WO2020227761A1

WO2020227761A1 - An optical beam scanner

Info

Publication number: WO2020227761A1
Application number: PCT/AU2020/050459
Authority: WO
Inventors: Thomas Michael STACE; Mark Adam BAKER; Benjamin Robert HAYLOCK; Mirko LOBINO
Original assignee: The University Of Queensland; Griffith University
Priority date: 2019-05-10
Filing date: 2020-05-08
Publication date: 2020-11-19

Abstract

An optical beam scanner, including: a body composed of an electro-optically active material and having formed therein a plurality of optical waveguides arranged to define a branching tree of optical paths, the optical waveguides including at least one input waveguide and a plurality of mutually spaced output waveguides; and electrodes located at each of a plurality of junctions of the branching tree and configured to control optical coupling between adjacent portions of corresponding ones of the optical waveguides such that optical signals received at the input waveguide can be selectively and dynamically directed to any selected one of the mutually spaced output waveguides by applying corresponding electrical signals to corresponding ones of the electrodes to control the optical coupling at each junction of an optical path of the branching tree therebetween.

Description

AN OPTICAL BEAM SCANNER

TECHNICAL FIELD

The present invention relates to photonics, and in particular to an optical beam scanner and a LIDAR system including an optical beam scanner.

BACKGROUND

Optical beam scanners capable of high speed steering of an optical beam are essential for many imaging techniques, including LIDAR and medical imaging applications. The first commercial demonstrations of multi-pixel LIDAR sensors relied on cumbersome spinning mirrors. Similarly, full field optical coherence tomography relied on sample stage movement or mechanical mirror steering to scan a sample. Recent advances have moved to integrated beam scanning techniques, including MEMS mirrors, optical phase arrays, and VCSELs (Vertical Cavity Surface-Emitting Lasers). Other significant approaches include liquid crystal electro-optic scanners, electro-optic beam deflectors, and spectral scanning. These new beam scanning techniques have allowed improved sensing performance by increasing the size and refresh rate of the generated point cloud. However, most of these beam scanning technologies still limit the point cloud size and refresh rate due to speed limitations.

It is desired, therefore, to overcome or alleviate one or more difficulties of the prior art, or to at least provide a useful alternative. SUMMARY

In accordance with some embodiments of the present invention, there is provided an optical beam scanner, including :

a body composed of an electro-optically active material and having formed therein a plurality of optical waveguides arranged to define a branching tree of optical paths, the optical waveguides including at least one input waveguide and a plurality of mutually spaced output waveguides; and

electrodes located at each of a plurality of junctions of the branching tree and configured to control optical coupling between adjacent portions of corresponding ones of the optical waveguides such that optical signals received at the input waveguide can be selectively and dynamically directed to any selected one of the mutually spaced output waveguides by applying corresponding electrical signals to corresponding ones of the electrodes to control the optical coupling at each junction of an optical path of the branching tree therebetween.

In some embodiments, the plurality of optical waveguides further includes a plurality of intermediate waveguides for coupling the at least one input waveguide to the output waveguides. In some embodiments, at least some of the intermediate waveguides and corresponding electrodes are configured so that an optical signal travelling along an intermediate waveguide can be selectively coupled to any one of a plurality of corresponding waveguides immediately downstream of the intermediate waveguide.

In some embodiments, the optical beam scanner includes one or more optical deflection components configured so that optical signals emitted from each of the mutually spaced output waveguides are deflected at a corresponding angle.

In some embodiments, the optical deflection components are configured so that optical signals emitted from the mutually spaced output waveguides are deflected at respective different angles.

In some embodiments, each of the optical deflection components includes a refractive exit surface whose spatial orientation determines the corresponding deflection angle. In some embodiments, the one or more optical deflection components includes a lens component configured so that optical signals emitted from the mutually spaced output waveguides are incident upon respective different portions of the lens component, and are thereby emitted from the lens component at different angles in dependence upon which of the mutually spaced output waveguides emitted the optical signals.

In some embodiments, the electro-optically active material is selected so that the optical signals can be selectively switched between different ones of the mutually spaced output waveguides at sub-microsecond timescales.

In some embodiments, the optical beam scanner includes a plurality of instances of any one of the above optical beam scanners, arranged to provide a two-dimensional array of the output waveguides.

In some embodiments, the plurality of instances of the optical beam scanner are planar and arranged to be mutually parallel.

