Patent Description:
Light Detection and Ranging (LIDAR) systems are known in the art, and have been identified as a useful technology for machine vision systems for use in various applications such as robotics, autonomous vehicles, and so-called driverless or self-driving cars. In very general terms, a LIDAR system includes a transmitter for transmitting pulses of light into a defined field of view of the LIDAR, and a receiver for detecting light reflected from objects within the defined field of view. A processor can then analyse the reflected light detected by the receiver to infer the presence and location of those objects. In some cases, a pulse (or "shot") may be made up of multiple sub-pulses. <CIT> describes laser radar devices adapted to ensure that the output from the laser is eye-safe. A means for applying spatial dither to the output of the laser source, such as a moveable optical arrangement is therein described. This causes the point of focus of the transmitted beam to traverse a target area by small amounts, reducing the overall radiation exposure at any particular point of focus, but having negligible impact on wind speed measurement for example. Alternative arrangements are therein described for ensuring eye-safety include periodically reducing the laser power density, gating the output or altering the focussing of the transmitted beam. <CIT> describes systems and methods for improved scanning ladar transmission, where closed loop feedback control is used to finely control mirror scan positions.

The transmitter is configured to transmit pulses (or "shots") of light in a narrow beam that can be steered to enable the entire field of view to be scanned within a predetermined scanning period. When a pulse (or shot) illuminates an object within the field of view of the LIDAR system, some of the light is scattered back toward the LIDAR system, and may be detected by the receiver. The "time of flight" between the transmission of a pulse and detection of the corresponding scattered light is indicative of distance to the point from which the light was scattered, while the direction of the transmitter beam (as determined by the steering device) can be used to determine the direction to the point from which the light was scattered. The distance and direction information associated with each shot can be processed to derive a "point cloud" indicative of the locations from which scattered light has been detected. This point cloud can be further processed to infer the size, location and possibly other characteristics of objects within the field of view.

It is desirable to maximize the power of the light pulses transmitted by the transmitter. However, eye safety regulations as defined in the American National Standards Institute (ANSI) standard Z136. <NUM>-<NUM> and in the International Electrotechnical Commission (IEC) standard <NUM>-<NUM> limit the maximum permissible optical power incident on a defined aperture to about 200nJ in a <NUM> interval.

An object of embodiments of the present invention is to provide methods and apparatus for increasing the optical power of the light emitted by a transmitter as defined by the independent claims, while conforming to applicable eye safety regulations.

Accordingly, an aspect of the present invention provides an optical apparatus comprising: a light source configured to emit light composed of a sequence of shots; and a steering device optically coupled to the light source and configured to steer the shots emitted by the light source in accordance with a predefined scan pattern such that at least one intermediate shot is emitted by the light source between a first shot directed by the steering device within an aperture defined by an eye safety regulation and a subsequent, second shot directed by the steering device within the same aperture, each intermediate shot being directed by the steering device outside the aperture.

A further aspect of the present invention provides a method of controlling an optical apparatus comprising a light source configured to emit light comprising a sequence of shots, and a steering device optically coupled to the light source. The method comprises controlling the steering device to steer the shots emitted by the light source in accordance with a predefined scan pattern such that at least one intermediate shot is emitted by the light source between a first shot directed by the steering device within an aperture defined by an eye safety regulation and a subsequent, second shot directed by the steering device within the same aperture, each intermediate shot being directed by the steering device outside the aperture.

<FIG> schematically illustrates elements of a Light Detection and Ranging (LIDAR) system <NUM>. In the example of <FIG>, the LIDAR system <NUM> comprises a transmitter <NUM> configured to transmit light <NUM>, and a receiver <NUM> configured to detect reflected light <NUM>. One or more windows <NUM> are provided to permit light <NUM> emitted from the transmitter <NUM> to exit the LIDAR system <NUM>, and to permit reflected light <NUM> to enter the LIDAR system and impinge on the receiver <NUM>. In the example of <FIG>, the transmitter <NUM> comprises a light source <NUM>, a steering device <NUM> and a controller <NUM> which operates to control the light source <NUM> and steering device <NUM>.

The light source <NUM> is preferably provided as a laser configured to emit light <NUM> at a predetermined wavelength and optical power level. The light source <NUM> may be for example an Infra-Red (IR) laser emitter configured to emit light having a wavelength of <NUM>-<NUM>. As may be seen in <FIG>, the light <NUM> may be emitted as a series of "shots" <NUM>. Each of the shots may include a plurality of optical pulses <NUM>. The number of pulses <NUM> in each shot <NUM>, along with the power level and duration (w) of each pulse <NUM> may be selected to enable reliable detection of reflected light <NUM> by the receiver <NUM>. In some embodiments each shot <NUM> may include <NUM> pulses <NUM>, while other embodiments may use as many as <NUM> or more pulses <NUM> in each shot <NUM>. A low-cost laser of a type usable in LIDAR systems may emit laser pulses having a duration (w) of <NUM> ns, and a pulse energy of <NUM> nJ, for a peak power level of <NUM> Watts. The frequency (<NUM>/T) at which shots are emitted may vary between <NUM> and <NUM>, depending largely on limitations of the steering device <NUM>.

