CA2288349C - Long period optical fiber grating filter device - Google Patents
Long period optical fiber grating filter device Download PDFInfo
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- CA2288349C CA2288349C CA002288349A CA2288349A CA2288349C CA 2288349 C CA2288349 C CA 2288349C CA 002288349 A CA002288349 A CA 002288349A CA 2288349 A CA2288349 A CA 2288349A CA 2288349 C CA2288349 C CA 2288349C
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- optical fiber
- long period
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
- G02B6/02085—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the grating profile, e.g. chirped, apodised, tilted, helical
- G02B6/02095—Long period gratings, i.e. transmission gratings coupling light between core and cladding modes
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02171—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes
- G02B6/02176—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes due to temperature fluctuations
- G02B6/0219—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes due to temperature fluctuations based on composition of fibre materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/105—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
- H01S3/1055—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length one of the reflectors being constituted by a diffraction grating
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Physics & Mathematics (AREA)
- Diffracting Gratings Or Hologram Optical Elements (AREA)
- Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
- Light Guides In General And Applications Therefor (AREA)
Abstract
There is provided a long period optical fiber grating filter device. The long period optical fiber grating filter device includes a core having long period optical fiber gratings formed therein at every predetermined periods, a cladding surrounding the core, a coating covering a cladding portion free from the long period optical fiber gratings, a recoating covering a cladding portion having the long period optical fiber gratings, a core/cladding refractive index changing portion where a coupling wavelength has a negative wavelength shift range with respect to a temperature change according to the amount of a dopant added to the core, and a cladding/recoating refractive index changing portion where a refractive index decreases at an increased temperature and a coupling wavelength logs a positive wavelength shift range. Therefore, the core shows a negative coupling wavelength shift by the amount of a positive coupling wavelength shift in the recoating material the refractive index of which decreases at an increased temperature.
Description
LONG PERIOD OPTICAL FIBER GRATING FILTER DEVICE
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates generally to a long period optical fiber grating filter device, and in particular, to a temperature compensating long period optical fiber grating filter device which shows no coupling shift characteristics with respect to a temperature change.
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates generally to a long period optical fiber grating filter device, and in particular, to a temperature compensating long period optical fiber grating filter device which shows no coupling shift characteristics with respect to a temperature change.
2. Description of the Related Art An optical fiber grating is generally used as a filter for selecting an optical signal at a specific wavelength propagating along a core. The optical fiber grating can eliminate or reflect light at a specific wavelength by inducing a periodic change in a refractive index of an optical fiber using an ultraviolet (UV) laser.
Optical fiber gratings are categorized into short period optical fiber gratings and long period optical fiber gratings.
The short period optical fiber gratings reflect only light at a specific wavelength signal in filtering, whereas the long period optical fiber gratings couple a core mode in which an optical signal propagates along the core of an optical fiber to a cladding mode in the same propagating direction. Long period optical fiber gratings of a period ranging from several tens of ~m to several hundreds of ~m are used as a gain flattening filter in an EDFA (Erbium Doped (-~ fiber Amplifier) due to its capability of removing light at an intended wavelength by shifting light in a core mode to a cladding mode in the same propagating direction.
The long period optical fiber gratings are fabricated by varying a refractive index in the core of an optical fiber sensitive to UV radiation for every predetermined period. The refractive index increases in a core portion exposed 1 (> to the UV radiation and is not changed in a core portion experiencing no UV
exposure, resulting in a periodic change in the refractive index along the longitudinal axis of the optical fiber.
The long period optical fiber gratings are sensitive to temperature and its 1 ~ optical characteristics are influenced by an ambient refractive index of an optical fiber cladding. Micro bending of the optical fiber significantly influences the central wavelength and extinction ratio of the long period optical fiber gratings, which are determined by coupling between a core mode and a cladding mode.
20 A recoating exhibiting stable optical characteristics against influences of an extel-nal environment is required for use of the long period optical fiber gratings. The external environment factors are temperature, moisture, dust introduction, and micro cracks and micro bending of an optical fiber.
2 > Coupling occurs in a long period optical fiber grating filter device when the phase matching condition of Eq. 1 is satisfied.
f'cn -f cm) = 2?L' ..... (1) A
P8950ST3(~~~ off- o~T71 ~ ~I o~~~ ) (38267/1999) where p « is a propagation constant in a core mode, ~;~"~ IS a propagation constant in an m-order cladding mode, and A is a grating period.
If /~ = 2~r ~ (n is a refractive index and ~, is a wavelength), ~"~~ _ 'i ~ { ) n~.~, - ra~~ -Light at a wavelength can be shifted to a cladding mode by determining the grating period n and a refractive index difference (n~." - n~;~) .
The refractive difference is obtained by appropriately irradiating a UV-sensitive optical fiber with UV light. That is, the optical fiber is masked with a mask with a specific grating period A and UV light is projected onto the mask.
fl'ien, the optical fiber reacts to the UV radiation in such a way that the refractive 1 ~ index of a core increases and a coupling wavelength increases to a long wavelength. In order to obtain an intended spectrum (i.e., intended coupling wavelength and extinction ratio) of the long period optical fiber grating filter device, the UV light should be projected for an appropriate time, accurately controlling a masking period.
The coupling wavelength of the thus-fabricated optical fiber gratings is influenced by temperature. A shift in the coupling wavelength with respect to a temperature change is determined by variations in a refractive index and lengthwise thermal expansion with the temperature change. This can be expressed as d~,~"'> d~~"'~ do d~,~'"~ d~
dT do dT + d~ dT
P8950ST3(~.rs~ o~ o~T~l ~ ~l~ o~~l ) (38267/1999) I
_4_ inhere T is temperature.
When a long period optical fiber grating filter device is fabricated of a ~_~neral communication optical fiber or distribution shifted optical fiber.
