Abstract
The terahertz (THz) quantum cascade laser (QCL) provides a versatile tool in a plethora of applications ranging from spectroscopy to astronomy and communications. In many of these fields, compactness, single mode frequency emission, and low threshold are highly desirable. The proposed approach, based on line defects in a photonic crystal (PhC) matrix, addresses all these features while offering unprecedented capabilities in terms of flexibility, light waveguiding, and emission directionality. Nine line-defect QCLs were realized in a triangular lattice of pillars fabricated in the laser active region (AR), centered around ∼2 THz by tuning the photonic design. A maximal 36% threshold reduction was recorded for these ultraflat dispersion line-defect QCLs in comparison to standard metal-metal QCL. The mode selectivity is an intrinsic property of the chosen fabrication design and has been achieved by lithographically scaling the dimension of the defect pillars and by acting on the PhC parameters in order to match the AR emission bandwidth. The measured line-defect QCLs emitted preferentially in the single frequency mode in the propagation direction throughout the entire dynamic range. An integrated active platform with multiple directional outputs was also fabricated as proof-of-principle to demonstrate the potential of this approach. The presented results pave the way for integrated circuitry operating in the THz regime and for fundamental studies on microcavity lasers.
Highlights
Quantum cascade lasers (QCLs) are well-established, compact semiconductor sources of coherent infrared and terahertz (THz) radiation
The proposed line-defect waveguides (LDWs) concept was extended to integrate QCLs in active photonic circuits. This is a unique and fundamental feature offered by this approach that cannot be reproduced in standard QCL ridges or omnidirectional photonic crystal (PhC)
The light-current-voltage (LIV) characteristics of all the QCLs were acquired with a Tydex Golay cell and a lock-in amplifier gated at 9 Hz, with QCLs typically pulsed at 100 kHz repetition rate and 30% duty cycle
Summary
Quantum cascade lasers (QCLs) are well-established, compact semiconductor sources of coherent infrared and terahertz (THz) radiation. Lasing occurs in the modes supported by the defects introduced in a PhC matrix These devices exhibit single frequency emission and low current threshold density Jth compared to commensurate metal-metal (MM) QCLs of equivalent area that display multimode operations and are in agreement with previously reported THz PhC QCLs. The proposed LDW concept was extended to integrate QCLs in active photonic circuits. The proposed LDW concept was extended to integrate QCLs in active photonic circuits This is a unique and fundamental feature offered by this approach that cannot be reproduced in standard QCL ridges or omnidirectional PhCs. the line-defect (LD) architecture offers an excellent platform to study fundamental effects such as slow-light, Purcell enhancement,[17] or the investigation of nonconventional microcavity lasers.[18,19]
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