Laser and method of manufacturing a laser

Abstract

This invention discloses a laser and a method for fabricating the laser. The laser includes a distributed feedback laser and a filter. The distributed feedback laser comprises an active layer, a coupling layer, and a passive layer. The light field generated in the active layer is coupled into the passive layer through the coupling layer for transmission and then enters the filter. The filter includes a straight waveguide and a ring waveguide, which are made of an extended passive layer. The filter shapes the signal from the distributed feedback laser. The distributed feedback laser and filter can be integrated without docking growth and can effectively reduce the chirp problem when the distributed feedback laser is directly modulated. It has advantages such as low chirp, high extinction ratio, low power consumption, and simple fabrication. It can replace electroabsorption modulated lasers for long-distance transmission, and the fabrication process is simpler, the cost is lower, the structural design is more reasonable, and the application range is wider.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic technology, and in particular to a laser, a method for preparing a laser, an optical communication device, and an optical network system. Background Technology

[0002] In recent years, with the rapid development of internet services, cost, size, and power consumption have become constraints on the development of optical devices towards higher bandwidth, higher speed, and longer distance. Lasers, as core components in communication network optical devices, are generally divided into directly modulated lasers and externally modulated lasers. Distributed Feedback Lasers (DFBs) are a type of directly modulated laser, widely used in short-to-medium distance (below 10km) transmission due to their low cost, small size, high speed, and high linearity. However, during direct modulation, thermal effects and changes in injection current alter the effective refractive index of the laser's active region, causing wavelength drift and chirp. This is one of the limiting factors for the application of DFBs in fiber optic transmission links exceeding 10km. Correspondingly, Electroabsorption Modulated Lasers (EMLs) are a typical type of externally modulated laser, integrating a DFB with an Electroabsorption Modulator (EAM) using a butt-joint growth technique, with the electrical signal applied to the EAM for external modulation. EML has advantages such as high speed, high extinction ratio and low chirp, and can be used for long-distance transmission over 40km. However, EML is difficult to manufacture, and its power consumption and cost are also high, which limits its large-scale use in optical communication networks. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a laser, a method for fabricating the laser, an optical communication device, and an optical network system, which can effectively reduce the chirp problem during DFB direct modulation, and has advantages such as high extinction ratio and low power consumption, making it more practical and reliable.

[0004] In a first aspect, embodiments of the present invention provide a laser, comprising:

[0005] A distributed feedback laser includes an active layer, a coupling layer, and a passive layer. The coupling layer is located between the active layer and the passive layer and is used to couple the optical field generated in the active layer to the passive layer for transmission.

[0006] A filter comprising a straight waveguide and a ring waveguide, wherein optical field coupling exists between the straight waveguide and the ring waveguide, and the passive layer extends to form the straight waveguide so that the filter is monolithically integrated with the distributed feedback laser;

[0007] The substrate on which the distributed feedback laser and the filter are formed are located.

[0008] Secondly, the present invention also provides a method for fabricating a laser, comprising:

[0009] A passive layer, a coupling layer, and an active layer are sequentially grown on the substrate.

[0010] The active layer and above are partially removed to form a filter region;

[0011] The passive layer and the coupling layer in the filter region are etched to form a straight waveguide and a ring waveguide, so that optical field coupling can be performed between the straight waveguide and the ring waveguide.

[0012] Thirdly, the present invention also provides an optical communication device, including the laser described in the first aspect embodiment above.

[0013] Fourthly, the present invention also provides an optical network system, including an optical line terminal and a plurality of optical network units, wherein the optical line terminal is connected to the plurality of optical network units through an optical distribution network; wherein the optical line terminal and / or the optical network units include a laser as described in the first aspect embodiment above.

[0014] The laser, laser fabrication method, optical communication equipment, and optical network system provided in this invention include a distributed feedback laser and a filter. Compared to a traditional DFB (Diverterless Laser), the distributed feedback laser in this invention adds a passive layer and a coupling layer. The passive layer is extended to form a straight waveguide for the filter, allowing the distributed feedback laser and filter to be monolithically integrated. The optical field generated in the active layer is coupled to the passive layer for transmission through the coupling layer. No butt joint growth is required between the distributed feedback laser and the filter, effectively reducing the chirp problem during direct DFB modulation. This results in advantages such as low chirp, high extinction ratio, low power consumption, and simple fabrication. The filter reshapes the output optical field of the distributed feedback laser to achieve low chirp and a high extinction ratio, enabling it to replace EML (Electronic Motion Filter) lasers for long-distance transmission. It offers lower power consumption than EML lasers and eliminates the need for complex butt-joint growth techniques, resulting in a simpler fabrication process, lower cost, more rational structural design, and greater practicality and reliability. The laser is suitable for optical communication equipment and optical network systems, with a wider range of applications.

