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Plastic Optical Materials

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

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Plastic Optical Materials

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  1. Plastic Optical Materials Sheng-Huei Derek Lu College of Optical Sciences University of Arizona

  2. 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!!

  3. 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

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

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

  6. Main Advantages • Cost • Production volume • Weight reduction • Aspheric and diffractive surfaces • Integral features – can have mounting features or multifunction parts

  7. 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

  8. Material Properties of Plastic Optical Element

  9. 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

  10. 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

  11. 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.

  12. 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

  13. Tolerance Analysis: wavefont error budget for the plastic optical component 1 mold costs $200,000!

  14. 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

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