High-Power Distributed Feedback Terahertz Quantum Cascade Lasers

Abstract

Single-mode operation of distributed feedback (DFB) terahertz quantum cascade lasers based on metal-stripe surface grating structure is reported. Strong DFB coupling and low waveguide loss conditions are obtained while maintaining a high laser output power. A record high edge-emitting optical power of 57 mW, ∼96.2 µm at 10 K together with a well-shaped far-field pattern is presented. Reliable dynamic single-mode emission at all injection currents and operating temperatures is realized with a side-mode suppression ratio >17 dB.Index Terms-Distributed feedback lasers, quantum cascade lasers, single-mode lasers.

Tri-channel single-mode terahertz quantum cascade laser

“…In order to emit a series of discrete wavelengths from one laser array, three different grating periods (Λ 12.9, 13.1, and 13.3 μm) were designed for the three tapered DFB lasers according to the calculated effective index (n 3.6) and central wavelength (λ ∼ 94 μm) of F-P devices, respectively. The grating depth and duty cycle are similar to reference [13].…”

“…The sample was processed into arrays using the method described in [12]. Metal-stripe surface plasma DFB grating was adopted to ensure single longitudinalmode emission [13]. The tapered profile was selected in order to enhance the output power and maintain single transverse mode.…”

“…Limited by the performance of our spectrometer, laser spectra were collected in rapid scan mode with a resolution of only 0.5 cm −1 . Based on the previous works [13,14], single-mode emission should be recognized under this resolution. For each laser in the array, the spectrum was measured at maximum peak output power.…”

“…The beam profile in the vertical direction is determined by the semi-insulating surface plasma waveguide structure and nearly the same as Ref. [13]. Beam quality factor M 2 was introduced to quantitatively analyze the in-plane laser beam and it can be expressed as the following equation [20]:…”

Power Amplification and Coherent Combination Techniques for Terahertz Quantum Cascade Lasers

“…At terahertz wavelengths, the DFB QCLs are well-defined single-mode emission by means of surface grating and lateral waveguide grating. Wang et al studied the tapered DFB THz QCLs based on metal-stripe surface grating with different grating periods of 13, 13.2 and 13.4 μm [18] (see Figure 3). The collected spectral peaks of 95 and 96.2 μm in Figure 4 indicate that the single mode emission has been demonstrated for lasers with grating period at 13.2 and 13.4 μm, respectively.…”