High-density photonic integrated circuits and on-chip optical interconnects require on-chip light sources with strict spectral stability. While all-dielectric quasi-bound states in the continuum offer a promising platform for compact nanolasers, the structural asymmetry required to excite high-Q modes inevitably induces severe resonance wavelength shifts, severely limiting their practical deployment. In this work, we propose a robust, CMOS-compatible device blueprint that employs a geometric area-compensation mechanism to completely decouple Q-factor tuning from wavelength variations. By systematically compensating for the air-hole volume altered during symmetry breaking, the typical 30 nm redshift is completely suppressed. Consequently, the resonance wavelength remains strictly pinned at approximately 1417.5 nm, falling squarely within the telecommunication E-band, while the Q-factor can be continuously tuned from 109 to 103. Crucially, the compensated design exhibits exceptional fabrication tolerance, confining wavelength fluctuations to approximately 1.8 nm even under realistic modern fabrication errors, including up to 3% area deviation and up to 5° sidewall-angle deviation. Furthermore, we validate the active performance of this design through rigorous device-level numerical experiments. Using a custom three-dimensional FDTD solver coupled with a four-level atomic gain model, we demonstrate that these wavelength-invariant qBIC metasurfaces can sustain highly stable, single-mode E-band lasing. This approach provides a highly reliable framework for precision spectral control in advanced optical communication components.
We present the first direct experimental comparison of quantum well infrared photodetectors (QWIPs) employing either single-quantum-well (SQW) or double-quantum-well (DQW) integrated with patch antenna nanophotonic cavities. While nanophotonic cavities theoretically can enable high-performance SQW infrared photodetector (SQWIP) by confining a large fraction of incident light in the SQW layer and thus eliminate the need for multiple quantum wells employed in conventional QWIPs, experimental realization of SQWIP suffers from severe carrier depletion and scattering due to proximal surface states. Transitioning to a DQW infrared photodetector (DQWIP) architecture can effectively mitigate the negative impacts of surface states and maintain large light absorption in each quantum well layer, leading to significantly improved device performance. Our DQWIP achieves a record-breaking peak responsivity of ~11.6 A/W and a photoconductive gain of ~10 around the 7 μm wavelength region at 80 K. These results establish a new benchmark for GaAs-based QWIPs and pave the way towards further development of the next-generation cost-effective and high-performance mid-infrared focal plane arrays.
The effect of two-photon absorption in high-power diode lasers is investigated numerically. The numerical simulation is based on the solution of coupled drift–diffusion and waveguide equations describing a broad-area Fabry–Pérot laser diode. Such an approach allows us to distinguish the direct effect due to inter-band absorption from the indirect effect due to intra-band absorption caused by the generated electron-hole pairs. The influence of two-photon absorption on continuous wave and pulsed laser operation is considered. The phenomenon of a reversed current of minority carriers is demonstrated.
Supercontinuum generation based on orbital angular momentum (OAM) modes offers a pathway toward broadband vortex light sources with expanded functional capabilities. Silica-based optical fibers have been successful in OAM supercontinuum generation; however, the strong absorption limits the application in the mid-infrared (>2500 nm) region. Fluoride glasses, characterized by their wide transmission window, provide an alternative platform for extending OAM supercontinuum spectra toward longer wavelengths. Here, we present a ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) dual-ring-core fiber designed for dispersion-engineered OAM supercontinuum generation. The optimized OAM1,1 mode exhibits a flat dispersion variation within ±50 ps/(nm·km) over 3830-nm bandwidth from 970 to 4800 nm range, enabling spectral broadening from 1414 nm to 6626 nm under normal-dispersion pumping. Through structural parameter modulation, the OAM4,1 mode achieves a flatter dispersion response with variation in ± 50 ps/(nm·km) between 800 nm and 5200 nm, accompanied by four zero-dispersion wavelengths. Under pulsed excitation, this mode supports a spectrum spanning 592-5240 nm, exceeding three octaves. Further structural refinement extends the OAM4,1 supercontinuum to 848-6880 nm, corresponding to more than 3 octaves and an additional 1640 nm expansion on the long-wavelength side.
