Dongpeng Kang

Efficient generation of correlated photon pairs through spontaneous four-wave mixing (SFWM) in silicon devices serves as a crucial resource for integrated quantum photonic technologies. Enhancing the intracavity field in high-quality-factor (Q) resonators enables energy-efficient photon-pair generation, with the photon-pair generation rate (PGR) scaling cubically with the Q factor. In this work, we demonstrate a high-brightness on-chip photon-pair source based on a racetrack resonator with a high Q factor of 1.75 × 10⁵, fabricated on a silicon-on-insulator (SOI) platform requiring only a single-etch process. By combining uniform multimode waveguides with optimized Euler bends, we suppress fundamental mode loss and minimize round-trip cavity dispersion, thereby improving both field enhancement and frequency matching for SFWM processes. With a continuous-wave pump of only 44.67 µW, we achieve an on-chip brightness of 1.54 GHz·mW⁻²·nm⁻¹. These results establish a fabrication-friendly and efficient photon-pair source architecture for integrated quantum photonic systems.

This paper investigates the performance of interference-limited and interference-free dual-hop mixed radio frequency (RF)/free space optical (FSO) systems with partial relay selection (PRS) for the variable-gain (VG) amplify-and-forward (AF) relaying scenario. We concentrate on the generalized channel model that not only describes different application scenarios but also allows a more accurate description of the channel characteristics. Specifically, the PRS-aided RF link is modeled by the κ-μ shadowed distribution, and the FSO link is expressed in terms of Fox’s H-function, which unifies Fisher-Snedecor F, Gamma-Gamma (GG), and Malága (M) distributions for atmospheric turbulence along with pointing errors and detection modes. The interference signals at the selected relay are modeled by independent identically κ-μ shadowed distributions. Using our analytical framework, new unified closed-form expressions for the cumulative distribution function (CDF), the average bit error rate (BER), and the ergodic capacity are derived. Additionally, we provide asymptotic expressions of the average BER at high SNR. The analysis quantifies the impact of co-channel interference, pointing errors, number of relays, and rank of the selected relay on the considered system’s performance. Finally, numerical results and Monte Carlo (MC) simulations are presented to confirm the effectiveness of the derived expressions. Note that our results provide a generalized framework for comprehensive studies of this kind of systems.

The performance of a dual-hop mixed radio frequency (RF)/free space optical (FSO) system with co-channel interferences (CCIs) is studied for both fixed-gain and variable-gain amplify-and-forward(AF) relaying scenarios. The RF link and interference link undergo the $\kappa$ - $\mu$ shadowed fading and the FSO link experiences the Fisher-Snedecor ${\cal F}$ distribution with pointing errors. For the considered system, we derive new closed-form expressions for the probability density function (PDF), cumulative distribution function (CDF), and average bit error rate (BER) of the end-to-end signal-to-interference-plus-noise ratio (SINR). In addition, efficient numerical expressions for the ergodic capacity are also obtained. Moveover, the asymptotic expressions for the CDF and average BER are derived. Our results can be regarded as a generalization of the previous results. Finally, numerical and simulation results are presented to verify the correctness of the proposed expressions.

Photon pairs generated by spontaneous parametric downconversion are essential for optical quantum information processing, in which the quality of biphoton states is crucial for the performance. To engineer the biphoton wave function (BWF) on-chip, the pump envelope function and the phase matching function are commonly adjusted, while the modal field overlap has been considered as a constant in the frequency range of interest. In this work, by using modal coupling in a system of coupled waveguides, we explore the modal field overlap as a new degree of freedom for biphoton engineering. We provide design examples for on-chip generations of polarization entangled photons and heralded single photons. This strategy can be applied to waveguides of different materials and structures, offering new possibilities for photonic quantum state engineering.