~ii""~ do d~r~n d~ d~.~"'' dr1 - is larger than - by several tens of times and thus dA ~T is cln c!T ~ d,'1 dT
ne~,lected. For example, the coupling wavelength of Flexcor 1060 of Corning shifts by ~nm per 100°C. In a typical distribution shifted optical fiber, a coupling wavelength shifts by 0.3nm per 100°C with respect to lengthwise wpansion and by ~nm per 100°C with respect to a refractive index change.
I i ~ Temperature stability of about 0.3nm per 100°C is required for a gain flattening f i l ter being one of applications of a long period optical fiber grating filter in an e~ctual applied system.
For compensating a temperature change, a refractive index distribution in I ~ an optical fiber is designed or the grating period of the optical fiber is selected so that in Eq. 3 has a negative value in prior art. Alternatively, B,_O; is c!.\
added to the optical fiber to get ~T = 0.
d~.~""
If ~~ < 100~m in a general long period optical fiber grating filter, d~~
(~ is a negative value in the conventional method of controlling the refractive index d;~ 'm, of the filter by setting d,, to a negative value. When A = 40q.m, the dependence of wavelen~h on temperature in the Flexcor 1060 fiber is 0.1 ~-f n-~snm! 100°C but a i.''"' mode is in a I .1 ~m region, thus deviating from a ~ommunicat~on region.
*Trademark A temperature compensating long period optical fiber grating filter device is disclosed in detail in Korea Application No. 99-8332 entitled "Temperature Compensating Long Period Optical Fiber Grating Filter", filed by the 5 present applicant.
While a recoating of the long period optical fiber grating filter in the above application is formed of a material the refractive index of which increases with temperature, the refractive index of a general recoating, especially a polymer recoating decreases due to thermal expansion at an increased temperature. Therefore, when recoating a long optical fiber grating filter formed of a general optical fiber, a long wavelength shift effect of the recoating adds to a long wavelength shift characteristic of the long optical fiber grating filter and thus a particular recoating material reducing a refractive index should be used. This recoating material is yet to be developed.
SUGARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a temperature compensating long period optical fiber grating filter device which shows no coupling shift characteristics with respect to a temperature change.
It is a further object of the present invention to provide a temperature compensating long period optical fiber grating filter device which is resistant against moisture and soft enough to prevent micro bending.
To achieve the above objects, there is provided a long period optical fiber grating filter device comprising:
a core having long period optical fiber gratings formed therein at predetermined periods; a cladding surrounding the core; a coating covering a cladding portion free from the long period optical fiber gratings; a recoating covering a cladding portion having the long period optical fiber gratings; a core/cladding refractive index changing portion where a coupling wavelength has a negative wavelength shift range with respect to a temperature change according to the amount of a dopant added to the core; and a cladding/recoating refractive index changing portion where a refractive index decreases at an increased temperature and a coupling wavelength has a positive wavelength shift range;
wherein the dopant includes B203 and Ge02 and the sum of coupling wavelength shifts caused by a refractive index increased according to the amount of Ge02 and by a refractive index decreased according to the amount of B203 has a negative wavelength shift value.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
FIG. lA is a perspective view of a long period optical fiber grating filter device packaged;
FIG. 1B is a perspective view of the long period optical fiber grating filter with a recoating removed;
FIG. 1C is a sectional view of the long period optical fiber grating filter device with the recoating removed;
6a FIGS. 2A to 2D are graphs showing a coupling wavelength shift with respect to an ambient refractive index of a cladding;
FIG. 3 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding;
FIG. 4 is a graph showing a coupling wavelength shift with respect to the ambient refractive index of the cladding when it is smaller than the refractive index of the cladding;
_7_ FIG. SA is a graph showing a refractive index variation with temperature of a recoating when it is formed of a general polymer material;
FIG. SB is a graph showing a refractive index variation with temperature of a recoating when it is formed of silicon resin;
FIG. 6 is a graph showing a coupling wavelength shift with respect a temperature change in a recoating material;
FIG. 7 is a graph showing a refractive index variation with temperature at different dopant concentrations in an optical fiber core;
FIG. 8 is a graph showing a wavelength dependence on temperature at I 0 d i ffercnt dopant concentrations in the optical fiber core;
FIG. 9 is a graph showing a temperature compensation effect of a long period optical fiber grating filter device according to the present invention;
FIG. l0A is a graph showing a temperature dependence of a general long period optical fiber grating device with a recoating removed;
1 ~ FIG. l OB is a graph showing a temperature dependence of the general long period optical fiber grating filter device with the recoating;
FIG. 11 is a graph showing a temperature dependence of the long period optical fiber grating filter device according to the present invention; and FIG. 12 is a sectional view of the long period optical fiber grating filter 20 device according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be described 2s hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
An optical fiber coating is removed for a predetermined length to forni P8950ST3( '~L-~.~. o~ o~-~r-~~ ~ ~)- o~~~) (28267/1999) _g_ long period optical fiber Gratings in an optical fiber. Then, the long period «ptical fiber gratings are formed on the exposed portion using a LJV' laser and an amplitude mask. The uncoated long period optical fiber gratings are influenced l,v an external environment including temperature, moisture, dust, micro cracks, and micro bending and thus needs protection to prevent a change in optical characteristics.
Furthermore, a plurality of long period optical fiber gratings formed along the length of an optical fiber for a predetermined period function as a filter I t~ tar coupling a core mode to a cladding mode. Therefore, the refractive index of :~ recoatin~ material should be considered. -As shown in FIGS. lA, 1B, and 1C, a packaged long period optical fiber ~~ratin~ filter device 100 includes a core 10 having long period optical fiber i ~ ~_ratings formed thereon at every predetermined periods, a cladding I
surrounding the core 10, a coating 14 surrounding the cladding 12, and a recoating 18 coated on the long period optical fiber gratings 16. A recoating is applied to a portion from which the coating 14 is removed to protect the long period optical fiber Gratings 16.
