JPH02217807A - Electromagnetic radiation transmission method and apparatus - Google Patents

Abstract

PURPOSE: To make an optical fiber usable as an optical demodulator capable of transducing output to an electrical analog signal by making electromagnet radiations incident on the inside of the optical fiber produced by etching a fiber consisting of the core material of the optical fiber and using the optical fiber as an energy sensor. CONSTITUTION: The electromagnet radiations are transmitted by using the etched optical fiber having a mode of low order. The section 3-3 of the optical fiber having a large diameter is a core material having a diameter F. The thin fiber having the diameter G reduced as shown by the etched section 4-4 is formed. The etched single mode fiber is used as the energy sensor. The optical fiber energy sensor operated by elongating or compressing the etched single mode fiber in a longitudinal direction renders the higher modulation to the signal energy of a given quantity and exhibits high sensitivity. As a result, the optical demodulator required by an electronic demodulator is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for transmitting electromagnetic radiation using etched optical fibers having low topographical dispersion.

For example, prior art techniques in either phase modulation or frequency modulation of light passing through an optical fiber are used to mechanically or acoustically excite the fiber with signals to be imposed on the light propagating through the optical fiber. The acousto-optic effect was utilized in this respect.

This mechanical or acoustic excitation causes a change in the optical index of the fiber's core. As a result, the optical distance of light traveling through the fiber changes.

This light is therefore modulated in phase and frequency by the signal. In glass fibers, the change in optical index is extremely small for a given mechanical or acoustic excitation energy. To obtain sufficient modulation, this means that the high level signal energy requires either a long interaction length, which is the length of the fiber that must be acoustically excited at the point where the modulation occurs. It's about that. The sensitivity of an optical fiber to direct acoustic modulation is J, ^8uc
Applied htics by aro, Vol.
18, Nc6.

It is explained in the March 15, 1979 issue.

The present invention constructs a single mode fiber with a thin cladding for use in a sensor where signal energy stretches the single mode fiber to cause phase modulation. The present invention also constructs lower order mode optical fibers from larger diameter optical fibers. The present invention accomplishes these two optical fibers by etching currently available optical fibers.

S, to 5heen and J, H, Co1e to 0p
ticsLetters, Vat, 4. Nn10
．． October 1979 issue [^coustic 5ens
ity of SinglOHodeOpti
In the prior art, a single mode fiber is etched to reduce its optical conductivity without considering changes in its increasing or decreasing sound W sensitivity or mode structure, as explained in Cal Power [1 ividcrs J. Such an effect, reduced photoconductivity, is considered undesirable for purposes of the present invention, and the present invention specifically provides an apparatus for minimizing it.

The present invention can be used in a distributed wavelength reflector of length tIIJ to reflect light within a single mode optical fiber. Such a reflex is rHethod An
d Apparatus For Radiant E
ner(II/Modulation In 0pti
U.S. Patent Application No. 0 entitled cal FibresJ
No. 88579 and App by K. 0.1lill et al.
Lied Physics 1etters, 32
(10).

rPhotoO8ensrtrVrtV 1n01)ti in the May 15, 1978 issue
cal FibreWaVOQIJrdeS :＾1)
Dlication tORerlecmouth On File
terFabrication J.

The present invention can also be used in reflectors that cause reflections within optical fibers in devices similar to Fabry-Bello interferometers. Such devices are P,G.

AI)I)t by C1e1o September 1, 1979 issue
iedOptics, Vol, 18, Pkll
7 “Fibre 0ptic Hydrophone
: Improved 5train conrigu
ramouth0nand EnVirOnll(ntal N
otse protect+on".

A novel detection device is provided that uses this reflector device as one of its multiple components.

As an example of an application of the present invention, an etched single mode fiber is used as an energy sensor. This energy sensor works as follows.

Signal energy to be sensed or detected is generated and stretches the etched single mode fiber. Etched single mode fiber is a single mode lath clad fiber whose cladding thickness has been reduced to a certain thickness to reduce its strength. When it is necessary to preserve the photoconductive properties of an etched single-mode fiber, the present invention provides a method for removing the portion of the glass cladding that has an optical index greater than that of the material of the core of the single-mode fiber. Assume that the plastic material is replaced with a plastic material that is also lower and whose modulus is lower than that of the glass crund being replaced.

Such etched single mode fibers are weaker and therefore more sensitive to stretching and compression. For a given signal energy of n, a single mode fiber will elongate by a larger amount after it is etched.

The prior art teaches that increasing the length of a single mode fiber changes the optical distance in the lff1 radiation propagating through its core.

The prior art further teaches that this change in optical distance increases as the amount that the single mode fiber is stretched increases. Prior art uses this change in optical distance to modulate electromagnetic radiation propagating through the core of the fiber. The prior art also teaches that as the magnitude of the change in optical distance increases, the amount of modulation increases. Therefore, an optical fiber energy sensor that consists of an etched single-mode fiber and operates by longitudinally stretching or compressing this etched single-mode fiber will generate a larger energy for a given amount of signal energy. modulation resulting in higher sensitivity.

The present invention also uses this etching process to produce optical fibers with reduced morphology dispersion from larger diameter optical fibers.

The present invention also utilizes an etched optical fiber.
The manufacturing process for constructing the A-position is given. This process allows the mold to be constructed of material that is not affected by the etching process. These molds are used to hold the fibers to be etched in the same alignment as they are in the actual device. Various means for allowing the mold to be removed if it is not present in the actual device are also detailed.

