HK1169162A - Spectrophotometer - Google Patents

Abstract

A spectrophotometer comprising a monolithic semiconductor substrate, one or more wavelength dispersing means, and one or more wavelength detecting means, wherein the monolithic substrate (1) has waveguide means (2) and one or more resonators (3-14) acting as detectors of particular light wavelengths and disposed in proximity to the waveguide means in such a way that evanescent light coupling can occur for said light wavelengths.

Description

Spectrophotometer

Technical Field

The present invention relates to a device for identifying and quantifying substances, and more particularly to a spectrophotometer in which there is no physical separation between a light dispersing means and a light detecting means. The invention also relates to a spectrophotometer without moving parts.

Background

Spectrophotometry is the study of the electromagnetic spectrum. Spectrophotometry involves the use of a spectrophotometer. A spectrophotometer is a photometer that can measure the intensity of light according to the wavelength of the light-a device for measuring the intensity of light. Such spectrophotometers are used in many fields such as chemistry, biology, forensic science, space and earth observation, security, and various industries. Spectrophotometers have additional widespread applications in color recognition, for example in flat panel displays or electronic cameras, color control for xerography, environmental monitoring, and process control related to color/wavelength recognition.

The most common application of spectrophotometers is the measurement of light absorption, but spectrophotometers can be designed to measure, for example, the diffuse reflectance and transmission or emission spectra of materials or devices. A spectrophotometer may in principle operate over the entire wavelength range of the electromagnetic radiation spectrum of light. However, most spectrophotometers operate in the visible, infrared, near infrared, mid infrared or ultraviolet wavelength ranges of the electromagnetic spectrum. The wavelength region and range of a spectrophotometer is determined in part by the spectral data that the spectrophotometer is designed to collect, the type of light dispersion, and the light detection system used. This in turn limits the acquisition speed, sensitivity and resolution capabilities of the spectrophotometer.

Conventional spectroscopy systems can be divided into two categories: (a) dispersive systems and (b) interferometric (FTIR) systems. In both cases, the basic system consists of a device used for light to be dispersed (spectrally or temporally) with a grating or linear drive mechanism plus a detection element (usually a semiconductor-based photodetector or photomultiplier). Such a system thus consists of at least two components. Indeed, such systems require a number of additional optical elements, such as lenses, mirrors, shutters, slits and optical choppers, for the spectrophotometer to operate effectively. Historically, spectrophotometers have used monochromators to analyze spectra, but there are also spectrophotometers that use arrays of light sensors, such as CCD arrays. Such a system is shown, for example, in GB 0525408.1. Such spectrophotometers are complex due to the number of components. These systems typically contain mechanical grating monochromators, slits, baffles and cooled photodetectors that color the light, and lenses, mirrors and shutters, all of which must be properly aligned for the spectrophotometer to function properly. Due to the complexity and large number of components, these systems are prone to failure, have relatively slow acquisition times, are expensive to manufacture, and have problems associated with stray light, which reduces signal strength because each additional component introduced into the optical system causes a loss of photons. This problem is compounded when there is a large spatial separation between components of the spectrophotometer, including the light dispersion and light detection components (optical paths). Furthermore, array-based spectrometers have the additional disadvantage that their optical characteristics are fixed, making it impossible, for example, to increase spectral resolution or sensitivity by varying the width of the slit as is possible in conventional grating-based spectrometers.

Furthermore, in critical applications, such as those requiring the spectrophotometer to be portable, these systems are not ideal because they are heavy, large in size, and prone to failure due to damage or misalignment of the optical path, due to stress failure, and the like. This is exacerbated when the system is used in space, aviation and other harsh environments, as conventional FTIRs and grating-based instruments with mechanically driven moving parts are fragile instruments that do not handle vibrational stresses and the extremes of emitted stress, space vacuum and temperature well. The quality and size are additional consumption of resources allocated to the payload. CCD arrays for the visible region slightly reduce stress on energy resources when used in a spectrophotometer, but can be susceptible to cosmic radiation and alignment errors.

Many additional applications of interest arise if the spectrophotometer in the instrument has significantly lower cost, lighter weight, smaller size, stringent and combined signal processing capabilities.

To overcome some of these disadvantages, miniaturized spectrophotometric systems have been developed in the art, such as micro-electromechanical systems (MEMS), such as that of U.S. patent No. US7106441 entitled "Structure and method for electrochemical fluorescence diffraction spectroscopy", which discloses a tunable MEMS spectrophotometer with a rotating cylindrical reflective diffraction grating integrated with a photodetector and a fiber optic light source on a rowland circle on a single silicon substrate.

Other examples include: a spectrophotometer disclosed in US2008198388, US2008198388 describes a compact fourier transform spectrophotometer with a moving scanning mirror; US2006132764 describes an integrated optics based high resolution spectrophotometer having an arrayed waveguide grating coupled to a photodetector; US2004145738 describes a MEMS spectrophotometer with a rotating grating; DEl0216047 describes a multi-reflecting optical cell with an internal sample-holding chamber, a light entrance port and a light exit port, without a movable mirror or other movably attached optical component, the reflecting surface of which can take the form of opposing parabolic or parallel pairs of multiple mirrors, cylindrical, circular or spiral arrangements; and US6249346 describes a micro-spectrophotometer integrally constructed on a silicon substrate. The spectrophotometer includes a concave grating for dispersing the light wave and focusing the reflected light onto an array of photodiodes located on a silicon bridge.

All the above-mentioned methods of spectrophotometers overcome the above-identified problems, since they provide a reduction in the size of the spectrophotometer, however they all have the following disadvantages: they have one or more moving parts, are structurally not unitary or complex, or have poor optical dispersion characteristics and poor resolution due to miniaturization. Therefore, these techniques do not fully solve the above-described problems because they are prone to malfunction, have stray light problems, and are generally expensive and difficult to produce, or have poor light dispersion characteristics and poor resolution due to miniaturization.

