Telecommunication Wavelengths Research Articles

Carbon defect qubit in two-dimensional WS2

Identifying and fabricating defect qubits in two-dimensional semiconductors are of great interest in exploring candidates for quantum information and sensing applications. A milestone has been recently achieved by demonstrating that single defect, a carbon atom substituting sulphur atom in single layer tungsten disulphide, can be engineered on demand at atomic size level precision, which holds a promise for a scalable and addressable unit. It is an immediate quest to reveal its potential as a qubit. To this end, we determine its electronic structure and optical properties from first principles. We identify the fingerprint of the neutral charge state of the defect in the scanning tunnelling spectrum. In the neutral defect, the giant spin-orbit coupling mixes the singlet and triplet excited states with resulting in phosphorescence at the telecom band that can be used to read out the spin state, and coherent driving with microwave excitation is also viable. Our results establish a scalable qubit in a two-dimensional material with spin-photon interface at the telecom wavelength region.

Cylindrical-lens-embedded photonic crystal based on self-collimation.

Photonic crystals can be engineered so that the flow of optical power and the phase of the field are independently controlled. The concept is demonstrated by creating a self-collimating lattice with an embedded cylindrical lens. The device is fabricated in a photopolymer by multi-photon lithography with the lattice spacing chosen for operation around the telecom wavelength of 1550 nm. The lattice is based on a low-symmetry rod-in-wall unit cell that strongly self-collimates light. The walls are varied in thickness to modulate the effective refractive index so light acquires a spatially quadratic phase profile as it propagates through the device. Although the phase of the field is altered, the light does not focus within the device because self-collimation forces power to flow parallel to the principal axes of the lattice. Upon exiting the device, ordinary propagation resumes in free space and the curved phase profile causes the light to focus. An analysis of the experimentally observed optical behavior shows that the device behaves like a thin lens, even though the device is considerably thick.

Temperature Dependence of Low-Dose Radiation-Induced Attenuation of Germanium-Doped Optical Fiber at Infrared Wavelengths

Ge-doped optical fibers (OFs) are considered radiation-tolerant waveguides. Even if their transmission in the infrared (IR) domain is degraded under irradiation, for most of the applications, their radiation-induced attenuation (RIA) remains acceptable. Space harsh environment is characterized by low dose and dose-rate constraints meaning that germanosilicate fibers are often employed for data links. However, the temperature can largely vary in space and is known to impact the RIA levels and kinetics. We studied here systematically the combined temperature and radiation effects induced on the transmission, at the telecom wavelengths, of a Ge-doped fiber, between −80 °C and 80 °C up to a total ionizing dose (TID) of 10 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )–1 Mrad. Our measurements highlight larger RIA levels at low temperatures than at room temperature (RT). At our highest TID, it increases by a factor of ~40 and ~20, respectively, at 1310 and 1550 nm, when the irradiation is performed at −80 °C instead of RT. A model is reported to study the activation energy of the radiation-induced point defects responsible for the IR-RIA. This simple model could help in predicting the fiber vulnerability for various mission profiles.

Ultralarge anti-Stokes lasing through tandem upconversion

Coherent ultraviolet light is important for applications in environmental and life sciences. However, direct ultraviolet lasing is constrained by the fabrication challenge and operation cost. Herein, we present a strategy for the indirect generation of deep-ultraviolet lasing through a tandem upconversion process. A core–shell–shell nanoparticle is developed to achieve deep-ultraviolet emission at 290 nm by excitation in the telecommunication wavelength range at 1550 nm. The ultralarge anti-Stokes shift of 1260 nm (~3.5 eV) stems from a tandem combination of distinct upconversion processes that are integrated into separate layers of the core–shell–shell structure. By incorporating the core–shell–shell nanoparticles as gain media into a toroid microcavity, single-mode lasing at 289.2 nm is realized by pumping at 1550 nm. As various optical components are readily available in the mature telecommunication industry, our findings provide a viable solution for constructing miniaturized short-wavelength lasers that are suitable for device applications.

