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 Sample image is 2592x1936 pixels (5.0 MP, 4.02:3) Don't throw away your FourThird, APS-C or full frame SLR  Cost is Everything!!

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 Plastic optical material application Advantages Disadvantages Issues: Structural Stability Thermal Stability Moisture Absorption Injection Molding Wavefont error budget Reference

What are optical elements made of plastic? Cellphone/ NB/ Car/ Camera Lens Bar code scanners in CD players Prisms LED collimator Diffractive Optical Elements

Main Advantages 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 Plastic with 1/3 resonant frequency than glass Deflection per thickness 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 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 Shrinkage - 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