CN113835152A

CN113835152A - Waveguide grating and grating spectrometer with adjustable range

Info

Publication number: CN113835152A
Application number: CN202111161525.XA
Authority: CN
Inventors: 赵浩辰; 佘轶; 叶志成
Original assignee: Yantai Information Technology Research Institute Shanghai Jiaotong University
Current assignee: Yantai Information Technology Research Institute Shanghai Jiaotong University
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2021-12-24
Anticipated expiration: 2041-09-30
Also published as: CN113835152B

Abstract

The application provides a waveguide grating, including waveguide and grating, characterized in that, the waveguide with the grating is in periodic structure department of grating connects, the waveguide is configured as after incident light passes through the grating reflection, produces free space diffraction light and waveguide mode light simultaneously. The application also provides a grating spectrometer comprising the waveguide grating, and the function of adjustable measuring range is realized by arranging a plurality of waveguide gratings on the tray. The optical path of the reflected light is increased by the arrangement of the waveguide emergent face and the arrangement of the matched reflector, so that the light with different wavelength components is fully separated in space, and the measurement sensitivity is improved. And the structure is simple, the cost is low, and the method is suitable for large-scale production.

Description

Waveguide grating and grating spectrometer with adjustable range

Technical Field

The application relates to the field of analytical instrument equipment, in particular to a waveguide grating and a grating spectrometer with adjustable range.

Background

Grating spectrometers are well-established industrial devices that function to accurately separate the different wavelength components of an input spectrum and measure the power content thereof for different wavelengths. The high-precision spectral information generated by analysis can be used as the input of a subsequent analysis tool, the emission spectrum, the reflection spectrum and the absorption spectrum information of an input light source or a reflection light source can be obtained from the spectral information, and the spectral information can be used as the important basis for light source performance analysis and material composition analysis.

With the current requirements of people on high efficiency, miniaturization and integration of optical devices and the development of micro-nano technology and MEMS micro-manufacturing technology, micro spectrometer technology has become a popular research direction at present.

The most central optical device in a grating spectrometer is the grating. A grating operating in free space, whether it is of a reflective or transmissive type, has a diffraction capability range that only includes light with a wavelength less than the grating period, and light with a wavelength greater than the grating period cannot be detected, which makes the range of the grating spectrometer limited. If the period of the grating is increased for enlarging the measuring range, on one hand, the volume and the cost of the grating spectrometer are increased, and waste is caused when a smaller wavelength is detected; on the other hand, the sensitivity of the grating spectrometer is in an inverse relationship with the measuring range, and the larger the measuring range is, the lower the sensitivity is. Some miniature spectrometer products exist in the prior art, have small and compact structures, are convenient to carry, and can cover visible light and near infrared light wave bands. The micro spectrometers can be used in the fields of identifying the content of specific substance molecules of articles, analyzing gemstones, identifying material evidence and the like, and have great practical significance for production life. However, at present, the design of the products is complex, the price is high, the cheapest product is also 299 dollars, and the large-scale popularization cannot be realized.

Therefore, there is an incentive for those skilled in the art to develop a waveguide grating and a grating spectrometer with adjustable range to solve the technical problems in the prior art.

Disclosure of Invention

The application provides a waveguide grating, including waveguide and grating, the waveguide with the grating is in periodic structure department of grating connects, the waveguide is configured as after incident light passes through the grating reflection, produces free space diffraction light and waveguide mode light simultaneously.

Further, the waveguide includes an upper surface from which incident light is configured to be incident and a side surface from which reflected light generated by the grating is configured to exit, the upper surface and the side surface being provided with antireflection structures thereon configured to increase transmittance of exiting light.

Further, the side surface is perpendicular to the upper surface.

Furthermore, the side surface is an inclined surface and forms a non-vertical included angle with the upper surface.

Further, the side surface is a cylindrical surface.

Further, the position of the circle center corresponding to the cylindrical surface is the incident position of the incident light on the grating.

