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Photonics, Volume 3, Issue 2 (June 2016)

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Research

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Open AccessArticle Equalization Enhanced Phase Noise in Coherent Optical Systems with Digital Pre- and Post-Processing
Photonics 2016, 3(2), 12; doi:10.3390/photonics3020012
Received: 15 February 2016 / Revised: 22 March 2016 / Accepted: 22 March 2016 / Published: 26 March 2016
Cited by 2 | PDF Full-text (1652 KB) | HTML Full-text | XML Full-text
Abstract
We present an extensive study of equalization enhanced phase noise (EEPN) in coherent optical system for all practical electronic dispersion compensation configurations. It is shown that there are only eight practicable all-electronic impairment mitigation configurations. The non-linear and time variant analysis reveals that
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We present an extensive study of equalization enhanced phase noise (EEPN) in coherent optical system for all practical electronic dispersion compensation configurations. It is shown that there are only eight practicable all-electronic impairment mitigation configurations. The non-linear and time variant analysis reveals that the existence and the cause of EEPN depend on the digital signal processing (DSP) schemes. There are three schemes that in principle do not cause EEPN. Analysis further reveals the statistical equivalence of the remaining five system configurations resulting in EEPN. In three of them, EEPN is due to phase noise of the transmitting laser, while in the remaining two, EEPN is caused by the local oscillator. We provide a simple look-up table for the system designer to make an informative decision regarding practicable configuration choice and design. Full article
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Open AccessArticle A High-Temperature Solar Selective Absorber Based upon Periodic Shallow Microstructures Coated by Multi-Layers Using Atomic Layer Deposition
Photonics 2016, 3(2), 13; doi:10.3390/photonics3020013
Received: 29 February 2016 / Revised: 21 March 2016 / Accepted: 22 March 2016 / Published: 29 March 2016
Cited by 2 | PDF Full-text (4009 KB) | HTML Full-text | XML Full-text
Abstract
Regarding the fabrication of solar selective absorbers, the ability to create microstructures on top of metal surfaces is a promising technology. Typically, these materials are able to possess spectrally-selective absorption properties for high-temperature usage. Solar-selective absorbers that function at temperatures up to 700
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Regarding the fabrication of solar selective absorbers, the ability to create microstructures on top of metal surfaces is a promising technology. Typically, these materials are able to possess spectrally-selective absorption properties for high-temperature usage. Solar-selective absorbers that function at temperatures up to 700 °C and possess shallow honeycomb cylindrical microcavities coated with a metal-dielectric multi-layer have been investigated. Honeycomb array cylindrical microcavities were fabricated on W substrate with interference lithography and multi-layers consisting of Pt nano-film sandwiched by Al2O3 layers were created for a uniform coating via atomic layer deposition. The absorbance spectrum of fabricated samples reveals results consistent with a simulation based on a rigorous coupled-wave analysis method. A solar absorbance value of 0.92 and a hemispherical total emittance value of 0.18 at 700 °C was determined from the fabricated solar-selective absorber. Additionally, thermal stability of up to 700 °C was confirmed in vacuum. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessArticle Dynamic Tuning of Transmission Wavelength of MEMS-Based Ge Waveguides on a Si Beam
Photonics 2016, 3(2), 14; doi:10.3390/photonics3020014
Received: 1 March 2016 / Revised: 15 March 2016 / Accepted: 17 March 2016 / Published: 30 March 2016
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Abstract
Three-dimensional structures of microelectro-mechanical systems (MEMS)-based Ge waveguide on a Si beam were fabricated for dynamic tuning of the fundamental absorption edge of Ge by external stressing. The application of various amounts of external forces up to 1 GPa onto the Si beam
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Three-dimensional structures of microelectro-mechanical systems (MEMS)-based Ge waveguide on a Si beam were fabricated for dynamic tuning of the fundamental absorption edge of Ge by external stressing. The application of various amounts of external forces up to 1 GPa onto the Si beam shows clear red-shifts in the absorption edge of Ge waveguides on the Si beam by ~40 nm. This shift was reproduced by the deformation potential theory, considering that mode of propagation in the Ge waveguide. The wavelength tuning range obtained makes it possible to cover the whole C-band of optical communication, indicating it to be a promising approach to electro-absorption Ge modulators to get them to work with a broader wavelength range than previously reported. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessArticle An Energy-Efficient High-Throughput Mesh-Based Photonic On-Chip Interconnect for Many-Core Systems
