KR100346780B1 - Integration polymeric arrayed waveguide grating wavelength multiplexer with photodetectors using GaAs substrate and a fabrication method - Google Patents

Abstract

The present invention relates to a polymer waveguide thermal lattice wavelength division optical device having a structure in which an InGaAs photodetector using a GaAs substrate is integrated on a single substrate, and a method of fabricating the same. The polymer waveguide thermal lattice wavelength division optical device integrated with a photodetector using a GaAs substrate according to the present invention includes an input / output waveguide composed of 1 × N, N × 1, or N × N, an input plate waveguide for dispersing an optical signal introduced through the input waveguide, and the dispersion. An output plate waveguide in which the collected optical signals are focused, a waveguide thermal lattice aligned between the two plate waveguides to transmit a signal, and an optical intensity of each wavelength signal integrated in the output waveguide and separated from the output waveguide A photodetector is provided. In addition, when the polymer waveguide thermal lattice wavelength division optical device using the GaAs substrate proposed in the present invention is fabricated, an InGaAs photodetector can be integrated in the output waveguide portion of the polymer waveguide thermal lattice wavelength division optical device, and the residual thermal stress of the polymer optical device is Si. Compared with the case of using a board | substrate, it can reduce and performance of elements, such as polarization dependence, improves.

Description

Integrated polymeric arrayed waveguide grating wavelength multiplexer with photodetectors using GaAs substrate and a fabrication method}

The present invention relates to a polymer waveguide thermal lattice wavelength division optical device having a structure in which an InGaAs photodetector using a GaAs substrate is integrated on a single substrate, and a method of fabricating the same.

The waveguide grating wavelength division optical elements and photodetectors are essential optical elements for constructing a wavelength division multiplexing (WDM) optical communication system. In order to integrate these optical devices have been urgently required.

The conventional polymer waveguide thermal lattice wavelength division optical device is fabricated on a Si substrate, and thus, single integration of a long wavelength photodetector in the 1.55m band is impossible, and also due to the large thermal expansion coefficient difference between the polymer material and the Si substrate, the residual thermal stress in the fabricated device is increased. This may cause problems such as deterioration of device performance.

As a waveguide grating wavelength division optical element of this kind,

1. Y. Hida et al., IEE Electron. Lett., Vol. 30, no. 12, pp. 959-960, 1994.

A waveguide thermal lattice wavelength division optical element fabricated using a polymer material using a Si substrate;

2. H. Okayama et al., IEEE J. Lightwave Technol., Vol. 14, No. 6, pp. 985-990, 1996.

A wavelength division optical device fabricated using a total reflection mirror between a waveguide column and a waveguide column grating on a lithium niobate substrate;

3. M. Zirngible et al., IEEE Photon. Technol. Lett., Vo4. 5, No. 11, pp. 1250-1253, 1992.

A wavelength division optical device fabricated by using a waveguide grating on an indium phosphite (InP) substrate;

H. Takahashi et al., IEEE I. Lightwave Technol., Vol. 12, No. 6, pp. 989-995, 1994.

A wavelength division optical device fabricated using a waveguide thermal grating in an optical waveguide device using silica;

5. J.B.D. Soole et al., IEE Electronics letters, Vo 31, No. 15, pp. 1289-1291, 1995.

Wavelength division optical devices fabricated using a waveguide grating in which a photodetector is integrated on an indium phosphite (InP) substrate.

An object of the present invention is that the polymer waveguide thermal lattice wavelength division using a SiA substrate improves the characteristics of the device, and the polymer waveguide thermal lattice wavelength division integrated with a photodetector using a GaAs substrate that can be integrated with other active devices An object of the present invention is to provide an optical device and a method of manufacturing the same.

The polymer waveguide thermal lattice wavelength division optical element integrated with a photodetector using the GaAs substrate of the present invention for achieving the above object is an input and output waveguide composed of 1xN, Nx1 or NxN, and an input plate for dispersing the optical signal introduced through the input waveguide A waveguide, an output plate waveguide in which the scattered optical signals are focused, a waveguide column grating aligned between the two plate waveguides to transmit a signal, and each wavelength signal integrated in the output waveguide and separated from the output waveguide And a photodetector for detecting the light intensity.

