WO2000028352A2

WO2000028352A2 - System for information/data interface to optical fibers and method of fabrication

Info

Publication number: WO2000028352A2
Application number: PCT/US1999/025749
Authority: WO
Inventors: Stephen C. Jacobsen; Michael R. Mcneely; David L. Wells
Original assignee: Sarcos, Inc.
Priority date: 1998-11-05
Filing date: 1999-11-05
Publication date: 2000-05-18
Also published as: AU2842800A

Abstract

An interface/modulator system for interfacing with an optical fiber and modulating an optical signal has in one preferred embodiment a Bragg grating formed in an optical fiber and an active material layer formed about the cladding of the optical fiber at the Bragg grating location. The Bragg grating has a spatial period defining a Bragg wavelength at which modes of the optical signal are reflected to develop a reflected signal. The active material layer is responsive to an applied electric field to physically strain the material layer and the optical fiber. As the fiber strains, the grating period and Bragg wavelength are altered, thus modulating the reflected signal which can be monitored, for example, by using a monochromator or diffrication grating and photodiode array. An electro-optic material layer may also be deposited in an opening in the cladding and onto the core or into the core. The electro-optic material is responsive to an applied electric field to change its index of refraction to change the wavelength, amplitude, and/or phase of the optical signal. The material layer may be sandwiched between two electrode layers. The interface/modulator is fabricated by removing a section of cladding as required, depositing a first layer of conductive material, patterning the first conductor layer, depositing a layer of active or electro-optic material, depositing a second layer of conductive material, patterning the second conductor layer, and jacketing the layers.

Description

SYSTEM FOR INFORMATION/DATA INTERFACE TO OPTICAL FIBERS AND METHOD OF FABRICATION

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a system and method for interfacing with an optical fiber, modulating an optical signal traveling therein, and a method of fabricating an optical modulator and interface device. More particularly, the present invention relates to material layers disposed on the optical fiber for modulating the wavelength, amplitude, and/or phase of a transmitted or reflected optical signal traveling through the fiber. The material has means for varying the wavelength, amplitude and/or phase of the optical signal by either straining the optical fiber and/or by changing the refractive index of the fiber core, cladding, or surrounding medium.

2. Prior Art

Optical fibers, or fiberoptics, are becoming the standard means for communication of data. Data, in the form of an optical signal or light, travels along the optical fiber. An optical fiber typically has an inner core and an exterior or outer cladding surrounding the core. A protective jacket may also surround the cladding. An optical signal, in the form of light, is constrained within the fiber because of total internal reflection at the core-cladding interface, provided the angle of incidence of the light ray with the interface is greater than the critical angle. (The incident angle and critical angle are taken with respect to the normal of the core-cladding interface.) Light traveling in modes which have an incident angle greater that the critical angle are reflected. Thus, the light travels along the fiber by reflecting off the core-cladding interface. Light traveling in modes which have an incident angle less than the critical angle are partially reflected and partially transmitted out of the fiber. The critical angle can only be achieved when the index of refraction of the cladding material is smaller than that of the core material. The core typically has an index of refraction of 1.48 and the cladding typically has an index of refraction of 1.45. In many situations it is desirable to connect to an optical fiber and put data/information onto an optical fiber transmission line at some point or points along the length of the fiber in order to transmit information. Such a situation may be, for example, a chip based micro-sensor located somewhere along the length of the fiberoptic. Other situations might be interfacing towed hydrophone arrays onto an optical fiber; connecting building/structural or ship state sensors (temperature, acceleration, vibration, strain, fire, etc.) to a data network which is monitoring system state or health; or connecting chip-based position, force, velocity, and acceleration sensors on a robot to an optical fiber data line for use in feedback control systems.

There is not presently a good way, however, of "tapping" into an optical fiber at a location other than the beginning of the fiber. Present methods for connecting to fibers and transmitting data require cutting the fiber at the interface location, inserting a signal modulator that is large (typically the size of a deck of cards), and reconnecting (splicing) the fiber. One disadvantage of this method is that breaking and splicing the fiber creates optical losses at the interface location. The optical losses reduce the efficiency of the optical communication line. Another disadvantage of this method is that the optical modulators and their requisite electronic drive systems are large, and thus not well suited for or compatible for interface with small chip-based sensors. Another disadvantage is that present fiber modulators are large and bulky, thus increasing the size and weight of the system. Size is a considerable concern in some applications, such as those in which fibers are embedded in a composite structure which needs to maintain the small and smooth profile of the optical fibers. Another problem of interfacing with fiberoptics is their small size and round shape. Lithographic techniques have been utilized for some time in the manufacture especially of integrated circuit boards and semiconductor devices and related products. The products manufactured have typically included planar surfaces to which the lithographic techniques were applied. Such techniques have proven extremely effective in the precise manufacturing and formation of very small details in the product. However, attempts to apply such techniques to other than planar surfaces have proven difficult, if not unachievable, until recently. With recent developments in nonplanar microlithography, the fabrication of microstructures, including both three-dimensional mechanical parts and three- dimensional electrical components, has become more readily achievable. U.S. Patent 5,106,455, issued April 21, 1992, to Jacobsen et al. discloses a method and apparatus for fabricating microstructures using nonplanar, exposure beam lithography. Using this method and apparatus, very fine, precise and detailed physical structures can be formed on very small three-dimensional objects such as, for example, cylinders. U.S. Patent 5,269,882, issued December 14, 1993, to Jacobsen discloses a method and apparatus for fabricating thin-film semiconductor devices using nonplanar, exposure beam lithography. In particular, a variety of semiconductor devices can be formed on three-dimensional substrates, again such as cylinders. The methods and apparatus disclosed in the above two patents provide for fabrication of individual microstructures or thin-film semiconductor devices in a type of batch processing approach. U.S. Patent 5,273,622, issued December 29, 1993, to Jacobsen discloses a continuous processing approach for fabricating microstructures and thin-film semiconductor devices. Such microstructures are finding use in a variety of areas including medical devices, robotics, navigation equipment, motors and similar equipment. U.S. Patent 5,481,184, issued January 2, 1996, to Jacobsen discloses a system for movement actuators and sensors on very small mechanical parts, such as fibers and filaments.

U.S. Patent 5,270,485, issued December 14, 1993, to Jacobsen discloses a three- dimensional circuit structure with electrical components formed on the surfaces of elongated cylindrical substrates. With the development of these very small (termed "micro") mechanical devices and electrical elements, the ability to fabricate detailed features of such devices and elements in an efficient and precise way has become feasible.

There has been recent growing interest in the formation and application of distributed Bragg gratings in single mode optical fibers. See B. Malo, D.C. Johnson, F. Bilodeau, J. Albert and K.O. Hill, Optics Letters 18, 1277-1279 (1993); G. Meltz, W.W. Morey, W.H. Glenn, Optics Letters 14, 823-825 (1989); and W.W. Morey, G. Meltz, W.H. Glenn, Proceedings of SPIE, 1169, 98 (1989). A Bragg grating is a series of lines formed in the core of the optical fiber. The grating consists of a spatial variation in the refractive index of the core. The grating causes a strong Bragg-reflected signal at the grating Bragg wavelength. The optical signal transmission is almost lossless at other wavelengths. Thus, light at the Bragg grating wavelength is reflected while light at other wavelengths is largely unaffected. The Bragg gratings have found uses as mirrors for all-fiber lasers, distributed fiber sensors, wavelength division multiplexers and filters for telecommunications, and instrumentation components.

