Selective opening of airholes in photonic crystal fiber

Abstract

We introduce a femtosecond-laser-based technique for selective opening of airholes in photonic crystal fibers (PCFs). With this technique, selective filling and inflation of the airholes in the PCF cladding are demonstrated. The technique may find important applications in tailoring or altering PCF characteristics and make it possible to seamlessly integrate various components/functions into PCFs. © 2010 Optical Society of America OCIS codes: 060.2310, 060.2340, 060.2400.The photonic crystal fiber (PCF) with a periodic array of airholes running along its length has attracted significant interest recently [1,2]. The precise arrangement of airholes and their index profiles throughout the cladding region allow various types of PCFs with novel properties to be designed. Endlessly single-mode operation, lightguidance in hollow air-core, and very high nonlinearity and birefringence are a few of the novel properties of PCFs that may not be achieved with conventional singlemode fibers (SMFs) [3,4]. Apart from the high level of flexibility in the PCF fabrication process, novel functionality may be added to PCFs by postprocessing [5][6][7][8].Techniques for postprocessing PCFs include tapering and inscription of periodic structures that are widely adopted for conventional fibers and selective filling or pressurization of airholes, which is unique to PCFs. Examples of PCF postprocessing include selective filling of airholes with an index tunable polymer to realize birefringence tunability [5], inflating/deflating airholes to reduce splice loss and to achieve in-fiber mode conversion [6,7], and infiltrating submicrometer gold into a selected hole of a polarization maintaining PCF to achieve polarizationand wavelength-dependent transmission [8]. All these examples rely on the selective opening or closing of airholes within the cladding region. We previously demonstrated selective filling of PCFs by using a conventional fusion splicer [9], but it lacks the freedom to choose arbitrary airholes for filling. In this Letter, we report a technique for selective opening of airholes and demonstrate the selective filling and inflation of arbitrary holes in the PCF cladding. Our approach starts by sealing all the airholes of a PCF by a thin layer of silica and then drilling individual holes through the layer by a femtosecond IR laser (fs-laser). With reference to Fig. 1(a), the PCF is first spliced to a conventional SMF by a fusion splicer. The SMF is then cleaved at a location about 30 μm from the splicing point. The splicing parameters are adjusted so that airhole deformation during splicing is minimized, while the splice is reasonably strong to survive the cleaving [10]. The thin layer of SMF seals all the airholes, but the end facet of the PCF beneath the thin silica layer can be clearly viewed under a microscope, allowing an individual airhole to be selected and located. Figure 1(b) shows the microscopic view of the end facet of a large-mode-area PCF [LMA-10, NKT Photonics A/S, scanning electron micrograph (SEM) photograph is sho...

Temperature Sensor Based on an Asymmetric Two-Hole Fiber Using a Sagnac Interferometer

“…As we mentioned before, the liquid insertion in MSF improves the temperature sensitivity. However, they also have several drawbacks that limit their use such as the cost, preform design, hole-matrix fabrication in the MSF structure, and complex technique in the partial or total filling mechanism [31,32].…”

Highly birefringent suspended-core photonic microcells for refractive-index sensing

“…2(a), are selectively opened by use of a femtosecond laser-assisted selective opening technique. 12 The other end of the PCF is spliced to a single mode fiber (SMF) to seal all the air-holes at this end. Second, high pressure gas is applied to the four selected air-columns of the PCF via the openings.…”

Partially liquid-filled hollow-core photonic crystal fiber polarizer

“…The microstructured holey cladding provides extra degrees of freedom in tailoring the waveguiding properties of the fibers and a number of PCFs with unique optical properties such as endlessly singlemode, high-birefringence, and high-nonlinearity have been fabricated [1,2]. In addition to the flexibility in fiber fabrication, the optical properties of PCFs can also be modified by post processing stock PCFs by, for example, selectively filling air holes with a liquid [3][4][5] or a gas [6], modifying the fiber geometry with a CO 2 laser [7,8] or fiber tapering [9] and incorporating quantum dots into the fibers [10]. In particular, selective filling is considered an important way to modify PCFs to achieve unique optical properties [3][4][5][6].…”

“…In addition to the flexibility in fiber fabrication, the optical properties of PCFs can also be modified by post processing stock PCFs by, for example, selectively filling air holes with a liquid [3][4][5] or a gas [6], modifying the fiber geometry with a CO 2 laser [7,8] or fiber tapering [9] and incorporating quantum dots into the fibers [10]. In particular, selective filling is considered an important way to modify PCFs to achieve unique optical properties [3][4][5][6]. A number of functional PCFs, such as birefringent-tunable PCF [3] and bending-sensitive PCF [5], are realized by the selective filling of the air holes.…”

“…In [4], selective filling was mainly based on the different filling speeds that depend on the sizes of air holes and the technique was limited to filling PCFs with different air hole sizes. In [5,6], selective filling was achieved by use of a femtosecond IR laser to selectively open some of the air holes, which involves complex laser processing and a higher experimental cost.…”