Tuomo Ritari

Gas sensing using air-guiding photonic bandgap fibers

We report on experimental studies of gas sensing using air-guiding photonic bandgap fibers. The photonic bandgap fibers have at one end been spliced to standard single mode fibers for ease of use and improved stability

Experimental study of polarization properties of highly birefringent photonic crystal fibers.

We analyze experimentally the polarization properties of highly nonlinear small-core photonic crystal fibers (PCFs) with no intentional birefringence. The properties of recently emerged polarization maintaining PANDA PCFs are also investigated. The wavelength and temperature dependence of phase and group delay of these fibers are examined in the telecommunications wavelength range. Compared to a standard PANDA fiber, the polarization characteristics and temperature dependence are found to be qualitatively different for both types of fibers.

Supercontinuum generation in large mode-area microstructured fibers

Supercontinuum generation in large mode-area microstructured fibers is demonstrated by launching into the fiber ns pulses from a passively Q-switched Nd:YAG laser. The special properties of these fibers open the way to compact, single-mode, high-power supercontinuum sources with a low divergence of the output beam. The nonlinear phenomena leading to the formation of the broad spectrum are also described.

Hollow-core photonic crystal fiber with square lattice

Most works on photonic crystal fibers with a photonic bandgap are concerned with structures made of silica glass with a hexagonal lattice. However, there are many other possible choices for the crystal structure of the fiber. In this paper, we study the optical properties of photonic bandgaps in a hollow-core photonic crystal fiber with a square lattice fabricated from multi-component glass. A composition of oxides was chosen to obtain a refractive index contrast higher than in fused silica fibers. The core size of the fiber is 11 microns and the cladding is made of an array of 17 x 17 air capillaries. A full-vector mode solver using the biorthonormal basis method is employed to analyze the modal properties of the fiber. We verify the guiding properties of the fiber by FDTD simulations. The transmission properties for several lengths of the fiber were measured by using broadband light from a nanosecond-pulse supercontinuum source and an optical spectrum analyzer. Preliminary results show that light is guided around 1650 nm. Possible modifications of the structure and potential applications will be discussed.

Experimental investigation of wavelength and temperature dependence of phase and group birefringence in photonic crystal fibers

Small-core photonic crystal fibers are often strongly birefringent, and consequently lend themselves to polarization maintaining applications or to polarimetric fiber sensors. For both types of use, it is important to have detailed knowledge not only of the fibers polarization characteristics, but also of its sensitivity to changes in environmental conditions. For the first time, experimental results of the dependence of phase and group delay on temperature are shown for the important 1500-1600 nm wavelength range. Both the polarization characteristics and its temperature dependence are found to be qualitatively different in a photonic crystal fiber compared to a standard PANDA fiber.

Generation of wide supercontinuum in a weakly nonlinear microstructured fiber

We report on the generation of a wideband supercontinuum in a microstructured fiber with a very weak nonlinearity. This type of fiber allows for producing broadband sources with higher spectral density than with narrow-core fibers.

Supercontinuum and gas cell in a single microstructured fiber

We exploit both the high nonlinearity and holey structure of microstructured fibers to combine an ultra-broadband light source and a gas cell in a single microstructured fiber filled with acetylene.

Optical properties of photonic band gap fibers made of silicate glass

We report on the fabrication of photonic band gap fiber made of multicomponent glass. This fiber has a hexagonal lattice made of an array of 17 x 17 air capillaries with a lattice constant Λ=6.0 μm and air holes of diameter equal to d=5.7 μm. A hollow core is created by omitting seven central microcapillaries and have diameter of 16 μm. Characterization results show that the fiber can guide the light in the visible range with a central wavelength of 510 nm. The transmission properties for the presented PCFs are measured by using a broadband light source and an optical spectrum analyzer. In the paper we discuss also possible future modifications of the structures and their potential applications.

Photonic bandgap fibers: optical properties and device applications

Recently emerged photonic bandgap fibers with their extraordinary optical properties offer many interesting device applications. We present the status of our work on the use of this kind of a fiber in sensing and wavelength referencing both in the 1300 and 1500 nm wavelength regions. The photonic bandgap fibers are spliced to standard single-mode fibers at input end for easy coupling and filled with gas through the other end placed in a vacuum chamber. The technique is applied to measure absorption lines of strongly absorbing gases such as acetylene and hydrogen cyanide by employing tunable lasers and LEDs as light sources. The measurement of weakly absorbing gases such as methane and ammonia is also explored. To realize a permanent wavelength reference sealing of a photonic bandgap fiber using index-matching UV-curable adhesive is demonstrated.

Birefringent microstructured fibers: Properties and applications

Development of sophisticated techniques for manufacturing microstructured fibers has enabled the production of fibers with precisely controlled structures. For instance, fibers with very low or high birefringence have been demonstrated. We present the status of our work on characterization of the dispersion properties of birefringent microstructured fibers and discuss their use for generation of supercontinuum radiation.