Technology to Improve Fiber Optic Scanning Systems

Abstract

The present invention relates to techniques for improving fiber optic scanning systems. A fiber optic scanning system can have optimized performance by substantially matching the natural frequency of an actuator of the fiber optic scanning system and the natural frequency of a fiber optic scanning element. By matching the natural frequencies, the fiber optic scanning system can increase the maximum distance that the end of the fiber optic scanning element can be driven relative to a stationary position. This effect occurs because matching the natural frequency of the fiber optic scanner allows for greater amplitudes to be achieved. It should be noted that the natural frequency of the scanning system can be selected to avoid excitation frequencies that may make the system unstable. In this way, the entire system can act as a tuned mass damper or a tuned resonant structure, thereby improving scanning performance while maintaining a stable scanning system.

Description

[0001] This application is a divisional application of an application with a filing date of March 13, 2018, a PCT international application number of PCT / US2018 / 022254, a Chinese national phase application number of 201880017818.0, and an invention name of “Technology for Improving Fiber Optic Scanning Systems”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 471,913, filed on March 15, 2017, entitled “DYNAMIC ABSORBER MODE FIBERSCANNER,” the entire disclosure of which is incorporated herein by reference for all purposes. Background Art

[0004] An image projector may be an optical device that projects an image (or moving image) for viewing by a user. Recently, innovations have enabled head mounted devices to include image projectors. Such image projectors may project images to the eyes of a user wearing the head mounted device. However, image projectors that are small enough to be used with head mounted devices typically project images with a narrow field of view. Therefore, there is a need in the art for an improved design of an image projector for use with a head mounted device. Summary of the invention

[0005] Methods, systems, and computer program products for improved designs of fiber optic scanning systems are provided. For example, the performance of a fiber optic scanning system can be optimized by substantially matching the natural frequency of an actuator of the fiber optic scanning system and the natural frequency of a fiber optic scanning element. By matching the natural frequencies, the fiber optic scanning system can increase the maximum distance that the tip of the fiber optic scanning element is driven relative to the stationary position of the fiber optic scanning element. This effect occurs because matching the natural frequency of the fiber scanner allows for greater amplitudes to be achieved. It should be noted that the natural frequency of the scanning system can be selected to avoid excitation frequencies that may make the system unstable. In this way, the entire system can act as a tuned dynamic absorber or modal energy transfer optimizer for an oscillator, thereby improving scanning performance while maintaining a stable scanning system.

[0006] According to an embodiment of the present invention, a method for increasing the field of view of a fiber scanning system is provided. The method includes configuring the fiber scanning system to act as a tuned dynamic absorber by selecting (1) an actuator characterized by a first actuator natural frequency and (2) a fiber optical scanning element characterized by a first fiber natural frequency, wherein the first fiber natural frequency is within a threshold of the first actuator natural frequency. Alternatively, the method includes configuring the fiber scanning system to act as a tuned dynamic absorber by selecting (1) a fiber optical scanning element characterized by a second fiber natural frequency and (2) an actuator characterized by a second actuator natural frequency, wherein the second actuator natural frequency is within a threshold of the second actuator natural frequency. The method also includes driving the fiber scanning system at an operating frequency.

[0007] According to another embodiment, a method for increasing the field of view of a fiber scanning system is provided. The method includes configuring the fiber scanning system to act as a tuned dynamic absorber by providing (1) an actuator characterized by an actuator natural frequency and (2) a fiber optical scanning element characterized by a fiber natural frequency, wherein the fiber natural frequency is within a threshold of the actuator natural frequency. A first displacement gain is associated with the operation of the fiber scanning system at the fiber natural frequency. The method also includes determining an operating frequency range. The range extends from a first operating frequency less than the fiber natural frequency and associated with the first displacement gain to a second operating frequency greater than the fiber natural frequency and associated with the first displacement gain. The method further includes driving the actuator at an operating frequency within the range.

[0008] In some examples, a fiber scanning system may include an actuator (e.g., a piezoelectric tube) and a fiber optical scanning element. In such examples, the fiber scanning system may be optimized so that the actuator natural frequency (of the actuator) may be determined to match the fiber natural frequency (of the fiber optical scanning element). In this way, energy from the actuator may be more efficiently transferred to the fiber optical scanning element, thereby increasing the overall deflection of the fiber optical scanning element, which may provide a wider field of view for the fiber scanning system.

[0009] Through the present disclosure, many benefits over conventional techniques are achieved. For example, embodiments of the present disclosure provide increased deflection of the fiber optic scanning element tip for a given energy input, thereby increasing the field of view of the scanning fiber system.

