Patent Description:
Electronic components such as laser circuitry can generate unwanted heat during use. Cooling systems such as oscillating heat pipes can be used to transfer heat away from such components and improve their functioning.

<NPL> relates to a number of heat exchange methods. In particular a "spaghetti" heat pipe is disclosed. The "spaghetti" heat pipe consists of a large evaporator region and a compact condenser, with working ammonia fluid flowing between the regions. It operates due to the oscillating motion of the two phases of working fluid within, with the gaseous part of the fluid generated via evaporation within the evaporator and the liquid phase generated through condensation at the condenser region. The condenser is enveloped in a porous material and is in thermal contact with the evaporator region of an adsorption refrigerator.

<CIT> relates to a heat transport device that can be used for cooling electronics equipment. It includes a container with a hollow structure in which a fluid channel is formed, a thermal-receiver-type heat exchanged and thermal-radiator-type heat exchanger arranged side by side on an outer wall of the container along the fluid channel, and driving heat exchangers provided at both terminal portions of the container. In this heat transport device, both ends of the fluid channel are closed to prevent intrusion of external air, and a liquid and gas are sealed in the fluid channel. The driving heat exchangers cause the liquid to oscillate in the container along its fluid channel. A porous element may be provided at the terminal portions of the container where the driving heat exchangers are provided.

<CIT> discloses a planar pulsating heat pipe which may have a wick structure located within the evaporator tubing region. The evaporator region is in the middle, adjacent to a heat source, and the condenser regions are on either side where the u-shaped bends are located. Working liquid in two phases pulsates around the device in a closed loop, driven by alternating boiling and condensing which transports heat away from the evaporator regions.

<CIT> discloses an open-cell foam metal heat pipe-fin combined CPU radiator. It consists of a heat source, base, open-cell foam metal, an air collecting chamber, hollow needle pins and a heat sink. Liquid is injected into the base cavity and evacuated into the foam metal, the bottom of the device is the hot evaporation end and the top of the device at the top of the hollow pin fins is the cool end. When the device is heated at the bottom end, evaporated water vapour flows into the hollow pins from the foam metal via the air collecting chamber. The vapour condenses back into water droplets on the walls of the pin and flow below, circulating continuously. Thus, heat is transferred away from the evaporator region.

According to the invention, there is provided an oscillating heat pipe comprising:.

The wick structure may be located within at least one evaporator region.

The oscillating heat pipe may comprise a plurality of U-shaped bends within the evaporator region.

The at least one wick structure may be located at, at least one of, the U-shaped bends.

A single wick structure may be fluidically connected to a plurality of different sections of evaporator regions of the oscillating heat pipe.

A plurality of wick structures may be connected to a plurality of different evaporator regions of the oscillating heat pipe.

The wick structure may comprise a gating portion and an evaporator portion.

According to various, but not necessarily all, examples of the disclosure there may be provided an apparatus comprising an oscillating heat pipe as claimed in any preceding claim and one or more heat sources wherein the oscillating heat pipe is configured to cool the one or more heat sources.

The one or more heat sources may comprise laser circuitry configured to enable light detection and ranging and wherein the oscillating heat pipe is configured to cool the laser circuitry.

The laser circuitry may be configured for light detection and ranging is configured to provide light in at least two distinct bands of wavelengths.

The laser circuitry may comprise at least two different reflective semiconductor optical amplifiers configured to provide light in, at least two distinct bands of wavelengths.

According to various, but not necessarily all, examples of the disclosure there may be provided an electronic device comprising an apparatus as described herein wherein the electronic device comprises at least one of; a communication device, a camera, a vehicle, and a part of a vehicle.

<FIG> schematically shows an example oscillating heat pipe <NUM>. The oscillating heat pipe <NUM> comprises a condenser region <NUM>, an evaporator region <NUM> and an adiabatic section <NUM>.

The evaporator region <NUM> comprises any means for transferring heat from a heat source into the working fluid within the oscillating heat pipe <NUM>. The evaporator region <NUM> is thermally coupled to a heat source. The heat source could be laser circuitry for a LiDAR device or any other suitable type of circuitry. The oscillating heat pipe <NUM> could be machined into the outer surfaces of components of the laser circuitry or other components.

The condenser region <NUM> comprises any means for transferring heat out of the working fluid within the oscillating heat pipe <NUM>. The condenser region <NUM> can be thermally coupled to a heat sink or any other suitable type of means for transferring heat out of the working fluid.

