We demonstrate a novel optical receiver for direct-detection of QPSK signals using microring-based photonic integrated circuit. The QPSK signal is converted into a PAM7 electrical signal, and demodulated without the need for a local oscillator.

We report 10 Gbps all-optical switching using a photonic molecule based on two lattice-shifted coupled photonic crystal nanocavities in Indium Phosphide. The process is enhanced by the asymmetric Fano resonance lineshape leading to 0.4 dB OSNR penalty at error rates smaller than 10−9 with switching energies as low as 19.5 fJ/bit or 39 fJ/pulse.

We demonstrate all-optical switching using a multi-mode membranized photonic crystal nanocavity exploiting the free-carrier induced dispersion in InP and the sharp asymmetric lineshape of Fano resonances. A multi-mode cavity is designed to sustain two spatially overlapping modes with a spectral spacing of 18 nm. The measured transmission spectrum of the fabricated device shows multiple asymmetric Fano resonances as predicted by optical simulations. The capabilities of the device are benchmarked by comparing a wavelength conversion from 1538.2 nm to 1565.2 nm with a single-mode wavelength conversion at 1566.2 nm on the same device. The results show an improvement in signal quality with a 5.6 dB power penalty reduction at the receiver as well as in energy efficiency with a reduction of the pump power from 534 fJ/bit to 445 fJ/bit.

We report the use of Fano resonances as compact optical switches by exploiting their sharp asymmetric lineshape together with thermo-optic effects. This enables low footprint and efficient on chip integrated systems. The device consists of a photonic crystal (PhC) membrane with a waveguide side-coupled to a nanocavity surrounded by a p-i-n junction. We demonstrate the thermal tuning of an asymmetric Fano resonances with low power requirements and a response time of 16.1μs. Their high extinction ratio and close spectral separation between maximum and minimum of transmission makes Fano resonances suitable candidates for such optical switching.

Nanocavity devices enabling concentration of light in a very small volume have resulted in several interesting applications over the past years. Of particular interest are the asymmetric resonance lineshapes known as Fano resonances, which result from the interference between a discrete mode of the nanocavity and a continuum of background modes. Compared to the conventional symmetric Lorentzian lineshape, asymmetric Fano lineshapes enable novel or improved device structures for use in optical switches, sensors, lasers, and narrow band filters. Herein, the use of Fano lineshapes in photonic crystal membranes for realizing various optical signal processing functionalities is reviewed. The basic theory of Fano resonances is presented, different photonic crystal Fano device geometries are discussed, the nonlinear processes empowering the devices are explained, and an overview of all-optical signal processing demonstrations based on Fano resonances is given.

Fano resonances occur as a result of the interference between a discrete mode and a continuum of modes. We have realized a Fano structure using a planar indium phosphide photonic crystal membrane device, which consists of a point-defect nanocavity side-coupled to a line-defect waveguide. Compared to the traditional symmetric Lorentzian lineshape, the asymmetric Fano lineshape is characterized by having a transmission maximum and minimum in close spectral vicinity, leading to new opportunities for optical switching, lasing, sensing and narrow band filtering. Here, we present our recent work on optical switches exploiting the sharp asymmetric Fano lineshape in combination with strong carrier-induced nonlinear resonance shifts. This unique combination has enabled femtojoule per bit all-optical switching at tens of gigahertz operation speed. Focus is given to our experimental and theoretical investigations aiming at achieving faster recovery of the switches by using a p-i-n junction around the nanocavity to sweep out carriers.

In article number 1900054 by Jesper Mork and co-workers, the properties of Fano resonances and their use in integrated photonics for realizing optical signal processing are reviewed. The cover image shows a photonic crystal structure, where a Fano resonance is used to realize all-optical switching. The light beam enters through a line-defect waveguide and excites a nanocavity, where the light is concentrated and induces nonlinear effects. Interference with the waveguide field leads to switching for ultra-small light intensity.

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

We experimentally demonstrate the use of a photonic crystal Fano resonance for carving-out short pulses from long-duration input pulses. This is achieved by exploiting an asymmetric Fano resonance combined with carrier-induced nonlinear effects in a photonic crystal membrane structure. The use of a nanocavity concentrates the input field to a very small volume leading to an efficient nonlinear resonance shift that carves a short pulse out of the input pulse. Here, we demonstrate shortening of ∼500  ps and ∼100  ps long pulses to ∼30  ps and ∼20  ps pulses, respectively. Furthermore, we demonstrate error-free low duty cycle return-to-zero signal generation at 2 Gbit/s with energy consumption down to ∼1  pJ/bit and power penalty of ∼2  dB. The device physics and limitations are analyzed using nonlinear coupled-mode theory.