As may be appreciated, in order to increase the range at which objects within the LIDAR field of view may be detected, it is desirable to increase the energy of each pulse <NUM>. However, since light having a wavelength in the <NUM>-<NUM> range can be focussed and absorbed by the eye, the maximum output of such a laser is limited by eye safety regulations, such as those defined in the American National Standards Institute (ANSI) standard Z136. <NUM>-<NUM> and in the International Electrotechnical Commission (IEC) standard <NUM>-<NUM>. These two standards have similar technical rules, albeit expressed in slightly differing language. In the present disclosure, embodiments of the invention will be described with reference to the nomenclature of ANSI Z136. <NUM>-<NUM>, but it should be understood that the invention also applies to IEC <NUM>-<NUM>, as well as successors and counterparts of both of these standards. For example, ANSI Z136. <NUM>-<NUM> defines a Maximum Permissible Exposure (MPE) and an Accessible Emission Limit (AEL). The MPE is the maximal optical radiation level a person can be exposed to before undergoing immediate or long term injuries. This maximum permissible exposure was established from the energy density limits, or the power-per-surface-unit (intensity) limits, that can be admitted on the cornea and on the skin. The MPE is calculated as a function of the radiation wavelength, the pulse duration, the exposure duration of the exposed tissue (skin or eye), and the size of the image on the retina. While the MPE defines the maximum pulse energies in terms of risk of injury, the AEL is derived from the radiation wavelength, power and energy emitted by the laser and accessible to a user (as represented by a defined aperture <NUM> (<FIG>) at a specified distance from the window <NUM>. Such definitions are use by eye safety regulations as they represent a realistic closest approach to a window by a human eye or an observation instrument such as a telescope. For example, using the definitions of ANSI Z136. <NUM>-<NUM> the aperture <NUM> may be defined as a circular area having a diameter of <NUM> at a distance of <NUM> from the window. The AEL therefore enables the classification of lasers according to the related radiation hazard, depending on the characteristics of each laser. For example, the ANSI Class <NUM> AEL for a wavelength of <NUM> is defined as: AEL=<NUM> nJ in a time interval (t) of 5ps<t≤<NUM>, and as AEL = (t<NUM> * <NUM>) mJ for <NUM><t≤<NUM>, where t is defined in units of seconds.

The steering device <NUM> is configured to direct the light <NUM> to scan a selected field of view of the LIDAR system. Example beam steering devices include moving (e.g. rapidly rotating) mirrors, or Spatial Light Modulator (SLM) devices such as Liquid Crystal on Silicon (LCoS) devices. In one embodiment, an Optical Waveguide Tunable Phased Array or Optical Waveguide Phased Array with a Tunable laser may be used to steer the beam. <FIG> schematically illustrates an example Optical Waveguide Tunable Phased Array steering device. In the example of <FIG>, the steering device, comprises a <NUM>:n optical power splitter <NUM> which is configured to divide the light emitted from the light source <NUM> into a sent of n optical paths <NUM>. Each path <NUM> includes an optical phase shifter <NUM> and an emitter <NUM>. The emitters <NUM> may take any suitable form (such as mirrors, waveguide tapers, or diffraction gratings, for example) such that light entering the emitter <NUM> from its corresponding phase shifter <NUM> will be emitted within a predetermined emission cone (not shown). Each phase shifter <NUM> operates to impose a phase shift on light propagating within the respective optical path <NUM> in accordance with a respective control signal <NUM> from the controller <NUM>. With this arrangement, light emitted from the light source <NUM> is divided by the <NUM>:n splitter <NUM> and supplied to each optical path <NUM>. The light propagating within each optical path <NUM> is then subjected to a respective phase shift before being emitted from the corresponding emitter <NUM>. The lights emitted from the emitters <NUM> recombine (due to constructive and destructive interference) to form one or more beams that propagate away from the emitters <NUM> (out of the page of the drawing of <FIG>) at an angle that is dependent on the phase shifts imposed by each of the phase shifters <NUM>. The direction of the (or each) beam can therefore be controlled by controlling the respective phase shift imposed by each phase sifter <NUM>.

