Exemplary embodiments pertain to the art of encoded optical fibers using Fiber Bragg Gratings (FBGs). FBGs are wavelength-selective reflectors that can be use in fiber optic communication and sensing. FBGs can be used to encoded digital information, such as a serial number, into an optical fiber. However, the amount of information that can be encoded is constrained by wavelength band, fiber length, etc. These limitations restrict the encoded optical fibers from being used in applications that require the encoding of high levels of digital information.
Disclosed is a method of encoding information in an optical fiber. Light is propagated through the optical fiber, the optical fiber having a first encoder Fiber Bragg grating (FBG) therein. A first encoded reflection of light indicative of an interaction of the propagated light with the first encoder FBG is received at a detector, wherein information for the first encoder FBG is encoded in an intensity of the first encoded reflection. The intensity of the first encoded reflection is measured to read the information of the first encoder FBG.
The method of claim 1 further includes receiving a reference reflection of light indicative of an interaction of the propagated light with a reference FBG in the optical fiber and comparing a reference intensity of the reference reflection to the intensity of the first encoded reflection to determine the encoded value.
The method further includes encoding the information for the first encoder FBG based on the first encoder intensity, a time of arrival of the first encoded reflection and a wavelength of the first encoded reflection.
In an embodiment, the optical fiber includes a second encoder FBG therein, wherein the first encoder FBG reflects light at a first wavelength and the second encoder FBG reflects light at a second wavelength.
In an embodiment, the first encoder FBG and the second encoder FBG are included within one of a plurality of FBG groups within the optical fiber.
In an embodiment, the intensity of the encoded reflection is an integer multiple of the reference intensity in one of (i) an arithmetic sequence; and (ii) a geometric sequence.
The method further includes performing a signal reversal operation when the first encoded reflection of light is received before the reference reflection at a detector.
Also disclosed herein is an optical fiber. The optical fiber includes a reference Fiber Bragg grating (FBG) configured to reflect a light propagating in the optical fiber at a reference intensity and a first encoder FBG configured to reflect the light at a first encoder intensity, wherein information is encoded in the optical fiber based on the reference intensity and the first encoder intensity.
The information includes a digit encoded in the optical fiber based on a comparison of the first encoder intensity to the reference intensity.
The optical fiber further includes a second encoder FBG, wherein the first encoder FBG reflects light at a first encoder wavelength and wherein the second encoder FBG reflects light at a second encoder wavelength. The information is further encoded by the first encoder FBG and the second encoder FBG based at least one of: (i) a time of arrival of a signal from each of the first encoder FBG and the second encoder FBG relative to the reference; and (ii) a first encoder wavelength of first encoder FBG and a second encoder wavelength of the second encoder FBG related to the reference.
In an embodiment, the first encoder FBG and the second encoder FBG are included within one of a plurality of FBG groups within the optical fiber.
In an embodiment, the first encoder intensity is an integer multiple of the reference intensity in one of (i) an arithmetic sequence; and (ii) a geometric sequence.
Also disclosed is an optical system. The optical system includes an optical fiber, a light source, a detector, and a processor. The optical fiber includes a reference Fiber Bragg grating (FBG) configured to reflect a light propagating in the optical fiber at a reference intensity and a first encoder FBG configured to reflect the light at a first encoder intensity. The light source is configured to propagate light along the optical fiber. The detector is configured to detect the light reflected from the reference FBG and from the encoder FBG. The processor is configured to decode information encoded in the optical fiber based on the reference intensity and the first encoder intensity.
The processor is configured to decode the information by comparing the first encoder intensity to the reference intensity.
The optical fiber further includes a second encoder FBG, the first encoder FBG reflecting light at a first encoder wavelength and the second encoder FBG reflecting light at a second encoder wavelength.
The processor is further configured to decode the information encoded by the first encoder FBG and the second encoder FBG based at least one of: (i) measuring a time of arrival of a signal from each of the first encoder FBG and the second encoder FBG; and (ii) measuring a first encoder wavelength of first encoder FBG and a second encoder wavelength of the second encoder FBG.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
The plurality of FBGs includes a reference Fiber Bragg grating (reference FBG 112) and at least one encoder Fiber Bragg grating (encoder FBG 114). The Bragg wavelength of the reference FBG 112 and the Bragg wavelength of the encoder FBG 114 are different, in order to facilitate distinguishing their signals from each other. The reference FBG 112 is formed within the optical fiber 102 to have a selected reflectivity coefficient and thus to reflect a selected percentage of the test signal. Thus, for a given intensity of the test signal, the reflected light from the reference FBG 112 has a given intensity, which is referred to herein as the reference intensity. Similarly, the encoder FBG 114 is formed in the optical fiber 102 to have a selected reflectivity coefficient and therefore to reflect the test signal at a given intensity, which is referred to herein as the encoder intensity. The encoder intensity can be the same as or different from the reference intensity. In various embodiments, the encoder intensity is an integer value of the reference intensity. Thus, for a reference FBG 112 having reflectivity Rref, the encoder FBG 114 is designed to have a reflectivity as given in Eq. (1):
R
enc
=q·R
ref Eq. (1)
where Renc is the reflectivity of the encoder FBG 114 and qε{0, 1, . . . , Q−1}, where Q is a positive integer. In an illustrative embodiment, Q=5. Thus, for a reference FBG 112 having reflectivity Rref=0.1%, the encoder FBG 114 can having a reflectively selected from a group Rref E {0, 0.1%, 0.2%, 0.3%, 0.4%}. By forming a ratio of the encoder intensity to the reference intensity, the encoder intensity is converted into a digit. In the illustrative embodiment in which Q=5, the encoded digits are selected from the group of qε{0, 1, 2, 3, 4}. Although in the illustrative embodiment, the group of encoder ratios is an arithmetic sequence, in another embodiment, this group can be a geometric sequence, (e.g., qε{0, 1, 2, 4, 8}) and the encoded digit is selected from this group.
