Resonant opto-mechanical accelerometer for use in navigation grade environments

An accelerometer includes a controller, a light source operatively coupled to the controller, and a bifurcated waveguide coupled to the light source and configured to receive light output by the light source. The bifurcated waveguide includes a first waveguide portion and a second waveguide portion. The accelerometer also includes a first resonator operatively coupled to the controller and configured to receive light from the first waveguide portion, and a second resonator operatively coupled to the controller and configured to receive light from the second waveguide portion. The first resonator includes a first proof mass, and the second resonator includes a second proof mass.

BACKGROUND

The subject matter disclosed herein relates to a resonant opto-mechanical accelerometer and, more particularly, to a resonant opto-mechanical accelerometer for use in navigation grade environments.

At least some known accelerometers have been developed on micro-electro-mechanical systems (“MEMS”) architectures. Some of these accelerometers may include a proof mass mounted on a piezoelectric substrate. As the proof mass experiences a change in acceleration, the proof mass compresses the piezoelectric substrate to generate an output current proportional to the acceleration of the proof mass. Other known accelerometers may include a deformable optical resonator that is compressed, like a piezoelectric substrate, when a proof mass coupled to the optical resonator experiences a change in acceleration.

Many such accelerometers have demonstrated high performance for targeting and inertial applications through the use of temperature postcompensation at accelerations of approximately one μg, where one “g” corresponds to the acceleration due to gravity at the Earth's surface and is approximately equal to 9.806 m/s2. However, such accelerometers may not be well suited to service under certain environmental conditions and may not exhibit a dynamic range of operation suitable for use with some inertial navigation systems.

BRIEF DESCRIPTION

In one aspect, an accelerometer is provided. The accelerometer includes a controller, a light source operatively coupled to the controller, and a bifurcated waveguide coupled to the light source and configured to receive light output by the light source. The bifurcated waveguide includes a first waveguide portion and a second waveguide portion. The accelerometer also includes a first resonator operatively coupled to the controller and configured to receive light from the first waveguide portion, and a second resonator operatively coupled to the controller and configured to receive light from the second waveguide portion. The first resonator includes a first proof mass, and the second resonator includes a second proof mass.

In another aspect, a resonator for use in an accelerometer is provided. The resonator includes a substrate, a transparent cover, and a proof mass mounted between the substrate and the transparent cover. The proof mass includes a central portion, a first spring, a first portion coupled to the central portion by the first spring, a second spring, and a second portion coupled to the central portion by the second spring.

In yet another aspect, an accelerometer is provided. The accelerometer includes a light source, a waveguide coupled to the light source configured to receive light output by the light source, and a resonator, which includes a proof mass, and which is configured to receive light from the waveguide.

DETAILED DESCRIPTION

As used herein, the terms “processor” and “computer” and related terms, e.g., “processing device,” “computing device”, and “controller” are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. In the embodiments described herein, memory includes, but is not limited to, a computer-readable medium, such as a random access memory (RAM), and a computer-readable non-volatile medium, such as flash memory. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with a user interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, a user interface monitor.

Further, as used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by personal computers, workstations, clients and servers.

As used herein, “g-force” acceleration is a measurement of acceleration caused by a mechanical force exerted on a body, such as an accelerometer, in a direction by a surface supporting the object and preventing the object from free fall. Similarly, as used herein, a unit of measurement of acceleration may be expressed as a “g,” which in the international system of units, corresponds to m/s2. One g is thus the acceleration due to gravity at the Earth's surface and is approximately equal to 9.806 m/s2.

Embodiments of the present disclosure relate to a resonant opto-mechanical accelerometer and, more particularly, to a resonant opto-mechanical accelerometer for use in navigation grade environments. As described herein, navigation grade environments include environments associated with and/or onboard various navigational systems, such as, for example, aircraft systems, marine systems, terrestrial systems, and/or munitions systems, such as missile and other ballistic systems. As such, navigation grade environments may expose the resonant opto-mechanical accelerometer to rapidly fluctuating g-forces as well as to extreme environmental conditions.