<FIG> schematically illustrates an example illustrates an Optical Waveguide Tunable Array steering device with a tunable laser. In the example of <FIG>, the steering device <NUM>, comprises an optical path <NUM> that includes a diffraction grating <NUM>, which will generate a reflected light beam <NUM> at an angle (α) that is dependent on the optical frequency. In this example, the laser <NUM> is preferably configured as a tunable laser capable of emitting light at a desired frequency (or wavelength) in accordance with a suitable control signal <NUM> from the controller <NUM>. Optionally, the frequency response of the light source <NUM> may be supplemented by a phase shifter <NUM> operating in accordance with a suitable control signal <NUM> from the controller <NUM>. This control signal <NUM> may be computed making use of the differential relationship between phase and frequency. With this arrangement, light emitted from the light source <NUM> is supplied to the diffraction grating <NUM>. The reflected light emitted from the diffraction grating <NUM> will form one or more beams <NUM> that propagate away from the diffraction grating <NUM> (in the plane of the page of the drawing of <FIG>) at an angle that is dependent on the relationship between the frequency (or wavelength) of the light and the spacing of the diffraction grating <NUM>. The direction of the (or each) beam can therefore be controlled by controlling the optical frequency of the light incident on the emitter <NUM>.

In a further alternative arrangement, a fixed frequency light source <NUM> may be used to generate the light beam, which is made incident on an LCoS SLM <NUM>. In this case, the beam is steered solely by the LCoS SLM <NUM> in accordance with the control signal <NUM> from the controller <NUM>.

For ease of illustration and description, the example steering devices <NUM> shown in <FIG> are configured to steer the light beam in <NUM> dimension. It is contemplated that extension of these examples to enable steering of the light beam in <NUM> dimensions will be well within the purview of hose of ordinary skill in the art.

The steering device <NUM> may be operated to direct the light <NUM> to trace a specific pattern across the field of view, such as a raster-scan pattern or a Lissajous-figure scan pattern, for example. With all scanning patterns, the light <NUM> is directed to scan the LIDAR field of view so as to illuminate any objects within the field of view and enable detection of a point cloud from which information about illuminated objects may be inferred.

In the example of <FIG>, the receiver <NUM> comprises a photodetector <NUM>, an Analog-to-Digital Converter (ADC) <NUM>, and a Digital Signal Processor (DSP) <NUM>. Other optical and electronic devices, such as lenses, mirrors, filters or amplifiers may be used, but are not illustrated in <FIG> in order to simplify the description. The photodetector <NUM> operates in a conventional manner to detect reflected light <NUM> a generate a corresponding photodetector signal <NUM>. The ADC samples the photodetector signal <NUM> at a predetermined sample rate, and supplies a corresponding digital sample stream <NUM> to the DSP <NUM>. With this arrangement, the time of flight may be determined by the DSP <NUM> in various ways. For example, in some embodiments, the time of flight may be determined by the sample rate of the ADC. For example, a sample rate of <NUM> represents a sample period of 1ns. This allows the time of flight to be determined (to a resolution of 1ns) by counting the number of samples received by the DSP <NUM> between the time at which a shot of light <NUM> is emitted by the transmitter <NUM> and detection of the corresponding scattered light <NUM>. Furthermore, the distance to the point from which the reflected light <NUM> was scattered can be estimated (e.g. to a resolution of ±<NUM>) by recognising that light travels in air approximately <NUM> in 1ns.

The present invention provides techniques for controlling the light source <NUM> and the steering device <NUM> to increase (in comparison to conventional techniques) the optical pulse energy output by the LIDAR transmitter <NUM> while maintaining safe levels of pulse energy accessible to a user as represented by a predetermined aperture <NUM> (<FIG>) at a specified distance from the window <NUM> of the LIDAR unit <NUM>. An advantage of the present invention is that the pulse energy emitted by the LIDAR system <NUM> may be significantly greater than prior art systems, without exceeding limits imposed by eye safety regulations.

For the purposes of the present disclosure, the aperture <NUM> shall be considered to be defined by the applicable eye safety regulations, such as, for example, the American National Standards Institute (ANSI) standard Z136. <NUM>-<NUM>. It is convenient to describe the size of the aperture as a "reference dimension". Where the aperture <NUM> is defined as a circular planar area at a defined distance from the LIDAR window <NUM> (as shown in <FIG>), the "reference dimension" may conveniently be considered to be the diameter of the planar area. Thus, for example, in ANSI standard Z136. <NUM>-<NUM>, the aperture <NUM> is a circular planar area positioned <NUM> from the LIDAR window <NUM>, and having a diameter of <NUM>. In this case, the reference dimension is <NUM>, corresponding with the diameter of the aperture. For ease of description in the present disclosure, this nomenclature will be used. However, it will be appreciated that the aperture (and therefore the reference dimension) may be defined in other ways. For example, the aperture may be defined as a region bounded by a circle that is at a defined distance from a given center point. In such a case, the dimensions of the aperture may be defined using polar coordinates, and the reference dimension may therefore be an angle subtending the aperture.

