JP6459296B2 - Light emitting module and multi-channel light emitting module - Google Patents

Description

  The present invention relates to a light emitting module and a multi-channel light emitting module.

  Patent Document 1 discloses an optical semiconductor module. This optical semiconductor module includes a semiconductor laser that emits laser light, a lens that condenses the laser light from the semiconductor laser, and an optical connector that outputs the laser light condensed by the lens to the transmission path of the fiber ferrule. ing. The optical connector includes a fiber ferrule including an optical fiber having an incident surface on which laser light is incident, and an optical attenuator provided so as to cover the incident surface. The light attenuator is, for example, polarizing glass. The transmittance of the laser light in the light attenuating portion varies depending on the rotational position of the light attenuating portion around the optical axis. The above-described semiconductor laser, lens, and optical connector are aligned so that the spot diameter of the laser light on the incident surface is smaller than the diameter of the core of the optical fiber.

  By the way, in a light emitting module, even when a laser diode (hereinafter referred to as “LD”), a lens and an optical fiber are appropriately optically aligned (optically coupled), when a predetermined current is applied to the LD, The light output (the intensity of light output from an end face different from the fiber end face taken out of the module and optically coupled to the lens) may exceed a predetermined value. Further, if the value of the applied current applied to the LD is lowered in order to ensure a predetermined light output, there arises a problem that the relaxation oscillation frequency of the LD is lowered and the high frequency characteristics of the LD are impaired.

  Therefore, as described in Patent Document 1, the optical connector is moved in the Z-axis direction (optical axis direction), and the end face of the fiber is moved to a position offset from the focal point of the lens, thereby entering the fiber core. The proportion of light that is being reduced. This is referred to as de-focus.

JP 2007-212795 A

  In the multiwavelength integrated module, a plurality of optical signals independent from each other are finally coupled to the end face of one optical fiber. In the method of defocusing the optical coupling point as described above, the power adjustment for one LD light can be appropriately performed. However, for example, when adjusting the power of four LD lights, the difference in fiber coupling power increases due to variations in the light emission power of the LD, coupling efficiency of optical components, or variations in the position or angle of the four optical axes. There arises a problem that a stable light output cannot be obtained.

  In addition, since the LD light of 4 lanes is finally coupled to the end face of the fiber by one condensing lens, when the light amount adjustment by defocusing is performed for one LD light, for other LD light There is also a problem that the light quantity adjustment is not always optimal. That is, the optical axis of each LD light in the condensing lens is consistent in design, but actually varies slightly with each LD light. Therefore, even if the end surface of the lens or fiber is moved along the optical axis of the condenser lens, each LD light is not necessarily incident on the lens along the optical axis, and an appropriate offset amount with respect to each LD light. Since they are often different, a stable light output cannot be obtained.

  Further, even when each LD light propagates on the optical axis of the lens and is incident on the end surfaces of the lens and the fiber, the IL characteristics (applied current-light output) of the LD naturally vary. Therefore, a unique offset amount between LDs is not guaranteed.

  The present invention has been made in view of such problems, and an object thereof is to provide a light-emitting module and a multi-channel light-emitting module that can obtain a stable light output.

  A light-emitting module according to an aspect of the present invention includes a light-emitting element, a first lens in which one condensing point coincides with a light emission point of the light-emitting element, and a second light that emits light emitted from the first lens as divergent light. A lens, a third lens that causes the light emitted from the second lens to enter the optical fiber, and a temperature control element that mounts the light emitting element, the first lens, and the second lens. The light emitted from the lens is disposed closer to the first lens than the position where the light becomes parallel light, and the light emitted from the third lens is collected inside the optical fiber.

  A multi-channel light emitting module according to an aspect of the present invention is a multi-channel light emitting module including a plurality of lanes having a light emitting element, a first lens, and a second lens, and is emitted from each second lens and combined. A third lens that causes light to enter the optical fiber; and a temperature control element on which each light emitting element, each first lens, and each second lens is mounted. In each lane, the light is condensed on the light emitting element side of the first lens. The point is located at the light emission point of the light emitting element, the second lens is provided at a position for converting the light emitted from the first lens into divergent light, and the divergent light emitted from the second lens is The light is optically coupled to the optical fiber via the three lenses, and the light emitted from the third lens is collected inside the optical fiber.

