MXPA00012645A - Monolithic coaxial device - Google Patents

Abstract

The present invention provides environmentally stable interferometric and lattice devices that exhibit low excess loss and polarization dependent loss. The modal noise at the splices between the device pigtails and the system fiber is minimized or eliminated. The present invention is an optical device (10) for filtering a light signal. The optical device (10) has a tunable spectral response. The optical device includes a first optical fiber (25) having a first core region (30) and a cladding (34) with refractive index n2. The first core region (30) includes a core (32) having refractive index n1 and a first fiber coupling regulator (300) integral with the first optical fiber (25). The first fiber coupling regulator (300) couples the light signal between a first optical path and second optical path and substantially prevents the light signals from coupling into a third optical path.

Description

MONOLITHIC COAXIAL DEVICE CROSS REFERENCE TO RELATED REQUESTS This is a continuation in part of the patent application of E.U.A. Serial No. 60/091, 092 filed July 29, 1998, the contents of which are hereby incorporated and incorporated by reference in their entirety, and the priority benefit pursuant to Civil Code 35 § is hereby claimed. 120 BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to monolithic filters and particularly to single-fiber and grid coaxial Mach-Zehnder devices, and to their applications.

PREVIOUS TECHNIQUE There is a need that arises from multiplexes and filters for narrowband wavelength division (WDM). Some important applications include broadband gain uniformator filters for rare earth and Raman amplifiers. For example, such devices can be used in the 1550 nm window to modify the gain spectrum of the erbium fiber amplifiers. They will also be widely used in trunk lines as well as in fiber-to-subscriber architectures. These components must be usually stable and very reliable. Mach-Zehnder filters are known for their narrowband wavelength capabilities. It has been proposed to form filters having pass bands as narrow as 1 nm, by connecting two evanescent couplers with unequal fiber lengths between them. However, it is difficult to reproduce an environmentally stable device with this procedure. The connecting fibers are subject to external destabilizing conditions, such as temperature changes and random bending forces. An environmentally stable Mach-Zehnder device that is insensitive to temperature gradients and capable of withstanding forces that would tend to cause inadvertent bending has been proposed. The device includes an elongated body of germ glass through which the first and second dissimilar optical fibers extend. The body includes a region of phase change in which the fibers have different propagation constants, whereby the optical signals are propagated through the optical fibers at different speeds in the region of phase change. At opposite ends of the phase change region, the body further includes three separate and tapered coupling regions in which the diameter of the body and the diameters of the fibers are smaller than the region of phase change. Although the propagation constants of the fibers are different in the region of phase change, the difference in the propagation constants of the fundamental modes propagating in those fibers within the tapered coupler regions is negligible due to the small size of the cores. in the tapered regions where coupling occurs. It has been proposed to use coated Mach-Zehnder couplers for uniform uniformator gain applications. The typical sinusoidal dependence of the two-coupler device is useful for filtering the red band and blue band gain of erbium-doped fiber amplifiers. Broadband gain filters require a non-sinusoidal filter function. Such broadband functionality has been demonstrated, using a grid structure coated with three couplers and two cores. However, it has been found that narrow-band Mach-Zehnder filters coated with two fibers tend to be polarization sensitive, because the cores deform in the phase change region of the device, as the tube collapses on the fibers during the manufacture of the device. A coaxial geometric configuration has been proposed to eliminate polarization sensitivity. Such devices are formed of an optical fiber which defines two waveguides, a rod waveguide (central core of the fiber) and a tubular or annular coaxial waveguide. The refractive indices of the central core and the annular waveguides are raised in relation to the refractive index of the coating layer that is intermediate to the core and the annular waveguides, and in relation to the refractive index of the outer coating that surrounds the annular waveguide. The execution of the design is difficult for the following reasons. In order to couple light from the core waveguide to the ring mode and the ring waveguide, the propagation constants of these modes in the tapered regions are required to be similar. But dissimilar propagation constants are required for good filtration. It is difficult to form a coaxial fiber coupler that satisfies these requirements. More importantly, in a coaxial device formed of a fiber having a central core waveguide and an annular waveguide, the annular mode may be tightly attached to the annular waveguide, which can not easily be stripped from the same with the protective coating of the spiral fiber output cable. This may necessitate the use of an additional bath of an indexing fluid to prevent the light propagating in the annular waveguide from reaching the output power of the device. If the ring mode reaches the junction between the output spiral cable and the system fiber, modal noise is generated. In addition, the characteristic of insertion loss with respect to the wavelength of Mach-Zehnder devices made of coaxial fiber having core and annular waveguides was highly non-reproducible.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides environmentally stable grid and interferometric devices that exhibit low excess loss and low polarization dependent loss. The interferometric and grid devices of the present invention are inexpensive and simple to make. The modal noise in the joints between the spiral cables of the device and the fiber of the system is minimized or eliminated. One aspect of the present invention is an optical device for filtering a light signal. The optical device has a tunable spectral response. The optical device comprises: a first optical fiber having a first core and a first coating with refractive index n2; the first core including a first central region having a refractive index n-i; and a first integral fiber coupling regulator with the first optical fiber, the first coupled fiber coupling coupling the light signal between a first optical path and a second optical path and substantially preventing the light signal from coupling to a third. optical path. In another aspect, the present invention includes a coaxial device for operating at an operational wavelength? 0, the device comprising: a single optical fiber having a core having a refractive index or maximum wrapped by a coating having an index of maximum refraction n2, and a pedestal of refractive indexes that has a maximum refractive index ns located between the core and the cladding, where n? > n5 > n2; at least one region tapered in the fiber, that portion of the fiber extending from one end of the tapered region having a protective coating thereon and constituting a fiber-exiting cable, the taper angle of the fiber being taper region large enough to cause coupling between modes LP01 and LP02, but not so large as to cause coupling to LP03 mode, where the optical fiber has a cut-off wavelength? Co more than 200 nm less than the length of Operational wave? In another aspect, the present invention includes a coaxial device comprising: a single optical fiber having a core having a maximum refractive index or wrapped by a coating having a maximum refractive index n2 and a pedestal of refractive indexes that has a maximum refractive index ns located between the core and the cladding, where n? > n2 > n2; at least one first and second axially tapered regions spaced apart along the fiber; a region of phase change of the fiber extending between the tapered regions; and a first fiber spiral cable extending from the end of the first tapered region opposite the phase change region, the taper angles of the tapered regions being large enough to cause coupling between the modes LP01 and LP02 , but not so big to cause the coupling to LP03 mode.

