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Development of fiber Bragg gratings technology and their complex structures for sensing, telecommunications and microwave photonics applications

Osuch T., Gąsior P., Markowski K., Jędrzejewski K.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2014

Vol. 62, nr 4

627--633

In this paper research on the development of the fiber Bragg grating (FBG) technology which has been conducted at the Institute of Electronic Systems (IES), Warsaw University of Technology (WUT) since 2004 is presented. In particular the directions in the development of advanced set-ups employing the phase mask inscription scheme are discussed and supported with the descriptions of structures designed and fabricated with the use of the laboratory stages constructed at the IES. The novelty of the presented solutions is based on the combination of numerous techniques of the external modification of the interferometric patterns (projected onto cores of photosensitive fibers to modulate their refractive index) as well as application of the modification of the internal properties of the waveguides themselves by the means of introducing strain or tapering. The development of these sophisticated set-ups resulted in the inscription of FBGs with precisely designed spectral characteristics which found application in telecommunications and sensor technology are also illustrated here. The paper is summarized with the specification of the most important achievements attained at the lab and drafting of the possible directions of further research.

Influence of tapering process on changes of optical fiber refractive index distribution along a structure

Stasiewicz K. A., Krajewski R., Jaroszewicz L. R., Kujawińska M., Świłło R.

Opto-Electronics Review

2010

Vol. 18, No. 1

102-109

Investigations of internal structure changes along an optical fiber during the manufacture of biconical taper have been described. Basing on the constant volume theory, classification of biconical structures manufactured on a special set-up is presented and discussed. The interferometric tomography method has been used for determination of 3D geometry and refractive index distribution in manufactured optical fiber tapers. The experiments provide detailed information on external (diameter of cladding) as well as internal (core diameter and refractive index profile) changes along the taper region. The results have been discussed in relation to the parameters of the manufacturing process.

Poszerzenie widma impulsu laserowego poprzez zastosowanie przewężki dwustronnej na standardowym włóknie jednomodowym

Stasiewicz K. A., Młyńczak J., Jaroszewicz L. R., Kopczyński K.

Biuletyn Wojskowej Akademii Technicznej

2007

Vol. 56, nr 4

155-165

Praca przedstawia eksperymentalne wyniki poszerzenia impulsu laserowego dużej mocy w standardowych światłowodach telekomunikacyjnych. Poszerzenie uzyskano poprzez wykorzystanie technologii przewężki dwustronnej, której optymalizacja dla danego typu włókna pozwala na sterowanie tak szerokością impulsu jak i składem widmowym wychodzącej wiązki, prowadząc w konsekwencji do generacji światła białego.

The papers describes the results of a laser pulse broadening in tapered standard single mode fiber. Additional description of a set - up for taper manufacturing, with a principle of its operation, based on elongation procedure of fiber-optics in a low-pressure gas burner, is also presented. A virtue of such a set-up is the possibility of different kinds of taper manufacturing, like punctual, long distance on regular or increasing distance. Tapering process allows us to change a diameter of an optical fiber what means boundary condition changes, beam is propagating in a core (made from silica) surrounded by air. There is a large refractive index step between these two media, allowing for confined pulse (with high power) in a very small area. This effect causes increasing intensity of a propagated beam and amplifies nonlinear effects, like self-phase modulation etc. The article presents the results of pulse broadening obtained in different tapers, made on a single-mode fiber for a wavelength of 1310 nm and a core diameter of about 9 žm. As a light source, the pumped laser operated at a wavelength of 532 nm, which emitted the pulses of 0.6 ns with a repetition rate of about 1 kHz, has been used. All the measured fibers with a taper have a length of about 3 m, where about 1.2 m was for the input (for easier launching) and the output (for easier connection with an optical spectrum analyzer). Experimental results show the pulse broadening in the used taper structures. The best result are obtained for a long distance taper, where the elongated part was about 50 mm (flame brush is travelling to and from along the constant length). For this taper, it can be observed more flat spectrum broadening to the longer wavelength, together with increasing average power of a laser. Theoretically the best broadening we should obtain for a taper length of about 100 mm what will be one of the next subjects of our research. Other tapers also cause broadening effects but their spectra are not so flat. Interesting example is a taper with an increasing length of elongation. We observed additional spectral pick at the wavelength of about 630 nm and 950 nm. These picks are connected with the smaller core diameter obtained in this type of tapering process (the smaller core, the larger broadening). The worst results were for a punctual taper. In this case, a diameter of a taper is very small (about several micrometers) but the losses are very high. The presented results show that biconical tapered single mode optical fiber is a good way to obtain spectral broadening (supercontinuum effect).