JP2013072984A - Glass polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass polarizer having a high extinction ratio, low insertion loss and a low phase difference in a wide band.SOLUTION: A method for manufacturing a glass polarizing element comprises: a melting step of melting glass adjusted so that a glass component after melting the glass contains silver ions of 0.2-0.3 wt.% and chlorine ions of 0.25-0.35 wt.%; a silver chloride depositing step of uniformly depositing silver chlorides inside the melted glass by heat-treatment at a temperature lower by 10-50°C than the softening point of the glass; a preform manufacturing step of processing the glass into a desired size; a drawing step of heating and drawing the preform and elongating the silver chloride particles in an uniaxial direction to form a glass sheet; and a reduction step of reducing the elongated silver chlorides in the glass sheet under a pressure equal to or less than the atmospheric pressure.

Description

  The present invention relates to a glass polarizing element and a method for manufacturing the same. In particular, the present invention relates to a glass polarizing element having polarization characteristics that can be industrially used for light in the near infrared region.

  An optical communication isolator is an important device used to block the return light due to reflection and improve the S / N ratio. The isolator is composed of a Faraday rotator, two polarizers, and a magnet. However, since high reliability is required, high performance and miniaturization have been advanced recently, and the demand for polarizers is also increasing.

  However, for example, in a birefringent crystal or a polarizing beam splitter, the thickness of the polarizer cannot be made thinner than the effective beam diameter. In addition, a polarizer of a type obtained by stretching a dichroic polymer cannot realize a sufficient extinction ratio and is inferior in environmental resistance.

  As a polarizer capable of realizing high reliability, a glass polarizer using a polarization characteristic caused by surface plasmon resonance by stretching nano metal particles such as silver and copper in a uniaxial direction can be mentioned. Such glass polarizers are widely used in optical communication isolators because they can obtain a high extinction ratio and can realize environmental resistance.

  The glass polarizer melts and molds a glass batch composed of silver and at least one halide composed of chloride, bromide and iodide. Next, the molded glass is subjected to a heat treatment to precipitate silver halide grains. The glass is stretched under an appropriate tension, and the silver halide grains are stretched and aligned in the tension direction. Finally, the elongated silver halide grains are heat-treated in a reducing atmosphere to precipitate the silver grains, thereby obtaining a glass polarizer (Patent Documents 1, 2, 3, 4, 5).

  The glass polarizer produced by the above production method is an excellent polarizer having an extinction ratio of 50 dB or more and having excellent environmental resistance.

  On the other hand, with the increase in communication capacity, wavelength division multiplex communication in which a plurality of wavelengths are simultaneously loaded as optical signals has become mainstream. Since light of various wavelengths is used, the performance of signal lasers and pump lasers has dramatically increased, and the performance requirements for isolators have become severe. In particular, it is required to reduce the insertion loss of the isolator and widen the wavelength region showing the polarization characteristics.

  As a method for reducing the insertion loss of the isolator, for example, as shown in Patent Document 6, there is a method of adjusting the halide content, but even with this method, the insertion loss can be reduced only to 0.04 dB.

  Patent Documents 7 and 8 disclose polarizers in which the wavelength region exhibiting polarization characteristics is expanded. In Patent Document 7, although it is a wide band, the extinction ratio is 40 dB or more, and the extinction performance is inferior. Patent Document 8 discloses a glass polarizer having an extinction ratio of 50 dB or more and a wavelength band of 600 nm or more. However, these use a special technique of high pressure for reduction, which is problematic from the viewpoint of safety and cost. In addition, there is no description about the insertion loss, and the insertion loss is about the same as the conventional one.

JP-A-2-248341 Japanese Patent Laid-Open No. 5-208844 JP 2007-171982 JP 2004-086100 A JP 2010-150132 A JP-A-9-86956 Special Table 2003-517634 JP 2010-204677 A

  In communication systems, noise reduction on the time axis as well as insertion loss is an important issue. In order to reduce noise on the time axis, the stability of the laser is the most important factor, and improvement in isolation performance is required. The isolation performance is generally determined by the quenching performance of garnet and glass polarizer. However, glass, which is an isotropic medium, develops optical anisotropy by stretching in a uniaxial direction like a glass polarizer. Further, the precipitation of uniaxially stretched silver chloride grains adds even greater optical anisotropy.

Optical anisotropy causes a phase difference when polarized light passes through a glass polarizer. When the phase difference occurs, the linearly polarized light becomes elliptical and the quenching performance is lowered. The phase difference is defined by the following equation and depends on the difference between n ₀ (ordinary refractive index) and n _e (extraordinary refractive index) and the optical path length d.

