Low-crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating

Abstract

The invention relates to a low-crosstalk wavelength division multiplexer based on cascaded arrayed waveguide gratings, and belongs to the technical field of semiconductor optical signal transmission. The invention comprises a substrate of a wafer, a buried oxide layer of the wafer, a device layer and a SiO2 upper cladding layer of the device from bottom to top, wherein the device layer comprises an input waveguide, a plurality of array waveguide gratings, a transmission waveguide, a cross waveguide and an output waveguide. When input optical signals pass through the first array waveguide grating, the optical signals with different wavelengths are separated to different positions where the first array waveguide grating outputs the slab waveguide, and then the optical signals are input to the second array waveguide grating through the transmission waveguide and the cross waveguide. The distance between the input waveguides of the second array waveguide grating is twice that between the output waveguides of the first array waveguide grating, and finally, target wavelengths filtered twice are respectively output at the output slab waveguides of the second array waveguide grating. The wavelength division multiplexer is used for realizing ultra-low adjacent channel crosstalk of the arrayed waveguide grating, and is an improvement of a traditional wavelength division multiplexer.

Description

Technical Field

[0001] The invention relates to a low crosstalk wavelength division multiplexer based on a cascade array waveguide grating, and belongs to the technical field of semiconductor optical signal transmission. Background Art

[0002] In the past three decades, the research on silicon-based optical interconnects has achieved the integration of various optical functional devices on-chip, such as on-chip lasers, edge couplers, electro-optic modulators, optical wavelength division multiplexers, photodetectors, etc. Arrayed waveguide gratings (AWGs) are key wavelength division multiplexing devices in silicon photonic integrated chips. At present, arrayed waveguide gratings have been applied to a certain extent on multiple material platforms, such as silicon dioxide (SiO2), silicon on insulator (SOI), silicon nitride (Si3N4), indium phosphide (InP) and other low refractive index contrast material systems. High-performance (low insertion loss, low inter-adjacent / inter-band crosstalk, etc.) arrayed waveguide gratings have been achieved on these material platforms. However, these arrayed waveguide gratings often have large device sizes, complex process preparation requirements, or are not easy to integrate with other photonic devices. In recent years, arrayed waveguide gratings based on silicon nanowire waveguides have been widely studied because their high refractive index contrast waveguide structure can achieve compact size. This is due to the high refractive index contrast characteristics of silicon on insulator (SOI) waveguides, which can achieve sharp bending. Furthermore, its fabrication is compatible with CMOS technology, offering a promising solution for large-scale integration with other silicon-based devices in high-density photonic chips.

[0003] The current research on silicon photonic integrated devices is based on high-speed transmission characteristics, so the SOI (silicon on insulator) wafer with thin (220nm) top silicon has become the first choice for device design. Silicon photonic PN junctions based on thin top silicon can achieve high-speed modulation and detection of optical signals. However, it is difficult to obtain satisfactory channel crosstalk characteristics for silicon-based arrayed waveguide gratings on thin top silicon SOI wafers. This is because the deviations caused by existing process conditions and designs can easily cause large phase errors in the nanowire waveguides of the high refractive index core layer, and the arrayed waveguide grating is very sensitive to phase errors. Large phase errors will lead to poor channel crosstalk. After years of research, several solutions have been proposed to improve the crosstalk characteristics of silicon photonic AWGs, but there are still some problems. At present, the crosstalk of AWGs on thin top silicon is a bottleneck that limits its widespread application. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the crosstalk problem of arrayed waveguide grating on thin top silicon, the present invention provides a low crosstalk wavelength division multiplexer for achieving a significant reduction in the crosstalk of adjacent output channels of the arrayed waveguide grating.

[0005] The technical solution of the present invention is: a low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide gratings, which includes, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer and a SiO2 upper cladding of the device layer, wherein the device layer includes an input waveguide 100, two or more cascaded arrayed waveguide gratings or wavelength division multiplexers; the input waveguide 100 is connected to an input optical fiber; each arrayed waveguide grating includes an arrayed waveguide grating input flat waveguide, an arrayed waveguide, and an arrayed waveguide grating output flat waveguide; the arrayed waveguide grating input flat waveguide, the arrayed waveguide, and the arrayed waveguide grating output flat waveguide are connected in sequence; two adjacent arrayed waveguide gratings are connected in sequence through a transmission waveguide 400 and a cross waveguide 500, and the output end of the last arrayed waveguide grating is connected to an output waveguide 600.

