TW475072B - Long-length continuous phase Bragg reflectors in optical media - Google Patents

Abstract

A long length continuous phase Bragg reflector and the method and an apparatus for writing the gratings into an optical fiber. The method includes the steps of providing a photosensitive optical fiber and a writing beam. A periodic intensity distribution of period Λ is created from the writing beam and the optical fiber is translated relative to the intensity distribution at a velocity v(t). The intensity of the writing beam is modulated as a function of time at a frequency f(t), where v(t)/f(t) ≈ Λ. The intensity of the writing beam is varied further to control the envelope of the refractive index profile to write apodized gratings. The gratings measure at least 2.5 meters in length.

Description

475072 A7 B7 V. Description of the invention (1) Related applications The present invention is US Application Serial No. 08 / 942,59, and the title is ^ Method For Fabrication Of in. Line 〇ptical Waveguide

Refractive Index Gratings Of Any Length,% Continuation Part Application on October 2, 1997, which is hereby incorporated by reference. Field of invention

The present invention relates to a method for making a coaxial optical waveguide refractive index grid of any desired length and an article manufactured using the method. More specifically, the present invention guides a method of making pure apodization of arbitrary length, fine fiber Bragg grid (FBG), by moving a fiber with the interference of actinic chirp, and performing amplitude modulation on an intensity Is a function of time and a long continuous phase Bragg grid manufactured using this technology. BACKGROUND OF THE INVENTION Coaxial optical waveguide refractive index grids have periodic, non-periodic or quasi-periodic variations in the refractive index of the guided waves. The grid can be formed, for example, by physical imprint-modulation on a waveguide, by using

It may cause variations in the refractive index on the waveguide, or other methods known in the art. In particular, the grid of the nester 1 banged into the core of the advancement is a key component of many optical fiber communication and sensor system applications. Dopants, such as wrong, are added to the waveguide material area to make it sensitive, making the area's refractive index susceptible to infection and increasing exposure to light. The currently preferred method for writing coaxial coaxial grids involves interference between the waveguide of the exposure section and the light emission of the two photochemical beams (usually UV). The ㈣ structure with two beams as the feeder is projected in the 帛 direction to disturb _ 4-

475072 A7 B7 V. Description of the invention (2 That is, a mode of optical interference. The angle between the two beams (and the wavelength of the Korean radiation) defines the interference light fringe interval. Generally, the photochemically transmitted two beams The two sides are generated by emitting a single beam through a phase mask. This phase mask method is generally considered to be more suitable for large-scale manufacturing of coaxial gratings because it has high repeatability and is less subject to optical settings. The effect of mechanical vibrations' can be done with beams written with much shorter coherence lengths.

The advantages of fiber coaxial grids over competing technologies include full fiber geometry, low insertion loss, high slew loss or reduction, and potentially low cost. But one of the biggest differentiating features of fiber grids is that the grid provides the flexibility to achieve the desired spectral characteristics. Numerous physical parameters of the grid can be changed, including the change of the sensitivity at the desired wavelength, the length, apodization, the period is meticulous, the grid correction is tilted, and whether the grid supports linking to a common delay (long_period or Transmission grid) or counter deferred link (Prague grid). By changing these parameters, the grid can be adapted to the specified application.

The versatility of a coaxial grid depends largely on two factors, the body length of the thumb grid structure and the shape of the reflective (or transmission) grid structure itself. The fine radiating shape can be achieved by carefully controlling the refractive index in the waveguide length, χ. The perturbation of this rate is characterized by the period of the phase and amplitude modulation. Number = αι0 (χ) · s Α (χ) + /;/(.〇- cos 1κ Λ, · ν + ㈣ 0) where electricity (; 〇 is the average of the grid period A (χ) in space_ Rate change 'A (x) is a vertical distance (usually called A) ❿ (X) is rate change

Fifth, invent V. Visibility of light lines, A is a very small period, which means that the grid is fine. To automate the manufacturing process, it is hoped that the arbitrary refractive index profile enters the waveguide in a single-processing step, that is, the laser beam passes through the waveguide once without physically changing the writing device. 1 The complete flexibility of the grid manufacturing requires Independently control each parameter plus (χ). In particular, the apodization of the grid spectrum can be achieved by controlling the length of the tree lattice such as 0) and p (X). Once the finite length of the refractive index is adjusted, the main learning value of the co-axial grid in the reflection spectrum # is accompanied by a series of adjacent side wavelengths. Reduce the reflection of the round coating on this side, or "apodization. The reflection spectrum of this grid is desired in devices that require high reflection of non-resonant light. Apodization can also improve the dispersion of fine grids. Compensation characteristics. In most of these applications, it is believed that the hope of dispersion and apodization caused by maintaining the average length across the grid length and the constant A (X) when m (x) changes, it is believed that It is achieved by controlling the laser beam in a single step (with complete flexibility). By changing the rate modulation change of the size of the ultraviolet exposure over the grid length, it also causes the refractive index modulation and the average light Induces changes in the refractive index. Changes in the average rate modulation cause an actual meticulous resonance wavelength of the unwanted grid and widens the spectral response of the grid. To mitigate this symptom, it is desirable to have pure apodization, This grid, that is, produces a non-uniformly modulated ultraviolet light streak pattern and compensation & DC exposure, which automatically ensures that this average light-induced refractive index is fixed over the length of the fiber. Some researchers have produced Come up The desired apodized shape by scattering the phase mask relative to this interference. This scattering reduces the visibility of the light streaks and thus -6-

