chapter 19. acousto optics - hanyangoptics.hanyang.ac.kr/~choh/degree/[2014-1] photonics...nonlinear...
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Nonlinear Optics Lab. Hanyang Univ.
Chapter 19. Acousto-Optics
19.1 Interaction of Light and Sound
19.2 Acousto-Optic Devices
19.3 Acousto-Optics of Anisotropic Media
Nonlinear Optics Lab. Hanyang Univ.
Acousto-Optic effect : The refractive index of an optical medium is altered by the presence of sound.
Light can be controlled by sound~
Applications : Optical Modulators, Switches, Filters, Isolators,
Frequency shifters, Spectrum analyzers, …
Change in refractive index of material by sound wave :
- Gas : Density modification by dynamic strain(sound wave)
- Solid, Liquid : Alternation of the optical polarizability by
the vibrations of molecules
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An acoustic wave creates a perturbation of the refractive index in the form of a wave.
Therefore, the medium becomes a “dynamic” graded-index medium (an inhomogeneous
medium with a time-varying stratified refractive index).
The theory of acousto-optics deals with the perturbation of the refractive index, and with the
propagation through the perturbed time-varying inhomogeneous medium.
However, since optical frequencies are much greater than acoustic frequencies. As a
consequence, it is possible to use an adiabatic approach in which the optical propagation
problem is solved separately at every instant of time, always treating the medium as if it were
a static inhomogeneous medium. In this quasi-stationary approximation, acousto-optics
becomes the optics of an inhomogeneous medium (usually periodic) that is controlled by
sound.
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19. 1 Interaction of light and sound
A. Bragg Diffraction
Considering an acoustic plane wave traveling in the x direction, the strain is
where, : angular frequency, : wavenumber
Acoustic intensity:
Refractive index change is given by [analogous to the Pockels effect in (20.1-4)]
where, : Photoelastic constant (strain-optic coefficient)
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Substituting from (19.1-2) into (19.1-5),
sI (19.1-6)
where, : Figure of merit for the strength of the AO effect in the material
Consequently, refractive index of medium is
where,
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Nonlinear Optics Lab. Hanyang Univ.
Nonlinear Optics Lab. Hanyang Univ.
Nonlinear Optics Lab. Hanyang Univ.
Figure of merit of the material
relative to water
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Consider an optical plane wave traveling through the acousto-optic medium,
Refractive index can be regarded as a static “frozen” sinusoidal function
(Adiabatic approach),
where, 𝜑 = Ω𝑡 : fixed phase
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Amplitude reflection
Divide the medium into incremental planar layers orthogonal to the x axis, since the optical
plane wave is partially reflected at each layer because of the refractive-index change.
And, assume that the reflectance is sufficiently small (transmitted light is not depleted),
Total complex amplitude reflectance :
Included since the reflected wave at x is advanced by a distance 2xsinq, corresponding to a
phase shift 2kxsinq, relative to the reflected wave at x=0. (refer to p.178, “Intro. to Optics”, Pedrotti)
Independent of x
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][)sin( )qx(j)qx(j eeqx Using complex notation,
where,
Performing the integral, and substituting 𝜑 = Ω𝑡,
where,
-r ,r: upshifted and downshifted reflections, respectively
L is sufficiently large, two maxima at 𝜃 = ±sin−1(𝑞/2𝑘) are sharp, so that any slight
deviation from the angles makes the counter term negligible. Thus, only one of these
two term is significant at a time.
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Bragg condition (upshifted reflection)
Sinc function has maximum when the argument is zero: 0sin 2 qk q (for upshifted reflection)
: Bragg angle is the angle for which the incremental reflection from planes
separated by an acoustic wavelength L have a phase shift of 2p
(2𝑘𝑥 sin 𝜃 = 2𝑘Λ ∙ 𝜆/2Λ = 2𝜋) so that they interfere constructively.
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Bragg condition (𝑞 = 2𝑘𝑥 sin 𝜃𝐵) is equivalent to the vector relation,
Nonlinear Optics Lab. Hanyang Univ.
Tolerance in the Bragg condition
(19.1-14)
])2sinsinc[(sin
]2)sin(sin2sinc[]2)sin2sinc[(
pqqpq
/L
/Lk/Lqk
B
B
qk B qsin 2
First zero at .
Since L is typically much greater than . This is an extremely small angular width.
