System and method for detecting end face reflectivity of DFB laser chip

Abstract

The invention provides a system and method for detecting the reflectivity of the end face of a DFB laser chip, and the system comprises a light source part which employs a broadband laser as a detection light source, an optical adjustment part which sequentially comprises an optical fiber collimator, a half-wave plate, a polarization splitting prism and a quarter-wave plate, and a beam expanding lens group. The quarter-wave plate is used for converting incident light into circularly polarized light, and the circularly polarized light irradiates the end face of the DFB laser chip through the beam expanding lens group and then is converted into specific polarized light after being reflected by the DFB laser chip so that the specific polarized light can be accurately measured by the optical power meter. According to the invention, the reflectivity of the end face of the DFB laser chip can be rapidly and accurately measured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic technology, in particular to a system and method for detecting the reflectivity of the end face of a distributed feedback (DFB) laser chip. BACKGROUND

[0002] DFB laser chip is an important semiconductor laser chip, which is used as a light emitting source in optical communication systems and widely applied in high-speed data transmission, optical fiber communication network, etc. By constructing a Bragg grating structure inside the chip, it realizes the feedback and oscillation of specific wavelength light, thereby outputting stable single longitudinal mode laser. However, the reflectivity characteristics of the DFB laser chip have a key influence on its performance. Inaccurate or unstable reflectivity may cause laser output power fluctuation, wavelength drift, etc., thereby affecting the performance and reliability of the entire optical communication system.

[0003] At present, the traditional DFB laser chip reflectivity detection method has certain limitations. For example, some detection methods based on fiber coupling have very high requirements for the flatness of the chip end face. Since the size of the DFB laser chip end face is very small, usually in microns, and its flatness requirement is very high, reaching nanometer level flatness deviation may have a significant impact on the detection result. And in the coupling process, loss and error are easily introduced. In addition, methods such as using complex optical interferometer for detection have high equipment cost and complex operation, which requires professional technicians to debug and measure, and is not convenient for large-scale chip detection and quality control in the production process. SUMMARY

[0004] The present application is dedicated to breaking through the bottleneck of the existing DFB laser chip end face reflectivity detection technology. By carefully optimizing the optical path design, using advanced optical elements, and combining with accurate measurement algorithm, a high-precision and high-reliability DFB laser chip end face reflectivity detection system and method is constructed. This scheme aims to realize the rapid and accurate measurement of the DFB laser chip end face reflectivity, provide key data support for chip research and development, ensure production quality, and help DFB laser chip expand application range. The detection is of great significance for evaluating the performance of DFB laser chip and ensuring its reliable application in the field of optical communication, etc.

[0005] The present application proposes a detection system for the reflectivity of a DFB laser chip, comprising: A light source part adopts a broadband laser as a detection light source, and its output end is connected with a fiber collimator through an optical fiber. The optical adjustment part comprises a fiber collimator, a half-wave plate, a polarization beam splitter prism and a quarter-wave plate, and a beam expander lens group, wherein the fiber collimator collimates the laser output by the optical fiber into a parallel light beam, and then the light beam sequentially passes through the half-wave plate, the polarization beam splitter prism and the quarter-wave plate; the half-wave plate is used for adjusting the polarization direction of the laser, and the light power passing through the polarization beam splitter prism can be changed by rotating the half-wave plate; the polarization beam splitter prism can divide the incident light into two beams with different polarization directions, one of which is used for subsequent detection light path, and the quarter-wave plate is used for converting the incident light into circularly polarized light; the beam expander lens group is arranged between the quarter-wave plate and the DFB laser chip, the circularly polarized light passes through the beam expander lens group and irradiates on the end face of the DFB laser chip, and then is converted into specific polarized light by the DFB laser chip after reflection, so as to be accurately measured by the optical power meter; The chip fixing and adjusting part comprises a volume grating fixing clamp and a two-dimensional adjusting frame, the volume grating fixing clamp is arranged on the two-dimensional adjusting frame and is used for fixing the DFB laser chip, and the two-dimensional adjusting frame can accurately adjust the front, back, left and right positions of the DFB laser chip and the pitch angle of the incident face; The power measurement part: the optical power meter is used for measuring the light power after the reflection of the DFB laser chip.