In addition, as described below, the resonant opto-mechanical accelerometer may be a single axis accelerometer (e.g., a z-axis accelerometer) configured to measure acceleration perpendicular to a resonator plane. However, the resonant opto-mechanical accelerometer may also measure accelerations about other axes (e.g., depending upon the orientation of the accelerometer) and may, in addition, measure accelerations about a plurality of axes (e.g., where a plurality of resonator and/or resonator pairs are utilized).

The resonant opto-mechanical accelerometer includes a light source, such as a laser, a first resonator, and a second resonator. A resonance frequency of each resonator is responsive to an acceleration, and the light source shines a light beam on each resonator. The resonators modulate the light to a frequency that corresponds to the resonance frequency, and the modulated light is sensed at each resonator by a corresponding photodetector. The photodetectors generate first and second electrical output signals in response, and these electrical output signals are used to generate a temperature independent acceleration measurement. More particularly, the first and second resonator are operated as a pair, each having and opposite scale factor, to provide robustness against common mode errors, such as temperature drift. Moreover, a plurality of electrodes are disposed in relation to each resonator, such that one or more proof masses associated with each resonator may be dynamically balanced and/or a scale factor associated with the modulated light increased or decreased as a function of acceleration.

FIG. 1is a perspective view of an exemplary resonant opto-mechanical accelerometer (“ROMA”)102. ROMA102includes a printed circuit board (“PCB”)104. A controller108is mounted on PCB104. As described elsewhere herein, controller108coordinates the operation of ROMA102. In the exemplary embodiment, controller108includes one or more processors communicatively coupled to one or more tangible, non-transitory, computer-readable memories.

A light source110is also mounted on PCB104. Light source110is any light source capable of generating a beam of monochromatic light and/or any other beam of radiation. In the exemplary embodiment, light source110is a laser, such as a continuous-wave laser and/or a pulsed operation laser. Light source110may, in addition, be a low power laser, such as, in some embodiments, a laser having an output power ranging from ten milliwatts to fifty milliwatts. Further, in various embodiments, more than one light source may be implemented with ROMA102. Light source110may be operatively coupled to controller108, such that controller108provides one or more control instructions or control signals to light source110for the operation of light source110.

An optical waveguide112is coupled to light source110, such that optical waveguide112is capable of receiving and guiding a light beam generated by light source110. In the exemplary embodiment, optical waveguide112is bifurcated and branches into a first branch or first portion114and a second branch or second portion116. Optical waveguide112includes any waveguide suitable for the transmission of light, such as any light guide, any fiber optic waveguide structure, any integrated waveguide structure patterned on a cover of ROMA102(as described below), and the like.

A first photodetector122is disposed at a first output coupler or first end118of first portion114. Similarly, a second photodetector124is disposed at a second output coupler or second end120of second portion116. First end118may include a mirror, prism reflector, or grating coupler (not shown) configured to redirect a beam of light traveling within first portion114of optical waveguide112towards a first resonator126. Likewise, second end120may include a mirror, prism reflector, or grating coupler (not shown) configured to redirect a beam of light traveling within second portion116of optical waveguide112towards a second resonator128.

In the exemplary embodiment, first resonator126and second resonator128are mounted on PCB104and form a resonator package or resonator pair. In other embodiments, first resonator126and/or second resonator128are not mounted on PCB104, and may be located or mounted apart from PCB104, controller108, and/or other control electronics.

First resonator126and/or second resonator128are operatively coupled to controller108, such that controller108provides one or more control instructions or control signals to first resonator126and/or second resonator128for the operation of first resonator126and/or second resonator128. For example, in some embodiments, controller108provides one or more control signals to first resonator126and/or second resonator128to control the voltages generated by one or more electrodes coupled to each resonator126and/or128(as described below). Similarly, in various embodiments, controller108provides one or more control signals to first resonator126and/or second resonator128to control the output power of light source110.