V. Invention Description (4) The refractive index modulation at a specific position on the waveguide length. The mechanical fixture must be accurately determined by vibration: this phase: mask: two = specific rate disturbance in the guide, the grid length in the fiber-optic pass: and the specific application in the knife sensor system is also very As important as /, long detailed fiber Bragg grids have been proposed as a means of making decentralized :: attractive. High-speed, long-distance data transmission, especially: the original non-dispersed shift optical fiber network is limited by the color gamut in the optical fiber. Because the transmission bandwidth is usually determined by the requirements of the system, it can be used as dispersion compensation in practice. The fine Bragg grid needs to exhibit dispersion compensation in the frequency bandwidth, which will cover the typical semiconductor laser wavelength error. Moreover, such f-band devices may cause unusable wavelengths in the area where the FBG band transition occurs, so it is more desirable to have a large and detailed FBGS that can compensate for the full Er + bandwidth. At present, most telecommunications systems have a mounting base for optical fiber, which is transmitting at 1300 nm, but not at 1550 nm. Because of the availability of 1550 Ω, heterogeneous fiber amplifiers, and low loss limits for fibers that occur in the same wavelength range, high-bit-rate transmission systems have been upgraded to the 1550 nm wavelength range. For non-dispersion-shifted fibers, the fiber dispersion at ⑸ ^ _ is close to 17 ps / nm / km. For distances exceeding 80 km, this results in an excessive dispersion of roughly -1360 ps / nm, which needs to be corrected before the light pulse can be detected. A dispersion-compensated fiber is a better choice for correcting gamut dispersion in this wavelength range. The extremely high nonlinearity of the fiber in a wide frequency band is the disadvantage of this technology. A long and continuous phase fiber grid, which can compensate 475072 A7 B7 V. Description of the invention (5 large-bandwidth color gamut dispersion, may be an alternative to this fiber solution for phase-continuous fibers used for dispersion compensation The Bragg grid usually has a bandwidth of 0.5, 1 and _ at 1360 ps / nm used to correct excessive dispersion. Frequent grids of 0.5 and 1.5 are usually 10 to 30 cm in length and are usually Manufactured with e_beam written in phase mask. Long, wide-band fine grids are usually manufactured using some form of phase mask / fiber scanning technology. The ideal grid based on dispersion compensator will cover the entire blend The bandwidth of the bait's fiber amplifier and the dependence on wavelength dispersion are properly compensated. Such a thumbgrid has a bandwidth of more than 40 nm and requires a length> 800 cm to compensate for the 80-fold connection length. Longer The connection length will require a longer grid. For example, the transmission distance of _ will require a bandwidth of 40 nm and the length of the fiber grid> 120 cm. The grid-based dispersion compensator has a new increase in package size and is smaller than the fiber Advantages to lose The low non-linearity at power means a long delay response. At present, the available phase mask length of grids embossed with traditional methods and phase masks is about ten to two. Production under conditions is also limited to < 2 5 which requires an accurate long Bragg thumb and can be produced in a cost-effective manner. There is a complex grid structure, one of the methods already described, which has a fixed centimeter of u Long phase: mask on the upper ::: For optical fiber :: The structure is modified by changing the exposure time or post-processing this grid and adding the m-knot method to discuss the fixed phase phase mask relative to the special design, its -8 -

V. Description of the invention (6) The structure of the invention has been embossed in a mask, and the fiber is used in a fixed position. However, as indicated above, the length of the available phase masks simultaneously limits these techniques. First, some attempts have been made for long installations by moving the optical fiber with a high accuracy arrangement relative to the interference of the 11 乂 ray. The location of this arrangement is trace interference, and the triggering of this laser is determined by the feedback of the arrangement for the next exposure when the fiber reaches the desired location. The positive 0-cycle phase between these sub-grids can be controlled to produce certain complex structures, such as fine details, and apodization can be achieved by scattered interference / optical fiber locations. Utilization = Talents * In Nortel's group, the Royal Institute of Technology (Swiss ^ 'University ofampton (UK) has reported that the length exceeds the phase mask S. Report. The longest FBGs6々 length < 2 5 meters It is not long enough to :: == 80 km. The complete W of a non-dispersion-shifted fiber is Ϊ = the dispersion of the frequency bands. These methods of connecting the sub-grids to one another are Chang Lu, where 1 Λ 'Γ is the grid The length of the grid is limited to effective and accurate movement-level movements and / or a length of several meters, and requires feedback from the interference meter. The development of = attempts to sweep ζ on a phase mask; nest into the sub-grid (Several elements of the grid and then the smoke is added to the A j.) The growing grid of the surgery room is a complex grid, and its increase force == U between the two is made into almost continuous phase. Want one. UV-fix h Force two, 'Several sub-grids can be connected to another-bit grid ...: two: the grid to move between the appropriate continuous phase of tens of centimeters. The position of this level is traced 1 = still accurate Degree arrangement—touch the desired position of each sub-grid and this transport is triggered when the fiber reaches the position. Position 475072 V. Description of the invention (7 can be controlled to produce complex structures, such as meticulous. And apodization can be achieved by scattered interference / relative position of the fiber. The processing of this connection must be quasi-phase Eye-cutting can only be done by using an interferometer. Shi zmin cry ± zL L · Very Mo The grid produced is often made of quality and time consuming. The maximum practicality that can be achieved by this method. At present only linear motion arrangements can be used Interfering with the 'rotary arrangement' must use a linear encoder. Therefore, the length of the connected fiber grid is limited by the linear movement that can be used with accurate arrangement and acceptable writing errors. Second: Another method The problem is that the protective jump around the fiber must be removed to make a grid. The long fiber that contains this thumb must be removed and wrapped for packaging. So your AA L,, /, is ...: ΐ The longer the length of the naked fiber, the more manufacturing complexity (increasing the processing process) is added, which complicates the automation of production and may reduce the mechanical strength of the fiber. Optical applications and the need for cost-effective writing technology for very long coaxial optical waveguide grids with complex reflection profiles remain. SUMMARY OF THE INVENTION The present invention discloses an innovative method for producing a grid of any length, and The control of each parameter that defines the rate perturbation is independent. The thumb length achieved by the present invention is not limited by the phase mask size and the length of the interferometer that needs to provide i resolution. The limitation of the linear movement stage requirements. The length that cannot be measured is a continuous phase Bragg reflection achieved with the revolutionary grade of innovative characteristics. -10- This paper size is suitable for the standard BS standard (CNS) A4 (21G_X tear public love) Order A7

