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Photonics
Volume 7
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Photonics, Volume 7, Issue 1 (March 2020) – 22 articles

Cover Story (view full-size image): Hybrid integrated diode lasers are introducing a new paradigm to photonics, due to their unprecedented coherence, full spectral control, and seamless embedding in high-functionality photonic circuits. Most promising is hybrid integration with ultra-low-loss dielectric feedback circuits, as these render the widest spectral coverage including the visible range. We present work on various types and operational modes of hybrid integrated diode lasers based on low-loss dielectric feedback circuits using silicon nitride waveguides. Highlights are the demonstration of sub-100-Hz intrinsic linewidth, up to 120 nm wide spectral coverage around a 1.55 µm wavelength, and more than 100 mW output power. Functionalities include dual-wavelength generation, dual-gain operation, laser frequency comb generation, and wavelength tunable feedback circuits for hybrid lasers in the visible range.View this paper.
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10 pages, 1767 KiB  
Review
Routes to Chaos of a Semiconductor Laser Subjected to External Optical Feedback: A Review
by Alexandre Locquet
Photonics 2020, 7(1), 22; https://doi.org/10.3390/photonics7010022 - 5 Mar 2020
Cited by 13 | Viewed by 4179
Abstract
This paper reviews experimental investigations of the route to chaos of a semiconductor laser subjected to optical feedback from a distant reflector. When the laser is biased close to threshold, as the feedback strength is increased, an alternation between stable continuous wave (CW) [...] Read more.
This paper reviews experimental investigations of the route to chaos of a semiconductor laser subjected to optical feedback from a distant reflector. When the laser is biased close to threshold, as the feedback strength is increased, an alternation between stable continuous wave (CW) behavior and irregular, chaotic fluctuations, involving numerous external-cavity modes, is observed. CW operation occurs on an external-cavity mode whose optical frequency is significantly lower than that of the solitary laser. The scenario is significantly different for larger currents as the feedback level is increased. At low feedback, the laser displays periodic or quasiperiodic behavior, mostly around external-cavity modes whose frequency is slightly larger than that of the solitary laser. As the feedback level increases, the RF and optical frequencies involved progressively lock until complete locking is achieved in a mixed external-cavity mode state. In this regime, the optical intensity and voltage oscillate at a frequency that is also equal to the optical frequency spacing between the modes participating in the dynamics. For even higher feedback, the locking cannot be maintained and the laser displays fully developed coherence collapse. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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18 pages, 2457 KiB  
Article
Photodetector with Controlled Relocation of Carrier Density Peaks: Concept and Numerical Simulation
by Ivan Pisarenko and Eugeny Ryndin
Photonics 2020, 7(1), 21; https://doi.org/10.3390/photonics7010021 - 5 Mar 2020
Cited by 5 | Viewed by 2944
Abstract
Modern electronics faces the degradation of metal interconnection performance in integrated circuits with nanoscale feature dimensions of transistors. The application of constructively and technologically integrated optical links instead of metal wires is a promising way of the problem solution. Previously, we proposed the [...] Read more.
