Radial wedge and central quadrant photodetector

Abstract

A photodetector for receiving a beam spot. The photodetector has a plurality of independent inner quadrant sections, each having a first anode, and a plurality of independent radial wedge sections each having a second anode. A separate first lead connects the first anode of each of the inner quadrant sections to a corresponding first anode bond pad. A separate second lead connects the second anode of each of the radial wedge sections to a corresponding second anode bond pad. The photodetector also has a single shared and common cathode located on the side of the photodetector opposite the first and second anodes. In some embodiments, the photodetector may include an individual third anode associated with each radial wedge section. Further provided is an optical detector system including the photodetector.

Description

RADIAL WEDGE AND CENTRAL QUADRANT PHOTODETECTORRELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial Number 63 / 528.539. filed on July 24. 2023. the contents of which are incorporated in this application by reference.TECHNICAL FIELD

[0002] The present disclosure relates generally to optoelectronic devices and, more particularly, to photodetectors having an array of active segments, sections, or detectors.BACKGROUND OF THE DISCLOSURE

[0003] As explained in an article by R. Paschotta titled "‘Position-Sensitive Detectors,” available at https: / / www.rp- photonics.com / position_sensitive_detectors.html and accessed on May 16, 2023, position-sensitive detectors are photodetectors with which one can measure the position of a light spot (or, as disclosed in U.S. Patent No. 11.424,827 titled “Optical Tracking System,” a non-spot impingement on the photodetector, such as those impingements illustrated in Fig. 9 of the patent, created by a non-spot beam shape) in one or two dimensions, normally with a relatively high speed. The light spot is usually caused by a laser beam hitting the photodetector. Such photodetectors can be used to monitor beam position and, therefore, optical system alignment (laser spot trackers). Another application is (within a feedback system) to stabilize the position of a laser beam (auto aligners). Still another application is to measure distances by triangulation.

[0004] Position-sensitive detectors can be based on different operation principles. One measurement principle for position sensing is to use a kind of segmented photodetector, which can measure optical intensities for a few or evenmany different spatial positions (pixels). From the resulting data, the position of the light spot can be calculated. The uniformity of response between different detector segments is of course an important quality feature of such devices.

[0005] In the simplest case, as illustrated in Fig. 1, a photodiode 10 with two active segments, sections, or detectors 12 and 14 (a dual-segment photodiode or dualcell photodiode) is used, with a narrow gap 16 between them. The incident beam forms a light spot 18 on the photodiode 10. The beam radius of the incident beam is chosen such that at least for beam positions in the intermediate range both detectors 12, 14 obtain some optical power. Fig. 2 is a graph depicting the output signals from the photodiode 10 with two signals as functions of the beam position. From the relative signals related to the two detectors 12, 14 (the detector 12 is the “left” detector and the detector 14 is the “right” detector) the beam position can be calculated. The gap 16 between the adjacent detectors 12, 14 is a transition region. The device design ultimately determines whether charge can be collected from light incident upon the transition zone (“gap”), where charge may be shared across multiple devices, or there may be a reduction in signal, or changed optical performance. Thus, the segmented device may result in perturbations or may result in “blind spots” or areas in w hich no output signal is produced by incident light.

[0006] Note that for this kind of device one obtains a nonlinear dependence of the signal on the position; therefore, a linearization technique may have to be applied. In addition, the relative intensities depend not only on the beam position, but also on the beam radius. For those reasons, such segmented diodes are not ideally suited for quantitative position measurements. They are useful, however, for checking whether a beam is properly centered (centering indicators), e.g., within a feedback system for automatic alignment. For example, such devices are used in devices for optical data storage (CD-ROM. DVD, etc ).

[0007] Similarly, one can use a quadrant photodiode 20 with four active segments, sections, or detectors 22, 24, 26, and 28 having a narrow7gap 30 betw een them as shown in Fig. 3. The incident beam forms a light spot 18 on the quadrant photodiode 20. The quadrant photodiode 20 can be used to monitor positions in twodimensions. For further information about the quadrant photodiode 20, see D. Marett, “A Four Quadrant Photo Detector for Measuring Laser Pointing Stability,’' available at https: / / www.conspiracyoflight.com (2012).

[0008] Segmented photodiodes like the photodiode 10 and the quadrant photodiode 20 are often based on silicon PIN technology, with sensitivity in the visible spectral range and up to about 1 pm. (They are also available with other semiconductors, however, such as indium gallium arsenide (InGaAs) for detection at longer infrared wavelengths.) The quadrant photodiode 20 often consists of four separate P on N silicon photosensitive surfaces separated by the small gap 30. In one example, the gap 30 is about 42 pm. The laser beam is usually pointed towards the dead center among the four quadrants and the beam diameter is selected to fit inside of the total quadrant area. Although light may fall on all four quadrants, the difference between the left and right quadrants (X output) and the top and bottom quadrants (Y output) can be adj usted to zero by centering the beam, whereas the SUM is at a maximum. The device X and Y output voltages thereby become very sensitive to slight deviations in the position of the beam from this initial centered setting. On the other hand, the SUM value can be used to measure changes in the beam intensity, so this can be used to correct the X and Y output values for voltage changes that are due to intensity fluctuations rather than actual beam deviations. In order to present the outputs of the four quadrants as X, Y, and SUM, it is necessary to first amplify the individual quadrant outputs, and then combine them using a series of sum and difference amplifiers (for X and Y) or just a sum amplifier (for the SUM output). Further, the spot size and location determine whether a signal can be collected from more than one pixel element. If in some instances light is fully within one single pixel, with no light incident upon a gap or another pixel, this can cause ambiguity' as to spot location, causing the system to raster, slew, or “search” for the precise location of the beam.

