JPS62500807A - Foam birefringent fiber and manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Foam birefringent fiber and manufacturing method Background of the invention FIELD OF THE INVENTION This invention relates generally to fiber optical waveguides and specifically relates to fiber optic waveguides. For example, it concerns a fiber optical waveguide whose core has two refractive indices; More specifically, a fiber propagating a single mode of optical energy with a defined polarization It relates to ohmic (form) birefringent optical fibers.

When two layers of materials with different refractive indices are layered optically and periodically , the optical wave action is different from the action in a homogeneous medium. The thickness of each layer is compared to the wavelength of light. When small enough and when the number of layers is large enough, the composite medium is birefringent. Huo Although the beam birefringence is large compared to the molecules of the material, it is Ordered layers of optically isotropic material, having small dimensions in comparison arises from placement. Fiber optic devices using foam birefringent fibers are Helps configure rososcopes, sensors, frequency shifters, and communication systems .

Several problems arise when forming the devices listed above using conventional fibers. Ru. Strictly speaking, a normal axially symmetric single mode fiber consists of two It is a "two-mode" fiber because it propagates orthogonally polarized HE modes. . Each polarized light has one propagation constant, but in normal optical fiber, there are two propagation constants. Since the numbers are almost the same, degeneracy occurs. By propagating two orthogonal polarizations , when geometric perturbations occur in the fiber, instability of the polarization state of the propagated mode occurs. Jiru. The propagation of degenerate polarization states also causes the two polarization modes to be slightly different. Polarization mode dispersion occurs due to the velocity. Polarization instability and mode content Optical fibers are widely used in applications of single mode fibers in communication and measurement systems. This reduces the performance of the driver.

In optical communication systems, the received signal level fluctuates when the receiver is sensitive to polarization. do. This variation is caused by optical integrated circuits in receivers and heterogain optical communication systems. Occurs when used in Polarization instability causes signal failure in traditional communication systems. appears in optical interferometer systems in a manner similar to

The slight elliptical deformation of the fiber is designed such that the fiber is axially symmetrical. It may occur even when The ellipticities are otherwise mutually degenerate2 separate the propagation constants of two orthogonally polarized HE modes, and separate the polarization modes. Causes scattered delay.

Single-polarization single-mode (SPSM) optical fibers are characterized by polarization instability. Developed to prevent effects. The three basic types of SPSM fiber are elliptical and circular core fibers, stress-induced sharply refractive fibers, and side bit fibers. It's a bar.

Previous attempts to provide polarization stability have We have used one of several methods to maximize the difference. Elliptical core fiber is a non- Provides a symmetric propagation constant distribution and provides the necessary difference in propagation constants. bend the fiber The same result is achieved by giving an asymmetric stress distribution.

Elliptical core fibers produce the desired birefringence in this manner and exhibit unacceptable transmission losses. In addition, such fibers can be spliced together. are impractical due to the difficulties involved in connecting them to other devices. with stress The induced birefringence occurs when the fiber optic material flows over an extended period of time. When it undergoes relaxation, it reduces stress. Stress is applied to the fiber to induce birefringence. As a result, fiber breakage often occurs during the fabrication of fiber optic devices. .

Summary of the invention This invention describes a fiber optic rotation sensing system whose operating characteristics are polarization dependent. and two types of foam birefringent fibers suitable for use in communications systems. including. The invention also provides that the fiber is stable over long periods of time; and the relaxation caused by the low-velocity flow characteristics of the suitably cooled liquid from which ordinary optical fibers are formed. Includes a method of fabricating a foam birefringent fiber with non-summable birefringence. nothing.

Form birefringent fiber and its fabrication method in relation to single mode fiber As discussed herein, the invention also includes multimode fibers.

The form drag-refractive fiber of this invention is a polarization-maintaining fiber and a polarization fiber. Including both. Polarization-maintaining fiber maintains its polarization while the signal is propagating along the fiber. maintains the polarization of the optical signal in its initial state. Polarized fiber only propagates one polarization do. If a randomly polarized signal is input into a polarizing fiber within a short distance, one of the polarization component is present in that fiber, and that of the other polarization component. All are removed from the polarizing fiber.

Polarization maintaining fiber has a layered core and a peripheral cladding. The core has different polarization have a different refractive index for light waves, so the propagation constant of the core depends on the polarization . The cladding has a refractive index that is less than both of the refractive indices of the core. bigger bend Light that enters the interface between two different dielectric materials from a material with a refractive index has an angle of incidence of It is well known that if the angle is smaller than the critical angle, it will be reflected internally. Hence , a polarization-maintaining fiber guides light of both polarizations. The core propagation constants are different. or non-degenerate, so energy does not easily combine between polarizations. Hence, Light propagated through polarization-maintaining fibers undergoes no change in polarization.

