KR102191682B1 - Sagnac interferometer having the nearly zero temperature sensitivity made by different birefringent optical fibers - Google Patents

Abstract

The Sanac interferometer with offset temperature sensitivity using heterogeneous birefringent optical fibers according to a preferred embodiment of the present invention comprises: a first optical fiber, and a first optical fiber that is bonded to the first optical fiber such that at least one optical axis is perpendicular to the optical axis of the first optical fiber. It includes 2 optical fibers, and each length of the first optical fiber and the second Guam Seongyu is set to offset temperature sensitivity.

Description

Sagnac interferometer having the nearly zero temperature sensitivity made by different birefringent optical fibers} using heterogeneous birefringent optical fibers

The present invention relates to a Sagnac interferometer made of heterogeneous birefringent optical fibers, and more particularly, to a Sagnac interferometer having a predetermined interference fringe spacing while the temperature sensitivity is canceled.

In general, the Sanac interferometer is configured such that two beams traveling in the same optical path in the opposite direction interfere.

The general structure of a conventional Sanak interferometer is an input port, an output port, an optical branching device made of an optical fiber coupler or a flat plate splitter, and a birefringence connected inside the Sanak loop. It consists of an optical waveguide (Birefringent fiber). The input optical waveguide, the output optical waveguide, the optical branching device, and the birefringent optical waveguide can be easily constructed using optical fibers.

Conventional sagnac interferometers are easy to downsize due to their simple structure, easy to change the free spectral range (FSR) in the light transmission spectrum, and can be used as an optical filter due to the high extinction ratio of the light transmission spectrum, and the light transmission characteristics are vibrated. It has various advantages such as high stability against the back and not affected by the polarization state of incident light.

In the case of a conventional fiber optic Sanac interferometer, despite various advantages, it has a light transmission characteristic that changes due to temperature, that is, it has a temperature sensitivity, so when you want to measure other physical quantities such as strain. It has a problem that must compensate for the amount of distortion caused by.

In order to solve this problem, by combining an additional optical element, that is, Fiber Bragg Grating (FBG), Long Period Grating (LPG), MZI, FP, or other Sagnac interferometer, to create a cross measurement structure, A method of measuring and analyzing an optical signal to which a physical quantity is applied and separating the temperature from it has been used.

However, in the case of this method, it is only a method of measuring the temperature by separating the temperature from other physical quantities applied to the optical signal by the cross-measurement technique, and the light transmission characteristics of the Sanac interferometer itself are changed by the temperature.

Recently, in the case of using the Sagnac interferometer as a signal analyzer (e.g., sweep source) that analyzes the characteristics of a sensor or a light source analyzer that measures the wavelength of a light source, a technology to remove and control the temperature sensitivity of the light transmission characteristics of the Sanak interferometer is essential to be.

As one of the means for solving the temperature sensitivity problem of the above-described Sagnac interferometer, there is a temperature maintaining device, and by maintaining the Sagnac interferometer at a certain level, it can be used as a signal analyzer or a sensor probe. In the case of such a temperature maintaining device, since it has an additional configuration such as a thermoelectric element (TEC), the structure is complicated and the cost is increased.

In addition, even if a thermoelectric element is used to maintain the temperature at a constant level, when a Sanac interferometer is constructed using a PANDA optical fiber, one of the birefringent optical fibers, the temperature sensitivity (dλ/dT= -1900pm/K) is very high, so the temperature of the thermoelectric element Due to the limit of the maintenance range (the minimum temperature maintenance deviation is about ±0.1 to 0.01°C), inaccuracy in wavelength measurement of about ±190 to 19pm may occur.

As another means of solving this problem, an optical fiber with low temperature sensitivity can be used. For example, in the case of a Sanac interferometer using a birefringent photonic crystal optical fiber (PCF) made of a single silica material, the temperature sensitivity (dλ/dT) can be reduced to about -2.5 to -0.3 pm/K.

However, even in the case of a Sanac interferometer based on a birefringent photonic crystal optical fiber (PCF) having a low temperature sensitivity, if the temperature changes in the range of tens to several hundred degrees Celsius or more, a very large inaccuracy of about several tens of pm to several hundreds of pm is brought about. These characteristics become a problem to be solved in the development of high-performance optical devices using the Sanac interferometer.

Korean Patent Registration No. 10-0088132

Accordingly, the present invention was devised in view of the above circumstances, and an object of the present invention is to provide a Sanac interferometer having a predetermined interference fringe spacing with a temperature sensitivity canceling out by using a heterogeneous birefringent optical fiber having a structure that cancels the temperature sensitivity. .

A Sanak interferometer with offset temperature sensitivity using heterogeneous birefringent optical fibers according to a preferred embodiment of the present invention for achieving the above object includes: a first optical fiber; A second optical fiber that is bonded to the first optical fiber so that at least one optical axis forms a right angle with the optical axis of the first optical fiber, wherein the lengths of the first optical fiber and the second guam oil offset temperature sensitivity. It characterized in that it is set.

