System and method for testing vertical cavity surface emitting laser
By using a beam splitter and polarizer to separate the beam and multiple optical sensors to detect optical power data, the problem of low efficiency in polarization stability testing of vertical cavity surface-emitting laser chips is solved, enabling rapid and effective polarization stability assessment and performance evaluation.
Patent Information
- Application Number
- CN202510332104.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-07-10
- Filing Date
- 2025-03-20
- Publication Date
- 2026-01-13
AI Technical Summary
Existing technologies suffer from low efficiency when testing the polarization stability of vertical-cavity surface-emitting laser chips, especially in mass production where the testing time of optical goniometer systems is too long.
A test system including a beam splitter, polarizer, and optical sensors is used to split and polarize the light beam. Multiple optical sensors are used to detect optical power data in different polarization directions. The data is then analyzed by a processor to determine the polarization stability and performance of the chip.
This enables rapid and efficient evaluation of the polarization stability and performance of vertical-cavity surface-emitting laser chips, reducing production costs and improving testing efficiency.
Smart Images
Figure CN121323933A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a laser testing apparatus, and more particularly to a system and method for testing the polarization stability of a vertical cavity surface-emitting laser chip. Background Technology
[0002] When transferring a vertical-cavity surface-emitting laser (VCSEL) chip from a wafer to a predetermined position, the VCSEL chip may be damaged or rotated due to parameter deviations in the pick and place equipment. Therefore, it is necessary to test the VCSEL chip.
[0003] Traditionally, the polarization stability of VCSEL chips is tested using an optical goniometer system, but this is impractical for mass production testing due to the long testing time.
[0004] The information disclosed in the background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the relevant information constitutes prior art known to those skilled in the art. Summary of the Invention
[0005] In view of this, the present invention provides a system and method for testing the polarization stability and chip performance of a vertical cavity surface-emitting laser (VCSEL) chip.
[0006] This invention provides a system for testing VCSEL chips, comprising a first beam splitter, a second beam splitter, a first polarizer, a second polarizer, a first optical sensor, a second optical sensor, and a third optical sensor. The first beam splitter splits an emitted light beam into a first beam and a second beam. The second beam splitter splits the second beam into a third beam and a fourth beam. The first polarizer has a first polarization direction for the passage of the third beam. The second polarizer has a second polarization direction for the passage of the fourth beam. The first optical sensor receives the first beam. The second optical sensor receives the polarized third beam. The third optical sensor receives the polarized fourth beam.
[0007] The present invention also provides a method for operating a system for testing a VCSEL chip. The testing method includes the following steps: driving the VCSEL chip with a drive current increasing by a predetermined step; recording first optical power data from a first optical sensor, second optical power data from a second optical sensor, and third optical power data from a third optical sensor; determining whether the first optical power data meets a predetermined power requirement; if it meets the predetermined power requirement, calculating a second fitting curve for the second optical power data and a third fitting curve for the third optical power data; calculating second residual data based on the second optical power data and the second fitting curve; and calculating third residual data based on the third optical power data and the third fitting curve.
[0008] This invention also provides a testing method for a system for testing VCSEL chips. The system includes a first optical sensor, a second optical sensor, and a third optical sensor. The testing method includes the following steps: outputting non-polarized optical power data using the first optical sensor; outputting optical power data in a first polarization direction using the second optical sensor; outputting optical power data in a second polarization direction using the third optical sensor; determining whether the non-polarized optical power data meets a predetermined power requirement; and if it meets the predetermined power requirement, determining the polarization performance of the VCSEL chip based on the residual data and determination coefficient of the first polarization direction optical power data and the second polarization direction optical power data.