[0009] As illustrated in Fig. 4, the PIN diode 40 that forms the basis for segmented photodiodes like the photodiode 10 and the quadrant photodiode 20 is an alteration of the PN-j unction diode having an area A. Unlike the PN-j unction diode, the PIN diode 40 has an undoped, wide intrinsic semiconductor region 44 (with awidth W) between a P-type semiconductor region 42 and an N-type semiconductor region 46. Thus, the PIN diode 40 has three regions: namely, the P-region 42, the I- region 44, and the N-region 46. The P and N regions 42, 46 are normally heavily doped because they are used for Ohmic contacts. The inclusion of the intrinsic region 44 in the PIN diode 40 can significantly increase the break down voltage for the application of high voltage. The intrinsic region 44 also offers advantageous properties when the PIN diode 40 operates at high frequencies in the range of radio waves and microwaves.

[0010] The working principle of the PIN diode 40 is exactly the same as the PN-junction diode. The main difference is that the depletion region, which normally exists between the P and N regions 42, 46, is larger. In any PN-junction diode, the P region 42 has been doped to contain holes. Likewise, the N-region 46 has been doped to have excess electrons. The intrinsic region 44 between the P and N regions 42, 46 includes no charge carriers because any electrons or holes merge. Therefore, the depletion region functions as an insulator. Fig. 5 outlines the structure of the PIN diode 40. One application of the PIN diode 40 is use as a photodetector to convert light (optical signals) into current (electrical signals).

[0011] Segmented photodiodes are also known having more complex arrays than the two active segments, sections, or detectors of the photodiode 10 and the four active segments, sections, or detectors of the quadrant photodiode 20. There are photodiode arrays containing a larger number of photodiode segments either in a linear array for one-dimensional position sensing or on a two-dimensional grid. Such devices can contain hundreds or thousands of diodes. In principle, one could derive the spot position simply by taking the coordinates of the pixel (detector segment) receiving the highest optical pow er. The spatial resolution would then be identical to the pixel spacing. A much better resolution can be achieved by using data from several pixels, assuming that the light spot 18 is large enough. For example, one may fit a calculated curve to the pixel data, calculating the position and the beam radius as fit parameters. A computationally simpler approach is to calculate the centroid via first moments of the intensity distribution, possibly after discarding pixels which haveintensity values below a certain threshold value or are spatially too far away from the intensity maximum.

[0012] One example of segmented photodiodes having a more complex array is disclosed in Fig. 6, which illustrates a known InGaAs PIN double quadrant photodetector 50 having eight independent active-area sections, segments, or detectors. The double quadrant photodetector 50 is available from Princeton Lightwave, Inc. of Cranbury, New Jersey. As illustrated, the eight-section double quadrant photodetector 50 has four inner quadrant sections 52 and four outer quadrant sections 54. The hermetically sealed packaging for the double quadrant photodetector 50 is a T0-8 through-hole metal can with an anti-reflection coated window cap (not shown) and twelve pins, terminals, or leads 56. Eight leads 56 connect the sections 52, 54 of the inner and outer quadrants of the double quadrant photodetector 50 to respective bond pads 58, and the remaining four leads are connected to the common cathode (substrate) of the detectors. (Neither the remaining four leads nor the cathode are shown in Fig. 6.) All twelve leads are isolated from the package case. The common cathode connection is made to each center pin of each of the four groups of three in-line pins. The overall detector optically active diameter, D, is typically 1 mm.

[0013] Another example of segmented photodiodes having a more complex array is disclosed in U.S. Patent No. 3,689,772 titled “Photodetector Light Pattern Detector.” The array includes first and second semi-circular sub-arrays. The first sub-array has a plurality (i.e., eight) of concentric annular detectors, such as hemirings. The second sub-array has a plurality (i.e., thirty four) of detectors extending approximately radially from near to the center of the first sub-array. Each detector of the array is provided with a separate attached electrical conductor. The conductors attached to the ring detectors are positioned in portions of approximately radial sector gaps separating the two sub-arrays.

[0014] Yet another example of segmented photodiodes having a more complex array is disclosed in U.S. Patent No. 11,646,384 titled “Optoelectronic Devices With Non-Rectangular Die Shapes.” Fig. 7 of the patent is a top plan viewillustration of multiple photodiodes within a detector assembly. More specifically, the photodiodes may be non-rectangular shaped, such as a trapezoid, and can be further arranged in configurations that increase surface area use.

[0015] Despite these attempts, a need exists for a photodetector having an array of independent active-area sections, segments, or detectors that allows for high sensitivity, high resolution, and high sample acquisition rates during operation. Therefore, objects of the present disclosure are to accept small, focused light beams without ambiguity and to minimize the size of the center of the array without sacrificing wide-field accuracy. Another object is to better accommodate “blind spots” or areas in which no output signal is produced by incident light. A further object is to provide a photodetector that provides both a radial distance and an angular position to vastly improve guidance when used for beam steering.SUMMARY OF THE DISCLOSURE

[0016] To meet this and other needs, to achieve these and other objects, and in view of its purposes, the present disclosure provides a photodetector for receiving a beam spot. The photodetector has a center, a top, a bottom, and a perimeter. The photodetector includes a plurality of independent inner quadrant sections each separated by a first gap, the inner quadrant sections located on the top and proximate the center of the photodetector; an individual first anode associated with each inner quadrant section; and a separate first lead connecting the first anode of each of the inner quadrant sections to a corresponding first anode bond pad located on the top and proximate the perimeter of the photodetector. The photodetector further includes a plurality of independent radial wedge sections each separated by a second gap, the radial wedge sections located on the top and each having a pie shape with a narrower head proximate the center of the photodetector and a wider foot proximate the periphery of the photodetector; an individual second anode associated with each radial w edge section, the second anode located proximate the foot of the radial wedge section; and a separate second lead connecting the second anode of each of the radial wedge sections to a corresponding second anode bond pad located on the top and at the perimeter of the photodetector. The photodetector still further includes a singleshared and common cathode located on the bottom of the photodetector opposite the first and second anodes. In some embodiments, the photodetector may include an individual third anode associated with each radial wedge section.