In another aspect, the present invention includes a method for filtering a light signal with an optical device having a predetermined spectral response, the optical device including a first optical fiber having a first core region and a first coating with the optical index. refraction n2, the first core region including a first core having a refractive index nj, the method comprising: providing a first integral fiber coupling regulator with the first optical fiber; directing the light signal to the first optical fiber; and coupling the light signal in an LP0 mode? or an LP02 mode, in which the first fiber coupling regulator couples the light signal between an LP01 mode and an LP02 mode and substantially prevents the light signal from being coupled to an LP03 mode. Additional features and advantages of the invention will be set forth in the detailed description that follows and will be readily apparent to those skilled in the art by the description or will be recognized by practicing the invention as described herein., including the detailed description that follows, the claims, as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide a general overview or structure for understanding the nature and character of the invention as claimed. The accompanying drawings are included to provide a better understanding of the invention and are incorporated and constitute a part of this specification. The drawings illustrate various embodiments of the invention. And together with the description, they serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a first embodiment of the present invention; Figure 2 is a profile representative of the refractive index of the device shown in Figure 1; Figure 3 shows the Mach-Zehnder configuration of two couplers used in the second, third and fourth embodiments of the present invention; Figure 4 is a cross-sectional view of the second embodiment of the present invention; Figure 5 is a profile of refractive indexes of the second embodiment of the present invention; Figure 6 is a graph of the insertion loss with respect to the wavelength for a Mach-Zehnder according to the second embodiment of the present invention; Figure 7 is a cross-sectional view of the third and fourth embodiments of the present invention.

Figure 8 a profile of refractive indexes according to the third embodiment of the present invention; Figure 9 is a profile of refractive indexes according to the fourth embodiment of the present invention; Figure 10 is a graph of the intensity with respect to the wavelength for the Mach-Zehnder according to the second, third and fourth modes configured as a filter to be used in a soliton transmission system; Figure 11 is * a soliton transmission system using the Mach-Zehnder device of Figure 10; Figure 12 shows a pair of Mach-Zehnder devices in cascade. Figures 13A-13D depict the channel filtering functionality of a Mach-Zehnder device chain; Figure 14 shows a coaxial grid device according to the fifth embodiment of the present invention. Figures 15A-15D are graphs illustrating examples of spectral responses obtained from the coaxial grid apparatus shown in Figure 14. Figure 16 is a Raman amplifier using a coaxial grid device of Figure 14; Figure 17 is a fiber amplifier involved with erbium using the coaxial device of Figure 14; Figure 18 is a plot of the intensity with respect to the wavelength of the erbium gain spectrum in a silica glass base; Figure 19 is a gain uniformator filter that is produced by cascading two devices of two or three tapers; Figure 20 is a spectral response of the gain uniformator filter shown in Figure 20; Figure 21 is a gain uniformer filter that is produced by cascading a Mach-Zehnder device as a three-taper grating device; Figure 22 is a schematic illustration of an apparatus for crushing a capillary tube on a fiber and stretching a tube to form a coupling region; Figure 23 is a graph of the concentration of chlorine with respect to the fiber radius for an optical fiber specific to the device.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Reference will now be made in detail to the present preferred embodiments of the invention, the examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers will be used in all the drawings to refer to the same or similar parts. An exemplary embodiment of the coaxial optical device 10 of the present invention is shown in Figure 1 and is generally designated throughout by the reference number 10. The following symbols are used herein to characterize the features of the present invention. . Is the term used? to indicate the relative differences of the refractive indexes between two light-propagating materials. Thus,? -? - 2 equal to (n? 2-n22) / 2n-? 2,? 5-2 (n52-n22) / 2n22 and? 2-3 (n22-n32) / 2n22, where m, n2, n3 and n5 are the refractive indices of the core region of the fiber core, the fiber coating, the device overcoat and the fiber pedestal in the core region, respectively. The core region may also include a valley. According to the invention, the present invention for a monolithic coaxial device 10 includes a lighting regulator 300.

The coupling regulator 300 includes an optical coupler 302 and a coupling inhibitor 304. The coupler 302 couples a light signal between the two optical paths, mode LP01 and mode LP02. Coupling inhibitor 304 allows the light signal to be coupled between LP01 mode and LP02 mode, but prevents the light signal from coupling to any higher order modes, such as LP03 mode. Coupling controller 300 is tunable to provide a predetermined desired spectral response. In addition, the optical device 10 may be cascaded or concatenated to provide spectral responses having very complex shapes.

The coupling regulator 300 includes one, two or three couplers and individual coupling, depending on the application. The coupling regulator 300 provides a variety of applications including: channel filtration, a filter to be used in soliton transmission systems to eliminate jitter, bandpass filters, notch filters, Raman amplifier filters, amplifier filters of rare earth and for gain uniformal filters that have a spectral response that conforms to any desired or predetermined shape. The optical device 10 has other features and advantages. It is relatively simple and economical to do. It is an environmentally stable device that exhibits low excess loss, low loss dependent on polarization and eliminates or minimizes the total noise in the joints between the spiral cables of the device and the system fiber. As is modalized herein and depicted in Figure 1, the optical device 10 includes the optical fiber 25 and the coupling regulator 300. The optical fiber 25 includes the core region 30 and the liners 34. The coupling regulator 300 is integral with the optical fiber 25 includes the coupler 302 and the coupling inhibitor 304. The simple single-taper device 10 shown in FIG. 1 is an example of a non-interferometric filter. The principles discussed with respect to the optical device 10 as depicted in Figure 1 are applicable to two-taper Mach Zehnder filters and three-taper grating filters discussed below.