[0006] As a further solution of the present invention, the arrayed waveguide grating includes a first arrayed waveguide grating AWG1 and a second arrayed waveguide grating AWG2; the first arrayed waveguide grating AWG1 includes a first arrayed waveguide grating input slab waveguide 310, an arrayed waveguide I210, and a first arrayed waveguide grating output slab waveguide 320; and they are connected in sequence; the second arrayed waveguide grating AWG2 includes a second arrayed waveguide grating input slab waveguide 330, an arrayed waveguide II220, and a second arrayed waveguide grating output slab waveguide 340, and they are connected in sequence;

[0007] The input waveguide 100 is connected to the first arrayed waveguide grating input slab waveguide 310, the first arrayed waveguide grating output slab waveguide 320 is connected to the transmission waveguide 400, the transmission waveguide 400 is connected to the cross waveguide 500, the cross waveguide 500 is connected to the second arrayed waveguide grating input slab waveguide 330, and the second arrayed waveguide grating output slab waveguide 340 is connected to the output waveguide 600.

[0008] As a further solution of the present invention, the output channel spacing of all cascaded arrayed waveguide gratings is consistent, which is d, and the input channel spacing of each arrayed waveguide grating cascaded after the first arrayed waveguide grating is twice the output channel spacing of the first arrayed waveguide grating, that is, 2×d.

[0009] As a further solution of the present invention, the optical signal input by the input optical fiber passes through the input waveguide 100, the first arrayed waveguide grating input slab waveguide 310, the arrayed waveguide I210, the first arrayed waveguide grating output slab waveguide 320, the transmission waveguide 400, the cross waveguide 500, the second arrayed waveguide grating input slab waveguide 330, the arrayed waveguide II220, the second arrayed waveguide grating output slab waveguide 340, and the output waveguide 600 to output the twice filtered optical signal.

[0010] As a further solution of the present invention, the planar waveguide and arrayed waveguide structures of the first arrayed waveguide grating AWG1 and the second arrayed waveguide grating AWG2 are completely consistent and are arrayed waveguide gratings with arbitrary channel spacing and arbitrary number of channels, so as to reduce crosstalk after cascading two arrayed waveguide gratings.

[0011] As a further solution of the present invention, the first arrayed waveguide grating AWG1 and the second arrayed waveguide grating AWG2 have five output channels, and the second arrayed waveguide grating AWG2 has five input channels; the optical signal output by the first output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the first input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500, and the optical signal output by the second output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the second input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500, and so on, the optical signal output by the fifth output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the fifth input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500.

[0012] As a further solution of the present invention, the arrayed waveguide grating is of a disk type or a saddle type.

[0013] As a further solution of the present invention, any type of N×N wavelength division multiplexer can be used instead of the arrayed waveguide grating to achieve the function of reducing crosstalk.

[0014] As a grating device, arrayed waveguide grating (AWG) can separate and output mixed input wavelengths, which is also called wavelength demultiplexing. Figure 1 As shown, the first arrayed waveguide grating AWG1 has five output channels. According to the dispersion characteristics of the AWG, different wavelengths are focused on different output channels of the output slab waveguide. Therefore, each channel outputs λ1-λ5 in turn. There is a wavelength difference Δλ between the response wavelengths output by each output channel, which is also called the channel spacing, that is, λ1+Δλ=λ2, λ2+Δλ=λ3, ...λ4+Δλ=λ5. The above is the output channel response based on the input of the center channel. If the arrayed waveguide grating input slab waveguide is input from the edge input channel, then according to the optical characteristics of the arrayed waveguide grating, the focused wavelength of the output channel will become λ±nΔλ (n is the ratio of the spacing Δx between the edge input channel and the center input channel to the output channel spacing d, that is, ), that is, when the light field is input from the nth input channel near the central channel, the output channel focusing wavelength is shifted from λ1,λ2,...λ5 to λ1±nΔλ,λ2±nΔλ,...λ5±nΔλ. For example, when the light field is input from the left adjacent channel of the central channel of the arrayed waveguide grating, that is, when n=-1, the output wavelength of the arrayed waveguide grating output channel output1-5 will be shifted from λ1,λ2,...λ5 to λ1-Δλ,λ2-Δλ,...λ5-Δλ. When the light field is input from the right adjacent channel of the central channel of the arrayed waveguide grating, that is, when n=1, the output wavelength of the arrayed waveguide grating output channel output1-5 will be shifted from λ1,λ2,...λ5 to λ1+Δλ,λ2+Δλ,...λ5+Δλ.

