External cavity lasers and devices

Abstract

This application belongs to the field of lasers, specifically disclosing an external cavity laser and device. The external cavity laser includes a gain chip, an external resonant cavity, and a coupling module. The gain chip and the external resonant cavity are coupled together via the coupling module. The external resonant cavity includes a waveguide structure, a grating, and a phase change material layer. The grating is disposed on the waveguide structure, and the phase change material layer is stacked on the surface of the grating, including interconnected planar portions and protrusions. The protrusions fill the grooves in the grating. Therefore, this external cavity laser can achieve rapid wavelength tuning while reducing energy consumption.

Description

Technical Field

[0001] This application belongs to the field of lasers, specifically relating to an external cavity laser and device. Background Technology

[0002] With the expanding applications of narrow-linewidth lasers capable of rapid and continuous frequency tuning, such as long-range laser sensing, precise ranging, continuous-wave tuned (FMCW) lidar, optical atomic clocks, and quantum technology, the demand for rapidly tunable lasers is constantly increasing. Compared to solid-state and fiber lasers, semiconductor lasers have a simpler structure and smaller size. External-cavity semiconductor lasers, in particular, combine linewidth compression with tuning capabilities, making them a promising candidate for widespread applications. However, coupling losses caused by the integration methods between semiconductor devices can affect the tuning speed of the laser. Therefore, further research is needed to reduce coupling losses and improve the accuracy of external-cavity lasers. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art. To this end, this application proposes an external cavity laser and device with rapidly tunable wavelength, low device loss, or low power consumption.

[0004] The first aspect of this application discloses an external cavity laser, comprising a gain chip, an external resonant cavity, and a coupling module. The gain chip and the external resonant cavity are coupled together via the coupling module. The external resonant cavity includes a waveguide structure, a grating, and a phase change material layer. The grating is disposed on the waveguide structure, and the phase change material layer is stacked on the surface of the grating and includes interconnected planar portions and protrusions. The protrusions fill the grooves in the grating. Therefore, this external cavity laser can quickly and accurately tune its wavelength, has low power consumption, and is widely applicable.

[0005] In some embodiments, the phase change material comprises germanium-antimony-selenium-tellurium. This enables rapid and stable multi-level state tuning, thereby improving the applicability and accuracy of external cavity lasers.

[0006] In some embodiments, the grating includes a Bragg grating. This allows for wavelength selection of the incident light, further compression of the linewidth, and thus gain of light at a specific wavelength.

[0007] In some embodiments, the grating period of the grating is 350 nm to 359 nm. This helps to reduce grating loss and increase the effective refractive index of the grating.

[0008] In some embodiments, the duty cycle of the grating is 50%.

[0009] In some embodiments, the depth of the grating is 40 nm to 50 nm.

[0010] Setting the parameters of the grating within the above range is beneficial for improving the coupling coefficient of the grating and achieving the maximum Bragg reflectivity.

[0011] In some embodiments, the thickness of the planar portion is 10 nm to 15 nm. This allows for more uniform deposition of the phase change material, thereby enabling rapid wavelength tuning.

[0012] In some embodiments, the waveguide structure is made of SiN. This enables the external cavity laser to withstand high voltages, reduces the overall loss of the external cavity laser, and thus lowers the laser emission threshold voltage.

[0013] In some embodiments, the thickness of the waveguide structure is 300 nm to 600 nm.

[0014] In some embodiments, the width of the waveguide structure is 800 nm to 1000 nm.

[0015] The thickness and width of the waveguide structure are within the above range, which is beneficial to improving the effective refractive index of the waveguide, thereby enabling rapid wavelength tuning.

[0016] In some embodiments, the coupling module includes a photonic wire bonding structure. This reduces mode profile mismatch between the gain chip and the waveguide, thereby reducing coupling losses and further improving the wavelength tuning accuracy of the external cavity laser.

[0017] In some embodiments, the gain chip includes an active region made of indium gallium arsenide phosphide. This allows for more efficient absorption and emission of light.

[0018] The second aspect of this application discloses a device including the external cavity laser described in the first aspect of this application. This improves the overall operational efficiency of the device.

[0019] In some embodiments, the device includes at least one of a fiber optic sensor, an optical communication device, a lidar, and a high-resolution spectrometer. Therefore, this external cavity laser has a wide range of applications and broad prospects. Attached Figure Description

[0020] Figure 1 This is a front view of a structural schematic diagram of an embodiment of this application.

[0021] Figure 2 This is a top view of a structural schematic diagram of an embodiment of this application.

[0022] Figure 3 This is a side view of a structural schematic diagram of an embodiment of this application.

