WO2001001090A1 - Interferometre de fabry-perot a fibre optique mono-mode - Google Patents

Interferometre de fabry-perot a fibre optique mono-mode Download PDF

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Publication number
WO2001001090A1
WO2001001090A1 PCT/GB2000/002495 GB0002495W WO0101090A1 WO 2001001090 A1 WO2001001090 A1 WO 2001001090A1 GB 0002495 W GB0002495 W GB 0002495W WO 0101090 A1 WO0101090 A1 WO 0101090A1
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WO
WIPO (PCT)
Prior art keywords
interferometer
fibre
polymer film
optical
single mode
Prior art date
Application number
PCT/GB2000/002495
Other languages
English (en)
Inventor
Timothy Noel Mills
Paul Beard
Original Assignee
University College London
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University College London filed Critical University College London
Priority to AU55564/00A priority Critical patent/AU5556400A/en
Publication of WO2001001090A1 publication Critical patent/WO2001001090A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
    • G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02023—Indirect probing of object, e.g. via influence on cavity or fibre
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/25—Fabry-Perot in interferometer, e.g. etalon, cavity

Definitions

  • This invention relates to optical fibre interferometers, particularly, but not exclusively, for use in a hydrophone for detecting pressure variations caused by the propagation of acoustic waves.
  • a known optical fibre hydrophone using an interferometer is described in the article "Miniature optical fibre ultrasonic hydrophone using a Fabry-Perot polymer film interferometer" by P C Beard and T N Mills published in Electronics Letters 24 April 1997, Volume 33 No. 9.
  • This article describes an interferometer arrangement in which a polymer sensing film is provided at a cleaved end of the fibre, two opposite faces of the polymer film providing the two reflecting surfaces of the interferometer. An incident acoustic wave modulates the thickness of the film which influences the output of the interferometer.
  • the hydrophone uses a multi-mode fibre, which does not require high alignment tolerances. However, mode coupling within a multi-mode fibre gives rise to non-uniform fibre characteristics and thereby degrades the performance of the sensing device.
  • Optical fibre hydrophones of this type may be used for monitoring any source of acoustic signals or characterising acoustic signals propagating within a sample of interest.
  • the hydrophone may be used to monitor, analyse or tune the operation of an ultrasonic cleaning system.
  • hydrophones may be used for analysing acoustic signals used to study biological tissue in medical examination equipment.
  • thermal signals may modulate the optical thickness of the sensing film and can therefore be detected by the hydrophone.
  • an optical fibre interferometer for sensing an incident wave comprising an optical fibre and a polymer film against one end of the fibre, two opposite faces of the polymer film providing reflecting surfaces of the interferometer, the optical thickness of the film being modulated by the incident wave, and wherein the optical fibre comprises a single mode fibre.
  • the use of a single mode fibre improves the stability of the interferometer, and enables the interferometer to have a small active area (corresponding to the mode field diameter of the fibre), preferably of width less than 15 ⁇ m, and preferably around 10 ⁇ m. This enables the interferometer to detect input signals of a wide range of wavelengths at non-normal angles of incidence. In particular, omnidirectional response can be achieved at high frequencies, for example to detect oblique signals having wavelengths as small as 20 ⁇ m.
  • the output of a single mode fibre has a power distribution which may be approximated as a Gaussian beam, and propagates with a diffraction-limited profile. Consequently, the output from the single mode fibre close to the fibre tip has a limited divergence profile.
  • the diffraction-limited divergence of the output profile enables high finesse operation to be achieved.
  • the face of the polymer film against the fibre may be associated with a coating giving rise to a reflectivity of between 70% and 95 %
  • the other face of the polymer film may be associated with a coating giving rise to a reflectivity of approximately 100% .
  • the coatings may be provided on the respective faces of the polymer film and may comprise dielectric coatings.
  • the interferometer is preferably used as a hydrophone for detecting incident acoustic waves.
  • Such acoustic waves may be used in numerous applications. Taking as one example the use of ultrasound in medical ultrasound equipment, the signals may typically have frequencies between 0.5 and 50 MHz. The corresponding wavelengths of acoustic signals in fresh water are 2.8mm and 28 ⁇ m (taking the speed of sound in fresh water to be 1410m/s).
  • the interferometer of the invention can be arranged to detect these signals for all angles of incidence.
  • Figure 1 shows an interferometer of the invention and represents the use of the interferometer in medical ultrasound equipment by way of example
  • Figure 2 shows the diffraction-limited propagation of an optical beam having a Gaussian distribution
  • Figure 3 illustrates some preferred dimensions for the components of the interferometer of Figure 1.
  • Optical fibre interferometers are well-known for measuring physical parameters. This invention is particularly directed to a measurement device operating according to the principles of a Fabry-Perot interferometer. Such a device may be used to study signals generated from any ultrasound source, and for any purpose, but Figure 1 illustrates medical ultrasound equipment by way of example.
  • the equipment comprises an excitation source 2 which produces a signal which is modified by a sample 4 to produce a signal 6 representing a physical parameter of the sample 4, the signal 6 being detectable by the interferometer device 8.
