Optical phase control chip and radar device with same

Abstract

The invention provides an optical phase control chip and a radar device with the optical phase control chip, and the optical phase control chip comprises an input coupler, a beam splitter, a phase shifter and a transmitting antenna array, and the input coupler, the beam splitter, the phase shifter and the transmitting antenna array are sequentially connected through an optical path. The transmitting antenna array comprises a plurality of optical antenna arrays which are arranged in series. According to the technical scheme, the problems of complex chip control, high power consumption and large chip area in the prior art can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of radar, and in particular, to an optical phased chip and a radar device having the same. Background Art

[0002] A lidar (light detection and ranging) is a device that can emit a laser beam towards a target object and receive the beam reflected from the target object (i.e., an echo signal). Based on the echo signal, the lidar can detect the distance of the target object and thus accurately reproduce the external environment. A lidar system generally includes a controller, a transmitting element, and a receiving element, where the core component in the transmitting element is an optical device that deflects the beam.

[0003] Currently, commercially mass-produced lidars mostly use mechanical optical devices, which are large in size, high in cost, and limited in lifespan and stability. Especially for high-speed scenarios such as autonomous driving, mechanical optical devices are difficult to meet the relevant performance requirements due to their own need to move. In contrast, all-solid-state lidars are small in size and low in cost, have no moving parts inside, and their reliability and durability have been greatly improved, so they have more competitive advantages. Currently, all-solid-state lidars mainly have technical solutions such as optical phased arrays (OPAs).

[0004] All-solid-state lidars need to have a large field of view to achieve comprehensive detection. To achieve a large field of view, current technical solutions generally adopt a method of combining multiple OPA chips, which leads to technical problems such as complex chip control, high power consumption, and large chip area, greatly limiting the performance and application of OPA chips. Summary of the Invention

[0005] The main object of the present invention is to provide an optical phased chip and a radar device having the same, so as to solve the problems of complex chip control, high power consumption, and large chip area in the related art.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided an optical phased chip, including: an input coupler, a beam splitter, a phase shifter, and a transmitting antenna array, which are optically connected in sequence; wherein, the transmitting antenna array includes a plurality of optical antenna arrays arranged in series.

[0007] Further, each optical antenna array includes N transmitting antennas arranged side by side in a first direction, where N is a positive integer greater than 1.

[0008] Further, for two adjacent optical antenna arrays, the N transmitting antennas in one optical antenna array are optically connected to the N transmitting antennas in the other optical antenna array in a one-to-one correspondence.

[0009] Further, the detection ranges of multiple optical antenna arrays partially overlap or do not overlap in a second direction perpendicular to the first direction.

[0010] Further, the input coupler is configured to receive input light and couple it to the beam splitter; the beam splitter, optically connected to the input coupler, is configured to receive the input light and split the input light into M detection beams; the phase shifters are respectively optically connected to the beam splitter and the transmitting antenna array, and the phase shifters are configured to receive the corresponding detection beams and adjust the phases of the detection beams.

[0011] Further, the input coupler is an end-face coupler or a grating coupler; and / or, the beam splitter is a Y-type beam splitter, a multimode interference type beam splitter, or a directional coupling type beam splitter; and / or, the phase shifter is a delay line, a thermo-optic phase shifter, or an electro-optic phase shifter.

[0012] According to another aspect of the present invention, a radar device is provided, including an optical phased array chip, wherein the optical phased array chip is the above-mentioned optical phased array chip.

[0013] Further, the radar device further includes a laser, which is optically connected to the input coupler to emit laser light to the input coupler.

[0014] Further, the radar device further includes a receiving unit, which is integrated in the optical phased array chip or separately provided; and / or, the receiving unit is configured to receive the reflected beam corresponding to the detection beam.

[0015] Further, the radar device further includes a signal processing device, which is optically connected to the receiving unit to obtain information from the reflected beam.

[0016] Applying the technical solution of the present invention, an input coupler is used to couple input light into a beam splitter. The beam splitter divides the input light into multiple detection beams. A phase shifter can modulate the phase of the detection beams. A transmitting antenna array is optically connected to the phase shifter and can transmit the detection beams into an external detection area. Among them, the transmitting antenna array includes a plurality of optical antenna arrays arranged in series. The optical antenna array at the starting end can receive the detection beams transmitted by the phase shifter and transmit them into the external space. The remaining optical antenna arrays are optically connected to the previous-level optical antenna array in sequence, and receive the remaining detection beams of the previous-level optical antenna array and transmit them into the external space. In specific implementation, designers can design the transmission power, detection area, etc. of each-level optical antenna array according to needs, thereby realizing that multiple optical antenna arrays share a set of input couplers, beam splitters, and phase shifters, and further realizing the expansion of the detection area under a limited chip area, reducing the volume, power consumption, and cost of the optical phased array chip. Therefore, the technical solution of this application can effectively solve the problems of complex chip control, high power consumption, and large chip area in the related art. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0018] Figure 1 Shows a structural schematic diagram of an embodiment of an optical phased array chip according to the present invention;