?(l In FIG. 1 C, arrows indicating a wavelength propagating direction denotes coupling from a core mode to a cladding mode in the long period optical fiber ~;ratin~ filter device. The thickness of an arrow indicates the intensity of light at a wavelength.
,;
An optical signal at a central wavelength traveling in a fundamental ~_uide mode in the core 10 is scattered at a refractive index changing portion, that is. in the lone period optical fiber gratings 16. As the scattered light is coupled to the cladding 12, light at a wavelength satisfying a phase matching condition is coherently reinforced. The light goes outside the cladding 12 and the long period optical fiber grating filter device 100 acts as a wavelength dependent attenuator.
The intensity of the light traveling in the fundamental guide mode is reduced while passing through the long period optical fiber gratings 16, as indicated by a decrease in the thickness of an arrow, and the intensity of the light at the wavelength coupled to the cladding 12 is increased as indicated by an i ncrease in the thickness of arrows.
An external condition of the cladding I2, namely air has a refractive index of 1. If the cladding 12 is recoated with a material with a refractive index n after formation of the long period optical fiber gratings 16, a coupling condition is changed and thus a coupling wavelength is shifted to a long or short 1 > w avelength.
FIGS. 2A to 2D are graphs showing shifts of a coupling wavelength with respect to an ambient refractive index of the cladding.
20 FIG. 2A is a graph showing an optical transmittance characteristic when an ambient refractive index (the refractive index of air) of the cladding surrounding the long period optical fiber gratings is 1.
FIG. 2B is a graph showing an optical transmittance characteristic when the ambient refractive index of the cladding is 1.400. It is noted that an optical transmittance is increased and a coupling wavelength shifts to a short wavelength by about 4.8nm, as compared to the graph of FIG. 2A.
FIG. 2C is a graph showing an optical transmittance characteristic when P8950ST3(-Q-~~ o~ o~-~r71 ~~l- o~~l) (~S267/1999) the ambient refractive index of the cladding is 1.448. The coupling wavelength shifts to a short wavelength by l6.Snm, as compared to FIG. 2A.
FIG. 2D is a graph showing an optical transmittance characteristic when tl~e ambient refractive index of the cladding is 1.484. The coupling wavelength shifts to a long wavelength, as compared to FIG. 2A.
If the ambient refractive index of the cladding increases from 1 but is smaller than the refractive index of the cladding, the coupling wavelength shifts I () to a short wavelength, as shown in FIGs. 2B and 2C. On the other hand, if the ambient refractive index of the cladding exceeds the refractive index of the cladding, the coupling wavelength shifts to a long wavelength, as shown in FIG.
2 D. If the ambient refractive index of the cladding is equal to the refractive index of the cladding, a full reflection condition is released and a coupling peak I ~ disappears.
FIG. 3 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding. The coupling wavelength shifts to a short wavelength as the ambient refractive index increases 2() From 1.0, the coupling peak disappears when the ambient refractive index is equal to the refractive index of the cladding, and then the coupling wavelength shifts to a long wavelength when the ambient refractive index exceeds the refractive index of the cladding.
2 ~ FIG. 4 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding when the ambient refractive index is smaller than the refractive index of the cladding.
Refernng to FIG. 4, as the ambient refractive index decreases, the coupling wavelength shifts to a long wavelength, only if the ambient refractive index is smaller than the P8950ST3(~-~~ o~ o~T~~ ~~1~ o~~~) (38267/1999) refractive index of the cladding.
The results shown in FIGS. 2A to 4 are described in detail in a thesis by the present inventor "Displacement of the Resonant Peaks of a Long period Fiber (hating Induced by a Change of Ambient Refractive Index", 1997 Optics Letters, December 1, 1997/VoI. 22, No. 23.
FIG. ~A is a graph showing a change in the refractive index of a general recoating material with respect to a temperature change, and FIG. SB is a graph ( () slowing a change in the refractive index of silicon resin taken as an example of tl~e general recoating material, with respect to a temperature change.
Referring to FIG. ~A, a general recoating material, that is, a polymer experiences thermal expansion at an increased temperature and has a reduced 1 > retractive index. Referring to FIG. SB, silicon resin also experiences thermal expansion at an increased temperature and has a reduced refractive index.. The refractive index variation with temperature of the silicon resin is -2.4x10-2/100°C.
FIG. 6 is a graph showing a coupling wavelength shift of a recoating 20 material with respect to a temperature change. It is noted from the drawing that the coupling wavelength shifts to a long wavelength as the refractive index of the recoating material decreases with a temperature increase. The shift of the coupling wavelength to a long wavelength implies that it has a positive wavelength shift range.
~>
FIG. 7 is a graph showing a coupling wavelength shift with respect to a tcmperaW re change at a different concentration of a dopant added to an optical Iiber core. Temperature compensation by adding Bz03 and GeO, as dopants to a core is disclosed in detail in EP 0 800 098 A2 entitled "Optical Waveguide P8950ST3(~ ~~ off- o~T 71 ~ ~)- 0~ ~1 ) (38267/1999) Grating and Production Method Thereof '. As shown in FIG. 7, with B,O, more than GeO,, the long period optical fiber gratings have a negative wavelength shift range when temperature increases. That is, a refractive index variation with mmperature has a negative value. In the present invention, a temperature change is compensated by setting the wavelength shift range of the coupling wavelength to a negative value in the long period optical fiber gratings and to a positive value in a recoating material.
