OADM device based on si3n4 gratings

Abstract

The application relates to an OADM device based on a Si3N4 grating and belongs to the field of semiconductor optical signal transmission. The application comprises, from bottom to top, a substrate layer, a bottom waveguide core layer, a middle waveguide core layer and a top electrode layer; the bottom waveguide core layer comprises a 2*2 multimode interference coupler and a tapered output / input waveguide; the middle waveguide core layer comprises a Si3N4 grating, a tapered input / output waveguide and a straight input / output waveguide; the application separates wavelengths through the Si3N4 grating by Bragg condition and realizes signal interaction through interlayer coupling; the application realizes wavelength separation of multiple wavelengths by changing the refractive index of the Si3N4 grating through thermo-optic modulation; the application realizes the function of wavelength selection by combining the multimode interference coupler with the Bragg grating and constructing a double-layer structure and realizes the light output of different channels through the multimode interference coupler; and the grating made of Si3N4 material has a longer grating period than the grating made of Si material, and the actual manufacturing process is simpler.

Description

Technical Field

[0001] This invention relates to an OADM device based on a Si3N4 grating, belonging to the field of semiconductor optical signal transmission technology. Background Technology

[0002] Optical networks enable high-capacity interconnection of information across most parts of the world. The growing demand for bandwidth from new services and users has spurred innovation in the optical industry, including the enticing prospect of directly connecting all network users to gigabit optical links. This massive increase in bandwidth demand is pushing the utilization of fiber optic infrastructure to its limits. To meet this demand, allocating communication channels to partitions within the optical spectrum has established wavelength division multiplexing (WDM) transmission as a standard method for increasing capacity. WDM combines multiple carrier signals of different wavelengths at the transmitting end via a multiplexer and couples them to the same optical fiber for transmission. At the receiving end, a demultiplexer separates the various wavelengths of the optical carriers, and the optical receiver further processes them to recover the original signal. Under WDM, optical add-drop multiplexers (OADMs) are introduced into access networks, enabling selective addition and filtering of optical channels and making optical methods for implementing network functions possible. OADM devices have become a hot application area due to their ability to utilize low-loss, low-cost passive components. Bragg gratings, in particular, have attracted significant attention in the design of OADMs due to their selectable wavelength capabilities. The center wavelength and period of the Bragg grating can be selected by the user, thus allowing the wavelength to be chosen according to application requirements. Summary of the Invention

[0003] Based on the above needs, this invention provides an OADM device based on a Si3N4 grating, which utilizes the beam splitting characteristics of a multimode interference coupler and the beam splitting characteristics of the grating to achieve wavelength selection; by using a Si3N4 grating, the grating period is lengthened, reducing the difficulty of fabrication process; the signal interaction form of interlayer coupling reduces the large size problem of current grating-type OADM devices to a certain extent; and realizes the capacity increase of optical fiber in optical networks.

[0004] The technical solution of this invention is: an OADM device based on a Si3N4 grating, the structure of which, from bottom to top, consists of a substrate layer, a bottom waveguide core layer 4, a middle waveguide core layer 5, and a top electrode layer 6, with each layer separated by a cladding layer; the bottom waveguide core layer 4 includes a 2×2 multimode interference coupler I1, a 2×2 multimode interference coupler II3, a tapered output waveguide X1, a tapered output waveguide X2, a tapered input waveguide X3, and a tapered input waveguide X4; the 2×2 multimode interference coupler I1 is connected to the tapered output waveguide X1 and the tapered output waveguide X2 respectively, and the tapered input waveguide X3 and the tapered input waveguide X4 are connected to the 2×2 multimode interference coupler II3 respectively;

[0005] The middle waveguide core layer 5 includes Si3N4 grating I2, tapered input waveguide Y1, tapered input waveguide Y2, tapered output waveguide Y3, tapered output waveguide Y4, input straight waveguide Z1, input straight waveguide Z2, output straight waveguide Z3, output straight waveguide Z4, and Si3N4 grating II7.

[0006] The electrodes in the top electrode layer 6 are distributed above the multimode waveguide regions I15 and II35 of the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3, as well as above the Si3N4 grating I2.

[0007] The 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 are located symmetrically distributed about the center of the middle waveguide core layer 5, below the beginning and end of the middle waveguide core layer 5.

[0008] The tapered input waveguide Y1, the input straight waveguide Z1, the Si3N4 grating I2, the output straight waveguide Z3, and the tapered output waveguide Y3 are connected in sequence.

[0009] The tapered input waveguide Y2, the input straight waveguide Z2, the Si3N4 grating II7, the output straight waveguide Z4, and the tapered output waveguide Y4 are connected in sequence.