The coupler 302 may be of any suitable well-known type but is shown by way of example, the tapered region 18, the diameter of the central region 32 and the valley 37 of the refractive indices which is integrated into the core region 30. If the adapter 18 is non-adiabatic, the light signal will propagate between the LP01 and higher modes, and the voucher 37 is not needed. In this case, the taper angle must be greater than a certain minimum taper angle to cause non-adiabatic coupling between modes LP01 and LP02 The taper angle is typically defined by a taper ratio. The taper ratio is the radius change (dr) of the optical fiber 25 with respect to the change in length (dz). It is desirable that dr / dc > r / Z02 where Zo2 = 2p / (ßo? -ßo2). However, the angle of the taper can not be too pronounced since that would cause the acute coupling LP03. Thus, the taper angle should not be so large that dr / dz is greater than r / Z03 where, in addition, a smaller taper angle is easier to control during the manufacturing process. In the previous relationships, ß0 ?, ßo2, and ßo3 are the preparation constants of the modes LP01, LP02 and LP03 in the tapered regions. As discussed above, the coupler 302 can be brought into use by using a refractive indices 37. If the tapered region 18 is adiabatic, it will not support the coupling between the modes LP01 and LP02 and the valley 37 is integrated to the core region 30. The valley 37 couples the light between the modal path LP01 and the modal path LP02, but not to higher modes. One skilled in the art will also recognize that the coupling between the modes LP01 and LP02 can also take effect., increasing the core diameter. The coupling inhibitor 304 can be of any suitable well known type, but the example shows the tapered region 18 and the pedestal of refractive indices 33 that were integrated into the core 30. As discussed above. If the taper region 18 is adiabatic, it will inhibit the coupling between the modes LP01 and LP02 and the valley 37 should be used. The coupling inhibitor 304 is also affected with the pedestal region 33. When a tapered region 18 is used it does not Pronounced adiabatic, the light is easily coupled to LP02 and higher modes. The pedestal region 33 is integrated to the core 30 to avoid coupling to the LP03 or higher modes. As is modeled herein and shown in Figure 2, a representative profile of refractive indices of the optical device 10 according to the present invention. Figure 2 shows the relationship between the core 30, the central core region 32, the pedestal 33, the coating 34 and the valley 37 with respect to the radius of the optical fiber 25. The central core region 32 is characterized by an index of refraction ni. The coating 34 is characterized by a refractive index n2. The pedestal 33 and the valley 37 have refractive indices of n5 and GQ, respectively. As shown in figure 2, n? >; n5 > n2 > n6 Note also that the optical device 10 typically includes the overcoated region 17 having the refractive index n3. The coupling of modes occurs more immediately between the modes LP01 and LP02 when the refractive index n3 of the body 17 is smaller than the refractive index n2 of the fiber coating, as shown in Figure 2. Since the fiber coating is Typically formed of silica, the tube index can be made smaller than that of the coating, formed the silica tube doped with B2O3 or fluorine. The refractive index n4 of the fiber covering material 38 is greater than that of n2, of the fiber covering 34. In addition, the index of the fiber coating n4 must be equal to or greater than the index n5 of the pedestal 33, to allow LP02 mode propagating from device 10 overflows from the fiber of the spiral cable. Thus, the modal noise in the joints between the spiral cable and the system fiber is eliminated. It is convenient to use chlorine as the dopant and increase the refractive index of the pedestal, since it makes possible the precise formation of a pedestal having a very small refractive index? S-2 with respect to the fiber coating. However, other chlorine impurifiers can be used to create fibers having a pedestal region 33 (Figure 3) in their refractive index profile. The doping agent that is used to form the core region 32 can also be used to form the pedestal 33. Germania, which is commonly used to form the fiber cores, can also be used for the pedestal 33 impurifier. more dopants that increase the refractive index, which could be used to form the core 32 and / or the pedestal 33. The pedestal region 33 could also be formed, from a glass such as silica, formed in the fiber coating region 34 of impurified silica with a doping agent that lowers the refractive index, such as fluorine or boron. In the specific couplers described herein, the device fiber 25 is wrapped in the coupling region by the germ glass body 17. The enclosing medium could also be any material having a refractive index n3, which is smaller than the fiber coating, such as plastic, air or the like. The difference in the propagation constants of the fibers between the modulos LP01 and LP02 in the tapered regions would be much greater, if the air were the surrounding medium. Therefore, a taper for such a device would have to be more pronounced thus making the taper angle more difficult to control. Also, with air in the highest taper portion of the tapered region, light can be coupled from mode LP02 to LP03. Thus, the taper must be formed very carefully, when the air is the surrounding medium. These negative effects are eliminated when the tube with the highest refractive index n4 is used. As is modalized herein and shown in Figure 3, a monolithic coaxial coated Mach-Zehnder device is provided. Subsequently, alternative Mach-Zehnder modalities will be discussed according to the second, third and fourth embodiments of the present invention. The first and second coated fiber optic cables 1 1 and 12, extending from the device 10 are connected to the fibers of the system 13 and 14 via the splices 15 and 16, respectively. The device 10 includes a germ glass body 17 having tapered engagement regions 18 and 19 therein. The phase change region 20 is located between the regions 18 and 19. A factor affecting the filter function of the present invention is the wavelength dependence of part of the couplers, which depend on the taper ratio and the values of the propagation constants of the LP01 and LP02 modes in the tapered regions. The taper angle must be greater than some minimum taper angle to cause non-adiabatic coupling between modes LP01 and LP02. The taper angle can not be too pronounced, since that would cause the coupling to LP03 mode. In addition, a less pronounced angle is easier to control during the manufacturing process. It is desirable that dr / dz >; r / Zo2 where Z02 = 2p (ßo? -ßo2) - However, the taper angle must not be so large that dr / dz is greater than r / Z03 where Z03 = 2p) ßo -? - ßo3) . In the previous relationships, r is the fiber radius, z is the distance along the fiber longitudinal axis and ßi ß2 and ß3 are the propagation constants of the LP01, LP02 and LP03 modes in the tapered regions. The coupling equation for mode LP01 to LP02 is given in Optical Waveguide Concepts by C. Vassailo, Elsevier 1991.

It was found that the coupling that occurs in the tapered regions is dependent on the cut-off wavelength of the fiber. If the cut-off wavelength was close to operating wavelength, no coupling occurred. For a device operating in the 1500 nm region, a fiber having a cut-off wavelength of approximately 200 nm below the operating wavelength produced some coupling in the tapered regions. When the cut-off wavelength of the fiber is about 950 nm, a significant coupling occurred. This illustrates an important intermediate design solution. Excellent coupling results were obtained when the cut-off wavelength was more than 500 nm below the operating wavelength. This result is obtained because ßi and ß2 are relatively close to each other. However, the close proximity of ßi and ß2 causes modal dispersion effects that result in longer intermodal interference. This results in a device of longer duration. Of course, it is the intermodal interference that is generated by the device that produces the filtering effects of the device. In order to produce a smaller device, ßi and ß2 must be relatively very apart. This results in a higher cutting wavelength. In smaller devices, it is required that the refractive index valley 37 generates the intermodal coupling. This will be discussed later, with respect to the third and fourth embodiments of the present invention.

