Dual-band aspheric zoom optical system for on-chip spectral probes

Abstract

This invention discloses a dual-band aspherical zoom optical system suitable for on-chip spectral detectors, belonging to the technical field of spectral imaging and zoom optical systems. The system, along its optical axis, sequentially comprises a front fixed group, a zoom group, a compensation group, a rear fixed group, and an on-chip integrated spectral detector. The zoom group and the compensation group work in tandem along the optical axis to achieve 3.5x continuous zoom and compensate for image plane shift. The system operates in the visible light bands of 460–643 nm and the near-infrared bands of 700–900 nm, sharing a single optical path and a single detector for both bands. The aperture stop is located between the compensation group and the rear fixed group, or inside the rear fixed group. The object-side surface of the 18th lens in the rear fixed group is aspherical. Within a zoom range of 20–70 mm, the image-side F-number remains at 3, the principal ray angle is controlled within 3°, and the maximum difference in exit pupil distance at different focal lengths does not exceed 1 mm. This invention maintains a stable incident beam state at different zoom positions, improves spectral coding response consistency and reconstruction accuracy, and features a compact structure suitable for UAVs and portable remote sensing platforms.

Description

Technical Field

[0001] This invention belongs to the technical field of spectral imaging and zoom optical systems, specifically relating to a dual-band aspherical zoom optical system suitable for on-chip spectral detectors. The on-chip integrated spectral detector encodes and modulates the incident spectrum through an on-chip spectral modulation structure, acquires the modulated light intensity signal using a photoelectric image sensor, and reconstructs the target's spectral information through a spectral demodulation module. This invention, through the combined design of a zoom group, compensation group, aperture stop, rear fixation group, and aspherical surface, achieves continuous zoom imaging in both visible and near-infrared bands while controlling the image-side principal ray angle, beam cone angle, and image plane illuminance distribution at different zoom positions and fields of view, thereby improving the consistency of the on-chip spectral detector's encoding response and the stability of spectral reconstruction. This invention can be applied to fields such as agricultural remote sensing, environmental monitoring, target recognition, UAV payloads, and portable spectral imaging. Background Technology

[0002] With the continuous development of agricultural technology, modern agriculture has an increasing demand for precise and efficient monitoring technologies, especially in field crop health monitoring, soil analysis, and environmental change monitoring. Spectral imaging technology can simultaneously acquire two-dimensional spatial and spectral information of a target, and based on the target's reflection, absorption, or radiation characteristics at different wavelengths, achieve target identification, material classification, and state analysis. The visible light band can reflect the target's color, texture, and morphological information, while the near-infrared band can provide information such as vegetation water content, chlorophyll content, material composition, and target spectral differences. Therefore, integrating the visible and near-infrared bands into the same imaging system is of great significance for agricultural monitoring, remote sensing, environmental analysis, and target identification.

[0003] Traditional spectral imaging systems typically employ beam-splitting elements such as gratings, prisms, dichroic mirrors, or external filters to separate light of different wavelengths and project it onto one or more photodetectors. While these systems can obtain relatively defined spectral channels, they usually require long beam-splitting paths or multiple independent imaging channels, which can easily increase the system's size and weight. Furthermore, they may introduce problems such as dual-band line-of-sight deviation, image registration errors, and inconsistent magnification across different channels, making it difficult to meet the miniaturization, lightweight, and high integration requirements of UAVs, unmanned ground vehicles, and portable devices.

[0004] With the development of micro-nano fabrication, semiconductor manufacturing, and computational imaging technologies, spectral detectors that integrate spectral modulation structures, photoelectric image sensors, and spectral demodulation functions onto a single chip have emerged. These on-chip integrated spectral detectors do not rely on traditional gratings or prisms to spatially unfold incident light; instead, they utilize multiple modulation structure units with different spectral response characteristics to encode and modulate the incident spectrum. The photoelectric image sensor acquires multiple aliased light intensity signals after modulation, and the spectral demodulation module then reconstructs the target's spectral information based on a pre-calibrated spectral encoding response relationship.

[0005] For the i-th spectral modulation unit, its output signal can be expressed as:

[0006] In the formula, For the incident spectrum, Let be the encoding response function of the i-th spectral modulation unit, and gi be the encoded light intensity signal obtained in the corresponding detection region. To detect noise.

[0007] After discretizing the working band, the above relationship can be expressed as:

[0008] In the formula, s is the spectral vector to be reconstructed, g is the coded light intensity vector collected by the detector, A is the spectral coded response matrix composed of the response functions of each spectral modulation unit, and n is the noise vector. The spectral demodulation module reconstructs the incident spectrum based on the pre-calibrated response matrix through matrix solving, regularized inversion, compressed sensing, or neural networks.

[0009] On-chip integrated spectrometers offer advantages such as compact structure, elimination of traditional dispersive optical paths, high light energy utilization, high spatial resolution, and the ability to achieve snapshot-style spectral acquisition. However, their spectral reconstruction accuracy depends on whether the spectral encoding response under actual operating conditions matches the encoding response under calibration conditions. When the incident angle, beam cone angle, polarization state, illuminance distribution, or spot coverage relationship at the spectral modulation structure changes, the actual response function of each modulation unit may deviate from the calibration response function, causing inconsistencies between the actual encoded response matrix and the calibration matrix, thus resulting in spectral reconstruction errors.