  In the light emitting module and the multi-channel light emitting module according to one embodiment of the present invention, stable light output can be obtained.

It is a perspective view which shows the internal structure of the light emitting module which concerns on embodiment. It is a top view which shows the internal structure of the light emitting module of FIG. It is a schematic diagram which shows the optical system of the light emitting module of FIG. It is a figure explaining alignment of the lens system in the light emitting module of FIG. It is a graph which shows XY tolerance in a sleeve. (A) shows the case where the second lens is moved to the LD side, and (b) shows the case where the second lens is moved to the optical fiber side. It is a graph which shows the relationship between the direction which displaces a 2nd lens, and the amount of reflected return light. It is a figure which shows the positional relationship of LD, a 1st lens, a 2nd lens, a 3rd lens, and an optical fiber. It is a graph which shows the relationship between the coupling loss of the light in the end surface of an optical fiber, and temperature. It is a figure explaining the conventional adjustment method.

  Hereinafter, embodiments of a light emitting module and a multi-channel light emitting module according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows the internal structure of the light emitting module 1 according to this embodiment. FIG. 2 is a plan view showing the internal structure of the light emitting module 1. As shown in FIGS. 1 and 2, the light emitting module 1 includes a rectangular parallelepiped housing 2 and a flanged columnar optical coupling portion 3. The light emitting module 1 includes four LDs (light emitting elements) 11a to 11d, four first lenses 12a to 12d, a beam splitter 13, four second lenses 14a to 14d, and a first WDM filter 15. A second WDM filter 16, a mirror 17, an isolator 18, and a polarization beam synthesis filter 19 are provided. The light emitting module 1 is a four-channel light emitting module including LDs 11a to 11d, first lenses 12a to 12d, and second lenses 14a to 14d.

  Each first lens 12a to 12d is provided corresponding to each LD 11a to 11d, and each second lens 14a to 14d is provided corresponding to each first lens 12a to 12d. In the following description, the LDs 11a to 11d, the first lenses 12a to 12d, and the second lenses 14a to 14d may be simply referred to as the LD 11, the first lens 12, and the second lens 14, respectively. LD11 indicates any one of LD11a to 11d, the first lens 12 indicates any one of the first lenses 12a to 12d, and the second lens 14 indicates any one of the second lenses 14a to 14d.

  Hereinafter, in the drawings, the terms “front-rear direction”, “vertical direction”, and “left-right direction” are used, but these terms are for convenience based on the illustrated state. In the following description, the front direction is a direction in which the LDs 11 a to 11 d are provided when viewed from the first lenses 12 a to 12 d, and the rear direction is a direction in which the optical coupling unit 3 is provided as viewed from the housing 2. The left-right direction is a direction in which the LDs 11a to 11d, the first lenses 12a to 12d, or the second lenses 14a to 14d are arranged in parallel. Further, the vertical direction is a direction orthogonal to the front-rear direction and the left-right direction.

  In the light emitting module 1, the LDs 11a to 11d functioning as light sources are independently driven, and the respective LDs 11a to 11d output optical signals. The output lights output from the LDs 11a to 11d are input to the first lenses 12a to 12d, which are condenser lenses, respectively. Since the LDs 11a to 11d are placed apart from the focal points of the corresponding first lenses 12a to 12d, the first lenses 12a to 12d function as condenser lenses.

  The lights condensed by the first lenses 12a to 12d are respectively input to the second lenses 14a to 14d and converted into substantially parallel light by the second lenses 14a to 14d. The focal points of the second lenses 14a to 14d on the LD 11a to 11d side are arranged so as to coincide with the condensing points of the first lenses 12a to 12d. Therefore, the divergent light having the light condensing point as a light source is converted into a parallel beam by the second lenses 14a to 14d whose own focal point coincides with the condensing point.

