Hybrid integrated single-longitudinal-mode narrow-linewidth complex-cavity laser and working method

Abstract

Disclosed is a hybrid integrated single-longitudinal-mode narrow-linewidth compound cavity laser, which comprises: a distributed feedback gain chip (1), a micro-ring resonant cavity; the two ends of the distributed feedback gain chip are respectively coated with a first anti-reflection film (5) and a second anti-reflection film (6), and the internal reflection structure is a continuous periodic grating (3) along the cavity; the distributed feedback gain chip is a continuous uniform grating distributed feedback gain medium (4); and the micro-ring resonant cavity is a micro-ring resonant cavity with a reflection function. A working method is also provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical communication and optoelectronics, in particular to a hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser and a working method of the hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser. BACKGROUND

[0002] Narrow-linewidth semiconductor lasers are widely used in high-speed optical communication, coherent detection, long-distance sensing and other fields. Distributed feedback semiconductor lasers (DFB) are commonly used narrow-linewidth semiconductor light sources in integrated microsystems, which set a distributed feedback grating in the internal gain medium region or waveguide region, and use the mode selection characteristics of the grating to achieve narrow-linewidth output. In order to break the mode degeneracy and achieve single-longitudinal-mode lasing, a quarter-wavelength phase shift is usually introduced in the design of the grating or a high-reflectivity (HR) film is coated on the back reflection end. These designs of the DFB laser achieve single-longitudinal-mode output with a linewidth of about 500 kHz, but this still cannot meet the current application in the fields of communication and sensing.

[0003] The composite cavity lasers that have been realized at present include: 1. Semiconductor optical amplifier / reflective semiconductor optical amplifier coupled with a multi-micro-ring resonant cavity, which uses the vernier effect, and the composite cavity has an equivalent single passband within the gain bandwidth, thereby realizing single-mode output and a linewidth of 10 kHz to 100 kHz. 2. DFB laser coupled with a high-Q external cavity, which introduces feedback self-injection, and under the condition of strong self-injection locking, the linewidth of the DFB laser is narrowed to the order of Hz. This method sacrifices the output optical power because it feeds back and injects part (about 10%) of the output light of the DFB. SUMMARY

[0004] To overcome the defects of the prior art, the technical problem to be solved by the present application is to provide a hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser, which can realize a side mode suppression ratio of greater than 60 dB, single-longitudinal-mode output, and a linewidth of 1.5 kHz.

[0005] The technical scheme of the present application is: the hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser comprises a distributed feedback gain chip (1) and a micro-ring resonant cavity; the two ends of the distributed feedback gain chip are respectively coated with a first anti-reflection film (5) and a second anti-reflection film (6), and the internal reflection structure is a continuous periodic grating (3) along the cavity; the distributed feedback gain chip is a continuous uniform grating distributed feedback gain medium (4); and the micro-ring resonant cavity is a micro-ring resonant cavity with a reflecting effect.

[0006] The application also provides a working method of the mixed integrated single-longitudinal-mode narrow-line-width compound cavity laser, the first anti-reflection film has a lasing spectrum of degenerate double-longitudinal modes λ1 and λ2; one of the reflection resonance peaks is aligned with λ1 in the degenerate mode by tuning the resonance wavelength of the compound cavity, so that the longitudinal mode with wavelength λ1 is selected and the other longitudinal mode with wavelength λ2 is suppressed; under the mode competition in the cavity, the output longitudinal mode is only the longitudinal mode with wavelength λ1.

[0007] The application is characterized in that: the two ends of the distributed feedback gain chip are respectively plated with a first anti-reflection film and a second anti-reflection film, the internal reflection structure is a continuous periodic grating along the cavity, the distributed feedback gain chip is a continuous uniform grating distributed feedback gain medium; the micro-ring resonant cavity is a micro-ring resonant cavity with a reflection function; the first anti-reflection film has a lasing spectrum of degenerate double-longitudinal modes λ1 and λ2; one of the reflection resonance peaks is aligned with λ1 in the degenerate mode by tuning the resonance wavelength of the compound cavity, so that the longitudinal mode with wavelength λ1 is selected and the other longitudinal mode with wavelength λ2 is suppressed; under the mode competition in the cavity, the output longitudinal mode is only the longitudinal mode with wavelength λ1. Therefore, a single-longitudinal-mode output with a side mode suppression ratio greater than 60 dB and a line width of 1.5 kHz can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A structure schematic diagram of a first embodiment of the mixed integrated single-longitudinal-mode narrow-line-width compound cavity laser according to the application is shown.

