Itof real-time self-calibration ranging device with built-in calibration optical fiber and ranging method thereof

Abstract

This invention discloses an iToF real-time self-calibration ranging device and method with built-in calibration fibers. The device includes a modulation light source, an imaging lens, a resonant cavity with a built-in electro-optic crystal, a CMOS image sensor, multiple calibration fibers with different and known optical paths, and a processing unit. A portion of the modulated light emitted by the modulation light source is used to illuminate the target object, while the other portion is transmitted via the calibration fibers to the central image plane of the imaging lens, and then, after passing through the resonant cavity, forms a preset calibration area on the CMOS image sensor. The processing unit corrects the measured distance of the target object based on the calibration phase of the preset calibration area and pre-stored reference information. This scheme can form multiple built-in fixed optical path references during the ranging process, correct system drift in real time, reduce the need for offline calibration, and improve ranging stability.

Description

Technical Field

[0001] This invention relates to the field of optical ranging and three-dimensional imaging technology, and more specifically, to an iToF real-time self-calibration ranging device with built-in calibration fiber and its ranging method. Background Technology

[0002] Indirect Time of Flight (iToF) ranging technology calculates the distance to a target object by emitting modulated light towards it and receiving the modulated light reflected back from the target object, based on the phase difference between the emitted and reflected light. Because iToF technology can acquire depth information from multiple points in a scene, it is widely used in industrial inspection, robot obstacle avoidance, vehicle sensing, augmented reality, and human-computer interaction.

[0003] Traditional continuous-wave iToF systems typically employ dedicated phase-demodulated image sensors. For example, sensor pixels using a current-assisted photonic demodulator structure can integrate photogenerated charges at different phase states through multiple sets of transmission gates and integrating capacitors, thereby achieving phase calculation. Such dedicated phase sensors are complex in structure and generally cannot be used directly as ordinary imaging sensors.

[0004] Another type of iToF system uses a conventional CMOS image sensor in conjunction with a resonant cavity containing an embedded electro-optic crystal to achieve phase measurement. In this type of system, a modulated light source emits light modulated at a preset frequency toward the target object. The reflected light from the target object passes through an imaging lens and enters the resonant cavity, where it demodulates the incident light. This allows the CMOS image sensor to acquire light intensity signals under different modulation states to obtain information for phase calculation. Since conventional CMOS image sensors themselves have imaging capabilities, this approach is advantageous for simultaneously acquiring image and depth information of the target scene.

[0005] However, in the iToF system combining the resonant cavity and CMOS image sensor described above, the modulation frequency of the modulation light source, the modulation delay of the electro-optic crystal in the resonant cavity, and the system circuit delay can all drift with changes in temperature, humidity, device aging, or operating conditions. The phase-distance calibration relationship established at the factory may become invalid after environmental changes, resulting in systematic depth shifts in multiple pixels and potentially nonlinear errors at different distances. To ensure ranging accuracy, offline recalibration is usually required, increasing production, maintenance, and field usage costs.

[0006] In existing solutions, one iToF camera obtains the error of a single reference optical path through a second light source, a light guide structure, and a reference photosensitive unit, and corrects the target distance based on this error. Another fiber optic calibration device uses multiple optical fibers of different lengths to form multiple calibration distances and fits the error curve based on the theoretical optical path and the actual flight distance. The former does not disclose setting multiple built-in optical path references in the iToF system composed of a resonant cavity and a conventional CMOS sensor, while the latter's calibration optical path is relatively independent, and it also does not disclose injecting calibration light at the central image plane of the imaging lens and directing the calibration light through the resonant cavity to the same CMOS image sensor.

[0007] Therefore, how to set up a stable built-in multi-distance reference in an iToF ranging device based on a resonant cavity and a CMOS image sensor, so that the calibration light can reflect the drift of the light source and the resonant cavity in real time during the operation of the device, and at the same time solve the problem of stable arrangement of multiple optical fibers in a compact imaging optical path, is a technical problem that needs to be solved in this field. Summary of the Invention

[0008] (a) The technical problem to be solved by the present invention How to provide an iToF real-time self-calibration ranging device and method with built-in calibration fiber, so as to form multiple built-in fixed optical path references in the iToF ranging system based on resonant cavity and CMOS image sensor, so that the calibration light and the target ranging light are from the same source and share at least the resonant cavity and CMOS image sensor receiving link, thereby correcting the depth measurement error caused by system drift in real time during the operation of the device, and reducing the dependence on external calibration equipment and offline calibration process.

