Silicon-based integrated external cavity tunable laser based on micro-ring interference

Abstract

The invention relates to the technical field of optical communication, in particular to a silicon-based integrated external cavity tunable laser based on micro-ring interference, comprising a filter chip which comprises an optical waveguide, a first micro-ring resonator, a second micro-ring resonator, a first beam splitting and combining device, a second beam splitting and combining device and a third beam splitting and combining device; the common waveguide of the first beam splitting and combining device is connected with the optical waveguide, one branch waveguide of the first beam splitting and combining device is connected with the common waveguide of the second beam splitting and combining device, and the other branch waveguide of the first beam splitting and combining device is connected with the common waveguide of the third beam splitting and combining device; the first micro-ring resonator is arranged between the two branch waveguides of the second beam splitting and combining device, and the second micro-ring resonator is arranged between the two branch waveguides of the third beam splitting and combining device. The micro-ring resonators and the corresponding beam splitting and combining devices form a Sagnac interferometer, and the two independent Sagnac interferometers are connected in parallel, so that the wavelength adjusting range of the laser is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of optical communication, and in particular to a silicon-based integrated external cavity tunable laser based on micro-ring interference. Background Art

[0002] Digital coherent optical communications are considered to be the development direction of the next generation of optical communication systems due to their potential to achieve high capacity and long-distance transmission. Increasing demand has pushed fiber capacity to 100Gbs / wavelength or higher, and as fiber capacity increases, the number of coherent optical systems deployed continues to increase. Coherent tunable lasers are an important and advantageous element of such networks. In order for such tunable lasers to meet the emerging needs and requirements of upcoming coherent systems, tunable lasers are required to have the largest possible adjustment range of laser wavelengths, the narrowest possible linewidth, low size, and low energy consumption.

[0003] In order to achieve the above goals, the external cavity tunable laser (ECL) based on cascade microrings came into being. However, the wavelength tunable range of the external cavity tunable laser based on cascade microrings is inversely proportional to the difference in the free spectral range (FSR) of different cascade microrings. Reducing the difference in FSR of different cascade microrings can increase the adjustment range of the tunable laser, but it also reduces the transmittance difference between the main mode and the side mode of the cascade microring, which will greatly reduce the performance of the tunable laser. The transmittance difference between the main mode and the side mode of the cascade microring is usually caused by the difference in the refractive index of the cascade microring. When the refractive index increases, the transmittance difference will increase accordingly. On the other hand, due to the large nonlinear coefficient of silicon materials, nonlinear effects (such as two-photon absorption) will limit the output power of the tunable laser.

[0004] In view of this, overcoming the defects of the prior art is an urgent problem to be solved in the field of this technology. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the problem that the existing cascaded micro-ring external cavity tunable laser cannot take into account both the large wavelength adjustment range and the high transmittance difference between the main mode and the side mode of the cascaded micro-ring; and to overcome the problem that the nonlinear coefficient of silicon material is large and the nonlinear effect limits the output power of the tunable laser.

[0006] The present invention adopts the following technical solution:

[0007] To solve the above problems, the present invention provides a silicon-based integrated external cavity tunable laser based on microring interference, comprising: a filter chip 1, wherein the filter chip 1 comprises an optical waveguide 10, a first microring resonator 12, a second microring resonator 13, a first beam splitter and combiner 110, a second beam splitter and combiner 111 and a third beam splitter and combiner 112;

[0008] The common waveguide of the first beam splitter and combiner 110 is connected to the optical waveguide 10, one of the branch waveguides of the first beam splitter and combiner 110 is connected to the common waveguide of the second beam splitter and combiner 111, and the other branch waveguide of the first beam splitter and combiner 110 is connected to the common waveguide of the third beam splitter and combiner 112;

[0009] The first microring resonator 12 is disposed between two branch waveguides of the second beam splitter / combiner 111 , and the second microring resonator 13 is disposed between two branch waveguides of the third beam splitter / combiner 112 .

