Low threshold current density 1.5 mu m strained-MQW laser by n-type modulation-doping

1.5 mu m. n-type modulation-doping InGaAsP/InGaAsP strained multiple quantum wells grown by low pressure metalorganic chemistry vapor decomposition technology is reported for the first time in the world. N-type modulation-doped lasers exhibit much lower threshold current densities than conventional lasers with undoped barrier layers. The lowest threshold current density we obtained was 1052.5 A/cm(2) for 1000 mu m long lasers with seven quantum wells. The estimated threshold current density for an infinite cavity length was 94.72A/cm(2)/well, reduced by 23.3% compared with undoped barrier lasers. The n-type modulation doping effects on the lasing characteristics in 1.5 mu m devices have been demonstrated.

Lowered laser threshold in photonic crystals investigated by semiclassical theory

Using the response formula of the photonic crystals and the Bloch equations, the lasing threshold in arbitrary 2D photonic crystals was obtained by an investigation of steady-state laser behavior. The lasing threshold is expressed by the population inversion. It shows that the population inversion threshold is proportional to the second order of the group velocity, and to the relaxation coefficient. (c) 2004 Elsevier B.V. All rights reserved.

Fabrication of photonic crystal on semiconductor materials by using focued ion-beam

A method of manufacturing two-dimensional photonic crystals on several kinds of semiconductor materials in near infrared region by a focused ion beam is introduced, and the corresponding fabrication results are presented and show that the obtained parameters of fabricated photonic crystals are identical with the designed ones. Using the tunable laser source, the spectra of the fabricated passive photonic crystal and the active photonic crystal are measured. The experiment demonstrates that the focused ion-beam can be used to fabricate the perfect two-dimensional photonic crystals and their devices.

Q-switched and mode-locked diode-pumped Nd : GdVO4 laser with low temperature GaAs saturable absorber

Low temperature GaAs (LT-GaAs) was successfully grown at the temperature of 550 degrees C by metal organic vapor phase epitaxy on a semi-insular GaAs substrate. With such an absorber as well as an output coupler we obtain Q-switched mode-locked (QML) 1064 nm Nd:GdVO4 laser pumped by diode laser with high repetition rate, formed with a simple flat-flat cavity. The repetition rate of the Q-switched envelope increased from 100 to 660 kHz as the pump power increased from 2.28 to 7.29 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of similar to 1.36 GHz. A maximum average output power of 953 mW was obtained. The dependence of the operational parameters on the pump power was also investigated experimentally. (C) 2005 Elsevier B.V. All rights reserved.

Progress of Si-based nanocrystalline luminescent materials

Si-based nanomaterials are some new photoeletronic and informational materials developed rapidly in recent years, and they have potential applications in the light emitting devices, e. g. Si light emitting diode, Si laser and integrated Si-based photoelectronics. Among them are nano-scale porous silicon (ps), Si nanocrystalline embedded SiO2 (SiOx, x < 2.0) matrices, Si nanoquantum dot and Si/SiO2 superlattice, etc. At present, there are various indications that if these materials can achieve efficient and stable luminescence, which are photoluminescence (PL) and electroluminescence (EL), it is possible for them to lead to a new informational revolution in the early days of the 21st century. In this article, we will mainly review the progress of study on Si-based nanomaterials in the past ten years. The involved contents are the fabricated methods, structural characterizations and light emitting properties. Finally, we predicate the developed tendency of this field in the following ten years.

Raman study of low-temperature-grown Al0.29Ga0.71As/GaAs photorefractive materials

We report on the observation of resonant Raman scattering in low-temperature-grown AlGaAs/GaAs structure. Two kinds of excitation lights, 632.8 and 488 nm laser lines, were used to detect scattering signal from different regions based on different penetration depths. Under the outgoing resonant condition, up to fourth-order resonant Raman peaks were observed in the low-temperature-grown AlGaAs alloy, owing to a broad exciton luminescence in low-temperature-grown AlGaAs alloy induced by intrinsic defects and As cluster after post-annealing. These resonant peaks were assigned according to their fundamental modes. Among the resonant peaks, besides the overtones of the GaAs- or AlAs-like mode, there exist combination bands of these two kinds of modes. In addition, a weak scattering peak similar to the bulk GaAs longitudinal optical mode was observed in low-temperature Raman experiments. We consider the weak signal correlated with GaAs clusters appearing in AlGaAs alloys. The accumulation of GaAs in AlGaAs alloys was enhanced after annealing at high temperatures. A detailed study of the dependence of vibration modes on measuring temperature and post-annealing conditions is given also. In light of our experiments, it is suggested that a Raman scattering experiment is a sensitive microscopic probe of local disorder and, especially performed at low temperature, is a superior method in detecting and analyzing the weak interaction between phonons and electrons.