[0009] Figure 2 A realization principle of the narrow-line-width single-mode laser is shown.

[0010] Figure 3 An external cavity reflection spectrum schematic diagram is shown.

[0011] Figure 4 A distributed feedback gain chip lasing spectrum is shown.

[0012] Figure 5 A compound cavity laser output spectrum is shown.

[0013] Figure 6 A compound cavity line width is shown.

[0014] Figure 7 A structure schematic diagram of a second embodiment of the mixed integrated single-longitudinal-mode narrow-line-width compound cavity laser according to the application is shown. DETAILED DESCRIPTION

[0015] As Figure 1 , 7As shown, the mixed integrated single-longitudinal-mode narrow linewidth compound cavity laser includes: a distributed feedback gain chip 1, a micro-ring resonant cavity; the two ends of the distributed feedback gain chip are respectively coated with a first anti-reflection film 5 and a second anti-reflection film 6, and the internal reflection structure is a continuous periodic grating 3 along the cavity, and the distributed feedback gain chip is a distributed feedback gain medium 4 with a continuous uniform grating; and the micro-ring resonant cavity is a micro-ring resonant cavity with a reflecting function.

[0016] Preferably, as shown in the figure, Figure 1 the micro-ring resonant cavity is a reflecting type micro-ring resonant cavity 2, and the Input end and the Drop end of the micro-ring resonant cavity are connected to form a reflecting structure through a multimode interferometer.

[0017] Alternatively, as shown in the figure, Figure 7 the micro-ring resonant cavity is an All-Pass type micro-ring resonant cavity 7 based on a subwavelength reflecting point.

[0018] Preferably, the reflectivity of the first anti-reflection film and the second anti-reflection film is 0.5%.

[0019] A working method of the mixed integrated single-longitudinal-mode narrow linewidth compound cavity laser is also provided, and the lasing spectrum from the first anti-reflection film is degenerate double-longitudinal-mode λ1 and λ2; by tuning the resonant wavelength of the compound cavity, one of the reflecting resonant peaks is aligned with λ1 in the degenerate mode, then the longitudinal mode with the wavelength λ1 is selected, and the other longitudinal mode with the wavelength λ2 is suppressed, and under the mode competition in the cavity, the output longitudinal mode is only the longitudinal mode with the wavelength λ1.

[0020] The two ends of the distributed feedback gain chip are respectively coated with a first anti-reflection film and a second anti-reflection film, the internal reflection structure is a continuous periodic grating along the cavity, the distributed feedback gain chip is a distributed feedback gain medium with a continuous uniform grating, the micro-ring resonant cavity is a micro-ring resonant cavity with a reflecting function, the lasing spectrum from the first anti-reflection film is degenerate double-longitudinal-mode λ1 and λ2, by tuning the resonant wavelength of the compound cavity, one of the reflecting resonant peaks is aligned with λ1 in the degenerate mode, then the longitudinal mode with the wavelength λ1 is selected, and the other longitudinal mode with the wavelength λ2 is suppressed, and under the mode competition in the cavity, the output longitudinal mode is only the longitudinal mode with the wavelength λ1. Therefore, a single-longitudinal-mode output with a side mode suppression ratio greater than 60 dB and a linewidth of 1.5 kHz can be realized.

[0021] Preferably, the spectral characteristics of the reflecting spectrum are as follows: the reflecting resonant peak FSR is greater than the interval of the degenerate mode of the gain chip, and is 20 GHz to 100 GHz; the full width at half maximum of the reflecting resonant peak is as narrow as 80 MHz to 1 GHz, and the corresponding resonant cavity quality factor is 10 5 ~ 10 6The coupling end of the reflection cavity is provided with a mode spot transformer for matching the waveguide mode field size and the output size of the gain chip. The reflection type micro-ring external cavity is coupled to the right side of the gain chip to form a composite cavity.