[0017] Further provided is an optical detector system including the photodetector summarized above. The optical detector system includes one or more optical elements, wherein the one or more optical elements receive incoming light and generate the beam spot on the photodetector, and a computer system configured to determine, based on output signals received from the photodetector, first data indicative of a direction of the beam spot relative to a predetermined point on the photodetector and second data indicative of a distance between the beam spot and the predetermined point.

[0018] Still further provided are a related sy stem and at least one computer- readable non-transitory storage media embodying software. The one or more computer-readable non-transitory storage media embodying software is operable when executed, in one embodiment, to perform a series of steps using the optical detector system including the photodetector.

[0019] It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the disclosure.BRIEF DESCRIPTION OF THE DRAWING

[0020] The disclosure is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures:

[0021] Fig. 1 illustrates a conventional dual-segment photodiode with a light spot of a beam impinging on the photodiode;

[0022] Fig. 2 is a graph depicting the output signals from the photodiode illustrated in Fig. 1 with two signals as functions of the beam position;

[0023] Fig. 3 illustrates a conventional quadrant photodiode with a light spot impinging on the quadrant photodiode;

[0024] Fig. 4 provides an outline of a PIN diode;

[0025] Fig. 5 illustrates the structure of a PIN diode;

[0026] Fig. 6 illustrates a known InGaAs PIN quadrant photodetector having eight independent active-area sections, segments, or detectors;

[0027] Fig. 7 illustrates an equivalent circuit for a single-element photodiode;

[0028] Fig. 8 illustrates an equivalent circuit for a one-dimensional position sensing device;

[0029] Fig. 9 illustrates one embodiment of an optical detector system according to the present disclosure including a photodetector having an improved geometrical pattern or array of detectors with a single anode contact per detector;

[0030] Fig. 10 depicts the optical detector system illustrated in Fig. 9 with a light beam impinging on the photodetector;

[0031] Fig. 11 illustrates another embodiment of the optical detector system according to the present disclosure including shorting links;

[0032] Fig. 12 illustrates yet another embodiment of the optical detector system according to the present disclosure including two anode contacts per detector in the radial wedge section of the array of detectors; and

[0033] Fig. 13 illustrates an example computer system for use in connection with the optical detector system according to the present disclosure.DETAILED DESCRIPTION OF THE DISCLOSURE

[0034] In this specification and in the claims that follow, reference will be made to a number of terms which shall be defined to have the following meanings ascribed to them. The term “substantially,” as used in this document, is a descriptiveterm that denotes approximation and means “considerable in extent” or “largely but not wholly that which is specified” and is intended to avoid a strict numerical boundary to the specified parameter. Directional terms as used in this disclosure — for example up, down, right, left, front, back, top, bottom — are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0035] The term “about” means those amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When a value is described to be about or about equal to a certain number, the value is within ± 10% of the number. For example, a value that is about 10 refers to a value between 9 and 11, inclusive. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point. Whether or not a numerical value or end-point of a range in the specification recites “about.” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about” and one not modified by “about.” It will be further understood that the endpoints of each of the ranges are significant both in relation to the other end-point and independently of the other end-point.

[0036] The term “about” further references all terms in the range unless otherwise stated. For example, about 1, 2, or 3 is equivalent to about 1, about 2, or about 3, and further comprises from about 1-3, from about 1-2, and from about 2-3. Specific and preferred values disclosed for components and steps, and ranges thereof, are for illustration only; they do not exclude other defined values or other values within defined ranges. The components and method steps of the disclosure include those having any value or any combination of the values, specific values, more specific values, and preferred values described.

[0037] The indefinite article “a” or “an” and its corresponding definite article “the” as used in this disclosure means at least one. or one or more, unless specified otherwise. “Include.” “includes.” “including,” “have.” “has,” “having,” comprise,”“comprises,” “comprising,” or like terms mean encompassing but not limited to, that is, inclusive and not exclusive.

[0038] The ability to transmit data wirelessly provides tremendous utility. Wireless transmission uses one or more frequencies of electromagnetic signals, such as optical wavelengths, to send information. Optical wavelengths may include, but are not limited to, infrared wavelengths, visible light wavelengths, ultraviolet wavelengths, and so forth. Optical wavelengths may move from one location to another in free space, including the atmosphere, a vacuum, and so forth.

[0039] A free space optical communication system may be used in a variety of different situations. For example, optical transceivers (include both a transmitter to send and a receiver to receive signals at optical wavelengths) may be used to provide an intersatellite link between a first satellite and a second satellite, allowing data to be sent from the first satellite to another. In another example, a ground station may communicate with a satellite using an optical transceiver. In still another example, fixed terrestrial stations may communicate with one another using optical transceivers. As with any system using electromagnetic signals, including optical wavelengths, the desired communication requires that the received signal must be received.

[0040] To maintain communication, it is necessary' for the transmitter and the receiver to be pointed at one another and to maintain that pointing. The transmitter is positioned so that light from the transmitter is directed towards the receiver. Likewise, the receiver is positioned so that the light from the transmitter is received. For example, the light source that is transmitting needs to radiate light in the direction of the receiver, and the receiver needs to gather that light and process it with a detector.

[0041] In the ideal situation in which the transmitter and the receiver are not in motion and neither is subject to any sort of vibration or other disturbance, maintaining such careful pointing could be done once and never repeated. Unfortunately, all structures have some mechanical motion or vibration. Thesemotions can result in a failure of the receiver to remain properly pointed at the transmitter and of the beam from the transmitter to remain properly pointed at the receiver. A device that is in motion and using optical communication, such as a satellite in orbit, introduces further complications. To account for these motions, some form of active adjustment or feedback may be used.

[0042] The active adjustment may include an optical detector system that provides output about how far a beam of incoming light deviates from a specified reference. The output signal(s) from the optical detector system may then be used to operate actuators affixed to an optical element. A feedback loop attempts to keep the incoming light aligned to a particular predetermined point, such as the center of a detector array, by using the output to operate the actuators. For example, the detector array may comprise photodetectors with each photodetector generating an output signal as light impinges on the individual photodetector.

