KR100319537B1 - Fiber optic temperature sensor using evanescent field coupling of the thermo-optic polymer planar waveguide - Google Patents
Fiber optic temperature sensor using evanescent field coupling of the thermo-optic polymer planar waveguide Download PDFInfo
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- 229920000642 polymer Polymers 0.000 title claims abstract description 14
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- 238000010168 coupling process Methods 0.000 title claims abstract description 12
- 238000005859 coupling reaction Methods 0.000 title claims abstract description 12
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- 239000013307 optical fiber Substances 0.000 claims abstract description 68
- 238000005253 cladding Methods 0.000 claims abstract description 26
- 230000010287 polarization Effects 0.000 claims abstract description 21
- 230000003287 optical effect Effects 0.000 claims abstract description 18
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- 238000000034 method Methods 0.000 claims abstract description 14
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052814 silicon oxide Inorganic materials 0.000 claims abstract description 7
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- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/3206—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres at discrete locations in the fibre, e.g. using Bragg scattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
Abstract
본 발명은 측면연마된 광섬유와 열광학 평면도파로 결합기를 이용하여 새로운 형태의 온도센서의 개발에 관한 것이다. 또한 온도의 검출시 센서의 감도를 향상시키고 조절하는 방법과 편광의존성이 없는 센서의 구조를 제공함에 그 특징이 있다.The present invention relates to the development of a new type of temperature sensor using a side polished optical fiber and a thermo-optic planar waveguide coupler. In addition, there is a feature that provides a method of improving and adjusting the sensitivity of the sensor when detecting the temperature and the structure of the sensor without polarization dependency.
측면 연마된 광섬유와 열광학 폴리머 평면도파로을 결합기는 광결합시 파장영역의 여과특성이 나타나고 온도가 변화함에 따라 열광학 평면도파로의 굴절률이 변하게 되어 공진파장이 이동하므로 이를 이용한 온도의 변화를 감지한다.The combiner of the side polished optical fiber and the thermo-optic polymer planar waveguide exhibits the filtration characteristics of the wavelength region during optical coupling and the refractive index of the thermo-optic planar wave changes as the temperature changes.
본 발명은 평면도파로의 상부클래딩의 굴절률을 광섬유의 클래딩의 굴절률(1.440)과 같은 산화실리콘(SiO2)층을 올리므로 편광의존성이 없는 우수한 감도를 가진 온도센서를 구현하고, 열광학 폴리머의 재질에 따라 온도감지 범위와 분해능을 달리하는 광섬유형 온도센서를 제공함에 목적이 있다.According to the present invention, since the refractive index of the upper cladding of the planar waveguide is raised to the silicon oxide (SiO 2 ) layer equal to the refractive index of the cladding of the optical fiber (1.440), a temperature sensor having excellent sensitivity without polarization dependency is realized and the material of the thermo-optic polymer. It is an object of the present invention to provide an optical fiber type temperature sensor that varies the temperature detection range and resolution.
Description
본 발명의 온도의 변화를 열광학 폴리머의 열광학계수의 변화에 의해 감지하고 이러한 재료적인 변화를 광학적인 방법으로 감지함에 목적이 있다. 이러한 효과는 열광학 폴리머의 재질에 따라 온도감지 범위와 분해능을 달리할 수 있고 또한 편광의존성을 구조적으로 해결함으로써 기존의 광섬유형 온도센서보다 더욱 유동적으로 사용할 수 있다.The purpose of the present invention is to sense the change in temperature by the change of the thermo-optic coefficient of the thermo-optic polymer and to detect this material change by an optical method. This effect can vary the temperature detection range and resolution depending on the material of the thermo-optic polymer, and can be used more flexibly than the conventional optical fiber type temperature sensor by structurally solving the polarization dependence.
종래기술은 온도센서에는 써미스터, 열전대, 초전형, 내장형(P-N접합형), 광섬유형이 있으며, 최근에는 기계적 안정성, 고감도, 원거리 측정, 전자기파의 영향에 무관 등의 장점으로 광섬유형 온도센서가 많이 연구되고 있다. 현재 많이 알려진 광섬유형 온도센서의 종류와 그 특성은 다음과 같다.Conventional technologies include thermistors, thermocouples, pyroelectrics, built-in (PN junction type), and optical fiber types in the temperature sensor, and recently, many optical fiber type temperature sensors have advantages such as mechanical stability, high sensitivity, long distance measurement, and independent of the influence of electromagnetic waves. Is being studied. The types and characteristics of optical fiber type temperature sensors that are known at present are as follows.
