KR100921508B1 - Polarization insensitivity slab waveguide, multiplexer/demultiplexer and method for making polarization insensitivity slab waveguide - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical devices used in wideband transmission networks, and more particularly, to optical devices having an improved polarization compensation function of optical signals and a method of manufacturing the same.

To this end, a polarization independent slab waveguide according to an embodiment of the present invention includes: an optical waveguide region formed on one side of a substrate and guiding an input optical signal; And a polarization compensation region formed on the other side of the substrate and compensating for the polarization of the optical signal that is input from the optical waveguide region and reflected and diffracted in the diffraction grating, wherein the optical waveguide region is in turn on the upper side of the substrate. A lower clad layer, a first core layer, and an upper clad layer formed, wherein the polarization compensation region extends from the optical waveguide region and is formed in turn on the other side of the substrate; And a second core layer formed between the first core layer and the upper clad layer, the present invention provides an optical device having improved reliability compared to conventional polarization compensation optical devices.

Slab Waveguide, Multiplexer, Diffraction Grating, Polarization Compensation

Description

POLARIZATION INSENSITIVITY SLAB WAVEGUIDE, MULTIPLEXER / DEMULTIPLEXER AND METHOD FOR MAKING POLARIZATION INSENSITIVITY SLAB WAVEGUIDE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical devices used in wideband transmission networks, and more particularly, to optical devices for compensating polarization of optical signals and methods of manufacturing the same.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2007-S-011-01, Title: Development of Optical Switch Technology for ROADM] ].

Recently, technologies for solving a wideband transmission network such as wavelength division multiplexing (hereinafter, referred to as WDM) have been rapidly developed in order to process a large amount of information due to the development of information and communication technology. Accordingly, problems of performance improvement and safety of optical devices such as a multiplexer (MUX) and a demultiplexer (DEMUX) used in a WDM method and the like have arisen.

As the optical signals transmitted in such an optical band transmission network propagate through the optical fiber waveguide, polarization is changed regularly or irregularly by environmental factors such as temperature and pressure. Therefore, when the optical signals transmitted in such a wideband transmission network are incident on the optical device for multiplexing, demultiplexing, switching, wavelength conversion and amplification, the optical signals are incident because the polarization characteristics of the incident optical signals are random. Optical devices are required to be polarization insensitivity.

On the other hand, optical devices generally include group III-V semiconductors such as silicon (Si), silica (SiO ₂ ), polymers, lithium niobate (LiNbO ₃ ), and gallium arsenide (GaAs) or indium phosphorus (InP). It is fabricated as an optical waveguide structure.

Signals emitted from the optical fiber and coupled to the optical waveguide structure are propagated in a mode suitable for the waveguide structure, that is, a guided mode, which is the basis of the waveguide mode (TE) (Transverse Electric) Since the mode and the transverse magnetic (TM) mode have different boundary conditions between media, propagation constants of the two modes are different. The propagation constant β is defined as in Equation 1.

Here, the effective refractive index n _eff , which is the eigen value of the waveguide mode, is determined by the optical waveguide structure (waveguide width, refractive index of the core material and the thickness of the clad layer, etc.) with respect to the polarized light.

On the other hand, since the phase of the traveling light varies in the light propagation direction for each mode, a phase difference occurs between the TE mode and the TM mode. The phase of the traveling light is defined as in Equation 2.

This phase difference greatly affects the characteristics of devices (optical couplers, wavelength converters, diffraction gratings, etc.) using interference phenomena according to the optical path length, and in particular, optical elements using diffraction characteristics, that is, waveguide-type concave diffraction gratings (planar-type concave diffraction grating (CDG)) and arrayed waveguide grating (AWG) have a significant impact on the performance. Problems caused by such a phase difference will be described below with reference to FIG.

1 is an exemplary view showing a demultiplexer using a conventional waveguide-type concave diffraction grating.

Conventional demultiplexers using concave diffraction gratings include input waveguides, slab waveguides, concave diffraction gratings, and output waveguide columns, and typically grow the lower clad layer, the core layer, and the upper clad layer on the substrate, followed by patterning and etching. It is implemented through work.

