GB2575442A - Passive thermal compensation of electromagnetic systems and components - Google Patents

Passive thermal compensation of electromagnetic systems and components Download PDF

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Publication number
GB2575442A
GB2575442A GB1811140.1A GB201811140A GB2575442A GB 2575442 A GB2575442 A GB 2575442A GB 201811140 A GB201811140 A GB 201811140A GB 2575442 A GB2575442 A GB 2575442A
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Prior art keywords
electromagnetic
change
arrangement
fluid
volume
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GB201811140D0 (en
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Hill Calum
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Thales Holdings UK PLC
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Thales Holdings UK PLC
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06704—Housings; Packages
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08013—Resonator comprising a fibre, e.g. for modifying dispersion or repetition rate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/083—Ring lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking
    • H01S3/1109—Active mode locking
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/139—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1305—Feedback control systems

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)

Abstract

A passively thermally compensated electromagnetic arrangement 2, may be a fibre laser system (Figure 1) comprising an electromagnetic element, for example an optical fibre (6, Figure 2) for interaction with an electromagnetic field. A bellows (40, Figure 2) includes a body (41, Figure 3B) and a fluid which may be olive oil ( 2 , Figure 3B). The body 41 contains the fluid and may expand or contraction with the fluid. The electromagnetic arrangement expands or contracts when there is a change in pressure and/or volume of the fluid occurring as a result of a change of temperature that acts through the body to cause a change in the interaction between the electromagnetic element and the electromagnetic field to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid. Alternatively, the arrangement may be used for the passive thermal compensation of an electromagnetic system or, component such as an optical system or, an optical component for example an isolator (Figure 4).

Description

PASSIVE THERMAL COMPENSATION OF ELECTROMAGNETIC SYSTEMS AND COMPONENTS
FIELD
Passive thermal compensation of electromagnetic systems and components is described herein and, in particular though not exclusively, passive thermal compensation of optical systems such as optical fibre lasers, including mode-locked fibre lasers, and optical fibre interferometers, and passive thermal compensation of optical components such as optical isolators and optical circulators.
BACKGROUND
It is known to use passive thermal compensation in actively mode-locked optical fibre lasers to stabilise the output from mode-locked optical fibre lasers. Known passive thermal compensators rely upon the thermal expansion of a metal member or the differential thermal expansion of two different metallic members to stretch a length of optical fibre of the fibre laser. Such known passive thermal compensators may be relatively large, relatively heavy and/or prone to vibrations or mechanical instabilities. Such known passive thermal compensators may not be able to provide a sufficient range of motion and/or a sufficient force to compensate the actively mode-locked optical fibre laser for a given temperature variation. This may be particularly true for large temperature variations such as those occurring in harsh environments.
It is also known to use active thermal compensation in actively mode-locked optical fibre lasers to stabilise the output from mode-locked optical fibre lasers. However, all active thermal compensation methods increase power consumption and require the measurement of the cavity length in situ which may be difficult and/or which may increase system complexity.
For example, it is known to use an optical fibre wrapped around a piezoceramic cylinder and to apply a voltage to the piezoceramic cylinder causing its diameter to change and stretching the optical fibre and providing a change in the optical length of the cavity of the optical fibre laser. However such known active thermal compensation methods may require high voltages to operate. This may further increase system complexity. Also, such known active thermal compensation methods may suffer from hysteresis in the piezoceramic cylinder.
It is also known to actively control cavity length changes in an optical fibre laser resulting from a change in temperature using a translation stage to control the distance between two fibre collimators. However, such methods may introduce optical alignment issues that can degrade laser performance due to the introduction of a freespace optical path within the laser cavity.
SUMMARY
It should be understood that any of the features of any one of the following aspects or embodiments may apply alone or in any combination in relation to any one or more of the other aspects or embodiments.
According to an aspect or embodiment of the present disclosure there is provided a passively thermally compensated electromagnetic arrangement, comprising:
an electromagnetic element configured for interaction with an electromagnetic field; and a bellows arrangement including a body and a fluid, wherein the body contains the fluid and is configured for expansion and contraction with the fluid, wherein the electromagnetic arrangement is configured so that the change in pressure and/or volume of the fluid occurring as a result of a change of temperature acts through the body to cause a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
Use of a bellows arrangement may provide a passively thermally compensated electromagnetic arrangement which is simpler, smaller or more compact, lighter and/or less susceptible to vibrations or mechanical instabilities than known passively thermally compensated electromagnetic arrangements. Use of a bellows arrangement may provide a range of motion and/or a force which is sufficient to passively thermally compensate for a larger temperature variation than known passively thermally compensated electromagnetic arrangements.
