WO2022101349A1

WO2022101349A1 - Ranging detection

Info

Publication number: WO2022101349A1
Application number: PCT/EP2021/081401
Authority: WO
Inventors: Håvard TØRRING
Original assignee: Tørring Invest As
Priority date: 2020-11-11
Filing date: 2021-11-11
Publication date: 2022-05-19

Abstract

A light-based ranging system (1), such as LIDAR, comprises: • a light source (2) arranged to emit time varying light signals; • a detection subsystem arranged to receive incoming light signals comprising reflections of said time varying light signals from an object (10), the detection subsystem comprising: • a lens (6) an adjustable deflecting element (4); and a detector (14). The lens is arranged to direct the reflections onto said adjustable deflecting element and the adjustable deflecting element is adjustable into a plurality of configurations, such that in each of the plurality of configurations the adjustable deflecting element deflects reflections from different corresponding directions onto said detector. The detection subsystem is arranged to measure a time between said light source emitting a given signal and said detector receiving a corresponding incoming signal and to calculate a distance to the object based on said time. The detection subsystem may thus have an effective aperture greater than a physical aperture of the adjustable deflecting element. The ranging system can be used for example in autonomous vehicles.

Description

Ranging Detection

This application relates to arrangements for detection of the range to an object, particularly, although not exclusively, based on the LIDAR principle. This may have applications, for example, in the field of autonomous or semi-autonomous vehicles which need to be able to detect obstacles and other vehicles reliably.

With the increasing focus on the development of autonomous and semi- autonomous vehicles, some of the most important enabling technologies are those that allow the detection of objects, pedestrians and other vehicles. A popular such technology is light detection and ranging (LIDAR). One of the challenges that is faced by LIDAR is that of extending the detection range. As LIDAR systems rely on light transmission, their effective detection range is limited by the fundamental property that the power of light which is received after reflection from the object being detected is attenuated as the inverse square of distance travelled, itself of course double the detection range. However, equally important are the rate at which the environment is scanned in order reliably to detect objects when the vehicle is travelling at speed and the resolution of the detection system.

As will be appreciated, there is conflict between two requirements mentioned above, since achieving a sufficiently high scanning rate limits the amount of light energy which can be received from a given direction which limits the achievable range and resolution. For example, practical implementations of LIDAR ranging systems on autonomous vehicles tend to have a range of only about 50 metres.

The present invention seeks to address some of the issues set out above and when viewed from a first aspect provides a light-based ranging system comprising: a light source arranged to emit time varying light signals; a detection subsystem arranged to receive incoming light signals comprising reflections of said time varying light signals from an object, the detection subsystem comprising: a lens an adjustable deflecting element; and a detector wherein the lens is arranged to direct said reflections onto said adjustable deflecting element and the adjustable deflecting element is adjustable into a plurality of configurations, such that in each of said plurality of configurations the adjustable deflecting element deflects reflections from different corresponding directions onto said detector wherein the detection subsystem is arranged to measure a time between said light source emitting a given signal and said detector receiving a corresponding incoming signal and to calculate a distance to said object based on said time.

Thus it will be seen by those skilled in the art that in accordance with the invention there is provided a light based ranging system, e.g. LIDAR. In which an adjustable deflecting element is disposed between the lens and the detector. As will be explained below, this arrangement enables an increase in the effective aperture size of the detection system than the physical aperture defined by the fixed elements thereof.

When viewed from a second aspect the invention provides a light-based ranging system comprising: a light source arranged to emit time varying light signals; a detection subsystem arranged to receive incoming light signals comprising reflections of said time varying light signals from an object, the detection subsystem comprising: a lens an adjustable deflecting element; and a detector wherein the lens is arranged to direct said reflections onto said adjustable deflecting element and the adjustable deflecting element is adjustable into a plurality of configurations, such that in each of said plurality of configurations the adjustable deflecting element deflects reflections from different corresponding directions onto said detector such that the detection subsystem has an effective aperture greater than a physical aperture of the adjustable deflecting element, wherein the detection subsystem is arranged to measure a time between said light source emitting a given signal and said detector receiving a corresponding incoming signal and to calculate a distance to said object based on said time. Moreover adjustment of the deflecting element allows light from a greater range of directions to be directed at the detector than if it were not adjustable. The result of this is that the system may have a wider field of view for a given size which allows for a more beneficial implementation of such a light-based ranging system with an extended effective range without sacrificing an acceptable resolution because it can collect a greater amount of light. Furthermore such an arrangement may allow an optimal trade-off to be chosen between the effective aperture of the detection subsystem and the field of view.