[0023] Figure 4 This is a partial enlarged view of a grating according to an embodiment of this application.

[0024] Figure 5 This is a top view of a PWB photonic wire bonding structure according to an embodiment of this application.

[0025] Figure 6 This is a front view of a PWB photonic wire bonding structure according to an embodiment of this application.

[0026] Figure label:

[0027] 1-Gain chip; 2-External resonant cavity; 3-Coupled module; 4-Waveguide structure; 5-Grate; 6-Phase change material layer; 7-Indium phosphide substrate; 8-N-doped region; 9-Active region; 10-P-doped region; 11-Electrode; 12-High reflectivity coating; 13-Anti-reflective coating; 14-SiO2 substrate; 15-PWB; 16-First waveguide; 17-Second waveguide. Detailed Implementation

[0028] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0029] The first aspect of this application discloses an external cavity laser, with reference to... Figure 1 The external cavity laser includes a gain chip 1, an external resonant cavity 2, and a coupling module 3. The gain chip and the external resonant cavity are coupled together through the coupling module. The external resonant cavity includes a waveguide structure 4, a grating 5, and a phase change material layer 6. The grating is disposed on the waveguide structure, and the phase change material layer is stacked on the surface of the grating and includes interconnected planar portions and protrusions. The protrusions fill the grooves in the grating (see reference). Figure 4 Furthermore, a top view of this external cavity laser can be found by referring to... Figure 2 The side view can be referenced. Figure 3 .

[0030] This application integrates a phase change material (PCM) and a grating. By applying a voltage to the PCM, its phase state is changed within nanoseconds (ns). Because the effective refractive index varies greatly between different PCM phase states, integration with the grating allows for adjustment of the grating's effective refractive index. Since the grating's reflection wavelength is directly related to its effective refractive index, rapidly changing the PCM's effective refractive index is equivalent to rapidly changing the grating's effective refractive index, thus enabling rapid wavelength tuning. Regarding the PCM configuration, this application fills the grating groove with PCM and then covers it with another layer of PCM to avoid uneven groove filling caused by the deposition process, thereby further improving the stability and accuracy of the external cavity laser.

[0031] It should be noted that, referring to Figure 1 Common gain chips typically include a substrate (7), an N-doped region (8), an active region (9), a P-doped region (10), and an electrode (11). The specific choice of gain chip is not limited and can be flexibly configured according to specific needs. In this application, the active region is made of indium gallium arsenide phosphide (InGaAsP). InGaAsP possesses the characteristics of a direct bandgap semiconductor, effectively absorbing and emitting light. Furthermore, it has good lattice matching with the indium phosphide (InP) substrate, allowing them to be easily integrated onto the same platform to form a composite material structure. After applying a certain voltage, particle inversion occurs within the active region of the gain chip, promoting the recombination of charge carriers and holes. During recombination, energy is released in the form of photons. These photons excite more photons during resonance in the resonant cavity. When the gain can compensate for the cavity losses, laser light is emitted.

[0032] In some embodiments, the phase change material includes germanium-antimony-selenium-tellurium (GSST). There are many types of phase change materials, with two main types currently: transition metal oxides and chalcogenide phase change materials. Due to the thermal sensitivity and volatility of transition metal oxides, this application chooses non-volatile materials like chalcogenide phase change materials to combine with the external cavity laser. However, chalcogenide phase change materials are diverse in type and quantity, and the phase switching time, thermal expansion coefficient, crystallization temperature, melting temperature, and refractive index of each phase vary, making it challenging to select a suitable material to ensure stable and rapid wavelength tuning of the laser. GSST, due to its fast phase switching speed, large refractive index difference between crystalline and amorphous states, high crystallization temperature, and small extinction coefficients between crystalline and amorphous states, can achieve rapid and stable multi-level state tuning, making rapid and precise wavelength tuning of the laser possible. Its non-volatility allows it to adapt to various harsh environments without affecting the normal operation of the laser, thereby improving the applicability and accuracy of the external cavity laser.

[0033] In some embodiments, the grating includes a Bragg grating, which can be directly etched onto the waveguide structure. The Bragg grating is a reflective grating, and its working principle is that the forward-propagating guided mode and the reverse-propagating guided mode generate energy coupling in the grating region, forming a reflected wave of a specific wavelength. This application uses a waveguide in the form of a Bragg grating to select the incident light, further compress the linewidth, and thus increase the gain of light at a specific wavelength.

