Optical system comprising a polarization controller and method of operation

Abstract

An optical system comprising: (i) a light source, (ii) at least one polarization controller positioned downstream of the light source and comprising: an optical fiber and a carrier surrounding the optical fiber, the carrier comprising an off-center through-hole having at least one collapsed region, such that the optical fiber is positioned within the through-hole and contacts the at least one collapsed region of the through-hole, (iii) at least one optical fiber coupled to the polarization controller; and (iv) at least one optical detector positioned downstream of the at least one optical fiber.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Serial No. 63 / 059604, filed July 31, 2020, pursuant to 35 USC §119, the contents of which are incorporated herein by reference in their entirety. Background Technology

[0003] This disclosure generally relates to polarization controllers, and more specifically to dynamic polarization controllers utilizing a carrier having an offset via and an optical fiber positioned therein, optical systems including such controllers, and methods of operating thereof.

[0004] Current polarization controllers utilize stress-induced birefringence to rotate the initial polarization state (SOP) to the desired output SOP. However, such polarization controllers are typically lossy, unreliable, and lead to long-term fiber fatigue and breakage. Furthermore, such polarization controllers either (i) apply external force directly to the fiber (e.g., directly squeeze the fiber before rotation) to induce birefringence, which typically causes considerable damage to the fiber; or (ii) involve fabricating a polarization controller that includes a planar waveguide and utilizes electro-optic techniques to rotate the polarization, thereby increasing power consumption and introducing losses due to coupling and activation.

[0005] No references cited herein are acknowledged as prior art. The applicant expressly reserves the right to question the accuracy and relevance of any cited documents. Summary of the Invention

[0006] One embodiment of this disclosure relates to an optical system, including:

[0007] (i) Light source,

[0008] (ii) At least one polarization controller, the at least one polarization controller being positioned downstream of the light source and

[0009] include;

[0010] (a) Optical fiber,

[0011] (b) A carrier surrounding an optical fiber, the carrier comprising an eccentric through-hole having at least one collapsed region, such that the optical fiber is positioned within the through-hole and in contact with the at least one collapsed region of the through-hole.

[0012] (iii) At least one optical fiber coupled to the polarization controller; and

[0013] (iv) At least one optical detector located downstream of at least one optical fiber.

[0014] One embodiment of the present disclosure relates to a polarization controller, which includes:

[0015] (i) An optical fiber,

[0016] (ii) A carrier surrounding the optical fiber, the carrier including an eccentric through-hole having at least one collapsed region, such that the optical fiber is positioned within the through-hole and in contact with the at least one collapsed region of the through-hole, and the collapsed region applies pressure to the optical fiber.

[0017] According to at least one embodiment, the carrier is configured such that when a force is applied to the carrier at the location of the collapsed region, the pressure on the optical fiber changes and the optical signal propagating through the optical fiber undergoes a polarization change.

[0018] According to some embodiments, the carrier is positioned within a plastic (e.g., nylon) tube.

[0019] According to at least one embodiment, the through-hole has a symmetry axis located at a distance D from the center of the carrier, such that 0.25 < D / R < 0.95, where R is the half-width of the cross-section of the carrier.

[0020] One embodiment of the present disclosure relates to a polarization controller, which includes:

[0021] (i) An optical fiber,

[0022] (ii) A carrier surrounding the optical fiber, the carrier including glass and an eccentric through-hole having at least one collapsed region, such that the optical fiber is positioned within the through-hole and at least in contact with the collapsed region of the through-hole, and the at least one collapsed region applies pressure to the optical fiber.

[0023] According to some embodiments, the carrier includes glass and an eccentric through-hole having a plurality of collapsed regions.

[0024] According to some embodiments, the carrier has a circular cross-section, and the center of the through-hole is located at a distance D from the center of the carrier, such that 0.25 < D / R < 0.95, where R is the radius of the cross-section of the carrier.

[0025] According to some embodiments, the carrier is a glass tube. According to some embodiments, the optical fiber is a single-mode optical fiber, a multi-mode optical fiber, or a polarization-maintaining optical fiber with a glass cladding; and

[0026] The carrier is a fluorine- and / or boron-doped glass tube. According to some embodiments, the glass tube is coated with titanium.

[0027] According to some embodiments, the carrier is a fluorine- and / or boron-doped glass tube, the through-hole has a cross-section of 0.5 μm to 275 μm and a symmetry axis located at a distance D from the center of the carrier, such that 0.25 < D / R < 0.95, where R is the half-width of the cross-section of the carrier.

[0028] According to some embodiments, the carrier has a circular cross-section, and the center of the through-hole is located at a distance D from the center of the carrier such that 0.25 < D / R < 0.95, where R is the radius of the cross-section of the carrier. Preferably, 0.65 < D / R < 0.85. According to some embodiments, 0.7 < D / R < 0.8.

[0029] According to some embodiments, the collapsed region contacts the optical fiber. According to some embodiments, at least a portion of the optical fiber positioned within the through-hole includes an outer glass surface that is fused to the collapsed region of the through-hole. According to some embodiments, the collapsed region contacts the fiber cladding and is fused to the cladding.

[0030] According to some embodiments, the carrier is plastic. According to some embodiments, the carrier is a plastic (i.e., polymer) tube. According to some embodiments, the carrier is a fluorine- or boron-doped plastic tube, and the through-hole of the carrier has a cross-section of 0.5 μm < d 孔 –d 光纤 < 400 μm (and preferably, 0.5 μm to 275 μm) and a symmetry axis located at a distance D from the center of the carrier such that 0.25 < D / R < 0.95, where R is the half-width of the cross-section of the carrier. More preferably, 5 μm < d 孔 –d 光纤 < 275 μm.

[0031] According to some embodiments, the collapsed region contacts the optical fiber. According to some embodiments, at least a portion of the optical fiber positioned within the through-hole includes a plastic cladding that is fused to the collapsed region of the through-hole of the plastic carrier.

[0032] One embodiment of the present disclosure relates to a polarization controller that includes:

[0033] (i) at least two optical fibers; and

[0034] (ii) a carrier surrounding the optical fibers, the carrier including glass and an eccentric through-hole having at least one collapsed region such that the optical fibers are positioned within the through-hole and contact at least one collapsed region of the through-hole, and

[0035] at least one collapsed region applies pressure to the optical fibers.

[0036] One embodiment of the present disclosure relates to a polarization controller that includes:

[0037] (i) an optical fiber, and

[0038] (ii) a carrier surrounding the optical fiber, the carrier including an eccentric through-hole having a plurality of collapsed regions such that the optical fiber is positioned within the through-hole and contacts at least the collapsed regions of the through-hole, and the plurality of collapsed regions apply pressure to the optical fiber.

