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Photonic
Frequency
Generator Unit

 

Photonics Frequency Generator Unit (FGU)

The frequency generation unit or FGU equipment comprises the generation, amplification and distribution of photonic local oscillator signals to facilitate the RF Photonic conversion process. Below we focus on local oscillators, high power OFAs and fibre splitters. EO‐MZMs have been discussed in RPC equipment section and AWG is discussed in the optical switching equipment section.
The FGU units and the basic equipment‐level requirements are:
- A Local Oscillator laser:
The FGU equipment deploys laser arrays to provide the optical signals used for RF frequency conversion using the optical domain. In the FGU equipment, lasers will be system integrated together with their current drivers and temperature control electronics.

FGU Simplified Block Diagram

- An Optical Fibre Amplifier:
The OFA is required to boost the output of the local oscillators (LOs). In the FGU equipment OFAs will be system integrated as modules comprising passive and active components together with their electronic drivers. Optical powers in excess of >1W are required to enable a high splitting ratio. Given the reported sensitivity of doped fibres under gamma Radiation Induced Absorption the basic FGU equipment requirement from OFAs is radiation hardness. During a 2014 research, iXFiber has developed a radiation hardened Er fibre with Cerium co‐dopant and HACC protection coating, with excellent performances: degradation less than 10% after 300 krad. In addition, OFAs have to be developed with Polarization Maintaining components and PM active fibres since the cascaded MZMs operate optimally with a specific state of polarization. For low electrical power FGU equipment, OFAs should deploy cooler‐less components with a wide operating temperature range.
- A fibre optic splitter:
These are passive components used to split and route the LO output to the EO MZMs. The components must be fabricated and packaged with high‐rel compatible processes.
- The potential of microwave technologies:
To generate RF signals with superior phase stability, also permitting simultaneous generation of multiple RF carriers has been demonstrated in the literature.
This simplifies considerably the distribution of LO signals, for instance, enabling the beam forming of wideband signals in Phased Array Antennas, the implementation of Tunable Filtering or other signal processing or the implementation of paralleled up/down converter schemes that can be even combined with optical switching for reconfigurable payloads.
In OPTIMA, DAS will evolve its current photonic frequency generation units (PFGU) by developing, jointly with Partner Cordon, an integrated Laser Diode plus Mach‐Zehnder modulator and RF stages reducing significantly the SWaP.

Schematic of the FGU Unit that will be Developed by DAS in OPTIMA and Details of the Proposed Package for the Laser Diode and MZM