JP5793837B2 - Optical module - Google Patents

Description

  The present invention relates to an optical module connected to an optical cable.

  An optical module for transmission used in optical communication uses light from a laser diode (LD) as signal light, and the signal light is collected by a lens and coupled to a communication optical fiber. . The receiving optical module collects the signal light transmitted through the optical fiber with a lens and receives the light with a receiving photodiode (PD). There is also a single-fiber bidirectional transmission / reception optical module that performs both transmission and reception using a single optical fiber.

  When optical coupling between such an optical device and an optical fiber is performed with two lenses, a parallel beam is formed with the optical fiber and one lens, and a parallel beam is formed with the other lens and the optical device. Two parallel beams are aligned. For example, Patent Documents 1, 2, and 3 are cited as documents disclosing optical modules using such a parallel beam optical system.

JP 2008-90231 A JP 2005-309370 A US Pat. No. 6,201,908

  However, in an optical module using a parallel beam optical system, there is a problem that adjustment of a parallel beam for obtaining a large light output becomes complicated and productivity of the optical module is lowered. Specifically, the adjustment of the parallel beam requires an accuracy of about ± several μm, and the angle tolerance is small and the number of adjustment axes is increased. Furthermore, since it is determined whether or not the adjustment has been made by visually confirming an image showing the parallel beam, it is difficult to quantify the degree of adjustment, which makes the adjustment of the parallel beam even more difficult.

  In particular, since the optical module of Patent Document 1 employs a parallel beam optical system, four optical filters, a fiber collimating lens provided at the fiber end of the optical fiber, and four collimating lenses having a condensing position on the laser diode. Is required. When assembling this optical module, the fiber collimating lens is first installed at a predetermined reference position, and the positions of the optical fiber, optical filter, and collimating lens are adjusted so that the beam is parallel to the installed fiber collimating lens. The

  Also, when assembling the optical module, in order to optically couple the laser diode and the optical fiber with high efficiency, it is necessary to match the spot size of the laser diode (about 1 μm) with the spot size of the optical fiber (about 5 μm). is there. In this case, it is preferable to first assemble the laser diode and the collimating lens, and then assemble the optical fiber and the fiber collimating lens. This is because if the optical fiber and the fiber collimating lens are assembled first, the spot size of the laser diode is about 1 μm, so that it is necessary to optically couple the optical fiber and the laser diode with this accuracy. However, in the optical module of Patent Document 1, since it is necessary to optically couple four laser diodes to one optical fiber, it is necessary to finally assemble a laser diode and a collimating lens, and high accuracy is required for optical coupling. Will be.

  Another problem is that the optical coupling between the collimating lenses has a small tolerance for the angle. FIG. 9 is a diagram illustrating a test result of coupling loss of optical coupling due to a deviation of the light incident angle with respect to the collimating lens. In this test, as shown in FIG. 9B, the separation distance between the collimating lens and the objective lens is 5 mm, the work distance between the collimating lens and the fiber end is 1.762 mm, and the work distance between the objective lens and the laser diode is 0.297 mm. Then, the incident angle of the light is changed by shifting the position of the laser diode in the direction orthogonal to the optical axis, and the coupling loss at each position is measured. FIG. 9A shows that a coupling loss of −0.5 dB occurs when the light incident angle is shifted by 5 degrees. For this reason, in the optical module of Patent Document 1, it is necessary to adjust the incident angle of light with high accuracy.

  In addition, in the optical module of Patent Document 1, four lights having different wavelengths are combined using four optical filters. However, when considering miniaturization of the optical module, the angle between the optical filter and the incident light is changed. It needs to be 45 degrees. In this case, if the wavelength interval of the four lights is reduced, the angle of the optical filter can be adjusted with high accuracy and the spread angle of the light transmitted through the collimating lens can be adjusted with high accuracy due to the dependency of the optical filter on the light incident angle. It becomes necessary to do.

