01 Silicon photonics technology introduction and advantages
As we all know, in order to make network transmission faster and carry more information, optical fibre broadband has replaced traditional broadband, and the transmission of signals in the form of optical pulses has greatly improved the transmission speed. However, the current optical network only realises the all-optical between nodes, and still adopts the electrical parts at the network nodes, so it needs to frequently carry out the photoelectric conversion, as shown in the figure below. The photoelectric conversion is aided by optical modules.
Figure: Schematic diagram of photovoltaic conversion
(Source: Electronically Speaking)
The main chips involved in the optical module are optical chip and electrical chip. Optical chip is the optical module is mainly responsible for photoelectric signal conversion chip, is divided into detector chip and laser chip. While the electrical chip is mainly to achieve the optical chip to work with the support, power regulation of electrical signals and complex DSP (digital signal processing). The higher the rate of the optical module, the optical chip cost compared to the electrical chip accounted for a higher proportion, and even up to 60% -70% of the cost of the optical module. Considering that in addition to the high rate module in the higher cost of the optical chip problem, the original to three five semiconductor laser chip that is indium phosphide (InP) and gallium arsenide (GaAs) and other rare metal materials made of optical chips are also constrained by the capacity of the optical communication line, so silicon as the material for the production of the device silicon photonics technology should come into being.
Compared with the traditional optical module, silicon photonics technology is based on silicon and silicon substrate liner materials, the information throughput required for a variety of photonic, electronic, optoelectronic devices, including light source, detector, optical waveguide, modulator, etc. are all integrated in the silicon photonics chip, so as to meet the market demand for optical modules of low-energy, low-cost, high-performance and small size, the specific advantages of the following:
(1) Low energy consumption and low cost. Not only silicon as the world's second largest reserves of material costs are relatively inexpensive, but also has the natural advantages of high refractive index of silicon-based materials, high optical confinement capabilities, can be optical waveguide bending radius reduced to less than 5 microns, that is, the Array Waveguide Gratings (AWG) bending radius of silicon photonics platform for the one-thousandth of a silicon dioxide platform, and its higher density of integration brought about by the significant reduction of the chip size, so the silicon photonics Chip in the traditional high-speed module in the electric chip area has reached the physical limit of more low-cost, low-power, miniaturisation and other unique advantages.
(2) Strong integration, easy integration. Silicon photonics technology using large-scale semiconductor manufacturing process can be achieved on a very small insulator thin film silicon wafer optoelectronics technology and microelectronics technology for efficient integration, especially in data centres and other size-sensitive areas will have a broader application space.
(3) Large bandwidth and high speed. Silicon photonics technology uses optical pathways to replace data circuits between chips, achieving high-capacity optical interconnections while maintaining low energy consumption and low heat dissipation, efficiently solving problems such as network congestion and delay. At the same time, the use of laser beams instead of electronic signals to transmit data is to achieve high data transmission rates.
In 2015, Intel first verified that the performance of silicon photonics devices has surpassed that of similar traditional optoelectronic devices; in 2019, silicon photonics devices have been speeding up by 8 times the peak speed per second compared with traditional optoelectronic devices, and energy consumption and cost are reduced by 85% and 84% respectively; according to Intel's silicon photonics industry development plan, by 2022, silicon photonics devices will be 64 times faster in terms of peak speed per second compared with traditional optoelectronic devices, and 64 times faster in terms of energy consumption and cost. According to Intel's silicon photonics industry development plan, by 2022, the peak speed per second of silicon photonics devices may be 64 times faster than that of traditional optoelectronic devices, and energy consumption and cost will be reduced by 98%.
Figure: Internal structure of optical modules made based on silicon photonic chips
(Source: Silicon Photonics Technology Report)
02 Silicon Photonics Technology Development and Bottlenecks
Silicon photonics technology was first proposed by the renowned Bell Labs in 1969. Based on the development of related devices for more than 50 years, Huawei divides the evolutionary trend of silicon photonics technology into four stages:
Stage 1, Packet Silicon Photonics: Silicon based devices are gradually replacing discrete components, i.e., silicon is used to make the underlying devices for optical communications to achieve process standardisation.
