Statement of Problem: Modern best structural solutions of microwave photonic systems for instantaneous frequency measurement (IFM) are based on “frequency-amplitude” measurement conversion using fiber Bragg gratings. The main disadvantage of microwave photonic systems for IFM with FBG is the monotonicity of the conversion characteristic in the area near the central wavelength of grating, which reduces the resolution of conversion at “low” radio frequencies (0.04 – 4 GHz). Methodology & Theoretical Orientation: A new method for measuring the instantaneous frequency of the microwave signal, based on the transformation of the "frequency-amplitude" in the classical fiber Bragg grating with a Gaussian spectral outline is presented. Previously measuring frequency components of microwave signals are shifted additively in electrooptical Mach-Zehnder modulator at a frequency equal to half width of the grating spectral contour. Findings: Using of these operations allows the instantaneous frequency measurements with high resolution and accuracy in the "low" frequency range. The proposed method is characterized by a simple realization and thermal stability as compared to methods using Bragg grating with special spectral contours: linear triangular and with a phase -shift, which are used to remove small slope of "frequency-amplitude" transformation and the monotonicity of the grating spectral contour at this frequencies. Conclusion & Significance: We described the principles of microwave photonic instantaneous frequency measurement system based on “frequency-amplitude” transformation in FBG. We identified possible way to improve their metrological characteristics in terms of available frequency range and resolution of low frequency identification by means of additional frequency shifting. Therefore, the low frequencies are measured on linear slope of FBG with good resolution and accuracy.
Tomomasa Ohkubo has his expertise in development of solar-pumped laser and numerical analysis of laser processing. He has completed his PhD from Tokyo Institute of Technology. He is Senior Assistant Professor of Department of Mechanical Engineering at Tokyo University of Technology. He is also Senior Assistant Professor of Department of Media Science at Tokyo University of Technology.
We developed solar-pumped laser system with Fresnel lens and solar cavity. The output power of the laser system was 120 W and the collection efficiency was 30W/m2. To keep the global environment, we must develop renewable energy systems, which replaces energy system with fossil fuels. Solar-pumped laser is one of a promising new technology to utilize solar energy for our society. For example, laser space solar power systems (L-SSPS) is proposed by Japan Aerospace Exploration Agency. L-SSPS proposes transmission of collected solar energy in the space to the earth by solar-pumped laser. In addition, energy cycle using magnesium as energy career is proposed by Yabe et al. Solar-pumped laser is expected as an energy source of reduction of magnesium in this energy cycle. We designed 2 m x 2 m of Fresnel lens to realize high power concentration of solar energy. Nd:YAG single crystal or Cr:Nd:YAG ceramic was used as laser medium. Whole system is installed on a Sun tracking system to realize continuous lasing. Using these equipment, we developed several type of solar cavity to confine solar energy and make it absorbed by laser medium. 80 W of peak output was realized as shown in green line in Figure 1 by a solar cavity, which is cone-shaped inner mirror holding laser medium at that of the central axis. 80 W of stable laser output was realized as shown in red line in Figure 1 by solar cavity, which is combined cone-shaped solar cavity and compound parabolic mirror (CPC). Furthermore, 120 W of stable output was realized using cone-shaped cavity and glass tube filled with water surrounding the laser medium. We called this system as liquid light-guide lens (LLGL) because the water works not only as coolant but also as a refractive optics.