Driven by cloud computing, the optical module will move towards 400g. As an important active optical device, the optical module realizes the electrical optical conversion and optical electrical conversion of signals at the transmitter and receiver respectively. The upstream of the optical module is mainly optical chips and passive optical devices, and the downstream customers are mainly used in three scenarios: Telecom bearer network, access network, data center and Ethernet. Among them, the data center and Ethernet markets mainly include data center internal interconnection, data center interconnection (DCI), enterprise Ethernet and other scenarios. Optical interconnects are mainly used for long-distance and high-capacity transmission of backbone network and core network. With the super large-scale data center becoming the mainstream, the high-speed blade ridge architecture has become the main development direction, and the number of high-end optical modules is about dozens of times that of the traditional architecture. Therefore, cloud computing will boost the iterative upgrading of optical modules. According to Cisco's prediction, there will be 628 super large-scale data centers in the world by 2021, accounting for nearly 50% of the data center server share. The optical module market is facing a huge opportunity, and how to seize the opportunity depends on technological innovation. Today, let's discuss the technological innovation trend of the optical module market.

Market requirements for optical modules

First of all, we all know that the requirements of the market for the optical module of the data center can be summarized into the following six points:

Low price: the data center is the basis of extensive use of optical modules, which is also the driving force to promote the development of the data center;

Low power consumption: comply with the concept of human green development and promote industrial development on the premise of protecting the environment;

High speed: meet the growing requirements of cloud computing, big data and other data communication;

High density: increase the number of optical transmission channels in unit space to improve the data transmission capacity;

Short cycle: the characteristics of the rapid development of data communication in recent years. The general life cycle is 3-5 years;

Narrow temperature: the application of data center optical module is in the room with temperature and humidity control, so it is proposed that the working temperature can be defined as a narrow temperature range between 15 degrees and 55 degrees - which is a reasonable way to tailor.

By analyzing the above six requirements, we can know that the optical module market has the characteristics of actively opening up, welcoming the introduction of new technologies, and the atmosphere of discussing new standards and application conditions. At the same time, the data center optical module market is a market that reasonably defines the service life and working conditions of optical modules according to the actual requirements, and fully optimizes the cost performance of optical modules. This provides excellent conditions for the development of optical data center technology.

Technology trend 1: realize non airtight packaging

Since the cost of optical components (OSA) accounts for more than 60% of the cost of optical modules, and the space for reducing the cost of optical chips has become smaller and smaller, the packaging cost is the most likely to reduce the cost. While ensuring the performance and reliability of optical modules, it is the key to promote the packaging technology from expensive airtight packaging to low-cost non airtight packaging.

Under the premise of optimizing the airtightness of components and non optical packaging materials, it is necessary to improve the airtightness of components at the same time. Among them, the non airtightness of optical devices (especially lasers) is the most challenging. If the laser device is non airtight, expensive airtight packaging is indeed not needed. Fortunately, in recent years, manufacturers in the industry have publicly claimed that their lasers can be suitable for non airtight applications. Throughout the large number of data center optical modules shipped now, most of them are mainly non airtight packaging. It seems that the non airtight packaging technology has been well accepted by the data center optical module industry and customers.

Technology trend 2: hybrid integration technology becomes a reality

Hybrid integration technology usually refers to the integration of different materials together. The structures of partial free space optics and partial integrated optics are also called hybrid integration. Driven by the demand of multi-channel, high rate and low power consumption, the larger the data transmission capacity that the optical module with the same volume can provide, the better. Therefore, photonic integration technology has gradually become a reality.

The significance of photonic integration technology is also extensive: for example, silicon based integration (planar optical waveguide hybrid integration, silicon light, etc.), indium phosphide based integration, etc. Typical hybrid integration is to integrate active optical devices (lasers, detectors, etc.) into substrates with optical path connection or other passive functions (demultiplexers, etc.) (planar optical waveguides, silicon light, etc.). Hybrid integration technology can make optical modules very compact, comply with the trend of optical module miniaturization, facilitate the use of mature automatic IC packaging technology, and is conducive to mass production. It is an effective method of optical module technology in data center in the near future.