The second stage, silicon photonics integration: integration technology from the coupling integration to monolithic integration evolution to achieve partial integration, that is, through the combination of different devices integrated different chips;
The third stage, all-optical fusion: full integration of optoelectronics, to achieve the complexity of the function of the combined seal;
The fourth stage, programmable chip: device decomposition for multiple silicon unit arrangement and combination, the local needle characterisation class; the kind of programming to change the internal structure of the chip, can be customised full functionality.
Although silicon photonics technology is known as the "breakthrough Moore's Law dawn appears", but the current worldwide silicon photonics technology in the optical switch, optical waveguide, silicon-based detector (Ge detector) and optical modulator (SiGe modulator) has achieved a breakthrough, but still in the process of simplifying and enhancing the efficiency of the second stage to the third stage of the evolutionary period. The evolutionary period of the process of simplifying process flow and improving efficiency is still in the second to the third stage.
Figure: Structures that can be processed by the silicon photonics technology process
(Source: Demonstration materials of Shenzhen Optical Expo)
One of the most important reasons for the application of silicon photonics technology is that the silicon-based material itself is very low luminous efficiency, can not detect the 1310nm and 1550nm light, resulting in the cost of optical chips once accounted for the largest proportion of optical lasers has become a silicon photonics technology development challenges, the market has only silicon-based quantum level chain lasers, silicon-based nanocrystalline lasers and other preliminary programmes have not yet been applied to a large scale. As a result, the current silicon photonics technology is still mainly embodied into two basic forms, in addition to the use of large-scale integrated circuit technology (CMOS) process integration of monolithic silicon photonics engine program, the market is more common for the hybrid integration program, mainly light chip is still using the traditional three-five family of materials, the use of discrete mounting or wafer bonding, and so on, different ways of the three-five family of lasers and silicon integration of modulators, coupled optical paths etc. processed together.
Figure: silicon photonics integration of mainstream solutions
Hybrid integration scheme process is mainly divided into two kinds: the first is the built-in integration process, the use of three five materials and silicon photonic chip heterogeneous integration technology to achieve monolithic integration of silicon photonics transceiver built-in, although the realization of the integration of the power consumption reduction, hardware costs, but because the laser in the core devices have always been the highest failure rate, and near the power consumption of the switching chip after the work of the faster temperature, the reliability and failure rate of laser is a serious test, and once the failure of maintenance and replacement costs are also higher, at the same time, this kind of "photoelectricity combined seal" module packaging is difficult, maintenance and replacement costs are also higher. Reliability and failure rate is a serious test, and once the failure of maintenance and replacement costs are also higher, while the "photoelectric seal" module packaging difficult, low yield; the second for the external integration process, although not in the true sense of the word "silicon photon", but the laser light source is made separately into a plug-and-play. The laser light source is made into a separate plug module can be flexible light sharing, not only in the switch layout on the design away from the "hot spot", but also in the single chip design to make bold attempts to improve application efficiency, for example, the current market of the 400G DR4 silicon-photonics module single chip bandwidth performance can be achieved in the same density of the same package 800G single-module output at the same packaging density.
03 Silicon Photonics Technology Application Market
The scientific and technological needs of social and economic construction are increasingly inseparable from the support of cloud computing, and the data centre supporting cloud computing at home and abroad has also maintained a high rate of expansion in recent years. Meanwhile, with the growth of data, low-rate transmission to high-speed transmission, silicon photonics technology application scenarios become more and more rich. 100G era, silicon photonics technology can be applied to parallel single-mode 4-channel (PSM4) and single-mode Coarse Wavelength Division Multiplexing 4-channel (CWDM4) two product forms; 400G era, it can be applied to DR4, FR4/DR4+ and LR4/LR8 and other more, longer, and more efficient products, including DR4, FR4, FR4 and LR4. LR8 and other more, longer distance programme; 800G era, silicon photonics technology can be basically applied to the full range of optical module type. Therefore, according to LightCounting and Yole's forecast on the optical module industry, the silicon photonics market will grow from 14% of the overall optical module market in 2018-2019 to 45% in 2025, with double-digit annual growth during that period. And over 90% of the demand in the $3.9 billion silicon photonics market space in 2025 will come from data centres.
The current 100G era of some of the digital pass silicon photonics module has matured into a steady shipment stage, but in the case of long distance (2 km and above) lower yield, reference Intel in Amazon, Facebook in the 100G silicon photonics module offer its cost advantage is not obvious, mainly because the cost of the traditional three-five family of solutions 100G module has fallen significantly. Therefore, silicon photonics technology on the 100G product market impact is actually limited.
