Mode-division Multiplexing Networks Research Articles

Reconfigurable Mode (De) Multiplexer via 3-D Triple-Waveguide Directional Coupler With Optical Phase Change Material

A three-dimensional reconfigurable mode (de) multiplexer (3DRM-(De)MUX) is proposed based on a triple-waveguide directional coupler with optical phase change material, which consists of an input waveguide on the upper layer, a bus waveguide on the lower layer, and an intermediate waveguide on the upper layer with a Ge2Sb2Se4Te1 (GSST) cap layer. The self-holding “ off ” and “ on ” states of the proposed 3DRM-(De)MUX can be switched by triggering the amorphous and crystalline states of GSST, respectively. The proposed 3DRM-(De)MUX is optimized by using the full-vectorial finite element method and 3-D full-vectorial finite difference time domain method. The simulated results show that the proposed 3DRM-(De)MUX for switching between the quasi-TE0 and quasi-TE1 modes is with a compact coupling length of only 12.0 μm, a broad bandwidth of 100 nm, the mode extinction ratios of 18.25 dB and 14.0 dB, and the insertion losses (ILs) of –0.38 and –1.14 dB for the “ off ” and “ on ” states, respectively. A more compact 3DRM-(De)MUX can also be achieved for the quasi-TM1 mode with the coupling length of 8.28 μm, IL of –0.12 dB (–1.98 dB), and mode crosstalk of –16.37 dB (–13.23 dB) for the “ off ” (“ on ”) state, respectively. The proposed 3DRM-(De)MUX can be applied in 3-D on-chip mode division multiplexing networks for flexible mode routing and switching.

Reconfigurable On-Chip Mode Exchange for Mode-Division Multiplexing Optical Networks

Data exchange plays a key role in enhancing network resources utilization and optimizing network performance. In this paper, a data exchange device based on mode-division multiplexing (MDM) technology is proposed and demonstrated, which is capable of exchanging data information between a fundamental mode (TE0) signal and an arbitrary high-order mode (TE x ) signal. We experimentally demonstrate the exchange between a TE0 mode signal and a TE1 mode signal using single microring resonator. The insertion loss is about 7.5 dB, including terminal coupling loss, the extinction ratio is more than 20 dB within the C -band. The crosstalk for the TE1-to-TE0 and TE0-to-TE1 mode conversions is measured to be less than −22 and −16 dB, respectively. Clear and open-eye diagrams of two different wavelength signals at 10 Gb/s are obtained. The proposed scheme is expected to be used for on-chip MDM networks in the future due to its scalability, compact size, and low power consumption.

Nonvolatile and ultra-low-loss reconfigurable mode (De)multiplexer/switch using triple-waveguide coupler with Ge2Sb2Se4Te1 phase change material

Mode-division multiplexing (MDM) is a promising approach to dramatically enhance the transmission capacity. A reconfigurable mode (De)multiplexer/switch (RMDS) is a key component for the flexible mode routing in the MDM network. A nonvolatile and ultra-low-loss RMDS is proposed via a triple-silicon-waveguide directional coupler with the Ge2Sb2Se4Te1 (GSST) phase change material (PCM). The nonvolatile property of GSST makes it attractive to reduce the switching power-consumption. Benefiting from the low loss of the GSST-PCM at both amorphous and crystalline states, an RMDS with an ultra-low loss and a high extinction-ratio can be realized. The proposed RMDS is optimally designed by using the full-vectorial finite element method and 3D full-vectorial finite difference time domain method. The numerically simulated results show that a compact RMDS is with the extinction ratios of 18.98 dB and 22.18 dB, ultra-low insertion losses of 0.10 dB and 0.68 dB for the “OFF” and “ON” states, respectively at the operating wavelength of 1550 nm. An ultra-wide bandwidth of 100 nm is achieved for both the “OFF” and “ON” states.

Reconfigurable three-dimensional mode (de)multiplexer/switch via triple-silicon-ITO-waveguide directional coupler.