[0009] (II) The technical solution adopted in this invention To achieve the above objectives, this application provides an iToF real-time self-calibration ranging device with built-in calibration fibers, including a modulation light source, an imaging lens, a resonant cavity with a built-in electro-optic crystal, a CMOS image sensor, multiple calibration fibers, and a processing unit. The modulation light source emits light modulated at a preset frequency. A first part of the light modulated at the preset frequency is used to illuminate the target object, and a second part is coupled into each calibration fiber. The imaging lens receives the first part reflected by the target object and forms an intermediate image plane. The resonant cavity is disposed in the imaging optical path between the intermediate image plane and the CMOS image sensor, and is used to perform electro-optic demodulation on the light transmitted to the CMOS image sensor via the intermediate image plane, so as to make the CMOS image sensor more accurate. The sensor outputs a light intensity signal for phase calculation; the optical path lengths of each calibration fiber are different and known. The input end of each calibration fiber is fixed at the modulation light source, and the output end of each calibration fiber is located at the intermediate image plane. The second part transmitted through each calibration fiber enters the resonant cavity from the intermediate image plane and forms a preset calibration area on the CMOS image sensor corresponding to each calibration fiber. The processing unit is used to obtain multiple calibration phases based on the light intensity signal output from the preset calibration area during the ranging process, obtain the measurement phase of the target object based on the light intensity signal output from the imaging area, and correct the target distance determined by the measurement phase based on the multiple calibration phases and the pre-stored reference information corresponding to each calibration fiber.

[0010] In some embodiments, the modulation light source is a vertical-cavity surface-emitting laser (VCSEL); the input end of the calibration fiber can be a flat-cut end face, with the axis of the calibration fiber at the input end perpendicular to the emitting surface of the VCSEL; or it can be a beveled end face at a 45° angle relative to the axis of the calibration fiber, with the axis of the calibration fiber at the input end parallel to the emitting surface of the VCSEL. Both of these input end structures are used to stably couple a portion of the modulation light emitted from the modulation light source into the calibration fiber.

[0011] In some embodiments, four calibration fibers are used, and four preset calibration areas are located at the edge regions of the CMOS image sensor and outside the effective display area of ​​the final output image. By setting four different optical path references, four sets of phase correction information can be obtained, while reducing the impact of the calibration spot on the effective display area.

[0012] In some embodiments, the light-emitting part of the calibration fiber is provided with a tapered light guide. The tapered light guide is used to adjust the divergence angle of the calibration light emitted from the light-emitting part, so that the divergence angle of the calibration light matches the divergence angle of the imaging beam reflected by the target object at the intermediate image plane, thereby improving the stability of the calibration light entering the subsequent imaging optical path and making the spot shape in the preset calibration area more stable.

[0013] In some embodiments, the calibration fiber is wound around an optical fiber axis, and the light-emitting part includes a light-emitting hole formed in the sidewall of the calibration fiber. The light-emitting hole faces the field stop of the imaging lens, and the light-emitting position of the light-emitting hole is aligned with the central image plane. This arrangement can utilize the space around the lens to house the calibration fiber, and the light-emitting position is aligned with the central image plane through lateral light emission, making it suitable for structures with limited internal installation space in the lens.

[0014] In some embodiments, the pre-stored reference information includes the equivalent object distance and reference phase corresponding to each calibration fiber; the equivalent object distance is determined based on the correspondence between the calibration phase of the corresponding calibration fiber collected during the factory calibration stage and the measurement phase of the known object distance target.

[0015] In some embodiments, the processing unit calculates the phase deviation between each currently obtained calibration phase and the corresponding reference phase, and constructs a phase-distance correction relationship based on the equivalent object distance of each calibration fiber and the corresponding phase deviation; the processing unit is also used to correct the target distance using the phase-distance correction relationship.

