WO2024073815A1

WO2024073815A1 - Reflective optical element and uses thereof

Info

Publication number: WO2024073815A1
Application number: PCT/AU2023/050973
Authority: WO
Inventors: Antony Martin; William Palmer; Selene Rodd-Routley
Original assignee: Rapid Phenotyping Pty Limited
Priority date: 2022-10-06
Filing date: 2023-10-06
Publication date: 2024-04-11

Abstract

The present invention relates to, in a first aspect, a reflector for an optical system, comprising a reflective surface, and an aperture extending from an aperture opening through the reflective surface, the aperture and aperture opening being adapted for light to pass therethrough, wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface. Also provided are an optical interface including a reflector having an aperture, and an optical device comprising an optical interface.

Description

REFLECTI VE OPTI CAL ELEMENT AN D USES TH EREOF

PRI ORI TY CLAI M

[0001 ] The present application claims priority from Australian provisional application No. 2022902905, filed on 06 October 2022. The contents of the priority application are hereby incorporated herein by reference.

TECHNI CAL Fl ELD

[0002] The present invention relates generally to the field of optics, and more particularly to means of improving efficiency of optical systems.

BACKGROUN D

[0003] Optical systems for the analysis of absorption or transm ission spectra typically use a m ultitude of different optical elements. Many of these are simple lenses and m irrors for the focusing or redirection of light beams for a single light path. However it is not uncom mon for light paths to overlap, and there needs to be a means of dividing the overlapping light rays apart. The most com mon prior art optical element for providing this is a beam-splitter, which, as the name suggests, ‘splits’ a beam into m ultiple beams. The most typical beam splitter arrangement divides a single incident beam into two output beams of equal intensity, such that each beam will possess 50% of the incident beam ’s intensity - although different splits are possible.

[0004] Figure 1 depicts a prior art optical system arranged for reflection spectroscopy of a sample, having a prior art light source P02 emitting light having 100% of initial intensity I , a beam-splitter P04, sample P06 and detector P08. Upon entering beam-splitter P04, 50% of the light is reflected and 50% is transm itted through to a reflective sample P06. Assum ing that all of the light is reflected from the reflective sample P06, the light returning to the beam splitter has an intensity 50% that of the initial intensity. This is halved again upon reflecting from the beam splitter P06 towards the spectrometer detector P08. I n reality, the sample P06 is unlikely to reflect all of the light - it will only reflect light wavelengths characteristic of its reflection spectrum . However, the specific intensity of each wavelength that is successfully reflected will be around 25% of what was originally em itted by the light source P02.

[0005] The loss factor applying to both the ‘incident’ beam and the ‘returning beam ’ is unavoidable in this situation due to the Helm holtz Reciprocity Principle. Because reflection spectroscopy involves reflecting light from a sample and the returning light path is essentially a reverse of the source light path, the beamsplitter encounters light from both directions and so will apply the same optical effect to both the source light and the return light. All conventional beam-splitters, whether polarising or non-polarising, are reciprocal and thus suffer from this drawback.

[0006] The end result of this problem is that, in order to achieve the m inimum signal intensity required in order for the signal to be detected by a detector, eye or any other light receiving means, the light source m ust em it at an increased power level that is a least four times greater than the m inim um detectable light power/intensity. By using a higher-powered light source, intensity loss through etendue or through polarisation may be compensated for - this, however, has major drawbacks in that larger and more powerful power sources are required, increasing the weight and size of the optical system . This means that handheld spectrometers, for example, tend to be bulky in order to hold the oversize battery cells and light sources needed for extended operation.

[0007] There is, therefore, a clear benefit to providing a means of improving the efficiency of an optical system or device by reducing, inhibiting or ameliorating loss of signal intensity. These and other benefits may be provided by at least one embodiment of the invention as disclosed below.

DI SCLOSURE OF THE I NVENTI ON

[0008] I n a first aspect, the present invention comprises a reflector for an optical system , comprising a reflective surface, and an aperture extending from an aperture opening through the reflective surface, the aperture and aperture opening being adapted for light to pass therethrough, wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface. [0009] I n an embodiment, a cross-sectional area of the aperture at a particular aperture depth within the reflector is greater than the cross-sectional area of the aperture opening. I n an embodiment, for at least a portion of a length of the aperture, the cross-sectional area of the aperture increases as aperture depth increases. I n an embodiment, the aperture is frustoconical in shape for at least a portion of its length.

