BOX package semiconductor laser operable at ambient temperature up to 105 DEG C

Abstract

The application discloses a BOX packaged semiconductor laser which can work at an ambient temperature of 105 DEG C, comprising a laser package shell and a semiconductor refrigerator, a semiconductor laser chip, a heat sink, a thermistor, a backlight diode, a pedestal, a coupling lens, an optical isolator and an optical fiber assembly arranged in the laser package shell; the pedestal is arranged on the semiconductor refrigerator; the heat sink, the coupling lens and the optical isolator are arranged on the pedestal; the semiconductor laser chip, the thermistor and the backlight diode are arranged on the heat sink; the optical fiber assembly comprises an optical fiber pedestal, a head Kovar capillary and a bare optical fiber; the optical fiber pedestal is arranged on one side of the semiconductor refrigerator, the head Kovar capillary is sleeved on the head of the bare optical fiber, the head Kovar capillary is arranged on the optical fiber pedestal, and the tail of the bare optical fiber extends out of the laser package shell.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a BOX-packaged semiconductor laser that can operate at ambient temperatures up to 105°C. Background Technology

[0002] To ensure the performance of semiconductor lasers, the semiconductor laser chip needs to operate at a stable temperature. For example, the wavelength of a DFB semiconductor laser chip drifts with temperature, with a temperature drift coefficient of 0.1 nm / ℃. Furthermore, the threshold current and optical output power of the semiconductor laser chip at a given injection current also change with temperature. In most applications of semiconductor lasers, it is required to strictly control parameters such as the output wavelength within specific values, but the temperature of the environment in which the semiconductor laser operates varies greatly.

[0003] To meet application requirements, temperature control of the semiconductor laser chip is often necessary when using semiconductor lasers. The operating temperature range of a semiconductor laser varies depending on its application. These operating temperature ranges are generally categorized as follows: Commercial grade: 0℃~+70℃, Industrial grade: -40℃~+85℃, Automotive grade: -40℃~125℃, and Military grade: -55℃~+125℃. Previously, semiconductor lasers were mostly used in fiber optic communication, where the applicable operating temperature range was limited to commercial and industrial grades, meaning the maximum operating temperature was 85℃. However, in recent years, the application of semiconductor lasers has expanded to areas such as laser sensors and lidar. Therefore, due to application needs, the operating temperature requirements for semiconductor lasers are no longer limited to commercial and industrial grades. Automotive lidar is a representative example.

[0004] Automotive LiDAR is a radar system that uses lasers as a detection method, emitting beams to detect the position, speed, and other characteristics of targets. LiDAR acts like the "eyes" of a car, possessing powerful and complex information perception and processing capabilities. It helps the car perceive the road environment, plan its driving route, and control the vehicle to reach predetermined targets. The core component of automotive LiDAR is the laser, with semiconductor lasers being the most commonly used. Automotive LiDAR requires precise control over the output wavelength, linewidth, and power of the semiconductor lasers it uses; in other words, it requires precise temperature control of the semiconductor laser chip.

[0005] Although current automotive-grade requirements specify an operating environment of -40℃ to 85℃ for automotive-grade LiDAR, the temperature inside the sealed housing of the LiDAR will rise by at least 20℃ at an ambient temperature of 85℃. Therefore, the actual casing temperature of the semiconductor laser used in automotive LiDAR can reach 105℃. Currently, there is no semiconductor laser that can operate at an ambient temperature as high as 105℃. Summary of the Invention

[0006] Purpose of the invention: To address the problem that existing semiconductor lasers cannot operate in environments with ambient temperatures of 105°C or higher, this invention proposes a BOX-packaged semiconductor laser that can operate at ambient temperatures up to 105°C.

[0007] Technical solution: A BOX-packaged semiconductor laser that can operate at ambient temperatures up to 105°C, comprising: a laser package housing and a semiconductor cooler, a semiconductor laser chip, a heat sink, a thermistor, a backlight diode, a base, a coupling lens, an optical isolator, and an optical fiber assembly disposed within the laser package housing;

[0008] The base is mounted on the semiconductor cooler; the heat sink, coupling lens, and optical isolator are all mounted on the base; the semiconductor laser chip, thermistor, and backlight diode are all mounted on the heat sink.

[0009] The optical fiber assembly includes an optical fiber base, a Kovar head capillary, and a bare optical fiber. The optical fiber base is disposed on one side of the semiconductor cooler. The Kovar head capillary is fitted over the head of the bare optical fiber and is disposed on the optical fiber base. The tail of the bare optical fiber extends outward from the laser encapsulation shell.