The gratings can be formed in the fiber by several methods, for example by interfering crossed excimer laser beams directed at the fiber. The excimer laser at 248 nm forms color centers or other defects in the doped silica core, or melts and recrystalljzes the core. Gratings with greater than 99.5% reflectance have been fabricated with spectral bandwidths of less than 0.4 nm and a total length of 4mm, with excellent long-term stability. More recently, gratings with linewidths of 0.05 to 0.2 nm have been formed with reflectances of 50 to 70%. See D.A. Jackson, A.B. Lobo Ribeiro, L. Reekie and J.L. Archambault, Optics Letters 18, 1192-

1194 (1993).

A variety of sensor applications have been proposed, including the use of fiber gratings as strain sensors in structures. See W.W. Morey, Proceedings of the Seventh Optical Fiber Sensors Conference (IREE Australia), Sydney, Australis, 285-288, (1990); A.D. Kersey, T. A. Berkoff ans W.W. Morey, Proceedings of the

First European Conference on Smart Structures and Materials (SPIE, Bellingham, WA), 61-67 (1992). The key advantages of the sensor result from its inherent nature. The formation of the grating uses a non-contact process which does not alter the physical geometry of the fiber. Gratings can be formed at any location along a fiber. The Bragg wavelength can be continuously tuned by simply altering the spatial period of the interference pattern formed by the two intersecting UV laser beams. The Bragg gratings can be extremely efficient, thermally stable, continuously adjustable in their reflectance and bandwidth, and they are nearly transparent for wavelengths longer than the Bragg Wavelength. For wavelengths shorter than the Bragg wavelength, some gratings form efficient broadband optical couplers. Many Bragg sensors can be located along a single fiber. Sensing is achieved by optically monitoring changes in the Bragg wavelength, which varies as the fiber is strained. Changes in the effective spatial period of the grating will result in a Bragg wavelength shift.

Therefore it would be advantageous to develop a system for interfacing with an optical fiber data line without interrupting or breaking the optical fiber. It would also be advantageous to develop such a system for modulating an optical signal within the optical fiber. It would also be advantageous to develop such a system where the interface can be integrated on the optical fiber and be made small enough to be driven by electronics on a chip-based sensor. It would also be advantageous to develop such a system where the interface is small. It would also be advantageous to develop a method for fabricating such an interface/modulator.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a system for interfacing with an optical fiber data line without interrupting or breaking the optical fiber. It is another object of the present invention to provide such a system with an interface that can be integrated on the optical fiber.

It is another objective of the present invention to provide such a system with an interface that is small.

It is another objective of the present invention to provide such a system for modulating an optical signal within the optical fiber.

It is yet another object of the present invention to provide a method for fabricating such an interface/modulator.

These and other objects and advantages of the present invention are realized in an optical fiber interface/modulator apparatus for interfacing with an optical fiber and for modulating an optical signal in the optical fiber. The apparatus has a Bragg grating formed in the core and an active, such as an acousto-optic, material layer disposed around the optical fiber at the Bragg grating for straining the fiber and grating.

The Bragg grating is a spatial variation in the refractive index of the optical fiber at the core/cladding interface. The grating has a spatial period defining a Bragg wavelength for selectively reflecting modes of the optical signal having the Bragg wavelength. This creates a reflected optical signal at the Bragg wavelength.

The strain inducing material layer, which could for example be an acousto- optic material layer, is responsive to an applied voltage, current, or electric field for activating the material and physically straining the optical fiber. As the optical fiber strains, the refractive index and length of the fiber changes. As a result, the wavelength of the light reflected by the Bragg grating changes because of the strain-induced changes in the Bragg grating. The altering of the grating period and Bragg wavelength modulates the wavelength of the reflected signal. The reflected signal is monitored for changes in the wavelength. An example of a monitoring means includes a high resolution monochromator and a low noise photodiode/amplifier used as a slope filter. Any change in the wavelength of the reflected signal changes the photodiode/amplifier output. For multiple interface sites, a grating in conjunction with a linear photodiode array could be used. Or the monochromator could be scanned across the wavelengths representing the different interfaces.

The active material layer may be disposed on the cladding. Alternatively, a first layer of conductor material may be disposed on the optical fiber, defining a first electrode. The active, for example acousto-optic, material layer may be disposed on the first conductor layer. A second layer of conductive material may be disposed on the active layer, defining a second electrode. The first and second conductor layers may be patterned in a desired electrode shape. The active material layer may be a piezoelectric film or tube.

Multiple and thicker active layers may be used to increase the physical strain. In addition, opposed sections of active material layers disposed on opposite sides of the fiber may be used synergistically in a push/pull fashion to increase the physical strain.

Multiple gratings may be formed in the core, each with a unique Bragg grating wavelength lying within the bandwidth of the optical signal. Multiple active material layers each may be disposed about the multiple gratings. In this fashion, multiple modulators may be multiplexed on a single optical fiber. One method for detecting the signals from multiple gratings would use pairs of gratings. The first grating in a pair is a sensor grating, and the second grating is a reference grating (the grating pairs need not be physically adjacent). A piezoelectric transducer may continually tune the reference grating and sweep it at twice the maximum sensor bandwidth desired. When the sensor and reference gratings are tuned to the same wavelength, a strong signal is reflected from the reference grating, thus identifying the sensor grating and its optical signal. Another method for demultiplexing signals from multiple interfaces involves a grating which reflects the optical signal from the fiber and spatially spreads it over a linear photodiode array according to wavelength. Individual elements of the array, corresponding to specific, but different wavelengths would then receive and transduce the signals from the different interface nodes.

A method for fabricating the optical fiber interface/modulator described above includes first providing an optical fiber. The optical fiber preferably has an exposed section exposing the cladding. Alternatively, the cladding may not be exposed, but have a jacket. A layer of conductive material is deposited on the cladding, or jacket, defining the first electrode. The first electrode may be patterned by removing unwanted portions of the conductive material. A segment of the conductive material also may be masked to provide a location for future electrical connection. A layer of active material is deposited onto at least a portion of the first electrode. The active material may be annealed if necessary. A second layer of conductive material is then deposited on at least a portion of the acousto-optic material layer, defining the second electrode. The second electrode may be patterned by removing unwanted material. The active material is then processed as necessary, such as by being poled. The active material may be poled by applying an electrostatic field across the active material while it is in a heated oil bath (for a piezoelectric material). The exposed portion may then be covered with a jacket material to protect it. The cladding does not have to be exposed. The active material can be put on the jacket, although it is not as efficient. An alternative embodiment of the present invention takes advantage of the principle of total internal reflection to modulate the amplitude of the optical signal. An opening is formed in the cladding of the optical fiber and extends through the cladding to the core. An electro-optic material layer is disposed in the opening. The electro-optic material has an index of refraction that changes in the presence of an electric field. A pair of conductors connect to the electro-optic material layer for activating the material and changing its index of refraction. As the index of refraction of the electro-optic material changes, the amount of attenuation of the optical signal changes to modulate the amplitude of the optical signal.

