Compact projector with high optical performance

A projector includes an illuminating system and an imaging system. The illuminating system includes a light source module, a lens array, a condenser lens and a display panel, in which light beams are generated by the light source module, uniformly dispersed by the lens array, condensed by the condenser lens, and reflected by the display panel to obtain image light, and the condenser lens has an effective focal length substantially equal to a product of an f-number of the illuminating system and a thickness of the lens array. The imaging system outwardly projects the image light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a projector with small volume and optimum optical performance.

2. Description of the Related Art

Electronic devices (e.g., mobile phones, cameras and notebook computers, etc.) with a pico projector contained are already seen in the present market. To be installed in the electronic products, the projector is necessarily limited in volume. The smaller of the volume of the projector, the more electronic devices can be collocated therewith. However, the minimized-volume projectors usually have poor optical performance. Therefore, it is a significant issue that how to keep the optical performance of a projector as the volume thereof is reduced.

BRIEF SUMMARY OF THE INVENTION

In view of this, the invention provides a projector capable of keeping the optical performance as the volume thereof is reduced by means of adjusting an effective focus length of a condenser lens and a thickness of a lens array.

A projector in accordance with an exemplary embodiment of the invention includes an illuminating system and an imaging system. The illuminating system includes a light source module, a lens array, a condenser lens and a display panel, in which light beams are generated by the light source module, uniformly dispersed by the lens array, condensed by the condenser lens, and reflected by the display panel to obtain image light, and the condenser lens has an effective focal length substantially equal to a product of an f-number of the illuminating system and a thickness of the lens array. The imaging system outwardly projects the image light.

In another exemplary embodiment, the effective focal length of the condenser lens is ranged between 8.25 mm and 19.2 mm.

In yet another exemplary embodiment, the light source module includes a first light source and a second light source.

In another exemplary embodiment, the first light source includes a green light-emitting diode, and the second light source includes a red light-emitting diode and a blue light-emitting diode.

In yet another exemplary embodiment, the projector further including a plurality of collimating lenses configured to convert the light beams generated by the first light source and the second light source into collimated beams.

In another exemplary embodiment, the projector further including a light source synthesizer, in which the collimated beams are combined by the light source synthesizer and projected to the lens array.

In yet another exemplary embodiment, the light source synthesizer is disposed at an intersection of the collimated beams.

In another exemplary embodiment, the lens array includes 3×5 spherical or aspherical micro biconvex lenses.

In yet another exemplary embodiment, the projector further including a reflecting mirror configured to reflect the light beams passing through the lens array to the condenser lens.

In another exemplary embodiment, the projector further including a polarization beam splitter configured to receive the light beams passing through the condenser lens, separate polarized light in a particular direction from the light beams passing through the condenser lens, and project the polarized light to the display panel.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a schematic view of a projector2of the invention is shown. The projector2includes an imaging system21and an illuminating system22. The structure of the imaging system21and the illuminating system22are described below.

The illuminating system22includes a light source module221,221′, a plurality of collimating lenses222, a light source synthesizer223, a lens array224, a reflecting mirror225, a condenser lens226, a polarization beam splitter227and a display panel228. The light source module, including a first light source221(e.g., a green light-emitting diode) and a second light source221′ (e.g., a red light-emitting diode and a blue light-emitting diode), is utilized to generate divergent light beams of different colors, in which the divergent light beams are converted into collimated beams when passing through the collimating lenses222, and the light source synthesizer is disposed at a intersection of the collimated beams, so that the collimated beams combined by the light source synthesizer223are emitted toward the lens array224. The lens array224includes at least 3×5 spherical or aspherical micro biconvex lenses. The light beams generated by the light source module are uniformly dispersed by the lens array224, reflected to the condenser lens226by the reflecting mirror225for convergence, and emitted to the polarization beam splitter227for separating polarized light in a particular direction therefrom. The polarized light is projected to the display panel228which adds image information into the polarized light to obtain image light. Then, the image light enters the imaging system21.

The imaging system21includes a plurality of lenses, through which the image light generated by the illuminating system22passes and is projected to a screen (not shown in Figs.).

An f-number (F/#) of the imaging system21is required to match an f-number (F/#) of the illuminating system22, so that the image light generated by the illuminating system22can be fully utilized by the imaging system21.

An F/# (or named f-number) of an optical system can be expressed by the following equation:
F/#=EFL/D(1)

wherein EFL represents an effective focus length, and D represents a diameter of clear aperture.

Referring toFIG. 2, a design principle of a projector of the invention is illustrated. In the illuminating system22, the light beams passing through the lens array224and the condenser lens226are projected to the display panel228. It can be seen fromFIG. 2that the diameter of clear aperture D is equal to the thickness of the lens array224. Accordingly, the above-described equation (1) can be rewritten as:
F/#Illuminating system=EFLCondenser lens/TLens array
or
EFLCondenser lens=F/#Illuminating system×TLens array(2)

wherein EFLCondenser lensrepresents an effective focus length of the condenser lens226, F/#Illuminating systemrepresents an f-number of the illuminating system22, and TLens arrayrepresents a thickness of the lens array224.

Thus, if the F/#Illuminating systemof the illuminating system22and the TLens arrayof the lens array224are known, then the EFLCondenser lensof the condenser lens226can be calculated by the equation (2). For example, the F/#Illuminating systemof the illuminating system22is practically ranged between 1.5 and 2.4, and the TLens arrayof the lens array224is practically ranged between 5.5 mm and 8 mm. Accordingly, the EFLCondenser lensof the condenser lens226is necessarily limited in the range between 8.25 mm and 19.2 mm.

In accordance with the calculated EFLCondenser lensof the condenser lens226, a pico projector can be designed with optimum optical performance and a minimized volume.