KR20210151480A - Polymeric waveguide Bragg reflecting tunable wavelength filters - Google Patents

Abstract

In a WDM optical communication systems required for 5G communication network, a narrow bandwidth that satisfies a channel spacing of 100 GHz, the wide wavelength tunability that can accommodate multiple channels, and high SMSR characteristics are required. In order to realize a wavelength filter that satisfies the complicated conditions, the present invention proposes a polymer waveguide-based Bragg grating filter having an original structure that was not previously available. The structure in which asymmetric mode-separated optical waveguides and inclined Bragg gratings are combined can separate a reflected signal without an external circulator, and through two Bragg grating reflections of a two-stage connection, a reflection bandwidth can be more narrowed and the SMSR characteristics can be improved. In addition, by passing through two mode-separating elements, a crosstalk signal caused by abnormal mode coupling can be suppressed. The proposed device exhibits a 20-dB bandwidth of 1 nm and the SMSR characteristics of over 35 dB, and enables tunable wavelength filtering over a wide wavelength range.

Description

Polymeric waveguide Bragg reflecting tunable wavelength filters

Various embodiments relate to a tunable filter used for the purpose of filtering only one specific wavelength in an optical signal transmitted by mixing several different wavelengths in a WDM optical communication system.

In the optical communication system required for the rapidly expanding 5G communication network, a wavelength signal that provides a data transmission rate of 10 Gbps per channel is transmitted by multiplexing 40 wavelengths at 100 GHz channel intervals over the C-, L-, and O-band bands. Wavelength division multiplexing (WDM) technology is used. For this purpose, a polymer Bragg grating-based tunable laser having a wide tunable wavelength range and low price due to a simple device structure is used as a light source for this purpose. By modulating a tunable laser using a data signal to be transmitted, an optical signal corresponding to a specific wavelength can be obtained. The core of WDM technology is to generate different wavelengths using several of these tunable lasers, modulate each with a desired data signal, collect several different optical wavelength signals at once and transmit them through one optical fiber. In this way, it is possible to maximize the amount of data transmitted per hour that can be transmitted through one optical fiber. When the generated and transmitted optical signal reaches the receiving end, it is necessary to separate the combined optical signals of different wavelengths again.

In the early WDM optical communication system with a small number of channels, a thin film filter was mainly used to separate wavelength signals. The thin film filter was a filter that was easy to access due to its simple fabrication and high yield, but as the number of channels increases and the channel spacing decreases in the WDM optical communication system, the number of deposition layers increases exponentially, complicating the manufacturing process and lowering the yield. do. On the other hand, by using an Arrayed Waveguide Grating (AWG), which separates signals of different wavelengths into different paths, it is possible to spatially separate signals of different wavelengths to advance to different optical fiber outputs. However, when the WDM system needs to change the wavelength of the tunable laser when necessary, the use of an AWG-like device causes a problem in which the output path of a specific wavelength is changed. A troublesome situation arises. Tunable Wavelength Filter (TWF) does not spatially separate wavelength signals, but selects only one wavelength signal and sends it out to the same output optical fiber. The wavelength is changed using a tunable laser in 5G WDM system. Even if you do this, it is possible to filter and detect a specific wavelength without switching the output optical fiber.

Among TWFs of various structures, the simplest possible wavelength tunable filter is a structure using an optical fiber Bragg grating and a piezo-electric transducer (PZT). However, it is difficult to make the device size small, and the change in characteristics of PZT with time remains a problem to be solved. In the case of a wavelength tunable filter of a ring resonator structure manufactured using a silicon optical waveguide, thanks to a very small device structure, it has an excellent advantage in integration. However, since the ring resonator has a narrow free spectral range (FSR), there is a problem in that wavelengths other than the desired wavelength are also output when the WDM optical signal in which several channel wavelengths are mixed passes through. In order to increase the FSR, it is necessary to connect several ring resonators to obtain an output. In this case, the yield of the manufacturing process decreases and it is not easy to change the wavelength. Optical waveguides using lithium niobate crystals and tunable wavelength filters using acoustic wave-based acousto-optic effects have also been widely studied. Compared to general thermo-optical devices, devices using acousto-optic effects have the advantage of having quick response characteristics, but the insertion loss of the devices is large and the manufacturing process is complicated, so there are many problems to be solved for mass production.

Compared with the other technologies above, the polymer optical waveguide device has a low driving power due to its high thermal-optical effect and low heat transfer characteristics, and the ability to vary the reflection wavelength of the Bragg grating by several tens of nm or more using only a simple micro-heater. have it The advantages of such polymer Bragg gratings were primarily applied to the development of external resonator-type tunable lasers, and were adopted as necessary parts for 5G optical communication networks. In addition, development of a variable optical attenuator device and a digital optical switch device using the high thermo-optical characteristics of the polymer optical waveguide device has been completed.