The index of refraction of the electro-optic material may change within a range defined at an upper limit by the index of refraction of the core and at a lower limit by the index of refraction of the cladding. Thus, the index of refraction of the electro-optic material layer is greater than that of the cladding, but less than that of the core. In this way, the optical signal is amplitude modulated by changing the amount of the optical signal reflected by the material layer at an interface between the core and the material layer. Alternatively, the index of refraction of the electro-optic material may change to be greater than the index of refraction of the core. In this way, the optical signal is amplitude modulated by changing the amount of the light leaking out of the fiber.

The electro-optic material layer may be disposed on the core with the conductors disposed on top of the electro-optic material layer. Alternatively, the electro-optic material layer and the conductors may be disposed on the core. Alternatively, a first layer of transparent conductive material may be disposed on the optical fiber, defining a first electrode. The electro-optic material layer may be disposed on the first conductor layer. A second layer of conductive material may be disposed on the electro-optic layer, defining a second electrode. The first and second conductor layers may be patterned in a desired electrode shape.

A method for fabricating the optical fiber interface/modulator described above includes first removing a section of the cladding down to the core to form an opening in the cladding. A layer of electro-optic material is deposited onto at least a portion of the core. Electrodes are then connected to the layer of electro- optic material. The electrodes may be mechanically connected to the material or may be deposited on the material layer or on the core. An alternative embodiment takes advantage of the principle of attenuated total reflection and modulates the amplitude of the optical signal. An opening is formed in the cladding and extends through the cladding to the core, similar to the above embodiment. A first layer of conductive material is disposed in the opening on the core, defining a first electrode. The electro-optic material layer is disposed on the first conductor layer. The electro-optic material has a dielectric constant that changes in the presence of an electric field. A second layer of conductive material is disposed on the electro-optic layer, defining a second electrode. An applied electric field changes the dielectric constant of the electro-optic material which changes the angle at which attenuated total reflection occurs, thus modulating the amplitude of the optical signal.

The method of manufacturing the above embodiment is similar to that described above.

In an alternative embodiment, an opening is formed in the cladding and extends through not only the cladding, but into the core as well. An electro-optic material is disposed in the opening and in the core. The electro-optic material changes its index of refraction and the index of refraction of the core. Thus, the pathlength of the optical signal is changed to modulate the phase of the optical signal. The method of fabricating the above embodiment is similar to that described above, only the opening is formed into the core as well as through the cladding.

These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of an interface/modulator apparatus of the present invention on an optical fiber. FIG. 2 is a cross-sectional view of the preferred embodiment of the interface/modulator apparatus of the present invention on an optical fiber taken along line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of the preferred embodiment of the interface/modulator apparatus of the present invention on an optical fiber taken along line 3-3 of FIG. 1.

FIG. 4A is a schematic view of an example system for interfacing with an optical fiber and modulating and detecting the optical signal therein using a monochromator and a photodiode/amplifier. FIG. 4B is a schematic view of an example system for interfacing with an optical fiber and modulating and detecting the optical signal therein using a diffraction grating and a linear photodiode array.

FIG. 4C is a schematic view of the diffraction grating and the linear photodiode array of FIG. 4B. FIG. 5 is a perspective view of an alternative embodiment of an interface/modulator apparatus of the present invention on an optical fiber.

FIG. 6 is a cross-sectional view of the alternative embodiment of the interface/modulator apparatus of the present invention on an optical fiber taken along line 6-6 of FIG. 5. FIG. 7 is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention.

FIG. 8 is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention.

FIG. 9A is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention.

FIG. 9B is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention.

FIG. 9C is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention. FIG. 10 is a cross-sectional view of an alternative embodiment of an interface/modulator apparatus of the present invention. FIG. 11 is a perspective view of a fixture for clamping onto an optical fiber about the interface/modulator apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention.

As illustrated in figs. 1-3, a preferred embodiment of an optical fiber interface/modulator system of the present invention includes an optical fiber interface/modulator apparatus, indicated generally at 10, for interfacing with an optical fiber data line 12 and modulating an optical signal in the optical fiber. Data, in the form of an optical signal or light, travels along the optical fiber 12. The optical fiber 12 has an inner core 14 and an exterior or outer cladding 16 surrounding the core. A protective jacket (not shown) may also surround the cladding.

The light or optical signal is constrained within the fiber because of total internal reflection at the core-cladding interface, provided the angle of incidence of the light ray with the interface is greater than the critical angle. (The incident angle and critical angle are taken with respect to the normal of the core-cladding interface.) Light traveling in modes which have an incident angle greater that the critical angle are reflected. Thus, the light travels along the fiber by reflecting off the core-cladding interface. Light traveling in modes which have an incident angle less than the critical angle are partially reflected and partially transmitted out of the fiber. The critical angle can only be achieved when the index of refraction of the cladding material is smaller than that of the core material. The core typically has an index of refraction of 1.48 and the cladding typically has an index of refraction of 1.45.

Referring to FIG. 3, a Bragg grating 20 is formed in the core 14. As described above, the Bragg grating consists of a periodic spatial variation of the index of refraction at the core/cladding interface. The grating 20 has a spatial period defining the Bragg wavelength. Light with modes or wavelengths the same as the grating Bragg wavelength is selectively reflected while light with other modes or wavelengths is largely unaffected. Therefore, a reflected signal of light at the Bragg wavelength is caused by the grating.

One way the grating may be formed in the fiber is by interfering excimer laser beams which are focused on the fiber. The excimer laser at 248 nm forms color centers or other defects in the doped silica core, or melts and recrystallizes the core. The formation of the grating uses a non-contact process which does not alter the physical geometry of the fiber. Gratings can be formed at any location along a fiber. The Bragg wavelength can be continuously tuned by simply altering the spatial period of the interference pattern formed by the two intersecting laser beams. The Bragg gratings can be extremely efficient, thermally stable, continuously adjustable in their reflectance and bandwidth, and they are nearly transparent for wavelengths longer than the Bragg wavelength. Many Bragg gratings can be located along a single fiber. Referring again to FIGS. 1-3, an active material layer 30 (such as an acousto-optic material) advantageously is disposed around the optical fiber 12 at the location of the Bragg grating 20. The material layer 30 may be disposed about the cladding 16 or the jacket (not shown). Preferably, the material layer is disposed on the cladding. The material layer 30 is responsive to an applied electric field, voltage, or current indicated at 32, for activating the material layer or causing it to physically strain.

