TECHNICAL FIELD

[0001] Various aspects of this disclosure relate to an optical system. Various aspects of this disclosure relate to a method of forming an optical system.

BACKGROUND

[0002] Imaging lenses (also known as “objectives”, such as photographic and microscope objectives) are commonly used together with optical filters for a variety of applications, such as (but not limited to) color photography and fluorescence detection. When filters are applied to imaging lenses, they are ordinarily either mounted in front of the lens or behind the lens.

SUMMARY

[0003] Various embodiments may provide an optical system. The optical system may include a plurality of lens elements. The optical system may also include a filter configured to be arranged between any two lens elements of the plurality of lens elements. The plurality of lens elements may be configured to concentrate electromagnetic beams from a first area onto a second area smaller than the first area.

[0004] Various embodiments may provide a method of forming an optical system. The method may include providing a plurality of elements. The method may further include providing a filter configured to be arranged between any two lens elements of the plurality of lens elements. The plurality of lens elements may be configured to concentrate electromagnetic beams from a first area onto a second area smaller than the first area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

FIG. 1 A shows a high aperture objective with a filter in front of the lenses.

FIG. IB shows the high aperture objective with a filter behind the lenses.

FIG. 2 A shows a wide aperture objective with a filter in front of the lenses. FIG. 2B shows the wide aperture objective with a filter behind the lenses.

FIG. 3 is a general illustration of an optical system according to various embodiments.

FIG. 4 is a general illustration of a method of forming an optical system according to various embodiments.

FIG. 5 shows a schematic of an optical system according to various embodiments.

FIG. 6 shows a schematic of an optical system according to various embodiments.

FIG. 7A is a schematic of an optical system in which a plurality of filters is mounted on a rotating stage according to various embodiments.

FIG. 7B is a schematic of an optical system in which a plurality of filters is mounted on a linear scanning stage according to various other embodiments.

FIG. 8A is a schematic showing a conventional optical imaging system.

FIG. 8B shows a schematic illustrating the modification of the base model to insert a 2 mm thick filter according to various embodiments.

FIG. 8C shows a schematic illustrating the optimized optical imaging system according to various embodiments after the first optimization process.

FIG. 8D shows a schematic illustrating the final design of the optical imaging system with 6 mm gaps catered for mechanical mounting.

FIG. 8E shows a schematic illustrating that the total lens thickness of the final design of the optical imaging system according to various embodiments is 62 mm.

FIG. 8F shows the optical imaging system with the filter arranged in front of the base model lens.

FIG. 8G shows the optical imaging system with the filter arranged at the back of the base model lens.

FIG. 8H shows the optical imaging system with the filter placed between two lens elements according to various embodiments.

DETAILED DESCRIPTION

[0006] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0007] Embodiments described in the context of one of the methods or optical systems are analogously valid for the other methods or optical systems. Similarly, embodiments described in the context of a method are analogously valid for an optical system, and vice versa.

[0008] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments. [0009] The device as described herein may be operable in various orientations, and thus it should be understood that the terms “top”, “bottom”, etc., when used in the following description are used for convenience and to aid understanding of relative positions or directions, and not intended to limit the orientation of the system.

[0010] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements. [0011] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.

[0012] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0013] As examples, FIGS. 1A-B and 2A-B show imaging lenses with filters mounted in the stated common configurations (i.e., either in front or behind the lenses). FIG. 1 A shows a high aperture objective with a filter in front of the lenses. FIG. IB shows the high aperture objective with a filter behind the lenses. The high aperture objective is shown in US2,828,671. FIG. 2A shows a wide aperture objective with a filter in front of the lenses. FIG. 2B shows the wide aperture objective with a filter behind the lenses. The wide aperture objective is shown in US3,468,600. In FIGS. 1 A-B and 2A-B, the rays are traced from left to right, where they strike the image plane. As can be seen in FIGS. 1 A and 2 A, when a filter has to be mounted in front of the lens, the filter may be required to be quite large in order to fit all rays through the filter. Optical filters are sometimes mounted behind the lens as shown in FIG. IB and 2B. However, mounting filters behind the lens may lead to stray light at the image, caused by reflection of rays off the surfaces of a filter that is near the image plane when mounting the filter behind the objective.