Mode crossing induced soliton frequency comb generation in high-Q yttria-stabilized zirconia crystalline optical microresonators

We demonstrate for the first time, to the best of our knowledge, the fabrication of high- Q crystalline optical microresonators from cubic yttria-stabilized zirconia (YSZ). Intrinsic Q factors up to 80 million are obtained, indicating an upper bound absorption coefficient of 0.001 cm − 1 for YSZ crystals at the telecom wavelength. Through laser-scanned spectroscopy on a few-mode YSZ microresonator with a radius of 300 μm, we find that the mode crossing effect in the case of weak coupling can induce a repelling disruption of free spectral range values between transverse mode families. Generation of soliton and soliton crystals in such a YSZ microcomb platform operated in the normal dispersion regime is observed. A breathing comb behavior is also reported. Our finding has enriched comb generation platforms with potential multidisciplinary capabilities linked to properties of YSZ crystals in superconducting films and sensors.

Theoretical analysis of VO2 filled double rectangular cavity-based coupled resonators for plasmonic active switch/modulator and band pass filter applications

In this paper, we have designed an electrically tunable nano-plasmonic waveguide-based band pass filter which works on the phenomena of phase transition of Vanadium dioxide. The device operates on telecommunication wavelength and can work as a modulator and a switch with a modulation depth of 26.40 dB. It has shown its promising applications in the area of filtering by providing a high-quality factor of 156. Whereas, the modulation depth and quality factor of the device can be increased and decreased by changing various device parameters. A large tunability of 280 nm in the resonant wavelength is achieved by changing the applied voltage on the device between 0 V and 2.7 V in switch-on and switch-off states. Figure of merit of 12 is also attained by the device. Our device consists of a main waveguide which is coupled to two uneven length rectangular cavities filled with Vanadium dioxide. Active material present as the dielectric of rectangular cavities transforms its state from insulator to metallic and vice versa according to the applied voltage. However, single band transmission is obtained for the device and this can be tuned by changing different geometrical parameters of the device. The device can find its applications in nano plasmonic on-chip applications due to its small size, good modulation depth, and large quality factor with moderate loss.

Ultra-low loss visible light waveguides for integrated atomic, molecular, and quantum photonics

Atomic, molecular and optical (AMO) visible light systems are the heart of precision applications including quantum, atomic clocks and precision metrology. As these systems scale in terms of number of lasers, wavelengths, and optical components, their reliability, space occupied, and power consumption will push the limits of using traditional laboratory-scale lasers and optics. Visible light photonic integration is critical to advancing AMO based sciences and applications, yet key performance aspects remain to be addressed, most notably waveguide losses and laser phase noise and stability. Additionally, a visible light integrated solution needs to be wafer-scale CMOS compatible and capable of supporting a wide array of photonic components. While the regime of ultra-low loss has been achieved at telecommunication wavelengths, progress at visible wavelengths has been limited. Here, we report the lowest waveguide losses and highest resonator Qs to date in the visible range, to the best of our knowledge. We report waveguide losses at wavelengths associated with strontium transitions in the 461 nm to 802 nm wavelength range, of 0.01 dB/cm to 0.09 dB/cm and associated intrinsic resonator Q of 60 Million to 9.5 Million, a decrease in loss by factors of 6x to 2x and increase in Q by factors of 10x to 1.5x over this visible wavelength range. Additionally, we measure an absorption limited loss and Q of 0.17 dB/m and 340 million at 674 nm. This level of performance is achieved in a wafer-scale foundry compatible Si3N4 platform with a 20 nm thick core and TEOS-PECVD deposited upper cladding oxide, and enables waveguides for different wavelengths to be fabricated on the same wafer with mask-only changes per wavelength. These results represent a significant step forward in waveguide platforms that operate in the visible, opening up a wide range of integrated applications that utilize atoms, ions and molecules including sensing, navigation, metrology and clocks.

