Optical limiter and method for limiting radiant flux

Abstract

One aspect relates to an optical limiter (200) for limiting the radiation flux of a light source beam, the optical limiter comprising: an optical control port (221) irradiated by an optical control beam originating from a source beam; an optical input port (221) irradiated by an optical transmission beam originating from the source beam; an optical output port (225) irradiated by the transmission beam; and a thermally driven optical windmill (211, 212); wherein the optical windmill is arranged relative to the input port, the control port and the output port such that: illumination of the control beam on the control port drives the optical windmill to rotate only when the control beam has a radiation flux equal to or exceeding a predetermined radiation flux threshold; and the rotation of the optical windmill causes the area of ​​the output port irradiated by the transmission beam to change.

Description

Technical Field

[0001] The present disclosure is concerned with limiting the radiant flux of a light beam; that is, limiting the radiant energy delivered by the light beam per unit time - its power.

[0002] More particularly, aspects relate to optical limiters and methods for limiting the radiant flux of a light source beam. Background Art

[0003] Optical networks are used to transmit data encoded as light signals over fiber-optic cables. To ensure that the optical signal successfully travels from source to destination without damaging any network components, it may be necessary to limit the radiant flux of the light beam carrying the optical signal. This can be achieved using an optical limiter.

[0004] An optical limiter is a device used to limit the radiant flux of a light beam to no more than a predetermined maximum value. Figure 1A1 An idealized graph of input radiant flux versus output radiant flux for a flat maximum optical limiter is shown, where the output rises proportionally to the input until a maximum output value M is reached, at which point the output remains at that level M regardless of how much the input rises.

[0005] Optical limiters can, for example, be formed using a material with a negative thermal index coefficient, where the heat generated by absorbing the light beam lowers the material's refractive index, causing the light rays to spread out in a defocused pattern, so that only some of these rays are received by the collimating lens. Other types of optical limiters use a stabilized optical amplifier whose output is kept constant by a feedback loop or is saturated at its input.

[0006] An optical fuse is a specific type of optical limiter used to interrupt the passage of an optical beam when the radiation flux of the optical beam exceeds a predetermined maximum value. Figure 1A2 A graph of input radiant flux versus output radiant flux for an idealized optical fuse is shown in , where the output rises proportionally to the input until a maximum output value, M, is reached, at which point the output drops to zero and remains zero for all higher input values.

[0007] Optical fuses can be constructed, for example, using light-absorbing materials that are either destroyed by the heat generated when an intense light beam is incident on them, or whose transmittance is altered by the heat (e.g., making them opaque). Consequently, optical fuses are typically single-use; they must be replaced to reestablish an optical connection along the path in which they reside.

[0008] What is needed is an alternative optical limiter that is reusable and does not require the use of exotic materials. Summary of the Invention

[0009] According to a first aspect, there is provided a light limiter for limiting the radiant flux of a light beam of a light source, the limiter comprising:

[0010] an optical control port illuminated by an optical control beam originating from the source beam;

[0011] an optical input port illuminated by the optical transmission beam originating from the source beam;

[0012] a light output port illuminated by the transmitted light beam; and

[0013] heat-driven light windmills;

[0014] The optical windmill is arranged relative to the input port, the control port and the output port so that:

[0015] The illumination of the control port by the control light beam drives the optical windmill to rotate only when the control light beam has a radiation flux that is equal to or exceeds a predetermined radiation flux threshold; and

[0016] The rotation of the optical windmill causes the area of ​​the output port illuminated by the transmitted light beam to change.

[0017] The light windmill comprises:

[0018] Axis; and

[0019] At least one blade:

[0020] is arranged to rotate about the axis of the shaft in an environment containing a fluid, and

[0021] The optical windmill has a first side and a second side thermally insulated from each other, so that the optical windmill is driven by irradiating the first side with the control light beam, so that the first side absorbs more light energy than the second side, and a temperature gradient is established from the second side to the first side, so that the blades rotate around the axis of the shaft while the first side is dragged.

[0022] The predetermined radiation flux threshold value depends on the inertia of the light windmill.

[0023] The limiter may be configured to allow the optical windmill to rotate through a sufficiently large angle such that the area of ​​the output port illuminated by the transmission light beam is zero, such that the limiter acts as a reusable optical fuse.

[0024] The source beam may be derived from a laser.

[0025] The side of the blade of the optical windmill arranged to be illuminated by the control light beam may have a higher light absorption rate than the opposite side of the blade.

[0026] Alternatively or additionally, the side of the blade of the light windmill that is configured to be illuminated by the control beam and the opposite side of the blade can be shaped so that within the allowed rotation range of the light windmill, the side of the blade that is illuminated by the control beam receives a larger amount of radiation energy from the control beam than the opposite side.

[0027] The limiter may further comprise optical baffle means arranged to prevent a portion of the transmission light beam from illuminating the output port, the size of the portion being dependent on the angle of rotation of the optical windmill.

[0028] The spacer device may include:

[0029] one or more light guides; and / or

[0030] One or more beam blockers.

[0031] The input port and the output port may be coaxial with each other;

[0032] The baffle arrangement may include one or more beam blockers arranged to rotate with the light windmill; and

[0033] The one or more beam blockers may be arranged to define an aperture through which the transmission beam must pass to reach the output port.

[0034] When the angle is zero, the aperture may be coaxial with the input port and the output port.

[0035] The input port may be the control port, the source beam itself serving as both the transmission beam and the control beam.

[0036] The limiter may further comprise a beam splitter configured to split the source beam into the transmission beam and the control beam.