  Therefore, it is necessary to make the phase difference as small as possible for the stability of the laser. However, in order to compensate for the decrease in the extinction performance due to the phase difference, the glass polarizer currently on the market increases the absorption area by increasing the particle diameter, and realizes an extinction performance that has no problem as an isolator. Its extinction ratio is at least 60 dB. For this reason, light scattering by large particles cannot be avoided, and low insertion loss has not been realized. In addition, large particles cause a large phase difference, and the insertion loss due to the ovalization of polarized light is one factor that cannot achieve a low insertion loss.

  Under the background as described above, an object of the present invention is to provide a glass polarizer having a wide band, a high extinction ratio, a low insertion loss, and a low phase difference.

  In order to solve the above-mentioned problems, the present inventors manufactured glass compositions having various silver ion and chloride ion concentrations, heat-treated at various temperatures, and precipitated silver chloride particles, so that the quenching performance and insertion loss were reduced. As a result of examining the phase difference and the bandwidth, a region satisfying all of the quenching performance, the insertion loss, the phase difference and the bandwidth at a certain concentration was discovered, and further studies were made to complete the present invention.

That is, the present invention provides the following glass polarizer.
(1) A glass polarizer having an extinction ratio of 50 dB or more in a wide range of 1260 to 1630 nm, an insertion loss of 0.015 dB or less, and a retardation in the thickness direction of λ / 2 or less.
(2)
In the manufacturing method of the glass polarizing element,
A melting step of adjusting the glass components after melting to 0.2 to 0.3% by weight of silver ions and 0.25 to 0.35% by weight of chlorine ions to melt the glass;
A silver chloride precipitation step of heat-treating the molten glass at a temperature lower by 10 to 50 ° C. than the softening point to uniformly precipitate silver chloride;
A preform manufacturing process for processing the glass into a desired size;
A stretching step in which the preform is heated and stretched to form a glass sheet by stretching the silver chloride particles in a uniaxial direction;
The glass polarizer manufactured by the reduction | restoration process which reduces the extended | stretched silver chloride in the said glass sheet at the pressure below atmospheric pressure.

As described above, in the present invention, silver ions in the glass composition after melting are adjusted to 0.2 to 0.3% by weight and chloride ions to 0.25 to 0.35% by weight, and 10 to 50 from the softening point. By performing heat treatment at a temperature as low as ° C, uniform silver chloride of 300 nm or less can be deposited. This particle size suppresses the influence of Rayleigh scattering, and can achieve a quenching performance of 50 dB or more even in reduction under atmospheric pressure. Furthermore, since the particle diameter is kept small, the phase difference can be reduced and a low insertion loss can be realized. In addition, it is possible to produce a broadband polarizer by performing stretching at an appropriate temperature of 10 ⁸ Woise or more. Although a large stretching tension of 300 kgf / cm ² or more is required, by processing the preform surface to 20 to 100 nm with Ra roughness, the frictional force with the roller increases and the slip during stretching is remarkably reduced. It is possible to greatly reduce the damage. Moreover, the tension can be uniformly transmitted to the entire surface of the tape by increasing the frictional force.

  The content of silver ions and chloride ions and the heat treatment temperature in the present invention will be described in detail. The content of silver ions and chloride ions greatly affects the extinction ratio insertion loss and phase difference. If the content is large, the extinction ratio tends to be high, but the insertion loss and the phase difference increase. In addition, silver is precipitated at the time of melting, and it becomes difficult to deposit uniform silver chloride particles. On the contrary, if the concentration of silver ions and chloride ions is small, the insertion loss and the phase difference are lowered, but it is difficult to obtain a high extinction ratio.

  Similarly to these contents, the silver chloride particle diameter greatly affects the extinction ratio insertion loss and the phase difference. The particle diameter of silver chloride increases as the heat treatment temperature increases and the heat treatment time increases, and the particle diameter decreases as the heat treatment temperature decreases and the heat treatment time decreases. Larger particle diameters tend to increase the extinction ratio, but increase insertion loss and phase difference. On the contrary, if the particle diameter is small, the insertion loss and the phase difference are reduced, but it is difficult to obtain a high extinction ratio, and the band showing the polarization characteristics is shifted to the short wavelength side and the bandwidth is narrowed. When heat treatment is performed at a temperature exceeding 10 ° C lower than the softening point, it is possible to achieve a low insertion loss of less than 0.015 dB by increasing the particle size, no matter how much the content of silver ions and chloride ions is reduced. It becomes impossible. In addition, if the heat treatment temperature is 50 ° C. or more lower than the softening point, the particle size becomes too small, and the wavelength region exhibiting polarization characteristics becomes shorter than the communication wavelength region even when stretched with a large tension. . Accordingly, the heat treatment is preferably performed at a temperature below the softening point, preferably at least 10 ° C. lower than the softening point and 50 ° C. lower than the softening point.