The application also provides a grating spectrometer with an adjustable range. The waveguide grating spectrometer comprises a tray, a side wall, a reflector, a detector and a grating component, and is characterized in that the tray is arranged at the bottom of the spectrometer, the grating component is arranged on the tray, and the grating component is the waveguide grating mentioned above.

Furthermore, the total number of the side walls is six, the side walls are sequentially connected and surround into a hexagonal prism shape, the reflecting mirrors are arranged on five of the side walls, and the detector is arranged on one of the side walls.

Further, the tray is a rotatable disc, and three grating components are arranged on the tray.

Furthermore, the incident light is reflected by the grating component and then sequentially passes through the five reflectors to reach the detector.

Compared with the prior art, the method has the following technical effects:

1. the grating spectrometer is combined with the grating of the waveguide, so that the measuring range of the grating spectrometer is expanded to a part with the wavelength larger than the grating period.

2. The optical path of the reflected light is increased by the arrangement of the waveguide emergent face and the arrangement of the matched reflector, so that the light with different wavelength components is fully separated in space, and the measurement sensitivity is improved.

3. This application has realized the select function of multiple range through setting up a plurality of waveguide grating and rotatable tray setting.

4. The device is simple in structure, low in cost and suitable for large-scale production.

The conception, specific structure and technical effects of the present application will be further described in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present application.

Drawings

FIG. 1 is a schematic diagram of a waveguide grating in one embodiment of the present application;

FIG. 2 is a schematic diagram of a waveguide grating structure according to an embodiment of the present application;

FIG. 3 is a schematic diagram of a waveguide grating structure according to an embodiment of the present application;

FIG. 4 is a schematic diagram of the operation of a waveguide grating in one embodiment of the present application;

FIG. 5 is a schematic diagram of the operation of a waveguide grating in one embodiment of the present application;

FIG. 6 is a schematic diagram of the operation of a waveguide grating in one embodiment of the present application;

FIG. 7 is a schematic diagram of a grating spectrometer in an embodiment of the present application;

FIG. 8 is a schematic diagram of a side-wall unfolded configuration of a grating spectrometer in an embodiment of the present application;

FIG. 9 is an optical simulation of a waveguide grating in an embodiment of the present application.

Detailed Description

The embodiments of the present application will be described below with reference to the accompanying drawings for clarity and understanding of technical contents. The present application may be embodied in many different forms of embodiments and the scope of the present application is not limited to only the embodiments set forth herein.

Fig. 1 shows an embodiment of a waveguide grating provided in the present application. Comprising a waveguide 2 and a grating 1.A periodic structure 11 is provided on the surface of the grating 1 and the waveguide 2 is provided on the surface of the grating 1 having the periodic structure. Preferably, the grating 1 is formed by plating a metal layer on a titanium oxide substrate. The waveguide 2 is made of a material transparent to light of the operating wavelength, such as silicon dioxide, PET, etc.

The waveguide 2 has an upper surface 7 and side surfaces 3, the side surfaces 3 being arranged perpendicular to the upper surface 7 in this embodiment. The waveguide 2 is connected to the grating 1 at the periodic structure 11. Incident light 6 is incident from the upper surface 7 of the waveguide 2, and is reflected and diffracted at the periodic structure 11 of the grating 1, thereby forming a diffraction spectrum. For different wavelength components of the incident light 6, the angles between the diffracted light and the normal are different, so that a series of outgoing light with different angles is formed. Due to the existence of the waveguide, free space diffraction light with a diffraction angle smaller than 90 degrees in air and waveguide mode light which meets the air interface total reflection condition and is transmitted in the waveguide can be generated simultaneously; the free space diffraction light of the grating and the waveguide mode light form a spectrum signal which is collected by the detector array at the same time, so that the measuring range of the spectrometer can be expanded, the precision of the spectrometer is improved, and the application range of the spectrometer is expanded.

