Abstracts:We demonstrate, a colliding-pulse mode-locked Bragg reflection laser (CPMBRL). A methodical study of a two-sections CPMBRL shows that these devices can generate pulse widths down to <inline-formula> <tex-math notation="LaTeX">$sim 130$ </tex-math></inline-formula> fs with a &#x2212;3 dB spectral bandwidth of 5.45 nm: time-bandwidth product of 0.348 indicating the formation of near transform limited pulses. Average power of 1.5 mW, a repetition rate of 42.4 GHz and peak power of <inline-formula> <tex-math notation="LaTeX">$sim 240$ </tex-math></inline-formula> mW enable a record difference frequency generation conversion efficiency of &#x2212;38 dB.

Abstracts:We report on the design, fabrication and characterization of red <inline-formula> <tex-math notation="LaTeX">$mu $ </tex-math></inline-formula>-LEDs directly grown on large-scale silicon wafers through a superior-quality Ge buffer. 300mm Ge/Si substrates with a threading dislocation density (TDD) of &#x007E;107 cm&#x2212;2 were successfully achieved, then followed by the growth and process of visible 649nm AlGaAs-based red emitters. The electro-optical properties of various red <inline-formula> <tex-math notation="LaTeX">$mu $ </tex-math></inline-formula>-LEDs with diameters ranging from 10 to <inline-formula> <tex-math notation="LaTeX">$100mu text{m}$ </tex-math></inline-formula> are investigated, showing promising performances. Those results coupled with numerical analysis with a model based on transfer-matrix with dipole source-terms help us better identify the main challenges limiting the efficiencies of our devices, while providing optimization routes to alleviate them. We believe that these results could pave the way for a monolithic large-scale and low-cost integration of red <inline-formula> <tex-math notation="LaTeX">$mu $ </tex-math></inline-formula>-LEDs on 300mm Si-CMOS driving circuits and for the fabrication of high-resolution RGB microdisplays that see use in various applications in optoelectronics.

Abstracts:A frequency-modulated interrupted continuous waveform (FMICW) generator with an ultra-large bandwidth based on optical heterodyne detection is proposed and experimentally demonstrated. The FMICW generator is implemented through the heterodyne detection of a stable optical carrier and a gate-function-modulated frequency-chirped optical pulse. A stable sub-kHz optical fiber laser operates the optical carrier. The optical pulse is generated from a three-electrode distributed Bragg reflector (DBR) laser diode (LD), which is gate-function modulated by a current source via the passive phase control section. By beating the optical carrier and the optical pulse at a photodetector (PD), an FMICW is generated. The bandwidth of the FMICW is over 20 GHz, and the temporal duration is around 200 <inline-formula> <tex-math notation="LaTeX">$mu text{s}$ </tex-math></inline-formula>. The compression ratio is obtained as large as <inline-formula> <tex-math notation="LaTeX">$3.78times 10 ^{6}$ </tex-math></inline-formula>. Thanks to the tunability of the gate-function-modulated frequency-chirped optical pulse, the generated FMICW is fully tunable in terms of gate-function period and duty ratio.

Abstracts:Gallium Oxide (Ga2O3), an emerging ultra-wide band gap semiconductor, has drawn great attention for application in radiation detection. In this letter, ultrafast X-ray detectors have been fabricated using a high resistivity unintentionally-doped (UID) <inline-formula> <tex-math notation="LaTeX">$varepsilon $ </tex-math></inline-formula>-Ga2O3 film grown on sapphire by metal-organic chemical vapor deposition (MOCVD). The detector featuring a lateral metal&#x2013;semiconductor&#x2013;metal (MSM) structure exhibited a low dark current &#x003C; 2 nA at 100 V and its sensitivity was as high as 28.6 nC/Gy or &#x007E;<inline-formula> <tex-math notation="LaTeX">$1.0,,times 10^{6}$ </tex-math></inline-formula> nC/(<inline-formula> <tex-math notation="LaTeX">$text {Gy}cdot text {cm}^{3}$ </tex-math></inline-formula>) at 40 V and an X-ray dose rate of 0.383 Gy/s. A stable and repeatable transient response was observed for the detectors under switching X-ray illumination. Furthermore, the detector achieved a pulsed X-ray detection with 50 ns in full width and its time resolution was revealed to be &#x007E;7.1 ns. These results imply the great potential of the MOCVD-grown high-resistivity UID <inline-formula> <tex-math notation="LaTeX">$varepsilon $ </tex-math></inline-formula>-Ga2O3 film for ultrafast X-ray detection.

Abstracts:To meet the miniaturization of all-solid-state high-power microwave drive technology based on photoconductive semiconductor switches (PCSSs), a vertical gallium nitride (GaN) PCSS that is triggered by a micro-joules energy and picoseconds pulse width laser is presented. The device has showed low triggering optical energy and fast response. When the bias-voltage is 3 kV and optical energy is 33 <inline-formula> <tex-math notation="LaTeX">$mu text{J}$ </tex-math></inline-formula>, the photocurrent, on-state resistance, rise-fall time and quantum efficiency of the PCSS are 4.28 A, <inline-formula> <tex-math notation="LaTeX">$650.5~Omega $ </tex-math></inline-formula>, 412/370 ps and 0.28&#x0025;, respectively. It is anticipated that GaN-based PCSS will have a practical application in future radio frequency (RF) microwave systems for military purposes.

Abstracts:Phase unwrapping is always the necessary procedure in fringe projection profilometry (FPP). This letter presents an efficient phase unwrapping-free FPP method. Both the wrapped phase maps of the measured object and the reference plane are extracted by phase-shifting algorithm. If the depth range of the measured object is within <inline-formula> <tex-math notation="LaTeX">$2pi $ </tex-math></inline-formula> in phase domain, the three-dimensional (3D) shape can be directly reconstructed by converting the wrapped phase difference into absolute phase difference without phase unwrapping process. Simulations and experiments are carried out, and their results demonstrate the effectiveness and robustness of the proposed method.