[0015] The first arrayed waveguide grating output slab waveguide 320 and the second arrayed waveguide grating input slab waveguide 330 are connected through the transmission waveguide 400 and the cross waveguide 500. Figure 2 and Figure 3 As shown, output1-5 are connected to input1-5 respectively, that is, λ1-λ5 are input to input1-5 respectively, and the waveguide spacing between input1-5 is 2d, which is twice the spacing of output1-5. The beneficial effect produced is that the output slab waveguide of the second arrayed waveguide grating has 340 channels output1 * -5 * The focusing response wavelengths are λ1+4Δλ=λ5, λ2+2Δλ=λ4, λ3, λ4-2Δλ=λ2, λ5-4Δλ=λ1. At this time, the channel responses of the second arrayed waveguide grating output slab waveguide 340 are λ5, λ4, ... λ1, which are consistent with the output channel response wavelengths of the first arrayed waveguide grating. Compared with the traditional six arrayed waveguide gratings with different designs cascaded to achieve double filtering, only two arrayed waveguide gratings are used to complete the same filtering to reduce crosstalk.

[0016] The beneficial effects of the present invention are:

[0017] 1. The present invention can separate mixed input wavelengths and reduce the crosstalk level by cascading two or more planar waveguides and arrayed waveguide-consistent arrayed waveguide gratings;

[0018] 2. It can achieve double filtering effect for a single wavelength, greatly reducing the crosstalk level of the same channel;

[0019] 3. The present invention can arbitrarily cascade multiple wavelength division multiplexers to filter multiple times;

[0020] 4. Compared with the traditional solution of integrating an arrayed waveguide grating for filtering in each arrayed waveguide grating output channel, it is more compact in size and provides a wavelength division multiplexing solution suitable for large-scale integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention provides a schematic structural diagram of a low crosstalk wavelength division multiplexer based on a cascaded array waveguide grating;

[0022] Figure 2 is a schematic structural diagram of a first arrayed waveguide grating output slab waveguide 320 provided by the present invention;

[0023] Figure 3 is a schematic structural diagram of a second arrayed waveguide grating input slab waveguide 330 provided by the present invention;

[0024] Figure 4 is a schematic structural diagram of a second arrayed waveguide grating output slab waveguide 340 provided by the present invention;

[0025] The numbers in the figure are: 100-input waveguide, AWG1-first arrayed waveguide grating, AWG2-second arrayed waveguide grating, 310-first arrayed waveguide grating input slab waveguide, 210-arrayed waveguide I, 320-first arrayed waveguide grating output slab waveguide, 400-transmission waveguide, 500-cross waveguide, 330-second arrayed waveguide grating input slab waveguide, 220-arrayed waveguide II, 340-second arrayed waveguide grating output slab waveguide, 600-output waveguide. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0027] Example 1: Figure 1 As shown, a low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide gratings includes, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer and a SiO2 upper cladding of the device layer, the device layer includes an input waveguide 100 and two cascaded arrayed waveguide gratings; the input waveguide 100 is connected to an input optical fiber; the two arrayed waveguide gratings have the same structure, one of the arrayed waveguide gratings includes a first arrayed waveguide grating AWG1 and a second arrayed waveguide grating AWG2; the first arrayed waveguide grating AWG1 includes a first arrayed waveguide grating input slab waveguide 310, an arrayed waveguide I210, and a first arrayed waveguide grating output slab waveguide 320; and they are connected in sequence; the second arrayed waveguide grating AWG2 includes a second arrayed waveguide grating input slab waveguide 330, an arrayed waveguide II220, and a second arrayed waveguide grating output slab waveguide 340, and they are connected in sequence;

[0028] The input waveguide 100 is connected to the first arrayed waveguide grating input slab waveguide 310, the first arrayed waveguide grating output slab waveguide 320 is connected to the transmission waveguide 400, the transmission waveguide 400 is connected to the cross waveguide 500, the cross waveguide 500 is connected to the second arrayed waveguide grating input slab waveguide 330, and the second arrayed waveguide grating output slab waveguide 340 is connected to the output waveguide 600, thereby realizing the double filtering output of the arrayed waveguide grating on the optical signal, greatly reducing the crosstalk level of the optical signal.