In a set of embodiments the adjustable deflecting element comprises a mirror. In a set of such embodiments the mirror is adjusted by tilting. This is not essential however - the Applicant has envisaged a number of different implementations which can deflect light in an adjustable direction such as suitable metamaterials . These may be configured so that a substrate thereof does not physically move but rather the material properties are changed - e.g. by application of an electric field - to alter the degree of deflection provided.

In a set of embodiments the light source is arranged to emit discrete light pulses. In some situations these may be the most straightforward to detect. In another set of embodiments the light source is arranged to emit a modulated continuous wave - e.g. a frequency modulated continuous wave (FMCW).

In a set of embodiments the ranging system is able to reflections from objects more than 50 metres away, e.g. more than 75 metres away, e.g. more than 100 metres away.

In a set of embodiments the detection subsystem has an angular resolution of less than 0.5 degrees, e.g. less than 0.2 degrees, e.g. less than 0.1 degrees.

The ranging system could be used in any of a number of applications, but in a set of embodiments it is suitable for use in a vehicle for determining a distance to an object or another vehicle. In a set of such embodiments the ranging system is provided in a housing suitable for installation in or on a vehicle. From a further aspect the invention extends to a vehicle comprising a ranging system of the kind described herein. In a set of embodiments the vehicle comprises a control system arranged at least partially to control the vehicle based on said calculated distance.

In accordance with the invention, the physical aperture of the detection subsystem may be defined by a projection of the deflection element onto a plane normal to a central axis of the incoming light. In this way, by positioning the lens (and thus the front principal plane of the lens) in front of the deflecting element (such that the deflecting element is disposed between the lens and the detector) the physical aperture may be effectively enlarged by a geometrical magnification factor to provide an effective aperture. The geometrical magnification factor may be dependent on variables such as, the focal length of the lens and the tilting angle of the deflecting element.

A particular embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a schematic block diagram of a ranging system embodying the invention;

Fig. 2 is a schematic diagram illustrating the wider effective aperture achievable in accordance with the invention;

Fig. 3 is a schematic diagram illustrating light entering the detection subsystem from the upper edge of the effective aperture thereof;

Fig. 4 is a schematic diagram illustrating light entering the detection subsystem from the lower edge of the effective aperture thereof;

Fig 5. is a schematic view similar to Fig. 2 showing the mirror in the position shown in Fig. 3;

Fig 6. is a schematic view similar to Fig. 2 showing the mirror in the position shown in Fig. 4; and Fig 7. is a schematic showing the superposition of Figs. 5 and 6.

Fig 8. is a photograph showing an experimental set up of part of a system in accordance with the invention;

Fig 9. shows simulation data of the actual size of the aperture of the system of Fig. 8 as a function of the angle of the deflecting element;

Fig 10. shows a comparison of simulation data to experimental results obtained from the system of Fig. 8;

Fig 11. shows experimental results showing received power as a function of mirror angle;

Fig 12. shows simulation data of spot size and shape as a function of mirror angle.

Fig 13. shows experimental results comparable to simulations shown in Fig 12.

Turning to Fig. 1 there may be seen the main components of a LIDAR range detection system 1 in accordance with an embodiment of the invention. The system could, for example, be installed on an autonomous vehicle for detecting other vehicles, pedestrians or stationary hazards.

The system comprises a light source 2, such as a 1550nm laser configured to produce 500W 10ns pulses. Light from the light source 2 is deflected by an adjustable deflecting element in the form of a steerable mirror 4 (the function of which is described in greater detail below) before passing through a lens 6. The mirror 4 may be moved by a non-commutated DC linear actuator, also known as a ‘voice coil’. Arrangements such as those described in WO 2016/055253 could be used. Alternatively a micro-electrical mechanical systems (MEMS) arrangement could be used. The mirror may for example have a diameter of 10 mm and be able to be deflected through an angle of +/- 12.5 degrees.

