Multichannel Phenomenon of Symmetrical Structure Optical Filter Guoxun Tian April 23, 2007 ATMS790 Seminar (Dr. Pat Arnott)

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

1. 1. Mutiple reflection in Multilayer film  A multilayer

A Fabry-Perot filter showing multiple reflections in the spacer layer 2. Fabry-Perot filter

Mirror Cavity 2. Fabry-Perot filter C  Structure of Fabry-Perot Filter This is a symmetrical structure and the position of channel was calculated by equivalent surface method

Structure of this Fabry-Perot filter: (HL) 7 H C (LH) 7, where the number “7” is the periodic number and c is the periodic thickness of the cavity layer. 1H=1L=n H d H =n L d L =λ 0 /4, where d H and d L are the physical thickness of high and low refractive index material respectively, λ 0 =600 nm. Vertical incidence, n H =2.3 and n L =1.44. Refractive index of substrate is n=1.52. Absorbance of the material of material is neglected to simplify the theoretical calculation.  Simulated conditions 2. Fabry-Perot filter

 Equivalent surface method 2. Fabry-Perot filter

 Equivalent surface method Maintains two mirrors invariably It means that  1 and  2 are constants C is the thickness of Layer C  （  =2  nC/ ） Changes the thickness of layer C to satisfy the following formula  1 +  2 － 2  nC/ =2k  (k=±1 ， 2 ， 3 ） = 2  nC/ [2k  +(  1 +  2 )]  Calculation of channel’s position 2. Fabry-Perot filter

 Multichannel Fabry-Perot Filter Two-channel filter 492nm/598nmThree-channel filter487nm/550nm/632nm 2. Fabry-Perot filter

 Channel can be moved continuously by changing 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.  Deficiency in this structure 2. Fabry-Perot filter

Fabry-Perot structure Coupling layer CCd Double-symmetrical structure based on Fabry Perot structure  Double-symmetrical structure based on Fabry Perot structure 3. Multichannel Phenomenon in double-symmetrical structure

Movement of Channel position while d changes and C is fixed  Adjustment of Channel position 3. Multichannel Phenomenon in double-symmetrical structure  Calculated spectrum of double-symmetrical structure

3. Multichannel Phenomenon in 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) 3 HL C H(HL) 3 L D (HL) 3 HL C H(HL) 3 3. Multichannel Phenomenon in double-symmetrical structure (a) d changes and C is fixed (b) C changes and d is fixed Here H=L=n H d H =n L d L =λ 0 /4 ， λ 0 =749nm ， n H =2.2 ， n L =1.44

3. Multichannel Phenomenon in double-symmetrical structure  Calculated spectrum and experiment spectrum (1H1L) 3 1H1L C 1H(1H1L) 3 1L D (1H1L) 3 1H1L C 1H(1H1L) 3 (a) d changes and C is fixed (b) C changes and d is fixed

 Film structure of double-linear filter 4. Design of double-linear filter

 Relationship between incident point and spectrum  Incident point move along X axis 4. Design of double-linear filter

 Relationship between incident point and spectrum  Incident point move along Y axis

CC  Film structure of two-chamber filter 5. Two-chamber integrated multichannel narrowband filter The original structure of the filter designed to be (HL) 4 H 4.64 LH(LH) 4 L(HL) 4 H 4.64 LH(LH) 4 with design wavelength =777.4nm

 Flow sheet of the preparation of two-chamber integrated narrowband filter 5. Two-chamber integrated multichannel 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) 4 H 4.64 LH(LH) 4 L(HL) 4 H 4.64 LH(LH) 4 5. Two-chamber integrated multichannel narrowband filter  Calculated spectrum of two-chamber integrated narrowband filter

 Experiment spectrum of two-chamber integrated narrowband filter 5. Two-chamber integrated multichannel narrowband filter (HL) 4 H 4.64 LH(LH) 4 L(HL) 4 H 4.64 LH(LH) 4

 Instrument and experiment condition 5. Two-chamber integrated multichannel narrowband filter 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 and 12 mm, respectively. Material: TiO 2 and SiO Two-chamber integrated multichannel narrowband filter  Instrument and experiment condition