As the material layer 30 strains, it also physically strains the optical fiber 12. The physical strain varies the refractive index and length of the optical fiber. The change in the refractive index and length of the fiber alters the grating period and the Bragg wavelength. As the Bragg wavelength changes, the wavelength of the reflected signal is changed. Thus, as the active material layer physically strains the optical fiber, the wavelength of the reflected signal from the Bragg grating is modulated. Therefore, the material layer interfaces with the optical fiber and modulates the optical signal. The modulated signal, or reflected signal, is caused by selectively applying a voltage or electric field to the material layer and may be monitored or sensed as discussed further below. The active material layer 30 and conductors or electrodes used to activate the acousto-optic material may be structured about the optical fiber 12 in various ways. For example, a first layer of conductive material 34 may be directly disposed around the optical fiber 12. The first conductive layer 34 forms a first electrode. The active material layer 30 may be disposed on at least a portion of the first layer 34 or first electrode. A second layer of conductive material 36 may be disposed on at least a portion of the active material layer 30. The second conductive layer 36 forms a second electrode.

The first and second electrodes or conductive layers 34 and 36 apply an electric field, voltage, or current across the active material layer 30. The applied voltage causes the material layer 30 to strain itself and the optical fiber 12. The first and second electrodes are formed of any appropriate conductive material. In addition, the first and second electrodes may be patterned in a desired electrode pattern. Furthermore, the layers may be protected by a coating or potted in a compliant sealant such as RTV silicone.

The active material layer 30 may be, for example, a piezoelectric film (e.g.

PZT or ZnO), a magnetostrictive film, an electrostictive film, shape memory alloy film, etc. As an example, a piezoelectric filt is poled to be oriented radially for e₃₃ and longitudinally for e₃₁. The strain is related to the applied field through the equation

S=eE/c where e is the piezoelectric coefficient,

E is the applied electric field, and c is the elastic stiffness of the piezoelectric/fiber composite structure.

When the core is strained, the grating period is altered through variations in the refractive index and through a physical length change of the fiber. For a wavelength of 0.8 μm, a grating pitch length of 0.5 nm is needed to provide very high contrast digital signals. This corresponds to a strain of 6.2 x 10^"4.

For a PZT-4 material layer with good poled characteristics, the effective piezoelectric constant is e₃, = -5.1 C/m², and c = 11.5 x 10¹⁰ N/m². The resulting strain for 5 μm thick film with an applied field of 10 V/μm (50 Volts total potential) is S = 4.4 x 10^"4, which is comparable to the strain needed for creating a very high contrast digital signal. Using alternative embodiments, the voltage necessary can be greatly reduced (an order of magnitude or more).

The wavelength of the signal reflected by the grating is shifted as a function of the applied electric field. By selectively applying a voltage or electric field to the material layer, the reflected signal is modulated.

In order to increase the physical strain, multiple or thicker active material layers may be disposed about the optical fiber. In addition, opposed sections of active material layers disposed on opposite sides of the fiber may be used synergistically in a push/pull fashion to increase the physical strain in the fiber at the grating location. Furthermore, bulk strain motors, which for example may be piezoelectric, can be bonded directly to the fiber.

In addition, although the above embodiment has been described and illustrated as having an active material layer, it is of course understood that the active material may take other forms. For example, the active material layer may be an active material tube disposed about the optical fiber. As another example, the active material layer may be a bulk material disposed on the optical fiber.

The interface/modulator apparatus of the present invention represents a significant advantage over prior art interfaces and/or modulators. The apparatus described above is capable of interfacing with an optical fiber without interrupting or breaking the fiber. In addition, the interface of the present invention is small enough to be integrated on the fiber itself and be driven by chip-based sensors. Furthermore, the apparatus described above is capable of modulating the optical signal within the optical fiber. As indicated above, the modulated reflected signal may be optically monitored for changes in the Bragg wavelength by measuring directly or indirectly the wavelength of the reflected signal, which is varied as the fiber is strained. Any change in the effective spatial period of the grating will result in a Bragg wavelength shift. The signal reflected by the grating is wavelength shifted as a function of the applied electric field.

The Bragg wavelength shift or wavelength of the reflected signal may be detected in various ways. As illustrated in FIG. 4 A. an example of one possible embodiment of the interface/modulation system or apparatus, indicated generally at 40, is shown. The modulation system demonstrates how the reflected signal may be optically monitored using a high resolution monochromator 50 as a slope filter and a low noise photodiode/amplifier 52. An interface/modulator device 10, is formed on the optical fiber 12, as described above. The optical fiber 12 is coupled by a wavelength-flattened, 2x2 coupler 42 to a light source 44, such as a super luminescent diode with the appropriate spectral range. The diode simulates an optical signal. The diode is only an illustrative example, other light sources are possible. A laser diode driver 46 is used to provide the regulated drive current for the diode 44. FC connectorized pigtails 48 are used to connect the diode 44 with the 2x2 coupler 42 and to connect the 2x2 coupler 42 with the optical fiber 12. The modulator device 10 is driven by the generator (not shown) of the signal that is transmitted down/interfaced to the fiber, which for example, could be a chip-based sensor. The modulated light, or reflected signal, is reflected by the grating of the modulator device 10 back through fiber 12 and the coupler 42 to the monochromator 50. The monochromator is tuned to the nominal Bragg reflected wavelength. The monochromator 50 is used to condition the modulated light signal for the photodiode/amplifier combination 52 from which a voltage representing the sensor data can be read. The photodiode response matches the wavelength spectrum of the light source and the Bragg grating. Any change in the wavelength of the reflected signal changes the photodiode/amplifier output. The monochromator and photodiode/amplifier form an optical receiver. It is of course understood that other embodiments and system components are possible, and that the system discribed above and illustrated is merely an example of a monitoring means to monitor changes in the wavelength at the interface.

Multiple interface/modulator devices may be multiplexed on a single optical fiber, as shown in FIG 4A, using, for example, wavelength-division multiplexing. Each modulator device may be shifted in grating wavelength within the bandwidth of the optical signal or interrogating light source. Alternatively, each modulator device may be weakly reflecting and its identity determined using time-domain techniques. Alternatively, signals form multiple gratings could be detected using pairs of gratings, with the first grating being the sensor/interface grating. A second grating is used as a reference and is continually tuned using a piezoelectric transducer. The grating pairs need not be physically adjacent. When the sensor grating and reference grating are tuned to the same wavelength, a strong signal is reflected from the reference grating. By sweeping the reference grating at twice the maximum sensor bandwidth desired, and calibrating the reference grating in Volts/nm shift to tune it to the sensor, the strain of the sensor grating (i.e. the transmitted signal) can be extracted in real time. Referring to FIGs. 4B and 4C, another method for demultiplexing signals form multiple interfaces involves a diffraction grating 54 which reflects the optical signal from the fiber and projects or spatially spreads it over a linear photodiode array 55 according to wavelength. Individual elements of the array, corresponding to specific, but different wavelengths would then receive and transduce the signals from the different interface nodes.

Referring to FIG. 4C, a collimating lens 56 may be disposed before the diffraction grating 54. In addition, a focusing lens 57 may be disposed after the diffraction grating 54, but before the linear photodiode array 55. It is of course understood that other embodiments and system components are possible, and that the system discribed above and illustrated is merely an example.

A large number of gratings can be wavelength-multiplexed using this approach.

The first step in a method for fabricating an optical fiber interface/modulator apparatus described above is to split the jacket of the optical fiber at the location of the Bragg grating to expose a section of the cladding. The fiber is then rinsed in de-ionized water.

