Improving the optical profile of electroabsorption modulator using single-sided large optical cavity structure

An electroabsorption modulator with large optical cavity was designed and fabricated successfully. Both the simulated and experimental results show that, the larger optical cavity structure introduced could obviously improve the optical profile of EA modulator, the traditional elliptical near-field spot becomes more rounded, so it will match better with the optical fiber and is beneficial for raising the coupling efficiency.

A Single Mode 980nm InGaAs/GaAs/AlGaAs Large Optical Cavity Quantum Well Laser with Low Vertical Divergence Angle

To achieve high optical power as well as low vertical divergence angle, a new kind of optimized large optical cavity (LOC) structure is applied to a ridge waveguide 980nm InGaAs/GaAs/AlGaAs multi-quantum well laser. The optical power density in the waveguide is successfully reduced. The maximum output power is more than 400mW with a slope efficiency of 0.89W/A and the far-field vertical divergence angle is lowered to 23°.

A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells

This paper reports a novel traveling-wave electroabsorption modulator (TWEAM) with a large optical cavity waveguide and an intrastep quantum well structure designed to achieve a high bandwidth, high saturation power and better fiber-matched optical profile, which is good for high coupling efficiency. The optical mode characteristic shows a great improvement in matching the circular mode of the fiber and the saturation power of 21 dBm, and a 3 dB bandwidth of 23 GHz was achieved for the fabricated TWEAM.

Design of novel three port optical gates scheme for the integration of large optical cavity electroabsorption modulators and evanescently-coupled photodiodes

This paper presents a novel scheme to monolithically integrate an evanescently-coupled uni-travelling carrier photodiode with a planar short multimode waveguide structure and a large optical cavity electroabsorption modulator based on a multimode waveguide structure. By simulation, both electroabsorption modulator and photodiode show excellent optical performances. The device can be fabricated with conventional photolithography, reactive ion etching, and chemical wet etching.

High efficiency, low vertical divergence angle 980nnn Al-free active region lasers with novel large optical cavity and asymmetrical cladding layers

980nm InGaAs/InGaAsP/AlGaAs strained quantum well lasers,vitta novel large optical cavity and asymmetrical claddings was fabricated bg MOCVD. Very high differential quantum efficiency elf 90% (1.15W/A) and low vertical divergence angle of 24 degrees at long cavity length were obtained for 100 mu m stripe lasers. The differential quantum efficiency is up to 94% (1.20) at cavity length of 500 mu m.

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).

Design,Fabrication,and Testing of Single-Side Alignment of 16×0.8nm Arrayed-Waveguide Grating

A novel design of 100GHz-spaced 16channel arrayed-waveguide grating (AWG) based on silica-on-silicon chip is reported.AWG is achieved by adding a Y-branch to the AWG and arranging the input/output channel in a neat row,so the whole configuration can be aligned and packaged using only one fiber-array.This configuration can decrease the device's size,enlarge the minimum radius of curvature,save time on polishing and alignment,and reduce the chip's fabrication cost.

Novel coupled multi-active region high power semiconductor lasers cascaded via tunnel junction

A novel semiconductor laser structure is put forward to resolve the major difficulties of high power laser diodes. In this structure, several active regions are cascaded by tunnel junctions to form a large optical cavity and to achieve super high efficiency. This structure can solve the problems of catastrophic optical damage of facet, thermal damage and poor light beam quality effectively. Low-pressure metalorganic chemical vapor deposition method is adopted to grow the novel semiconductor laser structures, which are composed of Si:GaAs/C:GaAs tunnel junctions, GaAs/InGaAs strain quantum well active regions. External differential quantum efficiency as high as 2.2 and light power output of 2.5 W per facet (under 2A drive current) are achieved from an uncoated novel laser device with three active regions.

Influence of a tilted cavity on quantum-dot optoelectronic active devices

Quantum-dot laser diodes (QD-LDs) with a Fabry-Perot cavity and quantum-dot semiconductor optical amplifiers (QD-SOAs) with 7° tilted cavity were fabricated. The influence of a tilted cavity on optoelectronic active devices was also investigated. For the QD-LD, high performance was observed at room temperature. The threshold current was below 30 mA and the slope efficiency was 0.36 W/A. In contrast, the threshold current of the QD-SOA approached 1000 mA, which indicated that low facet reflectivity was obtained due to the tilted cavity design.A much more inverted carrier population was found in the QD-SOA active region at high operating current, thus offering a large optical gain and preserving the advantages of quantum dots in optical amplification and processing applications. Due to the inhomogeneity and excited state transition of quantum dots, the full width at half maximum of the electroluminescence spectrum of the QD-SOA was 81.6 nm at the injection current of 120 mA, which was ideal for broad bandwidth application in a wavelength division multiplexing system. In addition, there was more than one lasing peak in the lasing spectra of both devices and the separation of these peak positions was 6-8 nm,which is approximately equal to the homogeneous broadening of quantum dots.

