NL2036028B1 - An optomechanical pressure-measurement system as well as a method for determining an ambient pressure level using such optomechanical pressure-measurement system. - Google Patents

An optomechanical pressure-measurement system as well as a method for determining an ambient pressure level using such optomechanical pressure-measurement system. Download PDF

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Publication number
NL2036028B1
NL2036028B1 NL2036028A NL2036028A NL2036028B1 NL 2036028 B1 NL2036028 B1 NL 2036028B1 NL 2036028 A NL2036028 A NL 2036028A NL 2036028 A NL2036028 A NL 2036028A NL 2036028 B1 NL2036028 B1 NL 2036028B1
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light beam
optomechanical
membrane element
measurement system
light
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NL2036028A
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Dutch (nl)
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Louis Hendriks Arthur
Fiore Andrea
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Univ Eindhoven Tech
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Priority to NL2036028A priority Critical patent/NL2036028B1/en
Priority to PCT/NL2024/050566 priority patent/WO2025080140A1/en
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Publication of NL2036028B1 publication Critical patent/NL2036028B1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L7/00—Measuring the steady or quasi-steady pressure of a fluid or a fluent solid material by mechanical or fluid pressure-sensitive elements
    • G01L7/02—Measuring the steady or quasi-steady pressure of a fluid or a fluent solid material by mechanical or fluid pressure-sensitive elements in the form of elastically-deformable gauges
    • G01L7/08—Measuring the steady or quasi-steady pressure of a fluid or a fluent solid material by mechanical or fluid pressure-sensitive elements in the form of elastically-deformable gauges of the flexible-diaphragm type
    • G01L7/086—Measuring the steady or quasi-steady pressure of a fluid or a fluent solid material by mechanical or fluid pressure-sensitive elements in the form of elastically-deformable gauges of the flexible-diaphragm type with optical transmitting or indicating means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
    • G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
    • G01L9/0016—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a diaphragm
    • G01L9/0017—Optical excitation or measuring
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
    • G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
    • G01L9/0019—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a semiconductive element
    • G01L9/002—Optical excitation or measuring
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
    • G01L9/0076—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means
    • G01L9/0077—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means for measuring reflected light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
    • G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
    • G01L9/0076—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means
    • G01L9/0077—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means for measuring reflected light
    • G01L9/0079—Transmitting or indicating the displacement of flexible diaphragms using photoelectric means for measuring reflected light with Fabry-Perot arrangements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Measuring Fluid Pressure (AREA)

Abstract

A B S T R A C T The present disclosure proposes an optomechanical pressure- measurement system for measuring an ambient pressure level, the system comprising a fiber having a first fiber end and a second fiber end, an optomechanical cavity being mounted at the first fiber end and composed of a first membrane element and a second membrane element spaced apart from each other, with the first membrane element contacting the first fiber end, at least one light beam generating device coupled to the second fiber end and structured to generate and direct light beams, each light beam having a certain optical frequency, via the fiber on the optomechanical cavity, and a light sensing member coupled to the second fiber end, wherein the at least one light beam generating device is structured to direct a first light beam with a first optical frequency on the optomechanical cavity, wherein the first light beam is modulated at a modulation frequency within a bandwidth of a mechanical resonance frequency of the second membrane element, wherein the at least one light beam generating device is structured to direct a second light beam with a second optical frequency on the optomechanical cavity; and wherein the light sensing member is structured to detect part of the second light beam reflected by the optomechanical cavity and to determine the ambient pressure around the optomechanical cavity based on a change of the oscillation amplitude of the second membrane element.

Description

TITLE
An optomechanical pressure-measurement system as well as a method for determining an ambient pressure level using such optomechanical pressure- measurement system.
TECHNICAL FIELD
The present disclosure relates to techniques for determining an ambient pressure level in particular inside deposition and measurement systems operating at low pressure (below atmospheric pressure).
BACKGROUND OF THE DISCLOSURE
Low pressure control is essential for deposition processes (e.g. electron beam evaporation, chemical vapour deposition, molecular beam epitaxy) in the semiconductor industry to be conducted in an accurate and controlled manner. It is also required for measurement systems which involve electron or ion beams (e.g. electron microscopes) or operate at cryogenic temperatures (cryostats). The measurement of low pressures mostly requires bulky pressure gauges (e.g. Pirani and capacitance gauges) which take up useful space inside vacuum systems. Additionally, these gauges are subject to electromagnetic interference and in some cases to corrosion in for example, a plasma system.