[0043] Optical detector systems use an incoming beam with a beam shape that is typically (although not necessarily) circular in cross section, presenting a circular pattern (or “spot”) of light on the detector array. (A non-spot beam shape is a beam shape, where it impinges upon the detector array, that is non-circular in cross section.) The combined characteristics of the detector array and spot produce information about how much the output of the detector array changes in response to a change in the position of the light incident on the detector array. For example, the information describes how amplitude of an output signal from the photodetectors in the array changes as the spot moves across the detector array.

[0044] The accuracy of the information is affected by several factors. One factor is how much of the incoming beam of light that impinges on the detector array produces output. The portion of the beam that impinges on photodetectors in the array produces output. The portion of light that impinges on gaps between or among the photodetectors does not. For example, if the spot of light falls entirely within a gap between photodetectors, no output is produced.

[0045] The optical detector system provides output that is indicative of a relative position of an incoming beam of light relative to the detector array as well as distance of the incoming beam of light relative to the detector array. This output may then be used to operate one or more devices to provide active tracking of a beam of incoming light. The system may be used in a variety of applications including, but not limited to, intersatellite communications, communications between a satellite and ground station, communications between a satellite and user terminals, between vehicles, between terrestrial stations, and the like. For example, the system may be used in terrestrial applications, mobile applications, and so forth. Some of the applications are described in U.S. Patent No. 11,424,827, mentioned above, which is incorporated by reference in this document.

[0046] Conventional optical detector systems use a single element as discussed above. Fig. 7 illustrates an equivalent circuit for a single-element photodiode (PD). The single-element PD has two terminals: a single, discrete anode located on one surface of the PD (on w hich an illuminated spot impinges) and a common cathode that extends substantially along the entire opposite surface of the PD. The single-element PD is position ambiguous.

[0047] Fig. 8 illustrates an equivalent circuit for a one-dimensional position sensing device (1 D PSD). The 1 D PSD has three terminals: two, discrete anodes located on one surface of the ID PSD (on which an illuminated spot impinges) and a common cathode that extends substantially along the entire opposite surface of the ID PSD. Both anodes reference the same cathode. The ID PSD is able to provide positional data in a single axis, typically within a single pixel. For a photonic ID PSD, the position is relative to the location of the illuminated spot. The longitudinal position X is measured by the ratio Ii : h, where Ii is the current in Anode 1 and h is the current in Anode 2. More specifically, if L is the distance between the two anodes, the applicable formula is: (I2 - I i) / (l2 + Ii) = 2X / L.

[0048] The optical detector system 100 according to the present disclosure includes a photodetector 102 having an improved geometrical pattern or array of detectors. The array combines a center quadrant (or segmented PSD) with radialwedges (a ID PSD) that extend outw ard from the center quadrant to the periphery7of the photodetector 102 . Several embodiments of the optical detector system 100 are disclosed.

[0049] As illustrated in Fig. 9, the center quadrant of the photodetector 102 has four, discrete and independent inner quadrant sections 110 each separated by a gap 112. Each quadrant section 110 has an individual anode 114 associated with it. A separate lead 1 16 connects the anode 114 of each of the four quadrant sections 1 10 to a corresponding anode bond pad 118 located at the perimeter of the photodetector 102.

[0050] As also illustrated in Fig. 9, the radial wedges of the photodetector 102 include twenty -four, discrete and independent radial wedge sections 120 each separated by a gap 122. Each radial wedge section 120 has an individual anode 124 associated with it. A separate lead 126 connects the anode 124 of each of the radial wedge sections 120 to a corresponding anode bond pad 128 located at the perimeter of the photodetector 102. Each radial wedge section 120 has a pie shape with a narrower head proximate the center of the photodetector 102 and a wider foot proximate the periphery of the photodetector 102. In the example illustrated, each radial wedge section 120 has an inner diameter of about 1.16 mm and an outer diameter of about 4.4 mm, and extends at an angle of about 14 degrees. Although twenty -four radial wedge sections 120 are illustrated in the embodiment show n in Fig. 9, the number of radial wedge sections 120 may be increased (to, for example, tw enty -eight, thirty-two, thirty-six, or more) or decreased (to, for example, twenty, sixteen, twelve, or less) depending upon the application and specified performance requirements. A circular opening 130 separates the inner quadrant sections 110 from the radial wedge sections 120.

[0051] The width, length, and number of the individual radial w edge sections 120 can be optimized to accommodate a small spot beam so that there is no positional ambiguity. Therefore, the photodetector 102 of the optical detector system 100 avoids the ambiguity found in existing position sensing detectors when small beam diameters are used. Further, the radial wedge sections 120 can be electrical configured toprovide both a radial distance and an angular position to vastly improve guidance when the optical detector system 100 is used for beam steering. The optical detector system 100 can support a simple optical window or specific lensing can be used to manipulate an incoming beam into a unique output so as to fall onto the radial wedge sections 120 or the inner quadrant sections 110 to provide a unique photoelectric displacement output. The optical detector system 100 can also minimize the size of the center of the array, without sacrificing wide-field accuracy, and can better accommodate blind spots.

[0052] Fig. 10 depicts the optical detector system 100 illustrated in Fig. 9 with a light beam impinging on the photodetector 102 to create a spot 140. Typically, the light beam emanates from a laser. A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word “laser” originated as an acronym for “light amplification by stimulated emission of radiation.” A laser differs from other sources of light in that it emits light that is coherent. Spatial coherence allows a laser to be focused to a tight spot. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation).

