Optical detector system having a ring photodetector and an annular beam lens design

Abstract

An optical detector system providing output signals. The system includes a ring-type photodetector, having an open center and multiple ring detector segments each separated by a gap, and an integral lens for receiving incident light and generating a beam spot on the photodetector. The lens includes an axicon and an asphere with a surface defined by both odd and even polynomial terms. The light does not fall outside or inside of the ring detector segments when the incident light is moved laterally off an optical center line but an intensity of the light is shifted around the ring detector segments. The detector system also may include a computer system configured to determine, based on the output signals, 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.

Description

OPTICAL DETECTOR SYSTEM HAVING A RING PHOTODETECTORAND AN ANNULAR BEAM LENS DESIGNRELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial Number 63 / 544,714, filed on October 18, 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 or another type of light source focused on the photodetector. Such photodetectors can be used to monitor beam position and, therefore, optical system alignment (laser spot trackers); and (within a feedback system) to stabilize the position of a laser beam (auto aligners). 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 ofsegmented photodetector, which can measure optical intensities for a few or even multiple photodiode configurations. 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 size 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 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 which 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 segmented diodes 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, for example, from GPD Optoelectronics Corp, of Salem, New Hampshire and 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 TO-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 inline 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 an optical detector system. The optical detector system transmits output signals and includes a ring-type photodetector having an open center and multiple ring detector segments each separated by a gap. The optical detector system also includes an integral lens for receiving incident light and generating a beam spot on the photodetector. The lens includes an axicon and an asphere with a surface defined by both odd and even polynomial terms. The light does not fall outside or inside of the ring detector segments when the incident light is moved laterally off an optical center line but an intensity of the light is shifted around the ring detector segments. The optical detector system also may include a computer system configured to determine, based on the output signals, 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.

[0017] Still further provided are a related system and at least one computer- readable non-transitory storage media embodying software. The one or morecomputer-readable non-transitory storage media embodying softw are is operable when executed, in one embodiment, to perform a series of steps using the optical detector system including the photodetector.

[0018] 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

[0019] 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:

[0020] Fig. 1 illustrates a conventional dual-segment photodiode with a light spot of a beam impinging on the photodiode;

[0021] 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;

[0022] Fig. 3 illustrates a conventional quadrant photodiode with a light spot impinging on the quadrant photodiode;

[0023] Fig. 4 provides an outline of a PIN diode;

[0024] Fig. 5 illustrates the structure of a PIN diode;

[0025] Fig. 6 illustrates a known InGaAs PIN quadrant photodetector having eight independent active-area sections, segments, or detectors;

[0026] Fig. 7 illustrates an equivalent circuit for a single-element photodiode;

[0027] Fig. 8 illustrates an equivalent circuit for a one-dimensional position sensing device;

[0028] 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;

[0029] Fig. 10 depicts the optical detector system illustrated in Fig. 9 with a light beam impinging on the photodetector;

[0030] Fig. 11 illustrates another embodiment of the optical detector system according to the present disclosure including wire bond links which combine radial detectors;

[0031] 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;

[0032] Fig. 13 is a top view of a ring-type photodetector;

[0033] Fig. 14 is a top view of a multi-segment ring-tj pe photodetector;

[0034] Fig. 15 is a top view of the multi-segment ring-type photodetector shown in Fig. 14 with connections to conventional electronics;

[0035] Fig. 16 illustrates yet another embodiment of the optical detector system according to the present disclosure including a multi-segment ring-type photodetector having a radial w edge section of detectors;

[0036] Fig. 17 illustrates an aspheric axicon lens;

[0037] Fig. 18 illustrates a configuration used for analysis and optimization of the lens design included in the optical detector system according to the present disclosure;

[0038] Fig. 19 provides the data for the design of the lens that optical analysis showed achieved the best performance for a Gaussian incident light beam in the configuration shown in Fig. 18;

[0039] Fig. 20 is a curve of beam shift versus signal for the lens defined in Fig. 19; and

[0040] Fig. 21 illustrates an example computer system for use in connection with the optical detector system according to the present disclosure.DETAILED DESCRIPTION OF THE DISCLOSURE

[0041] 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 descriptive term 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.

[0042] 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.

[0043] 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, orabout 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.

[0044] 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.

[0045] 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.

[0046] 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 transmitted signal must be received.

