Terahertz laser diode using field emitter arrays

High-power and broad-tunable terahertz wave generating source on chip, which has broad application prospects, remains an unachieved goal of researchers after decades of pursuing. Here, we propose a concept of terahertz laser diode, which is a dc-biased self-excited microelectronic laser oscillator using collectively modulated free electrons emitted by field-emitter-arrays as the active medium and using an inherent Fabry-Pérot interferometer formed by port reflections as the frequency selector. It is sub-millimeter to centimeter in size and can generate continuous-wave coherent terahertz radiation with several watts of power per square millimeter. Its frequency can be tuned to cover a wide terahertz band by changing the cathode-to-anode distance and the bias voltage. It has the potential to outperform the conventional free-electron or solid-state terahertz devices in terms of portability, tunability, and output power, signifying a promising class of tunable and high-power terahertz source on chip.

Figure 1

(a) Schematic model of the proposed TLD without output windows. (b) The two-dimensional (2D) model of TLD with a dc electron beam. (c) The 2D model of TLD with a modulated beam and THz emission.

Figure 2

Simulated electric field at the surface of the cathode (a) and the emitted beam current density (b), together with their frequency spectra. (c) Simulated THF $E$ (in blue) and charge density $\rho$ (in pink) in the time domain detected at different longitudinal positions (from $z=0.05d$ to $z=0.9d$). $\rho$ is negative since the electron carries a negative charge. The yellow regions denote the decelerating regions and the purple ellipses approximately locate the electron bunches.

Figure 3

(a) The calculated power as a function of cathode-anode distance $d$ and frequency. Here the bias voltage is $V_a=1.5$ kV. (b) The calculated power as a function of bias voltage $V_a$ and frequency. Here $d=10 \mu \mathrm{m}$. The negative power regions denote the possible operation regions.

Figure 4

(a) Calculated (lines) and simulated (dots) operating frequencies of the TLD as a function of $w$. Here two FP modes with $n=1$ and $n=2$ are shown. (b) Simulated electric field distribution at 0.8 THz for $d=10 \mu \mathrm{m}$ and $w=0.5 \mu \mathrm{m}$. (b) Simulated electric field distribution at 0.71 THz for $d=10 \mu \mathrm{m}$ and $w=1 \mu \mathrm{m}$.

Figure 5

Calculated power (a) and efficiency (b) of the TLD as functions of $d$ and $V_a$.