Photonics 2016, 3(2), 15; doi:10.3390/photonics3020015
Received: 25 February 2016 / Revised: 27 March 2016 / Accepted: 28 March 2016 / Published: 31 March 2016
Cited by 1 | PDF Full-text (2668 KB) | HTML Full-text | XML Full-text
Abstract
Future high-performance embedded and general purpose processors and systems-on-chip are expected to combine hundreds of cores integrated together to satisfy the power and performance requirements of large complex applications. As the number of cores continues to increase, the employment of low-power and high-throughput
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Future high-performance embedded and general purpose processors and systems-on-chip are expected to combine hundreds of cores integrated together to satisfy the power and performance requirements of large complex applications. As the number of cores continues to increase, the employment of low-power and high-throughput on-chip interconnect fabrics becomes imperative. In this work, we present a novel mesh-based photonic on-chip interconnect, named PHENIC-II, for future high-performance many-core systems. The novel architecture is based on an energy-efficient non-blocking photonic switch and a contention-aware routing algorithm. Simulation results show that the proposed system provides better bandwidth and energy efficiency when compared to conventional hybrid photonic NoC systems. Full article
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Open AccessArticle Continuous Emission Monitoring of Tetrafluoromethane Using Quantum Cascade Lasers
Photonics 2016, 3(2), 16; doi:10.3390/photonics3020016
Received: 11 March 2016 / Revised: 29 March 2016 / Accepted: 29 March 2016 / Published: 1 April 2016
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Abstract
Recent developments in quantum cascade lasers have enabled the development of new sensors for in-situ applications that have so far only been possible with extractive systems. In this work, a sensor is presented using a unique Wavelength Modulation Spectroscopy approach to measure tetrafluoromethane,
[...] Read more.
Recent developments in quantum cascade lasers have enabled the development of new sensors for in-situ applications that have so far only been possible with extractive systems. In this work, a sensor is presented using a unique Wavelength Modulation Spectroscopy approach to measure tetrafluoromethane, a strong greenhouse gas. The sensor was characterized in a laboratory environment indicating a long-term detection limit of 20 ppb·m and a short-term value of well below 10 ppb·m. To demonstrate the feasibility of the sensor in a real-world environment, it was installed at an Alcoa aluminum smelter. A co-located Fourier Transform Infrared Spectrometer allowed direct comparison measurements of both systems. General agreement between the two methods was observed, leading to the conclusion that the developed in-situ quantum cascade laser based sensor has the potential to continuously measure tetrafluoromethane at aluminum smelters. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Wide Spectral Characteristics of Si Photonic Crystal Mach-Zehnder Modulator Fabricated by Complementary Metal-Oxide-Semiconductor Process
Photonics 2016, 3(2), 17; doi:10.3390/photonics3020017
Received: 29 February 2016 / Revised: 27 March 2016 / Accepted: 29 March 2016 / Published: 2 April 2016
Cited by 3 | PDF Full-text (4079 KB) | HTML Full-text | XML Full-text
Abstract
Optical modulators for optical interconnects require a small size, small voltage, high speed and wide working spectrum. For this purpose, we developed Si slow-light Mach-Zehnder modulators via a 180 nm complementary metal-oxide-semiconductor process. We employed 200 μm lattice-shifted photonic crystal waveguides with interleaved
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Optical modulators for optical interconnects require a small size, small voltage, high speed and wide working spectrum. For this purpose, we developed Si slow-light Mach-Zehnder modulators via a 180 nm complementary metal-oxide-semiconductor process. We employed 200 μm lattice-shifted photonic crystal waveguides with interleaved p-n junctions as phase shifters. The group index spectrum of slow light was almost flat at ng ≈ 20 but exhibited ±10% fluctuation over a wavelength bandwidth of 20 nm. The cutoff frequency measured in this bandwidth ranged from 15 to 20 GHz; thus, clear open eyes were observed in the 25 Gbps modulation. However, the fluctuation in ng was reflected in the extinction ratio and bit-error rate. For a stable error-free operation, a 1 dB margin is necessary in the extinction ratio. In addition, we constructed a device with varied values of ng and confirmed that the extinction ratio at this speed was enhanced by larger ng up to 60. However, this larger ng reduced the cutoff frequency because of increased phase mismatch between slow light and radio frequency signals. Therefore, ng available for 25 Gbps modulation is limited to up to 40 for the current device design. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessArticle Spectroscopic Properties of Gold Curvilinear Nanorod Arrays
