JP2005032840A - Optical transmission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission module which can be set easily in an optical transmission system by suppressing a variation in the light receiving current of a light receiving element. <P>SOLUTION: The optical transmission module comprises a lens 20 for converting laser light emitted from the other end face of a light emitting element 16 into pseudo-parallel light, a beam splitter 22 for branching the laser light, a first light receiving element 23 for receiving the one branched laser light, a second light receiving element 24 for receiving the other branched laser light, a first optical filter 25 disposed between the beam splitter 22 and the first light receiving element 23 and passing only a laser light of a specified wavelength band, and a second optical filter 26 disposed between the beam splitter 22 and the first light receiving element 23 and passing only a laser light of a specified intensity. A light receiving current of the first light receiving element 23 having a specified level regulated by the second optical filter 26 is supplied to a means 27 for controlling the wavelength of the laser light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmission module used in an optical communication system, and more particularly to an optical transmission module having a structure suitable for monitoring a wavelength.
[0002]
[Prior art]
In a wavelength division multiplexing (WDM) communication system, it is indispensable that the wavelength and optical output of optical communication are stable over a long period of time. For this reason, the wavelength and optical output monitoring functions are included in the housing of the optical transmission module. An optical transmission module with a built-in wavelength and optical output monitor has been developed (for example, see Patent Document 1).
[0003]
FIG. 11 shows a configuration of an optical transmission module including a wavelength and optical output monitor disclosed in Patent Document 1.
[0004]
As shown in FIG. 11, a conventional optical transmission module 101 with a built-in wavelength and optical output monitor includes a light emitting element 102 that outputs laser light of a predetermined wavelength, and one end surface of the light emitting element 102 (on the right side on the paper surface). An optical fiber connecting portion 103 for sending the output laser light to the outside, a lens 112 for making the laser light output from the other end face (left side on the paper surface) of the light emitting element 102 pseudo-parallel light, and this pseudo-parallel light A beam splitter 104 composed of a half mirror that divides the laser light into a transmission direction (left side on the paper surface) and a reflection direction perpendicular to the transmission direction (lower side on the paper surface), and the beam splitter 104 branched the laser light. A first PD having an end face mounted with a first light receiving element 106 that receives one laser light through an optical filter 105 that transmits only laser light of a predetermined wavelength band. A carrier 107, a second PD carrier 109 having a second light receiving element 108 for receiving the other laser beam dispersed by the beam splitter 104 on its end surface, a Peltier module 110 for adjusting the temperature of the light emitting element 102, And a control unit 111 that controls the Peltier module 110 so as to control the wavelength of the light emitting element 102 based on the light receiving current output from the first light receiving element 106 and the second light receiving element 108.
[0005]
Then, the laser light output from the other end face of the light emitting element 102 is quasi-parallelized by the lens 112 and is branched by the beam splitter 104 into two directions of a transmission direction and a reflection direction perpendicular to the transmission direction. The laser beam branched in the direction is subjected to wavelength filtering by the optical filter 105 (dielectric multilayer film in Patent Document 1), and then received by the first light receiving element 106 and the wavelength is monitored.
[0006]
On the other hand, the laser beam branched in the reflection direction is received by the second light receiving element 108 and the light output is monitored.
[0007]
In the optical transmission module having such a structure, first, the light emitting element 102 is mounted on the LD carrier 113, and then the LD carrier 113 is fixed to the Peltier module 110. Next, the lens 112 is fixed to the LD carrier 113, while the first PD carrier 107 on which the first light receiving element 106 is mounted, the second PD carrier 109 on which the second light receiving element 108 is mounted, and the beam splitter 104. , And the optical filter 105 are fixed to the metal substrate 114, respectively.
[0008]
Then, laser light is output from the light emitting element 102, and the angle and position of the metal substrate 114 with respect to the LD carrier 113 are adjusted so that the light receiving currents of the first light receiving element 106 and the second light receiving element 108 become as large as possible. Are fixed.
[0009]
However, in the optical transmission module 101 disclosed in Patent Document 1, the mounting positions of the first light receiving element 106 and the second light receiving element 108 vary due to mounting errors, and the other of the light emitting elements 102 The extraction efficiency of the laser light from the end face has a problem in that the light receiving current of the first light receiving element 106 also varies for each optical transmission module 101 due to variations in the reflectance of the end face for each laser production lot. .