In accordance with the present invention, the optical pulse energy may be increased without exceeding eye safe exposure limits by providing an optical apparatus comprising light source configured to emit light composed of a sequence of shots; and a steering device optically coupled to the light source. The steering device is configured to steer the shots emitted by the light source in accordance with a predefined scan pattern such that at least one intermediate shot is emitted by the light source between a first shot directed by the steering device within an aperture defined by an eye safety regulation and a subsequent, second shot directed by the steering device within the same aperture. Each intermediate shot is directed by the steering device outside the aperture. Preferably, more than one intermediate shots are emitted between the first shot directed within the aperture and the subsequent second shot directed within that same aperture. Preferably, the first shot directed within the aperture and the subsequent second shot directed within that same aperture form a non-zero angle therebetween. For the purposes of this disclosure, a shot is considered to be directed within the aperture if the center (or "aim point") of that shot falls within the aperture.

In some embodiments, the light source <NUM> and the steering device <NUM> are configured to output a single beam. In such embodiments, the scan pattern is selected to provide a separation between any two successive shots that is at least equal to the reference dimension. This ensures that there will be at least one intermediate shot between a first shot directed within a given aperture and a next shot directed within that same aperture.

In other embodiments, the light source and the steering device <NUM> are configured to output two or more beams simultaneously. In such embodiments, the steering device <NUM> is further configured to provide a separation between any two of the beams that is at least equal to the reference dimension, and the scan pattern is selected to provide, for all of the beams, a separation between any two successive shots that is at least equal to the reference dimension.

Example embodiments are described below with reference to <FIG>.

<FIG> illustrates an embodiment in which a single beam is used to scan a linear field of view <NUM> of the LIDAR system <NUM>. In the example of <FIG>, the reference dimension is represented by a dashed circle <NUM> corresponding to the aperture <NUM>. The light <NUM> emitted by the LIDAR transmitter <NUM> is considered to form a beam spot <NUM> in the plane of the aperture <NUM>. The beam spot <NUM> has a diameter corresponding to the height of the field of view <NUM> of the LIDAR system <NUM>. In the illustrated embodiment, the beam spot <NUM> has a radius equal to <NUM>/<NUM> of the reference dimension <NUM>. In order to scan the entire field of view <NUM>, the controller <NUM> operates (for example in accordance with firmware stored in a memory) to control the steering device <NUM> to direct the light <NUM> through a set of <NUM> positions (labeled as r=<NUM>. r=<NUM> in <FIG>) along the length of the field of view <NUM>, with each position offset from its neighbors by the radius of the beam spot <NUM>. With this arrangement, the entire field of view <NUM> may be scanned using a series of <NUM> shots, which may be emitted by the transmitter <NUM> at times T1-T12.

In accordance with the present invention, the steering device <NUM> is controlled to direct the light <NUM> to each one of the set of <NUM> positions in accordance with a scan pattern is selected to provide a separation between any two successive shots that equal to or greater than the reference dimension. In the example, of <FIG>, the scan pattern is implemented as a multi-pass scan, in which three passes are used to reach all of the <NUM> positions (r=<NUM>. Thus, in a first pass, shots emitted at times T1, T2, T3 and T4 are directed to positions r=<NUM>, r=<NUM>, r=<NUM> and r=<NUM>, respectively. In a second pass, shots emitted at times T5, T6, T7 and T8 are directed to positions r=<NUM>, r=<NUM>, r=<NUM> and r=<NUM>, respectively. Finally, in the third pass, shots emitted at times T9, T10, T11 and T12 are respectively directed to positions r=<NUM>, r=<NUM>, r=<NUM> and r=<NUM>.

As may be seen, within each pass, successive shots are directed to respective positions that are separated by a distance of <NUM>*r, which corresponds with the reference dimension <NUM>. Furthermore, between each pass, successive shots (i.e., shots T4 and T5, and shots T8 and T9) are directed to respective positions which are separated by a distance of <NUM>*r, which is greater than the reference dimension <NUM>.

Inspection of <FIG> also shows that for any position of the aperture <NUM>, there are <NUM> intermediary shots between a first shot that is directed within any given aperture <NUM> and a subsequent second shot directed within that same aperture. For example, the circle <NUM> shown in <FIG> represents an aperture <NUM> located at the extreme left end of the field of view <NUM>. This aperture <NUM> receives light <NUM> from shots T1, T5 and T9, each of which is separated by <NUM> intermediary shots which are directed outside of the aperture. Furthermore, it will be seen that the aim point of each of shots T1, T5 and T9 are separated from each other by a non-zero angle. The interval between successive shots incident on a common aperture is therefore equal to <NUM> times the shot period T. The presence of intermediary shots increases the allowable optical energy of each pulse as compared to conventional techniques, without violating the eye safety regulations. The three examples described below illustrate this advantage.

It may be recognised that there may be positions of the aperture for which some light from two successive shots may be incident on a common aperture. For example, the circle <NUM> shown in <FIG> represents an aperture <NUM> located md-way between positions r=<NUM> and r=<NUM>. This aperture <NUM> receives light <NUM> from shots T3, T7, T11 and T4. However, less than half of the shot energy from each of shots T3 and T4 falls within the aperture, so that the combined optical energy received by the aperture (from shots T3 and T4) is less than the total energy emitted by the transmitter <NUM> in a single shot. Consequently, for the purposes of calculating eye safe optical power levels, the two partial shots at r=<NUM> and r=<NUM> can be replaced by a single whole shot at the timing of either T3 or T4.