Modern electronics faces the degradation of metal interconnection performance in integrated circuits with nanoscale feature dimensions of transistors. The application of constructively and technologically integrated optical links instead of metal wires is a promising way of the problem solution. Previously, we proposed the advanced design of an on-chip injection laser with an AIIIBV nanoheterostructure, and a functionally integrated optical modulator. To implement the efficient laser-modulator-based optical interconnections, technologically compatible photodetectors with subpicosecond response time and sufficient sensitivity are required. In this paper, we introduce the concept of a novel high-speed photodetector with controlled relocation of carrier density peaks. The device includes a traditional p-i-n photosensitive junction and an orthogonally oriented control heterostructure. The transverse electric field displaces the peaks of electron and hole densities into the regions with low carrier mobilities and lifetimes during the back edge of an optical pulse. This relocation results in the fast decline of photocurrent that does not depend on the longitudinal transport of electrons and holes. We develop a combined numerical model based on the Schrodinger-Poisson equation system to estimate the response time of the photodetector. According to the simulation results, the steep part of the photocurrent back edge has a duration of about 0.1 ps. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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10 pages, 2849 KiB  
Article
Side-lobe Level Reduction of an Optical Phased Array Using Amplitude and Phase Modulation of Array Elements Based on Optically Injection-Locked Semiconductor Lasers
by Anh Hang Nguyen, Jun-Hyung Cho, Ho-Jun Bae and Hyuk-Kee Sung
Photonics 2020, 7(1), 20; https://doi.org/10.3390/photonics7010020 - 24 Feb 2020
Cited by 13 | Viewed by 4723
Abstract
The side-lobe level (SLL) in optical phased array (OPA) systems should be reduced to ensure their high performance. We investigate theoretically the performance of an OPA based on optically injection-locked (OIL) semiconductor lasers. The phase and amplitude of the OIL laser are modulated [...] Read more.
The side-lobe level (SLL) in optical phased array (OPA) systems should be reduced to ensure their high performance. We investigate theoretically the performance of an OPA based on optically injection-locked (OIL) semiconductor lasers. The phase and amplitude of the OIL laser are modulated by controlling the injection-locking parameters to reduce the SLL as well as to achieve beam steering. We successfully achieved an SLL reduction of >16 dB when compared with the uniform amplitude profile based on the application of the Taylor window function profile to the injection-locked OPA elements. The reduced SLL and high power efficiency achieved in this study can expedite the use of OPA in real field applications, such as free-space communication, imaging, and light detection and ranging (LIDAR). Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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13 pages, 359 KiB  
Article
Quantum Theory of Multisubband Plasmon– Phonon Coupling
by Sofia Ribeiro, Angela Vasanelli, Yanko Todorov and Carlo Sirtori
Photonics 2020, 7(1), 19; https://doi.org/10.3390/photonics7010019 - 20 Feb 2020
Cited by 5 | Viewed by 3650
Abstract
We present a theoretical description of the coupling between longitudinal optical phonons and collective excitations of a two-dimensional electron gas. By diagonalizing the Hamiltonian of the system, including Coulomb electron–electron and Fröhlich interactions, we observe the formation of multisubband polarons, mixed states partially [...] Read more.
We present a theoretical description of the coupling between longitudinal optical phonons and collective excitations of a two-dimensional electron gas. By diagonalizing the Hamiltonian of the system, including Coulomb electron–electron and Fröhlich interactions, we observe the formation of multisubband polarons, mixed states partially phonon and partially multisubband plasmon, characterized by a coupling energy which is a significant fraction, up to ∼ 40 % , of the phonon energy. We demonstrate that multisubband plasmons and longitudinal optical phonons are in the ultra-strong coupling regime in several III–V and II–VI material systems. Full article
(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)
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11 pages, 8376 KiB  
Article
Topological Protection and Control of Quantum Markovianity
by Gian Luca Giorgi, Salvatore Lorenzo and Stefano Longhi
Photonics 2020, 7(1), 18; https://doi.org/10.3390/photonics7010018 - 8 Feb 2020
Cited by 9 | Viewed by 4672
Abstract
Under the Born–Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is [...] Read more.
