Telecommunication Wavelengths Research Articles

Implementation of a Quantum Memory Protocol Based on the Revival of Silenced Echo in Orthogonal Geometry at the Telecommunication Wavelength

An optical quantum memory protocol has been implemented on the basis of the revival of silenced echo at the telecommunication wavelength for signal light fields with a small number of photons. To this end, a long-lived (>1 s) absorption line has been initialized and the orthogonal geometry of the propagation of the signal and rephasing fields has been chosen. An efficiency of revival of (17 ± 1)% has been reached for the orthogonal polarization components of a signal pulse at a storage time of 60 μs. The input pulse contains ~38 photons on average, the revived echo signal includes ~6 photons, and the signal-to-noise ratio is 1.3.

Resonant silicon waveguide with strong transverse electric field rotation for magnetic-field-induced non-reciprocity.

Non-reciprocal devices suitable for on-chip implementation are of high importance in modern photonics. In most cases, non-reciprocity is caused by the magneto-optical effect. At the same time, the external magnetic field is convenient to apply in the normal direction to the chip plane, which leads to Voigt geometry and modes with in-plane transverse rotations of the electric field. Here, we propose two resonant magnetic material-free silicon waveguides supporting such modes. The first one is a rectangular waveguide with air holes inside, whose modes have higher rotations at the telecom wavelength, but the silicon thickness is non-standard. The second one is based on a 220-nm-thick silicon waveguide compatible with commercially available silicon-on-insulator wafers. We also propose the scheme of an optical isolator based on a Mach-Zehnder interferometer with a rotation elements delay in its arms.

Hyperfine states of erbium doped yttrium orthosilicate for long-coherence-time quantum memories

Due to their unique optical transition at 1.5 μm, erbium-doped crystals are one of the best candidates for the realization of quantum memories at telecommunication wavelengths. While the hyperfine states of erbium doped yttrium orthosilicate hold the possibility of achieving ultra-long coherence times for a quantum memory, the complexity of their hyperfine structures leads to inaccurate theoretical prediction, thus hindering the extending of the coherence times. Here, we report a set of spin-Hamiltonian parameters with sufficient predictive power on the coherence times of the erbium hyperfine states. Our calculation simultaneously takes into account both the data measured in Electron-Paramagnetic-Resonance and Raman-heterodyne experiments. Based on the new parameters, the coherence properties of the hyperfine ground states are discussed. At zero applied magnetic field, all hyperfine transitions between the ground states are transitions with zero-first-order-Zeeman (ZEFOZ) effect, manifesting both long coherence times and strong transition strengths. By turning up the magnetic field, it is possible to further extend the coherence times to the scale of hours. The long coherence times at ZEFOZ transitions can be an important step forward in creating long-lived telecommunication quantum memories.

Entangling microwaves with light.

Quantum entanglement is a key resource in currently developed quantum technologies. Sharing this fragile property between superconducting microwave circuits and optical or atomic systems would enable new functionalities, but this has been hindered by an energy scale mismatch of >104 and the resulting mutually imposed loss and noise. In this work, we created and verified entanglement between microwave and optical fields in a millikelvin environment. Using an optically pulsed superconducting electro-optical device, we show entanglement between propagating microwave and optical fields in the continuous variable domain. This achievement not only paves the way for entanglement between superconducting circuits and telecom wavelength light, but also has wide-ranging implications for hybrid quantum networks in the context of modularization, scaling, sensing, and cross-platform verification.

Hundredfold increase of stimulated Brillouin-scattering bandwidth in whispering-gallery mode resonators

Backward stimulated Brillouin scattering (SBS) is widely exploited for various applications in optics and optoelectronics. It typically features a narrow gain bandwidth of a few tens of megahertz in fluoride crystals. Here we report a hundredfold increase of SBS bandwidth in whispering-gallery mode resonators. The crystalline orientation results in a large variation of the acoustic phase velocity upon propagation along the periphery, from which a broad Brillouin gain is formed. Over 2.5 GHz wide Brillouin gain profile is theoretically found and experimentally validated. SBS phenomena with Brillouin shift frequencies ranging from 11.73 to 14.47 GHz in ultrahigh Q Z-cut magnesium fluoride cavities pumped at the telecommunication wavelength are demonstrated. Furthermore, the Brillouin–Kerr comb in this device is demonstrated. Over 400 comb lines spanning across a spectral window of 120 nm are observed. Our finding paves a new way for tailoring and harnessing the Brillouin gain in crystals.