[0010] Tapered input waveguides Y1 and Y2 are located directly above tapered output waveguides X1 and X2, respectively, while tapered output waveguides Y3 and Y4 are directly above tapered input waveguides X3 and X4, respectively.

[0011] As a further embodiment of the present invention, the 2×2 multimode interference coupler I1 includes a single-mode input waveguide I11, a single-mode input waveguide II12, a multimode waveguide region I15, a single-mode output waveguide I13, and a single-mode output waveguide II14; the single-mode input waveguide I11 and the single-mode input waveguide II12 are both connected to the multimode waveguide region I15, the multimode waveguide region I15 is connected to the single-mode output waveguide I13 and the single-mode output waveguide II14 respectively, and the single-mode output waveguide I13 and the single-mode output waveguide II14 are respectively connected to the tapered output waveguide X1 and the tapered output waveguide X2;

[0012] The 2×2 multimode interference coupler II3 includes a single-mode input waveguide III31, a single-mode input waveguide IV32, a multimode waveguide region II35, a single-mode output waveguide III33, and a single-mode output waveguide IV34; tapered input waveguides X3 and X4 are connected to single-mode input waveguides III31 and IV32 respectively, and both single-mode input waveguides III31 and IV32 are connected to multimode waveguide region II35, which in turn is connected to single-mode output waveguides III33 and IV34 respectively.

[0013] The tips of the conical output waveguides X1 and X2 are facing right, and the tips of the conical input waveguides X3 and X4 are facing left; the tips of the conical input waveguides Y1 and Y2 are facing left, and the tips of the conical output waveguides Y3 and Y4 are facing right.

[0014] As a further embodiment of the present invention, the bottom waveguide core layer 4 is located below the middle waveguide core layer 5. The interlayer coupling between the bottom waveguide core layer 4 and the middle waveguide core layer 5 is specifically as follows: after the optical signal is split by the 2×2 multimode interference coupler I1, it enters the tapered output waveguide X1 and tapered output waveguide X2 and is then coupled into the tapered input waveguide Y1 and tapered input waveguide Y2. After passing through the Si3N4 grating I2 and Si3N4 grating II7, the optical signal that conforms to the Bragg wavelength is reflected back to the 2×2 multimode interference coupler I1 according to the Bragg condition. The optical signals of other wavelengths are coupled into the tapered input waveguide X3 and tapered input waveguide X4 after passing through the output straight waveguide Z3 and output straight waveguide Z4 and the tapered output waveguide Y3 and tapered output waveguide Y4, and then enter the 2×2 multimode interference coupler II3.

[0015] As a further embodiment of the present invention, a heating electrode is provided in the top electrode layer 6. Thermo-optic modulation is performed by the heating electrode in the top electrode layer 6 to change the refractive index of Si3N4 grating I2 and Si3N4 grating II7 with temperature, thereby achieving modulation of the grating Bragg wavelength. Thermo-optic modulation is performed on 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 to select the output channel of the optical signal and achieve the function of switching.

[0016] As a further embodiment of the present invention, the substrate material is Si, the bottom waveguide core layer 4 is made of Si to fabricate a 2×2 multimode interference coupler, the middle waveguide core layer 5 is made of Si3N4 to fabricate a Bragg grating, the top electrode layer 6 is made of TiN to fabricate electrodes, the tapered output waveguide X1, tapered output waveguide X2, tapered input waveguide X3, and tapered input waveguide X4 are made of Si, the tapered input waveguide Y1, tapered input waveguide Y2, tapered output waveguide Y3, and tapered output waveguide Y4 are made of Si3N4, the input straight waveguide Z1, input straight waveguide Z2, output straight waveguide Z3, and output straight waveguide Z4 are made of Si3N4; and the cladding layer is SiO2.

[0017] The top electrode layer 6 includes electrodes for phase modulation of the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 and for thermo-optic modulation of the Si3N4 grating I2 and Si3N4 grating II7. The present invention mainly uses the Si3N4 grating I2 and Si3N4 grating II7 in the middle waveguide core layer 5 to separate wavelengths and achieve signal interaction through interlayer coupling.

[0018] The 2×2 multimode interference coupler I1 includes a single-mode input waveguide I11, a single-mode input waveguide II12, a multimode waveguide region I15, a single-mode output waveguide I13, and a single-mode output waveguide II14; the 2×2 multimode interference coupler II3 includes a single-mode input waveguide III31, a single-mode input waveguide IV32, a multimode waveguide region II35, a single-mode output waveguide III33, and a single-mode output waveguide IV34; the 2×2 multimode interference couplers I1 and II3 constitute the optical switch section. The multimode interference coupler is based on the self-image effect, inputting the optical field from the single-mode waveguide into the multimode waveguide region. It excites constructive interference between different modes in the multimode waveguide region, forming one or more images of the input mode field, which can be used for the propagation of multiple modes of optical waves. Furthermore, based on the structural characteristics of the multimode interference coupler, the phase of the optical signal can be changed by applying electrical modulation, realizing the function of an optical switch and distributing the optical signal to the two output waveguides, finally coupling it into the optical network system.