[0053] The goal of the optical detector system 100 is to position the spot 140 precisely at the center of the photodetector 102 (where the spot 140’ is shown in Fig. 10). The recommended diameter of the spot 140 is between about 50% and 75% of the diameter of the inner quadrant sections 110. Small spots 140, not spanning more than one detector 110, 120, become “ambiguous” within that detector, losing spatial resolution until either (a) the size of the spot 140 increases to encompass more than one detector, or (b) the spot 140 moves. The radial wedge sections 120 offer position resolution only to the limit of indicating that the spot 140 is within a particular radial wedge section 120 and not where the spot 140 is located within that radial wedge section 120. If the dimensions of the photodetector 102 are predetermined with respect to the size of the spot 140, then when the spot 140 is in one of the radial wedge sections 120, the centering direction can easily be determined because the spot 140 would cover at least tw o radial wedge sections 120. By “predetermined” is meantdetermined beforehand, so that the predetermined characteristic must be determined, i.e., chosen or at least known, before construction of the optical detector system 100.

[0054] The embodiment of the optical detector system 100 illustrated in Figs. 9 and 10 has one, single anode contact per detector (i.e., per inner quadrant section 110 and per radial wedge section 120). Therefore, position sensing is dependent upon the detector only. The photodetector 102 of the optical detector system 100 has a single shared and common cathode. The cathode is located on the side of the photodetector 102 opposite the anodes 114, 124 and preferably extends entirely along that side.

[0055] The optical detector system 100 requires flip chip for connectivity (i) between the four quadrant sections 110 and their corresponding anode bond pads 118; and (ii) between the radial wedge sections 120 and their corresponding anode bond pads 128. Therefore, the optical detector system 100 is preferably back-side illuminated. Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, integrated circuit chips, integrated passive devices, and microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry7(e.g., a circuit board or another chip or wafer), it is flipped over so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit, and then the solder is reflowed to complete the interconnect. The flip chip connectivity is in contrast to wire bonding, in which the chip is mounted upright and fine wires are welded onto the chip pads and lead frame contacts to interconnect the chip pads to external circuitry .

[0056] A back-illuminated sensor, also known as a backside illumination (BI) sensor, is a ty pe of digital image sensor that uses a novel arrangement of the imaging elements to increase the amount of light captured and thereby improve low -light performance. A traditional, front-illuminated sensor is constructed in a fashion similar to the human eye, with a lens at the front and photodetectors at the back. Thistraditional orientation of the sensor places the active matrix of the sensor — a matrix of individual picture elements — on its front surface and simplifies manufacturing. The matrix and its wiring reflect some of the light, however, and thus the photocathode layer can only receive the remainder of the incoming light; the reflection reduces the signal that is available to be captured.

[0057] A back-illuminated sensor contains the same elements as the front- illuminated sensor, but arranges the wiring behind the photocathode layer by flipping the silicon wafer during manufacturing and then thinning its reverse side so that light can strike the photocathode layer without passing through the wiring layer. This change can improve the chance of an input photon being captured from about 60% to over 90%. The greatest difference is realized when pixel size is small, because the light capture area gained in moving the wiring from the top (light incident) to bottom surface is proportionately smaller for a larger pixel.

[0058] The embodiment of the optical detector system 100 illustrated in Figs. 9 and 10 offers excellent performance for relatively large spots 140 where position accuracy is required. It works well for both Gaussian and top-hat beams. In optics, a Gaussian beam is a beam of electromagnetic radiation with high monochromaticity whose amplitude envelope in the transverse plane is given by a Gaussian function; this also implies a Gaussian intensity (irradiance) profile. This fundamental transverse Gaussian mode describes the intended output of most (but not all) lasers, as such a beam can be focused into the most concentrated spot. A flat-top beam (or top- hat beam) is a light beam (often a transformed laser beam) having an intensity profile which is flat over most of the covered area. This is in contrast to Gaussian beams, where the intensity smoothly decays from its maximum on the beam axis to zero.

[0059] Fig. 11 illustrates another embodiment of the optical detector system 100 that includes one or more shorting links 150. Each radial wedge section 120 can be individually addressed or permanently configured (during manufacture of the optical detector system 100) with one or more shorting links 150. The shorting links 150 reduce the number of pie-shaped radial wedge sections 120 downward to, ultimately, one continuous outer ring. An advantage of reducing the number of radialwedge sections 120 is that the number of outputs, which need to be processed, is also reduced.

[0060] Another variation in the embodiment of the optical detector system 100 illustrated in Figs. 9 and 10 seeks to lower the capacitance of the detectors in the radial w edge section 120. This goal is achieved by reducing the detector area in each of the radial wedge sections 120. Several design variations reduce the detector area, including a contiguous photodetector stmcture and an island photodetector structure in which the islands are wire bonded together (e.g., using shorting links 150 such as those illustrated in Fig. 11) to form a parallel capacitive network in each of the radial wedge sections 120.

[0061] More specifically, the number and / or geometry of each of the radial wedge sections 120 can be reduced to reduce the detector area. Rather than twenty- four, discrete and independent radial wedge sections 120 each separated by a gap 122, there may be only twelve discrete and independent radial wedge sections 120 each separated by a larger gap 122. Rather than having a pie shape, each radial wedge section 120 may have a substantially rectangular shape separated from adjacent radial wedge sections 120 by gaps 122 that have both a relatively large area and a substantially rectangular shape themselves. Each radial wedge section 120 may have a diamond shape. Each radial wedge section 120 may be configured as a sparse or relatively thin line detector. Although the radial wedge sections 120 may have a pie shape, the sections may not extend from a narrower head proximate the center of the photodetector to a wider foot proximate the periphery of the photodetector, i.e.. the radial wedge sections 120 may extend instead from a narrower head somewhat removed from the center of the photodetector and a wider foot proximate the periphery of the photodetector. Similarly, other shapes (e.g., diamond and line) may not extend fully from the center to the periphery of the photodetector.

[0062] The result of wire bonding the design variations outlined above for reducing the detector area in each of the radial wedge sections 120 would be that the parallel capacitance in the outer quadrant sections 120 can be made greater than (e.g., pie-shaped detectors), less than (e.g., thin line detectors), or equal to (e.g., diamond-shaped detectors) the capacitance of the inner quadrant sections 110 depending on application requirements.

