CN111880267A - Silicon nitride-assisted lithium niobate thin film waveguide-based fully-integrated optical transceiving system - Google Patents

Abstract

The invention proposes a fully integrated optical transceiver system based on silicon nitride-assisted lithium niobate thin film waveguide, which includes a transmitting module and a receiving module connected by a multi-mode waveguide; the optical frequency comb laser source includes a connected on-chip single-wavelength laser source and an optical frequency comb device; the wavelength-mode modulation module includes a wavelength demultiplexer, a power divider group, an electro-optical modulator array and a mode multiplexer connected in sequence; the optical frequency comb device is connected to the wavelength demultiplexer, and the mode is multiplexed The converter is connected to the wavelength-mode demultiplexing module through a multimode waveguide. The optical system can realize the full integration of multi-wavelength lasers, electro-optic modulators, wavelength (de)multiplexers, mode (de)multiplexers, photodetectors and other devices on the same chip using only standard commercial CMOS processes. Integration greatly reduces the process difficulty and manufacturing cost of the chip. It greatly expands the communication capacity of the system and doubles the processing speed of the system.

Description

Fully integrated optical transceiver system based on silicon nitride assisted lithium niobate thin film waveguide

technical field

The invention belongs to the technical field of integrated optics, and relates to a fully integrated optical transceiver system based on a silicon nitride-assisted lithium niobate thin film waveguide.

Background technique

In the prior art, the electrical interconnection and electrical information processing have limited bandwidth, high delay, and high power consumption, and have gradually been unable to meet the demand for improved device performance due to the increase in information capacity. Light has the characteristics of high speed, anti-electromagnetic interference and parallel processing, and is very suitable as a carrier of information. In addition, in addition to space division multiplexing, time division multiplexing, and code division multiplexing, light also has its own unique wavelength division multiplexing, mode division multiplexing, polarization multiplexing, etc., which can double the communication capacity and processing capacity of the system. speed. Therefore, optical communication technology has attracted extensive attention of researchers. Among them, optical fiber communication technology is the most mature and widely used, but the structural stability of optical fiber devices is poor, and the design methods are also very limited. In recent years, with the continuous development of the microelectronics industry, integrated photonic chips have received extensive attention from academia and industry, and the most representative one is silicon-based photonic integration technology. In terms of chip fabrication process, silicon-based photonic integration technology can utilize standardized metal-oxide-semiconductor (CMOS) processes to achieve mass production of chips on the existing microelectronics processing technology platform, which greatly reduces industrial costs. In terms of chip performance, various active or passive devices can be flexibly designed, and these devices can be integrated on the same silicon-based chip to achieve multiple functions while greatly reducing the chip area and power consumption. However, silicon materials have some natural defects, such as two-photon absorption and weak electro-optic effect. Among them, due to the two-photon absorption effect of silicon material, it is difficult to use silicon material for nonlinear optics research. Since silicon material does not have significant electro-optic effect, it is usually necessary to perform carrier injection or extraction after doping, and to complete the electro-optic modulation of the device by means of the plasmon dispersion effect of silicon material. This method is not only a complicated process, but also material doping will cause additional losses. These natural defects have become obstacles in the further development of silicon-based photonic integration technology.

Compared with silicon materials, lithium niobate has some excellent material properties, such as significant linear electro-optic effects and second-order nonlinear effects. Based on this, bulk lithium niobate waveguides have been widely used in the field of electro-optic modulators. However, the fabrication process of state-of-the-art bulk lithium niobate waveguides is not compatible with standard commercial CMOS processes, which limits the hybrid integration of electro-optic modulators with other photonic devices. As a result, devices based on lithium niobate thin-film waveguides entered the researchers' field of vision. At present, the most common method to realize lithium niobate thin film waveguide is still direct etching, but it is difficult for the waveguide structure formed by the direct etching method to have a smooth boundary. When it is necessary to strictly consider the chamfer that may be formed by etching in the design process, it increases the difficulty of device design. To sum up, whether it is based on silicon waveguide or based on lithium niobate thin film waveguide, it is difficult to complete the monolithic full integration of the main functional devices in the optical communication system through the existing technical means.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a fully integrated optical transceiver system based on silicon nitride assisted lithium niobate thin film waveguide, which includes multi-wavelength laser source, electro-optic modulation, wavelength division (de-multiplexing), The optical transceiver system, including mode division (de)multiplexing, photoelectric detection, etc., realizes the single-chip full integration of the main functional devices in the optical communication system.

