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This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector. The laser operated at the temperature settings of 15°C and 20°C. The experiment was conducted over a distance of 1 m and in a lab as a controlled environment. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including non-return-to-zero on-off keying (NRZ-OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15°C, the studied LWIR FSO system achieves net bitrates of 15 Gbps with an NRZ-OOK signal and 16.9 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps NRZ-OOK below the 2.7% overhead Reed-Solomon RS(528,514) pre-FEC (KR-FEC limit). At 20°C, we obtained net bitrates of 14.1 Gbps with NRZ-OOK, 16.9 Gbps with PAM4, and 16.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems., Horizon 2020 Framework Programme cFLOW project (828893); Vetenskapsr\u00E5det (2019-05197); Project \u2019BRAIN\u2019 (2022-04798); EU COST Action CA19111 NEWFOCUS; The LZP FLPP Project \u2019MIR-FAST\u2019 (lzp-2023-1-0503); The Strategic innovation program smarter electronic systems - a joint venture by Vinnona, Forms and the Swedish Energy Agency A-FRONTHAUL Project (2023-00659).

The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s−1. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s−1 communication., QC 20240927

We summarize our recent experimental studies of free-space communications enabled by directly modulated quantum cascade lasers at both MWIR and LWIR regions. Different detector types with different characteristics are compared., QC 20240612

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector. The laser operated at the temperature settings of 15°C and 20°C. The experiment was conducted over a distance of 1 m and in a lab as a controlled environment. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including non-return-to-zero on-off keying (NRZ-OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15°C, the studied LWIR FSO system achieves net bitrates of 15 Gbps with an NRZ-OOK signal and 16.9 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps NRZ-OOK below the 2.7% overhead Reed-Solomon RS(528,514) pre-FEC (KR-FEC limit). At 20°C, we obtained net bitrates of 14.1 Gbps with NRZ-OOK, 16.9 Gbps with PAM4, and 16.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems., Horizon 2020 Framework Programme cFLOW project (828893); Vetenskapsr\u00E5det (2019-05197); Project \u2019BRAIN\u2019 (2022-04798); EU COST Action CA19111 NEWFOCUS; The LZP FLPP Project \u2019MIR-FAST\u2019 (lzp-2023-1-0503); The Strategic innovation program smarter electronic systems - a joint venture by Vinnona, Forms and the Swedish Energy Agency A-FRONTHAUL Project (2023-00659).

Distributed-MIMO (D-MIMO) is a prospective solution for next-generation mobile networks to increase capacity and coverage. We experimentally validate 1024-QAM coherent joint transmissions in a two transmitter D-MIMO network including radio-over-LWIR FSO fronthaul links facilitating deployment and achieving diversity and power gains close to theoretical values., Part of ISBN 979-8-3503-1261-4QC 20240209

This study explores the potential of long-wave infrared free-space optical (FSO) transmission that leverages multilevel signals to attain high spectral efficiency. The FSO transmission system consists of a directly modulated-quantum cascade laser (DM-QCL) operating at 9.15 mu m and a mercury cadmium telluride (MCT) detector. To fully understand the system, we conduct measurements on the DM-QCL chip and MCT detector and assess the overall amplitude response of the DM-QCL, MCT detector, and all electrical components. We apply various signals, including on-off keying (OOK), 4-level pulse amplitude modulation (PAM4), 6-level PAM (PAM6), and 8-level PAM (PAM8) to maximize the bit rate and spectral efficiency of the FSO transmission. Through a two-dimensional sweeping of the laser bias current and MCT detector photovoltage, we optimize the transmission performance. At the optimal operation point, the FSO system achieved impressive results which are up to 6 Gbaud OOK, 3.5 Gbaud PAM4, 3 Gbaud PAM6, and 2.7 Gbaud PAM8 signal transmissions, with a bit error rate performance below 6.25% overhead hard decision-forward error correction limit when the DM-QCL operates at 10 degrees C. We also evaluate the eye diagrams and stability of the system to showcase its remarkable transmission performance. Our findings suggest that the DM-QCL and MCT detector-based FSO transceivers offer a highly competitive solution for the next generation of optical wireless communication systems., QC 20231115

Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching., QC 20231013

Buried heterostructure quantum cascade lasers (BH-QCLs) operating at high temperature in mid-infrared (MIR) to THz spectral range are desired for chemical sensing and free-space optical communication (FOC). In this work, Fe doped semi-insulating InP (SI-InP) regrowth is demonstrated in a hydride vapor phase epitaxy (HVPE) reactor for advanced MIR and THz BH-QCLs grown by MBE and MOCVD. SI-InP regrowth is implemented in THz QCL pillar arrays and narrow width and reverse-taper MIR BH-QCLs for efficient heat dissipation. By exploiting SI-InP regrowth, the parasitic capacitance in MIR distributed feedback BH-QCL can be suppressed, which is exploited for high speed FOC application., Part of ISBN 9781510659858QC 20231030

We experimentally demonstrate a Long-Wave IR FSO link with a 9.15-hm directly modulated quantum cascade laser at room temperature. Up to 8.1 Gb/s PAM8 transmission over 1.4 meter is achieved with a wideband MCT detector., QC 20230810

We experimentally test the compliance with 5G/NR 3GPP technical specifications of an analog radio-over-FSO link at 9 mu m. The ACLR and EVM transmitter requirements are fulfilled validating the suitability of LWIR FSO for 6G fronthaul., QC 20230810Part of ISBN 979-8-3503-1229-4

GaAsP/Si with high crystalline quality fabricated by cost-effective heteroepitaxial technology is a promising pathway for realizing low-cost Si-based tandem solar cell with efficiency higher than 30%. Herein, hydride vapor-phase epitaxy is used to perform selective area growth of GaAsP with high lateral coverage, referred to as epitaxial lateral overgrowth (ELOG). The ELOG is performed on GaAs-based substrates as a prestudy, followed by GaAs/Si and GaAsP/Si seed wafers employing chemical mechanical polishing to fabricate full 2 00 GaAsP/Si templates. These are subsequently used to grow and process GaAsP/Si pn-junction structures for electrical characterization. The ELOG GaAsP is studied by spatially resolved photoluminescence (PL) mapping and high-resolution X-ray diffraction measurements. PL analysis of the GaAsP/GaAs ELOG samples reveals an enhanced P-incorporation during lateral growth of GaAsP. This is also observed for the GaAsP/Si ELOG templates along with evidence of improved material quality, clearly distinguishing the laterally grown GaAsP from the planar growth directly above the Si substrate. Leakage pathways causing reduced electrical performance of the ELOG GaAsP/Si pn-junction structures are identified., QC 20230607

High bitrate mid-infrared links using simple (NRZ) and multi-level (PAM-4) data coding schemes have been realized in the 8 pm to 14 pm atmospheric transparency window. The free space optics system is composed of unipolar quantum optoelectronic devices, namely a continuous wave quantum cascade laser, an external Stark-effect modulator and a quantum cascade detector, all operating at room-temperature. Pre- and post-processing are implemented to get enhanced bitrates, especially for PAM-4 where inter-symbol interference and noise are particularly detrimental to symbol demodulation. By exploiting these equalization procedures, our system, with a full frequency cutoff of 2 GHz, has reached transmission bitrates of 12 Gbit/s NRZ and 11 Gbit/s PAM-4 fulfilling the 6.25 % overhead hard-decision forward error correction threshold, limited only by the low signal-to-noise ratio of our detector., QC 20230626

