Feedback cooling and detection for opto-mechanical devices
阅读说明：本技术 用于光机械装置的反馈冷却和检测 (Feedback cooling and detection for opto-mechanical devices ) 是由 约书亚·多尔 查德·费尔蒂希 亚瑟·萨夫琴科 史蒂文·廷 尼尔·克吕格尔 于 2020-02-21 设计创作，主要内容包括：本发明题为“用于光机械装置的反馈冷却和检测”。本发明提供了一种用于调制光信号以降低热噪声并跟踪检测质量块组件的机械共振的光机械装置,该光机械装置包括电路,该电路被配置用于：从发光装置接收光信号,并且调制光信号以移除热噪声并使用冷却反馈信号和机械共振反馈信号将机械响应频率驱动至检测质量块组件的机械共振。电路被进一步配置用于：使用调制光信号生成冷却反馈信号,以对应于总回路增益为零并且相位差为180度的调制光信号的热噪声信号；并且使用调制光信号生成机械共振反馈信号,以将调制光信号的机械响应频率驱动至机械共振。(The invention provides feedback cooling and detection for opto-mechanical devices. The present invention provides an opto-mechanical device for modulating an optical signal to reduce thermal noise and track mechanical resonance of a proof mass assembly, the opto-mechanical device comprising circuitry configured to: the method includes receiving an optical signal from a light emitting device, and modulating the optical signal to remove thermal noise and drive a mechanical response frequency to a mechanical resonance of the proof mass assembly using a cooling feedback signal and a mechanical resonance feedback signal. The circuitry is further configured to: generating a cooling feedback signal using the modulated optical signal to correspond to a thermal noise signal of the modulated optical signal having zero overall loop gain and a phase difference of 180 degrees; and generating a mechanical resonance feedback signal using the modulated optical signal to drive the mechanical response frequency of the modulated optical signal to mechanical resonance.)
1. An opto-mechanical device for modulating an optical signal to reduce thermal noise and track mechanical resonance of a proof mass assembly, the opto-mechanical device comprising circuitry configured for:
receiving the light signal from a light emitting device;
modulating the optical signal to remove thermal noise and driving a mechanical response frequency to the mechanical resonance of the proof mass assembly using a cooling feedback signal and a mechanical resonance feedback signal;
generating the cooling feedback signal using the modulated optical signal to correspond to a thermal noise signal of the modulated optical signal having a total loop gain of zero and a phase difference of 180 degrees; and
generating the mechanical resonance feedback signal using the modulated light signal to drive the mechanical response frequency of the modulated light signal to the mechanical resonance.
2. The opto-mechanical device according to claim 1, wherein the optical signal comprises an optical frequency driven to:
a sum of an optical resonance frequency of the proof mass assembly and a full width at half maximum (FWHM) of the optical resonance; or
The proof mass assembly has a difference between the optical resonance frequency and a quarter FWHM of the optical resonance.
3. The opto-mechanical device according to claim 1, wherein the circuit is configured for: measuring acceleration at the proof mass assembly using the mechanical resonance feedback signal.
4. The opto-mechanical device according to claim 1,
wherein to modulate the optical signal, the circuitry is configured to cancel no more than 20dB of the optical signal using the cooling feedback signal; and is
Wherein to modulate the optical signal, the circuit is configured to generate the modulated optical signal with a drive signal comprising a power of the optical signal greater than 20dB using the mechanical resonance feedback signal.
5. The opto-mechanical device according to any one of claims 1 to 4, wherein the circuitry is configured to output the modulated light signal to the proof mass assembly and receive the modulated light signal reflected from the proof mass assembly,
wherein to generate the cooling feedback signal, the circuitry is configured to generate the cooling feedback signal using the modulated optical signal after reflection from the proof mass assembly, and
wherein to generate the mechanical resonance feedback signal, the circuitry is configured to generate the mechanical resonance feedback signal using the modulated light signal after reflection from the proof mass assembly.
6. The opto-mechanical device according to claim 5,
wherein the circuit is configured to split the modulated light signal into a first portion of the modulated light signal and a second portion of the modulated light signal,
wherein to generate the cooling feedback signal, the circuitry is configured to generate the cooling feedback signal using the first portion of the modulated optical signal, and
wherein to generate the mechanical resonance feedback signal, the circuitry is configured to generate the mechanical resonance feedback signal using the second portion of the modulated light signal.
7. The opto-mechanical device according to claim 6,
wherein the first portion of the modulated optical signal comprises half of the modulated optical signal; and is
Wherein the second portion of the modulated optical signal comprises half of the modulated optical signal.
8. The opto-mechanical device according to claim 6, wherein the circuit is configured for:
converting the first portion of the modulated optical signal to a first electrical signal, wherein to generate the cooling feedback signal, the circuitry is configured to generate the cooling feedback signal using the first electrical signal; and
converting the second portion of the modulated optical signal to a second electrical signal, wherein to generate the mechanical resonance feedback signal, the electrical circuit is configured to generate the mechanical resonance feedback signal using the second electrical signal.
9. The opto-mechanical device according to claim 8, wherein to generate the cooling feedback signal, the circuitry is configured to:
applying the total loop gain of zero to the first electrical signal; and
the phase of the first electrical signal is adjusted by 180 degrees.
10. The opto-mechanical device according to claim 8, wherein to generate the mechanical resonance feedback signal, the circuitry is configured for:
measuring a frequency of the mechanical resonance of the proof mass assembly using the second electrical signal; and
driving a signal generator using the measured frequency of the mechanical resonance.
Technical Field
The present disclosure relates to opto-mechanical devices, such as accelerometers configured to measure acceleration using modulated light signals.
