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Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Mobile phone objective camera optical design

February 2014

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2 Kennes 2/2014

Mobile phone camera objective unique requirements: Small packaging and cost effectiveness. Small packaging dimensions - mobile phones tend to be as thin as possible.

This leads to total optics length (first optical surface to image sensor) of 4-5mm.

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

3 Kennes 2/2014

In order to reduce optics length, small pixel size is needed, that reduces image sensor format, which leads in turn to reduced focal length and system length:

f = D/(2*tan (ϴ/2))

where: D - image sensor diagonal, ϴ - field of view.

Usually the field of view (ϴ) is about 68° and the image sensor diagonal (D) is 5.5mm, that lead to a focal length (f) of 4.08mm, which can be designed in a total length of less than 5mm.

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

4 Kennes 2/2014

Resolution of optics is measured in lp/mm.

1.1μm pixel, smallest cycle is a black and white pixels. 1.1μm pixel the cycle will be 2.2μm.

spatial frequency of 1000/2.2 = 455lp/mm.

This cutoff frequency is called the Nyquist frequency (Ny).

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

5 Kennes 2/2014

MTF specification of optics refer to this frequency, or lower frequencies:

half Nyquist frequency (Ny/2) of two black and two white pixels, 4.4μm for a 1.1 pixel size: 1000/4.4μm = 227lp/mm.

Ny/3 = 152lp/mm

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

6 Kennes 2/2014

Low cost phones use a fixed focus objective.

Smart phones usually use a focus mechanism ,based on voice coil magnetic (VCM) technology:a motor made of a coil and a permanent magnet .These modules are compact and cheap .

New technologies are emerging :

Corephotonics (Magnetic reluctance auto focus actuator)

MEMS type (Tessera) and others .

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

7 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Until recently some mobile phones employed

Extended Depth Of Focus (EDOF) technology.

This technology replaces the need of moving focus mechanism. The optics is designed to have lower

MTF level, but with higher MTF for objects out of focus .

8 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Image processing can improve the overall camera MTF and imitates the mechanical moving lens focusing .

This method has the big advantage of non moving parts but the performance is not as good as the mechanical focusing.

9 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Optical design considerations: F-number - a low F-number improves performance at

dim light .

On the other hand it decreases the depth of field ,the sensitivity to focusing error and the sensitivity to manufacturing errors. Most cameras usually have an F-number value of 2.4 Focal length - derived from the image sensor format size and field of view requirements.

 

10 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

 Distortion - Usually smaller than 2% and TV distortion (departure from a line object) Less than 1%. Usually the distortion is negative to improve relative illumination.

11 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

 Relative illumination - ideal lens it decreases with field of view according to cosine fourth law .

For a 34degree half field the cosine is 0.829 ,which leads to a 47% relative illumination at the field edge.

Usually the requirement is not less the 50% (relative to field of view center). This can be increased above theoretical limit by using negative distortion, which shrinks the image at the field edge and therefore increases light concentration.

12 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

 Lateral color - Usually the requirement is not greater than 2 pixels. Practically most designs meet 1 pixel lateral color.

 

13 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

  CRA (Chief Ray Angle) - increases with field angle. In order for the sensor to collect the light efficiently, a micro-lens array focuses the light on the pixel active

area .

The lens array is optimized for specific chief ray angles defined by the camera manufacturer. Usually this data is dictated for the optical design as the tendency is to use an on the shelf camera and to avoid a change in camera production line due to the optical design

14 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

  Manufacture guide lines - the optical design should take into account manufacturer guidelines that may differ from one manufacturer to another: optical materials preferred by the manufacturer, maximum surface slope angles, minimal edge/center thickness, etc.

15 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

  Manufacture technologies: Aspheric plastic injection molded optics. The plastic is melted to liquid (relatively low temperature of about 160°C) and injected to a mold. As plastic is less rigid and stable than glass, this technology is applicable for small lenses such as mobile phone optics.  

Tolerance analysis - This market is sensitive to cost and to yield. Therefore an extensive effort is invested in order to reduce design sensitivity to manufacture/assembly errors. Extensive simulations are made to estimate the production yield and to finding the optimal tradeoff between performance and yield.

16 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

   Larger lenses are produced from glass. Due to the glass high melting temperature, the glass is heated to softening temperature and than compressed by a mold (compression molding). Plastic molding is less expensive than glass molding. On the other hand glass has a wider optical choice of refractive index/Abbe properties, which improves the optical design. 

Tolerance analysis - This market is sensitive to cost and to yield. Therefore an extensive effort is invested in order to reduce design sensitivity to manufacture/assembly errors. Extensive simulations are made to estimate the production yield and to finding the optimal tradeoff between performance and yield.

17 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

   Wafer level, low cost technology - usually for a VGA camera. This technology uses UV replication technology, where a liquid polymer is dispensed on the wafer and the lenses are imprinted by using a transparent stamp or mold and UV-light for curing. This method allows the manufacture of a large scale of lens arrays with a sub-micron surface accuracy on a 10’’ wafer size. A mold with lens stamps is filled with liquid polymer. This mold is covered by glass wafer: 

Tolerance analysis - This market is sensitive to cost and to yield. Therefore an extensive effort is invested in order to reduce design sensitivity to manufacture/assembly errors. Extensive simulations are made to estimate the production yield and to finding the optimal tradeoff between performance and yield.

18 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

   Wafer level, low cost technology - usually for a VGA camera. This technology uses UV replication technology, where a liquid polymer is dispensed on the wafer and the lenses are imprinted by using a transparent stamp or mold and UV-light for curing. This method allows the manufacture of a large scale of lens arrays with a sub-micron surface accuracy on a 10’’ wafer size. A mold with lens stamps is filled with liquid polymer. This mold is covered by glass wafer: 

19 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Removing the mold after UV curing

Repeating process on the opposite wafer side:

20 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Removing the mold after UV curing

Combining several wafers, to create multiple lens system and inserting spacers between wafers (for simplicity only edge spacers are shown and not all the spacers needed between all lenses), and then cutting all the array into single channels (dashed line). See a real design in the last design example.

21 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

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3 Mpixel, F2.0, 2.9mm sensor diagonal

22 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

3 Mpixel, F2.0, 2.9mm sensor diagonal

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23 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

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8 Mpixel, F2.4, 4.54mm sensor diagonal

24 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

8 Mpixel, F2.4, 4.54mm sensor diagonal

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25 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

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3 Mpixel, F2.6, 4.6mm sensor diagonal, wafer level design

Light blue plates are wafer glass plates.

26 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

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3 Mpixel, F2.6, 4.6mm sensor diagonal, wafer level design

27 Kennes 2/2014

Micha Dror Electro Optics5 Eliyahu Meron st., Nes Ziona 74019, Israel

Tel:08-9409388, Cellular: 052-5866551

E-mail: michad@bezeqint.net

Applicable patents:

•US 7079330 B2 - 4 lens design•US 8305699 B2 - Wafer level design