Photonics 2016, 3(2), 18; doi:10.3390/photonics3020018
Received: 4 March 2016 / Revised: 2 April 2016 / Accepted: 4 April 2016 / Published: 8 April 2016
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Abstract
We designed and fabricated gold curvilinear nanorod periodical arrays using microfabrication techniques. The gold curvilinear nanorods had two distinct resonant peaks in the near-infrared region between 1630 nm and 3000 nm. Similar peak was observed in gold straight nanorods at specific lengths. At
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We designed and fabricated gold curvilinear nanorod periodical arrays using microfabrication techniques. The gold curvilinear nanorods had two distinct resonant peaks in the near-infrared region between 1630 nm and 3000 nm. Similar peak was observed in gold straight nanorods at specific lengths. At lengths identical to the arc length of the curvilinear nanorod, the peak was in the relative range of 3000 nm, which corresponds to the longitudinal plasmon mode (L-mode). At lengths identical to half of the arc length of the curvilinear nanorod, the peak was close to 1630 nm. Plasmon resonant peaks were tunable in the infrared region by changing the arc length of the curve, the line width, and distance between the curvilinear nanorods. In particular, when two curvilinear nanorods were closely packed in a range of less than 100 nm, the peak wavelength of curvilinear nanorod was shifted due to the plasmonic coupling of each mode. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessArticle Enhanced Crystal Quality of AlxIn1-xAsySb1-y for Terahertz Quantum Cascade Lasers
Photonics 2016, 3(2), 20; doi:10.3390/photonics3020020
Received: 31 March 2016 / Revised: 14 April 2016 / Accepted: 15 April 2016 / Published: 20 April 2016
Cited by 2 | PDF Full-text (4556 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work provides a detailed study on the growth of AlxIn1-xAsySb1-y lattice-matched to InAs by Molecular Beam Epitaxy. In order to find the conditions which lead to high crystal quality deep within the miscibility gap, Al
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This work provides a detailed study on the growth of AlxIn1-xAsySb1-y lattice-matched to InAs by Molecular Beam Epitaxy. In order to find the conditions which lead to high crystal quality deep within the miscibility gap, AlxIn1-xAsySb1-y with x = 0.462 was grown at different growth temperatures as well as As2 and Sb2 beam equivalent pressures. The crystal quality of the grown layers was examined by high-resolution X-ray diffraction and atomic force microscopy. It was found that the incorporation of Sb into Al0.462In0.538AsySb1-y is strongly temperature-dependent and reduced growth temperatures are necessary in order to achieve significant Sb mole fractions in the grown layers. At 480 C lattice matching to InAs could not be achieved. At 410 C lattice matching was possible and high quality films of Al0.462In0.538AsySb1-y were obtained. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
Open AccessArticle Estimation of BER from Error Vector Magnitude for Optical Coherent Systems
Photonics 2016, 3(2), 21; doi:10.3390/photonics3020021
Received: 22 March 2016 / Revised: 18 April 2016 / Accepted: 19 April 2016 / Published: 21 April 2016
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Abstract
This paper presents the estimation of bit error ratio (BER) from error vector magnitude (EVM) for M-ary quadrature amplitude modulation (QAM) formats in optical coherent systems employing carrier phase recovery with differential decoding to compensate for laser phase noise. Simulation results show
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This paper presents the estimation of bit error ratio (BER) from error vector magnitude (EVM) for M-ary quadrature amplitude modulation (QAM) formats in optical coherent systems employing carrier phase recovery with differential decoding to compensate for laser phase noise. Simulation results show that the relationship to estimate BER from EVM analysis for data-aided reception can also be applied to nondata-aided reception with a correction factor for different combined linewidth symbol duration product at the target BER of 10 3 . It is demonstrated that the calibrated BER, which would otherwise be underestimated without the correction factor, can reliably monitor the performance of optical coherent systems near the target BER for quadrature phase shift keying (QPSK), 16-QAM, and 64-QAM. Full article
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Open AccessArticle Influence of Ethanol on Breath Acetone Measurements Using an External Cavity Quantum Cascade Laser
Photonics 2016, 3(2), 22; doi:10.3390/photonics3020022
Received: 31 March 2016 / Revised: 22 April 2016 / Accepted: 24 April 2016 / Published: 27 April 2016
Cited by 4 | PDF Full-text (2379 KB) | HTML Full-text | XML Full-text
Abstract
Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as
[...] Read more.
Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as narrow scanning mode around 1216 cm−1, respectively, for detection of acetone in exhaled breath. This wavelength region is essential for accurate determination of breath acetone due to the relative low spectral influence of other endogenous molecules like water, carbon dioxide or methane. We demonstrated that ethanol has a strong spectroscopic influence on the acetone concentration in exhaled breath, an important detail that has been overlooked so far. An ethanol correction is proposed and validated with the reference measurements from a proton-transfer reaction mass spectrometer (PTR-MS) for the same breath samples from ten persons. With the ethanol correction, both broadband and narrowband molecular spectroscopy represent an attractive way to accurately assess the exhaled breath acetone. The importance of considering spectroscopic ethanol influence is essential, especially for the narrowband scans, (e.g., 1216 cm−1), for which the error in determining the acetone concentrations can rise up to 39% if it is not considered. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Aluminum Nitride Ceramic as an Optically Stimulable Luminescence Dosimeter Plate
Photonics 2016, 3(2), 23; doi:10.3390/photonics3020023
Received: 4 April 2016 / Revised: 25 April 2016 / Accepted: 27 April 2016 / Published: 30 April 2016
Cited by 2 | PDF Full-text (1566 KB) | HTML Full-text | XML Full-text
Abstract
Photostimulable storage phosphors have been used in a wide range of applications including radiation measurements in one- and two-dimensional spaces, called point dosimetry and radiography. In this work, we report that an aluminum nitride (AlN) ceramic plate, which is practically used as a
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Photostimulable storage phosphors have been used in a wide range of applications including radiation measurements in one- and two-dimensional spaces, called point dosimetry and radiography. In this work, we report that an aluminum nitride (AlN) ceramic plate, which is practically used as a heat sink (SHAPAL®, Tokuyama Corp., Yamaguchi, Japan), shows good optically-stimulated luminescence (OSL) properties with sufficiently large signal and capability for imaging applications, and we have characterized the AlN plate for OSL applications. Upon interaction with X-rays, the sample color turns yellowish, due to a radiation-induced photoabsorption band in the UV-blue range below ~500 nm. After irradiating the sample with X-rays, an intense OSL emission can be observed in the UV (360 nm) spectral region during stimulation by red light. Although our measurement setup is not optimized, dose detection was confirmed as low as ~3 mGy to over 20 Gy. Furthermore, we have successfully demonstrated that the SHAPAL® AlN ceramic plate has great potential to be used as an imaging plate in radiography. Full article
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Open AccessArticle Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis
Photonics 2016, 3(2), 24; doi:10.3390/photonics3020024
Received: 31 March 2016 / Revised: 27 April 2016 / Accepted: 28 April 2016 / Published: 30 April 2016
Cited by 3 | PDF Full-text (4790 KB) | HTML Full-text | XML Full-text
Abstract
We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping
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We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping during long (>5 µs) current pulses. The theoretical aspects of the observed behavior are discussed using a combination of finite element method simulations and transfer matrix method calculations of dual-section DFB structures. Based on these results, we demonstrate how the internal etaloning can be minimized using anti-reflective (AR) coatings. Finally, the potential and benefits of these devices for high precision trace gas analysis are demonstrated using a laser absorption spectroscopic setup. Thereby, the atmospherically highly relevant compounds CO2 (including its major isotopologues), CO and N2O are simultaneously determined with a precision of 0.16 ppm, 0.22 ppb and 0.26 ppb, respectively, using a 1-s integration time and an optical path-length of 36 m. This creates exciting new opportunities in the development of compact, multi-species trace gas analyzers. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Widely Tunable Monolithic Mid-Infrared Quantum Cascade Lasers Using Super-Structure Grating Reflectors
Photonics 2016, 3(2), 25; doi:10.3390/photonics3020025
Received: 1 April 2016 / Revised: 28 April 2016 / Accepted: 29 April 2016 / Published: 3 May 2016
Cited by 1 | PDF Full-text (2845 KB) | HTML Full-text | XML Full-text
Abstract
A monolithic, three-section, and widely tunable mid-infrared (mid-IR) quantum cascade laser (QCL) is demonstrated. This electrically tuned laser consists of a gain section placed between two super structure grating (SSG) distributed Bragg reflectors (DBRs). By varying the injection currents to the two grating
[...] Read more.
A monolithic, three-section, and widely tunable mid-infrared (mid-IR) quantum cascade laser (QCL) is demonstrated. This electrically tuned laser consists of a gain section placed between two super structure grating (SSG) distributed Bragg reflectors (DBRs). By varying the injection currents to the two grating sections of this device, its emission wavelength can be tuned from 4.58 μm to 4.77 μm (90 cm−1) with a supermode spacing of 30 nm. This type of SSG-DBR QCLs can be a compact replacement for the external cavity QCL. It has great potential to achieve gap-free and even further tuning ranges for sensor applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
Open AccessArticle Advanced Fabrication of Single-Mode and Multi-Wavelength MIR-QCLs
Photonics 2016, 3(2), 26; doi:10.3390/photonics3020026
Received: 22 March 2016 / Revised: 30 April 2016 / Accepted: 2 May 2016 / Published: 11 May 2016
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Abstract
In this article we present our latest work on the optimization of mid-infrared quantum cascade laser fabrication techniques. Our efforts are focused on low dissipation devices, broad-area high-power photonic crystal lasers, as well as multi-wavelength devices realized either as arrays or multi-section distributed
[...] Read more.