[0010] I n an embodiment, an inner surface of the aperture is substantially reflective for at least a portion of its length.

[001 1 ] I n an embodiment, the cross-sectional area of the aperture opening is less than about 20% , less than about 10% , less than about 5% , less than about 2% , or less than about 1 % of a cross-sectional area of the reflective surface of the reflector.

[0012] I n an embodiment, the reflector further comprises a light source within the aperture and arranged to direct produced light out through the aperture opening.

[0013] I n an embodiment, the aperture extends substantially therethrough, and the reflector further comprises a second opening at a distal end of the aperture, and the second opening has a cross-sectional area that is greater than the cross- sectional area of the aperture opening.

[0014] A further aspect of the invention may lie in an optical interface comprising a reflector having a reflective surface and an aperture extending from an aperture opening through the reflective surface, wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface, and the reflector is arranged such that light from a light source passes through the aperture, out from the aperture opening, and into an observation region, and the reflective surface is angled to reflect a substantial majority of light returning from the observation region in a particular direction. [0015] I n an embodiment, the optical interface further comprises a concentrator lens arranged to focus light from the light source to a focal point positioned within or substantially proximal to the aperture opening.

[0016] I n an embodiment, the optical interface further comprises a second reflector arranged such that light from a further light source passes through the aperture of the second reflector, out from the aperture opening, and into the observation region, and the reflective surface of the second reflector is angled to reflect a substantial majority of light returning from the observation region in a particular direction.

[0017] I n an embodiment, the reflector is a reflector of an embodiment of the first aspect of the invention.

[0018] A further aspect of the invention may lie in an optical device, comprising a light source, optical elements defining a source optical pathway, an observation region and a return optical pathway, a receiving means, and an optical interface comprising a reflector having a reflective surface and an aperture extending from an aperture opening through the reflective surface, wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface, the source optical pathway extends from the light source, through the aperture of the reflector, to the observation region, and the return optical pathway extends from the observation region, via the reflective surface of the reflector, to the receiving means.

[0019] I n an embodiment, the optical device further comprises a second light source and optical elements defining a second source optical pathway and a second return optical pathway, the optical interface comprises a second reflector, the second source optical pathway extends from the second light source, through the aperture of the second reflector, to the observation region; and the second return optical pathway extends from the observation region, via the reflective surface of the second reflector, to the receiving means.

[0020] I n an embodiment, the reflector is a reflector of an embodiment of the first aspect of the invention. [0021 ] I n an embodiment, the optical interface is an embodiment of an optical interface of the second aspect of the invention.

[0022] Further or alternative embodiments of the invention may be disclosed herein or may otherwise become apparent to the person skilled in the art through the disclosure herein. These and other embodiments are considered to fall within the scope and object of the invention.

DESCRI PTI ON OF Fl GURES

[0023] Embodiments of the present invention will now be described in relation to figures, wherein:

Figure 1 is a prior art optical arrangement employing a beam splitter;

Figures 2A-2C are embodiments of a reflector of the present invention;

Figures 3A-3C are embodiments of a reflector having a reflective internal surface; Figures 4A & 4B are embodiments of the reflector of the present invention having alternate aperture embodiments;

Figures 5 & 6 are embodiments of an optical interface of the present invention, depicted within an embodiment of an optical system ; and

Figures 7 & 8 are embodiments of an optical device of the present invention.

DETAI LED DESCRI PTI ON OF PREFERRED EMBODI MENTS

[0024] I n a first aspect, the present invention relates to an optical element configured to enable light from a first direction to be transm itted therethrough and light from a second direction to be reflected, while m inim izing loss of intensity of light from either direction.

[0025] I n an embodiment and with reference to Figures 2A-2C, the optical element may be a reflector 100 comprising a reflective surface 102and an aperture 104 that extends from an aperture opening 106, through the reflective surface. I n an embodiment, the aperture and aperture opening are adapted for light to pass therethrough.

[0026] I n an embodiment, a cross-sectional area of the aperture opening 106 is less than a cross-sectional area of the reflective surface 102. Without lim iting the scope of the invention through theory, it is envisaged that light falling onto the reflective surface 102 will be almost entirely reflected therefrom . Even though the reflective surface 102 comprises the aperture opening 106, this opening 106 is a mere fraction of the surface area of the reflective surface 102. Therefore, only a very small portion of light approaching the reflective surface 102 will be lost by passing into the aperture opening 106, with the remainder being reflected therefrom .