[0010] Preferably, the silicon-based integrated external cavity tunable laser based on micro-ring interference further includes a gain chip 3, the gain chip 3 is connected to the filter chip 1 via a transmission medium, and the gain chip 3 is used to generate laser.

[0011] Preferably, the transmission medium is a pattern spot converter 4.

[0012] Preferably, one side of the gain chip 3 connected to the filter chip 1 is coated with an anti-reflection film to reduce reflection, and the other side of the gain chip 3 is coated with a reflective film to establish a standing wave condition.

[0013] Preferably, the silicon-based integrated external cavity tunable laser based on microring interference further includes a control chip 2, the gain chip 3 is connected to the control chip 2, and the control chip 2 is used to increase current to the gain chip 3 to generate laser gain.

[0014] Preferably, the filter chip 1 is made of one of silicon on insulator, silicon germanium, indium phosphide or gallium arsenide.

[0015] Preferably, when the filter chip 1 is made of silicon on insulator, the filter chip 1 includes silicon dioxide upper and lower cladding layers 14, a silicon waveguide device layer 15, a bottom silicon substrate layer 16 and a heater 17, the silicon dioxide upper and lower cladding layers 14 are arranged on the bottom silicon substrate layer 16, the silicon waveguide device layer 15 is wrapped in the silicon dioxide upper and lower cladding layers 14, the heater 17 is located on the upper surface of the silicon dioxide upper and lower cladding layers 14, and the heater 17 is connected to the control chip 2;

[0016] The optical waveguide 10 , the first beam splitter / combiner 110 , the second beam splitter / combiner 111 , the third beam splitter / combiner 112 , the first microring resonator 12 , and the second microring resonator 13 are arranged on the silicon waveguide device layer 15 .

[0017] Preferably, the coupling point of the first microring resonator 12 along the two branch waveguides of the second beam splitter / combiner 111 is symmetrical to the line connecting the center point of the first microring resonator 12, and the coupling point of the second microring resonator 13 along the two branch waveguides of the third beam splitter / combiner 112 is symmetrical to the line connecting the center point of the second microring resonator 13.

[0018] Preferably, the first beam splitter / combiner 110 splits the optical signal into the second beam splitter / combiner 111 and the third beam splitter / combiner 112 in equal phases at a ratio of 1:1.

[0019] Preferably, the optical waveguide 10 is in a zigzag shape or a spiral shape.

[0020] The beneficial effects of the present invention are as follows: On the first aspect, the present invention connects two independent Sagnac interferometers in parallel by combining the first microring resonator 12 and the second beam splitter / combiner 111 to form a Sagnac interferometer, and combining the second microring resonator 13 and the third beam splitter / combiner 112 to form another Sagnac interferometer, thereby expanding the adjustment range of the laser wavelength.

[0021] And in the preferred embodiment, the filter chip 1 is heated by the control chip 2, and the refractive index of the first microring resonator 12 and the second microring resonator 13 changes due to the thermo-optical effect. The refractive index increases with the increase of temperature, thereby increasing the transmittance difference of the microring resonator.

[0022] Secondly, by setting the second beam splitter and combiner 111 and the third beam splitter and combiner 112 as secondary beam splitters and combiners to receive the optical signal of the first beam splitter and combiner 110, the optical power is reduced by 1 / 2 each time after splitting, and the optical power is reduced by 1 / 4 after the second beam splitter and combiner 111 and the third beam splitter and combiner 112. Since the nonlinear effect is proportional to the square of the optical power, after two splittings, the nonlinear effect will be reduced to 1 / 16 of the traditional structure, and 16 times the output power can be obtained under the same conditions.