For example, if 20mo1% of GeO, and 1 ~mol% of B,03 are added to the core, a change in the refractive index of the long period optical fiber gratings formed on the core with respect to a temperature change has a negative value and thus the coupling wavelength has a negative wavelength shift range. This is illustrated in FIG. 8.
FIG. 8 is a graph showing a shift of the coupling wavelength to a short wavelength at an increased temperature when the amount of B=O; is larger than that of GeO, in the core and the long period optical fiber gratings are not recoated.
In FIG. S, the coupling wavelength shifts to a short wavelength when temperature increases. This implies that the coupling wavelength in the long period optical ?() fiber grating filter device has a negative wavelength shift range.
FIG. 9 is a graph showing a long wavelength shift effect of a recoating material like silicon resin at an increased temperature in the long period optical trber grating filter device and temperature compensation resulting from a short wavelength shift effect produced by use of B,03 more than GeO~. Reference numeral 1 indicates a shift of the coupling wavelength to a long wavelength due to a refractive index changing portion of the cladding%recoating according to a temperature change, and reference numeral 3 indicates a shift of the coupling wavelength to a short wavelength due to a refractive index changing portion of X5998-'2 the coreicladding according to a temperature change.
The long wavelength shift and the short wavelength shift of the coupling wavelength concurrently occur in the long period optical fiber grating filter ;i~vice, thereby achieving temperature compensation in the present invention, as indicated by reference numeral 2.
FIGS. l 0 A and l OB are graphs showing wavelength shifts with respect to a temperature change in the cases that a general long period optical fiber orating I c> filter device showing no short wavelength shift effect in a core is not recoated ,end is recoated with silicon resin, respectively.
FIG. 8 is a graph showing a wavelength shift with respect to a temperature change when the long period optical fiber grating filter device of the present invention is not recoated while it has a negative wavelength shift range with B.O; more than Ge0= used. FIG. 11 is a graph showing a wavelength shift with respect to a temperature change when the long period optical fiber grating filter device of the present invention is recoated with silicon resin while it has a ne~,ative wavelen~h shift range with B,03 more than GeO, used.
Temperature compensation of the present invention will be described hereinbelow by comparing FIGS. l0A and lOB showing the conventional technology with FIGS. 8 and 9 according to the present mvennon.
As shown in FIG. 1 OA, when the general long period optical fiber grating f i l ter device is not recoated, the coupling wavelength shifts to a long wavelength as temperature increases, and a temperature dependence of the wavelength is about ~.08nmi 100°C.
In FIG. lOB, when the general long period optical fiber grating filter device is recoated with silicon resin, the coupling wavelength shifts to a long wavelength at an increased temperature, and a temperature dependence of the wavelength is about lOnm/100°C.
It can be noted from FIGS. l0A and lOB that recoating the general long period optical fiber gratings with silicon resin incurs a synergy between a long wavelength shift effect of the optical fiber core and the long wavelength shift effiect of silicon resin to thereby further the long wavelength shift effect.
That is, 1 () temperature dependence is further increased.
In FIG. 8, when the optical fiber core includes BZ03 more than GeO, and the long period optical fiber grating filter device is not recoated in the present invention, the coupling wavelength shifts to a short wavelength at an increased l > temperature, and a temperature dependence of the wavelength is about -4.7nm/ 100°C.
In FIG. 11, when the optical fiber core includes Bz03 more than GeO, and the long period optical fiber grating filter device is recoated with silicon resin ?0 in the present invention, a short wavelength effect of the core and a long wavelength shift effect of the recoating material concurrently occur, thereby compensating for a temperature change. As a result, there is no change in the coupling wavelength with respect to a temperature change. Here, a temperature dependence of the wavelength is about 0.7nm/100°C.
The thus-fabricated long period optical fiber grating filter device of the present invention is shown in FIG. 12. Reference numeral 120 denotes a core with B,O~ more than Ge02, reference numeral 122 denotes a cladding surrounding the core 120, and reference numeral 126 denotes a plurality of long P8950ST3(-Q-rs~'o o~~ 7~ ~ ~}~ ~1-~l ) (38267/1999) period optical fiber gratings formed along the length of the core 120.
Reference numeral 128 denotes a silicon resin recoating which covers the long period optical fiber gratings 126.
It can be concluded that if a coupling wavelength shifts within a positive wavelength shift range at an increased temperature by using Bz03 more than GeO,, in an optical fiber core, and a refractive index decreases with an increase in temperature and the coupling wavelength shifts within a positive range in a rccoating, a temperature change can be compensated for without little coupling 1 (> wavelength shift.
As described above, the long period optical fiber grating filter device according to the present invention includes a core where a coupling wavelength shifts within a negative range at an increased temperature according to the 1 > amount of a dopant added, and a recoating where a refractive index decreases with the temperature increase and the coupling wavelength shifts within a positive range. Thus, the coupling wavelength shift of the long period optical fiber gratings attributed to a temperature change can be compensated for, and temperature compensation thereof is facilitated.
2 ~) While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended 2~ claims.
ps9sosT3l~-~~ o~ ~~-T~l ~y o~~l) (3az~ot~~9~
Optical fiber gratings are categorized into short period optical fiber gratings and long period optical fiber gratings.
The short period optical fiber gratings reflect only light at a specific wavelength signal in filtering, whereas the long period optical fiber gratings couple a core mode in which an optical signal propagates along the core of an optical fiber to a cladding mode in the same propagating direction. Long period optical fiber gratings of a period ranging from several tens of ~m to several hundreds of ~m are used as a gain flattening filter in an EDFA (Erbium Doped (-~ fiber Amplifier) due to its capability of removing light at an intended wavelength by shifting light in a core mode to a cladding mode in the same propagating direction.