In some embodiments, the plurality of instances of the optical beam scanner are planar and include a first instance of the optical beam scanner and a plurality of second instances of the optical beam scanner, wherein respective input waveguides of the second instances of the optical beam scanner are optically coupled to respective output waveguides of the first instance of the optical beam scanner.

In some embodiments, the optical beam scanner is a component of a LIDAR system configured to detect the range and relative velocity of objects from the optical signals.

In some embodiments, the optical switch is a component of an autonomous vehicle navigation system. In accordance with some embodiments of the present invention, there is provided a LIDAR system, including :

any one of the above optical beam scanners;

a laser;

first and second optical modulators, each configured to receive output from the laser via an optical coupler and to generate a corresponding modulated optical signal;

an optical circulator configured to receive the modulated optical signal from the first optical modulator and to send the received modulated optical signal to the optical beam scanner, wherein the optical beam scanner emits the optical signal at different spatial locations, and receives corresponding reflected optical signals reflected from objects and sends the received reflected optical signals to the circulator;

an optical coupler configured to receive the reflected optical signals from the circulator and the modulated optical signal from the second optical modulator and to provide the resulting combined optical signals to a homodyne detector component to generate corresponding electrical signals; and

a processing component configured to determine ranges and relative velocities of the objects from the corresponding electrical signals.

In accordance with some embodiments of the present invention, there is provided a LIDAR system, including :

any one of the above optical beam scanners;

a laser;

an optical modulator configured to receive output from the laser and to generate a corresponding modulated optical signal;

an optical circulator configured to receive the modulated optical signal from the optical modulator and to send the received modulated optical signal to the optical beam scanner, wherein the optical beam scanner emits the optical signal at different spatial locations, and receives corresponding reflected optical signals reflected from objects and sends the received reflected optical signals to the circulator;

a detector component configured to receive the reflected optical signals from the circulator and to generate corresponding electrical signals; and

a processing component configured to determine ranges and relative velocities of the objects from the corresponding electrical signals. In accordance with some embodiments of the present invention, there is provided an optical beam scanning process for use with any one of the above optical beam scanners, including the steps of:

directing optical signals to the input waveguide of the optical beam scanner; and

applying electric signals to the electrodes of the optical beam scanner to cause the directional couplers to route the optical signals to sequential ones of the output waveguides.

a plurality of instances of any one of the above optical beam scanners, distributed at mutually spaced locations of a vehicle and coupled to a centralised optical source and controller via optical fibres.

In accordance with some embodiments of the present invention, there is provided an optical beam scanning process for use with any one of the above optical beam scanners, including the steps of:

applying electric signals to corresponding ones of the electrodes of the optical beam scanner to cause the optical signals to be routed to selected ones of the output waveguides.

In some embodiments, the electric signals applied to the electrodes of the optical beam scanner cause the optical signals to be routed to corresponding selected ones of the output waveguides and, for the optical signals emitted from each selected output waveguide, allow corresponding optical signals reflected from objects within range of the LIDAR system to be received by the selected output waveguide and routed to the input waveguide for detection. In some embodiments, the optical beam scanning process further includes:

providing any one of the above optical beam scanners; and controlling the application of signals to the electrodes to cause the optical signals to be emitted from corresponding ones of the output waveguides of the optical bean scanner in a corresponding sequence.

In some embodiments, the step of controlling the application of signals to the electrodes includes controlling the application of signals to the electrodes to :

(i) randomise the sequence;

(ii) increase or decrease resolution in one region, or across the whole of a scanned region;

(iii) optimise power use;

(iv) avoid or concentrate a selected region;

(v) speed up scanning;

(vi) optimise a search pattern;

(vii) facilitate machine based vision;

(viii) optimise the amount of data to be processed; and/or

(ix) assist algorithmic object detection.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, wherein:

Figure 1 is a perspective view of an optical beam scanning structure (or "scanner") in accordance with an embodiment of the present invention;

Figure 2 is a graph showing the frequency response of an optical beam scanner having three output waveguides or channels, in accordance with an embodiment of the present invention;

Figure 3 is a block diagram of a LIDAR system incorporating the optical beam scanner in accordance with an embodiment of the present invention;

Figure 4 is a schematic illustration showing the optical signals generated by the electro-optic modulators of the LIDAR system of Figure 3 and unwanted back reflections from the optical beam scanner;

Figure 5 is a graph showing a Fourier spectrum of LIDAR signals generated by the LIDAR system of Figure 3; Figures 6 and 7 are perspective views of respective optical beam scanners in accordance with alternative embodiments of the present invention ;

Figure 8 is a perspective view of a portion of an optical beam scanner having faceted exit surfaces to deflect optical signals at respective angles;

Figure 9 is a close-up plan view of an optical beam scanner in accordance with an embodiment of the present invention; and

Figure 10 is a schematic cross-sectional side view of a switching portion of the optical beam scanner of Figure 9.

