A device comprising a photonic integrated circuit and a method of manufacturing the same

Abstract

This invention provides a device, and a method of manufacturing said device, the device comprising: a container containing an atomic vapour; and a Photonic Integrated Circuit, PIC, positioned inside the container, the PIC comprising: a substrate comprising a surface and a first optical path, wherein the substrate defines a first opening extending from the surface of the substrate to a first section of the first optical path, the first opening being exposed to the atomic vapour of the container such that the first section of the first optical path passes across the first opening through the atomic vapour.

Description

[0001] A DEVICE COMPRISING A PHOTONIC INTEGRATED CIRCUIT AND A METHOD OF MANUFACTURING THE SAME

[0002] Field of the Invention

[0003] The present invention relates to a device comprising a photonic integrated circuit and a method of manufacturing said device.

[0004] Background

[0005] An optical technology may require a containment of an atomic vapour (e.g. a vapour of alkali metal, such as Rubidium, Caesium or Strontium atoms). It is a requirement in many optical technologies to lock an output of an optical signal generator (e.g. laser) to a specific frequency. There are a variety of locking techniques and many utilise an atomic reference as a fundamental physical property to which the output signal can be referenced to. A containment of atomic vapour may be used as the atomic reference.

[0006] There are also many optical technologies that require a containment of atomic vapour in which the atomic vapour is controllably excited. These optical technologies include quantum receivers, quantum memory, quantum metrology and quantum gravity sensing.

[0007] In a laboratory environment, the atomic vapour may be contained in a vessel and used as part of a free space optical assembly. The vessel may contain the atomic vapour for a period of years. However, a free space optical assembly is not suitable for componentisation and mass market application. It is therefore desirable to miniaturise the atomic vapour containment vessel to enable integration with photonic systems such as Photonic Integrated Circuits (PICs). However, the relatively large surface area to volume ratio of the miniaturised vessel results in a relative high rate of loss of the atomic vapour (relative to the relatively large vessel used in the free-space optical assembly).

[0008] Summary of the Invention

[0009] According to a first aspect of the invention, there is provided a device comprising: a container containing an atomic vapour; and a Photonic Integrated Circuit, PIC, positioned inside the container, the PIC comprising: a substrate comprising a surface and a first optical path, wherein the substrate defines a first opening extending from the surface of the substrate to a first section of the first optical path, the first opening being exposed to the atomic vapour of the container such that the first section of the first optical path passes across the first opening through the atomic vapour.

[0010] The PIC may further comprise a second optical path.

[0011] The first section of the first optical path may overlap with a first section of the second optical path such that the first opening defined by the substrate extends from the surface of the substrate to the respective first sections of the first and second optical paths.

[0012] The substrate may define a second opening extending from the surface of the substrate to a first section of the second optical path, the second opening may be exposed to the atomic vapour of the container such that the first section of the second optical path passes across the first opening through the atomic vapour.

[0013] The container may comprise at least one connection interface.

[0014] The at least one connection interface may be configured to receive a first optical signal and communicate the first optical signal to the first optical path such that the first optical signal propagates through the first section of the first optical path and interacts with the atomic vapour.

[0015] The device may further comprise at least one optical source configured to generate a first optical signal and communicate the first optical signal to the first optical path such that the first optical signal propagates through the first section of the first optical path and interacts with the atomic vapour.

[0016] The first optical path may be configured to communicate the first optical signal from the first section of the first optical path to the at least one connection interface so as to output the first optical signal.

[0017] The at least one connection interface may be further configured to receive a second optical signal and communicate the second optical signal to the second optical path such that the second optical signal propagates through the first section of the second optical path and interacts with the atomic vapour. The device may further comprise at least one optical source configured to generate a second optical signal and communicate the second optical signal to the second optical path such that the second optical signal propagates through the first section of the second optical path and interacts with the atomic vapour.

[0018] The at least one optical source may be a component of the PIC.

[0019] The first and second signals may counter-propagate.

[0020] The second optical path may be configured to communicate the second optical signal from the first section of the second optical path to the at least one connection interface so as to output the second optical signal.

[0021] The at least one connection interface may be configured to receive an electrical signal for powering and / or controlling the at least one optical source and communicate the electrical signal to the at least one optical source.