The oscillating heat pipe <NUM> is configured in a meandering or serpentine configuration comprising a plurality of bends. A first plurality of bends is located in the evaporator region <NUM> and a second plurality of bends is located in the condenser region <NUM>. In the example shown in <FIG> three U-shaped bends are shown in the evaporator region <NUM> and two U-shaped bends are shown in the condenser region <NUM>. Other configurations and numbers of bends could be used in other examples of the disclosure. The meandering or serpentine configuration is configured so that the working fluid within the oscillating heat pipe <NUM> is alternately heated in the evaporator region <NUM> and cooled in the condenser region <NUM> of the oscillating heat pipe <NUM>.

In the example shown in <FIG> an adiabatic section <NUM> is provided between the evaporator region <NUM> and the condenser region <NUM>. The adiabatic section <NUM> extends between the bends in the condenser region <NUM> and the bends in the evaporator region <NUM>. The adiabatic section <NUM> ensures that heat that is transferred into the working fluid in the evaporator region <NUM> is retained within the oscillating heat pipe <NUM> until the working fluid reaches the condenser region <NUM>. In some examples the oscillating heat pipe <NUM> does not comprise an adiabatic section <NUM>. Whether or not the oscillating heat pipe <NUM> comprises an adiabatic section <NUM> can depend on the application and system geometry of the oscillating heat pipe <NUM> and any other suitable factors.

When the oscillating heat pipe <NUM> is in use, heat is applied to the working fluid in the bends within the evaporator region <NUM>. This heat causes, at least some of, the working fluid to evaporate. This evaporation results in an increase of vapour pressure inside the oscillating heat pipe <NUM> which causes the growth of bubbles <NUM> within the evaporator region <NUM>. The growth of the bubbles <NUM> and the increase in vapour pressure forces liquid slugs <NUM> of the working fluid towards the condenser region <NUM>. The working fluid that is pushed to the condenser region <NUM> is then cooled by the condenser. This cooling reduces the vapour pressure within the working fluid and causes condensation of the bubbles <NUM> and provides a restoring force that pushes the working fluid back towards the evaporator region <NUM>. This process of alternate bubble growth and condensation causes oscillation of the working fluid within the oscillating heat pipe <NUM> and allows for the transfer of heat between the evaporator region <NUM> and the condenser region <NUM>.

<FIG> schematically shows an oscillating heat pipe <NUM> with wick structures <NUM>. The addition of the wick structures <NUM> increases the efficiency with which the oscillating heat pipe <NUM> can transfer heat. This can enable the oscillating heat pipe <NUM> of <FIG> to be used to cool components that generate large amounts of unwanted heat. For example, the oscillating heat pipe <NUM> could be used to cool laser circuitry for a LiDAR devices or any other suitable type of circuitry or electronic components.

The oscillating heat pipe <NUM> comprises a channel <NUM> that is configured to enable flow of working fluid between at least one condenser region <NUM> and at least one evaporator region <NUM>. In the example of <FIG> one condenser region <NUM> and one evaporator region <NUM> are shown. In other examples the oscillating heat pipe <NUM> could comprise a plurality of condenser regions <NUM> and/or a plurality of evaporator regions <NUM>. The number of condenser regions <NUM> and evaporator regions <NUM> could be determined by the number and locations of heat sources that are to be cooled by the oscillating heat pipe <NUM>, the number and locations of heat sinks that enable heat to be transferred from the condenser regions <NUM> and/or any other suitable factor.

The oscillating heat pipe <NUM> comprises a plurality of bends in the evaporator region <NUM>. The bends allow the channel <NUM> of the oscillating heat pipe <NUM> to extend in different directions. In this example they enable the channel <NUM> to double back on itself so that different sections of the channel <NUM> extend in opposing directions. The sections that extend in opposing directions can be parallel, or substantially parallel. In the example of <FIG> the plurality of bends are U-shaped, or substantially U-shaped. In the example of <FIG> the oscillating heat pipe <NUM> comprises four U-shaped bends in the evaporator region. The oscillating heat pipe <NUM> could comprise a different number of U-shaped bends in other examples of the disclosure.

In the example of <FIG> the oscillating heat pipe <NUM> comprises a wick structure <NUM>. The wick structure <NUM> is located external to the channel <NUM> of the oscillating heat pipe <NUM>. In the example of <FIG> the wick structure <NUM> is located within the evaporator region <NUM>. In examples where the oscillating heat pipe <NUM> comprises a plurality of evaporator regions the wick structure <NUM> could be provided in all of the evaporator regions <NUM> or could be provided in just a subset of the evaporator regions <NUM>. In other examples the wick structure <NUM> could be located in a different position of the oscillating heat pipe <NUM>.

The wick structure <NUM> can be provided adjacent to the bends in the evaporator region <NUM>. In the example of <FIG> the wick structure <NUM> is located at the U-shaped bends. In the example of <FIG> the wick structure <NUM> is located on each of the U-shaped bends. In other examples the wick structure <NUM> could be provided on just a subset of the U-shaped bends.