[0029] As a further solution of the present invention, the output channel spacing of all cascaded arrayed waveguide gratings is consistent, which is d, and the input channel spacing of each arrayed waveguide grating cascaded after the first arrayed waveguide grating is twice the output channel spacing of the first arrayed waveguide grating, that is, 2×d.

[0030] As a further solution of the present invention, the optical signal input by the input optical fiber passes through the input waveguide 100, the first arrayed waveguide grating input slab waveguide 310, the arrayed waveguide I210, the first arrayed waveguide grating output slab waveguide 320, the transmission waveguide 400, the cross waveguide 500, the second arrayed waveguide grating input slab waveguide 330, the arrayed waveguide II220, the second arrayed waveguide grating output slab waveguide 340, and the output waveguide 600 to output the twice filtered optical signal.

[0031] As a further solution of the present invention, the planar waveguide and arrayed waveguide structures of the first arrayed waveguide grating AWG1 and the second arrayed waveguide grating AWG2 are completely consistent and are arrayed waveguide gratings with arbitrary channel spacing and arbitrary number of channels. According to the transmission waveguide connection method of the present invention, it is possible to reduce crosstalk after cascading two arrayed waveguide gratings.

[0032] As a further solution of the present invention, the first arrayed waveguide grating AWG1 and the second arrayed waveguide grating AWG2 have five output channels, and the second arrayed waveguide grating AWG2 has five input channels; the optical signal output by the first output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the first input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500, and the optical signal output by the second output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the second input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500, and so on, the optical signal output by the fifth output waveguide from the left of the first arrayed waveguide grating AWG1 is input into the fifth input waveguide from the left of the second arrayed waveguide grating AWG2 through the transmission waveguide 400 and the cross waveguide 500.

[0033] As a further solution of the present invention, the arrayed waveguide grating is of a disk type or a saddle type.

[0034] The input waveguide 100 inputs the mixed wavelengths λ1-λ5 and simultaneously enters the first arrayed waveguide grating AWG1, and then the wavelength λ1 is transmitted from Figure 2 The wavelength λ is output from Output 1 of the first arrayed waveguide grating output slab waveguide 320, the wavelength λ2 is output from Output 2 of the first arrayed waveguide grating output slab waveguide 320, the wavelength λ3 is output from Output 3 of the first arrayed waveguide grating output slab waveguide 320, the wavelength λ4 is output from Output 4 of the first arrayed waveguide grating output slab waveguide 320, and the wavelength λ5 is output from Output 6 of the first arrayed waveguide grating output slab waveguide 320. Figure 2 The first array waveguide grating output is output in Output 5 of the slab waveguide 320.

[0035] When the wavelength λ1 enters through the transmission waveguide 400 and the cross waveguide 500 Figure 3 When the second arrayed waveguide grating inputs input 1 of the slab waveguide 330, the input waveguide spacing between input 1 and input 3 is 4d. Therefore, the focused output wavelengths of the five output channels of the second arrayed waveguide grating output slab waveguide 340 are λ1-4Δλ, λ2-4Δλ, λ3-4Δλ, λ4-4Δλ, and λ5-4Δλ. At this time, since the wavelength input through the input 1 channel of the second arrayed waveguide grating AWG2 is only λ1, and λ1=λ5-4Δλ. Therefore, after the wavelength λ1 is filtered by AWG2, it is focused on Figure 4 The second arrayed waveguide grating output slab waveguide 340 ouput5 * location, ultimately through ouput5 * Output wavelength λ1.

[0036] When the wavelength λ2 enters through the transmission waveguide 400 and the cross waveguide 500 Figure 3 When the second arrayed waveguide grating inputs input2 of the slab waveguide 330, the input waveguide spacing between input2 and input3 is 2d. Therefore, the focused output wavelengths of the five output channels of the second arrayed waveguide grating output slab waveguide 340 are λ1-2Δλ, λ2-2Δλ, λ3-2Δλ, λ4-2Δλ, and λ5-2Δλ. At this time, since the wavelength input through the input2 channel of AWG2 is only λ2, and λ2=λ4-2Δλ. Therefore, after the wavelength λ2 is filtered by the second arrayed waveguide grating AWG2, it is focused on Figure 4 ouput4 of medium flat waveguide 340 * location, ultimately through ouput4 * Output wavelength λ2.

