A large-tolerance wavelength tunable narrow linewidth external cavity laser
By optimizing the coupling region structure and adiabatic widening design of the microring resonator, the problem of insufficient processing tolerance of external cavity lasers in micro-nano fabrication is solved, the processing robustness is improved, and the stability and performance consistency of the laser are ensured under standard micro-nano fabrication conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2024-01-05
- Publication Date
- 2026-07-21
AI Technical Summary
Existing on-chip wavelength-tunable narrow-linewidth external cavity lasers have insufficient processing tolerance in micro- and nano-fabrication, resulting in poor processing robustness and failing to meet the requirements of applications such as lidar.
By optimizing the coupling region structural parameters and adiabatic widening design of the microring resonator, the coupling efficiency of TE polarized light between the bus waveguide and the ring waveguide remains unchanged, while reducing the loss caused by sidewall roughness, increasing the Q value of the microring resonator, and achieving large tolerance wavelength selection and tuning.
It significantly improves the manufacturing tolerance of external cavity lasers in micro-nano fabrication, enhances processing robustness, and ensures the stability and performance consistency of lasers under standard micro-nano fabrication conditions.
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Figure CN117856036B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of optoelectronic devices, specifically relating to a large-tolerance wavelength-tunable narrow-linewidth external cavity laser. Background Technology
[0002] CMOS-compatible on-chip optical waveguide technology has driven the development of high integration and miniaturization in lasers. Lasers based on on-chip optical waveguides are characterized by ease of large-scale integration, light weight, and low cost. These advantages make them promising for applications in lidar, free-space optical communication, optical detection, and ranging.
[0003] Robustness is a crucial performance indicator for on-chip wavelength-tunable narrow-linewidth external cavity lasers. A typical lidar system requires a detection range of 200m, corresponding to a coherence length of 400m and a Lorentz linewidth of 300kHz. This corresponds to an effective filter length of less than 1mm. Within this range, even a small change in the effective filter length can cause a significant change in the laser's Lorentz linewidth. The effective length is determined by the coupling efficiency of the microring coupling region. Generally, a 1% change in the coupling efficiency of the microring resonator can lead to a 50% change in linewidth due to the change in effective length and coherence length. In practical applications, this cannot guarantee product yield. Therefore, improving the robustness of the manufacturing process, i.e., improving manufacturing tolerance, is of great significance and application value. Summary of the Invention
[0004] To address the limitations of existing technologies, the present invention aims to overcome these limitations and effectively improve the robustness of lasers under existing standard micro-nano fabrication conditions. The present invention proposes a high-tolerance wavelength-tunable narrow-linewidth external cavity laser and a method to stabilize the coupling efficiency of the microring resonator and the insulation broadening of the microring, which will significantly improve the fabrication robustness of the wavelength-tunable narrow-linewidth external cavity laser.
[0005] This invention proposes a large tolerance wavelength tunable narrow linewidth external cavity laser, which consists of the following components: a semiconductor optical amplifier (1), a mode converter (2), a multimode interference beam splitter (3), a first-stage microring resonator (4), a second-stage microring resonator (5), and a tapered extinction port (6).
[0006] The spontaneous emission light generated by the semiconductor optical amplifier (1) is output from one side and enters the external cavity composed of a multimode interference beam splitter (3), a first-stage microring resonator (4), and a second-stage microring resonator (5) through a mode converter (2). When the spontaneous emission light is output from the mode converter (2), the large mode field beam is converted into a single-mode waveguide TE polarization mode by the mode converter (2). After passing through the multimode interference beam splitter (3), the TE polarized light passes through the first-stage microring resonator (4) and the second-stage microring resonator (5). Due to the slight difference in the free spectral range of the two microring resonators, the resulting vernier effect can filter the TE polarized light. The returned TE polarized light returns to the semiconductor optical amplifier (1) through the mode converter (2) to form a resonant cavity and generate gain on the returned TE polarized light, generating a narrow linewidth laser output on the other side of the semiconductor optical amplifier (1). By optimizing the structural parameters of the coupling region of the microring resonator, the coupling efficiency of TE-polarized light between the bus waveguide and the ring waveguide remains almost constant within a standard micro / nano fabrication error range of ±20 nm. In the ring resonator, TE-polarized light enters the uncoupled wide waveguide region from the coupling region via adiabatic coupling, reducing the overlap between the waveguide mode and the waveguide sidewalls, minimizing losses caused by sidewall roughness, and increasing the Q value of the microring resonator. Compared with existing technologies, under the same standard micro / nano fabrication conditions, this invention significantly improves the manufacturing tolerance of external cavity lasers in micro / nano fabrication and enhances fabrication robustness.