The body may define a sealed cavity. The sealed cavity may contain the fluid.
The body may comprise a bellows portion or part.
The bellows portion or part may have a radius in the range of 1 to 100 mm, 5 to 15 mm or a radius of 8 mm. The bellows portion or part may have a length of 10 to 200 mm, a length of 20 to 100 m or a length of 50 mm. The bellows portion or part may provide a displacement of 0.1 - 10 mm, 0.5 - 5 mm, 1-3 mm or 2 mm over a 50° C temperature range.
The bellows portion or part may comprise, or be formed from, metal, for example aluminium.
The body may comprise a rigid body portion or part.
The rigid body portion or part may comprise, or be formed from, metal, for example aluminium.
The bellows portion or part and the rigid body portion or part may be connected, joined, coupled, attached or fastened together in any way.
The fluid may comprise a liquid.
The fluid may comprise an oil such as olive oil.
The fluid may comprise a gas.
The body may define an aperture to allow the body to be filled with the fluid.
The bellows arrangement may comprise a seal arrangement for sealing the aperture.
The seal arrangement may comprise a screw and a seal member.
The aperture in the body may define a female thread. The screw may comprise a head and a shank, the shank defining a male thread. The seal member may define an aperture through which the shank of the screw extends. The male thread of the screw may engage the female thread defined by the aperture in the body so as to compress the seal member between the head of the screw and the body.
The seal arrangement may comprise a cap.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a force exerted between the body and the electromagnetic element.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body and a relative movement between the body and the electromagnetic element. The relative movement between the body and the electromagnetic element may be linear with temperature.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in stress and/or strain of the electromagnetic element. A change in stress and/or strain of the electromagnetic element may result in a change in an electromagnetic length of the electromagnetic element. The change in the electromagnetic length of the electromagnetic element may be linear with temperature.
The electromagnetic element may be attached to, extend around, and/or be wrapped around the body.
The electromagnetic arrangement may comprise first and second members, wherein the electromagnetic element interacts mechanically with the first and second members and the body is attached, directly or indirectly, between the first and second members so that the change in pressure and/or volume of the fluid acts through the body so as to exert a force between the first and second members and/or so as to move the first and second members relative to one another, resulting in a change in stress and/or strain of the electromagnetic element.
The movement between the first and second members relative to one another may be linear with temperature.
The electromagnetic element may be attached to, extend between, and/or be wrapped around the first and second members.
The first and second members may each comprise a mandrel.
One or both of the first and second members may comprise a cylinder or a hemi-cylinder.
The electromagnetic arrangement may comprise an interaction element which is configured to interact non-mechanically with the electromagnetic element so as to vary an electromagnetic property of the electromagnetic element according to the nature and/or degree of the non-mechanical interaction between the interaction element and the electromagnetic element.
The body and the interaction element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a relative movement between the interaction element and the electromagnetic element so as to vary the electromagnetic property of the electromagnetic element and thereby change the interaction between the electromagnetic element and the electromagnetic field. The movement between the interaction element and the electromagnetic element may be linear with temperature.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a movement of the electromagnetic element relative to the electromagnetic field. The movement between the electromagnetic element and the electromagnetic field may be linear with temperature.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a change in position and/or orientation of the electromagnetic element relative to the electromagnetic field.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a movement of the electromagnetic element relative to a further electromagnetic element. The movement between the electromagnetic element and the further electromagnetic element may be linear with temperature.
The body and the electromagnetic element may be mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a change in position and/or orientation of the electromagnetic element relative to the further electromagnetic element.
The electromagnetic element may comprise an optical element and the electromagnetic field may comprise an optical field.
The electromagnetic element may comprise a passive optical element.
The electromagnetic element may comprise an optical fibre. Such an electromagnetic arrangement may provide thermal compensation for changes in an optical length of an optical fibre in an “all-fibre” optical system architecture.
The electromagnetic element may comprise a lens or a mirror.
The electromagnetic arrangement may comprise an optical isolator or an optical circulator. The electromagnetic element may form part of an optical isolator or an optical circulator. The electromagnetic element may comprise a Faraday rotator. The interaction element may comprise a magnet.
The electromagnetic element may comprise an RF element and the electromagnetic field may comprise an RF electromagnetic field.
The electromagnetic element may comprise an RF delay line having first and second parts and the electromagnetic arrangement may be configured so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby resulting in a relative movement between the first and second parts of the RF delay line and a change in an RF delay associated with the RF delay line.
The body may be attached, directly or indirectly, between the first and second parts of the RF delay line.