(1) FBG(Fiber Bragg Grating)형 온도센서(1) Fiber Bragg Grating (FBG) type temperature sensor
FBG형 온도센서는 높은 감도를 지니고 소형이며 제작하기가 용이하다는 장점 때문에 널리 사용된다. 하지만 온도의 물리량은 브래그 파장의 변화를 가지고 측정하게 되는데 일반적으로 온도에 따른 파장의 변화가 매우 작아 분해능이 떨어진다. 이러한 문제를 해결하기 위하여 간섭계를 이용한 센서시스템과 금속클래드를 이용한 방법이 제안되었다. 하지만 간섭계는 안정화 하기가 매우 힘들며 금속 클래드를 이용한 방법은 온도감도가 고정되는 단점이 있다.FBG type temperature sensors are widely used because of their high sensitivity, compactness and ease of manufacture. However, the physical quantity of temperature is measured with the change of Bragg wavelength. In general, the resolution of the wavelength is very small due to the change of wavelength. In order to solve this problem, a sensor system using an interferometer and a method using a metal clad have been proposed. However, the interferometer is very difficult to stabilize, and the method using the metal clad has the disadvantage that the temperature sensitivity is fixed.
(2) LPG(Long Period Grating)형 온도센서(2) Long Period Grating (LPG) type temperature sensor
일반적으로 LPG는 투과 스펙트럼이 매우 넓기 때문에 그것을 스캔하여 중심파장을 알아 내는데 긴시간이 소비되는데 이로 인하여 정적과 준 동적측정은 가능하나 빠른 동적 측정은 불가능하다. 또한 LPG의 브래그 파장을 찾기 위한 부가적인 소자도 필요하다.In general, LPG has a very large transmission spectrum, and therefore, it takes a long time to scan the center wavelength by scanning it, so that static and quasi-dynamic measurements are possible, but fast dynamic measurement is not possible. There is also a need for additional devices to find the Bragg wavelength of LPG.
(3) FBG/LPG 혼합센서(3) FBG / LPG mixed sensor
FBG/LPG 혼합센서는 스펙트럼 면에서 두 FBG의 브래그 파장 가운데 LPG의 브래그 파장이 있는 형태로 되어 있다. 이 센서에서는 FBG와 LPG가 서로 다른 온도에 대해 측정한다. 그러나 정확도를 높이기 위해서는 LPG의 스펙트럼이 아주 정밀하여 거의 완벽해야 하며 2개의 FBG와 LPG의 위치 조정이 용이하지 않다. 그리고 LPG는 온도에 의한 브래그 파장의 변화가 심한데 이로 인하여 이 센서의 온도측정 범위가 매우 좁다.The FBG / LPG mixed sensor has a spectral aspect in which the Bragg wavelength of LPG is among the Bragg wavelengths of two FBGs. In this sensor, the FBG and LPG are measured for different temperatures. However, to increase accuracy, the spectrum of the LPG must be very precise and nearly perfect, and the positioning of the two FBGs and LPGs is not easy. And LPG has a big change in Bragg wavelength due to temperature, which makes the temperature measurement range of this sensor very narrow.
