WO2019218807A1

WO2019218807A1 - Spectrometer

Info

Publication number: WO2019218807A1
Application number: PCT/CN2019/082030
Authority: WO
Inventors: 杨旻蔚; 孙竹; 彭世昌
Original assignee: 深圳市太赫兹科技创新研究院; 深圳市太赫兹科技创新研究院有限公司
Priority date: 2018-05-17
Filing date: 2019-04-10
Publication date: 2019-11-21
Also published as: CN108593108A

Abstract

Provided is a spectrometer, comprising: a collimating element (2) for converting a broadband beam into parallel light; a dispersion device (8) for dispersing the parallel light into a plurality of beams of dispersed light based on the wavelengths thereof; a focusing element (5) for focusing dispersed light with the same wavelength, the focusing element (5) focusing dispersed light with different wavelengths onto different positions in a focal plane, and focal spots of all the dispersed light being arranged along a straight line; and a detecting device (6) performing detection at a plurality of positions in the focal plane, the detecting device being used for detecting multiple types of dispersed light with different preset wavelengths. When an incident angle of the parallel light incident to the dispersion device (8) is fixed, the dispersion device (8) and the focusing element (5) cooperate with each other in such a manner that the focusing positions of the multiple types of dispersed light with different preset wavelengths and the multiple detection positions are in one-to-one correspondence; and the difference between the wave numbers of any two adjacent beams of the dispersed light among the dispersed light with the different preset wavelengths is equal, thereby greatly reducing the number of operations during imaging by means of the spectrometer, saving on the imaging time, and improving the imaging speed.

Description

spectrometer

Technical field

The present invention relates to the field of optical spectrum analysis instruments, and in particular to a spectrometer.

Background technique

Optical Coherence Tomography (OCT) adopts the principle of ultrasonic flaw detection. It uses the broad spectrum infrared beam to penetrate the test sample, superimposes the backscattered light at different depths of the sample, and connects with the reference light. Coherent detection is performed into the Michelson interferometer to obtain optical scattering characteristics at different depths inside the sample, thereby imaging the internal cross section of the sample tissue. OCT technology has non-radiative, non-contact, high-resolution axial direction, non-destructive, easy-to-see integration and moderate price characteristics. Therefore, OCT technology is a promising optical imaging tool. At present, OCT technology has been widely used in medical diagnosis and industrial flaw detection.

Spectral domain OCT (abbreviated as SD-OCT) is one of many different principles of OCT systems. Since the SD-OCT does not use a mechanical scanning component to scan the sample axially (here, the axial direction refers to the propagation direction of the probe inside the sample), the hierarchical information of the sample axis can be directly obtained by the Fourier transform of the spectrum, thereby enabling Greatly improve the imaging speed of the system. Thanks to the development of semiconductor broadband light sources and high-speed line-and-line photodetection cameras, SD-OCT performance has achieved rapid development, achieving higher axial resolution, system sensitivity, depth of detection, and more stable phase measurement results. The signal to noise ratio is higher. At the same time, SD-OCT uses the characteristic wavelength of water molecules to absorb very little, and thus has achieved great success in the field of ophthalmology and diagnosis. In general, the conventional SD-OCT includes a spectrometer for analyzing the spectrum of the interference spectrum emitted by the Michelson interferometer to obtain optical scattering characteristics at different depths inside the sample, thereby imaging the internal cross section of the sample tissue.

However, spectrometers used in conventional SD-OCT systems include photodetectors and dispersive elementing elements (typically diffraction gratings). The dispersive spectral element disperses the incident broad-spectrum optical signal at different wavelengths to form dispersive light. The photodetector includes a number of pixels that are arranged in a straight line. Each pixel of the photodetector corresponds to receiving different wavelengths of dispersive light, and the wavelength difference of the beams sampled by any two adjacent pixels remains the same. Thus, such spectrometers are equally spaced sampling spectrometers in the wavelength domain. According to the imaging algorithm of the traditional SD-OCT system, the wavelength domain spectrum detected by the photodetector first needs to convert the wavelength domain (wavelength is λ) to the wavenumber domain (wavenumber is k), and the transformation formula is: λ =2π/k. Spectral samples that are equally spaced in the wavelength domain are transformed into the wavenumber domain and no longer have equally spaced sampling properties. After converting the sampling spectrum to the wavenumber domain, the sampling in the low frequency band with smaller wave number is more dense, and the sampling in the high frequency band with larger wave number is more sparse. The Fourier transform in the imaging algorithm requires that the spectral samples be equally spaced samples in the wavenumber domain. Therefore, in the traditional SD-OCT system, before performing Fourier transform on the optical signal in the wavenumber domain, it is necessary to perform a certain interpolation transformation on the spectral sampling of the wavenumber domain (usually using cubic spline interpolation). Fourier transform. Therefore, the computational complexity of the conventional SD-OCT system is large, resulting in a slower imaging speed and longer imaging time for the SD-OCT system.

