JPS63184384A - Wavelength-tunable laser apparatus - Google Patents

Abstract

PURPOSE:To obtain a laser whose wavelength can be varied in a wide band by providing a rotator which is conposed of 1st rotating part which turns a crystal for a light wavelength converter (2nd harmonic generator) in a plane parallel to a light axis and 2nd rotating part which turns the crystal in a olane vertical to the light axis. CONSTITUTION:An ordinary light (o-component) of the output light of optical parametric oscillator (OPO) 1 is applied to a 2nd harmonic generator (SHG) 2 and a SHG crystal 9 is turned in a plane parallel to a light axis 10 by the 1st rotating part 16 of a rotator 18. If the rotation angle (theta) is varied within the range of 90-50 degrees, an output wavelength is varied as shown by a characteristic curve (C). Then, if the motor 27 of the 2nd rotating part 17 of the rotator 18 is turned 360 degrees, an index table 23 is turned 90 degrees with the light axis 10 as a center of turning by a parallel index cam 24. Then, an e-component, which is an extraordinary light for the SHG crystal 9, is turned into an ordinary light. In this state, the SHG crystal 9 is turned by the motor 20 of the 1st rotating part 16 for phase matching and the wavelength conversion is applied to the ordinary light component of the SHG output as shown by a characteristic curve (D). As a result, even if the rotation range is 90-50 degrees, a laser whose wavelength can be varied over the whole range of 250-1230 nm can be obtained.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention converts light emitted from an optical parametric oscillator (OPO) into an optical wavelength converter (for example, a second harmonic generator/5H
This invention relates to a wavelength tunable laser device in which a broadband optical wavelength tunable laser is obtained by inputting the signal into the crystal of G) and rotating the crystal for phase matching.

"Prior Art" In general, a wavelength tunable laser device, as shown in FIG.
It is equipped with an optical parametric oscillator (OPO) (1) and a second harmonic generator (SHG) (2) as an optical wave quality converter, of which 0PO (1) is a power density converter of the incident laser beam. It consists of a collimator part (3) for increasing the height, an input reflection mirror (4) and an output reflection mirror (5) having a predetermined reflectance in a predetermined bandwidth, and a rotatable nonlinear optical crystal (6), Further, 5HG (2) consists of lenses (7) (8) that increase power density and a crystal (9).

In such a configuration, the OPO crystal (6) is excited with a strong laser beam to generate two lights having different wavelengths from the excitation light. The excitation light is called pumping light, one of the two output lights is called signal light, and the other is called idler light. These signal lights and idler lights are transmitted by an OPO crystal (6
) is amplified and oscillated within a cavity made up of input and output mirrors (4) and (5).

Let the angular frequencies of the pumping light (p), signal light (s), and idler light (i) be ωp, ωS, and ωi, respectively,
Letting the wave number vectors be kp, ks, and ki, respectively,
A wavelength that satisfies the condition ωp=ωS+ωi −3=kp=ks+ki oscillates. Generally, only one of these two wavelengths is extracted.

In addition, in the above 5HG (2), when the crystal (9) is a uniaxial crystal, no(λ)=ne (0m, λ/2) (]/ne (Om, λ/2)”=cos2(3m/no
The phase matching angle can be found from the relationship ``+5in20 m/ne2.Here, n.

is the refractive index of ordinary light, and ne is the refractive index of extraordinary light.

For example, at 355 nm of Nd-YAG laser, urea crystal (6
), the rotation angle (O
) is 90 degrees as shown in Figure 5, 500 nm and 1
By generating two lights of 230 nm and further rotating them at a rotation angle of 60 degrees as shown in Figure 6, the light of 600 nm is generated.
It generates two lights of 870nm and 870nm. Thus, by changing the rotation angle (ill), coherent light in the range 500-1230 nm can be obtained. The laser beam emitted from the crystal (6) oscillates between the input and output mirrors (4) and (5) and is output. When the light emitted from 0PO (1) is incident on 5HG (2) and the crystal (9) is rotated for phase matching,
Frequency multiplication is possible, and even wider band 250-1230
It is possible to obtain nanometer oscillation light. In Figure 4, the optical axes (10) of crystals (6) and (9) are parallel to the plane of the paper, and the pumping light is ordinary light, and one of the two lights (signal light, idler light) generated is If it is an ordinary light, the other will be an extraordinary light. Since the SHG crystal (9) has a phase matching condition of TYPE 4, it is phase matched to the ordinary ray by crystal rotation and outputs a multiplied harmonic.