[0010] Furthermore, the semiconductor cooler is a two-stage semiconductor cooler.

[0011] Furthermore, the secondary semiconductor cooler includes a cold surface, a hot surface, an intermediate surface, and multiple thermoelectric pairs. The intermediate surface is disposed between the cold surface and the hot surface, and the multiple thermoelectric pairs are disposed between the cold surface and the intermediate surface, and between the hot surface and the intermediate surface.

[0012] Furthermore, 18 thermocouples are arranged between the cold side and the middle side, and 24 thermocouples are arranged between the hot side and the middle side; the column height of each thermocouple is 0.41mm.

[0013] Furthermore, the laser packaging shell is a BOX packaging shell, which includes a base plate and a frame disposed on the upper part of the base plate. A sleeve is disposed on the frame, and the optical fiber assembly passes through the sleeve and is disposed inside the laser packaging shell. The thickness of the base plate is greater than or equal to 3mm, and the base plate is fixed to an external heat sink through a positioning threaded hole, which is located in the middle of the base plate.

[0014] Furthermore, the tail of the bare optical fiber is sealed to the laser packaging shell through a tail Kovar capillary, so that the tail of the bare optical fiber extends outward from the laser packaging shell. The tail of the bare optical fiber is sealed and fused to the bare optical fiber using a low melting point glass material.

[0015] This invention discloses a BOX-packaged semiconductor laser that can operate at ambient temperatures up to 105°C, comprising: a laser package housing and a semiconductor cooler, a semiconductor laser chip, a heat sink, a thermistor, a backlight diode, a base, a coupling lens, an optical isolator, and an optical fiber assembly disposed within the laser package housing.

[0016] The base is mounted on the semiconductor cooler; the heat sink, coupling lens, and optical isolator are all mounted on the base; the semiconductor laser chip, thermistor, and backlight diode are all mounted on the heat sink.

[0017] The optical fiber assembly includes a Kovar head capillary and a bare optical fiber; the Kovar head capillary is fitted over the head of the bare optical fiber and is mounted on a base, with the tail of the bare optical fiber extending outwards to form a laser encapsulation shell.

[0018] Furthermore, the semiconductor cooler is a two-stage semiconductor cooler, including a cold surface, a hot surface, an intermediate surface, and multiple thermocouples. The intermediate surface is disposed between the cold surface and the hot surface. There are 18 thermocouples between the cold surface and the intermediate surface, and 24 thermocouples between the hot surface and the intermediate surface. The column height of each thermocouple is 0.41 mm.

[0019] Furthermore, the laser packaging shell is a BOX packaging shell, which includes a base plate and a frame disposed on the upper part of the base plate. A sleeve is disposed on the frame, and the optical fiber assembly passes through the sleeve and is disposed inside the laser packaging shell. The thickness of the base plate is greater than or equal to 3mm, and the base plate is fixed to an external heat sink through a positioning threaded hole, which is located in the middle of the base plate.

[0020] Furthermore, the tail of the bare optical fiber is sealed to the laser packaging shell through a tail Kovar capillary, so that the tail of the bare optical fiber extends outward from the laser packaging shell. The tail of the bare optical fiber is sealed and fused to the bare optical fiber using a low melting point glass material.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0022] (1) The semiconductor laser obtained by the present invention can operate at an ambient temperature of 105°C, and under stable injection current conditions, the operating temperature of the semiconductor laser chip is stable, thereby achieving stable wavelength and power output, while limiting the power consumption of the semiconductor laser cooler to a reasonable and acceptable range.

[0023] (2) The present invention overcomes the problem of bending and deformation of the bottom plate of the BOX packaging shell at high temperature by thickening the bottom plate of the BOX packaging shell and removing the four feet with positioning screw holes at the front and rear of the packaging shell, and by opening a threaded hole in the middle of the thickened bottom plate to achieve positioning of the BOX packaging shell.

[0024] (3) The present invention reduces the heat conduction of the optical fiber assembly into the packaging shell by adopting an assembly configuration in which the optical fiber assembly extends into the packaging shell and by using a method of sealing the Kovar capillary to the optical fiber in the optical fiber assembly with low melting point glass.

[0025] (4) By treating the coupling head of the optical fiber assembly and the bracket and optical fiber base used to fix this part as independent parts without cooling, the present invention can reduce the passive heat load of the semiconductor laser in the high temperature environment. This configuration is suitable when the active heat load of the semiconductor laser is large (such as when the semiconductor laser needs to output high power).

