WO2018198115A1

WO2018198115A1 - An optical arrangement and method for use in continuously scanning an optical sensor

Info

Publication number: WO2018198115A1
Application number: PCT/IL2018/050448
Authority: WO
Inventors: Dan Alon; Noam Cohen
Original assignee: Oryx Vision Ltd.
Priority date: 2017-04-23
Filing date: 2018-04-22
Publication date: 2018-11-01
Also published as: WO2018198113A1

Abstract

An optical arrangement is described for use in a coherent detection system. This arrangement comprises a light beam generating source for conveying a series of modulated optical signals, an optical receiver, a plurality of optical sensors and means to enable continuously scanning of optical energy across the optical sensors. The arrangement is characterized in that: a) part of the optical energy generated by the light generating source is conveyed towards the optical sensors for use as reference light signals; and b) part of the optical energy generated by the light generating source is directed towards an optical transmitter for transmitting optical signals that are reflected off objects present within the field of view. Consequently, at least a portion of the optical sensors is simultaneously illuminated by reference light signals and by the signals reflected from objects present within the field of view.

Description

AN OPTICAL ARRANGEMENT AND METHOD FOR USE IN CONTINUOUSLY SCANNING AN

OPTICAL SENSOR

TECHNICAL FIELD

The present disclosure generally relates to systems implementing coherent detection. More particularly, the present disclosure relates to systems utilizing depth sensing sensors.

BACKGROUND

Optical coherent detection is a method of extracting information encoded as modulation of the phase and/or frequency of electromagnetic radiation in the wavelength band of visible or infrared light. The received light signal is compared with a brighter standard or reference light, often called a "local oscillator" (LO) , by analogy with a superhetrodyne receiver.

The comparison of the two light signals is typically accomplished by combining them in a non linear element such as a photodiode detector. The two light frequencies may be similar enough that their difference or beat frequency produced by the detector is in the radio or microwave band that can be conveniently processed by electronic means.

Various prior art scanning techniques are available for use in passive and active optical detection systems, for all frequency ranges. Scanning techniques are typically utilized for the following reasons:

1. Achieving a large field of view and/or high-resolution imaging, while using a small array of sensors.

2. Improving system sensitivity by increasing integration time and/or focusing available optical energy to a limited field. However, prior art scanning systems suffer from certain the disadvantages, among which are:

1. Blurred images are created when objects in the field move at rates comparable with the scanning rate.

2. Moving parts in the scanning system result in reduced reliability .

The impact of these disadvantages is further increased in active detection systems (i.e. systems that actively illuminate the field of view) that utilize long pulses. Coherent detection systems are an example of such systems. Because the transmitted pulses are long relative to the scanning time, the system is required to scan and stare at objects in the field. In other words, the scanning cannot be continuous; after each scanning step, the system must stop and stare, allowing the pulse time and its flight time to elapse before stepping to scan the next point .

SUMMARY

The disclosure may be summarized by referring to the appended claims .

It is an object of the present disclosure to provide an arrangement and a method for continuously scanning an array of optical sensors to ensure that at least a portion (or a sub array) of the optical sensor array is illuminated by both LO and Rx signals for the entire duration of the pulse length and flight time, while the optical arrangement is operative.

It is another object of the present invention to provide an arrangement and a method implementing a continuous scanning technique, that allows detection of long pulses without the need to stop and stare.

Other objects of the present disclosure will become apparent from the following description. According to a first embodiment of the present disclosure, there is provided an optical arrangement for use in a coherent detection system, wherein the optical arrangement comprises a light beam generating source configured to convey a series of modulated optical signals, an optical receiver, a plurality of optical sensors (e.g. detectors) and means configured to enable continuously scanning of optical energy across the plurality of optical sensors (e.g. a large optical sensors' array), and wherein the arrangement is characterized in that: a) part of the optical energy generated by the light beam generating source (i.e. of modulated optical signals) is conveyed towards the plurality of optical sensors for use as reference light signals; and b) part of the optical energy generated by the light beam generating source is directed towards an optical transmitter for transmitting optical signals that are reflected off objects that are present within the field of view, thereby ensuring that while continuously scanning optical energy across the plurality of optical sensors, each time a different portion of the plurality of optical sensors is simultaneously illuminated by both reference light signals and the signals reflected from objects that are present within the field of view, while the optical arrangement is operative.