In addition, a method for manufacturing a polymer waveguide thermal lattice wavelength division optical device in which a photodetector is integrated using a GaAs substrate of the present invention for achieving the object of the present invention is a polymer optical waveguide lower cladding layer and a polymer optical waveguide core layer on a GaAs substrate. Forming a polymer waveguide thermal wavelength split optical element, and depositing an n-GaAs lower cladding layer, an i-InGaAs absorbing layer, a p-GaAs lower cladding layer, and a p-InGaAs layer on a GaAs substrate, respectively, to form a photodetector. And a third step of forming a photodetector waveguide mesa pattern by patterning the photodetector, a fourth step of coating polyimide around the mesa pattern, and forming a metal layer on the upper and lower portions of the detector. A fifth step of depositing a SiNx thin film on the surface of the photodetector as a whole, and a polymer optical waveguide by patterning the polymer optical waveguide core layer A seventh process of forming a pattern of a core layer, an eighth process of forming an upper cladding layer of a polymer optical waveguide, a ninth process of removing a polymer material and a SiNx thin film deposited on the photodetector, and an input / output of light waves And a tenth step of forming a cross section for forming a polymer waveguide thermal lattice wavelength division optical device in which a photodetector is integrated.

1 is a schematic diagram illustrating a polymer waveguide thermal lattice wavelength division optical device having a structure in which a photodetector is integrated according to an embodiment of the present invention;

2 is a schematic view showing a polymer waveguide thermal lattice wavelength division optical device region having a structure in which a photodetector is integrated according to an embodiment of the present invention;

3 is a schematic view showing a manufacturing process of a polymer waveguide thermal lattice wavelength division optical device having a structure in which a photodetector is integrated according to an embodiment of the present invention.

<Description of Symbols on Main Parts of Drawing>

1: GaAs substrate 2: n ^- GaAs lower clad layer

3: i-InGaAs absorption layer 4: p-GaAs upper clad layer

5: p + InGaAs layer 7: p-ohmic metal layer

8: n-ohmic metal layer 9: polymer optical waveguide lower clad layer

10 polymer optical waveguide core layer 11 SiNx thin film

12: polymer optical waveguide upper cladding layer

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

1 is a schematic diagram illustrating a polymer waveguide thermal lattice wavelength division optical device having an integrated photodetector according to an embodiment of the present invention.

As shown in FIG. 1, an optical device having an optical waveguide device and a photodetector integrated with a waveguide grating integrated into an optical waveguide, two flat waveguides and a waveguide grating, and an output end optical waveguide, as shown in FIG. 1. It consists of a photodetector.

The input / output waveguide is composed of 1xN, Nx1 or NxN. The optical signal entering through the input waveguide spreads out of the input plate waveguide and is excited in the waveguide grating. The waveguide grating is aligned between two planar waveguides and transmits a signal. Neighboring waveguides of the waveguide grating have a constant length difference and cause a phase shift difference between adjacent waveguides according to the input wavelength, thus affecting the direction of the optical signal focused in the output plate waveguide. Therefore, signals of different wavelengths excited at the same input terminal are transferred to different output terminals according to the wavelength. The light intensity of each wavelength signal separated in the output waveguide is detected in the integrated photodetector.

When the polymer waveguide thermal lattice wavelength division optical device using the GaAs substrate proposed in the present invention is fabricated, a long wavelength InGaAs photodetector having a band of 1.55 μm can be integrated in the output waveguide portion of the polymer waveguide thermal wavelength division optical device.

In addition, the residual thermal stress generated in the manufacturing process of the polymer optical element fabricated on the GaAs substrate can be reduced as compared with the case of using the Si substrate, thereby improving the performance of devices such as polarization dependence.

Here, the polymer waveguide thermal lattice wavelength division optical element in which a photodetector using a GaAs substrate is integrated has a function of a router capable of multiplexing and demultiplexing input optical signals and regularly connecting signals between input and output waveguides. And it has a function of directly detecting the output optical power through the photodetector.

The influence of the residual thermal stress of the GaAs substrate and the polymer material on the characteristics of the aforementioned polymer waveguide thermal lattice wavelength division optical device is expressed by Equation 1 below.