Determination of nonlinear refractive index of large area monolayer MoS2 at telecommunication wavelength using time-resolved Z-scan technique

The nonlinear refractive index of large area monolayer molybdenum disulfide (MoS2) thin film at the 1,550[Formula: see text]nm wavelength band is determined using time-resolved z-scan technique. MoS2 exhibits positive nonlinear phase shift with a large nonlinear refractive index, [Formula: see text] value of [Formula: see text]. The obtained value is similar to the [Formula: see text] value of monolayer MoS2 film measured at 2.0[Formula: see text][Formula: see text]m, and is approximately five and seven orders of magnitude larger than silicon and common bulk dielectrics. The large [Formula: see text] indicates that MoS2 can be used as nonlinear refractive 2D material for photonics applications operating in the 1,550[Formula: see text]nm optical telecommunications wavelength band.

Tunable topological phase transition in the telecommunication wavelength

Recent progress in the Valley Hall insulator has demonstrated a nontrivial topology property due to the distinct valley index in 2D semiconductor systems. In this work, we propose a highly tunable topological phase transition based on valley photonic crystals. The topological phase transition is realized by the inversion symmetry broken due to the refractive index change of structures consisting of optical phase change material (OPCM) with thermal excitation of different sites in a honeycomb lattice structure. Besides, simulations of light propagation at sharp corners and pseudo-spin photon coupling are conducted to quantitatively examine the topological protection. Compared with other electro-optical materials based on reconfigurable topological photonics, a wider bandwidth and greater tunability of both central bandgap frequency and topological phase transition can happen in the proposed scheme. Our platform has great potential in practical applications in lasing, light sensing, and high-contrast tunable optical filters.

Enhanced light absorption in Tamm metasurface with a bound state in the continuum

We consider light absorption in a germanium grating placed on top of photonic-crystalline substrate. Such a system supports an optical Tamm state decoupled from the continuous spectrum with its frequency within the photonic band gap. We have demonstrated that application of the Tamm state makes in possible to engineer extremely narrow absorber which provides a 100 % absorption in a semiconductor grating in the critical coupling regime. The proposed design may be used at both normal and oblique incidence at the telecom wavelength.

Linear and nonlinear characterization of a broadband integrated Si-rich silicon nitride racetrack ring resonator for on-chip applications.

We demonstrate the linear and nonlinear characterization of a plasma-enhanced chemical vapor deposited silicon-rich silicon nitride (SRSN) racetrack ring resonator for on-chip applications within the telecommunication wavelength range. The SRSN waveguide parameters are optimized by employing the refractive index profile measured by ellipsometry to achieve flat dispersion in the telecom band. Furthermore, we measure the thermo-optic coefficient of the micro-resonator by analyzing the temperature-dependent transmission spectra and assess it to be 3.2825×10-5 ∘ C -1. Additionally, we study power-dependent transmission spectra to investigate the effect of local heating and nonlinear absorption. The power-dependent transmission spectra exhibit a blueshifting of the resonance peak in the visible and near-IR regions, which indicates the presence of nonlinear losses in that range. The power-dependent transmission spectra almost remain unchanged in the telecom band, revealing the absence of nonlinear losses and excellent thermal stability in that wavelength range. Our experimental results reveal that the SRSN-based structure can be employed potentially to realize linear and nonlinear applications in the telecom band.

Integrated photon-pair source with monolithic piezoelectric frequency tunability

This work demonstrates the capabilities of an entangled photon-pair source at telecom wavelengths, based on a photonic integrated Si$_3$N$_4$ microresonator with monolithically integrated piezoelectric frequency tuning. Previously, frequency tuning of photon-pairs generated by microresonators has only been demonstrated using thermal control, however these have limited actuation bandwidth, and are not compatible with cryogenic environments. Here, the frequency-tunable photon-pair generation capabilities of a Si$_3$N$_4$ microresonator with a monolithically integrated aluminium nitride layer are shown. Fast-frequency locking of the microresonator to an external laser is demonstrated, with a resulting locking bandwidth orders of magnitude larger than reported previously using thermal locking. These abilities will have direct application in future schemes which interface such sources with quantum memories based on e.g. trapped-ion or rare-earth ion schemes.