An example of an application using the present invention is to make the energy sensor more effective by actually optically sensing the output of the energy sensor, thus substantially reducing the previously extremely large bandwidth required of the electronic demodulator. An optical demodulator is provided. The provided optical demodulator also allows for multiplexing several energy sensors on the same optical fiber, thus substantially lowering the cost of multiple sensor devices such as hydrophone arrays.

Is the optical demodulator optical? Each energy sensor is disposed between a pair of length III Bragg reflector members configured inside the fiber.

Each pair of reflectors arranged constitutes a 7 Abrie-Bello interferometer that only contains resonances in that portion of the electromagnetic spectrum in which the Bragg reflector operates. Since each energy sensor is placed between a pair of reflectors, the resulting change in optical distance of the sensor spectrally shifts the resonance of the Fapley-Bello interference 4 when signal energy is detected. The device then converts this spectral transition into a second
It is partially demodulated using a 77 Priebello interferometer. This analytical interferometer resonance has a spectral separation that is proportional to the spectral separation of the interferometer containing the energy sensor so as to provide amplification of the spectral transition. The output of the combined energy sensor interferometer and analytical interferometer is spectrally shifted more than the original spectral shift by an amplification constant times the equation given in the detailed description of the invention. The device also allows the use of one or more analytical interferometers, each performing its own amplification. The resulting amplification can be made to provide outputs corresponding to eight distinct digits, each of which represents the original spectral transition, thus reducing the bandwidth of the electronic detector and time demodulator.

This optical detector finally multiplies several energy sensors into the same fiber by making each anti-Q4 reflector pair corresponding to each sensor have a different reflection band than every other reflector pair. I'm considering doing a plex.

This device uses a wavelength-scanning laser whose output scans the resonance of one reflector pair at a time.

The sensitive optical fiber of the present invention can be used in energy sensors and optical demodulation systems that can convert the output of the energy sensors into electrical analog signals. First, I will explain the energy sensor, then the light ma.
Let's explain the device.

Is the current technology of optical fiber energy sensors single-mode optical fiber? When the ipa is radially compressed or stretched or longitudinally compressed,
This teaches that the optical distance of electromagnetic radiation propagating through the core of a single mode optical fiber changes. This technique further teaches that as the single mode fiber is stretched or shortened, the change in optical distance also increases. Current technology uses this change in optical distance to cause phase modulation of light propagating through the core. The length of the optical fiber where modulation occurs is called the interaction length.

The present invention provides an etched single mode fiber, energy sensor, for use in optical fibers. A single mode fiber is a fiber configured to propagate only the lowest order modes. This lowest order mode in a single mode fiber configuration is doubly degenerate. In these cases, the lowest order modes contain two states of propagation that are distinguished by the fact that their polarizations are mutually perpendicular.

Etched single-mode fibers are characterized in that their cladding thickness is etched by a chemical reaction (e.g., etching in a solution of hydrofluoric acid or ammonium fluoride) or by ion etching. It is defined as a single mode optical fiber thinly combed by milling.

FIG. 1 is an enlarged cross-sectional view of the fiber before etching. FIG. 2 is an enlarged cross-sectional view of the fiber after etching. FIG. 1 illustrates that the glass crund, generally designated 2-1, has a thickness designated K. In FIG. In FIG. 2, the cladding 2-2 is shown to have a reduced thickness indicated by R. In both FIGS. 1 and 2, the cores designated 1-1 and 1-2 have a diameter .largecircle. which remains unchanged due to the nature of the etching process which occurs only at the exposed surface of the fiber.

The usefulness of such fibers will first be explained in terms of sensitivity, and then the ease of manufacture using etched single mode fiber will be explained. For a given maximum signal energy E to be detected, the fiber of FIG. 1 of length L and total area 81 will extend by an amount ΔL.

Here, yo is the elastic modulus of the fiber material and may be assumed to be constant and equal to the elastic modulus of fused silica for purposes of explanation. Substituting the thickness of the tardding, calculated as above, however, into Equation (I) gives the elongated 5 ΔL2, and the etched fiber is Follow.

Here, 82 is the cross-sectional area of the etched fiber. Since S is larger than S2, from equations (I) and (I), ΔL2>ΔL1. Current technology in optical fiber sensing therefore suggests that for a given amount of signal energy, an etched single-mode fiber will have a larger change in optical distance than a regular single-mode fiber, thus propagating through the core. This means that a larger amount of phase modulation of the light can be obtained.

Another utility can be appreciated in that fibers with very small overall diameters are difficult to construct using current methods and, even when constructed, are difficult to process. The teachings of the present invention allow devices that may use thin clad combed fibers to be constructed with readily available larger diameter fibers.

Once such a device has been assembled to a point where the larger fiber is in place, the fiber can then be etched, thereby precluding further processing of thin fibers, i.e. fibers with thin cladding. Indulge. A more detailed explanation of this wrestling will follow later.

Another utility is recognized when it becomes necessary to construct fibers with small core diameters, and the present invention allows such fibers to be constructed from larger diameter fibers. FIG. 3 shows a cross-section, 3-3, of a large diameter optical fiber, which is a core material of diameter F (eg, fused silica). The larger diameter fiber is etched, thus creating a thinner fiber having a reduced diameter G, the cross section of which is shown at 4--4 in FIG. The invention further provides a fiber having a diameter G of the Genera IElec
RTV670 manufactured by tric corp
It is further provided that it can then be coated with a material 5-4 having a lower refractive index than the fiber itself, such as silicone rubber, thus creating an optical fiber with a small core diameter. Such small core diameter fibers are effective in providing a low number of guided optical modes.

As an example of the etching process, in FIG.
The etched core 4-4 of FIG. 4 may have a diameter in the range of 50 .mu.m to 5 .mu.m.

