March 30, 2012
We have achieved the world's highest level of reliability in the vertical cavity surface emitting laser (VCSEL) functioning at 10 Gbps (10 gigabits per second; a gigabit is one billion bits) for supercomputers and data centers.(Note 1) The latest version of the VCSEL has also achieved the world's highest level of low-electricity-consumption operation. Aside from its high reliability, the low-electricity-consumption laser contributes to the reduction of greenhouse gas emissions and is expected to spur the introduction of optical interconnections within supercomputers or data centers (Note 2). Applying the technologies accumulated in long-distance communication, our contribution will expand to the field of computers, more specifically an innovative shift from electronics to photonics.
The high-speed, low-electricity-consumption operation has been evaluated by IBM Research - Tokyo, and has been reported at numerous international conferences.
Operable at 10 Gbps or faster, the VCSEL involves high current (current density) per unit area to secure high-speed characteristics despite its low operating current, ranging between 1/5 and 1/10, in comparison with conventional, end-surface emitting semiconductor lasers. This makes it difficult for the VCSEL to ensure reliability, and the analysis of reliability based on a sufficient number of pieces and time was lacking.
For the first time, we performed a reliability test on thousands of VCSEL elements capable of operating at 10 Gbps to calculate reliability. As a result, the highest-ever reliability of 30 FIT (Note 3) for a high-speed (10 Gbps or faster) VCSEL has been verified. The result of the reliability test has been continuously applied, and further improvements in reliability can be expected. Ten FIT is considered to be the index required in a high-performance computer. This requirement has almost been met.
According to supercomputer performance projections, performance improves at a rate of 10 times ever four years (or 1,000 times every 10 years). One thousand petaflops (Note 4), or 100 times faster than the K computer, the world's fastest supercomputer today, is expected to be achieved by 2020. In a trial calculation, this would require one million to five million elements capable of transmitting 10 Gbps. A higher level of reliability and lower electricity consumption in operations are imperative. Based on this manufacturing technology, we have also launched the development of a VCSEL operable at 25 Gbps, which is expected to serve for use in the next generation. This R&D initiative is partly implemented as NEDO's activity for the research and development of low-electricity-consumption surface emitting laser arrays for energy-saving innovative technology development projects/leading research/green optical link technologies.
Details of the above will be presented in a guest lecture at the MRS (Material Research Society) Spring Meeting to be held in San Francisco from April 9 to 13.
(Note 1) The development used the InGaAs strained quantum well in the luminescent layer to gain an advantage in securing reliability. This was combined with knowledge of semiconductor materials whose degradation mechanism is owned by us, material evaluation technology, and material analysis technology in the area of nano order to achieve high reliability after repeating detailed analyses and discussions. The operation with high laser efficiency based on material properties also helped achieve low electricity consumption and high-speed operation.Back to Main Content
(Note 2) In the past, the inter-board connections between computer racks and within computers were made by means of electricity. As supercomputers improve in terms of performance, transmission rates increase and the limitations of electric connections are beginning to show. The optical interconnection where the abovementioned connection is made by means of light has attracted attention as requirements for increased transmission rates and lower electricity consumption grow. Supercomputers are divided into the Top500 and the Green500. The former is evaluated based on a performance index of operation speed, while the latter is evaluated based on electricity consumption. The K computer ranks 1st in the performance index, but is in 32nd place in the Green category. All the supercomputers occupying the top positions in the Green category employ a considerable number of optical interconnections.Back to Main Content
(Note 3) FIT (Failures in Time) is the scale of device reliability. One FIT represents one failure in one billion pieces per hour, or one failure in 100,000 pieces per 10,000 hours (approximately one year), meaning very small rates of failure.
The recent test result showed that only three pieces undergo a failure in a system using one million pieces during 1,000 hours of use. This represents a higher level of reliability, since the actual system was designed in consideration of redundancy. Back to Main Content
(Note 4) A petaflop is a unit representing computer processing speed. It means that 1,000 trillion operations (real number calculation) can be performed in one second. Back to Main Content
Supplementary note: About VCSEL
VCSEL is a domestically developed semiconductor laser invented by Kenichi Iga, President of the Tokyo Institute of Technology. With the following major characteristics, the VCSEL is beginning to find applications in numerous areas.
- Unlike conventional types of semiconductor laser, the VCSEL laser resonator forms vertically and does not necessitate an operation to cleave the laser crystal. As a result, the VCSEL can be tested on a wafer, like the LED (light-emitting diode) can, and is applicable to one- and two-dimensional laser arrays.
- The volume of the luminescent layer is about one tenth that of conventional lasers. This keeps the electric current for laser oscillation (threshold current) small and facilitates low electricity consumption, and is also optimal for application to one- or two-dimensional laser arrays. Large-volume transmissions are also available.
- The circular-shaped luminescent beam facilitates strong connections with optical fiber. Currently, the VCSEL is used in transceivers, computer mice, laser printers and other devices.