[0015] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0017] Figure 1 This is a longitudinal cross-sectional structural diagram of a laser according to an embodiment of the present invention;

[0018] Figure 2 This is a top view of the laser structure according to the first embodiment of the present invention;

[0019] Figure 3 This is a top view of the laser structure according to the second embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram of a distributed feedback laser structure according to an embodiment of the present invention;

[0021] Figure 5 This is a schematic diagram illustrating the principle of achieving low chirp and high extinction ratio in a laser according to an embodiment of the present invention;

[0022] Figure 6 This is a flowchart illustrating a method for fabricating a laser according to an embodiment of the present invention;

[0023] Figure 7 This is a flowchart illustrating the fabrication process of a wedge-shaped waveguide in a laser fabrication method according to an embodiment of the present invention.

[0024] Figure 8 This is a flowchart illustrating the fabrication process of a thermally tuned resistor in a laser fabrication method according to an embodiment of the present invention.

[0025] Figure 9 This is a flowchart illustrating the fabrication process of a total reflection mirror in a laser fabrication method according to an embodiment of the present invention.

[0026] Figure label:

[0027] Laser 100, distributed feedback laser 110, active layer 111, coupling layer 112, passive layer 113, filter 120, straight waveguide 121, ring waveguide 122, thermally tuned resistor 123, mode converter 124, total reflection mirror 125, wedge waveguide 130, substrate 140, metal electrode 150. Detailed Implementation

[0028] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0029] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0030] In the description of this invention, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.

[0031] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0032] The following is for reference. Figures 1 to 5 The laser 100 of this embodiment is described.

[0033] See Figure 1 As shown, the laser 100 of this embodiment includes a distributed feedback laser 110 and a filter 120. The distributed feedback laser 110 includes an active layer 111, a coupling layer 112, and a passive layer 113. The coupling layer 112 is located between the active layer 111 and the passive layer 113. This distributed feedback laser 110 is a direct modulation laser. Compared with the traditional DFB, it adds a passive layer 113 and a coupling layer 112. The function of the coupling layer 112 is to couple the light field generated in the active layer 111 to the passive layer 113. The passive layer 113 is used to transmit the light field to the filter 120. The filter 120 is used to reshape the light signal generated by the distributed feedback laser 110. The distributed feedback laser 110 and the filter 120 are fabricated on a substrate 140.

[0034] See Figure 1 and Figure 2As shown, the filter 120 includes a straight waveguide 121 and a ring waveguide 122. The straight waveguide 121 can be understood as a waveguide with a straight shape, and the ring waveguide 122 can be understood as a waveguide with a ring shape. The ring waveguide 122 is positioned close to the straight waveguide 121, so that the straight waveguide 121 and the ring waveguide 122 can be coupled in the optical field. The straight waveguide 121 and the ring waveguide 122 are both fabricated on the extended passive layer 113. The three are located in the same plane, and the straight waveguide 121 is directly connected to the passive layer 113, so that the filter 120 and the distributed feedback laser 110 can be monolithically integrated.

[0035] It can be understood that during the epitaxial growth of the distributed feedback laser 110, a passive layer 113 and a coupling layer 112 are added. The straight waveguide 121 is a waveguide structure defined within the passive structure of the passive layer 113. That is, the straight waveguide 121 and the passive layer 113 belong to the same passive structure. The monolithic integration of the filter 120 and the distributed feedback laser 110 can be understood as the filter 120 and the distributed feedback laser 110 sharing the same passive structure, without the need for docking growth technology. It should be noted that the monolithic integration of DFB and filter conventionally adopts the docking growth method, that is, the active waveguide of the laser and the passive waveguide of the filter are on the same layer, and good docking at the interface is required. The docking is difficult, and if the docking is not done well, the light will suffer very large loss at the interface. It is understood that in the embodiments of the present invention, the straight waveguide 121 of the filter 120 is an extension of the passive layer 113 of the distributed feedback laser 110. Compared with conventional DFB epitaxy, it does not increase the number of epitaxy cycles, does not require complex docking growth technology, effectively reduces the chirp problem during DFB direct tuning, and effectively solves the problem of large chirp and small extinction ratio of existing DFB, which is not conducive to long-distance transmission.