"Problems to be Solved by the Invention" In the angle-matched OPO (1), birefringence cannot be avoided in the OPO crystal (6), and as shown in Figure 2, one of the output lights is the ordinary light ( 0 component), and the other is extraordinary light (e
component). Here, in order to multiply by 5HG(2) based on the first type of matching (TYPEI), only the fundamental wave of a single polarization component, either the 0 component or the e component, can be used. For example, in Fig. 4, the OPO crystal (6) is a urea crystal, the SHG crystal (9) is β-BaB204, the pumping light is an ordinary light of 355 nm, the signal light of 0PO (1) is an ordinary light (0 component), and the 0PO (1) is an ordinary light (0 component). )'s idler light as extraordinary light (
e component), 5HG (2) fundamental wave as ordinary light (0 component), 5
When the second harmonic of HG (2) is taken as extraordinary light (e component), when the angle (0) of the OPO crystal (6) is rotated by 50 to 90 degrees around the optical axis (10), the seventh harmonic is As shown in the characteristic lines (A) and (B) in the figure, the e component of 0PO(1) is 6
60-1230nm, the 0 component of 0PO(1) is 780-
It changes to 500 nm. In SHG (2), 0PO(1
) is multiplied as ordinary light, a laser with a wavelength of 390 to 250 nm is obtained, as shown by the characteristic line (C) in FIG. However, in Figure 7, 390
A laser with a wavelength in the range (X) of ~500 nm cannot be obtained. If the rotation angle of the OPO crystal (6) is greatly rotated to 50° or less, the wavelength range of ordinary light (0 component) extends to the long wavelength side, and
The wavelength range multiplied by HG(9) also extends to the long wavelength side. However, when the rotation angle (θ) is increased, the following problems arise.

The deviation of the optical axis (10) due to the refractive index of the crystal increases. If the optical axis (10) shifts, it deviates from the plane of incidence of the SHG crystal (9), so the size of the SHG crystal (9) must be increased. , the reflectance at the end face of the crystal increases, and even if you try to increase the conversion efficiency by applying an AR coating to reduce the reflectance, the AR will increase when the incident angle is widened.
There were problems such as the difficulty of the court.

"Means for Solving the Problems" The present invention has been made to solve the above-mentioned problems, and it excites the nonlinear optical crystal of the optical parametric oscillation section with pumping light to generate signal light and idler light. In a wavelength tunable laser device, the light emitted from the optical parametric oscillation section is multiplied by rotation of a crystal in an optical wavelength conversion section (for example, a second harmonic generation section) to output a multiplied harmonic. A rotating device consisting of a first rotating section that rotates the crystal for the conversion section (second harmonic generation) in a plane parallel to the optical axis and a second rotating section that rotates the crystal in a plane perpendicular to the optical axis. It is equipped with.

"Operation" The nonlinear optical crystal of the optical parametric oscillator is excited by pumping light and emits signal light and idler light. By changing the rotation angle of the optical crystal, the wavelength of the output light is varied and a laser beam in a predetermined wavelength range can be obtained. Among the output lights of the optical parametric oscillator, for example, one ordinary light is made incident on the second harmonic generator to generate the second harmonic crystal.
The rotary unit rotates the light in a plane parallel to the optical axis to cause phase matching of the ordinary light, thereby obtaining output light in a multiplied wavelength range. If only the ordinary light is multiplied, the matching condition is not satisfied for the extraordinary light, and a broadband output cannot be obtained.

Therefore, the second harmonic crystal is rotated by 90 degrees in a plane perpendicular to the optical axis by the second rotating section. Then, the component that was previously extraordinary light for that crystal becomes ordinary light,
Furthermore, the first rotating section rotates within a plane parallel to the optical axis to cause phase matching, thereby obtaining output light in a multiplied wavelength range. In this way, a broadband optical wavelength tunable laser can be obtained.

"Example" An embodiment of the present invention will be described below with reference to FIG.

(1) is an optical parametric oscillator (hereinafter referred to as OPO)
, (2) is an optical wavelength conversion device, specifically a second harmonic generation section (hereinafter referred to as SHG). The 0PO (1) has a collimator section (3), an input reflection mirror (4) as shown in FIG.
), an output reflection mirror (5), and a nonlinear optical crystal (6).

This nonlinear optical crystal (6) is stored together with matching oil (14) in a container (13) with an entrance window (11) and an exit window (12) formed on both sides, and the table of the rotating device (
15) so as to be rotatable.

The above 5) IG (2) is β-BaB2 as in FIG.
The SHG crystal (9) consists of an SHG crystal (9) made of 04 and lenses (7) and (8) provided on both sides of the SHG crystal (9).
A rotating device (18) consisting of a rotating section (16) and a second rotating section (17) that rotates in a plane perpendicular to the optical axis (10).
installed on. That is, the first rotating part (1
6) is a rotary table on which the SHG crystal (9) is placed and fixed (
19) and a stepping motor (20) that rotates the rotary table (19) around its central axis, and rotates the SHG crystal (9) within a plane parallel to the optical axis (10). Set the angle (θ). Further, the second rotating portion (17) is mounted on a support frame (21) with a bearing (22) (
An index table (23) rotatable about the optical axis (10) while being supported by the index table (22) is provided, and the first rotating part (16) is attached to the index table (23)=8-. and meshes with the parallel index cam (24) divided into four parts, and also engages with the rotation shaft (25) of this parallel index cam (24).
) is connected to the motor (27) by a coupling (26). And when the motor (27) rotates once,
The index table (23) is rotated 90 degrees.