Optical signals of different wavelengths output from the optical fiber propagate through the input waveguide and the slab waveguide to the concave diffraction grating. Optical signals propagated to the concave diffraction grating are reflected at each grating plane. Wavelengths of which the phase difference is an integer multiple of 2π among the optical signals reflected from adjacent grating planes are subjected to constructive interference, so that the wavelengths have corresponding directions, that is, diffraction angles. Reflected. The diffraction characteristic described above is defined as in <Equation 3>.

Here, m represents a diffraction order, and in the waveguide type diffraction grating structure, since the effective refractive index of the waveguide is larger than that of air (refractive index = 1), m has a high order (m> 1) diffraction grating structure.

Meanwhile, optical signals focused at different diffraction angles β for each wavelength are propagated to output waveguides at different positions by the diffraction characteristics of the concave diffraction grating. The change in diffraction angle according to the wavelength is called angular dispersion and the change in position is called linear dispersion.

In the structure shown in FIG. 1, the input waveguide and the output waveguide columns may be implemented to be independent of polarization by controlling the transverse structure (the width of the waveguide and the shape of the waveguide) within a limited region with respect to the longitudinally grown material structure. . However, the slab waveguide is determined only by the longitudinal structure, and in most cases, the effective refractive index of each polarization mode is not the same, that is, birefringence, so that the TE mode component and the TM mode component of the output optical signal for the input optical signal Phase changes. This will be described with reference to FIG. 2.

2 is an exemplary diagram for showing a phase difference of an output optical signal to an input optical signal in a conventional slab waveguide.

FIG. 2 (a) is an exemplary diagram showing the phase of an optical signal input from an input waveguide to a slab waveguide, wherein the optical signal is an optical signal having an arbitrary polarization in which a TE mode and a TM mode are mixed. FIG. 2B is an exemplary diagram showing the phase difference of the output optical signal when the input optical signal as shown in FIG. 2A is reflected and diffracted in the diffraction grating and propagated on the output waveguide column.

Referring to FIGS. 2A and 2B, it can be seen that the phase of the output optical signal is different from that of the TE mode component and the TM mode component compared to the input optical signal. The phase change can also be expressed as a wavelength due to linear dispersion.

Therefore, there is a need for a technology that can solve the problems caused by the phase difference in the optical device using diffraction characteristics, that is, a technology capable of developing an optical device that is independent of polarization by implementing a waveguide having a birefringence of zero. . The reason why a waveguide with zero birefringence is required is that the difference in phase difference or propagation constant between the TE mode and the TM mode can be expressed by the birefringence which is the effective refractive index difference.

On the other hand, in order to solve the polarization characteristics due to the birefringence of the slab waveguide used in the demultiplexer as described above, the polarization compensation structure for each region by implementing a difference in the thickness of the upper clad layer of the polarization compensation region in the slab waveguide A method (He et al. "Optical Grating-based device having a slab waveguide polarization compensating region", US Patent no. 5,937,113, Date of patent Aug. 19, 1999; hereinafter referred to as Reference 1) has emerged. The above method will be described below with reference to FIG. 3.

3 is an exemplary diagram for describing a slab waveguide having a conventional polarization compensation structure.

Referring to FIG. 3A, a slab waveguide having a conventional polarization compensation structure includes a region 1 having an effective refractive index of n _TE1 , a birefringence of Δn ₁ , and an effective refractive index of n _TE2 , and a birefringence of Δn ₂ . Consists of area 2 for.

FIG. 3B is an exemplary diagram for showing the change of the effective refractive index and the birefringence according to the thickness of the upper clad layer of the slab waveguide having the structure as shown in FIG. 3A at the wavelength of 1550 nm. Referring to (b) of FIG. 3, as the thickness of the upper clad layer (t _clad ) becomes thinner, the effective refractive index n _TE of the TE mode and the effective refractive index n _TM of the TM mode decrease, and the birefringence Δn (n _TE − n _TM It can be seen that increases.