The wick structure <NUM> can be formed from any suitable material. In some examples the wick structure <NUM> can be formed from a thermally conductive material such as copper or silicon to enable efficient transfer of heat into the wick structure <NUM>. In some examples different portions of the wick structure <NUM> can be formed from different materials, such as glass or ceramic.

The wick structure <NUM> comprises microfluidic channels. Working fluid from the oscillating heat pipe <NUM> can flow through the microfluidic channels of the wick structure <NUM> by capillary action. This can provide for a higher fluidic resistance compared to the channel <NUM> of the oscillating heat pipe <NUM>, but also enable lower thermal resistance.

The wick structure <NUM> is external to the channel <NUM> of the oscillating heat pipe <NUM> but is provided in fluidic connection with the channel <NUM> of the oscillating heat pipe <NUM>. This fluidic connection enables working fluid from the channel <NUM> of the oscillating heat pipe <NUM> to flow from the channel <NUM> into the wick structure <NUM>.

Different arrangements of the wick structure <NUM> can be used in different examples of the disclosure. In some examples a single wick structure <NUM> can be fluidically connected to a plurality of different sections of evaporator regions <NUM> of the oscillating heat pipe <NUM>. For example, a single continuous wick structure <NUM> could be connected to a plurality of U-shaped bends, or other suitable sections, of the evaporator region <NUM>. An example of this is shown in the top half of <FIG> where the wick structure <NUM> is continuous between two of the U-shaped bends of the oscillating heat pipe <NUM>. In this arrangement the wick structure <NUM> is not thermally isolated for the different bends of the oscillating heat pipe <NUM>.

In some examples different wick structures <NUM> can be fluidically connected to different sections of evaporator regions <NUM> of the oscillating heat pipe <NUM>. For example, a plurality of separate wick structures <NUM> could be connected to a plurality of U-shaped bends, or other suitable sections, of the evaporator region <NUM>. An example of this is shown in the lower half of <FIG> where the wick structure <NUM> is discontinuous between two of the U-shaped bends of the oscillating heat pipe <NUM>. In this example the discontinuous wick structures <NUM> can be thermally isolated from the wick structures <NUM> on different bends of the oscillating heat pipe <NUM>. In some examples an isolation wall <NUM> can be provided between the different wick structures <NUM>. The isolation wall <NUM> can be configured to separate different sections of the wick structure <NUM>. The isolation wall <NUM> can comprise any suitable thermally insulating material that can prevent the transfer of heat and/or working fluid between the different wick structures <NUM> on the different bends. In some examples the isolation wall <NUM> can also enable pressure distributions across the different wick structures <NUM> to be controlled.

In the example of <FIG> the wick structure <NUM> comprises a plurality of different portions. The different portions of the wick structure can be configured to enable different functions to be performed. In the example of <FIG> the wick structure <NUM> comprises a gating portion <NUM> and an evaporator portion <NUM>. Both of these portions can be external to the channel of the oscillating heat pipe <NUM>.

The gating portion <NUM> can cover a section of the outer surface of the channel <NUM> of the oscillating heat pipe <NUM>. The gating portion <NUM> is configured to enable fluid to flow out of the channel <NUM> of the oscillating heat pipe <NUM> into the wick structure <NUM>. The gating portion <NUM> can be configured to allow liquid to pass through preferentially to vapour. The gating portion <NUM> can enable working fluid to flow from the channel <NUM> of the oscillating heat pipe <NUM> through the gating portion <NUM> and into the evaporator portion <NUM>. The flow of working fluid from the channel <NUM> of the oscillating heat pipe <NUM> through the gating portion <NUM> and into the evaporator portion <NUM> is indicated by the arrows <NUM> in <FIG>.

The evaporator portion <NUM> of the wick structure <NUM> is configured to enable heat to be transferred to the working fluid in the wick structure <NUM>. The evaporator portion <NUM> can be in good thermal contact with a heat source. The evaporator portion <NUM> can be configured to enable efficient heat transfer between the heat source and the working fluid in the evaporator portion <NUM>. For example, the evaporator portion <NUM> could have a large surface area to facilitate the transfer of heat and/or the evaporation of the working fluid.

The oscillating heat pipe <NUM> also comprises at least one vent <NUM>. The vent <NUM> is configured to enable working fluid in an, at least partial, vapour phase to be returned from the wick structure <NUM> to the channel <NUM> of the oscillating heat pipe <NUM>.

The vent <NUM> extends from the wick structure <NUM> into the channel <NUM> of the oscillating heat pipe <NUM>. The vent <NUM> is configured to enable evaporated, or partially evaporated, working fluid to flow from the wick structure <NUM> back into the channel <NUM> of the oscillating heat pipe <NUM>.

