CN117199996A

CN117199996A - Grating spectroscope and silicon-based external cavity laser

Info

Publication number: CN117199996A
Application number: CN202311100389.2A
Authority: CN
Inventors: 郑宇�; 黄颖; 廖仲扬
Original assignee: Yushu Optics Shenzhen Co ltd
Current assignee: Yushu Optics Shenzhen Co ltd
Priority date: 2023-08-29
Filing date: 2023-08-29
Publication date: 2023-12-08

Abstract

The application discloses a grating spectroscope and a silicon-based external cavity laser, belonging to the technical field of integrated optics of optical communication and optical sensing; in the grating spectroscope, the Bragg grating is a sector, and one end of the center of the Bragg grating is an optical input end and an optical reflection end; the end of the Bragg grating, which is far away from the light input end, is an arc end; the waveguide is a triangular body, one side edge of the waveguide is connected with the arc end, and a corner part of one end of the waveguide, which is far away from the arc end, is a light output end. In the silicon-based external cavity laser, an optical amplifier is connected with a silicon optical chip to form a resonant cavity, and a grating spectroscope is arranged in the resonant cavity. The application can realize single-path light reflection by using the grating spectroscope as the external cavity reflector and the laser output port without dividing light into two paths, thereby enhancing the output stability of the silicon-based external cavity laser and having the advantages of ultra-wide reflection spectrum, high reflectivity and small size.

Description

Grating spectroscope and silicon-based external cavity laser

Technical Field

The application belongs to the technical field of integrated optics of optical communication and optical sensing, and particularly relates to a grating spectroscope and a silicon-based external cavity laser.

Background

With the continuous miniaturization and portability of commercial products, the application of semiconductor integrated devices is becoming wider and wider, and especially the application of optical semiconductor products in the fields of communication and sensing. Silicon optical semiconductor devices have taken an important place in commercial applications by virtue of their compatibility with CMOS processes, small size, rich functionality, etc. However, since silicon is an indirect bandgap material, development of silicon-based light sources is still slow.

One solution to the silicon-based integrated light source is to integrate a III-V semiconductor optical amplifier with a silicon-based external cavity to form a silicon-based external cavity laser. Silicon-based external cavity lasers employ external cavity feedback to achieve wavelength selectivity, which has several unique features and advantages such as wavelength tunability, narrow linewidth, high output power, low threshold current, etc., over conventional semiconductor lasers using internal cavity structures.

In the existing silicon-based external cavity laser structure, the reflection structure of the external cavity is composed of a Sagnac (Sagnac) reflection ring, and the structure divides a light beam into two parts, one part of the light is reflected back to the laser cavity to resonate, and the other part of the light is output as laser.

In addition, in another type of silicon-based external cavity laser structure, the reflection structure of the external cavity is also composed of a Sagnac (Sagnac) reflection ring, and the 2×2 coupler splits the light into two beams of light propagating in opposite directions in the Sagnac reflection ring, and at the same time, the filtering structure of the external cavity is also placed in the Sagnac reflection ring. The other two ports of the coupler reflect a portion of the light back into the laser cavity for resonance and another portion of the light is output as laser light.

However, a Sagnac (Sagnac) reflective ring divides the optical path into two, and the two paths of light may be affected differently when there is a defect in the optical path or an external environmental factor varies. When the two paths of light are affected differently, the light intensity and the phase of the reflected light may change, and the reflectivity of the reflective ring may also change, eventually causing unstable laser output.

Disclosure of Invention

In order to solve the above-mentioned technical problems, the present application aims to provide a grating spectroscope and a silicon-based external cavity laser, which can realize single-path light reflection without dividing light into two paths, thereby enhancing the output stability of the silicon-based external cavity laser, and have the advantages of ultra-wide reflection spectrum, high reflectivity and small size.

The technical scheme adopted for solving the technical problems is as follows:

in a first aspect, the present application discloses a grating beam splitter having a light input direction, the grating beam splitter comprising:

the Bragg grating is a sector, and one end of the center of the Bragg grating is provided with an optical input end and an optical reflection end; one end of the Bragg grating, which is far away from the optical input end, is an arc end;

the waveguide is a triangular body, one side edge of the waveguide is connected with the arc end, and a corner part of one end of the waveguide, which is far away from the arc end, is a light output end.