The field pertaining to the interaction between light and nanomechanical motion which are mediated by radiation pressure forces present a promising alternative for accurate pressure level measurement. Nevertheless, the practical applications of these nano-optomechanical structures are hindered by the complexity and the limited efficiency of light coupling to and from the sensor, related to the tight optical confinement and the narrow linewidths which are typically employed.
Accordingly, it is a goal of the present disclosure to provide an improved optomechanical pressure-measurement system capable of accurate measurement of low ambient pressure levels, whilst enabling a large coupling efficiency without any external optics. The optomechanical structure according to the disclosure can readily be used in relevant sensing applications, for example in particular, inside deposition and measurement systems.
SUMMARY OF THE DISCLOSURE
According to a first example of the disclosure, an optomechanical pressure-measurement system for measuring an ambient pressure level is proposed.
The system comprises a fiber having a first fiber end and a second fiber end, an optomechanical cavity being mounted at the first fiber end and composed of a first membrane element and a second membrane element spaced apart from each other, with the first membrane element contacting the first fiber end, at least one light beam generating device coupled to the second fiber end and structured to generate and direct light beams, each light beam having a certain optical frequency, via the fiber on the optomechanical cavity, and a light sensing member coupled to the second fiber end.
In particular, in the optomechanical pressure-measurement system according to the disclosure, the at least one light beam generating device is structured to direct a first light beam with a first optical frequency on the optomechanical cavity, wherein the first light beam is modulated at a modulation frequency within a bandwidth of a mechanical resonance frequency of the second membrane element, wherein the at least one light beam generating device is structured to direct a second light beam with a second optical frequency on the optomechanical cavity; and wherein the light sensing member is structured to detect part of the second light beam reflected by the optomechanical cavity and to determine the ambient pressure around the optomechanical cavity based on a change of the oscillation amplitude of the second membrane element.
With this example, an optomechanical cavity mounted to the tip of the fiber is presented. The first and second membrane elements are patterned to form an optical resonance, whose electromagnetic field extends over both membrane elements. The second membrane element forms a mechanical oscillator, which can be excited by a first light beam through the optical or photothermal force, when said first light beam is modulated at a frequency close to the mechanical resonance frequency of the second membrane element.
By irradiating the optomechanical cavity with the first light beam having a modulation frequency within a bandwidth of a mechanical resonance frequency of the second membrane element, the optomechanical cavity is excited at that particular mechanical resonance frequency. This is achieved by selecting the modulation frequency of the first light beam within the bandwidth, such that the modulation frequency is conformal (nearly equal) to the particular mechanical resonance frequency of the second membrane element.
The displacement of the vibrating second membrane element results in a change in the frequency of the optical resonance and can be monitored by measuring the reflection of a second light beam, which said second light beam has been directed through the fiber towards the optomechanical cavity and has been reflected back by the second membrane element. Due to the collisions with the ambient gas molecules, the mechanical damping rate of the second membrane element depends on the ambient pressure. By exciting the mechanical motion of the second membrane element with the first light beam and measuring its oscillations as a function of time or frequency through (part of} the reflected second light beam using the light sensing element the mechanical damping rate and thereby the pressure can be determined.
In an implementation, in the optomechanical pressure-measurement system according to the disclosure, the at least one light beam generating device is structured to direct the first light beam with the modulation frequency only for a first time-interval, and to direct the second light beam with the second optical frequency at least during a second time interval following the first time-interval, and wherein the light sensing member is structured to detect part of the reflected second light beam as a function of time, and to determine the ambient pressure based on a temporal decay of the oscillations in part of the reflected second light beam during the second time interval.
With this example, a direct and accurate pressure level measurement can be obtained. By irradiating, during the first time-interval, the optomechanical cavity with the first light beam, the second membrane is excited and starts oscillating as the modulation frequency of the first light beam is selected such that it is within the bandwidth of the mechanical resonance frequency and preferably is conformal to that particular mechanical resonance frequency.
Next, during the second time-interval immediately following the first time- interval, the part of a second light beam being reflected by the optomechanical cavity is measured. The reflected power of the second light beam depends on the position of the oscillating second membrane, and therefore also oscillates at the mechanical resonance frequency. As the second membrane element is only excited during the first time-interval using the first light beam, the mechanical oscillation of the second membrane element is damping out, and its damping rate depends on the ambient pressure level around the optomechanical cavity. By fitting the decay of these oscillations, it is possible to measure the damping rate and therefore the ambient pressure level near the optomechanical cavity.