In addition, when the thickness of the upper clad layer increases by 1 μm or more, the effective refractive indices of the TE mode and the TM mode gradually converge to a constant value, and in this case, the birefringence also converges. Meanwhile, in FIG. 3B, the change of the refractive index with respect to the upper cladding layer thickness depends on the core layer thickness and the refractive index, and the thicker the core layer or the higher the refractive index, the more the waveguide mode is collected in the core layer. The clad layer thickness is reduced.

FIG. 3C illustrates the response of the TE mode and the TM mode before the polarization compensation region having the structure as shown in FIG. 3A is implemented, that is, when the thickness of the upper clad layer is 1 μm in the structure as shown in FIG. 1. 3 is an exemplary diagram illustrating a spectral response, and FIG. 3 (d) shows a thickness of the upper clad layer of region 1 having a thickness of 1 μm and an upper portion of region 2 in the structure shown in FIG. It is an exemplary figure which shows the response spectrum of TE mode and TM mode when the thickness of a clad layer is 0.3 micrometer.

Referring to FIG. 3C, in the slab waveguide before the polarization compensation region is implemented, it can be seen that a phase difference of about 0.4 nm occurs between the TE and TM modes of the output optical signal.

Referring to (d) of FIG. 3, by introducing a polarization compensation region having a thickness of 0.3 μm of the upper clad layer with respect to the phase difference of 0.4 nm shown in FIG. It can be seen that polarization compensation has been made. This compensation pattern is based on diffraction conditions where the phase difference of the propagation path of the incident optical signal in the diffraction grating structure is an integer multiple of 2π (Monolithically integrated grating cavity tunable lasers, IEEE Photonics Technology Letter, vol. 17, no.9, PP.1794- 1796, Sept. 2005, Oh Kee Kwon.

FIG. 3E is an exemplary view showing light distribution according to a waveguide mode for each region of a slab waveguide having the structure as shown in FIG. 3A. For convenience of explanation, only the light distribution for the TM mode is shown and described.

Referring to FIG. 3E, the light distribution in the region 1 represents a typical light distribution in which the peak value of the light intensity is located in the core layer because the refractive index of the core layer is the highest. It can be seen that the light distribution exhibits an abnormal light distribution characteristic in which the central axis of the light distribution deviates from the core layer due to the thickness of the upper clad layer which is relatively thin compared to the region 1.

Therefore, the waveguide mode of the region 2 is structurally unstable, and because the birefringence characteristic and the retardation variation are very sensitive to the upper clad layer thickness (in FIG. 3 (b), the thickness of the upper clad layer of the region 2 (0.3 mu m) If the change is ± 0.05㎛, the birefringence is 5 × 10 ⁻⁴ , and the phase difference occurs at 0.075 nm.

Meanwhile, an accurate etching depth is required to perform an etching process for implementing the region 2 as described above. In this case, since the etching depth alone is difficult to precisely control the etching depth, in Reference 1, selective wet etching and dry etching of InP using an etch stop layer using InGaAsP is used. In parallel, the thickness of the upper cladding layer is realized.

However, in hydrochloric acid and phosphoric acid-containing etchant (HCl: H ₃ PO ₄ ) which is widely used as an etchant for wet etching the InP material having the above structure, the hydrochloric acid may be etched according to the lattice direction of the material. Uniform etching for polarization compensation boundary due to anisotropic etching characteristics (Handbook of semiconductor lasers and photonic integrated circuits, Chapman & Hall, pp. 495-495, 1994, Y. Suematsu and ARAdams) There is a problem that is difficult to implement.

Meanwhile, FIG. 8 of Reference 1 discloses a structure in which an electrode is deposited in the region 2 and an additional polarization compensation is performed by injecting a current into the electrode pattern. However, when the metal pattern such as the electrode is deposited on the thin clad layer as described above, the perturbation of the waveguide mode is large due to the reflection of the metal material, and also, when the thermal annealing for the ohmic contact is performed. There is a difficulty in the manufacturing process because a metal material such as (Au) penetrates into the semiconductor material and increases light absorption.

On the other hand, the diffraction grating is implemented through dry etching in the vertical direction in the waveguide structure of the region 2, the verticality and uniformity in the etching depth direction affects the performance of the diffraction grating. Therefore, considering that the width corresponding to 1 / e ² (about 0.135) of the optical intensity of the area 2 is 2.7 μm, the dry etching equipment for the light intensity width can guarantee verticality and uniformity. It is required to be very precise equipment.

