Method and system for controlling stray light reflections in an optical system

Systems and methods for controlling stray light reflections are provided. An optical system includes an aperture having an optical axis passing therethrough, one or more optical elements disposed along an optical path, and a detector disposed along the optical path. The system further includes an optical housing disposed between the aperture and the detector. The interior surface of the optical housing includes a predetermined surface feature adapted to control reflections of stray light along the optical path between the aperture and the detector. A method of fabricating an optical housing includes forming a pattern comprising a predetermined surface feature on an interior surface of the optical housing. The predetermined surface feature is configured to control reflections of stray light along an optical path between an aperture at a proximal end of the optical housing and a detector at a distal end of the optical housing.

BACKGROUND OF THE INVENTION

Optical systems are used with optical devices such as cameras, telescopes, and microscopes. In an optical system, stray light is light which was not intended in the design. Stray light may be from an intended source, but follow paths other than intended. Stray light can also originate from a source other than the intended source. Stray light can enter into a lens from a peripheral source, which can be a light source coming from outside the expected field of view. One example of stray light is sunlight outside a field of view of an optical lens. Stray light can result in unwanted background noise or signals relative to the intended image. Thus, stray light can interfere with an intended image. Stray light can also limit the dynamic range of an optical system. For example, stray light can limit the signal-to-noise ratio or contrast ratio of an optical system, by limiting how dark the optical system can be.

Therefore, there is a need in the art for improved methods and systems to reduce or minimize the amount of stray light in optical systems.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate generally to optical systems. More specifically, embodiments of the present invention relate to methods and systems for reducing stray light in optical systems. Merely by way of example, the present invention has been applied to a method and system for forming a modified thread pattern on the internal surface of an optical housing (e.g., a lens hood) that reduces scattering of stray light. Some embodiments utilize an operating principle that is reflective in nature. Accordingly, embodiments of the present invention are applicable to all commonly used wavelengths of light in a variety of optical systems.

According to an embodiment of the present invention, an optical system is provided. The optical system includes an aperture (e.g., an input aperture) having an optical axis passing therethrough and one or more optical elements disposed along an optical path. The optical system also includes a detector disposed along the optical path and an optical housing disposed between the aperture and the detector. The optical housing can also be referred to as an optical cover or a lens barrel. An interior surface of the optical housing includes a predetermined surface feature adapted to control reflections of stray light along the optical path between the aperture and the detector. The predetermined surface feature can include a series of mechanical structures arranged substantially transverse to the optical axis. The series of structures can be characterized by a symmetric or non-symmetric pattern. These patterns include, without limitation, a sawtooth pattern, a rounded sawtooth pattern, a seagull pattern, combinations thereof, or the like. For symmetric patterns, the individual structures have symmetric geometries. In certain embodiments, non-symmetric patterns include an upstream surface facing toward the aperture that is characterized by a first surface feature and a downstream surface facing toward the detector that is characterized by a second surface feature differing from the first surface feature. For example, according to these embodiments, the first surface feature of a non-symmetric pattern can be curved and the second surface feature can be substantially planar or planar. According to one embodiment of the present invention, a non-symmetric pattern is a half-sawtooth and half-curved pattern. Individual structures comprising such non-symmetric patterns have asymmetric geometries.

According to another embodiment of the present invention, a method of fabricating an optical housing is provided. The method includes forming a pattern of geometric structures on an interior surface of the optical housing. The pattern of structures comprises a predetermined surface feature configured to control reflections of stray light along an optical path between the aperture and the detector. In some embodiments, the pattern is fabricated on an object, which can be referred to as an “insert,” that is inserted into the optical housing. Thus, embodiments in which the pattern is fabricated directly on the optical housing, as well as on an insert disposed inside the optical housing, are included within the scope of the present invention.