To overcome some of these disadvantages, other types of spectrophotometers have been developed. These spectrophotometers include, for example, U.S. application No. US 11/015,482 entitled "Integrated optics based high resolution photometer"; WO2007072428 entitled "Spectrophotometer and spectrometrological processing using Fabry-Perot detectors"; japanese patent application No. JP1990128765 entitled "Multiple-wavelet spectrophotometer and phosphorescent arrayed photodetector"; U.S. patent No. 6785002 entitled "variable filter based optical spectrometer"; U.S. Pat. No. 6249346 entitled "Monolithic spectrophotometer"; U.S. patent application No. 11/206,900 entitled "Chip-scale optical analyzers with enhanced resolution". All of the above prior art techniques utilize separate components for light dispersion and detection, resulting in problems and performance degradation during manufacturing.

All of the above spectrophotometers still have separate monochromator and detection optics, meaning that on a micro scale they will lack resolution (due to the limited spatial separation between the dispersive and detection elements), are difficult to manufacture (due to the need for precise alignment), and have problems associated with the effects of stray light (since intense light can be easily scattered in the spectrophotometer).

Disc resonators, also known as micro-disc resonators or resonators, for adding and removing specific wavelengths from a fiber optic cable in telecommunications are known in the art. Examples of the disk resonator include: U.S. patent application No. 10/323195 entitled "Tuneable optical filter" describes a tunable filter having a resonator with a resonator frequency that depends on the variable gap provided. Although this application describes an optical filter, it is not used for detection; OpticalExpress, 2006, vol 14, no 11, p4703-4712(Lee and Wu), article entitled "tunable coupling registers of silicon micro disk actuators". This paper describes a tunable coupling mechanism for silicon micro-disk resonators controlled by MEMS actuation. This publication describes a tunable optical filter that requires MEMS moving parts to function, and the micro-disk is not used for detection; U.S. patent application No. 10/678354, entitled "ultra-high Q micro-resonators and methods of manufacture," describes a microcavity resonator comprising a microcavity and a silicon substrate capable of high and ultra-high Q values. This application describes tunable optical filters, but does not envisage means for the use of detection or dispersion; applied Physics Letters, 2002, vol 80, no 19, p3467-3469, entitled "Gain trimming of the resonator characteristics in vertically coupled InP micro disk switches", describes a vertically coupled micro disk resonator/waveguide switch device that exhibits single mode operation. Optical switches for use in communication applications are described. The resonator is not used for detection.

The above described prior art is all in the field of telecommunications where disc resonators are used to guide/divert/add or remove specific wavelengths from optical cables or waveguides. None of the above prior art considers using micro-disk resonators for detection, spectroscopy as monochromators or even as detectors of the intensity of light at that wavelength.

Disclosure of the invention

Technical problem

Several problems in spectrophotometer technology have been identified in the art and are described above. Such spectrophotometers are complex due to the number of components. These systems typically contain mechanical grating monochromators to disperse the light, slits, baffles, cooled photodetectors, lenses, mirrors and shutters, all of which must be properly aligned for the spectrophotometer to function properly. Due to the complexity and large number of components, these systems are prone to failure, have slow acquisition times, are expensive to produce and have problems associated with stray light, reducing signal strength because each additional component introduced into the optical system causes a loss of photons.

Furthermore, array-based spectrometers have the additional disadvantage that their optical characteristics are fixed, making it impossible to improve spectral resolution or sensitivity by varying the width of the slit as is possible in conventional grating-based spectrometers. These systems are typically heavy and therefore not suitable for portable applications.

MEMS systems overcome some of these disadvantages. However, these systems have the following disadvantages: they have one or more moving parts, are not unitary in structure or complex in their structure, or have poor optical dispersion characteristics and differential resolution due to miniaturization. Therefore, these techniques do not fully solve the above-described problems because they are prone to malfunction, have stray light problems and are generally expensive and difficult to produce, or have poor light dispersion characteristics and poor resolution due to miniaturization.

To overcome these disadvantages, chip-based components are used. However, all the spectrophotometer approaches described above have separate monochromator and detection optics, meaning that on a micro scale they will lack resolution (due to the limited spatial separation between the dispersive and detection elements), be difficult to manufacture (due to the need for precise alignment), and have problems associated with the effects of stray light (since intense light can be easily scattered within the spectrophotometer).

Thus, the prior art does not address the problems identified above.

Technical solution

It is therefore an object of the present invention to provide a spectrophotometer that addresses one or more of the problems identified above. In particular, the invention relates to a spectrophotometer comprising a monolithic semiconductor substrate (1), one or more wavelength dispersive devices (3-14) and one or more wavelength detection devices (3-14), characterized in that there is no physical separation between the dispersive devices (3-14) and the detection devices (3-14).

Advantageous effects

Advantageously, such a spectrophotometer will have a small input photon loss and a high signal to low noise ratio and therefore will have an improved signal strength.

Accordingly, embodiments of the present invention also provide spectrophotometers without physically moving parts.

Advantageously, such a spectrophotometer would result in a system that is not complex, low maintenance, and free of grating-detector alignment or stray light problems. Such a system would also produce a spectrophotometer with fast acquisition time and high resolution.

In a preferred embodiment, the spectrophotometer comprises a monolithic substrate, characterized in that the monolithic substrate (1) is a semiconductor having one or more waveguide means (2) and one or more resonators (3-14), wherein each resonator (3-14) forms part of the waveguide means (2) or each resonator (3-14) is optimally positioned close to the waveguide means (2).

Advantageously, a spectrophotometer of this type without moving parts of the type described can be manufactured with the following characteristics.

