JP4868311B2 - Faraday rotator for short wavelength light and optical isolator equipped with the Faraday rotator - Google Patents

Description

  The present invention relates to a Faraday rotator that is capable of suppressing a temperature rise due to light absorption when short-wavelength light is incident and is thinned, and an optical isolator including the Faraday rotator.

  An optical isolator is an irreversible optical device that allows light to pass in one direction and prevents light from passing in the opposite direction. For example, in an optical communication system using a semiconductor laser as a light source, an optical signal is reflected by reflection. Used to prevent returning to the light source side. In general, such an optical isolator includes a Faraday rotator, two polarizers, and a permanent magnet. Faraday rotators used for optical isolators in the near-infrared wavelength region (1310 nm to 1550 nm) commonly used in optical communications include bismuth-substituted rare earth iron garnet single crystals (hereinafter referred to as “garnet single crystals” ")") Is used.

  Furthermore, with the development of optical communication, optical fiber amplifiers are attracting attention as a technique for amplifying optical signals in the near infrared wavelength region. For example, an optical fiber amplifier using 1017 nm band pumping is used for an optical signal in the 1310 nm band, and an optical fiber amplifier pumping using 980 nm band is used for an optical signal in the 1550 nm band. For this purpose, an optical isolator near 1000 nm is required for the 980 nm band and the 1017 nm band.

  Alternatively, a laser with a wavelength between 1030 nm and 1090 nm is used as an optical sensor or a light source for precision processing, and in order to prevent return light to this light source, it is considered to install an optical isolator on the light source side. Has been.

  The aforementioned bismuth-substituted rare earth iron garnet single crystal has a remarkably large Verde constant per unit length. Therefore, by applying the bismuth-substituted rare earth iron garnet single crystal to the Faraday rotator, the optical isolator can be significantly reduced in size. Is possible. However, in the bismuth-substituted rare earth iron garnet single crystal having a lattice constant of about 12.50 mm, the absorption of Fe trivalent having a peak near 900 nm has spread to more than 1000 nm, so the light absorption is large in the wavelength region near 1000 nm. Become. Therefore, when a bismuth-substituted rare earth iron garnet single crystal is used for an optical isolator used for a light source having a wavelength shorter than the near infrared wavelength region, the garnet single crystal is likely to absorb light. Furthermore, the absorbed light is converted into heat, which causes a large temperature rise in the light transmission part of the garnet single crystal. This temperature rise changes the Faraday rotation angle of the garnet single crystal, which causes problems such as deterioration of the extinction ratio of the optical isolator and deterioration of reliability due to thermal damage.

  In order to solve such problems, a Faraday rotator in which a paramagnetic garnet substrate is provided on at least one surface of a bismuth-substituted rare earth iron garnet single crystal and an optical isolator using such a Faraday rotator have been devised. (For example, see Patent Documents 1, 2, and 3).

JP-A 2000-66160 (page 3-5, FIG. 1) Patent 3472339 (4th page, Fig. 1) JP 2006-30442 (page 2-6, Fig. 2)

  An example of an optical isolator using the above-described garnet single crystal with a garnet substrate is shown in FIG. The optical isolator 100 of FIG. 20 uses a bismuth-substituted rare earth iron garnet single crystal film 101 (hereinafter referred to as “garnet single crystal film 101”) manufactured by the LPE method as a Faraday rotator, and this garnet single crystal film. A structure in which a paramagnetic garnet substrate 102 is left on one side of 101 is disposed between a polarizer 103 and another polarizer 104 (analyzer).

Further, a polarizer 103 is in close contact with the other surface of the garnet single crystal film 101. The garnet substrate 102 is desirably as transparent as possible in the wavelength range of light to be transmitted. In Patent Document 1, a lattice constant having Gd as a host rare earth element as a SGGG substrate is 1.2490 nm to 1.2515 nm. Paramagnetic garnet [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] is selected (see paragraph (0014) of Patent Document 1). Since the lattice constant of the garnet single crystal 101 grown on the garnet substrate 102 having such a lattice constant of 1.2490 nm to 1.2515 nm depends on the lattice constant of the garnet substrate 102 which is the growth substrate, it is in the range of about 12.49 to 12.51 mm. It will be around 12.50mm as expressed.

Patent Document 2 teaches that Gd ₃ Sc ₂ Ga ₃ O ₁₂ having Gd as a host rare earth element is used for the garnet substrate (see paragraph (0020) of Patent Document 2). Teaches the use of gadolinium gallium garnet (GGG) (see (Claim 1) of Patent Document 3).

  The above Patent Documents 1 to 3 all have a basic technical idea that heat generated in a garnet single crystal is conducted to a garnet substrate and radiated to the outside of the garnet single crystal. Therefore, it has not been considered to reduce the amount of heat generated in the magneto-optical element having the Faraday effect (in the above Patent Documents 1 to 3 garnet single crystal). Since the paramagnetic garnet substrate taught in Patent Documents 1 to 3 using Gd as a host rare earth element has almost no Faraday effect, it is virtually impossible to make this garnet substrate function as a Faraday rotator. Met.

  Thus, various paramagnetic garnet single crystals having Tb as a host rare earth element have been devised as Faraday rotators that have the Faraday effect but have very high light transmittance and little light absorption (for example, Patent Document 4). 5).

Japanese Patent Laid-Open No. 2001-51236 (page 2-4, FIG. 1) WO2004 / 29339

Patent Document 4 includes a Faraday rotator formed of a Tb ₃ Ga ₅ O ₁₂ (hereinafter referred to as “TGG”) single crystal as a paramagnetic garnet single crystal having Tb as a host rare earth element. An optical isolator is taught. Since TGG single crystal has a light transmittance of over 99%, the forward insertion loss and light absorption are extremely low. Therefore, when the TGG single crystal is used as a Faraday rotator, the amount of heat generated inside the Faraday rotator can be reduced.

Further, “Background Art” of Patent Document 5 teaches a terbium-aluminum-based paramagnetic garnet single crystal (Tb ₃ Al ₅ O ₁₂ : hereinafter “TAG”). TAG single crystals have a large Verde constant compared to other paramagnetic garnet single crystals and provide a sufficiently high light transmittance (over 99%) over a wide wavelength range of 500 nm to 1400 nm. It is also a preferable single crystal material.

  However, the paramagnetic garnet single crystal having Tb as the host rare earth element has a problem that the thickness becomes very large because the Verde constant is much smaller than that of the bismuth-substituted rare earth iron garnet single crystal. In particular, when the paramagnetic garnet single crystal is used for an optical isolator, a Faraday rotation angle of 45 degrees is required. Therefore, the thickness of the Faraday rotator is required to be 10 mm (1 cm) or more, and the optical isolator becomes large. TAG single crystal has the largest Verde constant among paramagnetic garnet single crystals, but the Verde constant when transmitting light with a wavelength of 633 nm is about 0.01 deg / (Oe · cm) even though it is large. . From this point of view, it is concluded that a paramagnetic garnet single crystal having a practical size as a Faraday rotator has not yet been obtained.

  The present invention has been made in view of the above problems, and its purpose is to use the thickness of a paramagnetic garnet single crystal having almost no light absorption Tb as a host rare earth element for a Faraday rotator while suppressing light absorption. It is to realize a Faraday rotator and an optical isolator that can be used for a light source in a relatively short wavelength range than the near-infrared wavelength range by making it as thin as possible.

The Faraday rotator for short wavelength light according to claim 1 of the present invention comprises a paramagnetic garnet single crystal,
Including bismuth-substituted rare earth iron garnet single crystal,
The paramagnetic garnet single crystal has Tb as a host rare earth element, and has a light transmittance of more than 99% for light in a wavelength region of 1030 nm or more and 1090 nm or less,
The paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal rotate the plane of polarization of incident light, and the Faraday rotation directions of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal, respectively. Are set in the same direction when viewed from the light propagation direction,
A magnetic field that sets the total Faraday rotation angle of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal to 45 degrees is applied to the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, applied to the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal by a permanent magnet,
When the wavelength of the light incident on the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal is λ (nm), λ is set to a wavelength condition of 1030 nm or more and 1090 nm or less,
The bismuth-substituted rare earth iron garnet single crystal is provided on at least one side of the paramagnetic garnet single crystal ,
The total thickness of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal
The total is less than 1cm,
The Faraday rotator for short wavelength light, wherein the paramagnetic garnet single crystal has a thickness of 5 mm or more .

Furthermore, in the Faraday rotator for short wavelength light according to claim 2 , the paramagnetic garnet single crystal has a chemical formula of Tb ₃ Ga ₅ O ₁₂ , Tb ₃ Al ₅ O ₁₂ , or Tb ₃ Sc ₂ Ga ₃ O ₁₂ . The Faraday rotator for short wavelength light according to claim 1 , having the composition shown.

Further Faraday rotator for short wavelength light according to claim 3, wherein the bismuth-substituted rare earth iron garnet single crystal in lattice constant, according to claim 1 or 2, characterized in that it is set below 12.56Å more and 12.58Å The Faraday rotator for short wavelength light described in 1.

Furthermore, the Faraday rotator for short wavelength light according to claim 4 is:
Two bismuth-substituted rare earth iron garnet single crystals are provided;
The Faraday rotation directions of the two bismuth-substituted rare earth iron garnet single crystals and the paramagnetic garnet single crystal are set in the same direction when viewed from the light propagation direction,
Furthermore, a magnetic field that sets the total Faraday rotation angle of the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals to 45 degrees is
Applied to the bismuth-substituted rare earth iron garnet single crystal ,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, and is applied to the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals by a permanent magnet;
Thickness of the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals
The sum of the total is less than 1cm,
Claims 1 to 3, wherein the thickness of the paramagnetic garnet single crystal is not less than 5mm
The Faraday rotator for short wavelength light according to any one of the above.