[0016] This application also provides a ranging method for an iToF real-time self-calibrating ranging device with built-in calibration fibers. The method includes: controlling a modulated light source to emit light modulated at a preset frequency, such that a first part illuminates a target object, and a second part couples into multiple known calibration fibers with different optical path lengths; causing the first part, reflected by the target object, to pass through an imaging lens and then through an intermediate image plane and a resonant cavity to reach a CMOS image sensor; causing the second part, transmitted through each calibration fiber, to enter the resonant cavity from the intermediate image plane and form a corresponding preset calibration area on the CMOS image sensor; within the same ranging cycle, obtaining multiple calibration phases based on the light intensity signal output from the preset calibration area, and obtaining the measurement phase of the target object based on the light intensity signal output from the imaging area; and correcting the target distance determined by the measurement phase based on the multiple calibration phases and pre-stored reference information corresponding to each calibration fiber.

[0017] In some embodiments, before ranging, factory calibration is performed: the initial calibration phase corresponding to each calibration fiber is collected; the measurement phase corresponding to multiple known object distance targets is collected; the equivalent object distance and reference phase corresponding to each calibration fiber are determined according to the correspondence between the initial calibration phase and the measurement phase of the known object distance targets; and the equivalent object distance and reference phase of each calibration fiber are stored.

[0018] In some embodiments, correcting the target distance based on the multiple calibration phases and pre-stored reference information corresponding to each calibration fiber includes: calculating the phase deviation between each currently obtained calibration phase and the corresponding pre-stored reference phase; generating a phase-distance correction relationship based on the equivalent object distance of each calibration fiber and the corresponding phase deviation; determining the distance to be corrected based on the measured phase, and determining the correction amount corresponding to the distance to be corrected using the phase-distance correction relationship; and correcting the distance to be corrected using the correction amount to obtain the target distance. The phase-distance correction relationship can be updated in real time during continuous ranging, can be updated according to a preset period, or can be updated when a change in environmental conditions is detected.

[0019] (III) Beneficial Effects (1) The calibration light and the target ranging light come from the same modulation source. The calibration result can reflect the modulation state change of the modulation source itself. The calibration light enters the resonant cavity from the intermediate image plane and reaches the same CMOS image sensor. It can reflect the delay change of the resonant cavity and subsequent receiving link.

[0020] (2) Multiple calibration optical fibers have different and known optical paths, which can form multiple fixed distance references inside the ranging device. This can not only correct the uniform system offset, but also correct the phase deviation or nonlinear error at different distances.

[0021] (3) The light output part of the calibration fiber is set at the middle image plane of the imaging lens, which can inject calibration light into the imaging optical path without significantly increasing the external calibration equipment, which is beneficial to the miniaturization and internalization of the ranging device.

[0022] (4) The preset calibration area can be set in the edge area of ​​the CMOS image sensor and outside the effective display area, thereby reducing the impact of the calibration spot on the final image and depth output.

[0023] (5) The tapered light guide can match the divergence angle of the calibration light with the divergence angle of the imaging beam at the middle image plane, thereby improving the position and intensity stability of the calibration spot; the fiber optic axis and side light outlet structure can utilize the space around the lens to arrange a longer calibration fiber, thus solving the problem of installing multiple fibers in a compact lens structure. Attached Figure Description

[0024] Figure 1 This is an overall structural diagram of an iToF real-time self-calibrating ranging device with built-in calibration fiber according to one or more embodiments.

[0025] Figure 2 for Figure 1 A magnified schematic diagram of a local structure.

[0026] Figure 3This is a distribution diagram of a preset calibration region on a CMOS image sensor according to one or more embodiments. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Before describing the various embodiments of this application in detail, the technical concept of this application is first briefly described: In an iToF ranging system using a resonant cavity with a built-in electro-optic crystal and a common CMOS image sensor, the system no longer relies on an external calibration plate or independent calibration device. Instead, a portion of the modulation light is extracted from the same modulation light source and passed through multiple known calibration fibers with different optical paths. This light is then re-injected into the imaging optical path at the central image plane of the imaging lens. The injected calibration light and the target reflected light pass through the resonant cavity together and reach the same CMOS image sensor, forming a stable calibration spot in the preset calibration area of ​​the CMOS image sensor. Since each calibration fiber corresponds to a different equivalent object distance, the processing unit can correct the correspondence between phase and distance in real time according to the phase change of each preset calibration area, thereby achieving online correction of system drift. The specific principle of the iToF real-time self-calibration ranging device with built-in calibration fibers of this application will be described below with reference to more embodiments.

