A return light test system and test method for a laser

Abstract

The present invention provides a return light test system and a test method for a laser. The return light test system sequentially includes a return light energy adjustment unit and a reflector along the laser transmission direction of the laser output. By adjusting the light intensity of the return light until the laser fails, the return light resistance threshold of the laser is determined. By using a reflector to form return light, on the one hand, it will not introduce any interference or influence on the laser transmitted in the optical path, and on the other hand, the return light is synchronized with the wavelength of the output light in real time. Therefore, the influence of the return light during the use of the laser can be truly simulated, and the return light resistance ability of the laser during actual use can be measured with very high measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor lasers, and in particular, to a return light test system and a test method for a laser. Background Art

[0002] The front cavity surface of a laser is coated with an optical film layer. Due to the reversibility of the optical path, in the case where no isolator or other devices are added to the optical path, part of the light beam is reflected back to the front cavity surface of the laser. The optical film layer is extremely sensitive to temperature. The absorption of the return light by the optical film layer will cause the temperature of the film layer to increase, thereby reducing the COMD threshold of the film layer on the front cavity surface of the laser, resulting in the premature failure of the original design structure and reducing the reliability of the laser. Therefore, it is very necessary to test the anti-return light ability of the laser.

[0003] Common return light ability test systems for lasers include the following two types:

[0004] (1) Using a fiber optic structure to build a return optical path, the laser emitted by the light source is returned to the light-emitting cavity surface through the optical fiber. There is edge loss when the laser emitted from the front cavity surface of the laser is coupled into the optical fiber, and during the transmission in the optical fiber, the light beam is shaped, rotated, and the bending of the optical fiber will cause abnormal return light and other effects. Therefore, when building the return light through the optical fiber, due to the above effects brought by the optical fiber itself during the transmission of the return light, it is impossible to truthfully simulate the effect of the return light on the chip cavity surface during the actual use of the laser, resulting in low measurement accuracy.

[0005] On the other hand, the power that the optical fiber can carry is relatively low. For a laser with a relatively large output optical power, such as about 100W, it exceeds the power range that the optical fiber can carry and transmit the light beam, and it is impossible to use the optical fiber for coupled transmission and measurement of the anti-return light ability.

[0006] (2) Introducing external light as a light source to simulate the return light. Since the optical film layer is sensitive to the wavelength of light, and during the operation of each laser, there are some random wavelength drifts due to its own heat dissipation. Even if a laser with the same wavelength is introduced as the external light, due to the difference in the heat dissipation temperature drift during operation, it is impossible to real-time simulate and reproduce the wavelength of the laser to be tested. Therefore, introducing an external laser cannot simulate the influence of the return light that the laser to be tested is actually subjected to during the actual use process.

[0007] Therefore, in the prior art, it is impossible to truly simulate the return light that the laser is subjected to during the use process, and thus it is impossible to accurately measure the anti-return light ability of the laser during the use process. Summary of the Invention

[0008] The present invention provides a return light test system and a test method for a laser. Along the laser transmission direction of the laser, the return light test system sequentially includes: a return light energy adjustment unit and a reflector;

[0009] The reflector is arranged on the propagation path of the laser for reflecting the laser to form return light and making the return light incident on the active region of the laser;

[0010] The return light energy adjustment unit is arranged on the propagation path of the return light for adjusting the light intensity of the return light until the laser fails, so as to determine the return light resistance threshold of the laser.

[0011] Further, the return light energy adjustment unit includes a half-wave plate and a polarization beam splitter prism arranged in sequence along the laser transmission direction. The polarization beam splitter prism adjusts the light intensity of the return light by adjusting the rotation angle of the half-wave plate.

[0012] Further, the return light energy adjustment unit further includes a power meter. The polarization beam splitter prism divides the return light into two partial light beams. One partial light beam passes through the polarization beam splitter prism and is incident on the active region of the laser, and the other partial light beam is reflected by the polarization beam splitter prism and enters the power meter.

