UV-inscription, polarization-dependant loss characteristics and applications of 45° tilted fiber gratings

We have UV-inscribed and theoretically and experimentally analyzed fiber gratings with the structure tilted at 45° and implemented this type of devices as an in-fiber polarizer. A systematic investigation has been carried out on the characterization of 45° tilted fiber gratings (45° TFGs) in terms of the polarization-dependant loss (PDL) and thermal response. The detailed theoretical modeling has revealed a linear correlation between the grating length and the PDL, which has been proved by the experimental results. For the first time, we have examined the UV beam diffraction from a tilted phase mask and designed the UV-inscription system to suit the 45° TFG fabrication. Experimentally, a 24 mm long 45° TFG UV-inscribed in standard telecom single-mode fiber exhibited around 25 dB PDL at 1530 nm and an over ~300 nm bandwidth of PDL spectrum. By the concatenation method, a 44 mm long grating showed a PDL as high as 40 dB that is close to the high polarization extinction ratio of commercial products. Moreover, we have revealed that the PDL of 45° TFGs has low thermal influence, which is desirable for real application devices. Finally, we experimentally demonstrated an all-fiber twist sensor system based on a 45° and an 81° TFG.

Superstructure fiber gratings via single step femtosecond laser inscription

We present the development of superstructure fiber gratings (SFG) in Ge-doped, silica optical fiber using femtosecond laser inscription. We apply a simple but extremely effective single step process to inscribe low loss, sampled gratings with minor polarization dependence. The method results in a controlled modulated index change with complete suppression of mode coupling associated with the overlapping LPG structure leading to highly symmetric superstructure spectra, with the grating reflection well within the Fourier design limit. The devices are characterized and compared with numerical modeling by solving Maxwell's equations and calculating the back reflection spectrum using the bidirectional beam propagation method (BiBPM). Experimental results validate our numerical analysis, allowing for the estimation of inscription parameters such as the ac index modulation change, and the wavelength, position and relative strength of each significant resonance peak. We also present results on temperature and refractive index measurements showing potential for sensing applications.

Polymer fiber bragg gratings

This chapter deals with gratings recorded in polymeric optical fibers (POFs); predominantly those based on poly (methyl methacrylate) (PMMA). We summarize the different mechanical and optical properties of POFs which are relevant to the application of POF Bragg gratings and discuss the existing literature on the subject of the UV photosensitivity of PMMA. The current state of the art in POF grating inscription is presented and we survey some of the emerging applications for these devices. © 2011 Bentham Science Publishers Ltd. All rights reserved.

Novel optical chemsonsor based on etched D-fiber bragg gratings

A novel optical chemsensor concept based on the cladding etched Bragg gratings in D-fiber is demonstrated. Two etched devices have been used to measure the concentrations of sugar solution, giving sensitivity as high as 0.02nm/%.

Generation of infrared surface plasmon resonances with high refractive index sensitivity utilizing tilted fiber Bragg gratings

We demonstrate the use of tilted fiber gratings to assist the generation of localized infrared surface Plasmons with short propagation lengths and a sensitivity of dλ/dn = 3365 nm in the aqueous index regime. It was also found that the resonances could be spectrally tuned over 1000 nm at the same spatial region with high coupling efficiency (in excess of 25 dB) by altering the polarization of the light illuminating the device. © 2007 Optical Society of America.

Femtosecond inscription of superimposed, non-overlapping fibre Bragg gratings

A method for direct inscription of fibre Bragg gratings laterally separated by inscription in separate segments of the fibre core is demonstrated for the first time.

Theory of parabolic pulse generation in tapered fiber

We examine similarities and differences between high-power parabolic pulse generation in an active medium and in tapered fiber with decreasing normal dispersion. Using a realistic tapered fiber design, we demonstrate the possibility of parabolic pulse generation without an external pump and determine the limitations of this approach. © 2007 Optical Society of America.

