The present specification relates to an optical microcavity device comprising an alignment system, to an optical microcavity device comprising an alignment structure, to an alignment system for an optical microcavity device, and to a method for aligning an optical microcavity device. In particular, but not exclusively, the present specification relates to an optical microcavity device in the form of a sensor, and an alignment system therefor.
An example of a microcavity device is a particle sensor including a micro-cavity for detecting particles in a fluid introduced into a sample space between the cavity reflectors. However, optical micro-cavities require careful alignment, and this requires significant skill and time. Even for an experienced user, there is a significant probability of damaging or destroying the cavity reflectors during the alignment process.
Aspects of the present disclosure are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as set out in the claims.
According to a first aspect of the present disclosure, there is provided an optical microcavity device as defined by the claims.
In an embodiment there is provided an optical microcavity device comprising:
a first optical reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the first and second optical reflectors being spaced from each other forming an open space therebetween;
wherein the first optical reflector comprises a first cavity reflector and a first alignment reflector,
wherein the second optical reflector comprises a second cavity reflector and a second alignment reflector, the second cavity reflector comprising a recess to provide an optical microcavity between the first and second cavity reflectors, the optical microcavity having an optical cavity length of at most 50 μm and/or an optical mode volume of 100 μm3 or less;
a first EM radiation source configured for illuminating the optical microcavity with EM radiation to cause multi-pass interference within the optical microcavity; and
an alignment system configured to:
the alignment system further comprising an actuator system configured to move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation.
By including an alignment system configured to determine a relative orientation and/or separation of the first and second optical reflectors and to move the optical reflectors relative to each other to change the relative orientation and/or separation of the optical reflectors based on the relative orientation and/or separation determined by the alignment system, the optical microcavity device of the present invention is able to automatically determine and correct the alignment of the first and second optical reflectors, and therefore of the optical microcavity defined by the first and second cavity reflectors, towards a desired relative orientation and/or separation. This may save significant time, both in terms of time required to train a person to manually perform this task, and in terms of operator time required to perform the correction, and may reduce the likelihood of damage to the first and second optical reflectors during alignment. In addition, the alignment system may enable drifts in the alignment of the first and second optical reflectors to be corrected, including drifts which are faster than human operators are able to correct for, leading to improvements in stability of the optical microcavity device.
The alignment system may be configured to determine the relative orientation and/or separation of the first and second optical reflectors and to adjust the optical reflectors accordingly during a manufacturing process of the optical microcavity device, or during use of the optical microcavity device. For example, in the case of an optical microcavity device in the form of a sensing device, the alignment system may be used to determine and adjust the relative orientation and/or separation of the first and second optical reflectors prior to a measurement or sample detection.
The alignment system may be configured to move the first and second optical reflectors relative to each other, to change the relative orientation and/or separation of the first and second optical reflectors to a desired orientation and/or separation, either in a single step, or in a series of steps. The alignment system may be configured to repeatedly detect the optical interference pattern, determine a relative orientation and/or separation of the first and second optical reflectors based on the detected optical interference pattern, and move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation, until the desired relative orientation and/or separation is attained.
In some embodiments, the optical microcavity is configured for stable resonance in at least one mode, and the EM radiation source is configured for illuminating the optical microcavity with EM radiation to cause resonance within the optical microcavity. However, for some embodiments of the optical microcavity device, resonance is not required, only multi-pass or multi-path interference.
In some embodiments, the recess may have a radius of curvature of 50 μm or less.
In some embodiments, the optical microcavity may have an optical mode volume of 10 μm3 or less.
In some embodiments, the optical microcavity device is a sensor, for example a sensor for detecting or characterising nanoparticles, a chemical sensor, a seismometer or a strain gauge. The open space may be configured to receive a sample to be sensed, for example a fluid sample, or a solid sample, for example fixed on a surface.
In other embodiments, the optical microcavity device may be a light source with application-specific properties. For example, a fluorescent material provided in the open space may be caused to emit into a cavity mode, with applications in spectroscopy and quantum simulation or computation.
The alignment system may be further configured to:
detect the optical interference pattern for at least two different relative orientations and/or separations of the first and second optical reflectors and/or at two or more different frequencies of EM radiation;
determine a difference between the detected optical interference patterns; and
determine the relative orientation and/or separation of the first and second optical reflectors based on the difference between the detected optical interference patterns.