Orientation-patterned gallium phosphide (OP-GaP) has been grown heteroepitaxially on OP gallium arsenide (GaAs) templates using hydride vapor phase epitaxy (HVPE). The effect of OP-GaAs template fabrication methods of epitaxial-inversion and wafer bonding on the heteroepitaxial OP-GaP growth has been investigated. OP-GaP layers with a growth rate of up to 35 mu m/h and excellent domain fidelity were obtained. The growth rate and the domain fidelity have been revealed/studied by scanning electron microscope (SEM). In addition, we demonstrate that the crystalline quality of the individual domains, namely, the substrate-oriented domains (ODs) and the inverted domains (IDs), can be investigated by high-resolution x-ray diffraction reciprocal space mapping (HRXRDRSM), which can also indicate the domain fidelity. Attempts to increase the growth rate and improve the domain fidelity by increasing the III and V group precursors resulted in either an increase in the growth rate in the OP-GaP layers grown on epitaxial inversion OP-GaAs template at the expense of the domain crystalline quality and fidelity or an improvement in the crystalline quality of the domains at the expense of the growth rate in the OP-GaP layers grown on wafer-bonded OP-GaAs templates. In the case of OP-GaP grown on OP-GaAs templates prepared by epitaxial inversion, the crystalline quality of the ODs is better than that of the IDs, but it shows that the quality of the inverted layer in the template influences the quality and fidelity of the grown domains. To the authors' knowledge, exploitation of HRXRDRSM studies on OP-GaP to establish the crystalline quality of its individual domains (ODs and IDs) is the first of its kind. OP-ZnSe grown on OP-GaAs templates has also been included in this study to further emphasize the potential of this method. We propose from this study that once the growth rate is optimized from SEM studies, HRXRDRSM analysis alone can be used to assess the structural quality and to i, QC 20230316

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

Heteroepitaxial Zn-doped p-GaP was grown on (001) GaAs, (001) Si and (111) Si substrates by hydride vapor phase epitaxy for solar-driven photoelectrochemical applications of hydrogen generation by water splitting and CO2 reduction. Growth of GaP on Si was realized through the implementation of a low-temperature buffer layer, and the morphology and crystalline quality were enhanced by optimizing the precursor flows and pre-heating ambient substrate. The p-GaP/GaAs and p-GaP/Si samples were processed to photoelectrodes with an amorphous TiO2 coating for CO2 reduction and a combination of TiO2 layer and mesoporous tungsten phosphide catalyst for water splitting. P-GaP/GaAs with suitable Zn-doping concentration exhibited photoelectrochemical performance comparable to homoepitaxial p-GaP/GaP for water splitting and CO2 reduction. Degradation of photocurrent in p-GaP/Si photoelectrodes is observed in PEC water splitting due to the high density of defects arising from heteroepitaxial growth., QC 20230124

We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 mu m, a novel-geometry device that can scale the output power while maintaining good beam quality. Buried-ridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth - the tapered region scales the output power, while the emitting facet is located at the narrow-end taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M-2) measurements along with beam-stability measurements were performed - a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M-2 values close to 1 up to similar to 1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation., QC 20220506

Record 11 Gb/s LWIR FSO transmission is demonstrated with a 9.6-mu m directly-modulated QCL and a fully passive QCD without cooling, surpassing the previous bitrate record of DM-QCL-based FSO in this spectral window by 4 times., QC 20220812Part of proceedings: ISBN 978-155752466-9

A roadmap for future wireless communications is expected to exploit all transmission-suitable spectrum bands, from the microwave to the optical frequencies, to support orders of magnitude faster data transfer with much lower latency than the deployed solutions nowadays. The currently under-exploited mid-infrared (mid-IR) spectrum is an essential building block for such an envisioned all-spectra wireless communication paradigm. Free-space optical (FSO) communications in the mid-IR region have recently attracted great interest due to their intrinsic merits of low propagation lass and high tolerance of atmospheric perturbations. Future development of viable mid-IR FSO transceivers requires a semiconductor source to fulfill the high bandwidth, low energy consumption, and small footprint requirements. In this context, quantum cascade laser (QCL) appears as a promising technological choice. In this work, we present an experimental demonstration of a mid-IR FSO link enabled by a 4.65-mu m directly modulated (DM) QCL operating at room temperature. We achieve a transmission data rate of up to 6 Gbps over a 0.5-m link distance. This achievement is enabled by system-level characterization and optimization of transmitter and receiver power level and frequency response and assisted with advanced modulation and digital signal processing (DSP) techniques. This work pushes the QCL-based FSO technology one step closer to practical terrestrial applications, such as the fixed wireless access and the wireless mobile backhaul. Such a QCL-based solution offers a promising way towards the futuristic all-spectra wireless communication paradigm by potentially supporting the whole spectrum from the MIR to the terahertz (THz)., QC 20220429