[0013] Further, the return light test system further includes a wedge prism. The wedge prism is arranged in front of the return light energy adjustment unit along the laser transmission direction; along the laser transmission direction, the wedge prism sequentially includes an incident surface and an exit surface. The beam emitted by the laser is refracted by the wedge prism and exits from the exit surface and then enters the return light energy adjustment unit.

[0014] Further, the return light test system further includes a near-field imaging unit. The near-field imaging unit is located on one side of the exit surface of the wedge prism. The laser passes through the wedge prism, is reflected by the exit surface of the wedge prism back to the incident surface, and then exits from the exit surface and enters the near-field imaging unit.

[0015] Further, the return light test system further includes a spectrometer; the spectrometer is located on one side of the incident surface of the wedge prism, and the beam emitted by the laser is reflected by the incident surface of the wedge prism and enters the spectrometer.

[0016] Further, the return light test system further includes an adjustment device for adjusting the position and angle of the reflector until the return light is reflected by the reflector and then enters the active region of the laser through the return light energy adjustment unit.

[0017] On the other hand, the present application also provides a return light test method for a laser. The return light test method includes:

[0018] Provide a laser;

[0019] Apply excitation to the laser, so that the laser light emitted by the laser forms retroreflected light through the retroreflected light test system of the laser as described above and is incident on the active region of the laser;

[0020] Adjust the light intensity of the retroreflected light through the retroreflected light energy adjustment unit until the laser fails, so as to determine the retroreflected light resistance threshold of the laser.

[0021] Further, adjusting the light intensity of the retroreflected light through the retroreflected light energy adjustment unit until the laser fails to determine the retroreflected light resistance threshold of the laser includes: rotating the half-wave plate of the retroreflected light test system of the laser to a preset rotation angle, gradually increasing the excitation of the laser until the laser fails, and obtaining the rotation angle of the half-wave plate and the excitation corresponding to the laser failure; determining the retroreflected light resistance threshold of the laser based on the rotation angle of the half-wave plate and the excitation.

[0022] Further, if the laser still does not fail when the excitation increases to the maximum value, adjust the rotation angle of the half-wave plate to increase the intensity of the retroreflected light until the laser fails; determine the retroreflected light resistance threshold of the laser based on the rotation angle of the half-wave plate and the excitation.

[0023] Further, applying excitation to the laser, so that the laser light emitted by the laser forms retroreflected light through the retroreflected light test system of the laser as described above and is incident on the active region of the laser includes: applying excitation to the laser, coarsely adjusting the reflector, adjusting the position and angle of the reflector, and observing the near-field image on the near-field imaging unit at the same time. When a sudden change in brightness of the near-field image is observed, the retroreflected light has been incident near the active region of the laser, and fix the reflector; finely adjust the reflector, adjust the position and angle of the reflector, and obtain the power change trend of the power meter. When the reading of the power meter reaches the maximum value, the retroreflected light is accurately incident on the active region of the laser, and fix the position of the reflector.

[0024] Further, the excitation is 20%-80% of the threshold excitation.

[0025] The present invention provides a retroreflected light test system and test method for a laser, which have the following technical effects:

[0026] (1) For the retroreflected light test system and test method of the laser of the present invention, a reflector is used to form retroreflected light. On the one hand, the reflector will not cause any interference or influence on the laser transmitted in the optical path. On the other hand, the retroreflected light is synchronized with the wavelength of the emitted light in real time. Therefore, the influence of retroreflected light during the use of the laser can be truly simulated, and the retroreflected light resistance ability of the laser during actual use can be measured, and the measurement accuracy is very high.

[0027] (2) The return light test system and method for the laser of the present invention use a mirror to form return light. Since the mirror does not cause any interference or influence on the laser transmitted in the optical path, the light intensity distribution of the return light on the front cavity surface is the same as that of the outgoing light on the cavity surface. The light intensity distribution of the outgoing light can be obtained from the light intensity distribution of the return light on the front cavity surface, and further judge the light intensity distribution of the semiconductor front cavity surface, such as whether there are points with abnormal light intensity distribution. Based on this, the laser is optimized subsequently. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is a structural diagram of the return light test system for the laser of the present invention.