Background
Opto-mechanical devices include devices for detecting acceleration (i.e., accelerometers), velocity, vibration, and other parameters. For example, in an opto-mechanical accelerometer, the resonant frequency of the mechanical structure shifts under acceleration in the opto-mechanical device. The mechanical resonance frequency can be read out with an optical field by applying near-resonance light to the optical resonance of the structure and measuring the transmitted or reflected light.
Disclosure of Invention
In general, the present disclosure relates to devices, systems, and techniques for feedback "cooling" an opto-mechanical device. As used herein, cooling may refer to mitigating the effects of thermal noise on the opto-mechanical resonator. For example, at room temperature, thermal noise may limit performance by causing instability (e.g., random fluctuations) in mechanical frequency. This instability can limit the resulting noise floor and therefore limit the performance of the opto-mechanical device. In particular, the opto-mechanical device may be configured to cool the mechanical temperature using a tuned cooling feedback loop while injecting a large (e.g., gain greater than 20dB), stable mechanical drive signal to drive the opto-mechanical device at a desired mechanical amplitude, which may help mitigate the effects of thermal noise on the opto-mechanical resonator.
In one example, an opto-mechanical device for modulating an optical signal to reduce thermal noise and track mechanical resonance of a proof mass assembly includes a circuit configured to: receiving an optical signal from a light emitting device; modulating the optical signal to remove thermal noise and driving a mechanical response frequency to a mechanical resonance of the proof mass assembly using the cooling feedback signal and the mechanical resonance feedback signal; generating a cooling feedback signal using the modulated optical signal to correspond to a thermal noise signal of the modulated optical signal having zero total loop gain and a phase difference of 180 degrees; and generating a mechanical resonance feedback signal using the modulated optical signal to drive the mechanical response frequency of the modulated optical signal to mechanical resonance.
In another example, a method for modulating an optical signal to reduce thermal noise and track mechanical resonance of a proof mass assembly includes: receiving an optical signal from a light emitting device through a circuit; modulating the optical signal by circuitry to remove thermal noise and using a cooling feedback signal and a mechanical resonance feedback signal to drive a mechanical response frequency to a mechanical resonance of the proof mass assembly; generating, by the circuitry, a cooling feedback signal using the modulated optical signal to correspond to a thermal noise signal of the modulated optical signal having zero total loop gain and a phase difference of 180 degrees; and generating, by the circuit, a mechanical resonance feedback signal using the modulated optical signal to drive the mechanical response frequency of the modulated optical signal to mechanical resonance.
In another example, an opto-mechanical system for modulating an optical signal to reduce thermal noise and track mechanical resonance of a proof mass assembly includes a light emitting device configured to emit an optical signal, a proof mass assembly, and a circuit. The circuit is configured to: receiving an optical signal from a light emitting device; modulating the optical signal to remove thermal noise and driving a mechanical response frequency to a mechanical resonance of the proof mass assembly using the cooling feedback signal and the mechanical resonance feedback signal; generating a cooling feedback signal using the modulated optical signal to correspond to a thermal noise signal of the modulated optical signal having zero total loop gain and a phase difference of 180 degrees; and generating a mechanical resonance feedback signal using the modulated optical signal to drive the mechanical response frequency of the modulated optical signal to mechanical resonance.
This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive description of the systems, apparatuses, and methods described in detail in the following figures and description. Further details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
Drawings
FIG. 1 is a block diagram illustrating an electro-optic-mechanical system according to one or more techniques of the present disclosure.
Fig. 2 is a block diagram illustrating the circuit of fig. 1 in greater detail in accordance with one or more techniques of this disclosure.
Fig. 3 illustrates a conceptual diagram of the proof mass assembly of fig. 1 including a proof mass suspended within a frame by a first double-ended tuning fork (DETF) structure, a second DETF structure, and a set of tethers in accordance with one or more techniques of this disclosure.
Fig. 4 illustrates a conceptual diagram of the accelerometer system of fig. 1 according to one or more techniques of this disclosure.
Figure 5 illustrates additional aspects of the accelerometer system of figure 1 according to one or more techniques of the present disclosure.
FIG. 6 is a conceptual diagram illustrating an example process for cooling the mechanical temperature of a photo-mechanical device according to one or more techniques of this disclosure.
FIG. 7 is a conceptual diagram illustrating exemplary results for cooling a mechanical temperature of a photo-mechanical device according to one or more techniques of the present disclosure.
FIG. 8 is a flow chart illustrating an exemplary process for cooling the mechanical temperature of the opto-mechanical device according to one or more techniques of the present disclosure.
Like reference characters designate like elements throughout the specification and drawings.
Detailed Description
This disclosure describes devices, systems, and techniques for cooling a photo-mechanical device to mitigate the effects of thermal noise. For example, the opto-mechanical device may include an electro-optical-mechanical system configured to accurately measure very high acceleration values (e.g., up to 500,000 meters per second squared (m/s)2)). Electro-optical-mechanical systems may use a combination of electrical, optical, and mechanical signals to determine the acceleration of an object.
