Propagation of light beams through scattering or multimode systems may lead to the randomization of the spatial coherence of the light. Although information is not lost, its recovery requires a coherent interferometric reconstruction of the original signals, which have been scrambled into the modes of the scattering system. Here we show that we can automatically unscramble optical beams that have been arbitrarily mixed in a multimode waveguide, undoing the scattering and mixing between the spatial modes through a mesh of silicon photonics tuneable beam splitters. Transparent light detectors integrated in a photonic chip are used to directly monitor the evolution of each mode along the mesh, allowing sequential tuning and adaptive individual feedback control of each beam splitter. The entire mesh self-configures automatically through a progressive tuning algorithm and resets itself after significantly perturbing the mixing, without turning off the beams. We demonstrate information recovery by the simultaneous unscrambling, sorting and tracking of four mixed modes, with residual cross-talk of −20 dB between the beams. Circuit partitioning assisted by transparent detectors enables scalability to meshes with a higher port count and to a higher number of modes without a proportionate increase in the control complexity. The principle of self-configuring and self-resetting in optical systems should be applicable in a wide range of optical applications.
As photonics moves from the single-device level toward large-scale, integrated, and complex systems on a chip, monitoring, control, and stabilization of the components become critical. We need to monitor a circuit non-invasively and apply a simple, fast, and robust feedback control. Here, we show non-invasive monitoring and feedback control of high-quality-factor silicon (Si) photonic resonators assisted by a transparent detector that is directly integrated inside the cavity. Control operations are entirely managed by a CMOS microelectronic circuit that is bridged to the Si photonic chip and hosts many parallel electronic readout channels. Advanced functionalities, such as wavelength tuning, locking, labeling, and swapping, are demonstrated. The non-invasive nature of the transparent monitor and the scalability of the CMOS readout system offer a viable solution for the control of arbitrarily reconfigurable photonic integrated circuits aggregating many components on a single chip.
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A photonic integrated circuit performing simultaneous mode and wavelength demultiplexing for few-mode-fiber transmission is demonstrated for the first time. The circuit is realized on an InP-based technological platform; it can handle up to eight mode- and wavelength-division-multiplexed (MDM/WDM) channels and allows all-optical multiple-input-multiple-output processing to unscramble mode mixing generated by fiber propagation. A single arrayed waveguide grating is used to demultiplex the WDM channels carried by all the propagating modes, optimizing circuit complexity, chip area, and operational stability. Combined with an integrated wideband mode multiplexer the circuit is successfully exploited for the transmission of 10 Gbit/s on-off-keying non-return-to-zero channels with a residual cross talk of about -15 dB.
A mixed-signal electronic system allowing closed-loop control of 16 independent integrated photonic devices equipped with CLIPP transparent optical probes (-35 dBm sensitivity, 50 kHz speed) is presented. It features a 32-channel CMOS lock-in front-end (203 nV /â\u88\u9aHz noise, 100 dB dynamic range), interfaced via conditioning chains to multiple ADCs and DACs driven by a Xilinx Spartan-6 FPGA for real-time processing, including the generation and demodulation of multiple pilot tones for channel labeling and dithering-based feedback. The results of the platform characterization are reported, along with the first application of automatic control applied to a novel all-optical unscrambler for mode-division multiplexing
HE transmission of data channels on different orthogonal modes of a single fiber is currently envisioned as the primary path to scale the capacity of optical fiber networks and to address the continuous traffic growth [1]. This solution is typically implemented in systems using multimode and multicore fibers [2], and operating according to space-division multiplexing (SDM) and polarization-division multiplexing (PDM) schemes. In this scenario, several components such as mode converters, wavelength selective switches and amplifiers are needed in order to support fiber networks with multiple spatial paths [3].Silicon (Si) photonics offers a versatile integrated platform to manipulate spatial modes and to carry out fundamental operations for SDM-PDM systems, such as space multiplexing/ demultiplexing [4]-[7] and all-optical multiple-input-multiple-Manuscript
This paper provides detailed guidelines for the optimal design of contactless integrated photonic probes suitable to track and control the local optical power in photonic circuits. With reference to current technology platforms, this paper provides a guide to extract the electrical parameters of the probe and to highlight their role in defining the achievable resolution. Crucial technological and geometrical choices are discussed, together with layout and interconnection solutions oriented to a highly dense integration of the probes. Finally, the criteria for the optimal coupling of the probes to the most suitable readout electronics providing the maximization of the SNR are presented. With these guidelines in mind, transparent in-line local power monitors featuring -35 dBm sensitivity, 40 dB of dynamic range, broadband response from 1.3 to 1.6 μm, a speed down to tens of microsecond and a minimum size of tens of micrometer can be effectively designed for high performance reconfiguration and closed-loop control of complex photonic circuits
The performance of a ring-resonator based passive wavelength router, suitable for optical networking at chip level, is evaluated through bit error rate measurements in single channel 10 Gb/s and 3-channel 10 Gb/s WDM configurations. As the routing path involves a different number of routing elements, depending on the wavelength used for the propagating signal, the performance of three output ports with respect to a specified input one are experimentally evaluated and discussed. Measurements show that low rejection on the filter elements due to fabrication issues mostly affect the channel on the through path with respect to the dropped ones
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