CN100456064C - High-order golden section Hamming function apodizing edition and method for making chirp optical fiber grating - Google Patents
High-order golden section Hamming function apodizing edition and method for making chirp optical fiber grating Download PDFInfo
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- CN100456064C CN100456064C CNB2006101697367A CN200610169736A CN100456064C CN 100456064 C CN100456064 C CN 100456064C CN B2006101697367 A CNB2006101697367 A CN B2006101697367A CN 200610169736 A CN200610169736 A CN 200610169736A CN 100456064 C CN100456064 C CN 100456064C
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Abstract
A kind of high order golden Hamming function apodizion edition and the preparation method of chirp fiber-optic grating, both ends of the through-carved part of the apodizion edition are narrow, the middle is broad. The ratio of the length of the two ends slowly varying area 502 and 504 and the length of the entire apodizion edition is golden section ratio 0.618, the two ends slowly varying area 502 and 504's length ratio is also golden section ratio 0.618. The curve of the two ends slowly varying area 502 and 504 is Hamming function. The apodizion edition is set up between the light source and the phase mask plate when it is to be used, to make the slowly varying area 502 of the apodizion edition faces to the short wavelength end of the phase mask plate of the chirp, the slowly varying area 504 faces to the long wavelength end of the phase mask plate, the apodizion edition will adjust the exposure intensity of the light source in the two side of the grating in the process of grating fabrication. That this apodized method makes the grating gain good performance, it is easy to handle, the light path system structure is simple and reliable, the repetitiveness is nice.
Description
Technical field:
The present invention relates to a kind of high-order golden section Hamming function apodizing edition, belong to the technical field that fiber grating is made.
Background technology:
Fiber grating be a kind of in optical fiber communication and sensory field of optic fibre important optical fibre devices of extensive application all.One of method for making that fiber grating is the most frequently used is the phase mask method, when utilizing this method to make the high-performance optical fiber grating, except needing high-precision phase mask, also will use the suitable toe technology of cutting.Do not cut Fabry-Perot (Fabry-Perot) effect that refractive indexes sudden change in toe fiber grating two ends causes the grating reflection spectrum will be gone up with strong ripple and sidelobe, and make the group delay curve of grating present big ripple yet, as shown in Figure 1.For the chirped fiber grating that is applied in the dense wavelength division multiplexing system, the reflectance spectrum sidelobe can reduce the isolation between the passage, and the group delay ripple can make the signal through grating produce additional noise or intersymbol interference, the reflectance spectrum characteristic of desirable grating should be smooth and negative edge is precipitous in the reflectance spectrum passband, desirable delay character should be that passband internal linear degree is good, and the time delay fluctuation is little.Cutting toe is exactly that grating index modulation is increased to the center gradually from the two ends of grating, to eliminate the grating characteristic degradation that the index modulation sudden change of grating two ends causes, particularly, cut the toe technology and can reduce the time delay ripple, and reduce reflectance spectrum ripple and sidelobe, make the negative edge at reflectance spectrum two ends become more precipitous.The index modulation change curve of cutting the toe introducing can be functions such as Gauss (Gauss), Blacknam (Blackman), tanh (Tanh) and Hamming, compare through the experimental performance to various apodizing functions, it is best to the inhibition effect and the grating time delay linearity of optical grating reflection spectrum sidelobe that we find that Hamming function is cut toe.
Traditional toe technology of cutting adopts in the one-sided exposure of optical fiber, and the symmetry of the toe ratio of the cutting unanimity at grating two ends is cut the toe mode, though also can reduce time delay ripple and reflectance spectrum sidelobe to a certain extent, but owing to thisly cut the variation that toe can cause grating refractive index modulation DC component, make it to present and cut toe curve similar trend, shown in Fig. 2 (a), provided two kinds of differences in Fig. 2 (a) and (b) respectively and cut two kinds of index modulation distributions that the optical grating axial direct current index modulation that obtains under the toe mode is not constant and maintenance constant.It is asymmetric to cause optical grating reflection spectrum short wavelength end and long wavelength to hold, and the long wavelength of time delay hold present bigger non-linear, as shown in Figure 3.Be head it off, a United States Patent (USP) was once arranged, and (No.US 6,574,395 B1, photic Bragg grating apodization) as shown in Figure 4, adopt two amplitude versions, one is the amplitude apodizing edition, and one for amplitude compensation version, in the preparing grating process, shine on the optical fiber 408 after passing through apodizing edition 405 and compensating plate 406 from the front and back of optical fiber respectively behind the ultraviolet light 402 process beam splitters 403 that laser instrument 401 produces and a plurality of catoptron 404,407 is phase mask.Though theoretically, adopt this technology, can make the direct current index modulation of grating become constant (as Fig. 2 (b)), thereby obtain good reflectance spectrum symmetry, and less reflectance spectrum and time delay ripple.But this method requires the strict conjugation of apodizing edition and compensation version, and require the strictness aligning of optical fiber front and back light path system and have very high stability, requirement to each mirror angle is also very strict, otherwise amplitude compensation version will not have predictive role, can bring negative effect on the contrary.Because system complex realizes that difficulty and repeatability are difficult to guarantee.