[0023] In a preferred embodiment, by configuring the optical waveguide 10 to be in a zigzag or spiral shape, the length of the optical waveguide 10 is lengthened within a limited space. The longer the optical waveguide 10 is, the longer the cavity length of the laser is. The longer the cavity length is, the narrower the light width output by the laser is. At the same time, since the area occupied by the optical waveguide 10 is smaller, the heating area of ​​the optical waveguide 10 is smaller, thereby reducing the power consumption, thereby achieving the requirement of reducing the energy consumption of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a schematic diagram of the overall structure of a silicon-based integrated external cavity tunable laser based on micro-ring interferometry provided by an embodiment of the present invention;

[0026] Figure 2 It is a cross-sectional schematic diagram of a filter chip made of silicon on insulator of a silicon-based integrated external cavity tunable laser based on microring interference provided by an embodiment of the present invention;

[0027] Figure 3 It is a schematic diagram of the symmetrical structure of a first microring resonator and a second microring resonator of a silicon-based integrated external cavity tunable laser based on microring interference provided by an embodiment of the present invention;

[0028] Figure 4 is a schematic structural diagram of a conventional external cavity tunable laser based on a cascaded micro-ring structure provided by an embodiment of the present invention;

[0029] Figure 5 It is a schematic diagram of the combined free spectral range of a conventional external cavity tunable laser based on a cascaded micro-ring structure and a silicon-based integrated external cavity tunable laser based on micro-ring interference provided by an embodiment of the present invention;

[0030] Figure 6 It is a schematic diagram of the joint free spectral range of a silicon-based integrated external cavity tunable laser based on microring interferometry provided in an embodiment of the present invention.

[0031] Wherein, the accompanying drawings are marked as follows:

[0032] 1-filter chip, 10-optical waveguide, 110-first beam splitter and combiner, 111-second beam splitter and combiner, 112-third beam splitter and combiner, 12-first microring resonator, 13-second microring resonator, 14-silicon dioxide upper and lower claddings, 15-silicon waveguide device layer, 16-bottom silicon substrate layer, 17-heater, 2-control chip, 3-gain chip, 4-mode spot converter. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] In the description of the present invention, the orientation or position relationship indicated by the terms "upper" and "lower" is based on the orientation or position relationship shown in the drawings and is only for the convenience of describing the present invention rather than requiring the present invention to be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0035] The terms "first", "second", etc. in the present invention are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0036] In the present invention, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, the term "coupling" can be a way of achieving electrical connection for signal transmission.

[0037] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Embodiment 1:

[0039] Embodiment 1 of the present invention provides a silicon-based integrated external cavity tunable laser based on micro-ring interferometry, such as Figure 1 As shown, it includes: a filter chip 1, the filter chip 1 includes an optical waveguide 10, a first microring resonator 12, a second microring resonator 13, a first beam splitter and combiner 110, a second beam splitter and combiner 111 and a third beam splitter and combiner 112; wherein the optical waveguide 10 is one of a zigzag line shape and a spiral line shape. Specifically, in an actual application scenario, a heater 17 (such as Figure 2As shown in the figure, the main purpose of the heater 17 is to heat the optical waveguide 10, the first microring resonator 12 and the second microring resonator 13. The silicon-based integrated external cavity tunable laser based on microring interference also includes a control chip 2, and the control chip 2 is electrically connected to the heater 17 to control the heating temperature and duration of the heater 17. The area where the optical waveguide 10 is located is a phase modulation area. The optical waveguide 10 receives the optical signal transmitted from the gain chip 3 and performs phase modulation on the optical signal. The purpose of phase modulation is to change the effective optical path of the entire laser cavity so as to change the output wavelength of the laser. The purpose of heating the phase modulation zone is that, firstly, heating the phase modulation zone can change the refractive index of its optical waveguide 10, thereby achieving precise control of the laser output phase, which is crucial for the stable operation of the laser and meeting the requirements of specific applications; secondly, by heating the phase modulation zone, the beam quality can also be improved. When the beam passes through the heated phase modulation zone, the coherence of the beam can be improved, thereby making the output laser beam more stable and of high quality; thirdly, heating the phase modulation zone can also improve the optical efficiency. When the beam passes through the heated phase modulation zone, the energy conversion efficiency of the beam can be improved, thereby making the output laser energy more concentrated and efficient.

