WO2023236669A1

WO2023236669A1 - Hybrid integrated external-cavity diode laser device resistant to external optical feedback

Info

Publication number: WO2023236669A1
Application number: PCT/CN2023/089984
Authority: WO
Inventors: 李若林
Original assignee: 珠海映讯芯光科技有限公司
Priority date: 2022-06-07
Filing date: 2023-04-23
Publication date: 2023-12-14
Also published as: CN116316059A

Abstract

A hybrid integrated external-cavity diode laser device resistant to external optical feedback. The hybrid integrated external-cavity diode laser device is composed of an active gain amplification chip (201) and a passive photonic chip (205), wherein a waveguide phase control area (207), a waveguide filtering feedback area (208) and a waveguide polarization rotator (211) are sequentially arranged on an optical waveguide (206) of the passive photonic chip (205); light emitted by an optical waveguide (203) of the active gain amplification chip (201) is coupled into the optical waveguide (206) of the passive photonic chip (205); and an optical anti-reflection film is plated on one end face of the active gain amplification chip (201), which end face is coupled to the passive photonic chip (205), and an optical high-reflection film is plated on the other end face of the active gain amplification chip (201). An external-cavity waveguide structure composed of the waveguide phase control area (207) and the waveguide filtering feedback area (208) is asymmetric in terms of polarization, that is, the effective refractive index of a TE base mode and the effective refractive index of a TM base mode are different; and a laser generated by an external-cavity diode laser device (209) enters the waveguide polarization rotator (211) and the waveguide polarization rotator (211) turns the polarization direction of the incident light by 45 degrees. By means of the diode laser device, the anti-interference operation of an external-cavity laser device without an optical isolator is realized, thereby reducing the cost and the process complexity.

Description

Hybrid integrated external cavity semiconductor laser resistant to external light feedback

Technical field

The present invention relates to an external-cavity semiconductor laser that is resistant to external light feedback, and in particular to a hybrid integrated external-cavity semiconductor laser that is resistant to external light feedback and can be integrated into a chip without an optical isolator.

Background technique

The development trend of photonic integrated chips is the shift to CMOS-based silicon semiconductor platforms. The specific representative is silicon photonics technology, which uses CMOS semiconductor processes and technologies on silicon wafers to achieve high-performance, low-cost optical devices and Large-scale integration and manufacturing of systems.

In the development and application of silicon photonics integration technology (including but not limited to silicon-based silicon oxide, silicon, silicon nitride, etc.), since silicon is an indirect band gap semiconductor and cannot emit light, any functions related to light emitting must rely on compound semiconductors. accomplish. The integration of compound semiconductor light-emitting functions into silicon photonic chips is achieved through hybrid integration.

Generally speaking, for semiconductor lasers, due to their operational stability requirements, an optical isolator is placed in the optical path before the laser light when the device is packaged to prevent some laser feedback or reflection back into the laser cavity caused by external optical reflections. , which in turn causes laser instability and film jump. Generally, optical isolators are in free space form, and the core is composed of magneto-optical materials. The polarization state of light during transmission is changed through the polarization rotation of the Faraday effect, and the isolation of the returned reflected light is achieved through orthogonal polarizers.

However, in silicon photonic integrated chip technology, one way to achieve isolation of lasers from external light feedback generated during transmission is to integrate optical isolators based on magnetic materials and silicon photonic chips on-chip. However, because they belong to different material systems, the integration of magnetic material optical isolators into silicon wafers has strict process requirements and is very difficult. Due to reasons such as yield, the implementation cost is very expensive and the performance is poor. Therefore, how to achieve tolerance to reflection or external feedback in silicon-integrated lasers is a big challenge.

In the current on-chip integrated laser system of silicon photonic chips, in addition to the quantum dot gain structure laser which has a certain degree of immunity to external light feedback, other types of lasers include multi-quantum well FP lasers, DFB lasers and DBRs. Lasers all require optical isolators on the output optical path, and silicon chip-integrated external cavity lasers also require optical isolators.

