Fabrication Techniques of Optical ICs

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Duane Andrews
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1 Fabrication Techniques of Optical ICs Processing Techniques Lift off Process Etching Process Patterning Techniques Photo Lithography Electron Beam Lithography

Photo Resist ( Microposit MP1300) Electron Beam Resist ( PMMA, PGMA) Resist Techniques Exposed area is removed Positive resist after development Exposed area remains Negative

2 Photo Resist ( Microposit MP1300) Electron Beam Resist ( PMMA, PGMA) Resist Techniques Exposed area is removed Positive resist after development Exposed area remains Negative resist after development Lift off techniques widly used for the fabrication of metal thin film electrodes and the patterning of relatively thin waveguide film or cladding layers.

3 Etching techniques Wet etching ( uses liquid chemicals) Dry etching ( uses gaseous chemicals) Plasma etching, Sputter etching, Rective ion etching, Ion beam etching.

4 Example Fabrication of Strip Waveguide First photoresist spin coated on (2μm thickness) fused silica substrate ( at 3000 rpm rotation rate) # Az spin coated resist prebaked at 95 o Cfor30mins or 70 o C for 20 mins( overhanging pattern) immersed in substrate drying C6H5 Cl ( chlorobenzene)

5 Example Fabrication of Strip Waveguide Second spin coated resist development exposed touv light through an photomask RF sputtered with corning #7059 glassing in Ar gas atmosphere for 1hour 0.56μm thick film Final immersed in glass acetone removing photoresist

6 Table 5.4 Waveguide Structures and Fabrication Techniques Waveguide structure Guiding layer Substrate Fabrication Ti LiNbO 3 LiNbO 3 Selective Ti indiffusion H + LiNbO 3 LiNbO 3 Selective proton exchange K +, Ag +, Tl + Glass Soda-lime Selective ion exchange glass SiO 2 -B 2 O 3 -GeO 3 Fused quartz Sputter etching + CVD As 40 Se 10 S 40 Ge 10 Glass Light or electronbeam direct writing Ti LiNbO 3 LiNbO 3 Ti indiffusion + Dry etching Nb 2 O 5 LiNbO 3 Sputtering + Lift off Corning #7059 Pyrex Sputtering + Lift off Ta 2 O 5 -SiO 2,Al 2 O 3 Fused quartz Dry etching Photopolymer Fused quartz Development, Hardening SiO 2 cladding / Ti LiNbO 3 LiNbO 3 Ti indiffusion + Lift off SiO 2 cladding / Corning #7059 Pyrex Sputtering + Lift off Al-cladding LiNbO 3 Chemical etching / Ti LiNbO 3

7 Coupling of Beams to Planar Waveguides End Coupling ( end fire or head on method) a light wave ( with a profile simial to the guided mode profile) fed into waveguide end face ( normal to the wave propagation direction) Grating Coupling a dielectric grating excite through phase matching between the incident wave and a guided mode waveguide a guided wave Taper Coupling a tapered section in the waveguide couple light out of the waveguide

8 Prism Coupling a high index prism excite through phase matching between the incident wave and a guided mode waveguide a guided wave 1 sinθ The phase velocity in the z direction of the incident beam in the prism and in the gap between the prism and waveguide v z = c ( 5 1) n sinθ where c is velocity of light in free space, n is refractive index of prism, θ = sin + α p n p p p is the angle of the light beam to the normal at the prism base.

9 The angle θ efficient coupling chosen such that v is equal to the phase velocity of one of the guided modes z v z ω c = = ( 5 2) β β k where β is propagation constant for the guided mode, k = 2 π λ is the wave number in free space. So the effecient coupling condition β sinθ = n = + k 1 psinθ npsin sin αp ( 5 3) n p ( also applies to coupling light out of the waveguide)

10 Prism Material Table 5.5 Example of Prism Couplers Heavy flint glass (TaFD 16) (λ=0.633 µm) TiO 2 n o =2.584, n e =2.872 rutile (λ=0.633 µm) GaP (λ=0.633 µm) GaAs 3.6 (λ=0.9 µm) Refractive index Wavelength region Applicable waveguide Visible (0.1µm) ~ near infrared(10µm) Visible ~ near infrared red ~ near infrared near infrared materials Glass, organic polymer (1.45~1.6) LiNbO 3, LiTaO 3, ZnO, Si 3 N 4 LiNbO 3, ZnO, Si 3 O 4 Chalcogenide glass (As 2 S 3 ) Ga(Al)As

11 Advantages High efficiency (~ 80% for input and ~ 100% output); Any one of the guided modes can be selectively excited; Applied to channel waveguides as well as slab waveguides; The prism is detachable in the experiment. DisAdvantages The necessary adjustment of gap separation and beam position is very critical; Therefore the stability is rather poor; An expensive high index high precision prism and the adjustment mechanism are required.

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OPTI510R: Photonics. Khanh Kieu College of Optical Sciences, University of Arizona Meinel building R.626

OPTI510R: Photonics. Khanh Kieu College of Optical Sciences, University of Arizona Meinel building R.626 OPTI510R: Photonics Khanh Kieu College of Optical Sciences, University of Arizona kkieu@optics.arizona.edu Meinel building R.626 Announcements Homework #3 is due today No class Monday, Feb 26 Pre-record