WO2018115566A1

WO2018115566A1 - Spectroscopic detection apparatus and method

Info

Publication number: WO2018115566A1
Application number: PCT/FI2016/050894
Authority: WO
Inventors: David BITAULD
Original assignee: Nokia Technologies Oy
Priority date: 2016-12-19
Filing date: 2016-12-19
Publication date: 2018-06-28

Abstract

According to an example aspect of the present invention, there is provided an apparatus comprising: an optic input (23); a waveguide structure for guiding input light (2) with given bandwidth into a set of narrower bandwidth standing waves (5); and a plurality of photonic detectors (3) arranged to sample the standing waves (5), wherein standing wave sample collection is arranged directly without intermediate etched nanoscale features.

Description

SPECTROSCOPIC DETECTION APPARATUS AND METHOD

FIELD

[0001] The present invention relates to detectors for obtaining spectral information about an electromagnetic field. BACKGROUND

[0002] Development of optical sensors has been under great interest commercially and in research literature. Optical spectroscopy has demonstrated a wide range of applications related to monitoring health as well as factors affecting it, such as monitoring water and food quality. However the dimensions and price of typical equipment does not allow its use in consumer electronics, which could be game changer in Digital Health. Early stages of cancer, diabetes, infections could be detected before they are dangerous. Continuous monitoring of the environment quality and everyday food could be performed. A powerful class of integrated photonic spectrometer has been demonstrated and is now commercialized. However, there is need to develop lower-cost photonic spectrometers. SUMMARY

[0003] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0004] According to a first aspect, there is provided an apparatus, comprising:

- an optic input;

- a waveguide structure for separating input light with a given bandwidth into a set of narrower bandwidth standing waves; and

a plurality of photonic detectors arranged to sample the standing waves, wherein standing wave sample collection is arranged directly without intermediate etched nanoscale features.

[0005] According to a second aspect, there is provided a method, comprising: receiving input light with given bandwidth by an optic input; separating input light from the optic input to a set of narrower bandwidth standing waves by a waveguide structure; and sampling the standing waves by a plurality of photonic detectors, wherein standing wave sample collection is arranged directly without intermediate etched nanoscale features.

[0006] According to an embodiment, the standing wave light collection is arranged on the whole length of detector pixels. [0007] According to an embodiment, the standing wave sample collection is arranged by or based on at least one of: evanescent coupling, coupling using artificially and/or naturally occurring impurities in the waveguide, artificial and/or naturally occurring roughness of a surface of the waveguide, and translucent thin film deposited on the waveguide. [0008] According to an embodiment, the apparatus further comprises: a splitter connected to the input to split the input light into first channel and a second channel, wherein the first channel is connected to a first separator and the second channel is connected to a second separator, and a set of waves from the first separator is arranged to be coupled/joined to a set of waves from the second separator to form the standing waves. [0009] According to an embodiment, a reflective edge is provided at an edge of the waveguide structure to guide the waves as standing waves.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGURES la and lb illustrate cross-section views of spectrometer elements in accordance with at least some embodiments of the present invention; [0011] FIGURES 2 and 3 illustrate example apparatuses capable of supporting at least some embodiments of the present invention;

[0012] FIGURE 4 illustrates measurement of broadband light and narrowband light; and

[0013] FIGURE 5 illustrates a method in accordance with at least some embodiments of the present invention.

EMBODIMENTS

[0014] Currently available integrated photonic spectrometers require cutting edge nanotechnology tools, such as electron beam lithography to implement nanowires. Furthermore, such spectrometers sample waves by applying nanoscopic diffusers in order to obtain broadband high-resolution spectrometry.

[0015] There is now provided a standing wave spectrometer apparatus with several sampling standing waves established in multiple waveguides, capable of providing substantial advantages over currently known integrated photonic spectrometers. FIGURES la and lb illustrate some example embodiments of such apparatus.

[0016] The apparatus comprises an optic input connected to a waveguide structure.

Input light 2 is connected to a waveguide 1 and guided to form a standing wave. The waveguide structure may be provided with a reflective edge 4 to form the standing wave 5. The apparatus further comprises a set or array of photonic detectors 3 arranged to sample the standing waves 5. In some embodiments, the detectors are charge-coupled devices (CCD). The standing wave 5 can be directly sampled with conventional image sensors and conventional size pixels, such as conventional size CCDs. The broadband input light may be guided into a set of narrow bandwidth or sub-bandwidth channels, to form several narrower bandwidth standing waves at respective waveguides 4. The several sub- bandwidth standing waves can be sampled in parallel with a two-dimensional array of detectors 3, such as a standard CCD camera.