The next step is to deposit a first layer of conductive material onto the cladding of the fiber. Alternatively, the conductive material may be deposited onto the jacket of the fiber. The conductive material may be deposited by physical vapor deposition (PVD), such as sputtering, or by other deposition techniques, such as chemical vapor deposition. The first conductor may be patterned in a desired electrode pattern by removing any unwanted portion of the conductive material. A segment of the first conductor is masked (e.g. lighographically or mechanically) to provide a location for future electrical connection to the electrode.

The next step is to deposit the active material layer (e.g. PZT) over the unmasked portions of the first layer of conductive material. The active material may be deposited by physical vapor deposition, dip-coating, or other methods. Alternatively, the active material layer may be tube, such as a PZT tube, disposed over the fiber, or may be a bulk actuator. The active material is then annealed if necessary. The annealing may be done by a laser annealing process, furnace annealing process, or other annealing process. A segment of the active material is masked (e.g. lithographically or mechanically) to allow for future electrical connection to the electrodes.

The next step is to deposit a second layer of conductive material over the active material layer. Again, the conductive material may be deposited by physical vapor deposition, such as sputtering, or other deposition methods, such as chemical vapor deposition. The second conductor may be patterned in a desired electrode pattern by removing any unwanted portion of the conductive material.

The next step is to pole the active material, if necessary. The electrodes are electrically connected to a voltage source and the optical fiber is placed in a heated oil bath. An electrostatic field is then applied across the material.

The exposed fiber may be re-jacketed to protect it from surface scratches and other environmental insults. The modulator device may then be tested by using the modulator system described above.

As illustrated in FIGS. 5-8, an alternative embodiment of an interface/modulator apparatus, indicated generally at 60, is shown on an optical fiber 12 and takes advantage of the principle of total internal reflection to modulate the amplitude of the optical signal. The optical fiber 12 has a cladding with an index of refraction and a core with an index of refraction. The index of refraction of the cladding material is smaller than the index of refraction of the core material. Thus, the optical signal or light traveling in the fiber is constrained within the fiber because of total internal reflection at the core-cladding interface 62, as illustrated in FIG. 6, as long as the angle of incidence of the light ray with the interface is greater than the critical angle. (The incident angle and critical angle are taken with respect to the normal of the core-cladding interface.) The critical angle can only be achieved when the index of refraction of the cladding material is smaller than the index of refraction of the core material. Light traveling in modes which have an incident angle less than the critical angle are partially reflected and partially transmitted out of the fiber. The smaller the incident angle the greater the attenuation of light out of the fiber.

An opening 64 is formed in the optical fiber 12 which extends through the cladding 16 to the surface of the core 14. The opening 64 may be formed all around the circumference of the fiber 12 or core 14, as illustrated, or may be formed only around a portion of the circumference of the fiber 12.

An electro-optic material layer 66 is disposed in the opening 64 and on the surface of the core 14. The electro-optic material may not be disposed on the surface of the core as discussed below. The electro-optic material has an index of refraction that changes in presence of an electric field. A pair of conductors 68 and 70 are connected to the electro-optic material layer 66 for activating the material and changing its index of refraction. The pair of conductors 68 and 70 may be placed on opposing ends of the electro-optic material layer 66 and on the surface of the core 14, as shown in FIG. 6, or at opposing ends of the material layer 66 and on the material layer, as shown in FIG. 7. Placing the conductors on the electro-optic material layer provides more efficient E-field generation in the material, but placing the conductors on the core is more easily realized.

Referring to FIG. 8, a first layer of transparent conductive material 74 is disposed in the opening 64 and on the core 14, defining a first electrode. The first electrode 74 must be optically transparent at the appropriate wavelengths. An electro-optic material layer 66 is disposed on at least a portion the first layer of conductive material 74. A second layer of conductive material 78 is disposed on at least a portion of the electro-optic material layer 66, defining a second electrode. The electro-optic material layer 66 forms a different cladding for the core or creates a core/modulator, or core/material, interface 72, as shown in FIGS. 6, 7 and 8. Changing the index of refraction of the cladding material, or the electro- optic material layer 66, will change the critical angle experienced by the fiber at that section. The change in the critical angle will in turn change the amount of light in the fiber undergoing attenuation by changing the reflectance and transmittance at the core/material interface. Therefore, the material layer interfaces with the optical fiber and modulates the optical signal in it. The modulated signal is developed by selectively applying a voltage or electric field to the material layer and may be monitored.

In order to be effective, the change in the index of refraction of the electro-optic material layer 66 must be within the interval between the core and cladding indicies. The index of refraction for the core material is typically 1.48 while the index of refraction for the cladding material is typically 1.45. Therefore, the electro-optic material must have an index of refraction that can change within the interval of 1.45-1.48, at least for these core/cladding materials. If the electro- optic material has an index of refraction greater than 1.48, then total internal reflection will not exist. If the electro-optic material has an index of refractions less than 1.45 then the critical angle will be shifted lower to accept modes of light that do not exist because of previous attenuation.

Selecting a material with an appropriate index of refraction for the electro- optic material layer is difficult. The electro-optic material may be an electro-optic polymer, or ceramic such as lithium niobate or PLZT. It is desirable that the material have a large change in index of refraction for a given E-field strength across it.

The first step in a method for fabricating an optical fiber interface and interface/modulator as illustrated in FIGs. 6 and 7 and described above is to form an opening in the fiber by removing a section of the cladding down to the core.

The cladding may be removed by mechanically grinding, ion milling, or chemical etching. The surface of the core may also be polished.

The next step is to deposit a layer of electro-optic material onto at least a portion of the surface of the core. The electro-optic material may be deposited on the core using sol-gel processing. The material may also be deposited by sputtering, Langmuir-Blodgett film coating techniques, or other deposition methods. The next step is to connect conductors to the electro-optic material. The conductive material may be deposited by physical vapor deposition, such as sputtering, or other deposition techniques, and then etched as desired to delineate electrode patterns. Alternatively, the conductors may be mechanically connected to the electro-optic material layer and held there by pressure, such as by a clamp device.

It may also be necessary to pole the electro-optic material to align the molecular structure in the appropriate orientation.

Alternatively, the first step in a method for fabricating an optical fiber interface and interface/modulator as shown in FIG. 8, is to form an opening in the fiber by removing a section of the cladding down to the core. The first electrode may be deposited on the core, for example by sputtering, and patterned as necessary. The electro-optic material is then deposited, such as by sputtering, and patterned as necessary. Then the second electrode is similarly deposited over the electro-optic material layer and patterned as necessary.

As illustrated in FIGs. 9 A, an alternative embodiment of an interface/modulator apparatus, indicated generally at 80, is shown on an optical fiber 12 and takes advantage of the principle of attenuated total reflection to modulate the amplitude of the optical signal. When one side of an optical material, e.g. a glass prism, is coated with a thin layer of silver or other suitable metal and a thin coating of a dielectric is applied, a surface plasmon resonance may be established when light is incident on the silvered face. Surface plasmon resonance occurs when the energy of incident photons resonates with the electron gas of the metal and generates longitudinal oscillations known as plasmons. The photons are not reflected as they normally would be, and a sharp decrease in the reflected light intensity can be measured (i.e. the attenuated total reflection). The surface plasmon resonance condition is a function of the angle of incidence of the incoming light and of the index of refraction, or dielectric constant, of the thin dielectric layer. It is also a function of the metal and prism (or optical) materials and the frequency of the light used.