[0036] See Figure 1 and Figure 2As shown, the laser 100 has a substrate 140, an active layer 111, a coupling layer 112 and a passive layer 113 are distributed on the substrate 140 in a vertical direction. The light field generated by the active layer 111 is transmitted from top to bottom and then transmitted to the filter 120 through the passive layer 113. The straight waveguide 121 of the filter 120 is located in the same plane as the passive layer 113. The specific working process is as follows: when a current signal is applied to the distributed feedback laser 110, an optical field is generated in the active layer 111. The optical field is coupled from the active layer 111 to the passive layer 113, and then enters the straight waveguide 121 of the filter 120. The optical field that meets certain conditions will enter the ring waveguide 122. After being reshaped, the optical field will be emitted along the straight waveguide 121. In this way, by means of the filter 120 reshaping the output optical field of the distributed feedback laser 110, low chirp and high extinction ratio are achieved. It can be applied to the OLT (Optical Line Terminal) of 10 Gigabit Passive Optical Network (XGPON) / 10 Gigabit Ethernet Passive Optical Network (XGEPON) to replace the original EML. It is suitable for long-distance transmission, has lower power consumption than EML, and does not require complex docking growth technology. The manufacturing process is easier to implement, the cost is lower, the structural design is reasonable, and the application range is wider.

[0037] See Figure 1 As shown, both the active layer 111 and the passive layer 113 are waveguide structures. The active layer 111 can be understood as an active waveguide, and the passive layer 113 as a passive waveguide. Both the active and passive waveguides can transmit optical fields, and they are distributed vertically to form a vertical double waveguide structure. After applying a current signal to the distributed feedback laser 110, the active layer 111 generates an optical field, which propagates forward along the waveguide. During propagation, the optical field is coupled to the passive layer 113 through the coupling layer 112. The waveguide structure region in the distributed feedback laser 110 can be understood as the waveguide region, such as... Figure 1 As shown, the waveguide region of the distributed feedback laser 110 includes an active layer 111, a passive layer 113, and a coupling layer 112. The optical field is coupled from the active layer 111 to the passive layer 113 for transmission. It should be noted that the distributed feedback laser 110 also includes an ohmic contact layer, a grating layer, and a cladding layer, etc. The specific structures are not shown in the attached figures and are conventional structures, so they will not be described in detail here. Figure 2 and Figure 3 The distributed feedback laser 110 shown has a metal electrode 150, and an optical field can be generated by energizing the active layer 111 through the metal electrode 150.

[0038] It is understood that in the distributed feedback laser 110, the active layer 111, passive layer 113, and coupling layer 112 are distributed vertically. In the filter 120, the straight waveguide 121 is connected to the passive layer 113, and the filter 120 does not have an active layer 111. Therefore, the optical field generated in the active layer 111 needs to be coupled vertically to the passive layer 113, and then transmitted to the filter 120 via the passive layer 113. One end of the waveguide region gradually narrows towards the filter 120. The shape of this gradual narrowing can be varied and is not limited to a specific shape. This gradually narrowing portion can be understood as a wedge-shaped waveguide (Taper) 130, i.e., a wedge-shaped waveguide 130 is provided at the end of the waveguide region near the filter 120. Specifically, this wedge-shaped waveguide 130 is part of the waveguide region. With the help of the gradually narrowing structure, the optical field can be coupled vertically from the active waveguide to the passive waveguide, which helps reduce optical loss.

[0039] It should be noted that the active layer 111 emits light to generate a mode field, and the coupling layer 112 acts as a coupling transition for the mode field. The coupling layer 112 can be understood as a mode field coupling layer. By adjusting the thickness of the coupling layer 112 and the width, length, and other parameters of the wedge waveguide 130, the optimal waveguide parameters of the wedge waveguide 130 can be obtained, so that the optical field can be coupled to the passive layer 113 to the maximum extent.

[0040] See Figure 4 As shown, taking the nonlinear wedge waveguide 130 as an example, the optical field in the active waveguide is coupled from the active waveguide into the passive waveguide through the wedge waveguide 130. By optimizing the waveguide parameters and the thickness of each layer, and with the help of the wedge waveguide 130, the optical field generated in the active waveguide can be transmitted to the passive waveguide to the maximum extent, reducing the coupling loss between the active layer 111 and the passive layer 113.