Specifically, in the present embodiment, a part of the outgoing light 5 exits from the upper surface 7 of the waveguide 2, and another part of the outgoing light 4 exits from the side surface 3 of the waveguide 2. In a similar embodiment as shown in fig. 2, 3, the side surface 3 is a slope with a non-perpendicular angle to the upper surface 7, or the side surface 3 is a cylinder. When the side surface 3 is a slope and is provided with a suitable size and position, both

outgoing light

4, 5 exits from the side surface 3. When the side surface 3 is a cylindrical surface, the position of the center of the circle corresponding to the cylindrical surface is the incident position of the incident light 6 on the periodic structure 11 of the grating 1, and therefore the incident light is emitted perpendicularly to the side surface 3 regardless of the angles of the emitted

light

4 and 5. The upper surface 7 and the side surfaces 3 of the waveguide 2 are provided with anti-reflection structures, such as anti-radiation gratings, at locations where light may exit. The anti-reflection grating can enable diffracted light to fully leave the waveguide, and utilization efficiency is improved. The anti-reflection structure can be a one-dimensional line or a two-dimensional lattice structure with the structure period smaller than the ratio of the minimum wavelength of the working waveband to the refractive index of the waveguide.

The working principle of the waveguide grating in this application is shown in fig. 4-6:

incident light is vertically incident on the grating 1 through the waveguide 2, and the angle theta between the general reflected light and the normal is described by the following formula:

n₁*sin(θ)*T＝m*λ

wherein n is₁The refractive index of the transparent waveguide is shown, theta is the included angle between the reflected light and the normal line, T is the period of the metal grating, m is the diffraction order, 1 is taken here, and lambda is the wavelength of the reflected light. This equation shows that for a conventional free space grating, n ₁1, with a maximum diffraction angle corresponding to λ ═ T, and the introduction of the waveguide, with a maximum diffraction angle corresponding to λ ═ n₁T, which is the theoretical basis for the design to improve the wavelength range.

Where h is the thickness of the optical waveguide and L is the length of the optical waveguide. In particular, theta₀At a critical angle, corresponding to the transition of diffracted light from the top surface to exit from the side surface. When diffraction angles theta and theta₀When different relationships are satisfied, the diffracted light is emitted into the air along different directions. Since the refractive index n of air is 1, the relationship is as follows:

(1) when theta is₁＜θ₀I.e., λ n1 sin (θ)₁) When T is less than T, the reflected light is emitted from the upper surface of the transparent waveguide, and the included angle between the reflected light and the normal line

(2) When theta is equal to theta₀When the transparent waveguide is used, reflected light is directly emitted from the intersection line of the upper surface and the side surface of the transparent waveguide;

(3) when theta is₂＞θ₀I.e., λ n1 sin (θ)₂) When T is larger than T, the reflected light is emitted from the side surface of the transparent waveguide, and the incident angle theta is₄＝π/2-θ₂Angle of reflected light to normal

Angle of total reflection theta of waveguide 2_FIRBy such asThe following formula describes:

θ_FIR＝arcsin(1/n₁)

discussion of the different paths of light that, when reaching the top or side surfaces, may exit back into the air under what conditions and thus be received by the detector array.

(1) When theta is₁＜θ₀I.e., λ n1 sin (θ)₁) T < T, the light should exit the upper surface at an angle of incidence θ₁Solving for theta₁＜θ_FIRλ of the relationship, resulting in λ < T

(2) When theta is₂＞θ₀I.e., λ n1 sin (θ)₂) When T is larger than T, the reflected light is emitted from the side surface of the transparent waveguide, and the incident angle theta is₄＝π/2-θ₂Solving for theta₄＜θ_FIRλ of the relationship, obtaining

According to the above discussion, in order to ensure that all wavelengths can be emitted from the top surface or the side surface in the measurement range, and the measurement range does not generate band break, it is necessary to ensure that the minimum value of the side wavelength is smaller than the maximum value of the top wavelength, that is, the side wavelength is smaller than the maximum value of the top wavelength

Solving to obtain n₁＜1.618。

The above discussion gives an upper limit on the refractive index of the waveguide material, but does not discuss the effect of the waveguide geometry, which is discussed further herein.

