CN109656029B - Static laser speckle suppression method combining multimode optical waveguide and diffractive optical device - Google Patents
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Abstract
一种结合多模光波导和衍射光学器件的静态激光散斑抑制方法，包括以下步骤：步骤1：将激光束准直后输入衍射光学器件，衍射光学器件将入射的准直激光束输出为具有不同衍射级的衍射光束；步骤2：不同衍射级的衍射光束被透镜聚焦，聚焦光束输入多模光波导中，所述多模光波导调制不同衍射光束的传输时延，使所有衍射级的衍射光束以时延差δT从多模光波导输出；步骤3：以不同时延输出的衍射光束被成像透镜收集，并成像在投影屏幕上，所述投影屏幕具有粗糙表面，所述投影屏幕上的图像由数字相机接受并处理，实现静态激光散斑抑制。本发明可靠性高、不需要电能供应、响应时间快、无机械运行机构、系统简单、尺寸小、成本低廉。
A static laser speckle suppression method combining a multimode optical waveguide and a diffractive optical device, comprising the following steps: Step 1: collimating a laser beam and then inputting it into a diffractive optical device, and the diffractive optical device outputs the incident collimated laser beam as a Diffracted beams of different diffraction orders; Step 2: The diffracted beams of different diffraction orders are focused by a lens, and the focused beam is input into a multi-mode optical waveguide, which modulates the transmission delay of different diffracted beams, so that all diffraction orders are diffracted The light beam is output from the multi-mode optical waveguide with the time delay difference δT; Step 3: The diffracted light beam output with different time delays is collected by the imaging lens, and is imaged on the projection screen, the projection screen has a rough surface, and the Images are received and processed by a digital camera for static laser speckle suppression. The invention has high reliability, does not need electric power supply, has fast response time, has no mechanical operating mechanism, has simple system, small size and low cost.
Description
Technical Field
The invention belongs to the field of laser display projection, and particularly relates to a method for inhibiting fully static space/time hybrid laser speckle by combining a multimode optical waveguide and a diffractive optical device.
Background
Laser projection display systems are receiving more and more attention and popular because of their advantages of rich colors, high picture quality, long service life, high reliability, high efficiency, low energy consumption, etc. However, since the laser is a high-coherence light, a picture noise called laser speckle is inevitably generated, and the laser speckle is formed by the random coherent superposition of signals, which seriously affects the quality of the image. In the field of laser projection display, speckle can reduce the quality of a projection display picture, so that a viewer can generate symptoms such as fatigue, dizziness and the like, the experience of a laser projector user is seriously influenced, and the speckle is a core factor for restricting the development of a laser projection display system and instruments. In the prior art, for inhibiting laser speckle, technical methods of reducing polarization coherence, time coherence and space coherence are mainly adopted, wherein the technical method of a motion diffraction optical device for performing time averaging on a random laser speckle pattern is the most common. The method for moving the diffraction optical device belongs to a dynamic laser speckle suppression method, and can reduce laser speckles, but the method needs a mechanical operation mechanism and an electrical control system, so that the reliability is poor, the energy consumption is high, the system is complex, the structure is huge, and the cost is high. Therefore, there is a need to develop speckle reduction methods and systems that are static (i.e., without power supply, without moving parts).
Heretofore, two technical schemes based on electro-optical, magneto-optical, acousto-optical modulation techniques (a.l. andreev, n.v. zalyapin, t.b. andreeva, i.n. kompanes, electro-optical despeckler based on helix-free optoelectronic crystal, Quantum Electronics, 2017, 47(11): 1064-. The former technical scheme has theory and preliminary experiment reports at present, and cannot be practically applied in a short period due to too low response speed, and meanwhile, the technical scheme still needs electric energy supply. The latter scheme only has theoretical analysis, no specific technical scheme and implementation system is proposed, and the speckle suppression effect is not ideal.