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

Transition metal phosphates (TMPs) are regarded as efficient co-catalysts for photoanodes, but they are rarely applied in hydrogen production reactions. In this work, iron phosphate (FePi), a co-catalyst for hydrogen production, is introduced onto the Fe2O3 surface by facile surface phosphorization under low-temperature conditions. The surface FePi leads to a shift of the onset potential by +201 mV and an increase in the photocurrent density by more than 10 mA cm−2 at 0 VRHE for the Fe2O3/p-Si photocathode in a strong alkaline electrolyte. The role of FePi stems from the smaller transfer resistance, efficient photogenerated carrier separation and electron injection, and preferable H* adsorption energy, as suggested by Kelvin probe force microscopy and density functional theory (DFT) calculation. The surface phosphorization presents a facile and attractive strategy for the treatment of transition metal oxide catalyzed photocathodes for green hydrogen production., QC 20230516

High crystal quality GaAsP/Si fabricated by cost effective heteroepitaxial technology is promising to realize low-cost Si based tandem solar cell with efficiency higher than 30%. In this work, epitaxial lateral overgrowth (ELOG) of GaAsP/GaAs and GaAsP/GaAs/Si by hydride vapor phase epitaxy (HVPE) and their properties are studied by photoluminescence (PL) mapping. High crystal quality ELOG GaAsP/Si is obtained with enhanced PL intensity and narrow line width indicating reduced defect density provided by ELOG approach., QC 20230622

Record 11 Gb/s LWIR FSO transmission is demonstrated with a 9.6-µm directly-modulated QCL and a fully passive QCD without cooling, surpassing the previous bitrate record of DM-QCL-based FSO in this spectral window by 4 times., Part of ISBN 9781557528209QC 20230626

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

This work investigates the impurity effects on the generalized stacking fault energy (GSFE) of InP via first-principles calculations. The impurity elements of group Ⅴ and VI, which substitute the P sublattice preferentially, are studied here. It is found that the GSFEs of InP will decrease considerably when these impurities are incorporated in the glide plane. The charge density maps indicate that the reduction of GSFEs is predominantly attributed to the electronic effects. These results could contribute to understanding the stacking fault characteristics of III-Ⅴ compounds incorporated by different impurities., QC 20210216

In this report, we summarize our recent achievements in free-space communications in the mid-infrared (MIR) region enabled by directly modulated quantum cascaded laser (QCL) at 4.65 mu m (similar to 65 THz). We have experimentally demonstrated a multigigabit free- space transmission link in the lab environment with the QCL operating at room temperature. The QCL chip is mounted on a commercial QCL mount with a water-cooled Peltier element. Multilevel modulation formats at different baud rates are generated and combined with the laser driving current at a custom-made bias-tee to drive and modulate the QCL. A commercial mercury cadmium telluride (MCT, HgCdTe) photovoltaic (PV) MIR detector with a built-in trans-impedance amplifier was used to receive the MIR free-space signal. With the receiver to be the bottleneck of the system bandwidth, the end-to-end 3-dB bandwidth was measured to be around 320 MHz, and the 6-dB bandwidth was around 450 MHz. We have successfully demonstrated up to 6 Gbps free space transmission with multilevel modulation formats, assisted with effective digital equalization techniques despite the limited bandwidth., QC 20220406

Direct heteroepitaxy and selective area growth (SAG) of GaP and GaAs on Si(100) and Si(111) are implemented by low-pressure hydride vapor phase epitaxy (LP-HVPE), which are facilitated by buffer layers grown at 410–490 °C with reactive gas mixing directly above Si substrates. High-density islands observed on GaP buffer layers on Si result in rough morphology and defect formation in the subsequent GaP layers grown at 715 °C. The impact of growth temperature of GaAs buffer layers on the crystal quality of GaAs/Si is studied. A decreased nucleation temperature significantly improves the morphology and crystalline quality of the overall GaAs growth on Si. It is observed that Si(111) substrates are favorable for both GaP and GaAs growths in comparison with Si(100). In SAGs of GaP/Si and GaAs/Si, the high selectivity innate to HVPE is maintained in the used unconventional growth regime. The spatially resolved photoluminescence mapping reveals the material quality of GaAs/Si is enhanced by defect filtering by SAG. The outcomes of this work will pave the way of III–V/Si integration realized by cost-effective HVPE for photonic device applications., QC 20210323

Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 mu m-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M-2 < 1.2 up to 1 W for similar to 5 mu m-wide ridges. 5 mu m-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of similar to 1.25 cm over a distance of 100 m., QC 20210217

We report our recent studies in photonics-assisted free-space transmissions in both the lower (0.3-0.5 THz) and upper- (similar to 64.5 THz) terahertz bands. We adopt the hybrid electro-optical approach for the lower-THz signal transmission, whereas a directly modulated quantum cascade laser is used for the upper-THz band., Part of proceedings: ISBN 978-1-6654-3868-1QC 20220810

We report on an experimental demonstration of a mid-infrared free-space communication link enabled by a directly modulated quantum cascade laser operating at room temperature. A record high transmission rate up to 6 Gbps over 50-cm link distance is demonstrated at 4.65 mu m wavelength., QC 20220811Part of proceedings: ISBN 978-1-6654-3868-1

Novel-geometry, 4.6 mu m-emitting BH QCLs were fabricated, where a tapered region scales the output power and, ahead of the emitting aperture, a narrow section provides mode filtering for suppressing high-order spatial modes. Beam-stability measurements indicate a small degree of collimated-beam centroid motion (< 0.25 mrad)., Part of proceedings: ISBN 978-1-6654-4133-9QC 20220509

We propose a comb-locked multi-channel transmitter with high-speed VCSELs injection-locked by an optical frequency comb. VCSEL dynamics are analyzed with various injection parameters including number of comb tones, frequency detuning and injection ratio. We evaluate the performance of filtering and amplification effect when multiple comb tones injection into single VCSEL, and estimate the transmission performance considering the reflection from VCSEL. Compared to intrinsic parameters of VCSEL, a 2-fold increase in frequency response and a 2.6 10 4-fold reduction in linewidth have been verified experimentally when the bandwidth-limited VCSEL locked to an incident comb line. 14-Gb/s single-lane transmission is demonstrated through 20 km single-mode fiber based on a 3.4-GHz VCSEL without any dispersion compensation. The similar performance can be achieved for all generated 25 comb tones, verifying a potential high-capacity transmitter with distinct feature of two-dimensional VCSELs, QC 20211207

This work investigates the optical and interfacial properties of epitaxially fused direct GaInP/Si heterojunctions realized by the corrugated epitaxial lateral overgrowth (CELOG) approach. To provide a broad analysis of the above heterojunction, photoluminescence (PL), cathodoluminescence (CL), Raman, and high-resolution transmission electron microscopy (TEM) were employed in this study. The enhanced luminescence intensity was observed in the direct GaInP/Si heterojunction in the cross-sectional CL because of the reduced defect density in the CELOG GaInP. The spatial resolution dependent PL and CL spectra of GaInP on Si yielded the composition variation of GaInP arising from the anisotropic growth behavior of CELOG. The Ga composition, x, in GaxIn1-xP/Si at the interface deduced from the lattice constant measured by TEM has a good agreement with the results of PL and CL. Low thermal and lattice mismatch strain in CELOG GaInP on Si were revealed by the Raman spectra. TEM investigation further revealed the atomic structure of some planar defects in CELOG GaInP over Si. It is confirmed that although a thin atomic disorder was observed on the surface of Si substrate, an epitaxially fused GaInP/Si heterojunction with a reduced threading dislocation density of similar to 6.4x10(7) cm(-2) in comparison to similar to 4.8x10(8) cm(-2) in the InP seed on Si has been successfully fabricated by the CELOG technique despite about 4% lattice mismatch between GaInP and Si. The findings of this study demonstrate the great potential of the CELOG technique for promoting monolithic integration of III-V/Si-based optoelectronics., QC 20201118