The spectrophotometer can be manufactured in a small size. Such a spectrophotometer may therefore find new use as part of, for example, a mobile phone or other device capable of transmitting information from the spectrophotometer (mounted on the surface of or within the mobile phone) from a remote location, allowing the development of networks of mobile or static chemical sensors. Such small sized sensors would also find use in spectrophotometers that are not desirable in weight or size, for example, in space applications. For example, in xerography, a spectrophotometer may be a key component in a closed-loop color control system that will enable a printer to produce reproducible color images in a networked environment. In a camera, a spectrophotometer chip may be used in place of the currently available light sensing chips to produce a camera capable of detecting light in the entire visible range, rather than only a discrete range.

The spectrophotometer described has low power requirements. Advantageously, such a spectrophotometer would find use in a portable spectrophotometer or a spectrophotometer that is not connected to a mains power supply.

Advantageously, such a spectrophotometer would allow for rapid acquisition of data since all wavelengths of light would be read in simultaneously. The entire spectrum can be read in milliseconds or less.

Advantageously, such a spectrophotometer will have excellent spectral characteristics, since such a spectrophotometer will have low stray light, thus producing a high resolution spectrum. In addition, such spectrophotometers can be manufactured with high resolution and wide wavelength coverage.

Advantageously, such spectrophotometers are cheaper than those currently on the market, since they have no moving parts, gratings, MEMS, etc.

Advantageously, such a spectrophotometer has no moving parts. Thus, the spectrophotometer will not suffer from failure due to failure of moving parts. Such a spectrophotometer would be more robust and reliable than currently available spectrophotometers.

In a preferred embodiment, the spectrophotometer comprises a monolithic substrate, characterized in that the monolithic substrate (1) is a semiconductor having one or more waveguide means (2) and one or more resonators (3-14), wherein the waveguide may be at an angle with respect to the direction of incidence of the input light, wherein each resonator (3-14) constitutes part of the waveguide means (2), or each resonator (3-14) is optimally positioned close to the waveguide means (2), the resonators being optimally dimensioned for a given electromagnetic wave wavelength and ordered such that the resonator of the smallest diameter is closest to the point of incidence of the input light entering the waveguide means and the resonator of the largest diameter is furthest from the point of incidence of the input light entering the waveguide means, the substrate being divided into three functional regions, wherein the first region is a substrate layer (17) made of a p-or n-type doped semiconductor, the second active region (16) is composed of a semiconductor in which band gaps are combined to cover the wavelength range of the spectrophotometer and have a refractive index greater than that of the substrate, and a third optical cladding region (18) having a refractive index lower than that of the second active region (16), wherein the second active region (16) is located between the first active region (17) and the third active region (18), the third region (18) is a common electrical contact with the first region (17), and the resonators (3-14) have electrical contacts (19, 20) on their surfaces.

Drawings

Embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which,

fig. 1 is a concept of a spectrophotometer.

Fig. 2 is two cross sections through the semiconductor chip [1] corresponding to the semiconductor chips indicated by a and B in fig. 1.

Fig. 3 is a three-dimensional representation of a semiconductor chip showing resonators (3-18) coupled to waveguide (2) either horizontally (a) or vertically (B).

Figure 4 is an epitaxial design of a typical spectrometer chip operating in the NIR region and designed with resonators aligned horizontally, as depicted in figure 3A.

It should be noted that certain aspects of the drawings are not to scale and that certain aspects are exemplified or omitted to facilitate clarity.

Best mode for carrying out the invention

The invention will be illustrated with reference to its most preferred embodiments. However, the present invention is not limited to the embodiments.

The present invention relates to a spectrophotometer in which there is no physical separation between the light dispersing means and the light detecting means, the spectrophotometer having no moving parts. For the reasons given above, the inventors have found that some spectrophotometers with moving parts are prone to failure or cannot be miniaturized, or are expensive/difficult to manufacture, or have other related problems.

It is therefore an object of the present invention to provide a spectrophotometer without moving parts. Accordingly, embodiments of the present invention provide a spectrophotometer comprising a monolithic semiconductor substrate (1), one or more wavelength dispersive devices (3-14) and one or more wavelength detection devices (3-14), characterized in that there is no physical separation between the dispersive devices (3-14) and the detection devices (3-14). It is envisaged that such a spectrophotometer will have no moving parts. Advantageously, a spectrophotometer of the type described can be manufactured with the following characteristics.

The spectrophotometer can be manufactured in a small size. Such a spectrophotometer may therefore find new use as part of, for example, a mobile phone or other device capable of transmitting information from the spectrophotometer (mounted on the surface of or within the mobile phone) from a remote location, allowing the development of networks of mobile or static chemical sensors. Such small sized sensors would also find use in spectrophotometers where weight or size is not desirable. For example, in xerography, a spectrophotometer may be a key component in a closed-loop color control system that will enable a printer to produce reproducible color images in a networked environment. In a camera, a spectrophotometer chip may be used in place of the currently available light sensing chips to produce a camera capable of detecting light in the entire visible range, rather than only a discrete range.

MODE OF THE INVENTION

The spectrophotometer described below will have low power requirements. Advantageously, such a spectrophotometer would find use in a portable spectrophotometer, or a spectrophotometer that is not connected to a mains power supply or that operates in difficult environments such as space, defense, etc.

Advantageously, such a spectrophotometer would allow for rapid acquisition of data as all wavelengths of light would be read in simultaneously. The entire spectrum can be read in milliseconds or less.

Advantageously, such a spectrophotometer will have excellent spectral characteristics, since such a spectrophotometer will have low stray light, thus producing a high resolution spectrum. In addition, such spectrophotometers can be manufactured with high resolution and wide wavelength coverage.

Advantageously, such spectrophotometers are cheaper than those currently on the market, since they have no moving parts, gratings, MEMS, etc.

Advantageously, such a spectrophotometer has no moving parts. Thus, the spectrophotometer will not suffer from failure due to failure of moving parts. Such a spectrophotometer would be more robust and reliable than currently available spectrophotometers.

