Fiber-optic spectrum monitoring of wavelength-division-multiplexed telecommunication signals with MHz update rates.

We propose a novel (to our knowledge) and simple real-time optical monitoring (RTOM) system for dynamic spectral analysis of telecommunication signals, involving electro-optic (EO) temporal sampling followed by dispersion-induced frequency-to-time mapping and high-speed photodetection. This system enables tracking of the presence and relative intensity of multiple wavelength-division-multiplexed (WDM) data streams that span over a broad frequency band with high resolution, accuracy, and fast measurement update rates. We derive the design conditions and trade-offs of the proposed scheme and report proof-of-concept experiments and a numerical result that demonstrate successful spectral monitoring of dense-WDM signals with different modulation formats and bit rates, over the full C-band, with the needed resolution to discern channels separated by a few tens of GHz, and with an unprecedented fast measurement update rate in the MHz range.

Ultra-compact silicon photonics highly dispersive elements for low-latency signal processing.

On-chip optical group-velocity dispersion (GVD) is highly desired for a wide range of signal processing applications, including low-latency and low-power-consumption dispersion compensation of telecommunication data signals. However, present technologies, such as linearly chirped waveguide Bragg gratings (LCWBGs), employ spectral phase accumulation along the frequency spectrum. To achieve the needed specifications in most applications, this strategy requires device lengths that are not compatible with on-chip integration while incurring in relatively long processing latencies. Here, we demonstrate a novel design strategy that utilizes a discretized and bounded spectral phase filtering process to emulate the continuous spectral phase variation of a target GVD line. This leads to a significant reduction of the resulting device length, enabling on-chip integration and ultra-low latencies. In experiments, we show GVD compensation of both NRZ and PAM4 data signals with baud rates up to 24 GBd over a 31.12-km fibre-optic link using a 4.1-mm WBG-based on-chip phase filter in a silicon-on-insulator (SOI) platform, at least 5× shorter compared to an equivalent LCWBG, reducing the processing latency down to ∼ 100 ps. The bandwidth of the mm-long device can be further extended to the THz range by employing a simple and highly efficient phase-only sampling of the grating profile. The proposed solution provides a promising route toward a true on-chip realization of a host of GVD-based all-optical analog signal processing functionalities.

On-chip generation of high-dimensional entangled quantum states and their coherent control.

Optical quantum states based on entangled photons are essential for solving questions in fundamental physics and are at the heart of quantum information science. Specifically, the realization of high-dimensional states (D-level quantum systems, that is, qudits, with D > 2) and their control are necessary for fundamental investigations of quantum mechanics, for increasing the sensitivity of quantum imaging schemes, for improving the robustness and key rate of quantum communication protocols, for enabling a richer variety of quantum simulations, and for achieving more efficient and error-tolerant quantum computation. Integrated photonics has recently become a leading platform for the compact, cost-efficient, and stable generation and processing of non-classical optical states. However, so far, integrated entangled quantum sources have been limited to qubits (D = 2). Here we demonstrate on-chip generation of entangled qudit states, where the photons are created in a coherent superposition of multiple high-purity frequency modes. In particular, we confirm the realization of a quantum system with at least one hundred dimensions, formed by two entangled qudits with D = 10. Furthermore, using state-of-the-art, yet off-the-shelf telecommunications components, we introduce a coherent manipulation platform with which to control frequency-entangled states, capable of performing deterministic high-dimensional gate operations. We validate this platform by measuring Bell inequality violations and performing quantum state tomography. Our work enables the generation and processing of high-dimensional quantum states in a single spatial mode.

Broadly tunable and ultra-highly selective detection of radio frequency signals enabled by a silicon photonic chip.

Precise and agile detection of radio frequency (RF) signals over an ultra-wide frequency range is a key functionality in modern communication, radar, and surveillance systems, as well as for radio astronomy and laboratory testing. However, current microwave solutions are inadequate for achieving the needed high performance in a chip-scale format, with the desired reduced cost, size, weight, and power. Photonics-based technologies have been identified as a potential solution but the need to compensate for the inherent noise of the involved laser sources have prevented on-chip realization of wideband RF signal detection systems. Here, we report an approach for ultra-wide range, highly-accurate detection of RF signals using a conceptually novel feed-forward laser's noise cancelling architecture integrated on chip. The technique is applied to realization of an RF scanning receiver as well as a complete radar transceiver integrated on a CMOS-compatible silicon-photonics chip, offering an unprecedented selectivity > 80 dB, spectral resolution < 1 kHz, and tunability in the full 0.5-35 GHz range. The reported work represents a significant step towards the development of integrated system-on-chip platforms for signal detection, analysis and processing in cognitive communication and radar network applications.

