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[Optoelectronic communication] Future trend, six important technologies of optical module!

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In 2019, the sales volume of optical modules in the data center will exceed 50 million, and the market scale is expected to reach 4.9 billion dollars in 2021. All the above data show that the optical module market is facing a huge opportunity. How to seize the opportunity, the key point is technological innovation, so today we will discuss the technological innovation trend of the optical module market.

Market requirements for optical modules

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

Ø Low price: the basis for the data center to use a large number of optical modules is also the driving force for the development of the data center;

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

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

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

Ø Short cycle: the characteristics of rapid development of data communication in recent years, with a general life cycle of 3-5 years;

Ø Narrow temperature: The application of the optical module in the data center 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 -- this is a reasonable way to tailor.

Through the analysis of the above six requirements, we can know that the optical module market has the characteristics of positive opening, welcome the introduction of new technologies, and explore the atmosphere of new standards and application conditions. At the same time, the data center optical module market is a market where the service life and working conditions of optical modules are reasonably defined according to the actual requirements, and the cost performance of optical modules is fully optimized. All these provide excellent conditions for the development of optical module technology in data center.

Technology trend 1: realize non-airtight packaging

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

The non-airtight packaging needs to optimize the design of optical components, improve the packaging materials and process while ensuring the non-airtightness of optical devices. Among them, the most challenging is the non-airtightness of optical devices (especially lasers). If the laser device is not airtight, the expensive airtight packaging is indeed unnecessary. Fortunately, in recent years, manufacturers in the industry have publicly announced that their lasers can be applied to non-airtight applications. Throughout the large number of data center optical modules shipped today, most of them are 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. There are also structures that combine part of free space optics and part of integrated optics as hybrid integration. Driven by the requirements of multi-channel, high-speed and low power consumption, it is required that optical modules with the same volume can provide as much data transmission as possible, so photonic integration technology is gradually becoming a reality.

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

Technology trend 3: Flip chip welding technology tends to mature

Flip chip is a high-density chip interconnection technology from the IC packaging industry. With the rapid development of optical module speed, it is an effective option to shorten the interconnection between chips. The optical chip is directly flip welded to the substrate by gold-metal bonding or eutectic bonding, which 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 easily transferred 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 the IC packaging industry, there are many commercial automatic flip chip welding machines for IC packaging. Optical components require high precision because of the need for optical path coupling. In recent years, high-precision flip chip welding machines for optical module processing are very eye-catching. In many cases, passive aiming has been achieved, which has greatly improved productivity. Because flip chip welding (also known as automatic bonding) machine has the characteristics of high precision, high efficiency, high quality, etc., flip chip welding technology has become an important process in the data center optical module industry.

Technology trend 4: COB technology is widely adopted

COB (Chip On Board) technology is to fix the chip or optical module on the PCB through the adhesive die bonding process, and then conduct electrical connection through wire bonding, and finally drip the rubber seal on the top. The advantage of this non-airtight packaging process is that automation can be used. For example, optical components can be regarded as a "chip" after being mixed and integrated by flip chip soldering. Then it is fixed on the PCB using 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 packaged using 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, to transform the current separated opto-electric conversion (optical module) into local opto-electric conversion in opto-electric integration, and further promote the integration of the system. It is undeniable that silicon light technology can achieve many functions, but at present, silicon modulators are still more dazzling. There are three reasons why silicon optical technology is difficult to enter the optical module market:

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

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

The wide application of silicon light also depends on the openness and acceptance of technology in the industry.

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

Ø Due to the large demand of the data center optical module market concentrated within 2 kilometers, and the strong requirements of low cost, high speed, high density, etc., it is more suitable for a large number of applications of silicon light.

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

Ø 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, this will greatly promote the application of silicon light.

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

Technology trend 6: application of onboard optics

If OEIC is the ultimate optoelectronic integration solution, onboard optics is a technology between OEIC and optical modules. On-board optics moves the photoelectric conversion function from the panel to the side of the motherboard processor or associated electrical chip. Because of saving space, the density is increased, and the routing distance of high-frequency signal is also reduced, thus reducing power consumption.

At the beginning, onboard optics was mainly concentrated in short-range multimode fibers using VCSEL arrays. However, recently, there are also plans to use silicon optical technology in single-mode fibers. In addition to the composition of pure photoelectric conversion function, there are also forms of packaging photoelectric conversion function (I/O) and associated electrical chip (processing). Although the onboard optics has the advantages of high density, the manufacturing, installation and maintenance costs are still high. At present, most of them are applied in the supercomputing field. It is believed that with the development of technology and the needs of the market, onboard optics will gradually enter the field of data center optical interconnection.



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