The opto-mechanical device may be configured to measure acceleration, velocity, vibration, etc. of the object in real time or near real time, such that the processing circuitry may analyze the acceleration, velocity, vibration, etc. of the object over a period of time to determine the positional displacement of the object during the period of time. For example, the opto-mechanical device may be part of an Inertial Navigation System (INS) for tracking the position of the object based at least in part on the acceleration of the object. Additionally, the opto-mechanical device may be located on or within the object such that the opto-mechanical device accelerates, moves, vibrates, etc. with the object. Thus, when an object accelerates, moves, vibrates, etc., the opto-mechanical device (including the proof mass) accelerates, moves, vibrates, etc. with the object. In some examples, since acceleration over time is a derivative of velocity over time and velocity over time is a derivative of position over time, in some cases, the processing circuitry may be configured to determine the position displacement of the object by performing a double integration of the acceleration of the object over a period of time. Determining the location of an object using an accelerometer system positioned on the object without using a navigation system separate from the object, such as a Global Positioning System (GPS), may be referred to as "dead reckoning.
The opto-mechanical device may be configured to achieve a high level of sensitivity in order to improve the accuracy of acceleration, velocity, vibration, etc. The high sensitivity may enable the opto-mechanical device to detect very small acceleration, velocity, vibration, etc., detect very small changes in acceleration, velocity, vibration, etc., detect a wide range of acceleration, velocity, vibration, etc., or any combination thereof. Additionally, while the object is experiencing high levels of acceleration, velocity, vibration, etc., the opto-mechanical device may be configured to accurately determine the acceleration, velocity, vibration, etc., of the object. As such, the opto-mechanical device may be configured to enable the INS to accurately track the position of the object when the magnitude of the acceleration, velocity, vibration, etc. of the object is very high.
In some examples, the opto-mechanical device may include a micro-electromechanical system (MEMS) accelerometer including a light emitting device, circuitry, and a proof mass assembly including a proof mass suspended within a frame by a Double Ended Tuning Fork (DETF) structure. In some examples, the opto-mechanical device may include a single-ended tuning fork or another structure.
In some examples, the DETF structure can be configured to carry optical signals. In addition, the optical signal can cause mechanical vibrations in the DETF structure. In some cases, acceleration causes displacement of the proof mass relative to the frame, which displacement affects the mechanical vibration frequency (mechanical resonance frequency) corresponding to the DETF structure. In this way, there can be a mathematical relationship between the acceleration and the mechanical vibration frequency of the DETF structure. Thus, the acceleration may be determined using the mathematical relationship. In some examples, the accelerometer device uses a combination of optical and electrical signals to measure the mechanical vibration frequency corresponding to the DETF structure and calculates the acceleration based on the mechanical vibration frequency.
For example, the processing circuit may be configured to modulate the optical signal emitted by the light emitting device using an electro-optical modulator (EOM). The modulated light signal propagates through the DETF structure of the proof mass assembly causing mechanical vibrations in the DETF structure. In addition, the mechanical vibration also modulates the modulated light signal such that the mechanical vibration frequency of the DETF structure is reflected in the modulated light signal after the modulated light signal passes through the DETF structure. The modulated optical signal reaches an optical receiver, which converts the modulated optical signal into an electrical signal. Additionally, the optical receiver can preserve the properties of the modulated optical signal (e.g., maintain the mechanical vibration frequency of the DETF structure) when generating the electrical signal. In this way, the electrical circuit can process the electrical signal and analyze the processed electrical signal to determine the mechanical vibration frequency of the DETF structure. Based on the mechanical vibration frequency, the processing circuitry may determine an acceleration of an object carrying the accelerometer system.
The opto-mechanical device may employ a positive feedback loop to simplify the way in which the acceleration of the object is measured. For example, the electrical circuit may direct the processed electrical signal to an EOM that modulates the optical signal emitted by the light emitting device based on the processed electrical signal. In this way, the optical signal input to the proof mass block assembly is at least partially dependent on the optical signal output from the proof mass block assembly to the circuit. By using a positive feedback loop, the accelerometer system can improve the efficiency of the circuit in calculating acceleration (e.g., reduce the number of steps required to calculate acceleration). For example, to calculate the acceleration value, the processing circuitry may subtract from the mechanical vibration frequency of the DETF structureA baseline frequency value to obtain a frequency difference value. In some cases, the baseline frequency value may represent when the proof mass is not displaced along the proof mass displacement axis (i.e., an acceleration of 0 m/s)2) Mechanical vibration frequency of the DETF structure. In some examples, the frequency difference is correlated to the acceleration such that the processing circuit can use the correlation to determine the acceleration based on the frequency difference. Thus, a positive feedback loop may ensure that a small number of calculation steps are required to determine the acceleration.
However, at room temperature, thermal noise can limit performance by causing instability (e.g., random fluctuations) in the mechanical frequency of the proof mass assembly (e.g., DETF structure). This instability can limit the ultimate noise floor (and hence impact performance) of the accelerometer device. Accordingly, the present disclosure describes a cooling feedback loop that applies cooling feedback 180 degrees out of phase with temperature induced noise fluctuations to mitigate the effects of thermal noise on the proof mass assembly (e.g., DETF structure). Although the foregoing examples are discussed with respect to acceleration, the opto-mechanical device may be configured to determine velocity, vibration, or another parameter.
Although examples of opto-mechanical devices are described with respect to an exemplary accelerometer, the techniques described herein for cooling thermal noise may be applied to opto-mechanical devices configured to measure various parameters including, but not limited to, acceleration, velocity, vibration, and other parameters. Further, although examples of opto-mechanical devices are described with respect to an exemplary proof mass assembly including a DETF structure, other structures may be used, such as, but not limited to, a single-ended tuning fork structure or another structure.
