CN110727052A - A low-loss infrared high nonlinear optical waveguide preparation method - Google Patents

Abstract

The invention relates to the field of micro-nano processing of on-chip waveguides, in particular to a preparation method of a low-loss infrared high-nonlinearity optical waveguide. The method comprises the following steps: s1, analyzing the transmission characteristics of the chalcogenide optical waveguide in the infrared wave band; s2, analyzing the influence of each parameter of electron beam exposure and the type of electron beam glue on the preparation of the chalcogenide waveguide, selecting proper exposure parameters and the type of electron beam glue to prepare a mask, and realizing the preparation of the waveguide through plasma reaction etching; s3, secondly, realizing the growth of a polymer cladding by a spin-coating method; and S4, finally, smoothing the side wall of the waveguide again by combining a cladding thermal annealing process, and performing loss test by a truncation method. According to the invention, the preparation of the on-chip chalcogenide waveguide with ultralow loss is realized by optimizing the electron beam exposure and adjusting the etching parameters of the plasma reaction and combining the thermal annealing process, and the preparation method is suitable for preparing large-scale high-nonlinearity photonic integrated devices.

Description

A low-loss infrared high nonlinear optical waveguide preparation method

technical field

The invention relates to the fields of micro-nano processing and nonlinear optics, and more particularly, to a method for preparing a low-loss infrared high nonlinear optical waveguide.

Background technique

The infrared band includes three bands: near-infrared, mid-infrared and far-infrared. The near-infrared band includes the communication band, and the mid-to-far infrared band includes the fingerprints of many biomolecules, typical toxic gas and dangerous goods molecules, and the fluorescence spectrum band of atmospheric greenhouse gases. Therefore, The highly integrated infrared waveguide has extremely important research significance. In addition, infrared waveguides also have important application backgrounds in the fields of laser transmission, thermal pixel transmission, and infrared spectroscopy research.

At present, the main materials used in on-chip infrared waveguides are germanium, silicon, and chalcogenide materials. Among them, germanium waveguides not only have large losses in infrared waveguides, but also the transmission band is mainly after 3 μm, excluding the communication band. In addition to the large absorption and loss, there are also problems such as the limitation of the transmission band and the difficulty of preparation.

Chalcogenide waveguide is an amorphous material formed by covalent bonds of sulfur, selenium, tellurium and some other metals and non-metallic materials, which has a very wide transmission band (from visible light band to 20μm), high nonlinearity, and It has the advantages of extremely low two-photon absorption, etc., and it is easier to prepare thin films by thermal evaporation, magnetron sputtering, etc. and process them into waveguides; however, chalcogenide waveguides also have problems such as large losses, which seriously limit their application performance. The main reason is that the sidewalls of the chalcogenide waveguides are rough due to the uneven etching rate during the processing of the chalcogenide waveguides, so that the sidewalls of the chalcogenide waveguides have very large scattering and lead to large losses of the chalcogenide waveguides.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned defects in the prior art, the present invention provides a low-loss infrared high nonlinear optical waveguide preparation method.

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is: a low-loss infrared high nonlinear optical waveguide preparation method, comprising the following steps:

S1. Analyze the transmission characteristics of chalcogenide optical waveguides in the infrared band;

S2. Analyze the influence of various parameters of electron beam exposure and the type of electron beam glue on the preparation of chalcogenide waveguides, and realize the preparation of waveguides by plasma reactive etching;

S3. The growth of the polymer cladding layer is realized by spin coating;

S4. Combined with the thermal annealing process of the cladding, the waveguide device is placed in an annealing furnace and heated to a temperature exceeding the glass transition temperature of the chalcogenide material, so that the waveguide is in a molten state, and its sidewalls become relatively relatively under the action of surface tension. Smooth and tested for loss by the truncation method.

Preferably, the cross-sectional structure of the waveguide is a ridge or a rectangle, and the selected material is a chalcogenide material.

Preferably, in the selected waveguide structure, if the structure is a rectangular waveguide, its cross-sectional width ranges from 1 micron to 10 microns, and its height ranges from 300 nanometers to 5 microns. If the structure is a ridge waveguide, the ridge height depends on the transmission band. Design required.

Preferably, the waveguide structure includes a lower cladding layer, a fiber core, and an upper cladding layer; the refractive index of the fiber core is higher than that of the upper and lower cladding layers, and the contact interface between the fiber core and the cladding layer is smooth.

Preferably, the preparation of low-loss infrared chalcogenide optical waveguide is realized by adjusting the parameters of plasma reactive etching, and the etching process includes chemical etching and physical etching; chemical etching mainly uses CHF3 or CF4+H2 gas; physical Etching is achieved by Ar or He gas.