In the production method according to the present invention, a photosensitive waveguide is provided, such as a photochemical light beamer, such as a uv_laser beam, which is 2 ′ ″, into an optical fiber. To obtain a periodic intensity distribution, use : Disturbance pattern generator ', such as a phase mask positioned in the middle of the writing beam and the waveguide, to generate a period Λ of interference. This waveguide then moves at this accurately controlled relative velocity V⑴ via this relative to the nested beam. Alternatively, For grid applications (but not limited to long FBGS), 1 fiber can be knotted to a reel, its rotation to pull the fiber through the periodic intensity distribution at a speed of V⑴, most ~; the modulator uses a time function f⑴ Intensity changes q / ⑺ two intensity " and width d. Delivery to ⑩ 丨 装 4 (1 2 ,, (

Φ (χ) «; COS ύ) (χ)

X (2) where ω = 2π · ί, v or ω can be held at a fixed value during the writing process or the 疋 parameter can be de-rounded to finely perturb the rate over the length of the grid χ = ν t.

The ordering also includes the step of further controlling the intensity of the writing beam to change the rate of change, the visibility of m, the peak intensity of the exposure to this fiber, and [0]. The distance perturbed by this oscillation rate, A, can also be controlled. The flux delivered to the fiber 0 is then determined by the equation -11-this paper is suitable for financial reasons ^^ s (21〇 X 2_iy ou / z A7

4 ν (χ) | Umbrella) Yiqi os bu)] [2 Lv (x) J will change the visibility and change the visibility, m, so that pure and apodized grids can be made. (3): = This parameter is also changed, that is, the amplitude and deviation of the refractive index oscillation, and the refractive index profile on the fiber length can be accurately controlled. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic representation of a fiber Bragg grid with possible refractive index profiles. Figure 2 is a simplified diagrammatic representation of a refractive index writing component of a coaxial optical waveguide written into a fiber optic grid in accordance with the present invention. Fig. 3 is a simplified diagrammatic representation of the refractive index profile modulation of a coaxial optical waveguide chirp rate writing assembly written to an optical fiber grid according to the present invention. Figure 4 is a simplified representation of a specific example of the present invention, in which the optical fiber is pulled by a spool. Fig. 5 is a graph showing a fine refractive index profile of a waveguide produced according to the present invention.

Fig. 6 is a graph showing a pure apodized refractive index profile of a waveguide produced according to the present invention. FIG. 7 is a simplified schematic diagram of dispersion compensation according to the present invention. FIG. 8 is a flowchart of a specific example of the method of the present invention. Fig. 9 is a reflection and delay curve of a first fiber optic grid according to the present invention. Fig. 0

FIG. 10a is a graph of transmission of a second fiber optic grid according to the present invention. Fig. 10b is a graph of the delay of a second fiber grid according to the present invention. -12- This paper size applies to China National Standard (CMS) A4 (210X 297mm)

DESCRIPTION OF THE INVENTION (10) FIG. 11 is a curve of a transmission spectrum of a third fiber optic grid according to the present invention. FIG. 12 is a view of the first fiber optic grid heated at a distance of ~ 1.5 meters from the end of the short wavelength endpoint. A graph of the spectral difference before and after. Figure 13 is a graph of the spectral difference before and after heating of the third fiber grid at a distance of ~ 6 meters from the start of the short wavelength endpoint. Figure 14 shows the dispersion compensator according to the present invention. Block diagram. Figure 15 is a block diagram of a broadband light generator according to the present invention. Figure 16 is a block diagram of a fast spectral pulse interrogator according to the present invention. Figure 17 is a diagrammatic representation of a sensor according to the present invention. is is a graphical representation of the m system, which queries the already written fiber grid phase and uses this signal and a processor to control the Ao modulator frequency as the grid moves through the laser beam. Details of the invention For the sake of simplicity, several examples provided in this specification will lead to the formation of a long Bragg grid in the light .. However, those skilled in the art can perceive that the grid can be other Formation of optical media, silk Direct exposure or exposure through photolithography after traditional lithographic processing. Similarly, the method and article of the present invention can be applied to other forms of grids, such as reflective grids. ^ Long Prague in the present invention Grid (llfbgs) is defined as grid = traditional Bragg grid with traditional Bragg length that can be obtained by traditional methods-an optical fiber 1 with a long grid 20 of length L is illustrated in the figure}. This optical fiber 1G usually contains oxidized debris, although Others known in the art are -13-297 mm.) B7. 5. Description of the Invention (11) Examples of examples may include plastic compounds. This optical fiber includes a core wire i 2 and one or more claddings 1 4. This grid 20 is a series of periodic 'aperiodic or quasi-periodic changes on the core line n 2 and one or more coatings 14 of this fiber. As illustrated in the pairing graph shown in FIG. 1, the grid 20 contains the change in the refractive index of the optical fiber 10. FIG. 2 illustrates a rate writing device 100 using the writing method of the present invention. This rate writing component includes a light source that generates the light beam 132, an interference mode f generator 140, a modulator 150 ', and an optical fiber support component 6o which supports the optical fiber 11o. More than one waveguide can be placed in this rate writing assembly at the same time. Germanium or other photosensitive dopants are added to the oxidized glass region of the optical fiber 110, so that the refractive index of this region of the optical fiber is easily affected and increased by the increase in the photochemical II exposure. It is possible to use a mass-produced photosensitive fiber ’such as c〇rning⑧ CPC6 (Corning

Incorporated, Corning, Nγ). Those skilled in the art will recognize that the method of the present invention can also be used to modify not only the refractive index of optical fibers, but also other waveguides, such as planar waveguides. " Light source 130 is a source of photochemical radiation, such as v laser light or X_ light. Select this light source to deliver sufficient intensity and to write a grid of «. Other light sources developed in this technology can be used, depending on the form of fiber used and the desired grid pattern. The light source 130 generates a light beam 132 having a peak value of 10 and a diameter of 0. The interference pattern generator 140 generates an intensity distribution with a period of eight and is located between the optical fiber 110 and the light source 130. The period of this intensity distribution usually matches the desired grid spacing. The intensity distribution is a repetitive light intensity mode that varies with space -14-