[0040] In addition, the purpose of the heater 17 heating the first microring resonator 12 and the second microring resonator 13 is to achieve output wavelength adjustment of the external cavity tunable laser. When current flows through the heater 17, the temperature of the heater 17 and the surrounding materials increases, and the refractive index of the first microring resonator 12 and the second microring resonator 13 changes due to the thermo-optical effect. The refractive index increases when the temperature increases, and decreases when the temperature decreases. This change in the refractive index causes the resonant frequency of the first microring resonator 12 and the second microring resonator 13 to shift. When the refractive index increases, the propagation speed of light in the microring resonator will slow down, resulting in a decrease in the resonant frequency; when the refractive index decreases, the propagation speed of light in the microring resonator will increase, resulting in an increase in the resonant frequency, thereby controlling the resonant frequency of the laser.

[0041] The common waveguide of the first beam splitter and combiner 110 is connected to the optical waveguide 10, one of the branch waveguides of the first beam splitter and combiner 110 is connected to the common waveguide of the second beam splitter and combiner 111, and the other branch waveguide of the first beam splitter and combiner 110 is connected to the common waveguide of the third beam splitter and combiner 112; the first microring resonator 12 is arranged between the two branch waveguides of the second beam splitter and combiner 111, and the second microring resonator 13 is arranged between the two branch waveguides of the third beam splitter and combiner 112. Specifically, the first beam splitter and combiner 110 is connected to the optical waveguide 10, that is, the first beam splitter and combiner 110 is connected to the phase modulation zone. The function of the beam splitter is to divide the input optical signal into two or more paths. Here, the first beam splitter and combiner 110 divides the optical signal passing through the phase modulation zone into two paths. The two branch waveguides are connected to the common waveguide of the first beam splitter and combiner 110, and are respectively connected to the second beam splitter and combiner 111 and the third beam splitter and combiner 112. The first microring resonator 12 and the second beam splitter and combiner 111 form a Sagnac interferometer, and the second microring resonator 13 and the third beam splitter and combiner 112 form a Sagnac interferometer. The Sagnac interferometer can perform frequency selection or filtering on the optical signal. The return light of the two independent Sagnac interferometers is combined through the first beam splitter and combiner 110. The interference in the input optical waveguide 10 further improves the coherence of the laser.

[0042] To summarize, in the first aspect, the present invention connects two independent Sagnac interferometers in parallel by combining the first microring resonator 12 and the two beam splitters 111 into a Sagnac interferometer, and combining the second microring resonator 13 and the third beam splitter 112 into another Sagnac interferometer, thereby expanding the adjustment range of the laser wavelength.

[0043] And in the preferred embodiment, the filter chip 1 is heated by the control chip 2, and the refractive index of the first microring resonator 12 and the second microring resonator 13 changes due to the thermo-optical effect. The refractive index increases with the increase of temperature, thereby increasing the transmittance difference of the microring resonator.

[0044] Secondly, by setting the second beam splitter and combiner 111 and the third beam splitter and combiner 112 as secondary beam splitters and combiners to receive the optical signal of the first beam splitter and combiner 110, the optical power is reduced by 1 / 2 each time after splitting, and the optical power is reduced by 1 / 4 after the second beam splitter and combiner 111 and the third beam splitter and combiner 112. Since the nonlinear effect is proportional to the square of the optical power, after two splittings, the nonlinear effect will be reduced to 1 / 16 of the traditional structure, and 16 times the output power can be obtained under the same conditions.

[0045] In a preferred embodiment, by configuring the optical waveguide 10 to be in a zigzag or spiral shape, the length of the optical waveguide 10 is lengthened within a limited space. The longer the optical waveguide 10 is, the longer the cavity length of the laser is. The longer the cavity length is, the narrower the light width output by the laser is. At the same time, since the area occupied by the optical waveguide 10 is smaller, the heating area of ​​the optical waveguide 10 is smaller, thereby reducing the power consumption, thereby achieving the requirement of reducing the energy consumption of the laser.