[0010] For an on-chip spectral detector with different spectral modulation structures, the actual response of the i-th modulation unit can be expressed as:

[0011] In the formula, Principal ray incident angle, Let be the image-side numerical aperture of the incident beam. This indicates the polarization state of the incident light. This indicates the position of the spectral modulation unit on the detector image plane. Therefore, the actual coded response matrix is ​​not only related to the modulation structure itself, but also affected by the output beam state of the front imaging optical system.

[0012] In fixed-focus imaging systems, the spectral detector can be calibrated for a given focal length, field of view, and aperture, ensuring that the actual operating state is essentially consistent with the calibration state. However, in continuous zoom systems, the movement of the zoom and compensation groups along the optical axis alters the system's power distribution and beam propagation path, causing changes in the exit pupil position, image-side principal ray angle, image-side numerical aperture, and relative illumination distribution. In this case, even if the system maintains a fixed image plane position and a high modulation transfer function at different focal lengths, it cannot guarantee that the beam state received by the on-chip spectral modulation structure will be consistent with the calibration state.

[0013] Existing four-element continuous zoom optical systems typically consist of a front fixed group, a zoom group, a compensation group, and a rear fixed group arranged sequentially along the optical axis. The zoom group moves along the optical axis to change the system's focal length, the compensation group moves along a corresponding trajectory to compensate for image plane displacement, and the front and rear fixed groups are used to complete beam propagation and aberration correction. The design objectives of this type of system usually include focal length, field of view, image plane stability, distortion, relative illumination, modulation transfer function, and mechanical travel, but rarely consider the response characteristics of on-chip coded modulation spectrometers, or jointly constrain the exit pupil position and image-side beam state during zooming.

[0014] Combining a conventional dual-band zoom lens directly with a coded modulation on-chip spectral detector may present the following problems: The exit pupil position changes during zooming, causing the incident angle of the principal ray at the detector image plane to change with the focal length; The differences in the principal ray angle and beam cone angle between the central field of view and the peripheral field of view cause the same type of spectral modulation unit to have different coding responses at different image plane positions; The numerical aperture of the image square changes with the zoom position, which causes the angular distribution received by the spectral modulation structure to change, resulting in the actual coded response matrix deviating from the calibration matrix; The relative illumination and vignetting state change at different focal lengths, causing a change in the proportional relationship between the output signals of each spectral modulation unit. The visible and near-infrared bands may differ in image plane position, magnification, principal ray angle and energy distribution due to material dispersion and residual chromatic aberration. Traditional aspherical designs are mainly used to correct imaging aberrations such as spherical aberration, coma, and astigmatism, without simultaneously optimizing for exit pupil aberration, principal ray angle, and spectral coding response consistency. Once a spectral detector is calibrated under a fixed beam condition, it is difficult to apply it directly to the entire zoom range. It may be necessary to establish calibration matrices for multiple focal length positions, which increases the complexity of system calibration and data processing.

[0015] Therefore, it is necessary to provide a dual-band aspherical zoom optical system suitable for on-chip integrated spectral detectors. While retaining the four-element structure and 3.5x continuous zoom capability, the coding modulation and computational demodulation characteristics of the on-chip spectral detector are incorporated into the optical system design. Through the coordinated movement of the zoom group and compensation group, the aperture stop position design, the telecentric design of the rear fixed group, and the joint correction of imaging aberrations and exit pupil aberrations by the aspherical surface, the image-side beam state remains stable under different focal lengths, different fields of view, and visible-near-infrared dual-band conditions. This reduces the variation in the beam state received by the on-chip spectral modulation structure at different zoom positions, providing an optical basis for reducing the difference between the actual coding response and the calibrated coding response, and improving the reconstruction accuracy and consistency of dual-band spectral images.

[0016] The shortcomings of existing technologies and the technical problems to be solved by this invention: 1) Multi-band imaging is difficult to achieve focus consistency: Existing optical systems typically support only single-band imaging or require multiple independent optical systems to process visible and near-infrared light bands separately. This approach not only increases system size and weight but also makes it difficult to maintain consistent focus for different wavelengths of light during imaging. In dynamic environments, such as those operating on drones or airborne platforms, inconsistent focus can cause image blurring, reduced resolution, and hinder the analysis and fusion of multi-band data.

[0017] This invention proposes a dual-band optical system design that ensures that visible light and near-infrared light are always focused on the same image plane position within the zoom range, achieving dual-band focus consistency and thus guaranteeing image quality and the accuracy of multispectral data.

[0018] 2) Aberrations and chromatic aberrations are difficult to control during zooming. Traditional optical zoom systems are prone to image plane drift, spherical aberration, coma, and chromatic aberration when adjusting the focal length. This is especially true in multi-band imaging, where different wavelengths of light can cause focus shifts due to differences in optical materials and lens combinations, leading to decreased image quality and uneven resolution. This makes existing systems less stable in dynamic environments, making it difficult to meet the requirements of high-precision agricultural remote sensing or environmental monitoring.