DETAILED DESCRIPTION

As an alternative to the spatial beam manipulation devices and methods described above, the inventors have developed integrated or 'monolithic' optical beam scanning structures with distinct spatially separated outputs, and that are able to perform arbitrary discrete 'point-by-point' scans between the outputs, rather than a continuous sweep in a fixed direction or sequence. The optical beam scanners described herein each includes a dynamically reconfigurable waveguide network to perform such a discrete scan, ensuring high speed, side-lobe-free, single mode, and single wavelength beam steering with a one or two-dimensional field of view, and with spatial resolution determined by the scanner configuration and associated output optics.

Each of the described optical beam scanning structures (also referred to herein as "scanners" for brevity) is in the form of an integrated electro-optic switch for high speed, solid-state, single-mode output optical beam steering. The switch is formed by a sequential network of waveguides and directional couplers arranged as a branching tree structure wherein optical signals received at an input waveguide can be selectively switched to any of a plurality of output waveguides, and switched between any of the output waveguides in any desired sequence or order.

As shown in Figure 1, in the described embodiments, an optical beam scanner includes a body 102 composed of an electro-optically active material and having formed therein a plurality of optical waveguides 104 and directional couplers 112, arranged as a branching tree structure wherein optical signals travelling along each upstream waveguide or waveguide portion (and in a direction generally from left to right in Figure 1) can be selectively switched to any one of a desired plurality of corresponding downstream waveguides or waveguide portions. Thus the plurality of optical waveguides 104 includes at least one input waveguide 106 and a plurality of mutually spaced output waveguides 108. In general, the input waveguide(s) 106 will be coupled to the output waveguides 108 via intermediate waveguides 110.

In the embodiment shown in Figure 1, the tree structure is in the form of a generally symmetrical branching tree wherein, at each and every branching point or junction, the optical path branches either left or right along a corresponding one of a corresponding pair of curved arcs that are symmetrically arranged relative to the preceding linear path segment; however, this need not be the case in other embodiments. For example, Figure 6 shows an alternative embodiment wherein both the input waveguide 106 and a corresponding one of the output waveguides 108 are portions the same linear waveguide extending through the electro-optically active material from its input end to its output end, and each of the other output waveguides has a corresponding curved portion branching away from the linear waveguide, and a linear portion extending to the output end of the body 102 of electro-optically active material.

Similarly, Figure 7 shows an embodiment that includes multiple instances of each type of waveguide, wherein the waveguide portions extending from some branching points or junctions are curved and symmetrically arranged, and the waveguide portions extending from other branching points or junctions are a combination of linear and curved waveguide segments. Moreover, although each branching point or junction in the described embodiments couples one input waveguide to only two output waveguides, in other embodiments there can be more than two output waveguides. Other configurations and/or combinations will be apparent to those skilled in the art in light of this disclosure.

Returning to the embodiment of Figure 1, each of the plurality of optical waveguides 106, 110 other than the output waveguides 108 is coupled to a corresponding pair of the optical waveguides downstream of the waveguide by a corresponding directional coupler 112. Electrodes 114 are used to control optical switching at each said directional coupler 112 such that optical signals travelling along any of the optical waveguides 106, 110 other than the output waveguides 108 can be selectively directed along a selected one of the corresponding pair of waveguides downstream of the waveguide. This configuration means that optical signals received at the input waveguide 106 can be selectively directed to any selected one of the output waveguides 108 by controlling the - Si - switching of the optical signals at each directional coupler 112 along the optical pathway between the input waveguide 106 and the selected output waveguide. Accordingly, an optical beam or signals received at the input waveguide 106 can be spatially scanned in a step-wise manner to be sequentially or randomly emitted from the different output waveguides by applying corresponding time-dependent signals to the electrodes 114.