In an additional implementation, the at least one light beam generating device is structured to vary the modulation frequency of the first light beam within the bandwidth of the mechanical resonance frequency, and the light sensing member is structured to detect part of the reflected second light beam, wherein the amplitude of the oscillations in the part of the reflected second light beam is measured as a function of the modulation frequency, wherein the width of the peak in the oscillation amplitude around the mechanical resonance frequency is used to measure the pressure.
The configuration of the optomechanical cavity mounted at the free fiber tip end can be very small (approximately 100 um diameter and smaller than 1 4m in thickness). Therefore, the optomechanical pressure-measurement system can be easily integrated into any part of a deposition or measurement system. It contains no electrical parts and the system is insensitive to electromagnetic interference.
In a preferred example, the at least one light beam generating device can be structured as a single at least one light beam generating device structured to generate and emit the first light beam and the second light beam, whereas in another advantageous example the at least one light beam generating device is comprised of a first light beam generating device structured to generate the first light beam with the first frequency and a second light beam generating device structured to generate the second light beam with the second frequency.
In a preferred example, a fiber coupler is used to combine the first light beam and the second light beam into a single fiber, and a circulator or a fiber coupler is used to separate the light beams directed towards the optomechanical cavity from the beams reflected by it.
In a specific example, the double membrane optomechanical cavity may comprise spacer members structured to orient the first membrane element and the second membrane element at a certain distance from each other. In particular, the spacer members are made from a material selected from the group containing at least 5 InGaAs, AlGaAs, SiOz, SiaN, or other semiconductor or dielectric materials and may have a thickness of 200-250 nm.
Preferably, the first membrane element and the second membrane element are made from a semiconductor material for example Silicon or Indium phosphide (InP) or Gallium Arsenide (GaAs), or a dielectric material, for example
SisN4. The double membrane photonic crystal membranes may be fabricated using standard semiconductor growth, lithography, and etching techniques. In particular, the first membrane element and the second membrane element have the same thickness or approximately have a same thickness, for example a thickness laying in the range of 150-200 nm.
Accordingly, the mechanical resonance frequency of the optomechanical cavity may be in a range of typically 1-4 MHz. However, it is to be noted that the mechanical resonance frequency is not limited to the range of 1-4 MHz, as lower of higher mechanical resonance frequencies are likewise feasible. The optical fiber can be construed as a single mode optical fiber.
In a further advantageous example of the optomechanical pressure- measurement system according to the disclosure, the light sensing member may comprise a filter centered at the optical frequency of the second light beam, a light detector, and a sensing unit, wherein the sensing unit is structured to determine the ambient pressure at the second membrane element based on a change of the oscillation amplitude of the reflected second light beam detected by the light detector as a function of time or modulation frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure will now be discussed with reference to the drawings, which show in:
Figure 1, a first example of an optomechanical pressure-measurement system for measuring an ambient pressure level according to the disclosure;
Figure 2a, the optical resonance of the optomechanical cavity showing absolute reflectance as a function of wavelength;
Figure 2b, the power spectral density of the second light beam reflected by the optomechanical cavity as a function of the modulation frequency of the first light beam implemented in the optomechanical pressure-measurement system according to the disclosure;
Figure 3, a further detail of the optomechanical pressure-measurement system for measuring an ambient pressure level according to the disclosure;
Figure 4, the measured linewidth of the mechanical resonance as a function of the ambient pressure.
DETAILED DESCRIPTION OF THE DISCLOSURE
For a proper understanding of the disclosure, in the detailed description below corresponding elements or parts of the disclosure will be denoted with identical reference numerals in the drawings.
Low pressure control is essential for deposition processes (e.g. electron beam evaporation, chemical vapour deposition and molecular beam epitaxy) in the semiconductor industry to be conducted in an accurate and controlled manner. It is also required for measurement systems which involve electron or ion beams (e.g. electron microscopes) or operate at cryogenic temperatures (cryostats). The measurement of low pressures mostly requires bulky pressure gauges (e.g. Pirani and capacitance gauges) which take up useful space inside vacuum systems. Additionally, these gauges are subject to electromagnetic interference and in some cases to corrosion in for example, a plasma system.
An improved optomechanical pressure-measurement system capable of accurate measurement of low ambient pressure levels is proposed in this application, whilst enabling a large coupling efficiency without any external optics. The optomechanical structure according to the disclosure can readily be used in relevant sensing applications, for example in particular use inside deposition and measurement systems.
Figure 1 depicts a first example of such improved optomechanical pressure-measurement system for the measurement of low ambient pressure levels.