According to an aspect or embodiment of the present disclosure there is provided a passive thermal compensator for passively thermally compensating an interaction between an electromagnetic element and an electromagnetic field, the passive thermal compensator comprising:
a bellows arrangement including a body and a fluid, wherein the body contains the fluid and is configured for expansion and contraction with the fluid, wherein the passive thermal compensator is configured so that a change in pressure and/or volume of the fluid occurring as a result of a change in temperature acts through the body and is capable of causing a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
According to an aspect or embodiment of the present disclosure there is provided a passively thermally compensated electromagnetic system comprising the passively thermally compensated electromagnetic arrangement or the passive thermal compensator described above.
According to an aspect or embodiment of the present disclosure there is provided a fibre interferometer comprising the passively thermally compensated electromagnetic arrangement or the passive thermal compensator described above.
According to an aspect or embodiment of the present disclosure there is provided a fibre laser comprising the passively thermally compensated electromagnetic arrangement or the passive thermal compensator described above.
According to an aspect or embodiment of the present disclosure there is provided a mode-locked fibre laser comprising the passively thermally compensated electromagnetic arrangement or the passive thermal compensator described above. Such a mode-locked fibre laser may be used to generate an optical pulse train with exceptional timing stability. The optical pulse train may then be used as a sampling signal for analogue to digital converters and/or for time correlated measurements.
According to an aspect or embodiment of the present disclosure there is provided a passively thermally compensated electromagnetic component comprising the passively thermally compensated electromagnetic arrangement or the passive thermal compensator described above.
According to an aspect or embodiment of the present disclosure there is provided a method for passively thermally compensating the interaction between an electromagnetic element and an electromagnetic field, the method comprising:
containing a fluid in a body of a bellows arrangement, the body being configured for expansion and contraction with the fluid;
configuring the bellows arrangement and the electromagnetic element such that a change in pressure and/or volume of the fluid occurring as a result in a change in temperature acts through the body to cause a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
Passively thermally compensated electromagnetic arrangements and systems are described herein by way of non-limiting example only with reference to the following drawings of which:
Figure 1 shows a thermally compensated actively mode-locked fibre laser;
Figure 2 shows a passively thermally compensated fibre stretching assembly of the mode-locked fibre laser of Figure 1;
Figure 3A shows the components of a bellows assembly of the fibre stretching assembly of Figure 2 prior to assembly of the components to form the bellows assembly;
Figure 3B shows the bellows assembly formed by assembling the components of Figure 3A; and
Figure 4 shows a passively thermally compensated optical isolator.
DETAILED DESCRIPTION OF THE DRAWINGS
One of skill in the art will understand that one or more of the features of the embodiments described below with reference to the drawings may produce effects or provide advantages when used in isolation from one or more of the other features of the embodiments and that different combinations of the features are possible other than the specific combinations of the features of the embodiments described below.
Referring initially to Figure 1 there is shown a passively thermally compensated electromagnetic system in the form of a passively thermally compensated actively mode-locked fibre laser system generally designated 2. The fibre laser system 2 includes an optical gain medium in the form of a semiconductor optical amplifier SOA and a Mach-Zehnder modulator MZM for mode-locking. The fibre laser system 2 includes a circulator ‘Circ’, a chirped fibre Bragg grating mirror CBM and a first optical fibre coupler OC1. The fibre laser system 2 further includes a passively thermally compensated electromagnetic arrangement in the form of a passively thermally compensated fibre stretching assembly generally designated 4 for the passive thermal compensation of the fibre laser system 2 and an actively thermally compensated fibre stretching assembly PZT for the active thermal compensation of the fibre laser system
2. The fibre laser system 2 also includes an electromagnetic element in the form of an optical fibre 6 which optically couples the semiconductor optical amplifier SOA, the circulator ‘Circ’, the Mach-Zehnder modulator MZM, the first optical fibre coupler OC1, the passive fibre stretching assembly 4 and the active fibre stretching assembly PZT in a loop which defines a 15.3 m long ring cavity of the mode-locked fibre laser system 2.
The chirped fibre Bragg grating mirror CBM is optically coupled to a second port of the circulator ‘Circ’ so that light entering a first port of the circulator is directed out through the second port of the circulator ‘Circ’ to the chirped fibre Bragg grating mirror CBM and light reflected back from the chirped fibre Bragg grating mirror CBM through the second port of the circulator ‘Circ’ is directed out through a third port of the circulator ‘Circ’ for onward transmission around the loop of optical fibre 6.
The fibre laser system 2 further includes a second optical fibre coupler OC2 and a pair of optical detectors PD1 and PD2. In addition, the fibre laser system 2 includes an electrical signal generator 8 for electrically driving the Mach-Zehnder modulator MZM and a controller 10.
