Experimental evaluation of an ultrafast free-space optical analog-to-digital conversion scheme using a tunable semiconductor laser

Johan Stigwall; Sheila Galt; Sverker Hard

doi:10.1117/12.547443

1 September 2004 Experimental evaluation of an ultrafast free-space optical analog-to-digital conversion scheme using a tunable semiconductor laser

Johan Stigwall, Sheila Galt, Sverker Hard

Author Affiliations +

Proceedings Volume 5466, Microwave and Terahertz Photonics; (2004) https://doi.org/10.1117/12.547443
Event: Photonics Europe, 2004, Strasbourg, France

Abstract

Using a tunable semiconductor laser diode and an array of diffractive optical elements (DOEs), a time-continuous, free-space optical analog to digital converter (ADC) with five bits of resolution was experimentally evaluated. The signal to be A/D-converted was fed to the tuning sections of a grating coupled twin-guide sampled reflector (GCSR) laser diode, giving a quasi-continuous tuning range of 10 nm that spanned 40 longitudinal modes. The 32 central modes were mapped to specific digital output values by first converting wavelength to deflection angle using a diffraction grating and then focusing on an array of beam splitting DOEs. Each DOE element generated a five-spot digital code word in the detector plane. Using Gray code, only one code bit changed value at a time. Thus, the beam could straddle two adjacent DOE elements without large read out errors. Furthermore, the grating components of the elements in the DOE array were all in-phase to keep the spot focused when such straddling occurs. The SNR of a converted 10 MHz sine signal covering 23 modes was 21 dB, mainly limited by tuning hysteresis. This SNR corresponds to 3.2 effective bits. The laser's analog tuning bandwidth was found to be 45 MHz, probably limited by the carrier lifetime in the passive tuning sections, but we also measured the ADC performance at 100 MHz. As the studied ADC system is time-continuous, the sampling was done in the digital domain.

Citation Download Citation

Johan Stigwall, Sheila Galt, and Sverker Hard "Experimental evaluation of an ultrafast free-space optical analog-to-digital conversion scheme using a tunable semiconductor laser", Proc. SPIE 5466, Microwave and Terahertz Photonics, (1 September 2004); https://doi.org/10.1117/12.547443

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