阅读说明：本技术 一种集成外腔窄线宽激光器的微环反射镜及其设计方法 (Micro-ring reflector of integrated external cavity narrow linewidth laser and design method thereof ) 是由 陈明华 李佳琛 于 2019-11-01 设计创作，主要内容包括：公开了一种集成外腔窄线宽激光器的微环反射镜,其有助于压窄线宽、结构简单、尺寸小、调谐简便、易于获得高Q值和大的延时、十分适合应用在窄线宽外腔激光器、同时也在其他场景中有潜在的应用价值。这种集成外腔窄线宽激光器的微环反射镜,在单臂耦合型微环反射镜的微环波导上添加一个亚波长大小的微结构来构成反射点,激励起反向传播的模式,通过反射点引起背向散射耦合,使得部分光能从输入端口输出。还提供了设计方法。(The micro-ring reflector is beneficial to narrow line width pressing, has a simple structure, small size, simple and convenient tuning, easily obtains a high Q value and large time delay, is very suitable for being applied to the narrow line width external cavity laser, and has potential application value in other scenes. According to the micro-ring reflector of the integrated external cavity narrow-linewidth laser, a sub-wavelength micro-structure is added on a micro-ring waveguide of a single-arm coupling type micro-ring reflector to form a reflection point, a backward propagation mode is excited, and back scattering coupling is caused through the reflection point, so that part of light energy is output from an input port. A design method is also provided.)

1. A micro-ring reflector of an integrated external cavity narrow linewidth laser is characterized in that: a micro-structure with sub-wavelength size is added on a micro-ring waveguide of the single-arm coupling type micro-ring reflector to form a reflection point, a backward propagation mode is excited, and back scattering coupling is caused through the reflection point, so that part of light energy is output from an input port.

2. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 1, wherein: the micro-structure is a circular, strip-shaped or fracture type sub-wavelength structure.

3. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 2, wherein: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is less than or equal to 0.3 um.

4. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 3, wherein: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is equal to 0.1 um.

5. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 3, wherein: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is equal to 0.2 um.

6. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 1, wherein: the micro-structure is arranged on a silicon nitride platform, the micro-ring waveguide is in a runway shape, the width of the micro-ring waveguide is 1.4um, the radius of the micro-ring is 125um, the length of a straight waveguide of the runway-shaped micro-ring waveguide is 250um, the coupling interval of the micro-ring is 0.8um, the micro-structure is circular, the micro-structure is arranged on the straight waveguide of the runway-shaped micro-ring waveguide, and the diameter of the micro-ring waveguide is 0.2 um.

7. The micro-ring mirror of an integrated external cavity narrow linewidth laser of claim 2, wherein: on a silicon nitride micro-ring waveguide which is 2.8um wide and 0.1um thick, the micro-ring reflector is in a circular shape with the radius of 600um, the coupling distance between the micro-ring and the waveguide is 0.9um, and the reflecting point is in a strip structure with 0.5 x 0.2 um.

8. A method for designing a micro-ring mirror of an integrated external cavity narrow linewidth laser according to claim 1, wherein: the sub-wavelength micro-structure is etched out by single exposure through layout design in the waveguide.

9. The design method of the micro-ring reflector of the integrated external cavity narrow linewidth laser according to claim 8, characterized in that: the feedback wavelength of the micro-ring reflector is tuned through the heating electrode, the heating electrode grows and etches on the surface of the chip, the local temperature around the heating electrode is changed by changing the voltage of the heating electrode, the heat is diffused to the waveguide to correspondingly change the refractive index of the waveguide, and further the central wavelength of the micro-ring reflector is changed.

10. The design method of the micro-ring reflector of the integrated external cavity narrow linewidth laser according to claim 8, characterized in that: the feedback wavelength of the micro-ring mirror is tuned by either piezo-optical tuning or electro-optical tuning.