L/B 2sin sin qq L/B 2qq
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Doppler shift
(19.1-14) )exp( tjr
Incident light field is proportional to [ ],
so the reflected wave has the form of ,
and has angular frequency
)exp( tjE )exp( tj
])(exp[ tjErEr
: The frequency as well as the propagation direction of the reflected wave is changed.
The frequency shift equal to the frequency of sound.
This can almost be thought as a Doppler shift.
q q
r vs
vssinq
Doppler shifted frequency :
LL pp )]2)(2)(2(21[ ///r
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Peak reflectance (skip)
Reflectance at the Bragg angle q=qB is [from (19.1-12)]
From (6.2-8), (6.2-9),
n1→n+Dn, n2=n, q1=90o-q, n1sinq1=n2sinq2, and neglect term of 2nd order in Dn,
(TE)
(TM) For small q, cos2q ~1
Report)
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From (19.1-18), by using ,
or, by (19.1-6)
sinq=/2L
- R : : typical light-scattering phenomena. 44
0
- R : valid only low intensity region since this result
is obtained from the approximation theory
(19.1B : Coupled-wave theory)
sI
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Downshifted Bragg Diffraction
qk B qsin 2
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Quantum interpretation
)( k, )( k,r
)( q,
Photon (, k) interacts with acoustic phonon (, q),
and generates a new reflected photon (r , k)
Energy and momentum conservation conditions:
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B. Coupled-wave theory
Bragg diffraction as a scattering process
Wave equation in a homogeneous medium with a slowly varying inhomogeneous
refractive-index perturbation Dn, (5.2-20)
where,
Radiation Source Term
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First Born approximation :
Assume that the scattering source S is induce by the incident field
[not by the actual (local) field].
- Incident field (plane wave),
- Perturbation in n caused by acoustic wave (plane wave),
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Coupled-wave equations (upshifted Bragg diffraction)
where,
(19.1-28)
Refer to Appendix II ~…
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Small-angle Bragg diffraction
For the case of small-angle diffraction(q<<1), two waves travel approximately in the z direction
(19.1-35)
where,
Boundary condition : 00 )(Ar
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Reflectance :
D
0
02sin
p dn2
0
0
D
p dn
d
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C. Bragg diffraction of beams
Diffraction of an optical beam from an acoustic plane wave
For an optical beam of width D interacting with an acoustic plane wave, the optical beam
can be decomposed into plane waves with directions occupying a cone of half-angle,
Rectangular: 1𝜆
𝐷, Circular: 1.22
𝜆
𝐷,
Gaussian(waist diameter=2w0 ): 𝜆
𝜋𝑤0= 0.64
𝜆
𝐷
Although there is only one wave-vector
q, there are many wave-vectors k within
a cone angle. But there is only one
direction k for which the Bragg
condition is satisfied.
The reflected wave is plane wave
with only one wave-vector kr.
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Diffraction of an optical beam from an acoustic beam
Suppose now that the acoustic wave itself is a beam of width Ds. Then angular divergence,
If the acoustic beam divergence is greater than the optical beam divergence (𝛿𝜃𝑠 ≫ 𝛿𝜃),
and if the central direction of two beams satisfy the Bragg condition, every optical plane
wave find acoustic match and the reflected light beam has the same divergence as the
incident beam.
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Diffraction of an optical plane wave from a thin acoustic beam :
Raman-Nath Diffraction
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Thin acoustic beam act as a thin phase (diffraction) grating.
Quantum interpretation :
One incident photon combines with two phonons to form a photon of second-order
reflected wave. Conservation of momentum condition is 𝑘𝑟 = 𝑘 ± 2𝑞. The energy
conservation condition is 𝜔𝑟 = 𝜔 ± 2Ω. Similar interpretations apply to higher orders.
Raman-Nath diffraction
(Debye-Sears scattering)
Refer to Appendix III~ multiple order diffraction
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19. 2 Acousto-optic devices
A. Modulators
Using an electrically controlled acoustic transducer (PZT), the intensity of the
reflected light can be varied. can be used as a modulator or switch.
D
0
02sin
p dnRe
(19.1.B), Reflectance, can be unity : 100% reflection
Efficient frequency shifter
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Modulation bandwidth
Bandwidth : Maximum frequency range(band) in which modulator can efficiently modulate.
[In idealized condition]
When both the optical and the acoustic waves are
plane waves, the frequency of sound corresponds
to a Bragg angle,
For a fixed angle of incidence q, an incident monochromatic optical plane wave of
wavelength interacts with one and only one acoustic wave frequency f satisfying (19.2-1).
The frequency of reflected wave is +f.