The system is denoted with reference numeral 100 whereas reference numeral 50 denoted the ambient pressure surrounding the optomechanical pressure- measurement system 100. The optomechanical pressure-measurement system 100 comprises a fiber 11 with a first fiber end 11a and a second fiber end 11b.
Reference numeral 110 denotes an optomechanical cavity that is mounted at the first fiber end 11a of the fiber 11. The optomechanical cavity 110 is formed of a first membrane element 111a and a second membrane element 111b, which are spaced apart from each other, for example yet not necessarily, by means of spacer members 112. The spacer members 112 orient the first membrane element 111a and the second membrane element 111b at a certain distance from each other, thus enveloping a gap 113. As shown in Figure 1, the first membrane element 111a contacts the first fiber end 11a.
The spacer members 112 can be manufactured from a material selected from the group containing at least InGaAs, AlGaAs, SiO2 and SizN4. Any other type of semiconductor or dielectric material are similarly suitable for the spacer members 112.
The thickness of the spacer members 112 can be in the range of 200-250 nm.
Preferably, the first membrane element 111a and the second membrane element 111b are made from a semiconductor material for example Silicon or Indium phosphide (InP) or Gallium arsenide (GaAs), or a dielectric material, for example SizNs.
The double membrane photonic crystal membranes 111a and 111b may be fabricated using standard semiconductor growth, lithography, and etching techniques.
Using metalorganic vapor-phase epitaxy (MOVPE) a sacrificial layer of lattice matched InGaAs of 300 nm is grown on top of a [100] InP substrate followed by two 180 nm InP membranes spaced by a 220 nm layer of InGaAs. Afterwards a 200 nm layer of SisN4 is deposited on top of the wafer using plasma enhanced chemical vapor deposition (PECVD) to act as a hard mask. Electron beam lithography (EBL) or optical lithography is used to pattern both the membranes 111a and 111b and the surrounding spacer members 112. Then, the pattern is transferred into the hard mask by reactive ion etching (RIE) with a CHF; plasma, which is followed by etching into the two InP membranes and the InGaAs spacer layer using inductively coupled plasma reactive ion etching (ICP-RIE) with a CH4/H2 chemistry at 60 °C.
Subsequently the hard mask is removed by buffered hydrofluoric acid (BHF 7:1) and replaced by a 250 nm thick SisN4 protection layer, followed by a 400 nm thick SisN4 hard mask on the substrate side using PECVD. Afterwards a second
EBL is performed to pattern large windows on the substrate side which are aligned with a few micrometer precision with respect to the pattern on the device layer. This is then followed by dry etching of the SisN4, wet etching of the InP substrate by a
HCL:H3PO4 = 7:2, removal of the Si3N4 by BHF 7:1, and then the etching of the sacrificial layer by H2O:H28504:H202 = 10:1:1. Finally, the sample is dried using critical point drying (CPD) so the suspended membranes do not collapse due to capillary forces.
In particular, the first membrane element 111a and the second membrane element 111b have the same thickness or approximately have a same thickness, for example a thickness in the range of 150-200 nm.
Accordingly, the configuration of the optomechanical cavity 110 mounted at the free fiber tip end 11a can be very small (approximately 100 um in diameter and smaller than 1 um in thickness: being the thicknesses of the two membrane elements 111a and 111b and that of the spacer member 112 combined). Therefore, the optomechanical pressure-measurement system 100 can be easily integrated into any part of a deposition or measurement system. It contains no electrical parts and the system is insensitive to electromagnetic interference.
The mechanical resonance frequency of the optomechanical cavity 110 may be in a range of typically 1-4 MHz. However it is to be noted that the mechanical resonance frequency is not limited to the range of 1-4 MHz, as lower of higher mechanical resonance frequencies are likewise feasible.
Also, it is noted that the optical fiber 11 can be construed as a single mode optical fiber.
The optomechanical pressure-measurement system 100 furthermore comprises at least one light beam generating device denoted with reference numeral 12. The at least one light beam generating device 12 is at least optically coupled to the second fiber end 11b and is structured to generate and direct light beams of various light characteristics. Each light beam may have a certain optical frequency / optical wavelength and may be emitted and directed via the optical fiber 11 on the optomechanical cavity 110. Also, the optomechanical pressure-measurement system 100 may comprise a light sensing member 13 that is likewise optically coupled to the second fiber end 11b.
The at least one light beam generating device 12 may direct a first light beam 14 with a first optical frequency fa / wavelength A, on the optomechanical cavity 110. The first light beam 14 is modulated in one example, by means of an amplitude modulator 131 which is part of the optomechanical pressure-measurement system 100 (see Figure 3) at a modulation frequency fn within a bandwidth of a mechanical resonance frequency of the second membrane element 111b. Also, the at least one light beam generating device 12 is structured to emit and direct a second light beam 15 with a second optical frequency f, / wavelength A, on the optomechanical cavity 110.