[0029] In this article, "calibration fiber" refers to the optical fiber fixed inside the ranging device and used to provide a known optical path reference; "inlet end" is the end of the calibration fiber that receives the light emitted from the modulated light source; "outlet section" is the part of the calibration fiber that allows the calibration light to leave the fiber and enter the imaging optical path. The outlet section can be the end face of the fiber or an outlet hole opened on the side wall of the fiber; "equivalent object distance" is the virtual target distance corresponding to the calibration fiber in the factory calibration relationship, rather than the physical length of the fiber itself.

[0030] Specifically, such as Figure 1 As shown, the iToF real-time self-calibration ranging device with built-in calibration fiber in this embodiment includes a modulation light source 10, an optical fiber fixing component 20, multiple calibration optical fibers 30, an imaging lens 40, a resonant cavity 50, a CMOS image sensor 60, and a processing unit (not shown). The modulation light source 10 is preferably a vertical-cavity surface-emitting laser (VCSEL). The processing unit is connected to the modulation light source 10, the resonant cavity 50, and the CMOS image sensor 60, respectively, and is used to control the modulation emission, control the electro-optic modulation state of the resonant cavity 50, read the light intensity signal output by the CMOS image sensor 60, and perform phase calculation and distance correction.

[0031] The light emitted by the modulation light source 10, modulated at a preset frequency, comprises a first part and a second part. The first part illuminates the target object; the second part is received by the light-incident end of the calibration fiber and transmitted within the calibration fiber. Fiber optic fixing components are disposed near the modulation light source to fix the light-incident ends of each calibration fiber, ensuring that the position of each light-incident end relative to the modulation light source remains stable.

[0032] The imaging lens 40 receives the first portion reflected from the target object and forms an intermediate image plane 41 inside the imaging lens 40. The resonant cavity 50 is located on the image side of the intermediate image plane 41, and the CMOS image sensor 60 is located on the image side of the resonant cavity. The target reflected light passes through the intermediate image plane and the resonant cavity to form a target image on the CMOS image sensor 60.

[0033] For example, both the imaging optical path L1 and the fiber optic correction optical path L2 reach the CMOS image sensor 60. S1 represents the central field of view, and S2 represents the edge field of view. The imaging lens 40 can image objects within the range from the central field of view S1 to the edge field of view S2.

[0034] For example, the light-emitting section of each calibration fiber 30 is located at the intermediate image plane. After the calibration light is emitted from the light-emitting section, it enters the image-side optical path of the intermediate image plane, is transmitted to the CMOS image sensor via the resonant cavity, and forms a preset calibration area on the CMOS image sensor that corresponds one-to-one with each calibration fiber. Since the calibration light is injected from the intermediate image plane, the calibration light can pass through the resonant cavity and the CMOS image sensor receiving link together with the target reflected light.

[0035] For example, the optical path lengths of each calibration fiber 30 are different. The optical path length can be determined by the physical length of the fiber, the effective refractive index of the fiber material, and the coupling paths at both ends of the fiber. Since the positions of each calibration fiber 30 within the device are relatively fixed, the optical path length corresponding to each calibration fiber 30 remains relatively stable during the operation of the device.

[0036] For example, the CMOS image sensor includes an imaging region and a preset calibration region. The imaging region is used to receive light reflected from the target object and output a light intensity signal for calculating the phase of the target object; the preset calibration region is used to receive calibration light emitted from a corresponding calibration fiber and output a light intensity signal for calculating the calibration phase. Preferably, the preset calibration region is located in the edge region of the CMOS image sensor and outside the effective display area of ​​the final output image.

