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Rapidly tunable RF signals at high frequency (>10 GHz) with high purity is a challenge that is more and more faced with optical solutions. Optical mixing of two laser fields has extensively been studied for that purpose. However, when the two fields come from independent laser sources, their phase locking remains a tour de force. Direct generation of two optical fields with close frequency difference in a single laser, so-called dual frequency laser (DFL), greatly reduces the drifts, as the cavity is shared [1]. We here report our last achievements in the generation of Ka-band RF signal generation with DFL technology.

Accurate microwave material characterization is essential for reliable high frequency circuit design. Therefore, various characterization techniques have been developed, comprising advantages and drawbacks for the respective conditions. In this paper, a material characterization system is presented, which enables a broadband measurement for both dielectric loss and relative permittivity of bulk substrates with variant geometrical dimensions. Strips of different dielectric bulk materials under test (MUTs) are mounted on top of an open semi double-ridged waveguide. Differential phase and amplitude broadband measurements with the MUTs are performed by a vector network analyzer, providing information on the introduced change in electrical length and dampening. The combined evaluation by measurement and electromagnetic simulations allow broadband assignments of the complex permittivity to the MUTs.

The generation of optically carried microwave signals is of great interest for a wide range of fields, from long-range transmission of RF to wideband radar signal processing. Among the available generation techniques, the potentialities of optical heterodyning are firmly established. However, it leads to severe constraints in optical phase-locked loop (OPLL) design. In this paper, we report on the realization of a compact and ruggedized Er, Yb:glass DFL at 1.5 µm stabilized with three servo-loops.

A new seeded stimulated Brillouin scattering (SBS) beam cleanup scheme to convert the aberrated output of a pulsed multimode fiber master-oscillator power-amplifier (MOPA) while maintaining the spectral width of the master oscillator is proposed. The pulsed master oscillator is a distributed feedback (DFB) laser diode amplified through two single mode preamplifiers.

We present a large core Er:Yb co-doped fiber amplifier followed by a beam quality recovery system. The multimode output (220 muJ, M2 ~6) is converted in a good quality beam (M2=1.6, 110 muJ) through SBS beam cleanup.