A method of fabricating a form-birefringent, polarization-maintaining single mode fiber according to the present invention is , first form multiple motifs from alternating layers of materials with different refractive indices.

The motif is then an essentially monolithic block with many alternating layers. stacked and heated to form a block.

The block is the core of an optical fiber preform that may be drawn into a fiber. pulled through successive dies to reduce the size to a value suitable for use as a may be extended or otherwise by methods well known in the art. Therefore, it may be stretched. Before stretching, the block has a core with a circular cross section may be ground to form a cylinder. From both refractive indices of the core A cladding with a small refractive index can be produced using several standard techniques, e.g. bulk dioxide. By melting silicone 5i02 onto the core and crushing the SLog tubing onto the core. 7 or may be added thereto by Sing's reaction precipitation from a gaseous mixture. stomach.

Form birefringent polarizing fibers also have a layered core that increases the refractive index depending on the polarization. have The form birefringent polarizing fiber preferably has a birefringence of about 0 for the two polarizations. ．． They have refractive indices that differ by 0.004. Polarizing fiber has a core refractive index of polarizing fibers by including a cladding with a refractive index greater than or equal to It is different from having fiber. Because of the favorable difference in the refractive index of the core, one side of the refractive index of the core is A cladding with a higher refractive index can be added.

Therefore, light of one polarization is guided by the core while light of the other polarization is guided by the core. during which it propagates across the interface between the core and cladding. Therefore, the form compound Refractive polarizing fibers propagate light waves of only one polarization. That is the preferred polarization The light emitted from the core-clad interface while all other polarized light radiates to the core. This is because it remains guided by the core as it is internally reflected. This issue Bright form birefringent polarizing fibers reject light of undesired polarization over very short distances. radiates to the cladding. Form birefringent polarizing fiber is a form birefringent polarizing fiber. It is formed in the same way as the holding fiber. After the core is melted, the cladding is made using a suitable technique , for example, by reactive precipitation of a gas mixture of 5iC1* and GeC1, It will be done.

Brief description of the drawing FIG. 1 is a cross-sectional view showing a periodic multilayer dielectric structure.

Figure 2 graphically represents the birefringence of a multilayer stack of alternating layers of two dielectric materials. vinegar.

Figure 3 shows a periodic structure formed from alternating layers of two materials with different refractive indices. 1 is a cross-sectional view of a multilayer dielectric structure illustrating the concept and arrangement of motifs.

FIG. 4 is a simplified cross-section of a form-birefringent polarization-maintaining fiber according to the present invention. It is a diagram.

FIG. 5 is a cross-sectional view of a conventional optical fiber having a core and a cladding.

Figure 6 shows the fused silicone positioned between the stack of motifs and the graphite block. FIG. 3 is an elevational view showing the casing.

FIG. 7 is a plan view of the structure of FIG. 6.

FIG. 8 is a cross-sectional view of a foam birefringent polarizing fiber according to the present invention.

Description of the preferred embodiment ■, form birefringence Referring to FIG. 1, a periodic multilayer dielectric structure 10 comprises multiple layers having different refractive indices. A number of alternating layers 12.14 are provided.

Layers 12 and 14 each have a wavelength smaller than the wavelength of the light to be propagated therethrough. It has a large thickness t and t2. With optical rotation sensing system (not shown) , the optical wavelength is typically about 820 nm.

The refractive index of the multilayer structure 10 depends on the polarization state of the propagating light. to simplify , 2 A plane wave that is linearly polarized by an electric field in one direction has an X-axis pointing out of the plane of FIG. Assume that it propagates along. According to the well-known boundary conditions of "electromagnetic waves at dielectric interfaces" Therefore, the standard component of the electric displacement vector D must be continuous as follows. Of course, D + z = D2 z - D (1) And therefore, εIEI−ε2E2 (2) , where ε and ε2 are the dielectric constants of the two materials.

The average electric field for one period of the layered structure 10 is:

<　E　>-(t + D/ε, +t2D/ε2) (tl"t2)-'2 one direction The effective permittivity ε2 for a wave polarized is therefore:

εz=D/<E> (4) εz = [(L+ + tz) ε, ε2] [εzt+ + ε, t2] -4 notation For convenience, the fractional thickness f, and f2 are as follows: It is defined as follows.

f+ = t+ / (tl + t2) (6) and f knee t2/ (tl +t2) (7) Using equations (6) and (7) in equation (5), we get the following: I'm going to growl.

ε2−(ε, ε2)(ε2fl　+ε+fz)−’ (8) y polarized in one direction The tangential component of the wave must be continuous as follows:

The average value of electrical displacement for one period is as follows.

