Techniques for compensating for errors in optical interferometer system

Abstract

To solve the following problem that: the tilted input and output surfaces of the Fabry-Perot etalon cause a path length of each reflected optical signal and a path length of the reference optical signal to differ, and the velocity projection calculations by the LIDAR system may be erroneous.SOLUTION: An input surface 321-3 of an optical interferometer is tilted around a first axis X and offset at a first angle with respect to a second axis Y, and an output surface 321-4 is tilted around the first axis and offset at a second angle with respect to the second axis. The optical signal is configured to propagate toward the input surface in a third axis Z orthogonal to the first and the second axes. The input surface is on a first optically clear material 321-1, the output surface is on a second optically clear material 321-2, and the first optically clear material and the second optically clear material are separated from one another.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] Light or laser detection and ranging (LIDAR) systems may be used on aircraft to determine one or more state variables of the aircraft, including, for example, speed, rate of climb or descent, angle of attack, and / or sideslip angle. The LIDAR system may use an optical interferometer system configured to form and project an optical interference pattern onto a photodetector of the optical interferometer system. Speed may be derived from the interference pattern detected by the photodetector using, for example, the techniques described in U.S. Pat. No. 7,106,447, which is incorporated herein by reference in its entirety.

[0002] The optical interferometer system includes a ferrule and optical processing components such as a lens, a photodetector, optionally an optical filter, and a Fabry-Perot etalon. The Fabry-Perot etalon includes, for example, first and second optically transparent components separated by free space. The input face of the first optically transparent component is configured to receive a Fabry-Perot etalon input optical signal from a first external component. The output face of the second optically transparent component is configured to emit a Fabry-Perot etalon output optical signal. Each of the input and output faces is tilted about a first axis (e.g., the X-axis) and offset at an angle relative to a second axis (e.g., the Y-axis) that is orthogonal to the first axis. The first and second axes are each orthogonal to or parallel to a third axis (e.g., the Z-axis) along which both the etalon input and output optical signals propagate.

[0003] The separation between the first optically transparent component and the second optically transparent component causes the Fabry-Perot etalon output optical signal to generate a desired interference pattern that is emitted as the output optical signal. The input and output faces are tilted to reduce undesired optical effects.

[0004] Typically, three or more transmitted light signals are emitted, each in a different area outside the aircraft, so that a vector variable can be determined.

[0005] Conventionally, three or more reflected optical signals and a single reference optical signal are emitted from a conventional ferrule. The reference optical signal is derived from an optical source, e.g., a laser, configured to provide three or more transmitted optical signals. The reflected optical signals are portions of the emitted optical signal that are reflected from an area outside the aircraft and subsequently received by the LIDAR system. The reference optical signal and each reflected optical signal are separately projected onto an input face of a Fabry-Perot etalon from different locations on the ferrule. As a result, the Fabry-Perot etalon projects interference patterns (which are separate Fabry-Perot etalon output optical signals) at the same relative locations of the reference optical signal and each reflected optical signal.

[0006] The interference pattern emitted at the relative position of the reflected optical signal is compared with the interference pattern emitted at the relative position of the reference optical signal to derive a velocity projection corresponding to the direction of the reflected optical signal. The tilted input and output faces of the Fabry-Perot etalon cause the path length of each reflected optical signal through the Fabry-Perot etalon to differ from the path length of the reference optical signal through the Fabry-Perot etalon. As a result of such different path lengths, the velocity projection calculation by the LIDAR system may be erroneous. Summary of the Invention

[0007] In some aspects, the technology described herein relates to an apparatus for transmitting an optical signal to an input face of an optical interferometer, the optical interferometer further including an output face, the input face tilted about a first axis and offset at a first angle relative to a second axis orthogonal to the first axis, the output face tilted about the first axis and offset at a second angle relative to the second axis orthogonal to the first axis, the optical signal configured to propagate toward the input face in a third axis orthogonal to the first and second axes, the input face being on a first optically transparent material and the output face being on a second optically transparent material, and N pairs of optical emitters within a surface of the ferrule, each pair including a receiving optical emitter configured to emit a received optical signal toward the input face and a reference optical emitter configured to emit a reference optical signal toward the input face, where N is an integer greater than 0; the surface of the ferrule lies in a plane formed by a fourth axis and a fifth axis that are orthogonal to each other; cross sections of the optical emitters of each pair are arranged symmetrically about the fifth axis; and for each pair, the receiving optical emitter lies in one half of the plane divided by the fifth axis and the reference optical emitter lies in the other half of the plane.

[0008] In some aspects, the technology described herein relates to a method for transmitting an optical signal to an input face of an optical interferometer, the optical interferometer further comprising an output face, the input face tilted about a first axis offset at a first angle relative to a second axis orthogonal to the first axis, the output face tilted about the first axis offset at a second angle relative to the second axis, the optical signal configured to propagate toward the input face at a third axis orthogonal to the first and second axes, the input face being on a first optically transparent material, and the output face being on a second optically transparent material. The optically transparent material is on a transparent material, and the first and second optically transparent materials are separated from each other, and the method includes receiving N received optical signals, where N is an integer greater than or equal to 1; receiving M reference optical signals, where M is an integer less than or equal to O and O is an integer greater than or equal to N; and emitting N pairs of received optical signals and reference optical signals, where a cross section of the optical signal of each of the N pairs is emitted symmetrically about a fifth axis in a plane in which each emitter is located and defined by a fourth axis and a fifth axis that are orthogonal to each other.

