CN114465089A

CN114465089A - Laser and preparation method of laser

Info

Publication number: CN114465089A
Application number: CN202011140489.4A
Authority: CN
Inventors: 朱瑞
Original assignee: Zte Photonics Technology Co ltd
Current assignee: Zte Photonics Technology Co ltd
Priority date: 2020-10-22
Filing date: 2020-10-22
Publication date: 2022-05-10

Abstract

The invention discloses a laser and a preparation method thereof, wherein the laser comprises a distributed feedback laser and a filter, the distributed feedback laser comprises an active layer, a coupling layer and a passive layer, a light field generated in the active layer is coupled into the passive layer through the coupling layer for transmission and enters the filter; the filter comprises a straight waveguide and a ring waveguide, the straight waveguide and the ring waveguide are made of extended passive layers, and the filter plays a role in shaping signals of the distributed feedback laser. The distributed feedback laser and the filter can be integrated without butt growth, the chirp problem during direct adjustment of the distributed feedback laser can be effectively reduced, the distributed feedback laser has the advantages of low chirp, large extinction ratio, low power consumption, simple process and the like, the distributed feedback laser can be applied to remote transmission instead of an electro-absorption modulation laser, the manufacturing process is simpler, the cost is lower, the structural design is reasonable, and the application range is wider.

Description

Laser and preparation method of laser

Technical Field

The present invention relates to the field of optoelectronic technologies, and in particular, to a laser, a method for manufacturing a laser, an optical communication device, and an optical network system.

Background

In recent years, with the rapid development of internet services, cost, size and power consumption become burdensome for the development of optical devices in the directions of large bandwidth, high speed and long distance. Lasers, which are core devices in optical devices of communication networks, are generally classified into direct modulation lasers and external modulation lasers. Distributed Feedback Laser (DFB) is a direct modulation Laser, which is widely used for medium and short distance (below 10 km) transmission due to its low cost, small size, high speed and high linearity. However, during the direct modulation process, the effective refractive index of the active region of the laser is changed by the change of the thermal effect and the injection current, so that the wavelength drift is caused, and the chirp is caused, which becomes one of the limiting factors of applying the DFB to an optical fiber transmission link with the length of more than 10 km. Accordingly, an electro-absorption Modulated Laser (EML) is a typical external modulation Laser, in which a DFB and an electro-absorption Modulator (EAM) are integrated by a Butt-joint growth technique (but-joint), and an electrical signal is applied to the EAM to perform external modulation. The EML has the advantages of high speed, high extinction ratio, low chirp and the like, and can be applied to long-distance transmission of more than 40 km. However, EML is difficult to manufacture, high in power consumption and cost, and has limited its large-scale use in optical communication networks.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a laser, a preparation method of the laser, optical communication equipment and an optical network system, which can effectively reduce the chirp problem during DFB direct tuning, have the advantages of high extinction ratio, low power consumption and the like, and are more practical and reliable.

In a first aspect, an embodiment of the present invention provides a laser, including:

a distributed feedback laser including an active layer, a coupling layer and a passive layer, the coupling layer being located between the active layer and the passive layer, the coupling layer being for coupling an optical field generated in the active layer to the passive layer for transmission;

a filter comprising a straight waveguide and a ring waveguide, optical field coupling between the straight waveguide and the ring waveguide, the passive layer extending to form the straight waveguide to monolithically integrate the filter with the distributed feedback laser;

a substrate on which the distributed feedback laser and the filter are formed.

In a second aspect, the present invention further provides a method for manufacturing a laser, including:

sequentially growing a passive layer, a coupling layer and an active layer on a substrate;

removing part of the active layer and the above layer structure to form a filter region;

and etching the passive layer and the coupling layer in the filter region to form a straight waveguide and an annular waveguide so as to enable optical field coupling between the straight waveguide and the annular waveguide.

In a third aspect, the present invention further provides an optical communication device, including the laser described in the embodiment of the first aspect.

In a fourth aspect, the present invention further provides an optical network system, including an optical line terminal and a plurality of optical network units, where 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 unit comprises a laser as described in the embodiments of the first aspect above.