Under the Born–Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is responsible for non-Markovian effects and information backflow from the environment into the system owing to Anderson localization. This turns disorder into a resource for enhancing non-Markovianity in the system–environment dynamics, which could be of relevance in cavity quantum electrodynamics. Here we consider the decoherence dynamics of a qubit weakly coupled to a two-dimensional bath with a nontrivial topological phase, such as a two-level atom embedded in a two-dimensional coupled-cavity array with a synthetic gauge field realizing a quantum-Hall bath, and show that Markovianity is protected against moderate disorder owing to the robustness of chiral edge modes in the quantum-Hall bath. Interestingly, switching off the gauge field, i.e., flipping the bath into a topological trivial phase, allows one to re-introduce non-Markovian effects. Such a result indicates that changing the topological phase of a bath by a tunable synthetic gauge field can be harnessed to control non-Markovian effects and quantum information backflow in a qubit-environment system. Full article
(This article belongs to the Special Issue Topological Photonics)
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8 pages, 2319 KiB  
Article
Fast Frame Synchronization Design and FPGA Implementation in SF-BOTDA
by Qiuyi Pan, Xincheng Huang, Rui Min and Weiping Liu
Photonics 2020, 7(1), 17; https://doi.org/10.3390/photonics7010017 - 8 Feb 2020
Cited by 2 | Viewed by 3468
Abstract
To address the issues of high time consumption of frame synchronization involved in a scanning-free Brillouin optical time-domain analysis (SF-BOTDA) system, a fast frame synchronization algorithm based on incremental updating was proposed. In comparison to the standard frame synchronization algorithm, the proposed one [...] Read more.
To address the issues of high time consumption of frame synchronization involved in a scanning-free Brillouin optical time-domain analysis (SF-BOTDA) system, a fast frame synchronization algorithm based on incremental updating was proposed. In comparison to the standard frame synchronization algorithm, the proposed one significantly reduced the processing time required for the BOTDA system frame synchronization by about 98%. In addition, to further accelerate the real-time performance of frame synchronization, a field programmable gate array (FPGA) hardware implementation architecture based on parallel processing and pipelining mechanisms was also proposed. Compared with the software implementation, it further raised the processing speed by 13.41 times. The proposed approach could lay a foundation for the BOTDA system in the field with the associated high real-time requirements. Full article
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16 pages, 862 KiB  
Article
Ultra-Wideband WDM Optical Network Optimization
by Stanisław Kozdrowski, Mateusz Żotkiewicz and Sławomir Sujecki
Photonics 2020, 7(1), 16; https://doi.org/10.3390/photonics7010016 - 21 Jan 2020
Cited by 27 | Viewed by 4788
Abstract
Ultra-wideband wavelength division multiplexed networks enable operators to use more effectively the bandwidth offered by a single fiber pair and thus make significant savings, both in operational and capital expenditures. The main objective of this study is to minimize optical node resources, such [...] Read more.
Ultra-wideband wavelength division multiplexed networks enable operators to use more effectively the bandwidth offered by a single fiber pair and thus make significant savings, both in operational and capital expenditures. The main objective of this study is to minimize optical node resources, such as transponders, multiplexers and wavelength selective switches, needed to provide and maintain high quality of network services, in ultra-wideband wavelength division multiplexed networks, at low cost. A model based on integer programming is proposed, which includes a detailed description of optical network nodal resources. The developed optimization tools are used to study the ultra-wideband wavelength division multiplexed network performance when compared with the traditional C-band wavelength division multiplexed networks. The analysis is carried out for realistic networks of different dimensions and traffic demand sets. Full article
(This article belongs to the Section Optical Communication and Network)
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5 pages, 195 KiB  
Editorial
Acknowledgement to Reviewers of Photonics in 2019
by Photonics Editorial Office
Photonics 2020, 7(1), 15; https://doi.org/10.3390/photonics7010015 - 21 Jan 2020
Viewed by 1866
Abstract
The editorial team greatly appreciates the reviewers who have dedicated their considerable time and
expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether
the papers are finally published or not [...] Full article
17 pages, 5514 KiB  
Review
Ultrahigh-Resolution Optical Vector Analyzers
by Oleg Morozov, Ilnur Nureev, Airat Sakhabutdinov, Artem Kuznetsov, Gennady Morozov, German Il’in, Samvel Papazyan, Alexander Ivanov and Roman Ponomarev
Photonics 2020, 7(1), 14; https://doi.org/10.3390/photonics7010014 - 20 Jan 2020
Cited by 33 | Viewed by 5963
Abstract
The optical vector analyzer is a device used to measure the magnitude, phase responses, and other parameters of optical devices. There have been increasingly higher demands placed on optical vector analyzers during the development of optical technologies, which are satisfied by the creation [...] Read more.
