JP2013050429A - Characteristics measuring method of input light of optical interference element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a characteristics measuring method of input light of an optical interference element capable of accurately measuring characteristics of the input light input to the optical interference element without adjusting interference characteristics of the optical interference element.SOLUTION: An optical interference element comprises: an input coupler; a plurality of semiconductor arms connected to the input coupler; and an output coupler for interfering with output of the plurality of semiconductor arms. A characteristics measuring method of input light of the optical interference element includes: a first step of performing control that causes optical absorption characteristics to be generated in all but one semiconductor arms out of the plurality of semiconductor arms; and a second step of measuring characteristics of the input light output from the output coupler subsequent to the first step.

Description

  The present invention relates to a method for measuring characteristics of light input to an optical interference element.

  An optical semiconductor device in which a semiconductor laser as a light source and an optical interference element are integrated is known (for example, see Patent Document 1). In such an optical semiconductor device, when the characteristics of a semiconductor laser serving as a light source are to be inspected, the output from the optical interference element is observed.

JP 2004-78002 A

  In order to inspect the characteristics of the semiconductor laser using light that has passed through the optical interference element from the semiconductor laser, it is preferable to avoid the influence of the optical interference element. For this purpose, there is a method of adjusting the interference characteristics so that the output of the optical interference element becomes a peak. However, the interference characteristics of individual optical interference elements may differ due to manufacturing variations of semiconductor arms. Therefore, in order to avoid the influence of the optical interference element, it is necessary to adjust the interference characteristics different for each optical interference element to obtain an appropriate light output.

  Of course, the adjustment of the interference characteristics of the optical interference element is carried out in any process up to the shipment of the optical semiconductor device. However, the characteristics of the semiconductor laser cannot be inspected until the adjustment of the interference characteristics of the optical interference element. Therefore, when a defect of the semiconductor laser is found after the adjustment of the interference characteristics of the optical interference element, the troublesome man-hours for adjusting the interference characteristics of the optical interference elements that have been performed individually are wasted.

  The present invention provides an input light of an optical interference element that can accurately measure the characteristics of the input light input to the optical interference element without adjusting the interference characteristics of the optical interference element by changing the conditions for each element. An object of the present invention is to provide a method for measuring the characteristics.

  An optical interference element comprising: an input coupler; a plurality of semiconductor arms connected to the input coupler; and an output coupler that interferes with an output of the semiconductor arm. The method for measuring the characteristics of the input light of the first step, wherein a control is performed to generate a light absorption characteristic in all other semiconductor arms excluding one of the plurality of semiconductor arms, and after the first step. And a second step of measuring a characteristic of the input light output from the output coupler. The light absorption characteristic of the semiconductor arm depends on the semiconductor material, and the difference between elements is smaller than the interference characteristic. For this reason, according to the method for measuring the input light characteristics of the optical interference element according to the present invention, the characteristics of the input light input to the optical interference element without adjusting the interference characteristics of the optical interference element for each element. Can be measured with high accuracy.

  The optical interference element may be a Mach-Zehnder modulator. In the first step, a light absorption characteristic may be generated by applying a reverse bias to the semiconductor arm. The semiconductor arm may include a phase control unit and a modulation control unit, and in the first step, the reverse bias may be applied to either or both of the phase control unit and the modulation control unit.

  An output of a semiconductor laser may be connected to the input coupler of the optical interference element. The optical interference element may be provided on a semiconductor substrate common to the semiconductor laser. The semiconductor laser may be a wavelength tunable semiconductor laser. The light absorption rate in the first step may be 20 dB or more.

  According to the method for measuring the characteristics of the input light of the optical interference element according to the present invention, the characteristics of the input light input to the optical interference element can be accurately measured without adjusting the interference characteristics of the optical interference element. .