According to yet another embodiment of the present invention, a method of designing an optical housing is provided. The method includes providing an optical lens assembly comprising an optical housing and receiving a selection of a shape of an internal structure to be included in a pattern disposed on an internal surface of the optical housing. The shape of the internal structure can be selected from a plurality of defined shapes having respective, predetermined surface features. The method computes, based on the shape of the internal structure and properties of components of the optical lens assembly, light intensity at a detector. The method then determines if the light intensity exceeds a threshold. If the intensity does not exceed the threshold, the design of the optical housing is fixed to include the selected shape of the internal structure. Otherwise, if the intensity exceeds the threshold, the shape of the internal structure is iteratively modified and the light intensity is re-computed based on the modified shape until the intensity no longer exceeds the threshold.

Numerous benefits are achieved by way of the present invention over conventional techniques. For example, embodiments of the present invention reduce stray light in optical systems and improve the perceived image quality by reducing unwanted background noise or signals relative to the intended image. Also, for example, embodiments of the present invention reduce stray light from sources that, while outside of a field of view of a lens, reach the front of the lens. Stray light can enter into lenses from peripheral sources, which can be any source of light coming from outside the expected field of view and interfering with an intended image. Some conventional optical systems include lens barrels having smooth or planar surfaces. Such smooth and planar surfaces reflect stray light rays within conventional optical systems, which results in problems stemming from unwanted background noise or signals relative to the intended image. In contrast to such conventional optical systems, embodiments of the present invention reduce stray light by incorporating surface features into internal surfaces of a lens barrel. These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention provide features that can be machined, formed, molded, or otherwise fabricated in the interior surfaces of an optical assembly, providing the function of reducing unwanted reflections, which can be referred to as “stray light” within the interior surfaces of the optical assembly. The features includes a mechanical structure, usually in a circular pattern, with a predetermined shape that re-directs light energy ultimately away from the primary image plane or detector location. Shapes include threadlike patterns with surfaces that are shaped or curved in a specific manner to control the direction and spread of the reflected beam. According to embodiments, the features may be helical (i.e., akin to a screw thread). In alternative or additional embodiments, the features can have a circular geometry.

As illustrated inFIG. 1A-FIG. 5, embodiments of the present invention utilize unique shapes of threadlike profiles that efficiently diffuse stray light in a desired direction within an optical system. Embodiments avoid issues associated with standard thread patterns consisting of nominally flat surfaces, which in turn can result in excessive stray light energy reaching the image plane, particularly for specific incidence angles.

In an alternative embodiment, an optical system is provided that contains one or more emitters, for example, a display assembly. A display assembly can include an emitter and a lens assembly. A human eye is used to look into the display assembly to view a magnified image of the display. In such a system, stray light could arise from light leaving the emitter and reflecting/scattering off the interior wall of the housing. Accordingly, the use of embodiments of the present invention extends not only to include opto-electronic detectors (e.g., mid-infrared focal plane arrays and the like), but optical systems suitable for use by a human viewer. In some embodiments, the “image plane”116illustrated inFIG. 1can be an object plane, with the housing including the pattern of internal structures disposed between the object plane and the user's eye.

In some implementations, optical elements are components that direct light beams and may include lenses, mirrors, prisms, gratings, and the like. An emitter is a light emitting component such as a display device that may include an array of pixels. The emission process for such display devices includes, but is not limited to, LCD (Liquid Crystal Display), OLED (Organic Light Emitting Diode) technology, and the like.

FIG. 1is a cross sectional view of an objective lens assembly (OLA)100according to one embodiment. In the illustrated embodiment, OLA100includes an input aperture102having an optical axis passing therethrough and one or more optical elements104disposed along an optical path between input aperture102and an image plane116. In certain embodiments, optical elements104can be lenses separated by a spacer106. As shown, OLA100includes an optical housing108. Optical housing108can also be referred to as an optical cover or a lens barrel. In the exemplary embodiment shown inFIG. 1, optical housing108is conical. It should also be understood that embodiments of OLA100can include a cylindrical or substantially cylindrical optical housing108.