475072 A7 B7 V. Description of the invention (12) Formula ′ may be periodic or pseudo-periodic, such as interference. This interference pattern generator 1 40 is a phase mask MMMLasirus PM-248-1.078-25.4 (Lasirus Inc. 5 Saint-Laurent, Quebec 5 Canada) with a period 2 Λ of a period U78 μm, which generates an interference of 0.539 μm . This interference can be caused by other methods, such as interferometers. Alternatively, those skilled in the art can perceive that the intensity distribution of the periodic (or pseudo-periodic) photochemical radiation used to make the grid need not be obtained by constructing a disturbance. For example, an image reduction system using amplitude masking can be used to generate this intensity distribution. Fig. 3 illustrates a specific example of electronic signal control of the modulator 150. The electronic signal control of the modulator 150 includes the amplitude modulation function 5 2, the frequency modulation function 1 5 4 and d · c. Offset 1 5 6. There are many different types of modulators that can be used. For example, a light modulator (for example, IntraActiOI1 ’s

IntraAction ASM-1251LA3, BellWood, IL). This modulator 1 50 0 'modulates the light beam 1 3 2 at an amplitude f (t). In addition, as shown in FIG. 3, the electronic signal that controls the modulator can be given a shape by a function generator, such as Stanford Research Systems DSM345 (Stanford Research Systems, Sunnyvale, CA), to fit the shape of this rate perturbation over the fiber length. Creates a detailed and apodized result grid. This optical fiber 110 moves at a speed v (t) with respect to the intensity distribution. More than one waveguide can be moved simultaneously via this periodic intensity distribution. A laser light number is amplitude modulated as a function of time and a phase mask is used to generate FBGS of any desired length. In this example, the optical fiber 1 10 moves at an accurate speed v (t) and transmits the laser light through a phase mask 14. The laser light is -15- This paper size applies the Chinese National Standard (CNS) A4 specification (210X297 mm) ) A7

It is based on the light-emitting frequency ω (ω = 2π · f), where / (0, v (〇 beam 1 32 Λ is taken as the desired shape and the desired shape 'f⑴ and ν⑴ can both be variable gates = 1 = ί Fixed value. Of course, the term fixed value is defined in the receivable parameters of the optical fiber compartment 4 (δΛ) due to disturbances or errors. 'In the modulator of the moving mechanism. This disturbance causes the grid circumference error. . 1

The movement of the fiber 110 relative to the intensity distribution is accurately controlled by the movement mechanism. This optical fiber 110 is mounted on the optical fiber supporting assembly 6o, a very accurate speed control motion stage, which can be a rotary or linear stage. In an alternative specific example, illustrated in Fig. 4, a continuous length of light: is wound on a reel 170 and the position of the writing beam is tracked and held on the light as the reel rotates. The movement of this stage or reel is linked to synchronize with the modulator '. In another alternative embodiment, this movement mechanism

The motion of the light source 130 and the interference generator 140 can be controlled. In another specific example 7 0, as shown in FIG. 8, a feedback signal from the processor 7 6 〇 is fed to the modulator 7 7 〇 and the modulator 7 7 〇 according to the detector 7 The relative phase detected at 20 is switched. The feedback signal 7 2 0 is generated by measuring the relative phase between the reflected reflected light 7 3 0 and the diffracted light beam 7 4 0, and both are emitted from the source 7 1 0. The reflected light is reflected by a mirror 7 1 5 and the interference between the two beams is detected by a detector 7 2 0. A phase mask 790 and a laser beam 780 are written into a grid on the optical fiber 750 according to the method of the present invention. When the fiber is moved, the beam passes in the direction 795. This feedback signal can be used to switch the beam on or off or modulate the signal in a sinusoidal manner. Therefore, -16- this paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 475072 A7 B7 V. Description of the invention (14 If the speed of this level is 2; The switching time (1 / f (t)) of the selected transformer in the grid phase will change in a corresponding manner, so that / (/) = eight is maintained at this set point. A fine grid can be generated using this feedback method 'By adding a phase error signal to the modulation feedback signal. Adding a linear phase error will cause the linearity of the grid to be fine. The phase of this grid can be diffracted by the first order from the grid To measure the reflection of the laser from the fiber. Assuming that the position of the fiber in space changes perpendicular to the axis of the fiber, the phase of the interference between this reflection and the diffraction beam will be identified relative to the position on the fiber The grid phase according to the present invention can be produced by using the device of FIG. 8 and the modulator guides light to write into the grid. It is only guided when the caret causing the phase interference of the grid light is written. Also, this grid can be made in tone The light guide is introduced to the grid only if the pilot signal plus the added phase errors cause interference optical phase grating writing the added function causes the number of fine fibers combined phase grid.

The laser beam 1 3 2 does not need to be moved relative to the phase mask 1 4 0. It can be expressed mathematically as

line

φ (.ν) = J y0.sin:-/ 2

(4) This credit can be simplified as: -17- This paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 5. Description of the invention (15 Φ〇): ν 1-sine 1. --Sine 2 2π Τ D -sincf £) ν2 · ν cos ω ω '— · X Η ---—. Γ) v 2 · ν D · rln: ω,-土-• cos soil ^ ~ · X- D ·-L Bayi ν Yi IU ν 丄 (5) ν 7, 1 〇 is the peak intensity of the irradiated fiber, D is the desired grid spacing defined as Λ, where ~ 土 v (〇 八 直 仏 is greater than the phase mask Equation (5) is simplified as the straight line of the beam to 'Φ (χ) is the flux sent to the fiber, m is the rate change and A (x) is the offset of the oscillation rate disturbance. The third term It is pointed out that in the use of small write beams, such as sub-micron diameter lasers, or alternative specific examples where the laser beam is smaller than the desired fiber grid spacing, a phase mask is not required. * 士 Λ. 广 / ν Λ If the beam 4 ν • sine n (2 / τ ω ^ i2 / r VI DA — ± — • cos ± --Λ.-Z) · LUW · \ · l The first term in AV person ⑹ () (which Actually two) with one adjustment 2 .K CQ \ 一 f (t \ 1 妖 Λ ν — if — = 丁 (where ω = 2πί), beij ij v (t) Λ φ⑴