The long period optical fiber gratings are fabricated by varying a refractive index in the core of an optical fiber sensitive to UV radiation for every predetermined period. The refractive index increases in a core portion exposed 1 (> to the UV radiation and is not changed in a core portion experiencing no UV
exposure, resulting in a periodic change in the refractive index along the longitudinal axis of the optical fiber.
The long period optical fiber gratings are sensitive to temperature and its 1 ~ optical characteristics are influenced by an ambient refractive index of an optical fiber cladding. Micro bending of the optical fiber significantly influences the central wavelength and extinction ratio of the long period optical fiber gratings, which are determined by coupling between a core mode and a cladding mode.
20 A recoating exhibiting stable optical characteristics against influences of an extel-nal environment is required for use of the long period optical fiber gratings. The external environment factors are temperature, moisture, dust introduction, and micro cracks and micro bending of an optical fiber.
2 > Coupling occurs in a long period optical fiber grating filter device when the phase matching condition of Eq. 1 is satisfied.
f'cn -f cm) = 2?L' ..... (1) A
P8950ST3(~~~ off- o~T71 ~ ~I o~~~ ) (38267/1999) where p « is a propagation constant in a core mode, ~;~"~ IS a propagation constant in an m-order cladding mode, and A is a grating period.
If /~ = 2~r ~ (n is a refractive index and ~, is a wavelength), ~"~~ _ 'i ~ { ) n~.~, - ra~~ -Light at a wavelength can be shifted to a cladding mode by determining the grating period n and a refractive index difference (n~." - n~;~) .
The refractive difference is obtained by appropriately irradiating a UV-sensitive optical fiber with UV light. That is, the optical fiber is masked with a mask with a specific grating period A and UV light is projected onto the mask.
fl'ien, the optical fiber reacts to the UV radiation in such a way that the refractive 1 ~ index of a core increases and a coupling wavelength increases to a long wavelength. In order to obtain an intended spectrum (i.e., intended coupling wavelength and extinction ratio) of the long period optical fiber grating filter device, the UV light should be projected for an appropriate time, accurately controlling a masking period.
The coupling wavelength of the thus-fabricated optical fiber gratings is influenced by temperature. A shift in the coupling wavelength with respect to a temperature change is determined by variations in a refractive index and lengthwise thermal expansion with the temperature change. This can be expressed as d~,~"'> d~~"'~ do d~,~'"~ d~
dT do dT + d~ dT
P8950ST3(~.rs~ o~ o~T~l ~ ~l~ o~~l ) (38267/1999) I
_4_ inhere T is temperature.
When a long period optical fiber grating filter device is fabricated of a ~_~neral communication optical fiber or distribution shifted optical fiber.
~ii""~ do d~r~n d~ d~.~"'' dr1 - is larger than - by several tens of times and thus dA ~T is cln c!T ~ d,'1 dT
ne~,lected. For example, the coupling wavelength of Flexcor 1060 of Corning shifts by ~nm per 100°C. In a typical distribution shifted optical fiber, a coupling wavelength shifts by 0.3nm per 100°C with respect to lengthwise wpansion and by ~nm per 100°C with respect to a refractive index change.
I i ~ Temperature stability of about 0.3nm per 100°C is required for a gain flattening f i l ter being one of applications of a long period optical fiber grating filter in an e~ctual applied system.
For compensating a temperature change, a refractive index distribution in I ~ an optical fiber is designed or the grating period of the optical fiber is selected so that in Eq. 3 has a negative value in prior art. Alternatively, B,_O; is c!.\
added to the optical fiber to get ~T = 0.
d~.~""
If ~~ < 100~m in a general long period optical fiber grating filter, d~~
(~ is a negative value in the conventional method of controlling the refractive index d;~ 'm, of the filter by setting d,, to a negative value. When A = 40q.m, the dependence of wavelen~h on temperature in the Flexcor 1060 fiber is 0.1 ~-f n-~snm! 100°C but a i.''"' mode is in a I .1 ~m region, thus deviating from a ~ommunicat~on region.
*Trademark A temperature compensating long period optical fiber grating filter device is disclosed in detail in Korea Application No. 99-8332 entitled "Temperature Compensating Long Period Optical Fiber Grating Filter", filed by the 5 present applicant.
While a recoating of the long period optical fiber grating filter in the above application is formed of a material the refractive index of which increases with temperature, the refractive index of a general recoating, especially a polymer recoating decreases due to thermal expansion at an increased temperature. Therefore, when recoating a long optical fiber grating filter formed of a general optical fiber, a long wavelength shift effect of the recoating adds to a long wavelength shift characteristic of the long optical fiber grating filter and thus a particular recoating material reducing a refractive index should be used. This recoating material is yet to be developed.
SUGARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a temperature compensating long period optical fiber grating filter device which shows no coupling shift characteristics with respect to a temperature change.
It is a further object of the present invention to provide a temperature compensating long period optical fiber grating filter device which is resistant against moisture and soft enough to prevent micro bending.