[0037] The limiter may further include a biasing element;

[0038] wherein the optical windmill is coupled to the biasing element such that the optical windmill is biased toward a first rotational position in which an area of ​​the output port illuminated by the transmission light beam is maximized relative to any other rotational position of the optical windmill.

[0039] The biasing element may be configured to be adjustable such that the biasing force exerted by the biasing element on the light windmill may be modified.

[0040] The biasing element may be configured to:

[0041] preventing the optical windmill from rotating away from the first rotational position when the radiant flux of the source light beam is below a predetermined threshold; and

[0042] When the radiation flux of the source beam is equal to or exceeds a predetermined threshold, the optical windmill is allowed to rotate from the first rotation position by a sufficiently large angle so that the area of ​​the output port illuminated by the transmission beam is zero.

[0043] The limiter may further include one or more limiters, each limiter being configured to prevent the optical windmill from rotating beyond a specific rotational position.

[0044] The limiter may further include a housing enclosing the optical windmill, the housing including a hole configured to partially drain fluid around the optical windmill.

[0045] According to a second aspect, there is provided a method for limiting the radiant flux of a light beam of a light source, the method comprising:

[0046] irradiating the input port of the optical limiter according to the first aspect above with an optical transmission beam originating from the source beam; and

[0047] The control port of the optical limiter according to the first aspect above is illuminated with an optical control beam originating from the source beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Various aspects of the present disclosure will now be described by way of example with reference to the accompanying drawings, in which:

[0049] Figure 1A1 It is an ideal curve of input radiant flux versus output radiant flux of a planar maximum optical limiter;

[0050] Figure 1A2 is a graph of input radiant flux versus output radiant flux for an idealized fuse;

[0051] Figure 1B1 The Crookes radiometer light windmill is shown;

[0052] Figure 1B2 Shown Figure 1B1 The force on each blade of the Crookes radiometer;

[0053] Figure 1C Another design of a light windmill is shown;

[0054] Figure 2A An example optical limiter is shown in a first position;

[0055] Figure 2B Shown Figure 2A a limiter in a second position;

[0056] Figure 3A An example optical fuse is shown in the "on" position;

[0057] Figure 3B Shown Figure 3A A fuse in the "off" position;

[0058] Figure 3C Shown Figure 3A Some internal parts of the fuse;

[0059] Figure 3D Shown Figure 3A Some external parts of the fuse;

[0060] Figure 4A Another example optical limiter is shown in a first position;

[0061] Figure 4B Shown Figure 4A a limiter in a second position;

[0062] Figure 5A Another example optical fuse is shown in the "on" position;

[0063] Figure 5B Shown Figure 5A A fuse in the "off" position;

[0064] Figure 6A Another example optical limiter is shown in a first position;

[0065] Figure 6B Shown Figure 6A a limiter in a second position;

[0066] Figure 7A Another example optical fuse is shown in the "on" position;

[0067] Figure 7B Shown Figure 7A A fuse in the "off" position;

[0068] Figure 8A Another example optical limiter is shown in a first position;

[0069] Figure 8B Shown Figure 8A a limiter in a second position;

[0070] Figure 9A Another example optical fuse is shown in the "on" position; and

[0071] Figure 9B Shown Figure 9AA fuse in the "off" position; DETAILED DESCRIPTION

[0072] The following description is presented to enable any person skilled in the art to make and use the system, and is provided in the context of a specific application. Various modifications to the disclosed embodiments will be apparent to those skilled in the art.

[0073] The terms "top," "bottom," "side," "front," "back," "forward," "backward," "clockwise," "counterclockwise," and other terms describing the orientation of features are not intended to be limiting and, where used, are included purely to describe the relative positions of these features in the context of the drawings. These features may be arranged in other orientations during use or storage.

[0074] It is proposed to use the optical windmill effect to route an optical signal between an input end and an output end of an optical limiter so that the radiation flux of an output light beam carrying the signal is limited to not exceed a predetermined maximum value.

[0075] A heat-driven light windmill includes at least one blade / paddle, the two sides of which are thermally insulated from each other so that when one side is heated by light or other electromagnetic radiation, it remains hotter than the other side. The blades are positioned in a fluid (typically low-pressure air) such that convection currents established in the fluid due to the temperature asymmetry between the two sides of each blade are sufficient to cause the light windmill to rotate.

[0076] In order to start a stationary optical windmill, the effect of the rotating optical windmill (and therefore the radiant flux of the light source causing the effect) must be sufficient to overcome the inertia of the optical windmill. In order to keep the optical windmill rotating, the optical windmill effect (and therefore the radiant flux of the light source causing the effect) must be sufficient to overcome the friction forces acting on the optical windmill relative to its mounting and the surrounding fluid during rotation.

[0077] Alternatively, the two sides of each blade may have different electromagnetic absorption characteristics in order to increase the rate at which a temperature differential is established and / or to allow a temperature differential to be established if the two sides of the blade are exposed to radiation.

[0078] Figure 1B1Crookes radiometer 1100 is shown, a classic demonstration of the optical windmill effect. Crookes radiometer 1100 includes four blades 1110 arranged to rotate about axis 1120 within a partially evacuated canister 1130. Each blade 1110 is painted white on one side and black on the other, and the blades are arranged so that the black and white sides alternate around the radiometer. (The black sides are indicated by cross-hatching.) When light is shone onto radiometer 1100 from the direction indicated by arrow L1, the blades rotate about axis 1120 in the direction indicated by arrow R1 (i.e., the black sides are dragged).