[0019] This invention achieves effective control of aberrations and chromatic aberrations during zooming by precisely designing the front lens group, zoom lens group, relay lens group, and rear lens group, and optimizing the lens curvature, thickness, and material selection. This ensures that the two wavelengths of light maintain consistent focus throughout the zoom range, while guaranteeing high resolution and stability of the image.

[0020] 3) The system is large in size, complex in structure, and has poor airborne adaptability. Existing multi-band optical systems typically rely on multiple independent optical channels or large lens groups, resulting in bulky and heavy systems that are unsuitable for mounting on drones or other airborne platforms. Furthermore, these systems are prone to optical path shifts or imaging instability under dynamic environments (such as vibration, acceleration changes, or temperature fluctuations), reducing system reliability and practical application performance. Summary of the Invention

[0021] In view of this, and in response to the problem that existing dual-band continuous zoom optical systems experience changes in exit pupil position, image-side principal ray angle, beam cone angle, and relative illumination during zooming, leading to deviations in the actual spectral encoding response of the on-chip integrated spectrometer from the calibration response and thus reducing the accuracy of spectral reconstruction, this invention provides a dual-band aspherical zoom optical system suitable for on-chip spectrometers.

[0022] A dual-band aspherical zoom optical system suitable for on-chip spectral detectors, comprising, from the object side to the image side along the imaging optical axis, a front fixed group, a zoom group, a compensation group, a rear fixed group, and an on-chip integrated spectral detector. The front fixed group and the rear fixed group remain fixed relative to the detector image plane during the zoom process. The zoom group and the compensation group move along the imaging optical axis respectively. The zoom group is used to change the equivalent focal length of the system. The compensation group is used to compensate for the image plane displacement generated during the zoom process. The on-chip integrated spectral detector includes a broadband coding modulation structure layer, a photoelectric image sensor module, and a spectral demodulation module. The broadband coding modulation structure layer is disposed on the light-incident side of the photoelectric image sensor module and includes multiple modulation structure units with different spectral response characteristics for coding modulation of the incident spectrum. The photoelectric image sensor module acquires the modulated coded light intensity signal. The spectral demodulation module is used to reconstruct the spectral information of the target according to the pre-calibrated spectral coding response relationship. The system operates in the visible light band and the near-infrared band, with the visible light band ranging from 460nm to 643nm and the near-infrared band ranging from 700nm to 900nm. The aperture stop is disposed between the compensation group and the rear fixing group or inside the rear fixing group; At least one of the optical surfaces in the front fixed group, zoom group, compensation group, or rear fixed group is an aspherical surface; The equivalent focal length at the short focal length end of the system is The equivalent focal length at the telephoto end is ,satisfy: ; Within the continuous zoom range, the system's image-side F-number remains at 3, the maximum angle between the principal ray of the image plane and the normal of the detector image plane does not exceed 3°, and the maximum difference in the image-side exit pupil distance corresponding to different zoom positions does not exceed 1mm.

[0023] Preferably, the aspherical surface is disposed in the rear fixing group and located on the image side of the aperture stop.

[0024] Preferably, the aspherical surface is an XY polynomial aspherical surface, and its surface sag is expressed as: ; in, For vertex curvature, Let be the radius of curvature at the vertex. The conic coefficient, For polynomial coefficients, It is the highest order of the polynomial.

[0025] Preferably, the front fixing group includes a combination of a positive power lens and a negative power lens for correcting primary chromatic aberration in the visible and near-infrared bands.

[0026] Preferably, the axial movement trajectories of the zoom group and the compensation group satisfy the following: during zooming, the axial offset of the actual image plane relative to the fixed image plane of the detector is not greater than the image plane drift allowed by the optical system.

[0027] Preferably, the focal plane position deviation of the visible light band and the near-infrared band in short focal length, medium focal length and long focal length states is not greater than the allowable depth of focus of the optical system.

[0028] Preferably, the axial positions of the zoom group and the compensation group are determined by the zoom cam curve, which allows the system's equivalent focal length to continuously vary within the range of 20mm to 70mm.

[0029] Preferably, the rear fixing group includes multiple lenses for correcting spherical aberration, coma, astigmatism, field curvature, distortion, and dual-band residual chromatic aberration, and for converging the light beam onto the image plane of the on-chip integrated spectral detector.

[0030] Preferably, the output signal of the \(i\)th modulation structure unit of the on-chip integrated spectral detector is represented as: ; in, For the target incident spectrum, For the first The spectral coding response function of each modulation structure unit, This refers to the encoded light intensity signal output from the corresponding detection area. To detect noise.

[0031] Preferably, the system is installed on a drone, unmanned ground vehicle, or fixed remote sensing platform for agricultural monitoring, remote sensing detection, or environmental monitoring.