  • the interferometer comprises an optical fibre having a cleaved and polished end face 12. Butted against the end face 12 is a polymer film 14 having opposite parallel faces 16, 18 which are least partially reflective to incident light from a given direction (from left to right in Figure 1) .
  • the face 16 is partially reflective so that some of the interrogation source signal is able to penetrate into the polymer film 14, and the face 18 may be 100% reflective.
  • An optical signal 20 is supplied to the optical fibre 10 by a light source and detector assembly 22.
  • Light is reflected from the two faces 16, 18.
  • the signal 6 modulates the thickness of the film 14 and hence the optical phase difference between the light reflected from the two faces 16, 18. This produces a corresponding intensity modulation of the light reflected from the film 14.
  • the interferometer should be operated at a phase bias that corresponds to quadrature. In other words, the phase bias is set half way between the maximum and the minimum of the interferometer transfer function.
  • the signal 6 may comprise an acoustic wave, which carries information to be monitored.
  • the characteristics of the acoustic wave may give information concerning a biological sample being examined.
  • the presence of the acoustic signal may be used to indicate that the ultrasound cleaning system is operating correctly.
  • the excitation source 2 may comprise an ultrasound source for imaging or treatment, and the interferometer may then be provided for taking safety-related exposure measurements.
  • the excitation source may comprise a source of laser excitation pulses which are absorbed in a target absorber, resulting in the production of acoustic and thermal waves. These waves may be detected by the sensor as a result of a change to the optical thickness of the film, and therefore the optical phase difference between the reflected signals.
  • the optical fibre 10 comprises a single mode fibre. This enables the interferometer to have a small active area. Furthermore, the provision of the film 14 butted against the end of the fibre enables the low divergence close to the exit of the single mode fibre to be utilized to form a high finesse device. The widespread availability and low cost of the components required to form the interferometer enable it to be disposable, whilst having high performance.
  • Figure 2 shows the diffraction-limited propagation of a Gaussian beam.
  • the shaded area in Figure 2 represents the area within which the power density profile ranges from 1/e 2 to 1 times the peak power density.
  • the radius r 0 is the radius at which the power density distribution is 1/e 2 times the peak. This radius is approximately equal to the radius of the core 1 1 of the single mode fibre, since part of the energy of the beam propagates in the cladding of the fibre.
  • the Gaussian profile is representative of the output power distribution of the fundamental transverse mode of oscillation of a cylindrical laser source and of the single mode carried by the single mode fibre.
  • the envelope 30 of the optical output diverges at a uniform rate from a point 32 at the centre of the fibre output.
  • the rate of divergence is a function of the light wavelength ⁇ as well as the radius r 0 .
  • the outer envelope 34 maintains a substantially constant size so that limited divergence takes place.
  • the active area of the interferometer corresponds to the mode field diameter, which is the diameter of the shaded area in Figure 2.
  • the active area is of less significance and the measuring device will be responsive to the input signal 6 provided the detector assembly 22 has sufficient frequency response.
  • the interferometer will integrate the input signal over the active area of the measuring device. Therefore, for detection of input signal 6 oblique to the faces 16, 18, the active area of the measuring device must extend over a distance which is small in relation to the wavelength of the signal 6 to be measured.
  • the measurement signal 6 comprises an acoustic wave of frequency up to around 50MHz.
  • the device will be positioned within an area of interest of a patient's body and for the purposes of illustration, we shall assume that the acoustic wave travels with the speed of sound in pure water, which is 1410m/s. At 50MHz, this corresponds to a wavelength of 28.2 ⁇ m.
  • the polymer film 14 may have a thickness of approximately 10 ⁇ m, which is less than the distance 1 0 within which the divergence of the beam from the output of the fibre remains limited. A high finesse device can thus be formed.
  • low absorption coatings on the opposite faces of the polymer film 14 are required.
  • dielectric coatings may be used.
  • the coating on the face 16 may have reflectivity approaching (but not exceeding) 100% , for example 95 % , whereas the coating on the face 18 is preferably arranged to be as close to 100% reflective as possible (for the optical signal 20).
  • the core 36 of the optical fibre 10 has an approximate diameter of 6 ⁇ m, the core being surrounded with an appropriate depth of cladding 38, for example having an outside diameter of 125 ⁇ m, and an outer buffer giving a total outside diameter of 250 ⁇ m.
  • the small active area of the interferometer also facilitates the production of a polymer film 14 having extremely parallel and uniform faces 16, 18 over the area of interest.
  • the sensing film may comprise a disc of PET (polyethylene terepthalate) . Such discs may be cut from a larger film, and the smaller the required area the more uniform will be the film thickness.
  • An additional advantage of the use of a single mode fibre is that mode crossings may be avoided and that the power distribution within the fibre is more uniform.
  • the light source may comprise a tunable laser diode, which may produce light of around 850nm.
  • the detector assembly within unit 22 may comprise a photodiode having an integral transimpedance amplifier.
  • the laser source may be tuned to obtain quadrature operation of the interferometer.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

