Red-emitting master-oscillator power-amplifier for holographic applications
Fig. 1: top: Sketch of the beam propagating through various optics, bottom: MOPA experiment with the camera hovering above the detector D1
Fig. 2: MOPA power current characteristics for various temperatures at a constant input power of 40 mW
Fig. 3: Output power as a function of input power into the TTA at 15°C, inset: spectrum at about 800 mW
Holography requires lasers with a coherent beam at wavelengths visible to the human eye. Until now, large gas lasers, such as HeNe lasers and Kr lasers, have been widely employed as small-sized semiconductor lasers so far lacked the required linewidths and output power.
However, the FBH recently developed red-emitting lasers with internal gratings (DBR-RWL), which feature a single-mode diffraction-limited beam with an optical output power of up to 100 mW. While this performance is sufficient for small holograms up to 20 cm in diameter, larger holograms require a larger output power. Now, the FBH demonstrated the successful amplification of the radiation of a DBR-RWL to optical output powers beyond 500 mW while maintaining the high coherence.
The amplifier chips used for the master-oscillator power-amplifier (MOPA) experiment featured a tapered contact stripe with a width of 30 µm at the input and 100 µm at the output facet (TTA). In order to suitably guide the laser beam through the amplifier a set of four lenses was used in front of and another two behind the TTA chip (see Fig. 1). This allows directing the horizontal focus outside the amplifier chips, which greatly improves the damage threshold of the device. The optical power behind the TTA is shown in Fig. 2 as a function of the input current for three different temperatures. From this graph it is easily discernable that a high output power requires sufficient cooling and that output powers in excess of 500 mW can be reached.
At high output powers of about 800 mW the MOPA is still longitudinal single mode (see inset in Fig. 3) with coherence lengths of several meters and a nearly diffraction-limited beam, well suitable for holography. As the output power strongly depends on the input power (see main plot of Fig. 3) a master oscillator with a higher output power should potentially enable even higher MOPA output powers. Another research focus is on further miniaturizing the MOPA –a prototype is expected in the near future.
Publications
D. Feise, G. Blume, J. Pohl, K. Paschke, "Distributed Bragg Reflector Ridge Waveguide Lasers Emitting Longitudinal Single Mode at 647 nm", IEEE J. Sel. Top. Quantum Electron., vol. 21, no. 6, 1501706 (2015).
G. Blume, J. Pohl, D. Feise, M. Jendrzejewski, M. Greiner, P. Ressel, K. Paschke, "Single-mode master-oscillator power amplifier at 647 nm with more than 500 mW output power", Opt. Lett., vol. 40, no. 8, pp. 1757-1759 (2015).
G. Blume, M. Schiemangk, J. Pohl, D. Feise, P. Ressel, B. Sumpf, A. Wicht, K. Paschke, "Narrow Linewidth of 633-nm DBR Ridge-Waveguide Lasers", IEEE Photonics Technol. Lett., vol. 25, no. 6, pp. 550-552 (2013).
G. Blume, O. Nedow, D. Feise, J. Pohl, K. Paschke, "Monolithic 626 nm single-mode AlGaInP DBR diode laser", Opt. Express, vol. 21, no. 18, pp. 21677-21684 (2013).
X. Wang, G. Erbert, H. Wenzel, P. Crump, B. Eppich, S. Knigge, P. Ressel, A. Ginolas, A. Maaßdorf, G. Tränkle, "17-W Near-Diffraction-Limited 970-nm Output From a Tapered Semiconductor Optical Amplifier", IEEE Photonics Technol. Lett., vol. 25, no. 2, pp. 115-118 (2013).
D. Feise, W. John, F. Bugge, G. Blume, T. Hassoun, J. Fricke, K. Paschke, G. Erbert, "96 mW longitudinal single mode red-emitting distributed Bragg reflector ridge waveguide laser with tenth order surface gratings", Opt. Lett., vol. 37, no 9, pp. 1532-1534 (2012).