400G era, due to single-channel optical chip rate constraints, PAM4 electric modulation scheme is indispensable. The traditional scheme of electric modulation brought about by a large number of losses, as well as the requirements of the internal device compact performance upgrade, the laser by the possibility of environmental losses increased significantly, has become a constraint on the yield of the optical module to improve the main factors. If the dual-density four-channel small pluggable package (QSFP-DD) programme, the doubling of the number of channels and lead to an increase in the number of devices, multi-device operating temperature increase brought about by the temperature drift can not be ignored. Silicon photonics solutions can save some of the devices and CMOS process to bring a high degree of integration than the traditional scheme has obvious advantages. Currently 400G silicon photonics products long-distance programme cost advantage is more prominent, but the integration is more difficult; and medium-distance programme has been part of the manufacturers to achieve single-chip integration and from 2020 small batch into the 2021 mass production, fortunately, 400G commercial time is slightly delayed also for the development of silicon photonics technology for a favourable period of time. Overall, the 400G market will first become the main battlefield of silicon photonics technology, the current three foreign giants Amazon, Microsoft, Google and domestic headlines have also taken the lead in the construction of the relevant high-speed data centre network.
800G era, silicon photonic module can be introduced on a large scale also depends on the silicon photonics industry in recent years in the cost of optical modules, power consumption, packaging yields, as well as the scale of the mass production of breakthroughs, the current 400G products have not yet been fully on the volume of the market is also mainly in North America and Europe, the industry's interest in the 800G products are constantly surging.
Unlike the non-coherent field of data centres continue to upgrade the development of multi-channel technology, silicon photonics technology flexibility can be expected. In the coherent optical application scenarios, silicon photonics technology has actually been achieved from 100G, 200G to 400G upgrade scale applications, thanks only to the product needs to be customised according to the customer's requirements, the adaptability of its stronger but in the power consumption and performance on the overall advantage is not obvious, and shipments of coherent areas of the price is not low, and the market is mainly by the main equipment vendors, such as Huawei, ZTE, etc., to divide themselves. Therefore, more vendors are still relying on the cost reduction advantages of silicon photonics technology in the competition for 400G technology in the data centre interconnection of commercial scale, while starting to enter the pre-research phase of the 800G programme.
04 Silicon Photonics Industry Chain
Currently, the corresponding silicon photonics industry chain has gradually matured, mainly including three categories of device products, namely, silicon photonics devices, silicon photonics chips and silicon photonics modules. Among them, silicon photonic devices and silicon photonic modules are basically no different from the traditional optical module industry chain. Silicon photonic chip, on the other hand, is as a highly integrated single chip rather than the traditional separation of multiple device combinations, so there are differences in the chip industry chain.
Silicon photonics technology as a global optical communication in the past decade the source of change, the traditional communications equipment giants and various competitive enterprises have entered the layout of the industry segments, foreign companies such as Intel, Acacia, etc. have launched a variety of devices based on silicon photonics technology and take the lead in achieving mass production, becoming the industry leader. Domestic enterprises are generally late to enter the field, mainly through mergers and acquisitions or collaboration with foreign enterprises to cut into the silicon photonics market, there is a significant gap in the progress of product development and technology research. In terms of the overall market, the acquisition and integration of silicon photonics technology in the optical communications market has never stopped. For example, Cisco has acquired Lightwire, luxtera, Acacia and other three industry-renowned silicon photonics company; Huawei acquired the Belgian silicon photonics vendor Caliopa; Nokia acquired Elenion, the three mergers and acquisitions has a total value of more than $ 5 billion, the industry vendors can be seen on the development of silicon-photonics technology expectations.
As optical communications silicon photonics technology applications compared to 100G products, in 400G and higher rates compared to discrete optical modules have significant cost advantages. Currently, many companies in the market have released high-rate silicon photonics solutions, the details are as follows:
We can see that silicon photonics technology in the industrialisation of the road will be more and more mature, although the current silicon photonics programme module can not completely replace the traditional programme under the optical module, but the supply of high-rate silicon photonics products share is bound to increase significantly in recent years, the corresponding market size is very promising. Silicon photonics technology beyond the traditional optical module after the full commercialisation will eventually lead the optical communication network to the real all-optical.
From ICCSZ Reprinted
http://www.iccsz.com//Site/CN/News/2021/08/24/20210824032914408892.htm