1 is a plan view showing an overall configuration of an optical semiconductor device that is an object of a method for measuring characteristics of input light of an optical interference element according to Example 1. FIG. (A) is an enlarged plan view of the semiconductor laser, and (b) is a cross-sectional view taken along the line α-α of (a). (A) is an example of a schematic top view of an optical interference element, (b) is an example of a schematic cross-sectional view between β and β in (a), and (c) is between γ and γ in (a). It is an example of a cross-sectional schematic diagram. It is a figure which shows the extinction ratio of the output from each semiconductor arm at the time of making it absorb light by applying a reverse bias to one semiconductor arm, and an optical interference element. (A) is a figure which shows the example of the optical output power of the optical interference element 300 at the time of applying a reverse bias to one semiconductor arm, (b) is a reverse bias applied to a semiconductor arm, and passes the said semiconductor arm It is a figure which shows the relationship with the optical power to do. (A) shows the flow of the measuring method which concerns on Example 1, (b) is an apparatus figure used for the measuring method which concerns on Example 1. FIG. FIG. 6 is an apparatus diagram used for a measurement method according to Example 2. FIG. 10 is a diagram illustrating a flow of a method for measuring characteristics of input light of an optical interference element according to Example 2.

  Hereinafter, modes for carrying out the present invention will be described.

  FIG. 1 is a plan view illustrating an entire configuration of an optical semiconductor device 100 that is a target of a method for measuring characteristics of input light of an optical interference element according to a first embodiment. As shown in FIG. 1, the optical semiconductor device 100 has a structure in which a semiconductor laser 200 and an optical interference element 300 are integrated. In this embodiment, a tunable laser is used as the semiconductor laser 200. A Mach-Zehnder modulator is used as the optical interference element 300. In FIG. 1, the optical waveguide of the optical semiconductor device 100 is seen through.

  FIG. 2A is an enlarged plan view of the semiconductor laser 200. FIG. 2B is a cross-sectional view taken along the line α-α in FIG. As shown in FIG. 2A and FIG. 2B, the semiconductor laser 200 includes an SG-DFB (Sampled Distributed Distributed Feedback) region A, a CSG-DBR (Chired Sampled Distributed Reflector) region B light, , And an SOA (Semiconductor Optical Amplifier) region D is connected. In this embodiment, the SOA region D, the SG-DFB region A, the CSG-DBR region B, and the light absorption region C are connected in this order.

  The SG-DFB region A has a structure in which a lower cladding layer 2, an active layer 3, an upper cladding layer 6, a contact layer 7, and an electrode 8 are stacked on a substrate 1. The CSG-DBR region B has a structure in which a lower cladding layer 2, an optical waveguide layer 4, an upper cladding layer 6, an insulating film 9, and a plurality of heaters 10 are stacked on a substrate 1. Each heater 10 is provided with a power supply electrode 11 and a ground electrode 12. The light absorption region C has a structure in which a lower cladding layer 2, a light absorption layer 5, an upper cladding layer 6, a contact layer 13, and an electrode 14 are laminated on a substrate 1. The SOA region D has a structure in which an n-type lower cladding layer 2, an optical amplification layer 19, a p-type upper cladding layer 6, a p-type contact layer 20, and an electrode 21 are stacked on a substrate 1. The insulating film 9 is also formed between the electrode 8 and the electrode 21.

  In the SG-DFB region A, CSG-DBR region B, light absorption region C, and SOA region D, the substrate 1, the lower cladding layer 2, and the upper cladding layer 6 are integrally formed. The active layer 3, the optical waveguide layer 4, the light absorption layer 5, and the optical amplification layer 19 are formed on the same plane.

The diffraction grating (corrugation) 18 is formed at a plurality of positions with a predetermined interval in the lower cladding layer 2 of the SG-DFB region A and the CSG-DBR region B. SG-DFB area A and CSG-DBR area B are composed of a plurality of segments. Here, the segment refers to a region in which a region where the diffraction grating 18 is provided and a space portion where the diffraction grating 18 is not provided are continuous one by one. The diffraction grating 18 is made of a material having a refractive index different from that of the lower cladding layer 2. When the lower cladding layer 2 is InP, for example, Ga _0.22 In _0.78 As _0.47 P _0.53 can be used as the material constituting the diffraction grating.

  In the CSG-DBR region B, the optical lengths of at least two segments are different from each other. Thereby, the intensity | strength of the peak of the wavelength characteristic of CSG-DBR area | region B comes to have wavelength dependence. On the other hand, the optical length of each segment in the SG-DFB region A is substantially the same. By combining these SG-DFB region A and CSG-DBR region B, the laser oscillation can be stably performed at a desired wavelength by utilizing the vernier effect.

  The substrate 1 is a crystal substrate made of n-type InP, for example. The lower cladding layer 2 is n-type, and the upper cladding layer 6 is p-type, and each is made of, for example, InP. The lower cladding layer 2 and the upper cladding layer 6 confine the active layer 3, the optical waveguide layer 4, the light absorption layer 5, and the optical amplification layer 19 vertically.

The active layer 3 is composed of a semiconductor having a gain. The active layer 3 has, for example, a quantum well structure, for example, a well layer made of Ga _0.32 In _0.68 As _0.92 P _0.08 (thickness 5 nm), Ga _0.22 In _0. It has a structure in which barrier layers made of ₇₈ As _0.47 P _0.53 (thickness 10 nm) are alternately stacked. The optical waveguide layer 4 can be composed of, for example, a bulk semiconductor layer, and can be composed of, for example, Ga _0.22 In _0.78 As _0.47 P _0.53 .

  For the light absorption layer 5, a material having absorption characteristics with respect to the oscillation wavelength of the semiconductor laser 200 is selected. As the light absorption layer 5, a material whose absorption edge wavelength is located on the long wavelength side with respect to the oscillation wavelength of the semiconductor laser 200 can be selected, for example. Of the oscillation wavelengths of the semiconductor laser 200, the absorption edge wavelength is preferably located on the longer wavelength side than the longest oscillation wavelength.

The light absorption layer 5 can be configured, for example, by a quantum well structure, for example, a Ga _0.47 In _0.53 As (thickness 5 nm) well layer and a Ga _0.28 In _0.72 As _0. It has a structure in which ₆₁ P _0.39 (thickness 10 nm) barrier layers are alternately stacked. Moreover, the light absorption layer 5 may be a bulk semiconductor, and a material made of, for example, Ga _0.46 In _0.54 As _0.98 P _0.02 may be selected. The light absorption layer 5 may be made of the same material as that of the active layer 3, and in that case, the active layer 3 and the light absorption layer 5 can be manufactured in the same process, so that the manufacturing process is simplified. Is done.

The optical amplification layer 19 is a region to which gain is given by current injection from the electrode 21, thereby performing optical amplification. The optical amplification layer can be configured, for example, with a quantum well structure. For example, a well layer of Ga _0.35 In _0.65 As _0.99 P _0.01 (thickness 5 nm) and Ga _0.15 In _0.85 A structure in which barrier layers of As _0.32 P _0.68 (thickness 10 nm) are alternately stacked may be employed. Further, as another structure, for example, a bulk semiconductor made of Ga _0.44 In _0.56 As _0.95 P _0.05 can be adopted. The contact layer 20 is made of, for example, p-type Ga _0.47 In _0.53 As crystal. Note that the optical amplification layer 19 and the active layer 3 can be made of the same material. In this case, since the optical amplification layer 19 and the active layer 3 can be manufactured in the same process, the manufacturing process is simplified.

The contact layers 7 and 13 can be composed of, for example, p-type Ga _0.47 In _0.53 As crystal. The insulating film 9 is a protective film made of an insulator such as SiN or SiO ₂ . The heater 10 is a thin film resistor made of NiCr or the like. Each heater 10 may be formed across a plurality of segments of the CSG-DBR region B.

  The electrodes 8, 14, the power supply electrode 11 and the ground electrode 12 are made of a conductive material such as gold. A back electrode 15 is formed at the bottom of the substrate 1. The back electrode 15 is formed across the SG-DFB region A, the CSG-DBR region B, and the light absorption region C.

  Next, the optical interference element 300 will be described. FIG. 3A is an example of a schematic top view of the optical interference element 300. As shown in FIG. 3A, the optical interference element 300 is configured by combining paths of mesa-shaped optical waveguides on a semiconductor substrate. In FIG. 3A, each optical waveguide is seen through. 3B is an example of a schematic cross-sectional view between β and β in FIG. 3A, and FIG. 3C is an example of a schematic cross-sectional view between γ and γ in FIG. is there.

  With reference to FIG. 3B, the optical waveguide is formed on the semiconductor substrate 41. The semiconductor substrate 41 may be a semiconductor substrate common to the semiconductor substrate 1 of FIG. The optical waveguide has a structure in which a lower cladding layer 42a, a core 43, and an upper cladding layer 42b are stacked in this order on a semiconductor substrate 41. A passivation film 44 and an insulating film 45 are sequentially stacked on the upper surface of the semiconductor substrate 41 and the upper surface and side surfaces of the optical waveguide.

  The semiconductor substrate 41 is made of a semiconductor such as InP. The lower cladding layer 42a and the upper cladding layer 42b are made of a semiconductor such as InP. The core 43 is made of a semiconductor having a band gap energy smaller than that of the lower cladding layer 42a and the upper cladding layer 42b, and is an InGaAsP bulk layer, an AlGaInAsP quantum well structure layer, or the like. The light passing through the core 43 is confined by the lower cladding layer 42a and the upper cladding layer 42b. The passivation film 44 is made of a semiconductor such as InP. The insulating film 45 is made of an insulator such as SiN.

  Referring to FIG. 3A, the optical interference element 300 is provided with a first input optical waveguide 32a connected to the first input end 31a, and a second input optical waveguide connected to the second input end 31b. 32b is provided. The first input optical waveguide 32a and the second input optical waveguide 32b join at the input coupler 33, and branch to the first semiconductor arm 34a and the second semiconductor arm 34b. When the longitudinal direction of the optical interference element 300 is the axis of symmetry, the first semiconductor arm 34a is disposed on the same side as the first input end 31a, and the second semiconductor arm 34b is disposed on the same side as the second input end 31b. ing. In the present embodiment, the input coupler 33 is a 2 × 2 MMI (Multi Mode Interference). The output end of the semiconductor laser 200 is optically coupled to the first input end 31a.

  The first semiconductor arm 34a and the second semiconductor arm 34b join at the output coupler 35, and the first output optical waveguide 36a connected to the first output end 37a and the second output optical waveguide connected to the second output end 37b. Branch to 36b. When the longitudinal direction of the optical interference element 300 is the axis of symmetry, the first output end 37a is disposed on the same side as the second semiconductor arm 34b, and the second output end 37b is disposed on the same side as the first semiconductor arm 34a. ing. In this embodiment, the output coupler 35 is a 2 × 2 MMI.

  Each of the first semiconductor arm 34a and the second semiconductor arm 34b is provided with a phase adjustment electrode 46 and a modulation electrode 47. The phase adjustment electrode 46 and the modulation electrode 47 are separated from each other. The positional relationship between the phase adjustment electrode 46 and the modulation electrode 47 is not particularly limited, but in the present embodiment, the phase adjustment electrode 46 is disposed closer to the light input end than the modulation electrode 47. .

  Referring to FIG. 3C, the modulation electrode 47 is disposed on the upper cladding layer 42b via the contact layer 49. The contact layer 49 is made of a semiconductor such as InGaAs. Note that the passivation film 44 and the insulating film 45 are not provided between the upper cladding layer 42 b and the contact layer 49. The phase adjustment electrode 46 and the modulation electrode 47 are made of a metal such as Au.

  When a voltage is applied to each phase adjustment electrode 46 and each modulation electrode 47, the refractive index of the core 43 changes in the first semiconductor arm 34a and the second semiconductor arm 34b, and the first semiconductor arm 34a and the second semiconductor The phase of the light passing through the arm 34b changes. When the optical interference element 300 is used as a modulator, a differential signal is input to each modulation electrode 47, and the light passing through the first semiconductor arm 34 a and the second semiconductor arm 34 b are connected to each phase adjustment electrode 46. A DC voltage for adjusting the phase difference from the light that has passed is applied.

  In the optical interference element 300, the input light input from the semiconductor laser 200 is evenly distributed by the input coupler 33 to the first semiconductor arm 34a and the second semiconductor arm 34b. In the output coupler 35, the light that has passed through the first semiconductor arm 34a and the light that has passed through the second semiconductor arm 34b interfere with each other in accordance with the phase difference, and are transmitted from the first output optical waveguide 36a and the second output optical waveguide 36b. An optical signal is output.

  A predetermined relationship is given between the length of the first semiconductor arm 34a and the length of the second semiconductor arm 34b during manufacturing. However, since individual differences occur during manufacturing, the phase difference between the light that has passed through the first semiconductor arm 34a and the light that has passed through the second semiconductor arm 34b may vary from 0 to π. Accordingly, the light output is distributed to the first output optical waveguide 36a and the second output optical waveguide 36b. Accordingly, even if the voltages applied to the first semiconductor arm 34a and the second semiconductor arm 34b are set to be the same, all the light input in the output coupler 35 is transmitted from the first output optical waveguide 36a due to individual differences. There is a possibility that there is a variation from the case of being output to the case of being output from the second output optical waveguide 36b. Therefore, when observing the characteristics of the semiconductor laser 200 through the output of the optical interference element 300, it is difficult to accurately measure the characteristics of the semiconductor laser 200. Therefore, in this embodiment, a method for accurately measuring the characteristics of the input light input to the optical interference element 300 while avoiding variations caused by individual differences of the optical interference elements 300 will be described.

  By applying a reverse bias to any one of the semiconductor arms and shifting the absorption band edge to the long wavelength side, the semiconductor arm can have a light absorption characteristic. In this way, by causing a light absorption characteristic in one of the semiconductor arms, the influence of optical interference in the output coupler 35 can be avoided. In this case, the optical intensity of the optical signal output from the first output optical waveguide 36 a and the second output optical waveguide 36 b is an intensity correlated with the optical intensity input to the optical interference element 300. In the present embodiment, the light intensity of the optical signals output from the first output optical waveguide 36a and the second output optical waveguide 36b is made to be the light of the optical interference element 300 by sufficiently absorbing light in one semiconductor arm. It becomes 1/4 of the output peak value. For this reason, the intensity of the input light input to the optical interference element 300 can be accurately measured. Note that there may be a difference in intensity between the optical signals output from the first output optical waveguide 36a and the second output optical waveguide 36b. As a factor of this intensity difference, there is a loss difference of the input coupler 33, the output coupler 35, the first semiconductor arm 34a, the second semiconductor arm 34b, and the like. However, the variation of the loss for each element is sufficiently small compared to the variation in interference of the optical interference element 300, and can be ignored.

  Since the reverse bias for sufficiently absorbing light in the semiconductor arm is a value determined by the material of the optical interference element 300, the reverse bias value does not vary greatly from element to element. Therefore, since the reverse bias value can be set uniformly for any element, it is not necessary to adjust the interference characteristic with respect to the optical interference element 300.

  If the light absorption of the semiconductor arm is not sufficient, the light output may fluctuate due to interference in the output coupler. When practicing the present invention, it is desirable to keep this fluctuation within an allowable range for the optical fiber output coupled to the output coupler. For example, when the output fluctuation of the optical fiber is kept within +/− 1 dB, it is necessary to give a loss of about 20 dB to the semiconductor arm. Further, when a loss of about 30 dB is given to the semiconductor arm, the output fluctuation of the optical fiber can be suppressed to about +/− 0.3 dB. As an example, the reverse bias for causing the semiconductor arm to absorb light of about 20 dB is about −8V, and the reverse bias for making light absorption of about 30 dB is about −10V.

  FIG. 4 shows the output from each semiconductor arm and the extinction ratio of the optical interference element 300 when the second semiconductor arm 34b absorbs light by applying a reverse bias to the second semiconductor arm 34b. In FIG. 4, the horizontal axis indicates the power loss in the second semiconductor arm 34b due to the application of the reverse bias, and the left vertical axis indicates the output ratio of the first semiconductor arm 34a to the output peak value of the optical interference element 300 and the second semiconductor arm 34b. The right vertical axis indicates the extinction ratio of the optical interference element 300.

  As shown in FIG. 4, if the contribution from the first semiconductor arm 34a and the second semiconductor arm 34b is equal, the variation in the output due to the initial phase difference becomes infinite. However, in an actual device, as described above, there is a variation of about 20 dB due to a loss difference between the input coupler 33, the output coupler 35, the first semiconductor arm 34a, the second semiconductor arm 34b, and the like (light output is 1 to 1/100). Will vary). Increasing the amount of light absorption in the second semiconductor arm 34b decreases the extinction ratio of the optical interference element 300. When the absorption loss of the second semiconductor arm 34b is about 30 dB, the variation is about +/− 0.3 dB. From the above, the dispersion of the light output of the optical interference element 300 can be sufficiently reduced by sufficiently absorbing the light in one of the semiconductor arms. As a result, the characteristics of the input light input to the optical interference element 300 can be accurately measured. In this embodiment, the characteristics of the semiconductor laser 200 can be measured with high accuracy.

  FIG. 5A is a diagram illustrating an example of the optical output power of the optical interference element 300 when a reverse bias is applied to the first semiconductor arm 34a or the second semiconductor arm 34b. Each line in FIG. 5A shows an example in which a reverse bias is applied to the modulation electrode 47 of the first semiconductor arm 34a, an example in which a reverse bias is applied to the phase adjustment electrode 46 of the first semiconductor arm 34a, and a second semiconductor arm. An example in which a reverse bias is applied to the modulation electrode 47 of 34b and an example in which a reverse bias is applied to the phase adjustment electrode 46 of the second semiconductor arm 34b are shown.

  As shown in FIG. 5A, the optical output power of the optical interference element 300 decreases while fluctuating as the reverse bias is applied. As the reverse bias value is increased, the decrease in the optical output power of the optical interference element 300 is as follows. Stabilize. In the example of FIG. 5A, by applying a reverse bias of about −10 V, the optical output power of the optical interference element 300 is stabilized by a decrease of about 6 dB from the state where no reverse bias is applied (−8 dB). (Stable at about one quarter). This means that most of the light is absorbed by one semiconductor arm.

  FIG. 5B is a diagram showing the relationship between the reverse bias applied to the semiconductor arm and the optical power passing through the semiconductor arm. As shown in FIG. 5B, the semiconductor arm can sufficiently absorb light by applying a reverse bias of about −10V.

  Next, a specific example of a method for measuring the characteristics of the input light of the optical interference element will be described. Fig.6 (a) shows the flow of the measuring method based on a present Example. FIG. 6B is an apparatus diagram used for the measurement method according to the present embodiment. As shown in FIG. 6B, in the measurement method according to the present embodiment, a control device 400, a plurality of DC power sources 500, an optical power meter 600, and the like are used. The control device 400 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like. The DC power source 500 is an electric probe or the like, and supplies a DC current corresponding to an instruction from the control device 400 to each unit. The optical power meter 600 measures the output light intensity from one of the first output optical waveguide 36a and the second output optical waveguide 36b, and gives the measurement result to the control device 400.

  With reference to Fig.6 (a), the optical semiconductor device 100 is mounted in a carrier, and it fixes to the stage which can be temperature-controlled (step S1). Next, a light absorption characteristic is generated in one semiconductor arm of the optical interference element 300 (step S2). Specifically, a reverse bias voltage is applied to one of the first semiconductor arm 34a and the second semiconductor arm 34b using the DC power source 500. In this embodiment, a reverse bias voltage is applied so that light absorption of about 20 dB occurs in the second semiconductor arm 34b. The reverse bias voltage can be applied to one or both of the phase adjustment electrode 46 and the modulation electrode 47.

  Next, the semiconductor laser 200 is caused to oscillate (step S3). Specifically, a predetermined driving current is injected into the electrode 8 of the semiconductor laser 200 using the DC power source 500, and each heater 10 is caused to generate heat at a predetermined temperature. Further, the temperature of the semiconductor laser 200 is controlled to a predetermined value by a temperature control device (TEC: Thermoelectric cooler) (not shown). In this case, the SG-DFB region A and the CSG-DBR region B function as a resonator unit. As a result, laser oscillation is performed with the wavelength selected by the SG-DFB region A and the CSG-DBR region B.

  Next, by measuring the output light from the first output optical waveguide 36a or the second output optical waveguide 36b of the optical interference element 300 using the optical power meter 600, the characteristics such as the output light intensity of the semiconductor laser 200 are measured. (Step S4).

  According to the above procedure, adjustment of the interference characteristics of the optical interference element 300 can be omitted. In addition, the characteristics of the semiconductor laser 200 can be measured while avoiding the influence of interference in the output coupler 35 of the optical interference element 300. Thereby, the characteristics of the input light input to the optical interference element 300 can be accurately measured.

  When measuring the output light of the semiconductor laser 200 after adjusting the interference characteristics of the optical interference element 300, the interference characteristics are adjusted for each individual of the optical interference elements 300, and appropriate Mach-Zehnder interference is performed. It is necessary to carry out the process of obtaining the realized state in advance. In the manufacturing process of the optical semiconductor device 100, the adjustment of the interference characteristics of the optical interference element 300 is always performed in any of the processes. Therefore, the output light of the semiconductor laser 200 is adjusted after adjusting the interference characteristics at first glance. It seems that there is no demerit even if it is measured.

  However, since the electrical characteristics of the semiconductor laser 200 change before and after the package encapsulation, the electrical characteristics of the semiconductor laser 200 must be implemented after the package encapsulation. In this case, the adjustment of the interference characteristics of the optical interference element 300 is performed after the optical semiconductor device 100 is sealed in a package. Therefore, when a defect of the semiconductor laser 200 is confirmed, the package enclosing process and the interference characteristic adjusting process are wasted. On the other hand, according to the present embodiment, since the characteristics of the semiconductor laser 200 can be measured without adjusting the interference characteristics, it is possible to eliminate the waste of man-hours.

  In the second embodiment, a measurement method including a step of performing wavelength tuning of the semiconductor laser 200 after enclosing the package will be described. FIG. 7 is an apparatus diagram used in the measurement method according to the present embodiment. A difference from FIG. 6A is that a wavelength meter 700 is newly provided. FIG. 8 is a diagram illustrating a flow of a method for measuring characteristics of input light of the optical interference element according to the second embodiment.

  As shown in FIG. 8, the optical semiconductor device 100 is mounted on a carrier and fixed to a temperature-controllable stage (step S1). Next, a light absorption characteristic is generated in one semiconductor arm of the optical interference element 300 (step S2). Next, the semiconductor laser 200 is caused to oscillate (step S3). Next, by measuring the output light from the first output optical waveguide 36a or the second output optical waveguide 36b of the optical interference element 300 using the optical power meter 600, the characteristics such as the output light intensity of the semiconductor laser 200 are measured. (Step S4).

  Next, the optical semiconductor device 100 is sealed in a package, and the package is fixed to a stage that can be temperature-controlled (step S5). Next, a light absorption characteristic is generated in one semiconductor arm of the optical interference element 300 (step S6). Next, the semiconductor laser 200 is caused to oscillate (step S7). Next, the wavelength tuning of the semiconductor laser 200 is performed using the wavelength meter 700 (step S8).

  According to the present embodiment, it is possible to accurately measure the characteristics of the input light input to the optical interference element 300 without adjusting the interference characteristics of the optical interference element 300. As a result, the characteristics of the semiconductor laser 200 can be accurately measured.

(Other examples)
Example 1 may be implemented after the optical semiconductor device 100 is sealed in a package. Even in this case, the characteristics of the semiconductor laser 200 can be measured before adjusting the interference characteristics. Therefore, when the semiconductor laser 200 is defective, the step of adjusting the interference characteristics can be omitted.

  In each of the above embodiments, the semiconductor laser 200 and the optical interference element 300 are integrated, but the present invention is not limited to this. For example, the semiconductor laser 200 and the optical interference element 300 may be independent chips. Even in this case, after the positional relationship between the semiconductor laser 200 and the optical interference element 300 is fixed by being mounted on a package or the like, only measurement of the output light after passing through the optical interference element 300 of the semiconductor laser 200 can be performed. The effects of the above embodiments can be obtained.

  In addition, even if the positional relationship between the semiconductor laser 200 and the optical interference element 300 is not fixed, the characteristics of the input light input to the optical interference element 300 can be accurately adjusted without adjusting the interference characteristics of the optical interference element 300. It can be measured well.

  In each of the above embodiments, the optical interference element having two semiconductor arms has been described. However, the present invention can also be applied to an optical interference element having three or more semiconductor arms. Specifically, light absorption characteristics are generated in all other semiconductor arms except for one of the plurality of semiconductor arms, and the characteristics of the input light output from the output coupler are measured. The characteristics of the input light input to the optical interference element 300 can be accurately measured without adjusting the interference characteristics.

  In each of the above embodiments, a Mach-Zehnder modulator is used as an optical interference element. However, the present invention can be applied to any optical interference provided with an input coupler, a plurality of semiconductor arms, and an output coupler. For example, the present invention can be applied to an optical frequency doubler. In each of the above embodiments, 2 × 2 MMI is used as the input coupler and output coupler, but 1 × 2 MMI (2 × 1 MMI) or the like may be used. Or a directional coupler etc. may be used as an input coupler and an output coupler.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

33 Input coupler 34a First semiconductor arm 34b Second semiconductor arm 35 Output coupler 46 Phase adjustment electrode 47 Modulation electrode 100 Optical semiconductor device 200 Semiconductor laser 300 Optical interference element 400 Controller 500 DC power supply 600 Optical power meter 700 Wavelength meter

Claims (8)

A method for measuring characteristics of input light of an optical interference element comprising: an input coupler; a plurality of semiconductor arms connected to the input coupler; and an output coupler that interferes with an output of the semiconductor arm,
A first step of performing control to generate light absorption characteristics in all other semiconductor arms except for one of the plurality of semiconductor arms;
And a second step of measuring the characteristics of the input light output from the output coupler after the first step, and a method for measuring the characteristics of the input light of the optical interference element.   2. The method of measuring characteristics of input light of an optical interference element according to claim 1, wherein the optical interference element is a Mach-Zehnder modulator.   3. The method of measuring characteristics of input light of an optical interference element according to claim 1 or 2, wherein in the first step, a light absorption characteristic is generated by applying a reverse bias to the semiconductor arm. The semiconductor arm has a phase control unit and a modulation control unit,
4. The method of measuring characteristics of input light of an optical interference element according to claim 3, wherein, in the first step, the reverse bias is applied to one or both of the phase control unit and the modulation control unit.   5. The method of measuring characteristics of input light of an optical interference element according to claim 1, wherein an output of a semiconductor laser is connected to the input coupler of the optical interference element.   6. The method of measuring characteristics of input light of an optical interference element according to claim 5, wherein the optical interference element is provided on a semiconductor substrate common to the semiconductor laser.   7. The method of measuring characteristics of input light of an optical interference element according to claim 6, wherein the semiconductor laser is a wavelength tunable semiconductor laser. 8. The method for measuring characteristics of input light of an optical interference element according to claim 1, wherein the light absorptance in the first step is set to 20 dB or more.

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