[0022] The device may further comprise an optical signal detector, wherein the first optical path may be configured to communicate the first optical signal from the first section of the first optical path to the optical signal detector.

[0023] The second optical path may be configured to communicate the second optical signal from a first section of the second optical path to the optical signal detector.

[0024] The device may be a Rydberg-atom based electromagnetic field detector, wherein the first and second optical signals may have respective frequencies to excite electrons of the atomic vapour to a predetermined Rydberg state so as to induce an Electromagnetic Induced Transparency, EIT, effect such that an incident electromagnetic field causes a detectable change in the atomic vapour.

[0025] The first optical path may comprise a waveguide section configured to guide an optical signal to the first section of the first optical path, and propagation of the optical signal as the optical signal passes across the first opening may be predominately characterised by free-space propagation. According to a second aspect of the invention, there is provided a method of manufacturing a device, the method comprising the steps of: providing a vessel having an interior section; positioning a Photonic Integrated Circuit, PIC, in the interior section of the vessel, the PIC comprising: a substrate comprising a surface and a first optical path, wherein the substrate defines a first opening extending from the surface of the substrate to a first section of the first optical path, the first opening being exposed to the atomic vapour of the container such that the first section of the first optical path passes across the first opening through the atomic vapour; connecting a connector to the PIC, the connector passing out of the interior section of the vessel; and sealing the vessel so as to form a containment vessel.

[0026] The method may further comprise the step of evacuating the containment vessel.

[0027] The method may further comprise the step of filling the containment vessel with an amount of material to form an atomic vapour.

[0028] Brief Description of the Figures

[0029] In order that the present invention may be better understood, embodiments thereof will now be described, byway of example only, with reference to the accompanying drawings in which:

[0030] Figure 1 is a schematic diagram of a first device;

[0031] Figure 2 is a schematic diagram of a Photonic Integrated Circuit (PIC) of the first device of Figure 1 ;

[0032] Figure 3 is a cross-sectional view of the PIC of Figure 2;

[0033] Figure 4 is a schematic diagram of a system comprising the first device of Figure 1 ;

[0034] Figure 5 is a schematic diagram of a second device;

[0035] Figure 6 is a schematic diagram of the second device of Figure 5;

[0036] Figure 7 is a schematic diagram of a system comprising the second device of Figure 5; and

[0037] Figure 8 is a flow diagram of a method of manufacturing a device.

[0038] Detailed Description

[0039] Figure 1 illustrates a first device 100 comprising a containment vessel 110 and Photonic Integrated Circuit (PIC) 120. The containment vessel 110 may be a hollow cylinder and be around 20-200mm in length and around 10-20mm in diameter. The containment vessel 110 may therefore be similarly sized to those used in tree-space optical assemblies. The containment vessel 110 therefore comprises a wall 112 (constructed from, for example, Quartz or borosilicate glass) defining an interior section of the containment vessel 110. The containment vessel 110 contains an atomic vapour in its interior section, such as a vapour of alkali metal (e.g. Rubidium, Strontium or Caesium).

[0040] Figure 1 also illustrates the PIC 120 being positioned inside the containment vessel 110. That is, the PIC 120 is positioned in the interior section of the containment vessel 110. The PIC 120 is supported in its fixed position by a support member 114 such that there is a gap between the wall 112 of the containment vessel 1 10 and each part of the PIC 120. The PIC 120 is therefore exposed to the atomic vapour contained within the containment vessel 110.

[0041] Figure 1 further illustrates a feedthrough optical fibre 130 and evacuation and filling nozzle 1 16. The feedthrough optical fibre 130 extends through the wall 112 of the containment vessel 110 to the PIC 120 and may be used to connect the PIC 120 to a circuit (as described in more detail below). The evacuation and filling nozzle 116 is used during manufacture of the first device 100 to evacuate the interior section of the containment vessel 110 and fill the containment vessel 110 with the atomic vapour (as described in more detail below).

[0042] Figure 2 illustrates the PIC 120 in more detail. The PIC 120 comprises a first optical fibre interface 121 and a second optical fibre interface 123. A first optical core 130a of the feedthrough optical fibre 130 may terminate at the first optical fibre interface 121 and therefore enable an optical signal to be propagated between the first optical core 130a of the feedthrough optical fibre 130 and the PIC 120. A second optical core 130b of the feedthrough optical fibre 130 may terminate at the second optical fibre interface 123 and therefore enable the optical signal to be propagated between the PIC 120 and the second optical core 130b of the feedthrough optical fibre 130.

