We investigate the microhole collapse property of different photonic crystal fibers (PCFs) and its effect on the splice loss using an electric arc fusion splicer. The physical mechanism of the splice loss for different kinds of PCFs is studied, and a guideline for splicing these PCFs and conventional single-mode fibers (SMFs) is proposed. We demonstrate a low-loss fusion splicing of five different PCFs with SMFs, including large-mode PCF, hollow-core PCF, nonlinear PCFs, and polarization-maintaining PCF.

/pdf/fusion-splicing-photonic-crystal-fibers-and-conventional-2xqkw1tafm.pdf

Fusion Splicing Photonic Crystal Fibers and Conventional Single-Mode Fibers: Microhole Collapse Effect

This paper presents a systematic review of long period fiber gratings (LPFGs) written by the CO2 laser irradiation technique. First, various fabrication techniques based on CO2 laser irradiations are demonstrated to write LPFGs in different types of optical fibers such as conventional glass fibers, solid-core photonic crystal fibers, and air-core photonic bandgap fibers. Second, possible mechanisms, e.g., residual stress relaxation, glass structure changes, and physical deformation, of refractive index modulations in the CO2-laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the CO2-laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.

/pdf/review-of-long-period-fiber-gratings-written-by-co2-laser-19six9u5nt.pdf

Review of long period fiber gratings written by CO2 laser

Environmental monitoring has become essential in order to deal with environmental resources efficiently and safely in the realm of green technology. Environmental monitoring sensors are required for detection of environmental changes in industrial facilities under harsh conditions, (e.g. underground or subsea pipelines) in both the temporal and spatial domains. The utilization of optical fiber sensors is a promising scheme for environmental monitoring of this kind, owing to advantages including resistance to electromagnetic interference, durability under extreme temperatures and pressures, high transmission rate, light weight, small size, and flexibility. In this paper, the optical fiber sensors employed in environmental monitoring are summarized for understanding of their sensing principles and fabrication processes. Numerous specific applications in petroleum engineering, civil engineering, and agricultural engineering are explored, followed by discussion on the potentials of OFS in manufacturing.

A review on optical fiber sensors for environmental monitoring

A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is orga- nized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long-period gratings and interferometric structures; the fourth one reports applica- tions of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in pho- tonic crystal fibers for sensing. A brief review about splicing with photonic crystal fibers is also included.

/pdf/optical-sensing-with-photonic-crystal-fibers-2g41xr66t6.pdf

Optical sensing with photonic crystal fibers

We present experimental results on coupling to surface plasmon modes on gold nanowires selectively introduced into polarization-maintaining photonic crystal fibers. Highly polarization- and wavelength-dependent transmission is observed. In one sample 24.5 mm long, the transmission on and off resonance differs by as much as 45 dB. Near-field optical images of the light emerging from such a gold-filled fiber show light guided on the wire at surface plasmon resonances. Finite element simulations are in good agreement with the experimental results. These gold-filled fibers can be potentially used as in-fiber wavelength-dependent filters and polarizers and as near-field tips for sub-wavelength-scale imaging.

Polarization-dependent coupling to plasmon modes on submicron gold wire in photonic crystal fiber

Silica photonic crystal fiber (PCF) is a new type of fiber that has an array of microscopic air holes running along its length. Splicing PCF to standard single-mode fiber (SMF) is a challenging task, but it is also important because of the potential broad applications. Proper splicing of SMF to PCF is imperative in order to avoid collapsing of the PCF on the air holes; however, the two types of fiber require different laser powers for melting. A laser splicing system is developed to demonstrate its effectiveness at splicing between the large-mode-area PCF and SMF with low splice loss.

Development of a system for laser splicing photonic crystal fiber.

Splicing between single-mode fiber (SMF) and photonic crystal fiber (PCF) using a conventional electric-arc splicer is not easily achieved. It is reported, for the first time, that the condensation within the capillaries resulted in a bubble developed at the fiber ends in the midst of splicing. A novel and effective splicing technique using a CO/sub 2/ laser has successfully eliminated this limitation and a complete splicing process is achieved within 3-5 s. The splice losses have been recorded to be in the range of 1.3-2.8 dB; the high splice losses are possibly due to the field-mode discrepancy of the sampled PCF with a diameter of 100 /spl mu/m.

An effective splicing method on photonic crystal fiber using CO 2 laser

A strong resonance and extremely short length long-period grating (LPG) has been fabricated in a large-mode-area photonic crystal fiber (PCF) by use of a CO2 laser heat source. We believe that such a longperiod grating in pure silica PCF is the first example of a point-by-point technique. The fabrication method is simple and repeatable. The resulting LPG has been developed with eight periodic collapses within a 2.8-mmlong period of the fiber, which gives the strong resonance of core-cladding mode coupling. The lowest mode of LP01 is at a 1529.2-nm wavelength with a full width at half-maximum of ~0.7 nm and a resonance strength of -31.5 dB. The principal advantages of this LPG are that (1) it is temperature insensitive and stable, (2) the device is compact when it is packaged, and (3) it provides practical, low-cost all-fiber filters and PCF-based devices for optical fiber communications and sensing systems.

Strong resonance and a highly compact longperiod grating in a large-mode-area photonic crystal fiber.

Fiber Bragg grating (FBG) based rearrangeable nonblocking optical cross connects (OXC's) using multiport optical circulators are proposed in this letter. The use of multiport optical circulators instead of three-port circulators can be more efficient for large optical cross connects systems. Performance evaluations of proposed large dimension optical cross connects are investigated.

Fiber Bragg grating-based rearrangeable nonblocking optical cross connects using multiport optical circulators

We report the development and demonstration of a long-period grating refractometer. The principle of operation is based on in the use of a long-period grating that is structurally induced by a CO/sub 2/ laser, and where the resonance wavelengths are shifted by the refractive index of the medium surrounding the cladding of the long-period grating. The different concentrations for three types of solutions (ethylene glycol, salt, and sugar) were experimentally measured, and results show that, as a refractometer, this fiber-based device can not only differentiate chemicals based on their refractive index, but it can also become a concentration indicator of a particular chemical solution, and applied in the oil and petroleum industry.

M.K. Rao

Papers

Development of a system for laser splicing photonic crystal fiber.

An effective splicing method on photonic crystal fiber using CO 2 laser

Strong resonance and a highly compact longperiod grating in a large-mode-area photonic crystal fiber.

Fiber Bragg grating-based rearrangeable nonblocking optical cross connects using multiport optical circulators

A long-period grating refractometer: measurements of refractive index sensitivity