Method for manufacturing a device and a structure

Abstract

Laser radar includes a two-part objective lens used to image the target and direct a probe beam at the target. Portions of the tracer beam that would degrade the target image are attenuated by a dichroic filter that blocks the central portion of the tracer beam. A local oscillator beam is generated using a blending lens that directs the probe beam at a waveplate or through a polarizing beam splitter to focus it on a waveplate, so that its reflection becomes the local oscillator beam. An imaging system that is confocal with the probe beam is coupled to provide target measurements or establish the focus of the probe beam.

Description

Technical Field

[0001] The present disclosure relates to lidar and laser tracking systems, optical systems and components for such systems, and associated measurement methods and apparatuses.

Background Art

[0002] Lidar systems generally generate an estimated value of an object distance based on detection of a part of a return beam. High-sensitivity detection is provided using a heterodyne method in which the return beam is mixed with a local oscillator signal and the distance is estimated based on measuring the frequency difference between the return beam and the local oscillator. By transmitting the beam with an appropriate chirp, these measurements can be made even when there is movement of an object that can cause a Doppler shift.

[0003] In an actual embodiment, the camera images a target surface that receives both a probe (measurement) beam and a pointing (or tracer) beam used for visual alignment. The camera includes a lens adjusted to generate a target image, and the probe beam and the tracer beam are imaged onto the target using separate adjustable lenses. Using different lenses for visual / visible images and a beam focusing lens for the IR probe beam enables a simple lens design. Unfortunately, using two movable lenses requires a movement or other stage for each, and it is difficult to maintain alignment between the camera axis and the probe beam axis, and the alignment deviation makes it difficult to use the camera image more than a rough visual alignment.

[0004] Another difficulty in heterodyne laser radar is based on the variation in the path length between the signal path associated with the object to be measured and the local oscillator (LO) path. LO path variations not only cause ranging errors, but also signal variations due to changes in the relative state of polarization between the returned probe beam portion and the LO beam. For example, reflections by optical components such as metal or dielectric mirrors or beam splitters can introduce a phase shift between different polarization states. Such variations can reduce the distance sensitivity or lead to dropout, i.e., complete signal loss.

[0005] The actual use of lidar typically requires alignment to the part being measured, and one or more sets of tooling balls must be placed around the part. Such setups can be slow and limit the rate at which parts can be measured. Therefore, improvement is needed. Summary of the Invention Means for Solving the Problems

[0006] The apparatus comprises a dichroic beam splitter and an optical fiber arranged to direct a probe beam along the axis towards the dichroic beam splitter. The objective lens is arranged on the axis and comprises a fixed lens and a movable lens arranged to receive the probe beam from the dichroic beam splitter. The image sensor is optically coupled to the dichroic beam splitter and is arranged on the axis to receive an imaging beam from the target via the dichroic beam splitter, and the movable lens is movable to form a target image on the image sensor and to focus the probe beam on the target. In some examples, the dichroic beam splitter is arranged such that the probe beam is transmitted through the dichroic beam splitter to the movable lens and the imaging beam is reflected by the dichroic beam splitter to the image sensor. In other examples, the objective lens is arranged to receive a tracer beam from the dichroic beam splitter and to direct the probe beam and the tracer beam towards the target, the probe beam having a wavelength in the range of 1200 nm to 1800 nm and the tracer beam having a wavelength in the range of 400 nm to 700 nm. In some alternative forms, the dichroic beam splitter is arranged such that the probe beam is reflected by the dichroic beam splitter to the movable lens and the imaging beam is sent by the dichroic beam splitter to the image sensor. In a typical embodiment, the dichroic beam splitter is a cube dichroic beam splitter, a plate dichroic beam splitter, or a double reflection dichroic beam splitter.

[0007] In a further embodiment, the dichroic beam splitter is a dual-reflection dichroic beam splitter that includes a first surface facing the movable lens and a dichroic reflective surface arranged to direct the imaging beam towards the image sensor and a portion of the probe beam returned from the target towards the optical fiber. In other embodiments, the dichroic beam splitter is a dual-reflection dichroic beam splitter that includes a first surface facing the movable lens and a dichroic reflective surface arranged to direct the imaging beam towards the first surface such that the imaging beam is reflected by the first surface towards the image sensor and a portion of the probe beam returned from the target to the optical fiber is sent to the optical fiber by the reflective surface. In a further additional example, the dichroic beam splitter is a dual-reflection dichroic beam splitter that includes a first surface facing the movable lens and a dichroic reflective surface arranged to direct a portion of the probe beam returned from the target towards the first surface, and the imaging beam is sent to the image sensor by the dichroic reflective surface. In another representative example, the first surface is arranged at an angle greater than the critical angle with respect to the imaging beam received from the dichroic reflective surface, and the dual-reflection dichroic beam splitter includes an output surface arranged such that a portion of the probe beam returned from the target and reflected by the dichroic reflective surface towards the first surface is reflected and incident perpendicularly on the output surface. In some embodiments, the dual-reflection dichroic beam splitter includes a first prism having an apex angle β between the first surface and the dichroic reflective surface, and β is greater than sin -1 (1 / n), where n is the refractive index of the prism. According to some examples, the dichroic reflective surface of the dual-reflection dichroic beam splitter is defined on the surface of the first prism or the second prism. In some cases, the dual-reflection prism includes a first prism and a second prism fixed to each other at their respective mating surfaces, and the dichroic reflective surface is arranged on the mating surface. In some specific examples, the dichroic reflective surface is defined on at least one of the mating surfaces.

[0008] In other alternative forms, the dichroic beam splitter includes a dichroic plate and a planar reflector, and the dichroic plate is arranged to direct a part of the probe beam returned from the target towards the planar reflector and send the imaging beam to the image sensor. In still other examples, the dichroic beam splitter includes a dichroic plate and a planar reflector, and the dichroic plate is arranged to reflect the imaging beam to the planar reflector and send a part of the probe beam returned from the target.

[0009] In some representative examples, the optical fiber is a polarization retaining single mode (PRSM) optical fiber and further includes a polarizing beam splitter (PBS). The PBS is arranged such that the probe beam from the PRSM optical fiber is received in a polarization state (typically a linearly polarized state) substantially sent to the dichroic beam splitter by the PBS. The apparatus may include a waveplate arranged between the PBS and the dichroic beam splitter to generate a circular polarization state in the probe beam and reflect a part of the probe beam towards the optical fiber to generate a local oscillator beam. In a further example, the waveplate has an input surface arranged to receive the probe beam from the PBS and an output surface arranged to receive the probe beam from the input surface of the waveplate. One of the input surface or the output surface is anti-reflection coated, and the other of the input surface and the output surface reflects a part of the probe beam as a local oscillator beam.

[0010] Typically, a mixing lens is arranged to receive the measurement beam from an optical fiber, and a dichroic filter is arranged along the axis of the axial portion of the mixing lens. The dichroic filter transmits the measurement beam and is substantially non-transmissive to the tracer beam. In other examples, the dichroic filter is a dichroic reflector that transmits the measurement beam and reflects the tracer beam. In some examples, the dichroic filter is a wavelength-dependent polarizer that is substantially non-transmissive to the tracer beam. According to a representative embodiment, the dichroic reflector is arranged along the axis of the axial portion of the mixing lens. The dichroic reflector transmits the measurement beam and reflects the tracer beam, and the dimensions of the dichroic reflector are based on the corresponding dimensions of the image sensor. In some embodiments, the mixing lens is arranged to receive the measurement beam and focus the measurement beam within the beam angular diameter α. The dichroic reflector is arranged along the axis of the axial portion of the mixing lens. The dichroic reflector transmits the measurement beam and reflects the tracer beam, and the dimensions of the dichroic reflector are based on the corresponding dimensions of the image sensor. In a representative example, the dimensions of the dichroic reflector are at least 0.5, 0.75, 1.0, or 1.5 times the product of the corresponding dimensions of the image sensor and the ratio of the optical distance along the axis from the focus of the mixing lens to the dichroic reflector to the optical distance from the focus of the mixing lens to the image sensor. For convenience, the dichroic filter is arranged on the lens surface of the movable lens.

[0011] The apparatus comprises an optical fiber and a hybrid lens arranged to receive a measurement beam from the optical fiber and generate a measurement beam focus. An optical element having a surface is arranged close to the measurement beam focus and reflects a part of the measurement beam back to the optical fiber as a local oscillator beam. The objective lens is arranged to receive the measurement beam from the optical element, direct a part of the measurement beam as a probe beam towards the target, and direct a part of the probe beam returned from the target towards the optical fiber to form a signal beam. In some examples, the optical element is a waveplate having an incident surface for receiving the measurement beam from the hybrid lens and an exit surface on the opposite side of the incident lens, and the exit surface is arranged close to the measurement beam focus to reflect a part of the measurement beam. In other examples, the waveplate has an incident surface for receiving the measurement beam from the hybrid lens and an exit surface on the opposite side of the incident lens, and the incident surface is arranged close to the measurement beam focus to reflect a part of the measurement beam. In a typical example, one of the incident surface and the exit surface of the waveplate includes an anti-reflection coating arranged to receive the measurement beam from the hybrid lens, and the other of the incident surface and the exit surface has an uncoated portion arranged to receive the measurement beam from the hybrid lens. In some alternative forms, a polarization beam splitter is arranged to receive the measurement beam from the hybrid lens and couple the measurement beam to the waveplate. In some cases, the optical element having a surface arranged close to the measurement beam focus is a polarization beam splitter (PBS). In other examples, the optical element includes a PBS and a waveplate fixed to the PBS. In yet further examples, the PBS has an incident surface coupled to receive the measurement beam from the optical fiber, and the waveplate includes an exit surface arranged to couple the measurement beam from the PBS to the objective lens and reflect a part of the measurement beam back to the optical fiber as a local oscillator beam.

[0012] In some examples, the PBS is arranged to reflect the probe beam portion of the measurement beam off a waveplate, and the photodetector receives a portion of the probe beam from the target and the local oscillator beam and is coupled to an optical fiber to generate a heterodyne electrical signal. The detection system provides an estimated target distance based on the heterodyne electrical signal.

[0013] In some examples, the apparatus includes first and second measurement beam sources that generate first and second measurement beams at first and second wavelengths, respectively. The beam combiner receives the first and second measurement beams and is arranged to combine the first and second measurement beams to form a combined measurement beam, and the optical fiber directs the combined measurement beam toward a mixing lens. The mixing lens focuses the combined beam at an optical element and reflects a portion of the combined measurement beam back toward the optical fiber as first and second local oscillator beams. According to other examples, the first and second photodetectors are arranged to receive a portion of the probe beam from the target as well as the first and second local oscillator beams and generate first and second heterodyne electrical signals. In some cases, the first and second photodetectors are coupled to the optical fiber or are coupled to receive a portion of the probe beam from a fiber and / or a polarization beam splitter. The detection system provides an estimated target distance based on the first and second heterodyne electrical signals. In a further example, the mixing lens receives the measurement beam and a tracer beam from the optical fiber, a dichroic filter is disposed on the axis of the objective lens, and the dichroic filter is non-transmissive to the tracer beam.

[0014] The method includes the step of directing a tracer beam having an associated beam aperture towards a beam splitter. A portion of the tracer beam aperture is blocked, obscured, attenuated, and scattered such that the beam splitter receives a measurement beam and a partially obscured / attenuated tracer beam. The partially obscured tracer beam from the beam splitter is directed towards a target having an objective lens, and the imaging beam is received at a beam splitter directed towards a detector having a beam splitter, and the obscured portion of the tracer beam corresponds to the imaging detector.

[0015] The method includes the steps of focusing a measurement beam from an optical fiber at a measurement beam focus and reflecting a portion of the measurement beam back towards the optical fiber to generate a local oscillator beam. Optionally, the measurement beam is focused via a beam splitter onto an optical element having a surface that reflects a portion of the measurement beam back towards the optical fiber. In an example, the optical element is a waveplate and the reflective surface is the surface of the waveplate. In other embodiments, the optical element is a polarizing beam splitter (PBS) and the reflective surface is the surface of the PBS.

[0016] In some examples, the apparatus includes a lidar arranged to direct a probe beam along an axis towards a target and generate an estimated value of at least one target dimension, the lidar including a probe beam scanner coupled to scan the probe beam axis. An imaging unit is optically arranged along the axis to generate an image of the target, and the probe beam scanner is coupled to the imaging unit to direct the probe beam to a target position based on at least one feature identified within the target image. In some examples, the imaging unit is an image sensor and the image processor identifies at least one feature within the target image. In some examples, the at least one feature is a design feature and the target position is associated with the design feature. In other examples, the at least one feature is a golf ball or an eyeball sphere and the target position is determined based on the position of the golf ball or the eyeball sphere. In a further example, the target position is determined based on the position of the eyeball sphere.

