CN107991738B - A silicon-based multifunctional reconfigurable optical filter - Google Patents

Abstract

The invention discloses a silicon-based multifunctional reconfigurable optical filter, comprising: a first straight waveguide, a second straight waveguide and a plurality of microrings, and the first straight waveguide and the second straight waveguide connect the plurality of microrings in parallel; The optical field coupling occurs between the microring and the two straight waveguides, and the optical field coupling does not occur between the multiple microrings, and the multiple microrings are equally spaced, and the optical filter composed of the multiple microrings and the two straight waveguides includes multiple resonant peaks; by controlling the spacing of the microrings, the phases introduced by the transmission of the optical field with adjacent resonant peak wavelengths in the straight waveguides between two adjacent microrings are odd multiples and even multiples of π respectively, and the adjacent resonance peaks The optical field of the wavelength produces resonances of different intensities, so that the optical filter has different filtering characteristics. The invention uses the same filter structure to realize filtering functions with different filtering characteristics, and can also ensure that the central wavelength and bandwidth of the filter can be adjusted.

Description

A silicon-based multifunctional reconfigurable optical filter

technical field

The invention belongs to the technical field of optical fiber communication and integrated photonics, and more specifically relates to a silicon-based multifunctional reconfigurable optical filter.

Background technique

With the advent of the era of big data, communication systems are developing towards ultra-high speed, low cost, and large capacity. Optical communication has become one of the most important ways of modern information transmission. Filtering technology plays an important role in making full use of the wavelength resources of the optical network and protecting the maximum unimpeded flow of channels in the network system.

According to the frequency selection function of the filter, it can be divided into two types: band-pass filter and band-stop filter. The band-pass filter can obtain signals of certain specific frequencies, and the band-stop filter can eliminate signals of certain specific frequencies. . Bandpass filters are mainly used in Dense Wavelength Division Multiplexing (DWDM) local area networks as wavelength selection, distribution, diversity, routing and user transceiver multiplexers, etc. Box filters are bandpass filters. The notch filter is a special band-stop filter with a very narrow stop band, which is mainly used to filter out unnecessary high-amplitude interference signals in the system, and can effectively eliminate the impact of noise.

Although traditional optical filters have reached a relatively high level in some indicators, they can basically only achieve a single filtering function, which is difficult to meet the needs of the growing communication system, and is large in size, which is not conducive to integration.

Contents of the invention

Aiming at the defects of the prior art, the purpose of the present invention is to solve the technical problem that the traditional optical filter basically can only realize a single filtering function, is difficult to meet the needs of the growing communication system, and is large in size, which is not conducive to integration.

To achieve the above object, the present invention provides a silicon-based multifunctional reconfigurable optical filter, including: a first straight waveguide, a second straight waveguide and a plurality of microrings, the first straight waveguide and the second straight waveguide combine multiple The microrings are connected in parallel;

The optical field coupling occurs between the microring and the two straight waveguides, and the optical field coupling does not occur between the multiple microrings, and the multiple microrings are equally spaced, and the optical filter composed of the multiple microrings and the two straight waveguides includes multiple resonant peaks; by controlling the spacing of the microrings, the phases introduced by the transmission of the optical field with adjacent resonant peak wavelengths in the straight waveguides between two adjacent microrings are odd multiples and even multiples of π respectively, and the adjacent resonance peaks The optical fields of the wavelengths respectively produce resonance weakening and resonance enhancing effects, so that the optical filter has different filtering characteristics.

It should be noted that "reconfigurable" mentioned in the present invention refers to tunable, which means that the bandwidth and center wavelength of the filter are adjustable.

Optionally, the plurality of microrings are of the same size.

Optionally, under the condition that no coupling occurs between microrings and microrings, the spacing L of multiple microrings satisfies:

Where m is a natural number, and R is the radius of the microring. At this time, the phases introduced by the first straight waveguide and the second straight waveguide to the optical field of the adjacent resonant peak wavelength are respectively odd and even times of π, so the adjacent resonant The light field at the peak wavelength produces resonance-weakening and resonance-enhancing effects, respectively.

