D Domenico D'Agostino

A High-

The design, fabrication, and optical characterization of the sensing element of a photonic InP-based gyroscope intended for applications in the field of aerospace and defense are reported in this paper. The sensing element is a spiral resonator coupled to a straight bus waveguide through a multimode interference coupler and exhibits a Q factor of approximately 600 000 with a footprint of approximately 10 mm 2. The design of each component of the sensor is based on some well-established numerical methods such as the Finite Element Method, the beam propagation method, and the film mode matching method. The spiral cavity was designed using the standard transfer matrix method. The selected fabrication process, which is an enhanced version of the standard COBRA process, allows the monolithic integration of the sensing element with the other active components of the gyroscope, e.g., lasers, photodiodes, and modulators. Each component of the fabricated sensing element was optically characterized using an appropriate setup, which was also used for the optical characterization of the whole sensor. Based on the results of the characterization, the gyro performance was evaluated, and a way to improve both the resolution and the bias drift, i.e., down to 10°/h and 1°/h, respectively, was also clearly identified. The achieved results demonstrate, for the first time, the actual feasibility of a photonic gyro-on-chip through a well-established InP-based generic integration process.

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We report the experimental demonstration of two coupled laser cavities via self-imaging interference in a multimode waveguide. The coupling is optimized by considering images formed by two coherent phase-delayed signals at the input of a 3×3 splitter. As a result, the complex transfer coefficients of the coupling element can be chosen to increase the mode selectivity of the coupled system. A demonstration is given by the successful fabrication of a tunable laser with a side-mode suppression ratio (SMSR) up to 40 dB and a 6.5 nm tuning range. The laser delivers milliwatts of output power to a lensed fiber and is fully compatible with processes supporting vertically-etched sidewalls.

InP Resonant Angular Velocity Sensor for a Monolithically Integrated Optical Gyroscope

Generic InP foundry processes allow monolithic integration of active and passive elements into a common p-n doped layerstack. The passive loss can be greatly reduced by restricting the p-dopant to active regions. We report on a localized Zn-diffusion process based on MOVPE, which allows to reduce waveguide loss from 2 dB/cm to below 0.4 dB/cm. We confirm this value by fabrication of a 73 mm long spiral ring resonator, with a record quality factor of 1.2 million and an extinction ratio of 9.7 dB.

Coupled cavity laser based on anti-resonant imaging via multimode interference.

We present a 26 nm tunable Coupled Cavity Laser based on a novel interferometer and fabricated in a low-cost generic foundry process, with SMSR above 40 dB and fibre coupled power > 5mW.

Low-loss passive waveguides in a generic InP foundry process via local diffusion of zinc

Integrated spot size converters (SSCs) are key components for efficient coupling between Photonic Integrated Circuits (PICs) and fibre-arrays. We report a compact SSC which is suitable for integration into dense arrays with a pitch down to 25 μm and compatible with our generic InP-based platform technology, which supports integration of SOAs and Electro Optical Modulators with a range of passive components. The small pitch supports coupling tens of on-chip optical waveguide ports to fiber arrays via a low-loss dielectric interposer chip. The density allows the design of a customized optical bus between the InP PIC and the interposer chip. The dielectric chip may simply expand to the pitch of a fiber array but also contain low-loss passive circuitry like delay-lines, high Q-filters and multiplexers. The latter enables the formation of a hybrid integration platform with our InP-based technology. Efficient coupling is obtained by adiabatically transforming the sub-micron modes of the InP waveguides to the 3 μm diameter mode of the interposer. We tested our SSCs by coupling to a lensed fibre with a mode field diameter of 2.5 μm. Coupling losses were found to be as low as 0.6 dB per fiber chip coupling for device lengths of a few 100 μm. We also measured the crosstalk from one input port to output ports adjacent to the targeted output port. We present simple design rules for reducing the crosstalk to neighbouring output ports below -50 dB. The quality and uniformity of the SSCs is demonstrated by fabrication of an 8 x 8 AWG demultiplexer between two SSC arrays placed at input and output ports. We measured an insertion loss between fibres of 4 dB for the central channel of the AWG, which is record low for an InP-based device.

Widely tunable Coupled Cavity Laser based on a Michelson interferometer with doubled free spectral range

Coupling of two Fabry-Perot cavities via a 3x3 Multimode Interference Reflector is presented. We measure SMSR close to 40 dB and a tuning range of 7 nm for 1.2 mm cavities with 5% length difference.

A dense spot size converter array fabricated in a generic process on InP

We present the monolithic integration of an extended tuning range coupled-cavity laser with traveling-wave Mach–Zehnder modulators in a low-cost generic photonic foundry platform for 10 Gb/s operation. Using an intra-cavity Michelson interferometer combined with on-chip reflectors, the coupled-cavity laser shows a tuning range of 25 nm. The modulator building blocks with optimized traveling wave electrodes exhibit efficient modulation and 8.5-GHz electro-optic bandwidth, enabling 10 Gb/s ON–OFF keying. We demonstrate error-free operation of the tunable transmitter in a full photonic circuit environment. The laser modulator combination neither requires Bragg grating formation for wavelength tuning nor additional growth steps for multiquantum-well material in the modulator section and is therefore well suited for cost effective foundry platforms specifically for low-cost applications.

Tunable Coupled Cavity Laser based on a 3x3 Multimode Interference Reflector

We experimentally demonstrate a monolithically integrated laser with built-in weak optical feedback, which shows broad regions of operation without relaxation-oscillation-induced instabilities. The side mode suppression is >40 dB for all values of the feedback phase. The measured linewidth varied from 740 KHz to 14 MHz, depending on the feedback phase value.

Monolithic Tunable Coupled-Cavity WDM Transmitter in a Generic Foundry Platform

Progress on the development of a long wavelength (~2 μm) generic monolithic photonic integration technology on indium phosphide substrate and a novel concept of a tunable laser realized as a photonic integrated circuit using such technology are presented. Insights into the development of active and passive waveguide structures which are used to define a limited set of on-chip functionalities in the form of building blocks will be given. A novel tunable laser was proposed and designed using such predefined set of basic building blocks. The laser geometry features an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers in a nested configuration. The photonic integrated circuit chip was fabricated within the first long wavelength multi-project wafer run. The experimental evaluations of the fabricated device show a record tuning range of 31 nm around 2027 nm and successful measurements of a 0.86 GHz wide absorption line of carbon dioxide. These results provide a demonstration of a fully functional photonic integrated circuit operating at wavelengths that are much longer than those in the typical telecommunication windows as well as the use of indium phosphide based generic photonic integration technologies for gas sensing applications.

Integrated Laser With Optical Feedback Shows Suppressed Relaxation-Oscillation Dynamics

In this letter, the fabrication and the characterization of angled and straight etched facets in InP-based technology are reported. In addition, we report on etched facets combined with coupler mirrors for vertical outcoupling, realized with a wet-etching process.