The Time-Stretch Analog-to-Digital Converter (TS-ADC) takes a high speed analog electronic signal, slows it down by a photonic time-stretch preprocessor, and digitizes that with a relatively slow but high resolution electronic analog-to-digital converter.

With this calculator, you will be able to determine the stretch factor, RF bandwidth, and required optical bandwidth amongst other parameters.

Schematics (Click on image to expand)

References

  1. F. Coppinger, A. S. Bhushan and B. Jalali, "Time magnification of electrical signals using chirped optical pulses," Electronics Letters, 34(4), 399-400 (1998). PDF
  2. A. S. Bhushan, F. Coppinger, and B. Jalali, "Time-stretched analogue-to-digital conversion," Electronics Letters 34(9), 839-841 (1998). PDF
  3. Y. Han and B. Jalali, "Photonic Time-Stretched Analog-to-Digital Converter: Fundamental Concepts and Practical Considerations," Journal of Lightwave Technology 21(12), 3085-3103 (2003). PDF
  4. A. M. Fard, S. Gupta and B. Jalali , "Photonic time-stretch digitizer and its extension to real-time spectroscopy and imaging," Laser & Photonics Reviews, Vol. 7, Issue 2, pp. 207-263, Mar. 2013. PDF

Explanation

Like all optical links, the photonic Time-Stretch preprocessor exhibits RF-fading, a phenomenon that, if not compensated, limits its maximum RF frequency. This phenomenon is called the dispersion penalty (DP). As the two RF sidebands on the optical pulse experience different phase shifts in the fiber due to dispersion, they beat in and out of phase. Using this simulator, you can explore the effect of dispersion on the amount of stretching, the dispersion penalty (DP) bandwidth, and the time aperture at the electrooptic modulator (EOM) and receiver. Dispersive elements, such as fibers or chirped fiber bragg gratings (CFBG) are not loss-less. Here you can also see the impact of this loss on the RF signal. The dispersion penalty can be entirely eliminated by one of three techniques: (1) phase diversity, (2) single-sideband modulation or (3) coherent detection. In that case, the maximum RF input frequency is only limited by the bandwidth of the electrooptic modulator.

RF Transfer Function

*PD: phase diversity **SSB: single-sideband ***Coherent demodulation

Maximum Frequency (GHz)

Schematic

Explanation

The single channel version of the photonic Time-Stretch preprocessor (Time-Stretch Enhanced Recording oscilloscope, or TiSER) captures and digitizes a finite signal length (a burst), called the time aperture of the system. The multi-channel version captures the signal continuously, so there is no limitation. When using the single-channel architecture, one way of increasing the time aperture is to increase the length of the first dispersing element. Doing so, however, increases the required optical bandwidth for a desired RF bandwidth due to the dispersion penalty. Thus, there is a trade-off between the time aperture and RF bandwidth, which is proportional to the ratio of optical and RF bandwidths. You can explore that trade-off here.

Click on each parameter for further explanation.

Input Parameters (Adjustable)

Stretch Factor - S
Back-end ADC Sample Rate (MS/s) - fs
Dispersion Penalty Bandwidth (GHz) - BDP
# of Samples Per Pulse (or Segment) - N
Mode-locked Laser Wavelength (nm) - λ

Schematic