Selective excitation of parabolic-index optical fibers by Gaussian beams

Saijonmaa, J.; Sharma, Awuashilal B.; Halme, Seppo J.

doi:10.1364/ao.19.002442

Cited by 40 publications

(28 citation statements)

References 5 publications

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“…Figure 12 (right) shows the predicted coupling efficiency into the two modes as a function of beam offset in the two lateral dimensions. The result strikingly shows that scan position in the cone aperture strongly influences efficiency of the modes, a result that was insensitive to IS length (lengths from 10 μm to 80 μm were investigated) and consistent with the literature for conventional optical fibers [54]. As shown in the figure, when the scan beam is near the cone aperture center (x and y offset near zero), coupling efficiency of LP 01 is greater and when displaced horizontally (x offset) LP 11 is greater.…”

Section: Influence Of the Ao-oct Scan Pattern On Excitation Of Cone Msupporting

confidence: 87%

“…It is well established that mode excitation in optical waveguides is sensitive to the launch conditions of the illumination beam, including lateral offset from fiber core center, tilt, width, and wavefront curvature [54,55]. The latter three conditions are fixed in our experiment due to the eye geometry and our focusing protocol.…”

Section: Influence Of the Ao-oct Scan Pattern On Excitation Of Cone Mmentioning

confidence: 99%

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Modal content of living human cone photoreceptors

Liu

Kocaoglu

Turner

et al. 2015

Biomed. Opt. Express

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Decades of experimental and theoretical investigations have established that photoreceptors capture light based on the principles of optical waveguiding. Yet considerable uncertainty remains, even for the most basic prediction as to whether photoreceptors support more than a single waveguide mode. To test for modal behavior in human cone photoreceptors in the near infrared, we took advantage of adaptive-optics optical coherence tomography (AO-OCT, λc = 785 nm) to noninvasively image in three dimensions the reflectance profile of cones. Modal content of reflections generated at the cone inner segment and outer segment junction (IS/OS) and cone outer segment tip (COST) was examined over a range of cone diameters in 1,802 cones from 0.6° to 10° retinal eccentricity. Second moment analysis in conjunction with theoretical predictions indicate cone IS and OS have optical properties consistent of waveguides, which depend on segment diameter and refractive index. Cone IS was found to support a single mode near the fovea (≤3°) and multiple modes further away (>4°). In contrast, no evidence of multiple modes was found in the cone OSs. The IS/OS and COST reflections share a common optical aperture, are most circular near the fovea, show no orientation preference, and are temporally stable. We tested mode predictions of a conventional step-index fiber model and found that in order to fit our AO-OCT results required a lower estimate of the IS refractive index and introduction of an IS focusing/tapering effect.

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Section: Influence Of the Ao-oct Scan Pattern On Excitation Of Cone Msupporting

confidence: 87%

Section: Influence Of the Ao-oct Scan Pattern On Excitation Of Cone Mmentioning

confidence: 99%

Modal content of living human cone photoreceptors

Liu

Kocaoglu

Turner

et al. 2015

Biomed. Opt. Express

View full text Add to dashboard Cite

show abstract

“…9 differs noticeably. It can be shown analytically that for an infinite parabolic profile there exists an excitation spot size at each excitation radius which inserts the maximum power into the most excited mode group [8,9]. Our calculations indicate that these results are approximately valid for finite radius fiber profiles although slight differences appear at large radii due to the presence of the cladding region.…”

Section: Experimental Considerationsmentioning

confidence: 56%

Correcting Multimode Fibers Profiles with Differential Mode Delay

Stoltz¹,

Yevick²

1983

Journal of Optical Communications

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We employ a numerical method based on direct integration of the scalar wave equation to study differential mode delay in perturbed near-optimal multimode fibers. At the same time, we investigate the validity of a simple geometrical optics method due to Petermann for determining the refractive index profile from the group velocities of the fiber's modegroups in the presence of strong ellipticity-induced mode coupling. While this method is approximate in nature, if we combine the method with our wave equation analysis, we can determine a new type of optimal cladded fiber profile. A further analysis indicates that low frequency profile ripple can be accurately detected with the method. Near the profile center however, the resolution falls off sharply.

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“…The mode-field diameter (MFD) of the SMF used is about 60% of the MFD of the fundamental mode (HE11) of the GI-MMF. This choice is a practical compromise for exciting nearly as few PMGs as possible for different offset positions [10]. The MFD of the SMF is around 6.9 μm (7.6 μm) at 850 nm (940 nm), while the MFD of the HE11 mode of the GI-MMF is around 11.6 μm (12 μm) at 850 nm (940 nm).…”

Section: Spatial-spectral Multiplexing In Gi-mmfsmentioning

confidence: 99%

Scaling multimode fibre IM/DD transmission capacity through spatial-spectral multiplexing

Tsekrekos

Varithimiadis

Kassos

et al. 2016

2016 18th International Conference on Transparent Optical Networks (ICTON)

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Data centre connections can greatly benefit from parallel transmission channels on one multimode fibre (MMF). Shortwave wavelength division multiplexing (SWDM) achieves parallel transmission through spectral multiplexing. Furthermore, MMFs offer a spatial dimension that should be exploited to increase parallel transmission, albeit in a cost-effective way. In this paper, it is shown that SWDM and spatial multiplexing can be combined in intensity modulation and direct detection MMF transmission systems that use selective offset excitation and mode-selective spatial filtering. Keywords: space division multiplexing, wavelength division multiplexing, multimode fibre, data centre network INTRODUCTIONIntra-data-centre optical connections are extensively employing graded-index (GI) multimode fibres (MMFs). Such MMF connections do not normally exceed a 500-m reach and should support the Gbps needs of the massive data centre networks. To achieve transmission of 100 Gbps and beyond, the following approaches have been considered: parallel optics in terms of parallel MMFs and MPO connectors, using advanced modulation formats such as pulse amplitude modulation and discrete multitone, and introducing shortwave wavelength division multiplexing (SWDM) by extending the 850-nm window and employing wideband MMFs [1], [2]. These approaches lead to solutions based on intensity modulation and direct detection (IM/DD). However, it is also the case that the MMF modes can be exploited by applying space division multiplexing (SDM) techniques. This can have significant advantages such as increasing the bit-rate-distance product, or reducing the number of parallel MMFs required. Applying SDM with IM/DD on GI-MMFs is possible and can be realized with selective offset excitation and mode-selective spatial filtering (MSSF) [3], [4].In this paper, we explore the application of IM/DD SDM with offset excitation and MSSF on 50/125 μm GIMMFs in a SWDM scenario. This scenario would require wavelength-selective optical filters that do not impact the mode power distribution that forms each spatial channel. This requirement can be met by WDM filters based on free-space optics and thin film filters [5]. It remains, though, crucial to investigate the application of SDM in terms of offset excitation and MSSF over the wavelength range proposed for SWDM. It is shown here that this IM/DD SDM approach can apply similarly on each SWDM channel, although the mode volume of the GI-MMF varies significantly within the SWDM wavelength range. Furthermore, the case of two IM/DD SDM channels can be realized without any additional signal processing requirements, presenting a very simple and straightforward scenario.

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Selective excitation of parabolic-index optical fibers by Gaussian beams

Cited by 40 publications

References 5 publications

Modal content of living human cone photoreceptors

Modal content of living human cone photoreceptors

Correcting Multimode Fibers Profiles with Differential Mode Delay

Scaling multimode fibre IM/DD transmission capacity through spatial-spectral multiplexing

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