On-chip ultra-narrow linewidth lasers

Abstract

The present invention provides an on-chip ultra-narrow linewidth laser, comprising a laser generation gain unit, a distributed scattering feedback unit, a first optical collimating lens and a second optical collimating lens. The laser generation gain unit performs wavelength selection on an initial optical signal of a wide spectrum generated by the laser generation gain unit to obtain an optical signal of a specific wavelength. A part of the optical signal of the specific wavelength is transmitted to the distributed scattering feedback unit through the first optical collimating lens, and the other part is output through the second optical collimating lens. The distributed scattering feedback unit performs linewidth compression on the optical signal of the specific wavelength, and transmits the optical signal fed back after linewidth compression to the laser generation gain unit through the first optical collimating lens. The laser generation gain unit performs gain amplification on the fed-back optical signal, a part of the gain-amplified optical signal is output through the second optical collimating lens, and the other part is transmitted to the distributed scattering feedback unit again through the first optical collimating lens for further linewidth compression.

Description

Technical Field

[0001] The invention belongs to the field of laser line width compression, and in particular relates to an on-chip ultra-narrow line width laser. Background Art

[0002] Ultra-narrow linewidth lasers operating in a single longitudinal mode have important application prospects in the fields of fiber-optic sensing, fiber-optic communication, lidar, and gravitational wave detection due to their ultra-long coherence length and extremely low phase noise. The single longitudinal mode operation of the laser is the prerequisite for achieving laser linewidth compression. So far, in addition to mode selection methods including the use of short cavity structures and saturated absorbers, optical injection feedback has become a common method for narrowing the laser linewidth. However, as a single-path power feedback, the traditional optical injection feedback is difficult to achieve single longitudinal mode operation of the laser due to the additional cavity length introduced, which will lead to a reduction in the free spectral range (FSR) under the same conditions. At the same time, since it is only a power feedback, the limited feedback cavity length will limit the further compression of its linewidth. In addition, it is difficult to achieve the integration and miniaturization of the laser by increasing the feedback cavity length to achieve laser linewidth narrowing. Therefore, finding a method for deep compression of laser linewidth that can make the laser output longitudinal-mode-free and has the potential for integration is an important issue facing the current field of ultra-narrow linewidth lasers. Summary of the invention

[0003] The present invention provides an on-chip ultra-narrow linewidth laser to solve the problem that it is difficult to achieve deep compression of the laser linewidth while obtaining mode selection by using traditional optical feedback methods in the field of narrow linewidth lasers; at the same time, the invention overcomes the problem that it is difficult to achieve integration and miniaturization of the laser by increasing the feedback cavity length to achieve narrowing of the laser linewidth.

[0004] According to one aspect of the present invention, there is provided an on-chip ultra-narrow linewidth laser, comprising a laser generating gain unit, a distributed scattering feedback unit, a first optical collimating lens, and a second optical collimating lens, wherein a first output end of the laser generating gain unit is connected to a first end of the distributed scattering feedback unit through the first optical collimating lens, and a second output end is connected to a first end of the second optical collimating lens; the laser generating gain unit is used to generate an initial optical signal with a wide spectrum, and to perform wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength, wherein a part of the optical signal with the specific wavelength is transmitted to the first end of the distributed scattering feedback unit through the first optical collimating lens, and another part is output through the second optical collimating lens;

[0005] After receiving the optical signal of a specific wavelength, the first end of the distributed scattering feedback unit performs line width compression on the optical signal, and transmits the optical signal fed back after line width compression to the laser generating gain unit through the first optical collimating lens. After receiving the fed back optical signal, the laser generating gain unit performs gain amplification on the fed back optical signal. For the gain-amplified optical signal, a part of it is output through the second optical collimating lens, and the other part is transmitted to the first end of the distributed scattering feedback unit again through the first optical collimating lens for further line width compression. When reaching a steady state, the optical signal of the specific wavelength is cyclically line width compressed by the distributed scattering feedback unit, and the obtained single longitudinal mode ultra-narrow line width optical signal is output from the second optical collimating lens.

[0006] In an optional implementation, the distributed scattering feedback unit includes a special optical fiber with a high scattering coefficient, a special gas material waveguide, or a special scattering waveguide inscribed on a substrate.

