Radiation-hardened (RH) photonic crystal fiber (PCF)

Abstract

The disclosure teaches radiation-hardened (rad-hard or RH) photonic crystal fibers (PCFs) comprising a RH core region surrounded by a micro-structured cladding region. The micro-structured cladding region comprises a RH inner cladding region that surrounds the RH core region. An outer cladding region surrounds the RH inner cladding region. The RH inner cladding region comprises an inner RH silica web formed by an inner set of holes. The outer cladding region comprises an outer silica web formed by an outer set of holes. The RH core region comprises a first RH silica material. The inner RH silica web comprises a second RH silica material. The second RH silica material is substantially identical in radiation hardness to the first RH silica material. The outer silica web comprises an outer silica material.

Description

RADIATION-HARDENED (RH) PHOTONIC CRYSTAL FIBER (PCF)CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patent application serial number 63 / 734,236, filed 2024-Dec-16, with first-named inventor David DiGiovanni, and having the title "Radiation-Hard Microstructure Photonic Crystal Fiber," which is incorporated herein by reference in its entirety.BACKGROUNDFIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to optical fibers and, more particularly, photonic crystal fibers (PCFs).DESCRIPTION OF RELATED ART

[0003] In optical systems, one of the causes of data loss and deterioration of signal integrity is attenuation of optical signals. Consequently, there are ongoing efforts to mitigate issues arising from attenuation of optical signals.SUMMARY

[0004] The present disclosure teaches radiation-hardened (rad-hard or RH) photonic crystal fibers (PCFs). Briefly described, one embodiment of a RH-PCF comprises a RH core region surrounded by a RH micro-structured cladding region. The RH micro-structured cladding region comprises a RH inner cladding region that surrounds the RH core region and, also, an outer cladding region that surrounds the RH inner cladding region. The RH inner cladding region comprises an inner RH silica web formed by an inner set of holes. The outer cladding region comprises an outer silica web formed by an outer set of holes. The RH core region comprises a first RH silica material. The inner RH silica web comprises a second RH silica material. The second RH silica material is substantially identical in radiation hardness to the first RH silica material. The outer silica web comprises an outer silica material. For some embodiments, the outer silica material is substantially identical in radiation hardness tothe second RH silica material. For other embodiments, the outer silica material is different in radiation hardness than the second RH silica material.

[0005] Other systems, devices, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure.Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0007] FIG. l is a diagram showing one embodiment of a micro-structured photonic crystal fiber (PCF) with a core region and a micro- structured cladding region.

[0008] FIG. 2 is a diagram showing another embodiment of a micro-structured PCF with a core region and a micro-structured cladding region.

[0009] FIG. 3 is a diagram showing an embodiment of a micro-structured PCF multiple cladding rings of radiation-hardened (RH) silica.

[0010] FIG. 4 is a diagram showing an embodiment of a micro-structured PCF with a seven (7) unit cell core and a micro-structured cladding region.

[0011] FIG. 5 is a diagram showing an embodiment of a micro-structured PCF with a nineteen (19) unit cell core and a micro- structured cladding region.

[0012] FIG. 6 is a diagram showing an embodiment of a micro-structured PCF with a honeycomb design.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] Optical attenuation of silica-based optical fibers increases as the fiber is exposed to ionizing radiation. Fibers with low sensitivity to radiation are typically free of conventional index -raising dopants (e.g., Germanium (Ge), Phosphorous (P), Aluminum(Al), etc.) but include more than trace levels of Chlorine (Cl) or Fluorine (F). For optical fibers to guide light, the fiber core must have a higher index of refraction than the fiber cladding, which typically requires different glass compositions for the core with radiationsensitive index-raising dopants than for the cladding with fewer (if any) index-raising dopants. These differences in composition result in differences in radiation sensitivity. In other words, ionizing radiation has a different effect on the core (with one composition) than it has on the cladding (with a different composition). Additionally, mitigating for bend sensitivity often requires an even more exaggerated difference in index, which in turn results in a higher difference in radiation sensitivity.