Compared with the traditional DFB, the distributed feedback laser in the embodiment of the invention is additionally provided with the passive layer and the coupling layer, the passive layer is extended to form the straight waveguide of the filter, so that the distributed feedback laser and the filter are monolithically integrated, an optical field generated in the active layer is coupled to the passive layer through the coupling layer for transmission, butt joint growth is not needed between the distributed feedback laser and the filter, the chirp problem during DFB direct adjustment is effectively reduced, and the distributed feedback laser has the advantages of low chirp, large extinction ratio, low power consumption, simple process and the like; the low chirp and the large extinction ratio are realized by reshaping of the output light field of the distributed feedback laser by using the filter, the distributed feedback laser can replace an EML laser to be applied to remote transmission, has lower power consumption than the EML laser, does not need a complex Butt joint growth technology (Butt-join), has simpler manufacturing process, lower cost, reasonable structural design, more practicability and reliability, is suitable for optical communication equipment and an optical network system, and has wider application range.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

The invention is further described with reference to the following figures and examples, in which:

FIG. 1 is a schematic diagram of a longitudinal cross-sectional structure of a laser according to an embodiment of the present invention;

fig. 2 is a schematic top view of a laser according to a first embodiment of the present invention;

fig. 3 is a schematic top view of a laser according to a second embodiment of the present invention;

FIG. 4 is a schematic diagram of a distributed feedback laser configuration according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a laser according to an embodiment of the present invention to achieve a low chirp high extinction ratio;

FIG. 6 is a flow chart illustrating a method for fabricating a laser according to an embodiment of the present invention;

FIG. 7 is a flow chart of the fabrication of a wedge waveguide in a method of fabricating a laser according to an embodiment of the invention;

FIG. 8 is a flow chart illustrating the fabrication of a thermal tuning resistor in a method of fabricating a laser according to an embodiment of the present invention;

fig. 9 is a flowchart illustrating a process of fabricating a total reflection mirror in a method of fabricating a laser according to an embodiment of the present invention.

Reference numerals are as follows:

the laser comprises a laser 100, a distributed feedback laser 110, an active layer 111, a coupling layer 112, a passive layer 113, a filter 120, a straight waveguide 121, a ring waveguide 122, a thermal tuning resistor 123, a spot size converter 124, a total reflection mirror 125, a wedge waveguide 130, a substrate 140 and a metal electrode 150.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

In the description of the present invention, it should be understood that the orientation or positional relationship referred to, for example, the upper, lower, etc., is indicated based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, but does not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention.

In the description of the present invention, if there are first, second, etc. described, it is only for the purpose of distinguishing technical features, and it is not understood that relative importance is indicated or implied or the number of indicated technical features is implicitly indicated or the precedence of the indicated technical features is implicitly indicated.

In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.

A laser 100 according to an embodiment of the present invention will be described with reference to fig. 1 to 5.

Referring to fig. 1, a laser 100 according to an embodiment of the present invention includes a distributed feedback laser 110 and a filter 120, wherein 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, the distributed feedback laser 110 belongs to a direct modulation laser, the passive layer 113 and the coupling layer 112 are added with respect to a conventional DFB, the coupling layer 112 functions to couple an optical field generated in the active layer 111 to the passive layer 113, transmit the optical field to the filter 120 using the passive layer 113, reshape an optical signal generated by the distributed feedback laser 110 using the filter 120, and the distributed feedback laser 110 and the filter 120 are formed on a substrate 140.

Referring to fig. 1 and 2, the filter 120 includes a straight waveguide 121 and a ring waveguide 122, the straight waveguide 121 may be understood as a straight waveguide, and the ring waveguide 122 may be understood as a ring waveguide, wherein the ring waveguide 122 is disposed near the straight waveguide 121 to enable optical-field coupling between the straight waveguide 121 and the ring waveguide 122, the straight waveguide 121 and the ring waveguide 122 are both formed on the extended passive layer 113, and are located in the same plane, and the straight waveguide 121 is directly communicated with the passive layer 113, so that the filter 120 and the distributed feedback laser 110 are monolithically integrated.