Although the acoustic wave is modulated, the reflected optical wave is not. That is, under
this idealized condition the bandwidth of the modulation is zero!
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Bandwidth : or : Transit time of sound wave
Necessary time for the sound wave
to interact at all point The light beam should be more tightly focused
in order to increase the bandwidth.
[ Modulation with a bandwidth B]
The sound wave is still planar, but the incident light is a beam of width D, and then
angular divergence 𝛿𝜃 = 𝜆/𝐷.
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B. Scanners
Relation between the angle of deflection and the sound frequency :
By changing sound frequency, the deflection angle can be varied. But both the angle of
incidence and the sound frequency must be changed simultaneously.
Tilting the sound beam!
The angle of tilt must be
synchronized with the
acoustic frequency f~
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[Another method instead of tilting]
To use a sound beam with an angular divergence equal to or greater than the entire range of
directions to be scanned.
As the sound wave frequency is changed, the Bragg angle is altered and incoming light wave
selects only one acoustic plane-wave with the matching direction. Efficiency is low~
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Scan angle
The incident light wave interacts with the sound wave of frequency f at an angle
𝜃 = (𝜆/2𝑣𝑠 ) 𝑓, and is deflected by an angle 2𝜃 = (𝜆/𝑣𝑠 ) 𝑓.
Scan angle of deflection to cover the bandwidth B is
The divergence of sound beam should be equal or greater than this angle, that is
Larger scan angles are obtained by use of materials in which the sound velocity is smaller~
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Number of resolvable spots
Number of resolvable spots :
Number of nonoverlapping angular widths of light within the scanning range
Angular width of the optical wave : 𝛿𝜃 = 𝜆/𝐷
Assuming that 𝛿𝜃 ≪ 𝛿𝜃𝑠 , the number of resolvable spots is
or
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The acousto-optics scanner as a spectrum analyzer
Sound waves with different frequencies are deflected in different directions. By this,
the spectrum of sound wave can be analyzed. Spectrum analyzer
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C. Space switches
Space switch : transfers information carried by one or more optical beams to one or more
selected directions.
Routing an optical beam to one of N directions by applying acoustic wave of frequencies fi.
Routing an optical beam to M directions simultaneously by applying acoustic wave of
frequencies fi simultaneously.
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Routing each of two(N) optical beams to a set of specified directions simultaneously by
applying acoustic wave of frequencies fi successively.
Each pulse duration : T/N
where, T=W/vs : transit time
Spatial light modulator(SLM)
Acoustic wave frequency f is the
same, but with different
amplitudes in different segments.
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Random access switch that routing each of L optical beams to M directions simultaneously
by applying acoustic wave of frequencies fi successively.
Acoustic cell is divides into
L segments, each of which
carries an acoustic wave
with M frequencies.
Interconnection capacity If an acoustic cell is used to route each of L incoming optical beams to a maximum of M
directions simultaneously, then product ML cannot exceed the time-bandwidth product N=TB.
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Nonlinear Optics Lab. Hanyang Univ.
D. Filters, frequency shifters, and isolators
Tunable acousto-optic filters Bragg condition, sin𝜃 = 𝜆/2Λ. Optical wavelength is the function of q and L(f).
Therefore, an optical wave with a wavelength can be selected successively by
adjusting the angle q (or the sound frequency f ).
Frequency shifters Bragg diffracted light is frequency shifted (up or down) by the frequency of sound, (𝜈 ± 𝑓).
Applications : Optical heterodyning (mixing two optical beams with different frequencies to
detect the beat signal), optical FM modulators, and laser Doppler velocimeters, …
Optical isolators
The frequency of returning light differs from that of
original light by twice the sound frequency.
A filter may be used to block the returning light.
Even without a filter, laser action may be insensitive
to the frequency-shifted light.
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19. 3 Acousto-optics of anisotropic media
Acoustic waves in anisotropic materials
Position of molecules :
Displacement :
Strain :
- Tensile(Normal) strain (i=j) : Strain along the stress
- Shear strain (i≠j) : Strain orthogonal to the stress
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The photoelastic effect (Refer to Appendix I~)
Photoeleastic effect : Change in refractive index of material by mechanical strain
In the presence of strain, the electric impermeability tensor is modified. Each of the
nine functions hij(skl) may be expanded in terms of nine variables skl in Taylor series.
where, : strain-optic (elasto-optic) tensor
Since both {hij}and {skl} are symmetrical tensors, the coefficients are invariant to
permutation of i and j, and to permutation of k and l. There are therefore only six
independent values for the set (i,j)→I and six independent values for (k,l)→K. The
fourth-rank tensor is thus described by a 6×6 matrix .
