Multi-wavelength laser based on vertical gain cavity

Abstract

The invention discloses a multi-wavelength laser based on a vertical gain cavity, and belongs to the field of semiconductor lasers. Comprising a vertical emission array chip and a silicon-based external cavity chip, the vertical emission array chip is mainly characterized in that light is vertical to the surface of the chip and emits light, the vertical emission array chip comprises at least two vertical emission devices serving as an optical vertical gain area, and the silicon-based external cavity chip comprises a coupler, a phase modulation area, a light reflector, a wavelength division multiplexer and an output area. Mode selection is carried out through the light reflector, light feedback of different wavelengths is achieved, a laser resonant cavity is formed by the light reflector and the vertical emission array chip, and work of multiple single wavelengths is achieved; and finally, wave combination is carried out through a wavelength division multiplexer to form the multi-wavelength laser. The device is high in integration level, good in stability, simple in process and low in cost, and the technical effects of ultra-multiple channels, ultra-narrow linewidth, large output optical power and large-area integration can be achieved at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor lasers, and particularly relates to a multi-wavelength laser based on a vertical gain cavity. Background Art

[0002] For applications such as short-distance dense data communication, ultra-high bandwidth optical interconnection, high-speed free-space optical communication, and high-precision spectral detection, a multi-wavelength narrow linewidth semiconductor laser is required to provide a light source signal with low phase noise, high coherence, and multiple wavelengths to meet the requirements of wavelength division multiplexing and comb spectra of the system.

[0003] Currently, the mainstream of multi-wavelength narrow linewidth lasers is to achieve comb spectra based on DFB laser arrays, microcavity optical frequency combs, and microwave modulation.

[0004] Among them, the DFB laser array adopts a monolithic integration scheme. Due to material limitations and thermo-optical crosstalk, only 4 - 8 channels can be integrated, and the linewidth is generally on the order of MHz due to the characteristics of the active material.

[0005] The microcavity optical frequency comb scheme generates multiple wavelengths by highly exciting the microcavity nonlinear effect. Currently, it is still a laboratory research scheme. The main problems are poor stability, small output power, and unequal power among multiple channels.

[0006] The microwave modulation scheme generates multiple wavelengths by inducing four-wave mixing through microwave modulation of a single light source. The advantage of this scheme is good stability, and the disadvantage is that it is difficult to integrate, and the modulator requires a large amount of microwave power. Summary of the Invention

[0007] The object of the present invention is to propose a multi-wavelength laser based on a vertical gain cavity for the problems existing in the background art, aiming to achieve a multi-wavelength laser with ultra-high channels, ultra-narrow linewidth, large output optical power, and large-area integration by utilizing the characteristics of high silicon photonic integration and good stability, as well as the characteristics of simple process and low cost of the vertical emission array chip.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows: A multi-wavelength laser based on a vertical gain cavity includes a vertical emission array chip and a silicon-based external cavity chip;

[0009] The vertical emission array chip includes a reflector, an upper cladding layer, a quantum well region, a lower cladding layer, and a contact layer connected in sequence. The contact layer is connected to the silicon-based external cavity chip, and after the quantum well region emits light, the light is vertically fed back to the silicon-based external cavity chip through the reflector;

[0010] The silicon-based external cavity chip includes a coupler, a phase modulation region, a light reflector, a wavelength division multiplexer, and an output region;

[0011] The coupler is used to connect the vertical emission array chip and the silicon-based external cavity chip, and is connected to the phase modulation region, the optical reflector, the wavelength division multiplexer and the output region in sequence through a waveguide, and serves as the output port of the multi-wavelength laser through the output region.

[0012] On the other hand, the connection method between the vertical emission chip and the silicon-based external cavity chip includes: fixing the vertical emission chip on the silicon-based external cavity chip through a contact layer, erecting the vertical emission chip, and directly realizing coupling with the silicon-based external cavity chip through end-to-end coupling or lens coupling;

[0013] Among them, when the vertical emission chip is installed on the silicon-based external cavity chip, the coupling methods between the coupler and the vertical emission chip include end face coupling, evanescent wave, grating coupling, lens coupling, flip-chip packaging or wafer bonding methods.