[0017] In a further example, the apparatus comprises a lidar arranged to direct a probe beam along an axis towards a target, the lidar comprising a probe beam scanner coupled to scan the probe beam axis. The imaging system comprises an image sensor optically arranged along the axis to generate an image of the target and a focusing mechanism coupled to an objective lens to adjust the focus of the target image at the image sensor. The image processor is coupled to the imaging system to generate an estimate of at least one target dimension based on the image of the target and an estimate of the distance to the target. In some examples, the lidar is configured to generate an estimate of the distance to the target or the estimate of the distance to the target is based on the adjustment of a focusing mechanism such as an autofocus mechanism. In one example, the target position is determined based on the position of the eyeball. In some examples, the imaging system is configured to generate a plurality of image portions and the image processor is configured to stitch the plurality of image portions together into a common image. In an additional example, the image processor is configured to at least partially correct the distortion of at least one image portion, such as at least one of the plurality of image portions, based on a test grid image.

[0018] The measuring device comprises a lidar providing a scanable laser probe beam and a remote mirror system including a movable mirror. The lidar is configured to direct the scanable laser probe beam towards the movable mirror of the remote mirror system for reflection towards the target to measure at least one feature of the target. In some examples, the remote mirror system includes at least one ball bearing or eyeball and the lidar is arranged to determine the position of the remote mirror system by directing the scanable laser probe beam towards the at least one ball bearing or eyeball. In a typical example, the lidar is coupled to the remote mirror system to initiate adjustment of the movable mirror such that the scanable laser probe beam is directed towards at least one feature of the target.

[0019] The above and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Brief Description of the Drawings

[0020]

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DETAILED DESCRIPTION OF THE INVENTION

[0021] As used in this application and the claims, the singular forms "a", "an", and "the" include the plural unless the context clearly dictates otherwise. Further, the term "includes" means "comprises". Further, the term "coupled" does not necessarily exclude the presence of intermediate elements between the coupled items. In some cases, elements are said to be directly coupled to exclude intermediate elements.

[0022] The systems, devices, and methods described herein should not be construed as being limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with each other. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, and the disclosed systems, methods, and devices do not require the presence of any one or more particular advantages or the solving of any particular problems. The theory of operation is for ease of explanation, but the disclosed systems, methods, and devices are not limited to such theory of operation.

[0023] Some of the operations of the disclosed methods are described in a particular sequential order for convenient presentation, but it should be understood that this description method includes permutations unless a particular order is required by the specific language described below. For example, the operations described sequentially may, in some cases, be permuted or performed simultaneously. Further, for simplicity, the accompanying figures may not show the various ways in which the disclosed systems, methods, and devices can be used in combination with other systems, methods, and devices. Further, the description may use terms such as "produce" and "provide" to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the particular embodiment and are readily identifiable by those skilled in the art.

[0024] In the following description, for convenience, the terms "light" and "optical radiation" refer to electromagnetic radiation propagating in the wavelength range of 300 nm to 10 μm, although other wavelengths can also be used. Such radiation can be directed at one or more targets to be investigated by profiling, detection, or other means. This radiation is referred to herein as typically propagating one or more "beams" based on optical radiation generated by a laser such as a laser diode. As used in this application, a beam need not be collimated, and radiation propagating in a waveguide is also referred to as a beam. A beam can have a spatial extent associated with one or more laser transverse modes and can be substantially collimated. Wavelengths for which optical fibers or other optical waveguides and coherent laser sources are readily available are convenient. In some examples, a laser diode having a wavelength of about 1550 nm is used.

[0025] For the sake of simplicity, a beam is described as propagating along one or more axes. Since such axes are generally based on one or more line segments, the axes can be bent, folded, or otherwise conformed to include several non - collinear segments when responding to mirrors, prisms, lenses, and other optical elements. The term "lens" is used herein to refer to a single refractive optical element (singlet), or a compound lens including one or more singlets, doublets, or other compound lenses. In some examples, the beam is shaped or directed by refractive optical elements, while in other examples, reflective optical elements such as mirrors are used, or a combination of refractive and reflective elements is used. Such optical systems can be referred to as refractive optical systems, reflective optical systems, and catadioptric optical systems, respectively. Advantageously, other types of refractive elements, reflective elements, diffractive elements, holographic elements, and other optical elements can be used. In some examples, a beam splitter such as a cube beam splitter is used to separate an input beam into a transmitted beam and a reflected beam. Any of these beams can be configured to function as a measurement beam or a local oscillator beam in a coherent detection system, as may be advantageous. The beam splitter can also be provided as a fiber coupler, and in some embodiments, a polarization beam splitter is preferred. The term "beam splitter" is also typically used to refer to a beam combiner. Fiber couplers and fiber wavelength division multiplexers (WDMs) can combine or separate beams.

[0026] In the disclosed examples, the lidar system is configured to scan a probe or measurement beam over a scanning path that can be a polygon, a portion of a closed curve, a raster, a w-pattern, or other pattern, and the scanning can be periodic or aperiodic. In response to the measurement beam or probe beam directed at the target, a return beam is obtained based on reflection, scattering, diffraction, refraction, or other processes at the target. Evaluation of the return beam enables estimation of target characteristics. The following examples are provided with respect to a lidar configured to provide an estimate of surface topography based, for example, on the portion of a light beam returned to a receiver directed at the surface. The disclosed methods and apparatuses can also be incorporated into a laser tracker system.

[0027] In some of the examples described herein, the measurement light beam is split into a probe beam directed at the target, a reference beam that can be used for calibration by being directed at a reference length, and / or a local oscillator beam that is used in combination with the probe beam for heterodyne detection and target distance estimation. In other examples, the beam directed at the target is called the probe beam, and the portion returned for detection is called the signal beam. In the disclosed examples, a portion of one or more light beams is directed at the target, the detector, or transmitted from one to one or more destinations. As used herein, a beam portion refers to any portion of a light beam, including the entire light beam. In many examples, a pointing or tracer beam propagates to the target along with one or more probe beams. The tracer beam is at a visible wavelength and enables the user to confirm that the probe beam is directed at the intended target position. Such a tracer beam would otherwise be unused and, in some cases, unwanted tracer beam reflections can interfere with the target's boresight camera image. The probe beam is typically at a wavelength greater than about 900 nm, and often suitable beam sources have wavelengths of about 1300 nm and 1500 nm. Other wavelengths can also be used.

[0028] The disclosed system generally includes one or more beam splitters, such as a polarizing beam splitter (PBS), and dichroic beam splitters (DBS), such as a cube beam splitter or a plate beam splitter. The beam splitter surface can be provided on a plate surface, a prism surface, a lens surface, or other curved or flat surfaces. As used herein, a DBS is a beam splitter that preferentially reflects (or transmits) in a first wavelength range and preferentially transmits (or reflects) in a second wavelength range. For the sake of explanation, the angle (tilt angle) of the beam splitter surface is measured from an axis perpendicular to the beam splitter surface with respect to the optical axis. PBSs and DBSs enable efficient use of the probe beam and excellent target image intensity, but non-polarization- and wavelength-dependent (neutral) beam splitters can also be used.

[0029] In some examples, rotation is described with reference to azimuth and elevation angles. Such angles are typically defined with respect to a vertical axis and a horizontal axis as used herein, but an orientation having a vertical axis and a horizontal axis is not required. Typically, the system is described with reference to such angles and the system is assumed to be in a standard orientation during use.

[0030] In the typical examples described below, the probe beam directed at the target is polarized, but non-polarized or randomly polarized beams can be used. An optical filter is called non-transmissive when its transmittance is 5%, 2%, 1%, or less. Beams, such as the probe beam and the tracer beam, can be focused on or near the surface of interest. As used herein, a beam is said to be focused on a surface when the beam waist is within ±0.5, 1, 2, 5, or 10 Rayleigh ranges of the surface.

[0031] Swept-frequency lidar Various configurations and aspects of a lidar system are disclosed below. The disclosed systems, system components, modules, and associated methods can be used in various lidar systems. In a typical example, a so-called swept frequency lidar system is provided. A typical coherent radar system generally uses one or more laser diode light sources. The laser diode frequency is directly modulated by modulating the laser diode injection current, or by modulating the laser diode temperature, or by some other method. The laser frequency is generally modulated in a waveform to generate a linear frequency sweep or linear "chirp". The laser frequency f(t) can be expressed as follows as a function of time t. f(t)=f0+(Δf / Δt)t=f0+γt,

[0032] where f0 is the initial laser frequency, and γ = Δf / Δt is the laser frequency change rate. Linear sweep is not required, and any laser frequency variation as a function of time, such as stepwise or other discontinuous frequency variations, or continuous variations based on polynomials or other functions, is theoretically useful, but linear chirp is generally more convenient and practical. The frequency modulated (FM) measurement beam is focused on the target, and a portion of the beam is scattered, reflected, refracted, or directed to be collected by the receiver optics. The local oscillator beam (“LO beam”) is generally obtained as a portion of the same laser beam used to generate the measurement beam. The round-trip transit time associated with the propagation of the measurement beam to and from the target results in a frequency difference obtained when the return portion of the measurement beam (return beam) and the local oscillator are optically mixed. This frequency difference can be used to determine the target distance. The return beam and the LO are directed to a detector such as a PIN photodiode (typically called a square-law detector) to generate a sum frequency signal and a difference frequency signal. The sum frequency (hundreds of THz for a 1.5 μm measurement beam) exceeds the available detector bandwidth, but the return beam and the LO beam also generate a difference frequency Δf (heterodyne frequency) within the detector bandwidth. The distance R to the target position can be calculated as R = cΔf / 2γ, where Δf is the heterodyne frequency associated with the return beam, γ is the chirp rate, and c is the speed of light. Heterodyne frequency generation also requires that the LO and the return beam are not orthogonally polarized, but since the range is determined based on the frequency difference rather than the amplitude, the polarization effect reduces the heterodyne signal level but does not change the heterodyne frequency.

[0033] Since the accuracy of distance measurement can be limited by the linearity of laser frequency modulation, successful lidar systems accurately control or measure the laser frequency. For example, when the target is 1 meter away, to ensure an accuracy of 1 mm, linearity of 1 in 1000 is required. Therefore, the laser source for an FM lidar is configured to provide a highly linear chirp, and variations from linearity are detected and corrected. In some cases, range measurements can have an accuracy in the range of a few microns.

[0034] In an FM lidar system, since signal detection is based on the heterodyne beat frequency, it is hardly affected by changes in ambient lighting conditions and surface reflectivity. The heterodyne beat frequency does not depend on the signal amplitude and is not affected by stray light radiation. Therefore, amplitude or intensity fluctuations in the return beam, measurement beam, or LO beam tend to have little effect on distance measurement. In addition, coherent heterodyne detection enables an FM coherent lidar to successfully detect an optical signal up to the shot noise limit so that reliable measurements can be made with a return beam output of only 1 picowatt corresponding to a 9-digit dynamic range.

[0035] In several of the following examples, systems using a probe beam of one or two wavelengths are shown. In general, one or more probe beams can be used, and the use of two counter-chirp beams enables the correction, modification, or elimination of Doppler shift errors associated with the relative motion between the lidar and the target.

[0036] In some examples, the disclosed system uses a single objective lens (having a fixed lens and a movable lens) to direct and focus a probe and a signal beam onto a target to generate an image of the target. This tends to maintain alignment between the bore site image and the probe beam. Due to the difference in wavelength between the probe beam and the image beam, as well as the high numerical aperture (NA) used, chromatic aberration correction can be difficult, and imaging with a dichroic prism type beam splitter can introduce a significant amount of other aberrations such as coma aberration. When an additional lens is used to shape the combined probe / tracer beam before focusing by the objective lens, an additional lens can be used to correct probe beam aberrations (such as chromatic aberration between the visible wavelength tracer beam and the infrared wavelength of the probe beam) independent of the imaging beam. In some cases, using such an additional lens can cause excessive tracer beam reflection, and shaping the tracer beam can reduce beam portions such as reflective portions that can interfere with target imaging. In some examples, the additional lens provides a beam focus on an optical surface such as a waveplate surface and uses a cat's eye retroreflector configuration to generate a local oscillator (LO) beam to provide LO stability.

[0037] In the following, for simplicity of explanation, representative examples of the disclosed technology are provided. Any features and aspects of any example can be combined with the features and aspects of other examples.

[0038] Example 1 Referring to FIG. 1, an optical system 100 for a lidar or other device includes an optical fiber 101 that emits a measurement (or probe) beam and a pointing (or tracer) beam from an optical fiber end 102. A beam splitter 104 is arranged to receive the probe beam and the tracer beam and direct a portion thereof to an objective lens 108 that includes fixed lenses 109, 112 and a movable lens 110 (shown in two places). The movable lens 110 is generally movable along an axis 120 to adjust the focus provided by the objective lens 108. The fixed lens 112 couples the combined probe / tracer beam 114 to a target 116. In a typical example, the probe beam wavelength is from 1200 nm to 1700 nm, the tracer beam wavelength is from 400 nm to 700 nm, typically from 650 nm to 700 nm, and an easily available laser diode can be used.