Research on TWF for WDM optical communication has been continuously conducted using a polymer Bragg grating with such unique properties. In this process, we focused on achieving narrow bandwidth, large side-mode suppression ratio and low insertion loss. In order to narrow the bandwidth, an epodized Bragg grating filter with a gradual change in depth using a shadow mask has been studied. Epodized Bragg gratings are fabricated using a shadow mask, which reduces bandwidth and significantly improves SMSR, but requires an external circulator to receive the reflected signal. A device structure using an asymmetric Y-branching waveguide and a tilted Bragg grating is proposed to extract the output light in a different direction from the input optical fiber in a device in which all components are integrated without using an external circulator. However, the side mode suppression ratio (SMSR) measured in the fabricated device is not large enough due to the combined reflection between the even modes in the inclined Bragg grating and the crosstalk in the asymmetric mode separator. did In addition, the 20-dB bandwidth of the Bragg grating reflection spectrum was 4.6 nm, which was too wide, and the adjacent channel crosstalk was very high as -12 dB, showing insufficient characteristics to filter the WDM signal at the 100 GHz channel interval.

Various embodiments are to implement tunable wavelength filters (TWF) that can filter and extract only one desired wavelength among multiple multiplexed wavelength signals separated by 100 GHz (1.6 nm) intervals in a 5G WDM optical communication system. . For this, the pass bandwidth must be narrow enough to satisfy the 100 GHz channel spacing while the wavelength tunable range is wide enough, and the SMSR value of 30 dB or more must be secured to cleanly remove other adjacent wavelengths. TWF that can satisfy these requirements has not yet been published, and various embodiments are to solve the problem by proposing a unique structure connecting the inclined Bragg lattice in two stages. Two stage cascaded tilted grating TWF can further narrow the reflection bandwidth and improve SMSR through two Bragg grating reflections. In addition, it is possible to significantly reduce the crosstalk signal due to abnormal mode coupling by going through two mode isolation elements.

In order to implement TWF using a polymer Bragg grating, a circulator device is needed to extract the signal reflected from the Bragg grating as an optical waveguide to another path, which increases the overall volume and makes integration difficult. In order to redirect the wavelength reflected from the Bragg grating to a different path without an external circulator, a tilted Bragg grating can be used to reflect and cause optical coupling between an even mode and an odd mode. At this time, in order to make the direction of the input previous mode and the reflected right mode different from each other, the Y-branch of the asymmetric optical waveguide is also required. 1 shows a basic tilting lattice TWF structure connecting these two elements. The normal mode conversion process in the slanted grid TWF is as follows. The previous mode component excited in the two mode optical waveguide through the Y-branch narrow waveguide changes to the right mode when it is reflected by the tilted Bragg grating. Thereafter, the reflected right mode is output along a wide waveguide in the mode-separated Y-branching optical waveguide. This normal mode conversion reflection process can be called NOEW conversion. In an actual device, various mode conversions occur due to the angle error of the Bragg grating and the crosstalk phenomenon of the mode separation device, resulting in unwanted reflection peaks. These cause deterioration of SMSR and adjacent channel crosstalk characteristics.

Various embodiments propose a two-stage connection TWF structure as shown in FIG. 2 that can be implemented by connecting the above-mentioned basic TWF element in two stages. In this device, the light reflected from the first-stage structure and returned to the wide waveguide is propagated through the tapered optical waveguide to the narrow optical waveguide of the second-stage device. The subsequent process again undergoes the NOEW mode conversion described in the first stage device, and the final output is directed in the opposite direction to the input, which facilitates packaging. In this way, in the process of undergoing two reflections and mode separation, the reflection spectrum becomes narrower and the surrounding modes caused by mode crosstalk are suppressed and disappear.

According to various embodiments, the structure in which the asymmetric mode separation optical waveguide and the inclined Bragg grating are combined can separate the reflected signal without an external circulator, and the reflection bandwidth through two Bragg grating reflections through the two-stage connection can be made narrower and the SMSR characteristics can be improved. Also, a crosstalk signal due to abnormal mode coupling can be suppressed while passing through the two mode isolation elements. The proposed device exhibits a 20-dB bandwidth of 1 nm and an SMSR characteristic of over 35 dB, enabling tunable wavelength filtering over a wide wavelength range. Through this, the tunable wavelength filter, which will play a key role in the currently active 5G WDM optical communication market, can be manufactured and supplied inexpensively using a polymer Bragg grating element. In addition, it can be presented as a good alternative in the next-generation optical communication network such as NG-PON2, which requires a narrow channel interval and a wide tunable wavelength range.