OLA100includes internal structures110disposed on an internal surface of optical housing108between input aperture102and image plane116. As described below with reference toFIG. 1A-FIG. 5, the internal structures110are mechanical structures shaped so as to reduce or minimize the amount of stray light reaching image plane116. As shown inFIG. 1, housing108is disposed between input aperture102and image plane116. Light from a scene gets passed through input aperture102on to image plane116. However, at the same time, some stray light can get through to image plane116, which is undesirable. Embodiments described herein reduce or minimize the amount of stray light that gets to image plane116. According to embodiments, a detector measures an amount of light received at image plane116after entering input aperture102and being passed along the optical path via optical housing108. For example, the detector can measure the intensity, or power, of light at image plane116, including stray light entering input aperture102and being passed through optical housing108and intermediate aperture112of focus lens cell114. As shown in the exemplary embodiments ofFIGS. 6 and 7, in embodiments, the detector can measure the intensity of light arriving at image plane116in terms of watts per square centimeter. In additional or alternative embodiments, the detector measures the intensity of light from a scene in other units, such as, for example, watts per square meter. In certain embodiments, image plane116comprises the detector.

FIG. 1Adepicts a perspective view of a portion of the example internal structures110shown inFIG. 1. As illustrated inFIG. 1A, internal structures110include a modified “sharktooth” geometry with a non-symmetric profile. The modified sharktooth geometry used for internal structures110includes an upstream surface118facing toward input aperture102that is characterized by a first surface feature and a downstream surface120facing toward the detector and image plane116that is characterized by a second surface feature differing from the first surface feature. In the example provided inFIG. 1A, the first surface feature of the modified sharktooth geometry is curved and the second surface feature can be substantially planar. Although the exemplary embodiment shown inFIG. 1Aincludes a convex first surface feature, it is to be understood that in alternative embodiments, the curved first surface feature can be concave.

FIGS. 2-5provide cross sectional views of internal structures usable to control reflections of stray light, according to various embodiments of the present invention.

FIG. 2depicts a cross sectional view of a sawtooth structure geometry200. As shown, sawtooth structure geometry200is a symmetric profile including planar surfaces forming triangular ridges spaced apart by a width210and separated by a trough with a depth212. With continued reference toFIG. 1, sawtooth structure geometry200includes an upstream surface218facing toward input aperture102and a downstream surface220facing toward the detector and image plane116. As seen inFIG. 2, each of surfaces218and220are planar surfaces. Upstream surface218is angled to control the direction and spread of stray light rays214so as to minimize reflection of stray light rays214in the downstream direction towards the detector. In one non-limiting embodiment, width210is 0.051 inches and depth212is 0.036 inches.

FIG. 3depicts a cross sectional view of a half-sawtooth half-curved structure geometry300. As shown, half-sawtooth half-curved structure geometry300is a non-symmetric profile including a curved upstream surface318and planar downstream surface320forming ridges resembling shark fins. The ridges are spaced apart by a width310and separated by a trough with a depth312. Upstream surface318is curved to control the direction and spread of stray light rays314in order to minimize reflection of stray light rays314in the downstream direction towards the detector. According to a non-limiting embodiment, width310is 0.042 inches and depth312is 0.038 inches. Although the exemplary embodiment shown inFIG. 3includes a convex curved upstream surface318, it is to be understood that in alternative embodiments, the curved upstream surface318can be concave.

FIG. 4depicts a cross sectional view of a rounded sawtooth structure geometry400having a symmetric profile including substantially planar upstream and downstream surfaces418and420forming ridges with rounded peaks. The ridges are spaced apart by a width410and separated by a trough with a depth412. Upstream surface418is angled to control the direction and spread of incoming stray light rays414in order to minimize reflection of stray light rays414in the downstream direction towards the detector. In accordance with one exemplary embodiment, width410is 0.051 inches and depth412is 0.033 inches. According to embodiments of the present invention, the general shape of a pattern can be different at different points along the optical axis. For example, the half-sawtooth half-curved structure geometry300shown inFIG. 3could be employed in the front half of a lens barrel or optical housing and the rounded sawtooth structure geometry400shown inFIG. 4could be employed in the back half of the barrel or housing.