[0009] To make the above and other objects, features and advantages of the present invention more apparent, a detailed description will be provided below with reference to the accompanying drawings. Furthermore, in the description of the present invention, the same components are denoted by the same reference numerals, which will be stated herein as well. Attached Figure Description
[0010] Figure 1 This is a schematic diagram of a test system for a vertical cavity surface-emitting laser chip according to an embodiment of the present invention;
[0011] Figure 2A and Figure 2B This is a schematic diagram of the output power of the photodetector in the test system of this invention embodiment;
[0012] Figure 3 yes Figure 2A A partially enlarged schematic diagram of the output power data of a photodetector; and
[0013] Figure 4 This is a flowchart of a test method for a system for testing vertical-cavity surface-emitting laser chips according to an embodiment of the present invention.
[0014] Explanation of reference numerals in the attached figures
[0015] 100 Test System
[0016] 11 Power Supply Measurement Module
[0017] 131 First Beam Spectroscope
[0018] 132 Second beam splitter
[0019] 13G beam splitter gap
[0020] 151 First polarizer
[0021] 152 Second polarizer
[0022] 170 First Sensor
[0023] 171 Second Sensor
[0024] 172 Third Sensor
[0025] 19 processors
[0026] 90 chips under test
[0027] L0 emits a beam
[0028] L1 First Beam
[0029] L2 Second Beam
[0030] L21 Third Beam
[0031] L22 Fourth Beam Detailed Implementation
[0032] One object of this invention is to provide a system and method for testing the polarization stability of a vertical-cavity surface-emitting laser (VCSEL) chip. The system uses a beam splitter to split the emitted beam of the chip under test (DUT) into a first beam and a second beam. The first beam is received directly by a photodetector without passing through a polarizer. The second beam is split by another beam splitter and then passed through polarizers with different polarization directions before being received by different photodetectors.
[0033] Please refer to Figure 1 The diagram shown is a schematic of a test system 100 for testing vertical-cavity surface-emitting laser (VCSEL) chips according to an embodiment of the present invention. The test system 100 is used to perform failure / performance testing on the chip under test (i.e., VCSEL chip) 90.
[0034] The test system 100 includes a first beam splitter 131, a second beam splitter 132, a first polarizer 151, a second polarizer 152, a first optical sensor 170, a second optical sensor 171, a third optical sensor 172, a power supply measurement module (SMU) 11, and a processor 19. The first beam splitter 131 and the second beam splitter 132 are, for example, 50 / 50 beam splitters.
[0035] The first beam splitter 131 is used to split the emitted beam L0 of the VCSEL chip 90 into a first beam L1 and a second beam L2. The second beam splitter 132 is used to split the second beam L2 into a third beam L21 and a fourth beam L22. Furthermore, to reduce the light loss of the second beam L2, the first beam splitter 131 and the second beam splitter 132 are positioned along the travel direction of the second beam L2 (i.e.,...). Figure 1 The smaller the distance (in the vertical direction), the better, for example, less than 1 millimeter.
[0036] The first polarizer 171 has a first polarization direction for the passage of the third beam L21. The second polarizer 152 has a second polarization direction for the passage of the fourth beam L22. In one embodiment, one of the first polarization direction and the second polarization direction is 45 degrees and the other is 0 degrees. In this description, the first polarization direction is 45 degrees and the second polarization direction is 0 degrees as an example.
[0037] The first optical sensor 170, the second optical sensor 171, and the third optical sensor 172 are, for example, optoelectronic devices capable of converting detected light energy into electrical signals, such as complementary metal-oxide-semiconductor field-effect transistor (CMOS) image sensors, charge-coupled device (CCD) image sensors, or single-photon avalanche diode (SPAD) sensors. The first optical sensor 170 is used to receive a first light beam L1 to generate first optical power data (e.g., ...). Figure 2A and Figure 2B The first optical power data (D1) is displayed to the processor 19, wherein the first optical power data is unpolarized optical power data. The second optical sensor 171 is used to receive the polarized third beam L21 (denoted by the same symbol as the third beam) to generate the second optical power data (e.g., ...). Figure 2A and Figure 2B The displayed D2) is sent to the processor 19, wherein the second optical power data is the optical power data of the first polarization direction. The third optical sensor 172 is used to receive the polarized fourth beam L22 (represented by the same symbol as the fourth beam) to generate third optical power data (e.g., Figure 2A and Figure 2B Displayed as D3) to processor 19, wherein the third optical power data is the second polarization direction optical power data.