It can be understood that the passive layer 113 and the coupling layer 112 are added in the epitaxial growth process of the distributed feedback laser 110, the straight waveguide 121 is a waveguide structure defined in 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, and the monolithic integration of the filter 120 and the distributed feedback laser 110 can be understood that the filter 120 and the distributed feedback laser 110 share the same passive structure without using a butt-joint growth technique. It should be noted that, the conventional butt joint growth method is adopted for monolithic integration of the DFB and the filter, that is, the active waveguide of the laser and the passive waveguide of the filter are on the same layer, and the butt joint at the junction is required to be good, the butt joint difficulty is high, and if the butt joint is not good, the light will have very large loss at the junction. It can be understood that the straight waveguide 121 of the filter 120 in the embodiment of the present invention is an extension of the passive layer 113 of the distributed feedback laser 110, and compared with the conventional DFB epitaxy, the number of epitaxy is not increased, and a complex butt-joint growth technique is not required, so that the chirp problem during DFB direct tuning is effectively reduced, and the problems that the existing DFB has large chirp and small extinction ratio and is not favorable for long-distance transmission are effectively solved.

Referring to fig. 1 and 2, the laser 100 has a substrate 140, the active layer 111, the coupling layer 112 and the passive layer 113 are distributed on the substrate 140 along a vertical direction, an optical 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, and the straight waveguide 121 of the filter 120 and the passive layer 113 are located on the same plane. In particular, when a current signal is applied to distributed feedback laser 110, an optical field is generated in active layer 111, which is coupled from active layer 111 to passive layer 113, then enters the straight waveguide 121 of the filter 120, the optical field meeting certain conditions enters the annular waveguide 122, the reshaped optical field is emitted along the straight waveguide 121, this achieves low chirp and large extinction ratio by means of reshaping of the distributed feedback laser 110 output optical field by filter 120, can be applied to an OLT end (optical line terminal) of a gigabit passive optical network (XGPON)/gigabit Ethernet passive optical network (XGPON), replaces the prior EML, is suitable for long-distance transmission, has lower power consumption than the EML, and a complex butt-joint growth technology is not needed, the manufacturing process is easier to realize, the cost is lower, the structural design is reasonable, and the application range is wider.

Referring to fig. 1, it can be understood that the active layer 111 and the passive layer 113 are both waveguide structures, the active layer 111 can be understood as an active waveguide, the passive layer 113 can be understood as a passive waveguide, both the active waveguide and the passive waveguide can transmit an optical field, and the active waveguide and the passive waveguide are distributed in a vertical manner to form a vertical dual-waveguide structure. Upon application of a current signal to distributed feedback laser 110, active layer 111 generates an optical field that propagates along the waveguide, where it is coupled to passive layer 113 via coupling layer 112. The region of the waveguide structure in the distributed feedback laser 110 may be understood as a waveguide region, as shown in fig. 1, the waveguide region of the distributed feedback laser 110 includes an active layer 111, a passive layer 113, and a coupling layer 112, and an optical field is transmitted by coupling from the active layer 111 to the passive layer 113. It should be noted that the distributed feedback laser 110 further includes an ohmic contact layer, a grating layer, a cladding layer, and the like, and a specific structure is not shown in the drawings, and belongs to a conventional structure, and details are not described here. The distributed feedback laser 110 shown in fig. 2 and 3 has a metal electrode 150 thereon, and the optical field can be generated by energizing the active layer 111 through the metal electrode 150.

It is understood that the active layer 111, the passive layer 113 and the coupling layer 112 in the distributed feedback laser 110 are distributed in the vertical direction, while the straight waveguide 121 is communicated with the passive layer 113 in the filter 120, and the filter 120 does not have the active layer 111, so that the optical field generated in the active layer 111 needs to be coupled into the passive layer 113 in the vertical direction and then transmitted to the filter 120 through the passive layer 113. One end of the waveguide region is gradually narrowed toward the filter 120, and the gradually narrowed shape may be various and is not limited to a specific shape. This narrowing may be understood as a tapered waveguide (Taper)130, i.e., a tapered waveguide 130 is disposed at an end of the waveguide region adjacent to the filter 120. In particular, the tapered waveguide 130 is a portion of the waveguide region, and the optical field can be coupled from the active waveguide to the passive waveguide in a vertical direction by means of the narrowing structure, which is advantageous for reducing optical loss.