[0037] In one embodiment, the resonant cavity and CMOS phase calculation are as follows: An electro-optic crystal is disposed within the resonant cavity. The processing unit controls the operating state of the resonant cavity according to a preset modulation sequence, so that the target reflected light and calibration light passing through the resonant cavity form corresponding light intensity signals on the CMOS image sensor. The processing unit calculates the measurement phase or calibration phase of the corresponding pixel based on the light intensity signals collected under multiple modulation states. Since both the target reflected light and the calibration light pass through the resonant cavity, the modulation delay change of the resonant cavity will be reflected in both the measurement phase and the calibration phase simultaneously. Detailed phase calculation methods can be employed using methods well-known to those skilled in the art, and will not be elaborated here.

[0038] The processing unit obtains the initial distance to the target object based on the measured phase of each pixel in the imaging region, and corrects the initial distance based on the calibration phase in the preset calibration region. The imaging region and the preset calibration region can use the same phase calculation method to reduce system differences caused by different calculation methods.

[0039] In some embodiments, the processing unit performs averaging, weighted averaging, or central region statistics on multiple pixel signals within a preset calibration area to obtain the calibration phase corresponding to the preset calibration area. This processing method can reduce the impact of individual pixel noise on the calibration phase.

[0040] The optical fiber input end structure can adopt the following two structures.

[0041] In one embodiment, the input end of the calibration fiber is a flat-cut end face. The fiber fixing device makes the axis of the calibration fiber at the input end perpendicular to the emitting surface of the VCSEL, so that a portion of the modulated light emitted from the VCSEL directly enters the calibration fiber.

[0042] In another embodiment, the input end of the calibration fiber is a 45° beveled end face relative to the axis of the calibration fiber. The fiber fixing component ensures that the axis of the calibration fiber at the input end is parallel to the emitting surface of the VCSEL. The beveled end face is used to change the coupling direction of the incident light, allowing the modulated light to couple into the calibration fiber. This structure facilitates the placement of the calibration fiber to the side of the VCSEL emitting surface, reducing obstruction of the target illumination optical path at the input end.

[0043] Each calibration fiber can sample from the output light of the same VCSEL, or they can be centrally mounted at the front end of the VCSEL using the same fiber optic fastener. Regardless of the arrangement, the calibration light and the modulation light used to illuminate the target object should both originate from the same modulation source, so that the calibration phase can reflect changes in the modulation state of the modulation source.

[0044] In one embodiment, the structural positional relationship between the light-emitting part and the intermediate image plane is as follows.

[0045] like Figure 2As shown, the light-emitting section of the calibration fiber is located at the intermediate image plane formed by the imaging lens. The calibration light emitted from the light-emitting section does not pass through the target object for reflection, but directly enters the image-side optical path of the intermediate image plane. Since the intermediate image plane is located upstream of the resonant cavity, the calibration light emitted from the light-emitting section can still pass through the resonant cavity and reach the CMOS image sensor.

[0046] The light-emitting section of each calibration fiber corresponds to a preset calibration area on the CMOS image sensor at the intermediate image plane. These preset calibration areas can be arranged along the edge of the CMOS image sensor. For example, when there are four calibration fibers, the four preset calibration areas can be located outside the effective display area of ​​the final output image, thereby reducing the impact of calibration light spots on the effective image display while retaining the calibration function.

[0047] In some embodiments, the emitting portion of the calibration fiber is provided with a tapered light guide. The tapered light guide is connected to the emitting portion of the calibration fiber and is located near the intermediate image plane. The tapered light guide matches the divergence angle of the emitted calibration light with the divergence angle of the imaging beam of the target reflected light at the intermediate image plane, thereby enabling the calibration light to stably enter the image-side optical path of the intermediate image plane and form a relatively stable spot in size and position on the CMOS image sensor.

[0048] The tapered light guide can also increase the assembly tolerance between the light-emitting part and subsequent optical structures. When there is a slight deviation in the position of the fiber end face, the tapered light guide can reduce the positional offset of the calibration spot on the CMOS image sensor, which is beneficial to improving the stability of the preset calibration area.

[0049] In other embodiments, the improved structure for side-emitting light is as follows.