[0030] Figure 2(a) is a schematic diagram of the near-field image (I).

[0031] Figure 2(b) is a schematic diagram of the near-field image (II).

[0032] Figure 3 It is a relationship diagram between the rotation angle of the half-wave plate and the ratio of the return light intensity to the laser light intensity emitted by the laser.

[0033] Figure 4 It is a schematic flow chart of the return light test method for the laser of the present invention.

[0034] In the figure, 1. Laser, 2. Fast-axis collimating mirror, 3. Slow-axis collimating mirror, 4. Wedge mirror, 5. Half-wave plate, 6. Polarizing beam splitter prism, 7. Mirror, 8. Power meter, 9. Spectrometer, 10. Converging lens, 11. Near-field imaging unit, 12. Incident surface, 13. Exit surface. Detailed Embodiments

[0035] The technical solutions in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention.

[0036] Embodiment 1

[0037] This embodiment provides a return light test system for a laser, as Figure 1 shown, successively including along the laser transmission direction of the laser 1: a wedge mirror 4, a return light energy adjustment unit and a mirror 7, as well as an adjustment device.

[0038] The laser emitted by the laser 1 passes through the fast-axis collimating mirror 2 and the slow-axis collimating mirror 3 and is incident on the wedge mirror 4. Along the laser transmission direction, the wedge mirror 4 sequentially includes an incident surface 12 and an exit surface 13. The beam emitted by the laser 1 enters the wedge mirror 4 from the incident surface 12, and after being refracted by the wedge mirror 4, it exits from the exit surface 13 and then enters the retroreflected light energy adjustment unit.

[0039] The reflecting mirror 7 is used to reflect the laser to form retroreflected light, and the adjusting device is used to adjust the position and angle of the reflecting mirror 7 so that the retroreflected light is reflected by the reflecting mirror 7 to the active region of the laser 1. The retroreflected light energy adjustment unit is used to adjust the light intensity of the retroreflected light until the laser 1 fails, so as to determine the retroreflected light threshold of the laser 1.

[0040] The retroreflected light energy adjustment unit includes a half-wave plate 5 and a polarization beam splitter prism 6 arranged in sequence along the laser transmission direction. The polarization beam splitter prism 6 adjusts the light intensity of the retroreflected light by adjusting the rotation angle of the half-wave plate 5. Further, the retroreflected light energy adjustment unit further includes a power meter 8. The polarization beam splitter prism 6 divides the retroreflected light into two partial beams. One partial beam passes through the polarization beam splitter prism 6 and is incident on the active region of the laser 1, and the other partial beam is reflected by the polarization beam splitter prism 6 and enters the power meter 8. The power meter 8 is used to measure the light intensity of the beam reflected by the polarization beam splitter prism 6.

[0041] Further, the retroreflected light test system further includes a near-field imaging unit 11. The near-field imaging unit 11 is used to determine the near-field image of the laser emitted by the laser 1. The near-field imaging unit 11 is located on one side of the exit surface 13 of the wedge mirror 4. The laser passes through the wedge mirror 4, is reflected back to the incident surface 12 by the exit surface 13 of the wedge mirror 4, and then exits through the exit surface 13 and enters the near-field imaging unit 11. A converging lens 10 can be added before the near-field imaging unit 11 so that the near-field image of the laser is imaged on the near-field imaging unit 11 after passing through the converging lens 10.

[0042] Further, the retroreflected light test system further includes a spectrometer 9. The spectrometer 9 is used to determine the wavelength of the laser emitted by the laser 1, so as to determine the retroreflected light threshold at a specific wavelength emitted by the laser 1. The spectrometer 9 is located on one side of the incident surface 12 of the wedge mirror 4. The beam emitted by the laser 1 is reflected by the incident surface 12 of the wedge mirror 4 and enters the spectrometer 9.