Another factor that affects the filter function of the present invention are the "L" lengths (for example, when there is more than one in a three-taper device) of the region 20 and the wavelength dependence of part of the phase change regions which depends at the same time on the propagation constants of the modes LP01 and LP02 in the non-tapered phase change region 20. Simple sinusoidal wavelength filters or WDM couplers exhibit excellent performance characteristics, when couplers 18 and 19 have substantially identical coupling characteristics. The second coupler 19 is therefore preferably formed near the tube end opposite the taper 18, subjecting the appropriate region of the tube to stretching conditions which are identical to those used to form the tapered coupler 19. Of course, for shaped spectral responses more complex, couplers 18 and 19 would be identical. As discussed above, prototypical Mach-Zehnder devices of the type shown in Figure 3 and grid devices of the type shown in Figure 4 can be "tuned" to obtain the desired transfer function. First, the desired profile of refractive indexes is obtained by an appropriate selection of the materials. Secondly, optical and spectral characteristics of optical device 16 are measured during manufacturing. The taper ratio, stretching distances or elongation of device 10 is adjusted to achieve the desired spectral characteristics. By this tuning procedure, optimum material selection, taper ratios, stretch distances and phase change separation L for a given filter are achieved. The fiber core must have a field diameter so that it is reasonably close to the system fibers to which the spiral cables of the device will melt or connect. Also, B2O3 can be added to the fiber core to form devices having improved thermal characteristics. As discussed below, core parameters such as the refractive index and radius must be such that the operational wavelength? S of the device is sufficiently greater than the cut wavelength? 8 in a single mode. As is modalized herein and shown in Figure 4, a second embodiment of the present invention is disclosed, the device 10 includes a single glass optical fiber 25 wrapped by the glass body 17. The taper ratio is approximately equal to 3 to 1. A silica tube was used, and purified with 8% by weight of B2O3, to form a Mach-Zehnder device according to a method that will be described later. The length of the tube (X) is 4.5 cm. The interaction length of both tapered regions is 0.75 cm and the separation L between the tapered regions is 1.0 cm. The fiber core consists of silica and purified with 15% by weight of GeO2 and 3% by weight of B2O3, and the A <The coated core is approximately 1.0%. The radii rc, rcr and rrevestim.ent are approximately 3 μm, approximately 12 μm and 62.5 μm, respectively. The cut-off wavelength is approximately 961 nm. The loss dependent on the polarization of the device is less than 0.1 dB. Figure 5 is a profile of refractive indexes of the fiber 25 and at least of the inner portion of the body 17. The profile of refractive indexes of the fiber 25 and at least of the outer portion of the body 17. In the profile of refractive indices of Figure 5, no attempt has been made to represent the indices and radii to scale and / or exact relative magnitude. The fiber 25 of the device includes a core region 30 having a maximum refractive index ni and a coating region 34 of lower refractive index n 2. The salient feature of this embodiment of the invention is a pedestal 33 of refractive indexes located between the center region 32 and the liner 34. The pedestal region 33 has a refractive index ns that is intermediate a ni and n2. For the clarity of the illustration, the core regions, which include the center 32 in the pedestal region 33, are illustrated as constant index regions of the fiber. Alternatively, the center region 32 and the pedestal region 33 could have a variable profile of refractive indices such as a gradient profile, a profile formed of a plurality of steps or the like, provided that the pedestal supports the coupling only to the mode LP02 as described herein. The refractive index profile of the pedestal should preferably remain essentially constant or slightly decrease with respect to the radius. The radii of the core, the pedestal and the fiber surface are rc and rcr respectively. In the profile shown in Fig. 5, the propagation constants of the modes LP01 and LP02 propagating in the fiber are very dissimilar in the region of phase change 20, but they approximate sufficiently in value in the tapered regions 18 and 19 to achieve a mode coupling. The fibers having such profiles provide adequate phase differences between the modes in the phase change region without exposing the mode coupling in the tapered regions. The value of? -? - 2 in the second mode is approximately equal to 1.0%. The value of? 15-2 must be small and yet it must be sufficient to make possible the coupling of light between the modes LP01 and LP02 of the fiber, while at the same time avoiding coupling to the LP03 mode. The LP02 mode is a guided mode that propagates in the Mach-Zehnder device in which the coating is surrounded by a medium such as the germ glass body. ? 5-2 should be less than 0.5% because larger values require a large ratio of tapers. ? 5-2 must be greater than 0.01% to allow coupling to the LP02 mode in the tapered region, while coupling to the LP03 mode is avoided. The rCT value should be between 10 μm and between 25 μm, and is preferably less than 15 μm. Figure 6 is a graph of the insertion loss with respect to the wavelength of the optical device 10 according to the second embodiment of the present invention. The spectral response of the optical device 10 is that of a one-stage Mach-Zehnder channel filter. The optical device 10 exhibits excellent attenuation properties, having a high insertion loss in the 1550 nm region of the spectrum. As is modalized herein and shown in FIG. 7, the third and fourth embodiments of the optical device 10 are approximately one-half the length of the second embodiment. As discussed above, there is an intermediate solution between the size of the device and the ease of coupling. Both the third and the fourth modes, the refractive index valley 37 is integrated into the optical fiber 25 as part of the optical coupler 302. The valley 37 makes possible the intermodal coupling between LP01 and LP02. Figure 8 is a refractive index profile of a Mach-Zehnder filter according to the third embodiment of the present invention. The value of ?? _ 2 in the third modality is approximately equal to 2.0%. The core diameter is enlarged to approximately 7 microns to drive the coupling. Note that valley 37 is very deep, tending a? -? - 6 in the approximate range between 0.1% and 0.4%. Valley 37 is used to begin a small ratio of tapers and ia? ß large. Due to the large ß, the cutting wavelength is much higher. It is approximately equal to 1200 nm. Coupling inhibitor 304 includes a small taper region and pedestal 33. The taper ratio is less than 2 to 1. Normally, this tapering relationship is adiabatic and inhibits intermodal coupling! However, the optical coupler 302 includes a very pronounced valley 37 which has the effect of counteracting the effects of the small taper ratio. The pedestal 33 should avoid coupling between modes LP02 and LP03 or higher. Figure 9 is a profile of refractive indexes according to the fourth embodiment of the present invention. The value of? -? - 2 in the third mode is approximately equal to 0.8%. The core diameter is enlarged to approximately 10 microns to promote intermodal coupling. In this modality, valley 376 is shallower, having a? - 6 in the approximate range between 0.03% and 0.07%. The valley is used 37 to compensate for the small ratio of tapers and the large ßß, but in this case its effects are milder. Again, the cut wavelength is much higher than the second mode. It is approximately equal to 1280 nm. The taper ratio is less than 2 to 1. As in the third embodiment, the coupling inhibitor includes a taper ratio that is normally adiabatic. Optical coupler 302 includes a small valley 37 that counteracts these effects. Coupling inhibitor 304 does not include pedestal 33. It is not required to avoid coupling between modes LP02 and LP03 or higher. Figure 10 is a graph of the intensity with respect to the wavelength for the Mach-Zehnder according to the second, third and fourth modes configured as a filter to be used in a soliton transmission system. As discussed above, the optical device 10 can be tuned to produce any number of predetermined spectral responses. In Figure 10, the Mach-Zehnder device is tuned in such a way that the maxima transmit approximately 100% of the incident light and the minimums transmit approximately 70% of the incident light signal. In soliton transmission systems, timing oscillation is a fundamental factor in the performance of soliton communication systems. One way to solve this problem is the use of sliding frequency filters. Fig. 11 is a block diagram of a powerful soliton 100 transmission system using a Mach-Zehnder device 10 having the spectral response shown in Fig. 10 the transmitter 200 is connected to the amplifier 202. The output signal from the amplifier 202 to the Mach-Zehnder filter 10. The amplifiers 202 and the filters 10 are distributed in the link to compensate for the losses. Theoretically, the soliton impulses can be amplified many times without losing their shape. The amplifiers 202 add noise due to the amplified spontaneous emission (ASE). The filter 10 is an optical bandpass filter that blocks unwanted ASE. Each filter 10 in the link has a different center frequency. A series of sliding frequency filters is formed, increasing the center frequency of the successive filters. The timing fluctuation is reduced because the soliton frequency slides with the filters, while the ASE is filtered out.