In this work, we put forward technological solutions for the key challenges in phase-based (coherent and quantum) free-space optical communication (FSOC) systems. We introduce an active transceiver (TRX) terminal for laser transmission and pilot-assisted- (PA-) based reception, and contrast it to the conventional terminal with laser transmission and local-oscillator- (LO-) based reception. From our measurements of error vector magnitude, at received signal powers above –24 dBm, we see that the active PA-TRX terminal can better mitigate turbulence-induced distortion on the propagating signal beam, in contrast to the active LO-TRX terminal. We also introduce a phase-based modulating retroreflector (MRR), in a passive MRR-TRX terminal, that can apply phase modulation onto incident beams (to encode data) and retroreflection (to return the beams to their active terminals with the encoded data). This lets the passive MRR-TRX terminal operate without the payload and complexity of active terminals (having lasers and targeting systems). Our experimental characterizations reveal that the active PA-TRX and passive MRR-TRX terminals can establish effective communication through weak, moderate, and strong turbulence, with received signal powers well above the system's sensitivity (–30 dBm) and bit-error-rates below our limit in the absence of forward error correction (10–3). Ultimately, we see that the proposed technologies can offer superior performance for emerging phase-based (coherent and quantum) FSOC systems.
In this article, we present the fabrication and detailed characterization of an aluminum gallium nitride-based ultraviolet (UV) solar-blind metal–semiconductor–metal photodetector. We have also demonstrated the carrier transport mechanism of the fabricated device under dark conditions, which supports the thermal stability of the device at high temperatures. The plasma assisted molecular beam epitaxy grown device exhibits high crystalline quality (screw-type threading dislocation density = ~108 cm−2) and smooth surface morphology (root-mean-square roughness = ~724 pm), enabling us to fabricate the UV solar-blind photodetector. The fabricated device performs well at room temperature (RT), as it demonstrates low dark current on the order of a few tens of pA (6.53 × 10−11 A), high photocurrent (3.91 × 10−6 A), high sensitivity (photocurrent-to-dark current ratio = ~105), high responsivity (~13 A/W), high UV-to-visible rejection ratio (> 103), good detectivity (~1011 Jones), and fast response time (rise time = ~24 μs and fall time = ~23 μs) at 5 V. The analysis of dark currents at high temperatures (300–475 K) suggests that carriers undergo thermionic emission in the low-field regime (E < 1.67 kV/cm), thermionic field emission in the mid-field regime (1.67 < E < 10 kV/cm), and Poole–Frenkel emission in the high-field regime (E > 10 kV/cm). These mechanisms govern carrier transport and limit the increase in dark current to only two orders of magnitude relative to RT, thereby confirming the stable behaviour of the device at high temperatures. Therefore, the superior RT performance metrics, along with the demonstrated thermal stability under dark conditions at high temperatures, motivate further optimization of the device and its potential commercialization for scientific and industrial applications.
In this work, we establish physical models and propose optically continuous reflections by grading the Al-composition in both n-waveguide and p-waveguide layers (WGLs) for GaN-based Fabry-Perot laser diodes. For the devices with constant-indexed WGLs, only one-time optical reflection occurs at the waveguide layer/cladding layer interface. However, optical reflection always occurs when the light propagates in the graded-indexed WGLs. Hence, such continuous optical reflections more effectively reduce the optical leakage into the passive layers. As a result, an increased optical confinement factor can be achieved, and thus stronger laser power can be obtained. We also find that the Al-composition-graded p-WGL very remarkably affects the electron and hole injections, such that the reduced energy band offset between the p-WGL and p-type electron blocking layer increases the electron leakage level. This sacrifices the electron-hole recombination efficiency in spite of the increased optical confinement factor. This work then makes comprehensive investigations so that the optimized device structure that favors the most improved net modal gain can be obtained.