An example of an application using the present invention is given in the particular underwater acoustic energy sensor illustrated in FIGS. 5 and 6 and, in part, in FIG. FIG. 5 is an end view of the sensor illustrating its cylindrical shape. FIG. 6 is a cross-sectional view of the sensor. The sensor consists of a rigid cylindrical framework, shown at 6 in FIG. 6, probably made of aluminum. The outer surface of this internally shaped skeleton is a plane H
and the plane J, the diameter becomes smaller. Surrounding this cylindrical framework is a membrane of flexible material, generally designated 7, within which a single mode optical fiber, generally designated 8, is radially wound. Such a flexible material may be, for example, silicone rubber or PVC. This sleeve is joined as at 13 to the larger diameter end 13' of the cylindrical framework, or tightened as at 14, or is tightened as at 14, so that the diameter of the flexible mya and the rigid form is reduced. Drill a hole 1if9 between the rigid cylindrical frame and the bolt. The wall of this rigid cylindrical skeleton of reduced diameter is provided with an equalization hole 10 extending from the inner wall of the cylindrical skeleton to the space between the flexible membrane and the rigid skeleton. On the inner wall of the cylindrical framework there is a protrusion, designated 11 in FIG. Similarly, inside the cylindrical framework there is a flexible bladder 1 which serves as a ballast supply.
2 extends and forms a tank 16, which communicates with the space 9 by an equalization hole 1o.

Spaces 16 and 9 are filled with air, helium, or another viscous flexible material, such as silicone oil. An end cap 17 is also provided which creates an additional space 16', shown in FIG. 6, and is provided with a hole 15 extending through the thickness of each end cap. Figure 5, Figure 6,
The Hydro 7-on shown in FIG. 7 operates as follows.

The Hydro 7-on is immersed in a fluid containing the sound wave to be measured. At any particular depth, according to the invention, a portion of this fluid is admitted through the hole 15 into the Hydro7on and then:
As shown by the dashed line indicated at 12', the protrusion 1
By stretching the bladder 12 around J3 and thus compressing the second viscous flexible material in spaces 16 and 9, the static pressure in spaces 9 and 16 J3 is reduced to the static pressure in the fluid outside of Hydro 7. be equal to When the pressure in spaces 16 and 9 equals the external pressure plus the additional pressure created in stretching bladder 12, fluid ceases to flow through hole 15. Hole 15 and equalization hole 1
0 or one of them is small enough to slow the rate of equalization to a much longer time period than the time period between the sound pressures to be measured.

The acoustic signal to be measured or sensed by the Hydro7On consists of alternating changes in ambient fluid pressure. Since these changes are not equalized by the bladder mechanism described above, they instead cause the flexible membrane 7 to expand and contract radially, thus longitudinally stretching and compressing the etched single mode fiber 8. or

The underwater acoustic sensors of FIGS. 5, 6, and 7 are used to sense underwater acoustic signals. In these applications that require being in motion, the use of a rigid cylindrical A reinforcing strand, for example fiber 8' in FIGS. 6 and 7, is provided parallel to the axis. Fibers 8' are bonded to the outside and/or inside surfaces of the flexible N membrane 7 and extend below each clamping ring 14 around the rigid cylinder 6. The clamping element is a rigid cylindrical part 13' to which the flexible membrane 7 is attached. Such reinforcing fiber 8' is evlar.

Namely, 1) Tire cord fiber manufactured by uPOnt;
Or it could be made of glass. Such reinforcing fibers 8' are arranged so as to increase the longitudinal strength of the flexible 1llllW7. Therefore, if the underwater acoustic sensor of FIGS. 5, 6, and 7 is accelerated in the axial direction of the rigid cylinder 6, the resulting deformation of the flexible membrane 7 will be It is made smaller by the reinforcing fiber 8' in FIG. Furthermore, this reinforcing fiber 8', when placed parallel to the axis of the rigid cylinder 6, does not substantially increase the resistance of the flexible membrane to radial contraction as would be caused by the acoustic signal to be sensed. Furthermore, the flexible thin film pawn can be varied as well as the density of the single mode fiber turns l1I8, which has the effect of shifting the underwater acoustic frequency response.

As an application example using the present invention, underwater acoustic sensors shown in FIGS. 8 and 9 are provided. FIG. 8 is an end view of an underwater acoustic sensor and FIG. 9 is a cross-sectional view of the sensor of FIG. This shows a thin film. The assembly also includes an inner cylinder 202 of a resilient, flexible material, such as silicone rubber, which is in contact with the inner wall of the flexible wJ membrane 7-9. reinforcing strands, e.g. fiber 20
1 is a flexible thin film [17-9] arranged parallel to the axis of the inner cylinder material 202 and brought into mechanical contact with the inner cylinder material 202 to increase the longitudinal strength of the inner cylinder without significantly changing its radial flexibility. . The reinforcing fiber 201 may be made of evlar or glass, may extend long beyond the end of the flexible material, and may be used to secure the sensor in place. Flexible inner circle 5202
may also be elongated to position or secure the sensor in position. The present invention also provides reinforcing fiber 2
01 is made of flexible thin 1g1 to increase its longitudinal strength.
This [! 7-9 is also provided for mechanical attachment to the outside.

Considering the longitudinal strength of the sensor also reduces the durability of the sensor during radial expansion and contraction caused by longitudinal acceleration of the sensor, but it also reduces the sensor's response to acoustic signals, i.e. Radial expansion and contraction do not decrease.

The underwater acoustic sensor of FIGS. 8 and 9 operates as follows. The sensor is immersed in a solution containing the acoustic signal. Sound W
1117- where the periodic changes in pressure appearing in the signal are flexible
Expand and deflate 9. ill[ll7-
9 expands or contracts, the etched single-mode optical fiber 8-9 is stretched or compressed, so that, as already explained, )? iba8
The electromagnetic radiation propagating within the -9 core is modulated.

