CN113253537B - Mach-Zehnder interferometer type adjustable fractional order optical field differentiator prepared based on SOI material - Google Patents

Abstract

The invention discloses a Mach-Zehnder interferometer type adjustable fractional light field differentiator based on SOI material, which includes a 2×2 directional coupler based on SOI material, two interference arms with different lengths and 2 ×1 multimode interference coupler (MMI), additionally including a thermode above the coupling region of the directional coupler. Among them, the directional coupler divides the modulated input light into two beams according to a certain ratio, and the interference arms with different lengths make the input light form a phase difference of π at the exit of the interference arm, and then form destructive interference through the MMI to complete the input light differential operation. The hot electrode is loaded with an electric signal, and by changing the light splitting ratio at the output end of the directional coupler, the interference intensity of the input light at the working wavelength can be changed, so that the differential order of the differentiator can be adjusted.

Description

A Mach-Zehnder interferometer-type tunable fractional light based on SOI material field differentiator

technical field

The invention belongs to the technical field of optical communication, and in particular relates to a Mach-Zehnder interferometer type adjustable fractional-order light field differentiator prepared based on SOI material.

Background technique

Due to process constraints, the development of electronic chips has gradually slowed down, and the number of integrated transistors has slowed down, while problems such as power consumption, noise, and crosstalk have become more and more obvious. Compared with electrical signal processing, optical signal processing has large bandwidth, fast transmission speed, anti-electromagnetic interference and rich multiplexing methods, and all-optical processing can match the transmission rate of optical fiber, thereby increasing the data processing rate and effectively reducing the previous signal processing. "Optical-electrical-optical" conversion costs and maintenance costs.

SOI (Silicon on Insulator, silicon on insulator) benefits from the large refractive index difference between silicon and silicon dioxide, so that optical signals can be well confined in silicon, and silicon has the same magnitude of thermo-optic coefficient as polymer , very suitable for waveguide material. SOI also has the advantages of low bending loss, mature manufacturing process, low manufacturing cost, and compatibility with CMOS technology, which is conducive to the miniaturization of waveguide devices for large-scale integration.

In order to realize all-optical processing, it is necessary to design basic calculation modules for optics, such as optical time-domain integrators, optical time-domain differentiators, and optical Fourier transformers. Among them, the optical time domain differentiator, as one of the components of optical computing, can be used for optical computing, pulse coding, pulse shaping, etc., and can also achieve more complex calculations in combination with other devices. Adding an auxiliary hot electrode on SOI can change the temperature of the waveguide, and then change the effective refractive index of the mode in the waveguide to realize the change of the optical amplitude and phase. It is one of the important modulation methods of the adjustable order differentiator.

In order to achieve on-chip integration, silicon-based micro-ring resonators (micro-ring resonators, MRRs), silicon-based Bragg gratings, silicon-based photonic crystal resonators, silicon-based Mach-Zehnder interferometers (Mach-Zehnder interferometer, MZI) and autonomous The optical time-domain differentiator scheme of self-coupled optical-waveguide (SCOW) has been proposed one after another. The more common types are MRR and MZI. The MRR differentiator has a high degree of integration and accurate differential results, but its working bandwidth is small and it is difficult to cope with high-speed signal processing; the MZI differentiator has a simple working principle and a relatively large working bandwidth, but its integration is relatively low.

For the adjustable MZI differentiator, the principle is to change the splitting ratio of the upper and lower interference arms to achieve the change of the final interference depth and phase change. The general solution is to introduce an additional loss in one arm to achieve different outgoing light intensities of the two arms, which leads to a large waste of energy. And the introduction loss must be based on the change of the waveguide refractive index, which will cause a large shift in the working wavelength of the differentiator, and the carrier frequency of the input light needs to be adjusted every time, which affects its practicability.

Contents of the invention

Aiming at the MZI type optical time domain differentiator with adjustable order, the present invention discloses a Mach-Zehnder interferometer type adjustable fractional order optical field differentiator based on SOI material, which provides a simple and effective MZI Compared with the existing MZI-type optical differentiator, the solution of the type optical differentiator reduces unnecessary waste of input signals, has a stable working wavelength, and has a large working bandwidth to adapt to high-speed information processing.

