[Ultra-small Projectors Teardown] Resin PBS Integrates Multiple Functions [Part 4]

Dec 31, 2008
Nikkei Electronics Teardown Squad
Fig 1: The optical module of the MPro110: In the photo, the LCOS is located on the lower side and the white LED on the right side. The module seemed to be made in China.
Fig 1: The optical module of the MPro110: In the photo, the LCOS is located on the lower side and the white LED on the right side. The module seemed to be made in China.
[Click to enlarge image]
Fig 2: The LCOS was removed from the optical module. The LCOS is attached to the optical module by the part seen at the bottom of the photo.
Fig 2: The LCOS was removed from the optical module. The LCOS is attached to the optical module by the part seen at the bottom of the photo.
[Click to enlarge image]
Fig 3: The white LEDs were mounted on a compact board.
Fig 3: The white LEDs were mounted on a compact board.
[Click to enlarge image]
Fig 4: The resin PBS. The lower right surface faces the projection lens, the lower left surface faces the LED light source and the upper left surface faces the LCOS. Part of the PBS was colored black to avoid excessive incident light.
Fig 4: The resin PBS. The lower right surface faces the projection lens, the lower left surface faces the LED light source and the upper left surface faces the LCOS. Part of the PBS was colored black to avoid excessive incident light.
[Click to enlarge image]
Fig 5: The Fresnel lens-shaped optical part was attached to the back of the black holder. The optical part in front is the reflective polarizing plate.
Fig 5: The Fresnel lens-shaped optical part was attached to the back of the black holder. The optical part in front is the reflective polarizing plate.
[Click to enlarge image]

The teardown of the ultra-small projectors has come to its final stage. The only thing we had left to break down was the optical module of the MPro110 (Fig 1). So, we started to take out the LCOS display device and the white LED light source from the module.

Judging from the logo printed on the driver LSI, the LCOS is probably a product of Himax Technologies Inc of Taiwan (Fig 2) (See related article). Its size is 0.55 inches, and the resolution is 640 x 480 pixels. It seemed that a color filter is provided on the LCOS side because there is no optical system to separate white light from the light source into RGB three colors.

As can be seen from the package and the electrode structure, the white LED "is most likely Cree Inc's XLamp," said a marketer of an LED manufacturer (Fig 3). Though it depends on the product class, the XLamp can output light with a luminance of up to approximately 100lm.

The light utilization efficiency (the ratio of output light intensity to incident light intensity) of an optical system in a projector is usually about 10%. The nominal luminance of images projected by the MPro110 is about 10lm. Thus, assuming that the light utilization efficiency is 10%, the light source is expected to have a luminance of about 100lm. This coincides with the luminance of the XLamp.

Multiple functions on resin PBS

The optical module is composed mainly of three optical parts. Of those three, what struck us most was a plastic PBS (polarizing beam splitter).

"It has such a unique shape," an engineer who is familiar with projectors said. "This is interesting!"

With diversified shapes on its surfaces, the PBS integrated multiple functions in addition to the basic function to transmit/reflect specific polarization components (Fig 4). For example, it apparently has a function to adjust light from the light source to the aspect ratio of the LCOS. It also seemed to work as part of the projection lens.

"This component can only be realized by resin, which has superior workability," said a researcher specializing in projector optical systems.

With multiple functions integrated in the PBS, the projector has a smaller and simpler optical system.

The other two components are an projection lens and an optical part shaped like a Fresnel lens. The latter seemed to collect light from the LEDs and process it into parallel light. This optical part is fixed to a black holder together with a reflective polarizing plate (Fig 5).

"This component was probably designed to feed back the light reflected on the polarizing plate to the LEDs," said the engineer. "Then, the light is reflected on the bottom face of the LED chip and supplied back again into the optical path to be reutilized."