[0014] FIG. 3 is a general illustration of an optical system according to various embodiments. The optical system may include a plurality of lens elements 302. The optical system may also include a filter 304 configured to be arranged between any two lens elements of the plurality of lens elements 302. The plurality of lens elements may be configured to concentrate electromagnetic beams from a first area onto a second area smaller than the first area.

[0015] In other words, the optical system may include multiple lens elements 302, and a filter 304 placed at a space between any two lens elements 302 of the multiple lens elements 302. For instance, the optical system may include three lens elements 302, and the optical filter 304 may be placed at a space between the first lens element and the second lens element, or at a space between the second lens element and the third lens element. The optical system may be such that light beams or rays converge from a bigger area onto a smaller area.

[0016] Various embodiments may seek to address or mitigate the various issues of mounting filter before or after the lens elements 302. By arranging the filter 304 between any two lens elements of the plurality of lens elements 302, various embodiments may require a smaller filter than the case if the filter is placed in front of the lens elements 302, and may also reduce stray light at the image compared to the case if the filter is placed behind the lens elements 302.

[0017] A lens element as described herein may be a standalone lens, or may be joined or cemented to one or more other lens elements to form a lens.

[0018] The filter 304 may be an optical filter. The 304 filter may be configured to allow electromagnetic waves or lights of certain characteristics, e.g. a predetermined wavelength or a predetermined range of wavelengths to pass through, while blocking or reducing the intensity of electromagnetic waves or lights of other characteristics, e.g. another predetermined wavelength or another predetermined range of wavelengths. The optical filter may be an interference filter. The optical filter may include any suitable glass or plastic.

[0019] In various embodiments, instead of a single filter 304 placed between the any two lens elements, the optical system may further include additional filters placed between the any two lens elements. In other words, the optical system may include multiple filters placed between the any two lens elements. [0020] In various embodiments, the optical filter may include arranging one or more other filters between another two lens elements of the plurality of elements. As an example, the filter may be arranged between a first lens element and a second lens element, and another filter may be arranged between the second lens element and a third lens element.

[0021 ] In various embodiments, the optical system may be an imaging system. The plurality of lens elements may be configured to concentrate electromagnetic beams, e.g. light beams, from an object having the first area onto the second area on an imaging surface, thereby demagnifying the object. The optical system may be a demagnification system. The plurality of lens elements may be imaging lenses or lens elements. The second area may be on an imaging plane or an imaging surface, e.g. an imaging surface of a detector, such as a charge- coupled device (CCD), or a complementary metal oxide semiconductor (CMOS) image sensor. Electromagnetic beams may travel from the first area, which may be a light source or an object, through the plurality of lens elements 302 onto the second area of an imaging place or surface. [0022] In various other embodiments, the optical system may be a non-imaging system, such as a concentrating solar collector. The plurality of lens elements 302 may be non-imaging lenses or lens elements. Light or electromagnetic beams may travel from a first area, which may be a source or object, through the plurality of lens elements 302 onto the second area of a target, a target surface, or a target plane. The non-imaging lenses may focus light or electromagnetic beams in such a way as to optimize the amount of flux at the target plane. The resulting distribution of light or electromagnetic waves at the target plane may not form a sharp image.