[0022] Preferably, λ1=1547.65 nm and λ2=1548.21 nm. After coupling the laser with an external cavity, the external cavity resonance peak is tuned to obtain a single longitudinal mode λ=1548.74 nm, and the side mode suppression ratio is 63.7 dB.

[0023] Preferably, the output linewidth of the laser is measured by a 20 km delay self-heterodyne experiment, a beat note figure is obtained, the full width at half maximum of the beat note is 3 kHz, and the output linewidth of the laser is 1.5 kHz.

[0024] The application will be described in more detail below.

[0025] The distributed feedback chip of structure 1 is coated with an anti-reflection film at both ends, the reflectivity is about 0.5%, and the internal reflection structure is a continuous periodic grating along the cavity. The lasing spectrum of the gain chip of the structure from the left side of the AR film is degenerate double longitudinal mode λ1, λ2, and the spectrum is shown in Figure 2 Structure 2 is a micro-ring resonant cavity with a reflection type. The structure can be a 2Add-Drop type micro-ring as shown in Figure 1 (111) micro-ring structure mentioned in patent CN202010279703.8), the Input end and the Drop end of the micro-ring are connected through a multimode interferometer to form a reflection structure. The structure can also be an All-Pass type micro-ring resonant cavity based on a subwavelength reflection point as shown in Figure 1 7 of reference document 1 (reference document 1: Li J, Zhang B, Yang S, et al. Robust hybrid laser linewidth reduction using Si 3N 4-based subwavelength hole defect assisted microring reflector [J]. Photonics Research, 2021, 9(4): 558-566.). The common point of the two resonant cavities is that they have a reflection effect. Their reflection spectrum at the input end is represented by , where I in is the light intensity entering the resonant cavity, and I out is the light intensity reflected from the same port. Their reflection spectrum is shown in Figure 3 , and the spectral characteristics are: 1. The reflection resonance peak FSR needs to be greater than the interval of the degenerate mode of the gain chip, about 20 GHz-100 GHz. 2. The reflection resonance peak full width at half maximum is as narrow as 80 MHz-1 GHz, and the quality factor of the resonant cavity is 10 5~10 6 .3. The coupling end of the reflection cavity is provided with a mode spot transformer to match the waveguide mode field size and the output size of the gain chip. The reflection type micro-ring external cavity is coupled to the right side of the gain chip to form a composite cavity. By tuning the resonance wavelength of the composite cavity, one of the reflection resonance peaks is aligned with one of the degenerate modes (for example, λ1), and the longitudinal mode with a wavelength of λ1 is selected, and another longitudinal mode with a wavelength of λ2 is suppressed, as shown in Figure 2 The schematic diagram of the composite cavity is shown. Under the mode competition in the cavity, the output longitudinal mode is only the longitudinal mode with a wavelength of λ1, and the side mode suppression ratio is significantly improved, and finally the output spectrum of the composite cavity laser is as shown in Figure 2 The output of the composite cavity laser is shown.

[0026] The difference between the patent CN202010279703.8 and the present application is as follows:

[0027] The silicon-based external cavity and the DFB laser coupled in the patent CN202010279703.8 form a narrow linewidth laser, and the present application couples a distributed semiconductor gain chip with the external cavity. The "distributed semiconductor gain chip" used in the present application is different from the traditional DFB laser. The DFB laser in the patent CN202010279703.8 is a distributed grating with a phase shift structure, which can make the DFB output a single longitudinal mode, and one end of the DFB is coated with an anti-reflection film and the other end is coated with an anti-reflection film. The internal structure of the "distributed semiconductor gain chip" of the present application is a distributed grating without a phase shift structure, and both ends are coated with an anti-reflection film, and the output spectrum is an unstable multi-longitudinal mode.

