DBR tapered laser at 660 nm as miniaturized pump source for quantum optical coherence tomography
Fig. 1: 660 nm DBR-TPL mounted on screening submounts for characterization and future module integration.
Fig. 2: Optical output power as a function of taper current and heat sink temperature.
The FBH has developed a red-emitting DBR tapered laser at a wavelength of 660 nm. With an almost single-mode emission and more than 1 W optical output power, this laser is suitable to generate entangled photons for quantum-OCT.
Optical coherence tomography (OCT) in the mid-infrared (MIR) is in strong demand for non-destructive testing of thin films that are opaque at visible wavelengths. However, detecting MIR photons is challenging, as common silicon-based detectors are blind in this spectral region, and MIR detectors are not available with the needed performance. Fortunately, our experience in quantum entanglement techniques offers us an elegant solution. Specifically, FBH scientists have been able to entangle (critical, but undetected) MIR photons with (detectable) near-infrared photons that act as “witness” photons. As a result, measurements such as OCT in the MIR are now possible, by detecting the entangled near-infrared photons using common Si detectors [1]. The necessary entanglement for this quantum-OCT is created using the well-established spontaneous parametric down conversion (SPDC) technique. The SPDC process requires a high optical power pump source at visible wavelengths with very good coherence properties. Previously, the FBH had already developed a suitable laser source at 660 nm that used two chips in a master-oscillator power-amplifier configuration with an optical output power of up to 500 mW [2].
To further miniaturize the pump source, FBH scientists now realized a dedicated single-chip solution based on a tapered laser with internal distributed Bragg reflector (DBR-TPL) for the wavelength of 660 nm [3]. The chips were mounted p-side down on dedicated diamond heat spreaders and on screening submounts (see Fig. 1). This enables optimized heat extraction and future module integration.
Our lasers feature an almost diffraction-limited, single longitudinal mode emission with an optical output power of more than 1 W, when suitably cooled (see Fig. 2). The coherence length exceeds 80 cm, which is sufficient to generate entangled photons via SPDC.
The DBR-TPL will be used for a miniaturized sensor module to enable the development of a portable quantum-OCT scanner in the near future, which will be employed in the non-destructive testing of ceramic layers in a production environment.
The work was funded by the German Federal Ministry of Education and Research (BMBF) within the QUIN project under project reference 13N15403.
Publications
[1] A. Vanselow, P. Kaufmann, I. Zorin, B. Heise, H.M. Chrzanowski, and S. Ramelow, "Frequency-domain optical coherence tomography with undetected mid-infrared photons", Optica 7 (12), pp. 1729-1736 (2020).
[2] G. Blume, C. Kaspari, J. Pohl, D. Feise, H. Wenzel, J. Fricke, P. Ressel, A. Ginolas, A. Sahm, A. Knigge and K. Paschke, "Single mode 660 nm master-oscillator power-amplifier with 500 mW optical output power", Proc. of SPIE, 11667, 116670C (2021)
[3] G. Blume, O. Matalla, H. Wenzel, A. Maaßdorf, D. Feise, J. Fricke, P. Ressel, S. Kreutzmann, A.Ginolas, A. Sahm, A. Knigge and K. Paschke "Single mode 660 nm DBR tapered laser with 1 W optical output power", Proc. SPIE 12402, 12402-7 (2023).