FIG. 5depicts a cross sectional view of a seagull structure geometry500. As shown, seagull structure geometry500has a symmetric profile including curved upstream and downstream surfaces518and520forming rounded ridges. The ridges are spaced apart by a width510and separated by a trough with a depth512. Upstream surface518is curved so as to control the direction and spread of incoming stray light rays514by minimizing reflection of stray light rays514in the downstream direction towards the detector. According to one exemplary embodiment, width510is 0.051 inches and depth512is 0.021 inches. While the example embodiment shown inFIG. 5includes convex curved upstream and downstream surfaces518and520, it is to be understood that in alternative embodiments, one or more of curved upstream and downstream surfaces518and520can be concave.

FIGS. 6 and 7illustrate results of using exemplary internal structures to control stray light reflections within an optical system, according to embodiments.FIG. 6provides a plot600showing the results of using a sawtooth structure geometry to control stray light in an optical system. In particular, plot600indicates the intensity of light632received at an image plane relative to horizontal input angles634of stray light beams when using a sawtooth geometry with a 90-degree angle for one of its surfaces. Horizontal input angles634are indicated in terms of degrees where the degrees indicate the angle of incidence of an incoming stray light beam, where the angle of incidence is the angle between the stray light beam and an interior surface of an optical housing. As shown, when employing the 90-degree sawtooth structure geometry, the amount of stray light reaching the image plane is minimal at most horizontal input angles634. Plot600also shows that with the 90-degree sawtooth structure geometry, when the horizontal input angle634of a stray light beam is between 20 and 22 degrees, the amount of stray light reaching the image plane is relatively high. In optical systems where angles of incidence for stray light is expected to fall within the range of 20-22 degrees, another structure geometry can be selected. Exemplary results of using another geometry are shown inFIG. 7

FIG. 7provides a plot700showing the results of using a half-sawtooth half curved geometry to control stray light in an optical system. In particular, plot700indicates the intensity of light732received at an image plane relative to horizontal input angles734of stray light beams when using a half-sawtooth half-curved geometry having shark fin shaped ridges. Horizontal input angles734are indicated in terms of degrees where the degrees indicate the angle of incidence of an incoming stray light beam, where the angle of incidence is the angle between the stray light beam and an interior surface of an optical housing. Plot700shows that with the half-sawtooth half curved structure geometry, the amount of stray light reaching the image plane remains relatively low across all horizontal input angles734.

In the examples ofFIGS. 6 and 7, the intensity of light632and732are indicated in terms of watts per square centimeter. It should also be understood that depending on the type of optical system, embodiments can employ detectors configured to measure power, or intensity of light in other units, such as, for example, watts per square meter. Similarly, althoughFIGS. 6 and 7include respective ranges between 0 and 35 degrees for horizontal input angles634and734, it is to be understood that additional embodiments can measure stray light beams having smaller or larger ranges of input angles.

FIG. 8depicts an example flow chart of a method for designing internal structures for controlling stray light reflections within an optical system, according to embodiments. In particular,FIG. 8illustrates steps of a method800for determining an optimum shape of internal structures, wherein method800takes into account the shapes of various optical elements of a given optical system. The determined structure shape or geometry is dependent on the shape of the optical elements, including the shapes of lenses, the shape of an optical housing or a lens barrel, the shape and dimensions of a spacer, and/or shapes of other optical elements included in the optical system. By taking into account the properties and characteristics of the optical components, method800is able to determine an internal structure for the optical housing that will best control stray light reflections within the optical system.

Method800begins at step808where an optical lens assembly is provided. The assembly provided in this step comprises an optical housing. In embodiments, the optical lens assembly provided in this step can also include optical elements, such as, for example, one or more lenses, mirrors, prisms, gratings or other optical elements that can have an influence on stray light. In the example ofFIG. 8, the optical housing can be substantially conical or cylindrical. Method800then proceeds to step810where a selection of a shape of an internal structure is received. As shown, the selected shape received in step810is to be disposed on an internal surface of the optical housing. In an embodiment, step810can comprise receiving a selection of one of a plurality of predefined shapes having respective, predetermined surface features. According to embodiments, the plurality of predefined shapes include one or more of the structure geometries shown inFIGS. 1A-5. After the selection is received, control is passed to step812.