Discussion of Angle and θ₀Two beams of light close to each other, theta₀For the critical angles mentioned hereinbefore, note

Respectively has an angle slightly larger than or slightly smaller than theta₀The two lights have physical meanings corresponding to the wavelength maximum light of the upper surface and the wavelength minimum light of the side surface respectively. The geometric parameters of the waveguide need to be ensured, and when the two beams of light respectively enter the upper surface and the side surface, the two beams of light do not generate full lightAnd (4) internal reflection. Column write corresponding condition

Simultaneous substitution into

Solved to obtain

Meanwhile, in order to ensure the existence of h/L, the method needs to ensure

Further solving to obtain n₁＜1.414。

In summary, the waveguide material satisfies n₁< 1.414 and the waveguide geometry design satisfies

When the wavelength is n, the light with full wavelength can be emitted from the upper surface and the side surface of the waveguide, and the maximum resolution wavelength of the grating in the waveguide is n₁The light of T, both combine, can expand grating system working wavelength range to promote the range of measurement system.

The above discussion mainly verifies that the design can improve the resolvable wavelength range of the grating. Furthermore, the waveguide incident surface and the waveguide emergent surface should be provided with an antireflection structure to improve the transmission efficiency.

Further, as shown in fig. 5, the side surface 3 of the grating 2 may be provided with an inclined surface from which diffracted light exits, and the exit angle and the diffraction angle have a one-to-one correspondence relationship, and the angles corresponding to different wavelengths do not overlap.

Further, as shown in fig. 6, the side surface 3 of the grating may be a cylindrical surface, and the incident position of the incident light is the position of the center of the circle corresponding to the cylindrical surface. When the diffracted light is emitted from the cylindrical surface, the diffracted light is normally incident on the cylindrical surface, and the direction is not changed, so that the emergent angle and the diffraction angle form a one-to-one corresponding relation, and the angles corresponding to different wavelengths cannot be overlapped.

Fig. 7-8 show tunable grating spectrometers using waveguide gratings in this embodiment. The grating spectrometer is generally hexagonal prism shaped including sidewalls and a bottom. Six side walls and the bottom enclose a hexagonal prism-shaped space. Wherein a circular tray 14 is arranged at the bottom, and the circular tray 14 is rotatably connected to the bottom through a rotating shaft 13. A grating member is provided on the circular tray 14. Preferably, the grating component is a waveguide grating as described in this embodiment. As shown in fig. 7, preferably three grating parts 11.a, 11.b, 11.c are provided. Six side walls are arranged perpendicular to the bottom, and a detector 8 is arranged on one side wall 7. Preferably, the detector 8 is a CCD with a rectangular detection surface. The incident light 6 is collimated composite light from the object to be measured, and has a plurality of wavelength components, so that a diffraction spectrum is generated after the light is reflected by the grating parts 11.a, 11.b and 11. c. If the diffraction spectra emitted from the grating members 11.a, 11.b, 11.c are directly irradiated onto the detector 8, the spatial distance between the light beams of different wavelength components is short, and the detector 8 is difficult to distinguish, which affects the detection sensitivity, so that the mirrors 10 are provided on the other five side walls in the present embodiment, and the emission mirrors 15 are provided near the operating positions of the grating members 11.a, 11.b, 11. c. In the diffraction spectra emitted from the grating parts 11.a, 11.b, 11.c, the light with different wavelength components has a certain angular distribution, and after passing through the emission reflector, the light sequentially passes through the five reflectors 10 arranged on the side walls, so that the optical path is increased, and the angular distribution is converted into the spatial distribution. In the present embodiment, the diffraction spectrum is preferably reflected by the two exit mirrors 16.a, 16.b, then enters the mirrors 10 disposed on the side walls at an incident angle of 60 °, and then sequentially reflected by the five mirrors 10 counterclockwise, and then reaches the detector 8. In other similar embodiments, a suitable number of exit mirrors may be provided, and the reflections from the mirrors 10 provided on the side walls may be passed in other sequences. Eventually reaching the detector 8, the detector 8 has been able to clearly resolve the light of the different wavelength components in the diffraction spectrum. Preferably, the plurality of grating elements 11.a, 11.b, 11.c provided on the circular tray 14 correspond to different ranges. The range adjustment of the grating spectrometer can be achieved by rotating the tray 14 to move the different grating elements to the operating position. In this embodiment, three grating elements are provided, and in other similar embodiments, other suitable numbers of grating elements may be provided. Because the measurement sensitivity of the grating spectrometer is in inverse proportion to the measurement range, the multi-range setting of the embodiment can provide large-range measurement and simultaneously still maintain the measurement sensitivity under the condition of small-range measurement.

