Patent Grant
11320594
The disclosure relates generally to the optical systems coupled to the optical fibers and more particularly to an optical system utilizing an optical fiber with an expanded Mode Field Diameter (“MFD”) coupled to an optical assembly.
A number of optical systems comprised of “free space” optical assemblies and/or optical assemblies for micro-optics applications, (e.g., optical collimators, wavelength division multiplexing assembly, etc.) provide an output signal that needs to be coupled to a standard optical fiber. For example, optical assemblies comprising optical elements such as mirrors, lenses, optical signal routers, or filters are used to route the optical signal from one part of the optical assembly to another. One end of the optical assembly may be connected to an optical source (e.g., laser diode) with the optical signal collected at the other end of the optical assembly and coupled to the optical fiber. As the optical signal is transported from one end of the optical assembly to the other, it interacts with multiple optical elements along the way.
A typical single mode optical fiber F has a very small core diameter and the optical signal collected or processed by the optical system needs to be provided to the optical fiber at the precise location where the fiber core FC is situated. Thus, the optical signal output beam provided from the optical assembly to the fiber needs to have a very small diameter intersect the fiber core with very high accuracy. Signal light that misses the fiber core results in the loss of optical system performance. For example, any misalignment in the optical elements results in a loss of the signal and thus negatively impacts the optical assembly performance. However, precise alignment requirements increase the assembly time and result in additional expense.
A key issue for cost sensitive applications is to efficiently and inexpensively couple optical systems and/or optical assemblies of multiple optical elements to an optical fiber. Therefore, there is a need for optical systems that provide efficient coupling between optical assemblies that include laser(s) or similar signal light sources and multiple optical elements to single mode fiber with low cost.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.
One embodiment of the disclosure relates to an optical system comprising:
According to some embodiments, an optical system comprises:
(I) a first Cl doped silica based core comprising:
(II) a silica based cladding surrounding the Cl doped silica based core;
In some embodiments the tapered core region has a taper profile, the tapered profile having: a linear taper, a parabolic taper, an exponential taper, or a Gaussian taper. In some embodiments tapered core region has an adiabatic taper and satisfies the following condition:
In some embodiments the tapered core region has a substantially adiabatic taper and satisfies the following condition
In some embodiments the maximum concentration of Cl in the core is between 1.1 wt. % and 5 wt. %. In some embodiments the core comprises at least one region with maximum Cl concentration between 1.4 wt. % and 5 wt. %.
In some embodiments 0.0%≤|Δc (at Dmax)|≤0.3%, relative to undoped silica, for example wherein 0.0%≤|Δc (at Dmax)|≤0.2%.
In some embodiments the length L2 is less than 3 cm. In some embodiments L2 is 0.05 mm to 30 mm, in some embodiments 0.1 mm to 30 mm, in some embodiments 0.5 mm to 20 mm, and in some embodiments 1 mm to 2 cm. In some embodiments the length L2 is less than 10 mm, for example L2 may be 0.1 mm to 10 mm.
According to at least some of embodiments the cladding is an F doped silica based cladding. According to some embodiments the maximum F concentration in the fiber cladding is 1 wt %. According to some embodiments the maximum F concentration in the fiber cladding is, for example, 0.05 wt % to 0.75% wt %.
According to some embodiments the Cl doped tapered core region has an adiabatic taper.
According to some embodiments the tapered core region has a taper induced loss of ≤0.2 dB at 1550 nm. According to some embodiments the tapered core region has a taper induced loss of ≤0.2 dB at 1310 nm. According to some embodiments the tapered core region has a taper induced loss of ≤0.1 dB at 1310 nm.
According to some embodiments the refractive index delta Δc at a location corresponding to the maximum diameter maximum Dmax is about −0.2% to about 0.8% relative to pure silica (i.e., −0.2%≤Δc (at Dmax)≤0.8%). According to some embodiments the refractive index delta Δc at a location corresponding to the maximum diameter maximum Dmax is ≤0.4% (i.e., Δc (at Dmax)≤0.4%, relative to undoped silica. According to some embodiments, |Δc (at Dmax)|≤0.2% relative to undoped (pure) silica. According to some embodiments, |Δc (at Dmax)|≤0.15% relative to undoped (pure) silica. According to other embodiments, |Δc (at Dmax)≤0.1%, relative to undoped (pure) silica. According to some embodiments, 0%≤Δc (at Dmax)|≤0.3%, relative to undoped silica. In some embodiments 0.0%≤|Δc (at Dmax)|≤0.2%, %, relative to undoped silica. According to some embodiments 0.15%≤[Δ0−Δc (at Dmax)]≤0.37%.
