Telecommunication Wavelengths Research Articles

An optical transition-edge sensor with high energy resolution

Optical transition-edge sensors (TESs) have shown an energy resolution for resolving the number of incident photons at the telecommunication wavelength. However, a higher energy resolution is required for biological imaging and microscopic spectroscopy. In this study, we tested an Au/Ti (10/20 nm) bilayer TES that showed a high energy resolution. The high energy resolution was achieved by lowering the critical temperature to 115 mK, and the resultant energy resolution was 67 meV full width at half maximum (FWHM) at 0.8 eV. When was reduced to 115 mK, the theoretical resolution would scale up to 30 meV FWHM, considering that the typical energy resolution of optical TESs was 150 meV and was 300 mK. To investigate the difference between the theoretical expectation (30 meV) and the measured value (67 meV), we measured the complex impedance and current noise of the TES. We found excess Johnson noise in the TES; the excess Johnson noise term M was 1.5 at a bias point where the resistance was 10% of the normal resistance. For reference, the above mentioned TES was compared with a TES showing typical energy resolution (156 meV FWHM). We also discussed factors that improved or inhibited the energy resolution.

Quantum Defects: What Pairs with the Aryl Group When Bonding to the sp2 Carbon Lattice of Single-Wall Carbon Nanotubes?

Aryl diazonium reactions are widely used to covalently modify graphitic electrodes and low-dimensional carbon materials, including the recent creation of organic color centers (OCCs) on single-wall carbon nanotube semiconductors. However, due to the experimental difficulties in resolving small functional groups over extensive carbon lattices, a basic question until now remains unanswered: what group, if any, is pairing with the aryl sp3 defect when breaking a C═C bond on the sp2 carbon lattice? Here, we show that water plays an unexpected role in completing the diazonium reaction with carbon nanotubes involving chlorosulfonic acid, acting as a nucleophilic agent that contributes -OH as the pairing group. By simply replacing water with other nucleophilic solvents, we find it is possible to create OCCs that feature an entirely new series of pairing groups, including -OCH3, -OC2H5, -OC3H7, -i-OC3H7, and -NH2, which allows us to systematically tailor the defect pairs and the optical properties of the resulting color centers. Enabled by these pairing groups, we further achieved the synthesis of OCCs with sterically bulky pairs that exhibit high purity defect photoluminescence effectively covering both the second near-infrared window and the telecom wavelengths. Our studies further suggest that these diazonium reactions proceed through the formation of carbocations in chlorosulfonic acid, rather than a radical mechanism that typically occurs in aqueous solutions. These findings uncover the unknown half of the sp3 defect pairs and provide a synthetic approach to control these defect color centers for quantum information, imaging, and sensing.

Storage and analysis of light-matter entanglement in a fiber-integrated system.

The deployment of a full-fledged quantum internet poses the challenge of finding adequate building blocks for entanglement distribution between remote quantum nodes. A practical system would combine propagation in optical fibers with quantum memories for light, leveraging on the existing communication network while featuring the scalability required to extend to network sizes. Here, we demonstrate a fiber-integrated quantum memory entangled with a photon at telecommunication wavelength. The storage device is based on a fiber-pigtailed laser-written waveguide in a rare earth-doped solid and allows an all-fiber stable addressing of the memory. The analysis of the entanglement is performed using fiber-based interferometers. Our results feature orders-of-magnitude advances in terms of storage time and efficiency for integrated storage of light-matter entanglement and constitute a substantial step forward toward quantum networks using integrated devices.

Fiber optical parametric oscillator made of soft glass

Fiber optical parametric oscillators (FOPOs) are compact optical sources of coherent and broadly tunable light compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band, but the strong material absorption of silica glass at wavelengths >2 µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two proof-of-concept FOPOs are presented, one driven by pure parametric gain leading to wavelength-tunable Stokes emission within the range 2.088-2.139 µm, and the other driven by Raman-assisted parametric gain leading to Stokes emission within the range 2.023-2.048 µm. This demonstration is a promising first step toward the development of fully fiberized MIR light sources.