1 is a perspective view of a tunable filter including an asymmetric Y-branching optical waveguide including a narrow optical waveguide and a wide optical waveguide, and an inclined Bragg grating, according to an exemplary embodiment.
FIG. 2 is a perspective view of a tunable filter configured in two stages by connecting an output unit of the tunable filter element shown in FIG. 1 to an input unit of a second tunable filter element through an optical waveguide taper, according to another embodiment.
3A is a design result for finding an effective index of a waveguide mode that can exist in an optical waveguide included in a tunable filter.
3B is a result of calculating the reflectance generated in the inclined Bragg grating according to the change in the length of the grating. Mode-coupling reflection between right-modes in the first-stage Bragg grating and reflection values by the previous mode-right mode combination are shown, and the second-stage Bragg grating shows the reflection values by the previous-right mode combining.
3C is a result of calculating an output reflection spectrum appearing through one-stage reflection or two-stage reflection in the proposed tunable filter.
FIG. 3D is a result of checking the 0.5 dB, 10 dB, and 20 dB bandwidth values in the reflection spectrum calculated in FIG. 3C according to the change in the grating length.
4 is a perspective view showing a flow chart of a manufacturing process of the two-stage connection tunable wavelength filter shown in FIG. 2 .
5A is a photograph of a Bragg grating fabricated on a 4-inch silicon wafer using a laser interferometer.
5B is an SEM photograph of a Bragg lattice pattern appearing when photoresist is exposed.
FIG. 5c is an SEM photograph of the state in which the photoresist Bragg lattice pattern produced in FIG. 5b is engraved into the lower cladding layer through oxygen plasma etching.
6A is a perspective view of a reflection spectrum measuring apparatus of a tunable wavelength filter.
6b is a spectrum result of confirming the initial reflection wavelength of the proposed two-stage connection tunable filter through OSA.
FIG. 6c is a spectrum result obtained by checking the wavelength reflected by the integrated application of light to Port A and Port B of FIG. 6A through OSA.
6d is a result of the output reflection spectrum confirmed after applying a small bias power to the Bragg grating on the Port A side in order to make the reflection wavelength condition of the two Bragg gratings the same.
7A shows a change in the reflection spectrum that appears when heat is generated by supplying power to the integrated micro-heat.
7B is a result of measuring the wavelength peak value of the reflection spectrum moving in proportion to the electric power applied to the micro-heater.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view of a tunable filter including an asymmetric Y-branching optical waveguide including a narrow optical waveguide and a wide optical waveguide, and an inclined Bragg grating, according to an embodiment.

Referring to FIG. 1 , a tunable filter 100 according to an exemplary embodiment may include a substrate 110 , a core and a cladding layer 120 , and a tunable filter element 130 .

The substrate 110 may support components of the tunable filter 100 .

The core and the cladding layer 120 may be stacked on the substrate 110 . The core and cladding layer 120 may include a lower cladding layer, a core layer, and an upper cladding layer. The lower cladding layer may be stacked on the substrate 110 , the core layer may be stacked on the lower cladding layer, and the upper cladding layer may be stacked on the core layer. Here, the core layer may be made of a polymer material.

The tunable filter element 130 may include optical waveguides 131 , 133 , and 135 , an inclined Bragg grating 137 , and a microheater 139 . In this case, the tunable filter element 130 may be disposed inside the core and the cladding layer 120 . For example, the optical waveguides 131 , 133 , and 135 and the inclined Bragg grating 137 may be disposed on the core layer, and the microheater 139 may be disposed on the upper cladding layer. The optical waveguides 131, 133, and 135 include an input unit (hereinafter, used interchangeably with the term “narrow optical waveguide”) 131, and a mode separation unit (hereinafter, used with the term “mode-separated optical waveguide”) (133) and an output unit (hereinafter, used interchangeably with the term “wide optical waveguide”) 135 . The input unit 131 and the output unit 135 are branched from the mode separation unit 133 , and the width of the input unit 131 may be narrower than the width of the output unit 135 . Accordingly, the optical waveguides 131 , 133 , and 135 may exhibit an asymmetric Y-branch structure. The inclined Bragg grating 137 may be disposed adjacent to the mode separation unit 133 . The microheater 139 may be disposed opposite the inclined Bragg grating 137 with the mode separation unit 133 interposed therebetween.

According to an embodiment, the input unit 131 may allow light to be incident therein. In addition, the inclined Bragg grating 137 together with the mode separation unit 133 may generate a prior-mode coupling with respect to the incident light, thereby reflecting at least a portion of the incident light. Through this, the output unit 135 may output the reflected light.

In a typical Bragg grating optical waveguide device, the filtered wavelength signal is returned to the input port to which the light source is connected. In order to send such a reflected signal to the photodetector, an external circulator is absolutely necessary. If the device structure is improved so that the reflected light can be extracted through a different path without using an external circulator, the optical waveguides 131, 133, and 135 having an asymmetric Y-branch structure such as the tunable filter 100 according to an embodiment. ) and an inclined Bragg grating 137 are required.

According to an embodiment, the light incident through the narrow optical waveguide 131 undergoes a mode evolution process in which a mode shape is gradually changed while passing through the mode separation optical waveguide 133 . The light that is incident through the narrow optical waveguide 131 and undergoes the mode evolution process forms a default mode in the dual-mode optical waveguide 133 manufactured on the inclined Bragg grating 137, and this default mode is the inclined Bragg grating 137. It is reflected in the right mode form by the grating 137 . The reflected right mode undergoes a mode evolution process again while passing through the mode separation optical waveguide 137 in the opposite direction, and this time evolves toward the optical waveguide 135 having a wider width than the input direction. The above process describes the ideal mode conversion process, and the optical signal goes through the mode, the previous mode, the right mode, and the wide optical waveguide mode of the narrow optical waveguide 131. Defined by mode conversion.

