CN111856497A - Single photon imaging method and system - Google Patents
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Abstract
The invention provides a single photon imaging method and a system, wherein the method comprises the following steps: the main controller receives an image acquisition instruction input from the outside, generates a laser trigger signal and sends the laser trigger signal to the fiber laser; the fiber laser emits laser pulses according to the laser trigger signal, and the laser pulses are transmitted to a target scene after optical processing; the timing electronic system starts to record the number of the laser pulses, generates a first number and sends TTL pulses to the scanning mirror servo driver; the telescope collects the reflected light pulse and then reaches the SPAD detector after optical treatment; when the timing electronic system judges that the first quantity is equal to the first preset quantity, the scanning mirror is triggered to change the position according to preset position data, the reflected light pulse received by the SPAD detector is subjected to time marking, and first pixel data are generated and sent to the main controller; and when the main controller judges that the scanning mirror completes the change of all the positions, carrying out depth image reconstruction according to the obtained data to obtain the depth image data of the target scene.
Description
Technical Field
The invention relates to the field of data processing, in particular to a single photon imaging method and system.
Background
In recent years, there has been an increasing interest in single photon counting lidar for remote three-dimensional imaging for a variety of remote sensing applications. One reason for this is the recent emergence of Geiger-Mode (GM) arrays that can provide full frame data acquisition with single photon sensitivity and picosecond resolution. The technique also finds application in aerial surveillance where remote target identification by turbulence is an engineering challenge. In particular, efforts are being focused on developing a wide range of applications such as wide-field-of-view airborne surveillance and remote object recognition and identification sensors.
While each application impacts specific requirements of design and component selection, there is clearly a need for a system that can provide long range three-dimensional high resolution imaging and has nighttime imaging capabilities. The use of a low power laser source means that single photon detection will be more covert and unlikely to exceed eye safety thresholds. Applications such as on-board monitoring using active imaging impose limits on system weight, size and volume, and require low power laser sources and high sensitivity optical detection. Single photon laser imaging technology is a potential candidate to meet these challenging requirements.
The timing resolution of single photon detection is not limited by the duration or rise time of the voltage pulses, but is determined by the variation of the rise time of the detector or the timing jitter. Thus, single photon detection can provide orders of magnitude better timing error than analog optical detectors, thereby significantly improving depth resolution. Furthermore, the high sensitivity of single photon detectors allows the use of lower power laser sources and allows time of flight data to be measured from significantly greater distances. The possibility of using lower power sources means that single photon lidar systems can be smaller, lighter and consume less power, which is required for integration onto onboard platforms.
The imaging distance of the single-photon three-dimensional imaging system disclosed by the prior art can reach the kilometer level. However, the imaging distance cannot reach a long-distance imaging range of more than 9 kilometers, and the imaging effect is not ideal due to the influence of the solar background and atmospheric loss.
Disclosure of Invention
Aiming at the defects of the prior art, the embodiment of the invention aims to provide a single photon imaging method and system, which effectively solve the problem of back reflection through reasonable light path design, simplify complex optical alignment, enable the imaging distance to reach 10.5 kilometers and effectively improve the imaging effect.
In order to solve the above problem, in a first aspect, the present invention provides a single photon imaging method, including: the main controller receives an image acquisition instruction input from the outside, generates a laser trigger signal and sends the laser trigger signal to the fiber laser;
the fiber laser sends laser pulses at a first preset frequency according to the laser trigger signal, and the laser pulses generate first laser pulses after collimation treatment, beam expansion treatment and light path change treatment and are transmitted to a target scene; the digital delay pulse generator starts a Field Programmable Gate Array (FPGA) of the scanner according to the laser trigger signal, the FPGA records the number of the laser pulses to generate a first number, and transmits TTL pulses to a scanning mirror servo driver;
the target scene reflects the first laser pulse to obtain a reflected light pulse; the reflected light pulse is collected by a telescope, is subjected to light path change treatment by a light path change system and then is guided to a single photon avalanche diode SPAD detector;
when the FPGA judges that the first quantity is equal to a first preset quantity, the FPGA triggers the scanning mirror to change the position according to preset position data, and releases the TTL pulse to the time interval analyzer;
the time interval analyzer acquires a time label according to the TTL pulse, and time marks the reflected light pulse received by the SPAD detector to generate photon data; recording the number of the transmitted light pulses received within a second preset time length to generate a second number;
the SPAD generates first pixel data according to the photon data and the second quantity, and sends the first pixel data to the main controller;
and when the main controller judges that the scanning mirror finishes the change of all positions according to the preset position data, carrying out depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain depth image data of the target scene.