Δλ: center wavelength transition, ΔL: waveguide path difference

m: diffraction order, B: birefringence

n _{TM, TE} : refractive index, K: photoelastic coefficient

E: Young's modulus, α _sub , _cladding : Coefficient of thermal expansion

The thermal expansion coefficients of the GaAs substrate and the conventional Si substrate used in the present invention are 3.5 x 10 ^-6 / C and 6.8 x 10 ^-6 / C, respectively, and the polymer is 10 x 10 ^-5 / C, where a GaAs substrate is used. The thermal expansion coefficient difference with the polymeric material can be reduced by about 2 times, thereby lowering the residual thermal stress.

Accordingly, as can be seen from Equation 1, the birefringence of the TE and TM modes is reduced, and thus the polarization dependency of the device can be reduced.

2 (a) and 2 (b) are schematic diagrams illustrating a waveguide thermal lattice wavelength division optical device region having an integrated photodetector structure.

Figure 2 (a) is a cross-sectional view of the horizontal coupling region in the single integration of the polymer optical element and InGaAs photodetector, Figure 2 (b) is a schematic cross-sectional view of the photodetector element.

As shown in Fig. 2 (a), the basic polymer wavelength division optical device includes a substrate 1, a polymer optical waveguide lower clad layer 9, a polymer optical waveguide core layer 10 and a poly optical waveguide upper clad layer 12. It consists of. The signals of different wavelengths coming from the polymer wavelength-division optical element are detected in the photodetector element. The photodetector element structure is n-GaAs substrate (1), n ^- GaAs lower clad layer (2) as shown in FIG. , an i-InGaAs absorbing layer 3, a p-GaAs upper cladding layer 4, and a p ⁺ InGaAs layer 5. In FIG. 2B, the width W of the photodetector is 3-10 μm, the length L of the photodetector is 10-100 μm, and the thickness of the i-InGaAs absorption layer 3 is 0.2-1 μm.

The optical signal from the polymer optical waveguide core layer 10 is horizontally optically coupled to the i-InGaAs absorption layer 3 of the photodetector element, and the photodetector element detects the light intensity of the signal.

The manufacturing process of the optical waveguide thermal lattice wavelength division optical device having the structure in which the photodetector of the present invention is integrated is shown in FIG. 3.

3 (a) to 3 (d) show a process for manufacturing a photodetector.

First, an n ^- GaAs lower cladding layer 2 (deposition thickness: 3-7 μm) and an i-InGaAs absorbing layer were formed on an n-GaAs substrate 1 prepared by MOCVD, which is a semiconductor thin film deposition apparatus, to fabricate a photodetector. 3) (Deposition thickness: 0.2-1 mu m), p-GaAs upper clad layer 4 (deposition thickness: 0.5-1 mu m), and p ⁺ InGaAs layer 5 (deposition thickness: 0.2 mu m), respectively.

A waveguide pattern of a photodetector having a width of 6 microns is prepared by using an optical etching technique using photoresist on the epitaxial layer grown using the MOCVD apparatus as described above (FIG. 3 (b)). After that, the GaAs and InGaAs epilayers around the photodetector are etched using dry etching equipment. Thereafter, the polyimide is coated around the photodetector mesa pattern to limit the electrical characteristics of the detector element as shown in FIG. 3 (c). Next, as shown in FIG. 3 (d), metal layers 7 and 8 are formed on the upper and lower photodetectors. The upper and lower p-ohmic metal layers 7 and n-ohmic metal layers 8 are formed of Ti / Pt / Au (7) and Cr / Au (8), respectively.

3 (e) -2, 3 (f) -2, 3 (g) -2, and 3 (h) -2 are cross-sectional views showing photodetector sites when fabricating a polymer wavelength division optical device.

First, in order to fabricate the polymer wavelength-division optical device in which the photodetector is integrated, the SiNx thin film 11 is entirely deposited on the GaAs substrate on which the photodetector is manufactured using PECVD (FIG. 3 (e) -2). Next, the SiNx thin film is etched except for the part where the photodetector is manufactured. Subsequently, the polymer optical waveguide lower clad layer 9 (deposition thickness: 3-5 mu m) and the polymer optical waveguide core layer 10 (deposition thickness: 4-6 mu m) were respectively produced by spin coating (FIG. 3 ( e) -1).