[0019] Figure 2 Shows Figure 1 A structural schematic diagram of the phase shifter and the transmitting antenna array of the optical phased array chip;

[0020] Figure 3 Shows Figure 1 A structural schematic diagram of the transmitting antenna array of the optical phased array chip;

[0021] Figure 4 Shows Figure 3 A structural schematic diagram of the transmitting antenna of the transmitting antenna array;

[0022] Figure 5 Shows the detection range of an embodiment in which the transmitting antenna array has two optical antenna arrays.

[0023] Among them, the above-mentioned drawings include the following reference numerals:

[0024] 11. Input coupler; 12. Beam splitter; 13. Phase shifter; 14. Transmitting antenna array; 141. Optical antenna array; 1411. Transmitting antenna;

[0025] a. First direction; b. Second direction. Detailed implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. As used herein, unless otherwise clearly specified in the context, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that for the convenience of description, the dimensions of the various parts shown in the drawings are not drawn according to the actual proportional relationship. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the said technologies, methods, and devices should be regarded as a part of the specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0029] As Figure 1 and Figure 2 shown, the present application provides an optical phased chip, including: an input coupler 11, a beam splitter 12, a phase shifter 13, and a transmitting antenna array 14, wherein the input coupler 11, the beam splitter 12, the phase shifter 13, and the transmitting antenna array 14 are optically connected in sequence; wherein, the transmitting antenna array 14 includes a plurality of optical antenna arrays 141 arranged in series.

[0030] Applying the technical solution of this embodiment, the input coupler 11 is used to couple the input light into the beam splitter 12. The beam splitter 12 divides the input light into multiple detection beams. The phase shifter 13 can modulate the phase of the detection beams. The transmitting antenna array 14 is optically connected to the phase shifter 13 and can transmit the detection beams into the external detection area. Among them, the transmitting antenna array 14 includes a plurality of optical antenna arrays 141 arranged in series. The optical antenna array 141 at the starting end (i.e., the optical antenna array 141 directly optically connected to the phase shifter 13) can receive the detection beams transmitted by the phase shifter 13 and transmit them into the external space. The remaining optical antenna arrays 141 are optically connected to the previous-level optical antenna array 141 in sequence, and receive the remaining detection beams of the previous-level optical antenna array 141 and transmit them into the external space. In specific implementation, designers can design the transmission power, detection area, etc. of each-level optical antenna array 141 according to needs, thereby realizing that a plurality of optical antenna arrays 141 share a set of input coupler 11, beam splitter 12, and phase shifter 13, and further realizing the expansion of the detection area under a limited chip area, reducing the volume, power consumption, and cost of the optical phased array chip. Therefore, the technical solution of this embodiment can effectively solve the problems of complex chip manipulation, high power consumption, and large chip area in the related art.

[0031] Perturbation is an important parameter affecting the light output of the optical antenna array 141, and the optical performance can be adjusted or optimized by fine-tuning the structural parameters. Perturbation needs to be combined with the antenna length. If the perturbation is strong, the antenna can be made short, and vice versa.

[0032] It should also be noted that in order to achieve uniform light output of the multi-level optical antenna array 141, in the light transmission direction, the perturbation of the multi-level optical antenna array 141 can be gradually enhanced, which is convenient for design.

[0033] Of course, the solution of this application is not limited to the gradually increasing perturbation. The solution with no specific rule for perturbation is also within the protection scope of this application.

[0034] The antenna parameters are related to the grating period. In order to facilitate the gradual increase or decrease of the period so that the detection range of the optical antenna array 141 changes in one direction from the first level to the last level is a preferred implementation manner. Of course, it is also feasible if the above rules are not satisfied.

[0035] Specifically, the transmission power and detection area of the optical antenna array 141 can be regulated by reasonably setting the antenna parameters of the optical antenna array 141. Among them, the above antenna parameters include: material, antenna form, antenna length, waveguide width, adjacent waveguide interval, grating form, grating width, grating duty cycle, and grating period, etc.