Accordingly, an object of the present invention is to implement a waveguide in which the light distribution in the polarization compensation region is less sensitive to waveguide material and structural parameters, thereby improving the performance and reliability of the optical device and at the same time increasing the yield.

In addition, another object of the present invention, to implement the waveguide is to prevent the irregular pattern caused by the anisotropy of the etchant.

In addition, another object of the present invention is to reduce the perturbation of the waveguide mode due to the reflective properties of the metal material generated by electrode deposition in implementing the waveguide.

In addition, another object of the present invention is to implement a waveguide requiring an etching condition lower than the etching conditions used in the prior art.

In addition, another object of the present invention can be understood by the following description and an embodiment of the present invention.

To this end, a polarization independent slab waveguide according to an embodiment of the present invention includes: an optical waveguide region formed on one side of a substrate and guiding an input optical signal; And a polarization compensation region formed on the other side of the substrate and compensating for the polarization of the optical signal that is input from the optical waveguide region and reflected and diffracted in the diffraction grating, wherein the optical waveguide region is in turn on the upper side of the substrate. A lower clad layer, a first core layer, and an upper clad layer formed, wherein the polarization compensation region extends from the optical waveguide region and is formed in turn on the other side of the substrate; And a second core layer formed between the first core layer and the upper clad layer.

In addition, the polarization independent multiplexer / demultiplexer according to an embodiment of the present invention for this purpose, the optical waveguide for receiving an optical signal from the outside or outputs the optical signal to the outside; A slab waveguide optically connected to the optical waveguide and receiving an optical signal from the optical waveguide or outputting an optical signal to the optical waveguide; And a concave diffraction grating for reflecting and diffracting an optical signal input from the slab waveguide and outputting the light signal to the slab waveguide, wherein the slab waveguide includes: an optical waveguide region formed on one side of a substrate and guiding an input optical signal; And a polarization compensation region formed on the other side of the substrate and compensating for the polarization of the optical signal that is input from the optical waveguide region and is reflected and diffracted by the concave diffraction grating, wherein the optical waveguide region is on the upper side of the substrate A lower cladding layer, a first core layer, and an upper cladding layer, which are formed in turn, wherein the polarization compensation region extends from the optical waveguide region and sequentially forms a lower clad layer, a first core layer, and an upper portion of the other side of the substrate; A clad layer and a second core layer formed between the first core layer and the upper clad layer.

In addition, the slab waveguide manufacturing method according to an embodiment of the present invention, to compensate for the polarization of the optical waveguide for guiding the optical signal input and the optical signal reflected and diffracted in the diffraction grating input from the optical waveguide region A slab waveguide manufacturing method comprising a polarization compensation region, comprising: (a) sequentially forming a lower clad layer, a first core layer, an etch stop layer, a second core layer, and a first upper clad layer on a substrate; (b) removing the first upper clad layer and the second core layer of the optical waveguide region by forming a first mask pattern on the first upper clad layer and performing dry etching and selective wet etching, and then the first mask Removing the pattern; And (c) forming a second upper clad layer on top of the optical waveguide region and the polarization compensation region.

As described above, in the present invention, since the refractive index and the birefringence characteristics are determined by the structure of the second core layer due to the introduction of the polarization compensation region in which the second core layer is formed, the thickness of the cladding layer is not affected by the thickness of the cladding layer as compared with the prior art. There is an advantage to implement a waveguide.

In addition, the present invention has a merit that a very accurate device can be realized because the thickness precision of 1 nm or less can be obtained through the growth equipment when the second core layer is grown.

In addition, the present invention, by forming an etch stop layer of the InP material and etching the InGaAsP material that can be etched by the anisotropic etchant to solve the problems caused by the irregular pattern caused by the anisotropy of the etchant There is this.

In addition, since the polarization compensation can be realized by making the thickness of the cladding layer of the polarization compensation region thicker than the thickness of the cladding layer of the conventional structure, the perturbation of the waveguide mode due to the reflection characteristic of the metal material due to electrode deposition can be reduced. There is an advantage to that.