The vents <NUM> can be located so as to bias the flow of working fluid within the channel <NUM> of the oscillating heat pipe <NUM>.

In the example shown in <FIG> a vent <NUM> is provided on each bend of the evaporator region <NUM>. Other arrangements for the vents <NUM> could be used in other examples. The arrangements used for the locations of the vents <NUM> may be determined by the locations of the wick structure <NUM>, the geometry of the channel of the oscillating heat pipe <NUM> or any other suitable factor.

The vents <NUM> can be configured so that any working fluid that flows from the channel <NUM> into the wick structure <NUM> is returned to the channel <NUM> via the vent <NUM>. This can maintain the mass of working fluid within the oscillating heat pipe <NUM>. The return of the working fluid back into the channel <NUM> of the oscillating heat pipe <NUM> can enable the oscillating heat pipe <NUM> to function as a closed loop. In the closed loop the evaporated working fluid is returned to the oscillating heat pipe <NUM> rather than being lost to the environment.

Any suitable processes can be used to form the oscillating heat pipe <NUM> and the wick structure <NUM>. In some examples the oscillating heat pipe <NUM> and/or the wick structure <NUM> can be machined into the walls and/or other surfaces of an electronic device that comprises the oscillating heat pipe <NUM>. The oscillating heat pipe <NUM> and/or the wick structure <NUM> can be formed using dry etching, selective laser wet etching or any other suitable processes.

<FIG> schematically shows a cross section of the oscillating heat pipe <NUM> shown in <FIG>. The cross section is taken through the line A-A' as shown in <FIG>. Corresponding reference numerals are used for corresponding features.

The cross section shows the different portions <NUM>, <NUM> of the wick structure <NUM>. This shows the gating portion <NUM> and the evaporator portion <NUM> of the wick structure <NUM>.

The gating portion <NUM> is provided adjacent to the channel <NUM> of the oscillating heat pipe <NUM>. In this example there are no intervening components between the channel <NUM> of the oscillating heat pipe <NUM> and the gating portion <NUM> of the wick structure <NUM>. The gating portion <NUM> can be configured to provide a part of the wall of the channel <NUM> of the oscillating heat pipe <NUM>. The gating portion <NUM> is directly connected to the channel <NUM> so that the working fluid can flow from the channel <NUM> into the gating portion <NUM>. The working fluid can flow from the channel <NUM> into the gating portion <NUM> by capillary action.

The gating portion <NUM> is provided between the channel <NUM> of the oscillating heat pipe <NUM> and the evaporator portion <NUM> of the wick structure <NUM> so that the evaporator portion <NUM> of the wick structure <NUM> is provided adjacent to the gating portion <NUM>. In this example there are no intervening components between the gating portion <NUM> and the evaporator portion <NUM>. The wick structure <NUM> is configured so that working fluid flows from the gating portion <NUM> into the evaporator portion <NUM> as indicated by the arrow <NUM> in <FIG>.

In the example shown in <FIG> the evaporator portion <NUM> is arranged in a different orientation to the gating portion <NUM>. The evaporator portion <NUM> is arranged in a perpendicular orientation, or substantially perpendicular orientation, to the gating portion <NUM>. As shown in <FIG> the gating portion <NUM> extends in a largely vertical plane while the evaporator portion <NUM> extends in a largely horizontal plane. This arrangement of the evaporator portion <NUM> can provide for a larger surface area which can facilitate the transfer of heat and the evaporation of the working fluid.

In some examples the different portions of the wick structure <NUM> can be formed from different materials. The gating portion <NUM> mainly enables the transfer of fluid rather than the transfer of heat and so does not need to be as thermally conductive as the evaporator portion <NUM>. As an example, the evaporator portion <NUM> could be formed from a thermally conductive material such as a metal so as to enable efficient transfer of heat through the evaporator portion <NUM> and the gating portion <NUM> could be formed from a different material such as glass.

A cavity <NUM> is positioned underneath the evaporator portion <NUM>. The cavity <NUM> provides a space for evaporated working fluid. The cavity <NUM> can be fluidically connected to the vent <NUM> as shown in <FIG> so that evaporated working fluid, or partially evaporated working fluid, can flow from the cavity <NUM> into the vent <NUM> and be returned to the channel <NUM> of the oscillating heat pipe <NUM>.

When the oscillating heat pipe <NUM> as show in <FIG> is in use heat <NUM> from a heat source is applied to the evaporator portion <NUM> of the wick structure <NUM>. The heat source could be circuitry or electronic components that generate unwanted heat during use, or any other suitable heat sources. This causes the heating and evaporation of working fluid within the wick structure <NUM>. As the working fluid evaporates more working fluid is drawn out of the channel <NUM> of the oscillating heat pipe <NUM> and into the wick structure <NUM>.