As shown in Figure 1, there is an existing semiconductor laser and optical isolator packaging system 107. The semiconductor laser chip 101 is generally based on compound semiconductor materials, such as (but not limited to) GaAs or InP. When current is injected, Next, photons are emitted through electro-optical conversion. The left end face 102 of the semiconductor laser chip 101 is generally a highly reflective end face and is plated with a high reflective mold. The right end face 103 of the semiconductor laser chip 101 is the light emitting end face and is coated with an anti-reflective film. The laser light generated by the semiconductor laser chip is gain amplified and transmitted in the optical waveguide 104, and is emitted from the right end surface 103 of the chip 101. The collimating optics 105 collimate the light emitted by the semiconductor laser 104 and then emit it from the exit window 108 of the packaging system 107 through the free space optical isolator 106 . The purpose of the optical isolator 106 is to prevent laser light that is reflected in and outside the optical window (right) from being fed back to the laser, because these reflected lights can cause interference that can lead to instability of the laser cavity, high noise, or even mode hopping. Generally, the core of a free optical isolator is composed of magneto-optical materials. The polarization state of light during transmission is changed through the light polarization rotation of the Faraday effect (TE/TM is converted to TM/TE), and this is achieved through orthogonal dual polarizers. Matting isolation of returned reflected light. The integration of optical isolators and chips has always been a problem and challenge due to free space components and magnetic materials.

Contents of the invention

The purpose of the present invention is to provide a hybrid integrated external cavity semiconductor laser that is resistant to external light feedback, does not require an optical isolator and can be chip integrated. It can also achieve hybrid integration through a simple docking process and a passive photonic integrated chip to achieve wireless integration. The interference-resistant operation of the optical isolator's external cavity laser reduces cost and process complexity.

The object of the present invention is achieved through the following technical measures: a hybrid integrated external cavity semiconductor laser that is resistant to external light feedback, which is characterized in that it consists of an active gain amplification chip and a passive photonic chip, and the active gain amplification chip and The passive photonic chips are all integrated with an optical waveguide. The optical waveguide of the passive photonic chip is successively provided with a waveguide phase control area, a waveguide filter feedback area and a waveguide polarization rotator. The active gain amplifies the light emitted by the optical waveguide of the chip. Coupled to the optical waveguide of the passive photonic chip, the coupling end surface of the active gain amplification chip and the passive photonic chip is coated with an optical anti-reflection film, and the other end surface of the active gain amplification chip is coated with an optical high-reflection film , the active gain amplifier chip, the optical waveguide of the passive photonic chip, the waveguide phase control area and the waveguide filter feedback device constitute an external cavity semiconductor laser, and the external cavity waveguide structure is composed of the waveguide phase control area and the waveguide filter feedback area. It has polarization asymmetry, that is, the effective light refractive index of the TE fundamental mode and the TM fundamental mode is different; the laser light generated by the external cavity semiconductor laser enters the waveguide polarization rotator, and the waveguide polarization rotator rotates the polarization direction of the incident light by 45 degrees. .

The present invention improves the laser's resistance to external feedback interference by optimizing the external cavity feedback and the waveguide polarization rotator. The optical waveguide of the external cavity semiconductor laser only supports basic TE and TM modes, and the external cavity waveguide structure has very strong polarization asymmetry. , resulting in a significant difference in the effective refractive index of TE and TM. The laser resonance of the external cavity semiconductor laser occurs in the TE mode. When the TE mode laser passes through the waveguide polarization rotator, the polarization is rotated 45 degrees or becomes circularly polarized light. If reflection is encountered during the transmission process, when the reflected light passes through the waveguide polarization rotator, the polarization is rotated 45 degrees again and becomes TM polarization, and in the TM polarization state, the wavelength is in the TM mode of the waveguide filter feedback Outside the curve, therefore, it is suppressed by the gain in the laser cavity and cannot form laser resonance or amplification, which will not cause interference to the already operating laser mode or cause mode hopping. This achieves interference-resistant operation of external cavity lasers without optical isolators. The phase controller in the external cavity laser can ensure that TE polarized photons achieve ring-pass coherent resonance amplification in the cavity of the external cavity laser.

The active gain amplification chip of the present invention adopts simple side butt coupling to the corresponding optical waveguide in the passive photonic chip as the gain light source of the external cavity laser, and the passive photonic chip integrates an optical waveguide loop and a waveguide device including waveguide polarization rotation. The waveguide polarization rotator and the waveguide loop use the same silicon-based material (including but not limited to silicon, silicon dioxide, or silicon nitride) instead of magnetic materials. In this way, all waveguide devices, including waveguide polarization rotators, can be integrated on the same chip through the semiconductor CMOS process, and the active gain amplification chip can also be integrated on the passive photonic chip through flip chip.

The active gain amplification chip and the passive photonic chip of the present invention are arranged separately.