In the described embodiments, the electro-optically active material is congruent lithium niobate (LiNbCh), and the waveguides are formed by the reverse proton exchange technique described in J. L. Jackel and J. J. Johnson, "Reverse exchange method for burying proton exchanged waveguides," Electron. Lett. 27, 1360 (1991) and F. Lenzini, S. Kasture, B. Haylock, and M. Lobino, "Anisotropic model for the fabrication of annealed and reverse proton exchanged waveguides in congruent lithium niobate," Opt. Express 23, 1748 (2015). In an alternative embodiment, the electro-optically active material is Lead Zirconate Tantalate (PLZT). However, other suitable electro-optically active materials will be apparent to those skilled in the art in light of this disclosure, including Lithium Tantalate (LiTa03), Lead Zirconate Tantalate (PLZT) and Potassium Titanyl Phosphate (KTP), for example.

Figure 9 shows a close-up plan view of a typical binary branch junction of a beam scanner, wherein an optical signal travelling from the left-hand side of this Figure to the right-hand side, enters the Figure travelling along an input waveguide portion 902, and can be selectively and dynamically switched to travel along either an upper branch waveguide portion 904 or a lower branch waveguide portion 906 of the branching tree network, in dependence on an electrical signal applied to a corresponding directional coupler 112, in the described embodiment being in the form of a pair of switching electrodes 908, 910 disposed about a corresponding switching portion 912 of the input waveguide 902.

In the embodiment of Figure 9, the upper branch waveguide portion 904 and the input waveguide portion 902 are respective portions of the same ("first") waveguide, but as will be apparent from the description above, this need not be the case in other embodiments. The lower branch waveguide portion 906 in this embodiment is defined by a separate ("second") waveguide having a switching portion 914 located close to, but spaced apart from, the switching portion 912 of the input waveguide 902, these switching portions 912, 914 being disposed about one 910 of the switching electrodes 908, 910.

A switching signal can be applied across the switching electrodes 908, 910 via a corresponding pair of electrical contacts 916. If no signal is applied to these electrodes 908, 910, then an optical signal passing along the switching portion 912 of the first waveguide will continue to travel along the first waveguide to the upper branch waveguide portion 904. If, however, an appropriate switching signal is applied across the electrodes 908, then the resulting electric field has the effect of coupling the switching portions 912, 914 of the first and second waveguides such that an optical signal entering the switching portion 912 of the first waveguide is effectively switched to the switching portion 914 of the second waveguide, and consequently the lower branch waveguide portion 906 of the branching tree network.

Figure 10 is a schematic cross-sectional view through the body 102 of electro-optically active material, the switching portions of the first and second waveguides, and the pair of switching electrodes 908, as viewed from left-hand side of Figure 9, showing an electric field line passing through the switching portion of the first waveguide when an appropriate signal is applied to the switching electrodes 908 or 910, and the elliptical shaded regions 912 and 914 indicating the locations of the waveguides and light guided therein with respect to the applied electric field.

The splitting ratio of each directional coupler 112 is selectable between 0 and 100% by applying a corresponding voltage to the corresponding pair of electrodes 114 disposed about the corresponding pair of evanescently coupled waveguides. For example, Figure 2 is a graph showing the measured frequency response of a LiNbCh switch formed as described above, with three output channels and a total device loss of ~4dB, for a sinusoidal switching signal of amplitude 10 dBm. Clearly, the scanner is suitable for use at switching rates up to ~300MHz. The inventors consider that the performance of the optical scanners described herein is only limited by electrode design, and by improving the designs (for example, by following the methods described in S. Haxha, B.M. A. Rahman, K. T. V. Grattan. "Bandwidth estimation for ultra-high-speed lithium niobate modulators," Appl. Opt. 42, 15, 2674-2682 (2003), and E.L. Wooten, K.M. Kissa A. Yi- Yan, E.J. Murphy, D.A. Lafaw, P.F. Hallemeier, D. Maack, D.V. Attanasio, D.J. Fritz, G.J. McBrien, D.E. Bossi. "A Review of Lithium Niobate Modulators for Fiber-Optic Communications Systems," IEEE J. Sel. Top. Quant. Electron, 6, 1 69-82 (2000)), the response of such a system should reach the GHz range.

An embodiment of the beam scanner for beam steering in an amplitude modulated continuous wave (AMCW) LIDAR system is described below. However, it should be understood that embodiments of the present invention can alternatively be used in other typoes of LiDAR systems, such as Phase-Modulated CW (PMCW) LiDAR, for example.

