KR20090089190A - Simultaneous rgb generation by qpm ultra-broadband optical parametric generation in periodically poled crystal - Google Patents

Abstract

A simultaneous RGB generating method by QPM ultra-broadband optical parametric generation in periodically poled crystals is provided to enable efficient ultra-broadband optical parametric generation, the second harmonic wave generation and SFG(sum-frequency generation). A beta-BBO (barium borate) crystal generates a weak signal and an idler light according to a suitable direction of a crystal. A monochromator and a PbS detector measure a light intermediation generation band. Band pass filters(F1,F2) transmit only 1.2~2.5 micrometer bands in order to cut pump light.

Description

Simultaneous RGB generation by QPM ultra-broadband optical parametric generation in periodically poled crystal}

The present invention relates to a method for simultaneously generating three primary colors using a secondary nonlinear medium. In particular, an efficient broadband secondary harmonic wave can be generated by group velocity matching and level matching in a secondary nonlinear medium, and the three primary colors can be simultaneously generated by a single pump. The present invention relates to a method for simultaneously generating three primary colors by quasi-phase matched ultra-wideband optical mediation in polarized inverted crystals.

Simultaneous generation of red, green and blue, ie, three primary colors (RGB) visible laser light is an essential element in laser-based projection displays. Laser displays offer many advantages over conventional displays, such as pure spectral colors, deep focus, high brightness and spatial resolution. This is due to the unique nature of the laser, and the demand for such a projection display is increasing.

Several attempts have been made to realize the simultaneous generation of these three primary colors, and most of the reported techniques have used nonlinear crystals using a plurality of nonlinear crystals, pump lights, or aperiodic polarization inverted structures.

In general, nonlinear optical frequency conversion is well known as a technique for converting near infrared into visible light. For effective frequency conversion, birefringent phase matching or quasi-phase matching conditions must be met in nonlinear optical materials.

In order to satisfy such birefringent phase matching or quasi-phase matching conditions, periodically polarized inverted lithium niobate crystals are widely used, which is well known as a quasi-phase matching device for realizing optical frequency conversion. This is because the lithium niobate crystal has a large nonlinear coefficient d ₃₃ .

In order to enable efficient frequency conversion in a secondary nonlinear medium such as lithium niobate, a phase matching or quasi phase matching (QPM) condition must be satisfied. This allows the interacting waves to phase each other as they progress through the nonlinear medium, allowing for efficient and coherent interaction.

However, these phase matching conditions are very strict, limiting the frequency bandwidth of the wave to be obtained. Therefore, when converting frequency into very short pulses, a thin medium is mainly used, but there is a side effect of decreasing the conversion efficiency in proportion to the length.

In order to solve the above problems, efficient broadband optical mediation, secondary harmonic wave generation, and sum frequency generation are possible by group speed matching and level matching in a secondary nonlinear medium, and the three primary colors can be simultaneously generated by a single pump. The task is to generate a phase-matched ultra-wideband photomediation method and to simultaneously generate three primary colors in periodically polarized inverted lithium niobate (LiNbO ₃ ).

In order to solve the above problems, the present invention generates a pumping light source by passing the pump light supplied by the pulsed laser to the OPG-OPA device, and generates the pumping light source by supplying the pumping light source to the polarized inverted crystal periodically Simultaneous generation of three primary colors by phase-matched ultra-wideband photomediation in the crystallization of periodic polarization inversion through group velocity matching and phase matching between signal and idler light in the ultra-wideband infrared band It is a technical point.

In addition, it is preferable that in the photo-mediation amplifier device, photo-mediation and photo-mediated amplification are performed by rotating a pair of β-BBO (β-Barium Borate) crystals.

Here, the periodically polarized inverted crystal is preferably a ferroelectric crystal of LiNbO ₃ or LiTaO ₃ series.

Further, the group speed matching is preferably performed near a degeneracy point or near a wavelength at which the group speed dispersion becomes zero.

Further, green light and red light are generated due to the generation of sum frequencies due to phase matching by the signal light, idler light, and pump light in the ultra-wide band infrared band, and generation of higher-order quasi-phase matching secondary harmonics by the pump light source. It is preferable to generate blue light by.

According to the above configuration, the present invention enables efficient wideband photomediation, secondary harmonic wave generation, and sum frequency generation by group speed matching and level matching by a single pumping light source using a periodically inverted crystal. There is a possible effect.

In addition, there is almost no change in the generation of the spectrum of the three primary colors even when the temperature changes, there is an effect that can be put to practical use.

In case of second harmonic wave generation, it is possible to solve by group velocity matching (GVM) method in order to obtain broadband bandwidth by efficient frequency conversion in secondary nonlinear media, and to match the group speed of fundamental and harmonic wave, and to use quasi-phase matching. If you can.

In the present invention, an efficient parametric optical parametric method is achieved by matching the group speed between a signal and an idler near a degeneracy point in a periodically polarized lithium niobate (PPLN). generation: OPG). This ultra-wideband gain band is applicable to optical parametric amplification (OPA) of very short pulses. In addition, the present invention implements the simultaneous generation of trichromatic light (RGB) insensitive to temperature changes due to ultra-wideband optical mediation.