In this article we present our latest work on the optimization of mid-infrared quantum cascade laser fabrication techniques. Our efforts are focused on low dissipation devices, broad-area high-power photonic crystal lasers, as well as multi-wavelength devices realized either as arrays or multi-section distributed feedback (DFB) devices. We summarize our latest achievements and update them with our most recent results. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessArticle Cascade Type-I Quantum Well GaSb-Based Diode Lasers
Photonics 2016, 3(2), 27; doi:10.3390/photonics3020027
Received: 7 April 2016 / Revised: 2 May 2016 / Accepted: 4 May 2016 / Published: 11 May 2016
Cited by 4 | PDF Full-text (1927 KB) | HTML Full-text | XML Full-text
Abstract
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in a spectral region from 1.9 to 3.3 μm. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in
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Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in a spectral region from 1.9 to 3.3 μm. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in GaSb/AlSb/InAs heterostructure complemented with optimized electron and hole injector regions. Coated devices with an ~100-μm-wide aperture and a 3-mm-long cavity demonstrated continuous wave (CW) output power of 1.96 W near 2 μm, 980 mW near 3 μm, 500 mW near 3.18 μm, and 360 mW near 3.25 μm at 17–20 °C—a nearly or more than twofold increase compared to previous state-of-the-art diode lasers. The utilization of the different quantum wells in the cascade laser heterostructure was demonstrated to yield wide gain lasers, as often desired for tunable laser spectroscopy. Double-step etching was utilized to minimize both the internal optical loss and the lateral current spreading penalties in narrow-ridge lasers. Narrow-ridge cascade diode lasers operate in a CW regime with ~100 mW of output power near and above 3 μm and above 150 mW near 2 μm. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Recent Advances and Applications of External Cavity-QCLs towards Hyperspectral Imaging for Standoff Detection and Real-Time Spectroscopic Sensing of Chemicals
Photonics 2016, 3(2), 28; doi:10.3390/photonics3020028
Received: 31 March 2016 / Revised: 27 April 2016 / Accepted: 30 April 2016 / Published: 13 May 2016
Cited by 6 | PDF Full-text (5798 KB) | HTML Full-text | XML Full-text
Abstract
External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a
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External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a broad gain spectrum and a resonantly driven micro-opto-electro-mechanical (MOEMS) scanner with an integrated diffraction grating in Littrow configuration. The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets, as well as on hazardous substances, such as explosives. Furthermore, different applications for the EC-QCL technology in spectroscopic sensing are presented. These include the fields of process analysis with on- or even inline capability and imaging backscattering spectroscopy for contactless identification of solid and liquid contaminations on surfaces. Recent progress in trace detection of explosives and related precursors in relevant environments as well as advances in food quality monitoring by discriminating fresh and mold contaminated peanuts based on their MIR backscattering spectrum is shown. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study
Photonics 2016, 3(2), 29; doi:10.3390/photonics3020029
Received: 31 March 2016 / Revised: 6 May 2016 / Accepted: 9 May 2016 / Published: 13 May 2016
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Abstract
In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current
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In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. Here, we study the influence of two important quantum-dot material parameters, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. However, by minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Modeling the Electro-Optical Performance of High Power Mid-Infrared Quantum Cascade Lasers
Photonics 2016, 3(2), 30; doi:10.3390/photonics3020030
Received: 24 March 2016 / Revised: 10 May 2016 / Accepted: 10 May 2016 / Published: 17 May 2016
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Abstract
Performance modeling of the characteristics of mid-infrared quantum cascade lasers (MIR QCL) is an essential element in formulating consistent component requirements and specifications, in preparing guidelines for the design and manufacture of the QCL structures, and in assessing different modes of operation of
[...] Read more.