[0007] In another optional implementation, by adjusting the scattering coefficient and signal feedback ratio of the distributed scattering feedback unit, deep compression of the optical signal line width and single longitudinal mode output are achieved.

[0008] In another optional implementation, the laser generating gain unit includes a gain medium and a fiber grating FBG, the gain medium generates an initial optical signal with a wide spectrum under electrical excitation, the generated optical signal is transmitted to the FBG, the FBG performs wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength, a part of the optical signal with the specific wavelength is transmitted to the first end of the distributed scattering feedback unit through the first optical collimating lens, and the other part is output through the second optical collimating lens;

[0009] The first end of the distributed scattering feedback unit receives an optical signal of a specific wavelength and compresses the line width of the optical signal, and then transmits the optical signal fed back after the line width compression to the gain medium through the first optical collimating lens and the FBG in sequence. After receiving the fed-back optical signal, the gain medium performs gain amplification on the fed-back optical signal. For the gain-amplified optical signal, a part of it is output through the FBG and the second optical collimating lens in sequence, and the other part is transmitted to the first end of the distributed scattering feedback unit again through the FBG and the first optical collimating lens in sequence for further line width compression.

[0010] In another optional implementation, a first optical isolator is further included, and the second end of the second optical collimating lens is connected to the first optical isolator.

[0011] In another optional implementation, a second optical isolator is also included, and the second end of the distributed scattering feedback unit is connected to the second optical isolator. After receiving the optical signal, the first end of the distributed scattering feedback unit performs line width compression on the optical signal, and then outputs the optical signal after line width compression and forward transmission through the second optical isolator; when a steady state is reached, the optical signal of a specific wavelength is cyclically line-width compressed by the distributed scattering feedback unit, and the obtained single longitudinal mode ultra-narrow line width optical signal is output from the second optical isolator.

[0012] In another optional implementation, the distributed scattering feedback unit is all distributed scattering mechanisms including Rayleigh scattering, and the self-matching of the laser wavelength and the effective distributed feedback cavity is achieved through the distributed scattering feedback unit.

[0013] In another optional implementation, the gain medium of the laser generating gain unit can cover any wavelength band of laser gain, has no wavelength selectivity, and is suitable for deep compression of any wavelength band and any type of laser line width.

[0014] In another optional implementation, at least the laser generation gain unit, the distributed scattering feedback unit, the first light collimating lens, the second light collimating lens, the first light isolator and the second light isolator are integrated on a substrate.

[0015] The beneficial effects of the present invention are:

[0016] 1. The present invention is provided with a laser generating gain unit, a distributed scattering feedback unit, a first light collimating lens and a second light collimating lens. Before transmitting the light signal to the distributed scattering feedback unit for cyclic line width compression, the laser generating gain unit first selects a light signal of a specific wavelength, and then transmits the light signal of the specific wavelength to the distributed scattering feedback unit for cyclic line width compression, thereby improving the compression efficiency; the present invention realizes self-matching of the output wavelength and the effective feedback cavity through the distributed scattering feedback unit, thereby realizing deep compression of the laser line width while selecting the mode, obtaining a single longitudinal mode output with relatively high side mode suppression, and the entire laser has a simple structure and a small volume;

[0017] 2. The present invention can realize single-end stable output or double-end stable output of a single longitudinal mode ultra-narrow linewidth optical signal by selectively setting a first optical isolator and a second optical isolator.

[0018] 3. The present invention can achieve integration and stability by integrating corresponding components on a substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 11 is a schematic diagram of the structure of an embodiment of an on-chip ultra-narrow linewidth laser of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of another embodiment of the on-chip ultra-narrow linewidth laser of the present invention.