ROMA102may, in addition, be enclosed within a housing106, which may serve as an environmental enclosure suitable to shelter ROMA102from air and moisture. In some embodiments, housing106is also heat resistant and functions as a heat shield suitable to shelter ROMA102from heat generated by a navigation or propulsion system to which ROMA102is mounted or coupled.

FIG. 2is an exploded view of first resonator126and second resonator128. As shown, first resonator126and second resonator128are substantially identical. In addition, first resonator126and second resonator128are mounted between a substrate202and a cover204. Substrate202and cover204are manufactured as micro-electro-mechanical systems (“MEMS”) wafers, such as silicon-on-insulator (“SOI”) wafers. For example, substrate202and cover204may be manufactured as SOI wafers and/or as floated borosilicate glass (e.g., PYREX) wafers. In the exemplary embodiment, substrate202is manufactured as an SOI wafer, and cover204is manufactured as a PYREX wafer.

However, in various embodiments, cover204is manufactured as an SOI wafer and is not substantially absorptive to light, such as light having a wavelength of approximately 1300 nanometers. As a result, cover204transmits and reflects light, such that one or more excitation signals, such as, for example, a first light beam206and a second light beam208, are able to pass through cover204. For example, light at a wavelength of 1300 nanometers may be 20% reflected by cover204and 80% transmitted. Thus, cover204may absorb some light, but in some embodiments, the absorption should be minimal. For example, in some embodiments, the absorption is less than 10%. If it is desired to make cover204from a transparent material, such as glass, such that cover204does not reflect a substantial amount of light, a separate thin film layer (not shown) may be deposited on cover204to obtain the desired reflectance. For example, a layer of Ta2O5having a thickness between 100 and 250 nanometers can be deposited onto a glass cover204to obtain a reflectance of approximately 20% to 25%. Accordingly, as used here, “transparent” means that light is able to be transmitted, at least partially, and with or without some attenuation through cover204.

Excitation by light source110may result in amplitude self-stabilized oscillation frequencies and may improve frequency stability. In addition, optical interactions may serve to decouple conventional quality factor and gain detection trade-offs and may simplify device fabrication by facilitating uniform, large-gap, layouts as opposed to micron-sized electrode spacing within high aspect ratio etching steps. Further, the optical drive and readout features described herein may reduce or eliminate traditional error sources, such as errors introduced as a result of AC and/or DC drive signals applied to conventional electrostatic MEMS devices.

First resonator126includes a first proof mass210. First proof mass210includes a first mounting perimeter214, a central portion216, a first leaf or a first portion218, a first spring220, a second leaf or a second portion222, and a second spring224. First portion218is coupled to central portion216by first spring220, and second portion222is coupled to central portion216by second spring224. Thus, first resonator126may be referred to as a “tuning fork” or “butterfly pattern” resonator. In some embodiments, first resonator126may also be a multiple beam opto-mechanical resonator that uses an out-of-plane linear vibrational oscillation. More generally, first resonator126may include any suitable resonator geometry or form factor. Central portion216may include a first reflective and absorptive surface or coating225, which may be deposited on the surface of first resonator126that is closest to cover204. If first resonator126is non-absorbing, first reflective coating225may also be deposited the surface of first resonator126that is furthest from the cover204. However, in various embodiments, first reflective coating225cannot be a perfect reflector, and must permit some portion of first light beam206shining upon its surface to pass into central portion216for absorption.

Likewise, second resonator128includes a second proof mass212. Second proof mass212includes a first mounting perimeter226, a central portion228, a first leaf or a first portion230, a first spring232, a second leaf or a second portion234, and a second spring236. First portion230is coupled to central portion228by first spring232, and second portion234is coupled to central portion228by second spring236. Thus, second resonator128may be referred to as a “tuning fork” or “butterfly pattern” resonator. Central portion228may include a second reflective surface or coating237, which may be deposited on the surface of second resonator128that is closest to cover204. If second resonator128is non-absorbing, second reflective coating237may also be deposited on the surface of second resonator128that is furthest from cover204. However, in some embodiments, second reflective coating237cannot be a perfect reflector, and must permit some portion of second light beam208shining upon its surface to pass into central portion228for absorption.