Furthermore, since the inner cylinder is also radially flexible, this provides less resistance to the expansion and contraction of the flexible membrane. The sensors in FIGS. 8 and 9 are connected to a single mode fiber 8.
It is shown that it is advantageous to use a single mode fiber etched as -9.

Etched single mode fibers are useful in all energy sensors, where one signal energy is used to longitudinally stretch or compress the single mode fiber to cause a change in the optical distance of the optical fiber. Some energy sensors may use lower order mode optical fibers if the morphological dispersion of such fibers is low enough to maintain sufficient optical coherence over the interaction length. For these energy sensors, the present invention provides the thin fiber of FIG. It should be noted that any optical fiber can be etched to increase its sensitivity to longitudinal stretch or contraction, such as multimode step index or hierarchical index fibers.

When the glass cladding of a step index or hierarchical index fiber is etched away to reduce its conductivity for fff6fi radiation, the present invention provides a method for removing the resulting fiber as shown in Figure 2-2' of the drawings. J3 provides that the fiber core may be coated with a material having a lower optical index than the fiber core, such as RTV670 silicone rubber, to restore its ability to conduct magnetic radiation. Therefore, the present invention includes "etched single mode optical fiber" as well as "etched optical fiber," and throughout the detailed description and claims, it is understood that etched fiber will be used to ensure proper operation of the device. These terms can be interchanged whenever the etched optical fiber has a low enough morphological dispersion to retain sufficient coherence of the light and the intended use of the etched optical fiber is sensitivity to longitudinal stretch or contraction. This is true when the objective is to provide a low order mode fiber, ie a fiber with low morphology dispersion, or for both of these objectives at the same time.

As an application example of the present invention, an optical fiber energy sensor preferably using an etched A-mode fiber is manufactured by the following manufacturing method. First, a mold is made that holds the fibers to be etched into the same arrangement or configuration that is to be used in the particular sensor being manufactured. In the case of the Hydro7on of FIGS. 5, 6, and 7, the fibers are arranged in a helical configuration. The appropriate type for this Hydro7on is the 10th
It is a circle 1118 as shown in the figure, around which a spiral groove 19' is cut, into which the unetched optical fiber 20' is wound. If it is desired to remove the mold by etching, the mold material must be a substance that can be melted or dissolved into a liquid state at a temperature or with a solution that will not damage the fiber or flexible film material. There must be. Such material is beeswax. Furthermore, some mold materials can jeopardize even the etching of the fiber (simply rubbing the wax in the right places on the fiber, thus protecting the fiber from the etching agent); The mold of the material is first coated with a thin layer of protective material 21' in FIG. 11 by dipping or spraying the solution. Once this protective material 21' hardens, it does not affect the etching process. A suitable protective material is TVI) 0139 Low Andex Pla manufactured by 0DteleCO1.
stic Cladding Solution, Kaniy
nar i.e. Pennwalt Chemical
Vinylidene fluoride manufactured by CO0. If the fiber to be etched does not have sufficient glass cladding to conduct light, the invention provides that the protective material has a lower optical refractive index than the fiber core. ■yp
e 139 Low AndexPlastic
C1addino 5solution or Kynar
has a lower optical index than quartz glass.

If necessary, the present invention allows the fiber to be
It is also determined that the etched core is bonded to the mold at both ends, as shown at 2'. As the protective material already explained, a bonding agent is sufficient.

If it is necessary to protect sections of the fiber from etching agents, these sections should also be protected as shown in FIG.
As shown in 3', it may be covered with the protective material already described.

If a fiber optic energy sensor is to use an etched single mode fiber, an example application using the present invention will now include a fiber 20' in the appropriate position as illustrated in FIG. Type 18' with hydrofluoric acid or ammonium hydrogen fluoride! llj in a solution of either hydrofluoric acid or any other chemical that can dissolve or remove the glass cladding of the fiber. Typically, the etching solution is ultrasonically agitated, if necessary, to promote entrainment of the etching agent around all portions of the fiber that are to be etched.

At the end of the etching period (which can be determined empirically), the mold with the bonded etched fibers in place is removed from the solution, rinsed with water, dried and then exposed to a solution of dissolved or molten coating material. or sprayed with or otherwise coated with a solution of a substance that becomes a pliable 11 material when cured, dried, or cooled. Ultrasonic agitation of the solution is performed when necessary to promote coating liquid around all parts of the fiber. The invention also provides that the application of the coating material may be carried out in a vacuum for the purpose of coating uniformity and eliminating air pockets.

When using such a fiber that does not have a cladding thickness sufficient to conduct electromagnetic radiation into the core after etching, the present invention provides that the cladding has a lower index of refraction than the material of the core. stipulate that Such a solution may be the protective material mentioned above or General El.
Any silicone rubber such as RTV670 from Electric Company may be used. The viscosity of the coating solution can be varied as a means of controlling the thickness of the coating remaining on the mold upon removal from the solution. A lower viscosity of the coating solution provides a thinner coating. The mold, removed from the coating solution, is then rotated until the coating hardens to achieve a uniform coating where the grooves are. FIG. 12 shows the completed mold and fiber of FIG. 10 after the etching and immersion process. The etched fiber is designated at 20-E and the flexible thin film material is designated at 124.

After the coating in FIG. 12 has solidified, a hole is drilled extending through the coating and protector into the mold material. The location of such holes must be selected so that the material of the mold can be removed by melting or melting, yet does not expose the fibers in the coating to am. Such a hole 125 is shown in FIG.