In use, the semiconductor optical amplifier SOA amplifies light circulating in the loop of optical fibre 6 defining the cavity of the fibre laser system 2 and the electrical signal generator 8 drives the Mach-Zehnder modulator MZM under the control of the controller 10 so as to modulate an intracavity loss in the optical fibre 6 at a rate which is matched to the cavity’s resonant frequency so as to stimulate mode-locking and thereby generating a stream of optical pulses from the fibre laser system 2 at a repetition rate of 7.2 GHz. The chirped fibre Bragg grating mirror CBM controls dispersion in the fibre laser system 2 so as to control the quality of the optical pulses emitted by the fibre laser system 2 via the first optical fibre coupler OC1.
The optical length of the cavity of the fibre laser system 2 defined by the loop of optical fibre 6 changes by 12 mm over a temperature range of 0° to 50° C. This change in optical length causes the pulse repetition rate of the fibre laser system 2 to vary or drift. The optical pulse train generated by the fibre laser system 2 is also optimised for low phase noise and timing jitter so that if the cavity length shifts from its optimum length, additional noise may be coupled into the fibre laser system 2. Consequently, the fibre laser system 2 is thermally compensated by both the passively thermally compensated fibre stretching assembly 4 and the actively thermally compensated fibre stretching assembly PZT so as to maintain the optical length of the loop of optical fibre 6 and, therefore, the optical length of the cavity of the fibre laser system 2 constant over a pre-determined temperature range. Specifically, as explained in more detail below, the passively thermally compensated fibre stretching assembly 4 passively changes a fibre stretching force and/or degree of fibre stretching in response to a temperature change. The controller 10 monitors the fibre stretching force and/or degree of fibre stretching provided by the passively thermally compensated fibre stretching assembly 4 and controls the fibre stretching force and/or degree of fibre stretching provided by the actively thermally compensated fibre stretching assembly PZT accordingly. In effect, the passively thermally compensated fibre stretching assembly 4 provides coarse thermal compensation over the predetermined temperature range whilst the actively thermally compensated fibre stretching assembly PZT provides fine thermal compensation over the pre-determined temperature range.
The actively thermally compensated fibre stretching assembly PZT includes a piezoceramic cylindrical mandrel 20. The controller 10 applies a high voltage electrical signal to the piezoceramic mandrel 20 so as to vary a diameter of the piezoceramic cylindrical mandrel 20.
The passively thermally compensated fibre stretching assembly 4 is shown in more detail in Figure 2 and includes a base member 30, a fixed cylindrical mandrel 32 which is fixed to the base member 30, and a moveable cylindrical mandrel 34 which is slidable relative to the base member 30 along a rail or slot 36. As will be described in more detail below with reference to Figures 3A and 3B, the passively thermally compensated fibre stretching assembly 4 further includes a bellows arrangement in the form of a bellows assembly 40 for moving the moveable mandrel 34.
Referring to Figure 3B, the bellows assembly 40 includes an aluminium body generally designated 41 and a fluid in the form of olive oil 42, wherein the body 41 is configured for expansion and contraction with the olive oil 42. The body 41 includes a generally cylindrical rigid body portion or part 43 and a bellows portion or part 44. As shown more clearly in Figure 3A, the rigid body portion 43 defines a first aperture 46 at a first end thereof for the communication of the olive oil 42 between the rigid body portion 43 and the bellows portion 44. The rigid body portion 43 defines a second aperture 48 at a second end thereof for receiving a seal screw generally designated 50. The rigid body portion 43 defines a female thread profile 48A around the second aperture 48.
The seal screw 50 includes a head 52, a shank 54 extending from the head 52, and a seal member 56 mounted on the shank 54. The shank 54 defines a male thread profile 54A.
The bellows assembly 40 is assembled by attaching the bellows portion 44 to the first end of the rigid body portion 43 as shown in Figure 3B. The rigid body portion 43 and the bellows portion 44 may define one or more complementary inter-engaging features for this purpose. For example, the rigid body portion 43 and the bellows portion 44 may each define complementary threaded profiles for this purpose (not shown). One of the rigid body portion 43 and the bellows portion 44 may define a circumferential slot (not shown) and the other of the rigid body portion 43 and the bellows portion 44 may define a circumferential ridge, rib, flange, lip or the like (not shown) which is configured to snap into the slot (not shown). Additionally or alternatively, the rigid body portion 43 and the bellows portion 44 may be attached together using epoxy, adhesive, solder or the like. Additionally or alternatively, the rigid body portion 43 and the bellows portion 44 may be welded together, for example laser welded together.
