CN103235363A - Array waveguide grating demodulation integration micro system - Google Patents

Abstract

The invention discloses an arrayed waveguide grating demodulation integrated microsystem, which includes a C-band on-chip LED light source, a 2×2 optical waveguide coupler, a fiber Bragg grating array, a 1×8 arrayed waveguide grating, and a photodetector array. Electron beam exposure and reaction coupled plasma process, fabricate coupler and arrayed waveguide grating on SOI wafer, couple the light emitted by LED light source made of InP material to coupler waveguide 1 through grating, and then enter fiber Bragg grating through coupler waveguide 2 The light reflected by the fiber Bragg grating array enters the arrayed waveguide grating through the coupler waveguide 3, and the light output from the arrayed waveguide grating is also coupled to the InGaAs photodetector array above it through the grating. The arrayed waveguide grating demodulation integrated microsystem disclosed by the invention has the advantages of compact structure, device integration, low cost, high demodulation precision, high speed, improved optical path stability and reliability, and the like.

Description

An Arrayed Waveguide Grating Demodulation Integrated Microsystem

technical field

The invention relates to the research on the heterogeneous integration of arrayed waveguide grating demodulation microsystems, and belongs to the field of optoelectronic integration.

Background technique

The research on fiber Bragg grating sensing technology abroad is earlier, and the commercialization and engineering of fiber Bragg grating sensors have been basically realized in developed countries. At present, the most widely used field of fiber Bragg grating sensors in foreign countries is the safety monitoring of bridges. At the same time, the application of fiber Bragg grating sensing technology has gradually extended to various industrial fields such as electric power, petroleum, and petrochemical. Domestic research on fiber Bragg grating sensors began in the late 1970s. At present, hundreds of units have carried out research work in this field. Fiber Bragg grating sensors have been applied in some industries in my country, and can be used to measure strain, temperature, pressure and all physical quantities that can be converted into strain or temperature.

At present, the fiber Bragg grating demodulation system is large in size and expensive, which limits the popularization and application of fiber Bragg grating sensing technology. The arrayed waveguide grating demodulation method is a new type of fiber Bragg grating demodulation method with great potential, which has the characteristics of high precision and fast demodulation speed. The invention performs heterogeneous integration on the light source, the optical waveguide coupler, the array waveguide grating and the photodetector of the arrayed waveguide grating demodulation system. The arrayed waveguide grating demodulation integrated microsystem after heterogeneous integration has the advantages of compact structure, device integration, high integration, low cost, and improved stability and reliability of the optical path. The invention will surely play an important role in promoting the development of the fiber Bragg grating sensing and demodulation field, and meanwhile has great significance for the research of future all-silicon optoelectronic integrated chips. The arrayed waveguide grating demodulation integrated microsystem can be widely used in bridges, buildings, health monitoring, petroleum industry and other fields, and even the arrayed waveguide grating demodulation integrated microsystem is implanted into clothing to complete the real-time measurement of human physiological parameters , which is also of great significance and application value for the timely diagnosis and treatment of human infectious diseases, tumors, heart and other diseases, and further expands the application of fiber Bragg grating sensing technology in health, life sciences and aerospace.

Contents of the invention

The purpose of the present invention is to solve the problems of large volume and high price of the fiber Bragg grating demodulation system, and provide an arrayed waveguide grating demodulation integrated microsystem with compact structure, high demodulation accuracy, fast demodulation speed and low cost.

The present invention is realized through the following technical solutions:

(1) The basic structure of the C-band on-chip LED light source is to continuously grow four layers on the InP substrate, followed by the n-InP buffer layer, the InGaAsP active layer, the p-InP confinement layer and the p-InGaAsP top layer. The central wavelength of the C-band on-chip LED light source is 1550nm. When the forward bias voltage is 0.8V, the luminous power is 2mW and the wavelength bandwidth is 100nm.

(2) Use the grating coupler to couple the light emitted by the C-band LED light source to the waveguide 1 of the 2×2 optical waveguide coupler, etch the grating on the SOI wafer to determine the etching depth, grating period and duty cycle of the waveguide layer. A distributed Bragg reflector is added to the opposite direction of the grating coupling to improve the coupling efficiency, and the end of the grating coupling direction is connected to the waveguide 1 of the 2×2 optical waveguide coupler through a tapered waveguide.