[0009] In some aspects, the technology described herein relates to an apparatus for transmitting an optical signal to an input face of a Fabry-Perot etalon tilted about a first axis and offset at a first angle with respect to a second axis orthogonal to the first axis, the optical signal being configured to propagate to the input face of the Fabry-Perot etalon on a third axis orthogonal to each of the first and second axes, the apparatus including: a first set of N optical emitters each emitting a reflected optical signal from a ferrule surface, where N is an integer greater than 0; and a second set of O optical emitters each emitting a reference optical signal from the ferrule surface, where O is an integer greater than or equal to N, the ferrule surface lying in a plane formed by a fourth axis and a fifth axis, the positions of each pair of optical emitters in the first set and the second set being arranged symmetrically about the fifth axis. [Brief explanation of the drawings]

[0010] Example embodiments will be described with additional specificity and detail through the use of the accompanying drawings, with the understanding that the drawings illustrate example embodiments only and therefore should not be considered limiting in scope. [Figure 1] FIG. 1 illustrates a block diagram of one embodiment of a vehicle including a ferrule-based LIDAR system, in accordance with embodiments of the present invention. [Figure 2] 1 shows a diagram of one embodiment of an optical interferometer system including a ferrule, in accordance with an embodiment of the present invention. [Figure 3] 1 shows a diagram of one embodiment of an optical interferometer, in accordance with an embodiment of the present invention; [Figure 4] 1 illustrates one embodiment of a surface of a ferrule where the end of each light emitter is optically visible. [Figure 5] 1 shows a diagram of a photodetector onto which the full optical interference pattern is projected. [Figure 6] 1 illustrates one embodiment of a surface of a ferrule with an exemplary pair of a first receiving optical signal emitter and a first reference optical signal emitter and a mirror image cross section of each emitter. [Figure 7] FIG. 1 illustrates a flow diagram of an exemplary method for transmitting an optical signal from a surface of a ferrule, according to an embodiment of the present invention.

[0011] According to common practice, the various features described are not drawn to scale but rather to emphasize particular features relevant to the exemplary embodiments. Reference characters denote like elements throughout the figures and text. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which specific exemplary embodiments are shown by way of illustration. However, it is to be understood that other embodiments may be utilized and structural, mechanical, and / or electrical changes may be made. Furthermore, the methods presented in the drawings and specification should not be construed as limiting the order in which the individual steps may be performed. The following detailed description is not to be construed in a limiting sense.

[0013] For instructional purposes, embodiments of the present invention are described with respect to an optical interferometer system of a LIDAR system. However, embodiments of the present invention may be used in other applications. The optical spectrum includes the ultraviolet spectrum, the visible spectrum, and the infrared spectrum.

[0014] An embodiment of the invention that reduces the aforementioned error sources in a LIDAR system, including, for example, an optical interferometer system, is as follows: In a ferrule, each reflected signal light emitter is paired with a reference signal emitter whose position in the ferrule is unique relative to the position of the corresponding reflected signal light emitter. Each pair of reflected signal light emitter and reference signal light emitter is arranged symmetrically about an axis that defines the plane of the surface of the ferrule, and optionally each such emitter also has the same cross section.

[0015] 1 shows a block diagram of one embodiment of a vehicle 100 including a ferrule-based LIDAR system 101, in accordance with an embodiment of the present invention. The LIDAR system 101 is mounted on and / or within the vehicle 100. The vehicle 100 may be an airborne vehicle (e.g., an aircraft), a space vehicle, a terrestrial vehicle, a waterborne vehicle, or any other type of vehicle.

[0016] LIDAR system 101 includes laser 101-1, optical splitter 101-2, one or more pairs of transmitting and receiving optical components TO1, RO1 through TON, RON, an optical interferometer system 101-4 including a ferrule according to an embodiment of the present invention, and processing system 101-3. Processing system 101-3 optionally includes at least one processor circuit and at least one memory circuit. Optionally, processing system 101-3 is configured to determine a velocity, e.g., vector velocity, of vehicle 100 by analyzing an interference pattern received from optical interferometer system 101-4. Exemplary techniques for doing so are described in U.S. Patent No. 7,106,447. Optionally, processing system 101-3 is further configured to control the power level of laser 101-1 using control signal 113 and based on information in electrical signal 118 representing the light intensity of the total optical interference pattern.

[0017] Laser 101-1 is configured to transmit optical signal 103 to optical splitter 101-2. Optical splitter 101-2 is configured to provide each of N transmit optical signals 105-1 through 105-N to a unique one of N transmit optical components TO1 through TON, where N is an integer greater than or equal to 1.

[0018] 1 shows, for instructional purposes, that optical splitter 101-2 is further configured to provide each of M reference optical signals REF1 through REFM to optical interferometer system 101-4, where M is an integer less than or equal to O, e.g., less than or equal to N, and greater than 0. Optionally, when fewer than O reference optical signals are received from optical splitter 101-2, at least one reference optical signal is split such that O reference optical signals are provided to optical interferometer system 101-4.

[0019] M is equal to 1, optical splitter 101-2 provides a single reference signal to optical interferometer system 101-4, and optical interferometer system 101-4, e.g., an optional optical splitter within optical interferometer system 101-4, e.g., a ferrule therein, may split the single reference signal into O reference signals, where O is an integer greater than or equal to N, and the reference signals beyond N may be used for purposes other than those described herein.

[0020] Each of the N transmitting optical components TO1 through TON is paired with a unique one of the N receiving optical components RO1 through RON. Each of the N transmitting optical components TO1 through TON includes at least one optical lens and / or at least one optical mirror. Each of the N transmitting optical components TO1, TO2 is configured to emit a transmitting optical signal 107-1, 107-N using a transmitting optical signal.