[0047] 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 ispositioned 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.

[0048] 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. These motions 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.

[0049] 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.

[0050] 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 informationdescribes how amplitude of an output signal from the photodetectors in the array changes as the spot moves across the detector array.

[0051] 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.

[0052] 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.

[0053] 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 which 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.

[0054] Fig. 8 illustrates an equivalent circuit for a one-dimensional position sensing device (ID PSD). The ID 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 IDPSD. 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 : T2, where Ti is the current in Anode 1 and I2 is the current in Anode 2. More specifically, if L is the distance between the two anodes, the applicable formula is: (I2 - Ii) / (h + Ii) = 2X / L.

[0055] 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 radial wedges (a ID PSD) that extend outward from the center quadrant to the periphery of the photodetector 102 . Several embodiments of the optical detector system 100 are disclosed.

[0056] 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 1 12. Each quadrant section 110 has an individual anode 114 associated with it. A separate lead 116 connects the anode 114 of each of the four quadrant sections 110 to a corresponding anode bond pad 118 located at the perimeter of the photodetector 102.

[0057] As also illustrated in Fig. 9, the radial w edges 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. In another example, each radial wedge section 120 has an inner diameter of about 0.5 mm and an outer diameter of about 5 mm, and extends at an angle of about 14 degrees. Although twenty-fourradial wedge sections 120 are illustrated in the embodiment shown in Fig. 9, the number of radial wedge sections 120 may be increased (to, for example, twenty-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.

[0058] 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 electrically configured to provide 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 1 10 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.

[0059] 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 w ord ’‘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).

[0060] 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 two radial wedge sections 120. By “predetermined" is meant determined beforehand, so that the predetermined characteristic must be determined, i.e., chosen or at least known, before construction of the optical detector system 100.

[0061] 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 1 10 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.

[0062] 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 w afer during the final wafer processing step. In order to mount the chip to external circuitry (e.g., a circuit board or another chip or wafer), it is flipped over sothat 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'.

[0063] 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. This traditional 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.

[0064] 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.

[0065] 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, assuch 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 profde 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.

[0066] Fig. 11 illustrates another embodiment of the optical detector system 100 that includes one or more wire bond links 150 which combine radial detectors. Each radial wedge section 120 can be individually addressed or permanently configured (during manufacture of the optical detector system 100) with one or more links 150. The 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 radial wedge sections 120 is that the number of outputs, which need to be processed, is also reduced.

[0067] 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 wedge sections 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 structure and an island photodetector structure in which the islands are wire bonded together (e.g., using links 150 such as those illustrated in Fig. 1 1) to form a parallel capacitive network in each of the radial wedge sections 120.

[0068] 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 pieshape, 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.

[0069] 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., diamondshaped detectors) the capacitance of the inner quadrant sections 110 depending on application requirements.

[0070] 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.

[0071] 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.

[0072] 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 of photons, a statistical probability (reality is always in most cases) 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.

[0073] 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 at least 1 part in 100 position accuracy. Both embodiments work well for both Gaussian and top-hat beams.

[0074] 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 areseparated 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 1 pm, about 10 pm, about 20 pm. about 30 pm. about 40 pm, about 50 pm, about 100 pm, about 1,000 pm (1 mm), or in the range between 1 and 1,000 pm, between 10 and 100 pm, 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 system that includes a processor, database, and stored instructions to configure the processor to process data in accordance with the methods of the disclosure. An example computer system 200 is discussed below.

[0075] Fig. 13 illustrates a ring-type photodetector 102 that can be used in yet another embodiment of the optical detector system 100. As illustrated, the photodetector 102 includes an intrinsic photodetector ring 170, a common cathode 172 for the photodiode or detector that forms the intrinsic photodetector ring 170, and a common anode 174 for that detector. Unfortunately, the ring-type photodetector 102 illustrated in Fig. 13 is not helpful in locating a beam or light spot 18 on the photodetector 102. It would be advantageous to sense where the beam hits the photodetector 102 so that adjustments can be made to center the beam on the photodetector 102.