Preferably, the generating of the first laser pulse after the laser pulse is subjected to the collimation processing, the beam expansion processing and the optical path changing processing specifically includes:
the laser pulse is transmitted to a collimator through an optical fiber to be collimated, and a collimated laser pulse is obtained;
the beam expander carries out beam expanding processing on the collimated laser pulse to obtain a beam expanded laser pulse;
and the beam expanding laser pulse is subjected to light path changing treatment by a light path changing treatment system to obtain the first laser pulse.
Further preferably, the beam expanding laser pulse is subjected to optical path changing processing by an optical path changing processing system, and obtaining the first laser pulse specifically includes:
the expanded beam laser pulse is reflected by the first reflecting mirror surface and then projects to the first scanning mirror through the small hole of the annular reflecting mirror;
the expanded beam laser pulse reflected by the first scanning mirror is projected to a second scanning mirror through a relay lens group;
the expanded beam laser pulse reflected by the second scanning mirror is projected to the surface of the second scanning mirror;
and the expanded beam laser pulse reflected by the second reflecting mirror surface passes through the eyepiece, is subjected to calibration treatment and then penetrates through the telescope to generate a first laser beam.
Preferably, the method further comprises:
and the main controller adjusts the current driver of the optical fiber laser according to preset current data so as to adjust the output power of the optical fiber laser.
Preferably, the duration of the laser pulse is a first preset duration.
Further preferably, the first preset time period is 800 ps.
Preferably, the first predetermined frequency is 125 khz.
Preferably, the collecting of the reflected light pulse by the telescope, and the guiding of the reflected light pulse to the single photon avalanche diode SPAD detector after the light path changing processing by the light path adjusting module specifically include:
the reflected light pulse penetrating through the telescope is projected to a second reflecting mirror surface after being calibrated through an ocular lens;
reflected light pulses emitted by the second reflecting mirror surface are projected to the second scanning mirror;
the emitted light pulse reflected by the second scanning mirror is projected to the first scanning mirror through the relay lens group;
reflected light pulses emitted by the first scanning mirror are reflected by the annular reflecting mirror and then are projected onto the focusing lens;
the reflected pulse after being focused by the focusing lens passes through a spectral filter and is focused on an effective area of the SPAD detector.
Preferably, the main controller performs depth image reconstruction according to the plurality of first pixel data and the preset position data, and obtaining the depth image data of the target scene specifically includes:
the main controller generates a time histogram of photon return according to the first pixel data;
the main controller performs peak positioning analysis processing on the histogram by using a least square curve fitting algorithm according to a preset time width to obtain a peak position corresponding to the first pixel data;
and the main controller carries out depth image reconstruction according to the time marks corresponding to the plurality of peak positions and the preset position number to obtain depth image data of the target scene.