Many types of LIDAR system are used for automotive applications. Companies use a variety of technologies, including pulsed time of flight, frequency modulated continuous wave (FMCW), flash, and coherent flash protocols. Any system used for automotive purposes must support an encoding that can ignore interfering signals from other road users. Pulsed systems can achieve this easily using random amplitude pulse encoding, however flash and FMCW systems are reliant on spectral separation, a technology not suitable for producing millions of unique units. AMCW offers a Doppler measurement capable technology similar to pulsed time of flight, however it does not require optics capable of handling high peak pulse powers, and instead can be achieved with eye-safe average and peak powers.

Figure 3 is a block diagram of an AMCW implementation that allows for simultaneous measurement of range and velocity across discrete pixels in one dimension using only a single coherent detector. Additionally, the switch architecture allows for temporal multiplexing of the detection electronics, since all pixels are measured by a single detector.

For example, an AMCW LIDAR system of this form and with between 2¹⁰ and 2¹³ output channels can operate in the following manner. An input modulated laser beam enters the beam scanner through a circulator, and the beam scanner is controlled via the signals applied to its electrodes so as to direct the laser beam to one of the array of output waveguides/channels. In one example, it dwells on this channel for two microseconds. Over this duration, the leading optical signal is reflected from a target object at a distance of up to 1 light-microsecond (approximately 300 m). In the embodiment shown in Figure 3, a portion of this reflected signal is received by the same output waveguide that emitted the signal. However, in other embodiments the reflected signal may be received by a secondary collection lens attached to a separate fibre waveguide. In either case, the reflected signal is directed back to the circulator, which in turn directs the reflected light to a homodyne detector. The electronic output of the detector contains information from which the range and speed of the target object can be determined, as described in Y. Lin, X. Mao, J. Fang and T. Zhang, "Doppler Laser Radar for Range and Speed Measurement of Road Targets", Advanced Sensor Systems and Applications VII, edited by T. Liu, S. Jiang, R. Landgraf, Proc. of SPIE Vol. 10025, 100250G 2016, doi : 10.1117/12.2245136. When the dwell time period expires, or if a control system determines that the signal has been received before the expiry time (e.g., if an object is closer than the maximum range), the beam scanner then switches the laser beam to the next output channel, and the process continues in this manner so that the laser beam is sequentially emitted from each of the output channels. In 0.01 seconds, the laser beam can be switched and its reflection received and processed 5000 times, achieving the desired sample size and frame rate.

In a single instance of the monolithic beam scanner, the output light channels are coplanar, allowing a large range of possible output directions to be addressed within a single plane. However, multiple instances of the beam scanner can be arranged to provide a two-dimensional array of the output waveguides. In some embodiments, multiple instances of the beam scanner are stacked together in a parallel arrangement. In some other embodiments, multiple instances of the beam scanner include a first optical beam scanner and a plurality of second instances of the optical beam scanner, wherein the input waveguides of the second instances of the optical beam scanner are optically coupled to respective output waveguides of the first optical beam scanner. The latter embodiments can be used to form an m x /c-channel optical scanner by optically bonding an m-channel beam scanner to a set of m beam scanners, each having k output channels, and oriented orthogonal to the m-channel beam scanner. In total, m x k output channels are provided, allowing an optical beam to be rastered over a two- dimensional region.

In some embodiments, the optical beam scanner includes optical deflection components configured so that optical signals emitted from each of the mutually spaced output waveguides are deflected at a corresponding angle. In the described embodiments, each corresponding angle is a corresponding fixed angle, although it will be apparent to those skilled in the art that the angles can be dynamically controlled using beam scanning components known to those skilled in the art (micro-mirror optical switching devices, for example).

Although the deflection angles can be the same in some embodiments, typically the optical deflection components are configured so that optical signals emitted from the mutually spaced output waveguides are deflected at respective different angles.

In some embodiments, each of the optical deflection components includes a planar exit surface whose spatial orientation determines the corresponding deflection angle. For example, Figure 8 is a schematic view of a portion of the exit end of a beam scanning structure, showing the output waveguides 108 of electro-active material and respective deflection components 802 to 810 whose outwardly facing exit faces are planar and inclined at respective different angles relative to the plane containing the output waveguides 108. The deflection components 802 to 810 can be produced separately (either individually or as an integral component) and subsequently attached to the body 102 of electro-active material using an optical adhesive, or alternatively can be produced simply by polishing the exit surfaces of the output waveguides 108 at different angles and applying an anti-reflection coating. A collimation lens can be arranged downstream of the optical deflection components 802 to 810 to deflect and focus the optical signals emitted from the deflection components 802 to 810.

