Alexandre Marceaux

Optically beamformed beam-switched adaptive antennas for fixed and mobile broad-band wireless access networks

In this paper, a 3-bit optical beamforming architecture based in 2/spl times/2 optical switches and dispersive media is proposed and demonstrated. The performance of this photonic beamformer is experimentally demonstrated at 42.7 GHz in both transmission and reception modes. The progress achieved for realizing these architectures with integrated optics is also reported. Due to its advanced features (i.e., potential fast-switching, huge bandwidth, and immunity to electromagnetic interference), the architecture is a very promising alternative to traditional beamforming technologies for implementing beamformed base-station antennas in fixed and mobile broad-band wireless access networks operating in the millimeter-wave band. The study presented here has been carried out in the frame of the IST 2000-25390 OBANET project.

Simulation of microwave optical links and proof of noise figure lower than electrical losses

The operation of a microwave photonic link is thoroughly investigated both theoretically and experimentally. To this aim, we have developed a simulation tool based on an accurate physical model embedded in a radio frequency (RF) chain simulator. The theoretical predictions are tested on an intensity modulation-direct detection (IMDD) link we have specifically developed to this purpose. Our simulation tool takes into account both optical and electrical characteristics of the link components including the laser dynamics and impedance matching networks. It thus enables an accurate understanding of the different physical and electrical phenomena governing the links performances even under unusual operation conditions. Specifically, we were able to isolate an unusual behavior and to confirm it experimentally. It is thereby clear that the noise figure of a microwave optical link can be lower than the electrical losses, such as a mismatched output passive electrical network. This state is reached when the optical losses are high enough and when the links output impedance is mismatched, too.

Discussion on RIN improvement using a standard coupler

It is possible to increase the signal-to-noise ratio (SNR) of radio-frequency optical links by a factor of N by combining the light of N individual lasers. The individual relative intensity noises (RINs) are then averaged, and the equivalent noise is lowered. However in some cases, while using a standard 3-dB coupler for combining two lasers, some additional noise appears which limits the RIN (and, thus, the SNR) improvement. This noise is proved, in this letter, to originate from heterodyne beating between the peak of one laser and the sidemodes of the other laser. It is possible to suppress this additional noise by injecting the light beams in crossed polarization in the coupler. The experimental data found by doing so matches perfectly the expected behavior. A 3-dB RIN improvement can be achieved if the two lasers have the same output optical power and similar RIN.

Optical Summation of RF Signals

We present two concepts dedicated to the optical summation of RF signals for radar applications. The first technique is based on a traveling wave detector array. We experimentally demonstrate the summation of four signals in the whole 25 GHz photodiodes bandwidth. However, a deeper study reveals that amplitude and phase errors increase dramatically at high frequency, limiting the practical application to 10 GHz. The second technique relies on a photodiode simultaneously illuminated on its top and back sides. We experimentally demonstrate the summation of two signals covering the whole 25 GHz photodiode bandwidth, with amplitude and phase errors below plusmn1dB and plusmn4deg, respectively. The heterodyne beating noise which occurs in this type of summation remains below -40 dB

Developement and optimization protocol of an additive phase noise measurement bench dedicated to long-haul microwave analog optical links

We propose a microwave additive phase noise measurement scheme dedicated to long-haul microwave analog optical links. We describe here the protocol to follow and precautions to take in order to ensure a reliable measurement with a reduced noise floor level.

Fabrication process for low-cost GaInAsP/InP etched-facet photodetectors

The optical waveguide entry facet of high-speed, 40 GHz waveguide photodetectors is usually obtained by manual cleaving, which has limited accuracy (± 10 μm) and reduces fabrication yields. In our new fabrication process, the waveguide facet is obtained with Chemically Assisted Ion Beam Etching (CAIBE). Length is therefore precisely controlled by photolithography. The antireflection coating is also deposited collectively on the whole wafer, which further reduces costs. The bandwidth of the photodiodes is 50 GHz, and their optical responsivity is 0.6 A/W at 1.55 μm wavelength. Other techniques, such as Inductively Coupled Plasma Etching (ICP), were also investigated for reducing leakage current.

Advanced packaging of 40-GHz photoreceiver

This paper presents recent developments in the packaging of 40GHz receivers for radio over fiber applications. First, we present a hybrid 40GHz photoreceiver module. It integrates 40GHz waveguide photodiode technology and narrow band MMIC amplifier. We give key elements for the design and the realisation of such photoreceiver. With an input optical power of 0dBm, an RF ouptut power of -3dBm is obtained in the 38-44GHz frequency range with a flatness of ±0.5dBm. The maximal input optical power is +6dBm. Secondly, a small footprint 40GHz photoreceiver scheme is presented. It includes high optical coupling tolerances 40GHz tapered waveguide photodiodes and the same type of MMIC amplifier than used in the hybrid package. The interconnect of the several elements (MMIC, capacitors, photodiode biasing network) uses Microwave High Density Integration (MHDI) technology on a Si substrate. The photodiode is flip-chip mounted on the same substrate. This technology is very promising for packaging of optoelectronic devices, since it combines compactness and reproducibility thanks to wire bonding suppression.