[0014] To reduce the difference in radiation sensitivity between the core and the cladding, this disclosure teaches an optical fiber in which both the core region and the cladding region are radiation hardened. By radiation hardening both the core region and the cladding region of an optical fiber preform, an optical fiber that is eventually drawn from the preform has a RH core region and a RH cladding region that are both relatively insensitive to ionizing radiation. More particularly, this disclosure teaches photonic crystal fibers (PCFs) with a lower-index RH cladding region surrounding a higher-index RH core region.

[0015] Having provided a broad technical solution to a technical problem, reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. However, to be clear before proceeding to the detailed embodiments, because different processes for radiation hardening of silica (e.g., irradiating (either pre-irradiating or re-irradiating) with ionizing radiation) are processes that are well known to those having skill in the art, only a truncated discussion of the actual process of radiation hardening is provided herein as necessary for the understanding of the disclosed embodiments.

[0016] FIG. l is a diagram showing one embodiment of a micro-structured optical photonic crystal fiber (PCF) 100 with a radiation-hardened (RH) core region 120 and a RH micro-structured cladding region 110. Specifically, FIG. 1 shows an axial cross-section of a PCF 100.

[0017] As shown in FIG. 1 , the RH core region 120 is located substantially in the center of the PCF 100 and comprises a RH silica material (designated with an ordinal as a first RH silica material to avoid ambiguity). The RH core region 120 is surrounded by the RH micro-structured cladding region 110. The RH micro-structured cladding region 110 comprises a set of holes 130 that form a RH silica web 140 around the RH core region 120.

[0018] The RH silica web 140 comprises a second RH silica material that is substantially identical in radiation hardness to the first RH silica material. In other words, because the first RH silica material and the second RH silica material are substantially identical in radiation hardness, both the silica RH core region 120 and the RH silica web 140 have substantially the same sensitivity or susceptibility to ionizing radiation.

[0019] To accommodate insensitivity to micro-bending, the PCF 100 exhibits an effective numerical aperture (NA) that is greater than approximately 0.18 (i.e., NA > 0.18) as defined by the difference between the refractive index of the RH core region 120 and the effective refractive index of the RH micro- structured cladding region 110. Preferably, the effective NA of the waveguide formed by the RH core region and the RH micro-structured cladding region is greater than approximately 0.26 (i.e., NA > 0.26) for better bend insensitivity. Insofar as various aspects of NA (e.g., wavelength dependency, etc.) are known to those having skill in the art, only a truncated discussion of NA is provided herein. However, for some embodiments, the operating wavelength (or center wavelength) for which the NA is computed is 1550 nanometers (nm). For other embodiments, the NA is computed for an operating wavelength of approximately one micrometer (1pm).

[0020] For purposes of manufacturing, a preferred embodiment of the PCF 100 is drawn from an optical fiber preform that has a uniform RH glass composition, but which has been precision drilled with multiple holes that eventually become the set of holes 130 shown in FIG. 1 upon drawing of the preform to the PCF 100. In an alternative preferred embodiment, the PCF 100 is drawn using known stack-and-draw procedures that begin with a RH glass rod that is surrounded by stacked RH capillary tubes, with both the RH glass rod and the RH capillary tubes having substantially the same RH glass composition. Of course, the RH capillary tubes eventually form the set of holes 130 and the RH silica web 140. Insofar as precision drilling procedures and stack-and-draw procedures are known to those having skill in the art, only a truncated description of both processes is described herein.

[0021] It should, however, be noted that if the capillary tubes have Fluorine (F) and the glass walls between the capillary tubes are thin, then deformation of the glass matrix (or web) may occur through outgassing of the F, which can thereafter react with water to form hydrofluoric (IFF) acid, a glass etchant. Nevertheless, more than a trace amount of F is needed for sufficient radiation hardness. Thus, in preferred embodiments of the PCF 100, the RH silica material comprises more than trace amounts of F, while also being substantially free of F to the extent that there is minimal negative effects of F outgassing. Insofar as those having skill in the art will understand what is meant by trace amounts of F (including a range of F concentrations), only a truncated discussion of the F concentration is provided herein.