The terms "reference light signal" and "LO signal" as used herein throughout the specification and claims is used to denote bright standard or reference light, that is used for comparing it with a weaker received light signal. The term "Local Oscillator" is used by analogy with superhetrodyne detection systems. The information carried by the received light is encoded as an amplitude, frequency and/or phase shift from the reference signal. The received signal and the reference signal may be introduced to a nonlinear signal-processing device (such as a photodiode) usually referred to as a mixing device {e.g. a multiplier or square law detector), to yield an output signal.

The term "continuous scanning" as used herein throughout the specification and claims is used to denote a scanning process having one or more degrees of freedom (length, width, angles etc.) where the scanning is carried out at an essentially constant speed. i.e. without staring, stopping, pausing, or slowing, when the optical arrangement is operative.

The term "optical transmitter" as used herein through the specification and claims, is used to denote an arrangement comprising at least one optical element designed to collect optical energy and shape it to illuminate a pre-defined field of view .

The term "optical receiver" as used herein through the specification and claims, is used to denote an arrangement comprising at least one optical element designed to collect optical energy and focus it onto an optical sensor array plane. Subject to the limitations of the optical arrangement and the sensor directivity, each sensing element within the array views a unique portion of the field of view.

According to another embodiment, the optical receiver is designed to facilitate collection of the reflected signals and to reflect the field of view onto the plurality of optical sensors (e.g. a sensors' array) .

In order to ensure that at least a part of the optical sensors is simultaneously illuminated by both reference and reflected signals while the optical arrangement is operative, attention should be given to the optical spot critical dimension and scanning velocity that are applied. For example, they should be applied in a manner that would comply with the following limitation : where V is the scanning velocity;

D is the critical dimension of the optical spot size;

T is the time duration of the modulated signal length; and t is the maximal allowed time of flight from the transmitter to the field of view and back to the receiver.

Scanning can be accomplished by various means that can roughly be divided into two general categories: a) mechanical scanning means that comprise moving parts which are configured to enable spinning, rotating, sliding, shifting, bending, tilting etc. of the optical energy. This group also comprises micro moving parts such as MEMs, piezo electric actuators and the like, b) Scanning means (or beam steering) that do not comprise moving parts, and the scanning is carried out by varying the physical properties of materials over time. This group comprises photo acoustic devices, index of diffraction manipulations through E field, temperature control and the like.

Those skilled in the art should appreciate that even though the present description relates to scanning that is being carried out for signals received at the receiving side (Rx) of the optical arrangement disclosed herein, in fact there will not be a substantial difference if the scanning is physically conducted on the signals at the transmitting side (Tx) . As both options would result in a similar scanning effect on the sensor plane, they both should be understood as being encompassed by the present invention.

According to another embodiment, the optical arrangement is configured to enable scanning only received (Rx) signals, while the LO signals are used to statically illuminate all optical sensors of the plurality of optical sensors (the entire sensors' array) .

In accordance with another embodiment, the optical arrangement is configured to enable scanning only LO signals, while the received (Rx) signals are used to statically illuminate all optical sensors of the plurality of optical sensors (the entire sensors' array) .

By yet another embodiment, the optical arrangement is configured to enable simultaneous scanning of both LO signals and received (Rx) signals, while ensuring that both the LO signals and the received signals are aligned to illuminate the same optical sensors from among the plurality of optical sensors (the same sub-array of the sensors ' array) .

In accordance with another embodiment, the optical arrangement is configured to enable scanning essentially all of the optical energy across the plurality of the optical sensors and direct the energy reflected therefrom towards the transmitter. In this embodiment, the reciprocity of light propagation will insure that the received signals will return to the appropriate illuminated sub-array of pixels.

By still another embodiment, the light beam emitted from the optical transmitter, is emitted in a pre-defined pattern.

According to another embodiment, the light beam generation source is a gas laser.