Disclosure of Invention
In order to overcome the defects of poor speckle suppression effect, poor reliability, complex system, slow response time, electric energy supply requirement, large size, high cost and the like in the prior art, the invention provides the static laser speckle suppression method which combines the multimode optical waveguide and the diffractive optical device and has the advantages of high reliability, no electric energy supply requirement, quick response time, no mechanical operation mechanism, simple system, small size and low cost. The technical method of the invention does not need electric energy supply and mechanical operation mechanisms, and can realize completely static laser speckle suppression.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method of static laser speckle suppression in combination with multimode optical waveguide and diffractive optics, the method comprising the steps of:
step 1: the laser beam is collimated and then input into a diffraction optical device, the diffraction optical device is manufactured on transparent glass or plastic materials and is provided with a one-dimensional or two-dimensional binary diffraction optical structure, and the diffraction optical device outputs the incident collimated laser beam into diffraction beams with different diffraction orders;
step 2: the diffraction beams of different diffraction orders are focused by the lens, the focused beams are input into the multimode optical waveguide, and the multimode optical waveguide modulates the transmission time delay of the different diffraction beams, so that the diffraction beams of all diffraction orders are output from the multimode optical waveguide with time delay difference delta T;
and step 3: the diffraction light beams output with different time delays are collected by the imaging lens and imaged on the projection screen, the projection screen is provided with a rough surface, and the image on the projection screen is received and processed by the digital camera to realize static laser speckle suppression.
Further, in step 1, the diffractive optical element has a one-dimensional or two-dimensional relief structure, and the relief structure is manufactured by using a binary-coded mask, and is called a binary diffractive optical structure.
The binary code may be, but is not limited to, a pseudo-random sequence code, a barker code, a Hadamard matrix.
The two-dimensional binary diffraction optical structure can be a specific two-dimensional binary coding structure, and can also be formed by overlapping two one-dimensional binary coding structures at a set angle.
Still further, the diffractive optical element is made of transparent glass or plastic material plated with metal, wherein the transparent glass or plastic material is transparent to visible light bands including red, green and blue light; the metal material is used for shielding light, and the light transmitting part and the light shielding part jointly form binary codes.
The glass material includes but is not limited to K9 optical glass, and the plastic material includes but is not limited to transparent hard plastic such as PMMA (polymethyl methacrylate).
Furthermore, in step 2, the multimode optical waveguide may be a multimode optical fiber or a multimode rectangular optical waveguide, where the multimode refers to a plurality of optical conduction modes existing in the waveguide, and the time delay difference of the diffracted light beam must be greater than the time coherence length of the laser, and the following inequality must be satisfied:
δT＞2πλ2/(c·δλ) (1)
δ T in formula (1) represents a time delay difference when the diffracted beam is output from the multimode optical waveguide, λ represents a wavelength of the laser, δ λ represents a spectral width of the laser, and c represents a speed of light in vacuum;
maximum delay difference deltaT of conduction mode in the multimode optical waveguidemaxCalculated from the following equation (2):
δ T in equation (2)maxRepresenting the maximum delay difference of the propagation modes in the multimode optical waveguide, l representing the length of the multimode optical waveguide, n1And n2Respectively, the refractive indices of the core and cladding of the multimode optical waveguide, and Δ represents the relative refractive index difference between the core and cladding of the multimode optical waveguide.
Further, the multimode optical waveguide may also be a multimode fiber bundle, or a multimode optical waveguide in which the core layer is structurally designed.
The static laser speckle suppression system for realizing the static laser speckle suppression method by combining the multimode optical waveguide and the diffractive optical device comprises a laser, a collimating lens, the diffractive optical device, a focusing lens, the multimode optical waveguide, an imaging lens, a projection screen and a digital camera, wherein the digital camera consists of an incident diaphragm, a camera lens and an image sensor, and the laser, the collimating lens, the diffractive optical device, the focusing lens, the multimode optical waveguide and the imaging lens are positioned on the same optical axis.
Laser beams emitted by the laser are expanded, shaped and calibrated through the collimating lens, and are normally incident on the diffractive optical device, the diffractive optical device decomposes incident laser beams into diffracted beams of different diffraction orders to be output, the diffracted beams of different diffraction orders are focused by the focusing lens and input into the multimode optical waveguide, the interval of light pulses output by the multimode optical waveguide is larger than the time coherence length of the laser, and the light pulses are projected onto a projection screen through an imaging lens; the projection screen records laser projection imaging and can be directly observed visually, and the digital camera records the laser projection imaging on the projection screen and utilizes the image sensor to perform data processing.