The mold is shrunk and released from the flexible ngI and protective material, thus forming II in the plane marked P in FIG.
The mold may be made of a material such as Teflon that can be cooled with liquid nitrogen to facilitate removal of the mold through the much larger opening 126 in FIG. 12 formed by cutting out the I. In general, it would be nice if the mold collapsed to aid its removal. Figure 5, Figure 6,
In the hydrophone of FIG. 7 and FIG. 7, a suitable collapsible form is shown in FIG. 13 in end view.

FIG. 13 is an end view of cylinder 257. The removed portion of this cylinder, called the key, is indicated at 256. key 25
6 extends parallel to the axis of the cylinder and over the entire length of the cylinder. The arrows marked zZ illustrate the movement of the key to assist in its removal. By removing the key, circle n2
57 collapses radially so that it can be removed from the flexible thin film material after etching and immersion.

If it is desired to manufacture a fiber optic energy sensor that uses a flexible sleeve or shroud to provide the unetched optical fiber, the present invention can also eliminate the etching and cleaning steps from the manufacturing process described above. .

FIG. 14 shows an optical demodulator as an application example using the present invention. Referring to FIG. 14, reference numeral 24 designates an optical fiber onto which are mounted several pairs of distributed Bragg reflectors 25 of limited length. A distributed Bragg reflector of length υ1, as used in the present invention, partially reflects a specific wavelength band of electromagnetic radiation propagating in an optical fiber back to the source. The light that is spectrally outside of these particular wavelength bands is transmitted forward and passed through an optical fiber that receives little chromatic tube. Such a reflector causes a spatial periodic perturbation of the optical index of the cladding surrounding the core of the optical fiber so that the spatial periodicity exists in a direction parallel to the axis of the core and there is no interference of light in the optical fiber. The structure can be constructed by ensuring that the spatial period does not exceed the quality that maintains the property.

Spatial periodic perturbations can be achieved by partially removing the cladding from a length of the fiber and then orienting the fiber towards an optical grating so that the teeth of the grating are perpendicular to the axis of the core. I can wake you up.

The magnitude of the reflectance can be increased or decreased by removing more or less of the cladding and thus moving the optical grating closer or further away from the core. Disclosed in US Patent Application No. 088579@. Such a reflector was developed by Ifi I et al.
nsitivity in 0ptical fiber
rllaVeOllid(!S :^pplicati
on to ReflectionFilter F
f! bricatiOn J^pplicd Phys
icsLetters; #32 (10), 197
It can also be constructed using the method described in May 15, 2008, where it is shown that the reflected wavelength band occurs when:

λCH~2nd M (I[[) where λc
H is the center of the reflected wavelength band for a particular value of M, n is the effective optical index in the optical fiber core, d is the spatial period of the perturbation that creates the Bragg reflector, M is an integer greater than zero and reflects This is called the band order.

The width, Δλ, is the total spectral width of a particular reflection band measured at half the rest of the CM' reflection intensity that a particular Bragg reflector can have. This has been shown in the prior art to be the case.

Here 1 is the length of the length-limited Bragg reflector.

Referring again to FIG. 14, anti-Ql pair 25 has A,
B, C, . . . are attached. The reflectors in each pair are made to spatially reflect the same wavelength band and have the same transmission spectrum, for example by adjusting d and 1. However, each pair is again d and 1
is made to reflect a particular wavelength band that is spectrally different from any other pair of reflective wavelength bands by adjusting it according to Equation (III) and Equation (rV), so that in each reflector to be used A wavelength interval w that includes at least one of these specific wavelength bands only, 1. exists.

Each pair 25 constitutes a Fabry-Perot interferometer inside single mode fiber 24. This Fapley-Bello interferometer is sensitive only to [1tj4] spectrally within the reflection wavelength band of the distributed Bragg reflectors forming a particular pair.

FIG. 15 is an illustration of the transmission of a particular pair of reflectors. Referring to FIG. 15, the ordinate represents the transmission of electromagnetic radiation through a particular reflector pair and the abscissa represents the wavelength of ff1iff radiation propagating through fiber 24 and incident on the reflector pair. There is. ff1la radiation that is spectrally outside a particular pair of reflected wavelength bands is transmitted virtually unaffected. Such radiation is shown in FIG. 15 as area a.

)? The largest population of electromagnetic radiation propagating in the fiber and spectrally within the reflection band of a particular reflector pair is anti-I8.
The wavelength is transmitted forward through the pair of reflectors, where OPL is the optical distance between the reflectors and N is a positive integer.

The least amount of electromagnetic radiation, if any, is transmitted forward through the reflector pair.

As a result, spectrally periodic transmission occurs as shown in the region of FIG.

As taught in the field of interferometry, the spectral width of the transmission peak, shown at 300 in FIG. The spectral separation Δλ of the transmission peaks can be varied by changing the magnitude of the reflectance of the filter. This can be achieved as already explained.

The number of peaks 300 in the wavelength range of FIG. 15 is given as follows.

X ~ - (■) where 2 is the geometric length between the reflectors as measured along the axis of the single mode fiber, 1 is the distribution Bragg as measured along the axis of the fiber is the length of the reflector.

As the optical distance between a pair of two reflectors changes, the transmission peak within the wavelength range shown in FIG.
V) spectrally shifts within this region.

In this application using the present invention, a portion or all of the length of optical fiber 24 disposed between a pair of two reflectors may be used as an optical fiber energy sensor, e.g. Let it be the interaction length of the acoustic energy sensor in Figure 7. As previously discussed, such sensors operate by using the detected signal energy to lengthen or shorten the length of the optical fiber, thereby changing its optical distance. Therefore, for example, in reflector pair B, within which the interaction length of the optical fiber energy sensor detecting the signal is located, the transmission peak in the area of FIG. spectrally shifted as caused by the signal energy being applied.