Determining a difference between the optical interference patterns detected at two different relative orientations and/or separations of the first and second optical reflectors may be useful in determining the relative orientation of the first and second optical reflectors, including both the magnitude and sense of a relative angle between the alignment reflectors. In embodiments in which the first and second alignment reflectors are planar, an optical interference pattern detected at a single relative orientation and/or separation of the first and second optical reflectors would not be sufficient to determine the sense of a relative angle between the first and second alignment reflectors.
Determining a difference between the optical interference patterns detected at two different frequencies of EM radiation may be useful in determining the separation of the first and second optical reflectors, for example by determining the difference in position of fringes in the interference pattern obtained at each frequency. Combining this with detection of the optical interference pattern for at least two different relative orientations and/or separations of the first and second optical reflectors may further be useful in overcoming an ambiguity in the determination of separation between the optical reflector of half-integer units of the wavelength of the EM radiation used by the alignment system to illuminate the first and second alignment reflectors.
In some embodiments, at least one of the first and second alignment reflectors comprises an alignment structure comprising at least two reflective surface portions having different angular orientations, and the alignment system is configured to detect an optical interference pattern by detecting the optical interference patterns generated by each of said at least two reflective surface portions of the alignment structure.
This may be useful in enabling the alignment system to determine the relative orientations of the first and second optical reflectors from an interference pattern detected at a single relative orientation of the first and second optical reflectors, and may improve the speed, accuracy and/or reliability with which the alignment system operates. The alignment structure may also increase the range over which the relative orientation of the first and second optical reflectors can be determined, which may be useful when the reflectors are very misaligned.
The at least two reflective surface portions of the alignment structure may be provided by two or more distinct reflective surfaces at different angular orientations, or by at least one continuous surface having a varying angular orientation.
In some embodiments, the alignment structure has a configuration which effectively defines a plane. For example, a plane may effectively be defined relative to two planar portions, each sloping at an equal but opposite angle to the plane, and cutting the plane at, for example, their lower edges. A plane may also be effectively defined relative to a cone, the cone having a symmetry axis orthogonal to the plane and an end point at a predetermined spacing from the plane. In such configurations, the alignment system may be used to align a plane effectively defined by the alignment structure on one of the first and second alignment reflectors with the other one of the first and second alignment reflectors.
The alignment structure may comprise at least one of the following configurations:
(i) wherein the at least two reflective surface portions comprise at least two planar reflectors having different angular orientations;
(ii) wherein the at least two reflective surface portions comprise surfaces of a pyramid-shaped structure;
(iii) wherein the at least two reflective surface portions are provided by respective portions of a spherical or spherical-cap surface;
(iv) wherein the at least two reflective surface portions are provided by respective portions of a hyperbolic or saddle-shaped surface; and/or
(v) wherein the at least two reflective surface portions are provided by respective portions of a conical or frusto-conical structure.
By providing an alignment structure comprising planar reflectors (e.g. the surfaces of a pyramid), an interference pattern comprising fringes with a simple periodic pattern is obtained, which can be analysed with relative ease. Spherical and spherical-cap surfaces or structures (including structures having surfaces corresponding to parts of a spherical surface, e.g. hem i-spherical) may be useful as the fringes obtained from spherical surfaces are always circular, and therefore relatively simple to detect, even if they are not equally spaced. By providing a conical or frusto-conical alignment structure, an interference pattern comprising elliptical fringes may be obtained, in which one focus of the ellipse is centred on the cone, and the eccentricity of the elliptical fringes indicates an angle of a plane orthogonal to the axis of the cone. These elliptical fringes may be used for aligning a plane orthogonal to the axis of the cone relative to a plane defined by the other optical reflector.
In some embodiments, at least one of the first and second alignment reflectors comprises an alignment structure comprising an array of recesses, said first and second alignment structures providing a corresponding array of optical microcavities, and the alignment system is configured to detect an optical interference pattern by detecting the optical interference pattern generated by said array of optical microcavities.
For example, the array of recesses may comprise an array of concave recesses arranged in a closely-packed structure. Transmission occurs at the optical modes of each optical microcavity corresponding to a respective recess. In addition, an interference pattern across the array of optical microcavities may be detected when the angle between the first and second alignment reflectors is non-zero. The interference pattern may be in the form of fringes having a periodicity dependent on the relative angle between the first and second alignment reflectors.