Integrated optical beam steering device using switchable nanoantennas and a reflective metalens

In this paper, an integrated optical device is proposed in which a reflective meta-lens and five switchable nano-antennas are combined to provide optical beam steering at the standard telecommunication wavelength of 1550 nm. For this purpose, a graphene-based switchable power divider is designed and integrated with nano-antennas to control the flow of the light entering the device. To achieve a higher angular accuracy in the radiated beams, a new algorithm is proposed and utilized to optimize the location of feeding nano-antennas in accordance with the reflective meta-lens. In order to achieve a minimum fluctuation in the light intensity when the beams are rotated in the space, an algorithm is developed to select optimum unit cells for the engineered meta-lens. The whole device is numerically analyzed using Electromagnetic full-wave simulations illustrating an optical beam steering with high accuracy (better than 1 degree) in the beam direction, and a low variation (less than 1 dB) in the radiated light intensity. The proposed integrated device can be used for many applications such as inter- and intra-chip optical interconnects, optical wireless communication systems, and advanced integrated LIDARs.

Perspective: Nanophotonic electro-optics enabling THz bandwidths, exceptional modulation and energy efficiencies, and compact device footprints

The growth of integrated photonics has driven the need for efficient, high-bandwidth electrical-to-optical (EO) signal conversion over a broad range of frequencies (MHz–THz), together with efficient, high bandwidth photodetection. Efficient signal conversion is needed for applications including fiber/wireless telecom, data centers, sensing/imaging, metrology/spectroscopy, autonomous vehicle platforms, etc., as well as cryogenic supercomputing/quantum computing. Diverse applications require the ability to function over a wide range of environmental conditions (e.g., temperatures from <4 to >400 K). Active photonic device footprints are being scaled toward nanoscopic dimensions for size compatibility with electronic elements. Nanophotonic devices increase optical and RF field confinement via small feature sizes, increasing field intensities by many orders of magnitude, enabling high-performance Pockels effect materials to be ultimately utilized to their maximum potential (e.g., in-device voltage-length performance ≤0.005 V mm). Organic materials have recently exhibited significant improvements in performance driven by theory-guided design, with realized macroscopic electro-optic activity (r33) exceeding 1000 pm/V at telecom wavelengths. Hybrid organic/semiconductor nanophotonic integration has propelled the development of new organic synthesis, processing, and design methodologies to capture this high performance and has improved understanding of the spatial distribution of the order of poled materials under confinement and the effects of metal/semiconductor-organic interfaces on device performance. Covalent coupling, whether from in situ crosslinking or sequential synthesis, also provides a thermally and photochemically stable alternative to thermoplastic EO polymers. The alternative processing techniques will reduce the attenuation of r33 values observed in silicon organic hybrid and plasmonic organic hybrid devices arising from chromophore-electrode electrostatic interactions and material conductance at poling temperatures. The focus of this perspective is on materials, with an emphasis on the need to consider the interrelationship between hybrid device architectures and materials.

All-optical logic gates using E-shaped silicon waveguides at 1.55 μm

Owing to the advanced fabrication technology of silicon, silicon waveguides are particularly attractive for implementing all-optical signal processing devices and switches. Therefore, in this paper, a silicon-on-silica waveguide that consists of four slots arranged in the shape of letter E is proposed to be employed as the building block for simulating fundamental all-optical logic gates (AOLGs), including XOR, AND, OR, NOT, NOR, NAND, and XNOR, at 1.55 μm telecommunications wavelength. The operation concept of these logic gates relies on the constructive and destructive interference that results from the phase difference induced by optical beams that are incident on the E-shaped waveguide. The performance of the target logic gates is assessed against the contrast ratio (CR) metric. Moreover, the dependence of the spectral transmission on the device's key operating parameters is investigated and assessed. Compared to other reported designs, the results obtained by conducting simulations using the finite-difference-time-domain in lumerical commercial software show that the proposed waveguide can operate at a higher speed of 80 Gb/s and attain higher CRs of 36, 39, 35.5, 28.8, 30, 38, and 36.7 dB for logic XOR, AND, OR, NOT, NOR, NAND, and XNOR, respectively. This suggests that by using the proposed scheme, AOLGs could be realized more feasibly with greater performance and faster operation toward satisfying the present and future needs of light wave circuits and systems.

