David Garcia-Rodriguez

Mode-Selective Couplers for Two-Mode Transmission at 850 nm in Standard SMF

The optimal design of a low-loss fused fiber mode-selective coupler for two-mode fiber transmission in the 850-nm band is presented. The coupler is based on precise phase matching of the propagation constants in each arm of a weakly fused fiber coupler. The designed component permits both mode converter and mode multiplexer/demultiplexer operation, thus enabling modal multiplexing transmission in this band with no additional component. The presented design is evaluated by simulation considering two types of structures, leading to asymmetric and symmetric coupler configurations. Mode converter and mode multiplexer operation is achieved with 93.5% efficiency in the band of 845-855 nm. Mode demultiplexer operation is achieved with an extinction ratio better than 20.4 dB in the same band.

Dimensional variation tolerant mode converter/multiplexer fabricated in SOI technology for two-mode transmission at 1550 nm

The use of an integrated asymmetrical directional coupler for two-mode transmission at 1550 nm is analyzed. The design is based on silicon-on-insulator (SOI) technology and permits mode conversion and mode multiplexing/demultiplexing. In the nominal design, mode conversion and mode (de)multiplexing are achieved with 97% efficiency and a 23.4 dB crosstalk level in the 1540-1560 nm band using a 0.1 μm gap. The dimension tolerance of the SOI process has been taken into account in the selection of the optimum design, and the coupling efficiency would remain above 82.3% (corresponding to 0.8 dB excess loss) with 3σ accuracy. A 90% efficiency has been experimentally obtained.

Towards multidimensional multiplexing in multicore fiber optical data links

This paper describes our current research in optical transmission technology targeting to overcome the capacity limitations in high-bitrate optical data links. In particular, the enabling steps taken towards multidimensional multiplexing (M2) transmission schemes for transmission in multicore fiber are described. The development of an integrated device capable of performing mode conversion for modal division multiplexing (MDM) is reported in this work. This device enables the generation of a mode-division multiplexed signal to be transmitted through the different cores of a multi-core optical fiber (MCF) employing spatial division multiplexing (SDM). The transmission performance is limited by the crosstalk from each core in the MCF. A theoretical and experimental analysis of the inter-core crosstalk expected when several cores are excited simultaneously is herein presented.

Demonstration of a spatially multiplexed multicore fibre-based next-generation radio-access cellular network

This paper proposes and demonstrates a next-generation radio-access network employing multicore fibre in the optical wireless fronthaul and mode-division multiplexing in the backhaul to overcome the capacity limitation of single-mode fibre systems. The proposed optical fronthaul is based on radio-over-fibre (RoF) transmission on multicore fibre. The combination of RoF and multicore fibre permits cost- and energy-efficient support of MIMO wireless present in actual 4G cellular systems, which is a key requirement for next-generation 5G radio technology. The performance of RoF transmission in a 4-core fibre using LTE-Advanced radio signals implementing 2×2 MIMO coding is reported in this paper altogether with the crosstalk performance with different bending radius and random twist. The proposed backhaul optical network is based on modal-division multiplexing over a single wavelength. Few-mode transmission is employed in order to increase the transmission capacity of the backhaul network. Few-mode transmission performance is analysed considering the propagation of two LP mode groups taking into account both modal and chromatic dispersion transmission impairments in the optical backhaul.

Few-mode optical transmission systems in the visible band

This paper introduces the principles and current technology of few-mode transmission in guided optical medium for systems operating in the visible band. The visible band opens up the possibility of using standard single mode fibre, as few-mode propagation media, with the advantage of lower cost than equivalent C+L components. Few-mode transmission performance is analysed in detail considering the propagation of two degenerated modes with modal and chromatic dispersion transmission impairments. The results indicate that few-mode optical transmission systems can be used as high-capacity optical interconnects and high-performance computing networks providing 1 Gbps at 322 m operating at 850 nm or 10 Gbps at 11.8 km with 1064 nm.

Spatial division multiplexing in the short and medium range: From the datacenter to the fronthaul

This paper reports the experimental performance of spatial division multiplexing (SDM) optical transmission systems. These SDM systems are intended to support key short- and medium-range low-latency applications as optical fronthaul in cellular networks, point-to-point optical backhaul and baseband optical links in datacentre applications. In particular, the experimental demonstration of optical fronthaul of 3GPP LTE-A wireless supporting up to 4×4 MIMO on a 4-core multicore fibre (MCF) is reported. The results indicate that successful multiple-antenna transmission is achieved at 150 m MCF range. SDM implementation in SSMF by modal multiplexing is a complementary approach to MCF and is also experimentally investigated. The key limiting factor in this case is the optical mode conversion stage. An efficient mode-conversion coupler is proposed and evaluated for 850 nm and 1550 nm operation. For 1550 nm, a coupler has been fabricated in silicon-on-insulator (SOI) technology. Few-mode transmission performance is analysed considering the propagation of two LP mode groups. The experimental results indicate that the SDM system is suitable for short-range datacentre applications operating at 850 nm where integration capability is of great importance, and medium-range point-to-point optical backhaul links operating at 1550 nm can also benefit from the proposed device architecture.

Mode-converter and multiplexer based on SOI technology for few-mode fiber at 1550 nm

The Asymmetric Directional Coupler (ADC) based on SOI (Silicon-on-Insulator) technology converts and couples the fundamental mode to the first higher order mode. The ADC is designed to achieve phase-matching condition, which is accomplished when both propagation constants are equal in each waveguide arm. Devices are fabricated in a SOI wafer with a 220 nm thick silicon layer. The refractive indexes of Si and SiO2 are nSi=3.47 and nSi02=1.46 respectively. The access waveguides (W1=0.45 μm) have been designed to propagate just the fundamental mode, TE0. The optimum width for the second waveguide was chosen to achieve the phase-matching condition for the TE1 mode, which corresponds to W2=0.962 μm. The coupling to the input and output waveguides is achieved through grating couplers. The input grating coupler will need to couple the LP01 mode from the SSMF (Standard Single-Mode Fiber) to the TE0 mode in the SOI waveguide; thus a typical design for a SOI coupler can be used. However, the output coupler must simultaneously couple the TE0 and TE1 modes in the SOI wide waveguide to the LP01 and LP11 modes in the FMF (Few-Mode Fiber). Input gratings are designed to have an area of 12x12 μm2 and a period of Λ=610 nm in order to maximize the optical power coupled between the fiber and the waveguide for an incident angle of 10 degrees. Output gratings are designed with the same period but distinct area (12.5x12.5 μm2) to correctly couple the LP01 and LP11 modes in the FMF.