Summary of the invention

Based on this, it is necessary to provide a spectrometer for the problem that the conventional SD-OCT system has a slow imaging speed.

A spectrometer for equally spaced sampling of a wideband beam in a wavenumber domain, the broadband beam comprising optical signals of different wavelengths; the spectrometer comprising:

a collimating element for converting the broadband beam into parallel light;

a dispersing device for dispersing the parallel light into a plurality of dispersive lights by wavelength;

a focusing element for focusing the dispersive light having the same wavelength, and the focusing element focuses the dispersive light having different wavelengths at different positions on a focal plane thereof, and the focused spot of each of the dispersive lights Arranged in a straight line; and

a detecting device having a plurality of detecting positions on the focal plane, the detecting device for detecting the scattered light of a plurality of different preset wavelengths;

Wherein, when the incident angle of the parallel light incident into the dispersing device is constant, the dispersing device and the focusing element cooperate such that a plurality of different preset wavelengths of the dispersing light have a focus position and the plurality of The detection positions are matched one by one; in the dispersive light of different preset wavelengths, the wavenumber difference of any two adjacent adjacent dispersion lights is equal.

The spectrometer, the dispersing device and the focusing element cooperate to determine the focus of a plurality of different predetermined wavelengths of dispersive light when the incident angle of the parallel light entering the dispersing device is constant. position. Among the plurality of dispersive lights of different preset wavelengths, the wavenumber difference of any two adjacent dispersive lights is equal, that is, the wave number difference is also a preset value. The dispersing device and the focusing element cooperate such that a focus position of the plurality of different predetermined wavelengths of the dispersive light is matched with the plurality of detecting positions in a one-to-one correspondence. In this way, the multi-beam dispersion light detected by the detecting device is equally spaced sampling in the wavenumber domain, thereby avoiding interpolation operations from equally spaced sampling in the wavelength domain to equally spaced sampling in the wavenumber domain. Therefore, the operation of the above spectrometer in the imaging process is greatly reduced, the imaging time is saved, and the imaging speed is improved.

In one embodiment, the dispersing device includes at least two dispersive elements, respectively a first dispersive element and a second dispersive element; the first dispersive element disperses the parallel light by wavelength a plurality of transition beams; the second dispersive element transforms each of the transition beams into a plurality of dispersions dispersed in wavelengths, and each of the dispersive lights is projected onto the focusing element; the parallel light is incident When the incident angle of the dispersing device is constant, the optical parameters, the relative position of the first dispersive element and the second dispersive element, and the focal length of the focusing element determine the focus position of each of the dispersive lights.

In one embodiment, the first dispersive element and the second dispersive element are each a diffraction grating, and an extending direction of the first dispersive element and an extending direction of the second dispersive element have a preset angle .

In one of the embodiments, the first dispersive element and the second dispersive element are both blazed gratings.

In one embodiment, the first dispersive element is a transmissive or reflective diffraction grating; the second dispersive element is a transmissive or reflective diffraction grating.

In one embodiment, the first dispersive element employs a positive first order diffraction or a negative first order diffraction; the second dispersive element employs a positive first order diffraction or a negative first order diffraction.

In one embodiment, the detecting device comprises a photodetector comprising a plurality of pixels, a plurality of the pixels being arranged in a line, and one of the pixels receiving a dispersive light of a corresponding wavelength .

In one embodiment, the photodetector is configured to detect dispersive light of a center wavelength of the broad spectrum beam, and the photodetector is further configured to detect a part of wavelengths of dispersed light on both sides of the center wavelength; The dispersive light detected by the photodetector is equally spaced on the focal plane.