According to some embodiments the cladding is an F doped cladding and |Δc (at Dmax)|≤0.2% relative to pure silica. According to some embodiments the cladding is an F doped cladding, and |Δc (at Dmax)|≤0.15% relative to pure silica.
According to some embodiments the optical an optical system comprises:
(a) a light source,
(b) an optical assembly comprising a plurality of optical elements, said optical assembly coupled to the light source
(c) an optical fiber comprising a core with a tapered core region coupled to said optical assembly,
the tapered core region comprising Cl and having an outer diameter Dc that changes along the length L2 of the tapered core region and a maximum outer diameter Dmax such that 8 microns≤Dmax≤70 microns; the tapered core region further comprising a maximum core refractive index Δc that decreases along the length L2 of the tapered core region; said fiber further comprising a silica based cladding surrounding the core; and
(c) a single mode fiber optically coupled to the optical fiber comprising a tapered core region.
According to some embodiments optical assembly comprises at least 3 optical elements and said optical elements are chosen from a group comprising mirrors, lenses, optical signal router, filters or combination thereof. According to some embodiments the optical assembly comprises at least 5 optical elements and said optical elements are chosen from a group comprising mirrors, lenses, optical signal router, filters or combination thereof.
According to some embodiments the optical assembly comprises an optical collimator, and/or an optical collimator array unit; and/or optical filter device (e.g., multiport filter device), or a variable optical attenuator.
The embodiments described herein advantageously provide one or more of the following: low insertion loss; low manufacturing cost; improved yields; improved optical performance.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.
The thermally diffused expanded core method described herein uses the phenomenon of dopant diffusion in a heated fiber to expand the mode field diameter. One approach to the fusion connection of two fibers with different mode field diameters is to continuously or adiabatically vary the core diameters of one or both fibers so that the mode field diameters match at their boundaries. During the process of dopant diffusion, the core diameter becomes larger locally, and the relative refractive index difference becomes smaller locally compared to the ordinary fiber part. The result is a tapered core and thus tapered mode field diameter within the fiber. The embodiments of the method for making thermally diffused expanded core described herein provide one or more of the following advantages: it is effective for many applications, is relatively inexpensive, and can be accomplished relatively quickly and inexpensively.
More specifically, the optical fiber 10 includes a core 20, and a cladding (preferably with a constant outer diameter Dc) surrounding the core 20. The core 20 comprises two core regions: a constant core region 22 and tapered core region 24 situated adjacent to the constant core region. The term “constant outer diameter” as used herein refers to the fiber having an outer cladding diameter variation along the length of less than 3 microns.
The core region 22 (also referred to herein as the constant core segment, or constant core region 22) has a length L1, for example L1>10 cm (and preferably L1>12 cm, or L1>15 cm), a substantially constant maximum refractive index delta Δ0, and substantially constant outer diameter D0 along the length L1. The term “substantially constant”, as used herein means that the diameter D0 and the maximum refractive index delta Δ0 of the core region 22 may have small variations, i.e., variations within typical manufacturing tolerances. The core region 22 has a constant maximum refractive index. The term “constant maximum refractive index” herein refers to the fiber core having a maximum refractive index variation along the length of less than 10 percent. In some embodiments, the fiber core region 22 has a maximum refractive index variation along the length of less than 5 percent.
The tapered core region 24 of the fiber 10 has a length L2 of less than 5 cm, i.e., 0 cm<L2<5 cm and is situated adjacent to the first end face 12 of the fiber. In some embodiments 0.2 cm<L2<3 cm. The tapered core region 24 has a changing outer core diameter Dc along its length L2. In some embodiments, the fiber has an outer diameter variation along the length of less than 1 micron. In some embodiments, for example, 15 cm≤L1≤50 m and L2<3 cm. In some embodiments L2<2 cm, for example 2 mm to 1 cm, or 2 mm to 5 mm. The tapered core region 24 has a maximum refractive index delta Δc at each position z along the length L2 of the tapered region, such that Δc changes along the length L2 of the tapered core region 24.
The exemplary optical fiber 10 has a constant outer cladding diameter. The term “constant outer diameter” refers to herein the fiber having an outer diameter variation along the length of less than 3 microns.