Referring again to FIG. 14, a wavelength-scanning laser 26 is used to provide electromagnetic radiation, and the electromagnetic radiation
5 into a single mode fiber 24 in which a suitable condenser lens 27 is placed. The output of laser 26 is scanned or chirved over a particular wavelength range.

FIG. 16 is a graph of laser power suitable for the present invention.

The scanning range is Δλ, and is marked as such in FIG.

The scanning time interval is 6 pairs, also shown in FIG. 16, and the present invention selects the scanning range of the laser 26 to be the wavelength interval U, [, as already explained, so that each pair 25 in FIG. What is the reflector wavelength in Figure 15? ! 11! [b
is spectrally within the scanning range.

Referring again to FIG. 14, the assembly includes a beam splitter 127 for directing a portion of the laser output beam to a Fapley-Bello interferometer 28, hereinafter referred to as the "Reference Fapley-Bello" interferometer. Laser output wavelength λ
, where Q is a positive integer and is the dark optical distance of the reflectors making up the Fapley-Bello interferometer 28.

A reference Fapley-Bello interferometer 28 directs a portion of this radiation to the first
The four-source photodetector 29 generates the R74 reference signal. Photodetector 329 is a commercially available device, for example, Texas Instr.
#TIX manufactured by uments Inc.
L, the output of which is an electrical signal whose amplitude is a well-known function of the amplitude of the incident radiation. If the laser is scanning as in Figure 16, criterion 7? The transmitted output of the Fapley-Bello interferometer 28 is a series of time-separated peaks, each corresponding to a resonance of the reference Fapley-Bello interferometer 28.

Is this invention a standard)? The optical distance of the Pribero interferometer 28 is determined to determine the spatial period of the reflectors in each reflector pair 25 as the laser scanning range Δλ.

The odor is selected such that the transmission peak of the reference Fapley-Bello interferometer 28 occurs at a wavelength very close to the reflector wavelength band of each reflector of the pair 25.

Referring again to FIG. 14, the output end of the single mode fiber 24, the end opposite to where the laser beam is incident, is focused into the Fapley-Bello interferometer 30 as illustrated in FIG. is connected to a suitable focusing e[32. The output of this interferometer 30 is directed to a photodetector 31.

Interferometric prior art and reflector pairs 25
From the above explanation of the spectral transmission of , the following can be seen. If a scanning laser is injecting into the fiber at a particular time a particular wavelength λ of electromagnetic radiation falling within the wavelength range shown in Figure 15 of a particular pair of reflectors Δ, then this Since this 1m radiation then passes through a particular reflector pair A, through the remaining fiber, and through all other reflector pairs, the present invention provides another reflector pair, B, C, etc. ), the incident radiation wavelength λ, transmitted through the Fapley-Bello interferometer 30 and transmitted to the photodetector 31, has a specific anti-Q4f! ! ! 15 of the pair A, and this particular transmission peak is also spectrally concentrated in the transmission of the Two-Ply-Bello interferometer 30, hereinafter referred to as the Analytical Fapley-Bello interferometer. When spectrally matched to a peak, it is transmitted at maximum intensity.

For example, optical type 11 between reflector pair B, anti-lFJ
The reflector pair B is determined to generate the SR transmission peak in a specific wavelength region between 1IT and (n)(z)1D and λ2D0. This happens if.

λ1. and 22. If the following equation holds in the same wavelength region between .

Here ■^ is the optical distance between the reflectors of the analytical Fapley-Bello interferometer 30.

As already explained, if a signal is detected by an optical fiber energy sensor placed, for example, between the length-limited Bragg reflectors of pair B, the transmission of region 1i1b in FIG. The peak indicates the spectral shift within the region, ΔλSR'. By adjusting the relative values of S and SR using equations (r , spectral shift of transmission,
This spectral shift, Δλ, R is actually amplified by ΔλSA@the following equation.

Δλ　〜UΔλ8R(XI) S.A. Here, U is the amplification coefficient, for example, given by the following equation: 5R-8A However, SA-(f)(SR)±1 where SA and SR are greater than 2 and f is a positive integer.

In order to better explain the demodulator and to show fewer obvious limitations to consider for its completion, the i! Let us walk through two laser scanning intervals in detail to explain one embodiment of the system. Laser scanning begins at λ1, which does not fall within any of the reflection wavelength bands at the back of pair 25. As the laser output wavelength scans over time, it will eventually begin to scan across the transmission peak of a particular pair of Δ. Reference interferometer 28 then transmits pulses of the laser beam to photodetector 29, which in turn provides electrical pulses to time demodulator 33. This electrical reference pulse is used to reset or start the electrical clock at time viW4 unit 33. The time demodulator 33 also counts the reference pulses in one scan interval and, depending on the number of pulses, determines which one of the electrical outputs corresponds to the particular reflector pair whose transmission peak is being scanned at the time.
Transmit the last output of the electrical clock to one. Such electronic circuits are readily available from commercially available products.

Referring to one embodiment of this device, the laser output is now
We are beginning to scan the transmission peak of . The laser output wavelength is
At λ2, when within the range of the first peak of pair A,
The laser beam passes through pair A and all other pairs and finally propagates to the analytical interferometer 30. For illustration purposes, the apparatus of FIG. 14 uses the equation x■ as 5R-10 to calculate the amplification factor
Assume that it is designed to give o. Also, for the sake of simplicity, λ1. and λ2o is assumed to spectrally match the region ll1tb of FIG. 15 in each reflector equation. Therefore, Ll-100
, S-10, it becomes 5A-99.