(3) Fabricate a 2×2 optical waveguide coupler with a center wavelength of 1550nm on the SO1 chip, receive the light diffracted by the grating through the waveguide 1, introduce the light into the fiber Bragg grating array through the waveguide 2, and then pass the optical fiber through the waveguides 2 and 3 The light reflected by the Bragg grating array is introduced into the 1×8 arrayed waveguide grating. The additional loss of the 2×2 optical waveguide coupler is not more than 0.5dB, the non-uniformity is not more than 0.1dB, the size is not more than 6×100μm ² , and the splitting ratio is close to 50:50, so that the 1×8 arrayed waveguide grating can receive as much light as possible .

(4) Fabricate a 1×8 arrayed waveguide grating working at a center wavelength of 1550nm on an SOI wafer, with a saddle-shaped structure, insertion loss not greater than 25.5dB, crosstalk not greater than 3.2dB, and size not greater than 270μm×390μm. A tapered multimode waveguide is connected to the front end of the 1×8 arrayed waveguide grating input slab waveguide, and a section of tapered pre-stretched waveguide is inserted before the tapered multimode interference coupler and after the arrayed waveguide grating output slab waveguide to obtain spectral flattening. 1×8 arrayed waveguide grating, which can obtain a flattened spectrum with low chromatic dispersion, and reduce the output spectral crosstalk of the arrayed waveguide grating.

(5) The grating coupler is used to vertically diffract the light propagating in the SOI waveguide to the photodetector array above it. The photodetector is made of InGaAs/InP, and three layers are continuously grown on the InP substrate, which are: n-InP buffer layer, i-InGaAs intrinsic absorption layer, and p-InP capping layer. The size of the photodetector is not larger than 460×460×170μm ³ , the dark current under 5V bias is less than 0.5nA, the sensitivity is about 3nW, the photosensitive area is 40μm, and the responsivity in the 1.1μm-1.65μm band exceeds 0.9A/W;

In the above step (1), an LED light source model on an InP substrate with a luminous center wavelength of 1550nm is established, and Silvaco simulation software is used to simulate the LED structure and solve the LED spectral curve.

In the above step (2), the grating coupler model is established, and the grating coupler is simulated based on the FDTD algorithm to calculate its coupling efficiency. In the case of vertical illumination of the light source, the coupling efficiency of the grating is not lower than 40%.

In the above step (3), the mathematical model of the 2×2 optical waveguide coupler is established, its basic parameters are determined, and the interconnection with the 1×8 arrayed waveguide grating is realized on the premise of ensuring the transmission efficiency. The beam propagation method (BPM) is used to simulate and optimize the design of the 2×2 optical waveguide coupler to reduce its additional loss, improve its polarization characteristics and inhomogeneity, and make the additional loss of the designed 2×2 optical waveguide coupler Less than 0.5dB, non-uniformity less than 0.1dB, size not larger than 6×100μm ² . The layout of the 2×2 optical waveguide coupler is derived, the parameters of the SOI wafer are determined, and the photolithography plate is made by electron beam exposure and reactive coupled plasma technology.

In the above step (4), based on the transmission theory of the beam transmission method, parameters such as the structural composition, diffraction order, length difference of adjacent array waveguides, focal length and free spectral region of the 1×8 arrayed waveguide grating were analyzed. Design, establish a mathematical model of 1×8 arrayed waveguide grating, and optimize the design to make its spectral distribution uniform, the loss not greater than 3.2dB, the crosstalk not greater than 25.5dB, and the size not greater than 270μm×390μm. Loss and crosstalk are reduced compared to equivalent micron-scale arrayed waveguide gratings. A 1×8 arrayed waveguide grating for spectral flattening is designed to obtain a flattened spectrum with low chromatic dispersion and reduce the crosstalk of the output spectrum. The layout of the 1×8 arrayed waveguide grating is derived, the parameters of the SOI wafer are determined, and the fabrication of the 1×8 arrayed waveguide grating is completed by electron beam exposure and reactive coupled plasma technology.

In the above step (5), the InP-based photodetector model is established. In order to eliminate the harmful absorption of light by the electrode and meet the phase matching conditions of optical coupling, the electrode structure and the thickness of the intrinsic absorption layer are respectively improved and optimized. Silvaco The simulation software simulates the structure of the photodetector. The sensitivity of the photodetector is about 3nW, and the responsivity in the 1.1μm-1.65μm band exceeds 0.9A/W.