[0006] The beam expander lens group expands the laser processed by the front optical elements, so that the laser can uniformly irradiate on the end face of the DFB laser chip, and the beam expander lens group can be combined by multiple lenses, and the expansion multiple can be adjusted according to actual needs.

[0007] Optionally, the optical power meter is located below the polarization beam splitter prism, the probe of the optical power meter receives the reflected light signal and converts it into an electric signal, which is transmitted to the optical power meter display to display the optical power value.

[0008] Optionally, the optical adjustment part further comprises a zero-degree plane mirror located between the beam expander lens group and the fiber collimation grating fixing clamp, which is used for changing the propagation direction of the light beam while keeping the optical characteristics of the light beam basically unchanged, so as to guide the light beam to the subsequent fiber collimation grating fixing clamp and the DFB laser chip to be measured. The zero-degree plane mirror has multiple layers of high reflectivity dielectric films with a reflectivity of ≥99.5% @ 1300nm-1600nm.

[0009] The application provides a detection method of the reflectivity detection system based on the DFB laser chip, which comprises the following steps: 1) System establishment and calibration: Optical path establishment: according to the system components, the optical elements are sequentially installed on the optical fixing support, and the optical fiber and other components are connected; System collimation and leveling: visible light is used to collimate the entire optical path, and the position of the light after passing through each optical element is observed through a reticle card. The positions and angles of the elements are adjusted so that the light can propagate along the predetermined optical path and accurately enter the end face of the DFB laser chip. Phase angle adjustment of half-wave plate and quarter-wave plate: the angles of the half-wave plate, polarization beam splitter prism, and quarter-wave plate are adjusted to ensure that the polarization state of the light meets the detection requirements. 2) Transmission loss measurement: a zero-degree plane mirror coated with multiple layers of high-reflectivity dielectric film is placed between the beam expander lens group and the DFB laser chip. A power meter is placed in the first position to measure the incident power of the incident light onto the zero-degree plane mirror . A power meter is placed in the second position to measure the calibrated reflected power after reflection by the zero-degree plane mirror . The optical path transmission loss is calculated according to the formula , where is the reflectivity of the zero-degree plane mirror. 3) DFB laser chip placement and preparation: the DFB laser chip is placed on the fixture, and then the knobs of the two-dimensional adjustment stand are adjusted to make the end face of the DFB laser chip perpendicular to the incident laser beam and ensure that the laser can accurately enter the active region of the chip. The display value of the optical power meter is cleared before testing to exclude the influence of background stray light on the measurement results. 4) Incident power measurement: the power meter is placed in the first position to ensure that the laser beam accurately enters the active region of the DFB laser chip, and the incident power of the incident light onto the DFB laser chip is measured . 5) Reflection power measurement The power meter is placed in the second position so that the laser enters the end face of the DFB laser chip, and the power reflected by the DFB laser chip is measured . 6) Reflectivity calculation The reflectivity of the DFB laser chip is calculated according to the formula .

[0010] Wherein the phase angle adjustment of the half-wave plate and the quarter-wave plate in step 1) includes: turning on the broadband laser switch, adjusting the angles of the half-wave plate and the quarter-wave plate, first placing the optical power meter probe behind the polarization beam splitter prism, i.e. in the first position, rotating the half-wave plate so that the light power transmitted through the polarization beam splitter prism is moderate, then moving the probe to the second position, rotating the quarter-wave plate so that the reflected light power measured by the optical power meter is maximum, at this time the angle of the quarter-wave plate is adjusted to the right position.

[0011] ​Wherein in order to improve the accuracy of measurement, the step 5) can be measured multiple times, and the data of each measurement is recorded. Then take the average of these measurements as the reflected power .

