G Giovanni Gilardi

An introduction to InP-based generic integration technology

Photonic integrated circuits (PICs) are considered as the way to make photonic systems or subsystems cheap and ubiquitous. PICs still are several orders of magnitude more expensive than their microelectronic counterparts, which has restricted their application to a few niche markets. Recently, a novel approach in photonic integration is emerging which will reduce the R&D and prototyping costs and the throughput time of PICs by more than an order of magnitude. It will bring the application of PICs that integrate complex and advanced photonic functionality on a single chip within reach for a large number of small and larger companies and initiate a breakthrough in the application of Photonic ICs. The paper explains the concept of generic photonic integration technology using the technology developed by the COBRA research institute of TU Eindhoven as an example, and it describes the current status and prospects of generic InP-based integration technology.

All-optical intensity modulation of near infrared light in a liquid crystal channel waveguide

We demonstrate a nonlinear optical channel waveguide made of E7 nematic liquid crystal infiltrated in a silica on silicon groove. Near infrared light at the wavelength of 1560 nm fiber coupled to the core of the liquid crystal waveguide was optically modulated by an optical beam with power below 25 mW by exploiting the optical Freedericks transition. By modeling the optical molecular reorientation in the nematic liquid crystal confined in a waveguiding geometry we are able to reproduce the experimental results.

Observation of tunable optical filtering in photosensitive composite structures containing liquid crystals

We report on the investigation and characterization of an optically tunable filtering effect, observed in a waveguide grating made of alternated strips of photocurable polymer and a mixture of azo-dye-doped liquid crystal. The grating is sandwiched between two borosilicate glasses, one of which includes an ion-exchanged channel waveguide, which confines the optical signal to be filtered. Exposure to a low power visible light beam modifies the azo-dye molecular configuration, thus allowing the filtered wavelength to be tuned over a 6.6 nm range. Simulations of the filtering response are well described with our experimental findings.

Liquid-crystal tunable filter based on sapphire microspheres

We design an integrated optoelectronic device based on the whispering-gallery modes of a sapphire microsphere integrated with a liquid-crystal tuning medium to produce a narrowband, electrically tunable, channel-dropping filter. The sapphire microsphere is glued over a diffused waveguide in a glass substrate. At the base of the microsphere, a small volume of liquid crystal is infiltrated. We numerically evaluate the performance of the device and demonstrate a voltage tuning of the narrowband resonances.

Experimental and Numerical Study of Electrical Crosstalk in Photonic-Integrated Circuits

This paper presents measurement results on electrical crosstalk between interconnect lines and electro-optical phaseshifters in photonic-integrated circuits. The results indicate that overall crosstalk originates from radiative and substrate coupling between lines and from shared ground connections. The latter is the main noise source in the structures measured in this paper and keeps crosstalk above -25 dB for interconnects and above -20 dB for phase-shifters independent of coupling distance. Measurements on the effect of electrical crosstalk on optical modulation show that -20 dB of coupling degrades modulation performance significantly, leading to at least 2-dB power penalty. A simulation approach is presented that reproduces the experimental results and gives insight into crosstalk mechanisms.

Generic InP-Based Integration Technology: Present and Prospects

The generic foundry approach will lead to a revolution in micro and nanophotonics, just as it did in microelectronics thirty years ago. Generic integration leads to a drastic reduction in the entry costs for developing Photonic Integrated Circuits. Integrated circuits using generic integration open up a whole new range of applications including data communications, flber-to-the-home, flber sensors, gas sensing, medical diagnostics, metrology and consumer photonics. Present status and prospects of InP-based photonic foundry technology are reviewed.

Substrate thickness effects on thermal crosstalk in InP-based photonic integrated circuits

We experimentally demonstrate the substrate thickness effect on thermal crosstalk between active and passive components in Indium Phosphide based photonic integrated circuits. The thermal crosstalk is quantified by measuring the effects on the electro-optical response of a MZ modulator considered as a test structure. The heat sources are represented by semiconductor optical amplifiers placed at different distances with respect to the position of the MZ. For a fixed substrate thickness (t), the dc switching curve drift reduces exponentially with the increase of distance (d) between MZ and heating source. We show how the amount of drift depends on the ratio between d and t. d/t >1 is the best condition to minimize the thermal effects, while d/t <; 1 heavily affects the MZ dc switching curve resulting in a reduction of its extinction ratio.

Integrated optics nano-opto-fluidic sensor based on whispering gallery modes for picoliter volume refractometry

We propose and numerically investigate an integrated optics refractometric nano-opto-fluidic sensor based on whispering gallery modes in sapphire microspheres. A measurand fluid is injected in a micromachined reservoir defined in between the microsphere and an optical waveguide. The wavelength shift due to changes in the refractive index of the measurand fluid are studied for a set of different configurations by the finite element method and a high sensitivity versus fluid volume is found. The proposed device can be tailored to work with a minimum fluid volume of 1 pl and a sensitivity up of 2000 nm/(RIUnl). We introduce a figure of merit which quantifies the amplifying effect on the sensitivity of high quality factor resonators and allows us to compare different devices.

Performance degradation of integrated modulator arrays due to electrical crosstalk

This paper reports on the performance degradation of optical modulators in an array due to electrical crosstalk. Bit-Error-Rate measurements reveal that additional power penalties are introduced due to crosstalk noise.

Realization of a Liquid Crystal Electrically Controlled Optical Waveguide on Micromachined Silicon

In this paper we report the major fabrication steps and preliminary electro-optical characterization of a novel integrated liquid crystal optical waveguide on silicon substrate. The optical waveguide is made of a SiO2/Si V-groove with a triangular cross-section filled with nematic liquid crystal E7. The optical propagation in the channel waveguide is controlled by an external voltage which induces a refractive index variation by means of molecular director reorientation. For TM polarized light at a wavelength of 1.55 μm, a threshold voltage of only about 2 V and an extinction ratio higher than 35 dB were measured with 6.5 V applied.