No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: "The advancement in the MEMS industry has enabled the development of mechanical resonators to measure physical parameters such as temperature, mass, pressure, radiation, stress, acceleration and chemical changes with unprecedented sensitivity. A conventional MEMS system used to measure such a physical parameter consists of a transducer to actuate the mechanical system into vibration and a detector to sense changes in this resonance frequency of the mechanical system. Any of the parameters to be measured affects the resonance frequency of the mechanical element, and the measurement system is designed to read this change in resonance frequency and to convert it to a measurement of the parameter desired. Although such prior art devices generally utilize nanoscale mechanical elements constructed on-chip, the need for external electronic excitation or actuation systems, which may be bulky, or which may require careful alignment with the on-chip resonator, remains a disadvantage of such passive MEMS devices. An active mechanical system of such a type, including a resonating optical cavity in an on-chip device configuration has been described in an article by Stay Zaitsev et al, entitled 'Forced and self-excited oscillations of an optomechanical cavity', published in Phys. Rev. E 84, 046605 (2011), incorporated herein by reference in its entirety. In this design, a high finesse optical cavity is formed between the reflecting surface of the mechanical resonator element and another static optical interface located nearby. The disadvantage of this set-up is the need for precise 3-dimensional nanoscale alignment of optical elements, and the complexity of supplying the electrical drive to the capacitative driving element in close proximity to the mechanical resonator.
"In the article entitled 'Optical fiber tip acoustic resonator for hydrogen sensing', by
"Reference is now made to FIG. 2, which illustrates schematically a complete prior art optomechanical measurement system, using a vibrating resonator beam 11 suspended over a cavity etched in the end of an optical fiber, as shown in FIG. 1. The mechanical resonance in the suspended resonator beam 11 is excited by means of a modulated laser beam 20 having a wavelength .lamda..sub.1 transmitted through the fiber, with the optical-mechanical energy transfer to the resonator beam 11 being described in Ma and Wang as occurring through the processes of radiation pressure and the photothermal effect. In order to detect the vibrations of the resonator, another laser beam 21 having a wavelength .lamda..sub.2 is directed down the fiber into the cavity. This second beam--the detection beam--is a CW beam at a different wavelength .lamda..sub.2 from that of the modulated exciting beam .lamda..sub.1, so that the detection beam can be wavelength filtered 22 from the modulated exciting beam and the detection measurement thus performed without interference between the two beams. The detection beam is reflected from the two surfaces forming the optical cavity at the tip of the fiber, one being the reflective surface of the freely suspended vibrating gold beam 11, and the other being the bottom surface of the cavity 13 etched out in the end of the fiber, which is a fiber-to-air interface having an approximately 4% reflectivity. According to the explanation given in Ma and Wang, the detection beam reflected from the vibrating gold beam is phase modulated by the Doppler frequency shift from the vibrating gold beam, and on interference with the detection beam reflected from the cavity floor, generates an intensity-modulated signal at the same frequency as the vibration; the signal strength is proportional to the amplitude of the vibration. The filtered detection beam is detected on a detector 24, and the output OUT is converted into the relevant measurement of the parameter being measured by the system.
"Consequently, this prior art method is complicated by the need to utilize two incident laser beams, and the associated optical elements to avoid interference between them, in order to perform the measurement.
"There therefore exists need for a simpler optomechanical cavity measurement device, which overcomes at least some of the disadvantages of the prior art systems and methods, to enable lower-cost and more compact sensor configurations.
"In general, throughout this disclosure, in order to avoid nomenclature confusion, an attempt has been made to distinguish between the mechanical resonant element and the optical resonator, by referring to mechanical resonant element as a mechanical resonator, or a mechanical element, while the optical resonator is called an optical cavity.
"The disclosures of any publications mentioned in this section and in other sections of the specification, are incorporated herein by reference, each in its entirety."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present disclosure describes new exemplary systems for the measurement of environmental parameters, using an optomechanical cavity constructed on the end of an optical fiber. The systems of the present disclosure differ from prior art systems firstly in that only a single laser is used to excite the optomechanical cavity, and furthermore, in that the laser is a CW laser, without the need for any modulation. The optomechanical cavity comprises two reflective elements, the first one of which being fixed within the end section of the fiber. The opposing mirror is a surface of a mechanical element, supported at the end of the fiber in such a manner that it can vibrate at its natural resonance frequency, and facing the first reflective element, so as to form the optomechanical cavity. As the mechanical element vibrates at its characteristic frequency, the length of the cavity also 'vibrates' at the same frequency, with the result that the light reflected from the cavity back down the fiber is modulated at that same frequency. Detection of that modulation frequency therefore enables the frequency of vibration of the mechanical element to be determined. An advantageous geometry to use is that of a cavity etched into the end of the fiber, with the mechanical element supported over the etched cavity by being attached rigidly to the outer edges of the fiber.