(Invited) Light-Emitting Devices Based on Defect-Enhanced Group-IV Nanostructures

Combining Si-based integrated optics with Si-based microelectronics is crucial for next-generation applications ranging from data transfer on short distances to sensing and, potentially, to quantum cryptography at telecom wavelengths. However, Si's intrinsically poor light-emitting properties, i.e., its indirect energy bandgap, inhibit a straightforward implementation of telecom devices such as light-emitting diodes and lasers operating at room temperature.We argue that adding Ge heterostructures, nanostructures, intentionally-induced defects, and defects within nanostructures to the Si platform can be a viable way to overcome the limitations of Si as a light-emitting material [1]. Significant progress for light-emission from group-IV nanostructures can be achieved by intentionally incorporating extended point defects inside the QDs upon in-situ low-energy ion implantation [2],[3]. This work discusses the superior light-emission properties from such defect-enhanced quantum dots (DEQDs) and our present understanding of their structural formation and light-emission mechanisms [4], indicating that optically direct recombination paths play a role in room-temperature light emission.As compared to other group-IV systems with pronounced optical emission, contact doping and hence fabrication of electrically driven devices is relatively straightforward in this nanosystem since DEQDs are embedded into a defect-free Si matrix [5],[6]. We show that useful electrically driven devices, such as light-emitting diodes (LEDs), can be fabricated employing optically active DEQD material. These LEDs exhibit exceptional temperature stability of their light-emission properties even up to 100°C, unprecedented for purely group-IV-based optoelectronic devices [7]. We discuss the role of vital parameters, such as the temperature stability of the structural properties [8],[9], the scalability of the light-emission with the nanostructure density [6], and passivation schemes to further improve the optical properties [8],[10]. Additionally, we elaborate on schemes for advanced layouts for electrically-pumped devices.References[1 ] M. Brehm, Silicon Photonics IV, 67-103, Silicon Photonics IV: Innovative Frontiers, edited by David J. Lockwood and Lorenzo Pavesi, Springer series Topics in Applied Physics (2021).[2] M. Grydlik et al., ACS Photonics 3, 298–303 (2016).[3] M. Grydlik et al., Nano Lett. 16, 6802–6807 (2016).[4] F. Murphy-Armando et al., Phys. Rev. B 103, 085310 (2021).[5] M. Brehm and M. Grydlik, Nanotechnology 28, 392001 (2017).[6] H. Groiss et al., Semicond. Sci. Technol. 32, 02LT01 (2017).[7] P. Rauter et al., ACS Photonics 5, 431-438 (2018).[8] L. Spindlberger et al., Crystals 10, 351 (2020).[9] L. Spindlberger et al., Physica Status Solidi (a) 216, 1900307 (2019).[10] L. Spindlberger et al., Appl. Phys. Lett. 118, 083104 (2021).

Mirror symmetric on-chip frequency circulation of light

Integrated circulators and isolators are important for developing on-chip optical technologies such as laser cavities, communication systems and quantum information processors. These devices seem to inherently require mirror symmetry breaking to separate backwards from forwards propagation, and thus existing implementations rely on magnetic materials or interactions driven by propagating waves. By contrast to past works, we exhibit a mirror-symmetric non-reciprocal device that comprises three coupled photonic resonators implemented in thin-film lithium niobate. Applying radiofrequency modulation, we drive conversion between the frequency eigenmodes of this system. We measure nearly 40 dB of isolation for approximately 75 mW of radiofrequency power near 1,550 nm. We simultaneously generate non-reciprocal conversion between all of the eigenmodes to demonstrate circulation. Mirror-symmetric circulation simplifies the fabrication and operation of non-reciprocal integrated devices. Finally, we consider applications of such on-chip isolators and circulators, such as full-duplex isolation within a single waveguide. Researchers demonstrate an integrated mirror-symmetric non-reciprocal device enabled by three coupled photonic resonators. Nearly 40 dB of isolation is achieved at telecommunications wavelengths using 75 mW of radiofrequency power.