[0039] The objective lens 108 also receives, typically along with the imaging beam based on broadband or ambient illumination of the target 116, a part of the probe beam and the tracer beam returned from the target 116. The returning part of the probe beam is directed through the beam splitter 104 towards the fiber end 102 so as to propagate within the fiber 101. The imaging beam is coupled to the image sensor 118 together with a part of the tracer beam by the beam splitter surface 106. The beam splitter surface 106 is generally a thin-film dichroic filter that preferentially transmits the probe beam and reflects the imaging beam (or, if necessary, reflects the probe beam and transmits the imaging beam). By adjusting the position of the movable lens 110 along the axis 120, the probe beam and the tracer beam are focused onto the target 116, and the imaging beam is focused onto the image sensor 118. Thus, the objective lens 108 must operate over a wide wavelength range (e.g., 250 nm to 1700 nm). However, by using a single lens 108 for the probe, tracer, and imaging beams, beam alignment is maintained and the beam does not displace during beam scanning. As shown in FIG. 1, the lens 108 and the beam splitter 104 form a projection system 130 that projects the probe beam and the tracer beam onto the target and projects the image of the target 116 onto the image sensor 118. In some cases, the image sensor 118 and the fiber end 102 are optically conjugate or approximately conjugate at visible wavelengths. However, due to chromatic aberration, at the probe beam wavelength, the image sensor 118 and the fiber end 102 are generally not optically conjugate without correction for chromatic aberration. In some examples, it is possible to provide such chromatic aberration, which is convenient but not essential.

[0040] Example 2 Referring to FIG. 2, a portion of a representative lidar 200 includes a projection optical system 202 disposed along an axis 204 that includes an objective lens 206 having a fixed lens 210 and a movable lens 208. The movable lens 208 is movable along the axis 204 to form an image of the target on the image sensor 212 and to focus the probe beam and the tracer beam from the fiber end 214 of the target along the scan axis 216. A beam splitter 218 (typically a dichroic beam splitter) couples the image beam to the image sensor 212 and couples the probe beam and the tracer beam between the target and the fiber end 214.

[0041] The focus beam and the probe beam are fixed to a shaft 222 held by a bearing 224 and scanned by an elevation reflector 220 that is rotatable about an axis 204 parallel to the z-axis of the coordinate system 250. The rotation of the shaft is measured using an encoder 230 disposed on the shaft 216. Some components are disposed within a housing 232.

[0042] Example 3 Figure 3 shows an optical system 300 that communicates a probe beam and a tracer beam between the target. An optical fiber 302 having a fiber end 304 couples the probe beam and / or the tracer beam or both to a beam splitter 306. The beam splitter 306 includes a first prism 308 and a second prism 310 having dichroic (or other reflective surface) reflectors 312 disposed on respective prism faces. In some cases, the dichroic reflector 312 is defined by a thin film coating applied to one or both of the prisms 308, 310, or a separate coating on a separate substrate is used. It is convenient to fix the prisms 308, 310 to each other at the dichroic reflector 312. The dichroic reflector is disposed at an angle θ with respect to the propagation axis 316. The propagation axis 316 is substantially perpendicular to the prism face 314 facing the objective lens, the prism face 318 facing the fiber end 304, and the prism face 320 facing the image sensor 324. As described above, the image sensor 324 and the fiber end 304 can be optically conjugate, particularly at the imaging / tracer wavelength.

[0043] The dichroic reflector 312 is arranged to direct the imaging beam received from the target and the objective lens to the prism face 314, such that the imaging beam is reflected to the prism face 320, for example, by total internal reflection. The angle θ is generally selected to provide total internal reflection at the surface 314, but a coating can be provided to provide an appropriate reflectivity. An angle θ greater than 45 degrees reduces the angle of incidence of the beam on the dichroic reflector 312, such that the dichroic reflector exhibits fewer angle-dependent variations, such as variations in reflectivity as a function of wavelength and / or variations in reflectivity as a function of polarization state. For example, the angle θ that reduces the beam angle of incidence can be 50°, 55°, 60°, 65°, 70°, 75°, or more.

[0044] Example 4 Referring to FIG. 4, the beam combiner / separator optical system 400 includes an optical fiber 401 having a fiber end 402 that transmits a tracer beam and / or a probe beam to a plate beam splitter 406. The probe beam and / or the tracer beam are coupled by the plate beam splitter 406 (transmitted in this example) along axis 416 to an objective lens. The imaging beam returned from the objective lens is coupled by the plate beam splitter 406 via a narrowband filter 408 and focused on an image sensor 410. In this example, the plate beam splitter 406 is a dichroic beam splitter such that the probe beam is efficiently coupled to the target and the imaging beam is efficiently coupled to the image sensor 410. The narrowband filter 408 attenuates at the tracer beam wavelength. A model transmission curve of such a filter is shown in FIG. 5A, a graph 500 of a representative transmission curve 502 of an exemplary dichroic filter is shown in FIG. 5B, and FIGS. 5C-5D are representative images obtained with and without using such a filter, respectively.

[0045] A dichroic filter (beam splitter) having the characteristics shown in FIG. 5B can be disposed, for example, on the prism surface 320 (see FIG. 3). Typically, a suitable filter is disposed on the prism surface closest to the image sensor (such as the image sensor 324 in FIG. 3) and provided as a coating on the selected prism surface. The dichroic filter can function as a band-pass optical filter with a transmission bandwidth of 480 to 630 nm in a range 504 where the average transmittance at an incident angle of 0 degrees is 90% or more. The dichroic filter also serves as a notch filter in a wavelength range of 652 nm to 662 nm where the transmittance is 5% ± 3% as shown at 506. Longer wavelengths are not used and the dichroic filter performance at these wavelengths is irrelevant. The example of FIG. 5B is easier to manufacture than the model of FIG. 5A. The transmittance for imaging using an image sensor is preferably over 50%, 75%, 80%, or 90% in the range of about 480 nm to 630 nm, and the transmittance at the tracer wavelength is preferably less than 10%, 5%, 2.5%, 1%, or 0.5%.

[0046] Example 5 Referring to FIG. 6A, a representative lidar system 600 includes an objective lens 602 having a fixed lens 604 and a movable (focusing) lens 606 disposed along axis 608. The focusing lens 606 is generally fixed to a stage so as to be movable along axis 608. (The focusing lens 606 is shown in dashed lines at the second focal position). The fiber end 610 couples a probe beam and / or a tracer beam to a hybrid optical system 609 including a polarization beam splitter 612, a hybrid lens 614, and a quarter-wave plate 616. As will be further described below, the hybrid lens 614 focuses the probe beam onto the surface 617 of the waveplate 616 such that the reflected portion of the probe beam functions as a local oscillator beam and is directed back toward the fiber end 610. The combined probe / tracer beam is focused onto a target by the objective lens 602 via a dual-reflection beam splitter 618 having planes 620, 622, 626 perpendicular to axis 608. The dichroic surface 623 (or other beam splitter surface) directs the imaging beam from the target to the image sensor 630 and transmits the returning portion of the probe beam from the target to the fiber end or toward the fiber end 610. To reduce the portion of the tracer beam reaching the image sensor 630, an appropriate narrowband filter 629 can be provided as shown in FIGS. 5A-5B. Otherwise, a notch filter or other filter can be used to reduce the portion of the tracer beam that might reach the image sensor 630. Passing through the quarter-wave plate 616 twice causes the returned probe beam and a portion of the probe beam reflected at the surface 617 (forming the LO beam) to be in a common linearly polarized state orthogonal to the polarization of the probe beam emitted from the fiber end 610. The returned probe beam and the LO beam then interfere at detector 611 for homodyne or heterodyne detection. As shown in FIG. 6A, the PBS 612 is arranged to transmit the probe beam from the fiber end 610 and reflect the returned signal and the LO beam, but the PBS 612 can be arranged to reflect the probe beam and transmit the returned probe and LO beams.As described above, the dichroic surface 623 can be designed to be used at a smaller angle of incidence, i.e., an angle less than 45 degrees typical of a cube beam splitter, and is tilted to enable improvement of dichroic coating performance. In addition, fluctuations in reflectivity due to defocus are reduced, and the target image position tends not to shift in response to defocus. The prism surface is conveniently perpendicular to the axis 608, although other angles can also be used. The double reflection beam splitter 618 also provides additional clearance 650.

[0047] Example 6 In another example shown in FIG. 6B, one or more probe beams are emitted by the fiber 652 and directed towards the target via the PBS 654, the probe beam lens or lens assembly 656, the quarter-wave plate 657, the two-reflection prism 658, the movable lens 660, and the fixed lens 662. A portion of the probe beam is returned to the detector or detector assembly 670, and the observation beam is coupled to the image sensor 672 by the two-reflection prism 658. The LO beam is also directed to the detector 670 by the PBS 654. In other examples, the LO beam is generated by reflection from the surface of the wave plate 657.

[0048] In order to acquire a high-quality image in the image sensor 672, it is necessary to sufficiently reduce chromatic aberration at visible wavelengths. However, obtaining an acceptably low value of chromatic aberration both at visible wavelengths and between the probe (IR) and the pointing (red laser) is a difficult problem in lens design. FIG. 6C shows the chromatic aberration at the visible wavelength (range 690, chromatic aberration indicated by arrow 691) shown at 695, and at the probe (i.e., IR) wavelength as well as at the pointing beam wavelength at 694. The hybrid lens 656 is selected to reduce or eliminate chromatic aberration between the pointing beam and the probe beams (visible and IR), and the lenses 660, 662 are selected to reduce chromatic aberration in the visible range 690). The focus shift is shown for target distances in the range from 0.5 m to infinity, and the curves almost overlap except for the curve 697 associated with the target distance of 0.5 m.

[0049] Example 7 FIG. 7A shows an optical assembly 700 that communicates one or both of a probe beam and a tracer beam with a target and receives imaging light (sometimes called an imaging beam) from the target, including an objective lens 702. The objective lens 702 includes a fixed lens 704 and a movable lens 706 that focus the probe beam and the tracer beam onto the target and enable imaging the target onto an image sensor 708. A beam splitter 710 transmits at least a return portion of the probe beam from the target to couple to one or more detectors (not shown in FIG. 7A) by sending the probe beam and the tracer beam to the target through the objective lens 702. The beam splitter 710 includes optical surfaces 712, 714, 716 that are disposed perpendicular to a beam propagation axis 718 (the optical surface 714 is perpendicular to the propagation axis in a folded state at 716, 720). The propagation axis 718 is defined by axis segments at various angles relative to each other. The beam splitter 710 includes a first prism 710A, a second prism 710B, and a beam splitter layer 720 that is typically a multilayer thin film coating that provides wavelength-dependent reflection and transmission. The imaging beam used to form an image of the target is shown as 722 in FIG. 7, is reflected by the beam splitter layer 720, and is then reflected by the optical surface 716 to the image sensor 708. The prism angle β is typically selected such that the imaging beam is incident at an angle greater than the critical angle, i.e., an angle greater than sin 1 (1 / n), where n is the refractive index of the prism 710B. In some examples, the probe beam(s) have an intermediate focus on a plane 740, such as the surface of a waveplate, as described above.

[0050] Referring to FIG. 7B, the optical system for beam combining and separation is similar to the beam splitter 710 of FIG. 7A, but reflects one or more probe beams (and a portion of the tracer beam) from the source / detector system 760 to the target and has a dichroic surface 754 that combines the return portion of the one or more probe beams to the source / detector system 760, including a beam splitter 752. The image beam is sent to the image sensor 764 along axis 762. As in other examples, axis 762 is defined by axis segments at various angles relative to each other, and a portion of axis 762 extends to the x-ray source / detector system 760 and the image sensor 764.

[0051] Example 8 Referring to FIG. 8A, the optical system 800 includes an optical fiber end 802 arranged to couple a probe beam and / or a tracer beam to a beam splitter 804. The objective lens 806 includes a fixed lens 810 and a movable (focus) lens 808 so as to be able to focus the probe beam(s) on the target. The optical filter 820 is arranged to receive the probe beam and the tracer beam and send at least the probe beam to the target. The filter 820 includes a dichroic layer 822 having an aperture 824. The dichroic layer 822 is typically ring-shaped and is selected to be transmissive at the probe beam wavelength and attenuating at visible wavelengths or other wavelengths used by the image sensor 830. Thus, the filter 820 can reduce the numerical aperture of the imaging beam and simplify the design of the objective lens 806. It will be appreciated that it can be difficult to design a lens suitable for simultaneous precision imaging and beam focusing in the wavelength ranges of 400 nm to 700 nm (for target imaging) and 1300 to 1600 nm (for probe beam focusing). Using a filter such as the filter 820, the probe beam numerical aperture can remain large to enable fine focusing, but by restricting the imaging beam numerical aperture, a satisfactory image is provided. Although a dichroic layer 822 is shown in FIG. 8A, a similar absorption layer can be used. The diameter or other dimensions of the aperture 824 can be selected in conjunction with the objective lens design. In the example of FIG. 8A, the optical path length difference for propagation through the dichroic layer 822 through the aperture 824 is generally kept small enough to avoid introducing a focus error into the probe beam.