However, in the actually fabricated device, the output spectrum is not ideal due to the combined reflection between the crosstalk phenomenon occurring in the optical waveguides 131 , 133 , and 135 of the asymmetric Y-branch structure and the right mode occurring in the inclined Bragg grating 137 . Wavelength components are included. Due to this, the SMSR value of the tunable filter is lowered and cross-channel crosstalk occurs in adjacent channels.

FIG. 2 is a perspective view of a tunable filter configured in two stages by connecting an output unit of the tunable filter element shown in FIG. 1 to an input unit of a second tunable filter element through an optical waveguide taper, according to another embodiment.

Referring to FIG. 2 , a tunable filter 200 according to another embodiment includes a substrate 210 , a core and a cladding layer 220 , a first tunable filter element 230 , and a second tunable filter element 240 . may include

The substrate 210 may support components of the tunable filter 200 .

The core and the cladding layer 220 may be stacked on the substrate 210 . The core and cladding layer 220 may include a lower cladding layer, a core layer, and an upper cladding layer. The lower cladding layer may be stacked on the substrate 210 , the core layer may be stacked on the lower cladding layer, and the upper cladding layer may be stacked on the core layer. Here, the core layer may be made of a polymer material.

The first tunable filter element 230 may include first optical waveguides 231 , 233 , 235 , a first inclined Bragg grating 237 , and a first microheater 239 . The second tunable filter element 240 may include second optical waveguides 241 , 243 , and 245 , a second inclined Bragg grating 247 , and a second microheater 249 . In this case, the first tunable filter element 230 and the second tunable filter element 240 may be disposed inside the core and the cladding layer 220 . For example, the first optical waveguides 231 , 233 , and 235 , the first inclined Bragg grating 237 , the second optical waveguides 241 , 243 , 245 , and the second inclined Bragg grating 247 are a core layer. The first microheater 239 and the second microheater 249 may be disposed on the upper cladding layer.

The first optical waveguides 231 , 233 , and 235 include a first input unit (hereinafter, the term “first narrow optical waveguide” is used interchangeably) 231 and a first mode separation unit (hereinafter, first mode separation light) 231 . It may include a first output unit (hereinafter, used interchangeably with the term "a waveguide") 233 and a first output unit (hereinafter, referred to as a "first wide optical waveguide") 235 . The first input unit 231 and the first output unit 235 are branched from the first mode separation unit 233 , and the width of the first input unit 231 may be smaller than the width of the first output unit 235 . Accordingly, the first optical waveguides 231 , 233 , and 235 may exhibit an asymmetric Y-branch structure. The first inclined Bragg grating 237 may be disposed adjacent to the first mode separation unit 233 . The first microheater 239 may be disposed opposite the first inclined Bragg grating 237 with the first mode separation unit 233 interposed therebetween.

The second optical waveguides 241 , 243 , and 245 include a second input unit (hereinafter, the term second narrow optical waveguide is used interchangeably) 241 and a second mode separation unit (hereinafter, second mode separation light). and a second output unit (hereinafter, used interchangeably with the term “second wide optical waveguide”) 245 ). The second input unit 241 and the second output unit 245 may be branched from the second mode separation unit 243 , and the second input unit 241 may be connected to the first output unit 235 . In addition, the width of the second input unit 241 may be narrower than the width of the first output unit 235 and may be narrower than the width of the second output unit 245 . Accordingly, the second optical waveguides 241 , 243 , and 245 may exhibit an asymmetric Y-branch structure. The second inclined Bragg grating 247 may be disposed adjacent to the second mode separation unit 243 . The second microheater 249 may be disposed opposite the second inclined Bragg grating 247 with the second mode separation unit 243 interposed therebetween.

According to another embodiment, the first input unit 231 and the second output unit 245 may extend in opposite directions to each other in the core layer. In this case, in the core layer, two axes passing through the center point of the core layer may be defined. In other words, the core layer may lie on a plane defined by the axes. In addition, the core layer may be divided into four regions by axes. In this case, the first mode separating unit 233 and the second mode separating unit 243 may be respectively disposed in any two of the regions located in a diagonal direction to each other. In addition, the first input unit 231 and the second output unit 245 extend in the other two of the regions in the core layer, respectively, so that the first mode separation unit 233 and the second mode separation unit 243 are respectively extended. can be connected to each.

According to another embodiment, the first input unit 231 may incident the light. In addition, the first inclined Bragg grating 237 together with the first mode separation unit 233 may generate a prior-right mode coupling with respect to the incident light to reflect at least a portion of the incident light. Thereafter, the first output unit 235 may output the reflected light to the second input unit 241 , and through this, the second input unit 241 may transmit the light output from the first output unit 235 . In addition, the second inclined Bragg grating 247 together with the second mode separation unit 243 may generate a prior-right mode coupling with respect to the transmitted light, thereby further reflecting at least a portion of the transmitted light. . Through this, the second output unit 245 may additionally output reflected light.