La présente invention concerne un interféromètre à fibre optique permettant de détecter une onde incidente et comprenant une fibre optique (10) et un film polymère (14) appliqué à l'une des extrémités (12) de la fibre. Les deux faces opposées (16, 18) du film polymère constituent les surfaces de réflexion de l'interféromètre, l'épaisseur optique du film étant modulée par l'onde incidente (6). La fibre optique (10) comprend une fibre mono-mode. Présentant une bonne stabilité pour une petite surface active, le dispositif permet une réponse omnidirectionnelle, même à hautes fréquences.
PCT/GB2000/002495 1999-06-28 2000-06-23 Interferometre de fabry-perot a fibre optique mono-mode WO2001001090A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU55564/00A AU5556400A (en) 1999-06-28 2000-06-23 Fabry perot single mode fibre interferometer

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9915081.5 1999-06-28
GBGB9915081.5A GB9915081D0 (en) 1999-06-28 1999-06-28 Optical fibre interferometer

Publications (1)

Publication Number Publication Date
WO2001001090A1 true WO2001001090A1 (fr) 2001-01-04

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PCT/GB2000/002495 WO2001001090A1 (fr) 1999-06-28 2000-06-23 Interferometre de fabry-perot a fibre optique mono-mode

Country Status (3)

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AU (1) AU5556400A (fr)
GB (1) GB9915081D0 (fr)
WO (1) WO2001001090A1 (fr)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6810062B2 (en) 2001-04-11 2004-10-26 Axsun Technologies, Inc. Passive optical resonator with mirror structure suppressing higher order transverse spatial modes
WO2005010511A1 (fr) * 2003-07-24 2005-02-03 Corning Incorporated Interferometre a reseau de fibres permettant d'inspecter des feuilles de verre
DE102006002605A1 (de) 2006-01-13 2008-07-24 Technische Universität Berlin Optisches Modul mit einer Lichtleitfaser und einer Fabry-Perot Schichtstruktur als elektrooptischer Modulator und abstimmbares Filter
CN110017890A (zh) * 2019-05-14 2019-07-16 广西师范大学 一种提高边沿滤波法线性解调区域的方法
CN110044468A (zh) * 2019-05-15 2019-07-23 重庆大学 一种用于球形聚焦集声器声场测量的光纤Fabry-Perot水听器系统
CN110044467A (zh) * 2019-05-15 2019-07-23 重庆大学 测量球形聚焦集声器声场的光纤Fabry-Perot水听器径向耦合系统
CN110186548A (zh) * 2019-05-13 2019-08-30 天津大学 基于光纤微结构膜片的光纤f-p声传感器及其制作方法
WO2019183137A1 (fr) * 2018-03-23 2019-09-26 Digonnet Michel J F Capteur acoustique à fibre basé sur une membrane
WO2019239148A1 (fr) 2018-06-15 2019-12-19 Ucl Business Plc Sonde d'imagerie à ultrasons