[0079] Figure 1B2 Shown Figure 1B1 The force on each blade 1110 of the Crookes radiometer 1100. Figure 1B2 , the blades 1110 are shown side by side, with the white side 1111 on the left and the black side 1112 on the right. The white side 1111 and the black side 1112 are thermally insulated from each other. The black side 1112 absorbs more light energy than the white side 1111. Therefore, a thermal conductivity is established from the white side 1111 to the black side 1112 ( Figure 1B2 The temperature gradient (from left to right in the figure) is generated by a convection current in the rarefied air surrounding the blade, resulting in an unbalanced force on the blade. A "thermal creep" force TC acts in the opposite direction of the temperature gradient. An additional "Einstein effect" force E acts on the surface edge perpendicular to the temperature gradient, also in the opposite direction. Consequently, forces TC and E cause blade 1110 to rotate about axis 1120, while the black side 1112 is dragged along.

[0080] The Hettner radiometer is similar to the Crookes radiometer, but has horizontal (as opposed to vertical) blades, with the exposed side of each blade painted half black and half white, with the black and white sides alternating around the radiometer. The Einstein effect is absent in the Hettner radiometer, but it still rotates due to thermal creep forces, and the black side of the blade is dragged along.

[0081] Figure 1C is a plan view showing another design of a light windmill 1200, in which the difference in light absorption between the two sides of each blade 1210 is caused by their geometry rather than color. The blades 1210 are shaped so that they each have a concave side 1211 and a convex side 1212, with the convex and concave sides alternating around the radiometer. Figure 1CThe shading in FIG2 shows where shadows fall when light shines onto light windmill 1200 from the direction indicated by arrow L2. It can be seen that throughout the rotation process, the convex side 1212 of blade 1210 receives more light energy than the concave side 1211. This creates a temperature gradient from the concave side 1211 to the convex side 1212 of each blade 1210, causing thermal creep forces and the Einstein effect to cause blade 1210 to rotate about the axis in the direction indicated by arrow R2, i.e., the convex side 1212 is dragged.

[0082] The exemplary light windmill designs described above all include blades with an asymmetry between the light absorption properties of the two sides of the blade. However, even without this asymmetry, motion will be caused by thermal creep forces and (depending on the geometry of the design) the Einstein effect, as long as a temperature gradient can be established between the two sides of the blade so that it is thermally driven.

[0083] Thermally driven optical windmills typically operate in a low-pressure gas or gas mixture, such as air, but generally can operate in any fluid capable of carrying convection currents.

[0084] Although the exemplary optical windmill designs described above all include four blades, any number of blades will be amenable to the optical windmill effect.

[0085] It will also be appreciated that the optical windmill may be driven by other forms of electromagnetic radiation besides visible light, for example infrared or ultraviolet radiation may also be used.

[0086] Several example designs of optical limiters for limiting the radiant flux of a light source beam will now be described. Each example limiter includes an optical input port, an optical output port, and an optical control port. The control port is configured to be irradiated by an optical control beam originating from the source beam. The input port is configured to be irradiated by an optical transmission beam also originating from the source beam. The output port is arranged to be irradiated by the transmission beam. In addition, each exemplary limiter includes a thermally driven optical windmill, which is arranged so that the irradiation of the control beam on the control port only drives the optical windmill to rotate when the control beam has a radiant flux equal to or exceeding a predetermined radiant flux threshold. The rotation of the optical windmill, in turn, causes the area of ​​the output port irradiated by the transmission beam to change. In this way, the radiant flux of the output beam emitted through the output port can be limited.

[0087] Figure 2A and Figure 2B Schematic plan views of an example optical limiter 200 are shown, the optical limiter 200 including an optical windmill in a first position and a second position, respectively. To avoid cluttering the two figures, reference numerals not relevant to the specific description of each figure are omitted in the figures, although all components involved are present in the limiter 200 as shown in each of the two figures.

[0088] The optical windmill comprises a rigid assembly configured to rotate about an axis 214, the rigid assembly being centered on the axis 214. The rigid assembly comprises a first blade 211 rigidly connected to a second blade 212, the second blade 212 acting as a counterweight for the first blade 211. The optical windmill is housed in a sealed housing 240 that maintains the air surrounding the optical windmill at a low pressure but not completely evacuated.

[0089] A relatively low-power beam (such as a laser beam) Figure 2A In the preceding sentence, both uses of "relatively" indicate the same thing as Figure 2B ) The light beam enters the housing 240 through the input port 221 to be incident on the first blade 211. The surface of the first blade 211 on which the light beam is incident is partially reflective, so a portion of the light beam is reflected off the first blade 211 to be incident on the output port 225. The various components of the limiter 200 are arranged so that when the light windmill is in Figure 2A In the position shown, all reflected portions of the light beam are incident on the output port 225.

[0090] The surface of the first blade 211 on which the light beam is incident is configured to absorb some of the electromagnetic radiation carried by the light beam (the portion that is not reflected). This surface is thermally insulated from the surface on the opposite side of the first blade 211, so that a temperature gradient appears from the shadow side to the illuminated side. Therefore, the light windmill effect tends to cause the light windmill to rotate clockwise, causing the illuminated first blade 211 to retreat from the light beam incident thereon. However, Figure 2A The light beam shown has a sufficiently low power that the optical windmill effect is insufficient to overcome the inertia of the optical windmill. Therefore, the optical windmill remains in its initial position adjacent to the first stop 281.

[0091] The first stopper 281 is a column that prevents the counterclockwise movement of the light windmill from exceeding Figure 2A The initial position shown is such that the reflected portion of the light beam is not mistakenly directed partially or completely to the right side of the output port 225, for example, in response to external vibration. For example, it can be formed of a material capable of absorbing impact force to reduce wear of the stopper 281 and the portion of the light windmill that contacts the stopper 281.