A reconfigurable mode (de)multiplexer/switch (RMDS) is a pivotal component for the mode routing in mode-division multiplexing (MDM) networks. Here, we propose a three-dimensional (3D) RMDS via a triple-waveguide directional coupler, consisting of a lower doped silicon waveguide, a central plasmonic horizontal-slot waveguide with indium-tin-oxide (ITO) and an upper doped polycrystalline-silicon waveguide. The enhanced light-matter-interactions can be achieved via the central plasmonic metal-oxide-semiconductor (MOS) mode. The multiplexing states of the proposed 3D-RMDS can be switched by adjusting the applied voltage bias on the ITO layer. The simulation results reveal that a 3D quasi-TM0 and quasi-TM1 RMDS is with a compact length of 8.429 μm, the mode crosstalk of -20.3 dB (-9.2 dB) and the insertion loss of 0.06 dB (1.47dB) at the wavelength of 1550 nm for the "OFF" ("ON") state, respectively. The proposed 3D-RMDS can be applied in future 3D on-chip MDM networks to achieve a flexible mode-routing and further enhance the transmission capacity.

Design of weakly-coupled three-spatial-mode rectangular-ring core fiber for short-reach MDM networks in C + L band

We propose a novel weakly-coupled three-spatial-mode rectangular-ring core fiber for short-reach mode-division multiplexing (MDM) networks in C + L band. We investigate the influence of geometrical parameters on neff, min∆neff, and Aeff with regions that meet the three-spatial-mode condition of the proposed fiber. Bending loss of each guided mode and DMD between adjacent spatial modes are also studied. Large effective refractive index difference between adjacent spatial modes is achieved with min∆neff ~ 0.004. Results imply that the designed fiber can simplify or eliminate MIMO-DSP for short-reach MDM networks such as optical interconnects, data centers, and optical access networks.

Fused-fiber-based 3-dB mode insensitive power splitters for few-mode optical fiber networks

We propose a 3-dB mode insensitive power splitter (MIPS) capable of broadcasting and combining optical signals. It is fabricated with two identical few-mode fibers (FMFs) by a heating and pulling technique. The mode-dependent power transfer characteristic as a function of pulling length is investigated. For exploiting its application, we experimentally demonstrate both FMF-based transmissive and reflective star couplers consisting of multiple 3-dB mode insensitive power splitters, which perform broadcasting and routing signals in few-mode optical fiber networks such as mode-division multiplexing (MDM) local area networks using star topology. For experimental demonstration, optical on-off keying signals at 10 Gb/s carried on three spatial modes are successfully processed with open and clear eye diagrams. Measured bit error ratio results show reasonable power penalties. It is found that a reflective star coupler in MDM networks can reduce half of the total amount of required fibers comparing to that of a transmissive star coupler. This MIPS is more efficient, more reliable, more flexible, and more cost-effective for future expansion and application in few-mode optical fiber networks.

3 × 104 Gb/s Single-λ Interconnect of Mode-Division Multiplexed Network With a Multicore Fiber

In this paper, we study the use of silicon microring modulators in an integrated mode-division multiplexing (MDM) network for short-reach interconnects using discrete multitone (DMT) modulation. A fiber grating coupler array is used as a high-speed optical interface between the on-chip mode channels and off-chip multicore fiber (MCF). The whole link has a crosstalk level lower than –23.1 dB. The MDM network can work without the crosstalk compensation of digital signal processing. We present experimental results of the linearity of the silicon microring modulator in terms of spurious-free dynamic range (SFDR). The third-order intermodulation distortion SFDR is 93.4 dB/Hz 2/3 at 20 GHz. We can improve system performance by using adaptive nonlinear equalizer at the DMT receiver to mitigate transmitter and transmission impairments. An aggregate bitrate above 312 Gb/s is achieved with a bit error ratio of 3.8 × 10−3. With the addition of nonlinear equalizer, the line rates of the MDM network can be further increased to about 330 Gb/s. The experimental results demonstrate the feasibility of single wavelength DMT transmission in MDM network with MCF.

Reconfigurable all-fiber mode exchange enabled by mechanically induced LPFG for short-reach MDM networks

Data exchange is an attractive network function for enhancing efficiency and flexibility and it has been widely investigated in the wavelength domain. Recently, mode division multiplexing (MDM) based on few-mode fiber (FMF) has been proposed to increase network capacity by transmitting signals over parallel spatial modes. In this paper, we propose a reconfigurable all-fiber mode exchange (ME) scheme based on mechanically induced long period fiber grating (LPFG) for short-reach MDM networks. The reconfigurable functionality is realized by changing the loaded pressure on LPFG. We experimentally demonstrate flexible data exchange between two linear polarization (LP) modes with on–off-keying (OOK) modulation and direct detection. Error-free performance is achieved for wavelength division multiplexing (WDM) signals in each LP mode.

