1. Technical Field
Embodiments of the invention relate to optical imaging lens systems and mounting arrangements thereof, and methods of fabricating.
2. Description of Related Art
A common type of variable focus system involves multiple solid lenses in which relative distances between two or more lenses can be varied to alter the focal length of the lens system. A drawback of this system is the relatively large form factor which limits the size of a device incorporating the variable focus system.
With increasing demand for miniaturized devices, an optical system having smaller form factor and improved performance is desired.
Embodiments of the invention relate to optical imaging lens systems having a lens assembly configured to simultaneously focus light rays originating from objects disposed at various distances onto a first focal plane which is maintained at a fixed distance from the lens assembly. The objects may be disposed at a near distance or at near-infinity distance from the lens assembly. To this purpose, the lens assembly has at least one non-uniform optical property.
Various arrangements may be envisaged to achieve the at least one non-uniform optical property in the lens assembly. In one embodiment, at least one of the lenses may have at least one graded optical property, i.e. graded lens. In another embodiment where at least some of the lenses have a susbtantially uniform optical property within each lens, i.e., non-graded lens, at least two of the lenses may have at least one different optical property. In certain embodiments, at least some of the lenses may be disposed in different directions.
In certain embodiments, a retainer structure may be provided to support the lenses. In certain applications, a suitable actuator, e.g. piezo actuator, may be employed in cooperation with embodiments of the invention to perform a zoom or focus function.
Embodiments of the invention are particularly advantageous in providing an optical imaging lens system which is capable of simultaneously focusing light rays originating from objects disposed at various distances onto a first focal plane which is maintained at a fixed distance from the lens assembly. Hence, embodiments of the invention enable imaging devices in small and compact form factor while still providing quality focus and, in some applications, zooming functions.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative embodiments of the present invention. It will be understood, however, to one skilled in the art, that embodiments of the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure pertinent aspects of embodiments being described. In the drawings, like reference numerals refer to same or similar functionalities or features throughout the several views. It is to be appreciated that
Embodiments of the invention such as, but not limited to, those illustrated in
The lens assembly of the optical system is operable to simultaneously focus light rays originating from various distances onto a first focal plane. More particularly, parallel, convergent or divergent light rays from objects at near distances (e.g. at least a few millimetres), and parallel or near parallel light rays from far objects or objects at near-infinity distances may be simultaneously focused onto a first focal plane while maintaining quality focus of a formed image with an acceptable tolerance limit. In certain embodiments, a separation distance between a second focal plane where an image of a near object may be formed and a third focal plane where an image of a far object may be formed should have an acceptable tolerance limit, e.g., at most about ±300 micrometres, at least about ±300 micrometres. The first focal plane may be suitably maintained at a fixed distance from the lens assembly whether the optical system is focussing on objects at near distances, or objects at near-infinity distances, or both. Thus, when focussing objects at various distances, the optical sytem does not require varying a relative distance between the lens assembly and a first focal plane or an image plane on which images of the objects are focussed on to be captured by an image sensor. In other words, the first focal plane for forming capturing images disposed at various distances, including near distances and near-infinity distance, is fixed relative to the lens assembly. Since a relative movement between lenses is not necessary when performing a focus function, the optical system would require less space and less power. The image plane may be provided as part of an image sensor, such as but not limited to, a charge-coupled device (CCD), a complementary metal-oxide-semiconductor (CMOS) active-pixel sensor and a photographic film.
Simultaneous focussing of objects at near distances and objects at near-infinity distances without varying a relative distance of the first focal plane and the lens assembly may be achieved by having at least one non-uniform optical property within the lens assembly. Various arrangements may be employed for this purpose, some of which are described as follows. In one embodiment, at least one of the lenses may have at least one graded optical property (also referred to as a graded lens) in which at least one optical property varies gradually or abruptly within the lens according to a predetermined or non-predetermined profile. Grading may be achieved by controlling the impurity content of the lens material, or by controlling the temperature profile or growth environment profile during the lens fabrication process. In another embodiment where at least some of the lenses have susbtantially uniform optical property within each lens (also referred to as a non-graded lens), at least two of the lenses may have at least one different optical property. In yet another embodiment, the lens assembly may include both graded and non-graded lenses. In certain embodiments, at least two of the lenses may be arranged in different directions. The above-described arrangements of achieving at least one non-uniform optical property in a lens assembly, and other arrangements not described, generally apply to embodiments of the invention and hence will not be further reproduced in the following paragraphs relating to each embodiment.