[0019] Si3N4 gratings I2 and II7 are formed by etching Si3N4, with the height of the grating region being 305±5nm and the number of exposed gratings being n (which can be designed according to application requirements). According to coupled-mode theory, when a multi-wavelength optical signal is incident on the grating, mode coupling will occur, and wavelengths satisfying the Bragg condition will be reflected.

[0020] The center wavelength of the reflected light satisfies:

[0021] λ Bragg =2n eff Λ. Where, n eff Λ is the refractive index of Si3N4 material, and Λ is the grating period.

[0022] In this implementation, when an optical signal is coupled into the system by the single-mode input waveguide I11 or the single-mode input waveguide II12 of the 2×2 multimode interference coupler I1, the wavelength that satisfies the Bragg condition will be reflected after the optical signal enters the Si3N4 grating I2 or the Si3N4 grating II7. The light reflected in the Si3N4 grating I2 or the Si3N4 grating II7 returns to the 2×2 multimode interference coupler I1 and is connected to other devices through the single-mode input waveguide I11 or the single-mode input waveguide II12 for use or discard. Other wavelengths of optical signals are unaffected and freely propagate along the grating direction through Si3N4 grating I2 and Si3N4 grating II7. At this time, the multi-wavelength optical signals transmitted by Si3N4 grating I2 and Si3N4 grating II7 are then input to the 2×2 multimode interference coupler II3 for splitting and then transmitted to other parts of the system through single-mode output waveguide III33 or single-mode output waveguide IV34. Through this process, a certain wavelength of light is separated to realize the optical wavelength addition-drop multiplexing function in the system.

[0023] Since the refractive index of Si3N4 material changes under the influence of temperature, the refractive index of Si3N4 grating can be changed by adding a heating electrode and thermo-optic modulation, thereby changing the Bragg wavelength of the grating and increasing the range of wavelengths that the device can separate.

[0024] Si3N4 has a lower refractive index than Si. When fabricating gratings, Si3N4 requires a longer grating period at the same wavelength, making it easier to manufacture.

[0025] In the top electrode layer 6, the electrodes are located above the multimode waveguide regions I15 and II35 of the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3. The electrodes are used to perform thermo-optical modulation to change the phase difference of the transmitted light, thereby determining the output of the optical signal by changing the phase difference.

[0026] The electrodes in the top electrode layer 6 are located above Si3N4 grating I2 and Si3N4 grating II7. They are used to modulate the refractive index of the Si3N4 grating under temperature changes, thereby changing the center wavelength of the grating and separating different wavelengths.

[0027] The coupling between the bottom and middle waveguide core layers is achieved by adding tapered waveguides, specifically as follows:

[0028] After being split by the 2×2 multimode interference coupler I1, the optical signal enters the tapered output waveguide X1 and X2, and is then coupled into the tapered input waveguide Y1 and Y2. After passing through the Si3N4 grating I2 and Si3N4 grating II7, the optical signals of different wavelengths are coupled into the tapered input waveguide X3 and X4 according to the Bragg condition, and then enter the 2×2 multimode interference coupler II3.

[0029] The substrate material is Si. The bottom waveguide core layer 4 uses Si to fabricate a 2×2 multimode interference coupler, the middle waveguide core layer 5 uses Si3N4 to fabricate a Bragg grating, and the top electrode layer 6 uses TiN to fabricate electrodes. The cladding material is SiO2. The buried oxide layer thickness is 2.5±0.5μm. The spacing between the bottom waveguide core layer 4 and the middle waveguide core layer 5 is 0.25±0.05μm, and the spacing between the middle waveguide core layer 5 and the top electrode layer 6 is 0.5±0.5μm. The overall thickness of the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 in the bottom waveguide core layer 4 is 220nm. The length of the multimode waveguide region I15 and the multimode waveguide region II35 are both 18±1μm, and the width is both 4±0.5μm. In the middle waveguide core layer 5, the Si3N4 gratings I2 and II7 have an overall thickness of 300 nm, an etching depth of 305 ± 5 nm, a length of 12 ± 1 μm, and a width of 4 ± 0.5 μm. The tapered output waveguides X1, X2, X3, and X4 are made of Si, while the tapered input waveguides Y1, Y2, Y3, and Y4 are made of Si3N4. The width of the wide end of the tapered waveguides is 0.5 ± 0.5 μm, and the width of the narrow end is 0.6 ± 0.2 μm; these dimensions can be adjusted according to specific requirements.

