High Numerical Aperture Fiber Research Articles

Fiber based polarization filter for radially and azimuthally polarized light

We demonstrate a new fiber based concept to filter azimuthally or radially polarized light. This concept is based on the lifting of the modal degeneracy that takes place in high numerical aperture fibers. In such fibers, the radially and azimuthally polarized modes can be spectrally separated using a fiber Bragg grating. As a proof of principle, we filter azimuthally polarized light in a commercially available fiber in which a fiber Bragg grating has been written by a femtosecond pulsed laser.

Fusion Splicing Holey Fibers and Single-Mode Fibers: A Simple Method to Reduce Loss and Increase Strength

We demonstrate a novel method for low-loss splicing Ge-doped holey fibers (HF) with subwavelength core size and high numerical aperture fibers by using a conventional fusion splicer. We found that a large overlap distance of the fibers during fusion would decrease the splice loss and increase the splice strength. The lowest splice loss achieved for a fiber with a core diameter of 1.27 mu m and air-filling fraction of >0.95 was ~ 1 dB at 1550 nm, with a bend failure radius of 0.8 cm. With the same method, we also observed improvement in terms of loss and strength with larger core size HF.

Integration of femtosecond laser written optical waveguides in a lab-on-chip

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica lab-on-chip (LOC). We fabricate high quality waveguides intersecting the microfluidic channels and use them to optically address with high spatial selectivity their content. Fluorescence from the photoexcited volume is efficiently collected at a 90 degrees angle by a high numerical aperture fiber, resulting in a compact and portable setup. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs, fabricated with standard techniques. By taking advantage of the unique three-dimensional capabilities of femtosecond laser writing, more complex functionalities, such as splitters or Mach-Zehnder interferometers, can be implemented.

Optical sensing in microfluidic lab-on-a-chip by femtosecond-laser-written waveguides

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica capillary electrophoresis chip. High-quality waveguides crossing the microfluidic channels are fabricated and used to optically address, with high spatial selectivity, their content. Fluorescence from the optically excited volume is efficiently collected at a 90 degree angle by a high numerical aperture fiber, resulting in a highly compact and portable device. To test the platform we performed electrophoresis and detection of a 23-mer oligonucleotide plug. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs fabricated with standard techniques.

A 5-$\mu$m-Thick SOI Waveguide With Low Birefringence and Low Roughness and Optical Interconnection Using High Numerical Aperture Fiber

A 5-m-thick silicon-on-insulator waveguide possessing low birefringence of and 9-nm lithography roughness is investigated using arrayed waveguide grating and an atomic force microscope. Instead of complex processing using a 3-D mode size converter, the high numerical aperture fiber is utilized as the bridge between the corresponding waveguide and single-mode fiber (SMF-28) to obtain a competitive coupling loss of 0.4 dB.

采用基本空间充填模式的掺铒多孔光纤分析

Erbium-doped holey fiber with hexagonal lattice was modeled by using effective index method. In order to calculate the equivalent step index of the periodic structure of the cladding holey optical fiber, all-vectorial fundamental space filling mode approach was utilized. By using EH11 mode, we have numerically solved the rate equations of a three-level pumping scheme for a fiber laser. The obtained results have shown a good agreement with the other experimental results, recently. The results have predicted amplifiers with gain efficiencies as high as 10 dB/mW. OCIS codes: 060.2310, 060.2410, 060.2320, 140.3500, 140.4480. doi: 10.3788/COL20080609.0644. In erbium doped fiber amplifiers (EDFAs), to obtain high gain efficiency one needs to use fibers with high numerical aperture (NA) to achieve the maximum population inversion of the erbium ions. It is useful to confine the erbium ions to the central part of the core to enforce the pumping light propagating with the fundamental HE11 mode [1,2] . Germanium-doping, which is used in the core of high NA fiber, reduces the emission bandwidth of the Er 3+ ions and limits its concentrations. This results in narrower gain bandwidths and increases the device

A MOX fuel attribute monitor

Euratom performs safeguards monitoring of Fresh MOX fuel for domestic power production in the European Union. Video cameras monitor the reactor storage ponds. If video surveillance is lost for a certain amount of time a measurement is required to verify that no fuel was diverted. The attribute measurement to verify the continued presence of MOX fuel is neutron emission. Ideally this measurement would be made without moving or handling the fuel rod assembly. A prototype attribute measurement system was made using scintillating neutron sensitive glass waveguides developed by Pacific Northwest National Laboratory. Short lengths (5–20 cm) of the neutron sensitive fiber were mechanically spliced to 15 m lengths of commercial high numerical aperture fiber optic cable (Ceramoptec Optran Ultra 0.44). The light detector is a Hamamatsu R7400P photomultiplier tube. An electronics package was built to use the sensors with a GBS Elektronik MCA-166 multichannel analyzer and user interface. The MCA-166 is the system most commonly used by Euratom inspectors. It can also be run from a laptop computer using Maestro (Ortec) or other software. A MCNP model was made to compare to measurements made with several neutron sources including NIST traceable 252Cf.

Narrowband, polarization insensitive all-fiber acousto-optic tunable bandpass filter

We demonstrate an all-fiber acousto-optic tunable bandpass filter exhibiting narrow optical bandwidth and negligible polarization dependence by employing a novel ultraviolet (UV)-induced core-mode blocker written in a high numerical aperture (NA) fiber. It was demonstrated that the device had the measured 3-dB optical bandwidth of 0.65 nm, the polarization-dependent center-wavelength splitting of 0.05 nm and the extinction ratio of -22dB at the wavelength around 1550 nm. The details of the transmission characteristics and the loss mechanism of the core-mode blocking element inscribed in the high NA fiber are discussed.