As noted above, the ANSI Class <NUM> AEL for a wavelength of <NUM> is defined as: AEL=<NUM> nJ in a time interval (t) of 5ps<t≤<NUM>, and as AEL = (t<NUM> * <NUM>) mJ for <NUM><t≤<NUM>. For the purposes of this example, we will consider the case of a <NUM> interval, so the AEL is 200nJ. For the laser properties, we may consider a laser <NUM> configured to generate shots at a frequency of <NUM>, so that the period T=<NUM>. Eye safety regulations specify that the allowable AEL is defined according to the worst-case scenario. In this example, in any given <NUM> interval there are either <NUM> or <NUM> shots, and thus in the worst case <NUM> shots will be incident on a given aperture within a <NUM> interval. Furthermore, we will consider that the laser <NUM> is configured to generate a total of <NUM> pulses in each shot. This means that the maximum allowable laser energy is <NUM> nJ per interval /<NUM> shots per interval = <NUM> nJ per shot. For the case of <NUM> pulses per shot , the maximum allowable energy per pulse is <NUM> nJ.

In the example of <FIG>, the scan pattern ensures that the interval between successive (whole) shots directed on a common aperture is equal to <NUM> times the shot period T. For the case of T=<NUM>, the interval is <NUM>. An AEL of 200nJ per <NUM> interval is equivalent to 320nJ per <NUM> interval. Since the scan pattern ensures that no more than one (whole) shot will be incident on any given aperture in this <NUM> interval, the maximum safe laser energy is 320nJ per shot, or <NUM> nJ per pulse. This represents <NUM> times more energy per pulse than would be permitted using conventional techniques.

According to the invention, the energy of each shot is determined as:
<MAT>
where Es is the energy of each shot, AEL is the defined amount of energy incident on the defined aperture during the predetermined time interval, t is the duration of the predetermined time interval, N is the number of intermediate shots, and T is the shot period. In the example of <FIG>, the number of intermediary shots, N, is <NUM>; AEL-<NUM> and t=<NUM>. Using this nomenclature, the energy of each pulse is simply<MAT>
where: Ep is the energy of each pulse, and P is the number of pulses in each shot.

The example of <FIG> is simplified for ease of description and understanding. In a practical LIDAR system, the number of intermediary shots between any two shots that are incident on a given aperture may be significantly greater. For example, consider a LIDAR system having a field of view <NUM> that is <NUM>° wide, each shot <NUM> has a radius of <NUM>°, and the aperture <NUM> has a diameter of <NUM>°. As may be seen in <FIG>, the scan pattern is similar to the example of <FIG>, except that the laser beam is steered through <NUM> discrete positions (r=<NUM>. r=<NUM>), and the reference dimension is equal to four times the beam radius. A total of four passes are required to scan the entire field of view <NUM>, and any given aperture <NUM> will receive energy from four separate shots. This implies that the interval between successive shots incident on any given aperture is equivalent to <NUM> positions/<NUM> passes=<NUM> times the shot period T. For the case of T=<NUM>, the interval between successive shots incident on any given aperture is <NUM>. An AEL of 200nJ per <NUM> interval is equivalent to 1200nJ per <NUM> interval. Since the scan pattern ensures that no more than one shot will be incident on any given aperture in this <NUM> interval, the maximum safe laser energy is 1200nJ per shot, or <NUM> nJ per pulse (assuming <NUM> pulses per shot). This represents <NUM> times more energy per pulse (equivalent to an increase of 13dB of optical signal strength) than would be permitted using conventional techniques.

As may be appreciated, increasing the energy per pulse produces a corresponding increase in the performance of the LIDAR system. For example, it is useful to calculate a distance through fog at which the LIDAR receiver <NUM> can reliably detect light <NUM> reflected from an object. For this purpose, it is common to consider fog as attenuating light via absorption and scattering at a rate of 4dB per <NUM> meters. Since the light reaching the receiver <NUM> is first emitted from the transmitter <NUM> before reflecting off the object, the round-trip loss due to fog is equivalent to 4dB per <NUM> meters of separation between the object and the LIDAR system <NUM>. Furthermore, increasing the distance (d) between the LIDAR receiver <NUM> and an object reduces the energy of the reflected light <NUM> detected by the receiver in accordance with the inverse square law ( <MAT>). Taking these factors into account, and assuming that the energy of the reflected light <NUM> at the receiver <NUM> must remain unchanged to ensure accurate detection of objects, a 13dB increase in the energy of each pulse emitted by the transmitter translates into an increased detection range of approximately <NUM> meters, relative to conventional systems.