[0043] The PIC 120 further comprises a loopback 122 for aligning each optical core 130a, 130b of the feedthrough optical fibre 130. The PIC 120 further comprises an optical path comprising a first waveguide section 125, a first variable section 126, an interaction section 127, a second variable section 128, and a second waveguide section 129.

[0044] The first waveguide section 125, first variable section 126, second variable volume 128 and second waveguide section 129 are formed as etchings within the PIC 120. Turning to Figure 3, being a cross-sectional view of the PIC 120 along line A-A of Figure 2, it is shown that the PIC 120 comprises a wafer of Silicon having a naturally forming layer of Silicon Oxide. A thin film of Silicon Nitride (SisN^, deposited on the layer of Silicon Oxide, is etched to define the first waveguide section 125, first variable section 126, second variable section 128 and second waveguide section 129 (that is, the remaining Silicon Nitride following the etching process - illustrated by the upward diagonal fill pattern - forms the first waveguide section 125, first variable section 126, second variable section 128 and second waveguide section 129). The Silicon, Silicon Oxide and Silicon Nitride layers are protected by a coating layer (that is, a layer encompassing all sides of the Silicon, Silicon Oxide and Silicon Nitride layers) of Chemical Vapour Deposited Oxide (CVD Oxide). The CVD Oxide coating layer provides protection against corrosion which may otherwise be experienced by the Silicon, Silicon Oxide and / or Silicon Nitride layers when exposed to the atomic vapour of the containment vessel 110.

[0045] The first waveguide section 125, first variable section 126, second variable section 128 and second waveguide section 129 are hereinafter referred to as "channels” in the PIC 120, being channels of Silicon Nitride in the PIC 120.

[0046] The PIC 120 has a milled cavity - illustrated by the backward diagonal fill pattern in Figure 3 - extending from a top face of the PIC 120 (being the face illustrated in Figure 2) to a bottom face of the PIC 120 through the interaction section 127. The milled cavity has a width and length corresponding with the interaction section 127, and its depth corresponds with the distance between the top and bottom faces of the PIC 120. Figure 3 also shows the interaction section 127 - illustrated by the diamond fill pattern - as being a section of the milled cavity that is open on a top face (corresponding with the top face of the PIC 120), open on a bottom face (corresponding with the bottom face of the PIC 120) and closed on its side faces. The following description relates to an example optical signal being communicated between the first and second optical core 130a, 130b of the feedthrough optical fibre 130 across the PIC 120 in a first direction from the first optical fibre interface 121 to the second optical fibre interface 123 (as shown by the arrowed lines in Figure 2). The first waveguide section 125 receives the optical signal at the first optical fibre interface 121 and guides the optical signal to the first variable section 126. The first variable section 126 is provided between the first waveguide section 125 and the interaction section 127. A spatial dimension of the channel defining the first variable section 126 (e.g. width and / or depth) varies across its length (that is, it varies along the direction of propagation of the optical signal) between a first cross sectional area - defined by the cross sectional area of the first variable section 126 at its junction with the first waveguide section 125 - and a second cross-sectional area - defined by the cross sectional area of the first variable section 126 at its junction with the interaction section 127 - the first cross sectional area being less than the second cross sectional area (or in other words, the second cross sectional area being greater than the first cross sectional area). In the example shown in Figure 2, the width of the channel defining the first variable section 126 increases from its junction with the first waveguide section 125 to its junction with the interaction section 127 (and the depth of the channel defining the first variable section 126 remains constant).

[0047] Following the passage of the optical signal along the optical path as shown in Figure 2, the optical signal is guided by the first waveguide section 125 to the first variable section 126, at which point the channel width increases. Propagation of the optical signal may transition during the optical signal’s passage of the first variable section from being predominantly characterised as a guided wave to being predominantly characterised as free-space propagation. The optical signal then passes from the first variable section 126 to the interaction section 127.

