Patent Description:
Some types of optical sensing systems include an optical transmitter, which transmits a beam of optical radiation toward a target, and an optical receiver, which collects and senses the optical radiation that is reflected from the target. (The term "optical radiation," in the context of the present description and in the claims, refers to electromagnetic radiation in any of the visible, infrared, and ultraviolet spectral ranges, and may be used interchangeably with the term "light. ") For example, in some depth sensing systems, the transmitter emits pulses of radiation toward a target, and the optical receiver senses the times of flight (ToF) of the pulses, and thus measures the distance to the target.

For many sensing applications, including ToF-based depth sensing, it can be advantageous to package the transmitter and receiver together on the same substrate in a compact package. An integrated optoelectronic module of this sort is described, for example, in <CIT>.

ToF-based depth sensing devices are almost inevitably subject to stray reflections, which reflect or otherwise scatter from optical surfaces within the device back toward the receiver. In general, such stray reflections are regarded as noise, and designers of the devices do their best to eliminate them. On the other hand, <CIT>, describes a ToF-based scanner in which the stray reflections are used intentionally in calibrating the ToF measurements. In the disclosed scanner, a transmitter emits a beam comprising optical pulses toward a scene, and a receiver receives reflections of the optical pulses and outputs electrical pulses in response thereto. Processing circuitry is coupled to the receiver so as to receive, in response to each of at least some of the optical pulses emitted by the transmitter, a first electrical pulse output by the receiver at a first time due to stray reflection within the apparatus and a second electrical pulse output by the receiver at a second time due to the beam reflected from the scene. The processing circuitry generates a measure of the time of flight of the optical pulses to and from points in the scene by taking a difference between the respective first and second times of output of the first and second electrical pulses.

<CIT> relates to a distance measuring device comprising a distance measuring unit, which has at least one transmission device for emitting reference and measurement radiation and at least one sensor device for detecting reference and measurement radiation, wherein the reference radiation is a partial beam of divergent radiation emitted by the transmission device.

<CIT> relates to a structure of an optical path for laser range finding, including a main body and a light-emitting unit assembled in the main body. The main body has a transmitting channel, a receiving channel and a calibration channel, wherein an internal optical beam is emitted to the receiving channel via the calibration channel.

The present invention provides an optical device and a method for optical sensing as set out in the appended independent claims. Embodiments of the present invention that are described hereinbelow provide improved devices for optical transmission and reception.

There is therefore provided, in accordance with an embodiment of the invention, an optical device, including a substrate and an optical transmitter, which is mounted on the substrate and includes an optical emitter, which is configured to emit a beam of optical radiation, and a transmission lens assembly, which is configured to direct the beam along a transmit axis toward a target. An optical receiver is mounted on the substrate alongside the optical transmitter and includes an optical sensor and an objective lens assembly, which is configured to focus the optical radiation that is reflected from the target along a receive axis onto the optical sensor. An optical baffle is disposed asymmetrically relative to the transmit axis and has an asymmetrical shape configured to block preferentially stray radiation emitted from the optical transmitter toward the receive axis.

In some embodiments, the substrate includes an electrical circuit substrate on which the optical emitter and the optical sensor are mounted, and the device includes ancillary electronic components, which are mounted on the electrical circuit substrate and connected to the optical emitter and the optical sensor by electrical circuit traces. In a disclosed embodiment, the device includes a case, which contains the transmission lens assembly and the objective lens assembly and is fixed to the substrate so that the transmission lens assembly and the objective lens assembly are positioned respectively over the optical emitter and the optical sensor.

The transmission lens assembly includes one or more lenses mounted in a lens barrel, and the optical baffle protrudes asymmetrically from the lens barrel toward the substrate in a location between the transmit axis and the receive axis. In an example useful for understanding the invention, the optical baffle is an integral part of the lens barrel. In the claimed invention, the optical baffle includes a collar mounted on the lens barrel. Optionally, the optical baffle includes an aperture configured to pass a predefined fraction of the emitted beam through the baffle toward the optical sensor.

In an example useful for understanding the invention, the device includes a light guide extending through the baffle and configured to pass a predefined fraction of the emitted optical radiation through the baffle toward the optical sensor.

In another example useful for understanding the invention, the optical baffle includes a compressible radiation-absorbing material, which is compressed upon assembly of the device, thereby preventing the stray radiation from reaching the optical sensor.