Once the rigid body portion 43 and the bellows portion 44 are attached to form the body 41, the body 41 is submerged in a bath of the olive oil 42 and subjected to ultrasonic waves to remove air from the cavity defined by the body 41 and thereby ensure that the cavity is filled completely with the olive oil 42. The bellows portion 44 is then compressed into a contracted state and the shank 54 of the seal screw 50 is inserted into the second aperture 48 defined in the second end of the rigid body portion 43 until the male threaded profile 54A defined by the shank 54 of the seal screw 50 is in threaded engagement with the female threaded profile 48A defined by the second aperture 48 defined in the second end of the rigid body portion 43. With the body 41 still submerged in the olive oil 42, the seal screw 50 is rotated so as to insert the seal screw 50 further into the cavity defined by the body 41 causing the bellows portion 44 to expand as olive oil 42 is pushed into the bellows portion 44 until the seal member 56 is compressed between the head 52 of the seal screw 50 and the rigid body portion 43.
The volume of the shank 54 of the seal screw 50 is carefully selected so as to control the volume of the olive oil 42 contained in the body 41. In particular, for a given diameter of the shank 54, the length of the shank 54 is carefully selected so as to control the volume of olive oil 42 contained in the body 41.
Returning to Figure 2, the rigid body portion 43 of the bellows assembly 40 is attached to the base member 30. The tip or end of the bellows portion 44 is attached to the moveable mandrel 34, for example using epoxy or adhesive. The optical fibre 6 is wrapped around the mandrels 32, 34 five times and held in tension such that any change in pressure of the olive oil 42 in the body 41 of the bellows assembly 40 occurring as a result of a change in temperature causes a change in the force applied by body 41 of the bellows assembly 40 to the movable mandrel 34, thereby causing a change in the stress experienced by the optical fibre 6. Similarly, any change in volume of the olive oil 42 resulting from a change in temperature causes a change in volume of the body 41 of the bellows assembly 40 thereby causing the movable mandrel 34 to move relative to the fixed mandrel 32 and causing a change in the strain experienced by the optical fibre 6. With five loops of the optical fibre 6 around the mandrels 32, 34, the body 41 of the bellows assembly 40 is designed to provide a linear travel range of 1.2 mm from 0° C to 50° C so that the passive fibre stretching assembly 4 compensates for the change of 12 mm in the optical length of the optical fibre 6 over the same temperature range. The expansion or contraction of the fluid may be calibrated to control the degree or rate of thermal compensation provided by the passive fibre stretching assembly 4 to minimise any variation in the optical length of the loop of the optical fibre 6 and, therefore, also minimise any variation in the pulse repetition rate of the fibre laser system 2. As such, the passive fibre stretching assembly 4 may decrease overall system complexity and allow thermal compensation to be performed over relatively large temperature ranges whilst also eliminating the need for a free-space optical path in the laser system. The use of the “all-fibre” architecture shown in Figure 1 also avoids the alignment issues associated with solidstate lasers which include free-space optical components. Compared with known passive thermal compensation arrangements, the passive fibre stretching assembly 4 may be more compact. For example, it is estimated that a 15.3 m long fibre laser that experiences an optical path length change of 11 mm for a 50°C temperature change, would require a piece of aluminium which is approximately 1 m in length to provide passive thermal compensation.
Although the passively thermally compensated fibre stretching assembly 4 has been described above for the passive thermal compensation of the actively modelocked fibre laser system 2, one of ordinary skill in the art will understand that the passively thermally compensated fibre stretching assembly 4 may be employed to passively thermally compensate other optical fibre systems. For example, the passively thermally compensated fibre stretching assembly 4 may be used for the passive thermal compensation of a passively mode-locked fibre laser system, a fibre interferometer of any kind, or optical fibre system where the passive thermal compensation of the optical length of an optical fibre is required.
Figure 4 shows an alternative passively thermally compensated electromagnetic arrangement in the form of a passively thermally compensated optical isolator generally designated 102 including an electromagnetic element in the form of a generally cylindrical Faraday rotator 106 and a non-mechanical interaction element in the form of a generally tubular magnet 160 located around the Faraday rotator 106. The Faraday rotator 106 and the magnet 160 are moveable relative to one another along an optical axis 162. The optical isolator 102 further includes an input polariser P1 arranged on the optical axis 162 before the Faraday rotator 106 and the magnet 160 and an output polariser P2 arranged on the optical axis 162 after the Faraday rotator 106 and the magnet 160. The input polariser P1 is oriented so as to transmit vertically polarised light, whereas the output polariser P2 is oriented so as to transmit light polarised at an angle of 45° relative to the vertical. It should be understood that the Faraday rotator 106 and the rigid body portion 43 of the bellows assembly 40 are fixed relative to one another. For example, the Faraday rotator 106 and the rigid body portion 43 of the bellows assembly 40 may both be fixed to a base member (not shown). The bellows portion 44 of the bellows assembly 40 is attached to the magnet 160.