In one embodiment, the spectrometer further includes an entrance slit, the broadband beam sequentially passes through the entrance slit and the collimating element; the incident slit is used to shield external stray light from interfering with the broadband beam .

In one embodiment, the collimating element is a collimating lens, the focusing element is a converging lens, and the collimating lens and the converging lens are both achromatic lenses.

DRAWINGS

1 is a schematic diagram of an optical system of a spectrometer of an embodiment;

2 is a schematic view showing an optical path of parallel light propagation in the spectrometer of the embodiment shown in FIG. 1;

FIG. 3 is a schematic diagram showing the relationship between the wave number of the beam sampled by the spectrometer and the offset distance according to an embodiment.

Detailed ways

The above described objects, features and advantages of the present invention will become more apparent from the aspects of the appended claims.

As in the background art, the spectrometer can be applied to a spectral domain OCT imaging system to obtain optical signal scattering characteristics at different depths within the sample, thereby enabling imaging of the internal cross section of the sample tissue.

A spectrometer for equally spaced sampling of a wideband beam in the wavenumber domain. The band beam includes optical signals of different wavelengths. For example, broadband beams have a spectral wavelength range of 800-900 nm.

1 is a schematic diagram of an optical system of a spectrometer of an embodiment. The spectrometer comprises a collimating element 2, a dispersing device 8, a focusing element 5 and a detecting device 6.

The collimating element 2 is used to convert the broadband beam into parallel light. In general, the collimating element 2 can be a collimating lens. Specifically, the collimating lens is a convex lens. The collimating lens converts the divergent broadband beam into parallel light. The collimating element 2 is a lens (for example, a double-glued or triple-glued lens) that is achromatically optimized for the spectrum of the incident light signal. That is, the collimating lens is an achromatic lens, so that different wavelength components of the broad spectrum beam can be collimated into parallel light.

Dispersion device 8 is used to disperse parallel light into multiple beams of dispersive light. Dispersive light of different wavelengths is arranged in order of the wavelength.

The focusing element 5 is used to focus the dispersive light of each wavelength. The focusing element 5 focuses the dispersive light of the same wavelength together. The focusing element 5 focuses the dispersive light of different wavelengths at different positions on its focal plane, and the focused spots of the respective scattered lights are arranged in a straight line. The focusing element 5 is a converging lens. In particular, the focusing element 5 is also a convex lens. Converging lenses are achromatic lenses.

The detecting device 6 has a plurality of detecting positions on the focal plane, and the detecting device 6 is configured to detect the scattered light of a plurality of different preset wavelengths. That is, the detecting device 6 can detect the focused spot at different positions on the focal plane, thereby detecting beams of different wavelengths.

Wherein, when the incident angle of the parallel light incident into the dispersing device 8 is constant, the dispersing device 8 and the focusing element 5 are matched such that the focusing positions of the plurality of different predetermined wavelengths of the dispersive light are matched with the plurality of detecting positions one-to-one; In the dispersion light of the preset wavelength, the wavenumber difference of any two adjacent adjacent dispersion lights is equal. Therefore, the wavenumber difference of any two adjacent scattered light beams detected by the detecting device 6 is equal. Specifically, for any predetermined wavelength of dispersive light, the above-mentioned incident angle, the optical parameters of the dispersing device 8, and the focal length of the focusing element 5 determine the focus position of the dispersive light of the predetermined wavelength on the focal plane. Therefore, the incident angle, the optical parameter of the dispersing device 8, or the focal length of the focusing element 5 can be adjusted to adjust the focus position of the dispersive light of the predetermined wavelength so that the detecting device 6 can detect the dispersive light. In this embodiment, the incident angle and the optical parameters of the dispersing device 8 are unchanged. The focal length of the focusing element 5 can be adjusted. In this way, the optical system of the spectrometer will be easier to adjust.