To address the issue of concave damage in the ring core that occurs during the fabrication of ring-core photonic crystal fiber (PCF), this work investigates its influence on the transmission performance of orbital angular momentum (OAM) modes. Meanwhile, two different compensation structures—adding an inner cladding and thickening the ring core are introduced into the ring-core PCF, and their compensation effects are compared. Simulation based on the COMSOL software platform shows that the concave damage of the ring core reduces the walk-off distance and effective mode field area, but has a slight impact on the mode quality. Analysis within the range of central angle 20°-40° and bending curvature radius 20 -60 μm reveals that the thickened ring core structure can maintain high mode quality and increase the effective mode field area, but it exacerbates mode walk-off in high-order modes; in contrast, the inner cladding structure performs well in increasing the walk-off distance yet slightly reduces the mode quality. This work addresses a research gap in the analysis of the effects of ring-core concave damage in PCF research and provides an important reference for the precise fabrication and structural optimization of high-performance optical OAM fibers.
Multicore-fibres (MCF) have emerged as an attractive solution for capacity scaling in optical communication. Securing such links with Quantum Key Distribution (QKD) is critical with the advent of Quantum computers. For practical deployment, QKD is required to operate alongside high-speed classical communication over field-deployed fiber infrastructure. In this work, the performance of QKD is experimentally evaluated in coexistence with high-speed classical data transmission over field-deployed underground and aerial multicore fiber links. The QKD system is implemented with Coherent One-Way Slim protocol, with dedicated Quantum and classical channels for Quantum communication and QKD post-processing. The deployed 4-core MCF infrastructure at IIT Madras provides an effective transmission length of 48 km through loopback operation. QKD performance over the MCF is evaluated in terms of quantum bit error rate (QBER) under varying attenuation, controlled noise injection, and inter-core crosstalk over both singlecore fiber and MCF links. The experimental results show that inter-core crosstalk has a stronger impact in MCF, leading to increased excess noise at the quantum receiver. For a 32-GBaud PM 16-QAM classical modulation format, stable QKD operation is maintained when the spectral separation is approximately six to eight times the occupied bandwidth.
A framework for the theoretical modeling and parameter estimation of erbium-doped fiber ring laser (EDFRL) is proposed based on physics-informed neural network (PINN). By introducing multi-dimensional parameterized input architecture, numerical transformation mapping and physics-consistent constraint strategy, this framework effectively addresses numerical stiffness and nonseparable boundary conditions in the closed-loop laser system. On this basis, forward prediction and inverse retrieval models were established. Within a multi-dimensional parameter space, the forward model exhibits a superior advantage in global generalization and computational efficiency, achieving high prediction fidelity (R2 > 0.99) and a maximum speedup by four orders of magnitude. Simultaneously, physical parameters were effectively retrieved from sparse data by the inverse model. Therefore, a collaborative workflow can be established, offering a novel and physically rigorous paradigm for the modeling, optimization, and calibration of nonlinear laser systems including EDFRL.
We present a realistic numerical model based on data-driven machine-learning (ML) techniques for generating high-energy ultrashort pulses at 4.5 μm. To achieve this objective, we propose a nonlinear amplifying loop mirror (NALM) configuration employing a self-similarly designed Praseodymium doped As2S3 (Pr3+: As2S3) tapered photonic crystal fiber (TPCF) compressor, which enables simultaneous pulse amplification and compression. Owing to the increasing complexity of Pr3+: As2S3 TPCF design, arising from the large parameter space associated with both fiber geometry and pulse characteristics, conventional numerical optimization becomes computationally expensive. Therefore, ML techniques are employed to optimize the TPCF structure and the input pulse parameters. Using the optimized design, we demonstrate that a 5 ps pulse at 4.5 μm can be compressed to 282.6 fs after propagation through 1.65 m of fiber, corresponding to a maximum compression factor of 17.68, with a pedestal energy of 2.217%.