[0021] In the figure: 1. distributed scattering feedback unit, 2. first light collimating lens, 3. laser generating gain unit, 4. second light collimating lens, 5. optical isolator, 300. gain medium, 301. FBG. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0023] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0024] See also Figure 1, is a schematic diagram of the structure of the on-chip ultra-narrow linewidth laser of the present invention. The on-chip ultra-narrow linewidth laser may include a laser generating gain unit 3, a distributed scattering feedback unit 1, a first optical collimating lens 2, and a second optical collimating lens 4. The first output end of the laser generating gain unit 3 is connected to the first end of the distributed scattering feedback unit 1 through the first optical collimating lens 2, and the second output end is connected to the first end of the second optical collimating lens 4; the laser generating gain unit 3 is used to generate an initial optical signal with a wide spectrum, and perform wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength. A part of the optical signal with a specific wavelength is transmitted to the first end of the distributed scattering feedback unit 1 through the first optical collimating lens 2, and the other part is output through the second optical collimating lens 4; the distributed scattering feedback unit 1 After receiving the optical signal of a specific wavelength, the first end of the optical signal performs line width compression on the optical signal, and transmits the optical signal fed back after line width compression to the laser generating gain unit 3 through the first optical collimating lens 2. After receiving the fed back optical signal, the laser generating gain unit 3 performs gain amplification on the fed back optical signal. For the gain-amplified optical signal, a part of it is output through the second optical collimating lens 4, and the other part is transmitted again to the first end of the distributed scattering feedback unit 1 through the first optical collimating lens 2 for further line width compression. When reaching a steady state, the optical signal of the specific wavelength is cyclically line width compressed by the distributed scattering feedback unit 1, and the obtained single longitudinal mode ultra-narrow line width optical signal is output from the second optical collimating lens 4.

[0025] In this embodiment, the distributed scattering feedback unit 1 includes a special optical fiber with a high scattering coefficient, a waveguide structure made of a special gas material, or a special scattering waveguide engraved on a substrate. The present invention can achieve cyclic compression of the optical signal line width and regulation of single longitudinal mode output by adjusting the scattering coefficient and signal feedback ratio of the distributed scattering feedback unit 1; the distributed scattering feedback unit 1 includes all distributed scattering mechanisms including Rayleigh scattering, and the optical signal transmitted by the distributed scattering feedback unit 1 is a distributed scattering feedback signal covering the Rayleigh scattering characteristics, and the distributed scattering feedback unit is used to achieve self-matching of the laser wavelength with the effective distributed feedback cavity. The present invention realizes self-cavity length matching and longitudinal mode-free output of the laser wavelength through the backward feedback signal generated by the distributed scattering feedback unit, and the influence of other nonlinear effects on the laser line width compression can be avoided by designing the structure of the distributed scattering feedback unit. Since the distributed scattering feedback unit 1 represented by Rayleigh scattering generates a backward scattered signal with a narrower frequency domain line width than the original injection signal during each oscillation of the laser and feeds back to the laser generating gain unit 1 for gain amplification, the present invention can achieve deep compression of the laser line width.

[0026] The laser generating gain unit 3 comprises a gain medium 300 and a fiber Bragg Grating (FBG) 301. The gain medium 300 generates an initial optical signal with a wide spectrum under the action of electrical excitation. The generated optical signal is transmitted to the FBG 301. The FBG 301 performs wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength. A part of the optical signal with the specific wavelength is transmitted to the first end of the distributed scattering feedback unit 1 through the first optical collimating lens 2, and the other part is output through the second optical collimating lens 4. After receiving the optical signal with the specific wavelength, the first end of the distributed scattering feedback unit 1 performs line width compression on the optical signal, and then transmits the optical signal fed back after line width compression to the gain medium 300 through the first optical collimating lens 2 and the FBG 301 in sequence. After receiving the feedback optical signal, the gain medium 300 performs gain amplification on the feedback optical signal. For the optical signal after gain amplification, a part of it is output through the FBG 301 and the second optical collimating lens 4 in sequence, and the other part is output through the FBG 301, the first light collimating lens 2 transmits it again to the first end of the distributed scattering feedback unit 1 for further line width compression. Among them, the gain medium 300 of the laser generating gain unit 3 can cover any band of laser gain, it has no wavelength selectivity, and is suitable for deep compression of any band and any type of laser line width. The gain medium 300 can be linear, and the FBG 301 can be engraved on the lower side of the linear gain medium 300. The gain medium 300 interacts with the FBG 301 through its lower side for optical signal. The left end of the FBG 301 serves as the first output end of the laser generating gain unit 3, and the right end serves as the second output end of the laser generating gain unit 3.