Technical Field

The invention relates to the technical field of optical communication and photoelectron, in particular to a micro-ring reflector of an integrated external cavity narrow line width laser and a design method of the micro-ring reflector.

Background

The micro-ring reflector is an important component of the integrated external cavity narrow linewidth laser. By integrating the high-Q micro-ring mirror with a semiconductor gain amplifier or commercial lasers such as FP, DFB, etc., the outgoing line width of the laser can be effectively narrowed. This is mainly because the micro-ring has a larger group delay at the resonance point (generally, the larger the Q value, the larger the group delay), which is equivalent to increasing the equivalent length of the external cavity. Moreover, the position of the resonance peak of the micro-ring reflector can be tuned to change the emergent wavelength of the laser.

Related micro-ring mirror structures have been proposed that include: the device comprises a multi-ring coupled single-arm coupled micro-ring reflector, an input-output coupled double-arm coupled micro-ring reflector, a reflector based on intrinsic Rayleigh scattering of the side wall of a micro-ring waveguide and the like. The multi-ring coupled single-arm coupled micro-ring reflector needs to tune the wavelength of a plurality of micro-rings respectively, and the complexity is high; the input-output coupled double-arm coupled micro-ring reflector needs double-arm coupling, the Q value is difficult to be improved compared with the single-arm coupled micro-ring reflector, and unnecessary physical phenomena or loss can be introduced; the reflector based on the intrinsic Rayleigh scattering of the side wall of the micro-ring waveguide can be realized only under the condition that the Q value of the micro-ring is extremely high, and cannot be generally applied.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides the micro-ring reflector of the integrated external cavity narrow-linewidth laser, which is beneficial to narrowing linewidth, has a simple structure, a small size, is convenient to tune, is easy to obtain a high Q value and a large time delay, is very suitable for being applied to the narrow-linewidth external cavity laser and has potential application value in other scenes.

The technical scheme of the invention is as follows: according to the micro-ring reflector of the integrated external cavity narrow-linewidth laser, a sub-wavelength micro-structure is added on a micro-ring waveguide of a single-arm coupling type micro-ring reflector to form a reflection point, a backward propagation mode is excited, and back scattering coupling is caused through the reflection point, so that part of light energy is output from an input port.

The invention adds a micro-structure with sub-wavelength size on the micro-ring waveguide of the single-arm coupling type micro-ring reflector to form a reflection point, excites a mode of back propagation, the modes (clockwise propagation and anticlockwise propagation) of two propagation directions cause back scattering coupling through the reflection point, so that part of light energy is output from an input port, thereby realizing the function of the micro-ring reflector of light, because only the single-arm coupling is adopted and the reflection point is added, the group delay of the cavity is approximately doubled compared with the condition of double-arm coupling, which is equivalent to obtaining longer equivalent cavity length, is beneficial to narrowing line width, is easy to obtain high Q value and large delay, is very suitable for being applied to a narrow line width external cavity laser, and has potential application value in other scenes; because the micro-structure is only composed of a sub-wavelength micro-structure, the trouble of independently tuning multiple cavities can be avoided, and the tuning is simple and convenient; because a sub-wavelength micro-structure is added on the existing micro-ring waveguide, the micro-ring reflector has simple structure and small size.

The design method of the micro-ring reflector of the integrated external cavity narrow linewidth laser is also provided, and the micro-structure with the sub-wavelength is etched out through single exposure by carrying out layout design in the waveguide.

Drawings

Fig. 1 shows a schematic structural diagram of a micro-ring mirror of an integrated external cavity narrow linewidth laser according to the present invention.

FIG. 2a shows a circular microstructure; FIG. 2b shows a microstructure in the form of a bar; fig. 2c shows a microstructure of the fracture type.

Fig. 3 shows the relationship between the circular microstructure and the coupling coefficient.

Fig. 4 shows the relationship between the circular microstructure and the loss.

Fig. 5 shows a schematic structural diagram of a micro-ring mirror of an integrated external cavity narrow linewidth laser according to one embodiment of the present invention.