  The present invention has been made in view of the above-described actual situation, and enables the laser diode and the optical fiber to be optically coupled with an appropriate adjustment allowance, and can realize downsizing easily and at low cost. An object of the present invention is to provide an optical module that can be used.

An optical module according to the present invention is an optical module that multiplexes light having different wavelengths emitted from at least four optical elements and optically couples each optical element with an optical fiber, and is emitted from the first optical element. The first wavelength λ1, the second wavelength λ2 emitted from the second optical element, the third wavelength λ3 emitted from the third optical element, and the fourth wavelength λ4 emitted from the fourth optical element A first condensing lens that condenses the light of each wavelength , and the collected light of the first wavelength λ1 and the condensed light of the third wavelength λ3. The first multiplexing filter for multiplexing, the second multiplexing filter for multiplexing the collected light of the second wavelength λ2 and the collected light of the fourth wavelength λ4, and the first multiplexing filter. A synthesis filter for synthesizing the waved light and the light multiplexed by the second multiplexing filter, and the synthesis filter A second condensing lens that condenses the light synthesized by the filter, and the position of the beam waist by the first condensing lens of the light of the first wavelength λ1 and the light of the third wavelength λ3 is the first The position of the beam waist by the first condenser lens of the light of the second wavelength λ2 and the light of the fourth wavelength λ4 is on the surface of the second multiplexing filter. The position of one beam waist of the second condenser lens is on the surface of the first combining filter and the surface of the second combining filter.

The optical module according to the present invention may have an optical isolator disposed in the optical path between the optical fiber and the synthesis filter.
The first to fourth wavelengths can be set to λ1 <λ2 <λ3 <λ4.
Also, the image magnification of the second focusing lens is a magnification for example.

  According to the optical module of the present invention, it is possible to optically couple a laser diode and an optical fiber with an appropriate adjustment tolerance, and it is possible to easily realize downsizing at a low cost.

FIG. 1 is a diagram illustrating an example of an optical module according to the present embodiment. FIG. 2 is a conceptual diagram illustrating an optical isolator. FIG. 3 is a diagram showing the relationship between the coupling loss of the optical isolator according to this embodiment and the separation distance between ordinary light and extraordinary light. FIG. 4 is a diagram showing the relationship between P-wave transmission loss and wavelength. FIG. 5 is a diagram illustrating the relationship between the spot size, the spread angle of incident light, and the distance from the beam waist. FIG. 6 is a diagram showing the relationship between S-wave transmission loss and wavelength. FIG. 7 is a diagram showing the relationship between the P-wave insertion loss and S-wave insertion loss and the wavelength. FIG. 8 is a diagram illustrating an example of dimensions of the optical module according to the present embodiment. FIG. 9 is a diagram illustrating a test result of coupling loss of optical coupling due to a deviation of the light incident angle with respect to the collimating lens.

  An outline of an optical module according to the present invention will be described. FIG. 1 is a diagram illustrating an example of an optical module 10 according to the present embodiment. The optical module 10 is a transmission optical module including four laser diodes 14a to 14d that generate signal lights (wavelengths λ1 to λ4) having different wavelengths.

  The optical module 10 includes a fiber condensing lens holder 11, a multiplexing filter holder 12, laser diodes 14a to 14d, a sleeve 15, transmission units 16a to 16d, joint sleeves 17a to 17d, first condensing lenses 18a to 18d, A second condenser lens 19, an optical isolator 20, first and second multiplexing filters 21 a and 21 b (WDM (Wavelength Division Multiplexing) filters), and a synthesis filter 22 are provided. Here, the first multiplexing filter 21a is installed at an angle of about 45 degrees with respect to the traveling direction of the light emitted by the transmission units 16a and 16c. The second multiplexing filter 21b is installed at an angle of about 45 degrees with respect to the traveling direction of the light emitted by the transmission units 16b and 16d. The synthesis filter 22 is installed at an angle of about 45 degrees with respect to the traveling direction of the light combined by the first and second multiplexing filters 21a and 21b. The synthesis filter 22 is a filter that synthesizes polarized waves. In the present embodiment, the synthesis filter 22 includes a P wave (parallel) component of light combined by the first combining filter 21a and an S wave (senkrecht) of light combined by the second combining filter 21b. Synthesize ingredients.