[0048] As noted above, the interaction section 127 is part of the milled cavity of the PIC 120 which is open on its top face and bottom face. Propagation of the optical signal is therefore predominantly characterised by free-space propagation (although the side faces of the interaction section 127 may guide the optical signal to an extent) as it traverses the interaction section 127 from its junction with the first variable section 126 to its junction with the second variable section 128. Passage of the optical signal across the interaction section 127 is described in more detail below. The second variable section 128 is provided between the interaction section 127 and the second waveguide section 129. A spatial dimension of the channel defining the second variable section 128 (e.g. width and / or depth) varies across its length (that is, it varies along the direction of propagation of the optical signal) between a first cross sectional area - defined by the cross sectional area of the second variable section 128 at its junction with the interaction section 127 - and a second cross-sectional area - defined by the cross sectional area of the second variable section 128 at its junction with the second waveguide section 129 - the first cross sectional area being greater than the second cross sectional area (or in other words, the second cross sectional area being less than the first cross sectional area). In the example shown in Figure 2, the width of the channel defining the second variable section 128 decreases from its junction with the interaction section 127 to its junction with the second waveguide section 129 (and the depth of the channel defining the second variable section 128 remains constant).

[0049] The optical signal is thereafter guided by the second waveguide section 129 to the second optical fibre interface 123.

[0050] As described above in relation to Figure 1 , the PIC 120 is positioned in the interior section of the containment vessel 110 and is exposed to the atomic vapour contained in the containment vessel 110. The cavity of the PIC 120 (and therefore the interaction section 127 of the optical path) therefore receives the atomic vapour such that the atomic vapour fills the cavity and the interaction section 127. The atomic vapour may also flow through the cavity from one side of the PIC 120 to an opposing side of the PIC 120. Accordingly, as the optical signal passes through the cavity of the PIC 120 (that is, as it propagates across the interaction section 127), it interacts with atoms of the atomic vapour.

[0051] The first device 100 therefore provides a PIC 120 in which an optical signal interacts with an atomic vapour, wherein the PIC 120 is provided inside the containment vessel 110 of the atomic vapour. An alternative design comprises a PIC in which the atomic vapour is contained in a miniaturised containment vessel that is a component of the PIC (that is, it is integrated with the PIC). Therefore, by positioning the PIC 120 of the first device 100 inside the containment vessel 110 in such a way that an optical path defined by the PIC 120 may still pass through an atomic vapour, the first device 100 may advantageously use a relatively large containment vessel 110 which benefits from an increased lifespan (due to the relatively low loss of the atomic vapour). The advantages of utilising a PIC, such as componentisation and mass-market application, may therefore be realised for an optical technology requiring an atomic vapour containment vessel.

[0052] In a further alternative design using a free-space optics assembly, free-space light is passed through the containment vessel. This requires a high quality and transparent optical window on the containment vessel. In contrast, the first device 100 passes the optical signal through the wall 112 of the containment vessel 110 via an optical fibre and excites the atomic vapour inside the containment vessel 110. The containment vessel 110 may therefore advantageously be constructed with desired properties, such as electromagnetic shielding to protect the interaction between the optical signal and atomic vapour from electromagnetic interference, a reflective or partially reflective surface to boost in-bound signals, or provide directionality in detection.

[0053] Figure 4 illustrates a first application of the first device 100. A first system is provided comprising the first device 100, the optical fibre 130, a laser source 140, and a photodiode 150. The laser source 140 generates an optical signal which may be varied in frequency, polarisation, power and / or linewidth. The optical signal passes from the laser source 140 to the first device 100 via the optical fibre 130. The optical signal is received at the input first optical fibre interface 121 of the PIC 120 of the first device 100, passes through the interaction section 127 of the cavity of the PIC 120 and interacts with the atomic vapour contained in the containment vessel 110, and is output at the second optical fibre interface 123 to the optical fibre 130. The optical signal then passes from the first device 100 to the photodiode 150 via the optical fibre 130.

[0054] This first system therefore utilises the first device 100 as an inline component and enables the atomic states of the atomic vapour contained in the containment vessel 110 to be measured, tracked and / or used as a reference. The first device 100 may therefore be used for locking the laser source 140 to a particular frequency. The first device may also be used for identifying electromagnetic fields interacting with the atomic vapour of the containment vessel 110 by frequency scanning the laser source 140 and measuring the absorption of the optical signal at the photodiode 150. The optical signal may be split from the optical fibre 130 (e.g. using a splitter, not shown) either before its passage of the first device 100 at a first arm 160 or after its passage of the first device 100 at a second arm 170. Additionally, the optical signal can be converted to an electrical signal. Figure 5 illustrates a second device 200. The second device 200 is substantially the same as the first device 100 and comprises a containment vessel 210 having a wall 212 defining an interior section of the containment vessel 210. The containment vessel 210 contains an atomic vapour in its interior section, such as a vapour of alkali metal (e.g. Rubidium, Strontium or Caesium).