Subsequently, a 6-micron waveguide pattern having the same width as a photodetector is fabricated using photolithography using photoresist. The polymer around the waveguide pattern is etched using a plasma dry etching technique using oxygen gas (FIG. 3 (f) -1). After etching, the SiNx thin film used as an etching mask is removed using a BOE etchant. Thereafter, the polymer optical waveguide upper cladding layer 12 (deposition thickness: 4-8 μm) is formed by spin coating (FIG. 3 (g) -1). The polymer material deposited on the photodetector site and the SiNx thin film 11 are removed using a BOE etchant (Fig. 3 (h) -2).

Finally, the use of end face cleaving or end face polishing to form a cross section for input and output of light waves completes the fabrication of the device.

As described above, when the polymer waveguide thermal lattice wavelength division optical device using the GaAs substrate proposed in the present invention is fabricated, an InGaAs photodetector can be integrated in the output waveguide portion of the polymer waveguide thermal lattice wavelength division optical device, and the residual heat of the polymer optical device The stress can be reduced as compared with the case of using a Si substrate, and the performance of devices such as polarization dependence is improved. In addition, the polymer waveguide thermal lattice wavelength-division optical device having an InGaAs photodetector using the proposed GaAs substrate integrated on a single substrate can be integrated with active devices such as semiconductor lasers and modulators, and is advantageous for making high-performance products. . Such integrated optical devices are applied to optical signal processing in wavelength division optical communication systems.

Claims (4)

I / O waveguide consisting of 1xN, Nx1 or NxN, An input plate waveguide for dispersing an optical signal introduced through the input waveguide, An output plate waveguide through which the distributed optical signals are focused; A waveguide column grating arranged between the two planar waveguides and transmitting a signal; And a photodetector integrated in the output waveguide for detecting the light intensity of each wavelength signal separated from the output waveguide. A first step of forming the polymer optical waveguide lower wavelength cladding layer 9 and the polymer optical waveguide core layer 10 on the GaAs substrate 1 to form a polymer waveguide thermal wavelength division optical element; A photodetector is formed by depositing an n-GaAs lower cladding layer 2, an i-InGaAs absorbing layer 3, a p-GaAs upper cladding layer 4, and a p ⁺ InGaAs layer 5, respectively, on the GaAs substrate 1. The second process, A third step of patterning the photodetector to form a photodetector waveguide mesa pattern; A fourth step of coating a polyimide around the mesa pattern; A fifth process of forming metal layers 7 and 8 on the upper and lower portions of the detector, A sixth step of depositing the SiNx thin film 11 as a whole on the surface of the photodetector; A seventh step of patterning the polymer optical waveguide core layer 10 to form a pattern of the polymer optical waveguide core layer; An eighth step of forming the polymer optical waveguide upper cladding layer 12, A ninth process of removing the polymer material and the SiNx thin film 11 deposited on the photodetector; A polymer waveguide thermal lattice wavelength division optical device in which a photodetector is integrated using a GaAs substrate, comprising a tenth step of forming a cross-section for input and output of light waves to form a polymer waveguide thermal lattice wavelength division optical device in which a photodetector is integrated. How to make. The method of claim 2, In the first process, the polymer optical waveguide lower clad layer 9 is deposited to a thickness of 3-5 μm, and the polymer optical waveguide core layer 10 is deposited to a thickness of 4-6 μm. A method for fabricating a polymer waveguide thermal lattice wavelength division optical device in which a photodetector using a substrate is integrated. The method of claim 2, In the second process, an n-GaAs lower clad layer 2 is deposited on the GaAs substrate 1 to a thickness of 3-7 μm, and an i-InGaAs absorber layer 3 is deposited to a thickness of 0.2-1 μm, and p Photo-detection integrated polymer waveguide column using a GaAs substrate, characterized in that the GaAs upper cladding layer 4 is deposited to a thickness of 0.5-1 탆 and the p ⁺ InGaAs layer 5 is deposited to a thickness of 0.2 탆. Method for manufacturing a grating wavelength division optical device.