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Final Report Summary - GETPICS (Generic Technologies for WDM Transmitter PhotonicIntegrated Circuits)

Photonic integrated chips play a key role in our daily lives, without our awareness of its significance. Sending a message through a chat program, watching an online movie, having a video call − all of this would look much more different if it was not for photonics. Specific materials, from III-V group of elements, allow us to use the most out of the light interaction inside these materials. Starting from a simple functionalities such as light generation on chip from a laser structure, modulation in modulator sections and combination of multiple light paths on a single chip, we are able to make very complex circuits. These circuits can be used in telecommunications, environmental sensing, medicine, and many more fields. All of the functionalities are implemented on a single chip, typically what we make is 4 × 4.5 mm2 area. This area is sufficient to make a transmitter or receiver circuit in optical communications, with at least 10 different channels if properly designed.
Wavelength division multiplexing makes way for bandwidth scaling by sending more information through different wavelengths in the same transmission medium. Transmitter devices have advanced rapidly with the introduction of photonic integrated circuits. Providing more bandwidth is the roadmap of the future and the next challenge is to make transmitters more compact and energy efficient.
The project promotes the use of a generic integration technology through the use of building blocks, processes and products for applications defined by the end user. Starting from the COBRA generic integration platform, the next generation of building blocks is being developed. Challenges addressed include:
• buried heterostructure active regions for high efficiency and high performance gain blocks which are integrated with the full generic platform,
• selective area growth to enable many different bandgap devices on the same chip, exploiting a rich range of established generic building blocks, and
• high speed electro-absorption modulators and radio-frequency transmission lines on n-InP and semi-insulating (SI) substrate for the wavelength division multiplexing circuits.
The test vehicles validated in GeTPICs project are focused on the design and fabrication of high bit-rate transmitter device.

Generic integration platform extension:

The generic COBRA platform comprises of diverse components, such as simple waveguides, multimode interferometers, arrayed waveguide grating (AWG), etc. Integration of buried heterostructure active sections shows, both theoretically and experimentally, an improved thermal resistance of 36%, allowing energy efficient operation. Optimized small footprint electro-absorption modulator ensures operation at 25 Gbps per channel for SI-substrate. High speed transmission lines on the same substrate exhibit very low loss, as low as 0.2 dB/mm in a wide frequency range, ensuring the integrity of the radio-frequency signal, important for high speed operation. Selective area growth technology allows local tuning of the bandgap of quantum well active structures during a single epitaxy growth. In this way an array of lasers with a range over 200 nm is possible to integrate, and wavelength division multiplexing sources on a single chip are now technologically easier to implement.
All of these developments have been enabled in GETPICs. A comprehensive range of designs, starting from test structures for validating the new functionalities of the platform, to a more complex ones such as multi-channel directly modulated laser sources and externally modulated laser sources in a WDM configuration, are implemented, exploiting the novelties in the platform.

Conclusions and potential impact:

The GeTPICs project enabled the development of key technologies to expand significantly the COBRA generic integration platform. High speed electro-absorption modulators are ready for being used by designers of the platform, all challenges for the integration of buried heterostructures have been addressed and a fabrication of such devices is ongoing, and the first implementation of selective area growth show successful results.
Thanks to the development of the COBRA platform through the GeTPICs project higher speed for telecommunication can be achieved, low consumption devices can be fabricated for embedded applications, on-chip coarse WDM is available for long range telecommunication, and wide wavelength range is reachable for sensing applications.
The development of the generic platform opens new possibilities for photonic chip designers. Extending the capability of such a platform is a leverage for the development of photonics since it has for only limit the creativity of designers around the world to make the most of the available technology.

Contact details:
Dr. Mohand Achouche, Leading the Nokia III-V Lab,
Dr. Kevin Williams, Leading the Photonic integration group at the Eindhoven University of Technology,

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Life Sciences
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