Similarly, assume that analytical interferometer 30 has a peak that spectrally matches the first peak of pair A. Therefore, when the laser beam is transmitted to the photodetector 31, the photodetector 31 generates an electrical output which, when applied to the time demodulator 33, pauses the electrical clock and its final output is the time in the clock. is applied to the S wire or lead wire marked 8. As the laser continues to scan, the wavelength of its output finally approaches the transmission peak of pair B. Again, the reference interferometer 28 transmits a pulse of light that causes the photodetector 29 to generate a pulse that resets or starts the clock and connects the output of the clock to the conductor or lead B. Prepare.

As the signal being detected by the energy sensor of pair A changes, the transmission peak of pair A shifts spectrally. Assume that the signal has already shifted its peak by -(Δλ) at some time before the second laser scan. 2
When the second laser scan begins, the output wavelength becomes λ1 again. Shortly after the start of the scan, the laser output is again close to the first transmission peak of pair A, and the output wavelength is such that no light is transmitted to field 31 and the output is not paused. However, as the laser continues to scan, its output will later become λ2 + - Δλ + Δλ, which is the spectral position d of the second transmission peak of pair A. #&! regarding the amplification factor U of the device of this embodiment. (7)
t′″0・)2+,−,lsA”620ゞ51 Interferometer 3
This is the spectral position of the transmission peak at λ2, which is spectrally adjacent to the peak located at λ2. therefore,
The transmission is done through an analytical interferometer 30 and the light is detected! a31
generates a signal that causes the clock to pause. Even if the transmission peak of pair A shifts by only one (Δλ), the output of the combination of pair A and interferometer 30 cannot be optically detected because the laser output wave does not match the peak of analytical interferometer 30. It would not have occurred until the amplification was 100. The remainder of the second scan WA interval continues as described for the first laser scan interval.

Completion of the demodulator d requires special attention to the bandwidth of the optical fiber 24. The bandwidth must be high enough to preserve the narrowness of the transmission peak of the returning reflector pair. It should be noted that the optical demodulator can be used whenever it is desired to measure the spectral movement of the Fapley-Bello interferometer fringes, with or without the use of optical fibers. In addition, the laser beam is analyzed using a Fapley-Bello interferometer! It is also recognized that the signal can be first passed through and then transmitted to a Fapley-Bello interferometer where one of the intervals is to be measured. However, if an optical fiber is used to transmit the laser beam to the Fapley-Bello interferometer being measured, if the laser beam is first passed to the analytical interferometer, then the beam is transferred from the analytical interferometer to the Fapley-Bello interferometer. It is necessary to select an optical fiber with low dispersion for transmission to. This is because this beam has an additional amplitude time dependence as caused by the spectrally periodic transmission of the analytical interferometer. Furthermore, the features of both the analytical interferometer and the sensor interferometer are chosen such that even if there are no spectrally exactly matched transmission peaks, there is still just enough overlap to produce a significant combined output. Must. Finally, the apparatus of the embodiment produces an ambiguous output if the spectral shift of the transmission peak of the reflector pair is allowed to be greater than 1 Δλ or less than 1 Δλ.

Finally, it is specified that the electrical reference signal may be derived from the same signal that causes the laser to scan. The criterion governing the reference signal is that it must have a known position in time with respect to the position in time of any particular wavelength of the laser scan. Furthermore, criteria in proper laser scanning are that the scanning interval must occur frequently enough in the time period to detect the highest frequency of oscillation of the temporal position of the output of the reflector pair and analytical interferometer combination. Next, the output wavelength of the scanning laser must be scaled as a well-known function of time.

Another analysis interferometer 308, illustrated in FIG. 17, is added to eliminate the obscurity in excessive peak migration. FIG. 17 is a schematic diagram of a subsystem that replaces the subsystem W surrounded by broken lines in FIG. 14. This additional analyzer 30B is configured, for example, to give a lower magnification when used with the same output of the reflector pair according to equation X. From the foregoing discussion, it can be seen that coupling lower amplification can give the transmission peak shift a higher threshold at which obscurity initially occurs. Using equation XI to determine the amplification factor U, the spectral shift of the threshold becomes:

fΔλ <xm> A device using two analytical interferometers, each with a different amplification, is given by:

The first interferometer 30 may have a transmission peak of S-99 between λ, 0 and λ2° as in the previous embodiment of the detection device. A pair of reflectors allows the peak of 5R-10 to be λ1. and λ2. An additional interferometer 308 may have a peak at 5A-9 between λ1o and λ2. It may be between. For example, if time 1 [vessel 33
and 33B give an analog output, then at a particular transition Δλ8((() corresponding to the pair A), the electrical output of the time demodulator 33B corresponding to the pair Δ would be a voltage e such that:

e = Δλ5RU1 (Xlv) where K is the constant U is the amplification factor equal to R 10 at S −10 and 5A=9 and Δλ3R is the spectral shift of the peak of the region S in FIG. 15 corresponding to conductor A.

The output e2 of the demodulator 33 will be:

e - to Δλ5RU2 (xv)-100 to Δλ8R Here, 100 is the amplification coefficient, U2, that is JH-valued for 5R-10 and 5A-99.

Such a device can of course be expanded to include a large number of such analytical interferometers with optical amplification, and easily add more beam splitters such as 127' and reflector pairs. The output of the analysis interferometer may be divided between the analytical interferometers.

It should be noted from the foregoing discussion that analytical interferometer 30B can begin to exhibit obscurity at spectral transitions smaller than 1Δλ.