FIG. 1 is a block diagram illustrating an electro-optic mechanical system 10 according to one or more techniques of the present disclosure. Fig. 1 is merely one non-limiting example system architecture in which the techniques of this disclosure may be utilized. As shown in fig. 1, the system 10 includes a light emitting device 12, circuitry 14, a proof mass assembly 16, and a housing 32. Additionally, in the example shown in fig. 1, the circuit 14 includes electro-optic modulators (EOMs) 22A, 22B (collectively "EOMs 22"), optical receivers 24A, 24B (collectively "optical receivers 24"), feedback units 26A, 26B (collectively "feedback units 26"), frequency counters 28A, 28B (collectively "frequency counters 28"), and a processing circuit 30. Although the example of fig. 1 includes two EOMs, two optical receivers, and two frequency counters, in some examples, the electro-opto-mechanical system may include only one EOM, one optical receiver, and one frequency counter or may include more than two EOMs, two optical receivers, and two frequency counters.
In the example of fig. 1, the light emitting device 12, the proof mass assembly 16, the EOM22A, the optical receiver 24A, the feedback unit 26A, and the frequency counter 28A form a first positive feedback loop. Additionally, in the example of fig. 1, the light emitting device 12, the proof mass assembly 16, the EOM22B, the optical receiver 24B, the feedback unit 26B, and the frequency counter 28B form a second positive feedback loop. In some examples, the second positive feedback loop may be omitted.
In some examples, system 10 may be configured to determine an acceleration associated with an object (not shown in fig. 1) based on a measured vibration frequency of the tuning fork structure of the proof mass assembly. For example, the system 10 may be configured to determine an acceleration associated with an object (not shown in fig. 1) based on a measured frequency of vibration of a set of Double Ended Tuning Fork (DETF) structures suspending a proof mass of the proof mass assembly 16, wherein the vibration of the DETF structures is caused by a light signal emitted by the light emitting device 12. In some examples, the first positive feedback loop generates a first frequency value representing a vibration frequency of the first DETF structure, and the second positive feedback loop generates a second frequency value representing a vibration frequency of the second DETF structure. Based on the first and second vibration frequencies, the system 10 may determine first and second acceleration values, respectively. In some examples, system 10 determines the acceleration of the object based on the first acceleration value and the second acceleration value. In some examples, the system 10 determines the acceleration of the object based only on the first acceleration value (e.g., omitting the second positive feedback loop). In some examples, the system 10 determines the acceleration of the object based only on the second acceleration value (e.g., omitting the first positive feedback loop).
In some cases, light-emitting device 12 may include a laser device configured to emit photons. In some examples, light emitting device 12 emits photons with an optical power in a range between 0.1 microwatts (μ W) to 100 μ W. In some examples, the light emitting device 12 is a semiconductor laser including a laser diode.
In some examples, the electrical circuit 14 may include a set of electronic components for processing and analyzing the electrical signals received by the optical receiver 24. The components of circuit 14 are described in further detail below.
The EOM22 may represent an optical device configured to modulate the optical signal emitted by the light emitting device 12 based on the electrical signal generated and processed by the electrical circuit 14. For example, EOM22A may include a set of crystals (e.g., lithium niobate crystals) in which the refractive index of the set of crystals varies with the electric field adjacent to the set of crystals. The refractive index of the crystal may determine the manner in which the EOM22A modulates the optical signal. For example, the crystal of EOM22A may receive an optical signal from light emitting device 12 while EOM22A is also receiving an electrical signal from feedback unit 26A of circuit 14. Thus, the electrical signal may affect the electric field of the crystal adjacent the EOM22A, causing the EOM22A to modulate the optical signal. In some examples, the EOM22A modulates the optical signal by modulating the refractive index of the crystal using an electrical signal. In some cases, the EOM22A may send a modulated light signal to the proof mass block assembly 16. In some examples, EOM22B is substantially similar to EOM22A, with EOM22B being controlled by an electrical signal from feedback unit 26B.
The light receivers 24 may each include one or more transistors configured to absorb photons of the optical signal and output an electrical signal in response to absorbing the photons. As such, the optical receiver 24 may be configured to convert the optical signal to an electrical signal. For example, optical receiver 24A may include a p-n junction that converts photons of an optical signal into an electrical signal, where the electrical signal retains at least some parameters of the optical signal. In response to optical receiver 24A receiving the optical signal, one or more frequency values and intensity values associated with the optical signal may be reflected in the electrical signal generated by optical receiver 24A. For example, in response to receiving a stronger (e.g., greater power) optical signal, optical receiver 24A may generate a stronger electrical signal (e.g., a greater current magnitude). Additionally, in some cases, optical receiver 24A may generate an electrical signal to reflect one or more frequency values corresponding to the received optical signal. In other words, the processing circuitry (e.g., processing circuitry 30) may analyze the electrical signal to determine one or more frequency values corresponding to the optical signal. The optical receiver 24A may include a semiconductor material, such as any combination of indium gallium arsenide, silicon carbide, silicon nitride, gallium nitride, germanium, or lead sulfide. In some examples, optical receiver 24B is substantially similar to optical receiver 24A.
The feedback units 26 may each comprise a set of circuit components for processing the electrical signals. In some examples, the set of circuit components included in feedback unit 26A may include any combination of bandpass filters, phase shifters, electronic amplifiers, and voltage limiters. Such components may process or filter the electrical signal such that certain aspects of the electrical signal (e.g., frequency values or intensity values) may be more effectively measured. In the example of fig. 1, feedback unit 26A may receive electrical signals from optical receiver 24A and output processed electrical signals to EOM22A and frequency counter 28A. In this way, the feedback unit 26A acts as part of a first positive feedback loop by processing an electrical signal that is used by the EOM22A to modulate the optical signal emitted by the light emitting device 12, where the modulated optical signal passes through the proof mass assembly 16 before the return circuit 14 is processed by the feedback unit 26A. Feedback unit 26B may be substantially similar to feedback unit 26A in that feedback unit 26B receives electrical signals from optical receiver 24B and delivers processed electrical signals to frequency counter 28B and EOM 22B. Thus, the feedback unit 26B operates within the second feedback loop in a manner similar to the way the feedback unit 26A operates within the first feedback loop. Also, the feedback unit 26B may be omitted.