Optionally, one end of the first straight waveguide is the first output end, and one end of the second straight waveguide is the second output end. According to different needs, the first output end of the optical filter has a narrow bandwidth by adjusting the temperature of the microring The box-type filtering function, the band-pass filtering function or the narrow bandwidth notch filtering function enable the second output end of the optical filter to have the notch filtering function.

Optionally, the radius R of the microring satisfies: 2um≤R≤300um, if the radius is too small, the bending loss will be large; if the radius is too large, the wavelength interval between resonance peaks is small, and when used as an optical filter, multiple wavelengths will be filtered out, which is difficult to distinguish.

Optionally, the microring is a ridge waveguide device, and the microring can also be called a microring waveguide; the width W of the microring waveguide and the straight waveguide satisfies: 450nm≤W≤600nm, the waveguide width is too narrow, and the transmission loss is large; the waveguide width is too large Wide, there will be multi-mode transmission in the waveguide, resulting in multiple resonance peaks, which reduces the transmittance of the required fundamental mode resonance peak; the height h of the micro-ring waveguide and the straight waveguide meets: 150nm≤h≤300nm to ensure Only the archetype is transmitted.

Optionally, both ends of the first straight waveguide and the second straight waveguide have a coupling grating design, and all input light and output light are coupled through the coupling grating; the first straight waveguide, the second straight waveguide, multiple microrings and The coupling gratings are located in the same plane, and are etched once by a photolithography process.

Optionally, the cross section of the optical filter from top to bottom is the heating electrode, the upper cladding layer of silicon dioxide, the silicon device and the silicon dioxide substrate; the first straight waveguide, the second straight waveguide and the plurality of microrings are Silicon device; the heating electrode is above the microring and the coupling area between the microring and the straight waveguide, the heating electrode is connected to an external power supply, and the effective refractive index of the waveguide is changed by heating to adjust the central wavelength and bandwidth of the optical filter.

Specifically, silicon-based materials have the characteristics of high integration, manufacturing process compatibility with Complementary Metal Oxide Semiconductor (CMOS), good stability, and high thermal-optic coefficient, and are suitable for multifunctional reconfigurable optical filters. manufacture.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

Compared with the prior art, the present invention utilizes multiple micro-ring parallel structures, uses the same filter structure to realize filtering functions with different filtering characteristics, and can also ensure that the central wavelength and bandwidth of the filter can be adjusted.

Description of drawings

Fig. 1 is the structural representation of the multifunctional reconfigurable filter based on the silicon-based parallel microring provided by the present invention;

Figure 2 is a partial schematic diagram of a multifunctional reconfigurable filter based on silicon-based parallel microrings provided by the present invention and a cross-sectional view at the microring waveguide;

Fig. 3 is the multifunctional reconfigurable filter Output1 port output filtering characteristic based on the silicon-based parallel microring provided by the present invention, wherein, Fig. 3 a is the characteristic transmission spectrum of the narrow bandwidth box type filter, and Fig. 3 b is the characteristic transmission spectrum of the bandpass filter , Fig. 3c is the characteristic transmission spectrum of the narrow bandwidth notch filter;

Fig. 4 is the multifunctional reconfigurable filter Output2 port output filter characteristic based on the silicon-based parallel micro-ring provided by the present invention;

Figure 5 is a schematic diagram of the influence of the number of parallel microrings on the filtering characteristics in the multifunctional reconfigurable filter based on silicon-based parallel microrings provided by the present invention, wherein Figure 5a is a box-type filter and a bandpass filter at the output of Output1 Schematic diagram of the change law of 3dB bandwidth with the number of microrings. Figure 5b is a schematic diagram of the change law of the 3dB bandwidth of the notch filter at the Output1 output port and Output2 output port with the number of microrings;

Fig. 6 is the relationship curve of the effective refractive index of the waveguide with the control power in the multifunctional reconfigurable filter based on the silicon-based parallel microring provided by the present invention;