[0007] The semiconductor optical amplifier (1) is connected to a DC power supply and generates spontaneous emission light.
[0008] The mode converter (2) realizes the function of converting the light spot size. When the spontaneous emission light generated by the semiconductor optical amplifier (1) is output from one side, the mode converter (2) outputs the single-mode waveguide TE mode light on the right side; when the single-mode waveguide TE mode light is input from the right side, the mode converter (2) outputs the light similar to the light spot of the semiconductor optical amplifier (1) on the left side.
[0009] The first-stage microring resonator (4) and the second-stage microring resonator (5) have large-tolerance wavelength selection and tuning characteristics. They comprise two directional couplers, a ring waveguide, and a heating wire; the drop ends of the two microring resonators are connected. The directional couplers ensure that the optical coupling efficiency of the TE mode between the bus waveguide and the ring waveguide remains unchanged within the standard micro / nano fabrication error range; the ring waveguide is thermally broadened from the coupling region into the uncoupled wide waveguide region, reducing the overlap between the waveguide mode and the waveguide sidewalls, reducing losses caused by sidewall roughness, and increasing the Q value of the microring resonator; the heating wire is located above the ring waveguide, and heating it can change the refractive index of the ring waveguide, achieving the function of selecting and tuning the TE polarization wavelength.
[0010] The method proposed in this invention for improving the fabrication robustness of large-tolerance wavelength selection and tuning micro-ring resonator structures is as follows:
[0011] The wavelength selection and tuning of the microring resonator are determined by the coupling efficiency between the bus waveguide and the ring waveguide and the effective refractive index of the optical modes in the ring waveguide. The coupling efficiency between the bus waveguide and the ring waveguide is related to the effective index difference between the symmetric and antisymmetric supermodes in the waveguide cross-section of the coupling region. Waveguide widening and gap narrowing caused by manufacturing directly affect the change in the effective index difference between the symmetric and antisymmetric supermodes. By optimizing the parameters of the waveguide cross-section (waveguide width w, waveguide gap g, waveguide plate thickness t), the changes in the effective index difference caused by the changes in each parameter can be mutually canceled, thus keeping the coupling efficiency between waveguides constant within a certain range. At the same time, the ring waveguide is adiabatically widened from the coupling region to the wide waveguide in the uncoupled region, reducing the overlap between the waveguide modes and the waveguide sidewalls. At this time, the change in the effective refractive index of the waveguide modes caused by the sidewall roughness will be greatly reduced, which helps to stabilize the resonance peak and also reduces the loss caused by the sidewall roughness, increasing the Q value of the microring resonator.
[0012] The beneficial effects of this invention are:
[0013] This invention addresses existing standard micro / nano fabrication processes by proposing a high-tolerance wavelength-tunable narrow-linewidth external cavity laser based on on-chip optical waveguides. The proposed methods for stabilizing the coupling efficiency of the microring resonator and widening the insulation of the microring significantly improve the manufacturing tolerance and robustness of the external cavity laser in micro / nano fabrication under current standard micro / nano fabrication processes. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the structure of a high-tolerance wavelength-tunable narrow-linewidth external cavity laser according to the present invention.
[0015] Figure 2 This is a schematic diagram showing the sensitivity of the coupling efficiency of the microring resonator of the present invention relative to the waveguide width in the coupling region compared with other microring resonators.
[0016] Figure 3 This is a schematic diagram showing the changes in center wavelength and FSR of the microring resonator of the present invention and other microring resonators under a 20nm manufacturing size variation.
[0017] Figure 4 This is a schematic diagram of the wavelength shift of the present invention.
[0018] In the figure: semiconductor optical amplifier (1), mode converter (2), multimode interference beam splitter (3), first-stage micro-ring resonator (4), second-stage micro-ring resonator (5), tapered extinction port (6). Detailed Implementation
[0019] The invention will now be further described with reference to the accompanying drawings.
[0020] like Figure 1 As shown, a large-tolerance wavelength-tunable narrow-linewidth external cavity laser is composed of the following components: a semiconductor optical amplifier (1), a mode converter (2), a multimode interference beam splitter (3), a first-stage micro-ring resonator (4), a second-stage micro-ring resonator (5), and a tapered extinction port (6).