[0055] The second device 200 also comprises a PIC 220 positioned inside (that is, in the interior section) of the containment vessel 210. The PIC 220 is supported by a support member 214 such that there is a gap between the wall 212 of the containment vessel 210 and each part of the PIC 220. The PIC 220 is therefore exposed to the atomic vapour contained within the containment vessel 210.

[0056] Figure 5 further illustrates a feedthrough optical fibre 230 and evacuation and filling nozzle 216. The feedthrough optical fibre 230 extends through the wall 212 of the containment vessel 210 to the PIC 220 and may be used to connect the PIC 220 to a circuit (as described in more detail below). The evacuation and filling nozzle 216 is used during manufacture of the first device 200 to evacuate the interior section of the containment vessel 210 and fill the containment vessel 210 with the atomic vapour (as described in more detail below).

[0057] The PIC 220 of the second device 200 is shown in more detail in Figure 6. The PIC 220 of the second device 200 is similar to the PIC 100 of the first device 100 but differs as it enables two optical signals to be at least partially counter-propagated. The PIC 220 of the second device 200 will now be described in more detail.

[0058] The PIC 220 of the second device 200 comprises a first single-signal waveguide section 224a, a second single-signal waveguide section 224b, a first multiple-signal waveguide section 225, a first variable section 226, an interaction section 227, a second variable section 228, and a second multiple-signal waveguide section 229. The PIC 220 further comprises an Arrayed Waveguide Grating (AWG) 222.

[0059] A first optical path of the PIC 220 of the second device 200 may be defined as the path between the first and second optical fibre interfaces 221 , 223 defined by the first singlesignal waveguide section 224a, the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229. A second optical path of the PIC 220 of the second device 200 may defined as the path between the first and second optical fibre interfaces 221 , 223 defined by the second single-signal waveguide section 224b, the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229. A plurality of optical signals may therefore propagate (e.g. counter-propagate) along the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229, but only a single optical signal may propagate along each of the first and second single-signal waveguide sections 224a, 224b.

[0060] The PIC 220 further comprises a loopback for aligning each optical core of the feedthrough optical fibre 230.

[0061] In the following example, a first optical signal propagates from the first optical fibre interface 221 to the second optical fibre interface 223 along the first optical path, and a second optical signal propagates from the second optical fibre interface 223 to the first optical fibre interface 221 along the second optical path. The first and second optical signals therefore counter-propagate. The first and second optical signals are combined / split (depending on direction of propagation) at the AWG 222.

[0062] The first single-signal waveguide section 224a, the second single-signal waveguide section 224b, the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229 are all formed as etchings within the PIC 220, in the same or similar manner as described above in relation to the PIC 120 of the first device 100. The first single-signal waveguide section 224a, the second single-signal waveguide section 224b, the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229 are hereinafter referred to as “channels” in the PIC 220, being channels of Silicon Nitride in the PIC 220. The PIC 220 of the second device 200 also has a milled cavity (the same or similar to the milled cavity of the PIC 120 of the first device 100) extending from a top face of the PIC 220 (being the face illustrated in Figure 2) to a bottom face of the PIC 220 through the interaction section 227. The milled cavity has a width and length corresponding with the interaction section 227, and its depth corresponds with the distance between the top and bottom faces of the PIC 220. The interaction section 227 is therefore a section of the milled cavity that is open on a top face (corresponding with the top face of the PIC 220), open on a bottom face (corresponding with the bottom face of the PIC 220) and closed on its side faces.

[0063] The first optical signal is communicated from the first optical fibre interface 221 to the second optical fibre interface 223 in the same manner as described above in relation to the first PIC 120 of the first device 100, with the addition of being combined with the second optical signal at the AWG 220 and thereafter counter-propagated (during its passage along the first multiple-signal waveguide section 225, the first variable section 226, the interaction section 227, the second variable section 228, and the second multiple-signal waveguide section 229). The second optical signal is communicated from the second optical fibre interface 223 to the first optical fibre interface 221 (and is split from the first optical signal at the AWG 222).