In a preferred example, the at least one light beam generating device 12 can be structured as a single light beam generating device 12 capable of generating and emitting both the first light beam 14 and the second light beam 15. In another example, which is also depicted in Figure 1, the at least one light beam generating device 12 to is comprised of a first light beam generating device 12a structured to generate the first light beam 14 with the first frequency fa and a second light beam generating device 15 structured to generate the second light beam 15 with the second frequency fb.
Modulation of the first light beam 14 by means of the amplitude modulator 131 is not a requirement for a proper and functional operation of the optomechanical pressure-measurement system 100. In an alternative example which also implements modulation of the first light beam 14, the amplitude modulator 131 may be incorporated in, or be part of, the at least one light beam generating device 12, or the first light beam generating device 12a.
The light sensing member 13 detects part of the second light beam 15 reflected by the optomechanical cavity 110, for example with an optical detector or light sensing surface 13a and converted in a proper processing signal by means of light sensing unit 13b. Said reflected part of the second light beam 15 is denoted with reference numeral 15r.
The whole construction of the optomechanical pressure-measurement system 100 is capable of determining the ambient pressure 50 around the optomechanical cavity 110 based on a change of the oscillation amplitude of the second membrane element 111b.
The first and second membrane elements are patterned to form an optical resonance cavity 110, whose electromagnetic field extends over both membrane elements 111a and 111b and across the gap 113 between both membranes. The second membrane element 111b forms a mechanical oscillator, which can be excited by the first light beam 14 through the optical or photothermal force, when the first light beam 14 is modulated at a frequency close to the mechanical resonance frequency of the second membrane element 111b. The mechanical resonance frequency of the second membrane element 111b is, amongst others, defined by its constructional dimensions and materials used and can be approximated in advance. Accordingly, with the mechanical resonance frequency being known by approximation, a frequency bandwidth can be defined in which the modulation frequency of the first light beam 14 can be chosen.
Reference is made to Figure 2a depicting the optical resonance of the optomechanical cavity showing absolute reflectance as a function of wavelength and
Figure 2b depicting the modulation of second light beam reflected by the optomechanical cavity as a function of the modulation frequency of the first light beam implemented in the optomechanical pressure-measurement system 100 according to the disclosure.
By radiating the optomechanical cavity 110 with the first light beam 14 having a modulation frequency fm within a bandwidth of a mechanical resonance frequency of the second membrane element 111b, the vibration of the second membrane element 111b is excited. This is achieved by selecting the modulation frequency fn, of the first light beam 14 within that bandwidth, such that the modulation frequency fm is conformal (nearly equal) to the particular mechanical resonance frequency of the second membrane element 111b.
The displacement of the vibrating second membrane element 111b results in a change in the frequency of the optical resonance and can be monitored by measuring the reflection beam 15r of a second light beam 15, which second light beam 15 has been directed through the fiber 11 towards the optomechanical cavity 110 and has been reflected back by it. Due to the collisions with the ambient gas molecules, the mechanical damping rate of the second membrane element 111b depends on the ambient pressure 50 surrounding the optomechanical cavity 110. By exciting the mechanical motion of the second membrane element 111b with the first light beam 14 and measuring its oscillations as a function of time or frequency fn of (part of) the reflected second light beam 15r using the light sensing element 13 the mechanical damping rate and thereby the pressure 50 can be determined.
In one implementation, the at least one light beam generating device 12 directs the first light beam 14 with the modulation frequency fm only for a first time- interval ti, and directs the second light beam 15 (not modulated) with the second optical frequency f, at least during a second time-interval tz following (preferably directly following) the first time interval t.
During the first time-interval ty the first light beam 14 having a modulation frequency fi, within a bandwidth of the mechanical resonance frequency of the second membrane element 111b (and more in particular nearly equal or very close to the mechanical resonance frequency of the second membrane element 111b) causes excitation of the second membrane element 111b at that particular modulation frequency. After that first time-interval ty the first light beam 14 is switched off such that the continuous excitation at the modulation frequency is removed.
During the second time-interval t2 following the first time-interval t4, the second light beam 15 is being directed towards the oscillating optomechanical cavity 110 (and the oscillating second membrane element 111b) and the light sensing member 13 detects part of the reflected second light beam 15r as a function of time.