[0030] This invention enables multiple interconnections and allows for the separation and utilization of multiple wavelengths by modulating the refractive index of the grating. This invention is an active OADM device.

[0031] The beneficial effects of this invention are:

[0032] 1. This invention combines 2×2 multimode interference coupler I and 2×2 multimode interference coupler II with Si3N4 grating I and Si3N4 grating II and achieves signal propagation through interlayer coupling, thereby realizing the wavelength separation function of the OADM system and enabling selective channel selection of optical signals.

[0033] 2. By introducing 2×2 multimode interference coupler I and 2×2 multimode interference coupler II, the present invention can distribute optical signals to multiple output waveguides, realize the controllable switching of channels, and better couple signals into the optical network system, thereby reducing losses.

[0034] 3. This invention introduces Si3N4 grating I and Si3N4 grating II to separate and utilize wavelengths that meet the Bragg condition by reflecting and receiving them while allowing other wavelengths to pass through, thereby increasing the capacity of optical fiber in the optical network and improving its utilization efficiency.

[0035] By utilizing the beam splitting characteristics of a multimode interference coupler and the beam splitting characteristics of a Bragg grating, wavelength selection can be achieved. That is, wavelengths that meet the Bragg condition are affected and strongly reflected to the download port for further use, while other wavelengths of optical signals are almost unaffected by the Bragg grating and will continue to be transmitted through the grating.

[0036] 4. The present invention uses Si3N4 material to make gratings. Since the refractive index of Si3N4 is smaller than that of Si, when making gratings, Si3N4 requires a longer grating period at the same wavelength, and is easier to manufacture.

[0037] 5. This invention reduces device size through interlayer coupling.

[0038] 6. This invention is compatible with CMOS technology, has a simple structure, low loss and low crosstalk, and achieves a wavelength division multiplexing system with significantly improved performance compared to the previous one. Attached Figure Description

[0039] Figure 1 This is a partial structural schematic diagram of an OADM device based on a Si3N4 grating according to the present invention;

[0040] Figure 2 This is a cross-sectional interlayer structure diagram of an OADM device based on a Si3N4 grating according to the present invention;

[0041] Figure 3 This is a schematic diagram of the 2×2 multimode interference coupler structure of the present invention;

[0042] Figure 4 This is a schematic diagram of the structural dimensions and tapered waveguide of the 2×2 multimode interference coupler of this invention;

[0043] Figure 5 This is a schematic diagram of the structure, design dimensions, and tapered waveguide of the Si3N4 grating of the present invention.

[0044] Figure 1-5 The labels in the text are as follows: 1-2×2 multimode interference coupler I; 2-Si3N4 grating I; 3-2×2 multimode interference coupler II; 4-bottom waveguide core layer; 5-middle waveguide core layer; 6-top electrode layer; 7-Si3N4 grating II;

[0045] 11-Single-mode input waveguide I, 12-Single-mode input waveguide II, 13-Single-mode output waveguide I, 14-Single-mode output waveguide II, 15-Multimode waveguide region I;

[0046] 31-Single-mode input waveguide III, 32-Single-mode input waveguide IV, 33-Single-mode output waveguide III, 34-Single-mode output waveguide IV, 35-Multimode waveguide region II. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1: As Figure 1 As shown, an OADM device based on a Si3N4 grating has a structure consisting of a substrate layer, a bottom waveguide core layer 4, a middle waveguide core layer 5, and a top electrode layer 6, with each layer separated by a cladding layer. In this embodiment, an SOI wafer is used, and the substrate material is Si with a thickness of 725 μm.

[0049] In this embodiment, the buried oxide layer thickness is 2.5 μm. The spacing between the tapered output waveguides X1 and X2 and the tapered input waveguides Y1 and Y2 in the middle waveguide core layer 5 is 0.3 μm, and the spacing between the middle waveguide core layer 5 and the top electrode layer 6 is 1 μm. These can be set according to specific requirements.

