JP2006284937A - Wavelength converting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized wavelength converting device which has excellent wavelength conversion efficiency. <P>SOLUTION: The wavelength converting device includes a pseudo-phase matching type wavelength converting means which is made of a LiNbO3 crystal having an optical waveguide 11 whose polarizing direction is periodically inverted and wavelength-converts an infrared light I incident from an incidence end 11a of the optical waveguide into blue lights B1 and B2 while guiding it along the optical waveguide, a DBR 20 which is provided on the side of a projection reflecting end 11b of the optical waveguide and transmits only the blue light B1 wavelength-converted by the wavelength converting element 10 to project it from the side of the projection reflecting end of the optical waveguide and also reflects the remaining infrared light I to return it to the optical waveguide, and a multiplexing device 40 which multiplexes the blue light B1 projected from the projection reflecting end side of the optical waveguide and the blue light B2 wavelength-converted by the wavelength converting element and projected from the incidence end side of the optical waveguide after being returned to the optical waveguide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical wavelength conversion device used for a laser light source or the like.

  In recent years, there is an increasing expectation for a wavelength conversion device capable of producing beautiful blue light as a blue light source of a projection television. As shown in FIG. 4A, this wavelength conversion device forms an optical waveguide 101 in a LiNbO 3 crystal 100 as a wavelength conversion element, and forms a periodically poled structure (shown in a striped pattern) by applying a voltage thereto. Thus, the infrared light I is converted into the blue light B.

In the conventional wavelength conversion device, in order to increase the wavelength conversion efficiency, the pitch interval of the periodically poled structure is adjusted to satisfy the phase matching condition of the infrared light I and the blue light B (for example, Patent Document 1). reference.).
JP 2000-171844 A

  By the way, the LiNbO3 crystal, which is the material of the wavelength conversion element, has absorption in the vicinity of the 400 nm band corresponding to blue. Therefore, on the exit end side of the optical waveguide where the abundance ratio of blue light increases, as shown in FIG. 4B, the crystal temperature rises due to heat generated by the absorption of blue light, and the expansion and refractive index of the LiNbO3 crystal increase. Change occurs. As a result, the phase matching condition described above may be deviated on the output end side of the optical waveguide, and the effective working length of the wavelength conversion element may be shortened.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a small wavelength conversion device with good conversion efficiency.

  In order to solve the above problems and achieve the object, the wavelength converter of the present invention is configured as follows.

(1) In a wavelength conversion device, a pseudo crystal that is made of a nonlinear crystal having an optical waveguide whose polarization direction is periodically reversed and that converts the wavelength of light incident from one end of the optical waveguide while guiding the light along the optical waveguide. Phase matching type wavelength conversion means, provided on the other end side of the optical waveguide, transmits only the light wavelength-converted by the wavelength conversion means, emits it from the other end side of the optical waveguide, and the remaining Reflecting and transmitting means for reflecting light back to the optical waveguide, light emitted from the other end of the optical waveguide, and returning to the optical waveguide and wavelength-converted by the wavelength converting means, the optical waveguide Synthesizing means for synthesizing the light emitted from the one end side.

(2) The wavelength conversion device described in (1) further includes control means for uniformly heating or cooling the nonlinear crystal and controlling the temperature to be constant.

(3) In the wavelength converter described in (1), the nonlinear crystal is a LiNbO3 crystal, and converts infrared light into blue light.

  According to the present invention, the wavelength conversion efficiency can be improved. In addition, the wavelength converter can be reduced in size.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram of a wavelength converter according to an embodiment of the present invention. As illustrated in FIG. 1, the wavelength conversion device includes a wavelength conversion element 10, a DBR 20, an electric circuit 30, a synthesis device 40, and a control device 50.