Performance modeling of the characteristics of mid-infrared quantum cascade lasers (MIR QCL) is an essential element in formulating consistent component requirements and specifications, in preparing guidelines for the design and manufacture of the QCL structures, and in assessing different modes of operation of the laser device. We use principles of system physics to analyze the electro-optical characteristics of high power MIR QCL, including thermal backfilling of the lower laser level, hot electron effects, and Stark detuning during lasing. The analysis is based on analytical modeling to give simple mathematical expressions which are easily incorporated in system-level simulations of defense applications such as directed infrared countermeasures (DIRCM). The paper delineates the system physics of the electro-optical energy conversion in QCL and the related modeling. The application of the performance model to a DIRCM QCL is explained by an example. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Liver Status Assessment by Spectrally and Time Resolved IR Detection of Drug Induced Breath Gas Changes
Photonics 2016, 3(2), 31; doi:10.3390/photonics3020031
Received: 31 March 2016 / Revised: 28 April 2016 / Accepted: 30 April 2016 / Published: 20 May 2016
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Abstract
The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20
[...] Read more.
The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 to 60 min. Fast administration of 13C-labelled methacetin induces a fast response of liver metabolism and is tracked in real-time by the increase of 13CO2 in exhaled air. The 13CO2 concentration increase in exhaled air allows the determination of the metabolic liver capacity (LiMAx-test). Fluctuations in CO2 concentration, pressure and temperature are minimized by special gas handling, and tracking of several spectrally resolved CO2 absorption bands with a quantum cascade laser. Absorption measurement of different 12CO2 and 13CO2 rotation-vibration transitions in the same time window allows for multiple referencing and reduction of systematic errors. This FLIP (Fast liver investigation package) setup is being successfully used to plan operations and determine the liver status of patients. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessCommunication Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators
Photonics 2016, 3(2), 32; doi:10.3390/photonics3020032
Received: 5 April 2016 / Revised: 13 May 2016 / Accepted: 16 May 2016 / Published: 20 May 2016
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Abstract
Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric
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Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric (vertically radiative but low quality factor Q) and anti-symmetric (non-radiative, high Q) modes is indeed here fully overcome, offering a concrete perspective of highly efficient vertical emitting resonators. We here exploit electrically pumped terahertz quantum cascade heterostructures to devise two-dimensional seven-fold quasi-crystal resonators, exploiting rotational order or irregularly distributed defects. By lithographically tuning the lattice quasi-periodicity and/or the hole radius of the imprinted patterns, efficient multimode surface emission with a rich sequence of spectral lines distributed over a 2.9–3.4 THz bandwidth was reached. We demonstrated multicolor emission with 67 mW of peak optical power, slope efficiencies up to ≈70 mW/A, 0.14% wall plug efficiencies and beam profile results of the rich quasi-crystal Fourier spectrum that, in the case of larger rotational order, can reach very low divergence. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Rapid and Sensitive Quantification of Isotopic Mixtures Using a Rapidly-Swept External Cavity Quantum Cascade Laser
Photonics 2016, 3(2), 33; doi:10.3390/photonics3020033
Received: 31 March 2016 / Revised: 16 May 2016 / Accepted: 17 May 2016 / Published: 23 May 2016
Cited by 3 | PDF Full-text (3944 KB) | HTML Full-text | XML Full-text
Abstract
A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O
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A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O liquid near the open-path Herriott cell, allowing the H/D exchange reaction with ambient H2O to produce HDO. Fluctuations in the ratio of D2O and HDO on timescales of <1 s due to the combined effects of plume transport and the H/D exchange chemical reaction are observed. Noise-equivalent concentrations (1σ) (NEC) of 147.0 ppbv and 151.6 ppbv in a 25-ms measurement time are determined for D2O and HDO, respectively, with a 127-m optical path. These NECs are improved to 23.0 and 24.0 ppbv with a 1-s averaging time for D2O and HDO, respectively. NECs <200 ppbv are also estimated for N2O, 1,1,1,2–tetrafluoroethane (F134A), CH4, acetone and SO2 for a 25-ms measurement time. The isotopic precision for measurement of the [D2O]/[HDO] concentration ratio of 33‰ and 5‰ is calculated for the current experimental conditions for measurement times of 25 ms and 1 s, respectively. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Semiconductor Three-Dimensional Photonic Crystals with Novel Layer-by-Layer Structures
Photonics 2016, 3(2), 34; doi:10.3390/photonics3020034
Received: 5 April 2016 / Revised: 16 May 2016 / Accepted: 17 May 2016 / Published: 20 May 2016
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Abstract
Three-dimensional photonic crystals (3D PhCs) are a fascinating platform for manipulating photons and controlling their interactions with matter. One widely investigated structure is the layer-by-layer woodpile structure, which possesses a complete photonic bandgap. On the other hand, other types of 3D PhC structures
