Room temperature surface emission on large-area photonic crystal quantum cascade lasers

Abstract

We design and fabricate large-area (1.1 mm × 1.1 mm) photonic crystal quantum cascade lasers, enabling single-mode (wavelength ∼ 8.5 µm) surface emission at room temperature, with a maximum peak power up to 176 mW. The beam divergence is < 1 • and without side-lobes. Moreover, by introducing asymmetry into the photonic crystal pillar shape, a single-lobed far-field is realized. The photonic band structure is measured with high spectral (0.72 cm −1 ) and angular (0.1 • ) resolution by using the photonic crystal quantum cascade laser itself as a detector.Quantum cascade lasers (QCLs) are semiconductor laser sources that operate in the both mid-infrared [1] and terahertz region [2]. Nowadays, QCLs are the sources of choice for many laser-based applications, e.g., trace gas spectroscopy [3], process control [4], and biological sensing [5]. Surface emitting lasers are advantageous for their beam shape and the ease of two-dimensional (2D) integration [6]. Based on intersubband transitions, the selection rule of QCL determines the light to be transverse magnetic (TM) polarized.Therefore, conventional vertical cavity surface emission design is not suitable for QCLs.In order to realize a surface-emitting QCL, novel coupling structures have been implemented, for example, photonic crystal (PhC) [7-10], second-order distributed feedback (DFB) grating [11,12], microdisk and ring resonators [13][14][15]. Compared to these other 1 arXiv:1811.08786v1 [physics.optics]

Large area photonic crystal quantum cascade laser with 5 W surface-emitting power

“…The slope efficiencies in both measurements are around 130 mW/A, which are significantly enhanced compared to our previous published result (17.5 mW/A) [13]. This improvement can be attributed to the strain-balanced active region used for this laser [15], the stronger effective index contrast (2 µm-thick PhC layer) and the additional grid-like contact which enhances the current injection.…”

“…1(a), the top-view shape of the PhC pillar is a square with a missing corner. This asymmetry enhances the surface power extraction at the Γ 2 point, by increasing the radiation constant in the surface-normal direction [3,13]. A 600 nm-thick active region layer remains unetched to maintain a high optical overlap factor and to prevent over-etching into the InP substrate.…”

“…After processing, the laser is cleaved and epi-down mounted on an AlN submount. One limitation on the performance of large area surface-emitting PhC-QCLs is the uniformity of the current injection [13]. In this work, the influence of the additional grid-like contact is investigated with a 2D COMSOL simulation, as shown in Fig.…”

“…Because of the unique 2D in-plane coupling mechanism [4], photonic crystals (PhCs) [5][6][7][8][9][10] provide a powerful solution for surface-emitting QCLs. Furthermore, large-area surface-emitting lasers are advantageous for realizing high output power with a narrow and symmetrical beam shape [11][12][13].…”

“…Previously, our group has demonstrated room-temperature large-area PhC-QCLs by using the buried heterostructure and buried grating technique [13,14]. However, the peak output power was below 1W.…”