The technical conception of the invention is as follows: the method is characterized in that irrelevant diffracted light beams generated by a diffraction optical device are used for destroying the spatial coherence of laser, and light pulses with intervals larger than the time coherence length of a laser are generated by a multimode optical waveguide for destroying the time coherence of the laser, so that the effect of inhibiting speckles is achieved.
Furthermore, the diffractive optical device and the multimode optical waveguide are fixed, and no electric energy supply or mechanical operation mechanism is needed, so that completely static laser speckle suppression can be realized.
Furthermore, as no electric energy supply and mechanical operation mechanism is needed, the method has the advantages of high reliability, high response speed, low energy consumption, small size, simple system and easy maintenance.
The invention has the following beneficial effects:
(1) the method does not need electric energy supply and mechanical operation mechanisms, and is a completely static laser speckle suppression method.
(2) Both the temporal and spatial coherence of the laser can be reduced.
(3) The whole speckle suppression system has the advantages of high reliability, high response speed, low energy consumption, small size and simple and easy maintenance.
(4) Compared with the existing speckle suppression device in the market, the speckle suppression device is simple to manufacture, low in cost and suitable for mass production.
Drawings
FIG. 1 is a schematic diagram of a system for implementing the static laser speckle suppression method in combination with a multimode optical waveguide and diffractive optics according to the present invention, wherein 1 is a laser; 2 is a collimating lens; 3 is a diffractive optic; 4 is a focusing lens; 5 is a multimode optical waveguide; 6 is an imaging lens; 7 is a projection screen; 8 is a digital camera; 9 is the entrance diaphragm of the digital camera; 10 is a camera lens; 11 is an image sensor of a digital camera. L is1Is the distance of the diffractive optic to the focusing lens; l is2Is the distance from the imaging lens to the projection screen; l is3Is the distance of the projection screen from the entrance aperture of the digital camera in the direction of the optical axis.
FIG. 2 is a schematic diagram of a diffractive device unit in a static laser speckle suppression method of the present invention incorporating a multimode optical waveguide and diffractive optics (binary encoding is exemplified by a pseudo-random sequence), (a) is a one-dimensional binary encoding schematic diagram; (b) is a two-dimensional binary coding diagram.
FIG. 3 is a schematic diagram of a multimode optical waveguide (taking multimode optical fiber and multimode optical fiber bundle as examples) in the static laser speckle suppression method of the invention combining the multimode optical waveguide and diffractive optical device, wherein (a) is a schematic diagram of multimode optical fiber, n is1And n2Respectively representing the refractive indexes of the core layer and the cladding layer of the multimode optical fiber; (b) is a schematic view of a multimode fiber bundle.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1-3, a method of static laser speckle suppression in combination with a multimode optical waveguide and diffractive optics, the method comprising the steps of:
step 1: the laser beam is collimated and then input into a diffraction optical device, the diffraction optical device is manufactured on transparent glass or plastic materials and is provided with a one-dimensional or two-dimensional binary diffraction optical structure, and the diffraction optical device outputs the incident collimated laser beam into diffraction beams with different diffraction orders;
step 2: the diffraction beams of different diffraction orders are focused by the lens, the focused beams are input into the multimode optical waveguide, and the multimode optical waveguide modulates the transmission time delay of the different diffraction beams, so that the diffraction beams of all diffraction orders are output from the multimode optical waveguide with time delay difference delta T;
and step 3: and 2, collecting the diffracted light beams output with different time delays by a lens, imaging the diffracted light beams on a projection screen, wherein the projection screen is provided with a rough surface, and receiving and processing the image on the projection screen by a digital camera to realize static laser speckle suppression.
Further, in step 1, the diffractive optical element has a one-dimensional or two-dimensional relief structure, and the relief structure is manufactured by using a binary-coded mask, and is called a binary diffractive optical structure.
The binary code may be, but is not limited to, a pseudo-random sequence code, a barker code, a Hadamard matrix.
The two-dimensional binary diffraction optical structure can be a specific two-dimensional binary coding structure, and can also be formed by overlapping two one-dimensional binary coding structures at a specific angle.
Still further, the diffractive optical element is made of transparent glass or plastic material plated with metal, wherein the transparent glass or plastic material is transparent to visible light bands including red, green and blue light; the metal material is used for shielding light, and the light transmitting part and the light shielding part jointly form binary codes.
The glass material includes but is not limited to K9 optical glass, and the plastic material includes but is not limited to transparent hard plastic such as PMMA (polymethyl methacrylate).
