Multichannel Phenomenon of Symmetrical Structure Optical Filter

Multichannel Phenomenon of SymmMultichannel Phenomenon of Symm

etrical Structure Optical Filteretrical Structure Optical Filter

Guoxun TianGuoxun TianApril 23, 2007April 23, 2007

ATMS790 Seminar (Dr. Pat ArnotATMS790 Seminar (Dr. Pat Arnott)t)

Outline

1. Mutiple reflection in Multilayer film

2. Introduction of Fabry-Perot filter

3. Multichannel Phenomenon in double-symmetrical structure

4. Design of double-linear filter

5. Two-chamber integrated multichannel narrowband filter

6. Review

High index

Low index

High index

Low index

High indexSubstrate

Incident lightReflected light =combination of

many beamsAir

Transmitted light

Multilayer

1.1. Mutiple reflection in Multilayer film

A multilayerA multilayer

A Fabry-Perot filter showing multiple reflections A Fabry-Perot filter showing multiple reflections in the spacer layerin the spacer layer

Spacer layer

Incident light

Reflected light =combination of many beamsAir

Transmitted light

High-reflectance

Multilayer

High-reflectance

Multilayer

2. Fabry-Perot filter

Mirror MirrorCavity


C

Structure of Fabry-PerotStructure of Fabry-Perot Filter Filter

77 )()( LHHHL C

This is a symmetrical structure and the position of channel was calculated by equivalent surface method

Structure of this Fabry-Perot filter: (HL)7HC(LH)7, where the number “7” is the periodic number and c is the periodic thickness of the cavity layer. 1H=1L=nHdH=nLdL=λ0/4, where dH and dL are the physical thickness of high and low refractive index material respectively, λ0 =600 nm. Vertical incidence, nH=2.3 and nL =1.44. Refractive index of substrate is n=1.52. Absorbance of the material of material is neglected to simplify the theoretical calculation.

Simulated conditionsSimulated conditions2. Fabry-Perot filter

)2(21

sin)1(

41

1

)1(21

2

221

212

21

21

δϕϕ −+−

+−

=

RRRRRR

TTT

κπδϕϕ 2221 =−+ )3,2,1( LLL±=κ

221

21max

)1( RR

TTT

−=

EEquivalent surface methodquivalent surface method


EEquivalent surface methodquivalent surface method

Maintains two mirrors invariably It means that 1 and

2 are constants

C is the thickness of Layer C δ （ δ =2πnC/ ）

Changes the thickness of layer C to satisfy the following formula

1+ 2 － 2πnC/=2kπ (k=±1 ， 2 ，3 ）

= 2πnC/ [2k π+( 1+ 2)]

Calculation of channel’s position


Multichannel Fabry-PerotMultichannel Fabry-Perot Filter Filter

Two-channel filter 492nm/598nm Three-channel filter487nm/550nm/632nm


Channel can be moved continuously by Channel can be moved continuously by changing layer Cchanging layer C

The position of channels are correlated. It is difficult to design a useful two-channel filter by this structure because we can not ensure every channel on it’s position.

500 550 600 650 700 750

5010050

10050

10050

10050

100C=5.6H

C=5.2H

C=4.8H

C=4.4H

C=4H

Wavelength(nm)

Transmittance(%)

Deficiency in this structure


Fabry-PerotFabry-Perot structurestructure Fabry-Perot structureFabry-Perot structure

Coupling layerCoupling layer

C Cd

7777 )()()()( LHHHLLLHHHL CdC

Double-symmetrical structure based on Double-symmetrical structure based on Fabry Perot structureFabry Perot structure


Movement of Channel position while d changes and C is fixed

Adjustment of Channel position



Calculated spectrum of double-symmetrical structure


Adjustment of Channel position Calculated spectrum of double-symmetrical structure

Movement of Channel position while C changes and d is fixed


Calculated spectrum and experiment spectrum

(HL)3HLCH(HL)3LD(HL)3HLCH(HL)3


(a) d changes and C is fixed (b) C changes and d is fixed

Here H=L=nHdH=nLdL=λ0/4， λ0=749nm， nH=2.2 ， nL=1.44


Calculated spectrum and experiment spectrum (1H1L)31H1LC1H(1H1L)31LD(1H1L)31H1LC1H(1H1L)3

(a) d changes and C is fixed (b) C changes and d is fixed

Film structure of double-linear filter



Relationship between incident point and spectrumIncident point move along X axis




Relationship between incident point and spectrumIncident point move along Y axis


C C

Film structure of two-chamber filter


The original structure of the filter designed to be (HL)4H4.64LH(LH)4L(HL)4H4.64LH(LH)4 with design wavelength =777.4nm0

Flow sheet of the preparation of two-chamber integrated narrowband filter


(a) Depositing the first resonant cavity, (b) etching the first resonant cavity, (c) second depositing, (d) depositing the second resonant cavity, (e) etching the second resonant cavity, (f) deposition the residual film.

(HL)4H4.64LH(LH)4L(HL)4H4.64LH(LH)4


Calculated spectrum of two-chamber integrated narrowband filter

780 800 820 840 860 880 900 920-0.10.00.10.20.30.40.50.60.70.80.91.0

%Transmittance

Wavelength / nm

Experiment spectrum of two-chamber integrated narrowband filter


(HL)4H4.64LH(LH)4L(HL)4H4.64LH(LH)4

Instrument and experiment condition


Thickness of two spacer layer of which equivalently decreases by the optical thickness of 0.02L through the etching technique.

Coating machine: ZZSX-800 (Beijing Beiyi Innovation Vacuum Technology Co., Ltd, Beijing, China) optical multilayer coating machine, which uses the electron-beam vapor-deposition method assisted by ionic bombardment to fabricate the multilayer. Etching machine: the LKJ-1C (Beijing Institute of Radio Measurement, Beijing, China) ion-beam etching machine, which uses the dry etching method. The entrance angle of the ion beam is normal. The depth of the 32 parallel etched notches is gradually increased, and their width and length are 0.375 and 12 mm, respectively. Material: TiO2 and SiO2.


Instrument and experiment condition

Thank you_ _

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Multichannel Phenomenon of Symmetrical Structure Optical Filter