Microwave generation in an electro-absorption modulator integrated with a DFB laser subject to optical injection

This paper presents a new technique to generate microwave signal using an electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser subject to optical injection. Experiments show that the frequency of the generated microwave can be tuned by changing the wavelength of the external laser or adjusting the bias voltage of the EAM. The frequency response of the EAM is studied and found to be unsmooth due to packaging parasitic effects and four-wave mixing effect occurring in the active layer of the DFB laser. It is also demonstrated that an EA modulator integrated in between two DFB lasers can be used instead of the EML under optical injection. This integrated chip can be used to realize a monolithically integrated tunable microwave source. (C) 2009 Optical Society of America

Narrow-channel-spacing 32-channel arrayed-waveguide-grating multiplexer with an innovative alignment method

A 32-channel 50-GHz spaced arrayed-waveguide grating with our innovative configuration has been designed and fabricated. The performance of the device has been fully tested by using a tunable laser light source, optical power meter, and polarization controller. The insertion loss (IS) of the device is 4.2 similar to 7.4 dB. The crosstalk is about -28 clB. The IS uniformity is less than 3.2 dB. With our configuration, the performance of the device has been enhanced effectively and the difficulty in alignment process has been decreased obviously. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Giant and zero electron g factors of dilute nitride semiconductor nanowires

The electronic structures and electron g factors of InSb1-sNs and GaAs1-sNs nanowires and bulk material under the magnetic and electric fields are investigated by using the ten-band k.p model. The nitrogen doping has direct and indirect effects on the g factors. A giant g factor with absolute value larger than 900 is found in InSb1-sNs bulk material. A transverse electric field can increase the g factors, which has obviously asymmetric effects on the g factors in different directions. An electric field tunable zero g factor is found in GaAs1-sNs nanowires. (C) 2007 American Institute of Physics.

Structure tuning of line-defect waveguides based on silicon-on-insulator photonic crystal slabs

We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a siliconon-insulator substrate and characterize them using a tunable laser source over a wavelength range from 1510nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant. We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.

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.

Material growth and device fabrication of highly strained InGaAs/InGaAsP long wavelength distributed feedback lasers

1.6-1.7 mu m highly strained InGaAs/InGaAsP distributed feedback lasers was grown and fabricated by low pressure mentalorganic chemical vapor deposition. High quality highly strained InGaAs/InP materials were obtained by using strain buffer layer. Four pairs of highly strained quantum wells were used in the devices and carrier blocking layer was used to improve the temperature characteristics of the devices. The uncoated 1.66 mu m and 1.74 mu m lasers with ridge wave guide 3 mu m wide have low threshold current (< 15mA) and high output power (> 14mW at 100mA). In the temperature range from 10 degrees C to 40 degrees C, the characteristic temperature T-0 of the 1.74 mu m laser is 57K, which is comparable to that of the 1.55 mu m-wavelength InGaAsP/InP-DFB laser.

Improved optical heterodyne methods for measuring. frequency responses of photodetectors

An improved optical self-heterodyne method utilizing a distributed Bragg reflector (DBR) tunable laser and an optical fiber ring interferometer is presented in this paper. The interference efficiency can be increased by 7 dB compared with the scheme using the conventional Mach-Zehnder interferometer. The unsteady process that the beating frequency experiences in each tuning period is investigated. According to the measurement results, the wavelength and optical power of the tunable laser will be steady when the square-wave frequency is lower than 300 kHz. It has been shown that when a square-wave voltage is applied to the phase section of the tunable laser, the laser linewidths vary in a wide range, and are much larger than that under dc voltage tuning. The errors caused by the variations in the linewidth of the beat signal and optical power can be eliminated using the proposed calibration procedures, and the measurement accuracy can, therefore, be significantly improved. Experiments show that the frequency responses obtained using our method agree well with the data provided by the manufacturer, and the improved optical self-heterodyne method is as accurate as the intensity noise technique.

Spatial interference effect of two-photon in femtosecond-pulse pumped spontaneous parametric down-conversion

We have used the transverse correlated properties of the entangled photon pairs generated in the process of spontaneous parametric down-conversion, which is pumped by a femtosecond pulse laser, to perform Young's interference experiment. Unlike the case of a continuous wave laser pump, a broadband pulse laser pump can submerge an interference pattern. In order to obtain a high visibility interference pattern, we used a lens with a tunable focal length and two interference filters to eliminate the effects of the broadband pump laser. It is proven that the process of two-photon direct interference is a post-selection process.