  FIG. 3 is a schematic diagram showing an optical system of the light emitting module 1. As shown in FIG. 3, each light from the second lenses 14 a to 14 d is combined by an optical circuit including a first WDM filter 15, a second WDM filter 16, a mirror 17, an isolator 18, and a polarization beam combining filter 19. The signal is output to the outside of the casing 2 through a window 2a provided on the rear wall 2A of the casing 2. The light output to the outside of the housing 2 is collected by the third lens 4 provided in the optical coupling unit 3. The light condensed by the third lens 4 is coupled to the end face of the optical fiber 5 that is positioned behind the third lens 4 and held by the fiber stub 6.

  Here, conventionally, the power of light coupled to the end face of the fiber (hereinafter also referred to as fiber coupling power) is adjusted by a system (sleeve defocusing) in which the end face of the fiber is offset in the optical axis direction. It was. However, in this embodiment, by changing the position of each of the second lenses 14a to 14d in the housing 2 in the optical axis direction, the fiber coupling power by the output light from each of the LDs 11a to 11d is within a predetermined range. And

  In the above method, the output light from the LDs 11a to 11d is converted into parallel light by the second lenses 14a to 14d, and the parallel light is incident on the optical circuit to perform multiplexing. The light output from the housing 2 becomes parallel light, and this parallel light is collected by the third lens (condensing lens) 4 located outside the housing 2 and coupled to the end face of the optical fiber 5. If parallel light is incident within the effective diameter of the third lens 4, the light is concentrated at one point even if a shift in the optical axis direction occurs in the four lights passing through the second lenses 14 a to 14 d. Further, the fiber coupling power depends on the variation in the light intensity output from each of the LDs 11a to 11d and the variation in the optical coupling efficiency of the optical system. The variation due to these is generally about 3 dB.

  The average optical output of the direct modulation type LDs 11a to 11d is about 10 dBm under a predetermined driving current condition. Further, since the coupling loss to the end face of the optical fiber 5 by the optical multiplexer and the lens system is about 2 to 3 dB, the intensity of the signal light output from the optical fiber 5 is about 7 to 8 dBm. On the other hand, the light output of LR4 (100 GBASE-LR4) defined by IEEE is set to 4.5 dBm at the maximum, and it becomes an overpower condition when the coupling efficiency to the optical fiber 5 is not adjusted.

  Here, the conventional method for adjusting the coupling efficiency has been performed by a defocus method in which the position of the end face of the fiber is moved away from (or brought closer to) the focusing position (focus). However, when the defocus method is applied to the light emitting module 1, adjustment to one optical axis that is in an ideal state is possible, but in reality, the optical axis variation due to mounting variation or the like, and the LD 11a. Therefore, it is difficult to adjust the power for all (four) optical axes.

  The cause of the variation in the fiber coupling power will be specifically described. As shown in FIG. 9, when the four parallel lights L0 to L3 are incident on the third lens 4 that is a condenser lens, if the optical axes of the parallel lights L0 to L3 are shifted, the third lens Therefore, the angles of the optical axes of the light beams from 4 toward the optical fiber 5 of the fiber stub 6 are different from each other. However, if the deviation of the optical axis in each of the parallel lights L0 to L3 is within the range of the effective diameter of the third lens 4, each light traveling from the third lens 4 toward the optical fiber 5 is condensed at one point. In the fiber 5, significant fiber coupling power can be obtained.

  However, if the coupling position of the light in the optical fiber 5 is shifted from the condensing position in order to adjust the light output from the light emitting module 1, the optical fiber from the third lens 4 is displaced by the deviation of the four optical axes. Since the angles of the optical axes of the respective light beams directed toward 5 are different from each other, the positional shift of the four optical axes after the coupling position is shifted becomes large. As a result, there arises a problem that variations in fiber coupling power become large.

  Therefore, in order to solve the above-described problem, the positions of the second lenses 14a to 14d with respect to the respective LDs 11a to 11d in the housing 2 are monitored until the fiber coupling power reaches a desired optical output power. Adjustment to displace in the optical axis direction is performed. By performing such adjustment, a desired fiber coupling power can be obtained in all of the four LDs 11a to 11d.