The effect and benefits of the arrayed waveguide grating demodulation integrated microsystem of the present invention are: to provide a new type of fiber Bragg grating demodulation method with great potential, which has the advantages of compact structure, device integration, high integration, low cost, and improved optical path. advantages of stability and reliability.

Description of drawings

Figure 1 is a schematic diagram of an arrayed waveguide grating demodulation integrated microsystem;

Figure 2 is a schematic diagram of the structure of the C-band on-chip LED light source;

Fig. 3 is a schematic diagram of the connection between the light source and the grating coupler;

Fig. 4 is a structural schematic diagram of a grating coupler;

Figure 5 is a layout of a 2×2 multimode interference coupler;

Fig. 6 is a 2 * 2 multimode interference coupler optical field and optical power distribution diagram;

Figure 7 is a physical diagram of a 2×2 multimode interference coupler;

Figure 8 is the saddle-shaped 1×8 arrayed waveguide grating layout;

Fig. 9 is a 1×8 arrayed waveguide grating output spectrum diagram;

Figure 10 is a spectrum flattened 1 × 8 arrayed waveguide grating layout;

Figure 11 is a scanning electron microscope image of a 1×8 arrayed waveguide grating;

Fig. 12 is a structural schematic diagram of a photodetector;

Fig. 13 is a schematic diagram of the connection between the photodetector and the grating coupler;

Figure 14 is the output spectrum diagram of the 2×2 multimode interference coupler obtained in the experimental test;

Fig. 15 is the output spectrum diagram of the 1×8 arrayed waveguide grating obtained in the experimental test.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with technical solutions and accompanying drawings.

The present invention carries out heterogeneous integration of LED light source, 2×2 optical waveguide coupler, fiber Bragg grating array, 1×8 arrayed waveguide grating, and photodetector array. The steps are:

1. C-band on-chip LED light source

The basic structure of the InP-based C-band on-chip LED light source is shown in Figure 2. Four layers are grown continuously on the InP substrate, which are n-InP buffer layer, InGaAsP active layer, p-InP confinement layer and p-InGaAsP top layer. The thickness of the n-InP buffer layer is 0.5 μm, the thickness of the InGaAsP active layer is 0.1 μm, the thickness of the p-InP confinement layer is 0.5 μm, and the thickness of the p-InGaAsP top layer is 0.5 μm. Using Silvaco simulation software to model and simulate the LED, the basic structure, output spectrum curve and output optical power curve of the LED are obtained. When the forward bias voltage is 0.8V, the maximum forward bias current of the LED is 100mA, the luminous power is 2mW, and the wavelength bandwidth is 100nm. A 2×2 LED array is used as the input light source of the arrayed waveguide grating demodulation integrated microsystem.

2. Grating coupler

The C-band on-chip LED light source is coupled with the 2×2 optical waveguide coupler waveguide 1 by grating coupling method. In Figure 3, the on-chip LED light source is vertically irradiated to the grating coupler, and the light is diffracted into the waveguide 1 of the 2×2 optical waveguide coupler through the grating. In Figure 4, the grating is etched on the SOI wafer. The etching depth of the waveguide layer is 50nm, the period is 570nm, and the duty cycle is 0.74. A distributed Bragg reflector is added in the opposite direction of the grating coupling to improve the coupling efficiency. The end of the grating coupling direction passes through The tapered waveguide is connected with the waveguide 1 of the 2×2 optical waveguide coupler, so as to realize the coupling of the light source and the waveguide 1 of the 2×2 optical waveguide coupler. The grating coupler model is established according to the above parameters, and the FDTD algorithm is used to simulate the grating coupler. In the case of vertical illumination of the light source, the coupling efficiency can reach 49%.

3.2×2 Optical Waveguide Coupler

The 2×2 optical waveguide coupler adopts SOI-based 2×2 multimode interference coupler. The input/output waveguide of the multimode interference coupler adopts an inverted tapered shape, and the width of the large end of the tapered waveguide is set to 1 μm. In order to match the size of the input waveguide of the arrayed waveguide grating, the end width of the tapered waveguide connected to the arrayed waveguide grating is set to 0.35 μm. The end width of the remaining tapered waveguides was set to 0.65 μm. In Figure 5, the size of the coupler is 6 μm×100 μm, and the size of the multimode interference area is 6 μm×57 μm. Before optimization, the additional loss of the coupler is 1.09dB, and the non-uniformity is 0.44dB. After optimization, the additional loss is reduced and the polarization characteristics are significantly improved. In Figure 6, when the TE polarization center wavelength is 1.55μm, the additional loss of the device is 0.46dB, and the non-uniformity is 0.06dB. The additional loss of the coupler is less than 1.55dB in the wavelength range of 1.49-1.59μm. The results show that the designed 2×2 multimode interference coupler has the advantages of small size, low additional loss, wide wavelength response range and uniform light splitting. The layout of the 2×2 optical waveguide coupler is derived, and the SOI wafer with the thickness of the top silicon layer of 0.22 μm and the thickness of the buried SiO ₂ layer of 2 μm is selected, and the photolithography plate is made by electron beam exposure and reactive coupled plasma technology. Figure 7 shows the 2× 2 The physical picture of the multimode interference coupler.