[0038] The power supply measurement module 11 provides a drive current If to the VCSEL chip 90, and this drive current If increases monotonically in predetermined steps. In one embodiment, the drive current If increases from 0 to 9 milliamperes, and the predetermined step is 50 microamperes. It is understood that the smaller the predetermined step, the more data points can be obtained.
[0039] The processor 19 is, for example, a microcontroller unit (MCU), a central processing unit (CPU), an application-specific integrated circuit (ASIC), or a programmable gate array (FPGA). The processor 19 is used to post-process the first optical power data, the second optical power data, and the third optical power data using software, firmware, and / or hardware to determine the performance of the chip under test 90, including maximum output power and polarization stability.
[0040] Please refer to Figure 4 As shown, it is used Figure 1 A flowchart of the testing method for the testing system 100 in this embodiment is shown. The testing method of this embodiment includes the following steps:
[0041] Step S401: After the test begins, a DC test is first performed on the VCSEL chip 90 to identify failed components early. If the DC test fails, the next chip is tested. DC testing is known and not the primary objective of this invention, therefore it will not be described in detail here.
[0042] Step S402: Next, the power supply measurement module 11 drives the VCSEL chip 90 using a drive current If that gradually increases in predetermined steps. As described above, the drive current If can increase from 0 to 9 milliamperes, and the predetermined steps are 50 microamperes. During the driving of the VCSEL chip 90, the first optical sensor 170 outputs first optical power data D1, the second optical sensor 171 outputs second optical power data D2, and the third optical sensor 172 outputs third optical power data D3, for example, referring to... Figure 2A As shown.
[0043] Step S403: During the driving process, the processor 19 receives and records (e.g., in its memory) the first optical power data D1, the second optical power data D2, and the third optical power data D3, along with their associated parameters. In one embodiment, the associated parameters include, for example, the critical current Ith (representing the driving current If when optical energy is first detected), the maximum power Pmax, and the 1 milliwatt power current (e.g., ...) of the first optical power data D1. Figure 3 Displayed as I@1mW, it represents the drive current If when the optical sensor outputs 1 milliwatt of optical power. For example, the relevant parameters also include the critical currents Ith45 and Ith0 of the second optical power data D2 and the third optical power data D3, the maximum power Pmax45 and Pmax0, and the 1 milliwatt power current.
[0044] Step S404: After obtaining the first optical power data D1, the second optical power data D2, and the third optical power data D3, the processor 19 first determines whether the relevant parameters of the first optical power data D1 meet the predetermined power requirements. For example, the processor 19 determines whether the maximum power of the first optical power data D1 is higher than a first power threshold. (Refer to...) Figure 2A and Figure 2B , assuming the first power threshold is 1.5 mW, when the maximum power exceeds the first power threshold (e.g., Figure 2A Pmax > 1.5 mW), it meets the predetermined power requirement; when the maximum power does not exceed the first power threshold (e.g., Figure 2B Pmax' < 1.5 mW), it does not meet the predetermined power requirement. For example, the processor 19 determines whether the difference between the critical current Ith of the VCSEL chip 90 and the 1 mW power current meets a predetermined difference, e.g., Figure 2A and Figure 2B shows that when the maximum power of the first optical power data D1 is relatively low (e.g., Pmax' < Pmax), the difference between the critical current Ith of the VCSEL chip 90 and the 1 mW power current becomes larger (e.g., Diff2 > Diff1). For example, the first power threshold and the predetermined difference can be determined in advance through theoretical derivation or historical empirical values.
[0045] When the relevant parameters of the first optical power data D1 meet the predetermined power requirement, it enters step S405; otherwise, it indicates that the currently tested chip 90 does not meet the specification (spec), and then measures the next VCSEL chip.