[0036] The following describes the impact of the main antenna parameters on the transmission power and detection area of the optical antenna array 141:

[0037] Antenna length:

[0038] Under normal circumstances, a longer antenna length may result in more directional radiation, while a shorter antenna may result in a wider radiation beam. A more directional antenna can better direct and focus the light beam, thus affecting the resolution and directivity of the detection area. The antenna length also affects the detection sensitivity. The selection of the antenna length can make the antenna more sensitive to light signals in a specific direction, thus affecting the specificity of the detection area.

[0039] Waveguide width:

[0040] The waveguide width directly affects the modes supported in the waveguide. Different waveguide modes have different characteristics for the coupling and transmission of light. Selecting an appropriate waveguide width can prompt the waveguide to support a specific mode, thus affecting the transmission power. The waveguide width affects the coupling efficiency between the antenna and the waveguide. Appropriately selecting the waveguide width can optimize the coupling efficiency, enabling more light energy to be effectively transmitted from the waveguide to the antenna, thereby increasing the transmission power.

[0041] The waveguide width affects the modes supported by the waveguide and the radiation pattern. A wider waveguide may result in a wider radiation pattern, while a narrower waveguide may result in a narrower radiation pattern. This affects the radiation directivity and beam width of the antenna, and thus affects the directivity and resolution of the detection area. The waveguide width also affects the matching between the waveguide and the antenna. Appropriate matching can improve the response of the antenna to the light signal in the waveguide, thus affecting the sensitivity of the detection area.

[0042] Adjacent waveguide spacing:

[0043] The spacing between adjacent waveguides affects the mutual interference between the waveguides. If the spacing between adjacent waveguides is too small, it may cause mutual interference and reduce the transmission power. An appropriate spacing can reduce the mutual interference between the waveguides and improve the stability of the transmission power. The selection of the waveguide spacing can affect the mode coupling between the waveguides. A suitable waveguide spacing can prompt effective mode coupling between the waveguides, which helps the light signal to be transmitted from one waveguide to the adjacent waveguide, increasing the transmission power.

[0044] The spacing between adjacent waveguides affects the radiation pattern and beam width of the antenna array. An appropriate spacing can affect the shape of the radiation pattern and the width of the beam, thus affecting the directivity and resolution of the detection area.

[0045] Grating form:

[0046] The grating form directly affects the optical coupling efficiency between the antenna and the waveguide. Different grating forms may lead to different coupling mechanisms, affecting the efficiency of light reaching the antenna from the waveguide. An appropriate grating form can improve the coupling efficiency, thereby increasing the emission power. The grating form also affects the emission, transmission, and reflection of light. Some special forms of gratings may have specific optical properties, resulting in more light emission, transmission, or reflection. This affects the propagation and utilization of light in the system.

[0047] The grating form has a direct impact on the radiation pattern and beam width of the antenna array. Different grating forms may result in different radiation patterns, thereby affecting the directivity and resolution of the detection area. Some grating forms may have directivity, while others may be more suitable for applications with wide coverage. The grating form may also affect the modes inside the waveguide, thus affecting the performance of the antenna array. A specific grating form may help to achieve specific waveguide modes and optimize the transmission and coupling of light.

[0048] Grating width:

[0049] The grating width directly affects the optical coupling efficiency between the antenna and the waveguide. A wider grating generally improves the coupling efficiency. However, an overly large width may lead to excessive light coupling, resulting in light loss. The grating width also affects the transmission loss inside the waveguide. An appropriate grating width can reduce the transmission loss and improve the transmission efficiency of the emission power.

[0050] The grating width has a direct impact on the radiation pattern and beam width of the antenna array. A larger grating width may result in a wider radiation pattern and beam, while a smaller width may lead to sharper directivity. The choice of grating width also affects the detection sensitivity of the antenna to optical signals in a specific direction or wavelength. An appropriate grating width can optimize the detection performance of the antenna.

[0051] Grating duty cycle:

[0052] The grating duty cycle directly affects the width of the emission area. A higher grating duty cycle usually results in more light emission. This helps to increase the perturbation intensity and enables more light emission in an antenna of the same length.

[0053] The grating duty cycle has a direct impact on the radiation pattern and beam width of the antenna array. A higher grating duty cycle may result in a wider radiation pattern and beam, while a lower duty cycle may lead to sharper directivity. The choice of grating duty cycle also affects the detection sensitivity of the antenna to optical signals in a specific direction or wavelength. An appropriate grating duty cycle helps to optimize the detection performance of the antenna.

[0054] Grating period:

[0055] The grating duty cycle directly affects the detection range of the antenna array. Under the condition that other conditions are the same, a larger grating period can make the detection range closer to the optical axis perpendicular to the chip surface, and a smaller grating period can make the detection range farther from the optical axis perpendicular to the chip surface.