[0039] Additional embodiments of this disclosure relate to a method for manufacturing a polarization controller, the method comprising:

[0040] (i) A polarization carrier comprising an eccentrically positioned through-hole having at least one collapsed region surrounding an optical fiber at at least one location, and

[0041] (ii) Apply force to the carrier.

[0042] According to some embodiments, the collapsed region is curved.

[0043] Additional embodiments of this disclosure relate to a method for manufacturing a polarization controller, the method comprising:

[0044] (i) providing a carrier with an offset hole; (ii) inserting an optical fiber through the hole; and (iii) collapsing the carrier in at least one region to form a collapsed region around the optical fiber, and splicing the interface of the optical fiber to the carrier at the collapsed region.

[0045] According to one embodiment, the method includes collapsing a carrier in multiple regions to form multiple collapsed regions around an optical fiber, and splicing an interface of the optical fiber to the carrier at the multiple collapsed regions. According to some embodiments, the length of the collapsed regions is at least 0.5 cm, and preferably at least 1 cm. For example, the length of the collapsed regions (multiple regions) can be from 2 cm to 15 cm, or from 2 cm to 6 cm.

[0046] According to some embodiments, the step of collapsing the carrier to form a collapsed region around the optical fiber includes heating at least a portion of the carrier to above 1000°C. According to some embodiments, the step of collapsing the carrier in at least one region to form a collapsed region around the optical fiber includes applying a vacuum to the vias of the carrier.

[0047] According to some embodiments, the step of collapsing the carrier in at least one region to form a collapsed region around the optical fiber includes placing the carrier into a heater such that the carrier is positioned asymmetrically within the heater.

[0048] According to some embodiments, the side of the carrier closest to the through hole is closer to the flame than the side of the carrier positioned further away from the through hole.

[0049] According to some embodiments, a method for controlling the polarization of light propagating through an optical fiber includes: (i) supporting a polarization controller with an eccentric through-hole having at least one partially collapsed region surrounding the optical fiber at at least one location, and (ii) applying a force to the polarization controller at another location corresponding to the partially collapsed region.

[0050] According to some embodiments, a method for controlling the polarization of light propagating through an optical fiber includes:

[0051] (i) supporting a polarization controller with an eccentric through-hole having at least one partially collapsed region around an optical fiber at at least one location, and (ii) applying a force to the polarization controller at another location corresponding to the partially collapsed region.

[0052] The polarization controller described in this paper advantageously provides high-precision polarization control, reliability, and low loss. This polarization controller can be operated relatively inexpensively and can be used in both classical and quantum optics applications. The offset position of the optical fiber relative to the center of the carrier results in increased birefringence due to internal stress in the fiber, and advantageously rotates the polarization of the optical signal propagating through the fiber.

[0053] The offset position of the optical fiber within the carrier allows for greater polarization control sensitivity, and a polarization controller utilizing a carrier with an optical fiber offset relative to the center of the carrier offers the following advantages:

[0054] 1.) Lower power consumption

[0055] 2.) Higher precision

[0056] 3.) Due to its high reliability and minimal fiber optic damage,

[0057] 4.) Lower optical loss compared to polarization controllers using planar electro-optic systems.

[0058] Additional features and advantages will be set forth in the following detailed description, and will be apparent in part to those skilled in the art, or will be recognized by practicing the embodiments as described in the written description and as described in the claims herein and the accompanying drawings.

[0059] It should be understood that the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework for understanding the nature and characteristics of the claims.

[0060] Various accompanying drawings are included to provide further understanding and are incorporated in and form a part of this specification. The drawings illustrate one or more embodiments and, together with the description, serve to explain the principles and operation of the embodiments. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of one embodiment of a quantum key distribution system;

[0062] Figure 2 This is a side view of one embodiment of a polarization controller including multiple collapsed regions surrounding the stripped optical fiber;

[0063] Figure 3An exemplary polarization controller is depicted as rotating an arbitrary input polarization state (SOP), shown as labeled M1, to another polarization state M2 for output;

[0064] Figure 4 It is a cross-sectional view of the geometry of the carrier, borehole, and flame;

[0065] Figure 5 This is a cross-sectional view of a polarization controller according to an exemplary embodiment;

[0066] Figure 6 It is a cross-sectional image of simulated compression / tension along the glass rod when an external force is applied.

[0067] Figure 7 The simulation shows the force applied along the length of the polarization controller when both ends of the polarization controller are fixed.

[0068] Figure 8 The simulation shows the applied forces and stresses experienced by the polarization controller when it is supported at one end;

[0069] Figure 9A and Figure 9B The polarization rotation of two embodiments of the polarization controller is shown when the polarization controller is subjected to an applied external force of 0-100 gF.

[0070] Figure 10 The good repeatability of the polarization controller during testing was demonstrated;

[0071] Figure 11 The measured loss of the polarization controller provided by the backscattering OTDR measurement is shown;

[0072] Figure 12 An embodiment of a polarization controller is shown, wherein the optimal positioning for the borehole center is when D / R = 0.7072. Detailed Implementation

[0073] One embodiment of this disclosure relates to a polarization controller 100, the polarization controller 100 comprising:

[0074] (i) Fiber optic cable 120,

[0075] (ii) A carrier 150 surrounding the optical fiber 120, the carrier 150 including an eccentric through-hole 160 having at least one collapsed region 170, such that the optical fiber 120 is positioned within the through-hole and in contact with the at least collapsed region 170 of the through-hole, and the collapsed region 170 applies pressure to the optical fiber 120.

[0076] According to at least one embodiment, the carrier 150 is configured such that when a force is applied to the carrier 150 at the location of the collapse region 170, the pressure on the optical fiber 120 changes and the optical signal propagating through the optical fiber 120 undergoes a polarization change (i.e., a change in polarization state).

[0077] According to some embodiments, an optical system includes:

[0078] (i) Light source,

[0079] (ii) at least one polarization controller 100, the polarization controller 100 comprising;

[0080] A carrier 150 surrounding the optical fiber includes an eccentric through-hole having at least one collapsed region, such that the optical fiber is positioned within the through-hole and in contact with the at least one collapsed region of the through-hole.

[0081] At least one optical fiber coupled to the polarization controller;

[0082] (iii) and at least one optical detector located downstream of at least one optical fiber.

[0083] According to some embodiments, the polarization controller is a polarization state generator.

[0084] According to some embodiments, the optical system is a quantum key distribution (QKD) system, wherein the quantum key distribution (QKD) system includes at least two polarization controllers, a quantum channel including optical fibers located at the two polarization controllers, and at least two optical detectors.