[0064] The first and second optical signals therefore both pass through the interaction section 227 and interact with the atomic vapour received within the interaction section 227.

[0065] As described above in relation to Figure 5, the PIC 220 is positioned in the interior section of the containment vessel 210 and is exposed to the atomic vapour contained in the containment vessel 210. The cavity of the PIC 220 (and therefore the interaction section 227) therefore receives the atomic vapour such that the atomic vapour fills the cavity and the interaction section 227. The atomic vapour may also flow through the cavity from one side of the PIC 220 to an opposing side of the PIC 220. Accordingly, as the first and second optical signals pass through the cavity of the PIC 220 (that is, as they propagate across the interaction section 227), both the first and second optical signals interact with atoms of the atomic vapour.

[0066] The second device 200 therefore provides a PIC 220 in which multiple optical signals interact with an atomic vapour, wherein the PIC 220 is provided inside the containment vessel 210 of the atomic vapour so as to realise the benefits of relatively large containment vessels (relative to a miniaturised containment vessel that may be integrated with an alternative PIC design). The advantages of utilising a PIC, such as componentisation and mass-market application, may therefore be realised for an optical technology requiring an atomic vapour containment vessel that is excited by multiple optical signals.

[0067] Figure 7 illustrates a first application of the second device 200. A second system is provided comprising the second device 200, the optical fibre 230, a first optical source 240 (e.g. a first laser), a second optical source 250 (e.g. a second laser) and a photodetector 260. A first optical signal may be transmitted by the first optical source 240 to the second device 200 via the optical fibre 230. A second optical signal may be transmitted by the second optical source 250 to the second device 200 via the optical fibre 230. The first and second optical signals may counter-propagate. The first and second optical signals both propagate across the interaction section 227 of the PIC 220 of the second device 200 and excite the atomic vapour contained in the containment vessel 210. At least one of the first and second optical signals is thereafter communicated to the photodetector 260, via the optical fibre 230, for analysis.

[0068] The second system may represent a Rydberg-atom based electromagnetic field detector (or receiver), such that the first optical source 240 transmits a probe signal for exciting electrons of the atomic vapour from a first state to a second state, and the second optical source 250 transmits a coupling signal for exciting electrons of the atomic vapour to a predetermined Rydberg state. The probe signal may be analysed at the photodetector 260 for detecting an incoming electromagnetic field and optionally for demodulating data encoded in the incoming electromagnetic field.

[0069] The second device may also be excited by two optical signals from a single optical source, such as in a system comprising a splitter. The second system may also be used for performing sub-Doppler spectroscopy with counter-propagated saturation absorption spectroscopy measurements.

[0070] The first and second devices 100, 200 are described as being entirely optical devices in which the one or more optical signals are received at the device and the device outputs the at least one optical signal (following interaction with the atomic vapour of the PIC 120, 220). However, this is non-essential. The device 100, 200 may further comprise an optical source, such as a laser diode, which may be integrated as a component of the PIC 120, 220. Additionally or alternatively, the device 100, 200 may comprise an optical detector / receiver, such as a photodiode, which may be integrated as a component of the PIC 120, 220. In these alternative configurations, the first and second devices 100, 200 may utilise alternative feedthrough connections (that is, the connection passing from outside the containment vessel 110, 210 to the PIC 120, 220 in the interior section of the containment vessel 110, 210). The feedthrough connection may comprise both an optical and electrical component (for example, an electrical connection to control and / or power the optical source of the PIC 120, 220 and an optical connection to receive the optical signal output by the PIC 120, 220, or an optical connection to provide an optical signal to the PIC 120, 220 and an electrical connection to receive an electrical signal output by the optical detector / receiver on the PIC 120, 220). The feedthrough connection may alternatively be entirely electrical, for example, to control and / or power the optical source of the PIC 120, 220 and to receive an electrical signal output by the optical detector / receiver on the PIC 120, 220. The electrical component may also be used to control and / or power further components of the device 100, 200, such as a ThermoElectric Cooler (TEC). The electrical and optical connections may be connected through the containment vessel 110, 120 via separate connectors.

