Fabrication of Blue Photonic Quantum Ring Laser and Study of High Power Flower Photonic Quantum Ring Laser
- Fabrication of Blue Photonic Quantum Ring Laser and Study of High Power Flower Photonic Quantum Ring Laser
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- Light-emitting diodes (LEDs) are under intensive development worldwide for their advanced display technology applications. However, high- power LEDs are bulk devices, suffering therefore from inherent heating problems, and limited to low frequencies far below conventional lasers’ GHz ranges.
The photonic quantum ring (PQR) laser is similar in structure to VCSELs, but its lasing characteristics should be classified as a three-dimensional (3D) Rayleigh-Fabry-Perot (RFP) WCM (whispering cave mode) laser. The PQR laser of 3D WCMs exhibits unique operating characteristics attendant on its quantum-wire-like nature, such as ultra-low threshold currents and -dependent thermally stable spectra in the typical operating temperature range. The resonance of the PQR laser results in 3D WC modes of helical standing waves, which is surface-normal dominant 3D fashion, in contrast to the in-plane 2D WG mode.
For display applications, we make GaN-based 3D WCM blue PQR laser using the LLO (Laser Lift-off) GaN wafer. For the vertical resonance effect, like a VCSEL or RCLED, we have used high-reflectivity dielectric DBRs and metal reflector as top and bottom mirrors respectively. The threshold for a 20um circular blue PQR is about 6uA and this value is consistant with other PQR lasers studied before. This extremely low threshold current is due to the PQR’s unique operating characteristics attendant on its quantum-wire-like nature. The emission spectra for the vertical structure blue PQR lasers can be defined by the 3D RFP resonance conditions. Emission spectra are collected at view angles of θ =0°, 15° and 30° with an injection current of 4㎃. It should be noted that as θ increases, the envelope is blue-shifted successively while the discrete sub-modes within different envelopes remain the same regardless of θ. These polar angle-dependent multi-chromatic emission characteristics, observed over the regime of a 70° polar angle, were reported before.
Although the PQR laser has the advantages above mentioned, it still needs to deliver output power sufficiently large to compete with high-power LEDs. We thus provide a proof-of-concept report on the design, fabrication and performance of multi-petal flower-type (“flower”) PQR lasers consisting of concave and convex WCM modes. We observed enhancements of light output power roughly in proportion to the number of petals of the flower PQR laser, up to the point where the total PQR perimeter reached a critical length corresponding to that of a circular PQR laser of about 50 ㎛ diameter. This indicates that dense arrays of small but multi-petal flower PQR lasers can compete with high- power LEDs while individual lasers are operating in power-saving and thermally stable modes.
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