[0092] Figure 2B A relatively high power light source beam is shown entering housing 240 through input port 221, as indicated by the relatively narrow transverse cross-hatching lines. (Both uses of "relatively" in the preceding sentence indicate relative to Figure 2AIn this case, the radiant flux of the light beam striking the first blade 211 is high enough to generate a sufficient temperature gradient between the illuminated side and the shadowed side of the first blade 211, and the optical windmill effect causes the optical windmill to rotate clockwise about the axis 214, away from the first stop 281 and toward the second stop 282. Therefore, the input port 221 serves as a control port for the rotation of the optical windmill, and the light beams shown entering and traveling within the housing 240 are all the source beams, transmission beams, and control beams described above.

[0093] A biasing element (not shown) in the form of a resilient member attaching the light windmill to the housing 240 is provided to bias the light windmill towards Figure 2A The position shown is slightly offset. (The elastic member may alternatively be shaft 214.) This reduces the risk of the optical windmill rotating clockwise under any influence other than the optical windmill effect (e.g. in response to external vibrations). (The biasing element also increases the threshold radiant flux required to start the optical windmill rotation relative to an optical windmill whose acceleration is limited only by its own inertia.) Such a correctly calibrated biasing element can also be used to control the response of the limiter 200. This is because the rotation of the optical windmill will stop at the point where the optical windmill effect force is balanced by the biasing force. For example, if the optical windmill is connected to the housing 240 via an elastic member, the optical windmill will stop at the point where the optical windmill effect force is balanced by the biasing force. Figure 2A The angle of rotation of the position shown will be roughly proportional to the input beam power. Such a biasing element may be adjustable; for example, the tension of the elastic member may be adjusted by winding or unwinding the elastic member from a spool. Suitable biasing elements may take forms other than elastic members, such as springs or magnetic devices.

[0094] In the light windmill is Figure 2B In the position shown, a portion of the beam is still reflected generally toward the output port 225, but at an angle such that only some of the reflected portion of the beam is incident on the output port 225, with the remainder being blocked by the beam blocker 290. Figure 2B , the radiant flux of the output light beam leaving the housing 240 via the output port 225 is lower than the radiant flux of the source ( / control / transmission) light beam entering the housing 240 via the input ( / control) port 221. It can be seen that the higher the radiant flux of the light beam entering via the input port 221, the more the light windmill will rotate, and therefore the smaller the area of ​​the output port 225 that will be illuminated. Thus, the reflector provided by the reflective surface of the first blade 211 and the beam blocker 290 together form an optical baffle device that is arranged to prevent a portion of the light beam from irradiating the output port 225, the size of which portion depends on the angle of rotation of the light windmill.

[0095] A second stop 282 similar to the first stop 281 is provided by another column to set the light windmill from Figure 2AThe maximum rotation angle of the initial position shown. This prevents the second blade 212 from rotating to the extent of striking the housing 240. The positioning of the second stop 282 can be selected to have one of two effects on the response of the limiter 200 to high power input. If the second stop 282 is positioned far enough around the rotation path of the optical windmill so that the optical windmill can rotate far enough so that the light beam completely misses the output port 225, the limiter 200 will act to limit the output power to a certain input power and then effectively act as a fuse so that the output power drops to zero for all higher input powers. Alternatively, the second stop 282 can be positioned to limit the rotation of the optical windmill more so that if an input signal is present, the output radiation flux can be prevented from dropping to zero at any time. That is, the second stop 282 can be positioned so that the clockwise rotation of the optical windmill stops just at the point where the reflected portion of the light beam completely misses the output port. (However, this will allow the output power to increase to levels beyond what the limiter is intended to limit, so the use of a backup optical fuse in conjunction with this type of limiter may be advisable if there is a risk of damage to network equipment due to power surges exceeding the limiter level.)

[0096] The beam blocker 290 can be omitted from the limiter 200 and the light windmill is in Figure 2B Even with the position shown, a portion of the beam will still miss the output port 225 and instead strike the housing 240 near the output port 225. However, by using a dedicated beam blocker 290, the response of the limiter 200 can be controlled to be flatter than if the housing 240 surrounding the output port 225 were relied upon as part of a baffle arrangement.

[0097] Figure 3A and Figure 3B Shown with Figure 2A and Figure 2B Schematic plan view of an example optical fuse 300 of similar design to the optical limiter 200 of FIG. To avoid cluttering the two figures, reference numerals not relevant to the specific description of each figure are omitted in the figure, although all components involved are present in the limiter 300 as shown in each of the two figures. The optical fuse 300 includes an optical windmill having first blades 311 and second blades 312, which are configured to rotate about an axis 314. The optical windmill is enclosed in a housing 340 having an input port 321 and an output port 325. The rotation of the optical windmill is limited by a first limiter 381 and a second limiter 382. All of these components are arranged in accordance with Figure 2A and Figure 2B The corresponding components of limiter 200 function in the same manner.

[0098] However, in contrast to limiter 200, fuse 300 does not include the resilient member present in limiter 200. In addition, second blade 312 of fuse 300 is magnetic (e.g., by being made of iron or coated with a layer of iron), and fuse 300 also includes a biasing element in the form of a magnet 385. (In the illustrated design, magnet 385 is external to housing 340 to facilitate adjustment, as will be described below, but it could also be internal to housing 340.) As long as the radiant flux of the light beam input through input port 321 remains below a threshold, the magnetic attraction between magnet 385 and second blade 312 causes the optical windmill to be in a biased state. Figure 3A The position shown remains adjacent to the first stop 381 .

