1 W master oscillator power amplifier laser modules with narrow linewidth for applications in space
Fig. 1: Micro-integrated MOPA module consisting of a DBR laser as a master oscillator and a tapered amplifier. Beam forming is realized by micro lenses. The inset shows the collimation of the oscillator in more detail.
Fig. 2: FWHM and intrinsic spectral linewidth in dependence of the optical output power of the oscillator. The FWHM is rather constant whereas the intrinsic linewidth follows the theoretically expected 1/P dependence
Narrow-linewidth high-power lasers find application in a variety of fields like coherent optical communication, precision measurements, spectroscopy, and laser cooling. For some of these applications, semiconductor lasers have not been extensively used so far due to their relatively large linewidth and potential problems originating from mode instabilities and uncontrollable optical feedback effects. Instead, optically pumped solid state or fiber lasers are used e.g. in free space optical communication applications, specifically in space. However, semiconductor lasers would be beneficial due to their lower weight, higher conversion efficiency and better mechanical stability. The FBH succeeded to realize a compact and rugged micro-integrated master oscillator power amplifier (MOPA) that features a narrow linewidth with high-power output.
The MOPA module is depicted in fig. 1. The oscillator (MO) is a distributed Bragg reflector laser which is optimized for narrow-linewidth operation. The amplifier (PA) consists of a tapered amplifier and a ridge waveguide entry section. The output of the MO is collimated by a pair of aspherical cylindrical micro-lenses. The collimated beam is then guided through a micro isolator in order to suppress feedback effects and subsequently coupled into the amplifier by another pair of micro-lenses. The output of the MOPA is collimated by a three lens optical system in order to obtain a circular beam. All semiconductor components and optics are integrated on a footprint of 50 x 10 mm2. The output power of the module exceeds 1 Watt in stable single-mode operation with a conversion efficiency of 25%. The results of a heterodyne linewidth measurement are depicted in fig. 2. The full width at half maximum (FWHM) linewidth is approximately 100 kHz over the entire power range. The intrinsic linewidth Dnint (a measure for the linewidth that excludes technical noise) is following the theoretically expected 1/P dependence with a minimum value of 3.6 kHz at a total output power of the MOPA (Pout, MOPA) of 1.25 W (output of the oscillator Pout,MO = 85 mW).
To our knowledge, this is the first micro-integrated MOPA concept that provides an output power in the Watt level with narrow linewidth emission and that addresses the challenging demands of space applications like mechanical stability, compactness, and efficiency. Furthermore, this concept can be transferred to any other wavelength that is accessible with semiconductor lasers.
Publikations:
S. Spießberger, M. Schiemangk, A. Sahm, A. Wicht, H. Wenzel, A. Peters, G. Erbert, G. Tränkle, "Micro-integrated 1 Watt semiconductor laser system with a linewidth of 3.6 kHz", Optics Express, 2011.
S. Spießberger, M. Schiemangk, A. Sahm, A. Wicht, H. Wenzel, J. Fricke, G. Erbert, "1 W semiconductor based laser module with a narrow linewidth emitting near 1064 nm", Photonics West, SPIE, 7953-36, 2011.
S. Spießberger, M. Schiemangk, A. Sahm, A. Wicht, H. Wenzel, J. Fricke, G. Erbert, G. Tränkle, "1 W narrow linewidth semiconductor-based laser module emitting near 1064 nm for coherent optical communication in space", IEEE ICSOS, 2011.
S. Spießberger, M. Schiemangk, A. Wicht, G. Erbert, "Compact narrow linewidth laser sources for coherent optical communication", Laser Optics Berlin, Berlin, 2010.
S. Spießberger, M. Schiemangk, A. Wicht, G. Erbert, "<link /fileadmin/fbh-berlin/english/ver10/pub60.htm _blank internal-url-new-window>Narrow linewidth DBR-RW lasers emitting near 1064 nm", Conference on Lasers and Electro-Optics, OSA, CtuKK6, 2010.
S. Spießberger, M. Schiemangk, A. Wicht, H. Wenzel, O. Brox, G. Erbert, "<link /fileadmin/fbh-berlin/english/ver10/pub72.htm _blank internal-url-new-window>Narrow linewidth DFB lasers emitting near a wavelength of 1064 nm", Journal of Lightwave Technology, vol. 28, pp. 2611-2616, 2010.
FBH research: 14.03.2011