In such embodiments, the recess of the second cavity reflector may be provided by one of the recessed of said array of recesses. This may simplify an optical microcavity device in which the second cavity reflector comprises an optical microcavity array, in that the first and second alignment reflectors may be provided by the same structures as the first and second cavity reflectors, and a single EM radiation source may be used both for illuminating the optical microcavities to cause multi-pass interference within each optical microcavity (e.g. to operate the device as a sensor), and for illuminating the first and second alignment reflectors to generate an optical interference pattern (i.e. for aligning the first and second optical reflectors).
The actuator system may comprise a plurality of actuators arranged to adjust the position and relative orientation of at least one of the first and second optical reflectors. In some embodiments, the actuators may have a resolution of less than 100 nm. In some embodiments, the actuators may comprise piezo-inertial actuators. In some embodiments, multiple actuator types may be combined, for example a standard piezo actuator plus a piezo-inertial actuator, or a piezo plus a stepper motor.
The alignment system may comprise a control device for controlling the actuator system, wherein the control device is configured to adjust the relative orientations of the optical reflectors without adjusting the separation between the optical reflectors.
By controlling the actuators to adjust the relative angular orientations of the optical reflectors without adjusting the optical cavity length, the relative orientations of the optical reflectors may be corrected prior to approaching the reflectors towards each other. This may be useful due to the proximity of the optical reflectors required to achieve a short optical cavity, which can lead to collision between the first and second optical reflectors if they are moved towards each other without first ensuring that a relative angle between the optical reflectors is sufficiently small. This feature may also be useful for adjusting the alignment of the optical microcavity without significantly changing the cavity length.
The alignment system may comprise an EM radiation source for illuminating the first and second alignment reflectors of the respective first and second optical reflectors to generate an optical interference pattern, wherein the EM radiation source of the alignment system is either the same or different from the EM radiation source configured for illuminating the optical microcavity with EM radiation to cause multi-pass interference within the optical microcavity.
The alignment system may comprise an EM radiation source for illuminating the first and second alignment reflectors of the respective first and second optical reflectors to generate an optical interference pattern, wherein the EM radiation source of the alignment system comprises one or more low coherence light sources.
By low coherence, we mean that the EM radiation source of the alignment system may simultaneously excite multiple non-degenerate or quasi-degenerate modes of the optical cavity formed between the alignment reflectors. For example, the EM radiation source of the alignment system may comprise an LED.
The alignment system may comprise image capture and image analysis components configured to:
capture an image of the optical interference pattern; and
determine at least one parameter of the optical interference pattern.
The at least one parameter may comprise a spatial frequency of the optical interference pattern.
The spatial frequency of the optical interference pattern may be determined from a single image of the optical interference pattern, or from a difference image obtained by subtracting a first image of the optical interference pattern from a second image of the optical interference pattern obtained by changing the relative separation of the optical reflectors by a small amount (typically by less than one quarter of a wavelength of the EM radiation illuminating the first and second alignment reflectors in the intra-cavity medium) to shift the interference pattern by a correspondingly small amount (i.e. by less than half a fringe). The spatial frequency of the optical interference pattern may be determined, for example, by obtaining a 2D Fourier transform or an autocorrelation function of the image of the optical interference pattern (either the single image or the difference image). The image capture and image analysis components may be configured for filtering the image of the optical interference pattern, and/or for filtering the 2D Fourier transform or autocorrelation function. Further computational image analysis techniques may also be used, including general image feature recognition methods such as Hough transforms, least squares regression fitting, pattern or template matching, or machine-learning methods.
In embodiments in which an elliptical fringe pattern is produced, the at least one parameter determined by the image analysis components of the alignment system may comprise the foci and/or major and minor axes and/or the eccentricity of the elliptical fringe pattern.
In some embodiments, the optical microcavity device further comprises a detector arranged to detect EM radiation from the optical microcavity. The detector may be a photodiode. Alternatively, the detector may be provided by the image capture and image analysis components configured to capture an image of the optical interference pattern.
The alignment system may be configured to determine and correct the relative orientation and/or separation of the first and second optical reflectors at predetermined time intervals and/or in response to predetermined events.