The grating spectroscope provided by the application has at least the following beneficial effects: in the process that laser sequentially enters the Bragg grating and the waveguide through the light input end and is emitted from the light output end, the Bragg grating adopts a sector shape design, and the waveguide adopts a triangle shape design, so that the Bragg grating can reflect most of light, so that most of light returns to and is emitted from the light reflection end, and a small part of light is transmitted into the waveguide through the Bragg grating and is emitted from the light output end of the waveguide to form laser output, thereby playing the role of a spectroscope and reducing the coupling loss of the spectroscope.

Compared with the traditional Bragg reflector, the grating spectroscope has ultra-wide reflection spectrum, can be suitable for lasers in a large wavelength range and is used for manufacturing tunable lasers, and grating structure design is not required for specific wavelengths; for the Sagnac reflecting ring structure, the grating spectroscope can be used as an external cavity reflecting mirror and a laser output port to realize single-path light reflection without dividing the light path into two parts, so that the output stability of the laser can be enhanced.

As a further improvement of the technical scheme, the Bragg grating comprises a sector waveguide and a plurality of arc waveguides, all the arc waveguides are arranged outside the arc side of the sector waveguide at intervals, the length of the arc waveguides increases along with the increase of the distance between the arc waveguides and the sector waveguide, and the plurality of arc waveguides form a grating structure.

As a further improvement of the above technical solution, the bragg grating is symmetrically disposed about the light input direction with the light input end as a center, the waveguide is an isosceles triangle, one end of the top angle of the waveguide is the light output end, the waveguide is symmetrically disposed about the light input direction with the light output end as a center, and the bottom edge of the waveguide is connected with the arc end.

As a further improvement of the above technical solution, the center angle of the bragg grating is identical to the angle of the apex angle of the waveguide.

As a further improvement of the technical scheme, the center angle of the Bragg grating is 60-70 degrees.

In a second aspect, the present application discloses a silicon-based external cavity laser comprising:

an optical amplifier;

a silicon optical chip connected with the optical amplifier and forming a resonant cavity;

a grating beam-splitter as described in the first aspect, disposed within the resonant cavity.

The silicon-based external cavity laser provided by the application has at least the following beneficial effects: the grating spectroscope with the structure is arranged in the resonant cavity, when light emitted by the optical amplifier enters the grating spectroscope, most of laser is reflected by the grating spectroscope and returns to a gain medium of the optical amplifier through an original path, then the laser is reflected back to the resonant cavity by the optical amplifier, and another small part of laser is transmitted by the grating spectroscope and outputs the laser, so that a Sagnac reflecting ring is not needed, the output of the silicon-based external cavity laser is more stable, and the laser has ultra-wide reflection spectrum.

As a further improvement of the technical scheme, the opposite ends of the optical amplifier are a first end and a second end respectively, the reflectivity of the first end is larger than 90%, the reflectivity of the second end is smaller than 0.01%, and the second end is coupled and connected with the silicon optical chip through the spot-size converter.

As a further improvement of the technical scheme, the silicon-based external cavity laser further comprises a phase shifter and a vernier filter, wherein the mode spot converter, the phase shifter, the vernier filter and the grating spectroscope are sequentially connected.

As a further improvement of the technical scheme, the spot-size converter is an inverted cone coupler; and/or the phase shifter is a thermo-optic effect phase shifter or an electro-optic effect phase shifter.

As a further improvement of the above technical solution, the vernier filter includes a first micro-ring filter and a second micro-ring filter, and the first micro-ring filter and the second micro-ring filter form a vernier filtering effect.

Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application 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 application is further described below with reference to the drawings and examples;

FIG. 1 is a schematic diagram of a grating beam splitter according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a silicon-based external cavity laser according to an embodiment of the present application;

FIG. 3 is a reflection spectrum of a grating beam splitter according to an embodiment of the present application;

FIG. 4 is a diagram of the transmission spectrum of a grating beam splitter according to an embodiment of the present application.