For reaching said goal, technical scheme of the present invention is as follows:

A Mach-Zehnder interferometer-type adjustable fractional light field differentiator based on SOI material, comprising SiO ₂ cladding, the inside of the SiO ₂ cladding is provided with a waveguide layer arranged horizontally, and the waveguide layer is composed of Si material preparation;

The waveguide layer includes: a directional coupler, two interference arms with different lengths and a multimode interference coupler, the directional coupler, the interference arm and the multimode interference coupler are sequentially cascaded to form a Mach-Zehnder interference instrument;

The upper port Input A of the input end of the directional coupler is the input end of the differentiator, and the output port Output of the multimode interference coupler is the output end of the differentiator; a hot electrode is arranged directly above the coupling region of the directional coupler, and its The width covers the entire coupling area and some surrounding areas; there is SiO ₂ as a buffer layer between the hot electrode and the directional coupler.

Further, the directional coupler includes two input straight waveguides, four curved waveguides, two coupled straight waveguides, and transition waveguides transitioning from the ridge waveguide to the strip waveguide, and the two coupled straight waveguides are formed with a distance The coupling region C1. Further, the coupling spacing of the directional coupler is adjusted according to the modulation efficiency of the modulation system. If the modulation system has a low level of modulation of the waveguide refractive index, the range of refractive index changes that can be achieved is small, and the coupling distance of the directional coupler is reduced. spacing to increase the sensitivity of the split ratio to changes in the refractive index.

Further, the interference arm is a strip waveguide, including eight quarter-ring waveguides with a radius of 15 μm, and an interference arm straight waveguide for adjusting the optical path difference.

Further, the length difference of the two interference arms is determined by the requirement for the working wavelength of the differentiator, that is, after the working wavelength of the differentiator is determined, the length difference of the two interference arms is designed so that the light at the working wavelength is interfered Inversion is achieved after the arm.

Further, the multimode interference coupler includes three straight waveguides, three Taper waveguides for reducing propagation loss, and a multimode interference cavity.

Further, the upper arm of the output end of the directional coupler is connected to the upper arm of the input end of the interference arm through a transition waveguide, and the lower arm of the output end of the directional coupler is connected to the lower arm of the input end of the interference arm through a transition waveguide; The upper arm of the output end of the arm is connected with the upper arm of the input end of the multimode interference coupler through a Taper waveguide, and the lower arm of the output end of the interference arm is connected with the lower arm of the input end of the multimode interference coupler through a Taper waveguide.

Further, the thickness of the waveguide layer is 220nm, the directional coupler is a ridge waveguide, and the etching depth is 150nm; the interference arm and the multimode interference coupler are strip waveguides, and the cross-sectional size of the waveguide is 500nm×220nm.

Further, a variable voltage is applied to both ends of the thermode to realize a proportional change of the optical power output by the directional coupler, so as to adjust the differential order of the final output of the differentiator.

Further, under the condition of no modulation, the optical power ratio at the working wavelength of the transmission port A and the coupling port B output from the directional coupler should be less than 1:1, so as to ensure that the differential order is less than 1 under the condition of no modulation .

The beneficial effects of the present invention are:

The invention proposes a Mach-Zehnder interferometer-type adjustable fractional-order light field differentiator based on SOI material, which splits the input light through a directional coupler, and then transmits it through two waveguides of different lengths. will have a phase difference of π. Then the two beams of anti-phase light will form destructive interference around the carrier frequency in the multi-mode interference coupler (MMI), where the extinction ratio of the carrier is the largest, and the differential operation of the input light field is completed. Through the modulation of the directional coupler, the light splitting ratio of the two ports will be changed, thereby realizing the adjustment of the differential order.

Compared with the common MZI-based adjustable differentiator, the present invention does not enlarge the occupied area, but ensures the stability of the working wavelength to reduce the cost of additionally introduced wavelength conversion, and reduces the waste of input light energy. Compared with the adjustable differentiator based on MRR, this scheme can handle large signal bandwidth and can process high-speed input information.