[0010] A fiber optic scanning system is provided. For example, a fiber optic scanning system can include an actuator (e.g., a piezoelectric tube) characterized by operation at an actuator natural frequency and a fiber optic scanning element coupled to the actuator. In some examples, the fiber optic scanning element can be characterized by a fiber natural frequency that is determined to match the actuator natural frequency. In examples with a piezoelectric tube, the piezoelectric tube can have a cylindrical geometry having a central axis, wherein the fiber optic scanning element passes through the piezoelectric tube along the central axis.

[0011] In some examples, one or more properties of the actuator can be configured to produce operation of the actuator natural frequency. In such examples, the one or more properties can be Young's modulus, second moment of area, density, cross-sectional area, length, or mode constant.

[0012] In some examples, the actuator natural frequency and the fiber natural frequency may match within a threshold value (eg, 10%). In such examples, when the fiber optical scanning element is separated from the actuator, operation of the actuator natural frequency characterizes the actuator.

[0013] A method for increasing the field of view of a fiber optic scanning system is also provided. For example, the method may include providing an actuator characterized by operation at an actuator natural frequency. In some examples, the fiber optic scanning system may include an actuator. The method may further include providing a fiber optic scanning element coupled to the actuator. In some examples, the fiber optic scanning element is characterized by a fiber natural frequency, and the fiber natural frequency is determined to match the actuator natural frequency. In such an example, the fiber optic scanning system may further include the fiber optic scanning element. The method may further include driving the actuator at an operating frequency.

[0014] In some examples, the displacement gain of the fiber scanning system can be characterized by two separate frequency peaks that define the natural frequency of the actuator. In such examples, the operating frequency can be close to a first peak in the frequency peaks (i.e., at a frequency within a threshold of the first peak), where the first peak is less than the natural frequency of the actuator. In other examples, the operating frequency can be close to a second peak in the frequency peaks (i.e., at a frequency within a threshold of the second peak), where the second peak is greater than the natural frequency of the actuator. In other examples, the operating frequency can be close to the natural frequency of the actuator (i.e., at a frequency within a threshold of the natural frequency of the actuator). In some examples, the actuator can be driven by a sinusoidal voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments are described in detail below with reference to the following drawings.

[0016] Figure 1 An example of a fiber scanning system according to an embodiment of the present disclosure is shown;

[0017] Figure 2 An example of an image projector using a fiber scanning system according to an embodiment of the present disclosure is shown;

[0018] Figure 3 shows an example of a spiral pattern formed by a moving fiber scanning system according to an embodiment of the present disclosure;

[0019] Figure 4A shows an example of a cross section for a dynamic absorption design for a fiber scanning system according to an embodiment of the present disclosure;

[0020] Figure 4B shows an example of a cross section of an alternative design for a fiber optic scanning system according to an embodiment of the present disclosure;

[0021] Figure 4C An example of a cross section of a fiber optic scanning system indicating a hub and a plate is shown;

[0022] Figure 5A An example of a Bode plot showing an alternative design of a fiber scanning system according to an embodiment of the present disclosure;

[0023] Figure 5B An example of a Bode plot showing a dynamic absorption design of a fiber scanning system according to an embodiment of the present disclosure;

[0024] Figure 5C shows an example of a Bode plot for comparing a dynamic absorption design and an alternative design of a fiber optic scanning element according to an embodiment of the present disclosure;

[0025] Figure 5D shows an example of a Bode plot for comparing a dynamic absorption design and an alternative design of an actuator according to an embodiment of the present disclosure; and

[0026] Figure 6 An example of a process for increasing the field of view of a fiber scanning system is shown. DETAILED DESCRIPTION

[0027] In the following description, for the purpose of explanation, specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it is apparent that various embodiments can be practiced without these specific details. The drawings and descriptions are not intended to be limiting.

[0028] The following description provides exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the following description of the exemplary embodiments will provide those skilled in the art with instructions to enable the exemplary embodiments to be implemented. For example, although the description describes a piezoelectric tube, it should be recognized that any type of actuator may be used. It should also be understood that various changes may be made to the function and arrangement of the elements without departing from the spirit and scope of the present disclosure as set forth in the appended claims.

[0029] An image projector can be an optical device that projects an image (or moving image) for viewing by a user. In some examples, the image projector can project an image in the form of light into one or more eyes of the user. In such examples, the image projector can take the form of one or more fiber optic scanning systems, each of which can use fiber optic scanning elements and actuators to project light into one or more eyes of the user in various patterns (e.g., raster scanning, spiral scanning, Lissajous, etc.). In addition to projecting light, the fiber optic scanning system can also receive emitted light. In particular, the same fiber optic scanning system that projects light can be used to receive light.

[0030] Figure 1 An example of a fiber optic scanning system 100 according to an embodiment of the present disclosure is shown. The fiber optic scanning system 100 may include an actuator 110 (e.g., a piezoelectric tube) and a fiber optic scanning element 120 (e.g., a single-fiber or multi-core fiber optic scanning element). In some examples, the actuator 110 may be coupled to the fiber optic scanning element 120 so that the fiber optic scanning element 120 is cantilevered. In such an example, the actuator 110 may be used to scan (or move) the end of the fiber optic scanning element 120 to project light into one or more eyes of a user.