The figures are marked as follows: 100. a grating beam splitter; 110. a Bragg grating; 120. a waveguide; 200. a micro-loop filter; 300. a phase shifter; 400. a spot-size converter; 500. a silicon optical chip; 600. a semiconductor optical amplifier.

Detailed Description

Reference will now be made in detail to the present embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein the accompanying drawings are used to supplement the description of the written description so that one can intuitively and intuitively understand each technical feature and overall technical scheme of the present application, but not to limit the scope of the present application.

In the description of the present application, it should be understood that references to orientation descriptions such as upper, lower, front, rear, left, right, etc. are based on the orientation or positional relationship shown in the drawings, are merely for convenience of description of the present application and to simplify the description, and do not indicate or imply that the apparatus or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present application.

In the description of the present application, if there is a word description such as "a plurality" or the like, the meaning of the plurality is one or more, the meaning of the plurality is two or more, and greater than, less than, exceeding, etc. are understood to exclude the present number, and above, below, within, etc. are understood to include the present number. The description of first, second, and third is for the purpose of distinguishing between technical features only and should not be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of technical features indicated.

In the description of the present application, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present application can be reasonably determined by a person skilled in the art in combination with the specific contents of the technical scheme.

Referring to fig. 1 to 4, several embodiments of the grating beam splitter and the silicon-based external cavity laser according to the present application are shown below. It may be noted that the arrows appearing in fig. 1 to 4 indicate the propagation direction of the laser light.

As shown in fig. 1, the first embodiment of the present application provides a grating beam splitter 100, where the grating beam splitter 100 can be used as an external cavity reflector and a laser output port to implement single-path light reflection, and the light is not required to be split into two paths, so that the output stability of a silicon-based external cavity laser can be enhanced, and the grating beam splitter 100 has the advantages of ultra-wide reflection spectrum, high reflectivity and small size.

The grating spectroscope 100 provided in this embodiment may be applied to a silicon-based external cavity laser, and may also be used in other silicon optical devices or systems.

The grating beam-splitter 100 has a first direction and a light input direction, wherein the first direction is perpendicular to the light input direction. The structure of the grating beam splitter 100 includes a Bragg grating 110 and a waveguide 120.

The bragg grating 110 is a sector, that is, the bragg grating 110 has a sector contour line, and the bragg grating 110 has a center and an arc. The end of the bragg grating 110 where the center of the circle is located is an optical input end and is also an optical reflection end, the end of the bragg grating 110 away from the optical input end is an arc end, the optical input end is far away from the waveguide 120, and the arc end is close to the waveguide 120, as shown in fig. 1.

The waveguide 120 is a triangular body, one side of the waveguide 120 is fixedly connected to the arc end of the bragg grating 110, one end of the waveguide 120 away from the arc end has a corner, the side is an opposite side of the angle, and the corner is a light output end.

It will be appreciated that the bragg grating 110 is fan-shaped and the waveguide 120 is triangular when viewed in a first direction as shown in fig. 1. In the present embodiment, assuming that the first direction is the up-down direction and the light input direction is the front-back direction, as shown in fig. 1, the bragg grating 110 is designed in a fan shape and the waveguide 120 is designed in a triangle shape as viewed from the top.

The light input end and the light reflection end are located at a side of the bragg grating 110 away from the waveguide 120, and the bragg grating 110 is arranged in bilateral symmetry about the light input direction with the light input end as a center. The left-right dimension of the bragg grating 110 increases along the light input direction.

Specifically, as shown in fig. 1, the bragg grating 110 includes a sector waveguide and a plurality of arc waveguides. All the arc-shaped waveguides are arranged outside the arc side of the sector-shaped waveguide, in this embodiment, the sector-shaped waveguide and all the arc-shaped waveguides are sequentially arranged along the light input direction, and all the arc-shaped waveguides are arranged at intervals, and the length of the arc-shaped waveguide increases along with the increase of the distance between the arc-shaped waveguides and the sector-shaped waveguide. Several arc waveguides form a grating structure.