[0032] The present invention has the following beneficial effects: (1) The present invention adopts a four-element structure consisting of a front fixed group, a zoom group, a compensation group and a rear fixed group. By linking the zoom group and the compensation group along the optical axis, a 3.5x continuous zoom is achieved and the image plane displacement during the zoom process is compensated, so that the system keeps the image plane of the on-chip integrated spectral detector fixed within the zoom range of 20 to 70 mm.

[0033] (2) The present invention adopts a common optical path design for visible light and near infrared, so that the 460-643 nm visible light band and the 700-900 nm near infrared band share a set of zoom optical path and an on-chip integrated spectral detector, which is beneficial to reduce the system volume, mass, line-of-sight deviation, magnification difference and dual-band image registration error.

[0034] (3) This invention maintains the image-side F-number of 3 within a 3.5x continuous zoom range through the coordinated movement of the zoom group and the compensation group, as well as the combined design of the aperture stop, the rear fixing group, and the aspherical surface. This ensures that the beam cone angle reaching the on-chip integrated spectrometer remains consistent across different focal lengths. Simultaneously, the maximum angle between the principal ray of the image plane and the normal of the detector image plane is controlled within 3°, and the maximum difference in the image-side exit pupil distance under different focal lengths is controlled within 1 mm. As a result, the beam center direction, beam cone angle, and exit pupil position reaching the on-chip spectral modulation structure remain relatively stable under each focal length. This helps to reduce the difference between the actual coding response and the calibration coding response, improves the consistency of the spectral demodulation results, and reduces the need for repeated calibration of the on-chip spectrometer under different focal lengths. This provides an optical basis for sharing or simplifying spectral calibration parameters across multiple zoom positions.

[0035] (4) In this invention, the aspherical surface is set on the object-side surface of the 18th lens in the rear fixed group, i.e., the 31st surface of the optical system, so that it is located on the image-side side of the aperture stop. The aspherical surface at this position can not only correct the advanced imaging aberrations in the combined visible and near-infrared bands, but also adjust the exit pupil imaging state of the aperture stop, the propagation state of the principal ray in the edge field of view, and the cone angle of the image-side beam. Thus, while ensuring the spatial imaging quality of the dual-band, it meets the requirements of the on-chip spectrometer for the incident beam state, avoiding the separation of imaging quality optimization and spectrometer detection adaptation.

[0036] (5) The present invention achieves visible light and near-infrared imaging, 3.5x continuous zoom, fixed image plane and on-chip spectral detection adaptation in a set of four-element zoom optical paths without the need to add traditional gratings, prisms, dichroic mirrors or independent dual-channel lenses. It has a compact structure and is suitable for application platforms with limited size and weight, such as UAVs, unmanned ground vehicles and portable remote sensing equipment. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the zoom structure in Example 1 of the present invention; Figure 2 MTF curves for different focal lengths of visible light; Figure 3 MTF curves for different focal lengths in the near-infrared spectrum; Figure 4 MTF curves for different focal lengths in the visible and near-infrared ranges; Figure 5 A dot plot for the visible band; Figure 6 A dot plot for the near-infrared band; Figure 7 A dot plot of visible and near-infrared wavelengths; Figure 8 This is a curve diagram of the zoom cam. Figure 9 This is a schematic diagram of the zoom structure in Example 2 of the present invention; Figure 10 This is the MTF curve of visible light and near-infrared light in Example 2 of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] A dual-band aspherical zoom optical system design suitable for on-chip integrated spectral detectors is provided. The system includes, along the imaging optical axis from the object side to the image side, a front fixed group Lf, a zoom group Lv, a compensation group Lc, a rear fixed group Lb, and an on-chip integrated spectral detector Is. The aperture stop is disposed between the compensation group and the rear fixed group or inside the rear fixed group.

[0040] The front fixed group Lf and the rear fixed group Lb remain fixed relative to the detector image plane during zooming, while the zoom group Lv and the compensation group Lc move along the imaging optical axis. The zoom group Lv is used to change the equivalent focal length of the system, and the compensation group Lc is used to compensate for the image plane displacement generated during zooming, and together with the zoom group Lv, controls the system exit pupil position and image-side beam state.

[0041] The equivalent focal length at the short focal length end of the system is The equivalent focal length at the telephoto end is ,satisfy: ; The on-chip integrated spectral detector includes a broadband coded modulation structure layer, a photoelectric image sensor module, and a spectral demodulation module. The broadband coded modulation structure layer is located on the light-incident side of the photoelectric image sensor module and includes multiple modulation structure units with different spectral response characteristics. Different modulation structure units respectively encode and modulate the incident spectrum. The photoelectric image sensor module acquires the modulated coded light intensity signal, and the spectral demodulation module calculates and demodulates the coded light intensity signal according to a pre-calibrated spectral coding response relationship to obtain the spectral information of the target.

[0042] The system operates in both visible and near-infrared bands, with the visible band ranging from 460 to 643 nm and the near-infrared band from 700 to 900 nm. Through the design of the optical power allocation, material combination, radius of curvature, axial thickness, and air gaps of each lens group, the two operating bands share the same zoom optical path, and are imaged onto the same on-chip integrated spectral detector image plane in short-focus, medium-focus, and long-focus states.