[0085] Figure 1 An exemplary optical system utilizing a polarization controller 100 is schematically illustrated. In this embodiment, the optical system is a quantum key distribution (QKD) system 10 that utilizes the polarization controller 100 as a polarization state generator. In this embodiment, the sender (Alice) transmits a signal to the receiver (Bob). The polarization state generator (e.g., the polarization controller 100) changes the polarization of the optical signal received from the signal source to a specific state that can be linearly (parallel or perpendicular) or circularly (left or right). At the receiver (used by Bob), the polarization controller 100 again shifts or converts the polarization state of the received signal to a specified state (e.g., linear or circular).

[0086] More specifically, Figure 1The exemplary quantum key distribution system 10 is shown to include: an optical signal source 20 coupled to a polarization state generator PGS (30) (which in this embodiment is also a polarization controller 100); a quantum channel 40 for quantum communication coupled to the polarization controller 100; a second polarization controller 100 (PSC) coupled to and receiving signals from the quantum channel 40; a polarization beamsplitter 50 coupled to and receiving signals from the quantum channel 40; and two detectors (D1, D2) 60 configured and positioned to receive the optical signals provided by the polarization beamsplitter 50. In this embodiment, the beamsplitter 40 is a polarization beamsplitter and splits the optical signal into two components with different polarizations. The quantum channel 40 includes an optical fiber 40A that receives (multiple) optical signals from the first polarization controller 100 (e.g., PGS 30) and provides (multiple) optical signals to the second polarization controller. The first polarization controller changes the polarization state of the optical signal received from the optical signal source 20 and provides that polarization state to the quantum channel 40. Two detectors 60 enable detection of two optical polarizations, allowing one to obtain the quantum key. Preferably, the polarization controller 100 utilized by the quantum key distribution system 10 includes two, and preferably three, collapsed regions 170. The terms "communication," "connection," and "coupling" can refer to the relationship between components that supports the flow of signals between components.

[0087] According to some exemplary embodiments described herein, the polarization controller 100 includes:

[0088] (i) Fiber 120, and

[0089] (ii) A carrier 150 surrounding the optical fiber 120, the carrier 150 including an eccentric through-hole 160 having a plurality of collapsed regions 170, such that the optical fiber 120 is positioned within the through-hole 160 and in contact with at least some of the collapsed regions 170 of the through-hole 160.

[0090] Various embodiments will be further illustrated through the following examples.

[0091] According to one embodiment, the polarization controller 100 includes a carrier 150 (e.g., a rod 150') comprising a partially collapsed through-hole 160' with an off-center center, and a stripped portion (i.e., the uncoated portion of the fiber) of an optical fiber 120 positioned within the off-center through-hole 160'. Because the fiber is positioned inside the carrier, no external force is directly applied to the fiber. The fiber is not directly compressed, and external forces applied to the carrier(s) 150 cause stress along the length of the fiber. The off-center position of the fiber 120 within the carrier 150 advantageously provides the fiber with high sensitivity to polarization rotation. (The farther the center of the hole is radially positioned from the centerline of the carrier, the greater the stress on the carrier for a given force or bending, and therefore the greater the birefringence exhibited by the fiber core.)

[0092] Fiber 120 may be, for example, a stripped single-mode fiber. According to some embodiments, one end of fiber 120 may be stripped from its coating (i.e., exposed), and the stripped end may be inserted into a via 160. The via 160 then collapses around the stripped portion of the fiber (e.g., around the glass cladding) and is fused to the exposed fiber (i.e., to the fiber cladding). The stripped portion of fiber 120 exiting the via can then be coupled (e.g., fused) to another fiber (e.g., a pigtail).

[0093] In another embodiment, a portion of the optical fiber 120 is stripped of its coating 121, such that the stripped portion of the optical fiber is positioned between coated segments of the optical fiber. Then, a coated segment 121A of the optical fiber 120 is inserted into a via 160, and the optical fiber 120 passes through the via 160, such that the coated segment of the optical fiber exits the via, and the stripped segment of the optical fiber 120 is positioned within the via. The via 160 then collapses around the stripped portion 120' of the optical fiber 120 (e.g., around the cladding) and is fused to the optical fiber cladding, thereby forming the polarization controller 100.

[0094] The rod 150' may be composed of glass, such as pure quartz glass, doped glass, coated glass, and / or coated-doped glass. In this embodiment, the optical fiber 120 has a glass cladding. The through-hole 160 may be, for example, an eccentrically drilled hole. The optical fiber 120 is positioned at an offset location relative to the center of the carrier 150 (e.g., rod 150'). The carrier 150 (e.g., rod 150') collapses around the optical fiber at high temperatures (e.g., 1000°C-2000°C for a glass rod), as described below. The collapse region 170 may be of any length, but the longer the collapse region, the more birefringence the propagating light encounters, and the greater the polarization rotation. According to some embodiments, the optical fiber 120 has a glass outer surface 122 with a stripped portion and a surface corresponding to the glass cladding. The collapse region 170 may completely or partially surround the stripped portion of the optical fiber 120. As described above, the collapse region 170 surrounds the optical fiber and is fused to it. In these embodiments, the interface between the optical fiber 120 and the carrier at the collapsed region is a fusion splice.

[0095] According to another exemplary embodiment, the optical fiber 120 has a plastic cladding, and the carrier 150 is plastic. A through-hole 160 of the carrier 150 collapses around a stripped portion of the optical fiber (in this embodiment, the portion surrounding the plastic cladding of the optical fiber), and the plastic material of the carrier is fused to the plastic material of the optical fiber cladding. In this embodiment, the carrier 150 (e.g., rod 150') collapses around the optical fiber at a relatively low temperature (e.g., 200°C-750°C for a plastic rod) and is fused to the cladding of the optical fiber to form a polarization controller 100.

[0096] The polarization controller 100 includes one or more collapsed regions 170 surrounding the optical fiber 120. For example, as Figure 2 As schematically shown, the polarization controller 100 may include three (3) collapsed regions 170 surrounding the optical fiber 120.