The optical vector analyzer is a device used to measure the magnitude, phase responses, and other parameters of optical devices. There have been increasingly higher demands placed on optical vector analyzers during the development of optical technologies, which are satisfied by the creation of new devices and their operating principles. For further development in this area, it is necessary to generalize the experience gained during the development of optical vector analyzers. Thus, in this report, we provide an overview of all the basic types of approaches used for the realization of optical vector analyzers, including the advanced ones with the best performances. The principles of their working, as well as their associated advantages, disadvantages, and existing solutions to the identified problems, are examined in detail. The presented approaches could be of value and interest to those working in the field of laser dynamics and optical devices, as we propose one use of the optical vector analyzer as being the characterization of Fano resonance structures. Full article
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10 pages, 1373 KiB  
Article
Equivalent Circuit Model of High-Performance VCSELs
by Marwan Bou Sanayeh, Wissam Hamad and Werner Hofmann
Photonics 2020, 7(1), 13; https://doi.org/10.3390/photonics7010013 - 18 Jan 2020
Cited by 4 | Viewed by 6517
Abstract
In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do [...] Read more.
In this work, a general equivalent circuit model based on the carrier reservoir splitting approach in high-performance multi-mode vertical-cavity surface-emitting lasers (VCSELs) is presented. This model accurately describes the intrinsic dynamic behavior of these VCSELs for the case where the lasing modes do not share a common carrier reservoir. Moreover, this circuit model is derived from advanced multi-mode rate equations that take into account the effect of spatial hole-burning, gain compression, and inhomogeneity in the carrier distribution between the lasing mode ensembles. The validity of the model is confirmed through simulation of the intrinsic modulation response of these lasers. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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12 pages, 3199 KiB  
Article
Development of an Interference Filter-Stabilized External-Cavity Diode Laser for Space Applications
by Linbo Zhang, Tao Liu, Long Chen, Guanjun Xu, Chenhui Jiang, Jun Liu and Shougang Zhang
Photonics 2020, 7(1), 12; https://doi.org/10.3390/photonics7010012 - 18 Jan 2020
Cited by 21 | Viewed by 7335
Abstract
The National Time Service Center of China is developing a compact, highly stable, 698 nm external-cavity diode laser (ECDL) for dedicated use in a space strontium optical clock. This article presents the optical design, structural design, and preliminary performance of this ECDL. The [...] Read more.
The National Time Service Center of China is developing a compact, highly stable, 698 nm external-cavity diode laser (ECDL) for dedicated use in a space strontium optical clock. This article presents the optical design, structural design, and preliminary performance of this ECDL. The ECDL uses a narrow-bandwidth interference filter for spectral selection and a cat’s-eye reflector for light feedback. To ensure long-term stable laser operation suitable for space applications, the connections among all the components are rigid and the design avoids any spring-loaded adjustment. The frequency of the first lateral rocking eigenmode is 2316 Hz. The ECDL operates near 698.45 nm, and it has a current-controlled tuning range over 40 GHz and a PZT-controlled tuning range of 3 GHz. The linewidth measured by the heterodyne beating between the ECDL and an ultra-stable laser with 1 Hz linewidth is about 180 kHz. At present, the ECDL has been applied to the principle prototype of the space ultra-stable laser system. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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9 pages, 4707 KiB  
Article
Tuning of Fiber Optic Surface Reflectivity through Graphene Oxide-Based Layer-by-Layer Film Coatings
by Catarina S. Monteiro, Maria Raposo, Paulo A. Ribeiro, Susana O. Silva and Orlando Frazão
Photonics 2020, 7(1), 11; https://doi.org/10.3390/photonics7010011 - 18 Jan 2020
Cited by 6 | Viewed by 3332
Abstract
The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, [...] Read more.