3323321331
23221221
131211
hhhhh
hhhh
hhh
Symmetrical tensor (example):
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Example) Strain-optic matrix for cubic crystal (or isotropic media):
Additional constraint: There are only two independent coefficients!
(miss print !)
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0
0
0
)cos(
)cos(
)cos(
0
0
0
)cos(
0
0
00000
00000
00000
000
000
000
011
012
012
0
44
44
44
111212
121112
121211
qztSp
qztSp
qztSp
qztS
p
p
p
ppp
ppp
ppp
sp ijIK
From example 19.3-1,
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z
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Bragg diffraction (Refer to Appendix II~)
Bragg condition:
(z-component)
(x-component)
Nonlinear Optics Lab. Hanyang Univ.
From (19.3-18), when 𝜃𝑟 = 𝜋/2
L
0sin
cos0
q
q
nn
n
r
2/pq
2)1 /pq L
0nnr
2)2 /pq L
0nnr
Nonlinear Optics Lab. Hanyang Univ.
Appendix
References :
A. Ghatak, K. Thyagarajam, “Optical Electronics”, Cambridge Univ. Press
A. Yariv, P. Yeh, “Optical Waves in Crystals”, John Wiley & Sons
I. Photoelastic effect
II. Bragg diffraction (Coupled-wave theory)
III. Raman-Nath diffraction
Nonlinear Optics Lab. Hanyang Univ.
Photoelastic effect
: Mechanical strain Index of refraction
Index ellipsoid for Principal axes : 12
3
2
2
2
2
2
1
2
n
z
n
y
n
x
Strain tensor elements, S :
zxxz
zyyz
yxxy
zzyyxx
Sx
wz
uS
Sy
wz
vS
Sx
vy
uS
zwS
yvS
xuS
,,
where, u, v, w : displacements along the x, y, z axes
xyzxyz
zzyyxx
SSSSSS
SSSSSS
654
321
,,
,, : Tensile(Normal) strain
: Shear strain
I. Photoelastic effect
Nonlinear Optics Lab. Hanyang Univ.
Change in index of refraction due to the mechanical strain :
)6,,1()1
(6
12
D
iSpn j
jiji
where, Pij : Elasto-Optic (Strain Optic) Coefficient (6x6 matrix) Table 9.1 / 9.2
The equation of the index ellipsoid in the presence of a strain field :
1222
111
654
32
3
2
22
2
2
12
1
2
j
jj
j
jj
j
jj
j
jj
j
jj
j
jj
SpxySpxzSpyz
Spn
zSpn
ySpn
x
Yariv, P. Yeh,
“Optical Waves in Crystals”,
John Wiley & Sons
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Nonlinear Optics Lab. Hanyang Univ.
Nonlinear Optics Lab. Hanyang Univ.
Example) Sound wave propagating along the z direction in water
Sound wave : )cos(ˆ),( KztzAtzw
0)/()/(,0)/()/(,0)/()/(
)sin()sin(/,0/,0/
654
321
xvyuSSxwzuSSywzvSS
KztSKztKAzwSSyvSSxuSS
xyzxyz
zzyyxx
Elasto-Optic Coefficient for the water (isotropic, Table 9.1) :
)(2
100000
0)(2
10000
00)(2
1000
000
000
000
1211
1211
1211
111212
121112
121211
pp
pp
pp
ppp
ppp
ppp
pij
0)1
(
),sin()1
(
),sin()1
()1
(
6,5,42
1132
122212
D
D
DD
n
KztSpn
KztSpnn
The new index ellipsoid :
1)sin(1
)sin(1
)sin(1
112
2
122
2
122
2
KztSp
nzKztSp
nyKztSp
nx
Nonlinear Optics Lab. Hanyang Univ.