Optionally, the waveguide of the spectrophotometer may be angled with respect to the direction of incidence of the light to prevent back reflection of the light.

Alternatively, the waveguide of the spectrophotometer may be between about 1 micron and about 50 microns wide, about 1000 microns long, and about 1 micron to about 20 microns deep.

In preferred embodiments, each resonator is dimensioned to be optimised for a given wavelength, and each resonator may be cylindrical, cup-shaped, spherical, conical, stepped conical, plate-shaped, or comprise one or more flat or curved surfaces. In the most preferred option, each resonator is spherical, cylindrical or cup-shaped in shape and the diameter of each sphere or cylinder is determined by the formula D ═ n λ/pi μ, where λ is the free space wavelength of light, n is the resonance order and μ is the effective refractive index of the resonator.

Alternatively, the waveguide arrangement may be formed from resonators (3-14), the resonators (3-14) being arranged such that the resonators (3-14) are arranged in a linear manner, wherein the resonators are arranged from small to large such that the smallest resonator is positioned in a first position and the largest resonator is positioned in the last position. In a preferred embodiment, the resonators are ordered such that the resonator of the smallest diameter is closest to the point of incidence of the incident light entering the waveguide device and the resonator of the largest diameter is furthest from the point of incidence of the incident light entering the waveguide device.

Alternatively, compositional grading or doping of the absorbing layer may also be used to select a particular wavelength for each resonator, instead of or in addition to resonator size. A set of resonators with the same diameter can be used and the resonance is changed by manipulating the refractive index. For example, for a resonator having a diameter of about 1 micron, a total refractive index step of less than 0.02 between 10 resonators would produce resonances spaced 1 nanometer apart, e.g., from 1500 nanometers to 1510 nanometers, by composition/doping (with impurities) grading, without changing the diameter of the resonator.

Alternatively, the spectrometer chip may use a bias as a means to adjust the refractive index. Thus, part of chip testing may be to determine whether the bias on any given resonator may be optimized to shift one or more resonances. This is also a very good way to change the resolution of the spectrometer chip.

In a preferred embodiment, the resonator operates in the first order and responds only to a single wavelength in the spectrometer. Alternative embodiments contemplate using resonators that operate at higher orders (and are therefore larger and more easily manufactured with sufficient tolerances). When larger resonators are used on higher orders, there are three ways in which unwanted wavelengths can be excluded:

1. the absorbing layer is chosen to have its own fixed spectral absorption bandwidth so that it is not responsive to wavelengths above a certain limit.

2. The use of a thin film filter on the front side (optical input) of the chip may be used to suppress shorter wavelengths that are not of interest but that may couple into and be absorbed by the resonator.

3. The waveguide itself will absorb wavelengths below a certain cut-off wavelength and can therefore be used as a filter.

The resonator may be placed horizontally or vertically with respect to the waveguide for horizontal or vertical coupling. Fig. 3B shows an embodiment of vertical coupling where the resonator spans two ridges. This configuration is particularly suitable when the resonator is operating at higher orders.

The spectrophotometer is fabricated from a substrate that may include group IV, III-V, II-VI, II-IV semiconductors or other semiconductors with semiconductor alloys added thereto. Preferably, the substrate is doped p-type or n-type.

In a preferred embodiment, the substrate is divided into three functional regions, wherein the first region is a substrate layer (17) made of a p-type or n-type doped semiconductor, the second active region (16) is composed of a semiconductor in which the band gaps are combined to cover the wavelength range of the spectrophotometer and have a refractive index greater than the refractive index of the substrate, and the third optical cladding region (18) has a refractive index lower than the second active region (16), wherein the second active region (16) is located between the first active region (17) and the third active region (18). The third region (18) is in common electrical contact with the first region (17). Preferably, the electrical contact (18) is a gold electrical contact, a gold alloy electrical contact or an electrical contact made of other electrically conductive material or a composition thereof, such as silver or a composition thereof.

Preferably, the resonators (3-14) have electrical contacts (19, 20) on their surface, which contacts comprise gold electrical contacts, gold alloy electrical contacts or electrical contacts comprising other electrically conductive materials.

Alternatively, the cleaved surface of the semiconductor wafer may be coated with multiple layers of coatings to accept or reject light over a particular range of wavelengths. Such coatings are known to those skilled in the art.

In another option, the substrate may include one or more solid state shutters/modulators or light guide optics.

In a more preferred embodiment, the spectrophotometer comprises a monolithic substrate, characterized in that the monolithic substrate (1) is a semiconductor having one or more waveguide means (2) and one or more resonators (3-14), wherein the waveguide is at an angle with respect to the direction of incidence of the input light, wherein each resonator (3-14) constitutes part of the waveguide means (2), or each resonator (3-14) is optimally positioned close to the waveguide means (2), the resonators being optimally dimensioned for a given electromagnetic wave wavelength and ordered such that the resonator of the smallest diameter is closest to the point of incidence of the input light entering the waveguide means and the resonator of the largest diameter is furthest from the point of incidence of the input light entering the waveguide means, the substrate being divided into three functional regions, wherein the first region is a substrate layer (17) made of a p-or n-type doped semiconductor, the second active region (16) is composed of a semiconductor in which band gaps are combined to cover the wavelength range of the spectrophotometer and have a refractive index greater than that of the substrate, and the third optical cladding region (18) has a refractive index lower than that of the second active region (16), wherein the second active region (16) is located between the first active region (17) and the third active region (18), the third region (18) is a common electrical contact with the first region (17), and the resonators (3-14) have electrical contacts (19, 20) on their surfaces.