The active gain amplification chip of the present invention is integrated on the passive photonic chip. The waveguide filter feedback area of the present invention is a waveguide reflection grating, which is designed using apodized grating. Its reflection peak curve is Gaussian or Lorentzian linear, and there is no high-order or marginal reflection peak.

The linewidth at half maximum and half width (HWHM) of the TE fundamental mode and the TM fundamental mode reflection peak of the external cavity filter feedback Bragg waveguide reflection grating of the present invention is smaller than the distance between the center wavelengths of the TE fundamental mode and the TM fundamental mode reflection peak.

The waveguide filter feedback area of the present invention is an equivalent reflection feedback area formed by multiple ring resonators.

The waveguide polarization rotator of the present invention is slanted or has other special structures.

The docking coupling end of the optical waveguide of the passive photonic chip and the optical waveguide of the active gain amplification chip is provided with a waveguide mode matcher.

Both end surfaces of the passive photonic chip of the present invention are coated with optical anti-reflective films.

In the present invention, a waveguide mode converter is provided on the optical waveguide of the passive photonic chip, and the laser light generated by the external cavity semiconductor laser enters the waveguide polarization rotator through the waveguide mode converter.

Compared with the prior art, the present invention has the following significant effects:

⑴ This invention uses the waveguide polarization rotator on the passive photonic chip so that the light reflected from the outside is changed to the original orthogonal polarization state when entering the laser cavity, and is suppressed by the gain in the cavity, so that it cannot form laser resonance or amplification. The anti-interference operation of external cavity laser without optical isolator is achieved, which reduces the cost and process complexity.

⑵ The waveguide polarization rotator and optical waveguide of the present invention use the same silicon-based material (including but not limited to silicon, silicon dioxide, or silicon nitride, etc.) instead of magnetic materials, and are compatible with standard semiconductor CMOS processes.

⑶ All waveguide devices of the present invention, including the waveguide polarization rotator, can be manufactured and integrated on the same chip through the semiconductor CMOS process.

⑷The active gain amplification chip of the present invention can be integrated on the passive photonic integrated chip through flip-chip chip, making full use of the advantages of silicon photonic integrated chip.

Description of the drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Figure 1 is a schematic structural diagram of an existing semiconductor laser and optical isolator packaging system;

Figure 2 is a schematic diagram of the composition and structure of Embodiment 1 of the present invention;

Figure 3 is one of the spectral curves of Embodiment 1 of the present invention;

Figure 4 is the second spectrum curve diagram of Embodiment 1 of the present invention;

Figure 5 is a schematic structural diagram of Embodiment 2 of the present invention.

Detailed ways

Example 1

As shown in Figure 2, it is a hybrid integrated external cavity semiconductor laser that is resistant to external light feedback according to the present invention. It is composed of an active gain amplification chip 201 and a passive photonic chip 205. The active gain amplification chip 201 integrates an optical waveguide 203. , the active gain amplification chip 201 is usually based on compound semiconductor materials such as (but not limited to) InP, etc., when current is injected, broadband spontaneous emission photons are generated through electro-optical conversion, and these photons emit light on the active gain chip 201 Propagation amplification in waveguide 203. The left end face 202 of the active gain amplification chip 201 is a high-reflection end face and is coated with an optical high-reflection film, and the right end face 204 is a low-reflection end face. The emitting surface is coated with optical anti-reflective coating. The light transmitted in the optical waveguide 203 of the active gain chip 201 is emitted from the right end surface 204 .

The integration of the active gain amplification chip 201 and the passive photonic chip 205 can be achieved through the butt coupling of two discrete devices, or through the flip-chip of the active gain amplification chip 201 and the end-face butt coupling of the passive photonic chip 205 .

There are optical waveguides 206 and waveguide devices on the passive photonic chip 205 based on silicon-based materials (including but not limited to silicon, silicon dioxide, or silicon nitride, etc.). The optical waveguide 206 and the optical waveguide 203 of the active gain amplifier chip 201 are butt-coupled, and a waveguide mode matcher (taper) can be provided on the butt side 214 to improve the coupling efficiency. The optical waveguide 206 is sequentially provided with a waveguide phase control area 207, a waveguide filter feedback area 208, waveguide mode converters (waveguide taper) 210, 212 and a waveguide polarization rotator (waveguide polarization rotator) 211. The highly reflective left end face 202 of the active gain chip 201, the optical waveguide 203 of the active gain chip 201, the optical waveguide 206 of the passive photonic chip 205, the waveguide phase control area 207 and the waveguide filter feedback area 208 constitute the external cavity semiconductor laser 209. The left end surface 214 and the right end surface 215 of the passive photonic chip 205 may be coated with an optical anti-reflection film. The collimating optics 216 collimate the light emitted by the external cavity semiconductor laser from the right end surface of the passive photonic chip 205 and then output it.