  The wavelength conversion element 10 is made of a LiNbO3 crystal having a nonlinear optical effect, and an optical waveguide 11 that transmits infrared light and converts it into blue light is formed at a predetermined position. The optical waveguide 11 has a so-called periodic polarization reversal structure (shown in a striped pattern), one end of which forms an incident end 11a for incident infrared light, the other end that reflects infrared light, and blue light. Is formed as an outgoing reflection emitting end 11b. The periodic polarization reversal structure is a structure in which the polarization direction of the crystal is reversed at a predetermined interval with respect to the optical axis direction of the optical waveguide 11.

  The periodic pitch of the periodically poled structure is designed to satisfy the phase matching condition of infrared light and blue light at the reference temperature. The phase matching condition is a condition for preventing infrared light and blue light mixed in the optical waveguide 11 from weakening each other.

  The length of the optical waveguide 11 is designed so that approximately half of the infrared light is converted into blue light in one way of the optical waveguide 11. In other words, the length of the optical waveguide 11 is determined while infrared light propagates from the incident end 11a of the optical waveguide 11 to the outgoing reflection end 11b or during propagation from the outgoing reflection end 11b of the optical waveguide 11 to the incident end 11a. In addition, it is designed so that approximately half of it is converted into blue light.

The DBR (distributed Bragg reflector) 20 is composed of a plurality of Bragg reflector films 21 and is provided at the output reflection end 11 b of the optical waveguide 11. The lamination pitch (hereinafter referred to as “DBR period”) Λ of the Bragg reflection film 21 is set as shown in Equation [1] based on the Bragg reflection condition. Here, Λ is the DBR period, λ _I is the wavelength of infrared light, and n is the effective refractive index of the Bragg reflection film 21.

Λ = 2λ _I n ... [1]
As a result, the DBR 20 reflects only infrared light and transmits blue light.

  FIG. 2 is a relationship diagram of the wavelength conversion element and the electric circuit 30 according to the embodiment. As shown in FIG. 2, the electric circuit 30 includes a first system 31 and a second system 32. The first and second systems 31 and 32 are alternately connected to electrodes (not shown) formed on the side surface of the wavelength conversion element 10, and respectively apply reverse polarity voltages to the LiNbO 3 crystal. . As a result, the above-described periodic polarization inversion structure is formed in the optical waveguide 11 of the wavelength conversion element 10.

  The synthesizer 40 includes a dichroic mirror 41, a first mirror 42, a second mirror 43, a polarizing optical element 44, and a polarizer 45.

  The dichroic mirror 41 is disposed opposite to the incident end 11 a of the optical waveguide 11, transmits infrared light from a light source or the like (not shown) and enters the incident end 11 a of the optical waveguide 11, and the incident end of the optical waveguide 11. The blue light emitted from 11 a is reflected substantially at a right angle and guided to the first mirror 42.

  The first mirror 42 is disposed on the side of the dichroic mirror 41, reflects blue light reflected by the dichroic mirror 41 at a substantially right angle, and guides it to the second mirror 43.

  The second mirror 43 is disposed on the side of the polarizer 45, reflects the blue light reflected by the first mirror 42 at a substantially right angle, and guides it to the polarizing optical element 44.

  The polarization optical element 44 is disposed between the second mirror 43 and the polarizer 45, and rotates the polarization angle of the blue light reflected by the second mirror 43 and traveling to the polarizer 45 by 90 degrees.

  The polarizer 45 is disposed opposite to the output reflection end 11 b of the optical waveguide 11, transmits the blue light emitted from the output reflection end 11 b of the optical waveguide 11, and has a polarization angle rotated by 90 degrees by the polarization optical element 44. Are reflected at a substantially right angle to synthesize them.

  The control device 50 cools the wavelength conversion element 10 uniformly and controls the temperature so that the temperature becomes the above-described reference temperature.