[0043] Embodiment 2

[0044] As Figure 4 shown, based on the retroreflected light test system provided in Embodiment 1 of the present application, the method for testing the retroreflected light of the laser 1 includes:

[0045] Applying an excitation to the laser 1 so that the laser emitted by the laser 1 forms retroreflected light through the retroreflected light test system and is incident on the active region of the laser 1;

[0046] Adjust the optical intensity of the retro-reflected light through the retro-reflected light energy adjustment unit until the laser 1 fails, so as to determine the anti-retro-reflected light threshold of the laser 1.

[0047] Further, apply an excitation to the laser 1 so that the laser emitted by the laser 1 forms a retro-reflected light through the retro-reflected light test system and is incident on the active region of the laser 1, including the following two steps:

[0048] Step (1), apply an excitation to the laser 1 and roughly adjust the mirror 7 so that the retro-reflected light is incident near the active region of the laser 1, as shown in Fig. 2(a).

[0049] Specifically, adjust the position and angle of the mirror 7, and at the same time obtain the near-field image on the near-field imaging unit 11. When the brightness of the near-field image changes suddenly, it indicates that the retro-reflected light has been incident near the active region of the laser 1. The reason is that in addition to the electrical excitation of the laser 1 itself, the retro-reflected light can be used as another optical excitation for the laser 1. When the retro-reflected light has been incident near the active region of the laser 1 by adjusting the mirror 7, the retro-reflected light can then act on the laser 1 itself as another optical excitation, causing a population inversion in the laser 1 to emit laser light. Therefore, a sudden change in brightness can be observed from the near-field image formed by the near-field imaging unit 11, as shown in the change from Fig. 2(a) to Fig. 2(b).

[0050] To observe the sudden change in the brightness of the near-field image in step (1), the electrical excitation applied to the laser 1 is 20% - 80% of the threshold current. That is, in the case of only electrical excitation, no population inversion is formed in the laser 1, and no laser light is emitted but spontaneous emission fluorescence is generated. The near-field image formed by the near-field imaging unit 11 is shown in Fig. 2(a).

[0051] Step (2), finely adjust the mirror 7 so that the retro-reflected light is accurately incident on the active region of the laser 1.

[0052] Specifically, adjust the position and angle of the mirror 7, and observe the power change trend of the power meter 8. When the reading of the power meter 8 reaches the maximum value, it indicates that the retro-reflected light has been accurately incident on the active region of the laser 1, that is, most of the energy of the retro-reflected light has been applied to the laser 1 as an optical excitation, and the optical excitation applied to the laser 1 reaches the maximum value. Therefore, the intensity of the laser emitted by the laser 1 reaches the maximum value, and the intensity of the retro-reflected light in the optical path is also the largest. Fix the position and angle of the mirror 7 at this time.

[0053] Among them, the method for determining that the reading of the power meter 8 reaches the maximum value may include but is not limited to determining the maximum value based on the power value measured by the power meter 8 for the nth time, the power value measured for the (n - 1)th time, and the power value measured for the (n + 1)th time; during the process of adjusting the position and angle of the mirror 7, it is always ensured that the power value measured for the nth time is greater than the power value measured for the (n - 1)th time. When the power value measured for the nth time is greater than the power value measured for the (n + 1)th time, it is determined that the power value measured by the power meter 8 for the nth time is the maximum value.

[0054] Further, the return light energy adjustment unit adjusts the light intensity of the return light until the laser 1 fails to determine the anti - return light threshold of the laser 1, including:

[0055] Rotate the half - wave plate 5 to a preset rotation angle, gradually increase the electrical excitation of the laser 1 until the laser 1 fails, and obtain the rotation angle of the half - wave plate 5 and the electrical excitation corresponding to the failure of the laser 1; determine the anti - return light threshold of the laser 1 based on the rotation angle of the half - wave plate 5 and the electrical excitation of the laser 1.