(Invited) Opportunities and Challenges for Quantum Emitters in One and Two Dimensional Materials

The last five years have witnessed dramatic advances in realization of quantum emitters (QEs) in one dimensional carbon nanotubes and two dimensional layered semiconductors. These novel QEs offer exciting opportunities for not only storing, processing and transducing of quantum information but also sensing physical phenomena beyond classical detection limits. Realization of these opportunities also present multiple challenges including: (1) realizing room temperature, telecommunication wavelength operation; (2) controlling fundamental as well as quantum optical properties such as QE emission wavelengths, linewidths, polarization, coherent times, single photon purity and indistinguishability; (3) deterministic placement and integration of QEs into photonic, plasmonic, and mangnonic platforms for quantum sensing and transduction applications. Here in this talk I will present recent efforts toward meeting these challenges. In 1D carbon nanotubes, we recently demonstrated that chemical binding configuration of covalent quantum defects can be controlled through the spin multiplicity of photoexcited intermediates. This enable us to control the emission wavelength of QEs by creating previously inaccessible chemical configuration. In 2D semiconductor, we have successfully created the telecommunication wavelength quantum emitters by local strain engineering of MoTe2. We have also realized chiral quantum emitters via exploit of magnetic proximity interaction between quantum emitters of WSe2 monolayer and localized magnetization crated in NiPS3 anti-ferromagnetic insulator by nanoscale stain engineering.

(Keynote) Van Der Waals Active Metasurfaces and Heterostructures for Phase Modulation and Polarization Conversion

A grand challenge for nanophotonics is the realization of tunable metasurfaces enabling active control of the key constitutive properties of light – amplitude, phase, wavevector and polarization. Active metasurfaces that enable dynamic modulation of reflection amplitude, phase and polarization have been recently explored using several active materials and modulation phenomena, including carrier index in plasmonic ENZ structures, reorientation of liquid crystal molecules, electrooptic effects in quantum well heterostructures and index change in phase change materials. The rapid advances in understanding of exciton resonances in layered van der Waals materials has now stimulated thinking about active metasurfaces that exploit excitonic modulation phenomena to enable ‘van der Waals active metasurfaces’. As one example, I will describe recent advances in electrically reconfigurable polarization conversion across the telecommunication wavelength range in van der Waals layered materials, integrated in a Fabry-Pérot cavity. The large electrical tunability of the excitonic birefringence in tri-layer black phosphorus enables spectrally broadband polarization conversion over nearly half the Poincaré sphere. We observe both linear to circular and cross-polarization conversion with voltage, demonstrating dynamic access to polarization diversity. As a second example, we discuss the observed large gate tunability of the complex refractive index in monolayer MoSe2 by Fermi level modulation near the A and B excitonic resonances for temperatures between 4 K to 150 K. By tuning the charge density, we observe both temperature and carrier dependent epsilon-near-zero response in the permittivity and transition from metallic to dielectric near the A exciton energy, and directly observe active phase modulation in monolayer MoSe2 gated heterostructures, whose voltage dependence is consistent with our complex index measurements. These results have broad implications for the use of monolayer transition metal dichalcogenides in active metasurfaces, and I also will give a general outlook for the wide range of possibilities for active van der Waals metasurfaces.

Super Broadband at Telecom Wavelengths From RE3+-Doped SiO2-Ta2O5 Glass Ceramics Planar Waveguides.