<D>-(t, ε, E+t2εz E)(tl+t2)-'(1G) From the definition of electrical displacement, ε, −<D>/E (11) and this becomes as follows.

ε − (j + ε, +t2ε2) (t, +t2) −’ Fracsidual thickness fl and and f2, the permittivity εX for a wave polarized in one direction is: given to.

εY−εIff+ε2f2 (13) Equations (8) and (13) are used to calculate the refractive index in the 2 and y directions. It may also be used for The definition of refractive index is as follows, n+　”　[ε+　/eo　IX　(15) and Ω2−[ε, /ε01” (16) Here ε0 is the dielectric constant of free space.

Using equations (14), (15) and (16) for equations (8) and (13) If there is, it will look like this:

nZ − (n + nZ) [nz 2 f, +n, 2 f21 Birefringent crystal is It has a normal refractive index n's and an extraordinary refractive index ne. By convention 2-axis Waves polarized along some optical axis encounter an extraordinary refractive index ne. abnormal refraction If the index is greater than the normal refractive index, birefringence is said to be positive and an abnormal refraction A refractive index is negative if the index is less than the normal refractive index. In this case, a multilayer dielectric structure The structure 10 has the following refractive indices nx, na, and nZ, and n/! 1m1lx >nz (19) This means that the normal refractive index n is greater than the extraordinary refractive index n2. that Therefore, the multilayer dielectric structure 10 resembles a uniaxial crystal with negative birefringence a.

Equations (17) and (18) show that the birefringence properties of the materials for layers 12 and 14 By properly selecting the materials to have a specific refractive index and can be synthesized by correctly selecting the functional thickness f and f2. Show that you can do it. The effective permittivity is for polarized light parallel to layers 12 and 14. and the other value for polarization perpendicular to layers 12 and 14. Therefore, the birefringence of the layered structure 10 is called "form birefringence."

As shown in Figure 5, the refractive index for polarized light along the 2-axis is smaller than the refractive index for polarized light.

Figure 2 shows the difference in refractive index Δn””n7−nz for normal and abnormal waves. , illustrated as a function of fractional thickness. The graph in FIG. 2 shows that the layer 12 is Al. The form obtained when formed from 2O3 and layer 14 is formed from AIF. It represents a one-party refraction.

Referring to FIG. 4, the form birefringent single mode fiber 15 according to the present invention is , a layer of a first material 18-20, and a layer of a second material having a different refractive index than the first material. It includes a core 16 made up of layers 22,23. Core 16 has many layers of two amulets. but for convenience of illustration and explanation, five layers 1g-20 and Only 22.23 is shown.

The core 16 is circular in cross section, as in most optical fibers. shown. Form birefringent single mode fiber 15 has a cluster surrounding core 16. head 26. The material comprising core 16 and cladding 26 is - choosing the refractive index for polarization along the axis to be greater than the refractive index of the cladding 26; be done. Therefore, input into the form birefringent single mode fiber 15, y A wave that is polarized along one or two directions is polarized along one or two directions. Preserves polarization.

A typical optical fiber 30 shown in FIG. 5 has a refractive index greater than that of the cladding 34. It has a core 32 having a refractive index.

The diameter of the core 32 is such that all light propagating through it is at a critical angle for total internal reflection. small enough to hit the interface between core 32 and cladding 34 at a large angle. stomach. Therefore, nearly all of the optical energy propagating within the fiber 30 is transferred to the core 3 It is in 2.

Unlike the normal optical fiber 30, the form birefringent single mode fiber 15 is It maintains the polarization state of waves propagating through it. In fiber 15, due to the two polarizations The difference between the refractive indices of is the substantial difference between the propagation constants of waves with two orthogonal polarizations. It's big enough. The difference between the propagation constants eliminates the degeneracy between polarization states and under these conditions, waves of one polarization are prevented from coupling into the other polarization. of energy between waves Coupling requires that the waves have essentially the same speed.

If the velocities are different, there is less coupling between the two states.

Il, design and design of submillimeter beat length form birefringence polarization maintaining fibers. and production A, design Highly birefringent fibers can be optimized for spectral optimization with some frequency shifter designs. Necessary for purity and dynamic range. This measure of birefringence is length, or the length required to bring the most effectively aligned quadrature waves back into the same phase relationship. is the distance in a birefringent medium. Beat length measures vacuum wavelength and birefringent medium is a function of the refractive index of In other words, L-λo / Ct]y nz) (20), where ny>nz and λO is the vacuum wavelength of the light wave. For λo = 820OA, ny nz is 1 mi. Must be greater than 0.00082 for beat lengths less than millimeters. It is easy to see that there is no such thing. Conventional birefringent fibers range from 0.00016 to 0. with an nZ-nZ value of 00027 and a beat length of 3 to 5 mm. Ru. This birefringence is usually caused by anisotropic stress applied to the core and more Applying large stresses requires that the mechanical stability of the fiber be preserved. If not, it is not practical.

