KR101896113B1 - Interferometer optic structure and bias-free optical current sensor using of the same and manufacturing method of optical integrated circuit device for the same - Google Patents

Abstract

The present invention relates to an optical interferometer structure and a photocurrent sensor using the same.
A photocurrent sensor according to the present invention includes a sine wave plate connected to a polarization maintaining optical fiber for transmitting light and converting the transmitted light into circularly polarized light, an optical fiber coil for delaying the phase of light converted into circularly polarized light, A sensing head unit disposed at an end of the sensing head unit, the sensing head unit including a mirror for reflecting light, and a light source connected to the polarization maintaining optical fiber to transmit light incident from the light source to the sensing head unit, And the optical integrated circuit device forms a return path of light that is reflected from the sensing head and returns to the optical integrated circuit device, and the sequential branching is performed based on the return direction, And a light path of light branched by at least the third Y branching path A quarter wave plate (HWP) inclined by 22.5 DEG with respect to the substrate; a quadrature wave plate (QWP) provided at the other path of the third Y branch and inclined by 45 DEG with respect to the substrate; and a waveguide The two optical signal input / output characteristic curves output through the waveguide polarizer include a polarizer, and have a phase difference of 90 ° with respect to each other, so that the current / voltage signal can be measured regardless of the initial phase state of the interferometer.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical interferometer structure, a photocurrent sensor using the same, and a manufacturing method of an optical integrated circuit device for the same.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical interferometer for effectively detecting a phase change of a light wave caused by a change in a physical quantity such as a magnetic field and an electric field due to a current voltage and a photocurrent sensor using the same.

The photocurrent sensor has various advantages compared with the electric current measuring device which is widely used in the past, and has received great attention in the electric power industry at present.

In the non-patent documents [1, 2], technologies related to the use of optical sensors for measuring current and voltage through optical fibers have been published and have proved to be effective for performing stable power monitoring in large-scale power generation and distribution systems.

A photocurrent sensor composed of an insulator without a metal conductor can safely operate the sensor without the danger of heat or explosion due to surge current. (See Non-Patent Document 3)

On the other hand, the magnetic field generated by the current induces an instantaneous refractive index change in the optical fiber, and the optical interferometer type current sensor can measure the rapidly changing fault current in real time (Non-Patent Document 4) (See non-patent literature [5]), because the photocurrent sensor is a small circular birefringence in the optical fiber, the photocurrent sensor has a linear and broad dynamic range without saturation.

In addition, since the optical signal is not affected by electromagnetic interference (EMI), it is possible to obtain a noise-suppressed sensing signal at a facility generating high power. The photocurrent sensor is smaller and lighter than the conventional electric current transducer (CT), which makes it easy to install, less maintenance cost, and is made of insulating material, unlike electric CT, so there is no need of gas and insulating oil. See [6]).

In the non-patent document [7], a polarization rotated reflection interferometry (PRRI) structure has been proposed to improve the operational stability of a photocurrent sensor. Non-patent documents [8] and [9] And two orthogonal polarization components are used to measure minute circular birefringence.

The polarization rotation interferometer structure compensates for the phase change caused by the influence of the surrounding environment such as temperature or vibration, thereby providing stability of operation.

However, PRRI-type optical current transducers (OCTs) require various types of optical components that complicate the structure and lower the production yield. Therefore, in order to integrate various optical components on a single substrate, (See non-patent documents [10] to [12]).

On the other hand, the optical interferometer for measuring the phase difference of two waves can basically obtain a linear response with the maximum sensitivity only when the operating point is adjusted to the point of λ / 4. However, when the birefringence of the optical fiber changes due to the influence of ambient vibration or temperature change, the operating point changes with time.

Therefore, in the non-patent document [13], a phase modulator made of PZT or LiNbO3 is used to compensate for the change of the operating point in real time.

Another method is to change the operating point using a passive optical device such as a polarizer or a wave plate in Non-Patent Documents [12], [14] and [15], and US 6,636,321 "Fiber-optic the polarization state of light can be easily changed due to the change in characteristics of the optical fiber coil portion which winds the wire according to changes in the external environment such as temperature and vibration, in the "optical sensor" and "optical fiber electric current sensor and electric current measurement method" A polarization rotation reflection type photocurrent sensor using a polarization maintaining optical fiber is disclosed.