This paper reports on the preparation of Er3+/Yb3+/Tm3+, Er3+/Yb3+/Nd3+, and Er3+/Tm3+/Nd3+ triply doped and Er3+-doped SiO2-Ta2O5 glass ceramic nanocomposites and active planar waveguides by the sol–gel process using the dip-coating technique as deposition method. The investigation of their structural, morphological, and luminescent properties using XRD, AFM, and photoluminescence analysis, are reported here. The XRD results showed the presence of L-Ta2O5 nanocrystals dispersed in the SiO2-based amorphous host for all the nanocomposites and films. The rare earth ion (RE3+) doping concentration affected both the crystallinity, and the crystallite sizes of the Ta2O5 dispersed into SiO2-Ta2O5 nanocomposites and waveguides. AFM characterization revealed crack free and smooth surface roughness and differences in viscoelasticity on the Er3+-doped SiO2-Ta2O5 films surface, which allows the identification of Ta2O5 nanocrystals on the SiO2 amorphous host. The Er3+ doped and triply doped SiO2-Ta2O5 nanocomposites displayed broad- and super broadband NIR emissions with a FWHM up to 173 nm achieved in the telecom wavelengths. The lifetime of the 4I13/2 emitting level of the Er3+-doped SiO2-Ta2O5 waveguides is strongly dependent on Er3+ concentration and an emission quenching was negligible up to 0.81 mol%. The structural and luminescent investigations indicated that RE3+-doped SiO2-Ta2O5 glass ceramics are promising candidates for photonic applications in optical devices operating in wide wavelengths at the telecom bands.

Interplay of Leakage Radiation and Protection in Topological Photonic Crystal Cavities

AbstractThe introduction of topological concepts to the design of photonic crystal cavities holds great promise for applications in integrated photonics due to the prospect of topological protection. This study examines the signatures of topological light confinement in the leakage radiation of 2D topological photonic crystal cavities. The cavities are implemented in an all‐dielectric platform that features the photonic quantum spin Hall effect at telecom wavelengths and supports helical edge states that are weakly coupled to the radiation continuum. The modes of resonators scaling down to single point defects in the surrounding bulk lattice are characterized via spectral position and multipolar nature of the eigenstates. The mode profiles in real and momentum space are mapped using far‐field imaging and Fourier‐spectropolarimetry, revealing how certain properties of the cavity modes reflect on their origin in the topological bandstructure. This includes band‐inversion‐induced confinement and inverted scaling of mode spectra for trivial and topological defect cavities. Furthermore, hallmarks of topological protection in the loss rates are demonstrated, which are largely unaffected by cavity shape and size. The results constitute an important step toward the use of radiative topological cavities for on‐chip confinement of light, control of emitted wave fronts, and enhancement of light–matter interactions.

Picosecond pulsed squeezing in thin-film lithium niobate strip-loaded waveguides at telecommunication wavelengths

Achieving a high level of pulsed squeezing, in a platform which offers integration and stability, is a key requirement for continuous-variable quantum information processing. Typically highly squeezed states are achieved with narrow band optical cavities and bulk crystals, limiting scalability. Using single-pass parametric down conversion in an integrated optical device, we demonstrate quadrature squeezing of picosecond pulses in a thin-film lithium niobate strip-loaded waveguide. For on-chip peak powers of less than 0.3 W, we measure up to −0.33 ± 0.07 dB of squeezing with an inferred on-chip value of −1.7 ± 0.4 dB. This work highlights the potential of the strip-loaded waveguide platform for broadband squeezing applications and the development of photonic quantum technologies.

Semimetal hR6-CaSi2 thin film: A transparent contact for Si optoelectronics

Transparent conducting materials (TCMs) provide low cost and effective solution for the modern optoelectronics. However, simultaneous high electrical conductivity and optical transparency in the near-infrared (NIR) and middle-infrared (MIR) spectral ranges remain challenging. This study proposes thin film of the semimetal calcium disilicide (CaSi2) with hR6 polymorph modification to fill this niche. Investigation of the electrical, magnetoresistance and magnetic properties shed light on its semimetal behavior. CaSi2 film grown on Si substrate demonstrates competitive electrical and optical properties from the NIR to MIR ranges compared to commonly used TCMs reaching maximum transmittance of 47% at an important telecommunication wavelength of 1550 nm in addition to the low sheet resistance of 6.6 Ω/sq, which results in high TCM figure of merit of 0.2 Ω−1. Moreover, demonstrated for the first time partial optical transparency of the CaSi2 in the visible range could significantly heighten its applicability for Si-based optoelectronics.