In addition, the present invention has the advantage of improving the reliability of the device under the same equipment and conditions as the etching equipment and etching conditions used in the prior art.

The multiplexer serves to spatially combine input optical signals of different wavelengths coming from different ports into a single waveguide, and the demultiplexer separates optical signals of multiple channels coming from one input port by wavelength. Since there is a reversible relationship with each other, a demultiplexer will be described below for convenience of description. However, the scope of the present invention by the following description is not limited to the demultiplexer but also includes a multiplexer.

In addition, the optical device performing the multiplexing and demultiplexing includes a waveguide-type concave diffraction grating and an array waveguide diffraction grating as described above. Hereinafter, the waveguide-type concave diffraction grating will be described. However, the scope of the present invention by the following description is not limited to the waveguide concave diffraction grating but also includes an array waveguide diffraction grating.

Figure 4 is an example attempt to show a polarization independent demultiplexer according to an embodiment of the present invention. A polarization independent demultiplexer according to an embodiment of the present invention includes an input waveguide, an output waveguide column, a slab waveguide, and a concave diffraction grating. Hereinafter, the structure and role of the polarization independent demultiplexer according to an embodiment of the present invention will be described in detail with reference to FIG. 4.

As described above, optical signals having arbitrary polarizations of different wavelengths input from the outside are propagated to the concave diffraction grating through an input waveguide and a slab waveguide optically connected to the input waveguide, and diffraction characteristics of the concave diffraction grating plane Depending on the wavelength, it propagates to the output waveguide at different positions. In this case, in order to solve the above problems caused by the phase difference between the TE mode and the TM mode of the output optical signal, the polarization independent demultiplexer according to the embodiment of the present invention may include an optical waveguide region and a polarization compensation region for polarization compensation. A slab waveguide is included. Such a slab waveguide according to an embodiment of the present invention will be described in more detail below.

Referring to FIG. 4, a slab waveguide according to an embodiment of the present invention includes a substrate, an optical waveguide region including a lower cladding layer, a first core layer, and an upper cladding layer sequentially formed on one side of the substrate; Polarization compensation including a lower clad layer, a first core layer, an upper clad layer, and a second core layer formed between the first core layer and the upper clad layer extending from the optical waveguide region and sequentially formed on the other side of the substrate; It includes an area.

In the above structure, the substrate, the lower clad layer and the upper clad layer may be made of a group III-V combination, preferably made of InP material or GaAs material.

In addition, the first core layer and the second core layer may be made of InGaAsP material. At this time, if the band gap wavelength of the second core layer material is longer than the operating wavelength of the optical signal, the band gap wavelength of the second core layer material should be shorter than the operating wavelength of the optical signal.

On the other hand, in order to effectively change the characteristics (refractive index, birefringence) of the waveguide mode due to the introduction of the second core layer, when the refractive index of the second core layer is designed to be smaller than the first core layer refractive index, that is, When the band gap wavelength is shorter than the band gap wavelength of the first core layer material, it is preferable to make the thickness of the second core layer thicker than the thickness of the first core layer. In this case, however, the overall core layer thickness is increased, so that the multi-mode characteristics are easily shown. Therefore, it is necessary to design within the range to obtain the single mode characteristics. When the band gap wavelength of the second core layer material is long, the single core characteristic and the birefringence change characteristic can be easily satisfied by designing the second core layer thickness to be thinner than the first core layer thickness. At this time, it is preferable that the band gap wavelength of the first core layer material is higher than 1.05 mu m, and the band gap wavelength of the second core layer material is higher than 1.05 mu m.

In addition, the thickness of the upper clad layer can be arbitrarily adjusted during the slab waveguide manufacturing process according to an embodiment of the present invention described below. Such a method for manufacturing a slab waveguide according to an embodiment of the present invention will be described in detail with reference to FIG. 5 below.

5 is an exemplary view showing a method of manufacturing a slab waveguide according to an embodiment of the present invention.

First, as shown in FIG. 5A, a lower clad layer, a first core layer, an etch stop layer, a second core layer, and a first upper clad layer are sequentially formed on a substrate.