[0097] The polarization controller 100 is preferably positioned within a soft plastic (nylon) tube 150A (not shown) and supported or held by one or more supports H. Multiple supports may be positioned adjacent to each end of the polarization controller, allowing the carrier 150 to move slightly (slide) along its central axis or in directions perpendicular to the central axis (e.g., in the X, Y, and Z directions). This minimizes the possibility of breakage or snapping of the optical fiber 120 and also minimizes the total loss caused by the polarization controller. For example, a V-shaped clamp (not shown) may be clamped onto the plastic tube 150A supporting the polarization controller (not shown), allowing the carrier to move slightly (slide) within the plastic tube along its central axis or in directions perpendicular to the central axis. The plastic tube 150A also protects the carrier from scratches or other damage. A force F is then applied to regions 170 (e.g., as indicated by arrows) to induce birefringence within the core of the optical fiber 120. For example, by slightly bending each region 170 of the polarization controller 100 individually, any input polarization state of light propagating through the optical fiber 120 can be converted to any desired output polarization state. Such bending can be applied using, for example, electromechanical methods. External forces can be applied individually to each region 170, directly to the carrier 150, or preferably through a plastic tube 150A supporting the carrier. For example, each region 170 can be individually bent, allowing movement toward a fully polarized state at any location on the Poincaré sphere. In some embodiments, the polarization controller 100 (or carrier 150) is preferably held in place by one or more rigid supports, for example, using high-modulus epoxy resin. In some embodiments, the carrier 150 is held or supported by clamps, preferably by a plastic tube surrounding the carrier.

[0098] Figure 3 As shown, the polarization controller 100 can rotate an arbitrary input polarization state (SOP), shown as label M1, to a desired arbitrary output polarization state, shown as label M2. In this embodiment, the selected desired polarization state output is linear.

[0099] When an external force is applied to rotate to an arbitrary polarization, the polarization controller 100 utilizes the birefringence phenomenon caused by stress. Due to the offset position of the fiber 120 within the polarization controller 100, the initial input polarization of the light coupled to the fiber 120 can be easily rotated. This is because the fiber 120 experiences an antisymmetric and stronger stress distribution at the collapse region 170 compared to the stress distribution generated in the same fiber in the carrier positioned within the central bore. This stress distribution causes a change in the refractive index within the fiber core, thereby rotating / converting the initial arbitrary polarization of the light propagating through the fiber core to the desired (arbitrary) output polarization.

[0100] As described above, the polarization controller 100 utilizes stress-induced birefringence to alter the polarization of light propagating through the core of the optical fiber 120. Birefringence is the phenomenon where polarized light encounters two different refractive indices of a material, depending on how the polarization is aligned with the birefringence axis. Multiple collapsed regions 170 introduce stress into the fiber core located within these regions, thereby inducing birefringence in the core material (e.g., glass).

[0101] The length l of the (multiple) collapsed regions 170 contributes to the amount of polarization rotation. The longer the length l of the (multiple) collapsed regions 170, the greater the polarization rotation. More specifically, the longer the collapsed region, the more hindrance (the difference in velocity between the orthogonal polarization states of light) accumulates between the two orthogonal polarization states due to stress-induced birefringence, thus better controlling the polarization rotation. For light propagating within the fiber core located within the collapsed region, the glass refractive index of light polarized parallel to the stress direction is different from that of light polarized perpendicular to the stress direction. Therefore, when light passes through a segment with stress-induced birefringence, a phase difference is generated between the two polarization components. At the fiber output, the net polarization state changes due to the accumulated phase difference.

[0102]

[0103]

[0104]

[0105]

[0106]

[0107] Where K represents two different signal polarizations (parallel and perpendicular, i.e., Kp) ∥ and K ⊥ The propagation constant of ). Parallel and perpendicular ( and ) represents the phase of light propagating in these two different polarizations, l is the length of the collapsed region 170 around the fiber, and n is parallel and n is perpendicular (n ∥ and n ⊥ ) is the refractive index of the fiber core corresponding to these two different polarizations.

[0108] The via region preferably undergoes adiabatic collapse to reduce micro-bending fiber loss during the collapse process. The length l of the transition region (also referred to herein as the tapered region) t (Transition length) can be, for example, from 2000 μm to 1 cm. Before the collapse region forms, the diameter d of the through-hole 160 (e.g., drill hole 160') is compared to the diameter of the fiber portion entering the hole. 孔Formed to make 0.5μm <d 孔 -d 光纤 <400μm, where d 光纤 This is the maximum outer diameter of the optical fiber 120 passing through aperture 160. For example, in some embodiments, it is 0.5 μm. <d 孔 -d 光纤 <300μm, or 0.5μm <d 孔 -d 光纤 <250μm, and preferably, 10μm <d 孔 -d 光纤 <250μm. More preferably, if only a single fiber is positioned within the aperture, then 5μm. <d 孔 -d 光纤 <60μm, or 5μm <d 孔 -d 光纤 <30μm, or 10μm <d 孔 -d 光纤 <30μm. Most preferably, if only a single fiber is positioned within aperture 160, then 5μm is required to achieve low loss (before the collapse step). <d 孔 -d 光纤 <15μm, or even 5μm <d 孔 -d 光纤 <10μm. When 5μm <d 孔 -d 光纤 <15μm, or even 5μm <d 孔 -d 光纤 When the diameter is <10 μm, macro-bending loss is minimized at wavelengths between 1250 nm and 1660 nm. 光纤 It is the diameter of the coated or uncoated fiber (bare fiber), depending on whether the segment of coated or uncoated fiber first passes through the through-hole 160.

[0109] For example, if a typical fiber cladding diameter is approximately 125 micrometers and the coated fiber diameter is 250 micrometers, then the diameter of the via 160 needs to be determined so that the coated segment of fiber 120 can pass through before the formation of the collapse regions 170. In this exemplary embodiment, d 光纤 It is the diameter of the coated optical fiber that has passed through the 160mm through-hole.

[0110] For example, in one embodiment, the aperture 160 is greater than 250 μm, such that the coated fiber 120 (with an outer coating diameter of 250 μm) will be able to pass through the aperture 160 before creating multiple collapse regions 170 around the uncoated portions of the fiber. In embodiments where the coated portion of the fiber 120 is inserted into the aperture 160, the aperture diameter d 孔The aperture diameter can be, for example, 0.5 μm to 300 μm larger than the diameter of the coated optical fiber. Preferably, to minimize loss, the aperture diameter d... 孔 The diameter of the via 160 can be 5 μm to 300 μm larger than the diameter of the coated fiber, more preferably 5 μm to 50 μm larger, even more preferably 5 μm to 30 μm larger, and most preferably 5 μm to 15 μm larger. Therefore, in such exemplary embodiments, if the diameter of the coated fiber is 250 μm and only one fiber passes through the via 160, the diameter of the via 160 can be 255 μm to 280 μm, or 255 μm to 275 μm (e.g., 260 μm or 270 μm). Thus, according to some embodiments, if the diameter of the via 160 needs to accommodate the coated fiber (before the carrier collapses onto the uncoated fiber segment), the diameter d of the via 160... 孔 Preferably, the diameter d of the coated optical fiber 光纤 Large 5μm-30μm (e.g., 5μm-15μm or 5μm-10μm).