In the present disclosure, the term “optical property” includes, but are not limited to, refractive index, light transmission coefficient, absorption coefficient, dispersion power, polarization, stretchability, Abbe number, focal length, optical power, reflective performance, refractive performance, spot size, resolution, modulation transfer function (MTF), distortion, and diffractive performance.
According to some embodiments of the invention, a retainer structure may be provided to support the lenses. In certain other embodiments, a retainer structure may not be required. Depending on the intended application of the optical system, the retainer structure may include a heat-resistant material such as, but not limited to, a liquid crystal plastic, a black liquid crystal plastic, an epoxy, a polymer and a monomer. The liquid crystal plastic may include glass fibers or frits. If required, the retainer structure may include threads to facilitate installation or mounting of the optical system to an external body or device. The retainer structure may be formed of a transparent or a non-transparent (opaque) material. If heat-resistant materials are used, the optical system may be employed in a high-temperature environment, e.g. a reflow oven.
The embodiments of
The piezo materials 710 coupled to opposed surfaces of an actuating substrate 720 may be electrically connected to an appropriate control circuit 740 to provide a deflection on the actuator substrate 720 or a compressive and/or decompressive force when the actuator 700 is activated.
The input voltage to control circuit 740 may be received from an image sensor or autofocus driver circuit. The output voltage from the control circuit 740 may be applied to the piezo materials (piezo actuator) in order to deform the actuator body to generate a compressive or decompressive force which is applied to the lens. When the piezo actuator 700 is activated, the piezo actuator 700 applies a compressive or decompressive force to the lens or substrate layer connected thereto to vary at least one of an optical property of the lens, and a physical property of the lens. As a result of varying at least one of a physical property and an optical property, the lenses may deform or may not deform. In the present description, the term “physical property” includes, but are not limited to, mass, shape, volume, density, thermal property, magnetic property, hardness, energy conversion factor, length, width, and radius of curvature.
Depending on the material used, the lenses of the lens assembly may be deformable or non-deformable, and/or compressible or non-compressible by the operation of the piezo actuator 700. More particularly, lenses which are deformable by the piezo actuator may be compressible or non-compressible; lenses which are non-deformable by the piezo actuator may be compressible or non-compressible. Thus, by using one or more piezo actuators, the optical system is operable to perform a zoom function. In the present description, while a piezo actuator is used to enable focus and/or zoom function in the optical system, it is to be appreciated that other types of actuators including, but not limited to, a voice coil motor, an electromagnet actuator, a thermal actuator, a bi-metal actuator, and an electrowetting device may be used with suitable modifications.
While the above paragraphs and
In the above embodiments as illustrated in
For the sake of clarity in the illustrations, the lens assembly has been illustrated as having well-defined boundaries between adjacent lenses or substrate layers or graded layers. It is to be appreciated that the boundaries between adjacent lenses or substrate layers may be less clearly defined. In particular, the variation of the optical properties between lenses may occur in a gradual manner.
Further, a graded lens may have a same optical effect as a composite lens being formed of multiple lenses having at least one different optical property. Theoretically, each of the multiple lenses may have a minute thickness, e.g. having a thickness of an atomic layer, and therefore a graded lens may be construed as being formed of a very large number or near-infinite number of lenses with minute thickness.
Embodiments of the invention may be employed in a variety of optical applications including, but not limited to a barcode reader, a digital camera, an analogue camera, mobile phone camera, camera using photographic film, and an eye implant. Such digital and analogue cameras may be used in devices and applications, including but not limited to, automotive cameras, security cameras, remote control cameras, remote control devices, mobile device cameras, endoscopic capsule cameras, endoscope camera, cameras used in medical applications, cameras used in telescopes, cameras used in space applications.
A method of fabricating an optical system as described in the above embodiments is described as follows. A retainer structure and a first lens may be separately molded, such as by two-colour molding or by in-mold decoration. Either the retainer structure or the intermediate lens may or may not be molded first. Subsequently, a lens assembly having a non-uniform optical property may be formed by disposing the first lens and a second lens in the retainer structure in a juxtaposed arrangement. Materials for the lenses are suitably selected so that at least one of the first and the second lens has a graded optical property. Further, but optionally, at least one of the first and the second lens may be a non-graded lens. The above-described method is exemplary, and it is to be understood that other methods of fabrication may be used with suitable modifications.
Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the embodiments as disclosed. The embodiments and features described above should be considered exemplary, with the invention being defined by the appended claims.
Number | Date | Country | Kind |
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PCT/SG2208/000136 | Apr 2008 | SG | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SG09/00151 | 4/23/2009 | WO | 00 | 10/24/2010 |