In the examples illustrated above, the field of view is linear, so that a <NUM>-dimensional scan pattern (as shown in <FIG> and <FIG>, for example) is needed to cover the entire field of view. It will be appreciated that these scan patterns may be extended to cover a polygonal field of view, if desired. For example, LIDAR systems commonly are capable of scanning a rectangular field of view, which, for example, may have <NUM> spots laterally and <NUM> spots vertically, for total of <NUM> spots. The spot positions may be separated by ¼ of the reference dimension, in which case a reference aperture receives energy from 4x4=<NUM> spots. <FIG> is a table illustrating a <NUM>-dimensional scan pattern suitable for such a <NUM>-dimensional field of view. In the example of <FIG>, the rectangular field of view <NUM> may conveniently be represented as a table having <NUM> rows and <NUM> columns. Each cell <NUM> of the table corresponds with a respective position in the field of view <NUM> to which light <NUM> may be directed by the steering device <NUM>. The time at which each position in the field of view is illuminated by the light <NUM> is indicated by the number in the corresponding cell of <FIG>. The reference dimension is illustrated by the circle <NUM> in the table, and the positions for which light is directed into the corresponding aperture are shown as a shaded region <NUM>.

As may be seen in <FIG>, the scan pattern follows a 4x4 modified raster scan. Accordingly, in a first pass, shots are directed to row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>, etc. until rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM> have been scanned. In the second pass shots are directed to row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>; row <NUM>, columns <NUM>, <NUM>, <NUM>, <NUM>. <NUM>, etc. until rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM> have been scanned. This pattern is repeated though passes <NUM> and <NUM> until all of the columns in rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM> have been scanned. Passes <NUM>-<NUM> repeat the pattern for passes <NUM>-<NUM>, but for rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. Passes <NUM>-<NUM> repeat the pattern for passes <NUM>-<NUM>, but for rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. Finally, passes <NUM>-<NUM> repeat the pattern for passes <NUM>-<NUM> for rows <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

In the example of <FIG>, a total of <NUM> shots (four shots in each of four adjacent rows) are required to completely cover a given aperture, and the minimum interval between two successive shots directed within the aperture is <NUM> (pertaining to shots <NUM> and <NUM>) times the shot period T. For the case of T=<NUM>, the minimum interval between successive shots incident on any given aperture is <NUM> *<NUM> = <NUM>. An AEL of 200nJ per <NUM> interval is equivalent to 9680nJ per <NUM> interval. This yields a maximum safe laser energy (based on the AEL calculation) of 9680nJ per shot, or <NUM> nJ per pulse (assuming <NUM> pulses per shot). However, this exceeds the maximum permissible energy of 200nJ for a single pulse (AEL=<NUM> nJ for 5ps<t≤<NUM>), as defined by ANSI standard Z136. <NUM>-<NUM> or IEC <NUM>-<NUM>. Accordingly, the laser energy in the embodiment of <FIG> would be limited to 200nJ per pulse. However, this still represents <NUM> times more energy per pulse (equivalent to 18dB) than would be permitted using conventional techniques. Following the calculations above, it will be seen that an 18dB increase in the energy of each pulse emitted by the transmitter translates into an increased detection range through fog of approximately <NUM> meters relative to conventional systems.

The examples of <FIG> describe scan patterns in which the light <NUM> is steered in each row such that the separation between any two successive shots is equal to the reference dimension. In the example of <FIG>, this pattern is extended to two dimensions such that the separation between any two successively scanned rows is also equal to the reference dimension. This achieves the objective of ensuring that at least one intermediary shot is emitted by the transmitter <NUM> between a first shot directed within a given aperture <NUM> and a next shot directed within that same aperture. However, it is contemplated that there are many alternative scan patterns that may also be used to ensure that the separation between any two successive shots is equal to or greater than the reference dimension. Thus it will be appreciated that the specific scan patterns described in the present disclosure are illustrative, and not limitative of the present invention.

Based on the foregoing discussion, it will be seen that increasing the number of intermediary shots enables a corresponding increase in the laser output power, up to the single pulse limit (for example AEL=200nJ for 5ps<t≤<NUM>) imposed by the eye safety regulations. Beyond this point, no further increase in laser output power can be obtained by increasing the number of intermediary shots, without exceeding eye safety limits.

The embodiments described above with reference to <FIG> the laser <NUM> and the steering device <NUM> are configured to output a single beam. As noted above, the laser <NUM> and the steering device <NUM> may alternatively be configured to output two or more beams simultaneously. For example, <FIG> schematically illustrates an example LIDAR system <NUM> in which light emitted by the laser <NUM> is split into four beams 504A-504D, which are then directed by the steering device <NUM> (operating under control of the controller <NUM>) to scan the field of view. The receiver <NUM> is similarly configured to detect reflected light 508A-508D corresponding to each of the transmitted beams 504A-504D, and compute corresponding time-of-flight and distance information for each beam. In such embodiments, the steering device <NUM> is further configured to provide a separation between any two of the beams <NUM> that is at least equal to the reference dimension, and the scan pattern is selected to provide, for all of the beams 504A-504D, a separation between any two successive shots that is at least equal to the reference dimension. <FIG> illustrates an example scan pattern.