Example) y-polarized Shear wave propagating along the z direction in Ge
Sound wave : )cos(ˆ),( KztyAtzv
0)/()/(,0)/()/(
),sin()sin()/()/(
,0/,0/,0/
65
4
321
xvyuSSxwzuSS
KztSKztKAywzvSS
zwSSyvSSxuSS
xyzx
yz
zzyyxx
Elasto-Optic Coefficient for the Ge (cubic, Table 9.1) :
44
44
44
111212
121112
121211
00000
00000
00000
000
000
000
p
p
p
ppp
ppp
ppp
pij
0)1
(
),sin()1
(
,0)1
()1
()1
(
6,52
4442
322212
D
D
DDD
n
KztSpn
nnn
The new index ellipsoid :
1)sin(2)(1
44
222
2 KztSyzpzyx
n
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II. Bragg diffraction (Coupled-wave theory)
In this regime, we can no longer consider the refractive index perturbation to act as a thin
phase grating. We should consider the propagation equation of light ;
e)sin(e2
2
0
2 Kztt
D
2
2
02
2
0
2 )sin()(t
eKzte
t
D
2
2)()(
02
2
02
2
2
2
)(2
1
t
eee
it
e
z
e
x
e KztiKzti
D
: )dependencey (no problem D-2 toconverting
eeee 0
: e-field Total
where,
])[)(
)(
0
)(
00
),(),(
),(),(
zxtiti
zxtiti
ezxAezxAe
ezxAezxAe
rk
rk
Nonlinear Optics Lab. Hanyang Univ.
222
0
2
222
0
2
)(
k
k
z
Ak
z
A
x
Ak
x
A
2
2
2
2
,
Let,
And, slow varying approximation ;
)]zxt)[(i)]zxt)[(i)]zxt[(i
)Kzt(i)Kzt(i
)]zxt)[(i
)]zxt)[(i
)zxt(i
eA)(eA)(eA
eei
ez
A
x
Ai
ez
A
x
Ai
ez
A
x
Ai
D
22
0
0
00
2
1
2
2
2
Nonlinear Optics Lab. Hanyang Univ.
])([
00
2)(
])([])([
0
2)(00
2
12
2
12
zKxizxi
zKxizKxizxi
eAi
ez
A
x
Ai
eAeAi
ez
A
x
Ai
D
D
Nonlinear Optics Lab. Hanyang Univ.
(1) Small Bragg angle diffraction
00
z
Aq
])([
00
2)(
])([])([
0
2)(0
2
12
2
12
zKxizxi
zKxizKxizxi
eAi
edx
dAi
eAeAi
edx
dAi
D
D
KK & : Bragg condition
Nonlinear Optics Lab. Hanyang Univ.
D
D
D
D
AA
AA
eAkdx
Ad
eAkdx
Ad
ix
ix
2/1
0
0
2/1
00
2/10
2
0
0
2
~
2
~
)(4 where,
~~
~~
These equations have a solution for when only , The solutions for , are independent each other, so let
A
0~
~
)(
~
0
20
2
0
2
D Adx
Adi
dx
Ad
2/12
412
)(
0
)(
00
)(
)(~
:solution
where,
21
21
D
DD
k
eDeCxAixix
021
021
)()(
,
)(~
where
21
21
DiD
CiC
eeDeCxA ixixix
D
D
DD
D
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Diffraction efficiency, h
DD
41
21
041
21
0
0
,
condition) (initial0)0(~
,1)0(~
DC
xAxA
)(sin)(~
)(
)(sin2
)(cos)(~
)(
222
22
22
00
xxAxP
xxxAxP
D
0-th and 1-st diffraction powers :
i) 2
4122
0 )(1)()( D xPxP
ii) Maximum transfer : D ;0
)(sin)(
)(cos)(
2
2
0
xxP
xxP
Diffration efficiency :
,2
3,2
1
)(sin)( 2
p
ph
h
L
LLp
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DD
2
0
11
nexpressionscalar :4
0 SpnD
B
B
nc
Spn
cq
q
cos
cos4
3
23
2
1SvI aa rAcoustic intensity :
2/1
2 )(cos2
a
B
IMq
p
326
2 / where, avpnM r : Figure of Merit
Diffraction efficiency :
LIM a
B
2/1
2
2 )(cos2
sinq
ph
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Acoustic intensity for maximum efficiency :
2
2
22
2
cos
LMI B
am
q
Acoustic power for maximum efficiency
(LH cross-section, maximum impedance matching case) :
22
22 1
2
cos
ML
H
MLHIp B
aam
q
Diffraction figure of merit
of the material relative to water
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(2) Large Bragg angle diffraction
02/
x
Apq
])([
00
2)(
])([])([
0
2)(0
4
1
4
1
zKxizxi
zKxizKxizxi
eAez
A
eAeAez
A
D
D
x-dependent term
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These equations have a solution for when only , The two solutions are independent each other, so let
1) K (Co-directional coupling)
A K
zi
zi
eAz
A
eAz
A
)(
0
)(0
~~
~~
s
s
D
D
k
AA
AA
c
D
D
D
s
2/1
0
0
2/1
00
2/1
0
2
2
2/1
0
2
2
~
2
~
)(
1
4)(4 where, 2/12
412
)(
0
)(
00
)( ,
)(~
where
21
21
D
DD iziz
eDeCzA
Solutions :
021
021
)()(
)(~
where,
21
21
DiD
CiC
eeDeCzA iziziz
s
s
D
D
DD
D
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Diffraction efficiency, h
0)0(~
,1)0(~
0 zAzA
DD41
21
041
21
0 , DC
0-th and 1-st diffraction powers :
)(sin)(~
)(
)(sin2
)(cos)(~
)(
222
22
22
00
zzAxP
zzzAzP
s
D
Diffraction efficiency :
]4
1[sin4/1
1
)(sin
2/1
2
2
2
22
2
2
D
D
s
s
s
sh
L
L
Nonlinear Optics Lab. Hanyang Univ.