In some other embodiments, the optical deflection components include or are in the form of a lens component configured so that optical signals emitted from the mutually spaced output waveguides are incident upon respective different portions of the lens component, and are thereby emitted from the lens component at different angles in dependence upon which of the mutually spaced output waveguides emitted the optical signals.

In the LiDAR system embodiment of Figure 3, a low noise CW laser at 1550nm (Koheras Boostik, NKT Photonics) 302 is split by a 3dB coupler 304 between two electro-optic modulators (EOMs) 306, 308. One channel is passed through an optical circulator 310 and into the 1x3 fast electro-optic switch 312 whose frequency response is shown in Figure 2. The average power of each switch output is approximately 200uW, limited by the maximum input power of the EOMs 306, 308 (lOOmW). To obtain higher output powers, and therefore better signal to noise ratios, a low noise erbium doped fiber amplifier can be used after the EOM 306 in the signal arm, or a lower loss EOM.

To demonstrate the performance of the LIDAR system, the output channels of the electro-optic switch 312 were imaged through a lens 314 onto a test object, in this case being a spinning wheel target 316 (radius 64 ± 1 mm) with a diffuse surface, located approximately 4.7 m away from the lens 314. Depending on the position of the output channel with respect to the axis of the lens 314, the output beam propagated at a different angle, as shown schematically in Figure 3. In this demonstration testbed, the separation between output waveguides or 'channels' 1 and 2 was 9.4 mm, and between output waveguides or channel 2 and 3 was 4.7 mm.

After reflection from the object, the return signal is recombined with the other arm of the 3 dB splitter 304, that acts as local oscillator, and is detected using a homodyne detector 318 with bandwidth 100MHz, as described in Kumar, E. Barrios, A. MacRae, E. Cairns, E. H. Huntington, and A. I. Lvovsky, "Versatile wideband balanced detector for quantum optical homodyne tomography," Opt. Commun. 285, 5259-5267 (2012). Distance and velocity are determined from the Fourier spectrum of the output signal which in the described demonstration testbed was captured at a sampling rate of 200MSPS using an oscilloscope.

The signal channel EOM 306 is modulated to produce a square wave pulse train with a repetition rate of 10MHz and a pulse width of 10ns, which, included with the intrinsic loss, gives the EOM 306 a transmission of -18.8 dB. The second channel's EOM 308 is modulated to produce a pulse sequence that is the inverse of the pulse sequence from the first EOM 306, and with a delay selected so that back- reflect! on from the input of the electro-optic switch 312 is not mixed with light from the other arm before being incident on the homodyne detector 318, as demonstrated in Figure 4. The total loss of the second EOM is -6.1dB. This modulation of the reference signal reduces the detection of the back reflection from the electro-optic switch 312, and allows an increase in the dynamic range of the LIDAR measurement. Alternatively, in other embodiments this could be achieved with a standard anti-reflection coating on the facets of the electro optic switch 312, and the second channel EOM 308 could be omitted. The electro-optic switch 312 was operated to send and receive light from each output waveguide consecutively, i.e. a measurement was taken from channel 1, then channel 2, and so on, with the cycle looping back to 1 after the last channel. A timing signal was sent from the switch control electronics to the oscilloscope to identify the channel that received the corresponding signal.

Both range and velocity information can be extracted from the measured signal, whose Fourier transform is shown in Figure 5. The Doppler shift from a moving object changes the frequency of the return pulse train. From the frequency difference, the velocity of the target object 316 can be found to be equal to v = lD/ = 1.55 x 10 ⁶ D/ms^-1.

From the relative phase of the residual signal reflected from the input of the electro optic switch 312 and the return signal, the time delay (and therefore the distance to the target object 316) can be calculated. The uncertainty in range and velocity is determined by the number of samples per channel and the signal to noise ratio. For these measurements, the switching rate between different outputs was set to 10 kHz, with a duty cycle of 10% per channel, meaning 10000 samples were taken per channel per measurement. The frequency (velocity) resolution was calculated from the full width at half maximum of the lowest frequency Doppler peak, which was ±33 kHz (±25 mm/s ). The best position resolution is set by the sampling rate (200 MSPS, ± 1.5 m), however the random phase of the noise in the signal increases this uncertainty proportional to the signal to noise ratio (SNR). This phase uncertainty is summarized in Table 1 below.

Longer acquisition times or averaging over many acquisitions improves the SNR and therefore the accuracy. From the Doppler LIDAR measurements, using a known radius, the tangential velocity of the spinning target can be calculated as well as the angle at which the light is incident. In this example, the tangential velocity of the target was determined to be 15.3 ± 0.1 m/s, and the incidence angles with respect to the normal of the target surface are summarized in Table 1 below.

