Suping Liu

Researching the 915 nm high-power and high-brightness semiconductor laser single chip coupling module

Based on the high-speed development of the fiber laser in recent years, the development of researching 915 nm semiconductor laser as main pumping sources of the fiber laser is at a high speed. Because the beam quality of the laser diode is very poor, the 915 nm laser diode is generally based on optical fiber coupling module to output the laser. Using the beam-shaping and fiber-coupling technology to improve the quality of output beam light, we present a kind of high-power and high-brightness semiconductor laser module, which can output 13.22 W through the optical fiber. Based on 915 nm GaAs semiconductor laser diode which has output power of 13.91 W, we describe a thoroughly detailed procedure for reshaping the beam output from the semiconductor laser diode and coupling the beam into the optical fiber of which the core diameter is 105 μ m and the numerical aperture is 0.18. We get 13.22 W from the output fiber of the module at 14.5 A, the coupling efficiency of the whole module is 95.03% and the brightness is 1.5 MW/cm 2 -str. The output power of the single chip semiconductor laser module achieves the advanced level in the domestic use.

Improved spectral characteristics of 980 nm broad area slotted Fabry-Perot diode lasers

A novel broad area slotted Fabry-Perot diode laser is designed and fabricated. Using a new semi- analytical method, we introduce effective refractive index perturbations in the form of etched slot features into a conventional 980 nm broad area Fabry-Perot cavity, and the spectral characteristics of the device are expected to be noticeably improved. A low density of slot features is formed by using standard optical lithography and induc- tively coupled plasma dry etching. The experimental results show that the full spectral width at half-maximum is less than 0.4 nm, meanwhile, the thermal shift of the emission spectrum is decreased from 0.26 to 0.07 nm/ C over a temperature range of 10 to 60 C. The improved spectral characteristics of the device are proved to be attributed to such slotted Fabry-Perot laser structures.

Study of high-power broad area distributed-feedback laser

High-power semiconductor laser is commonly used for pump source, but the absorption spectra width of the ion which is pumped by the laser is often small. In order to improve the pumping efficiency of high-power semiconductor laser to solid or fiber laser, the current and thermal drift coefficient of wavelength should be decreased. The influence of grating depth and grating duty cycle with the laser wavelength stabilized effect are analyzed theoretically. The appropriate grating parameter is obtained by experimental verification. And the appropriate laser cavity length is obtained according to the optimized condition. The first broad area distributed-feedback(DFB) laser whose wavelength is well-locked is fabricated interiorly. The broad area DFB laser single emitter with2.4 mm cavity length,100μm stripe width produce continuous-wave output power of400 mW at15°C heatsink temperature and its wavelength is954 nm. The current drift of wavelength on this DFB laser is0.67 nm/A and the thermal drift coefficient of wavelength on this DFB laser is0.046 nm/K.

Segregation and precipitation formation for in situ oxidised 9Cr steel powder

Powder and sintered bulk materials of a reduced activation steel with oversaturated Ti and Y are prepared by gas atomisation and sintering. Segregation on both the surface and interior of the powder particles are observed after an thermal treatment. The oxidation of the segregates promotes formation of clusters of large Y oxide crystals and thick continuously distributed Ti oxide layers on the surface of the powder particles. The oxidation also occurs within the powder particles and mainly forms larger Ti oxide dispersoids in the grain boundaries of the powder. The coarsening and aggregation of the oxide dispersoids occur with increasing duration of the thermal treatment. Yttrium is also segregated and precipitated in the grains of the powder particles.

Thermal investigation of high-power GaAs-based laser diodes

The thermal characteristics of high-power AlGaAs/GaAs laser diodes (LDs) at high current (2-10 A) are studied with electrical transient method. The temperature rise increases linearly with the current. The thermal resistance of chip is the largest proportion of total thermal resistance. By increasing the width of the chip from 500 to 800 μm, the temperature rise and thermal resistance decrease by 8.5% and 8.8%, respectively.

1.06 μ m high-power InGaAs/GaAsP quantum well lasers

The high power and low internal loss 1.06 μ m InGaAs/GaAsP quantum well lasers with asymmetric waveguide structure were designed and fabricated. For a 4000 μ m cavity length and 100 μ m stripe width device, the maximum output power and conversion efficiency of the device are 7.13 W and 56.4%, respectively. The cavity length dependence of the threshold current density and conversion efficiency have been investigated theoretically and experimentally; the laser diode with 4000 μ m cavity length shows better characteristics than that with 3000 and 4500 μ m cavity length: the threshold current density is 132.5 A/cm 2 , the slope efficiency of 1.00 W/A and the junction temperature of 15.62 K were achieved.

High power 980 nm broad area distributed feedback laser with first-order gratings

To achieve high pumping efficiency and stability, a wavelength stabilized 980 nm broad area distributed feedback laser was realized. A nanoimprint lithography technique was used to fabricate the first-order gratings. The stripe width was 90 μm and the cavity length was 2 mm. Under continuous wave condition, the output laser power reached 1.2 W, with the slope efficiency of 0.7 W/A. The current and thermal dependence of the spectrum peak was measured to be approximately 0.19 nm/A and 0.064 nm/K respectively, and the wavelength-locking range reached over 50 ℃.

Life prediction of 808nm high power semiconductor laser by accelerated life test of constant current stress

High power semiconductor laser is widely used because of its high transformation efficiency, good working stability, compact volume and simple driving requirements. Laser’s lifetime is very long, but tests at high levels of stress can speed up the failure process and shorten the times to failure significantly. So accelerated life test is used here for forecasting the lifetime of 808nm CW GaAs/AlGaAs high power semiconductor laser that has an output power of 1W under 1.04A. Accelerated life test of constant current stress based on the Inverse Power Law Relationship was designed. Tests were conducted under 1.3A, 1.6A and 1.9A at room temperature. It is the first time that this method is used in the domestic research of laser’s lifetime prediction. Applying Weibull Distribution to describe the lifetime distribution and analyzing the data of times to failure, characteristics lifetime’s functional relationship model with current is achieved. Then the characteristics lifetime under normal current is extrapolated, which is 9473h. Besides, to confirm the validity of the functional relationship model, we conduct an additional accelerated life test under 1.75A. Based on this experimental data we calculated the characteristics lifetime corresponding to 1.75A that is 171h, while the extrapolated characteristics lifetime from the former functional relationship model is 162h. The two results shows 5% deviation that is very low and acceptable, which indicates that the test design is reasonable and authentic.

An exploration of slab-coupled semiconductor lasers

To obtain a high-power and efficient single-mode laser, a new laser called the slab coupled optical waveguide laser (SCOWL) has been developed. We have simulated its structure and grown the chip with this structure by low-pressure metal organic chemical vapor deposition. We have also produced the broad-area SCOWL and compared it with the traditional structure laser in terms of some performances. This work lays the foundation for further research of ridged lasers with the same structure.

Asymmetric wide-coupled waveguide 980nm laser diode with high power and low vertical divergence angle

A novel asymmetric wide-coupled waveguide structure is put forward. We optimize the thickness of N-type waveguide and cladding through theoretical calculation of this structure, and adopt LP-MOCVD to grow the designed semiconductor lasers. The fabricated 980nm laser with 1200μm cavity length has a threshold current of 590mA, slope efficiency of 0.96W/A. When the operating current is 2.6A, the output power is 2000mW and the far field divergence angle is 16.1° (vertical) by 10.2° (horizontal). Experimental results indicate that the novel asymmetric wide-coupled waveguide structure can achieve high power output, effectively reduce the vertical far field divergence angle and improve the beam quality of the device.