Patent Description:
In many camera applications, it is necessary to align the optical elements of the system lens with the center of the active area of the Focal Plane Array (FPA), also known as the optical axis. This typically requires specialized equipment in order to assure consistent mounting of the camera to the alignment test fixture, and then the imaging of a test card or other suitable pattern so that the optics positioning can be adjusted to bring the test image to the required location. Multiple individual items (camera, test card, and lens mount) must be well-controlled in order to achieve an accurate, repeatable alignment outcome. In addition, if different test fixtures are used, the outcome may vary due to physical differences (manufacturing tolerances etc.) between the fixtures.

<CIT> discloses a system for aligning components of an imaging device including a board on which the imaging device is mounted. The board includes light emitting devices and light receiving devices to receive reflected light from the light emitting devices which is used to align the components of the imaging device.

<CIT> discloses an alignment system configured to sense a state of alignment between a lens and a sensor of an imaging device, the system comprises alignment markers that are self-illuminating and may include a light-emitting diode.

The conventional techniques have been considered satisfactory for their intended purpose. However, there is a need for improved systems and methods for aligning components of an imaging device. This disclosure provides a solution for this need.

The present invention provides a system for aligning components of an imaging device as claimed in claim <NUM>.

In accordance with some embodiments, the FPA includes imaging pixels defining a pixel area, guard pixels defining a guard pixel area positioned around a perimeter of the pixel area, and test pixels defining a test pixel area positioned around a perimeter of the guard pixel area. Each of the at least two test elements can include a cluster of forward biased diodes positioned in the test pixel area. Each of the at least two test elements can be configured and adapted to emit alignment reference light through the lens of the imaging device. The forward biased diodes of each cluster can be arranged in at least one of a square shape, a round shape, a diamond shape, and/or an "L" shape. The at least two test elements can include four test elements. The FPA can define a rectangular imaging area. The rectangular imaging area can be a square imaging area. The at least two test elements can be positioned proximate to respective corners of the rectangular imaging area. The at least two test elements can be positioned at respective mid-points of respective sides of the rectangular imaging area.

Two test elements can define an axis. Each test element can include a cluster of forward biased InGaAs diodes configured and adapted to emit alignment reference light through the lens of the imaging device. The at least two test elements can be configured and adapted to emit light in a wavelength ranging from <NUM>-<NUM>. The at least two additional test elements can be configured and adapted to emit light in a wavelength ranging from <NUM>-<NUM>, <NUM> - <NUM>, and/or <NUM> - <NUM>. Each cluster of forward biased diodes are configured and adapted to emit alignment reference light through the lens of the imaging device. The test elements can be forward biased InGaAs diodes configured and adapted to emit alignment reference light through the lens of the imaging device.

The present invention also provides a method of testing and aligning a lens of an imaging device as claimed in claim <NUM>.

The method can include mounting the test camera to the lens of the imaging device so that a test camera FPA is rotated ninety degrees relative to the FPA of the imaging device. The method can include mounting the test camera to the lens of the imaging device so that a test camera FPA is rotated forty five degrees relative to the FPA of the imaging device. Adjusting the lens of the imaging device can include at least one of moving the lens along a horizontal and/or a vertical axis, and/or rotation about the FPA. The method can include focusing the lens of the imaging device to infinity such that the light emitted from the at least two test elements will be collimated and rays emerging from the lens will be parallel to the optical axis. The method can include focusing a test camera lens to the at least two test elements.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a schematic view of an exemplary embodiment of the system for aligning components of an imaging device in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments of the system for aligning components of an imaging device in accordance with the disclosure, or aspects thereof, are provided in <FIG>, as will be described. The systems and methods described herein can be used to simplify the testing process for imaging devices by using test features on the FPA of the imaging device itself as the source of the test image, instead of a traditional test card. This eliminates the test card and its associated alignment process.