D * {ι • cos .v (7) Finely adjust the frequency of optical amplitude modulation or change the speed of the fiber. ^ In the field mode, you can produce detailed FBGs of any length. Figure 5 illustrates an exemplary fine refractive index profile of an optical fiber made in accordance with the present invention. The small phase mask of the field period (assuming "..d ·) can be used to make very long: -18-

Grid, which is detailed over a very wide wavelength range. In the present example, this dispersion compensation product covers the entire doped range from ⑽ to 1568 nm. The fineness of -40nm is written into the single-FBG by the micrometer laser beam, and # is maintained by the argument of the sinc function in equation (6) being less than redundant. A fine 4nm fbg can be written with a beam of ~ 100 microns. These diameters are mathematically upper bounds: In practice, you should use a diameter less than half of this size to write the grainy visibility into this raster. When the frequency of the optical modulation or the speed of the fiber changes, the adjustment of the S Π1 C function parameter in equation (6) will increase from zero and reduce the spatial modulation size of the cosine function. If these parameters are changed too much, no net modulation will occur. This reduction in size is proportional to the straight a of the laser beam, which can be focused to make a wide range of wavelength finesse possible. The limitations of this relationship S 丄, V⑴ Λ are in the limit that sufficient refractive index modulation can be written into this wave tube to produce an acceptable grid. Depending on the shape and accuracy of the grid to be written, the difference between the two sides of the above equation can be, for example, as large as 〇0%. The key difference between this inventive method and other coaxial grid fabrication technologies is that in the present invention, the motion between the optical fiber and the interference is speed controlled. Conversely, other technologies for producing long grids rely on precise positioning devices (rate reduction) ', which are based on position control as defined by the Michelson interferometer. Because of the disturbance in the equipment, the deviation of the fiber grid spacing (δδ) can be modeled by this level of speed 2; = 2; 〇 ± 52 > and {= (〇 ± 5 (, where δ υ and δ f Are the respective perturbations. This fiber grid spacing will be -19-

The paper size is suitable for SS Home Standard (CNS) Λ grid (210 X 297 Mod W 475072 A7 B7 V. Description of the invention f〇 ± Sf / 〇1 Soil νΛ / 〇 (8) FBG resonance wavelength results due to equipment disturbance The grade of the deviation is δλ δ, δ f-= Toast ——— Enter 0 ′, 〇— / 〇 * (9) Such a speed or modulation error produces an error in the grid cycle phase, which can be obtained by this level The speed control can be reduced by providing a feedback deduction derived from the grid phase in which it is written. To produce a grid with a longer operating range than an accurate motion level, the fiber can be pushed through the mesh to interfere with the system This fiber will be placed in a V-groove, or an accurate v-groove pulley, similar to the fiber support assembly 16 illustrated in Figure 2, to maintain the fiber's accurate alignment in interference mode. Because this The invented method requires speed control. In contrast to accurate positioning, this fiber can be rolled onto a reel, as illustrated in Figure 4, which rotates to move the laser beam modulated by the phase mask from the 74 The continuous length of the fiber before the interference The reel 170 is part of a reel system. The reel speed of these reels is achieved by using the spindle horsepower controlled by a simple phase-locked loop circuit 76 to provide accurate edge speed. As illustrated in Fig. 4, the light beam 174 is held on the optical fiber 172 by moving the light beam 174 synchronously with the rotation of the reel 17 by moving vertically. The position of the writing beam 174 can be tracked, for example, with a laser beam, and rotates on a rotation axis. It is maintained on the optical fiber 1 7 2 at all times. = In another alternative embodiment of the present invention, the uncoated optical fiber can be permanently fixed on the reel, and the reel with the grid can be packaged, thereby reducing

Binding

Line -20

Processing of optical fibers. The inventive method can also be used to generate an apodized fiber Bragg grid, A has a refractive index profile as illustrated in FIG. 6. A pure apodized grid can be produced by the method of the present invention 'by modulating the amplitude of this sine wave signal, by another function generator or appropriate electronics, when the optical fiber moves through interference. To achieve pure apodization, control and seal the T mountain before applying an offset .. {伞) __). Cos ω {χ) [2 Bu (X) J where if Α (χ) = 1 Then amplitude modulation, m, change between zero and one (10)

Φ (χ) «Z〇ίί) ._ ^ 4 ν (χ) Motion. Those skilled in the art can perceive that the intensity of the irradiated optical fiber, 10, the speed of movement, V, and the deviation of the perturbation of the oscillation rate, A, can also be controlled to fit the refractive index profile of the grid. If this peak intensity, speed, and deviation remain constant as a function of time, the average flux to the fiber is a sufficient value ', that is, regardless of the level of amplitude modulation. 4 ν

