PRECISION MICROWAVE GENERATION
In the last years the demand for ultra-low noise microwave (MW) and radio-frequency (RF) signal sources increased drastically. Standard industrial applications and high-end academic experiments require ever higher precision:
- Radar systems
- Defence communications
- Photonic ADC
- Ultra-stable clocking
- Test and measurement
- Satellite communications
- Particle accelerators, FELs
- Coherent communications
Ultra-low phase noise generation from modelocked lasers offers a simple solution to achieve RF or MW signals with sub-femtosecond RMS timing jitter. Ultra-low noise quartz oscillators show phase noise higher by orders of magnitude. Cryogenically cooled sapphire oscillators on the other hand require an extensive cooling system, which limits their range of application due to their complexity. Although, the more recently developed ultra-low noise microwave signal generation from optical frequency comb based system can achieve extremely high phase stability and low phase noise, the installation and maintenance of these systems are technically difficult and cost intensive .
For many high performance applications in signal processing and communications (sampling clocks, ADC, master oscillators for signal source analyzers) high frequency phase noise and accumulated timing jitter impact the system performance most critically. For these applications, one may generate microwave directly from a free-running modelocked laser by simply using a photodiode signal and optional electronic amplification. To suppress the phase noise at lower noise frequencies, one may lock or synchronize the modelocked laser to a low-noise and electronic oscillator  for long-term stability. For applications, that require a high frequency microwave reference oscillator (e.g. 10 GHz) it may also be a solution to synchronize a low-noise voltage controlled oscillator to a modelocked laser .
Digitalization of data opens unprecedented opportunities in telecommunication, radar and signal processing. Almost all sensing systems in use today require analog signals to be converted to digital ones. Signal rates have grown at a rate that has outpaced electronic analog to digital conversion (ADC). This demand for higher bandwidth, speed or digitalization precision puts stringent requirements on the aperture jitter of ADC setups. One way to improve ADC is to use a lower timing-jitter clock source provided by photonic solutions. Photonic ADCs benefit from much more than only improved timing-jitter. Using mode-locked laser sources like the MENHIR‑1550 laser enables a wide variety of new ultra-fast photonic digitization techniques.
We show here how the MENHIR-1550 can be used to clock an ADC at much higher bandwidths while at same time achieving timing-jitter below 1 fs.
Radiofrequency (RF) sources are widely used in our modern world. All the radar systems, GPS and a broad range of other technologies are based on generating and comparing RF signals. The need to have more precise measurement systems and faster communication solutions puts stringent requirements on phase noise and timing-jitter.
We show here how a photonic solution, using the MENHIR-1550 laser as a low phase-noise oscillator, meets the current and future needs for RF generation. This solution is straightforward to integrate with current RF technology and can be used in harsh environments as well as in laboratory conditions.
Menhir Photonics added values
Menhir Photonics offers modelocked lasers with the lowest phase-noise available on the market today combined with extreme reliability. Fig. 1 shows a typical phase noise measurement for a free-running laser of the MENHIR-1550 series, measured on the 10 GHz carrier i.e. the 40th harmonics (250 MHz pulse repetition rate). Note that the noise floor of the measurement limits the integrated timing jitter to approximately 500 as (attoseconds).
Fig 1.: 1) Phase noise power spectrum of a free-running MENHIR-1550 250MHz laser measured at the 10 GHz harmonics. 2) Integrated timing jitter starting at 10 MHz for the same free-running laser.
All lasers of the MENHIR-1550 SERIES have an optional fast repetition rate tuning with a modulation bandwidth of >50 kHz for repetition rate locking or synchronization. In addition, there is also the option for fast modulation of the pump current.
The MENHIR-1550 SERIES reaches unmatched levels of industrial quality and environmental stability. It has been excessively tested for vibrations, shocks and other external disturbances (space and aerospace related standard tests). For integration into space-critical applications, customized small-sized versions are available.
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 Schlatter, B. Rudin, S. C. Zeller, R. Paschotta, G. J. Spühler, L. Krainer, N. Haverkamp, H. R. Telle, and U. Keller, ”Nearly quantum-noise-limited timing jitter from miniature Er:Yb:glass lasers”, Opt. Lett. 30, 1536 (2005)
 N. V. Nardelli, T. M. Fortier, M. Pomponio, E. Baumann, C. Nelson, T. R. Schibli, and A. Hati 10 GHz generation with ultra-low phase noise via the transfer oscillator technique, APL Photonics 7, 026105 (2022).