[0010]
Therefore, in the control unit 111 that controls the wavelength of the laser light based on the light reception current, when the input current range of the control unit 111 is set to the light transmission module 101 with a large light reception current, the light transmission module 101 with a small light reception current. In this case, the input current becomes too small, and there is a possibility that the wavelength resolution indicating the change amount of the wavelength with respect to the change amount of the received light current is insufficient.
[0011]
On the other hand, when the input current range of the control unit 111 is set to the optical transmission module 101 having a small light reception current, the input current becomes excessive in the optical transmission module 101 having a large light reception current, and wavelength control may not be possible.
[0012]
Therefore, it is necessary to prepare a plurality of input current ranges in the control unit 111 and switch the ranges according to the magnitude of the light reception current of the first light receiving element 106.
[0013]
[Patent Document 1]
JP 2000-56185 A (page 4, FIG. 2)
[0014]
[Problems to be solved by the invention]
In the optical transmission module disclosed in Patent Document 1 described above, there is a problem that the light reception current of the light receiving element for monitoring the wavelength varies. Therefore, the wavelength control means includes a plurality of input current ranges, and the light receiving element receives light. It is necessary to adjust individually according to the current level. Therefore, the work of incorporating the optical transmission module into the optical transmission system is complicated, and the installation time becomes long.
[0015]
The present invention has been made to solve the above problems, and provides an optical transmission module that facilitates incorporation of an optical transmission module into an optical transmission system by suppressing variations in output current of a light receiving element. With the goal.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, in an optical transmission module of one embodiment of the present invention, a light emitting element that outputs laser light having a predetermined wavelength and light that emits laser light output from one end face of the light emitting element to the outside. A fiber connection portion; a lens that converts the laser light output from the other end face of the light emitting element into quasi-parallel light; a beam splitter that divides the quasi-parallel laser light; and the one of the branched laser lights. A first light receiving element that receives light, a second light receiving element that receives the other branched laser beam, and a laser beam having a predetermined wavelength band disposed between the beam splitter and the first light receiving element. And a second optical filter that is disposed between the beam splitter and the first light receiving element and transmits laser light having a predetermined intensity, and the second optical filter. The light receiving current of the first light receiving element is adjusted to a predetermined value by an optical filter, and the light receiving current adjusted to the predetermined value is supplied to the wavelength control means for controlling the wavelength of the laser light. It is a feature.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
(First embodiment)
1 and 2 are views showing an optical transmission module according to a first embodiment of the present invention. FIG. 1 is a plan view of the optical transmission module as seen from a state where a lid attached to a box-shaped housing is removed. FIG. 2 is a side view of the housing with the side wall plate removed from FIG.
[0019]
As shown in FIGS. 1 and 2, the optical transmission module 11 according to the present embodiment includes a rectangular box-shaped housing 12 having an open top, and a fiber that is inserted into a through hole in a side wall portion of the housing 12. An optical fiber connecting portion 13 for connecting the optical fiber, a substrate 14 on which optical components housed in the housing 12 are mounted, a Peltier module 15 for placing the substrate 14, and a lid (see FIG. Not shown).
[0020]
The substrate 14 includes a light emitting element 16 that outputs laser light of a predetermined wavelength, a heat sink 17 that dissipates heat generated by the light emitting element 16 to the housing 12, a thermistor 18 that detects the temperature in the vicinity of the light emitting element 16, and a light emitting element. The first lens 19 that converts the laser beam output from one end surface 16 (right side on the paper surface) into quasi-parallel light, and the monitor light output from the other end surface (left side on the paper surface) of the light emitting element 16 A second lens 20 that converts laser light (monitor light) into pseudo-parallel light and a substrate 21 on which monitor components are mounted are mounted.
[0021]
This substrate 21 has a beam splitter 22 that branches pseudo-parallel light in two directions, a transmission direction (left side on the paper surface) and a reflection direction perpendicular to the transmission direction (upper side on the paper surface), and branches in the transmission direction. The first light receiving element 23 for receiving the laser beam, the second light receiving element 24 for receiving the laser beam branched in the reflection direction perpendicular to the transmission direction, the second lens 20 and the first light receiving element 23, between the first optical filter 25 that transmits only laser light of a predetermined wavelength band, and between the first optical filter 25 and the first light receiving element 23, and to transmit laser light of a predetermined intensity. A second optical filter 26 to be transmitted is mounted.
[0022]
Further, the first light receiving element 23 is connected to wavelength control means 27 that controls the Peltier module 15 based on the light receiving current Im and controls the wavelength of the light emitting element 16.