  Hereinafter, a specific light output adjustment method capable of obtaining a desired fiber coupling power will be described. As shown in FIG. 3, the optical system of the light emitting module 1 is a three-lens system, and the output light from the LDs 11a to 11d is condensed at a magnification of 5 to 6 in each of the first lenses 12a to 12d. To do. In general, the optical magnification capable of optimally coupling the output light of the DFB-LD to an SMF (Single-mode Fiber) is 5 to 6 times. That is, in the first lenses 12a to 12d, the output light from the LDs 11a to 11d is condensed at a magnification of 5 to 6 times. The third lens 4 located outside the housing 2 collects the parallel light that has passed through the rear wall 2 </ b> A of the housing 2 on the end surface of the optical fiber 5.

  Here, the focal length of the first lenses 12a to 12d is 0.45 mm, and the magnification of the first lenses 12a to 12d is 5 to 6. The focal length of the second lenses 14a to 14d is 0.85 mm, and the magnification of the second lenses 14a to 14d is 1. The focal length of the third lens 4 is 0.85 mm, and the magnification of the third lens 4 is 1. In the light emitting module 1 having such a three-lens system, the optical magnifications of the first lenses 12a to 12d are 5 to 6, and the optical magnifications of the second lenses 14a to 14d and the third lens 4 are 1. Then, by mounting the second lenses 14a to 14d behind the first lenses 12a to 12d for which the highest positional accuracy is required, the second lenses 14a to 14d having a low magnification can be used as optical axis adjusting lenses. It is possible to reduce optical coupling loss due to misalignment during mounting.

  In the light emitting module having two lens systems, the mounting accuracy of the collimating lens is required to be 0.3 μm or less, whereas in the light emitting module 1 having three lens systems, the mounting accuracy of the second lens 14 is 1.5 μm. Equivalent performance can be achieved if Note that optical components such as lenses are fixed with an adhesive such as an epoxy UV curable resin in order to achieve miniaturization. Such fixing is difficult to mount with an accuracy of 1 μm or less due to shrinkage during curing of the resin or expansion due to heat during curing.

  Moreover, in the light emitting module 1, since the magnification of the first lenses 12a to 12d is an optical system of 5 to 6, the diameter of the beam pattern of parallel light located behind the second lenses 14a to 14d can be reduced. (It can be reduced from about 0.6 mm to about 0.2 mm), and the optical system that performs optical multiplexing can be made compact.

  Next, a lens system alignment procedure in the light emitting module 1 will be described. First, the LDs 11a to 11d are mounted at predetermined locations in the light emitting module 1, and predetermined wiring is performed on the LDs 11a to 11d so that the LDs 11a to 11d can be electrically operated. Thereafter, as shown in FIG. 4, the step of determining the position of the first lens 12a with respect to the LD 11a, the step of determining the initial position of the second lens 14a with respect to the first lens 12a, and the alignment of the second lens 14a are performed. The process to perform is performed. Below, these each process is demonstrated in detail.

  First, as shown in FIG. 4A, a step of determining the position of the first lens 12a with respect to the LD 11a is performed. In this step, it is necessary to take out the light generated by the LDs 11 a to 11 d arranged in the light emitting module 1 to the outside of the light emitting module 1. This is performed by translating the optical axes of the LDs 11 a to 11 d out of the light emitting module 1.

  And the infrared camera 30 is arrange | positioned in the far point (location about 1000 mm away from the housing | casing 2) with respect to the housing | casing 2, and the position adjustment of the 1st lens 12a is performed using the infrared camera 30. FIG. Specifically, the light output from the first lens 12a is taken out of the light emitting module 1 using the jig so that the light output from the LD 11a becomes parallel light by the first lens 12a, and the first light is output by the infrared camera 30. While confirming the field pattern of the light from the first lens 12a, the position of the first lens 12a with respect to the LD 11a is determined.

  At this time, since the light emission point of the LD 11a is located on the focal point of the first lens 12a, the light output from the LD 11a is parallel light from the first lens 12a to the far point where the infrared camera 30 is located. Become. Then, the position of the first lens 12a in the optical axis direction is offset by a predetermined amount. That is, by moving the first lens 12a away from the LD 11a, the relationship between the LD 11a and the first lens 12a having a magnification of 5 to 6 can be obtained.

  Subsequently, as shown in FIG. 4B, a step of determining an initial position of the second lens 14a with respect to the first lens 12a is executed. In this process, the initial position of the second lens 14a is determined while adjusting the position of the second lens 14a using the infrared camera 30 disposed at the far point. Specifically, the direction of the optical axis is such that the light reaching the infrared camera 30 from the second lens 14a becomes parallel light while checking the field pattern of the light emitted from the second lens 14a by the infrared camera 30. The initial position of the second lens 14a is determined.

  Next, as shown in FIG. 4C, a position adjusting jig 40 is installed. The jig 40 includes a condensing lens 44 and an optical fiber 45 simulating the third lens 4 and the optical fiber 5, and the positional relationship between the condensing lens 44 and the optical fiber 45 is the same as that of the third lens 4 described above. The positional relationship with the optical fiber 5 is the same. That is, in the jig 40, the condenser lens 44 and the optical fiber 45 are arranged so that the end surface of the optical fiber 45 is on the optical axis of the condenser lens 44 and at the focal position of the condenser lens 44. .

  The jig 40 as described above is disposed at a position (design position) where the third lens 4 and the optical fiber 5 are actually disposed with respect to the rear wall 2A of the housing 2. Thereafter, a step of aligning the second lens 14a is performed so that light emitted from the other end face of the optical fiber 45 (opposite side of the condensing lens 44) in the jig 40 has a predetermined intensity. Here, the initial position of the second lens 14a is determined in the previous step, and at this time, the focal position of the second lens 14a coincides with the condensing point of the first lens 12a. Therefore, since the light that has passed through the second lens 14a is parallel light, in the step of aligning the second lens 14a, the second lens 14a is used as the optical axis so that a predetermined light output can be obtained. Make adjustments to move in a vertical plane. Further, as shown in FIG. 4D, by displacing the second lens 14a in the optical axis direction, the second lens 14a is adjusted so that the power of light coupled to the end face of the optical fiber 45 becomes a desired value. Adjust the position of. Thereafter, the second lens 14 a is fixed inside the housing 2 with an adhesive.

  As described above, after performing the step of determining the position of the first lens 12a with respect to the LD 11a, the step of determining the initial position of the second lens 14a with respect to the first lens 12a, and the step of aligning the second lens 14a. The step of determining the position of the first lens 12b with respect to the LD 11b, the step of determining the initial position of the second lens 14b with respect to the first lens 12b, and the step of aligning the second lens 14b are performed in the same manner as described above. Here, the position of the jig 40 relative to the housing 2 is not changed.

  Specifically, (1) the position of the first lens 12b is determined using the infrared camera 30 located at the far point so that the output light of the LD 11b becomes parallel light by the first lens 12b, and (2) the first The light passing through the second lens 14b is observed by the infrared camera 30, and the position of the second lens 14b where the observed light becomes parallel light is determined as the initial position of the second lens 14b. The second lens 14b is fixed after the second lens 14b is offset along the optical axis and the fiber coupling power is adjusted so as to obtain the light output. Thereafter, the first lens 12c, the second lens 14c, the first lens 12d, and the second lens 14d are arranged in this order using the same method as the above (1) to (3).

  As described above, after the first lenses 12a to 12d and the second lenses 14a to 14d are arranged, the jig 40 is removed from the rear wall 2A of the housing 2. Then, the regular optical coupling unit 3 including the third lens 4 and the optical fiber 5 is attached to the rear wall 2A of the housing 2, and after the optical coupling unit 3 is aligned with the housing 2, the optical coupling unit 3 is aligned. Is fixed to the housing 2. Specifically, an optical coupling system incorporating the third lens 4 and a fiber stub 6 that holds the optical fiber 5 is firstly attached after the third lens 34 is attached to the housing 2. The wall 2A is slid to perform alignment within a plane perpendicular to the optical axis, and then alignment within the plane between the fiber stub 6 and the third lens 4 is performed. By repeating the alignment of the third lens 4 and the alignment of the fiber stub 6, the position of the optical coupling system where the light intensity emitted from the other end face of the fiber stub 6 is maximized is found, and the optical coupling system is determined at this position. It fixes to the housing | casing 2 by welding.

  Thus, a YAG alignment welding equipment can be used as equipment for fixing by welding. In the YAG alignment welding equipment, the three-body alignment of the housing 2, the third lens 4 and the sleeve is performed while maintaining the positional relationship in the optical axis direction between the third lens 4 and the sleeve of the optical coupling unit 3. By doing so, all four light outputs can be adjusted to the adjusted fiber coupling power.

  As described above, the light emitting module 1 is assembled through the process of aligning the second lenses 14a to 14d by displacing the second lenses 14a to 14d in the optical axis direction. Thus, by performing alignment with respect to each of the second lenses 14a to 14d, alignment can be performed with an appropriate offset amount for each LD light output from each of the LDs 11a to 11d. Therefore, the light output from the optical fiber 5 can be stabilized.

  In the step of aligning the second lenses 14a to 14d, the fiber coupling power is adjusted by displacing each of the second lenses 14a to 14d in the optical axis direction, but the second lenses 14a to 14d are moved. There are LD 11a to 11d side and optical fiber 5 side as directions to be made.

  However, as shown in FIG. 5B, when the second lenses 14a to 14d are displaced toward the optical fiber 5 (in the direction away from the first lenses 12a to 12d), the second lenses 14a to 14d are moved to the LD 11a. The coupling tolerance of the optical fiber 5 can be increased as compared with the case of being displaced toward the ˜11d side (direction approaching the first lenses 12a to 12d). Therefore, when the second lenses 14a to 14d are displaced toward the optical fiber 5, the amount of change in light can be reduced, so that the light output from the optical fiber 5 can be further stabilized. 5A shows the coupling tolerance when the second lenses 14a to 14d are displaced toward the LDs 11a to 11d, and FIG. 5B illustrates the displacement of the second lenses 14a to 14d toward the optical fiber 5. The coupling tolerance is shown.

  Further, as shown in the graph of FIG. 6, when the second lenses 14a to 14d are displaced toward the optical fiber 5, the second lenses 14a to 14d are displaced toward the LDs 11a to 11d. Thus, the amount of reflected return light can be reduced. This is because the distance between the first lenses 12a to 12d and the second lenses 14a to 14d is widened, so that the influence of reflection by the light incident surfaces of the second lenses 14a to 14d is reduced. Further, as the second lens 14a to 14d and the third lens 4, for example, a lens having a focal length of about 1.5 to 2.5 mm is used, so that the effect of expanding the coupling tolerance and the amount of reflected return light are reduced. It is possible to enhance the effect to be made.

  Here, the direction in which the second lens 14 is moved will be described in detail. FIG. 7 shows the relative positional relationship between the second lens 14 and the third lens 4. Specifically, FIG. 7A shows a state where the focal point on the LD 11 side of the second lens 14 and the condensing point on the optical fiber 5 side of the first lens 12 coincide. In this state, the light emitted from the second lens 14 is collimated light. FIG. 7B shows a state where the second lens 14 is located closer to the optical fiber 5 than the state of FIG. At this time, light emitted from the second lens 14 becomes convergent light. FIG. 7C shows a state in which the second lens 14 is positioned closer to the LD 11 than the state of FIG. At this time, the light emitted from the second lens 14 becomes divergent light.

  As shown in FIGS. 7B and 7C, when the light emitted from the second lens 14 is convergent light or divergent light, the light emitted from the third lens 4 is the optical fiber 5. The light is not condensed on the end face of the optical fiber 5, and this condensing position is a place inside the optical fiber 5. That is, when the light emitted from the second lens 14 is convergent light or divergent light, the condensing position of the light emitted from the third lens 4 is that the light emitted from the second lens 14 is parallel light. The position is farther from the third lens 4 than in the case. Therefore, when the outgoing light from the second lens 14 is convergent light or divergent light, the light coupling efficiency in the optical fiber 5 is lower than when the outgoing light from the second lens 14 is parallel light. .

  Here, a tracking error, which is a phenomenon in which the coupling efficiency varies depending on temperature, will be verified. Due to the tracking error, the physical dimension of each component varies depending on the coefficient of thermal expansion of each component in the light emitting module 1, and the relative position of each component is also affected.