As is modalized herein and shown in Figure 12, which exposes a two-stage channel 200 filter in a fifth embodiment of the present invention. The output spiral wire 53 of the Mach-Zehnder is connected to the input spiral wire 54 of the Mach-Zehnder 11. One skilled in the art will recognize that two or more Mach-Zehnder devices can be concatenated to form a channel filter. of step M. The output transfer melt of the optical device 200 is shown in FIG. 13. FIG. 13A shows the wavelength channels of the system. In Figure 13B, the spectral response of a single-stage Mach-Zehnder device is shown. The answer is similar to that shown in figure 6 and is repeated here for clarity of illustration. The spectral response of the two-stage device shown in Fig. 12 is shown in Fig. 13C. Assuming it is twice that of a single-stage device. Each successive Mach-Zehnder added to the chain doubles the size of the period. The spectral response of a step device M is shown in FIG. 13D. A spectrum in the art will recognize that the step device M functions as a bandpass filter. In Fig. 13D, the bandpass filter is used to arrive at channel 0, shown in Fig. 13A. As is modalized herein and depicted in Figure 14, a monolithic coaxial coated grid filter 10 having three tabs is exposed according to a mode sect of the present invention. The device 10 includes a germ glass body 17 having the tapered coupling regions 170, 180 and 190 in it. The phase lag regions 20 and 21 are located between the coupling regions 170, 180 and 190. The phase lag region 20 has a length L-n and the phase lag region 21 has a length L-? 2. The grid device 10 is tunable to perform a multiplicity of filter functions that have more complicated spectral responses than the sinusoidal responses of the Mach-Zehnder devices discussed above. However, the principles set forth above with respect to the tuning of Mach-Zehnder coaxial devices also apply to the three-taper grating filters set forth herein. The taper ratio, the phase delay lengths Ln and L? 2, the refractive index valley, the pedestal, the blocking diameter, the delta values and other characteristics discussed above are used to obtain the desired spectral response . Figures 15A-15D are graphs illustrating examples of spectral responses obtained from the coaxial grid device 10 shown in Figure 14. Figure 15A shows a spectral response that is substantially Gaussian in form. This gain uniformator filter 10 attenuates the signal of a spectral window of 1529 nm at 1540 nm. This filter is characterized by a maximum insertion loss of approximately 1532 nm, which corresponds to a sharp point in the gain spectrum of an erbium impurified fiber amplifier. The maximum insertion loss at 1532 nm is approximately 7.0dB. Figure 15C represents a spectral response that is very similar to that shown in Figure 15A. That filter has a smaller window between 1528 nm and 1538 nm. The maximum insertion loss is 3.5dB at 1533 nm. The grid filter 10 can be tuned to filter any portion of the spectrum. Figure 15B represents a spectral response that covers the lengths of a rock in an approximate spectral window between 1548 nm and 1560 nm. This response is characterized by a maximum at 1550 nm followed by a non-linear curve that decreases monotonically as the wavelength increases. Figure 15D depicts an L-band filter response having a spectral window between 1565 nm and 1600 nm. The response of this filter is very similar to that shown in Figure 15B and is characterized by a maximum at 1572 nm followed by a non-linear curve that decreases monotonically as the wavelength increases. As discussed above, the invention should not be limited to the responses shown in Figures 15A-15D. The grid device 10 is versatile and lends itself to a variety of applications. As is modalized herein and shown in Figure 16, a Raman amplifier using the coaxial grid device of Figure 14 is exposed. The optical pump 154 supplies a pump signal to the coupler 150. The optical signal is directed to the coupler 150 from the communications fiber 13. Energy is transferred from the pump signal to the optical signal as the two signals propagate in the fiber 140. The spontaneous Raman diffusion due to the grenade noise occurs only wide range of frequencies and limits the effectiveness of the amplifier. The grid filter 10 improves the performance of the Raman amplifier because it is tunable over a wide band of wavelengths. As modalized herein and depicted in Figure 17, an erbium doped filter amplifier using the coaxial device of Figure 14 is exposed. The optical pump 154 supplies a pump signal to the selective wavelength coupler 150. . The optical signal is directed to the coupler 150 from the communications fiber 13. The doped fiber with erbium 140 is connected to the output of the coupler 150 and the signal is amplified by an erbium ion stimulated mission caused by the pumping signal. HE connects the insulator 152 to the figure of erbium 140 and decouples the pump signal of 980 nm from the optical signal. Figure 18 is a graph of the intensity with respect to the wavelength of the erbium gain spectrum on a silica glass base. The erbium-contaminated filter is very important in amplifier applications as will be discussed later. Note the peak in the gain spectrum centered near the 150 nm region. Bandpass filters are needed at the EDFA output for gain equalization. A) Yes, the grid filter 10 is connected to the isolator 152 and functions as a uniform charge filter. The spectral responses represented in Figures 15A and 15C are appropriate for this application. These responses have patterned attenuation bands to uniform the peak of the erbium gain spectrum.

As is modalized herein and shown in Fig. 19, a uniform uniformer gain filter 700 is manufactured by cascading the three-taper grating device 71 with the three-taper grating device 72. The filter 700 is particularly useful in the applications of erbium impurified amplifiers discussed above. Figure 20 is a spectral response that can be achieved using the uniform gain filter shown in Figure 19. This complex shape is made possible by the design of two or three tapers. It produces a mirror image of the erbium spectrum in the 1530-1540 nm window and results in extremely uniform gain in this spectral window. As it is modalized herein and shown in Figure 21, a gain-uniformal filter is exposed which is produced by cascading a Mach-Zehnder device 71 with a three-taper grating device 72. It is also possible to tune that design of filter to provide a complex spectral response. Figure 22 is a schematic illustration of an apparatus for crushing a capillary tube on a fiber and stretching a tube to form a coupling region. The optical devices 10 of the present invention can be formed last having a composition that varies with the radius as set forth in the patent E.U.A. 5,521, 277. if such a tube is used, the inner portion thereof would contain silica and the impurificant which decreases the refractive indices.