The feedback units 26 may each include a cooling feedback loop that applies cooling feedback 180 degrees out of phase with the temperature induced noise fluctuations to mitigate the effects of thermal noise on the proof mass assembly 16. For example, the feedback unit 26A may include cooling feedback 180 degrees out of phase with temperature induced noise fluctuations to mitigate the effects of thermal noise on the proof mass assembly 16. In examples in which feedback unit 26A is included, feedback unit 26B may include cooling feedback 180 degrees out of phase with temperature-induced noise fluctuations to mitigate the effects of thermal noise on proof mass assembly 16.
The frequency counters 28 are circuit components each configured to measure a frequency of the electrical signal. For example, frequency counter 28A may determine one or more frequency values corresponding to the processed electrical signal generated by feedback unit 26A. Frequency counter 28A may measure the frequency value corresponding to the processed electrical signal in real time or near real time such that frequency counter 28A tracks the frequency value over time. Frequency counter 28B may be substantially similar to frequency counter 28A, except that frequency counter 28B receives an electrical signal from feedback unit 26B instead of from feedback unit 26A.
Processing circuitry 30 and circuitry 14 may generally include one or more processors configured to implement functions and/or process instructions for execution within system 10. For example, the processing circuit 30 is capable of processing instructions stored in a memory device (not shown in FIG. 1). The processing circuitry 30 may comprise, for example, a microprocessor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing. Thus, the processing circuit 30 may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, for performing the functions attributed herein to the processing circuit 30. Processing circuitry 30 and circuitry 14 may include analog-only circuitry, digital-only circuitry, or a combination of analog and digital circuitry. The term "processor" or "processing circuitry" may generally refer to any of the foregoing analog circuitry and/or digital circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.
The proof mass assembly 16 can include a proof mass, a frame, a set of tethers, and a set of DETF structures. In some examples, the proof mass is suspended within the frame by the set of tethers and the set of DETF structures. For example, the proof mass assembly 16 can include a set of DETF structures that can suspend the proof mass in a first direction relative to the frame. Additionally, the set of tethers may suspend the proof mass in the second direction and the third direction relative to the frame. The first direction, the second direction, and the third direction may represent three axes (e.g., an x-axis, a y-axis, and a z-axis) of a cartesian space. In some cases, the set of DETF structures enables displacement of the proof mass in a first direction. Additionally, in some cases, the set of tethers prevent displacement of the proof mass in the second direction and the third direction. In this way, the mass assembly 16 may only allow displacement of the proof mass along a single axis (e.g., displacement axis). Since the displacement of the proof mass can determine the acceleration measured by the circuitry 14, the system 10 can be configured to determine the acceleration relative to the displacement axis.
In some examples, a first positive feedback loop (e.g., the device 12, the proof mass assembly 16, the EOM22A, the optical receiver 24A, the feedback unit 26A, and the frequency counter 28A) and a second positive feedback loop (e.g., the light emitting device 12, the proof mass assembly 16, the EOM22B, the optical receiver 24B, the feedback unit 26B, and the frequency counter 28B) are configured to independently determine acceleration values representing acceleration of an object comprising the system 10. For example, the light emitting device 12 may emit a light signal, the EOM22A may modulate the light signal to obtain a first modulated light signal, and the EOM22A may send the first modulated light signal to the proof mass block assembly 16. The optical receiver 24A can receive the first modulated optical signal from the proof mass assembly 16, wherein properties of the first modulated optical signal received by the optical receiver 24A can be affected by mechanical vibrations of the first DETF structure of the proof mass assembly 16. The optical receiver 24A converts the first modulated optical signal into a first electrical signal and sends the first electrical signal to the feedback unit 26A.
In some examples, feedback unit 26A processes the first electrical signal to obtain a first processed electrical signal. For example, feedback unit 26A may process the first electrical signal using any combination of a first band pass filter, a first phase shifter, a first electronic amplifier, and a first voltage limiter. Frequency counter 28A may receive the first processed electrical signal and determine a first frequency value corresponding to the first processed electrical signal. In some cases, the first frequency value represents a mechanical vibration frequency of a first DETF structure of the proof mass assembly 16 that carries the first modulated optical signal that is ultimately received by the optical receiver 24A.
In addition to sending the first processed electrical signal to frequency counter 28A, feedback unit 26A may also send the first processed electrical signal to EOM 22A. In turn, the EOM22A may modulate the optical signal emitted by the light emitting device 12 based on the first processed electrical signal, wherein the first modulated optical signal is sent to the optical receiver 24A via the first DETF structure of the detection mass block assembly 16, thereby completing a first positive feedback loop. Thus, the future mechanical vibration frequency of the first DETF structure depends at least in part on the current mechanical vibration frequency of the first DETF structure.
Additionally, in some examples, a second positive feedback loop may determine a second frequency value. For example, the light emitting device 12 may emit a light signal, the EOM22B may modulate the light signal to obtain a second modulated light signal, and the EOM22B may send the second modulated light signal to the proof mass block assembly 16. The optical receiver 24B can receive the second modulated optical signal from the proof mass assembly 16, wherein properties of the second modulated optical signal received by the optical receiver 24B can be affected by mechanical vibrations of the second DETF structure of the proof mass assembly 16. The optical receiver 24B converts the second modulated optical signal into a second electrical signal and sends the second electrical signal to the feedback unit 26B.