4.1×8 arrayed waveguide grating

The SOI-based 1×8 arrayed waveguide grating adopts a saddle-shaped arrayed waveguide grating structure as shown in Figure 8. The waveguide width is 0.35 μm, the device size is only 267 μm×381 μm, and the length difference between adjacent arrayed waveguides of the arrayed waveguide grating is 19.7 μm. The focal length of the waveguide is 67 μm, and the free spectral region is 55.39 μm. Figure 9 shows that the central wavelengths of the eight output channels are 1.5427 μm, 1.5446 μm, 1.5461 μm, 1.548 μm, 1.550 μm, 1.5528 μm, 1.5549 μm, and 1.5567 μm, the channel interval is about 0.002526 μm, and the spectral distribution is uniform. The insertion loss of the optimally designed 1×8 arrayed waveguide grating is only 3.15dB and the crosstalk is only 25.5dB. Compared with the same micron arrayed waveguide grating, the loss and crosstalk are both reduced.

A tapered multimode waveguide is connected to the front end of the 1×8 arrayed waveguide grating input slab waveguide, and a section of tapered pre-stretched waveguide is inserted before the tapered multimode interference coupler and after the 1×8 arrayed waveguide grating output slab waveguide. The spectrally flattened 1×8 arrayed waveguide grating shown in FIG. 10 can obtain a flattened spectrum with low chromatic dispersion, which reduces the output spectral crosstalk of the arrayed waveguide grating. The results show that the central wavelengths of the eight output channels of the spectrally flattened 1×8 arrayed waveguide grating are 1.542μm, 1.544μm, 1.546μm, 1.548μm, 1.550μm, 1.552μm, 1.554μm, 1.556μm, 1.558μm. The spacing is 2nm, the 3dB bandwidth is 1.31nm, the insertion loss is 4.36, and the crosstalk is about 21.9dB. After the spectrum is flattened, the channel interval of the 1×8 arrayed waveguide grating is widened, and the crosstalk between adjacent channels is reduced.

The layout of the 1×8 arrayed waveguide grating is derived, the parameters of the SOI wafer are determined, and the fabrication of the 1×8 arrayed waveguide grating is completed by electron beam exposure and reactive coupled plasma technology. Fig. 11 is a scanning electron microscope image of a 1×8 arrayed waveguide grating.

5. Photodetector array

The InGaAs/InP PIN photodetector structure is shown in Figure 12. Three layers are continuously grown on the InP substrate, which are: n-InP buffer layer, i-InGaAs intrinsic absorption layer, and p-InP layer. The thickness of the n-InP buffer layer is 1 μm, the thickness of the i-InGaAs intrinsic absorption layer is 3 μm, and the thickness of the p-InP layer is 1 μm. In order to eliminate the harmful absorption of light by the electrode and meet the phase matching conditions of optical coupling, the electrode structure and the thickness of the intrinsic absorption layer were improved and optimized, and the photodetector structure was simulated using Si1vaco simulation software. Utilizing the heterogeneous integration technology of silicon and III-V materials, the silicon-based InGaAs/InP PIN photodetector is fabricated by using the benzocyclobutene (BCB) polymer wafer bonding process. The grating coupler is used to vertically diffract the light from the output waveguide of the 1×8 arrayed waveguide grating to the photodetector array above it. The advantage of the coupling method shown in Figure 13 is that a relatively thick BCB adhesive layer can be used. The size of the photodetector is not larger than 460×460×170μm ³ , the dark current under 5V bias is less than 0.5nA, the sensitivity is about 3nW, the photosensitive area is 40μm, and the responsivity in the 1.1μm-1.65μm band exceeds 0.9A/W. By optimizing and stabilizing the process parameters, a photodetector array with 8 photodetectors was fabricated.