Each length of the first optical fiber and the second optical fiber may be set such that the Sanac interferometer has a predetermined free spectral range (FSR).

The first optical fiber and the second optical fiber may have a birefringence coefficient temperature sensitivity of the same sign.

Input optical fiber; Output optical fiber; And an optical branch unit in which the input optical fiber and the output optical fiber are coupled to an external port, and the first optical fiber and the second optical fiber are coupled to an internal port.

Each length of the first optical fiber and the second optical fiber may be set to have a positive temperature sensitivity in order to further cancel the temperature sensitivity.

The length ratio of the first optical fiber and the second optical fiber may be selected from an inverse ratio of the temperature sensitivity of the birefringence coefficient of the first optical fiber and the temperature sensitivity of the birefringence coefficient of the second optical fiber.

The inverse ratio between the temperature sensitivity of the birefringence coefficient of the selected first optical fiber and the temperature sensitivity of the birefringence coefficient of the second optical fiber may include an error range within ±10%.

The temperature sensitivity ratio of the birefringence coefficient of the first optical fiber and the birefringence coefficient of the second optical fiber may be selected from 500:1 to 1:1.

The first optical axis of the first optical fiber may coincide with the first optical axis or the second optical axis of the second optical fiber.

The first optical fiber or the second optical fiber may be a birefringent optical fiber structure having an elliptical core mode.

The birefringent optical fiber having the elliptical core mode may be a photonic crystal optical fiber.

The birefringent optical fiber having the elliptical core mode may have a core to which Ge, P, or Al is added.

It is possible to provide a light source analyzer including a Sanac interferometer whose temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention for achieving the above object.

It is possible to provide an optical sensor signal analyzer including a Sanac interferometer whose temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention for achieving the above object.

It is possible to provide an optical sensor probe including a Sanac interferometer whose temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention for achieving the above object.

Therefore, according to the Sanac interferometer in which the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention, the lengths of the two optical fibers are set to cancel the temperature sensitivity, and the optical axes of the two optical fibers form a right angle. By bonding, the temperature sensitivity is canceled.

In addition, unlike the existing cross-measurement technology, it is about a technology that removes and controls the temperature sensitivity of the Sanac interferometer itself, and can be used for a high-performance light source analyzer, a signal analyzer for an optical sensor, and an optical sensor probe.

In addition, by selecting the optical fiber length of the birefringent optical fiber having two different characteristics and the characteristics of the birefringent optical fiber, it can be made to have a predetermined interval between the interference fringes.

In addition, unlike conventional techniques such as optical fiber structure or material change, it is possible to make a Sanac interferometer having a negative temperature sensitivity to have a positive temperature sensitivity.

In addition, even in the case of a Sanac interferometer made of birefringent photonic crystal fiber having low temperature sensitivity, it can be made to have a lower temperature sensitivity.

In addition, since an additional device such as TEC (Thermoelectric Cooler) is not used, the structure is simple and the manufacturing cost is low.

In addition, since it is a technology that uses a single Sanac interferometer, the volume of the system can be minimized.

In addition, since it is constructed using a birefringent optical fiber, a vibration-resistant system can be made.

1 is a block diagram of a Sanac interferometer with a temperature sensitivity canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention.
FIG. 2 is a diagram illustrating a state in which a third connection point of FIG. 1 is disconnected.
3 is a graph showing a light transmission spectrum according to a wavelength of a typical Sagnac interferometer.
4 is a graph showing a light transmission spectrum of a Sanac interferometer for an optical sensor probe according to a preferred embodiment of the present invention.
5 is a block diagram of a signal analyzer for an optical fiber sensor using a Sanak interferometer according to a preferred embodiment of the present invention.
6 is a graph showing the transmission spectrum according to the wavelength of the Sanac interferometer and sensor of FIG. 5.
7 is a graph showing a light transmission spectrum of an optical filter using a Sanac interferometer used in a signal analyzer for an optical fiber sensor according to a preferred embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to elements of each drawing, it should be noted that the same elements have the same numerals as possible, even if they are indicated on different drawings. In addition, a preferred embodiment of the present invention will be described below, but the technical idea of the present invention is not limited thereto or is not limited thereto, and may be modified and variously implemented by a person skilled in the art.

First, prior to the description of the configuration of the Sanac interferometer whose temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention, temperature sensitivity will be described.

It is known that the temperature sensitivity (dλ/dT) of the Sanac interferometer using a commercial birefringent optical fiber known to date has a negative value. For example, a PANDA optical fiber, which is one of the birefringent optical fibers, has a temperature sensitivity of dλ/dT= -1.9nm/℃. In addition, the Bow-tie optical fiber, the IEC optical fiber, and the D-type birefringent optical fiber have temperature sensitivity of approximately -1.2nm/°C, -0.70nm/°C, and -0.34nm/°C, respectively. The reason why the temperature sensitivity of the optical fiber Sanak interferometer has a negative value is because the temperature sensitivity of the birefringence coefficient has a negative value as an inherent characteristic of the optical fiber material itself.