In a second aspect, the present invention provides a single photon imaging system comprising: the system comprises a main controller, a fiber laser, a collimator, a beam expander, a light path changing and processing system, a telescope, a timing electronic system and a Single Photon Avalanche Diode (SPAD) detector; the timing electronic system further comprises a digital delay pulse generator, a scanner Field Programmable Gate Array (FPGA) and a time interval analyzer;
the main controller is used for receiving an image acquisition instruction input from the outside, generating a laser trigger signal and sending the laser trigger signal to the optical fiber laser;
the optical fiber laser is used for sending laser pulses at a first preset frequency according to the laser trigger signal;
the collimator is used for collimating the laser pulse;
the beam expander is used for performing beam expanding processing on the laser pulse;
the light path changing processing system is used for carrying out light path changing processing on the laser pulse to generate a first laser pulse and transmitting the first laser pulse to a target scene;
the digital delay pulse generator is used for starting a Field Programmable Gate Array (FPGA) of the scanner according to the laser trigger signal;
the scanner field programmable gate array FPGA is used for recording the number of the laser pulses, generating a first number and sending TTL pulses to the scanning mirror servo driver;
the target scene reflects the first laser pulse to obtain a reflected light pulse;
the telescope is used for collecting the reflected light pulse, and guiding the reflected light pulse to the single photon avalanche diode SPAD detector after the reflected light pulse is subjected to light path change treatment by the light path change treatment system;
the FPGA is further used for triggering the scanning mirror to change the position according to preset position data and releasing the TTL pulse to the time interval analyzer when the first quantity is judged to be equal to a first preset quantity;
the time interval analyzer is used for acquiring a time label according to the TTL pulse, and performing time marking on the reflected light pulse received by the SPAD detector to generate photon data; recording the number of the transmitted light pulses received within a second preset time length to generate a second number;
the SPAD detector is further used for generating first pixel data according to the photon data and the second quantity and sending the first pixel data to the main controller;
and the main controller is further configured to perform depth image reconstruction according to the plurality of first pixel data and the preset position data after the scanning mirror is judged to complete the change of all the positions according to the preset position data, so as to obtain depth image data of the target scene.
The embodiment of the invention provides a single photon imaging method, which is based on a single photon imaging system, solves the problem of back reflection by using a reasonable light path, simplifies the alignment of an optical pair applied on the single photon imaging system, enables the imaging distance to reach 10.5 kilometers, and obviously improves the imaging effect.
Drawings
FIG. 1 is a block diagram of a single photon imaging system according to an embodiment of the present invention;
fig. 2 is a flowchart of a single photon imaging method according to an embodiment of the present invention.
Detailed Description
The present application will be described in further detail with reference to the following drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be further noted that, for the convenience of description, only the portions related to the related invention are shown in the drawings.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
The single photon imaging method provided by the invention is realized based on the single photon imaging system provided by the embodiment of the invention, and in order to better explain the single photon imaging method provided by the embodiment of the invention, the single photon imaging system is introduced firstly. Fig. 1 is a block diagram of a single photon imaging system according to an embodiment of the present invention, and as shown in the figure, the system includes: the system comprises a main controller 1, a fiber laser 2, a collimator 3, a beam expander 4, a light path change processing system 5, a telescope 6, a timing electronic system 7 and a single photon avalanche diode SPAD detector 8; the timing electronic system 7 further includes a digital delay pulse generator (not shown), a Field Programmable Gate Array (FPGA) (not shown), and a time interval analyzer (not shown).
The main controller 1 is a control device of the whole system, and when a user needs to image a target scene, an image acquisition instruction is sent to the main controller 1 through a wireless communication device, or the image acquisition instruction is input to the main controller through a hardware starting device which is in limited connection with the main controller. After receiving an image acquisition instruction input from the outside, the main controller 1 generates a laser trigger signal according to the image acquisition instruction, and sends the laser trigger signal to the fiber laser.
The fiber laser 2 starts to emit laser pulses at a first preset frequency after receiving the laser trigger signal sent by the main controller 1. The first preset frequency is a preset laser pulse emission frequency. In an embodiment of the present invention, the first predetermined frequency is 125 khz. And the wavelength of the laser pulse is 1550 nm.