[0043] For the i-th modulation structure unit, its corresponding coded optical intensity signal is represented as:

[0044] In the formula, For the incident spectrum, Let be the spectral coding response function of the i-th modulation structure unit, and gi be the coded light intensity signal output from the corresponding detection region. To detect noise.

[0045] After discretizing the operating band, the coded detection process of the on-chip integrated spectrometer is represented as follows:

[0046] In the formula, To encode the light intensity vector, Let be the incident spectrum vector to be reconstructed. The encoded response matrix is ​​composed of the spectral responses of multiple modulation structure units. This represents the noise vector. The spectral demodulation module reconstructs the incident spectrum based on the encoded light intensity vector and the pre-calibrated encoded response matrix.

[0047] Since the spectral response of the modulation structure unit may be affected by the incident angle of the principal ray, the beam cone angle, and the image plane illuminance distribution, this invention uses the image-side beam state under different focal lengths and fields of view as an optimization constraint during the design of the zoom optical system. The zoom group and the compensation group move in tandem along the imaging optical axis according to a preset trajectory, thereby changing the system focal length and compensating for image plane displacement while limiting the changes in the system exit pupil position and the principal ray angle of the image plane.

[0048] normalized zoom parameters Indicates the system zoom position, where The axial positions of the scaling group and the compensation group are respectively represented as:

[0049] The motion trajectories of the zoom group and the compensation group must at least satisfy:

[0050] In the formula, For the system's equivalent focal length, This represents the axial offset of the actual image plane relative to the fixed image plane of the on-chip integrated spectral detector during zooming. The allowable image plane drift.

[0051] The aperture stop is positioned between the compensation group and the rear fixed group, or inside the rear fixed group. Through the joint design of the aperture stop position, the optical power of the rear fixed group, and the lens structure within the group, the image-side principal ray angle and beam cone angle under different zoom positions and different fields of view are controlled to reduce the changes in the beam state received by the on-chip integrated spectrometer.

[0052] Preferably, the incident angle of the principal ray on the image plane corresponding to any zoom position u, field of view angle ω, and working wavelength λ satisfies:

[0053] In the formula, The angle between the principal ray and the normal to the image plane of the on-chip integrated spectrometer detector. The threshold is determined based on the allowable incident angle of the on-chip spectrometer.

[0054] The change in the principal ray incident angle between different zoom positions satisfies:

[0055] In the formula, This refers to the allowable variation in the principal ray incident angle between different zoom positions. and Determined based on the modulation structure response characteristics of the on-chip integrated spectral detector.

[0056] The focal plane position difference between the visible light band and the near-infrared band satisfies:

[0057] In the formula, The wavelength within the visible light band. The wavelength is in the near-infrared band. This refers to the permissible dual-band focal plane deviation. The dual-band focal plane deviation is not greater than the permissible depth of focus of the optical system.

[0058] In a preferred embodiment, the image-side F-number of the optical system is 3 in short-focal, medium-focal, and long-focal states, ensuring that the image-side beam cone angle at the on-chip integrated spectrometer remains consistent during zooming. At each zoom position and field of view, the angle between the principal ray of the image plane and the normal to the image plane of the on-chip integrated spectrometer does not exceed 3°; the maximum difference in image-side exit pupil distance corresponding to different zoom positions does not exceed 1 mm.

[0059] , ,

[0060] To further correct imaging aberrations in the visible and near-infrared bands and constrain the image-side beam state at different zoom positions, at least one aspherical surface is provided in the front fixed group, zoom group, compensation group, or rear fixed group. Preferably, the aspherical surface is provided in the rear fixed group and located on the image-side side of the aperture stop, so as to utilize the aspherical surface to jointly correct dual-band imaging aberrations, exit pupil aberrations, and principal ray angle deviations in different fields of view.

[0061] The aspherical surface adopts a surface shape composed of a reference quadratic surface and polynomial additional terms, and its surface sag is expressed as:

[0062] In the formula, For aspherical sag, For vertex curvature, Let be the radius of curvature at the vertex. The conic coefficient, For polynomial coefficients, It is the highest order of the polynomial.

[0063] By optimizing the vertex curvature, conic coefficient, and polynomial coefficients of the aspherical surface, the aspherical surface can correct spherical aberration, coma, astigmatism, and advanced chromatic aberration, while improving the exit pupil imaging state of the aperture stop and the light propagation state of the edge field of view.

[0064] This optical system is particularly well-suited for airborne platform applications. Thanks to its compact design and optimized optical components, it can operate efficiently on airborne platforms and maintain image stability in dynamic environments. The system can be widely used in scenarios requiring rapid zoom and hyperspectral imaging, such as agricultural monitoring, remote sensing, and environmental monitoring.

[0065] This invention provides a dual-band aspherical zoom optical system suitable for on-chip integrated spectral detectors. The optical system operates in the 460–643 nm visible light band and the 700–900 nm near-infrared band, with a zoom ratio of 3.5x. The system comprises, along the imaging optical axis from the object side to the image side, a front fixed assembly. Variable multiplication group Compensation Group Rear fixed group and on-chip integrated spectral detector .