[0027] The skilled person may appreciate that an embodiment of the reflector 100 may therefore substantially preserve the intensity of light that is transm itted therethrough and/or reflected thereby.

[0028] Without lim iting the scope of the invention through theory, it is envisaged that an embodiment of the reflector 100 may provide a replacement or an alternative to optical elements such as ‘half-silvered m irrors’ or beam-splitters, which reflect or transm it light based on the light’s polarity and so represent significant sources of loss of light intensity. At least one embodiment of the present invention may enable transm ission of light from a first direction (e.g., from a light source), and reflection of light returning from a second direction (e.g., from an illum inated sample) , while substantially preserving light intensity. This may be contrasted against a beam-splitter, which is able to sim ilarly provide for both reflection and transm ission of light, but the intensity of a light beam is reduced by 50% each time it interacts therewith.

[0029] It is further envisaged that, in contrast to optical systems employing beam splitters in a sim ilar arrangement - which require that the light source produce light with an intensity that is at least four times greater than the m inim um detectable intensity of a light detector receiving reflected light - at least one embodiment of the first aspect of the present invention may enable the use of reduced-power light sources, improving energy efficiency of optical systems and devices, and reducing power requirements. Additionally, certain optical devices may be able to be made more compact, with source and return optical pathways at least partially overlapping, without increasing power demands (unlike prior art systems employing beam splitters) . I n some uses, optical devices may even be able to be made into lightweight devices due to reduced power requirements enabling the use of lighter batteries and smaller light sources, reducing weight.

[0030] I n an embodiment, the cross-sectional area of the aperture opening 106 may be, in particular, less than about 20% , less than about 10% , less than about 5% , less than about 2% , or less than about 1 % of a cross-sectional area of the reflective surface 102.

[0031 ] I n an embodiment, the aperture 104 of the reflector 100 may extend at a non-perpendicular angle relative to the reflective surface 102. The angle between the aperture and the reflective surface 102 may be dependent upon the relative orientation of other optical elements within an optical system or device utilising the reflector 100.

[0032] I n an embodiment, the aperture may be adapted to funnel or otherwise direct light towards a focal point / that is located within or substantially proximal to the aperture opening 106. With particular reference to Figure 2C, in an embodiment of the invention, a cross-sectional area of the aperture 104 at a particular aperture depth d within the reflector 100 may be greater than the cross- sectional area of the aperture opening 106, wherein depth d is a distance into the aperture as measured from the aperture opening. I n a further embodiment, for at least a portion of a length of the aperture 104, the cross-sectional area of the aperture 104 may increase as aperture depth d increases. I n a particular embodiment thereof, the aperture may be frustoconical in shape for at least a portion of its length.

[0033] I n an embodiment and with reference to Figures 3A-3C, an inner surface 108 of the aperture 104 may be substantially reflective for at least a portion of its length. It is envisaged that a reflective inner surface 108 may substantially enable the aperture 104 to ‘funnel’ light passing therethrough towards the focal point f by reflecting any light that is not completely aligned with the focal point f. To explain by way of non-lim iting example, light from a light source may first pass through a collimator and/or concentrator lens in order to focus the light to pass through the aperture and to the focal point f. However, as the skilled person is aware no lens can perfectly focus light to a point. Therefore, by providing a reflective inner surface 108 within the aperture 104, any portion of the light that is not properly focused and directed towards the focal point f - and thus would otherwise be absorbed by or dispersed upon the aperture wall - may subsequently be reflected and thus keep traversing the aperture towards the aperture opening 106.

[0034] An embodiment of the aperture 104 having a reflective inner surface 108 may be combined with an embodiment wherein the aperture increases in cross- sectional area as depth d increases for at least a portion of its length. It is envisaged that the combination of the inner surface being both angled (due to increasing cross-sectional area) and reflective may synergistically act to prevent loss of light intensity, further improving power efficiency of an optical system employing such an embodiment of the invention.

[0035] I n an embodiment and with reference to Figure 4A, the reflector 100 may further comprise a light source 1 10 located within the aperture 104 and arranged to direct produced light out through the aperture opening 106. I n an alternate embodiment and with reference to Figure 4B, the aperture 104 may instead extend substantially completely through the reflector. I n such an embodiment, the reflector 100 may further comprise a second opening 1 12 at a distal end of the aperture 104, which has a cross-sectional area that is greater than the cross- sectional area of the aperture opening 106. Such an embodiment may be adapted to receive light into the aperture from a separate light source (not shown) .