[0028] The output port of the external cavity laser in the patent CN202010279703.8 is from one port of the external cavity chip, and the output of the composite cavity laser proposed in the present application is one end of the semiconductor gain chip.

[0029] The patent CN202010279703.8 is based on the self-injection locking principle of the DFB laser, and the DFB output light is self-injected back to the gain medium to form injection locking. The present application is based on the principle of composite cavity, and the spectrum of the distributed feedback gain chip and the reflection spectrum of the external cavity form a composite cavity, and the external cavity plays the function of a mirror. By using the mode selection principle, a single longitudinal mode output is realized.

[0030] The gain chip used in the composite cavity laser is a continuous uniform grating distributed feedback gain medium, and its output spectrum is a multi-longitudinal mode, as shown in Figure 4 The most important double longitudinal mode wavelengths of the degenerate state are λ1=1547.65nm and λ2=1548.21nm, respectively, and the longitudinal mode working state is unstable. After coupling the laser with an external cavity, the external cavity resonance peak is tuned to obtain Figure 5The single longitudinal mode λ = 1548.74 nm is shown, and the side mode suppression ratio is 63.7 dB. The output linewidth of the laser is measured by a 20 km delay self-heterodyne experiment, and the beat frequency diagram is shown in Fig. 3. Figure 5 As shown in Fig. 3, the full width at half maximum of the beat frequency is 3 kHz, and thus the output linewidth of the laser is 1.5 kHz.

[0031] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Any simple modification, equivalent change and modification made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser, characterized in that: It includes: Distributed feedback gain chip (1), micro-ring resonator; the two ends of the distributed feedback gain chip are respectively coated with a first anti-reflection film (5) and a second anti-reflection film (6), the internal reflection structure is a continuous periodic grating (3) along the cavity, the distributed feedback gain chip is a distributed feedback gain medium (4) with a continuous uniform grating; the micro-ring resonator is a micro-ring resonator with a reflection function; a mode converter is set at the coupling end of the micro-ring resonator to match the waveguide mode field size with the output size of the gain chip. When this micro-ring resonator is coupled to the right side of the above-mentioned gain chip, a composite cavity is formed, and the micro-ring resonator is used as the outer cavity; The lasing spectrum of the first antireflective coating is a degenerate dual-longitudinal mode. , By tuning the resonant wavelength of the composite cavity, one of the reflected resonant peaks is made to coincide with the degenerate mode. If aligned, the wavelength is... The longitudinal mode was selected, and another wavelength was... The longitudinal mode is suppressed; under intracavity mode competition, the output longitudinal mode is only the wavelength of [wavelength value missing]. The longitudinal modulus.

2. The hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to claim 1, characterized in that: The micro-ring resonator is a reflective micro-ring resonator (2), and the Input and Drop ends of the micro-ring resonator are connected by a multimode interferometer to form a reflective structure.

3. The hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to claim 1, characterized in that: The micro-ring resonator is an All-Pass type micro-ring resonator based on subwavelength reflection points.

4. The hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to any one of claims 1-3, characterized in that: The reflectivity of the first antireflective film and the second antireflective film is 0.5%.

5. The operating method of the hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to claim 4, characterized in that: The spectral characteristics of the reflection spectrum are as follows: the FSR of the reflection resonance peak is greater than the spacing of the degenerate modes of the gain chip, ranging from 20 GHz to 100 GHz; the full width at half maximum (FWHM) of the reflection resonance peak is narrow from 80 MHz to 1 GHz, corresponding to a resonant cavity quality factor of [missing value]. .

6. The operating method of the hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to claim 1, characterized in that: ， After coupling the laser to the external cavity, the resonant peak of the external cavity is tuned to obtain a single longitudinal mode. The side-mode suppression ratio is 63.7 dB.

7. The operating method of the hybrid integrated single-longitudinal-mode narrow-linewidth composite cavity laser according to claim 6, characterized in that: The laser output linewidth was measured using a 20km delay self-heterodyne experiment to obtain the beat frequency diagram. The beat frequency half-width was 3kHz, and the laser output linewidth was found to be 1.5kHz.

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