JP2011100754A - Optical device made of fluoride glass having optical thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device having an optical thin film deposited on fluoride glass where the bonding performance of the optical thin film is improved. <P>SOLUTION: Optical glass having the fluoride glass and the optical thin film is characterized in that the optical thin film is deposited on the surface of the fluoride glass containing oxygen in a range of ≥300 and ≤5,000 mass ppm on the surface and in the vicinity thereof. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical device having fluoride glass and an optical thin film.

  In recent years, fluoride materials have attracted attention as materials capable of directly emitting visible light. For example, a laser in the visible light region is obtained by exciting a rare earth-doped optical waveguide using a gallium nitride based semiconductor light source (Non-Patent Documents 1, 2, 3, 4). Further, since the fluoride material is transparent in the infrared region, it goes without saying that it is used as an infrared laser optical waveguide, a transmission optical waveguide, or the like.

  In order to realize a highly efficient laser, it is necessary to use a low-loss resonator as an optical device to be used. Non-Patent Document 4 and the like constitute a resonator by abutting a mirror against the end face of a rare earth-doped fluoride fiber cleaved to constitute a laser resonator. However, in the configuration of the laser resonator by the abutment of the mirror, since the laser light passes through the air layer, unnecessary reflection may occur, and the stability of the laser output may be deteriorated. Furthermore, since it is difficult to hit a thin fiber having a diameter of 1 mm or less perpendicularly to the mirror, there is a possibility that the resonator loss may be increased due to the influence of angular deviation or the like.

  In general, one means for avoiding this is to use an optical device in which a mirror film is directly formed on the end face of a rare earth-doped optical waveguide that is a laser medium. An optical thin film such as a dielectric multilayer film formed on the end face of the optical waveguide is required to have high damage resistance against light having a high power density and an oscillation wavelength. Therefore, the optical multilayer film has an absorption coefficient of almost 0 in a wide range from the visible range to the infrared range, a film structure with a high laser damage threshold, and adhesion to the end face of the optical waveguide to be formed. It is important to be good.

  In addition, if the difference in thermal expansion coefficient between the optical thin film and the optical waveguide is large, a large film stress is generated at the interface, and there is a risk of laser damage reduction due to microcracks and further film peeling.

For example, when a multilayer film is formed on a ZBLAN fluoride glass using an oxide material such as Ta ₂ O ₅ which is a high refractive index material and SiO ₂ which is a low refractive index material, the heat of the ZBLAN fluoride glass While the expansion coefficient is 196 × 10 ⁻⁷ / ° C., the thermal expansion coefficient of the multilayer film is 40 to 50 × 10 ⁻⁷ / ° C., which is 1/4 to 1/5 compared with the ZBLAN fluoride glass. Therefore, a large film stress is generated at the interface between the fluoride glass and the multilayer film after film formation.

  As described above, in order to configure a high-efficiency laser, a low loss can be achieved by using an optical device in which an optical thin film is formed directly on the end face of the optical waveguide or by directly hitting a mirror on the end face of the optical waveguide However, it is also necessary to appropriately set the NA of the optical waveguide as described below.

  Non-Patent Documents 1, 3, and 4 describe fiber parameters of a fluoride fiber used for a fiber laser, and in particular, for NA, a fiber in the range of 0.12 to 0.39 is used. . However, when producing a fiber having an NA exceeding 0.22, it is necessary to add lead or the like to increase the refractive index of the core, but this is not preferable because of environmental problems. Further, when the NA is smaller than 0.10, it becomes difficult to handle an optical fiber, particularly in an optical fiber in which the radius of the optical waveguide is easily changed, because it is easily affected by bending or the like. Therefore, the NA of the optical fiber is preferably in the range of 0.10 to 0.22.

U. WEICHMANN, J.M. BAIER, J.A. BENGOECHEA and H. MOENCH,: 'GaN-diode pumped Pr3 +: ZBLAN fiber-lasers for the visible waverange range', Proc. CLEO / Europe-IQEC, European Conference on., Munich, Germany, 2007 Magazine "Laser Focus World Japan", July 2009, 50-52 pages Michel J. F. Edited by Diginet, “Rare-Earth-Doped Fiber Lasers and Amplifiers Second Edition”, Marchel Dekker, Inc, pp, 186, 187, 225, 232, 479, 484, 495, 501 and 508 H. OKAMOTO, K.M. KASUGA, I.K. HARA, Y. et al. KUBOTA, 'ULTRA-Wideband Tunable RGB Fiber Laser', Proc. CLEO 2009, Baltimore, United States, 2009

  As described above, it is known that, for example, a highly efficient laser can be realized by using an optical device in which an optical thin film is formed on the end face of the optical waveguide. Since the difference in thermal expansion coefficient between the optical thin film and the fluoride glass is large, a large film stress is generated at the interface, which may reduce the adhesion strength between the optical thin film and the optical waveguide.

