| Laser projector has many advantages such as wide color gamut,high saturation,bright in color,high resolution,low power consumption,easy miniaturization and so on. It will be the mainstream in the future.The paper contains the following two aspects: First, the beam of light matching is studied from the theory of the color matching and spectral tristimulus value. Second, the input and output characteristics of LD-pumped all-solid-state red,green,blue lasers are investigated, especially on the research about the Polarization of LD-pumped Green-light Solid Laser, after analysising the reasons we bring forward two solving projects and we get high polarization finally.I,Theoritical study on ChrominanceAccording to my experiment, how to match the red light,the green light,the blue to compound the white light which is used as the light source for the micro-projector is my work. About it, I make the numerical simulation.(i)Formula of spectral tristimulus values is devided :Ki is radiance in the formula(1) , Ki=kφ(λi ) i=1,2,3, x, y, z are the chromaticity coordinate. According to the formula(1), we deduce that the ratio of power about the red650nm,the green532nm,the blue473nm is 3.008 to 0.8524 to 1.(ii)Keep the wavelength of the red 650nm and the green 532nm and change the wavelength of the blue from 400nm to 490nm, using the tricolor we couple the equal energy white light. We get the relationship between the ratio of power of the red 650nm,the green 532nm and the blue as the wavelength variation of the blue in theThe vertical coordinatesηis the ratio of power, abscissa is the wavelength of the blue .When we vary the wavelength of the blue lasers, the ratio of the power between the red 650nm,the green 532nm and the blue will change. Every point of the Red curve is the power ratio between the red 650nm and the blue, Every point of the Green curve is the power ratio between the green 532nm and the blue. For a given blue 473nm, from the Red and the Green curves, we read that the ratio of the red 650nm and the blue 473nm is 3.01 to 1 and the power ratio of the green 532nm and the blue 473nm is 0.85 to 1, so the power ratio of the red 650nm,the green 532nm,the blue 473nm is 3.01 to 0.85 to 1. So we can read the power ratio from the Figure 1 when we change the wavelength of the blue.(iii)Keep the wavelength of the red 650nm and the blue 532nm and change the wavelength of the green from 500nm to 580nm, using the tricolor we couple the equal energy white light. We get the relationship between the ratio of power of the red 650nm,the blue 473nm and the green as the wavelength variation of the green in the Figure 2. When we change the wavelength of the green and keep the wavelength of the red 650nm and the blue 473nm, we can read the power ratio of the tricolor from the Figure 2.(iv)Keep the wavelength of the green 532nm and the blue 473nm and change the wavelength of the red from 500nm to 580nm, using the tricolor we couple the equal energy white light. We get the relationship between the ratio of power of the green 532nm,the blue 473nm and the red as the wavelength variation of the red in the Figure 3.When we change the wavelength of the red and keep the wavelength of the green 532nm and the blue 473nm, we can read the power ratio of the tricolor from the Figure 3.In summary, using any group (such as the red 650nm,the green 532nm,the blue 473nm and so on )of the spectral tricolor couples the equal energy white light, we can read the ratio of the power of the group in the Figure 1,Figure 2,Figure 3. The numerical simulation will be helpful for the optical coupling light source in our micro-projector.II,Experiment research on LD-pumped all-solid-state red, green, blue lasers(1) All-solid-state micro-green laser and the polarization(i) The light source is semiconductor laser diode whose the highest output power is 1W and the diode emissions Center wavelength is 808nm.The light of 808nm focuses on the laser crystal(Nd:YVO4) through the self-focusing lens, and produces fundamental frequency light of 1064nm, and then traverses the frequency-doubling crystal(KTP), so the output light is 532nm. The experimental schematic diagram is displayed in Figure 4.The room temperature is 24.2°C, we measure the output power of 532nm green light, the experimental result is displayed in Figure 5.By the curve of Figure 5, we can see the green light output power increases as the input current increasing, although it is not completely linear change, closing to linear. The highest output power is 172mW.The degree of the polarization is the mark on the characteristics of the lasers, the higher is the degree of the polarization, the better is the characteristics and the coherences of the lasers .The experimental schematic diagram measuring the polarization of green laser is displayed in Figure 6.The output green light is divided into two part through the PBS, one part is vertically polarized light, the other one is horizontally polarized light. We measure the polarization ratio of LD-pumped micro-green laser, the results is displayed in Figure 7By the curve of Figure 7, the polarization ratio of LD-pumped micro-green laser varies from 0.7 to 1.5, maintaining at about 1. We need the vertically polarized light in the miro-projctor only and about one half is wasted. To increase the polarization ratio is our primary thing.