This invention is based on juxtaposing materials with different bulk refractive indexes in appropriate proportions. Thus, a configuration of foam birefringent fibers is used. These parameters are related to each other by equations (17) and (18) above.

The following describes one way to create a frame birefringent core 16 that meets the above requirements. A preferred method is described. Whether nZ-1,4582 and ny=1.4592 For example, birefringence is 0. QOl, and the beat length is 0.8 at a wavelength of 0.82 μ. It will be 20 mm. Because of this selection, the form birefringence stack allows for low refraction. Fused silica (n+-1,453) can be used as a rate component .

If n is -1,453, then f is -0,9578.

And as a corollary, nz=1.593 and fractional thickness f2 It becomes -0.0422. These parameters are suitable for the high refractive index of the form birefringence stack. It is shown that Ge0z (nz -1,593) is used as the refractive index component. vinegar. Both silica and germania are preferred due to their low loss and physical compatibility. Therefore, it is used in virtually all single mode and multimode fibers. given When bonded non-uniformly with fractional thickness, they are bonded by fused silica. Form the core 16 with both nZ and ny large enough to be coated. However, fabricated from two conventional low-loss components, silica and germania. Form 1 (refractive frame) with a beat length of 0.820 mm, which may fibers are generated.

To form birefringent polarization-maintaining fibers at dimensions that are practically achievable. In other words, the fabrication techniques and constraints closely match the rules of form birefringence.

Due to the unwieldy size of fibers (kilometers in length and microns in diameter), All dimensions need to be constrained until the final steps of fabrication. This is the spatial ratio The ratio, angular relationship, and refractive index are determined by successive draw steps well known in the art. Construct a preform that is the same as in the finished fiber made by It is conveniently achieved by doing. In the stretching process, these three Retaining properties allows traditional single and multimode fibers to be fabricated . Considering these factors, it is possible to define the core geometry and process it. It is possible to scale to any size.

Regarding form birefringence, the scale of the completed fiber is smaller than that of the waveguide. The refractive index periodicity of the small core must be exhibited. used to determine the amount of this request. The structural device involved is denoted by the term "motif". periodic structure mochi The surface is the smallest size that preserves the proportions of its components. The file being discussed The motif of the ohmic birefringent core is then f SiO2 layer thickness + 1 G It is the thickness of the eO2 layer. A, B, C and D in Figure 3 represent various motifs. Illustrate the arrangement. The length of the structure in Figure 3 is four motifs along two axes.

Since there is no periodicity along the x-axis or y-axis, nZ represents the form birefringence. This is a refractive index suitable for use in determining the size M of the largest motif.

As noted above, form birefringence means that the size of the motif M depends on the material being discussed. It begins to appear when it is equal to or smaller than the optical wavelength of the material. This is This is called the system birefringence threshold. Therefore, the form birefringence threshold is It seems like.

Mkuλo/nz=820OA/1.4582-5G23A (21) Form duplication The threshold of refraction occurs for motifs smaller than 5623A and therefore It is.

M<5623A-λz (22) To guarantee form birefringence, M must be significantly smaller than the threshold. For example, it must be as follows:

M-λZ /8 (23) Or M-703A (24) For a final core diameter equal to C-2,8μ, i.e. 2800OA, core 16 then contains the C/M-28000A/703A-40 motif.

B. Production FIG. 6 shows a plurality of graphite blocks 42. 43. The module held between 44 Chief's stack 42 is represented. The stack 41 must be supported on five sides. However, only three graphite blocks are shown in FIG. preform The motif is set to Q, 5mm, and the size is 0.5X20X50mm. Each of the 40 motifs required was manufactured as a thin rectangular plate. Thus, a complete core is a rectangular solid with dimensions of 20X20X50mm. can be assembled. The 5i02 component of the motif has the following thickness: It exists.

f + (M) - (0,9578) (0,5ma+) -478,9μ (25 ) The GeO2 component of the motif has the following thickness:

f　2　(M)　-(0,0422)(0,5+u)-21,1μ　(26) So The amount of the core 26 configured as follows is (20 mm) (20 mm) (50 mm) = 20000 mm' and kept constant during the stretching process. 2 for each side. The length L of the finished fiber with a square cross section of 8μ is calculated as It is possible, (2,8μ) (2,8μ) (L) -2000hm　(27) This is as follows. give similar results.