[0034] In some embodiments, the grating period of the grating is 350nm to 359nm, for example, it can be 350nm, 351nm, 352nm, 353nm, 354nm, 355nm, 356nm, 357nm, 358nm, or 359nm. It can be understood that different wavelengths can be obtained by adjusting the grating period; if a wavelength of 1310nm is required, a grating period of 303nm is used; if a wavelength of 1550nm is required, a grating period of 359nm is used. This helps to reduce grating loss and improve the effective refractive index of the grating.

[0035] In some embodiments, the duty cycle of the grating is 50%. The grating duty cycle refers to the ratio of transparent to opaque areas in the grating. Different grating duty cycles can be obtained by setting the width and spacing of the transparent and opaque areas during the grating fabrication process.

[0036] In some embodiments, the depth of the grating is 40nm to 50nm, for example, it can be 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47nm, 48nm, 49nm or 50nm, etc.

[0037] Setting the grating parameters within the above range is beneficial for improving the grating coupling coefficient and achieving the maximum Bragg reflectivity at a wavelength of 1550nm.

[0038] In some embodiments, the thickness of the planar portion is 10nm to 15nm, for example, 10nm, 11nm, 12nm, 13nm, 14nm, or 15nm. This application fills the grooves of the grating with phase change material and then deposits another layer of phase change material on the surface. By applying a specific voltage, the phase change material achieves rapid conversion between an amorphous and crystalline state. Utilizing the differences in refractive index and extinction coefficient between the crystalline and amorphous states, the overall effective refractive index of the waveguide changes, causing a change in the Bragg wavelength, thereby achieving rapid wavelength tuning.

[0039] In some embodiments, the waveguide structure is made of SiN. Due to its wide bandgap, the SiN waveguide has the ability to withstand high voltages, and its low-loss characteristics can reduce the overall loss of the external cavity laser, thereby lowering the laser emission threshold voltage.

[0040] In some embodiments, the thickness of the waveguide structure is 300nm to 600nm, for example, it can be 300nm, 350nm, 400nm, 450nm, 500nm, 550nm or 600nm.

[0041] In some embodiments, the width of the waveguide structure is 800nm ​​to 1000nm, for example, it can be 800nm, 850nm, 900nm, 950nm or 1000nm.

[0042] The thickness and width of the waveguide structure are within the above range, which is beneficial to improving the effective refractive index of the waveguide, thereby enabling rapid wavelength tuning.

[0043] In some embodiments, the coupling module includes a photonic wire bonding structure, and a specific structural diagram can be found in the following figures. Figure 5 and Figure 6 Among these technologies, photonic wire bonding technology controls high-energy pulsed light beams to induce multiphoton polymerization of photoresist at specific locations, forming three-dimensional polymer waveguides. These waveguides completely confine light within, enabling efficient and low-loss transmission of optical signals between different photonic devices or chips.

[0044] The external cavity laser described in this application has at least the following beneficial effects:

[0045] 1. Wavelength tuning speed has been optimized: Thanks to the nanosecond-level phase switching speed of phase change materials, the wavelength of external cavity lasers can be tuned in a very short time, making them applicable to applications requiring rapid tuning.

[0046] 2. Reduced device losses: Thanks to the use of SiN waveguides and GSST phase change materials, the coupling loss and transmission loss of the device are reduced to a certain extent, which reduces the required threshold current and helps to achieve low power consumption.

[0047] 3. Low power consumption: Compared with the traditional design of applying a large voltage to the waveguide to achieve wavelength tuning, lasers using phase change materials can achieve material phase change at a voltage of about 2V, saving energy.

[0048] The second aspect of this application discloses a device including the external cavity laser described in the first aspect of this application. This improves the overall operational efficiency of the device.

[0049] In some embodiments, the device includes at least one of a fiber optic sensor, an optical communication device, a lidar, and a high-resolution spectrometer. Therefore, this external cavity laser has a wide range of applications and broad prospects.

[0050] Specifically, this external cavity laser can be applied in the following fields:

[0051] 1. Grating sensing field:

[0052] Fiber optic sensors are susceptible to environmental noise and electromagnetic interference in practical applications, thus placing higher demands on their anti-interference capabilities. External cavity lasers, through appropriate coupling and packaging techniques, can effectively suppress noise during measurement, enhancing the anti-interference ability of fiber optic sensors. The phase transition process of phase change materials enables wavelength tuning of the laser, improving the measurement accuracy of the sensor.

[0053] 2. High-speed optical communication field

[0054] With the growth of applications such as cloud computing, the Internet of Things, and video streaming, the demand for data transmission continues to rise. This places new demands on the bandwidth of fiber optic communication technology. External cavity lasers, by combining optical components such as gratings, can achieve wavelength division multiplexing, improving bandwidth utilization. Phase change materials, through wavelength tuning, can address the problem of limited spectrum resources.