[0021] Each of the N transmitted optical signals is emitted toward a region 102-1 through 102-N, impinges on the region 102-1 through 102-N, and is scattered by components of the region 102-1 through 102-N around the vehicle 100, such as molecules, particles, etc. Each region may be a volume of space and may be formed by at least one gas, at least one solid, and / or at least one liquid. A portion of each transmitted optical signal, a reflected optical signal 108-1 through 108-N, is reflected back to a corresponding receiving optical component RO1 through RON, and optionally, such receiving optical component RO1 through RON is adjacent to the transmitting optical component TO1 through TON that transmitted the transmitted optical signal 107-1 through 107-N whose reflected portion is received by the receiving optical component RO1 through RON. Each of the N receiving optical components RO1 through RON includes at least one lens and / or at least one mirror.

[0022] Each of the N receiving optical components RO1 through RON is configured to provide a received optical signal 106-1 through 106-N to the optical interferometer system 101-4, e.g., to a ferrule therein. Each of the N receiving optical signals 106-1 through 106-N is derived by a unique receiving optical component from a unique reflected optical signal.

[0023] 2 shows a diagram of one embodiment of an optical interferometer system 201-4 including a ferrule 222, in accordance with an embodiment of the present invention. The illustrated optical interferometer system 201-4 includes the ferrule 222, at least one collimating lens 223, an optical interferometer 221, at least one imaging lens 225, and an optical sensor 226. The optical sensor 226 is configured to generate an electrical signal 118 representative of the light intensity of the total optical interference pattern.

[0024] Ferrule 222 is configured to receive N received optical signals 106-1 through 106-N and M reference optical signals REF1 through REFM. Optionally, M is equal to O. If M is less than N, ferrule 222 may be combined with or include optical splitter 222-2 configured to provide O reference optical signals from the M reference optical signals REF1 through REFM. O is an integer greater than or equal to N. If O is greater than N, excess reference optical signals beyond the N reference optical signals may be used for other purposes in optical interferometer system 101-4.

[0025] The ferrule 222 includes a set of N receiving optical emitters RecE1 to RecEN, each of which is configured to emit a unique receiving optical signal 106-1 to 106-N towards the input face 221-3 of the optical interferometer 221. The ferrule 222 also includes a set of O reference optical emitters RefE1, RefE1, each of which is configured to emit a unique reference optical signal REF1, REFN towards the input face 221-3 of the optical interferometer 221. Optionally, the ferrule surface 222-1 of the ferrule 222 and each of the at least one collimating lens 223 may be tilted about a first axis, e.g., the X-axis, at an angle α with respect to a second axis, e.g., the Y-axis (orthogonal to the first axis). 1 The first and second inner surfaces 221-5, 221-6 are parallel to each other. The at least one collimating lens 223 is configured to collimate the N received optical signals and the N reference signals emitted by the ferrule 222 before they enter the input face 221-3 of the optical interferometer 221. 1 An optical axis passing through an intersection 445 (shown in FIG. 4) of the fourth axis 441 and the fifth axis 442 is perpendicular to the first and second inner surfaces 221-5 and 221-6 of the optical interferometer 221.

[0026] Optical interferometer 221 includes a first piece of optically transparent material 221-1 and a second piece of optically transparent material 221-2 separated by, for example, free space, air, etc. First piece of optically transparent material 221-1 includes a first inner surface 221-5 and an input surface 221-3 configured to receive N received optical signals and N reference signals collimated by at least one collimating lens and emitted. Second piece of optically transparent material 221-2 includes a second inner surface 221-6 and an output surface 221-4 configured to emit interference patterns formed by optical interferometer 221 for each of the N received optical signals and the N reference signals.

[0027] All such interference patterns are referred to as total optical interference pattern 227 and are configured to be emitted from output face 221-4. Each piece of optically transparent material can be glass, quartz, or any other material that is optically transparent at the wavelength of optical signal 103 emitted by laser 101-1.

[0028] 3 shows a diagram of one embodiment of an optical interferometer 321, in accordance with an embodiment of the present invention. The optical interferometers 221 and 321 shown in FIGS. 2 and 3 are Fabry-Perot interferometers. However, the optical interferometer 321 may be any optical interferometer including a first piece of optically transparent material 321-1 separated from a second piece of optically transparent material 321-2 by a third piece of optically transparent material 321-7 (e.g., air or vacuum), and having at least one of: (a) an input surface 321-3 of the first piece of optically transparent material 321-1 tilted about a first axis (e.g., the X-axis) and offset at an angle δ with respect to a second axis (e.g., the Y-axis) orthogonal to the first axis; and (b) an output surface 321-4 of the second piece of optically transparent material 321-2 tilted about the first axis (e.g., the X-axis) and offset at an angle β with respect to a second axis (e.g., the Y-axis) orthogonal to the first axis. Optionally, offset angle β is equal to offset angle δ, although such offset angles may be different. The first and second axes are each orthogonal to a third axis (e.g., the Z axis) that propagates along or parallel to the received optical signal and the reference optical signal and the overall optical interference pattern (and its components). The first piece of optically transparent material 321-1 includes an input face 321-3 and a first inner face 321-5. The second piece of optically transparent material 321-2 includes an output face 321-4 and a second inner face 321-6.

[0029] Returning to FIG. 2, the total-optical interference pattern 227 is propagated from output face 221 - 4 to at least one imaging lens 225 configured to focus the total-optical interference pattern 227 onto a photosensor 226 .

[0030] Optionally, both the sensor surface 226-1 of the optical sensor 226 and the vertical axis 225-1 of each of the at least one focusing lenses 225 may be tilted about a first axis, e.g., the X-axis, at an angle α' with respect to a second axis, e.g., the Y-axis (orthogonal to the first axis), so that the total optical interference pattern 227 propagates in orthogonal directions from the first and second inner surfaces 221-5, 221-6 of the optical interferometer 221. Optionally, the angle α' is equal to the angle α', although both angles may be different.