However, in such a case, the alignment between the respective components must be precisely matched, and the optical waveguide requires a low birefringence optical waveguide.

On the other hand, a quadrature interferometer using two operating characteristic curves having a phase difference of 90 [deg.] Can achieve stable current measurement irrespective of changes in operating point (see Non-Patent Documents 16 and 17).

In the non-patent document [18], OCT based on a quadrature interferometer is proved by integrating MMI to confirm the possibility of current sensing without operating point control.

However, the interference characteristics of the MMI structure are sensitive to the dimensional deviation and the refractive index deviation of the optical waveguide, making it difficult to fabricate a device having accurate characteristics.

US 6636321 B2 US 2005-0088662 A1

[1] K. Kurosawa, "Development of fiber optic current sensing technique and its applications in electric power systems," Photon. Sens. 4 (1), 12-20 (2014). [2] K. Bohnert, P. Gabus, J. Nehring, H. Brandle, and M. G. Brunzel, "Fiber optic current sensor for electrowinning of metals," J. Lightwave Technol. 25 (11), 3602-3609 (2007). [3] J. D. P. Hrabluik, "Optical current sensors eliminate CT saturation," in Proc. 2002 IEEE PES Winter Meeting, 2, pp.1478-1481. [4] Y. N. Ning, Z. P. Wang, A.W. Palmer, K. T. V. Grattan, and D.A. Jackson, " Recent progress in optical current sensing techniques, " Rev. Sci. Instrum. 66 (5), 3097-3111 (1995). [5] K. Bohnert, P. Gabus, J. Kostovic, and H. Brandle, "Optical fiber sensors for the electric power industry," Opt. Lasers Eng. 43 (3-5), 511-526 (2005). [6] R. M. Silva, H. Martins, I. Nascimento, J. M. Baptista, A. L. Ribeiro, J. L. Santos, P. Jorge, and O. Frazao, "Optical current sensors for high power systems: a review," Appl. Sci. 2 (4), 602-628 (2012). [7] K. Bohnert, P. Gabus, J. Nehring, and H. Brandle, "Temperature and vibration insensitive fiber-optic current sensor," J. Lightwave Technol. 20 (2), 267-276 (2002). [8] A. Enokihara, M. Izutsum and T. Sueta, "Optical fiber sensors using the method of polarization-rotated reflection," J. Lightwave Technol. 5 (11), 1584-1590 (1987). [9] G. Frosio and R. Dandliker, "Reciprocal reflection interferometer for a fiber-optic Faraday current sensor," Appl. Opt. 33 (25), 6111-6122 (1994). [10] M.-C. Oh, J.-K. Seo, K.-J. Kim, H. Kim, J.-W. Kim, and W.-S. Chu, " Optical current sensors consisting of polymeric waveguide components, " J. Lightwave Technol. 28 (12), 1851-1857 (2010). [11] M.-C. Oh, W.-S. Chu, K.-J. Kim, and J.-W. Kim, " Polymer waveguide integrated-optic current transducers, " Opt. Express 19 (10), 9392-9400 (2011). [12] GM Muler, L. Yang, A. Frank, and K. Bohnert, "Simple fiber-optic current sensor with integrated-optics polarization splitter for interrogation," in Applied Industrial Optics: Spectroscopy, Imaging and Metrology Conference, Technical Digest Series (Optical Society of America, 2014), paper AM4A.3. [13] T. Masao, K. Sasaki, and K. Terai, "Optical Current Sensor for DC Measurement," Proceedings of IEEE Conference on Asia Pacific IEEE / PES Transmiss. Distrib. Conf. Exhibit. (IEEE, 2002) 1, 440-443. [14] F. Briffod, L. Thevenaz, P.-A. Nicati, A. Kung, and P. A. Robert, "Polarimetric current sensor using an in-line faraday rotator," IEICE Trans. Electron. E83-C (3), 331-335 (2000). "Design and development of a low-cost optical current sensor," Sensors (Basel) 13 (10), J. Zubia, L. Casado, G. Aldabaldetreku, A. Montero, E. Zubia, and G. Durana, , 13584-13595 (2013). [16] D. W. Stowe and T.-Y. Hsu, " Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator, " J. Lightwave Technol. 1 (3), 519-523 (1983). [17] H.-J. Park and M. H. Song, "Fiber grating sensor interrogation using a double-pass mach-zehnder interferometer," IEEE Photon. Technol. Lett. 20 (22), 1833-1835 (2008). [18] S.-M. Kim, W.-S. Chu, S.-G. Kim and M.-C. Oh, "Integrated-optic current sensors with a multimode interference waveguide device," Opt. Express 24 (7), 7426-7435 (2016). [19] W.-S. Chu, S.-M. Kim, and M.-C. Oh, "Integrated-optic current transducers incorporating photonic crystal fiber for reduced temperature dependence," Opt. Express 23 (17), 22816-22825 (2015). [20] S.-H. Park, J.-W. Kim, M.-C. Oh, Y.-O. Noh, and H.-J. Lee, " Polymer waveguide birefringence modulators, " IEEE Photon. Technol. Lett. 24 (10), 845-847 (2012).

