Generation of ultra-narrow, stable and tunable millimeter- and terahertz- waves with very low phase noise

Abstract

The interference between two spectral lines of the frequency comb of a fiber femtosecond laser is used to generate millimeter-wave and terahertz tones. The two lines are selected by stimulated Brillouin scattering (SBS) amplification. All other modes are strongly rejected based on polarization discrimination, using the polarization-pulling effect that is associated with SBS. The inherent high spectral quality of a femtosecond fiber laser comb allows generation of millimeter-and terahertz waves with linewidths below 1 Hz, and a phase noise of -105 dBc/Hz at 10 kHz offset. The generation, free-space transmission and detection of continuous waves at 1 THz are demonstrated as well. Lastly, the generated millimeterwave carriers are modulated by 40 Gbit/s data. The entire system consists of a fiber laser and standard equipment of optical telecommunications. Besides metrology, spectroscopy and astronomy, the method can be utilized for the emergent field of wireless millimeter-wave and THz-communications at ultra-high data rates. Abstract: The interference between two spectral lines of the frequency comb of a fiber femtosecond laser is used to generate millimeter-wave and terahertz tones. The two lines are selected by stimulated Brillouin scattering (SBS) amplification. All other modes are strongly rejected based on polarization discrimination, using the polarization-pulling effect that is associated with SBS. The inherent high spectral quality of a femtosecond fiber laser comb allows generation of millimeter-and terahertz waves with linewidths below 1 Hz, and a phase noise of -105 dBc/Hz at 10 kHz offset. The generation, free-space transmission and detection of continuous waves at 1 THz are demonstrated as well. Lastly, the generated millimeter-wave carriers are modulated by 40 Gbit/s data. The entire system consists of a fiber laser and standard equipment of optical telecommunications. Besides metrology, spectroscopy and astronomy, the method can be utilized for the emergent field of wireless millimeter-wave and THz-communications at ultra-high data rates.

Laser system design for table-top X-ray light source

“…For instance, mode-locked Yb:YAG thin-disk oscillators support pulse durations as short as 49 fs [43] . At high energy 1.5 nm [41,42] or 1.1 nm [43] , pulse spectral width has been achieved. The bandwidth is limited to <1.3 nm at cryogenic temperature [29,32,44] , and typically 0.4 nm pulse spectral width is achieved, limiting the central frequency of generated THz pulses to 100 GHz [21] .…”

Generation of highly stable millimeter waves with low phase noise and narrow linewidth

“…Frequencies up to 1 THz have been generated with nonlinear fiber optics. For frequencies up to 110 GHz a linewidth of 1 Hz and a phase noise of -llOdBc/Hz at a 10 kHz offset has been measured [7]. In [8] frequencies up to 39.8 GHz are generated with conventional optical filters with a phase noise of -102 dBcIHz at 10 kHz frequency offset.…”

Flat, rectangular frequency comb generation with tunable bandwidth and frequency spacing

“…The contrast of the lines seems to be lower due to the limited resolution bandwidth of the OSA. However, the width of the lines equals the linewidth of the initial lines, which is below 1 Hz for the comb lines generated by a femtosecond-fiber laser [12]. The longterm stability of the amplitudes of the comb lines is within 3 dB over several hours.…”

“…Another possibility represents the stimulated Brillouin scattering (SBS). This nonlinear effect has a very narrow bandwidth and can be used for the amplification of independent frequency lines [12]. The bandwidth can be as low as 3 MHz [13,14].…”

“…Due to the narrow bandwidth, it is possible to separate the frequencies of a femtosecond laser with a repetition rate of 80-100 MHz, with a pump wave generated by a DFB-LD. The pump lasers are locked to the line, which they have to separate by an electronic circuit [12] (not shown in Fig. 2).…”