[0046] In order to illustrate the complete solution provided by the embodiment of the present invention, the details of the above solution are further described below.

[0047] With respect to the filter chip 1 and the control chip 2, the silicon-based integrated external cavity tunable laser based on microring interference further includes a gain chip 3, which is connected to the filter chip 1 through a transmission medium, and is used to generate laser light; specifically, the transmission medium is a mode spot converter 4. The gain chip 3 and the filter chip 1 together constitute a laser, and usually the two mode field sizes of the outgoing light of the gain chip 3 and the light entering the filter chip 1 are inconsistent. The mode spot converter 4 couples as much light emitted by the gain chip 3 as possible into the filter chip 1 to reduce light loss by providing a light mode spot size that matches the rear end face of the gain chip 3.

[0048] In order to improve the efficiency of the laser, the side of the gain chip 3 connected to the filter chip 1 is coated with an anti-reflection film to reduce reflection, and the other side of the gain chip 3 is coated with a reflective film to establish a standing wave condition. The anti-reflection film is mainly used to reduce the reflection of light, thereby improving the penetration of light in the gain chip 3. In the laser, light reflects back and forth in the gain chip 3, and light loss will be generated in this process. In order to reduce light loss, in one embodiment, an anti-reflection film can be coated on the side of the gain chip 3 connected to the filter chip 1, so that the light can better penetrate the gain chip 3, thereby improving the efficiency of the laser. On the other hand, the reflective film is mainly used to establish a standing wave condition. In the laser, a standing wave refers to light reflecting back and forth in the gain chip 3, but the total energy remains unchanged. This standing wave condition can help the laser produce a more stable and powerful laser output. In order to establish a standing wave condition, a reflective film can be coated on the other side of the gain chip 3, so that the light reflects back and forth in the gain chip 3, thereby forming a standing wave.

[0049] In order to control the laser output of the gain chip 3 and realize real-time monitoring and stable control of the gain chip 3, the silicon-based integrated external cavity tunable laser based on micro-ring interference also includes a control chip 2, and the gain chip 3 is connected to the control chip 2, and the control chip 2 is used to add current to the gain chip 3 to generate laser gain. In order to achieve laser gain, the control chip 2 needs to provide appropriate current and voltage to the gain chip 3. When the current passes through the gain chip 3, the electrons will transition from a high energy level to a low energy level and release energy. The energy is absorbed by photons and converted into laser output. The control chip 2 can control the output power and wavelength of the laser by adjusting the magnitude and frequency of the current.

[0050] In one embodiment, the filter chip 1 is made of one of silicon on insulator, silicon germanium, indium phosphide or gallium arsenide. Preferably, when the filter chip 1 is made of silicon on insulator, Figure 2 As shown, it is a cross-sectional view of the filter chip 1, that is, Figure 1 for Figure 2 The filter chip 1 includes upper and lower silicon dioxide claddings 14, a silicon waveguide device layer 15, a bottom silicon substrate layer 16 and a heater 17. The upper and lower silicon dioxide claddings 14 are arranged on the bottom silicon substrate layer 16, the silicon waveguide device layer 15 is wrapped in the upper and lower silicon dioxide claddings 14, the heater 17 is located on the upper surface of the upper and lower silicon dioxide claddings 14, and the heater 17 is connected to the control chip 2; the optical waveguide 10, the first beam splitter and combiner 110, the second beam splitter and combiner 111, the third beam splitter and combiner 112, the first microring resonator 12 and the second microring resonator 13 are arranged on the silicon waveguide device layer 15. The advantages of choosing silicon on insulator as the material of the filter chip 1 are that silicon on insulator has excellent thermal stability and chemical stability, can adapt to high temperature and harsh environment, and thus can achieve higher reliability and longer service life; silicon on insulator has a lower dielectric constant, which can reduce the size of the filter, thereby reducing the volume of the entire system; silicon on insulator has a higher thermal conductivity, which can quickly dissipate the heat generated by the chip, thereby ensuring the stable performance of the chip; silicon on insulator has lower stress, which can reduce the risk of damage to the chip during packaging and use; silicon on insulator has good chemical inertness and can resist corrosion from various chemical substances, thereby ensuring the long-term stability and reliability of the chip.