The number of the arc-shaped waveguides may be selected according to practical situations, and in this embodiment, the number of the arc-shaped waveguides is three. Moreover, the further the arc-shaped waveguide is from the sector-shaped waveguide, the longer the arc-shaped waveguide is. The vertical distance between the arc-shaped waveguide closest to the sector-shaped waveguide and the sector-shaped waveguide is defined as a first vertical distance, the vertical distance between any two adjacent arc-shaped waveguides is defined as a second vertical distance, and the first vertical distance and the second vertical distance can be set according to practical situations.

The waveguide 120 is an isosceles triangle, specifically, when viewed along the first direction, the waveguide 120 is an isosceles triangle, the isosceles triangle waveguide 120 has a vertex angle, two base angles and a base, wherein, one end of the vertex angle of the waveguide 120 is a light output end, the light output end is located at one side of the waveguide 120 away from the bragg grating 110, the base of the waveguide 120 is located at one side of the waveguide 120 near the bragg grating 110, and the waveguide 120 is arranged in bilateral symmetry about the light input direction with the light output end as a center. The bottom edge of the waveguide 120 is connected to the rounded end of the bragg grating 110. The left-right dimension of the waveguide 120 decreases along the light input direction.

The axis of symmetry of the bragg grating 110 and the axis of symmetry of the waveguide 120 coincide such that the grating beam splitter 100 has reflective symmetry in the light input direction.

In this embodiment, the bragg grating 110 is located at the front side of the waveguide 120, when the laser propagates from front to back and enters the bragg grating 110 from the light input end of the bragg grating 110, since the bragg grating 110 is in a fan-shaped design, most of the laser can be reflected and promoted to return in the original path, and is emitted from the light reflection end of the bragg grating 110, and a small part of the laser is transmitted into the waveguide 120 by the bragg grating 110, propagates all the way back along the waveguide 120, and is emitted from the light output end of the waveguide 120.

It is understood that the grating beam splitter 100 may be comprised of a silicon waveguide and surrounding silicon dioxide cladding. The bragg grating 110 may be fabricated by an etching process, among others. The structure of the bragg grating 110 is very compact and its size may be no more than 15 μm x 10 μm.

When the grating spectroscope 100 of this embodiment is used, in the process that laser sequentially enters the bragg grating 110 and the waveguide 120 through the light input end and is emitted from the light output end, since the bragg grating 110 adopts a fan-shaped shape design and the waveguide 120 adopts a triangle-shaped shape design, the bragg grating 110 can reflect most of the light, so that most of the light returns to the light source and is emitted from the light reflection end, and a small part of the light is transmitted into the waveguide 120 through the bragg grating 110 and is emitted from the light output end of the waveguide 120, so as to form laser output, thereby playing the role of the spectroscope and reducing the coupling loss of the grating spectroscope 100.

Compared to the conventional bragg reflector, the grating beam splitter 100 of the present embodiment has an ultra-wide reflection spectrum, and is applicable to lasers in a large wavelength range and for manufacturing tunable lasers, without the need of designing a grating structure for a specific wavelength. Compared with the sagnac reflection ring structure, the grating spectroscope 100 of the present embodiment can be used as an external cavity reflector and a laser output port to realize single-path light reflection, and the optical path is not divided into two parts, so that the output stability of the laser can be enhanced.

Of course, it is not excluded that the bragg grating 110 and the waveguide 120 are designed with an asymmetric arrangement with respect to the light input direction.

The center angle of the bragg grating 110 and the apex angle of the waveguide 120 are set according to actual conditions.

In some embodiments, the center angle of the Bragg grating 110 is coincident with the apex angle of the waveguide 120. That is, the central angle α of the bragg grating 110 is equal to the apex angle β of the waveguide 120. The two sides of the bragg grating 110 are respectively disposed corresponding to the bottom corner end points passing through the waveguide 120.

In some embodiments, the center angle of the bragg grating 110 ranges from 60 ° to 70 °, and then the apex angle of the waveguide 120 ranges from 60 ° to 70 °.

In addition, as shown in fig. 1 to 4, a silicon-based external cavity laser is provided according to a first embodiment of the present application, and the structure of the silicon-based external cavity laser includes an optical amplifier, a phase shifter 300, a vernier filter, a silicon optical chip 500, and the grating spectroscope 100 of the above embodiment.