[0023]
Further, on the side wall of the housing 12, a fiber connecting portion 13 for connecting the optical fiber 28, a third lens 29 for condensing the parallel light from the first lens 19 and coupling it to the optical fiber, and the housing A sapphire glass 30 for sealing the body 12 is attached.
[0024]
FIG. 3 is a diagram showing the second optical filter 26, FIG. 3 (a) is a plan view thereof, and FIG. 3 (b) is cut along the line AA in FIG. FIG. As shown in FIG. 3, the second optical filter 26 is a pinhole plate 41, for example, a pinhole 42 provided in the center of a rectangular stainless steel plate.
[0025]
FIG. 4 is a plan view showing an optical coupling relationship among the light emitting element 16, the lens 20, the beam splitter 22, the first optical filter 25, the second optical filter 26, and the first light receiving element 23. .
[0026]
As shown in FIG. 4, the diameter of the laser beam output from the light emitting element 16 and quasi-parallelized by the second lens 20 is D0, and the diameter of the pinhole 42 of the second optical filter 26 is D1. The laser beam output from the infrared light emitting element 16 used in the WDM communication system is a laser beam having a spread angle θ1 of generally 30 ° to 40 ° and a substantially circular cross section. The intensity distribution of the cross section of the laser light is almost Gaussian distribution, and the diameter thereof is defined as a size that makes the intensity of the light 1 / e.
[0027]
In the present embodiment, the laser beam having the diameter D0 is adjusted to have a predetermined light intensity by cutting the outer peripheral light of the laser beam through the pinhole 42 having the diameter D1, and then irradiates the first light receiving element 23. is doing.
[0028]
FIG. 5 schematically shows the relationship between the intensity I of the laser beam having the diameter D 0 that has passed through the first optical filter 25 and the diameter D 1 of the pinhole 42. As shown in FIG. 5, FIG. 5A shows the diameter of the pinhole 42 when the intensity I is Ia so that the light quantity S (area of the hatched portion) received by the first light receiving element 23 is substantially constant. FIG. 5B shows the case where the diameter of the pinhole 42 is set to D1b when the intensity I is Ib, and FIG. 5C shows the case where the diameter of the pinhole 42 is set to D1c when the intensity I is Ic. Show.
[0029]
FIG. 6 is a flowchart showing a method for suppressing variations in the light receiving current Im of the first light receiving element 23. As shown in FIG. 6, with reference to the statistical variation data of the light receiving current Im of the first light receiving element 23 obtained in advance, a light receiving current Im large enough for wavelength control can be obtained with a predetermined yield. Then, the input range of the wavelength control means 27 is determined, and the light reception current Im large enough for the wavelength control is set as the standard light reception current Ims (step S01).
[0030]
For example, if the standard light receiving current Ims is twice the average value-standard deviation of the light receiving current Im, a yield of 95% is obtained. If the average value of the light receiving current Im-three times the standard deviation, a yield of 99% is obtained. It is common knowledge to expect.
[0031]
Next, the optical transmission module is assembled (step S02), the light reception current Im of the optical transmission module is measured (step S03), and it is determined whether the light reception current Im is larger than the standard light reception current Ims (step S04).
[0032]
When the light reception current Im is larger than the standard light reception current Ims, the second optical filter 26 is attached between the beam splitter 22 and the first light receiving element 23 of the optical transmission module 11, and the light reception current Im is substantially equal to the standard light reception current Ims. The diameter D1 of the pinhole 42 is adjusted so as to be equal (step S05 and step S06).
[0033]
For this purpose, a plurality of pinhole plates 41 having different diameters of the pinholes 42 are prepared in advance, and the pinhole plates 41 having the pinholes 42 having appropriate diameters are selected by being sequentially replaced.
[0034]
As a result, the light reception current Im of the optical transmission module 11 can be aligned with the standard light reception current Ims, and variations in the light reception current Im can be suppressed.
[0035]
On the other hand, if the light reception current Im is smaller than the standard light reception current Ims, the variation in the light reception current Im cannot be suppressed. Therefore, the assembly of the optical transmission module 11 is readjusted (step S07), and the process proceeds to step S03. Repeat until Im becomes larger than the standard light receiving current Ims.
[0036]
As described above, in the optical transmission module according to the first embodiment, the pinhole having the pinhole 42 as the second optical filter 26 between the first optical filter 25 and the first light receiving element 23. Since the plate 41 is provided to suppress variations in the light reception current Im of the first light receiving element 23, it is not necessary to prepare a plurality of input current ranges corresponding to the variations in the light reception current Im in the wavelength control means 27. . Therefore, it is easy to incorporate the optical transmission module 11 into the optical transmission system, and the integration time can be shortened.