An object of the present invention is to provide a quadrature interferometer for generating a 90 DEG phase shift signal using two kinds of wave plates, a waveguide polarizer and a birefringent modulator, Thereby providing an optical interferometer structure that is not required.

It is another object of the present invention to provide an optical sensor capable of improving stability of an interferometer and increasing productivity of a product by integrating optical components for forming a quadrature interferometer on one substrate.

The optical interferometer structure according to the present invention includes an optical integrated circuit device that sends input light to an optical fiber coil constituting a sensing head unit and forms a path for transmitting reflected light reflected by a mirror provided in the optical fiber coil to a photodetector, And a sensing head connected to the optical integrated circuit device through a polarization maintaining optical fiber to transmit light and being reflected by the mirror after the transmitted light is converted into two circularly polarized states through a sine wave plate, A first Y branch path for transmitting light returning from the sensing head unit to the photodetector is formed in the optical integrated circuit element, and light transmitted to the photodetector by the first Y branch path is branched by the second Y branch path Half of the branched light goes to the MPD monitoring the power change of the light source, the remaining light passes through the third Y branch path, In one path among the paths branched by the third Y branching path, it passes through the half wave plate (HWP) and the waveguide type polarizer which are inclined at 22.5 ° with the substrate. In the other path, the quarter wave plate (QWP) The current changes from the photodetector to the current through the polarizer.

And a phase modulator is further provided on an incident path of the input light.

In another aspect of the present invention, there is provided a photocurrent sensor comprising: a sine wave plate connected to a polarization maintaining optical fiber to transmit light and converting the transmitted light into circularly polarized light; an optical fiber coil for delaying the phase of light converted into circularly polarized light; A sensing head disposed at an end of the optical fiber coil and including a mirror for reflecting light, and a light source connected to the polarization maintaining optical fiber for transmitting light incident from the light source to the sensing head, The optical integrated circuit device includes a return path for returning light reflected from the sensing head unit, and a return path for returning light reflected from the sensing head unit is sequentially The first to the third Y branching paths and the at least the third Y branching path, A quarter wave plate (HWP) provided on the path and inclined at 22.5 DEG with respect to the substrate, a quarter wave plate (QWP) provided at the other path of the third Y branch and inclined at 45 DEG to the substrate, And the two optical signal input / output characteristic curves output through the waveguide type polarizer have a phase difference of 90 [deg.] From each other, so that the current / voltage signal can be measured regardless of the initial phase state of the interferometer .

According to another aspect of the present invention, there is provided a method of fabricating an optical interference device, comprising: forming a lower cladding layer on a silicon substrate; forming a core layer by forming an optical waveguide pattern on the lower cladding layer; Forming a first upper cladding layer by coating a polymer on the first upper cladding layer, depositing chromium (Cr) and gold (Au) on the first upper cladding layer and then etching the first upper cladding layer to form a waveguide polarizer; Forming a second upper cladding layer by spin-coating a polymer on the first upper cladding layer; forming a phase modulator using a Cr-Au metal thin film after forming the second upper cladding layer; A mounting step of mounting a wave plate on the waveguide, and a packaging step of aligning and connecting the optical fiber array to the optical waveguide after the wave plate is installed, and connecting wires to the phase modulator In the wave plate mounting step, a groove line is formed by using a dicing saw, and a four-sided wave plate is installed on the groove line at an angle of 45 ° with the half wave plate inclined by 22.5 ° with respect to the optical axis of the substrate.

