Mode-locked lasers, and in particular solid-state femtosecond lasers, are oscillators with a unique physics capable to exhibit extremely low-phase noise of the emitted pulse train. Here we report ultra-low phase noise microwave generation with a self-referenced, fully-stabilized mode-locked femtosecond laser. The system involves a 395-MHz repetition rate 1560nm laser which is self-referenced and whose repetition rate is locked to a cavity-stabilized continuous-wave laser. The selfreferencing is achieved with a f-3f nonlinear interferometer realized in a silicon nitride highly-nonlinear waveguide. Prior to optical-to-electrical conversion for X-band microwave generation, the 395-MHz repetition rate of the mode-locked laser pulse train is multiplied in a fiber interleaver to 3.16 GHz. A high-power handling photodiode converts the optical pulse train to an electrical frequency comb with 3.16 GHz frequency spacing. Finally, the 9.5-GHz harmonics is bandpassfiltered and phase noise measurements have shown a record-low phase noise floor of -175 dBc/Hz at 1-MHz offset frequency.
This contribution summarizes the status of our current development of a novel, high-power and high-linearity photodiode. This photodiode is specifically designed to operate over an exceptionally wide optical input power range from below - 10 dBm up to + 20 dBm without relying on self-biasing effects, making it a versatile solution in many potential analog optical RF applications. The backside illuminated photodiode offers a large active diameter, which enables high coupling efficiency, allows optimization of the optical launch conditions to improve the optical saturation current and linearity as well as to improve the thermal power dissipation, which is required for high power operation. The high-power photodiodes, flip-chip-bonded to their heat-dissipation carriers, have been integrated in a hermetically sealed, rugged package with built-in matching circuit and bias-T. The thermal design and the opto-electrical characterization such as bandwidth and linearity will be presented. Preliminary gamma and proton irradiation testing, have been performed with promising results.
The EU-SIPhoDiAS project deals with the development of critical photonic building blocks needed for highperformance and low size, weight, and power (SWaP) photonics-enabled Very High Throughput Satellites (VHTS). In this presentation, we report on the design and fabrication activities during the first year of the project concerning the targeted family of digital and microwave photonic components. This effort aims to demonstrate components of enhanced reliability at technology readiness level (TRL) 7. Specifically, with respect to microwave photonic links, we report: (i) the design of Ka and Q-bands analogue photodetectors that will be assembled in compact packages, allowing for very high bandwidth per unit area and (ii) on the design of compact V-band GaAs electro-optic modulator arrays, which use a folded-path optical configuration to manage all fiber interfaces packaged opposite direct in-line RF feeds for ease of board layouts and mass/size benefits. With respect to digital links, we report on the development of 100 Gb/s (4 x 25 Gb/s) digital optical transceiver sub-assemblies developed using flip-chip mounting of electronic and opto-parts on a high-reliability borosilicate substrate. The transceiver chipset developed specifically for this project refers to fullycustom 25 Gb/s radiation hard (RH) VCSEL driver and TIA ICs designed in IHP’s 130 nm SiGe BiCMOS Rad-Hard process.
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