[0041] It should be noted that the substrate 140 is made of indium phosphide (InP) material, and the substrate 140 can be understood as the substrate for the distributed feedback laser 110 and the filter 120. It can be understood that during epitaxial wafer fabrication, a passive layer 113 is first grown on the InP substrate 140, followed by a coupling layer 112, then an active layer 111, and finally the other layers above the active layer 111. Conventional distributed feedback laser fabrication steps are performed on the epitaxial wafer. Then, when fabricating the filter 120, the active layer 111 and the portion above it in the filter 120 region are completely removed. The pattern of the filter 120 is then fabricated on the coupling layer 112 and the passive layer 113, forming a straight waveguide 121 and a ring waveguide 122. In this way, the distributed feedback laser 110 and the filter 120 are fabricated on the substrate 140.

[0042] In this embodiment, the passive layer 113 uses a material with a larger bandgap than the active layer 111. The active layer 111 is an active waveguide containing multiple quantum wells (MQWs), while the passive layer 113 uses a material with a larger bandgap than the MQW. The material of the passive layer 113 can be understood as a waveguide material that does not absorb optical power. This prevents light field absorption during transmission in the passive waveguide. It should be noted that, like active waveguides, passive waveguides must meet the single-mode transmission condition of the optical field. Specifically, when the distributed feedback laser 110 is powered, the active waveguide emits light. Through the design of the waveguide width and height, the mode field generated by the active waveguide can be made single-mode. The passive waveguide, however, does not require power and does not generate light; it only serves to transmit light. Therefore, the passive waveguide needs to maintain a single-mode mode field to meet the single-mode transmission condition of the optical field, preventing the single-mode generated in the active waveguide from becoming multimode after entering the passive waveguide. Furthermore, the material systems of active and passive waveguides are the same, for example, indium gallium arsenide phosphide (InGaAsP) or indium aluminum gallium arsenide (InGaAlAs), which are quaternary compounds. By adjusting the proportion of these quaternary elements, the desired active or passive waveguide can be obtained. The material systems of active and passive waveguides are conventional materials and will not be elaborated further.

[0043] In addition, the coupling layer 112 is made of InP material. The optical field in the active waveguide is coupled to the passive waveguide through the coupling layer 112. The thickness and waveguide parameters of the active layer 111, passive layer 113 and coupling layer 112 can be optimized and adjusted. The optical field transmission process is aided by the wedge waveguide 130, which can transmit the optical field from the active waveguide to the passive waveguide to the maximum extent.

[0044] See Figure 2 and Figure 3As shown, in some embodiments, the passive layer 113, the straight waveguide 121, and the ring waveguide 122 are all located on the same plane. It can be understood that the straight waveguide 121 is an extension of the passive layer 113, and the straight waveguide 121 communicates with the passive layer 113, thereby achieving monolithic integration of the filter 120 and the distributed feedback laser 110. Simultaneously, the straight waveguide 121 and the ring waveguide 122 are also located on the same plane and have the same waveguide structure. The straight waveguide 121 is close to the ring waveguide 122, enabling optical field coupling between the straight waveguide 121 and the ring waveguide 122. The straight waveguide 121 and the ring waveguide 122 constitute the filter 120, which is also called a micro-ring filter. The optical field is coupled from the active layer 111 to the passive layer 113, and then enters the straight waveguide 121 of the filter 120. Since the straight waveguide 121 is very close to the ring waveguide 122, the light will enter the ring waveguide 122 from the straight waveguide 121. The light that satisfies the resonance equation will stay in the ring waveguide 122, and the light that does not satisfy the condition will return to the straight waveguide 121 and be emitted. The filter 120 reshapes the non-return-to-zero line code (NRZ) signal generated by the distributed feedback laser 110.

[0045] See Figure 2 As shown, specifically, the ring waveguide 122 includes two oppositely arranged straight edges, which are parallel to each other and parallel to the straight waveguide 121. The gap between the straight edge closer to the straight waveguide 121 and the straight waveguide 121 is in the range of submicron to micron. This gap affects the coupling coefficient between the straight waveguide 121 and the ring waveguide 122. The straight edge closer to the straight waveguide 121 forms a coupling region with the straight waveguide 121. The optical field can be coupled from the straight waveguide 121 into the ring waveguide 122, and can also be coupled from the ring waveguide 122 back into the straight waveguide 121.