[0022] Similar to F, if the capillary tubes have Chlorine (Cl), then outgassed Cl can react with other elements to form chlorides that can also degrade optical performance of the PCF 100. Again, more than a trace amount of Cl is needed for sufficient radiation hardness. Consequently, in preferred embodiments of the PCF 100, the RH silica material will also have more than a trace amount of Cl, but not so much Cl that its detrimental effects are minimized. Insofar as those having ordinary skill will understand how to balance the proper amount of Cl, only a truncated discussion of the Cl concentration is provided herein.

[0023] As demonstrated from FIG. 1, by using substantially the same RH silica composition (or silica composition with substantially identical radiation hardness) for both the core region 120 and the cladding region 110, the light-guiding portions of the PCF 100 are affected by ionizing radiation to the same degree. Furthermore, by using silica material that has been radiation hardened, the light-guiding properties of the PCF 100 remain sufficiently immune to the effects of ionizing radiation, thereby mitigating for radiation- induced attenuation.

[0024] Continuing, FIG. 2 is a diagram showing another embodiment of a RH microstructured PCF 200 with a RH core region 220 and a micro-structured cladding region 210. Similar to FIG. 1, the RH core region 220 comprises a RH silica material (again, for clarity, designated with an ordinal as first RH silica material). However, unlike the embodiment of FIG. 1, the micro-structured cladding region 210 comprises two (2) distinct cladding regions, namely, a RH inner cladding region and an outer cladding region.

[0025] More particularly, as shown in FIG. 2, the micro-structured cladding region 210 comprises an inner set of holes 230 and an inner RH silica web 240 (or matrix) that isformed by the inner set of holes 230. Together, the inner set of holes 230 and the inner RH silica web 240 form the RH inner cladding region. The inner RH silica web 240 comprises a second RH silica material that is substantially identical in radiation hardness to the first RH silica material of the RH core region 220.

[0026] The reason for having substantially the same silica composition is because the inner RH silica web 240 also guides light (in conjunction with the RH core region 220. As such, if the inner RH silica web 240 had a different composition than the RH core region 220, then ionizing radiation would potentially affect the inner RH silica web 240 differently than the RH core region 220. That difference would create a difference in light-attenuation properties within the light-guiding portion of the PCF 200.

[0027] Continuing with FIG. 2, the outer cladding region of the PCF 200 comprises an outer set of holes 250 and an outer silica web 260 that is formed by the outer set of holes 250. The outer silica web 260 comprises an outer silica material. For some embodiments, the outer silica material is substantially identical in radiation hardness to the second RH silica material, in which case the embodiment of the PCF 200 of FIG. 2 becomes substantially the same as the embodiment of the PCF 100 of FIG. 1.

[0028] For other embodiments, the outer silica material is different in radiation hardness than the second RH silica material. This difference is acceptable for the PCF 200 because the outer cladding (formed by the outer set of holes 250 and the outer RH silica web 260) do not form a part of the light guide for the PCF 200. Thus, the effects of ionizing radiation on non-light-guiding portions of the PCF 200 are relatively unimpactful to the integrity of the optical signal because the ionizing radiation has little-to-no impact on optical attenuation in the outer cladding region (as compared to the inner cladding region).

[0029] Similar to FIG. 1, the embodiment of FIG. 2 accommodates insensitivity to micro-bending when the effective NA > 0. 18 at the interface between the RH core region 120 and the RH micro-structured cladding region 110. Preferably, for better bend insensitivity, the effective NA > 0.26 at the interface between the RH core region and the RH microstructured cladding region.