Light 8 exiting the lens 6 passes into the environment and strikes an object 10, which could be over a hundred metres away. Light 12 which is reflected from the object 10 passes back through the lens 6 and is deflected by the mirror 4 onto a detector 14, such as a 200 pm InGeAs (Indium-gallium-arsenide) avalanche photodiode (APD).

In use the laser 2 emits a series of light pulses which are directed through the lens 6 by the mirror 4. They reflect from an object 10 before following a path back through the lens 6 to be deflected by the mirror 4 onto the detector 14. A timer and processor subsystem (not shown) calculates a time of flight of the light pulses and uses this to calculate a distance between the ranging system 1 and the object 10.

Fig. 2 show schematically the physical arrangement of some of the components of the ranging system of Fig. 1. More particularly it shows parts of the detection subsystem for receiving incoming light signals arising from reflections from the object 10, including the lens 6, steerable mirror 4 and detector 14. The incoming light 12 which is depicted as a two horizontal collimated beams is focussed by the lens 6 onto the mirror 4 which deflects the light through a variable angle, the median of which is a right angle, onto the detector 14.

As will be appreciated, the physical aperture 16 of the detection subsystem is defined by the projection of the mirror 4 onto the plane normal to the central axis 18 of the incoming light 12. Incoming rays of different angles will pass along different optical paths through the lens 6 and will be focussed onto different parts of the focal plane. However, since the back principal plane of the lens 6 is placed in front of the physical aperture 16, the effective aperture 20 is enlarged by a geometrical magnification factor, e.g. 2.5, dependent on the focal length of the lens.

Moreover, as will be explained with reference to Figs. 3 to 5, by moving the steerable mirror 4, a scanning function is achieved.

Turning to Fig. 3, there can be seen a configuration where the mirror 4 is tilted to a minimum angle with respect to the central axis 18. A light beam 12a is shown which is at the greatest angle above the axis 18 which will be focussed by the lens 6 onto the mirror 4 so as to be able to hit the detector. This therefore defines one edge of the field of view of the detection subsystem. By contrast Fig. 4 there shows a configuration where the mirror 4 is tilted to a maximum angle with respect to the central axis 18. A light beam 12b is shown which is at the greatest angle below the axis 18 which will be focussed by the lens 6 onto the mirror 4 so as to be able to hit the detector. This therefore defines the other edge of the field of view of the detection subsystem.

The field of view which is available by tilting the mirror 4 is defined by the angle of tilt (e.g. +/- 12.5 degrees of the mirror which results in +/- 25 degrees of movement of the reflected rays) and the geometrical magnification factor (e.g. 2.5) mentioned above. As will be explained below with further reference to Figs. 5 and 6, the scanning field of view is determined by the magnification factor of the lens 6 as the width of the effective aperture 20 is. This means that by selecting different focal lengths, and thereby using different geometrical magnification factors, different trade-offs between scanning field of view and effective aperture size can be achieved.

As will be appreciated by those skilled in the art, the scanning field of view is important to ensure that a sufficiently wide area in front of the vehicle can be surveyed whilst the effective aperture size is important as a wider effective aperture will allow more light to be collected for a given transmit power and will thus extend the range of detection as a greater attenuation with distance can be tolerated if more light is collected.

Referring to Fig. 5, the mirror 4 is shown in the minimum angle position shown in Fig. 3. From here can be seen three parallel rays 22a, 22b, 22c at a maximum angle A+ above the horizontal. This angle A+ is determined by the tilt of the mirror 4 and the magnification factor of the lens 6. In the example previously given, the mirror 4 can tilt 12.5 degrees in each direction from its central position and thus the reflected rays are tilted by twenty five degrees in each direction. With a magnification factor of 2.5, this means that the angle A+ is ten degrees (25/2.5).