[0012] Wherein the zero plane mirror plated with multiple layers of high reflectivity dielectric film has a reflectivity ≥99.5% in the range of 1300nm~1600nm.

[0013] The above and other objects, advantages and features of the present application will become more apparent from the following detailed description of the embodiments thereof, when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0014] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments with reference to the drawings. The drawings are for purposes of illustration only and are not intended to limit the present application thereto. Like reference numerals are used to refer to like elements throughout. In the drawings: Figure 1 is a system schematic diagram for detecting the end face reflectivity of a DFB laser chip according to an embodiment of the present application; Figure 2 is a detection flowchart of the system for detecting the end face reflectivity of a DFB laser chip according to an embodiment of the present application. DETAILED DESCRIPTION

[0015] Embodiments of the present application will be described below with reference to the accompanying drawings, and those skilled in the art should understand that these embodiments are only used to explain the present application, but are not limiting.

[0016] The embodiments of the present application propose a system for detecting the end face reflectivity of a DFB laser chip, as Figure 1 shown, the detection system of the reflectivity of the DFB laser chip of the embodiments of the present application can include a light source part, an optical adjustment part, a chip fixing and adjustment part, and a power measurement part.

[0017] Light source part: a broadband laser is used as a detection light source, and its output end is connected with a fiber collimator through an optical fiber. The broadband laser can provide laser with a wide wavelength range, meeting the needs of reflectivity detection of the DFB laser chip at different working wavelengths. For example, a super-continuous broadband laser with a wavelength coverage range of 1510~1630nm can be selected, and its output laser power is stable and adjustable, generally set to less than 5mW to avoid damage to the DFB laser chip.

[0018] Optical adjustment part: the optical fiber collimator collimates the laser output by the optical fiber into a parallel light beam, and then passes through a half-wave plate, a polarization beam splitter prism and a quarter-wave plate in turn. The half-wave plate is used to adjust the polarization direction of the laser. By rotating the half-wave plate, the light power passing through the polarization beam splitter prism can be changed, thereby avoiding damage to the optical power meter due to saturation. The polarization beam splitter prism can divide the incident light into two beams with different polarization directions, one of which is used for subsequent detection. The quarter-wave plate is used to convert the light into circularly polarized light, which is reflected by the DFB laser chip and then converted into a specific polarized light for accurate measurement by the optical power meter.

[0019] The beam expander lens group expands the laser beam after being processed by the front optical elements, so that the laser beam can uniformly irradiate the end face of the DFB laser chip, ensuring the accuracy of detection. The beam expander lens group can be composed of multiple lenses, and the expansion multiple can be adjusted according to actual needs.

[0020] Chip fixing and adjusting part: the grating fixing clamp is used to fix the DFB laser chip, and the fixing clamp is arranged on the two-dimensional adjusting frame. The two-dimensional adjusting frame can accurately adjust the front, back, left and right positions of the DFB laser chip and the pitch angle of the incident face. When installing the DFB laser chip, first place the chip on the clamp, and then adjust the knobs of the two-dimensional adjusting frame to make the end face of the DFB laser chip perpendicular to the incident laser beam, and ensure that the laser can accurately enter the active area of the chip. For example, the adjustment accuracy can reach microns, to ensure the repeatability and accuracy of detection.

[0021] Power measurement part: the optical power meter is used to measure the optical power reflected by the DFB laser chip. The probe of the optical power meter has high sensitivity and accuracy, and can accurately measure weak optical signals. During measurement, the optical power meter converts the optical signal into an electrical signal and displays the corresponding power value. The optical power meter is located below the polarization beam splitter prism, and the probe receives the reflected light signal and converts it into an electrical signal, which is transmitted to the optical power meter display to display the optical power value. The zero-degree plane mirror belongs to the optical collimation and reflection system of the optical adjustment part, and is located between the beam expander lens group and the optical fiber collimation grating fixing clamp. Its main function is to change the direction of the light beam while keeping the optical properties of the light beam basically unchanged, so as to guide the light beam to the subsequent optical fiber collimation grating fixing clamp and the DFB laser chip to be measured.