[0037] When the wavelength λ3 enters through the transmission waveguide 400 and the cross waveguide 500 Figure 3When the second arrayed waveguide grating inputs input3 of the slab waveguide 330, input3 is the central input waveguide. Therefore, the focused output wavelengths of the five output channels of the second arrayed waveguide grating output slab waveguide 340 are λ1, λ2, λ3, λ4, and λ5 respectively. At this time, since the wavelength input through the input3 channel of AWG2 is only λ3, the wavelength λ3 is filtered by the second arrayed waveguide grating AWG2 and focused on Figure 4 The output of the second arrayed waveguide grating slab waveguide 340 is ouput3 * Location, ultimately through ouput3 * Output wavelength λ3

[0038] The wavelength λ4 enters through the transmission waveguide 400 and the cross waveguide 500 Figure 3 When the second arrayed waveguide grating inputs input 4 of the slab waveguide 330, the input waveguide spacing between input 4 and input 3 is 2d. Therefore, the focused output wavelengths of the five output channels of the second arrayed waveguide grating output slab waveguide 340 are λ1+2Δλ, λ2+2Δλ, λ3+2Δλ, λ4+2Δλ, λ5+2Δλ. At this time, since the wavelength input through the input2 channel of AWG2 is only λ4, and λ4=λ2+2Δλ. Therefore, after the wavelength λ4 is filtered by AWG2, it is focused on Figure 4 The second arrayed waveguide grating output slab waveguide 340 ouput2 * location, ultimately through ouput2 * Output wavelength λ4.

[0039] The wavelength λ5 enters through the transmission waveguide 400 and the cross waveguide 500 Figure 3 When the second arrayed waveguide grating inputs input5 of the slab waveguide 330, the input waveguide spacing between input5 and input3 is 4d. Therefore, the focused output wavelengths of the five output channels of the second arrayed waveguide grating output slab waveguide 340 are λ1+4Δλ, λ2+4Δλ, λ3+4Δλ, λ4+4Δλ, λ5+4Δλ. At this time, since the wavelength input through the input1 channel of AWG2 is only λ5, and λ5=λ1+4Δλ. Therefore, after the wavelength λ5 is filtered by AWG2, it is focused on Figure 4 The ouput 1 of the second arrayed waveguide grating output slab waveguide 340 * Location, ultimately through ouput1 * Output wavelength λ5.

[0040] The present invention can cascade two or more arrayed waveguide gratings to achieve filtering and reduce crosstalk;

[0041] Any type of N×N wavelength division multiplexer can replace the arrayed waveguide grating to achieve the function of reducing crosstalk.

[0042] Exemplarily, the preparation process of the present invention can be as follows: take a pure silicon wafer, clean it, obtain a buried oxide layer after thermal oxidation, and chemically polish the obtained surface using CMP technology to obtain a smooth surface. A silicon layer is deposited on the prepared buried oxide layer using LPCVD technology, polished, and then photolithography is performed. Photolithography includes spinning, exposure, development, drying, etching, and finally degumming and cleaning to prepare a complete ridge structure and strip waveguide structure, and complete the array waveguide grating and transmission waveguide structure. After cleaning, the PECVD method is used to deposit the SiO2 cladding on the Si waveguide. In order to obtain a smooth and flat upper surface, CMP chemical mechanical polishing is used to obtain a smooth upper surface. At this point, the passive silicon-based low crosstalk wavelength division multiplexing device is completed.

[0043] Embodiment 2, a low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide gratings. This embodiment is different from Embodiment 1 in that the number of cascaded arrayed waveguide gratings is 2. In Embodiment 2, the number of cascaded arrayed waveguide gratings is 3, the number of output channels of the arrayed waveguide grating is 8, and other structures remain unchanged.

[0044] The channel spacing of the three arrayed waveguide gratings is 3.2 nm, the output waveguide spacing d of the three arrayed waveguide gratings is 4 nm, and the input waveguide spacing of the second and third arrayed waveguide gratings is 8 nm.

[0045] All input / output waveguides are defined to be numbered 1, 2, ... 8 from left to right. The output waveguide 1 of the first arrayed waveguide grating is connected to the input waveguide 8 of the second arrayed waveguide grating, the output waveguide 2 of the first arrayed waveguide grating is connected to the input waveguide 7 of the second arrayed waveguide grating, and so on, and finally the output waveguide 8 of the first arrayed waveguide grating is connected to the input waveguide 1 of the second arrayed waveguide grating.

