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Title:
INTEGRATED SPECTROMETER
Document Type and Number:
WIPO Patent Application WO/2020/065355
Kind Code:
A1
Abstract:
An integrated spectrometer (200). The spectrometer may comprise a substrate bearing set of waveguides; these may be arranged in a plane of the substrate. The waveguides may be configured to transmit a respective set of wavelength bands. Each waveguide may be configured to transmit a wavelength band with a different center wavelength. The spectrometer may further comprise one or more graphene photodetectors (220). The one or more graphene photodetectors (220) may be located at an end of each of the waveguides so that when the substrate is illuminated from above or beneath light couples into the waveguides and is guided into the one or more graphene photodetectors. The spectrometer may be configured to differentiate between the light guided by each waveguide to distinguish the wavelengths bands present in the illumination.

Inventors:
FERRARI PROFESSOR ANDREA C (GB)
OCCHIPINTI LUIGI (GB)
RUOCCO ALFONSO (GB)
Application Number:
PCT/GB2019/052758
Publication Date:
April 02, 2020
Filing Date:
September 30, 2019
Export Citation:
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Assignee:
CAMBRIDGE ENTPR LTD (GB)
International Classes:
G01J3/18; G01J3/02; G02B6/12; G02B6/34; G01N21/3504
Domestic Patent References:
WO2014089454A22014-06-12
WO2015162197A22015-10-29
Foreign References:
US20170138789A12017-05-18
US20160238447A12016-08-18
US20170088944A12017-03-30
CN103439808A2013-12-11
JP2016161890A2016-09-05
Other References:
HYUNGJUN HEO ET AL: "A Study on a Compact Coupler between an Optical Fiber and a Grating-assisted Graphene-embedded Silicon Waveguide for a Wavelength-selective Photodetector", CURRENT OPTICS AND PHOTONICS, 1 October 2017 (2017-10-01), pages 514 - 524, XP055647164, Retrieved from the Internet [retrieved on 20191127], DOI: 10.3807/COPP.2017.1.5.514
HYUNGJUN HEOSANGIN KIM: "A Study on a Compact Coupler between an Optical Fiber and a Grating-assisted Graphene-embedded Silicon Waveguide for a Wavelength-selective Photodetector", CURR. OPT. PHOTON., vol. 1, 2017, pages 514 - 524
"PhD thesis", 2001, MCMASTER UNIVERSITY, article "Segmented Waveguide Photodetectors For Wavelength Monitoring"
NANO LETT., vol. 16, no. 11, 2016, pages 7107 - 7112
Attorney, Agent or Firm:
MARKS & CLERK LLP (GB)
Download PDF:
Claims:
CLAIMS

1. An integrated spectrometer comprising:

a substrate bearing set of waveguides configured to transmit a respective set of wavelength bands, wherein each waveguide is configured to transmit a wavelength band with a different center wavelength;

one or more graphene photodetectors, wherein the one or more graphene photodetectors are located at an end of each of the waveguides;

wherein when the substrate is illuminated from above or beneath light couples into the waveguides and is guided into the one or more graphene photodetectors; and wherein the spectrometer is configured to differentiate between the light guided by each waveguide to distinguish the wavelengths bands present in the illumination.

2. A spectrometer as claimed in claim 1 comprising one graphene photodetector for each waveguide.

3. A spectrometer as claimed in claim 1 comprising at least one shared graphene photodetector located at the ends of a group of the waveguides, and a modulator between the end of each waveguide of the group and the shared graphene photodetector.

4. A spectrometer as claimed in claim 3 wherein the modulator is a graphene- based modulator. 5. A spectrometer as claimed in claim 3 or 4 configured to control each modulator to modulate light from a respective waveguide of the group so that a signal component of the light from the respective waveguide is distinguishable in a signal from the shared graphene photodetector. 6. A spectrometer as claimed in claim 5 further comprising a demodulator to separate the signal components from each waveguide of the group to distinguish the wavelengths bands present in the illumination.

7. A spectrometer as claimed in any preceding claim wherein the waveguides comprise gratings.

8. A spectrometer as claimed in any preceding claim wherein the waveguides are fabricated from silicon nitride.

9. A method of fabricating a spectrometer as claimed in any preceding claim wherein the method uses a CMOS or CMOS-compatible process.

10. A method of detecting gas or glucose wherein the method uses the spectrometer of any one of claims 1 -9.

Description:
INTEGRATED SPECTROMETER

FIELD

This invention relates to generally to spectrometers, in examples to an integrated broadband spectrometer.

The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 649953.

BACKGROUND

Background prior art can be found in: US20170088944A1 “Method Of Manufacturing Large Area Graphene And Graphene-Based Photonics Devices”; CN103439808B“A New Electro-Optic Modulator Structure Of Graphene”; JP2016161890A “Optical Device”; Hyungjun Heo and Sangin Kim, "A Study on a Compact Coupler between an Optical Fiber and a Grating-assisted Graphene-embedded Silicon Waveguide for a Wavelength-selective Photodetector," Curr. Opt. Photon. 1 , 514-524 (2017); and PhD thesis “Segmented Waveguide Photodetectors For Wavelength Monitoring”, A Densmore 2001 , McMaster University, Ontario - see section 5.2.4 at page 88.