[0056] If the laser 1 still does not fail when the electrical excitation increases to the maximum value, then adjust the rotation angle of the half - wave plate 5 to increase the intensity of the return light until the laser 1 fails. The relationship between the rotation angle of the half - wave plate 5 and the light feedback intensity curve of the return light is as Figure 3 shown; determine the anti - return light threshold of the laser 1 based on the rotation angle of the half - wave plate 5 and the electrical excitation of the laser.

[0057] Specifically, the greater the excitation applied to the laser, the higher the power of the laser emitted by the laser (i.e., the higher the power of the return light). By adjusting the rotation angle of the half - wave plate 5, the light intensity of the beam returning to the active region of the laser 1 can be adjusted. That is, by adjusting the half - wave plate 5, a certain proportion of the light intensity of the laser emitted by the laser 1 can be returned to the active region of the laser 1. Figure 3 is a graph of the relationship between the rotation angle of the half - wave plate 5 and the proportion of the return light intensity relative to the light intensity of the laser emitted by the laser 1; further, the anti - return light threshold of the laser 1 can be determined according to the proportion and the light intensity of the laser emitted by the laser 1.

[0058] Specifically, in this embodiment, the principle of adjusting the return light energy by the half - wave plate 5 and the polarization beam splitter prism 6 is as follows: The half - wave plate 5 has two main axes, namely the fast axis and the slow axis. The refractive indices on the two axes are different, so the light speeds are also different. The angle between the polarization direction of the outgoing light and the polarization direction of the incident light is twice the angle between the polarization direction of the incident light and the main axis of the wave plate. When the polarization direction of the incident light coincides with the fast axis or the slow axis, the polarization direction remains unchanged. The half - wave plate 5 can continuously adjust the polarization direction. Assuming that the angle between the polarization direction and the slow axis is θ, after the light beam passes through the half - wave plate 5, the optical phase of the fast axis adds π, and the rotation angle of the polarization direction is 2θ.

[0059] The polarization beam splitter prism 6 is an optical element that splits an incident light beam into two light beams with perpendicular propagation directions. However, different from general optical beam splitting elements, there is a special relationship between the two light beams split by it, that is, both light beams are linearly polarized light, and the polarization directions are perpendicular to each other. In this embodiment, the intensity of the return light is mainly determined by the return light energy adjustment unit composed of the half-wave plate 5 and the polarization beam splitter prism 6, and the intensity of the return light can be adjusted by adjusting the angle of the half-wave plate 5. The half-wave plate 5 can change the polarization direction of light, and the polarization beam splitter prism 6 can allow the P light (parallel polarized light, that is, the light with the electric field vibration direction parallel to the incident plane, and the incident plane is the plane formed by the incident light ray and the normal line. For P light, its electric vector is located in the incident plane) to pass through and reflect the S light (perpendicular polarized light, that is, the light with the electric field vibration direction perpendicular to the incident plane, and its electric vector is perpendicular to the incident plane). The combination of the two can achieve continuous adjustment of the return light energy.

[0060] Based on the return light test system and method provided in this embodiment, the return light is formed by using the mirror 7. On the one hand, the mirror 7 will not cause any interference or influence on the laser transmitted in the optical path. On the other hand, the return light is synchronized with the wavelength of the outgoing light in real time. Therefore, the influence of the return light during the use of the laser 1 can be truly simulated, and the anti-return light ability of the laser 1 during actual use can be measured, and the measurement accuracy is very high.

[0061] On the other hand, in this embodiment, the mirror 7 is used to form the return light. Since the mirror 7 will not cause any interference or influence on the laser transmitted in the optical path, the light intensity distribution of the outgoing light on the front cavity surface of the laser 1 can be simulated by measuring the light intensity distribution of the return light on the front cavity surface of the laser 1. The light intensity distribution of the outgoing light can be obtained by measuring the light intensity distribution of the return light on the front cavity surface, and further judge the light intensity distribution of the front cavity surface of the laser 1, such as whether there are points with abnormal light intensity distribution. Based on this, the laser 1 can be optimized subsequently.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser return light testing system, characterized in that: The laser transmission direction along the laser output of the laser includes: a return light energy adjustment unit and a reflector; The reflector is arranged in the propagation path of the laser, and is used to reflect the laser to form return light, and make the return light incident on the active area of ​​the laser; The return light energy adjustment unit is arranged in the propagation path of the return light, and is used to adjust the light intensity of the return light until the laser fails, so as to determine the anti-return light threshold of the laser; the return light energy adjustment unit includes a half-wave plate and a polarization beam splitter prism arranged in sequence along the laser transmission direction, and the polarization beam splitter prism adjusts the light intensity of the return light by adjusting the rotation angle of the half-wave plate.