[0066] Front fixed group and rear fixed group The zoom group remains fixed relative to the image plane of the on-chip integrated spectral detector during zooming. and compensation group Move along the imaging optical axis respectively. Magnification group Axial movement is used to change the equivalent focal length of the system, compensation group It moves along a trajectory that matches the zoom group to compensate for the image plane displacement generated during zooming, so that the image plane in short focal length, medium focal length and long focal length states coincides with the photosensitive surface of the on-chip integrated spectral detector.

[0067] Example 1: Spherical four-element dual-band zoom optical system Example 1 is used to illustrate the basic structure and zoom principle of the four-element dual-band continuous zoom system, and serves as the basis for the aspherical optimization design in Example 2.

[0068] like Figure 1 As shown, this embodiment employs a four-element continuous zoom structure consisting of a front fixed group, a zoom group, a compensation group, and a rear fixed group. The front and rear fixed groups remain fixed during zooming, while the zoom group and the compensation group move along the imaging optical axis according to a predetermined trajectory. The system focal length continuously changes from 20mm to 70mm, with a zoom ratio of 3.5x. Figure 1 The optical structure and motion group positions are shown for focal lengths of 20mm, 50mm, 60mm and 70mm.

[0069] Front fixed group Located on the object side of the system, it is used to receive dual-band beams from the target, initially control the incident beam aperture, field of view, and optical power, and correct primary chromatic aberration in the visible and near-infrared bands. In this embodiment, the front fixed group includes the first to third lenses. Through the combination of positive and negative optical power lenses and the matching of different dispersive optical materials, it reduces axial and lateral chromatic aberration over a wide spectral range and provides the subsequent zoom group with an incident beam that meets the aperture requirements.

[0070] Variable multiplication group Located after the front fixed group, this embodiment includes a fourth lens. The zoom group moves along the imaging optical axis, changing the overall optical power and equivalent focal length of the system by altering the air gap between it and the front fixed group and the compensation group, thus enabling the system to continuously transition from a short focal length state to a long focal length state.

[0071] Compensation Group Following the zoom group, this embodiment includes a 5th and a 6th lens. The compensation group moves along the imaging optical axis according to a predetermined non-linear trajectory to compensate for image plane drift caused by the movement of the zoom group. By jointly designing the axial positions of the zoom group and the compensation group, the system maintains a fixed image plane throughout the entire 3.5x zoom range.

[0072] Rear fixed group Located between the compensation group and the on-chip integrated spectrometer, this embodiment includes lenses 7 through 18. The rear fixing group is used to gather the beam after passing through the zoom group and the compensation group, further correcting spherical aberration, coma, astigmatism, field curvature, distortion, and dual-band residual chromatic aberration, and finally image the beam onto the image plane of the on-chip integrated spectrometer.

[0073] The aperture stop is located inside the rear fixed assembly, between the 10th and 11th lenses. By combining the position of the aperture stop with the optical power of the rear fixed assembly, the system's aperture, image-side beam cone angle, and the propagation state of the principal ray in different fields of view are controlled.

[0074] The on-chip integrated spectral detector Is is located at the image-side focal plane of the rear fixed group and includes a broadband coding modulation structure layer, a photoelectric image sensor module, and a spectral demodulation module.

[0075] A broadband coded modulation structure layer is disposed on the light-incident side of the photoelectric image sensor module, and includes multiple modulation structure units with different spectral response functions. After the incident light passes through different modulation structure units, it forms multiple coded light intensity signals with different spectral weights. The photoelectric image sensor module converts the coded light intensity signals into digital electrical signals, and the spectral demodulation module reconstructs the visible light and near-infrared spectral information of the target according to the pre-calibrated coded response matrix.

[0076] The first on-chip integrated spectral detector The output signal of each modulation structure unit is represented as:

[0077] In the formula, For the target incident spectrum, For the first The spectral coding response function of each modulation structure unit, This refers to the encoded light intensity signal output from the corresponding detection area. To detect noise.

[0078] The zoom optical system in this embodiment serves as the front imaging optical system for the on-chip integrated spectrometer, primarily performing target dual-band beam collection, continuous zoom, aberration correction, and fixed image plane imaging. The materials, dimensions, arrangement, and spectral demodulation algorithms of the specific modulation structure within the on-chip integrated spectrometer can be determined based on the actual detector model and spectral reconstruction requirements; this invention does not impose any limitations on these aspects.

[0079] This embodiment first establishes a basic dual-band four-element continuous zoom structure. The system consists of 18 lenses, each with a spherical surface. The variable air gaps in the system include: the air gap between the front fixed group and the zoom group; the air gap between the zoom group and the compensation group; and the air gap between the compensation group and the rear fixed group.

[0080] The three air gaps mentioned above change as the zoom group and the compensation group move, but their changes are not independent of each other, but are jointly determined by the axial positions of the two motion groups.

