On-chip integrated optical frequency comb generation structure and optical frequency comb generation method

Abstract

The invention discloses an on-chip integrated optical frequency comb generation structure and an optical frequency comb generation method, the structure is formed by heterogeneous integration of a laser chip and an integrated optical microcavity chip, and the integrated optical microcavity chip comprises a polarization beam splitter, two ring filters, an Add-drop type microcavity and two output ports; the polarization beam splitter is used for dividing laser injected by the laser chip into a TE mode and a TM mode, and the TE mode and the TM mode have different power ratios and are injected into the two ring filters respectively. The two ring filters are respectively provided with a heating electrode for controlling the size of the passing wavelength, and the two ring filters have different diameters for transmitting different wavelengths; the Add-drop type microcavity is used for generating an optical frequency comb, and a heating electrode is arranged above the microcavity and used for controlling the resonant wavelength passing through the microcavity. The problems that an existing optical frequency comb debugging system is large and debugging is complex can be solved, the size of the microcavity optical frequency comb can be greatly reduced, and power consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of integrated photonics, and particularly relates to an on-chip integrated optical comb generation structure and an optical comb generation method. BACKGROUND

[0002] Microcavity Kerr optical comb technology has shown disruptive potential in multiple fields due to its advantages of miniaturization, low power consumption, and high integration, but also faces challenges such as manufacturing process, system integration, and stability.

[0003] With the continuous progress of on-chip waveguide technology, integrated optics has been continuously developed, and more and more optical systems can be realized through on-chip waveguide devices, which also provides the possibility for the miniaturization and integration of Kerr optical combs. The optical comb based on the principle of self-injection locking is the most integrated Kerr optical comb. Although this method has high integration, it is very difficult to debug, and the reproducibility and stability are poor. The commonly used optical comb debugging method is based on the debugging of auxiliary laser method, which uses a backward transmission laser to compensate for the power jitter of the pump laser after entering the red detuning cavity, to realize stable cavity power, so that it stably enters the soliton state, and the generated soliton optical comb also has robustness. However, the optical and electrical debugging systems of this system are relatively large, and the debugging means are also relatively complex, which restricts the development of optical combs towards miniaturization. SUMMARY

[0004] The purpose of the present application is to provide an on-chip integrated optical comb generation structure and an optical comb generation method, which can solve the problems of large and complex debugging of existing optical comb debugging systems, and can greatly reduce the volume and power consumption of microcavity optical combs.

[0005] In order to achieve the above purpose, one aspect of the present application provides an on-chip integrated optical comb generation structure, which is heterogeneously integrated by a laser chip and an integrated optical microcavity chip. The integrated optical microcavity chip includes a polarization beam splitter, two ring filters, an Add-drop type microcavity, and two output ports. The laser injected by the laser chip enters the integrated optical microcavity chip, and the integrated optical microcavity chip generates a microcavity optical comb and outputs from one of the two output ports. The polarization beam splitter is used to divide the injected laser into TE and TM modes with different power ratios and inject them into the two ring filters respectively. The two ring filters are respectively provided with heating electrodes for controlling the wavelength size passing through them. The two ring filters have different diameters for transmitting different wavelengths. The add-drop type microcavity is used for generating an optical frequency comb, the Input and Through ends are used for transmitting TE mode and TM mode through two ring filters respectively, and the Add and Drop ends are used for outputting the optical frequency comb, corresponding to two output ports of an integrated optical microcavity chip, and a heating electrode is arranged above the microcavity and is used for controlling the resonant wavelength through the microcavity.

[0006] Another aspect of the present application provides an optical frequency comb generation method, which generates an optical frequency comb by using the above structure, comprising: The laser generated by the laser chip is divided into TE mode and TM mode through a polarization beam splitter and is sent into two ring filters respectively, the heating electrode of the ring filter is finely adjusted to accurately control the through wavelength, so that the ring filter has a certain wavelength difference, after filtering through the ring filter, the optical frequency comb is generated by injecting the add-drop type microcavity in a direction, using the one with lower power in the TE mode and the TM mode as auxiliary laser and the other as pump laser, adjusting the heating electrode on the add-drop type microcavity, so that the microcavity is reduced from high temperature to low temperature, until the optical frequency comb is generated, and the generated optical frequency comb is output through one of the two output ports of the integrated optical microcavity chip.

[0007] According to the on-chip integrated optical frequency comb generation structure and the optical frequency comb generation method of the above aspect of the present application, the problems of large and complex optical frequency comb debugging system can be solved, the volume of the microcavity optical frequency comb can be greatly reduced, and the power consumption can be reduced. BRIEF DESCRIPTION OF DRAWINGS

[0008] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Figure 1 is a top view of the on-chip integrated optical frequency comb generation structure of an embodiment of the present application. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described clearly and completely in the following combined with the drawings. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0010] An embodiment of the present application provides an on-chip integrated optical frequency comb generation structure, which comprises: Figure 1As shown, the on-chip integrated optical comb generation structure of the embodiment of the present application is composed of a laser chip 1 and an integrated optical microcavity chip 2, and the laser chip 1 and the integrated optical microcavity chip 2 are heterogeneous substrates. A spacer with a proper height is placed below the respective substrates to align the waveguide end face of the laser waveguide 10 of the laser chip 1 with the waveguide end face of the microcavity waveguide 20 of the integrated optical microcavity chip 2. After alignment, the two are fixed by dispensing, and the heterogeneous integration of the two is completed.

[0011] The laser chip 1 is a semiconductor laser chip, and the output can be single-mode or multi-mode laser, and the typical wavelength is 1550 nm. The integrated optical microcavity chip 2 includes, from left to right, a polarization beam splitter 21, two ring filters (a first ring filter 22 and a second ring filter 23), an Add-drop type microcavity 24, and two output ports (a first output port 25 and a second output port 26). The laser output by the laser chip 1 is injected into the integrated optical microcavity chip 2 through the laser waveguide 10, and the microcavity optical comb generated by the integrated optical microcavity chip 2 is output from one of the two output ports. The polarization beam splitter 21 is, for example, a Y-type polarization beam splitter.

[0012] The polarization beam splitter 21 of the integrated optical microcavity chip 2 divides the injected laser into TE and TM modes, and has different power ratios, and is injected into the two ring filters, respectively, and prevents the light after passing through the microcavity from being re-injected back into the laser chip 1, and also facilitates filtering out different mode parts in the output optical comb, reducing phase noise.

[0013] The two ring filters of the integrated optical microcavity chip 2 are each provided with a heating electrode for accurately controlling the wavelength size passing through the filter. The two ring filters have different diameters for transmitting different wavelengths, and the wavelength difference is close to the wavelength difference corresponding to the TE and TM modes within N microcavity FSR (free spectral range) periods, and N is an integer greater than or equal to 0. Specifically, the wavelengths transmitted by the two ring filters are the resonance wavelengths in the corresponding modes, and the wavelength difference within the same period is N times the FSR, so that the wavelength difference of the two ring filters capable of generating an optical comb is N×FSR+ n n .

[0014] The Add-drop type microcavity of the integrated optical microcavity chip is used to generate an optical comb, and the Input and Through ends are used to transmit the TE and TM modes passing through the ring filters, respectively, and the Add and Drop ends are used to output the optical comb (corresponding to the two output ports of the integrated optical microcavity chip 2), and a heating electrode is also provided above the microcavity for controlling the resonance wavelength passing through the microcavity.

[0015] ​The integrated optical microcavity chip is prepared by the following steps: Step S1: growing a lower cladding layer of silicon dioxide on a silicon or SOI or lithium niobate substrate, and the thickness is generally greater than 2 microns; Step S2: growing a thin film of silicon nitride or lithium niobate as a waveguide layer on the lower cladding layer of silicon dioxide, and the thickness of the waveguide layer needs to be selected according to the design of the dispersion structure to be within the designed spectral range; Step S3: realizing pattern transfer of the waveguide layer by photolithography or electron beam exposure combined with ICP etching or wet etching to obtain a polarization beam splitter, two ring filters and an Add-drop type microcavity structure; Step S4: growing a layer of silicon dioxide as an upper cladding layer on the waveguide layer with a pattern formed; Step S5: performing photolithography on the upper cladding layer of silicon dioxide again, and using a lift-off process to prepare a heating layer located above the polarization beam splitter, the ring filter and the Add-drop type microcavity; Step S6: growing a layer of silicon dioxide on the heating layer again, and etching the position and depth of the contact electrode by photolithography and lift-off process to prepare the contact electrode of the heating layer; Step S7: after the contact electrode is completed, a layer of silicon dioxide is grown again, and then photolithography and etching are performed to remove the photoresist to obtain a through hole of the contact electrode, and the silicon dioxide grown in steps S4, S6 and S7 collectively serves as an upper cladding layer of the integrated optical microcavity chip, and the thickness of the upper cladding layer is generally greater than 2 microns.

[0016] The method for generating the optical frequency comb is that the laser generated by the laser is divided into TE mode and TM mode by the polarization beam splitter and is sent into two ring filters, the heating electrode of the ring filter is finely adjusted to accurately control the passing wavelength, so that the ring filter has a certain wavelength difference, and after filtering, the ring filter is injected into the Add-drop type microcavity, one of the two paths with lower power is used as auxiliary laser, and the other path is used as pump laser, the heating electrode on the Add-drop type microcavity is adjusted to reduce the temperature from high to low until the optical frequency comb is generated, and the generated optical frequency comb is output through one of the two output ports of the integrated optical microcavity chip 2, and the output depends on the path with higher transmission power as the pump laser.

[0017] In summary, the on-chip integrated optical frequency comb generation structure and method of the embodiment of the present application combines on-chip waveguide technology to realize a set of optical system with robustness through on-chip devices combined with on-chip debugging method, the optical system debugging steps are simple, and robust optical frequency comb can be generated only by temperature control, the problems of large and complex debugging system of the existing optical frequency comb are solved, and the volume of the miniaturized microcavity optical frequency comb can be greatly reduced, and the power consumption is reduced.

[0018] The foregoing merely illustrates some exemplary embodiments of the application, and it will be appreciated that those skilled in the art will be able to devise various modifications without departing from the spirit and scope of the application. The appended drawings and description are illustrative only, and are not intended to be limiting.

Claims

1. An on-chip integrated optical frequency comb generation structure, characterized in that, It consists of a laser chip and an integrated optical microcavity chip heterogeneously integrated. The integrated optical microcavity chip includes a polarization beam splitter, two ring filters, an add-drop microcavity, and two output ports. The laser output from the laser chip is injected into the integrated optical microcavity chip, and the integrated optical microcavity chip generates a microcavity optical frequency comb and outputs it from one of the two output ports. The polarization beam splitter is used to split the injected laser into TE mode and TM mode with different power ratios, which are injected into two ring filters respectively; the two ring filters are respectively equipped with heating electrodes to control the wavelength passed through, and the two ring filters have different diameters to transmit different wavelengths. Add-drop type microcavities are used to generate optical frequency combs. Their Input and Through terminals are used to transmit TE and TM modes after passing through two ring filters, respectively. The Add and Drop terminals are used to output the optical frequency comb, corresponding to the two output ports of the integrated optical microcavity chip. Heating electrodes are provided above the microcavity to control the resonant wavelength passing through the microcavity.

2. The structure as described in claim 1, characterized in that, The wavelength difference between the transmission wavelengths of the two ring filters is N×FSR+ n Where FSR is the free spectral range of the microcavity, and N is the number of FSR periods. n This represents the wavelength difference between the TE mode and the TM mode within the same period.

3. The structure as described in claim 1 or 2, characterized in that, The laser chip is a semiconductor laser chip that outputs single-mode or multi-mode laser, and the polarization beam splitter is a Y-type polarization beam splitter.

4. The structure as described in claim 1 or 2, characterized in that, The integrated optical microcavity chip is prepared through the following steps: Step S1: Grow a lower cladding layer of silicon dioxide on a silicon, SOI, or lithium niobate substrate; Step S2: Grow a silicon nitride or lithium niobate thin film as a waveguide layer under silicon dioxide; Step S3: The waveguide layer is patterned by photolithography or electron beam exposure combined with ICP etching or wet etching to obtain a polarization beam splitter, two ring filters and an add-drop microcavity; Step S4: Use ICP-CVD to grow a layer of silicon dioxide as the top cladding on the patterned waveguide layer; Step S5: Photolithography is performed on the cladding layer on silicon dioxide, and a heating layer is prepared above the polarization beam splitter, two ring filters and add-drop microcavity using a lift-off process; Step S6: Grow another layer of silicon dioxide on the heating layer, etch the position and depth of the contact electrode by photolithography, and fabricate the contact electrode of the heating layer using a lift-off process; Step S7: Grow another layer of silicon dioxide, and then perform photolithography etching to obtain the through-hole of the contact electrode.

5. The structure as described in claim 4, characterized in that, The silicon dioxide grown in steps S4, S6 and S7 together serve as the upper cladding layer of the integrated optical microcavity chip, and the thickness of the upper cladding layer is greater than 2 μm.

6. The structure as described in claim 4, characterized in that, The waveguide end face of the laser chip is aligned with the waveguide end face of the integrated optical microcavity chip. After alignment, it is fixed by dispensing adhesive to complete the heterogeneous integration of the laser chip and the integrated optical microcavity chip.

7. The structure as described in claim 4, characterized in that, The thickness of the lower cladding layer of silica is greater than 2 μm.

8. A method for generating an optical frequency comb, characterized in that, Generating an optical frequency comb using the structure of any one of claims 1-7 includes: The laser generated by the laser chip is split into TE and TM modes by a polarization beam splitter and fed into two ring filters respectively. The heating electrodes of the ring filters are finely adjusted to precisely control the wavelength of the transmitted light, so that they have a certain wavelength difference. After being filtered by the ring filters, the light is injected into the add-drop type microcavity in opposite directions. The lower power of the TE mode and TM mode is used as the auxiliary laser, and the other is used as the pump laser. The heating electrodes on the add-drop type microcavity are adjusted to cool the microcavity from a high temperature to a low temperature until an optical frequency comb is generated. The generated optical frequency comb is output through one of the two output ports of the integrated optical microcavity chip.

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