[0076] This advantage is achieved by segmenting the ring-type photodetector 102 as shown in Fig. 14. The number of segments in the multi-segment ring-type photodetector 102 can be predetermined depending on the application; any suitable number of segments is possible. There are sixteen segments in the multi-segment ring-type photodetector 102 shown in the example illustrated in Fig. 14. Thus, there are sixteen arc-shaped photodiodes that form the intrinsic photodetector ring 170 with sixteen individual arc-shaped cathode segments forming the cathode 172 and sixteen individual arc-shaped anode segments forming the anode 174. The gaps 16 separate each of the sixteen photodiodes and their corresponding cathode and anode segments. The multi-segment ring-type photodetector 102 provides the ability to locate where the beam hits the photodetector 102 and. therefore, to make adjustments so that thebeam illuminates all sixteen of the segments of the photodetector 102 (i.e., the beam is centered on the photodetector 102).

[0077] Fig. 15 is a top view of the multi-segment ring-type photodetector 102 shown in Fig. 14 with connections (albeit the connections are not fully illustrated) to the conventional electronics used to obtain signals from the photodetector 102 and make the adjustments necessary to steer and center the beam. For the example shown, each of the sixteen segments of the anode 174 are connected to an 8 to 12 channel HXR6112 transimpedance limiting amplifier array 176, which is commercially available from Integrated Device Technology, Inc. (IDT) of San Jose, California. Together with the photodetector 102, the HXR6112 transimpedance limiting amplifier array 176 allows high-capacity, high-availability links for datacom applications. The HXR6112 transimpedance limiting amplifier array 176 is a 3.3 V, SiGe device that integrates a transimpedance pre-amplifier, a limiting post-amplifier, and a versatile current mode logic (CML) output stage for 8 to 12 optical channels.

[0078] Signals from the HXR6112 transimpedance limiting amplifier array 176 are transmitted through 8x-12x low pass filter channels 178. A low' pass filter is a circuit that passes low-frequency signals but blocks high-frequency signals. The low pass filter allows signals below a cutoff frequency (known as the passband) and attenuates signals above the cutoff frequency (known as the stopband).

[0079] The signals that leave the low' pass filter channels 178 are transmitted to a 16+ channels analog-to-digital converter (ADC) 180 for the position sensing device (PSD). In electronics, an ADC is a system that converts an analog signal, such as light illuminating a photodetector, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or cunent. Typically the digital output is a two’s complement binary number that is proportional to the input, but there are other possibilities.

[0080] Signals are transmitted from the transimpedance limiting amplifier array 176 to a 16 channel RF (radio frequency) power combiner 182. An RF powercombiner is a passive device that combines or sums a number of RF input signals to a common output, while maintaining the characteristic impedance of the inputs. The output of the RF power combiner is transmitted to a data channel 184, which is a computer path used to transfer data from one device to another.

[0081] Fig. 15 illustrates just one example of the electrical configurations that combine with the multi-segment ring-type photodetector 102 to form an embodiment of the optical detector system 100. The electrical configurations may include both two-terminal and three-terminal configurations. Electrical interconnections can be made to these terminals via either wire bonds to packaging interconnects or by flip chip bumps to packaging interconnects when the photodetector 102 is a back illuminated configuration.

[0082] Fig. 16 illustrates yet another embodiment of the optical detector system 100 according to the present disclosure including a multi-segment ring-type photodetector 102 having radial wedge sections 120. In the example illustrated, the optical detector system 100 has a chip or die substrate 8 that is about 5. 1 mm square (although other sizes and shapes for the substrate 8 are possible depending on the application). As illustrated in Fig. 16, the open center 6 of the photodetector 102 has four, discrete and independent ring-type inner quadrant sections 110 each separated by the gap 112. In the example illustrated, each ring-type inner quadrant section 110 has an inner diameter of about 0.88 mm and an outer diameter of about 1.2 mm so that each ring-ty pe inner quadrant section 110 has a width of about 0.32 mm or 320 pm. The gaps 112 are about 20 pm and are located at the top (0°), right (90°), bottom (180°), and left (270°) positions of the open circle 6 formed by the ring-ty pe inner quadrant sections 110. Each of the ring-type inner quadrant sections 110 has two anodes 114 associated with it. A separate lead 116 connects each anode 114 to a corresponding anode bond pad 118 located at the perimeter of the photodetector 102. Thus, the four, ring-type inner quadrant sections 1 10 provide signals to eight anode bond pads 118.