Similarly in Fig. 6 the mirror 4 is shown in the maximum angle position shown in Fig. 4. From here can be seen three further parallel rays 22d, 22e, 22f at a maximum angle A- which is the same magnitude as A+ but below the horizontal. With reference to Fig. 7 which shows a superposition of Figs. 5 and 6 (with some rays removed) showing the scanning field of view. As may be appreciated, as the effective aperture 20 increases (by using a larger geometrical magnification factor) the size of the scanning field of view angle A+, A- will decrease and vice versa.

The Applicant has found that by employing the principles mentioned above, a LIDAR system with a range of over 200 metres and a scanning angle of +/- 10 degrees can be achieved will be recognised by those skilled in the art as a significant improvement over known arrangements. The arrangement described above recognises that whilst the mirror can move the reflected rays though +/- 25 degree angle, only a +/- 10 degree scanning field of view is required. This allows a 2.5 magnification factor provided by the lens to be used to increase the effective aperture compared to the physical aperture which beneficially captures a corresponding greater amount of light and thereby extends the effective range of the system.

Fig 8. shows an experimental bench set up of the transmission light path of the ranging system which is used to measure the experimental data shown in Figs 10, 11 and 13, as discussed below. With reference to Fig 8, light is output from a fiber laser output 2a and directed onto the deflecting element mirror (not visible in the photograph due to the mount 5 which obscures the mirror face) which in turn deflects the laser light through the lens 6 to provide light beam 8 which is directed onto an object. A goniometer 11 is used to simulate the tilting angles of the deflecting element mirror. It will be appreciated, as shown in Fig. 1, that the light reflected from the object will be reflected back through the lens 6 and onto the deflecting element mirror to be directed into the detector (not shown).

Fig 9. shows simulation data of the effective size of the aperture as a function of the horizontal scanning angle (a) from -12.5° and +12.5° and the vertical scanning angle (P) from -25° to +25° of the deflecting element. As can be seen, at 0° (denoting the central position of the deflecting mirror) the effective size of the aperture is at a maximum. As the deflecting element is tilted away from 0° the effective size of the aperture decreases. Fig 10. shows a comparison of simulated beam positions to experimentally determined beam positions. As can be seen, the simulated data correlates well to the experimentally observed data points (measured using the experimental set up of Fig 8) thus verifying that the geometric relationship used to calculate the beam position for the simulated data is accurate.

Fig 11. shows experimental results showing the received power as a function of mirror angle. As can be seen, the power of the beam detected is non-linearly dependent on the scanning angle with the maximum power measured at the centre of the beam having a horizontal scanning angle of 0° and a vertical scanning angle of between 0° and 5°. It has been appreciated that increasing the field of view of the system as described by the present invention results in a compromise in the received power of the reflected light. However, the inventors have appreciated that the increase in the field of view presents more advantages as the power of the received beam can be sufficiently high to be detected, and higher than that of systems whereby a collimated beam is scanned.

Fig 12. shows simulation data of the spot size and shape as a function of mirror angle measured at 200 m. As can be seen, at a horizontal scanning angle (a) of 0° and a vertical scanning angle (P) of 0° (denoting the central position of the deflecting mirror) the spot is simulated to be circular with high and uniform power density across the spot. As the horizontal scanning angle (a) is varied away from 0°, it can be seen that the spot maintains a substantially circular shape but increases in size with a more reduced uniformity in the power density across the radius of the spot. As the vertical scanning angle (P) is varied away from from 0°, it can be seen that the spot shape becomes less circular.

Fig 13A. shows an experimentally observed spot having a horizontal scanning angle (a) of 0° and a vertical scanning angle (P) of 0° which is comparable to the simulated spot having a horizontal scanning angle (a) of 0° and a vertical scanning angle (P) of 0° shown in Fig 12.

Figure 13B shows an experimentally observed spot having a horizontal scanning angle (a) of 10° and a vertical scanning angle (P) of 20° which is comparable to the spot that would be expected if the simulation data shown in Fig 12 was extrapolated to these values.

Thus, as can be seen, the data described above in relation to Fig 9-13 shows that the present invention provides a light based ranging system which increases the effective aperture size of the detection system.