[0031] Figure 2 2 shows an example of an image projector using a fiber scanning system 200 according to an embodiment of the present disclosure. In some examples, the fiber scanning system 200 may include an actuator 210 (which may be coupled to a Figure 1 ) and a fiber optic scanning element 220 (which may be associated with the actuator 110 in Figure 1 2). In such an example, the fiber optic scanning element 220 can be scanned by the actuator 210 to produce a set of beamlets having multiple angles of incidence and intersections that are delivered to the eye 240 via the waveguide 230. For example, a collimated light field image can be injected into the waveguide 230 and then moved to the eye 240.

[0032] Figure 3An example of a spiral pattern formed by a mobile fiber scanning system according to an embodiment of the present disclosure is shown. Specifically, spiral 310 shows a multi-core fiber optical scanning element 330, and spiral 320 shows a single fiber optical scanning element 340. In some examples, a fixed pattern spacing can provide a uniform display resolution. In such an example, the spacing can be the distance between consecutive spiral passes along a common vector from the origin of the multi-core fiber optical scanning element 330.

[0033] Figure 4A 4 shows an example of a cross section of a dynamic absorption design for a fiber scanning system 400 according to an embodiment of the present disclosure. The fiber scanning system 400 may include an actuator 410 (which may be coupled to a Figure 1 The fiber optic scanning system 400 may also include a fiber optic scanning element 420 (which may be associated with the actuator 110 in FIG. 1 ). Figure 1 As described below, the fiber optic scanning element 420 can be used as a scanning fiber in a fiber optic scanning display system.

[0034] exist Figure 4A In the present disclosure, the actuator of the fiber scanning system is implemented as a piezoelectric tube, and for clarity, the discussion herein utilizes the term "piezoelectric tube", but it should be understood that embodiments of the present disclosure may use actuators other than piezoelectric tubes. For example, voice coil actuators, thermal actuators, electrostatically driven actuators, electromagnetic actuators, etc. may be used. Therefore, the description of piezoelectric tubes should be understood to include a description of a more general class of actuators, and the present disclosure is not limited to actuators implemented as piezoelectric tubes.

[0035] exist Figure 4A In the illustrated example embodiment, the actuator 410 is characterized by a cylindrical geometry. In addition, the fiber optic scanning element 420 passes through the actuator 410 along the central axis of the fiber optic scanning element 420 and is mechanically coupled to the actuator 410 at a central position 412. Although the fiber optic scanning element 420 is coupled to the actuator 410 at the central position 412 (i.e., at a radial position of zero radius), this is not required by the present disclosure, and other coupling positions may also be utilized according to embodiments of the present disclosure. Therefore, it should be recognized that the fiber optic scanning element 420 may be coupled to other positions of the actuator 410. In some examples, the fiber optic scanning element 420 may be coupled to the actuator 410 using epoxy.

[0036] In some examples, the fiber scanning system 400 may further include an intermediate element between the fiber optical scanning element 420 and the actuator 410. In such examples, the intermediate element may be a fused silica ferrule or a micromachined (eg, fused silica or single crystal silicon) joint.

[0037] In some examples, the outer diameter of the fiber optic scanning element 420 at the center location 412 and the inner diameter of the actuator 410 at the center location 412 can be the same. In other examples, the diameters can be different (i.e., the outer diameter can be smaller than the inner diameter). In such examples, a retention collar can be used to surround and contact the fiber optic scanning element 420.

[0038] In some examples, the fiber optic scanning element 420 can be coupled to the actuator 410 using epoxy, filled epoxy (e.g., carbon nanotube, nano rubber, graphene, or nano silica additives, etc.), solder glass, solder, any adhesive, etc.

[0039] In some examples, the actuator 410 can have a natural frequency (sometimes referred to as an actuator natural frequency or eigenfrequency) based on one or more properties of the actuator 410 (described below). The actuator natural frequency can be described as the frequency at which the actuator 410 oscillates on its own without an external force after an initial disturbance (as described in Rao SS, Mechanical Vibrations, p. 53, Addison-Wesley Publishing Company, New York, 1995). In some examples, the actuator natural frequency is a characteristic of the actuator 410 that is separate from the fiber optic scanning element 420.

[0040] In some examples, the fiber optic scanning element 420 may also have a natural frequency (sometimes referred to as a fiber natural frequency). The fiber natural frequency (sometimes referred to as a fiber resonant frequency) may be the frequency at which the fiber optic scanning element 420 (independent of or separate from the actuator 410) tends to oscillate in the absence of any driving or damping forces. The fiber natural frequency may be the same as or different from the actuator natural frequency. In some examples, the fiber natural frequency may be much smaller than the actuator natural frequency (e.g., Figure 4B In some examples, when the oscillation frequency of the fiber optic scanning element 420 matches the actuator natural frequency, the fiber optic scanning element 420 can absorb more energy.