Conventional spectroscopic systems can be divided into two categories: (a) dispersive systems and (b) interferometric (FTIR) systems. In both cases, the basic system consists of a device used for light to be dispersed (spectrally or temporally) with a grating or linear drive mechanism plus a detection element (usually a semiconductor-based photodetector or photomultiplier). Such a system thus comprises at least two components, a light dispersing means and a light detecting means. Indeed, such systems require a number of additional optical elements, such as lenses, mirrors, shutters, slits and optical choppers, examples of which are shown in GB 0525408.1. In addition, the output of the spectrometer is connected to signal processing devices such as lock-in amplifiers, gate-integrated averagers (box-car averagers), and other signal conditioning circuits that allow decoding of the output signal. Furthermore, the resolution (minimum resolvable wavelength feature) is inversely proportional to the physical size of the cell, thus requiring large instruments for high resolution. Therefore, the conventional spectrophotometer having a high resolution is large as necessary, and thus heavy and bulky. This results in limitations on the use of spectrophotometers. Furthermore, such spectrophotometers are delicate in nature and therefore tend not to be portable in nature.

This application describes spectrometers (elements) based on monolithic semiconductor chips. The element can be fabricated using standard semiconductor fabrication processes. The chip includes an optical dispersion system and an optical detection system, wherein one or more resonators serve as both an optical dispersion device and an optical detection device. Furthermore, in particular embodiments, the chip may include shutters/modulators (solid state) and other light guide optics.

The basic concept is shown in fig. 1. [1] Representing a semiconductor chip having a typical size of 200 microns wide by 1000 microns long by 100 microns thick. The material comprising the semiconductor chip may comprise any one of a group IV semiconductor, a group II-VI semiconductor, or a group III-V semiconductor alloy wherein: GaAs, GaN, GaP, GaSb, InAs, InN, InP, InSb, AlAs, AlN, AlP, and AlSb, the choice of materials being determined by the desired wavelength range of the spectrometer chip. In addition, the inclusion of dopant impurities can be used to fine tune the optical and electrical characteristics of the chip. [2] An optical waveguide composed of the material for [1] is shown. The waveguide is intentionally angled with respect to the semiconductor chip [1] in order to avoid back reflections. The waveguides are typically between 1 and 50 microns wide, 1000 microns long, and 1-20 microns deep. In addition, the end faces of the chips may be coated to accept and/or reject incident light in a particular wavelength range. [3-14] are representative examples of circular resonators that can be any number. A larger number of resonators will provide a wider wavelength range and/or higher spectral resolution. Typical implementations typically contain 10-1000 resonators on a single chip. The dimensions of the resonator are chosen such that the diameter (D) of the resonator is equal to the wavelength (λ) of interest multiplied by the order of resonance (n) divided by pi and the refractive index (μ) of the semiconductor comprising the resonator (i.e. D ═ n λ/pi μ). Therefore, assuming that a semiconductor with a refractive index of 3 operates on the first order (n ═ 1), a resonator with a diameter of 0.164 micrometers is required to detect light at a wavelength of 1.55 micrometers. Larger discs operating on n > 1 (e.g., for n 10, D1.64 microns) may also be fabricated, assuming the light is pre-filtered to remove other orders of forming resonances within the micro-disc. The resonators are ordered with the smallest diameter resonator nearest the point of incidence of the incident ray, as shown in figure 1. Resonance can also be controlled by the refractive index μ, which can be varied by changing the alloy composition and/or by introducing doping impurities in the resonator.

FIG. 2 shows a through semiconductor chip [1]]Which correspond to the semiconductor chips indicated by a and B in fig. 1. [17 ] in FIG. 2]Is represented by the formula for [1]A base material made of the listed materials and doped either n-type or p-type. The substrate is typically about 90 microns thick and serves as a template for the spectrometer chip. On top of the substrate an active region is grown (typically by molecular beam epitaxy or metal organic vapor phase epitaxy) [16 ]]The region is formed by]But the bandgap is designed to cover the target wavelength range of the spectrometer and has a refractive index greater than the refractive index of the substrate. Band gap (E) of semiconductor_g) Is selected to determine the maximum detection wavelength of the resonator, where λ ═ hc/E_gWhere h is the Planck constant and c is the speed of light in vacuum, the equation may be approximated as λ (nm) ═ 1240/E_g(eV). In the case of low-dimensional structures such as quantum wells, quantum wires or quantum dots, the thickness of the absorbing semiconductor layer is selected such that λ (nm) 1240/(E)_g+E_e+E_h) (eV) in which E_eIs electron confinement energy, and E_hThe energy is constrained for the aperture. [18]Is an upper optical coating layer comprising a metal oxide layer for [1]]And is selected to have a specific layer [16 ]]A larger bandgap and a lower refractive index. [18]Which represents the common electrical contact of the lower surface of the device and is generally made of gold and its alloys. [19]And [20]Electrical contacts made directly to the upper surface of the resonator are shown, which are typically made of gold and its alloys. The resonators may be placed in any order along the waveguide. However, the best positioning is to place the resonator with the smallest diameter closest to the light entrance on the resonator and with the diameter being the smallestThe largest is placed farther. The resonators interposed between the first and last resonators sequentially increase in diameter.

FIG. 3A provides a topology diagram of a specific embodiment in which resonators [3-13] and waveguides [2] are defined by etching of a semiconductor structure grown on top of a substrate. Electrical contacts are provided by evaporated and/or sputtered conductors and contact pads, as in [19, 20 ]. In this embodiment, the optical coupling between the waveguide [2] and the resonator [3-13] is horizontal. FIG. 3B shows an alternative embodiment in which light is coupled from waveguide [2] into resonators [3-14], whereby the resonators are defined by etching on the waveguide. The electrical contacts are provided by evaporated and/or sputtered conductors, an example of which is labeled [19 ].

