Amado M. Velázquez-Benítez

Time-division-multiplexed few-mode passive optical network.

We demonstrate the first few-mode-fiber based passive optical network, effectively utilizing mode multiplexing to eliminate combining loss for upstream traffic. Error-free performance has been achieved for 20-km low-crosstalk 3-mode transmission in a commercial GPON system carrying live Ethernet traffic. The alternative approach of low modal group delay is also analyzed with simulation results over 10 modes.

Low-Differential-Mode-Group-Delay 9-LP-Mode Fiber

We report the fabrication of low-differential-mode-group-delay 9-LP-mode fibers using a standard bend-insensitive 50μm-diameter-core multimode process. Such 9-LP-mode fibers exhibit DMGDs <; 155ps/km at 1550nm.

10-Mode mode-multiplexed transmission over 125-km single-span multimode fiber

We demonstrate combined wavelength- and mode-multiplexed transmission over a 125-km multimode single span composed of 10- and 15-mode fibers with a spectral efficiency of 29 b/s/Hz. A transmission capacity of 115.2 Tb/s is achieved over a distance of 87 km.

Demonstration of world's first few-mode GPON

We demonstrate the first few-mode-fiber based passive optical network, effectively utilizing mode multiplexing to eliminate combining loss for upstream traffic. Error-free performance has been achieved for 20-km 3-mode transmission in a commercial GPON system carrying live Ethernet traffic.

10 Spatial mode transmission using low differential mode delay 6-LP fiber using all-fiber photonic lanterns.

To unlock the cost benefits of space division multiplexing transmission systems, higher spatial multiplicity is required. Here, we investigate a potential route to increasing the number of spatial mode channels within a single core few-mode fiber. Key for longer transmission distances and low computational complexity is the fabrication of fibers with low differential mode group delays. As such in this work, we combine wavelength and mode-division multiplexed transmission over a 4.45 km low-DMGD 6-LP-mode fiber by employing low-loss all-fiber 10-port photonic lanterns to couple light in and out of the fiber. Hence, a minimum DMGD of 0.2 ns (maximum 0.357 ns) is measured after 4.45 km. Instrumental to the multi-mode transmission system is the employed time-domain-SDM receiver, allowing 10 spatial mode channels (over both polarizations) to be captured using only 3 coherent receivers and real-time oscilloscopes in comparison with 10 for conventional methods. The spatial channels were unraveled using 20 × 20 multiple-input multiple-output digital signal processing. By employing a novel round-robin encoding technique, stable performance over a long measurement period demonstrates the feasibility of 10x increase in single-core multi-mode transmission.

First Demonstration of Six-Mode PON Achieving a Record Gain of 4 dB in Upstream Transmission Loss Budget

The power budget and costs are the two primary concerns for access networks. A major challenge is to minimize upstream power combining loss to increase the power budget. Spatial modes multiplexing offers the possibility to minimize upstream combining loss without significant added costs. We demonstrate the first integrated six-mode passive optical network, utilizing spatial modes to eliminate upstream combining loss. A record 4-dB net gain in power budget was achieved by fusion splicing a photonic lantern with a FMF, in contrast to the traditional power combining scheme with a single-mode power combiner/splitter. BERs <;10-9 were obtained for all the six modes enabling Ethernet transmission using commercial GPON equipment. The packet loss of all six modal channels was tested for 12 h. Finally, we discuss some special issues of few-mode PON regarding its practical application.

Scaling the fabrication of higher order photonic lanterns using microstructured preforms

We fabricate ten- and fifteen-mode photonic lanterns by using microstructured preforms that enables a repeatable fabrication process and scalability to large number of modes. Mode selective capability is demonstrated by independently exciting individual LP mode.

Bending sensor combining multicore fiber with a mode-selective photonic lantern

A bending sensor is demonstrated using the combination of a mode-selective photonic lantern (PL) and a multicore fiber. A short section of three-core fiber with strongly coupled cores is used as the bend sensitive element. The supermodes of this fiber are highly sensitive to the refractive index profiles of the cores. Small bend-induced changes result in drastic changes of the supermodes, their excitation, and interference. The multicore fiber is spliced to a few-mode fiber and excites bend dependent amounts of each of the six linearly polarized (LP) modes guided in the few-mode fiber. A mode selective PL is then used to demultiplex the modes of the few-mode fiber. Relative power measurements at the single-mode PL output ports reveal a high sensitivity to bending curvature and differential power distributions according to bending direction, without the need for spectral measurements. High direction sensitivity is demonstrated experimentally as well as in numerical simulations. Relative power shifts of up to 80% have been measured at radii of approximately 20 cm, and good sensitivity was observed with radii as large as 10 m, making this sensing system useful for applications requiring both large and small curvature measurements.

Thermocapillary Flow in Glass Tubes Coated with Photoresponsive Layers

Thermocapillary flow has proven to be a good alternative to induce and control the motion of drops and bubbles in microchannels. Temperature gradients are usually established by implanting metallic heaters adjacent to the channel or by including a layer of photosensitive material capable of absorbing radiative energy. In this work we show that single drops can be pumped through capillaries coated with a photoresponsive composite (PDMS + carbon nanopowder) and irradiated with a light source via an optical fiber. Maximum droplet speeds achieved with this approach were found to be ~300 μm/s, and maximum displacements, around 120% of the droplet length. The heat generation capacity of the coatings was proven having either a complete coating over the capillary surface or a periodic array of pearls of the photoresponsive material along the capillary produced by the so-called Rayleigh-Plateau instability. The effect of the photoresponsive layer thickness and contact angle hysteresis of the solid-liquid interface were found to be important parameters in the photoinduced thermocapillary effect. Furthermore, a linear relationship between the optical intensity I(o) and droplet velocity v was found for a wide range of the former, allowing us to analyze the results and estimate response times for heat transfer using heat conduction theory.

Six spatial modes photonic lanterns

Low-loss all-fiber mode selective photonic-lanterns capable of exciting six spatial fiber modes (4 LP modes) are demonstrated. Mode field profile characterization of photonic lanterns using both step and graded index fibers is presented.