In order to achieve the above object, the technical solution adopted in the present invention is: a fully integrated optical transceiver system based on a silicon nitride-assisted lithium niobate thin film waveguide, comprising a sending module and a receiving module, and the sending module and the receiving module pass through the multi-mode waveguide. connected;

The sending module includes a connected optical frequency comb laser source and a wavelength-mode modulation module;

The receiving module includes a connected photodetector array and a wavelength-mode demultiplexing module; the optical frequency comb laser source includes a connected on-chip single-wavelength laser source and an optical frequency comb device; the wavelength-mode modulation module includes sequentially connected wavelength demultiplexing modules. The optical frequency comb device is connected with the wavelength demultiplexer, and the mode multiplexer is connected with the wavelength-mode demultiplexer module through the multi-mode waveguide.

The fully integrated optical transceiver system of the present invention is based on a silicon nitride assisted lithium niobate thin film waveguide. This type of waveguide uses a silicon nitride assisted lithium niobate thin film as the waveguide core layer and silicon dioxide as the waveguide cladding/substrate. Lasers, electro-optic modulators, wavelength (de)multiplexers, mode (de)multiplexers, The full integration of devices such as photodetectors greatly reduces the process difficulty and manufacturing cost of the chip. In addition, the optical transceiver system combines optical wavelength division multiplexing technology and mode division multiplexing technology, which greatly expands the communication capacity of the system and doubles the processing speed of the system.

Description of drawings

FIG. 1 is an overall architecture diagram of an optical transceiver system of the present invention.

FIG. 2 is a schematic structural diagram of a receiving module in the optical transceiver system of the present invention.

FIG. 3 is a schematic structural diagram of a transmitting module in the optical transceiver system of the present invention.

FIG. 4 is a schematic structural diagram of the lithium niobate thin film waveguide in the optical transceiver system of the present invention.

FIG. 5 is a mode field diagram formed when light is transmitted in the lithium niobate thin film waveguide of FIG. 4 .

In the figure: 1. Transmitting module, 2. Receiving module, 3. Optical frequency comb laser source, 4. Wavelength-mode modulation module, 5. Multimode waveguide, 6. Photodetector array, 7. Wavelength-mode demultiplexing Module, 8. On-chip single-wavelength laser source, 9. Optical frequency comb device, 10. Wavelength demultiplexer, 11. Power divider group, 12. Electro-optic modulator array, 13. Mode multiplexer, 14. Dioxide Silicon cladding layer, 15. Silicon nitride layer, 16. Lithium niobate layer, 17. Silicon dioxide buried layer, 18. Substrate layer.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , the optical transceiver system of the present invention includes a sending module 1 and a receiving module 2 , and the sending module 1 and the receiving module 2 are connected through a multimode waveguide 5 .

The transmitting module 1 includes a connected optical frequency comb laser source 3 and a wavelength-mode modulation module 4 .

The receiving module 2 includes a connected photodetector array 6 and a wavelength-mode demultiplexing module 7, as shown in FIG. 2 .

The wavelength-mode modulation module 4 is connected to the wavelength-mode demultiplexing module 7 through the multimode waveguide 5 .

The optical frequency comb laser source 3 in the transmitting module 1 includes a connected on-chip single-wavelength laser source 8 and an optical frequency comb device 9; the wavelength-mode modulation module 4 in the transmitting module 1 includes a wavelength demultiplexer 10, a function The splitter group 11, the electro-optic modulator array 12 and the mode multiplexer 13 are shown in Figure 3; the optical frequency comb device 9 is connected to the wavelength demultiplexer 10, and the mode multiplexer 13 is connected to the wavelength-mode demultiplexer through the multimode waveguide 5. The multiplexing module 7 is connected.

The power divider group 11 is composed of N 1×M power dividers, the input ends of all 1×M power dividers are connected to the output end of the wavelength demultiplexer 10, and the output ends of all 1×M power dividers are connected to Input of the electro-optic modulator array 12 . The electro-optic modulator array 12 is composed of N×M electro-optic modulators, and a 1×M power divider is connected to the M electro-optic modulators.

Optical transmission and optical information processing devices can be arranged between the sending module 1 and the receiving module 2 according to the user's needs. At present, a variety of integrated optoelectronic devices for optical transmission and optical information processing have been reported successively, including switches, routing, logic operation devices, etc., involving multiple wavelengths and multiple modes, and will not be described one by one here.

The multi-mode waveguide 5 in the optical transceiver system of the present invention is a silicon nitride-assisted lithium niobate thin film waveguide with a structure as shown in FIG. 17. The lithium niobate layer 16 and the silicon dioxide cladding layer 14 . The lithium niobate layer 16 is further provided with a silicon nitride layer 15 , and the silicon nitride layer 15 is located in the silicon dioxide cladding layer 14 .