And the collimator 3 is used for collimating the laser pulse to obtain a collimated laser pulse. In an alternative of the embodiment of the present invention, the collimator is a collimating lens, one end of the collimating lens is coupled to the fiber laser by using an optical fiber, the laser pulse emitted by the fiber laser 2 is transmitted to the collimator 3 through the optical fiber, and the collimator 3 generates a collimated laser pulse after collimating the received laser pulse.
And the beam expander 4 is used for performing beam expanding treatment on the laser pulse to obtain the parallel laser pulse with the increased diameter. In an alternative of the embodiment of the present invention, the beam expander 4 is composed of two lenses with fixed relative positions, and the relative distance between the two lenses is reasonably set according to the optical principle of the lenses in the experimental stage of the system. And the beam expander 4 of the invention is used for diffusing the received collimated laser pulse and reducing the divergence angle of the laser pulse. In a specific example of an alternative embodiment of the present invention, the beam expander 4 expands the collimated laser pulses into expanded laser pulses having a diameter of 20 cm.
The optical path changing processing system 5 is configured to change a direction of the received laser pulse, so that the laser pulse incident to the optical path changing processing system 5 can pass through an eyepiece (not shown in the figure) to generate a first laser pulse after passing through the telescope 6, and the first laser pulse is emitted to a target scene. On the other hand, the single photon avalanche diode SPAD detector is used for carrying out light path change processing on the collected reflected light pulse of the telescope 6 and guiding the reflected light pulse to the single photon avalanche diode SPAD detector 8;
in a preferred embodiment of the present invention, the optical path changing processing system 5 further includes a first reflecting mirror surface (not shown in the figure), an annular reflecting mirror (not shown in the figure), a first scanning mirror (not shown in the figure), a second reflecting mirror surface (not shown in the figure), an eyepiece (not shown in the figure), a focusing lens (not shown in the figure), and a spectral filter (not shown in the figure), before the system is put into use, the positions of the components are set according to the optical principle of the components, so that the received laser pulses can be emitted to a target scene according to a required direction. In the present invention, the optical path changing system does not use exactly the same components as those used in the optical path changing process for the reflected pulse. The components commonly used in the course of both changing processes include a ring mirror (not shown in the drawings), a first scanning mirror (not shown in the drawings), a second mirror surface (not shown in the drawings), and an eyepiece (not shown in the drawings).
And the digital delay pulse generator (not shown in the figure) is used for starting the field programmable gate array FPGA of the scanner according to the laser trigger signal.
A scanner field programmable gate array FPGA (not shown in the figures) for recording the number of laser pulses, generating a first number, and sending TTL pulses to the scan mirror servo driver. And the FPGA (not shown in the figure) is also used for triggering the scanning mirror (not shown in the figure) to change the position according to the preset position data and releasing the TTL pulse to the time interval analyzer when the first quantity is judged to be equal to the first preset quantity.
A time interval analyzer (not shown in the figure) for obtaining a time tag according to the TTL pulse, and time-stamping the reflected light pulse received by the SPAD to generate photon data; and recording the number of the received emitted light pulses within a second preset time period to generate a second number.
The main controller 1 is further configured to reset the time interval analyzer to an initial state when the second number is equal to the first preset number. And generating first pixel data according to the photon data and the second quantity at the SPAD detector 8, sending the first pixel data to the main controller 1, judging that the scanning mirror completes the change of all positions according to preset position data, and performing depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain depth image data of the target scene.
In the photon imaging system provided by the embodiment of the present invention, the connection relationship between each component includes: the main controller 1 is in communication connection with the optical fiber laser 2, the optical fiber laser 2 is electrically connected with the timing electronic system, and the SPAD detector 8 is in wired or wireless communication connection with the timing electronic system 7.
The single photon imaging system provided by the invention is introduced above, and the single photon imaging method provided by the invention is explained in detail based on the single photon imaging system. Fig. 2 is a flowchart of a single photon imaging method according to an embodiment of the present invention, as shown in the figure, the method includes the following steps:
and 101, receiving an image acquisition instruction input from the outside by a main controller, generating a laser trigger signal and sending the laser trigger signal to the optical fiber laser.