[0052] Typical filters 850, 860 are shown in FIGS. 8B - 8C. Filter 850 includes an attenuation ring 852 and a transmission central region 854 provided on one side, one side or both sides of the substrate. The attenuation ring 852 can be provided with an absorptive, reflective, polarizing, or other layer that preferentially attenuates an imaging beam (typically 400 nm to 700 nm, although imaging at other wavelengths can also be used). The attenuation ring 852 and the transmission central region 854 can have a common thickness or a common optical thickness in order to eliminate or reduce a probe beam focusing error associated with a phase difference between the attenuation ring 852 and the transmission central region 854. In the example of FIG. 8C, filter 860 includes an attenuation ring 862 disposed around a transmission region 864.

[0053] Example 9 FIG. 9A shows an optical system 900 including an optical fiber end 902 arranged to direct one or more probe beams and a tracer beam toward a polarizing beam splitter (PBS) 904 and an imaging lens 906. The imaging lens 906 focuses the probe beam onto the surface 908 of a waveplate 910, generally a quarter-wave plate that generates a circular state of polarization (SOP) within the probe beam. Typically, the imaging lens 906 forms an image of the optical fiber end 902 on the surface 908 of the waveplate 910. The surface 908 reflects a portion of the probe beam back to the imaging lens 906 so that it is directed either back to the fiber end 902 or otherwise normally used as a local oscillator beam. The surface 908 can be an uncoated surface since a reflectivity of a few percent is generally sufficient to produce a sufficient local oscillator beam output. By placing the surface 908 at the focus of the imaging lens 906, the local oscillator beam tends to be returned to the fiber end 902 with reduced variations in response to the tilt of the waveplate 908. A dichroic beam splitter 912 receives the probe beam and the tracer beam, and an objective lens 914 focuses the probe beam onto a target 916. The returned portion of the probe beam is recombined and directed back toward the fiber end 902, and the imaging beam is reflected by the beam splitter 912 to an image sensor 920.

[0054] As shown in FIGS. 9A-9B, the imaging lens 906 also includes a central shield 922 arranged to block one or more central portions of the probe beam or the tracer beam. In most examples, a portion of the tracer beam is blocked or attenuated within an angular diameter selected such that all or part of the tracer beam reflected by the surface 926 facing the target of the beam splitter 912 does not reach the image sensor 920. This blocking reduces the portion of the tracer beam that reaches the image sensor, resulting in the generation of an excellent target image. The beam portions 930, 931 are displaced from the axis 936 (i.e., the beam portion with a larger numerical aperture) and propagate towards the target 916. The corresponding beam portions are reflected by the beam splitter 912 but do not reach the image sensor 920. The central portion 932 (low numerical aperture portion) of the tracer beam is blocked or attenuated and does not reach the image sensor 920 or reaches the image sensor with a reduced beam power. The central shield 922 is typically provided by a dichroic reflector that transmits the probe beam and reflects at the tracer beam wavelength. The dimensions of the dichroic reflector are based on the corresponding dimensions of the image sensor. In some examples, the imaging lens 906 focuses the probe beam within the beam angular diameter α, and the dimensions of the dichroic reflector are at least 0.5, 0.75, 1.0, or 1.5 times the product of the corresponding dimensions of the image sensor and the ratio of the optical distance along the axis from the hybrid lens focus to the dichroic reflector to the optical distance from the hybrid lens focus to the image sensor. As shown in FIG. 9C, the shielding dimension d obs that attenuates the portion of the tracer beam reflected to the image sensor 920 obs can be determined as d SENSOR =(Z MIXLENS / Z SENSOR )D, where D is the image sensor dimension and Z MIXLENSis the axial distance from the hybrid lens focus to the image sensor 920 and the central shielding portion 922. Larger or smaller dimensions can also be used depending on the degree to which removal of the tracer beam portion is desired. (For convenience, FIG. 9C shows the optical system of FIG. 9A that is not folded.)

[0055] FIG. 9D shows another technique for reducing the tracer beam portion from reaching the image sensor. In an optical system similar to the optical system of FIG. 9A, the imaging lens 952 generates probe beam focusing on the surface 958 of the waveplate 960 or other optical element. The dichroic coating 956 is provided on the imaging lens 952 and provides variable transmittance as a function of the incident angle and wavelength. Typically, the central portion of the dichroic coating 956 is highly reflective to the tracer beam but transmissive to the probe beam. Other portions of the dichroic reflector, such as those associated with higher incident angles, tend to transmit both the tracer beam and the probe beam. Such a coating can be disposed on other surfaces such as the plane of a beam splitter or waveplate. FIG. 9E is the transmittance curve of a representative dichroic coating. As shown in FIG. 9E, the probe beam is transmitted at an incident angle of up to 30 degrees, but the transmittance at the tracer wavelength changes substantially, with low transmittance at normal incidence and increasing transmittance as a function of the angle.

[0056] Example 10 Referring to FIG. 10, the optical system 1000 includes an objective lens 1002 and a hybrid optical system 1004 that directs a probe beam and a tracer beam toward the objective lens 1002 to focus on the target 1008. In some cases, two counter-chirped probe beams are used. The hybrid optical system 1004 includes a fiber end 1010 that directs one or more probe beams and a tracer beam as a combined beam 1013 toward a PBS 1012 and then toward a hybrid lens 1014. The hybrid lens 1014 focuses the combined beam 1013 onto the surface 1018 of a waveplate 1016, and the reflected portion of the probe beam from the surface 1018 is returned toward the fiber end 1010 to function as a local oscillator beam. The state of polarization (SOP) of the reflected portion from the surface 1018 is rotated by 90 degrees. The opposite side of the waveplate 1016 typically has an anti-reflection coating.

[0057] The combination of the hybrid lens 1014 and the waveplate 1016 functions as a cat's eye retroreflector 1030 that is less responsive to the tilt of the waveplate 1016. A portion of the probe beam(s) and the local oscillator beam(s) is directed by the PBS 1012 toward a detector assembly 1032 that typically includes respective detectors coupled to receive a probe beam portion and an LO portion for each probe beam wavelength.

[0058] Example 11 FIG. 11 shows an optical system similar to FIG. 10 in which the probe / tracer beam is reflected by a PBS 1112 to a hybrid lens 1114 and focused onto the target-side surface 1118 of a waveplate 1116 such that the state of polarization (SOP) of the reflected portion from the surface 1118 is rotated by 90 degrees. The opposite side of the waveplate 1116 has an anti-reflection coating 1121. In this example, the return beam portion is sent by the beam splitter 1112 to a detector 1132.

[0059] Example 12 Referring to FIG. 12A, the lidar system 1200 includes a pointing laser 1202, a first probe laser 1204, and a second probe laser 1206 coupled to a fiber module 1210, the fiber module being temperature controllable and including a sealed container 1211 that can be filled with an exhaust or inert gas. The probe lasers 1204, 1206 are coupled via respective optical isolators 1205, 1207 and then coupled to a wavelength division multiplexer (WDM) 1212 that combines the first and second probe beams for output to the fiber module 1210. The fiber module 1210 includes a fiber coupler 1214 that directs a portion of the combined probe beam towards the WDM 1216, the WDM combining a portion of the probe beam with a tracer or pointing beam (such as a red or other visible beam) from the tracer laser 1202 and outputting the combined probe / pointing beam at the fiber end 1218. In other examples, the WDM 1212 and the fiber coupler 1214 are replaced by a single coupler disposed within the sealed container 1211. The coupler 1214 also directs the probe beam portion towards the coupler 1222, which couples the beam portion to the coupler 1224 via two different paths, one of which includes a reference fiber 1226. The coupler 1224 then combines the beam portions associated with the different paths and directs the combined beam towards the WDM 1228, which directs the beam portions from each path towards reference detectors 1230, 1232 associated with the wavelengths of the first probe laser 1202 and the second probe laser 1204, respectively. The beam portions at each of the reference detectors 1230, 1232 generate heterodyne signals at frequencies associated with the length of the reference fiber 1226 and the frequency chirps in the first and second probe beams. Based on these heterodyne signals and the known length of the reference fiber 1226, the probe laser frequency chirps and the measurement signals obtained from the target 1250 can be used for calibration or verification of the distance measurements.

[0060] The fiber end 1218 couples the combined beam to the mixing optical system 1234. The PBS 1236 receives the combined beam, and the mixing lens 1238 forms a beam focus on the surface 1240 of the quarter-wave plate 1239 that reflects the local oscillator portion back to the PBS 1236. The other portion of the combined beam passes through the beam splitter 1244 (shown as a plate, but a cube, double reflection, or others can be used) and propagates to the projection optical system 1242 having a fixed lens 1248 and a movable lens 1246 for focusing the combined beam on the target 1250. The beam splitter directs the imaging beam towards the camera 1257. One or more scanning mirrors 1249 (typically as shown in FIG. 2) direct the combined beam towards the target 1250, and the return portion of the combined beam from the target 1250 is directed back towards the projection optical system 1242 and the mixing optical system 1234. The beam portion returned from the target 1250 together with each local oscillator beam is reflected by the PBS 1236 to the dichroic beam splitter 1260. The detectors 1262, 1264 are arranged to receive the beam portions and the local oscillator beams associated with their respective wavelengths and generate corresponding heterodyne signals. In other examples, a normal beam splitter (i.e., non-polarizing and non-dichroic) is used together with a wavelength filter in front of each detector. Such a configuration is generally associated with some additional signal loss but can be more convenient to generate.

[0061] As shown in FIG. 12A, the local oscillator (LO) beam is generated using reflection from the surface of a quarter-wave plate at the focus of the hybrid lens. The composite lenses 1238 and the quarter-wave plate 1239 function as a cat's eye retroreflector for the incident beam focused on the surface of the quarter-wave plate 1239. Even with an inclination of the quarter-wave plate 1239, alignment of the LO and the return portion of the probe beam is provided. For example, for a hybrid lens focal length of 7.5 mm, the beam offset (spot offset) as a function of the wave plate inclination for displacements from the exact focus between -0.6 mm and 0.6 mm is plotted in FIG. 13A. For the exact focus, the spot offset is 0 for all inclinations. FIG. 13B shows the signal loss as a function of the spot offset, and FIG. 13C shows the spot offset (SO) at the detector surface between the beams 1302, 1304.

[0062] FIG. 12B shows a lidar 1280 similar to the lidar 1200 of FIG. 12A. However, in the example of FIG. 12B, a temperature-controlled oven 1290 is shown that includes some or all of the components of a reference path such as the fiber 1226. Generally, it is preferred to place all optical fiber components inside the oven and evacuate and seal the oven. The fiber end 1218 directs the combined beam towards a local oscillator optical assembly 1291 that includes a PBS 1292 that directs a portion of the probe beam towards the detector assembly 1293. Note that the PBS is not perfect, and thus a portion of the "wrong" polarization is reflected, and the reflected portion is a part of the total beam. The other part of the probe beam is directed towards the quarter-wave plate 1294, and the portion returned from the target is reflected by the PBS 1292 towards the quarter-wave plate 1294 and then towards the retroreflector 1295. The probe beam is then directed towards the detector assembly 1293 as shown. Instead of the plate beam splitter 1244 of FIG. 12A, a cube beam splitter 1296 is arranged to reflect a portion of the observation beam towards the camera 1297. The lens 1238 enables independent focusing of the probe beam and the imaging beam using the lenses 1246, 1248.

[0063] FIG. 12C shows a hybrid optical system 1279 including a cat's eye assembly 1284 and a detector module 1281. The cat's eye assembly 1284 includes a lens 1285 that focuses an input probe beam onto the surface of a wave plate 1286 to generate an LO beam by reflection. The detector module 1281 includes a PBS 1283 that directs the LO and return probe beam portions toward a dichroic beam splitter 1287 such that the transmitted portion of the first wavelength is directed toward a detector 1288 and the reflected portion of the second wavelength is directed toward a detector 1289. The wavelength difference between the first wavelength and the second wavelength can be 1, 2, 5, 10, 20, 50, or 100 nm or more for separation by the dichroic beam splitter 1287. The hybrid optical system 1279 can be made compact (total volume less than 2 cubic inches), has few components required, and can be easily and stably aligned.

[0064] Example 13 FIGS. 14A - 14D relate to a double - reflection beam splitter. FIG. 14A shows a double - reflection prism beam splitter 1400 in which a dichroic surface 1404 is disposed at an angle β defined as the apex angle of a prism 1406. FIG. 14B is a detailed view of the prism 1406 showing the prism angle and the angles of incidence and reflection with respect to an axis 1408 perpendicular to the beam splitter surfaces 1410, 1412. FIG. 14C shows another alternative double - reflection beam splitter 1420 that can include a prism such as prism 1406. As shown in FIG. 14D, the double - reflection beam splitter 1452 includes a plate dichroic beam splitter 1454 and a reflector 1460. The plate dichroic beam splitter 1454 and the reflector 1460 are disposed on an axis 1456. The reflector 1460 can be defined, for example, on the surface 1458 of a transmissive plate.