Fig. 7 is a schematic diagram of different filtering characteristics obtained by adding different control power to the electrode above the microring waveguide of the multifunctional reconfigurable filter based on the silicon-based parallel microring provided by the present invention, wherein Fig. 7a is the electrode above the microring waveguide A schematic diagram of the influence of different control powers on the central wavelength of the output box-type filter characteristics at the Output1 end. Figure 7b is a schematic diagram of the influence of different control powers on the central wavelength of the output band-pass filter characteristics of the Output1 end by adding different control powers to the upper electrode of the microring waveguide;

Fig. 8 is a schematic diagram of different filtering characteristics obtained under different control powers of the multifunctional reconfigurable filter based on silicon-based parallel microrings provided by the present invention, where Fig. 8a is a box-type filter output at the Output1 port Figure 8b is a schematic diagram of the filter characteristics of the Output1 port output bandpass filter changing with the electrode control power of the coupling area, and Figure 8c is the filter characteristic of the narrow bandwidth notch filter output by the Output1 port Schematic diagram of power variation with electrode control in the coupling region.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Aiming at the defects of the prior art, the present invention provides a multifunctional reconfigurable optical filter based on silicon-based parallel microrings, the purpose of which is to use the same filter structure to achieve different filtering functions, while ensuring that the center Adjustable wavelength and bandwidth.

FIG. 1 is a schematic structural diagram of a multifunctional reconfigurable optical filter based on silicon-based parallel microrings provided by the present invention. As shown in Figure 1, the present invention provides a multi-functional reconfigurable optical filter based on silicon-based parallel microrings, including sequentially setting a group of multiple (X, X≥2) microrings of the same size and upper and lower Two straight waveguides, the two straight waveguides connect multiple microrings in parallel. By precisely designing the phase introduced by the straight waveguide, the resonator can produce different resonance intensities for the light fields with different resonant peak wavelengths, so that different filtering functions can be obtained from the output end.

Wherein, for the convenience of distinction, the two straight waveguides may include a first straight waveguide and a second straight waveguide. One end of one of the straight waveguides (such as the first straight waveguide) can be used as the input terminal Input of the optical filter, the other end can be used as the second output terminal Output2 of the optical filter, and the other straight waveguide (such as the second straight waveguide) is connected to the Input terminal. The end on the same side as the port can be used as the first output end Output1 of the optical filter.

Furthermore, optical field coupling occurs between the microring and the straight waveguide, and no optical field coupling occurs between the microrings. The radius R of the microrings is the same, and the spacing L between the microrings is the same, and multiple parallel microrings and straight waveguides form a similar grating structure and multiple resonant cavity structures.

Furthermore, in the case of ensuring that there is no coupling between the microrings and the microrings, the length L satisfies where m is a natural number. At this time, the phases introduced by the straight waveguide to the optical fields of adjacent resonance peak wavelengths are odd multiples and even multiples of π respectively, so the resonance weakening and resonance strengthening effects will be produced on the optical fields of adjacent resonance peak wavelengths.

Furthermore, the signal light is input from the Input terminal to the multifunctional reconfigurable optical filter based on the silicon-based parallel microring, and according to different needs, the narrow bandwidth box filter function, bandpass filter function and Narrow bandwidth notch filter function, get the notch filter function from Output2.

Furthermore, the four ports of the multifunctional reconfigurable optical filter based on silicon-based parallel microrings are designed with coupling gratings, and all input light and output light are coupled through the coupling gratings.

Furthermore, the straight waveguide, the microring and the coupling grating are all located in the same plane, and are etched by a photolithography process at one time.

Furthermore, the radius R of the microring satisfies: 2um≤R≤300um, if the radius is too small, the bending loss will be large; if the radius is too large, the wavelength interval between resonance peaks will be small, and when used as a filter, multiple wavelengths will be filtered out, which is difficult to distinguish. The width W of the microring waveguide and the straight waveguide meets: 450nm≤W≤600nm, if the waveguide width is too narrow, the transmission loss will be large; if the waveguide width is too wide, there will be multi-mode transmission in the waveguide, resulting in multiple resonance peaks, making the required base The mode resonance peak transmittance decreases. The height h of the microring waveguide and the straight waveguide satisfies: 150nm≤h≤300nm, which is also to ensure that only the fundamental mode is transmitted in the waveguide.