Nonlinear optical properties of PVD-grown Cr2Te3 film and its nonlinear switching application

Recently, two-dimensional (2D) nanomaterials have been investigated extensively in the field of nonlinear photonics. Cr2Te3, which is one of the 2D transition metal chalcogenides, has garnered attention in the field of spintronics and optoelectronics because of its fascinating magnetic and optical properties. Despite its potential in optoelectronics, Cr2Te3 has rarely been studied in the field of nonlinear photonics. This study investigates the nonlinear optical responses of nanoscale-layered Cr2Te3 films grown by physical vapor deposition at telecommunication wavelengths. A large nonlinear absorption coefficient of –(1.43 ± 0.06) × 105 cm/GW and a nonlinear refractive index of –1.22 ± 0.04 cm2/GW at 1560 nm obtained through Z-scan measurements indicate that the Cr2Te3 film shows saturable absorption and self-defocusing properties at telecommunication wavelengths. Density functional theory calculation show that Cr2Te3 is suitable for broadband optical device. The potential of the nanoscale-layered Cr2Te3 film as a base medium for a nonlinear optical switch was evaluated by fabricating a saturable absorption mirror (SAM). Stable Q-switched pulses with a maximum repetition rate of 33.35 kHz and minimum temporal width of 2.62 μs were readily achieved from a fiber laser cavity incorporating the SAM.

Optically enhanced single- and multi-stacked 1.55 μm InAs/InAlGaAs/InP quantum dots for laser applications

For the development of InAs/InP quantum dot (QD) lasers for 1.55 μm telecom wavelength, there are two main challenges: (1) morphological preference for quantum dashes over QDs, and (2) generally poor size uniformity of QDs (dashes). This study addresses the issues, in synchronous, by demonstrating the improved optical properties of 1.55 μm InAs/InP QDs at room temperature with excellent reproducibility. A high-density (∼4 × 1010 cm−2) dot-like morphology was initially attained via adjusting the growth parameters, albeit with a large full-width at half-maximum (FWHM) of ∼80 meV and a peak position of a wavelength longer than 1.55 μm. For improvement, the indium-flush technique was employed, which enhanced the uniformity of InAs QDs and substantially lowered the FWHM of five (single) stacked QDs to 50.9 meV (47.9 meV). This technique also blue-shifted the emission peak to 1530.2 nm (1522 nm). The InAs/InP QDs presented are appropriate for the fabrication of high-performance 1.55 μm lasers on InP (001) and, potentially, emerging light sources on the important Si (001).

Ultra-high birefringence with tuneable double zero chromatic dispersion-PCF: a theoretical analysis

This work presents photonic crystal fibres made up of four hexagonal shape of four rings. Four structures have been designed and configured. The structures show improvement in optical properties consecutively to achieve the optimum configuration. The full vectorial finite-element method is adopted for this work. COMSOL Multiphysics is used for the simulation. The results show a birefringence of 1.308 × 10−2 at 1.55 µm and tuneable double zero dispersion at wavelengths of 0.99 µm and 1.8 µm for x-polarisation mode. Also, the chromatic dispersion of − 24.062 ps/km nm and nonlinear coefficient of 30.32 W−1 km−1 are obtained at a telecommunication wavelength of 1.55 µm. The proposed photonic crystal fibre can be beneficial in nonlinear and supercontinuum applications since photonic crystal fibres of double zero dispersion demonstrate higher power spectral densities than single zero dispersion.