[0083] As also illustrated in Fig. 16, the photodetector 102 also includes twenty -four, discrete and independent radial wedge sections 120 each separated by thegap 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. Thus, the twenty -four radial wedge sections 120 provide signals to twenty-four anode bond pads 128 and the photodetector 102 shown in Fig. 16 has thirty -two anode elements (24 plus 8).

[0084] 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 E16 mm and an outer diameter of about 4.4 mm, and extends at an angle of about 14 degrees. Although twenty-four radial w edge sections 120 are illustrated in the embodiment shown in Fig. 16, the number of radial w edge 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. The circular opening 130 separates the ring-type inner quadrant sections 1 10 from the radial wedge sections 120.

[0085] As illustrated in Figs. 13-16 and described above, the optical detector system 100 may include a photodetector 102 fabricated in the shape of a ring and / or a segmented ring with terminals on the inner diameter and outer diameter of the ring detectors or on ends of each segment for each individual detector (segment) on the ring. Light is directed to the ring-type photodetector 102 through a lens configuration so that light does not fall outside or inside of the ring-type photodetector 102 when the incident beam is moved laterally off the optical center line, but does shift the intensity of the light around the ring. Specific lenses are required to manipulate an incoming light beam 4 into a ring optical output so that the light spot 18 falls on the specially optimized ring-type photodetector 102. Attention is now directed to the design of the lens of the optical detector system 100 that is used to create the annular light spot 18 incident on the ring-type photodetector 102.

[0086] The glass elements which make up a traditional or ordinary lens can be thought of as cross-sections of a large sphere in which the curvature of each surface is even. The problem with spherical lens designs is that light passing through the outer edges of curved lenses focuses at different points from light passing through the center — creating a blur. This causes focus errors, or spherical aberration, and other forms of optical problems. Spherical lenses work fine if the recording surface is also spherical (e.g., the human eyeball), but in the case of photodetectors the surface is not spherical. Instead, the photodetector surface or chip surface is always substantially flat.

[0087] One way to fix the problem is to add additional lens elements to correct for the aberration. A generally more efficient way to address aberration is to make a lens element which is not a sphere in cross section. In other words the curvature of the lens varies from the middle to the edges. Such an aspherical lens can help simplify lens design by minimizing the number of elements required and can result in a sharper image. Aspherical elements are particularly useful for correcting distortion in wide-angle lenses.

[0088] An asphere (also called an aspheric lens) is a lens whose surface profiles are not portions of a sphere or cylinder. An aspheric lens can be designed to minimize aberration by adjusting the conic constant and aspheric coefficients of the curved surface of the lens. Fig. 17 illustrates an aspheric axicon lens. As illustrated, the optic axis lies in the z direction, and z(r) is the sag or the z-component of the displacement of the surface from the vertex at a distance r from the axis. R is the radius of curvature. The relatively complex surface profile of an asphere can reduce or eliminate spherical aberration, and can also reduce other optical aberrations, compared to an ordinary lens. The most unique geometric feature of aspheric lenses is that the radius of curvature changes with distance from the optical axis, unlike a sphere which has a constant radius. This distinctive shape allows aspheric lenses to deliver improved optical performance compared to standard spherical surfaces.

[0089] Aspheric lenses have been traditionally defined with the surface profile (sag) given by Z(s) = (Cs2 / (1 + (1 - ( l+k)C2s2)1 2) + A2S2+ A4S4+ Aes6+ . . .(Equation 1). In this Equation, Z is the sag of the surface parallel to the optical axis; s is the radial distance from the optical axis; C is the curvature, inverse of radius; k is the conic constant; and A2. A4. Ae. etc. are the second, fourth, sixth, etc. order aspheric coefficients. When the aspheric coefficients are odd, the lens is called an odd asphere; when the aspheric coefficients are even, the lens is called an even asphere. The preferred aspheric lens identified in the present disclosure has both even and odd polynomial terms. When the aspheric coefficients are equal to zero, the resulting aspheric surface is considered to be a conic with the actual conic surface generated depending on the magnitude and sign of the conic constant, k: the conic surface is a sphere if k is 0; the conic surface is an ellipse if k is greater than negative 1; the conic surface is a parabola if k is equal to negative 1; and the conic surface is a hyberbola if k is less than negative 1.

[0090] There are several ways to manufacture an aspheric lens. The cheapest way is to cement a plastic resin aspheric surface to the top of a glass spherical element. Such lenses are known as replicated aspherical elements. Other alternatives include precision glass molding, precision polishing, and diamond turning.

