Improving response speed of electrooptical switch in silicon-on-insulator by modifying modulation area structure

This paper reports on the simulation of two 2 x 2 electrooptical switches with different modulation area structures in silicon-on-insulator (SOI). A two-dimensional (2D) semiconductor device simulation tool PISCES-II has been used to analyze the dc and transient behaviors of the two devices. The modeling results show that the switch with an N+-I-P+-I-N+ modulation structure has a much faster response speed than the device with a P+-I-N+ modulation structure, although the former requires slightly stronger injection power.

A new method of restraining the Fabry-Perot resonance

In the paper, we present a new method of restraining the Fabry-Perot resonance. The method is to combine dip angle with taper angle in the structure of the device and avoids the process of antireflection coatings. The experimental results show that restraining effect is apparent. A high threshold current has been obtained for the sample with both dip angle and taper angle structure. It provides a new method to make traveling-wave optical amplifiers.

High performance of 1.55 mu m DFB integrated with vertically tapered self-aligned spot-size converter

A new type of self-aligned spotsize converter (SSC) integrated 1.55 mum DFB lasers had been proposed in this article. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously, which not only offered the separate optimization of the active region and the integrated SSC, but also reduced the difficulty of the butt-joint selective regrowth. The vertical and horizontal far field angles were 9degrees and 12degrees respectively, the 1- dB misalignment tolerance were both 3.6 and 3.4 mum. The directed coupling efficiency to tapered single mode fiber was 48%.

High-performance 980-nm quantum-well lasers using a hybrid material system of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm(2) (at a cavity length of 1500 mu m), internal quantum efficiency of similar to 95%, and low internal loss of 1.8 cm(-1). Both broad-area and ridge-waveguide laser devices are fabricated. For 100-mu m-wide stripe lasers with a cavity length of 800 Irm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T-0) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-mu m-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A.

980nm InGaAs/InGaAsP quantum well lasers with AlGaAs cladding grown by metal organic chemical vapour deposition

The authors report on the fabrication of 980 nm InGaAs strained quantum well lasers with hybrid materials of InGaAsP as waveguide and AlGaAs as cladding grown by metal organic chemical vapour deposition. The InGaAs/InGaAsP/AlGaAs diode lasers (100 x 800 mu m) with broadened waveguide structure exhibit a threshold current of 180 mA, a slope efficiency of 1.0 W/A, and a high characteristic temperature coefficient (T-0) of 230 K.

Oscillatory magneto-conductance in quantum waveguides with lateral multi-barrier structures

The magneto-transport properties of a narrow quantum waveguide with lateral multibarrier modulation are investigated theoretically. It is found that the magnetoconductance as a function of Fermi energy or magnetic field exhibits square-wave-like oscillations. In the presence of magnetic field, the edge states are formed near each barrier and the boundaries. Therefore, the number of edge states increases with the number of lateral barriers, leading to the increase of the propagating modes. On the other hand, owing to the tunneling effect a pair of edge states around the barrier region with opposite moving directions may be coupled and formed a circulating localized state, leading to the quenching of the related propagating states. The resulting dispersion relation exhibits oscillation structures superimposed on the bulk Landau levels. These novel conductance characteristics may provide potential applications to the fabrication of new quantum devices.

Tunneling transmission in two quantum wires coupled by a magnetically defined barrier

A numerical analysis of an electron waveguide coupler based on two quantum wires coupled by a magnetically defined barrier is presented with the use of the scattering-matrix method. For different geometry parameters and magnetic fields, tunneling transmission spectrum is obtained as a function of the electron energy. Different from that of conventional electron waveguide couplers, the transmission spectrum of the magnetically coupled quantum wires does not have the symmetry with regard to those geometrically symmetrical ports, It was found that the magnetic field in the coupling region drastically enhances the coupling between the two quantum wires for one specific input port while it weakens the coupling for the other input port. The results can be well understood by the formation of the edge states in the magnetically defined barrier region. Thus, whether these edge states couple or decouple to the electronic propagation modes in the two quantum wires, strongly depend on the relative moving directions of electrons in the propagating mode in the input port and the edge states in the magnetic region. This leads to a big difference in transmission coefficients between two quantum wires when injecting electrons via different input ports. Two important coupler specifications, the directivity and uniformity, are calculated which show that the system we considered behaves as a good quantum directional coupler. (C) 1997 American Institute of Physics.