The fibers of the devices can be made by a device similar to that disclosed in the U.S. patent. 5,295,211, which is incorporated herein by reference. A porous core preform is formed comprising a core region and a coating glass inlet layer on a cylindrical mandrel. The mandrel is removed and the resulting tubular preform is gradually inserted into a consolidation glazing oven, whose maximum temperature is between 1200 ° C and 1700 ° C, preferably about 1490 ° C for high silica glass. Chlorine, which is normally present during the consolidation step of the preform to achieve drying, can be supplied to the preform by flowing a drying beam consisting of helium and chlorine to the preform opening. A minimum of about 1% by volume chlorine is required in the drying gas mixture to achieve proper core drying. The end of the opening is plugged to cause gas to flow through the pores of the preform. A helium flooding gas is flowed simultaneously through the muffle. Approximately 0.06-0.07 weight in chlorine remains in the consolidated preform after this first drying / consolidation step. The resulting tubular glass article is heated and stretched in a typical traction oven, while a vacuum is applied to the opening to form a "core rod" in which the opening has been closed. A suitable length of the core rod is supported in a lathe in which the silica particles are deposited thereon. The coated rod is dried and consolidated in a furnace muffle through which a mixture of helium and 9% by volume of chlorine is flowed. The resulting concrete intermediate rod is supported on a lathe in which the silica particles are deposited therein. This final porous preform is inserted into a consolidation furnace in which it is subjected to a third drying / consolidation step, while a mixture of helium and 0.06% by volume of chlorine is flowed up through the muffle. This outer portion of the preform will constitute the covering 34 (FIG. 3) of the fiber 25. The resulting fiber preform is closed to form an optical fiber. The amount of coating glass particles applied to the core rod to form the intermediate preform determines the radius of the pedestal. The amount of chlorine to which the porous portion of the preform is subjected in the second and third drying / consolidation steps determines the value of? 5.2. Figure 23 is a graph of the concentration of chlorine with respect to the fiber radius for an optical fiber specific to the device. When the fiber 25 of the device was formed according to the above method by which the coating consisted of silica containing a minimum amount of chlorine to achieve drying and the pedestal consisted of silica containing more than about 0.12 wt.% Chlorine, the minimum excessive demand was achieved by using a glass body of doped silica germ with more than 4% by weight of B2O3. To characterize this distinctive feature, three types of devices were made. The devices were similar except for the boron content in the body 17. The excessive loss of the device was approximately 1.0 dB and approximately 0.8 dB, when the tube consisted of silica impurified with 2% by weight of B2O3 and 4% in weight of B203, respectively, there was essentially no excess loss, when the device was formed from a tube formed of silica and purified with 8% by weight of B2? 3. As indicated above, fluorine can also be used as the impurifier which lowers the refractive index. Regardless of whether B2O3 fluorine is used,? 2-3 must be greater than 0.1% to achieve devices that exhibit low excess loss. The device is formed according to the methods set forth in the U.S. Patents. 5,011, 251 and 5,295,205, which is incorporated herein by reference. Referring to FIGS. 2 and 4, a length of coating slightly shorter than the section of germ glass tube 39 is removed from the central region of a length of coated fiber. Those portions of the fiber coated on opposite ends of the stripped region will constitute the spiral wires 11 and 12 of coated fiber. The glass fiber 25 uncovered to the tube core 39 is inserted in such a way that the fiber sheaths 26 and 27 to the mouths which are provided to the ends of the tube core to facilitate the insertion of the fiber. The fiber and tube combination is referred to as a coupler preform 40.

Referring to Fig. 22, the preform 40 is inserted through a ring burner and fastened to traction plates 42 and 43 which are mounted in motor controlled stages 44 and 45. The burner is schematically represented as the 41st box. , representing the arrow that extends from it the flame. The fiber is threaded through vacuum fittings (not shown) which are then sealed to the ends of the preform 40. Typical vacuum fittings are exposed in the U.S. patent. 5,011, 251 That portion of the tube between points a and b is initially crushed on the fiber (Figure 4). This is done by evacuating the core by vacuum fittings and heating the tube near one end to cause them to collapse in the region of applied heat. The plates 42 and 43 move the preform relative to the burner to gradually extend the crushed region towards the opposite end of the tube until the desired length of the collapsed tube is obtained. The tapered region 18 is formed near one end of the preform, heating a region of the tube and moving the computer controlled stages 45 and 46 in opposite directions to stretch the heated region. The operation of stretching the tube can be performed according to the teachings of the U.S. patent. 5,011, 251. It is known that the coupling characteristics of the tapered region is determined by parameters such as the optical and mechanical characteristics of the tube 39 and the fiber 25 and taper parameters such as the length and shape of the tapered regions. Thereafter the tube is moved relative to the burner and the second tapered region 19 similarly formed. Adhesive material 28 and 29 can be added to the ends of the tube to improve the tensile strength of the fiber spiral cables. It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention, without departing from the spirit and scope of the invention. It is intended that the present invention cover the modifications and variations of this invention as long as they fall within the scope of the appended claims and their equivalents.

Claims (68)