[0021] The spontaneous emission light generated by the semiconductor optical amplifier (1) is output from one side and enters the outer cavity composed of a multimode interference beam splitter (3) and microring resonators through a mode converter (2). When the spontaneous emission light is output from the mode converter (2), the large mode field beam is converted into a single-mode waveguide TE polarization mode through the mode converter (2). The TE polarized light passes through two microring resonators after passing through the multimode interference beam splitter (3). Due to the slight difference in the free spectral range of the two microring resonators, the resulting vernier effect filters the TE polarized light. The returned TE polarized light returns to the semiconductor optical amplifier (1) through the mode converter (2) to form a resonant cavity and generate gain on the returned light, generating a narrow linewidth laser output on the other side of the semiconductor optical amplifier (1).
[0022] The multimode interference beam splitter (3) described above uses special mathematical line optimization to realize a 3dB power divider with large bandwidth and large tolerance, and features low phase error and power balance within a large bandwidth range.
[0023] The first-stage microring resonator (4) and the second-stage microring resonator (5) have large tolerance wavelength selection and tuning characteristics. The first-stage microring resonator (4) and the second-stage microring resonator (5) optimize the ring shape by using an adiabatic wide waveguide on a ridge waveguide structure. The constructed silicon-based external cavity chip can realize the functions of large bandwidth, large tolerance wavelength selection and tuning, and the resonant peak wavelength can be changed by heating the electrodes to change the refractive index of the ring waveguide, thereby achieving tuning over a wide range of wavelengths.
[0024] The first-stage microring resonator (4) and the second-stage microring resonator (5) each contain two directional couplers, a ring waveguide, and a heating wire; the drop ends of the two microring resonators are connected. The wavelength selection and tuning of the microring resonator are determined by the coupling efficiency between the bus waveguide and the ring waveguide and the effective refractive index of the optical mode in the ring waveguide. The coupling efficiency between the bus waveguide and the ring waveguide is related to the effective index difference between the symmetric and antisymmetric supermodes in the waveguide cross-section of the coupling region. The specific relationship is as follows:
[0025]
[0026] Where Δn is the effective exponent difference between the symmetric and antisymmetric supermodes, L is the length of the coupler, and λ is the wavelength. Substituting α for the waveguide geometry parameters, which include waveguide width w, waveguide gap g, and plate thickness t, the relationship between coupling efficiency and the geometry parameters is obtained as follows:
[0027]
[0028] This indicates that the change in coupling efficiency K can be determined by the sensitivity parameter. Characterization shows that in a symmetric directional coupler, Δn is stable with respect to asymmetric changes in waveguide width w. Increasing the waveguide width w increases mode constraint, thereby reducing Δn. However, Δn is also affected by the waveguide gap g. Decreasing the waveguide gap g increases mode overlap between the two waveguides and Δn. Therefore, to maintain constant waveguide coupling, the following equation must be satisfied (Δn1 and Δn2 are the changes in the effective exponent difference between the symmetric and antisymmetric supermodes caused by changes in waveguide width w and waveguide gap g, respectively):
[0029]
[0030] The ring waveguide is thermally extended from the coupling region into the uncoupled wide waveguide region, reducing the overlap between the waveguide mode and the waveguide sidewall, reducing the loss caused by sidewall roughness, and increasing the Q value of the micro-ring resonator. The heating wire is located above the ring waveguide, and heating can change the refractive index of the ring waveguide, thereby achieving the function of selecting and tuning the TE polarization wavelength.
[0031] Figure 2 The sensitivity of the coupling efficiency of the microring resonator relative to the waveguide width in the coupling region compared to other microring resonators is demonstrated. Figure 2 The left image shows the full etching process, and the right image shows the etching sensitivity at 150nm. The coupling efficiency of the coupling region of the microring resonator is less sensitive to changes in manufacturing dimensions.
[0032] Figure 3 The changes in center wavelength and FSR of the microring resonator and other microring resonators under a 20nm manufacturing size variation are shown. Figure 3 The upper left image shows the wavelength shift of the fully etched waveguide, while the upper right image shows the wavelength shift of the designed structure. The microring resonator is less sensitive to changes in manufacturing dimensions and its performance is minimally affected.
[0033] like Figure 4 As shown, the FSR variation of the fully etched waveguide in the lower left corner; the FSR variation of the designed structure in the lower right corner.