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Three-dimensional photonic crystals (3D PhCs) are a fascinating platform for manipulating photons and controlling their interactions with matter. One widely investigated structure is the layer-by-layer woodpile structure, which possesses a complete photonic bandgap. On the other hand, other types of 3D PhC structures also offer various possibilities for controlling light by utilizing the three dimensional nature of structures. In this article, we discuss our recent research into novel types of layer-by-layer structures, including the experimental demonstration of a 3D PhC nanocavity formed in a <110>-layered diamond structure and the realization of artificial optical activity in rotationally stacked woodpile structures. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
Open AccessArticle Heterogeneously Integrated Distributed Feedback Quantum Cascade Lasers on Silicon
Photonics 2016, 3(2), 35; doi:10.3390/photonics3020035
Received: 28 April 2016 / Revised: 29 May 2016 / Accepted: 30 May 2016 / Published: 2 June 2016
Cited by 7 | PDF Full-text (4476 KB) | HTML Full-text | XML Full-text
Abstract
Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated
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Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Pérot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for mid-infrared (MIR) silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon has been reported to date. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-on-insulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle Two-Stage n-PSK Partitioning Carrier Phase Recovery Scheme for Circular mQAM Coherent Optical Systems
Photonics 2016, 3(2), 37; doi:10.3390/photonics3020037
Received: 25 April 2016 / Revised: 31 May 2016 / Accepted: 1 June 2016 / Published: 4 June 2016
Cited by 2 | PDF Full-text (4948 KB) | HTML Full-text | XML Full-text
Abstract
A novel two-stage n-PSK partitioning carrier phase recovery (CPR) scheme for circular multilevel quadrature amplitude modulation (C-mQAM) constellations is presented. The first stage of the algorithm provides an initial rough estimation of the received constellation, which is utilized in the second stage for
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A novel two-stage n-PSK partitioning carrier phase recovery (CPR) scheme for circular multilevel quadrature amplitude modulation (C-mQAM) constellations is presented. The first stage of the algorithm provides an initial rough estimation of the received constellation, which is utilized in the second stage for CPR. The performance of the proposed algorithm is studied through extensive simulations at the forward error correction bit error rate targets of 3.8 × 103 and 1 × 102 and is compared with different CPR algorithms. A significant improvement in the combined linewidth symbol duration product (ΔνTs) tolerance is achieved compared to the single-stage n-PSK partitioning scheme. Superior performance in the ΔνTs tolerance compared to the blind phase search algorithm is also reported. The relative improvements with respect to other CPR schemes are also validated experimentally for a 28-Gbaud C-16QAM back-to-back transmission system. The computational complexity of the proposed CPR scheme is studied, and reduction factors of 24.5 | 30.1 and 59.1 | 63.3 are achieved for C-16QAM and C-64QAM, respectively, compared to single-stage BPS in the form of multipliers | adders. Full article
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Open AccessArticle Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers
Photonics 2016, 3(2), 38; doi:10.3390/photonics3020038
Received: 4 May 2016 / Revised: 5 June 2016 / Accepted: 7 June 2016 / Published: 10 June 2016
Cited by 3 | PDF Full-text (640 KB) | HTML Full-text | XML Full-text
Abstract
We present a quantum transport simulation of a 4.6-μm quantum cascade laser (QCL) operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian
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We present a quantum transport simulation of a 4.6- μ m quantum cascade laser (QCL) operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian master equation in the presence of applied electric field and relevant scattering mechanisms. We show that it is important to allow for both position-dependent effective mass and for effective lowering of very thin barriers in order to obtain the band structure and the current-field characteristics comparable to experiment. Our calculations agree well with experiments over a wide range of temperatures. We predict a room-temperature threshold field of 62 . 5 kV/cm and a characteristic temperature for threshold-current-density variation of T 0 = 199 K . We also calculate electronic in-plane distributions, which are far from thermal, and show that subband electron temperatures can be hundreds to thousands of degrees higher than the heat sink. Finally, we emphasize the role of coherent tunneling current by looking at the size of coherences, the off-diagonal elements of the density matrix. At the design lasing field, efficient injection manifests itself in a large injector/upper lasing level coherence, which underscores the insufficiency of semiclassical techniques to address injection in QCLs. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
Open AccessArticle Effective Linewidth of Semiconductor Lasers for Coherent Optical Data Links
Photonics 2016, 3(2), 39; doi:10.3390/photonics3020039
Received: 12 May 2016 / Revised: 7 June 2016 / Accepted: 9 June 2016 / Published: 15 June 2016
Cited by 1 | PDF Full-text (1773 KB) | HTML Full-text | XML Full-text
Abstract