We present our recent experimental work involving nanocavities which enable efficient light-matter interaction in small optical mode volumes. To achieve this, we investigated photonic crystal membrane platforms for designing high-quality (Q) factor nanocavities and efficient planar waveguides. Particularly, we discuss waveguide-nanocavity coupled systems for realization of asymmetric Fano resonances which are characterized by having transmission maximum and minimum in close spectral separation (~1nm) suitable for optical switching applications.

Summary form only given. Ultra-compact photonic structures that perform high-speed low-energy optical signal processing are essential for enabling integrated photonic chips that can meet the growing demand for information capacity [1]. Here, we demonstrate all-optical 40 Gbit/s to 10 Gbit/s demultiplexing of an optical time domain multiplexed (OTDM) signal using an InP photonic crystal switch. The device is realized using a membrane structure, where a point-defect nanocavity is side coupled to a photonic crystal line-defect waveguide as shown in Fig. 1(a). The discrete cavity mode interacts with continuum modes of the waveguide creating a Fano resonance [2]. By placing a partially transmitting element (PTE) in the waveguide, the coupling between the waveguide and the cavity can be controlled [3]. The Fano lineshape is characterized by a large on-off transmission ratio with small spectral separation making it suitable for switching applications (Fig. 1(b)).

We show that Fano resonances can be realized in photonic crystal membrane structures by coupling line-defect waveguides and point-defect nanocavities. The Fano resonance can be exploited to realize optical switches with very small switching energy, as well as Fano lasers, that can generate short optical pulses.

We present our work on photonic crystal membrane devices exploiting Fano resonance between a line-defect waveguide and a side coupled nanocavity. Experimental demonstration of fast and compact all-optical switches for wavelength-conversion is reported. It is shown how the use of an asymmetric structure in combination with cavity-enhanced nonlinearity can be used to realize non-reciprocal transmission at ultra-low power and with large bandwidth. A novel type of laser structure, denoted a Fano laser, is discussed in which one of the mirrors is based on a Fano resonance. Finally, the design, fabrication and characterization of grating couplers for efficient light coupling in and out of the indium phosphide photonic crystal platform is discussed.

We discuss the realization of active photonic devices exploiting Fano resonances in photonic crystal membranes.

Island-type two-dimensional high-index-contrast grating mirror based on a standard silicon-on-insulator wafer have been experimentally demonstrated. The measured spectra shows a bandwidth of ~192 nm with a reflectivity over 99% as well as polarization independence. Numerical simulations show that the designed mirror has large tolerance to fabrication errors.

Silicon photonics offers tremendous potential for inexpensive high-yield photonic-electronic integration by enabling fabless fabrication and joint processing of photonic and electronic circuitry. Silicon as an optical material, however, falls short of certain properties that are indispensable for high-performance devices. In particular, bulk silicon does not feature any second-order optical nonlinearity due to crystal symmetry, thereby making efficient electro-optic modulators challenging. These deficiencies can be overcome by silicon-organic hybrid (SOH) integration, which combines silicon-on-insulator (SOI) waveguides with electro-optic organic materials. We give an overview on our recent progress in the field of SOH modulators, covering highly efficient devices with energy consumptions of a few femtojoule per bit and modulator-based frequency comb generators that enable WDM data transmission at terabit/s data rates.

We demonstrate frequency comb generation using silicon-organic hybrid (SOH) electro-optic modulators. The frequency combs are used for WDM data transmission at terabit/s data rates and distances of up to 300 km.

We give an overview on our recent achievements in the field of SOH integration, covering in-device electro-optic coefficients r33 in excess of 200 pm/V, highly efficient Mach-Zehnder modulators, IQ modulators, and modulator-based frequency comb generators.

In this paper an evaluation of state-of-the-art binary keypoint descriptors, namely BRIEF, ORB, BRISK and FREAK, is presented. In contrast to previous evaluations we used the Stanford Mobile Visual Search (SMVS) data set because binary descriptors are mainly used in mobile applications. This large data set does provide a lot of characteristic transformations for mobile devices, but no ground truth data. The often used Oxford data set is used only for validation purposes. We use ratio-test and RANSAC (RANdom SAmple Consensus) for evaluation and present results for accuracy, precision and average number of best matches as performance metrics. The validity of the results is also checked by evaluating these binary keypoint descriptors on Oxford data set. The obtained results show that BRISK is the keypoint descriptor which gives highest percentage of precision and largest number of best matches among all the binary descriptors. Next to BRISK is FREAK, which offers comparably good result.