[0063] Fig. 12 illustrates yet another embodiment of the optical detector system 100 that includes two anode contacts per detector in the radial wedge section of the array of detectors. The embodiment illustrated in Fig. 12 has all of the components of the embodiment illustrated in Figs. 9 and 10. In addition to the anode 124 associated with each radial wedge section 120, however, each radial wedge section 120 of the optical detector system 100 illustrated in Fig. 12 has a second anode 154. The second anode 154 is an inner anode (closer to the center of the photodetector 102) labeled “Anode 1” in Fig. 12; the anode 124 is an outer anode (closer to the periphery of the photodetector 102) labeled “Anode 2” in Fig. 12. Thus, each radial wedge section 120 has two anode contacts.

[0064] The embodiment of the optical detector system 100 illustrated in Fig. 12 has one. single anode contact per detector for the inner quadrant sections 110 and two anode contacts per detector for the radial wedge sections 120. The center quadrant performs as a traditional segmented PSD, losing fine resolution if the spot 140 is fully within any single detector. Position sensing in the radial wedge sections 120 is provided by utilizing the known “lateral effect” to provide for ID position sensing along the radial length of each detector. Such functionality allows a small spot 140 to provide additional spatial data relative to a single-contact detector. Lateral effect photodiodes sense the position of the spot 140 by measuring the change of current between the opposite anodes 124, 154 and the common cathode. They either require a bias current or the current is photogenerated. In either case, their linearity is affected by the non-uniformity of the current distribution between the anodes 124, 154.

[0065] More generally, lateral effect sensors use a detector longitudinally to share charge in a ratio of geometric proportion consistent with the gradient of electrical -resistivity uniformity and / or geometric shape. A photon may fall between the two anodes, resulting in a shared charge. The sheet resistance between a spot at location “x” causes charge to flow to the contact of least resistance. With a flux ofphotons, a statistical probability based upon diffusion conditions causes the ratio of charge collected at one anode to be directly proportional to the distance between the two anodes. For sensors where the resistivity is non-uniform (gradient), or the geometry is not linear (as in a wedge or pie-shape), this must be taken into account, but can be measured by transmission line measurement test structures or modeled with accurate coefficients for material and electrical properties and geometric dimensions.

[0066] Like the embodiment of the optical detector system 100 illustrated in Figs. 9 and 10, the embodiment illustrated in Fig. 12 has a single shared and common cathode, requires flip chip for connectivity, and is preferably back-side illuminated. The embodiment of the optical detector system 100 illustrated in Fig. 12 offers excellent performance for relatively large and small spots 140 where position accuracy is required. High resolution is achieved, which means 1 part in 10,000 position accuracy or better. Each embodiment works well for both Gaussian and top- hat beams.

[0067] The photodetector 102 in each embodiment of the optical detector system 100 provides an output signal that is indicative of light incident upon its active area. For example, light incident on an active portion of a photodetector may produce an output current that is proportionate to the power of the incident light. As disclosed above, the individual inner quadrant sections 110 of the photodetector 102 are separated from one another by a gap 112 and the individual radial wedge sections 120 of the photodetector 102 are separated from one another by a gap 122. The gap 112, 122 may have a width of about 20 pm, about 30 pm, about 40 pm, about 50 pm, or in the range between 20 and 50 pm, between 20 and 40 pm, between 20 and 30 pm, between 30 and 50 pm, or between 40 and 50 pm. The output signals may be processed by a computer apparatus that includes a processor, database, and stored instructions to configure the processor to process data in accordance with the methods of the disclosure.

[0068] Fig. 13 illustrates an example computer system 200. In particular embodiments, one or more computer systems 200 engage with one or morecomponents, and perform one or more steps of one or more methods, described or illustrated in this document. In particular embodiments, one or more computer systems 200 provide functionality described or illustrated in this document. In particular embodiments, software running on one or more computer systems 200 performs one or more steps of one or more methods described or illustrated in this document or provides functionality described or illustrated in this document. Particular embodiments include one or more portions of one or more computer systems 200. In this document, reference to a computer system may encompass a computing device, and vice versa, where appropriate. Moreover, reference to a computer system may encompass one or more computer systems, where appropriate.

[0069] This disclosure contemplates any suitable number of computer systems 200. This disclosure contemplates the computer system 200 taking any suitable physical form. As example and not by way of limitation, the computer system 200 may be an embedded computer system, a system-on-chip (SOC), a single-board computer system (SBC) (such as, for example, a computer-on-module (COM) or system-on-module (SOM)), a desktop computer system, a laptop or notebook computer system, an interactive kiosk, a mainframe, a mesh of computer systems, a mobile telephone, a personal digital assistant (PDA), a server, a tablet computer system, or a combination of two or more of these devices. Where appropriate, the computer system 200 may include one or more computer systems 200; be unitary or distributed; span multiple locations; span multiple machines; span multiple data centers; or reside in a cloud, which may include one or more cloud components in one or more networks. Where appropriate, one or more computer systems 200 may perform without substantial spatial or temporal limitation one or more steps of one or more methods described or illustrated in this document. As an example and not by way of limitation, the one or more computer systems 200 may perform in real time or in batch mode one or more steps of one or more methods described or illustrated in this document. The one or more computer systems 200 may perform at different times or at different locations one or more steps of one or more methods described or illustrated in this document, where appropriate.

[0070] In particular embodiments, the computer system 200 includes a processor 202, memory 204, storage 206, an input / output (I / O) interface 208, a communication interface 210, and a bus 212. Although this disclosure describes and illustrates a particular computer system having a particular number of particular components in a particular arrangement, this disclosure contemplates any suitable computer system having any suitable number of any suitable components in any suitable arrangement.