We demonstrate a surface emitting 1.5 mu m multi-quantum well (MQW) light-emitting diode (LED) on a 3-inch epitaxial lateral overgrowth (ELOG) InP/Si wafer. The enhanced crystalline quality of ELOG InP/Si is revealed by various characterization techniques, which gives rise to a MQW with high photoluminescence intensity at 1.5 mu m and interference fringes arising from the vertical Fabry-Perot cavity. The LED devices exhibited strong electroluminescence intensity that increased with pump current. Moreover, transparency current measurements indicate optical gain in the 1.5 mu m MQW on InP/Si. The results are encouraging for obtaining wafer scale 1.5 mu m surface emitting laser structures on silicon with further optimization., QC 20201105

Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE., QC 20200603

Heteroepitaxial growth of orientation‐patterned (OP) GaP (OP‐GaP) on wafer‐bonded OP‐GaAs templates is investigated by low‐pressure hydride vapor phase epitaxy for exploiting the beneficial low two‐photon absorption properties of GaP with the matured processing technologies and higher‐quality substrates afforded by GaAs. First, GaP homoepitaxial selective area growth (SAG) is conducted to investigate the dependence of GaP SAG on precursor flows and temperatures toward achieving a high vertical growth rate and equal lateral growth rate in the [110] and [-110]‐oriented openings. Deteriorated domain fidelity is observed in the heteroepitaxial growth of OP‐GaP on OP‐GaAs due to the enhanced growth rate on domain boundaries by threading dislocations generated by 3.6% lattice matching in GaP/GaAs. The dependence of dislocation dynamics on heteroepitaxial growth conditions of OP‐GaP on OP‐GaAs is studied. High OP‐GaP domain fidelity associated with low threading dislocation density and a growth rate of 57 μm h−1 are obtained by increasing GaCl flow. The properties of heteroepitaxial GaP on semi‐insulating GaAs is studied by terahertz time‐domain spectroscopy in the terahertz range. The outcomes of this work will pave the way to exploit heteroepitaxial OP‐GaP growth on OP‐GaAs for frequency conversion by quasi‐phase‐matching in the mid‐infrared and terahertz regions., QC 20191111

We fabricate and study direct InP/Si heterojunction by corrugated epitaxial lateral overgrowth (CELOG). The crystalline quality and depth-dependent charge carrier dynamics of InP/Si heterojunction are assessed by characterizing the cross-section of grown layer by low-temperature cathodoluminescence, time-resolved photoluminescence and transmission electron microscopy. Compared to the defective seed InP layer on Si, higher intensity band edge emission in cathodoluminescence spectra and enhanced carrier lifetime of InP are observed above the CELOG InP/Si interface despite large lattice mismatch, which are attributed to the reduced threading dislocation density realized by the CELOG method.

We present a large-area (1.5 mm x 1.5 mm) photonic crystal quantum cascade laser, with over 2 W peak power at room temperature (289 K), and symmetrical, narrow (<1 degrees), single-lobed surface-emitting beam., QC 20190917

Quantum cascade lasers (QCLs) are the sources of choice for many laser-based applications in the mid-infrared region. Because of the unique 2D in-plane coupling mechanism, a photonic crystal (PhC)QCL [1] has superior advantages on mode selection, surface emission, and beam control. In this work, we present a large-area (1.5 mm × 1.5 mm) PhC-QCL operating under pulsed mode at room temperature (289 K). The surface-emitting peak power is as high as 1 W., QC 20200623

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is an attractive technology for achieving mid-IR and terahertz (THz) radiation enabled by nonlinear frequency conversion, because of its low two-photon absorption (2PA) down to 1 µm. High crystalline quality of OP-GaP template and subsequent thick layer growth is required to exploit the benefit of low 2PA of GaP pumped with short wavelength lasers [1]. In this work, we present the development of heteroepitaxial growth of OP-GaP on wafer fused OP-GaAs template with high growth rate and good domain fidelity. The conductivity of the GaP grown on planar GaAs was investigated in the THz region., SyskonpostNot duplicate with DiVA 1429993QC 20200623