[0022] The reflectivity detection system of the DFB laser chip of the embodiment of the present application carefully optimizes the optical path design, uses advanced optical elements, and enables fast and accurate measurement of the reflectivity of the DFB laser chip, providing key data support for chip research and development, ensuring production quality, and helping to expand the application range of DFB chips.

[0023] The embodiment of the present application also provides a detection method for reflectivity of a DFB laser chip. Figure 2 As shown in the figure, the detection method for reflectivity of the DFB laser chip of the embodiment of the present application can include the following steps: 1. System setup and calibration Optical path setup: according to the above system components, sequentially install each optical element on the optical fixing support, and connect the optical fiber and other components. Ensure the stability of the optical path, and avoid interference of external vibration and other factors on the optical path. For example, the optical fixing support can be placed on a vibration isolation platform to reduce the influence of environmental vibration on the optical path.

[0024] System collimation and leveling: collimate the entire optical path with visible light, observe the position of light after passing through each optical element through the cursor card, adjust the position and angle of each element, so that the light can propagate along the predetermined optical path and accurately incident on the end face of the DFB laser chip. During the adjustment process, special attention should be paid to the angle of the half-wave plate, the polarization beam splitter prism and the quarter-wave plate, to ensure that the polarization state of the light meets the detection requirements, and the spot position and shape of the light after passing through each optical element need to be observed through the cursor card. For example, the angle of the half-wave plate needs to be adjusted to make the polarization direction of the light form a specific 45° angle with the transmission axis or reflection axis of the polarization beam splitter prism, so as to realize the polarization state conversion of the light and make the linearly polarized light be correctly separated by the polarization beam splitter prism.

[0025] Phase angle adjustment: turn on the broadband laser switch, and adjust the angles of the half-wave plate and the quarter-wave plate according to the method described above. First, place the optical power meter probe behind the polarization beam splitter prism, that is, at the first position, rotate the half-wave plate so that the light transmitted through the polarization beam splitter prism has moderate power, then move the probe to the second position on the direction of the reflected light of the DFB laser chip reflected by the polarization beam splitter prism again, rotate the quarter-wave plate so that the reflected light power measured by the optical power meter is maximum, at this time the angle of the quarter-wave plate is adjusted to the right position.

[0026] 2. Transmission loss measurement Place a zero-degree plane mirror coated with multiple layers of high reflectivity dielectric film (reflectivity ≥ 99.5% @ 1300nm~1600nm) between the beam expander lens group and the DFB laser chip.

[0027] Place the power meter at the first position to measure the incident power incident on the zero-degree plane mirror .

[0028] Place the power meter at the second position to measure the calibrated reflected power after reflection by the zero-degree plane mirror . Calculate the optical path transmission loss according to the formula (where is the reflectivity of the zero-degree plane mirror) This step requires accurate measurement of power values and ensures the surface of the zero-degree plane mirror is clean and flat to ensure the accuracy of the measurement.

[0029] 3. DFB laser chip placement and preparation Carefully fix the DFB laser chip on the volume grating fixing clamp, ensuring good contact between the chip and the clamp without shaking or deviation. Avoid mechanical damage to the chip during the fixing process. Set the wavelength range of the broadband laser output laser to 1510-1630 nm, and stabilize the output laser power in a suitable range (less than 5 mW). Before testing, clear the display value of the optical power meter to exclude the influence of background stray light on the measurement results.

[0030] 4. Incident power measurement Place the power meter in the first position to measure the incident power incident to the DFB laser chip At this time, ensure that the laser beam is accurately incident to the active area of the DFB laser chip, and the probe of the power meter can accurately receive all the incident light.