For example, in embodiments in which the optical microcavity device is a sensor, the alignment system may be configured to determine and, if necessary, to correct the relative orientation and/or separation of the first and second optical reflectors prior to a measurement by the optical microcavity device. As another example, during a measurement using the optical microcavity device in the form of a sensor, the alignment system may be configured to determine and correct the relative orientation and/or separation of the first and second optical reflectors in response to a measured or inferred signal being outside of a pre-defined range. The measured or inferred signal may be a difference between the resonant frequencies of two nearby optical microcavities, which depends directly on the angle between the first and second optical reflectors along an axis between the microcavities.
The alignment system may be configured to determine and correct the relative orientation and/or separation of the first and second optical reflectors during a process for manufacturing the optical microcavity device.
The alignment system may be configured to determine and correct the relative orientation and/or separation of the first and second optical reflectors prior to and/or while bonding the first and second reflectors to each other.
According to another aspect of the present disclosure, there is provided an optical microcavity device comprising:
a first optical reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the opposed first and second optical reflectors being spaced apart from each other forming an open space therebetween;
wherein the first optical reflector comprises a first cavity reflector and a first alignment reflector,
wherein the second optical reflector comprises a second cavity reflector and a second alignment reflector, the second cavity reflector comprising a recess to provide an optical microcavity between the first and second cavity reflectors, the optical microcavity having an optical cavity length of at most 50 μm and/or an optical mode volume of 100 μm3 or less; and
an EM radiation source configured for illuminating the optical microcavity with EM radiation to cause multipass interference within the optical microcavity;
wherein at least one of the first and second alignment reflectors comprises an alignment structure comprising at least two reflective surface portions having different angular orientations.
According to another aspect of the present disclosure, there is provided an alignment system for an optical microcavity device, the optical microcavity device comprising:
a first optical reflector comprising a first cavity reflector and a first alignment reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the first and second optical reflectors being spaced from each other forming an open space therebetween, the second optical reflector comprising a second cavity reflector and a second alignment reflector, the second cavity reflector comprising a recess to provide an optical microcavity between the first and second cavity reflectors,
the optical microcavity having an optical cavity length of at most 50 μm and/or an optical mode volume of 100 μm3 or less;
the alignment system being configured to:
the alignment system further comprising an actuator system configured to move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation.
According to another aspect of the present disclosure, there is provided a method for aligning an optical device, the optical device comprising:
a first optical reflector comprising a first cavity reflector and a first alignment reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the first and second optical reflectors being spaced from each other forming an open space therebetween, the second optical reflector comprising a second cavity reflector and a second alignment reflector;
the method comprising:
The method may further comprise:
after the step of controlling the actuator system, bonding the first and second optical reflectors to each other at a fixed relative orientation and separation; and
removing the alignment system from the optical microcavity device.
Bonding the first and second optical reflectors may include applying an adhesive to the first and second optical reflectors, glass frit bonding or glass soldering.
The method may further comprise:
applying an adhesive to the first and second optical reflectors for bonding the first and second optical reflectors to each other at a fixed relative orientation and separation;
after applying said adhesive, determining a relative orientation and/or separation of the first and second optical reflectors based on the detected optical interference pattern, and controlling the actuator system to move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation. This step may be repeated until the first and second optical reflectors are fixedly bonded together at a desired relative orientation and separation.
The adhesive may be a UV-light cured adhesive and the method may further comprise:
irradiating the applied adhesive with UV light to cure the adhesive.
According to a further aspect of the present disclosure, there is provided an optical microcavity device comprising:
a first optical reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the first and second optical reflectors being spaced from each other forming an open space therebetween;
wherein the first optical reflector comprises a first cavity reflector and a first alignment reflector,
wherein the second optical reflector comprises a second cavity reflector and a second alignment reflector;
an EM radiation source configured for illuminating the first and second cavity reflectors with EM radiation to cause multi-pass interference between the first and second cavity reflectors; and
an alignment system configured to:
the alignment system further comprising an actuator system configured to move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation.
According to another aspect of the present disclosure, there is provided an optical microcavity device comprising:
a first optical reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the opposed first and second optical reflectors being spaced apart from each other forming an open space therebetween;
wherein the first optical reflector comprises a first cavity reflector and a first alignment reflector,
wherein the second optical reflector comprises a second cavity reflector and a second alignment reflector; and
an EM radiation source configured for illuminating the first and second cavity reflectors with EM radiation to cause multi-pass interference between the first and second cavity reflectors;
wherein at least one of the first and second alignment reflectors comprises an alignment structure comprising at least two reflective surface portions having different angular orientations.
