Measurement of higher order chromatic dispersion in a photonic bandgap fiber: comparative study of spectral interferometric methods

Abstract

Chromatic dispersion of a 37 cm long, solid-core photonic bandgap (PBG) fiber was studied in the wavelength range of 740-840 nm with spectral interferometry employing a Mach-Zehnder interferometer and a high resolution spectrometer. The interferometer was illuminated by a Ti:sapphire laser providing 20 fs pulses. A comparative study has been carried out to find the most accurate spectral phase retrieval method that is suitable for measuring higher order chromatic dispersion. The stationary phase point, the minima-maxima, the cosine function fit, the Fourier transform, and the windowed Fourier transform methods were tested. It was shown that out of these five techniques, the Fourier-transform method provided the dispersion coefficients with the highest accuracy, and it could also detect rapid phase changes in the vicinity of leaking mode frequencies within the transmission band of the PBG fiber.

Monitoring the dominance of higher-order chromatic dispersion with spectral interferometry using the stationary phase point method

“…Note that this is not caused by polarization mode dispersion [28], nor by intermodal dispersion [32] but due to the prevalent presence of third-order chromatic dispersion as in Refs. [23,24]. Accordingly, in order to get the correct GD curve of the sample both SPPs should be monitored.…”

“…The precision of the Fourier-transform evaluation method in measuring higher-order dispersion is already demonstrated [23,24], however if dispersion retrieval in a wide wavelength range is of interest, thus a lower resolution spectrometer is used, the method becomes inaccurate. On the other hand, the so-called stationary phase point (SPP) method [25][26][27][28][29], also known as equalization wavelength, is one of the most common evaluation methods, the applicability of which has already been demonstrated in measuring the dispersion of various optical elements, including fibers [23,24,[30][31][32]. The SPP method is advantageous as regardless of the value of the dispersion and the resolution of the spectrometer the positions of the SPPs can be precisely determined [28].…”

“…The SPP method is advantageous as regardless of the value of the dispersion and the resolution of the spectrometer the positions of the SPPs can be precisely determined [28]. Up until now this method was mainly used only in the case of optical elements and fibers where the GDD was the decisive dispersion term, however, recent studies show that even fifth-order dispersion (QOD) has significance when the GDD is reduced and the TOD becomes dominant [23,24]. In that case two SPPs were detected at certain delays, and the group delay curve was determined from the positions of both SPPs.…”

Phase and polarization changes of pulsed Gaussian beams during focusing and propagation

“…So, to have an experimental method to measure the phase or shape of a pulse, the only step remaining is to get the phase difference ∆ϕ(ω) from the measured interferogram I ifg (ω). Several methods exists for this [190], one of the most widely used ones is Fourier-transform spectral interferometry (FTSI) [191], which was shown to be the most reliable one from the several others, in specific applications [190]. Apart from its general usage for ultrafast measurements [104], this is the evaluation method in all previous examples of CEP-change measurement with SI [186][187][188][189].…”

“…Using FTSI to evaluate an interferogram is technically very simple [104,190,191]. The first step is to apply an inverse Fourier transform XII on the interferogram, which yields a temporal signal (like the one in 2.13(a), obtained by transforming the interferogram of 2.12(a)).…”