[0046] The output waveguides 1, 2, ... 8 of the second arrayed waveguide grating are sequentially connected to the input waveguides 1, 2, ... 8 of the third arrayed waveguide grating.

[0047] The specific embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide gratings, comprising, from bottom to top, a wafer substrate, a wafer buried oxide layer, a device layer, and a SiO2 upper cladding layer of the device layer, characterized in that: The device layer includes an input waveguide (100), two or more cascaded arrayed waveguide gratings or wavelength division multiplexers; The input waveguide (100) is connected to the input optical fiber; each arrayed waveguide grating comprises an arrayed waveguide grating input flat waveguide, an arrayed waveguide, and an arrayed waveguide grating output flat waveguide; the arrayed waveguide grating input flat waveguide, the arrayed waveguide, and the arrayed waveguide grating output flat waveguide are connected in sequence; two adjacent arrayed waveguide gratings are connected in sequence through a transmission waveguide (400) and a cross waveguide (500); and the output end of the last arrayed waveguide grating is connected to an output waveguide (600).

2. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 1, characterized in that: The arrayed waveguide grating (AWG1) comprises a first arrayed waveguide grating (AWG1) and a second arrayed waveguide grating (AWG2); the first arrayed waveguide grating (AWG1) comprises a first arrayed waveguide grating input slab waveguide (310), an arrayed waveguide I (210), and a first arrayed waveguide grating output slab waveguide (320), which are connected in sequence; the second arrayed waveguide grating (AWG2) comprises a second arrayed waveguide grating input slab waveguide (330), an arrayed waveguide II (220), and a second arrayed waveguide grating output slab waveguide (340), which are connected in sequence; The input waveguide (100) is connected to the first arrayed waveguide grating input slab waveguide (310), the first arrayed waveguide grating output slab waveguide (320) is connected to the transmission waveguide (400), the transmission waveguide (400) is connected to the cross waveguide (500), the cross waveguide (500) is connected to the second arrayed waveguide grating input slab waveguide (330), and the second arrayed waveguide grating output slab waveguide (340) is connected to the output waveguide (600).

3. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 1, characterized in that: The output channel spacing of all cascaded array waveguide gratings is consistent, which is d. The input channel spacing of each array waveguide grating cascaded after the first array waveguide grating is twice the output channel spacing of the first array waveguide grating, that is, 2×d.

4. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 2, characterized in that: An optical signal inputted from an input optical fiber passes through an input waveguide 100, a first arrayed waveguide grating input flat waveguide (310), an arrayed waveguide I (210), a first arrayed waveguide grating output flat waveguide (320), a transmission waveguide (400), a cross waveguide (500), a second arrayed waveguide grating input flat waveguide (330), an arrayed waveguide II (220), a second arrayed waveguide grating output flat waveguide (340), and an output waveguide (600) in sequence to output a twice-filtered optical signal.

5. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 2, characterized in that: The planar waveguide and arrayed waveguide structures of the first arrayed waveguide grating (AWG1) and the second arrayed waveguide grating (AWG2) are completely consistent and are arrayed waveguide gratings with arbitrary channel spacing and arbitrary channel numbers.

6. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 2, characterized in that: The first arrayed waveguide grating (AWG1) and the second arrayed waveguide grating (AWG2) have five output channels, and the second arrayed waveguide grating (AWG2) has five input channels; an optical signal outputted from the first output waveguide from the left of the first arrayed waveguide grating (AWG1) is inputted into the first input waveguide from the left of the second arrayed waveguide grating (AWG2) through a transmission waveguide (400) and a cross waveguide (500), and an optical signal outputted from the second output waveguide from the left of the first arrayed waveguide grating (AWG1) is inputted into the second input waveguide from the left of the second arrayed waveguide grating (AWG2) through a transmission waveguide (400) and a cross waveguide (500), and by analogy, an optical signal outputted from the fifth output waveguide from the left of the first arrayed waveguide grating (AWG1) is inputted into the fifth input waveguide from the left of the second arrayed waveguide grating (AWG2) through a transmission waveguide (400) and a cross waveguide (500).

7. The low crosstalk wavelength division multiplexer based on cascaded arrayed waveguide grating according to claim 1, characterized in that: The arrayed waveguide grating is of a disk type or a saddle type.

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