6. Experimental test results

The finished 2×2 optical waveguide coupler and 1×8 arrayed waveguide grating were tested by end-face coupling method, and the tapered optical fiber was used to connect with the optical waveguide to improve the coupling efficiency. Figure 14 is the output spectrum diagram of the 2×2 multimode interference coupler, where P is the output spectrum of the light source, PO is the spectrum when the optical fiber is connected, and P1 and P2 are the output spectra of the two output waveguides of the 2×2 optical waveguide coupler. The experimental results show that the additional loss of the 2×2 optical waveguide coupler is 0.5423dB, and the non-uniformity is 0.0053dB. Figure 15 is the output spectrum of the 8 output channels of the 1×8 arrayed waveguide grating. The experimental results show that the channel spacing of the 1×8 arrayed waveguide grating is 1.91nm, the insertion loss is 3.18dB, the crosstalk is -23.1dB, and the non-uniformity is 1.35dB.

Claims (6)

1. integrated micro-system of array waveguide grating demodulation, it is characterized in that comprising led light source on the C-band sheet that links to each other successively, 2 * 2 optical waveguide couplers, the Fiber Bragg Grating FBG array, 1 * 8 array waveguide grating, photodetector array, above-mentioned each ingredient isomery is integrated on a slice backing material, wherein 2 * 2 optical waveguide couplers and 1 * 8 AWG Fabrication are on the SOI wafer, and C-band led light source, photodetector array are produced on the InP substrate.

2. the integrated micro-system of array waveguide grating demodulation according to claim 1, it is characterized in that: C-band led light source luminescent center wavelength is 1550nm, wavelength bandwidth is 100nm, basic structure is to grow 4 layers continuously on the InP substrate, is followed successively by n-InP cushion, InGaAsP active layer, p-InP limiting layer and p-InGaAsP top layer.

3. the integrated micro-system of array waveguide grating demodulation according to claim 1, it is characterized in that: at 2 * 2 optical waveguide coupler input waveguide place etched diffraction gratings, add distributed bragg reflector mirror in the other direction in the grating coupling, grating coupling direction end links to each other with 2 * 2 optical waveguide coupler waveguides 1 by tapered transmission line, the led light source vertical irradiation is to grating coupler on the C-band sheet, with optical diffraction to 2 * 2 optical waveguide coupler waveguides 1, thus the coupling of realization light source and 2 * 2 optical waveguide coupler waveguides 1.

4. the integrated micro-system of array waveguide grating demodulation according to claim 1, it is characterized in that: make 2 * 2 optical waveguide couplers at the SOI wafer, waveguide 1 links to each other with grating by one section tapered transmission line, waveguide 2 links to each other with the Fiber Bragg Grating FBG array, waveguide 3 links to each other with 1 * 8 array waveguide grating input waveguide, receive the light of optical grating diffraction by waveguide 1, waveguide 2 is introduced the Fiber Bragg Grating FBG array with light, by waveguide 2,3 Fiber Bragg Grating FBG array reflected light is introduced 1 * 8 array waveguide grating again.

5. the integrated micro-system of array waveguide grating demodulation according to claim 1, it is characterized in that: make 1 * 8 array waveguide grating at the SOI wafer, its structure is saddle-shape, input waveguide links to each other with 2 * 2 optical waveguide coupler waveguides 3, output waveguide links to each other with photodetector array, by one section taper multimode waveguide of termination before 1 * 8 array waveguide grating input planar waveguide, before the taper multi-mode interference coupler and after 1 * 8 array waveguide grating output planar waveguide, respectively insert one section pre-broadening waveguide of taper, obtain 1 * 8 array waveguide grating of spectrum planarization, can obtain to have the planarization spectrum of low chromatic dispersion, reduce the output spectrum of array waveguide grating and crosstalk.

6. the integrated micro-system of array waveguide grating demodulation according to claim 1, it is characterized in that: at 1 * 8 array waveguide grating output waveguide place etched diffraction grating, with the light vertical diffraction of 1 * 8 array waveguide grating output waveguide photodetector array to its top, it comprises 8 photodetectors, the light signal of 8 output channels of 1 * 8 array waveguide grating is converted to electric signal, photodetector is substrate with the InP material, on the InP substrate, grow 3 layers continuously, be followed successively by n-InP cushion, i-InGaAs intrinsic absorption layer, p-InP layer.

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