We present experimental results on coherent beam combining from large arrays of high power broad-area semiconductor
lasers. Our laser array consists of 47 high-power anti-reflection coated broad-area semiconductor lasers and each laser
emitter is capable of emitting 1.8 W when uncoated with a maximum array output power of 80W. The total available
power from the AR coated array is approximately 40W. By using an external V-shape cavity design, we experimentally
demonstrated a coherently combined beam at the output power of ~13 W with the 0.07 nm FWHM spectrum linewidth
that is limited by the sensitivity of the optical spectrum analyzer. We also discuss coherent beam combining of highpower
broad area laser diode array in current driver pulse mode operation.
Pulsed lasers with pulse durations of nanosecond to millisecond are very important tools for free-space optical communication, LADAR, laser material processing, and optical sensing. Although Q-switched solid-state lasers or gas lasers are currently the most popular light sources for these purposes, pulsed semiconductor lasers have the potential for the above applications because of their compactness, accessibility of direct modulation, and inherently large electrical to optical conversion efficiency. The drawbacks with high-power semiconductor lasers are their poor beam quality and low coherence factors. This work addresses the above issues through experimental demonstration of frequency locking, wavelength tuning, and synchronization of nanosecond pulsed broad-area semiconductor lasers. Nanosecond optical pulses with the peak power of 25 W and the repetition rates of 4 KHz to 240 KHz are generated from a broad-area laser. An external cavity with a diffractive grating is used to reduce the linewidth of the laser from over 5 nm to less than 0.1 nm. The wavelength of the pulsed laser is tunable over more than 10 nm. We have conducted injection locking of a nanosecond pulsed broad-area laser with optical injection from a frequency-locked master laser. Successful injection locking strongly support the feasibility of synchronization and beam combination of pulsed broad-area lasers.
We present experimental results on the locking of a 19-broad-area semiconductor laser array using a novel design of external cavity containing a lens array, projection optics, and a diffractive grating. All lasers are locked to single longitudinal mode. Significant improvement of the spatial profile of the entire laser array output beam has been observed. The center lobe of the far-field pattern of the laser array shows a single wavelength which can be tuned over a range more than 10 nm. The proposed technology can be applied to larger arrays including the stacked arrays.
A synchronized broad-area laser array (SBLA) can produce a highly coherent light source whose output intensity is proportional to the square of the number of lasers in the array. High contrast optical intensity modulation can be achieved by utilizing the nonlinear response of the total output intensity to the injected light, resulting in fast optical switching. SBLA can be applied to phased array antenna and beam steering. Semiconductor laser array capability provides a unique opportunity not only for free-space adaptive optical communication but also for free-space quantum adaptive optical communications through the atmosphere. In this paper, we propose a paradigm that illustrates how quantum communication (which provides quantum ultra-security) can take advantage of ultrashort pules, high repetition rate, high power density (due to coherent beam coupling), and spatial beam control.
This paper describes experimental results on the injection locking of high-power broad-area semiconductor lasers in a commercially available 19-laser array driven by a common current source. Single-frequency optical spectrum and single lobe far-field pattern are observed as a result of injection locking. We discuss the temporal dynamics, the amplification of the injection light, and the phase coherence between the injection-locked lasers, which are key issues in their applications to free-space laser communication.
This paper describes a method of enhancing coherence and intensity of a broad-area laser array. An experimental scheme has been proposed to injection lock a single or multiple broad-area high-power lasers in a commercially available 19-laser array driven by a common current source. We experimentally demonstrate both the injection locking of each individual broad-area laser and the simultaneous injection of two broad-area lasers in a 19-laser array using a single-mode laser as the source of injection. The method and required conditions for the simultaneous locking of all 19 lasers have been discovered from the experimental results.