During manufacturing, first proof mass210and second proof mass212are bonded or mounted between substrate202and cover204. Specifically, first mounting perimeter214of first proof mass210is bonded or mounted between a substrate mounting surface238of substrate202and a cover mounting surface240of cover204, such that first proof mass210is suspended between substrate202and cover204within a first cavity242defined between substrate202and cover204. Similarly, first mounting perimeter226of second proof mass212is bonded or mounted between substrate mounting surface238of substrate202and cover mounting surface240of cover204, such that second proof mass212is suspended between substrate202and cover204within a second cavity244defined between substrate202and cover204. First cavity242and second cavity244may be sealed and filled with a gas or a mixture of gases, sealed under vacuum, and/or manufactured to include an aperture or opening (not shown) through which a gas or mixture of gases may be introduced into or evacuated from the device.

In addition, in the exemplary embodiment, a first electrode246and a second electrode248are bonded or mounted on an internal surface250of substrate202, such that first electrode246is disposed substantially in proximity to, or under, first portion218of first proof mass210, and second electrode248is disposed substantially in proximity to, or under, second portion222of first proof mass210. In addition, a third electrode252and a fourth electrode254are bonded or mounted on an internal surface257of cover204, such that third electrode252is disposed substantially in proximity to, or over, first portion230of second proof mass212, and fourth electrode254is disposed substantially in proximity to, or over, second portion234of second proof mass212.

In operation, and as described in greater detail below, first light beam206is directed by optical waveguide112through cover204onto central portion216of first proof mass210, and second light beam208is directed by optical waveguide112through cover204onto central portion228of second proof mass212. Each proof mass210and212oscillates or vibrates at a particular resonance frequency (as described in greater detail below) under the influence of an applied acceleration (or g force).

As first light beam206makes contact with central portion216of first proof mass210, a reflected portion256of first light beam206is reflected by first reflective coating225, and an absorbed portion of first light beam206is absorbed, as heat energy, by central portion216. Reflected portion256is modulated to the resonance frequency of first proof mass210as it reflects from central portion216of first proof mass210.

This modulation may be variously accomplished. For example, with respect to first resonator126, the surfaces of cover204reflect some light, as does first resonator126, such as, for example, central portion216of first proof mass210. These surfaces form an optical cavity310having a length, L, and the reflected light from these surfaces interferes when it recombines at first photodetector122to cause the total reflected light intensity on first photodetector122to vary with the length, L, of optical cavity310between cover204and central portion216. The variation is periodic with distance and the period is equal to half of the wavelength of light within optical cavity310. Therefore, as resonator126vibrates, thereby changing the length, L, of optical cavity310, the light intensity on photodetector122may also vary synchronously with the vibration of resonator126. Other techniques may also be used to generate an oscillating light intensity on photodetector122, such as depositing a reflective mirror (not shown) on a portion of resonator126that moves in and out of first light beam206as first resonator126vibrates, and/or fabricating a structure within ROMA102that partially shadows or prevents first light beam206from striking first resonator126, where the amount of shadowing may vary as resonator126vibrates. These modulation techniques may be applied, in similar fashion, to second resonator128.

Likewise, as second light beam208makes contact with central portion228of second proof mass212, a reflected portion258of second light beam208is reflected by second reflective coating237, and an absorbed portion of second light beam208is absorbed, as heat energy, by central portion228. Reflected portion258is modulated to the resonance frequency of second proof mass212as it reflects from central portion228of second proof mass212.

Thus, the frequencies associated with reflected portions256and258correspond to the resonance frequencies of first proof mass210and second proof mass212, respectively, which depend upon the acceleration on ROMA102as well as the electromechanical stiffnesses of each proof mass210and212.