The power of the reflected second light beam 15r depends on the position of the oscillating second membrane element 111b, and therefore the power of the reflected second light beam 15r also oscillates at the modulation frequency fn. As the second membrane element 111b is only excited during the first time-interval t: using the first light beam 14, the mechanical oscillation of the second membrane element 111b is damping out, and its damping rate depends on the ambient pressure level 50 around the optomechanical cavity 110. By fitting the decay of the resulting oscillations of the power of the reflected second light beam 15r, it is possible to measure the damping rate and therefore the ambient pressure level 50 near the optomechanical cavity 110.
This is depicted in Figure 4.
In another implementation, the at least one light beam generating device 12 varies the modulation frequency fn, of the first light beam 14 within the bandwidth of the mechanical resonance frequency of the optomechanical cavity 110. In this implementation the light sensing member 13 detects part of the reflected second light beam 15r as a function of time, wherein the amplitude of the oscillations in the part of the reflected second light beam 15r is measured as a function of the modulation frequency fn, wherein the width of the peak in the oscillation amplitude around the mechanical resonance frequency is used to measure the pressure.
With the examples as described, an ambient pressure level can be measured in an efficient and accurate manner. In particular, the optomechanical pressure-measurement system 100 is suited to measure pressure levels in the range of 0.001 mbar till 100 mbar.
In a preferred example, see Figure 3, a fiber coupler 132 is used to combine the first light beam 14 and the second light beam 15. The first light beam 14 is modulated by means of the amplitude modulator 131 with a voltage produced by a signal generator 138. As outlined above, the amplitude modulator 131 can be implemented as a separate component of the optomechanical pressure-measurement system 100 or form part of the at least one light beam generating device 12 or the first light source 12a. From the fiber coupler 132 the light beams 14 and 15 are directed into a circulator 133 towards the optomechanical cavity 110. The first light beam 14 increases the amplitude of the oscillation of the second membrane element 111b and the second beam 15 measures this oscillation. Both the reflected light beams go back through the circulator 133 and pass through a tunable bandpass filter 134, which removes or filters out the first light beam 14. Only the reflected second light beam 15r is measured by an optical detector 13a and processed in the light sensing unit 13b.
The electronic signal from a bandpass filter 134 / the light sensing unit 13b can be measured and analyzed in the time domain 135 or in the frequency domain 136 and displayed by the use of a computer 137, which in turn can alter the modulation frequency of the signal generator 138.
In a further advantageous example of the optomechanical pressure- measurement system according to the disclosure, the light sensing member may comprise a filter centered at the optical frequency of the second light beam, a light sensor, and a sensing unit, wherein the sensing unit is structured to determine the ambient pressure at the second membrane element based on a change of oscillation amplitude of the reflected second light beam detected by the light sensor.
LIST OF REFERENCE NUMERALS USED
50 ambient pressure 100 optomechanical pressure-measurement system 11 fiber 11a first fiber end 11b second fiber end 12 light beam generating device 12a first light source 12b second light source 13 light sensing member 13a optical detector / light sensing surface 13b light sensing unit 14 first light beam fy first optical frequency fin modulation frequency 15 second light beam fo second optical frequency 15r reflected part of the second light beam 110 optomechanical cavity 111a first membrane element 111b second membrane element 111a-z array of holes of first membrane element 111b-z array of holes of second membrane element 112 spacers 113 resonance cavity 131 amplitude modulator 132 fiber coupler 133 circulator 134 bandpass filter 135 time domain analyzer 136 frequency domain analyzer 137 computer 138 signal generator

Claims (13)

CONCLUSIESCONCLUSIONS 1. Een optomechanisch drukmeetsysteem voor het meten van een omgevingsdrukniveau, waarbij het systeem bestaat uit: een vezel met een eerste vezeluiteinde en een tweede vezeluiteinde, een optomechanische ruimte die geplaatst is op het eerste vezeluiteinde en gevormd is uit een eerste membraan element en een tweede membraan element, die op afstand van elkaar zijn geplaatst, waarbij het eerste membraan element contact maakt met het eerste vezeluiteinde, ten minste één lichtbundel genererende inrichting welke is gekoppeld met het tweede vezeluiteinde en is ingericht om lichtbundels te genereren en af te geven via de vezel naar de optomechanische holte, waarbij elke lichtbundel een bepaalde optische frequentie bezit, en een lichtdetectie element dat is gekoppeld met het tweede vezeluiteinde, waarbij de ten minste ene lichtbundel genererende inrichting is ingericht om een eerste lichtbundel met een eerste optische