However, the analyzer 30 has a 51
Significant output is generated in spectral transitions below Δλ. One may therefore wish to add analytical interferometers that will provide either lower or higher amplification than the analytical interferometers already provided in one device.

Time 11! A jig is an electrical device that performs two functions: First, how can a reference pulse be received and analyzed from a Fapley-Bello interferometer, for example by its amplitude, frequency of vibration, or phase of vibration? Receiving the IY magnetic radiation is a pulse from the photodetector, called the ANΔL pulse, which generates an electrical signal that contains or transmits the time taken during the 2. To transmit this electrical signal to a specific output line or group of specific output lines of the tree. There are a number of electrical circuits that can accomplish this, one of which is schematically illustrated in FIG. Referring to FIG. 18, Ul and (J2 are voltage comparators, e.g., National Semiconductor
or Corp, part #LM311, U4
and U5 are counters, such as TexasInStru■
ents part #74161, U3 is a clock generator, e.g.
Part #74LS124 manufactured by S company, U6 is demu
x, for example, Texas Instruments part #74155, U7. U8 and U9 are latches, e.g. also TeXaS lll5trUIQn
It is part #74175 manufactured by tS.

This circuit operates as follows. ul and ()2, the voltage comparators, operate to convert the reference pulse and the additional pulses to standard TTL logic voltage levels for use in Wa devices. As driven by generator U3, it serves to reset a counter U4 which is continuously counting at a rate approximately 16 times the rate of reference pulse repetitions.The resulting output of counter U4 is the reference pulse repetition rate. is the number that starts at O when a reference pulse is taken, counts upward, resets again with another reference pulse, and starts counting anew when it reaches 0. Meanwhile, each time a reference pulse is taken, , counter U5 is incremented. After counting the appropriate number of channels (3 in this case) it is set to automatically return to O. When the ANAL pulse is sent, this causes deltlX L12 to The number on the output of the counter represents the time between the appropriate channel latch latch reference pulse and the ANAL pulse.The next ANAL pulse is such that the channel latches of are stored with numbers representing the time between these M monopulses and the ANAL pulses, etc. Each time a new time count is latched,
The trailing edge of the latch pulse alerts the user that new data is available.

An improved optical fiber energy sensor and method of manufacturing the same is provided, as well as an improved optical demodulator that is particularly sensitive to elongation and IE contraction due to the signal energy to be sensed or detected.

[Brief explanation of the drawing]

FIG. 1 is a greatly enlarged cross-sectional view of a single mode optical fiber, and FIG.
3 is a greatly enlarged cross-sectional view of the single mode optical fiber of FIG. 3, FIG. 4 is a greatly enlarged cross-sectional view of a large diameter fiber comprising a core material, and FIG. FIG. 4 is a greatly enlarged cross-sectional view of the large diameter fiber of FIG. 3; Figures 15 to 18
The diagram is a tree! This is an application example using the invention, and Figure 5 is an example of application using the invention.
7 is an end view of the acoustic energy sensor illustrated in FIG. 6, FIG. 6 is a cross-sectional illustration of the acoustic energy sensor of FIG. FIG. 8 is an end view of the acoustic energy sensor; FIG. 9 is a cross-sectional view of the acoustic sensor of FIG. 8 taken along line 9--9; Figure 10 shows a constructed mold and single mode optical fiber for manufacturing an optical fiber energy sensor. FIG. 11 is a cross-sectional view of only the mold in FIG. 10 after being coated with a protective film, and FIG. 12 is a cross-sectional view of the mold in FIG. 10 after etching and coating and the single mode optical FIG. 13 is an end view of a collapsible mold that can be used in the etching process; FIG. 14 is an illustration of the applied light v! FIG. 15 is a typical transmission i) illustration of the pair 25 of reflectors in FIG. 14, and FIG. FIG. 17 is a graph of appropriate laser output, and FIG. 17 is a graph of a large number of analytical interferometers 111 that substitutes for the part of the optical demodulator surrounded by the broken line w't' in FIG. 14.
FIG. 18 is a schematic diagram of the time demodulation circuit exemplarily shown in FIGS. 14 and 17. Explanation of symbols 1-1...Core, 2-1...Glass clad, 6.
...Skeleton, 7.7-9...Flexible membrane, 8.8-9
．． 24...Single mode optical fiber, 8', 201
-9... Reinforced strut, 9.16'... Space, 1
6...Storage, 10.15...N port, 11...Protrusion, 12...Bladder 14...Tightening with ring, 17.
...End cap, 202-9...Inner cylinder, 257
...Cylinder, 18'18-12...Type, 19'...
Spiral groove, 125...hole, 126...opening, 25.
...pair of Bragg reflectors of length i, 11 limited, 26
...Wavelength scanning laser, 127°127'...Beam splitter-128...Reference Fabry-Perot interferometer, 29, 31, 31B...Photodetector, 30.308.
・・Analysis F7 Breebeloy interferometer, 33.33B・・Time demodulator.

Claims (4)

[Claims] (1) A method of transmitting electromagnetic radiation to provide low morphological dispersion, the method comprising injecting said radiation into an optical fiber made by etching a fiber comprising an optical fiber core material. The electromagnetic radiation transmission method as described above. (2) Claim (1) is characterized in that the optical fiber manufactured by etching a fiber made of a core material of the optical fiber is coated with a substance having an optical index lower than that of the core. The electromagnetic radiation transmission method. (3) An electromagnetic radiation transmission device characterized in that it includes an etched optical fiber with low topographical dispersion. (4) The electromagnetic radiation transmission device according to claim (3), characterized in that the optical fiber having low morphological dispersion is coated with a material having a lower optical index than the core of the fiber.