 Crimia October 1-5, 2001
Magneto-optical circulator
Prism polarizer A
Faraday rotator
Reflection prism
Half wave plate
Port 2
Port 1
Port 4
Port 3
Prism polarizer B
ICFM2001 Crimia October 1-5, 2001
Optical absorption in YIG
ICFM2001 Crimia October 1-5, 2001
Waveguide type isolators
ICFM2001 Crimia October 1-5, 2001
Mach-Zehnder type isolator
ICFM2001 Crimia October 1-5, 2001
Current-field sensor
ICFM2001 Crimia October 1-5, 2001
Current sensors used
by power engineers
Before installation
Magnetic core
After installation
Aerial wire
Hook
Magneto-optical
sensor head
Fail-safe string
Fastening
screw
Optical fiber
ICFM2001 Crimia October 1-5, 2001
Field sensor using
optical fibers
ICFM2001 Crimia October 1-5, 2001
SUMMARY
• Basic concepts of magneto-optics are
described.
• Macroscopic and microscopic origins of
magneto-optics are described.
• Some of the recent development of
magneto-optics are also given.
• Some of the recent application are
summarized.
ICFM2001 Crimia October 1-5, 2001

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