  A transmission unit in which a sleeve 15 for accommodating and holding the optical fiber 13 is joined to one end of the fiber condensing lens holder 11, and a laser diode 14a for emitting signal light of wavelength λ1 is mounted on the opposite end. 16a is joined. Further, a transmission unit 16c on which a laser diode 14c that emits signal light having a wavelength λ3 is mounted is joined to one side surface of the fiber condensing lens holder 11.

  A multiplexing filter holder 12 that accommodates the second multiplexing filter 21 b is joined to the opposite side surface of the fiber condensing lens holder 11. Further, a transmission unit 16b on which a laser diode 14b that emits signal light having a wavelength λ2 is mounted is joined to the side surface of the multiplexing filter holder 12. Further, on the other side surface of the multiplexing filter holder 12, a transmission unit 16d on which a laser diode 14d that emits signal light having a wavelength λ4 is mounted is joined.

  In the optical path in the fiber condenser lens holder 11, a first multiplexing filter 21 a, a synthesis filter 22, a second condenser lens 19, and an optical isolator 20 are arranged. A second multiplexing filter 21 b is disposed in the optical path in the multiplexing filter holder 12. The optical isolator 20 is a polarization-independent isolator that does not depend on the polarization state of incident light, and is a press-fit, resin, YAG (yttrium-aluminum-garnet) laser so as to match the dimensions of the fiber condenser lens holder 11. It is fixed by welding or the like. The optical isolator 20 may be disposed between the second condenser lens 19 and the synthesis filter 22.

  FIG. 2 is a conceptual diagram illustrating the optical isolator 20. As shown in FIG. 2, the optical isolator 20 includes birefringent crystal plates 20a and 20d made of rutile or the like, a Faraday rotator 20b, and a λ / 2 wavelength plate 20c. When light is incident on the optical isolator 20 in the forward direction (in the case of FIG. 2A), the birefringent crystal plate 20a makes the incident light normal light (straightly traveling light) and abnormal depending on the polarization direction of the incident light. It separates into two components of light (refracted light). The separation distance between ordinary light and extraordinary light is generally about 1/10 of the crystal optical axis direction. The Faraday rotator 20b and the λ / 2 wavelength plate 20c rotate the polarization direction of the light incident in the forward direction clockwise with respect to the traveling direction of the light. Then, the birefringent crystal plate 20 d recombines ordinary light and extraordinary light, and causes the combined light to enter the optical fiber 13.

  On the other hand, when light is emitted from the optical fiber 13 (in the case of FIG. 2B), the birefringent crystal plate 20d separates light into ordinary light and extraordinary light, whereas the λ / 2 wavelength plate 20c is ordinary light. And the polarization direction of the extraordinary light is rotated clockwise with respect to the traveling direction of the light. Since the Faraday rotator 20b rotates the polarization directions of ordinary light and extraordinary light counterclockwise with respect to the light traveling direction, the light is separated when the ordinary light and extraordinary light are transmitted through the birefringent crystal plate 20a. It will be in a state as it is.

  The optical isolator 20 uses this principle to remove the reflected light by diverting the optical path of the reflected light emitted from the laser diodes 14a to 14d. However, when the thickness of the birefringent crystal plates 20a and 20d is, for example, 0.5 mm and the incident light is a parallel beam, the separation distance at which the optical isolator 20 separates ordinary light and extraordinary light is at most about 50 μm. Therefore, the separation distance cannot be made sufficiently large. Therefore, the optical isolator 20 according to the present embodiment employs a condensed beam optical system using the first condenser lenses 18 a to 18 d and the second condenser lens 19. Thereby, the reflected light can be effectively removed.