In order to realize the ultra-wideband optical mediation, the pump wavelength, the phase match period, and the driving temperature should be selected so that the group speeds of the signal wave and the idler wave match. In order to enable three primary colors to be generated simultaneously based on such ultra-wideband photomediation, the pump must be additionally considered to generate blue light by generation of higher order phase matched secondary harmonic waves.

Hereinafter, as illustrated in FIG. 1, an experimental method for simultaneous generation of three primary colors by a single pump using crystals in which polarization is periodically inverted will be described in detail.

Lithium niobate was used as the crystal that was periodically polarized and then simulated using refractive index dispersion of lithium niobate, and then a pump wavelength of 933 nm, a phase match period of 27 µm, and a driving temperature of 24 ° C were selected.

355nm, the third harmonic of mode-locked Nd: YAG laser (Quantel, YG900, repetition rate: 10 Hz, pulse width: 35 ps), is used to determine a pair of β-BBO (β-barium borate) crystals. An optical mediation amplification (OPG-OPA) device manufactured by incident light was used. Here, the first β-BBO crystal generates weak signal light and idler light according to the proper crystal direction, and is further amplified by the β-BBO crystal collinear with the second 355 nm beam.

Periodically polarized inverted lithium niobate has a length of about 20 mm, and when measuring the photo-mediated band generated by the monochromator (monochromater, SPEX 1702) and PbS detector, only 1.2-2.5 μm band is used to cut the pump light. Band pass filters F1 and F2 were used to transmit, and the observation of the three primary colors was measured by a CCD spectrometer. Converging lenses L were installed on both sides of the lithium niobate crystal so that the pump light had a focal length of 5 cm.

Figure 2 shows the measured ultra-wideband broad spectrum. The measured bandwidth was about 1200 nm and was almost identical to that calculated by the Sellmeier equation except for the long wavelength region limited by the band pass filter. Photovoltaic generation of 1.7 μJ was possible when pumping with an energy of 22 μJ per unit pulse. The narrow and large depletion of four special places (λ ₁ , λ ₂ , λ ₃ , λ ₄ ) in the photomediated band is explained in connection with subsequent three primary color developments.

3 is the measured RGB spectrum. The red light (648 nm) is due to the second-order matched phase generation (SFG) between the pump light (933 nm) and λ ₃ (2122 nm) in FIG. The green light (575 nm) is due to the generation of the third order phase matched frequency between the pump light (933 nm) and λ ₁ (1498 nm) in FIG. λ ₂ and λ ₄ are mutually depleted in pairs of λ ₃ and λ ₁ , respectively, in photomediating.

On the other hand, the blue light (467 nm) is due to the higher order of the pump, that is, the sixth phase matched secondary harmonic generation. The phase difference of even difference can be generated by the variation in duty ratio of the cycle inevitably involved in the fabrication of periodically polarized and reversed lithium niobate. The total energy of the three primary colors generated was about 0.5 μJ with the above pump energy.

Figure 4 shows the characteristics of the three primary colors generated by the drive temperature change. When the driving temperature was changed from 24 ° C. to 55 ° C., there was no significant change in the spectrum smaller than 1 nm without significant change in the intensity of the three primary colors. This is because the broadband generation band changes as the driving temperature changes, but is still strong and wide enough to generate three primary colors. This feature can be a great advantage at the stage of practical use.

FIG. 1 shows schematic experimental settings for photomediated generation and three primary colors simultaneously due to periodically polarized inverted lithium niobate crystals.

FIG. 2 shows the ultra-wideband photomediation spectrum measured in accordance with the present invention. FIG.

3 shows a three primary color spectrum measured according to the invention.

4 is a view showing a characteristic change according to the drive temperature change of the three primary colors generated by the present invention.

Claims (5)

The pump light supplied by the pulsed laser is passed through an OPG-OPA device to generate a pumping light source, and the pumping light source is periodically supplied to a polarized inverted crystal to generate a signal of an ultra wide band infrared band. 3) Simultaneous generation of three primary colors by phase-matched ultra-wide band optical mediation in periodically polarized and inverted crystals through group velocity matching and phase matching between light and idler light. The method of claim 1, wherein the periodically polarized inverted crystal, Simultaneous generation of three primary colors by phase-matching ultra-wideband photomediation in a periodically polarized inverted crystal characterized in that the ferroelectric crystal of LiNbO ₃ or LiTaO ₃ series. The method of claim 1, wherein the group speed matching is Simultaneous generation of three primary colors by phase-matched ultra-wideband photomediation in crystals that are periodically polarized inverted when near the degeneracy point or near the wavelength at which the group velocity dispersion becomes zero. The polarized and inverted crystals according to claim 1, characterized in that green light and red light are generated by generating the sum frequency by matching the phase of the signal light, the idler light and the pump light in the ultra-wide band infrared band. Simultaneous Generation of Three Primary Colors by Quasi-Phase Matching 3. The simultaneous generation of three primary colors due to the phase-matched ultra-wideband photo-mediated generation in a periodically polarized inverted crystal, characterized in that for generating blue light due to the generation of higher-order phase-matched secondary harmonic waves by the pump light source. Way.

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