The core 20 has a maximum outer core diameter Dmax in the tapered core region 24, and an outer diameter D0 in the constant region of the fiber—i.e., in the core region 22, for example, at or adjacent to the end face 14. Preferably the tapered core region 24 has an adiabatic taper—i.e., the diameter of the core Dc changes adiabatically. In other embodiments the taper profile (change in outer core diameter Dc within the tapered core region 24 along the length of the fiber) of the tapered core region 24 is linear, parabolic, or exponential. In some embodiments the taper is a Gaussian taper. The core 20 contains chlorine (Cl), and the maximum Cl concentration in the core is between 0.5 wt % and 5 wt %, for example 1 wt % to 5 wt %, or 1.1 wt % to 5 wt %, or 1.2 wt % to 5% wt %, or 1.3 wt % to 5 wt %.
In this embodiment the fiber core 20 is constructed such that: Dmax>D0. In some embodiments 5 μm≤D0≤11 μm, 8 μm≤Dmax≤50 μm, 0.005%≤Δ0≤1% (for example, 0.05%≤Δ0≤0.6%, or 0.2%≤Δ0≤1%), and the refractive index delta Δc at a location corresponding to the maximum diameter maximum Dmax is smaller than Δ0. In some embodiments Δc (at Dmax) is <Δ0, for example Δc (at Dmax)<0.940, or Δc (at Dmax)<0.8Δ0. In some embodiments |Δc (at Dmax) is <0.7Δ0, for example |Δc (at Dmax)| is <0.540, and in some embodiments |Δc (at Dmax)| is ≤0.2Δ0.
In some embodiments, Δ0−Δc (at Dmax)>0.05%. For example, according to some embodiments Δ0−Δc (at D1)≥0.08%, or Δ0−Δc (at Dmax)≥0.1%, or Δ0−Δc (at Dmax)≥0.12. In some embodiments, 0.35%≥Δ0−Δc (at Dmax)≥0.05%.
According to some embodiments, 10 microns/mm≤(Dmax−D0)/L2≤100 microns/mm. According to some embodiments, 14 microns/mm≤(Dmax−D0)/L2≤86 microns/mm. According to some embodiments, 14 microns/mm≤(Dmax−D0)/L2≤35 microns/mm.
The constant core region 22 has a mode field diameter of MFD0. In some embodiments, MFD0 is similar to that of standard single mode fiber, for example MFD0 is between 8 to 10 μm at 1310 nm, and between 9.5 to 11.5 μm at 1550 nm. In some fiber embodiments, MFD0 is smaller than standard single mode fiber, for example MFD0 is between 4 to 8 μm at 1310 nm, and between 5 to 9 μm at 1550 nm.
In the tapered core region 24 the mode field diameter MFD is expanded from the mode field diameter MFD0 of the constant core region 22 to a larger diameter. The fiber's maximum mode field diameter MFDMAX —i.e., MFD corresponding to Dmax, is, for example, between 8 μm and 50 μm at 1310 nm, and between 8.5 and 50 μm at 1550 nm. The maximum MFD may be, for example, at one end of the tapered core region 24, e.g., end face 12. In the embodiments described herein MFDMAX>MFD0, for example MFDMAX≥1.5 MFD0, or MFDMAX≥2 MFD0. In some embodiments, for example, 15 MFD0≥MFDMAX≥1.5 MFD0; and in some embodiments 15 MFD0≥MFDMAX≥2 MFD0.
As shown in
As shown in
The core diameter (Dmax) of the tapered core region 24 at the end face 12 of the fiber 10 is preferably the same, substantially the same, or larger than the laser beam diameter incident on the end face 12 of optical fiber 10. Having a large core diameter (Dmax) at the end face 12 of the fiber 10 minimizes coupling loses between the optical assembly 200 and the optical fiber 10 and provides efficient coupling between the optical assembly 200 and the optical fiber 10. Having a large core diameter (Dmax) at the end face 12 of the fiber 10 offers large (relaxed) spatial alignment tolerances, minimizing coupling loses between the optical assembly 200 and the optical fiber 10.