[0065] Example 14 Figures 15A - 15C illustrate exemplary methods that can be used individually or in combination in a lidar or laser tracker system or other optical measurement system. As shown in Figure 15A, method 1500 includes a step of combining a probe beam and a tracer beam at 1502, and a step of directing the combined beam towards a target using an objective lens having a fixed portion and a movable portion at 1504. The probe beam portion received from the target is returned to a dichroic beam splitter and directed towards a detector at 1506. At 1508, an image beam is directed towards an image sensor, and at 1510, the focus of the probe beam at the target and the focus of the imaging beam at the image sensor are adjusted by a movable lens.

[0066] As shown in Figure 15B, method 1530 includes a step of combining one or more probe beams and a tracer beam at 1532, and a step of focusing the combined beam onto a reflective surface to generate a retropropagating local oscillator (LO) beam containing each portion of the probe beam at 1534. At 1536, a portion of the probe beam received from the target is received and directed towards one or more detectors along with the LO beam. At 1538, the target distance or height is estimated based on the heterodyne frequency between the returned probe beam portion and the corresponding LO beam.

[0067] As shown in FIG. 15C, method 1550 includes, at 1552, coupling a beam (such as one or more probe beams and a tracer beam) to a beam splitter such as fiber-based WDM, and at 1554, blocking the center or low NA portion of the tracer beam. At 1556, the combined beam (excluding the central portion of the tracer beam) is directed to a dichroic beam splitter. At 1558, an imaging beam is directed from the dichroic beam splitter to an image sensor, and at 1560, the return portion of one or more probe beams is processed to generate a distance or height estimate. Typically, the return beam portion is mixed with a corresponding local oscillator beam to generate an electrical signal at a different (heterodyne) frequency, and the heterodyne frequency is calibrated with respect to distance / height.

[0068] Example 15 FIG. 16A shows a representative lidar 1600 including a fiber module 1602 disposed generally within a temperature-controlled, sealed, inert gas-filled or evacuated enclosure 1603. The fiber module 1602 includes an optical isolator 1606 and a fiber coupler 1608 coupled to a probe laser 1604. The WDM 1610 is coupled to receive a portion of the probe beam from the probe laser 1604 and a tracer beam from the tracer laser 1612 and couples the combined probe / tracer beam to a mixing optical system 1614. The mixing optical system 1614 couples a portion of the probe beam returned from the target to one or more detectors 1616 to generate an electrical signal that is processed to determine the target distance or height. The mixing optical system 1614 couples the combined probe / tracer beam to a projection optical system 1618 and then to a beam scanner 1620 for transmission to the target. The projection optical system 1618 also directs an imaging beam to an image sensor that functions as a boresight camera 1617 in combination with an objective lens provided in the projection optical system 1618. The beam scanner 1620, the projection optical system 1618, and the mixing optical system 1614 also direct a return portion of the probe beam from the target to one or more detectors 1616. Further, a reference photodiode 1630 is coupled to fiber couplers 1632, 1634 such that a portion of the probe beam received from the coupler 1608 is directed to a reference fiber 1636 having a predetermined length so that the heterodyne signal frequency can be associated with distance or height. The lidar 1600 can use any of the mixing optical system, the projection optical system, and the beam scanner disclosed herein and, in some cases, one or more can be omitted. In one variation, the detector 1616 is omitted and a detector 1622 is coupled to a fiber coupler 1624 of the fiber module 1602 to receive the signal beam.

[0069] The example of FIG. 16A shows only a single probe laser, but typically two probe lasers of different wavelengths are used, and the lasers generate a counter-chirp beam that reduces or eliminates the Doppler shift associated with the target motion to enable heterodyne detection. As in most examples, the tracer beam is used to confirm alignment but is otherwise unused.

[0070] Example 16 Referring to FIG. 16B, a representative optical system 1650 includes a first probe laser 1654, a second probe laser 1658, and a visible (typically red-emitting) laser 1652. A portion of each probe laser beam is directed to respective reference paths 1666, 1668 to generate a heterodyne signal at respective detectors 1656, 1658. The coupler 1670 combines the portion of the probe beam that is combined with the visible beam from the visible laser 1652 at the visible / probe coupler 1672. Typically, a hermetically sealed temperature controller enclosure 1664 is provided to stabilize the reference heterodyne frequency.

[0071] Example 17 An alternative optical system 1680 is shown in FIG. 16C. An actuator 1690 is attached to the output fiber end 1688 to enable displacement of the fiber end 1688 and the associated output beam. A voice coil, piezoelectric, or other device can function as the actuator. The displaced beam is directed, as described above, through the beam coupler 1684 and the hybrid optical system 1682, to a lens 1691 that images the output beam onto a target. The beam displacement results in a small movement or scan of the output beam at the target. For relatively small fiber movements, the LO beam and the measurement beam generated by the hybrid optical system remain efficiently overlapped at the detector 1686 to provide a useable RF (heterodyne) signal. By using a small and fast actuator such as a voice coil or a piezoelectric stack, the beam can be swept very rapidly and accurately. A dual actuator can be used to sweep in two lateral directions. This provides a way to measure carefully selected points on a target, typically to rapidly measure features such as holes or posts without using a much slower scanning mirror. A larger area detector may be convenient to accommodate the beam displacement associated with this scan, but excessive detector size can limit the detector bandwidth and potentially reduce the magnitude of the heterodyne signal. In one example, a 1 mm fiber displacement generates a 0.4 mrad angular beam scan. Only a single probe beam of a single wavelength is shown in FIG. 16C, but two or more wavelengths can be used with their respective detectors.

[0072] Example 18 As shown in FIGS. 17A - 17C, measurement system 1700 can include a plurality of fiber outputs 1701 to provide a plurality of measurement positions where measurements can be made simultaneously. Measurement system 1700 includes a visible laser 1702 and a probe laser 1704 coupled via an optical isolator 1705. A portion of the probe laser beam is directed by a reference arm tap (typically a fiber coupler) 1706 towards a reference arm 1712 and a visible / probe coupler 1703. A 1 - row N - column coupler 1708 receives the combined visible / probe beam and generates N combined visible / probe output beams. Alternatively, a 1×N switch can be used. These N beams can be directed towards a common scanning projection optical system. For the sake of simplicity, the associated local oscillator beams and detectors are not shown.

[0073] FIGS. 17B - 17C show a representative array 1720 of optical fibers configured to direct N beams towards a mixing optical system. Representative fiber ends 1722 - 1726 are arranged in a cross - shape and each has its own core such as core 1727. If the output fibers are standard 125 - μm - diameter PM fibers and the fibers are in contact, the cores are 125 μm apart. Focusing this array onto a target generates the beam pattern 1750 shown in FIG. 17D, where beam spots 1753 - 1756 are directly shown on the visible target surface and beam spot 1752 is within the recess 1706 of the target. The angular separation of the combined beams can be 0.5, 1, 2, 5, 10, or 20 mrad or more. A large separation requires attention to the objective lens characteristics to maintain an appropriate beam focus and large beam separations (e.g., 0.5, 1, 2, 5, 10, 20 mm) can be achieved. In the example of FIG. 17D, the bean spots 1753 - 1756 surrounding the hole 1706 simultaneously provide a return probe beam associated with the area up to the plane of the hole 1706 and can process the image of the recess 1706 to provide the hole diameter along with range information. Such measurements are much faster than conventional techniques that require scanning.

[0074] FIG. 18 is a diagram showing a representative multi-fiber optical configuration. In this configuration, the detector array 1810 is arranged to capture the mixed signal of each fiber (i.e., the returned probe beam portion and the LO beam). A plurality of fiber ends 1802 (including representative fiber ends 18021, 18022) direct the probe beam towards a cat's eye assembly 1807 including a polarization beam splitter and the above-described lenses and quarter-wave plates. The cat's eye assembly 1807 generates an LO beam by reflecting a portion of the probe beam from the surface of the quarter-wave plate. The probe beam is directed towards an object 1812 by an objective lens 1811, and the probe beam from each fiber of the plurality of fiber ends 1802 provides a beam spot corresponding to the object 1812 (e.g., representative beam spots 18081, 18082). The probe beam portion from the object 1812 is returned to the objective lens 1811, the cat's eye assembly 1807, and the PBS, and each detector of the detector array 1810 (e.g., representative detectors 18101, 18102). When a dual-wavelength probe beam is used, a dichroic beam splitter and an additional detector array can be used. Only the beams from two fiber ends are shown, the beam from fiber end 18021 is shown as 18041, 18061, and the beam from fiber end 18022 is shown as 18042, 18062. The heterodyne signals associated with each of the plurality of fiber ends 1802 are processed by corresponding processing elements 1820 (such as processing elements 18201, 18202, etc.) to establish an estimated value of distance, range, or dimension. In other examples, a single processing system is used and the heterodyne signals are processed one at a time. For example, an electrical switch can receive all the heterodyne signals and sequentially combine the selected heterodyne signals for processing. In FIG. 18, the fiber ends are shown distributed along a single direction, but a cross-shaped or other distribution (e.g., along the diagonals, curves, edges, and / or inside of a polygon) can be used.

[0075] Example 19 The lidar can include a camera aligned along the lidar axis. Such an implementation can use an inexpensive surveillance camera having calibration parameters that vary with the spatial orientation with respect to environmental conditions such as gravity and temperature. The camera data is processed and presented independently of the lidar scan data, and real-time alignment between the camera and the lidar data can be difficult. In some of the disclosed examples, the measurement camera is arranged to use a common focusing optical system having a lidar measurement path, and such a camera is referred to herein as a confocal camera, and the associated lidar is referred to as a confocal lidar (cLR). This provides measurements over six degrees of freedom (DOF) between the camera and the lidar. Such a camera can be a high-definition camera and can be coupled to provide camera data at a low level within the system architecture to minimize or reduce the latency between the data that enables real-time alignment of the LR and the camera data. By using two measurement modes (LR and camera) in the confocal lidar, it becomes possible to optimally measure features of interest with respect to the LR. Further, a low-latency data interface enables real-time algorithms and tracking of distinguishable features within the camera.

[0076] The lidar measures the azimuth, elevation, and distance to the surface of interest. The azimuth and elevation are read from appropriate on-axis encoders. The distance measurement is achieved by heterodyne interferometry and can be performed on almost all surfaces without interference from ambient light. The conversion of the distance (R), azimuth (A), and elevation (E) to the Cartesian coordinates XYZ is achieved by the well-known conversion from spherical coordinates to Cartesian coordinates as follows. X LR =R*cos(E)*cos(A) Y LR =R*cos(E)*sin(A) Z LR =R*sin(E)

[0077] A calibrated camera can be regarded as an angle measurement device that can determine the azimuth and elevation angles of all pixels in an image. Since the LR and the camera have a confocal relationship, distance measurement can provide a scale to the camera image. Due to this relationship, the central pixel of the camera can be directly associated with the XYZ LR It is not possible to guarantee that the projection of the camera focal plane onto the scene is perpendicular to the central axis of the LR, but the actual relationship can be determined by the calibration process.

[0078] In a calibrated camera, when the distance is determined by the LR, planar features can be directly measured by the camera. Once the distance is established, other features with known geometric shapes such as spheres can also be measured.

[0079] Referring back to FIG. 12A, an auto-focus (AF) linear translation stage 1253 is coupled to one or more of the lenses 1246, 1248 to enable probe beam focusing over a measurement distance (such as 0.5 m to 30 m or 50 m). The beam splitter 1244 reflects visible light (or other imaging radiation) from the target or other scene to the camera 1257 so that the beam position can be displayed on a camera screen or other display device. The camera 1257 is coupled to one or more processing systems 1258 and can also use the output to provide an input image for a computer-based measurement algorithm. Since the camera 1257 and the probe beam share the same focusing optics, the relationship between the camera sensor array and the position (measurement point) of the measurement beam on the target remains invariant as long as the camera mounting is stable. This invariance establishes the camera 1257 as a confocal camera and enables scanning beam focusing using the auto-focus stage 1253. In one example, the focus is adjusted to provide maximum contrast in the image generated by the camera 1257. In such a configuration, the probe beam can be quickly focused and directed to a selected position within the camera image. Variations in the position of the probe beam relative to the camera at different focus positions, if present, can be corrected by calibration, similar to any variations due to ambient temperature. Additional focus correction can be performed using a focus signal based on the lidar probe beam, as provided by the lidar focus controller 1255. In other examples described below, the processing system 1258 is used to stitch images together to form a larger image, correct the distortion of the stitched-together images, and identify or track target features or objects such as a cue ball or an eyeball sphere.

[0080] Example 20 Referring to FIG. 19, a method 1900 for establishing a target feature size or dimension includes the step of establishing the distance to the target surface at 1902. If the target surface is planar as determined at 1903, an image of the target feature is acquired at 1904. If the target surface is not planar, the shape, inclination, and distance of the target surface are established at 1905, usually by additional scanning. Alternatively, the distortion of a preliminary image of the shape or structure of a known geometric shape can be evaluated. At 1906, the magnification of the image is determined for some or all of the image (i.e., target) positions. Based on the determined image magnification, the feature size on the image can be appropriately scaled to actual dimensions at 1910. These scaled dimensions can be reported or stored at 1910. In some examples, the scaled dimensions are compared to the design dimensions to determine whether the features are properly sized.