As shown in <FIG>, a system <NUM> for aligning components of an imaging device <NUM> includes imaging device <NUM>, and a test camera <NUM>. Imaging device <NUM> includes a lens <NUM> and a focal plane array (FPA) <NUM>. FPA <NUM> defines an optical axis A and four test elements 112a-112d configured and adapted to emit a light through lens <NUM>. In the embodiment of <FIG>, the wavelength of the emission from test elements 112a-112d is at an upper end of the SWIR (shortwave infrared) spectrum, ranging from about <NUM> - <NUM>. Test elements 112a-112d can be forward biased InGaAs diodes. Test camera <NUM> is configured and adapted to be mounted to and pre-aligned with lens <NUM> of imaging device <NUM> to receive a light from test elements 112a-112d. Test camera <NUM> includes a test camera lens <NUM>. Because test camera <NUM> mounts directly to lens <NUM>, the position of test camera <NUM> is not independent (as the test card was) and therefore it is, in essence, pre-aligned. This pre-alignment results in a more accurate alignment of lens <NUM>, a simpler set up and faster alignment process, all of which result in reduced cost due to reduced labor hours needed to align lens <NUM> with the optical axis A.

With continued reference to <FIG>, a variety of mechanical attachment devices can be used, for example existing alignment test fixtures. Those skilled in the art will readily appreciate that there are a variety of commercially available lenses equipped with a cylindrical threaded receptacle used to mount filters or other optical elements. In the embodiment of <FIG>, a threaded adaptor <NUM> is configured and adapted to thread into threads <NUM> on lens <NUM> and threads <NUM> of test camera lens <NUM>, thereby attaching the test camera <NUM> to imaging device <NUM>. Alternatively, if the lens <NUM> is of custom design, said design may incorporate suitable mounting or alignment details (threaded adapters similar to above, pegs/locating holes, mechanical guides etc.) which will serve to affix the test camera <NUM> to lens <NUM>. Test camera <NUM> will respond to the light emitted by test elements 112a-112d, and their relative positions can therefore be determined by test camera <NUM>. Lens <NUM> alignment is achieved by adjusting the position of lens <NUM> until the detected positions of the test features 112a-112d matches the desired (pre-calculated) positions expected to be seen by test camera <NUM>. Embodiments of the present disclosure can be used to eliminate offsets in both the horizontal axis X (schematically shown to be extending in and out of the page in <FIG>) direction and the vertical axis Y direction (shown perpendicular to horizontal axis X), as well as rotation about the FPA optical axis A.

With continued reference to <FIG>, FPA <NUM> is positioned on a printed circuit board assembly (PCBA) <NUM> of imaging device <NUM>. Test elements 112a-112d are electrically coupled to control circuitry <NUM> positioned on the PCBA <NUM> to drive the light emission. Control circuitry <NUM> can be positioned in a variety of suitable places, such as off-chip, meaning it does not need to be incorporated into the PCBA or readout integrated circuit (ROIC). These test elements 112a-112d are positioned within FPA diode arrays <NUM>. These FPA diode arrays <NUM> typically surround a rectangular imaging area <NUM>, where rectangular includes a square shape. Diode arrays <NUM> around the imaging area <NUM> are generally used to test for dark current and other parameters to ensure FPA <NUM> meets specifications. In testing for dark current and/or other parameters (and in normal operation of the imaging area <NUM> of the array), the diodes of diode array <NUM> of the present disclosure are reverse biased. In embodiments of the present disclosure, test elements 112a-112d are forward biased diodes such that they will emit light in the same manner as a standard light-emitting diode (LED).