It should be noted that the light emitted from the active layer 111 generates a mode field, the coupling layer 112 plays a role of coupling transition of the mode field, and the coupling layer 112 can be understood as a mode field coupling layer. By adjusting the thickness of coupling layer 112 and the width and length of wedge waveguide 130, optimized waveguide parameters of wedge waveguide 130 can be obtained, so that the optical field can be maximally coupled into passive layer 113.

Referring to fig. 4, a nonlinear wedge waveguide 130 is taken as an example for illustration, an optical field in an active waveguide is coupled from the active waveguide into a passive waveguide through the wedge waveguide 130, and by optimizing waveguide parameters and thicknesses of layers and by means of the wedge waveguide 130, the optical field generated in the active waveguide can be maximally transferred into the passive waveguide, and the coupling loss between the active layer 111 and the passive layer 113 is reduced.

Note that the substrate 140 is made of indium phosphide (InP) material, and the substrate 140 can be understood as a base of the distributed feedback laser 110 and the filter 120. It can be understood that, when an epitaxial wafer is made, the passive layer 113, the coupling layer 112, the active layer 111 and other layers on the active layer 111 are grown on the InP substrate 140, and the conventional distributed feedback laser processing is performed on the epitaxial wafer; then, in the filter 120, the active layer 111 and the upper part of the filter 120 are completely removed, and the filter 120 is patterned on the coupling layer 112 and the passive layer 113 to form a straight waveguide 121 and a ring waveguide 122, so that the distributed feedback laser 110 and the filter 120 are formed on the substrate 140.

In an embodiment, the passive layer 113 is made of a material having a larger bandgap than that of the active layer 111, wherein the active layer 111 is an active waveguide containing a multi-Quantum Well (MQW), the passive layer 113 is made of a material having a larger bandgap than the MQW, and the material of the passive layer 113 is a waveguide material that does not absorb optical power. Thus, when the optical field is transmitted in the passive waveguide, the optical field absorption phenomenon can not occur. It should be noted that the passive waveguide is the same as the active waveguide, and the passive waveguide needs to satisfy a single-mode transmission condition of the optical field, specifically, when the distributed feedback laser 110 is powered on, the active waveguide can emit light, and by designing the width and height of the waveguide, the mode field generated by the active waveguide can be single-mode, while the passive waveguide does not need to be powered on, and the passive waveguide does not generate light, but only plays a role in transmitting light. Therefore, the passive waveguide needs to maintain a single-mode field, so that the single-mode transmission condition of the optical field is met, and the situation that a single mode generated in the active waveguide enters the passive waveguide and then becomes a multi-mode is avoided. In addition, the material systems of the active waveguide and the passive waveguide are the same, for example, indium gallium arsenide phosphide (InGaAsP) or aluminum gallium indium arsenide (InGaAlAs) are used, and are all quaternary compounds, and the desired active waveguide or passive waveguide is obtained by adjusting the proportion of the quaternary elements, and the material systems of the active waveguide and the passive waveguide belong to conventional materials and are not described again.

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 thicknesses and waveguide parameters of the active layer 111, the passive layer 113 and the coupling layer 112 can be optimally adjusted, and the optical field can be maximally transferred from the active waveguide to the passive waveguide by means of the wedge waveguide 130 in the optical field transmission process.

Referring to fig. 2 and 3, in some embodiments, the passive layer 113, the straight waveguide 121, and the annular waveguide 122 are all located in the same plane, and it is 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, so that the filter 120 is monolithically integrated with the distributed feedback laser 110. Meanwhile, the straight waveguide 121 and the annular waveguide 122 are also located on the same plane, the waveguide structures are also the same, the straight waveguide 121 is close to the annular waveguide 122, so that the straight waveguide 121 and the annular waveguide 122 can perform optical field coupling, the straight waveguide 121 and the annular waveguide 122 form a filter 120, and the filter 120 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, because the straight waveguide 121 is close to the annular waveguide 122, light enters the annular waveguide 122 from the straight waveguide 121, light satisfying the resonance equation remains in the annular waveguide 122, light not satisfying the condition returns to the straight waveguide 121 and is emitted, and the filter 120 reshapes a Non-return-to-zero Line (NRZ) signal generated by the distributed feedback laser 110.