[0026] (5) The present invention mounts all components except the TEC inside the package housing, including the Kovar capillary at the head of the optical fiber assembly and its fixing bracket, onto a narrow gold-plated tungsten copper base, which is then eutectic bonded to the TEC, which also has a narrow dimension. This can appropriately reduce the passive heat load of the semiconductor laser and help reduce the tracking error of the output power of the coupled semiconductor laser in a high-temperature environment.

[0027] (6) The bare lens and optical isolator of the present invention are fixed with adhesive, which can avoid introducing additional passive heat load in high temperature environment. Attached Figure Description

[0028] Figure 1 This is a side view of a secondary semiconductor cooler;

[0029] Figure 2 Performance curves for a secondary semiconductor cooler;

[0030] Figure 3 This is a schematic diagram of the packaged outer shell after deformation;

[0031] Figure 4 A schematic diagram showing the thickening of the base plate of the encapsulation housing and the relocation of the positioning threaded holes to the middle of the base plate;

[0032] Figure 5 This is a diagram illustrating the structure of an optical fiber assembly.

[0033] Figure 6 This is a package assembly diagram of the semiconductor laser in Example 1;

[0034] Figure 7 This is a packaged assembly diagram of the semiconductor laser in Example 2. Detailed Implementation

[0035] The technical solution of the present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0036] Example 1:

[0037] Assuming the operating environment temperature of the semiconductor laser is -40℃ to 105℃, the operating temperature of the semiconductor laser chip is determined from this ambient temperature. Since the cooling efficiency of the cooler is lower than its heating efficiency, the operating temperature of the semiconductor laser chip can be set slightly higher than room temperature. Considering the characteristics of the semiconductor laser chip itself, setting its operating temperature between 35℃ and 40℃ is reasonable. When the semiconductor laser chip operates within this temperature range, the threshold current will not rise too high, and the chip is less prone to degradation over long-term operation. When the operating temperature of the semiconductor laser chip is 35℃, and the temperature difference DT between the semiconductor laser chip and the laser casing at the highest ambient temperature is 70℃, this embodiment first designs a reasonable semiconductor cooler (TEC) and a heat load consisting of the semiconductor laser chip, chip heat sink, base, and other components. This ensures that, with a reasonable TEC power consumption, when the laser package casing is at an ambient temperature of 105℃, the TEC can stably control the temperature of the semiconductor laser chip at the set operating temperature, such as 35℃. Secondly, this embodiment optimizes the structure of the laser package housing and the coupling system of the semiconductor laser to overcome the degradation effect of optical coupling efficiency caused by the deformation of the laser housing due to thermal expansion at an ambient temperature of 105°C.

[0038] The structure of a thermoelectric cooler (TEC) determines its maximum achievable temperature difference (DT). A single-stage TEC can achieve a maximum temperature difference of approximately 70°C, but at this point, it can no longer pump heat. A two-stage TEC can achieve a maximum temperature difference (DT) of approximately 85°C-95°C. Therefore, when a temperature difference of 70°C is required, a two-stage TEC can still pump heat and operate normally. Figure 1A side view of a secondary thermoelectric cooler is shown, comprising a cold surface 11, a hot surface 12, an intermediate surface 13, and thermocouples 14. The cold surface 11 is the top surface of the upper stage of the secondary thermoelectric cooler, made of a ceramic sheet with dimensions of 4.7 mm (L) * 4.4 mm (W). The hot surface 12 is the bottom surface of the lower stage of the secondary thermoelectric cooler, made of a ceramic sheet with dimensions of 5.5 mm (L) * 4.4 mm (W). The intermediate surface 13 is located between the cold surface 11 and the hot surface 12, connecting the upper and lower stages of the secondary thermoelectric cooler. Eighteen thermocouples 14 are arranged between the cold surface 11 and the intermediate surface 13, and 24 thermocouples are arranged between the intermediate surface 13 and the hot surface 12. The height of each thermocouple post is 0.41 mm, and the total height of the secondary thermoelectric cooler is 1.85 mm. The temperature difference between the cold surface 11 and the hot surface 12 is DT. Based on this design model, calculations show that when the semiconductor laser's package temperature is 108℃, the temperature difference DT = 70℃, and the heat load Qc is 0.35W, the secondary thermoelectric cooler current I = 0.6A, and the corresponding secondary thermoelectric cooler voltage Vin is approximately 2.3V. When the heat load Qc is 0.5W, the secondary thermoelectric cooler current I = 0.7A, and the corresponding secondary thermoelectric cooler voltage Vin is approximately 2.5V. Figure 2 Figure (a) shows the calculated results of the heat load Qc as a function of the secondary semiconductor cooler current I when the temperature difference DT = 70℃. Figure 2 (b) shows the calculated results of the voltage Vin of the secondary thermoelectric cooler as a function of the current I of the secondary thermoelectric cooler when the temperature difference DT = 70°C. When the secondary thermoelectric cooler current I = 0.6A, the coefficient of performance (COP) of the secondary thermoelectric cooler is 0.25; when the secondary thermoelectric cooler current I = 0.7A, the COP of the secondary thermoelectric cooler is slightly higher than 0.25, both near the peak COP. When the heat load Qc is approximately 0.35W, the power consumption Pin of the secondary thermoelectric cooler is 1.38W, and when the heat load Qc is approximately 0.5W, the power consumption Pin of the secondary thermoelectric cooler is 1.75W. These power consumptions are acceptable. This indicates that as long as the total heat load of the semiconductor laser is controlled below 0.5W, the temperature of the semiconductor laser chip can be stably controlled at 38°C (or 35°C, Th = 105°C), thus verifying that the semiconductor laser of this embodiment can stably operate at an ambient temperature of 105°C.