Technology trend 3: flip chip welding technology tends to be mature

Flip chip bonding is a high-density chip interconnection technology from IC packaging industry. With the rapid development of optical module rate, shortening the interconnection between chips is an effective option. The direct flip chip welding to the substrate by gold gold or eutectic welding is much better than the high-frequency effect of gold wire bonding (short distance, low resistance, etc.). In addition, for the laser, because the active area is close to the solder joint, the heat generated by the laser is easy to transfer from the solder joint to the substrate, which is very helpful to improve the efficiency of the laser at high temperature. Because flip chip welding is a mature technology in IC packaging industry, there are many kinds of commercial automatic flip chip welding machines for IC packaging. Because optical components need optical path coupling, they require high precision. In recent years, the high-precision flip chip welding machine for optical component processing is very eye-catching. In many cases, passive light alignment has been realized, which greatly improves the productivity. Because the flip chip welding (also known as automatic bonding chip) machine has the characteristics of high precision, high efficiency and high quality, flip chip welding technology has become an important process in the optical module industry of data center.

Technology trend 4: extensive adoption of cob Technology

Cob (chip on board) technology is to fix the chip or optical component on the PCB through epoxy die bonding, then connect it electrically by wire bonding, and finally drip glue seal on the top. The advantage of this non hermetic packaging process is that automation can be used. For example, after the optical component is mixed and integrated through flip chip welding, it can be regarded as a "chip". Then fix it on PCB by cob technology. At present, cob technology has been widely used, especially when VCSEL array is used in short-range data communication. Silicon light with high integration can also be encapsulated by cob technology.

Technology trend 5: application of silicon optical technology

First of all, the trend of silicon optical technology will be opto electric integrated circuits (OEIC), that is, turning the current separated photoelectric conversion (optical module) into local photoelectric conversion in photoelectric integration, so as to further promote the integration of the system. It is undeniable that silicon optical technology can achieve many functions, but at present, silicon modulator is the most dazzling. There are three reasons why silicon optical technology is difficult to enter the optical module Market:

Silicon optical technology requires huge initial investment, which is a very important limiting factor.

At 100g rate, the traditional optical module has been very successful, and it is not easy for silicon light to enter in large quantities.

A large number of applications of silicon light also depend on the openness and acceptance of technology in the industry.

At the same time, silicon optical technology also has the following three technical advantages:

As a large number of demands in the data center optical module market are concentrated within 2km, coupled with the strong requirements of low cost, high speed and high density, it is more suitable for a large number of applications of silicon light.

At speeds above 200g and 400g, because the traditional direct modulation is close to the limit of bandwidth and the cost of EML is relatively high, it will be a good opportunity for silicon light.

If the characteristics of silicon light are taken into account when formulating standards or protocols, and some indicators (wavelength, extinction ratio, etc.) are relaxed on the premise of meeting the transmission conditions, it will greatly promote the application of silicon light.

Therefore, if silicon optical technology can finally overcome the limiting factors and successfully integrate into the optical module, it will undoubtedly promote the development of optical module technology.

Technology trend 6: application of onboard optics

If OEIC is the ultimate photoelectric integration scheme, onboard optics is a technology between OEIC and optical module. Onboard optics moves the photoelectric conversion function from the panel to the motherboard processor or the associated electrical chip. Because of saving space, the density is improved, and the routing distance of high-frequency signals is reduced, so as to reduce power consumption.

   At first, onboard optics was mainly concentrated in short-range multimode fiber using VCSEL array. However, recently, there are also schemes using silicon optical technology in single-mode fiber. In addition to the composition of simple photoelectric conversion function, there are also co packages that encapsulate photoelectric conversion function (I / O) and associated electrical chip (processing). Although onboard optics has the advantages of high density, the cost of manufacturing, installation and maintenance is still high. At present, it is mostly used in the field of supercomputing. It is believed that with the development of technology and the needs of the market, onboard optics will gradually enter the field of optical interconnection in data center.

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