Traditional heterogeneous networks (HetNets) are constrained by their hardware design and configuration. These HetNets have a limited ability to adapt to variations in network dynamics. Software-defined radio technology has the potential to address this adaptability issue. In this paper, we introduce a software-defined radio (SDR)-based long-term evolution licensed assisted access (LTE-LAA) architecture for next-generation communication networks. We show that with proper design and tuning of the proposed architecture, high-level adaptability in HetNets becomes feasible with a higher throughput and lower power consumption. Firstly, maximizing the throughput and minimizing power consumption are formulated as a constrained optimization problem. Then, the obtained solution, alongside a heuristic solution, is compared against the solutions to existing approaches, showing our proposed strategy is drastically superior in terms of both power efficiency and system throughput. This study is then concluded by employing artificial intelligence techniques in multi-objective optimization, namely random forest regression, particle swarm, and genetic algorithms, to balance out the trade-offs between maximizing the throughput and power efficiency and minimizing energy consumption. These investigations demonstrate the potential of employing the proposed LTE-LAA architecture in addressing the requirements of next-generation HetNets in terms of power, throughput, and green scalability.

Ultra-low-noise laser sources are crucial for a variety of applications, including microwave synthesizers, optical gyroscopes, and the manipulation of quantum systems. Silicon photonics has emerged as a promising solution for high-coherence applications due to its ability to reduce system size, weight, power consumption, and cost (SWaP-C). Semiconductor lasers based on self-injection locking (SIL) have reached fiber laser coherence, but typically require a high-Q external cavity to suppress coherence collapse through frequency-selective feedback. Lasers based on external-cavity locking (ECL) are a low-cost and turnkey operation option, but their coherence is generally inferior to SIL lasers. In this work, we demonstrate quantum-dot (QD) lasers grown directly on Si that achieve SIL laser coherence under turnkey ECL. The high-performance QD laser offers a scalable and low-cost heteroepitaxial integration platform. Moreover, the QD laser's chaos-free nature enables a 16 Hz Lorentzian linewidth under ECL using a low-Q external cavity, and improves the frequency noise by an additional order of magnitude compared to conventional quantum-well lasers.

A parametric study was conducted on coupled-cavity on-chip lasers to investigate the feasibility of reducing the lasing linewidth. The study showed that the coupled-cavity structure achieved up to 7 orders of magnitude linewidth reduction. Increasing the number of QW/QD layers (or QD density-per-layer) resulted in higher optical power and narrower linewidths. However, in the QW case, increasing the layers reduced efficiency and increased the input-power requirement for locking, while in the QD case, increasing the QD layers/density increased the efficiency and decreased the input-power requirement. The study recommends minimizing the number of QW layers and maximizing the number of QD layers at moderate and low current injection, respectively.

Stable laser emission with narrow linewidth is of critical importance in many applications, including coherent communications, LIDAR, and remote sensing. In this work, the physics underlying spectral narrowing of self-injection-locked on-chip lasers to Hz-level lasing linewidth is investigated using a composite-cavity structure. Heterogeneously integrated III-V/SiN lasers operating with quantum-dot and quantum-well active regions are analyzed with a focus on the effects of carrier quantum confinement. The intrinsic differences are associated with gain saturation and carrier-induced refractive index, which are directly connected with 0- and 2-dimensional carrier densities of states. Results from parametric studies are presented for tradeoffs involved with tailoring the linewidth, output power, and injection current for different device configurations. Though both quantum-well and quantum-dot devices show similar linewidth-narrowing capabilities, the former emits at a higher optical power in the self-injection-locked state, while the latter is more energy-efficient. Lastly, a multi-objective optimization analysis is provided to optimize the operation and design parameters. For the quantum-well laser, minimizing the number of quantum-well layers is found to decrease the threshold current without significantly reducing the output power. For the quantum-dot laser, increasing the quantum-dot layers or density in each layer increases the output power without significantly increasing the threshold current. These findings serve to guide more detailed parametric studies to produce timely results for engineering design.