According to another aspect of the present disclosure, there is provided an alignment system for an optical microcavity device, the optical microcavity device comprising:
a first optical reflector comprising a first cavity reflector and a first alignment reflector;
a second optical reflector opposed to the first optical reflector along an optical axis, the first and second optical reflectors being spaced from each other forming an open space therebetween, the second optical reflector comprising a second cavity reflector and a second alignment reflector;
the alignment system being configured to:
the alignment system further comprising an actuator system configured to move the first and second optical reflectors relative to each other to change the relative orientation and/or separation of the first and second optical reflectors based on the determined relative orientation and/or separation.
The optical microcavity device 10 further comprises an electromagnetic (EM) radiation source 50 configured for illuminating the optical microcavity with an electromagnetic radiation beam 52 to cause multi-pass interference within the optical microcavity. Imaging optics in the form of an input lens 54 and an output lens 56 may be provided for focussing the beam 52. The input lens 54 and output lens 56 may be arranged in a confocal configuration. The optical microcavity is generally configured for stable resonance in at least one mode, and the EM radiation source 50 and/or the cavity length is tuned or tunable to cause resonance within the optical microcavity. However, in some applications, resonance may not be required.
A detector 60, for example a photodiode, is arranged to detect electromagnetic radiation from the optical microcavity. Further imaging optics in the form of a lens 62 may be provided for focussing radiation from the optical microcavity onto the detector 60. In some embodiments, multiple detectors 60 may be provided. By detecting the electromagnetic radiation from the optical microcavity, the optical microcavity device 10 may function as a sensor, for example a seismometer, a strain gauge, or a sensor for detecting and measuring the properties of particles or chemicals. The open space between the optical reflectors 20, 30 may provide a sample space for receiving a fluid or solid sample. However, in some embodiments of the device, for example a device for use as a light source, the detector 60 may not be required.
The optical microcavity device 10 further comprises an alignment system, comprising a further electromagnetic (EM) radiation source 70 configured to illuminate the first and second alignment reflectors 24, 34 with an electromagnetic radiation beam 72 to generate an optical interference pattern 74. In some embodiments, the EM radiation source 70 is an LED. The EM radiation source 70 may comprise multiple sources, for example multiple LEDs, or may be tunable for changing the frequency of the beam 72. In one embodiment, the two EM radiation beams 52, 72 have different wavelengths to increase transmission of the EM radiation beam 72 of the alignment system. The wavelength of the EM radiation beam 72 of the alignment system is centred at the edge of the stop-band of the dielectric mirrors forming the first and second alignment reflectors 24, 34, while the wavelength of the EM radiation beam 52 for illuminating the optical microcavity is selected to be at the centre of the stop-band. A beam splitter 76 is provided for combining the two EM radiation beams 52, 72 so that both illuminate the optical reflectors 20, 30. The beam splitter 76 is a dichroic beam splitter, taking account of the different wavelengths of the two EM radiation beams 52, 72. However, a simple non-polarising beam splitter could be used. A further beam splitter 78 is provided for separating the two EM radiation beams 52, 72 for detection by the detector 60 and sensor 80 respectively. Additional filters (not shown) are used to further improve the wavelength selection at the detector 60 and sensor 80. In other embodiments, the two electromagnetic radiation sources 50, 70 may be replaced by a single electromagnetic radiation source, for example an LED or other low coherence light source, or by a single source with broad spectrum but high coherence, such as a pulsed, mode-locked laser or a frequency comb.
The alignment system further comprises image capture and processing components in the form of a sensor 80 and processor 90. The sensor 80 is configured to detect the optical interference pattern 74 and to output data representing the optical interference pattern 74 to the processor 90. Imaging optics in the form of a lens 82 may be provided for focussing the optical interference pattern 74 onto the sensor 80. The processor 90 is configured to determine a relative orientation and/or separation of the first and second optical reflectors 20, 30 based on the optical interference pattern 74 detected at the sensor 80. In some embodiments, the detector 60 and sensor 80 may be replaced by a single sensor, with suitable discrimination between the two EM radiation beams 52, 72 (e.g. a colour sensor if the two EM radiation beams 52, 72 are different colours, temporal multiplexing or spatial resolution using different pixels of a detector array).
