Surface Emitting Devices Based on a Semiconductor Coupled Multilayer Cavity for Novel Terahertz Light Sources

Abstract

SUMMARYCompact and room-temperature operable terahertz emitting devices have been proposed using a semiconductor coupled multilayer cavity that consists of two functional cavity layers and three distributed Bragg reflector (DBR) multilayers. Two cavity modes with an optical frequency difference in the terahertz region are realized since two cavities are coupled by the intermediate DBR multilayer. In the proposed device, one cavity is used as the active layer for two-color lasing in the near-infrared region by current injection and the other is used as the second-order nonlinear optical medium for difference-frequency generation of the two-color fundamental laser light. The control of the nonlinear polarization by face-to-face bonding of two epitaxial wafers with different orientations is quite effective to achieve bright terahertz emission from the coupled cavity. In this study, two-color emission by optical excitation was measured for the waferbonded GaAs/AlGaAs coupled multilayer cavity containing self-assembled InAs quantum dots (QDs). We found that optical loss at the bonding interface strongly affects the two-color emission characteristics when the bonding was performed in the middle of the intermediate DBR multilayer. The effect was almost eliminated when the bonding position was carefully chosen by considering electric field distributions of the two modes. We also fabricated the current-injection type devices using the wafer-bonded coupled multilayer cavities. An assemble of self-assembled QDs is considered to be desirable as the optical gain medium because of the discrete nature of the electronic states and the relatively wide gain spectrum due to the inhomogeneous size distribution. The gain was, however, insufficient for two-color lasing even when the nine QD layers were used. Substituting two types of InGaAs multiple quantum wells (MQWs) for the QDs, we were able to demonstrate two-color lasing of the device when the gain peaks of MQWs were tuned to the cavity modes by lowering the operating temperature.

Near-infrared dual-wavelength surface-emitting light source using InAs quantum dots resonant with vertical cavity modes

“…Similar to VCSELs, vertical external-cavity surface-emitting lasers (VECSELs), 6) which possess a gain material in a thin VC with a lower DBR and an external upper mirror, have been extensively developed. 7) Recently, multiwavelength surface-emitting lasers based on VCSELs 8,9) and VECSELs [10][11][12][13][14][15] have been intensively studied for various applications, such as wavelength-multiplexed optical communications in free space, 16) dual-wavelength interferometry, 17,18) and nonlinear optical phenomena [19][20][21][22][23] (e.g. THz-DFG).…”

Sublattice reversal in GaAs/Ge/GaAs (113)B heterostructures and its application to THz emitting devices based on a coupled multilayer cavity

“…To obtain terahertz emission through DFG without external light sources, we have fabricated the structure by current injection from the viewpoint of practical device application. [20][21][22][23] The opposite signs of χ (2) (second-order nonlinear susceptibility) in the two cavity regions are necessary to realize a stronger THz-DFG of two modes. The sign of χ (2) can be inverted by the 180°rotation of the crystal around the appropriate axis.…”

Room-temperature two-color lasing by current injection into a GaAs/AlGaAs coupled multilayer cavity fabricated by wafer bonding

“…A similar device was also fabricated and studied using the waferbonded GaAs=AlGaAs coupled cavity. 33,34) The threshold behavior was observed in the current-light output (I-L) curve. However, two-color lasing was not realized at room temperature because of the wavelength mismatch between the cavity modes and the gain peaks of the MQWs.…”