The use of the quadrature interferometer according to the present invention does not require the operation point control necessarily required in the operation of a general interferometer type optical sensor.

Therefore, the optical sensor operation control algorithm and the control electronic circuit are simplified, and more stable sensor operation becomes possible.

In addition, according to the present invention, various optical components for forming the quadrature interferometer can be integrated on one substrate, thereby improving the stability of the interferometer and enhancing productivity of the product.

In addition, the optical sensor according to the present invention has an advantage that the current / voltage signal can be measured regardless of the initial phase state of the interferometer by outputting the two optical signal input / output characteristic curves having a phase difference of 90 degrees with each other.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the structure of a polymer optical waveguide-based optical integrated circuit device and a photocurrent sensor including the same according to the present invention; FIG.
FIG. 2 is a view showing a manufacturing process of the optical IC device shown in FIG. 1; FIG.
3 is a view showing a state in which an optical fiber pigtail process and a packaging process are completed in the optical integrated circuit device shown in FIG.
Fig. 4 (a) is a view showing a result of a polarization state appearing on a Poincare sphere in which input linearly polarized light with an angle of 45 degrees is converted at an output unit due to a change in birefringence due to heat. Fig.
4 (b) is a graph showing the relative phase difference between TE and TM polarized light according to the power applied to the micro-heater.
FIG. 5A is a diagram showing interference signals appearing at PD1 and PD2 when a voltage is applied to the phase modulator. FIG.
FIG. 5 (b) is a cross-sectional image drawn using two interference signals to confirm the phase difference of the two measured interference signals.
6 is a set-up of current toroids used to amplify the magnetic field applied to the sensing fiber coil 10 times.
7 is a graph showing the linearity of the sensor output measured when the applied current is varied from 0.3 to 5.5 kA (toroidal applied current 0.03 to 0.55 kA) and a relative error compared with the electric current sensor value.
8A to 8C are diagrams showing the result of measuring a long-time current in a state in which there is no operating point control.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. It is to be understood, however, that the spirit of the invention is not limited to the embodiments shown and that those skilled in the art, upon reading and understanding the spirit of the invention, may easily suggest other embodiments within the scope of the same concept.

FIG. 1 shows a structure of a polymer optical waveguide-based optical integrated circuit device and a photocurrent sensor including the same according to the present invention.

Referring to these drawings, a photocurrent sensor 100 according to the present invention includes a sensing head unit 200 and an optical integrated circuit device (OIC device) 400.

The optical integrated circuit device 400 according to the present embodiment transmits the input light to the optical fiber coil 230 of the sensor head unit 200 based on the Y-branch structure of the optical waveguide and transmits the reflected light to a photo detector ) To the destination.

In this embodiment, a quadrature interferometer is formed so that the interference signal detected through the photodetector has a phase difference of? / 4.

More specifically, the sensor head 200 includes a quarter wave plate 210 (QWP) made of an optical fiber coil 230, a mirror 220, and a polarization maintaining optical fiber 300.

The s-wave plate 210 is disposed on the front side of the optical fiber coil 230 and is formed of a photonic crystal fiber (PCF) that is aligned by rotating the optical axis by 45 °.

In the sine wave plate 210 manufactured as described above, the linearly polarized light of the fast axis component and the slow axis component is converted into Left-Handed Circular Polarization (LHCP) and Righ-Handed Circular Polarization (RHCP) .

Two circular polarizations passing through the optical fiber coil 230 accumulate phase delay due to the Faraday effect and are reflected by a mirror 220 provided at the end of the optical fiber coil 230 Reflection.

The two circularly polarized lights reflected by the mirror 220 are again converted into linearly polarized light while passing through the optical fiber coil 230 and the quarter wave plate 210.

At this time, the linearly polarized light of the output fast axis component is the slow axis component of the slow axis component at the time of input, and the linearly polarized light of the slow axis component is converted at the input of the slow axis component and passes through the polarization maintaining optical fiber 300 .