Eigenmode confinement in semiconductor microcavity lasers with an equilateral triangle resonator

We analyze the mode behaviors for semiconductor lasers with an equilateral triangle resonator by deriving the mode field distribution and the eigenvalue equation. The eigenvalue equation shows that the longitudinal mode wavelength interval is equivalent to that of a Fabry-Perot cavity with the cavity length of 1.5a, where a is the side length of the equilateral triangle resonator. The transverse waveguiding is equivalent to as a strip waveguide with the width of root 3a/ 2, and the number of transverse modes supported by the resonator is limited by the total reflection condition on the sides of the equilateral triangle. Semiconductor microcavity laser with an equilateral triangle resonator is suitable to realize single mode operation, and the mode wavelength can be adjusted by changing the side length.

Characters of Surface Deformation and Surface Wave in Thermal Capillary Convection

In the field of fluid mechanics, free surface phenomena is one of the most important physical processes. In the present research work, the surface deformation and surface wave caused by temperature difference of sidewalls in a rectangular cavity have been investigated. The horizontal cross-section of the container is 52 mmx42 mm, and there is a silicon oil layer of height 3.5 mm in the experimental cavity. Temperature difference between the two side walls of the cavity is increased gradually, and the flow on the liquid layer will develop from stable convection to un-stable convection. An optical diagnostic system consisting of a modified Michelson interferometer and image processor has been developed for study of the surface deformation and surface wave of thermal capillary convection. The Fourier transformation method is used to interferometer fringe analysis. The quantitative results of surface deformation and surface wave have been calculated from a serial of the interference fringe patterns.The characters of surface deformation and surface wave have been obtained. They are related with temperature gradient and surface tension. Surface deformation is fluctuant with time, which shows the character of surface wave. The cycle period of the wave is 4.8 s, and the amplitudes are from 0 to 0.55 mu m. The phase of the wave near the cool side of the cavity is opposite and correlative to that near the hot side. The present experiment proves that the surface wave of thermal capillary convection exists on liquid free surface, and it is wrapped in surface deformation.

Designing a coupler for the intersatellite optical communication system

Coupling a single-mode laser diode with 200 mW to a single-mode fiber (SMF) through an orthonormal aspherical cylindrical lens and a GRIN lens for the intersatellite optical communication system is proposed and demonstrated. We experimentally studied how the coupling efficiency changes with the SMF's position displacement and axial angle variation, and obtained 80 mW output power at the end of the SMF, which shows that the coupling units have satisfied the designed request. (c) 2007 Elsevier GmbH. All rights reserved.

Three-photon absorption-induced fluorescence and optical limiting effects in a fluorene derivative

This paper reports on the steady-state fluorescence, three- photon absorption-induced fluorescence emission and subsequently induced optical limiting behaviour of a fluorene derivative with D-pi-D structural motifs. The lifetime of the steady-state fluorescence is 0.903 ns. Large optical limiting behaviour induced by 3PA has also been demonstrated, and the nonlinear absorption coefficient gamma derived from 3PA fitting curves is 5.92 x 10(-20) cm(3)/W-2 and the corresponding molecular 3PA cross-section sigma(3)' is 1.14 x 10(-76) cm(6) s(2).

Fiber Dispersion and Nonlinearity Influences on Transmissions of AM and FM Data Modulation Signals in Radio-Over-Fiber System

Transmission properties of data amplitude modulation (AM) and frequency modulation (FM) in radio-over-fiber (RoF) system are studied numerically. The influences of fiber dispersion and nonlinearity on different microwave modulation schemes, including double side band (DSB), single side band (SSB) and optical carrier suppression (OCS), are investigated and compared. The power penalties at the base station (BS) and the eye opening penalties of the recovered data at the end users are both calculated and analyzed. Numerical simulation results reveal that the power penalty of FM can be drastically decreased due to the larger modulation depth it can achieve than that of AM. The local spectrum broadening around subcarrier microwave frequency of AM due to fiber nonlinearity can also be eliminated with FM. It is demonstrated for the first time that the eye openings of the FM recovered data can be controlled by its modulation depths and the coding formats. Negative voltage encoding format was used to further decrease the RF frequency thus increase the fluctuation period considering their inverse relationship.