Referring to fig. 2, specifically, the annular waveguide 122 includes two straight sides disposed oppositely, the two straight sides are parallel to each other and parallel to the straight waveguide 121, wherein a gap between one of the straight sides close to the straight waveguide 121 and the straight waveguide 121 is in a range from submicron to micron, the gap affects a coupling coefficient between the straight waveguide 121 and the annular waveguide 122, the straight side close to the straight waveguide 121 and the straight waveguide 121 form a coupling region, and an optical field can be coupled into the annular waveguide 122 from the straight waveguide 121 or coupled back into the straight waveguide 121 from the annular waveguide 122.

Referring to fig. 2 and 3, a thermal tuning resistor 123 is disposed inside the annular waveguide 122, the thermal tuning resistor 123 is distributed along the inside of the annular waveguide 122, and the resonant wavelength of the filter 120 can be thermally tuned by the thermal tuning resistor 123. The refractive index of the passive waveguide material changes along with the temperature change, the resonance wavelength meeting the resonance equation also changes correspondingly, and the purpose of thermal tuning is achieved through the thermal effect. In this embodiment, the thermal tuning resistor 123 may be made of platinum, but may be made of other materials, and is not limited to the platinum material shown in the embodiment.

It can be understood that the laser 100 of the embodiment can operate the laser 100 with only a small thermal modulation power consumption applied to the filter 120, in addition to the power consumption of the distributed feedback laser 110, and the total power consumption is lower than that of the EML, thereby achieving the purpose of low power consumption. Moreover, compared with the manufacturing process of the EML, butt-joint growth is not needed, and compared with the DFB process, only the steps of etching the passive waveguide and manufacturing the thermal tuning resistor 123 are added, so that the manufacturing process is easy to realize, and the cost is reduced.

Referring to fig. 2 and 3, in some embodiments, a Spot Size Converter (SSC) 124 is disposed at an end of the straight waveguide 121, a front end of the straight waveguide 121 communicates with the passive layer 113, a distal end of the straight waveguide 121 is coupled to an external optical fiber, the Spot Size Converter 124 is disposed at the distal end, and the Spot Size Converter 124 is configured to reduce coupling loss between the laser 100 and the external optical fiber.

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 is transmitted into the filter 120 through the passive layer 113, and by designing parameters of the filter 120, including the waveguide width, the gap, the circumference of the circular waveguide 122, and the like, the NRZ zero-order signal satisfies the wavelength resonance condition, and is further coupled into the circular waveguide 122, and the rest of the light except the loss exits from the SSC at the end of the straight waveguide 121. That is, when the "1" and "0" signals of NRZ pass through the filter 120 in a serial form, the attenuation of the "1" stage signal is lower than that of the "0" stage signal, thereby achieving the purpose of reducing chirp and increasing extinction ratio.

It is understood that the filter 120 has the best filtering effect when in the critical coupling state, and the following two embodiments are taken as examples to realize the critical coupling.

Referring to fig. 2, in the first embodiment, the filter 120 includes three parts, namely a straight waveguide 121, a racetrack-type annular waveguide 122 and a thermal tuning resistor 123, and the straight waveguide 121, the annular waveguide 122 and the passive waveguide in the distributed feedback laser 110 are in the same layer and are all etched from a passive material layer. The optical field in the active waveguide of the distributed feedback laser 110 is coupled in the vertical direction through the wedge waveguide 130, the optical field enters the straight waveguide 121, when passing through the annular waveguide 122, the optical field is coupled to the straight edge of the annular waveguide 122 through the gap between the straight waveguide 121 and the annular waveguide 122 and is transmitted in the annular waveguide 122, the optical field meeting the wavelength resonance equation is continuously transmitted in the annular waveguide 122, and the optical field not meeting the resonance equation is coupled back to the straight waveguide 121 in the coupling region after circulating for one circle, and is coupled into an external optical fiber through the SSC, so that light is emitted.

It can be 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 also has individual differences, in the present embodiment, the thermal tuning resistor 123 is added in the inner ring of the ring waveguide 122, and by energizing the thermal tuning resistor 123, the effective refractive index of the passive waveguide is changed due to the thermal effect, and the wavelength satisfying the resonance equation is correspondingly changed, so as to complete the thermal tuning of the resonance wavelength (filtering wavelength).