Detailed FBGs with pure apodization can be produced in a one-step write process without the need for special phase masks, attenuated convex mirrors, or controlled laser beam attenuation. For example, a linear fine FBG with a width of 4 nm and a length of 160 cm can be crossed by moving the fiber at a speed of 1 mm / s over a period of 73 μm with a phase mask of 9 μm to produce 'linearity in the frequency of the laser beam chirp When the ground moves from 1859.98 wheat to 1864.76 Hz (4.784033 Hz amplitude). Because this grid takes 1600 seconds to write, the apodization of the protruding sine can be done by modulating the output of this function generator with a sine of 0 · 3 12 mHz. Other amplitude chirped profiles can be used to fit Fbg for specific applications. -21-This paper size is in accordance with Chinese National Standard (CNS) A4 (210X 297 mm) V. Description of the invention (19) Long optical fiber bra produced according to the present invention-used in applications. Figure 7 illustrates the use of a long fiber Bragg: = device 200. The signal 28 0 is in operation 2 10 is in the knife government patch (usually a level of several hundred kilometers), bearing: when the length of the fiber rear loop device 2 84, its guide signal z 2 domain is scattered. This signal is connected to each of these; the soil spoon is a detailed Bragg grid 2 1 0. = #Running 11: = over the fiber Bragg grid. The extra running distance recompresses this signal and sends out the knife compensation 唬 k 2 2 2 to the circulation device 2 8 4. = Conductivity of: a flowchart of the production method of the grid in fact be coaxial any length of light waves emitted invention to work. Provided-actinic projection of the nest. If this beam is smaller than the desired inter-grid interference pattern generator, otherwise the tone & Λ ΛΑ, and the periodic intensity distribution of the eighth period Λ will be generated from this beam. A light-sensitive waveguide is provided and placed between paths across the write beam. Then "this waveguide modulates the intensity of the writing beam as a function of time at a speed relative to the speed of the writing beam" and adjusts at a frequency f⑴ as a function of which 7 ^ ΓΛ. If a desirably grid is desired, the intensity of the embedded beam can be further varied to control the envelope of refractive index perturbations. The method of the present invention provides the ability to write a refractive index grid of a coaxial optical waveguide with a complex refractive index profile of virtually any length. Availability grids longer than one meter allow, for the first time, grids to be used effectively in many different applications. In the pending US application No. 08 / 942,59, the title is "Method Fab Fabrication of In-Line Optical Waveguide inactive Index Gratings of Any Length", which is also incorporated herein by reference, the present invention The method can also be applied to write long-period gates of any length -22-degrees. Applicable to China Standard (CNS) A4 [Grid (210X297 public love) 475072 A7 B7

Grid without using a phase mask. As will be apparent to those skilled in the art, the innovative methods disclosed in this document can be used to modify not only the refractive index of optical fibers, but also planar waveguides. Long fiber Bragg grids (LL FBG) have been written into optical fibers using the method of the present invention. 633 and 1055 cm long phase continuous fiber grids 30, written on 3M photosensitive fiber, which are at ~ 2000 ps and 60. 〇 > Hydrogen loading for 3 days. A length of 3MS-sensitive optical fiber is stripped of its protective cover and wound on a reel in a spiral manner. A beam of photochemical radiation, such as ultraviolet laser light at a wavelength of 244 nm, is focused and emitted through a phase mask to cause interference on the fiber. The reel then rotates at an accurate angular velocity to move the fiber across the writing beam, and the intensity of the writing beam is modulated at a frequency determined by the fiber's moving speed and the interference period. Spectroscopy is recorded using erbium-doped fiber to amplify the self-emission source and a spectrum analyzer or a trimmer laser and wavelength meter. The measurement of the delay is recorded using a trimmer laser, a wavelength meter, and an optical network analyzer at 25 GHz. The optical and delay curves are recorded with a resolution of 1 pm and a modulation frequency of 0.2 GHz. Example 1 FIG. 9 is a graph showing reflection and delay of a 30 cm, 2 bandwidth fiber grid written on a 3 M photosensitive fiber according to the present invention. The small ripple in the wavelength-dependent delay curve is about 75 ps. This grid shows a short fiber grid suitable for reasonably high quality.

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Example 2 A wide-band, long grid was fabricated in a 3 M photosensitive fiber exposed to ~ 2000 ps, 60 t: for 3 days. In this case, a long (> 6 · 5 meter) optical fiber was stripped in a hot sulfuric acid solution and then wound on a 300 cm circumference reel. This reel rotates at a speed of 12 rpm to move the fiber at ~ 6.33251 mm / s across the 244-nm wavelength of light provided by the frequency-doubling Ar + laser, the writing beam of light. A phase mask of ι · 〇739-micron period is used to establish a spatial modulation period of 0.553695-micron interference. The intensity of the writing beam is modulated by a photodiode converter in a linear range from 1793 478516 to 1 1823.886698 Hz (in the range of 60.816364 Hz), while the grid is written to produce 8 nm Wide fine grid. The resulting 63 cm long grid was made in 1000 seconds. The transmission spectrum of the resulting grid is illustrated in Fig. 10. The light emitted from the amplified self-emission source (Er + doped fiber base) enters the grid and is analyzed by a spectrum analyzer (HP 70952B), which has ~ The spectral resolution of oi nm is measured by measuring this transmitted light. As shown, the result is a 6-meter long grid with an optical bandwidth of ~ 8 nm. The optical delay of this grid is obtained from an adjustable laser (Hp 8 丨 68F), which decays at 0.2 GHz, emits a light into the grid and then measures the phase shift of the reflected light modulation as Network Analyzer (HP 8353D) as a function of wavelength. The optical path length for each wavelength is constructed from this information. As shown in the delay curve illustrated in Figure 11, a differential delay of ~ 7754 ps / nm is measured at a wavelength ranging from ~ 1556 nm to 1562 nm. This transmission spectrum was recorded using a spectrum analyzer with a resolution of 0.1 nm.