[0051] In order to improve the symmetry and stability of the light field of the microring resonator and achieve better coupling efficiency, the first microring resonator 12 and the second microring resonator 13 are symmetrical structures.

[0052] In one embodiment, Figure 3As shown in the figure on the left, the coupling point of the first microring resonator 12 along the two branch waveguides of the second beam splitter and combiner 111 is symmetrical with the line connecting the center point of the first microring resonator 12, and the coupling point of the second microring resonator 13 along the two branch waveguides of the third beam splitter and combiner 112 is symmetrical with the line connecting the center point of the second microring resonator 13.

[0053] In one embodiment, Figure 3 As shown in the right figure, the first microring resonator 12 and the second microring resonator 13 are symmetrical along the dotted line.

[0054] The purpose of the symmetrical design is to: enhance the symmetry of the light field. Since the geometric structure of the microring resonator is symmetrical along the line, the symmetry of the light is enhanced when it is reflected back and forth in the microring resonator. This symmetry helps to reduce the fluctuation and instability of the light field, thereby improving the coherence and stability of the light; achieve better coupling efficiency. Since the coupling points of the microring resonator and the branch waveguide are symmetrically distributed along the line, the coupling of light between the microring resonator and the branch waveguide is more uniform and efficient. This symmetry helps to reduce the loss and leakage of light energy and improve the utilization rate of light and the efficiency of the laser; it is easy to control the propagation direction of light. Since the geometric structure of the microring resonator is symmetrical, the propagation direction and mode of light can be more easily controlled. This symmetry helps to achieve better optical performance and more flexible optical control; improve the stability of optical elements. The symmetrical structure of the microring resonator along the line helps to improve the stability of optical elements. This symmetry enables the optical elements to maintain better stability and reliability when subjected to external interference (such as temperature changes, mechanical vibrations, etc.).

[0055] In the scheme of the embodiment of the present invention, expanding the adjustment range of the laser wavelength is one of the goals that the scheme of the embodiment of the present invention wants to achieve. In addition to forming two independent parallel Sagnac interferometers with the first microring resonator 12, the second microring resonator 13, the second beam splitter and combiner 111, and the third beam splitter and combiner 112, the first microring resonator 12 and the second microring resonator 13 have different radii. The reason for this design is that the microring resonator acts as a wavelength selector, which can reflect light of a specific wavelength back to the laser cavity and let light of other wavelengths pass through. If the radii of the two microring resonators are different, they will select different wavelengths, so that the laser can generate lasers of multiple wavelengths at the same time; in addition, when the radii of the two microring resonators are different, their resonant frequencies will also be different. Therefore, by changing the radius of the microring, the frequency of the laser can be changed.

[0056] In summary, the working principle of the silicon-based integrated external cavity tunable laser based on microring interference provided in the embodiment of the present invention is: the gain chip 3 emits the generated laser into the mode spot converter 4, the mode spot converter 4 matches the mode field of the output light of the gain chip 3 and the mode field size of the light in the filter chip 1, and the output light enters the optical waveguide 10 area for phase modulation; the modulated optical signal enters the first beam splitter and combiner 110, the first beam splitter and combiner 110 splits the optical signal in a 1:1 ratio to the second beam splitter and combiner 111 and the third beam splitter and combiner 112, and the Sagnac interferometer formed by the first microring resonator 12 and the second microring resonator 13 interferes with the optical signal to roughly adjust the wavelength of the optical signal; the roughly adjusted optical signal returns to the first beam splitter and combiner 110 after passing through the second beam splitter and combiner 111 and the third beam splitter and combiner 112, and reaches the phase modulation area of ​​the optical waveguide 10 for interference, and finely adjusts the wavelength of the optical signal, thereby adjusting the output wavelength of the laser.

