Bandwidth density optimization of misaligned optical interconnects

In this paper, the bandwidth density of misaligned free space optical interconnects (FSOIs) system with and without coding under a fixed bit error rate is considered. In particular, we study the effect of using error correction codes of various codeword lengths on the bandwidth density and misalignment tolerance of the FSOIs system in the presence of higher order modes. Moreover, the paper demonstrates the use of the fill factor of the detector array as a design parameter to optimize the bandwidth density of the communication. The numerical results demonstrate that the bandwidth density improves significantly with coding and the improvement is highly dependent on the used codeword length and code rate. In addition, the results clearly show the optimum fill factor values that achieve the maximum bandwidth density and misalignment tolerance of the system.

FPGA-Implemented Fractal Decoder with Forward Error Correction in Short-Reach Optical Interconnects

Forward error correction (FEC) codes combined with high-order modulator formats, i.e., coded modulation (CM), are essential in optical communication networks to achieve highly efficient and reliable communication. The task of providing additional error control in the design of CM systems with high-performance requirements remains urgent. As an additional control of CM systems, we propose to use indivisible error detection codes based on a positional number system. In this work, we evaluated the indivisible code using the average probability method (APM) for the binary symmetric channel (BSC), which has the simplicity, versatility and reliability of the estimate, which is close to reality. The APM allows for evaluation and compares indivisible codes according to parameters of correct transmission, and detectable and undetectable errors. Indivisible codes allow for the end-to-end (E2E) control of the transmission and processing of information in digital systems and design devices with a regular structure and high speed. This study researched a fractal decoder device for additional error control, implemented in field-programmable gate array (FPGA) software with FEC for short-reach optical interconnects with multilevel pulse amplitude (PAM-M) modulated with Gray code mapping. Indivisible codes with natural redundancy require far fewer hardware costs to develop and implement encoding and decoding devices with a sufficiently high error detection efficiency. We achieved a reduction in hardware costs for a fractal decoder by using the fractal property of the indivisible code from 10% to 30% for different n while receiving the reciprocal of the golden ratio.

Unidirectional single mode lasing realization and temperature induced mode switching in asymmetric GaN coupled cavities

Effective lasing mode control and unidirectional coupling of semiconductor microlasers are vital to boost their applications in optical interconnects, on-chip communication and bio-sensors. In this paper, symmetric and asymmetric GaN...

BER Illusion Methodology: A Novel, Open Sourced and Scalable Approach to Troubleshooting High Radix Photonics Interconnects in a Modern Hyperscale Datacenter

Facebook Datacenter consists of a large number of servers that run diverse Facebook services aggregated to serve any given user request. To allow this aggregation, servers have to interact with each other via different traffic flows which are managed by networking fabric. The underlying connection powering this fabric consists of a large number of pluggable optical interconnects and On Board Optical (OBO) modules carrying production data. This connectivity at scale requires fast and reliable detection of the link failures to ensure resolution. In the first generation of the deployments, detection of the link failure was sequential and a slow process. The troubleshoot process was equally tedious as the available tools required characterizing one optical transceiver at a time. Further, the failure analysis also presented a majority of resolution with no failed optics as a root cause resulting in high No Trouble Found (NTF) rate. In this paper we introduce a novel link failure detection and resolution method that improves on the previous method across three dimensions: faster resolution, reliable troubleshooting and scalable implementation. We introduce BER Illusion Methodology (BIM) that is a highly scalable and resource efficient solution that significantly reduces the time taken to troubleshoot pluggable optical interconnects. This is also scalable to next-gen OBO modules at Facebook datacenters aiming to lower the NTF rate and optimally utilizing the available resources. BIM, which is based on Open Compute Platform (OCP) network switches, can be used to troubleshoot 128 QSFP28, 64 QSFP56 or 32 OBO modules simultaneously in under 30 minutes. The tool is easy to implement and capable of also reporting diagnostics on the transceiver such as Transmitter Power, Transmitter Bias Current, Receiver Power, Case Temperature, Bit Error Rate result per channel, Vendor information and Manufacturing part number. This additional test data report along with true failure indication helps optic suppliers gain confidence and build customer credibility. The open-source nature and the universal applicability of this tool offers possibility for other users to adopt and further customize it for their networking needs.