Meanwhile, a method of controlling the temperature sensitivity by changing the material or structure of the birefringent optical fiber for the Sanac interferometer may be considered. However, in this case, the geometric structure of the birefringent optical fiber, the core constituting the optical fiber, and the thermal optical coefficient and the thermal expansion coefficient of the cladding material must be comprehensively changed, so it is not possible to make it using materials and structures that are limitedly used for commercial optical fibers. There is a limit. In addition, it is difficult to reduce the temperature sensitivity to a sufficient level.

1 is a block diagram of a Sanac interferometer with a temperature sensitivity canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention. FIG. 2 is a diagram illustrating a state in which the third connection point P3 of FIG. 1 is disconnected.

1 and 2, the Sanac interferometer 100 whose temperature sensitivity is canceled using a heterogeneous birefringent optical fiber according to a preferred embodiment of the present invention is connected to each other in a series structure in order to remove the temperature sensitivity as described above. It is a birefringent optical fiber and includes two independent first optical fibers 110 and second optical fibers 120. In addition, the Sanak interferometer 100 is configured to further include an input optical fiber 130, an output optical fiber 140, and an optical branching device 150.

The Sanac interferometer 100 is configured in a loop shape on one side based on the optical branching device 150, and the input optical fiber 130 and the output optical fiber 140 are connected to an external port located on the other side of the optical branching device 150. Each is connected. Here, the optical branching device 150 has 2x2 external ports and internal ports. For example, in the optical branch device 150, two optical waveguides may be formed on a flat substrate. The two optical waveguides may be formed to be close to each other to form an optical coupling characteristic. In addition, the optical signal input to the external port of the optical branch device 150 connected to the input optical fiber 130 may be designed to be branched to two inner ports of the optical branch device 150.

In order to increase the extinction ratio of the Sanac interferometer 100, a 2x2 optical branching device 150 having a coupling ratio of approximately 3dB is used, but an optical branching device 150 having a different coupling ratio may be used as necessary.

In order to implement a loop shape, the Sanac interferometer 100 connects one end of the first optical fiber 110 to one of the inner ports of one side of the optical branching device 150 at a first connection point P1.

Then, by connecting one end of the second optical fiber 120 to the other end of the first optical fiber 110, the first optical fiber 110 and the second optical fiber 120 are connected in series to the third connection point P3. Make it possible.

In addition, a loop shape is implemented by connecting the other end of the second optical fiber 120 to the remaining one of the inner ports on one side of the optical branching device 150 at the second connection point P2.

Here, the first optical fiber 110 and the second optical fiber 120 are not directly connected to the inner port of one side of the optical branching device 150, but separate optical fibers 160 and 170 for loops directly connected to the inner port. Can be connected to The first optical fiber 110 and the first optical fiber 160 for loops are connected to a first connection point P1, and the second optical fiber 120 and the second optical fiber 170 for loops are connected to a second connection point P2. Is connected to The first optical fiber 160 and the second optical fiber 170 for loop may be of the same material as the input optical fiber 130 or the output optical fiber 140, but the first optical fiber 110 and the second optical fiber 120 It is preferably made of a different material than. Here, a widely known fusion splicing method may be used for the connection between optical fibers.

On the other hand, when implementing the loop of the Sanak interferometer 100, it is preferable to rotate the first optical axis (axis1) of the second optical fiber (120) by 90 degrees with respect to the first optical axis (axis1) of the first optical fiber (110). . At this time, the bonding surface 111 of the first optical fiber 110 and the contact surface 121 of the second optical fiber 120 are bonded at the third connection point P3. Meanwhile, the first optical fiber 110 may be formed of a PANDA optical fiber as shown in FIG. 3, but is not limited thereto.

When the angle formed by the first optical axis aixs1 of the first optical fiber 110 and the first optical axis 1 of the second optical fiber 120 is not 90 degrees, the light transmission characteristic of the sagnac interferometer 100 is one sagnac It does not have the FSR (Free Spectral Range) characteristic with a single period like an interferometer. That is, when the angle formed by the first optical axis (axis1) of the first optical fiber 110 and the first optical axis (axis1) of the second optical fiber 120 is not 90 degrees, the Sanac interferometer 100, an interrogater ), it becomes unsuitable for use as an optical device such as a light source analyzer. When the angle formed by the first optical axis (axis1) of the first optical fiber 110 and the first optical axis (axis1) of the second optical fiber 120 is 0 degrees, FSR characteristics having a single period are obtained. It is not easy to implement because a birefringent optical fiber with temperature sensitivity is required.

In addition, it is preferable not to connect the single mode optical fiber for optical connection between the first optical fiber 110 and the second optical fiber 120 connected in series at the third connection point P3. In the case of using a single-mode optical fiber for optical connection between the first optical fiber 110 and the second optical fiber 120, the polarization axis is easily twisted while the light moves through the single-mode optical fiber due to bending, vibration, and temperature change. There is a problem that the optical properties of the Sanac interferometer are distorted.