Influence of combined InAlAs and InGaAs strain-reducing laser on luminescence properties of InAs/GaAs quantum dots

We have fabricated self-organized InAs/GaAs quantum dots (QDs) capped by 1 nm In0.2Al0.8As and 5 nm In0.2Ga0.8As strain-reducing layer (SRL). The luminescence emission at a long wavelength of 1.33 mum with narrower half width is realized. A wider energy separation between the ground and first excited radiative transitions of up to 102meV was observed at room temperature. Furthermore, the comparative study proves that luminescence properties of InAs/GaAs QDs overgrown with combined InAlAs and InGaAs SRLs are much better than that of one capped with InGaAs or InAlAs SRL. (C) 2002 Elsevier Science B.V. All rights reserved.

The research of range-gated laser night vision system on cars - art. no. 68351V

The characteristic of several night imaging and display technologies on cars are introduced. Compared with the current night vision technologies on cars, Range-gated technology can eliminate backscattered light and increase the SNR of system. The theory of range-gated image technology is described. The plan of range-gated system on cars is designed; the divergence angle of laser can be designed to change automatically, this allows overfilling of the camera field of view to effectively attenuate the laser when necessary. Safety range of the driver is calculated according to the theory analysis. Observation distance of the designed system is about 500m which is satisfied with the need of safety driver range.

Wavelength tunable distributed Bragg reflector laser integrated with electro-absorption modulator by a combined method of selective area growth and quantum well intermixing - art. no. 68240N

Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed, small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity, the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing (QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML has been fabricated by this technique for the first time. The component has superior characteristics as following: threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited with power penalties less than 2.2 dB at a bit error ratio (BER) of 10(-10) after 44.4 km standard fiber transmission.

Design and performance of monolithic integrated electro-absorption modulated distributed feedback laser - art. no. 67820Y

High performance InGaAsP/InGaAsP strained compensated multiple-quantum-well (MQW) electroabsorption modulators (EAM) monolithically integrated with a DFB laser diode have been designed and realized by ultra low metal-organic vapor phase epitaxy (MOVPE) based on a novel butt joint scheme. The optimization thickness of upper SCH layer for DFB and EAM was obtained of the proposed MQW structure of the EAM through numerical simulation and experiment. The device containing 250(mu m) DFB and 170(mu m) EAM shows good material quality and exhibits a threshold current of 17mA, an extinction ratio of higher than 30 dB and a very high modulation efficiency (12dB/V) from 0V to 1V. By adopting a high-mesa ridge waveguide and buried polyimide, the capacitance of the modulator is reduced to about 0.30 pF corresponding to a 3dB bandwidth more than 20GHz.

High-speed photodetector characterization using tunable laser by optical heterodyne technique - art. no. 60200A

An ultra-wide-band frequency response measurement system for optoelectronic devices has been established using the optical heterodyne method utilizing a tunable laser and a wavelenath-fixed distributed feedback laser. By controlling the laser diode cavity length, the beat frequency is swept from DC to hundreds GHz. An outstanding advantage is that this measurement system does not need any high-speed light modulation source and additional calibration. In this measurement, two types of different O/E receivers have been tested. and 3 dB bandwidths measured by this system were 14.4GHz and 40GHz, respectively. The comparisons between experimental data and that from manufacturer show that this method is accurate and easy to carry out.

High-output very small aperture laser and its near-field distribution properties - art. no. 60200L

A Very-Small-Aperture Laser with a 250 X 500 nm(2) aperture has been created on a 650nm edge emitting LD. The highest far-field output power is 1.9mW and the power per unit emission area is about 15 MW/mu m(2). The special fabrication process and high output power mechanism are demonstrated respectively. The near-field distribution properties are also analyzed theoretically and experimentally.

Electroabsorption-modulated DFB laser integrated with dual-waveguide spot-size converter - art. no. 60200N

A 1.55-mu m ridge DFB laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum well intermixing and dual-core technologies. These devices exhibit threshold current of 28 mA, side mode suppression ratio of 38.0 dB, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0 dB dc. The output beam divergence angles of the spot-size converter in the horizontal and vertical directions are as small as 8.0 degrees x 12.6 degrees, respectively, resulting in 3.2 dB coupling loss with a cleaved single-mode optical fiber.

Tandem electroabsorption modulators integrated with DFB laser by ultra-low-pressure selective-area-growth MOCVD for 10 GHz optical short pulse generation - art. no. 60200O

A novel device of tandem multiple quantum wells (MQWs) electroabsorption modulators (EAMs) monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 mbar) selective area guowth (SAG) MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mX output light power of 4.5 mW and over 20 dB extinction ratio when coupled into a single mode Fiber. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using I this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with a width of 13.7 ps without any compression elements is obtained.

Wavelength-selectable DFB laser with wide gain bandwidth realized in nonidentical quantum well - art. no. 60200W

Width varied quantum wells show a more flat and wide gain spectrume (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an selectable DFB laser based on this material grown identical chip using traditional holographic exposure. A wavelength by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.