1. NOVELTY OF THE INVENTION CLAIMS 1. - An optical device for filtering a light signal, said optical device having a tunable spectral response, said optical device comprising: a first optical fiber having a first core and a first coating with refractive index n2, said first core including a first central region having a refractive index ni and a first integral fiber coupling regulator with said first optical fiber, said first fiber coupling regulator coupling the light signal between a first optical path and a second optical path and substantially avoiding that the light signal is coupled to the third optical path.
2. 2. The optical device according to claim 1, further characterized in that the first fiber coupling regulator comprises: a first optical coupler integral with the first optical fiber for coupling the light signal between the first path and the second path and producing a first output signal, in which the first path is a mode LP01 of the light signal and the second path is a mode LP02 of the light signal; and a first integral coupling inhibitor with at least one of said first optical coupler or the first optical fiber, said first coupling inhibitor substantially avoiding that the light signal is coupled to the third path, wherein the third path is any mode of the light signal higher than said mode LPo2- 3. The optical device according to claim 2, further characterized in that the first optical coupler comprises a tapered region in the first optical fiber, wherein said tapered region is characterized by a taper ratio defined as a change of a radius of the first optical fiber with respect to a change in a length of said tapered region 4. The optical device according to claim 3, further characterized in that the first coupling inhibitor comprises a pedestal of refractive indices in the first region of the core disposed between the first region c entral and the first coating, said pedestal region having refractive indexes a refractive index n5, wherein 5. - The optical device according to claim 3, further characterized in that the tapered region is characterized by a taper ratio approximately equal to 3 to 1. 6. The optical device according to claim 3, further characterized in that the first coupler optical comprises a valley region disposed in the first core between the first central region and the first coating, said valley region having a refractive index n6, wherein n1 > n2 > n6 7. - The optical device according to claim 6, further characterized in that the first coupling inhibitor comprises a pedestal region of refractive indexes disposed in the first core region between the valley region and the first coating, said pedestal region having of refractive indexes a refractive index n5, where n? > ns > n2 > n6 8. The optical device according to claim 7, further characterized in that the valley region has a radial dimension in an approximate range between 3 microns and 10 microns, and? -i-ß is within a range of approximately 0.1% and 0.4%. 9. The optical device according to claim 6, further characterized in that the first coupling inhibitor comprises the tapered region and the tapered region is characterized by a taper ratio of less than 2 to 1, such that the intermodal coupling. 10. The optical device according to claim 9, further characterized in that the valley region has a radial dimension in an approximate range between 5 micras and 10 micras and? -t-6 is in an approximate range between 0.03% and 0.07 %, in such a way that the intermodal coupling between mode LP01 and mode LP02- 11 is made possible. The optical device according to claim 2, further characterized in that the first fiber coupling regulator also comprises: a second optical coupler integral with the first optical fiber and separated from the first optical coupler by a phase delay distance Ln, said second optical coupler coupling the first optical signal between the LP01 mode of the first output signal and the LP2 mode of the first output signal to produce a second output signal, in which the first coupler and the second coupler form a Mach-Zehnder device; and a second integral coupling inhibitor with at least one of said second optical coupler or the first optical fiber, said second coupling inhibitor substantially avoiding that the first output signal is coupled to any mode of the higher output signal than said one. mode LP02- 12. The optical device according to claim 1 1, further characterized in that said first optical coupler comprises a first tapered region that is characterized by a first taper ratio and the second optical coupler comprises a second tapered region that is characterized by a second taper relationship, wherein said first taper ratio and said second taper ratio are defined as a change of a radius of the first optical fiber with respect to a change of a length of the first optical fiber. 13. The optical device according to claim 12, further characterized in that the spectral response is tunable as a function of the first taper ratio, the second taper ratio and the phase delay distance L-n. 14. The optical device according to claim 13, further characterized in that the spectral response includes the channel wavelength? C, a wavelength channel passage band, a channel blocking band of length of wave and a gain as a function of wavelength. 15. The optical device according to claim 14, further characterized in that the spectral response is a periodic function of approximately sinusoidal shape having a short period including a maximum and a minimum, in which said maximum corresponds to the pass band of wavelength channel and said minimum corresponds to the wavelength channel blocking band. 16. The optical device according to claim 15, further characterized in that the maxima transmit approximately 100% of the light signal and the minimums transmit approximately 70% of the light signal. 17. A fiber optic transmission system comprising: at least one soliton transmitter for modulating data and transmitting soliton pulses over a channel wavelength to carry said data; an optical fiber connected to said soliton transmitter for propagating said soliton pulses; at least one amplifier connected to said optical fiber to amplify said soliton pulses; the optical device according to claim 16 connected to said amplifier which is at least one and tuned to a center frequency; and at least one soliton receiver connected to said optical fiber to demodulate said soliton pulses and recover said data. 18. - The fiber optic transmission system according to claim 17, further characterized in that the amplifier which is at least one comprises a plurality of amplifiers that are separated in the transmission system, and in which the center frequency of each of the optical devices according to claim 16 connected to said plurality of amplifiers is different, forming a series of sliding frequency filters that substantially reduce the timing fluctuation of the transmission system. 19. An optical device according to claim 15, further comprising: a second optical fiber connected to the first optical fiber, having second optical fiber card a second core and a second coating with refractive index n, including said second core a second central region having a refractive index n3; and a second integral fiber coupling regulator with said second optical fiber, said second fiber coupling regulator coupling the light signal between the first optical path and second optical path and substantially preventing the light signal from coupling to the third path. optics. 20. The optical device according to claim 19, further characterized in that the second fiber coupling regulator comprises: a third optical coupler integral with the second optical fiber for coupling the light signal between the first path and the second path and produce a third output signal; and a third integral coupling inhibitor with at least one of said third optical coupler or the second optical fiber, said second coupling inhibitor substantially avoiding that the light signal is coupled to the third path. 21. The optical device according to claim 20, further characterized in that the second fiber coupling regulator also comprises: a fourth optical coupler integral with the second optical fiber and separated from the third optical coupler by a phase delay distance L21 , said fourth optical coupler coupling the third output signal between the first path and the second path and producing a fourth output signal, wherein the third coupler and the fourth coupler form a Mach-Zehnder device; a fourth integral coupling inhibitor with at least said fourth optical coupler or the second optical fiber, said fourth coupling inhibitor substantially avoiding that the third output signal is coupled to the third path. 22. The optical device according to claim 21, further characterized in that the spectral response is a periodic function of approximately sinusoidal shape and having a second period that is twice that of the first period. 23. The optical device according to claim 11, further characterized in that the first fiber coupling regulator also comprises: a third optical coupler integral to the first optical fiber and separated from the second optical coupler by a phase delay distance L - | 2, said optical coupler coupling the second output signal between the first path and the second path to produce a third output signal, wherein the first optical coupler, the second optical coupler and said third optical coupler form a filter device of grid; and a third integral coupling inhibitor with at least one of said optical coupler or the first optical fiber, said third coupling inhibitor being a material property that substantially prevents the second output signal from coupling to the third path. 24. The optical device according to claim 23, further characterized in that the first optical coupler comprises a first tapered region that is characterized by a first taper ratio, the second optical coupler comprises a second tapered region that is characterized by a second taper ratio and the third optical coupler comprises a third tapered region that is characterized by a third taper relationship, wherein said first taper ratio, said second ratio The taper and said third taper relationship are defined as a change of a radius of the first optical fiber with respect to a change of a length of the first optical fiber. 25. The optical device according to claim 24, further characterized in that the spectral response is tunable as a function of the first taper ratio, the second taper ratio, the third taper ratio and the phase delay distances L? ? and L | . 26. - The optical device according to claim 25, further characterized in that the spectral response is tuned to thereby cause an insertion loss of the optical device to vary as a function of the wavelength, such that a predetermined spectral window is filtered. 27. A fiber Raman amplifier system comprising: an optical pump for supplying a pump signal; a WDM coupler having a first input connected to said pump and a second input connected to the light signal; an optical fiber connected to an output of said WDM coupler, in which the energy of said pump signal is transferred to the light signal by stimulated Raman diffusion; and a broadband filter comprising the optical device according to claim 26 connected to said optical fiber to filter the light signal. 28. An erbium impurified fiber amplifier system comprising: an optical pump for supplying a pump signal; a wavelength selective coupler having a first input connected to the light signal and a second input connected to said optical pump; an erbium doped fiber connected to an output of said selective wavelength coupler, in which an output light signal is amplified by a stimulated emission of erbium particles caused by said pump signal; an insulator connected to said erbium doped fiber; and a gain uniformator filter comprising the optical device according to claim 26, wherein the transfer function 4d causes a gain of the output light signal to be substantially uniform in the predetermined spectral response. 