[0091] Precision glass molding is a manufacturing technique in which optical glass cores are heated to high temperatures until the surface becomes malleable enough to be pressed into an aspheric mold. After the cores cool down to room temperature, the resulting lenses maintain the shape of the mold. Creating the mold has high initial startup costs because the mold must be precisely made from very durable material that can maintain a smooth surface, while the mold geometry needs to take into account any shrinkage of the glass in order to yield the desired aspheric shape. Once the mold is finished, how ever, the incremental cost for each lens is lower than that of standard manufacturing techniques for aspheres, making this technique a good option for high volume production.

[0092] For decades, machined aspheric lenses have been ground and polished to the right shape one lens at a time. This technique is quite difficult given the extreme precision required to achieve the complex geometry. Although this process of individually producing machined aspheres has not changed dramatically and is themost expensive way to manufacture an aspheric lens, significant fabrication technology advancements in precision polishing have elevated the achievable level of accuracy possible from this production technique. In precision polishing, small contact areas on the order of square millimeters are used to grind and polish aspheric shapes. These small contact areas are adjusted in space to form the aspheric profile during computer-controlled precision polishing. If even higher quality polishing is required, magneto-rheological finishing (MRF) is used to perfect the surface using a similar small area tool that can rapidly adjust the removal rates to correct errors in the profile. MRF technology provides high-performance finishing in less time than standard polishing techniques because of its precise control of the removal location and high removal rate. Although other manufacturing techniques generally require a special mold unique to each lens, precision polishing uses standard tooling, making it the best option for prototyping and low-to-medium volume production.

[0093] A third way to manufacture an aspheric lens is to use single-point diamond turning (SPDT). Similar to grinding and polishing, SPDT can be used to manufacture single lenses one at a time. The tool size used in SPDT is significantly smaller than in precision polishing, however, producing surfaces with improved finishes and form accuracies. Material options are also much more limited with SPDT than with other techniques because glass cannot be shaped through diamond turning, whereas plastics, metal, and crystals can. SPDT can also be used in making metal molds utilized in glass and polymer molding.

[0094] In a preferred embodiment, the aspheric lens is made using SPDT. The advantages of using SPDT include easy programming; quick setup changes for short runs of optics; a high degree of precision in mechanics; accommodation of variations in surface shape and in aspheric, toroidal, and diffractive optics; cost effectiveness; and speed (the surface can be directly turned to its finished tolerances). Specifically, a single-crystal diamond cutting tool is used to accurately turn the surfaces to finished tolerances. The tool includes a vacuum chuck, a spindle with an air bearing, and a computer-controlled cutting tool that is monitored by an interferometer. The linear axes position feedback resolution is about 8.6 nm and the rotary axis encoder angular resolution is about 0.25 arc sec. The tool achieves a lens having a minimal grooveheight of about 10 nm and a surface roughness of about 20 A rms; grooves and surface roughness are undesirable because they scatter and diffract light.

[0095] Like an aspheric lens, an axicon (also called an axicon lens) is another specialized ty pe of optical lens. Whereas an ordinary7lens has a curved surface, an axicon has a conical surface. Generally, one side is conical, with the tip looking outwards, and the other surface is flat (forming a plano-convex axicon). In most cases, the transverse cross-section is a circle, as for an ordinary lens. The inclination angle of the surface (called the axicon angle) does not change with increasing distance from the optical axis, while it continuously changes for an ordinary lens. Refraction thus leads to a constant ray deflection angle within a range of input ray positions. An axicon transforms a laser beam into a ring shaped distribution. Axicons can be made of any optical material, such as glass or silicon. The combination with other axicons or lenses allows a wide variety' of beam patterns to be generated.

[0096] In the present application, an integral lens 190 combining an asphere 190a (with a surface defined by Equation 1 having both even and odd polynomial terms) with an axicon 190b has proven through design and analysis to be preferred. Fig. 18 illustrates the configuration that was used for analysis and optimization of the lens design. Analysis and optimization of the lens design was completed using the OpticStudio* (formerly Zemax*) optical design software available from Zemax LLC, an Ansys, Inc. company, of Canonsburg, Pennsylvania. See www.Ansys.com.