[0039] The total thermal load of a semiconductor laser consists of two parts: active thermal load and passive thermal load. The active thermal load is determined by the operating current and voltage of the semiconductor laser chip. When a 1550nm semiconductor laser is used in an automotive lidar system, the minimum required output power, converted to CW output, is equivalent to 4-5mW. For a 1550nm semiconductor laser, the injection current required for this output power does not exceed 60mA. If the laser chip voltage is approximately 1.6V, then the active thermal load of the semiconductor laser is approximately 0.1W. Therefore, the total thermal load of the semiconductor laser mainly comes from the passive thermal load. To reduce the total thermal load of the semiconductor laser, the passive thermal load should be reduced. The passive thermal load of a semiconductor laser in high-temperature environments is closely related to the dimensions and configuration of the components within the semiconductor laser housing.

[0040] Considering the required dimensions of the secondary thermoelectric cooler and the large heat output Qh (Qh = Qc + Pin) from the hot end (Th end) of the secondary thermoelectric cooler, the semiconductor laser should use a large BOX package with good heat dissipation in this case, with a butterfly package being a readily available option. To achieve a high thermal conductivity, the base plate of the butterfly package is made of tungsten copper, while the frame above the base plate, which needs to be sealed to ceramic or glass materials, uses Kovar alloy, whose coefficient of thermal expansion is close to that of ceramics or glass. Since the coefficient of thermal expansion of tungsten copper is greater than that of Kovar alloy, at high temperatures, the linear expansion of the length and width of the base plate of the butterfly package will be greater than the corresponding linear expansion of the frame. Therefore, the bottom of the frame will be widened due to the expansion of the base plate, causing the four sides of the frame, especially the front and back, to tilt and deform. The base plate of the butterfly package, under the influence of the shear force in the opposite direction of the frame, will also bend and deform due to its limited extension. When the base plate is fixed to the heat sink through the holes of the four feet at the front and back of the butterfly-shaped package base plate, the thermal expansion of the butterfly-shaped package base plate is greatly restricted, and its flexural deformation will be greater. Figure 3 A schematic diagram of the downward flexing deformation of the base plate of the butterfly-shaped package is shown (upward flexing deformation may also occur depending on the degree of obstruction to the expansion of the base plate). For clarity, Figure 3 The bending deformation of the butterfly-shaped package shell is exaggerated. The Kovar alloy frame 31 is mounted on the base plate 34 of the butterfly-shaped package shell, and a window and its sleeve 35 are provided on the front end face 32 of the Kovar alloy frame 31. Figure 3 The number 33 in the figure corresponds to the rear end face of the Kovar alloy frame 31.