Integrated silicon photonics has sparked a significant ramp-up of investment in both academia and industry as a scalable, power-efficient, and eco-friendly solution. At the heart of this platform is the light source, which in itself, has been the focus of research and development extensively. This paper sheds light and conveys our perspective on the current state-of-the-art in different aspects of application-driven on-chip silicon lasers. We tackle this from two perspectives: device-level and system-wide points of view. In the former, the different routes taken in integrating on-chip lasers are explored from different material systems to the chosen integration methodologies. Then, the discussion focus is shifted towards system-wide applications that show great prospects in incorporating photonic integrated circuits (PIC) with on-chip lasers and active devices, namely, optical communications and interconnects, optical phased array-based LiDAR, sensors for chemical and biological analysis, integrated quantum technologies, and finally, optical computing. By leveraging the myriad inherent attractive features of integrated silicon photonics, this paper aims to inspire further development in incorporating PICs with on-chip lasers in, but not limited to, these applications for substantial performance gains, green solutions, and mass production.

This paper presents our recent progress on integrated Si photonics, focusing specifically on on-chip lasers. In addition, we discuss the future perspectives of incorporating this technology into various applications, spanning a wide range from optical communication to quantum technologies.

Spectrally-pure lasers are paramount in various fields. Progression to Hz-level lasing linewidth in III-V/SiN lasers with quantum-dot active regions is predicted here. Using parametric studies, one can produce timely results in engineering designs.

We performed a parametric study of the design of an integrated III-V/SiN distributed feedback (DFB) quantum well (QW) and quantum dot (QD) lasers involving detailed and comprehensive modeling and multi-objective performance optimization. The study aims to maximize the potential laser linewidth reduction in InP/Si lasers coupled with SiN microring resonators. The design of the complex structures in such devices requires a large parameter space to explore for design engineering. This investigation and the formulated theory serve as an analytical tool for parametric studies to produce timely results for design engineering and optimization.

We report on the generation and transmission of millimeter-wave (MMW) beat-tone at 28 GHz from an external injection-locked InAs/InP quantum-dash laser-based comb source emitting in mid L-band. The MMW beat-tone exhibited a narrow linewidth, and low phase noise of similar to -122 dBc/Hz at 1.0 MHz offset frequency, thus demonstrating superior characteristics. Thereafter, we achieved a successful transmission of 2 Gbps quadrature-phase-shift-keying (QPSK) signal over 28 GHz MMW beat-tone carrier on 4 m wireless channel as well as 20 km single-mode fiber and 4 m wireless hybrid channel, exhibiting receiver sensitivities of -1.0 and -0.5 dBm, respectively. This demonstration paves the way for the potential deployment of this new-class of MMW photonic source in future passive optical networks and 5G, enabling exploiting hybrid architectures and extended L-band wavelength operation besides the conventional C-band.

We report on the generation and transmission of a millimeter-wave (MMW) signal with a frequency of 28 GHz by employing an InAs/InP quantum-dash dual-wavelength laser diode (QD-DWL) emitting in the ~1610 nm extended L-band window. The self-injection locking (SIL) technique has been engaged to improve the linewidth and reduce the noise of the optical tone. Besides, the transmission of a 2 Gbits/s quadrature phase-shift keying (QPSK)-modulated 28-GHz MMW beat tone over a hybrid 20-km radio-over-fiber combined with 5-m radio-over-free-space-optics and up to 6-m radio frequency wireless link has been demonstrated. Moreover, comparing the proposed QD-DWL with a commercial laser showcased similar performance characteristics, making the QD-DWL a candidate source for MMW applications.

Wireless transmission of unmodulated 28, 38, and 60GHz millimeter-wave (MMW) sub-carriers, generated by L-band quantum-dash laser-based comb-source, is investigated in terms of RF-characteristics. Low-frequency MMWs showcased ~4 to 5dB/m power-attenuation and ~−2 to −3dBc/Hz/m phase-noise degradation, while the 60GHz signal exhibited twice these values.

Generation of tunable millimeter-wave signals with frequencies 60, 38, and 28 GHz are reported from an injection-locked InAs/InP quantum-dash-laser emitting in L-band, for the first time. High performance with small-linewidths and phase-noise are demonstrated.

Effect of DP-QPSK modulation (28GBaud) and transmission on RF-characteristics is investigated for a 3-channel multiplexed system employing InAs/InP quantum-dash laser comb-source showing 3dB-bandwidth increase by ~16.7%, linewidth by ~7 kHz, and phase-noise by ~4.7 dBc/Hz.

