Product & Research in Focus


Product in Focus

Micro-integrated laser sources with watt-level output power in the yellow-green spectral range

The FBH has developed very compact laser modules emitting at 561 nm and 576 nm with power levels in the watt range. They additionally provide a polarization-maintaining single-mode fiber output option. The diode-based laser systems, measuring only 76 x 54 x 15 mm³, use a novel butterfly housing and are aimed at biomedical and spectroscopic applications. They are used, for example, in ophthalmology and high-resolution confocal microscopy and enable a significantly higher degree of miniaturization of the corresponding systems. In cw mode, they achieve output powers of more than 2 W at 561 nm and 1.5 W at 576 nm in free-space configuration.

The FBH uses second harmonic generation to generate high-brightness visible light, combining a full semiconductor master oscillator power amplifier (MOPA) with nonlinear crystals. An integrated micro-optical isolator shields the laser structure against back reflections, thereby retaining the spectral properties of the emission. The MOPA approach also allows for direct modulation without affecting the emission wavelength.

Further information regarding our activities in the field of laser systems using frequency doubling and laser sources emitting in the yellow wavelength region between 550 nm and 590 nm

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Research in Focus

Fully GaN-based all-digital transmitter chain for massive MIMO

The FBH has developed a fully digital GaN-based transmitter module aiming to replace the analog transmitter chain. It extends the boundary of the digital domain behind the power amplifier (PA), yielding several benefits including compactness, low energy consumption and flexibility. It is therefore predestined for any (massive) MIMO application, utilizing beam forming techniques to multiple receivers. The module can be mounted right underneath each antenna element.

The upconverter is replaced by a modulator (FBH patent) that translates complex baseband signals into a purely binary data stream. The transition from the digital signal into the analog domain takes place in the band-pass filter only. The FBH module applies for the first time a novel robust and compact digital GaN PA chip with greatly reduced complexity compared to earlier designs. Full-scale output power at 30 V supply voltage was measured to exceed 3 W at 80 % drain efficiency. The realized module represents an ideal candidate for software-defined radio.

Further information on FBH's activitites regarding digital power amplifiers and research news on digital transmitter chain for massive MIMO

Ultra-narrow linewidth diode laser for LISA satellite mission

The upcoming Laser Interferometer Space Antenna (LISA) mission aims at detecting and characterizing gravitational waves. For this purpose, changes of the distance between test masses on board three satellites that are spaced 2.5 million km apart need to be measured with a sensitivity corresponding to a few pm. To accomplish this, three laser interferometers will be used that require very low-noise seed lasers like Nd:YAG NPRO.

As part of an ESA project, FBH has developed a micro-integrated ultra-narrow linewidth diode laser module (footprint 80 x 30 mm2) as potential alternative to the NPRO seed laser. The module emitting at 1064 nm consists of an external cavity, a semiconductor gain chip with an anti-reflective coating on both facets, and a volume holographic Bragg grating. Here, the external cavity acts as a mirror and the resonant feedback is re-injected into the gain chip. As the light travels back and forth inside the external cavity before feeding back to the gain chip, this setup effectively implements a very long cavity, but at the same time avoids problems related to very long conventional ECDL setups. The module achieves a Lorentzian linewidth of 13 Hz and is at the same time capable of fast frequency tuning. It is suited for a variety of further applications like coherent optical communications.

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