Furthermore, in step 2, the multimode optical waveguide may be a multimode optical fiber or a multimode rectangular optical waveguide; the multimode refers to that a plurality of optical conduction modes exist in the waveguide, the time delay difference of the diffracted light beams must be larger than the time coherence length of the laser, and the following inequality must be satisfied:
δT＞2πλ2/(c·δλ) (1)
δ T in formula (1) represents a time delay difference when the diffracted beam is output from the multimode optical waveguide, λ represents a wavelength of the laser, δ λ represents a spectral width of the laser, and c represents a speed of light in vacuum.
Maximum delay difference deltaT of conduction mode in the multimode optical waveguidemaxCalculated from the following equation (2):
δ T in equation (2)maxRepresenting the maximum delay difference of the propagation modes in the multimode optical waveguide, l representing the length of the multimode optical waveguide, n1And n2Respectively, the refractive indices of the core and cladding of the multimode optical waveguide, and Δ represents the relative refractive index difference between the core and cladding of the multimode optical waveguide.
Further, the multimode optical waveguide may also be a multimode fiber bundle, or a multimode optical waveguide in which the core layer is structurally designed.
The static laser speckle suppression system for realizing the static laser speckle suppression method by combining the multimode optical waveguide and the diffractive optical device comprises a laser 1, a collimating lens 2, the diffractive optical device 3, a focusing lens 4, the multimode optical waveguide 5, an imaging lens 6, a projection screen 7 and a digital camera 8 which are sequentially arranged along a light path, wherein the digital camera 8 consists of an incident diaphragm 9, a camera lens 10 and an image sensor 11, and the laser 1, the collimating lens 2, the diffractive optical device 3, the focusing lens 4, the multimode optical waveguide 5 and the imaging lens 6 are positioned on the same optical axis.
The laser beam emitted by the laser 1 is expanded, shaped and calibrated through the collimating lens 2, and is normally incident on the diffractive optical device 3, the diffractive optical device 3 decomposes the incident laser beam into diffracted beams with different diffraction orders to be output, the diffracted beams with different diffraction orders are focused by the focusing lens 4 and input into the multimode optical waveguide 5, the interval of light pulses output by the multimode optical waveguide 5 is larger than the time coherence length of the laser and projected onto a projection screen 7 through an imaging lens 6, the projection screen 7 records laser projection imaging and can directly conduct visual observation, and the digital camera 8 records the laser projection imaging on the projection screen 7 and utilizes an image sensor to conduct data processing.
Example 1:
a static laser speckle suppression method combining a multimode optical waveguide and a diffraction optical device is characterized in that the diffraction optical device adopts two one-dimensional pseudo-random sequence binary codes which are orthogonally overlapped to form a two-dimensional binary code (see figure 2), the overlapping angle of the two-dimensional binary codes is 90 degrees, the minimum code width of the binary code is 6 microns, and the number of the pseudo-random sequence code bits is 13.
Referring to fig. 3(a), the multimode optical waveguide is a multimode optical fiber, a core layer of the multimode optical fiber is a cylindrical optical waveguide with a diameter of 400 micrometers, and a length l of the multimode optical fiber is 1500 millimeters.
Referring to fig. 1, the function of the static laser speckle suppression method combining the multimode optical waveguide and the diffractive optical device is realized by a static laser speckle suppression system. The static laser speckle suppression system comprises a laser, a collimating lens, a diffraction optical device, a focusing lens, a multimode optical waveguide, an imaging lens, a projection screen and a digital camera, wherein the digital camera consists of an incident diaphragm, a camera lens and an image sensor. The laser, the collimating lens, the diffractive optical element, the focusing lens, the multimode optical waveguide and the imaging lens are positioned on the same optical axis.
A532-nanometer laser 1 with a wavelength is used as a light source, emitted laser beams are expanded, shaped and calibrated through the collimating lens 2, and are normally incident on the diffraction optical device 3, the diffraction optical device decomposes the incident laser beams into diffracted beams with different diffraction orders to be output, the diffracted beams with different diffraction orders are focused by the focusing lens 4 and input into the multimode optical waveguide 5, the interval of light pulses output by the multimode optical waveguide is larger than the time coherence length of the laser, and the light pulses are projected onto a projection screen 7 through the imaging lens 6. The projection screen records laser projection imaging and can be directly observed visually, and the digital camera 8 records the laser projection imaging on the projection screen and performs data processing by using an image sensor.