In this case, the substrate may use an InP substrate, and the lower clad layer, the etch stop layer, and the first upper clad layer may use a III-V group bond, preferably an InP material or a GaAs material.

In addition, the first core layer and the second core layer may use InGaAsP material, and the refractive index of the second core layer material is higher than that of the first core layer material. That is, the band gap wavelength of the second core layer material should be longer than the band gap wavelength of the first core layer material, and the band gap wavelength of the first core layer material is 1.05 μm (thickness = 0.6 μm), that of the second core layer material The band gap wavelength is at least 1.05 탆, preferably 1.3 탆.

Thereafter, as shown in FIG. 5B, a mask pattern is formed on the first upper clad layer, and dry etching and selective wet etching are performed to remove the first upper clad layer and the second core layer of the optical waveguide region. Remove the mask pattern.

In this case, it is preferable to use an insulating material such as silicon nitride (SiN _X ) or silica (SiO ₂ ) in the mask pattern forming step.

In addition, the etchant used in the selective wet etching of InGaAsP is preferably an etchant having isotropy with respect to the medium. The etchant is a solution of phosphoric acid, hydrogen peroxide and water (H ₃ PO ₄ : H ₂ O ₂ : H ₂ O) or a solution of sulfuric acid, hydrogen peroxide and water (H ₂ SO ₄ : H ₂ O ₂ : H ₂ O).

As described above, the present invention, unlike the prior art of forming the etch stop layer of the InGaAsP material and wet etching the InP, etching the InGaAsP material that can form the etch stop layer of InP material and can be etched by an anisotropic etchant As a result, problems caused by irregular patterns due to anisotropy of the etchant may be solved.

Subsequently, after removing the mask pattern as shown in FIG. 5C, the second upper clad layer is formed of the same material as that of the first upper clad layer. At this time, the formation thickness of the second upper clad layer may be appropriately adjusted according to the structural parameters for polarization compensation.

Subsequently, after forming a mask pattern on the second upper clad layer and performing dry etching to bond the diffraction grating as shown in (d) of FIG. 5, the mask pattern is removed when the mask pattern is removed. A polarization independent slab waveguide according to one embodiment of the invention is completed. A polarization independent slab waveguide according to an embodiment of the present invention manufactured as shown in FIG. 5 will be described below with reference to FIG. 6.

FIG. 6 is an example attempt to explain a polarization independent slab waveguide manufactured according to the method for manufacturing a polarization independent slab waveguide according to an embodiment of the present invention described with reference to FIG. 5.

6 (a) is a cross-sectional view of the optical waveguide region of the slab waveguide according to an embodiment of the present invention, Figure 6 (b) is a cross-sectional view of the polarization compensation region of the slab waveguide according to an embodiment of the present invention, Figure 6 (C) is an exemplary diagram showing the effective refractive index and the birefringence according to the structural parameters of the slab waveguide according to an embodiment of the present invention. The input optical signal was simulated using a 1550 nm wavelength and the substrate using InP material. 6 (a) and 6 (b), the thickness of the first upper clad layer was 0.2 µm and the thickness of the second upper clad layer was 1 µm.

6C is a graph simulating the effective refractive index and the birefringence of the TE mode and the TM mode when the thickness t _core of the second core layer is changed. Referring to FIG. 6C, when the thickness t _core of the second core layer is 0 μm, that is, the effective refractive index of the TE mode in the region 1 is 3.19638, the birefringence is 0.001652, and It can be seen that as the thickness t _core increases, the effective refractive index and the birefringence increase.

Meanwhile, in order to implement a polarization compensator, the birefringence of the polarization compensation region should be about 2.5 times or more than the birefringence of the optical waveguide region to design the polarization compensation region pattern in the slab waveguide region. In addition, as the birefringence of the polarization compensation region increases, polarization compensation may be performed in a narrow region, and a stable polarization compensation structure may be realized in a region where the change in birefringence is small with respect to the thickness change of the second core layer.