Summary of the invention
Shortcomings such as it is too high to the objective of the invention is to overcome above-mentioned apodization complexity, and repeatability is bad realize the raising of grating performance by adopting comparatively simple apodization.
The objective of the invention is to be achieved through the following technical solutions.
The present invention utilizes high-order golden section Hamming function apodizing edition to replace symmetrical expression apodizing edition or the apodizing edition in the conjugation apodization in the classic method and compensates the toe of cutting that version realizes grating.High-order golden section Hamming function apodizing edition, it is characterized in that: it is narrow that the hollow out zone at apodizing edition 501 centers is two ends, middle wide, gradual regional 502 and 504 length and (L2+L4) be golden section 0.618 with the ratio of the length L 6 of whole apodizing edition 501, gradual area part 502 and 504 length ratio (L2/L4) they also are golden section 0.618; Apodizing edition vacancy section length of field L6 is determined by grating length; The hot spot width decision in vertical direction that the width L5 of apodizing edition flat region is sent by ultraviolet source 601; The curvilinear function of the gradual part in two ends is a Hamming function.
Utilize high-order golden section Hamming function apodizing edition to make the method for chirped fiber grating, it is characterized in that comprising the steps:
1) apodizing edition 501 settings are positioned in the middle of ultraviolet source 601 and the phase mask 606, make the short wavelength end of the short side in gradual zone of apodizing edition facing to the phase mask of warbling, and the long side in gradual zone faces toward long wavelength's end of phase mask, and the centre-height of apodizing edition is consistent with the centre-height that light source sends hot spot.
2) in the preparing grating process, after the ultraviolet light 602 that light source 601 sends changes an angle of 90 degrees through catoptron 603, shine on light-sensitive optical fibre 607 after will passing through apodizing edition 501, convergent lens 604 and phase mask 606 successively, wherein catoptron 603 and convergent lens 604 be fixed in one can be by on the computer-controlled mobile platform 605, in the preparing grating process, mobile platform 605 drives the two when moving and moves, thereby form the scan exposure of optical fiber 607 and realization is simultaneously cut toe.
Key content of the present invention is the design of high-order golden section Hamming function apodizing edition, and its design concept is as follows:
The symmetrical apodization of the single exposure of using compensation version does not make optical grating axial direct current index modulation not be constant, causes the optical grating reflection spectrum asymmetric, and reflectance spectrum and time delay all have big ripple at long wavelength's end.Because grating long wavelength end-grain cutting toe is stronger to the inhibiting effect of time delay ripple and reflectance spectrum sidelobe than short wavelength's end-grain cutting toe, so, the toe amount of cutting of appropriateness increase long wavelength end can reduce the bigger ripple of asymmetric and long wavelength end of sidelobe, but long wavelength's toe ratio of cutting to short wavelength's end of holding needs optimization.In addition, if it is to cut the ratio that toe length accounts for the grating total length that the toe ratio is cut in definition, cut then that the toe ratio will influence that the optical grating reflection bands of a spectrum are wide, the Key Performance Indicator of grating such as reflectance spectrum flatness and time delay ripple, therefore the toe ratio of cutting of grating also needs to be optimized, it is excessive to cut the toe amount, can make the bandwidth of reflectance spectrum too small, cut the too small meeting of toe ratio and cause the inhibition effect of grating time delay ripple well inadequately, make the mis-behave of grating.