[0097] Fig. 18 shows that the incident light beam 4 initially contacts the asphere 190a portion of the lens 190. The asphere 190a may have a maximum height, for example, of about 0.38 mm. The light travels through the asphere 190a into the axicon 190b portion of the lens 190. The axicon 190b may have a base diameter, for example, of about 2 mm and a conic shape defined by an angle of about 5 degrees. The light leaves the axicon 190b and forms the light spot 18 on the photodetector 102. In the example shown, the photodetector 102 includes a chip or die substrate that is about 3 mm square. The air space or gap between the top of the asphere 190a and the photodetector 102 is between about 0.9 and 1.1 mm (analyses showed almost no change in performance of the photodetector 102 even for a defocus or change in thegap of about ± 0.1 mm). Analyses were run by moving the incident light beam 4 laterally away from the conic center by incremental distances and analyzing the results. Some of the more relevant analytical results are summarized below.

[0098] The critical angle (0c) for silicon is about 16.7°. Therefore, an axicon angle of about 17° for an axicon made of silicon will result in a totally internally reflected (TIR) beam. The critical angle is unaffected by providing an antireflective coating (ARC) on the axicon. The reason is as follows. An ARC is designed to reduce the reflection of light at the surface to which it is applied, by interfering with the light waves that are reflected. On the other hand, the critical angle is the angle at which light is TIR at the boundary between two media, when the angle of incidence exceeds a certain value. The reason why an ARC does not affect the critical angle is that the critical angle is determined by the refractive index of the two media and the angle of incidence of the light, and is not affected by the amount of reflection at the surface. The ARC may reduce the amount of reflection, but it does not change the refractive index of the media, which is the main factor that determines the critical angle. Therefore, although an ARC may improve the efficiency of light transmission through a surface, it does not have any direct impact on the critical angle - and the axicon 190b may be provided with an ARC. The transmittance of the axicon 190b with an ARC was determined to be about 83%.

[0099] The angle of incidence (AOI) is the angle that a line (such as a ray of light) falling on a surface or interface makes with the normal drawn at the point of incidence. The angle of incidence tolerances for the incident light beam 4 were determined to be about ± 2 or 3°. Analyses showed almost no change in performance of the photodetector 102 regardless of the wavelength in the range of about 1.2 pm to 1.6 pm for the incident light beam 4.

[0100] The photodetector 102 may be made of InGaAs. The reflectance of an InGaAs photodiode can be affected by several factors, including the angle of incidence, the surface finish of the photodiode, and the polarization and w avelength of the incident light. To minimize reflectance and improve the sensitivity of an InGaAs photodiode, the surface of the photodiode can be coated w ith an ARC. Thereflectance of an InGaAs photodiode can also be affected by its material properties, such as the thickness of the InGaAs layer and the doping concentration of the material. These factors can affect the refractive index of the material and alter the reflection properties of the photodetector. Analyses show that the spectral reflection of InGaAs is about 10% for an angle of incidence of about 38° to 60°.

[0101] Fig. 19 provides the data for the design of the lens 190 that analysis showed achieved the best performance for a Gaussian incident light beam 4 in the configuration shown in Fig. 18. The lens 190 includes the asphere 190a defined by the parameters highlighted by the boxes in the top of Fig. 19 and the axicon 190b having an angle of 13°. The center of Fig. 19 shows that the incident light beam 4 was shifted during analyses from 0.0 mm to 1.0 mm in increments of 0. 1 mm. The bottom of Fig. 19 shows the spot diagrams that resulted after each beam shift. The left-most beam spot shows that, when the beam is centered, the energy is distributed around the photodetector 102. The right-most beam spot shows that, when the beam is shifted the maximum of 1 .0 mm off center, all of the energy falls into a small segment of the photodetector 102.

[0102] Understanding and calculating the performance of a lens such as the lens 190 can be a difficult task. There are many variables that will affect the performance of a lens, including the laws of physics, design criteria and philosophy, and manufacturing tolerances and errors. In order to obtain optimal system performance, both optical designers and the end users have access to several metrics that can be used to measure the performance of a lens. One of these metrics is a curve of beam shift versus signal, as shown in Fig. 20 for the lens 190 defined in Fig. 19. Such curves can be provided to help optimize the lens design. As shown in Fig. 20, the curve has an “S” shape. It is desirable for a lens design to achieve an S-curve having a large maximum slope and a large peak value (PV, defined between the top and bottom of the curve) which reflects more signal. The design of the lens 190 defined in Fig. 19 showed the best S-curve of all designs analyzed with the largest maximum slope (4.2384) and the largest PV (1.9102) due to the narrowest beam width.

