Patent Application
20210003830
There are numerous applications in which it is beneficial to be able to collect image data in multiple wavelength ranges (wavebands) concurrently, such as visible and infrared, or different regions of the infrared. Conventional sensors for multiple wavebands use multiple windows with the respective optics for each waveband. This approach adds cost and weight to the system, and is difficult to implement in volume-constrained platforms, such as weapon sights, missiles, and unmanned aerial vehicles (UAVs), for example. Certain other approaches, such as described in U.S. Pat. No. 6,174,061, for example, involve the use of dichroic beamsplitters to separate the light collected in the different wavebands, which results in the optical configurations being limited to collimated beams and/or reflective, long-F # or reimaged optics to accommodate the beamsplitter(s). Accordingly, these designs are also challenging to implement in volume-constrained platforms.
Aspects and embodiments are directed to a compact dual-band sensor optical design with a shared aperture that may be particularly useful for volume constrained platforms.
According to one embodiment, a dual-band optical system comprises an all-reflective shared optical sub-system configured to receive combined optical radiation including first optical radiation having wavelengths in a first waveband and second optical radiation having wavelengths in a second waveband different from the first waveband, and an optical element positioned to receive the combined optical radiation from the all-reflective shared optical sub-system and having a dichroic coating configured to transmit the first optical radiation and to reflect the second optical radiation, the optical element being configured to transmit the first optical radiation toward a first focal plane and to reflect and focus the second optical radiation to a second focal plane, wherein the all-reflective shared optical sub-system and the optical element are each positioned symmetrically in a first dimension about a primary optical axis extending along a second dimension between the first focal plane and the second focal plane, the first and second dimensions being orthogonal to one another.
In one example, the all-reflective shared optical sub-system includes a primary mirror, a secondary mirror, and a tertiary mirror, the primary mirror being positioned and configured to receive the combined optical radiation via a system aperture and to reflect the combined optical radiation to the secondary mirror, the secondary mirror being positioned and configured to receive the combined optical radiation reflected from the primary mirror and to reflect the combined optical radiation to the tertiary mirror, and the tertiary mirror being positioned and configured to receive the combined optical radiation reflected from the secondary mirror and to reflect the combined optical radiation to the optical element. In one example, the optical element is a quaternary mirror. In another example, the quaternary mirror is a monolithic piece fabricated on a single substrate with the secondary mirror. In another example, the primary mirror and the tertiary mirror are formed as surface regions on a common first substrate. In another example, the secondary mirror and the quaternary mirror are formed as surface regions on a common second substrate. In one example, the common second substrate is made of zinc sulfide. In another example, the common second substrate is made of a material that transmits the first optical radiation.
In certain examples, the dual-band optical system further comprises a refractive optical sub-system configured to receive the first optical radiation from the optical element and to focus the first optical radiation onto the first focal plane, the refractive optical sub-system being positioned symmetrically in the first dimension about the primary optical axis. In one example, the refractive optical sub-system includes at least one lens configured to correct aberrations in the first waveband.
The dual-band optical system may further comprise a first imaging sensor positioned at the first focal plane and configured to produce a first image of at least a portion of a viewed scene from the first optical radiation, and a second imaging sensor positioned at the second focal plane and configured to produce a second image of the viewed scene from the second optical radiation. In one example, the first waveband is a visible waveband ranging from 380 nanometers (nm) to 740 nm, and the first imaging sensor is a visible-band imaging sensor, the second waveband is a long-wave infrared (LWIR) waveband ranging from 8 micrometers (μm) to 15 μm, and the second imaging sensor is an LWIR-band sensor. In another example, the first waveband is a shortwave infrared (SWIR) waveband ranging from 1.4 micrometers (μm) to 3 μm, and the first imaging sensor is a SWIR-band imaging sensor, the second waveband is a LWIR waveband ranging from 8 μm to 15 μm, and the second imaging sensor is an LWIR-band sensor. In another example, the first imaging sensor is one of a visible-band imaging sensor and a SWIR-band imaging sensor, and the second imaging sensor is one of a LWIR-band imaging sensor and a mid-wave infrared (MWIR)-band imaging sensor.
According to another embodiment, a dual-band optical imaging system comprises a primary mirror configured to receive and reflect optical radiation from a viewed scene, a secondary mirror positioned and configured to receive and reflect the optical radiation reflected by the primary mirror, a tertiary mirror positioned and configured to receive and reflect the optical radiation reflected by the secondary mirror, a quaternary mirror positioned and configured to receive the optical radiation reflected by the tertiary mirror, the quaternary mirror including a dichroic coating configured to separate the optical radiation into a first waveband and a second waveband, the quaternary mirror being configured to transmit the first waveband toward a first focal plane and to reflect and focus the second waveband to a second focal plane, and at least one lens element configured to receive the first waveband from the quaternary mirror and to focus the first waveband onto the first focal plane.