As shown in <FIG>, the imaging area <NUM> of FPA <NUM> includes imaging pixels <NUM> defining a pixel area <NUM>, and guard pixels <NUM> defining a guard pixel area <NUM> positioned around a perimeter of the pixel area <NUM>. Guard pixels <NUM> are contiguous with the imaging pixels <NUM> and extend out for several rows and columns along each edge. Guard pixels <NUM> act to mitigate any 'edge effects' that might occur at the periphery of pixel area <NUM>. Test diode array <NUM> includes test diodes <NUM> positioned around a perimeter of guard pixel area <NUM>. Test diodes <NUM> are located just beyond guard pixels <NUM> and act to check dark current, as described above. Each test element 112a-112d includes a cluster of forward biased diodes <NUM> (which are test diodes <NUM> in a forward biased position) positioned in the test diode array <NUM> (test element 112b is shown in <FIG> and test elements 112a, 112c and 112d are all similar). In accordance with the embodiment of <FIG>, test diodes <NUM> are fabricated from InGaAs and when forward biased, like forward biased diodes <NUM>, they will emit SWIR light in the same manner of a standard LED. Those skilled in the art will readily appreciate that a variety of light-emitting diodes may be used for to make up suitable test elements 112a-112d and that a variety of wavelengths can be emitted. It is contemplated that light with other wavelengths in the electromagnetic spectrum can also be emitted by test elements 112a-112d, such as, visible light (<NUM>-<NUM>), UltraViolet light (<NUM>-<NUM>), and the like. Those skilled in the art will readily appreciate that as long as test diodes <NUM> are capable of emitting light when they are forward biased, they will provide suitable diodes to make up test elements 112a-112d. By forward-biasing already existing test diodes <NUM> in test diode array <NUM>, the forward biased diodes <NUM> that make up test elements 112a-112d are allowed to be fabricated on the detector material as part of the existing processing - so the test elements 112a-112d incur no additional cost. Forward biased diodes <NUM> are configured and adapted to emit alignment reference light through lens <NUM> of imaging device <NUM>. Forward biased diodes <NUM> of test element 112b are shown arranged in a diamond shape, but those skilled in the art will readily appreciate that a variety of suitable shapes may be used, such as a square shape, a round shape, and/or an "L" shape.

With reference to <FIG>, it is contemplated that only two of test elements 112a-112d may be needed to provide proper alignment, e.g. test elements 112a and 112b. Two test elements 112b and 112c are positioned adjacent to opposite corners of FPA <NUM>. In this way, in some embodiments of the invention, only two of test elements 112a-112d may be needed to provide proper alignment of lens <NUM>. Those skilled in the art will readily appreciate that the two elements used could be test elements 112a and 112c, or 112a and 112d. The test camera <NUM> is set up so that a test camera FPA <NUM>, shown in <FIG>, is rotated <NUM>° from FPA <NUM>. <FIG> schematically shows the area of the test camera FPA <NUM> overlaid on the FPA <NUM>. The rotation of test camera <NUM> allows for test elements 112a-112d to fall within an imaging area of FPA <NUM> of test camera <NUM> so that the position of the test elements 112a-112d can be determined. In general, test elements 112a-112d should be close to the edges of FPA <NUM> so they can be as far apart as possible (while still falling within the detecting area of FPA <NUM> of test camera <NUM>. Having test elements 112a-112d as far apart as possible, while still falling within the detecting area of FPA <NUM>, provides for the best possible accuracy in measurement, as any measurement error will result in smallest angular distortion.

As shown in <FIG>, another embodiment of an FPA <NUM> for use in imaging device <NUM> of system <NUM> is shown. FPA <NUM> is the same as FPA <NUM> except that FPA <NUM> has a square shape where two test elements <NUM> are positioned at the midpoints of respective edges, instead of being toward the corners of FPA <NUM>. FPA <NUM> includes an imaging area <NUM>, similar to imaging area <NUM>. Imaging area <NUM> defines a pixel area <NUM> and a guard pixel area <NUM>, which are the same as pixel area <NUM> and guard pixel area <NUM>, except for the square shape. Test elements <NUM> are positioned within a test diode array <NUM>. Test diode array <NUM> is the same as test diode array <NUM>, except that the four edges of test diode array <NUM> are the same length and test elements <NUM> are positioned at the mid-points of respective edges. Each test element <NUM> includes a cluster of forward biased diodes and is positioned in the test diode array <NUM>. By having each test element <NUM> positioned at the mid-point of a respective edge, a square test camera FPA <NUM> can be rotated <NUM> degrees relative to the edges of FPA <NUM> or a rectangle test camera FPA <NUM> can be rotated <NUM> degrees relative to the edges of FPA <NUM> and the test elements <NUM> will fall within the imaging area of the test camera defined by the test camera FPA <NUM>. Test camera FPA <NUM> can be used in test camera <NUM>. Those skilled in the art will readily appreciate that if the original FPA is square, such as FPA <NUM>, and the test camera has a square test camera FPA <NUM>, the test camera should be rotated. Those skilled in the art will appreciate that you can use any test camera with a given FPA shape, as long as in the un-aligned state, the test features will be within the imaging area defined by the FPA of the test camera.