Moreover, the manufacturing process of the present invention is compatible with CMOS, and has potential characteristics and advantages of fast response speed, low transmission loss, and low power consumption.

Description of drawings

Fig. 1 is a schematic diagram of a three-dimensional structure of the present invention.

Fig. 2 is a schematic diagram of the top view structure of the waveguide of the present invention; (a) a model diagram of the overall waveguide; (b) a directional coupler part; (c) an interference arm part; (d) a multimode interference coupler part.

Fig. 3 is a partial cross-sectional schematic view of the thermode of the present invention.

Fig. 4 is the frequency spectrum of the output port when there is no external power in the present invention (take the incident from Input A as an example); (a) amplitude-frequency response curve; (b) phase-frequency response curve.

Fig. 5 is the spectrogram of the differential results of integer order differential (1st order) and high order differential (greater than 1st order, less than 2nd order) of the present invention; (a) amplitude-frequency response curve; (b) phase-frequency response curve.

Fig. 6 is the time-domain representation of the differential results of the three differential orders of the present invention.

Fig. 7 is a graph showing the relationship between the applied power and the temperature change of the waveguide according to the present invention.

1. Directional coupler; 2. Interference arm; 3. Multimode interference coupler; 4. Thermal electrode; 5. SiO ₂ cladding;

1-1. Input straight waveguide; 1-2. Bending waveguide; 1-3. Coupling straight waveguide; 1-4. Transition waveguide; 2-1. Quarter ring waveguide; 2-2. Interference arm straight waveguide; 3-1. Straight waveguide; 3-2. Taper waveguide; 3-3. Multimode interference cavity.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the drawings, and the words "inner" and "outer" refer to is the direction towards or away from the geometric center of a particular part.

As shown in Figure 1 and Figure 2 (a), the present invention designs a Mach-Zehnder interferometer-type adjustable fractional-order light field differentiator based on SOI material, and its waveguide layer is embedded in SiO ₂ The Si waveguide in the layer (5), the thickness of the waveguide layer is 220nm;

The main components include: a directional coupler 1 , two waveguide interference arms 2 with unequal lengths and a multimode interference coupler 3 .

As shown in Figure 2(b), the directional coupler 1 is a ridge waveguide process with an etching depth of 150nm, including: two input straight waveguides 1-1, four curved waveguides 1-2, two coupling straight waveguides 1- 3 and transition waveguides 1-4 transitioning from ridge waveguides to strip waveguides. The two coupled straight waveguides 1-3 constitute a spaced coupling region C1. The input ports of the directional coupler 1 (ie, the input ports of the differentiator) are Input A and Input B, and only one of the ports is used in actual work. The coupling spacing of the directional coupler 1 is adjusted according to the modulation efficiency of the modulation system. If the modulation system has a low modulation level for the waveguide refractive index, the range of refractive index changes that can be realized is small, and the coupling spacing of the directional coupler 1 is reduced. To increase the sensitivity of the split ratio to changes in the refractive index.

As shown in Figure 2(c), the interference arm 2 is a strip waveguide process, including: eight quarter-ring waveguides 2-1 with a radius of 15 μm (only one is marked for simplicity in the figure), and a Path difference of the interference arm straight waveguide 2-2. The length difference of the two interference arms 2 is determined by the requirement for the working wavelength of the differentiator, that is, after the working wavelength of the differentiator is determined, the length difference of the two interference arms 2 is designed so that the light at the working wavelength passes through the interference arm 2 to achieve inversion.

As shown in Figure 2(d), the multimode interference coupler 3 is a strip waveguide process, including three straight waveguides 3-1, three Taper waveguides 3-2 for reducing propagation loss, and a multimode interference cavity 3-3. The interference arm 2 and the multimode interference coupler 3 are strip waveguides with a cross-sectional size of 500nm×220nm.

