JP2006146092A - Single core bidirectional optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single core bidirectional optical module in which the reduction of the coupling efficiency between an optical fiber and a laser diode due to a temperature rise can be prevented. <P>SOLUTION: The single core bidirectional optical module is equipped with; a supporting stand on which a photodiode and a laser diode are mounted; a 1st lens and a diffraction grating which are fixed to a module housing so as to be located between the optical fiber and the supporting stand; and a holding member which is provided on the supporting stand, and which holds the laser diode, and the optical module is characterized in that the zero-order diffracted light which is emitted from the optical fiber, and is diffracted by the diffraction grating is converged by the 1st lens to be optically coupled with the photodiode, and ±1st or higher-order diffracted light beams which are emitted from the laser diode, and are diffracted by the diffraction grating are converged by the 1st lens to be optically coupled with the optical fiber, and the holding member displaces the laser diode to a direction separating from the optical axis of the zero-order diffracted light in accordance with the temperature rise. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a single-fiber bidirectional optical module used for bidirectional communication using two or more wavelengths through a single optical fiber.

  FIG. 4 is a cross-sectional view showing a conventional single-fiber bidirectional optical module. As shown in the figure, the 0th-order diffracted light emitted from the laser diode 41 and diffracted by the diffraction grating 42 is converged by the lens 43 and optically coupled to the optical fiber 44. The first-order or higher-order diffracted light emitted from the optical fiber 44 and diffracted by the diffraction grating 42 is converged by the lens 43 and optically coupled to the photodiode 45.

  That is, in the conventional single-core bidirectional module, 0th-order diffracted light is used as transmitted light, and high-order diffracted light is used as received light (see, for example, Patent Document 1).

  Here, since the diffraction angle of the 0th-order diffracted light is 0 degrees irrespective of the wavelength, high coupling efficiency can be stably obtained even if the wavelength of the laser diode changes depending on the temperature. On the other hand, although the diffraction angle of the higher-order diffracted light changes depending on the wavelength, the use of a photodiode having a large light diameter can prevent a decrease in coupling efficiency. However, the received light is subjected to first-order or higher-order diffraction and the diffraction efficiency is lowered, so that there is a problem that sufficient reception sensitivity cannot be obtained.

  Thus, a single-fiber bidirectional optical module has been proposed that uses 0th-order diffracted light as received light and high-order diffracted light as transmitted light (see, for example, Patent Document 2). By using 0th-order diffracted light with high diffraction efficiency as received light, the dynamic range between transmission and reception can be expanded, and signals can be transmitted to a longer distance and optically distributed.

US Patent 4,834,485 “Integrated Fiber Optics Transmitter / Receiver Device” JP-A-5-241049

  However, since the emitted light of the laser diode changes to the longer wavelength side due to the temperature rise, the diffraction angle of the emitted light increases. Therefore, when high-order analysis light is used as the transmitted light, the condensing position of the emitted light of the laser diode is shifted in the direction away from the optical axis of the 0th-order diffracted light due to the temperature rise, and the coupling efficiency between the optical fiber and the laser diode is lowered. There was a problem to do.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a single-fiber bidirectional optical module that can prevent a reduction in coupling efficiency between an optical fiber and a laser diode due to a temperature rise.

  A single-fiber bidirectional optical module according to the present invention includes a support base on which a photodiode and a laser diode are mounted, a first lens and a diffraction grating fixed to the module housing so as to be positioned between the optical fiber and the support base. And a holding member for holding the laser diode, and the zero-order diffracted light emitted from the optical fiber and diffracted by the diffraction grating is converged by the first lens and optically applied to the photodiode. The first-order or higher-order diffracted light that is coupled, emitted from the laser diode, and diffracted by the diffraction grating is converged by the first lens and optically coupled to the optical fiber. Then, the laser diode is displaced in a direction away from the optical axis of the 0th order diffracted light. Other features of the present invention will become apparent below.

  According to the present invention, it is possible to prevent a decrease in the coupling efficiency between the optical fiber and the laser diode due to temperature rise.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing a single-fiber bidirectional optical module according to Embodiment 1 of the present invention. As shown in the figure, the first lens 13 and the diffraction grating 14 are fixed to the module housing 15 so as to be positioned between the optical fiber 11 and the support base (stem) 12. A photodiode 16 is mounted on the support base 12 at the condensing position of the 0th-order diffracted light emitted from the optical fiber 11, and a laser diode 18 is mounted on the holding member 17. A second lens 19 is integrally provided in the laser beam emission direction of the laser diode 18.