The tapered core region 24 of the optical fiber 10 facilitates coupling a laser source 50 to the optical assembly 200 as shown, for example, in the embodiment of
The fiber 10 is designed to have numerical aperture (NA) and MFD that match those of the light source appearing in front of the fiber 10. Matched MFDs means that the mode field diameter MFD of the optical fiber's end face facing the light source appearing immediately in front of it (e.g., fiber end face that faces optical component 60 or 60′ shown in
Optical fibers with chlorine as the core dopant are preferable for making mode field expanded optical fibers 10 because of the high chlorine diffusivity at high temperatures, for example, at temperatures greater than 1700° C., and preferably greater than 1800° C. (the higher the temperatures, the higher chlorine diffusivity). Mode field expansion can be achieved using a heat source 250, such as a heater, laser, splicer, plasma, flame, induction or combination thereof. This is shown, schematically, in
Preferably, the core diameter taper in region 24 is designed to have an adiabatic transition to minimize the light propagation loss through the taper. That is, the mode field conversion occurs in the wider portion of the core 20 (in the tapered core region 24), and the adiabatic shape or substantially adiabatic shape of the core region 24 provides nearly lossless transmission of light. In some embodiments described herein the light loss within the tapered core region 24 is less than 1 dB, and in some embodiments less than 0.5 dB, or even 0.2 dB or less. Taper loss can be measured by standard techniques in the industry such as launching light into the core at the input end of an optical fiber and measuring light coming out of the core at the end of the fiber using a power meter and comparing it to a fiber having a taper at the end of the fiber. The change on the core diameter Dc within the adiabatic region allows the first optical mode (LP01) to be confined in the tapered core region 24, without conversion to higher-order modes, or without radiating out through the cladding, and the length of the adiabatic region (taper length L2) should be long enough to achieve that purpose. Preferably, the adiabatic transition is such that that the change in core diameter satisfies the following condition:
where Dc is the core diameter in the core region 24 at location z within the length L2, λ is the transmission wavelength, neff is the effective index of the fundamental mode LP01, and ncl is the refractive index of the cladding at the wavelength λ.
In some embodiments the core taper (core radius shape) is approximately adiabatic (also referred to herein as a substantially adiabatic taper), such that that the change in core diameter satisfies the following condition
According to the embodiments described herein λ=1310 nm. However, in other embodiments λ may be 1550 nm or 980 nm.
Process for Making Tapered Core Fibers 10
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.
According to some embodiments, a method of forming a tapered core in a glass optical fiber comprising a chlorine doped core surrounded by a cladding comprises the step of applying heat for a cumulative duration of less than 60 seconds (e.g., 50 seconds or less, 45 seconds or less, 30 seconds or less) to a region of the optical fiber having a mode field diameter MFD0, thereby diffusing chlorine from the core of the optical fiber into the cladding of the optical fiber, and expanding the mode field diameter such that the maximum mode field diameter MFDMAX of the fiber (i.e., MFD corresponding to Dmax) is greater than MFD0, for example MFDMAX≥1.5 MFD0, or MFDMAX≥2 MFD0. In some embodiments, for example, 15 MFD0≥MFDMAX≥1.5 MFD0; and in some embodiments 15 MFD0≥MFDMAX≥2 MFD0. In some embodiments, the maximum (expanded) mode field diameter MFDMAX is, for example, between 8 μm and 50 μm m at 1310 nm, and between 8.5 μm and 50 μm m at 1550 nm.
According to some embodiments, a method of forming a tapered core in a glass optical fiber comprising a chlorine doped core surrounded by a cladding comprises the step of applying heat for a cumulative duration of less than 60 seconds to a region of the optical fiber, thereby diffusing chlorine from the core of the optical fiber into the cladding of the optical fiber, and expanding the mode field diameter MFD by at least 3 microns. According to some embodiments a method of forming a tapered core in a glass optical fiber comprises: (i) applying heat for a cumulative duration of less than 60 seconds to a region of the optical fiber, thereby diffusing chlorine from the core of the optical fiber into the cladding of the optical fiber, and expanding the mode field diameter MFD by at least 3 microns; and (ii) cleaving the optical fiber in the region of the fiber where the mode field MFD was expanded by at least 3 microns.
More specifically, a tapered core profile (tapered core region 24) can be made by thermal diffusion of the core dopants to the cladding and/or cladding dopants towards or into the fiber core.