To achieve the above objects, there is provided a long period optical fiber grating filter device comprising:
a core having long period optical fiber gratings formed therein at predetermined periods; a cladding surrounding the core; a coating covering a cladding portion free from the long period optical fiber gratings; a recoating covering a cladding portion having the long period optical fiber gratings; a core/cladding refractive index changing portion where a coupling wavelength has a negative wavelength shift range with respect to a temperature change according to the amount of a dopant added to the core; and a cladding/recoating refractive index changing portion where a refractive index decreases at an increased temperature and a coupling wavelength has a positive wavelength shift range;
wherein the dopant includes B203 and Ge02 and the sum of coupling wavelength shifts caused by a refractive index increased according to the amount of Ge02 and by a refractive index decreased according to the amount of B203 has a negative wavelength shift value.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
FIG. lA is a perspective view of a long period optical fiber grating filter device packaged;
FIG. 1B is a perspective view of the long period optical fiber grating filter with a recoating removed;
FIG. 1C is a sectional view of the long period optical fiber grating filter device with the recoating removed;
6a FIGS. 2A to 2D are graphs showing a coupling wavelength shift with respect to an ambient refractive index of a cladding;
FIG. 3 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding;
FIG. 4 is a graph showing a coupling wavelength shift with respect to the ambient refractive index of the cladding when it is smaller than the refractive index of the cladding;
_7_ FIG. SA is a graph showing a refractive index variation with temperature of a recoating when it is formed of a general polymer material;
FIG. SB is a graph showing a refractive index variation with temperature of a recoating when it is formed of silicon resin;
FIG. 6 is a graph showing a coupling wavelength shift with respect a temperature change in a recoating material;
FIG. 7 is a graph showing a refractive index variation with temperature at different dopant concentrations in an optical fiber core;
FIG. 8 is a graph showing a wavelength dependence on temperature at I 0 d i ffercnt dopant concentrations in the optical fiber core;
FIG. 9 is a graph showing a temperature compensation effect of a long period optical fiber grating filter device according to the present invention;
FIG. l0A is a graph showing a temperature dependence of a general long period optical fiber grating device with a recoating removed;
1 ~ FIG. l OB is a graph showing a temperature dependence of the general long period optical fiber grating filter device with the recoating;
FIG. 11 is a graph showing a temperature dependence of the long period optical fiber grating filter device according to the present invention; and FIG. 12 is a sectional view of the long period optical fiber grating filter 20 device according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be described 2s hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
An optical fiber coating is removed for a predetermined length to forni P8950ST3( '~L-~.~. o~ o~-~r-~~ ~ ~)- o~~~) (28267/1999) _g_ long period optical fiber Gratings in an optical fiber. Then, the long period «ptical fiber gratings are formed on the exposed portion using a LJV' laser and an amplitude mask. The uncoated long period optical fiber gratings are influenced l,v an external environment including temperature, moisture, dust, micro cracks, and micro bending and thus needs protection to prevent a change in optical characteristics.
Furthermore, a plurality of long period optical fiber gratings formed along the length of an optical fiber for a predetermined period function as a filter I t~ tar coupling a core mode to a cladding mode. Therefore, the refractive index of :~ recoatin~ material should be considered. -As shown in FIGS. lA, 1B, and 1C, a packaged long period optical fiber ~~ratin~ filter device 100 includes a core 10 having long period optical fiber i ~ ~_ratings formed thereon at every predetermined periods, a cladding I
surrounding the core 10, a coating 14 surrounding the cladding 12, and a recoating 18 coated on the long period optical fiber gratings 16. A recoating is applied to a portion from which the coating 14 is removed to protect the long period optical fiber Gratings 16.
?(l In FIG. 1 C, arrows indicating a wavelength propagating direction denotes coupling from a core mode to a cladding mode in the long period optical fiber ~;ratin~ filter device. The thickness of an arrow indicates the intensity of light at a wavelength.
,;
An optical signal at a central wavelength traveling in a fundamental ~_uide mode in the core 10 is scattered at a refractive index changing portion, that is. in the lone period optical fiber gratings 16. As the scattered light is coupled to the cladding 12, light at a wavelength satisfying a phase matching condition is coherently reinforced. The light goes outside the cladding 12 and the long period optical fiber grating filter device 100 acts as a wavelength dependent attenuator.
The intensity of the light traveling in the fundamental guide mode is reduced while passing through the long period optical fiber gratings 16, as indicated by a decrease in the thickness of an arrow, and the intensity of the light at the wavelength coupled to the cladding 12 is increased as indicated by an i ncrease in the thickness of arrows.
An external condition of the cladding I2, namely air has a refractive index of 1. If the cladding 12 is recoated with a material with a refractive index n after formation of the long period optical fiber gratings 16, a coupling condition is changed and thus a coupling wavelength is shifted to a long or short 1 > w avelength.
FIGS. 2A to 2D are graphs showing shifts of a coupling wavelength with respect to an ambient refractive index of the cladding.
20 FIG. 2A is a graph showing an optical transmittance characteristic when an ambient refractive index (the refractive index of air) of the cladding surrounding the long period optical fiber gratings is 1.
FIG. 2B is a graph showing an optical transmittance characteristic when the ambient refractive index of the cladding is 1.400. It is noted that an optical transmittance is increased and a coupling wavelength shifts to a short wavelength by about 4.8nm, as compared to the graph of FIG. 2A.
FIG. 2C is a graph showing an optical transmittance characteristic when P8950ST3(-Q-~~ o~ o~-~r71 ~~l- o~~l) (~S267/1999) the ambient refractive index of the cladding is 1.448. The coupling wavelength shifts to a short wavelength by l6.Snm, as compared to FIG. 2A.
FIG. 2D is a graph showing an optical transmittance characteristic when tl~e ambient refractive index of the cladding is 1.484. The coupling wavelength shifts to a long wavelength, as compared to FIG. 2A.
If the ambient refractive index of the cladding increases from 1 but is smaller than the refractive index of the cladding, the coupling wavelength shifts I () to a short wavelength, as shown in FIGs. 2B and 2C. On the other hand, if the ambient refractive index of the cladding exceeds the refractive index of the cladding, the coupling wavelength shifts to a long wavelength, as shown in FIG.
2 D. If the ambient refractive index of the cladding is equal to the refractive index of the cladding, a full reflection condition is released and a coupling peak I ~ disappears.
FIG. 3 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding. The coupling wavelength shifts to a short wavelength as the ambient refractive index increases 2() From 1.0, the coupling peak disappears when the ambient refractive index is equal to the refractive index of the cladding, and then the coupling wavelength shifts to a long wavelength when the ambient refractive index exceeds the refractive index of the cladding.