[0071] In the first and second devices, the cavity extends through the entirety of the PIC 120, 220. This is beneficial as it increases the effective aperture for receiving the atomic vapour and it also allows the atomic vapour to flow through the PIC 120, 220. Alternatively, the cavity may extend up to and including a section of the optical path of the PIC 120, 220 so as to provide an opening for receiving the atomic vapour and enable the optical signal to interact with the atomic vapour as it propagates along the optical path. In other words, the interaction section 117, 227 of the PIC 120, 220 may have a single open face. There are alternative benefits for this alternative arrangement in that the PIC 110, 120 is more structurally stable. The cavity may be, for example, milled or etched. Furthermore, the one or more openings may be tapered to further encourage the atomic vapour into the cavity.

[0072] As noted above, the PIC 120, 220 is positioned in the interior section of the containment vessel 110, 210 such that there is a gap between the PIC 120, 220 and the wall of the containment vessel 110, 210. This enables the atomic vapour to be received within (and pass through) the cavity of the PIC 120, 220. There are further benefits of this arrangement in that there is no direct thermal transfer to the PIC 120, 220 when the containment vessel 110, 210 is heated (which may be performed to ensure vapour desorption of the atomic vapour from the wall of the containment vessel 110, 210 and increase the partial pressure of the atomic vapour). However, this is non-essential and the PIC 120, 220 may be positioned in any way in the interior section of the containment vessel 120, 220 which enables the atomic vapour to be received within the cavity of the PIC 120, 220. For example, the PIC 120, 220 may be attached to the wall of the containment vessel 110, 210 at a side portion of the PIC 120, 220. Thermomechanical stability can be improved with the addition of Peltier coolers to regulate the temperature of the PIC 120, 220 and / or piezo driven expansion cancelling control.

[0073] In the above first and second devices 100, 200, the one or more optical signals interacted with the atomic vapour in a single interaction section. However, this is non-essential and there may be a plurality of interaction sections (each passing through a respective milled cavity in the PIC) which may be in series or in parallel.

[0074] The skilled person will also understand that the materials of the PIC 120, 220 noted above are non-essential, and any suitable material or materials may be used as a substrate of the PIC 120, 220, such as Indium Phosphide and Gallium Arsenide.

[0075] A method of manufacture will now be described with reference to Figure 8. The method of manufacture is applicable to both the first and second devices 100, 200 described above. In a first step, S101 , a PIC 120, 220 is constructed, the PIC 120, 220 defining an optical path. In step S103, an opening is created in a section of the optical path, the opening extending from a surface of the PIC 120, 220 to the optical path. The opening may be a milled cavity that extends partially or fully through the PIC 120, 220.

[0076] In a third step, S105, the PIC 120, 220 is positioned in an interior section of a vessel that is initially open on at least one end. The PIC 120, 220 may be fixed to a support member 114, 214 of the vessel.

[0077] In step S107, one or more connectors (e.g. an optical fibre, an electrical connector, or a composite connector comprising both an optical fibre and electrical connector) is / are connected to the PIC 120, 220 and extended out of an open end of the vessel. In step S109, an end cap is bonded to each open end of the vessel, with the one or more connectors passing through the end cap so as to form one or more feedthrough connectors. The end caps seal the vessel so as to create the containment vessel 110, 210.

[0078] In step S111 , the interior section of the containment vessel 110, 210 is evacuated and filled with an atomic vapour via the evacuation and filling nozzle 116, 216. The evacuation and filling nozzle 116, 216 may then be sealed and the device 100, 200 removed from the evacuation / f i 11 i ng apparatus.

[0079] The skilled person will understand that any combination of features is possible within the scope of the invention, as claimed.

Claims

CLAIMS1. A device comprising: a container containing an atomic vapour; and a Photonic Integrated Circuit, PIC, positioned inside the container, the PIC comprising: a substrate comprising a surface and a first optical path, wherein the substrate defines a first opening extending from the surface of the substrate to a first section of the first optical path, the first opening being exposed to the atomic vapour of the container such that the first section of the first optical path passes across the first opening through the atomic vapour.