[0056] The grating period has a direct impact on the radiation pattern and beam width of the antenna array. A higher grating duty cycle may result in a wider radiation pattern and beam, while a lower duty cycle may result in a sharper directivity. The choice of the grating duty cycle also affects the detection sensitivity of the antenna to optical signals in a specific direction or wavelength. An appropriate grating duty cycle helps to optimize the detection performance of the antenna.

[0057] Generally speaking, by adjusting the antenna parameters of the optical antenna array, flexible control of the transmission power and detection area can be achieved. In practical applications, comprehensive consideration and optimized design are required according to specific requirements and application scenarios.

[0058] Specifically, the "optical path connection" used when describing the embodiments of the present application refers to connection through a waveguide structure for optical transmission.

[0059] As Figure 3 shown, each optical antenna array 141 includes N transmitting antennas 1411 arranged side by side along the first direction a, where N is a positive integer greater than 1. Each optical antenna array 141 includes N transmitting antennas 1411. By means of the phase shifter 13, the phase of the light beam in the transmitting antenna 1411 can be controlled, thereby realizing scanning along the first direction a.

[0060] As Figure 3 shown, for two adjacent optical antenna arrays 141, the N transmitting antennas 1411 in one optical antenna array 141 are optically path-connected to the N transmitting antennas 1411 in the other optical antenna array 141 in a one-to-one correspondence. The remaining part of the light beam in each transmitting antenna 1411 after being emitted outward can be transmitted to the corresponding transmitting antenna 1411 in the next-level optical antenna array 141. Compared with the solution of only setting one-level optical antenna array in the related art, the energy of the light beam can be utilized as much as possible.

[0061] As Figures 1 to 3 shown, multiple optical antenna arrays 141 are arranged in sequence in the second direction b perpendicular to the first direction a. Such an arrangement has the advantages of simple structure and reasonable layout.

[0062] As Figure 3 and Figure 5As shown, the detection ranges of multiple optical antenna arrays 141 partially overlap or do not overlap in the second direction b. In specific implementation, designers can reasonably design the detection range of each optical antenna array 141 in the second direction b as needed to expand the detection range of a single optical phased chip, thereby reducing the overall cost of the radar device.

[0063] In this embodiment, the phase shifter 13 has N optical channels, and N transmitting antennas 1411 in the optical antenna array 141 adjacent to the phase shifter 13 are optically connected to the N optical channels in one-to-one correspondence. By setting N optical paths to correspond to the N transmitting antennas 1411 one by one, phase adjustment of each beam is achieved, and thus beam scanning can be realized.

[0064] In this embodiment, the input coupler 11 is used to receive input light and couple it to the beam splitter 12; the beam splitter 12 is optically connected to the input coupler 11. The beam splitter 12 is used to receive the input light and divide the input light into M detection beams; the phase shifter 13 is optically connected to the beam splitter 12 and the transmitting antenna array 14 respectively. The phase shifter 13 is used to receive the corresponding detection beams and perform phase adjustment on the detection beams.

[0065] Preferably, the input coupler 11 is an end-face coupler or a grating coupler; the beam splitter 12 is a Y-type beam splitter, a multimode interference type beam splitter or a directional coupling type beam splitter; the phase shifter 13 is a delay line, a thermo-optic phase shifter or an electro-optic phase shifter.

[0066] To enable those skilled in the art to better understand this solution, the technical solution of this application will be described in detail below with specific embodiments. These embodiments should not be construed as limiting the scope to be protected by this application.

[0067] As shown in Figures 4 to 5 the transmitting antenna array 14 includes two optical antenna arrays 141, and the structure of the transmitting antennas 1411 in each optical antenna array 141 is as shown in Figure 4 shown.

[0068] Among them, the specific parameters of the optical antenna array 141(a) at the first level are as follows: the antenna material is silicon nitride, the thickness is 200 nm, the period is 1 um, the duty cycle is 50%, the waveguide width is 1.5 um, the etching depth is 150 nm, the length is 230 um, the transmission power is 50%, the detection range in the second direction b is from -2.87° to 1.72°, and the wavelength of the detection beam is between 1.5 um and 1.6 um.

[0069] The specific parameters of the optical antenna array 141(b) at the second level are as follows: the antenna material is silicon nitride, the thickness is 200 nm, the period is 1.2 um, the duty cycle is 50%, the waveguide width is 1.5 um, the etching depth is 200 nm, the length is 770 um, the emission power is 50%, the detection range in the second direction b is from 7.76° to 11.54°, and the detection beam wavelength is between 1.5 um and 1.6 um.