[0014] On the other hand, when the vertical emission chip is installed on the silicon-based external cavity chip, it also includes a 45-degree rotation of the end face of the silicon-based external cavity chip to directly transfer the light of the chip waveguide to the vertical emission chip. The forms of the 45-degree rotation include grinding and polishing the end face of the silicon-based external cavity chip at 45 degrees, pasting a 45-degree corner prism or a 45-degree lens coupling on the end face of the silicon-based external cavity chip.

[0015] On the other hand, the connection methods of the components in the silicon-based external cavity chip include: one is that the coupler is connected to the phase modulation region, the optical reflector, the wavelength division multiplexer and the output region in sequence through a waveguide; the other includes that the phase modulation array is directly connected to each input port of the wavelength division multiplexer, and the output port of the wavelength division multiplexer is connected to the optical reflector.

[0016] On the other hand, the phase modulation region is used to adjust the wavelength phase of the laser, and the adjustment methods include electrical tuning and thermal tuning. The formed longitudinal mode interval is where n is the equivalent refractive index in the cavity, L is the equivalent cavity length of the laser, m is the order, and λ is the lasing wavelength.

[0017] On the other hand, the optical reflector includes a Sagnac mirror, a Bragg mirror, and a photonic crystal; it has a high Q band-pass effect, selects the mode of the longitudinal mode of the laser and realizes the optical feedback of different wavelengths, forms a laser resonant cavity with the vertical emission array chip, and realizes multiple single-wavelength operations.

[0018] On the other hand, the wavelength division multiplexer is used to multiplex different wavelengths of light, and at the same time plays a role in filtering or mode selection. It includes a cascaded MZI structure, an AWG, an EDG or a microring resonator.

[0019] On the other hand, the output methods of the output region include end face output, grating surface output, and lens coupling output.

[0020] On the other hand, the vertical emission array chip can be a vertical cavity FP array chip. Single modes are respectively formed through a silicon-based external cavity, and then multi-wavelength operation is achieved through a wavelength division multiplexer.

[0021] On the other hand, an optical resonator is introduced at the output end, including a micro-ring resonator, a Bragg reflector or an optical etalon, to form an injection locking structure.

[0022] On the other hand, the material of the silicon-based external cavity chip includes SOI, SiN, SiON, SiO2 or lithium niobate material.

[0023] Beneficial effects:

[0024] The vertical emission array chip has the characteristic of a large emission surface. It can not only achieve high-power output, but also be easily coupled with a silicon-based chip. The process is simple and has extremely high process tolerance; the silicon-based external cavity chip has a high integration level, achieving the technical effect of a small size; whether it is a silicon photonics chip or a vertical emission array chip, they are both widely used commercial technology platforms at present, and the prices are very low, having the technical effect of low cost; by designing an optical feedback mechanism with high Q band-pass performance and a wavelength division multiplexer structure to select modes for different wavelengths simultaneously, a DWDM multi-wavelength light source is realized. It not only has a large number of channels, but also achieves the narrow linewidth technical effect of an external cavity laser. Description of the Drawings

[0025] Figure 1 is a schematic cross-sectional structure diagram of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 1 of the present invention;

[0026] Figure 2 is a schematic top view structure diagram of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 1 of the present invention;

[0027] Figure 3 is a schematic working principle diagram of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 1 of the present invention;

[0028] Figure 4 is a schematic cross-sectional structure diagram of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 2 of the present invention;

[0029] Figure 5 is a schematic cross-sectional structure diagram of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 3 of the present invention. Detailed Embodiments

[0030] The following further describes the specific embodiments of the present invention in detail with reference to the drawings.