The present invention has adopted the golden section optimum seeking method of widely using.When selecting long wavelength's end-grain cutting toe ratio, objective function is indeterminate, and total number of test ratio do not have the characteristics of setting yet, adopt this rule can with minimum testing site the fastest find the optimum toe ratio of cutting.Therefore, we adopt the golden section optimum seeking method to the toe ratio of cutting of always cutting toe ratio and long wavelength end, cut under the toe ratio by comprehensive contrast difference, it is 0.618 that the key indexs such as symmetry of grating reflection spectrum and time delay ripple and reflectance spectrum have found the optimum toe ratio of cutting, be that to cut the ratio that toe length accounts for total length be golden section to grating, it also is 0.618 that optimum long wavelength's end-grain cutting toe length accounts for the ratio of always cutting toe length, and the toe length ratio of cutting of cutting toe length and long wavelength's end of short wavelength's end also is 0.618 in other words.
The high-order golden section Hamming function apodizing edition that utilizes the present invention to propose is realized the toe of cutting of grating, only needs grating is carried out once one-sided exposure in the preparing grating process, and the complexity of preparing grating system greatly reduces, reliability height, easy operating, good reproducibility.Simultaneously, the fiber grating reflectance spectrum of producing is smooth, and symmetry is good, and the time delay ripple is little, can better application in dense wavelength division multiplexing system.
Description of drawings
Fig. 1. be the reflectance spectrum and the delay character curve map of the chirped fiber grating of not cutting toe;
Fig. 2 (a) is that DC component is not the index modulation distribution plan of constant, (b) is the index modulation distribution plan of constant for DC component;
Fig. 3 cuts optical grating reflection spectrum and the delay character curve map that the toe mode is made for symmetrical one-sided exposure;
Fig. 4 is for adopting the preparing grating system construction drawing of conjugation symmetry apodization;
The high-order golden section Hamming function apodizing edition synoptic diagram that Fig. 5 proposes for the present invention;
The preparing grating system construction drawing that Fig. 6 proposes for the present invention;
Fig. 7 is hot spot scanning initial sum final position figure in the preparing grating process of the present invention's proposition;
Fig. 8 is the grating reflection spectral property curve map that the method for utilizing the present invention to propose is produced.
Embodiment
The invention will be further described below in conjunction with the drawings and specific embodiments.
The making of the apodizing edition of high-order golden section Hamming function:
As shown in Figure 5, the making key of the apodizing edition of high-order golden section Hamming function is to determine the size in hollow out zone, center.The hot spot that ultraviolet source sent is at the width L5 perpendicular to the decision of the width on optical fiber direction apodizing edition flat region.The length L 6 in the length decision apodizing edition hollow out zone of grating, gradual regional 502 and 504 length accounts for the ratio decision of apodizing edition vacancy section length of field L6 by it on the apodizing edition.For example, the width of ultraviolet hot spot on the vertical fiber direction is 3mm, and desire is made the long chirp grating of 140mm, and then the parameter of She Ji apodizing edition is as follows: the width L5 of apodizing edition flat region is 3mm, and length L 6 is 140mm; Gradual regional 502 length is L2=140 * 0.618 * 0.382=33mm; Gradual regional 504 length is L4=140 * 0.618 * 0.618=53mm.The curve in gradual zone is a Hamming function
Calculate each point coordinate of apodizing edition openwork part according to above-mentioned parameter, and, can on sheet metal, produce the apodizing edition of high-order golden section Hamming function with the molybdenum filament stroke of this control line cutting machine.
The making that high-order golden section Hamming function is cut the chirped fiber grating of toe:
As shown in Figure 6, the laser 602 that ultraviolet source 601 sends impinges perpendicularly on after catoptron 603 turn 90 degrees partially on the apodizing edition 501, and the hollow out zone on the light transmission 501 is incided on the cylinder convergent lens 604, optical convergence after phase mask 606 be exposed on the light-sensitive optical fibre 607.Wherein, catoptron 603 and convergent lens 604 are fixed on the precise mobile platform 605, so catoptron and convergent lens can be parallel to optical fiber with mobile platform 605 and move axially.The weak point gradual regional 502 of apodizing edition 501 faces toward phase mask 606 short wavelengths end, holds and face toward phase mask 606 long wavelengths than long gradual regional 504, and the centre-height of apodizing edition 501 is consistent with the centre-height that light source 601 sends hot spot.