Further, the Faraday rotator for short wavelength light according to claim 5 is:
Two Faraday rotators for short-wavelength light configured by providing the bismuth-substituted rare earth iron garnet single crystal on one side of the paramagnetic garnet single crystal, arranged in the light propagation direction,
The Faraday rotation directions of the two bismuth-substituted rare earth iron garnet single crystals and the two paramagnetic garnet single crystals are set in the same direction when viewed from the light propagation direction,
Furthermore, the magnetic field that sets the total Faraday rotation angle of the two paramagnetic garnet single crystals and the two bismuth-substituted rare earth iron garnet single crystals to 45 degrees includes two paramagnetic garnet single crystals and two Of the bismuth-substituted rare earth iron garnet single crystal ,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, and is applied to the two paramagnetic garnet single crystals and the two bismuth-substituted rare earth iron garnet single crystals by a permanent magnet;
Two single paramagnetic garnet single crystals and two single bismuth-substituted rare earth iron garnets
The total crystal thickness is less than 1 cm,
Two of the Faraday rotator for short wavelength light according to any one of claims 1 to 3, characterized in that the total thickness of the paramagnetic garnet single crystal is not less than 5 mm.

Furthermore, the Faraday rotator for short wavelength light according to claim 6 is:
Claim 4 wherein the bismuth-substituted rare earth iron garnet single crystal which is arranged on the incident side of the light, characterized in that said Faraday rotation angle than the other one of said bismuth-substituted rare earth iron garnet single crystal is smaller Or a Faraday rotator for short wavelength light as described in 5 above.

Furthermore, the Faraday rotator for short wavelength light according to claim 7 is:
Among both surfaces of the bismuth-substituted rare earth iron garnet single crystal, a paramagnetic net substrate having Gd or Y as a host rare earth element is provided on one side opposite to the one side on which the paramagnetic garnet single crystal is provided,
The garnet substrate has a thermal conductivity of 5 W / m · K or more.
6. The Faraday rotator for short wavelength light according to any one of 6 .

Further, the Faraday rotator for short wavelength light according to claim 8 is:
Among both surfaces of the bismuth-substituted rare earth iron garnet single crystal, a light transmission plate is provided on one side opposite to the one side on which the paramagnetic garnet single crystal is provided,
The light transmitting plate is short according to any one of claims 1 to 6, characterized in that it is formed of a material having more than four times the thermal conductivity of the thermal conductivity of the bismuth-substituted rare earth iron garnet single crystal This is a Faraday rotator for wavelength light.

Furthermore, the Faraday rotator for short wavelength light according to claim 9 is:
The light transmission plate is made of a single crystal, and the light transmission plate is made of the bismuth-substituted rare earth so that the optical isotropic axis of the single crystal is perpendicular to the optical surface of the bismuth-substituted rare earth iron garnet single crystal. 9. The Faraday rotator for short wavelength light according to claim 8 , wherein the Faraday rotator for short wavelength light is provided on one side of an iron garnet single crystal.

Furthermore, the Faraday rotator for short wavelength light according to claim 10 ,
The Faraday rotator for short wavelength light according to claim 7 , wherein the thickness of the garnet substrate is set to 1 mm or more.

Furthermore, the Faraday rotator for short wavelength light according to claim 11 ,
2. The short wavelength light Faraday rotator is applied to a side surface of the short wavelength light Faraday rotator which is a non-light transmitting surface, and the short wavelength light Faraday rotator is bonded to a Peltier element or a heat sink. The Faraday rotator for short wavelength light according to any one of 1 to 10 .

The Faraday rotator for short wavelength light according to claim 12 is:
The metal layer is formed on a side surface of the Faraday rotator for short wavelength light which is a non-light transmitting surface, and the Faraday rotator for short wavelength light is bonded to a Peltier element or a heat sink by soldering. The Faraday rotator for short wavelength light according to any one of 1 to 10 .

Further, the Faraday rotator for short wavelength light according to claim 13 is:
The Faraday rotator for short wavelength light, which is a non-light transmitting surface, is provided with a gold film on the side surface of the Faraday rotator for short wavelength light, and the Faraday rotator for short wavelength light is pressure bonded to the Peltier element or heat sink by thermocompression bonding. The Faraday rotator for short wavelength light according to any one of claims 1 to 10 .

The invention as set forth in claim 14
11. An optical isolator comprising the polarizer on the light incident side and the light emitting side of the Faraday rotator for short wavelength light according to any one of claims 1 to 10 .

The invention as set forth in claim 15
Of the Faraday rotator for short wavelength light according to any one of claims 11 to 13, an optical isolator formed by arranging a polarizer on the incident side and the exit side of the light.

Furthermore, the optical isolator according to claim 16 comprises:
Each side surface which is a non-light transmitting surface of the Faraday rotator for short wavelength light and the polarizer is held by a holder formed of a material having a thermal conductivity of 15 W / mK or more,
The optical isolator according to claim 14 , wherein the bismuth-substituted rare earth iron garnet is connected to a Peltier element or a heat sink via the holder.

Furthermore, the optical isolator according to claim 17 comprises:
Claim a thermosetting resin is applied to the side of the Faraday rotator for short wavelength light which is a non light transmitting surface, a Faraday rotator for the short wavelength light to said holder, characterized in that it is bonded 16
It is an optical isolator as described in above.

An optical isolator according to claim 18 is provided.
The metal layer is formed on the side surfaces of the Faraday rotator for short wavelength light which is a non light transmitting surface, to claim 16, characterized in that the Faraday rotator for the short wavelength light is joined by soldering to the holder It is an optical isolator of description.

An optical isolator according to claim 19 is provided.
The Faraday rotator for short wavelength light is provided on the side surface of the Faraday rotator for short wavelength light which is a non-light transmitting surface, and the Faraday rotator for short wavelength light is pressure bonded to the holder by thermocompression bonding the gold film. The optical isolator according to claim 16 .

Furthermore, the optical isolator according to claim 20 comprises:
The thermosetting resin is applied to the holder, the holder to the Peltier element or heat sink is a light isolator according to any one of claims 16 to 19, characterized in that it is bonded.

An optical isolator according to claim 21 is provided.
The metal layer is formed on the holder, an optical isolator according to any one of claims 16 to 19, wherein the holder by soldering to the Peltier element or heat sink is characterized in that it is joined.

The optical isolator according to claim 22 is an optical isolator.
The optical isolator according to any one of claims 16 to 19 , wherein a gold film is provided on the holder, and the holder is pressure-bonded to the Peltier element or a heat sink by thermocompression-bonding the gold film. is there.

Furthermore, the optical isolator according to claim 23 ,
Cross-sectional shape of the holder in the direction perpendicular to the propagation direction of the light, rectangular, concave, in the optical isolator according to any one of claims 16 to 22, characterized in that either the flat-plate is there.

The optical isolator according to claim 24 , further comprising:
The optical isolator according to any one of claims 16 to 23 , wherein a filler made of a material having thermal conductivity is filled in contact with the Faraday rotator for short wavelength light and the holder. It is.

Furthermore, the invention according to claim 25 provides
25. The Faraday for short wavelength light according to any one of claims 1 to 24 , wherein the Faraday rotator for short wavelength light or the optical isolator is used under a temperature condition of -10 degrees or more and 80 degrees or less. It is a rotor or an optical isolator.

According to the Faraday rotator for short-wavelength light according to claim 1 or 2 of the present invention, by using a paramagnetic garnet single crystal having Tb as a host rare earth element and a light transmittance of more than 99%, 1030 nm or more And light absorption for light below 1090nm can be suppressed to almost nothing,
By providing a paramagnetic garnet single crystal with a bismuth-substituted rare earth iron garnet single crystal with a large Verde constant, the insufficient rotation angle of the Faraday rotation angle of the paramagnetic garnet single crystal with a small Verde constant relative to 45 degrees is reduced. It can be compensated by the Faraday rotation angle of the garnet single crystal. Therefore, the paramagnetic garnet single crystal can be made thinner by the Faraday rotation angle of the bismuth-substituted rare earth iron garnet single crystal. Therefore, it is possible to realize a Faraday rotator that can be used for a light source having a wavelength of 1030 nm or more and 1090 nm or less that has a relatively short wavelength and a high power in the near infrared wavelength region.
Furthermore, it is possible to further increase the Faraday rotation angle of the paramagnetic garnet single crystal by applying a magnetic field of 2000 Oe or more and 3000 Oe or less to the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal. Therefore, the Faraday rotation angle of the bismuth-substituted rare earth iron garnet single crystal can be decreased by the amount of increase in the Faraday rotation angle of the paramagnetic garnet single crystal. The thickness can be reduced by the amount of decrease. In this way, by reducing the thickness of the bismuth-substituted rare earth iron garnet single crystal where light absorption occurs, it is possible to reduce the thickness of the paramagnetic garnet single crystal and further suppress the light absorption of the entire Faraday rotator. Become. Further, by setting the upper limit value of the magnetic field to 3000 Oe, it is possible to prevent the permanent magnet from becoming large.
Further, the Faraday rotator can be downsized even if a paramagnetic garnet single crystal is used.

Furthermore, according to the Faraday rotator for short-wavelength light according to claim 3 , by setting the lattice constant of the garnet single crystal in the range of 12.56 mm to 12.58 mm, light transmission associated with light absorption is achieved. The wavelength band at which the loss reaches a peak shifts to a shorter wavelength band than the peak wavelength band of a garnet single crystal having a lattice constant of about 12.50 mm around the conventional one. Along with this shift, the light transmission loss of the garnet single crystal in the wavelength range of 1030 nm and below 1090 nm is reduced, the amount of light absorption in the garnet single crystal is also reduced, and the amount of heat converted from the absorbed light is reduced. Further, the temperature increase of the garnet single crystal is further suppressed.

Furthermore, according to the Faraday rotator for short wavelength light according to claims 4 to 6 , it is possible to disperse the amount of heat generated by light absorption by dividing the garnet single crystal into two. . Furthermore, since the thickness of each garnet single crystal can be reduced, the amount of light absorption in each garnet single crystal is reduced, and the temperature increase of each garnet single crystal can be further suppressed. .

