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The Development Direction of Optical Module Technology in Data Center

Number of visits: Date:2018-3-13 09:33

Abstract:

 

With the commercial use of cloud computing, big data, etc, the traffic and bandwidth of data center grow exponentially. It is predicted by Cisco that the IP traffic in global data center will rise from annual 4.7ZB in 2015 to annual 15.3ZB in 2020, in which the compound annual growth rate is about 27%. In addition, it is predicted by LightCounting that the sales volume of optical module in data center will have exceeded 50 millions by 2019; and the sales of market will possibly have reached $4.9 billions by 2021, which will be a big opportunity for manufacturers of optical transceivers. Simultaneously, it is seen that the applications of optical transceivers in data centers differ in that of traditional telecom transmission market. Then in this article, the development direction of optical transceiver tech will be talked about.


At present, the requirements on the optical transceiver of the data center in the market include low cost, low power consumption, high density, short cycle and narrow temperature range. The following content will have a brief introduction:

Low price: The wide-range utilization of optical transceiver in the data center is the drive to promote the development of data center.

 

Low power consumption: to keep pace with the theory of Green Growth, to promote the development of industry based on the protection of environment.

 

High data rate: to satisfy the increasing requirements of data telecom such as cloud computing, big data, etc.

 

High density: to increase the amount of optical transmission channels in per space.

 

Short cycle: it is the recent features about rapid development of datacom. The life cycle is usually 3-5 years.

 

Narrow temperature range: the applications of optical transceiver in the data center are in the rooms with temperature and humidity control. Therefore, there are some users proposing that the range of working temperature can be defined in 15-55 degrees Celsius, which is a reasonable way that suits the case.


Macroscopically, the market of optical transceiver in data center is one in which the working life and working condition are reasonably defined according to the actual requirements, and the cost performance of optical transceiver is simultaneously fully optimized. On account of open trend of digital network, the market is open and positive to introduce new techs, and it is also with one atmosphere of exploring new standards and application conditions. It provides a good opportunity for the development of optical module tech in data centers. The following will introduce development directions of optical transceiver tech in data centers for reference.


Non-airtight Packaging Tech

 

The cost of optical components(OSA)accounts for over 60% of that of optical transceiver. Besides, the cost of optic chip is less possible to drop. After that, the possible way is to reduce the cost of form factor. While ensuring the performance and reliability of optical modules, it is necessary to push packaging technology from more expensive airtight packaging to low-cost non-airtight packaging. The main points of non airtight packaging include the non-airtightness of the optical device itself, the optimization in the design of the optical components, the packaging material and the improvement of the process, etc. Thereinto, the non-airtightness of lasers is most challenging, which is due to that once lasers achieve the non-airtightness, the expensive airtight form factor is not needed. It is worth mentioning that several manufacturers of laser have announced that their own lasers are available for non-airtight applications. In a large number of data center optical modules, most of which are mainly non-airtight packaging. The current optical transceivers in data centers shipped in large volumes are mainly with non-airtight form factor. It seems that non-airtight encapsulation technology has been well accepted by the industry and customers of the optical modules in data center.


Hybrid Integration Technology

 

With the drive of demands on multichannel, high data rate, and low power consumption, optical transceivers with same volumes need larger transmission capacity. Photonic integration tech is gradually achieved. Photonic integration tech has various types, such as the Silicon-based integration (Hybrid integration of planar optical waveguides, silicon photonics, etc), Integration of indium phosphide, etc. Hybrid integration technology usually refers to the integration of different materials. Moreover, parts of free-space optics and integrated optics can be also called as hybrid integration. The typical hybrid integration is to integrate active optical components into the baseplate(planar optical waveguides, silicon photonics)with passive function (optical WDM couplers). Hybrid integration tech can make the optical components compact to accord to the trend of optical transceiver miniaturization. It is convenient to use the mature automatic IC packaging technology, which is beneficial to batch production. It is an effective technique for the optical module of the data center in the near future.