The spectrometer, the dispersing device 8 and the focusing element 5 are matched. When the incident angle of the parallel light incident into the dispersing device 8 is constant, the dispersing device 8 and the focusing member 5 determine the focus positions of the plurality of different predetermined wavelengths of the dispersive light. Among the plurality of dispersive lights of different preset wavelengths, the wavenumber difference of any two adjacent dispersive lights is equal, that is, the wave number difference is also a preset value. The dispersing device 8 cooperates with the focusing element 5 such that the focusing positions of the plurality of different predetermined wavelengths of the dispersive light are matched one-to-one with the plurality of detecting positions. Specifically, if the wave number difference has been set, the wavelength of one of the wideband beams to be detected by the detecting device 6 is known, and the wavelengths of the other beams to be detected by the detecting device 6 can be derived. For example, the detecting device 6 is to detect a beam of a central wavelength of the broadband beam, and the wave number difference is known, and the wavelength of each astigmatism light to be detected by the detecting device 6 is known. As long as the dispersing device 8 and the focusing element 5 are matched, the multi-beam dispersion light detected by the detecting device 6 can be equally spaced in the wavenumber domain, thereby avoiding interpolation from equally spaced sampling in the wavelength domain to equally spaced sampling in the wavenumber domain. Operation. Therefore, the operation of the above spectrometer in the imaging process is greatly reduced, the imaging time is saved, and the imaging speed is improved. At the same time, since the operation of the spectrometer is greatly reduced, the hardware resources of the imaging system are saved and the cost is saved.

As shown in Fig. 1, the spectrometer further comprises an entrance slit 1 which is disposed between the broadband beam and the collimating element 2, the incident slit 1 being located at a focus position of the collimating lens. The entrance slit 1 is used to convert a broadband beam into divergent light. That is, the entrance slit 1 is used to form an image point of a broadband beam. Specifically, the incident slit 1 refers to an optical aperture for shielding a broadband optical signal into a spectrometer system while shielding external stray light interference to reduce system noise. Optionally, the slit may be a circular aperture for the fiber output interface.

The dispersing device 8 comprises at least two dispersive elements. As shown in FIG. 1, the two dispersive elements are the first dispersive element 3 and the second dispersive element 4, respectively. The first first dispersive element 3 disperses the parallel light into a plurality of transition beams by wavelength. The second dispersive element 4 converts each of the transitional beams into a plurality of dispersive lights dispersed in wavelengths, and projects the respective dispersive lights onto the focusing element 5. That is, the dispersing device 8 in the present embodiment employs the cascaded first dispersing element 3 and the second dispersing element 4. When the incident angle of the parallel light incident into the dispersing device 8 is constant, the optical parameters of the first dispersing element 3 and the second dispersing element 4, the relative position, and the focal length of the focusing element 5 determine the focus position of each dispersive light. Therefore, setting the optical parameters of the appropriate first dispersing element 3 and the second dispersing element 4, the relative position and the focal length of the focusing element 5 can be such that the focus position of the dispersive light of any predetermined wavelength and the detection of the detecting device 6 The locations match.

In the present embodiment, both the first dispersive element 3 and the second dispersive element 4 are diffraction gratings. That is, the first dispersive element 3 is a first diffraction grating. The second dispersive element 4 is a second diffraction grating. The extending direction of the first dispersing element 3 and the extending direction of the second dispersing element 4 have a preset angle. The diffraction grating is a dispersion beam splitting element. The surface of the diffraction grating creates a periodic structure by scribe lines. In the broadband beam, for different wavelengths of light, according to the grating diffraction Bragg equation, there are different exit angles, so as to separate the light components of different wavelengths. The grating Bragg equation is:

d(sinθ _i +sinθ _d )=mλ (1)

Where θ _d is the exit angle, θ _i is the incident angle, λ is the wavelength, d is the grating period constant, and m is the diffraction order (m=0, ±1, ±2, . . . ).