[0050] The calibration fiber is wound around a fiber optic axis. The fiber optic axis is positioned above or around the imaging lens to accommodate longer calibration fibers. After the calibration fiber is wound, a side light-emitting aperture is provided at a position facing the field stop of the imaging lens. The side light-emitting aperture constitutes the light-emitting part of the calibration fiber.

[0051] The calibration light exits from the side aperture and enters the field stop of the imaging lens, then enters the image-side optical path of the central image plane at a position aligned with the central image plane. Since the calibration fiber can be wound around the fiber optic axis, this structure allows for the arrangement of a longer fiber within a limited lens space and reduces the impact on the imaging optical path caused by the fiber end face directly extending into the lens.

[0052] The side light exit aperture can be formed by laser processing. By controlling the position and orientation of the side light exit aperture, the emission direction of the calibration light can be directed toward the field stop, and the calibration light can ultimately be imaged in a preset calibration area on the CMOS image sensor.

[0053] In one embodiment, the factory calibration process is as follows.

[0054] Before the device leaves the factory, the modulation light source is first controlled to emit light modulated by a preset frequency, so that the calibration light passes through each calibration fiber and forms a corresponding calibration spot on the CMOS image sensor. The processing unit obtains the initial calibration phase corresponding to each preset calibration area.

[0055] Simultaneously or sequentially, a target with a known object distance is placed in the measurement field of view of the ranging device. A modulated light source is controlled to illuminate the target with the known object distance, and the corresponding measurement phase is obtained based on the reflected light from the target. The above process is repeated for multiple targets with known object distances to obtain the correspondence between the target object distance and the measurement phase at the factory stage.

[0056] The processing unit maps the initial calibration phase of each calibration fiber to the measurement phase of multiple targets with known object distances, determining the equivalent object distance corresponding to each initial calibration phase. Thus, each calibration fiber corresponds to an equivalent object distance and a reference phase. The processing unit stores the equivalent object distance and reference phase of each calibration fiber as pre-stored reference information.

[0057] For example, the wavelength of the modulated light source 10 is The refractive index of the optical fiber is If the physical length of the calibration fiber is L1, then the equivalent object distance of the calibration fiber is... The method for calculating object distance using phase can be found in methods well-known to those skilled in the art, and will not be elaborated upon here.

[0058] Using factory calibration to determine the equivalent object distance, instead of calculating the equivalent object distance solely based on the physical length of the optical fiber, allows the fiber end-face coupling path, the refractive index of the fiber material, and the common optical path factors between the light-emitting part and the CMOS image sensor to be incorporated into the factory correspondence, thereby improving the accuracy of the pre-stored reference information.

[0059] In one embodiment, during ranging, the modulated light source 10 continuously or periodically emits light modulated at a preset frequency. The target reflected light passes through the imaging lens 40, the intermediate image plane, and the resonant cavity 50 to reach the imaging area of ​​the CMOS image sensor 60; the calibration light passes through the corresponding calibration fiber and enters the resonant cavity 50 from the intermediate image plane, reaching the corresponding preset calibration area.

[0060] The processing unit reads the light intensity signal of the imaging area and the light intensity signal of the preset calibration area within the same ranging cycle, and obtains the measurement phase of the target object and the current calibration phase corresponding to each calibration fiber. The processing unit calculates the phase deviation between the current calibration phase and the reference phase stored at the factory.

[0061] Since each calibration fiber corresponds to a known equivalent object distance, the processing unit can obtain multiple sets of corresponding data between the equivalent object distance and the phase deviation. Based on these multiple sets of corresponding data, the processing unit generates the current phase-distance correction relationship. This correction relationship can be achieved using piecewise interpolation, curve fitting, lookup tables, or other equivalent methods.

[0062] For any pixel in the imaging region, the processing unit determines the distance to be corrected based on the measured phase of that pixel, then determines the correction amount corresponding to that distance based on the current phase-distance correction relationship, and uses the correction amount to correct the distance to be corrected. By using the phase deviations corresponding to multiple equivalent object distances, the processing unit can not only correct the uniform distance offset across the entire image, but also correct the nonlinear error that varies with distance.