[0046] See Figure 2 and Figure 3 As shown, a thermally tuned resistor 123 is disposed inside the ring waveguide 122. The thermally tuned resistor 123 extends and is distributed along the inner side of the ring waveguide 122. The resonant wavelength of the filter 120 can be thermally tuned using the thermally tuned resistor 123. The refractive index of the passive waveguide material changes with temperature, and the resonant wavelength that satisfies the resonance equation will also change accordingly, achieving the purpose of thermal tuning through thermal effect. In this embodiment, the thermally tuned resistor 123 can be made of platinum. Of course, it can also be made of other materials, and is not limited to the platinum material shown in the embodiment.

[0047] It is understood that, apart from the power consumption of the distributed feedback laser 110, the laser 100 in this embodiment only requires a small amount of thermally tunable power to be applied to the filter 120 to enable the laser 100 to operate, resulting in lower total power consumption than the EML process and achieving the goal of low power consumption. Moreover, compared with the EML fabrication process, no docking growth is required, and compared with the DFB process, only the etching of the passive waveguide and the fabrication of the thermally tunable resistor 123 are added, making the fabrication process easy to implement and helping to reduce costs.

[0048] See Figure 2 and Figure 3 As shown, in some embodiments, a spot size converter 124 (SSC) is provided at the end of the straight waveguide 121. The front end of the straight waveguide 121 is connected to the passive layer 113, and the end of the straight waveguide 121 is coupled to an external optical fiber. The spot size converter 124 is located at the end position and is used to reduce the coupling loss between the laser 100 and the external optical fiber.

[0049] It should be noted that the optical field generated by the distributed feedback laser 110 in the active layer 111 is coupled into the passive layer 113 and then transmitted to the filter 120. By designing the parameters of the filter 120, including the waveguide width, gap, and perimeter of the ring waveguide 122, the NRZ zero-order signal satisfies the wavelength resonance condition and is thus coupled into the ring waveguide 122. Except for the loss, the remaining light exits from the SSC at the end of the straight waveguide 121. In other words, when the NRZ "1" and "0" signals pass through the filter 120 in sequence, the attenuation of the "1" order signal is lower than that of the "0" order signal, thereby achieving the purpose of reducing chirp and increasing the extinction ratio.

[0050] It is understandable that filter 120 has the best filtering effect when it is in a critical coupling state. The following two embodiments are used as examples to illustrate how critical coupling is achieved.

[0051] See Figure 2As shown, in the first embodiment, the filter 120 comprises three parts: a straight waveguide 121, a racetrack-shaped ring waveguide 122, and a thermally tuned resistor 123. The straight waveguide 121, the ring waveguide 122, and the passive waveguide in the distributed feedback laser 110 are on the same layer, all formed by etching a passive material layer. The optical field in the active waveguide of the distributed feedback laser 110 is vertically coupled through the wedge-shaped waveguide 130. The optical field enters the straight waveguide 121. When passing through the ring waveguide 122, the optical field is coupled into the straight edge of the ring waveguide 122 through the gap between the straight waveguide 121 and the ring waveguide 122, and propagates in the ring waveguide 122. The optical field that satisfies the wavelength resonance equation continues to propagate in the ring waveguide 122, while the optical field that does not satisfy the resonance equation circulates once and is recoupled back into the straight waveguide 121 in the coupling region. It is then coupled into the external optical fiber via the SSC, thereby emitting the light.

[0052] It is understood that, since the structure of the ring waveguide 122 is greatly affected by process errors and the output wavelength of the distributed feedback laser 110 may vary individually, this embodiment adds a thermal tuning resistor 123 to the inner ring of the ring waveguide 122. By applying power to the thermal tuning resistor 123, the thermal effect causes the effective refractive index of the passive waveguide to change, and the wavelength that satisfies the resonance equation also changes accordingly, thereby completing the thermal tuning of the resonant wavelength (filter wavelength).

[0053] Considering that the refractive index difference between the waveguide core and cladding of the III-V material is small, the waveguide bending radius usually needs to be above 200um to obtain a low-loss microring. Therefore, the size of the ring waveguide 122 in the first embodiment is relatively large.