The laser speckle suppression effect is a speckle suppression coefficient of 1.85.
Example 2:
referring to fig. 3(b), the multimode optical waveguide is a multimode optical fiber bundle, the diameter of the multimode optical fiber bundle is 5 mm, each multimode optical fiber in the multimode optical fiber bundle is a hexagonal cylindrical optical waveguide with a circumscribed circle diameter of 25 microns, and the length l of the multimode optical fiber bundle is 2500 mm. Other implementation parameters and procedures were the same as in example 1.
The laser speckle suppression effect is a speckle suppression coefficient of 2.4.
Claims (8)
1. A method of static laser speckle suppression in combination with multimode optical waveguide and diffractive optics, the method comprising the steps of:
step 1: the laser beam is collimated and then input into a diffraction optical device, the diffraction optical device is manufactured on transparent glass or plastic materials and is provided with a one-dimensional or two-dimensional binary diffraction optical structure, and the diffraction optical device outputs the incident collimated laser beam into diffraction beams with different diffraction orders;
step 2: the diffraction beams of different diffraction orders are focused by the lens, the focused beams are input into the multimode optical waveguide, and the multimode optical waveguide modulates the transmission time delay of the different diffraction beams, so that the diffraction beams of all diffraction orders are output from the multimode optical waveguide with time delay difference delta T;
and step 3: the diffraction light beams output with different time delays are collected by the imaging lens and imaged on the projection screen, the projection screen is provided with a rough surface, and the image on the projection screen is received and processed by the digital camera to realize static laser speckle suppression.
2. The method for static laser speckle suppression in conjunction with multimode optical waveguide and diffractive optics according to claim 1, wherein in step 1, said diffractive optics has a one-dimensional or two-dimensional relief structure made using binary-coded mask-based, called binary diffractive optics.
3. The method of claim 2, wherein the binary code is a pseudorandom sequence code, a barker code, or a Hadamard matrix.
4. The method for suppressing laser speckle in a static state by combining a multimode optical waveguide and a diffractive optical device according to claim 2, wherein said two-dimensional binary diffractive optical structure is a specific two-dimensional binary coded structure or is formed by two one-dimensional binary coded structures overlapped at a set angle.
5. The method for suppressing the speckle of the static laser combining the multimode optical waveguide and the diffractive optical device according to any one of claims 1 to 4, wherein the diffractive optical device is made of a transparent glass or plastic material plated with metal, and the transparent glass or plastic material is a material transparent to visible light bands including red, green and blue light; the metal material is used for shielding light, and the light transmitting part and the light shielding part jointly form binary coding.
6. The method of claim 5, wherein the glass material is K9 optical glass and the plastic material is Polymethylmethacrylate (PMMA).
7. The method for suppressing laser speckle in a static state by combining a multimode optical waveguide and a diffractive optical device according to any one of claims 1 to 4, wherein in the step 2, the multimode optical waveguide is a multimode optical fiber or a multimode rectangular optical waveguide, the multimode is that a plurality of optical conduction modes exist in the waveguide, the time delay difference of the diffracted light beam must be greater than the time coherence length of the laser, and the following inequality must be satisfied:
δT>2πλ2/(c·δλ) (1)
δ T in formula (1) represents a time delay difference when the diffracted beam is output from the multimode optical waveguide, λ represents a wavelength of the laser, δ λ represents a spectral width of the laser, and c represents a speed of light in vacuum;
maximum delay difference deltaT of conduction mode in the multimode optical waveguidemaxCalculated from the following equation (2):
δ T in equation (2)maxRepresenting the maximum delay difference of the propagation modes in the multimode optical waveguide, l representing the length of the multimode optical waveguide, n1And n2Respectively, the refractive indices of the core and cladding of the multimode optical waveguide, and Δ represents the relative refractive index difference between the core and cladding of the multimode optical waveguide.
8. The method for suppressing laser speckle in combination with a multimode optical waveguide and a diffractive optical device according to any one of claims 1 to 4, wherein in step 2, the multimode optical waveguide is a multimode fiber bundle or a multimode optical waveguide with a structured core layer.
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