On the other hand, when the second optical fiber 120 is directly connected to the first optical fiber 110 at the third connection point P3 as in the configuration of the present invention, the polarization axis, etc. due to vibration due to the polarization maintenance function of the birefringent optical fiber for the Sanac interferometer There will be no problem of this distortion.

In the general Sagnac interferometer 100, the transmission spectrum characteristic is determined by the phase difference due to birefringence, and the light transmission function is calculated as in Equation 1 below.

<Equation 1>

는 위상차, B는 복굴절 광섬유의 제1 광축(axis1)과 제2 광축(axis2) 사이의 굴절률 차이(복굴절계수), L은 복굴절 광섬유의 길이, 그리고 λ는 파장을 나타낸다.In Equation 1,

Is the phase difference, B is the refractive index difference (birefringence coefficient) between the first optical axis (axis1) and the second optical axis (axis2) of the birefringent optical fiber, L is the length of the birefringent optical fiber, and λ is the wavelength.

The light transmission function of the Sanak interferometer system configured by arranging independent Sanak interferometers each composed of the first optical fiber 110 and the second optical fiber 120 according to the prior art in a series structure is as follows: It is calculated as the product of trigonometric functions.

<Equation 2>

In Equation 2, T is a light transmission function of the entire Sanak interferometer system arranged in a series structure, T1 is a light transmission function of the first Sanak interferometer composed of the first optical fiber 110, and T2 is composed of the second optical fiber 120. It shows the light transmission function of the first Sanac interferometer.

In this case, the transmission spectrum according to the wavelength of the entire Sagnac interferometer system appears as a complex overlap as shown in FIG. 3 by overlapping individual optical fibers. Therefore, it is difficult to cancel the temperature sensitivity of the entire Sanac interferometer system or control it in a desired direction.

In the following, in order to cancel the temperature sensitivity of the Sanac interferometer 100 according to the present invention, the first optical fiber 110 and the second optical fiber 120 connected in the loop of a single Sanak interferometer 100 are selected and the length is derived. Explain the process.

The temperature sensitivity of the Sanac interferometer 100 is calculated as in Equation 3 below as the sum of the temperature sensitivity of the birefringence coefficient and the temperature sensitivity of the optical fiber length due to the thermal expansion effect.

<Equation 3>

는 사냑 간섭계(100)의 온도민감도,

는 복굴절계수의 온도민감도,

는 광섬유길이의 온도민감도를 나타낸다.In Equation 3,

Is the temperature sensitivity of the Sanac interferometer 100,

Is the temperature sensitivity of the birefringence coefficient,

Represents the temperature sensitivity of the optical fiber length.

The temperature sensitivity of the optical fiber length is relatively smaller than the temperature sensitivity of the birefringence coefficient and can be ignored as shown in Equation 4 below.

<Equation 4>

,

,

In a general case where the bandwidth of the FSR, that is, the interference fringe spacing (S) in the Sanac interferometer, does not change significantly, the temperature sensitivity of the phase difference and the temperature sensitivity of the wavelength have a linear relationship as shown in Equation 5 below.

<Equation 5>

According to the present invention, when the first optical axis (axis1) of the first optical fiber 110 and the first optical axis (axis1) of the second optical fiber 120 are connected to form 90 degrees within the loop of the Sanac interferometer 100, The transmission function is derived as follows. The Sanac interferometer 100 may be derived using the Jones matrix.

는 제1 광섬유(110)의 복굴절에 의한 B₁L₁과 제2 광섬유(120)의 복굴절에 의한 B₂L₂의 차이로 하기 수학식 6과 같이 계산된다.The total phase difference of the Sanac interferometer 100 connected so that the first optical axis (axis1) of the first optical fiber 110 and the first optical axis (axis1) of the second optical fiber 120 form 90 degrees according to the present invention

Is calculated as Equation 6 below as the difference between B ₁ L ₁ due to birefringence of the first optical fiber 110 and B ₂ L ₂ due to birefringence of the second optical fiber 120.

<Equation 6>

및

는 각각 제1 광섬유 및 제1 광섬유의 복굴절계수를 나타낸다. 또한

및

는 각각 사냑 간섭계의 루프내에 사용된 제1 및 제2 광섬유의 길이를 나타낸다. k는 두 광섬유의 제1 광축(axis1)이 90도로 서로 교차할 경우 -1 이고, 두 광섬유의 제1 광축(axis1)이 서로 일치할 경우 +1 이다.In Equation 6

And

Denotes the birefringence coefficient of the first optical fiber and the first optical fiber, respectively. Also

And

Denotes the lengths of the first and second optical fibers used in the loop of the Sanac interferometer, respectively. k is -1 when the first optical axes (axis1) of the two optical fibers cross each other by 90 degrees, and is +1 when the first optical axes (axis1) of the two optical fibers coincide with each other.

And the temperature sensitivity of the Sanac interferometer can be obtained by differentiating the phase difference term as shown in Equation 7 below.