Fig. 6 shows the transmission response of the input and output ends of the micro-ring mirror of fig. 5.

Fig. 7 shows a schematic structural diagram of a micro-ring mirror of an integrated external cavity narrow linewidth laser according to another embodiment of the present invention.

Fig. 8 shows the transmission response of the input and output ends of the micro-ring mirror of fig. 7.

Detailed Description

As shown in fig. 1, in the micro-ring reflector of the integrated external cavity narrow linewidth laser, a sub-wavelength micro-structure is added on the micro-ring waveguide of the single-arm coupling micro-ring reflector to form a reflection point, so as to excite a backward propagation mode, and cause back scattering coupling through the reflection point, so that part of the light energy is output from the input port.

The invention adds a micro-structure with sub-wavelength size on the micro-ring waveguide of the single-arm coupling type micro-ring reflector to form a reflection point, excites a mode of back propagation, the modes (clockwise propagation and anticlockwise propagation) of two propagation directions cause back scattering coupling through the reflection point, so that part of light energy is output from an input port, thereby realizing the function of the micro-ring reflector of light, because only the single-arm coupling is adopted and the reflection point is added, the group delay of the cavity is approximately doubled compared with the condition of double-arm coupling, which is equivalent to obtaining longer equivalent cavity length, is beneficial to narrowing line width, is easy to obtain high Q value and large delay, is very suitable for being applied to a narrow line width external cavity laser, and has potential application value in other scenes; because the micro-structure is only composed of a sub-wavelength micro-structure, the trouble of independently tuning multiple cavities can be avoided, and the tuning is simple and convenient; because a sub-wavelength micro-structure is added on the existing micro-ring waveguide, the micro-ring reflector has simple structure and small size.

Preferably, the shape of the sub-wavelength reflection point is arbitrary in the case where the processing condition is satisfied. For example, the microstructures are circular (as shown in fig. 2 a), stripe-shaped (as shown in fig. 2 b), or broken (as shown in fig. 2 c) subwavelength structures.

Specific subwavelength reflecting dot shapes and sizes need to be designed according to specific integration platforms and requirements. The scattering condition introduced by the sub-wavelength reflection point is characterized by a coupling coefficient and loss. The coupling coefficient represents the proportion of the clockwise (anticlockwise) light converted into the anticlockwise (clockwise) light by the sub-wavelength reflection point once, namely the coupling strength of the two kinds of light in the rotary directions; loss means loss introduced by light passing through a sub-wavelength reflection point except for conversion to light of two handedness (scattering in other directions, not efficiently converted to the desired mode). Furthermore, the backward coupling coefficient and the loss are in a positive correlation, that is, the stronger the two types of rotational optical coupling, the larger the size of the reflection point is required, but the more energy is lost, and the Q value is reduced correspondingly for the micro-ring. Therefore, the shape and size of the sub-wavelength reflection spot needs to be carefully designed in order to obtain sufficient reflection energy while reducing the extra loss of light energy.

Preferably, the micro-ring reflector of the integrated external cavity narrow linewidth laser is: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is less than or equal to 0.3 um.

Specifically, the micro-ring reflector of the integrated external cavity narrow linewidth laser is as follows: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is equal to 0.1 um.

For a 0.2um silicon nitride waveguide, the optimal circular reflection point for a narrow linewidth laser is the radius 0.2 um. Specifically designed for other applications.

Assuming a 1.4um wide, 0.2um thick silicon nitride waveguide has a circular defect in the center, the ratio of back-scattered and forward-transmitted light caused by this defect to the length of the fracture defect can be obtained as shown in fig. 3.

As can be seen from fig. 3 and 4, as the size of the circular subwavelength structure increases, the forward transmission ratio decreases, and the back scattering ratio increases. However, when the size of the reflection point is too large, the loss increases because the ratio in the other direction increases.