In the embodiment of <FIG>, the rectangular field of view <NUM> is divided into <NUM> rows of <NUM> positions each. Each of the four beams output from the laser <NUM> and the steering device <NUM> is directed to scan a respective quadrant <NUM> of the field of view <NUM>, using an identical scan pattern. The reference dimension is four times the radius of the beam spot, and the scan pattern is represented as a table having <NUM> rows and <NUM> columns. Each cell <NUM> of the table corresponds with a respective position in the field of view <NUM> to which light <NUM> may be directed by the steering device <NUM>. Each quadrant <NUM> of the field of view <NUM> may therefore be represented by a corresponding quadrant (in this example comprising <NUM> rows and <NUM> columns) of the table, as shown in <FIG>. The time at which each position in the field of view is illuminated by one of the beams is indicated by the number in the corresponding cell <NUM> of the table. The reference dimension is illustrated by the ellipse <NUM> in each quadrant <NUM> of the table of <FIG>, and the positions for which light is directed into the corresponding aperture are shown as a shaded region <NUM>.

As may be seen in <FIG>, each quadrant <NUM> is scanned using a scan pattern closely similar to that of <FIG>, except that it is truncated to <NUM> rows and <NUM> columns. Furthermore, it will be seen that the four beams 504A-504D are separated from one another by <NUM> rows and <NUM> columns, which is significantly larger than the reference dimension. Accordingly, the embodiment of <FIG> achieves the objective of providing a separation between any two of the beams that is at least equal to the reference dimension, and the scan pattern is selected to provide, for all of the beams, a separation between any two successive shots that is at least equal to the reference dimension. In this example, detection of scattered reflected light 508A-508D may be accomplished by providing respective different receivers (each similar to that described above with reference to <FIG>) and restricting the field of view of each receiver to the appropriate one o the four quadrants. In an alternative arrangement, the transmitter <NUM> may be configured to emit each of the beams 504A-504D using a respective different wavelength, in which case optical filtering may be used to separate the corresponding reflected lights 508A-508D.

In the example of <FIG>, a total of <NUM> shots (four shots in each of four adjacent rows) are required to completely cover a given aperture, and the smallest interval between any two shots directed into the aperture (in the illustrated example, shots <NUM> and <NUM>) is <NUM> times the shot period T. For the case of T=<NUM>, the smallest interval between successive shots incident on any given aperture is <NUM>*<NUM> = <NUM>. An AEL of 200nJ per <NUM> interval is equivalent to 2480nJ per <NUM> interval. This yields a maximum safe laser energy (based on the AEL calculation) of 2480nJ per shot, or <NUM> nJ per pulse (assuming <NUM> pulses per shot). This still represents approximately <NUM> times more energy per pulse (equivalent to approximately 16dB) than would be permitted using conventional techniques.

An advantage of the embodiment of <FIG> is that the entire field of view is scanned in <NUM> times the shot period T, which is significantly faster than the <NUM>*T that would be required if a single-beam was used.

In the embodiment of <FIG>, there are four beams 504A-504D, which are steered in unison to scan a respective quadrant <NUM> of the field of view. If desired, more or fewer than four beams may be used. Similarly, the beams may be steered independently of each other. For example, <FIG> schematically illustrates an example LIDAR system <NUM> in which light emitted by the laser <NUM> is split into two beams, which are then directed by independent steering devices 714A and 714B (operating under control of the controller <NUM>) to scan the field of view. In such a case, each of beams 704A-704B can be steered in any desired direction to scan its respective portion of the field of view. If desired, the respective portions of the field of view scanned by each beam may be arranged in quadrants or sectors, as in the embodiment of <FIG>. However, other options may also be used. If desired, the respective portions of the field of view scanned by each beam may have cover any suitable portion of the field of view, and may be interleaved in any suitable manner. The key limitation is that in all cases, there must be an interval of at least one (and preferably more than one) intermediary shot between a first shot (from any beam) incident on a given aperture and a next shot (again, from any beam) incident on that same aperture.

The example embodiments described above with reference to <FIG> describe linear and rectangular fields of view and scan patterns defined in terms of specific numbers of shots or positions. Clearly, the field of view may be defined in any suitable manner, and may have any desired shape. Similarly, <NUM>-dimensional and <NUM>-dimensional scan patterns may be defined in any suitable manner to cover the field of view.

If desired, the shot density (i.e. the spacing between adjacent shot positions) may be constant (as in the embodiments of <FIG>) or may be varied within the field of view. For example, in the embodiments of <FIG> and <FIG>, a rectangular field of view is scanned using a scan pattern represented as a table with a given number of rows and columns. Thus in the illustrated embodiments each row has the same number of columns, and so is scanned using the same number of shots. If desired, the number of columns in each row may be varied so that, for example, rows near the center of the field of view have more columns (and so are scanned using more shots) than rows near the periphery of the field of view. Alternatively, the spacing between shots may be varied within a row, so that, for example, shots directed near the center of the field of view are positioned closer together than shots directed near the periphery of the field of view. In all of these cases, the scan pattern must be selected to ensure that there is at least one (and preferably more than one) intermediary shot between a first shot directed to a given aperture and a next shot directed to that same aperture.