2. A device as claimed in Claim 1 , wherein the PIC further comprises a second optical path.

3. A device as claimed in Claim 2, wherein the first section of the first optical path overlaps with a first section of the second optical path such that the first opening defined by the substrate extends from the surface of the substrate to the respective first sections of the first and second optical paths.

4. A device as claimed in Claim 2, wherein the substrate defines a second opening extending from the surface of the substrate to a first section of the second optical path, the second opening being exposed to the atomic vapour of the container such that the first section of the second optical path passes across the second opening through the atomic vapour.

5. A device as claimed in any one of the preceding claims, wherein the container comprises at least one connection interface.

6. A device as claimed in Claim 5, wherein the at least one connection interface is configured to receive a first optical signal and communicate the first optical signal to the first optical path such that the first optical signal propagates through the first section of the first optical path and interacts with the atomic vapour.

7. A device as claimed in any one of Claims 1 to 5, further comprising at least one optical source configured to generate a first optical signal and communicate the first optical signal to the first optical path such that the first optical signal propagates through the first section of the first optical path and interacts with the atomic vapour.

8. A device as claimed in either Claim 6 or Claim 7 when dependent on Claim 5, wherein the first optical path is configured to communicate the first optical signal from the first section of the first optical path to the at least one connection interface so as to output the first optical signal.

9. A device as claimed in Claim 5 when dependent on any one of Claims 2 to 4, wherein the at least one connection interface is further configured to receive a second optical signal and communicate the second optical signal to the second optical path such that the second optical signal propagates through the first section of the second optical path and interacts with the atomic vapour.

10. A device as claimed in any one of Claims 2 to 5, further comprising at least one optical source configured to generate a second optical signal and communicate the second optical signal to the second optical path such that the second optical signal propagates through the first section of the second optical path and interacts with the atomic vapour.

11. A device as claimed in either Claim 7 or Claim 10, wherein the at least one optical source is a component of the PIC.

12. A device as claimed in either Claim 9, Claim 10, or Claim 11 when dependent on Claim 10, wherein the first and second signals counter-propagate.

13. A device as claimed in any one of Claims 9 to 12 when dependent on Claim 5, wherein the second optical path is configured to communicate the second optical signal from the first section of the second optical path to the at least one connection interface so as to output the second optical signal.

14. A device as claimed in either Claim 7 when dependent on Claim 5, or Claim 10 when dependent on Claim 5, wherein the at least one connection interface isconfigured to receive an electrical signal for powering and / or controlling the at least one optical source and communicate the electrical signal to the at least one optical source.

15. A device as claimed in any one of the preceding claims, further comprising an optical signal detector, wherein the first optical path is configured to communicate the first optical signal from the first section of the first optical path to the optical signal detector.

16. A device as claimed in Claim 15 when dependent directly or indirectly on Claim 2, wherein the second optical path is configured to communicate the second optical signal from a first section of the second optical path to the optical signal detector.

17. A device as claimed in any one of Claims 6 to 14 or either Claim 15 or Claim 16 when dependent on any one of Claims 6 to 14, being a Rydberg-atom based electromagnetic field detector, wherein the first and second optical signals have respective frequencies to excite electrons of the atomic vapour to a predetermined Rydberg state so as to induce an Electromagnetic Induced Transparency, EIT, effect such that an incident electromagnetic field causes a detectable change in the atomic vapour.

18. A device as claimed in any one of the preceding claims, wherein: the first optical path comprises a waveguide section configured to guide an optical signal to the first section of the first optical path, and propagation of the optical signal as the optical signal passes across the first opening is predominately characterised by free-space propagation.

19. A method of manufacturing a device, the method comprising the steps of: providing a vessel having an interior section; positioning a Photonic Integrated Circuit, PIC, in the interior section of the vessel, the PIC comprising: a substrate comprising a surface and a first optical path, wherein the substrate defines a first opening extending from the surface of the substrate to a first section of the first optical path, the first opening being exposed to the atomic vapour of the container such that the first section of the first optical path passes across the first opening through the atomic vapour;connecting a connector to the PIC, the connector passing out of the interior section of the vessel; and sealing the vessel so as to form a containment vessel.

20. A method as claimed in Claim 19, further comprising the step of: evacuating the containment vessel.21 . A method as claimed in either Claim 19 or Claim 20, further comprising the step of: filling the containment vessel with an amount of material to form an atomic vapour.

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