[0111] In embodiments where only the stripped portion of the fiber passes through the via 160 and the diameter of the fiber cladding is approximately 125 μm, the diameter of the via 160 is 0.5 μm to 300 μm larger than the diameter of the stripped (i.e., bare) fiber, and preferably 5-50 μm larger than the diameter of the stripped fiber (i.e., 5-50 μm larger than the diameter of the cladding). When the fiber passes through the via, a via 160 with a diameter only 0.5 to 5 μm larger than the diameter of the uncoated fiber being passed through can cause abrupt bending, which can lead to microbending losses in the fiber, or even microcracks, and reduce device life. If the via diameter d... 孔 If the diameter is significantly larger than the fiber diameter (e.g., greater than 400 μm), the air gap in the fiber within the via 160 surrounding the uncollapsed via(s) can also cause signal loss by inducing sharp fiber bending or twisting within the via 160. Preferably, to minimize losses generated by the polarization controller, in embodiments where only the stripped portion of the fiber passes through the via 160, the via diameter is 5 μm to 60 μm larger than the diameter of the uncoated (i.e., stripped) fiber, for example, 5 μm to 50 μm larger than the diameter of the uncoated fiber, and more preferably 5 μm to 30 μm or 5 μm to 20 μm larger than the diameter of the uncoated fiber. In such embodiments, the diameter of the uncoated (stripped) fiber is the outer diameter of the fiber cladding. Therefore, if the stripped fiber diameter is 125 μm, the diameter of the via 160 can be 135 μm to 185 μm, 135 μm to 175 μm, 135 μm to 160 μm, or 135 μm to 155 μm.

[0112] Preferably, in order to maximize the performance of the polarization controller 100 and to minimize microbending loss before the carrier collapses and forms the collapse region 170, the difference Δ (Δ = d) between the aperture diameter and the diameter of the fiber that has passed through the aperture is minimized. 孔 -d 光纤 The range is from 10 μm to 60 μm. For example, d 孔 -d 光纤 The aperture size can be 5μm, 6μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 35μm, 40μm, 50μm, 55μm, 60μm, or somewhere in between. If the aperture is too small, the fiber 120 will be jammed and will not be able to pass through. If it is too large, it can lead to macro-bending loss, micro-bending loss, and distortion that limits polarization control capabilities.

[0113] More preferably, d 孔 -d 光纤 The range is from 5 μm to 50 μm, for example, from 5 μm to 15 μm. In some embodiments, Δ = d 孔 -d 光纤 The value is 20 μm to 60 μm, or 20 μm to 55 μm, or 20 μm to 50 μm. Most preferably, d 孔 -d 光纤 The aperture size is 5 μm to 20 μm, for example, 5 μm to 15 μm, or 5 μm to 10 μm. It is believed that collapse taper loss (loss caused by macrobending) is a major factor contributing to signal loss in the polarization controller 100. The smaller the aperture 150, the lower the macrobending loss. Therefore, to minimize macrobending loss, preferably, d 孔 -d 光纤 The value can be 5 μm to 30 μm, or 10 μm to 20 μm, or 5 μm to 15 μm, or even 5 μm to 10 μm. In some embodiments, d 孔 -d 光纤 The range is from 10μm to 20μm.

[0114] The tapered (or arc-shaped) region 175 of the through-hole 150 is the transition region between the fully open region 172 and the collapsed region 170 of the through-hole 150. The size and geometry of the tapered region can also be used to minimize losses caused by bending. The longer the tapered region (i.e., the larger the tapered area), the better. t The longer the length of the cone, the more it minimizes bending losses. If the cone is too steep (i.e., if the length of the cone is l...),... t If the length is short, the tapered region will result in (multiple) macro-bending losses. In some embodiments, l t>2mm, for example, 2mm to 6mm. A longer tapered (e.g., arc-shaped) region can be achieved when the carrier 50 is moved through the heating zone during the collapse step. The optical fiber 120 can be bent due to the constraint of the collapsing inner wall of the through-hole 150, as the collapsing inner wall is fused to the optical fiber. The length l of the tapered hole region... t The length that allows the optical fiber 120 to be supported within the via 150 is such that when the optical fiber 120 bends due to the constraint of the collapsed inner wall, the region 175 does not result in a macro bending loss greater than 0.2 dB at 1550 nm, and preferably not greater than 0.1 dB at 1550 nm, when the slope or radius of the optical fiber 120 is such that.

[0115] As described above, to minimize microbending loss, a via 160 slightly larger than the diameter of the bare (stripped) fiber (e.g., 10 μm-30 μm or 10 μm-15 μm) can be used, allowing the stripped fiber to be inserted into the via 160. Then, after the insertion of fiber 120, before or after the collapse step forming the collapse carrier region 170, a pigtail or another fiber 122 (not shown) can be spliced ​​to fiber 120. This method will allow for minimal loss due to macrobending. Furthermore, splicing fiber 120 with another fiber 122 (e.g., with such...) SMF The splicing of single-mode fibers (such as single-mode fibers) can be done using a fusion splicer, resulting in low coupling loss (e.g., 0.01 to 1 dB) (measured by OTDR at 1550 nm wavelength).

[0116] Polarization controllers based on planar electro-optic (e.g., lithium niobate) chips used in quantum systems typically suffer from high coupling losses (~3 dB) due to the coupling between planar chips and single-mode fibers. In contrast, the polarization controller 100 described herein is an all-optical device utilizing fiber-to-fiber coupling. The coupling loss between the two fibers can be, for example, from 0.01 dB to 0.7 dB.

[0117] Another method to minimize microbending loss is to fill the excess space in the via 160 with one or more "dummy" fibers, if they are significantly larger than the stripped fiber diameter d. 光纤 For example, if the polarization controller 100 utilizes a typical single-mode fiber 120 with a cladding diameter of 125 μm and a via diameter d of 250 μm or greater. 孔 The offset via 160 allows at least one additional optical fiber (“dummy fiber”) to be inserted into the via 160 to minimize the microbending of the fiber 120 while creating a collapse carrier region 170 during the collapse process. The “dummy” fiber is an uncoated (stripped) fiber that does not propagate signal light and does not significantly affect optical loss. In such an embodiment, d 孔It can be, for example, about 200 - 550 μm, and the coupling loss between the two optical fibers 120, 122 is ≤1 dB, for example, 0.01 dB to 0.7 dB.