Semiconductor–Semimetal Transition‐Driven Photocurrent Spurt and Infrared Band Response in Lead Iodide at High Pressure

AbstractTopological semimetals have attracted flourishing interest as promising candidates for their unique advantages in achieving highly sensitive, low‐energy photodetection with ultrafast operation. Although various semimetals have been explored recently, new semimetals are still being pursued for high‐responsivity photodetectors with broadband response. Here, a pressure‐induced semiconductor–semimetal transition is observed in two‐dimensional wide‐band semiconducting lead iodide (PbI2). The photocurrent under visible light shows abrupt increases by two orders of magnitude at ≈25 GPa, where the crystalline structure transforms from the Pnma to I4/MMM phase. Meanwhile, the responding band expands from visible light to at least the telecom wavelength 1550 nm. The high‐pressure absorption spectra of PbI2 suggest that the electrical band is closed at the transition point, while the charge transport shows that the sample is still not metallic. Through first‐principles calculations, the photocurrent spurt and infrared band response are attributed to the appearance of a semimetal phase at high pressure, which well explains the nonmetallic transport. The prominent drop in lifetime to a few picoseconds in ultrafast spectroscopy under pressure further confirms the semiconductor–semimetal transition in PbI2. Pressure‐induced semimetallization opens a new strategy for designing a high‐performance photodetector with broadband response.

Waveguide‐Integrated Two‐Dimensional Material Photodetectors in Thin‐Film Lithium Niobate

Thin‐film lithium niobate on insulator (LNOI) is a promising platform for optical communications, microwave photonics, and quantum technologies. While many high‐performance devices like electro‐optic modulators and frequency comb sources have been achieved on LNOI platform, it remains challenging to realize photodetectors (PDs) on LNOI platform using simple and low‐cost fabrication techniques. 2D materials are excellent candidates to achieve photodetection since they feature strong light‐matter interaction, excellent mechanical flexibility, and potential large‐scale complementary metal–oxide–semiconductor‐compatible fabrication. Herein, this demand is addressed using an LNOI‐2D material platform, and two types of high‐performance LNOI waveguide‐integrated 2D material PDs, namely graphene and tellurium (Te), are addressed. Specifically, the LNOI‐graphene PDs feature broadband operations at telecom and visible wavelengths, high normalized photocurrent‐to‐dark current ratios up to 3 × 106 W−1, and large 3‐dB photoelectric bandwidths of ≈40 GHz, simultaneously. The LNOI‐Te PDs on the other hand provide ultrahigh responsivities of 7 A W−1 under 0.5 V bias for telecom signals while supporting GHz frequency responses. The results show that the versatile properties of 2D materials and their excellent compatibility with LNOI waveguides could provide important low‐cost solutions for system operating point monitoring and high‐speed photoelectric conversion in future LNOI photonic integrated circuits.

Active control of surface plasmon polaritons with phase change materials

Active control of surface plasmon polaritons (SPPs) is highly desired for nanophotonics. Here we employ a phase change material Ge2Sb2Te5 (GST) to actively manipulate the propagating direction of SPPs at the telecom wavelength. By utilizing the phase transition-induced refractive index change of GST, coupled with interference effects, a nanoantenna pair containing GST is designed to realize switchable one-way launching of SPPs. Devices based on the nanoantenna pairs are proposed to manipulate SPPs, including the direction tuning of SPP beams, switchable SPP focusing, and switchable cosine–Gauss SPP beam generating. Our design can be employed in compact optical circuits and photonics integration.

Visible-Light Integrated PIN Avalanche Photodetectors With High Responsivity and Bandwidth

Integrated photodetectors are key building blocks of scalable photonics platforms. Many recent improvements have been made for integrated avalanche photodetectors (APDs) operating at infrared telecommunications wavelengths, but their visible-spectrum counterparts remain relatively unexplored. Here, we demonstrate PIN-doped silicon APDs for visible light detection, monolithically integrated with a silicon nitride photonics circuit via end-fire coupling. An in-depth study of multiple PIN doping profiles reveals different optimal designs based on the desired operating regimes. At −49 dBm input power, they show 0.25 A/W (0.8 A/W) responsivity at reverse bias as low as 0.5 V (5.5 V), with corresponding dark current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 3 pA (50 pA). We also report fast RF response with an optimal 3 dB bandwidth of 11 GHz and gain-bandwidth product of 142 GHz, with all devices yielding open eye diagrams at 25 Gbps or above. Coupled with CMOS-compatible fabrication, our APDs will enable scalable photonics applications in sensing, communications, and quantum technologies at visible wavelengths.