Plastic Optical Materials
Sheng-Huei Derek Lu
College of Optical Sciences
University of Arizona
Apple iPhone 4 Camera Lens
• Apple iPhone 4 Camera Specs:
 5.0 Mpixels (2592 x 1936)
 3.85 mm lens focal length
 f/2.8 lens aperture
• Equivalent 35mm film camera
 30 mm f/22
image is 2592x1936 pixels
Cost isSample
Everything!!
(5.0 MP, 4.02:3)
• Don't throw away your FourThird, APS-C or full frame SLR 
iPhone 4 Camera Module
• Glass cell phone lenses cost $20-$40 in the market.
• Plastic cost: $3.55 only
• Manufacturer: Largan Precision Co., LTD, Taiwan
 Product#: 9457F
 Composition：4 Plastic Elements
• Very high production volumes
 Injection Molding: 8-Holes Method
 8 cavities at the same time
 Monthly volume = 207,306 parts
Outlines
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Plastic optical material application
Advantages
Disadvantages
Issues:
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


Structural Stability
Thermal Stability
Moisture Absorption
Injection Molding
• Wavefont error budget
• Reference
What are optical elements
made of plastic?
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•
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•
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Cellphone/ NB/ Car/ Camera Lens
Bar code scanners in CD players
Prisms
LED collimator
Diffractive Optical Elements
Main Advantages
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•
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•
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Cost
Production volume
Weight reduction
Aspheric and diffractive surfaces
Integral features – can have mounting features or multifunction
parts
Disadvantages
• Lower service temperature than glass
- max service 80-130 ºC
• Low structural stability
- soft, larger deflection while applying force, lower resonant
frequency than glass
• Poor thermal properties
– high dn/dT, high CTE
• Moisture Absorption
• Limited material selection
Material Properties of
Plastic Optical Element
Plastic Element Structural Stability
• ρ = 1 g/cm3, E = 3 Gpa
(glass: ρ=2.5 g/cm3, E=80 Gpa)
• Resonant frequency

k
m
EI E bh3
k 3  3
;
l
l 12
m  bhl

h
2 3l 3

E

• Plastic with 1/3 resonant frequency than glass
• Deflection per thickness
 

E
• Plastic with 10 times deflection than glass
Plastic Element Thermal Stability
• dn/dT = -8.5 ppm/ºC, CTE = 72 ppm/ºC, λ = 0.21 W/mK
(glass: dn/dT = 1.86 ppm/ºC, CTE = 7 ppm/ºC, λ = 1 W/mK)
• Defocus due to one degree change
• β = 89 ppm/ºC for plastic, β = 3.28 ppm/ºC for glass
• Linear thermal distortion of a constant heat flux Φ
T 


L

   T    ;
L0

• Plastic with 50 times thermal deflection than glass
Moisture Absorption
• Water absorption: change of volume, change of refractive index
-
The coefficient of moisture expansion (CME) for PMMA is about 0.5%
The change of refractive index for PMMA is about 900 ppm
• Cycloolefin Polymer (COP) and Cycloolefin Copolymer (COC) are
known as low moisture absorption.
Injection Molding
• Surface Imperfections
- Melt temperature is too high to cause gas evolution: bubbles
- Pressure is too low to cause incomplete filling of mold.
• Shrinkage
- If the part thickness is too thin, part will
shrink while cooling.
- Applying holding pressure is maintained
to compensate for material shrinkage
Tolerance Analysis: wavefont error budget
for the plastic optical component
1 mold costs $200,000!
Reference
• Selected plastic optical material characteristics are listed
in my tutorial: “Tutorial for Plastic Optical Materials”
• Great reference book: Stefan Bȁumer etc. “Hand Book of
Plastic Optics”, 2005 WILEY
• Formulas: Prof. Burge, Opti 521/421 class note