[0099] If the radiant flux of the input beam reaches or exceeds this threshold, the optical windmill effect overcomes the magnetic attraction and the optical windmill (not constrained by any elastic member) suddenly swings to Figure 3B The position shown is adjacent to the second stop 382, ​​wherein the reflected portion of the light beam completely misses the output port 325, causing the output power to drop sharply to zero.

[0100] Figure 3A and Figure 3B The light paths in the figure are represented by thin dashed lines and dotted lines (instead of Figure 2A and Figure 2B The shaded area in the figure indicates that the sharp response of the fuse at the threshold input power means that the width of the beam is irrelevant. The total width of the beam or Figure 3A as shown in the figure, or transmitted through the output port 325, or as shown in the figure. Figure 3B The output port 325 is completely missed. (Of course, when the output port 325 is illuminated by only a portion of the beam, the windmill Figure 3A and Figure 3B There are gaps between the positions shown, but these gaps are very brief.)

[0101] If and when the source beam is cut off, or its radiant flux drops below a threshold, magnet 385 causes the light windmill to rotate rapidly counterclockwise back to Figure 3A Thus, the fuse 300 is reusable and self-resetting.

[0102] The magnet 385 has an external member so that its position can be adjusted by screwing it closer to or further away from the second blade 312 within the internally threaded nut 386. In this way, the threshold power for causing the fuse to open can be adjusted. If the nut is long enough, the magnet 385 can even be retracted far enough from the second blade 312 so that the fuse 300 responds in much the same manner as the limiter 200. (In this case, a beam stopper similar to the beam stopper 290 of the limiter 200 can be added to flatten the response, as described above with respect to the Figure 2B ) Thus, the device 300 may be multifunctional in nature; providing an adjustable, reusable, self-resetting optical fuse / limiter.

[0103] Figure 3C The relative positions of the optical windmill (including first and second blades 311 and 312 configured to rotate about axis 314), input and output ports 321 and 325, first and second stoppers 381 and 382, ​​and magnet 385 of fuse 300 are three-dimensionally illustrated.

[0104] Figure 3D 3 is a plan view of the housing 340 and nut 386 of the fuse 300. The thickness of these components is indicated by the dashed lines on their inner walls. Also shown in dashed lines are two holes 341 and 345 in the housing 340, which are configured to help connect the input optical fiber (not shown) to the input port 321 and the output optical fiber (not shown) to the output port 325, respectively. The holes 341 and 345 have a stepped profile with a relatively narrow inner portion (e.g., a diameter of 3 mm) and a relatively wide outer portion (e.g., a diameter of 4.6 mm). The input port 321 and the output port 325 are sealed within the inner portion so that the housing is airtight, thereby allowing the air within the housing to be maintained at an optimal low pressure for the operation of the light windmill. The outer portion is configured to receive the optical fiber (not shown) with a tight interference fit.

[0105] The housing 240 of the limiter 200 can be identical to the housing 340 of the fuse 300. The housing 240 of the limiter 200 and the housing 340 of the fuse 300 can be, for example, approximately 11 mm high, 7 mm wide, and 27 mm long, with walls approximately 2 mm thick. They can be made, for example, of plastic, metal, or another impermeable solid.

[0106] In both the limiter 200 and the fuse 300, the housing 240, 340 ( Figures 2A to 3D A further port is provided in any one of the housings (not shown) for a vacuum device to be attached so that the air pressure within the housing can be maintained at a level that is optimal for the operation of the light windmill, for example between 300mTor and 600mTor.

[0107] The angles between the input and output ports 221 , 321 and 225 , 325 in the limiter 200 and the fuse 300 may be, for example, obtuse angles, such as approximately 120°.

[0108] The optical windmills of limiter 200 and fuse 300 may, for example, have blades that are approximately 1 mm thick and 10 mm long from axis to tip.

[0109] The entire limiter / fuse assembly 200, 300 may have a mass of approximately 15 g, for example.

[0110] The beam stopper 290 of the slicer 200 may be, for example, approximately 3 mm wide.

[0111] Now refer to Figures 4A to 9B Describes additional exemplary limiters and fuses. In these figures, the same Figures 2A to 3B That is: (i) to avoid cluttering the drawings, not all reference numerals are repeated across the multiple views of a particular device; (ii) relatively wide and narrow hatching is used in the depiction of the slicer to indicate relatively low-power and high-power beams; and (iii) thin dashed lines are used to indicate relatively low-power beams in the depiction of the fuse, while thin dot-dash lines are used to indicate relatively high-power beams.

[0112] Figure 4A and Figure 4B 1 and 2 show a schematic plan view of an example optical limiter 400 including an optical windmill in a first position and a second position, respectively. Figure 2A and Figure 2B The limiter 200 functions in a very similar manner. It comprises a light windmill having a first blade 411 and a second blade 412 configured to rotate about an axis 414. The light windmill is biased toward the housing 440 by being connected to the housing 440 via an elastic member (not shown). Figure 4A The light windmill is enclosed in a housing 440 having an input port 421 and an output port 425. The rotation of the light windmill is limited by a first stopper 481 and a second stopper 482. A beam blocker 490 is also provided. All of these components are arranged in accordance with Figure 2A and Figure 2B The corresponding components of the limiter 200 function in the same manner, the only difference being the geometry of their arrangement. Specifically, whereas the input port 421 is at an obtuse angle to the output port 425 in the limiter 200, the input port 421 is perpendicular to the output port 425 in the limiter 400.