Referring to (c) of FIG. 6, the thickness t _core of the second core layer is in a range of 0.28 μm to 0.34 μm (multi-mode occurs at 0.36 μm or more), and the birefringence is 0.3 μm. 0.00536, i.e., 3.35 times the optical waveguide region. The accuracy of the thickness of the second core layer can be obtained at 1 nm or less through growth equipment (Metal-Organic Chemical Vapor Deposition: MOCVD), and even if there is a slight thickness variation, the birefringence change is changed very slowly, so that the polarization compensation is stable. You can let The response spectrum when the thickness of the second core layer is 0.3 μm will be described below with reference to FIG. 7.

FIG. 7 is an exemplary view illustrating a response spectrum of a TE mode and a TM mode of a polarization independent slab waveguide according to an embodiment of the present invention as shown in FIG. 6.

Referring to FIG. 7, it can be seen that the response spectra of the TE mode and the TM mode coincide. That is, it can be seen that the polarization compensation of the output optical signal with respect to the input optical signal.

As described above, since the slab waveguide according to the embodiment of the present invention can implement polarization compensation by making the thickness of the cladding layer of the polarization compensation region thicker than the thickness of the cladding layer of the conventional structure, The perturbation in the waveguide mode can be reduced.

FIG. 8 is an exemplary view illustrating light distribution according to a waveguide mode for each region of a polarization independent slab waveguide according to an embodiment of the present invention as shown in FIG. 6.

Referring to FIG. 8, it can be seen that the peak value of the light distribution of the optical waveguide region is in the first core layer and the peak value of the light distribution of the polarization compensation region is in the second core layer.

As described above, in the polarization independent slab waveguide according to the exemplary embodiment of the present invention, the peak value of the light distribution in the polarization compensation region represents a normal waveguide mode in the second core layer, which is not affected by the cladding layer thickness compared to the conventional structure. It's a structure. In addition, in the structure in which the thickness of the upper cladding layer of the optical waveguide region and the polarization compensation region is infinitely increased with respect to the structure, the variation in the birefringence ratio of the polarization compensation region with respect to the optical waveguide region is within 5% and can be ignored.

폭이 약 1.6㎛를 나타내므로, 종래 기술에 의한 2.7㎛보다 식각 깊이에 대한 수직성과 균일성이 덜 요구되는 장비 또는 식각 조건을 사용할 수 있는 이점이 있다. 다시 말해, 종래 기술에 사용되는 장비 및 조건과 동일한 장비 및 조건을 사용하여 광 소자의 신뢰성 및 특성 향상을 이룰 수 있게 된다. In addition, the light intensity of the polarization compensation region

Since the width represents about 1.6 μm, there is an advantage in that it is possible to use equipment or etching conditions that require less perpendicularity and uniformity to the depth of etching than 2.7 μm in the prior art. In other words, it is possible to achieve the reliability and characteristics of the optical device by using the same equipment and conditions as those used in the prior art.

In the above description of the present invention, a specific embodiment has been described, but various modifications may be made without departing from the scope of the present invention. For example, the present invention can be applied not only to a waveguide-type concave diffraction grating but also to an array waveguide diffraction grating composed of input / output waveguides, slab waveguides, and array waveguide columns, in particular, the polarization in a slab waveguide, i.e., a free propagation range (FPR) region. Compensation structures can be applied. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the equivalents of the claims and the claims.

1 is an exemplary view showing a demultiplexer using a conventional waveguide-type concave diffraction grating,

2 is an exemplary diagram for showing a phase difference of an output optical signal with respect to an input optical signal in a conventional slab waveguide;

3 is an exemplary diagram for explaining a slab waveguide having a conventional polarization compensation structure;

4 is an exemplary view showing a polarization independent demultiplexer according to an embodiment of the present invention;

5 is an exemplary view showing a method of manufacturing a slab waveguide according to an embodiment of the present invention;

6 is an exemplary diagram for explaining a polarization independent slab waveguide manufactured according to an embodiment of the present invention;

7 is an exemplary view illustrating a response spectrum of a TE mode and a TM mode of a polarization independent slab waveguide according to an embodiment of the present invention;

8 is an exemplary view showing light distribution according to a waveguide mode for each region of a polarization independent slab waveguide according to an embodiment of the present invention.