  When a plurality of garnet single crystals are provided, the optimum number is two. The reason for this is to reduce the ease of assembly and cost, and if it is set to 3 or more, the number of optical elements increases excessively, making it difficult to assemble between optical elements and increasing the manufacturing cost.

Furthermore, according to the Faraday rotator for short wavelength light according to claim 5 , the manufacturing process can be shortened and the heat radiation efficiency can be improved.

Furthermore, according to the Faraday rotator for short wavelength light according to claim 6 , the incident side garnet single crystal having a relatively large calorific value by transmitting light first is made thinner than the garnet single crystal on the emission side. It is set. For this reason, the amount of heat generated in both garnet single crystals becomes equal, and the amount of heat generated in the incident-side garnet single crystal is reduced. As a result, the temperature rise values of the two garnet single crystals can be made substantially equal to perform optimum heat dispersion, so that the temperature rise of the entire garnet single crystal can be minimized.

Further, according to the Faraday rotator for short wavelength light according to claim 7 , Gd or Y is used as a host rare earth element and almost has a Faraday effect having a high thermal conductivity of 5 W / m · K or more. A non-paramagnetic garnet substrate can be provided on one side of a bismuth-substituted rare earth iron garnet single crystal. Accordingly, since the high thermal conductivity material is connected to the garnet single crystal, the heat dissipation efficiency of the garnet single crystal can be improved. Therefore, since heat generated by light absorption inside the garnet single crystal is efficiently and quickly radiated to the outside of the garnet single crystal, the temperature increase of the garnet single crystal can be further suppressed.

In addition, according to the Faraday rotator for short wavelength light according to claim 8 , since it has a structure in which a high thermal conductivity material is connected to the garnet single crystal, it is possible to improve the heat dissipation efficiency of the garnet single crystal. Become. Therefore, since heat generated by light absorption inside the garnet single crystal is efficiently and quickly radiated to the outside of the garnet single crystal, the temperature increase of the garnet single crystal can be further suppressed.

Furthermore, according to the Faraday rotator for short-wavelength light according to claim 9 , when the incident angle of light incident on the Faraday rotator for short-wavelength light is small, the effect of birefringence is small enough to be ignored. It becomes possible to suppress.

Furthermore, according to the Faraday rotator for short wavelength light according to claim 10 , since the thickness of the garnet substrate is set to 1 mm or more, the heat conduction volume is increased, and the heat dissipation efficiency of the garnet single crystal is increased. improves.

Furthermore, according to the Faraday rotator for short wavelength light or the optical isolator according to claims 11 to 13 or claims 17 to 22 , heat generated in the garnet single crystal can be conducted to the outside of the garnet single crystal. Since the garnet single crystal is thermally connected to the holder or the cooling element by the thermosetting resin, solder, or gold film, the garnet single crystal can be radiated efficiently and quickly.

In addition, according to the optical isolator according to claim 14 or 15 , by providing the Faraday rotator according to any one of claims 1 to 13 , it is possible to prevent deterioration of optical characteristics of the optical isolator and to ensure reliability. It becomes possible. Furthermore, an optical isolator applicable to an optical device or apparatus using a light source in a short wavelength band is realized.

Furthermore, according to the optical isolator according to claim 16 , since the garnet single crystal is connected to the cooling element through the holder of the material having a thermal conductivity of 15 W / m · K or more, the garnet is made of a high thermal conductivity material. A structure in which the single crystal and the cooling element are thermally connected can be provided, and the heat dissipation efficiency of the garnet single crystal can be improved.

Furthermore, according to the optical isolator according to claim 23 , by providing the holder with a plane portion in a part of the outer shape of the holder by making the cross-sectional shape of the holder either square, concave, or flat plate, The mounting on the cooling element can be facilitated. Further, since the holder is brought into surface contact with the cooling element by the flat portion, it is possible to quickly dissipate the garnet single crystal by securing a heat conduction area.

Furthermore, according to the optical isolator according to claim 24 , since the heat generated in the garnet single crystal is conducted not only from the garnet substrate or the light transmission plate but also from the filler, the heat dissipation efficiency of the garnet single crystal is further improved. It becomes possible to make it.

Further, according to the Faraday rotator or optical isolator for short wavelength light according to claim 25 of the present invention, the operating temperature condition of the Faraday rotator or optical isolator for short wavelength light is -10 degrees or more and 80 degrees or less. Therefore, the Verde constant of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal can be stabilized.

<First Embodiment>
Hereinafter, a first embodiment of a short wavelength light Faraday rotator 1 (hereinafter referred to as “Faraday rotator 1”) and an optical isolator 8 using the Faraday rotator 1 according to the present invention will be described with reference to FIG. It demonstrates in detail using-FIG.

As shown in FIG. 1, the Faraday rotator 1 according to the present embodiment includes a paramagnetic garnet single crystal 20 (hereinafter referred to as “paramagnetic garnet single crystal 20”), a bismuth-substituted rare earth iron garnet single crystal 2. (Hereinafter referred to as “garnet single crystal 2” if necessary) and a garnet substrate 3. The paramagnetic garnet single crystal 20, the garnet single crystal 2, and the garnet substrate 3 are all flat and formed into a rectangular outer shape. The garnet single crystal 2 is provided in contact with at least one side of the paramagnetic garnet single crystal 20 and one side of the paramagnetic garnet substrate 3. One side of the paramagnetic garnet single crystal 20 is in contact with one optical surface os1 of the garnet single crystal 2, and one side of the garnet single crystal 2 is opposite to the side on which the paramagnetic garnet single crystal 20 is provided. A garnet substrate 3 is provided on the optical surface os2 of the garnet single crystal 2 that is one side of the garnet single crystal 2.

The optical isolator 8 using the Faraday rotator 1 has two polarizers 4 and 5 in total, one on each of the light incident side and the light emission side of the Faraday rotator 1 as shown in FIG. It is composed by arranging.

  The garnet substrate 3 has a lattice constant set in the range of 12.56 mm or more and 12.58 mm or less, a composition having Gd or Y as a host rare earth element, and a thermal conductivity of 5 W / m · K or more. It is a substrate. Since Gd or Y is a host rare earth element, the garnet substrate 3 is a paramagnetic material having almost no Faraday effect. The garnet single crystal 2 has a lattice constant set in a range of 12.56 to 12.58.

Paramagnetic garnet single crystal 20 is a paramagnetic material having a composition in which Tb is a host rare earth element, and has a Faraday effect that rotates the polarization plane of incident light when an external magnetic field is applied. It is. Further, it is made of a material having a light transmittance of more than 99% with respect to light in a wavelength region of 1030 nm or more and 1090 nm or less. As an optimum material, a TGG single crystal having a composition represented by a chemical formula of Tb ₃ Ga ₅ O ₁₂ , Tb ₃ Al ₅ O ₁₂ , or Tb ₃ Sc ₂ Ga ₃ O ₁₂ , a TAG single crystal, or Examples include Tb ₃ Sc ₂ Ga ₃ O ₁₂ single crystal.

  Among them, the TAG single crystal has a Verde constant (deg / (Oecm)) that indicates the Faraday rotation angle per unit length and magnetic field of the paramagnetic material compared to other paramagnetic garnet single crystals. Very big. Therefore, since a sufficient Faraday rotation angle can be obtained even if the size of the paramagnetic garnet single crystal 20 is reduced, the Faraday rotator 1 and the optical isolator 8 can be downsized. Further, since the magnetic field can be reduced, the permanent magnet 6 can also be reduced, and not only the optical isolator 8 can be miniaturized, but also the influence of the magnetic field on other electronic components can be prevented to a minimum. Stabilize the function of the parts.

  Since the paramagnetic garnet single crystal 20 and the garnet single crystal 2 are both magneto-optical elements having a Faraday effect, the polarization plane of incident light is rotated. Further, the Faraday rotation directions of the paramagnetic garnet single crystal 20 and the garnet single crystal 3 are set in the same direction when viewed from the light propagation direction (arrow P direction) as shown in FIG. The

  The garnet single crystal 2 is grown on one side of the garnet substrate 3 by the LPE method. The flux that has been heated and melted in the platinum crucible is heated and melted and stirred sufficiently to produce a uniformly mixed melt. The garnet substrate 3 having a surface orientation {111} having a diameter of 2 to 3 inches and a thickness t2 of 1 mm or more is immersed in the liquid surface of the melt, and the {111} by the LPE method while rotating the garnet substrate 3 The garnet single crystal 2 is grown on the surface by epitaxial growth in an air atmosphere.

Since the grown garnet single crystal 2 has a lattice constant that depends on the lattice constant of the garnet substrate 3 and the composition of the melt, it is set in the range of 12.56 to 12.58. The garnet single crystal 2 having this lattice constant is polished to a predetermined thickness, and an AR coating for an arbitrary band having a wavelength of 1030 nm to 1090 nm is deposited on the surface. An example of the composition of the garnet single crystal 2 to be grown is GdBi ₂ Fe ₅ O ₁₂ .

  The paramagnetic garnet single crystal 20 may be manufactured by a known micro-pulling down method (μ-PD method), Czochralski method (Cz), or the like. Specifically, in the micro pull-down method, an opening is provided at the bottom of a crucible made of Pt, and a seed crystal is placed from the outside of the crucible at the opening of the crucible. The polycrystalline body separately put in the crucible is heated and melted to join the seed crystal and the polycrystalline body, and the paramagnetic garnet single crystal 20 is grown by pulling down the seed crystal from the outside.

In the case of the Czochralski method, a calcined mixed powder of starting materials (Tb ₄ O ₇ and Al ₂ O _{3 in} the case of a TAG single crystal) is filled in an Ir crucible and melted by high frequency induction heating. . The seed crystal is brought into contact with the melt and sufficiently blended, and then the paramagnetic garnet single crystal 20 is grown by pulling up the seed crystal while rotating it at a constant speed.