[0031] 5. Reflection power measurement Place the power meter in the second position to make the laser incident to the end face of the DFB laser chip, and measure the reflected power after the DFB laser chip. To improve the accuracy of the measurement, multiple measurements (such as 5 times) can be taken, and the data of each measurement is recorded. Then take the average of these measured values as the reflected power During the measurement process, keep the environment stable to avoid external factors interfering with the measurement results.

[0032] 6. Reflection rate calculation According to the formula Calculate the reflectivity of the DFB laser chip. Substitute the incident power , the reflected power and the calculated transmission loss into the formula to obtain the reflectivity value of the DFB laser chip. Pay attention to the accuracy of the data and the unity of the units during the calculation process.

[0033] Example demonstration: Use a DFB laser chip with a center wavelength of 1550 nm, and use a super-continuous broadband laser (output power 3 mW) with a wavelength coverage range of 1510-1630 nm as the light source to build the detection system. Adjust the positions and angles of each element through visible light collimation to ensure that the light path is accurately incident to the chip end face, and adjust the angles of the half-wave plate and quarter-wave plate to make the light power moderate and the reflected light power maximum. Use the zero-degree plane mirror to measure the light path transmission loss After fixing the DFB laser chip and clearing the optical power meter, the incident power is measured. 2.49mW, reflected power (Average of 5 measurements) is 0.01236mW, and the reflectivity of the DFB laser chip is finally calculated. Considering the application requirements of DFB laser chips in the field of optical communications, the normal reflectivity range is between 0.2% and 1.5%. The reflectivity of this DFB laser chip meets the performance requirements.

[0034] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A system for detecting the reflectivity of a DFB laser chip end face, characterized in that: include: In the light source part, a broadband laser is used as the detection light source, and its output end is connected to the fiber collimator through an optical fiber; The optical adjustment part includes a fiber collimator, a half-wave plate, a polarization beam splitter prism, a quarter-wave plate, and a beam expansion lens group. The fiber collimator collimates the laser output from the optical fiber into a parallel beam, which then passes through the half-wave plate, the polarization beam splitter prism, and the quarter-wave plate in sequence. The half-wave plate is used to adjust the polarization direction of the laser. The optical power passing through the polarization beam splitter prism can be changed by rotating the half-wave plate. The polarization beam splitter prism can split the incident light into two beams with different polarization directions, part of which is used for subsequent detection of the optical path. The quarter-wave plate is used to convert the incident light into circularly polarized light. The beam expansion lens group is located between the quarter-wave plate and the DFB laser chip. The circularly polarized light passes through the beam expansion lens group and is irradiated onto the end face of the DFB laser chip. After being reflected by the DFB laser chip, it is converted into a specific polarization light so that it can be accurately measured by the optical power meter. The chip fixing and adjustment part includes a volume grating fixing fixture and a two-dimensional adjustment frame. The volume grating fixing fixture is set on the two-dimensional adjustment frame to fix the DFB laser chip. The two-dimensional adjustment frame can accurately adjust the front, back, left, right and pitch angle of the DFB laser chip and the incident surface. Power measurement part: The optical power meter is used to measure the optical power after being reflected by the DFB laser chip.

2. The system for detecting the reflectivity of the end face of a DFB laser chip according to claim 1, characterized in that: The beam expansion lens group expands the laser beam processed by the previous optical elements so that the laser beam can be evenly irradiated onto the end face of the DFB laser chip. The beam expansion lens group can be composed of multiple lenses and the beam expansion multiple can be adjusted according to actual needs.

3. The system for detecting the reflectivity of the end face of a DFB laser chip according to claim 1, wherein: The optical power meter is located below the polarization beam splitter prism, and its probe receives the reflected light signal and converts it into an electrical signal, which is then transmitted to the optical power meter display to display the optical power value.