[0046] Step S405: The processor 19 calculates the second fitting curve of the second optical power data D2 and the third fitting curve of the third optical power data D3. For example, referring to Figure 3 , assuming the optical power data includes multiple data points P0 to P7 (only taking some data points as an example), the fitting curve FC of the multiple data points P0 to P7 can be calculated, which is, for example, a quadratic fitting curve, but is not limited to quadratic. Figure 3 The optical power data of
[0047] can be the second optical power data D2 and the third optical power data D3. The method of calculating the fitting curve FC can use the conventional method, so it will not be elaborated here. For example, the processor 19 has a related algorithm built in, which can calculate the corresponding fitting curves according to the second optical power data D2 and the third optical power data D3 respectively when it is executed. Figure 3 It also displays the offsets of certain data points from offset1 to offset4, with Residual45 being the largest and Min_offset45 being the smallest.
[0048] Please refer to Figure 2B As shown, when Max_offset45 is too large, a peak in Pf1 or a trough in Pf2 will appear, indicating that the polarization stability of the VCSEL chip 90 may have a problem. Therefore, in this invention, the processor 19 is configured to compare the maximum offset Max_offset45 with a second offset threshold as a judgment condition. In addition, the processor 19 is also configured to compare a second determination coefficient Rsquare45 with a second predetermined threshold (e.g., 0.95, but not limited to) as another judgment condition. These comparison results are recorded as test results of the test system 100.
[0049] Steps S407 to S408: Next, the processor 19 determines whether the maximum power Pmax45 of the second optical power data D2 is higher than the second power threshold (e.g., displayed as 0.3mW, but not limited to 0.3mW). If Pmax45 is not higher than the second power threshold, the process proceeds directly to step S410. If Pmax45 is higher than the second power threshold, the processor 19 calculates the second critical current offset of the critical current Ith45 based on the second optical power data D2 (e.g., displayed as Ith45_Offset, which is the difference between the critical current and the predetermined critical current or the critical current Ith of the first optical power data D1). Similarly, the maximum power Pmax45 and the second critical current offset Ith45_Offset calculated based on the second optical power data D2 represent the performance of the VCSEL chip 90 in the 45-degree polarization direction. If the maximum power Pmax45 and the second critical current offset Ith45_Offset exceed the predetermined range, it indicates that the VCSEL chip 90 has defects in the manufacturing and positioning process.
[0050] Step S409: Next, processor 19 calculates third residual data (e.g., displayed as Residual0) based on the third optical power data D3 and its third fitted curve. Processor 19 also calculates a third coefficient of determination (e.g., displayed as Rsquare0) based on the third optical power data D3, the third fitted curve, and the third residual data Residual0. The calculation of the third residual data and the third coefficient of determination can be performed using conventional statistical methods, and therefore will not be elaborated here. Processor 19 calculates the maximum offset (e.g., displayed as Max_offset0) and the minimum offset (e.g., displayed as Min_offset0) based on the third residual data Residual0.
[0051] Processor 19 is configured to compare the maximum offset Max_offset0 with a third offset threshold (which may be the same as or different from the second offset threshold) as a judgment condition. Furthermore, processor 19 is also configured to compare a third determination coefficient Rsquare0 with a third predetermined threshold (which may be the same as or different from the second predetermined threshold) as another judgment condition. These comparison results are recorded as test results of test system 100.
[0052] Steps S410 to S411: Next, the processor 19 determines whether the maximum power Pmax0 of the third optical power data D3 is higher than the third power threshold (e.g., displayed as 0.3mW, but may be the same as or different from the second power threshold). If Pmax0 is not higher than the third power threshold, the test ends directly and all test results are recorded. If Pmax0 is higher than the third power threshold, the processor 19 calculates the third critical current offset of the critical current Ith0 based on the third optical power data D3 (e.g., displayed as Ith0_Offset, which is the difference between the critical current and the predetermined critical current or the critical current Ith of the first optical power data D1). Similarly, the maximum power Pmax0 and the third critical current offset Ith0_Offset calculated based on the third optical power data D3 represent the performance of the VCSEL chip 90 in the 0-degree polarization direction. If the maximum power Pmax0 and the third critical current offset Ith0_Offset exceed the predetermined range, it indicates that the VCSEL chip 90 has defects in the manufacturing and positioning process.