[0030] Similar to the manufacture of the PCF 100 of FIG. 1, for purposes of manufacturing with reference to FIG. 2, a preferred embodiment of the PCF 200 is drawn from an optical fiber preform that has a uniform RH glass composition, but which has beenprecision drilled with multiple holes that eventually become the sets of holes 230, 250 shown in FIG. 2 upon drawing of the preform to the PCF 200. In an alternative preferred embodiment, the PCF 200 is drawn using known stack-and-draw procedures that begin with a RH glass rod that is surrounded by a first set of stack RH capillary tubes, which in turn is surrounded by a second stack of RH capillary tubes. The RH glass rod and the first set of RH capillary tubes have substantially the same RH glass composition, but the second set of RH capillary tubes need not have the same glass composition. Of course, both sets of RH capillary tubes eventually form their respective sets of holes 230, 250 and their respective RH silica webs 240, 260. In preferred embodiments of the PCF 200, the RH silica material (for the core region and the inner cladding region) is substantially free of F and Cl.

[0031] As demonstrated from FIG. 2, by using substantially the same RH silica composition for both the core region 220 and the inner cladding region, the light -guiding portions of the PCF 200 are affected by ionizing radiation to the same degree. Furthermore, by using silica material that has been radiation hardened, the light-guiding properties of the PCF 200 remain sufficiently immune to the effects of ionizing radiation, thereby mitigating for radiation-induced attenuation.

[0032] FIG. 3 is a diagram showing an embodiment of a micro-structured PCF 300 with multiple cladding rings of radiation-hardened (RH) silica. As shown in FIG. 3, the PCF 300 comprises a RH core region 320 and a micro-structured cladding region 310. Similar to FIG. 1 and FIG. 2, the RH core region 320 comprises a RH silica material (again, for clarity, designated with an ordinal as first RH silica material). Also, similar to FIG. 2, the microstructured cladding region 310 comprises two (2) distinct cladding regions, namely, a RH inner cladding region and an outer cladding region. However, unlike FIG. 2, the RH inner cladding region comprises two (2) layers of cladding rings with inner holes 330 and an inner RH silica web 340, which together form the RH inner cladding region. The outer cladding region comprises an outer set of holes 350 and an outer silica web 360. For some embodiments, the outer silica material is substantially identical in radiation hardness to the second RH silica material, in which case the embodiment of the PCF 300 of FIG. 3 becomes substantially the same as the embodiment of the PCF 100, 200 of FIG. 1 and FIG. 2. For other embodiments, the outer silica material is different in radiation hardness than the second RH silica material.

[0033] FIG. 4 is a diagram showing an embodiment of a micro-structured PCF with a seven (7) unit cell core 420 and a micro-structured cladding region 410. Unlike the embodiment of FIG. 2 (with a single-unit cell core 220), the embodiment of FIG. 4 comprises a larger, 7-unit cell core 420. Otherwise, the inner holes 430, inner RH silica web 440, the outer holes 450, and the outer silica web 460 are comparable to the corresponding components 230, 240, 250, 260 of FIG. 2. As such, only a truncated discussion of those components is provided herein.

[0034] FIG. 4 is a diagram showing an embodiment of a micro-structured PCF with a nineteen (19) unit cell core 520 and a micro-structured cladding region 410. Unlike the embodiment of FIG. 2 (with a single-unit cell core 220) or the embodiment of FIG. 4 (with a larger, 7-unit cell core 420), the embodiment of FIG. 5 comprises an even larger 19-unit-cell core 520. Otherwise, the inner holes 530, inner RH silica web 540, the outer holes 550, and the outer silica web 560 are comparable to the corresponding components 230, 240, 250, 260, 430, 440, 450, 460 of FIG. 2 of FIG. 2 and FIG. 4. As such, only a truncated discussion of those components is provided herein.