L=2551km (28) Approximately 2500 km of well-defined fiber available from one preform In the development of the prototype instrument and the entire production of the instrument, the same fiber is shared. can do. The calculated dimensions are calculated for a rectangular cross section for simplicity. 'C is given. A similar calculation is easier for a fiber core that has a circular cross section. may be carried out, in which case the well-known formula for the volume of the cylinder is Must be used to calculate length. The process explained in -1- The cylindrical fiber thus formed has a core diameter of approximately 2.8μ.

Well-established optical fabrication techniques produce 5i02 plates from pure bulk 5i02. It can be used for manufacturing. GeO2 components are not very thin They may be too large to be formed by mechanical fabrication techniques. Gem The second layer is Gem, by sputtering the film onto a 5in2 substrate. and in an easy but time consuming manner well known in the art. may be made. The GeO2 layer can also be coated with 5io2 and Ge0 layer. and oxidizing it to Gem2 in a tube furnace in a manner well known in the art. may be formed by. The resulting thickness of the Ge layer is: Ru: Icm' Ge weighs 5.36g, while GeO weighs 7.72g. It is oxidized to 2.

The density of GeO2 is 3.604 gm/cm3, and therefore, The amount of GeO2 is then 2.142 cm3.

The surface area of the Ge film both before and after oxidation to G , 5i02 is determined by the size of the plate, so the change in quantity upon oxidation is Only the thickness is changed. If GeO2 has a thickness of 21.1μ, the thickness of the Ge layer is ( 21.1μ) (1cm3/2.142cm3)-9°85μ . Due to the judicious placement of the motif (corresponding to C in Figure 3), the 5in2 plate You can give both sides half this thickness. With this selection, oxidation proceeds faster and the residual stress applies equal tension to both sides of the 5in2 plate. Ge size Threshold density is measured by the change in the resonant frequency of a crystal thickness monitor when deposited. It gives a change of 5.4kHz per 0.1μ of Ge, allowing precise and accurate thickness control. give.

The 40 motifs are then assembled into graphite blocks as shown in Figure 6. stacked and supported on five sides by. The whole assembly is placed in the furnace placed and heated to the softening point of GeO2, and then slowly brought to room temperature. cooled down. The graphite blocks are then removed (graphite is (one of the few materials that fused glass does not adhere to), and the fused core is removed. Ru.

From this point, the remaining steps in fiber preform fabrication are: Adjust the aspect ratio (preform length/preform diameter) to the finished file. Si Provision is made to provide an appropriate thickness of O2 cladding. Everything you need for a complete fiber If all claddings are added in proportion to the size of the molten core, the preform will be The diameter of the tube is 50cm, but the thickness is only 50mm, and as a result, it is difficult to stretch. It will be impossible to get rid of it.

Therefore, the cladding 26 has a size smaller than that given above by the stack 41. must be added after being subtracted by . Decrease the size of stack 41 During the process, it must be protected from chemical contamination and physical damage. Furnace temperature and stretch rate are adjusted to yield a precise and consistent core size. , sufficient material must be provided. Stack 41 with graphite block core 1 to prevent physical damage and chemical contamination from A stack 41 of motifs 40 forming 6 is shown in FIGS. 6 and 7. Also enclosed within four fused silica casings 46, 48, 52 and 54. good. A pair of melt cylinders was used to provide sufficient material for temperature and stretch rate adjustment. Recaplugs 47 and 49 are added at the ends of core 16. Motif 40 star The entire assembly of blocks 41, graphite blocks, and pieces of fused silica are Before solution, the data are collected as shown in FIGS. 7 and 8. Possible cases The size of the cleaning plate may be approximately 10 mm added to [i+11i. casing Two of the plates may have dimensions of 20 mm x 5 mm x 50 mm; And the other two casing plates are preferably 30mm x 5mm x It may have a size of 50 mm. Plugs 47, 49 of the assembly of FIG. The cross section is preferably approximately 30 mm x 30 mm x 5 Q mm. star The entire rack, casing and plug assembly is then assembled into a graphite block. While trapped between the locks it heats up and forms a monolith; It is then stretched to have a cross section of approximately 3 mm x 3 mm.

The cladding 26 is then formed using a method well known in the art to form optical fibers. Any of several methods, e.g. melt the bulk 5in2 onto the core and i Crushing the O2 tubing into cores or by reactive precipitation of 5i02 from the gas mixture. Therefore, it may be added to the core 16.

To simplify this discussion, core 16 is described as having a rectangular cross section. Ru. The advantages of the rectangular shape are for diode coherent light sources and integrated optical circuits. Contains a conduit match that joins. However, a rectangular cross section has significant damage. There may be a penalty for losing. The molten core is most preferably circular in cross section. , may be centerless ground into a cylindrical shape before providing the cladding. fused silica case The grinding is then preferably performed by centerless grinding techniques well known in the art. When the core 16 is made into a cylinder, it is ground.