Alternatively, a flux method may be used. In the case of the flux method, prepare a solution in which starting materials (Tb ₄ O ₇ and Al ₂ O _{3 in} the case of TAG single crystal) are dissolved as a solute in a solvent such as PbF ₂ and put seed crystals into this solution The bulk-type paramagnetic garnet single crystal 20 is obtained by slow cooling.

  As a joining method of the grown paramagnetic garnet single crystal 20 and the garnet single crystal 2, there is an adhesion method using an optical epoxy adhesive. When an optical epoxy adhesive is used, the temperature during bonding can be set to a low temperature of 100 ° C. or less, so that a remarkable effect appears in terms of suppressing stress distortion generated inside the Faraday rotator 1 during bonding.

  Or, instead of optical epoxy adhesive, room temperature vacuum bonding (method of activating the bonding surface with an ion beam etc. in ultra-high vacuum, bonding them together, pressurizing and bonding), hydrofluoric acid bonding (hydrofluoric acid solution) May be joined by glass joining using a low melting point glass.

  The AR coating is applied to the bonding surface of the paramagnetic garnet single crystal to the garnet single crystal 2 in order to suppress Fresnel reflection. Since the film configuration of the AR coating varies depending on the material of the substrate to be bonded and the bonding method, it is necessary to design an optimal AR coating according to the conditions. If the loss due to Fresnel reflection can be ignored and the influence of reflected light can be eliminated, the AR coating does not have to be formed.

  Next, the single body of the paramagnetic garnet single crystal 20, the garnet single crystal 2 and the garnet substrate 3 is cut into equal mm squares with a dicer or the like, and the paramagnetic garnet single crystal 20 and the garnet as shown in FIG. A 1 to 2 mm square Faraday rotator 1 composed of a single crystal 2 and a garnet substrate 3 is obtained.

  The Faraday rotator 1 thus obtained is coated with a thermosetting resin adhesive on the side which is a non-light transmitting surface, and the Faraday is applied to a Peltier element or heat sink 9 (hereinafter collectively referred to as a cooling element 9). The rotor 1 is bonded (see FIG. 2).

  A solder or gold film may be used instead of the thermosetting resin. When solder is used, a metal layer composed of three layers of Cr, Pt, and Au is formed on the side surface by vacuum deposition, and the Faraday rotator 1 is joined to the cooling element 9 by solder (for example, Au / Sn solder). When a gold film is used, gold (Au) is formed on the side surface, and the Faraday rotator 1 is bonded to the cooling element 9 by thermocompression bonding of the gold film.

  As shown in FIG. 3 (d), the polarizers 4 and 5 constituting the optical isolator 8 together with the Faraday rotator 1 are formed of anisotropic glass having dichroism and transmit a specific polarization component. The orthogonally polarized components absorb and block light. The polarizers 4 and 5 may be fixed to the cooling element 9 with thermosetting resin or solder.

  Furthermore, a U-shape was formed as shown in FIGS. 4D and 5D so as to cover the side surfaces of the three sides of the optical element 10 for the optical isolator (polarizers 4 and 5 and Faraday rotator 1). A permanent magnet 6 is installed in the vicinity of the paramagnetic garnet single crystal 20 and the garnet single crystal 2. The permanent magnet 6 is optimally Sm—Co or Ne—Fe—B. The magnitude of the magnetic field of the permanent magnet 6 is set such that when the magnetic field is applied to the paramagnetic garnet single crystal 20 and the garnet single crystal 2, the total Faraday rotation angle is set to 45 degrees.

  In the Faraday rotator and optical isolator according to the present invention, the predetermined value of the Faraday rotation angle is 45 degrees. Therefore, the greater the magnetic field, the greater the Faraday rotation angle of the paramagnetic garnet single crystal 20. Since the Faraday rotation angle of the garnet single crystal 2 can be decreased by the increase in the Faraday rotation angle of the paramagnetic garnet single crystal 20, the thickness of the garnet single crystal 2 is reduced by the decrease in the Faraday rotation angle. You can also Furthermore, the thickness t5 of the paramagnetic garnet single crystal 20 can be reduced. As the thickness t1 of the garnet single crystal 2 is reduced, the light absorption amount in the garnet single crystal 2 is also reduced, so that the light absorption of the entire Faraday rotator 1 can be further suppressed.

  The magnitude of the magnetic field that can provide the above effects is desirably set to 2000 Oe or more. However, in order to prevent the permanent magnet 6 from becoming large, a setting of 3000 Oe or less is preferable.

By placing the permanent magnet 6, a magnetic field is applied to the paramagnetic garnet single crystal 20 and the garnet single crystal 2 along the plate thickness direction, and a wavelength of 1030 nm or more that passes through the thicknesses t 1 and t 5 is 10
Linearly polarized light with an arbitrary wavelength of 0 nm or less was rotated 45 degrees. In this way, the total Faraday rotation angle of the paramagnetic garnet single crystal 20 and the garnet single crystal 3 is set to 45 degrees. For example, the Faraday rotation angle of the paramagnetic garnet single crystal 20 may be set to 20 degrees, and the Faraday rotation angle of one garnet single crystal 2 may be set to 25 degrees.

  Further, the total thickness t5 and t1 of the paramagnetic garnet single crystal 20 and the garnet single crystal 2 is preferably set to be less than 1 cm in view of miniaturization of the Faraday rotator 1. However, the Verde constant of the paramagnetic garnet single crystal 20 is very small. The object of the present invention is “to reduce the thickness of a paramagnetic garnet single crystal containing Tb as a host rare earth element to such an extent that it can be used for a Faraday rotator while suppressing light absorption”. Therefore, it is desirable to avoid increasing the thickness t1 of the garnet single crystal 2 that generates heat by light absorption in order to increase the Faraday rotation angle. Accordingly, it is desirable to set the thickness t5 to 5 mm or more in order to set the total thickness t5 and thickness t1 to less than 1 cm and to increase the Faraday rotation angle as much as possible in the paramagnetic garnet single crystal 20.

  The Faraday rotator 1 and the cooling element 9 are connected not only to the Faraday rotator 1 directly to the cooling element 9 as shown in FIG. 2, but also to hold the Faraday rotator 1 in the holder and through the holder. It may be connected to the cooling element 9. As shown in FIGS. 3A to 3C, the polarizers 4 and 5 and the Faraday rotator 1 constituting the optical isolator 8 are accommodated inside the holder (7a or 7b) or placed on the holder 7c. The side surfaces which are non-light transmitting surfaces of the polarizers 4 and 5 and the Faraday rotator 1 are held by holders 7a to 7c. The holders 7a to 7c are made of a material having a thermal conductivity of 15 W / m · K or more, such as copper, SUS, and aluminum.

  Furthermore, a U-shaped permanent magnet 6 shown in FIGS. 4A to 4C is provided so as to cover the side surfaces of the three sides of the optical element 10 for the optical isolator (the polarizers 4 and 5 and the Faraday rotator 1). In the vicinity of the garnet single crystal 2. Next, the holders 7a to 7c are mounted on the cooling element 9 as shown in FIGS. 5A to 5C, so that the garnet single crystal 2 is connected to the cooling element 9 through the holders 7a to 7c. Is done.

  As shown in FIGS. 3A to 3C, the holders 7a to 7c have a square cross section in a direction perpendicular to the light propagation direction (arrow P direction) (see FIG. 3A). It is molded so as to have any one of a concave shape (see FIG. 3 (b)) and a flat plate shape (see FIG. 3 (c)). When configuring the optical isolator 8, the paramagnetic garnet single crystal 20 and the garnet single crystal 2 are arranged on the light source side (not shown). With this arrangement, the reflected light at the interface between the garnet single crystal 2 and the garnet substrate 3 is further subjected to Faraday rotation by the garnet single crystal 2 and the paramagnetic garnet single crystal 20. Therefore, since it can be handled in the same manner as so-called return light from the optical isolator 8, the isolation of the optical isolator 8 is not lowered. Conversely, when the garnet substrate 3 is disposed on the light source side, the reflected light returns to the light source as it is without being subjected to Faraday rotation, and the isolation is lowered.

  When the Faraday rotator 1 is held by the holders 7a to 7c, a thermosetting resin adhesive is applied to the side of the Faraday rotator 1 which is a non-light transmitting surface, and the Faraday rotator 1 is bonded to the holders 7a to 7c. To do. A solder or gold film may be used instead of the thermosetting resin. In the case of using solder, a metal layer is formed on the side surface, and the Faraday rotator 1 is joined to the holders 7a to 7c by solder. When using a gold film, the Faraday rotator 1 is pressure-bonded to the holders 7a to 7c by providing a gold film on the side surface and thermocompression bonding the gold film. The polarizers 4 and 5 may be fixed to the holders 7a to 7c with a thermosetting resin or solder.

  Further, a thermosetting resin is applied to one surface of the holders 7a to 7c holding the optical element 10, and the holders 7a to 7c are bonded to the cooling element 9 as shown in FIGS. A solder or gold film may be used instead of the thermosetting resin. When solder is used, a metal layer is formed on the one surface, and the holders 7a to 7c are joined to the cooling element 9 by soldering. When a gold film is used, a gold film is provided on the one surface, and holders 7a to 7c are pressure bonded to the cooling element 9 by thermocompression bonding of the gold film.

  The usage environment of the paramagnetic garnet single crystal 20 and the garnet single crystal 2 connected to the cooling element 9 as described above is such that λ is 1030 nm or more and 1090 nm or less when the wavelength of incident light is λ (nm). Are set so as to satisfy any wavelength condition.

  Next, the optical operation of the optical isolator 8 will be described with reference to FIG. When light having an arbitrary wavelength of 1030 nm or more and 1090 nm or less is incident on the optical isolator 8 along the arrow I direction, the light is first incident on the polarizer 4. Here, the polarization direction of the incident light is limited to only the polarization component that matches the polarization direction of the polarizer 4. The light transmitted through the polarizer 4 (linearly polarized light) is then incident on the paramagnetic garnet single crystal 20 and the garnet single crystal 2 of the Faraday rotator 1 in order, and the plane of polarization is rotated by 45 degrees in total.