[0113] Figure 5A and Figure 5B Shown with Figure 4A and Figure 4B Schematic plan view of an example optical fuse 500 of similar design to the optical limiter 400. The optical fuse 500 includes an optical windmill having a first blade 511 and a second blade 512, which are configured to rotate about an axis 514. The optical windmill is enclosed in a housing 540 having an input port 521 and an output port 525. The rotation of the optical windmill is limited by a first limiter 581 and a second limiter 582. All of these components are similar to Figure 4A and Figure 4B The corresponding components of the limiter 400 are the same.

[0114] However, in contrast to the limiter 400, in the fuse 500 there is no resilient member, the second blade 512 is magnetic, and the fuse 500 further comprises a biasing element in the form of a magnet 585. The magnet 585 is arranged in accordance with Figures 3A to 3C The magnet 385 of fuse 500 functions in a similar manner, except that it is located within housing 540 and is not adjustable. Therefore, fuse 500 has a fixed threshold input power value that will cause the fuse to open and cannot be used as a limiter. However, like fuse 300, fuse 500 is reusable and self-resetting.

[0115] Figure 6A and Figure 6B 1 and 2 show a schematic plan view of another example optical limiter 600 including an optical windmill in a first position and a second position, respectively. The limiter 600 is similar to Figure 4A and Figure 4B It functions in the manner of the limiter 400 of FIG. It comprises a light windmill enclosed in a housing 640 having an input port 621 and an output port 625. The light windmill is attached to the housing 640 by an elastic member (not shown) which biases the light windmill toward Figure 6A A beam blocker 690 is provided which functions in the same manner as the beam blocker 490 of the slicer 400 .

[0116] However, the limiter 600 is Figure 4A and Figure 4B The limiter 400 differs in that the control of the rotation and direction of the light from the input port 621 to the output port 625 is provided separately, rather than being provided by the first blade of the light windmill as in the limiter 400. Figure 6A and Figure 6B As shown, a source beam arriving from the left-hand side encounters a beam splitter 661 which splits the source beam into a control beam and a transmission beam.

[0117] The control beam is directed to the reflector 671, which directs the control beam to the first blade 611 of the optical windmill through the control port 631. The first blade 611 absorbs some or all of the energy of the control beam. Figure 6B As shown, the control beam is strong enough to cause the optical pinwheel to rotate clockwise due to the optical pinwheel effect caused by this absorption.

[0118] The transmitted light beam continues to pass through the beam splitter 661 and the input port 621 to be incident on the light guide 613 such as a reflector. The light guide 613 is part of the rigid assembly of the light windmill, centered on the axis 614 and configured to rotate around the axis 614 together with the first blade 611 and the second blade 612. The transmitted light beam is reflected by the light guide at an angle that depends on the rotational position of the light windmill. When the light windmill is in Figure 6A When the optical windmill is in the position shown, the transmission beam is incident on the output port 625, so that the power of the output beam is maximized. Figure 6B In the illustrated position, a portion of the transmitted light beam is blocked by the beam blocker 690, thereby reducing the power of the output light beam. Thus, the light guide 613 and the beam blocker 690 together form an optical baffle arrangement that is configured to prevent a portion of the transmitted light beam from irradiating the output port 625, the size of which portion depending on the angle of rotation of the light windmill.

[0119] Any counterclockwise rotation of the windmill caused by effects other than the windmill effect (e.g., external vibrations) is constrained by the first stop 681. The clockwise rotation of the windmill is constrained by a pair of second stops 682. One of the stops 682 can be omitted, although including two stops balances the forces on both sides of the windmill when it abuts the two stops, thereby reducing the risk of it bending or breaking. Figure 2B As described above, the positioning of the second stopper 682 determines the response of the limiter 600 to the high power source beam.

[0120] Figure 7A and Figure 7B Shown with Figure 6A and Figure 6B Schematic plan view of an example optical fuse 700 of similar design to the optical limiter 600. The optical fuse 700 includes an optical windmill having a first blade 711, a second blade 712, and a light guide 713 rigidly connected therebetween. All of the first blades 711, the second blades 712, and the light guide 713 are configured to rotate together around an axis 714. The optical windmill is enclosed in a housing 740 having an input port 721, an output port 725, and a control port 731. The optical windmill is attached to the housing 740 by an elastic member (not shown) that directs the optical windmill toward the Figure 7A The position shown is offset. The beam splitter 761 is configured to split the source beam into a transmission beam incident on the input port 721 and a control beam incident on the control port 731 through reflection by the reflector 771. The rotation of the optical windmill is constrained by a first stopper 781 and a pair of second stoppers 782. All these components are arranged in accordance with Figure 6A and Figure 6B The corresponding components of limiter 600 function in the same manner.

[0121] However, in contrast to limiter 600, there is no resilient member in fuse 700, second blade 712 is magnetic, and fuse 700 further includes a biasing element in the form of magnet 785. Magnet 785 functions in the same manner as magnet 585 of fuse 500.

[0122] Figure 8A and Figure 8B 1 and 2 show a schematic plan view of another example optical limiter 800 including an optical windmill in a first position and a second position, respectively. The limiter 800 is similar to Figure 6A and Figure 6B It functions in the same manner as the limiter 600 of FIG. It comprises a light windmill enclosed in a housing 840 having an input port 821, an output port 825 and a control port 831. The light windmill is attached to the housing 840 by an elastic member (not shown) which directs the light windmill toward the housing 840. Figure 8A The beam splitter 861 is configured to split the source beam into a transmission beam incident on the input port 821 and a control beam incident on the control port 831 by reflection from the mirror 871, as in Figure 6A and Figure 6B The clockwise rotation of the optical windmill is restricted by a pair of stoppers 882 corresponding to a pair of second stoppers 682 of the stopper 600 .