[0041] To overcome the deformation of the frame and base plate under high temperatures, this embodiment removes the four feet of the base plate to avoid interference with the linear expansion of the base plate after the positioning screws are tightened, thus preventing the base plate from flexing. Furthermore, as is known from material and structural mechanics, the flexural deformation of sheet metal decreases with increasing sheet thickness. Increasing the thickness of the base plate can reduce the flexural deformation caused by the counter-shear force generated when the frame is stretched by the expanding base plate, which inhibits the linear expansion of the base plate. The counter-shear force of the frame has little effect on the flexural deformation of the base plate; after thickening the base plate, if the thickness is greater than or equal to 3mm, calculations show that its effect on the deformation of the base plate is negligible. In this embodiment, after thickening the base plate, the positioning screw holes of the outer shell are replaced with positioning threaded holes 41 and moved to the middle of the base plate. For the specific structure, please refer to [reference needed]. Figure 4 The center of the base plate exhibits minimal deformation. Furthermore, thermal grease is typically applied between the base plate and the heat sink beneath it. Therefore, securing the housing to the heat sink via screws from the top minimizes additional stress. The difference in thermal expansion coefficients between the tungsten copper base plate and the Kovar alloy frame, causing slight tilting of the frame's front and rear, is inherently unavoidable. However, as long as the base plate remains undeformed, this tilting deformation does not affect the internal structural configuration of the housing. However, if a window-type housing is used with fiber optic coupling externally, the efficiency of fiber coupling based on the window will significantly deteriorate at high temperatures due to the window tilting with the frame. To avoid the disadvantages of the window-type housing, this embodiment employs an internal encapsulation configuration where the fiber optic cable is inserted inside the housing for fiber coupling, thus mitigating the impact of frame surface tilting deformation on optical coupling at high temperatures. In addition to the semiconductor laser chip, the housing of the semiconductor laser includes: a heat sink for the laser chip, a thermistor and a backlight diode on the heat sink, a gold-plated tungsten copper base supporting the heat sink, a lens for coupling the laser from the chip to the optical fiber (considering single-lens coupling), an optical isolator, and an optical fiber assembly extending into the housing through a sleeve at the front end of the frame. Considering the small spot size of the chip, to ensure the accuracy of the lens position and the temperature characteristics of the optical isolator, this embodiment mounts the lens, optical isolator, and chip heat sink on the same gold-plated tungsten copper base.

[0042] When an optical fiber passes through a sleeve on the front end of the encapsulation housing and enters the housing, the traditional method to achieve hermetic sealing is to metallize a section of bare optical fiber, then attach a gold-plated Kovar capillary tube to the fiber head and the portion of the fiber within the sleeve, and solder the gold-plated capillary tube to the fiber. The optical fiber with two fixed Kovar capillary tubes forms an optical fiber assembly. After optical coupling of the optical fiber assembly is completed, the gold-plated capillary tube in the housing sleeve is soldered to the sleeve to achieve a hermetic seal. Because the optical fiber assembly is fixed to the sleeve with solder, the fiber head used for coupling is connected to the metallized optical fiber itself through high temperature.

[0043] This embodiment addresses the issue of heat conduction from the fiber optic coupling section by separating the fiber optic assembly extending into the housing. Specifically, the head of the fiber optic assembly, the support that fixes it, the Kovar base, and the gold-plated base containing the heat sink (which also houses the laser chip, thermistor, and backlight diode), the coupling lens, and the optical isolator are separated and not cooled. This is because the deformation of the housing base plate at high temperatures is negligible after removing the four positioning feet of the housing and thickening the base plate.

[0044] Figure 6 The diagram shows the internal package assembly of a semiconductor laser, which includes: a secondary semiconductor cooler 61, a gold-plated tungsten copper base 62 disposed on the secondary semiconductor cooler 61, a heat sink 63 disposed on the gold-plated tungsten copper base 62, a semiconductor laser chip 64 disposed on the heat sink 63, a thermistor 65 disposed on the heat sink 63, a backlight diode 66 disposed on the heat sink 63, a coupling lens 67 disposed on the gold-plated tungsten copper base 62, an optical isolator 68 disposed on the gold-plated tungsten copper base 62, a Kovar base 69 disposed next to the secondary semiconductor cooler 61, a capillary tube 510 at the head of the coupling fiber assembly, a saddle support 610 for fixing the capillary tube, and a bare optical fiber 512.

[0045] Among them, the semiconductor laser chip 64, the thermistor 65, and the backlight diode 66 are all fixed to the heat sink 63 by eutectic bonding, and the heat sink 63 is also fixed to the gold-plated tungsten copper base 62 by eutectic bonding.

[0046] The coupling lens 67 is the coupling lens from the semiconductor laser chip to the optical fiber. It is a bare lens with a diameter of 1mm*1mm*0.62mm, and its linear dimensions are very small, contributing very little to the passive heat load. The heat sink 63, semiconductor laser chip 64, thermistor 65, and backlight diode 66 are all components with very small linear dimensions, and their contribution to the passive heat load is also very small. In this configuration, the passive heat load mainly comes from the gold-plated tungsten copper base 62 and the optical isolator 68. Both the coupling lens 67 and the optical isolator 68 are fixed to the gold-plated tungsten copper base 62 with adhesive, which eliminates the additional passive heat load caused by the metal bracket required for YAG laser welding.