[0118] Preferably, to improve the sensitivity of the polarization controller, 0 < (D / R) < 1, where D is the distance from the center of the carrier 150 to the center of the through - hole 160, and R is the outer radius of the carrier 150 (or the average half - width of the carrier 150 if the carrier does not have a circular cross - section). Preferably, the through - hole 160 (e.g., a drilled hole) has a symmetry axis, which is positioned such that 0.25 < D / R < 0.9, and preferably 0.4 < D / R < 0.85. In at least some embodiments, the through - hole 160 has a cross - section with a width of 0.5 μm to 275 μm and a symmetry axis located at a distance D from the center of the carrier, such that 0.5 < D / R < 0.8. More preferably, 0.6 < D / R < 0.8, and still more preferably, 0.65 < D / R < 0.8. In some embodiments, 0.7 ≤ D / R ≤ 0.75. In one embodiment, as Figure 5 shown, the drilled hole and the optical fiber positioned therein are offset from the center such that they are located at 3 / 4 of the radius R from the center of the rod (i.e., D / R = 3 / 4). In this embodiment, this positioning is shown by simulation to experience the strongest amount of stress during bending, as Figure 6 shown. Figure 12 The figure shows that in one embodiment, the optimized positioning of the through - hole corresponds to the ratio D / R = 0.7072.

[0119] The through - hole 160 can be formed in any geometry or design, such as a spiral shape along the length of the carrier 150. It can also be circular, elliptical, triangular, rhombic, or any other shape. The collapse region can be of any length, but experiments show that a longer length is better, and in one exemplary embodiment, the collapse region is 6 cm long. The polarization controller 100 can include one or more collapse regions, such as multiple regions with different collapse lengths l. In some embodiments, 1 cm ≤ l ≤ 15 cm, 2 cm ≤ l ≤ 15 cm, 2 cm ≤ l ≤ 10 cm, or 2 cm ≤ l ≤ 8 cm, or 2 to 7 cm, and preferably, or 2 cm to 6.5 cm (to reduce the size of the carrier).

[0120] The polarization rotation is caused by the sum of the birefringences induced in the transverse and longitudinal directions across the polarization controller 100 of the device. This induced birefringence phenomenon results from the stress experienced by the carrier 150 when subjected to an external force field. The force F can be used in the configuration of two fixed ends, and the force F can be as Figure 7 shown, for example, applied to the collapse region. However, the force field can also be applied in such a configuration: a part (e.g., one end) of the polarization controller 100 is fixed by a holder H, as Figure 8 As shown in the diagram. The polarization controller 100 can be secured using a series of mounting brackets and can have a series of multiple collapse regions 170. In some embodiments, the polarization controller 100 includes two collapse regions 170. In some embodiments, the polarization controller 100 includes three or more collapse regions 170. Preferably, the polarization controller 100 includes 2 to 5 collapse regions 170.

[0121] Accordingly, a method for controlling the polarization of light propagating through optical fiber 120 includes:

[0122] (i) A polarization controller 100 is supported, the polarization controller 100 including a carrier 150 having an eccentric through-hole 160 having at least one partially collapsed region 170 surrounding an optical fiber 120 at at least one location, and

[0123] (ii) Applying a force to the carrier 150 at another location; wherein the other location corresponds to at least a partially collapsed region 170.

[0124] A method for controlling the polarization of light propagating through optical fiber 120 includes:

[0125] (i) A polarization controller 100 is supported, the polarization controller 100 including a carrier 150 having an eccentric through-hole 160 having at least one partially collapsed region 170 surrounding an optical fiber 120 at at least one location, and

[0126] (ii) Bending or twisting the carrier 150.

[0127] Other configurations of the polarization controller 100 may include, for example, a helical aperture 160, a collapse aperture 160 as a stress concentrator, which has been shaped as a cone, as well as a notch, horseshoe, or any other geometry. The through-hole 160 can be formed in any geometry or design, such as a helical shape along the length of the carrier 150. It can also be circular (in this embodiment), elliptical, triangular, rhomboid, or any other cross-sectional shape. Other types of stress concentrators are optical fibers with stress bars (e.g., panda-type polarization-maintaining fibers) or optical fibers containing pores (e.g., photonic crystal fibers). Other alternative methods can be implemented through any combination of the above embodiments. The applied force is applied in one, two, and / or three dimensions to better control the polarization rotation. For example, the force on the carrier can be applied in the XY plane (radially, toward the fiber, and not just along the fiber axis).

[0128] like Figure 9A and Figure 9BAs shown, the polarization rotation by the applied external force is caused by stress-induced birefringence. According to some embodiments, for a carrier diameter of 3 mm or less, the amount of force applied at each location is greater than 0 gF and not greater than 200 gF (200 g-force), preferably not greater than 100 gF. According to some embodiments, the amount of force applied at each location is greater than 1 gF and not greater than 100 gF, for example, 1 gF to 50 gF, preferably 1 gF to 20 gF, and more preferably 1 gF to 10 gF. A low force of 10 gF or less can produce a large radius bend, thereby minimizing any serious damage to the optical fiber by avoiding torsional forces. For example, in one embodiment, a 1 cm collapsed segment (L = 1 cm) can be moved to a bend radius of 0.5 meters using a force of 7 g. In another embodiment, 2 gF (2 g-force) is utilized, for example by (i) using a linear platform with fingers resting on the carrier; or (ii) a motor-driven cam.

[0129] The total cumulative birefringence along the transverse and longitudinal directions allows for rotation of more than 360 degrees in at least one direction. Figure 10 The repeatability of the polarization controller 100 when pressure is applied and removed is shown. The polarization rotation, as a function of bending, can be mathematically described using known algorithms. In this embodiment, the voltage relates to bending rather than an electro-optic effect. Figure 11 As shown, in one embodiment, the measurement loss of the transpolarization controller 100 is approximately 0.7 dB.

[0130] Forces are applied in one-dimensional, two-dimensional, and / or three-dimensional ways to better control polarization rotation. For example... Figure 9A and Figure 9B As shown, the polarization rotation is caused by the applied external force resulting from stress-induced birefringence. The optical hindrance caused by the accumulated birefringence along the length of the collapsed region has enabled the Bouincalle sphere to rotate more than 360 degrees in at least one direction. Figure 9A The polarization rotation results of the embodiment are shown, wherein the input of the device is excited by a Fabry-Perot semiconductor laser operating in multiple longitudinal modes, and wherein one end of the collapsed region is firmly held in place by a clamp, while forces of varying magnitudes are applied to the opposite ends of the collapsed region in a direction perpendicular to the glass rod. The length of the collapsed region is 6 cm, and the fiber waveguide is SMF-28. Figure 9B Another embodiment of polarization rotation results is shown, where the length of the collapsed region is 2 cm and the fiber waveguide is a polarization-preserving panda fiber. The input of the device in this example is excited by a single-frequency semiconductor laser operating at 1550 nm, the device has a transmission loss of 0.6 dB, and the degree of polarization is 92% during the polarization rotation measurement.