Bend sensing by measuring the resonance splitting of long-period fiber gratings

An application of long-period fiber gratings (fabricated in standard fiber) as bend sensors is reported. A simple model, taking account of the strain and compression in the fiber cladding, is used to calculate the splitting of the cladding modes and is found to be in excellent agreement with the experimental results. Over 80 nm resonance splitting was observed under a 5.6 m-1 bend curvature giving a bend sensitivity of 14.5 nm/(m-1), the best obtained data so far. © 2001 Elsevier Science B.V.

Blank beam fabrication of regenerated type IA gratings

We demonstrate an idealized method for the fabrication of regenerated type IA fibre Bragg gratings using commonly available apparatus. We use this technique to show that gratings written in the same fibre with the same period may have central wavelengths which are 14.4 nm apart and have an + 11.5% and - 1.2% difference in temperature and strain coefficients, respectively. We use these results to show that temperature compensated dual grating sensor heads, of an arbitrary length, may be quickly and consistently manufactured. © 2004 IOP Publishing Ltd.

Fiber Bragg gratings inscribed using 800nm femtosecond laser and a phase mask in singleand multi-core mid-IR glass fibers

For the first time, Fiber Bragg grating (FBG) structures have been inscribed in single-core passive germanate and three-core passive and active tellurite glass fibers using 800 nm femtosecond (fs) laser and phase mask technique. With fs peak power intensity in the order of 10(11)W/cm(2), the FBG spectra with 2nd and 3rd order resonances at 1540 and 1033 nm in the germanate glass fiber and 2nd order resonances at approximately 1694 and approximately 1677 nm with strengths up to 14 dB in all three cores in the tellurite fiber were observed. Thermal responsivities of the FBGs made in these mid-IR glass fibers were characterized, showing average temperature responsivity approximately 20 pm/ degrees C. Strain responsivities of the FBGs in germanate glass fiber were measured to be 1.219 pm/microepsilon.

Spectral modification of type IA fibre Bragg gratings by high-power near-infrared lasers

We report the first experimental measurements on the spectral modification of type IA fibre Bragg gratings, incorporated in an optical network, which result from the use of high-power, near-infrared lasers. The fibre grating properties are modified in a controlled manner by exploiting the characteristics of the inherent 1400 nm absorption band of the optical fibre, which grows in strength during the type IA grating inscription. If the fibre network is illuminated with a high-power laser, having an emission wavelength coincident with the absorption band, the type IA centre wavelength and chirp can be modified. Furthermore, partial grating erasure is demonstrated. This has serious implications when using type IA gratings in an optical network, as their spectrum can be modified using purely optical methods (no external heating source acts on the fibre), and to their long-term stability as the grating is shown to decay. Conversely, suitably stabilized gratings can be spectrally tailored, for tuning fibre lasers or edge filter modification in sensing applications, by purely optical means. © 2006 IOP Publishing Ltd.

Investigations on birefringence effects in polymer optical fiber Bragg gratings

Step-index polymer optical fiber Bragg gratings (POFBGs) and microstructured polymer optical fiber Bragg gratings (mPOFBGs) present several attractive features, especially for sensing purposes. In comparison to FBGs written in silica fibers, they are more sensitive to temperature and pressure because of the larger thermo-optic coefficient and smaller Young's modulus of polymer materials. (M)POFBGs are most often photowritten in poly(methylmethacrylate) (PMMA) materials using a continuous-wave 325 nm HeCd laser. For the first time to the best of our knowledge, we study photoinduced birefringence effects in (m)POFBGs. To achieve this, highly reflective gratings were inscribed with the phase mask technique. They were then monitored in transmission with polarized light. For this, (m)POF sections a few cm in length containing the gratings were glued to angled silica fibers. Polarization dependent loss (PDL) and differential group delay (DGD) were computed from the Jones matrix eigenanalysis using an optical vector analyser. Maximum values exceeding several dB and a few picoseconds were obtained for the PDL and DGD, respectively. The response to lateral force was finally investigated. As it induces birefringence in addition to the photo-induced one, an increase of the PDL and DGD values were noticed. © 2014 Copyright SPIE.