Therefore, the phase difference between the fast axis component and the slow axis component generated while passing through the polarization maintaining optical fiber 300 when input to the optical fiber coil 230 is canceled by returning to the opposite direction, and the two polarized light returned with the delayed phase information And is incident on the optical integrated circuit device 400.

The optical integrated circuit device 400 sends input light to the sensing head 200 based on a Y-branch optical waveguide in which a plurality of branch paths are formed, branches the reflected light, and outputs the MPD (monitoring PD 486) PD2 484, and PD1 482, as shown in Fig.

To this end, the optical waveguide includes a first Y branch path 422 that is first branched after the light incident from the light source is reflected through the sensing head 200, and a second Y branch path 422 that branches the light branched from the first Y branch path 422 A second Y branch path 424 for branching again, and a third Y branch path 426 for branching again the light branched from the second Y branch path 424.

In this embodiment, the light source uses an SLED 481 light source having a wide wavelength bandwidth and a short coherence length.

Two kinds of wave plates are provided in the optical waveguide in which the first Y branching path, the second Y branching path and the third Y branching path are formed as described above.

The wave plate is divided into a half-wave plate (HWP) and a quarter-wave plate (QWP), and the optical axis direction is 22.5 ° and 45 ° from the substrate, respectively.

Hereinafter, the half-wave plate is referred to as a 22.5 ° half-wave plate (464) and the four-sided wave plate is referred to as a 45 ° sine wave plate (462).

On the other hand, the 22.5 DEG half-wave plate 464 is located at the front side of the MPD 486 and the PD2 484 in the return path, which is located in the incident path and divides input light incident on the TE polarized light into TE and TM polarized light. To this end, the 22.5 DEG half-wave plate 464 may be formed as a single plate that can cover all the above-mentioned positions.

The 45 DEG sine wave plate 462 is located at the front side of the PD1 482 in the return path and further includes waveguide polarizers 420 at the front side of the PD2 484 and PD1 482, So that the interference signal detected through the PD1 482 and the PD2 484 has a phase difference of? / 4.

Further, a phase modulator 421 is further provided on the incident path of the optical waveguide.

The phase modulator 421 adjusts the birefringence of the optical waveguide by applying heat.

FIG. 2 is a view showing a manufacturing process of the optical IC device shown in FIG. 1, and FIG. 3 is a view showing a state in which an optical fiber pigtail process and a packaging process are completed in the optical IC device shown in FIG. Respectively.

Prior to the description, in this embodiment, the polymer material used for the core and the cladding was a polymer of ChemOptics Co., Ltd. in order to fabricate the polymer optical waveguide device, and materials having the refractive indexes of 1.455 and 1.440 were used, respectively. According to the effective index calculation method, the single mode optical waveguide is designed to have a width of 6 μm and a thickness of 6 μm.

In the manufacturing process of the optical integrated circuit device 400 according to the present invention, a lower cladding layer forming step of forming a lower cladding layer 412 on a silicon substrate is performed.

In this embodiment, the ZPU-440 polymer is spin-coated on the silicon substrate in the lower cladding layer formation step, UV cured, and thermally cured at 160 캜 to form a 17 탆 thick lower cladding layer 412.

After the lower cladding layer 412 is formed as described above, the optical waveguide core patterning step is performed.

In the present embodiment, the optical waveguide core patterning step was masked using AZ-5214 photoresist and etched to a depth of 3.6 탆 through an O2 plasma etching apparatus. Then, a core layer forming step is performed by spin-coating a ZPU-455 polymer to a thickness of 2.4 탆 on the etched optical waveguide pattern to form a core layer.

When the core layer forming step is completed as described above, the first upper cladding layer forming step is performed.

In this embodiment, a ZPU-455 polymer is spin-coated on the core layer in the first upper cladding layer formation step to form a first upper cladding layer having a thickness of 2 탆.

The chromium (Cr) and the gold (Au) are deposited to a thickness of 10 nm and 100 nm, respectively, on the first upper cladding layer formed as described above. Subsequently, a photolithography process and a wet etching process are performed, Type polarizer 420 is formed.

