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FLT
Photonics Inc. is dedicated to pioneering advancements in Fiber Light Tuning
Technology. Our fiber grating tuning devices are built upon innovative tuning
technology that employs purely compressive strain tuning to achieve extensive
wavelength tuning ranges. Our fiber grating tuner is designed for tuning the
wavelengths of various types of fiber gratings, including fiber Bragg
gratings, phase-shifted fiber gratings, and long-period fiber gratings. These
technologies have a wide range of applications, including tunable lasers,
nonlinear optics, quantum optics, optical fiber telecommunications, fiber
optic sensors, etc. We eagerly anticipate the opportunity
to collaborate with you to meet your specific needs. |
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1. FBG Tuning Technology |
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Fiber Bragg gratings (FBGs) are key photonic elements
with broad applications. There is great interest in tuning FBGs, either for
central wavelength shifts or for spectral response profiles enabling more
flexible and versatile applications. FBG tuning devices can provide tunable
platforms offering "all-fiber" advantages with extensive
applications in optical fiber communication systems, tunable fiber lasers, and fiber optic sensors. Practical applications require that
such tunable FBG devices have a relatively large tuning range, good
stability, and solid reliability. For
tuning the center wavelength of an FBG, temperature tuning offers only a
limited tuning range (tuning range <2 nm for ΔT=150 ºC).
Actually, applying a high temperature to the fiber is not practically
convenient since a normal acrylate-coated optical fiber has a suggested
operating limit of less than 85 ºC. Thus, strain tuning of FBGs has attracted
extensive attention. The simplest way to tune an FBG is by
applying tensile strain to the FBG through stretching. Unfortunately, the
strength of FBGs typically written by a phase mask under UV laser exposure is
reduced during the grating writing process. The ultimate tensile strain is
approximately 0.7-1%. As a result, tuning by elongating an FBG is limited to
about 8-12 nm. The optical telecommunication C-band has a bandwidth of 35 nm
so that tuning an FBG to cover the full C-band needs to apply an axial strain
of >3% to the FBG. High-purity fused silica has been shown to have much
more compressive strength as compared to tensile strength 21-23 times. This
suggests that tuning FBGs by compressive stain will achieve a larger tuning
range. However, applying such high compressive strain to the thin fiber
without buckling is a challenge. Up to now, much effort has been
focused on approaches to tuning FBGs by compressive strain. There are two
basic techniques: the ferrule guided axial compression
technique and the beam bending technique. However, these tuning techniques
have limited practical application due to their intrinsic drawbacks. In
ferrule guided technique, the fiber coating needs to be stripped from one end
of the fiber during the FBG mounting process in order to feed the FBG section
into guiding ferrules, and the guiding ferrules need to be aligned
perfectly. This is difficult to do,
especially when the FBG has a long grating length. For instance, in
distributed feedback (DFB) fiber lasers, a phase-shifted FBG written in active
fiber may have a grating length of 50 mm or more. In the beam bending
technique, the tuning strain is applied to the FBG through an elastic beam in
which the FBG adheres to the beam with polymer material. By bending the beam
in different directions, compressive or tensile strain can be applied to the
FBG. As a strain-applying element, the obtained bending beam needs to be
associated with polymer or polymer-based hybrid composite materials in order
to achieve a large tuning range. The beam bending technique has demonstrated an
impressive tuning range. However,
polymers are viscoelastic in nature. Since the tuning stress applied to an
FBG has to be transferred through a polymer, the tuning process is subject to
hysteresis and drift (e.g., a 1.56-nm drift resulting in a 30-nm wavelength shift), which
limits the practical application of this technique. Therefore, development of
FBG tuning devices must address such important challenges as large tuning
range, solid reliability and relative ease of fabrication. Here,
we introduce a novel deformable slide tuning technique that overcomes such
challenges. Fig. 1 shows the schematic
design of the FBG tuning device. The FBG section of an optical fiber is
sandwiched between a pair of deformable slides, which have a corrugated
structure and function as a deformable spring. The corrugated structure has a
spatial period of d1+d2.