2. A laser return light testing system as claimed in claim 1, characterized in that: The return light energy adjustment unit also includes a power meter. The polarization beam splitter prism splits the return light into two light beams. One light beam passes through the polarization beam splitter prism and enters the active area of ​​the laser. The other light beam is reflected by the polarization beam splitter prism and enters the power meter.

3. The laser return light testing system according to claim 1, characterized in that: The return light testing system further comprises a wedge mirror, which is arranged in front of the return light energy adjustment unit along the laser transmission direction; Along the laser transmission direction, the wedge-shaped mirror includes an incident surface and an exit surface in sequence. The light beam emitted by the laser is refracted by the wedge-shaped mirror, and enters the return light energy adjustment unit after being emitted from the exit surface.

4. A laser return light testing system as claimed in claim 3, characterized in that: The return light testing system also includes a near-field imaging unit, which is located on one side of the exit surface of the wedge-shaped mirror. The laser passes through the wedge-shaped mirror, is reflected back to the incident surface by the exit surface of the wedge-shaped mirror, and then enters the near-field imaging unit after being emitted through the exit surface.

5. The laser return light testing system as claimed in claim 3, characterized in that: The return light testing system further comprises a spectrometer; the spectrometer is located on one side of the incident surface of the wedge-shaped mirror, and the light beam emitted by the laser is reflected by the incident surface of the wedge-shaped mirror and enters the spectrometer.

6. A laser return light testing system as claimed in claim 1, characterized in that: The return light testing system also includes an adjusting device for adjusting the position and angle of the reflector until the return light is reflected by the reflector and incident on the active area of ​​the laser through the return light energy adjusting unit.

7. A method for testing the return light of a laser, characterized in that: The back-return light testing method comprises: Step S1, providing a laser; Step S2, applying excitation to the laser, so that the laser emitted by the laser forms reflected light incident on the active area of ​​the laser through the laser reflected light testing system according to any one of claims 1 to 6; Step S3, adjusting the light intensity of the returned light by a returned light energy adjustment unit until the laser fails, so as to determine the anti-return light threshold of the laser.

8. A laser return light testing method as claimed in claim 7, characterized in that: The step S3 comprises: Rotate the half-wave plate of the laser return light test system to a preset rotation angle, gradually increase the excitation of the laser until the laser fails, and obtain the half-wave plate rotation angle and excitation corresponding to the laser failure; determine the anti-return light threshold of the laser based on the rotation angle of the half-wave plate and the excitation.

9. A laser return light testing method as claimed in claim 8, characterized in that: If the laser does not fail when the excitation is increased to the maximum value, the rotation angle of the half-wave plate is adjusted to increase the intensity of the returned light until the laser fails; the anti-return light threshold of the laser is determined based on the rotation angle of the half-wave plate and the excitation.

10. A laser return light testing method as claimed in claim 7, characterized in that: The step S2 comprises: Applying excitation to the laser, roughly adjusting the reflector, adjusting the position and angle of the reflector, and observing the near-field image on the near-field imaging unit at the same time. When a sudden change in brightness of the near-field image is observed, the return light has been incident near the active area of ​​the laser, and the reflector is fixed; Fine-tune the reflector, adjust its position and angle, and obtain the power change trend of the power meter. When the power meter reading reaches the maximum value, the return light accurately enters the active area of ​​the laser, and the position of the reflector is fixed.

11. A laser return light testing method as claimed in claim 10, characterized in that: The incentive is 20%-80% of the threshold incentive.

Images