The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, by mounting combined bilayers of polyethylenimine (PEI) and GO layers using the Layer-by-Layer (LbL) technique. The reflectivity of optical fibers coated with graphene oxide layers is investigated for the telecom region allowing to both monitor layer growth kinetics and cavity characterization. Tunable reflective surfaces are successfully attained in both cleaved optical fibers and hollow microsphere fiber-based sensors by simply coating them with PEI/GO layers through the LbL film technique. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices)
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11 pages, 2562 KiB  
Article
Near-IR Plasmons in Micro and Nanoparticles with a Semiconductor Core
by Fahime Seyedheydari, Kevin Conley and Tapio Ala-Nissila
Photonics 2020, 7(1), 10; https://doi.org/10.3390/photonics7010010 - 17 Jan 2020
Cited by 5 | Viewed by 3283
Abstract
We computationally study the electromagnetic response of semiconductor micro and nanoinclusions for realizing highly reflective, plasmonically enhanced coatings in the visible and infrared regime. We first examine the influence of oxide coatings on the Mie resonances of microparticles of low-bandgap semiconductors (Si and [...] Read more.
We computationally study the electromagnetic response of semiconductor micro and nanoinclusions for realizing highly reflective, plasmonically enhanced coatings in the visible and infrared regime. We first examine the influence of oxide coatings on the Mie resonances of microparticles of low-bandgap semiconductors (Si and Ge) in the near-IR regime. We then study the influence of a semiconducting core on the localized surface plasmon resonances of Si@Ag and Ge@Ag core@shell nanoparticles. Our results show a strong interaction between the resonances of the plasmonic Ag shell and the semiconducting core material which allows tuning of the electromagnetic response for near-IR applications. Full article
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8 pages, 2790 KiB  
Article
RF Injection of THz QCL Combs at 80 K Emitting over 700 GHz Spectral Bandwidth
by Andres Forrer, Lorenzo Bosco, Mattias Beck, Jérôme Faist and Giacomo Scalari
Photonics 2020, 7(1), 9; https://doi.org/10.3390/photonics7010009 - 16 Jan 2020
Cited by 14 | Viewed by 5198
Abstract
We report about RF injection locking of an homogeneous THz quantum cascade laser operating at 3 THz central frequency. The extremely diagonal nature of the optical transition, combined with low-loss copper-based double-metal waveguides, allow CW operation up to 105 K and CW power [...] Read more.
We report about RF injection locking of an homogeneous THz quantum cascade laser operating at 3 THz central frequency. The extremely diagonal nature of the optical transition, combined with low-loss copper-based double-metal waveguides, allow CW operation up to 105 K and CW power in excess of 5.6 mW measured at 80 K. Terahertz emission spanning up to 600 GHz, together with a narrow beatnote, indicate comb operation at 80 K, and strong RF injection clearly modifies the laser spectrum up to 700 GHz spectral bandwidth making these devices ideal candidates for an on-chip dual comb spectrometer. Full article
(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)
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13 pages, 7466 KiB  
Article
Nonlinear Optical Study in a Set of Dibenzylideneacetone Derivatives with Potential for Optical Frequency Conversion
by Francisco A. Santos, Luis M. G. Abegão, Ruben D. Fonseca, Aline M. Alcântara, Cleber R. Mendonça, Márcio A. R. C. Alencar, Marcelo S. Valle, Kenji Kamada, Leonardo De Boni and José J. Rodrigues, Jr.
Photonics 2020, 7(1), 8; https://doi.org/10.3390/photonics7010008 - 9 Jan 2020
Cited by 10 | Viewed by 4258
Abstract
The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications [...] Read more.