[0054] See Figure 3 As shown, in the second embodiment, the ring waveguide 122 adopts a rectangular ring structure instead of a racetrack-shaped ring structure. In this embodiment, the ring waveguide 122 is rectangular, which can be understood as a rectangular waveguide. A total reflection mirror 125 is set at each of the four apex positions of the rectangular waveguide. The light field can complete a 90° turn with low radiation loss at the total reflection mirror 125, that is, the light field propagates along a rectangular path. The total reflection mirror 125 is fabricated by deep etching (etching to the InP substrate 140). Since it does not involve the bending loss of the waveguide and the radiation loss is small, the filter 120 using a rectangular waveguide can achieve the critical coupling state with a smaller size, making the device structure more compact and beneficial to reducing the size of the laser 100. The size of the laser 100 in this embodiment is comparable to that of EML, and the packaging process is also compatible with EML.

[0055] Similarly, a thermally tuned resistor 123 is provided on the inside of the rectangular waveguide. By energizing the thermally tuned resistor 123, a thermal effect is generated, thereby thermally tuning the resonant wavelength.

[0056] It should be noted that the NRZ signal generated by the distributed feedback laser 110 is affected by chirp, meaning that the wavelength λ1 of the "1" signal is different from the wavelength λ0 of the "0" signal. By designing parameters such as the perimeter of the ring waveguide 122 and the coupling gap of the filter 120, specific resonant wavelength λ0, free spectral range (FSR), and full width at half maximum (FWHM) bandwidth Δλ of the resonant peak are obtained. FWHM When the NRZ signal from the distributed feedback laser 110 enters the straight waveguide 121, the wavelength of the "0" signal satisfies the resonance equation and enters the racetrack-shaped or rectangular ring waveguide 122, where it resonates. The wavelength of the "1" signal does not satisfy the resonance equation and is coupled into the external optical fiber via the mode converter 124. Through this process, the wavelength of the "0" signal becomes λ. 00 Meanwhile, the wavelength λ1 of the "1" signal remains unchanged, the chirp decreases, and the extinction ratio increases by ΔER. Figure 5 The diagram shows the principle of how laser 100 achieves low chirp and high extinction ratio.

[0057] It can be understood that the "1" and "0" signals generated by a conventional DFB (Digital Fluorescent Blade) are produced by applying different magnitudes of current, resulting in output light of different magnitudes; a larger current corresponds to a "1" signal, and a smaller current corresponds to a "0" signal. Because different currents introduce different amounts of heat, there will be a difference in wavelength between the two signals. Figure 5 As shown, these correspond to λ1 and λ0 respectively, which is the chirp. Designing the resonant wavelength of filter 120 at λ0 allows for filtering of the "0" signal. The dashed line represents the resonant peak of filter 120 (the peak that can be filtered), which is periodic. After filtering, the wavelength of the "0" signal becomes λ. 00 The difference between λ1 and λ2 decreases, the chirp decreases, and the extinction ratio between "1" and "0" increases by ΔER, which is the desired result.

[0058] The following is for reference. Figures 6 to 9 The method for fabricating the laser according to the embodiments of the present invention is applicable to the fabrication of the laser 100 shown in the above embodiments.

[0059] See Figure 6 As shown, the method for fabricating the laser in this embodiment includes, but is not limited to, the following steps:

[0060] Step S100: A passive layer, a coupling layer and an active layer are sequentially grown on the substrate;

[0061] Step S200: Remove part of the active layer and above to form a filter region;

[0062] Step S300: Etch the passive layer and coupling layer in the filter region to form a straight waveguide and a ring waveguide, so that optical field coupling can be performed between the straight waveguide and the ring waveguide.

[0063] It is understandable that the fabricated laser comprises two parts: a distributed feedback laser 110 and a filter 120. Epitaxial growth technology is used to grow an epitaxial wafer on a substrate 140. Specifically, during the epitaxial wafer fabrication, a passive layer 113 is first grown on the InP substrate 140, followed by a coupling layer 112, and then an active layer 111. Of course, the distributed feedback laser 110 is not limited to including the passive layer 113, coupling layer 112, and active layer 111; it also includes other layers on the active layer 111, such as an ohmic contact layer, a grating layer, and a cladding layer. Therefore, after growing the active layer 111, other layers are grown on top of it, which will not be elaborated further.

[0064] It should be noted that after completing the passive layer 113, coupling layer 112, active layer 111, and other layers above, conventional distributed feedback laser fabrication processes are performed on the epitaxial wafer. These include steps such as ridge waveguide etching, dielectric layer growth, windowing, metal fabrication, and cavity surface coating for the distributed feedback laser 110, which will not be elaborated here. It is understood that the fabrication process for the laser is not limited to these steps. Figure 6 The sequence of steps in the illustrated embodiment, namely steps S100, S200, S300, and the fabrication process steps of a conventional distributed feedback laser on the epitaxial wafer, is not limited to the order shown in the above embodiment and can be reasonably adjusted according to actual design requirements.

