Algaas second-order nonlinear and linear optical waveguide integrated monolithic and manufacturing method thereof

Abstract

The application discloses an AlGaAs second-order nonlinear and linear optical waveguide integrated monolithic and a manufacturing method thereof. x Ga 1‑x As composition; the surface of the epitaxial layer is used to manufacture a photoetching mask, and then the Bragg upper reflection layer is etched to form a ridge waveguide structure comprising a second-order nonlinear waveguide region and a second-order linear waveguide region; the second-order nonlinear waveguide region is used to manufacture a photoetching mask, and then the Bragg lower reflection layer of the second-order linear waveguide region is etched to complete the manufacturing. The application can realize seamless monolithic integration of AlGaAs optical nonlinear waveguide and linear waveguide, and provides a simple and high-integration chip manufacturing method for the fields of nonlinear optics and integrated quantum optics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of integrated optical quantum devices, and particularly relates to an AlGaAs second-order nonlinear and linear optical waveguide integrated monolithic and a manufacturing method thereof. BACKGROUND

[0002] Utilizing quantum characteristics such as polarization and frequency of photons to realize quantum secure communication, optical quantum computing, optical quantum detection and other technologies is one of the main contents in the current quantum information technology system. The monolithic integration of quantum light sources (single photon source, entangled light source) in the optical quantum system and other quantum optical devices is the key to the large-scale application of optical quantum technology.

[0003] The spontaneous parametric down conversion (SPDC) process using a second-order optical nonlinear material can realize the conversion of a pump laser into a two-photon source or an entangled light source.

[0004] AlGaAs material has strong second-order optical nonlinearity. By designing a suitable Bragg reflection waveguide material structure, the Bragg reflection waveguide (BRW) mode of pump light in the waveguide and the total internal reflection (TIR) mode of down-converted photons can be phase-matched without additional processes such as periodic polarization, realizing efficient nonlinear photon conversion.

[0005] However, in an integrated optical quantum chip, it is often necessary to integrate and interconnect the quantum light source with other linear waveguide devices without optical nonlinear characteristics. Therefore, a manufacturing method is needed to interconnect and monolithically integrate the BRW second-order nonlinear waveguide and the linear waveguide with low loss for the AlGaAs material system. According to the investigation, there is no public report on the manufacturing method of the AlGaAs material second-order nonlinear and linear optical waveguide integrated monolithic at home and abroad. SUMMARY

[0006] The technical problem solved by the application is that the AlGaAs second-order nonlinear and linear optical waveguide integrated monolithic and the manufacturing method thereof can realize seamless monolithic integration of AlGaAs optical nonlinear waveguide and linear waveguide, and provide a simple and high-integration chip manufacturing method for the nonlinear optics and integrated quantum optics field.

[0007] Technical scheme: An AlGaAs second-order nonlinear and linear optical waveguide integrated monolithic manufacturing method includes the following steps:

[0008] S1. growing AlGaAs epitaxial layers on a substrate in sequence: Bragg lower reflection layer, core layer and Bragg upper reflection layer; the Bragg upper reflection layer and the Bragg lower reflection layer each comprise a plurality of periods, each period comprising two layers of BRW-a and BRW-b with different Al compositions x Ga 1-x As material composition;

[0009] S2. making a photoetching mask on the surface of the AlGaAs epitaxial layer to protect a rectangular area in the middle, and then etching the Bragg upper reflection layer to form a ridge waveguide structure comprising a second-order nonlinear waveguide area and a second-order linear waveguide area;

[0010] S3. making a photoetching mask on the second-order nonlinear waveguide area, and then etching the Bragg lower reflection layer of the second-order linear waveguide area to complete the fabrication.

[0011] Preferably, the substrate material is GaAs.

[0012] Preferably, the Al x Ga 1-x The value range of x in the AlGaAs material is 0-1.