2) K (Counter-directional coupling)
zi
zi
eAz
A
eAz
A
)(
0
)(0
~~
~~
s
s
D
D
KD where,
2/12
412
2121
2/)(
)(
011
)(
0
)(
1)(
~
)(~
where,
21
s
s
D
DD
D
DD
g
egQegPezA
eDeQePezA
gzigzizi
izgzgzzi
Solutions :
Nonlinear Optics Lab. Hanyang Univ.
0)(
~,1)0(
~0 DzAzA
{ gDgDg
gDgADP
gDgDg
gADP
22
2122
22
212
2
22
2122
22
00
sinhcosh
sinh~)(
sinhcosh
~)(
D
D
D
# Application : DBR reflector
Nonlinear Optics Lab. Hanyang Univ.
Acousto-Optic effect
Bragg diffraction & Raman-Nath diffraction
Bragg diffraction
: acoustic wave vector
is well defined
Raman-Nath diffraction
: acoustic wave vector
has an angular distribution
# Spread angle of Acoustic wave :
LnB
2~
q
L
L~
# Diffraction angle of Light :
L
L
acoustic wave
light wave
# Dimensionless parameter : 2
24
L
n
LQ B ppq
ndiffractioNath -Raman
ndiffractio Bragg
: 1
: 1
Vector Representation
III. Raman-Nath diffraction
Nonlinear Optics Lab. Hanyang Univ.
Raman-Nath diffraction :
Multiple order diffraction
Bragg diffraction :
Single order diffraction
Example) Water, n=1.33, W=6MHz (vs=1,500 m/s), l=632.8 nm
m250/ L sv
Regime Bragg
RegimeNath -Raman
: cm 2
: cm 2)2/(2
L pnL
Nonlinear Optics Lab. Hanyang Univ.
Moving periodic refractive index grating : Kztnntzn D sin, 0
Consider L is small enough so that the medium behave as a thin phase grating,
)sin(,2
10 KztLtzn D
p
where, 12p/)n0L, 12p/DnL
The transmitted field on the plane x=L :
)]sin([
010 Kztti
t eEE
qq im
m
m
i eJe
)(sin
)(
]}){(}){()([
where,
22
121110
)(
00
Kzt
eeJeeJJeEE iiiiti
t
q
qqqq
Nonlinear Optics Lab. Hanyang Univ.
])[(
])[(
)(
]2)2(]2)2(
120
])(])(
110
)(
100
00
00
0
KztiKzti
KztiKzti
ti
t
eeJE
eeJE
eJEE])([
100
0 0)(
Lxkti
t eJEEamplitude reduction
Frequency : ,
Wave vector :
2/1222
1
2/1222
1
]/)[(
,]/)[(
Kck
Kck
])()[(
110
])()[(
110
01
01
)(
)(
KzLxkti
KzLxkti
eJE
eJE
Propagation in x>L :
: +1 order
: -1 order
L
L
nk
K
nk
K
q
q
1
1
sin
sin
Diffraction angles : 1q
1q
Nonlinear Optics Lab. Hanyang Univ.
m-th order diffractive wave :
# Frequency :
# Diffraction angle :
m
L
nmm
qsin
D ,654.8,520.5,405.22
,0)( 110 nLJ
p
582.0)(85.1 111 J : First order diffraction maximum (diffraction efficiency ~ 33.9%)
!12 2
2
L
pL#
: The restriction on length of medium is
severe at higher frequency
Diffraction efficiency reduction
: zero order is absent