  An object of the present invention is to provide an optical device in which adhesion between a fluoride glass and an optical thin film is improved in an optical device on which an optical thin film is formed.

  As a result of intensive studies, the present inventors have found that when an optical thin film is formed on fluoride glass, the film adhesion is improved by forming the optical thin film on the surface of fluoride glass having a specific oxygen content. The present invention has been found to improve, and the present invention has been achieved.

  That is, in an optical device having a fluoride glass and an optical thin film, an optical thin film is formed on the surface of the fluoride glass containing oxygen within the range of 300 ppm to 5000 ppm by mass in the vicinity of the surface. An optical device is provided.

  Further, the fluoride glass is a fluoride glass optical waveguide, and the surface and the surface containing oxygen within the range of 300 ppm by mass to 5000 ppm by mass in the vicinity thereof are at least one of the fluoride glass optical waveguides. The optical device according to claim 1, wherein the optical device is an end face.

  According to the present invention, in an optical device in which an optical thin film is formed on fluoride glass, an optical device with improved adhesion of the optical thin film can be provided.

  The present invention is described in detail below.

  The optical device of the present invention can be obtained by forming an optical thin film on the surface of fluoride glass containing oxygen.

  The type of fluoride glass used is not limited with respect to the type thereof. For example, ZBLAN fluoride glass, Al-Zr fluoride glass (fluoride glass mainly composed of aluminum and zirconium), Al fluoride. Examples thereof include glass (fluoride glass mainly composed of Al).

  As a method of containing oxygen within the range of 300 ppm to 5000 ppm by mass on the surface of the fluoride glass and its vicinity, a thermal oxidation method in which heating is performed in the presence of oxygen, a method of irradiating the surface with oxygen ions or oxygen plasma, Although a method of leaving in an atmosphere in the presence of oxygen, a method of contacting with water, or the like can be used, the present invention is not limited to a method of containing oxygen.

The structure of the optical thin film formed on the surface of the fluoride glass containing oxygen within the range of 300 ppm to 5000 ppm in the vicinity of the surface is a film made of a high refractive index material or a low refractive index material Any one or a plurality of films made of these layers are laminated, such as Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , or ZnS as the high refractive index film, and SiO ₂ as the low refractive index film. And MgF ₂ .

  When the optical thin film is a single layer, an optical device such as a mirror or an optical component having a reflection suppressing function can be obtained.

When the optical thin film is an optical multilayer film having a laminated structure, the obtained optical device includes an ultra-wideband SWPF (short wave path filter), a notch filter, and the like. A combination of Ta ₂ O ₅ and SiO ₂ that does not change the film structure and optical characteristics even in film formation over time is suitable.

  As a film forming method for obtaining the optical device of the present invention, a general film forming method can be used, and the present invention is not limited to the film forming method.

For example, a film forming method such as an ion assist vapor deposition method, a plasma assist vapor deposition method, or an ion plate vapor deposition method that can obtain an optical multilayer film having excellent optical characteristics can be used. In these film-forming methods, it is necessary to increase the film-forming temperature, activate the vapor deposition material by ion or plasma irradiation, and form a high-density film while peeling the vapor-deposited material with weak adhesion from the substrate. . However, in film formation on the end face of an optical waveguide such as a fiber, if the film formation temperature is raised, degassing from the fiber coating resin may occur and absorption may occur in the film. Therefore, the substrate temperature during film formation is preferably 250 ° C. or less. However, when the substrate temperature is 250 ° C. or less, absorption of the formed film is likely to occur without the assistance of ions or plasma, and the refractive index is increased. May be low. In particular, when Ta ₂ O ₅ is used as the film material, the tendency is remarkable. Therefore, in forming the multilayer film, the substrate temperature is 50 to 250 ° C., preferably 100 to 230 ° C. or less, and ion or plasma assist is used in combination. Is preferred.

  By using the film forming method as described above, a film having high adhesion strength can be formed on the surface of a bulk fluoride glass that does not have an optical waveguide structure or on the end surface of the fluoride glass optical waveguide. In particular, an optical device such as a laser resonator mirror or an optical component having a non-reflective function can be obtained by forming a film on the surface of the optically polished bulk fluoride glass by using the film forming method as described above. it can.