Both the first dispersive element 3 and the second dispersive element 4 are blazed gratings. The surface of the blazed grating has a periodic groove surface, which can transfer the zero-order diffracted light (maximum energy) without splitting to a certain level (usually m=+1 order) diffraction spectrum, thereby obtaining the diffraction of the order maximum. energy. That is, the blazed grating achieves a position where the diffraction center maximum is shifted from the zero-order spectrum without dispersion to other spectral levels with dispersion. The first dispersive element 3 is a transmissive or reflective diffraction grating. The second dispersive element 4 is a transmissive or reflective diffraction grating. In this embodiment, both the first dispersive element 3 and the second dispersive element 4 are transmission gratings. The first dispersive element 3 employs a positive first order diffraction or a negative first order diffraction. The second dispersive element 4 employs a positive first order diffraction or a negative first order diffraction. The first dispersive element 3 employs a positive first order diffraction or a negative first order diffraction such that the first dispersive element 3 has the highest diffraction efficiency. The second dispersive element 4 employs a positive first order diffraction or a negative first order diffraction so that the diffraction efficiency of the first dispersive element 3 is the highest. In the present embodiment, the first dispersive element 3 and the second dispersive element 4 each adopt positive first-order diffraction. Therefore, for the formula (1), m is 1.

Figure 2 is a schematic illustration of the optical path of parallel light propagation in the spectrometer of the embodiment of Figure 1. It is assumed that the incident angle of the parallel light incident on the first diffraction grating is θ _B . θ _{B is} also the blazed angle of the first diffraction grating. After the broad-spectrum beam is diffracted by the first diffraction grating, the different wavelength components have different diffraction angles θ ₁ and are incident on the second diffraction grating. It can be seen from the grating diffraction equation (1) that the exit angle θ ₁ of the first-order diffraction grating is:

θ ₁ =arcsin[λ/d ₁ -sin(θ _B )] (2)

Where d ₁ is the period constant of the first-order diffraction grating. The angle between the two diffraction gratings is α, and according to the geometric relationship in Fig. 2, the incident angle incident on the second diffraction grating is obtained as follows:

θ ₂ =α-θ ₁ =α-arcsin[λ/d ₁ -sin(θ _B )] (3)

After being diffracted by the second-order diffraction grating, a diffracted beam having an exit angle of θ ₀ is formed, and again from the diffraction equation (1):

The exiting light of the second-order diffraction grating is incident on the converging lens and is concentrated by the converging lens to its focal plane. In particular, it is assumed that the exit angle of the beam 7 of the central wavelength of the broad-spectrum beam after passing through the second-order diffraction grating is θ _f . Assuming that the focal length of the converging lens is f, the focus position of the central wavelength beam 7 on the focal plane can be obtained from the geometric relationship shown in FIG. It can be seen from the geometric relationship shown in FIG. 2 that the expression of the offset distance x of the focused spot of the non-central wavelength beam 9 on the focal plane relative to the focused spot of the central wavelength beam 7 is:

x=f tan(θ _f -θ ₀ ) (5)

It is known from the formulas (1) to (5) that the focal length, the optical parameter of the first diffraction grating, the optical parameter of the second diffraction grating, the angle between the first diffraction grating and the second diffraction grating, or the first diffraction grating are known. The angle of incidence can change the above offset distance. In this embodiment, since the focal length of the converging lens is relatively easy to adjust, the offset distance of the dispersive light of any wavelength can be changed only by adjusting the focal length of the converging lens, so that a plurality of different predetermined wavelengths of dispersive light are The focus position is matched in one-to-one correspondence with the plurality of detection positions, so that the detecting device 6 can detect the dispersion light arranged at equal intervals in the wave number domain.

FIG. 3 is a schematic diagram showing the relationship between the wave number of the beam sampled by the spectrometer and the offset distance according to an embodiment. In this embodiment, the detecting device 6 includes a photodetector. The photodetector includes a plurality of pixels 61. A plurality of pixels 61 are arranged in a straight line. A pixel 61 receives the dispersive light of the corresponding wavelength. That is, the photodetector is a line photodetector. The photodetector can be a high speed detection device 6 based on a Complementary Metal-Oxide-Semiconductor (CMOS) sensor. The photosensitive material of the pixel 61 can be selected from GaAs, Si, or InGaAs or the like depending on the spectral range of the incident light to be detected.

Photodetectors are used to detect dispersive light at the center wavelength of a broad spectrum beam. Photodetectors are also used to detect partial wavelength dispersion light on either side of the center wavelength. The scattered light detected by the photodetector is equally spaced on the focal plane.