Η

Line-24- This paper size applies Chinese National Standard (CNS) A4 specification (210X 297 public love) ________ B7 _ V. Description of the invention (22) The low laser power and optical loss in this thumb make the reflected signal too weak It is not possible to measure delays in the range of ~ 1554 to 1556 with our measurement system. As shown ', this optical element is highly dispersed and can be used in several applications discussed below. Example 3 A second wideband, long grid is made with the same form of fiber and uses the same laser source, and is set up as described in Example 2. A 11-meter-long fiber segment was stripped and wound on a reel. This reel is rotated at 2 rpm to move the fiber at ~ 10 · 5542 mm / s. The intensity of the writing beam is adjusted 'text' by a light-coupled modulator at a frequency linearly ranging from 1963 458675 Hz to 19681.138980 Hz (in the range 50.680305 Hz) while the grid is written to produce 4 nm wide detail. The resulting grid of 10.55-meters in length was made in 1,000 seconds. The transmission spectrum of a 1055 cm long fiber Bragg grid is plotted in Figure 11. As shown, this 10-meter-long grid has an optical bandwidth of ~ 4.5 nm (-meticulous ~ 45 nm / m) and provides a maximum attenuation of 2 dB. Again, this grid can be used in applications described below. One application of this grid is as a distributed sensor, where localized disturbances to the grid can be detected by measuring changes in the transmission spectrum. A soldering iron is used to heat a short section of this grid at a short wavelength from the thumb, which starts at ~ 15 5 4 5 nm and ends at 5 meters. The wavelength shift due to heating is expected to occur at approximately 0.7 nm at 1555.2 nm. The difference spectra of the heated and unheated grids were taken, and the peak occurred at 1555.25 as expected. Figure 12 illustrates the result curve of this experiment, showing the difference spectrum before and after heating at the shortest -25-A7 B7 V. Invention Description (23) Wavelength end starting point ~ 1.5 meters. In order to further show the effectiveness of these long grids as distributed sensors, the first point on the grid, at the start point of the short wavelength end ~ 6 meters, is heated and the difference spectrum is recorded. The peak value of the difference spectrum at 1557.25 nm was generated by heating at about 450 cm from the first position. Figure 13 plots the results of this experiment. Therefore, the invention demonstrates for the first time the production of more than 2.5 m Ll FBGs. Utilizing the method of the present invention, measurement of LL FBGs previously impossible, four, acupoints, ten meters or any desired length are possible. The LL FBGs according to the present invention can be used in many different devices for several applications, such as in the area of discrete components for fiber optic communication and fiber optic sensors. A. Dividing element A color gamut dispersing element can be produced according to the present invention by varying the FBG period over its length. Grid dispersion over a specific optical bandwidth is directly related to the length of the grid; longer lengths can produce more dispersed structures than shorter lengths. ° FIG. 14 illustrates a dispersion compensator 300 according to the present invention, which includes a u FBGs 310, a grid similar to that described in Example 2, and a light cycling device 3 2 0. Color gamut dispersion in a long, non-dispersion-shifted silica fiber can cause considerable optical pulse distortion and lead to adverse consequences for the transmission system. Changing the original optical wave system to a channel of 10 Gb / s usually requires dispersion compensation, which can be achieved by passing the distorted signal through a device equal to or opposite to the connection of the transmission system. ^, The meticulous write in LL FBG 310 to compensate for differential delays in optical transmission systems, regardless of whether they are linear or non-linear wavelengths. Last name fruit from the grid Reflection experience-difference time delay r is equal to Yun = 2 „/ cC where C is a table: Cheng -26- This paper size applies the Chinese National Standard (CNS) A4 specification (210X297)

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The nm / cm grid is detailed, c is the speed of light, and n is the effective refractive index of the transmission mode in the fiber. Regardless of optical nonlinearity and higher-order dispersion, choose this carefully, so that the reflection of the transmission fiber length L / cancels out the grid dispersion, =, where D is the dispersion of the fiber (usually 17 ps / nm / km). This grid must also be long enough to ensure the entire recent signal spectrum △; ls is suitable, which is Lg > Δ As / c. For example, a grid of fine C3 0.05 nm / cm is needed to compensate for the dispersion introduced on a 1000 km standard communication fiber. To compensate for Er + doped fiber amplifiers with a wide width of 40 nm, carefully measure the length of ~ 8 meters with FBG 3 10. To compensate for the dispersion introduced by longer fiber links or wider optical bandwidths, grids that replace specific examples can be proportionally longer. The grid strength of LL FBG 3 10 can also be controlled over the grid length. When grid 3 1 0 is refined to produce a grid with reflective properties, it flattens the uneven gain profile of the doped fiber amplifier. Therefore, the compensator 300 compensates for the dispersion of the color gamut and finishes shaping the shape of the spectrum. Figure 15 illustrates a broadband light generator 400 according to the present invention. The generator 400 includes a long fine fiber grid 4 10 and a light recycling device 42. This generator is used as a pseudo-CW light source, for example, a high-performance interferometer fiber optic gyroscope. In high-performance interferometer fiber optics, it is important to use a light source with a very wide optical spectrum. A mode-locked fiber laser can be used as a source with a broader spectrum (50 nm wide and centered at 1570 nm) than the most commonly used extremely luminescent diodes. However, mode-locked pulses produce high learned intensity, which increases errors in the gyroscope due to Kerr nonlinearity. At present, -27- This paper size is applicable to Chinese National Standard (CNS) A4 specification (210X297 mm). __ —__ B7 V. Description of the invention (25) To avoid these errors, send a 25-kilometre fiber with a pulse. It is used as a blade element to smear one pulse in another. This highly detailed pulse then looks like C W radiation. In the generator 400, this detailed LLFBG 410 replaces a huge reel containing 25 kilometers of optical fiber. The fiber grid is long enough to detail the pulse over a 50 nm wide spectrum. It also controls the intensity of the grid over the length of the grid, when the grid is refined to fit the output of this spectrum. FIG. 16 illustrates a fast spectral pulse interrogator $ 00 according to the present invention. The interrogator 5 0 0 includes a detailed LL FBG 510, a circulation device 5 1 5, a high-speed photodetector 5 2 0, and a time / spectrum comparator 5 4 0. The output of the comparator 540, the spectrum derived from the known spectrum / delay effect of the grid 560, is also shown. The spectral shape of the light pulse is determined by sending a pulse to the detailed LL FBG 5 10 and detecting the reflection with a high-speed photodetector 5 2 0. If the short-term shape of the pulse is independent of the wavelength, or the relationship between the two is clearly known, the photodiode response can be recorded as a function of time and the spectral shape of the pulse can be taken from this information. For a specific optical bandwidth, the length of the grid 5 10 is directly related to the spectral resolution of the system. Therefore, it is highly desirable to have long FBGs. B. Fiber Optic Sensor FIG. 17 illustrates a sensor 600 including an LL FBG 610. This sensor 6 0 0 can be connected to the optical analyzer 6 2 0 and used to determine the intensity of uneven measurement over very long lengths, such as those of a car bridge or a road. Although most of this sensing technology based on short grids only utilizes the wavelength-encoding nature of this device, this device provides a more innovative approach that includes inter-grid sensing. This method involves a detailed analysis of the reflectance spectrum in order to obtain a continuous profile measured over the grid length. This technology makes use of this factor. When this grid spans its length -28- this paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 male sauce). 5. Description of the invention (26) has an uneven period. ' Different sections of the grid will cause different wavelengths to invert and analyze the intensity or phase components of the reflection spectrum.4 At the same time, both can allow the wavelength displacement to be derived as a function of the length of the grid and detect the grid. ^ Measure the distributed tensile force caused by I over the length. Phase-continuous LL will allow measurement of very long lengths in harmful or unreachable environments. The methods and specific examples described and illustrated here are only recorded in the journal, and should not be a reference to the scope of the present invention. Restrictions. Those skilled in the art will recognize that other changes and modifications can be made in accordance with the spirit and scope of the invention. Description of component symbols 1 〇 Optical fiber 1 7 2 Optical fiber 1 2 Core wire 1 7 4 Modulated laser writing beam 1 4 Cover 1 7 6 Simple phase-locked loop circuit 2 0 Shelf 2 0 0 Dispersion compensator 1 0 0 rate write component 2 1 0 long fiber Bragg grid 1 1 0 fiber 2 8 0 signal 1 3 0 light source 2 8 2 dispersion compensation signal 132 beam 2 8 4 loop device 140 interference pattern generator 3 0 0 dispersion compensator 1 50 modulator 3 1 OLL FBG 1 5 2 Amplitude modulation function 3 2 0 Optical cycle device 1 5 4 Frequency modulation function 400 Broadband light generator 1 5 6 d .c · Offset 4 1 0 Long fine fiber grid Grid 1 6 0 Optical fiber support assembly 4 2 0 Light circulation device 1 70 Reel 5 0 0 Fast optical language pulse interrogator-29- This paper size applies to China National Standard (CNS) Α4 size (210 X 297 mm) 475072 A7 B7 V. Description of Invention (27