In use, the bellows assembly 40 is configured to move the magnet 160 relative to the Faraday rotator 106 in response to a change in temperature so as to maintain the degree of isolation provided by the optical isolator 102 over a pre-determined temperature range. Specifically, the input light incident from the left-hand side of Figure 4 upon the input polariser P1 is vertically polarised by the input polariser P1 before entering an input side of the Faraday rotator 106. The bellows assembly 40 is configured to move the magnet 160 relative to the Faraday rotator 106 in response to a change in temperature within the pre-determined temperature range so that the Faraday rotator 106 rotates the linear polarisation of the vertically polarised light by 45° so that the light emerging from an output side of the Faraday rotator 106 has a linear polarisation at an angle of 45° to the vertical at any temperature within the predetermined temperature range. The light emerging from the output side of the Faraday rotator 106 then passes through the output polariser P2 as output light at any temperature within the pre-determined temperature range.
Any of the output light reflected from the right-hand side of Figure 4 with the same linear polarisation at an angle of 45° to the vertical is transmitted by the output polariser P2 before entering the output side of the Faraday rotator 106. The bellows assembly 40 is configured to move the magnet 160 relative to the Faraday rotator 106 in response to the change in temperature within the pre-determined temperature range so that the Faraday rotator 106 rotates the linear polarisation of the vertically polarised light by a further 45° in the same sense as before so that the light emerging from the input side of the Faraday rotator 106 is horizontally polarised at any temperature within the pre-determined temperature range. The horizontally polarised light emerging from the input side of the Faraday rotator 106 is then blocked by the input polariser P1 at any temperature within the pre-determined temperature range.
Although the bellows assembly 40 has been described above for the passive thermal compensation of the optical isolator 102, one of ordinary skill in the art will understand that the bellows assembly 40 may be employed for the passive thermal compensation of other optical elements, components, assemblies or systems. For example, the bellows assembly 40 may be used for the passive thermal compensation of an optical element which interacts with an optical field so as to maintain the interaction between the optical element and the optical field for any temperature in a pre-determined temperature range. The bellows assembly 40 may be used so as to maintain an optical property of the optical element for any temperature in a predetermined temperature range. The bellows assembly 40 may be used so as to maintain a position and/or orientation of the optical element for any temperature in a pre-determined temperature range. For example, the bellows assembly 40 may be used so as to maintain a position and/or orientation of a mirror or a lens for any temperature in a pre-determined temperature range.
Furthermore, one of ordinary skill in the art will understand that the bellows assembly 40 may be employed for the passive thermal compensation of electromagnetic elements, components, assemblies or systems other than optical elements, components, assemblies or systems. The bellows assembly 40 may be employed for the passive thermal compensation of an electromagnetic element that interacts with an electromagnetic field having a frequency other than an optical frequency. For example, the bellows assembly 40 may be employed for the passive thermal compensation of an RF element which interacts with an RF electromagnetic field. For example, the electromagnetic element may comprise an RF delay line having first and second parts and the bellows assembly 40 may be configured so that a change in the volume of the bellows assembly 40 causes a change in position and/or orientation of the first part of the RF delay line relative to a position and/or orientation of the second part of the RF delay line. For example, the bellows assembly 40 may be attached, directly or indirectly, between the first and second parts of the RF delay line so that the change in the volume of the body of the bellows assembly 40 causes a relative movement between the first and second parts of the RF delay line and a change in an RF delay associated with the RF delay line.
One of ordinary skill in the art will understand that various other modifications may be made to the passively thermally compensated electromagnetic arrangements previously described without departing from the scope of the present invention as defined by the appended claims. For example, rather than the rigid body portion 43 and/or the bellows portion 44 of the bellows assembly 40 being formed separately and then joined or attached to form the body 41 of the bellows assembly 40, the body 41 of the bellows assembly 40 may be unitary or formed integrally. Rather than the rigid body portion 43 and/or the bellows portion 44 of the bellows assembly 40 comprising, or being formed, from aluminium, the rigid body portion 43 and/or the bellows portion 44 may comprise, or be formed, from a metal or material of any kind. Rather than using olive oil 42 as the fluid within the bellows assembly 40, the bellows assembly 40 may contain a fluid of any kind. For example, the bellows assembly 40 may contain a liquid of any kind. The bellows assembly 40 may contain an oil of any kind. The bellows assembly 40 may contain a gas of any kind.