Preferably, the cladding layer of the low-loss infrared chalcogenide waveguide is passed through a spin coating method through a glue machine, that is, the glue machine is used for 1 minute at a rotation speed of 2000 rpm, so that a layer of polymer cladding layer is grown on the waveguide, and Combined with the cladding thermal annealing process, the waveguide device is placed in an annealing furnace, and heated for 8-12 hours at a temperature of 200°C to 240°C, depending on the specific material.

Preferably, the truncation method test needs to include at least two waveguide structures with different lengths. Make sure to exclude the effects of end-face coupling and coupling errors.

Preferably, the waveguide structure can measure the transmission power, loss coefficient and operating frequency of the waveguide transmission.

Compared with the prior art, the beneficial effects are as follows: the present invention realizes the preparation of a highly nonlinear waveguide with high precision and low sidewall roughness through electron beam exposure and adjusting the etching parameters of the plasma reaction, combined with the thermal annealing process , and compared with the traditional lithography, a preparation method of a low-loss infrared chalcogenide waveguide is provided, which realizes the low-loss transmission of light waves in the infrared band.

Description of drawings

FIG. 1 is a cross-sectional structural diagram of the waveguide of the present invention.

FIG. 2 is a SEM characterization diagram of the ridge waveguide of the present invention.

FIG. 3 is a simulated electric field model diagram of the ridge waveguide of the present invention.

Fig. 4 is the preparation flow chart of the present invention.

FIG. 5 is a schematic structural diagram of the testing system of the present invention.

Detailed ways

The accompanying drawings are for illustrative purposes only, and should not be construed as limiting the present invention; in order to better illustrate the present embodiment, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art It is understandable to the artisan that certain well-known structures and descriptions thereof may be omitted from the drawings. The positional relationships described in the drawings are only for exemplary illustration, and should not be construed as limiting the present invention.

Example 1:

As shown in FIG. 4 , the present embodiment will be described with reference to FIGS. 1 to 5 . As shown in FIG. 1 , the low-loss infrared chalcogenide optical waveguide includes: silicon substrate 201 , lower cladding 202 , and fiber core 203 in order from bottom to top , the upper cladding layer 204; the lower cladding layer 202 is silicon dioxide; the core 203 provided on the lower cladding layer 202 cladding layer and having an incident surface and an exit surface is an infrared chalcogenide; The upper cladding 204 is air; the refractive index of the core 203 is larger than that of the upper and lower cladding, and the interfaces between the core 203 and the upper cladding 204 and the lower cladding 202 are smooth.

This embodiment provides a method for preparing a low-loss infrared chalcogenide waveguide, which relates to the fields of micro-nano processing and nonlinear optics, and in particular to low-loss optical wave transmission in waveguides. Step 2: Analyze the influence of various parameters of electron beam exposure and electron beam glue on the preparation of chalcogenide waveguide, select appropriate exposure parameters and electron beam glue for mask preparation, and realize the waveguide through plasma reactive etching Step 3: realize the growth of the polymer cladding by spin coating method; Step 4: combine the thermal annealing process of the cladding layer, place the device in an annealing furnace and heat the device to exceed the glass transition temperature of the chalcogenide waveguide, so that the waveguide It is in a molten state, and the sidewall becomes relatively smooth under the action of surface tension, thereby reducing the transmission loss of the waveguide, and the loss test is performed by the truncation method.

Wherein, in the waveguide structure, the section length is 2 μm, the ridge height is 0.5 μm, and the total height is 0.8 μm, which can achieve better size matching with the Gaussian mode of the optical fiber and reduce coupling loss.

Additionally, the waveguide structure includes a lower cladding, a core, and an upper cladding. The refractive index of the core is higher than that of the upper and lower cladding layers, and the contact interface between the core and the cladding layers is smooth.

In this embodiment, the preparation method of the low-loss infrared chalcogenide waveguide is realized by adjusting the parameters of reactive plasma reactive etching, and the etching process mainly uses two reactive substances, Ar and CHF ₃ .

Specifically include the following steps:

Step 1: Cleaning: that is, cleaning the substrate that needs to be structured by certain means, so that the thickness of the glue can be more uniform during the gluing process. At present, the mainstream cleaning method is a three-step cleaning method, that is, ultrasonication is carried out in acetone, isopropanol and deionized water for 10 minutes by an ultrasonic cleaning machine respectively. Then, the moisture on the surface of the film is removed by soft baking to enhance the adhesion between the film and the electron beam glue.

Step 2: Gluing: put the substrate on the glue spinner, and suck the substrate by a vacuum pump. Then, the selected positron beam glue was dropped onto the substrate by a pipette until the entire substrate was covered with the electron beam glue. Finally, run the designed spin coating program. After the spin coating was completed, the substrate was placed on a heating table, and the temperature was 150°C for pre-baking.

Step 3: Sample injection: Transport the previously prepared sample to the exposure chamber through the sample stage.