The external cavity optical waveguide 206 supports but is not limited to the basic TE fundamental mode and TM fundamental mode. The design of the external cavity waveguide structure composed of the waveguide phase control area and the waveguide filter feedback area makes it have very strong polarization asymmetry, that is, TE There is a significant difference in the effective optical refractive index between the fundamental mode and the TM fundamental mode. The external cavity waveguide filter feedback area 208 may be a Bragg waveguide reflection grating, or an equivalent reflection feedback area formed by multiple ring resonators. For the reflection spectrum of the Bragg waveguide reflection grating, the linewidth at half maximum and half width (HWHM) of the TE fundamental mode and TM fundamental mode reflection peaks of the external cavity filter feedback Bragg waveguide reflection grating is smaller than the central wavelength of the TE fundamental mode and TM fundamental mode reflection peaks. As shown in Figure 3, the central wavelength positions of the reflection peaks of the waveguide filter feedback area 208 for the reflection curve 231 of the TM fundamental mode and the reflection curve 232 of the TE fundamental mode are clearly separated. In order to ensure the stability of the laser excitation mode, the waveguide reflection grating adopts the apodized grating design. The reflection peak curve is Gaussian or Lorentzian linear. There are no high-order or marginal reflection peaks, and the line width of the grating reflection peak is ( Full width at half maximum) is narrow enough so that there is almost no overlap in the reflection peak curves of the TE and TM fundamental modes. The waveguide phase control area 207 ensures that the round trip phase of the photon in the cavity of the external cavity semiconductor laser 209 is an integer multiple of 2 at the laser wavelength 234 to achieve coherent resonance amplification, as shown in Figure 4, the curve 233 represents the active The self-photon radiation curve emitted by the gain chip through the waveguide 203, 231a is the filter feedback curve of the TM mode, and 232a is the filter feedback curve of the TE mode. The gain resonance of the external cavity semiconductor laser generates laser light of a specific wavelength 234 of TE polarization. When it is transmitted to the right, it passes through the waveguide mode converter 210 and enters the waveguide polarization rotation. The structure of the waveguide polarization rotator 211 is different from that of the optical waveguide 206. It can be slanted or other special waveguide structure. The purpose of setting the waveguide mode converter 210 is to improve the modes of the optical waveguide 206 and the waveguide polarization rotator 211. matched to reduce optical coupling losses between them.

The waveguide polarization rotator 211 rotates the polarization of the laser passing through it by 45 degrees, that is, the TE polarization becomes circularly polarized light. Then, the laser is coupled to the optical waveguide 213 through the waveguide mode converter 212 and emitted from the right end surface 215 of the passive photonic chip 205 . Collimating optics 216 collimate the light emitted by optical waveguide 213 before exiting package 218 at output window 217. If the output laser is reflected during transmission, especially at a short distance, the reflected light will be transmitted back along the original optical path into the optical waveguide 213. When passing through the waveguide polarization rotator 211, its polarization is rotated 45 degrees again, and the polarization state is changes to the TM polarization state. In the TM polarization state, the light of wavelength 234 is outside the filter feedback curve 231a of the TM fundamental mode, and its effective optical refractive index will also cause it to pass through the waveguide phase control region 207 and then circulate within the cavity of the external cavity semiconductor laser 209. The phase mismatch, therefore, is suppressed by the gain in the cavity and cannot form laser resonance or amplification. It will not cause interference to the already operating laser mode or cause mode hopping. This enables interference-resistant operation of external cavity lasers without optical isolators.

Example 2

As shown in Figure 5, the difference between this embodiment and Embodiment 1 is that the active gain amplification chip 251 is pasted on the surface of the passive photonic chip 255 through a flip-chip process, and the optical waveguide 253 of the active gain amplification chip generates The broadband spontaneous emission light is coupled into the optical waveguide 256 of the passive photonic chip through the evanescent wave effect. The left end face 252 of the active gain amplification chip 251 is a high-reflection end face and is coated with an optical high-reflection film. The right end face 254 of the active gain amplification chip 251 is a low-reflection face and is coated with an optical anti-reflection film. The active gain amplification chip 251 The optical waveguide 253 realizes high-efficiency evanescent wave coupling with the optical waveguide 256 of the passive photonic chip 255 through the waveguide mode converters 260 and 262 (tapers). The left end face 252 of the active gain amplification chip 251, the optical waveguide 253 of the active gain amplification chip 251, the optical waveguide 256 of the passive photonic chip, the waveguide phase control area 257 and the waveguide filter feedback area 258 constitute an external cavity semiconductor laser 259.