"Although the mechanical element can begin vibrating at its resonance frequency without any input power merely as a result of a random positional excursion from its equilibrium rest position, the amplitude of its vibrations can be significantly increased by applying CW laser power, such that the mechanical element undergoes powered self oscillation. The CW laser power thus operates both to excite the mechanical element to vibrate at its resonance frequency, and to detect the frequency of these vibrations by analyzing the optical reflection from the optomechanical cavity.
"The mechanical element is responsive to the environmental parameter which it is desired to measure, either directly by the influence of that parameter on the vibration of the mechanical element, or by means of a temperature change of the mechanical element as a result of exposure to the environmental parameter. Such a temperature change generally causes the elasticity and the internal stress of the mechanical element to change, and this change causes a change in the frequency of vibration, which is detected by the optical system.
"One exemplary implementation involves a system for measuring an environmental parameter, comprising: (i) an optomechanical cavity constructed on the end section of an optical fiber, the cavity comprising:
"(a) a mechanical element responsive to the environmental parameter to be measured, and disposed on an end of the fiber, the mechanical element being connected to the end of the fiber such that it can vibrate at a resonance frequency, and the mechanical element reflecting light impinging thereon from the fiber, and
"(b) a second reflective element disposed at the end of the fiber, such that the mechanical element and the second reflective element form an optical cavity, (ii) a single laser source only, the single laser source being adapted to direct CW laser light into the optomechanical cavity through the fiber, and (iii) a detection system adapted to measure the modulation frequency of light reflected from the optomechanical cavity, such that the environmental parameter can be determined from the frequency measurement.
"In such a system, the second reflective element may be the floor of a cavity over which the first mechanical element is suspended, or it could be a fiber Bragg grating mirror disposed in the end section of the fiber.
"In any such systems, the mechanical element may be responsive to the environmental parameter by means of change in its mechanical properties when exposed to the environmental parameter, and this change of mechanical properties may then amend the vibration characteristics of the mechanical element. This change in mechanical properties may arise from a change in the temperature of the mechanical element.
"Alternatively, the mechanical element may be responsive to the environmental parameter by means of a direct change in its vibration characteristics when exposed to the environmental parameter.
"The laser source in any of the above described systems should have a constant power output, and this should be at a level such that the mechanical element is driven into self-oscillation vibrations by the laser source. In such cases, the mechanical element may be such that when exposed to the environmental parameter, its self-oscillation vibration frequency changes in accordance with the level of the environmental parameter.
"The environmental parameter may be any of temperature or pressure in the vicinity of the mechanical element, radiation power incident on the mechanical element, gas contamination in the vicinity of the mechanical element, or acceleration of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
"The presently claimed invention and its novelty and inventiveness over the prior art will be understood and appreciated more fully from the detailed description, taken in conjunction with the drawings in which:
"FIG. 1 shows a prior art optomechanical cavity structure constructed on the end of an optical fiber;
"FIG. 2 illustrates schematically a complete prior art optomechanical measurement system, using a cavity of the type shown in FIG. 2;
"FIG. 3 illustrates schematically a novel exemplary optomechanical measurement system, of the type described in the present disclosure;
"FIG. 4 illustrates schematically the output characteristic response of an optical cavity to a constant input power level CW beam;
"FIG. 5 illustrates schematically the thermal force acting on the resonant beam of the cavity of FIG. 3, as a function of the cavity geometrical parameters;
"FIG. 6 is a sketch representing an experimental plot showing the frequency of vibration of the suspended beam of the cavity of FIG. 3, as a function of the laser power level reflected from said cavity; and
"FIG. 7 illustrates an alternative construction of the fiber tip cavity device of FIG. 3, using a fiber Bragg grating (FBG) as a high reflectivity mirror opposite the high reflectivity mirror on the underside of the suspended beam"
For additional information on this patent application, see: DHAYALAN, Yuvaraj; BACHAR, Gil; BASKIN,
Keywords for this news article include: Patents, Nanoscale, Nanotechnology, Emerging Technologies.
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