<Equation 7>

와

는 복굴절계수의 온도민감도와 관련된 항인

와

보다 작으므로 무시할 수 있다. 이에 따라, 사냑 간섭계(100)의 전체 온도민감도는 제1 광섬유(110)의 복굴절계수의 온도민감도 및 제2 광섬유(120)의 복굴절계수의 온도민감도의 차이로 계산된다.In Equation 7, a term related to the temperature sensitivity of the optical fiber length

Wow

Is a term related to the temperature sensitivity of the birefringence coefficient

Wow

It is smaller than and can be ignored. Accordingly, the overall temperature sensitivity of the Sanac interferometer 100 is calculated as a difference between the temperature sensitivity of the birefringence coefficient of the first optical fiber 110 and the temperature sensitivity of the birefringence coefficient of the second optical fiber 120.

And in Equation 7, in order to remove the temperature sensitivity of the Sanac interferometer 100, the right term should be 0. When an optical fiber having a birefringence coefficient temperature sensitivity of the same sign is used as the first optical fiber 110 and the second optical fiber 120, the optical axes of the two optical fibers cross each other at 90 degrees to form an interferometer. At this time, k=-1, and the following Equation 8 can be derived from this.

<Equation 8>

,

,

가 제1 광섬유(110)와 제2 광섬유(120) 각각의 복굴절계수 온도민감도의 역수비

가 되도록 선택하면 된다.According to Equation 8, the length ratio of the first optical fiber 110 and the second optical fiber 120

Is the inverse ratio of the birefringence temperature sensitivity of the first optical fiber 110 and the second optical fiber 120

You can choose to be.

The length of the first optical fiber 110 and the appropriate length of the second optical fiber 120 for removing the temperature sensitivity of the Sanac interferometer 100 can be easily calculated using Equation 8 described above. That is, in order to efficiently remove or control the temperature sensitivity of the Sanac interferometer 100, instead of changing the structure and characteristics of the material of the birefringent optical fiber as in the conventional method, the two first optical fibers 110 used in the Sanak interferometer loop and A method of adjusting the length of the second optical fiber 120 is used. When this method is used, even if the first optical fiber 110 and the second optical fiber 120 have the same temperature sensitivity, the temperature sensitivity of the Sanac interferometer 100 can be removed.

는 제1 광섬유(110)와 제2 광섬유(120) 각각의 온도민감도의 역수비

에서 대략 ±10% 정도의 오차를 고려하여 계산되고, 이를 통해 제1 광섬유(110)와 제2 광섬유(120)의 길이를 선택하는 것이 바람직하다.Considering the error due to the thermal expansion effect of the first optical fiber 110 and the second optical fiber 120 used in the Shanac interferometer 100, more precisely, the length ratio of the first optical fiber 110 and the second optical fiber 120

Is the inverse ratio of the temperature sensitivity of each of the first optical fiber 110 and the second optical fiber 120

It is calculated in consideration of an error of approximately ±10%, and it is preferable to select the lengths of the first optical fiber 110 and the second optical fiber 120 through this.

In order to precisely control the temperature sensitivity of the Sanac interferometer 100, it is necessary to precisely control the lengths of the first optical fiber 110 and the second optical fiber 120. However, in cutting an optical fiber using an optical fiber cleaver, which is a general optical fiber cutting equipment, it is difficult to control the length of the optical fiber by cutting with an accuracy of 0.1 to 0.05 mm or less.

Therefore, in manufacturing the Sanac interferometer 100, the length accuracy of the first optical fiber 110 and the second optical fiber 120 is secured, and the first optical fiber 110 and the second optical fiber 120 having a predetermined length or longer are used. For this purpose, it is preferable to select a birefringent optical fiber having a temperature sensitivity ratio of the birefringence coefficient in the range of 500:1 to 1:1. Therefore, it is preferable to select a birefringent optical fiber having a length ratio of the first optical fiber 110 and the second optical fiber 120 in the range of 500:1 to 1:1.

In addition, in order to reduce excessive use of the length of the birefringent optical fiber used as the first optical fiber 110 and the second optical fiber 120, and to further improve the length accuracy of the used birefringent optical fiber, more preferably, birefringence It is possible to select a birefringent optical fiber having a coefficient of temperature sensitivity ratio in the range of 100:1 to 1:1.

If the temperature sensitivity of the Sanac interferometer 100 is removed by using the second optical fiber 120 having a temperature sensitivity opposite to that of the first optical fiber 110, the first optical axis (axis1) of the first optical fiber 110 ), the first optical axis (axis1) of the second optical fiber is aligned and connected.

The Sanac interferometer 100 according to the present invention configured as described above can be used as an optical filter. In addition, the Sagnac interferometer 100 can be used as a light source analyzer that measures the wavelength characteristics of a light source such as a laser. In addition, the Sagnac interferometer 100 measures the wavelength of an optical signal generated by an optical sensor using light including an optical fiber sensor such as an optical fiber Bragg grating (FBG), and measures the physical quantity applied to the optical sensor. It can be used as a terrorist). In addition, the optical fiber Sanak interferometer can be used as an optical sensor probe that measures various physical quantities including pressure, bending, rotation, and refractive index using light.