Flip Chip Technology

 

Flip welding is a high-density chip interconnection technology from the IC packaging industry. Shortening the interconnection between chips is an effective option in today's optical module. Optic chip is directly welded onto the substrate via gold-gold welding or eutectic welding, the high frequency effect much better than that of gold wire bonding (short distance, small resistance, etc.). Besides, for the laser, because the active area is near the solder joint, the heat generated by the laser is easier to transfer from the solder joint to the substrate, which is helpful to improve the efficiency of the laser under high temperature. The flip welding is a mature technology in the IC packaging industry, there have been many commercial automatic flip welding machines for IC packaging. Optical components require high precision because of the need for optical coupling. The process of optical components via high-precision flip chip bonding machine is very eye-catching, which has achieved passive light in many cases, and has greatly improved the productivity. Flip chip machine is with high precision, high efficiency, high quality and so on. Flip chip technology has become an important technology in the optical module industry.


COBChip On BoardTech

 

COB is also a technology from the IC packaging industry. Its principle is to fix the chip or optical components on PCB via the glue patch technology (epoxy die bonding) first, then to take electrical connection via the gold wire bonding (wirebonding), and finally to seal the top by dripping glue. It is clear that this is a non-airtight package. The advantage of this process is that automation can be used. For example, one optical component can be seen as a "chip" after a hybrid integration, such as flip welding. Then the COB technology is used to fix it on the PCB. At present, COB technology has been widely used, especially in the use of VCSEL array in short-distance data communication. The silicon light with high integration can also be encapsulated by using COB technology.


Silicon Photonics Tech

 

Silicon photonics tech is to explore the technology and techniques compatible with optoelectronic devices and silicon based integrated circuits, and is integrated on the same silicon substrate. Silicon photonics technology will eventually move towards OEIC(Opto-Electric Integrated Circuits), making the current separation photoelectric conversion (optical module) become a partial photoelectric conversion in the process of photoelectric integration, and further promoting the integration of the system.


Of course, silicon photonics technology can achieve many functions, but a silicon modulator currently is more attractive. From the perspective of industry, the requirements for a new technology to enter into the market are that it is competitive in performance and cost, which is indeed a great challenge for silicon technology with the need of a huge initial investment. In the data center optical module market, due to the large demand for 2 kilometers applications, and the requirements for low cost, high speed and high density, it is suitable for a wide range of application of silicon photonics. In one's opinion, the traditional optical module with 100G rate has made great achievements, then the silicon photonics is not easy to enter in a large batch. But, for 200G/400G optical transceivers, because the traditional optical module with direct modulation has reached the limit of bandwidth, and the cost of EML is relatively high, it will be a good opportunity for silicon photonics. The common applications of silicon photonics also depend on the degree of openness and acceptance of technology in the industry. If the characteristics of silicon photonics are taken into account when standards or protocols are defined, and some indicators (wavelength, extinction ratio, etc.) are reduced under the premise of satisfying transmission conditions, it will greatly promote the development and application of silicon photonics.


OnBoard Optics

 

If OEIC is the ultimate photoelectric integration scheme, onboard optics tech is a technology between OEIC and optical module. Onboard optics tech transfers the photoelectric conversion function from the panel to the processor on the main board or beside the associated electric chip. On account that the space saving increases the density and also reduces the line distance of the high frequency signal, the power consumption is also reduced. Onboard optics tech mainly focuses on multimode optic fiber for short distance using VCSEL array at the first time. However, silicon photoelectric technology has recently been applied in single-mode optical fiber. In addition to photoelectric conversion function, there is also a form that photoelectric conversion function(I/O) and associated chip (processing) are co-packaged. Although onboard optics is with high density, and the costs on manufacturing, installation and maintenance are 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, the onboard optics will gradually enter into the field of optical interconnection in the data center.


In order to cater for the upcoming data center challenge, Gigalight has launched complete 25G/100G product series, to provide various solutions for data center interconnect. At the same time, in order to provide more cost-effective interconnection scheme for customers, Gigalight also has launched 100G PSM4, 100G CWDM4 and 200G QSFP-DD. If there is any need, welcome to contact Gigalight.