[0065] In the laser fabrication method of this embodiment, the epitaxial wafer is divided into a distributed feedback laser region and a filter region. After epitaxial growth is completed, conventional distributed feedback laser fabrication steps are performed on the epitaxial wafer. Then, the active layer 111 and above in the filter region are removed, such as... Figure 1 In the illustrated embodiment, the left side of the laser 100 is a filter region, which does not have an active layer 111 or higher layer structure on the epitaxial wafer. Then, the coupling layer 112 and the passive layer 113 in the filter region are etched to form a straight waveguide 121 and a ring waveguide 122. The straight waveguide 121 and the ring waveguide 122 are located on the same plane and are positioned close to each other, allowing them to couple through an optical field for reshaping the optical signal generated by the distributed feedback laser 110. Thus, both the straight waveguide 121 and the ring waveguide 122 are fabricated on the passive layer 113, all three are located in the same plane, and the straight waveguide 121 is directly connected to the passive layer 113, enabling the filter 120 and the distributed feedback laser 110 to be monolithically integrated.

[0066] It can be understood that during the epitaxial growth process of the distributed feedback laser 110, a passive layer 113 and a coupling layer 112 are added. The straight waveguide 121 and the ring waveguide 122 are directly etched onto the coupling layer 112 and the passive layer 113. The filter 120 shares the same passive structure with the distributed feedback laser 110. Compared with the conventional docking growth method for monolithic integration of the DFB and the filter, this method does not increase the number of epitaxial cycles and does not require complex docking growth techniques. It effectively reduces the chirp problem during direct tuning of the DFB and effectively solves the problems of large chirp and small extinction ratio of existing DFBs, which are not conducive to long-distance transmission.

[0067] See Figure 7 As shown, the laser fabrication method of the embodiment further includes the following steps:

[0068] Step S400: Etch each layer near the filter region, including the passive layer, coupling layer and active layer, to form a wedge waveguide.

[0069] It can be understood that the wedge-shaped waveguide 130 is formed at one end of the distributed feedback laser region near the filter region. The wedge-shaped waveguide 130 gradually narrows towards the filter region and can have various shapes, not limited to a specific form. The waveguide region includes an active layer 111, a passive layer 113, and a coupling layer 112. In the filter 120, the straight waveguide 121 is connected to the passive layer 113. The optical field generated in the active layer 111 needs to be coupled to the passive layer 113 and then transmitted to the filter 120. The wedge-shaped waveguide 130 is part of the waveguide region. The structure of the wedge-shaped waveguide 130 enables the optical field to be coupled from the active waveguide to the passive waveguide in a vertical direction. Specifically, by optimizing the waveguide parameters and the thickness of each layer, and with the help of the wedge-shaped waveguide 130, the optical field generated in the active waveguide can be transmitted to the passive waveguide to the maximum extent, reducing the coupling loss between the active layer 111 and the passive layer 113.

[0070] See Figure 8 As shown, the laser fabrication method of the embodiment further includes the following steps:

[0071] Step S500: Fabricate a thermally tuned resistor inside the ring waveguide.

[0072] Understandably, after the straight waveguide 121 and the ring waveguide 122 are etched, a thermally tunable resistor 123 is fabricated inside the ring waveguide 122. The thermally tunable resistor 123 extends along the inner side of the ring waveguide 122. The resonant wavelength of the filter 120 can be thermally tuned using the thermally tunable resistor 123. The specific working principle will not be elaborated further. The fabrication steps of the thermally tunable resistor 123 are applicable to both racetrack-shaped ring waveguides 122 and rectangular waveguides. The fabrication process is easy to implement and helps reduce costs.

[0073] See Figure 9 As shown, when fabricating a rectangular waveguide, a total reflection mirror 125 needs to be placed at the apex corner of the rectangular waveguide. Specifically, the laser fabrication method of this embodiment also includes the following steps:

[0074] In step S600, when fabricating the rectangular waveguide, a deep etching process is used to form a total reflection mirror.