[0041] In some examples, the fiber scanning system 400 can be optimized so that when the fiber optical scanning element 420 is separated from or independent of the actuator 410, the fiber natural frequency can be within a threshold value (e.g., 10%) of the actuator natural frequency. By matching the natural frequency within the threshold value, the energy from the actuator 410 can be more efficiently transferred to the fiber optical scanning element 420, thereby making the overall deflection of the fiber optical scanning element 420 larger, which can lead to a larger (or wider) image field of view. As described herein, the equality or match between the actuator natural frequency and the fiber natural frequency enables efficient energy transfer from the actuator 410 to the fiber optical scanning element 420. The equality or match is discussed with respect to a threshold value of 10%, but this is not required by the present disclosure. In some examples, the threshold value is less than 10% (e.g., 5%, 2%, 1%, etc.). In other examples, the threshold value is greater than 10% (e.g., 15%, 20%, etc.). Those of ordinary skill in the art will recognize many variations, modifications, and substitutions.

[0042] As described above, the actuator natural frequency can be based on one or more properties of the actuator 410. In some examples, the one or more properties can be adjusted so that the actuator natural frequency is determined to match the fiber natural frequency (within a threshold of the fiber natural frequency). In such examples, the one or more properties of the actuator 410 can include, but are not limited to: Young's modulus, second moment of area, density, cross-sectional area, length, or mode constant. The actuator natural frequency can be expressed as: where f n may be the natural frequency of the actuator 410, β may be the mode constant, L may be the length of the actuator 410, i may be an integer representing the mode number, E may be the Young's modulus of the actuator 410, I may be the second moment of area of ​​the actuator 410, ρ may be the density of the actuator 410, and A may be the cross-sectional area of ​​the actuator 410. In some examples, the mode constant may be a function of the boundary conditions and the mode harmonics (e.g., first mode, second mode, etc.). The boundary conditions may be how the fiber optic scanning element is attached at its end. In some examples, the attachment may be fixed, indicating that the fixed end has no rotation and no displacement. In other examples, the attachment may be simple, indicating that no displacement, but rotation is allowed. In other examples, the attachment may be free-supported, indicating that rotation is allowed and displacement is allowed.

[0043] In one illustrative example, the actuator natural frequency and the fiber natural frequency can both be about 25,000 Hertz (Hz). In such an example, the length of the actuator 410 can be 3.903 millimeters (mm), and the length of the fiber optic scanning element 420 can be 1.970 mm. Other dimensions of the actuator 410 and the fiber optic scanning element 420 can include a piezoelectric outer diameter (OD) (e.g., 888 micrometers (μm)), a piezoelectric inner diameter (ID) (e.g., 296 μm), a diameter of the fiber optic scanning element 420 (e.g., 125 μm), a thickness of the joint flexure plate (e.g., 70 μm) (the plate is at Figure 4C ), the thickness of the joint flexure hub (eg, 40 μm) (the hub is Figure 4C ) and a nominal excitation voltage (eg, 100 μm). However, it should be appreciated that the dimensions and properties may vary depending on the specific application and / or actuator.

[0044] In some examples, when the fiber optic scanning element 420 is added to the actuator 410 to form a fiber optic scanning system, the natural frequency of the fiber optic scanning system can be less than the actuator natural frequency or the fiber natural frequency. For example, due to the added mass of the fiber optic scanning element 420, the natural frequency of the fiber optic scanning system can be reduced relative to the actuator natural frequency. In some examples, when the fiber optic scanning element 420 is combined with the actuator 410, the natural frequency of the fiber optic scanning system can be a function of the modal mass ratio of the fiber optic scanning element 420 and the actuator 410. In some examples, the modal mass ratio of the dynamic absorption design can be 1:1, where the actuator 410 has a modal mass equal to that of the fiber optic scanning element 420.

[0045] In some examples, the actuator 410 may be driven at a specific frequency or a specific frequency range, which may be referred to as an operating frequency. In such an example, the actuator 410 may be driven by a sinusoidal voltage. The operating frequency at which the actuator 410 is driven may cause the actuator 410 to reduce its own motion. For example, the actuator 410 may be driven at its natural frequency. By minimizing the motion of the actuator 410, energy may be stored by the actuator 410, which may then be transferred to the fiber optic scanning element 420 through a reaction force to obtain a greater overall deflection of the fiber optic scanning element 420. Therefore, embodiments of the present invention in which the actuator is driven at its natural frequency to produce an increased deflection of the fiber optic scanning element are in sharp contrast to conventional systems, in which the operating frequency (particularly the operating frequency of the tuned dynamic absorber) is significantly different from the resonant frequency to mitigate vibration. In contrast to conventional system operation, embodiments of the present invention do not mitigate the oscillation (i.e., deflection) of the fiber optic scanning element, but increase the deflection range.