기존의 온도센서는 구조적인 측면과 측정방법에서 온도감지의 한계를 지니고 있다. 또한 Grating을 사용할 경우 편광의존성을 갖게 된다. 본 발명에서는 이러한 점을 인지하여 물질의 열광학계수 변화에 따라 온도를 감지하고 편광의존성, 센서의 분해능과 감도를 센서의 구조적인 측면에서 고려하여 개선하였다. 측면연마된 광섬유와 열광학 폴리머 평면도파로 결합기의 구조에서 평면도파로와 광섬유사이의 광결합특성은 파장영역에서 여과특성으로 나타나고 형성되고 온도가 가해지면 열광학 평면도파도의 굴절률이 변하게 되어 공진파장이 이동하게 된다. 이때 공진파장의 이동은 열광학 평면도파로의 열광학계수에 따라 변화시킬 수 있고 이는 센서의 분해능과 관계가 있다. 또한 평면도파로의 상부클래딩의 굴절률을 광섬유의 클래딩의 굴절률(1.440)과 같은 산화실리콘(SiO2)을 사용하면 평면도파로와 광섬유 사이가 대칭적인 구조를 이루므로 편광의존성이 없어지게 된다. 따라서, 본 발명에서는 열광학 폴리머의 종류와 소자구조에 따라 센서의 특성을 제어하는 온도센서를 제안한다.Conventional temperature sensors have limitations in temperature sensing in terms of structure and measurement methods. In addition, when using grating, polarization dependence is obtained. In the present invention, by recognizing this point, the temperature is sensed according to the change of the thermo-optic coefficient of the material, and the polarization dependence, the resolution and sensitivity of the sensor are improved in consideration of the structural aspects of the sensor. The optical coupling characteristics between the planar waveguide and the optical fiber in the structure of the side-polished optical fiber and the thermo-optic polymer planar wave coupler are shown as filtration characteristics in the wavelength region, and when the temperature is applied, the refractive index of the thermo-optic planar wave changes and the resonance wavelength is shifted. Done. At this time, the shift of the resonant wavelength can be changed according to the thermo-optic coefficient of the thermo-optic planar wave, which is related to the resolution of the sensor. In addition, when the silicon oxide (SiO 2 ) such as the refractive index of the cladding of the optical fiber is used as the refractive index of the cladding of the optical fiber (1.440), the polarization dependency is eliminated because the planar wave and the optical fiber have a symmetrical structure. Accordingly, the present invention proposes a temperature sensor for controlling the characteristics of the sensor according to the type and device structure of the thermo-optic polymer.
도 1 : 측면 연마된 광섬유와 영광학 평면도파로의 결합구조를 이용한 온도센서1: Temperature sensor using a combination of side polished optical fiber and Glory plane waveguide
도 2 : 온도센서의 파장응답 특성2: Wavelength response characteristic of temperature sensor
도 3 : 소자의 제작공정3: Fabrication Process
도 4 : 평면도파로 상부클래딩의 굴절률에 따른 편광의존성4: Polarization dependence according to the refractive index of the top cladding of the planar waveguide
(가) 금(n2=0.4+j8.25) (나) 물(n2=1.33) (다) 산화실리콘(n2=1.440)(A) Gold (n 2 = 0.4 + j8.25) (b) Water (n 2 = 1.33) (c) Silicon oxide (n 2 = 1.440)
도 5 : 센서의 파장응답 특성5: Wavelength response characteristics of the sensor
(가) 평면도파로 : AZ4562 (나) 평면도파로 : THB-30(A) Floor plan wave: AZ4562 (b) Floor plan wave: THB-30
도 6 : 1.3㎛파장 영역에서의 온도에 따른 광세기 변화6: Light intensity change with temperature in 1.3㎛ wavelength region
도 1과 같이 측면이 코어 가까이 연마된 단일모드 광섬유와 다중모드를 가지는 평면도파로의 소산장 결합(evanescent field coupling)이 형성되면 두 광경로 사이에 광에너지 교환이 발생할 수 있다. 평면도파로는 여러 모드를 가질 수 있으며 이중에 광섬유 모드와 위상정합(phase matching) 조건을 만족하는 모드가 효과적인 광 결합을 일으킨다. 평면도파로의 코어층과 클래딩의 굴절률 차이를 크게 하면 매우 높은 분산특성을 가지게 된다. 여기서 분산특성이란 평면도파로의 유효굴절률이 파장에 따라 크게 달라지는 현상을 의미한다. 따라서 광섬유와 평면도파로의 유효굴절률은 특정한 파장과 모드에서 일치하게 되며 이때 광섬유로부터 입사된 광전력은 평면도파로로 이동하게 된다. 여기서 위상정합을 만족하는 광의 파장은 공진파장으로 정의된다. 단일모드 광섬유의 코어층과 클래딩층의 굴절률 차이는 0.01∼0.001 정도로서 매우 작으며 이것의 유효굴절률은 클래딩층보다 크고 코어보다 작은 범위 안에 있다. 따라서 광섬유의 파장에 대한 유효굴절률의 변화는 매우 미약하다. 이때 두 광경로 사이에 위상정합이 존재하기 위해서는 평면도파로의 상부클래딩 물질은 광섬유 클래딩 물질의 굴절률보다 같거나 작아야 한다. 다중모드를 가지는 평면도파로의 m번째 모드의 유효굴절률을 찾기 위한 고유치 방정식은 다음과 같다.As shown in FIG. 1, when an evanescent field coupling is formed between a single mode optical fiber polished near a core and a planar waveguide having a multimode, optical energy exchange may occur between two optical paths. The planar wave can have several modes, of which the fiber mode and the mode satisfying the phase matching conditions result in effective optical coupling. When the refractive index difference between the core layer and the cladding of the planar waveguide is increased, the dispersion characteristics are very high. Here, the dispersion characteristic means a phenomenon in which the effective refractive index of the planar waveguide varies greatly depending on the wavelength. Therefore, the effective refractive indices of the optical fiber and the planar waveguide coincide in a specific wavelength and mode, and the optical power incident from the optical fiber is moved to the planar waveguide. The wavelength of the light satisfying the phase match is defined as the resonance wavelength. The refractive index difference between the core layer and the cladding layer of the single mode optical fiber is very small, about 0.01 to 0.001, and its effective refractive index is in the range larger than the cladding layer and smaller than the core. Therefore, the change of effective refractive index with respect to the wavelength of the optical fiber is very small. In this case, in order for phase matching to exist between the two optical paths, the upper cladding material of the planar waveguide must be equal to or smaller than the refractive index of the optical fiber cladding material. The eigenvalue equation for finding the effective refractive index of the mth mode of a planar wave with multiple modes is as follows.