[0031] As Figure 1 shown, a multi-wavelength laser based on a vertical gain cavity is provided, including a vertical emission array chip 1 and a silicon-based external cavity chip 2;

[0032] The vertical emission array chip includes a mirror 10, an upper cladding layer 11, a quantum well region 12, a lower cladding layer 13, and a contact layer 14, wherein the contact layer 14 is connected to the silicon-based external cavity chip 2;

[0033] The silicon-based external cavity chip 2 is composed of a cover layer 211, a core layer 212, a box layer 213, and a substrate 214. Corresponding devices need to be fabricated on the core layer 212 to achieve functions, including a coupler 221, a phase modulation region 222, an optical reflector 223, a wavelength division multiplexer 224, and an output region 225;

[0034] The coupler 221 is used to connect the vertical emission array chip 1 and the silicon-based external cavity chip 2, and is connected to the phase modulation region 222, the optical reflector 223, the wavelength division multiplexer 224, and the output region 225 in sequence through a waveguide. The output region 225 serves as the output port of the multi-wavelength laser;

[0035] The quantum well region 12 of the vertical emission array chip 1 provides population inversion for the laser by applying a current to provide gain. The upper cladding layer 11 and the lower cladding layer 13 provide optical confinement. The reflectivity of the mirror 10 is 100%, and the light is fed back to the contact layer 14, causing the light to emit perpendicular to the chip surface. The light of the vertical emission array chip 1 is transmitted to the silicon-based external cavity chip 2 through the contact layer 14.

[0036] The mirror 10 includes a Bragg mirror and a metal electrode mirror.

[0037] The contact layer 14 is used to fix the vertical emission array chip 1 on the silicon-based external cavity chip 2, and the fixing method can be flipchip metal bonding, wafer bonding, or lens coupling.

[0038] Embodiment 1:

[0039] Figure 2 It is a top view schematic diagram of the structure of a multi-wavelength laser based on a vertical gain cavity according to Embodiment 1 of the present invention.

[0040] The coupler 221, the phase modulation region 222, the optical reflector 223, the wavelength division multiplexer 224, and the output region 225 are integrated on the silicon optical chip, and the core layer material of the optical transmission waveguide is SOI, SiN, SiON, SiO2, or lithium niobate material.

[0041] The coupler 221 realizes optical coupling between the vertical emission array chip 1 and the silicon-based external cavity chip 2, and the coupling methods include end-face coupling, evanescent wave, grating coupling, lens coupling, flip-chip packaging, and wafer bonding.

[0042] The phase region 222 can adjust the phase of light through a thermal control or an electrical control mechanism, and is used to control the light wavelength in the resonant cavity formed by the mirror 10 and the optical reflector 223 to meet the resonance condition, that is, to make the phase of the light be an integer multiple of 2π when it travels back and forth in the optical resonant cavity once, so as to emit the corresponding wavelength, as shown in the formula: That is, 2nL = mλ, and the formed longitudinal mode interval is where n is the equivalent refractive index in the cavity, L is the equivalent cavity length of the laser, m is the order, and λ is the lasing wavelength.

[0043] Figure 3 It is a schematic diagram of the working principle of the first embodiment of the present invention. Each device in the vertical emission array chip is the same and has a very wide gain spectrum. In each path, the optical reflector is a band-pass reflector with a high Q band-pass effect to achieve optical feedback of different wavelengths, as Figure 3 shown by various dotted lines. The feedback light and the mirror of one of the devices of the vertical emission array chip 1 together form a laser resonant cavity. Since the band-pass of the optical reflector is less than the longitudinal mode interval, the longitudinal modes of the laser are mode-selected to achieve single-wavelength operation. The wavelength division multiplexer is a passband filter, as Figure 3 shown by the solid line of, which can multiplex the light of different wavelengths formed and output from a single output port, and at the same time play a role in filtering or mode selection, so as to realize a multi-wavelength light source.

[0044] The optical reflector 223 includes a Sagnac mirror, a Bragg mirror, and a photonic crystal.

[0045] The wavelength division multiplexer 224 can have a cascaded MZI structure, an AWG, an EDG, or a microring resonator.

[0046] The output region 224 serves as the laser output port, and the output methods include end-face output, grating surface output, and lens coupling output.

[0047] The vertical emission array chip can be a vertical cavity FP array chip, including adding a mirror 10 between the early vertical emission chip contact layer 14 and the lower cladding layer 13, which can be a traditional III-V material grown or formed by coating. The vertical cavity FP laser emits a series of longitudinal modes, and then its mode is selected by a silicon-based external cavity. The effect produced is that the threshold of the single-mode laser is greatly reduced.

