Driven by cloud computing, optical modules will move toward 400G. As an important active optical device, the optical module realizes the electric-optical conversion and optical-electric conversion of signals at the transmitting and receiving ends, respectively. The upstream industrial chain of fiber optical transceivers is mainly optical chips and passive optical devices, and the downstream clients mainly apply optical modules to three scenarios: telecom bearer network and access network, data center, and Ethernet. Among them, the data center and Ethernet market mainly include data center internal interconnection, data center interconnection (DCI), enterprise Ethernet, and other scenarios.
With the large-scale data center becoming the mainstream, high-speed blade ridge architecture has become the main development direction. 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 fiber optical modules
The requirements of the market for the optical module of the data center can be summarized as follows:
- Low price: this is the basis for the massive use of optical modules in data centers and the driving force for the development of data centers.
- Low power consumption: this is to comply with the concept of green development of mankind and to promote the development of the industry under the premise of protecting the environment.
- High speed: this is to meet the growing requirements of data communication such as cloud computing, big data, etc.
- High density: this is to increase the number of optical transmission channels per unit space for the purpose of increasing data transmission capacity.
- Short cycle: This is the characteristic of the rapid development of data communication in the near future. Generally, the renewal cycle of optical modules is 3-5 years.
- Narrow temperature range: the application of optical modules in the data center is in a room with temperature and humidity control. Therefore, it is proposed that the working temperature can be defined as a narrow temperature range between 15 ° C and 55 ° C —which is a reasonable approach.
Top 6 Important Technology Trends in 2021
Following are some of the technology trends you might need to know.
Technology Trend #1: Achieving non-hermetic encapsulation
As the cost of optical components accounts for more than 60% of the cost of optical modules, and the optical chip has less and less room to reduce costs, so the most likely to reduce costs is the packaging. While ensuring the performance and reliability of the fiber optical transceiver, it is crucial to promote the packaging technology from the more expensive hermetic packaging to the low-cost non-hermetic packaging. Non-hermetic packaging needs to optimize the design of optical components, improve packaging materials and processes on the premise of ensuring the non-hermetic of optical devices. Among them, the non-hermetic of optical devices (especially lasers) is the most challenging. If the laser device is non-hermetic, expensive hermetic packaging is indeed not needed.
Technology Trend #2: Hybrid integration technology becomes a reality
Hybrid integration technology usually refers to the integration of different materials together. The structure of partial free-space optics and partially integrated optics is also called hybrid integration. Driven by the requirements of multi-channel, high rate, and low power consumption, the larger the data transmission capacity that can be provided by optical modules with the same volume, the better. Therefore, photonic integration technology has gradually become a reality. The significance of photonic integration technology is also broad: for example, silicon-based integration (planar optical waveguide hybrid integration, silicon optical integration, 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.). 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 process, and is conducive to mass production. It is an effective technical method for optical modules in data centers 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 the IC packaging industry. With the rapid development of optical module rates, shortening the interconnection between chips is an effective option. Soldering the optical chip directly to the substrate via gold to gold soldering or eutectic soldering is much more effective than gold wire bonding at high frequencies (shorter distance, lower 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 the IC packaging industry, there are many kinds of commercial automatic flip-chip welding machines for IC packaging. Optical components require high precision because of the need for optical path coupling. Moreover, because the flip-chip welding (also known as automatic bonding chip) machine has the characteristics of high precision, high efficiency, and high quality, it has become an important process of an optical module in the data centers.
Technology Trend #4: Extensive adoption of COB technology
Cob (chip on board) technology is to fix the chip or optical module on the PCB through epoxy die bonding, then conduct electrical connection through wire bonding, and finally drip glue seal on the top. For example, after the optical module 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 heavily adopted, especially in the case of short-range data communications using VCSEL arrays. Many 40G and 100G optical modules are available with COB technology, such as QSFP28 optical transceivers. Highly integrated silicon optical 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 optoelectronic integrated circuits (OEIC), that is, turning the current separated photoelectric conversion into local photoelectric conversion, so as to further promote the integration of the system. It is undeniable that silicon optical technology can achieve many functions.
However, 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, traditional optical modules have been very successful, and it is not easy for silicon photonic modules to enter this market in large quantities.
- A large number of applications of silicon photonic modules 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:
- Because 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 the application of silicon photonics modules.
- At speeds above 200G and 400G, such as 400G SR8 transceiver, 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 photonics modules.
- If the characteristics of silicon photonic modules are taken into account when formulating standards or protocols, and some indicators (wavelength, extinction ratio, etc.) are relaxed on the premise of meeting transmission conditions, it will greatly promote the application of silicon optical technology.
Therefore, if silicon optical technology can finally overcome the constraints and successfully integrate into the optical module, it will undoubtedly promote the development of optical module technology.
Technology Trend #6: The application of on-board optics
If OEIC is the ultimate optoelectronic integration solution, onboard optics is a technology that lies between OEIC and optical modules. Onboard optics move the photoelectric conversion function from the panel to the motherboard processor or the associated electrical chip. Because the density is improved, the routing distance of high-frequency signals is also reduced, so as to reduce power consumption. At first, onboard optics mainly focused on short-range multimode fiber using the VCSEL array.
However, recently, there are also schemes using silicon optical technology in single-mode fiber. In addition to the composition of a simple photoelectric conversion function, there is also a form of CO package that encapsulates the photoelectric conversion function (I/O) and the associated electrical chip. Although on-board optics has the advantages of high density, its manufacturing, installation, and maintenance costs are still high. At present, it is mostly used in the field of supercomputers. 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 the data centers.