frequentie naar de optomechanische holte af te geven, waarbij de eerste lichtbundel binnen een bandbreedte van een mechanische resonantie frequentie van het tweede membraan element is gemoduleerd op een modulatie frequentie, waarin de ten minste ene lichtbundel genererende inrichting is ingericht om een tweede lichtbundel met een tweede optische frequentie op de optomechanische holte af te geven; en waarin het lichtdetectie element is ingericht om een deel van de tweede lichtbundel te detecteren dat wordt gereflecteerd door de optomechanische holte en om de omgevingsdruk rondom de optomechanische holte vast te stellen op basis van een verandering van de oscillatie-amplitude van het tweede membraan element.1. An optomechanical pressure measurement system for measuring an ambient pressure level, the system comprising: a fiber having a first fiber end and a second fiber end, an optomechanical cavity disposed on the first fiber end and formed from a first membrane element and a second membrane element spaced apart, the first membrane element contacting the first fiber end, at least one light beam generating device coupled to the second fiber end and configured to generate and deliver light beams through the fiber to the optomechanical cavity, each light beam having a specific optical frequency, and a light detection element coupled to the second fiber end, the at least one light beam generating device configured to deliver a first light beam having a first optical frequency to the optomechanical cavity, the first light beam being modulated at a modulation frequency within a bandwidth of a mechanical resonance frequency of the second membrane element, wherein the at least a light beam generating device is configured to emit a second light beam having a second optical frequency to the optomechanical cavity; and wherein the light detection element is configured to detect a portion of the second light beam reflected by the optomechanical cavity and to determine the ambient pressure surrounding the optomechanical cavity based on a change in the oscillation amplitude of the second membrane element. 2. Het optomechanisch drukmeetsysteem volgens conclusie 1, waarbij de ten minste ene lichtbundel genererende inrichting is ingericht om de eerste lichtbundel met de modulatiefrequentie slechts gedurende een eerste tijdsinterval af te geven, en om de tweede lichtbundel met de tweede optische frequentie ten minste gedurende een tweede tijdsinterval volgend op het eerste tijdsinterval af te geven, en waarbij het lichtdetectie element is ingericht om een deel van de gereflecteerde tweede lichtbundel te detecteren als een functie van de tijd, en om de omgevingsdruk vast te stellen op basis van een tijdsverval van de oscillaties in een deel van de gereflecteerde tweede lichtbundel tijdens het tweede tijdsinterval.2. The optomechanical pressure measurement system of claim 1, wherein the at least one light beam generating device is configured to emit the first light beam with the modulation frequency only during a first time interval, and to emit the second light beam with the second optical frequency at least during a second time interval following the first time interval, and wherein the light detection element is configured to detect a portion of the reflected second light beam as a function of time, and to determine the ambient pressure based on a time decay of the oscillations in a portion of the reflected second light beam during the second time interval. 3. Het optomechanisch drukmeetsysteem volgens conclusie 1, waarbij de ten minste ene lichtbundel genererende inrichting is ingericht om de modulatiefrequentie van de eerste lichtbundel te variëren binnen de bandbreedte van de mechanische resonantie frequentie, en waarbij het lichtdetectie element is ingericht om een deel van de gereflecteerde tweede lichtbundel te detecteren, waarbij de amplitude van de oscillaties in het deel van de gereflecteerde tweede lichtbundel wordt gemeten als functie van de modulatiefrequentie, en waarbij de breedte van de piek in de oscillatieamplitude rondom de mechanische resonantie frequentie wordt gebruikt om de druk te meten.3. The optomechanical pressure measurement system of claim 1, wherein the at least one light beam generating device is configured to vary the modulation frequency of the first light beam within the bandwidth of the mechanical resonance frequency, and wherein the light detection element is configured to detect a portion of the reflected second light beam, wherein the amplitude of the oscillations in the portion of the reflected second light beam is measured as a function of the modulation frequency, and wherein the width of the peak in the oscillation amplitude around the mechanical resonance frequency is used to measure the pressure. 4. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij de optomechanische holte afstandselementen omvat bedoeld om het eerste membraan element en het tweede membraan element op een bepaalde afstand van elkaar te oriënteren.4. The optomechanical pressure measurement system according to any one or more of the preceding claims, wherein the optomechanical cavity comprises spacer elements intended to orient the first membrane element and the second membrane element at a certain distance from each other. 