13 GHz direct modulation of terahertz quantum cascade lasers

Abstract

By directly modulating the bias voltage of a double-metal waveguide, 2.8THz quantum cascade laser, we observe the appearance of multiple gigahertz sidebands in the emission spectrum, with a spacing that can be continuously tuned up to 13GHz. By using an upconversion technique, the terahertz spectrum is shifted at 1.57μm, and displayed on an optical spectrum analyzer. A marked increase in the number of sidebands is observed when the modulation frequency approaches the round-trip frequency (∼12.3GHz). The laser packaging high frequency response has been measured using a microwave rectification technique, and is limited by the bond-wire parasitic inductance.

Beat note analysis and spectral modulation of terahertz quantum cascade lasers with radio frequency injection

“…In all three curves we can see a broad "dip" around 6 GHz. Note that the modulation responses of intersubband QCLs are free of relaxation peaks, which has already been confirmed by several experiments [11,21] . Therefore, the dip around 6 GHz does not originate from the laser itself.…”

“…[11,13]. Figure 1(a) shows the V − I curve measured in continuous wave (cw) mode at 5 K. From the first-order derivative (right axis, red color) of the V − I curve, we can clearly see a "step" around 600 mA, which indicates the threshold of the laser.…”

“…Different from the interband diode lasers, quantum cascade lasers (QCLs) [7][8][9] are unipolar devices based on electron intersubband transitions in the conduction band of multiple quantum well structures. The fast radiative relaxation in QCLs results in a flat modulation frequency response that makes QCLs more suitable for fast modulation [10,11] . For multimode QCLs with a Fabry-Perot cavity geometry, the emission spectrum is inherently modulated due to the resonant cavity.…”

Efficient prediction of terahertz quantum cascade laser dynamics from steady-state simulations

“…From these data, an upper bound for the modulation bandwidth of the laser under various conditions can be determined-for example, to optimize bandwidth for short-range communications. 5,19 Our model predicts a 3 dB modulation bandwidth between 3 GHz and 10 GHz, with the maximum value being obtained close to the peak of the L-I curve (see inset in Fig. 3).…”

Wireless terahertz light transmission based on digitally-modulated terahertz quantum-cascade laser

“…The THz quantum-cascade laser (QCL) is one of the most promising sources in this frequency region, and has many advantages such as compact size, portability, long life-time, and easy integration [2−4] . Fast modulation [5,6] of THz QCLs, such as the midinfrared QCLs [7] , is a key element of transmission systems with high data-rate. Moreover, a spectrally-matched detector with fast response ability, such as the quantum-well infrared photodetector (QWIP) [8] , is also required.…”