[0023] In various embodiments, the electromagnetic beams passing from a first lens element to a second lens element of the any two lens elements may be collimated beams, or may be at least partially collimated beams. In some cases, mounting the filter 304 between the any two lens elements of the plurality of lens elements 302 may result in lower angles of incidence (AOI) for rays passing through the filter. In applications such as fluorescence detection, this may be advantageous. Filters used in fluorescence detection (or fluorescence imaging) may be interference filters. The spectral transmission of the filter may vary according to the angle of incidence (AOI) of a beam or ray that travels through the surfaces of the filter. As the AOI of a ray increases, the spectral transmission may shift towards shorter wavelengths, an effect often called “blue shift” or “spectral blue shift”. When a filter is mounted either in front or behind the plurality of lens elements (the objective), rays that are passing through the filter may have higher AOI compared to a filter mounted at a location between the lens elements within the objective. Accordingly, for interference filters which are designed optimally for use with collimated beams, arranging the interference filter between the any two lens elements may result in better spectral transmission.

[0024] In various other embodiments, the electromagnetic beams passing from a first lens element to a second lens element of the any two lens elements may be non-collimated beams. [0025] In various embodiments, the optical system may further include one or more further filters configured to be arranged between the any two lens elements of the plurality of lens elements. The filter and the one or more further filters may form a plurality of filters. The optical system may also include an actuator system configured to move the plurality of filters so that one filter of the plurality of filters is arranged between the any two lens elements at any one time.

[0026] In various embodiments, the actuator system may include a filter stage holding the plurality of filters. The actuator system may further include a motor configured to actuate the filter stage so as to move the plurality of filters.

[0027] In various embodiments, the filter stage may be a filter wheel configured to be rotated about a pivot point. The actuator system may include a stand or holder configured to hold the filter wheel at the pivot point of the filter wheel. When the filter wheel is rotated about the pivot point by the motor, the plurality of filters arranged circumferentially on the filter wheel may also be moved, such that one filter of the plurality of filters is between the any two lens elements at any one time.

[0028] In various other embodiments, the filter stage may be a linear-scanning mount configured to be moved in a linear manner along one direction, e.g. parallel to a length of the linear-scanning mount. The plurality of filters may be arranged along the length of the linear- scanning mount. When the linear-scanning mount is moved along a direction parallel to its length, the plurality of filters may also be moved, such that one filter of the plurality of filters is between the any two lens elements at any one time.

[0029] In various embodiments, the electromagnetic beams may be visible light beams. However, in various embodiments, the electromagnetic beams may be of any other suitable type of electromagnetic waves whose paths can be manipulated by the plurality of lens elements 304. For instance, the electromagnetic beams may be infrared beams. [0030] FIG. 4 is a general illustration of a method of forming an optical system according to various embodiments. The method may include, in 402, providing a plurality of elements. The method may further include, in 404, providing a filter configured to be arranged between any two lens elements of the plurality of lens elements. The plurality of lens elements may be configured to concentrate electromagnetic beams from a first area onto a second area smaller than the first area.

[0031] In other words, the method may include forming an optical system including a plurality of elements and one or more filters arranged between any two lens elements of the plurality of lens elements.

[0032] In various embodiments, the optical system may be an imaging system. The plurality of lens elements may be configured to concentrate electromagnetic beams from an object having the first area onto the second area on an imaging surface, thereby demagnifying the object.

[0033] In various other embodiments, the optical system may be a non-imaging system. [0034] In various embodiments, the electromagnetic beams passing from a first lens element to a second lens element of the any two lens elements may be collimated beams. In various other embodiments, the electromagnetic beams passing from a first lens element to a second lens element of the any two lens elements may be non-collimated beams.

[0035] In various embodiments, the method may include providing one or more further filters configured to be arranged between the any two lens elements of the plurality of lens elements. The filter and the one or more further filters may form a plurality of filters.

[0036] In various embodiments, the method may also include providing an actuator system configured to move the plurality of filters so that one filter of the plurality of filters is arranged between the any two lens elements at any one time.

[0037] The actuator system may include a filter stage holding the plurality of filters. The actuator system may also include a motor configured to actuate the filter stage so as to move the plurality of filters.

[0038] In various embodiments, the filter stage may be a filter wheel configured to be rotated about a pivot point. In various other embodiments, the filter stage may be a linear- scanning mount configured to be moved in a linear manner along one direction.