A two-sectioned quantum dash laser structure based on an InAs/InP chirped active region medium is investigated as a monolithic broadband tunable laser. A thorough parametric analysis on the effect of three tuning parameters (viz. injection current, cavity length, absorber-to-device length ratio) on the optical power-injection current (L-I) and spectral characteristics, particularly wavelength tunability and bandwidth broadening, is performed. A total emission wavelength tunability of ~20 nm is demonstrated in the mid-L-band (~1600 to ~1620 nm) window and ~2 times enhancement in the 3dB bandwidth. Furthermore, optical bistability in the two-sectioned InAs/InP quantum-dash laser device is observed at near room temperature in the form of L-I curve hysteresis. Further investigation displayed a direct relation between the absorber length and the hysteresis loop width with a maximum value of ~40 mA is demonstrated; a potential platform in fast optical switching and modulation applications. Finally, the two-sectioned structure is also proposed and investigated as a monolithic two-segment contact spectrum shaper to manipulate the lasing spectrum profiles to attain flat tops and effectively increase the spectrum 3dB bandwidth. As such, a maximum 3dB bandwidth was able to be pushed up to ~20 nm from ~7 nm by proper tuning of the current density distribution across the two segments of the device.

A two-sectioned InAs/InP quantum dash laser structure is proposed and investigated as a monolithic broadband multimodal tunable laser with an integrated semiconductor optical amplifier. The optical power-injection current and spectral characteristics of the device at different operating conditions demonstrated a total wavelength tunability of similar to 15.8 nm in the extended-L-band (similar to 1615 to similar to 1630.8 nm) window with similar to 2.0 times -3 dB bandwidth enhancement. Furthermore, due to the unique tunability mechanism of forward biasing the amplifier section, the device exhibits simultaneous wavelength tuning as well as optical amplification features, with an estimated gain of similar to 8.5 dB affirmed by an increase in the wall-plug efficiency up to 6.8% from 3.9%, shown by its single-section counterpart. This demonstration paves a potential platform for the deployment of broadband quantum-dash laser-amplifiers as unified light sources in next-generation optical access networks. (C) 2020 Society of Photo Optical Instrumentation Engineers (SPIE)

Electro-absorption and electro-optic characteristics of InAs/InP quantum-dash active region-based waveguide, emitting at ~1600 nm is investigated. Two major peaks were observed in the change of absorption spectrum with a maximum value of 7070 cm-1 at a bias voltage of -8V with an excellent uniform extinction ratio of ~15 dB across the wavelength range of operation (1460-1620 nm). The effect of temperature on electro-absorption (EA) measurement suggests a strong influence resulting in merging of two major change of absorption spectrum peaks with higher temperature. Furthermore, electro-optic measurements indicate a change in refractive index and its efficiency values of ~2.9 × 10-4 and ~0.5 × 10-4 V-1, respectively, hence exhibiting a low chirping factor of 0.9 and 1.5 at bias voltages of -2 V and -4 V, respectively. As a quasi-three-dimensionally confined structure possessing both quantum well- and quantum dot-like features, the quantum dash waveguide showed superior electro-absorption and electro-optic properties compared to quantum dots and close to that of quantum wells, while attaining low chirp and broad wavelength range of operation. This paves a way for potential realization of quantum dash-based EA and electro-optic modulator for future optical access networks, particularly operating in wide C- to L-band region.

Injection locked quantum-dash laser diode-based comb source is employed in wavelength-division multiplexed (WDM) optical transmission covering ~1610 nm L-band optical telecommunication window. An aggregate data rate of 192 Gbits/s (3 × 32 GBaud-QPSK reaching 7% FEC overhead) is demonstrated over three 50 GHz separated channels in coherent transmission over a 10 km-long single mode fiber. A thorough investigation of the radio-frequency (RF) characteristics of all channels is carried out in terms of the linewidth, phase, and frequency noises, showing minimum values of 44 kHz, -80 dBc/Hz, and 5.2 × 10 11 Hz 2 /Hz, respectively. Also, an integrated average relative intensity noise of ~-132 dB/Hz is reported for the central channel. To the best of our knowledge, this constitutes the first report and demonstration of a dense WDM (DWDM) in an extended L-band regime using a comb source.

Injection locked quantum-dash laser diode-based frequency-comb source is employed in wavelength-division multiplexed (WDM) transmission in ~1610nm L-band. An aggregate data rate of 192 Gbits/s (3×16 GBaud-DP-QPSK) is demonstrated over three channels separated by 50 GHz in coherent transmission over a 10 km-long single-mode fiber.

Investigation of non-uniform current-density distribution over a two-segmented InAs/InP quantum-dash laser at 1610nm displayed controllability of the emission spectrum profile and bandwidth, thus qualifying this configuration as a monolithic flat-top spectral shaper in optical communications.