In this paper, we numerically study the secrecy performance of the free-space optical (FSO) system by considering different eavesdropping scenarios. More precisely, we considered three possible eavesdropping scenarios for Eve: 1) Eve is between Alice and Bob; 2) Eve and Bob are in the same receiving plane; 3) Eve is behind Bob. We adopt the Málaga ( M )-distribution channel to model atmospheric turbulence due to the presence of link blockage while considering the non-zero boresight pointing error and path loss. To do so, we obtain a novel probability density function (PDF) and cumulative distribution function (CDF) under different eavesdropping scenarios, based on which we derived the secrecy outage probability (SOP) analytical expressions as well as their asymptotic expressions at a high SNR regime. We verified the results using Monte Carlo simulations, which showed that the parameters related to atmospheric turbulence and pointing errors, as well as the location of the eavesdropper, have different effects on different eavesdropping scenarios.

Optical satellite networks using laser intersatellite links are recognized as being capable of satisfying the increasing broadband communication demands. However, the Doppler shift due to relative movement between satellites must be taken into consideration. A convenient method that does not require complicated mathematical calculation is adopted to derive the relationship between the residual Doppler shift and the bit error rate (BER) for the balanced differential phase-shift keying (DPSK) detection system. It is shown that the DPSK receiver is sensitive to the residual Doppler shift; when the residual Doppler shift Δ f r e s / R b is 0.05, 0.10, and 0.15, the BER is reduced from a level of 10 − 17 to a level of 10 − 14 , 10 − 11 , and 10 − 6 , respectively. The BER of a certain node pair under different link assignment schemes is calculated in a typical multi-hop LEO constellation. The results show that the communication BER of the same node pair is not only related to the step change of the Doppler but also related to the accumulation of the Doppler shift in the optical path. The results obtained here will be helpful in routing selection, link assignment, topology design, and system compensation.

Here, we correct the mistakes about citations in our article [1]. This has no effect on the results and conclusions. The correct citation numbers are given here.

We investigate the performance of a dual-hop mixed free space optical (FSO) /radio frequency (RF) system with fixed-gain relaying under direct detection and heterodyne detection techniques. The FSO link is modeled by the Fisher–Snedecor F distribution, which matches well with the experimental data under weak-to-strong turbulence regimes. The RF link experiences κ − μ shadowed fading, which unifies popular RF fading models. The κ − μ shadowed distribution is approximated by an α − μ distribution. Capitalizing on this approximation, closed-form approximate expressions for the cumulative distribution function, the average bit error rate of different modulation schemes, and the ergodic capacity are derived in terms of the bivariate Fox’s H function. Moreover, asymptotic analysis is carried out at a high signal-to-noise ratio to further illustrate the obtained diversity order and the influence of system and channel parameters. Numerical results and Monte Carlo simulations are presented to validate the derived approximate expressions.

We investigate the performance of a dual-hop mixed radio frequency (RF)/free space optical (FSO) system with variable-gain relaying. The RF link is modeled by the $\kappa$ - $\mu$ shadowed distribution, which unifies popular RF channel models. The FSO link is subject to atmospheric turbulence with non-zero boresight pointing errors. The atmospheric turbulence channel is modeled by the Fisher-Snedecor ${\mathcal F}$ distribution, which fits well with the measurement data under weak-to-strong turbulence conditions. The pointing error is modeled by the Beckmann distribution, which includes popular pointing error models. We propose an approximation method to approximate the $\kappa$ - $\mu$ shadowed distribution using an $\alpha$ - $\mu$ distribution, which is more accurate than that using a gamma distribution in the existing literatures. Then, we derive closed-form expressions for the probability density function (PDF) and the cumulative distribution function (CDF) for the irradiance fluctuations. Based on these expressions, we derive closed-form approximate expressions for the CDF, the PDF, the moment generating function (MGF), the average bit error rate (BER), and the ergodic capacity (EC) of the considered system in terms of the bivariate Fox’s H function. Furthermore, asymptotic expressions for the CDF and the average BER at high signal-to-noise ratio (SNR) are derived in terms of simple elementary functions. Finally, numerical results and Monte Carlo (MC) simulations are provided to verify the derived approximate expressions.