In step812, light intensity is computed. In the exemplary embodiment provided inFIG. 8, the light intensity is computed as a result of the shape of the internal structure selected in step810and characteristics of the assembly provided in step808. As shown, the computation can be performed by measuring light intensity at a detector. In certain embodiments, step812is performed by providing input light beams (i.e., stray light beams) at various angles and computing respective light intensities for each of the various angles. Step812can comprise computing an aggregate, overall light intensity across a given range of input light angles. In additional or alternative embodiments, step812can be performed by simulating the direction and spread of reflected stray light beams. For example, step812can comprise performing computer simulations wherein light intensity is computed based on the shape of the selected internal structure and known characteristics of the provided assembly. After the light intensity is computed, method800proceeds to step814.

Next, in step814, a determination is made as to whether a light intensity computed in step812exceeds a threshold. According to embodiments, the threshold is a tunable value. In an embodiment, the threshold can be compared to an aggregate, overall light intensity computed in step812. In accordance with additional or alternative embodiments, step814can comprise comparing the threshold to a plurality of computed light intensities corresponding to various light beam angles. If it is determined that a light intensity exceeds the threshold, control is passed to step816. Otherwise, the light intensity does not exceed the threshold and control is passed to step818.

In step816, the shape of the internal structure is modified. The modification performed in this step is done in order to reduce stray light intensity. In an embodiment, this step can comprise receiving a selection of another shape differing from the shape previously selected in step810. After the shape is modified, control is passed back to step812where light intensity is re-computed based on the modified shape. In certain embodiments, step816can be performed by simulating modifications to the previously selected shape. For example, step816can comprise invoking computer software to make alterations to a previously selected internal structure and then providing properties of the modified shape as input to step812. According to an embodiment, steps812-816are iterated until the computed light intensity does not exceed the threshold.

In step818, the design of the optical housing is fixed to include the shape of the internal structure. This completes method800according to one example embodiment. In additional or alternative embodiments, additional steps can be performed to implement the designed optical housing. For example, method800can be expanded to include further steps for fabricating an optical housing according to the design resulting from completing steps808-818. Such a method can comprise forming a pattern on an interior surface of the optical housing, wherein the pattern comprises the internal structure.

Embodiments of the present invention include a method of fabricating an optical housing. The method includes forming a pattern comprising a predetermined surface feature on an interior surface of the optical housing. The method also includes configuring the predetermined surface feature to control reflections of stray light along an optical path between an aperture at a proximal end of the optical housing and a detector at a distal end of the optical housing.

In an embodiment, the pattern is fabricated on an object, which can be referred to as an “insert” that is inserted into the optical housing. Thus, the method of fabricating an optical housing include embodiments in which the pattern is fabricated directly on the optical housing, as well as on an insert disposed inside the optical housing. In an embodiment, the method includes mounting one or more input optics to the optical housing. For example, the optical housing can be operable to be mated to an objective lens assembly.

According to an embodiment, the predetermined surface feature comprises a series of geometric structures arranged substantially transverse to an optical axis of the optical housing. In exemplary embodiments, the series of geometric structures are characterized by a symmetric pattern. The symmetric pattern can comprise at least one of a sawtooth pattern or a rounded sawtooth pattern, such as, for example, the sawtooth pattern shown inFIG. 2or the rounded sawtooth pattern shown inFIG. 4. Further, for example, the symmetric pattern can include a seagull pattern, such as, for example the seagull pattern shown inFIG. 6.

In alternative or additional embodiments, the series of geometric structures are characterized by a non-symmetric pattern. For example, an upstream surface facing toward the aperture can be characterized by a first surface feature and a downstream surface facing toward the detector can characterized by a second surface feature differing from the first surface feature. In accordance with these embodiments, the first surface feature can be curved and the second surface feature can be substantially planar.

Provided below are descriptions of some devices (and components of those devices) that may be used in the systems and methods described above. These devices may be used, for instance, to receive, transmit, process, and/or store data related to any of the functionality described above. As will be appreciated by one of ordinary skill in the art, the devices described below may have only some of the components described below, or may have additional components.