The search for advanced optical materials, in particular, materials with nonlinear optical responses, has, in the last years, experienced substantial growth due to their vast applications in the photonics field. One of those applications is ultra-fast optical frequency conversion, in the optics communications field. Organic compounds have emerged as promising candidates for raw materials to develop nonlinear optical devices, such as optical converters, due to their intrinsic ultra-fast electronic responses. Also, the easy tailoring of organic molecular structures makes organic materials much more appealing than the inorganic ones. In this work, we have performed a linear and nonlinear optical characterization of a set of dibenzylideneacetone derivatives. The nonlinear optical responses investigated correspond to second- and third-order nonlinear processes, namely, first electronic molecular hyperpolarizability and two-photon absorption cross-section, respectively. The value of the first electronic molecular hyperpolarizability, up to 52 cm4·statvolt−1, could be considered a robust value when compared to the short-sized π-electron backbone length of the studied compounds. Such results suggest that these compounds exhibit the potential to be used as optical frequency converters. Quantum chemical calculations were used to predict the theoretical value of the first molecular hyperpolarizability, as well as to simulate the one- and two-photon absorption spectra for all compounds. Full article
(This article belongs to the Special Issue Advanced Optical Materials and Devices)
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8 pages, 397 KiB  
Article
Short Barriers for Lowering Current-Density in Terahertz Quantum Cascade Lasers
by Liang Gao, John L. Reno and Sushil Kumar
Photonics 2020, 7(1), 7; https://doi.org/10.3390/photonics7010007 - 8 Jan 2020
Cited by 8 | Viewed by 4470
Abstract
Scattering due to interface-roughness (IR) and longitudinal-optical (LO) phonons are primary transport mechanisms in terahertz quantum-cascade lasers (QCLs). By choosing GaAs/Al0.10Ga0.90As heterostructures with short-barriers, the effect of IR scattering is mitigated, leading to low operating current-densities. A series of [...] Read more.
Scattering due to interface-roughness (IR) and longitudinal-optical (LO) phonons are primary transport mechanisms in terahertz quantum-cascade lasers (QCLs). By choosing GaAs/Al0.10Ga0.90As heterostructures with short-barriers, the effect of IR scattering is mitigated, leading to low operating current-densities. A series of resonant-phonon terahertz QCLs developed over time, achieving some of the lowest threshold and peak current-densities among published terahertz QCLs with maximum operating temperatures above 100 K. The best result is obtained for a three-well 3.1 THz QCL with threshold and peak current-densities of 134 A/cm2 and 208 A/cm2 respectively at 53 K, and a maximum lasing temperature of 135 K. Another three-well QCL designed for broadband bidirectional operation achieved lasing in a combined frequency range of 3.1–3.7 THz operating under both positive and negative polarities, with an operating current-density range of 167–322 A/cm2 at 53 K and maximum lasing temperature of 141 K or 121 K depending on the polarity of the applied bias. By showing results from QCLs developed over a period of time, here we show conclusively that short-barrier terahertz QCLs are effective in achieving low current-density operation at the cost of a reduction in peak temperature performance. Full article
(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)
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16 pages, 10484 KiB  
Article
CMOS-Compatible Measures for Thermal Management of Phase-Sensitive Silicon Photonic Systems
by Pedro-Andrei Krochin-Yepez, Ulrike Scholz and Andre Zimmermann
Photonics 2020, 7(1), 6; https://doi.org/10.3390/photonics7010006 - 1 Jan 2020
Cited by 5 | Viewed by 4984
Abstract
To date, several photonic applications have been demonstrated without considerable thermal management efforts. However, in phase-sensitive photonic applications, thermal management becomes of utmost importance. Thermal management of photonic systems requires not only efficient heat dissipation, but also reduction of on-chip temperature gradients. Particularly [...] Read more.