  Since the paramagnetic garnet single crystal 20 uses Tb as a host rare earth element and has a light transmittance of over 99%, light absorption with respect to light of 1030 nm or more and 1090 nm or less can be suppressed almost completely. Therefore, almost no heat is generated in the paramagnetic garnet single crystal 20 due to light absorption.

  Since the paramagnetic garnet single crystal 20 has a small Verde constant, the thickness t5 becomes 1 cm or more when trying to obtain the Faraday rotation angle of 45 degrees necessary for the isolator function with the single paramagnetic garnet single crystal 20 alone. . In the Faraday rotator 1, in addition to the paramagnetic garnet single crystal 20, the garnet single crystal 2 having a large Verde constant is provided so that the insufficient rotation angle for 45 degrees can be compensated by the Faraday rotation angle of the garnet single crystal 2. It becomes possible. Therefore, the paramagnetic garnet single crystal can be made thinner by the Faraday rotation angle of the garnet single crystal 2. Therefore, it is possible to realize the Faraday rotator 1 that can be used for a light source having a wavelength of 1030 nm or more and 1090 nm or less that has a relatively short wavelength and high power in the near infrared wavelength region.

  Although the paramagnetic garnet single crystal 20 has a light transmittance of over 99%, it hardly absorbs light, but light absorption occurs in the light transmitting portion of the garnet single crystal 2 and a part of incident light is absorbed. However, as described above, the lattice constant of the garnet single crystal 2 is set in the range of 12.56 to 12.58. Therefore, as shown in FIG. 6, the wavelength band in which the transmission loss of light due to light absorption peaks is compared with the peak wavelength band of a garnet single crystal having a lattice constant of about 12.50 mm (12.49 to 12.51 mm). Shift to a shorter wavelength band. The light absorption peak wavelength of the conventional garnet single crystal having a lattice constant of about 12.50 mm is around 900 nm, whereas the light absorption peak wavelength of the garnet single crystal 2 of the present embodiment increases the lattice constant. Along with this, it shifts to around 890nm.

  In FIG. 6, the wavelength-light transmission loss characteristic of a conventional garnet single crystal having a lattice constant of about 12.50 mm (12.49-12.51 mm) is represented by a curve A-1, which is 12.56 mm or more and 12.58 mm according to the present embodiment. The wavelength-light transmission loss characteristic of the garnet single crystal 2 having the following lattice constant is represented by a curve A-2. The shift effect of the light absorption peak wavelength was not confirmed in a garnet single crystal having a lattice constant of more than 12.51 to 12.55 mm or less. As described above, the lower limit of the lattice constant of the garnet single crystal 2 is limited to 12.56 mm.

  The reason why the upper limit of the lattice constant of the garnet single crystal 2 is limited to 12.58 mm is that, in order to grow the garnet single crystal 2 having a lattice constant of more than 12.58 mm, neodymium that generates light absorption in the wavelength range from 1030 nm to 1090 nm. This is because a garnet substrate having a composition containing (Nd) must be used, and the growth limit of a garnet substrate having a composition that does not generate light absorption is 12.58 mm.

  Along with this shift, the light transmission loss of the garnet single crystal 2 in the wavelength band of 1030 nm or more and 1090 nm or less is reduced from 1.0 dB to 0.7 dB in the case of 120 μm thickness where the light of 1064 nm rotates 45 degrees ( FIG. 6 shows a case of 1064 nm as a representative example). Since the light transmission loss is reduced with the shift of the light absorption peak wavelength in this way, the light absorption amount in the garnet single crystal 2 is also reduced, and the amount of heat converted from the absorbed light is reduced. The temperature rise is further suppressed.

  The light absorbed by the garnet single crystal 2 is converted into heat inside the garnet single crystal 2. However, since the optical surface os2 of the garnet single crystal 2 is in contact with the garnet substrate 3, heat is diffused three-dimensionally and radially from the optical surface os2 to the garnet substrate 3. The heat conducted to the garnet substrate 3 is transmitted to the cooling element 9 and radiated.

  By providing Gd or Y as a host rare earth element and providing a paramagnetic garnet substrate 3 having a high thermal conductivity of 5 W / m · K or more and having almost no Faraday effect on one side of the garnet single crystal 2, A high thermal conductivity material can be connected to the garnet single crystal 2. Therefore, the heat dissipation efficiency of the garnet single crystal 2 can be improved. Therefore, the heat generated by light absorption inside the garnet single crystal 2 is efficiently and quickly dissipated to the outside of the garnet single crystal 2, so that the temperature rise of the garnet single crystal 2 is suppressed and the optical characteristics of the optical isolator 8 are deteriorated. Prevention and reliability can be ensured. Furthermore, the optical isolator 8 applicable to an optical device or apparatus using a light source in a short wavelength band is realized.

  Furthermore, since the thickness t2 of the garnet substrate 3 is set to 1 mm or more, the heat conduction volume is increased, and the heat dissipation efficiency of the garnet single crystal 2 is improved.

  Furthermore, the garnet single crystal 2 is thermally connected to the cooling element 9 by a thermosetting resin, solder, or gold film so that heat generated in the garnet single crystal 2 can be conducted to the cooling element 9. Therefore, the garnet single crystal 2 can be dissipated efficiently and quickly.

  Further, holders 7a to 7c were formed of a material having a thermal conductivity of 15 W / m · K or more, and the garnet single crystal 2 was connected to the cooling element 9 through the holders 7a to 7c. Therefore, a structure in which the garnet single crystal 2 and the cooling element 9 are thermally connected with a high thermal conductivity material can be provided, and the heat dissipation efficiency of the garnet single crystal 2 can be improved.

  Further, the holder 7a to 7c has a cross-sectional shape of any one of a square shape, a concave shape, and a flat plate shape, and a flat portion is provided on a part of the outer shape of the holders 7a to 7c, so In addition to facilitating the placement, the holders 7a to 7c are brought into surface contact with the cooling element 9 by the flat portion, so that the garnet single crystal 2 can be quickly dissipated by securing a heat conduction area.

Finally, light is incident on the polarizer 5. In the forward direction (arrow I direction), the polarization direction of the light transmitted through the polarizer 4 is polarized through the paramagnetic garnet single crystal 20 and the garnet single crystal 2. Since it is adjusted so as to coincide with the polarization direction of the polarizer 5, there is almost no polarization component absorbed by the polarizer 5, and light passes through.

  When there is return light due to reflection or the like, the light is converted into linearly polarized light by the polarizer 5, and then the 45-degree polarization plane is rotated by the garnet single crystal 2 and the paramagnetic garnet single crystal 20. However, since the garnet single crystal 2 and the paramagnetic garnet single crystal 20 are irreversible optical elements, the polarization direction of the rotated polarization plane differs from the polarization direction of the polarizer 4, and the return light is the polarizer 4. Cannot pass through.

  When the Faraday rotator 1 and the optical isolator 8 are used under a temperature condition in the range of -10 degrees or more and 80 degrees or less, the Verde constant of the paramagnetic garnet single crystal 20 and the garnet single crystal 2 can be stabilized. This is preferable.

In the Faraday rotator 1 and the optical isolator 8 described above, a light transmission plate may be used instead of the garnet substrate 3. As shown in FIGS. 7 (a) and 7 (b) and FIGS. 8 to 10, another form of Faraday is provided by providing the optical surface os2 of the garnet single crystal 2 in contact with one surface of the flat light transmitting plate 11. FIG. A rotor 12 is configured. That is, the light transmission plate 11 is provided on one side of the garnet single crystal 2 opposite to the side on which the paramagnetic garnet single crystal 20 is provided.

  The light transmission plate 11 is made of a material having a high thermal conductivity, and is further provided in surface contact with the optical surface os2 of the garnet single crystal 2, so that it is optically transparent and absorbs almost no light. There is no condition. Since the light transmission plate 11 is provided for the purpose of quickly conducting and dissipating heat generated in the garnet single crystal 2, its thermal conductivity is at least four times larger than that of the garnet single crystal 2. There must be.

  Since the garnet single crystal 2 is composed of a bismuth-substituted rare earth iron garnet single crystal, the thermal conductivity is about 2.1 W / m · K (25 degrees). The garnet single crystal 2 has a thermal conductivity 4 times higher than that of the garnet single crystal 2 and, as a transparent and transparent material, sapphire single crystal (42 W / m · K (25 degrees)), ZnSe single crystal (18 W / m · K (25 degrees)). The purpose of providing the light transmission plate 11 is to efficiently dissipate the heat of the garnet single crystal 2 generated with the incidence of light in a short wavelength band (1030 nm to 1090 nm). It is necessary to limit to 1090 nm or less. Therefore, it is optimal to use a material that can transmit light in the wavelength band of 1030 nm to 1090 nm, such as sapphire single crystal (light transmission wavelength range of 0.17 μm to 6.5 μm), for the light transmission plate 11.

  When using optically anisotropic single crystal such as sapphire single crystal for the light transmission plate 11, especially when used for optical elements that handle polarized light such as Faraday rotator, attention to the polarization state is required. It is. Specifically, the light transmission plate 11 is set so that the optical isotropic axis of the sapphire single crystal (for example, the C axis) is perpendicular to the optical surface os2. Contact and join to. By such joining, only when the incident angle of light (not shown) incident on the Faraday rotator 12 is small, the influence of birefringence can be suppressed to a negligible level.

  In such a Faraday rotator 12, after growing the garnet single crystal 2 on the garnet substrate, the garnet substrate is removed by polishing, and the light transmission plate 11 is brought into surface contact with the optical surface os2, and the optical surface os2 and the light transmission plate 11 and a paramagnetic garnet single crystal 20 are bonded and fixed to the other optical surface os1.

  As a method for joining the garnet single crystal 2 and the light transmission plate 11, adhesion using an optical epoxy adhesive may be mentioned. When an optical epoxy adhesive is used, the temperature during bonding can be set to a low temperature of 100 ° C. or less, so that a remarkable effect appears in that the stress distortion generated inside the Faraday rotator 12 during bonding is suppressed.

  By joining the garnet single crystal 2 and the light transmission plate 11 as described above, heat generated in the garnet single crystal 2 more quickly than when the light transmission plate 11 is simply brought into contact with the optical surface os2. Can be conducted to the light transmission plate 11 to diffuse and dissipate heat, so that the temperature rise of the garnet single crystal 2 can be more effectively suppressed.

  As other joining methods, if the thermal expansion coefficients of both (the garnet single crystal 2 and the light transmission plate 11) are close, joining at high temperature such as thermal diffusion joining is possible, but room temperature vacuum joining (joining in ultra-high vacuum) The surfaces may be activated by an ion beam or the like, bonded together, and then pressed and bonded), hydrofluoric acid bonding (method of tight bonding with a hydrofluoric acid solution), glass bonding with low-melting glass, or the like.

  Also, when materials with different refractive indexes such as garnet single crystal 2 and light transmission plate 11 are bonded, Fresnel reflection occurs due to the difference in refractive index at the bonding surface, so AR coating is applied to garnet single crystal 2. Reduces Fresnel reflection. Since the film configuration of the AR coating varies depending on the material of the substrate to be bonded and the bonding method, it is necessary to design an optimal AR coating according to the conditions. If the loss due to Fresnel reflection can be ignored and the influence of reflected light can be eliminated, the AR coating does not have to be formed.

  As in the case of the optical isolator 8 described above, the paramagnetic garnet single crystal 20 has almost no light absorption because the light transmittance is over 99%, but light absorption occurs in the light transmission portion of the garnet single crystal 2. Part of the incident light is absorbed and heat is generated. However, as described above, with the shift of the light absorption peak wavelength of the garnet single crystal 2, the amount of heat converted from the absorbed light decreases, so that the temperature increase of the garnet single crystal 2 is suppressed.

  The light absorbed by the garnet single crystal 2 is converted into heat inside the garnet single crystal 2. The garnet single crystal 2 has a high thermal conductivity because its optical surface os2 is in contact with the light transmission plate 11. The material is connected to the garnet single crystal 2 and the heat dissipation efficiency of the garnet single crystal 2 is improved. Accordingly, since heat is diffused three-dimensionally and radially from the optical surface os2 to the light transmission plate 11 and dissipated by the cooling element, the temperature rise of the garnet single crystal 2 is further suppressed, and the optical isolator 13 shown in FIG. It is possible to prevent deterioration of the optical characteristics and to ensure reliability. Furthermore, the optical isolator 13 applicable to an optical device or apparatus using a light source in a short wavelength band is realized.

<Second Embodiment>
Next, a second embodiment of the Faraday rotator according to the present invention and an optical isolator using the Faraday rotator will be described in detail with reference to FIGS. In addition, the same number is attached | subjected to the same location as 1st Embodiment, and the overlapping description is abbreviate | omitted or simplified and described.

The second embodiment is different from the first embodiment in that two garnet single crystals are provided. As shown in FIG. 12, the Faraday rotator 14 according to the present embodiment is configured by providing a total of two flat and square garnet single crystals 2 a and 2 b on both surfaces of the garnet substrate 3. . The optical surface os1 of the garnet single crystal 2a is in contact with one surface of the paramagnetic garnet single crystal 20, and the optical surface os3 of the garnet single crystal 2b is in contact with one surface of the garnet substrate 3. Furthermore, the other optical surface os2 of one garnet single crystal 2a is bonded to the garnet substrate 3.

  Further, as shown in FIG. 14, the optical isolator using the Faraday rotator 14 has a total of two polarizers 4 and 5 arranged on the light incident side and the light outgoing side of the Faraday rotator 14, respectively. Is made up of. The Faraday rotation directions of the paramagnetic garnet single crystal 20 and the garnet single crystals 2a and 2b are set in the same direction when viewed from the light propagation direction (arrow P direction) as shown in FIG. 12 (a). The

  The garnet substrate 3 is a paramagnetic substrate having a lattice constant set in the range of 12.56 mm or more and 12.58 mm or less, and the garnet single crystals 2a and 2b are set in the range of 12.56 mm or more and 12.58 mm or less. Has a lattice constant.

  After the garnet single crystals 2a and 2b are grown on the surfaces of the two garnet substrates by the LPE method, one garnet substrate is removed by polishing, and the paramagnetic garnet single crystal 20 is brought into surface contact with the optical surface os1. Bonded and fixed. Next, the other garnet substrate is left attached to the garnet single crystal 2b, and one surface of the garnet substrate and one optical surface os2 of the garnet single crystal 2a are bonded and fixed, whereby the Faraday rotator 14 is fixed. Is produced.

  Next, a method for producing the garnet single crystals 2a and 2b will be described in detail. As in the first embodiment, the heat-melted flux in the platinum crucible is heated and melted and sufficiently stirred to produce a uniformly mixed melt. Two garnet substrates 3 having a surface orientation {111} having a diameter of 2 to 3 inches and a thickness t2 of 1 mm or more are immersed in the liquid surface of the melt, and the garnet substrate 3 is rotated by the LPE method while rotating. On the {111} plane, the garnet single crystal 2a or 2b is grown by epitaxial growth in an air atmosphere.

  The garnet single crystals 2a and 2b are polished to a predetermined thickness, and an AR coat for an arbitrary wavelength band with a wavelength of 1030 nm to 1090 nm is deposited on the surface. There is no particular limitation on the composition of the garnet single crystals 2a and 2b to be grown. When it is difficult to set the Faraday rotation angles of the two garnet single crystals 2a and 2b uniformly, the Faraday rotation angles may be slightly biased. Therefore, the thicknesses t3 and t4 of the two garnet single crystals 2a and 2b are not necessarily equal. The garnet single crystals 2a and 2b, the paramagnetic garnet single crystal 20 and the garnet substrate 3 are cut into equal mm squares, and two garnet single crystals 2a and 2b and one paramagnetic garnet as shown in FIG. A 1-2 mm square Faraday rotator 14 composed of the single crystal 20 and the garnet substrate 3 is obtained.

  The Faraday rotator 14 thus obtained is fixed to the cooling element 9 by means of a thermosetting resin adhesive, solder, a gold film, etc. (FIGS. 13, 14 (d), 15 (d), (See FIG. 16 (d)).

  Alternatively, instead of directly connecting the Faraday rotator 14 to the cooling element 9, the Faraday rotator 14 may be held by a holder as shown in FIGS. As shown in FIGS. 14A to 14C, the polarizers 4 and 5 and the Faraday rotator 14 constituting the optical isolator 15 are accommodated in the holder 7a or 7b or placed on the holder 7c. Next, as shown in FIGS. 16A to 16C, the holders 7a to 7c are placed on the cooling element 9, so that the garnet single crystal 2a is attached to the cooling element 9 via the holders 7a to 7c. 2b is connected.

  When the Faraday rotator 14 is held by the holders 7a to 7c, the Faraday rotator 14 is fixed to the holders 7a to 7c with an adhesive of a thermosetting resin, solder, a gold film, or the like. Further, holders 7a to 7c holding optical isolators 16 (polarizers 4 and 5 and Faraday rotator 14) as shown in FIGS. 15 (a) to 15 (c) are bonded to a thermosetting resin adhesive, It is fixed to the cooling element 9 by solder, a gold film or the like.

  When the optical isolator 15 having the Faraday rotator 14 in which the thicknesses of the two garnet single crystals 2a and 2b are not equal is mounted on an optical device such as an optical sensor, it is arranged on the incident side of light from a light source (not shown). The garnet single crystal 2a to be formed is thin, and the exit-side garnet single crystal 2b is arranged to be thicker than that. That is, the Faraday rotation angle of the garnet single crystal 2a arranged on the light incident side is set smaller than the Faraday rotation angle of the other garnet single crystal 2b.

  The magnitude of the magnetic field of the permanent magnet 6 is set such that the total Faraday rotation angle is set to 45 degrees when a magnetic field is applied to the paramagnetic garnet single crystal 20 and the garnet single crystals 2a and 2b. For example, the Faraday rotation angle of the paramagnetic garnet single crystal 20 is set to 20 degrees, the Faraday rotation angle of the garnet single crystal 2a is set to 8 degrees, and the Faraday rotation angle of the other garnet single crystal 2b is set to 17 degrees. Just do it.

  Next, the optical operation of the optical isolator 15 will be described with reference to FIG. When light having an arbitrary wavelength of 1030 nm or more and 1090 nm or less is incident on the optical isolator 15 along the direction of arrow I, the light is first incident on the polarizer 4 to be converted into linearly polarized light, and then the Faraday rotator 14 is constantly switched. The light is incident on the magnetic garnet single crystal 20 and the two garnet single crystals 2a and 2b in order, and the plane of polarization is rotated by 45 degrees in total. At that time, light absorption occurs in the light transmitting portions of the garnet single crystals 2a and 2b, and a part of the incident light is absorbed.

  However, as described above, the lattice constants of the garnet single crystals 2a and 2b are set in the range of 12.56 to 12.58. Therefore, as shown in FIG. 6, the wavelength band where the light transmission loss due to light absorption peaks is shorter than the peak wavelength band of the conventional garnet single crystal having a lattice constant of about 12.50 mm. Shifted to. The light absorption peak wavelength of the conventional garnet single crystal having a lattice constant of about 12.50 mm is near 900 nm, whereas the light absorption peak wavelengths of the garnet single crystals 2a and 2b of this embodiment are of the lattice constant. It shifts to around 890nm with the increase.

  Along with this shift, the light transmission loss of the garnet single crystals 2a and 2b in the wavelength band of 1030 nm or more and 1090 nm or less is reduced from 1.0 dB to 0.7 dB when the wavelength of 1064 nm is rotated by 45 degrees and the thickness is 120 μm. The By reducing the light transmission loss, the light absorption amount in the garnet single crystals 2a and 2b is also reduced, and the amount of heat converted from the absorbed light is reduced, so that the temperature rise of the garnet single crystals 2a and 2b is suppressed.

  The light absorbed by the garnet single crystals 2a and 2b is converted into heat inside the garnet single crystals 2a and 2b. However, since the optical surfaces of the garnet single crystals 2a and 2b are in contact with the garnet substrate 3, heat is diffused three-dimensionally and radially from the optical surfaces os2 and os3 to the garnet substrate 3. The heat conducted to the garnet substrate 3 is transmitted to the cooling element 9 and radiated. By providing the garnet substrate 3 on the garnet single crystals 2a and 2b as described above, heat generated by light absorption inside the garnet single crystals 2a and 2b is efficiently and quickly radiated to the outside of the garnet single crystals 2a and 2b. Therefore, the temperature rise of the garnet single crystals 2a and 2b is suppressed, and it becomes possible to prevent deterioration of the optical characteristics of the optical isolator 15 and to ensure reliability. Furthermore, an optical isolator 15 applicable to an optical device or apparatus that uses a light source in a short wavelength band is realized.

  Furthermore, in the first embodiment, the amount of heat generated by light absorption is obtained by dividing the thickness t1 generated by the Faraday rotation angle, which was handled by one garnet single crystal 2, into two garnet single crystals 2a and 2b. Can be dispersed. Furthermore, since the thickness t3 or t4 per piece can be made thinner than the t1, the light absorption amount per garnet single crystal 2a or 2b is reduced, and the temperature of each garnet single crystal 2a or 2b is reduced. It is possible to further suppress the rise.

  Of the two garnet single crystals 2a and 2b, the amount of heat generated in the incident-side garnet single crystal 2a through which light is first transmitted is greater than the amount of heat generated in the exit-side garnet single crystal 2b. However, by making the garnet single crystal 2a on the incident side thinner than the garnet single crystal 2b on the output side and equalizing the amount of heat generated in both garnet single crystals 2a, 2b, the garnet single crystal 2a on the incident side The calorific value is reduced. As a result, the temperature rise values of the two garnet single crystals 2a and 2b can be made substantially equal to perform optimum heat dispersion, so that the temperature rise of the entire garnet single crystal can be minimized.

  When a plurality of garnet single crystals are provided, the optimum number is two. The reason for this is to reduce the ease of assembly and cost, and if it is set to 3 or more, the number of optical elements increases excessively, which makes it difficult to assemble between optical elements and increases the manufacturing cost. .

Finally, the light passes through the polarizer 5. When there is return light, the return light does not pass through the polarizer 4 due to the operation of the optical isolator 8 described above.

In the Faraday rotator 14 and the optical isolator 15 described above, by using the light transmission plate 11 instead of the garnet substrate 3, the garnet single crystals 2a and 2b are formed on both surfaces of the flat light transmission plate 11. Another form of Faraday rotator may be formed by providing the optical surfaces os2 and os3 in contact with each other.

  In such a Faraday rotator, after growing the garnet single crystals 2a and 2b on the surfaces of the two garnet substrates 3, both the garnet substrates 3 are removed by polishing, and the garnets are formed on both surfaces of the light transmission plate 11, respectively. The optical surfaces os12 and os3 of the single crystals 2a and 2b are brought into surface contact, and the optical surface os1 and the paramagnetic garnet single crystal 20 are bonded and fixed.

  In addition, as shown in FIGS. 17 and 18, two garnet single crystals are newly installed by arranging two Faraday rotators 1 having the structure shown in FIG. 1 in the light propagation direction (arrow P direction). This may be realized by configuring the Faraday rotator 17. The Faraday rotation directions of the two paramagnetic garnet single crystals 20a and 20b and the two garnet single crystals 2a and 2b are set to be the same when viewed from the light propagation direction.

  The magnitude of the magnetic field of the permanent magnet 6 (not shown) is such that when a magnetic field is applied to the two paramagnetic garnet single crystals 20a and 20b and the two garnet single crystals 2a and 2b, the total Faraday rotation angle is 45. The size is set to the degree. For example, the Faraday rotation angles of the paramagnetic garnet single crystals 20a and 20b are 10 degrees each, the Faraday rotation angle of the garnet single crystal 2a is 8 degrees, and the Faraday rotation angle of the other garnet single crystal 2b. Set to 17 degrees. Accordingly, the two paramagnetic garnet single crystals 20a and 20b have a uniform thickness t6. It may be non-uniform.

  Furthermore, when configuring an optical isolator, the paramagnetic garnet single crystals 20a and 20b and the garnet single crystals 2a and 2b are arranged on the light source side, and the garnet substrates 3 and 3 are arranged on the opposite side of the light source side. As described above, it is desirable in that a decrease in isolation of the optical isolator is prevented.

  By adopting such a configuration of the Faraday rotator 17, the polishing removal process of the garnet substrate 3 is eliminated, so that the manufacturing process is shortened. Further, by providing two garnet substrates 3 and 3, the heat conduction path generated in the garnet single crystals 2a and 2b can be ensured twice as compared with the Faraday rotator 14 of FIG. More improved.

  In the Faraday rotator 17 and the optical isolator described with reference to FIGS. 17 and 18, by using the light transmission plates 11 and 11 instead of the garnet substrates 3 and 3, a single garnet is provided on one side of the light transmission plates 11 and 11. Further, another Faraday rotator may be formed by providing the optical surfaces os2 of the crystals 2a and 2b in contact with each other.

  As an example, the optical isolator of the present invention is an optical isolator optical element (polarizers 4 and 5 and Faraday rotator 1) and a permanent magnet so as to come into contact with the Faraday rotator 1 and the holder 7c as shown in FIG. It is also possible to change so as to fill the filler 18 in the gap formed between the two.

  Filler 18 is made of a material having thermal conductivity, and has good thermal conductivity such as a solidified filler such as a thermal conductive resin, thermal conductive adhesive or low melting point alloy, or a non-solidified filler such as silicone paste for heat dissipation. The material which has property is suitable.

  When light having an arbitrary wavelength of 1030 nm or more and 1090 nm or less enters the optical isolator 19 in the direction of arrow I, heat is generated by light absorption in the light transmitting portion of the garnet single crystal 2 as described above. The heat is transmitted from the garnet substrate 3 to the cooling element 9 (not shown) through the holder 7c and dissipated. In the optical isolator 19, in addition to this heat dissipation path, the filler 18 in contact with the Faraday rotator 1 and the holder 7c conducts heat, so that the heat of the garnet single crystal 2 is also conducted from the filler 18 and from the cooling element 9. Heat is dissipated.

  Accordingly, the heat generated in the garnet single crystal 2 is conducted not only from the garnet substrate 3 but also from the filler 18 to the cooling element 9. The heat dissipation efficiency can be further improved.

Paramagnetic garnet substrates 20, 20a, 20b may be used as growth substrates for garnet single crystals 2, 2a, 2b. In this case, as a paramagnetic garnet single crystal, a Tb ₃ Sc ₂ Ga ₃ O ₁₂ single crystal having a lattice constant of 12.5235Å is more than 99% with respect to light in a wavelength region of 1030 nm or more and 1090 nm or less using Tb as a host rare earth element It is optimal because it has the largest lattice constant among the paramagnetic garnet single crystals having a light transmittance of.

By using the Faraday rotator and the optical isolator of the present invention for a passive optical device, it is possible to prevent return light to the light source due to reflection.

The perspective view of the Faraday rotator which concerns on the 1st Embodiment of this invention. The perspective view which shows the state which mounted the Faraday rotator of FIG. 1 on the cooling element. (a) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 1 in a square holder. (b) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 1 in a concave holder. (c) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 1 in a flat plate holder. (d) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 1 on a cooling element. (a) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of Fig.3 (a). FIG. 3B is an assembled perspective view in which a permanent magnet is mounted on the optical element for an optical isolator in FIG. (c) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of FIG.3 (c). (d) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of FIG.3 (d). (a) The perspective view which shows the state which mounted the optical isolator of Fig.4 (a) on the cooling element. (b) The perspective view which shows the state which mounted the optical isolator of FIG.4 (b) on the cooling element. (c) The perspective view which shows the state which mounted the optical isolator of FIG.4 (c) on the cooling element. (d) The perspective view which shows the state which mounted the optical isolator of FIG.4 (d) on the cooling element. Wavelength-light transmission loss graph for each lattice constant of garnet single crystal. (a) The assembly perspective view of the Faraday rotator which is another form of 1st Embodiment. (b) The perspective view which shows the Faraday rotator which the assembly of the figure (a) completed. The perspective view which shows the state which mounted the Faraday rotator of FIG.7 (b) on the cooling element. (a) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG.7 (b) in a square holder. (b) An assembled perspective view in which the Faraday rotator and polarizer of FIG. 7 (b) are mounted in a concave holder. (c) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG.7 (b) in a flat plate holder. (d) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG.7 (b) on a cooling element. (a) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of Fig.9 (a). FIG. 9B is an assembled perspective view in which a permanent magnet is mounted on the optical element for the optical isolator in FIG. (c) An assembled perspective view in which a permanent magnet is mounted on the optical element for an optical isolator in FIG. (d) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of FIG.9 (d). (a) The perspective view which shows the state which mounted the optical isolator of Fig.10 (a) on the cooling element. (b) The perspective view which shows the state which mounted the optical isolator of FIG.10 (b) on the cooling element. (c) The perspective view which shows the state which mounted the optical isolator of FIG.10 (c) on the cooling element. (d) The perspective view which shows the state which mounted the optical isolator of FIG.10 (d) on the cooling element. The perspective view of the Faraday rotator which concerns on the 2nd Embodiment of this invention. The perspective view which shows the state which mounted the Faraday rotator of FIG. 12 on the cooling element. (a) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 12 in a square holder. (b) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 12 in a concave holder. (c) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 12 in a flat plate holder. (d) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 12 on a cooling element. (a) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of Fig.14 (a). FIG. 14B is an assembled perspective view in which a permanent magnet is mounted on the optical element for the optical isolator shown in FIG. (c) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of FIG.14 (c). (d) The assembly perspective view which mounts a permanent magnet in the optical element for optical isolators of FIG.14 (d). (a) The perspective view which shows the state which mounted the optical isolator of Fig.15 (a) on the cooling element. (b) The perspective view which shows the state which mounted the optical isolator of FIG.15 (b) on the cooling element. (c) The perspective view which shows the state which mounted the optical isolator of FIG.15 (c) on the cooling element. (d) The perspective view which shows the state which mounted the optical isolator of FIG.15 (d) on the cooling element. The perspective view of the Faraday rotator which is another form of 2nd Embodiment. (a) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 17 in a square holder. (b) An assembled perspective view in which the Faraday rotator and polarizer of FIG. 17 are mounted in a concave holder. (c) An assembled perspective view in which the Faraday rotator and polarizer of FIG. 17 are mounted in a flat plate holder. (d) The assembly perspective view which mounts the Faraday rotator and polarizer of FIG. 17 on a cooling element. The perspective view which shows the optical isolator of another form of this invention. The schematic diagram which shows the structure of the conventional optical isolator.

Explanation of symbols

1, 12, 14, 17 Faraday rotator 2, 2a, 2b Garnet single crystal 3 Garnet substrate 4, 5 Polarizer 6 Permanent magnet
7a, 7b, 7c Holder 8, 13, 15, 19 Optical isolator 9 Peltier element or heat sink
10, 16 Optical elements for optical isolators
11 Light transmission plate
18 Filler
20, 20a, 20b Paramagnetic garnet single crystal

Claims (25)

The Faraday rotator for short wavelength light includes a paramagnetic garnet single crystal and a bismuth-substituted rare earth iron garnet single crystal,
The paramagnetic garnet single crystal has Tb as a host rare earth element, and has a light transmittance of more than 99% for light in a wavelength region of 1030 nm or more and 1090 nm or less,
The paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal rotate the plane of polarization of incident light, and the Faraday rotation directions of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal, respectively. Are set in the same direction when viewed from the light propagation direction,
A magnetic field that sets the total Faraday rotation angle of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal to 45 degrees is applied to the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, applied to the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal by a permanent magnet,
When the wavelength of the light incident on the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal is λ (nm), λ is set to a wavelength condition of 1030 nm or more and 1090 nm or less,
The bismuth-substituted rare earth iron garnet single crystal is provided on at least one side of the paramagnetic garnet single crystal ,
The total thickness of the paramagnetic garnet single crystal and the bismuth-substituted rare earth iron garnet single crystal
The total is less than 1cm,
A Faraday rotator for short wavelength light, wherein the thickness of the paramagnetic garnet single crystal is 5 mm or more . The paramagnetic garnet single crystal chemical formula _{Tb 3 Ga 5 O 12, Tb} 3 Al 5 O 12, or, according to claim 1, characterized in that it comprises a composition represented by Tb ₃ Sc ₂ Ga ₃ O ₁₂ Faraday rotator for short wavelength light. The bismuth-substituted rare earth iron garnet single crystal in lattice constant, a Faraday rotator for short wavelength light according to claim 1 or 2, characterized in that it is set below 12.56Å more and 12.58A. Two bismuth-substituted rare earth iron garnet single crystals are provided;
The Faraday rotation directions of the two bismuth-substituted rare earth iron garnet single crystals and the paramagnetic garnet single crystal are set in the same direction when viewed from the light propagation direction,
Furthermore, a magnetic field that sets the total Faraday rotation angle of the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals to 45 degrees is
Applied to the bismuth-substituted rare earth iron garnet single crystal ,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, and is applied to the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals by a permanent magnet;
Thickness of the paramagnetic garnet single crystal and the two bismuth-substituted rare earth iron garnet single crystals
The sum of the total is less than 1cm,
Claims 1 to 3, wherein the thickness of the paramagnetic garnet single crystal is not less than 5mm
The Faraday rotator for short wavelength light according to any one of the above. Two Faraday rotators for short-wavelength light configured by providing the bismuth-substituted rare earth iron garnet single crystal on one side of the paramagnetic garnet single crystal, arranged in the light propagation direction,
The Faraday rotation directions of the two bismuth-substituted rare earth iron garnet single crystals and the two paramagnetic garnet single crystals are set in the same direction when viewed from the light propagation direction,
Furthermore, the magnetic field that sets the total Faraday rotation angle of the two paramagnetic garnet single crystals and the two bismuth-substituted rare earth iron garnet single crystals to 45 degrees includes two paramagnetic garnet single crystals and two Of the bismuth-substituted rare earth iron garnet single crystal ,
The magnetic field is set to 2000 Oe or more and 3000 Oe or less, and is applied to the two paramagnetic garnet single crystals and the two bismuth-substituted rare earth iron garnet single crystals by a permanent magnet;
Two single paramagnetic garnet single crystals and two single bismuth-substituted rare earth iron garnets
The total crystal thickness is less than 1 cm,
Two of the Faraday rotator for short wavelength light according to any one of claims 1 to 3, characterized in that the total thickness of the paramagnetic garnet single crystal is not less than 5 mm. Claim 4 wherein the bismuth-substituted rare earth iron garnet single crystal which is arranged on the incident side of the light, characterized in that said Faraday rotation angle than the other one of said bismuth-substituted rare earth iron garnet single crystal is smaller Or the Faraday rotator for short wavelength light of 5 . Among both surfaces of the bismuth-substituted rare earth iron garnet single crystal, a paramagnetic garnet substrate having Gd or Y as a host rare earth element is provided on one side opposite to the one side on which the paramagnetic garnet single crystal is provided,
The garnet substrate has a thermal conductivity of 5 W / m · K or more.
The Faraday rotator for short wavelength light according to any one of 6 . Among both surfaces of the bismuth-substituted rare earth iron garnet single crystal, a light transmission plate is provided on one side opposite to the one side on which the paramagnetic garnet single crystal is provided,
The light transmitting plate is short according to any one of claims 1 to 6, characterized in that it is formed of a material having more than four times the thermal conductivity of the thermal conductivity of the bismuth-substituted rare earth iron garnet single crystal Faraday rotator for wavelength light. The light transmission plate is made of a single crystal, and the light transmission plate is made of the bismuth-substituted rare earth so that the optical isotropic axis of the single crystal is perpendicular to the optical surface of the bismuth-substituted rare earth iron garnet single crystal. The Faraday rotator for short wavelength light according to claim 8 , wherein the Faraday rotator for short wavelength light is provided on one side of an iron garnet single crystal. The Faraday rotator for short wavelength light according to claim 7 , wherein the thickness of the garnet substrate is set to 1 mm or more. 2. The short wavelength light Faraday rotator is applied to a side surface of the short wavelength light Faraday rotator which is a non-light transmitting surface, and the short wavelength light Faraday rotator is bonded to a Peltier element or a heat sink. The Faraday rotator for short wavelength light according to any one of 1 to 10 . The metal layer is formed on a side surface of the Faraday rotator for short wavelength light which is a non-light transmitting surface, and the Faraday rotator for short wavelength light is bonded to a Peltier element or a heat sink by soldering. The Faraday rotator for short wavelength light according to any one of 1 to 10 . The Faraday rotator for short wavelength light, which is a non-light transmitting surface, is provided with a gold film on the side surface of the Faraday rotator for short wavelength light, and the Faraday rotator for short wavelength light is pressure bonded to the Peltier element or heat sink by thermocompression bonding. The Faraday rotator for short wavelength light according to any one of claims 1 to 10 . 11. An optical isolator comprising the polarizer on the light incident side and the light emitting side of the Faraday rotator for short wavelength light according to any one of claims 1 to 10 . 14. An optical isolator comprising the polarizer on the light incident side and the light emitting side of the Faraday rotator for short wavelength light according to any one of claims 11 to 13 . Each side surface which is a non-light transmitting surface of the Faraday rotator for short wavelength light and the polarizer is held by a holder formed of a material having a thermal conductivity of 15 W / mK or more,
The optical isolator according to claim 14 , wherein the bismuth-substituted rare earth iron garnet is connected to a Peltier element or a heat sink via the holder. Claim a thermosetting resin is applied to the side of the Faraday rotator for short wavelength light which is a non light transmitting surface, a Faraday rotator for the short wavelength light to said holder, characterized in that it is bonded 16
The optical isolator according to 1. The metal layer is formed on the side surfaces of the Faraday rotator for short wavelength light which is a non light transmitting surface, to claim 16, characterized in that the Faraday rotator for the short wavelength light is joined by soldering to the holder The optical isolator described. The Faraday rotator for short wavelength light is provided on the side surface of the Faraday rotator for short wavelength light which is a non-light transmitting surface, and the Faraday rotator for short wavelength light is pressure bonded to the holder by thermocompression bonding the gold film. The optical isolator according to claim 16 . The thermosetting resin is applied to the holder, the optical isolator according to any one of claims 16 to 19, wherein the holder to the Peltier element or heat sink is characterized in that it is bonded. The metal layer is formed on the holder, the optical isolator according to any one of claims 16 to 19, wherein the holder by soldering to the Peltier element or heat sink is characterized in that it is joined. The optical isolator according to any one of claims 16 to 19 , wherein a gold film is provided on the holder, and the gold film is thermocompression bonded so that the holder is pressure bonded to the Peltier element or the heat sink. A cross-sectional shape of the holder in a direction perpendicular to the light propagation direction is square, concave,
The optical isolator according to any one of claims 16 to 22 , wherein the optical isolator is a flat plate. The optical isolator according to any one of claims 16 to 23 , wherein a filler made of a material having thermal conductivity is filled in contact with the Faraday rotator for short wavelength light and the holder. . 25. The Faraday for short wavelength light according to any one of claims 1 to 24 , wherein the Faraday rotator for short wavelength light or the optical isolator is used under a temperature condition of -10 degrees or more and 80 degrees or less. Rotor or optical isolator.

Images