D. Decoster

High performance evanescent edge coupled waveguide unitraveling-carrier photodiodes for >40-gb/s optical receivers

We have demonstrated a low-cost high-bandwidth and high-responsivity evanescent waveguide unitravelling-carrier photodiode (PD) fabricated using all 2-in InP processing including on-wafer mirrors and coating. Optimization of the optical input waveguide was made using the method of the genetic algorithm associated with a beam propagation method. Optical fiber coupling to the PD is based on a diluted multimode waveguide allowing simple material epitaxial growth. The fabricated PDs exhibit simultaneously 0.76-A/W responsivity at 1.55 /spl mu/m, >50-GHz bandwidth, and more than 22-mA average saturation photocurrent at 50 GHz. The light polarization dependence is less than 0.1 dB.

An improved time-domain beam propagation method for integrated optics components

An improved time-domain beam propagation method based on the propagation of a quasi-rectangular pulse is proposed to analyze and optimize the integrated components in which wide-angle of diffraction or reflection of light are possible. This method can overcome the drawback due to the modification of short pulse during propagation and reflection induced by the numerical errors and slow-varying envelope approximation in the usual TD-BPM. After validating this method for a planar waveguide, three 90/spl deg/ reflections on micromirrors are simulated.

Improving thermal stability of opto-electronic oscillators

Stable microwave oscillators are realized based on high-quality factor resonators, which in turn are realized using acoustic, electromagnetic, and optical technologies. This article provides an overview of close-in carrier phase noise and temperature stability of various oscillators

Modeling of waveguide PIN photodetectors under very high optical power

In this paper, the behavior under very high optical power of waveguide PIN photodetectors grown on InP substrate is simulated. The problem is solved using a pseudo-bidimensional drift-diffusion model which describes the electrical behavior of the device including the effects of the external circuit. The optical behavior of the device is analysed using FD 2D and 3D beam propagation method. First, we present the optical behavior of the device when the illumination conditions change. Influence of device structure, spot width, spot position and injection angle on the quantum efficiency of the photodetector is so studied. Second, the whole modeling is validated using experimental results given in the literature. Three typical multimode structures w hich allow a high cut-off frequency as well as a good responsivity are then modeled and compared. The smaller one has a cut-off frequency of 75 GHz in small signal conditions and the main effect decreasing the microwave output signal when the optical input power increases is the carrier effect in the depletion region of the photodetector. The maximum microwave power of each photodetector is calculated in typical conditions of use. >

Optical waveguide loss minimized into gallium nitride based structures grown by metal organic vapor phase epitaxy

The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.

Design, optimization, and fabrication of side-illuminated p-i-n photodetectors with high responsivity and high alignment tolerance for 1.3and 1.55-/spl mu/m wavelength use

We describe the design, optimization and fabrication of side-illuminated p-i-n photodetectors, grown on InP substrate, suitable for surface hybrid integration in low-cost modules. The targeted functionalities of these photodetectors were a very high responsivity at 1.3- and 1.55-/spl mu/m wavelengths and quasi-independent on the optical polarization, and had a high alignment tolerance. Moreover, in order to avoid any reliability problem, the principle of evanescent coupling was adopted. Two photodetectors were optimized, fabricated, and tested; the first was for classical cleaved fiber, and the second was for lensed fiber. Because the considered epitaxial structures were complicated to optimize, the method of the genetic algorithm was used, associated with a beam propagation method (BPM). The photodetectors are based on multimode diluted waveguides, which are promising structures in the field of optoelectronics and integrated optics. Starting from the presented comparisons between experimental and theoretical results, the interest of the design method is discussed and the complete performances of newly fabricated devices are presented. The aspect of the cutoff frequency is also considered.

Investigation of 3D semivectorial finite-difference beam propagation method for bent waveguides

A three dimensions of semivectorial finite difference beam propagation method (FD-BPM) in cylindrical coordinates is investigated in order to analyze the optical wave propagation in the bent waveguides with the strong lateral confinement which will keep low radiation loss. The three dimensional (3D) semivectorial wave propagation equation is programmed in the quick and unconditionally stable procedure by using the alternating direction implicit method. This version of FD-BPM could well express the polarization characteristics of modal field near the dielectric interfaces and accurately simulate the wave propagation in bent waveguides even at a very small radius (<100 /spl mu/m). Moreover, it is pointed out that the numerical precision of the algorithm is intensively affected by the propagation loss of bent waveguides along with the propagation step length of beam propagation method.

Theoretical study of p-i-n photodetectors' power limitations from 2.5 to 60 GHz

In this paper, we present a theoretical study and a numerical simulation of various long wavelength top-illuminated p-i-n photodetectors in the frequency range of 2.5-60 GHz under high optical modulated power at 1.55-/spl mu/m wavelength. The modeling includes a monodimensional drift-diffusion model for the device and takes into account the external circuit. We considered six InP/GaInAs/InP photodetectors especially designed to work at 2.5, 10, 20, 30, 40, and 60 GHz, respectively. For the one with the highest frequency, we intentionally sacrificed the quantum efficiency in order to compare them at the end with the results already obtained in the case of waveguide p-i-n photodetectors. The results show the maximum microwave-output power for each photodetector at its specific working frequency. Additionally, we present the effects of the modulation depth, the back illumination, and the wavelength of 1.3 /spl mu/m.

Photonic devices based on preferential etching

We introduce a design concept of optical waveguides characterized by a practical and reproducible process based on preferential etching of crystalline silicon substrates. Low-loss waveguides, spot-size converters, and power dividers have been obtained with polymers. We have also aligned liquid crystals in the waveguides and demonstrated guided propagation. Therefore this technology is a suitable platform for soft-matter photonics and heterogeneous integration.

Planar monolithic integrated photoreceiver for 1.3–1.55 μm wavelength applications using GaInAs‐GaAs heteroepitaxies

We report the first fabrication of a monolithic integrated circuit consisting of a Ga0.47In0.53As planar photoconductive detector (suitable for 1.3–1.55 μm wavelength optical communication systems) associated with a GaAs field‐effect transistor. The gain, response times, and noise properties of the photoconductive detector and the integrated photoreceiver have been investigated, taking into account particular aspects of the material and integrated circuit structure.