In accordance with another aspect, a method of testing and aligning a lens, e.g., lens <NUM>, of an imaging device, e.g., imaging device <NUM>, includes mounting a test camera, e.g. the test camera <NUM>, to the lens of the imaging device so that a test camera FPA, e.g. FPA <NUM>, is rotated ninety degrees relative to an FPA, e.g. FPA <NUM>, of the imaging device. Mounting the test camera to the lens of the imaging device includes mounting a first side of a threaded adaptor, e.g. threaded adaptor <NUM>, to the lens of the imaging device and then mounting the test camera lens to a second side of the threaded adaptor. Where a square FPA, e.g. square FPA <NUM>, is used, those skilled in the art will readily appreciate that mounting the test camera to the lens of the imaging device includes mounting the test camera such that a test camera FPA, e.g. test camera FPA <NUM>, is rotated at <NUM> degrees relative to the square FPA.

The method includes emitting light with at least two test elements, e.g., test elements 112a-112d, or <NUM>, positioned within a diode array, e.g. diode array <NUM> or <NUM>, of the FPA of the imaging device. The FPA defines an optical axis, e.g., optical axis A. The method includes focusing the lens of the imaging device to infinity such that the light emitted from the test elements will be collimated and rays emerging from the lens will be parallel to the optical axis. The method includes focusing a test camera lens, e.g., test camera lens <NUM>, to the test elements. The focus of the lens should be adjusted for sharpest detail on the test elements. The method includes detecting the light with the test camera mounted to the lens of the imaging device to determine if the light emitted is in a desired position. To determine this, the test camera will respond to the light emitted by the test elements (e.g. the SWIR light), and their relative positions can therefore be determined.

The method includes adjusting the lens of the imaging device until the light emitted by these test features is detected by the test camera in the desired position. The lens alignment is achieved by adjusting the position of the lens until the detected positions of the test elements matches the desired (pre-calculated) positions. Adjusting the lens of the imaging device includes moving the lens along a horizontal and/or a vertical axis, e.g., horizontal axis X and vertical axis Y, and/or rotation about the FPA about optical axis A. This method can be used to eliminate offsets in both horizontal and vertical axes, as well as rotation about the optical axis. Embodiments of the present disclosure include manufacturing and/or retrofitting a Readout Integrated Circuit (ROIC) or Photodiode Array (PDA) to include metallization to allow the test elements to be operated in LED mode.

Embodiments of system <NUM> provide for more accurate alignment as compared with the traditional test card approach, simpler set-up, and quicker test procedures. The faster set-up and quicker test procedure results in reduced labor hours and costs savings. The simpler set up stems from not having to align a test card with the FPA optical axis A. Instead, the test camera <NUM> and lens <NUM> attach directly to the lens <NUM> to be aligned. The faster alignment process results from the four, widely-separated test elements as the references, misalignment is magnified to the greatest extent possible, and the operator can see the effects of the alignment adjustment in real time.

Claim 1:
A system (<NUM>) for aligning components of an imaging device, the system comprising:
an imaging device (<NUM>) including a lens (<NUM>) and a focal plane array (<NUM>), FPA, wherein the FPA defines an optical axis (A) and includes at least two test elements (112a-112d) configured and adapted to emit a light through the lens; and characterized in that the system further comprises
a test camera (<NUM>) configured and adapted to be mounted to and pre-aligned with the lens of the imaging device to receive the light from the at least two test elements.