The optical amplifier is a III-V semiconductor optical amplifier 600, which is connected to the silicon optical chip 500 and which together form a resonant cavity. Specifically, the gain medium of the optical amplifier may be formed of a group iii-v quantum well or quantum dot material, the opposite ends of the optical amplifier have high reflectivity and low reflectivity, respectively, one of the ends of the optical amplifier is defined as a first end, the other end of the optical amplifier is defined as a second end, wherein the reflectivity of the first end of the optical amplifier is greater than 90%, and the reflectivity of the second end of the optical amplifier is less than 0.01%, so that the first end is a high-reflection end and the second end is a low-reflection end.

The second end of the optical amplifier is provided with a spot-size converter 400, and the optical amplifier is coupled with the silicon optical chip 500 through the spot-size converter 400, for example, the optical amplifier can be coupled in a butt coupling or flip-chip coupling mode.

The grating beam splitter 100 is disposed within the resonant cavity. The spot-size converter 400, the phase shifter 300, the vernier filter and the grating beam splitter 100 are sequentially connected to form a laser propagation path. The spot-size converter 400, phase shifter 300, vernier filter are disposed on a silicon optical chip 500. It is understood that the spot-size converter 400, the phase shifter 300, and the vernier filter are related to the prior art, and those skilled in the art will understand the specific structure and operation thereof, and will not be described in detail herein.

As shown in fig. 1 and 2, an input waveguide and an output waveguide are respectively provided at opposite ends of the grating beam splitter 100, wherein the input waveguide is positioned at the front side of the grating beam splitter 100 and connected to the optical input end of the bragg grating 110, the output waveguide is positioned at the rear side of the grating beam splitter 100 and connected to the optical output end of the waveguide 120, and the output waveguide extends to the output port of the silicon optical chip 500 so as to output laser light. The left and right dimensions of the input waveguide and the output waveguide may be set according to actual conditions, and are not particularly limited herein.

In this embodiment, the spot-size converter 400 may employ an angled back taper coupler, and the angle of the back taper coupler may be set according to the actual situation. By this arrangement, reflection at the coupling end face can be reduced. The phase shifter 300 can adopt a thermo-optical effect phase shifter 300 or an electro-optical effect phase shifter 300, and can complete the laser longitudinal mode adjustment work.

The vernier filter structure comprises two micro-ring filters 200, wherein the two micro-ring filters 200 are respectively defined as a first micro-ring filter and a second micro-ring filter, the first micro-ring filter and the second micro-ring filter are coupled and connected, and a vernier filtering effect is formed, so that the wide-range wavelength adjustability can be realized.

It will be appreciated that the first and second micro-ring filters each comprise a phase shifter 300, and that laser wavelength adjustment may be achieved by applying a DC signal, or FMCW (Frequency Modulated Continuous Wave ) signal generation may be achieved by applying an AC signal, wherein the FMCW laser signal may be used in lidar sensing applications.

When the silicon-based external cavity laser of the embodiment is used, light emitted by the optical amplifier enters the phase shifter 300 through the mode spot converter 400, after the longitudinal mode adjustment of the laser is completed through the phase shifter 300, the laser enters the vernier filter with vernier effect, and after the wavelength adjustment of the laser is completed, the laser enters the grating spectroscope 100 from the output end of the vernier filter; at this time, the grating beam splitter 100 plays an excellent beam splitting function, and the grating beam splitter 100 can reflect most of the laser light, and make the laser light return to the gain medium of the optical amplifier through the original path, and then be reflected back to the resonant cavity formed by the optical amplifier and the silicon optical chip 500 by the high reflection end of the optical amplifier, and at the same time, the grating beam splitter 100 transmits a small part of the laser light, and outputs the laser light from the output port of the silicon optical chip 500.

Therefore, the grating beam splitter 100 can reflect a part of the laser light output by the vernier filter into the resonant cavity, and transmit another part of the laser light out of the resonant cavity to form a laser light output, thereby functioning as a beam splitter.