As shown in Figure 1, the square TiN hot electrode 4 is directly above the coupling area of the directional coupler 1, and the temperature of the electrode is changed by applying a voltage across the hot electrode 4 to realize the proportional change of the optical power output by the directional coupler 1 to adjust The differential order of the final output of the differentiator. Under the condition of no modulation, the optical power ratio at the working wavelength of the transmission port A and the coupling port B output from the directional coupler should be less than 1:1, so as to ensure that the differential order is less than 1 under the condition of no modulation. The cross-sectional view of the thermal electrode 4 is shown in FIG. 3 , and there is a SiO ₂ cladding (buffer layer) 5 between the waveguide layer and the thermal electrode 4 .

The principle of the differentiator of the structure of the present invention is: for the Mach-Zehnder interferometer, two beams of anti-phase light will destructively interfere, and an approximately linear amplitude-frequency response curve will appear on the frequency spectrum, and reach the lowest point at the carrier , the phase-frequency response will have a π-phase jump at the carrier frequency, which is consistent with the transfer function of the ideal differentiator, so the first-order differential function can be realized; for the fractional-order differentiator, more attention should be paid to the accuracy of the phase response, the amplitude The frequency response does not need to be exactly the same, so the phase response of the fractional differentiator can be realized by adjusting the intensity difference between the two beams of the Mach-Zehnder interferometer.

Under the structure of the present invention, the input light carrying the signal enters the directional coupler 1 from Input A, and splits the light through the coupling region C1. In the case of no modulation, the ratio of the coupling energy to the passed energy should be greater than 1, so as to achieve less than 1 order For differential calculation, the two beams of light will be reversed after passing through the interference arm 2, and then destructively interfere in the multimode interference coupler 3 to complete the low-order differential calculation and output from Output. By applying a voltage across the thermode 4, the temperature of the thermode 4 can be changed, thereby changing the temperature of the coupling region of the directional coupler 1, that is, changing the effective refractive index of the waveguide, and changing the splitting ratio of the directional coupler 1 (coupling energy The ratio of the energy passed through gradually becomes smaller), the coupling order of the differentiator can be increased, and the adjustable function of the optical differentiator can be realized.

In order to verify that the present invention can realize this function, a verification example is given for illustration.

In this verification example, the time domain finite difference method is used for calculation and analysis. The main parameters used in the simulation calculation are: strip waveguide section width 500nm, height 220nm; ridge waveguide etching depth 150nm; silicon and silicon dioxide The thermo-optic coefficients are 1.84×10 ^-4 and 1×10 ^-5 respectively; for directional coupler 1, the length of coupled straight waveguides 1-3 is 6.5 μm, the coupling distance is 200nm, and the x-direction distance between the left and right ports of curved waveguides 1-2 is 10μm, y-direction distance of 2μm, ridge waveguide to strip waveguide transition zone 10μm; interference arm straight waveguide 2-2 length 123.32μm; MMI Taper waveguide 3-2 length 10μm, multimode interference cavity 3-3 length 59μm , 8 μm wide.

Taking light incident from Input A as an example, the calculated output port amplitude-frequency and phase-frequency curves are shown in Figure 4(a) and (b) respectively. According to the design, the operating wavelength of the differentiator is 1553.56nm. It can be seen that the differentiator realizes the differential processing at 1553.56nm, and the differential order is less than 1, and the working bandwidth is about 1.3nm. By applying modulation, the frequency response of the differentiator changes accordingly, as shown in Figure 5(a) and (b), where the solid line is the first-order differential result, and the dotted line is the high-order differential result, which can illustrate the adjustable differentiator Function.

The time-domain characteristics of the present invention are shown in Figure 6, wherein the dark solid line is the low-order differential result, the light-color solid line is the first-order differential result, and the dotted line is the high-order differential result, which also verifies the functionality of the differentiator and its adjustability.

Figure 7 shows the waveguide temperature change corresponding to different power consumption. It can be seen that the waveguide temperature change corresponding to the power consumption is approximately proportional, and the proportional coefficient is about 3.05K/mW. The approximately linear formant shift can be more Good for control of derivative order.

In summary, the Mach-Zehnder interferometer-type adjustable fractional-order light field differentiator based on SOI materials provided by the present invention can directly realize differential calculation processing of different differential orders for optical signals, and has a large working bandwidth and a wide operating wavelength. Stable, less waste of input signal energy, can better add all-optical processing. At the same time, it also has the potential characteristics and advantages of simple fabrication, compatibility with CMOS, and low power consumption.