Considering that the waveguide bending radius is usually more than 200um to obtain a low-loss micro-ring due to the small refractive index difference between the waveguide core layer and the cladding layer of the iii-v material, the size of the ring waveguide 122 of the first embodiment may be relatively large.

Referring to fig. 3, in the second embodiment, the annular waveguide 122 adopts a rectangular annular structure instead of a racetrack-type annular structure, in the embodiment, the annular waveguide 122 is rectangular, which can be understood as a rectangular waveguide, one total reflection mirror 125 is respectively disposed at four vertex angles of the rectangular waveguide, and the optical field can complete a 90 ° turn with low radiation loss at the total reflection mirrors 125, that is, the optical field is transmitted along a rectangular path. The total reflection mirror 125 is manufactured by deep etching (etching to the InP substrate 140), and since the bending loss of the waveguide is not involved and the radiation loss is small, the filter 120 using the rectangular waveguide can achieve a critical coupling state with a smaller size, so that the device structure can be more compact, and the size of the laser 100 can be reduced. The laser 100 of the embodiment of the invention has the size equivalent to that of the EML, and the packaging process is compatible with the EML.

Similarly, a thermal tuning resistor 123 is provided inside the rectangular waveguide, and the resonance wavelength is thermally tuned by energizing the thermal tuning resistor 123 to generate a thermal effect.

It should be noted that the NRZ signal generated by the distributed feedback laser 110 is affected by the chirp, i.e., the wavelength λ of the "1" signal₁Wavelength λ of AND 0 signal₀Different. The specific resonant wavelength lambda is obtained by designing parameters such as the perimeter of the annular waveguide 122 of the filter 120, the coupling region gap and the like₀Free Spectral Range (FSR) and full width half maximum bandwidth of the resonance peak Δ λ_FWHM. When the NRZ signal of the distributed feedback laser 110 enters the straight waveguide 121, the signal of "0" is transmittedThe wavelength satisfies the resonance equation to enter the racetrack or rectangular ring waveguide 122 and resonate, and the wavelength of the "1" signal does not satisfy the resonance equation to be coupled into the external optical fiber through the spot-size converter 124. Through the process, the wavelength of the '0' signal becomes lambda₀₀And "1" signal wavelength λ₁Without change, the chirp is reduced and the extinction ratio is increased by Δ ER. Fig. 5 is a schematic diagram illustrating the principle of the laser 100 to achieve a low chirp high extinction ratio.

It is understood that the "1" and "0" signals generated for a conventional DFB are generated by applying currents of different magnitudes, which produce output light of different magnitudes, with large light corresponding to the "1" signal and small light corresponding to the "0" signal. Since different currents are applied, the amount of heat introduced is different, so that there is a difference between the wavelengths, as shown in FIG. 5, corresponding to λ₁And λ₀This is the chirp. The resonant wavelength of the filter 120 is designed to be λ₀The "0" signal can be filtered and the dotted line is the harmonic peak (peak that can be filtered) of the filter 120, which is periodic. After filtering, the "0" signal wavelength becomes λ₀₀And λ₁The difference becomes smaller and the chirp becomes smaller, while the extinction ratio between "1" and "0" also increases Δ ER, which is the desired result.

A method for manufacturing a laser according to an embodiment of the present invention, which is suitable for manufacturing the laser 100 according to the above-described embodiment, is described below with reference to fig. 6 to 9.

Referring to fig. 6, the method for manufacturing the laser of the embodiment includes, but is not limited to, the following steps:

s100, growing a passive layer, a coupling layer and an active layer on a substrate in sequence;

step S200, removing part of the active layer and the layer structure above to form a filter area;

and step S300, etching the passive layer and the 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.

It will be appreciated that the laser is fabricated to include both the distributed feedback laser 110 and the filter 120, and epitaxial growth techniques are used to grow an epitaxial wafer on the substrate 140. Specifically, in the case of an epitaxial wafer, the passive layer 113 is grown on the InP substrate 140, the coupling layer 112 is grown, and the active layer 111 is grown. Of course, the distributed feedback laser 110 is not limited to include the passive layer 113, the coupling layer 112, and the active layer 111, and also includes other layers on the active layer 111, such as an ohmic contact layer, a grating layer, a cladding layer, and the like, and therefore, after the active layer 111 is grown, other layers are grown on the active layer 111, which will not be described in detail.