In accordance with another embodiment, the plurality of optical sensors (e.g. the optical sensors' array) comprises photo diodes.

In accordance with another embodiment, the plurality of optical sensors (e.g. the optical sensor's array) comprises rectifying antennas (rectennas) .

According to yet another embodiment, the optical arrangement further comprises a processor, wherein the processor is configured to execute a sub-array data analysis algorithm, which in turn is configured to accommodate specific signals' modulation types, according to each sub-array's relative location within the array.

According to yet another embodiment, the optical arrangement further comprises a processor, wherein the processor is configured to combine results obtained from a plurality of scanning operations, in order to obtain a unified result (e.g. a full frame) .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate several embodiments of the disclosure and, together with the description, serve to explain the principles of the embodiments disclosed herein.

FIG . 1 illustrates a prior art technique by which an optical sensor is scanned by steps;

FIG . 2 demonstrates an embodiment of the solution provided by the present invention by which a continuous scanning of the Rx signals is carried out while maintaining a static LO signal that illuminates the entire pixel array;

FIG . 3 illustrates an example of a linear frequency modulated signal that is used to continuously scan the sub-arrays of the optical sensor demonstrated in FIG. 2;

FIG . 4 demonstrates an embodiment which illustrates an optical arrangement construed in accordance with an embodiment of the present invention;

FIG . 5 illustrates an embodiment by which all of the available energy is used to scan the sensors' array and the reflected energy is forwarded to the optical transmitter; and FIG . 6 presents a flow chart demonstrating a method carried out in accordance with an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some of the specific details and values in the following detailed description refer to certain examples of the disclosure. However, this description is provided only by way of example and is not intended to limit the scope of the invention in any way. As will be appreciated by those skilled in the art, the claimed method and device may be implemented by using other methods that are known in the art per se. In addition, the described embodiments comprise different steps, not all of which are required in all embodiments of the invention. The scope of the invention can be summarized by referring to the appended claims .

FIG. 1 illustrates a prior art scanning technique, whereby the optical sensor is scanned by steps (i.e. using scan and stare technique for each step) , while keeping a sub-array of the sensors statically illuminated during each such step.

FIG. 2 demonstrates an embodiment of the solution provided by the present invention, by which a continuous scanning of the Rx signals is carried out, while at the same time a static LO signal that illuminates the entire pixel array is maintained. In this figure, sensor 400 comprises an array of pixels 410, optical LO signal 470 illuminates statistically the entire array, and the received optical energy (Rx) 420 illuminates sub- arrays of pixels. The light beam of the received signals (Rx) continuously scans across the sensor in the direction designated 480, at a speed assuring that sub- array 430 remains illuminated for the duration of the symbol length. In other words, the time required to move spot 420 from its left edge (430) to its right edge (440) is equal to or greater than the symbol length and flight time. The sub-arrays of pixels designated by 450 and 460 are illuminated at different times.

FIG. 3 illustrates an example of a linear frequency modulated signal 500, that is used to continuously scan the sub- arrays of the optical sensor shown in FIG. 2. Sub-array 440, being the first illuminated array in this example, is illuminated by signal 510. The illumination time of the next sub-array, 450, begins at a time delay relative to the time at which sub-array 440 began its illumination, and therefor sub- array 450 is illuminated by signal 520. Likewise, the illumination of sub-array 460 takes place in a further delay with respect to sub-array 450 so it is illuminated by signal 530. The delays in the illumination of the various sub-arrays are preferably predetermined by the system specific scanning parameters. In some modulation techniques, algorithmic compensation for the known delay, might be required.

FIG. 4 demonstrates another embodiment which illustrates an optical arrangement construed in accordance with an embodiment of the present invention, where essentially all of the optical energy is continuously scanned across the optical sensor and the reflected energy is presented to an optical transmitter.

In this example, available optical energy 100 which is comprised within the optical beam generated by the light source, is conveyed to the optical sensor 121 which, in the present example is printed on the surface of sensor die 120. This conveyance of optical energy is preferably done in a controlled manner in order to enable establishing a predetermined phase and spot size. In the present example, the desired phase and spot size are typical of a Gaussian beam waist created by lens 110 which is located along the optical path of the light beam.