[0047] The coupled fiber optic assembly includes a Kovar head capillary 510, a saddle support 610 for fixing the Kovar head capillary 510, and a bare fiber portion 512. The Kovar head capillary 510 is fixed to the Kovar base 69 by the saddle support 610. The Kovar base 69, the Kovar head capillary 510, the saddle support 610, and the bare fiber portion 512 are not mounted on the secondary semiconductor cooler 61, and therefore do not contribute to the passive heat load.

[0048] Both the secondary semiconductor cooler 61 and the Kovar base 69 are fixed to a thickened packaging shell base plate. The thickness of the packaging shell base plate is greater than or equal to 3mm, and it is positioned by a threaded hole in the middle of the base plate. Therefore, the deformation of the base plate is negligible at an ambient temperature of 105℃. In this embodiment, the gold-plated tungsten copper base 62 is 4.5mm long, 3.7mm wide, and 2.15mm high at its highest point. In order to support the coupling lens 67 and the optical isolator 68, the upper part of the gold-plated tungsten copper base 62 is processed into two steps.

[0049] In this package configuration, when the cold end of the secondary semiconductor cooler 61 is 35°C and the ambient temperature is 105°C (DT = 70°C), the total passive heat load of the semiconductor laser can be calculated to be 0.19W. Therefore, when the operating current of the secondary semiconductor cooler 61 is 0.6A, the permissible active heat load can reach 0.16W. If the voltage of the semiconductor laser chip is 1.6V, the current of the semiconductor laser chip can reach 100mA in this case. Under such a high current, assuming the optical coupling efficiency of the semiconductor laser is 50% (the coupling efficiency of a typical BOX-packaged semiconductor laser can reach over 70%), the output optical power of the semiconductor laser will be greater than 10mW. If the operating current of the secondary semiconductor cooler 61 is increased to 0.7A, this embodiment is more suitable for high-power laser output, i.e., packaging of semiconductor lasers with an output power of around 30mW.

[0050] Example 2:

[0051] The difference between this embodiment and Embodiment 1 is that in this embodiment, the head of the coupled fiber optic assembly and the support for fixing this part are integrated onto a gold-plated tungsten copper base. The passive thermal load of the semiconductor laser is reduced by adjusting the 2D linear shape of the gold-plated tungsten copper base and the secondary semiconductor cooler, and by reducing the conductive heat of the fiber optic assembly. Adjusting the 2D linear shape of the gold-plated tungsten copper base and the secondary semiconductor cooler involves designing the gold-plated tungsten copper base into a narrow, elongated shape to accommodate the fiber optic assembly head and the support for fixing this part, while maintaining an overall linear shape close to the overall linear shape of the gold-plated tungsten copper base without the fiber optic assembly head and the support for fixing this part. Furthermore, while keeping the secondary structure of the semiconductor cooler, the number of upper and lower thermocouples, and the height of the thermocouple pillars unchanged, the secondary semiconductor cooler is designed into a correspondingly narrow, elongated shape. This 2D linear adjustment of the secondary semiconductor cooler has virtually no impact on its original characteristics.

[0052] To reduce the conductive heat of the optical fiber assembly, in this embodiment, the optical fiber inserted into the front sleeve of the outer shell is hermetically fused to the optical fiber using a low-melting-point glass material with a Kovar capillary to avoid metallization of the optical fiber. Since quartz has a very low thermal conductivity, the heat flow conducted from high-temperature areas through the optical fiber can be significantly reduced. Figure 5The structure of the optical fiber assembly is shown. In the figure, the Kovar capillary 510 at the head of the optical fiber assembly is not gold-plated, while the tail Kovar capillary 513, which is sealed to the outer casing, is gold-plated. The non-metallized bare optical fiber portion 512 is fixed to the Kovar capillary by a low-melting-point glass ring 516. The bare optical fiber head 514 is ground to a 6° angle and positioned at the head of the optical fiber assembly. According to numerical calculations, when the length of the bare optical fiber between the two Kovar capillary tubes is 5 mm, DT = 70°C, and the outer casing temperature is 105°C, the heat flowing into the optical fiber head from the encapsulation casing does not exceed 0.4 mW.