2 ~ FIG. 4 is a graph showing a coupling wavelength shift with respect to a change in the ambient refractive index of the cladding when the ambient refractive index is smaller than the refractive index of the cladding.
Refernng to FIG. 4, as the ambient refractive index decreases, the coupling wavelength shifts to a long wavelength, only if the ambient refractive index is smaller than the P8950ST3(~-~~ o~ o~T~~ ~~1~ o~~~) (38267/1999) refractive index of the cladding.
The results shown in FIGS. 2A to 4 are described in detail in a thesis by the present inventor "Displacement of the Resonant Peaks of a Long period Fiber (hating Induced by a Change of Ambient Refractive Index", 1997 Optics Letters, December 1, 1997/VoI. 22, No. 23.
FIG. ~A is a graph showing a change in the refractive index of a general recoating material with respect to a temperature change, and FIG. SB is a graph ( () slowing a change in the refractive index of silicon resin taken as an example of tl~e general recoating material, with respect to a temperature change.
Referring to FIG. ~A, a general recoating material, that is, a polymer experiences thermal expansion at an increased temperature and has a reduced 1 > retractive index. Referring to FIG. SB, silicon resin also experiences thermal expansion at an increased temperature and has a reduced refractive index.. The refractive index variation with temperature of the silicon resin is -2.4x10-2/100°C.
FIG. 6 is a graph showing a coupling wavelength shift of a recoating 20 material with respect to a temperature change. It is noted from the drawing that the coupling wavelength shifts to a long wavelength as the refractive index of the recoating material decreases with a temperature increase. The shift of the coupling wavelength to a long wavelength implies that it has a positive wavelength shift range.
~>
FIG. 7 is a graph showing a coupling wavelength shift with respect to a tcmperaW re change at a different concentration of a dopant added to an optical Iiber core. Temperature compensation by adding Bz03 and GeO, as dopants to a core is disclosed in detail in EP 0 800 098 A2 entitled "Optical Waveguide P8950ST3(~ ~~ off- o~T 71 ~ ~)- 0~ ~1 ) (38267/1999) Grating and Production Method Thereof '. As shown in FIG. 7, with B,O, more than GeO,, the long period optical fiber gratings have a negative wavelength shift range when temperature increases. That is, a refractive index variation with mmperature has a negative value. In the present invention, a temperature change is compensated by setting the wavelength shift range of the coupling wavelength to a negative value in the long period optical fiber gratings and to a positive value in a recoating material.
For example, if 20mo1% of GeO, and 1 ~mol% of B,03 are added to the core, a change in the refractive index of the long period optical fiber gratings formed on the core with respect to a temperature change has a negative value and thus the coupling wavelength has a negative wavelength shift range. This is illustrated in FIG. 8.
FIG. 8 is a graph showing a shift of the coupling wavelength to a short wavelength at an increased temperature when the amount of B=O; is larger than that of GeO, in the core and the long period optical fiber gratings are not recoated.
In FIG. S, the coupling wavelength shifts to a short wavelength when temperature increases. This implies that the coupling wavelength in the long period optical ?() fiber grating filter device has a negative wavelength shift range.
FIG. 9 is a graph showing a long wavelength shift effect of a recoating material like silicon resin at an increased temperature in the long period optical trber grating filter device and temperature compensation resulting from a short wavelength shift effect produced by use of B,03 more than GeO~. Reference numeral 1 indicates a shift of the coupling wavelength to a long wavelength due to a refractive index changing portion of the cladding%recoating according to a temperature change, and reference numeral 3 indicates a shift of the coupling wavelength to a short wavelength due to a refractive index changing portion of X5998-'2 the coreicladding according to a temperature change.
The long wavelength shift and the short wavelength shift of the coupling wavelength concurrently occur in the long period optical fiber grating filter ;i~vice, thereby achieving temperature compensation in the present invention, as indicated by reference numeral 2.
FIGS. l 0 A and l OB are graphs showing wavelength shifts with respect to a temperature change in the cases that a general long period optical fiber orating I c> filter device showing no short wavelength shift effect in a core is not recoated ,end is recoated with silicon resin, respectively.
FIG. 8 is a graph showing a wavelength shift with respect to a temperature change when the long period optical fiber grating filter device of the present invention is not recoated while it has a negative wavelength shift range with B.O; more than Ge0= used. FIG. 11 is a graph showing a wavelength shift with respect to a temperature change when the long period optical fiber grating filter device of the present invention is recoated with silicon resin while it has a ne~,ative wavelen~h shift range with B,03 more than GeO, used.
Temperature compensation of the present invention will be described hereinbelow by comparing FIGS. l0A and lOB showing the conventional technology with FIGS. 8 and 9 according to the present mvennon.
As shown in FIG. 1 OA, when the general long period optical fiber grating f i l ter device is not recoated, the coupling wavelength shifts to a long wavelength as temperature increases, and a temperature dependence of the wavelength is about ~.08nmi 100°C.
In FIG. lOB, when the general long period optical fiber grating filter device is recoated with silicon resin, the coupling wavelength shifts to a long wavelength at an increased temperature, and a temperature dependence of the wavelength is about lOnm/100°C.
It can be noted from FIGS. l0A and lOB that recoating the general long period optical fiber gratings with silicon resin incurs a synergy between a long wavelength shift effect of the optical fiber core and the long wavelength shift effiect of silicon resin to thereby further the long wavelength shift effect.
That is, 1 () temperature dependence is further increased.
In FIG. 8, when the optical fiber core includes BZ03 more than GeO, and the long period optical fiber grating filter device is not recoated in the present invention, the coupling wavelength shifts to a short wavelength at an increased l > temperature, and a temperature dependence of the wavelength is about -4.7nm/ 100°C.