A New Edge-Coupled Two-Terminal Double Heterojunction Phototransistor (ECTT-DHPT) and Its DC Characteristics

A new ECTT-DHPT with InGaAsP(lambda=1.55 mu m) as base and InGaAsP(lambda=1.3 mu m) as collector as well as waveguide was designed and fabricated, the DC characteristics reveal that the ECTT-DRPT can perform good optoelectronic mix operation and linear amplification operation by optically biased at two appropriate value respectively. Responsivity of more than 52A/W and dark current of 70nA (when V-ce=1V) were obtained.

Fabrication and characterization of two-dimensional photonic crystal on silicon by efficient methods

Two-dimensional photonic crystals working in near infrared region are fabricated into silicon-on-insulator wafer by 248-nm deep UV lithography. We present an efficient way to measure the photonic crystal waveguide's light transmission spectra at given polarization states.

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.

1.55 mu m Ge islands resonant-cavity-enhanced narrowband detector

The high quality Ge islands material with 1.55 mu m photo-response grown on Sol substrate is reported. Due to the modulation of the cavity formed by the mirrors at the surface and the buried SiO2 interface, seven sharp and strong peaks with narrow linewidth are found. And a 1.55 mu m Ge islands resonant-cavity-enhanced (RCE) detector with narrowband was fabricated by a simple method. The bottom mirror was deposited in the hole formed by anisotropically etching, in a basic solution from the backside of the sample with the buried SiO2 layer in silicon-on-insulator substrate as the etch-stop layer. Reflectivity spectrum indicates that the mirror deposited in the hole has a reflectivity as high as 99% in the range of 1.2-1.65 mu m. The peak responsivity of the RCE detector at 1543.8 nm is 0.028 mA/W and a full width at half maximum of 5 nm is obtained. Compared with the conventional p-i-n photodetector, the responsivity of RCE detector has a nearly threefold enhancement.

Single-mode holey vertical-cavity surface-emitting laser with ultra-narrow beam divergence

We demonstrated oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs) with a two-dimensional petal-shaped holey structure composed of several annular-sector-shaped holes. Four types of devices with different hole numbers were designed and fabricated. The measured results showed that the larger hole number was beneficial to purifying the lasing mode, and realizing the single-mode operation. The side mode suppression ratio (SMSR) exceeded 30 dB throughout the entire drive current. Mode selective loss mechanism was used to explain the single-mode characteristic. The single-mode devices possessed good beam profiles, and the lowest divergence angle was as narrow as 3.2 degrees (full width at half maximum), attributed to the graded index profile and the shallow etching in the top distributed Bragg reflector (DBR).

Monolithic optical gates based on integration of evanescently-coupled uni-traveling-carrier photodiodes and electroabsorption modulators

We report on chip-scale optical gates based on the integration of evanescent waveguide unitraveling-carrier photodiodes (EC-UTC-PDs) and intra-step quantum well electroabsorption modulators (IQW-EAMs) on n-InP substrates. These devices exhibit simultaneously 2.1 GHz and -16.2 dB RF-gain at 21 GHz with a 450 Omega thin-film resistor and a bypass capacitor integrated on a chip.

Electronic states and magnetotransport in quantum waveguides with nonuniform magnetic fields

The electronic states and magnetotransport properties of quantum waveguides (QW's) in the presence of nonuniform magnetic fields perpendicular to the QW plane are investigated theoretically. It is found that the magnetoconductance of those structures as a function of Fermi energy exhibits stepwise variation or square-wave-like oscillations, depending on the specific distributions (both in magnitude and direction) of nonuniform magnetic fields in QW's. We have investigated the dual magnetic strip structures and three magnetic strip structures. The character of the magnetotransport is closely related to the effective magnetic potential and the energy-dispersion spectrum of electron in the structures. It is found that dispersion relations seem to be combined by different sets of dispersion curves that belong to different individual magnetic subwaveguides. The magnetic effective potential leads to the coupling of states and the substantial distortion of the original dispersion curves at the interfaces in which the abrupt change of magnetic fields appears. Magnetic scattering states are created. Only in some three magnetic strip structures, these scattering states produce the dispersion relations with oscillation structures superimposed on the bulk Landau levels. It is the oscillatory behavior in dispersions that leads to the occurrence of square-wave-like modulations in conductance.

Suppression of ballistic electron transmission through a semiconductor II-structure by an external transverse electric field

We have conducted numerical studies of ballistic electron transport in a semiconductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.