In some embodiments the heat source (e.g., heating element 250) may be placed away from the edge of the fiber 10A—i.e., somewhere adjacent to or around the middle of the fiber 10A. In one embodiment, the optical fiber with a chlorine doped core is held by a holding fixture and the heating element 250 surrounds the fiber 10A in a middle region of the fiber. Preferably the heat source heating element 250 is evenly distributed around the fiber to create a radially symmetric dopant diffusion profile. In this embodiment, the fiber end region of the fiber 10A is heated by a heating element to a desired temperature (fiber dopant diffusion temperature Td), for example 1500° C.≤Td<2200° C. and the fiber is moved relative to the heat source (or the heat source is moved relative to the fiber, to expand the mode field diameter of the fiber core (through dopant diffusion), through dopant diffusion, in a middle region of the fiber. In some embodiments 1500° C.≤Td<2100° C., and in some embodiments 1700° C.≤Td<2100° C., for example 1500° C.≤Td<2000° C., or 1700° C.≤Td<2000° C.
According to some embodiments a method of forming a low loss taper in a glass optical fiber comprising greater than 0.5 wt % chlorine in a core, the core having an initial mode field diameter MFD (at 1550 nm) and being surrounded by a cladding, comprises the steps of:
According to some embodiments, a method of forming an adiabatic taper or a substantially adiabatic taper in an optical fiber comprises the steps of:
According to another embodiment, a method of forming an adiabatic taper or a substantially adiabatic taper in an optical fiber, the method comprises the steps of: cleaving one end of an optical fiber having a small MFD (e.g., MFD≥5 μm, for example between 5 μm and ≤11 μm, at a wavelength of 1550 nm) and Cl doped core; applying heat to a segment of fiber with a predetermined length from the cleaved end by moving the fiber segment through the heat source;
controlling fiber moving velocity profile to expand the MFD adiabatically from inner end of the segment towards the cleaved end, wherein the step of applying heat is performed at a temperature Td for a time t that is less than 1 minute total (cumulative) in duration. Preferably, according to some embodiments 1500° C.≤Td<2200° C. According to some embodiments 1600° C.≤Td<2100° C., and even more preferably 1800° C.≤Td<2000° C. to facilitate the optimum diffusion of dopants within the fiber core while minimizing or avoiding undesirable fiber deformations. According to some embodiments t is 45 seconds or less, or for example, 30 seconds or less, 20 seconds or less, 10 seconds or less. For example, in some embodiments, 1 second≤t≤45 seconds, 1 second≤t≤30 seconds, or 1 second≤t≤20 seconds, or even 1 second≤t≤10 seconds. According to some embodiments t is 5 to 45 sec, or 5 to 45 sec, or 5 to 30 sec.
According to another embodiment, a method of forming an adiabatic taper or a substantially adiabatic taper in an optical fiber having Cl doped core, the method comprises the steps of:
In some embodiments the application of heat is provided for the time t that is 45 seconds or less, 30 seconds or less, 20 seconds or less, 10 seconds or less, or 1 to 10 seconds.
Preferably, according to some embodiments 1500° C.≤Td<2200° C. According to some embodiments 1500° C.≤Td<2100° C., and preferably 1600° C.≤Td<2100° C., 1700° C.≤Td<2000° C., or 1800° C.≤Td<2000° C. to facilitate the optimum diffusion of dopants within the fiber core within a minimum amount of time to minimize or avoid undesirable fiber deformations.
For example, a highly localized high temperature heat source, such as an arc fusion splicer (e.g., model no. FSU 975 manufactured by Ericsson Incorporated), a tungsten filament, or a CO2 laser can be used to expand the mode field diameter of the optical fiber 10 and thus form the tapered core region 24 (e.g., adiabatic taper) in the Cl doped fiber core. In one embodiment, the fiber with a Cl doped core (0.3%≤Δ0≤2.5%, Cl concentration about 0.2 wt % to about 2.5 wt %) and silica based cladding (e.g., F doped silica cladding) is stripped of its primary coating over a portion of its length exposing a small diameter core 20 bounded by a cladding 40 and then cleaved. Another fiber 10′ (with a larger mode field diameter) is then stripped of its coating, cleaved, and the two fibers (not shown) are in the fusion splicer such that the two cleaved ends face each other and the cores are in proper alignment. The arc is applied such that so that the larger portion of the smaller Cl doped fiber 10 lies the in arc region or heat region than that of the large mode field diameter fiber. That is, in this embodiment the arc region is offset from the splice seam, rather than being directly over the splice seam 50. The two fibers 10 and 10′ are initially fused at splice seam by delivery of an initial arc discharge current, for example, of approximately 10 to 20 mA for an arc time of approximately 2 seconds. Additional arc discharge current is intermittently applied over the arc region to maintain the fiber temperature at the temperature Td, in order to diffuse Cl, within the core of small mode field diameter fiber 10 residing in the arc region, to create a tapered region 24. In the exemplary embodiments described herein fiber temperature is maintained at the temperature Td over a total (or cumulative) time of less than 1 minute. In some embodiments the optical fiber is subjected to temperature Td for a total of 5 sec to 45 sec. The resultant fused fiber is then cleaved, resulting in fiber 10 with Cl doped core that has a tapered region similar to that shown in
Various embodiments will be further clarified by the following examples. Table 1 discloses fiber core parameters before the fiber is subjected to a temperature Td, while Table 2 shows fiber core parameters of the tapered core region 24, after the taper is created by subjecting the fiber to the temperature Td for 1 sec to 45 seconds.