Specifically, when a user needs to image a target scene or the target object, an image acquisition instruction is sent to the main controller through the external link device, and the main controller generates a laser trigger signal after receiving the image acquisition instruction and sends the laser trigger signal to the fiber laser.
102, sending laser pulses by a fiber laser, and transmitting the laser pulses to a target scene after optical treatment; the timing electronic system counts the laser pulses.
Specifically, the fiber laser emits laser pulses at a first preset frequency according to a laser trigger signal, and the laser pulses are subjected to collimation treatment, beam expansion treatment and light path change treatment to generate first laser pulses which are emitted to a target scene; the digital delay pulse generator starts a Field Programmable Gate Array (FPGA) of the scanner according to the laser trigger signal, the FPGA records the number of the laser pulses to generate a first number, and transmits TTL pulses to the scanning mirror servo driver. The method specifically comprises the following steps:
and when the fiber laser receives the laser touch signal sent by the controller, the fiber laser starts to emit laser pulses with the wavelength as the preset wavelength at the first preset frequency.
The fiber laser in the embodiment of the invention is an erbium-doped fiber laser with the working wavelength of 1550 nanometers, and the laser generates laser pulses at the repetition frequency of 125 kilohertz. The duration of the laser pulse is a first preset duration. The first preset time period is preferably 800ps in the embodiment of the present invention.
In the embodiment of the invention, the fiber laser is coupled with the collimation processor by using the optical fiber, and the emitted laser pulse is transmitted to the collimator through the optical fiber for collimation processing to obtain the collimated laser pulse. And the collimated laser pulse is incident to the beam expander to be subjected to beam expanding treatment, so that beam-expanded laser pulse is obtained. Then, the expanded beam laser pulse is transmitted to a light path changing processing system to change the light path, so as to obtain a first laser pulse, wherein the specific processing method comprises the following steps:
first, the expanded beam laser pulses are reflected by a first mirror surface and then projected through an aperture of an annular mirror onto a first scanning mirror.
And secondly, the expanded beam laser pulse reflected by the first scanning mirror is projected to a second scanning mirror through a relay lens group.
And thirdly, projecting the expanded beam laser pulse reflected by the second scanning mirror to the surface of the second scanning mirror.
And finally, the expanded beam laser pulse reflected by the second reflecting mirror surface passes through an ocular lens to be calibrated and then penetrates through a telescope to generate a first laser beam.
Thus, the laser pulse emitted from the fiber laser is irradiated to the corresponding position of the target scene in a predetermined direction.
When the fiber laser starts to emit laser pulses, the digital delay pulse generator starts a Field Programmable Gate Array (FPGA) of the scanner according to the received laser trigger signals, the FPGA starts to record the number of the laser pulses to generate a first number, and transmits TTL pulses to the scanning mirror servo driver.
103, reflecting the first laser pulse by the target scene to obtain a reflected light pulse; the reflected light pulse is collected by the telescope, and is guided to the single photon avalanche diode SPAD detector after being subjected to light path change treatment by the light path change system.
Specifically, after the first laser pulse is irradiated to the target scene, the first laser pulse is reflected by the target scene, and for convenience of description, in the embodiment of the present invention, the first laser pulse reflected by the target scene is referred to as a reflected pulse. The reflected light pulse is incident to a telescope, is projected to a light path changing system after passing through the telescope, and is guided to the SPAD detector by components in the light path changing system. The guiding process of the optical path changing system includes:
first, the reflected light pulse transmitted through the telescope is collimated by the eyepiece and then projected onto the second reflecting mirror surface.
The reflected light pulse, after being emitted by the second mirror surface, is then projected onto the second scanning mirror.
Then, the emitted light pulse reflected by the second scanning mirror is projected to the first scanning mirror through the relay lens group.