  When heat treatment is performed in the above temperature range, the silver ion concentration is adjusted to 0.2 to 0.3 by weight%, and the chloride ion is adjusted to 0.25 to 0.35 by weight%. When the silver ion concentration is less than 0.2% by weight and the chloride ion is less than 0.25% by weight, a high extinction ratio of 50 dB or more cannot be realized over the entire band of 1260 to 1630 nm. On the other hand, when the silver ion concentration exceeds 0.3 by weight% and the chloride ion exceeds 0.35 by weight%, the insertion loss becomes about 0.02 dB, and a high extinction ratio cannot be realized.

When stretching small particles, a large tension is required, so that damage due to slippage during stretching becomes a big problem. Since the preform manufactured under the above conditions requires a stress of at least 300 kgf / cm ² or more, the possibility of breakage increases. Therefore, the preform surface is adjusted to 20 to 100 nm, preferably 40 to 70 nm in terms of Ra in order to prevent breakage due to slip and transmit the tension uniformly. By stretching such a preform with a viscosity of 10 ⁸ Woise or more, it has an extinction ratio of 50 dB or more in a wide range of 1260 to 1650 nm, an insertion loss of 0.015 dB or less, and a retardation in the thickness direction of λ / 2. A glass polarizer characterized by the following can be obtained.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to these examples.

  Create a glass block containing multiple silver ions and chloride ions so that the content of silver ions is 0.08 to 0.4% by weight and chloride ions are 0.1 to 0.5% by weight. did.

  Next, these glasses were molded to 60 × 300 × 4.0 mm and subjected to heat treatment at a temperature from a softening point of −60 ° C. to a softening point to precipitate silver chloride grains. Both sides of this silver chloride-containing glass molding were ground so that the thickness was 2.3 mm. At this time, the surface roughness Ra was adjusted to 50 nm.

The produced preform was stretched with a tension of 300 to 600 kgf / cm ² depending on the heat treatment temperature. At this time, the temperature and the stretching speed were adjusted so that the width of the stretched tape was 26 mm.

  The produced stretched tape was cut into a size of 26 × 21 and optically polished so that the thickness was 0.5 mm and the flatness was λ or less.

  The glass molding was adjusted to a hydrogen reduction furnace so that the hydrogen partial pressure was 420 ° C. and 0.012 MPa, reduced for 8 hours, and then AR coated on both sides to produce a glass polarizer.

The obtained glass polarizer was measured for the extinction ratio and insertion loss using a laser light source, a Glan-Thompson prism, and a multimeter. In addition, the phase difference from 400 to 1100 nm was measured with a retardation measuring device, and the phase differences at 1260, 1430, and 1630 nm were calculated by extrapolation. The results are shown in Table 1.

  As described above, by appropriately adjusting the content of silver ions and chloride ions and the heat treatment temperature, it is possible to provide a glass polarizer having a wide band with a high extinction ratio, a low insertion loss, and a low phase difference. It becomes possible.

Claims (2)

  A glass polarizer characterized by having an extinction ratio of 50 dB or more, light having an insertion loss of 0.015 dB or less, and retardation in the thickness direction of λ / 2 or less with respect to light in the wavelength range of 1260 to 1630 nm. . In the manufacturing method of the glass polarizing element,
A melting step of adjusting the glass components after melting to 0.2 to 0.3% by weight of silver ions and 0.25 to 0.35% by weight of chlorine ions to melt the glass;
A silver chloride precipitation step of heat-treating the molten glass at a temperature lower by 10 to 50 ° C. than the softening point to uniformly precipitate silver chloride;
A preform manufacturing process for processing the glass into a desired size;
Heating and stretching the preform, and stretching the silver chloride particles in a uniaxial direction to form a glass sheet;
The glass polarizer of Claim 1 manufactured by the reduction | restoration process reduce | restored the extended | stretched silver chloride in the said glass sheet at the pressure below atmospheric pressure.