The working fluid that has evaporated from the wick structure <NUM> enters the cavity <NUM>. The evaporated, or partially evaporated, working fluid then returns to the channel <NUM> of the oscillating heat pipe <NUM> via the vent <NUM>.

The use of the wick structure <NUM> therefore provides for efficient transfer of heat to the working fluid and can improve the efficiency of heat transfer by the oscillating heat pipe <NUM>. This can make the oscillating heat pipe <NUM> suitable for use for colling components or circuitry that generate relatively large amounts of unwanted heat. For example, it could be used to cool laser circuitry as shown in <FIG> and <FIG> or any other suitable type of circuitry.

Variations to the structure and geometry of the oscillating heat pipe <NUM> and the wick structure <NUM> could be used in other examples of the disclosure. For instance, the wick structure <NUM> could be provided as s ingle portion rather than a gating portion <NUM> and an evaporator portion <NUM>.

<FIG> schematically shows an example apparatus <NUM> comprising an oscillating heat pipe <NUM> and one or more heat sources <NUM>. In the example of <FIG> only one heat source <NUM> is shown. It is to be appreciated that, in other examples of the disclosure, the apparatus <NUM> could comprise a plurality of heat sources. The apparatus <NUM> could be comprised within an electronic device such as a communication device, a camera, a vehicle, a part of a vehicle or any other suitable device.

The oscillating heat pipe <NUM> is configured within the apparatus <NUM> so as to cool the one or more heat sources <NUM>. The oscillating heat pipe <NUM> can comprise an evaporator region <NUM> and a condenser region <NUM>. The oscillating heat pipe <NUM> can comprise one or more wick structures <NUM>. The one or more wick structures <NUM> can be as shown in <FIG> and/or can be provided in any other suitable arrangement or configuration.

In the example of <FIG> the wick structure <NUM> is provided in the evaporator region <NUM> of the oscillating heat pipe <NUM>. In this example the wick structure <NUM> comprises a continuous structure that extends across a plurality of U-shaped bends of the channel <NUM> of the oscillating heat pipe <NUM>. Other arrangements of the wick structure <NUM> could be used in other examples of the disclosure.

The wick structure <NUM> could comprise a gating portion <NUM> and an evaporation <NUM> as shown in <FIG> or could be provided in a single portion.

The components of the apparatus <NUM> are arranged so that the wick structure <NUM> of the oscillating heat pipe <NUM> are in thermal contact with the one or more heat sources <NUM>. In examples where the wick structure <NUM> comprises a gating portion <NUM> and an evaporator portion <NUM> the evaporator portion <NUM> of the wick structure <NUM> can be in thermal contact with the one or more heat sources <NUM>. This thermal contact can enable heat from the heat sources to be transferred to working fluid in the wick structures <NUM>.

The heat sources <NUM> can comprise any components or circuitry that generate unwanted heat during use. In some examples the heat sources <NUM> can comprise laser circuitry configured to enable light detection and ranging (LiDAR). The LiDAR can be used to detect objects, obtain images of objects, determine positions of objects or for any other suitable purpose.

In the example shown in <FIG> the oscillating heat pipe <NUM> is configured to cool a single heat source <NUM>. In this example the oscillating heat pipe <NUM> comprises a single condenser region <NUM> and a single evaporator region <NUM>. In other examples the oscillating heat pipe <NUM> could comprise a plurality of condenser regions <NUM> and/or a plurality of evaporator regions <NUM>. The oscillating heat pipe <NUM> can be configured so that different evaporator regions <NUM> can be used to cool different heat sources <NUM>. In examples where the different heat sources <NUM> are provided in different locations with the device <NUM> the oscillating heat pipe <NUM> can be arranged so that the different evaporator regions <NUM> are also provided in different locations. Similarly, the condenser regions <NUM> can be provided in different locations to enable the device <NUM> to comprise a plurality of different heat sinks in different locations.

<FIG> and <FIG> schematically shows an example laser circuity <NUM> that could be one or more of the heat sources <NUM> in some examples of the disclosure. The laser circuitry can be configured for LiDAR applications or for any other suitable purpose. In this example the laser circuitry <NUM> is configured to provide light in at least two distinct bands of wavelengths. The two bands of wavelengths can be distinct in that the gap between the bands of wavelengths is much bigger than the gap between the wavelengths used within the bands of wavelengths.

The example laser circuitry <NUM> comprises an array <NUM> of gain sections and an optical wavelength multiplexer <NUM>. The gain sections can comprise Reflective Semiconductor Amplifiers (RSOAs) or any other suitable types of moderators.