29. A fiber optic transmission system comprising: a first network element for transmitting the light signal; an optical fiber to propagate the light signal; an erbium doped fiber amplifier system according to claim 28; and a second network element for receiving the light signal. 30.- An optical device in accordance with the claim 23, further comprising: a second optical fiber connected to the first optical fiber, said second optical fiber having a second core and a second coating with refractive index n4, said second core including a second central region having a refractive index n3 , where n3 < n; and a second integral fiber coupling regulator with the second optical fiber, said second fiber coupling regulator coupling the light signal between the first optical path and the second optical path and substantially preventing the light signal from coupling to the third. optical path. 31. The optical device according to claim 30, further characterized in that the second fiber coupling regulator comprises: a fourth integral optical coupler to the second optical fiber for coupling the light signal between the first path and the second path and produce a fourth output signal; a fourth integral coupling inhibitor with at least one of said fourth optical coupler or the second optical fiber, said second coupling inhibitor substantially avoiding that the light signal is coupled to the fourth path; a fifth integral optical coupler to the second optical fiber and separated from said fourth optical coupler by a phase delay distance L2- ?; said fifth optical coupler coupling said fourth output signal between the first path and the second path and producing a fifth output signal, wherein said fourth coupler and said fifth coupler form a Mach-Zehnder device; and a fifth integral coupling inhibitor with at least one of said fifth optical coupler or the second optical fiber, said fifth coupling inhibitor substantially avoiding that the fourth output signal is coupled to the third path. 32. The optical device according to claim 31, further characterized in that the second fiber coupling regulator also comprises: a sixth optical coupler integral with the second optical fiber and separated from said fifth optical coupler by a phase delay distance L22, said sixth optical coupler coupling said fifth output signal between the first path and the second path and producing a sixth output signal, wherein said fifth coupler and said sixth coupler form a Mach-Zehnder device; and a sixth integral coupling inhibitor with at least one of said sixth optical coupler or the second optical fiber, said sixth coupling inhibitor substantially preventing the fifth output signal from being coupled to the third path. 33. - The optical device according to claim 31, further characterized in that the spectral response is a mirror image of an erbium gain spectrum on a silica glass base with aluminum co-buffing. 34.- A coaxial device for operation at an operating wavelength? 0, said device comprising: a single optical fiber having a core having a maximum refractive index or wrapped by a coating having a maximum refractive index n2 and a pedestal of refractive indexes having a maximum refractive index n5 located between said core and sheath, where n? > n5 < n2; at least one region tapered in said fiber, the portion of said fiber extending from one end of said tapered region having a protective coating thereon and forming a spiral fiber cable, the taper angle of said tapered region being large enough to cause coupling between modes LP01 and LP02, but not so large as to cause coupling to LP03 mode; further characterized in that said optical fiber has a cut-off wavelength? co more than 200 nm less than said operating wavelength? 0. 35. The optical device according to claim 34, further characterized in that said cutting wavelength? Co is more than 500 nm less than said operating wavelength? 0. 36. The optical device according to claim 34, which further comprises a medium having a refractive index n3 that surrounds said tapered region, which is at least one, of said fiber, wherein n3 < n2. 37. The optical device according to claim 36, further characterized in that? 2-3 is greater than 0.1%, where? 2-3 equals (n22-n32) / 2n22. 38.- The optical device according to claim 36, further characterized in that said means comprises an elongated body of germ glass having two end regions and a middle region, said fiber extending longitudinally inside said body and melting together with the region means of said body, said middle region including said tapered region, which is at least one, and said region of phase change. 39.- The optical device according to claim 43, further characterized in that said means comprises a base glass and a doping agent that decreases the refractive indexes. 40.- The optical device according to claim 34, further characterized in that said first fiber spiral cable is wrapped by a protective coating, whose refractive index is sufficiently higher than that of said coating that said mode LP02 is deformed. said fiber in said first fiber spiral cable, said protective coating having a refractive index n4, where n4 = ns. 41. - The optical device according to claim 34, further characterized in that the radius r p of said pedestal in said region of phase change is between 10 μm and 25 μm. 42. The optical device according to claim 41, further characterized in that the radius r p is less than 15 μm. 43.- The optical device according to claim 34, further characterized in that said fiber contains chlorine, the amount of chlorine in said pedestal being greater than the amount of chlorine in said coating. 44. The optical device according to claim 34, further characterized in that said core contains silica and a doping agent that increases the refractive indexes. 45.- The optical device according to claim 44, further characterized in that said core and said pedestal contain the same dopant that increases the refractive indexes. 46.- The optical device according to claim 34, further characterized in that? 5-2 is in the range of 0.01% to 0.05%, where? 5-2 is equal to (n52 - n22) / n22 47.- The optical device according to claim 34, further characterized in that said tapered region, which is at least one, comprises a plurality of tapered regions . 48. A coaxial device comprising: a single optical fiber having a core that has a maximum refractive index nor wrapped by a coating having a maximum refractive index n2 and a pedestal of refractive indexes having a refractive index maximum ns located between said core and cladding, where n? >; n5 > n2; at least one first and second axially tapered regions spaced apart along said fiber; a region of phase change of said fiber extending between said tapered regions from the end of said first tapered region opposite said region of phase change; and the taper angles of said tapered regions that are large enough to cause coupling between modes LP01 and LP02, but not so large as to cause coupling to LP03 mode. 49.- The device according to claim 48, further characterized in that said device operates at a given operative wavelength? 0 and said optical fiber has a cut-off wavelength? Co more than 200 nm less than said wavelength operational? 50.- The device according to claim 49, further characterized in that said cutting wavelength? Co is more than 500 nm less than said operating wavelength? 0. 51. The device according to claim 48, which further comprises a means having a refractive index n3 that surrounds said tapered regions of said fiber, wherein n3 < n2. 52. The device according to claim 51, further characterized in that? 2-3 is greater than 0.1%. 53. The device according to claim 51, further characterized in that said means comprises an elongated body of germ glass having two end regions and a middle region extending said fiber longitudinally within said body and melting together with the middle region of said body. said body, said middle region including said tapered regions and said region of phase change. 54.- The device according to claim 51, further characterized in that said means comprises a phase medium and a doping agent that decreases the refractive indexes. 55.- The device according to claim 48, further characterized in that said first spiral fiber cable is wrapped by a protective coating whose refractive index is sufficiently higher than that of said coating that said mode LP02 of said fiber is stripped in said first fiber spiral cable, said protective coating having a refractive index n, where n4 = ns. 56.- The device according to claim 48, further characterized in that the radius rp of said pedestal in said region of phase change in between 10 μm and 25 μm. 57.- The device according to claim 56, further characterized in that the radius r p is less than 15 μm. 58.- The device according to claim 48, further characterized in that said fiber contains chlorine, the amount of chlorine in said pedestal being greater than the amount of chlorine in said coating. 59. The device according to claim 48, further characterized in that said core contains silica and a refugee that increases the refractive indexes and because said pedestal contains silica and a dopant that increases the refractive index. 60.- The device according to claim 49, further characterized in that said core and said pedestal contain the same dopant that increases the refractive index. 61.- The device according to claim 49, further characterized in that said core and said pedestal contain different impurifiers that increase the refractive indexes. 62.- A method for filtering a light signal with an optical device having a predetermined spectral response, said optical device including a first optical fiber having a first core and a first coating with refractive index n2, said first core including a first central region having a refractive index nor, said method comprising: providing a first integral fiber coupling regulator with said first optical fiber; directing the light signal to a first optical fiber; and coupling the light signal in an LP0 mode? to an LP02 mode, wherein said first fiber coupling regulator couples the light signal between an LP0? and an LP02 mode and substantially prevents the light signal from being coupled to an LP03 mode. 63. The method according to claim 62, further characterized in that the step of providing a first fiber coupling regulator includes tuning the spectral response. 64. - The method according to claim 63, further characterized in that the spectral response is a periodic function of approximately sinusoidal shape having maximums and minimums, and a first period that includes a maximum and a minimum, in which said maximum corresponds to the band of wavelength channel pitch and said minimum corresponds to the wavelength channel blocking band. The method according to claim 64, further characterized in that the maxima transmit approximately 100% of the light signal and the minimums transmit approximately 70% of the light signal. 66.- The method according to claim 62, further characterized in that the step of providing a first fiber coupling regulator includes tuning the spectral response to thereby cause an insertion loss to the optical device to vary as a function of the wavelength , such that a predetermined spectral window is filtered. 67.- The method according to claim 62, which further comprises the steps of: providing a second optical fiber connected to the first optical fiber, said second optical fiber having a second core and a second coating with refractive index n4, said core including a second central region having a refractive index n3 where n3 > n4; and providing a second integral fiber coupling regulator with said second optical fiber, said second fiber coupling regulator coupling the light signal between the first optical path and the second optical path and substantially preventing the light signal from coupling to the third optical path. 68.- The method according to claim 67, further characterized in that the spectral response is a mirror image of an erbium gain spectrum on a silica glass base with aluminum co-buffing.