Then, the reflected light emitted by the first scanning mirror is reflected by the annular reflecting mirror and then is projected onto the focusing lens.
And finally, the reflected pulse after being focused by the focusing lens passes through the spectral filter and is focused on the effective area of the SPAD detector.
In the embodiment of the invention, the arrangement position of the focusing lens is ensured, after the annular reflecting mirror reflects the reflected light pulse to the focusing lens, the radiant light pulse focused by the lens can just generate a focus in an active area of the SPAD detector, so that the SPAD detector can accurately detect the reflected light pulse.
In the embodiment of the present invention, the optical path changing process in step 102 and the optical path changing process in this step use the ring-shaped mirror, the first scanning mirror, the second reflecting mirror surface and the eyepiece at the same time, and this design enables the expanded laser pulse and the received reflected light pulse to be aligned through the same path, that is, this method of sharing the optical path can simplify the complexity of optical alignment.
And 104, when the FPGA judges that the first quantity is equal to the first preset quantity, triggering the scanning mirror to change the position according to preset position data, and releasing the TTL pulse to the time interval analyzer.
Specifically, in the system provided by the invention, the emission direction of the first laser pulse is changed by adjusting the position of the scanning mirror, so that the position scanned by the laser pulse is changed. The scanning mirror servo drive controls the position change of the scanning mirror. The single photon imaging method can complete imaging with various resolutions. The size of the resolution that can be provided and its corresponding scan mirror position data are generated in advance and stored in the system memory device, and the user can select one of the multiple resolutions as desired. For example, the resolution includes 85 × 85, 32 × 32, 40 × 80, 100 × 100, etc., and the selected resolution is 32 × 32, then the preset position data corresponding to the resolution of 32 × 32 is selected. When the FPGA judges that the first quantity is equal to the first preset quantity, the scanning mirror servo drive changes the position of the scanning mirror according to the preset position data, and the position of the scanning mirror at one time is not judged to be changed to the next position. Therefore, in the actual acquisition process, if the scanning mirror changes all the positions in the preset position data, the system finishes scanning all the points of the target scene. After each change of position, the scanning mirror servo drive releases a TTL pulse to the time interval analyzer.
105, the time interval analyzer acquires a time label according to the TTL pulse, and time marks the reflected light pulse received by the SPAD detector to generate photon data; and recording the number of the received emitted light pulses within a second preset time period to generate a second number.
Specifically, the time interval analyzer acquires the time tag after receiving the TTL pulse. Wherein the time stamp indicates the time period, for example, in an alternative of the embodiment of the present invention, the time stamp is 80 ps.
After the time tag is obtained, the SPAD detector starts to detect the transmitted light pulse, when the reflected light pulse is detected, timing processing of a second preset time duration is started, the reflected light pulse received by the SPAD detector starts to be marked, and photon data are generated. Where the frequency of the marks is determined by the time stamp, e.g., 80ps, then the SPAD detector is marked every 80 ps.
And 106, generating first pixel data by the SPAD detector according to the photon data and the second quantity, and sending the first pixel data to the main controller.
Specifically, when the second preset time period is reached, the SPAD detector is turned off, and at this time, the first pixel data is generated according to the photon data and the second quantity. At the same time, the time interval analyzer is reset to the initial state.
And 107, after the main controller judges that the scanning mirror completes the change of all the positions according to the preset position data, performing depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain depth image data of the target scene.
Specifically, the main controller judges whether the scanning mirror completes the change of the position corresponding to each point in the preset position data or not according to the preset position data, and when the scanning mirror completes the change of all the positions, the main controller calls a preset algorithm to perform depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain depth image data of the target scene.
In an alternative of the embodiment of the present invention, the process of depth image reconstruction includes:
first, the main controller generates a time histogram of photon returns from the first pixel data.