[0037]
Here, a case has been described in which a plurality of pinhole plates 41 having different diameters of pinholes 42 are prepared in advance, and the light receiving currents Im are aligned in order, but a plurality of pinholes having different diameters are arranged at predetermined intervals in advance. The arranged pinhole plate 41 may be used.
[0038]
Hereinafter, these modifications will be described.
[0039]
(Modification 1 of the first embodiment)
7A and 7B are diagrams showing a second optical filter 26 according to the first modification of the first embodiment of the present invention. FIG. 7A is a plan view thereof, and FIG. 7B is a plan view of FIG. It is sectional drawing cut | disconnected along the BB line | wire of () and looked at the direction of the arrow. In the present modification, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different portions will be described.
[0040]
This modification differs from the first embodiment in that a pinhole plate in which a plurality of pinholes having different diameters are arranged in advance at a predetermined interval is used.
[0041]
That is, as shown in FIG. 7, the second optical filter 26 of this modification is a pinhole plate 43. For example, three pinholes 44, 45, and 46 having different diameters are formed on a rectangular stainless steel plate. Are arranged at intervals L.
[0042]
As a result, the pinhole plate 43 can be slid in the horizontal direction to select a pinhole having an appropriate diameter that makes the light reception current Im close to the standard light reception current Ims.
[0043]
As described above, in the first modification of the first embodiment, since the pinhole plate 43 is provided with a plurality of pinholes, the work is more efficient than sequentially changing the pinhole plate 41 having a single pinhole. It is easy and the working time can be shortened.
[0044]
Although the case where a pinhole plate having three pinholes is used has been described here, a pinhole plate having a larger number of pinholes may be used.
[0045]
(Modification 2 of the first embodiment)
8A and 8B are diagrams showing a second optical filter 26 according to the second modification of the first embodiment of the present invention. FIG. 8A is a front view thereof, and FIG. 8B is a side view thereof. is there. In the present modification, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different portions will be described.
[0046]
This modification is different from the first embodiment in that an iris diaphragm is used as the second optical filter 26.
[0047]
That is, as shown in FIG. 8, by operating the level actuator 52 of the iris diaphragm 51, the diameter of the pinhole 53 of the iris diaphragm 51 can be changed steplessly. Thereby, the light receiving current Im can be adjusted to the pinhole 53 having an optimum diameter which becomes the standard light receiving current Ims.
[0048]
As described above, in the second modification of the first embodiment, the diameter of the pinhole 53 can be changed in a stepless manner by the iris diaphragm 51, so that the work can be performed more than sequentially changing the plurality of pinhole plates 41. It is easy and the working time can be further reduced.
[0049]
Here, a case has been described in which the diameter of the pinhole is mechanically changed by the iris diaphragm 51, but the diameter of the pinhole may be electrically changed by using a liquid crystal diaphragm. According to the liquid crystal diaphragm, the diameter of the pinhole can be set more smoothly, for example, in 10 μm micron steps.
[0050]
(Modification 3 of the first embodiment)
9A and 9B are diagrams showing a second optical filter 26 according to the third modification of the first embodiment of the present invention. FIG. 9A is a plan view thereof, and FIG. 9B is a plan view of FIG. It is sectional drawing cut | disconnected along CC line of a) and it looked at the method of the arrow. In the present modification, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different portions will be described.
[0051]
This modification is different from the first embodiment in that the second optical filter 26 is a slit plate 61. That is, as shown in FIG. 9, the second optical filter 26 is a slit plate 61, for example, a slit 62 is provided at the center of a rectangular stainless steel plate.
[0052]
Thereby, even when the beam shape 63 of the laser beam output from the light emitting element 16 is not circular, the width D2 and the length D3 of the slit 62 are formed in accordance with the beam shape 63 of the laser beam. Since the amount of transmission can be finely adjusted, a plurality of slit plates 61 with different widths and lengths of the slits 62 are prepared in advance, and the light receiving current Im can be adjusted by sequentially replacing them.
[0053]
As described above, in the third modification of the first embodiment, since the second optical filter 26 is the slit plate 61, the present invention can be applied even when the shape of the laser beam is not circular.
[0054]
Here, a case has been described in which a plurality of slit plates 61 having different widths and lengths of the slits 62 are prepared in advance, and the light receiving current Im is adjusted by sequentially changing them. A slit plate in which slits are arranged at a predetermined interval may be used.