[0123] However, the limiter 800 is Figure 6A and Figure 6B The limiter 600 differs from the limiter 800 in that the light windmill of the limiter 800 does not include a light guide. The limiter 800 has an optical baffle arrangement comprising two beam blocks 891 and 892 which define the boundaries of the aperture. (Alternatively, the optical baffle arrangement may be provided by a single annular beam block which appears identical in a cross section through the horizontal plane of the aperture.) The beam blocks 891 and 892 are rigidly connected between the first blade 811 and the second blade 812 and are configured to rotate with them about an axis not shown (because it is attached to the shown part of the light windmill above and / or below the horizontal plane of the aperture). The output port 825 is parallel to and coaxial with the input port 821. When the light windmill is in Figure 8A In the position shown, the hole between the beam blockers 891 and 892 is located in the middle of the input port 821 and the output port 825 and is coaxial with them, so that the power of the output beam is maximized. Figure 8B As shown, when the light windmill is Figure 8A Rotate the position shown to Figure 8B In the position shown, an increased area of ​​the transmitted beam is blocked by beam blockers 891 and 892, resulting in a reduced power output beam.

[0124] Although a stopper may be provided, no stopper is shown to hold the windmill in place. Figure 8A The initial position shown can be configured to resist effects other than the optical windmill effect, such as external vibrations. For example, one or both of the first and second blades 811, 812 and / or the spokes to which they are mounted can be configured to be weakly attracted to one or more magnets in corresponding positions on the base and / or top of the housing 840. Alternatively, an elastic member may be sufficient to perform this function.

[0125] Figure 9A and Figure 9B Shown with Figure 8A and Figure 8B Schematic plan view of an example optical fuse 900 of similar design to the optical limiter 800 of FIG. The optical fuse 900 includes an optical windmill having a first blade 911, a second blade 912 and two beam blocks 991 and 992, which define an aperture and are rigidly connected between the first blade 911 and the second blade 912. All of the first blades 911 and the second blade 912 and the first beam blocker 991 and the second beam blocker 992 are configured to rotate together around an axis (not shown). The optical windmill is enclosed in a housing 940 having an input port 921, an output port 925 and a control port 931. The beam splitter 961 is configured to split the source light beam into a transmission light beam incident on the input port 921 and a control light beam incident on the control port 931 via reflection from a reflector 971. All of these components are connected to Figure 8A and 8B The corresponding components of limiter 800 are the same.

[0126] However, in contrast to limiter 800, there is no resilient member in fuse 900, second blade 912 is magnetic, and fuse 900 also includes a biasing element in the form of magnet 985. Magnet 985 functions in the same manner as magnet 785 of fuse 700.

[0127] The fuse 900 further includes a first stopper 981 and a second stopper 982 to Figure 5A and Figure 5B The first limiting member 581 and the second limiting member 582 of the fuse 500 respectively constrain the counterclockwise rotation and the clockwise rotation of the optical windmill in a similar manner.

[0128] In all of the example limiters and fuses described above, at least one region of at least one face of at least one blade of each light windmill is configured to have light incident thereon and absorb energy from the light such that the light causes the at least one region to heat up relative to an opposing region of an opposite face of the blade. The absorbing region may be coated, for example, with graphite, black aluminum foil, anodized aluminum, or Litho-Black. TM . If the opposing regions are thermally insulated from each other and the absorbing region is illuminated to a greater extent than the opposing region, there need not be any asymmetry in their optical absorptivity. (Optical absorptivity is defined as the ratio of the absorbed radiant power to the incident radiant power.) The illuminating light, being a laser beam, is sufficiently narrow relative to the dimensions of the blade so that only one side of the blade is targeted, enhancing the effect. However, the optical windmill effect can be enhanced by providing an absorbing region with a higher optical absorptivity than the opposing region. For example, the opposing region may be covered with a reflective metal, such as silver or a dielectric material. Alternatively or additionally, the absorbing region may be shaped so that it receives a greater amount of radiant flux than the opposing region within the allowed rotation range of the optical windmill, utilizing the above description of Figure 1C The principle of description.

[0129] The optical windmills of all the exemplary fuses and limiters described above include two blades: a first blade and a second blade, with the first blade configured to be struck by the control beam and the second blade acting as a counterweight. The second blade can be omitted, and the optical windmill will still rotate in response to the control beam. Alternatively, the optical windmill can be provided with more than two blades.

[0130] Some of the example limiters and fuses described above include one or more light guides, such as reflectors. Such reflectors can be provided by at least partially reflecting surfaces. If the mirror needs to be able to absorb some light, such as in the above description of Figures 2A to 5B In the exemplary switches and limiters 200, 300, 400, and 500 described, their surfaces can be made partially reflective, for example, by laminating a thin dielectric on a light-absorbing surface (e.g., a surface coated with a light-absorbing material as described above). Other optical components (such as prisms) can also be used as light guides.

[0131] In all of the exemplary limiters and fuses described above, at least one component of the optical baffle arrangement is arranged to rotate with the optical pinwheel. However, other arrangements are contemplated in which the motion of the optical pinwheel causes the transmission light beam to be redirected or blocked in some other manner. For example, a cam arrangement may be used to convert the rotational motion of the optical pinwheel into linear motion of the light guide.

