Research Projects

The few mode fiber (FMF) technology is on the horizon with a novel multiplexing strategy termed as space or mode division multiplexing. The successful deployment of FMF technology would require a large number of devices and sub-systems to be made available. This project aims to develop multimode interference (MMI) devices on an all-fiber platform for achieving 1x4 power splitters to be used in passive optical networks with single mode fibers (SMFs) and FMFs. Additionally, the reverse propagation mechanism in the power splitter would be exploited to achieve a 4x1 coherent beam combiner for achieving high power levels at the output. We would be using the state-of-the-art MMI method to design these devices on an all-fiber platform using the square core multimode fiber (SCMMF). The MMI technique has already been widely exploited for fabricating various devices on the 1D waveguide platform. Using waveguide-based devices in an optical fiber network provides a compact solution, however, at the cost of non-optimal performance such as high insertion loss and cross talk. Additionally, the cost of these devices is also very high due to the specialized fabrication requirements. We aim to achieve MMI devices on the all-fiber platform (2D cross-section) to exploit various advantages including easy integration in fiber networks using simple connectors, lower device cost, ease of customization for SMF and FMF networks with similar design principles leading to back compatibility. The PI has already done preliminary research work showing the feasibility of power splitting for the SMF and FMF using MMI phenomenon in SCMMF. The propagation modelling of the electromagnetic field in the SCMMF has been achieved with in-house codes, and results have been tested by comparing them with that obtained from the commercial beam propagation software (BeamProp). The PI has also achieved in-principle agreement between theoretical understanding and the experimental data to assess the feasibility of the splitter device where the splitting due to SCMMF was observed on a CCD camera. The MMI devices require precise fabrication with fiber connections as input and output ports. This is essential to achieve complete characterization and establish its feasibility for practical usage. This necessitates cleaving a precise length of a large core diameter SCMMF with a precision requirement of the order of 10 um. Additionally, the splitter device would require alignment of 4 SMFs/FMFs at the output cross-section of the fiber. The cores of the fibers should be sufficiently apart such that there is no coupling between the output fibers. Thus, the investigation would involve analyzing the propagation behavior of the field and resultant multimode interference due to many modes (order of 1000) in a large core diameter SCMMF. In addition to this, the project also aims to develop and characterize the devices for their use as optical power combiners while using them in reverse propagation direction. We would be developing algorithms for achieving precise phase control for achieving coherent power combination using the devices. Achieving these multi-application devices on an all-fiber platform would have a significant impact on lowering the cost of the device due to simpler production procedures as compared to planar waveguide based devices. Furthermore, we would develop in-house mounts, connectors and adapters for setting up the configuration of the device with multiple ports being connected to the SCMMF. The successful implementation of this project would provide passive devices for deployment in existing SMF networks with similar processes being applicable for the development of devices for the future FMF technology. Additionally, the prototype development in this project would boost the prospects of this device to be a potent product for the Make in India initiative of the government of India.

Multimode Interference devices, square core fibers, few mode fibers, optical power splitters, coherent power combiner