The array <NUM> of gain sections and the optical wavelength multiplexer <NUM> are provided within a laser cavity <NUM>. A first reflective surface <NUM> is provided on a first side of the laser cavity <NUM> and a second reflective surface <NUM> is provided on a second side of the laser cavity <NUM>. The array <NUM> of gain sections and the optical wavelength multiplexer <NUM> are provided between the reflective surfaces.

The array <NUM> of gain sections, when coupled to the optical wavelength multiplexer <NUM>, are configured to provide a set of output light signals, each at a particular wavelength. A single output wavelength can be obtained from each of the gain sections when the light emitted by each of them is transmitted through the wavelength multiplexer <NUM>.

In the example of <FIG> six of the gain sections in the array <NUM> are shown. It is to be appreciated that the array <NUM> could comprise any suitable number of gain sections. The array <NUM> could comprise many more than six gain sections.

The array <NUM> can comprise a plurality of different subsets of gain sections. The different subsets of the gain sections can be configured to provide light in different wavelength bands. In the example of <FIG> the array <NUM> comprises two subsets of gain sections. The first subset are configured with a gain spectrum in a first wavelength band λA and the second subset are configured with a gain spectrum in a second, different wavelength band λB.

The different subsets of the gain sections within the array <NUM> can be arranged in any suitable configuration. In the example of <FIG> the different subsets are provided in an alternating configuration. In this example the array <NUM> comprises an alternating sequence of a gain section that provides light in the first wavelength band λA followed by a gain section that provides light in the second wavelength band λB. Other arrangements for the array <NUM> of gain sections could be used in other examples. For instance, a first subset of the gain sections could be provided at a first side of the laser cavity <NUM> and a second subset could be provided a second side.

The gain sections can generate unwanted heat during use. The gain sections could therefore provide a heat source <NUM> that could be cooled using an oscillating heat pipe <NUM> as described herein.

The optical wavelength multiplexer <NUM> can be configured to combine the outputs of the individual gain sections within the array <NUM> to provide a single combined output. Any suitable means could be used as the optical wavelength multiplexer <NUM>. In some examples the optical wavelength multiplexer <NUM> could be implemented using an arrayed waveguide grating. An example of an arrayed waveguide grating <NUM> that could be used is shown in <FIG>. Other suitable means could be used as the optical wavelength multiplexer <NUM>, such as for example echelle gratings or circuits formed by an arrangement of microring resonators, Mach-Zehnder interferometers or Bragg gratings.

<FIG> schematically shows a top-view of an arrayed waveguide grating <NUM>. The arrayed waveguide grating <NUM> comprises a first star coupler <NUM>, a second star coupler <NUM>, a plurality of input waveguides <NUM>, a plurality of connecting waveguides <NUM>, and an output waveguide <NUM>.

The plurality of input waveguides <NUM> are coupled to the input of the first start coupler <NUM>. In this example N input waveguides <NUM> are coupled to the input of the first star coupler <NUM>. The number of input waveguides <NUM> can be the same as the number of gain sections in the array <NUM>. An input waveguide <NUM> can be provided for each of the gain sections within the array <NUM>.

The input waveguides <NUM> can be coupled to the gain sections so that the input waveguides receive light emitted by the gain sections. In this example each of the input waveguides <NUM> is coupled to a different gain section so each waveguide receives an input from a different gain section. Optical coupling between the gain sections and the input waveguides <NUM> can be achieved through direct butt-coupling between the gain sections chips and the chip hosting the wavelength multiplexer or by using free-space components, such as for example lenses. Alternatively, in some materials platforms, the gain sections and the wavelength multiplexers can be fabricated monolithically on the same chip, so that the output of each gain section is directly connected to each of the waveguides <NUM>.

The first star coupler <NUM> can comprise any means that can be configured to distribute the input light to a plurality of outputs. In some examples the first star coupler <NUM> can be configured to uniformly distribute the input light to the plurality of outputs. The first star coupler <NUM> can be configured to function as a power splitter and splits power from each of the input waveguides <NUM> across the outputs of the star coupler <NUM>.

In this example the first star coupler <NUM> comprises a waveguide that has a larger width compared to a standard waveguide. For example, the width w of the first star coupler <NUM> can be much larger than the width of the input waveguides <NUM>. The width w of the first star coupler <NUM> can be large enough so that there is no lateral confinement of the light that is input to the first star coupler <NUM>.

The arrayed waveguide grating <NUM> also comprises a plurality of connecting waveguides <NUM> connecting the first star coupler <NUM> to the second star coupler <NUM>. In this example the arrayed waveguide grating <NUM> comprises P waveguides <NUM> connecting the first star coupler <NUM> to the second star coupler <NUM>. The number of waveguides <NUM> that are used can be selected based on specifications of the laser circuitry <NUM> or any other suitable factors.

