Nakita Vodjdani

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.

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.

An InP-based photonic integrated beamformer for phased-array antennas

An InP-based integrated beamformer for beamsteering of a four-element Phased-Array Antenna has been designed, fabricated and characterized. This beamformer consists of an AWG, 14 high-speed MZI switches, and 9delaylines integrated on a single compact chip.

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.