In some examples, feedback unit 26B processes the second electrical signal to obtain a second processed electrical signal. For example, feedback unit 26B may process the second electrical signal using any combination of a second bandpass filter, a second phase shifter, a second electronic amplifier, and a second voltage limiter. Frequency counter 28B may receive the second processed electrical signal and determine a second frequency value corresponding to the second processed electrical signal. In some cases, the second frequency value represents the mechanical vibration frequency of a second DETF structure of the proof mass assembly 16 that carries the second modulated optical signal that is ultimately received by the optical receiver 24B.
In addition to sending the second processed electrical signal to frequency counter 28B, feedback unit 26B may also send the second processed electrical signal to EOM 22B. The EOM22B may then modulate the light signal emitted by the light emitting device 12 based on the second processed electrical signal, wherein the second modulated light signal is sent to the light receiver 24B via the second DETF structure of the detection mass block assembly 16, thereby completing a second positive feedback loop. Thus, the future mechanical vibration frequency of the second DETF structure depends at least in part on the current mechanical vibration frequency of the second DETF structure.
The processing circuit 30 may be configured to calculate a first acceleration value based on the first frequency value. In some examples, to calculate the first acceleration value, processing circuitry 30 may subtract the baseline frequency value from the first frequency value to obtain a first frequency difference value. The baseline frequency value can represent the resonant mechanical frequency of the first DETF structure of the proof mass assembly 16 when the proof mass is not displaced from the rest point along the proof mass displacement axis. In other words, the modulated light signal emitted by the EOM22A can cause the first DETF structure to vibrate at this baseline frequency value when the proof mass is not displaced from the rest point along the proof mass displacement axis. Thus, when the object is not accelerating, the first frequency difference may be equal to zero because the first acceleration value representing the mechanical frequency of the first DETF structure is equal to the baseline frequency value when the proof mass is not displaced (e.g., the object carrying system 10 is not accelerating). In some examples, the first frequency difference may be related to an acceleration of the object. In other words, an increase in the magnitude of the first frequency difference may indicate an increase in acceleration of the object, and a decrease in the magnitude of the first frequency difference may indicate a decrease in acceleration of the object.
Additionally, the processing circuit 30 may be configured to calculate a second acceleration value based on the second acceleration value. In some examples, to calculate the second acceleration value, processing circuitry 30 may subtract the baseline frequency value from the second frequency value to obtain a second frequency difference value. In some examples, the second frequency difference may be related to an acceleration of the object. In other words, an increase in the magnitude of the second frequency difference may indicate an increase in acceleration of the object, and a decrease in the magnitude of the second frequency difference may indicate a decrease in acceleration of the object. In some cases, the first acceleration value and the second acceleration value calculated by the processing circuit 30 may be approximately equal.
In some examples, system 10 includes an optomechanical vibrating beam accelerometer as a self-oscillating optomechanical oscillator. Two pairs of nanoscale dielectric beams can form a pair of DETF structures that rigidly anchor the thin-film proof mass to the frame. Each DETF structure of the pair of DETF structures can have an optical resonance having a spectral width in a range defined by including 0.05 nanometers (nm) and 1nm (e.g., 0.1 nm). In some examples, the DETF structure can be excited and driven by an optical signal emitted by the light emitting device 12, wherein the optical signal is coupled to the optically active portion of the DETF structure via a waveguide. Mechanical motion of the DETF structure driven by the amplitude modulated optical signal can have an interactive effect on the optical signal, since the mechanical motion modulates the optical signal. In other words, the optical signal can both induce mechanical vibrations in the DETF structure and measure the mechanical vibration frequency of the DETF structure corresponding to the vibrations induced by the optical signal.
The optical signal can be outcoupled from the DETF structure. In some examples, the DETF structure is disengaged to reflect the laser field. In some examples, the optical signal passes through the DETF structure in transmission and the optical signal is incident on the optical receiver 24 with a suitable bandwidth to detect an Alternating Current (AC) photocurrent at the modulation frequency of the optical signal. The electrical signal generated by the optical receiver 24 may be conditioned (e.g., filtered, amplified, phase shifted, and voltage limited) by the feedback electronics, and output to a corresponding drive port of the EOM22 to modulate the optical signal. In this way, the system 10 can achieve closed loop electro-optical-mechanical self-oscillation at a mechanical resonance frequency (e.g., 1.33 megahertz (MHz)) under positive feedback standard conditions with 0 degree phase offset and 0dB round-trip signal gain. The acceleration experienced by the system 10 can cause a slight displacement of the proof mass assembly 16, thereby generating stresses in the DETF structure that shift the mechanical resonant frequency of the DETF structure, which are high relative to tensile stresses and low relative to compressive stresses. Thus, the instantaneous frequency of each DETF structure can be monitored by counting the frequency of the corresponding electrical signal using the frequency counter 28. To generate the acceleration values, in some examples, the processing circuitry 30 may apply a scaling factor to the measured frequency offset of the mechanical vibration frequency of the DETF structure.
Fig. 2 is a block diagram illustrating circuitry 14 of fig. 1 in greater detail in accordance with one or more techniques of the present disclosure. As shown in fig. 1, circuit 14 includes an EOM22, an optical receiver 24, a feedback unit 26, a frequency counter 28, and a processing circuit 30. Feedback units 26 may each include a bandpass filter 40A, 40B (collectively "bandpass filter 40"), a phase shifter 42A, 42B (collectively "phase shifter 42"), an electronic amplifier 44A, 44B (collectively "electronic amplifier 44"), a chiller 45A, 45B (collectively "chiller 45"), and a driver 47A, 47B (collectively "driver 47"). The first feedback loop includes bandpass filter 40A, phase shifter 42A, electronic amplifier 44A, cooler 45A, and driver 47A. The second feedback loop includes bandpass filter 40B, phase shifter 42B, electronic amplifier 44B, cooler 45B, and driver 47B.