[0031] Optical sensor 226 may be a complementary metal-oxide semiconductor (CMOS) sensor, a charge-coupled device (CCD) sensor, or any other type of optical sensor. Optical sensor 226 converts the total-optical interference pattern 227 into an electrical signal that conveys information about (or represents) the total-optical interference pattern 227, including its component interference patterns described elsewhere herein. Surface 226-1 of optical sensor 226 on which the total-optical interference pattern 227 is incident may or may not be parallel to the surface formed by the first and second axes, and is orthogonal to a third axis.

[0032] 4 illustrates one embodiment of a ferrule surface 422-1 where the end of each optical emitter is optically visible (i.e., at the wavelength of the optical signal 103 emitted by laser 101-1). For instructional purposes, the emitters are shown as having a circular cross-section; however, in other embodiments, the emitters may have different cross-sections, e.g., elliptical or rectangular. There are N pairs of emitters on surface 422-1. Each pair of optical emitters includes a unique receiving optical emitter (RecE1 or RecEN) and a unique reference optical emitter (RefE1 or RefEN, respectively), whose positions are arranged symmetrically about a fifth axis 442 (e.g., the Y' axis). 2 Optionally, each such emitter has the same cross section. Such symmetrical displacement of the positions of each pair of optical emitters reduces the difference in path lengths along which optical signals propagate in optical interferometers with tilted input and / or output faces described elsewhere herein. 2The fourth axis 441 and the fifth axis 442 intersect at an intersection point 445 such that the fourth axis 441 symmetrically divides the surface 222-1 of the ferrule 222 along the fourth axis 441, and the fifth axis 442 symmetrically divides the surface 222-1 of the ferrule 222 along the fifth axis 442. The fourth and fifth axes 441, 442 are axes that define the plane of the surface 422-1.

[0033] Such symmetry can be described in many different ways. For teaching purposes, such symmetry is described as follows. However, the following description is not intended to be limiting. Furthermore, for teaching purposes, FIG. 4 shows the number N of pairs of light emitters equal to 2. However, embodiments of the present invention are applicable when the number N of pairs of light emitters is 1 or greater.

[0034] The first pair 447 of optical emitters E1-1 and E1-2 includes a first optical emitter (e.g., either the first receiving optical emitter RecE1 or the first reference optical emitter RefE1) and a second optical emitter (e.g., either the first reference optical emitter RefE1 or the first receiving optical emitter RecE1, respectively). 3 C1 is disposed at a negative first angle −θ1 from the fifth axis 442 and at a first radius R1 from an intersection 445 of the fourth axis (X′ axis) 441 and the fifth axis (Y′ axis) 442. A center C2 of the second light emitter E1-2 is disposed at a first angle θ1 from the fifth axis 442 and at a first radius R1 from an intersection 445 of the fourth axis 441 and the fifth axis 442. 3 The centers described herein are geometric centers.

[0035] The second pair 448 of optical emitters E2-1, E2-2 includes a third optical emitter (e.g., either the Nth receiving optical emitter RecEN or the Nth reference optical emitter RefEN) and a fourth optical emitter (e.g., either the Nth reference optical emitter RefEN or the Nth receiving optical emitter RecEN, respectively). A center C3 of the third optical emitter E2-1 is disposed at a negative second angle −θ2 from the fifth axis 442 and at a second radius R2 from an intersection 445 of the fourth axis 441 and the fifth axis 442. A center C4 of the second optical emitter E2-2 is disposed at a second angle θ2 from the fifth axis 442 and at a second radius R2 from an intersection 445 of the fourth axis 441 and the fifth axis 442.

[0036] Each of the fourth and fifth axes 441, 442 is orthogonal to a sixth axis 443 (e.g., the Z′ axis). The aforementioned symmetrical arrangement of the receiving optical emitter and reference optical emitter of each pair 447, 448 about the fifth axis 442 reduces the difference between the path length of the reflected optical signal emitted by the receiving optical emitter and passing through the Fabry-Perot etalon and the path length of the reference optical signal emitted by the reference optical emitter and passing through the aforementioned optical interferometer 221. As a result, for example, the aforementioned errors in velocity measurements by the LIDAR system 101 are reduced.

[0037] Each of the first pair of light emitters E1-1, E1-2 has a cross-sectional area A1, A2. Each of the second pair of light emitters E2-1, E2-2 has a cross-sectional area A3, A4.

[0038] 5 shows a view of the photodetector 526 when the all-optical interference pattern 527 is projected onto the surface 526-1 of the photodetector 526. The plane of the surface 526-1 is defined by a seventh axis (X'') 542 and an eighth axis (Y'') 543 that are orthogonal to each other.

[0039] For teaching purposes, the illustrated total optical interference pattern 527 includes only one pair 559 of received optical interference pattern 552 and reference optical interference pattern 553 in the position shown, and for this single pair, the positions of received optical interference pattern 552 and reference optical interference pattern 553 can be reversed. Received optical interference pattern 552 is created by optical interferometer 221 from first received optical signal 106-1. Reference optical interference pattern 553 is created by optical interferometer 221 from first reference optical signal REF1.

[0040] The locations of the received optical interference pattern 552, the reference optical interference pattern 553, and the corresponding unwanted interference patterns, as well as their shapes, are specifically described below. However, such descriptions are for instructional purposes. The shapes may vary. The locations may be described in alternate and reversed ways, as described elsewhere herein.