[0027] It can be seen from the above embodiments that the present invention is provided with a laser generating gain unit, a distributed scattering feedback unit, a first light collimating lens and a second light collimating lens. Before transmitting the optical signal to the distributed scattering feedback unit for cyclic linewidth compression, the laser generating gain unit first selects the optical signal of a specific wavelength, and then transmits the optical signal of the specific wavelength to the distributed scattering feedback unit for cyclic linewidth compression, thereby improving the compression efficiency; the present invention realizes self-matching of the output wavelength and the effective feedback cavity through the distributed scattering feedback unit, so that deep compression of the laser linewidth can be achieved while realizing mode selection, and a single longitudinal mode output with relatively high side mode suppression is obtained, and the entire laser has a simple structure and a small volume.

[0028] In addition, the on-chip ultra-narrow linewidth laser of the present invention may further include a first optical isolator 5, combined with Figure 1As shown, the second end of the second optical collimating lens 4 is connected to the first optical isolator 5. The on-chip ultra-narrow linewidth laser may also include a second optical isolator 5, combined with Figure 2 As shown, the second end of the distributed scattering feedback unit 1 is connected to the second optical isolator 5. After receiving the optical signal, the first end of the distributed scattering feedback unit 1 performs line width compression on the optical signal, and then outputs the optical signal transmitted forward after line width compression through the second optical isolator 5; when the steady state is reached, the optical signal of the specific wavelength is cyclically line width compressed by the distributed scattering feedback unit 1, and the obtained single longitudinal mode ultra-narrow line width optical signal is output from the second optical isolator 5. The present invention can achieve single-end stable output of the single longitudinal mode ultra-narrow line width optical signal by connecting the second end of the second optical collimating lens to the first optical isolator or connecting the second end of the distributed scattering feedback unit to the second optical isolator. Of course, when the second end of the second optical collimating lens 4 is connected to the first optical isolator 5, and the second end of the distributed scattering feedback unit 1 is connected to the second optical isolator 5, the double-end stable output of the single longitudinal mode ultra-narrow line width optical signal can be achieved.

[0029] Since the laser of the present invention has a simple structure and a small size, the present invention is particularly suitable for the process of realizing laser integration and chipization, wherein at least the laser generation gain unit 3, the distributed scattering feedback unit 1, the first light collimating lens 2, the second light collimating lens 4, the first light isolator and the second light isolator are integrated on the substrate.

[0030] In the present invention, the Rayleigh scattering unit represented by Rayleigh scattering is used as an example to realize the deep compression of laser line width, and its principle can be explained as follows:

[0031]

[0032] in: represents the signal spectrum output during the kth laser oscillation process, represents the distributed feedback signal fed back to the laser gain medium for the k-1th time, F RBS The line width attenuation factor of each injected signal represented by Rayleigh scattering can be expressed as:

[0033]

[0034] Since this process is a linear scattering process, the line width attenuation F RBSis a constant. During the laser oscillation process, the Rayleigh scattering unit compresses the line width of each injected laser at a certain ratio and then feeds it back to the gain unit for amplification. Similar to a repetitive cycle, the line width will be deeply compressed when the laser reaches dynamic equilibrium.

[0035] It should be noted that the distributed scattering feedback unit is a material with a high scattering coefficient integrated on the laser chip, which can be a special optical fiber (Fiber) with a high scattering coefficient, a special gas material, or a special scattering waveguide written on the chip using femtosecond processing and other technologies. The laser band that the gain medium of the laser generating gain unit should have can cover any laser band. The invention does not have wavelength selectivity in line width laser line width deep compression and mode selection. The optical device can be connected by optical fiber or spatial coupling. In addition, regardless of whether the laser gain unit is a semiconductor type or a fiber laser gain type, the laser output line width can be compressed to the Hz level using this method.