[0050] The bottom waveguide core layer 4 includes a 2×2 multimode interference coupler I1, a 2×2 multimode interference coupler II3, a tapered output waveguide X1, a tapered output waveguide X2, a tapered input waveguide X3, and a tapered input waveguide X4; the 2×2 multimode interference coupler I1 is connected to the tapered output waveguide X1 and the tapered output waveguide X2 respectively, and the tapered input waveguide X3 and the tapered input waveguide X4 are connected to the 2×2 multimode interference coupler II3 respectively;

[0051] like Figure 3 As shown, the 2×2 multimode interference coupler I1 includes a single-mode input waveguide I11, a single-mode input waveguide II12, a multimode waveguide region I15, a single-mode output waveguide I13, and a single-mode output waveguide II14. The single-mode input waveguide I11 and the single-mode input waveguide II12 are both connected to the multimode waveguide region I15. The multimode waveguide region I15 is connected to the single-mode output waveguide I13 and the single-mode output waveguide II14, respectively. The single-mode output waveguide I13 and the single-mode output waveguide II14 are connected to the tapered output waveguide X1 and the tapered output waveguide X2, respectively.

[0052] The 2×2 multimode interference coupler II3 includes a single-mode input waveguide III31, a single-mode input waveguide IV32, a multimode waveguide region II35, a single-mode output waveguide III33, and a single-mode output waveguide IV34; tapered input waveguides X3 and X4 are connected to single-mode input waveguides III31 and IV32 respectively, and both single-mode input waveguides III31 and IV32 are connected to multimode waveguide region II35, which in turn is connected to single-mode output waveguides III33 and IV34 respectively.

[0053] The tips of the conical output waveguides X1 and X2 are facing right, and the tips of the conical input waveguides X3 and X4 are facing left; the tips of the conical input waveguides Y1 and Y2 are facing left, and the tips of the conical output waveguides Y3 and Y4 are facing right.

[0054] The middle waveguide core layer 5 includes a Si3N4 grating I2, a tapered input waveguide Y1, a tapered input waveguide Y2, a tapered output waveguide Y3, a tapered output waveguide Y4, an input straight waveguide Z1, an input straight waveguide Z2, an output straight waveguide Z3, an output straight waveguide Z4, and a Si3N4 grating II7.

[0055] The electrodes in the top electrode layer 6 are distributed above the multimode waveguide regions I15 and II35 of the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3, as well as above the Si3N4 grating I2.

[0056] The 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 are symmetrically distributed about the center of the middle waveguide core layer 5, located below the beginning and end of the middle waveguide core layer 5. The tapered input waveguide Y1, the input straight waveguide Z1, the Si3N4 grating I2, the output straight waveguide Z3, and the tapered output waveguide Y3 are connected in sequence. The tapered input waveguide Y2, the input straight waveguide Z2, the Si3N4 grating II7, the output straight waveguide Z4, and the tapered output waveguide Y4 are connected in sequence. The tapered input waveguides Y1 and Y2 are located directly above the tapered output waveguides X1 and X2, respectively, and the tapered output waveguides Y3 and Y4 are directly above the tapered input waveguides X3 and X4, respectively.

[0057] The bottom waveguide core layer 4 is located below the middle waveguide core layer 5. The interlayer coupling between the bottom waveguide core layer 4 and the middle waveguide core layer 5 is as follows: After the optical signal is split by the 2×2 multimode interference coupler I1, it enters the tapered output waveguide X1 and tapered output waveguide X2 and is then coupled into the tapered input waveguide Y1 and tapered input waveguide Y2. After passing through the Si3N4 grating I2 and Si3N4 grating II7, the optical signal that meets the Bragg wavelength is reflected back to the 2×2 multimode interference coupler I1 according to the Bragg condition. The optical signals of other wavelengths are coupled into the tapered input waveguide X3 and tapered input waveguide X4 through the output straight waveguide Z3 and output straight waveguide Z4 and the tapered output waveguide Y3 and tapered output waveguide Y4, and then enter the 2×2 multimode interference coupler II3.

[0058] The top electrode layer 6 is provided with a heating electrode. The thermo-optical modulation of the heating electrode in the top electrode layer 6 causes the refractive index of Si3N4 grating I2 and Si3N4 grating II7 to change with temperature, thereby achieving modulation of the grating Bragg wavelength. The thermo-optical modulation of 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 is used to select the output channel of the optical signal and realize the switching function.

[0059] The substrate material is Si, with a thickness of 725 μm. The bottom waveguide core layer 4 is made of Si to fabricate 2×2 multimode interference couplers. The overall thickness of the 2×2 multimode interference coupler I1 and the 2×2 multimode interference coupler II3 is 220 nm, the length of the multimode coupling region is 18 μm, and the width is 4 μm. The middle waveguide core layer 5 uses Si3N4 to fabricate Bragg gratings. The Si3N4 gratings I2 and II7 in the middle waveguide core layer 5 have an overall thickness of 300nm, an etching depth of 300nm, a length of 12μm, and a width of 4μm. The top electrode layer 6 uses TiN to fabricate electrodes with a thickness of 100nm. The tapered output waveguides X1, X2, X3, and X4 are made of Si, while the tapered input waveguides Y1, Y2, Y3, and Y4 are made of Si3N4. The input straight waveguides Z1, Z2, Z3, and Z4 are made of Si3N4. The cladding layer is SiO2. The tapered waveguides (X1, X2, X3, X4, Y1, Y2, Y3, Y4) have a width of 0.6 μm at the wide end and 0.8 μm at the narrow end.