It should be noted that after the passive layer 113, the coupling layer 112, the active layer 111 and other layers above are completed, a manufacturing process of a conventional distributed feedback laser is performed on the epitaxial wafer, for example, the steps of ridge waveguide etching, dielectric layer growth, windowing, metal manufacturing, cavity surface coating and the like of the distributed feedback laser 110 are performed, and details are not described here again. It can be understood that the flow of steps of the method for manufacturing a laser is not limited to the order of steps in the embodiment shown in fig. 6, that is, the steps S100, S200, and S300 and the steps of the conventional distributed feedback laser manufacturing process performed on the epitaxial wafer are not limited to the order shown in the above embodiment, and may be reasonably adjusted according to actual design requirements.

In the method for manufacturing the laser of this embodiment, the epitaxial wafer is divided into the distributed feedback laser region and the filter region, after the epitaxial growth is completed, the process steps of the conventional distributed feedback laser are performed on the epitaxial wafer, and then the active layer 111 and the layer structures above the active layer 111 in the filter region are removed, as shown in fig. 1, in the embodiment, the left side portion of the laser 100 is the filter region, and the filter region does not have the active layer 111 and the layer structures above the active layer 111 on the epitaxial wafer. Then, the coupling layer 112 and the passive layer 113 in the filter region are etched to form the straight waveguide 121 and the annular waveguide 122, and the straight waveguide 121 and the annular waveguide 122 are located on the same plane and are disposed close to each other, so that the straight waveguide 121 and the annular waveguide 122 can be coupled through an optical field and used for reshaping an optical signal generated by the distributed feedback laser 110. Thus, the straight waveguide 121 and the annular waveguide 122 are both formed on the passive layer 113, and the three are located in the same plane, and the straight waveguide 121 is directly communicated with the passive layer 113, so that the filter 120 and the distributed feedback laser 110 are monolithically integrated.

It can be understood that the passive layer 113 and the coupling layer 112 are added in the epitaxial growth process of the distributed feedback laser 110, the straight waveguide 121 and the annular waveguide 122 are directly formed by etching the coupling layer 112 and the passive layer 113, and the filter 120 and the distributed feedback laser 110 share the same passive structure. Compared with the conventional butt joint growth mode adopted by monolithic integration of the DFB and the filter, the method has the advantages that extra extension times are not increased, a complex butt joint growth technology is not needed, the chirp problem during DFB direct adjustment is effectively reduced, and the problems that the conventional DFB has large chirp and small extinction ratio and is not beneficial to long-distance transmission are effectively solved.

Referring to fig. 7, the method for manufacturing a laser according to the embodiment further includes the steps of:

step S400, etching the layers close to the filter region and including the passive layer, the coupling layer and the active layer to form the wedge waveguide.

It is understood that the wedge waveguide 130 is formed at one end of the distributed feedback laser region near the filter region, the wedge waveguide 130 is tapered in a direction toward the filter region, and the wedge waveguide 130 may have a variety of shapes, not limited to a specific shape. The waveguide region comprises an active layer 111, a passive layer 113 and a coupling layer 112, a straight waveguide 121 is communicated with the passive layer 113 in the filter 120, an optical field generated in the active layer 111 needs to be coupled into the passive layer 113 and then transmitted to the filter 120 through the passive layer 113, the wedge waveguide 130 is a part of the waveguide region, and the optical field can be coupled from the active waveguide to the passive waveguide in the vertical direction by means of the structure of the wedge waveguide 130. Specifically, by optimizing the waveguide parameters and the thickness of each layer and by means of the wedge waveguide 130, the optical field generated in the active waveguide can be maximally transferred into the passive waveguide, and the coupling loss between the active layer 111 and the passive layer 113 is reduced.

Referring to fig. 8, the method for manufacturing a laser according to the embodiment further includes the steps of:

step S500, manufacturing a thermal tuning resistor on the inner side of the annular waveguide.