It should be noted that the microring is a ridge waveguide device, and the microring may also be called a microring waveguide. The width W of the microring waveguide refers to the difference between its outer diameter and inner diameter. Wherein, the radius R of the microring refers to the average value of its inner and outer diameters. Specifically, FIG. 1 can be regarded as an xy plane view of the optical filter. Along the z direction, the thickness of the microring waveguide and the straight waveguide is their height h.

Furthermore, the cross-section of the multifunctional reconfigurable optical filter based on silicon-based parallel microrings is heating electrode, silicon dioxide upper cladding layer, silicon device and silicon dioxide substrate from top to bottom. The heating electrode is above the microring waveguide and the coupling area between the microring and the straight waveguide. The heating electrodes are respectively connected with external power sources, and the effective refractive index of the waveguide is changed by heating to adjust the wavelength and bandwidth of the optical filter.

Figure 2 is a partial schematic diagram of a multifunctional reconfigurable filter based on silicon-based parallel microrings and an AA cross-sectional view of the microring waveguide, where the dotted lines represent electrodes. The thickness of the silicon dioxide SiO ₂ substrate is 2 microns, the width of the straight waveguide and the micro-ring waveguide are both 500 nanometers, and the height is 220 nanometers. This size only allows the transmission of the fundamental mode, in order to avoid the inconsistent resonance peaks of various modes. The effect has a bad effect.

Among them, the waveguide silicon device includes each structural device shown in FIG. 1 . In order to avoid the influence of heating the metal electrode on the optical properties of the waveguide silicon device structure, a layer of 1.2 micron silicon dioxide (silicon dioxide upper cladding layer) is first deposited on the waveguide silicon device structure by PECVD process. Then, a layer of 120nm-thick metal titanium electrode is coated on the silicon dioxide directly above the coupling area between the micro-ring waveguide and the straight waveguide and directly above the ring waveguide by electron beam evaporation technology.

The present invention proposes a multi-functional reconfigurable filter based on parallel silicon-based microrings. By precisely designing the spacing L between the parallel microrings, the direct waveguide between the microrings is indirectly controlled to introduce additional phase shift, resulting in alternating high and low Q values. The resonant spectrum, so as to obtain different filtering characteristics.

Specifically, in the parallel microring structure, the radius R of the microrings is the same, and the distance L between the microrings is the same, the straight waveguide between the microrings will form a periodic grating, and each microring is used as a reflection element. These microring rings are simultaneously coupled to the straight waveguide, but not to each other.

For the optical field whose wavelength is the resonant wavelength λ _n , the phase change of one cycle of transmission in a single microring resonator satisfies the resonance condition: where n is a positive integer. Among them, λ _n represents the nth resonance wavelength, according to the resonance condition, we can get

For the nth resonant wavelength λ _n , the additional phase shift caused by the straight waveguide between the microrings in the parallel microring structure for:

where β is the propagation constant, n _eff is the effective refractive index of the silicon waveguide, and c is the speed of light. Will and Introduced into the above formula to get:

where β is the propagation constant n _eff is the effective refractive index of the silicon waveguide, and c is the speed of light. According to the principle of interference, when the additional phase shift introduced by the straight waveguide When it is an even multiple of π, the optical field of the resonant peak wavelength will produce resonance enhancement, and the projected spectrum at the download end will appear box-type filter spectral lines with high Q value and narrow bandwidth; when the additional phase shift introduced by the straight waveguide When π is an odd multiple of π, the optical field of the resonant peak wavelength will produce resonance weakening, and the projected spectrum at the download end will appear band-pass filter spectral lines with low Q value and wide bandwidth; where, the quality factor Q value of the resonant cavity is defined as In a photon vibration cycle, the ratio of the energy stored in the microring to the total energy consumed by coupling out of the microring and scattering, the stronger the resonance, the greater the energy stored in the cavity, the higher the Q value, and the narrower the bandwidth.