[0036] With reference to Figure 5, a second aspect of the present invention may lie in an optical interface 200, comprising a reflector 202 having a reflective surface 204 and an aperture 206 extending from an aperture opening 208 and outwards through the reflective surface. The reflector 202 is arranged such that light from a light source 210 (depicted as a dotted line) traverses a source optical pathway in which it passes through the aperture 206, out from the aperture opening 208, and into a defined observation region 212, and the reflective surface 204 is angled to reflect a substantial majority of light returning from the observation region 212 along a return optical pathway (depicted as a dot-dash line) in a particular direction. The particular direction may be, for example, towards further optical elements, one or more detectors (depicted in Figure 5 as detector 214) , or an eyepiece. I n an embodiment, a cross-sectional area of the aperture opening 208 is less than a cross-sectional area of the reflective surface 204. I n certain embodiments, the light source 210 may be located within the aperture 206 of the reflector 202, as depicted previously in Figure 4A. I n alternate embodiments, the aperture 206 may extend completely through the reflector 202.

[0037] The observation region 212 may be defined by one or more additional optical elements known in the art and which will not be elaborated upon here. Although the observation region 212 is depicted as circular in Figure 5 and elsewhere, the skilled person will appreciate that this is exemplary only and is not meant in any way to describe the shape of the observation region 212. The skilled person will also appreciate that the observation region 212 is depicted as being adjacent to the optical interface 200 for clarity purposes only, and that the arrangement depicted in Figure 5 and elsewhere is not to be construed as lim iting the physical arrangement of the optical interface 200 relative thereto.

[0038] I n an embodiment, the optical interface 200 may also comprise a collimator or a concentrator lens 216 arranged to focus light received by the optical interface from the light source to a focal point / positioned within or substantially proximal to the aperture opening. I n an alternative or further embodiment, an inner surface of the aperture 206 may be substantially reflective for at least a portion of its length in order to direct light towards the aperture opening. This may be alongside, or alternate to, an embodiment of the optical interface 200 comprising a collimator or a concentrator lens 216.

[0039] With reference to Figure 6, a further embodiment of the optical interface 200 may comprise at least two reflectors 202A, 202B arranged in different locations around the observation region 212. The second reflector 202B may be arranged such that light from a further light source 218 passes through the aperture of the second reflector 202, out from the aperture opening, and into the observation region 212, and the second reflector’s reflective surface 204 is angled to reflect a substantial majority of light that it receives from the observation region 212 in a particular direction. This may be the same particular direction as that of light reflected by the first reflector 202A, or may be a different direction. The skilled person will appreciate that each ‘particular direction’ may be dependent upon an arrangement of further optical elements (such as detectors) relative to the reflectors 202A, 202B.

[0040] I n an embodiment, the optical interface 200 may comprise one or more reflectors 202 that is or are reflector(s) 100 of an embodiment of the first aspect of the invention. Such an embodiment of the optical interface 200, in comprising an embodiment of a reflector 202 of a first aspect of the invention, may enable the use of a lower-powered light source to illum inate the observation region while also enabling the optical device to be made more compact by at least partially overlapping source and return optical pathways. This may be contrasted against a beam splitter, which may enable at least partially overlapping source and return optical pathways, but requires that the intensity of the light source be increased to at least four times that of the m inim um required intensity of the receiving means.