[0046] Figure 4B An example of a cross section of an alternative design for a fiber optic scanning system according to an embodiment of the present disclosure is shown. The alternative design can have different natural frequencies for the actuator 440 and the fiber optic scanning element 450. In particular, the actuator natural frequency can be about 50,000 Hz, while the fiber natural frequency can be about 25,000 Hz (half the actuator natural frequency). In some examples, the length of the actuator in the alternative design can be 2.767 mm, and the length of the fiber optic scanning element 450 can be 1.970 mm. In some examples, the modal mass ratio of the alternative design can be 2:1, where the modal mass of the actuator 440 can be twice the modal mass of the fiber optic scanning element 450.

[0047] Figure 5A Examples of Bode plots of alternative designs of fiber optic scanning systems according to embodiments of the present disclosure are shown. Figure 5A The Bode plot shown is similar to the one above for Figure 4B The discussed alternative design of the fiber optic scanning system, in which the natural frequency of the fiber optic scanning element is half the natural frequency of the actuator, is relevant. Figure 5A The Bode plots in can describe the frequency response and phase angle of components of the fiber scanning system (e.g., actuator 440 and / or fiber optic scanning element 450). In some examples, the Bode plots can be generated using one or more linear models. However, it should be appreciated that the Bode plots can be generated using one or more nonlinear models.

[0048] Specifically, the first Bode plot may plot the displacement gain of the actuator (e.g., piezoelectric tube plot 520) and the displacement gain of the fiber optic scanning element (e.g., fiber optic plot 510) as a function of the frequency at which the voltage is applied to the actuator. In some examples, the displacement gain may be related to the end of the fiber optic scanning element and / or the end of the actuator. In such an example, the displacement gain may be calculated using the following equation: Where δ refers to the dynamic value of the fiber scanning system and 1 refers to the approximation of the static value of the fiber scanning system. In such an example, the static value can be normalized to 1, which can be the expected static deflection of the fiber scanning system. In some examples, the static value can be the displacement of the actuator when a direct current (DC) voltage potential is applied. In such an example, the position of the actuator may not change over time. In some examples, the dynamic value can be the displacement of the actuator when an alternating current (AC) voltage potential is applied.

[0049] refer to Figure 5AFiber graph 510 may indicate that the displacement gain of the end of the fiber optic scanning element may increase until the frequency applied to the actuator reaches the natural frequency of the fiber optic scanning element (e.g., 25,000 Hz). In some examples, the displacement gain of the fiber optic scanning element may increase at a greater rate as the frequency approaches the natural frequency of the fiber. After fiber graph 510 reaches the natural frequency of the fiber, the displacement gain of the end of the fiber optic scanning element may decrease (e.g., asymptotically).

[0050] The piezoelectric tube graph 520 may indicate that the displacement gain at the end of the actuator also increases until the frequency applied to the actuator reaches the fiber natural frequency. In some examples, the frequency of the actuator may increase at a relatively linear rate on a logarithmic scale until the displacement gain of the fiber optic scanning element reaches a specific amount. Once the displacement gain of the fiber optic scanning element reaches the specific amount, more energy may be transferred from the actuator to the fiber optic scanning element so that the displacement gain of the actuator increases at a greater rate than before the displacement gain of the fiber optic scanning element reaches the specific amount. In some examples, the transfer of energy from the fiber optic scanning element to the actuator is disadvantageous because the transfer of the reaction force of the fiber optic scanning element to the actuator reduces the displacement gain that the fiber optic scanning element can experience.

[0051] Once the frequency applied to the actuator reaches the fiber's natural frequency, the actuator's displacement gain drops to about -10, which is equal to 20log 10 Output / input, so that output / input equals 0.31, indicating that the dynamic response is 31% of the static response. After the displacement gain of the actuator decreases, the displacement gain of the actuator can increase to a certain amount (the rate of change of the displacement amplitude as a function of frequency can depend on the order of the linear system), and then continue to increase (at a rate similar to the rate before the above certain amount) until the frequency applied to the actuator reaches the actuator natural frequency (e.g., 50,000 Hz). After the frequency applied to the actuator reaches the actuator natural frequency, the displacement gain of the actuator can decrease (e.g., asymptotically).

[0052] A second Bode plot may plot the phase angle of the actuator (e.g., piezoelectric tube 540) and the phase angle of the fiber optic scanning element (fiber diagram 530) in relation to the frequency at which the voltage is applied to the actuator. The phase angle may indicate the relationship between the response of the actuator and the fiber optic scanning element to the frequency input. In some examples, the phase angle may indicate a time delay, typically a delay between a command signal and a physical response. In such an example, the phase angle may indicate the controllability of the fiber optic scanning system.