[0053] Specifically, Figure 7 The diagram shows the internal package assembly of a semiconductor laser, which includes: a secondary semiconductor cooler 61, a gold-plated tungsten copper substrate 62 disposed on the secondary semiconductor cooler 61, a heat sink 63 disposed on the gold-plated tungsten copper substrate 62, a semiconductor laser chip 64 disposed on the heat sink 63, a thermistor 65 disposed on the heat sink 63, a backlight diode 66 disposed on the heat sink 63, a coupling lens 67 disposed on the gold-plated tungsten copper substrate 62, an optical isolator 68 disposed on the gold-plated tungsten copper substrate 62, a U-shaped bracket 611 disposed on the gold-plated tungsten copper substrate 62, and a bare optical fiber 512.

[0054] Among them, the semiconductor laser chip 64, the thermistor 65, and the backlight diode 66 are all fixed to the heat sink 63 by eutectic bonding, and the heat sink 63 is also fixed to the gold-plated tungsten copper base 62 by eutectic bonding.

[0055] The coupling lens 67 is the coupling lens from the semiconductor laser chip to the optical fiber. It is a bare lens with a diameter of 1mm*1mm*0.62mm, and its linear dimensions are very small, contributing very little to the passive heat load. The heat sink 63, semiconductor laser chip 64, thermistor 65, and backlight diode 66 are all components with very small linear dimensions, contributing very little to the passive heat load. In this configuration, the passive heat load mainly comes from the gold-plated tungsten copper base 62, the coupling lens 67, the optical isolator 68, the Kovar capillary tube 510 at the head of the coupled optical fiber assembly, and its U-shaped bracket 611. The coupling lens 67 and the optical isolator 68 are both fixed to the gold-plated tungsten copper base 62 with adhesive, which eliminates the additional passive heat load caused by the metal bracket required for YAG laser welding.

[0056] The coupled optical fiber assembly includes a Kovar head capillary 510 and a bare optical fiber portion 512; the Kovar head capillary 510 is fixed on a gold-plated tungsten copper base 62 by a U-shaped bracket 611.

[0057] In this embodiment, compared to Embodiment 1, the gold-plated tungsten copper base 62 has an additional Kovar head capillary tube 510 and a U-shaped bracket 611 mounted on it. Therefore, the gold-plated tungsten copper base 62 must be longer in this embodiment compared to Embodiment 1. While lengthening, to reduce the passive heat load, the width of the gold-plated tungsten copper base 62 is reduced, and correspondingly, the length and width of the secondary thermoelectric cooler 61 are also adjusted. The adjusted dimensions of the top surface of the secondary thermoelectric cooler 61 are 6.5mm (L) * 3.18mm (W). However, the first stage of the bottom layer of the secondary thermoelectric cooler 61 still has 24 thermocouples, and the second stage has 18 thermocouples. The height of these thermocouples remains unchanged, so the height of the secondary thermoelectric cooler 61 is still 1.85mm. Under this design, the performance of the secondary thermoelectric cooler 61 in this embodiment is basically the same as that in Embodiment 1. The dimensions of the bottom surface of the gold-plated tungsten copper base 62 are basically the same as those of the cold surface of the secondary semiconductor cooler 61, but the length and width are slightly reduced by 0.1mm-0.2mm. The upper part of the gold-plated tungsten copper base 62 is also processed into a stepped shape, and the height of the rest, except for the part that mounts the head Kovar capillary tube, is the same as in Embodiment 1. Since the width of the gold-plated tungsten copper base 62 is smaller than that of the gold-plated tungsten copper base in Embodiment 1, the overall effective dimension of the gold-plated tungsten copper base 62 that determines the passive heat load is not increased much compared to the gold-plated tungsten copper base 62 in Embodiment 1. A U-shaped bracket is used in this embodiment because the dimension of the U-shaped bracket is smaller than that of the saddle bracket, and correspondingly, its contribution to the passive heat load is also smaller. In addition, it is also suitable for the long and narrow gold-plated tungsten copper base 62.

[0058] In this embodiment, considering all components on the secondary semiconductor cooler 61, including the passive heat load caused by the heat introduced by the bonding wires and the conduction heat of the bare optical fiber, the total passive heat load of the semiconductor laser can be calculated to be 0.25W when the cold end of the secondary semiconductor cooler 61 is 35°C and the ambient temperature is 105°C (DT = 70°C). Although the total passive heat load of this embodiment is slightly higher than that of Embodiment 1, the optical coupling stability is better than that of Embodiment 1 because the optical fiber coupling part is also mounted on the secondary semiconductor cooler 61 and cooled together. The tracking error of the laser output power at high temperatures is smaller than that of Embodiment 1. When the operating current of the secondary semiconductor cooler 61 is 0.6A, the allowable active heat load can reach 0.10W. Assuming the voltage of the semiconductor laser chip is 1.6V, the current of the semiconductor laser chip reaches about 62mA. At this current, the output optical power of the semiconductor laser in this embodiment with a 50% coupling efficiency can also reach about 5-6mW.