According to the above analysis, when which is (m is a natural number), for the optical fields of adjacent resonant wavelengths λ _n and λ _n+1 , the additional phase shift caused by the straight waveguide and They are odd multiples and even multiples of π respectively. At this time, the resonance weakens and the resonance strengthens in the light field adjacent to the resonant peak, so the transmission spectrum at the Output1 end will appear alternating high-Q narrow-bandwidth resonant peaks and low-Q broadband resonant peaks. Due to the coupling of adjacent microrings and waveguides to form a new resonant cavity structure, according to the principle of light interference, side lobes will be generated between adjacent resonant peaks, and the notch filter characteristics can be formed by using the depressions between side lobes.

Taking a multifunctional reconfigurable optical filter with three parallel microrings as an example, the radius of the microrings is 50 microns, the coupling coefficient between the microrings and the straight waveguide is 0.3, and the distance between the microrings is 235.62 microns. There is no mutual coupling. Input the wide-spectrum light source from the Input port, and obtain the narrow-bandwidth box-type filter characteristic transmission spectrum, band-pass filter characteristic transmission spectrum and narrow-bandwidth notch filter characteristic transmission spectrum from the Output1 output port, as shown in Figures 3a, 3b, and 3c, respectively. . Among them, the bandwidth of the narrowband box filter is 7.5GHz, and the extinction ratio is greater than 10dB; the 3dB bandwidth of the bandpass filter is 20GHz, and the extinction ratio is greater than 25dB; the 3dB bandwidth of the narrow bandwidth notch filter is 3MHz, and the notch depth is greater than 90dB. The notch filter characteristic transmission spectrum can be obtained from the Output2 output port, as shown in Figure 4, the 3dB bandwidth is 3.125MHz, and the notch depth is greater than 80dB. According to the needs, the required filter characteristics can be selected at will, and different filter functions can be realized with the same filter structure.

The influence of the number of microrings on the filtering characteristics is shown in Figure 5. Figure 5a is a schematic diagram of the box filter characteristics and band-pass filter characteristics of the Output1 output port changing with the number of microrings, and Figure 5b is a schematic diagram of the notch filter characteristics of the Output1 output port and Output2 output port changing with the number of microrings. With the increase of the number of microrings, the bandwidth of the box filter characteristic and the narrow line width notch filter characteristic of the Output1 output port is narrower, and the bandwidth of the bandpass filter characteristic is larger; the bandwidth of the notch filter characteristic of the Output2 output port is narrower .

When the effective refractive index n _eff of the waveguide changes, the resonant wavelength also changes. The SOI waveguide material has a high thermo-optic coefficient. The thermal effect generated by electrifying the metal electrode causes the temperature of the local waveguide material to rise. The thermo-optic effect changes the effective refractive index of the waveguide, thereby realizing the tuning of the filtering center wavelength. When the control power loaded on the heating electrode changes, the change curve of the effective refractive index of the SOI waveguide with the control power is shown in Figure 6. The effective refractive index changes linearly with the control power. When the voltage increases, the effective refractive index increases. big.

The influence of the control power change of the microring waveguide heating electrode on the central wavelength of the filter is shown in Figure 7. Figure 7a shows the influence of different control power on the central wavelength of the output box-type filter characteristics at the Output1 end, and Figure 7b is The influence of different control powers on the electrodes above the microring waveguide on the central wavelength of the output bandpass filter characteristics at the Output1 port. As shown in Figure 7a and Figure 7b, when the control power increases, the output spectrum of the filter shifts red. When the control power is 20mW, the center wavelength of the filter shifts red by 1.298nm, and the tuning rate is 0.065nm/mW. Therefore, the control power can be appropriately changed according to different filtering requirements to obtain optical signals of different wavelengths.

The influence of the heating electrode control power change in the coupling area on the filter bandwidth is shown in Figure 8. Among them, Figure 8a is a schematic diagram of the filter characteristics of the output box filter at the Output1 port changing with the control power, Figure 8b is a schematic diagram of the filtering characteristics of the output bandpass filter at the Output1 port changing with the control power, and Figure 8c is a narrow bandwidth notch output at the Output1 port Schematic diagram of the filter characteristics of the filter changing with the control power. It can be seen that increasing the control power of the coupling region increases the effective refractive index and decreases the coupling coefficient, the bandwidths of the output box filter and the bandpass filter at the Output1 port decrease, and the center wavelength of the narrow bandwidth notch filter drifts.