  An optical thin film for forming a laser is formed on the input and output end faces of an optical waveguide made of fluoride glass containing oxygen in the range of 300 ppm to 5000 ppm by mass on and near the surface. By using the obtained optical device, the confinement effect of the excitation light and the laser light can be increased, so that a highly efficient laser can be configured. Furthermore, a laser may be configured using the optical device of the present invention as a mirror for reducing the interaction length.

  When using the fluoride glass optical waveguide comprised with fluoride glass, you may use what NA is contained in the range of 0.10-0.22 mentioned above.

When a fluoride glass optical waveguide is used as the fluoride glass to constitute the laser, the composition of the core material and the cladding material is, for example, ZrF ₄ is 53 ± 2 mol% and BaF ₂ is 21 ± 2 mol% in the case of ZBLAN glass. LaF ₃ is 0 to 4 mol%, AlF ₃ is 4 ± 2 mol%, YF ₃ is 2 ± 2 mol%, NaF ₃ is 18 ± 2 mol%, and trivalent rare earth fluorides other than La and Y are in the range of 0 to 4 mol%. , The core glass composition whose total is substantially 100 mol%, ZrF ₄ is 47 ± 8 mol%, HfF ₄ is 1 to 13 mol%, BaF ₂ is 21 ± 3 mol%, LaF ₃ is 3 ± 2 mol%, AlF ₃ clad There 4 ± 2mol%, YF ₃ is 2 ± 2 mol%, and the range NaF ₃ of 19 ± 3 mol%, the sum is substantially 100 mol% Las composition, in the case of Al-Zr glass, AlF ₃ is 28 ± 5mol%, ZrF ₄ is 13 ± 5mol%, BaF ₂ is 12 ± 2mol%, SrF ₂ is 13 ± 2mol%, CaF ₂ is 21 ± 2 mol% MgF ₂ is 4 ± 2 mol%, YF ₃ is 0 to 10 mol%, NaF is 2 ± 2 mol%, trivalent rare earth fluoride other than Y is in the range of 0 to 10 mol%, and the total is substantially 100 mol%. and one core glass composition, AlF ₃ is 30 ± 5mol%, ZrF ₄ is 0 to 5 mol%, HfF ₄ is 10 ± 5mol%, BaF ₂ is 11 ± 2mol%, SrF ₂ is 13 ± 2mol%, CaF ₂ is 20 Clad glass having a range of ± 2 mol%, MgF ₂ of 3 ± 2 mol%, YF ₃ of 9 ± 2 mol%, NaF of 4 ± 2 mol%, and the total thereof being substantially 100 mol% By combining the compositions, an NA (numerical aperture) in the range of 0.10 to 0.22 can be realized. Furthermore, a high-efficiency laser resonator can be configured by using these as a mirror of a laser resonator or a mirror including a light emitting medium.

  The trivalent rare earth fluoride is arbitrarily selected from, for example, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb, and contributes to light emission. It can be used as a rare earth element.

  The invention is disclosed in detail using the following examples.

[Examples 1-3, Comparative Examples 1-3]
In this example, the effect of the oxygen concentration on the fluoride glass surface is shown. Secondary ion mass spectrometry (SIMS) was used for oxygen concentration analysis. However, since quantitative analysis is difficult only by SIMS analysis, first a standard sample (fluoride bulk) with a known oxygen content is used. Glass, composition: ZrF ₄ (53.0) -BaF ₂ (22.0) -LaF ₃ (2.2) -AlF ₃ (3.5) -YF ₃ (2.0) -NaF ₃ (17.0 ) -PrF3 (0.3), the unit is mol%) to obtain a calibration curve. The oxygen content of the standard sample was measured in advance using the method described in Japanese Patent No. 3128027.

Next, six fluoride glasses whose surfaces were optically polished were prepared, and only five of them were irradiated with oxygen plasma for different times. Thereafter, SIMS analysis was performed based on the obtained calibration curve, and the oxygen concentration on the surface of the six fluoride glasses was measured. As a result, 150 mass ppm (no oxygen plasma irradiation), 210 mass ppm, 300 mass ppm, 2010 mass ppm. 4950 mass ppm and 6000 mass ppm. Thereafter, dielectric multilayer films (Ta ₂ O ₅ and SiO ₂ , total 20 layers, total film thickness 1 μm) are formed on each glass surface, cut into 5 × 5 mm squares, and each 100 sheets (600 sheets in total) A dielectric multilayer filter was obtained. A tape peeling test based on JIS D0202-1988 was performed using the obtained dielectric multilayer filter.
In the tape peeling test, CT-24 manufactured by Nichiban was used, and it was pressed with the belly of a finger to adhere closely to the film formation surface, and then the tape was peeled off to visually confirm the film peeling. The case where film peeling occurred at the edge portion was regarded as defective, and the case where film peeling did not occur at the edge portion was regarded as good.