[0060] The working principle of this invention is:

[0061] like Figure 1 As shown: When an optical signal is coupled into the system by the single-mode input waveguide I11 or the single-mode input waveguide II12 of the 2×2 multimode interference coupler I1, after the optical signal enters the Si3N4 grating I2 or the Si3N4 grating II7, the wavelengths that satisfy the Bragg condition will be reflected. The light reflected in the Si3N4 grating I2 or the Si3N4 grating II7 returns to the 2×2 multimode interference coupler I1 and is connected to other devices through the single-mode input waveguide I11 or the single-mode input waveguide II12 for use or discard. Other wavelengths of optical signals are unaffected and freely propagate along the grating direction through Si3N4 grating I2 and Si3N4 grating II7. At this time, the multi-wavelength optical signals transmitted by Si3N4 grating I2 and Si3N4 grating II7 are then input to the 2×2 multimode interference coupler II3 for splitting and then transmitted to other parts of the system through single-mode output waveguide III33 or single-mode output waveguide IV34. Through this process, a certain wavelength of light is separated to realize the optical wavelength addition-drop multiplexing function in the system.

[0062] like Figure 3As shown, the 2×2 multimode interference coupler I1 includes a single-mode input waveguide I11, a single-mode input waveguide II12, a multimode waveguide region I15, a single-mode output waveguide I13, and a single-mode output waveguide II14; the 2×2 multimode interference coupler II3 includes a single-mode input waveguide III31, a single-mode input waveguide IV32, a multimode waveguide region II35, a single-mode output waveguide III33, and a single-mode output waveguide IV34. The multimode interference coupler is based on the self-image effect, where the optical field input from the single-mode waveguide is input into the multimode waveguide region. It excites constructive interference between different modes in the multimode waveguide region, forming one or more images of the input mode field, which can be used for the propagation of multiple modes of optical waves. Furthermore, based on the structural characteristics of the multimode interference coupler, the phase of the optical signal can be changed by applying electrical modulation, realizing the function of an optical switch and distributing the optical signal to the two output waveguides, finally coupling it into the optical network system.

[0063] like Figure 2 As shown: Electrodes are added above the multimode waveguide region I15 and multimode waveguide region II35 in the 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 to perform thermo-optical modulation to change the phase difference of the transmitted light, thereby determining the output end of the optical signal by changing the phase difference.

[0064] The 2×2 multimode interference coupler I1 and 2×2 multimode interference coupler II3 are optical switches. When the phase difference between the optical signal input from the single-mode input waveguide I11 and the output light after entering the multimode waveguide region I15 is π, the optical signal enters the Si3N4 grating I2 through the single-mode output waveguide I13, and the optical switch is in a straight-through state. If the phase difference is 0, the optical signal enters the Si3N4 grating II7 through the single-mode output waveguide II14, and the optical switch is in a crossover state. When the phase difference is π / 2, the optical signal exits through both single-mode output waveguides I13 and II14 at a 50:50 ratio. If the phase difference between the optical signal input from single-mode input waveguide II12 and the output after entering multimode waveguide region I15 is π, then the optical switch entering Si3N4 grating II7 from single-mode output waveguide II14 is in a straight-through state. If the phase difference is 0, then the optical switch enters Si3N4 grating I2 from single-mode output waveguide I13, and the optical switch is in a crossover state. If the phase difference is π / 2, then the two channels of single-mode output waveguide I13 and single-mode output waveguide II14 output light at a 50:50 ratio. If the phase difference between the optical signal input from single-mode input waveguide III31 and the output light after passing through multimode waveguide region II35 is π, then the optical signal exits from single-mode output waveguide III33, and the optical switch is in a straight-through state. If the phase difference is 0, then the optical signal exits from single-mode output waveguide IV34, and the optical switch is in a crossover state. If the phase difference is π / 2, then the two channels of single-mode output waveguide III33 and single-mode waveguide IV34 output light at a 50:50 ratio. When the phase difference between the input and output light of the single-mode input waveguide IV32 is π, the light is emitted from the single-mode output waveguide IV34, and the optical switch is in a straight-through state; when the phase difference is 0, the light is emitted from the single-mode output waveguide III33, and the optical switch is in a crossover state; when the phase difference is π / 2, the light is emitted from both single-mode output waveguide III33 and single-mode output waveguide IV34 at a 50:50 ratio.