Broadband photonic tensor core with integrated ultra-low crosstalk wavelength multiplexers

Abstract The integration of artificial intelligence (AI) systems in the daily life greatly increases the amount of data generated and processed. In addition to the large computational power required, the hardware needs to be compact and energy efficient. One promising approach to fulfill those requirements is phase-change material based photonic neuromorphic computing that enables in-memory computation and a high degree of parallelization. In the following, we present an optimized layout of a photonic tensor core (PTC) which is designed to perform real valued matrix vector multiplications and operates at telecommunication wavelengths. We deploy the well-studied phase-change material Ge2Sb2Te5 (GST) as an optical attenuator to perform single positive valued multiplications. In order to generalize the multiplication to arbitrary real factors, we develop a novel symmetric multiplication unit which directly includes a reference-computation branch. The variable GST attenuator enables a modulation depth of 5 dB over a wavelength range of 100 nm with a wavelength dependency below 0.8 dB. The passive photonic circuit itself ensures equal coupling to the main-computation and reference-computation branch over the complete wavelength range. For the first time, we integrate wavelength multiplexers (MUX) together with a photonic crossbar array on-chip, paving the way towards fully integrated systems. The MUX are crucial for the PTC since they enable multiple computational channels in a single photonic crossbar array. We minimize the crosstalk between the channels by designing Bragg scattering based MUX. By cascading, we achieve an extinction ratio larger than 61 dB while the insertion loss is below 1 dB.

Heterogeneous integration of Si photodiodes on silicon nitride for near-visible light detection.

Silicon nitride (SiN) is used extensively to complement the standard silicon photonics portfolio. However, thus far demonstrated light sources and detectors on SiN have predominantly focused on telecommunication wavelengths. Yet, to unlock the full potential of SiN, integrated photodetectors for wavelengths below 850 nm are essential to serve applications such as biosensing, imaging, and quantum photonics. Here, we report the first, to the best of our knowledge, microtransfer printed Si p-i-n photodiodes on a commercially available SiN platform to target wavelengths <850 nm. A novel heterogeneous integration process flow was developed to offer a high microtransfer printing yield. Moreover, these devices are fabricated with CMOS compatible and wafer-scale technology.

Optical charge injection and coherent control of a quantum-dot spin-qubit emitting at telecom wavelengths

Solid-state quantum emitters with manipulable spin-qubits are promising platforms for quantum communication applications. Although such light-matter interfaces could be realized in many systems only a few allow for light emission in the telecom bands necessary for long-distance quantum networks. Here, we propose and implement an optically active solid-state spin-qubit based on a hole confined in a single InAs/GaAs quantum dot grown on an InGaAs metamorphic buffer layer emitting photons in the C-band. We lift the hole spin-degeneracy using an external magnetic field and demonstrate hole injection, initialization, read-out and complete coherent control using picosecond optical pulses. These results showcase a solid-state spin-qubit platform compatible with preexisting optical fiber networks.

Near-Zero-Index Slabs on Bloch Surface Wave Platform for Long-Range Directional Couplers and Optical Logic Gates.

Near-zero-index materials and structures, with their extraordinary optical behaviors of phase-free propagation resulting in directional radiation, provide a possible approach for directional coupling and optical logic gates in photonic integrated circuits. However, the radiation from the near-zero-index structures is limited to a short range of a few hundreds of nanometers. A Bloch surface wave (BSW), an electromagnetic surface wave that can be excited at the interface between an all-dielectric multilayer and a dielectric medium with a low-loss optical mode, provides a solution to increase the propagation length. In this work, we present a nanostructured near-zero-index slab integrated on the all-dielectric metal-free BSW platform for long-range surface wave radiation. By employing the long-range directional surface-wave radiation, a directional coupler and optical logic gates based on the BSW near-zero-index slabs are realized. The proposed directional couplers achieve long coupling distances (the electric-field magnitude ratio between the input slab and output slab is 0.22 with a 50 μm coupling distance), which is 2 orders of magnitude longer than that of conventional directional couplers based on evanescent wave coupling. By controlling the interference pattern of the BSW between the slabs, the XOR logic gate is experimentally demonstrated with a significant extinction ratio of 27.9 dB at telecommunications wavelengths. The BSW near-zero-index logic gates and the directional coupler with long-range light propagation provide an approach to the development of photonic integrated circuits and metal-free surface wave-based applications.

Direct f-3f self-referencing using an integrated silicon-nitride waveguide.