FIG. 9depicts an example block diagram of a data processing system upon which the disclosed embodiments may be implemented. Embodiments of the present invention may be practiced with various computer system configurations such as hand-held devices, microprocessor systems, microprocessor-based or programmable user electronics, minicomputers, mainframe computers and the like. For example, steps of the method800described above with reference toFIG. 8can be carried out by the data processing system900shown inFIG. 9. The embodiments can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a wire-based or wireless network.FIG. 9shows one example of a data processing system, such as data processing system900, which may be used with the present described embodiments. Note that whileFIG. 9illustrates various components of a data processing system, it is not intended to represent any particular architecture or manner of interconnecting the components as such details are not germane to the techniques described herein. It will also be appreciated that network computers and other data processing systems which have fewer components or perhaps more components may also be used. The data processing system ofFIG. 9may, for example, be a personal computer (PC), workstation, tablet, smartphone or other hand-held wireless device, or any device having similar functionality.

As shown, the data processing system900includes a system bus902which is coupled to a microprocessor903, a Read-Only Memory (ROM)907, a volatile Random Access Memory (RAM)905, as well as other nonvolatile memory906. In the illustrated embodiment, microprocessor903is coupled to cache memory904. System bus902can be adapted to interconnect these various components together and also interconnect components903,907,905, and906to a display controller and display device908, and to peripheral devices such as input/output (“I/O”) devices910. Types of I/O devices can include keyboards, modems, network interfaces, printers, scanners, video cameras, or other devices well known in the art. Typically, I/O devices910are coupled to the system bus902through I/O controllers909. In one embodiment, the I/O controller909includes a Universal Serial Bus (“USB”) adapter for controlling USB peripherals or other type of bus adapter.

RAM905can be implemented as dynamic RAM (“DRAM”) which requires power continually in order to refresh or maintain the data in the memory. The other nonvolatile memory906can be a magnetic hard drive, magnetic optical drive, optical drive, DVD RAM, or other type of memory system that maintains data after power is removed from the system. WhileFIG. 9shows that nonvolatile memory906as a local device coupled with the rest of the components in the data processing system, it will be appreciated by skilled artisans that the described techniques may use a nonvolatile memory remote from the system, such as a network storage device coupled with the data processing system through a network interface such as a modem or Ethernet interface (not shown).

With these embodiments in mind, it will be apparent from this description that aspects of the described techniques may be embodied, at least in part, in software, hardware, firmware, or any combination thereof. It should also be understood that embodiments can employ various computer-implemented functions involving data stored in a data processing system. That is, the techniques may be carried out in a computer or other data processing system in response executing sequences of instructions stored in memory. In particular, the instructions, when executed, enable microprocessor903to implement the processes of the present invention, such as the steps in the method800illustrated by the flowchart ofFIG. 8, discussed above. In various embodiments, hardwired circuitry may be used independently, or in combination with software instructions, to implement these techniques. For instance, the described functionality may be performed by specific hardware components containing hardwired logic for performing operations, or by any combination of custom hardware components and programmed computer components. The techniques described herein are not limited to any specific combination of hardware circuitry and software.

Embodiments herein may also be in the form of computer code stored on a computer-readable medium. Computer-readable media can also be adapted to store computer instructions, which when executed by a computer or other data processing system, such as data processing system900, are adapted to cause the system to perform operations according to the techniques described herein. Computer-readable media can include any mechanism that stores information in a form accessible by a data processing device such as a computer, network device, tablet, smartphone, or any device having similar functionality. Examples of computer-readable media include any type of tangible article of manufacture capable of storing information thereon such as a hard drive, floppy disk, DVD, CD-ROM, magnetic-optical disk, ROM, RAM, EPROM, EEPROM, flash memory and equivalents thereto, a magnetic or optical card, or any type of media suitable for storing electronic data. Computer-readable media can also be distributed over a network-coupled computer system, which can be stored or executed in a distributed fashion.

Throughout the foregoing description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to persons skilled in the art that these embodiments may be practiced without some of these specific details. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow as well as the legal equivalents thereof.