As reflected portion256is reflected back through cover204, reflected portion256is received by first photodetector122. Similarly, as reflected portion258is reflected back through cover204, reflected portion258is received by second photodetector124. In response, first photodetector122generates a first electrical output signal260proportional to the frequency of received reflected portion256, and second photodetector124generates a second electrical output signal262proportional to the frequency of received reflected portion258.

First electrical output signal260and second electrical output signal262are transmitted (e.g., over one or more electrical wires) to an electrical circuit264, such as a frequency counter or phase-locked-loop (“PLL”), that is configured to analyze first electrical output signal260and second electrical output signal262, and, based upon the analysis, to output either digital or analog signals that are related to the oscillation frequency of resonators126and128and, in some embodiments, to other parameters such as the temperature of resonators126and128. The digital signals from resonators126and128may in turn be subtracted from each other with either analog or digital electronics to provide an acceleration signal266that is representative of the acceleration measured by ROMA102. Specifically, in the exemplary embodiment, electrical circuit264is configured to subtract one of first electrical output signal260and second electrical output signal262from the other. The difference between the two signals260and262corresponds to the acceleration on ROMA102and is provided as acceleration signal266. Moreover, as described below, acceleration signal266is temperature independent.

FIG. 3is a schematic view of resonator126of ROMA102(shown atFIG. 1). Although resonator126is described with respect toFIG. 3, the same description applies to resonator128.

Accordingly, resonator126includes, in addition to the elements described above, a cap302and a window304. As described above, waveguide112terminates in first end118(e.g., an output coupler) that is constructed on either cap302or window304. Waveguide112may be composed of a high refractive index core layer320, such as a SiN or Si core layer, which may be surrounded above by a first low index layer322and below by a second low index layer324. First low index layer322and second low index layer324may be manufactured from, for example, SiO2. Because waveguide112may be directly attached to cover204, the cladding material between core layer320and the cover204may be sufficiently thick to substantially prevent laser light leakage from core layer320into cover204. For example, first low index layer322and second low index layer may be about 2 microns in thickness, which is generally sufficient to prevent substantial light leakage from core layer320into the cover204. In addition, and in various embodiments, first photodetector122is mounted on an outer surface306of window304.

As described above, central portion216of first resonator126may include a reflective surface coating, such as first reflective surface coating225, on either or both surfaces to partially reflect light towards photodetector122, thus forming optical cavity310for the purpose of generating modulated light intensity. In various embodiments, the reflected light intensity should be about 20%, but, in at least some embodiments, is preferably less than 50%. Moreover, the reflective coating, such as first reflective coating225, should not absorb a significant amount of the laser light. For example, the absorption should be less than 5% in some embodiments, and, in other embodiments, is preferably much less than 1%.

In the exemplary embodiment, optical cavity310is a Fabry-Perot cavity and is configured to produce a standing light wave interference absorption and reflection pattern to allow for optical self-oscillation and detection by using only a single constant power light source (e.g., light source110) As described previously, the reflectance of optical cavity310varies with the length, L, of optical cavity310between central portion216of first resonator126and cover204, and this generates an optical signal that is measured by photodetector122. For instance, when the reflected light intensity is large, then the amount of light absorbed in first resonator126(and/or a thin film on first resonator126), is small, and vice-versa. Therefore, as first resonator126vibrates, the amount of light that it is absorbed is also oscillating synchronously. The absorbed light heats central portion216of first resonator126and can cause its mechanical properties to vary (as described in greater detail below).

For example, Young's modulus may be applied to describe the amount of strain in first resonator126as a function of applied stress. Specifically, the modulus may vary with temperature and, hence, with the vibration of first resonator126. Variation in Young's modulus changes the stiffness of the first spring220and second spring224, which directly affects the resonance frequency of first resonator126. The dimensions of first resonator126may also vary due to the coefficient of thermal expansion of first resonator126. For example, heating first resonator126will cause it to expand, which will in turn cause it to bend and change the length, L, of optical cavity310. With a properly designed ROMA102, when first resonator1026is located at a positon of high absorption, the absorbed light heats first resonator126and causes it to move to a location of lower absorption by changing the length, L, of optical cavity310. With less absorbed light, first resonator126then cools down slightly and moves back into a position of larger absorption. The process repeats itself, causing first resonator126to oscillate at its natural frequency.