[0071] In particular embodiments, the processor 202 includes hardware for executing instructions, such as those making up a computer program. As an example and not by way of limitation, to execute instructions, the processor 202 may retrieve (or fetch) the instructions from an internal register, an internal cache, the memory 204, or the storage 206; decode and execute them; and then write one or more results to an internal register, an internal cache, the memoiy 204, or the storage 206. In particular embodiments, the processor 202 may include one or more internal caches for data, instructions, or addresses. This disclosure contemplates the processor 202 including any suitable number of any suitable internal caches, where appropriate. As an example and not by way of limitation, the processor 202 may include one or more instruction caches, one or more data caches, and one or more translation lookaside buffers (TLBs). Instructions in the instruction caches may be copies of instructions in the memory 204 or the storage 206, and the instruction caches may speed up retrieval of those instructions by the processor 202. Data in the data caches may be copies of data in the memory 204 or the storage 206 for instructions executing at the processor 202 to operate on; the results of previous instructions executed at the processor 202 for access by subsequent instructions executing at the processor 202 or for writing to the memoiy 204 or the storage 206; or other suitable data. The data caches may speed up read or write operations by the processor 202. The TLBs may speed up virtual- address translation for the processor 202. In particular embodiments, the processor 202 may include one or more internal registers for data, instructions, or addresses. This disclosure contemplates the processor 202 including any suitable number of any suitable internal registers, where appropriate. Where appropriate, the processor 202 may include one or more arithmetic logic units (ALUs); be a multi-core processor; orinclude one or more processors 202. Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor.

[0072] In particular embodiments, the memory 204 includes main memory for storing instructions for the processor 202 to execute or data for the processor 202 to operate on. As an example and not by way of limitation, the computer system 200 may load instructions from the storage 206 or another source (such as, for example, another computer system 200) to the memory 204. The processor 202 may then load the instructions from the memory 204 to an internal register or internal cache. To execute the instructions, the processor 202 may retrieve the instructions from the internal register or internal cache and decode them. During or after execution of the instructions, the processor 202 may write one or more results (which may be intermediate or final results) to the internal register or internal cache. The processor 202 may then write one or more of those results to the memory 204. In particular embodiments, the processor 202 executes only instructions in one or more internal registers or internal caches or in the memory 204 (as opposed to the storage 206 or elsewhere) and operates only on data in one or more internal registers or internal caches or in the memory 204 (as opposed to the storage 206 or elsewhere). One or more memory' buses (which may each include an address bus and a data bus) may couple the processor 202 to the memory 204. The bus 212 may include one or more memory buses, as described below. In particular embodiments, one or more memory' management units (MMUs) reside between the processor 202 and the memory 204 and facilitate accesses to the memory' 204 requested by the processor 202. In particular embodiments, the memory 204 includes random access memory (RAM). This RAM may be volatile memory, where appropriate. Where appropnate, this RAM may be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where appropriate, this RAM may be single-ported or multi-ported RAM. This disclosure contemplates any suitable RAM. The memory' 204 may include one or more memories 204, where appropriate. Although this disclosure describes and illustrates particular memory, this disclosure contemplates any suitable memory.

[0073] In particular embodiments, the storage 206 includes mass storage for data or instructions. As an example and not by way of limitation, the storage 206 mayinclude a hard disk drive (HDD), a floppy disk drive, flash memory', an optical disc, a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB) drive or a combination of two or more of these. The storage 206 may include removable or nonremovable (or fixed) media, where appropriate. The storage 206 may be internal or external to the computer system 200, where appropriate. In particular embodiments, the storage 206 is non-volatile, solid-state memory. In particular embodiments, the storage 206 includes read-only memory (ROM). Where appropriate, this ROM may be mask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM), or flash memory or a combination of two or more of these. This disclosure contemplates the storage 206 taking any suitable physical form. The storage 206 may include one or more storage control units facilitating communication between the processor 202 and the storage 206, where appropriate. Where appropriate, the storage 206 may include one or more storages 206. Although this disclosure describes and illustrates particular storage, this disclosure contemplates any suitable storage.

[0074] In particular embodiments, the I / O interface 208 includes hardware, software, or both, providing one or more interfaces for communication between the computer system 200 and one or more I / O devices. The computer system 200 may include one or more of these I / O devices, where appropriate. One or more of these I / O devices may enable communication between a person and the computer system 200. As an example and not by way of limitation, an I / O device may include a keyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker, still camera, stylus, tablet, touch screen, trackball, video camera, another suitable I / O device or a combination of two or more of these. An I / O device may include one or more sensors. This disclosure contemplates any suitable I / O devices and any suitable I / O interfaces 208 for them. Where appropriate, the I / O interface 208 may include one or more device or software drivers enabling the processor 202 to drive one or more of these I / O devices. The I / O interface 208 may include one or more I / O interfaces 208, where appropriate. Although this disclosure describes and illustrates a particular I / O interface, this disclosure contemplates any suitable I / O interface.

[0075] In particular embodiments, the communication interface 210 includes hardware, software, or both providing one or more interfaces for communication (such as, for example, packet-based communication) between the computer system 200 and one or more other computer systems 200 or one or more networks. As an example and not by way of limitation, the communication interface 210 may include a network interface controller (NIC) or network adapter for communicating with an Ethernet or other wire-based network or a wireless NIC (WNIC) or wireless adapter for communicating with a wireless network, such as a WI-FI network. This disclosure contemplates any suitable network and any suitable communication interface 210 for it. As an example and not by way of limitation, the computer system 200 may communicate with an ad hoc network, a personal area network (PAN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), or one or more portions of the Internet or a combination of two or more of these. One or more portions of one or more of these networks may be w ired or wireless. As an example, the computer system 200 may communicate with a wireless PAN (WPAN) (such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WLMAX network, a cellular telephone network (such as, for example, a Global System for Mobile Communications (GSM) network), or other suitable wireless network or a combination of tw o or more of these. The computer system 200 may include any suitable communication interface 210 for any of these networks, where appropriate. The communication interface 210 may include one or more communication interfaces 210, where appropriate. Although this disclosure describes and illustrates a particular communication interface, this disclosure contemplates any suitable communication interface.