[0131] Figure 10The repeatability of the polarization controller 100 when force is applied and removed in small steps is shown. During multiple cycles of force increase and decrease within the experimental range, the polarization on the Boynkall sphere is observed to follow the same path. Polarization rotation as a function of bending can be described and modeled. In this case, voltage involves bending rather than an electro-optic effect. The measured loss of the transpolarization controller 100 has been shown to be less than 2 dB or even less than 1 dB. In some embodiments, the loss of the transpolarization controller 100 is 0.3 dB to 1 dB. In some embodiments, the loss of the transpolarization controller 100 is 0.1 dB to 1 dB, for example 0.12 dB, 0.15 dB, 0.2 dB, 0.3 dB, 0.6 dB, 0.7 dB, 0.8 dB, or between therewith. Figure 11 As shown, in one embodiment, the measured loss of the polarization controller 100 is approximately 0.7 dB.

[0132] Example 1.

[0133] Carrier with offset drilling

[0134] In this exemplary embodiment, the center of the offset borehole 160' of the carrier 150' is located at a distance of 3 / 4 relative to the center of the carrier to obtain optimal stress distribution. In this particular embodiment, the carrier 150' is cylindrical. That is, in this embodiment, D / R = 3 / 4, where R is the radius of the carrier's cross-section. Therefore, the position of the optical fiber 120 from the center of the glass rod is offset by 3 / 4R from the radial center of the rod. In this embodiment, the outer diameter of the carrier 150 (rod 150') is approximately 2 mm. Therefore, R = 1 mm and the diameter of the borehole before the collapse step is approximately 175 μm.

[0135] The stripped fiber 120 (i.e., the fiber with at least a portion of the coating removed, exposing the outer surface of the cladding) is fed through the borehole 160'. Fiber 120 can be a single-mode fiber, a polarization-maintaining fiber, a multimode fiber, a few-mode fiber, a multi-core fiber, or any other type of fiber. In this embodiment, fiber 120 is a single-mode fiber with a glass core and a glass cladding (e.g., available from Corning Incorporated, New York City). SMF Optical fiber, specifically THORLABS PM fiber (“Panda” or “Bow” type) or Corning PM Panda fiber. In this embodiment, the fiber cladding diameter is 125 μm.

[0136] When this optical fiber is used in conjunction with a glass carrier 150, it can be advantageous for the polarization controller 100 to include a polarization-maintaining fiber (PM fiber) 120. When the glass carrier 150 cools to room temperature, the forces that cause the glass carrier 150 to collapse onto the glass fiber result in viscous forces freezing within the glass carrier 150. These stresses can vary significantly with length and can cause operational problems for the polarization controller 100. The performance of the polarization controller 100 is improved when the polarization mode is maintained as light propagates through the fiber positioned within the carrier. This can be advantageously achieved by using a polarization-maintaining fiber as fiber 120. Then, when the carrier 150 is bent, as light propagates through the fiber length within the carrier, one polarization mode acts in a continuous manner different from another polarization mode. If polarization mode coupling exists due to stress variations with fiber length, the bending force can have undesirable compensation due to the change in length. Using polarization-maintaining fiber (e.g., Corning PM15-U25D 1550nm fiber available from Corning, New York) prevents this from happening and allows the two propagation polarization modes to be separated continuously and smoothly within the bend.

[0137] It is noted that annealing the carrier spliced ​​to the optical fiber 120 minimizes changes caused by undesirable stresses in the collapsed region and also improves the performance of the polarization controller 100. However, these stresses may be difficult to completely eliminate through annealing.

[0138] Preferably, the beat length of the polarization-maintaining fiber 120 is no greater than 2 cm and greater than 1 mm at the operating wavelength (e.g., 1550 nm). The beat length of the polarization-maintaining fiber at the operating wavelength is preferably less than 1 cm. In some embodiments, the applicant utilizes a polarization-maintaining (PM) fiber 120 with a beat length of 2 mm to 5 mm.

[0139] The borehole 160' collapses at the desired location, thereby fusing the interface of the bare optical fiber to the carrier to form the polarization controller 100. The resulting collapsed region 170 can be of any length l, but in this exemplary embodiment, l = 6 cm. The carrier 150 can have one or more collapsed regions 170 spaced at any arbitrary length, but in this embodiment, the carrier 150 includes a collapsed region 170 positioned and fusing around the fiber cladding. In this exemplary embodiment, the transition region (also referred to herein as the tapered region) has a length l of 2600 micrometers. t (Transition length).

[0140] The carrier 150 is then subjected to an external force that causes it to bend and / or deviate from its central position, for example, via mechanical, thermal and / or piezoelectric methods.

[0141] In this embodiment, the rod 150' is composed of fluorine-doped SiO2 glass coated with titanium and includes an eccentrically drilled hole 160 (i.e., the center of the drilled hole is offset from the center of the carrier). In this embodiment, the carrier 150 is a glass carrier comprising silicon dioxide doped with 1.2 wt% fluorine.

[0142] The glass carrier 150 may also be doped with boron or any other type of dopant to reduce the thermal temperature required for collapse drilling without causing germanium to diffuse from the core, thereby minimizing mode field expansion. This helps maintain low loss (<0.7 dB). In some embodiments, the carrier is a silica-doped glass, and the amount of boron and / or fluorine is between 1 wt% and 8 wt%. In this embodiment, the single-mode fiber (e.g., SMF The optical fiber is fed through the borehole 160' before it collapses around the fiber.

[0143] While in other embodiments the polarization controller 100 includes multiple collapse regions, in this embodiment the polarization controller 100 has a single collapse region 170. In this embodiment, to cause the carrier to collapse in the desired region, a combustion flame from the heater (burner) 200 is introduced around the rod 150'. For SiO2-based rods, the temperature required to cause borehole collapse is between 1000°C and 2000°C, for example 1600-1800°C or 1700-1800°C. The required heat can also be applied by an infrared (IR) laser.

[0144] In this embodiment, the temperature inside the burner 200 is 1723°C. The desired temperature is achieved by changing the ratio of methane (CH4) to oxygen (O2).

[0145] According to some embodiments, a 2:1 ratio (CH4 = 0.5O2 = 0.8) is used to generate the desired temperature of at least 1700°C required for the SiO2-based carrier 150 to melt or soften the carrier glass. If, as in this embodiment, the carrier 150 comprises fluorine- or boron-doped silicon dioxide, the melting temperature of the carrier glass is reduced to below the melting temperature of pure silicon dioxide, and CH4 = 0.5O2 = 0.8. Type B thermocouples (range: 810°C to 1700°C) and Type K thermocouples (range: 293°C to 1260°C) are used to measure the temperature. The thermocouples are fixed at the same location where the actual burner will be placed. In this embodiment, the burner moves along the carrier at a rate of 0.5 mm / s to ensure the carrier has been heated to the desired temperature.