[0081] Example 21 Referring to FIG. 20, the lidar system 2000 includes a lidar ranging system 2002 that includes reporting and adjustment for establishing target azimuth and elevation angles, laser ranging measurement electronics for reporting distance, and motors for controlling azimuth and elevation angles. A confocal camera 2004 is also arranged to generate an image of the target, and both the lidar ranging system 2002 and the camera 2004 are coupled to an embedded processor 2006. Thus, lidar distance data and image data are provided to the embedded processor 2006 without increasing the latency associated with the communication of such data to a remote processor via a network or other communication connection such as Ethernet or Universal Serial Bus (USB). The exemplary system of FIG. 20 enables the collaborative use of the confocal camera and lidar data with the rapid operation obtained by closely coupling the lidar ranging system and the confocal camera. Each of these measurement systems continuously creates a data stream. As shown, this data is combined in an embedded computer physically associated with the confocal lidar. This use of an embedded computer with a confocal lidar facilitates the search for features selected based on computer aided design (CAD), which is a digital representation of the part being measured. Often, there is a list of features measured in CAD coordinates. Under normal circumstances where the actual part is measured, the features are not at the ideal CAD coordinates. Further, ideal measurements are preferably made when the measurement device, here the confocal lidar, is at the center of the feature being measured. Search algorithms must be executed to identify any preselected feature, but these search algorithms can be very inefficient. Due to the confocal and / or metrology relationship of the confocal lidar, when a feature is within the field of view of the camera, the feature of interest can be automatically and rapidly centered.

[0082] In other examples, a high-speed alignment can be obtained prior to measurement. In many applications, the system must perform an alignment to the part before measuring the feature of interest. The alignment can be of two types: (1) an absolute alignment where the lidar measures a set of tooling balls that have a known relationship to the part, or (2) an alignment to a set of features. As described above, features can be quickly found by searching with a camera. In the case of tooling balls, a confocal lidar has additional advantages. A camera can be used to center the lidar on the tooling ball. In all algorithms, generally, the radius of the tooling ball is assumed to be known so that the surface measurements of the tooling ball can be projected to the center of the tooling ball. After centering, four different algorithms can be used: (1) in the case of a shiny tooling ball, assume that the camera has accurately centered the lidar and is simply measuring the distance to the surface; (2) in the case of a shiny tooling ball, perform a W-shaped lidar scan to determine the exact angle to the tooling ball and then measure the distance to the surface; (3) in the case of a matte tooling ball, assume that the camera has accurately centered the lidar and is simply measuring the distance to the surface; (4) in the case of a matte tooling ball, scan the surface and perform a sphere fit to determine the position of the tooling ball. In all cases, the ability to center with a camera improves speed and overall productivity.

[0083] The camera can measure features (such as tooling balls) in conjunction with lidar distance measurements. Additionally, the camera can measure planar features such as holes, slots, polygons, etc. In these types of measurements, there is only a void at the center of the feature. Therefore, the lidar system must intentionally offset the camera field of view to point to the surface around the feature.

[0084] Example 22 Referring to FIG. 21, a representative tracking target 2100 is shown. The tracking target 2100 is based on a sphere 2101 having concentric rings 2102, 2104 defined on the sphere. The rings 2102, 2104 have different colors, reflectivities, surface finishes, patterns, or other features that are easily visible in a camera image. Other portions 2106, 2108 of the target can have a common surface color or finish, etc. In some cases, portions 2106, 2108 are shiny and highly reflective, while the rings 2102, 2104 have different colors. Such a tracking target can have 1, 2, 3, or more rings. For convenience in view of the appearance of such a tracking target, it is referred to herein as an "eyeball sphere" or "ES".

[0085] FIG. 22 shows a representative method 2200 of using an ES. The ES must first be placed within the field of view of the camera at 2202, for example, by using a spiral or angular search that may have a portion outside the field of view of the camera to search with a lidar. In some cases, the operator can adjust the target or lidar position. At 2204, the ES is tracked with a confocal camera. The ES can be tracked (or the tracking error reduced) by keeping the annular ring at the center of the camera field of view. When the ring moves away from the center of the field of view, one or more motors in the lidar are commanded to orient the lidar (and the confocal camera) so as to minimize the error. The speed of movement is continuously calculated, and when the speed falls below a threshold, it is declared at 2206 that the ES is not moving. Next, at 2208, a measurement of the position of the sphere is triggered. The returned measurement is the center of the sphere. Usually, the measurement of the object is the surface, and the measurement of the sphere is projected onto the surface.

[0086] ES is particularly convenient, but other tracking targets can be used, such as corner cubes attached to the sphere (referred to as "Spherically Mounted Retroreflectors: SMR"). Such a target should have a corner cube reflection point at the center of the sphere; otherwise, errors may occur. Unlike SMR, ES does not show misalignment in response to incorrect handling. The various regions of ES can be provided with paint, etched, frosted, or coated with reflective, metallic, dichroic, or other coatings.

[0087] ES or other tracking targets enable or hide the measurement of target areas having a high angle of incidence to the lidar 2304. Referring to FIG. 23, the tracking target 2302 is shown in different positions, enabling the probe beam 2301 from the lidar 2304 to reach the hidden area 2310 of the target 2308.

[0088] In some examples, ES is formed by modifying a precision sphere by adding rings of different colors. The rings can also be filled with retroreflective paint and made highly visible by flashing. The sphere can be made of either a matte material or a gloss finish in three measurement modes, namely (1) a matte finish where the angle is used from the camera and the distance to the center of the sphere is obtained from the lidar, (2) a matte sphere that conforms to the spherical surface, or (3) a matte material or gloss finish that creates a W-shaped lidar scan on the mirror point for finding the angle and then creates a distance measurement to the mirror point. In modes 2 and 3, the lidar performs all the measurements, and the camera positions the lidar at the center of the sphere and detects that the sphere is not moving. In mode 1, the camera is still used for tracking and detecting the lack of movement, but the angle measurement value of the camera is combined with the LR measurement value to perform the measurement almost instantaneously.

[0089] Example 23 Another type of hidden point tool can also be used with tracking. As shown in FIG. 24, a vector bar 2400 can be created. When the centers of ES2410, 2412 are measured by a lidar 2404 having probe beam axes 2416, 2417, the results can be projected onto the center of the measurement sphere 2403 or the measurement point. Such measurements can be called stadia measurements. A complete 6DOF tool can be created using three eyeballs placed at different positions, and these eyeballs do not have to be on the same straight line.

[0090] Using two eyeballs, two measurements are made at the XYZ positions of the two eyeballs (XYZ1, XYZ2). The distance between XYZ1 and XYZ2 is not important, but the distance D m between ES2512 and the measurement sphere 2403 must be known. If the centers of all three spheres are on the same straight line, excellent measurement results can be obtained. The center of the measurement sphere 2403 is projected onto the surface of the target using ordinary techniques. The sample calculation of the XYZ of the measurement sphere 2403 is as follows.

Equation

[0091] Such measurements are practical because the waiting time is short and each spherical ball can be measured in a fraction of 10 seconds. An instrument having two eyeballs and a measurement sphere that are fixedly separated is convenient, but such an instrument can use a single eyeball that can move to different positions along the shaft 2414. Then, the measured values at each position can be used.

[0092] Example 24 Automated measurement systems that use lidar require an expensive and time-consuming setup process, which can take several weeks to complete and may require skilled personnel. This specification discloses systems that utilize measurement-grade high definition (HD) or other cameras incorporated into lidar. Machine learning algorithms are provided for identifying and / or measuring features such as holes, slots, studs, and other features. So-called "collaborative robots" (usually including mirrors or other optical systems) enable blind spot measurements and local tracking of the measurement device, shortening the setup time and speeding up the measurement time.

[0093] In some of the disclosed examples, a tooling ball placed around the part to be measured is not required, and an augmented reality application can overlay the CAD image of the part and the camera image. This enables automatic detection of the part and can be used to instruct the lidar to measure / scan the selected target area. In that case, a long lidar scan is not required to identify the target area of interest. In some applications, an additional mirror is used with the lidar for measuring points that are hidden or difficult to reach that are not in direct line of sight. Such mirrors are generally small and thus provide a limited field of view from a fixed position. By attaching such a mirror to a robot, this limited field of view can be greatly expanded with automated movement. The use of a collaborative robot allows for easy positioning of the mirror and eliminates the need to protect the measurement area for safety. Thus, the collaborative robot can place the mirror in multiple reproducible and stable positions that enable a larger field of view than a static mirror position and also enable more measurements from a single lidar position.

[0094] Referring to FIG. 25A, mirror 2506 is attached to tool flange 2507 of collaborative robot (COBOT) 2504. Typically, the COBOT includes one or more translation stages and one or more rotation stages so that the mirror 2506 can be set to a selected position and angle. In some examples, the turret ball 2528 is attached to an offset in front of the mirror 2506 on a rigid shaft. (Although a turret ball is used in this example, a system including a measurement camera does not need to use a turret ball.) The lidar 2500 is placed at a single fixed position or fixed to a programmable position so that the lidar 2500 can be iteratively positioned. The position of the mirror 2506 is programmed into the robot 2504 manually or using simulation software so that hidden features of the object to be measured are visible from the selected lidar position. As shown in FIG. 25B, the initial position of the turret ball 2528 is measured both directly and indirectly (i.e., via reflection of the turret ball 2528 in the mirror 2506) using the lidar 2500 to determine the nominal position of the turret ball 2528 and define the surface of the mirror 2506 passing through the perpendicular bisecting plane of the line connecting the center of the turret ball 2528 and the turret ball image within the mirror 2506. In addition to the movement of the COBOT 2504, the arm 2505 to which the tool flange 2507 is fixed can be moved to access additional positions on the object 2508.

[0095] Following this setup, the COBOT 2504 can be driven to each of a plurality of programmed positions, and the lidar 2500 can automatically measure the turret ball based on the previously obtained nominal values. This enables an automatic and accurate determination of the mirror position for use in sample measurements. In some cases, typically when lower accuracy is sufficient, the repeatability of the robot may be sufficient.

[0096] To adjust mirror measurement and cobot positioning, digital or physical I / O from the cobot is provided with either a direct connection to the measurement PC or a connection via a programmable logic controller (PLC) based on OPC, Profinet, or other standard PLC interfaces. Interface software on the PC can coordinate movement and position signals from the cobot, as well as measurement signals from the lidar. This may involve a separate software platform connected to teach others, or may be part of a single software suitable for controlling both communication with the PLC and the lidar itself.

[0097] By using cobot 2504 and mirror 2506 in combination with the attached tooling ball 2528, faster measurements are possible, measurements with reduced lidar or part repositioning are possible, and the number of required tooling ball measurements is reduced. Multiple mirror positions can be created for a single lidar position, mirror movement can be performed during other measurements of the part, dead measurement time can be shortened, or it can be done simultaneously during repositioning movement. Cobot 2504 does not necessarily require safety fencing or zoning and can therefore be placed close to the part and even moved while the operator is nearby. Automatic cleaning of mirror 2506 can be based on the force feedback of cobot 2504 via a pad or from an air comb or blower to prevent material deposition on the mirror surface.

[0098] Figure 25A shows exemplary tooling balls 2520 - 2523 placed on the measurement object 2508 in addition to the tooling ball 2528 in cobot 2504. Tooling balls 2528 and 2520 - 2523 can be irradiated along their respective axes 2510 and 2511 - 2514 in response to beam scanning from the scanning plane 2501.

[0099] Example 25 The bore site camera / laser radar system enables the acquisition of a target image by stitching together a plurality of images associated with different parts of the target. Each camera image can be associated with the target distance obtained by the laser radar, and any camera tilt can be corrected using features of known shape as described above. In a representative method 2600 shown in FIG. 26, at 2602, a confocal laser radar is set at a fixed position, and at 2604, an image of at least a part of the target is acquired. At 2606, the distance to the target part is measured using the laser radar probe beam. At 2608, the acquired image and the associated distance, azimuth angle, elevation angle, and laser radar position coordinates are stored. At 2610, it is determined whether additional images are intended. If so, the laser radar position is set to 2602 and image acquisition is repeated. The laser radar position can remain fixed at the previous position or at a selected new position. When all the intended images are acquired, at 2612 the images are stitched together to create an image of a larger target area. This image can be used to identify the position of specific target features, provide feature measurements, identify the target area for additional laser radar measurements, or for other purposes. In a typical example, the laser radar is repositioned one or more times to generate an overall view of the target being evaluated.

[0100] In some cases, image stitching results in excellent results after camera / probe beam calibration. For example, in some examples, the camera field of view center is determined based on one or more images that include the image portion corresponding to the position on the target where the probe beam / tracer beam is incident. In another example, an image of a grid pattern can be evaluated to determine the image distortion introduced by the projection lens used by the camera and the probe beam. Such distortion can be corrected or compensated for the stitched images.