Since according to the underlying principle of the present disclosure all of the available optical energy is first delivered to the sensor as LO, its magnitude would obviously be greater than that which can be achieved while following prior art configurations.

Because the efficiency of the sensor' s energy conversion is less than 50%, the major part of the optical energy will be reflected off its surface. Preferably, the surface of the sensor 121 is designed to reflect the optical power and consequently to illuminate the system field of view.

The energy reflected from objects located within the field of view, will be reflected back to sensor die 120. According to the present invention, the proposed system configuration may preferably be such that it ensures (by implementing a proper design) that the field of view and the illuminated field are essentially identical, thus eliminating losses that would otherwise occur due to the phenomenon known as parallax.

In a preferred embodiment, radiation pattern 140 is reflected from the surface of sensor 121 in a way designed to match the aperture of lens 150. Lens 150 is designed so as to shape the transmitted beam to illuminate the field of view 160.

In another embodiment of the present disclosure, the arrangement further comprises a beam shaping means which is operative on the LO signal before the latter is introduced to the detector die. This beam shaping operation enables matching the beam profile with the sensor array shape. For example, if the sensor array is in an essentially rectangular shape, the LO beam profile can be made rectangular to ensure that all of the available energy would indeed be delivered to the sensor. Another potential use may be for example, spreading the beam energy uniformly across the optical sensor die.

Such a shaping operation may be done by lenses (110 in FIG.

4) or by means of reflective arrays techniques (e.g. by replacing mirror 130 with an array of reflective surfaces) . FIG. 5 illustrates an embodiment by which all of the available energy is used to scan the sensors' array, and the reflected energy is conveyed to the optical transmitter. Reciprocity of light propagation insures that the Rx signal returns to the illuminated area.

In the example described in this embodiment, sensor 400 comprises an array of pixels 410. The optical energy 420 illuminates a sub array of pixels 430. The beam continuously scans across the sensor at a rate that ensures that sub array 430 remains illuminated for the duration of a symbol length. In other words, the time required to move spot 420 from its left edge 430 to its right edge 440 is equal to or greater than the time period of a symbol length. It can be seen that subsequent sub-arrays will be illuminated at different phases of the symbol. However, the phase of each sub array is predetermined, allowing compensation to be affected during signal processing.

Typically, in prior art scanning systems small arrays of pixels are used (e.g. a single column or a single row, using the scanning as means to increase resolution and/or the field of view. The solution provided by the present invention preferably relies on the use of large sensors' arrays, in which only part of the sensors' array is operative at any given time, i.e. when that part is illuminated by both the LO signal and the Rx signal .

In other words, scanning is implemented in prior art systems in order to manipulate the field of view of their respective sensors' array (thereby shifting light from one region of the field of view to another) , whereas according to the present invention solution, the field of view of each pixel remains constant. The scanning carried out in the present solution allows to concentrate the available optical energy on fewer pixels, and consequently improving the system sensitivity .

The following steps exemplify a method for carrying out this embodiment:

A. The optical power is steered to illuminate a portion of the sensor. The scanning rate and the spot size are designed to ensure that each pixel remains continuously illuminated for the duration of the coherent system symbol length.

B. Due to the continuous scanning process, each column (or row) of pixels is exposed to the transmitted symbol at different times (i.e. out of phase) . Because the phase of exposure is predetermined, this can be accounted for during signal processing.

C. The continuous scanning carries on until the entire sensor has been illuminated.

D. The results from the scanning process are combined (or stitched together) into a single image representing the full field of view.

E. Steps (A) through (D) are repeated at a given frame rate.

FIG. 6 presents a flow chart demonstrating a method carried out in accordance with an embodiment of the present invention. First, in step 600 a light beam is generated by a light source and is optionally modulated. Part of the modulated light beam is conveyed towards an optical sensor for use as a reference light signal thereat in the coherent detection process, and the shape of that part of the modulated light beam is adapted to match that of the shape of the optical sensor (step 610) . Optionally, that part of the modulated light beam may be shaped to match a sub-array of sensors comprised in the optical sensor.