[0063] In some embodiments, the phase-distance correction relationship can be updated once per ranging cycle to achieve continuous tracking of system drift; it can also be updated once every preset ranging cycle to reduce computational load; or it can be updated when a change in ambient temperature is detected, the device is restarted, or the ranging error exceeds a preset threshold. All of the above update methods enable the device to perform self-calibration during operation without returning it to the calibration environment.

[0064] In one embodiment, the ranging and calibration processes are coordinated as follows.

[0065] The calibration light and the target reflected light can arrive at the CMOS image sensor simultaneously. Since the preset calibration area is separated from the effective display area of ​​the final output image, the processing unit can read the data of the imaging area and the preset calibration area separately in the same frame or the same ranging cycle, thereby obtaining the calibration phase without interrupting the target ranging.

[0066] In some embodiments, the processing unit may shield the preset calibration area when outputting the target image or depth map, or may not output the preset calibration area as a valid ranging pixel, thereby preventing the calibration spot from being mistaken for an actual measurement point on the target object.

[0067] In this embodiment, the calibration fiber does not provide a single global offset, but rather multiple fixed optical path references corresponding to different equivalent object distances. Compared to a single reference optical path, multiple fixed optical path references can reflect phase deviation changes at different distances, and are therefore more suitable for correcting nonlinear drift in the phase-distance relationship.

[0068] Compared to schemes using independent calibration light sources and independent reference detectors, the calibration light in this embodiment is taken from the same modulation light source and passes through the same resonant cavity and the same CMOS image sensor, which can more fully cover the drift factors jointly generated by the modulation light source, resonant cavity, and receiving link. Compared to relatively independent external fiber optic calibration devices, this embodiment fixes the calibration fiber inside the ranging device and injects the calibration light from the intermediate image plane into the imaging optical path, thus enabling real-time self-calibration during field operation.

[0069] The specific embodiments of the present invention have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that modifications and improvements can be made to these embodiments without departing from the principles and spirit of the present invention as defined by the claims and their equivalents, and such modifications and improvements should also be within the protection scope of the present invention.

Claims

1. A real-time self-calibrating ranging device for iToF with built-in calibration fiber, characterized in that, The iToF real-time self-calibration ranging device includes a modulation light source, an imaging lens, a resonant cavity with a built-in electro-optic crystal, a CMOS image sensor, multiple calibration optical fibers, and a processing unit. The modulated light source is used to emit light modulated by a preset frequency. The first part of the light modulated by the preset frequency is used to illuminate the target object, and the second part of the light modulated by the preset frequency is coupled into each of the calibration optical fibers. The imaging lens is used to receive the first portion reflected by the target object and form an intermediate image plane; The resonant cavity is disposed in the imaging optical path between the intermediate image plane and the CMOS image sensor, and is used to demodulate the light transmitted to the CMOS image sensor through the intermediate image plane, so that the CMOS image sensor outputs a light intensity signal for calculating the phase. The optical path lengths of each calibration fiber are different and known. The light-inlet end of each calibration fiber is fixedly disposed at the modulation light source, and the light-outlet part of each calibration fiber is disposed at the intermediate image plane, so that the second part transmitted through each calibration fiber enters the resonant cavity from the intermediate image plane and forms a preset calibration area on the CMOS image sensor corresponding to each calibration fiber. The processing unit is used to obtain multiple calibration phases based on the light intensity signal output by the CMOS image sensor in the preset calibration area during the ranging process, obtain the measurement phase of the target object based on the light intensity signal output by the CMOS image sensor in the imaging area, and correct the target distance determined by the measurement phase based on the multiple calibration phases and the pre-stored reference information corresponding to each calibration fiber.

2. The iToF real-time self-calibration ranging device with built-in calibration fiber as described in claim 1, characterized in that, The modulation light source is a vertical cavity surface-emitting laser; The input end of the calibration fiber is a flat-cut end face, and the axis of the calibration fiber at the input end is perpendicular to the emitting surface of the vertical cavity surface-emitting laser; or... The light-inlet end of the calibration fiber is a 45° beveled end face relative to the axis of the calibration fiber, and the axis of the calibration fiber at the light-inlet end is parallel to the light-emitting surface of the vertical cavity surface-emitting laser.