Similar to the embodiment described above, an opening 82 is formed in the optical fiber 12 which extends through the cladding 16 to the surface of the core 14. The opening 82 may be formed all around the circumference of the fiber 12 or core 14, as illustrated, or may be formed around only on a portion of the circumference of the fiber 12.

A first layer of conductive material 84 is disposed in the opening 82 and on the core 14, defining a first electrode. The first electrode 84 is preferably a thin silver layer. An electro-optic material layer 86 is disposed on at least a portion the first layer of conductive material 84. The electro-optic material has a dielectric constant that changes in presence of an electric field. The electro-optic material layer does not actually interface with the light, so it does not necessarily need to be transparent. Thus, any material that changes its electric constant in the presence of an electric field can be used. A second layer of conductive material 88 is disposed on at least a portion of the electro-optic material layer 86, defining a second electrode.

The first and second electrodes 84 and 88 apply an electric field which changes the dielectric constant of the electro-optic material layer 86. The change in the dielectric constant changes the angle at which attenuated total reflection occurs and modulates the amplitude of the optical signal. The modulated signal is developed by selectively applying a voltage or electric field to the material layer and may be monitored. The method of fabricating the optical fiber interface and modulator of the above embodiment is similar to that described above. An opening is first formed by removing a section of the cladding to expose the core. The first electrode may be deposited on the core, for example by sputtering, and patterned as necessary. The electro-optic material is then deposited, such as by sputtering, and patterned as necessary. Then the second electrode is similarly deposited over the electro- optic material layer and patterned as necessary. Therefore, the material layer interfaces with the optical fiber and modulates the optical signal.

Referring to FIGs. 9B and 9C, an opening 82 is formed in the optical fiber 12 which extends through the cladding 16 to the surface of the core 14. A metal layer 89 is disposed in the opening 82 and on the core 14. The metal layer 89 is not an electrode. Surface plasmon resonance occurs at the metal layer. An electro-optic material layer 86 is disposed on the metal layer 89 and a portion of the surface of the core 14. A pair of conductors 84 and 88 are connected to the electro-optic material layer 86 for activating the material. The pair of conductors 84 and 88 may be placed on opposing ends of the electro-optic material layer 86 and on the surface of the core 14, as shown in FIG. 9C, or at opposing ends of the material layer 86 and on the material layer, as shown in FIG. 9B.

The method of fabricating the optical fiber interface and modulator shown in FIGs. 9B and 9C is similar to that described above. An opening is first formed by removing a section of the cladding to expose the core. The metal layer may be deposited on the core, for example by sputtering, and patterned as necessary. The electro-optic material is then deposited, such as by sputtering, and patterned as necessary. The conductive material may be deposited by physical vapor deposition, such as sputtering, or other deposition techniques, and then etched as desired to delineate electrode patterns. Alternatively, the conductors may be mechanically connected to the electro-optic material layer and held there by pressure, such as by a clamp device.

Referring again to FIGS. 5-7, an alternative embodiment of an interface/modulator apparatus is structurally similar to the embodiments shown, but the index of refraction of the electro-optic material changes to be larger than that of core material, rather than within the range defined by the core and cladding. As described above, if the index of refraction of the cladding material is larger than that of the core material then light does not undergo total internal reflection but instead experiences both reflection off the interface and transmission through the interface. This reflectance and transmittance is a complex function of the permittivities and permeabilities of the core and cladding material, the angle of incidence of the light rays, and the polarization components of the light. By changing the index of refraction of the electro-optic material layer to be greater than the index of refraction of the core material, the reflectance and transmittance will be changed enough to measure the amount of light that is reflected by the cladding at that interface. Therefore, the optical signal is amplitude modulated. The electro-optic material may be a polymer, lithium niobate and other ceramics. The method for fabricating the above embodiment of the interface/modulator is similar to that described above. As illustrated in FIG. 10, an alternative embodiment of an interface/modulator apparatus, indicated generally at 90, is shown on an optical fiber 12. When light is traveling through a medium whose index of refraction is made to change, the light experiences a change in path length. The change can be measured as a change in the phase of the outgoing light.

An opening 92 is formed in the optical fiber 12 which extends through the cladding 16 and into the core 14. Unlike the above embodiments, the opening extends into the core, rather than just to the surface of the core. The opening 92 may be formed all around the circumference of the fiber 12 or core 14, as illustrated, or may be formed around only a portion of the circumference of the fiber 12.

An electro-optic material layer 94 is disposed in the opening 92 and into the core 14. The electro-optic material has an index of refraction that changes in presence of an electric field. A pair of conductors 96 and 98 are connected to the electro-optic material layer 94 for activating the material and changing its index of refraction. The conductors 96 and 98 may be disposed at opposing ends of the material layer 94, or the material layer 94 may be sandwiched between a first conductor layer 96 disposed on the core and a second conductor layer 98 disposed over the material layer. The electro-optic material layer 94 directly interferes with light conduction in the fiber. The material layer 94 extends into the core with enough depth to represent a significant amount of the light conduction. The material layer 94 changes the index of refraction of the core which changes the path length of the optical signal. Therefore, the material layer interfaces with the optical fiber and modulates the optical signal. The modulated optical signal illustratively may be monitored by causing the modulated signal to interfere with light in another fiber that has followed the same path but which does not undergo the change in path length. A shift in interference patterns occurs.

The method of fabricating the optical fiber interface and modulator of the present invention is similar to that described above. An opening is first formed which extends through the cladding and into the core. The cladding and core may be removed by mechanically grinding, ion milling, or chemical etching. The surface of the core may also be polished. The next step is to deposit a layer of electro-optic material into the core. The next step is to connect conductors to the electro-optic material. The conductive material may be deposited by physical vapor deposition, or other deposition process, and then etched as desired to delineate electrode patterns. Alternatively, the conductors may be mechanically connected to the electro-optic material layer and held there by pressure, such as by a clamp device.

With this embodiment, the requirements for the appropriate index of refraction are less important. There will be significant insertion loss and fiber fragility. Therefore, materials that will best match the fiber mechanically, such as ceramics, are more desirable.

Although the above embodiments have been described and illustrated as having an electro-optical material layer, it is of course understood that the electro- optical material may take other forms. For example, the material layer may be a material tube disposed about the optical fiber. As another example, the material layer may be a bulk material disposed on the optical fiber.

Referring to FIG. 11, a fixture 100 is shown for clamping the optical fiber 12 around the interface/modulator apparatus. The fixture 100 may be used to clamp the optical fiber during processing and/or to support other devices such as a chip based sensor 102 being interfaced with the fiber. The fixture 100 has a pair of arms 104 and 106 attached to the fiber. An opening is formed in each arm in which the fiber is disposed. The arms 104 and 106 are separated by a space 108 which defines a window in which the optical fiber interface/modulator device is located. A support member 109 may be located adjacent the optical fiber and extend between the arms 104 and 106 for supporting the optical fiber. The fixture also has a mounting plate 110 attached to both arms and upon which the chip based sensor 102 is disposed. The sensor and interface/modulator device may be coated (not shown) for protection.