Table 1 Summary of measurement results for three channel AMCW LIDAR. Range uncertainty limited by the SNR

Due to the low pulse repetition rate, the unambiguous velocity measurement range was only 7.75 m s^_1, and the unambiguous range measurement range was only 15m. This can be improved with higher pulse repetition rates and random modulation schemes, respectively. Alternatively, other LIDAR schemes such as frequency modulated continuous wave (FMCW) or phase-modulated continuous wave (PMCW), are also suitable to use with this beam steering method for simultaneous range and velocity measurements.

An advantage of the discrete beam steering scheme described herein is the possibility for distributed sensing heads for LIDAR. As the outputs of the electro-optic switch 100 can be easily redirected into optical fibers, the outputs can be easily routed to different places around a vehicle, with each fiber terminated by a taper or microlens. This means each 'sensor head' can be extremely small, unobtrusive and easily replaced. The TX/RX module, and the electro-optic switch 100 can be integrated onto a daughter board connected to a central processing unit. This is ideally suited to harsh environment sensing, where any external sensor head may be easily damaged, and must be cheaply and easily replaceable. Furthermore, the requirement of only one set of detection electronics for multiple sensors can reduce the total sensor cost for automotive LIDAR.

The high speed electro-optic beam scanners described herein have several advantages, including their speed, modularity, and single-mode outputs. Although the embodiment measured above included only three output channels, in general optical beam scanners as described herein can be made with any practical number of output waveguides. For example, in embodiments having only a binary tree configuration, in general beam scanners in accordance with the present invention will typically have 2ⁿ output waveguides or channels. For example, an optical beam scanner for autonomous vehicle navigation or other advanced driver assistance/object detection and avoidance systems and having ~ 1024 output waveguides can be made as described herein. Additionally, such a beam scanner can be complemented with acousto-optic deflectors such as those described in D. E. Smalley, Q. Y. J. Smithwick, V. M. Bove, J. Barabas, and S. Jolly, "Anisotropic leaky-mode modulator for holographic video displays," Nature 498, 313- 317 (2013) on the waveguide outputs to create a chip for 2D scanning, with one dimension discrete as described herein, and the other dimension continuous. Utilizing the amplitude modulated continuous wave technique for automotive LiDAR requires fast random modulation for improved positional accuracy. One source for this fast random modulation is a chaotic laser system as has been previously demonstrated for a 3D LiDAR system, as described in C.-H. Cheng, C.-Y. Chen, J.-D. Chen, D.-K. Pan, K.-T. Ting, and F.-Y. Lin, "3D pulsed chaos lidar system," Opt. Express 26, 12230-12241 (2018).

Finally, the ability to redirect optical signals to any of the outputs and in any order can be advantageous for many applications. For example, the order or sequence of outputs can be randomised, and where used to scan an optical beam over one or more regions of interest, the ability to control the output sequence can be used to, inter alia, :

(i) increase or decrease spatial resolution in one or more regions, or across the whole of a scanned region;

(ii) avoid or concentrate a selected region;

(iii) optimise a search pattern;

(iv) facilitate machine based vision;

(v) optimise power use;

(vi) speed up scanning;

(vii) optimise the amount of data to be processed; and/or

(viii) assist algorithmic object detection.

For example, in a LiDAR system, a high-level controller can have a dynamically selected schedule for addressing different spatial directions. For example, it may decide that regions in the field-of-view in which there is high activity should have higher density scans, while regions of low activity can be addressed with low density scans. Another example is where an object that has previously been scanned at low resolution requires a higher resolution scan, then the scanning schedule can be adapted to achieve this.

Another example is a situation in which objects nearby require less power to be identified, or even switched off for safety reasons. To achieve this, one of the spatial outputs on the chip can be a "dump" port, so that excess light can be partially or entirely switched to the dump port, leaving only a fraction of the power to be directed into free space. This is particularly relevant where a higher-level control system has detected a person's face in close proximity to the LIDAR sensor, requiring power to be quickly reduced for safety considerations. Another example is a situation where two objects in close proximity have different velocities (e.g., a bus overtaking a bicycle). These objects can be distinguished more easily by knowing both their spatial positions and their speeds, which is afforded by velocity-sensitive Doppler LIDAR. Since the two objects can have very different cross- sectional areas, the dynamical scanning capability allows higher density scans of the bicycle compared to the bus, so that both objects end up with approximately the same number of scan points associated with them. This assists a higher level processor that is capable of reliably disambiguating the two objects.

Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

CLAIMS:

1. An optical beam scanner, including :

2. The optical beam scanner of claim 1, wherein the plurality of optical waveguides further includes a plurality of intermediate waveguides for coupling the at least one input waveguide to the output waveguides.

3. The optical beam scanner of claim 2, wherein at least some of the intermediate waveguides and corresponding electrodes are configured so that an optical signal travelling along an intermediate waveguide can be selectively coupled to any one of a plurality of corresponding waveguides immediately downstream of the intermediate waveguide.

4. The optical beam scanner of any one of claims 1 to 3, including one or more optical deflection components configured so that optical signals emitted from each of the mutually spaced output waveguides are deflected at a corresponding angle.

5. The optical beam scanner of claim 4, wherein the optical deflection components are configured so that optical signals emitted from the mutually spaced output waveguides are deflected at respective different angles.

6. The optical beam scanner of claim 4 or 5, wherein each of the optical deflection components includes a refractive exit surface whose spatial orientation determines the corresponding deflection angle.

7. The optical beam scanner of claim 6, wherein the one or more optical deflection components includes a lens component configured so that optical signals emitted from the mutually spaced output waveguides are incident upon respective different portions of the lens component, and are thereby emitted from the lens component at different angles in dependence upon which of the mutually spaced output waveguides emitted the optical signals.

8. The optical beam scanner of any one of claims 1 to 7, wherein the electro- optically active material is selected so that the optical signals can be selectively switched between different ones of the mutually spaced output waveguides at sub-microsecond timescales.

9. An optical beam scanner, including a plurality of instances of the optical beam scanner of any one of claims 1 to 8 arranged to provide a two-dimensional array of the output waveguides.

10. The optical beam scanner of claim 9, wherein the plurality of instances of the optical beam scanner are planar and arranged to be mutually parallel.

11. The optical beam scanner of claim 9, wherein the plurality of instances of the optical beam scanner are planar and include a first instance of the optical beam scanner and a plurality of second instances of the optical beam scanner, wherein respective input waveguides of the second instances of the optical beam scanner are optically coupled to respective output waveguides of the first instance of the optical beam scanner.

12. The optical beam scanner of any one of claims 1 to 11, wherein the optical beam scanner is a component of a LIDAR system configured to detect the range and relative velocity of objects from the optical signals.

13. The optical beam scanner of claim 12, wherein the optical beam scanner is a component of an autonomous vehicle navigation system.

14. A LIDAR system, including :

the optical beam scanner of any one of claims 1 to 11;

a laser;

15. A LIDAR system, including :

the optical beam scanner of any one of claims 1 to 11;

a laser;

an optical coupler configured to receive the reflected optical signals from the circulator and the modulated optical signal from the second optical modulator and to provide the resulting combined optical signals to a homodyne detector component to generate corresponding electrical signals; and a processing component configured to determine ranges and relative velocities of the objects from the corresponding electrical signals.

16. A LIDAR system, including :

a plurality of instances of the optical beam scanner of any one of claims 1 to 11 distributed at mutually spaced locations of a vehicle and coupled to a centralised optical source and controller via optical fibres.

17. An optical beam scanning process for use with the optical beam scanner of any one of claims 1 to 11, including the steps of:

18. The optical beam scanning process of claim 17, wherein the electric signals applied to the electrodes of the optical beam scanner cause the optical signals to be routed to corresponding selected ones of the output waveguides and, for the optical signals emitted from each selected output waveguide, allow corresponding optical signals reflected from objects within range of the LIDAR system to be received by the selected output waveguide and routed to the input waveguide for detection.

19. An optical beam scanning process, including :

providing the optical bean scanner of any one of claims 1 to 13; and controlling the application of signals to the electrodes to cause the optical signals to be emitted from corresponding ones of the output waveguides of the optical bean scanner in a corresponding sequence.

20. The optical beam scanning process of claim 19, wherein the step of controlling the application of signals to the electrodes includes controlling the application of signals to the electrodes to :

(i) randomise the sequence;

(iii) optimise power use;

(iv) avoid or concentrate a selected region;

(v) speed up scanning;

(vi) optimise a search pattern;

(vii) facilitate machine based vision;

(viii) optimise the amount of data to be processed; and/or

(ix) assist algorithmic object detection.