Preferably, on a silicon nitride micro-ring waveguide 2.8um wide and 0.1um thick, the micro-ring mirror is circular with a radius of 600um, the coupling distance between the micro-ring and the waveguide is 0.9um, and the reflection point is a strip structure 0.5 x 0.2 um.

Two specific embodiments are described below.

As shown in fig. 5, the microstructure is disposed on a 0.2um thick silicon nitride platform (the platform may be other, and is only for illustration and not for limitation), the microring waveguide is a racetrack type (may not be racetrack type, and is only for illustration and not for limitation), the width is 1.4um, the radius of the microring is 125um, the length of the straight waveguide of the racetrack type microring waveguide is 250um, the coupling pitch of the microring is 0.8um, the microstructure is circular, and the diameter of the microstructure is 0.2um disposed on the straight waveguide of the racetrack type microring waveguide. In this structure, it is not preferable that the coupling coefficient is larger, but the coupling coefficient is larger in an ambiguous manner, and the additional light loss is larger, which is not favorable for improving the Q value. The specific dimensions mentioned above are not exclusive and are only examples.

If the sub-wavelength reflection point is not arranged on the micro-ring waveguide, the micro-ring waveguide is a pure single-arm coupling micro-ring, and no reflected light exists at an incident port; however, after the reflection point is added, a small part of light is coupled to the mode with the opposite propagation direction after passing once, and two stable modes with opposite rotation directions exist after the light is reflected and coupled for many times in the micro-ring. In this case, both the entrance and exit ports have light output and thus can act as mirrors. The transmission response of both ports is shown in fig. 6.

After adding the circular defect, the microring can be seen to have significant light reflection at the input port. The insertion loss of the mirror is 2.6dB, and the Q value reaches 1.1 x 10⁵Therefore, the requirement of the narrow linewidth external cavity laser on the external cavity can be well met. Moreover, because only single-arm coupling is adopted and the reflection point is added, the group delay of the cavity is approximately doubled compared with the double-arm coupling, which is equivalent to obtaining a longer equivalent cavity length, and the narrow line width is facilitated. The problem of independently tuning multiple cavities can be avoided because the micro-ring is only formed by one micro-ring. The sub-wavelength reflection point-assisted micro-ring reflector has the advantages of simple structure, small size, simple and convenient tuning, easy acquisition of high Q value and large time delay, suitability for being applied to narrow-linewidth external cavity lasers, and potential application value in other scenes.

For 100nm thick silicon nitride a suitable mirror design based on microstructured reflection points is given.

The waveguide width is 2.8um, and the micro-ring speculum is the circular of radius 600um, and the coupling interval of micro-ring and waveguide is 0.9um, and the reflection point is bar structure (0.5 x 0.2 um). The structure is shown in fig. 7.

This reflection point gives rise to a reflection coefficient of 2.72e-4, and the energy lost per pass of the reflection point is about 0.2%.

Due to this reflection point, also at the input end, reflected light is generated, as shown in fig. 8. The insertion loss of the reflected light was 3.8dB, and the Q value reached 4.6e 5. It is also very suitable as a reflector of a micro-ring with narrow line width.

The design method of the micro-ring reflector of the integrated external cavity narrow linewidth laser is also provided, and the micro-structure with the sub-wavelength is etched out through single exposure by carrying out layout design in the waveguide.

Preferably, the feedback wavelength of the micro-ring reflector is tuned through the heating electrode, the heating electrode is grown and etched on the surface of the chip, the local temperature around the heating electrode can be changed by changing the voltage of the heating electrode, the refractive index of the waveguide can be correspondingly changed by diffusing heat to the waveguide, and further the central wavelength of the micro-ring reflector is changed.

Alternatively, the feedback wavelength of the micro-ring mirror is tuned by either piezo-optical tuning or electro-optical tuning. All other tuning modes are also applicable to the proposed micro-ring mirror, and the structure itself does not limit the tuning mode.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.