[0146] like Figure 4As shown, the rod 150’ is asymmetrically positioned within the burner flame. The eccentric bore is positioned on the side closest to the flame 200A. Introducing such high temperatures around the bore is accompanied by an increase in pressure within the bore. For collapse to occur, the high-pressure air must be at least partially evacuated. A vacuum pump is utilized during the collapse step such that the rod collapses around the fiber cladding. In this embodiment, the pressure is -17 psi. The burner 200 (or a laser beam from an IR laser) is moved along the length of the rod to produce the desired length of the collapse region. The process of heating and collapsing the (multiple) rod regions around the fiber also causes the fiber to fuse to the inner surface of the rod at the collapse region.

[0147] Importantly, the transition from the fully non-collapsed region to the fully collapsed region of the carrier is smooth (i.e., not steep or abrupt) such that no microbend or macrobend perturbations are induced, which would cause light to couple from the first mode within the collapsed region to higher-order cladding modes.

[0148] In this exemplary embodiment, the fusion interface between the bore and the fiber 120 collapses adiabatically to reduce the microbend losses that occur during the collapse process, and the length of the transition region is 2600 microns.

[0149] Compared to the fiber size, the bore diameter is 0.5μm < d 孔 –d 光纤 <250μm, where d 光纤 is the diameter of the fiber cladding. In this embodiment, d 光纤 is the outer glass diameter of the fiber after the (multiple) coating layers have been stripped. In this exemplary embodiment, d 孔 –d 光纤 is approximately 50μm. The eccentric position of the bore / fiber is located at 3 / 4 of the distance from the center of the rod, as Figure 5 shown, and this distance is 3 / 4 of the radius from the center of the rod 150’. This positioning is shown by simulation to experience the strongest amount of stress during bending, as Figure 6 shown. However, although less efficient, the bore can be positioned anywhere within 0 < D / R < 1. For example, the carrier can be a fluorine- and / or boron-doped glass tube, the cross-section of the through-hole can be from 0.5μm to 275μm, and its axis of symmetry is located at a distance D from the center of the carrier such that 0.25 < D / R < 0.4, where R is the half-width of the cross-section of the carrier.

[0150] The collapse region 170 can be any length, but experiments have shown that longer lengths (>0.5 cm) are better, and in this embodiment, l = 6 cm. However, the polarization controller 100 can include more than one collapse region with varying collapse lengths.

[0151] The polarization rotation is caused by total birefringence in both the transverse and longitudinal directions of the cross-device polarization controller 100. This birefringence phenomenon originates from the stress experienced by the carrier 150 when subjected to an external force field. The force F can be used in a configuration with two fixed carrier ends, and as... Figure 7 As shown, it is applied to the collapsed region. However, as Figure 8 As shown, a force F can also be applied in a configuration where only one end of the polarization controller 100 is fixed. The polarization controller 100 can be held in place using a series of mounting brackets and can include a series of multiple collapse regions surrounding one or more optical fibers.

[0152] Typical commercial fiber polarization controllers utilize clamping-torsion motion applied directly to the fiber to induce stress birefringence. However, the polarization controller 100 described herein does not employ any direct twisting or clamping of the fiber 120. Instead, force is applied to the carrier 150. The fiber 120 does not experience direct damage and therefore does not degrade over time, making it more stable and reliable.

[0153] The polarization controller 100 is capable of high-precision polarization control. More specifically, due to the sum of the resulting birefringence, the length l of the multiple collapsed regions 170 allows the user to rotate the polarization over a wider angular range. The polarization controller 100 may include more than one collapsed region (e.g., three), which allows for complete control over polarization motion on the Bouincal sphere.

[0154] The polarization controller 100 can be advantageously used with low power consumption. Because the polarization controller 100 described herein includes a carrier and one or more optical fibers positioned at an offset location relative to the center of the carrier, this configuration allows for asymmetric stress induction and allows the optical fibers to be more sensitive to externally applied forces. Therefore, when using the polarization controller 100, very small external forces are required to rotate the polarization. Unless otherwise expressly stated, any method set forth herein should never be construed as requiring its steps to be performed in a particular order. Therefore, no particular order is intended to be inferred unless the method claims actually describe a sequence of steps to be followed, or unless such steps are otherwise specifically stated in the claims or specification.

[0155] 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, encompassing the spirit and essence of the invention, will be conceived by those skilled in the art, the invention should be understood to include everything within the scope of the appended claims and their equivalents.

Claims

1. An optical system, comprising: (i) a light source, (ii) at least one polarization controller positioned downstream of the light source and comprising; an optical fiber (iii) a carrier surrounding the optical fiber, the carrier comprising an eccentric through - hole having at least one collapsed region, such that the optical fiber is positioned within the through - hole and in contact with the at least one collapsed region of the through - hole, at least one optical fiber coupled to the polarization controller; and (iv) at least one optical detector positioned downstream of the at least one optical fiber, wherein each of the at least one polarization controllers is a polarization state generator, and wherein the at least one collapsed region exerts a pressure on the optical fiber.

2. The optical system of claim 1, wherein, The optical system is a quantum key distribution (QKD) system, wherein the quantum key distribution (QKD) system comprises at least two polarization controllers, a quantum channel comprising optical fibers positioned at the two polarization controllers, and at least two optical detectors.

3. The optical system of claim 1 or 2, wherein: The carrier is a fluorine - and / or boron - doped glass tube, the through - hole having a cross - section of 0.5 μm to 275 μm and a symmetry axis located at a distance D from the center of the carrier, such that 0.25 < D / R < 0.95, where R is the half - width of the cross - section of the carrier.

4. The optical system as claimed in any of the preceding claims, wherein: At least a portion of the optical fiber positioned inside the through - hole comprises an outer glass surface fused to the collapsed region of the through - hole.

5. A method of controlling the polarization of light propagating through an optical fiber, the method comprising: (i) supporting a polarization carrier, the polarization carrier comprising an eccentrically - positioned through - hole having at least one collapsed region surrounding the optical fiber at at least one location, wherein the optical fiber is in contact with the at least one collapsed region and the at least one collapsed region exerts a pressure on the optical fiber, and (ii) applying a force to the carrier.

6. The method of controlling the polarization of light propagating through an optical fiber of claim 5, wherein, The collapsed region is curved.

7. The method of controlling the polarization of light propagating through an optical fiber of claim 5, wherein, The force is 0 gF to 200 gF.

8. The method of controlling the polarization of light propagating through an optical fiber of claim 5, wherein, The force is 1 gF to 10 gF.

9. The method of claim 5, 6, or 7, wherein, The carrier is positioned inside a plastic tube.

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