It can be understood that after the straight waveguide 121 and the annular waveguide 122 are etched, the thermal tuning resistor 123 is fabricated inside the annular waveguide 122, the thermal tuning resistor 123 extends along the inside of the annular waveguide 122, the thermal tuning resistor 123 can be used to thermally tune the resonant wavelength of the filter 120, and the specific working principle is not described again. The manufacturing steps of the thermal tuning resistor 123 can be applied to the race track type annular waveguide 122 and the rectangular waveguide, and the manufacturing process is easy to implement and is beneficial to reducing the cost.

Referring to fig. 9, when a rectangular waveguide is manufactured, a total reflection mirror 125 needs to be disposed at a vertex angle of the rectangular waveguide, and in particular, the method for manufacturing a laser according to the embodiment further includes the following steps:

and S600, when the rectangular waveguide is manufactured, a total reflector is manufactured by utilizing a deep etching process.

It should be noted that the annular waveguide 122 is rectangular, a total reflection mirror 125 is etched at each of four vertex angles of the rectangular waveguide, and the optical field can complete a 90-degree turn with low radiation loss at the total reflection mirror 125, that is, the optical field is transmitted along a rectangular path. The deep etching process may be understood as a process of etching to the InP substrate 140 to form the total reflection mirrors 125. The filter 120 adopting the rectangular waveguide can achieve a critical coupling state with a smaller size, can make the device structure more compact, and is beneficial to reducing the size of the laser 100, the size of the laser 100 of the embodiment of the invention is equivalent to that of the EML, and the packaging process is compatible with the EML.

It should be noted that, steps S100, S200, S300, S400, S500, and S600 shown in the above embodiments are not limited to a specific sequence, and may be reasonably adjusted according to actual design requirements. Based on the laser 100 provided in the foregoing embodiment, 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, where the optical line terminal includes the laser 100 provided in the foregoing embodiment, and the optical network unit includes the laser 100 provided in the foregoing embodiment.

Based on the laser 100 provided in the foregoing embodiment, another embodiment of the present invention provides an optical network system, which includes an optical line terminal located in a central control station and a plurality of optical network units located at a user side, where the optical line terminal and the optical network units perform optical network communication, the optical line terminal includes a laser for providing a data modulation transmission function, and the laser is the laser 100 provided in the foregoing embodiment; the optical network unit includes a laser for providing a data modulation transmission function, and the laser is the laser 100 provided in the above embodiment.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.

Claims

1. A laser, comprising:

a substrate on which the distributed feedback laser and the filter are formed.

2. The laser of claim 1, wherein the active layer, the coupling layer, and the passive layer form a waveguide region that narrows proximate to an end of the filter.

3. The laser of claim 2, wherein the narrowing portion of the waveguide region is wedge-shaped in cross-section.

4. The laser of claim 1, wherein the passive layer has a material bandgap greater than that of the active layer.

5. The laser of claim 1, wherein the straight waveguide and the annular waveguide are both made of the extended passive layer, and the straight waveguide and the annular waveguide are located in the same plane and have the same waveguide structure.

6. The laser of claim 1, wherein the annular waveguide comprises a straight edge parallel to the straight waveguide, and a gap between the straight edge and the straight waveguide is in a range from submicron to micron order, so that a coupling region is formed between the straight waveguide and the annular waveguide.

7. The laser according to claim 1 or 6, wherein the annular waveguide is a racetrack or a rectangular ring structure, and total reflection mirrors are respectively arranged at rectangular vertex angles of the rectangular ring structure.

8. The laser of claim 1, wherein a thermal tuning resistor is disposed inside the annular waveguide for thermally tuning a resonant wavelength of the filter.

9. The laser of claim 1, wherein the end of the straight waveguide is provided with a mode spot converter for reducing coupling loss of the laser with an external optical fiber.

10. The laser of claim 1, wherein the substrate material is indium phosphide.

11. A method of fabricating a laser, comprising:

12. The method of manufacturing a laser according to claim 11, further comprising:

and etching the layers close to the filter region, including the passive layer, the coupling layer and the active layer to form a wedge-shaped waveguide.

13. The method of manufacturing a laser according to claim 11, further comprising:

and manufacturing a thermal tuning resistor on the inner side of the annular waveguide.

14. An optical communication device comprising a laser as claimed in any one of claims 1 to 10.

15. An optical network system, comprising 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 optical network unit comprises a laser according to any of claims 1 to 10.