Self-adaptive integrated photonic receiver for turbulence compensation in free space optical links

: In Free Space Optical (FSO) communication systems, atmospheric turbulence distorts the propagating beams, causing a random fading in the received power. This perturbation can be compensated using a multi-aperture receiver that samples the distorted wavefront on different points and adds the various signals coherently. In this work, we report on an adaptive optical receiver that compensates in real time for scintillation in FSO links. The optical front-end of the receiver is entirely integrated in a silicon photonic chip hosting a 2D Optical Antenna Array and a self-adaptive analog Programmable Optical Processor made of a mesh of tunable Mach-Zehnder interferometers. The photonic chip acts as an adaptive interface to couple turbulent FSO beams to single-mode guided optics, enabling energy and cost-effective operation, scalability to systems with a larger number of apertures, modulation-format and data-protocol transparency, and pluggability with commercial fiber optics transceivers. Experimental results demonstrate the effectiveness of the proposed receiver with optical signals at a data rate of 10 Gbit/s transmitted in indoor FSO links where different turbulent conditions, even stronger than those expected in outdoor links of hundreds of meters, are reproduced

Separating arbitrary free-space beams with an integrated photonic processor

: Free-space optics naturally offers multiple-channel communications and sensing exploitable in many applications. The different optical beams will, however, generally be overlapping at the receiver, and, especially with atmospheric turbulence or other scattering or aberrations, the arriving beam shapes may not even be known in advance. We show that such beams can be still separated in the optical domain, and simultaneously detected with negligible cross-talk, even if they share the same wavelength and polarization, and even with unknown arriving beam shapes. The kernel of the adaptive multibeam receiver presented in this work is a programmable integrated photonic processor that is coupled to free-space beams through a two-dimensional array of optical antennas. We demonstrate separation of beam pairs arriving from different directions, with overlapping spatial modes in the same direction, and even with mixing between the beams deliberately added in the path. With the circuit's optical bandwidth of more than 40 nm, this approach offers an enabling technology for the evolution of FSO from single-beam to multibeam space-division multiplexed systems in a perturbed environment, which has been a game-changing transition in fiber-optic systems

Self-Configuring Silicon-Photonic Receiver for Multimode Free Space Channels

A self-configuring mesh of silicon Mach-Zehnder Interferometers is employed to receive two spatially overlapped orthogonal beams modulated at 10 Gbit/s. These beams, sharing the same wavelength and state of polarization, are separated with more than 30 dB isolation, and sorted out with no signal degradation

Breaking the Delay-Bandwidth Product of Continuously-Tunable MZI Delay-Lines

We report on a novel integrated delay-line architecture enabling to break the delay-bandwidth product of Mach-Zehnder Interferometers delay-lines. A continuously tuneable delay from 0 to 100 ps is achieved across a bandwidth of 21 GHz

Continuously Tuneable MZI-based Delay Line Overcoming Delay-Bandwidth Product

A silicon photonic integrated circuit, implementing a novel delay-line architecture, is proposed. The device, based on a set of four nested Mach-Zehnder Interferometers, overcomes typical delay-bandwidth product. Showing a minimum bandwidth of 20 GHz, group delay can be continuously tuned between 0 and 100 ps

Variable optical true-time delay line breaking bandwidth-delay constraints

Continuously variable true-time optical delay lines are typically subject to a constraint of the bandwidth-delay product, limiting their use in several applications. In this Letter, we propose an integrated topology that breaks the bandwidth-delay product limit. The device is based on multiple Mach-Zehnder Interferometers (MZIs) arranged in parallel, providing easier control and a larger bandwidth compared to ring resonator-based solutions. The functionality of this architecture is demonstrated with a 4-stage delay line by performing measurements in both the time and frequency domains. The delay line introduces a delay of 90 ps over a bandwidth of more than 22 GHz with a negligible group delay distortion, operates on a wavelength range of about 60 nm, and is scalable to a higher number of MZI stages

Automatic Setting of Multiple FSO Orthogonal Communication Channels Between Photonic Chips

Multiple orthogonal free-space optical (FSO) communication channels are automatically established between photonic chips hosting programmable integrated processors. All-optical channel demultiplexing is achieved with a crosstalk < -30 dB even after co-propagation though arbitrary mode mixers

Determining the optimal communication channels of arbitrary optical systems using integrated photonic processors

Modes of propagation through an optical system are generally defined as the eigensolutions of the wave equation in the system. When propagation occurs through complicated or highly scattering media, however, modes are better identified as the best orthogonal communication channels to send information between sets of input and output apertures. Here we determine the optimal bidirectional orthogonal communication channels through arbitrary and scattering optical systems using photonic processors. The processors consist of meshes of electrically tuneable Mach–Zehnder interferometers in silicon photonics. The meshes can configure themselves based on simple power maximization or minimization algorithms, without external calculations or calibration or any prior knowledge of the optical system. The identification of the communication mode channels corresponds to a singular value decomposition of the entire optical system, autonomously performed by the photonic processors. We observe crosstalk below –30 dB between the optimized channels even in the presence of distorting masks or partial obstructions. In these cases, although the beams bear little resemblance to conventional mode families, they still show orthogonality. These findings offer potential for applications in multimode optical communication systems, promising efficient channel identification, adaptability to dynamic media and robustness against environmental challenges