  In the wavelength conversion device having the above-described configuration, approximately half of the infrared light I incident on the incident end 11a of the optical waveguide 11 is converted into the blue light B1 before reaching the output reflection end 11b of the optical waveguide 11. The The blue light B1 passes through the polarizer 45 after passing through the DBR 20. On the other hand, the infrared light I that has not been wavelength-converted before reaching the output reflection end 11 b of the optical waveguide 11 is reflected by the DBR 20, and then passes through the optical waveguide 11 in the reverse direction, that is, to the incident end 11 a of the optical waveguide 11. The light travels toward the incident end 11a of the optical waveguide 11 and is almost converted into blue light B2. The blue light B2 is emitted from the incident end 11a of the optical waveguide 11, and passes through the polarizer 45 through the first mirror 42, the second mirror 43, the polarizing optical element 44, and the polarizer 45. Synthesized with B1.

  According to the present embodiment, in the quasi phase matching type wavelength converter, the DBR 20 that reflects only the infrared light I is provided at the output reflection end 11b of the optical waveguide 11. The infrared light I that has not been converted between the incident end 11 a and the outgoing reflection end 11 b of the optical waveguide 11 is reflected by the DBR 20 and returned to the optical waveguide 11, so that the infrared light I is thereafter converted into the optical waveguide 11. The wavelength conversion is performed using the time until the incident end 11a is reached.

  That is, in the wavelength conversion device of this embodiment, the optical waveguide 11 is reciprocated with the infrared light I, and wavelength conversion is performed in both the forward path and the return path. Therefore, the working length can be increased up to about twice that of the conventional wavelength converter. In other words, the length of the wavelength conversion element 10 necessary for obtaining a desired amount of blue light can be reduced to about ½ of the conventional length.

  Further, since wavelength conversion is also performed in the return path in which the infrared light I travels toward the incident end 11 a of the optical waveguide 11, the blue light near the incident end 11 a of the optical waveguide 11 increases, and the blue light in the optical waveguide 11 is increased. The abundance ratio of B is uniform over the entire optical waveguide 11.

  Therefore, even when a LiNbO3 crystal having absorption in the 400 nm band is used as the wavelength conversion element 10, the temperature of the wavelength conversion element 10 can be made uniform as shown in FIG. Thus, it is possible to maintain the entire wavelength conversion element 10 at the reference temperature only by cooling the entire wavelength conversion element 10 uniformly.

  As a result, the phase matching conditions of the infrared light I and the blue light B are maintained, and the entire optical waveguide 11 of the wavelength conversion element 10 is used for wavelength conversion. Therefore, the wavelength conversion element 10 can be made smaller than before. it can.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a schematic configuration diagram of a wavelength conversion device according to an embodiment of the present invention. FIG. 3 is a relationship diagram between a wavelength conversion element and an electric circuit according to the embodiment. Schematic which shows the schematic structure and temperature distribution of the wavelength conversion element which concern on the same embodiment. Schematic which shows the schematic structure and temperature distribution of the conventional wavelength converter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Wavelength conversion element (wavelength conversion means), 11 ... Optical waveguide, 20 ... DBR (reflection / transmission means), 40 ... Synthesis apparatus (synthesis means), 50 ... Control apparatus (control means).

Claims (3)

A quasi-phase-matching wavelength converting means comprising a non-linear crystal having an optical waveguide whose polarization direction is periodically reversed, and performing wavelength conversion while guiding light incident from one end side of the optical waveguide along the optical waveguide; ,
The optical waveguide is provided on the other end side of the optical waveguide, transmits only the light wavelength-converted by the wavelength converting means, emits the light from the other end side of the optical waveguide, and reflects the remaining light. Reflection and transmission means to return to
Combining means for combining the light emitted from the other end side of the optical waveguide, and the light emitted from the one end side of the optical waveguide after being returned to the optical waveguide and wavelength-converted by the wavelength converting means;
A wavelength conversion device comprising:   2. The wavelength converter according to claim 1, further comprising control means for uniformly heating or cooling the nonlinear crystal and controlling the temperature to be constant.   2. The wavelength conversion device according to claim 1, wherein the nonlinear crystal is a LiNbO3 crystal and converts infrared light into blue light.

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