Cunzhu Tong

Semiconductor disk lasers (SDLs) combine the tailorable emission wavelength of semiconductor lasers and the high output power and good beam quality of solid-state disk lasers. It may be a potential candidate for many applications in special wavebands that cannot be accessed by solid-state gain medium. However, because of the very short lifetime of the carriers, it is difficult to generate high energy pulses by traditional methods such as Q- or gain-switching in a SDL. This work demonstrates a steady cavity-dumped SDL by inserting a high extinction ratio Pockels cell and a low insertion loss birefringent filter as both a polarizer and an output coupler into the resonant cavity. At the laser wavelength of 980 nm, output pulses with 10 ns pulse width, 1 kHz repetition rate and 271 mW average power are achieved. The energy of a single laser pulse is $271~\mu $ J, two orders of magnitude higher than the reported maximum value from similar SDLs. Meanwhile, good beam quality with the M2 factor of 1.13 in both x and y directions are also maintained at high-power operation.

In this paper, we present a beam-combining technique to boost GaSb-based 1940 nm diode laser output power through spectral beam combining (SBC), spatial beam combining, and polarization beam combining (PBC). Four spectral beam-combining (SBC) configurations were developed using commercially available standard bars. The four SBC configurations were paired to perform PBC after spatial beam combining. The total output power of the 1940 nm laser reached 23.4 W, with the beam qualities of the combined beam achieving 10.6 in the slow axis and 11 in the fast axis. The brightness of the combined laser reached 5.4 MW·cm⁻²·sr⁻¹.

This study presents the development of a high-speed, broadband InGaAs/InP photodiode suitable for advanced sensing and optical detection applications across the critical wavelength range of 850–1550 nm. By employing an InAlAs window layer to replace conventional InP, the device significantly improves sensitivity at 850 nm. Additionally, the substitution of traditional GaAs-based materials with InGaAs enhances responsivity and reduces carrier transit times, enabling precise, high-speed signal detection. The introduction of InGaAsP graded bandgap layers (GBLs) further improves device reliability and reduces absorption losses associated with defects, thus enhancing overall sensing performance. The fabricated photodiode, featuring an active area diameter of 35 µm, achieves high bandwidths of 20 GHz, 15 GHz, and 15.5 GHz at 850 nm, 1310 nm, and 1550 nm, respectively, along with responsivities of 0.5 A/W, 0.72 A/W, and 0.64 A/W. These characteristics make the device well suited for integration into multi-wavelength optical sensing systems, broadband photonic sensors, and high-speed optical communication platforms.

This study explores the impact of a dual-charge layer structure on the performance of InGaAs/InAlAs avalanche photodiodes (APDs) with a separate absorption, charge, multiplication, charge, and transit (SACMCT) structure. The dual-charge layer, consisting of p-doped and n-doped charge layers on either side of the avalanche layer, is designed to precisely control the internal electric field, effectively reduce the dark current, and extend the dynamic range. Simulation results guided the fabrication of a backside-illuminated APD, which achieved a linear operating range of 10–30 V and a dark current as low as 80 nA. The optimized design significantly reduced the dark current and increased the breakdown voltage compared to previously reported APDs. These improvements demonstrate the potential of dual-charge-layer APDs for high-speed optical communications and precision photodetection applications.

One of the primary goals in the development of underwater wireless optical communication (UWOC) is to extend the link length. Meanwhile, the key to increasing the link length of UWOC is to decrease the attenuation of the optical signals underwater. This work demonstrates that a decreased underwater attenuation coefficient and improved communication performance can be achieved by using a pulsed laser. The pulsed blue laser used in the experiment is a self-Q-switched semiconductor disk laser, whose Q-switching is initiated by the nonlinear Kerr effect of the multiple quantum wells in the active region of the gain chip. The width of the laser pulse is about a few nanoseconds and the repetition rate of the output pulse train is in the order of tens of megahertz. According to the measurements of the attenuation coefficients at various concentrations of Maalox solution, the pulsed laser has a significantly smaller attenuation coefficient than the continuous-wave laser, and this drop in attenuation coefficient is particularly noticeable in turbid water with a higher concentration of Maalox solution. The attenuation coefficient of the pulsed laser was only 62% of the continuous-wave laser at a Maalox concentration of 2905 mg·m ⁻³ . Subsequent tests reveal that the lower attenuation coefficient of the pulsed laser is mainly resulted from the reduced scattering it encounters underwater, rather than the ignorable decrease in the attenuation coefficient raised from the water's absorption of the laser. A UWOC system based on the above pulsed laser has also been built and much better communication performance compared to the continuous-waves laser has been obtained. The bit error rate of the UWOC based on the pulsed laser is 1–2 orders of magnitude lower than that of the UWOC with a continuous-wave laser when the data rate is 10 Mb/s and the link length is 18 m.

We report a compact high-power narrow-linewidth 509 nm widely tunable single-frequency vertical-external-cavity surface-emitting laser (VECSEL) for the preparation of cesium Rydberg states. A record output power of 6.3 W near 509.140 nm is achieved, and the measured Gaussian linewidth (100 μs integration time) and Lorentzian linewidth of the fundamental wave within 1 ms sampling time are 19.3 kHz and 142.5 Hz, respectively. When the absorbed pump power is 28 W, the laser wavelength can be tuned from 502 nm to 516 nm, the output power is maintained between 29 mW and 5.4 W. This type of single-frequency laser provides a high-performance light source for research involving cesium Rydberg atoms, such as quantum computing, microwave electric field measurement, and terahertz imaging.

We demonstrate a 1018 nm high-power tunable single-frequency VECSEL with kilohertz linewidth. The maximum output power of 5 W and linewidth of 1.16 kHz are experimentally achieved. The laser wavelength can be tuned from 1006 nm to 1032.6 nm, corresponds to a tuning range of 26.6 nm. Within the wavelength range of 1010 nm to 1020 nm, the output power of the tunable laser is maintained between 925 mW and 5 W, and the linewidth fluctuates between 0.94 kHz and 8.9 kHz. This type of high-power, narrow linewidth, and wide wavelength tuning single-frequency VECSEL provides a high-performance seed or pump source for applications such as optical lattice clocks, atomic cooling, and stimulated Raman scattering.

Benefitting from narrow beam divergence, photonic crystal surface-emitting lasers are expected to play an essential role in the ever-growing fields of optical communication and light detection and ranging. Lasers operating with 1.55 μm wavelengths have attracted particular attention due to their minimum fiber loss and high eye-safe threshold. However, high interband absorption significantly decreases their performance at this 1.55 μm wavelength. Therefore, stronger optical feedback is needed to reduce their threshold and thus improve the output power. Toward this goal, photonic-crystal resonators with deep holes and high dielectric contrast are often used. Nevertheless, the relevant techniques for high-contrast photonic crystals inevitably complicate fabrication and reduce the final yield. In this paper, we demonstrate the first continuous-wave operation of 1.55 μm photonic-crystal surface-emitting lasers by using a ‘triple-lattice photonic-crystal resonator’, which superimposes three lattice point groups to increase the strength of in-plane optical feedback. Using this geometry, the in-plane 180° coupling can be enhanced threefold compared to the normal single-lattice structure. Detailed theoretical and experimental investigations demonstrate the much lower threshold current density of this structure compared to ‘single-lattice’ and ‘double-lattice’ photonic-crystal resonators, verifying our design principles. Our findings provide a new strategy for photonic crystal laser miniaturization, which is crucial for realizing their use in future high-speed applications.