Nanoscale light field imaging with graphene

Modern nano-optics and nanophotonics rely heavily on the precise formation of nanostructured light fields. Accurate and deterministic light field formation and characterization are indispensable for device operation as well as for revealing the underlying physical mechanisms involved. Despite a significant progress made in detection of scattered light with extremely high precision down to 1 nm resolution, there are only a limited number of techniques for direct subwavelength light mapping which do not rely on measurements of light scattering, fluorescence, or non-linear light conversion. Hence, techniques for direct conversion of light to electrical signals with precise and non-destructive imaging of nanoscale light would be of great benefit. Here, we report a nanoscale light field imaging approach based on photodetection with a p-n junction that is induced and moved inside a graphene probe by gate voltage, formed by a set of external electrodes. The spatial resolution of this electrical scanning technique is determined by p-n junction width, reaching ~ 20 nm. The developed approach is demonstrated with mapping the electric field distribution of a plasmonic slot-waveguide at telecom wavelengths. Our method provides a non-invasive nanoscale light field imaging that ensures extremely high spatial resolution and precision.

Five-layer planar hot-electron photodetectors at telecommunication wavelength of 1550 nm.

Cost-effective and high-responsivity photodetectors at a telecommunication wavelength of 1550 nm are highly desired in optical communication systems. Differing from conventional semiconductor-based photodetectors, several planar hot-electron photodetectors (HE PDs) that operate at 1550 nm have been reported. However, these devices were often comprised of many planar layers and exhibited relatively low responsivities. Herein, we propose a design of high-performance planar HE PDs consisting of five layers. Utilizing Fabry-Pérot (FP) resonance, the nearly perfect absorption of the proposed device can be achieved at the targeted wavelength of 1550 nm. Simulation results show that FP resonance orders are crucial for the optical absorption efficiencies, and then electrical responses. Analytical electrical calculations reveal that, benefiting from the strong absorption (>0.6) in the ultrathin Au layer with a thickness of 5 nm and the low Schottky barrier (0.5 eV) of Au-MoS2 contact, predicted responsivity of proposed HE PD at zero-order FP resonance is up to ∼10 mA/W. Our design provides a new approach to realize low-cost and efficient photodetection for optical communication technology.

Fabrication of Hyperuniform Dielectric Networks via Heat‐Induced Shrinkage Reveals a Bandgap at Telecom Wavelengths

AbstractRecent studies report photonic bandgaps (PBGs) in disordered hyperuniform network structures numerically and experimentally for high enough refractive index contrast. However, the smallest experimental central gap wavelength that one can realize experimentally is not close to the essential near‐infrared light spectrum with adverse consequences for specific applications and more advanced experimental studies. Indeed, standard direct laser writing (DLW) lithography does not allow fabrication at a much higher resolution. Here, the authors demonstrate heat‐treatment induced uniform shrinkage of the network's polymer template obtained by DLW to reach smaller feature sizes and subsequent silicon coating, resulting in a pronounced gap near telecom wavelengths.

Effective Passivation of InGaAs Nanowires for Telecommunication Wavelength Optoelectronics

AbstractCatalyst‐free InGaAs nanowires are promising building blocks for optoelectronic devices operating at telecommunication wavelengths. Despite progress, the applications of InGaAs nanowires remain limited due to their high density of surface states that degrade their optical properties. Here, InGaAs nanowires with superior optical properties are achieved by effectively suppressing their surface states with an InP passivation shell. Optimal InP shell growth conditions and thickness to maximize the minority carrier lifetime are identified. The photoluminescence intensity of these passivated InGaAs nanowires is up to three orders of magnitude higher than that of their bare counterparts. Moreover, a long minority carrier lifetime of up to ≈13 ns is measured with these passivated nanowires at room temperature. Optimal passivation of InGaAs nanowires with an emission wavelength of 1530 nm results in an ultra‐low surface recombination velocity of ≈280 cm s−1. In addition to the shell, the crystal structure of these nanowires plays an important role in the luminescence intensity. Combined cathodoluminescence mapping and high‐resolution transmission electron microscopy along the nanowires reveal significantly lower emission intensities in wurtzite predominant sections of the nanowires than zinc blende predominant ones.These insights on the optimal passivation of InGaAs provide directions for engineering high‐performance nanoscale‐devices in the telecommunication wavelength.