The operation of the above configuration will be explained. As shown in Figure 1, when the OPO crystal (6) is excited with 355 nm pumping light, the angle (θ) of the OPO crystal (6) is 90
500 nm ordinary light (0 component) and 1230 nm extraordinary light (e component) are emitted, and when the angle (θ) of the laser light is changed, the characteristics of the laser light of these wavelengths are as shown in Figure 3 (A) and (B). Continuously changes.

Next, the ordinary light (0 component) of the output light of the 0PO (1) is incident on the SHG (2) and the SHG crystal (9) is moved along the optical axis ( 10)
Rotate in a plane parallel to . This rotation angle (0) is 90
When changing the range of ~50 degrees, the characteristic line (C) in Figure 3
It changes like this.

Next, when the motor (27) of the second rotating part (17) of the rotating device (18) is rotated once, the index table (23) is rotated 9 times through the parallel index cam (24).
Rotate around the optical axis (10) by 0 degrees. Then,
The e component, which was an extraordinary light for the SHG crystal (9), becomes an ordinary light. In this state, the motor (2) of the first rotating part (16)
0) rotates the SHG crystal (9) to cause phase matching, and the wavelength is converted into the ordinary component of the SHG output as shown by the characteristic line (D) in FIG. As a result, a wavelength tunable laser can be obtained over the entire range of 250 to 1230 nm even in a rotation range of 90 to 50 degrees.

In the embodiment described above, since the index cam (24) of the second rotating part (17) divides the index table (23) into four parts, phase matching does not occur between the ordinary light and the extraordinary light. However, a stepping motor is used for the motor (27), and a normal rotary table (23) is used for the index table (23) and index cam (24).
), the rotary table is rotated by a stepping motor to enable arbitrary positioning. With such a configuration, the phases of the ordinary light and the extraordinary light of the OPO output at any position can be matched with the ordinary light components of the SHG crystal (9). Therefore, by selecting the rotation angle, the second harmonics of ordinary light and extraordinary light can be obtained simultaneously at an arbitrary output ratio.

"Effects of the Invention" Since the present invention is configured as described above, it is possible to convert the optical wavelength of both the e component and the 0 polarization component of the laser emitted from the optical parametric oscillation section. It is possible to obtain a broadband optical wavelength tunable laser without using a large rotation angle. Furthermore, since there is no need to take a large rotation angle, correction of optical axis deviation is unnecessary, or even if it is necessary, it is extremely easy, and there is no need for an AR coating to reduce reflection.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a first embodiment of the optical wavelength tunable laser device according to the present invention, FIG. 2 is an explanatory diagram of wavelength changes in OPo and SHG, and FIG. 3 is a characteristic diagram of the device according to the present invention.
Figure 4 is an explanatory diagram of the conventional device, Figure 5 is an illustration of output light when the rotation angle (O) of the OPO crystal is 90 degrees, and Figure 6 is an illustration of the output light when the rotation angle (0) of the OPO crystal is 60 degrees. FIG. 7 is an explanatory diagram of output light in the case of , and is a characteristic diagram of a conventional device. (1)...Optical parametric oscillator (OPO), (2
)... Optical wavelength conversion section (second harmonic generation section) (SHG)
, (3)...collimator section, (4) (5)--reflection mirror, (6)-0PO crystal, (7) (8)...lens, (9)...SHG crystal, (10 )···optical axis,
(11) (12)...Window, (13)...Container, (14)
)... Matching oil, (15)... Rotary table, (16)... First rotating part, (7)... Second rotating part, (18)... Rotating device, (19)...Rotary table, (20)...Stepping motor, (21
)... Support frame, (22)... Bearing, (23)... Index table, (24)... Parallel index cam, (25)... Rotating shaft, (26)... Cup Ring, (27)...Motor. Applicant Hamamatsu Photonics Co., Ltd.

Claims (5)

[Claims] (1) Excite the nonlinear optical crystal of the optical parametric oscillator with pumping light and emit signal light and idler light,
In a wavelength tunable laser device in which the light emitted from the optical parametric oscillator is multiplied by rotating the crystal of the optical wavelength converter to emit harmonics, the crystal for the optical wavelength converter is placed in a plane parallel to the optical axis. What is claimed is: 1. An optical wavelength tunable laser device comprising a rotating device comprising a first rotating section that rotates in a plane perpendicular to an optical axis and a second rotating section that rotates in a plane perpendicular to an optical axis. (2) The optical wavelength tunable laser device according to claim 1, wherein the optical wavelength conversion section comprises a second harmonic generation section. (3) The optical wavelength tunable laser device according to claim 1, wherein the first rotating section comprises a rotating table on which a crystal for an optical wavelength converting section is installed, and a stepping motor that rotates this rotating table. (4) The optical wavelength tunable laser device according to claim 1, wherein the second rotating section comprises an index table on which the first rotating section is installed and a motor for rotating this index table. (5) The optical wavelength tunable laser device according to claim 1, wherein the second rotating section comprises a rotating table on which the first rotating section is installed and a stepping motor that rotates the rotating table.