[0132] In all the exemplary limiters and fuses described above, the movement of the windmill is constrained by a stop in the form of a buffer / shock absorber / support element provided for one or more of the windmill blades (and / or the spokes carrying them), but against an upward force. Alternatively, a single stop can be provided for a plurality of blades, for example so that in a two-blade example the windmill rotates almost a full circle between its two positions.

[0133] Other forms of stops may also be used; elements that prevent or inhibit rotation in one direction beyond a certain position while allowing (some) reverse rotation out of that position are suitable. For example, in addition to the magnetic stops described above, other types of mechanical stops, such as catches, may also be envisaged.

[0134] The optical transmission (input / output) ports and control ports used in the limiters and fuses according to the present disclosure can be used to couple light from fiber to fiber. They can optionally include lenses to focus or defocus the light appropriately.

[0135] Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein.The specification and embodiments are intended to be exemplary only.

[0136] In addition, where the application has listed the steps of a method or process in a particular order, it is possible, or even advantageous in some cases, to change the order in which some steps are performed, and unless such sequence specificity is explicitly stated, the specific steps of the method or process set forth herein are not to be construed as being sequence specific. That is, unless otherwise indicated, the operations / steps may be performed in any order, and embodiments may include more or fewer operations / steps than those disclosed herein. It is further contemplated that performing or executing a particular operation / step before, concurrently with, or after another operation is in accordance with the described embodiments.

Claims

1. An optical limiter for limiting the radiant flux of a light beam from a light source, the limiter comprising: a light control port, the light control port being illuminated by a light control beam originating from the light source beam; a light input port illuminated by a light transmission beam originating from the light source beam; a light output port, the light output port being illuminated by the light transmission beam; as well as heat-driven light windmills; The optical windmill is arranged relative to the optical input port, the optical control port and the optical output port such that: The illumination of the light control port by the light control beam drives the light windmill to rotate only when the light control beam has a radiation flux that is equal to or exceeds a predetermined radiation flux threshold; and The rotation of the optical windmill causes the area of ​​the optical output port illuminated by the light transmission beam to change.

2. The optical limiter according to claim 1, wherein The optical limiter is configured to allow the optical windmill to rotate by an angle large enough to make the area of ​​the optical output port illuminated by the optical transmission beam zero, so that the limiter acts as a reusable optical fuse.

3. The optical limiter according to claim 1 or 2, wherein: The optical limiter is configured to limit a radiation flux of a light source beam originating from a laser.

4. The optical limiter according to claim 1, wherein: The side of the blade of the light windmill which is arranged to be illuminated by the light control beam in use has a higher light absorption rate than the opposite side of the blade; and / or The side of the blade of the light windmill that is arranged to be illuminated by the light control beam during use and the opposite side of the blade are shaped so that in use, within the allowable rotation range of the light windmill, the side of the blade illuminated by the light control beam receives a larger amount of radiation energy from the light control beam than the opposite side.

5. The optical limiter according to claim 1, wherein The optical limiter further comprises an optical baffle device arranged to prevent a portion of the optical transmission beam from irradiating the optical output port, the size of the portion being dependent on the angle of rotation of the optical windmill.

6. The optical limiter according to claim 5, wherein The optical partition device comprises: one or more light guides; and / or One or more beam blockers.

7. The optical limiter according to claim 5 or 6, wherein: The optical input port and the optical output port are coaxial with each other; The optical baffle arrangement includes one or more beam blockers arranged to rotate with the optical windmill; as well as The one or more beam blockers are arranged to define an aperture through which the light transmission beam must pass in order to reach the light output port.

8. The optical limiter according to claim 1, wherein The light input port is the light control port, and the light source beam itself serves as the light transmission beam and the light control beam in use.

9. The optical limiter according to claim 1, wherein The optical limiter further includes a beam splitter configured to split the light source beam into the light transmission beam and the light control beam.

10. The optical limiter according to claim 1, further comprising a biasing element; in, The light windmill is coupled to the biasing element such that the light windmill is biased toward a first rotational position in which an area of ​​the light output port illuminated by the light transmission beam is maximized relative to any other rotational position of the light windmill.

11. The optical limiter according to claim 10, wherein The biasing element is configured to be adjustable so that the biasing force applied by the biasing element to the light windmill can be varied.

12. The optical limiter according to claim 10 or 11, wherein the optical limiter is configured to allow the optical windmill to rotate by an angle large enough to make the area of ​​the optical output port illuminated by the optical transmission beam zero, so that the limiter acts as a reusable optical fuse, wherein The biasing element is configured to: When the radiation flux of the light source light beam is lower than the predetermined radiation flux threshold, preventing the light windmill from rotating away from the first rotation position; as well as When the radiation flux of the light source beam is equal to or exceeds the predetermined radiation flux threshold, the light windmill is allowed to rotate from the first rotation position by a sufficiently large angle so that the area of ​​the light output port illuminated by the light transmission beam is zero.

13. The optical limiter according to claim 1, wherein The optical limiter further includes one or more limiters, each limiter being configured to prevent the optical windmill from rotating beyond a specific rotational position.

14. The optical limiter according to claim 1, wherein The optical limiter further includes a housing surrounding the optical windmill, the housing including a hole configured to partially drain fluid around the optical windmill.

15. A method for limiting the radiant flux of a light beam from a light source, the method comprising: irradiating the optical input port of the optical limiter according to any one of claims 1 to 14 with an optical transmission light beam originating from the light source light beam; as well as The optical control port of the optical limiter according to any one of claims 1 to 14 is irradiated with an optical control beam originating from the light source beam.

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