[0075] It should be noted that the ring waveguide 122 is rectangular, and a total reflection mirror 125 is etched at each of the four vertices of the rectangular waveguide. The light field can complete a 90° turn with low radiation loss at the total reflection mirror 125, that is, the light field propagates along the rectangular path. The deep etching process can be understood as fabricating the total reflection mirror 125 by etching onto the InP substrate 140. Using a rectangular waveguide filter 120 can achieve a critical coupling state with a smaller size, making the device structure more compact and beneficial for reducing the size of the laser 100. The size of the laser 100 in this embodiment of the invention is comparable to that of the EML, and the packaging process is also compatible with the EML.

[0076] It should be noted that steps S100, S200, S300, S400, S500, and S600 shown in the above embodiments are not limited to a specific order and can be reasonably adjusted according to actual design requirements. Based on the laser 100 provided in the above embodiments, another embodiment of the present invention provides an optical communication device, which includes, but is not limited to, an optical line terminal or an optical network unit. The optical line terminal includes the laser 100 provided in the above embodiments, and the optical network unit includes the laser 100 provided in the above embodiments.

[0077] Based on the laser 100 provided in the above embodiments, another embodiment of the present invention provides an optical network system, which includes an optical line terminal located at a central control station and multiple optical network units located on the user side. The optical line terminal and the optical network units communicate with each other via optical network. The optical line terminal includes a laser for providing data modulation and transmission functions, and the laser is the laser 100 provided in the above embodiments. The optical network units include lasers for providing data modulation and transmission functions, and the lasers are the laser 100 provided in the above embodiments.

[0078] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A laser, characterized in that, include: A distributed feedback laser includes an active layer, a coupling layer, and a passive layer. The coupling layer is located between the active layer and the passive layer and is used to couple the optical field generated in the active layer to the passive layer for transmission. The material bandgap of the passive layer is larger than that of the active layer. A filter comprising a straight waveguide and a ring waveguide, wherein optical field coupling exists between the straight waveguide and the ring waveguide, and the passive layer extends to form the straight waveguide so that the filter is monolithically integrated with the distributed feedback laser; The substrate on which the distributed feedback laser and the filter are formed are located.

2. The laser according to claim 1, characterized in that, The active layer, the coupling layer, and the passive layer form a waveguide region, which gradually narrows at one end near the filter.

3. The laser according to claim 2, characterized in that, The cross-section of the gradually narrowing portion of the waveguide region is wedge-shaped.

4. The laser according to claim 1, characterized in that, Both the straight waveguide and the ring waveguide are made of the extended passive layer, and the straight waveguide and the ring waveguide are located in the same plane and have the same waveguide structure.

5. The laser according to claim 1, characterized in that, The ring waveguide includes a straight edge parallel to the straight waveguide, and the gap between the straight edge and the straight waveguide is in the range of submicron to micron, so as to form a coupling region between the straight waveguide and the ring waveguide.

6. The laser according to claim 1 or 5, characterized in that, The annular waveguide is a racetrack-shaped structure or a rectangular annular structure, and a total reflection mirror is respectively set at the apex of the rectangle of the rectangular annular structure.

7. The laser according to claim 1, characterized in that, The inner side of the ring waveguide is provided with a thermal tuning resistor for thermally tuning the resonant wavelength of the filter.

8. The laser according to claim 1, characterized in that, The end of the straight waveguide is provided with a mode converter for reducing the coupling loss between the laser and the external optical fiber.

9. The laser according to claim 1, characterized in that, The substrate material is indium phosphide.

10. A method for fabricating a laser, characterized in that, The method, applied to the laser according to any one of claims 1 to 9, comprises: A passive layer, a coupling layer, and an active layer are sequentially grown on a substrate, wherein the material band gap of the passive layer is larger than that of the active layer. A portion of the active layer and the layer structure above the active layer are removed to form a filter region; The passive layer and the coupling layer in the filter region are etched to form a straight waveguide and a ring waveguide, so that optical field coupling can be performed between the straight waveguide and the ring waveguide.

11. The method for fabricating a laser according to claim 10, characterized in that, Also includes: The layers near the filter region, including the passive layer, the coupling layer, and the active layer, are etched to form a wedge-shaped waveguide.

12. The method for fabricating a laser according to claim 10, characterized in that, Also includes: A thermally tuned resistor is fabricated inside the ring waveguide.

13. An optical communication device, characterized in that, Including the laser as described in any one of claims 1 to 9.

14. An optical network system, characterized in that, It includes an optical line terminal and multiple optical network units, wherein the optical line terminal is connected to the multiple optical network units through an optical distribution network; wherein the optical line terminal and / or optical network units include a laser as described in any one of claims 1 to 9.

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