[0039] In various embodiments, the electromagnetic beams may be visible light beams. However, in various embodiments, the electromagnetic beams may be of any other suitable type of electromagnetic waves whose paths can be manipulated by the plurality of lens elements.

[0040] FIG. 5 shows a schematic of an optical system according to various embodiments. The optical system may include 9 optical elements 502a- 502i. Electromagnetic or light beams from the object may pass through the optical elements 502a - 502i to form an image on the image plane. As shown in FIG. 5, some of the lens elements, such as elements 502a, 502b, 502g may be standalone lenses. On the other hand, lens element 502c may be joined to lens element 502d, lens element 502e may be joined to lens element 502f, and lens element 502h may be joined to lens element 502L Lens elements 502a-b may each be a standalone meniscus lens with a convex surface towards the object. The lens element 502c may be plano-convex with the convex surface facing towards the object, while the lens element 502d that is cemented or joined to the lens element 502c may be plano-concave with the concave surface facing the image plane. The lens element 502e may be plano-concave with the concave surface facing the object, while the lens element 502f cemented or joined to the lens element 502e may be planoconvex, with the convex surface facing towards the image plane. Lens element 502g may be a standalone plano-convex lens with the convex surface facing the image plane. Lens element 502h may be concave, and the lens element 502i cemented or joined to lens element 502h may be convex, with the convex surface facing the object. The lens elements 502a-502i may form the objective.

[0041] In order to reduce the size of the filter as shown in FIG. 1A and also to address or mitigate issues associated by arranging the filter behind the objective as shown in FIG. IB, various embodiments may relate to increasing the distance within the objective, i.e. between any two elements of the plurality of elements 502a-h, to form a space, and mounting one of more filters 504 in that space.

[0042] For instance, as shown in FIG. 5, the system shown in FIGS. 1 A-B may be modified by increasing the space between the elements 502f and 502g. In this example, no further re optimization of the objective lens design may be performed. In practice, such as in lens design for a specific application that has a set of requirements, spaces between elements of an objective may be increased as the lens is being designed. As shown in FIG. 5, the electromagnetic or light beams from the object may pass through the filter 504 in addition to optical elements 502a - 502i to form the image on the image plane. [0043] In some other cases, there may be sufficient space between elements in an objective, such as the objective in FIGS. 2A-B. In such cases, one or more filters may be mounted in that space, as illustrated in FIG. 6.

[0044] FIG. 6 shows a schematic of an optical system according to various embodiments. The optical system may include 8 lens elements 602a - 602h, which may form the objective. Lens elements 602a, 602b, 602c and 602h may be standalone lenses, while lens element 602d may be joined with lens element 602e, and lens element 602f may be joined to lens element 602g. Lens element 602a may be a standalone lens having a slightly convex front surface facing the object and a concave rear surface facing the image plane. Lens elements 602b, 602c may be standalone convex lenses. Lens element 602d may be joined or cemented to lens element 602e. Lens element 602d may be concave, while lens element 602e may be convex. Lens element 602f may be convex, while lens element 602g may be concave. Lens element 602h may be a standalone plano-convex lens, with the convex surface facing the image plane. [0045] As there is sufficient space between the first lens element 602a and the second lens element 602b, a filter 604 may be mounted in this space.

[0046] In various embodiments, more than one filter may be mounted on a motorized stage (such as a filter wheel, or a linear scanning stage). The stage may be any suitable type that can provide motion in order to switch different filters into the objective. The motion of the stage may enable switching of the different filters into the objective, as illustrated in FIGS. 7A-7B. FIG. 7A is a schematic of an optical system in which a plurality of filters 704a-d is mounted on a rotating stage 706 according to various embodiments. FIG. 7B is a schematic of an optical system in which a plurality of filters 704a’-d’ is mounted on a linear scanning stage 706’ according to various other embodiments.