[0048] The traditional vertical emission chip is multimode. The present invention designs an optical feedback mechanism with high Q band-pass performance and combines the wavelength division multiplexer structure to simultaneously select modes for different wavelengths to meet the single-mode condition. Due to the advantages of the silicon photonics process node, the wavelength of this reflector can cover a very wide range. Combined with the wavelength division multiplexer, not only are there many channels, but also the narrow linewidth technical effect of an external cavity laser is achieved.

[0049] In the traditional structure, an edge-emitting chip is adopted, which is generally coupled through a lens. As the number of channels increases, it has a large volume, low coupling efficiency, and high cost. The vertical emission array chip adopted in the present invention has the characteristic of a large light-emitting surface. At present, a multi-layer quantum well, a multi-junction quantum well or an array vertical structure is adopted, and a high power output of 300 mW can be realized, which is much larger than that of the traditional edge-emitting laser structure. The light spots of the vertical emission array chips are all circular, which are easy to be coupled with the silicon-based chip. The vertical emission array chip integrally integrates multiple emission units at one time, and the laser lasing of dozens of wavelengths is completed in one coupling. The process is simple and has extremely high process tolerance. The wavelength division multiplexer structure can be designed to be more than 40 wavelengths, and it is very easy to realize a DWDM multi-wavelength light source with a super large number of channels, which is much more than that of the traditional DFB array multi-wavelength laser.

[0050] Make full use of the high integration advantage of the silicon-based external cavity chip to achieve a small size. Improve the linewidth performance by increasing the equivalent cavity length. At the same time, design an optical reflector with high Q band-pass performance to meet the single-mode working conditions of each wavelength. Through theoretical calculation, when the equivalent cavity length reaches 10 mm, the linewidth can reach below 20 kHz, which is one order of magnitude better than that of the commercial monolithic integrated narrow linewidth laser.

[0051] Finally, whether it is a silicon photonics chip or a vertical emission array chip, they are both currently widely used commercial technology platforms, and the prices are very low, having the technical effect of low cost.

[0052] Embodiment 2

[0053] As Figure 4 shown, it is a top view schematic diagram of Embodiment 2 of the present invention. The difference from Embodiment 1 is that the phase modulation array 222 is directly connected to each input port of the wavelength division multiplexer 224. The output port of the wavelength division multiplexer 224 is connected to the optical reflector 223, and finally connected to the output port 225. The advantage of doing this is that the optical reflector 223 does not need to be separately designed for each wavelength, and only needs to be designed as a wide spectrum. The structure can be a ring mirror or a Bragg reflector. To achieve single-mode operation, the optical bandwidth of each channel of the wavelength division multiplexer needs to be less than the longitudinal mode interval.

[0054] Embodiment 3

[0055] As Figure 5 shown, it is a top view schematic diagram of Embodiment 3 of the present invention. An optical resonator is introduced at the output end, including a micro-ring resonator, a Bragg reflector or an optical etalon, to form an injection locking structure, further improving the linewidth performance of the laser. The injection locking principle is known to professionals and will not be elaborated here. The order of the various structures included in the silicon-based external cavity chip can be interchanged.

[0056] Embodiment 4

[0057] The end face of the silicon-based external cavity chip is angled at 45 degrees, directly transferring the light of the chip waveguide to the vertical emission array chip 1. The forms of the 45-degree angle include grinding and polishing the end face of the silicon-based external cavity chip at 45 degrees, pasting a 45-degree angle prism on the end face of the silicon-based external cavity chip, and coupling with a 45-degree lens.

[0058] Example Five

[0059] The vertical emission array chip 1 is erected and coupled to the silicon-based external cavity chip directly through end-to-end connection or through lens coupling.

[0060] Example Six

[0061] The multi-wavelength laser can further be monolithically integrated with the silicon-based optoelectronic chip or heterogeneously integrated with other chips, greatly improving the integration of the system.

[0062] After considering the specification and practicing the content disclosed herein, those skilled in the art will readily conceive of other embodiments of the present application. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and examples are only illustrative, and the true scope and spirit of the present application are pointed out by the claims.

