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SIlicon Optomechanical optoellectronic Microwave Oscillator

Periodic Reporting for period 1 - SIOMO (SIlicon Optomechanical optoellectronic Microwave Oscillator)

Reporting period: 2020-06-01 to 2021-11-30

High-quality microwave sources are required in multiple applications (radar, wireless networks, satellites, etc.). Typically, low-noise microwave oscillators are made by applying frequency multiplication to an electronic source. This requires a cascade of frequency-doubling stages, which strongly reduces the power of the final signal. Recently, different techniques to produce microwave tones via optical means have been proposed. The resulting device is an optoelectronic oscillator (OEO). The advantages with respect to its electronic counterparts are immunity to electromagnetic interference, low weight, compactness, long-distance transport, amongst others.

In the FET-Open PHENOMEN project, aiming at the realization of RF processing using silicon-chip cavity optomechanics, UPV partner designed and demonstrated a novel OM cavity on a silicon chip displaying, for the first time, a localized mechanical mode at frequencies fm ≈4 GHz within a full phononic bandgap and with a large OM coupling rate. This property allows having a high-quality mechanical mode that can be efficiently excited and manipulated by an external input laser. When the laser is blue-detuned with respect to the resonance, the mechanical mode is amplified (as in SBS) and strongly modulates the laser, so after photodetection we have a pure microwave tone at fm. The phase noise of the generated microwave tone is as low as -101 dBc/Hz at 100 kHz, which is a remarkably good value for an OEO oscillating at GHz frequencies without any feedback mechanism. Therefore, the device behaves as an OEO of optomechanical nature: we have an optomechanical microwave oscillator (OMO).

The device demonstrated in PHENOMEN has three key advantages: i) it is fabricated in standard silicon technology, meaning that it can be manufactured in large volumes at low cost as well as that it can be easily interconnected with electronics; ii) it is extremely compact and low-weight, which makes it very suitable for space and satellite applications; iii) it can be easily connected to optical fibres. It is the aim of SIOMO to completely unveil its potential and address its transfer to the industrial sector via partner DAS, which will assess its potential for implementing an all-optical payload for SATCOM applications.

The main objectives of SIOMO are:
OEO performance assessment and application requirements (OBJ1).
Validation of the OEO in the DAS SATCOM testbed (OBJ2).
Benchmarking against competitors and elaboration of a technology transfer and exploitation plan (OBJ3).
Here we summarize the main activities that we have performed since the beginning of the project:

I. System and application-driven specifications. DAS Photonics provided system-level and application-level specifications, gathering their expertise in SATCOM applications following a top-down approach. These specifications were translated into subsystem parameters by DAS and then further to component and integration parameters by UPV.

II. Performance assessment. We assessed the achievable performance in terms of phase-noise, output power, frequency stability, power consumption, and so on. UPV performed simulations at a photonic integrated circuit (PIC) level and DAS at module and system-levels by using already developed libraries and commercial software. The results allowed us to establish the performance limits which will define the possible application of the new technology in Space applications.

III. Laboratory experiments in DAS SATCOM testbed. Initially, this step involved the adaptation of the OMO to the SATCOM lab set-up available at DAS facilities, equipped with the necessary test and measurement equipment required to assess the performances of the OMO at device, module, and system levels. Finally, we tested the OMO in the UPV labs where we move the OPTIMA equipment. DAS Photonics performed the measurements to validate the OMO in that SATCOM test bed. The main weaknesses of the OMO from a practical perspective were identified and the way towards further development was established.

IV. Industrialisation and product roadmap. DAS Photonics, in cooperation with UPV, performed an analysis of the industrialization of the product. This also included an analysis of the supply chain necessary to establish a product roadmap.

V. Commercialisation and business plan. DAS Photonics has provided the plans toward exploitation.
Beyond the state of the art:

For the first time, a photonic local oscillator operating at microwave frequencies implemented in an ultra-compact optomechanical cavity on a silicon chip has been validated in a test bed aimed at SATCOM application. This validation has allowed us to unveil the practical potential of the technology as well as to establish its current limitation towards practical implementation. The main conclusion of SIOMO is that silicon-based OMO is potentially suitable for SATCOM; applications but the device has to be improved in several ways, which requires further technological development. The next steps towards commercialization are: adapting the mechanical frequency to useful RF bands; engineering the interface with fibre optics and packaging

Socio-economical impact:

The main economic impact should be on the SATCOM market. This potential market is huge and growing, considering both geostationary (GEO) and low-Earth orbit (LEO) mega-constellations, and therefore opportunities for market exploitation of the results will arise naturally once the OMO is upgraded, and the technology is matured to higher TRLs. In particular, the optimisation and test of the device in DAS SATCOM demonstrators will increase the interest from satellite integrators, who are pushing for continuous price and SWaP reduction of payloads. According to “A Strategic Research and Innovation Agenda (SRIA) for EU-funded Space research supporting competitiveness “, SATCOM the main EU commercial segment and export market (EUR 3.5 billion sales in 2017). EU adaptation to this rapidly changing market requires accelerating a number of developments guided by a technology top-down approach targeting the final user application. In particular, photonics and optical communications are explicitly mentioned in the SRIA as technology enablers.
DAS is leading the development of Photonic technologies for SATCOM space applications, being the first company flying a photonic microwave converter working at Ku/Ka/V/Q bands in HISPASAT 30W-6 and in EUTELSAT 7C , both manufactured by the leading worldwide satellite manufacturer SSL/MAXAR. Since May 2017, DAS leads the ESA project “Single String Photonic Payload and Multi-String Photonic Payload” which is developing a photonics-based multiple frequency conversion chain also with SSL/MAXAR. DAS participated in the H2020 project OPTIMA , led by AIRBUS, developing analog and digital photonic SATCOM payloads. Besides, DAS coordinates H2020 projects PHLEXSAT and RETINA , developing also photonic technologies for SATCOM and space surface aperture RADAR (SAR), respectively, in cooperation with EUTELSAT, AIRBUS and MDA. DAS also leads the ESA project “KaBs” which aims to develop a generic electro-photonic, software-defined transceiver that allows complete reconfigurability of the microwave front end depending on the mission from ground stations. Therefore, DAS is well-positioned to introduce the OMO in the targeted SATCOM market as long as the device is improved following previous recommendations.
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