High power coherent PCSEL arrays

An efficient, organized and pressure tolerant electronic design is required to carry power to a 192-meter-long ocean acoustic coherent hydrophone array developed at North-eastern University. This oil filled linear towable large aperture hydrophone array is densely populated. The array consists of eight sub-sections, of which five are acoustic containing 160 hydrophone elements, two are non-acoustic sections, containing depth and heading sensors, and one vibration isolation module (VIM). This underwater acoustic array receives its power from a 5000W Power Supply housed on a research vessel (RV) or ship. The 300VDC output generated from the power supply travels through a 600-meter-long tow cable before it reaches the in-house designed main power board in the hydrophone array, bucking the voltage down to three independent 48V power rails. Multiple voltage rails were used to reduce current draw and voltage drop seen down the long-twisted pair of 16-gauge wires, feeding four other in-house designed power boards; 24V, 12V, 12V/-12V and 5V. During in-air operational testing while under high power producing conditions, thermal run-off was seen on the main power board. Although this is not critical for this application, precautions were made to allow for seamless testing. A commercial off-the-shelf (COTS) heat sink was cut and thermally epoxied around the main power integrated circuit (IC). Combining this with oil, which acts as a heat sink and the length of the array, an effective heat reservoir was produced. Detailed research and design were instrumental in the component selection, schematic and layout phases of this design to create a reliable, resilient, and cost-effective system. Future improvements and paths forward will also be discussed to improve reliability, energy efficiency and robustness.

Coherent Beam Combining (CBC) can scale the overall output power while maintaining high beam quality. In recent years, this technique has also been employed to generate the high-power Optical Vortex Beam (OVB). In this work, we designed a coherent phased array, and an Optical Vortex Beam Array (OVBA) was generated via the CBC technique. Numerical simulation was studied, and an experimental setup was set up. The results showed that the OVBA could be generated in the far field. Meanwhile, the phase detection results indicated that the OVBA included several phase singularities. This work can present a new idea for manipulating the high power structured optical fields.

A vertical-cavity surface-emitting laser (VCSEL) is easily made into a two-dimensional array to improve its output power. However, if the near-field complex amplitude output cannot be stabilized in the lowest supermode generated by the fundamental transverse mode, the spot cannot converge on the center normal of the far-field array geometry, and the energy will be diverged. The external cavity is prepared for the VCSEL array, and the output of the array can be stabilized in the lowest order supermode generated by the fundamental transverse mode by supermode control through diffraction coupling. In this study, the parallel-coupled model for the 2-dimensional VCSEL array based on Fresnel diffraction integration was established and used to numerically calculate and analyze the influence on the supermodes’ thresholds of different array distributions, array elements’ transverse modes and duty ratios versus the length of the external cavity. The simulation results show that the square array provides a wider range of external cavity control length (0.2d2/λ and approximately 0.9 to 1.0d2/λ). The lowest supermode of the fundamental transverse mode can be outputted. For the regular hexagonal array with the length of the external cavity of 0.15d2/λ and 0.6d2/λ. The results have important reference significance for the design of an external cavity VCSEL array, which can control the supermode and obtain VCSEL coherent array beams with high power and near diffraction limits.

Phase coupling of medium power high beam quality lasers are of great interest for achieving high power diffraction limited beam with high gain lasers. This make it possible to set up compact and efficient sources. In this paper, we review the work performed in our laboratory concerning the coherent array of CO<SUB>2</SUB> waveguide lasers. We report the various techniques used for phase coupling like Talbot effect, intra-cavity spatial filtering and anti-guiding effect and we give the relevant performances in terms of beam quality and efficiency. After, we discuss the advantages and drawbacks brought by each one. The far field diffraction pattern supplied by a series of coherent independent lasers is made of several asymmetric lobes. We then present lossless techniques making it possible to convert this multilobe asymmetric far field diffraction patterns into a single lobe symmetric beam. Last, we discuss the capability of slab CO<SUB>2</SUB> laser with a graded-phase mirror cavity for generating large stable mode and, then, improving the energy extraction efficiency.