  FIG. 3 is a diagram showing the relationship between the coupling loss of the optical isolator 20 according to this embodiment and the separation distance between ordinary light and extraordinary light. When the separation distance between ordinary light and extraordinary light is 50 μm, it is not shown in FIG. 3, but it is estimated that the coupling loss between the laser diodes 14 a to 14 d and the optical fiber 13 can be sufficiently increased. (At least −77 dB or less). In the example of FIG. 3, an aspheric lens in which the distance between the optical fiber 13 and the second condensing lens 19 is 4.35 mm and the condensing position is 5.8 mm from the first condensing lens 18 is used. The image magnification of the second condenser lens 19 used is approximately 1 (approximately equal magnification). By setting the image magnification to about 1, the variation in the condensing characteristic of the second condensing lens 19 can be reduced.

  Returning to the description of FIG. 1, a second condenser lens 19 having one beam waist position at the fiber end of the optical fiber 13 is disposed in the fiber condenser lens holder 11. The other beam waist position of the second condenser lens 19 is set to be on the surface of the first multiplexing filter 21a. Moreover, the 1st condensing lenses 18a-18d are distribute | arranged in transmission unit 16a-16d.

  One beam waist position of the first condenser lens 18a is set so as to be positioned at the light emitting portion of the laser diode 14a, and the other beam waist position of the first condenser lens 18a is set to the first multiplexing filter 21a. It is set to be on the surface of the first condenser lens 18a. In addition, one beam waist position of the first condenser lens 18b is set to be located in the light emitting portion of the laser diode 14b, and the other beam waist position of the first condenser lens 18b is the second multiplexing filter. 21b is set to be on the surface of the first condenser lens 18b side. In addition, one beam waist position of the first condenser lens 18c is set to be positioned at the light emitting portion of the laser diode 14c, and the other beam waist position of the first condenser lens 18c is the first multiplexing filter. 21a is set to be on the surface of the first condenser lens 18c side. Furthermore, one beam waist position of the first condenser lens 18d is set to be positioned at the light emitting portion of the laser diode 14d, and the other beam waist position of the first condenser lens 18d is the second multiplexing filter. 21b is set to be on the surface of the first condenser lens 18d side.

  The optical path of the second condenser lens 19 is branched in four directions using the first multiplexing filter 21 a, the second multiplexing filter 21 b, and the synthesis filter 22. The laser diode 14 a and the optical fiber 13 are optically coupled via the light transmission holes 11 a and 11 d of the fiber condenser lens holder 11, and the laser diode 14 b and the optical fiber 13 are the light transmission hole 12 a of the multiplexing filter holder 12. , 12c and the light transmission holes 11c and 11d of the fiber condensing lens holder 11, and the laser diode 14c and the optical fiber 13 are connected via the light transmission holes 11b and 11d of the fiber condensing lens holder 11. The laser diode 14 d and the optical fiber 13 are optically coupled via the light transmission holes 12 b and 12 c of the multiplexing filter holder 12 and the light transmission holes 11 c and 11 d of the fiber condenser lens holder 11. .

  Each of the transmission units 16a to 16d is aligned by adjusting the position in the x, y, and z directions, and fixed by adhesion or welding. The signal light (wavelength λ1) from the laser diode 14a is transmitted through the first condenser lens 18a, the first multiplexing filter 21a, the synthesis filter 22, the second condenser lens 19, and the light disposed in the optical path. The light enters the optical fiber 13 via the isolator 20. The signal light (wavelength λ2) from the laser diode 14b passes through the first condensing lens 18b, the second combining filter 21b, the synthesis filter 22, the second condensing lens 19, and the optical isolator 20, and an optical fiber. 13 is incident. The signal light (wavelength λ3) from the laser diode 14c passes through the first condenser lens 18c, the first multiplexing filter 21a, the synthesis filter 22, the second condenser lens 19, and the optical isolator 20, and the optical fiber. 13 is incident. The signal light (wavelength λ4) from the laser diode 14d passes through the first condensing lens 18d, the second combining filter 21b, the synthesis filter 22, the second condensing lens 19, and the optical isolator 20, and an optical fiber. 13 is incident.

