Generation of tunable high-purity microwave and terahertz signals by two-frequency solid state lasers

Abstract

We show that diode-pumped solid-state lasers can generate tunable high-purity microwave signals. In the case of a single-axis cavity containing an adjustable linear phase anisotropy, orthogonal linear eigenstates oscillate with a continuously tunable frequency difference. The maximum beat frequency is fixed by the laser cavity length and can reach a few tens of GHz. In order to reach the THz range, insertion of a double refraction crystal inside the laser cavity creates a two-axis laser that allows one to choose independently the frequencies of the two eigenstates. In this case the maximum beat frequency is fixed by the active medium gain bandwidth which is of a few THz for an Er:Yb:glass active medium. We show that doubling the two frequencies emitted by such a two-axis laser at 1.55 µm yields a source of tunable cw THz beat notes suitable for photomixing in GaAs-based THz emitters. Moreover, the beat notes generated by diode-pumped solid-state lasers can be phase-locked to microwave local oscillators. In particular, we show that a singleaxis Er:Yb:glass laser provides a beat note continuously tunable from 0 to 20 GHz with a 170 µHz line width. The phase noise of such a source is measured to be lower than -130 dBc/Hz at 100 kHz offset from the carrier.

Wideband dual-frequency lidar-radar for simultaneous velocity and high-resolution range profile measurements

“…To generate the waveform, we chose to use a dual-frequency laser (DFL) since it provides in a simple setup widely tunable high frequency modulated beams, with a 100 % modulation depth [18][19][20][21][22]. We included the DFL in a electronically controlled frequency locked loop realized with a fiber optics delay line [23][24][25][26][27] in order to generate a stepby-step chirp [11].…”

Frequency Difference Thermally and Electrically Tunable Dual-Frequency Nd:YAG/LiTaO3 Microchip Laser

“…Frequency difference tunable dual-frequency lasers have drawn a lot of attention in the last few years for their applications in the fields of absolute distance interferometry, Light Detection and Ranging (LIDAR) detection and terahertz wave generation [1][2][3]. In recent years, significant achievements have been made in the research of dual-frequency lasers, such as the intensity balance ratio, beat note stability and beat effect-based Q-switch regime [4][5][6].…”

Photonic generation of microwave signal using a rational harmonic mode-locked fiber ring laser

“…O PTICAL generation and distribution of millimeter-wave signals has many potential applications such as broad-band wireless access networks, radar, software-defined radio, and satellite communications, and has been intensively investigated over the past few years [1]- [8]. In general, the techniques to generate microwave signals in the optical domain can be divided into three categories, which are: 1) optical phase locking or injection locking of two laser diodes [1], [2] or the combination of the two [3]; 2) external modulation of a laser diode [4]- [6]; and 3) direct beating of dual-longitudinal or multilongitudinal modes of a laser at a photodetector (PD) [7], [8]. In the first category, two lasers are phase or injection locked to a microwave reference.…”