The structure of the foam birefringent polarizing fiber 60 is shown in FIG. The structure of the foam birefringent polarization maintaining fiber 15 is It is similar to structure. The core 62 includes a plurality of layers 6 of a first material having a first refractive index n. g-70, and a plurality of layers 72,73 of a second material having a second refractive index n2. Ru. However, as explained above, the cross section of the foam birefringent polarizing fiber 60 The refractive index of the rad 64 is greater than or equal to one of the refractive indices of the core 62. There must be. In mathematical notation, the relationship between the refractive indices is: n, > nc > nz (28) where ray and nz are defined before, and nc is the refractive index of the cladding. be.

The selection guidance of one state and the radiation of all other states are determined by the form sharply refractive core 1 It is known that 6 can be realized if the refractive index nx and n/ are as follows. ing.

Δn - ny - nz = 0.004 (29) The desired value of Δn of 0.004 is H Then, the refractive index nc of the cladding 64 is approximately equal to the smaller core refractive index Ω2. or slightly larger. The refractive index was explained above. 2-component polarization of all light input into fiber 60. The y-component is radiated to the cladding 64 while the y-component is radiated to the core 62. thus guided and maintained without crosstalk with the two-component.

The refractive index of the form step refractive polarizing fiber 60 is the same as that of the form birefringent polarization maintaining fiber. 15, the motif M of the form birefringent polarizing fiber 60 is In equations (21) to (24) above: 1 is different from the calculated value. Birefringence threshold The values are as follows.

Mkuλ0 / nz -8200A / 1.4781 (30) and M < 5548A-λz (31) To guarantee form birefringence, M is set well above the threshold as was written, M-λz/8 (32) This is for a final core diameter of C-2,illμ equal to 28000A as follows: I want to know the results.

M-693A (33) Core 62 therefore includes C/M-28000A/693A, which The result is that the core 62 of the ohmic birefringent polarizing fiber 60 also includes 40 motifs. give fruit.

B. Production Form birefringent polarizing fiber is about form birefringent polarization maintaining fiber. It is manufactured in a manner similar to that described in . The core 62 is shown in FIGS. 4, 7 and 7. It is formed from a stack 41 of 40 motifs 40, which is schematically represented in FIG.

The size of the stack 41 is related to the fabrication of the form birefringence polarization maintaining fiber 15. may be as described above. Form birefringence polarization maintaining fiber 15 Layers 68-70 may be SiO□ and layers 72,73 may be Ge. It may be formed from O2.

To achieve the desired Δn-0,004, the 5i02 component of motif 40 The fractional thickness is f.

−o, soo may be used, while the GeO2 component may be fractional The thickness is f2-0.200. Therefore, the thickness of the 5i02 layer 1g-20 is is given by the formula.

f + (M) - (0,800) (0,5a+m) -400tt (34) G The thickness of the e02 component is given by:

f2 (M>-(0,200)(0,5mo+)=100μ(36)S The layers of iO2 and GeO2 are associated with the form birefringence polarization maintaining fiber 15. 9] may be formed by any of the techniques described in 2. Motif 40 After the tack 41 is formed, the formation birefringence polarization maintaining fiber 15 is described above. The process described is such that the stack 41 is folded in order to reduce the size of the stack 41. It continues to be stretched to form the fiber core 62. The cladding is , must be formed to have a refractive index greater than the refractive index of 5t02 . S L CI, and GeC1, are both 5 by methane/oxygen flame It exists as a vapor that may be oxidized to a mixture of in2 and GeO2. results and The refractive index of the resulting mixture depends on its molar composition. Therefore, 5iC1 By controlling the flow rates of 4 and GeC1, 82.8 mo1% of Sing and 1 A soot consisting of 7.72 mo1% Gem2 can be precipitated on the core, and Form a rad. The refractive index of the cladding is then equal to the nz of the core.

The cladding 64 that must be added to the core 62 has a refractive index greater than 5i02. What must be the refractive index at or equal to it? Clad 64 is meta To oxidize a mixture of 5iCl, and GeCl, vapor in a gas/oxygen flame. Therefore, it may be added. The refractive index of the resulting mixture depends on its molar composition Dependent. Therefore, controlling the flow rates of Si CI4 and GeCl4 vapors and from 5i02 of 82.18mo1% and C02 of 17.72mo1%. A soot can be deposited onto the core 62 to form a cladding 64 . This program The refractive index of the cladding 64 formed according to the process is equal to 02 of the core 62. Ru.

