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Limitations of the interferometric side diffraction technique for fibre Bragg grating characterization
Acreo AB, Electrum, Kista.
Proximion AB, Kista.
KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
2002 (English)In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 201, no 4-6, 301-308 p.Article in journal (Refereed) Published
Abstract [en]

We make a quantitative investigation of the interferometric side diffraction technique for characterization of fibre Bragg gratings. As opposed to more commonly used non-interferometric alternatives, this method also allows for determination of the grating's distributed phase. It is shown that for weak gratings the detected power and phase are directly proportional to the amplitude and phase of the refractive index modulation in the fibre. While the phase measurement is only limited by the amount of noise present, the relation between modulation amplitude and detected power becomes non-linear when using small probe beam wavelengths and gratings with a modulation depth Deltan approximate to 10(-3) and above. This behavior is inherent to the side diffraction and thus care has to be taken when performing apodization measurements on very strong gratings. The sensitivity to noise is briefly discussed and using a crude estimate for the noise level. the theory indicates that this method is suitable down to a grating modulation depth of at least Deltan approximate to 10(-5).

Place, publisher, year, edition, pages
2002. Vol. 201, no 4-6, 301-308 p.
Keyword [en]
Acoustic noise; Diffraction; Interferometry; Modulation; Refractive index; Modulation depth; Fiber Bragg gratings
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-7130DOI: 10.1016/S0030-4018(01)01704-7ISI: 000173827000009OAI: oai:DiVA.org:kth-7130DiVA: diva2:12048
Note
QC 20100813Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-08-13Bibliographically approved
In thesis
1. Fibre Bragg Gratings: Characterization, Realization and Simulation
Open this publication in new window or tab >>Fibre Bragg Gratings: Characterization, Realization and Simulation
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The main topic of this thesis is realization and characterization of fibre Bragg gratings.

A novel versatile grating fabrication technique is developed and a number of gratings are realized, showing the potential of the system. Arbitrarily-shaped gratings are sequentially imprinted in the fibre by a moving interference pattern created with a continuous-wave ultraviolet (UV) source. This scheme allows for a very good control and stability of the grating shape, which is also shown experimentally. As opposed to most other present fabrication techniques, the proposed method offers a total control over the grating parameters by software, enabling simple implementation of new designs.

Different kinds of error sources when stitching long gratings are identified and investigated regarding impact on the final grating result.

Another important question within this field is how to characterize gratings. We propose a new characterization method based on optical low-coherence reflectometry (OLCR). A new interferometer design allows for simple simultaneous detection of the reflection response from two different points in the interrogated grating, so that differential measurements can be performed. The advantage of this is that the sensitivity to noise caused by e.g. thermal fluctuations in the system is substantially reduced. Several test gratings have been investigated and a very good agreement to the expected results is noted.

A second characterization technique using interferometric detection of the side diffraction from the grating under test is investigated both theoretically and experimentally. With aid of two-dimensional theory for wave propagation, it is shown that there is a linear relation between the detected phase and modulation depth and the corresponding grating properties. The technique is evaluated with a novel scheme of implementation where the UV source provided in a fabrication setup is used assource for the side probe. This approach results in a very simple implementation and opens for an integration of the characterization and fabrication systems.

Finally, a tuning method for transmission filters based on local heating of linearly chirped fibre Bragg gratings is analysed and further developed to allow for fully software-controlled operation. The potential of this technique is illustrated by some promising initial experimental results.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. viii, 64 p.
Series
Trita-ICT/MAP, 2007:4
Keyword
Bragg gratings, optical fibres, optical fibre components
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4381 (URN)978-91-7178-621-0 (ISBN)
Public defence
2007-06-01, N2, KTH-Electrum 3, Isafjordsgatan 28A/D, Kista, 10:15
Opponent
Supervisors
Note
QC 20100812Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-08-13Bibliographically approved

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