[0017] The optical spectrum of the light can be obtained by performing a Lippmann transform of the measured array of values. The resolution of the spectrum will be limited by the length of the waveguide:

[0018] δλ « λ²/Δΐ_,

[0019] wherein δλ represents resolution, λ central wavelength, and ΔΙ_ waveguide length. The measurable bandwidth is limited by the distance between features. This distance is fixed by the sensor array pixel pitch: [0020] Δλ « λ²/δΙ_,

[0021] wherein Δλ represents bandwidth, λ central wavelength, and 5L: distance between features/pixels. [0022] If the bandwidth of the measured light is larger than δΙ_, the standing wave will be undersampled, leading to an aliasing problem. This problem may be solved by dividing the input channel into several channels where nanoscopic features are slightly shifted from one channel to the other. [0023] In the presently developed apparatus standing wave sample collection may be arranged directly without requiring intermediate etched nanoscale features. This enables to achieve low-cost optical spectrometers for various consumer electronics applications. Cutting edge nanotechnology tools, such as electron beam lithography, are not required to implement nanowires. Such fabrication step can be avoided while maintaining comparable performance, enabling easier and cheaper mass-manufacture. It is to be appreciated that the direct sample collection without intermediate etched nanoscale features does not preclude use of a specific intermediate element or matter between the sensor array and the waveguide, as is the case in some embodiments.

[0024] The standing wave sample collection may be arranged to rely on weak diffusion of light, by or based on at least one of the following:

- evanescent coupling between the standing wave 5 and the set of detectors 3, in an embodiment appropriate proximity of CCD pixel array to the waveguide structure

- coupling using artificially and/or naturally occurring impurities in the waveguide 1, - artificial and/or naturally occurring roughness of a surface of the waveguide

1, and

- translucent thin film deposited on the waveguide.

[0025] There are different ways available to introduce artificial impurities inside the waveguide, depending on its material. For polymer waveguides, impurities such as nanoparticles (dielectric or metal) may be mixed with the monomer solution before it is polymerised on the substrate. In case of semiconductor materials, the impurities can be dopants, or integrated in a similar way, during the growth of the semiconductor layer. In most types of waveguides, such as polymer, oxide, and semiconductor, the impurities can be implanted after the waveguide layer is fabricated by using plasma implantation. [0026] There may be protective oxide or resin between the waveguide and the detectors 3. FIGURE lb illustrates deposition of a thin film 6 between the waveguide and the detectors 3. The translucent thin film diffuses the light from the evanescent wave towards the detectors. In order to reduce the amount of light directed towards the detectors, a transparent layer of appropriate thickness could be deposited between the waveguide and the translucent film. An example of one such applicable film is provided in [1].

[0027] According to at least some embodiments, accurately located nanoscale features between the detectors 3 and the waveguide 1 to scatter light towards the detectors 3 are not necessary. However, in some embodiments diffusive material is applied, and there may be nanoscale features in an intermediate material between the waveguide 1 and the detectors 3. However, in this case the material may be naturally and randomly available in the material, without requiring specific nanofabrication steps.

[0028] The standing wave 5 light may be collected on the whole length of the sensor

3. Here, undersampling will not lead to aliasing because the measurement is integrated along the whole length of the pixel. However if the light has a spectrum larger than Δλ <* λ²/δΙ_, the results will be blurred out.

[0029] This problem may be avoided by separating the broadband input light into several channels with narrower bandwidths. This can be done by arranging the waveguide structure to separate the broadband input light into a set of narrower band or sub- bandwidth channels by means of an arrayed waveguide grating (AWG), for example. Each such sub-bandwidth channel or light is guided in the waveguide 1 to form a standing wave 5. The AWG does not require any additional fabrication step. It can be fabricated during the same step as the waveguides 1 for sampling.

[0030] Reference is now made to FIGURES 2 and 3 illustrating top views of some embodiments of a photonic chip applying AWG. Input light via an optic input 23 of the chip 20, such as an optic fibre input, is connected to an AWG 21 placed on the chip 20. The AWG divides the broadband light into a set of narrow band channels, each of which is connected to the detector area 22. The standing wave is arranged at the detector area 22, in an embodiment by the reflective edge 4. Each of the standing wave channels in the detector area 22 is applied to respective set of detectors (not shown), such as the set of detectors 3 arranged as illustrated in Figure la or lb. [0031] As illustrated in FIGURE 3, the chip 20 may comprise a splitter 30 connected to the input 23 to split the input light into first channel and a second channel, wherein the first channel is connected to a first AWG 21a and the second channel is connected to a second AWG 21b. A set of waves from the first AWG 21a is arranged to be coupled or joined to a set of waves from the second AWG 21b to form the standing wave in detection area 32 with a set of detectors, such as the set of detectors 3 arranged as illustrated in Figure la or lb.

[0032] The presently disclosed features enable to achieve similar resolution and bandwidth as prior art but without having to fabricate etched nanoscale features. However, in some embodiments, the standing waves can be obtained by splitting the input in two channels that link to each other as on figure 3. In some embodiments, a phase shifter 31 is provided allowing shifting the position of the standing wave to optimize measurements.

[0033] FIGURE 4 illustrates measurement of narrow-band light versus broadband light with conventional size pixels. It can be seen that use of the present division to narrower bandwidth standing waves, illustrated in the lower graphs, enables easier measurement with conventional pixels.