” Single mode form step-refractive polarizing fiber according to the process steps described in 2. The fiber 60 may be formed to have the specifications given in Table I below.

table! Polarizing fiber specifications Core m configuration f + -0,800 (S10x) f z = 0.200 (Ge( 12) Core refraction nz = 1.4781 ny = 1.4821 rate Cladding 82.28io1%5iOz 17.72io1%GO02 composition Rirad 1.4718 refractive index Core diameter 2.8μ V number 1.2519 The V number of the optical fiber is as follows, V"kp (nz-n2cladd[n g” (37) ore where -2π/λ0 is the wave number, λ0 is the wavelength of the optical signal in vacuum, and p is the core radius. The V number is the amount of energy a fiber can carry in a single mode of electromagnetic energy at a particular frequency. Criteria for determining whether a fiber propagates only 1000 MHz or multiple modes. It is. V<2.405 for a given set of parameters in equation (37) If so, the fiber is a single mode fiber. When the V number is lowered, evanesene The size of the light field increases and the core of light guided by the core Field decreases. The GeO2 doping makes the cladding 64 more concentrated. A62 and heavy. Since GeO2 is the primary scattering agent in fiber 60, it is evanescent. Increasing the field and decreasing the field of the core 62 reduces scattering; A portion of the signal is thereby coupled to cladding 64. Therefore, form 1 4; i-refractive polarizing fiber 60 is formed to have a relatively low V number.

All information carried by optical fibers is carried by the propagation of light.

The portion of light guided by some mechanism, e.g. core 62, is get out of

If the intensity of the emitted light is not suppressed, it enters the fiber as a cladding mode. 60. The cladding mode is included in the light guided by the core 62. It is considered that the t-th information is not correlated with the information contained in the data and is not correlated with the noise. fiber Over the length of 60, the cladding mode portion tends to couple back to the core 62. the information integrity of the light guided by the core 62. Phi If the output of the core 60 is incident on a detector (not shown), the detector responds to both the light guided by the cladding mode and the noise carried in the cladding mode. .

Conventional mode and multimode fibers, such as fiber 30 in FIG. The brittle glass fiber 30 is ring-formed with a soft plastic material 76 under mechanical stress. prevent from damage. This coating is usually transparent or translucent and What is the refractive index of the fiber 30 that is greater than the refractive index of the cladding 34? Clad 34 bend Depending on the relationship between the refractive index and the jacket material 76, the radiation mode is It can be stripped away. Most traditional jackets come in four colors Meter lengths of fiber are required.

The rapid attenuation of a radiation mode results in one polarization regardless of the polarization of the signal input to it. It is known to increase the effectiveness of the form birefringent polarizing fiber 60 when propagating only It is being

Because the noise-producing mechanisms in a fiber are distributed along its length, the noise , the minimum possible length to minimize the detrimental effect of noise on signal strength. must be suppressed. Therefore, the signal/noise ratio of fiber 60 is reduced. In order to minimize the It may be added instead. Absorbing jacket 80 preferably covers polarizing fiber 6 to absorb cladding modes within a distance of a few centimeters along the length of 0 , finely divided into opaque materials, such as high refractive index plastic matrices. Contains carbon black. The absorbent layer 64 is a conventional jacket material made of carbon. It may be formed by adding black.

0. 2.4. 6, θ 1.0 7 rakun eaJ Copy and translation of amendment damage) Excavation (Article 184-7, Paragraph 1 of the Patent Law) June 1986 11th Mochi’, 1FtT’Ai Palace 1. International application number PC block/US85101988 2. Name of the invention Foam storage V-fiber j3 and “jAh95FA3, patent applicant Address: Beverly Hills Snow, California, 90210, United States Talented Drive, 360 Name Kutsu1-Systems Inc. Rated Representative Gilman, Herold Yee Address: Hirano-cho Yachiyo Building, 1-1, 2TI-18m, Hirano-cho, Higashi-ku, Osaka Telephone: Osaka ( 06) 222-・0381 (generation) unknown 6. Copy and translation of attached documents) 1 copy The scope of the claims 1. A fiber is formed from multiple layers of optical material and includes a core that propagates optical signals. , the core has a first core refractive index for light of a first polarization, and a first core refractive index for light of a second polarization. formed to have a second core refractive index of further comprising a cladding surrounding the core, the cladding including at least one The focus has a rad index of refraction such that polarized light is guided by the core. birefringent fiber optical waveguide.

2. The core consists of multiple cores that are fused together to form a monolithic structure. It is composed of motifs, each motif having at least two different indices of refraction. 2. A foam birefringent fiber according to claim 1, comprising a plurality of layers of dielectric material. Iba optical waveguide.

3. Claims wherein the core is formed from alternating layers of 5in2 and GeO2. The form birefringent fiber optical waveguide according to item 1.

4. The cladding index is adjusted so that both polarizations are guided by the core. A foam according to claim 2, which is less than both the first and second core refractive indices. Birefringent fiber optical waveguide.