High-speed serial deep learning through temporal optical neurons.

Deep learning is able to functionally mimic the human brain and thus, it has attracted considerable recent interest. Optics-assisted deep learning is a promising approach to improve forward-propagation speed and reduce the power consumption of electronic-assisted techniques. However, present methods are based on a parallel processing approach that is inherently ineffective in dealing with the serial data signals at the core of information and communication technologies. Here, we propose and demonstrate a sequential optical deep learning concept that is specifically designed to directly process high-speed serial data. By utilizing ultra-short optical pulses as the information carriers, the neurons are distributed at different time slots in a serial pattern, and interconnected to each other through group delay dispersion. A 4-layer serial optical neural network (SONN) was constructed and trained for classification of both analog and digital signals with simulated accuracy rates of over 79.2% with proper individuality variance rates. Furthermore, we performed a proof-of-concept experiment of a pseudo-3-layer SONN to successfully recognize the ASCII codes of English letters at a data rate of 12 gigabits per second. This concept represents a novel one-dimensional realization of artificial neural networks, enabling a direct application of optical deep learning methods to the analysis and processing of serial data signals, while offering a new overall perspective for temporal signal processing.

Group-velocity dispersion emulator using a time lens.

We report a novel method to continuously track the temporal evolution of an arbitrary complex waveform as it propagates through a group-velocity dispersion medium by using a single-frequency-driven phase modulator. The proposed method exploits the fact that the frequency spectrum of a given (input) waveform, following a suitable sinusoidal temporal phase modulation, exhibits the same shape as that of a dispersed version of the same temporal waveform after propagation through a prescribed amount of dispersion. In experiments, we track the dispersion-induced temporal evolution of different optical picosecond pulsed waveforms by tuning the frequency and/or amplitude of the phase modulation signal and observing the resulting shapes in the optical frequency domain. A good agreement is obtained between the measured spectra and predicted temporal shapes of the propagating waveform for different amounts of dispersion. Moreover, the method is successfully applied on a chirped optical pulse to find the optimal pulse compression conditions.

On-chip dispersive phase filters for optical processing of periodic signals.

We develop a dispersive phase filter design framework suitable for compact integration using waveguide Bragg gratings (WBGs) in silicon. Our proposal is to utilize an equivalent "discrete" spectral phase filtering process, in which the original continuous quadratic spectral phase function of a group velocity dispersion (GVD) line is discretized and bounded in a modulo 2π basis. Through this strategy, we avoid the phase accumulation of the GVD line, leading to a significant reduction in device footprint (length) as compared to conventional GVD devices (e.g., using a linearly chirped WBG). The proposed design is validated through numerical simulations and proof-of-concept experiments. Specifically, using the proposed methodology, we demonstrate 2× pulse repetition-rate multiplication of a 10 GHz picosecond pulse train by dispersion-induced Talbot effect on a silicon chip.

Real-time measurement of complex fast signals by bandwidth compression in frequency shifting loops.

We report coherent time-to-frequency mapping in frequency shifting loops (FSLs). We show that when seeded by a temporal signal shorter than the inverse of the frequency shift per roundtrip, the optical spectrum at the FSL output consists of a periodic replica of the input waveform, whose temporal amplitude and phase profiles are mapped into the frequency domain. We provide an experimental demonstration of this phenomenon and show how this simple setup enables real-time measurement of fast non-repetitive input RF signals with a detection chain two orders of magnitude slower than the input signal.

Nonlinear time-lens with improved power efficiency through a discrete multilevel pump: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 3557 (2020).OPLEDP0146-959210.1364/OL.396342.

Nonlinear time-lens with improved power efficiency through a discrete multilevel pump.