[0034] The spectrometer apparatus and chip 20 can be manufactured by using standard techniques. The chip can be manufactured on a variety of photonic platforms, such as silica or polymer based photonic integrated circuits (PIC), silicon on insulator (SOI), Indium Phosphide (InP), Gallium arsenide (GaAs), etc.

[0035] FIGURE 5 is a flow graph of a method. The phases of the illustrated method may be performed on a chip for reading multiple photonic detectors, such as the chip 1 according to at least some of the embodiments illustrated above. Input light of given bandwidth is received 500 by an optic input. The input light from the optic input is separated 510 by a waveguide structure to form a set of narrower bandwidth standing waves. The standing waves are sampled by photonic detectors by direct standing wave sample collection without intermediate etched nanoscale features.

[0036] It will be appreciated that some or all of the embodiments illustrated above in connection with Figures 1 to 4 may be applied in addition to the method illustrated in Figure 5. Furthermore, a chip, an apparatus or a device may be provided which may be configured to perform or comprise means for carrying out the phases of Figure 5 and its further embodiments.

[0037] The apparatus capable of supporting at least some embodiments illustrated above may be a standalone sensor device or applied in a wide variety of electronic devices. Such electronic device comprising the apparatus may be an optical biosensor or chemical sensor device, for example. The device may include one or more such spectrometer apparatuses and chips 20 in accordance with at least some of the embodiments illustrated above. For example, the chip 20 and/or the device may be applicable or configured for human or animal health monitoring, such as infection, cancer or diabetes detection purposes, food and water quality monitoring, environment quality monitoring, astronomy, chemistry, biochemistry, explosive and other illegal substances detection, forensic, textile, farming, etc.

[0038] The electronic device may further comprise various other units, such as at least one single- or multi-core processor with at least one processing core and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processing core cause the device to perform certain actions as defined in the computer program. The device may also comprise a transmitter, a receiver, and/or a user interface, for example.

[0039] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0040] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed. [0041] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0042] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. [0043] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0044] The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality. INDUSTRIAL APPLICABILITY

At least some embodiments of the present invention find industrial application in apparatuses applying optical detection.

ACRONYMS LIST

AWG Arrayed waveguide grating

CCD Charge-coupled devices

GaAs Gallium arsenide

InP Indium Phosphide PIC Photonic integrated circuit

SOI Silicon on insulator

CITATION LIST

[1] "Deposition of nanocrystalline translucent h-BN films by chemical vapor deposition at high temperature", Ghassan Younes et al, Thin Solid Films, Volume 520, Issue 7, 31 January 2012, Pages 2424-2428, ht p://fedoi r^lOJQi6/i.tsf.20ilJ9J82

Claims

CLAIMS:

1. A spectroscopic detection apparatus comprising:

- an optic input;

- a plurality of photonic detectors arranged to sample the standing waves, wherein standing wave sample collection is arranged directly without intermediate etched nanoscale features.

2. The apparatus of claim 1, wherein the standing wave light collection is arranged on the whole length of detector pixels.

3. The apparatus of claim 1 or 2, wherein the standing wave sample collection is arranged by or based on at least one of: evanescent coupling, coupling using artificially and/or naturally occurring impurities in the waveguide, artificial and/or naturally occurring roughness of a surface of the waveguide, and translucent thin film deposited on the waveguide.

4. The apparatus of any preceding claim, wherein a reflective edge is provided at an edge of the waveguide structure to guide the waves as standing waves.

5. The apparatus of any preceding claim, wherein the apparatus further comprises: a splitter connected to the input to split the input light into first channel and a second channel, wherein the first channel is connected to a first separator and the second channel is connected to a second separator, and a set of waves from the first separator is arranged to be coupled/joined to a set of waves from the second separator to form the standing waves.

6. The apparatus according to claim 5, wherein the apparatus further comprises a phase shifter connected to the first channel for shifting a position of the standing waves.

7. The apparatus of any preceding claim, wherein the waveguide structure comprises an arrayed waveguide grating.

8. The apparatus according to any preceding claim, wherein the photonic detectors are charge-coupled devices.

9. The apparatus according to any preceding claim, wherein the apparatus is an optical biosensor or a chemical sensor device.

10. A method for spectroscopic detection, comprising:

- receiving input light with given bandwidth by an optic input;

- separating the input light from the optic input to a set of narrower bandwidth standing waves by a waveguide structure; and

- sampling the standing waves by a plurality of photonic detectors, wherein standing wave sample collection is arranged directly without intermediate etched nanoscale features.

11. The method according to claim 10, wherein the standing wave light is collected on the whole length of detector pixels.

12. The method of claim 10 or 11, wherein the standing wave samples are collected by or based on at least one of: evanescent coupling, coupling using artificially and/or naturally occurring impurities in the waveguide, artificial and/or naturally occurring roughness of a surface of the waveguide, and translucent thin film deposited on the waveguide.