For example, as first spring220and second spring224increase in temperature, first portion218and second portion222may experience increased mechanical displacement about the z-axis as a result of acceleration of ROMA102, because the stiffness of first spring220and second spring224have decreased. Conversely, as first spring220and second spring224decrease in temperature, first portion218and second portion222may experience decreased mechanical displacement about the z-axis as a result of acceleration of ROMA102, because the stiffness of first spring220and second spring224have increased. Thus, as the temperature of resonator126varies, first proof mass210and second proof mass212may oscillate about the z-axis with increasing and/or decreasing resonance frequency.

In the exemplary embodiment, a first voltage may be applied to first electrode246, and a second voltage may be applied to second electrode248, to compensate for the change in temperature and/or to adjust the resonance frequency of first proof mass210. For example, as the voltage generated by first electrode246is adjusted, the electrostatic force between first electrode246and first portion218of first proof mass210may vary, such that the electromechanical stiffness of first portion218, which is suspended from central portion216by spring220, increases and decreases with corresponding increases and decreases in voltage. Similarly, as the voltage generated by second electrode248is adjusted, the electrostatic force between second electrode248and second portion222of first proof mass210may vary, such that the electromechanical stiffness of second portion222, which is suspended from central portion216by spring224, increases and decreases with corresponding increases and decreases in voltage.

These changes in electromechanical stiffness affect the resonance frequency of first proof mass210during operation. For example, as the electromechanical stiffness of first proof mass210increases, the resonance frequency of first proof mass210may also increase, and as the electromechanical stiffness of first proof mass210decreases, the resonance frequency of first proof mass210may also decrease. An increasing and/or decreasing voltage may thus be applied between first electrode246and/or second electrode248and first proof mass210to adjust the electromechanical stiffness of first proof mass210and, in turn, the resonance frequency of first proof mass210.

In addition, as reflected portion256of first light beam206reflects from central portion216, reflected portion256travels along the z-axis within optical cavity310and reflects from the top and bottom surfaces of cover204back towards central portion216. In other words, reflected portion256bounces back and forth between central portion216and the surfaces of the cover within optical cavity310. Some of this reflected light escapes optical cavity310(as reflected portion256) and travels along the z-axis towards photodetector122, where it is converted, as described above, into first electrical output signal260, which is proportional to the resonance frequency of resonator126.

Thus, ROMA102detects acceleration based, in part, upon the frequency of reflected portion256of first light beam206. As described above, however, the same resonation and detection processes occur within resonator128, where second photodetector124converts reflected portion258of second light beam208into second electrical output signal262.

More particularly, in the exemplary embodiment, first electrode246of first resonator126applies a bias voltage under first portion218of first proof mass210, and second electrode248of first resonator126applies a bias voltage under second portion222of first proof mass210. These bias voltages may, for example, increase the electromechanical stiffness of first proof mass210in a first direction312along the z-axis (because first proof mass210is attracted and/or repulsed by the electrostatic force developed as a result of the bias voltages), such that first proof mass210oscillates at a first resonance frequency in response to an acceleration in either first direction312or second direction314.

Similarly, third electrode252of second resonator128applies a bias voltage over first portion230of second proof mass212, and fourth electrode254of second resonator128applies a bias voltage over second portion234of second proof mass212. These bias voltages may, for example, increase the electromechanical stiffness of second proof mass212in a second direction314along the z-axis (because second proof mass212is attracted and/or repulsed by the electrostatic force developed as a result of the bias voltages), such that second proof mass212oscillates at a second resonance frequency in response to an acceleration in either first direction312or second direction314.