We have achieved the simultaneous generation of a 2.6-octave-wide supercontinuum (SC) spectrum over 400-2500 nm and third-harmonic light solely by a dispersion-controlled silicon-nitride waveguide (SiNW). To increase the visible intensity of the SC light component, we fabricated low-loss 5-mm-long deuterated SiNWs with spot-size converters by low-temperature deposition. We succeeded in measuring the carrier-envelope-offset (CEO) signal with a 34-dB signal-to-noise ratio because this short deuterated SiNW provides a large temporal overlap between the f and 3f components. In addition, we have demonstrated this method of CEO locking at telecommunications wavelengths with f-3f self-referencing generated solely by the SiNW without the use of highly nonlinear fiber and an additional nonlinear crystal. Compared with the method of CEO locking with a highly nonlinear fiber and a standard f-2f self-referencing interferometer, this method is not only simple and compact but also stable.

Dynamic routing through saturable absorption in graphene photonic resonators: Impact of carrier diffusion and finite relaxation time

We assess the continuous wave and dynamic routing performance of a compact silicon-on-insulator disk resonator overlaid with a graphene monolayer at telecommunication wavelengths. Switching action is enabled by saturable absorption in graphene, controlled by a pump wave of only a few milliwatts. Graphene saturable absorption is modeled through a carrier rate equation that incorporates both the finite relaxation time and diffusion of photo-generated carriers, providing a realistic account of carrier dynamics. The overall nonlinear response of the resonator is evaluated with a rigorous mathematical framework based on perturbation theory and temporal coupled-mode theory. We thoroughly investigate the effects of carrier diffusion and finite relaxation time, both separately and together. We also take into account nonlinear refraction via a Kerr effect term and quantify its impact on the overall response. In order to suppress the Kerr effect, we replace silicon with silicon-rich nitride, allowing for the individual contributions of the resonator core and graphene (of opposite sign) to exactly compensate each other. Our results contribute to the understanding of carrier dynamics and their impact on the performance of practical graphene-based switching components.

Topological cavity laser with valley edge states.

Topological edge states (ES) arise at the boundary between spatial domains with diverse topological properties in photonic crystals, which can transmit unidirectionally to suppress the backscattering and robustly to be immune to defects and disorders. In addition, optical devices with arbitrary geometries of cavities, such as lasers, are expected to be designed on the basis of ES. Herein, we first propose a topological cavity laser based on a honeycomb lattice of ring holes with the bearded interface in two-dimensional (2D) all-dielectric valley photonic crystals (VPhCs) at telecommunication wavelengths. Specifically, we construct a topological cavity using topological valley edge states (VES) and further study the lasing action of the optically pumped cavity with high-quality factors. Our findings could provide opportunities for practical applications of VES-based lasers as ultra-small light sources with the topological protection.

Avalanche photodiodes on silicon photonics

Silicon photonics technology has drawn significant interest due to its potential for compact and high-performance photonic integrated circuits. The Ge- or III–V material-based avalanche photodiodes integrated on silicon photonics provide ideal high sensitivity optical receivers for telecommunication wavelengths. Herein, the last advances of monolithic and heterogeneous avalanche photodiodes on silicon are reviewed, including different device structures and semiconductor systems.

Fabrication of hyperuniform dielectric networks via heat induced shrinkage reveals a bandgap at telecom wavelengths; Dataset

Fabrication of hyperuniform dielectric networks via heat induced shrinkage reveals a bandgap at telecom wavelengths; Dataset

A quantum key distribution testbed using a plug&amp;play telecom-wavelength single-photon source

Deterministic solid state quantum light sources are considered key building blocks for future communication networks. While several proof-of-principle experiments of quantum communication using such sources have been realized, most of them required large setups—often involving liquid helium infrastructure or bulky closed-cycle cryotechnology. In this work, we report on the first quantum key distribution (QKD) testbed using a compact benchtop quantum dot single-photon source operating at telecom wavelengths. The plug&amp;play device emits single-photon pulses at O-band wavelengths (1321 nm) and is based on a directly fiber-pigtailed deterministically fabricated quantum dot device integrated into a compact Stirling cryocooler. The Stirling is housed in a 19 in. rack module including all accessories required for stand-alone operation. Implemented in a simple QKD testbed emulating the BB84 protocol with polarization coding, we achieve an multiphoton suppression of g(2)(0)=0.10±0.01 and a raw key rate of up to (4.72 ± 0.13) kHz using an external pump laser. In this setting, we further evaluate the performance of our source in terms of the quantum bit error ratios, secure key rates, and tolerable losses expected in full implementations of QKD while accounting for finite key size effects. Furthermore, we investigate the optimal settings for a two-dimensional temporal acceptance window applied on the receiver side, resulting in predicted tolerable losses up to 23.19 dB. Not least, we compare our results with previous proof-of-concept QKD experiments using quantum dot single-photon sources. Our study represents an important step forward in the development of fiber-based quantum-secured communication networks exploiting sub-Poissonian quantum light sources.