[0047] As shown in FIG. 7A the rotating stage 706 may include the plurality of filters 704a- d. When the rotating stage 706 is rotated, one filter of the plurality of filters 704a-d may be arranged to be between two lens elements of the plurality of lens elements 702 such that electromagnetic or light beams from the object passes through the filter to the image plane. The plurality of filters 704a-d may have different optical characteristics from one another. For instance, the plurality of filters 704a-d may allow different ranges of wavelengths of light to pass through. Accordingly, by rotating the rotating stage 706, electromagnetic or light beams of different characteristics, e.g. different range of wavelengths, may be allowed to transmit through to the image plane. [0048] On the other hand, FIG. 7B shows the linear scanning stage 706’ including the plurality of filters 704a’ -d’. By moving the linear scanning stage in the scan direction as shown, one filter of the plurality of filters 704a’ -d’ may be arranged to be between two lens elements of the plurality of lens elements 702’ such that electromagnetic or light beams from the object passes through the filter to the image plane. The plurality of filters 704a’-d’ may have different optical characteristics from one another. By moving the linear scanning stage 706’ along the scan direction, electromagnetic or light beams of different characteristics, e.g. different range of wavelengths, may be allowed to transmit through to the image plane.

[0049] In yet various other embodiments, the motorized stage including optical filters may not be a rotating type or a linear scanning type.

[0050] Further, provided that there is sufficient space in the gap where the filters lie between elements, focusing of the objective may be performed without mechanical interference by the filters. Also, since an optical filter is a relatively thin flat window in the path of rays, the filters may remain stationary while the lens is focused, as once a window has been accounted for in the design of the objective (i.e., when it is included between two chosen elements during the design of the objective), the impact of the position of that window on image quality may be minimal.

[0051] Various embodiments may be different from an optical system of a fluorescence microscope in that the tube lens of the fluorescence microscope is not part of the objective, but is an external accessory. Further, as the tube lens is designed to accept rays from an infinity- corrected objective lens, the rays from the objective lens may be required to be collimated. In contrast, the rays or beams passing through the filter according to various embodiments may not be required to be collimated. In other words, in various embodiments, the rays or beams passing through the filter may be collimated, while in various other embodiments, the rays or beams passing through the filter may not be collimated.

[0052] Various embodiments may not be limited to imaging objectives. Various embodiments may be applied to non-imaging lenses. Non-imaging lenses may instead of forming sharp images at the image plane, focus the light in such a way to optimize the amount of flux at the plane wherein an image usually resides (e.g. a detector or a sensor mounted at that plane), and the resulting distribution of light at the detector or sensor plane may not be an image of the source or the object. In various embodiments, the distribution of light may be arbitrary. When filters are desired for non-imaging lenses, the one or more filters may be mounted in a space between elements of the non-imaging lens elements.

[0053] Example

[0054] Conventional optical imaging systems are usually designed to be compact, where lens elements are placed close to each other. On the other hand, for an optical imaging system to be usable for the method as described herein, space between two lens surfaces may be required which is enough to fit a filter of some thickness and its mechanical housing. An example of design process of such an optical imaging lens system is explained below. In this specific example, a 2 mm thick filter is chosen.

[0055] A design of a conventional optical imaging system may be used as the base model. This system has an Effective Focal Length (EFL) of 35mm at Wavelength 588nm. It has nine lens elements and a total lens thickness (i.e. the distance between the surface of the first lens element and the surface of the last lens element) of 45mm. The optical imaging system is optimized for Object Field of 40mm. Glass materials used in the lens elements are all from Schott.

[0056] FIG. 8A is a schematic showing a conventional optical imaging system. Table 1 shows a lens prescription of the base model shown in FIG. 8 A.

Base Model

Table 1: Lens prescription of the base model shown in FIG. 8A. The radius, thickness and semi diameter are in millimeters (mm).

[0057] The base model has been modified by inserting a 2 m thick filter between lens element surface #7 and lens element surface #8 as shown in FIG. 8A, such that the filter is 6mm away from the lens element centers of both sides. The total lens thickness is now increased from 45 mm to 51.3 mm.