  As described above, the third lens 4 and the optical fiber 5 are accommodated in the optical coupling portion 3 located outside the housing 2 together with the sleeve and the like. Therefore, the third lens 4 and the optical fiber 5 located inside the optical coupling unit 3 are directly affected by the temperature of the light emitting module 1 and the housing 2. On the other hand, the LD 11, the first lens 12 and the second lens 14 are disposed inside the housing 2. Furthermore, the LD 11, the first lens 12, and the second lens 14 are mounted on a TEC (temperature control element: Thermo-Electric Cooler) 20 inside the housing 2. Therefore, the temperatures of the LD 11, the first lens 12, and the second lens 14 are substantially stabilized.

  When the temperature rises, the optical coupling unit 3 is thermally expanded, and the optical fiber 5 moves in a direction away from the third lens 4. That is, in the state shown in FIG. 7B and FIG. 7C, the optical fiber 5 moves in a direction in which the end face of the optical fiber 5 approaches the condensing position of the third lens 4. On the other hand, mechanical distortion occurs in the upper substrate of the TEC 20 as the temperature changes. As a result, the second lens 14 moves away from the third lens 4 when the temperature rises.

  Here, in the state shown in FIG. 7B, the second lens 14 moves away from the third lens 4 as the temperature rises, so that the light coupling efficiency in the optical fiber 5 increases. Further, in the state shown in FIG. 7B, the coupling efficiency further increases because the end face of the optical fiber 5 approaches the condensing position of the third lens 4 as the temperature rises. As described above, in the state shown in FIG. 7B, the light coupling efficiency in the optical fiber 5 significantly increases when the temperature rises. However, in the state shown in FIG. 7B, the coupling efficiency is significantly lowered when the temperature is lowered.

  In the state shown in FIG. 7C, the second lens 14 is further away from the third lens 4 as the temperature rises, so that the light coupling efficiency in the optical fiber 5 is lowered. However, in the state shown in FIG. 7C, the end face of the optical fiber 5 moves in a direction approaching the condensing position of the third lens 4 as the temperature rises. This increases the light coupling efficiency in the optical fiber 5.

  That is, in the state shown in FIG. 7C, the coupling efficiency is lowered when the second lens 14 is separated from the third lens 4 due to the temperature rise, but the end face of the optical fiber 5 is focused on the third lens 4. Since the coupling efficiency is increased by approaching the position, the coupling efficiency is stabilized. Further, when the temperature decreases, the second lens 14 approaches the third lens 4 and the coupling efficiency increases. However, the coupling efficiency decreases when the end face of the optical fiber 5 moves away from the condensing position of the third lens 4. Also in this case, the coupling efficiency is stabilized. Accordingly, as shown in FIG. 7C, when the second lens 14 is positioned on the LD 11 side (first lens 12 side) and the light emitted from the second lens 14 becomes divergent light, the temperature dependence is increased. And the coupling efficiency can be stabilized. Therefore, the tracking error can be effectively reduced.

  FIG. 8 is a graph showing the relationship between the light coupling loss at the end face of the optical fiber 5 and the temperature. FIG. 8A shows the case where the second lens 14 is positioned on the optical fiber 5 side and the light emitted from the second lens 14 is convergent light (in the case of FIG. 7B), and FIG. ) Shows the case where the second lens 14 is positioned on the LD 11 side and the light emitted from the second lens 14 is divergent light (in the case of FIG. 7C).

  In FIG. 8, “Lane0” indicates a path of light that travels substantially straight from the LD 11 d (see FIG. 3) and is coupled to the optical fiber 5, and “Lane1” is light from the LD 11 b and includes the mirror 17 and the first light. 2 indicates the path of light reflected by the WDM filter 16, “Lane 2” indicates the path of light from the LD 11 c and repeated internal reflection by the polarization beam combining filter 19, and “Lane 3” indicates the path from the LD 11 a. A path of light that has been subjected to both reflection by the mirror 17 and the first WDM filter 15 and internal reflection by the polarization combining filter 19 is shown. The optical path length of each Lane is a value shown in the following Table 1, for example, and the optical path length of Lane 0 is the shortest and the optical path length of Lane 3 is the longest.