[0081] The specific optical parameters of the basic four-element optical structure are shown in Table 1. In the table, the surface number indicates the arrangement order of the optical surfaces from the object side to the image side; the radius indicates the radius of curvature of the corresponding optical surface; the thickness indicates the axial distance from the current optical surface to the next optical surface; and the material indicates the optical material used in the lens after the current optical surface. "Zoom 1", "Zoom 2", and "Zoom 3" indicate the air gap that changes with the movement of the zoom group and the compensation group.

[0082] Table 1

[0083] Figure 2 This figure shows the MTF curves for different focal lengths in the visible light band. The curves display the system's imaging performance at short, medium, and long focal lengths, especially its ability to resolve high-frequency components. This figure illustrates that the design of the front fixed group, zoom group, and compensation group effectively controls aberrations and chromatic aberration, ensuring high-resolution imaging in the visible light band during zooming.

[0084] Figure 3 , Figure 4 The MTF curves are shown for different focal lengths in the near-infrared band and for different focal lengths in combinations of visible and near-infrared bands.

[0085] Figure 5 and Figure 6 The diagrams show the imaging resolution and pixel accuracy of the system at different focal lengths in the visible light band, near-infrared band, and visible and near-infrared bands, illustrating the imaging clarity of the system in different bands.

[0086] Table 2 shows the axial positions of the zoom group and compensation group in short focal length, medium focal length, and long focal length states in Example 1. The axial positions in Table 2 are all based on the predetermined mechanical reference plane of the system object side as the origin, and the positive direction of the axial position is along the direction from the object side to the image side. The unit is millimeters.

[0087] Table 2 Axial position of motion group in Example 1

[0088] Table 2 shows the axial positions of the zoom group and the compensation group in Example 1 at short, medium, and long focal lengths. During zooming, the two motion groups move in tandem along mutually matched nonlinear trajectories, causing the system's equivalent focal length to change continuously and compensating for image plane displacement caused by the movement of the zoom group.

[0089] In Example 1, the variable magnification group and the compensation group are as shown in Table 2 and... Figure 8 The motion trajectory shown is linked. Figures 2-4 The modulation transfer functions of Example 1 in the visible light band, near-infrared band, and combined visible and near-infrared band are shown respectively. Figures 5-7 The corresponding spectral diagrams are shown separately.

[0090] Depend on Figures 2-7 It can be seen that Example 1 can correct the main imaging aberrations of the visible light and near-infrared bands under different focal lengths and obtain dual-band imaging on the same detector image plane.

[0091] Example 2: Aspherical Quad-Element Dual-Band Zoom Optical System Based on the four-element zoom structure shown in Example 1, in order to further improve the overall imaging quality of the visible and near-infrared bands, and to adjust the light propagation state on the image side of the aperture stop using an aspherical surface, an aspherical zoom optical system as shown in Example 2 is established.

[0092] like Figure 9 As shown, Example 2 also employs a four-element structure consisting of a front fixed group, a zoom group, a compensation group, and a rear fixed group. The system focal length continuously varies from 20mm to 70mm, with a zoom ratio of 3.5x. The positions of the front and rear fixed groups remain unchanged, while the zoom group and the compensation group move along the optical axis.

[0093] In Example 2, the aspherical surface is disposed on the object-side surface of the 18th lens in the rear fixed group, corresponding to the 31st surface of the optical system. The aspherical surface is located on the image-side side of the aperture stop, and its conic coefficient and XY polynomial coefficient are optimized together with other optical parameters to correct advanced imaging aberrations in the visible and near-infrared bands and to adjust the light propagation state in different fields of view.

[0094] Table 3 Aspherical Surface Implementation Cases

[0095] Table 4. Zoom Cam Curve Data (Absolute Position)

[0096] Table 5 Aspherical Data

[0097] The surface sag of the XY polynomial aspheric surface is expressed as:

[0098] In the formula, For aspherical sag, For vertex curvature, Let be the radius of curvature at the vertex. The conic coefficient, denoted as XY, where XY is the coefficient of the polynomial and N is the highest order of the polynomial.

[0099] In Table 5, X, Y, XY, X2, Y2, X2Y, XY2, and X2Y2 correspond to the respective polynomial terms in the above expressions.

[0100] Figure 10 The modulation transfer functions for short-focal, medium-focal, and long-focal states in Example 2 are shown under the combined visible and near-infrared bands. Figure 10 It can be seen that Example 2 can correct the main imaging aberrations of the visible light and near-infrared combined bands within the 3.5x zoom range, and maintain the dual-band imaging performance under different focal lengths.

[0101] In Example 2, when zooming from the short focal length end to the long focal length end, the zoom group and the compensation group are linked according to the axial positional relationship shown in Table 4. The front fixed group, the rear fixed group, and the on-chip integrated spectral detector remain fixed. The movement of the zoom group is used to change the equivalent focal length of the system, and the movement of the compensation group is used to compensate for the image plane displacement generated during zooming. The equivalent focal lengths at the short focal length end and the long focal length end satisfy: ;in, This is the equivalent focal length at the short focal length end. This is the equivalent focal length at the telephoto end.

[0102] By jointly optimizing the short, medium, and long focal length states, as well as several intermediate zoom positions, the zoom trajectory can maintain the stability of the system's image plane position while meeting the requirements for minimum air gap and motion travel between groups.