[0053] Figure 5B The optical fiber scanning system according to the embodiment of the present disclosure (as shown above) is shown. Figure 4A An example of a Bode plot for a dynamic absorption design where the fiber natural frequency can be approximately matched to the actuator natural frequency is shown. Figure 5A As described, the Bode plot may describe the frequency response and phase angle of components of the fiber optic scanning system (eg, the actuator 410 and / or the fiber optic scanning element 420).

[0054] refer to Figure 5B 550. The first Bode plot of the fiber optic scanning element can indicate that the displacement gain of the end of the fiber optic scanning element is characterized by two peaks in the fiber optic graph 550. The two peaks can represent the mode splitting caused by combining the fiber optic scanning element and the actuator together to form a single mechanical system with the fiber optic scanning element and the actuator having the same frequency. In particular, the first resonant mode of the actuator can be associated with a first peak (sometimes referred to as a first resonant frequency 552) formed at a frequency lower than the natural frequency of the actuator. In addition, the second resonant mode of the fiber optic scanning element can be associated with a second peak (sometimes referred to as a second resonant frequency 554) formed at a frequency higher than the natural frequency of the fiber.

[0055] In some examples, the displacement gain at the end of the fiber optic scanning element may decrease between the first peak and the second peak, such as Figure 5B The reduction in displacement gain may result in the end of the fiber optical scanning element having a displacement gain at the fiber natural frequency that is less than either peak; however, despite the reduction from the peak, the displacement gain may still be higher than the displacement gain of the end of an alternatively designed fiber optical scanning element at the fiber natural frequency (e.g. Figure 5A 550). In some examples, the distance between peaks in the fiber map 550 can be a function of the modal mass ratio. For example, if the actuator has a larger modal mass, the spacing between the first peak and the second peak is smaller. In addition, the shape of each peak can be based on the damping of the fiber scanning system. For example, one of the peaks can be higher than the other peak.

[0056] In some examples, the displacement gain of the fiber optical scanning element can be maximized at the first resonant frequency 552, the fiber natural frequency, and / or the second resonant frequency 554. In such examples, the fiber scanning system can be operated at or near the point where the displacement gain is maximized. In other examples, the fiber scanning system can be operated at one of the above points, that is, the point at which the operation is performed is not the maximum value. In such examples, the operating point of the fiber scanning system can be selected based on the rate of change around the point. For example, the first resonant frequency 552 and / or the second resonant frequency 554 may be unstable in terms of displacement gain (e.g., based on the amount of change in displacement gain in response to a small change in frequency), while the natural frequency 556 may be more stable. In such examples, the natural frequency 556 can be selected as the operating point of the fiber scanning system instead of the first resonant frequency 552 or the second resonant frequency 554.

[0057] In some embodiments, the operating point of the fiber scanning system is selected so that the displacement gain is greater than or equal to a predetermined displacement gain. In other words, during operation, the fiber scanning system can achieve a range of displacement gains by driving the actuator at an operating frequency within a frequency range.

[0058] refer to Figure 5B , the displacement gain at the 25kHz natural frequency is slightly greater than 40dB, which can be referred to as the natural displacement gain. A displacement gain greater than or equal to the natural displacement gain can be achieved by driving the fiber scanning system with a frequency (i.e., operating frequency) in the range of f1 to f2, where f1 is associated with a minimum frequency less than the first resonant frequency 552 (at which the displacement gain is equal to the natural displacement gain), and f2 is associated with a maximum frequency greater than the second resonant frequency 554 (at which the displacement gain is equal to the natural displacement gain). Therefore, by driving the fiber scanning system with an operating frequency within this range, a displacement gain greater than or equal to the natural displacement gain is achieved. In some embodiments, a particular operating frequency is selected based on the natural frequency of the actuator, while in other embodiments, a particular operating frequency is selected based on the natural frequency of the fiber optical scanning element.

[0059] The operating frequency may be selected such that the operating frequency is within a threshold of the first resonant frequency 552 or within a threshold of the second resonant frequency. The thresholds may be set such that the operating frequency is associated with a displacement gain that is greater than or equal to the inherent displacement gain. Figure 5B As shown, the threshold near the first resonant frequency can extend from frequency f1 to 25 kHz, and the threshold near the second resonant frequency can extend from 25 kHz to frequency f2.

[0060] Similar to the fiber optic diagram 550, the piezoelectric tube diagram 560 may also include two resonant frequencies. In some examples, the two resonant frequencies of the piezoelectric tube diagram 560 may be located at similar frequencies as the two resonant frequencies of the fiber optic diagram 550. However, the displacement gain at the end of the actuator may be reduced to approximately zero. In some examples, the combined kinetic and potential energy of the actuator may be transferred to the fiber optic scanning element at the actuator natural frequency, which may reduce the displacement gain of the actuator to approximately zero.