[0103] In this last embodiment, the optical detector system 100 includes the ring-type photodetector 102 in combination with the lens 190. The width and diameter of the projected ring light can be optimized to be a finite thickness and radius, respectively, via the lens design so the photoelectric lateral displacement gain, photoelectric sensitivity7, and photoelectric bandwidth of the ring detector can be maximized making this embodiment a large improvement over existing quad and octo cell position sensing detectors or tetralateral position sensing detectors. In this embodiment an asphere / axicon lens 190 was used, but other optical lens designs could make a projected light ring such as variants of axicons and diffractive vortex lenses.

[0104] Fig. 21 illustrates an example computer system 200 which can be included in, or at least operate in connection with, the optical detector system 100. In particular embodiments, one or more computer systems 200 engage with one or more components, 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.

[0105] 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, thecomputer 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.

[0106] 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.

[0107] 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 memory 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 retrievalof 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 memory 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; or include one or more processors 202. Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor.

[0108] 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 w ay 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 memorymanagement 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 appropriate, 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.

[0109] 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 may include 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.

[0110] 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 theseI / 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.

[0111] 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 netw ork (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 netw orks may be wired 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 WI-MAX 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 two or more of these. The computer system 200 may include any suitable communication interface 210 for any of these networks, whereappropriate. 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.

[0112] 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 Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology7attachment (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.

[0113] 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-transitory7storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate.

[0114] 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 or otherwise 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.

[0115] 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 w ithin the scope and range of equivalents of the claims and without departing from the spirit of the disclosure.

Claims

What is Claimed:

1. An optical detector system comprising: a ring-type photodetector having an open center and multiple ring detector segments each separated by a gap, the photodetector providing output signals; an integral lens for receiving incident light and generating a beam spot on the photodetector, the lens including an axicon portion and an asphere portion with a surface defined by both odd and even polynomial terms, wherein the light does not fall outside or inside of the ring detector segments when the incident light is moved laterally off an optical center line but an intensity of the light is shifted around the ring detector segments; 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 relative to a predetermined point on the photodetector and second data indicative of a distance between the beam spot and the predetermined point.

2. The optical detector system according to claim 1 wherein the ring detector segments are arc-shaped.

3. The optical detector system according to claim 2 wherein the photodetector includes a common arc-shaped cathode and a common arc-shaped anode.

4. The optical detector system according to claim 3 wherein the photodetector includes sixteen arc-shaped ring detector segments, sixteen arc-shaped common cathode segments, and sixteen arc-shaped common anode segments, and gaps separate each of the sixteen ring detector segments and their corresponding cathode and anode segments.

5. The optical detector system according to claim 3 further comprising a transimpedance limiting amplifier array being connected to the anode,transmitting signals through a low pass filter channel to an analog-to-digital converter, and transmitting signals through a radio frequency power combiner to a data channel.

6. The optical detector system according to claim 1 wherein the asphere portion of the integral lens is manufactured using single-point diamond turning.

7. The optical detector system according to claim 1 wherein the incident light initially contacts the asphere portion of the integral lens and travels through the asphere portion into the axicon portion of the integral lens.

8. The optical detector system according to claim 7 wherein the asphere portion of the integral lens has a maximum height of about 0.38 mm.

9. The optical detector system according to claim 7 wherein the axicon portion of the integral lens has a base diameter of about 2 mm and a conic shape defined by an angle of about 5 degrees.

10. The optical detector system according to claim 1 further comprising an antireflective coating on the axicon portion of the integral lens.

11. The optical detector system according to claim 1 further comprising an antireflective coating on the ring-type photodetector.

12. The optical detector system according to claim 1 wherein the ring detector segments are arc-shaped and the incident light initially contacts the asphere portion of the integral lens and travels through the asphere portion into the axicon portion of the integral lens.

13. The optical detector system according to claim 12 wherein the photodetector includes a common arc-shaped cathode and a common arc-shaped anode.

14. The optical detector system according to claim 12 further comprising an antireflective coating on the axicon portion of the integral lens.

15. The optical detector system according to claim 12 further comprising an antireflective coating on the ring-type photodetector.

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