Fiber Bragg grating temperature sensor for practical use

Fiber Bragg grating (FBG) is a promising measurement technology for future sensor system applications. Little attention has been given to the FBG sensor housing, however it is important that the FBG is embedded in a conventional electrical sensor housing so that it may be installed easily in instrumentation systems. We have experimentally fabricated a practical pass-through type FBG temperature sensor which is embedded in the conventional thermocouple housing. A small radius U-turn fiber spliced to the FBG is placed inside the top of a stainless sheath. Employing a high numerical aperture fiber with polyamide recoating, we have determined that the bending loss of the small radius U-turn fiber and heat resistance is less than 0.1 dB and up to 250°C respectively. The wavelength shift of this sensor due to temperature change is 10.3 pm/°C equal to that of general FBG. Consequently the practical use of this sensor has been confirmed.

Reduction of Bragg Grating-Induced Coupling to Cladding Modes

We discuss fiber designs that have been suggested for the reduction of Bragg-grating-induced coupling to cladding modes. The discussion is based on a theoretical approach that includes the effect of asymmetry in the UV-induced index grating, made by UV-side writing. Experimental results from gratings in a depressed-cladding fiber are compared with simulations. The model gives good agreement with the measured transmission spectrum and accounts for the pronounced coupling to asymmetrical cladding modes, even when the grating is written with smallest possible blaze. The asymmetry causing this is accounted for by the unavoidable attenuation of the UV light. It is found for the considered fiber designs that a high numerical-aperture fiber increases the spectral separation between the Bragg resonance and the onset of cladding-mode losses. A depressed-cladding fiber reduces the coupling strength to the lower order cladding modes, and the UV-sensitive cladding design reduces the cladding-mode coupling loss. The analysis suggests that the UV-sensitive cladding design is the most effective in reducing the cladding-mode-coupling losses.

Praseodymium-doped cadmium mixed halide glasses for 1.3 μm amplification

In the search for suitable glass hosts for 1300 nm amplification, the field has been narrowed to Pr-doped fluorozirconate, fluoroindate, cadmium mixed halide and sulphide glasses. This paper presents data identifying the cadmium mixed halide system as a leading candidate, based on the lifetime and quantum efficiency of the1G4 →3H5 fluorescence of Pr3+ in this system. Compositional studies to develop cladding and core glasses suitable for high numerical aperture fiber, as well as relevant physical and optical properties, are also discussed.

Erbium-doped optical fiber amplifiers pumped in the 660- and 820-nm bands

State-of-the-art erbium (Er)-doped optical fiber amplifiers (EDFA's) pumped in the 660- and 820-nm bands are described. We have demonstrated highly efficient EDFA's incorporating optimized 664- and 827-nm pump wavelengths and an Er-doped high numerical aperture (NA) fiber with thermally diffused expanded core (TEC) fiber ends. Gain coefficients of 3.8 and 1.3 dB/mW at respective wavelengths of 664 and 827 nm were achieved at a signal wavelength of 1535 nm. Noise figures of 3.1 and 4.1 dB at respective pump wavelengths of 670 and 827 nm were obtained at a signal wavelength of 1535 nm. A highly efficient Er-doped fiber amplifier module, in which an AlGaInP visible laser diode (LD) was used as the pump source, was successfully developed as a practical application of this technology. A maximum overall gain coefficient of 3.0 dB/mW was achieved at a signal wavelength of 1535 nm. The EDFA module realized a maximum overall signal gain of 33 dB at 1535 nm with a saturated output power of -1 dBm. A maximum saturated output power of 3.9 dBm was obtained at a signal wavelength of 1552 nm. The present EDFA design using a low-cost laser diode for optical disk memory use and a high NA Er-doped fiber has great potential for providing inexpensive, high-performance EDFA's.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dispersion Minimization in Dielectric Waveguides

The effect of dielectric dispersion on pulse transmission through singly clad, cylindrical fibers is formulated in terms of the effective group index for the waveguide. It is shown that two different solutions are possible for designing guides that give a minimum of distortion due to dispersion. One solution uses fibers with low numerical aperture made from glasses with low dispersion; here for sufficiently long wavelengths minimum distortion is possible while the guide parameters limit conduction to the lowest order mode. It is predicted, for example, that a pulse of radiation in the lowest order mode with a carrier wavelength of 1.06 micro can be conducted with minimum distortion by a fiber made from commercially available, low dispersion glass. In the other solution the fiber is designed so that the HE(11) mode provides an anomalous dispersive characteristic; this solution requires a high numerical aperture fiber with a core large enough to support the next higher order group of modes, namely the TE(01), TM(01), and HE(21) modes. For this second solution, it is shown that a dispersionless group index is possible for wavelengths at least as short as 0.77 micro.

Fiber Optics VII Image Transfer from Lambertian Emitters*

Light leakage between fibers for the particular case of their use with Lambertian emitters is discussed. The associated problems of the degree of optical contact between the fiber ends and the emitting source, and their effects on the over-all transmitting efficiency are considered in detail and results are presented for several representative emitters. A transmission theory of fibers based on meridional ray considerations alone is derived and shown to be adequate for high numerical aperture fibers. The general expressions, from which the simplified theory is deduced, are given in an appendix to the paper. Results are presented for an experimental system which has been constructed and tested. These results demonstrate that photometric gains of up to 40 or 140 are available when using a fiber optics cathode-ray tube in place of a standard tube and unit magnification f/1 and f/2.8 lens systems, respectively. The fusion processes entailed in the construction of such tubes and similar devices are considered. Fibers with a numerical aperture of 1.17 which retain their circular cross section during these processes are described.