[0063] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and do not limit the present application. The present application is not limited to the precise structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A multi-wavelength laser based on a vertical gain cavity, characterized in that, It includes a vertical emission array chip and a silicon-based external cavity chip; The vertical emission array chip includes a mirror, an upper cladding layer, a quantum well region, a lower cladding layer, and a contact layer connected in sequence. The contact layer is connected to the silicon-based external cavity chip. After the quantum well region emits light, the light is vertically fed back to the silicon-based external cavity chip through the mirror; The silicon-based external cavity chip includes a coupler, a phase modulation region, an optical reflector, a wavelength division multiplexer, and an output region; The coupler is used to connect the vertical emission array chip and the silicon-based external cavity chip, and is connected to the phase modulation region, the optical reflector, the wavelength division multiplexer, and the output region through a waveguide. The output region serves as the output port of the multi-wavelength laser; 2. The multi-wavelength laser based on a vertical gain cavity according to claim 1, characterized in that The connection method between the vertical emission chip and the silicon-based external cavity chip includes: fixing the vertical emission chip on the silicon-based external cavity chip through the contact layer, standing the vertical emission chip upright, and directly realizing coupling with the silicon-based external cavity chip through end-to-end coupling or lens coupling; Among them, when the vertical emission chip is installed on the silicon-based external cavity chip, the coupling method between the coupler and the vertical emission chip includes end-face coupling, evanescent wave, grating coupling, lens coupling, flip-chip packaging, or wafer bonding method; 3. The multi-wavelength laser based on a vertical gain cavity according to claim 2, wherein When the vertical emission chip is installed on the silicon-based external cavity chip, it also includes a 45-degree rotation of the end face of the silicon-based external cavity chip to directly transfer the light of the chip waveguide to the vertical emission chip. The form of the 45-degree rotation includes grinding and polishing the end face of the silicon-based external cavity chip by 45 degrees, pasting a 45-degree turning prism or a 45-degree lens coupling on the end face of the silicon-based external cavity chip; 4. A silicon-based external cavity laser based on a vertical gain cavity according to claim 1, characterized in that, The connection method of each component in the silicon-based external cavity chip includes: one is that the coupler is connected to the phase modulation region, the optical reflector, the wavelength division multiplexer, and the output region in sequence through a waveguide; the other includes that the phase modulation array is directly connected to each input port of the wavelength division multiplexer, and the output port of the wavelength division multiplexer is connected to the optical reflector; 5. The silicon-based external cavity laser based on a vertical gain cavity according to claim 1, characterized in that, The phase modulation region is used to adjust the wavelength phase of the laser, and the adjustment methods include electrical adjustment and thermal adjustment. The formed longitudinal mode interval is where n is the equivalent refractive index in the cavity, L is the equivalent cavity length of the laser, m is the order, and λ is the lasing wavelength.

6. The silicon-based external cavity laser based on a vertical gain cavity according to claim 1, wherein The optical reflector includes a Sagnac mirror, a Bragg mirror, and a photonic crystal; it has a high-Q band-pass effect, selects the mode of the laser longitudinal mode, and realizes the optical feedback of different wavelengths, and forms a laser resonant cavity together with the vertical emission array chip to realize multiple single-wavelength operations; 7. A silicon-based external cavity laser based on a vertical gain cavity according to claim 1, characterized in that, The wavelength division multiplexer is used to multiplex different wavelengths of light, and at the same time plays a role in filtering or mode selection. It includes a cascaded MZI structure, an AWG, an EDG, or a micro-ring resonator; 8. A silicon-based external cavity laser based on a vertical gain cavity according to claim 1, characterized in that, The vertical emission array chip is a vertical cavity FP array chip, and single modes are respectively formed through the silicon-based external cavity, and then multi-wavelength operation is realized through the wavelength division multiplexer; 9. The silicon-based external cavity laser based on a vertical gain cavity according to claim 4, wherein, Introducing an optical resonator at the output end includes a micro-ring resonator, a Bragg reflector, or an optical etalon to form an injection locking structure; 10. A silicon-based external cavity laser based on a vertical gain cavity according to claim 1, characterized in that, The material of the silicon-based external cavity chip includes SOI, SiN, SiON, SiO2, or lithium niobate material;

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