[0055] 3. LiDAR

[0056] LiDAR (Light Detection and Ranging) is a technology that uses laser beams for ranging and is widely used in fields such as autonomous driving, terrain mapping, construction, agriculture, and environmental monitoring. Continuous Wave Tuned (FMCW) mode in LiDAR typically uses a tunable laser as the light source to output a frequency-modulated optical signal. External cavity lasers based on phase change materials can achieve rapid wavelength tuning at the nanosecond level through the phase change material, improving the 3D recognition capability of LiDAR. Furthermore, rapid tuning can enhance the frequency response of the signal and reduce measurement delay, thereby improving the accuracy and performance of the system. This makes it a promising technology for automotive LiDAR applications.

[0057] 4. High-resolution spectrum

[0058] In high-resolution spectral analysis, background noise and environmental interference can cause signal distortion, thus requiring extremely high accuracy and reliability. External cavity lasers, due to their unique design, help reduce noise levels and improve signal clarity, thereby enhancing the quality of spectral data. Phase change materials can meet the need for high-resolution spectral measurements across different wavelength ranges.

[0059] In summary, wavelength-tunable external cavity lasers incorporating phase change materials have broad application prospects in various technological fields such as fiber optic sensing, high-speed optical communication, lidar, and high-resolution spectroscopy. With continuous technological development and innovation, these application areas will continue to expand and deepen.

[0060] Example 1

[0061] This external cavity laser is an improvement upon a common laser (specifically the ECDL-795). It comprises a gain chip and an external resonant cavity, connected via a coupling module (PWB photonic wire bonding technology). The external resonant cavity is bonded to a phase-change material GSST. A Bragg grating (359nm period, 50% duty cycle, 50nm etching depth) is directly etched onto a SiN waveguide (600nm thick, 1μm wide). GSST is filled into the grooves of the grating, and then a 15nm thick layer of GSST is deposited on top. A detailed structural diagram can be found in the provided image. Figure 1 .

[0062] Comparative Example 1

[0063] Same as Example 1, except that there is no phase change material, specifically model ECDL-795.

[0064] The embodiment 1 (external cavity laser incorporating phase change material) provided in this application is compared with Comparative Example 1. The work done in this application involves tuning the effective refractive index of a grating to change its reflectable wavelength. Adding a phase change material improves the speed and stability of this change. Specifically, the phase change material and the grating are integrated. By applying a voltage to the phase change material, its phase state changes within nanoseconds. Because the effective refractive index varies greatly between different phase states of the phase change material, its effective refractive index can be adjusted after integration with the grating. The reflection wavelength of the grating is directly related to its effective refractive index; rapidly changing the effective refractive index of the phase change material is equivalent to rapidly changing the effective refractive index of the grating, thus achieving rapid wavelength tuning. In contrast, a conventional grating without integrated phase change material does not have a changed effective refractive index, resulting in a fixed reflection wavelength and preventing wavelength tuning. Therefore, the external cavity laser incorporating phase change material provided in this application has faster wavelength tuning capability and experiences less coupling and propagation loss.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. An external cavity laser, characterized in that, It includes a gain chip, an external resonant cavity, and a coupling module. The gain chip and the external resonant cavity are coupled together through the coupling module. The external resonant cavity includes a waveguide structure, a grating, and a phase change material layer. The grating is disposed on the waveguide structure, and the phase change material layer is stacked on the surface of the grating and includes interconnected planar portions and protrusions. The protrusions fill the grooves of the grating. The phase change material layer includes germanium, antimony, selenium, and tellurium; The grating period of the grating is 350nm~359nm; The duty cycle of the grating is 50%; The depth of the grating is 40nm~50nm.

2. The external cavity laser according to claim 1, characterized in that, The grating includes a Bragg grating.

3. The external cavity laser according to claim 1, characterized in that, The thickness of the planar portion is 10nm~15nm.

4. The external cavity laser according to claim 1, characterized in that, The waveguide structure satisfies at least one of the following conditions: The waveguide structure is made of SiN; The thickness of the waveguide structure is 300nm~600nm; The width of the waveguide structure is 800nm~1000nm.

5. The external cavity laser according to claim 1, characterized in that, The coupling module includes a photonic wire bonding structure.

6. The external cavity laser according to claim 1, characterized in that, The gain chip includes an active region, and the active region is made of indium gallium arsenide phosphide.

7. A device, characterized in that, The external cavity laser includes any one of claims 1 to 6.

8. The device according to claim 7, characterized in that, It includes at least one of fiber optic sensors, optical communication equipment, lidar, and high-resolution spectrometers.

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