According to another embodiment, in order to improve the problems occurring in the single tunable filter element 130 as shown in FIG. 1 , as shown in FIG. 2 , the first tunable filter element 230 and the second tunable filter element 230 are The purpose is to improve SMSR and reduce adjacent channel crosstalk by connecting the wavelength filter element 240 in two stages. By connecting the first output unit 235 of the first tunable filter element 230 with the second input unit 241 of the second tunable filter element 240 through the optical waveguide tapered structure, the tunable filter 200 is performance can be improved.

In the design of the polymer optical waveguide of the tunable wavelength filter 200, core and cladding materials having refractive indices of 1.455 and 1.430, respectively, are used. A large difference in refractive index is advantageous for obtaining a high reflectance and a small bending radius in the inclined Bragg gratings 237 and 247. In the rib-type design with a core thickness of 2.5 μm and a side core layer thickness of 0.5 μm, a width of less than 4 μm satisfies the single-mode condition as shown in Fig. 3a. The mode-separated optical waveguides 233 and 243 with the inclined Bragg gratings 237 and 247 have a width of 8 μm to support both the right mode and the left mode. In the mode-separated optical waveguides 233 and 243, crosstalk for mode evolution is calculated using the beam propagation method, and varies according to the ratio of the narrow optical waveguide width to the wide optical waveguide width ratio or varies according to the branching angle. Crosstalk of less than -30 dB was confirmed in the structure where the branching angle was 0.3° and the width of the narrow optical waveguide and the wide optical waveguide was 4 and 3 μm, respectively. Due to the scattering of higher-order modes, the crosstalk increases as the angle increases.

The reflection spectra of the tilted Bragg gratings 237 and 247 may be calculated using a transmission matrix method. The reflectivity of the unit elements of the tilted Bragg gratings 237 and 247 is calculated by considering the mode overlap integral between modes having different mode distributions. The reflected power generated by ideal narrow-odd-even-wide (NOEW) and spurious narrow-even-even-wide is added to include the crosstalk effect of mode-separated optical waveguides (233, 243). Find the final reflection spectrum. In addition, the influence of NOOW mode and NEOW mode conversion, which have a small effect, is not considered. When the core thickness is 3.0 μm and the thickness modulation of the grating is 0.2 μm, the effective index is modulated to 0.0008. Reflection spectra from the 5 mm long inclined Bragg gratings 237 and 247 can be obtained as shown in FIG. 3B . Compared to single reflection tilted Bragg gratings (137), double reflection tilted Bragg gratings (237, 247) provide significantly improved SMSR, much narrower bandwidth, and lower adjacent channel crosstalk. The reflectance of the two-stage reflection inclined Bragg gratings 237 and 247 may be compared with the reflectance of the single reflection inclined Bragg grating 137 as shown in FIG. 3C . Since the two-stage reflection inclined Bragg gratings 237 and 247 are the square values of the single reflection spectrum, the reflectance is lower than that of the single reflection inclined Bragg grating 137 . To overcome this problem, it is necessary to increase the grating modulation depth and grating length of the two-stage reflection inclined Bragg gratings 237 and 247. When the reflectivity of the two-stage reflection tilted Bragg gratings 237 and 247 is increased, in order to achieve a higher reflectivity, the bandwidth of the reflection spectrum is affected as shown in FIG. 3D . However, the two-stage reflection inclined Bragg gratings 237 and 247 can generate a 20 dB bandwidth of 1.6 nm or less even when the reflectance reaches 100%. Therefore, crosstalk to an adjacent channel with a channel spacing of 0.8 nm can be kept below -20 dB.