We discuss the implications of using monolithically integrated semiconductor lasers in high capacity optical coherent links suitable for metro applications, where the integration capabilities of semiconductor lasers make them an attractive candidate to reduce transceiver cost. By investigating semiconductor laser frequency noise profiles
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We discuss the implications of using monolithically integrated semiconductor lasers in high capacity optical coherent links suitable for metro applications, where the integration capabilities of semiconductor lasers make them an attractive candidate to reduce transceiver cost. By investigating semiconductor laser frequency noise profiles we show that carrier induced frequency noise plays an important role in system performance. We point out that, when such lasers are employed, the commonly used laser linewidth fails to estimate system performance, and we propose an alternative figure of merit that we name “Effective Linewidth”. We derive this figure of merit analytically, explore it by numerical simulations and experimentally validate our results by transmitting a 28 Gbaud DP-16QAM over an optical link. Our investigations cover the use of semiconductor lasers both in the transmitter side and as a local oscillator at the receiver. The obtained results show that our proposed “effective linewidth” is easy to measure and accounts for frequency noise more accurately, and hence the penalties associated to phase noise in the received signal. Full article

Review

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Open AccessReview Progress in Rapidly-Tunable External Cavity Quantum Cascade Lasers with a Frequency-Shifted Feedback
Photonics 2016, 3(2), 19; doi:10.3390/photonics3020019
Received: 21 March 2016 / Revised: 11 April 2016 / Accepted: 13 April 2016 / Published: 18 April 2016
Cited by 6 | PDF Full-text (5089 KB) | HTML Full-text | XML Full-text
Abstract
The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance
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The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance for various critical applications requiring ultra-rapid wavelength tuning, including combustion and explosion diagnostics and standoff detection. In this paper, recent research results on these devices are summarized and the advantages of the new configuration are analyzed in the context of practical applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessReview Fabrication of 3D Photonic Crystals toward Arbitrary Manipulation of Photons in Three Dimensions
Photonics 2016, 3(2), 36; doi:10.3390/photonics3020036
Received: 26 April 2016 / Revised: 28 May 2016 / Accepted: 30 May 2016 / Published: 3 June 2016
Cited by 2 | PDF Full-text (5760 KB) | HTML Full-text | XML Full-text
Abstract
The creation of large-area, unintentional-defect-free three-dimensional (3D) photonic crystals in the optical regime is a key challenge toward the realization of the arbitrary 3D manipulation of photons. In this article, we discuss an advanced fabrication method of 3D silicon photonic crystals based on
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The creation of large-area, unintentional-defect-free three-dimensional (3D) photonic crystals in the optical regime is a key challenge toward the realization of the arbitrary 3D manipulation of photons. In this article, we discuss an advanced fabrication method of 3D silicon photonic crystals based on the highly accurate alignment and wafer bonding of silicon-on-insulator (SOI) wafers. We introduce an advanced alignment system, in which the alignment process is automated by image recognition and feed-back control of stages, and show that it achieves an alignment accuracy better than ~50 nm. The bonding of SOI wafers is also investigated to obtain 3D crystals composed of highly pure crystalline silicon. We show the fabrication results of large-area 3D photonic crystals based on such considerations and demonstrate the successful introduction of artificial defects as functional components, such as coupled waveguide pairs or waveguides/nanocavities. We expect that these will be pioneering results toward the arbitrary 3D control of photons using 3D photonic crystals. Full article
(This article belongs to the Special Issue 3D- and 2D-Nanofabrication for Photonic Devices)
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Open AccessReview Semiconductor Nanomembrane-Based Light-Emitting and Photodetecting Devices
Photonics 2016, 3(2), 40; doi:10.3390/photonics3020040
Received: 1 June 2016 / Revised: 13 June 2016 / Accepted: 14 June 2016 / Published: 17 June 2016
Cited by 2 | PDF Full-text (8587 KB) | HTML Full-text | XML Full-text
Abstract
Heterogeneous integration between silicon (Si), III-V group material and Germanium (Ge) is highly desirable to achieve monolithic photonic circuits. Transfer-printing and stacking between different semiconductor nanomembranes (NMs) enables more versatile combinations to realize high-performance light-emitting and photodetecting devices. In this paper, lasers, including
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Heterogeneous integration between silicon (Si), III-V group material and Germanium (Ge) is highly desirable to achieve monolithic photonic circuits. Transfer-printing and stacking between different semiconductor nanomembranes (NMs) enables more versatile combinations to realize high-performance light-emitting and photodetecting devices. In this paper, lasers, including vertical and edge-emitting structures, flexible light-emitting diode, photodetectors at visible and infrared wavelengths, as well as flexible photodetectors, are reviewed to demonstrate that the transfer-printed semiconductor nanomembrane stacked layers have a large variety of applications in integrated optoelectronic systems. Full article
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