In FIG. 11, when the optical fiber core includes Bz03 more than GeO, and the long period optical fiber grating filter device is recoated with silicon resin ?0 in the present invention, a short wavelength effect of the core and a long wavelength shift effect of the recoating material concurrently occur, thereby compensating for a temperature change. As a result, there is no change in the coupling wavelength with respect to a temperature change. Here, a temperature dependence of the wavelength is about 0.7nm/100°C.
The thus-fabricated long period optical fiber grating filter device of the present invention is shown in FIG. 12. Reference numeral 120 denotes a core with B,O~ more than Ge02, reference numeral 122 denotes a cladding surrounding the core 120, and reference numeral 126 denotes a plurality of long P8950ST3(-Q-rs~'o o~~ 7~ ~ ~}~ ~1-~l ) (38267/1999) period optical fiber gratings formed along the length of the core 120.
Reference numeral 128 denotes a silicon resin recoating which covers the long period optical fiber gratings 126.
It can be concluded that if a coupling wavelength shifts within a positive wavelength shift range at an increased temperature by using Bz03 more than GeO,, in an optical fiber core, and a refractive index decreases with an increase in temperature and the coupling wavelength shifts within a positive range in a rccoating, a temperature change can be compensated for without little coupling 1 (> wavelength shift.
As described above, the long period optical fiber grating filter device according to the present invention includes a core where a coupling wavelength shifts within a negative range at an increased temperature according to the 1 > amount of a dopant added, and a recoating where a refractive index decreases with the temperature increase and the coupling wavelength shifts within a positive range. Thus, the coupling wavelength shift of the long period optical fiber gratings attributed to a temperature change can be compensated for, and temperature compensation thereof is facilitated.
2 ~) While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended 2~ claims.
ps9sosT3l~-~~ o~ ~~-T~l ~y o~~l) (3az~ot~~9~
Claims (4)
1. A long period optical fiber grating filter device comprising:
a core having long period optical fiber gratings formed therein at predetermined periods;
a cladding surrounding the core;
a coating covering a cladding portion free from the long period optical fiber gratings;
a recoating covering a cladding portion having the long period optical fiber gratings;
a core/cladding refractive index changing portion where a coupling wavelength has a negative wavelength shift range with respect to a temperature change according to the amount of a dopant added to the core; and a cladding/recoating refractive index changing portion where a refractive index decreases at an increased temperature and a coupling wavelength has a positive wavelength shift range;
wherein the dopant includes B2O3 and GeO2 and the sum of coupling wavelength shifts caused by a refractive index increased according to the amount of GeO2 and by a refractive index decreased according to the amount of B2O3 has a negative wavelength shift value.
a core having long period optical fiber gratings formed therein at predetermined periods;
a cladding surrounding the core;
a coating covering a cladding portion free from the long period optical fiber gratings;
a recoating covering a cladding portion having the long period optical fiber gratings;
a core/cladding refractive index changing portion where a coupling wavelength has a negative wavelength shift range with respect to a temperature change according to the amount of a dopant added to the core; and a cladding/recoating refractive index changing portion where a refractive index decreases at an increased temperature and a coupling wavelength has a positive wavelength shift range;
wherein the dopant includes B2O3 and GeO2 and the sum of coupling wavelength shifts caused by a refractive index increased according to the amount of GeO2 and by a refractive index decreased according to the amount of B2O3 has a negative wavelength shift value.
2. The long period optical fiber grating filter device of claim 1, wherein the recoating is formed of a polymer material of which the refractive index decreases with an increase in temperature.
3. The long period optical fiber grating filter device of claim 2, wherein the polymer material is silicon resin.
4. The long period optical fiber grating filter device of claim 1, wherein the refractive index of the recoating is smaller than the refractive index of the cladding.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019990038267A KR100334801B1 (en) | 1999-09-09 | 1999-09-09 | Long period optical fiber grating filter device |
| KR38267/1999 | 1999-09-09 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2288349A1 CA2288349A1 (en) | 2001-03-09 |
| CA2288349C true CA2288349C (en) | 2002-06-25 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002288349A Expired - Fee Related CA2288349C (en) | 1999-09-09 | 1999-11-02 | Long period optical fiber grating filter device |
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| KR (1) | KR100334801B1 (en) |
| CA (1) | CA2288349C (en) |
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| US8488924B2 (en) | 2009-07-03 | 2013-07-16 | Electronics And Telecommunications Research Institute | Optical waveguide and bi-directional optical transceiver |
| CN103941330A (en) * | 2014-05-07 | 2014-07-23 | 南通大学 | Composite structure long-period fiber grating |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO1994000784A1 (en) * | 1992-06-24 | 1994-01-06 | British Telecommunications Public Limited Company | Photoinduced grating in b2o3 containing glass |
| KR100357247B1 (en) * | 1995-10-16 | 2003-01-24 | 스미토모덴키고교가부시키가이샤 | Optical fiber diffraction grating, production method thereof and laser light source |
| US5757540A (en) * | 1996-09-06 | 1998-05-26 | Lucent Technologies Inc. | Long-period fiber grating devices packaged for temperature stability |
| JPH10170736A (en) * | 1996-12-12 | 1998-06-26 | Sumitomo Electric Ind Ltd | Long-cycle fiber grating, and method and device for controlling loss wavelength |
| US6011886A (en) * | 1997-10-16 | 2000-01-04 | Lucent Technologies Inc. | Recoatable temperature-insensitive long-period gratings |
-
1999
- 1999-09-09 KR KR1019990038267A patent/KR100334801B1/en not_active IP Right Cessation
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| KR100334801B1 (en) | 2002-05-02 |
| KR20010026805A (en) | 2001-04-06 |
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