The technical means disclosed in the solutions of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims (8)

1. A Mach-Zehnder interferometer type adjustable fractional order optical field differentiator based on SOI material preparation comprises SiO ₂ A cladding (5), characterized in that: the SiO ₂ A waveguide layer horizontally arranged is arranged in the cladding layer (5), and the waveguide layer is prepared from a Si material;

the waveguide layer includes: the device comprises a directional coupler (1), two interference arms (2) with different lengths and a multimode interference coupler (3), wherein the directional coupler (1), the interference arms (2) and the multimode interference coupler (3) are sequentially cascaded to form a Mach-Zehnder interferometer;

an upper port Input A of the Input end of the directional coupler (1) is the Input end of the differentiator, and an Output port Output of the multimode interference coupler (3) is the Output end of the differentiator; a hot electrode (4) is arranged right above the coupling area of the directional coupler (1), and the width of the hot electrode covers the whole coupling area and the surrounding partial area; siO is arranged between the hot electrode (4) and the directional coupler (1) ₂ As a buffer layer (5);

applying a variable voltage across the hot electrode (4) to realize proportional change of the optical power output by the directional coupler (1) part so as to adjust the differential order of the final output of the differentiator;

under the no-modulation condition, the optical power ratio at the working wavelength of the transmission port A and the coupling port B output from the directional coupler (1) is less than 1, so as to ensure that the differential order under the no-modulation condition is less than 1.

2. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on an SOI material according to claim 1, wherein: the directional coupler (1) comprises two input straight waveguides (1-1), four bent waveguides (1-2), two coupling straight waveguides (1-3) and transition waveguides (1-4) which are transited from ridge type waveguide to strip type waveguide, wherein the two coupling straight waveguides (1-3) form a coupling area C1 with a distance.

3. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on an SOI material according to claim 2, wherein: the coupling space of the directional coupler (1) is adjusted according to the modulation efficiency of the modulation system, and if the modulation system has a low modulation level for the waveguide refractive index, namely the achievable refractive index change range is small, the coupling space of the directional coupler (1) is reduced to improve the sensitivity of the splitting ratio to the refractive index change.

4. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on an SOI material according to claim 1, wherein: the interference arm (2) is a strip waveguide and comprises eight quarter-ring waveguides (2-1) with the radius of 15 mu m and interference arm straight waveguides (2-2) for adjusting optical path difference.

5. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on an SOI material according to claim 1, wherein: the length difference of the two interference arms (2) is determined by the requirement on the working wavelength of the differentiator, namely after the working wavelength of the differentiator is determined, the length difference of the two interference arms (2) is designed to enable light at the working wavelength to realize phase inversion after passing through the interference arms (2).

6. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on SOI material as defined in claim 1 wherein: the multi-mode interference coupler (3) comprises three straight waveguides (3-1), three Taper type waveguides (3-2) for reducing propagation loss and a multi-mode interference cavity (3-3).

7. A Mach-Zehnder interferometer type adjustable fractional order optical field differentiator prepared based on SOI materials as claimed in claim 2 or 6, wherein: the upper arm of the output end of the directional coupler (1) is connected with the upper arm of the input end of the interference arm (2) through a transition waveguide (1-4), and the lower arm of the output end of the directional coupler (1) is connected with the lower arm of the input end of the interference arm (2) through a transition waveguide (1-4); the upper arm of the output end of the interference arm (2) is connected with the upper arm of the input end of the multimode interference coupler (3) through a Taper type waveguide (3-2), and the lower arm of the output end of the interference arm (2) is connected with the lower arm of the input end of the multimode interference coupler (3) through the Taper type waveguide (3-2).

8. A mach-zehnder interferometer type adjustable fractional order optical field differentiator prepared based on an SOI material according to claim 1, wherein: the thickness of the waveguide layer is 220nm, the directional coupler (1) is a ridge waveguide, and the etching depth is 150nm; the interference arm (2) and the multimode interference coupler (3) are strip waveguides, and the cross section of each waveguide is 500nm multiplied by 220nm.

Images