[0058] FIG. 8B shows a schematic illustrating the modification of the base model to insert a 2 mm thick filter according to various embodiments.

[0059] As the addition of the filter and the space may have a negative impact on the optics performance, the lens parameters may be required to be re-optimized. Constraints have been set to the optimization to ensure lens manufacturability, and that the effective focal length has been maintained at 35 mm. The software returns an optimized design as shown in FIG. 8C. [0060] FIG. 8C shows a schematic illustrating the optimized optical imaging system according to various embodiments after the first optimization process.

[0061 ] A second optimization has also been performed to further increase the space between the filter and its neighboring lens surfaces. In order to fit in mechanical housings for the filter, there should be at least 6 mm between the filter surface and the edge of its neighboring lens surfaces. Constraints have also been added to avoid getting lenses with overly sharp edges. After the second optimization, the software returns a design as shown in FIGS. 8D-E.

[0062] FIG. 8D shows a schematic illustrating the final design of the optical imaging system with 6 mm gaps catered for mechanical mounting. FIG. 8E shows a schematic illustrating that the total lens thickness of the final design of the optical imaging system according to various embodiments is 62 mm.

Final Design

Table 2: Lens prescription of the final design shown in FIGS. 8D-E. The radius, thickness and semi-diameter are in unit millimeters (mm).

[0063] In the final optimized optical imaging system, with the filter at the position of the “Stop”, the rear surface of the filter now acts as the aperture stop. The system's stop diameter may be given by the clear aperture of the rear surface of the filter.

[0064] FIG. 8F shows the optical imaging system with the filter arranged in front of the base model lens. FIG. 8G shows the optical imaging system with the filter arranged at the back of the base model lens. FIG. 8H shows the optical imaging system with the filter placed between two lens elements according to various embodiments.

[0065] Table 3 compares the filter size required if the filter is arranged in front of the lens elements, at the back of the lens elements, or between two lens elements as shown in FIGS.

8F-H.

Table 3: Comparison of filter size required

[0066] As indicated above, the filter may be reduced greatly when the filter is placed within the lens, i.e. between two lens elements.

[0067] Various embodiments may relate to an optical system including one or more optical filters arranged inside the objective. Various embodiments may relate to a method of mounting one or more optical filters inside the objective. The mounting of the one or more optical filter may be designed with commercially-available optical design software.

[0068] In various embodiments, mounting a filter between elements in an objective may be advantageous compared to mounting a filter behind the objective in the sense that there may be less stray light at the image, caused by reflection of rays off the surfaces of a filter that is near the image plane when mounting the filter behind the objective.

[0069] In some cases, mounting a filter between elements in an objective may result in lower angles of incidence for at least some of the rays passing through the filter. Compared to this, mounting a filter behind the objective may often result in higher angles of incidence (AOI) for rays passing through the filter (compare, e.g., the rays passing through the filter in FIG. 6 compared to FIGS. 2A-B). In applications such as fluorescence detection, this may be advantageous because filters used in fluorescence detection (or fluorescence imaging) are so- called “interference filters”, where the spectral transmission of the filter varies according to the angle of incidence (AOI) of a ray that travels through the filter’s surfaces. As the AOI of a ray increases, the spectral transmission may shift towards shorter wavelengths, an effect often called “blue shift” or “spectral blue shift”. As can be seen in FIGS. 2A-B, when a filter is mounted either in front or behind an objective, rays can have higher AOI than when mounting at a strategic location between elements within the objective, as in FIG. 6.

[0070] By mounting filters between elements inside an objective, the size of the filter may be reduced, which results in lower cost of the filters and a more compact optical system. Moreover, in some cases, a filter that is mounted between elements inside an objective may be subject to lower angles of incidence for rays passing through the filter. This may reduce or minimize spectral blue shifts for interference-type filters.

[0071] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.