5. Het optomechanisch drukmeetsysteem volgens conclusie 4, waarbij de afstandselementen zijn gemaakt van een materiaal gekozen uit de groep die ten minste InGaAs, AlGaAs, SiO2, SisNs of andere halfgeleider- of diëlektrische materialen bevat.5. The optomechanical pressure measurement system of claim 4, wherein the spacer elements are made of a material selected from the group comprising at least InGaAs, AlGaAs, SiO2, SisNs or other semiconductor or dielectric materials. 6. Het optomechanisch drukmeetsysteem volgens conclusie 4 of 5, waarbij de afstandselementen een dikte bezitten van 200-250 nm.6. The optomechanical pressure measuring system according to claim 4 or 5, wherein the spacer elements have a thickness of 200-250 nm. 7. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij het eerste membraan element en het tweede membraan element zijn vervaardigd uit een halfgeleidermateriaal, bijvoorbeeld silicium of indiumfosfide (InP) of galliumarsenide (GaAs) of een diëlektrisch materiaal, bijvoorbeeld SisNa.7. The optomechanical pressure measurement system according to one or more of the preceding claims, wherein the first membrane element and the second membrane element are made of a semiconductor material, for example silicon or indium phosphide (InP) or gallium arsenide (GaAs) or a dielectric material, for example SisNa. 8. Het optomechanisch drukmeetsysteem volgens conclusie 7, waarbij het eerste membraan element en het tweede membraan element dezelfde dikte bezitten, bijvoorbeeld 150-200 nm.8. The optomechanical pressure measurement system according to claim 7, wherein the first membrane element and the second membrane element have the same thickness, for example 150-200 nm. 9. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij het eerste membraan element en het tweede membraan element zijn voorzien van een patroon van openingen teneinde een fotonisch kristal te vormen.9. The optomechanical pressure measurement system according to any one of the preceding claims, wherein the first membrane element and the second membrane element are provided with a pattern of openings to form a photonic crystal. 10. Het optomechanisch drukmeetsysteem volgens conclusie 9, waarbij de optische frequenties van de eerste en de tweede lichtbundel zo worden gekozen dat ze dicht bij de frequentie van een optische resonantie van het fotonische kristal liggen.10. The optomechanical pressure measurement system according to claim 9, wherein the optical frequencies of the first and second light beams are selected to be close to the frequency of an optical resonance of the photonic crystal. 11. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij de mechanische resonantiefrequentie van de optomechanische holte tussen 1-4 MHz ligt.11. The optomechanical pressure measurement system according to any one of the preceding claims, wherein the mechanical resonance frequency of the optomechanical cavity is between 1-4 MHz. 12. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij de vezel een single-mode optische vezel is.12. The optomechanical pressure measurement system according to any one of the preceding claims, wherein the fiber is a single-mode optical fiber. 13. Het optomechanisch drukmeetsysteem volgens één of meer van de voorgaande conclusies, waarbij het lichtdetectie element een lichtdetector en een detectie-eenheid omvat, waarbij de detectie-eenheid is ingericht om de omgevingsdruk bij het tweede membraan element te bepalen op basis van een verandering van de oscillatieamplitude van de gereflecteerde tweede lichtbundel als een functie van tijd of modulatiefrequentie, zoals gedetecteerd door de lichtdetector.13. The optomechanical pressure measurement system according to any one or more of the preceding claims, wherein the light detection element comprises a light detector and a detection unit, the detection unit being adapted to determine the ambient pressure at the second membrane element based on a change in the oscillation amplitude of the reflected second light beam as a function of time or modulation frequency, as detected by the light detector.
NL2036028A 2023-10-13 2023-10-13 An optomechanical pressure-measurement system as well as a method for determining an ambient pressure level using such optomechanical pressure-measurement system. NL2036028B1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120096956A1 (en) * 2009-05-01 2012-04-26 The University Of Western Ontario Photonic crystal pressure sensor
US20140043614A1 (en) * 2012-06-28 2014-02-13 Technion Research And Development Foundation Ltd. On-fiber optomechanical cavity based sensor
US20200141805A1 (en) * 2018-11-06 2020-05-07 Commissariat A L'energie Atomique Et Aux Energies Alternatives Measuring device based on an optical measurement in an opto-mechanical cavity

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120096956A1 (en) * 2009-05-01 2012-04-26 The University Of Western Ontario Photonic crystal pressure sensor
US20140043614A1 (en) * 2012-06-28 2014-02-13 Technion Research And Development Foundation Ltd. On-fiber optomechanical cavity based sensor
US20200141805A1 (en) * 2018-11-06 2020-05-07 Commissariat A L'energie Atomique Et Aux Energies Alternatives Measuring device based on an optical measurement in an opto-mechanical cavity

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