Efficient photodetectors (PDs) and lasers are critical components in silicon photonics technology. Here, we demonstrate bufferless InP/InGaAs PDs, directly grown on (001) silicon-on-insulators. The nano-scale PDs exhibit a high photoresponsivity of 1.06 A/W at 1.55 µm, and a wide operating range from 1450 nm to 1650 nm. The bufferless feature of nano-PDs facilitates effective interfacing with Si waveguides, thus paving the path toward fully integrated silicon photonics circuits.We propose and demonstrate a method to generate a flat broadband chaotic laser by using an active optical feedback loop combined with a high nonlinear fiber. The feedback strength and nonlinear effect, especially the four-wave mixing effect of high nonlinear fiber, are studied to improve the bandwidth and flatness of chaos. When the feedback strength is 6.6 and injected fiber power is 1.0 W, a chaotic signal with a frequency range over 50 GHz, 80% bandwidth of 38.9 GHz, and flatness of 4.2 dB are experimentally achieved.With respect to the classical Shack-Hartmann (SH) wavefront sensor (WFS), the recently proposed reverse Hartmann (RH) sensor inverts the locations of the filtering and observation planes and forms a direct image of the pupil on a detector array. The slopes of the wavefront error (WFE) are then reconstructed by using a double Fourier transform algorithm. It turns out that the same algorithm can also be applied to the raw data acquired by SH sensors. This Letter presents the first, to the best of our knowledge, experimental results obtained with a simplified RH WFS and their comparison to those provided by a reference SH sensor, in both classical and double Fourier transform modes. They demonstrate that similar WFE measurement accuracy is achievable when using the three techniques, at least within the limit of our test bench that is estimated around $\lambda/10$λ/10 RMS.We propose a tri-band half-wave plate in the reflection mode, composed of rectangular silicon bar arrays on a 10-layer graphene substrate. By merely varying the Fermi energy of graphene from 0 to 0.25 eV, the three frequency bands shift in step and merge to a continuous dynamic bandwidth from 0.88 to 1.81 terahertz (THz). In addition, it can also dynamically switch the reflected wave among cross-linear polarization, right-handed and left-handed circular polarization in 0.93-1.35 THz. We found that the large dynamic bandwidth originates from the tunable reflection phase from the graphene layers. As it no longer depends on the plasmonic resonance in graphene, the proposed hybrid metasurface offers an alternative solution for active THz polarization devices with low biasing voltages.Bessel-like beams with controllable rotation of local linear polarization upon propagation are generated, which in fact achieve the evolution of polarization states along the equator of the Poincaré sphere during propagation. Based on the amplitude-phase joint modulation method, the rotation direction and rate of polarizations of the Bessel-like beam can be controlled easily by adjusting the radial indices and intensity ratio of two superposed beams. A rotation angle of $\sim$∼800 deg has been achieved after a propagation distance of 120 mm, corresponding to a rotation rate of $\sim$∼6.7 deg/mm, which is about three times higher than in previous works.We report a single-shot three-dimensional (3D) topographical imaging method, optical coherence factor (OCF) imaging, which uses optical coherence as the contrast mechanism to acquire the surface height ($z$z-direction) information of an object. A 4-f imaging system records the light field reflected from the surface of the object. The illumination of the imaging system comes from a laser source with the optical coherence length comparable to the depth of field (DoF) of the optical system. Off-axis holographic recording is used to retrieve the coherence factor from the interference fringes, which is then converted to $z$z-direction information. In this experiment, we validate our 3D imaging results comparing them to axial scanning full-field optical coherence tomography images. We also analyze the contrast mechanism of OCF and show that it is able to provide additional information over conventional coherent and incoherent imaging using the same imaging setup. This single-shot computationally efficient method may have potential applications in industrial quality control inspection.We demonstrate a pyrometric contact-less temperature sensor using a flexible fused silica fiber of 360 µm diameter able to measure down to 30°C with a precision better than 1°C at 10 Hz. Silica fibers, as opposed to dedicated mid-IR fibers, are non-degrading, low-cost, and bio-compatible. The large bandwidth (up to several kilohertz) and the broad temperature range (up to 235°C) of the sensor can be instrumental for time-resolved analysis and control of laser ablation and electrothermal surgery procedures.Cladding waveguide fiber Bragg gratings (FBGs) provide a compact and simple solution for fiber shape sensing. The shape sensing accuracy is limited by birefringence, which is induced by bending and the non-isotropic FBG structure (written by femtosecond laser point-by-point technique). An algorithm based on an artificial neural network for fiber shape sensing is demonstrated, which enables increased accuracy, better robustness, and less time latency. This algorithm shows great potential in the application of high-accuracy real-time fiber shape measurements.A high-temperature all-fiber non-destructive multi-parameter sensing system is developed. The system can operate consistently in a wide range of temperature changes by specially designed active signal generation and detection units. It is capable of monitoring temperature up to 600°C and cracks on metal pipes with an acoustic wave generation unit and an acoustic detection unit. A gold-coated multi-mode fiber is used to deliver a laser pulse for acoustic excitation while minimizing parasitic acoustic signals at high temperature. An in-fiber Fabry-Perot fiber Bragg grating (FP-FBG) is fabricated in another single-mode fiber and bonded to the test object for acoustic detection. Selumetinib mw The FP-FBG avoids strain redistribution inside the bonder at high temperature to ensure consistent operation. The feasibility of the system for temperature monitoring and crack detection in real-world applications is also demonstrated on an industry-standard P91 pipe.