  The optical fiber 11 is a single mode optical fiber, and transmits two wavelengths of light having wavelengths of 1.3 μm and 1.5 μm. Then, the 0th-order diffracted light emitted from the optical fiber 11 and diffracted by the diffraction grating 14 is converged by the first lens 13 and optically coupled to the photodiode 16. As a result, the 1.5 μm received light emitted from the optical fiber 11 is converted into an electrical signal by the photodiode 16. On the other hand, ± first-order or higher-order diffracted light emitted from the laser diode 18 and diffracted by the diffraction grating 14 is converged by the first lens 13 and optically coupled to the optical fiber 11. As a result, the 1.3 μm transmission light emitted from the laser diode 18 enters the optical fiber 11 and is transmitted far away.

  Further, assuming that the wavelength of light emitted from the optical fiber 11 is λ, the refractive index of the members constituting the diffraction grating 14 is n, N is an arbitrary integer of 1 or more, and the grating groove search of the diffraction grating 14 is d, d = It is configured to have a relationship of N · λ / (n−1). Thereby, the diffraction grating 14 can transmit almost 100% of the 0th-order diffracted light for reception.

  The holding member 17 is a bimetal obtained by bonding a copper plate (first metal plate) 17a and a Kovar plate (second metal plate) 17b having a lower thermal expansion coefficient than the copper plate 17a by cold rolling or hot rolling. It is. The holding member 17 is fixed on the support base 12 by silver brazing so that the copper plate 17a is closer to the optical axis of the 0th-order diffracted light than the Kovar plate 17b. The laser diode 18 is held on the side surface of the holding member 17 by soldering.

  The holding member 17 displaces the laser diode 18 in a direction away from the optical axis of the 0th-order diffracted light as the temperature rises. As a result, the laser diode 18 is displaced to the optimum coupling position as the temperature rises, so that the coupling efficiency between the optical fiber 11 and the laser diode 18 due to the temperature rise can be prevented. Further, by using a bimetal as the holding member 17, such an effect can be produced with an inexpensive configuration.

  Specifically, the oscillation wavelength of the laser diode 18 changes depending on the temperature, and the rate of change is about 0.4 nm / ° C. Therefore, when the temperature of the laser diode 18 changes by 100 ° C., the oscillation wavelength changes by about 40 nm, and accordingly, the first-order diffraction angle changes by about 0.01 °. On the other hand, the bimetal constituting the holding member 17 displaces the laser diode 18 and the second lens in the direction perpendicular to the optical axis by about 10 μm due to the temperature change of 100 ° C. As a result, the change in the first-order diffraction angle due to the change in the oscillation wavelength described above and the displacement caused by the holding member 17 cancel each other, and a constant coupling efficiency can be maintained.

  In addition, since the bimetal and the laser are joined close together, there is almost no temperature difference between them, and the oscillation wavelength change and the displacement due to the bimetal occur almost simultaneously, so that the coupling efficiency is always constant even in the transient state of the temperature change. Can keep. Since the copper plate has a high thermal conductivity, the heat generated by the laser diode 18 is effectively radiated to the periphery.

  In addition, since the laser diode 18 and the second lens 19 are integrally provided, the laser diode 18 and the second lens can be moved integrally, so that the optical fiber 11 and the laser due to temperature rise more reliably. A reduction in the coupling efficiency of the diode 18 can be prevented.

Embodiment 2. FIG.
FIG. 2 is a cross-sectional view showing a single-fiber bidirectional optical module according to Embodiment 2 of the present invention. Constituent elements similar to those in FIG.

  In the second embodiment, the thermal expansion coefficient of the constituent material of the module housing is asymmetric about the optical axis of the 0th-order diffracted light. The module housing 15a on the laser diode 18 side is made of Kovar material, and the module housing 15b on the other side is made of steel material. That is, the constituent material on the laser diode 18 side has a lower coefficient of thermal expansion than the constituent material on the other side. Further, the holding member 17 that holds the laser diode 18 is formed of a simple copper plate, not a bimetal. Other configurations are the same as those in the first embodiment.

  Then, as the temperature rises, the entire module housings 15a and 15b are warped, so that the first lens 13 is displaced in the direction perpendicular to the optical axis of the 0th-order diffracted light. As a result, the first lens is displaced to the optimum coupling position as the temperature rises, and as in the first embodiment, it is possible to prevent a reduction in the coupling efficiency between the optical fiber and the laser diode due to the temperature rise. Further, by making the coefficient of thermal expansion of the constituent material of the module casing asymmetric, such an effect can be produced with an inexpensive configuration.

  Although the 0th-order diffracted light incident on the photodiode 16 is slightly displaced with the temperature change, the coupling efficiency does not decrease because the light receiving diameter of the photodiode 16 is about 20 μm.

Embodiment 3 FIG.
FIG. 3 is a sectional view showing a single-fiber bidirectional optical module according to Embodiment 3 of the present invention. Constituent elements similar to those in FIG.

  In the third embodiment, the optical fiber 11 is held by the holding member 20. Further, the holding member 17 that holds the laser diode 18 is formed of a simple copper plate, not a bimetal. Other configurations are the same as those in the first embodiment.