[0057] Compared with the traditional external cavity tunable laser solution, the silicon-based integrated external cavity tunable laser solution based on micro-ring interference provided in the embodiment of the present invention has the following performance optimization effect.

[0058] In one embodiment, it is assumed that the light field coupled into the filter chip 1 by the gain chip 3 is The corresponding optical power is proportional to the square of the optical field intensity P 0 ∝|E 0 | 2 After passing through the two-stage beam splitter, the power of light in the branch waveguides of the first microring resonator 12 and the second microring resonator 13 is P = 1 / 4P 0 ∝1 / 4|E 0 | 2 In the traditional external cavity tunable laser based on cascade micro-ring structure (such as Figure 4 As shown), the optical power in the microring resonator branch waveguide is P 0 According to the fact that the two-photon absorption effect in the silicon waveguide is proportional to the square of the power, the two-photon absorption effect of the silicon-based integrated external cavity tunable laser based on microring interference provided by the embodiment of the present invention is 1 / 16 smaller than that of the traditional structure, which greatly suppresses the influence of the nonlinear effect of the silicon material.

[0059] In the conventional external cavity tunable laser based on cascaded micro-ring structure, the corresponding joint free spectral range is as follows Figure 5 As shown,

[0060]

[0061] FSR 1 and FSR 2 The distributions represent the free spectral ranges of the two microrings.

[0062] In one embodiment, it is assumed that the transmission coefficients of the two microring resonator filters are r 1 and r 2 , which includes the phase term. The combined transmission coefficient of the two microring resonators is 1 / 2*(r 1 +r 2 ), which is not only related to the transmittance of the two microring resonators, but also to the phase difference of the transmittance coefficients of the two microring filters. The transmittance coefficients of the two microring resonators at the peak can be expressed as:

[0063]

[0064]

[0065] Where n is the effective refractive index of the microring waveguide, λ is the resonant wavelength of the microring, and l 1 represents the distance difference between the two coupling points in the first microring resonator 12, l 2 represents the distance difference between the two coupling points in the second microring resonator 13. Define L 1 and L 2 denote the circumferences of the first microring resonator 12 and the second microring resonator 13 respectively, then the first peak point where the peaks of the first microring resonator 12 and the second microring resonator 13 are aligned satisfies:

[0066]

[0067]

[0068] Wherein, M and N are positive integers.

[0069] Furthermore, the adjacent second peak point satisfies:

[0070]

[0071]

[0072] Assume l 1 =L 1 / k,l 2 =L 2 / k, then the transmission coefficients of the first microring resonator 12 and the second microring resonator 13 at the first peak point are:

[0073]

[0074]

[0075] Similarly, the transmission coefficients of the first microring resonator 12 and the second microring resonator 13 at adjacent second peak points are:

[0076]

[0077]

[0078] From the above, it can be seen that the phase differences of the transmission coefficients of the micro-rings 106-1 and 106-2 at the two peak points are:

[0079]

[0080]

[0081] To make one of the two peak points in the interference addition state, i.e., φ=2π, and the other in the interference destructive state, i.e., φ=π, k=2 is required, that is, the first microring resonator 12 and the second microring resonator 13 are designed to be symmetrical structures. Under this design, the joint free spectrum range of the external cavity tunable laser based on the interference microring structure is as follows: Figure 6 As shown,

[0082]

[0083] Therefore, under the condition of the same FSR difference, compared with the traditional external cavity tunable laser based on the cascade micro-ring structure, the laser scheme provided by the embodiment of the present invention can obtain a combined free spectral range that is twice as large as that of the traditional scheme, that is, the laser obtains a larger wavelength adjustment range.