[0013] Preferably, the etching in step S2 is to the Bragg upper reflection layer, leaving 0-2 layers of BRW-a and / or BRW-b.

[0014] Preferably, the etching in step S3 is to the Bragg lower reflection layer, leaving 0-2 layers of BRW-a and / or BRW-b.

[0015] Preferably, ICP dry etching is adopted in steps S2 and S3.

[0016] Preferably, the Bragg upper reflection layer and the Bragg lower reflection layer each comprise 5-10 periods.

[0017] The AlGaAs second-order nonlinear and linear optical waveguide integrated monolithic obtained by the above fabrication method.

[0018] Beneficial effects: the first waveguide etching in the application unifies the etching of the second-order nonlinear waveguide area and the second-order linear waveguide area to form a waveguide ridge structure, ensuring the continuity of the TIR mode of the two areas; the second waveguide etching in the application etches most of the Bragg upper reflection layer material of the second-order linear waveguide area, leaving one or two layers as a protective layer of the core layer, thereby destroying the support of the waveguide structure to the BRW mode and only retaining the TIR mode. In this way, the phase matching between the pump light and the down-conversion light incident to the linear waveguide is destroyed, thereby prohibiting the occurrence of the second-order nonlinear process in the second-order linear waveguide area.

[0019] This method enables seamless monolithic integration of AlGaAs optical nonlinear waveguides and linear waveguides, providing a simple and highly integrated chip fabrication method for nonlinear optics and integrated quantum optics. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a chip after epitaxial layer growth has been completed;

[0021] Figure 2 This is a schematic diagram of the chip after the ridge waveguide structure etching is completed;

[0022] Figure 3 This is a schematic diagram of a chip with the under-Bracket reflector layer etched in the second-order linear waveguide region.

[0023] Figure 4 It shows a cross-section of a nonlinear optical waveguide and schematic diagrams of the BRW and TIR modes (TE, TM) it supports.

[0024] Figure 5 This is a cross-section of a linear optical waveguide and a schematic diagram of the TIR modes (TE, TM) it supports;

[0025] Figure 6 This is a schematic diagram of the integrated scheme of a two-photon source and a directional coupler implemented using the fabrication method of the present invention in Example 2. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] The method for fabricating a monolithic AlGaAs second-order nonlinear and linear optical waveguide integration includes the following steps:

[0029] S1. Growth of AlGaAs epitaxial layers on a GaAs substrate: lower Bragg reflective layer, core layer, and upper Bragg reflective layer. For example... Figure 1 As shown, the upper Bragg reflector and the lower Bragg reflector each contain 5 to 10 periods, and each period consists of two Al layers, BRW-a and BRW-b, with different Al contents. x Ga 1-x As material composition. For example, BRW-a uses Al. 0.2 Ga 0.8 As and BRW-b use Al 0.8 Ga 0.2 As; the Al content in the core layer is slightly lower, such as Al 0.3 Ga 0.8 As.

[0030] S2. A photolithographic mask is fabricated on the surface of the AlGaAs epitaxial layer to protect the central rectangular region. The Bragg reflector layer is then etched using an ICP dry etching machine, stopping at the BRW-a layer above the core layer, forming a ridged waveguide structure containing both second-order nonlinear and second-order linear waveguide regions. Figure 2 As shown.

[0031] S3. Fabricate a photolithographic mask in the second-order nonlinear waveguide region to completely cover the second-order nonlinear waveguide region, exposing only the second-order linear waveguide region. Then, etch the lower Bragg reflector layer of the second-order linear waveguide region using an ICP dry etching machine. The etching stops when only a single BRW-a layer remains as a protective layer, completing the fabrication. Figure 3 As shown.

[0032] Example 2

[0033] The AlGaAs second-order nonlinear and linear optical waveguide integrated monolith obtained by the fabrication method in Example 1 realizes seamless monolithic integration of AlGaAs optical nonlinear waveguide and linear waveguide.