[0061] The second Bode plot can plot the phase angle of the actuator (e.g., piezoelectric tube plot 520) and the phase angle of the fiber optic scanning element (e.g., fiber plot 510) as a function of the frequency at which the voltage is applied to the piezoelectric tube. In some examples, the second Bode plot can show the phase shift that may occur at each peak (e.g., a 180 degree phase shift).

[0062] Figure 5C An example of a Bode plot for comparing a dynamic absorber design and an alternative design of a fiber optic scanning element (described above) according to an embodiment of the present disclosure is shown. It can be seen that the peaks of the fiber optic scanning element of the dynamic absorber design provide the highest displacement gain. Although the displacement gain of the dynamic absorber design at the point between the peaks is lower than the alternative design, this is not always the case. In addition, even if the dynamic absorber design has a lower displacement gain at that point, the dynamic absorber design may be more stable. The ideal operating point can be determined by experimental investigation.

[0063] Figure 5D An example of a Bode plot for comparing a dynamic absorption design and an alternative design of an actuator (described above) according to an embodiment of the present disclosure is shown. In some examples, the example may show energy absorbed from the actuator by the fiber optic scanning element in the dynamic absorption design. In such an example, the response of the actuator may be lower than the static response of the dynamic absorption design.

[0064] Figure 6 An example of a process 600 for increasing the field of view of a fiber scanning system is shown.

[0065] Process 600 can include providing an actuator characterized by operation at an actuator natural frequency (610). In some examples, a fiber scanning system can include an actuator.

[0066] Process 600 can further include providing a fiber optic scanning element coupled to the actuator (620). In some examples, the fiber optic scanning element can be characterized by a fiber natural frequency that is determined to match the actuator natural frequency. In such examples, the fiber scanning system can further include a fiber optic scanning element.

[0067] Process 600 may further include driving the actuator at an operating frequency (630). In some examples, the displacement gain of the fiber scanning system may be characterized by two separate frequency peaks that define the natural frequency of the actuator. In such examples, the operating frequency may be close to a first peak of the separate frequency peaks (i.e., at a frequency within a threshold of the first peak), where the first frequency peak is less than the natural frequency of the actuator. In other examples, the operating frequency may be close to a second peak (i.e., at a frequency within a threshold of the second peak), where the second frequency peak is greater than the natural frequency of the actuator. In other examples, the operating frequency may be a frequency in a range between the first frequency peak and the second frequency peak, for example, at the natural frequency of the actuator. In some examples, the actuator may be driven by a sinusoidal voltage.

[0068] A number of examples have been described. However, it will be appreciated that various modifications may be made without departing from the scope of the present disclosure.

Claims

1. A fiber scanning system, comprising: an actuator configured to have an actuator natural frequency; as well as a fiber optic scanning element coupled to the actuator, the fiber optic scanning element being configured to have a fiber natural frequency that is within a threshold of the actuator natural frequency such that a displacement gain of the fiber optic scanning element as a function of operating frequency exhibits: a first peak at a first resonant frequency less than a natural frequency of the optical fiber; as well as a second peak located at a second resonant frequency greater than the natural frequency of the optical fiber, The difference between the natural frequency of the optical fiber and the natural frequency of the actuator is less than or equal to 10% or 20% of the natural frequency of the actuator.

2. The fiber scanning system according to claim 1, wherein the first peak value and the second peak value are greater than a displacement gain of the fiber optical scanning element at a natural frequency of the fiber.

3. The fiber scanning system of claim 1, wherein the displacement gain of the actuator is minimized when the actuator is driven at an operating frequency substantially equal to a natural frequency of the actuator.

4. The fiber optic scanning system of claim 3, wherein when the actuator is driven at an operating frequency substantially equal to the natural frequency of the actuator, movement of the actuator is minimized and movement of the fiber optic scanning element is maximized.

5. The fiber scanning system of claim 1, wherein the actuator comprises a piezoelectric tube.

6. The fiber optic scanning system of claim 1, wherein the actuator has a cylindrical geometry having a central axis, and wherein the fiber optic scanning element passes through the actuator along the central axis.

7. The fiber optic scanning system of claim 1, wherein the fiber optic scanning element comprises a multi-core optical fiber.

8. The fiber optic scanning system of claim 1, wherein the fiber optic scanning element is coupled to the actuator at a center location of the actuator.

9. The fiber optic scanning system of claim 8, wherein an outer diameter of the fiber optic scanning element at the center position is smaller than an inner diameter of the actuator.

10. The fiber optic scanning system of claim 9, further comprising a retaining collar surrounding and in contact with the fiber optic scanning element.