After the waveguide polarizer 420 is formed through the above process, a second upper cladding layer is formed.

In this embodiment, the second upper cladding layer is formed by spin-coating a ZPU-440 polymer to form a second upper cladding layer 414 having a thickness of 8 μm.

After the second upper cladding layer 414 is formed, a phase modulator forming step of fabricating a phase modulator 421 with Cr-Au metal thin film having a thickness of 10 nm and 100 nm is performed.

When the phase modulator 421 is formed as described above, a wave plate mounting step for mounting the wave plate on the completed optical waveguide is performed.

In the step of installing the wave plate, a grooved line (460) having a width of 30 μm is formed by using a dicing saw to insert a wave plate into the optical waveguide, and the 22.5 ° half wave plate (464) (462) is inserted into the groove line (460) and fixed using epoxy.

After the wavelength plate is installed as described above, the packaging completion step is performed.

In the packaging completion step, the optical fiber array is aligned and connected to the optical waveguide, and the wires are connected to the phase modulator 421 forming the birefringence modulator 440 to complete the packaging as shown in FIG.

Hereinafter, the operation of the optical IC 400 manufactured as described above will be described.

First, the input light from the SLED 481 as a light source is incident on the optical integrated circuit device 400 as TE polarized light, and after being passed through the 22.5 ° half wave plate 464, divided into TE and TM polarized light.

These field components pass through the first Y branching path 422 of the optical integrated circuit device 400 and are connected to the fastening optical fiber 300 of the polarization maintaining optical fiber 300 connecting the optical integrated circuit device 400 and the sensing head 200 axis component and the slow axis component.

The two linearly polarized light components proceeding toward the optical fiber coil 230 are converted into two circularly polarized light components by the quarter wave plate 210 of the sensing head 200. The circular birefringence proportional to the current in the optical fiber coil 230 generates a phase difference between the two circular polarization components, and the two polarized components are reflected by the mirror 220 at the end of the optical fiber coil 230.

The reflected circularly polarized light component moves along the return path and is converted into linearly polarized light again through the sine wave plate 210 to move to the optical integrated circuit device 400 along the polarization maintaining optical fiber 300.

The light returned to the optical integrated circuit device 400 is divided into a plurality of different lights through the birefringent modulator 440.

In detail, the light returned to the optical integrated circuit device 400 is divided into the first to third Y branching paths 422, 424 and 426 into the other lights proceeding to the MPD 486 and the PD2 484 and PD1 482 Loses.

The light traveling to the MPD 486 and the PD2 484 of the divided light passes through the 22.5 ° half wave plate 464 and passes through the 45 ° sine wave plate 462 ) Through the waveguide-type polarizers 420, respectively.

In this process, the interference signal detected through the PD1 482 and the PD2 484 may have a phase difference of? / 4.

In order to confirm that the characteristics of the quadrature phase shifted interferometer can be obtained by using the two types of wave plates, that is, the 22.5 ° half wave plate 464 and the 45 ° sine wave plate 462, the interference signal is induced using the Jones matrix Respectively.

The electric field of the waves finally detected in the PD1 482 and the PD2 484 in consideration of the optical elements included in the optical integrated circuit element 400 and the optical parts inserted into the sensing head 200 is expressed by the following equation .

.... 수식(1)

(1)

.... 수식(2)

(2)

는 외부 전류신호에 비례하며, 진폭

와 주파수 ω를 가지는 신호로 표현할 수 있다. 그리고, 이에 부가하여 위상변조기(421)에 의해 인가되는 바이어스 위상값을

라고 할 때, 두 편광간의 최종적인 위상차이는 다음과 같이 표현될 수 있다.Faraday rotation angle

Is proportional to the external current signal, and the amplitude

And the frequency ω. In addition, the bias phase value applied by the phase modulator 421 is set to

, The final phase difference between the two polarized lights can be expressed as follows.

....................................수식(3)

.................................... Equation (3)

The light intensity measured at PD1 482 and PD2 484 from equation (3) is expanded as follows.

..... 수식(4)

(4)

..... 수식(5)

(5)

,

은 Bessel functions of the first kind 함수들이다. here,

,

Are the Bessel functions of the first kind functions.