여기서 m은 모드의 차수를 나타내는 정수, λ는 광의 파장, d는 평면도파로의 코어층 두께, no는 평면도파로의 코어 굴절률 그리고 neo는 m번째 고차모드의 유효 굴절률이다. 1과 2는 평면도파로의 코어층과 클래딩층의 경계에서 발생하는 위상천이로서 다음과 같이 주어진다.Where m is an integer representing the order of the mode, λ is the wavelength of light, d is the core layer thickness of the planar waveguide, n o is the core refractive index of the planar waveguide, and n eo is the effective refractive index of the mth higher order mode. 1 lesson 2 is a phase shift occurring at the boundary between the core layer and the cladding layer of the planar waveguide.
여기서 TE편광 대해선=1, TM편광에 대해선=n0 2/n2 2을 대입하면 된다. n1은 광섬유의 클래딩층의 굴절률인 동시에 평면도파로의 하부클래딩층의 굴절률이다. n2는 평면도파로의 상부클래딩층의 굴절률이다. 평면도파로의 최고차 모드가 가장 작은 유효굴절률(neo)을 가지기 때문에 광섬유의 유효굴절률(nef)과 가장 근접하게 된다. 식(1)에서 i가 편광에 따라서 다른 값을 가지므로 유효굴절률이 편광에 따라 다소 차이가 발생할 수 있다. 광섬유형 온도센서의 특성으로 편광상태에 의존하지 않는 성질이 필요하다. 만일 광섬유형 온도센서 소자가 편광상태에 의존하는 특성을 가지면, 편광을 제어하는 소자가 추가로 필요해지기 때문이다. 따라서, 광섬유형 온도센서 소자의 편광의존성을 줄이는 방법으로 i의 절대치를 최소화시키는 기법이 유용하다. 이를 위하여 평면도파로의 상부클래딩 물질로 광섬유의 클래딩과 같은 물질을 사용하는 방법이 이용될 수 있다. 위상정합시 neo=nef를 만족하고, 광섬유의 코어와 클래딩 간의 굴절률 차이가 작기 때문에 nef ni를 식(2)에 대입하면 평면도파로의 상하부의 계면에서 발생하는 위상천이는 매우 작아진다. 그리고 모드의 차수(m)가 높을수록 i가 식(1)에서 상대적으로 작아지기 때문에 편광에 따른 중심파장의 차이가 줄어든다. 평면도파로가 대칭적 구조일 때 정성적 해석을 위해 식(1)에서 오른쪽항의i를 무시하여 아래와 같은 간단한 식을 유도하였다.TE polarized light here = 1 for TM polarization = n 0 2 / n 2 2 n 1 is the refractive index of the cladding layer of the optical fiber and the refractive index of the lower cladding layer of the planar waveguide. n 2 is the refractive index of the upper cladding layer of the planar waveguide. Since the highest order mode of the planar waveguide has the smallest effective refractive index n eo , it is closest to the effective refractive index n ef of the optical fiber. In equation (1) Since i has different values depending on the polarization, the effective refractive index may slightly vary depending on the polarization. As a characteristic of optical fiber type temperature sensor, it is necessary to have a property that does not depend on polarization state. If the optical fiber type temperature sensor element has a characteristic that depends on the polarization state, it is necessary to additionally need an element for controlling the polarization. Therefore, as a method of reducing the polarization dependence of the optical fiber type temperature sensor element Techniques to minimize the absolute value of i are useful. To this end, a method using a material such as cladding of an optical fiber as the upper cladding material of the planar waveguide may be used. Satisfy the phase match when n eo = n ef, and because of the small difference between the refractive index of the optical fiber core and the cladding n ef Substituting n i into equation (2), the phase shift occurring at the interface of the upper and lower parts of the planar wave becomes very small. And the higher the order (m) of the mode Since i becomes relatively small in equation (1), the difference in the center wavelength due to polarization is reduced. For qualitative analysis when the planar waveguide is symmetrical, the right term in Eq. (1) Ignoring i led to the following simple equation:
여기서 λ0는 평면도파로의 m차 모드와 광섬유 모드의 사이의 위상정합을 만족하는 파장이다. 공진파장은 식(3)으로부터 평면도파로의 두께(d)와 굴절률(n0)에 의해 결정된다. 그리고 광섬유의 유효굴절률(nef)은 광섬유의 구조와 파장에 의해 계산될 수 있는 수치이다. 여기서 m은 λ0에서 가질 수 있는 모드의 차수 중에 최고차이다. 그 이유는 평면도파로의 모드중 최고차 모드의 유효굴절률이 광섬유의 유효굴절률과 가장 근접해 있기 때문이다.Λ 0 is a wavelength that satisfies the phase matching between the mth order mode of the planar waveguide and the optical fiber mode. The resonance wavelength is determined from equation (3) by the thickness d of the planar waveguide and the refractive index n 0 . The effective refractive index n ef of the optical fiber is a numerical value that can be calculated by the structure and the wavelength of the optical fiber. Where m is the highest order among the possible orders of mode in λ 0 . This is because the effective refractive index of the highest-order mode among the planar waveguide modes is closest to the effective refractive index of the optical fiber.
식(2)에서는 평면도파로의 상부층의 굴절률이 하부 클래드층의 굴절률 (n=1.4440)에 가까워 질수록 TE, TM편광의존성이 작아짐을 알 수가 있다. 식(3)에서는 공진파장 λ0는 평면도파로의 두께와 굴절률(n0)에 의해 결정되므로 열광학 효과가 우수한 폴리머를 평면도파로의 코어층으로 사용하면 주위온도에 의하여 굴절률이 바뀌며 이는 결국 공진파장이 이동하는 결과를 가져온다. 따라서 광섬유-평면도파로 결합기를 공진파장의 온도 의존성을 이용한 온도센서에 적용할 수 있다. (도2 참조)Equation (2) shows that the TE and TM polarization dependence becomes smaller as the refractive index of the upper layer of the planar waveguide approaches the refractive index (n = 1.4440) of the lower cladding layer. In Eq. (3), the resonant wavelength λ 0 is determined by the thickness of the planar waveguide and the refractive index (n 0 ). Therefore, when a polymer having excellent thermo-optic effect is used as the core layer of the planar waveguide, the refractive index is changed by ambient temperature. This will result in moving. Therefore, the optical fiber-plane waveguide coupler can be applied to the temperature sensor using the temperature dependence of the resonance wavelength. (See Fig. 2)
본 발명에서 사용한 광섬유 재원은 광통신용 표준 단일모드 광섬유이다. 평면도파로의 재료로 열광학 폴리머를 사용하였다. 폴리머는 단순한 스핀 코팅으로 도파로제작이 가능하고 스핀코팅(spin coating)시 회전속도로 두께를 제어할 수 있다. 이러한 장점 때문에 본 발명에서는 평면도파로의 재료로 폴리머를 이용하였다. 단일모드 광섬유를 연마하는 방법으로는 화학적 식각방법, 석영을 광섬유연마 지지대로 만들어 연마하는 방법등이 알려져 있다. 본 발명에서는 보다 정확한 곡률과 연마공정을 위하여 반도체 이방성식 각 공정을 통하여 광섬유 연마 지지대를 만들고 그 위에 광섬유를 경화제를 이용하여 고정시킨후 연마하는 방법을 사용하였다.The optical fiber source used in the present invention is a standard single mode optical fiber for optical communication. Thermo-optic polymer was used as the material for the planar waveguide. The polymer can be made waveguide by simple spin coating and the thickness can be controlled by the rotational speed during spin coating. For this reason, the present invention uses a polymer as a material for the planar waveguide. As a method of polishing a single mode optical fiber, a chemical etching method, a method of polishing a quartz made of an optical fiber polishing support is known. In the present invention, for the more accurate curvature and polishing process, the optical fiber polishing support is made through each semiconductor anisotropic process, and the optical fiber is fixed thereon with a curing agent and then polished.