As a result, in the dielectric multilayer filter (Comparative Example 1) having an oxygen concentration of 150 mass ppm, the film is peeled off at the edge portion of 12 out of 100 sheets (film peeling rate is 12%), and the dielectric multilayer film having an oxygen concentration of 210 mass ppm In the filter (Comparative Example 2), about 11 out of 100 sheets, the film peeled off at the edge (film peeling rate 11%), oxygen concentration 300 mass ppm (Example 1), 2010 mass ppm (Example 2), 4950 mass ppm. In the dielectric multilayer filter of (Example 3), the film peels off at the edge portion (film peeling rate 3%) for 3 out of 100 sheets, and 5 out of 100 sheets in the filter with oxygen concentration of 6000 mass ppm (Comparative Example 3). The film peeled off at the edge of the sheet (film peeling rate 5%).
The film peeling rate of the filter having an oxygen concentration of 210 mass ppm is almost the same as that of the filter having an oxygen concentration of 150 mass ppm (no oxygen plasma irradiation), and no improvement in the film adhesion strength due to the formation of the oxygen-containing layer is observed. In the filter having an oxygen concentration of 6000 mass ppm, the film peeling rate is increased. As described above, it is better to avoid oxidizing the fluoride glass surface more than necessary. Therefore, it is desirable that the oxygen concentration on the surface of the fluoride glass is 300 mass ppm to 5000 mass ppm.
[Example 4, Comparative Example 4]
First, ZBLAN glass fiber (core composition: ZrF ₄ (53.0) -BaF ₂ (22.0) -LaF ₃ (2.2) -AlF ₃ (3.5) -YF ₃ (2.0) -NaF ₃ (17.0) -PrF ₃ (0.3), Cladding composition: ZrF ₄ (40.0) -BaF ₂ (18.0) -LaF ₃ (4.0) -AlF ₃ (3.0)- NaF ₃ (22.0) -HfF ₄ (13.0), the unit is mol%), and the fiber was cleaved every 10 cm in length to obtain 200 fibers. The cleaved surface was confirmed to be flat by an optical microscope image. Half of the 100 cleaved end faces were irradiated with oxygen plasma under the same conditions as in Example 2. Therefore, the oxygen concentration on the surface of the fluoride glass is 150 mass ppm at the fiber end face not irradiated with oxygen plasma and 2010 mass ppm at the fiber end face irradiated with oxygen plasma.

Dielectric multilayer films (Ta ₂ O ₅ and SiO ₂ , total 20 layers, total film thickness 1 μm) are formed on all 100 cleaved end faces of each of the two types of fibers, and a dielectric is formed on the end face having an oxygen concentration of 2010 mass ppm. 100 fibers (Example 4) obtained by molding the multilayer film and 100 fibers (Comparative Example 4) obtained by molding the dielectric multilayer film on the end face having an oxygen concentration of 150 ppm by mass were obtained. A tape peeling test was performed using 200 obtained fibers.

  In the tape peeling test, CT-24 manufactured by Nichiban was used and pressed with the belly of the finger to adhere to the film formation surface, and then the tape was peeled off and the film peeling was confirmed with an optical microscope. The case where film peeling occurred at the edge portion was regarded as defective, and the case where film peeling did not occur at the edge portion was regarded as good. Fibers not irradiated with oxygen plasma (Comparative Example 4) 12 out of 100 fibers peeled off at the edge (film peeling rate 12%), whereas fibers irradiated with oxygen plasma (Example 4) 100 The film peeling of the edge portion occurred in three of the books (film peeling rate of 3%). As described above, the oxygen concentration of the end surface before forming the dielectric multilayer film is increased to 2010 mass ppm by the irradiation of oxygen plasma, so that the adhesion strength of the dielectric multilayer film is increased.

By obtaining an optical device with improved adhesion strength of optical thin film to fluoride glass, a low-loss resonator can be realized, a high-power laser can be constructed, and a high-strength AR coating can be constructed. It can also be applied to all optical devices using fluoride glass, such as laser television, laser projection, laser microscope light source, ultrashort pulse light source, infrared light source, terahertz light source.

Claims (2)

In an optical device having fluoride glass and an optical thin film, an optical thin film is formed on the surface of the fluoride glass containing oxygen within the range of 300 ppm to 5000 ppm by mass in the vicinity of the surface. An optical device characterized by that. The fluoride glass is a fluoride glass optical waveguide, and the surface containing oxygen within the range of 300 ppm to 5000 ppm by mass in the vicinity thereof is at least one end face of the fluoride glass optical waveguide. The optical device according to claim 1, wherein: