Laser inspection method, laser production method, and inspection device

Abstract

A laser inspection method according to the present disclosure involves: acquiring a phase shift amount, which is the ratio of the wavelength difference between a main mode and one of side modes on both sides of the main mode in the spectrum of a laser to the wavelength difference between the side modes; acquiring a physical quantity related to a single mode property other than the phase shift amount from the spectrum; and determining whether the laser is a non-defective product on the basis of the physical quantity, wherein the determination criterion changes according to the phase shift amount.

Description

Laser inspection method, laser manufacturing method, and inspection apparatus

[0001] The present disclosure relates to a laser inspection method, a laser manufacturing method, and an inspection apparatus.

[0002] Patent Document 1 discloses a semiconductor laser inspection method capable of detecting kinks with high accuracy. In this method, a differential curve and an approximation curve are calculated from an I-L waveform, the kink rate is obtained by arithmetic processing, and the presence or absence of a kink is determined.

[0003] Japanese Patent No. 7134110

[0004] In a laser inspection process or manufacturing process, it is preferable to be able to accurately extract a laser with low single-mode characteristics that causes kink defects after assembly. However, the method of Patent Document 1 may require complex calculations.

[0005] An object of the present disclosure is to obtain a laser inspection method, a laser manufacturing method, and an inspection apparatus that can accurately and easily extract a laser with low single-mode characteristics.

[0006] The laser inspection method according to the first disclosure obtains a phase shift amount that is a ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum of the laser, obtains a physical quantity related to single-mode characteristics other than the phase shift amount from the spectrum, determines whether the laser is a good product based on the physical quantity, and the criterion for the determination is changed according to the phase shift amount.

[0007] The laser inspection apparatus according to the second disclosure includes a measurement circuit configured to obtain a spectrum of a laser and an arithmetic circuit. The arithmetic circuit calculates a phase shift amount that is a ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum, calculates a physical quantity related to single-mode characteristics other than the phase shift amount from the spectrum, and is configured to determine whether the laser is a good product based on the physical quantity, and the criterion for the determination is changed according to the phase shift amount.

[0008] The laser inspection method according to the third disclosure involves obtaining a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the laser spectrum, for each of the multiple drive currents that drive the laser; calculating the rate of increase of the phase shift amount with respect to the drive current from the phase shift amount for each of the multiple drive currents; and determining whether the laser is a good product or not based on the rate of increase.

[0009] The laser inspection apparatus according to the fourth disclosure comprises a measurement circuit configured to acquire the spectrum of the laser for each of a plurality of drive currents that drive the laser, and a calculation circuit, wherein the calculation circuit calculates a phase shift amount for each of the plurality of drive currents, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum, calculates the rate of increase of the phase shift amount with respect to the drive current from the phase shift amount for each of the plurality of drive currents, and is configured to determine whether the laser is a good product or not based on the rate of increase.

[0010] The fifth disclosure relates to a laser inspection method in which a laser unit and a modulator unit are integrated, and the modulator unit is driven to reduce the reflected light to the laser unit, a spectrum is acquired, a phase shift amount is calculated which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum, and it is determined whether the laser is a good product or not based on the phase shift amount.

[0011] The laser detection device according to the sixth disclosure includes a measurement circuit configured to acquire a spectrum in a laser in which a laser unit and a modulator unit are integrated, while driving the modulator unit to reduce the reflected light to the laser unit, and a calculation circuit, wherein the calculation circuit is configured to acquire a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum, and to determine whether the laser is good or not based on the phase shift amount.

[0012] In the laser inspection method and inspection apparatus described in the first and second disclosures, the criterion for determining whether a laser is good or not is changed according to the amount of phase shift. Therefore, lasers with low single-mode characteristics can be extracted with high accuracy and ease. In the laser inspection method and inspection apparatus described in the third and fourth disclosures, whether a laser is good or not is determined based on the rate of increase of the amount of phase shift relative to the drive current. Therefore, lasers with low single-mode characteristics can be extracted with high accuracy and ease. In the laser inspection method and inspection apparatus described in the fifth and sixth disclosures, the spectrum is acquired while the modulator unit is driven to reduce the reflected light to the laser unit. Whether a laser is good or not is determined from the amount of phase shift calculated based on this spectrum. Therefore, lasers with low single-mode characteristics can be extracted with high accuracy and ease.

[0013] This is a cross-sectional view of the laser according to Embodiment 1. This is a diagram illustrating the phase shift amount. This is a diagram illustrating the difference in phase shift amount due to the end face phase. This is a diagram illustrating the relationship between phase shift amount and SMSR. This is a block diagram illustrating the configuration of the inspection device according to Embodiment 1. This is a hardware configuration diagram of the inspection device according to Embodiment 1. This is a flowchart illustrating the laser inspection method according to Embodiment 1. This is a diagram illustrating the relationship between phase shift amount and normalized coupling coefficient. This is a flowchart illustrating the laser inspection method according to Embodiment 3. This is a diagram illustrating spectral shift due to drive current. This is a perspective view of the laser according to Embodiment 4. This is a cross-sectional view of the laser according to Embodiment 4. This is a flowchart illustrating the laser inspection method according to Embodiment 4.

[0014] The laser inspection method, laser manufacturing method, and inspection apparatus according to each embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.

[0015] Embodiment 1. Figure 1 is a cross-sectional view of a laser 100 according to Embodiment 1. The laser 100 to be inspected is, for example, a high-power phase-shift type DFB-LD (Distributed FeedBack-Laser Diode). The laser 100 has cladding layers 10 and 14 and an active layer 12 provided between the cladding layers 10 and 14. A diffraction grating 16 is provided on the cladding layer 14. An anti-reflective (AR) film 20 is formed on one end face of the laser 100 to emit the beam. The other end face of the laser 100 is a reflective end, and for example, a highly reflective film 18 is formed thereon. The reflective end may also be a cleavage surface. This improves the beam extraction efficiency. Note that components such as electrodes are omitted in Figure 1.

[0016] Figure 2 illustrates the phase shift amount ΔL. The phase shift amount ΔL is given by the following equation 1. In other words, the phase shift amount ΔL is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the two side modes on either side of the main mode in the spectrum of laser 100. The phase shift amount ΔL can also be said to be the relative position of the oscillation wavelength between the wavelengths of the side modes.

[0017]

[0018] Figure 3 illustrates the difference in phase shift amount ΔL depending on the end face phase. In a λ / 4 phase shift type DFB-LD like this embodiment, the phase shift amount ΔL is determined by the phase state of the end face. Ideally, when the phase shift amount ΔL matches λ / 4, the oscillation wavelength is selected to be the center of the stopband, i.e., the Bragg wavelength. However, the phase of the reflective end face in a DFB-LD is subject to uncertainty depending on the manufacturing precision of the LD chip. Therefore, the actual phase shift amount deviates from λ / 4.

[0019] When the phase shift amount ΔL deviates significantly from 0.5, the oscillation wavelength approaches the stopband edge. This can reduce the normalized threshold gain difference between the primary and secondary modes, potentially affecting the laser characteristics. Furthermore, the phase shift amount ΔL can fluctuate further due to disturbances such as mounting distortion, junction distortion, current injection amount, and temperature changes. For example, changes in refractive index during current injection can cause hall burning, altering the phase shift amount ΔL. Such fluctuations may lead to mode hopping to higher-order modes. In this case, sharp output fluctuations known as kinks, beam shape fluctuations, and discontinuous transitions in the oscillation wavelength may be observed. Such devices are judged to be defective.

[0020] The following describes an inspection method for accurately identifying lasers with low single-mode characteristics that cause the aforementioned defects. Single-mode characteristics refer to the stability of oscillation in a single mode. In the inspection method of this embodiment, the phase shift amount ΔL and other physical quantities related to single-mode characteristics are obtained from the spectrum of the laser 100. Next, it is determined whether the laser 100 is a good product or not based on these physical quantities. At this time, the criteria for determination are changed according to the phase shift amount ΔL. The physical quantities related to single-mode characteristics are, for example, the optical mode intensity ratio of the secondary mode, which has the next strongest intensity after the primary mode, to the primary mode. The optical mode intensity ratio is called SMSR (Side Mode Suppression Ratio).

[0021] Figure 4 illustrates the relationship between the phase shift amount ΔL and SMSR. In Figure 4, the threshold for determining whether the laser 100 is a good product or not is shown by a dashed line. In other words, the region above the dashed line is the good product region, and the region below the dashed line is the defective product region. A device exhibiting ΔL = 0.5 oscillating at the Bragg wavelength has high single-longitudinal mode stability and is resistant to disturbances. Therefore, it can maintain a single mode even with a low SMSR. On the other hand, devices with ΔL far from 0.5 are susceptible to disturbances. Therefore, even with a high SMSR, it may not be possible to maintain a single mode.

[0022] Therefore, if the phase shift amount ΔL is far from 0.5 to a predetermined value, the criteria for discrimination are made stricter compared to when it is not far. For example, as shown in Figure 4, the threshold may be set to 35 dB in the range 0.45 ≤ ΔL ≤ 0.55, and to 40 dB in the range ΔL < 0.45 or ΔL > 0.55. As another example, the threshold may be set to 40 dB in the range 0.48 ≤ ΔL ≤ 0.52, and to 43 dB in the range ΔL < 0.48 or ΔL > 0.52. The stability of a single mode is evaluated using such thresholds.

[0023] Figure 5 is a block diagram illustrating the configuration of the inspection device 50 according to Embodiment 1. The inspection device 50 includes a measurement circuit 60 configured to acquire the spectrum of the laser 100 and a calculation circuit 70. The measurement circuit 60 has a laser drive unit 61 and an optical spectrum measurement unit 62. The laser drive unit 61 can be any current application device for the laser. The optical spectrum measurement unit 62 is, for example, a spectrum analyzer capable of measuring a desired wavelength range. The laser drive unit 61 drives the laser 100 with a drive current value set by the measurement condition setting unit 72. The resulting optical output of the laser 100 is input to the optical spectrum measurement unit 62. As a result, the spectrum of the laser 100 is measured.

[0024] The calculation circuit 70 includes a condition setting unit 71, a determination unit 74, and a calculation unit 76. The condition setting unit 71 includes a measurement condition setting unit 72 and an evaluation condition setting unit 73. The measurement condition setting unit 72 sets the application conditions for the drive current in the laser drive unit 61 and the measurement conditions in the optical spectrum measurement unit 62. The evaluation condition setting unit 73 sets a threshold value for determining whether the laser 100 is a good product or not based on SMSR, using the phase shift amount ΔL calculated by the calculation unit 76.

[0025] The calculation unit 76 includes an optical mode intensity ratio calculation unit 77 and a phase shift amount calculation unit 78. The optical mode intensity ratio calculation unit 77 calculates the SMSR from the spectrum measured by the optical spectrum measurement unit 62. The phase shift amount calculation unit 78 calculates the phase shift amount ΔL from the spectrum measured by the optical spectrum measurement unit 62.

[0026] The determination unit 74 includes a single-mode determination unit 75. Based on the SMSR calculated by the optical mode intensity ratio calculation unit 77, the single-mode determination unit 75 uses a threshold value set by the evaluation condition setting unit 73 to determine whether the laser 100 is a good product or not.

[0027] Figure 6 is a hardware configuration diagram of the inspection apparatus 50 according to Embodiment 1. As described above, the function of the laser drive unit 61 can be realized by the current application device 61a, and the function of the optical spectrum measurement unit 62 can be realized by the spectrum analyzer 62a. In addition, the function of the arithmetic circuit 70 is realized by one or more control circuits such as a processor 70a. The control circuit may be dedicated hardware. Alternatively, the control circuit may be a CPU (Central Processing Unit) that executes a program stored in memory 70b. The CPU may be a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor).

[0028] If the control circuit is dedicated hardware, it may be, for example, a single circuit, a composite circuit, a programmed processor, or a parallel programmed processor. The control circuit may also be an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). Furthermore, the control circuit may be a combination of these. Each function of the arithmetic circuit 70 may be implemented by a separate control circuit. Alternatively, the functions of each part may be implemented together by a single control circuit.

[0029] When the control device is a CPU, the functions of the arithmetic circuit 70 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in one or more memories 70b. The control circuit realizes the functions of each part by reading and executing the programs stored in the memory 70b.

[0030] In other words, the memory 70b stores a program that calculates the phase shift amount ΔL and SMSR, determines whether the laser 100 is a good product or not based on the SMSR, and changes the criteria for determination according to the phase shift amount ΔL. These programs cause the computer to execute the procedures or methods in the calculation circuit 70.

[0031] Here, memory 70b may be non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, magnetic disk, flexible disk, optical disk, compact disk, minidisc, DVD, etc. RAM is an abbreviation for Random Access Memory. ROM is an abbreviation for Read Only Memory. EPROM is an abbreviation for Erasable Programmable Read Only Memory. EEPROM is an abbreviation for Electrically Erasable Programmable Read-Only Memory.

[0032] Furthermore, some of the functions of the arithmetic circuit 70 may be implemented using dedicated hardware, while others may be implemented using software or firmware. In this way, the control circuit can implement the above-mentioned functions using hardware, software, firmware, or a combination thereof.

[0033] Figure 7 is a flowchart showing the inspection method for the laser 100 according to Embodiment 1. First, the measurement condition setting unit 72 sets the laser driving conditions of the laser driving unit 61 and the spectrum measurement conditions of the optical spectrum measurement unit 62 (Step 1). Next, the measurement circuit 60 measures the spectrum under the set conditions (Step 2). The spectrum measurement is performed with the laser 100 in a bare chip state and not mounted on a submount. Next, the calculation unit 76 calculates the SMSR and the phase shift amount ΔL (Step 3). Here, the side modes used in the calculation of the phase shift amount ΔL are the two peaks closest to the main mode. The secondary mode used in the calculation of SMSR is the peak showing the second highest intensity within the measurement window. In most cases, the secondary mode is one of the side modes, but rarely, a mode other than the side modes may be the secondary mode.

[0034] Next, the evaluation condition setting unit 73 sets a threshold from the phase shift amount ΔL. If the difference between the phase shift amount ΔL and 0.5 is greater than or equal to a predetermined value θ (YES in step 4), the evaluation condition setting unit 73 sets threshold A (step 5). If the difference between the phase shift amount ΔL and 0.5 is less than a predetermined value θ (NO in step 4), the evaluation condition setting unit 73 sets threshold B (step 6). Threshold A has stricter judgment criteria than threshold B. Next, the single-mode determination unit 75 performs an evaluation based on SMSR using the set threshold (step 7).

[0035] From the above, in the laser inspection method and inspection apparatus 50 according to this embodiment, the criteria for determining whether the laser 100 is a good product or not are changed according to the phase shift amount ΔL. In other words, single-mode properties are determined from the values ​​of both the phase shift amount ΔL and SMSR. Therefore, lasers with low single-mode properties can be extracted with high accuracy. In particular, in the case of a phase-shift type DFB-LD, the value of the phase shift amount ΔL indicates the amount of shift in the end face phase. For this reason, by setting the judgment threshold of SMSR according to the phase shift amount ΔL, LDs that are resistant to disturbances can be selected.

[0036] Furthermore, in this embodiment, sorting is possible by simple bare chip inspection. In addition, in conventional SMSR evaluation, various current values ​​were input to the laser for measurement by inputting an RF (Radio Frequency) signal centered on current values ​​above the oscillation threshold. In contrast, in this embodiment, measurement can be performed with a single drive current value, and there is no need to apply an RF signal to the laser 100 during evaluation. For this reason, there is no need to install equipment to apply an RF signal to the inspection device 50, and evaluation can be performed with a simple inspection device 50. Furthermore, complex calculations for evaluation are not required. Accordingly, lasers with low single-mode characteristics can be easily extracted.

[0037] The configuration of the laser 100 in Figure 1 is just one example, and any semiconductor laser can be used as the laser 100 to be inspected. The laser 100 may also be an integrated device in which the laser unit and the modulator unit are integrated. Furthermore, the manufacturing method of the laser 100 may include the inspection method of the laser 100 described above.

[0038] The modifications described above can be appropriately applied to the laser inspection method, laser manufacturing method, and inspection apparatus according to the following embodiments. Since the laser inspection method, laser manufacturing method, and inspection apparatus according to the following embodiments have many similarities with Embodiment 1, the differences from Embodiment 1 will be explained in detail.

[0039] Embodiment 2. In this embodiment, instead of the SMSR in Embodiment 1, the physical quantity related to single-mode properties is the difference ΔκL between the normalized coupling coefficient κL obtained from the spectrum and the design value of the normalized coupling coefficient κL. In other words, in the calculation unit 76 of Figure 5, the difference ΔκL between the normalized coupling coefficient κL and the design value is calculated from the spectrum instead of the SMSR. Generally, if the normalized coupling coefficient κL deviates from the design value, the single-mode properties deteriorate. The single-mode property determination unit 75 determines whether the laser 100 is a good product or not based on the difference ΔκL calculated by the calculation unit 76, using a threshold value set by the evaluation condition setting unit 73. Similar to Embodiment 1, the threshold value is changed according to the phase shift amount ΔL.

[0040] In the case of a λ / 4 phase shift type laser, the normalized coupling coefficient κL can be calculated by Equation 2 below. In Equation 2, κ is the coupling coefficient, L is the resonator length of the laser 100, c is the speed of light. Δν is the Fabry-Perot mode interval during spectral measurement. The Fabry-Perot mode interval indicates the mode interval other than the oscillation mode of the DFB-LD.

[0041]

[0042] FIG. 8 is a diagram for explaining the relationship between the phase shift amount ΔL and the difference ΔκL. In FIG. 8, a threshold value for determining whether the laser 100 is a good product is shown by a broken line. The region above the broken line is the defective product region, and the region below the broken line is the good product region. Also in the present embodiment, when the phase shift amount ΔL is farther from 0.5 than a predetermined value, the discrimination criterion is made stricter as compared with the case where it is not far. Using such a threshold value, the stability of the single mode is evaluated.

[0043] Also in the present embodiment, by setting a determination threshold value of the difference ΔκL according to the phase shift amount ΔL, an LD that is resistant to disturbance can be selected highly accurately and easily. Furthermore, also in the present embodiment, it is not necessary to apply an RF signal to the laser 100 during evaluation, and the evaluation can be performed with a simple inspection device 50. In general, the larger the normalized coupling coefficient κL, the higher the single mode property. However, in a λ / 4 phase shift type DFB-LD, when the normalized coupling coefficient κL is large, the increase amount of ΔL with respect to the current increase becomes large, and thus the single mode property deteriorates. Therefore, for each laser, there is an appropriate design value of the normalized coupling coefficient κL, and the deviation from the design value of the normalized coupling coefficient κL becomes an important physical quantity related to the single mode property.

[0044] In Embodiments 1 and 2, an example in which the threshold values of physical quantities related to the single mode property such as SMSR and the difference ΔκL are changed by the phase shift amount ΔL has been described. The physical quantity related to the single mode property may be other than SMSR and the difference ΔκL. Examples of such a physical quantity include the light output ratio before and after the laser 100.

[0045] Embodiment 3. In the present embodiment, the acceleration V of the increase in the phase shift amount ΔL with respect to the drive currentΔＬ Based on this, it is determined whether the laser 100 is a good product or not. Specifically, the optical spectrum measuring unit 62 of the inspection device 50 is configured to acquire the spectrum of the laser 100 for each of the multiple drive currents that drive the laser 100. The calculation unit 76 acquires the phase shift amount ΔL for each of the multiple drive currents that drive the laser 100. From the phase shift amount ΔL for each of the multiple drive currents, the calculation unit 76 calculates the rate of increase of the phase shift amount ΔL relative to the drive current V ΔＬ The single-mode determination unit 75 calculates the calculated increase rate V. ΔＬ Based on this, it is determined whether or not the laser 100 is a good product.

[0046] Figure 9 is a flowchart showing the inspection method for the laser 100 according to Embodiment 3. First, the measurement condition setting unit 72 sets the laser driving conditions for the laser driving unit 61 and the spectrum measurement conditions for the optical spectrum measurement unit 62. At this time, the measurement condition setting unit 72 sets the number of driving current conditions n (step 31). Then, the laser 100 is driven by the laser driving unit 61 under one driving current condition, and the spectrum is measured by the optical spectrum measurement unit 62 (step 32). Next, the phase shift amount calculation unit 78 calculates the phase shift amount ΔL (step 33). The above steps of acquiring the spectrum and calculating the phase shift amount ΔL are repeated for all n set driving current conditions (steps 31 to 34).

[0047] From the multiple phase shift amounts ΔL obtained above and the corresponding drive current values, the calculation unit 76 calculates the rate of increase of the phase shift amount ΔL with respect to the drive current V ΔＬ The calculation is performed (step 35). The evaluation condition setting unit 73 sets the increase rate V ΔＬ The threshold Vth is defined. The single-mode determination unit 75 determines V ΔＬ If ≥ Vth, the single-mode characteristic is low and the product is determined to be defective (step 36). The single-mode characteristic determination unit 75 determines V ΔＬ If Vth is present, it indicates high single-mode characteristics and is judged to be a good product (step 36).

[0048] Figure 10 illustrates the spectral shift caused by the drive current. In phase-shift type DFB-LDs, a phenomenon called axial hole burning can occur in the phase-shift region, where optical confinement is strong and the carrier density is low. As a result, the refractive index becomes higher in the phase-shift region, the phase shift amount ΔL increases from the design value, and the stability of the single mode may deteriorate. If the amount of current injected into the LD is further increased from this state, the phase shift amount ΔL increases, the normalized threshold gain difference between the primary and secondary modes decreases, and mode hopping may occur.

[0049] The increase in the phase shift amount ΔL with respect to the increase in the drive current is due to the quality of the laser structure. Therefore, the increase in the phase shift amount ΔL with respect to the drive current value, i.e., the rate of increase V ΔＬ By inspecting this, lasers with low single-mode characteristics can be easily and accurately extracted. Therefore, it becomes possible to prevent LDs exhibiting mode defects from entering the market. The manufacturing method of the laser 100 may also include the above-described inspection method for the laser 100.

[0050] Embodiment 4. Figure 11 is a perspective view of the laser 400 according to Embodiment 4. Figure 12 is a cross-sectional view of the laser 400 according to Embodiment 4. Figure 12 is a cross-sectional view obtained by cutting Figure 11 along the α-β line. The laser 400 has a laser unit 22 and a modulator unit 26 integrated on a substrate 30. The modulator unit 26 is, for example, an EA (Electro Absorption) type modulator. The modulator unit 26 may also be an MZ (Mach-Zender) type modulator. The laser unit 22 and the modulator unit 26 are connected by a waveguide 24. A waveguide 24 is also provided on the output side of the modulator unit 26. An upper electrode 32 is provided on the upper surface of the substrate 30, and a back electrode 34 is provided on the back surface of the substrate 30. The upper electrode 32 includes the electrodes of the laser unit 22 and the electrodes of the modulator unit 26.

[0051] In the laser section 22, the cladding layer 22a, the active layer 22b, and the cladding layer 22c are stacked on the substrate 30 in this order. In the modulator section 26, the cladding layer 26a, the active layer 26b, and the cladding layer 26c are stacked on the substrate 30 in this order. In the waveguide 24, the cladding layer 24a, the waveguide layer 24b, and the cladding layer 24c are stacked on the substrate 30 in this order. In section B, the waveguide layer 24b connects the active layers 22b and 26b.

[0052] As shown in Figure 12, in the laser 400, light 80 is emitted through the laser unit 22 and the modulator unit 26. At this time, light 80 is reflected at the exit end face, passes through the modulator unit 26 again, and the returned light 81 is incident on the laser unit 22. In this case, the phase of the laser unit 22 changes due to the returned light 81, and a phase shift amount ΔL containing noise may be calculated.

[0053] Therefore, in this embodiment, the optical spectrum measurement unit 62 acquires a spectrum while the modulator unit 26 is driven by the laser drive unit 61 to reduce the reflected light 81 to the laser unit 22. From this spectrum, the phase shift amount calculation unit 78 acquires the phase shift amount ΔL, and the single-mode determination unit 75 determines whether the laser 400 is a good product or not based on the phase shift amount ΔL.

[0054] Figure 13 is a flowchart showing the laser inspection method according to Embodiment 4. First, the measurement condition setting unit 72 sets the laser driving conditions of the laser driving unit 61 and the spectrum measurement conditions of the optical spectrum measurement unit 62 (step 41). The measurement condition setting unit 72 also sets the driving conditions of the modulator unit to reduce the reflected light 81 to the laser unit 22 (step 42). Next, the optical spectrum measurement unit 62 acquires the spectrum while the modulator unit 26 is driven to reduce the reflected light 81 to the laser unit 22 (step 43). At this time, the spectrum measurement is performed by comparing it with the state in which the modulator unit 26 is not driven, for example, with the reflected light 81 extinguished by 3 dB.

[0055] Next, the phase shift amount calculation unit 78 calculates the phase shift amount ΔL from the spectrum (step 44). Then, the single-mode determination unit 75 determines whether the laser 400 is a good product or not based on the phase shift amount ΔL (step 45). In step 45, for example, it is evaluated whether the phase shift amount ΔL is farther from 0.5 than a predetermined value.

[0056] In this embodiment, the modulator unit 26 is driven to reduce the reflected light 81 from the exit end face to the laser unit 22, i.e., in an extinction state, and the spectrum is acquired, and the phase shift amount ΔL is calculated. Therefore, the original phase shift amount ΔL of the laser 400 can be calculated. In other words, the phase shift amount ΔL can be calculated accurately. By determining whether the laser is of good quality from this phase shift amount ΔL, lasers with low single-mode characteristics can be extracted with high accuracy and ease.

[0057] Furthermore, the manufacturing method of the laser 400 may include the inspection method of the laser 400 described above. Also, if the laser being inspected in Embodiments 1-3 includes a modulator section, the phase shift amount ΔL obtained by the method of this embodiment may be used in the evaluation of Embodiments 1-3. This allows for even higher accuracy in the evaluation of Embodiments 1-3.

[0058] The technical features described in each embodiment may be used in combination as appropriate.