5 1 0 Fine LLFBG 7 1 5 Mirror 5 1 5 Circulator 7 2 0 Detector 5 2 0 High-speed light detector 7 3 0 Reflected light 5 4 0 Time / spectrum comparator 7 4 0 Diffractive beam 5 6 0 Grid 7 5 0 Fiber 6 0 0 Sensor 7 6 0 Processor 6 1 OLL FBG 7 7 0 Modulator 6 2 0 Spectral Analyzer 7 8 0 Laser Beam 7 0 0-Example of Rate Writing Module 7 9 0 phase mask 7 1 0 source 7 9 5 optical fiber moving direction order

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Claims (1)

A8 B8 C8 D8 Patent application scope The grid l A method for producing a refractive index in a refractive index grid of an optical waveguide has a desired grid pitch Λ, the method includes steps. Provide a photosensitive waveguide (10); provide a photochemical radiation (132) writing beam; moving the waveguide at a speed V (t) relative to the writing beam; = the intensity of the writing beam is a function of time at the frequency f⑴, which is 2: method of applying for patent scope β It also includes the step of establishing this waveguide state from the intensity distribution of the writing beam with a period Λ and the movement of the knives with a strength of 8%. 3. ^ Method of applying for patent scope "or 2 items, providing the 写 of the human beam, including providing a strong value of t with the irradiated fiber. And wide tapping, gan r + > ft.»… A .. a_ knife Two jo D 4 v (x) LW-m (〇X) -cos ω (χ), 2 Lv (x) 'Φ (χ) where A is the offset and m is the visibility of the light pattern. 4. A long phase Continuous Bragg grid, its package · an optical waveguide (10); and-the grid (20) is embossed on the optical waveguide, where this is less 2.5 meters. J K / §: to 5 · For example, the Bragg grid of item 4 in the scope of the patent application is at least four meters. # The length of this grid in 6. The bragg grid in the scope of the patent application is 4 or 5, and the grid is -31-475072. A continuous phase Bragg grid 7. If the Bragg grid device of the patent application No. 4 '5 or ㈣ is a photosensitive optical fiber and this grid is-continuous grid, 8袼 grid: ,, refractive index perturbation. There is a periodic change in motion over the length of the grid. Among them, the refractive index 9 is as described in the patent application range 4, 5, 6, 7, or 8 and the grid is written using a revolution level. > The Brasserie grid of 10, such as the Brasserie grid of the dragon y bay of item 4, 5 or 9 of the scope of patent application, which is detailed. Dan T. Sanger 11. A light dispersion compensator (300) Bragg grid. 12 · —A kind of broadband light generator (400) Bragg grid. Where the waveguide disturbs It contains item 4 of the scope of patent application. It includes 13_ a fast spectral interrogator (500) including the scope of patent application, which contains the Bragg grid of the scope of patent application. 14. A sensor (600) comprising a Bragg grid of item 4 of the patent application. Line 15 · —A kind of optical medium reflector, comprising: an optical waveguide (10); and a grid (20) embossed on the optical waveguide, this grid: at least 2.5 meters in length, the grid The grid frequency bandwidth is greater than 0.0 5 nm, the reflection intensity is at least 0.1 dB, and the phase error in the grid period is at most 0.087 diameter. -32- This paper size is applicable to China National Standard (CNS) A4 (210 X 297 mm) 475072 AB c D The patent application scope The loss in the exposed part of the fiber is at least 2 0.1 dB / m, and the reflection intensity outside the band is less than -5 dB. 16. —An optical medium reflector, comprising: an optical waveguide (10); and a grid (20) embossed on the optical waveguide, of this grid: the grid bandwidth is greater than 0.0 5 nm, The length should be at least 4.0 meters, the reflection intensity should be at least 0.1 dB, the phase error in the grid period should be at most 0.087 diameter, the loss in the exposed part of the installed fiber should be at least 2 0.1 dB / m, and the reflection intensity outside the band should be less than -5 dB. . Line -33- This paper size applies to China National Standard (CNS) A4 (210X 297mm)