Step 4: Exposure: Expose the designed layout to the electron beam glue through "electron beam" to denature the exposed part.

Step 5: Development: The electron beam glue in the exposed part is removed by the corresponding developer, and the other excess electron beam glue is retained.

Step 6: Etching and degumming: Attach the sample to the carrier plate of the reactive ion etching machine. Then, a vacuum is drawn, the sample is fed into the reaction chamber, and the programmed program is run. The key lies in setting the parameters of Ar and CHF ₃ reactive species and the working power during the reaction. After etching, put the sample into the reactive ion etching machine and run the degumming procedure again to remove the residual electron beam glue.

Step 7: cladding growth and thermal annealing: the polymer cladding is applied to the entire waveguide structure by spin coating. Finally, the sample was placed in an annealing furnace and heated for 12 hours at a temperature of 220°C, depending on the specific material.

Example 2

This embodiment is described with reference to FIG. 5 . In this embodiment, the input and output powers of waveguides with different lengths are compared, and then the output powers of two waveguides with different lengths are used to make a difference to obtain the waveguide loss coefficient.

The test system for the waveguide loss factor test scheme includes the following steps:

Step 1: First, place the prepared waveguide structure on an adsorption table to ensure that the structure will not shake during the test.

Step 2: Pass the lens fiber through the three-dimensional adjustment frame, roughly adjust the input and output ends of the waveguide, observe through the CCD, and then input a beam of infrared band, 10dBm light source at the input end, and connect a power meter at the output end. And through fine adjustment of the three-dimensional adjustment frame, the lens fiber is just aligned with the input and output ports of the waveguide, which can be observed by a power meter, and the maximum output is obtained after a beam of light is coupled into the waveguide. Similarly, the output powers of other waveguides with different lengths are measured. In this implementation process, the measured long waveguide length L ₂ =8.28cm, the output power of the input beam after passing through the length of the waveguide is -0.84dBm, the short waveguide length L ₁ =0.7cm, the output power of the input beam after passing through the length of the waveguide is 1.10 dBm dBm. The formula α=(P ₂ -P ₁ )/(L ₂ -L ₁ ) for calculating the waveguide loss factor can be calculated according to the truncation method, and the waveguide loss factor α=0.26dB/cm. This loss factor, currently in the infrared chalcogenide waveguide with the same waveguide size, already belongs to the ranks of low loss.

Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the embodiments of the present invention. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (6)

1. a low-loss infrared high nonlinear optical waveguide preparation method, is characterized in that, comprises the following steps: S1. Analyze the transmission characteristics of chalcogenide optical waveguides in the infrared band; S2. Analyze the influence of various parameters of electron beam exposure and the type of electron beam glue on the preparation of chalcogenide waveguides, and realize the preparation of waveguides by plasma reactive etching; S3. The growth of the polymer cladding layer is realized by spin coating; S4. Combined with the thermal annealing process of the cladding, the waveguide device is placed in an annealing furnace and heated to a temperature exceeding the glass transition temperature of the chalcogenide material, so that the waveguide is in a molten state, and its sidewalls become relatively relatively under the action of surface tension. Smooth and tested for loss by the truncation method. 2 . The method for preparing a low-loss infrared high nonlinear optical waveguide according to claim 1 , wherein the cross-sectional structure of the waveguide is a ridge or a rectangle, and the selected material is a chalcogenide material. 3 . 3. The method for preparing a low-loss infrared high-nonlinear optical waveguide according to claim 2, wherein, in the selected waveguide structure, if the structure is a rectangular waveguide, its cross-sectional width ranges from 1 μm to 10 μm, The height ranges from 300 nanometers to 5 microns. If the structure is a ridge waveguide, the ridge height is designed according to the transmission band requirements. 4. The method for preparing a low-loss infrared high nonlinear optical waveguide according to claim 2, wherein the waveguide structure comprises a lower cladding, a fiber core, and an upper cladding; the refraction of the fiber core The rate is higher than that of the upper and lower cladding, and the contact interface between the core and the cladding is smooth. 5 . The method for preparing a low-loss infrared high nonlinear optical waveguide according to claim 1 , wherein the preparation of the low-loss infrared chalcogenide optical waveguide is realized by adjusting the parameters of plasma reactive etching, and the etching process Including chemical etching and physical etching; chemical etching mainly uses CHF ₃ or CF ₄ +H ₂ gas; physical etching is realized by Ar or He gas. 6. The method for preparing a low-loss infrared high nonlinear optical waveguide according to any one of claims 1 to 5, characterized in that, by spin coating, that is, using a glue dispenser to rotate 1 at a rotational speed of 2000 rpm minutes, grow a layer of polymer cladding above the waveguide, and combine the thermal annealing process of the cladding, place the waveguide device in an annealing furnace, at 200℃～240℃, the specific temperature is determined according to the specific material, heat for 8-12 Hour.

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