  In this optical module 10, when the wavelength has a relationship of λ1 <λ2 <λ3 <λ4, for example, the P wave component of the light with the wavelength λ1 emitted from the laser diode 14a and the wavelength λ3 emitted from the laser diode 14c. The P wave component of light is multiplexed by the WDM system using the first multiplexing filter 21a. FIG. 4 is a diagram showing the relationship between P-wave transmission loss and wavelength. For example, it is assumed that λ1 is 1295.56 nm, λ2 is 1300.05 nm, λ3 is 1304.58 nm, and λ4 is 1309.14 nm.

  FIG. 4 shows variations in P-wave transmission loss when the spread angle of light incident on the first multiplexing filter 21a is ± 0.5 degrees. The P-wave transmission characteristics of the first and second multiplexing filters 21a and 21b are greatly affected by the spread angle of incident light. With this degree of variation, the P-wave transmission loss of light of wavelength λ1 is almost equal. Since the P wave transmission loss at the wavelength λ3 is equal to or less than −20 dB, the P wave component of the light of the wavelength λ1 and the P wave component of the light of the wavelength λ3 are efficiently combined.

  FIG. 5 is a diagram illustrating the relationship between the spot size, the spread angle of incident light, and the distance from the beam waist. In the present embodiment, the beam waist positions of the first condenser lenses 18a to 18d and the second condenser lens 19 are set on the surfaces of the first or second multiplexing filters 21a and 21b. In this case, the spread angle of incident light is about 0 degrees, and the spot size is minimum. Further, by setting the beam waist position within a range of ± 50 μm from the surface of the first or second multiplexing filter 21a, 21b, the spread angle of incident light can be made ± 0.5 degrees or less. In this way, by setting the beam waist position to be substantially on the surface of the first or second multiplexing filter 21a, 21b, the spread angle of incident light can be set to about 0 degrees, and the first or second multiplexing filter can be made. The performance of the wave filters 21a and 21b can be sufficiently exhibited.

  Further, in this optical module 10, the S-wave component of the light of wavelength λ2 emitted from the laser diode 14b and the S-wave component of the light of wavelength λ4 emitted from the laser diode 14d are used by the second multiplexing filter 21b. Are multiplexed by the WDM method. FIG. 6 is a diagram showing the relationship between S-wave transmission loss and wavelength.

  FIG. 6 shows variations in S wave transmission loss when the spread angle of light incident on the second multiplexing filter 21b is ± 0.5 degrees. If the spread angle of the light is such a variation, the S wave transmission loss of the light of wavelength λ2 is about 0 dB, and the S wave transmission loss of the wavelength λ4 is −20 dB or less. The component and the S wave component of the light of wavelength λ4 are efficiently combined.

  The P wave component of the light combined by the first combining filter 21 a and the S wave component of the light combined by the second combining filter 21 b are combined by the combining filter 22. FIG. 7 is a diagram showing the relationship between the P-wave insertion loss and S-wave insertion loss and the wavelength.

  As shown in FIG. 7, for the wavelengths λ1 (129.56 nm), λ2 (1300.05 nm), λ3 (1304.58 nm), and λ4 (1309.14 nm) of the four incident lights, the P-wave insertion loss is −0. .05 dB or more, and the S-wave insertion loss is -20 dB or less. Therefore, since the synthesis filter 22 efficiently transmits the P wave and reflects the S wave, the P wave component of the light combined by the first multiplexing filter 21a and the second multiplexing filter 21b are combined. It is possible to efficiently combine the S wave component of the waved light.