The various embodiments of the interface/modulator apparatus and system of the present invention described above represent significant advantages over prior art interfaces or modulators. The above apparati are capable of interfacing with an optical fiber and modulating an optical signal therein without breaking the optical fiber. In addition, the interface/modulator apparatus of the present invention are small enough to be integrated on the optical fiber and driven by chip- based sensors.

It is to be understood that the described embodiments of the invention are illustrative only, and that modifications thereof may occur to those skilled in the art. For example, the active material layer may be a tube of active material. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed, but is to be limited only as defined by the appended claims herein.

Claims

CLAIMSWhat is claimed is:

1. An optical fiber interface/modulator apparatus for interfacing with an optical fiber data communication line without breaking the fiber and for modulating an optical signal in the optical fiber, the apparatus comprising: a Bragg grating formed in a core of the optical fiber, the grating having a spatial period defining a Bragg wavelength for selectively reflecting modes of the optical signal having the Bragg wavelength to develop a reflected optical signal at a given wavelength; and an active material layer disposed around the optical fiber at the

Bragg grating location and responsive to means for activating the material layer for physically straining the fiber, to thereby vary the refractive index and length of the optical fiber, to thereby alter the grating period and the Bragg wavelength, to thereby modulate the wavelength of the reflected optical signal.

2. The apparatus of claim 1, further comprising: monitoring means for optically monitoring changes in the Bragg wavelength by measuring the wavelength or wavelength shift of the reflected signal.

3. The apparatus of claim 2, wherein the monitoring means is a slope filter to detect the wavelength shift.

4. The apparatus of claim 3, wherein the slope filter is a high resolution monochromator.

5. The apparatus of claim 2, wherein the monitoring means is a diffraction grating projecting onto a linear photodiode array.

6. The apparatus of claim 1 , wherein the active material layer is a piezoelectric film.

7. The apparatus of claim 1 , wherein the active material layer is a magnetostrictive film.

8. The apparatus of claim 1 , wherein the active material layer is an electrostrictive film.

9. The apparatus of claim 1 , wherein the active material layer is a shape memory alloy film.

10. The apparatus of claim 1 , wherein the active material layer is an active material tube.

11. The apparatus of claim 1 , wherein the active material layer is a bulk material.

12. The apparatus of claim 1, further comprising: a first layer of conductive material disposed on the optical fiber forming a first electrode; wherein the active material layer is disposed on at least a portion of the first layer; and a second layer of conductive material disposed on at least a portion of the active material layer forming a second electrode.

13. The apparatus of claim 12, wherein either or both of the first or second layer is patterned in a desired electrode pattern.

14. The apparatus of claim 1, further comprising multiple active material layers to increase the physical strain.

15. The apparatus of claim 1, further comprising opposing sections of active material layers acting synergistically in a push/pull fashion to increase the physical strain.

16. The apparatus of claim 1, further comprising multiple gratings each shifted in grating wavelength within the bandwidth of the optical signal and multiple active material layers each disposed about one of the multiple gratings to multiplex multiple modulators onto a single optical fiber.

17. The apparatus of claim 1 , wherein the grating is a first grating defining a sensor grating; and further comprising: a second grating defining a reference grating; and a piezoelectric transducer for continuously tuning the reference grating and sweeping at twice the maximum sensor bandwidth desired such that when the sensor and reference gratings are tuned to the same wavelength a strong signal is reflected from the reference grating to identify the sensor grating.

18. The apparatus of claim 1, further comprising a chip-based sensor electrically coupled to the active material layer and adapted for physically coupling to the fiber optic.

19. The apparatus of claim 1, further comprising a fixture adapted for clamping to the optical fiber and having a pair of arms for attaching to the optical fiber, the arms separated by a space defining a window in which the grating and acousto-optic material are located, and having a mounting plate attached to the arms.

20. A method for fabricating an optical fiber interface comprising the steps of: (a) providing an optical fiber having an inner core and an exterior cladding surrounding the core; (b) depositing a layer of conductive material onto the optical fiber, defining a first electrode;

(c) depositing a layer of acousto-optic material onto at least a portion of the first electrode; and (d) depositing a layer of conductive material onto at least a portion of the layer of acousto-optic material, defining a second electrode.

21. The method of claim 20, wherein step (a) further comprises providing an optical fiber with a Bragg grating formed in the core.

22. The method of claim 20, wherein step (a) further comprises providing an optical fiber with an exposes section exposing the cladding; and wherein step (b) further comprises depositing a layer of conductive material onto the cladding of of the optical fiber at the exposed section.

23. The method of claim 20, wherein step (a) further comprises providing an optical fiber with a protective jacket surrounding the cladding; and wherein step (b) further comprises depositing a layer of conductive material onto the jacket of the optical fiber.

24. The method of claim 20, wherein step (b) further comprises (bl) patterning the first electrode by removing any unwanted portion of the conductive material, and (b2) masking a segment of the conductive material to provide a location for future electrical connection to the first electrode.

25. The method of claim 20, wherein step (c) further comprises depositing a layer of active material using physical vapor deposition, sol-gel deposition, chemical vapor deposition, or direct mechanical disposition of bulk active material on the fiber.

26. The method of claim 20, wherein step (c) further comprises (cl) annealing the active material.

27. The method of claim 20, wherein step (d) further comprises (dl) patterning the second electrode by removing any unwanted portion of the conductive material.

28. The method of claim 20, wherein steps (b) and (d) further comprise physical vapor deposition of the conductive material.

29. The method of claim 20, further comprising the step of (e) poling the active material by applying an electrostatic field across the acousto-optic material.

30. The method of claim 20, further comprising the step of (e) jacketing the exposed section to protect it.

31. An optical fiber interface/modulator apparatus for interfacing with an optical fiber data communication line and modulating an optical signal in the optical fiber, the apparatus comprising: an optical fiber having an inner core and an exterior cladding surrounding the core, the core and cladding each having an index of refraction, the index of refraction of the cladding being less than the index of refraction of the core; an opening formed in the cladding and extending through the cladding to the core; an electro-optic material layer disposed in the opening defining a core/material interface, the material having an index of refraction that changes in the presence of an electric field; and a pair of conductors connected to the electro-optic material layer for activating the material and changing its index of refraction, to thereby change the amount of attenuation of the optical signal by changing the reflectance and transmittance at the core/material interface and modulating the amplitude of the optical signal.

32. The apparatus of claim 31 , wherein the electro-optic material layer and at least one of the conductors are disposed in the opening and on the core.

33. The apparatus of claim 31 , wherein the electro-optic material layer is disposed on the core, and wherein at least one of the conductors is disposed on the material layer.

34. The apparatus of claim 31 , further comprising: a first layer of transparent conductive material disposed in the opening and on the core, defining a first electrode; wherein the electro-optic material layer is disposed on at least a portion the first layer of transparent conductive material; and a second layer of conductive material disposed on at least a portion of the electro-optic material layer, defining a second electrode.