[0059] This embodiment uses a specially designed secondary semiconductor cooler as the cooler for the semiconductor laser, providing sufficient temperature difference DT between the hot and cold ends of the TEC, and cooling capacity Qc under this DT. This embodiment overcomes the deformation of the shell structure at high temperatures through an improved BOX package shell structure, and through a reasonable configuration of the internal components of the package shell to suppress passive heat load, the semiconductor laser can operate normally in a high-temperature environment of 105°C.

Claims

1. A BOX-packaged semiconductor laser capable of operating at ambient temperatures up to 105°C, characterized in that: include: The laser package housing and the semiconductor cooler, semiconductor laser chip, heat sink, thermistor, backlight diode, base, coupling lens, optical isolator and fiber optic assembly disposed within the laser package housing; The base is mounted on the semiconductor cooler; the heat sink, coupling lens, and optical isolator are all mounted on the base; the semiconductor laser chip, thermistor, and backlight diode are all mounted on the heat sink. The optical fiber assembly includes an optical fiber base, a Kovar head capillary, and a bare optical fiber; the optical fiber base is disposed on one side of the semiconductor cooler, the Kovar head capillary is sleeved on the head of the bare optical fiber and the Kovar head capillary is disposed on the optical fiber base, and the tail of the bare optical fiber extends outward from the laser encapsulation shell. The laser packaging shell is a BOX packaging shell, which includes a base plate and a frame set on the upper part of the base plate. A sleeve is set on the frame. The optical fiber assembly passes through the sleeve and is set inside the laser packaging shell. The thickness of the base plate is greater than or equal to 3mm. The base plate is fixed to an external heat sink through a positioning threaded hole, which is located in the middle of the base plate. The tail of the bare optical fiber is sealed to the laser package shell through a tail Kovar capillary tube, so that the tail of the bare optical fiber extends outward from the laser package shell; the tail of the bare optical fiber is sealed by welding the tail Kovar capillary tube to the bare optical fiber using a low melting point glass material. The semiconductor cooler is a two-stage semiconductor cooler, including a cold surface, a hot surface, an intermediate surface, and multiple thermocouples. The intermediate surface is located between the cold surface and the hot surface. There are 18 thermocouples between the cold surface and the intermediate surface, and 24 thermocouples between the hot surface and the intermediate surface. The column height of each thermocouple is 0.41 mm.

2. A BOX-packaged semiconductor laser capable of operating at ambient temperatures up to 105°C, characterized in that: include: The laser package housing and the semiconductor cooler, semiconductor laser chip, heat sink, thermistor, backlight diode, base, coupling lens, optical isolator and fiber optic assembly disposed within the laser package housing; The base is mounted on the semiconductor cooler; the heat sink, coupling lens, and optical isolator are all mounted on the base; the semiconductor laser chip, thermistor, and backlight diode are all mounted on the heat sink. The optical fiber assembly includes a Kovar head capillary and a bare optical fiber; the Kovar head capillary is fitted over the head of the bare optical fiber and is mounted on a base, and the tail of the bare optical fiber extends outward from the laser encapsulation shell. The laser packaging shell is a BOX packaging shell, which includes a base plate and a frame set on the upper part of the base plate. A sleeve is set on the frame. The optical fiber assembly passes through the sleeve and is set inside the laser packaging shell. The thickness of the base plate is greater than or equal to 3mm. The base plate is fixed to an external heat sink through a positioning threaded hole, which is located in the middle of the base plate. The tail of the bare optical fiber is sealed to the laser package shell through a tail Kovar capillary tube, so that the tail of the bare optical fiber extends outward from the laser package shell. The tail of the bare optical fiber is sealed by welding the tail Kovar capillary tube to the bare optical fiber using a low melting point glass material. The semiconductor cooler is a two-stage semiconductor cooler, including a cold surface, a hot surface, an intermediate surface, and multiple thermocouples. The intermediate surface is located between the cold surface and the hot surface. There are 18 thermocouples between the cold surface and the intermediate surface, and 24 thermocouples between the hot surface and the intermediate surface. The column height of each thermocouple is 0.41 mm.

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