[0065] A Si3N4 grating is formed by etching a Si3N4 layer using a mask. According to coupled-mode theory, when a multi-wavelength light signal is incident on the grating, mode coupling will occur, and wavelengths that satisfy the Bragg condition will be reflected.

[0066] like Figure 2 As shown: The electrodes in the top electrode layer 6 are placed above Si3N4 grating I2 and Si3N4 grating II7. After being energized, the refractive index of the grating changes under temperature changes, thereby achieving the effect of changing the center wavelength of the grating.

[0067] Using Si3N4 material to make gratings is easier because Si3N4 has a lower refractive index than Si, requiring a longer period at the same wavelength compared to Si gratings.

[0068] This invention provides a manufacturing process as follows:

[0069] Step 1: Take an SOI wafer, clean it, and then perform photolithography on the wafer. The photolithography includes spin coating, exposure, development, drying, etching alignment marks, and then removing the photoresist and cleaning.

[0070] Step 2: Cleaning. Photolithography is performed on the wafer fabricated in Step 1, followed by etching of Si to a depth of 220 nm. The resist is removed, and the wafer is cleaned to obtain silicon-based nanowaveguides and their devices, including 2×2 multimode interference couplers I1, 2×2 multimode interference couplers II3, tapered output waveguide X1, tapered output waveguide X2, tapered input waveguide X3, and tapered input waveguide X4 in the bottom waveguide core layer 4.

[0071] Step 3: A SiO2 layer with a thickness of 0.4 μm is deposited as a cladding layer on the bottom waveguide core layer 4 fabricated in Step 2 using the PECVD method. Reverse etching is then performed, including photolithography, etching, resist removal, and cleaning. The deposited SiO2 layer is then subjected to CMP to obtain a smooth surface.

[0072] Step 4: A Si3N4 layer with a thickness of 301 nm is deposited on the cladding layer using LPCVD technology. After cleaning, CMP is performed to obtain a smooth Si3N4 surface. A mask is placed, and the layer is etched using an exposure machine for spin coating, exposure, development, drying, and etching to form the Si3N4 gratings I2 and II7 in the middle waveguide core layer 5, as well as the tapered input waveguides Y1, Y2, Y3, and Y4, and the input straight waveguides Z1, Z2, Z3, and Z4. The height of the grating region is 300 nm, the number of exposed gratings is n, the etching height is 300 nm, and finally, the resist is removed and the layer is cleaned.

[0073] Step 5: A SiO2 layer with a thickness of 1 μm was deposited using PECVD, and a TiN electrode layer with a thickness of 100 nm was deposited using PVD. The heated TiN electrode was obtained through photolithography and etching, and finally the resist was removed and the surface was cleaned.

[0074] Step 6: After depositing a 1μm thick SiO2 layer, lead holes are obtained through etching. Al is then deposited using PVD, followed by dry etching of Al lines with a length of 600nm. Metallic Al leads are obtained, which are connected to the heating electrode TiN.

[0075] Step 7: After cleaning, photolithography and deep etching are performed to obtain the thermal insulation trench. Finally, deep etching is performed on the Si substrate to obtain the deep etched trench for fiber coupling testing, thus completing the chip fabrication process.

[0076] This invention enables multiple interconnections, and by modulating the refractive index of the grating, multiple wavelengths can be separated and utilized.

[0077] This process increases the capacity of optical fiber in optical networks and improves fiber utilization efficiency.