(ii) The programs on increasing polarization ratio of LD-pumped micro-green laser. (①)Insert QWP(λ4) between the frequency-doubling crystal and the output coupler in order to compensate the polarization loss. The Schematic diagram is displayed in Figure 8.1) The room temperature is 24.2°C, after inserting QWP ,we adjust the cavity length as the input current is 1.0A. We measure the relationship between the cavity length and the output power, the result is displayed in Figure 9. When the cavity length is 34.6mm, the average power is the highest. We do the following experiment in this cavity .2) Keep the cavity to 34.6mm , we measure the relationship between the output power and the input current. By the curve of Figure 10, we can see that the green light output power increases as the input current increases. After fitting the curve we get that the electro-optical conversion efficiency is up to 23.3%. 3) Insert QWP between the frequency-doubling crystal (KTP) and the output coupler and rotate the QWP. When we rotate angle at 5 degree, we measure the relationship between polarization ratio of LD-pumped micro-green laser and the rotating angle of QWP in Figure 11.By the curve of Figure 11, the polarization ratio is different when we rotate the angle of QWP , the polarization ratio varies from 0.2 to 6.6. This program improves the polarization of the green laser. In order to entirely polarized green laser, we propose another program-polarization conversion. By the curve of Figure 12, horizontally polarized light OA traverses reflection primαandβ, the output light BC become vertically polarized light, the vertically polarized lights of BC and OK couple through the coupling devices, this program obtains the completely vertically polarized green light.(2) All-solid-state micro-blue laser and micro-red laser(①)All-solid-state micro-blue laserThe light source is semiconductor laser diode whose output power is 2W of the Beijing HI-Tech company , the diode emissions Center wavelength of 808nm, the beam is divergent. The light of 808nm focuses on the laser crystal (Nd:YAG) through the self-focusing lens, and produces fundamental frequency of 946nm, and then traverses the frequency-doubling crystal(BIBO), so the output blue light is 473nm. The experimental schematic diagram is displayed in Figure 13.In the experiment we use the frequency-doubling crystal(BIBO) and the phase-matching cutting angle of BIBO crystal isθ= 161.7 ,φ=90, the relationship between the output power and input current in Figure 14, from the curve we can see that the blue light output power increases as the input current increases, although it is not completely linear change, closing to linear. The highest output power is 75mW.(②) All-solid-state micro-red laserThe light source is semiconductor laser diode whose highest output power is 100mW of the Beijing HI-Tech company. In the room temperature , the diode emissions center wavelength of 650nm red light. The beam is divergent, so it need the self-focusing lens to focus. After traversing it, the beam is focused and collimated. The experimental schematic diagram is displayed in Figure 15, the radius of the output beam is 0.7mm. The relationship between the red light output power and the input current in the Figure 16. In the Figure 16, we can see the curve is closing to linear, the red light output power increases as the input current increasing. The high power is 126mW. In the chapter 3, we mix the green light 532nm,the blue light 473nm,the red light 650mn with the ratio of 0.8524 to 1 to3.008 in order to obtain the Equal Energy White Light according to the Figure 17. Take them as the light source of the laser-projector, we get the display image. In Figure 18, there are two images , the left is the one from the laser-projector, the right is from the LED- projector. From this two images, we can see the high saturation and colorful. In the left of Figure 18, we can see that the green horizontal stripes reduce because the polarization ratio of green light increase, so the quality of the image improves. |
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