35. The apparatus of claim 34, wherein either or both of the first or second conductive layers is patterned in a desired electrode pattern.

36. The apparatus of claim 31, wherein the electro-optic material layer has an index of refraction that changes within a range defined at an upper limit by the index of refraction of the core and at a lower limit by the index of refraction of the cladding so that the index of refraction of the material layer is greater than that of the cladding, but less than that of the core, and the optical signal is amplitude modulated by changing the amount of the optical signal undergoing attenuation by changing the reflectance and transmittance at the interface.

37. The apparatus of claim 31 , wherein the electro-optic material layer has an index of refraction that changes to be greater than the index of refraction of the core, and the optical signal is amplitude modulated by changing the amount of the optical signal reflected and transmitted by the material layer at an interface between the core and the material layer.

38. The apparatus of claim 31 , wherein the electro-optic material layer is a polymer film.

39. The apparatus of claim 31 , wherein the electro-optic material layer is a ceramic film.

40. The apparatus of claim 31 , wherein the electro-optic material layer is lithium niobate.

41. The apparatus of claim 31 , wherein the electro-optic material layer is PLZT.

42. The apparatus of claim 31 , further comprising a chip-based sensor electrically coupled to the electro-optic material layer and adapted for physically coupling to the fiber optic.

43. The apparatus of claim 41 , further comprising a fixture adapted for clamping to the optical fiber and having a pair of arms for attaching to the optical fiber, the arms separated by a space defining a window in which the opening and electro-optic material are located, and having a mounting plate attached to the arms.

44. A method for fabricating an optical fiber interface comprising the steps of: (a) providing an optical fiber line having an inner core and an exterior cladding surrounding the core;

(b) removing a section of the cladding down to the core to form an opening in the cladding;

(c) depositing a layer of electro-optic material onto at least a portion of the core;

(d) connecting electrodes to the layer of electro-optic material.

45. The method of claim 44, wherein step (d) includes mechanically connecting the electrodes to the layer of electro-optic material.

46. The method of claim 44, wherein step (d) includes physical vapor deposition of a conductive material onto the layer of electro-optic material or onto the core.

47. The method of claim 46, wherein step (d) further includes patterning the conductive material.

48. The method of claim 44, further comprising the step of (e) jacketing the opening to protect the optical fiber.

49. An optical fiber interface/modulator apparatus for interfacing with an optical fiber data communication line and for modulating an optical signal in the optical fiber, the apparatus comprising: an optical fiber having an inner core and an exterior cladding surrounding the core, the core and cladding each having an index of refraction, the index of refraction of the cladding being less than the index of refraction of the core; an opening formed in the cladding and extending through the cladding to the core; a first layer of conductive material disposed in the opening and on the core, defining a first electrode; an electro-optic material layer disposed on at least a portion of the first layer of conductive material and having a dielectric constant that changes in presence of an electric field; and a second layer of conductive material disposed on at least a portion of the electro-optic material layer, defining a second electrode, the first and second electrodes applying an electric field which changes the dielectric constant of the electro-optic material layer, to thereby change the angle at which attenuated total reflection occurs to thereby modulate the amplitude of the optical signal.

50. The apparatus of claim 49, wherein the electro-optic material layer has an index of refraction that changes within a range changing the level of attenuated total reflection, causing the optical signal to be amplitude modulated.

51. The apparatus of claim 49, wherein either or both of the first or second conductive layers is patterned in a desired electrode pattern.

52. The apparatus of claim 49, further comprising a chip-based sensor electrically coupled to the electro-optic material layer and adapted for physically coupling to the fiber optic.

53. The apparatus of claim 49, further comprising a fixture adapted for clamping to the optical fiber and having a pair of arms for attaching to the optical fiber, the arms separated by a space defining a window in which the opening and electro-optic material are located, and having a mounting plate attached to the arms.

54. An optical fiber interface/modulator apparatus for interfacing with an optical fiber data communication line and modulating an optical signal in the optical fiber, the apparatus comprising: an optical fiber having an inner core and an exterior cladding surrounding the core, the core and cladding each having an index of refraction, the index of refraction of the cladding being less than the index of refraction of the core; an opening formed in the cladding and extending through the cladding to the core; an electro-optic material layer disposed in the opening and having a dielectric constant that changes in the presence of an electric field; and a pair of conductors connected to the electro-optic material layer for activating the material and changing its dielectric constant, to thereby change the amount of attenuation of the optical signal by changing the angle at which attentuated total reflection occurs and to thereby modulate the amplitude of the optical signal.

55. The apparatus of claim 54, wherein the electro-optic material layer and at least one of the conductors are disposed in the opening and on the core.

56. The apparatus of claim 54, wherein the electro-optic material layer is disposed on the core, and wherein at least one of the conductors is disposed on the material layer.

57. The apparatus of claim 54, wherein a metal layer is disposed on the core between a portion of the electro-optic material layer and the core.

58. The apparatus of claim 54, further comprising: a first layer of conductive material disposed in the opening and on the core, defining a first electrode; wherein the electro-optic material layer is disposed on at least a portion the first layer of conductive material; and a second layer of conductive material disposed on at least a portion of the electro-optic material layer, defining a second electrode.

59. The apparatus of claim 54, wherein either or both of the first or second conductive layers is patterned in a desired electrode pattern.

60. An optical fiber interface/modulator apparatus for interfacing with an optical fiber data communication line and for modulating an optical signal in the optical fiber, the apparatus comprising: an optical fiber having an inner core and an exterior cladding surrounding the core, the core and cladding each having an index of refraction; an opening formed in the cladding and extending through the cladding and into at least a portion of the core; an electro-optic material layer disposed on at least a portion of the core and having an index of refraction that changes in the presence of an electric field; and a pair of conductors connected to the electro-optic material layer for activating the material and changing its index of refraction, thereby changing the index of refraction of the core, and thus changing the path length of the optical signal, thereby modulating the phase of the optical signal.

61. The apparatus of claim 60, further comprising: monitoring means for optically monitoring changes in the interference pattern by interfering the optical signal with light from another fiber that has followed the same path but which has not undergone a change in path length.

62. The apparatus of claim 60, wherein the electro-optic material layer and at least one of the conductors are disposed in the opening and on the core.

63. The apparatus of claim 60, wherein the electro-optic material layer is disposed on the core, and wherein at least one of the conductors is disposed on the material layer.

64. The apparatus of claim 60, further comprising: a first layer of conductive material disposed in the opening and on the core, defining a first electrode; wherein the electro-optic material layer is disposed on at least a portion the first layer of conductive material; and a second layer of conductive material disposed on at least a portion of the electro-optic material layer, defining a second electrode.

65. The apparatus of claim 64, wherein either or both of the first or second conductive layers is patterned in a desired electrode pattern.

66. The apparatus of claim 64, further comprising a chip-based sensor electrically coupled to the electro-optic material layer and adapted for physically coupling to the fiber optic.

67. The apparatus of claim 64, further comprising a fixture adapted for clamping to the optical fiber and having a pair of arms for attaching to the optical fiber, the arms separated by a space defining a window in which the opening and electro-optic material are located, and having a mounting plate attached to the arms.