[0103] Example 2, through the coordinated movement of the zoom group and the compensation group, and the combined setting of the aperture stop, the rear fixing group and the 31st aspherical surface, maintains the image-side F-number at 3 within the 3.5x continuous zoom range, controls the maximum angle between the principal ray of the image plane and the normal of the detector image plane to within 3°, and controls the maximum difference in the image-side exit pupil distance under different focal length states to within 1mm, thereby keeping the beam center direction, beam cone angle and exit pupil position of the on-chip integrated spectral detector relatively stable during the zoom process.

[0104] The dual-band aspherical zoom optical system described in Example 2 can be installed on UAVs, unmanned ground vehicles, or fixed remote sensing platforms. Visible and near-infrared light emitted or reflected by the target enters the system through the front fixed group, and then sequentially passes through the zoom group, compensation group, aperture stop, and rear fixed group before being imaged onto the on-chip integrated spectral detector.

[0105] An on-chip integrated spectrometer performs broadband coding modulation and photoelectric conversion on the incident light, and obtains a dual-band spectral image of the target through a spectral demodulation module. By adjusting the positions of the zoom group and the compensation group, the imaging scale of the target on the detector can be changed while keeping the detector image plane fixed, thereby meeting the dual-band spectral imaging requirements at different observation distances and spatial resolutions.

[0106] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-band aspherical zoom optical system suitable for on-chip spectral detectors, characterized in that, Along the imaging optical axis from the object side to the image side, it includes a front fixation group, a zoom group, a compensation group, a rear fixation group, and an on-chip integrated spectral detector. The front fixed group and the rear fixed group remain fixed relative to the detector image plane during the zoom process. The zoom group and the compensation group move along the imaging optical axis respectively. The zoom group is used to change the equivalent focal length of the system. The compensation group is used to compensate for the image plane displacement generated during the zoom process. The on-chip integrated spectral detector includes a broadband coding modulation structure layer, a photoelectric image sensor module, and a spectral demodulation module. The broadband coding modulation structure layer is disposed on the light-incident side of the photoelectric image sensor module and includes multiple modulation structure units with different spectral response characteristics for coding modulation of the incident spectrum. The photoelectric image sensor module acquires the modulated coded light intensity signal. The spectral demodulation module is used to reconstruct the spectral information of the target according to the pre-calibrated spectral coding response relationship. The system operates in the visible light band and the near-infrared band, with the visible light band ranging from 460nm to 643nm and the near-infrared band ranging from 700nm to 900nm. The aperture stop is disposed between the compensation group and the rear fixing group or inside the rear fixing group; At least one of the optical surfaces in the front fixed group, zoom group, compensation group, or rear fixed group is an aspherical surface; The equivalent focal length at the short focal length end of the system is The equivalent focal length at the telephoto end is ,satisfy: ; Within the continuous zoom range, the system's image-side F-number remains at 3, the maximum angle between the principal ray of the image plane and the normal of the detector image plane does not exceed 3°, and the maximum difference in the image-side exit pupil distance corresponding to different zoom positions does not exceed 1mm.

2. The system according to claim 1, characterized in that, The aspherical surface is disposed in the rear fixing group and is located on the image side of the aperture stop.

3. The system according to claim 1 or 2, characterized in that, The aspherical surface is an XY polynomial aspherical surface, and its surface sag is expressed as: ； in, For vertex curvature, Let be the radius of curvature at the vertex. The conic coefficient, For polynomial coefficients, It is the highest order of the polynomial.

4. The system according to claim 1, characterized in that, The front fixation group includes a combination of positive and negative power lenses, used to correct primary chromatic aberration in the visible and near-infrared bands.

5. The system according to claim 1, characterized in that, The axial movement trajectories of the zoom group and the compensation group satisfy the following: during zooming, the axial offset of the actual image plane relative to the fixed image plane of the detector is not greater than the image plane drift allowed by the optical system.

6. The system according to claim 1, characterized in that, The focal plane position deviation of the visible light band and the near-infrared band in short focal length, medium focal length and long focal length states is not greater than the allowable depth of focus of the optical system.

7. The system according to claim 1, characterized in that, The axial positions of the zoom group and the compensation group are determined by the zoom cam curve, which allows the system's equivalent focal length to continuously vary within the range of 20mm to 70mm.

8. The system according to claim 1, characterized in that, The rear fixation group includes multiple lenses for correcting spherical aberration, coma, astigmatism, field curvature, distortion, and dual-band residual chromatic aberration, and for converging the light beam onto the image plane of the on-chip integrated spectral detector.

9. The system according to claim 1, characterized in that, The output signal of the \(i\)th modulation structure unit of the on-chip integrated spectral detector is represented as: ； in, For the target incident spectrum, For the first The spectral coding response function of each modulation structure unit, This refers to the encoded light intensity signal output from the corresponding detection area. To detect noise.

10. The system according to claim 1, characterized in that, The system is installed on drones, unmanned ground vehicles, or fixed remote sensing platforms for agricultural monitoring, remote sensing detection, or environmental monitoring.

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