Utilize above-mentioned preparing grating system to make the main technique flow process of grating:
1) light-sensitive optical fibre 607 is peelled off about coat 142mm and clean, afterwards optical fiber is fixed on the back of phase mask 606, make it to try one's best but do not contact phase mask 606 with wipes of alcohol;
2), make the initial position of the hot spot irradiation optical fiber 607 of laser instrument be positioned at the extra-regional starting point of apodizing edition hollow out 701 places, as shown in Figure 7 by computer control mobile platform 605;
3) require to set the pulsed frequency of ultraviolet source 601 and pulse energy (for example can setpoint frequency be that 10Hz, single pulse energy are 100mJ) according to the grating reflection rate;
4) at the uniform velocity move (for example setting speed is 1mm/s) by computer control mobile platform 605 with certain speed, driving catoptron 603 and convergent lens 604 moves, when beginning to move, opens mobile platform 605 laser instrument 601, the ultraviolet hot spot that then exposes on optical fiber will move axially along optical fiber along with mobile platform, realize the scanning type exposure to optical fiber 607;
5) when hot spot moves to position 702, end exposure.The manufacturing process of fiber grating finishes.The coverage diagram of a fiber grating of producing as shown in Figure 8.
Above-mentioned specific embodiment has been described in realization in order to demonstrate the invention, but other variations of the present invention and modification it will be apparent to those skilled in the art that the present invention is not limited to described embodiment.Therefore, at the true spirit of the disclosed content of the present invention and any/all modifications, variation or the equivalent transformation in the cardinal rule scope, all belong to claim protection domain of the present invention.
Claims (1)
1. high-order golden section Hamming function apodizing edition, it is characterized in that: it is narrow that hollow out zone, apodizing edition (501) center is two ends, middle wide, the length (L2+L4) in gradual zone, two ends (502 and 504) and with the ratio of the length (L6) in whole apodizing edition hollow out zone (501) be golden section 0.618, the length ratio (L2/L4) of gradual zone, two ends (502 and 504) also is golden section 0.618; Apodizing edition vacancy section length of field (L6) is determined by grating length; The hot spot width decision in vertical direction that the width of apodizing edition flat region (L5) is sent by ultraviolet source (601); The curvilinear function of the gradual part in two ends is a Hamming function.
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| CNB2006101697367A CN100456064C (en) | 2006-12-28 | 2006-12-28 | High-order golden section Hamming function apodizing edition and method for making chirp optical fiber grating |
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| CNB2006101697367A CN100456064C (en) | 2006-12-28 | 2006-12-28 | High-order golden section Hamming function apodizing edition and method for making chirp optical fiber grating |
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| CN100456064C true CN100456064C (en) | 2009-01-28 |
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1014124A2 (en) * | 1998-12-21 | 2000-06-28 | OTC Optical Technologies Center | Method of and device for optical fibre grating fabrication |
| CN1278069A (en) * | 2000-06-23 | 2000-12-27 | 清华大学 | Optical fiber grating mfg. method with chirp and apodization function adjustment |
| CN1355441A (en) * | 2001-12-21 | 2002-06-26 | 清华大学 | Optical fibre raster iwth sine chirp structure |
| US20030156791A1 (en) * | 2001-12-06 | 2003-08-21 | De Groot Peter J. | Method and apparatus for writing apodized patterns |
| CN1607406A (en) * | 2003-10-13 | 2005-04-20 | 北京邮电大学 | Method for realizing optical fiber raster multiple function apodisation by single exposure |
-
2006
- 2006-12-28 CN CNB2006101697367A patent/CN100456064C/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1014124A2 (en) * | 1998-12-21 | 2000-06-28 | OTC Optical Technologies Center | Method of and device for optical fibre grating fabrication |
| CN1278069A (en) * | 2000-06-23 | 2000-12-27 | 清华大学 | Optical fiber grating mfg. method with chirp and apodization function adjustment |
| US20030156791A1 (en) * | 2001-12-06 | 2003-08-21 | De Groot Peter J. | Method and apparatus for writing apodized patterns |
| CN1355441A (en) * | 2001-12-21 | 2002-06-26 | 清华大学 | Optical fibre raster iwth sine chirp structure |
| CN1607406A (en) * | 2003-10-13 | 2005-04-20 | 北京邮电大学 | Method for realizing optical fiber raster multiple function apodisation by single exposure |
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