Secondly, the main controller performs peak positioning analysis processing on the histogram by using a least square curve fitting algorithm according to a preset time width to obtain a peak position corresponding to the first pixel data. The preset time width is the duration of the time label, and in the embodiment of the invention, the value is 80 ps.
And finally, the main controller carries out depth image reconstruction according to the time marks corresponding to the peak positions and the preset position number to obtain depth image data of the target scene. That is, each pixel obtains a time stamp corresponding to a peak value, and then according to each time stamp, a relative depth data value of each pixel can be obtained through the time stamp, and then, depth image data can be reconstructed according to a corresponding relationship between the relative depth value of each pixel and each pixel in the preset position data.
The embodiment of the invention provides a single photon imaging method, which is based on a single photon imaging system, solves the problem of back reflection by using a reasonable optical path design, simplifies complex optical pair alignment, enables the imaging distance to reach 10.5 kilometers, and simultaneously obviously improves the imaging effect.
The second embodiment of the present invention provides a single photon imaging system, including: the single photon imaging method comprises a main controller, a fiber laser, a collimator, a beam expander, a light path changing and processing system, a telescope, a timing electronic system and a single photon avalanche diode SPAD detector, and can be achieved.
Those of skill would further appreciate that the various illustrative components and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied in hardware, a software module executed by a processor, or a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The above embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A method of single photon imaging, said method comprising: the main controller receives an image acquisition instruction input from the outside, generates a laser trigger signal and sends the laser trigger signal to the fiber laser;
the fiber laser sends laser pulses at a first preset frequency according to the laser trigger signal, and the laser pulses generate first laser pulses after collimation treatment, beam expansion treatment and light path change treatment and are transmitted to a target scene; the digital delay pulse generator starts a Field Programmable Gate Array (FPGA) of the scanner according to the laser trigger signal, the FPGA records the number of the laser pulses to generate a first number, and transmits TTL pulses to a scanning mirror servo driver;
the target scene reflects the first laser pulse to obtain a reflected light pulse; the reflected light pulse is collected by a telescope, is subjected to light path change treatment by a light path change system and then is guided to a single photon avalanche diode SPAD detector;
when the FPGA judges that the first quantity is equal to a first preset quantity, the FPGA triggers the scanning mirror to change the position according to preset position data, and releases the TTL pulse to the time interval analyzer;
the time interval analyzer acquires a time label according to the TTL pulse, and time marks the reflected light pulse received by the SPAD detector to generate photon data; recording the number of the transmitted light pulses received within a second preset time length to generate a second number;
the SPAD generates first pixel data according to the photon data and the second quantity, and sends the first pixel data to the main controller;
and when the main controller judges that the scanning mirror finishes the change of all positions according to the preset position data, carrying out depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain depth image data of the target scene.
2. The single photon imaging method according to claim 1, wherein the generating of the first laser pulse after the laser pulse is subjected to the collimating process, the beam expanding process and the optical path changing process specifically comprises:
the laser pulse is transmitted to a collimator through an optical fiber to be collimated, and a collimated laser pulse is obtained;
the beam expander carries out beam expanding processing on the collimated laser pulse to obtain a beam expanded laser pulse;
and the beam expanding laser pulse is subjected to light path changing treatment by a light path changing treatment system to obtain the first laser pulse.
3. The single photon imaging method according to claim 2, wherein said beam expanding laser pulse is subjected to a light path changing process by a light path changing process system, and obtaining said first laser pulse specifically comprises:
the expanded beam laser pulse is reflected by the first reflecting mirror surface and then projects to the first scanning mirror through the small hole of the annular reflecting mirror;
the expanded beam laser pulse reflected by the first scanning mirror is projected to a second scanning mirror through a relay lens group;
the expanded beam laser pulse reflected by the second scanning mirror is projected to the surface of the second scanning mirror;
and the expanded beam laser pulse reflected by the second reflecting mirror surface passes through the eyepiece, is subjected to calibration treatment and then penetrates through the telescope to generate a first laser beam.