When using a Sanak interferometer as a signal analyzer or optical sensor probe composed of a filter, the Sanak interferometer must have a predetermined filtering characteristic and a periodic interference fringe characteristic with a constant interval and an extinction ratio. In addition, in order to be used as a signal analyzer and an optical device for an optical sensor probe, it is necessary to create an interference pattern having a predetermined filter slope or a predetermined wavelength characteristic. To do this, the Sanac interferometer must be configured to have the necessary FSR.

According to the present invention, the temperature sensitivity is canceled by using heterogeneous birefringent optical fibers having different characteristics in the loop of the Sanac interferometer, and an optical fiber interferometer having a predetermined FSR can be constructed.

The FSR (S) of the Sanac interferometer constructed using the first optical fiber and the second optical fiber is shown in Equation 9. Here, k is +1 when the first optical axes (axis1) of the two optical fibers coincide with each other, and -1 when the first optical axes (axis1) of the two optical fibers cross each other by 90 degrees.

<Equation 9>

When the same optical fiber is used as the first optical fiber and the second optical fiber, the birefringence coefficient temperature sensitivity (dB1/dT=dB2/dT) is the same, L1 = L2 by Equation 8, and the birefringence coefficient (B1 = B2) is also the same. The denominator in Equation 9 becomes 0. In this case, since the FSR (S) of the Sanac interferometer becomes infinite, it is difficult to use it as a signal analyzer or optical sensor probe because it is impossible to obtain a filtering characteristic with a slope or a periodic interference pattern.

을 만족하는 이종의 제1 광섬유 및 제2 광섬유를 선택한다. 이와 동시에 수학식 10 에 따라 소정의 FSR (S)를 갖도록 제1 광섬유 및 제2 광섬유의 길이를 선택할 수 있다.According to the present invention, the lengths of the first optical fiber and the second optical fiber can be selected so as to have a predetermined FSR while canceling the temperature sensitivity of the Sanac interferometer. For this purpose, so that the denominator of Equation 9 is not 0

Select the heterogeneous first optical fiber and the second optical fiber satisfying. At the same time, it is possible to select the lengths of the first optical fiber and the second optical fiber to have a predetermined FSR (S) according to Equation 10.

<Equation 10>

및

는 각각 제1 광섬유 및 제2 광섬유의 온도민감도이다. 수학식 10에 따라 사냑 간섭계의 온도민감도를 상쇄할 수 있으며 이와 동시에 제1 광섬유 및 제2 광섬유의 길이를 조절함으로써 소정의 FSR (S)를 갖도록 할 수 있다. 제1 광섬유(110) 및 제 2 광섬유(120)로 동일한 부호의 복굴절계수 온도민감도를 가진 광섬유를 사용할 경우 k=-1 이다.here

And

Is the temperature sensitivity of the first optical fiber and the second optical fiber, respectively. The temperature sensitivity of the Sanac interferometer can be canceled according to Equation 10, and at the same time, the lengths of the first optical fiber and the second optical fiber can be adjusted to have a predetermined FSR (S). When an optical fiber having a birefringence coefficient temperature sensitivity of the same sign is used as the first optical fiber 110 and the second optical fiber 120, k=-1.

<Example 1>

The Sagnac interferometer 100 according to the first preferred embodiment of the present invention is composed of a silica birefringent optical fiber having an internal elliptical cladding (IEC) structure made by forming a material having a stress in the first optical fiber 110 around a core, and 2 The optical fiber 120 is composed of a silica elliptical core optical fiber to which germanium (Ge) is added.

Hereinafter, a method of removing and controlling the temperature sensitivity of the Sanac interferometer 100 according to the first embodiment will be described. The first optical fiber 110 and the second optical fiber 120 each have a negative temperature sensitivity as shown in Equation 11 below.

<Equation 11>

,

,

As described above, the temperature sensitivity of the Sanak interferometer 100 configured by rotating and connecting the first optical axis 1 of the second optical fiber 120 by 90 degrees with respect to the first optical axis 1 of the first optical fiber 110 is shown below. It is summarized in Table 1.

First optical fiber 2nd optical fiber Length ratio
R=L2/L1 Temperature sensitivity before connecting the second optical fiber, dλ/dT
(pm/
o
C) Temperature sensitivity after connecting the second optical fiber, dλ/dT (pm/oC) Birefringence coefficient temperature sensitivity
, dB1/dT
(/
o
C) Length, L1 (mm) Birefringence coefficient temperature sensitivity
, dB2/dT
(/
o
C) Length, L2
(mm) ^-7.5x10-8 1000 -5.5x10-8 1300 1.300 -291 -21 -7.5x10-8 1000 -5.5x10-8 1364 1.364 -291 0.01 -7.5x10-8 1000 -5.5x10-8 2000 2 -291 301

Table 1 shows the temperature sensitivity of the Sanak interferometer 100 obtained by fixing the length L ₁ of the first optical fiber 110 to 1000 mm and varying the length L ₂ of the second optical fiber 120. It can be seen that when the length ratio (R) of the optical fiber is near the inverse ratio of the temperature sensitivity of the birefringence coefficients of the two optical fibers, that is, 1.364, the temperature sensitivity of the Sanac interferometer 100 is almost removed at 0.01 pm/℃.