  The holding member 20 is a bimetal obtained by bonding a copper plate (first metal plate) 20a and a Kovar plate (second metal plate) 20b having a thermal expansion coefficient lower than that of the copper plate 20a by cold rolling or hot rolling. It is. The holding member 17 is fixed to the support base 12 by silver brazing so that the copper plate 20a is closer to the optical axis of the 0th-order diffracted light than the Kovar plate 20b. The optical fiber 11 is held on the side surface of the holding member 17 by soldering.

  The holding member 20 displaces the optical fiber 11 in a direction away from the optical axis of the 0th-order diffracted light as the temperature rises. As a result, the optical fiber 11 is displaced to the optimum coupling position as the temperature rises, so that it is possible to prevent a reduction in the coupling efficiency between the optical fiber 11 and the laser diode 18 due to the temperature rise. Further, by using a bimetal as the holding member 20, such an effect can be produced with an inexpensive configuration.

  Since the light receiving diameter of the photodiode 16 is about 20 μm, the coupling efficiency does not decrease even if the optical fiber 11 is displaced.

It is sectional drawing which shows the single fiber bidirectional optical module which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the single fiber bidirectional optical module which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the single fiber bidirectional optical module which concerns on Embodiment 3 of this invention. It is sectional drawing which shows the conventional single fiber bidirectional optical module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Support stand 13 1st lens 14 Diffraction gratings 15, 15a, 15b Module housing 16 Photodiode 17 Holding member 18 Laser diode 19 Second lens 20 Holding member

Claims (8)

A support base on which a photodiode and a laser diode are mounted;
A first lens and a diffraction grating fixed to the module housing so as to be positioned between the optical fiber and the support;
A holding member provided on the support base and holding the laser diode;
The zero-order diffracted light emitted from the optical fiber and diffracted by the diffraction grating is converged by the first lens and optically coupled to the photodiode,
± 1st or higher order diffracted light emitted from the laser diode and diffracted by the diffraction grating is converged by the first lens and optically coupled to the optical fiber;
The single-fiber bidirectional optical module, wherein the holding member displaces the laser diode in a direction away from the optical axis of the 0th-order diffracted light as the temperature rises.   Assuming that the wavelength of the light emitted from the optical fiber is λ, the refractive index of the members constituting the diffraction grating is n, N is an arbitrary integer of 1 or more, and the grating groove search of the diffraction grating is d, d = N · The single-fiber bidirectional optical module according to claim 1, wherein the single-fiber bidirectional optical module has a relationship of λ / (n−1). The holding member is a bimetal obtained by bonding a first metal plate and a second metal plate having a lower thermal expansion coefficient than the first metal plate,
The holding member is fixed on the support base so that the first metal plate is closer to the optical axis of the 0th-order diffracted light than the second metal plate,
The single-fiber bidirectional optical module according to claim 1, wherein the laser diode is held on a side surface of the holding member.   4. The single-fiber bidirectional optical module according to claim 3, further comprising a second lens provided integrally in a laser beam emission direction of the laser diode. A support base on which a photodiode and a laser diode are mounted;
A first lens and a diffraction grating fixed to the module housing so as to be positioned between the optical fiber and the support;
The zero-order diffracted light emitted from the optical fiber and diffracted by the diffraction grating is converged by the first lens and optically coupled to the photodiode,
± 1st or higher order diffracted light emitted from the laser diode and diffracted by the diffraction grating is converged by the first lens and optically coupled to the optical fiber;
A single-fiber bidirectional optical module, wherein the first lens is displaced in a direction perpendicular to the optical axis of the 0th-order diffracted light by warping the entire module housing as the temperature rises.   In the module housing, the thermal expansion coefficient of the constituent material is asymmetric about the optical axis of the 0th-order diffracted light, and the constituent material on the laser diode side has a lower thermal expansion coefficient than the constituent material on the other side. 6. The single-fiber bidirectional optical module according to claim 5, wherein A support base on which a photodiode and a laser diode are mounted;
A first lens and a diffraction grating fixed to the module housing so as to be positioned between the optical fiber and the support;
A holding member for holding the optical fiber,
The zero-order diffracted light emitted from the optical fiber and diffracted by the diffraction grating is converged by the first lens and optically coupled to the photodiode,
± 1st or higher order diffracted light emitted from the laser diode and diffracted by the diffraction grating is converged by the first lens and optically coupled to the optical fiber;
The single-fiber bidirectional optical module, wherein the holding member displaces the optical fiber in a direction away from the optical axis of the 0th-order diffracted light as the temperature rises. The holding member is a bimetal obtained by bonding a first metal plate and a second metal plate having a lower thermal expansion coefficient than the first metal plate,
The holding member is fixed to the module housing such that the first metal plate is closer to the optical axis of the 0th-order diffracted light than the second metal plate,
The single-fiber bidirectional optical module according to claim 1 or 2, wherein the optical fiber is held on a side surface of the holding member.

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