의 핫플레이트 상에서 60 분동안 하드 베이킹 하였으며, 두께는 8.4 μm가 되었다. 제 1 기울어진 브래그 격자(237) 및 제 2 기울어진 브래그 격자(247) 제작을 위해, He-Cd laser 광원을 이용한 holographic interference 방법을 사용한다. 패턴 형성을 위해AZ MIR 703포토레지스트를 사용하였고 400 nm 정도의 얇은 두께를 확보하기 위해 PGMEA를 일정 비율 섞은 후 4000 rpm의 속도로 스핀코팅한다. 좀 더넓은 격자 영역을 확보하기 위해 확장되어 콜리메이션된 레이저빔을 일정 영역에 조사후, 샘플을 좌측으로 이동시켜 한번 더 조사한다. 이때 조사되는 영역간 중첩을 막기 위해` 쉐도우 마스크를 사용하여 조사될 수 있는 영역을 한정한다. 제 1 기울어진 브래그 격자(237) 및 제 2 기울어진 브래그 격자(247)는 도 5a와 같이 넓은 영역에 걸쳐 패터닝 되었으며, 도 5b의 SEM 이미지와 같이 주기가 538 nm이고 높이가 400 nm인 형상이 되었다. 제 1 기울어진 브래그 격자(237) 및 제 2 기울어진 브래그 격자(247)를 하부 클래딩층으로 전사시키기 위해, O2 plasma를 사용하여 15 초간 건식 식각하였고 도 5(c와 같이 236 nm 깊이로 식각 되었다. 제 1 기울어진 브래그 격자(237) 및 제 2 기울어진 브래그 격자(247)가 형성된 하부 클래딩층 위에 코어물질인 ZPU 13-455를 스핀코팅한 후 코어층 폴리머를 전면 에칭하여 코어 두께를 2.5 μm까지 줄이게 되었다. 광도파로 패터닝을 위해 AZ 5213를 4000 rpm의 속도로 스핀코팅한 후 MA6 mask aligner를 이용하여 UV조사하였다. 이때 제 1 광도파로(231, 233, 235)와 제 1 기울어진 브래그 격자(237), 및 제 2 광도파로(241, 243, 245)와 제 2 기울어진 브래그 격자(247)는 86.3°의 각도를 가지게 되며 하부 클래딩층 코팅 이전에 SU-8 물질로 미리 패터닝된 정렬 키패턴을 이용하여 정렬되었다. 제 1 광도파로(231, 233, 235) 와 제 2 광도파로(241, 243, 245)를 포함한 코어층은 ICP 내부에서3 분간 건식 식각 되어, 제 1 광도파로(231, 233, 235) 와 제 2 광도파로(241, 243, 245)의 두께가 2.5 μm, 남겨진 코어층의 두께가 0.5 μm인 립형태의 제 1 광도파로(231, 233, 235) 와 제 2 광도파로(241, 243, 245)를 형성하게 된다. 하부 클래딩 층과 같은 물질이 한번 더 코팅되어 총 두께는 17 μm가 되었으며, UV경화된 상부 클래딩 층 위에Cr-Au 진공 열 증착과 포토리소그라피를 통해 10-100 nm 두께의 제 1 마이크로히터(239)와 제 2 마이크로 히터(249)가 제작되었다. 마지막으로 샘플을 다이싱한 후 단면 폴리싱을 하여 광섬유와 연결할 준비를 마친다.As a core and a cladding layer 220 for manufacturing the tunable filter 200, ChemOptics Co.'s ZPU was used and the refractive indexes were 1.455 and 1.430, respectively. The manufacturing process sequence proceeds as shown in FIG. 4 . After removing the residual surface oxide on the silicon substrate 210, a ZPU 13-430 material, which is a lower cladding material, is spin-coated. Before coating the cladding layer, O2 plasma treatment is performed for 5 seconds and ZAP 1020 is coated to improve adhesion between the silicon wafer and the ZPU polymer. The coated ZPU material was 137 UV cured in a nitrogen chamber.

It was hard-baked for 60 minutes on a hot plate of For the production of the first inclined Bragg grating 237 and the second inclined Bragg grating 247, a holographic interference method using a He-Cd laser light source is used. AZ MIR 703 photoresist was used for pattern formation, and PGMEA was mixed in a certain ratio to secure a thin thickness of about 400 nm and then spin-coated at a speed of 4000 rpm. In order to secure a wider grid area, the expanded and collimated laser beam is irradiated to a certain area, and then the sample is moved to the left and irradiated once more. At this time, in order to prevent overlap between the irradiated regions, a shadow mask is used to limit the irradiated region. The first inclined Bragg grating 237 and the second inclined Bragg grating 247 were patterned over a wide area as shown in FIG. 5A, and a shape with a period of 538 nm and a height of 400 nm as shown in the SEM image of FIG. became In order to transfer the first inclined Bragg grating 237 and the second inclined Bragg grating 247 to the lower cladding layer, dry etching was performed for 15 seconds using O2 plasma and etched to a depth of 236 nm as shown in FIG. 5(c). ZPU 13-455, a core material, was spin-coated on the lower cladding layer on which the first inclined Bragg grating 237 and the second inclined Bragg grating 247 were formed, and then the core layer polymer was etched to reduce the core thickness to 2.5 μm. For optical waveguide patterning, AZ 5213 was spin-coated at a speed of 4000 rpm and then UV irradiated using a MA6 mask aligner At this time, the first optical waveguides 231, 233, 235 and the first inclined Bragg grating 237 , and the second optical waveguides 241 , 243 , 245 and the second inclined Bragg grating 247 have an angle of 86.3° and an alignment key pre-patterned with SU-8 material before coating the lower cladding layer. The core layer including the first optical waveguides 231, 233, 235 and the second optical waveguides 241, 243, and 245 was dry-etched inside the ICP for 3 minutes, and the first optical waveguide 231 was aligned using a pattern. , 233, 235) and the second optical waveguides 241, 243, 245 have a thickness of 2.5 μm, and the remaining core layer has a thickness of 0.5 μm, respectively. The waveguides 241, 243, and 245 are formed. The same material as the lower cladding layer was coated once more to a total thickness of 17 μm, and the UV-cured upper cladding layer was subjected to Cr-Au vacuum thermal evaporation and photolithography. A first micro-heater 239 and a second micro-heater 249 with a thickness of 10-100 nm were fabricated. Finally, after dicing the sample, it is prepared to be connected to the optical fiber by performing cross-sectional polishing.

