JP2006147769A - Cap for optical element, optical element and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module which can be easily assembled and is a built-in optical isolator type, as well as an optical element and a cap for the optical element which are used therefor. <P>SOLUTION: The cap for an optical element is provided with an optical isolator that is provided with an optical member joint body wherein rutile single crystals 44 and 45 are connected to both sides of a Faraday rotator crystal 46 and the rutile single crystal is spherically processed, a window glass 42 for hermetical sealing and light transmission, and a metallic cap (main body of cap) 41. The end face of a cylindrical magnet 47 which applies magnetic field to the Faraday rotator crystal 46 and holds the optical joint body is adhered and fixed to the inside of the metallic cap (main body of cap) 41. In addition, the cap for the optical element is used to manufacture an optical element with the optical isolator, and an optical fiber is aligned with the optical element and it is secured thereto, thereby obtaining the optical module of built-in optical isolator type. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element cap integrated with an optical isolator that transmits light only in one direction, and an optical element and an optical module using the cap.

  In general, as an optical module used for optical communication, an LD module for transmitting an optical signal and a PD module for receiving an optical signal are known. In particular, in the case of an optical information processing system that requires large capacity, high speed, and long-distance relay communication function, as a light emitting element for O / E conversion (light / electric conversion) mounted inside an LD module, A distributed feedback semiconductor laser (hereinafter referred to as a DFB laser) is used. This DFB laser has the characteristics that the oscillation spectrum is narrow and has excellent dispersion characteristics, but on the other hand, it is very sensitive to the return light due to the reflected light, and from the coupling end face to the optical fiber and other discontinuous interfaces. When the reflected light returns, the characteristic becomes unstable. Therefore, in the optical module, in order to prevent the reflected light from returning to the light emitting element, a one-way transmission function of light (transmits light in the forward direction and blocks light in the reverse direction) between the light emitting element and the optical fiber. The optical isolator having a function) is disposed, and the return light of the reflected light from the optical fiber in the direction of the light emitting element is blocked by the optical eyelator, so that the light emitting element is always stably operated.

  Therefore, as a means for blocking this kind of reflected return light, a structure in which light in the oscillation polarization direction is transmitted and a nonreciprocal element for blocking the return light is arranged in the vicinity of the semiconductor laser has become common. This optical isolator is often placed not in the vicinity of a semiconductor laser but in the middle of the optical circuit due to maintenance of the optical circuit and structural limitations.

  Incidentally, since the optical semiconductor element needs to be hermetically sealed, it is hermetically sealed with a metal cap 11 in which a window glass 12 that transmits light is sealed with a low melting point glass 13 as shown in FIG. In addition, as shown in FIG. 6, a metal cap 21 in which a lens 22 is sealed with a low-melting glass 23 instead of a window glass is used, so that a lens function is added to the cap. FIG. 7 shows a layout of an optical module including an optical semiconductor element having a cap as shown in FIG. 6 and an optical isolator. Reference numeral 34 denotes a stem, 35 denotes a semiconductor laser chip, 31 denotes a metal cap, 32 denotes a lens, 33 denotes low-melting glass, 36 denotes an optical isolator, and 37 denotes a ferrule with an optical fiber.

  Patent Document 1 discloses an optical semiconductor hermetic sealing container having a cap with an optical isolator.

JP 2004-79963 A

  When an optical module with an optical isolator is manufactured using the cap as shown in FIG. 5 or FIG. 6, it is necessary to dispose the optical isolator on the optical path. In the case of the optical module with the optical isolator using the optical element using the cap having the lens function of FIG. 6, the optical isolator is arranged between the lens and the ferrule with the optical fiber as shown in FIG. Not only is it necessary to provide mechanical parts that separately align the ferrule with an optical fiber, but it is difficult to reduce the number of assembly steps.

  On the other hand, in the case of the optical semiconductor hermetic sealing container according to claim 2 of Patent Document 1, a cap in which a lens and an optical isolator are arranged in series is used. However, because of the length in the optical path direction occupied by the optical isolator, There are many restrictions on the setting of the optical system for effectively coupling the light emission of the semiconductor to the optical fiber, and as a result, the entire mechanical component becomes large.

  In this situation, an object of the present invention is to provide an optical module with a built-in optical isolator that is easy to assemble, has a small size, and has a simple structure, an optical element used therefor, and an optical element cap.

  The present invention has been made to solve the above-described problems, and has been made by integrating an optical isolator having a spherically processed polarizer with a cap while maintaining hermetic sealing performance of the cap.

  The optical element cap of the present invention includes an optical isolator having an optical member assembly in which a polarizer is bonded to both sides of a Faraday rotation crystal and a spherical surface is applied to the polarizer, and for hermetic sealing and light transmission. And a cap main body. In this way, an optical isolator formed by applying spherical processing to a polarizer that selects specific polarized light bonded to both sides of a Faraday rotator that rotates the polarization direction of light non-reciprocally, and processing to give a lens action, By integrating the cap with a window glass that is hermetically sealed, the cap is placed while taking advantage of the optical isolator.

  The optical isolator may be disposed and integrated inside the window hermetically sealed. In this way, the above-described optical isolator is arranged inside the hermetic seal, the optical isolator having a lens action is brought close to the semiconductor laser chip, and the effective diameter of the optical isolator is reduced to reduce the cost.

  Further, the optical isolator may be arranged and integrated outside the window which is not hermetically sealed. By disposing the optical isolator outside the hermetic seal in this way, it is not necessary to reduce the degassing from the organic adhesive, and the range of usable organic adhesives can be increased to facilitate the overall design.

  The optical isolator may be formed by disposing the optical member assembly inside a cylindrical magnet, and an end surface of the cylindrical magnet and the cap body portion may be bonded. This structure facilitates the joining of the optical isolator and the cap body.

  The optical element of the present invention includes the optical element cap and a semiconductor laser chip. In this way, an optical element in which the optical isolator is integrated with a small and simple structure is obtained.

  The optical module of the present invention includes the optical element and an output optical fiber. Thus, an optical module with a built-in optical isolator that is small and simple in structure and easy to assemble is obtained.

  According to the present invention, since the optical isolator having a lens action is integrated into the optical element cap, the optical element with the optical isolator can be reduced in size and simplified in structure. In addition, it is possible to reduce the number of man-hours for assembling an optical module manufactured by coupling the output of the optical element to an optical fiber.

  That is, according to the present invention, it is possible to provide an optical module that is easy to assemble, has a small and simple structure, an optical element used therefor, and an optical element cap.

  The cap for an optical element according to an embodiment of the present invention is a bonded body composed of a Faraday rotating crystal that rotates the polarization plane of light nonreciprocally and two polarizers that select specific polarized light bonded to both sides thereof. On the other hand, an optical isolator formed by applying spherical processing to the polarizers on both sides and refracting the light transmitted through the polarizer to form an image is formed inside or outside the cap with window glass for hermetic sealing. It is made by fixing as one.

  An optical device according to an embodiment of the present invention is manufactured by hermetically sealing a semiconductor laser chip on a heat sink fixed to a stem having pin terminals with the optical device cap according to an embodiment of the present invention.

  An optical module according to an embodiment of the present invention is manufactured by arranging the output of the optical element according to an embodiment of the present invention so as to be coupled to an optical fiber.

  FIG. 1 is a cross-sectional view showing the basic structure of an optical element cap (a cap with a window integrated with an optical isolator) according to a first embodiment of the present invention. As a material (optical member) of the optical isolator, a GdBi iron garnet film (GdBiIG thick film) is used as a Faraday rotation crystal, and a rutile single crystal plate having a thickness of 0.9 mm is used as a polarizer. A non-reflective coating having a refractive index of 1.5 on one side was applied. The set wavelength of the antireflective coating applied to the GdBi iron garnet film and the rutile single crystal plate is 1550 nm. First, EPOTECH 353ND organic adhesive was applied to the antireflective coating with a refractive index of 1.5 on one rutile single crystal plate, and the GdBi iron garnet film was bonded and fixed with the respective edges aligned. Next, another rutile single crystal plate was fixed and cured in a state where the reverse loss was maximized. The cured sample was cut with a dicing saw and polished into a spherical shape by wet barrel polishing. In this way, an R1.0 mm spherical optical member assembly made of the rutile single crystals 44 and 45 and the Faraday rotation crystal 46 shown in FIG. 1 was obtained. Next, this optical member assembly was fixed inside the cylindrical magnet 47 using the organic adhesive 48 to complete the optical isolator.

  The optical isolator thus formed was adhered and fixed to the inner surface of the metal cap (cap body portion) 41 in which the window glass 42 was sealed with the low melting point glass 43 at the end face of the cylindrical magnet 47.

  At this time, characteristics of a forward loss of 0.8 dB and a backward loss of 45 dB were obtained at a wavelength of 1550 nm. The forward loss of about 0.7 dB corresponding to the Fresnel reflection loss was improved by re-applying the antireflection coating for air lost during barrel polishing.

  FIG. 2 is a cross-sectional view showing the basic structure of an optical element cap (a cap with a window integrated with an optical isolator) according to a second embodiment of the present invention. As the material of the optical isolator, a GdBi iron garnet film (GdBiIG thick film) was used as a Faraday rotation crystal. A rutile single crystal plate having a thickness of 0.9 mm was used as a polarizer, and a non-reflective coating with a single-sided refractive index of 1.0 and a single-sided refractive index of 1.5 was applied. The set wavelength of the antireflection coating applied to the GdBi iron garnet film and the rutile single crystal plate is 1310 nm. First, EPOTECH 353ND organic adhesive was applied to the antireflective coating with a refractive index of 1.5 on one rutile single crystal plate, and the GdBi iron garnet film was bonded and fixed with the respective edges aligned. Next, another rutile single crystal plate was fixed and cured. The cured sample was cut with a dicing saw and polished into a spherical shape by wet barrel polishing. In this way, an R1.0 mm spherical optical member assembly comprising the rutile single crystals 54 and 55 and the Faraday rotation crystal 56 shown in FIG. 2 was obtained. Next, this optical member assembly was fixed inside the cylindrical magnet 57 using the organic adhesive 58 to complete the optical isolator.

  The optical isolator thus formed was adhered and fixed to the outside of the metal cap 51 in which the window glass 52 was sealed with the low melting point glass 53 at the end face of the cylindrical magnet 57.

  At this time, characteristics of a forward loss of 0.8 dB and a backward loss of 45 dB were obtained at a wavelength of 1310 nm. The forward loss of about 0.7 dB corresponding to the Fresnel reflection loss was improved by re-applying the antireflection coating for air lost during barrel polishing.

  FIG. 3 is a partial cross-sectional view showing an optical element according to Example 3 of the present invention. Using the optical element cap of Example 2, the semiconductor laser chip 35 fixed through the heat sink 39 on the stem 34 provided with the pin terminals 38 was hermetically sealed, thereby producing the optical element of Example 3. As described above, when the optical element cap of the present invention is used, an optical element with an optical isolator can be manufactured in the same process as an optical element without an optical isolator.

  FIG. 4 is a partial cross-sectional view showing an optical module according to Embodiment 4 of the present invention. The optical module with built-in optical isolator of the present invention is obtained simply by aligning and fixing the ferrule 37 with an optical fiber so that the optical output of the optical element of Example 3 is narrowed down to the core on the end face of the optical fiber. If the optical element using the optical element cap of Example 1 is used, the distance between the semiconductor laser chip and the optical isolator having a lens function can be made closer, and the effective diameter of the optical isolator can be reduced. Therefore, not only can the material cost be reduced, but the distance between the optical isolator and the end face of the optical fiber can be reduced at the same time, so that the optical path can be downsized.

Sectional drawing of the cap for optical elements in Example 1 of this invention. Sectional drawing of the cap for optical elements in Example 2 of this invention. FIG. 9 is a partial cross-sectional view of an optical element in Example 3 of the present invention. The fragmentary sectional view of the optical module in Example 4 of the present invention. Sectional drawing of the conventional cap with a window glass. Sectional drawing of the conventional cap with a lens. FIG. 6 is a layout view of a conventional optical module with an optical isolator.

Explanation of symbols

11, 21, 31, 41, 51 Metal cap 12, 42, 52 Window glass 13, 23, 33, 43, 53 Low melting point glass 22, 32 Lens 34 Stem 35 Semiconductor laser chip 36 Optical isolator 37 Ferrule 38 pin with optical fiber Terminal 39 Heat sink 44, 45, 54, 55 Rutile single crystal 46, 56 Faraday rotating crystal 47, 57 Cylindrical magnet 48, 58 Organic adhesive

Claims (6)

  An optical isolator having an optical member assembly in which a polarizer is bonded to both sides of a Faraday rotating crystal and spherical processing is performed on the polarizer, a window for hermetic sealing and light transmission, and a cap body A cap for optical elements, comprising:   2. The optical element cap according to claim 1, wherein the optical isolator is disposed and integrated inside an airtight seal of the window.   2. The optical element cap according to claim 1, wherein the optical isolator is disposed and integrated outside the window not hermetically sealed.   4. The optical element cap according to claim 1, wherein the optical isolator includes the optical member assembly disposed inside a cylindrical magnet, and an end surface of the cylindrical magnet, the cap body portion, A cap for an optical element, characterized in that is bonded.   An optical element comprising the optical element cap according to claim 1 and a semiconductor laser chip.   An optical module comprising the optical element according to claim 5 and an output optical fiber.

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