5. The cladding refractive index is such that the core guides only the second polarized light and the first core such that all other polarized light propagates from the core to the cladding; the refractive index of the second core; Form birefringent fiber optical waveguide according to scope 2.

6. The cladding's second part is used to absorb the light propagated by the cladding. The foam birefringent fiber optic of claim 5 further comprising a coating. academic waveguide.

7. The cladding index is such that both the first and second polarized light are guided by the core. the refractive index of the first and second cores is smaller than both the first and second core refractive indices, such that Form birefringence according to claim 1, wherein the second polarized light has a non-degenerate propagation constant. Fiber optic waveguide.

8. The cladding refractive index is such that the core guides only the second polarized light and the first core cladding so that light of all polarizations radiates from the core to the cladding; at least as large as the refractive index and less than the second core refractive index. Form birefringent fiber optical waveguide according to claim 1.

9. Having a first core refractive index and a second core refractive index different from the first core refractive index 1. A method of fabricating a foam birefringent waveguide having a layered core, the method comprising: A structure consisting of a number of layers of at least two dielectric materials with different refractive indices form, To form a monolith, the structure is heated to the softening temperature of the dielectric material, and Tension is applied to the monolith to produce a layered fiber core of predetermined size. A method comprising the steps of:

10. The forming step is forming 112 motifs of alternating layers of 5iC)2 and GeO□; Stacking the motifs of the number of stages, and Claims include supporting stacked motifs with graphite blocks The method described in Scope Item 9.

11. Stacking the fused silica motif before heating to form the monolith. 10. The method of claim 9, further comprising the step of covering the cover.

12. Claim 9, further comprising the step of grinding the monolith into a cylinder. How to put it on.

13. A step that covers the core with a cladding having a smaller refractive index than the core refractive index. 10. The method of claim 9, further comprising:

14. A cladding having a refractive index at least as large as one of the core refractive indices. 10. The method of claim 9, further comprising the step of covering the core with a pad.

15. Covering the cladding with a material that absorbs the light propagated by the cladding. 15. The method of claim 14, further comprising:

Claims (12)

[Claims] 1. Fiber is formed from multiple layers of optical material and has a core that propagates optical signals. Eh, the core has a first core refractive index for light of a first polarization and a refractive index for light of a second polarization. a second core having a refractive index of the cladding further comprises a core, the cladding configured to allow light of at least one polarization to be transmitted through the core; Form birefringent fiber optical waveguide with cladding index such that it is guided by tube. 2. The core consists of multiple modules that are fused together to form a monolithic structure. each motif consists of at least two different motifs with different refractive indices. The foamed birefringent fiber of claim 1 comprising multiple layers of dielectric material. optical waveguide. 3. 10. The method of claim 1, wherein said core is formed from alternating layers of SiO2 and GeO2. A foam birefringent fiber optical waveguide according to item 1. 4. The cladding index is such that both polarizations are guided by the core. The lens according to claim 2, which is smaller than both the first and second core refractive indices. birefringent fiber optical waveguide. 5. The clad refractive index is such that the core guides only the second polarized light and is transparent. the first core such that light of other polarization propagates from the core to the cladding; at least as large as the refractive index and less than the second core refractive index. A foam birefringent fiber optical waveguide according to item 2. 6. A cord on the cladding to absorb light propagated by the cladding. 6. The foamed birefringent fiber optical guide of claim 5 further comprising: Wave tube. 7. The cladding refractive index is such that both the first and second polarized light are guided by the core. the first and second core refractive indexes are smaller than the first and second core refractive indices such that the first and second polarized A foam birefringent fiber according to claim 1, wherein the light has a non-degenerate propagation constant. optical waveguide. 8. The clad refractive index is such that the core guides only the second polarized light and the clad base is a glass base. the first core such that light of other polarization radiates from the core to the cladding; and at least the same magnitude as the refractive index and less than the refractive index of the second core. A foam birefringent fiber optical waveguide according to item 1. 9. A layer having a first core refractive index and a second core refractive index different from the first core refractive index. 1. A method of fabricating a foam birefringent optical waveguide having a birefringent core, the method comprising: Structure consisting of multiple layers of at least two dielectric materials with different refractive indices form, To form a monolith, the structure is heated to the softening temperature of the dielectric material, and Tension is applied to the monolith to create a layered fiber core of predetermined size. A method comprising the steps of: 10. A step that covers the core with a cladding having a cladding index smaller than the core refractive index. 10. The method of claim 9, further comprising: 11. has a cladding index that is at least as large as one of the core refractive indices 10. The method of claim 9, further comprising the step of covering the core with a cladding. 12. covering the cladding with a material that absorbs light propagated by the cladding 15. The method of claim 14, further comprising: