METHOD FOR FABRICATING KTP NONLINEAR RACETRACK MICRO-RING RESONATORS

Abstract

The present invention provides a method for fabricating KTP nonlinear racetrack micro-ring resonator, composed of six steps: KTP wafer processing, ion implantation, electron beam exposure, subsequent processing, reactive ion etching and final processing. A thin-film waveguide structure similar to the on-insulator lithium niobate thin-film can be achieved through only one process of ion implantation, which enables significantly simplified procedure, shortened time, and reduced cost. Meanwhile, the KTP micro-ring resonator produced according to the present invention has an optical damage threshold several times higher than the existing lithium niobate micro-ring resonator. It can output nonlinear frequency converted light to the power of milliwatts, and suitable for the case where both the input and output optical signals are pulsed lasers. Since Ion implantation, electron beam exposure, metal evaporation deposition, and reactive ion etching are all relatively developed micro-nano machining technologies, the present invention has wonderful operability and repeatability.

Claims

1. A method for fabricating a KTP nonlinear racetrack micro-ring resonator, comprising the following steps: Step 1: KTP wafer processing First, perform surface polishing operations on the cut KTP wafer. Then, clean the wafer, and store it for later use. Step 2: Ion Implantation Take out the spare KTP wafer in step 1, accelerate ions by an ion accelerator, and implant them into KTP wafer. After ion implantation, an isolated layer with decreased refractive index can be formed at a depth of several microns below the surface of the KTP wafer, the part above the isolated layer is the waveguide layer. Step 3: Electron Beam Exposure Spin-coat a layer of photoresist on the surface of the KTP wafer, transfer the two-dimensional pattern of the micro-ring resonator to the photoresist, with an electron beam exposure equipment, to achieve the sample to be processed. Step 4: Subsequent Processing Deposit a layer of metal on the sample with an evaporation deposition coating system. Soak and clean the sample with pure acetone to remove excess photoresist, to transfer the two-dimensional pattern of the micro-ring resonator to the metal and form a metal mask plated on the sample. Step 5: Reactive Ion Etching Perform etching on the sample plated with the metal mask from top to bottom using a reactive ion etching equipment. Since the micro-ring part is covered by a metal mask, and the etching rate of the reactive ions on the metal mask is significantly lower than that of the KTP crystal, reactive ion etching can only remove little fraction of the metal mask and parts of crystal other than the micro-ring. Step 6: Final Processing Dissolve the remaining metal mask with a chemical corrosion solution; the remaining part of ion-implanted KTP crystal is a micro-ring resonator structure.

2. The step 2 of claim 1, wherein the type of ion is Carbon ion or Oxygen ion.

3. The step 2 of claim 1, wherein “several microns” means 5-10 microns.

4. The step 3 of claim 1, wherein the thickness of the photoresist is 300-600 nm.

5. The step 4 of claim 1, wherein the metal is one of Aluminum or Chromium.

6. The step 5 of claim 1, wherein reactive ions are the mixed gas of argon and sulfur hexafluoride.

7. The step 6 of claim 1, wherein the chemical corrosion solution is one of hydrogen peroxide (to dissolve aluminum) or a mixed solution of 200 grams of cerium ammonium nitrate, 35 milliliters of acetic acid and 1 liter of water (to dissolve chromium).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following will briefly introduce the figures that need to be used in the description of the embodiments or the prior art. Obviously, the figures in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative work, other accompanying figures can be obtained from these figures.

[0026] FIGS. 1-9 correspond to the example 1, FIG. 10 corresponds to the example 2.

[0027] FIG. 1 is a schematic diagram of the steps for the fabrication of micro-ring resonator.

[0028] FIG. 2 is a schematic two-dimensional top view of a micro-ring resonator.

[0029] FIG. 3 is a schematic diagram of the ion implantation into KTP wafer.

[0030] FIG. 4 is a schematic side view of the KTP wafer after spin-coating of photoresist.

[0031] FIG. 5 is a schematic side view of the KTP wafer after electron beam exposure.

[0032] FIG. 6 is a schematic side view of the wafer after metal evaporation deposition.

[0033] FIG. 7 is a schematic side view of the wafer after a metal mask was formed.

[0034] FIG. 8 is a schematic side view of the wafer after reactive ion etching.

[0035] FIG. 9 is a schematic side view of the wafer after the metal mask was dissolved.

[0036] FIG. 10 (a) is a schematic diagram of the frequency doubling process of the 1064 nm laser of the KTP micro-ring resonator.

[0037] FIG. 10 (b) is a schematic diagram of simulated transmission mode of 1064 nm laser in the KTP micro-ring resonator.

DETAILED DESCRIPTION OF EMBODIMENTS

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying figures in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0039] In the description of the present invention, it should be noted that for the terms: “center”, “up”, “down”, “left”, “right”, “vertical”, “horizontal”, “inner”, “outer”, etc. the indicated azimuth or position relationship is based on the azimuth or position relationship shown in the figures. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation to the present invention. In addition, the terms: “first”, “second”, “third”, “fourth”, etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0040] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms “installation”, “connected”, and “connected” should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; It can be direct connection, or indirect connection through a medium, and can be a connection between two components. For those of ordinary skill in the art, the specific meanings of the above-mentioned terms in the present invention can be understood according to the specific situation.

Embodiment 1

[0041] This example shows a method for fabricating a KTP nonlinear racetrack micro-ring resonator, which includes the following steps:

Step 1: KTP Wafer Processing

[0042] First, perform surface polishing operations on the cut KTP wafer. Then, clean the wafer, and store it for later use.

Step 2: Ion Implantation

[0043] Take out the spare KTP wafer in step 1, accelerate ions by an ion accelerator, and implant them into KTP wafer, as shown in FIG. 2. After ion implantation, an isolated layer with decreased refractive index can be formed at a depth of several microns below the surface of the KTP wafer, the part above the isolated layer is the waveguide layer.

[0044] Here, the type of ion is carbon ion or oxygen ion; “several microns” means 5-10 microns.

Step 3: Electron Beam Exposure

[0045] Spin-coat a layer of photoresist (950 PMMA A4) on the surface of the KTP wafer, as shown in FIG. 3, transfer the two-dimensional pattern (FIG. 4) of the micro-ring resonator to the photoresist, with an electron beam exposure equipment, to achieve the sample to be processed. After electron beam exposure, the photoresist in the area where the two-dimensional pattern of the micro-ring resonator is located is removed, leaving a gap of the same size, as shown in FIG. 5.

[0046] Here, the thickness of the photoresist is 300-600 nm.

Step 4: Subsequent Processing

[0047] Deposit a layer of metal on the sample with an evaporation deposition coating system, as shown in FIG. 6. Soak and clean the sample with pure acetone to remove excess photoresist, to transfer the two-dimensional pattern of the micro-ring resonator to the metal and form a metal mask plated on the sample, as shown in FIG. 7.

[0048] Here, the metal is the one of Aluminum or Chromium.

Step 5: Reactive Ion Etching

[0049] Perform etching on the sample plated with the metal mask from top to bottom using a reactive ion etching equipment. Since the micro-ring part is covered by a metal mask, and the etching rate of the reactive ions on the metal mask is significantly lower than that of the KTP crystal, reactive ion can only etch little fraction of the metal mask and parts of crystal other than the micro-ring, as shown in FIG. 8.

[0050] Here, reactive ions are the mixed gas of argon and sulfur hexafluoride.

Step 6: Final Processing

[0051] Dissolve the remaining metal mask with a chemical corrosion solution; the remaining part of ion-implanted KTP crystal is a micro-ring resonator structure, as shown in FIG. 9.

[0052] Here, the chemical corrosion solution is one of hydrogen peroxide (to dissolve Aluminum) or a mixed solution of 200 grams of cerium ammonium nitrate, 35 milliliters of acetic acid and 1 liter of water (to dissolve chromium).

Embodiment 2

[0053] As shown in FIG. 10, this example demonstrates the frequency doubling (second harmonic generation) within the micro-ring resonator at the waveband of 1064 nanometer. The top of FIG. 10 is a schematic diagram of the 1064 nm frequency doubling in the micro-ring resonator, and the arrow indicates the direction of light propagation.

[0054] When the KTP crystal has been treated with proper phase matching (e.g., cut along a specific angle, when θ=90°, φ=23.5°, type II birefringent phase matching can be realized), it will satisfy the phase matching condition of nonlinear frequency doubling. At this time, when the 1064 nm laser passes through the straight waveguide, it will be coupled into the micro-ring resonator in the form of evanescent wave, cycle back and forth in the resonator, oscillate, and be continuously converted into frequency doubled light of around 532 nm in the propagation path.

[0055] The generated frequency doubled light will also be coupled into the straight waveguide in the form of evanescent wave, and finally optical signals around 532 nm will be output. Simulation result of transmission mode of 1064 nm laser oscillating in the KTP micro-ring resonator are shown in the bottom of FIG. 10.

[0056] Since KTP has a high optical damage threshold, the output power of frequency doubled optical signal can be improved to the order of milliwatts. Meanwhile, the light circulates back and forth in the micro-ring for many times, making full use of the nonlinear response characteristics of the material. Compared with that of a straight waveguide, the frequency doubling light conversion efficiency of the micro-ring can be increased by several tens of times or more.

[0057] The basic principles, main features and advantages of the present invention have been shown and described above. Technical personnel in this industry should understand. The above-mentioned embodiments and the description in the specification only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements. These changes and improvements should fall within the scope of the claimed invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.