3. The iToF real-time self-calibration ranging device with built-in calibration fiber as described in claim 1, characterized in that, The calibration optical fibers consist of four fibers; the four preset calibration areas are located at the edge regions of the CMOS image sensor and outside the effective display area of ​​the final output image.

4. The iToF real-time self-calibration ranging device with built-in calibration fiber as described in claim 1, characterized in that, The emitting section of the calibration fiber is provided with a tapered light guide; the tapered light guide is used to adjust the divergence angle of the calibration light emitted from the emitting section, so that the divergence angle of the calibration light matches the divergence angle of the imaging beam reflected by the target object at the intermediate image plane.

5. The iToF real-time self-calibration ranging device with built-in calibration fiber according to claim 1, characterized in that, The calibration fiber is wound on the fiber optic axis; the light-emitting part includes a light-emitting hole opened on the side wall of the calibration fiber, the light-emitting hole facing the field stop of the imaging lens, and the light-emitting position of the light-emitting hole is aligned with the intermediate image plane.

6. The iToF real-time self-calibration ranging device with built-in calibration fiber according to claim 1, characterized in that, The pre-stored reference information includes the equivalent object distance and reference phase corresponding to each of the calibration fibers; the equivalent object distance is determined based on the correspondence between the calibration phase of the corresponding calibration fiber collected during the factory calibration stage and the measurement phase of the known object distance target.

7. The iToF real-time self-calibration ranging device with built-in calibration fiber as described in claim 6, characterized in that, The processing unit is used to calculate the phase deviation between each of the currently obtained calibration phases and the corresponding reference phases, and to construct a phase-distance correction relationship based on the equivalent object distance of each calibration fiber and the corresponding phase deviation. The processing unit is also used to correct the target distance using the phase-distance correction relationship.

8. A ranging method for an iToF real-time self-calibrating ranging device with built-in calibration fiber as described in any one of claims 1 to 7, characterized in that, The ranging method includes: The modulated light source is controlled to emit light modulated at a preset frequency, so that the first part of the light modulated at the preset frequency illuminates the target object, and the second part of the light modulated at the preset frequency is coupled into multiple known calibration optical fibers with different optical paths. The first part reflected by the target object passes through the imaging lens and through the resonant cavity of the intermediate image plane and the built-in electro-optic crystal to reach the CMOS image sensor. The second portion transmitted through each of the calibration optical fibers enters the resonant cavity from the intermediate image plane and forms a preset calibration area on the CMOS image sensor corresponding to each of the calibration optical fibers respectively; Within the same ranging cycle, multiple calibration phases are obtained based on the light intensity signal output by the CMOS image sensor in the preset calibration area, and the measurement phase of the target object is obtained based on the light intensity signal output by the CMOS image sensor in the imaging area. The target distance determined by the measurement phase is corrected based on the pre-stored reference information corresponding to the multiple calibration phases and each calibration fiber.

9. The ranging method of the iToF real-time self-calibration ranging device with built-in calibration fiber as described in claim 8, characterized in that, Before performing distance measurement, the distance measurement method also includes a factory calibration step: The initial calibration phase corresponding to each of the calibration fibers is collected respectively; Collect the measurement phases corresponding to multiple targets at known distances; Based on the correspondence between each initial calibration phase and the measurement phase of the multiple known object distance targets, the equivalent object distance and reference phase corresponding to each calibration fiber are determined. Store the equivalent object distance and reference phase of each of the calibration fibers.

10. The ranging method of the iToF real-time self-calibrating ranging device with built-in calibration fiber as described in claim 8 or 9, characterized in that, Correcting the target distance based on multiple calibration phases and pre-stored reference information corresponding to each calibration fiber includes: Calculate the phase deviation between each of the currently obtained calibration phases and the corresponding pre-stored reference phases; Based on the equivalent object distance and corresponding phase deviation of each calibration fiber, a phase-distance correction relationship is generated; The distance to be corrected is determined based on the measured phase, and the correction amount corresponding to the distance to be corrected is determined using the phase-distance correction relationship; The target distance is obtained by correcting the distance to be corrected using the correction amount; The phase-distance correction relationship is updated in real time during continuous ranging, updated according to a preset cycle, or updated when a change in environmental conditions is detected.

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