There is additionally provided, in accordance with an embodiment of the invention, a method for optical sensing, which includes mounting an optical transmitter on a substrate. The optical transmitter includes an optical emitter, which is configured to emit a beam of optical radiation, and a transmission lens assembly, which comprises one or more lenses mounted in a lens barrel and is configured to direct the beam along a transmit axis toward a target. An optical receiver is mounted on the substrate alongside the optical transmitter. The optical receiver includes an optical sensor and an objective lens assembly, which is configured to focus the optical radiation that is reflected from the target along a receive axis onto the optical sensor. An optical baffle is positioned asymmetrically relative to the transmit axis. The optical baffle has an asymmetrical shape configured to block preferentially stray radiation emitted from the optical transmitter toward the receive axis. The optical baffle protrudes asymmetrically from the lens barrel toward the substrate in a location between the transmit axis and the receive axis. Positioning the optical baffle comprises mounting a collar comprising the optical baffle on the lens barrel.

In designing an optical module that includes a transmitter and a receiver, it is important to minimize the amount of stray radiation that reaches the receiver, and particularly stray radiation emitted from the transmitter toward the receiver. This radiation is "stray" in the sense that it does not exit the module along the intended transmit path toward the target and then return from there to the receiver through the objective lens assembly, but rather reflects internally with the module, typically from one or more of the optical or mechanical surfaces in the module. Even a small amount of this sort of stray radiation can severely degrade the performance of the optical module, by adding substantial noise to the signals output by the receiver.

Baffles are mechanical elements that are introduced into optical designs in order to block stray radiation and prevent it from reaching the target of the objective lens assembly (such as the sensor in a ToF sensing device). Baffles are usually designed to be a part of or attached to the barrel (i.e. the housing) of the objective lens assembly, with circular symmetry around the optical axis of the lens assembly.

Careful optical design and baffling can eliminate most stray reflections; but when the transmitter and receiver are mounted together on the same substrate in a compact package, it is generally not possible to close off all possible paths that stray radiation could follow. For example, when ancillary electronic components are mounted on the substrate together with the optical emitter and the optical sensor, it may not be possible to surround the emitter or the sensor completely with a baffle that extends all the way down to the substrate. Furthermore, in ToF sensing modules, it may actually be desirable to allow a small amount of stray radiation to reach the optical sensor from the emitter in order to serve as a zero-reference for the ToF measurements, for example as described in the above-mentioned <CIT>.

Embodiments of the present invention address these problems using an asymmetrical stray light baffle. In these embodiments, an optical device comprises an optical transmitter and an optical receiver, both mounted on a substrate, one alongside the other. The optical transmitter comprises an optical emitter, which emits a beam of optical radiation (a pulsed beam in the case of ToF measurement), and a transmission lens assembly, which directs the beam along a transmit axis toward a target. The optical receiver comprises an optical sensor and an objective lens assembly, which focuses the optical radiation that is reflected from the target along a receive axis onto the optical sensor. An optical baffle is disposed asymmetrically relative to the transmit axis and has an asymmetrical shape that is designed to preferentially block stray radiation emitted from the optical transmitter from propagating toward the receive axis.

The optical baffle protrudes asymmetrically from the lens barrel toward the substrate in a location between the transmit axis and the receive axis. This optical baffle is a separate piece in the form of a collar mounted on the lens barrel. The asymmetrical design makes it possible to mount ancillary electronic components on the substrate in close proximity to the emitter, typically on the side of the emitter opposite to the protruding baffle (i.e., on the opposite side from the receiver). The baffle can also be designed to permit a small, controlled amount of stray light to reach the optical sensor in order to serve as the zero reference. In one embodiment, the optical baffle comprises an aperture configured to pass a certain fraction of the emitted beam through the baffle toward the optical sensor.

Reference is now made to <FIG>, which schematically illustrate an optical device in the form of an optical module <NUM>, in accordance with an embodiment of the invention. <FIG> is a sectional view of the optical module, while <FIG> shows a pictorial view of a transmission lens assembly <NUM> in module <NUM>.