Quasi-phase-matched orientation-patterned GaP (OP-GaP) is an attractive technology for achieving mid-IR and terahertz (THz) radiation enabled by nonlinear frequency conversion, because of its low two-photon absorption (2PA) down to 1 pm. High crystalline quality of OP-GaP template and subsequent thick layer growth is required to exploit the benefit of low 2PA of GaP pumped with short wavelength lasers [1]. In this work, we present the development of heteroepitaxial growth of OP-GaP on wafer fused OP-GaAs template with high growth rate and good domain fidelity. The conductivity of the GaP grown on planar GaAs was investigated in the THz region., QC 20200513

Quantum cascade lasers (QCLs) are the sources of choice for many laser-based applications in the mid-infrared region. Because of the unique 2D in-plane coupling mechanism, a photonic crystal (PhC)-QCL [1] has superior advantages on mode selection, surface emission, and beam control. In this work, we present a large-area (1.5 mm × 1.5 mm) PhC-QCL operating under pulsed mode at room temperature (289 K). The surface-emitting peak power is as high as 1 W., QC 20200331Not duplicate with diva2:1354581

We fabricate and study direct InP/Si heterojunction by corrugated epitaxial lateral overgrowth (CELOG). The crystalline quality and depth-dependent charge carrier dynamics of InP/Si heterojunction are assessed by characterizing the cross-section of grown layer by low-temperature cathodoluminescence, time-resolved photoluminescence and transmission electron microscopy. Compared to the defective seed InP layer on Si, higher intensity band edge emission in cathodoluminescence spectra and enhanced carrier lifetime of InP are observed above the CELOG InP/Si interface despite large lattice mismatch, which are attributed to the reduced threading dislocation density realized by the CELOG method. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, QC 20190326

Room temperature surface emission is realized on a large area (1.5 mm x 1.5 mm) photonic crystal quantum cascade laser (PhC-QCL) driven under pulsed mode, at the wavelength around 8.75 mu m. By introducing in-plane asymmetry to the pillar shape and optimizing the current injection with a grid-like window contact, the maximum peak power of the PhC-QCL is up to 5 W. The surface emitting beam has a crossing shape with 10 degrees divergence., QC 20190925

QC 20191007

We fabricate and study direct InP/Si heterojunction by corrugated epitaxial lateral overgrowth (CELOG). The crystalline quality and depth-dependent charge carrier dynamics of InP/Si heterojunction are assessed by characterizing the cross-section of grown layer by low-temperature cathodoluminescence, time-resolved photoluminescence and transmission electron microscopy. Compared to the defective seed InP layer on Si, higher intensity band edge emission in cathodoluminescence spectra and enhanced carrier lifetime of InP are observed above the CELOG InP/Si interface despite large lattice mismatch, which are attributed to the reduced threading dislocation density realized by the CELOG method.

We fabricate and study direct InP/Si heterojunction by corrugated epitaxial lateral overgrowth (CELOG). The crystalline quality and depth-dependent charge carrier dynamics of InP/Si heterojunction are assessed by characterizing the cross-section of grown layer by low-temperature cathodoluminescence, time-resolved photoluminescence and transmission electron microscopy. Compared to the defective seed InP layer on Si, higher intensity band edge emission in cathodoluminescence spectra and enhanced carrier lifetime of InP are observed above the CELOG InP/Si interface despite large lattice mismatch, which are attributed to the reduced threading dislocation density realized by the CELOG method.

QC 20220301Conference ISBN: 978-1-7281-0469-0

Heteroepitaxial growth of orientation-patterned GaP on patterned GaAs template was developed by using hydride vapor phase epitaxy for quasi-phase-matching applications. We present the growth with well-defined periodic boundaries between (001) and (00 1) GaP domains. The GaP layer on planar GaAs was characterized by terahertz time-domain spectroscopy and the conductivity of GaP (0.16 S cm-1) was obtained in terahertz range., Not duplicate with DiVA 1366349Part of proceedings: ISBN 978-1-7281-0080-7QC 20230921