The alignment system further comprises an actuator system comprising actuators 100, 102 configured to move the first and second optical reflectors 20, 30 relative to each other to change the relative orientation and/or separation of the first and second optical reflectors 20, 30 based on the determined relative orientation and/or separation. Although only two actuators 100, 102 are shown in
The control device 92 may be configured to adjust the relative orientations of the first and second optical reflectors without adjusting the separation between the optical reflectors 20, 30, by coordinating the motion of two or more of the actuators 100, 102 at a time, so that it is possible to adjust the orientation and separation of the optical reflectors 20, 30 in separate steps. This may also be useful in reducing the likelihood of the two optical reflectors 20, 30 colliding with each other, which could cause the optical reflectors 20, 30 to become damaged or adhere to each other.
In the embodiment illustrated in
Although an image of the interference pattern 74 shown in
In the example illustrated by
The alignment system may also be configured to detect optical interference patterns 74 using two or more different frequencies of EM radiation generated by the EM radiation source 70. Determining a difference between the two or more detected optical interference patterns 74 obtained at non-commensurate frequencies, for example by determining a difference in the position of fringes in the optical interference pattern 74 detected using each frequency, can be used to determine the separation of the first and second optical reflectors 20, 30, overcoming an ambiguity in the determination of separation between the optical reflector of half-integer units of the wavelength of the EM radiation 72 used by the alignment system. Further overdetermination of the exact length by detection of optical interference patterns for several relative orientations and/or separations of the first and second optical reflectors may be useful in overcoming this ambiguity even in the presence of image distortion, detector noise or other instrumental uncertainties.
The alignment structure shown in
Various other alignment structures are possible, some of which are illustrated in
In
In the embodiment illustrated in
In the embodiment illustrated in
In this embodiment, the alignment system is configured to detect the optical interference pattern generated by the array of optical microcavities when illuminated with EM radiation.
By detecting the interference pattern 74 shown in
The second cavity reflector 32a of the second optical reflector 30a may also be provided one or more of the recesses 26a of the array of recesses 26a. Thus it is not necessary to provide a specific alignment structure in an optical microcavity device relying on an optical microcavity array for its principle function (e.g. as a sensor). Similarly, the first cavity reflector and the first alignment reflector of the first optical reflector (not shown) may be provided by a single reflector portion. In such configurations, a single EM radiation source may be used both for aligning the first and second optical reflectors of the optical microcavity device and for use of the optical microcavity device (e.g. for sensing).
In the above-described embodiments, the alignment structures and cavity recesses of the optical reflectors may be produced by using focused ion beam milling to ablate the surface of a substrate prior to coating with a reflective material, or with several pairs of layers of dielectric materials with alternating refractive index and controlled thickness, to form an optical reflector at the designed operating wavelengths. The alignment structures could also be produced using other techniques such as wet etching or laser ablation.
The alignment system may be used to repeatedly adjust the optical reflectors 20, 30 of the optical microcavity device 10 during manufacture and/or during use of the device 10. For example, the relative alignment of the optical reflectors 20, 30 may be determined, and, if necessary, adjusted by the alignment system at predetermined time intervals or in response to specific events, such as powering on the device or each time the device is used, or if the device's environment (temperature, humidity, air pressure) changes beyond some acceptable range. One example of a specific event could be when a measurement, for example a difference in the determined cavity lengths of neighbouring optical microcavities, falls outside a predetermined range. In the case of an optical microcavity device 10 in the form of a sensing device, a determination and adjustment (if necessary) of the relative alignment of the optical reflectors 20, 30 could be performed prior to each measurement or sample detection.
Although the embodiments described above comprise an optical microcavity device in which at least one of the optical reflectors includes a cavity reflector comprising a recess having a radius of curvature of at most 50 μm, the first and second cavity reflectors forming an optical microcavity having an optical cavity length of at most 50 μm and/or an optical mode volume of 10 μm3 or less, the present disclosure is also applicable to optical devices which do not necessarily include a microcavity. In particular, optical devices in which the first and second optical reflectors have a small separation, for example under 100 microns, would be difficult to align manually.
Although particular embodiments of this disclosure have been described, it will be appreciated that many modifications, additions and/or substitutions may be made within the scope of the claims.
Number | Date | Country | Kind |
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1914068.0 | Sep 2019 | GB | national |
Filing Document | Filing Date | Country | Kind |
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PCT/GB2020/052216 | 9/15/2020 | WO |