As a result of these opposing bias voltages, ROMA102may operate such that, as the resonance frequency of first resonator126increases, the resonance frequency of second resonator128decreases (and vice versa). Moreover, if the bias voltages applied to each resonator126and128are substantially equivalent, the difference between the first resonance frequency of first proof mass210and the second resonance frequency of second proof mass212will correspond to the actual acceleration upon ROMA102. For example, differential output signal266will not be affected by the temperature of ROMA102, because the variations in the first resonance frequency and the second resonance frequency arising as a result of temperature fluctuations will cancel in the difference calculation performed by electrical circuit264(as described above). ROMA102is thus capable of detecting acceleration independent of temperature.

As the acceleration on ROMA102varies during operation, it may be desirable to increase and/or decrease a scale factor associated with one or both of first resonator126and second resonator128to improve the dynamic range of ROMA102. For example, as the acceleration on ROMA102increases, it may be desirable to increase and/or decrease the scale factor associated with one or both of first resonator126and/or second resonator128. Similarly, as the acceleration on ROMA102decreases, it may be desirable to increase and/or decrease the scale factor associated with one or both of first resonator126and second resonator128.

To adjust the scale factor, the bias voltages generated by one or more of first electrode246, second electrode248, third electrode252, and/or fourth electrode254may be increased and/or decreased. For example, at large accelerations, the resonance frequencies of first resonator126and second resonator128may fluctuate rapidly. To accommodate for this frequency instability, one or more electrodes246,248,252, and/or254may be controlled (e.g., by controller108) to increase and/or decrease the bias voltage applied to first proof mass210and/or second proof mass212. For example, as the bias voltage is increased, the resonance frequency of each proof mass210and212may also increase. Thus, the resonance frequencies of first proof mass210and second proof mass212may be scaled up and down to accommodate increases and decreases in acceleration. In some embodiments, ROMA102may detect g forces ranging from 0 g to 50,000 g.

First resonator126and/or second resonator128may also be dynamically balanced as part of an initial calibration function and/or during operation. More particularly, first portion218of first proof mass210and second portion222of first proof mass210may vary slightly in mass (e.g., due to imperfections in the manufacturing process). Similarly, first portion230of second proof mass212and second portion234of second proof mass212may vary slightly in mass. These small deviations in mass may unbalance first proof mass210and second proof mass212, such that the resonance frequencies of first resonator126and second resonator128are affected.

To balance first resonator126and/or second resonator128, one or more bias voltages may be applied, as described above, to either or both of first proof mass210and/or second proof mass212. In particular, first electrode246and second electrode248may apply one or more bias voltages to first proof mass210, and third electrode252and fourth electrode254may apply one or more bias voltages to second proof mass212.

Embodiments of the resonant opto-mechanical accelerometer thus include a light source, such as a laser, a first resonator, and a second resonator. A resonance frequency of each resonator is responsive to an acceleration, and the light source shines a light beam on each resonator. The resonators modulate the light to a frequency that corresponds to the resonance frequency, and the modulated light is sensed at each resonator by a corresponding photodetector. The photodetectors generate first and second electrical output signals in response, and these electrical output signals are used to generate a temperature independent acceleration measurement. In addition, a plurality of electrodes are disposed in relation to each resonator, such that one or more proof masses associated with each resonator may be dynamically balanced and/or a scale factor associated with the modulated light increased or decreased as a function of acceleration.

Exemplary technical effects of the resonant electro-optical accelerometer described herein include, for example: (a) optical self-excitation and detection; (b) real-time dynamic resonator balancing; (c) real-time adjustments to scale factor; and (d) differential resonator output for temperature independent acceleration measurement.

Exemplary embodiments of a resonant opto-mechanical accelerometer and related components are described above in detail. The system is not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the configuration of components described herein may also be used in combination with other processes, and is not limited to practice with the systems and related methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many applications where acceleration measurement is desired.