Boson sampling is a leading platform for exploring many-body quantum interference in linear optical systems. However, identifying circuit-level operating regimes where quantum signatures remain robust under realistic conditions remains challenging. In this work, multimode photonic boson sampling is investigated using a programmable six mode integrated photonic circuit composed of cascaded beam splitters and tunable phase shifters. Each beam splitter is realized through directional couplers combined with local phase control, enabling arbitrary unitary transformations within the linear optical circuit. The circuit is modeled using a tight-binding Hamiltonian allowing controlled manipulation of optical phases and inter-mode coupling that directly governs multiphoton interference pathways. This set up is utilised to do the analysis of Heavy Output Generation (HOG), Total Variation Distance (TVD) and Linear Cross-Entropy Benchmarking (XEB), together with configuration-resolved probability differences, for up to five photons. Distinct dynamic regimes associated with coherent evolution, optimal interference and phase dispersion induced mixing is identified. The results further reveal a photon number dependent complexity–fragility trade-off and demonstrate the robustness of TVD to symmetric photon loss under post-selection. Overall, this work establishes a circuit-relevant validation framework linking programmable interferometer parameters, phase control and quantum interference metrics, providing guidance for scalable photonic boson-sampling implementations in the NISQ regime.
A passive mode-locked laser was demonstrated using an all-fibre ytterbium-doped fibre laser. Mode-locking was generated using a manganese (Mn (II)) material as a saturable absorber (SA) in a ring-cavity ytterbium-doped fibre laser. The Mn (II)-SA, fabricated via the hydrothermal method, using trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene linker and manganese(II) chloride tetrahydrate (MnCl (2)& sdot;4 H2O). The solution was then deposited onto a side-polished fibre, which exhibits a modulation depth of 18.1%, a saturation intensity of 0.74 MW/cm(2,) and a nonsaturable loss of 55.03%. The ring cavity outputs dissipative soliton mode-locked at 1030 nm, with a pulse duration of 9.1 ps and a repetition rate of 20.7 MHz.
A receiving improvement method is proposed and experimentally demonstrated based on hybrid spatial-modal diversity for single-input multi-output (SIMO) free-space optical (FSO) communication links. A moderate turbulence with a Rytov variance of 0.4665 is simulated using a rotatable phase plate. For 10 Gb/s quadrature phase shift keying (QPSK) signals, the hybrid spatial-modal diversity is realized by employing a two-aperture array with three-mode photonic lanterns. At the bit error rate (BER) of 1 x 10(-4), the transmitted power is reduced by about 2.8 dB due to the spatial diversity compared to a single aperture. Meanwhile, a 2.2-dB improvement is achieved using linear polarization modal diversity. The overall improvement reaches 3.9 dB through the hybrid spatial-modal diversity.
A high-precision all-fiber fluorescence temperature probe based on the fluorescence intensity ratio (FIR) technique was developed for human body temperature monitoring. Ionic substitution (KCa)(3+) for Y3+ ions in Er3+/Yb3+ codoped Y(2)Mo(3)O(12 )phosphors leads to significant enhancement of green upconversion emissions at 532 nm and 554 nm, which are 90-fold and 85-fold higher than those of the unsubstituted sample, respectively. In the temperature range of 253-423 K, a self-calibration relationship between FIR and 1/T was established with a linear regression coefficient R-2 of 0.999. The absolute sensitivity (S-a) reaches a maximum value of 0.016 K-1 at 423 K and the temperature measurement error is approximately +/- 0.12K. The real-time temperature monitoring of human body is demonstrated, which indicates that the as-built temperature probe can be used for real-time temperature measurement in different scenarios.
We propose a dual-pump phase-sensitive amplifier (PSA)-based all-optical framework for quadrature phase-shift keying (QPSK) de-aggregation and time-interleaved binary phase-shift keying (TI-BPSK) generation, offering spectrally efficient, reconfigurable transmission for next-generation optical networks. The scheme exploits coherent four-wave mixing (FWM) in a dual-pump highly nonlinear medium to generate a phase-conjugated idler, which coherently combines with the input QPSK signal to extract both in-phase and quadrature BPSK components. A half-bit-period temporal staggering repacks these components into a single TI-BPSK stream, achieving optical-domain baud rate doubling without digital signal processing (DSP). Numerical simulations using a vectorial split-step Fourier method (SSFM) capture nonlinear, dispersive, and polarization-dependent dynamics, while analytical formulations of PSA gain, phase mismatch, OSNR evolution, bit-error rate (BER), and error vector magnitude (EVM) provide independent validation. Monte Carlo analyses further establish robustness to birefringence and dispersion fluctuations. Results confirm high-fidelity TI-BPSK generation with BER and EVM performance consistent with analytical bounds. Compared with interferometer or DSP-based de-aggregation, the proposed single-stage optical approach delivers energy efficiency, scalability, and resilience, positioning it as a promising solution for elastic and software-defined optical networks (SDONs).