The waveguide polarization rotator 261 rotates the polarization of the laser passing through it by 45 degrees, that is, the TE polarization becomes circularly polarized light. Then, the laser is coupled to the optical waveguide 264 by the passive photonic chip 255 through the waveguide mode converter The right end face 263 emerges. Collimating optics 265 collimate the light emitted by optical waveguide 264 before exiting package 267 at output window 266. If the output laser is reflected during transmission, especially at a short distance, the reflected light will be transmitted back along the original optical path into the optical waveguide 264. When passing through the waveguide polarization rotator 261, its polarization is rotated 45 degrees again, and the polarization state changes to the TM polarization state. The light of this wavelength in the TM polarization state is outside the filter feedback curve of the TM mode, and its effective optical refractive index will also cause phase mismatch in the cavity of the external cavity semiconductor laser 209 after passing through the waveguide phase control region 207 , therefore, it is suppressed by the gain in the cavity, cannot form laser resonance or amplification, and will not cause interference to the already operating laser mode or cause mode hopping. This enables interference-free operation of external cavity lasers without optical isolators.

Each drawing of the present invention is a schematic diagram and does not represent the actual size or numerical value.

The embodiments of the present invention are not limited to this. According to the above content of the present invention, according to the common technical knowledge and common means in the field, without departing from the above basic technical ideas of the present invention, the present invention can also be made in various other forms. Modifications, replacements or changes all fall within the scope of protection of the present invention.

Claims

A hybrid integrated external cavity semiconductor laser that is resistant to external light feedback, characterized in that it consists of an active gain amplification chip and a passive photonic chip, and both the active gain amplification chip and the passive photonic chip integrate light Waveguide, a waveguide phase control area, a waveguide filter feedback area and a waveguide polarization rotator are arranged on the optical waveguide of the passive photonic chip in sequence. The light emitted by the optical waveguide of the active gain amplification chip is coupled into the optical waveguide of the passive photonic chip. , the coupling end face of the active gain amplification chip and the passive photonic chip is coated with an optical anti-reflection film, the other end face of the active gain amplification chip is coated with an optical high-reflection film, the active gain amplification chip, the passive photonic chip The optical waveguide, waveguide phase control area and waveguide filter feedback area of the source photonic chip constitute an external cavity semiconductor laser. The external cavity waveguide structure composed of the waveguide phase control area and waveguide filter feedback area has polarization asymmetry, that is, TE mode and The effective light refractive index of the TM mode is different; the laser light generated by the external cavity semiconductor laser enters the waveguide polarization rotator, and the waveguide polarization rotator rotates the polarization direction of the incident light by 45 degrees.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 1, characterized in that the active gain amplification chip and the passive photonic chip are provided separately.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 1, characterized in that the active gain amplification chip is integrated on the passive photonic chip.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 2 or 3, characterized in that: the waveguide filter feedback area is a waveguide reflection grating using an apodized grating.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 4, characterized in that: the line width at half maximum and half width of the TE fundamental mode and the TM fundamental mode reflection peak of the external cavity filter feedback Bragg waveguide reflection grating is less than TE The distance between the central wavelengths of the fundamental mode and TM fundamental mode reflection peaks.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 2 or 3, characterized in that the waveguide filter feedback area is an equivalent reflection feedback area formed by a plurality of ring resonators.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 5, characterized in that: the waveguide polarization rotator and the optical waveguide are made of the same silicon-based material.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 7, characterized in that: the butt coupling end of the optical waveguide of the passive photonic chip and the optical waveguide of the active gain amplification chip is provided with a waveguide mode matcher .
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 8, characterized in that: both end surfaces of the passive photonic chip are coated with optical anti-reflection films.
The hybrid integrated external cavity semiconductor laser resistant to external light feedback according to claim 9, characterized in that: a waveguide mode converter is provided on the optical waveguide of the passive photonic chip, and the laser light generated by the external cavity semiconductor laser passes through the waveguide. The mode converter goes into the waveguide polarization rotator.