The circuit 14 may be configured to: receive the modulated optical signal from the proof mass assembly 16; converting the optical signal into an electrical signal; processing the electrical signal; analyzing the processed electrical signal to determine an acceleration value; and modulating the optical signal using the processed electrical signal to complete the first feedback loop and the second feedback loop. For example, the optical receiver 24A can receive a first modulated optical signal from the first DETF structure of the proof mass assembly 16. The first modulated light signal can include frequency components associated with the first DETF structure itself, such as the frequency of vibration of the first DETF structure. The optical receiver 24A can convert the first modulated optical signal to a first electrical signal, thereby preserving frequency components indicative of the vibration frequency of the first DETF structure for the cooler 45A and the second electrical signal for the driver 47A. Optical receiver 24A may send the first and second electrical signals to feedback unit 26A, which includes bandpass filter 40A, phase shifter 42A, electronic amplifier 44A, cooler 45A, and driver 47A.
The band pass filter 40A may be an electronic filter that attenuates frequencies outside of the frequency range and "passes" frequencies within the frequency range. In some examples, band pass filter 40A includes a passive filter, an active filter, an Infinite Impulse Response (IIR) filter, a Finite Impulse Response (FIR) filter, a butterworth filter, a chebyshev filter, an elliptic filter, a bezier filter, a gaussian filter, a legendre filter, or any combination of linkwey-rayleigh filters. In some examples, band pass filter 40A includes a combination of a high pass filter that passes frequencies above a high pass cut-off point and a low pass filter that passes frequencies below a low pass cut-off point. In some cases, band pass filter 40A passes frequencies in a range between 100 kilohertz (kHz) and 10,000 kHz.
Phase shifter 42A may be configured to shift the phase of the first electrical signal and the second electrical signal. The phase may be characterized as the instantaneous position on a waveform cycle of a periodic waveform. For example, the first electrical signal may include a periodic waveform representing a frequency component of the first electrical signal. The maximum peak of the sine wave may be at a different phase than the minimum peak or zero crossing of the sine wave, for example. In some examples, phase shifter 42A may "delay" the first electrical signal by a time value so as to shift the time axis in which the frequency component of the first electrical signal oscillates, and delay the second electrical signal by a time value so as to shift the time axis in which the frequency component of the second electrical signal oscillates.
Electronic amplifier 44A may amplify the first electrical signal and/or the second electrical signal such that the amplitude of the first electrical signal is increased by a gain factor. In other words, electronic amplifier 44A may increase the power of the first and second electrical signals. By amplifying the first and second electrical signals using electronic amplifier 44A, circuitry 14 may improve the ability of processing circuitry 30 to analyze the first and second electrical signals and use EOM22A to modulate the optical signal emitted by light emitting device 12.
In some cases, electronic amplifier 44A may include a power amplifier, an operational amplifier, or a transistor amplifier, or any combination thereof. Additionally, in some examples, the electronic amplifier 44A is configured to limit the voltage of the first and second electrical signals to a maximum voltage value. In other words, electronic amplifier 44A may prevent the first and second electrical signals from exceeding a maximum voltage value, which means that the first and second processed electrical signals generated by feedback unit 26A may not exceed the maximum voltage value.
In some examples, the first and second electrical signals can pass through the feedback unit 26A in order from the band pass filter 40A, to the phase shifter 42A, to the electronic amplifier 44A, and then to the cooler 45A and the driver 47A, as shown in fig. 1. However, the order shown in FIG. 1 is not limiting. The band-pass filter 40A, the phase shifter 42A and the electronic amplifier 44A may be arranged to process the first electrical signal and the second electrical signal in any order.
The cooler 45A may be configured to cause the EOM22A to apply cooling feedback 180 degrees out of phase with the temperature-induced noise fluctuations to mitigate the effects of thermal noise on the proof mass block assembly 16. For example, the cooler 45A may be configured to generate a cooling feedback signal that causes the EOM22A to cancel the 20dB optical signal. For example, the cooler 45A may generate a cooling feedback signal to apply a 0dB gain 180 degrees out of phase with the noise fluctuations.
The driver 47A may be configured to cause the EOM22A to drive the optical signal to the mechanical resonance of the proof mass assembly 16. For example, driver 47A may be configured to generate a mechanical resonance feedback signal that causes EOM22A to operate near or at a mechanical resonance of proof mass assembly 16. For example, the driver 47A may generate a mechanical resonance feedback signal using a signal generator configured to detect mechanical resonance of the mass assembly 16.
Feedback unit 26A may send the first processed electrical signal to frequency counter 28A. Frequency counter 28A may determine a first frequency value, and processing circuitry 30 may determine a first acceleration value based on the first frequency value. In addition, the feedback unit 26A may combine and send the first processed electrical signal and the second processed electrical signal to the EOM22A, and the EOM22A may modulate the light signal emitted by the light emitting device 12 based on the first processed electrical signal and the second processed electrical signal. Thus, proof mass assembly 16, optical receiver 24A, band pass filter 40A, phase shifter 42A, electronic amplifier 44A, cooler 45A, driver 47A, EOM22A, and frequency counter 28A are the portions of the first positive feedback loop that produce the first acceleration value associated with the object that includes system 10.
