Photonic Crystal Mikaelian Lenses and Their Potential Use as Transverse Focusing Elements in Microstructured Fibers

Baghdasaryan, Tigran; Geernaert, Thomas; Thienpont, Hugo; Berghmans, Francis

doi:10.1109/jphot.2013.2274763

Cited by 14 publications

(8 citation statements)

References 45 publications

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“…Filling the air holes with index matching liquid and tapering of the MOF have been proposed as solutions to mitigate against their detrimental effect on grating writing [15]- [18]. New MOF designs allowing efficient light delivery to the core have been proposed as well [19]- [21]. The amount of experimental reports on FBG inscription with IR femtosecond pulses in MOFs is limited [16], [17], [22], [23] but most of these emphasize the importance of the angular orientation of the fiber relative to the writing beam.…”

Section: Introductionmentioning

confidence: 99%

The role of highly non-linear index change mechanism during femtosecond grating writing in microstructured optical fibers

et al. 2015

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New methods for fiber Bragg grating inscription in optical fibers use femtosecond laser sources, which can induce refractive index changes even in non-photosensitive fibers and which allow achieving gratings that remain stable at high temperatures. The index change takes place as a result of a highly non-linear multi-photon absorption process. Although such gratings were successfully inscribed in conventional fibers, there are still challenges involved when attempting to fabricate femtosecond gratings in microstructured optical fibers (MOFs). The air holes are usually impeding the delivery of optical power to the core region, which results in a lower grating writing efficiency.In this paper we report on our numerical computations that aim to estimate the influence of the MOF's holey cladding on the induced index change during interferometric grating inscription with an infrared (IR) femtosecond laser source. For high power femtosecond laser pulses at 800 nm the refractive index change in silica stems from a highly non-linear five photon absorption process. Using empirical data on refractive index changes from literature and intensity distribution data from our transverse coupling simulations we propose an approach to reconstruct the non-linear refractive index modification in the MOF core region. We then study the influence of the MOF angular orientation on the induced index change and we model the impact of MOF tapering as a possible way to increase the grating writing efficiency.

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Section: Introductionmentioning

confidence: 99%

The role of highly non-linear index change mechanism during femtosecond grating writing in microstructured optical fibers

et al. 2015

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“…After the parameter study of the previous section, we will now design the air cladding of the MOF in such a way that it will focus the transversely propagating grating writing beam into the core region [23], [26], [27]. This can be achieved by implementing a photonic crystal Mikaelian lens (PCML), which is a specific type of gradient index lens in a photonic crystal lattice.…”

Section: Dedicated Mof With Focusing Claddingmentioning

confidence: 99%

Opportunities for designing microstructured optical fibers for efficient femtosecond laser grating inscription

et al. 2015

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Microstructured optical fibers (MOFs) are a major achievement in the field of optical fiber technology. Owing to their unprecedented design flexibility, MOFs have found numerous applications in various fields of photonics. By adapting the parameters of the holey cladding, MOFs with tailored dispersion properties, large mode area, endlessly single mode operation and high non-linear response can be designed and fabricated. This paper deals with designing MOFs with a specific microstructure that would allow increasing the efficiency with which fiber gratings can be photo-inscribed in a MOF. The air holes are usually impeding the delivery of optical power to the core region, which results in a lower grating writing efficiency. This problem is exacerbated when using IR femtosecond laser sources for the inscription, as the induced refractive index changes stem from a highly non-linear multi-photon absorption process and are hence very dependent on the optical intensity that actually reaches the MOF core. In this paper we first study regular hexagonal lattice MOFs to find a range of lattice parameters that would facilitate femtosecond grating inscription, considering the non-linear nature of the index change. To assess the influence of the microstructured cladding on the transverse delivery of light to the core region, we introduce a figure of merit to which we refer as 'transverse coupling efficiency' (TCE). Second, we evaluate the index changes that would be obtained when implementing a special type of holey structure that acts as a transversely focusing microstructure -known as Mikaelian lens -in the cladding of the MOF.

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“…The idea is to have the average refractive index of such a primitive cell to vary in accordance with the Mikaelian formula introduced above. More details on the design procedure for each of those four structures can be found in [25].…”

Section: Focusing Properties Of Photonic Crystal Mikaelian Lenses In mentioning

confidence: 99%

“…Most fiber grating inscription techniques rely on side illumination of the fiber in order to induce a refractive index modification in the core region exploiting either the photosensitivity of the core material to UV light or non-linear absorption processes [17]. We have previously also reported on the issue of transverse light coupling to the MOF core and on possible ways to increase efficient grating writing in MOFs [16,[23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Photonic crystal lenses for transverse focusing of laser illumination in microstructured optical fibers

et al. 2014

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Transverse light propagation through the air holed cladding of microstructured optical fibers (MOFs) has recently attracted interest owing to its importance for several applications such as fiber grating writing, particle trapping in hollow core fibers, all optical switch devices, etc. The air holes in the MOF cladding region impede efficient delivery of transversely propagating light to the core region when the fiber is illuminated from the outside. To overcome this problem we designed MOFs with a gradient air holed cladding structure that will actually focus transversely propagating light to the fiber core. We used photonic crystal Mikaelian lenses (PCML) as focusing gradient media in the holey cladding. First, we considered and compared several PCML types with varying air hole diameter and air hole pitch, in both hexagonal and rectangular lattices. We studied the design rules of those structures and we carried out a frequency response analysis to identify the most efficient operational regions of the PCMLs. The polarization properties of the considered structures were investigated as well. Finally, we analyzed the transverse coupling properties of the MOF equipped with such a PCML structure in the cladding and we obtained a fiber that clearly focuses transversely incident light to its core region with a normalized focal intensity up to 18, whilst exhibiting good guiding properties.

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Photonic Crystal Mikaelian Lenses and Their Potential Use as Transverse Focusing Elements in Microstructured Fibers

Cited by 14 publications

References 45 publications

The role of highly non-linear index change mechanism during femtosecond grating writing in microstructured optical fibers

The role of highly non-linear index change mechanism during femtosecond grating writing in microstructured optical fibers

Opportunities for designing microstructured optical fibers for efficient femtosecond laser grating inscription

Photonic crystal lenses for transverse focusing of laser illumination in microstructured optical fibers

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