[0053] In one embodiment, the processor 19 is further configured to determine whether the second optical power data D2 (or the second maximum power Pmax45) is greater than the third optical power data D3 (or the third maximum power Pmax0), i.e. Figure 2A As shown in the diagram. If the second optical power data D2 is less than the third optical power data D3, it indicates that the placement orientation of the VCSEL chip 90 has been rotated.
[0054] In summary, the built-in algorithm in processor 19 first determines whether the unpolarized optical power data (e.g., D1) meets the predetermined power requirements. If D1 does not meet the requirements, it is determined that the performance of the current VCSEL chip 90 is not as expected; if D1 meets the requirements, processor 19 then uses the residual data and coefficient of determination (R²) of the first polarization direction optical power data (e.g., D2) and the second polarization direction optical power data (e.g., D3) to determine the performance. 2 Determine the polarization performance / stability of the VCSEL chip 90.
[0055] In one embodiment, the test system 100 of the present invention can be connected to a screen to display all or some of the above test results, or to display test statistics of multiple chips.
[0056] It must be noted that although the present invention is described using the example of the first polarizer 151 being separated from the second photosensitive sensor 171 and the second beam splitter 132, and the second polarizer 152 being separated from the third photosensitive sensor 172 and the second beam splitter 132, the present invention is not limited thereto. In other embodiments, the first polarizer 151 may be combined with the second photosensitive sensor 171 or the second beam splitter 132, and the second polarizer 152 may be combined with the third photosensitive sensor 172 or the second beam splitter 132, achieving the same effect.
[0057] It must be noted that although the first beam splitter 131 and the second beam splitter 132 of this embodiment are described using a 50 / 50 beam splitter as an example, the present invention is not limited thereto. The first beam splitter 131 and the second beam splitter 132 may have other beam splitting ratios, as long as the thresholds are configured accordingly, including thresholds for comparison with Pmax, Pmax45 and Pmax0, thresholds for comparison with Ith, Ith45 and Ith0, thresholds for comparison with Max_Offset45 and Max_Offset0, thresholds for comparison with Diff1 and Diff2, etc.
[0058] It must be noted that the numerical values in the embodiments of the present invention, such as current value, optical power, power threshold, spectral splitting ratio, polarization direction, etc., are only used for illustration and are not intended to limit the present invention.
[0059] In summary, conventional optical goniometer systems are unsuitable for batch testing due to their long testing duration. Therefore, this invention provides another testing system for VCSEL chips (see reference). Figure 1 ) and its testing methods (refer to Figure 4 It simultaneously determines the damage and angular deviation of the VCSEL chip based on the detection optical power of the unpolarized beam and the polarized beam.
[0060] While the present invention has been disclosed through the foregoing embodiments, it is not intended to limit the invention. Anyone skilled in the art to which this invention pertains can make various modifications and alterations without departing from the spirit and scope of the invention. Therefore, the scope of protection of this invention shall be determined by the scope defined in the claims.
Claims
1. A system for testing vertical-cavity surface-emitting laser (VCSEL) chips, the system comprising: A first beam splitter is used to split the emitted beam into a first beam and a second beam. The second beam splitter is used to split the second beam into a third beam and a fourth beam. A first polarizer has a first polarization direction for the passage of the third beam; A second polarizer has a second polarization direction for the passage of the fourth beam; A first optical sensor is used to receive the first light beam; A second optical sensor, which receives a polarized third beam of light; and The third optical sensor is used to receive the polarized fourth beam.