Claims (13)

An optical waveguide region formed on one side of the substrate and configured to guide the input optical signal; And A polarization compensation region formed on the other side of the substrate and compensating for polarization of an optical signal that is input from the optical waveguide region and is reflected and diffracted by a diffraction grating Including, The optical waveguide region includes a lower clad layer, a first core layer, and an upper clad layer, which are sequentially formed on one side of the substrate, The polarization compensation region extends from the optical waveguide region and includes a lower clad layer, a first core layer, an upper clad layer, and a second core formed between the first core layer and the upper clad layer, which are sequentially formed on the other side of the substrate. Covering layer Polarization independent slab waveguide. The method of claim 1, The band gap wavelength of the second core layer material is shorter than the operating wavelength Polarization independent slab waveguide. The method of claim 1, wherein the first core layer and the second core layer, Made of a material having a higher refractive index than the upper clad layer and the lower clad layer Polarization independent slab waveguide. The method of claim 1, wherein the first core layer and the second core layer, Made of InGaAsP material Polarization independent slab waveguide. The method of claim 1, wherein the upper clad layer and the lower clad layer, Made of InP material or GaAs material Polarization independent slab waveguide. The method of claim 1, The band gap wavelength of the second core layer material is longer than the band gap wavelength of the first core layer material. Polarization independent slab waveguide An optical waveguide configured to receive an optical signal from an external source or output an optical signal to an external device; A slab waveguide optically connected to the optical waveguide and receiving an optical signal from the optical waveguide or outputting an optical signal to the optical waveguide; A concave diffraction grating that reflects and diffracts an optical signal input from the slab waveguide and outputs the light signal to the slab waveguide Including but not limited to: The slab waveguide may include an optical waveguide region formed on one side of a substrate and configured to guide an input optical signal; And a polarization compensation region formed on the other side of the substrate and compensating for the polarization of the optical signal inputted from the optical waveguide region and reflected and diffracted by the concave diffraction grating. The optical waveguide region includes a lower clad layer, a first core layer, and an upper clad layer, which are sequentially formed on one side of the substrate, The polarization compensation region extends from the optical waveguide region and includes a lower clad layer, a first core layer, an upper clad layer, and a second core formed between the first core layer and the upper clad layer, which are sequentially formed on the other side of the substrate. Covering layer Polarization independent multiplexer / demultiplexer. A slab waveguide manufacturing method comprising an optical waveguide region for guiding an input optical signal and a polarization compensation region for compensating polarization of an optical signal inputted from the optical waveguide region and reflected and diffracted in a diffraction grating. (a) sequentially forming a lower clad layer, a first core layer, an etch stop layer, a second core layer, and a first upper clad layer on the substrate; (b) removing the first upper clad layer and the second core layer of the optical waveguide region by forming a first mask pattern on the first upper clad layer and performing dry etching and selective wet etching, and then the first mask Removing the pattern; And (c) forming a second upper clad layer on top of the optical waveguide region and the polarization compensation region; Slab waveguide manufacturing method comprising a. The method of claim 8, (d) forming a region for joining the diffraction grating by forming a second mask pattern over the second upper clad layer and performing dry etching Slab waveguide manufacturing method further comprising. According to claim 8, wherein step (b) is, Forming the first mask pattern from silicon nitride (SiN _X ) or silica (SiO ₂ ) Slab waveguide manufacturing method comprising a. The method of claim 9, wherein step (d) Forming the second mask pattern from silicon nitride (SiN _X ) or silica (SiO ₂ ) Slab waveguide manufacturing method comprising a. The method of claim 8, wherein step (a) comprises: Forming the first core layer and the second core layer from an InGaAsP material Slab waveguide manufacturing method comprising a. The method of claim 12, wherein step (b) comprises: In the case of selective wet etching of the second core layer, a solution in which phosphoric acid, hydrogen peroxide and water are mixed (H ₃ PO ₄ : H ₂ O ₂ : H ₂ O) or a solution in which sulfuric acid, hydrogen peroxide and water are mixed (H ₂ SO ₄ : H ₂ O ₂ : H ₂ O) as an etchant Slab waveguide manufacturing method comprising a.

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