  As shown in FIG. 8A, when the second lens 14 is moved to the optical fiber 5 side, a tracking error appears greatly, and a variation in tracking error between lanes is large. That is, when the second lens 14 is moved to the optical fiber 5 side, the coupling efficiency varies greatly as the temperature rises. As described above, the coupling efficiency greatly fluctuates because the second lens 14 moves away from the third lens 4 and the end surface of the optical fiber 5 approaches the condensing position of the third lens 4 as described above. This is because both 14 and the third lens 4 act in the direction of increasing the coupling efficiency. The reason why the tracking error varies greatly between the lanes is that the distance between the second lens 14 and the third lens 4 differs from one lane to another as shown in Table 1 above.

  As shown in FIG. 8B, when the second lens 14 is moved to the LD 11 side, the tracking error is small and the tracking error variation between the lanes is also small. That is, when the second lens 14 is moved to the LD 11 side, even if the temperature rises, the fluctuation of the coupling efficiency is small and stable. As described above, the coupling efficiency is stable because the second lens 14 is further away from the third lens 4 and the end surface of the optical fiber 5 is closer to the condensing position of the third lens 4 as described above. This is because the second lens 14 acts in a direction that decreases the coupling efficiency, whereas the third lens 4 acts in a direction that increases the coupling efficiency.

  As mentioned above, although preferred embodiment which concerns on this invention has been described, this invention is not limited to embodiment mentioned above. That is, it is easily recognized by those skilled in the art that various modifications and changes can be made within the scope of the present invention described in the claims. For example, in the above embodiment, the multi-channel light emitting module including a plurality of lanes including the LDs 11a to 11d, the first lenses 12a to 12d, and the second lenses 14a to 14d has been described. However, the LD, the first lens, and the second lens are described. May be provided one by one.

DESCRIPTION OF SYMBOLS 1 ... Light emitting module (multi-channel light emitting module), 2 ... Housing | casing, 3 ... Optical coupling part, 4 ... 3rd lens, 5 ... Optical fiber, 11, 11a-11d ... LD (light emitting element), 12, 12a-12d DESCRIPTION OF SYMBOLS 1st lens, 13 ... Beam splitter, 14, 14a-14d ... 2nd lens, 15 ... 1st WDM filter, 16 ... 2nd WDM filter, 17 ... Mirror, 18 ... Isolator, 19 ... Polarization combining filter, 30 ... Infrared Camera, 40 ... jig, 44 ... condensing lens, 45 ... optical fiber.

Claims (4)

A light emitting element;
A first lens having one condensing point coincident with the light emitting point of the light emitting element;
A second lens that emits the light emitted from the first lens as diverging light;
A third lens for allowing the light emitted from the second lens to enter the optical fiber;
A temperature control element on which the light emitting element, the first lens and the second lens are mounted;
The second lens is disposed closer to the first lens than a position where light emitted from the second lens becomes parallel light,
The light emitted from the third lens is condensed inside the optical fiber ,
The second lens moves away from the third lens as the temperature rises,
The end face of the optical fiber on which the light emitted from the third lens is incident moves in a direction approaching the condensing position of the third lens as the temperature rises.
Light emitting module. In the first lens, the output light from the light emitting element is condensed at a magnification of 5 to 6 times,
The light emitting module according to claim 1. A multi-channel light emitting module comprising a plurality of lanes having a light emitting element, a first lens and a second lens,
A third lens that makes the light emitted from each of the second lenses combined and incident on the optical fiber;
A temperature control element on which each light emitting element, each first lens and each second lens is mounted;
With
In each of the lanes, the condensing point on the light emitting element side of the first lens is located at the light emitting point of the light emitting element, and the second lens converts light emitted from the first lens into divergent light. It is provided at the position to convert,
The divergent light emitted from the second lens is optically coupled to the optical fiber via the third lens, and the light emitted from the third lens is condensed inside the optical fiber ,
The second lens in each of the lanes moves away from the third lens as the temperature rises,
The end face of the optical fiber on which the light emitted from the third lens is incident moves in a direction approaching the condensing position of the third lens as the temperature rises.
Multi-channel light emitting module. The first lens in each of the lanes collects output light from the light emitting element at a magnification of 5 to 6 times,
The multi-channel light emitting module according to claim 3 .

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