Fig. 9 shows a simulated diffraction pattern obtained using the commercial software LightTools for a waveguide grating as shown in fig. 3. The period of the grating 1 is set to 750.00nm and the height of the waveguide 2 is 2.00 mm. The radius of the cylindrical side surface 3 is 2.00mm, the wavelength range of the incident composite light is 400.00 nm-1200.00 nm, and the diameter of a light spot is 0.10 mm. The refractive index of the waveguide 2 was 1.50 and the distance from the center point of the incident light to the side surface was 2.00 mm. At this time, the total reflection angle of the waveguide 2 was 41.81 °. On the cylindrical side surface of the waveguide 2, diffracted light is emitted from the cylindrical side surface 3 from the center of a circle, and an absorption structure is added on the other side of the waveguide, so that the diffracted light is emitted only from the cylindrical side surface, and the interference on a detector is reduced.

The foregoing detailed description of the preferred embodiments of the present application. It should be understood that numerous modifications and variations can be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the concepts of the present application should be within the scope of protection defined by the claims.

Claims

1.A waveguide grating comprising a waveguide and a grating, wherein the waveguide and the grating are connected at a periodic structure of the grating, and wherein the waveguide is configured to generate two diffracted lights in free space and within the waveguide when incident light is reflected by the grating.

2. A waveguide grating as claimed in claim 1, wherein the waveguide comprises an upper surface from which incident light is arranged to be incident and a side surface from which reflected light generated by the grating is arranged to exit, the upper surface and the side surface having anti-reflection structures disposed thereon, the anti-reflection structures being arranged to increase the transmittance of exiting light.

3. A waveguide grating as claimed in claim 2, wherein the side surfaces are perpendicular to the upper surface.

4. A waveguide grating as claimed in claim 2, wherein the side surfaces are inclined at a non-perpendicular angle to the upper surface.

5. A waveguide grating as claimed in claim 2, in which the side surfaces are cylindrical.

6.A waveguide grating as claimed in claim 5, wherein the cylindrical surface corresponds to a centre of the circle at a position where the incident light is incident on the grating.

7. A grating spectrometer with adjustable range, comprising a tray, a sidewall, a mirror, a detector and a grating member, wherein the tray is disposed at the bottom of the spectrometer, the grating member is disposed on the tray, and the grating member is the waveguide grating of claim 6.

8. The tunable grating spectrometer of claim 7, wherein there are six sidewalls, the sidewalls being connected in series to enclose a hexagonal prism, wherein the mirrors are disposed on five of the sidewalls, and wherein the detector is disposed on one of the sidewalls.

9. The tunable grating spectrometer of claim 8, wherein the tray is a rotatable disk, and three grating elements are disposed on the tray.

10. The tunable grating spectrometer of claim 9 wherein the incident light is reflected by the grating member and then sequentially passes through the five mirrors to the detector.