The basic implementation method of the silicon nitride-assisted lithium niobate thin film waveguide: firstly, a silicon dioxide layer (silicon dioxide buried layer 17) is grown on a silicon or lithium niobate wafer (substrate layer 18), and then the lithium niobate The thin film (lithium niobate layer 16) is bonded to the silicon dioxide layer, and a layer of silicon nitride is sputtered, and the layer of silicon nitride is subjected to photolithography, etching and other processes to form a waveguide structure (silicon nitride layer 15). ), multiple modes of signal transmission can be achieved by etching silicon nitride waveguides with different widths. Finally, a silicon dioxide layer is deposited as the device cladding layer (silicon dioxide cladding layer 14). Among them, lithium niobate thin films were prepared by ion implantation and thermal stripping. The detailed preparation methods can be found in the literature (A. Rao, S. Fathpour, "Compact lithiumniobate electroopticmodulators," IEEE J. Sel. Top. QuantumElectron. 24(4), 1–14 (2018).); The silicon nitride layer was prepared by magnetron sputtering, and compared with plasma chemical vapor deposition (PECVD), the transmission loss of silicon nitride waveguide prepared by magnetron sputtering method Greatly reduced; compared with low pressure chemical vapor deposition (LPCVD), the silicon nitride waveguide prepared by magnetron sputtering is less prone to waveguide cracks, and the required process temperature is lower, which will not cause damage to the device structure and substrate . The preparation method of magnetron sputtering silicon nitride can be found in the literature (A. Frigg, A.Mitchell, et al. “Low loss CMOS-compatible silicon nitride photonicsutilizing reactive sputtered thin films,” Opt. Express 27(26), 37795-37805 ( 2019). ).

Figure 5 is a mode field diagram of light propagating in a silicon nitride-assisted lithium niobate thin-film waveguide. It can be seen that the silicon nitride-assisted lithium niobate waveguide has a good confinement effect on light. Due to the large refractive index of the lithium niobate material, most of the light field is confined in the lithium niobate film, which is convenient and sufficient. The linear electro-optic effect and second-order nonlinear effect of lithium niobate material are used effectively; and because the refractive index of silicon nitride material is very close to that of lithium niobate material, silicon nitride waveguide also has a certain constraining effect on the optical field, and light can travel along the As the silicon nitride waveguide is transmitted forward, the shape and structure size of the silicon nitride waveguide will affect a series of transmission characteristics of light, and the fabrication process of the silicon nitride waveguide is fully compatible with the standard commercial CMOS process, which reduces the design of the device. Difficulty and process cost.

The lithium niobate material has a significant electro-optic effect. In the specific implementation process, when the continuous light emitted by the on-chip single-wavelength laser source 8 is modulated by one or more electro-optic modulators, the output end of the modulator can be obtained with continuous light as the continuous light. In the center, the spectrum of N equally spaced frequency components whose modulation frequency is spaced is called an optical frequency comb. opticfrequency combgeneration in a lithium niobatemicroring resonator,"Nature568,373 (2019)). The wavelength demultiplexer 10 is used to demultiplex the multiple frequency components to different ports. After passing through the power divider 11 array, each frequency component is divided into M beams, and the M beams of continuous light with the same wavelength are electro-optical The modulator array 12 is modulated into a binary signal, which is then multiplexed into M different mode outputs in the multi-mode waveguide 5 through the mode multiplexer 13 . It can be seen that the single-wavelength CW laser input into the system by the on-chip single-wavelength laser source 8 is expanded into N×M optical signals transmitted in parallel, thereby multiplying the communication capacity of the system.

The wavelength-mode demultiplexer 7 demultiplexes the signals carried by different wavelength channels and different mode channels in the multi-mode waveguide 5 input by the transmitting module 1 to different ports, which are received by the photodetector array 6 and converted into electrical signals for output. , see Figure 2. It can be seen that the optical signals transmitted in parallel by N×M channels are successfully received, collected and processed, thereby multiplying the processing speed of the system.