[0041 ] With reference to Figure 7, a further aspect of the invention may lie in an optical device 300 incorporating an optical interface 302. The optical device 300 may comprise a reflector 304, a defined source optical pathway 306 to illum inate a defined observation region 308, a defined return optical pathway 310, and a receiving means 312 at an end of the return optical pathway. I n use, the source optical pathway 306 is a path for light to travel from a light source 314, through the aperture 318 of the reflector 304, to the defined observation region 308. Sim ilarly, a return optical pathway 310 extends from the observation region 308, via the reflective surface 316 of the reflector 304, to the receiving means 312. I n an embodiment, the source optical pathway may be defined by one or more optical elements in addition to the aperture 318 and aperture opening 320 of the reflector 304. I n an embodiment, the return optical pathway may be defined by one or more optical elements in addition to the reflective surface 316 of the reflector 304. The optical device 300 may include a light source 314 therewithin (as depicted in Figure 7), or in alternate embodiments the light source may be external. I n certain embodiments, the light source 314 may be located within the aperture 318 of the reflector 304, as depicted previously in Figure 4A. I n alternate embodiments, the aperture 318 may extend completely through the reflector 304. [0042] The skilled person will appreciate that the source and return optical pathways, the means of defining the observation region 308, the receiving means 312, and any additional optical elements, will depend upon what form the optical device 300 takes. Means of defining source and return pathways and observation regions, as well as means of providing for various receiving means, are known in the art. Some optical elements, including potential receiving means 312, that may be employed alongside or as part of an embodiment of the optical interface 302 without departing from the scope or object of the invention are focal, polarising, magnifying, objective and/or image lenses, collimators, diffraction gratings, m irrors and other reflective elements, refractive prisms, interferometer arrays, , and optical filters. Furthermore, the optical device 300 may include one or more detectors or detector arrays, sensors, recording means, either as an embodiment of the receiving means 312 or in addition thereto.

[0043] The optical interface 302 may enable the optical device 300 to function more efficiently than a prior art optical device. This may be through enabling employment of a relatively lower-powered light source, due to the reflector 304 substantially preserving the intensity of light that is transm itted therethrough and/or reflected thereby.

[0044] I n an embodiment, the optical interface 302 may be an embodiment of an optical interface 200 of a second aspect of the invention. I n an embodiment, the reflector 304 may be an embodiment of a reflector 100 of a first aspect of the invention.

[0045] An example embodiment of the optical device 300 will now be described, however this should not be considered to be the only form that the optical device 300 may take. I n an example embodiment and with further reference to Figure 7, the optical device 300 may be an optical analysis device 300-1 that is adapted to direct light from the observation region 308 onto a receiving means 312 comprising one or more detectors 312- 1 . The light may be reflected from or transm itted through the observation region 308, or may be em itted by a substance, sample or other object being observed therewithin. I n an embodiment, the optical analysis device may comprise a light source 314 arranged to direct light into the source optical pathway 306, a sampling means (not shown) defining the observation region 308, a receiving means 312 comprising a detector or detector array 312- 1 arranged at an end of the return optical pathway 310, and an optical interface 302 comprising a reflector 304 having a reflective surface 316 and an aperture 318 extending from an aperture opening 320 and outwards through the reflective surface. I n use, a sample may be arranged within the sample observation region 308 and illum inated by the light source 314. Return light received from the observation region 308 may be subsequently reflected by the reflective surface 316 towards the detector or detector array 312- 1 . I n a further embodiment (not shown) , the optical analysis device 300-1 may further comprise a reflection means arranged to capture light that passes through the observation region 308 or is em itted by a substance, sample or other object being observed therewithin.

[0046] I n a further embodiment and with reference to Figure 8, the optical analysis device 300- 1 may further comprise a second light source 322 and a second optical interface 302B that is substantially similar to the optical interface 302, 302A. A second source optical pathway 324 extends from the second light source 322, through the aperture 318 of the second reflector 304B, to the observation region 308. As before, a second return optical pathway 326 may extend from the observation region 308, via the reflective surface 316 of the second reflector 304B, to the one or more detectors 312- 1 . As the skilled person may appreciate, at least the present embodiment of the optical analysis device 300- 1 may therefore enable detection of one or more of the following:

• A first characteristic reflection spectrum from the observation region 308, dependent upon the first light source 314 {light traverses source optical pathway 306 to observation region 308, is reflected, and subsequently traverses return optical pathway 310) ;

• A first characteristic transm ission spectrum from the observation region 308, dependent upon the first light source 314 {light traverses source optical pathway 306 to observation region 308, passes therethrough, and subsequently traverses second return optical pathway 326) ;

• A second characteristic reflection spectrum from the observation region 308, dependent upon the second light source 322 {light traverses source optical pathway 306 to observation region 308, is reflected, and subsequently traverses return optical pathway 310) -, and

• A second characteristic transm ission spectrum from the observation region 308, dependent upon the second light source 322 {light traverses second source optical pathway 324 to observation region 308, passes therethrough, and subsequently traverses return optical pathway 310) .