[0101] Example 26 Referring to FIG. 27, a representative control and measurement device 2700 for use with a lidar such as a confocal lidar 2704 includes a measurement controller 2706 and an embedded feature processor 2708. One or both of these can be implemented in one or more central processing units, FPGAs, ASICs, or as a system on a chip (SOC). As shown, the feature set 2710 communicated to the measurement controller 2706 includes one or more features, and for each feature, a corresponding scan path requirement is communicated to the feature processor 2708. The scan path is returned, appropriate scanning of the lidar 2704 is performed, and lidar measurement data is returned to the feature processor 2708. Upon receiving satisfactory measurement data, the feature process 2708 communicates to the measurement controller 2706 that the measurement is complete. Similar messaging is performed for each feature of the feature set 2710, and data processing for one or more scan paths can be performed while scanning of one or more other scan paths is being processed. The feature set 2710 can include specifications of various target features such as part dimensions, hole sizes and positions, part shapes, orientations, etc. The scan data returned from the lidar 2704 can include lidar distance data and / or image data obtained with a confocal camera.

[0102] Example 27 In a lidar including a suitable imaging system (such as a high-definition camera), the lidar probe beam can be directed towards the region of interest based on features selected from the target image. Such measurements do not require a target ball. Further, the target design (such as a CAD image) can be overlaid or otherwise displayed in the camera image for component evaluation. The features to be evaluated can be identified from the camera image and the scan paths generated for feature measurement. The lidar can be driven along these scan paths for component evaluation. As described above, the mirror placed on the cobot can be used for measurements that would otherwise be impossible without repositioning the lidar. In some cases, the cobot is controlled based on the selected scan paths. The cobot can be placed in a space that requires strict safety measures for a human operator, thus simplifying the measurement process. In some cases, the position of the lidar or other measurement device can be determined using GPS, gyroscope, and / or accelerometer, and in some cases, such tracking can eliminate the need to use a target ball for alignment.

[0103] In contrast, conventional lidars require placing four target balls on the component for each robot position, and typically require more than 10 robot positions. A lidar that can be aligned without a target ball, as disclosed herein, can enable quick and easy component setup and measurement. Using a camera as described above, and using machine learning, features can be detected, features that appear to be in the wrong position can be identified, and feature parameters can be adjusted without relying on the assumption that the component conforms to the corresponding CAD design.

[0104] Example 28 FIG. 28 shows a representative manufacturing system 2800 suitable for manufacturing one or more components of a ship, an aircraft, or other systems or devices, and evaluating and reprocessing such manufactured components. System 2800 typically includes a shape or profile measurement system 2805 such as the lidar system described above. Manufacturing system 2800 also includes a design system 2810, a shaping system 2820, a controller 2830, and a repair system 2840. Controller 2830 includes a coordinate storage device 2831 configured to store the measurement and design coordinates or other characteristics of one or more manufactured structures that have been designed and / or measured. Coordinate storage device 2831 is generally a computer-readable medium such as a hard disk, random access memory, or other memory device. Typically, design system 2810, shaping system 2820, shape measurement system 2805, and repair system 2840 communicate via communication bus 2815 using network protocols.

[0105] Design system 2810 is configured to create design information corresponding to the shape, coordinates, dimensions, or other characteristics of the structure to be manufactured and transmit the created design information to shaping system 2820. Further, design system 2810 can communicate the design information to coordinate storage device 2831 of controller 2830 for storage. The design information typically includes information indicating the coordinates of some or all of the features of the structure to be generated.

[0106] Shaping system 2820 is configured to generate a structure based on the design information provided by design system 2810. The shaping process provided by shaping system 2820 can include casting, forging, cutting, or other processes. Shape measurement system 2805 is configured to measure the coordinates of one or more features of the manufactured structure and communicate information indicating the measured coordinates or other information associated with the structure shape to controller 2830.

[0107] The manufacturing inspection unit 2832 of the controller 2830 is configured to acquire design information from the coordinate storage unit 2831 and compare the information such as coordinates and other shape information received from the profile measuring device 100 with the design information read from the coordinate storage unit 2831. The manufacturing inspection unit 2832 is generally provided as a processor and a series of computer-executable instructions stored in a tangible computer-readable medium such as a random access memory, a flash drive, a hard disk, or other physical devices. Based on the comparison between the design and the actual structural data, the manufacturing inspection unit 2832 can generally determine whether the manufactured structure is formed according to the design information based on one or more design tolerances that can also be stored in the coordinate storage device 2831. That is, the manufacturing inspection unit 2832 can determine the quality of the manufactured structure. Then, when the structure is not formed according to the design information (defective), the manufacturing inspection unit 2832 determines whether the structure can be repaired. If it can be repaired, the manufacturing inspection unit 2832 can identify the defective part of the manufactured structure and provide appropriate coordinates or other repair data. The manufacturing inspection unit 2832 is configured to generate one or more repair instructions or repair data and transfer the repair instructions and repair data to the repair system 2840. Such repair data can include the location requiring repair, the degree of reshaping required, or other repair data. The repair system 2840 is configured to process the defective part of the manufactured structure based on the repair data.

[0108] Example 29 Figure 29 is a flowchart showing a representative manufacturing method 2900 that can incorporate the manufacturing system as shown in Figure 28. At 2902, design information is obtained or created corresponding to the shape of the structure to be manufactured. At 2904, the structure is manufactured or "formed" based on the design information. At 2906, the coordinates, dimensions, or other features of the manufactured structure are measured using a profile measurement system such as the above-described laser radar system to obtain shape information corresponding to the manufactured structure. At 2908, the manufactured structure is inspected based on a comparison of the actual dimensions with the design dimensions, coordinates, manufacturing tolerances, or other structural parameters. At 2910, if it is determined that the manufactured structure is a good product, the manufactured part is accepted and the process ends at 2914. At 2910, for example, if it is determined by the manufacturing inspection unit 1932 of the controller 1930 as shown in Figure 19 that the manufactured part is defective, at 2912, it can be determined whether the manufactured part can be repaired. If it can be repaired, the manufactured part is reprocessed or repaired at 2916 and then measured, inspected, and re-evaluated at 2906, 2908, and 2910, respectively. If it is determined at 2912 that the manufactured part cannot be repaired, the process ends at 2914.

[0109] According to the method of Figure 29, by using a profile measurement system to accurately measure or evaluate the coordinates or other features of the manufactured structure, the manufactured structure can be evaluated to determine whether the structure is defective. Further, if it is determined that the manufactured structure is defective and the part is considered repairable based on the dimensions and features of the designed and actual structures, a reprocessing process can be started. By repeating the measurement, inspection, and evaluation steps, defective products can be reprocessed or those that cannot be repaired even if they are defective can be discarded. The specific systems and methods of Figures 28 - 29 are merely illustrative and other configurations can be used.

[0110] In the above-described embodiment, the structure manufacturing system 2800 can include a profile measurement system such as the lidar and related optical systems disclosed herein, a design system 2810, a forming system 2829, a controller 2830 (inspection device) configured to determine whether a part is acceptable, and a repair system 2840. However, other systems and methods can be used, and the examples of FIGS. 28 to 29 are provided for simplicity of explanation.

[0111] Example 30 Additional embodiments of the reference assembly for a laser-based measurement system as disclosed above are shown in FIGS. 30A - 30B. Referring to FIG. 30A, a reference arm assembly 3000 includes vacuum-rated fiber feedthroughs 3002 - 3005 typically coupled to an airtight enclosure 3002 filled with exhaust or inert gas. Fiber feedthroughs 3002, 3003, 3004 are typically coupled to a pointing laser 3008, a probe laser 3009, and a reference detector 3010, respectively. Fiber feedthrough 3002 sends a tracer beam to a first coupler 3012. Fiber feedthrough 3003 sends a probe beam to an isolator 3014, which then couples the probe beam to the first coupler 3012. The combined probe / tracer beam is directed from the first coupler 3012 to fiber feedthrough 3005 and then to an optical fiber connector such as an FC / APC connector 3016 for sending to an appropriate scanning, focusing, and detection system as described above. The first coupler 3012 directs a portion of the probe beam from the isolator 3014 to a second coupler 3020 that splits this beam portion into first and second portions that propagate along respective paths 3022A, 3022B. Optionally, a fiber delay extension 3080 can be placed between the fiber feedthrough 3003 and the isolator 3014 to cause reflections from internal components (such as the probe laser) to generate a heterodyne frequency outside of a typical measurement range. Paths 3022A, 3022B typically have a stable fixed path difference provided by including additional fiber length in one of these paths. A third coupler 3024 receives the first and second beam portions from paths 3022A, 3022B, combines these portions, and directs the combined portion to the reference detector 3010 via fiber feedthrough 3004. The fixed path difference enables associating the beat signal between the first and second beam portions with a specific length.

[0112] The enclosure 3002 is typically made of copper and is temperature controlled by a thermoelectric (TEC) module 3083 and control electronics 3084. Outside the enclosure 3002, an insulator (not shown) that surrounds the enclosure 3002 is usually provided to insulate the enclosure 3002 from the ambient environment. The enclosure 3002 has a lid sealed by bolts and O-rings. A tube 3082 can be provided to evacuate or fill the enclosure 3002 with another gas such as nitrogen. The tube 3082 can be placed on the lid of the enclosure and can be made of copper. Such a tube is generally sealed by pinch-off or other means after evacuation or filling of the enclosure 3002. Copper is a convenient material, but other materials can also be used. In some cases, the enclosure is filled with a dry gas.

[0113] Referring to FIG. 30B, a reference arm assembly 3040 for use with a dual probe beam typically includes fiber feedthroughs 3043A - 3043F coupled to an airtight enclosure 3042 filled with an exhaust or inert gas. Fiber feedthroughs 3043A, 3043B, 3043C, 3043D, 3043F are typically coupled to a pointing laser or tracing laser 3048, a first probe laser 3049A, a second probe laser 3049B, a first reference detector 3050A, and a second reference detector 3050B, respectively. Fiber feedthrough 3043A sends a tracer beam to a first coupler 3052, and fiber feedthroughs 3043B - 3043B send probe beams to isolators 3054A - 3054B, which then couple the probe beams to a second coupler 3055. The combined probe beam is directed from the second coupler 3055 towards the first coupler 3052, and the combined probe / tracer beam is directed towards fiber feedthrough 3043F and then towards an optical fiber connector such as an FC / APC connector 3056 for sending to an appropriate scanning, focusing, and detection system. Fiber coupler 3052 includes an unused output 3090 and is terminated at 3070 to reduce or eliminate back reflection.

[0114] The second coupler 3055 directs a portion of the combined probe beams from the isolators 3054A, 3054B and then directs the combined beam portion towards a third coupler 3060 that splits it into a first portion and a second portion that propagate along respective paths 3062A, 3062B. Optionally, the fiber delay stretches 3045A, 3045B can be disposed between the fiber feedthroughs 3043B, 3043C and the isolators 3054A, 3054B. The paths 3062A, 3062B typically have a stable fixed path difference provided by including an additional fiber length 3047 in one of these paths. A third coupler 3064 receives the first and second beam portions from the paths 3062A, 3062B, combines these portions, and directs the combined portion towards respective reference detectors 3050A, 3050B via fiber feedthroughs 3043D, 3043E. The fixed path difference enables associating the beat signal between the first beam portion and the second beam portion with a specific length. In the most practical example, the optical filters 3080A, 3080B are arranged such that the reference detector 3050A receives only the beam portion of the first wavelength provided by the first probe laser 3049A and the reference detector 3050B receives only the beam portion of the second wavelength provided by the second probe laser 3049B. For example, the first and second wavelengths can be about 1550 nm and 1560 nm. The fiber delay stretches 3045A, 3045B may be disposed between the fiber feedthroughs 3043B, 3043C and the isolators 3054A, 3054B, such that reflections from internal components generate a heterodyne frequency that can be outside the typical measurement range. For wavelength separation, instead of the third coupler 3064 and the optical filters 3080A, 3080B, a wavelength demultiplexing coupler may be used.

[0115] In the examples of FIGS. 30A to 30B, the optical fiber used for the probe beam is typically a polarization retaining single mode (PRSM) fiber, and in the case of the tracer beam, a PRSM fiber is not normally used. The length difference used to establish the heterodyne frequency generally uses fibers with lengths of 1 m to 200 m, typically 5, 10, 15, 20, 25, or 50 m.

[0116] Example 31 Referring to FIG. 31, a representative lidar system 3100 with confocal imaging includes a beam splitter 3104 that directs a probe beam and a tracer beam along axis 3101 to a first lens 3106 and then to a waveplate 3108. The waveplate can be used to generate a local oscillator (LO) beam by reflection as described above. The LO beam can also be generated by other methods, and the reflection from the waveplate 3108 is just a convenient example. Then, the probe / tracer beam is directed through a beam splitter such as a cube beam splitter 3110 (or the plate beam splitter or double reflection beam splitter described above) to an objective lens 3112 that includes a fixed lens portion 3116 and a movable (focusing) lens portion 3114. A beam scanner 3120 receives the focused probe / tracer beam and directs the beam at the target. An image sensor 3122 is disposed on axis 3101 such that the lidar provides confocal imaging. A focus controller 3124 is coupled to the image sensor 3122 and provides autofocus of the image from the target by adjusting the movable lens 3114 using a moving stage or other moving mechanism 3126. The return portion of the probe beam is directed to the beam splitter 3104 and then to a detector 3128. The heterodyne or other signal generated at the detector 3128 enables the evaluation of the characteristics of the target surface.

