ABSTRACT Quantum photonic integrated circuits (QPICs) are a promising platform for scalable quantum technologies. A major outstanding challenge is the efficient interconnection of diverse quantum photonic components, where optical losses must remain below the ∼10% threshold required for advanced quantum applications. In this paper, the optical coupling between GaAs single‐photon sources and a low‐loss SiN interposer is investigated, where reliable high‐efficiency transitions have not yet been achieved. To address this, a fully numerical framework is introduced for the optimization of waveguide mode couplers that directly incorporates experimentally characterized fabrication variations critically impacting performance, including waveguide misalignment, width deviation, and sidewall roughness. Using this approach, low‐loss GaAs/SiN transitions are designed and experimentally demonstrated with reproducible coupling efficiencies of –0.43 dB ± 0.14 dB. These results establish a viable path toward low‐loss heterogeneous QPICs tailored to advanced quantum applications.

Next-generation scalable quantum photonic technologies operating at the single photon level rely on bringing together optimized quantum building blocks with minimal optical coupling losses. Achieving this necessitates the heterogeneous integration of different elements onto a single interposer chip. Integrated quantum emitters are key enablers for generating single photons, inducing quantum nonlinearities, and producing entanglement. In this work, we demonstrate the scalable integration of mature InGaAs quantum dots embedded in GaAs waveguides onto a low-loss SiN photonic platform, as evidenced by a high processing yield of 94.7

Quantum photonic integrated circuits (QPICs) offer a promising path toward scalable quantum technologies. QPICs rely on the integration of many quantum photonic components and interconnecting optical waveguides for generation, manipulation, and detection of single photons. A key challenge in QPICs is the management and minimization of optical losses, which is particularly critical for single-photon applications. In this paper, we investigate optical propagation losses in strip waveguides within suspended gallium arsenide (GaAs) platforms, which can directly host deterministic single-photon sources but suffer high scattering-related losses. We systematically analyze different scattering loss contributions by investigating four key waveguide perturbation types: sidewall roughness, top surface roughness, surface particles, and suspension tethers. Our approach combines rigorous 3D finite-difference time-domain (FDTD) simulations with experimental measurements to decouple and quantify individual contributions to the total propagation loss. We study two suspended GaAs platforms operating at different wavelengths: an established 930 nm platform and an emerging 1300 nm platform in the telecommunication O-band. Based on our findings, we identify the dominant scattering loss mechanisms and propose novel design-time guidelines and concrete strategies to reduce the main loss contributions by factors of 2.5-5. These improvements are crucial for enabling complex QPICs directly within the native platform of the single-photon source, supporting advances in integrated quantum technologies.

This paper presents a novel approach to addressing the issue of temperature-induced instability in an optical, single-sideband transmitter based on a micro-ring resonator (MRR) suitable for millimeter-wave (mmW) radio-over-fiber (RoF) communications. We propose utilizing the drop port of the MRR to provide a feedback signal to the closed-loop control (CLC) system. The latter serves to maintain the optimal alignment between the laser’s carrier and the MRR’s resonant wavelength, thus mitigating the adverse effects of chromatic-dispersion-induced power fading at the receiving end. Since the feedback information is extracted from the otherwise-wasted resonant energy at the drop port, the control system does not compromise the delicate optical signal at the through port. A CLC was synthesized, designed, and prototyped to provide real-time wavelength tuning of the heat-pump-controlled laser based on the feedback signal. Experimental evaluations demonstrate that the wavelength of the laser could be successfully locked to the MRR’s resonance with a wavelength dither of less than 0.004 nm (~491 MHz). This allowed us to limit the power-penalty deterioration to less than 2 dB for a RoF link with a 2.5-km standard telecommunication single-mode fiber (SMF), a modulation frequency of 37.8 GHz, and a carrier wavelength of 1563.97 nm (~191.820 THz). The proposed solution offers an alternative approach for the carrier and the MRR’s resonant wavelength interlocking without the need for complex photonics like thermo-optic or electro-optic structures to control the temperature or phase velocity, respectively.

A polarization beam splitter is an essential building block in integrated silicon photonics. We propose a polarization beam splitter design based on all-dielectric metamaterial cladding structures. Exceptionally high extinction ratio and low insertion loss were achieved in an ultra-wide bandwidth for both polarizations.

Photonic integrated circuits (PICs) play an important role in telecom and datacom applications. While in the past integrated transceivers were the main driver for technological advances in integrated photonics, nowadays PICs are emerging in various other fields, such as sensing, high-performance computing, quantum technologies, and more [1]. Various material platforms for PICs have been developed and successfully utilized, like III-V semiconductors (InP, GaAs), silicon-based materials (Si, Si 3 N 4 , SiO 2 ), lithium niobate (LiNbO 3 ), polymers and others.

In silicon and other photonic integrated circuit platforms many devices exhibit a large polarization dependency, therefore a polarization beam splitter (PBS) is an essential building block to split optical signal to transversal electric (TE) and transversal magnetic (TM) modes. In this paper we propose a concept of integrated silicon-based PBS exploiting unique properties of all dielectric metamaterial cladding to achieve a high extinction ratio (ER) and wide bandwidth (BW) polarization splitting characteristics. We start from a structure (PBS-1) based on a directional coupler with metamaterial cladding combined with a bent waveguide with metamaterial cladding at the outer side in the role of a TE polarizer at the Thru port of the device. To increase BW we propose the improved concept (PBS-2) - a metamaterial compact dual Mach-Zehnder Interferometer structure in combination with the TE polarizer. Numerical simulations reveal that an exceptionally high ER over 35 dB can be achieved in a BW of 263 nm with insertion loss (IL) below 1 dB in case of PBS-2. The designed device has a footprint of 82 µm. Measurement results reveal that an ER > 30 dB is achievable in a BW of at least 140 nm (limited by the laser tuning range).