It can be understood that the silicon-based external cavity laser of this embodiment integrates the iii-v semiconductor optical amplifier 600 with the silicon optical chip 500, and implements a laser resonator, on the basis of which the grating spectroscope 100 with a novel structure is used as a reflecting mirror/transmitting mirror to form the external cavity of the silicon optical laser, without using a sagnac reflection ring, and avoids using the sagnac reflection ring to divide the light beam into two parts, so that the laser output stability of the silicon-based external cavity laser can be enhanced, and the silicon-based external cavity laser has an ultra-wide reflection spectrum, and has high integration level, which is beneficial to mass production and reduces the cost of terminal products.

The grating spectroscope 100 and the silicon-based external cavity laser provided by the embodiment of the application can be applied to various fields including, but not limited to, laser radar and gas sensors, and can reduce the device cost.

Of course, the use of grating beam-splitter 100 in silicon-based external cavity lasers other than those described above is not precluded.

The grating spectroscope 100 has the characteristics of ultra-wide reflection spectrum, high reflectivity (C band reflectivity > 85%) and small size when applied to a silicon-based external cavity laser. As shown in FIG. 3, when the wavelength range is 1.35 μm to 1.7 μm, the reflectivity of the grating beam splitter 100 is greater than 80%, and when the wavelength range is C-band (i.e. the wavelength range is 1530nm to 1565 nm), the reflectivity is greater than 85%, and the high reflectivity can reduce the loss of the resonant cavity. As shown in fig. 4, the transmission spectrum of the grating beam splitter 100 shows a transmittance of about 2% in the wavelength range of 1.35 μm to 1.7 μm.

It will be appreciated that the reflectivity and transmissivity of the grating beam splitter 100 may be adjusted by the number of grating periods, the greater the number of periods, the greater the reflectivity and the lesser the transmissivity.

While the preferred embodiment of the present application has been described in detail, the application is not limited to the embodiments, and various equivalent modifications and substitutions can be made by those skilled in the art without departing from the spirit of the application, and these modifications and substitutions are intended to be included in the scope of the present application as defined in the appended claims.

Claims

1. A grating beam splitter having a light input direction, comprising:

2. The grating spectroscope of claim 1, wherein the bragg grating comprises a sector waveguide and a plurality of arc waveguides, all the arc waveguides are arranged outside the arc side of the sector waveguide and are arranged at intervals, the length of the arc waveguide increases with the distance between the arc waveguide and the sector waveguide, and the plurality of arc waveguides form a grating structure.

3. The grating spectroscope according to claim 2, wherein the bragg grating is symmetrically arranged about the light input direction with the light input end as a center, the waveguide is an isosceles triangle, an end of the waveguide where a vertex angle is located is the light output end, the waveguide is symmetrically arranged about the light input direction with the light output end as a center, and a bottom edge of the waveguide is connected to the circular arc end.

4. A grating beam-splitter according to claim 3 wherein the angle of the centre of the circle of the bragg grating coincides with the angle of the apex angle of the waveguide.

5. A grating beam-splitter according to claim 4, wherein the bragg grating has a center angle of 60 ° to 70 °.

6. A silicon-based external cavity laser, comprising:

an optical amplifier;

a grating beam splitter as described in any one of claims 1 to 5, disposed within the resonant cavity.

7. The silicon-based external cavity laser of claim 6, wherein the opposite ends of the optical amplifier are a first end and a second end, respectively, the first end has a reflectivity of greater than 90%, the second end has a reflectivity of less than 0.01%, and the second end is coupled to the silicon optical chip via a spot-size converter.

8. The silicon-based external cavity laser of claim 7, further comprising a phase shifter and a vernier filter, wherein the spot-size converter, the phase shifter, the vernier filter and the grating beam splitter are connected in sequence.

9. The silicon-based external cavity laser of claim 8, wherein the spot-size converter is an inverted cone coupler; and/or the phase shifter is a thermo-optic effect phase shifter or an electro-optic effect phase shifter.

10. The silicon-based external cavity laser of claim 8, wherein the vernier filter comprises a first micro-ring filter and a second micro-ring filter, the first micro-ring filter and the second micro-ring filter forming a vernier filter effect.