[0055]
FIG. 10 is a view showing the slit plate, FIG. 10 (a) is a plan view thereof, and FIG. 10 (b) is a cross-sectional view taken along the line DD in FIG. FIG.
[0056]
As shown in the figure, three slits 65, 66, 67 having different slit widths and lengths are arranged at a predetermined interval L on the slit plate 64.
[0057]
In the above-described embodiment, the case where the second optical filter 26 is provided between the first optical filter 25 and the first light receiving element 23 has been described. However, the present invention is not limited to this, It may be provided between the beam splitter 22 and the first optical filter 25.
[0058]
【The invention's effect】
As described above, according to the optical transmission module of the present invention, the variation in the light reception current of the light receiving element can be suppressed, so that it can be easily incorporated into the optical communication system.
[Brief description of the drawings]
FIG. 1 is a plan view showing an optical transmission module according to a first embodiment of the present invention.
FIG. 2 is a side view showing an optical transmission module according to the first embodiment of the present invention.
3A and 3B are diagrams showing the optical filter according to the first embodiment of the present invention, in which FIG. 3A is a plan view thereof, and FIG. 3B is a cross-sectional view taken along line AA.
FIG. 4 is a plan view showing the arrangement of optical coupling from the light emitting element to the light receiving element according to the first embodiment of the present invention.
FIG. 5 is a schematic diagram showing the relationship between the laser beam intensity and the pin pole according to the first embodiment of the present invention.
FIG. 6 is a flowchart showing a method of adjusting the light receiving current according to the first embodiment of the present invention.
FIGS. 7A and 7B are diagrams showing an optical filter of a first modification according to the first embodiment of the present invention, in which FIG. 7A is a plan view and FIG. 7B is cut along a line BB. FIG.
FIG. 8 is a diagram showing an iris diaphragm of a second modification according to the first embodiment of the present invention.
FIGS. 9A and 9B are diagrams showing an optical filter of a third modification according to the first embodiment of the present invention, in which FIG. 9A is a plan view and FIG. 9B is cut along the line CC. FIG.
10A and 10B are diagrams showing another optical filter according to the third modification of the first embodiment of the present invention, in which FIG. 10A is a plan view thereof, and FIG. 10B is taken along a line DD. FIG.
FIG. 11 is a plan view showing a conventional optical transmission module.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Optical transmission module 12 Case 13 Fiber connection part 14, 21 Board | substrate 15 Peltier module 16 Light emitting element 17 Heat sink 18 Thermistor 19, 20, 29 Lens 22 Beam splitter 23 1st light receiving element 24 2nd light receiving element 25 1st Optical filter 26 Second optical filter 27 Wavelength control means 28 Optical fiber 30 Sapphire glass 41, 43 Pinhole plates 42, 44, 45, 46, 53 Pinhole 51 Iris diaphragm 52 Level actuator 61, 64 Slit plates 62, 65, 66, 67 Slit 63 Laser beam diameter

Claims (7)

A light emitting element that outputs laser light of a predetermined wavelength;
An optical fiber connection for sending laser light output from one end face of the light emitting element to the outside;
A lens that makes the laser light output from the other end face of the light emitting element pseudo-parallel light;
A beam splitter for branching the quasi-parallelized laser beam;
A first light receiving element for receiving the one branched laser beam;
A second light receiving element for receiving the other branched laser beam;
A first optical filter disposed between the beam splitter and the first light receiving element and transmitting only a laser beam having a predetermined wavelength band;
A second optical filter disposed between the beam splitter and the first light receiving element and transmitting laser light having a predetermined intensity;
Comprising
The light receiving current of the first light receiving element is adjusted to a predetermined value by the second optical filter, and the light receiving current adjusted to the predetermined value is supplied to wavelength control means for controlling the wavelength of the laser light. An optical transmission module characterized by the above. The optical transmission module according to claim 1, wherein the second optical filter is a pinhole plate. 3. The optical transmission module according to claim 2, wherein a plurality of pinholes having different sizes are arranged on the pinhole plate at a predetermined interval. The optical transmission module according to claim 2, wherein the pinhole plate is an iris diaphragm. The optical transmission module according to claim 2, wherein the pinhole plate is a liquid crystal diaphragm. The optical transmission module according to claim 1, wherein the second optical filter is a slit plate. The optical transmission module according to claim 6, wherein a plurality of slits having different sizes are arranged at predetermined intervals on the slit plate.

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