[0036] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0037] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. An on-chip ultra-narrow linewidth laser, characterized in that: The invention comprises a laser generating gain unit, a distributed scattering feedback unit, a first optical collimating lens and a second optical collimating lens, wherein a first output end of the laser generating gain unit is connected to a first end of the distributed scattering feedback unit through the first optical collimating lens, and a second output end is connected to a first end of the second optical collimating lens; the laser generating gain unit is used to generate an initial optical signal with a wide spectrum, and to perform wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength, wherein a part of the optical signal with the specific wavelength is transmitted to the first end of the distributed scattering feedback unit through the first optical collimating lens, and another part is output through the second optical collimating lens; After receiving the optical signal of a specific wavelength, the first end of the distributed scattering feedback unit performs line width compression on the optical signal, and transmits the optical signal fed back after line width compression to the laser generating gain unit through the first optical collimating lens. After receiving the fed back optical signal, the laser generating gain unit performs gain amplification on the fed back optical signal. For the gain amplified optical signal, a part of it is output through the second optical collimating lens, and the other part is transmitted to the first end of the distributed scattering feedback unit again through the first optical collimating lens for further line width compression. When a steady state is reached, the optical signal of the specific wavelength is cyclically line width compressed by the distributed scattering feedback unit, and the obtained single longitudinal mode ultra-narrow line width optical signal is output from the second optical collimating lens. The laser generating gain unit includes a gain medium and a Bragg grating, wherein the gain medium generates an initial optical signal with a wide spectrum under the action of electrical excitation, and the generated optical signal is transmitted to the Bragg grating, and the Bragg grating performs wavelength selection on the generated optical signal to obtain an optical signal with a specific wavelength, and a part of the optical signal with the specific wavelength is transmitted to the first end of the distributed scattering feedback unit through the first optical collimating lens, and the other part is output through the second optical collimating lens; The first end of the distributed scattering feedback unit receives an optical signal of a specific wavelength, compresses the line width of the optical signal, and then transmits the optical signal fed back after the line width compression to the gain medium through the first optical collimating lens and the Bragg grating in sequence. After receiving the fed-back optical signal, the gain medium performs gain amplification on the fed-back optical signal. For the gain-amplified optical signal, a part of it is output through the Bragg grating and the second optical collimating lens in sequence, and the other part is transmitted to the first end of the distributed scattering feedback unit again through the Bragg grating and the first optical collimating lens in sequence for further line width compression. The Bragg grating is engraved on the lower side of the linear gain medium, and the gain medium interacts with the Bragg grating for optical signals through its lower side. The left end of the Bragg grating serves as the first output end of the laser generating gain unit, and the right end serves as the second output end of the laser generating gain unit.

2. The on-chip ultra-narrow linewidth laser according to claim 1, characterized in that: The distributed scattering feedback unit includes a special optical fiber with a high scattering coefficient, a special gas material waveguide, or a special scattering waveguide written on a substrate.

3. The on-chip ultra-narrow linewidth laser according to claim 1 or 2, characterized in that: By adjusting the scattering coefficient and signal feedback ratio of the distributed scattering feedback unit, deep compression of the optical signal line width and single longitudinal mode output can be achieved.

4. The on-chip ultra-narrow linewidth laser according to claim 1, characterized in that: It also includes a first optical isolator, and the second end of the second optical collimating lens is connected to the first optical isolator.

5. The on-chip ultra-narrow linewidth laser according to claim 1 or 4, characterized in that: It also includes a second optical isolator, the second end of the distributed scattering feedback unit is connected to the second optical isolator, and the first end of the distributed scattering feedback unit receives an optical signal, compresses the line width of the optical signal, and then outputs the optical signal transmitted forward after the line width compression through the second optical isolator; when a steady state is reached, the optical signal of a specific wavelength is cyclically line-width compressed by the distributed scattering feedback unit, and the obtained single longitudinal mode ultra-narrow linewidth optical signal is output from the second optical isolator.

6. The on-chip ultra-narrow linewidth laser according to claim 1 or 2, characterized in that: The distributed scattering feedback unit is all distributed scattering mechanisms including Rayleigh scattering, and the self-matching of the laser wavelength and the effective distributed feedback cavity is achieved through the distributed scattering feedback unit.

7. The on-chip ultra-narrow linewidth laser according to claim 1, characterized in that: The gain medium of the laser generating gain unit can cover any wavelength band of laser gain, has no wavelength selectivity, and is suitable for deep compression of any wavelength band and any type of laser line width.

8. The on-chip ultra-narrow linewidth laser according to claim 5, characterized in that: At least the laser generation gain unit, the distributed scattering feedback unit, the first light collimating lens, the second light collimating lens, the first light isolator and the second light isolator are integrated on the substrate.

Images