[0035] FIG. 6 is a diagram showing an embodiment of a micro-structured PCF 600 with a honeycomb design. As shown in FIG. 6, the PCF 600 comprises a central, single-unit- cell core 620 surrounded by a RH inner cladding layer, which comprises inner holes 630 and an inner RH silica web 640. Unlike the embodiments of FIGS. 1 through 5, the PCF 600 of FIG. 6 comprises outer holes 650 that form a honeycomb pattern around their respective RH silica web 660 (with the corresponding hexagonal web formed by the outer holes being designated with "X"). Insofar as the honeycomb pattern is evident from FIG. 6, only a truncated discussion of the honeycomb pattern is provided herein.

[0036] Although exemplary embodiments have been shown and described, it will be clear to those of ordinary skill in the art that a number of changes, modifications, or alterations to the disclosure as described may be made. All such changes, modifications, and alterations should therefore be seen as within the scope of the disclosure.

Claims

What is claimed is:

1. An optical photonic crystal fiber (PCF), comprising: a radiation-hardened (RH) core region comprising a first RH silica material; and a RH micro- structured cladding region surrounding the RH core region, the RH micro-structured cladding region comprising: a RH inner cladding region surrounding the RH core region, the RH inner cladding region comprising: an inner set of holes; and an inner RH silica web formed by the inner set of holes, the inner RH silica web comprising a second RH silica material, the second RH silica material being substantially identical in radiation hardness to the first RH silica material; and a RH outer cladding region surrounding the RH inner cladding region, the RH outer cladding region comprising: an outer set of holes; and an outer silica web formed by the outer set of holes, the outer silica web comprising an outer silica material, the outer silica material being substantially identical in radiation hardness to the second RH silica material.

2. An optical photonic crystal fiber (PCF), comprising: a radiation-hardened (RH) core region comprising a first RH silica material; and a micro- structured cladding region surrounding the RH core region, the microstructured cladding region comprising: a RH inner cladding region surrounding the RH core region, the RH inner cladding region comprising: an inner set of holes; and an inner RH silica web formed by the inner set of holes, the inner RH silica web comprising a second RH silica material, the second RH silica material being substantially identical in radiation hardness to the first RH silica material; and an outer cladding region surrounding the RH inner cladding region, the outer cladding region comprising:an outer set of holes; and an outer silica web formed by the outer set of holes, the outer silica web comprising an outer silica material, the outer silica material being different in radiation hardness than the second RH silica material.

3. An optical photonic crystal fiber (PCF), comprising: a radiation-hardened (RH) core region comprising a first RH silica material; and a micro- structured cladding region surrounding the RH core region, the microstructured cladding region comprising a second RH silica material, the second RH silica material being substantially identical in radiation hardness to the first RH silica material.

4. The optical PCF of claim 3, wherein the micro-structured cladding region comprises a RH inner cladding region surrounding the RH core region, the RH inner cladding region comprising: an inner set of holes; and an inner RH silica web formed by the inner set of holes, the inner RH silica web comprising the second RH silica material.

5. The optical PCF of claim 4, wherein the micro-structured cladding region further comprises an outer cladding region surrounding the RH inner cladding region, the outer cladding region comprising: an outer set of holes; and an outer silica web formed by the outer set of holes, the outer silica web comprising an outer silica material.

6. The optical PCF of claim 5, wherein the outer silica material is substantially identical in radiation hardness to the second RH silica material.

7. The optical PCF of claim 5, wherein the outer silica material is different in radiation hardness than the second RH silica material.

8. The optical fiber of claim 3, further comprising: an effective numerical aperture (NA) between the RH core region and the micro-structured cladding region, the effective NA being greater than approximately 0.18 (NA > 0.18).

9. The optical fiber of claim 3, further comprising: an effective numerical aperture (NA) between the RH core region and the micro-structured cladding region, the effective NA being greater than approximately 0.26 (NA > 0.26).

10. The optical fiber of claim 3: the first RH silica material comprising more than a trace level of Fluorine (F), the first RH silica material further comprising more than a trace level of Chlorine (Cl).

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