Mode-Division Multiplexing for Silicon Photonic Network-on-Chip

Optical interconnect is a potential solution to attain the large bandwidth on-chip communications needed in high performance computers in a low power and low cost manner. Mode-division multiplexing (MDM) is an emerging technology that scales the capacity of a single wavelength carrier by the number of modes in a multimode waveguide, and is attractive as a cost-effective means for high bandwidth density on-chip communications. Advanced modulation formats with high spectral efficiency in MDM networks can further improve the data rates of the optical link. Here, we demonstrate an intra-chip MDM communications link employing advanced modulation formats with two waveguide modes. We demonstrate a compact single wavelength carrier link that is expected to support 2x100 Gb/s mode multiplexed capacity. The network comprised integrated microring modulators at the transmitter, mode multiplexers, multimode waveguide interconnect, mode demultiplexers and integrated germanium on silicon photodetectors. Each of the mode channels achieves 100 Gb/s line rate with 84 Gb/s net payload data rate at 7% overhead for hard-decision forward error correction (HD-FEC) in the OFDM/16-QAM signal transmission.

User selective mode-forming remote switch in multi-mode fiber distributing networks using MIMO processing

A mode-forming remote switch in multi-mode fiber distributing networks has been proposed. It can transmit the desired data to the desired port by adjusting transmitter signals. Feasibilities of the proposed scheme are confirmed by switching sub-carrier BPSK signal to the selected port. A graded-index multi-mode fiber link whose output is divided into two ports by a mode-dependent optical coupler, is used as mode-division multiplexing network. Its channel matrix is obtained by using MIMO processing technologies. Amplitudes and phases of the data are adjusted according to the channel matrix. The data is successfully switched to the desired port. Also, wavelength independences are clarified.

Proposed Raised Cosine FMF for Dispersion Management in Next-Generation Optical Networks

Spatial mode-division multiplexing (MDM) that exploits the emerging few-mode fiber (FMF) technology is one potential candidate for next-generation petabyte optical communication links. In this paper, we focus on the design issues and specifications of the next-generation FMF that will better enable future MDM networks. These systems suffer from two main optical fiber impairments: intermodal coupling and dispersion. In this paper, we focus on the dispersion management issues through an FMF optical link. We first define two potential differential mode group delay (DMD) management strategies, namely, sawtooth and triangular. Moreover, we propose and investigate a novel parametric refractive index profile few-mode fiber, referred to as raised cosine (RC) function, which has been extensively used in digital communication pulse shaping. We investigate the achievable DMD for a wide range of the RC shape parameter and identify the design values of a two-mode FMF fiber. We then improve the RC profile by including additional shaping parameters. This enabled us to develop one four-mode fiber (4-FMF) and one six-mode fiber (6-FMF) having particularly attractive dispersion characteristics for three kinds of FMF applications: nz-, p-, and n-DMD.

Mode-selective optical packet switching in mode-division multiplexing networks.

A novel mode-selective optical packet switching, based on mode-multiplexers/demultiplexers and multi-port optical micro-electro-mechanical systems (MEMS) switches, has been proposed and experimentally demonstrated. The experimental demonstration was performed using the LP(01), LP(11a) and LP(11b) modes of a 30-km long mode-division multiplexed few-mode fiber link, utilizing 40 Gb/s, 16-QAM signals.

Low DSP complexity mid-haul mode-division multiplexing links utilizing wideband modal dispersion compensated two-mode fibers

Mode-division multiplexing (MDM) over wavelength division multiplexed (WDM) networks is studied, particularly for the deployment of metro area networks (MAN) using two-mode fibers (TMF). Full C-band differential mode group delay (DMGD)-compensated TMF links are adopted for decreasing the computational complexity of real-time multiple-input multiple-output (MIMO) signal processing. The effect of modal crosstalk to the maximum delay spread of the channel is validated through numerical simulations. Finally, the 2×2 MIMO channel state information (CSI) of a 102.6-km DMGD-compensated TMF link is experimentally estimated for mode path provisioning based upon routing and mode assignment (RMA) in MDM networks. The results confirm close-to-zero total DMGD value over the entire C-band.