We report a novel, to the best of our knowledge, all-optical discrete multilevel time-lens (DM-TL) design based on cross-phase modulation (XPM). In this approach, the pump is synthesized such as the quadratic phase modulation is applied to the probe in constant-level time-bins with a maximum phase excursion of 2π. As a result, a considerable reduction in the required pump power is achieved in comparison to the conventional approach based on a parabolic pump. To illustrate the concept, the proposed DM-TL is here applied to the energy-preserving conversion of a continuous-wave (CW) signal into a train of pulses according to the theory of temporal Talbot array illuminators. We demonstrate CW-to-pulse conversion gains up to 12 at repetition rates exceeding 16 GHz, with a power saving with respect to the conventional parabolic TL that is more significant for increasing conversion gains.

Generalized Talbot self-healing and noise mitigation of faulty periodic images.

Obtaining high-quality images from physical systems, objects, and processes is fundamental for a myriad of areas of science and technology. However, in many situations, the measured images contain defects and/or are accompanied by noise, degrading the quality of the measurement. Recently, a variant of the well-known Talbot self-imaging effect has been shown to redistribute the energy of a spatially periodic collection of images, obtaining output images with increased energy with respect to the input ones. In this work we experimentally demonstrate that such an energy redistribution method has the unique capabilities of increasing the coherent energy level of a periodic set of images over that of the incoherent noise, even allowing images completely buried under noise to be recovered. We further demonstrate that the process can mitigate potential faults of the periodic image structure, including blocked images, spatial jitter, and coherent noise, offering important enhancements (e.g., in regards to the quality of the recovered individual images) in the self-healing capabilities of Talbot self-imaging.

Expanding the phenotypes of congenital hemangiomas.

Congenital hemangiomas (CH) are benign vascular tumors that are present at birth and do not stain for the marker Glut-1. Herein, we describe five cases of CH with atypical presentations: 3 with late growth, 1 with slow involution, and 1 that partially involuted rapidly then manifested late growth.

Discretely programmable microwave photonic filter based on temporal Talbot effects.

We propose and experimentally demonstrate a reconfigurable microwave photonic filter based on temporal Talbot effects. The microwave signal is first uniformly sampled by a train of optical pulses through electro-optic intensity modulation. The sampled optical pulses are then directed to a Talbot-based optical signal processor, consisting of an electro-optic temporal phase modulator and a chromatic dispersion line. The Talbot-based microwave photonic filter (TMPF) exploits the inherent properties of the Talbot self-imaging effect for mitigating pulse-to-pulse intensity fluctuations of optical pulses to transmit some fluctuation frequencies and mitigate or entirely block other microwave spectral components. The output microwave signal is finally reconstructed from the processed optical pulses and the resultant RF response is measured by a network analyzer. The TMPF exhibits an RF response with periodic, symmetric-profile passbands whose center frequency and free spectral range (FSR) are defined by the sampling rate and the dispersion value. The filter passbands can be reconfigured electrically, in discrete steps, by adjusting the modulation function of the phase modulator, i.e., without the need for manual adjustment of the optical components. This enables the capability of selection of specific passbands among the primary passbands. The phase modulation function is provided using an arbitrary waveform generator, with the potential for fast tuning of the filter's spectral response. The bandwidth of the filter passband can also be easily customized by adjusting the sampling pulse's temporal width using an optical bandpass filter. Examples of filter performance in various passband configurations are also presented in the time domain to further validate the operation of the filter.

Novel and Recurrent PNPLA1 Mutations in Spanish Patients with Autosomal Recessive Congenital Ichthyosis; Evidence of a Founder Effect.

Autosomal recessive congenital ichthyosis (ARCI) is a group of rare non-syndrome diseases that affect cornification. PNPLA1 is one of the 12 related genes identified so far. Mutation screening of this gene has resulted in the identification of 13 individuals, from 10 families, who carried 7 different PNPLA1 mutations. These mutations included 2 missense, 2 frame-shift and 3 nonsense, 3 of them being novel. One of the identified variants, c.417_418delinsTC, was highly prevalent, as it was found in 6 out of 10 (60%) of our ARCI families with PNPLA1 mutations. Clinical manifestations varied significantly among patients, but altered sweating; erythema, palmar hyperlinearity and small whitish scales in flexor-extensor and facial areas were common symptoms. Haplotype analyses of c.417_418delinsTC carriers confirmed the existence of a common ancestor. This study expands the spectrum of the PNPLA1 disease, which causes variants and demonstrates that the c.417_418delinsTC mutation has founder effects in the Spanish population.