To date, several photonic applications have been demonstrated without considerable thermal management efforts. However, in phase-sensitive photonic applications, thermal management becomes of utmost importance. Thermal management of photonic systems requires not only efficient heat dissipation, but also reduction of on-chip temperature gradients. Particularly in highly integrated systems, in which several components are integrated within a single photonic integrated circuit, the reduction of on-chip temperature gradients is necessary to guarantee the correct functionality of the system. Due to their high integration density as well as their extreme temperature sensitivity, optical phased arrays are ideal examples of a system, where thermal management is required. Ideally, thermal management solutions of such systems should not require additional power for operation. Therefore, it is desired to improve the heat dissipation and to reduce temperature gradients by structural modifications of the photonic circuit. Furthermore, to cope with the advantages of silicon photonics, thermal management solutions must be compatible with series fabrication processes. In this work, complementary metal–oxide–semiconductor (CMOS)-compatible measures for thermal management of silicon photonic integrated circuits are proposed and validated by characterization of in-house fabricated thermal demonstrators. The proposed concepts are extremely efficient not only in reducing temperature gradients, but also in improving the heat dissipation from integrated heat sources. Full article
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22 pages, 5451 KiB  
Article
Numerical Study of Resonant Optical Parametric Amplification via Gain Factor Optimization in Dispersive Microresonators
by Özüm Emre Aşırım and Mustafa Kuzuoğlu
Photonics 2020, 7(1), 5; https://doi.org/10.3390/photonics7010005 - 25 Dec 2019
Cited by 7 | Viewed by 3698
Abstract
The achievement of wideband high-gain optical parametric amplification has not been shown in micrometer-scale cavities. In this paper we have computationally investigated the optical parametric amplification process in a few micrometer-long dispersive microresonator. By performing a gain medium resonance frequency dependent analysis of [...] Read more.
The achievement of wideband high-gain optical parametric amplification has not been shown in micrometer-scale cavities. In this paper we have computationally investigated the optical parametric amplification process in a few micrometer-long dispersive microresonator. By performing a gain medium resonance frequency dependent analysis of optical parametric amplification, we have found that it is possible to achieve a wideband high-gain optical amplification in a dispersive microresonator. In order to account for the effects of dispersion (modeled by the polarization damping coefficient) and the resonance frequency of the gain medium on optical parametric amplification, we have solved the wave equation in parallel with the nonlinear equation of electron cloud motion, using the finite difference time domain method. Then we have determined the resonance frequency values that yield an enhanced or a resonant case of optical parametric amplification, via gain factor optimization. It was observed that if the microresonator is more dispersive (has a lower polarization damping coefficient), then there are more resonance frequencies that yield an optical gain resonance. At these gain resonances, a very wideband, high-gain optical amplification seems possible in the micron scale, which, to our knowledge, has not been previously reported in the context of nonlinear wave mixing theory. Full article
(This article belongs to the Section Optical Interaction Science)
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33 pages, 11871 KiB  
Review
Hybrid Integrated Semiconductor Lasers with Silicon Nitride Feedback Circuits
by Klaus-J. Boller, Albert van Rees, Youwen Fan, Jesse Mak, Rob E. M. Lammerink, Cornelis A. A. Franken, Peter J. M. van der Slot, David A. I. Marpaung, Carsten Fallnich, Jörn P. Epping, Ruud M. Oldenbeuving, Dimitri Geskus, Ronald Dekker, Ilka Visscher, Robert Grootjans, Chris G. H. Roeloffzen, Marcel Hoekman, Edwin J. Klein, Arne Leinse and René G. Heideman
Photonics 2020, 7(1), 4; https://doi.org/10.3390/photonics7010004 - 21 Dec 2019
Cited by 106 | Viewed by 18573
Abstract
Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth, as well as compatibility for embedding into integrated photonic circuits, are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback [...] Read more.
Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth, as well as compatibility for embedding into integrated photonic circuits, are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si 3 N 4 in SiO 2 ) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around a 1.55 μ m wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser. Full article
(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)
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14 pages, 3303 KiB  
Article
Tunable Mode Converter Device Based on Photonic Crystal Fiber with a Thermo-Responsive Liquid Crystal Core
by Jorge Andres Montoya Cardona, Nelson Dario Gomez Cardona, Esteban Gonzalez Valencia, Pedro Torres Trujillo and Erick Reyes Vera
Photonics 2020, 7(1), 3; https://doi.org/10.3390/photonics7010003 - 19 Dec 2019
Cited by 11 | Viewed by 4305
Abstract
A compact tunable mode converter device based on the thermo-optically characteristics of liquid crystals (LCs) is proposed and numerically analyzed herein. The proposed mode converter consists of an asymmetric dual-core photonic crystal fiber (PCF) with a highly thermo-responsive LC core. The verification of [...] Read more.
