Ultrashort pulse generation by semiconductor mode-locked lasers at 760 nm.

We demonstrate the first semiconductor mode-locked lasers for ultrashort pulse generation at the 760 nm waveband. Multi-section laser diodes based on an AlGaAs multi-quantum-well structure were passively mode-locked, resulting in the generation of pulses at around 766 nm, with pulse durations down to ~4 ps, at pulse repetition rates of 19.4 GHz or 23.2 GHz (with different laser cavity lengths of 1.8 mm and 1.5 mm, respectively). The influence of the bias conditions on the mode-locking characteristics was investigated for these new lasers, revealing trends which can be ascribed to the interplay of dynamical processes in the saturable absorber and gain sections. It was also found that the front facet reflectivity played a key role in the stability of mode-locking and the occurrence of self-pulsations. These lasers hold significant promise as light sources for multi-photon biomedical imaging, as well as in other applications such as frequency conversion into the ultraviolet and radio-over-fibre communications.

1.06-µm InGaAs/GaAs multiple-quantum-well optical thyristor lasers with a PiNiN structure.

InGaAs/GaAs multiple quantum well (MQW)-depleted optical thyristor lasers operating at 1.06 µm with a waveguide-type PiNiN structure is presented for the first time. The optical thyristor lasers clearly show nonlinear S-shaped current-voltage and lasing characteristics. The measured switching voltage and current are 5 V and 1 mA, respectively. The holding voltage and current are 2.6 V and 3.6 mA, respectively. A relatively high output light power of 30 mW per facet at room temperature is achieved. The lasing wavelength is 1.055 µm at a bias current of 80 mA at 25 °C.

[The effect of temperature on the PL spectra of high power LED].

Two kinds of 1 W white high power light emitting diode (LED) were made by packaging blue chips from Taiwan and US. The chips were coated by the same phosphor and transparent silica gel. Optical properties of the two kinds of LEDs were investigated in the temperature range of 15-75 degrees C and at the current of 350 mA. The results show that temperature badly affects the optical parameters such as peak wavelength, radiant flux, color temperature and so on. After analyzing the PL spectrum, the relationship between temperature and LED performance was found. The reasons for optical parameters vs. temperature were theoretically analyzed. Some suggestions were given to reduce the influence of temperature on power LED.

[The property of white powder LED with different ratio of phosphor].

White powder light emitting diodes (LED) with different color temperature were made by using different ratio of yellow to orange silicate phosphor. When the ratio of yellow to orange phosphor was less than 7, the peak wavelength of yellow light in spectra was about 570 nm and the wavelength was about 590 nm as the ratio was greater than 7. With the color temperature increasing, the color rendering index and the luminous efficiency increased at the beginning and then decreased. And color temperature of 5 521 K is the optimal value. The reason was the ineffective excitation of blue light due to higher concentration of phosphor and excess red light in spectra. In contrast, blue light was not excited effectively and red light in spectra was little when the color temperature was higher than 5 521 K. The luminous efficiency was decreased, and the decreased magnitude was inconsistency with the testing temperature from 10 to 80 degrees C. This suggests that, besides Auger recombination, the decrease in excitation efficiency of yellow and orange phosphors is different as the temperature rises and orange phosphor's temperature characteristic is superior to that of yellow phosphor.