In addition, it can be seen that when the length of the second optical fiber 120 is adjusted to 2000mm, the temperature sensitivity of the Sanac interferometer 100 can have a positive value as 301pm/°C.

<Example 2>

In the Sagnac interferometer 100 according to the second preferred embodiment of the present invention, the first optical fiber 110 is composed of a birefringent optical fiber having an elliptical core photonic crystal structure made of a silica material, and the second optical fiber 120 is incorporated in the core ( It is composed of a silica elliptical core optical fiber to which P) and aluminum (Al) are added. Hereinafter, a method of removing and controlling the temperature sensitivity of the Sanac interferometer 100 according to the second embodiment will be described. Both of the first optical fiber 110 and the second optical fiber 120 have negative temperature sensitivity as shown in Equation 12 below.

<Equation 12>

,

,

As described above, the temperature sensitivity of the Sanac interferometer 100 configured by rotating and connecting the first optical axis 1 of the second optical fiber 120 by 90 degrees with respect to the first optical axis 1 of the first optical fiber 110 is shown below. It is summarized in Table 2.

First optical fiber 2nd optical fiber Length ratio
R=L2/L1 Temperature sensitivity before connecting the second optical fiber, dλ/dT
(pm/
o
C) Temperature sensitivity after connecting the second optical fiber, dλ/dT (pm/oC) Birefringence coefficient temperature sensitivity
, dB1/dT
(/
o
C) Length, L1 (mm) Birefringence coefficient temperature sensitivity
, dB2/dT
(/
o
C) Length, L2
(mm) -2.0x10-9 2000 -3.0x10-8 100 0.05 -2.6 -0.91 -2.0x10-9 2000 -3.0x10-8 133 0.066 -2.6 0 -2.0x10-9 2000 -3.0x10-8 400 0.2 -2.6 7.4

Table 2 shows the temperature sensitivity of the Sanac interferometer 100 obtained by fixing the length L ₁ of the first optical fiber 110 to 2000 mm and varying the length L ₂ of the second optical fiber 120. Similarly, when the length ratio (R) of the optical fiber is the inverse ratio of the temperature sensitivity of the birefringence coefficients of the two optical fibers, that is, near 0.066, it can be seen that the temperature sensitivity of the Sanac interferometer 100 is removed to 0 pm/℃.

<Example 3>

In addition, the optical fiber Sanac interferometer can be used as an optical sensor probe that measures various physical quantities including pressure using light. In order to be used as an optical sensor probe, an interference pattern having a predetermined wavelength and light transmission characteristics is required. When a physical quantity is applied to the optical sensor probe, the interference fringe of the Sanac interferometer moves and the light output changes at a predetermined wavelength.

FIG. 4 shows the light transmission spectrum of a Sanac interferometer with a temperature sensitivity canceled by using heterogeneous first optical fibers and second optical fibers having birefringence characteristics. Birefringent optical fibers (B1=4.35x10 ^-4 , B2=9.10x10 ^-5 ) with different physical properties were used as the first and second optical fibers in the Sanac interferometer configuration, and the temperature sensitivity of the birefringence coefficient was respectively -4.79x10 ^-7 / ^o C (first optical fiber) and -5.34x10 ^-8 / ^o C (second optical fiber). As can be seen in FIG. 4, it is confirmed that the extinction ratio is 23dB and has an interference pattern having a constant interval (S=~2.6 nm). Using this, the physical quantity can be measured from the movement of the interference fringe or the change in light output according to the application of the physical quantity. As shown in FIG. 4, in the case of the Sanac interferometer according to the present invention, the extinction ratio and the interval have a constant interference pattern characteristic. On the other hand, in the case of the Sanac interferometer according to the prior art, the interference fringe spacing as shown in FIG. 4 is not the same and the extinction ratio is not constant in terms of the interference fringe characteristics.

<Example 4>

A signal analyzer for an optical sensor for measuring the physical quantity applied to the optical sensor by measuring the wavelength of the optical signal generated by the optical sensor using light including an optical fiber sensor such as an optical fiber Bragg grating (FBG) using the Sanac interferometer 100 according to the present invention Can be used as

5 is a block diagram of a signal analyzer for an optical sensor using a Sanak interferometer according to a preferred embodiment of the present invention. 6 is a graph showing the transmission spectrum according to the wavelength of the Sanac interferometer and sensor of FIG. 5. For example, in order to measure the physical quantity applied to an optical fiber Bragg grating used as an optical fiber sensor, the position of the center wavelength of the optical fiber Bragg grating must be accurately calculated. To this end, as shown in FIG. 5, the position of the center wavelength of the optical fiber Bragg grating can be calculated by passing the optical signal generated by the optical fiber Bragg grating through a linear filter made of a Sanac interferometer and measuring the intensity of the passed optical signal. . For accurate measurement, the optical characteristics of the Sanac interferometer used to make the linear filter of the signal analyzer should not be affected by changes in the surrounding environment, especially temperature.

