Sumitomo Electric Industries, Ltd. has developed a multi-core optical fiber including 8 cores in the standard 125-µm cladding suitable for optical interconnects, and realized an ultra-high-density fiber optic cable with the highest core density ever reported.
To cope with the growing data traffic in the short-reach interconnects used for parallel processing in supercomputers and resource disaggregation in data centers*1, optical interconnect technologies for broadband high-density transmission are intensively researched and developed. At the same time, the multi-core optical fiber (MCF)*2 that has multiple cores in one fiber has been also intensively researched and developed. The MCF is expected as a next-generation optical fiber that can realize ultra-high-capacity transmission systems. Most of the ever-reported MCF developments had permitted the cladding diameter*3 thicker than the standard 125-µm optical fibers to increase core count while realizing good optical properties of each core and suppressing core-to-core crosstalk*2.
We developed, for the first time, an MCF that has a cladding diameter of 125 µm, equivalent to the standard optical fibers*1 and includes 8 cores with low core-to-core crosstalk. The MCF also has optical characteristics comparable to the standard single-mode fiber (SSMF) specialized for 1.3-μm wavelength band where signal distortion can be suppressed. Having such features, the 125-µm cladding realizes the mechanical reliability*3 equivalent to that of the standard optical fibers, and can utilize various technologies related to the standard optical fibers such as cabling and connecting technologies. The core count of 8 has been desired since full-duplex (2×) 100-Gb/s (4 × 25 Gb/s) signals can be transmitted over one MCF with a transmitting and receiving technology for the conventional 25-Gb/s signals. The realized optical characteristics have a high affinity to silicon photonics technology that realizes highly integrated optical devices operable at 1.3-μm band.
We fabricated a 12-MCF cable using the developed MCFs, in which 96 cores were included within an outer diameter of 3 mm. The achieved core density was more than 2 times higher than those of ever-reported fiber optic communication cables. We also evaluated the transmission characteristics in 1.3-μm band of the 1.1-km-long MCF cable. The evaluation test using 100G-ethernet (100GBASE-LR4) transceiver revealed that the MCF cable assures the error-free transmission for 800 Gb/s (8 cores × 4 wavelengths × 25 Gb/s) signals, which is 8 times higher than the SSMF case. The results of the transmission experiment indicate that the developed MCF cable has the transmission capacity no less than 9.6 Tb/s (12 fibers × 8 cores × 4 wavelength × 25 Gb/s). Improvements on transceivers can further enhance the transmission capacity.
Sumitomo Electric will continue the developments of various MCFs and related-technologies for their practical realization.
These results will be presented at the postdeadline paper*4 session of Optical Fiber Communication Conference (OFC 2015, 22–26 March 2015, Los Angeles, California, USA), one of the largest conferences on optical fiber communications.
This research is supported in part by the National Institute of Information and Communications Technology (NICT), Japan under “R&D of Innovative Optical Fiber and Communication Technology.”
*1 Resource disaggregation in data centers
In resource-disaggregated data centers, the internal resources (computing, memory, storage, communication, etc.) of a server are disaggregated. Such disaggregation makes more logical resource allocation and repair/upgrade of a specific resource easier, and enables efficient use of the resources.
- Standard optical fiber - Optical fibers standardized for communications. The standard cladding diameter is 125 µm. Cores vary by standards.
- Standard single-mode fiber - An optical fiber that has a thin (<10 µm) core. Only one optical path exist in the fiber.
- Multi-core optical fiber - An optical fiber having multiple cores. Suppression of core-to-core crosstalk is necessary to use individual cores as individual transmission paths.
*3 The cladding diameter and mechanical reliability of optical fiber
An optical fiber may break with a certain probability if the mechanical stress, e.g., bend-induced stress, is applied to the fiber for a long time. The mechanical reliability is high when the breakage probability is low. A tighter bend radius and thicker cladding diameter cause higher bend-induced stress. Thus, a cladding diameter larger than 125 µm is not preferable for the short-reach transmissions where tight bends are easily applied to the fiber.
*4 Postdeadline paper
The postdeadline papers are received after the deadline of regular submissions. Generally, these papers present new and significant materials in rapidly advancing areas. Only those papers judged to be truly excellent and compelling in their timeliness are accepted for presentation.