A photonic approach to generating multiple chirp rates microwave signal with frequency multiplying capability is reported based on a tunable optoelectronic oscillator (OEO). There is an option to select a single chirp signal of a particular chirp rate and center frequency out of multiple chirp rate signals without any modification in the experimental setup. In the proposed scheme, one balanced photodetector (BPD) is used for the detection of multiple chirp rate signals with multiple center frequencies and one PIN photodetector (PD) is used for the detection of frequency doubled un-chirp signal. A single dual linear chirp signal of the fixed tunable central frequency can be generated by the same experimental setup by adjusting the bias voltage of the phase modulator. In the proposed scheme, one Mach-Zehnder Modulator (MZM) and one Dual-Parallel Mach-Zehnder Modulator (DPMZM) are cascaded and operate at MITP (minimum transmission point) in push-pull mode to achieve the carrier suppression frequency modulated optical signal at the output end. The lower MZM is properly biased to serve as an intensity modulator and further constructs the closed-loop OEO to generate a microwave signal. When the OEO loop gain is slightly more than the total loss of the loop, an oscillating frequency centered at the frequency decided by the microwave photonic filter (MPF) can stably occur. The upper DPMZM is driven by the feedback signal obtained from the lower MZM with the combination of the base-band single-chirped signal to generate a multiple chirp rate microwave waveform with multiple central frequencies. Our proposed scheme alleviates the need for an external millimeter source due to the RF signal received from the OEO system, increasing the possibility of integration in the photonic integrated circuits. In this study, two cases of chirping have been considered: Linear and Nonlinear chirping. The effect of the nonlinear chirping case has been proved to be a more advantageous as compared to the linear chirping case. Also, in this connection, the simultaneous generation of multi-chirp rate microwave waveform with multiple center frequencies and chirp rates in the context of OEO has been studied for the first time. Our proposed scheme has potential applications in the next generation of multifunction RADAR and surveillance systems.
The development of large-scale quantum networks requires scalable interconnects operating from cryogenic to ambient temperatures. While conventional electrical interconnects pose thermal management and system complexity challenges, photonic interconnects enable efficient optical modulation and fiber transmission. Here, we present temperature-dependent characterization of a modified uni-traveling carrier photodetector (MUTC-PD) for quantum network applications. The 28 mu m device exhibits stable responsivity (> 0.56 A/W), > 9 GHz bandwidth at-5 V bias, and good linearity from 5 K to 300 K. These robust characteristics identify the MUTC-PD as a promising candidate for scalable quantum photonic interconnects and provide design insights for next-generation cryogenic photodetectors.
This work presents the design and optimization of a new lead-free high-performance dual-absorber solar cell combining Cu2SnS3 and MASnI(3). The remarkable performance results from the complementary bandgaps of the Cu2SnS3 and MASnI(3 )absorber layers, which enable broader light absorption, and the favorable band alignment of absorber and transport layers, that facilitates efficient carrier separation and extraction. The proposed structure, FTO/ETL/Cu2SnS3 /MASnI(3)/HTL/Pt, achieved a high PCE of 35.67%, with a $V_{ ext {OC}}$ of 0.94 V, $J_{ ext {SC}}$ of 43.64 mA/cm2, and FF of 86.80%. Key optimization of transport layers, thickness, doping, and defect densities, along with resistive and thermal loss analysis, ensured practical applicability. This research demonstrates the strong potential of lead-free solar cell configurations for environmentally safe and high-performance photovoltaic technologies.