There are micro-channel grooves inscribed between the deformable slides to
confine and guide the FBG, the channel grooves being fabricated to match the
size of the optical fiber. The two
fiber ends of the FBG are
fixed to the respective ends of the slides. The slides are driven by an
actuator to yield deformation in the longitudinal direction. Since both ends
of the FBG are fixed to the slides, the deformation of slides leads to strain
the FBG axially. A compressive or
tensile strain can be applied to the FBG depending on the deformation
direction of the slides, therefore the FBG can be tuned under either
compressive or tensile strain. |
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Fig.
1. Deformable slide structure for FBG tuning. (a) before mounting
of the FBG; (b) side view after
mounting of the FBG. |
Fig.2. Typical dimension of the FBGT:
124X55X40 mm |
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The
deformable slides are made of a metal alloy which has excellent elasticity,
good thermal conductivity and ease of machining, such as a beryllium-copper
alloy. The high elasticity of the deformable slides can minimize hysteresis
and drift during FBG tuning. A good
thermal conductivity is preferred for thermal dissipation in high power
applications. In the tuning structure shown in Fig. 1, the guided portion of
the FBG is equal to the sum of the distances, d1, and the unguided length is equal to the sum of the
corrugated gaps d2,
which should be narrow in order to prevent FBG
buckling during compression. According to buckling theory, for a
typical fiber with a 125-µm diameter to carry an axial compressive strain of
4% without buckling, the unguided length of fiber should be less than 0.5 mm.
The length of the corrugated section of the deformable slides depends on the
grating length of the FBG. The FBG section can be mounted in the channel
grooves easily. The tuning device is packaged in an aluminum alloy frame with
dimensions 124 mm × 39 mm × 55 mm, which is shown in Fig.2. Fig. 3
shows a tuning example of a 1550-nm FBG, in which Fig. 3(a) shows the
transmission spectra of the FBG during tuning, specifically the center
wavelength shift vs. displacement of actuator; and Fig. 3(b) shows the
reflection spectra of the FBG during tuning.
In the purely compressive tuning mode, a 45-nm tuning range has been
obtained. The tuning process has excellent linearity corresponding to the
displacement of actuator. Fig. 4
shows tuning example of a 2001-nm and 1073-nm FBG, in which around a
50-nm tuning range of center wavelength shift has been achieved in the purely
compressive strain tuning mode. |
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Fig.
3. Spectra of wavelength shifts observed
during tuning of a 1560-nm FBG.
(a) transmission spectra of the FBG and center wavelength shift versus
actuator displacement;
(b) reflection spectra of the FBG and -3dB spectral bandwidth
variations during tuning. |
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Fig.
4. Spectra of wavelength shifts during tuning
of a 2001-nm and a 1073-nm FBG (a) transmission and reflection
spectra of the 2001-nm FBG during tuning; (b) transmission and reflection
spectra of the 1073-nm FBG during tuning. |
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FLT Inc. is dedicated to advancing fiber optic products for use in
photonics. Our innovative technologies are embodied by intellectual property
rights, including patents, publications, and know-how, which we are eager to
share with our partners. We hold a strong commitment to respecting the
intellectual property rights of all parties and are open to discussions
regarding technology licensing, transfer, or partnerships.
We look forward to the opportunity to collaborate with you in the
development and manufacturing of fiber optic products to support your
application solutions. |
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2. Granted US patents: |
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1.
US 7801403B2, Optical fiber grating
tuning device and optical systems employing same, 2.
US 9864131B2, Tunable superstructure fiber
grating device 3.
US 9190799B2, Q-Switched all-fiber laser, 4.
US 9190800B2, Q-Switched all-fiber laser, |
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3. Publications: |
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Some of published technical works are
listed below:
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4. Technical Notes |
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Download PDF files of
our tunable fiber Bragg gratings and tunable fiber lasers. |
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Tunable
FBG Flier Tunable
Laser Flier
Tunable
laser with ASE |
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Please don't hesitate to contact us
with your requirements, and we look forward to collaborating with you to meet
your specific needs. |
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Massachusetts, USA.
info@fltphotonics.com
Copyright © 2023 FLT Photonics, all rights reserved. |
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