The optical fibers 10 of Table 2 exhibit taper induced loss of ≤0.2 dB at 1550 nm. For example, at least in some embodiments of fiber 10 the tapered region 24 of these fibers exhibits a taper induced loss of ≤0.2 dB at 1310 nm. For example, in at least in some embodiments of fiber 10 the tapered region 24 of these fibers exhibit a taper induced loss of ≤0.1 dB at 1310 nm.
Fiber Designs for Mode Field Expansion
To make a tapered core region adjacent to one the end of an optical fiber jumper (such as fiber 10) the fiber's core refractive index in this region needs to be decreased gradually and the core diameter in this region needs to be increased gradually. This can be achieved by core dopant diffusion by heating the fiber end.
Although the Ge dopant that is used in most single mode fibers can diffuse when the fiber is heated, creating a tapered core region, in such fibers at temperatures below 2200 C° the diffusion required for adequate mode field expansion will take very long time (many minutes or hours) because the diffusion coefficient of Ge is too low, making the process inefficient and expensive. If, however, a Ge doped fiber is subjected to a relatively fast heating time (1-2 min), the fiber needs to be heated to very high temperatures—i.e., above 2200° C. or above 2300° C., or even greater (the faster heating time, the higher the temperature), which creates undesirable fiber deformation(s), for example it creates fiber bends and/or significantly changes the outer diameter of the fiber.
Applicants realized that in order to increase the diffusion speed, without significantly deforming the fiber by heating it to very high temperatures, a fiber with Cl doped core having more than 0.5 wt % Cl should be used instead of typical fiber with Ge doped core. The exemplary fiber embodiments discussed herein thus utilize a Cl doped core, because Cl can diffuse easier and faster than Ge, at lower temperatures. Preferably, according to at least some embodiments the fiber utilizes a F doped cladding, because as Cl diffuses out toward the outer diameter of the fiber, the F simultaneously diffuses inward, toward the center of the fiber, and the two dopants (Cl and F) work synergistically to facilitate the fast creation of the tapered core region at smaller temperature Td, without causing fiber deformation (i.e., no unwanted bends, or significant changes in the outer diameter of the fiber).
At the Td temperatures where Td is below 2100° C., (e.g., greater than 1500° C. and less than 2100° C., or not greater than 2000° C., for example 1500° C. to 2000° C., or 1600° C. to 2000° C., or 1700° C. to 2000° C.), Cl dopant within the fiber core diffuses through silica much faster than Ge in the comparative fibers.
When the fiber is subjected to the temperature Td (e.g., 1500° C.≤Td≤2100° C.), Cl in the fiber core starts to diffuse out of the core towards and into the cladding. The diffusion of the Cl lowers the maximum refractive index of the core and simultaneously increases the core outer diameter. In the embodiments where the cladding 40 comprises fluorine, when the fiber is subjected to the temperature Td the fluorine from the cladding also starts to diffuse into from the cladding into the core, further lowering the refractive index of the core.
As can be seen from results presented in
Similarly,
We discovered that when the optical fiber has a Cl doped core with Cl concentration of at least 0.5 wt %, we can create adiabatic tapers in less than 1 minute (e.g., 1 sec to 45 sec, e.g., 5 sec to 45 sec, 10 sec to 45 sec, 15 sec to 45 sec, or 5 sec to 30 sec, or 15 sec to 45 sec), at temperatures between about 1500° C., and about 2100° C., without creating undesirable deformation(s). Preferable temperature range is 1700° C. to 2100° C., and more preferably 1700° C. to 2000° C.