SUMMARY In one aspect there is described an integrated spectrometer. The spectrometer may comprise a substrate bearing set of waveguides; these may be arranged in a plane of the substrate. The waveguides may be configured to transmit a respective set of wavelength bands. Each waveguide may be configured to transmit a wavelength band with a different center wavelength. The spectrometer may further comprise one or more graphene photodetectors. The one or more graphene photodetectors may be located at an end of each of the waveguides so that when the substrate is illuminated from above or beneath light couples into the waveguides and is guided into the one or more graphene photodetectors. The spectrometer may be configured to differentiate between the light guided by each waveguide to distinguish the wavelengths bands present in the illumination. In implementations such a spectrometer may have a wide bandwidth, for example from the visible to the near infrared (IR), for example up to wavelengths longer than 2000nm.

The use of graphene facilitates broadband operation using a single type of photodetector.

The graphene photodetector(s) may be of any convenient type including, for example, a detector based on the photo-thermoelectric effect (PTE) and/or photoconductivity (see Nano Lett., 2016, 16 (1 1 ), pp 7107-71 12 for examples).

In some implementations the waveguides are fabricated from silicon nitride, which facilitates sensitivity to the near IR although e.g. glass or silicon may also be used.

In implementations passive a grating or other frequency selective device is built into each waveguide. For example each waveguide may comprise a grating, as used herein any periodic perturbation of the waveguide structure. The FWHM (full width at half maximum) bandwidth of such a waveguide may be for example be in the range 5- 100nm.

In some implementations at least some waveguides each have a dedicated graphene photodetector.

In some of these or other implementations there is at least one shared graphene photodetector located at the ends of a group of the waveguides. For example each waveguide of the group may converge on a location of the graphene photodetector. A modulator may be provided between the end of each waveguide of the group and the shared graphene photodetector. In some implementations each modulator is a graphene-based modulator. A wide range of graphene-based modulators may be employed, e.g. an electro-absorption modulator (EAM).

The spectrometer may be configured to drive each modulator, for example with a driver, to modulate light from a respective waveguide of the group so that a signal component of the light from the respective waveguide is distinguishable in a signal from the shared graphene photodetector. The modulator drive may be electrical or optical. In some implementations the light from the waveguides may be time-domain multiplexed onto the shared graphene photodetector. Additionally or alternatively the light from the waveguides may be frequency-domain multiplexed onto the shared graphene photodetector. A demodulator may be used to separate the signal components from each waveguide of the group to distinguish the wavelengths bands present in the illumination.

The wide bandwidth of the spectrometer in implementations may be used for gas detection, for example to determine a spectral fingerprint of a gas over the bandwidth of the spectrometer. such a spectrometer may have a wide bandwidth, for example from the visible to the near infrared (IR), for example up to wavelengths longer than 2000nm. In some other applications the spectrometer may be employed to sense one or more components of a liquid. For example the wide bandwidth of the spectrometer in implementations may be used to identify one or more absorption bands of glucose in a region >2000nm (e.g. at ~2120nm and/or ~2270nm and/or ~2320nm) in conjunction with one or more absorption bands of glucose in a region <2000nm (e.g. ~1610-1740nm).

A substrate for an integrated spectrometer as described above, in particularly a substrate bearing the waveguides and photodetector(s), may be an independent article of commerce and may be fabricated using a CMOS or CMOS-compatible process.

DRAWINGS

These and other aspects of the invention will now be further described by way of example only, with reference to the accompanying Figures, in which:

Figure 1 shows a first example large bandwidth integrated spectrometer; and

Figure 2 shows a second example large bandwidth integrated spectrometer.

DESCRIPTION There is described a broadband spectrometer working from visible to SWIR with high resolution (limited by minimum feature size of the lithographic tool). In implementations the broadband absorption of graphene is combined with the wavelength selectivity of grating couplers.

Integrated graphene modulators allow heterodyne detection using single or multiple pixel detector.

The architecture does not require the integration of multiple materials for the different absorption wavelengths.

Thus in implementations a single CMOS compatible platform enables broadband but wavelength selective light detection.

Silicon nitride may be used for its transparency (VIS to SWIR); in implementations graphene is used both for light modulation (SWIR) and light detection (VIS-SWIR).

Grating couples selectively couple light to individual waveguides. In implementations modulators are present on each of the waveguides and these encode the signal into a carrier frequency. Then the carriers are detected by the graphene photodetector(s).

Off-chip lock-in detection for the individual carriers may be used to reconstruct the spectral content of the incoming light.

Applications include broadband spectrometry and low light level light detection spectrometry, and finger print analysis.

Figure 1 shows a perspective view of a first example large bandwidth integrated spectrometer 100. Passive waveguide gratings 1 10a-d filter the different wavelengths. Illumination is from above; there is a large collection area (the area of the grating). The graphene photodetectors 120a-d can produce -10V/W.

Figure 2 shows a perspective view of a second example large bandwidth integrated spectrometer 200. In this configuration passive waveguide gratings 1 10a-d converge on a single graphene photodetector 220 via respective graphene modulators 230a-d. No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.