Figure 4 shows a typical epitaxial structure of the particular embodiment shown in figure 3A for the concept of a device that is targeted to operate at around 1.5 microns. The chip is grown on InP substrate [21 ]]Doped n-type to 1x10¹⁸cm^-3And then thinned to a thickness of about 100 microns. On this chip, an In (0.601) Ga (0.399) As (0.856) P (0.144) layer [22 ] having a thickness of 200 nm was grown]Having an optical bandgap equal to 1.3 microns, followed by a layer [ 23.23 ] of In (0.601) Ga (0.399) As (0.856) P (0.144) having a thickness of 100 nm and an optical bandgap of 1.5 microns]. Followed by a second In (0.72) Ga (0.28) As (0.6) P (0.4) layer [24 ] with a thickness of 200 nm]Having an optical bandgap equal to 1.3 microns and subsequently doped to 2x10¹⁸cm^-3A p-type InP layer [25 ] of a thickness of 5 μm]. In this embodiment, the input light is in the waveguide (top InP layer [25 ]]And a bottom InP layer [21 ]]To [2] in]And [22-24]) Is guided mainly through a 1.3 micron layer [22, 24 ] of In (0.72) Ga (0.28) As (0.6) P (0.4)]And (5) spreading. Top InP layer [25 ]]And an In (0.72) Ga (0.28) As (0.6) P (0.4) layer is selectively etched In the resonator region, wherein the In (0.601) Ga (0.399) As (0.856) P (0.144) layer constitutes an absorber layer providing absorption at and below 1.5 microns. Other epitaxial structure implementations are contemplated and known in the art.

Principle of operation

The present invention differs from the prior art in at least three respects:

(a) there is no physical separation between the light dispersing means and the light detecting means,

(b) dispersing light over a range of wavelengths using a series of resonators, and

(c) detecting the level of light at a particular wavelength using a series of resonators.

Light emanating from the point of interest enters the device as shown by the arrows in fig. 1. The entrance face of the chip may be coated to reject/select the wavelength-prefilter of interest. The point of incidence may also include an electro-absorption modulator to optically isolate the chip at any given time. Due to the difference in refractive index between the waveguide [2] and its surroundings, light propagates along the waveguide. The electric field distribution (optical field distribution) of light is generally gaussian in distribution, decaying laterally and symmetrically across the chip and having a evanescent field tail. If a particular wavelength component of the incident light matches the resonant wavelength of one of the resonators (3-14 in the figure, although in practice there will be many more resonators), it will couple into that resonator, while the rest of the light continues to travel along the waveguide. As light passes through each resonator, any component of the light having a wavelength matching the resonator wavelength will couple into the resonator. Thus, each resonator selectively couples a portion of the incident light, effectively selecting a different wavelength. The semiconductor material comprising the resonator is chosen such that it absorbs light in a specific wavelength range. Thus, when light enters one of the resonators, it is also absorbed, creating electron-hole pairs in that resonator. When connected to an external circuit by electrical contacts (e.g. [18] and [19] or [18] and [20]), this forms a circuit proportional to the amount of light present in the resonator. Thus, each resonator acts as a detector sensitive to a particular wavelength and when the signal from each detector is connected to appropriate circuitry, a spectrum of light can be produced. The speed at which the spectrum can be recorded is limited only by the electron and hole escape times in the resonator (typically a few microseconds or less), allowing spectra to be obtained at speeds typically up to 100 tens of thousands per second.

Industrial applicability

The disclosed semiconductor chip provides a spectrophotometer with low mass and low power requirements, cosmic ray resistance, thermal stability, vibration resistance, oxygen atom immunity, space vacuum compatibility, and no moving parts, the chip will not require maintenance. Thus, this spectrophotometer is ideally suited for hyperspectral imaging, security monitoring and surveillance, chemical analysis, remote sensing, and imaging applications for earth observation (e.g., climate and atmospheric monitoring) and space observation across the entire environment, healthcare (including "wearable" monitoring systems for healthcare/medical devices), industrial and security markets. Hyperspectral imaging using such a spectrophotometer can be performed from space using a linear array of spectrophotometer chips, since each chip can provide broadband spectral information. Current methods using CCD detectors have typical integration times of about 7 seconds, allowing ground pixel sizes of about 50 meters. In conventional imaging systems, a 2D silicon CCD array is used, with one dimension providing spatial information and the other dimension providing spectral information. Faster acquisition times offer the potential to enhance a particular resolution window (ground pixel size) on earth. In our concept, a linear array of spectrophotometers provides both spectral and specific information. In applications requiring high resolution, each resonator will be used to target a particular wavelength. The resolution of this approach is related to the resonator size, for which we expect that a resolution of about 1 nanometer can be achieved using current technology. For applications where speed is much more important than resolution, multiple micro-discs (resonators) may be coupled together to cover a wider wavelength region with faster data acquisition, or data from a particular resonator may not be detected, thereby reducing data collection time. Thus, the spectrophotometer may be dynamically adjusted when not in operation to optimize acquisition time or resolution. For example, a spectrophotometer setting can be varied from covering a spectral range of 1000 to 2000 nanometers at a resolution of 1 nanometer (1000 data points) to covering the same range but with lower resolution, e.g., a coupled group of 10 resonators together providing a resolution of 10 nanometers, but with much faster data collection speed. This can be remotely controlled and reconfigured according to the requirements of a particular application. The acquisition time is limited by the transit time of the light-generated electrons from the chip and is expected to be less than 1 millisecond. Advantageously, such a system would also eliminate the need for mirrors and gratings that are severely degraded in space by cosmic radiation and reduce acquisition time. Such systems use resonator technology to develop optically effective direct bandgap semiconductor alloys such as those in groups III-V.

Therefore, it is very attractive to create a monolithic solution that targets different wavelength windows, each of which can be configured with dynamically variable resolution. This provides flexibility in selectivity in operation to meet the requirements of small ground pixel size or high spectral resolution.

