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Top DBR mirror replaced with CTF and chiral STF bilayers

Towards Circularly-Polarized Light Emission from Vertical-Cavity Surface-Emitting Lasers Fan Zhang, Jian Xu and Akhlesh Lakhtakia * Department of Engineering Science and Mechanics, Penn State University, State College, PA, 16802 *akhlesh@psu.edu, Tel: (814)863-4319, Fax: (814)865-9974.

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Top DBR mirror replaced with CTF and chiral STF bilayers

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  1. Towards Circularly-Polarized Light Emission from Vertical-Cavity Surface-Emitting Lasers Fan Zhang, JianXu and AkhleshLakhtakia* Department of Engineering Science and Mechanics, Penn State University, State College, PA, 16802 *akhlesh@psu.edu, Tel: (814)863-4319, Fax: (814)865-9974 Vacuum chamber Quartz crystal monitor Conventional mirror Right-handed chiral STF mirror Substrate Top chiral STF cv CTF (QWP) RCP LCP ml/2 cavity RCP RCP Vapor p-contact layer Active layer (MQWs) RCP RCP RCP LCP Source n-contact layer Bottom DBR mirror Conventional mirror Right-handed chiral STF mirror Vacuum pump Polarization control in external cavity diode laser CP emission from QDs LEDs Introduction • Device structure • System setup Compact circularly polarized (CP) light sources have recently attracted wide attention for direct chip-level integration due to potential applications in the fields of optical information processing and data storage, optical communication, quantum computing, and bio/chemical detection. So, it is highly desirable to have on-chip CP light emitters with precise controls over CP handedness and wavelength. The authors report the development of a class of chiral-mirror-based vertical-cavity surface-emitting lasers (VCSELs). The advances in sculptured thin film (STF) technology will eventually lead to the development of a new family of CP photonic devices that are efficient, compact, and fully integrable into optical/optoelectronic chips for a wide range of applications of CP light. 1-Laser diode; 2-collimating lens; 3-Soleil Babinet Compensator; 4-Left-handed Chiral STF mirror • LD: one facet is coated for enhanced reflectivity; the other is antireflection-coated. • The fast axis of the intra-cavity QWP was aligned at 45°with respect to the • polarization of the TE mode in the LD. • Chiral mirrors: left-handed STFs made of TiO2 with the circular Bragg regime • centered at 660nm. STF deposition • System lasing behavior Schematic of the device • CP ratio=112 • CP ratio=32 • Chiral mirrors: structurally left-handed STFs made of TiO2 with the circular Bragg • regime centered at 610 nm • Device characterization CTF Polar plot of the normalized analyzer transmission vs the angle between the optical axes of the analyzer and the Fresnel-rhomb retarder Light output energy as a function of driving current (Inset: spectrum of the LCP laser emission) • Ith = 46 mA • LCP lasing output • Side-mode suppression ratio is 26 dB Schematics of depositions of CTFs and chiral STFs Schematic of the basic system for PVD of STFs chiral STF CP emission from VCSELs • Oblique angle deposition • A tilted and rotating/fixed substrate corresponds to chiral STF/CTF deposition. • Atomic self-shadowing (Low energy adatom diffusion). LCP and RCP emission spectra of the NQDs confined in the chiral-STF-based microcavity Measured reflectance spectrum of the microcavity device for incident LCP light • Device design • Spectrally: narrower FWHM; higher peak intensity; large discriminable • difference between CP handedness. • LCP emission peak in good agreement with the position of spectral hole. Chiral-mirror microcavity • Top DBR mirror replaced with CTF and chiral STF bilayers • The CTF (QWP) introduces a pi/2 retardance to compensate the • polarization mismatch between the two reflectors. • Device characterization • Large discriminable difference between CP handedness is persistent under • different pumping light power. • Spatially: narrower emission angle (strongly directed normal to the surface). Acknowledgement Difference between chiral STF mirror and conventional mirror An example of well-developed circular Bragg regime The authors thank Sean M. Pursel and Dr. Mark W. Horn for providing help on initial STF depositions. • Circular Bragg phenomenon (CBP) • A well-developed CBP displays high selective reflection of CP light and is • confined to a defined spectral regime. • Microcavity built with chiral mirrors • Chiral STF mirror: CP states preserved by reflection. • Conventional mirror: CP states NOT preserved, due to p shift. References • Reflectance spectra of the CTF and • RH chiral STF bilayers (Inset: cross-section SEM image of the CTF and STF bilayers) A. Lakhtakia and R. Messier. Sculptured Thin Films: Nanoengineered Morphology and Optics, SPIE Press (2005). F. Zhang, J. Xu, A. Lakhtakia, S. M. Pursel, M. W. Horn, and A. Wang, Appl. Phys. Lett. 91, 023102 (2007). F. Zhang, J. Xu, A. Lakhtakia, T. Zhu, S.M. Pursel, and M.W. Horn, Appl. Phys. Lett. 92, 111109 (2008). F. Zhang, Ph.D. Dissertation, Pennsylvania State University (2008). Light output as a function of the pumping light energy (Inset: spectrum of the RCP lasing emission)

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