I just read the 2015 excellent paper , "Tunable microwave photonic notch filter based on sliced broadband optical source".
Is it possible to downconvert a microwave photonic notch filter to a visible light photonic notch filter? What is the tuning speed of this microwave photonic filter?
[EDIT: August 4 2016 9:26 P.M Frank . The tuning speed of this analog microwave photonic filter is limited primarily by the response time of the balanced photodiode. For example, the Newport Nanosecond Photodetector, Silicon, 350-1000 nm, 0.8 mm Diameter, 8-32 / M4 Model: 1621 with URL, [https://www.newport.com/p/1621], has a rise time of 1 nanosecond.]
[EDIT: August 6 2016 6:00 P.M. Frank . Today's laser pointers are almost exclusively continuous wave)(CW) laser pointers . Continuous wave laser pointers do not need chirp compensation. Currently, pulsed lasers are used for high speed telecommunications because narrow pulse widths are needed. In the near future, it is estimated that CW laser pointers will be replaced by pulsed laser pointers which require chirp compensation similar to fiber Bragg grating (FBG) with variable delay line(VDL). Chirping is defined as a waveform with a continuously increasing or decreasing frequency spectra where frequency equals speed of light divided by wavelength.]
[EDIT August 7 2016 7:00 P.M. Frank There are two types of balanced photodetectors. Free space and Fiber, which is faster and smaller. The ThorLabs PBD430A Fiber model takes the difference between two signals , subtracting them across the spectrum for visible or infrared light . The PDB430A has two different frequency ranges 0 Hz to 400 MHz and 30Khz to 350 Mhz. ThorLabs told me last Friday that their PDB430A has a switching speed fast enought to respond to laser pointer strikes within 50 millisecond , thereby protecting the pilots from permanent damage.]
[EDIT August 7 2016 7:00 P.M switching frequency = speed of light (3.0 x 10^8 meters/second divided by wavelength 532 nanometers = 500 Terahertz switching time which is so fast one cannot see fluctuations of the electric field]
[EDIT August 8 2016 2:30 A.M.
This paper is very important because we wish to protect pilot's vision from increasingly sophisticated laser pointers on the ground 150 meters away aimed at the Boeing 747-787 cockpit windows. If we can detect the presence and wavelength of a coherent laser light in an incoherent background within 10 milliseconds of arrival , could I then activate a tunable band-reject filter based on this paper centered at the visible red, green or blue wavelengths?
In addition, I read with great interest in this paper that:
"The frequency omega2 can be tuned by the MZI without changing the filter shape according to Eq. (9). Another slicing way is to directly use the FPOP to shape the spectrum of the BOS. In this way, the interferometer is not needed in the approach, but a FPOP with high resolution is required."
In December 2009, Yuuki Watanabe and Toshiki Itagaki wrote in SPIE Journal of Biomedical Optics Volume 14 Issue6 JBO Letters 2009, "Real-time display on Fourier domain optical coherence tomography(OCT) system using a graphical processing unit" that a display rate of 27.9 frames per second for processed images(2048 FFT size X 1000 lateral A-scans) is achieved in our OCT system using a line scan CCD camera operated at 27.9 kHz using the C and C++ programming language".
Given today's embedded microprocessors, could we boost the FDOP display rate of 27.9 frames per second to 500 frames per second to meet Boeing and Airbus passenger plane pilot's expectations?
Furthermore , I read with great interest in the paper that:
"In this paper, two filters are necessary. One filter is used to filter the BOS; the other one is used to split the single laser from the BOS. In order to quickly verify the principle, we use two waveshapers in the experiment. It results in a high system cost. Moreover, a way to reduce the cost is to use fiber Bragg gratings (FBG) with optical circulators to work as the filters. Take the second filter as an example, we can send the light into the FBG via an optical circulator. When the Bragg wavelength is just equal to the laser wavelength, the reflected light only includes the laser light and the transmitted light only contains the BOS part."
How could I estimate the performance loss associated with replacing the waveshaper with fiber Bragg gratings and optical circulator?
This paper is a very nice example of out-of-the box engineering because it has no moving elements or electro-optic Pockels or Kerr effect. Rather, the authors subtract a single frequency source from an allpass optical filter producing a band-reject filter.
The schematic diagram of the proposed microwave photonic filter (MPF) is illustrated in the above figure. The single-side-band modulator is a fancy name for a microwave frequency mixer. The optical power and optical angle frequency of the laser source is 𝑃 𝑜 and 𝜔 𝑜 , respectively. The spectrum-sliced broadband optical source (BOS) is first confined within the optical angle frequency range between 𝜔 1 and 𝜔 2 (𝜔 1 <𝜔 2 ) via the Fourier domain optical processor (FDOP), and then sliced via a Mache-Zehnder interferometer (MZI) which is constructed by two 50/50 optical couplers and a variable delay line (VDL). The FDOP works as a programmable optical filter. The single-frequency light and the broadband light are coupled together and then single-side-band modulated to carry the radio frequency (RF) signal. The modulated light is fed into a dispersion fiber, and then launched into a wavelength division multiplexer (WDM). The WDM splits the light into two parts: Port B only includes the laser part; Port C only includes the BOS part. A balanced photodetector (BPD) is employed to detect the two parts, respectively.
Please correct me if I have stated anything incorrect. The use of equations is appreciated.
Any help is greatly appreciated.