Viewpoint: Compact cryogenics for superconducting photon detectors

Abstract Superconducting detectors capable of registering single light quanta - single photons - are highly sought after in a host of emerging 21st century technologies [1]. Superconducting nanowire single-photon detectors (SNSPDs or SSPDs) [2] operating in the telecommunication wavelength range outperform conventional semiconductor detectors in the following metrics: dark count rate, system detection efficiency (SDE), photon counting rate and timing jitter [3, 4, 5, 6]. SNSPDs have been deployed in many important emerging photon-counting applications including single photon LiDAR [7, 8], quantum key distribution [9, 10], optical quantum computing [11], life sciences [12, 13], fibre sensing [14, 15], exoplanet spectroscopy [16] and free space optical communication [17].

Bias-free terahertz generation from a silicon-compatible photoconductive emitter operating at telecommunication wavelengths

We present a telecommunication-compatible bias-free photoconductive terahertz emitter composed of a bilayer InAs structure directly grown on a high-resistivity silicon substrate. The bilayer InAs structure includes p+-doped and undoped InAs layers, inducing a strong built-in electric field that enables terahertz generation without requiring any external bias voltage. A large-area plasmonic nanoantenna array is used to enhance and confine optical generation inside the photoconductive region with the highest built-in electric field, leading to the generation of a strong ultrafast photocurrent and broadband terahertz radiation. Thanks to a higher terahertz transmission through the silicon substrate and a shorter carrier lifetime in the InAs layers grown on silicon, higher signal-to-noise ratios are achieved at high terahertz frequencies compared with previously demonstrated bias-free terahertz emitters realized on GaAs. In addition to compatibility with silicon integrated optoelectronic platforms, the presented bias-free photoconductive emitter provides more than a 6 THz radiation bandwidth with more than 100 dB dynamic range when used in a terahertz time-domain spectroscopy system.

Zeeman and hyperfine interactions of a single Er3+167 ion in Si

Er-doped Si is a promising candidate for quantum information applications due to its telecom wavelength optical transition and its compatibility with Si nanofabrication technologies. Recent spectroscopic studies based on photoluminescence excitation have shown multiple well-defined lattice sites that Er occupies in Si. Here we report a measurement of the Zeeman and hyperfine tensors of a single $^{167}\mathrm{Er}^{3+}$ ion in Si. All the obtained tensors are highly anisotropic with the largest value principal axes aligning in nearly the same direction, and the trace of the lowest crystal field level $\mathbf{g}$-tensor is $17.78\ifmmode\pm\else\textpm\fi{}0.40$. The results indicate that this specific Er site is likely to be a distorted cubic site that exhibits monoclinic (${\mathrm{C}}_{1}$) symmetry. Finally, zero first-order-Zeeman fields are identified for this site and could be used to reduce decoherence of hyperfine spin states in future experiments.

Generation of highly pure single-photon state at telecommunication wavelength.

Telecommunication wavelength with well-developed optical communication technologies and low losses in the waveguide are advantageous for quantum applications. However, an experimental generation of non-classical states called non-Gaussian states at the telecommunication wavelength is still underdeveloped. Here, we generate highly-pure-single-photon states, one of the most primitive non-Gaussian states, by using a heralding scheme with an optical parametric oscillator and a superconducting nano-strip photon detector. The Wigner negativity, the indicator of non-classicality, of the generated single photon state is -0.228 ± 0.004, corresponded to 85.1 ± 0.7% of single photon and the best record of the minimum value at all wavelengths. The quantum-optics-technology we establish can be easily applied to the generation of various types of quantum states, opening up the possibility of continuous-variable-quantum-information processing at the telecommunication wavelength.