[0076] In particular embodiments, the bus 212 includes hardware, software, or both coupling components of the computer system 200 to each other. As an example and not by way of limitation, the bus 212 may include an Accelerated Graphics Port (AGP) or other graphics bus. an Enhanced Industry Standard Architecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a PeripheralComponent Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus. or another suitable bus or a combination of two or more of these. The bus 212 may include one or more buses 212, where appropriate. Although this disclosure describes and illustrates a particular bus, this disclosure contemplates any suitable bus or interconnect.

[0077] In this document, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (ICs) (such, as for example, field-programmable gate arrays (FPGAs) or applicationspecific ICs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or drives, any other suitable computer- readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate.

[0078] This disclosure contemplates one or more computer-readable storage media implementing any suitable storage. In particular embodiments, a computer- readable storage medium implements one or more portions of the processor 202 (such as, for example, one or more internal registers or caches), one or more portions of the memory 204. one or more portions of the storage 206. or a combination of these, where appropriate. In particular embodiments, a computer-readable storage medium implements RAM or ROM. In particular embodiments, a computer-readable storage medium implements volatile or persistent memory . In particular embodiments, one or more computer-readable storage media embody software. In this document, reference to software may encompass one or more applications, bytecode, one or more computer programs, one or more executables, one or more instructions, logic, machine code, one or more scripts, or source code, and vice versa, where appropriate . In particular embodiments, software includes one or more application programming interfaces (APIs). This disclosure contemplates any suitable software written orotherwise expressed in any suitable programming language or combination of programming languages. In particular embodiments, software is expressed as source code or object code. In particular embodiments, software is expressed in a higher- level programming language, such as, for example, C, Perl, or a suitable extension thereof. In particular embodiments, software is expressed in a lower-level programming language, such as assembly language (or machine code). In particular embodiments, software is expressed in C++. C#, Python, Java, JavaScript, Solidity, Vyper, Golang, Simplicity, or Rholang. In particular embodiments, software is expressed in Hyper Text Markup Language (HTML), Extensible Markup Language (XML). JavaScript Object Notation (JSON) or other suitable markup language.

[0079] Although illustrated and described above with reference to certain specific embodiments and examples, the present disclosure is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the disclosure.

Claims

What is Claimed:

1. A photodetector for receiving a beam spot, the photodetector having a center, a top, a bottom, and a perimeter and comprising: a plurality of independent inner quadrant sections each separated by a first gap. the inner quadrant sections located on the top and proximate the center of the photodetector; an individual first anode associated with each inner quadrant section; a separate first lead connecting the first anode of each of the inner quadrant sections to a corresponding first anode bond pad located on the top and proximate the perimeter of the photodetector; a plurality of independent radial wedge sections each separated by a second gap, the radial wedge sections located on the top with an opening separating the inner quadrant sections from the radial wedge sections; an individual second anode associated with each radial wedge section, the second anode located proximate the foot of the radial wedge section; a separate second lead connecting the second anode of each of the radial wedge sections to a corresponding second anode bond pad located on the top and at the perimeter of the photodetector; and a single shared and common cathode located on the bottom of the photodetector opposite the first and second anodes.

2. The photodetector according to claim 1 further comprising an individual third anode associated with each radial wedge section, the third anode located proximate the head of the radial wedge section.

3. The photodetector according to claim 1 wherein each of the plurality of independent radial wedge sections has a pie shape.

4. The photodetector according to claim 3 wherein each of the plurality of independent radial wedge sections has a narrower head proximate the center of the photodetector and a wider foot proximate the periphery of the photodetector.

5. The photodetector according to claim 4 wherein each of the plurality of independent radial wedge sections has an inner diameter of about 1.16 mm and an outer diameter of about 4.4 mm and extends at an angle of about 14 degrees.

6. The photodetector according to claim 1 wherein each of the plurality of independent radial wedge sections has a substantially rectangular shape or a diamond shape or is configured as a thin line.

7. The photodetector according to claim 1 wherein the single shared and common cathode located on the bottom of the photodetector extends entirely along the bottom.

8. The photodetector according to claim 1 further comprising controlled collapse chip connections between the inner quadrant sections and their corresponding first anode bond pads and between the radial wedge sections and their corresponding second anode bond pads.

9. The photodetector according to claim 1 further comprising one or more shorting links connecting the plurality of independent radial wedge sections.

10. The photodetector according to claim 1 wherein the photodetector achieves 1 part in 10,000 position accuracy or better.

11. The photodetector according to claim 1 wherein the first gap and the second gap each have a width in the range between 20 and 50 pm.

12. An optical detector system comprising: a photodetector according to claim 1 providing output signals; one or more optical elements, wherein the one or more optical elements receive incoming light and generate the beam spot on the photodetector; and a computer system configured to determine, based on the output signals provided by the photodetector, first data indicative of a direction of the beam spot relativeto a predetermined point on the photodetector and second data indicative of a distance between the beam spot and the predetermined point.

13. The optical detector system according to claim 12 wherein the beam spot generated by the optical elements has a diameter between about 50% and 75% of the diameter of the inner quadrant sections.

14. The optical detector system according to claim 12 further comprising backside illumination.

15. The optical detector system according to claim 12 wherein the photodetector further comprises an individual third anode associated with each radial wedge section, the third anode located proximate the head of the radial wedge section.

16. The optical detector system according to claim 12 wherein each of the plurality of independent radial wedge sections of the photodetector has a pie shape.

17. The optical detector system according to claim 16 wherein each of the plurality of independent radial wedge sections has a narrower head proximate the center of the photodetector and a wider foot proximate the periphery of the photodetector.

18. The optical detector system according to claim 12 wherein the single shared and common cathode located on the bottom of the photodetector extends entirely along the bottom.

19. The optical detector system according to claim 12 wherein the photodetector has controlled collapse chip connections between the inner quadrant sections and their corresponding first anode bond pads and between the radial wedge sections and their corresponding second anode bond pads.

20. The optical detector system according to claim 12 wherein the photodetector has one or more shorting links connecting the plurality of independent radial wedge sections.

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