[0070] Specifically, by arranging the two-level optical antenna array 141 as described above, the optical phased array chip can detect a larger area range, so as to reduce the number of optical phased array chips required in the radar device. In specific implementation, the designer can also set more levels of the optical antenna array 141 according to needs, or change the detection range and emission power by adjusting the antenna parameters.

[0071] This application also provides a radar device, including an optical phased array chip, and the optical phased array chip is the above-mentioned optical phased array chip. The above-mentioned optical phased array chip can effectively solve the problems of complex chip control, high power consumption, and large chip area in the related art, and the radar device with the above-mentioned optical phased array chip also has the above-mentioned advantages.

[0072] In this embodiment, the radar device further includes a laser, a receiving unit, and a signal processing device. The laser is optically connected to the input coupler 11 to emit laser light to the input coupler 11; the receiving unit is integrated on the optical phased array chip or is provided separately, and the receiving unit is used to receive the reflected light beam corresponding to the detection light beam. The number of receiving units can be one or more. Among them, the specific form of the receiving unit can be a detector array, an optical antenna array, etc.; the signal processing device is optically connected to the receiving unit to obtain information from the reflected light beam.

[0073] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the orientation words such as "front, back, up, down, left, right", "horizontal, vertical, perpendicular, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description. Without contrary explanation, these orientation words do not indicate and imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, so it cannot be understood as a limitation on the protection scope of the present invention; the orientation words "inside, outside" refer to the inside and outside relative to the contour of each component itself.

[0074] For ease of description, spatial relative terms, such as "above", "over", "on the upper surface", "upper", etc., may be used herein to describe the spatial positional relationship of one device or feature to other devices or features as shown in the figures. It should be understood that the spatial relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, a device described as "above" or "over" other devices or structures will then be positioned "below" or "under" the other devices or structures. Thus, the exemplary term "above" can include both the orientations of "above" and "below". The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the corresponding interpretations of the spatial relative descriptions used herein will be made accordingly.

[0075] In addition, it should be noted that the use of terms such as "first" and "second" to define components is only for the convenience of differentiating the corresponding components. Without further statement, the above terms have no special meanings and thus should not be construed as limiting the protection scope of the present invention.

[0076] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An optical phased array chip, characterized in that Comprising: An input coupler (11), a beam splitter (12), a phase shifter (13), and a transmitting antenna array (14), the input coupler (11), the beam splitter (12), the phase shifter (13), and the transmitting antenna array (14) are optically connected in sequence; Wherein, the transmitting antenna array (14) includes a plurality of optical antenna arrays (141) arranged in series.

2. The optical phased chip according to claim 1, wherein Each of the optical antenna arrays (141) includes N transmitting antennas (1411) arranged side by side along a first direction (a), where N is a positive integer greater than 1.

3. The optical phased chip according to claim 2, wherein For two adjacent optical antenna arrays (141), the N transmitting antennas (1411) in one of the optical antenna arrays (141) are optically connected to the N transmitting antennas (1411) in the other optical antenna array (141) in a one-to-one correspondence.

4. The optical phased chip according to claim 3, wherein The detection ranges of the plurality of optical antenna arrays (141) in a second direction (b) perpendicular to the first direction (a) partially overlap or do not overlap.

5. The optical phased chip according to claim 1, characterized in that The input coupler (11) is configured to receive input light and couple it to the beam splitter (12); The beam splitter (12), optically connected to the input coupler (11), is configured to receive the input light and split the input light into M detection light beams; The phase shifter (13) is optically connected to the beam splitter (12) and the transmitting antenna array (14) respectively, and the phase shifter (13) is configured to receive the corresponding detection light beam and adjust the phase of the detection light beam.

6. The optical phased chip according to any one of claims 1 to 5, characterized in that The input coupler (11) is an end-face coupler or a grating coupler; and / or, The beam splitter (12) is a Y-type beam splitter, a multimode interference type beam splitter, or a directional coupling type beam splitter; and / or, The phase shifter (13) is a delay line, a thermo-optic phase shifter, or an electro-optic phase shifter.

7. A radar device, comprising an optical phased array chip, characterized in that, The optical phased chip is the optical phased chip according to any one of claims 1 to 6.

8. The radar device according to claim 7, characterized in that The radar device further includes a laser, and the laser is optically connected to the input coupler (11) to emit laser light to the input coupler (11).

9. The radar device according to claim 7, characterized in that, The radar device further includes a receiving unit, and the receiving unit is integrated in the optical phased chip or is provided separately; and / or, The receiving unit is configured to receive the reflected light beam corresponding to the detection light beam.

10. The radar device according to claim 9, characterized in that, The radar device further includes a signal processing device, and the signal processing device is optically connected to the receiving unit to obtain information from the reflected light beam.

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