인 작은 신호

에 대해서,

과

로 부터의 AC 필터링에 의해 진폭신호

과

로 구해진다.

Small signal

about,

and

Lt; RTI ID = 0.0 > AC < / RTI >

and

.

로부터 얻을 수 있다.Finally,

Lt; / RTI >

A phase modulator 421 integrated in the optical integrated circuit device 400 is used to change the operating point of the sensor in the initialization step.

Since the thermo-optic effect of the polymer optical waveguide device has a small difference according to the polarization, the birefringence of the optical waveguide can be controlled by applying heat.

를 변화시키기 때문에 PD1(482) 및 PD2(484)에서 간섭신호를 얻을 수 있다.During the initialization step of normalizing the PD gain by operating the phase modulator 421, the phase modulator 421 modulates the PD gain by using Equations (4) and

The interference signal can be obtained at the PD1 482 and the PD2 484. [

In this way, it can be confirmed that the sensor operating curve shows a phase difference of exactly 90 °.

In order to confirm birefringence modulation characteristics of the optical integrated circuit device 400 manufactured through the above-described manufacturing process, a voltage is applied to a phase modulator fabricated on a linear optical waveguide, After generating heat, we looked at the polarization state of the output signal.

The fabricated phase modulator has a width of 40 μm, a length of 10 mm, and a resistance of 145 Ω.

The input light has a polarization extinction ratio of 30dB or more through a fiber polarizer, and the PM fiber optical axis of the fiber polarizer is aligned at 45 ° to the substrate to excite the TE and TM modes. The output polarized state is observed on the polarization analyzer's Poincare sphere Respectively.

4 (a) shows a result of a polarization state in which a 45-degree input linearly polarized light is converted at an output portion due to a change in birefringence due to heat, on a Poincare sphere, and FIG. 4 (b) A graph showing the relative phase difference between TE and TM polarized light according to the power applied to the heater is shown.

Referring to these figures, as the voltage increases, the polarization changes over a circular path connecting RHCP, + 45 ° linear polarization point on the Poincare sphere.

From the measured data, the phase difference between the TE and TM polarization components proportional to the heating power applied to the phase modulator can be obtained, as shown in Fig. 4 (b).

는 58.8mW로 확인되었다.Then, a heating power for obtaining a phase difference π between the two polarized lights,

Was confirmed to be 58.8 mW.

On the other hand, the initialization process of the optical integrated circuit device was performed prior to the current measurement experiment.

5A is a diagram showing an interference signal appearing at PD1 and PD2 when a voltage is applied to a phase modulator. FIG. 5B shows a phase difference between two measured interference signals A lithographic figure drawn using two interfering signals is shown.

의 함수로써 출력 간섭신호를 측정하였다.The phase modulator is driven so that the relative phase difference between TE and TM polarized light is 2π or more, and as shown in Fig. 5 (a)

The output interference signal was measured.

과

의 최대값과 최소값을 비교하여 동일한 modulation depth가 되도록 PD1과 PD2의 gain 값을 조정하였다.

and

The gain values of PD1 and PD2 were adjusted so that the same modulation depth was obtained.

In order to confirm that the phase difference of the two output interference signals becomes 90 °, the Lisa main figure is drawn, and a clean circle which is not distorted for one period can be confirmed as shown in FIG. 5 (b).

Meanwhile, in order to amplify the intensity of the magnetic field applied to the optical fiber, a 60 Hz AC signal was applied to the toroidal current loop as shown in FIG.

6 is a set of current toroids used to amplify the intensity of a magnetic field applied to a sensing fiber coil by 10 times. In order to confirm the linearity of the photocurrent sensor, the current applied to the toroid was gradually increased from 0.03 to 0.55 kA Again reduced.

FIG. 7 shows a graph showing the relative error of the sensor output measured when the applied current is varied from 0.3 to 5.5 kA (toroidal applied current 0.03 to 0.55 kA) and the electric current sensor value.

Referring to the figure, the current signal measured according to the toroidal applied current is compared with the output of the reference CT, and the same output value appears in the process of increasing and decreasing the current. The relative error is ± 0.5 %.

The stability of the sensor was verified by conducting a long time current measurement experiment without bias feedback, and normalization was performed using the signal of MPD to correct the power of the light source.