  When assembling the optical module 10, first, the first multiplexing filter 21a and the second multiplexing filter 21b are fixed, the position of the optical fiber 13 is adjusted in the x, y, and z directions, and the second The beam waist position of the condenser lens 19 is aligned so as to be on the filter surface of the first multiplexing filter 21a and the filter surface of the second multiplexing filter 21b. Whether the beam waist position is on the filter surface is determined by the reflected light reflected by the first multiplexing filter 21a and the second multiplexing filter 21b, or the first multiplexing filter 21a and the second multiplexing filter 21b. This can be determined by monitoring the power of the transmitted light that passes through the multiplexing filter 21b.

  Thereafter, each of the transmission units 16a to 16d is arranged so that the beam waist position of the first condenser lens 18a, 18c is on the filter surface of the first multiplexing filter 21a, and the first condenser lens 18b, The alignment is fixed by adjusting the position in the x, y, and z directions so that the beam waist position of 18d is on the filter surface of the second multiplexing filter 21b.

  In the optical module 10 according to the present embodiment, when the wavelength has a relationship of λ1 <λ2 <λ3 <λ4, the light of the wavelength λ1 and the light of the wavelength λ3 are combined by the first multiplexing filter 21a, and the wavelength Since the light having the wavelength λ4 and the light having the wavelength λ4 are combined by the second combining filter 21b, the first and second combining filters 21a and 21b are combined by combining the light having different wavelengths as much as possible. The performance of can be fully demonstrated.

  FIG. 8 is a diagram illustrating an example of dimensions of the optical module 10 according to the present embodiment. By adopting the configuration of the optical module 10 as described above, for example, the length from the end of the fiber condenser lens holder 11 to the end of the transmission unit 16a is 18 mm, and the end of the transmission unit 16b to the transmission unit. The optical module 10 can be downsized so that the length to the end of 16c is 13 mm.

DESCRIPTION OF SYMBOLS 10 ... Optical module, 11 ... Fiber condensing lens holder, 12 ... Multiplex filter holder, 13 ... Optical fiber, 14a-14d ... Laser diode, 15 ... Sleeve, 16a-16d ... Transmission unit, 17a-17d ... Joint sleeve, 18a to 18d: first condensing lens, 19: second condensing lens, 20: optical isolator, 20a, 20d: birefringent crystal plate, 20b: Faraday rotator, 20c: λ / 2 wave plate, 21a: 1st combining filter, 21b ... 2nd combining filter, 22 ... synthesis filter.

Claims (4)

An optical module that combines light of different wavelengths emitted from at least four optical elements and optically couples each optical element and an optical fiber,
The first wavelength λ1 emitted from the first optical element, the second wavelength λ2 emitted from the second optical element, the third wavelength λ3 emitted from the third optical element, and the fourth optical element A first condenser lens that is provided for each wavelength with respect to each light of the fourth wavelength λ4 emitted from the first condenser lens and condenses the light of each wavelength ;
A first combining filter that combines the collected light of the first wavelength λ1 and the light of the third wavelength λ3;
A second combining filter that combines the collected light of the second wavelength λ2 and the light of the fourth wavelength λ4;
A combining filter that combines the light combined by the first combining filter and the light combined by the second combining filter;
A second condenser lens for condensing the light synthesized by the synthesis filter;
With
The position of the beam waist by the first condenser lens of the light of the first wavelength λ1 and the light of the third wavelength λ3 is on the surface of the first multiplexing filter,
The position of the beam waist by the first condenser lens of the light of the second wavelength λ2 and the light of the fourth wavelength λ4 is on the surface of the second combining filter;
An optical module, wherein the position of one beam waist of the second condensing lens is on the surface of the first combining filter and on the surface of the second combining filter.   The optical module according to claim 1, wherein an optical isolator is disposed in an optical path between the optical fiber and the synthesis filter.   The optical module according to claim 1, wherein the first to fourth wavelengths satisfy λ1 <λ2 <λ3 <λ4.   The optical module according to claim 1, wherein an image magnification of the second condenser lens is equal.

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