The connecting waveguides <NUM> have different lengths. The connecting waveguides <NUM> have different lengths so that the light that travels through the connecting waveguides <NUM> travels through different distances depended upon which connecting waveguide <NUM> is used. The different lengths of the connecting waveguides <NUM> introduce different phase shifts into the light that travels through the different connecting waveguides <NUM>. Other means for introducing phase shifts into the light signals could be used in other examples of the disclosure.

The light that travels through the connecting waveguides <NUM> is input to the second star coupler <NUM>. The second star coupler <NUM> can have a similar structure to the first star coupler <NUM>. The second star coupler <NUM> also comprises a waveguide having a large width. The width of the second star coupler <NUM> can also be large enough so that there is no lateral confinement of the light in the second star coupler <NUM>.

The second star coupler <NUM> is configured to combine the input P signals from the connecting waveguides <NUM> and provide a single output via the output waveguide <NUM>. The single output comprises a combination of the plurality of input signals.

The arrayed waveguide grating <NUM> therefore provides the output <NUM> of the optical wavelength multiplexer <NUM> as shown in <FIG>. This output <NUM> is a single output that comprises light from each of the RSOAs in the array <NUM>.

<FIG> shows example bands of wavelengths that can be generated by the laser circuitry <NUM> as shown in <FIG> and <FIG>.

The example wavelengths comprise a first wavelength band λA and a second wavelength band λB. The first wavelength band λA comprises a plurality of wavelengths λ<NUM> to λN. Each of the wavelengths is separated by a difference Δλ. Similarly, the second wavelength band λB comprises a plurality of wavelengths λ<NUM>* to λM*. In an example, each of these wavelengths in the second band is also separated by a difference Δλ. The difference Δλ between the wavelengths can be different for the different wavelength bands λA, λB. A different separation between the wavelengths of the first wavelength band λA and of those of the second wavelength band λB can be achieved based on the configuration of gain sections.

The wavelength bands are distinct from each other. There is a difference ΔΛ between the two wavelength bands. The difference ΔΛ is much larger than the difference Δλ. This means that the gap between the two wavelength bands is much larger than the gaps between the wavelengths within the bands.

By way of non-limiting example, the difference ΔΛ between the two wavelength bands could be of the order of <NUM> while the difference Δλ between the wavelengths within the bands could be of the order of one nanometer. As an example, the first wavelength band λA could be centered around <NUM> and the second wavelength band λB could be centered around <NUM>. The gaps between the wavelengths within the bands could be around <NUM>. Other values for the wavelengths could be used in other examples of the disclosure.

The laser circuitry <NUM> that is configured to provide outputs in two different wavelength bands can be used to provide improved LiDAR systems. Having the outputs in the two different wavelength bands can enable the LiDAR system to be used to obtain information at different resolutions. For example, a higher resolution can be achieved with the outputs with the shorter wavelength while a lower resolution can be achieved with the outputs with the longer wavelengths. The different resolutions could be used to obtain different images and/or to detect or identify different objects. The laser circuitry <NUM> could be configured to enable a user to select which of the wavelength bands they want to use or whether to use both of the wavelength bands.

In examples of the disclosure an oscillating heat pipe <NUM> such as the oscillating heat pipe <NUM> shown in <FIG> could be used to cool the laser circuitry <NUM> or parts of the laser circuitry <NUM>. The laser circuitry <NUM> could be formed on a glass substrate or any other suitable type of material such as silicon, indium phosphide, silicon nitride. The oscillating heat pipe <NUM> could be formed within the glass substrate to enable cooling of the laser circuitry <NUM>. The glass substrate could be thermally insulating and so, to enable heat transfer, a plurality of thermally conducting vias could be provided within the substrate. The thermally conducting vias could be formed from metal or any other suitable thermally conducive materials. The thermally conducive vias can be positioned within the substrate so as to create areas of high thermal conductivity and areas of low thermal conductivity within the substrate. For instance, areas of high thermal conductivity could be created between the RSOAs or other heat sources and the evaporating portion <NUM> of the wick structure <NUM>.

In some examples a heat transfer path can be provided different components of the laser circuitry <NUM>. For example, a heat transfer path, defined by the OHP channels, could be provided between the RSOAs and the arrayed waveguide grating <NUM>. This heat can be used to enable the output wavelengths to be adjusted during the operation of the laser circuitry <NUM>.