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5311485A (en) * 1992-10-30 1994-05-10 The United States Of America As Represented By The United States Department Of Energy Fiber optic hydrophone
DE19541952A1 (de) * 1995-11-10 1997-05-15 Christian Dr Koch Faseroptisches Hydrophon

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5311485A (en) * 1992-10-30 1994-05-10 The United States Of America As Represented By The United States Department Of Energy Fiber optic hydrophone
DE19541952A1 (de) * 1995-11-10 1997-05-15 Christian Dr Koch Faseroptisches Hydrophon

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CH.KOCH: "Coated fiber optic hydrophone for ultrasonic measurement", ULTRASONICS, vol. 34, 1 June 1996 (1996-06-01), pages 687 - 689, XP000627319 *
P.C.BEARD AND T.N.MILLS: "Miniature optical fibre ultrasonic hydrophone using a Fabry Perot polymer film interferometer", ELECTRONICS LETTERS, vol. 33, no. 9, 24 April 1997 (1997-04-24), pages 801 - 803, XP000695342 *
V.WILKENS AND CH.KOCH: "Fiber optic multilayer hydrophone for ultrasonic measurement", ULTRASONICS, vol. 37, 1 January 1999 (1999-01-01), pages 45 - 49, XP004154492 *

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7327772B2 (en) 2001-04-11 2008-02-05 Axsun Technologies, Inc. Optical resonator with mirror structure suppressing higher order transverse modes
US6810062B2 (en) 2001-04-11 2004-10-26 Axsun Technologies, Inc. Passive optical resonator with mirror structure suppressing higher order transverse spatial modes
WO2005010511A1 (fr) * 2003-07-24 2005-02-03 Corning Incorporated Interferometre a reseau de fibres permettant d'inspecter des feuilles de verre
DE102006002605A1 (de) 2006-01-13 2008-07-24 Technische Universität Berlin Optisches Modul mit einer Lichtleitfaser und einer Fabry-Perot Schichtstruktur als elektrooptischer Modulator und abstimmbares Filter
WO2019183137A1 (fr) * 2018-03-23 2019-09-26 Digonnet Michel J F Capteur acoustique à fibre basé sur une membrane
US11629979B2 (en) 2018-03-23 2023-04-18 The Board Of Trustees Of The Leland Stanford Junior University Diaphragm-based fiber acoustic sensor
US11215481B2 (en) 2018-03-23 2022-01-04 The Board Of Trustees Of The Leland Stanford Junior University Diaphragm-based fiber acoustic sensor
WO2019239148A1 (fr) 2018-06-15 2019-12-19 Ucl Business Plc Sonde d'imagerie à ultrasons
CN110186548A (zh) * 2019-05-13 2019-08-30 天津大学 基于光纤微结构膜片的光纤f-p声传感器及其制作方法
CN110017890A (zh) * 2019-05-14 2019-07-16 广西师范大学 一种提高边沿滤波法线性解调区域的方法
CN110044467A (zh) * 2019-05-15 2019-07-23 重庆大学 测量球形聚焦集声器声场的光纤Fabry-Perot水听器径向耦合系统
CN110044467B (zh) * 2019-05-15 2021-09-28 重庆大学 测量球形聚焦集声器声场的光纤Fabry-Perot水听器径向耦合系统
CN110044468A (zh) * 2019-05-15 2019-07-23 重庆大学 一种用于球形聚焦集声器声场测量的光纤Fabry-Perot水听器系统

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Publication number Publication date
AU5556400A (en) 2001-01-31
GB9915081D0 (en) 1999-08-25

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