[0041] The received optical interference pattern 552 and the reference optical interference pattern 553 are each substantially symmetrically displaced about the eighth axis 542 because the received optical emitter and the reference optical emitter that emit the received optical signal 106-1 and the reference optical signal REF1, respectively, are disposed symmetrically about the eighth axis 542, e.g., as described above. The seventh axis 541 and the eighth axis 542 intersect at an intersection point 555. 4 Receive optical interference pattern 552 has a center 551A that is at a radius R3 from intersection point 555 and disposed at a negative third angle −θ3. Reference optical interference pattern 553 has a center 551B that is at a radius R3 from intersection point 555 and disposed at a third angle θ3. 4 The seventh axis 541 and the eighth axis 542 intersect at an intersection point 555 such that the first axis 541 symmetrically divides the surface 526-1 of the photodetector 526 along the seventh axis 541, and the eighth axis 542 symmetrically divides the surface 526-1 of the photodetector 526 along the second axis 542. A ninth axis, e.g., the Z axis, is orthogonal to each of the seventh axis 541 and the eighth axis 542.

[0042] Optical interferometer system 201-4 can suffer from another problem: reflections between component surfaces, for example, between the surface of a lens and the surface of optical interferometer 221, that cause a first unwanted optical interference pattern 557 and / or a second unwanted optical interference pattern 558 (sometimes individually or collectively referred to as "ghost" optical interference patterns). If the unwanted optical interference pattern overlaps with the desired, i.e., received or reference, interference pattern, this can induce further errors, for example, in velocity measurements by LIDAR system 101.

[0043] A first undesired optical interference pattern 557 is generated from the first reference optical signal REF1 used to create the reference optical interference pattern 553. A second undesired optical interference pattern 558 is generated from the first received optical signal 106-1 used to create the received optical interference pattern 552.

[0044] First undesired optical interference pattern 557 has center 551C. Center 551C of first undesired optical interference pattern 557 (a) occurs 180 degrees around intersection point 555 from center 551B of reference optical interference pattern 553, and (b) radial distance R3′ from center 551C of first undesired optical interference pattern 557 is substantially the same as radial distance R3 from center 551B of reference optical interference pattern 553.

[0045] Second undesired optical interference pattern 558 has center 551D. Center 551D of second undesired optical interference pattern 558 (a) occurs 180 degrees around intersection point 555 from center 551A of received optical interference pattern 552, and (b) radial distance R3'' from center 551D of second undesired optical interference pattern is substantially the same as radial distance R3 from center 551A of received optical interference pattern 552.

[0046] Each received optical interference pattern has a cross-sectional area. Each reference optical interference pattern has a cross-sectional area. The illustrated received optical interference pattern 552 has a first cross-sectional area 556A. The illustrated reference optical interference pattern 553 has a second cross-sectional area 556B.

[0047] Each unwanted optical interference pattern has a cross-sectional area. The first unwanted optical interference pattern 557 has a third cross-sectional area 556C. The second unwanted optical interference pattern 558 has a fourth cross-sectional area 556D. To reduce errors resulting from unwanted optical interference patterns, when there are more than one pair of receiver and reference light emitter (i.e., N is greater than 1), neither the receiver nor the reference optical interference pattern should overlap with the unwanted optical interference patterns.

[0048] The cross-sectional area of the received optical interference pattern is proportional to the cross-sectional area of the receive optical emitter that emits the receive optical signal from which optical interferometer 221 generates received optical interference pattern 552. The cross-sectional area of the reference optical interference pattern is proportional to the cross-sectional area of the reference optical emitter that emits the reference optical signal from which optical interferometer 221 generates reference optical interference pattern 553.

[0049] To avoid potential errors due to undesired interference patterns in a system having a ferrule 222 with two or more pairs of receive and reference optical signal emitters (i.e., N is greater than 1), neither a receive nor a reference optical emitter should be located within surface 222-1 of ferrule 222 within a cross section that is a mirror image of another receive or reference optical emitter within ferrule 222, e.g., within surface 222-1. Figure 6 illustrates this point.

[0050] 6 shows one embodiment of a surface 622-1 of a ferrule 222 with an exemplary pair of a first receiving optical signal emitter RecE1 and a first reference optical signal emitter RefE1 and a mirror image cross section (about the fourth and fifth axes 441, 442) of each emitter. Reference numbers that are the same or similar to those used in FIG. 4 have the same meaning in FIG. 6.

[0051] A cross section C1 of the mirror image 662-1 (around the fourth and fifth axes 441, 442) of the first receive optical signal emitter RecE1 occurs from a center point C1 of the first receive optical signal emitter RecE1 at 180 degrees around the intersection point 445. The cross section C1 of the mirror image 662-1 of the first receive optical signal emitter RecE1 has the same cross-sectional area A1 as the cross-sectional area A1 of the first receive optical signal emitter RecE1.

[0052] A cross section C2 of the mirror image 662-2 (about the fourth and fifth axes 441, 442) of the first reference optical signal emitter RefE1 occurs 180 degrees about the intersection point 445 from the center point C2 of the first reference optical signal emitter RefE1. The cross section C2 of the mirror image 662-2 of the first reference optical signal emitter RefE1 has the same cross-sectional area A2 as the cross-sectional area A2 of the first reference optical signal emitter RefE1. If the ferrule 222 includes additional pairs of unique receiving optical signal emitters and unique reference optical signal emitters (i.e., two or more pairs or N is greater than 1), the cross section of any emitter should not overlap with the mirror image of any other emitter.

[0053] For clarity, emitters E1-1, E1-2, E2-1, E2-2 in corresponding quadrants of surface 222-1, 422-1 of ferrule 222 will generate corresponding interference patterns in different quadrants of surface 226-1, 526-1 of photodetector 226 that are 180 degrees from the quadrants of surface 222-1, 622-1 of ferrule 222.