4. The single photon imaging method of claim 1 further comprising:
and the main controller adjusts the current driver of the optical fiber laser according to preset current data so as to adjust the output power of the optical fiber laser.
5. The single photon imaging method of claim 1 in which said laser pulses have a duration of a first predetermined duration.
6. The single photon imaging method in accordance with claim 5 wherein said first predetermined period of time is 800 ps.
7. The single photon imaging method of claim 1 in which said first predetermined frequency is 125 kilohertz.
8. The single photon imaging method according to claim 1, wherein said reflected light pulses are collected by a telescope, and are guided to a single photon avalanche diode SPAD detector after being subjected to light path change processing by a light path adjusting module, the method comprising:
the reflected light pulse penetrating through the telescope is projected to a second reflecting mirror surface after being calibrated through an ocular lens;
reflected light pulses emitted by the second reflecting mirror surface are projected to the second scanning mirror;
the emitted light pulse reflected by the second scanning mirror is projected to the first scanning mirror through the relay lens group;
reflected light pulses emitted by the first scanning mirror are reflected by the annular reflecting mirror and then are projected onto the focusing lens;
the reflected pulse after being focused by the focusing lens passes through a spectral filter and is focused on an effective area of the SPAD detector.
9. The single photon imaging method according to claim 1, wherein the performing, by the main controller, depth image reconstruction according to the plurality of first pixel data and the preset position data to obtain the depth image data of the target scene specifically includes:
the main controller generates a time histogram of photon return according to the first pixel data;
the main controller performs peak positioning analysis processing on the histogram by using a least square curve fitting algorithm according to a preset time width to obtain a peak position corresponding to the first pixel data;
and the main controller carries out depth image reconstruction according to the time marks corresponding to the plurality of peak positions and the preset position number to obtain depth image data of the target scene.
10. A single photon imaging system, said system comprising: the system comprises a main controller, a fiber laser, a collimator, a beam expander, a light path changing and processing system, a telescope, a timing electronic system and a single photon avalanche diode SPAD detector; the timing electronic system further comprises a digital delay pulse generator, a scanner Field Programmable Gate Array (FPGA) and a time interval analyzer;
the main controller is used for receiving an image acquisition instruction input from the outside, generating a laser trigger signal and sending the laser trigger signal to the optical fiber laser;
the optical fiber laser is used for sending laser pulses at a first preset frequency according to the laser trigger signal;
the collimator is used for collimating the laser pulse;
the beam expander is used for performing beam expanding processing on the laser pulse;
the light path changing processing system is used for carrying out light path changing processing on the laser pulse to generate a first laser pulse and transmitting the first laser pulse to a target scene;
the digital delay pulse generator is used for starting a Field Programmable Gate Array (FPGA) of the scanner according to the laser trigger signal;
the scanner field programmable gate array FPGA is used for recording the number of the laser pulses, generating a first number and sending TTL pulses to the scanning mirror servo driver;
the target scene reflects the first laser pulse to obtain a reflected light pulse;
the telescope is used for collecting the reflected light pulse, and guiding the reflected light pulse to the single photon avalanche diode SPAD detector after the reflected light pulse is subjected to light path change treatment by the light path change treatment system;
the FPGA is further used for triggering the scanning mirror to change the position according to preset position data and releasing the TTL pulse to the time interval analyzer when the first quantity is judged to be equal to a first preset quantity;
the time interval analyzer is used for acquiring a time label according to the TTL pulse, and performing time marking on the reflected light pulse received by the SPAD detector to generate photon data; recording the number of the transmitted light pulses received within a second preset time length to generate a second number;
the SPAD detector is further used for generating first pixel data according to the photon data and the second quantity and sending the first pixel data to the main controller;
and the main controller is further configured to perform depth image reconstruction according to the plurality of first pixel data and the preset position data after the scanning mirror is judged to complete the change of all the positions according to the preset position data, so as to obtain depth image data of the target scene.
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