TY - GEN
T1 - Design and analysis of terahertz surface-emitting distributed-feedback lasers with circular metal grating
AU - Yu, S. F.
AU - Li, X. F.
PY - 2010/1/3
Y1 - 2010/1/3
N2 - Circular surface-emitting quantum-cascade lasers (QCLs) are good candidate to provide high-power low-divergent single-mode terahertz (THz) waves. These devices employ the metallic cladding layer and 2nd-order circular metal grating to provide surface-coupling mechanism and ultra-high light confinement to improve the lasing efficiency. Under such a big index contrast in metal grating, high-order diffracted waves cannot be overlooked, leading to dramatic change of the transverse modal distribution with the variation of grating duty cycle. Therefore, the conventional coupled-wave technique used for small-index contrast grating becomes inapplicable for this investigation. To solve this problem, we express the field distribution as a Floquet-Bloch expansion of Hankel functions to take into account the high-order diffraction waves. First, the coupled-wave equations of transverse-magnetic mode are derived under the infinite-length approximation. The detailed transverse-mode characteristics of symmetric and anti-symmetric modes supported in the circular waveguide as well as the effects of device parameters are analyzed. Based on the results of infinite-length assumption, the coupled-mode equations of finite-length device are then derived, which allows us to investigate the threshold and modal characteristics of the considered THz surface-emitting circular QCLs. It is observed that the proposed structure has the potential to realize vertical THz radiation with beam quality of subwavelength dimension.
AB - Circular surface-emitting quantum-cascade lasers (QCLs) are good candidate to provide high-power low-divergent single-mode terahertz (THz) waves. These devices employ the metallic cladding layer and 2nd-order circular metal grating to provide surface-coupling mechanism and ultra-high light confinement to improve the lasing efficiency. Under such a big index contrast in metal grating, high-order diffracted waves cannot be overlooked, leading to dramatic change of the transverse modal distribution with the variation of grating duty cycle. Therefore, the conventional coupled-wave technique used for small-index contrast grating becomes inapplicable for this investigation. To solve this problem, we express the field distribution as a Floquet-Bloch expansion of Hankel functions to take into account the high-order diffraction waves. First, the coupled-wave equations of transverse-magnetic mode are derived under the infinite-length approximation. The detailed transverse-mode characteristics of symmetric and anti-symmetric modes supported in the circular waveguide as well as the effects of device parameters are analyzed. Based on the results of infinite-length assumption, the coupled-mode equations of finite-length device are then derived, which allows us to investigate the threshold and modal characteristics of the considered THz surface-emitting circular QCLs. It is observed that the proposed structure has the potential to realize vertical THz radiation with beam quality of subwavelength dimension.
UR - http://www.scopus.com/inward/record.url?scp=77951659200&partnerID=8YFLogxK
U2 - 10.1109/INEC.2010.5424694
DO - 10.1109/INEC.2010.5424694
M3 - Conference article published in proceeding or book
AN - SCOPUS:77951659200
SN - 9781424435449
T3 - INEC 2010 - 2010 3rd International Nanoelectronics Conference, Proceedings
SP - 291
EP - 292
BT - INEC 2010 - 2010 3rd International Nanoelectronics Conference, Proceedings
T2 - 2010 3rd International Nanoelectronics Conference, INEC 2010
Y2 - 3 January 2010 through 8 January 2010
ER -