[0054] 7 shows a flow diagram of an exemplary method 770 for transmitting an optical signal from a surface of a ferrule to an input face of an optical interferometer that is tilted about a first axis (e.g., the X-axis) and offset at a first angle relative to a second axis (e.g., the Y-axis) that is orthogonal to the first axis. The optical interferometer has an output face that is also tilted about the first axis and offset at a second angle relative to the second axis. The tilting of the surfaces and axes of the components of the optical interferometer is further described herein with respect to FIGS. 2 and 3. The optical signal is configured to propagate in a third axis (e.g., the Z-axis) that is orthogonal to each of the first and second axes.

[0055] The optical interferometer includes a first piece of optically transparent material separated from a second piece of optically transparent material by a third piece of optically transparent material (e.g., air), and has at least one of: (a) an input surface of the first piece of optically transparent material tilted about a first axis (e.g., the X-axis) and offset at an angle δ with respect to a second axis (e.g., the Y-axis) orthogonal to the first axis; and (b) an output surface of the second piece of optically transparent material tilted about the first axis (e.g., the X-axis) and offset at an angle β with respect to a second axis (e.g., the Y-axis) orthogonal to the first axis. Optionally, the offset angle δ is equal to the offset angle β, although such offset angles may be different. The first and second axes are each orthogonal to a third axis (e.g., the Z-axis) along which or parallel to which the received optical signal and the reference optical signal and the optical interference pattern (and their components) propagate. Optionally, the optical interferometer is a Fabry-Perot interferometer.

[0056] Exemplary method 770 may be implemented by one or more of the devices shown in Figures 1-6. To the extent that the methods herein are described herein as being implemented by one or more of the devices shown in Figures 1-6, it should be understood that other embodiments may be implemented in other ways. Techniques described with respect to the embodiments shown in Figures 1-6 may be applicable to method 770.

[0057] The blocks of the flow diagrams herein are generally organized sequentially for ease of explanation; however, it should be understood that this organization is merely exemplary and that the processing associated with the methods (and the blocks illustrated in the figures) may occur in a different order (e.g., at least some of the processing associated with the blocks may be performed in a parallel and / or event-driven manner).

[0058] In optional block 771, an optical signal is emitted, for example, by a laser. In optional block 772, the optical signal is split into N transmit optical signals and M reference optical signals, for example, by an optical splitter, where the integers M and N are defined and exemplified elsewhere herein.

[0059] In optional block 773, using N transmit optical signals, each of the N transmit optical signals is transmitted, e.g., from a unique transmit optical component, toward a unique region, e.g., of a gas, solid, and / or liquid. A portion of each transmit optical signal, a reflected optical signal, is reflected back to the LIDAR system and received by the LIDAR system, e.g., by a unique receive optical component. Thus, in optional block 774, each of the N reflected optical signals is received from a unique region, e.g., by a unique receive optical component.

[0060] At optional block 775, a unique received optical signal is derived from each reflected optical signal, for example, by a LIDAR system (e.g., by a unique receiving optical component). At optional block 776, each of the N received optical signals is received, for example, by an optical interferometer system, for example, by a ferrule therein.

[0061] At least one reference optical signal is received in block 777. Optionally, M reference optical signals are received, for example, by an optical interferometer system, for example, a ferrule therein. Optionally, if fewer than O reference optical signals are received, the at least one reference optical signal is split to provide O reference optical signals. If O is greater than N, the excess reference optical signals beyond the N reference optical signals may be used for other purposes, for example, in optical interferometer system 101-4.

[0062] At block 778, N pairs of unique reflected optical signals and unique reference optical signals are emitted. Each pair of the N pairs includes a unique reflected optical signal (of the N reflected optical signals) and a unique reference optical signal (of the N reflected optical signals) whose cross sections are emitted symmetrically about a fifth axis, and optionally, such optical signals have the same cross section. Optionally, the symmetric emission of the cross sections of the unique reflected optical signals and the unique reference optical signals about the fifth axis means that: (a) a center of a cross section of the unique reflected optical signal is disposed at a negative first angle −θ1 from the fifth axis and at a first radius R1 from an intersection of the fourth axis and the fifth axis; (b) The center of the cross section of the intrinsic reference optical signal is disposed at a first angle θ1 from the fifth axis and at a first radius R1 from the intersection of the fourth and fifth axes.

[0063] Optionally, if the ferrule includes more than one pair of receiving optical signal emitters and reference optical signal emitters (i.e., N is greater than 1), the cross section of any emitted optical signal should not overlap with the mirror image of any other emitted optical signal, a subject further described elsewhere herein with respect to optical emitters.

[0064] In optional block 779, the emitted N pairs of reflected optical signals and reference optical signals are collimated, for example, by at least one collimating lens. In optional block 780, the emitted N pairs of reflected optical signals and reference optical signals are received by an input face of an optical interferometer, example structures and operations of which are described elsewhere herein.

[0065] In optional block 781, a total optical interference pattern is generated in an optical interferometer using the N received and emitted pairs. Total optical interference patterns are further described elsewhere herein.

[0066] In block 782, the total optical interference pattern is emitted by an output face of the optical interferometer. In optional block 783, the total optical interference pattern is focused, for example, by at least one imaging lens onto an optical sensor. In optional block 784, the total optical interference pattern is received, for example, by an optical sensor. In optional block 785, the total optical interference pattern is converted, for example, by the optical sensor, into an electrical signal carrying information about (or representative of) the total optical interference pattern. In optional block 786, a state variable (of the vehicle on which the LIDAR system is mounted), for example, vector velocity, is derived from the electrical signal representing the total optical interference pattern, for example, by a processing system. Optionally, the electrical signal (e.g., information regarding light intensity) is also used to adjust the output power (e.g., of a laser) and / or the light pulse transmission time.