Review of integrated magneto-optical isolators with rare-earth iron garnets for polarization diverse and magnet-free isolation in silicon photonics [Invited

Passive optical isolators are needed in silicon photonics but unavailable due to challenges in rare-earth iron garnet processing and integration. Material challenges include incompatibility with silicon and high annealing temperatures, and design challenges include a need for polarization diversity and a preference for no external magnetic bias. These challenges have restricted optical isolation to discrete modules that require physical pick and place of bulk garnet pieces. This review presents developments in the processing of magneto-optical garnets on Si and the enhancement of their Faraday rotation that enables small footprint isolators on silicon waveguide structures. For example, seedlayers and/or new garnet compositions have enabled monolithic Si integration, and in some cases, hybrid integration of garnet-on-garnet or transfer-printed garnet nanosheets enable reduced on-chip thermal processing. Integrated isolators that utilize non-reciprocal phase shift (NRPS) or non-reciprocal mode conversion (NRMC) have been demonstrated to have isolation ratios up to 30 dB, insertion loss as low as 9 dB, polarization diversity and magnet-free operation in the desired telecommunication wavelengths. The advances in materials, processing techniques, and isolator designs shown here will pave the way for on-chip isolators and novel multi-lane photonic architectures.

Sigmoid Type Neuromorphic Activation Function Based on Saturable Absorption Behavior of Graphene/PMMA Composite for Intensity Modulation of Surface Plasmon Polariton Signals

For an optical technology to be feasible as a substitution of electronics one for neuromorphic applications, it is required the waveguides in which are capable of confining and directing light signals in much smaller dimensions than the operating wavelength of the light, i.e., subwavelength optical components must be realized. Hybrid nature of surface plasmon polariton addresses the problem with the diffraction limit of regular photonic components. Here, the authors present a two-dimensional numerical simulation of a passive photonic element based on a saturable absorber material as a hardware base analogy to the biological activation function existed at the cell body of neurons. They demonstrate that at telecom wavelengths, a highly confined SPP mode can be modulated in a nonlinear fashion by considering the carrier dynamics of graphene/PMMA polymeric composite as a two-level system. The hardware base sigmoid type nonlinear activation function derived from this study further characterized; and the parameters which appeared to be effective on the performance of the structure, such as saturation intensity, modulation depth, and thickness of the synaptic part as a Fabry–Pérot structure, have been studied.

Comparison and analysis of phase change materials-based reconfigurable silicon photonic directional couplers

The unique optical properties of phase change materials (PCMs) can be exploited to develop efficient reconfigurable photonic devices. Here, we design, model, and compare the performance of programmable 1 × 2 optical couplers based on: Ge2Sb2Te5, Ge2Sb2Se4Te1, Sb2Se3, and Sb2S3 PCMs. Once programmed, these devices are passive, which can reduce the overall energy consumed compared to thermo-optic or electro-optic reconfigurable devices. Of all the PCMs studied, our ellipsometry refractive index measurements show that Sb2S3 has the lowest absorption in the telecommunications wavelength band. Moreover, Sb2S3 -based couplers show the best overall performance, with the lowest insertion losses in both the amorphous and crystalline states. We show that by growth crystallization tuning at least four different coupling ratios can be reliably programmed into the Sb2S3 directional couplers. We used this effect to design a 2-bit tuneable Sb2S3 directional coupler with a dynamic range close to 32 dB. The bit-depth of the coupler appears to be limited by the crystallization stochasticity.