[0047] I n an embodiment, the return optical pathway 310 and second return optical pathway 326 may extend from the observation region 308, via the respective reflective surfaces 316 of the respective reflector 304A, 304B, to different ones of the one or more detectors 312- 1 .

[0048] While the invention has been described with reference to preferred embodiments above, it will be appreciated by those skilled in the art that it is not lim ited to those embodiments, but may be embodied in many other forms, variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, components and/or devices referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0049] I n this specification, unless the context clearly indicates otherwise, the word “comprising” is not intended to have the exclusive meaning of the word such as “consisting only of”, but rather has the non-exclusive meaning, in the sense of “including at least”. The same applies, with corresponding gram matical changes, to other forms of the word such as “comprise”, etc.

[0050] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as com monly understood to one of ordinary skill in the art to which the invention belongs.

[0051 ] Any prom ises made in the present document should be understood to relate to some embodiments of the invention, and are not intended to be prom ises made about the invention in all embodiments. Where there are prom ises that are deemed to apply to all embodiments of the invention, the applicant/patentee reserves the right to later delete them from the description and they do not rely on these prom ises for the acceptance or subsequent grant of a patent in any country.

Claims

CLAI MS

1 . A reflector for an optical system , comprising: a reflective surface; and an aperture extending from an aperture opening through the reflective surface, the aperture and aperture opening being adapted for light to pass therethrough; wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface.

2. The reflector of claim 1 , wherein a cross-sectional area of the aperture at a particular aperture depth within the reflector is greater than the cross- sectional area of the aperture opening.

3. The reflector of claim 2, wherein, for at least a portion of a length of the aperture, the cross-sectional area of the aperture increases as aperture depth increases.

4. The reflector of claim 2 or 3, wherein the aperture is frustoconical in shape for at least a portion of its length.

5. The reflector of any one of claims 1 - 4, wherein an inner surface of the aperture is substantially reflective for at least a portion of its length.

6. The reflector of any one of claims 1 - 5, wherein the cross-sectional area of the aperture opening is less than about 20% , less than about 10% , less than about 5% , less than about 2% , or less than about 1 % of a cross- sectional area of the reflective surface.

7. The reflector of any one of claims 1 - 6, further comprising a light source within the aperture and arranged to direct produced light out through the aperture opening.

. The reflector of any one of claims 1 - 6, wherein: the aperture extends substantially therethrough; the reflector further comprises a second opening at a distal end of the aperture; and the second opening has a cross-sectional area that is greater than the cross-sectional area of the aperture opening. . An optical interface comprising a reflector having a reflective surface and an aperture extending from an aperture opening through the reflective surface; wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface; and the reflector is arranged such that: light from a light source passes through the aperture, out from the aperture opening, and into a observation region; and the reflective surface is angled to reflect a substantial majority of light returning from the observation region in a particular direction. 0. The optical interface of claim 9, further comprising a concentrator lens arranged to focus light from the light source to a focal point positioned within or substantially proximal to the aperture opening. 1 . The optical interface of claim 9 or claim 10, further comprising a second reflector arranged such that: light from a further light source passes through the aperture of the second reflector, out from the aperture opening, and into the observation region; and the reflective surface of the second reflector is angled to reflect a substantial majority of light returning from the observation region in a particular direction. 2. The optical interface of any one of claims 9 - 1 1 , wherein the reflector is a reflector of any one of claims 1 - 8. 3. An optical device, comprising: a light source; optical elements defining a source optical pathway, an observation region and a return optical pathway; a receiving means; and an optical interface comprising a reflector having a reflective surface and an aperture extending from an aperture opening through the reflective surface; wherein a cross-sectional area of the aperture opening is less than a cross-sectional area of the reflective surface; the source optical pathway extends from the light source, through the aperture of the reflector, to the observation region; and the return optical pathway extends from the observation region, via the reflective surface of the reflector, to the receiving means. The optical device of claim 13, further comprising a second light source and optical elements defining a second source optical pathway and a second return optical pathway; wherein the optical interface comprises a second reflector; the second source optical pathway extends from the second light source, through the aperture of the second reflector, to the observation region; and the second return optical pathway extends from the observation region, via the reflective surface of the second reflector, to the receiving means. The optical device of claim 13 or 14, wherein the reflector is a reflector of any one of claims 1 - 8. The optical device of any one of claims 13 - 15, wherein the optical interface is an optical interface of any one of claims 9 - 12.