[0067] While the present teachings have been illustrated with respect to one or more embodiments, changes and / or modifications to the illustrated embodiments may be made without departing from the scope of the appended claims. In addition, while certain features of the present disclosure may be described with respect to only one of several embodiments, such features may be combined with one or more features of other embodiments as may be desirable or advantageous for any given or particular function. Furthermore, to the extent that the terms "including," "includes," "having," "has," "with," or variations thereof are used in either the Detailed Description and / or the Claims, such terms are intended to be as inclusive as the term "comprising." The term "at least one of" is used to mean that one or more of the listed items may be selected. As used herein, the term "one or more of," with respect to a list of items, such as A and B, or A and / or B, means A only, B only, or A and B. The term "at least one of" is used to mean that one or more of the listed items may be selected.

[0068] Relative position terms used in this application are defined based on a plane parallel to a conventional plane or working surface of a material (e.g., a layer or substrate), regardless of orientation. Terms such as "on," "higher," "lower," "over," "top," and "under" are defined with respect to a conventional plane or working surface that is on top of a layer or substrate, regardless of orientation. The terms "about" or "substantially" indicate that a specified value or parameter may be slightly modified as long as such modification does not result in non-compliance of the process or structure with the illustrated embodiment. Finally, "exemplary" indicates that the description does not imply ideality but is used as an example. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that any configuration expected to achieve the same purpose may be substituted for the specific embodiment shown. Therefore, it is manifestly intended that this invention be limited only by the claims and equivalents thereof.

[0069] Illustrative Embodiments Example 1 is an apparatus for transmitting an optical signal to an input face of an optical interferometer, the optical interferometer further including an output face, the input face tilted about a first axis and offset at a first angle relative to a second axis orthogonal to the first axis, the output face tilted about the first axis and offset at a second angle relative to the second axis orthogonal to the first axis, the optical signal being configured to propagate toward the input face at a third axis orthogonal to the first and second axes, the input face being on a first optically transparent material and the output face being on a second optically transparent material, the first optically transparent material and the second optically transparent material being separated from each other. and N pairs of optical emitters within a surface of the ferrule, each pair including a receiving optical emitter configured to emit a received optical signal toward the input face and a reference optical emitter configured to emit a reference optical signal toward the input face, where N is an integer greater than 0; the surface of the ferrule lies in a plane formed by a fourth axis and a fifth axis that are orthogonal to each other, and cross sections of the optical emitters of each pair are arranged symmetrically about the fifth axis, and for each pair, the receiving optical emitter lies in one half of the plane divided by the fifth axis and the reference optical emitter lies in the other half of the plane.

[0070] Example 2 includes the apparatus of example 1, wherein N is an integer greater than 2.

[0071] Example 3 includes the apparatus of any of Examples 1-2, wherein arranging the cross sections of each pair of light emitters symmetrically about the fifth axis means that the center of the pair of receiving light emitters is arranged at a negative third angle from the fifth axis and at a radius from an intersection of the fourth axis and the fifth axis, and the center of the pair of reference light emitters is arranged at the third angle from the fifth axis and at the radius from the intersection.

[0072] Example 4 includes the device of any of examples 1-3, wherein when N is greater than 1, no light emitter is located within the surface within a cross-sectional area that is a mirror image of another light emitter within the surface about the fourth axis and the fifth axis.

[0073] Example 5 includes the apparatus of example 4, wherein the center of the cross-sectional area of the mirror image is located 180 degrees about the intersection of the fourth axis and the fifth axis and at a radial distance from the intersection that is the same as the radial distance from the intersection to the center of the cross-sectional area of the other light emitter.

[0074] Example 6 includes the apparatus of any of Examples 1-5, further including at least one collimating lens configured to collimate the N pairs of optical signals emitted from the ferrule; an optical interferometer configured to receive the N pairs of optical signals at an input face, generate an interference pattern from each received optical signal and each reference optical signal received from the ferrule, and emit the interference pattern from an output face; at least one imaging lens configured to focus the interference pattern emitted from the output face; and a photodetector configured to convert the interference pattern into an electrical signal.

[0075] Example 7 includes the apparatus of example 6, wherein the optical interferometer is a Fabry-Perot interferometer.

[0076] Example 8 includes the apparatus of any of Examples 6-7, further including: a laser configured to emit a laser optical signal; an optical splitter configured to split the laser optical signal into N transmitted optical signals and M reference optical signals, where M is an integer less than or equal to O and O is an integer greater than or equal to N; N pairs of optical transmitters and optical receivers, where each optical transmitter is configured to transmit one of the N transmitted optical signals using the N transmitted optical signals to a region including at least one of at least one gas, at least one solid, and at least one liquid, and each optical receiver is configured to receive one of the N reflected optical signals reflected from the respective region and generate a received optical signal therefrom; the N pairs of optical transmitters and optical receivers, the ferrule configured to receive the N received optical signals from the N optical receivers and the M reference signals from the optical splitter; and a processing circuit configured to receive the electrical signals and use the electrical signals to determine a state variable of a vehicle on or in which the N pairs of optical transmitters and optical receivers are mounted.

[0077] Example 9 includes the apparatus of example 8, wherein M is less than N, and the ferrule is configured to split the M reference signals into O reference signals.

[0078] Example 10 is a method for transmitting an optical signal to an input face of an optical interferometer, the optical interferometer further comprising an output face, the input face tilted about a first axis offset at a first angle relative to a second axis orthogonal to the first axis, the output face tilted about the first axis offset at a second angle relative to the second axis, the optical signal configured to propagate toward the input face at a third axis orthogonal to the first and second axes, the input face being on a first optically transparent material, the output face being on a second optically transparent material, and the first and a second optically transparent material are separated from each other, the method including: receiving N received optical signals, where N is an integer greater than or equal to 1; receiving M reference optical signals, where M is an integer less than or equal to O and O is an integer greater than or equal to N; and emitting N pairs of received optical signals and reference optical signals, where a cross section of the optical signal of each of the N pairs is emitted symmetrically about a fifth axis in a plane in which each emitter is located and which is defined by a fourth axis and a fifth axis that are orthogonal to each other.