본 발명에서는 측면 연마된 광섬유와 평면도파로를 독립적으로 제작하여 물리적 결합으로 광섬유-평면도파로 결합기를 제작하였다. 단순히 소자의 특성을 관측할 때는 측면 연마된 광섬유 위의 연마된 부위에만 주사기로 약간의 정합액을 떨어뜨리고 평면도파로를 물리적 압력으로 붙힌다. 정합액의 굴절률은 광섬유 클래딩과 일치하는 물질을 사용해야 한다. 정합액은 광섬유와 평면도파로 사이에 공기층이 발생하는 것을 막아주는 동시에 측면 연마된 광섬유 표면의 불완전한 연마로 인한 산란손실을 막아 주는 역할을 한다. 준비한 평면도파로를 광섬유 블록 위에 붇힌 후 압력을 가하여 광결합이 발생하는지 측정장치로 확인한다. 원하는 특성이 나오면 에폭시 접착제를 이용하여 광섬유 블록과 평면도파로를 접착시킨다. 광섬유-평면도파로 결합기를 이용한 온도센서의 제작공정은 도3과 같다.In the present invention, a side polished optical fiber and a planar waveguide are independently manufactured to form an optical fiber-plane waveguide coupler by physical coupling. When simply observing the characteristics of the device, a small drop of the matching liquid is applied with a syringe only to the polished area on the side polished optical fiber, and the planar wave is subjected to physical pressure. The refractive index of the matching solution should be made of materials consistent with the fiber cladding. The matching solution prevents the formation of an air layer between the optical fiber and the planar waveguide, while preventing scattering loss due to incomplete polishing of the side polished optical fiber surface. The prepared planar waveguide is squeezed onto the optical fiber block, and then pressurized to check if the optical coupling occurs. Once the desired properties are produced, the optical fiber blocks are bonded to the planar waveguide using epoxy adhesive. The manufacturing process of the temperature sensor using the optical fiber-plane waveguide coupler is shown in FIG. 3.
소자의 광경합시 광결합의 여과깊이를 제어하는 방법은 광섬유와 평면도파로 사이의 간격(결합 간격)으로 조절하였다. 이는 광섬유 모드와 평면도파로 모드의중첩정도에 따라서 여과깊이가 결정되기 때문이다. 측면 연마된 광섬유와 평면도파로가 완벽하게 결합되면 연마 후 남은 클래딩의 두께와 결합간격이 일치하게 된다. 연마후 남은 광섬유 클래드의 두께(g0)를 구하기 위하여 측면 연마된 광섬유 표면 위에 광섬유의 코어보다 큰 굴절률을 가지는 용액을 떨어뜨려 이때 발생하는 손실로부터 결합간격(g0)를 구하는 방법을 도입하였다.The method of controlling the filtration depth of the optical coupling during photo-competition of the device was controlled by the interval (coupling interval) between the optical fiber and the planar waveguide. This is because the depth of filtration is determined by the degree of overlap between the optical fiber mode and the planar waveguide mode. When the side polished optical fiber and the planar waveguide are perfectly combined, the thickness and bonding interval of the remaining cladding after polishing are matched. In order to determine the thickness g 0 of the remaining optical fiber clad, a solution having a refractive index greater than that of the core of the optical fiber was dropped on the surface of the side polished optical fiber to obtain a coupling gap g 0 from the loss.
도4와 같이 평면도파로의 상부 클래드층 굴절률(n=1.4440)이 하부 클래드층 굴절률(n=1.4440)과 같은 산화실리콘(SiO2)의 경우 복굴절을 가지는 금이나 물에 비해 월등히 편광의존성이 감소함을 실험을 통해 알 수 있었으며, 그 때의 TE, TM 편광된 공진파장의 차이는 2nm 이하였다. 그리고 삽입 손실은 0.5dB 이하로 관측되었다.As shown in FIG. 4, in the case of silicon oxide (SiO 2 ) having the upper cladding layer refractive index (n = 1.4440) of the planar waveguide having the lower cladding layer refractive index (n = 1.4440), the polarization dependence is significantly reduced compared to gold or water having birefringence. It can be seen through the experiment, the difference of the TE, TM polarized resonant wavelength at that time was less than 2nm. And insertion loss was observed below 0.5dB.