In order to confirm the characteristics of the tunable filter 200 that has been manufactured, a measurement setup as shown in FIG. 6A was configured. The light output from the SLED light source having a center wavelength of 1550 nm and a 3-dB bandwidth of 60 nm passes through the polarization controller and is aligned with TE polarization and is directed to the narrow optical waveguide 231 of the first variable wavelength filter element 230. are entered Of the incident light, only the reflected light by the previous-right mode combination of the first inclined Bragg grating 237 passes through the first inclined Bragg grating 237 and the second inclined Bragg grating 247, and the second variable The wavelength filter element 240 is output through the wide optical waveguide 245 . Based on this, the results measured through OSA are shown in FIG. 6B . The measured central wavelength of the reflected light was 1528.3 nm, the 3-dB bandwidth was 0.3 nm, and the 20-dB bandwidth was 1.1 nm. Insertion loss was measured to be 5.5 dB and SMSR was confirmed to be 35 dB. Since the two inclined Bragg gratings 237 and 247 are manufactured at a distance of about 8.7 mm in the manufactured tunable filter 200, the reflected wavelengths of the gratings may appear different from each other. In order to confirm this, the spectrum of light reflected back through Port A and Port B shown in FIG. 6A rather than the first input unit 231 and the second output unit 245 was measured, and the result of FIG. 6C was obtained. Since Ports A and B are dual-mode optical waveguides, it is possible to make the right or left mode dominant depending on the conditions for aligning the optical fibers. By moving the optical fiber to the left and right from the center of the tunable filter 200, the state in which the peak value of reflected light appears the largest was adjusted, and in this case, the previous mode-right mode coupling efficiency was the highest. When light was incident on Port A and Port B, respectively, the central wavelengths of the reflected light were 1528.6 nm and 1528.0 nm, showing a difference of about 0.6 nm. In order to offset the difference in the Bragg reflection wavelength, a power of 12.6 mW is initially applied to the first microheater 239 of the first tilted Bragg grating 237 as a bias value. The reflection wavelength of the second tilted Bragg grating 247 matched with As a result, the output spectrum passing through the first tunable filter element 230 and the second tunable filter element 240 was shown as shown in FIG. 6d, and the insertion loss was reduced to 3.4 dB, and in the case of bandwidth, 0.5 dB was 0.28 nm, 3-dB was 0.5 nm and 20-dB was 1 nm. While the initial bias power was maintained, the reflected wavelength was measured as shown in FIG. 7A while increasing the additional power in steps of 15.8 mW to the two first micro-heaters 239 and the second micro-heaters 249 as shown in FIG. 7A . When a power of 206 mW was applied, a wavelength tunability of 11 nm and an adjacent channel crosstalk of -27.6 dB were confirmed. The TO coefficient of ZPU polymer is -1.8Х10-4, and the temperature change at the center of the optical waveguide to obtain 11 nm wavelength tunability is 56.8°. The result of plotting the peak position of the reflected wavelength with respect to the applied power is as shown in FIG. 7b, and the wavelength variable efficiency was found to be 54 nm/W. As the heater power increases, it is observed that the reflection pick gradually decreases and the bandwidth expands. As the temperature change value generated by the first microheater 239 and the second microheater 249 gradually decreases toward the substrate, the first optical waveguides 231, 233, 235 and the second optical waveguides 241, 243, 245 This is because the refractive index distribution is formed asymmetrically, which causes radiation of the waveguide mode. This problem is solved by forming the first microheater 239 and the second microheater 249 at the lower ends of the first optical waveguides 231, 233, 235 and the second optical waveguides 241, 243, 245, respectively. It can be solved by improving the uniformity. By using the lower electrode and the trench structure, the wavelength tunable efficiency can also be greatly improved. In particular, since the early mode has a weaker light binding force compared to the right mode, the radiation phenomenon can easily appear.

The tunable filter 200 according to various embodiments includes a first mode separation unit 233 and a first input unit 231 and a first output unit 235 branched from the first mode separation unit 233 . a first tunable filter element 230 including first optical waveguides 231, 233, 235, and a second input unit branched from the second mode separation unit 243 and the second mode separation unit 243 ( 241 ) and a second output unit 245 , and the second tunable filter element including second optical waveguides 241 , 243 , and 245 connected to the first output unit 235 with the second input unit 241 connected to the first output unit 235 . (240).

According to various embodiments, the first tunable filter element 230 may further include a first inclined Bragg grating 237 disposed adjacent to the first mode separation unit 233 .

According to various embodiments, the second tunable filter element 240 may further include a second inclined Bragg grating 247 disposed adjacent to the second mode separation unit 243 .

According to various embodiments, the tunable filter 200 includes a substrate, a lower cladding layer formed on the substrate, a lower cladding layer, and is made of a polymer material, and includes the first tunable filter element 230 and It may further include a core layer on which the second variable filter element 240 is formed, and an upper cladding layer formed on the core layer.

According to various embodiments, the first input unit 231 and the second output unit 245 may extend in opposite directions to each other in the core layer.