[0079] Example 11 includes the method of Example 10, wherein arranging each pair symmetrically around the fifth axis means that the center of the received optical signal of the pair is arranged at a negative third angle from the fifth axis and at a radius from the intersection of the fourth axis and the fifth axis, and the center of the reference optical signal of the pair is arranged at a third angle from the fifth axis and at the radius from the intersection.

[0080] Example 12 includes the method of any of Examples 10-11, wherein when N is greater than 1, a cross-section of any of the N pairs of emitted light signals should not overlap with a mirror image of any of the other N pairs of emitted light signals about the fourth axis and the fifth axis.

[0081] Example 13 includes the method of any of Examples 10-12, wherein N is greater than 2.

[0082] Example 14 includes the method of any of Examples 10-13, further including: collimating the emitted N pairs of received optical signals and reference optical signals; receiving the emitted N pairs of received optical signals and reference optical signals at an input face of an optical interferometer; generating by the input face a total-optical interference pattern using the received emitted N pairs, the total-optical interference pattern including an interference pattern for each received reflected optical signal and for each reference optical signal; emitting the total-optical interference pattern from the output face; focusing the emitted total-optical interference pattern; and generating an electrical signal representing the total-optical interference pattern.

[0083] Example 15 includes the method of example 14, further including: emitting an optical signal; splitting the optical signal into N transmitted optical signals and M reference optical signals; transmitting each of the N transmitted optical signals to an area including at least one of at least one gas, at least one solid, and at least one liquid; receiving N reflected optical signals, each reflected optical signal being a portion of the transmitted optical signal reflected from a respective area; deriving N received optical signals, each derived from the reflected optical signals; and determining a state variable of the vehicle from the electrical signals.

[0084] Example 16 includes the method of any of Examples 10-15, wherein when M is not equal to N, O reference optical signals are generated from M reference optical signals.

[0085] Example 17 includes an apparatus for transmitting an optical signal to an input face of a Fabry-Perot etalon tilted about a first axis and offset at a first angle with respect to a second axis orthogonal to the first axis, wherein the optical signal is configured to propagate to the input face of the Fabry-Perot etalon on a third axis orthogonal to each of the first axis and the second axis, the apparatus including: a first set of N optical emitters each emitting a reflected optical signal from a ferrule surface, where N is an integer greater than 0; and a second set of O optical emitters each emitting a reference optical signal from the ferrule surface, where O is an integer greater than or equal to N, and the ferrule surface lies in a plane formed by a fourth axis and a fifth axis, wherein the positions of each pair of optical emitters in the first set and the second set are arranged symmetrically about the fifth axis.

[0086] Example 18 includes the apparatus of example 17, wherein disposing each pair symmetrically about the fifth axis means that the center of the receiving light emitter of the pair is disposed at a negative second angle from the fifth axis and at a radius from an intersection of the fourth axis and the fifth axis, and the center of the reference light emitter of the pair is disposed at a second angle from the fifth axis and at the radius from the intersection.

[0087] Example 19 includes the device of any of examples 17-18, wherein when N is greater than 1, no optical emitter is located within the ferrule surface within a cross-sectional area that is a mirror image of another optical emitter within the ferrule surface about the fourth axis and the fifth axis.

[0088] Example 20 includes the apparatus of example 19, wherein the center of the cross-sectional area of the mirror image is located 180 degrees about the intersection of the fourth axis and the fifth axis and at a radial distance from the intersection that is the same as the radial distance from the intersection to the center of the cross-sectional area of the other light emitter.

[0089] Although specific embodiments have been illustrated and described herein, those skilled in the art will recognize that any configuration which is expected to achieve the same purpose may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.

Claims

1. 1. An apparatus for transmitting an optical signal to an input face of an optical interferometer, the optical interferometer further comprising an output face, the input face tilted about a first axis and offset at a first angle relative to a second axis orthogonal to the first axis, the output face tilted about the first axis and offset at a second angle relative to the second axis orthogonal to the first axis, the optical signal being configured to propagate towards the input face on a third axis orthogonal to the first and second axes, the input face being on a first optically transparent material and the output face being on a second optically transparent material, the first optically transparent material and the second optically transparent material being separated from one another, the apparatus comprising: A ferrule and N pairs of optical emitters within a surface of the ferrule, each pair of optical emitters including a receiving optical emitter configured to emit a received optical signal into the input surface and a reference optical emitter configured to emit a reference optical signal into the input surface, where N is an integer greater than 0; the surface of the ferrule lies in a plane formed by a fourth axis and a fifth axis that are orthogonal to each other; the cross sections of the light emitters of each pair are symmetrically disposed about the fifth axis; 1. An apparatus for transmitting optical signals to an input face of an optical interferometer, wherein for each pair, the receiving optical emitter is in one half of the plane divided by the fifth axis and the reference optical emitter is in another half of the plane.

2. 2. The apparatus of claim 1, wherein when N is greater than 1, no light emitter is located within the surface within a cross-sectional area that is a mirror image of another light emitter within the surface about the fourth axis and the fifth axis.

3. at least one collimating lens configured to collimate the N pairs of optical signals emitted from the ferrule; the optical interferometer configured to receive the N pairs of optical signals at the input surface, generate an interference pattern from each received optical signal and each reference optical signal received from the ferrule, and emit the interference pattern at the output surface; at least one imaging lens configured to focus the interference pattern emitted from the output surface; The apparatus of claim 1 , further comprising: a photodetector configured to convert the interference pattern into an electrical signal.

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