Figs. 8A to 8C are diagrams showing the result of measuring the long-term current in a state in which there is no operating point control.

> 과 <

>를 계산한 결과를 도 8의 (a)에 나타내었으며, 두 신호의 크기로 볼 때 각각의 초기 동작점은 λ/4 지점에서 많이 벗어나 있으며, 시간에 따라 약간의 변화가 나타났다. Using the interferometer output signal obtained from PD1 and PD2, time average power <

> And <

The results are shown in Fig. 8 (a). From the magnitudes of the two signals, each initial operating point deviates much from the? / 4 point and slightly changed with time.

The amplitude of the 60 Hz AC signal varied by about 10% according to the bias change as shown in FIG. 8 (b).

However, in Fig. 8 (c) showing the root sum square value of the two amplitude signals, the relative error is maintained within 1% of the signal.

100: photocurrent sensor 200: sensing head
300 ......... Polarization maintaining optical fiber 400 ......... optical integrated circuit element
462 ........ 45 ° sandwich plate 464 ........ 22.5 ° This sandwich plate

Claims (4)

An optical integrated circuit device which transmits an input light to an optical fiber coil constituting a sensing head and forms a path for transmitting reflected light reflected by a mirror provided in the optical fiber coil to a photodetector;
A sensing head connected to the optical integrated circuit device through a polarization maintaining optical fiber to transmit light and to be reflected by the mirror after the transmitted light is converted into two circularly polarized states through a sine wave plate, &Lt; / RTI &
In the optical integrated circuit device,
A first Y branch path for transmitting light returning from the sensing head to the photodetector is formed and the light transmitted to the photodetector by the first Y branch path is branched by the second Y branch path, Half goes to the MPD monitoring the power change of the light source, the remaining light goes through the third Y branch,
In one path among the paths branched by the third Y branching path, a half-wave plate (HWP) inclined at 22.5 ° with the substrate is passed through the waveguide-type polarizer. In the other path, the quarter wave plate (QWP) The structure of an optical interferometer that changes from a photodetector to a current through a polarizer.
The method according to claim 1,
And a phase modulator is further provided on an incident path of the input light.
An optical fiber coil for delaying the phase of the light converted into the circularly polarized light, and an optical fiber coil provided at the end of the optical fiber coil for transmitting the light, A sensing head including a mirror for reflecting light; And
And an optical integrated circuit device connected to the polarization maintaining optical fiber for transmitting light incident from a light source to the sensing head and forming a path for transmitting light reflected from the sensing head to a photodetector, ,
In the optical integrated circuit device,
First to third Y branching paths forming a return path of light reflected from the sensing head portion and sequentially branched based on a returning direction,
A half wave plate (HWP) provided at one side of the path of light branched at least by the third Y branching path and tilted at 22.5 DEG to the substrate,
A quarter wave plate (QWP) provided on the other path of the third Y branch and inclined by 45 [deg.] From the substrate,
And two waveguide-type polarizers provided on both sides of the third Y branch. The two optical signal input / output characteristic curves output through the waveguide polarizer have a phase difference of 90 ° with respect to each other, / &Lt; / RTI &gt; voltage signal.
Forming a lower cladding layer on a silicon substrate and forming an optical waveguide pattern on the lower cladding layer to form a core layer;
Forming a first upper cladding layer by coating a polymer on the upper side of the core layer; depositing chromium (Cr) and gold (Au) on the first upper cladding layer and then etching to form a waveguide polarizer;
Forming a second upper cladding layer by spin-coating a polymer on the first upper cladding layer after forming the waveguide polarizer;
A phase modulator forming step of forming a phase modulator with a Cr-Au metal thin film after the formation of the second upper cladding layer;
An installing step of installing a wave plate on the optical waveguide and
And a packaging step of arranging and connecting the optical fiber array to the optical waveguide after the wave plate is installed, and connecting wires to the phase modulator,
Wherein the grooved line is formed by using a dicing saw in the step of installing the wave plate, and the substrate is provided with a four-sided wave plate which is inclined by 45 DEG with respect to the substrate and the half wave plate tilted by 22.5 DEG with respect to the optical axis. &Lt; / RTI &gt;

Images