If desired, the LIDAR system controller may change the scan pattern during operation of the system. For example, the controller may store information defining a set of two or more different scan patterns, and select one of the set of scan patterns as a current pattern. The information defining the selected current pattern is subsequently used by the controller to direct the laser and steering device(s) to scan the field of view (or a selected region of it) in accordance with the selected current pattern. At a later time (for example in response to changing conditions) the controller may select a different one of the set of patterns as the current pattern. The information defining the new current pattern is subsequently used by the controller to direct the laser and steering device(s) to scan the field of view (or a selected region of it) in accordance with the new current pattern.

If desired, the LIDAR system controller may implement respective different scan patterns in respective different regions of the field of view. For example, a selected region of the field of view may be scanned more frequently than another region of the field of view, to thereby gather more accurate information or more timely information about objects in the selected region. For example, in a fast-moving vehicle, information about objects directly in front of the vehicle is more critical than information about objects to the sides or the rear of the vehicle, because objects directly in front of the vehicle represent a more imminent collision hazard. Thus, the scan pattern(s) may be designed such that one or more selected regions of the field of view are scanned more frequently than other regions of the field of view. <FIG> illustrates an example, in which a central region of the field of view is scanned more frequently than the rest of the field of view.

In the embodiment of <FIG>, the rectangular field of view <NUM> is divided into <NUM> rows of <NUM> positions each. This field of view <NUM> is further subdivided into a pair of regions, including a first region (which, in this example, is discontinuous) composed of rows <NUM>-<NUM> (Region 1A) and rows <NUM>-<NUM> (Region 1B), and a second region composed of rows <NUM>-<NUM> (Region <NUM>). Each of these regions can be scanned using a respective one of the beams <NUM>-704B emitted by the LIDAR system <NUM> of <FIG>. Region <NUM> may be scanned using a scan pattern that is closely similar to that of <FIG>, except that it is truncated to <NUM> rows and <NUM> columns, and so is scanned in a period equivalent to <NUM> times the shot period T. Region <NUM> may be scanned using a scan pattern that is also closely similar to that of <FIG>, except that it is truncated to <NUM> rows and <NUM> columns, and so is scanned in a period equivalent to <NUM> times the shot period T. With this arrangement, the Region <NUM> will be scanned at twice the frequency of Region <NUM>, so that information of objects within the Region <NUM> is updated at double the rate of Region <NUM>.

If desired, the selected region(s) in which the scan frequency is increased may be statically defined, and thus would not change during operation of the LIDAR system. Alternatively, the selected regions in which the scan frequency is increased may be dynamically defined, for example in accordance with software executing in a processor of the LIDAR system. In such a case, the LIDAR system may change the scan frequency in a selected region of the field of view during operation, for example in response to changing conditions such as the speed of a vehicle on which the LIDAR system is mounted, or the detection of other objects in the field of view (such as other vehicles around the vehicle on which the LIDAR system is mounted).

Embodiments of the present invention may be provided as any suitable combination of hardware and software. For example, the present invention may be embodied as a LIDAR system configured to implement techniques in accordance with the present invention, or as software (or, equivalently, firmware) stored on a non-transitory machine readable storage medium and including software instructions for controlling a processor of a LIDAR system to implement techniques in accordance with the present invention, or as a non-transitory machine readable storage medium storing software (or, equivalently, firmware) including software instructions for controlling a processor of a LIDAR system to implement techniques in accordance with the present invention. For example, in a LIDAR system of the type illustrated in <FIG>, specific embodiments of the present invention may take the form of software (or, equivalently, firmware) stored in a memory (not shown) of the controller <NUM> and including software instructions for controlling the controller <NUM> to implement techniques in accordance with the present invention.

Claim 1:
An optical apparatus comprising:
a light source configured to emit light composed of a sequence of shots; and
a steering device optically coupled to the light source and configured to steer the shots emitted by the light source in accordance with a predefined scan pattern such that at least one intermediate shot is emitted by the light source between a first shot directed by the steering device within an aperture defined by an eye safety regulation and a subsequent, second shot directed by the steering device within the same aperture, each intermediate shot being directed by the steering device outside the aperture., wherein an energy of each shot is determined based on an Accessible Emission Limit defined by the eye safety regulation as a defined amount of energy incident on the aperture during a predetermined time interval, and wherein the energy of each shot is: <MAT>
where Es is the energy of each shot, AEL is the defined amount of energy incident on the aperture during the predetermined time interval, t is the duration of the predetermined time interval, N is the number of intermediate shots, and T is the shot period.