In this embodiment, the wavelength of the incident spectrum is 800-900 nm, the grating period constant of the first diffraction grating is 1200 pl/mm, and the grating period constant of the second diffraction grating is 200 pl/mm. The angle between the first diffraction grating and the second diffraction grating is 30°. The focal length of the condenser lens is 50 mm. The center wavelength is approximately 849 nm, and the wavelength k of the center wavelength beam is 7.4 with an offset distance of zero. That is, the focus position of the center wavelength beam on the focal plane is the reference position. The offset distance of the beam detected by the detecting device 6 is taken as the reference point of the focus position of the beam of the center wavelength. As shown in FIG. 3, the horizontal axis represents the wave number, and the vertical axis represents the offset distance x of the light beam of a different wave number. With the above optical system, the offset distance of the beams arranged at equal intervals in the wave number domain sampled by the detecting device 6 of the spectrometer is substantially linear with the wave number. That is, when the wavenumber difference of any two adjacent beams sampled by the detecting device 6 is equal, the focus positions of any two adjacent beams on the focal plane are also equally spaced. This achieves the function of equally spaced sampling in the wavenumber domain of the spectrometer.

The technical features of the above-described embodiments may be arbitrarily combined. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be considered as the scope of this manual.

The above-described embodiments are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but is not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims

A spectrometer for performing equal-wave sampling of a broadband beam in a wavenumber domain, the broadband beam comprising optical signals of different wavelengths; the spectrometer comprising:

a collimating element for converting the broadband beam into parallel light;

a dispersing device for dispersing the parallel light into a plurality of dispersive lights by wavelength;

a focusing element for focusing the dispersive light having the same wavelength, and the focusing element focuses the dispersive light having different wavelengths at different positions on a focal plane thereof, and the focused spot of each of the dispersive lights Arranged in a straight line; and

a detecting device having a plurality of detecting positions on the focal plane, the detecting device for detecting the scattered light of a plurality of different preset wavelengths;

Wherein, when the incident angle of the parallel light incident into the dispersing device is constant, the dispersing device and the focusing element cooperate such that a plurality of different preset wavelengths of the dispersing light have a focus position and the plurality of The detection positions are matched one by one; in the dispersive light of different preset wavelengths, the wavenumber difference of any two adjacent adjacent dispersion lights is equal.
The spectrometer according to claim 1, wherein said dispersing device comprises at least two dispersive elements, said two dispersive elements being a first dispersive element and a second dispersive element, respectively; said first dispersive element The parallel light is dispersed into a plurality of transition beams by wavelength; the second dispersive element converts each of the transition beams into a plurality of dispersions dispersed by wavelength, and each of the dispersion lights is projected onto the focusing element; When the incident angle of the parallel light incident into the dispersing device is constant, the optical parameters, the relative position of the first dispersive element and the second dispersive element, and the focal length of the focusing element determine the respective scattered light Focus position.
The spectrometer according to claim 2, wherein said first dispersive element and said second dispersive element are each a diffraction grating, an extending direction of said first dispersive element and an extending direction of said second dispersive element Has a preset angle.
The spectrometer of claim 3 wherein said first dispersive element and said second dispersive element are each a blazed grating.
The spectrometer according to claim 3, wherein the first dispersive element is a transmissive or reflective diffraction grating; and the second dispersive element is a transmissive or reflective diffraction grating.
The spectrometer according to claim 3, wherein said first dispersive element employs a positive first order diffraction or a negative first order diffraction; and said second dispersive element employs a positive first order diffraction or a negative first order diffraction.
A spectrometer according to claim 1, wherein said detecting means comprises a photodetector, said photodetector comprising a plurality of pixels, said plurality of pixels being arranged in a line, one of said pixels Receives dispersive light of the corresponding wavelength.
The spectrometer according to claim 1, wherein said photodetector is for detecting scattered light of a center wavelength of said broad-spectrum beam, and said photodetector is further for detecting a partial wavelength of said central wavelength The dispersive light; the dispersive light detected by the photodetector is equally spaced on the focal plane.
The spectrometer according to claim 1, further comprising an entrance slit, said broadband beam sequentially passing through said entrance slit and said collimating element; said incident slit being for shielding an external stray light pair The interference of the broadband beam.
The spectrometer of claim 1 wherein said collimating element is a collimating lens, said focusing element is a converging lens, and said collimating lens and said converging lens are both achromatic lenses.