According to the above analysis, it can be seen that a reconfigurable optical filter based on parallel microrings according to the present invention can realize different filtering functions at different output ports according to the needs of actual filtering characteristics, and at the same time, the filter can be changed by controlling the power. Center wavelength and bandwidth.

The above are only preferred specific implementation methods of the present application, but the scope of protection of the present application is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application. All should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims (6)

1. a kind of silicon substrate multifunctional reconfigurable optical filter characterized by comprising the first straight wave guide, the second straight wave guide and The multiple micro-loop is connected in parallel by multiple micro-loops, the first straight wave guide and the second straight wave guide；

Light field occurs between micro-loop and two straight wave guides to couple, light field coupling does not occur to each other for the multiple micro-loop, and described more The optical filter that a micro-loop equidistantly distributed, the multiple micro-loop and two straight wave guides are constituted includes multiple resonance peaks；

By controlling the spacing of the micro-loop so that for adjacent resonance peak wavelength light field between two neighboring micro-loop straight wave guide The phase that middle transmission introduces is respectively the odd-multiple and even-multiple of π, produces resonance respectively to the light field of adjacent resonance wavelength and subtracts Weak and resonance reinforcing effect, to make the optical filter that there is different filtering characteristics；

Guarantee in the case where not coupled between micro-loop and micro-loop, the spacing L of the multiple micro-loop meets: Wherein m is natural number, and R is that micro-loop radius, at this time the first straight wave guide between two neighboring micro-loop and the second straight wave guide are directed to phase The introduced phase of the light field of adjacent resonance peak wavelength is respectively the odd-multiple and even-multiple of π, therefore can be to adjacent resonance peak wavelength Light field generate respectively resonance weaken and resonance booster action；

One end of first straight wave guide is the first output end, and one end of the second straight wave guide is second output terminal, according to different needs, is led to Crossing design micro-loop interannular spacing makes the first output end of the optical filter have narrow bandwidth box filter function, bandpass filtering function Energy or narrow bandwidth notch filter function, make the second output terminal of the optical filter have the function of notch filter.

2. silicon substrate multifunctional reconfigurable optical filter according to claim 1, which is characterized in that the ruler of the multiple micro-loop It is very little identical.

3. silicon substrate multifunctional reconfigurable optical filter according to claim 1, which is characterized in that the micro-loop radius R is full Foot: 2um≤R≤300um, the too small bending loss of radius are big；Radius is excessive, and wavelength interval is small between resonance peak, filters as light When device, multiple wavelength can be filtered out, are not easily distinguishable.

4. silicon substrate multifunctional reconfigurable optical filter according to claim 1, which is characterized in that the micro-loop is ridge wave Device is led, the micro-loop can be described as micro-loop waveguide again；

The micro-loop waveguide and straight wave guide width W meet: 450nm≤W≤600nm, duct width is narrow, and transmission loss is big；Wave It is wide to lead width, multimode transmissions are had in waveguide, leads to there are multiple resonance peaks, so that required fundamental resonance peak transmissivity drops It is low；

The micro-loop waveguide and straight wave guide height h meet: 150nm≤h≤300nm, to guarantee there was only basic mode transmission in waveguide.

5. silicon substrate multifunctional reconfigurable optical filter according to claim 1, which is characterized in that first straight wave guide and There is coupled grating design at the both ends of second straight wave guide, and all input lights and output light pass through coupling grating and coupled；

First straight wave guide, the second straight wave guide, the multiple micro-loop and the coupling grating are respectively positioned in same plane, are passed through Photoetching process once etches completion.

6. silicon substrate multifunctional reconfigurable optical filter according to claim 5, which is characterized in that the optical filter is cut Face is followed successively by heating electrode, silica top covering, silicon device and silicon dioxide substrates from top to bottom；

First straight wave guide, the second straight wave guide and multiple micro-loops are silicon device；

The heating electrode heats electrode and external power supply above the top of the micro-loop and micro-loop and straight wave guide coupled zone It is connected, changes the effective refractive index of waveguide by heating, the central wavelength and bandwidth of the optical filter are adjusted.