도5(가)는 AZ4562를 평면도파로의 물질로 사용하였을 때의 온도에 따른 파장응답 특성이다. 온도가 증가함에 따라 공진파장이 짧아지는 현상을 보이는데 이는 일반적으로 폴리머의 경우 열광학계수가 1차수 더 크기 때문에 온도가 올라감에 따라 굴절률이 감소하고 공진파장이 감소하는 현상으로 나타남을 알 수 있다. 온도에 따른 공진파장의 변화는 -0.54nm/℃의 변화를 보였다. 도5(나)는 THB-30을 평면도파로의 물질로 사용하였을 때의 온도에 따른 파장응답 특성이다. 이 때의 공진파장의 이동은 AZ4562보다 커짐을 알 수 있고 이는 물질에 따라 공진파장의 이동을 제어함을 알 수 있다. 또한 연마후 남은 클래딩의 두께를 적게하면 도5(나)와 같이 여과깊이가 깊어지면서 넓어지는데 이러한 경우 파장의 이동으로 온도를 감지할 수있을 뿐만 아니라 특정파장에서의 광세기 변화로도 측정이 가능하다.Fig. 5A is a wavelength response characteristic according to temperature when AZ4562 is used as the material of the planar waveguide. As the temperature increases, the resonant wavelength becomes shorter. In general, since the thermo-optic coefficient of polymer is larger by one order, the refractive index decreases and the resonant wavelength decreases as the temperature increases. The change of resonance wavelength with temperature showed -0.54nm / ℃. FIG. 5B shows wavelength response characteristics according to temperature when THB-30 is used as the material of the planar waveguide. In this case, it can be seen that the movement of the resonance wavelength is larger than that of AZ4562, which controls the movement of the resonance wavelength according to the material. In addition, if the thickness of the remaining cladding is reduced, the depth of filtration becomes wider and wider, as shown in Fig. 5 (b). In this case, not only the temperature can be detected by the shift of wavelength, but also the light intensity at a specific wavelength can be measured. Do.
도6은 도5(나)의 특성을 가지는 온도센서를 광통신파장인 1.3㎛ 단일파장에서 측정한 것이다. 이 때 온도에따른 분해능은 더욱 커지고 소자의 공정 조건과 측정 방법에 따라 센서의 분해능을 조절할 수 있다. 또한 단일 파장이 광통신 파장일 경우 센서의 원거리 모니터링이 가능하게 된다.FIG. 6 is a temperature sensor having the characteristics of FIG. 5 (b) measured at a single wavelength of 1.3 mu m, which is an optical communication wavelength. At this time, the resolution according to the temperature is further increased and the resolution of the sensor can be adjusted according to the process conditions and measurement methods of the device. In addition, remote monitoring of the sensor is possible when a single wavelength is an optical communication wavelength.
본 발명의 목적은 측면연마된 광섬유와 열광학 평면도파로 결합기를 이용하여 새로운 형태의 온도센서를 개발하고 평면도파로의 재질에 따라 온도감지 범위와 분해능을 달리하는 광섬유형 온도센서를 제공함에 있다. 또한 산화실리콘(SiO2)를 층을 사용하여 편광상태에 의존하지 않은 고감도의 광섬유형 온도센서를 구현하므로 편광을 제어하는 소자의 추가없이 간단하면서 소형의 고감도 광섬유형 온도센서를 구현할 수 있다.It is an object of the present invention to develop a new type of temperature sensor using a side polished optical fiber and a thermo-optic planar wave coupler, and to provide an optical fiber type temperature sensor having a different temperature sensing range and resolution depending on the material of the planar waveguide. In addition, by using a layer of silicon oxide (SiO 2 ) to implement a high-sensitivity optical fiber type temperature sensor that does not depend on the polarization state, it is possible to implement a simple and compact high-sensitivity optical fiber type temperature sensor without the addition of a device for controlling the polarization.
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| US5745231A (en) * | 1995-06-12 | 1998-04-28 | American Research Corporation Of Virginia | Method of fluorescence analysis comprising evanescent wave excitation and out-of-plane photodetection |
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| JPS6365413A (en) * | 1986-09-08 | 1988-03-24 | Sumitomo Electric Ind Ltd | Optical cable provided with bending mechanism |
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