The fluid may be selected so as to provide a pre-determined change in pressure and/or volume of the fluid over a pre-determined temperature range.
The fluid may be selected so that the bellows assembly 40 exerts a predetermined force over the pre-determined temperature range. The fluid may be selected so that the bellows assembly 40 undergoes a pre-determined change in volume and, therefore, a pre-determined change in length over the pre-determined temperature range. The fluid may be selected so that the bellows assembly 40 causes one or more members to move by a pre-determined distance relative to one another over the pre-determined temperature range.
The fluid may be selected so that the bellows assembly 40 causes an interaction element to move by a pre-determined distance relative to the electromagnetic element over the pre-determined temperature range.
The fluid may be selected so that the bellows assembly 40 causes the electromagnetic element to move by a pre-determined distance relative to the electromagnetic field and/or a further electromagnetic element over the pre-determined temperature range.
The expansion or contraction of the fluid and, therefore, the expansion or contraction of the body of the bellows assembly 40 may be calibrated to precisely control the amount of expansion or contraction of the body of the bellows assembly 40 over the pre-determined temperature range.
The volume of the fluid contained by the bellows assembly 40 may be selected so as to provide a pre-determined change in pressure and/or volume of the fluid over a pre-determined temperature range. The volume of the fluid contained by the bellows assembly 40 may be selected so that the bellows assembly 40 exerts a pre-determined force and/or so that the bellows assembly 40 undergoes a pre-determined change in volume and, therefore, a pre-determined change in length over a pre-determined temperature range. The volume of the shank 54 of the seal screw 50 may be selected so as to control the volume of the fluid contained by the bellows assembly 40. For example, the length of the shank 54 of the seal screw 50 may be selected so as to control the volume of the fluid contained by the bellows assembly 40.
Although the mandrels 32, 34 of the passively thermally compensated fibre stretching assembly 4 are cylindrical, one or both of the mandrels may have a different shape. For example, one or both of the mandrels may be hemi-cylindrical.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.

Claims (25)

1. A passively thermally compensated electromagnetic arrangement, comprising:
an electromagnetic element configured for interaction with an electromagnetic field; and a bellows arrangement including a body and a fluid, wherein the body contains the fluid and is configured for expansion and contraction with the fluid, wherein the electromagnetic arrangement is configured so that a change in pressure and/or volume of the fluid occurring as a result of a change of temperature acts through the body to cause a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
2. An electromagnetic arrangement as claimed in claim 1, wherein the body comprises or is formed from metal.
3. An electromagnetic arrangement as claimed in any preceding claim, wherein the fluid comprises a liquid or an oil such as olive oil.
4. An electromagnetic arrangement as claimed in any preceding claim, wherein the fluid comprises a gas.
5. An electromagnetic arrangement as claimed in any preceding claim, wherein the body defines an aperture to allow the body to be filled with the fluid and the bellows arrangement comprises a seal arrangement for sealing the aperture.
6. An electromagnetic arrangement as claimed in claim 5, wherein the seal arrangement comprises a screw and a seal member.
7. An electromagnetic arrangement as claimed in claim 6, wherein the aperture in the body defines a female thread and the screw comprises a head and a shank, the shank defining a male thread, wherein the seal member defines an aperture through which the shank of the screw extends, and wherein the male thread of the screw engages the female thread defined by the aperture in the body so as to compress the seal member between the head of the screw and the body.
8. An electromagnetic arrangement as claimed in any preceding claim, wherein the body and the electromagnetic element are mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a force exerted between the body and the electromagnetic element.
9. An electromagnetic arrangement as claimed in any preceding claim, wherein the body and the electromagnetic element are mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body and a relative movement between the body and the electromagnetic element.
10. An electromagnetic arrangement as claimed in any preceding claim, wherein the body and the electromagnetic element are mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in stress and/or strain of the electromagnetic element.
11. An electromagnetic arrangement as claimed in any preceding claim, wherein the electromagnetic element is attached to, extends around, and/or is wrapped around the body.
12. An electromagnetic arrangement as claimed in any preceding claim, comprising first and second members, wherein the electromagnetic element interacts mechanically with the first and second members and the body is attached, directly or indirectly, between the first and second members so that the change in pressure and/or volume of the fluid acts through the body so as to exert a force between the first and second members and/or so as to move the first and second members relative to one another resulting in a change in stress and/or strain of the electromagnetic element.