Module <NUM> comprises an optical transmitter <NUM> and an optical receiver <NUM>, which are mounted one alongside the other on a substrate <NUM>. Substrate <NUM> typically comprises an electrical circuit substrate, such as a printed circuit board. Transmitter <NUM> comprises an optical emitter <NUM>, for example a suitable light-emitting diode (LED) or laser, such as a vertical-cavity surface-emitting laser (VCSEL), or an array of such LEDs or lasers, which may emit pulsed, continuous, or modulated radiation. Receiver <NUM> comprises an optical sensor <NUM>, for example an avalanche photodiode (APD) or a single-photon avalanche diode (SPAD) or an array of such photon detectors, or alternatively a detector or detector array that is capable of continuous or gated sensing. Emitter <NUM> and sensor <NUM> are mounted on substrate <NUM> together with ancillary electronic components <NUM>, such as drivers, amplifiers and control circuits, which are typically connected to the emitter and the sensor by electrical circuit traces.

Emitter <NUM> emits a beam of optical radiation, and a transmission lens assembly <NUM> collects and directs the beam along a transmit axis <NUM> toward a target (not shown in the figures). Transmission lens assembly <NUM> comprises one or more lenses <NUM> (multiple lenses in the pictured example), which are mounted in a lens barrel <NUM>. Lenses <NUM> direct the beam through an exit window <NUM>, which opens through a case <NUM>.

Receiver <NUM> comprises an objective lens assembly <NUM>, comprising one or more lenses <NUM>, which are mounted in a barrel <NUM>. Lenses <NUM> focus the optical radiation that is reflected from the target along a receive axis <NUM> through an entrance window <NUM> in case <NUM> onto optical sensor <NUM>. Case <NUM> is fixed to substrate <NUM> so that transmission lens assembly <NUM> and objective lens assembly <NUM> are positioned respectively over optical emitter <NUM> and optical sensor <NUM>.

An optical baffle <NUM> protrudes asymmetrically from lens barrel <NUM> toward substrate <NUM> in a location between transmit axis <NUM> and receive axis <NUM>. The asymmetrical shape and disposition of baffle <NUM> relative to transmit axis <NUM> will preferentially block stray radiation emitted from emitter <NUM> toward receive axis <NUM> (including both rays emitted directly from the emitter itself and rays reflected from other elements of transmitter <NUM>, such as from the surfaces of lenses <NUM>). In examples useful for understanding the invention, optical baffle <NUM> is an integral part of lens barrel <NUM>. In the claimed invention, the baffle is produced separately and fastened to the lens barrel or otherwise mounted within case <NUM>.

The asymmetrical design of optical baffle <NUM> has a number of advantages in the context of module <NUM>. This design can relieve other packaging constraints, for example by making it possible to mount relatively large ancillary components, such as component <NUM> to the right of emitter <NUM> in <FIG>, in close proximity to the emitter. Furthermore, the baffle can be designed to permit a small amount of stray light to reach sensor <NUM>, in order to enable ToF calibration without causing excessive noise in receiver <NUM>.

Reference is now made to <FIG>, which schematically illustrate the design and operation of a stray light baffle <NUM>, in accordance with another embodiment of the invention. <FIG> is a pictorial view of baffle <NUM>, while <FIG> is a pictorial view of transmission lens assembly <NUM> incorporating baffle <NUM> inside case <NUM> of an optical module.

Baffle <NUM> in this embodiment comprises a collar <NUM>, which mounts on lens barrel <NUM>. An asymmetrical protrusion <NUM> extends above collar <NUM> in the area between transmit axis <NUM> and receive axis <NUM>, and thus preferentially blocks stray radiation emitted from the optical transmitter toward the receive axis. The use of this sort of separate collar component allows for greater flexibility of design and possibly easier assembly of the module. For example, the shape of baffle <NUM> can readily be molded as a separate component, but might be difficult to mold as an integral component of the lens barrel or might interfere with subsequent assembly of lenses <NUM> into the barrel. The use of a separate baffle of this sort also makes it possible to update and improve the baffle design without having to modify the entire lens barrel.

<FIG> is a schematic sectional view of an optical module <NUM>, in accordance with an example useful for understanding the invention. In this example, transmission lens assembly <NUM> is contained in a dual barrel, including an inner barrel <NUM> in which lenses <NUM> are mounted and an outer barrel <NUM>, which is fixed to substrate <NUM>. Outer barrel <NUM> includes a baffle <NUM>, which protrudes asymmetrically toward substrate <NUM>, between transmitter <NUM> and receiver <NUM>. In this case, however, baffle <NUM> has an aperture that is configured to pass a small fraction of the radiation output by emitter <NUM> through the baffle toward optical sensor <NUM>.

