Focal ratio degradation: a new perspective

Haynes, Dionne; Withford, Michael J.; Dawes, Judith M.; Haynes, Roger; Bland-Hawthorn, Joss

doi:10.1117/12.788735

Cited by 12 publications

(6 citation statements)

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“…This method of polishing the fibre is time-consuming, however visual and interferometric inspection of the end normally shows it to be high quality. Haynes et al [8] have shown that the quality of the polish has a large effect on the FRD by comparing fibres with end face roughness of 245 nm and 6 nm rms. Figure 1 shows the typical finish which can be expected when a fibre is cleaved or polished.…”

Section: Introductionmentioning

confidence: 99%

The dependence of the properties of optical fibres on length

Poppett¹,

Allington‐Smith²

2010

Monthly Notices of the Royal Astronomical Society

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We investigate the dependence on length of optical fibres used in astronomy, especially the focal ratio degradation (FRD) which places constraints on the performance of fibre-fed spectrographs used for multiplexed spectroscopy. To this end we present a modified version of the FRD model proposed by Carrasco and Parry \cite{Carrasco1994} to quantify the the number of scattering defects within an optical fibre using a single parameter. The model predicts many trends which are seen experimentally, for example, a decrease in FRD as core diameter increases, and also as wavelength increases. However the model also predicts a strong dependence on FRD with length that is not seen experimentally. By adapting the single fibre model to include a second fibre, we can quantify the amount of FRD due to stress caused by the method of termination. By fitting the model to experimental data we find that polishing the fibre causes more stress to be induced in the end of the fibre compared to a simple cleave technique. We estimate that the number of scattering defects caused by polishing is approximately double that produced by cleaving. By placing limits on the end-effect, the model can be used to estimate the residual-length dependence in very long fibres, such as those required for Extremely Large Telescopes (ELTs), without having to carry out costly experiments. We also use our data to compare different methods of fibre termination.Comment: 10 pages, 7 figure

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Section: Introductionmentioning

confidence: 99%

The dependence of the properties of optical fibres on length

Poppett¹,

Allington‐Smith²

2010

Monthly Notices of the Royal Astronomical Society

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“…A common method to investigate FRD of fibers is the far field method with selective angular excitation also known as "laser injection method" by Carrasco [16], "inverse farfield method" by Ferwana [10] "parallel laser beam" by Haynes [17] and "collimated beam" by Yan [4] and "ring test" by Belland [2].…”

Section: Far Field Methods With Selective Angular Excitationmentioning

confidence: 99%

Characterization of multi-clad fibers: approaches to measure the beam divergence angle and its degradation in the fiber

Schönfeld,

Reul,

Raithel

et al. 2024

High-Power Laser Materials Processing: Applications, Diagnostics, and Systems XIII

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Multi-cladding (MC) fibers with undoped silica core and alternating highly fluorine doped and undoped silica cladding layers are a new standard for high power laser beam transmission. Such MC-fibers allow tailoring the output beam profile of a single laser source to the desired application.An important factor for these applications is to avoid additional scattering of the guided light in the different regions leading to an increased output divergence, so-called focal ratio degradation (FRD).In this work, we compare two possible measurement concepts to determine the beam divergence angle under controlled launch conditions to quantify FRD of MC fibers. One approach is the pinhole setup historically used in astronomy; another approach is the inverse far field method with selective excitation. The objective is to define a reliable setup for quality inspection.We show measurement results for FRD of MC fibers with both methods and evaluate the differences between the lightguiding sections. To our knowledge, this is the first time such data are presented. The objective described above is best fulfilled by a modified far field method with defined broad angular excitation.

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“…Then, by relying on the azimuthal scrambling of light within a fiber, we simulate a full light cone at an input f-ratio of f/3.65. This approach allows us to couple light into all the fibers simultaneously, and is conceptually similar to laser-based tests for FRD (Haynes et al 2008). The collimated light is filtered with a broad (∼ 100Å) bandpass filter centered at 500 nm.…”

Section: Methodsmentioning

confidence: 99%

“…(Haynes et al 2011) However, despite these challenges, several groups have quantified FRD via a number of different techniques. (Ramsey 1988;Craig et al 1988;Schmoll et al 1998;Avila 1998;Carrasco & Parry 1994;Schmoll et al 2003;Crause et al 2008;Murphy et al 2008;Haynes et al 2008;Brunner et al 2010;Poppett & Allington-Smith 2010a) FRD is typically defined as any increase in the output angle (i.e output f-ratio, hereafter f/out) of light when compared to the input angle. In an ideal fiber, the input f/ratio (f/in) will be preserved through the fiber, with no rays being scattered to larger output angles.…”

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confidence: 99%

The influence of motion and stress on optical fibers

et al. 2012

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We report on extensive testing carried out on the optical fibers for the VIRUS instrument. The primary result of this work explores how 10+ years of simulated wear on a VIRUS fiber bundle affects both transmission and focal ratio degradation (FRD) of the optical fibers. During the accelerated lifetime tests we continuously monitored the fibers for signs of FRD. We find that transient FRD events were common during the portions of the tests when motion was at telescope slew rates, but dropped to negligible levels during rates of motion typical for science observation. Tests of fiber transmission and FRD conducted both before and after the lifetime tests reveal that while transmission values do not change over the 10+ years of simulated wear, a clear increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely due to microfractures that develop over time from repeated flexure of the fiber bundle, and stands in contrast to the transient FRD events that stem from localized stress and subsequent modal diffusion of light within the fibers. There was no measurable wavelength dependence on the increase in FRD over 350 nm to 600 nm. We also report on bend radius tests conducted on individual fibers and find the 266 µm VIRUS fibers to be immune to bending-induced FRD at bend radii of R ≥ 10 cm. Below this bend radius FRD increases slightly with decreasing radius. Lastly, we give details of a degradation seen in the fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory. The degradation is shown to be caused by a localized shear in a select number of optical fibers that leads to an explosive form of FRD. In a few fibers, the overall transmission loss through the instrument can exceed 80%. These results are important for the VIRUS instrument, and for both current and proposed instruments that make use of optical fibers, particularly when the fibers are in continual motion during an observation, or experience repeated mechanical stress during their deployment. Subject headings: Optical Fibers, Focal Ratio Degradation, VIRUS, VIRUS-P, Mitchell Spectrograph, HETDEX1. INTRODUCTION First proposed for use in astronomical instrumentation by Angel et al. (1977) optical fibers have revolutionized the field over the past 3 decades. This revolution has come about due to the flexibility optical fibers offer in re-routing the light from thetelescope focal plane to a more convenient location. The gain for this technological advance is clear as issues of instrument weight, size, stability, and temperature control are made largely obsolete. However, this advantage comes at a cost as fibers constitute an added element in the instrument's optical path. Moreover, optical fibers are not entirely stable light guides, and while their characteristics have been studied in a comprehensive and systematic way by several groups (Ramsey 1988;Schmoll et al. 2003;Crause et al. 2008; Poppett & Allington-Smith 2010b), little work has been focused on their behavior during periods of ...

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Focal ratio degradation: a new perspective

Cited by 12 publications

References 12 publications

The dependence of the properties of optical fibres on length

The dependence of the properties of optical fibres on length

Characterization of multi-clad fibers: approaches to measure the beam divergence angle and its degradation in the fiber

The influence of motion and stress on optical fibers

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