2. The system according to claim 1, wherein, The first beam splitter and the second beam splitter are 50 / 50 beam splitters.
3. The system according to claim 1, wherein, The distance between the first beam splitter and the second beam splitter in the direction of travel of the second beam is less than 1 mm.
4. The system according to claim 1, wherein, One of the first polarization direction and the second polarization direction is 45 degrees and the other is 0 degrees.
5. The system according to claim 1 further includes a power supply measurement module, wherein, The power supply measurement module is used to provide drive current to the VCSEL chip, and the drive current gradually increases in predetermined steps.
6. The system according to claim 5, wherein, The drive current increases from 0 to 9 milliamperes, and The predetermined step is 50 microamperes.
7. The system according to claim 6 further includes a processor for calculating, respectively, the fitting curve, residual, coefficient of determination, and critical current offset of the optical power data of the second optical sensor and the third optical sensor.
8. A testing method for the system of claim 1, the testing method comprising: The VCSEL chip is driven by a drive current that increases in predetermined steps; Record the first optical power data of the first optical sensor, the second optical power data of the second optical sensor, and the third optical power data of the third optical sensor; Determine whether the first optical power data meets the predetermined power requirements; If the predetermined power requirement is met, then calculate the second fitting curve of the second optical power data and the third fitting curve of the third optical power data; Calculate the second residual data based on the second optical power data and the second fitting curve; and The third residual data is calculated based on the third optical power data and the third fitting curve.
9. The test method according to claim 8, wherein, The first beam splitter and the second beam splitter are 50 / 50 beam splitters.
10. The test method according to claim 8, wherein, One of the first polarization direction and the second polarization direction is 45 degrees and the other is 0 degrees.
11. The test method according to claim 10, further comprising: Determine whether the second optical power data is greater than the third optical power data.
12. The test method according to claim 8, further comprising: The second determination coefficient is calculated based on the second optical power data, the second fitted curve, and the second residual data; and The third coefficient of determination is calculated based on the third optical power data, the third fitting curve, and the third residual data.
13. The test method according to claim 12, further comprising: Determine whether the maximum offset in the second residual data is within a second predetermined range; and Determine whether the maximum offset in the third residual data is within a third predetermined range.
14. The test method according to claim 8, further comprising: Determine whether the maximum power of the second optical power data is higher than the second power threshold; and Determine whether the maximum power of the third optical power data is higher than the third power threshold.
15. The test method according to claim 8, further comprising: Calculate the second critical current offset based on the second optical power data; and The third critical current offset is calculated based on the third optical power data.
16. The test method according to claim 8, wherein, The predetermined power requirement includes: The difference between the critical current of the first optical power data and the 1 milliwatt power current meets the predetermined difference value, and The maximum power of the first optical power data is higher than the first power threshold.
17. A testing method for a system for testing VCSEL chips, the system comprising a first optical sensor, a second optical sensor, and a third optical sensor, the testing method comprising: The first optical sensor outputs non-polarized optical power data; The second optical sensor outputs the optical power data in the first polarization direction; The third optical sensor outputs the second polarization direction optical power data; Determine whether the polarization-free optical power data meets the predetermined power requirements; as well as When the predetermined power requirement is met, the polarization performance of the VCSEL chip is determined based on the residual data and determination coefficient of the first polarization direction optical power data and the second polarization direction optical power data.
18. The test method according to claim 17, wherein, One of the first polarization direction and the second polarization direction is 45 degrees and the other is 0 degrees.
19. The test method according to claim 18, further comprising: Determine whether the maximum power of the optical power data in the first polarization direction is higher than the second power threshold. Determine whether the maximum power of the optical power data in the second polarization direction is higher than the third power threshold; and Determine whether the maximum power of the light power data in the first polarization direction is higher than the maximum power of the light power data in the second polarization direction.
20. The test method according to claim 17, further comprising: Calculate the second critical current offset of the optical power data in the first polarization direction; and Calculate the third critical current offset of the optical power data in the second polarization direction.