13. An electromagnetic arrangement as claimed in claim 12, wherein the electromagnetic element is attached to, extends between, and/or is wrapped around the first and second members.
14. An electromagnetic arrangement as claimed in any one of claims 1 to 7, comprising an interaction element which is configured to interact non-mechanically with the electromagnetic element so as to vary an electromagnetic property of the electromagnetic element according to the nature and/or degree of the non-mechanical interaction between the interaction element and the electromagnetic element.
15. An electromagnetic arrangement as claimed in claim 14, wherein the body and the interaction element are mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a relative movement between the interaction element and the electromagnetic element so as to vary the electromagnetic property of the electromagnetic element and thereby change the interaction between the electromagnetic element and the electromagnetic field.
16. An electromagnetic arrangement as claimed in any one of claims 1 to 7, wherein the body and the electromagnetic element are mechanically coupled so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby causing a movement of the electromagnetic element relative to the electromagnetic field and/or relative to a further electromagnetic element.
17. An electromagnetic arrangement as claimed in any preceding claim, wherein the electromagnetic element comprises an optical element and the electromagnetic field comprises an optical field.
18. An electromagnetic arrangement as claimed in claim 17 when dependent on any one of claims 1 to 13, wherein the electromagnetic element comprises an optical fibre.
19. An electromagnetic arrangement as claimed in claim 17 when dependent on claim 14 or 15, wherein at least one of:
the electromagnetic arrangement comprises an optical isolator or an optical circulator;
the electromagnetic element forms part of an optical isolator or an optical circulator; and the electromagnetic element comprises a Faraday rotator and the interaction element comprises a magnet.
20. An electromagnetic arrangement as claimed in claim 17 when dependent on claim 16, wherein the electromagnetic element comprises a lens or a mirror.
21. An electromagnetic arrangement as claimed in any one of claims 1 to 16, wherein the electromagnetic element comprises an RF element and the electromagnetic field comprises an RF electromagnetic field.
22. An electromagnetic arrangement as claimed in claim 21, wherein the electromagnetic element comprises an RF delay line having first and second parts and the electromagnetic arrangement is configured so that the change in pressure and/or volume of the fluid results in a change in a volume of the body, thereby resulting in a relative movement between the first and second parts of the RF delay line and a change in an RF delay associated with the RF delay line.
23. A passively thermally compensated electromagnetic system or component comprising the electromagnetic arrangement as claimed in any preceding claim, for example a passively thermally compensated optical system or component comprising the electromagnetic arrangement of claim 17, or a passively thermally compensated optical fibre laser or optical fibre interferometer comprising the electromagnetic arrangement of claim 18.
24. A passive thermal compensator for passively thermally compensating an interaction between an electromagnetic element and an electromagnetic field, the passive thermal compensator comprising:
a bellows arrangement including a body and a fluid, wherein the body contains the fluid and is configured for expansion and contraction with the fluid, wherein the passive thermal compensator is configured so that a change in pressure and/or volume of the fluid occurring as a result of a change in temperature acts through the body and is capable of causing a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
25. A method for passively thermally compensating the interaction between an 5 electromagnetic element and an electromagnetic field, the method comprising:
containing a fluid in a body of a bellows arrangement, the body being configured for expansion and contraction with the fluid;
configuring the bellows arrangement and the electromagnetic element such that a change in pressure and/or volume of the fluid occurring as a result in a change in 10 temperature acts through the body to cause a change in the interaction between the electromagnetic element and the electromagnetic field so as to at least partially compensate for a change in the interaction between the electromagnetic element and the electromagnetic field that would have otherwise occurred for the same change in temperature in the absence of the change in pressure and/or volume of the fluid.
GB1811140.1A 2018-07-06 2018-07-06 Passive thermal compensation of electromagnetic systems and components Withdrawn GB2575442A (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57100781A (en) * 1980-12-16 1982-06-23 Fujitsu Ltd Photo semiconductor device
US6229827B1 (en) * 1998-12-04 2001-05-08 Cidra Corporation Compression-tuned bragg grating and laser
WO2012075474A2 (en) * 2010-12-02 2012-06-07 Ofs Fitel, Llc Dfb fiber laser bend sensor and optical heterodyne microphone

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57100781A (en) * 1980-12-16 1982-06-23 Fujitsu Ltd Photo semiconductor device
US6229827B1 (en) * 1998-12-04 2001-05-08 Cidra Corporation Compression-tuned bragg grating and laser
WO2012075474A2 (en) * 2010-12-02 2012-06-07 Ofs Fitel, Llc Dfb fiber laser bend sensor and optical heterodyne microphone

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