The components of feedback unit 26B (e.g., bandpass filter 40B, phase shifter 42BN, electronic amplifier 44B, cooler 45B, and driver 47B) may be substantially similar to the corresponding components of feedback unit 26A. Thus, the second positive feedback loop may be substantially similar to the first positive feedback loop.
Fig. 3 illustrates a conceptual diagram of a proof mass assembly 16 including a
Proof mass assembly 16 is a mechanical component of electro-optic mechanical system 10. Since the system 10 measures acceleration, which is the rate at which the velocity of an object changes over time, it may be beneficial to include the proof mass assembly 16 so that acceleration can be measured based on a physical object, such as the
In some examples, the
To generate acceleration values indicative of the acceleration of the object to which the system 10 is secured, the system 10 may use the light signals to quantify the displacement of the
The
Additionally, the
The
The
The
Fig. 4 illustrates a conceptual diagram of the system 10 according to one or more techniques of this disclosure. The conceptual diagram of fig. 4 includes the light emitting device 12, components of the circuit 14, and the proof mass assembly 16.
In some examples, the object may be secured to the system 10. In some cases, the object may accelerate. The system 10 including the proof mass assembly 16 may be accelerated with the object. The
The light emitting device 12 may emit a light signal to the EOM 22. In turn, EOMs 22A and 22B may modulate the optical signal according to the first processed electrical signal generated by feedback unit 26A and the second processed electrical signal generated by feedback unit 26B, respectively. Thus, EOM22A may generate a first modulated light signal and EOM22B may generate a second modulated light signal. For example, the EOM22A may send a first modulated light signal to the proof mass block assembly 16. The first modulated optical signal may cross the
After exiting the proof mass assembly 16, the first modulated optical signal, which may include thermal noise, may reach the optical receiver 24A. Optical receiver 24A converts the first modulated optical signal into a first electrical signal for cooling thermal noise and a second electrical signal for driving EOM22A to mechanical resonance of proof mass assembly 16. The frequency counter 28A can determine a first frequency value corresponding to the first processed electrical signal, wherein the first frequency value is indicative of the mechanical vibration frequency of the
For example, the EOM22B may send a second modulated light signal to the proof mass block assembly 16. The second modulated optical signal may cross the
After exiting the proof-mass assembly 16, the second modulated optical signal (which may include thermal noise) may reach the optical receiver 24B. Optical receiver 24B converts the second modulated optical signal into a first electrical signal for cooling thermal noise and a second electrical signal for driving EOM22B to mechanical resonance of proof mass assembly 16. The frequency counter 28B can determine a second frequency value corresponding to the second processed electrical signal, wherein the second frequency value is indicative of the mechanical vibration frequency of the
Fig. 5 illustrates additional aspects of system 10 according to one or more techniques of this disclosure. For example, fig. 5 shows a
FIG. 6 is a conceptual diagram illustrating an example process for cooling the mechanical temperature of a photo-mechanical device according to one or more techniques of this disclosure. As shown, the electro-optic-
The
The
Light enters into EOM622, which may be an example of EOM 22A. The EOM622 modulates the optical signal to mechanical resonance while removing thermal noise using the cooling feedback signal and the mechanical resonance feedback signal output by the
The
The
In the cooling
While the cooling
Frequency servo and
As shown, the frequency servo and
The
Although the example of fig. 6 depicts a single feedback loop for the proof mass assembly, in some examples, the system of fig. 6 may be configured to utilize more than one feedback loop to measure, for example and without limitation, vibration at a proof mass assembly having a DETF structure. Although fig. 6 is described with respect to determining acceleration values, in some examples, the cooling described in fig. 6 may be applied to a system configured to measure velocity, vibration, and other parameters.
FIG. 7 is a conceptual diagram illustrating exemplary results for cooling a mechanical temperature of a photo-mechanical device according to one or more techniques of the present disclosure. In the example of fig. 7, the
FIG. 8 is a flow chart illustrating an exemplary method for cooling a mechanical temperature of a photo-mechanical device according to one or more techniques of the present disclosure. For convenience, fig. 8 is described with respect to fig. 1-7. However, the technique of fig. 8 may be performed by different components, such as the light emitting device 12, the circuitry 14, and the proof mass block assembly (e.g., single-ended tuning fork configuration, DETF configuration, etc.), or by additional or alternative means.
The
The EOM622 modulates the optical signal to remove thermal noise and drives the mechanical response frequency to mechanical resonance using the cooling feedback signal and the mechanical resonance feedback signal (808). The
The opto-mechanical devices described herein may include analog only circuits, digital only circuits, or a combination of analog and digital circuits. The digital circuitry may comprise, for example, a microcontroller on a single integrated circuit that includes a processor core, memory, inputs, and outputs. For example, the digital circuitry of the opto-mechanical device described herein may include one or more processors, including one or more microprocessors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term "processor" or "processing circuitry" may generally refer to any of the foregoing analog circuitry and/or digital circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.
The digital circuitry may utilize hardware, software, firmware, or any combination thereof to implement the described functionality. Those functions implemented in software may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media, such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, for example, according to a communication protocol. As such, the computer-readable medium may generally correspond to: (1) a non-transitory, tangible computer-readable storage medium, or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the techniques described in this disclosure.
The techniques of this disclosure may be implemented in various apparatuses or devices including an Integrated Circuit (IC) or a group of ICs (e.g., a chipset). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but the various components, modules, or units do not necessarily need to be implemented by different hardware units. Rather, the various units may be combined with or provided by a collection of interoperative hardware units (including one or more processors as described above) in combination with suitable software and/or firmware.
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