A compact tunable mode converter device based on the thermo-optically characteristics of liquid crystals (LCs) is proposed and numerically analyzed herein. The proposed mode converter consists of an asymmetric dual-core photonic crystal fiber (PCF) with a highly thermo-responsive LC core. The verification of the proposed mode converter was ensured through an accurate PCF analysis based on the vector finite element method. With an appropriate choice of the design parameters associated with the LC core, phase matching at a single wavelength is available in the important O-band wavelength region. The simulation results showed that high conversion efficiencies between LP01 and LP11 mode are readily achieved over a broad wavelength range from 1278 nm to 1317 nm. Likewise, the tunable capability of the proposed mode converter was evaluated when it was submitted to thermal changes; thus, we evidence the strong thermo-responsive dependence of the operating wavelength, mode conversion efficiency and full-width at the half maximum (FWHM) bandwidth. Finally, the fabrication tolerances of the devices were also investigated. Therefore, the thermo-responsive characteristics of this novel PCF mode converter can be of fundamental importance in the future space division multiplexing technology. Full article
(This article belongs to the Section Optical Communication and Network)
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17 pages, 2328 KiB  
Article
Electron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models
by Chiara Ciano, Michele Virgilio, Luigi Bagolini, Leonetta Baldassarre, Andrea Rossetti, Alexej Pashkin, Manfred Helm, Michele Montanari, Luca Persichetti, Luciana Di Gaspare, Giovanni Capellini, Douglas J. Paul, Giacomo Scalari, Jèrome Faist, Monica De Seta and Michele Ortolani
Photonics 2020, 7(1), 2; https://doi.org/10.3390/photonics7010002 - 18 Dec 2019
Cited by 5 | Viewed by 4806
Abstract
n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe [...] Read more.
n-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron–phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter- and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an experimental case study, we have epitaxially grown samples consisting of two asymmetric coupled quantum wells forming a three-level system, which we optically pump with a free electron laser. The benchmark quantity selected for model testing purposes is the saturation intensity at the 1→3 intersubband transition. The numerical quantum model prediction is in reasonable agreement with the experiments and therefore outperforms the discrete-energy-level analytical model, of which the prediction of the saturation intensity is off by a factor 3. Full article
(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)
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17 pages, 4236 KiB  
Article
Angle Multiplexing Optical Image Encryption in the Fresnel Transform Domain Using Phase-Only Computer-Generated Hologram
by Hsuan T. Chang, Yao-Ting Wang and Chien-Yu Chen
Photonics 2020, 7(1), 1; https://doi.org/10.3390/photonics7010001 - 18 Dec 2019
Cited by 13 | Viewed by 4022
Abstract
We propose an angle multiplexing method for optics-based image encryption using a phase-only computer-generated hologram (POCGH) in the tilted Fresnel transform (TFrT) domain. Modified Gerchberg-Saxton algorithms, based on the three types of rotation manipulation in both the hologram and reconstruction planes, are used [...] Read more.
We propose an angle multiplexing method for optics-based image encryption using a phase-only computer-generated hologram (POCGH) in the tilted Fresnel transform (TFrT) domain. Modified Gerchberg-Saxton algorithms, based on the three types of rotation manipulation in both the hologram and reconstruction planes, are used with their corresponding TFrT parameters to extract the phase-only functions (POFs) of the target images. All the extracted POFs are then phase-modulated and summed to obtain the final POCGH, which is capable of multiplexing and avoiding overlap in the reconstructed images. The computer simulation results show that the images corresponding to the various rotation manipulations at the hologram and image reconstruction planes can be successfully restored with high correlation coefficients. Due to the encrypted nature of the multiplexed images, a higher system security level can be achieved, as the images can only be correctly displayed when all the required parameters in the TFrT are available. The angle sensitivity on the image quality for each manipulation is also investigated. Full article
(This article belongs to the Section Optical Communication and Network)
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