[0034] In its second-order nonlinear waveguide region, such as Figure 4 As shown, this waveguide supports 780nm BRW mode and 1560nm TIR-TE and TIR-TM modes, enabling SPDC phase matching and completing the downconversion process for 780nm photons. In its second-order linear waveguide region, as... Figure 5 As shown, the waveguide supports 780nm or 1560nm TIR-TE and TIR-TM modes, but due to the damage to the AlGaAs Bragg reflector layer, it can no longer support the 780nm BRW mode. Due to the dispersion characteristics of AlGaAs material, SPDC phase matching cannot be formed between the 780nm and 1560nm TIR-TE and TIR-TM modes. Therefore, for the second-order nonlinear process SPDC, the waveguide in this region can be regarded as a linear optical waveguide.

[0035] like Figure 6As shown, an AlGaAs dual-photon source and directional coupler integration scheme is realized using the aforementioned optical waveguide integrated monolithic chip. The AlGaAs dual-photon source is constructed from the AlGaAs nonlinear waveguide of this invention, and the directional coupler is constructed from a linear waveguide. After a 780nm pump laser is input to the input end of the AlGaAs dual-photon source, through the SPDC second-order nonlinear process of the nonlinear waveguide, a portion of the pump photons coupled into the BRW mode are converted into pairs of 1560nm down-converted photons in the TIR mode, which are directly input into the linear waveguide region. Simultaneously, a portion of the 780nm pump photons are coupled into the linear waveguide and mixed with the 1560nm down-converted photons. In the directional coupler region of the linear region, appropriately designed adjacent waveguides can couple the 780nm photons to an adjacent optical path, thereby achieving the separation of the 780nm pump photons and the 1560nm down-converted photons. Using the technical solution of this invention, the functions of SPDC down-converted photon generation and pump light separation can be realized on a single chip, greatly improving the integration of the dual-photon source.

Claims

1. A method for fabricating an integrated monolithic AlGaAs second-order nonlinear and linear optical waveguide, characterized in that, The steps include the following: S1. An AlGaAs epitaxial layer is sequentially grown on the substrate: a lower Bragg reflector layer, a core layer, and an upper Bragg reflector layer; both the upper Bragg reflector layer and the lower Bragg reflector layer contain multiple periods, each period consisting of two Al layers, BRW-a and BRW-b, with different Al contents. x Ga 1-x As material composition; S2. A photolithographic mask is fabricated on the surface of the AlGaAs epitaxial layer to protect the rectangular region in the middle, and then the upper Bragg reflective layer is etched to form a ridge waveguide structure containing a second-order nonlinear waveguide region and a second-order linear waveguide region. S3. Fabricate a photomask in the second-order nonlinear waveguide region, and then etch the lower Bragg reflection layer in the second-order linear waveguide region to complete the fabrication; In steps S2 and S3, ICP dry etching is used; the upper Bragg reflective layer and the lower Bragg reflective layer each contain 5 to 10 cycles.

2. The method for fabricating an integrated monolithic AlGaAs second-order nonlinear and linear optical waveguide according to claim 1, characterized in that, The substrate material is GaAs.

3. The method for fabricating an integrated monolithic AlGaAs second-order nonlinear and linear optical waveguide according to claim 1, characterized in that, The Al x Ga 1-x The value range of x in material As is 0~1.

4. The method for fabricating an integrated monolithic AlGaAs second-order nonlinear and linear optical waveguide according to claim 1, characterized in that, In step S2, etching is performed until 0-2 layers of BRW-a and / or BRW-b remain on the Bragg reflective layer.

5. The method for fabricating an integrated monolithic AlGaAs second-order nonlinear and linear optical waveguide according to claim 1, characterized in that, In step S3, etching is performed down to the remaining 0-2 layers of BRW-a and / or BRW-b under the Bragg reflector layer.

6. An AlGaAs second-order nonlinear and linear optical waveguide integrated monolith obtained by the fabrication method described in claim 1.

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