To this end, a Sanac interferometer whose temperature sensitivity is canceled is used by using a heterogeneous birefringent optical fiber having a structure that cancels the temperature sensitivity according to the present invention. In the case of a signal analyzer configured using a Sanak interferometer as a filter, the Sanak interferometer must have a certain filter slope characteristic, and for this, a Sanak interferometer with a certain FSR must be configured.

According to the present invention, Fig. 7 shows the light transmission characteristics of the Sanac interferometer for an optical filter having an FSR of about 67 nm. As can be seen from the figure, it can be seen that the transmission characteristics of the Sanac interferometer have very linear optical filtering characteristics around 1552nm. As shown in FIG. 7, an optical sensor signal having a bandwidth of about 0.2-0.8 nm and whose position of the center wavelength varies according to the physical quantity is passed through a Sanac interferometer, and at this time, the change in light output that varies according to the physical quantity is measured. From this, the physical quantity can be calculated.

Meanwhile, when the Sanac interferometer 100 according to the present invention is used as an optical sensor probe, a polarimetric interferometer structure may be formed. In the case of a polarization-type interferometer structure, since the light transmission function is given in the same form as the above-described Sagnac interferometer 100, the temperature sensitivity can be controlled in the same manner.

)으로 사냑 간섭계의 온도민감도, 간섭무늬 간격(FSR) 등의 광특성을 제어할 수 있다.In addition, in the case of using an optical fiber having a birefringence coefficient temperature sensitivity of opposite sign as the first optical fiber 110 and the second optical fiber 120 according to the present invention (k=1), equations 6, 7, 9, and 10 Using the same way (

), it is possible to control optical characteristics such as temperature sensitivity and interference fringe spacing (FSR) of the Sanac interferometer.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the technical field to which the present invention belongs can make various modifications, changes, and substitutions within the scope not departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments and the accompanying drawings. .

100: Sanac interferometer
110: first optical fiber
120: second optical fiber
130: input optical fiber
140: output optical fiber
150: optical branching device
160, 170: optical fiber for loop

Claims (15)

A first optical fiber;
A second optical fiber splicing to the first optical fiber such that at least one optical axis is perpendicular to the optical axis of the first optical fiber;
Including,
Each length of the first optical fiber and the second optical fiber is set to cancel temperature sensitivity,
The length ratio of the first optical fiber and the second optical fiber is selected from an inverse ratio of the temperature sensitivity of the birefringence coefficient of the first optical fiber and the temperature sensitivity of the birefringence coefficient of the second optical fiber. Sanac interferometer with offset sensitivity. The method of claim 1,
Each length of the first optical fiber and the second optical fiber is set so that the Sanac interferometer has a predetermined free spectral range (FSR). The temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. The method of claim 1,
The first optical fiber and the second optical fiber have a temperature sensitivity of a birefringence coefficient of the same sign, and temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. The method of claim 1,
Input optical fiber;
Output optical fiber; And
An optical branching unit in which the input optical fiber and the output optical fiber are coupled to an external port, and the first optical fiber and the second optical fiber are coupled to an internal port; Sanac interferometer. The method of claim 1,
The length of each of the first optical fiber and the second optical fiber is set to have a positive temperature sensitivity in order to further cancel the temperature sensitivity, and the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. delete The method of claim 1,
The temperature sensitivity is canceled using a heterogeneous birefringence optical fiber, characterized in that the inverse ratio of the temperature sensitivity of the birefringence coefficient of the selected first optical fiber and the temperature sensitivity of the birefringence coefficient of the second optical fiber includes an error range within ±10%. interferometer. The method of claim 1,
The temperature sensitivity ratio of the birefringence coefficient of the first optical fiber and the birefringence coefficient of the second optical fiber is selected in the range of 500:1 to 1:1. The method of claim 1,
The first optical axis of the first optical fiber coincides with the first optical axis or the second optical axis of the second optical fiber, wherein the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. The method of claim 1,
The first optical fiber or the second optical fiber has a birefringent optical fiber structure having an elliptic core mode, wherein the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. The method of claim 10,
The birefringent optical fiber having the elliptical core mode is a photonic crystal optical fiber, wherein the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. The method of claim 10,
The birefringent optical fiber having the elliptical core mode has a core to which Ge, P, or Al is added, wherein the temperature sensitivity is canceled using a heterogeneous birefringent optical fiber. A light source analyzer comprising a Sanac interferometer whose temperature sensitivity is canceled using a birefringent optical fiber of any one of claims 1 to 5, and 7 to 12. An optical sensor signal analyzer comprising a Sanac interferometer whose temperature sensitivity is canceled using a birefringent optical fiber of any one of claims 1 to 5, and 7 to 12. An optical sensor probe comprising a Sanac interferometer whose temperature sensitivity is canceled using the heterogeneous birefringent optical fiber of any one of claims 1 to 5, and 7 to 12.

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