[0117] Auto - focusing by the focus controller and the movement mechanism 3126 enables maintaining the focus of the probe beam when the probe beam scans various target areas. In conventional systems, it may take time to establish the focus of the probe beam on the target. Using a confocal image sensor allows for rapid focus adjustment using the target image generated by the image sensor 3122. Thus, the focus can be established and adjusted, and the probe beam can be directed to any selected portion of the field of view using the image sensor 3122 and the focus controller 3124. A non - transient computer - readable memory or network connection 3130 receives images from the image sensor 312 for the process of identifying features to stitch together images to provide a panoramic image of the target.

[0118] Example 32 Figure 32 is a diagram showing a representative method of tracking a tooling ball (or tracking target features) fixed to a substrate or target. One or more tooling balls can be fixed to the target to provide a reference point for coordinate determination. Tooling balls generally include a reflective ball - shaped surface to provide sufficient reflection of the search beam in a laser - based measuring device such as a lidar.

[0119] As shown in Figure 32, at 3202, based on the return portion of the scanned search light beam, the position of the tooling ball is identified and recorded. The light beam can be scanned in various patterns such as circles, spirals, w - shapes, or zigzags to track the tooling ball. At 3204, the identified position is evaluated to determine the position relative to the primary scan. At 3206, the primary scan is adjusted so that the position of the tooling ball is at a preferred position relative to the primary scan. Typically, the primary scan is adjusted so that the tooling position is approximately at the center within the primary scan range. At 3208, a determination regarding additional scans is made.

[0120] Example 33 Figure 33 and the following description are intended to provide a brief and general description of an exemplary computing environment in which the disclosed technology, including any of the above methods, may be implemented. Although not required, the disclosed technology is described in the general context of computer-executable instructions, such as program modules, being executed by a personal computer (PC). Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Further, the disclosed technology may be implemented in other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, etc. The disclosed technology may also be implemented in a distributed computing environment where tasks are performed by remote processing devices linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.

[0121] Referring to FIG. 33, an exemplary system for implementing the disclosed technology includes a general-purpose computing device in the form of an exemplary conventional PC 3300, which includes one or more processing units 3302, a system memory 3304, and a system bus 3306 that couples various system components including the system memory 3304 to the one or more processing units 3302. The system bus 3306 may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The exemplary system memory 3304 includes a read only memory (ROM) 3308 and a random access memory (RAM) 3310. A basic input / output system (BIOS) 3312, which contains basic routines that help to transfer information between elements within the PC 3300, is stored in the ROM 3308. The memory 3304 also includes portions 3371 - 3373 containing computer-executable instructions and data for shape identification and processing, lidar and cobot control and communication, and acquisition of design data, respectively.

[0122] The exemplary PC 3300 further includes one or more storage devices 3330, such as a hard disk drive for reading from and writing to a hard disk, a magnetic disk drive for reading from or writing to a removable magnetic disk, and an optical disk drive for reading from or writing to a removable optical disk (such as a CD-ROM or other optical medium). Such storage devices can each be connected to the system bus 3306 by a hard disk drive interface, a magnetic disk drive interface, and an optical drive interface. The drives and their associated computer-readable media provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for the PC 3300. Other types of computer-readable media that can store data accessible by a PC, such as magnetic cassettes, flash memory cards, digital video disks, CDs, DVDs, RAM, ROM, etc., can also be used in the exemplary operating environment.

[0123] The plurality of program modules can be stored in a storage device 3330 including an operating system, one or more application programs, other program modules, and program data. A user can input commands and information into the PC 3300 via one or more input devices 3340 such as a keyboard and a pointing device such as a mouse. Other input devices can include a digital camera, a microphone, a joystick, a game pad, a satellite dish, a scanner, and the like. These and other input devices are often connected to one or more processing units 3302 via a serial port interface coupled to the system bus 3306, but may also be connected by other interfaces such as a parallel port, a game port, or a Universal Serial Bus (USB). A monitor 3346 or other type of display device is also connected to the system bus 3306 via an interface such as a video adapter. Other peripheral output devices such as speakers and printers (not shown) may be included.

[0124] The PC 3300 can operate in a network environment using a logical connection to one or more remote computers such as a remote computer 3360. In some examples, one or more networks or communication connections 3350 are included. The remote computer 3360 can be another PC, a server, a router, a network PC, or a peer device or other common network node, and typically includes many or all of the elements described above with respect to the PC 3300, but only the memory storage device 3362 is shown in FIG. 33. The personal computer 3300 and / or the remote computer 3360 can be connected to a logical local area network (LAN) and wide area network (WAN). Such networking environments are common in offices, enterprise-scale computer networks, intranets, and the Internet.

[0125] When used in a LAN networking environment, PC3300 is connected to the LAN via a network interface. When used in a WAN networking environment, PC3300 typically includes a modem or other means for establishing communication via a WAN such as the Internet. In a networked environment, program modules shown with respect to personal computer 3300 or portions thereof can be stored in a remote memory storage device or in other locations on a LAN or WAN. The network connections shown are exemplary, and other means of establishing a communication link between computers may be used.

[0126] It should be recognized that, considering the many possible embodiments to which the principles of the disclosed technology may be applied, the illustrated embodiments are only preferred examples and should not be construed as limiting the scope of the present disclosure.

Claims

1. A dichroic beam splitter, an optical fiber arranged to irradiate a probe beam toward the dichroic beam splitter, an objective lens that receives the probe beam from the dichroic beam splitter and includes a movable lens movable along the axis so as to irradiate the target along the axis with the probe beam, an image sensor arranged on the axis branched from the axis by the dichroic beam splitter and receiving, via the dichroic beam splitter, an imaging beam that is reflected by the target and forms an image of the target, and the movable lens is movable so as to focus the imaging beam on the image sensor and to focus the probe beam on the target. An apparatus.

2. The objective lens includes a fixed lens arranged to irradiate the target with the probe beam along the axis, and the movable lens is movable along the axis with respect to the fixed lens. The apparatus according to claim 1.

3. The optical fiber irradiates, together with the probe beam, a tracer beam having a wavelength different from that of the probe beam toward the dichroic beam splitter. The apparatus according to claim 1 or 2.

4. The objective lens receives a tracer beam from the dichroic beam splitter and is arranged to direct the probe beam and the tracer beam toward the target, the probe beam has a wavelength of 1200 nm to 1800 nm, and the tracer beam has a wavelength of 400 nm to 700 nm. The apparatus according to any one of claims 1 to 3.

5. The dichroic beam splitter is arranged such that the probe beam is reflected by the dichroic beam splitter to the movable lens and the imaging beam is transmitted by the dichroic beam splitter to the image sensor. The apparatus according to any one of claims 1, 2 or 4.

6. The dichroic beam splitter is a cube dichroic beam splitter, a plate dichroic beam splitter, or a double reflection dichroic beam splitter. The apparatus according to any one of claims 1, 2 or 5.

7. The dichroic beam splitter is a dual-reflection dichroic beam splitter including a first surface facing the movable lens, and a dichroic reflection surface arranged to direct the imaging beam toward the image sensor and a part of the probe beam returned from the target toward the optical fiber, according to the device of any one of claims 1 to 5.

8. The dichroic beam splitter is a dual-reflection dichroic beam splitter including a first surface facing the movable lens, and a dichroic reflection surface arranged to direct the imaging beam toward the first surface such that the imaging beam is reflected by the first surface toward the image sensor, A part of the probe beam returned from the target to the optical fiber is sent to the optical fiber by the reflection surface, according to the device of any one of claims 1 to 5.

9. The dichroic beam splitter is a dual-reflection dichroic beam splitter including a first surface facing the movable lens, and a dichroic reflection surface arranged to direct a part of the probe beam returned from the target toward the first surface, The imaging beam is sent to the image sensor by the dichroic reflection surface, according to the device of any one of claims 1 to 5.

10. The first surface is arranged at an angle greater than the critical angle with respect to the imaging beam received from the dichroic reflection surface, according to the device of any one of claims 7 to 9.

11. The dual-reflection dichroic beam splitter includes an output surface, and the output surface is arranged such that a part of the probe beam returned from the target and reflected by the dichroic reflection surface toward the first surface is reflected and normally incident on the output surface, according to the device of any one of claims 7 to 10.

12. The dual-reflection dichroic beam splitter includes an output surface, and the output surface is arranged such that the imaging beam returned from the target and reflected by the dichroic reflection surface toward the first surface is reflected and normally incident on the output surface, according to the device of any one of claims 7 to 11.

13. The dichroic beam splitter includes a first prism having a vertex angle between the first surface and the dichroic reflective surface. The apex angle is greater than sin －１ (1 / n), where n is the refractive index of the first prism, the apparatus according to any one of claims 7 to 12.

14. The device according to claim 13, wherein the dichroic reflective surface of the dichroic beam splitter is defined on the surface of the first prism.

15. The device according to claim 13, wherein the dichroic beam splitter includes a first prism and a second prism fixed to each other at their mating surfaces, and the dichroic reflective surface is disposed on the mating surface.

16. The device according to claim 15, wherein the dichroic reflective surface is defined on at least one of the mating surfaces.

17. The device according to any one of claims 1 to 5, wherein the dichroic beam splitter includes a dichroic plate and a plane reflector, and the dichroic plate is arranged to direct a part of the probe beam returned from the target towards the plane reflector and send the imaging beam to the image sensor.

18. The device according to any one of claims 1 to 5, wherein the dichroic beam splitter includes a dichroic plate and a plane reflector, and the dichroic plate is arranged to reflect the imaging beam to the plane reflector and send a part of the probe beam returned from the target.

19. The device according to any one of claims 1 to 18, wherein the optical fiber is a polarization-maintaining single-mode (PRSM) optical fiber and further includes a polarization beam splitter (PBS), and the PBS is arranged such that the probe beam from the PRSM optical fiber is received in a polarization state substantially sent to the dichroic beam splitter by the PBS.

20. The device according to claim 19, wherein the polarization state is a linearly polarized state.

21. The device according to claim 19 or 20, further comprising a wave plate disposed between the PBS and the dichroic beam splitter to generate a circular polarization state in the probe beam and reflect a part of the probe beam towards the optical fiber to generate a local oscillator beam.

22. The wavelength plate has an input surface arranged to receive the probe beam from the PBS, and an output surface arranged to receive the probe beam from the input surface of the wavelength plate. One of the input surface or the output surface is anti-reflection coated, and the other of the input surface and the output surface reflects a part of the probe beam as the local oscillator beam. The device according to claim 21.

23. The apparatus further comprises a hybrid lens arranged to receive the probe beam and the tracer beam from the optical fiber, and a dichroic filter arranged along the axis of the axial direction portion of the hybrid lens. The dichroic filter transmits the probe beam and does not transmit the tracer beam. The device according to claim 3.

24. The apparatus further comprises a dichroic reflector arranged along the axis of the axial direction portion of the hybrid lens. The dichroic filter is a dichroic reflector that transmits the probe beam and reflects the tracer beam. The device according to claim 23.

25. The dichroic filter is a wavelength-dependent polarizer that substantially does not transmit the tracer beam. The device according to claim 23.

26. The apparatus further comprises a dichroic reflector arranged along the axis of the axial direction portion of the hybrid lens. The dichroic reflector transmits the probe beam and reflects the tracer beam. The dimensions of the dichroic reflector are based on the corresponding dimensions of the image sensor. The device according to claim 23.

27. A hybrid lens arranged to receive the probe beam and focus the probe beam. The apparatus includes a dichroic reflector arranged along the axis of the axial direction portion of the hybrid lens, which transmits the probe beam and reflects the tracer beam. The dimensions of the dichroic reflector are based on the corresponding dimensions of the image sensor. The device according to claim 23.

28. The dimensions of the dichroic reflector are at least 0.5, 0.75, 1.0, or 1.5 times the product of the corresponding dimensions of the image sensor and the ratio of the optical distance along the axis from the focus of the hybrid lens to the dichroic reflector to the optical distance from the focus of the hybrid lens to the image sensor. The device according to any one of claims 24, 26, and 27.

29. The device according to claim 23, wherein the dichroic filter is disposed on the lens surface of the movable lens.

30. An apparatus for measuring the distance to the target with the probe beam returned from the target, using the apparatus according to any one of claims 1 to 29.

31. A design process for generating design information regarding the shape of a structure, A molding process for creating the structure based on the design information, A measurement process for measuring the shape of the fabricated structure using the apparatus according to claim 30, An inspection process for comparing the shape information obtained in the measurement process with the design information, and a method for manufacturing a structure having the same.

32. The method for manufacturing a structure according to claim 31, further comprising a repair process that is executed based on the comparison result of the inspection process and performs reprocessing of the structure.

33. The method for manufacturing a structure according to claim 32, wherein the repair process is a process of re-executing the molding process.

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