GaInNAs/GaAs multiple-quantum well resonant-cavity-enhanced photodetectors at 1.3 mu m

A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhanced photodetector (RCF-PD) operated at a wavelength of 1.3 mum with the full width at half maximum of 4nm has been demonstrated. The GaInNAs RCE - PD was grown by molecular beam epitaxy using a homemade ion-removed dc plasma cell as a nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at room temperature, which is very beneficial for applications in long-wavelength absorption devices. For a 100 mum diameter RCE-PD, the dark current is 20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltage is - 18 V. The measured 3 dB bandwidth is 308 MHz, which is limited by the resistance of p-type distributed Bragg reflector mirror. The tunable wavelength in a range of 18 nm with the angle of incident light was observed.

Experimental Demonstration on Structure-Parameter Dependence of Photonic Crystal Optical Spectrum

We present fabrication and experimental measurement of a series of photonic crystal waveguides and coupled structure of PC waveguide and PC micro-cavity. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-holes single-line-defect waveguide. We fabricated these devices on a silicon-on-insulator substrate and characterized them using tunable laser source. We've obtained high-efficiency light propagation and broad flat spectrum response of photonic-crystal waveguides. A sharp attenuation at photonic crystal waveguide mode edge was observed for most structures. The edge of guided band is shifted about 31 nm with the 10 nm increase of lattice constant. Mode resonance was observed in coupled structure. Our experimental results indicate that the optical spectra of photonic crystal are very sensitive to structure parameters.

Recent progresses of SOI-based photonic devices - art. no. 60201R

SOI (Silicon on Insulator) based photonic devices, including stimulated emission from Si diode, RCE (Resonant Cavity Enhanced) photodiode with quantum structure, MOS (Metal Oxide Semiconductor) optical modulator with high frequency, SOI optical matrix switch and wavelength tunable filter are reviewed in the paper. The emphasis will be played on our recent results of SOI-based thermo-optic waveguide matrix switch with low insertion loss and fast response. A folding re-arrangeable non-blocking 4x4 matrix switch with total internal reflection (TIR) mirrors and a first blocking 16 x 16 matrix were fabricated on SOI wafer. The extinction ratio and the crosstalk are better. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length and more bend and intersecting waveguides. The insertion losses are expected to decrease 2-3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

Recent progresses of silicon-based optoelectronic devices for application in fiber communication

Si-based optoelectronic devices, including stimulated emission from Si diode, 1.3 and 1.5mum SiGe photodetector with quantum structures, 1GHz MOS optical modulator, SOI optical switch matrix and wavelength tunable filter are reviewed in the paper.

A new method to realize configurable OADM by using Bragg waveguide grating

Our configurable optical add/drop multiplexers (OADM) are based on thermally tunable silicon-on-insulator (SOI) Bragg gratings. We have simulated the whole device and get ideal performance. We also tried experiments to explore the process of grating waveguide and got useful results.

Period Continuous Tuning of an Efficient Mid-Infrared Optical Parametric Oscillator Based on a Fan-out Periodically Poled MgO-Doped Lithium Niobate

We report a period continuously tunable, efficient, mid-infrared optical parametric oscillator (OPO) based on a fan-out periodically poled MgO-doped congruent lithium niobate (PPMgLN). The OPO is pumped by a Nd:YAG laser and a maximum idler output average power of 1.65 W at 3.93 mu m is obtained with a pump average power of 10.5 W, corresponding to the conversion efficiency of about 16% from the pump to the idler. The output spectral properties of the OPO with the fan-out crystal are analyzed. The OPO is continuously tuned over 3.78-4.58 mu m (idler) when fan-out periods are changed from 27.0 to 29.4 mu m. Compared with temperature tuning, fan-out period continuous tuning has faster tuning rate and wider tuning range.

Stretchable Graphene: A Close Look at Fundamental Parameters through Biaxial Straining

Tunable biaxial stresses, both tensile and compressive, are applied to a single layer graphene by utilizing piezoelectric actuators. The Gruneisen parameters for the phonons responsible for the D, G, 2D and 2D' peaks are studied. The results show that the D peak is composed of two peaks, unambiguously revealing that the 2D peak frequency (omega(2D)) is not exactly twice that of the D peak (omega(D)). This finding is confirmed by varying the biaxial strain of the graphene, from which we observe that the shift of omega(2D)/2 and omega(D) are different. The employed technique allows a detailed study of the interplay between the graphene geometrical structures and its electronic properties.