[0059] 10 Cladding layer, 12 Active layer, 14 Cladding layer, 16 Diffraction grating, 18 High-reflection film, 20 Anti-reflection film, 22 Laser section, 22a Cladding layer, 22b Active layer, 22c Cladding layer, 24 Waveguide, 24a Cladding layer, 24b Waveguide layer, 24c Cladding layer, 26 Modulator section, 26a Cladding layer, 26b Active layer, 26c Cladding layer, 30 Substrate, 32 Top electrode, 34 Back electrode, 50 Inspection device, 60 Measurement circuit, 61 Laser drive unit, 61a Current application device, 62 Optical spectrum measurement unit, 62a Spectrum analyzer, 70 Arithmetic circuit, 70a Processor, 70b Memory, 71 Condition setting unit, 72 Measurement condition setting unit, 73 Evaluation condition setting unit, 74 Judgment unit, 75 Single-mode determination unit, 76 Calculation unit, 77 Optical mode intensity ratio calculation unit, 78 Phase shift amount calculation unit, 80 Light, 81 Reflected light, 100 Laser, 400 Laser

Claims

1. A laser inspection method characterized by obtaining a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the laser spectrum; obtaining physical quantities related to single-mode nature other than the phase shift amount from the spectrum; determining whether the laser is a good product based on the physical quantities, and changing the criteria for the determination according to the phase shift amount.

2. The laser inspection method according to claim 1, characterized in that the physical quantity is the ratio of the optical mode intensity of the secondary mode, which has the next strongest intensity after the primary mode, to the primary mode.

3. The laser inspection method according to claim 1, characterized in that the physical quantity is the difference between the normalized coupling coefficient obtained from the spectrum and the design value of the normalized coupling coefficient.

4. The laser inspection method according to any one of claims 1 to 3, characterized in that if the phase shift amount is far from 0.5 to a predetermined value, the criteria for judgment are made stricter compared to when it is not far.

5. A method for manufacturing a laser, comprising the inspection method described in any one of claims 1 to 4.

6. An inspection device comprising: a measurement circuit configured to acquire the spectrum of a laser; and a calculation circuit, wherein the calculation circuit calculates a phase shift amount which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum; calculates physical quantities related to single-mode nature other than the phase shift amount from the spectrum; and is configured to determine whether the laser is a good product based on the physical quantities, wherein the criteria for the determination are changed according to the phase shift amount.

7. The inspection apparatus according to claim 6, characterized in that the physical quantity is the ratio of the optical mode intensity of the secondary mode, which has the next strongest intensity after the primary mode, to the primary mode.

8. The inspection apparatus according to claim 6, characterized in that the physical quantity is the difference between the normalized coupling coefficient obtained from the spectrum and the design value of the normalized coupling coefficient.

9. A laser inspection method characterized by obtaining a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the laser spectrum, for each of a plurality of drive currents that drive the laser; calculating the rate of increase of the phase shift amount with respect to the drive current from the phase shift amount for each of the plurality of drive currents; and determining whether the laser is a good product or not based on the rate of increase.

10. A method for manufacturing a laser, comprising the inspection method described in claim 9.

11. An inspection device comprising: a measurement circuit configured to acquire the spectrum of a laser for each of a plurality of drive currents that drive a laser; and a calculation circuit, wherein the calculation circuit calculates for each of the plurality of drive currents a phase shift amount which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum; calculates the rate of increase of the phase shift amount with respect to the drive current from the phase shift amount for each of the plurality of drive currents; and is configured to determine whether the laser is a good product or not based on the rate of increase.

12. A laser inspection method characterized by: acquiring a spectrum in a laser in which a laser unit and a modulator unit are integrated, while the modulator unit is driven to reduce the reflected light to the laser unit; calculating a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum; and determining whether the laser is a good product or not based on the phase shift amount.

13. A method for manufacturing a laser, comprising the inspection method described in claim 12.

14. An inspection device comprising: a measurement circuit configured to acquire a spectrum in a laser in which a laser unit and a modulator unit are integrated, with the modulator unit driven to reduce the reflected light to the laser unit; and a calculation circuit, wherein the calculation circuit is configured to acquire a phase shift amount, which is the ratio of the wavelength difference between one of the side modes and the main mode to the wavelength difference between the side modes on both sides of the main mode in the spectrum, and to determine whether the laser is a good product based on the phase shift amount.

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