Beam Combining for High Brightness

High-brightness applications, such as laser material processing, mostly use diode lasers as pump sources. With the aim of enabling their direct use, we develop and optimize beam combining methods such as "Dense Wavelength Division Multiplexing" (DWDM), polarization coupling and "Coherent Beam Combining" (CBC). These methods could help diode lasers achieve a market breakthrough in direct applications - we have made significant progress in this regard.

Single stack element of a 3.5 kW laser stack

kW-class QCW single diode laser bar on passive heat sink

Efficient beam bundling

Schematic diagram illustrating Dense Wavelength Division Multiplexing (DWDM) — Dense Wavelength Division Multiplexing (DWDM)

Schematic diagram illustrating Coherent Beam Combining (CBC) — Coherent Beam Combining (CBC)

In cooperation with partners in research and industry, various beam combining methods have been investigated. The developed light sources are able to combine the light of individual emitters with exceptional efficiency.

Basically, three different methods for combining high-power diode laser beams are available. They enable coupling by means of the following beam characteristics: wavelength, polarization and coherence of the individual emitters.

Dense Wavelength Division Multiplexing (DWDM) offers the possibility of spectrally coupling single-mode laser bars as well as individual lasers (e.g. DBR tapered lasers). With the help of optical gratings or special dichroic coated filters, different construction options can be realized. The external spectral stabilization and combination of broad-area lasers and bars is already used in commercially-available systems, which can, however, be made more efficient using optimized components.

For spectrally narrow-band power scaling of several light sources, Coherent Beam Combining (CBC) can be used, in which the spatial phase of several coherently-coupled lasers relative to each other is controlled. Novel amplifiers are suitable for this purpose, whose optical power is combined by means of CBC to form a nearly diffraction-limited beam.

These methods have been applied in various module classes within the scope of different projects. This covers the range from modules for pumping solid-state lasers to micromodules for direct material processing.

NIR range:

single-pass tapered semiconductor optical amplifiers with high beam quality for efficient coherent beam combining
laser bars with narrow vertical far field for low loss, smile-insensitive external spectral stabilization
efficient high-power bars of single-mode emitters for dense wavelength multiplexing (DWM) applications
high-brightness grating-stabilized mini-bars tailored for spectral beam combination applications
Micromodule with polarization coupling: P >12 W; M² < 2
Micromodule with spectral and polarization coupling: P > 30 W; M² < 3

Selected Publications

Miniaturizing a coherent beam combining system into a compact laser diode module

Appl. Opt., vol. 63, no. 9, pp. 2212-2217 (2024).

Phase Noise Reduction in Semiconductor Optical Amplifiers using Low-Index Quantum Barrier Structures

Conf. on Lasers and Electro-Optics (CLEO 2022), San Jose, USA, May 15-20, ISBN 978-1-957171-05-0, p. SM3G.3, doi:10.1364/CLEO_SI.2022.SM3G.3 (2022).

Externally Wavelength-Stabilized Single Mode Lasers with 65% Conversion Efficiency and 50 pm Spectral Width at 1 W Output

Conf. on Lasers and Electro-Optics/Europe and European Quantum Electronics Conf. (CLEO/Europe-EQEC 2021), Munich, Germany, Jun. 21-25, virtual event, ISBN: 978-1-6654-1876-8, cb-p-2 (2021).

Single-pass tapered semiconductor optical amplifiers and modules for efficient coherent beam combining

Proc. of SPIE, vol. 11705, Novel In-Plane Semiconductor Lasers XX, Photonics West, Online Only, Mar 6-11, 117050M (2021).

Highly Efficient High-Brightness 970nm Ridge Waveguide Lasers

IEEE Photonics Technol. Lett., vol. 32, no. 7, pp. 406-409 (2020).

Progress in GaAs-based Semiconductor Sources For High Brightness Beam-Combined Applications

Photonics Device Workshop 2020, Virtual Event, Nov. 20 (2020).

Low-index quantum-barrier single-pass tapered semiconductor optical amplifiers for efficient coherent beam combining

Semicond. Sci. Technol., vol. 35, no. 06, pp. 065018, doi:10.1088/1361-6641/ab804e (2020).

Efficient Narrow Stripe Ridge Waveguide Lasers for Single-Spatial Mode Operation up to 2.5 W

Conf. on Lasers and Electro-Optics/Europe and European Quantum Electronics Conf. (CLEO/Europe-EQEC 2019), Munich, Germany, Jun. 23-27, ISBN: 978-1-7281-0469-0, cb-5.3 (2019).

Coherent beam combining of high power quasi continuous wave tapered amplifiers

Opt. Express, vol. 27, no. 20, pp. 27891-27901 (2019).

Coherent combining of high brightness tapered amplifiers for efficient non-linear conversion

Opt. Express, vol. 27, no. 2, pp. 928-937 (2019).

Coherent combining of high brightness tapered lasers in Master Oscillator Power Amplifier configuration

Proc. SPIE 10514, High-Power Diode Laser Technology XVI, Photonics West, San Francisco, USA, Jan 27 - Feb 01, 105140T (2018).

High-Efficiency Broad-Ridge Waveguide Lasers

IEEE Photonics Technol. Lett., vol. 30, no. 6, pp. 545-548 (2018).

High-power operation of coherently coupled tapered laser diodes in an external cavity

Proc. SPIE 9733, Photonics West, San Francisco, USA, Feb. 13-18, 97330I (2016).

25-W Monolithic Spectrally Stabilized 975-nm Minibars for Dense Spectral Beam Combining

IEEE Photonics Technol. Lett., vol. 27, no. 15, pp. 1675-1678 (2015).

High brightness narrow-stripe broad-area lasers with 7 W optical output at 910, 935 & 970 nm for coarse spectral beam combining

Conf. on Lasers and Electro-Optics/Europe and European Quantum Electronics Conf. (CLEO/Europe-EQEC 2015), Jun. 21-25, Munich, Germany, ISBN: 978-1-4673-7475-0, paper CB_5_4 (2015).

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