The first encoder FBG 202 and the second encoder FBG 204 can be used to encode two digits within the optical fiber 102. Once, read, these digits can be combined at the processor 110 to form a digital word. In addition to encoding a digit based on the intensities of reflected light form an encoder FBG, the digit can be encoded based on the reflected wavelength of the FBG. The reference FBG 112 reflects light at a first wavelength (reference wavelength), while the first encoder FBG 202 reflects light at a first encoder wavelength and the second encoder FBG 204 reflects light at a second encoder wavelength. The reference wavelength, first encoder wavelength and second encoder wavelength are all different from each other. The digital word includes a first digit encoded by the first encoder FBG 202 at first encoder wavelength and a second digit encoded by the second encoder FBG 204 at the second encoder wavelength. In general, the reference FBG 112 is formed such that, as a test signal is swept through a range of wavelength, the reference wavelength is the first to be received at the optical interrogator 104.
The FBG groups are physically separated by a group separation distance LM between adjacent FBG groups. The first FBG group G1 is separated from the reference FBG 112 by a lead length LC. Each FBG group has a group length LG, which includes all of the encoder FBGs of the FBG group. The group separation distance LM is greater than the group length LG. Since the reference FBG 112 and each FBG within a single FBG group have different wavelength slots, both the lead length LC and the group length LG can be more than an order smaller than LM.
A total of w encoders FBGs can be arranged at different locations within an FBG group, each location being a position within the FBG group at which an FBG can be placed. With each FBG having its own individual reflection wavelength, up to w wavelengths can be represented in an FBG group. It is noted that the wavelengths are not necessarily arranged such that they always increase with distance along the optical fiber in the FBG group. In order words, the wavelengths can show up in any order within the FBG group. Also, it is possible that a location at which an encoder FBG might otherwise be positioned is left empty in order to encode a digit value of ‘0’ for the encoder FBG wavelength. The location is left by simply not forming an encoder FBG at the location.
For illustrative purposes, the first FBG group (G1) includes a first encoder FBG 302a, a second encoder FBG 302b and a third encoder FBG 302c. The second FBG group (G2) includes encoders FBGs 312a, 312b and 312c. The reference FBG 112 is located between the first FBG group G1 and the optical interrogator 104. In order to distinguish the reference wavelength, the encoder wavelengths are groups in a cluster, while the reference wavelength is separated from the cluster.
While encoder FBGs within an FBG group reflect light at different wavelengths, an encoder FBG of the first FBG group can reflect light at the same wavelength as an encoder FBG of the second group. For an encoder FBG within the first FBG group and an encoder FBG within the second FBG group that reflect light at the same wavelength, the time-of flight for their reflected signals can be used to distinguish between them. In general, time-of flight is used as a parameter for distinguishing FBG groups from one another.
In the illustrative optical system 300, a narrowband wavelength-stepping pulse-echo light source 106 is used. The wavelength range of the light source is selected so that it covers all of the wavelength slots for both the reference FBG and the FBG groups. The wavelength, spatial location, and amplitude of the reflected light for the FBG groups are used to determine the information encoded int the optical fiber. Error detection and correction techniques, such as Reed-Solomon code, hamming code and cyclic error correcting code, can be applied during the decoding process in order to add redundancy and increase the size of data to be encoded, as well as to ensure data integrity.
Digital data can be either be partitioned into differently sized multi-bit aggregates to fit into a single FGB group or lumped together so as to be distributed over all FBG groups. For example, a 64-bit binary data can be encoded as a single integer value. In an embodiment, with Q=4 and w=16, the integer can be converted into a base 32 number. This base 32 number can be encoded using two FBG groups.
The reference signal provides a directional reference, position reference, wavelength reference and amplitude reference for the encoder signals. Based on the arrangement of the optical interrogator (such as in
Box 410 shows a close-up of the encoder amplitudes of the first amplitude group 404a, along with the reference amplitude 402. In the illustrative embodiment, the amplitude group 404a includes the amplitudes at 10 wavelength slots (i.e., w=10), each of which corresponds to a location of an encoder FBG. The reference amplitude 402 defines a digit value of ‘1’. The amplitudes at the wavelength slots show digital values of ‘0’ (indicated by dashed lines), ‘1’ and ‘2’, which read spatially, from left to right, as ‘1021201102’.
In box 512, the center wavelength of the encoder FBGs are determined. In addition, the wavelength slots are determined with respect to the wavelength of the reference FBG. In box 514, the wavelength slot of each encoder FBG is cross-referenced to the wavelength slot of the reference FBG to determine its position and amplitude. In box 516, the positions and amplitudes of the encoder FBGs are quantized. Quantization uses the group separation LM and the reference intensity. In box 518, the quantized information is used to read the digits encoded in the encoder FBGs based on the amplitudes, positions, and wavelengths. In box 520, error correction algorithms are applied, if necessary, to verify the integrity of the information.
It is to be noted that the information encoded in the optical fiber can be related to other information obtained by the optical fiber, such as at one or more sensors at other locations along the optical fiber. In another embodiment, the optical fiber can be attached to an article of manufacture and the information can be related to the associated article of manufacture.
The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.