In the pictured example, a light guide <NUM> extends through baffle <NUM> order to control and direct the stray radiation from emitter <NUM> toward sensor <NUM>. Light guide <NUM> is designed to pass a predefined fraction of the emitted optical radiation through the baffle and direct it toward the optical sensor. Alternatively, baffle <NUM> may simply contain an aperture for such stray light, without the light guide.

<FIG> is a schematic pictorial view of light guide <NUM>, in accordance with an example useful for understanding the invention. Light guide <NUM> comprises a suitable transparent material, such as a glass or transparent plastic. An entrance face <NUM> of the light guide is angled in this example to receive stray radiation that is reflected from lower lens <NUM> in transmission lens assembly <NUM>. An exit face <NUM> of the light guide outputs the stray light toward sensor <NUM>. Entrance face <NUM> and/or exit face <NUM> may be masked and/or coated in order to control the amount of radiation that is passes through the light guide. Additionally or alternatively, light guide <NUM> itself may comprise a volume of material that absorbs radiation for this purpose.

Further additionally or alternatively, light guide <NUM> may be shaped or patterned to control the spatial distribution of the stray radiation that is emitted through exit face <NUM>. For example, light guide <NUM> may be configured to direct the radiation specifically toward certain reference pixels in sensor, while avoiding irradiation of the pixels that receive radiation from the target. For such purposes, exit face <NUM> may be cylindrical or wedged, or may be patterned with a nano-structured diffractive optical element to control the direction of the light. Alternatively, the stray light transmitted through light guide <NUM> may be diffused by roughening exit face <NUM> or adding a lenslet array on the exit face.

<FIG> is a schematic sectional view of an optical module <NUM>, in accordance with another example useful for understanding the invention. In this example, optical receiver <NUM> comprises a sensing assembly <NUM>, which includes a submount <NUM>, on which optical sensor <NUM> (not shown in this figure) is installed. An optical baffle <NUM> comprising a compressible radiation-absorbing material, such as a suitable closed-cell foam, surrounds the optical sensor. This compressible baffle <NUM> is used in conjunction with a baffle on barrel <NUM> of transmission lens assembly <NUM>, such as the asymmetrical barrels described above. Alternatively or additionally, optical transmitter <NUM> may comprise a compressible baffle of this sort.

When module <NUM> is assembled, barrel <NUM> of objective lens assembly <NUM> presses against and compresses baffle <NUM>, thus shutting out stray light from emitter <NUM>. Alternatively, barrel <NUM> and baffle <NUM> may be designed to permit a small, controlled amount of stray light to reach sensor <NUM> for ToF calibration purposes. The use of such a compressible material in baffle <NUM> is also helpful in relaxing the manufacturing tolerances of module <NUM> and in absorbing mechanical shocks to sensing assembly <NUM> from objective lens assembly <NUM>.

<FIG> is a schematic pictorial view of a sensing assembly <NUM> with compressible baffle <NUM>, in accordance with another example useful for understanding the invention. In this example, baffle comprises a compressible, radiation-absorbing foam disposed as a gasket around sensor <NUM> on the upper side of the chip package containing the sensor. Other configurations of this sort of compressible baffle will be apparent to those skilled in the art after reading the above description and are considered to be within the scope of the present invention.

Claim 1:
An optical device (<NUM>, <NUM>, <NUM>), comprising:
a substrate (<NUM>);
an optical transmitter (<NUM>), which is mounted on the substrate and comprises an optical emitter (<NUM>), which is configured to emit a beam of optical radiation, and a transmission lens assembly (<NUM>), which comprises one or more lenses (<NUM>) mounted in a lens barrel (<NUM>) and is configured to direct the beam along a transmit axis (<NUM>) toward a target;
an optical receiver (<NUM>), which is mounted on the substrate alongside the optical transmitter and comprises an optical sensor (<NUM>) and an objective lens assembly (<NUM>), which is configured to focus the optical radiation that is reflected from the target along a receive axis (<NUM>) onto the optical sensor; and
an optical baffle (<NUM>, <NUM>, <NUM>) disposed asymmetrically relative to the transmit axis and having an asymmetrical shape configured to block preferentially stray radiation emitted from the optical transmitter toward the receive axis,
wherein the optical baffle protrudes asymmetrically from the lens barrel toward the substrate in a location between the transmit axis and the receive axis; and
wherein the optical baffle comprises a collar (<NUM>) mounted on the lens barrel.