11. The fiber optic scanning system of claim 1, further comprising an intermediate element coupling the fiber optic scanning element and the actuator.

12. A method of operating a fiber optic scanning system, the method comprising: The fiber optic scanning system comprising an actuator and a fiber optic scanning element coupled to the actuator is configured by: configuring the actuator so that the actuator has an actuator natural frequency; and configuring the fiber optic scanning element such that the fiber optic scanning element has a fiber natural frequency that is within a threshold of a natural frequency of the actuator; determining an operating frequency range extending from a first frequency to a second frequency, the first frequency being less than a natural frequency of the optical fiber, and the second frequency being greater than the natural frequency of the optical fiber; as well as driving the actuator at an operating frequency within the operating frequency range, The difference between the natural frequency of the optical fiber and the natural frequency of the actuator is less than or equal to 10% or 20% of the natural frequency of the actuator.

13. The method of claim 12, wherein determining the operating frequency range comprises determining the first frequency and the second frequency such that a displacement gain of the fiber optic scanning element is greater than a predetermined value within the operating frequency range.

14. The method of claim 13, wherein the predetermined value is greater than or equal to a displacement gain of the fiber optical scanning element at a natural frequency of the fiber.

15. The method of claim 12, wherein the displacement gain of the fiber optic scanning element as a function of operating frequency exhibits a first peak at a first resonant frequency and a second peak at a second resonant frequency, the first resonant frequency and the second resonant frequency being within the operating frequency range.

16. The method of claim 15, wherein the first peak value and the second peak value are greater than a displacement gain of the fiber optic scanning element at a natural frequency of the fiber.

17. The method of claim 15, wherein the operating frequency is between the first resonant frequency and the second resonant frequency.

18. The method of claim 15, wherein the operating frequency is at the first resonant frequency or the second resonant frequency.

19. The method of claim 15, wherein the operating frequency is located at the fiber's natural frequency.

20. A method for increasing the field of view of a fiber scanning system, the method comprising: configuring the fiber scanning system, the fiber scanning system comprising an actuator and a fiber optical scanning element coupled to the actuator, wherein the fiber optical scanning element is configured to have a fiber natural frequency and the actuator is configured to have an actuator natural frequency, such that the fiber scanning system acts as a tuned dynamic absorber; determining an operating frequency range, wherein the range extends from a first operating frequency less than a natural frequency of the optical fiber to a second operating frequency greater than the natural frequency of the optical fiber; and driving the actuator at an operating frequency within the range, The difference between the natural frequency of the optical fiber and the natural frequency of the actuator is less than or equal to 10% or 20% of the natural frequency of the actuator.

21. The method of claim 20, wherein the fiber natural frequency is substantially matched to the actuator natural frequency.

22. The method of claim 20, wherein a displacement gain of the actuator is minimized when the actuator is driven substantially at the actuator natural frequency.

23. The method of claim 22, wherein when the actuator is driven substantially at the actuator natural frequency, movement of the actuator is minimized and movement of the fiber optic scanning element is maximized.

24. The method of claim 20, wherein a first displacement gain is associated with operating the fiber scanning system at a natural frequency of the fiber.

25. The method of claim 24, wherein determining the operating frequency range comprises determining the first operating frequency and the second operating frequency such that a displacement gain of the fiber optic scanning element is greater than or equal to the first displacement gain.

26. The method of claim 24, wherein: The operating frequency corresponds to a resonant frequency lower than a natural frequency of the optical fiber; and The displacement gain at the operating frequency is greater than the first displacement gain.

27. The method of claim 24, wherein: The operating frequency corresponds to a resonant frequency greater than a natural frequency of the optical fiber; and The displacement gain at the operating frequency is greater than the first displacement gain.

28. The method of claim 20, wherein the fiber optic scanning system is characterized by a displacement gain of the fiber optic scanning element as a function of operating frequency, the displacement gain exhibiting: a first peak at a first resonant frequency less than a natural frequency of the optical fiber; and A second peak is located at a second resonant frequency greater than the natural frequency of the optical fiber.

29. The method of claim 20, wherein a displacement gain of the actuator is reduced to zero when the actuator is driven substantially at the actuator natural frequency.

30. The method of claim 20, wherein the actuator comprises a piezoelectric tube.

31. The method of claim 29, wherein the actuator has a cylindrical geometry having a central axis, and wherein the fiber optic scanning element passes through the actuator along the central axis.

32. The method of claim 29, wherein the fiber optic scanning element comprises a multi-core optical fiber.

33. The method of claim 20, wherein the fiber optic scanning element is coupled to the actuator at a center location of the actuator.

34. The method of claim 33, wherein an outer diameter of the fiber optic scanning element at the central location is smaller than an inner diameter of the actuator.

35. The method of claim 34, wherein the fiber optic scanning system includes a retaining collar surrounding and in contact with the fiber optic scanning element.

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