[0034] As shown in the figure above, compared with the prior art, under the same micro-nano fabrication conditions, the present invention significantly improves the manufacturing tolerance of external cavity lasers in micro-nano fabrication and enhances the fabrication robustness.
Claims
1. A high-tolerance wavelength-tunable narrow-linewidth external cavity laser, characterized in that, It includes a semiconductor optical amplifier (1), a mode converter (2), a multimode interference beam splitter (3), a first-stage micro-ring resonator (4), a second-stage micro-ring resonator (5), and a tapered extinction port (6); The spontaneous emission light generated by the semiconductor optical amplifier (1) is output from one side and enters the external cavity composed of a multimode interference beam splitter (3), a first-stage microring resonator (4), and a second-stage microring resonator (5) through a mode converter (2). When the spontaneous emission light is output from the mode converter (2), the large mode field beam is converted into a single-mode waveguide TE polarization mode through the mode converter (2). After passing through the multimode interference beam splitter (3), the TE polarized light passes through the first-stage microring resonator (4) and the second-stage microring resonator (5) respectively. Since the free spectral range of the two microring resonators has a slight difference, the resulting vernier effect can filter the TE polarized light. The returned TE polarized light returns to the semiconductor optical amplifier (1) through the mode converter (2) to form a resonant cavity and generate a gain on the returned TE polarized light, generating a narrow linewidth laser output on the other side of the semiconductor optical amplifier (1). The first-stage micro-ring resonator (4) and the second-stage micro-ring resonator (5) have large tolerance wavelength selection and tuning characteristics; the first-stage micro-ring resonator (4) and the second-stage micro-ring resonator (5) optimize the ring shape by using the method of adiabatic wide waveguide on the ridge waveguide structure. The constructed silicon-based external cavity chip can realize the functions of large bandwidth, large tolerance wavelength selection and tuning, and achieve large-range wavelength tuning by changing the refractive index of the ring waveguide by heating the heating electrode, that is, changing the resonant peak wavelength; the drop ends of the two micro-ring resonators are connected; and each contains two directional couplers, one ring waveguide, and one heating wire; the directional coupler ensures that the optical coupling efficiency of the TE mode between the bus waveguide and the ring waveguide remains unchanged within the standard micro-nano fabrication error range; the ring waveguide is adiabatically widened from the coupling region to the wide waveguide in the non-coupling region, reducing the overlap between the waveguide mode and the waveguide sidewall, reducing the loss caused by the sidewall roughness, and increasing the Q value of the micro-ring resonator cavity; The heating wire is located above the ring waveguide. By heating, the refractive index of the ring waveguide is changed, thereby achieving the function of selecting and tuning the TE polarization wavelength. The coupling efficiency between the bus waveguide and the ring waveguide is related to the effective exponent difference between the symmetric and antisymmetric supermodes in the coupled region waveguide cross-section. The specific relationship is as follows: in The effective index difference between the symmetric and antisymmetric supermodes. The length of the coupler; For wavelength, use Instead of waveguide geometry parameters, waveguide geometry parameters include waveguide width. waveguide gap Plate thickness The relationship between coupling efficiency and geometric parameters is as follows: This indicates the coupling efficiency The change can be determined by the sensitivity parameter Characterization, in a symmetric direction coupler, For waveguide width The asymmetric change is stable, waveguide width Increasing the number of constraints will increase pattern constraints, thereby reducing the number of constraints. ;but, Also affected by waveguide gap The influence of waveguide gap The reduction makes the two waveguides and As the overlap between modes increases, the waveguide coupling must remain unchanged to satisfy the following equation: in, , They are respectively determined by the waveguide width waveguide gap The change in the effective index difference between the symmetric and antisymmetric supermodes caused by the variation.
2. The high-tolerance wavelength-tunable narrow-linewidth external cavity laser according to claim 1, characterized in that, The semiconductor optical amplifier (1) is connected to a DC power supply and generates spontaneous emission light.
3. The high-tolerance wavelength-tunable narrow-linewidth external cavity laser according to claim 1, characterized in that, The mode converter (2) realizes the function of converting the light spot size. When the spontaneous emission light generated by the semiconductor optical amplifier (1) is output from one side, the mode converter (2) outputs the single-mode waveguide TE mode light on the right side; when the single-mode waveguide TE mode light is input from the right side, the mode converter (2) outputs the light similar to the light spot of the semiconductor optical amplifier (1) on the left side.