Another part of the modulated light beam is conveyed towards an optical transmitter, and the shape of that part of the modulated light beam is adapted to match the Field of View (FOV) of the optical transmitter (step 620) . Optionally, that part of the modulated light beam may be shaped to match a sub- array of sensors.

Next, the optical signals are continuously scanned across the sensors' array in a manner that would allow each sensor of that array to be simultaneously illuminated by both LO and Rx signals for the whole period of time that is comprised of the signal length and its time of flight (step 630) .

In step 640, a coherent detection of signals being reflected off targets that are located within a pre-defined sub- FOV (field of view) is carried out, and information that relates to their distance and velocity relative to the detector is extracted therefrom.

An appropriate detection algorithm associated with each sub array of pixels is adapted to match the specific modulation scheme of the signals it receives, where the adaptation is based on its relative position in the scanning sequence (step 650) .

The data received during the continuous scanning process is compiled (stitch together) thereby enabling to obtain information on the objects that are present within the entire field of view (step 660) .

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

WHAT IS CLAIMED IS :

1. An optical arrangement for use in a coherent detection system, wherein the optical arrangement comprises a light beam generating source configured to convey a series of modulated optical signals, an optical receiver, a plurality of optical sensors and means configured to enable continuously scanning of optical energy across the plurality of optical sensors, and wherein the arrangement is characterized in that: a) part of the optical energy generated by the light beam generating source is conveyed towards the plurality of optical sensors for use as reference light signals; and b) part of the optical energy generated by the light beam generating source is directed towards an optical transmitter for transmitting optical signals that are reflected off objects that are present within the field of view, thereby ensuring that at least a portion of the plurality of optical sensors is simultaneously illuminated by both reference light signals and the signals reflected from objects that are present within the field of view, while the optical arrangement is operative.

2. The optical arrangement of claim 1, wherein the optical receiver is configured to enable collection of the reflected signals and reflection of the field of view onto the plurality of optical sensors.

3. The optical arrangement of claim 1, wherein the scanning velocity is defined by the relationship:

D

V <

T 5 ί

where V is the scanning velocity; D is the critical dimension of the optical spot size;

4. The optical arrangement of claim 1, wherein the scanning means are selected from a group that consists of: a) mechanical scanning means that comprise micro moving parts and b) non- mechanical scanning means selected from among photo acoustic devices, index of diffraction manipulations through E field, and temperature control .

5. The optical arrangement of claim 1, wherein said optical arrangement is configured to enable scanning only received (Rx) signals, while LO signals are used to statically illuminate all optical sensors that belong to said plurality of optical sensors .

6. The optical arrangement of claim 1, wherein said optical arrangement is configured to enable scanning only LO signals, while the received (Rx) signals are used to statically illuminate all optical sensors that belong to the plurality of optical sensors.

7. The optical arrangement of claim 1, wherein said optical arrangement is configured to enable simultaneous scanning of both LO signals and received (Rx) signals, while ensuring that both the LO signals and the received signals are aligned to illuminate the same optical sensors from among the plurality of optical sensors.

8. The optical arrangement of claim 1, wherein said optical arrangement is configured to enable scanning essentially all the optical signals across said plurality of the optical sensors and to direct the energy reflected therefrom towards an optical transmitter.

9. The optical arrangement of claim 1, wherein the light beam emitted from the optical transmitter, is emitted in a pre^¬ defined pattern.

10. The optical arrangement of claim 1, wherein the light beam generation source is a gas laser.

11. The optical arrangement of claim 1, wherein the plurality of optical sensors comprises at least one photo diode.

12. The optical arrangement of claim 1, wherein the plurality of optical sensors comprises at least one rectifying antenna.

13. The optical arrangement of claim 1, wherein the optical arrangement further comprises a processor, and wherein the processor is configured to execute a sub-array data analysis algorithm, which in turn is configured to accommodate specific signals' modulation types, according to each sub-array's relative location within the array.

14. The optical arrangement of claim 1, wherein the optical arrangement further comprises a processor, and wherein the processor is configured to combine results obtained from a plurality of scanning operations, in order to obtain a unified result .