It will of course be appreciated by those skilled in the art that many variations and modifications are possible within the scope of the invention. For example, it is not essential to use pulsed laser light; a frequency modulated continuous wave could be used instead. It is also not essential to use a mirror which can tilt; an adjustable metamaterial could equally be used, as well as non-mechanical beam steering.

Metamaterials, or metasurfaces, can be used for electromagnetic structures engineered on subwavelength scales to elicit tailored polarization responses, reflection, or refraction. Metasurfaces may refer to the two-dimensional counterparts of metamaterials. Metasurfaces modulate the behaviors of electromagnetic waves through specific boundary conditions. In the present disclosure the lens could for example be a flat lens lens whose flat shape allows it to provide distortion-free imaging. The aperture could then have any size. The tilting mirror could be made from metamaterial where the light enters the material and is then refracted or where a metasurface is the mirror changing the direction of the light similar to tilting a common mirror, but with no movable parts. Metasurfaces that can be used for a LIDAR system are described in Shaltout, Amr M., Vladimir M. Shalaev, and Mark L. Brongersma. "Spatiotemporal light control with active metasurfaces." Science 364, no. 6441 (2019). Flat optics are also discussed by Shalaginov, Mikhail Y., Sawyer D. Campbell, Sensong An, Yifei Zhang, Carlos Rios, Eric B. Whiting, Yuhao Wu et al. "Design for quality: reconfigurable flat optics based on active metasurfaces." Nanophotonics 1 , no. ahead-of-print (2020). Here different active switching mechanisms are reviewed and optical phase-change materials are further discussed.

Claims

Claims:

1. A light-based ranging system comprising: a light source arranged to emit time varying light signals; a detection subsystem arranged to receive incoming light signals comprising reflections of said time varying light signals from an object, the detection subsystem comprising: a lens an adjustable deflecting element; and a detector wherein the lens is arranged to direct said reflections onto said adjustable deflecting element and the adjustable deflecting element is adjustable into a plurality of configurations, such that in each of said plurality of configurations the adjustable deflecting element deflects reflections from different corresponding directions onto said detector wherein the detection subsystem is arranged to measure a time between said light source emitting a given signal and said detector receiving a corresponding incoming signal and to calculate a distance to said object based on said time.

2. A light-based ranging system comprising: a light source arranged to emit time varying light signals; a detection subsystem arranged to receive incoming light signals comprising reflections of said time varying light signals from an object, the detection subsystem comprising: a lens an adjustable deflecting element; and a detector wherein the lens is arranged to direct said reflections onto said adjustable deflecting element and the adjustable deflecting element is adjustable into a plurality of configurations, such that in each of said plurality of configurations the adjustable deflecting element deflects reflections from different corresponding directions onto said detector such that the detection subsystem has an effective aperture greater than a physical aperture of the adjustable deflecting element, wherein the detection subsystem is arranged to measure a time between said light source emitting a given signal and said detector receiving a corresponding incoming signal and to calculate a distance to said object based on said time.

3. The system as claimed in claim 1 or 2 wherein the adjustable deflecting element comprises a mirror.

4. The system as claimed in claim 3 wherein the mirror is adjustable by tilting.

5. The system of any preceding claim, wherein the adjustable deflecting element defines the physical aperture, and wherein a front principle plane of the lens is in front of the deflecting element to provide an effective aperture, said effective aperture comprising the physical aperture enlarged by a geometrical magnification factor.

6. The system of claim 5, wherein the geometrical magnification factor is dependent on at least one of, the focal length of the lens and a tilting angle of the deflecting element.

7. The system as claimed in any preceding claim wherein the light source is arranged to emit discrete light pulses.

8. The system as claimed in any preceding claim suitable for use in a vehicle for determining a distance to an object or another vehicle.

9. The system as claimed in any preceding claim comprising a housing suitable for installation in or on a vehicle.

10. A vehicle comprising the ranging system as claimed in any preceding claim.

11. The vehicle as claimed in claim 10 comprising a control system arranged at least partially to control the vehicle based on said calculated distance.