4. The system for detecting the reflectivity of the end face of a DFB laser chip according to claim 1, wherein: The optical adjustment part also includes a zero-degree plane reflector, which is located between the beam expansion lens group and the fiber collimator grating fixing fixture, and is used to change the propagation direction of the light beam while keeping the optical properties of the light beam basically unchanged, so as to guide the light beam to the subsequent fiber collimator grating fixing fixture and the DFB laser chip to be tested.

5. The system for detecting the reflectivity of the end face of a DFB laser chip according to claim 4, characterized in that: The zero-degree plane reflector has multiple layers of high-reflectivity dielectric films.

6. The system for detecting the reflectivity of the end face of a DFB laser chip according to claim 5, characterized in that: The reflectivity of the zero-degree plane reflector in the range of 1300nm to 1600nm is ≥99.5%.

7. A detection method for a system for detecting the reflectivity of a DFB laser chip end facet according to any one of claims 1 to 6, characterized in that: The following steps are involved: 1) System construction and calibration: Optical path construction: According to the system components, install each optical component on the optical fixed bracket in sequence, and connect the optical fiber and other components; System alignment and leveling: Use visible light to align the entire optical path. Use a cursor card to observe the position of light after passing through each optical component. Adjust the position and angle of each component to ensure that the light can propagate along the predetermined optical path and accurately enter the end face of the DFB laser chip. Phase angle adjustment of half-wave plate and quarter-wave plate: adjust the angles of half-wave plate, polarization beam splitter and quarter-wave plate to ensure that the polarization state of light meets the detection requirements; 2) Transmission loss measurement: Place a zero-degree plane mirror coated with multiple layers of high-reflectivity dielectric film between the beam expander lens group and the DFB laser chip; place the power meter in the first position and measure the incident power on the zero-degree plane mirror. ; Place the power meter in the second position and measure the calibrated reflected power after reflection from the zero-degree plane mirror According to the formula Calculate optical path transmission loss ,in is the reflectivity of the zero-degree plane mirror; 3) DFB laser chip placement and preparation: Place the DFB laser chip on the fixture, then adjust the knobs of the two-dimensional adjustment frame to make the end face of the DFB laser chip perpendicular to the incident laser beam, and ensure that the laser can accurately enter the active area of ​​the chip. Before testing, clear the optical power meter display to eliminate the influence of background stray light on the measurement results; 4) Incident power measurement: Place the power meter in the first position, ensure that the laser beam accurately enters the active area of ​​the DFB laser chip, and measure the incident power incident to the DFB laser chip. ; 5) Reflected power measurement Place the power meter in the second position, make the laser incident on the end face of the DFB laser chip, and measure the power after being reflected by the DFB laser chip. ; 6) Reflectivity calculation According to the formula Calculate the reflectivity of the DFB laser chip.

8. The detection method of a system for detecting the reflectivity of a DFB laser chip end face according to claim 7, characterized in that: In step 1), the phase angle adjustment of the half-wave plate and the quarter-wave plate includes: turning on the broadband laser switch, adjusting the angles of the half-wave plate and the quarter-wave plate, first placing the optical power meter probe behind the polarization beam splitter prism, that is, in the first position, rotating the half-wave plate to make the light power passing through the polarization beam splitter prism moderate, then moving the probe to the second position where the light reflected by the DFB laser chip is reflected again by the polarization beam splitter prism in the output direction, and rotating the quarter-wave plate to maximize the reflected light power measured by the optical power meter. At this point, the angle of the quarter-wave plate is adjusted to the correct position.

9. The detection method of a system for detecting the reflectivity of a DFB laser chip end facet according to claim 7, characterized in that: In step 5), in order to improve the accuracy of the measurement, you can measure multiple times and record the data of each measurement, and then take the average of these measured values ​​as the reflected power. .

10. The detection method of a system for detecting the reflectivity of a DFB laser chip end facet according to claim 7, characterized in that: The reflectivity of the zero-degree plane mirror coated with multiple layers of high-reflectivity dielectric film is ≥99.5% in the range of 1300nm~1600nm.

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