[0078] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An OADM device based on a Si3N4 grating, characterized in that: The structure, from bottom to top, consists of a substrate layer, a bottom waveguide core layer (4), a middle waveguide core layer (5), and a top electrode layer (6), with each layer separated by a cladding layer. The bottom waveguide core layer (4) includes a 2×2 multimode interference coupler I (1), a 2×2 multimode interference coupler II (3), a tapered output waveguide X1, a tapered output waveguide X2, a tapered input waveguide X3, and a tapered input waveguide X4; the 2×2 multimode interference coupler I (1) is connected to the tapered output waveguide X1 and the tapered output waveguide X2 respectively, and the tapered input waveguide X3 and the tapered input waveguide X4 are connected to the 2×2 multimode interference coupler II (3) respectively; The middle waveguide core layer (5) includes Si3N4 grating I (2), tapered input waveguide Y1, tapered input waveguide Y2, tapered output waveguide Y3, tapered output waveguide Y4, input straight waveguide Z1, input straight waveguide Z2, output straight waveguide Z3, output straight waveguide Z4, and Si3N4 grating II (7). The tapered input waveguide Y1, the input straight waveguide Z1, the Si3N4 grating I (2), the output straight waveguide Z3, and the tapered output waveguide Y3 are connected in sequence; The tapered input waveguide Y2, the input straight waveguide Z2, the Si3N4 grating II (7), the output straight waveguide Z4, and the tapered output waveguide Y4 are connected in sequence; Tapered input waveguides Y1 and Y2 are located directly above tapered output waveguides X1 and X2, respectively, and tapered output waveguides Y3 and Y4 are directly above tapered input waveguides X3 and X4, respectively. The electrodes in the top electrode layer (6) are distributed above the multimode waveguide regions I (15) and II (35) of the 2×2 multimode interference coupler I (1) and 2×2 multimode interference coupler II (3) and above the Si3N4 grating I (2); The 2×2 multimode interference coupler I (1) and 2×2 multimode interference coupler II (3) are located symmetrically distributed about the center of the middle waveguide core layer (5) below the beginning and end of the middle waveguide core layer (5); The 2×2 multimode interference coupler I (1) includes a single-mode input waveguide I (11), a single-mode input waveguide II (12), a multimode waveguide region I (15), a single-mode output waveguide I (13), and a single-mode output waveguide II (14); the single-mode input waveguide I (11) and the single-mode input waveguide II (12) are both connected to the multimode waveguide region I (15), the multimode waveguide region I (15) is connected to the single-mode output waveguide I (13) and the single-mode output waveguide II (14) respectively, and the single-mode output waveguide I (13) and the single-mode output waveguide II (14) are connected to the tapered output waveguide X1 and the tapered output waveguide X2 respectively; The 2×2 multimode interference coupler II (3) includes a single-mode input waveguide III (31), a single-mode input waveguide IV (32), a multimode waveguide region II (35), a single-mode output waveguide III (33), and a single-mode output waveguide IV (34); tapered input waveguide X3 and tapered input waveguide X4 are connected to single-mode input waveguide III (31) and single-mode input waveguide IV (32) respectively, and single-mode input waveguide III (31) and single-mode input waveguide IV (32) are both connected to multimode waveguide region II (35), and multimode waveguide region II (35) is then connected to single-mode output waveguide III (33) and single-mode output waveguide IV (34) respectively; The tips of the tapered output waveguides X1 and X2 are facing right, and the tips of the tapered input waveguides X3 and X4 are facing left; the tips of the tapered input waveguides Y1 and Y2 are facing left, and the tips of the tapered output waveguides Y3 and Y4 are facing right. The bottom waveguide core layer (4) is below the middle waveguide core layer (5). The interlayer coupling between the bottom waveguide core layer (4) and the middle waveguide core layer (5) is as follows: After the optical signal is split by the 2×2 multimode interference coupler I (1), it enters the tapered output waveguide X1 and tapered output waveguide X2 and is then coupled into the tapered input waveguide Y1 and tapered input waveguide Y2. After passing through the Si3N4 grating I (2) and Si3N4 grating II (7), the optical signal that meets the Bragg wavelength is reflected to the 2×2 multimode interference coupler I (1) according to the Bragg condition. The optical signals of other wavelengths are coupled into the tapered input waveguide X3 and tapered input waveguide X4 through the output straight waveguide Z3 and output straight waveguide Z4 and the tapered output waveguide Y3 and tapered output waveguide Y4 and then enter the 2×2 multimode interference coupler II (3). The top electrode layer (6) is provided with a heating electrode. The heating electrode in the top electrode layer (6) is used to perform thermo-optic modulation so that the refractive index of Si3N4 grating I (2) and Si3N4 grating II (7) changes with temperature, thereby achieving modulation of the grating Bragg wavelength. The phase of the optical signal can be changed by performing thermo-optic modulation on 2×2 multimode interference coupler I (1) and 2×2 multimode interference coupler II (3), which is used to select the output channel of the optical signal and realize the switching function.

2. The OADM device based on Si3N4 grating according to claim 1, characterized in that: The substrate material is Si. The bottom waveguide core layer (4) uses Si to fabricate a 2×2 multimode interference coupler. The middle waveguide core layer (5) uses Si3N4 to fabricate a Bragg grating. The top electrode layer (6) uses TiN to fabricate electrodes. The tapered output waveguide X1, tapered output waveguide X2, tapered input waveguide X3, and tapered input waveguide X4 are made of Si. The tapered input waveguide Y1, tapered input waveguide Y2, tapered output waveguide Y3, and tapered output waveguide Y4 are made of Si3N4. The input straight waveguide Z1, input straight waveguide Z2, output straight waveguide Z3, and output straight waveguide Z4 are made of Si3N4. The cladding layer is SiO2.

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