Such a spectrophotometer may also be used, for example, in a digital camera device that takes true color images with a sensor (spectrophotometer chip) instead of a currently available color sensor. In addition, a spectrophotometer chip may be used to ensure true color calibration of the television (measuring spectral irradiance and lux levels). Advantageously, such a spectrophotometer may have coarse resolution properties and be used to define visible light perception with a resolution of about 5 nanometers.

The present invention is an alternative to conventional imaging techniques based on the use of detectors with filter windows to provide substantial wavelength selectivity over a wide range of wavelengths (with the resulting low resolution), or spectroscopic methods using FTIR or grating-based instruments. The latter are complex systems, some with high maintenance mechanical moving parts and slow data acquisition, all with stray light problems and a large number of discrete optical components. Each additional component introduced into the optical system causes a loss of photons, thus reducing the signal strength. Thus, the development of monolithic systems where the resonator provides wavelength dispersion and detection capability would provide improved signal strength, no moving parts, no grating-detector alignment or stray light issues, and fast acquisition times and high resolution.

It is envisaged that such a spectrophotometer will have a resolution of about 1 nanometer and a fast acquisition time of about 1 millisecond and may evolve across the visible to infrared spectrum with a bandwidth of about 1000 nanometers.

The present invention relates to a tunable broadband monolithic semiconductor spectrophotometer chip that integrates wavelength dispersion and detection capabilities within a solid state optical circuit. Wavelength dispersion and detection occurs without the need for moving or spatially separated components, and because each component is embedded on a single robust chip, stray light is minimized while light intensity is maximized.

The present invention can operate over a large wavelength bandwidth. The bandwidth used will depend in part on the composition of the semiconductor used. Preferably, however, the spectrophotometer is designed to operate within the vis-NIR bandwidth from 400 nm to 2000 nm and allow flexibility in wavelength range/resolution within this bandwidth. For the design of spectrophotometers in the near infrared region (900 nm to 1700 nm), it is preferred to use group III-V compound semiconductor-based alloys, since the optical properties of group III-V semiconductor alloys are well known.

Although this method can be used with silicon, III-V alloys are optically more reactive and cover a large range of wavelengths. Typical materials include AlInGaN alloys for short wavelength spectrum, AlGaInAsP alloys for the visible range, and InGaAsP, InGaAsN n, and InGaAlAsSb alloys for near and mid-infrared light. The wavelength range of the chip can thus be adjusted by judicious use of different semiconductor alloys. Furthermore, the introduction of impurities such as Zn, C, and Te into the alloy can provide fine tuning of the optical and electronic properties of the chip and its components.

Core semiconductor design

Spectrophotometer chips are almost entirely semiconductor-based, in which a semiconductor alloy constitutes a waveguide for incident light and a resonator where the light is detected. The waveguide is composed of a bulk semiconductor material, with the alloy designed such that its bandgap is greater than the energy of the highest energy (shortest wavelength) photon of interest. The resonator is composed of a semiconductor multilayer with a bulk or quantum well active region forming a core absorption region such that the optical gap of the active region is greater than or equal to the minimum energy (maximum wavelength) photon. Thus, the exact composition and doping of the semiconductor alloy is determined for a particular target wavelength range, taking into account the electrical, optical and thermal properties of the material.

Waveguide and resonator structure

The waveguide may be constituted by a slanted rib waveguide. This is to prevent back reflection from the end face of the spectrophotometer chip. The height and width of the waveguide are optimized to allow for maximum throughput of light into the spectrophotometer. As shown in fig. 1-3, the cylindrical resonators would be tightly coupled to the waveguide to allow light to gradually leak into each resonator. Since each resonator is aimed at a particular wavelength, the diameter, thickness, and spacing relative to the waveguide are optimized to maximize optical coupling efficiency and minimize stray light. As a general design rule, the resonator diameter (D) will be designed such that D ═ wavelength × m/Pi × n, where n is the effective refractive index of the semiconductor and m is the resonator order. Thus, for a resonator operating at the second stage, having a typical refractive index of 3.2 and sensitive to 1.5 micron radiation, the diameter D is 300 nanometers. This is well within the capabilities of ultraviolet or electron beam lithography.

Tolerances of less than 20 nanometers are feasible using electron beam or deep ultraviolet lithography. In the prototype testing stage, it is envisaged that electron beam lithography will be used, as it is very versatile and current technology is much better for trying multiple designs on one wafer. Electron beam is also possible during the production phase, however, deep ultraviolet and holographic lithography techniques are much faster when producing large numbers of devices with such tolerances.

Optical coating

Optionally, the front and back surfaces of the spectrophotometer chip are coated to allow the spectrophotometer chip to operate at higher orders, such as first, second or third, 81 th order, etc. This is a desirable feature because it allows operation using larger resonators, thus making manufacture simpler. The exact composition, thickness and refractive index of the layers are optimized to match the wavelength of interest. The coating will typically consist of a plurality of dielectric layer pairs selected such that their total optical thickness is resonant over a particular wavelength range (passband). Alternatively, a nanoscale particle coating may be used to resonantly couple light of a particular wavelength into a chip.

Electric coupling

The electrons from the spectrometer chip produced by the light form a current that provides spectral intensity information. To extract current, a p-n junction is utilized which, when biased with a voltage, provides an electric field to sweep electrons away from the device.

Range of wavelengths

As stated above, the wavelength range of a spectrophotometer chip is determined by the semiconductor material of which it is composed. For spectrophotometers operating in near infrared applications in the wavelength range of 900-1700 nm, methods have been developed to achieve this range using cooled InGaAs detectors. Efficient multi-quantum well absorption regions based on ingaas (p) ZinP alloys may also be used. However, spectrophotometer chips operating in different wavelength ranges are envisioned with a judicious combination of semiconductor material, doping, and resonator dimensions.