Arbitrary energy-preserving control of the line spacing of an optical frequency comb over six orders of magnitude through self-imaging.

Spectral self-imaging (SI) is an efficient technique for controlling the line spacing (LS) of optical frequency combs (OFC). However, the degree of control is relatively limited, since the LS of the output comb must be set to be an integer sub-multiple of the input one. This technique can be extended to achieve arbitrary control of the comb LS by pre-conditioning the input comb with a properly designed spectral phase mask. This way, the output LS can be set to be any desired integer or fractional multiple of the input one. This generalized spectral SI process is intrinsically energy-preserving, which enables passive amplification of individual spectral lines of the comb when the scheme is designed for LS increase. Here we demonstrate the unique capabilities of generalized spectral SI in a simple dedicated fiber-optics platform, based on a frequency-shifting recirculating loop. When seeded with an external CW laser, the loop delivers a frequency comb with an arbitrary and reconfigurable quadratic spectral phase. We report lossless arbitrary control of the LS of the generated OFCs over six orders of magnitude, from the kHz to the GHz range, including passive amplification of individual comb lines by factors as high as 17 dB. The LS control is produced without modifying the features of the frequency comb. Practical applications of this LS control method are discussed.

Programmable passive Talbot optical waveform amplifier.

We introduce and experimentally demonstrate a new design for passive Talbot amplification of repetitive optical waveforms, in which the gain factor can be electrically reconfigurable. The amplifier setup is composed of an electro-optic phase modulator followed by an optical dispersive medium. In contrast to conventional Talbot amplification, here we achieve different amplification factors by using combinations of fixed dispersion and programmable temporal phase modulation. To validate the new design, we experimentally show tunable, passive amplification of picosecond optical pulses with gain factors from m = 2 to 30 using a fixed dispersive line (a linearly chirped fiber Bragg grating).

In-fiber high-speed recognition of incoherent-light broadband energy spectrum patterns.

A fiber-optic system is proposed and experimentally demonstrated for real-time, on-the-fly identification of an incoherent-light energy spectrum pattern based on dispersion-induced time-spectrum convolution. In the proposed system, the incoming frequency-spectrum patterns to be identified are modulated by a time-mapped version of the target intensity profile. Following propagation through a suitable fiber-optic dispersive medium, the measured output temporal waveform provides a correlation of the incoming spectra with the programmed target pattern. This enables direct, real-time detection of the matching energy spectra, without any further numerical post-processing. We experimentally demonstrate successful recognition of a target infrared spectral pattern, extending over a bandwidth of 1.5 THz with a resolution of ∼12 GHz, with sub-megahertz update rates. A path for further performance improvements is also suggested.

Fully digital programmable optical frequency comb generation and application.

We propose a fully digital programmable optical frequency comb (OFC) generation scheme based on binary phase-sampling modulation, wherein an optimized bit sequence is applied to phase modulate a narrow-linewidth light wave. Programming the bit sequence enables us to tune both the comb spacing and comb-line number (i.e., number of comb lines). The programmable OFCs are also characterized by ultra-flat spectral envelope, uniform temporal envelope, and stable bias-free setup. Target OFCs are digitally programmed to have 19, 39, 61, 81, 101, or 201 comb lines and to have a 100, 50, 20, 10, 5, or 1 MHz comb spacing. As a demonstration, a scanning-free temperature sensing system using a proposed OFC with 1001 comb lines was also implemented with a sensitivity of 0.89°C/MHz.

Bit-rate-transparent optical return-to-zero-to-nonreturn-to-zero format conversion based on linear spectral phase filtering of the RZ signal.

We propose a novel and simple design for all-optical bit-rate-transparent return-to-zero (RZ)-to-nonreturn-to-zero (NRZ) telecommunication data format conversion based on linear spectral phase filtering of the RZ signal. The proposed concept is numerically analyzed and experimentally validated through successful format conversion of a 640 Gbit/s coherent RZ signal into the equivalent NRZ time-domain data using a simple phase filter realized by a commercial optical waveshaper.