JP2012038972A - Method for manufacturing semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor laser module capable of reducing percent defective of semiconductor laser elements and the manufacturing cost of the semiconductor laser module.SOLUTION: The method for manufacturing a semiconductor laser module 1 having a semiconductor laser element 3 and a optical fiber 7, comprises: a detecting step for detecting an end face phase of the semiconductor laser element 3; an acquisition step for acquiring a driving current value Ib1 corresponding to the end face phase detected in the detecting step from the driving current value Ib1 set so that its frequency characteristic may be nearly constant in any end face phase of the semiconductor laser element 3; and an adjusting step for adjusting an optical axis between the semiconductor laser element 3 and the optical fiber 7 so that the light output from the optical fiber 7 may be nearly constant when the driving current value Ib1 acquired in the acquisition step is supplied to the semiconductor laser element 3.

Description

  The present invention relates to a method for manufacturing a semiconductor laser module, and more particularly to a method for manufacturing a semiconductor laser module including a distributed feedback (DFB) semiconductor laser element.

  As a distributed feedback type semiconductor laser module, a semiconductor laser element, an optical fiber disposed so that light emitted from the semiconductor laser element is input, a lens disposed between the semiconductor laser element and the optical fiber, and the like There is known a module provided with (for example, see Patent Document 1). As an index indicating the performance of such a semiconductor laser module, there are optical output and frequency characteristics. However, since semiconductor laser modules have particularly large variations in optical output among individuals, it is difficult to use them as they are.

  Therefore, conventionally, a predetermined drive current obtained by increasing a constant current from a constant current source or a constant drive current obtained by increasing a constant current from a threshold current Ith is given to each of a predetermined number of semiconductor laser elements, and the light output from the optical fiber at that time is The optical axis between the semiconductor laser element and the optical fiber is adjusted (also referred to as alignment) so as to be substantially constant between the individual. Then, after adjusting the optical axis, the member for holding the semiconductor laser element and the member for holding the optical fiber are fixed by a fixing means such as a YAG laser to obtain a final module product.

JP 10-039174 A

  By the way, in the adjustment method described above, although the optical output, which is one of the indexes indicating the performance of the semiconductor laser module, can be made substantially constant among the individuals, it is another index indicating the performance of the semiconductor laser module. A certain frequency characteristic is not substantially constant but depends on the performance of each semiconductor laser element, and varies from module to module. For this reason, when the frequency characteristics such as the relaxation oscillation frequency fr that determines the transmission band do not satisfy a predetermined standard, the semiconductor laser element or the semiconductor laser module is excluded as a defective product, and as a result, the manufacturing yield decreases, and the semiconductor This was one factor that increased the manufacturing cost of laser modules.

  Accordingly, an object of the present invention is to provide a method of manufacturing a semiconductor laser module that can reduce the rate at which a semiconductor laser element or the like is defective and reduce the manufacturing cost of the semiconductor laser module.

In order to solve the above-mentioned problems, the present inventor first paid attention to the relationship between the relaxation oscillation frequency fr of each semiconductor laser element and the end face phase of each semiconductor laser element in the course of earnest research (see FIG. 3). Further, as shown in the following formula (1), the relaxation oscillation frequency fr is also proportional to the square root of the difference between the bias current Ib and the threshold current Ith divided by the threshold current Ith, and is driven. It has been found that the value of the relaxation oscillation frequency fr can be adjusted to a substantially constant value between individuals by increasing or decreasing the bias current Ib corresponding to the current (see FIG. 9). FIG. 9 shows that the relaxation oscillation frequency fr is changed by changing the bias current Ib in the same laser element.

  On the other hand, to increase the relaxation oscillation frequency fr by 20%, for example, (Ib−Ith) in equation (1) is increased by approximately 44%, and the optical output of the semiconductor laser module is also increased by approximately 44%. As a result, the allowable range of light output may be exceeded. Therefore, the present inventor can adjust the value of the relaxation oscillation frequency fr to be substantially constant (predetermined range) between individuals while preventing the optical output of the semiconductor laser module from exceeding the allowable range. Obtaining knowledge that the number of semiconductor laser elements and the like that have been excluded as defective products can be reduced to reduce the manufacturing cost of the semiconductor laser module, the present invention has been completed.

  That is, in order to solve the above problems, a semiconductor laser module manufacturing method according to the present invention includes a distributed feedback semiconductor laser element having a predetermined end face phase, and an optical fiber into which light emitted from the semiconductor laser element is incident. A method for manufacturing a semiconductor laser module comprising: a detection step for detecting an end face phase of a semiconductor laser element; and a frequency characteristic set to be substantially constant regardless of the end face phase of the semiconductor laser element. An acquisition step for acquiring a drive current value corresponding to the end face phase detected in the detection step among the drive current values that are present, and an optical fiber when the drive current of the drive current value acquired in the acquisition step is given to the semiconductor laser element And an adjusting step for adjusting the optical axis between the semiconductor laser element and the optical fiber so that the optical output of the laser beam becomes substantially constant.

  In this manufacturing method, one drive current value corresponding to the detected end face phase is acquired from the drive current values set so that the frequency characteristics are substantially constant, and the drive current of the acquired drive current value is acquired. Is applied to the semiconductor laser element, and the optical axis is adjusted so that the light output thereof is substantially constant among the individual laser diodes. In this case, since the optical axis is adjusted using the drive current of the drive current value set so that the frequency characteristics are substantially constant in the adjustment step before the semiconductor laser module is completely assembled, Even if the light output is inevitably increased in order to increase the frequency characteristics, the adjustment of the optical axis can be performed so as to reduce the light output.

  In other words, once it is incorporated as a semiconductor laser module, the optical output must be increased in order to increase the frequency characteristics, and it is difficult to reduce only the optical output. Such a problem can be solved by making an adjustment before being incorporated into the semiconductor module. As a result, according to the manufacturing method of the present invention, it is possible to obtain a semiconductor laser module in which the frequency characteristics and the optical output are substantially constant among individuals, and the rate at which the semiconductor laser element and the like are defective products can be obtained. Thus, the manufacturing cost of the semiconductor laser module can be reduced. The defective products mentioned here include not only semiconductor laser elements that are at a level that cannot be used at all, but also those that may be used in certain applications but cannot be used in other higher-precision applications. included.

  In the above manufacturing method, the drive current value set so that the frequency characteristics are substantially constant regardless of the end face phase of the semiconductor laser element is the minimum value when the end face phase is 0.5π. It is preferable that the maximum value is set when the end face phase is 1.5π. By setting in this way, the acquisition process of acquiring the drive current value can be facilitated.

  In the manufacturing method described above, in the adjustment step, the coupling loss between the semiconductor laser element and the optical fiber is increased or decreased in proportion to the drive current value corresponding to the end face phase. It is preferable to adjust the optical axis in between. In this way, when the drive current value increases, the coupling loss also increases, and when the drive current value decreases, the coupling loss also decreases, so that the light between the semiconductor laser modules having different drive current values can be reduced. The output can be easily made substantially constant.

  In the manufacturing method described above, the semiconductor laser module further includes a drive circuit for driving the semiconductor laser element, and the drive circuit in which the drive current value used in the adjustment process is set is combined with the semiconductor laser element. You may make it further provide the incorporation process integrated in. In this case, since the drive current value used in the adjustment process is set in advance in the drive circuit, it is not necessary to set and input the drive current value when using the completed semiconductor laser module. Convenient.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the semiconductor laser module which can reduce the rate by which a semiconductor laser element is made defective, and can reduce the manufacturing cost of a semiconductor laser module can be provided.

It is the schematic of the system configuration | structure for performing the optical axis adjustment between a semiconductor laser element and an optical fiber. It is a flowchart which shows the manufacturing process of a semiconductor laser module. It is a figure which shows the relationship between relaxation vibration frequency fr and an end surface phase. It is a figure which shows that relaxation oscillation frequency fr etc. change according to an end surface phase, (a) shows the case where an end surface phase is 0.5 (pi), (b) shows the case where an end surface phase is (pi). It is a figure which shows that the waveform of a signal changes according to an end surface phase, (a) shows the case where an end surface phase is 0.5 (pi), (b) shows the case where an end surface phase is (pi). It is a figure which shows the relationship between the correction coefficient fr_Comp for correct | amending a drive current, and an end surface phase. It is a figure which shows that the relaxation oscillation frequency fr is in the substantially constant range by the manufacturing method which concerns on this invention. It is a figure which shows the dispersion | variation in the electric current by the manufacturing method which concerns on this invention. It is a figure which shows that relaxation oscillation frequency fr changes by changing bias current. It is a flowchart which shows the manufacturing process at the time of incorporating a drive circuit etc. further into an optical module.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  First, the semiconductor laser module 1 manufactured by the manufacturing method according to the present embodiment will be briefly described. As shown in FIG. 1, the semiconductor laser module 1 includes a semiconductor laser element 3, a holding member 5 that holds the semiconductor laser element 3, an optical fiber 7 into which light emitted from the semiconductor laser element 3 is incident, A holding member 9 that holds the fiber 7 and a lens 11 disposed between the semiconductor laser element 3 and the optical fiber 7 are provided.

  The semiconductor laser element 3 is, for example, a DFB laser with an oscillation wavelength of 1.55 μm, and is exemplified as a light source used in a long-distance optical communication system that requires stable single mode oscillation. The semiconductor laser element 3 which is a DFB laser is provided with a diffraction grating inside, and has a predetermined phase (end face phase) of the diffraction grating on the cleavage plane.

  As shown in FIG. 3, this end face phase is expressed in a range of 0 to 2π and has a predetermined relationship with the value of the relaxation oscillation frequency fr of the semiconductor laser element 3. The relaxation oscillation frequency fr is one of the factors that determine the transmission band of the semiconductor laser element 3. For example, the relaxation oscillation frequency fr and the like (including the frequency characteristic due to the CR time constant of the element) have a flat frequency characteristic as shown in FIG. 4A when the end face phase is 0.5π. As shown in FIG. 4B, when the end face phase is π, the frequency characteristic appears slightly deviated from the flat.

  Then, in the semiconductor laser element 3 (end face phase is 0.5π) shown in FIG. 4A, the signal waveform has a clean shape as shown in FIG. 5A. On the other hand, in the semiconductor laser element 3 (end face phase is π) shown in FIG. 4B, as shown in FIG. 5B, a part of the peak is distorted and the rise of the signal is delayed. It becomes a slightly deteriorated waveform. That is, the end face phase in the semiconductor laser element 3 and the accompanying relaxation oscillation frequency fr are important factors that determine the performance of the semiconductor laser module 1.

  Next, returning to FIG. 1, an optical axis adjustment system 21 for performing optical axis adjustment in the method of manufacturing the semiconductor laser module 1 will be described. The optical axis adjustment system 21 includes a current source 23 for giving a predetermined current to the semiconductor laser element 3, an optical PowerMeter 25 for measuring the optical output from the optical fiber 7, and the semiconductor laser element 3 and the optical fiber 7. An adjustment unit 27 that adjusts the optical axis, a PC 29 that controls the current source 23, the optical power meter 25, and the adjustment unit 27, and an element information provision unit 31 that outputs element information (end face phase information and the like) of the semiconductor laser element 3 to the PC 29 A YAG laser 33 for fixing the holding member 5 of the semiconductor laser element 3 and the holding member 9 of the optical fiber 7 is provided.

  As shown in FIG. 1, the adjustment unit 27 is a device that adjusts the optical axis by appropriately moving the optical fiber 7 in the three axial directions of the X axis, the Y axis, and the Z axis. Furthermore, you may make it provide the rotation mechanism (not shown) for angle adjustment.

  Next, a method for manufacturing the semiconductor laser module 1 according to the present embodiment will be described with reference to FIGS.

  First, a semiconductor substrate serving as a basis for the semiconductor laser element 3 is prepared (step S1). As a semiconductor substrate used here, for example, a semiconductor substrate made of InP doped with Sn is prepared. Subsequently, a clad layer, a diffraction grating formation layer, and the like are sequentially laminated on such a semiconductor substrate to form a laminated body. For example, when the oscillation wavelength of the semiconductor laser element 3 is 1.55 μm, the diffraction grating in the diffraction grating forming layer has an interval of about 240 nm.

  Subsequently, the laminated body in which the cladding layer, the diffraction grating formation layer, and the like are laminated is cleaved to form a chip (step S2). Since the interval between the diffraction gratings is about two orders of magnitude smaller than the cleavage accuracy, it is difficult to control the phase (end surface phase) of the diffraction grating at the end face of the semiconductor laser element 3. The end face phase varies. As a result of the change in the internal photon density distribution due to the difference in the end face phase, the frequency characteristics such as the relaxation oscillation frequency fr vary from one semiconductor laser element 3 to another as described above with reference to FIG.

  Subsequently, end faces such as HR coat and AR coat are formed on both end faces of each cleaved chip, and an electrode layer is further formed. Thereby, a plurality of semiconductor laser elements 3 are completed (step S2). The detailed manufacturing method of the semiconductor laser element 3 is omitted because the conventional technique can be used as appropriate.

Subsequently, various measurements for determining the quality of the semiconductor laser element 3 are performed (step S3). This measurement includes measurement of the end face phase of each semiconductor laser element 3. In order to measure the end face phase of the semiconductor laser element 3, for example, as disclosed in JP 2009-231830A, the optical output Im from the semiconductor laser element 3 is measured at two temperatures (25 ° C. and 80 ° C.). The change rate ΔIm can be measured and measured, and the light output Im ₂₅ at 25 ° C. and the change rate ΔIm can be calculated.

  Subsequently, based on the measurement in step S3, the semiconductor laser element 3 is selected for each end face phase (step S4). Then, the semiconductor laser element 3 selected in step S4 is mounted and fixed on the holding member 5, and the optical fiber 7 is introduced into the opening of the holding member 9 and temporarily fixed (step S5). At this time, the lens 11 and the like are also arranged.

Subsequently, the optical axis between the semiconductor laser element 3 and the optical fiber 7 is adjusted using the optical axis adjustment system 21 shown in FIG. 1 (step S6). Specifically, first, the PC 29 functioning as a control unit obtains information on the end face phase of the semiconductor laser element 3 that performs optical axis adjustment and the correction coefficient fr_Comp of the drive current Ib from the element information providing unit 31. This correction coefficient fr_Comp is used to set the drive current Ib of the semiconductor laser element 3 in order to make the relaxation oscillation frequency fr of each semiconductor laser element 3 having different end face phases substantially constant among the individual using the following formula (1). It is a coefficient for correcting according to the end face phase.

The drive current Ib1 corrected by the correction coefficient fr_Comp is expressed by the following equation (2). In formula (2), Ith represents a threshold current, and β is an additional value considering operation at a high temperature, and usually takes 1-2.
(Equation 2)
Ib1 = (fr_Comp) × Ith × (1 + β) (2)
Note that fr_Comp preferably takes a continuously changing value as shown in FIG. 6, but in the present embodiment, in order to facilitate the correction process, it is set to 16 levels shown in Table 1 below. .

  As is clear from the equation (2) and the graph of FIG. 6 (or Table 1), the value of the drive current Ib1 used in the optical axis adjustment step is a graph having a locus substantially equivalent to the graph of FIG. Become. That is, the corrected drive current Ib1 is set to take a minimum value when the end face phase is 0.5π and to take a maximum value when the end face phase is 1.5π.

  Next, after obtaining the correction coefficient fr_Comp and the like of the drive current Ib, in the optical axis adjustment step in step S6, the drive current Ib1 is corrected by correcting the drive current Ib with the correction coefficient fr_Comp according to the end face phase of the semiconductor laser element 3. Obtained and applied to the semiconductor laser element 3. Then, the semiconductor laser element 3 is used by using the adjusting unit 27 so that the light output from the optical fiber 7 is also substantially constant while the driving current Ib1 is set so that the relaxation oscillation frequency fr is substantially constant. The optical axis between the optical fiber 7 and the optical fiber 7. The optical output from the optical fiber 7 is measured by the optical PowerMeter, and the PC 29 controls the movement of the adjusting unit 27 to execute the optical axis adjustment described above.

Here, the principle for adjusting the optical axis between the semiconductor laser element 3 and the optical fiber 7 to make the optical output substantially constant will be briefly described. The light output used here is generally expressed by the following equation (3). Loss in equation (3) indicates the coupling loss between the semiconductor laser element 3 and the optical fiber 7, and Se indicates the light emission efficiency of the semiconductor laser element 3.
(Equation 3)
Optical output Pout = Loss × Se × (Ib−Ith) (3)

  Then, by providing the corrected drive current Ib1 as described above, the light output from the semiconductor laser element 3 may become higher than usual. In this embodiment, the position of the optical fiber is adjusted by the adjusting unit. By adjusting at 27, the loss (coupling loss) of the above-described equation (3) is also increased, and as a result, the optical output can be made substantially constant. In other words, by adjusting the coupling loss between the semiconductor laser element 3 and the optical fiber 7 according to the corrected value of the driving current Ib1, the optical axis between the semiconductor laser element 3 and the optical fiber 7 is adjusted. Is supposed to do.

  Subsequently, when the optical axis adjustment step of step S6 is completed, the holding member 5 holding the semiconductor laser element 3 and the holding member 9 holding the optical fiber 7 are fixed by the YAG laser 33, and the light output and the relaxation vibration frequency are fixed. An optical fiber module 1 in which fr becomes substantially constant between solids is obtained. Thereafter, predetermined inspection / sorting is performed on each optical fiber module 1 to complete the manufacture of the optical fiber module 1 (step S7).

  As described above, in the manufacturing method according to the present embodiment, one of the drive current values Ib1 that is set so that the relaxation oscillation frequency fr and the like are substantially constant among the individuals according to the detected end face phase. The drive current value Ib1 is acquired by correction, and the optical axis adjustment is performed so that the optical output becomes substantially constant among the individual while giving the drive current of the acquired drive current value Ib1 to the semiconductor laser element 3. ing.

  In this case, in the adjustment step before the semiconductor laser module 1 is completely assembled, the optical axis adjustment is performed using the drive current of the drive current value Ib1 set so that the relaxation oscillation frequency fr and the like become substantially constant. Therefore, even if the light output is inevitably increased in order to increase the relaxation oscillation frequency fr based on the equation (1), the adjustment step based on the equation (3) The optical axis can be adjusted so as to reduce the output.

  That is, once incorporated as a semiconductor laser module, the optical output must be increased in order to increase the frequency characteristics, and it is difficult to reduce only the optical output. In addition, this problem can be solved by making an adjustment before being incorporated into the semiconductor laser module 1. As a result, according to the manufacturing method according to the present embodiment, it is possible to obtain the semiconductor laser module 1 in which the relaxation oscillation frequency fr and the optical output are substantially constant among individuals (see FIGS. 7 and 8). The range shown by this method in FIGS. 7 and 8 means substantially constant.

  Thus, by making the relaxation oscillation frequency fr and the optical output substantially constant among the individual members, the rate at which the semiconductor laser element or the like is defective can be reduced, and the manufacturing cost of the semiconductor laser module 1 can be reduced. Can be lowered. Note that when the optical axis adjustment is performed in the present embodiment, as shown in FIG. 8, the variation in the drive current is slightly increased, but the level is practically not problematic.

  In the manufacturing method described above, the drive current value Ib1 set so that the relaxation oscillation frequency fr is substantially constant regardless of the end face phase of the semiconductor laser element 3 has an end face phase of 0.5π. In this case, the minimum value is set and the maximum value is set when the end face phase is 1.5π (see FIG. 6 and Expression (2)). With such a setting, the acquisition process of acquiring the drive current value Ib1 can be facilitated.

  Further, in the manufacturing method described above, in the adjustment step, the coupling loss Loss between the semiconductor laser element 3 and the optical fiber 7 is increased or decreased in proportion to the drive current value corresponding to the end face phase. Optical axis adjustment with the optical fiber 7 is performed. As described above, when the drive current value Ib1 is increased, the coupling loss Loss is also increased, and when the drive current value Ib1 is decreased, the coupling loss Loss is also decreased, so that the semiconductor laser modules 1 having different drive current values are connected. Therefore, their light outputs can be easily made substantially constant.

  By the way, when the drive current value Ib1 is adjusted in accordance with the end face phase of the semiconductor laser element 3 so that the relaxation oscillation frequency fr and the optical output are substantially constant, the drive current is particularly adjusted to exceed a predetermined value. In such a case, a so-called thermal runaway phenomenon of the drive current due to heat generation of the semiconductor laser may occur. This thermal runaway phenomenon is accompanied by a decrease in the optical output of the semiconductor laser due to the heat generation of the semiconductor laser as the drive current increases, and as a result, the drive current is increased to maintain the optical output constant. Since the control circuit functions so as to increase, it is considered that the cause is that the heat generation of the semiconductor laser element and the decrease in the optical output are increasingly caused. In order to avoid such a thermal runaway phenomenon, an upper limit value is set for the drive current of the semiconductor laser element, and a drive current control unit can be set in advance so as not to supply a current exceeding the upper limit value. . Alternatively, a drive current limiting circuit may be provided in the drive current supply power supply unit so that no current flows beyond the upper limit value of the drive current. In FIG. 8, the current limitation of the drive current is due to the setting of the upper limit value of the drive current.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  For example, in the above-described embodiment, the end face phase of the semiconductor laser element 3 is detected by the method described in JP 2009-231830 A. However, the end face phase is detected from the optical spectrum of the semiconductor laser element 3. Of course.

  Further, in the above-described embodiment, the manufacturing is finished as a module in which the holding unit 5 that holds the semiconductor laser element 3 and the holding unit 9 that holds the optical fiber 7 are fixed. However, the semiconductor laser module 1 may further include a drive circuit (not shown) for driving the semiconductor laser element 3. In this case, as shown in FIG. 10, the drive circuit (IC, electronic component) or mechanism component in which the drive current value Ib1 (module characteristic information) used in the adjustment process is set is combined with the semiconductor laser element 3 in the semiconductor laser module 1. You may make it further provide the incorporation process integrated in.

  In this case, since the drive current value used in the adjustment process is set in advance in the drive circuit, it is not necessary to set and input the drive current value Ib1 when using the completed semiconductor laser module 1. Convenient. Even in the semiconductor laser module 1 that has undergone such additional steps, the characteristic inspection is finally performed. In this drive circuit, the above-described upper limit value of the drive current can also be set.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser module, 3 ... Semiconductor laser element, 7 ... Optical fiber, 27 ... Adjustment part, 31 ... Element information provision part, 33 ... YAG laser

Claims (4)

A method of manufacturing a semiconductor laser module, comprising: a distributed feedback semiconductor laser element having a predetermined end face phase; and an optical fiber into which light emitted from the semiconductor laser element is incident.
A detection step of detecting an end face phase of the semiconductor laser element;
A drive current value corresponding to the end face phase detected in the detection step is acquired from drive current values set so that the frequency characteristics thereof are substantially constant regardless of the end face phase of the semiconductor laser element. An acquisition process to
When the drive current of the drive current value acquired in the acquisition step is applied to the semiconductor laser element, the optical output from the optical fiber is substantially constant between the semiconductor laser element and the optical fiber. An adjustment process for adjusting the optical axis;
A method of manufacturing a semiconductor laser module, comprising:   The drive current value set so that the frequency characteristic is substantially constant regardless of the end face phase of the semiconductor laser element takes a minimum value when the end face phase is 0.5π, and the end face phase is 2. The method of manufacturing a semiconductor laser module according to claim 1, wherein the semiconductor laser module is set to take a maximum value in the case of 1.5 [pi].   In the adjustment step, the coupling loss between the semiconductor laser element and the optical fiber is increased or decreased between the semiconductor laser element and the optical fiber so as to increase or decrease in proportion to the drive current value corresponding to the end face phase. 3. The method of manufacturing a semiconductor laser module according to claim 1, wherein the optical axis is adjusted. The semiconductor laser module further includes a drive circuit for driving the semiconductor laser element,
4. The method according to claim 1, further comprising an incorporation step of incorporating the drive circuit in which the drive current value used in the adjustment step is set into the semiconductor laser module together with the semiconductor laser element. The manufacturing method of the semiconductor laser module of description.

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