Quality and coverage area

The spectrophotometer chip itself has negligible mass. Assuming an InP based chip with dimensions of 1 mm x250 microns x200 microns, the InP density is 4.8g/cm3 and the chip mass is 24 mg. Thus, the main mass of a spectrophotometer would be the associated micro-optics (less than 100 grams). The equivalent quality of a typical CCD-based spectrophotometer that does not include optics is substantially higher. Typical dimensions of a CCD system are in the region of 5 cm x10 cm x15 cm. In a conventional spectrophotometer, resolution is limited by the size of the cassette (to maximize dispersion). In the present invention, resolution is inherently related to the wavelength of light, meaning that the spectrophotometer can be very small.

The claims as filed form part of the description.

Claims (23)

1. A spectrophotometer comprising a monolithic semiconductor substrate (1), one or more wavelength dispersive devices (3-14), and one or more wavelength detection devices (3-14), characterised in that there is no physical separation between the dispersive devices (3-14) and the detection devices (3-14).

2. Spectrophotometer according to claim 1, characterized in that said dispersive means (3-14) and said detection means (3-14) have no physically moving parts.

3. Spectrophotometer according to claim 1 or claim 2, characterized in that said dispersive means (3-14) and said detection means (3-14) are micro-resonators (3-14).

4. Spectrophotometer according to claim 3, characterized in that each microresonator (3-14) is dimensioned to optimally accept light of one wavelength or light of multiple wavelengths, since the diameter (D) of each resonator is determined by the formula D-n λ/π μ.

5. The spectrophotometer of claim 3 or claim 4, wherein each microresonator acts as a detector of the level of light at a particular wavelength.

6. Spectrophotometer according to any one of the preceding claims, characterized in that it comprises one or more waveguide means (2).

7. Spectrophotometer according to claim 5, characterized in that each resonator (3-14) constitutes part of the waveguide device (2) or each resonator (3-14) is optimally positioned close to the waveguide device (2).

8. Spectrophotometer according to claim 6 or claim 7, characterized in that the waveguide means (2) is angled to prevent back reflection of light.

9. The spectrophotometer of claim 6, 7 or 8, wherein said waveguide has a width of between about 1 micron and about 50 microns, a length of about 1000 microns, and a depth of about 1 micron to about 20 microns.

10. Spectrophotometer according to any one of the preceding claims, characterised in that each resonator is optimised in size for a given wavelength.

11. Spectrophotometer according to any one of the previous claims, characterized in that the resonators (3-14) are spherical, conical, stepped conical, flat plate-like, cylindrical cup-like or comprise one or more flat or curved surfaces.

12. Spectrophotometer according to any one of the previous claims, characterized in that the waveguide means (2) is constituted by cylindrical resonators (3-14), the cylindrical resonators (3-14) being arranged such that the resonators (3-14) are arranged in a linear manner, wherein the resonators are arranged from small to large such that the smallest resonator is positioned in a first position and the largest resonator is positioned in the last position.

13. The spectrophotometer of any one of claims 5-12, wherein the resonators are ordered such that the smallest diameter resonator is closest to the point of incidence of the incident light entering the waveguide device and the largest diameter resonator is furthest from the point of incidence of the incident light entering the waveguide device.

14. Spectrophotometer according to any one of the preceding claims, characterized in that the substrate comprises silicon or a group III-V semiconductor onto which a layer of an alloy based on a group III-V semiconductor is added.

15. The spectrophotometer of claim 14, wherein the substrate is doped p-type or n-type.

16. Spectrophotometer according to any one of the previous claims, characterized in that the substrate is divided into three functional areas, wherein the first area is a substrate layer (17) made of a p-type or n-type doped semiconductor, the second active area (16) consists of a semiconductor having a band gap therein to cover the wavelength range of the spectrophotometer and has a refractive index larger than the refractive index of the substrate, and the third optical cladding area has a refractive index smaller than the second active area (16), wherein the second active area (16) is located between the first active area (17) and the third active area (18).

17. Spectrophotometer according to claim 16, characterized in that said third area (18) is a common electrical contact with said first area (17).

18. Spectrophotometer according to claim 16 or claim 17, characterized in that said electrical contacts (18) are gold electrical contacts, gold alloy electrical contacts or electrical contacts made of other electrically conductive materials or composites thereof.

19. Spectrophotometer according to any one of the preceding claims, characterized in that the resonators (3-14) have electrical contacts (19, 20) on their surface.

20. Spectrophotometer according to claim 19, characterized in that said electrical contacts (19, 20) comprise gold electrical contacts, gold alloy electrical contacts or electrical contacts made of other conductive materials or composites thereof.

21. Spectrophotometer according to any one of the preceding claims, characterized in that the surface of the chip can be coated with a substance to accept or reject light over a specific wavelength range.

22. The spectrophotometer of any preceding claim, wherein the substrate may comprise one or more solid state shutters or light guide optics.

23. Spectrophotometer comprising a semiconductor, characterized in that a monolithic substrate (1) is a semiconductor with a waveguide device (2) and one or more resonators (3-14), wherein the waveguide is at an angle with respect to the direction of incidence of the input light, wherein each resonator (3-14) constitutes part of the waveguide device (2), or each resonator (3-14) is optimally positioned close to the waveguide device (2), the resonators being optimally dimensioned for a given electromagnetic wavelength and being ordered such that the resonator of the smallest diameter is closest to the point of incidence of the input light entering the waveguide device and the resonator of the largest diameter is furthest from the point of incidence of the input light entering the waveguide device, the substrate being divided into three functional regions, wherein the first region is a substrate layer (17) made of a p-type or n-type doped semiconductor, a second active region (16) consisting of a semiconductor having a band gap therein to cover the wavelength range of the spectrophotometer and having a refractive index greater than that of the substrate, and a third optical cladding region having a refractive index less than that of the second active region (16), wherein the second active region (16) is located between a first active region (17) and a third active region (18), the third region (18) being a common electrical contact with the first region (17), and the resonators (3-14) have electrical contacts (19, 20) on their surfaces.