In the specific implementation process, an asymmetric single-ring dual-waveguide micro-ring resonator can be used to realize a wavelength-mode (de)multiplexer. The principle and specific implementation method can be found in references (LW Luo, N. Ophir, CP Chen) , et al. “WDM-compatible mode-division multiplexing on a silicon chip,” Nat. Commun. 5, 3069 (2014)). Microring resonators (Z. Yu, Y. Tong, HK Tsang, et al. “High-dimensional communication on etchlesslithiumniobate platform with photonicbound states in the continuum,” Nat. Commun. 11, 2602 (2020)) or Mach augmentation can be used. The Del interferometer structure realizes the on-chip electro-optical modulator (ANR Ahmed, S.Nelan, S. Shi, et al. "Subvolt electro-optical modulator on thin-filmlithiumniobate and siliconnitride hybrid platform," Opt. Lett. 45(5), 1112 -1115 (2020)). On-chip lasers can be prepared by growing silicon and III-V materials on a silicon nitride layer. The principle and specific implementation methods can be found in the reference (C.Xiang, W.Jin, J. Guo, et al. "Narrow-linewidth III -V/Si/Si ₃ N ₄ laser usingmultilayer heterogeneous integration,” Optica 7(1), 20-21 (2020)). A photodetector can be prepared by growing germanium on a silicon nitride layer, and its principle and specific implementation methods can be found in the reference (H.Chen, P.Verheyen, P.DeHeyn, et al. "-1 V bias 67 GHz bandwidth Si- contactedgermanium waveguide pi-nphotodetector for optical links at 56 Gbps and beyond,” Opt. Express 24, 4622 (2016)).

The optical receiving system of the present invention includes two modules of sending and receiving. The optical frequency comb laser source 3 generates a multi-wavelength light source signal (that is, N×M wavelength-mode signals) into the wavelength-mode modulation module 4, and uses the wavelength division multiplexing and mode multiplexing technology to decompose the source signal. They are multiplexed to different ports, and respectively input to the photodetector array 12 composed of N×M photodetectors, and the photodetector array 12 processes and outputs electrical signals. That is, the modulated optical signal is input into a multi-mode waveguide 5 for output, and the transmission function is realized. At the receiving end, the signal entering the multimode waveguide 5 is input into the wavelength-mode demultiplexer 7, demultiplexed into multiple signals through the wavelength-mode demultiplexing operation, and received by the photodetector array 6, The receive function is implemented.

After the optical signals of N wavelengths generated by the optical frequency comb laser source 3 are demultiplexed by the wavelength demultiplexer 10, the light of a single wavelength is divided into M beams of continuous light of the same wavelength by N 1×M power dividers. After M beams of continuous light with the same wavelength are modulated into binary signals by the electro-optic modulator array 12 , they are multiplexed into M mode channels by the mode multiplexer 13 respectively, and N×M parallel channels are simultaneously output in a multimode waveguide 5 signal, the N×M parallel signals contain N wavelength channels and M mode channels.

Claims (3)

1. A fully integrated optical transceiver system based on a silicon nitride-assisted lithium niobate thin film waveguide, characterized in that it comprises a sending module (1) and a receiving module (2), a sending module (1) and a receiving module (2) connected through a multimode waveguide (5); The sending module (1) includes a connected optical frequency comb laser source (3) and a wavelength-mode modulation module (4); The receiving module (2) includes a connected photodetector array (6) and a wavelength-mode demultiplexing module (7); the optical frequency comb laser source (3) includes a connected on-chip single-wavelength laser source (8) and an optical frequency comb laser source (8) A comb device (9); a wavelength-mode modulation module (4) comprising a wavelength demultiplexer (10), a power divider group (11), an electro-optic modulator array (12) and a mode multiplexer (13) connected in sequence The optical frequency comb device (9) is connected with the wavelength demultiplexer (10), and the mode multiplexer (13) is connected with the wavelength-mode demultiplexer module (7) through the multimode waveguide (5). 2 . The fully integrated optical transceiver system based on silicon nitride assisted lithium niobate thin film waveguide according to claim 1 , wherein the power divider group ( 11 ) consists of N 1×M power dividers The input ends of all 1×M power dividers are connected to the output ends of the wavelength demultiplexer (10), and the output ends of all 1×M power dividers are connected to the input ends of the electro-optic modulator array (12); The electro-optic modulator array (12) is composed of N×M electro-optic modulators, and a 1×M power divider is connected to the M electro-optic modulators. 3 . The fully integrated optical transceiver system based on silicon nitride assisted lithium niobate thin film waveguide according to claim 1 , wherein the multi-mode waveguide ( 5 ) comprises substrate layers arranged sequentially from bottom to top. 4 . (18), a silicon dioxide buried layer (17), a lithium niobate layer (16) and a silicon dioxide cladding layer (14), the lithium niobate layer (16) is further provided with a silicon nitride layer (15), nitrogen A silicon oxide layer (15) is located within the silicon dioxide cladding (14).

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