The optical fibers 10 described herein are suitable for efficient coupling of optical signals to an optical assembly. The optical assembly may comprise multiple optical components (e.g., 3, 4, 5, or more) that are spatially separated from one another. According to at least some embodiments disclosed herein, the optical fiber 10 includes a Cl doped tapered core region 24 with a changing outer diameter and changing maximum core refractive index to provide improved coupling at wavelengths of interest to optical assemblies. The optical assemblies may comprise, for example, an optical collimator, an optical collimator array unit, an optical filter device (e.g., multiport filter device), a wavelength-division multiplexing unit, or variable attenuator. The optical assembly may operate, for example, at an operating wavelength λ that is at or near 1310 nm.
The present disclosure extends to optical systems (e.g., an integrated systems) 500 that incorporate the optical fibers 10. In one embodiment, the optical system 500 includes an optical signal source (for example a laser light source 50, e. g., a laser or LED), an optical assembly 200, and the optical fiber 10. In one embodiment, the light source 50 operates at a wavelength at or near 1310 nm (e.g., in the range from 1250 nm to 1350 nm, or in the range from 1260 nm to 1325 nm, or in the range from 1275 nm to 1325 nm, or in the range from 1290 nm to 1320 nm, or in the range from 1200 nm to 1400 nm). In another embodiment, the light source 50 operates at a wavelength at or near 1550 nm (e.g., in the range from 1500 nm to 1580 nm).
The optical assembly 200 may be coupled to the optical fiber 10 with a tapered core 24) for exchanging optical signals between the optical assembly and another (optional) optical fiber 105. The system 500 includes an optical fiber 10 of the type disclosed herein. In some embodiments the optical fiber 105 is coupled directly to optical assembly 200 through the optical fiber 10. The optical assembly 200 of the optical system 500 may be devices or components such as modulators, detectors, multiplexers, demultiplexers, etc. An exemplary embodiment of a wavelength division multiplexer optical assembly 200 coupled to optical fibers 10 is shown in
The large mode field diameters provided by the optical fibers 10 described herein reduce coupling losses between the optical fibers and optical assemblies 200.
According to some embodiments, system 500 comprises an optical assembly 200 and at least one optical fiber 10, but does not include the optical fiber 105. In such embodiments the length of the optical fiber 10 is longer, because the length L1 of the fiber 10 serves the function of the fiber 105, and the core portion with the outer diameter D0 in the core region 22 serves same the function as the core 106 of the optical fiber 105.
Referring again to
an optical assembly 200 optically coupled to at least one optical fiber 10, the optical fiber comprising:
According to one embodiment an optical system 500 comprises:
an optical assembly 200 comprising a first optical surface and a rear optical surface, said optical assembly 200 comprising at least three optical elements E1-E3,
an optical fiber 10 comprising an end face 12 and an adjacent core portion with a field expanded region optically coupled to the rear optical surface of the optical assembly, the optical fiber 10 comprising a core region doped with chlorine in a concentration greater than 0.5 wt %, and wherein the mode field expanded region is less than 5 cm in length, and the optical fiber 10 having, at an operating wavelength λ, a mode field diameter at the fiber end coupled to the optical assembly that is a least 20% greater than the optical fiber mode field diameter at other end of the optical fiber; and
an optical signal source 50 coupled to first optical surface of the optical assembly, such that the optical signal provided by the optical signal source 50 is routed along an optical path formed by the optical assembly 200 to the fiber end face 12 of the optical fiber 10.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C § 119 of U.S. Provisional Application Ser. No. 62/896,106 filed Sep. 5, 2019 the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Name | Date | Kind |
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| 10429589 | Bookbinder | Oct 2019 | B2 |
| 20180224607 | Bookbinder | Aug 2018 | A1 |
| 20210072462 | Gui | Mar 2021 | A1 |
| Entry |
|---|
| Shiraishi et al., “Beam expanding fiber using thermal diffusion of the dopant”, Journal of Lightwave Tech, vol. 8, No. 8, 1990, pp. 1151-1161. |
| Number | Date | Country | |
|---|---|---|---|
| 20210072462 A1 | Mar 2021 | US |
| Number | Date | Country | |
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| 62896106 | Sep 2019 | US |