<FIG> show a system not according to the invention that can be used to enable working fluid can be added to a cooling system. The cooling system could be a two-phase cooling system such as an oscillating heat pipe <NUM> or any other suitable two-phase cooling system. The cooling system could be used for cooling electronic components and devices such a LiDAR devices.

The system is suitable for enabling a small amount of working fluid to be added to the oscillating heat pipe <NUM>. The small amount of fluid could be less than <NUM>. <FIG> shows a system that is used for a first stage of the process of charging an oscillating heat pipe <NUM> and <FIG> shows a system that is used for second stage of the process of charging an oscillating heat pipe <NUM>. In the first stage a cylinder <NUM> is charged from a pressurized container <NUM>. In the second stage the oscillating heat pipe <NUM> is charged from the cylinder <NUM>. The oscillating heat pipe <NUM> can be an oscillating heat pipe <NUM> as shown in <FIG> or any other suitable type of cooling system. In examples where the cooling system comprises an oscillating heat pipe, the examples of the disclosure can be used to partially fill the oscillating heat pipe as needed.

At the start of the process the working fluid is comprised within the pressurized container <NUM>. The pressurized container <NUM> can be a bottle or any other suitable type of container. The pressurized container <NUM> can be a portable container. The cylinder <NUM> is connected to a plurality of valves. In the examples of <FIG> the cylinder <NUM> is connected to a first valve <NUM> and a second valve <NUM>. The first valve <NUM> and second valve <NUM> are provided on either side of the cylinder <NUM> so that the cylinder <NUM> is provided between the valves <NUM>, <NUM>. The valves <NUM>, <NUM> could be Schrader valves or any other suitable type of valve. The same type of valve <NUM>, <NUM> could be used for the first valve <NUM> and the second valve <NUM>.

The pressurized container <NUM> is also connected to the first valve <NUM>. In the example of <FIG> the pressurized container <NUM> is connected to the first valve <NUM> by the hose <NUM> and the third valve <NUM>.

A fourth valve <NUM> is configured to enable the cylinder <NUM> to be connected to a vacuum pump. The vacuum pump is not shown in <FIG>. The fourth valve <NUM> can be a three-way valve.

To enable working fluid to be discharged from the pressurized container <NUM> to the cylinder <NUM> a vacuum is created in the cylinder <NUM>. To create the vacuum in the cylinder the third valve <NUM> is closed while the other valves <NUM>, <NUM> in the system are opened. A vacuum pump connected to the fourth valve <NUM> can be used to create the vacuum.

Once the vacuum has been created the system can be pressurized by opening and closing the third valve <NUM>. The vacuum pump can then be disconnected and the fourth valve <NUM> can be closed. The system can then be filled with working fluid from the pressurized container <NUM>. The hose <NUM>, or other suitable parts of the system can be gradually heated to force the working fluid into the cylinder <NUM>.

The mass of working fluid in the cylinder <NUM> can be determined by weighing the system, or parts of the system, before and after the filling.

<FIG> shows a system that can be used for the second part of the process for adding working fluid to the oscillating heat pipe <NUM>. In this second part of the process the working fluid can be transferred from the cylinder <NUM> to the oscillating heat pipe <NUM>.

In the example of <FIG> the oscillating heat pipe <NUM> is connected to the cylinder <NUM> via a hose <NUM> and a three-way valve <NUM>. The oscillating heat pipe <NUM> can be connected to the three-way valve <NUM> via a capillary copper tube or by any other suitable means.

To enable the working fluid to be discharged from the cylinder <NUM> to the oscillating heat pipe <NUM> a vacuum is created inside the oscillating heat pipe <NUM>. The vacuum pump connected to the fourth valve <NUM> can be used to create the vacuum.

The system, including the oscillating heat pipe <NUM> can then be pressurized before the vacuum pump is disconnected.

The valves <NUM>, <NUM> between the cylinder <NUM> and the oscillating heat pipe <NUM> can then be opened to enable the working fluid to flow from the cylinder <NUM> to the oscillating heat pipe <NUM>. The appropriate parts of the system, such as the hose <NUM>, can be heated to force the working fluid into the oscillating heat pipe <NUM>. Once the working fluid has been forced into the oscillating heat pipe <NUM> the valve <NUM> can be closed.

Claim 1:
An oscillating heat pipe (<NUM>) comprising:
a channel (<NUM>) configured to enable flow of working fluid between at least one condenser region <NUM> and at least one evaporator region <NUM>; characterized in that the oscillating pipe further comprises:
at least one wick structure (<NUM>) in fluidic connection with the channel (<NUM>) so as to enable working fluid to flow from the channel into the wick structure (<NUM>); and
at least one vent (<NUM>) configured to enable working fluid in an, at least partial, vapour phase to be returned from the wick structure (<NUM>) to the channel (<NUM>).