According to various embodiments, the first mode separation unit 233 and the second mode separation unit 243 are in the core layer, in the diagonal direction of each other among the regions by two axes passing through the center point of the core layer. It may be respectively disposed in any two of the locations.

According to various embodiments, the first input unit 231 and the second output unit 245 extend in the other two of the regions in the core layer, respectively, to form the first mode separation unit 233 and the second mode Each of the separation units 243 may be connected.

According to various embodiments, the first tunable filter element 230 is disposed opposite to the first inclined Bragg grating 237 with the first mode separation unit 233 interposed therebetween, and the first inclined A first microheater 239 for varying the wavelength of reflection by the Jean Bragg grating 237 may be further included.

According to various embodiments, the second tunable filter element 240 is disposed opposite to the second inclined Bragg grating 247 with the second mode separation unit 243 interposed therebetween, and the second inclined A second microheater 249 for varying the wavelength reflected by the Jean Bragg grating 247 may be further included.

According to various embodiments, the first output unit 235 and the second input unit 241 may be connected in a tapered structure.

According to various embodiments, the width of the first input unit 231 is narrower than the width of the first output unit 235 , and the width of the second input unit 241 is narrower than the width of the first output unit 235 , and , may be narrower than the width of the second output unit 245 .

According to various embodiments, in the first tunable filter element 230 , the first input unit 231 causes light to be incident, and the first inclined Bragg grating 237 has a default mode ( ) with respect to the incident light. Odd mode) - by generating an even mode coupling, at least a portion of the incident light is reflected, and the first output unit 235 may output the reflected light to the second tunable filter element 240 . have.

According to various embodiments, in the second tunable filter element 240 , the second input unit 241 transmits the light output from the first output unit 235 , and the second inclined Bragg grating 247 . , may generate a prior-right mode coupling with respect to the transmitted light to further reflect at least a portion of the transmitted light, and the second output unit 245 may additionally output the reflected light.

According to various embodiments, the tunable filter 200 may further include a cladding layer stacked on the core layer and formed with a refractive index smaller than the refractive index of the core layer.

The various embodiments of this document and the terms used therein are not intended to limit the technology described in this document to a specific embodiment, but it should be understood to include various modifications, equivalents, and/or substitutions of the embodiments. In connection with the description of the drawings, like reference numerals may be used for like components. The singular expression may include the plural expression unless the context clearly dictates otherwise. In this document, expressions such as “A or B”, “at least one of A and/or B”, “A, B or C” or “at least one of A, B and/or C” refer to all of the items listed together. Possible combinations may be included. Expressions such as “first”, “second”, “first” or “second” can modify the corresponding components regardless of order or importance, and are only used to distinguish one component from another. It does not limit the corresponding components. When an (eg, first) component is referred to as being “connected (functionally or communicatively)” or “connected” to another (eg, second) component, that component is It may be directly connected to the component or may be connected through another component (eg, a third component).

According to various embodiments, each component of the described components may include a singular or a plurality of entities. According to various embodiments, one or more components or operations among the above-described corresponding components may be omitted, or one or more other components or operations may be added. Alternatively or additionally, a plurality of components may be integrated into one component. In this case, the integrated component may perform one or more functions of each component of the plurality of components identically or similarly to those performed by the corresponding component among the plurality of components prior to integration.

Claims (6)

In the tunable wavelength filter,
a first tunable filter element including a first mode separation unit and a first optical waveguide including a first input unit and a first output unit branched from the first mode separation unit; and
A second tunable filter comprising a second mode separation unit and a second input unit and a second output unit branched from the second mode separation unit, wherein the second input unit includes a second optical waveguide connected to the first output unit comprising a component,
The first tunable filter element comprises:
a first inclined Bragg grating disposed adjacent to the first mode separation unit;
The second tunable filter element comprises:
The tunable filter further comprising a second inclined Bragg grating disposed adjacent to the second mode separator.
The method of claim 1,
Board;
a lower cladding layer formed on the substrate;
a core layer formed on the lower cladding layer, made of a polymer material, and on which the first tunable filter element and the second tunable filter element are formed; and
The tunable filter further comprising an upper cladding layer formed on the core layer.
3. The method of claim 2,
The first input unit and the second output unit,
In the core layer, a tunable wavelength filter extending in mutually opposite directions.
The method of claim 1,
The first tunable filter element comprises:
A first microheater disposed opposite the first inclined Bragg grating with the first mode separation unit interposed therebetween, and further comprising a first microheater for varying a reflection wavelength by the first inclined Bragg grating,
The second tunable filter element comprises:
A tunable wavelength filter disposed opposite to the second inclined Bragg grating with the second mode separation unit interposed therebetween and further comprising a second microheater for varying a reflection wavelength by the second inclined Bragg grating. .
The method of claim 1,
The first output unit and the second input unit,
Tunable wavelength filters connected in a tapered structure.
The method of claim 1,
The width of the first input part is,
narrower than the width of the first output part,
The width of the second input unit is,
The tunable wavelength filter is narrower than a width of the first output unit and narrower than a width of the second output unit.

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