In this paper we address the limiting effect of power fading (PF) in fiber optic communication links, due to the fiber's dispersive properties, and suggest a mitigation approach in intensity-modulated radio-over-fiber (RoF) applications. The proposed method is independent of the length of the optical transmission path. PF is mitigated by employing a simple integrated photonic structure, i.e., a single micro-ring resonator. The latter features a periodic notch-filter response, employed to suppress one of the sidebands in an optical double sideband (ODSB) modulation, reducing the PF of the received RF signal. The suppression ratio measured by the optical spectrum analyzer is 24 dB. In this way we succeeded in reducing the RF signal's power ripple at the receiving end to 3 dB. The proposed approach promises an economic yet effective solution to overcoming the PF in point-to-multipoint-topology optical networks.

Evanescent coupling between optical waveguides (WGs) in photonic integrated circuits (PICs) is the origin of unwanted optical cross-talk between adjacent WG structures. Employing an all-dielectric metamaterial cladding, consisting of two periodically exchanging dielectric materials, can potentially reduce the cross-talk between WGs, and thus, paves the way towards higher integration density. In this contribution we present the results of numerical simulations in the process of optimization of all-dielectric metamaterial cladding of silicon strip WGs to achieve the lowest possible gap width between WG cores that still satisfies the chosen reference cross-talk level (-30 dB at the distance of 2 mm). We also investigate how the performance of WGs with metamaterial cladding is affected, if the metamaterial cladding is present only in the spacing between WGs. We show that the gap width can be in best case decreased by 60 % representing a 45 % improvement in integration density for the case of 450 nm core width. We also investigate the wavelength dependence of effects and determine the usable wavelength range of optimized structures. Furthermore, we extend the study to account for fabrication variability of the sub-wavelength structures. A general trend is observed that structures with the lowest achieved gap width exhibit the narrowest wavelength range and the highest sensitivity to fabrication variability. However, we still demonstrate a sizable decrease in gap width of 37 % and a relatively wide usable wavelength range of > 75 nm when accounting for a feature size variation in the range of ± 5 nm.

All-dielectric metamaterials can reduce the cross-talk in PICs. We present a numerical study and optimization of metamaterial cladding in silicon technology resulting in decreased minimal gap between waveguides by 53 %.

We employed numerical simulations to optimize optical performance of different photonic devices: light in-coupling in ultra-thin CIGS solar cells, light out-coupling in bottom-emitting OLEDs and reduction of optical crosstalk in silicon photonic integrated circuits.

All-dielectric metamaterial structures in the role of the cladding of optical waveguides (WGs) in photonic integrated circuits (PICs) are investigated and optimized by means of numerical simulations to increase the integration density of PICs. First the role of the refractive index (material platform) on the effects of metamaterial cladding is studied. The results of a quantitative analysis show that only material platforms with a high refractive index contrast (such as existing Si or membrane InP platform) can noticeably benefit from optimized metamaterial cladding in terms of integration density. Furthermore, we perform a comprehensive optimization of the geometry of metamaterial claddings in Si platform to achieve the lowest possible gap width between cores of two adjacent WGs, while keeping the cross-talk bellow the targeted limit of −30 dB at the length of 2 mm. By doing this we can, for the first time, explicitly show how much the integration density of a PIC can be increased. We demonstrate that a metamaterial cladding can, in best case, reduce the gap width by 60% compared to Si WGs with normal cladding in case of 450 nm wide core. The wavelength dependence and sensitivity to fabrication variability are also studied, revealing a trade-off between the lowest possible integration density and usable wavelength range. We show that a sizable decrease in gap width at a wide usable wavelength range is possible, demonstrating that waveguides with metamaterial cladding have the potential to be utilized in future applications requiring a high integration density of PICs.

Dense integration of photonic components in photonic integrated circuits presents an important challenge. To reduce the cross talk between the components and thus enable denser integration, sub-wavelength all-dielectric metamaterial claddings have been investigated. Such structures can be realized by patterning subwavelength ridges around the core of the integrated waveguide. In this contribution we present the results of analytical calculations and numerical simulations of optical systems with slab and strip waveguides with all-dielectric metamaterial cladding and investigate the effects on evanescent field in the cladding. We show that a high refractive index contrast between the core and surrounding material is vital for the performance of all-dielectric metamaterial claddings. In particular we include silicon, silicon oxide and silicon nitride materials in our investigation.

By introducing all-dielectric metamaterials into optical waveguide structures, the cross-talk between waveguides can be reduced enabling denser integration in photonic integrated circuits. In this work we present results of Finite Element Method simulations to optimize the metamaterial-based cladding of the so called e-skid waveguides in order to achieve the longest possible coupling length. We show that e-skid waveguides can have significantly longer coupling length compared to strip waveguides due to reduced skin depth. We optimize the Si based metamaterial structure in terms of number of silicon ridges, period and fill factor of silicon and show that results strongly depend on the chosen surrounding material (air or silicon dioxide).