In one example, the dual-band optical imaging system further comprises a first imaging sensor positioned at the first focal plane and configured to produce a first image of at least a portion of a viewed scene from the first waveband, and a second imaging sensor positioned at the second focal plane and configured to produce a second image of the viewed scene from the second waveband. In one example, the first waveband is a visible waveband ranging from 380 nanometers (nm) to 740 nm, and the first imaging sensor is a visible-band imaging sensor, and the second waveband is a long-wave infrared (LWIR) waveband ranging from 8 micrometers (μm) to 15 μm, and the second imaging sensor is an LWIR-band sensor. In another example, the first waveband is a shortwave infrared (SWIR) waveband ranging from 1.4 micrometers (μm) to 3 μm, and the first imaging sensor is a SWIR-band imaging sensor, and the second waveband is a LWIR waveband ranging from 8 μm to 15 μm, and the second imaging sensor is an LWIR-band sensor. In another example, the at least one lens includes a first lens and a second lens, the first lens being positioned between the quaternary mirror and the second lens along a primary optical axis of the optical system extending from the first focal plane to the second focal plane.
Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternate embodiment,” “various embodiments,” “one embodiment” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment.
Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the invention. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:
There are many applications in which both day and night operability are desirable. For example, most sensors in weapon sights, missile seekers, and Intelligence, Surveillance, and Reconnaissance (ISR) platforms, require day and night operability. This often necessitates the use of thermal or long-wave infrared (LWIR) or Mid-Wave Infrared (MWIR) cameras, which have poor resolution due to diffraction. Visible and short-wave infrared (SWIR) sensors can provide good resolution, but have poor night time imaging capability, particularly at long ranges. Accordingly, to achieve both day and night imaging capability, certain optical systems are dual-band, including both an LWIR sensor for night time imaging and a visible or SWIR sensor for higher resolution daytime imaging, for example. However, as discussed above, conventional dual-band systems use multiple windows and sets of optics and take up large volumes.
Aspects and embodiments provide a dual-band optical imaging system in a compact package that can be used in volume-constrained platforms and other applications where a highly compact form may be desirable. As discussed in more detail below, two imaging sensors for different wavebands, such as a MWIR or LWIR sensor and a visible or SWIR sensor, can be combined in a very compact optical design in which the sensors share a common window, primary mirror, secondary mirror, and tertiary mirror. Embodiments of the optical system discussed herein allow the use of both SWIR and LWIR imaging sensors for searching, acquisition, recognition, and tracking targets from volume-constrained platforms, such as weapon sights, missile seekers, UAVs, and satellites, for example.
Referring to
The system 100 includes a primary mirror 112, a secondary mirror 114, and a tertiary mirror 116. Incoming optical radiation 120, which may include light in both wavebands, is received via a system aperture 130 at the primary mirror 112, reflected by the primary mirror 112 to the secondary mirror 114, reflected from the secondary mirror 114 to the tertiary mirror 116, and reflected by the tertiary mirror 116. Thus, the aperture 130, the primary mirror 112, the secondary mirror 114, and the tertiary mirror 116 are all shared by (or common to) the optical radiation 120 in both wavebands. In one example, the primary mirror 112 and the tertiary mirror 116 are formed as different regions on the same physical structure. For example, a substrate may be produced, for example, by injection molding or other techniques, and a surface of the substrate machined, for example, using diamond point turning or other techniques and polishing to shape and polish regions of the surface into mirror surfaces corresponding to the primary mirror 112 and the tertiary mirror 116. In certain examples, the substrate may be made of magnesium or a magnesium alloy, or example. Using diamond point turning or similar techniques allows different regions of the surface of the substrate to be formed with the correct surface figure or shape (e.g., spherical, conical, etc.) and any aspheric departures or other characteristics needed to produce the mirror surfaces corresponding to the optical prescription that defines the primary and tertiary mirrors 112, 116. In certain examples, the mirror surfaces can be polished or coated (e.g., with a metallic coating) and then polished to be highly reflective to the optical radiation 120 in both wavebands of interest. An advantage of having the three dual-waveband shared optical elements, namely the primary mirror 112, the secondary mirror 114, and the tertiary mirror 116, be reflective optical elements (mirrors), rather than refractive optical elements, is that reflective systems are generally compact and free of chromatic aberrations over a wide spectral range, which is particularly useful where the shared optical elements need to accommodate two different wavebands.
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Thus, aspects and embodiments provide a dual-band optical imaging system capable of supporting infrared and visible imaging, and both daytime and night-time operation, in a compact package suitable for use in volume-constrained applications. Embodiments may combine advantageous properties of two different wavebands in a single compact system. For example, LWIR sensors provide a low-cost solution with both daytime and night-time operability, but have poor resolution, whereas SWIR (or visible) sensors provide better resolution but limited night-time operability. Embodiments of the optical system disclosed herein allow the use of both sensors in volume-constrained platforms. In certain examples, the optical system 100 can be configured with a short focal length and wide field of view for the lower-resolution LWIR or MWIR sensor, such that the optical system may be used for daytime or night-time detection and recognition of objects of interest, and configured with a long focal length and narrow field of view for the higher-resolution visible or SWIR sensor, such that the optical system 100 can also be used for identification of objects of interest detected using the LWIR sensor. Thus, a highly versatile, multi-function optical system with daytime and night-time operability can be provided in a highly compact volume.
The tables of
As discussed above, the optical system 100 may have a very compact physical form. For an example corresponding to the optical prescriptions given in the tables of
Embodiments of the optical system 100 may also provide good optical performance in both wavebands.
Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the foregoing description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.