[0084] The silicon-based integrated external cavity tunable laser based on micro-ring interference provided in an embodiment of the present invention comprises a filter chip 1 and a gain chip 3 based on silicon photonics (silicon on insulator), wherein the gain chip 3 is a semiconductor structure (e.g., a III-V semiconductor diode structure), and the filter chip 1 and the gain chip 3 are interconnected to form a tunable laser. In practical application scenarios, the laser provided in an embodiment of the present invention has a large wavelength tunable range, can provide a variety of wavelength options, and is convenient for use in optical communication systems. In optical fiber communication, optical signals of different wavelengths can be transmitted in the same optical fiber to increase the transmission capacity of the communication system, increase the adjustment range of the laser wavelength, and realize the transmission of more optical signals of different wavelengths, further enhancing the transmission capacity of the optical communication system. And by using the external cavity tunable laser provided in an embodiment of the present invention, the output wavelength can be adjusted as needed, thereby avoiding wavelength drift caused by factors such as temperature and time, and improving the stability of the communication system.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A silicon-based integrated external cavity tunable laser based on microring interferometry. It is characterized in that include: A filter chip (1), the filter chip (1) comprising an optical waveguide (10), a first microring resonator (12), a second microring resonator (13), a first beam splitter / combiner (110), a second beam splitter / combiner (111), and a third beam splitter / combiner (112); The common waveguide of the first beam splitter / combiner (110) is connected to the optical waveguide (10), one of the branch waveguides of the first beam splitter / combiner (110) is connected to the common waveguide of the second beam splitter / combiner (111), and the other branch waveguide of the first beam splitter / combiner (110) is connected to the common waveguide of the third beam splitter / combiner (112); The first microring resonator (12) is arranged between two branch waveguides of the second beam splitter / combiner (111), and the second microring resonator (13) is arranged between two branch waveguides of the third beam splitter / combiner (112).

2. The silicon-based integrated external cavity tunable laser based on microring interferometry according to claim 1, It is characterized in that The silicon-based integrated external cavity tunable laser based on micro-ring interference further comprises a gain chip (3), wherein the gain chip (3) is connected to the filter chip (1) via a transmission medium, and the gain chip (3) is used to generate laser light.

3. The silicon-based integrated external cavity tunable laser based on microring interferometry according to claim 2, It is characterized in that The transmission medium is a pattern spot converter (4).

4. The silicon-based integrated external cavity tunable laser based on microring interferometry according to claim 2, It is characterized in that The side of the gain chip (3) connected to the filter chip (1) is coated with an anti-reflection film to reduce reflection, and the other side of the gain chip (3) is coated with a reflection film to establish standing wave conditions.

5. The silicon-based integrated external cavity tunable laser based on microring interferometry according to claim 2, It is characterized in that The silicon-based integrated external cavity tunable laser based on micro-ring interference further comprises a control chip (2), the gain chip (3) is connected to the control chip (2), and the control chip (2) is used to increase current to the gain chip (3) to generate laser gain.

6. The silicon-based integrated external cavity tunable laser based on microring interferometry according to claim 1, It is characterized in that The filter chip (1) is made of one of silicon on insulator, silicon germanium, indium phosphide or gallium arsenide.

7. The silicon-based integrated external cavity tunable laser based on micro-ring interferometry according to claim 6, It is characterized in that When the filter chip (1) is made of silicon on insulator, the filter chip (1) comprises silicon dioxide upper and lower cladding layers (14), a silicon waveguide device layer (15), a bottom silicon substrate layer (16) and a heater (17); the silicon dioxide upper and lower cladding layers (14) are arranged on the bottom silicon substrate layer (16); the silicon waveguide device layer (15) is wrapped in the silicon dioxide upper and lower cladding layers (14); the heater (17) is located on the upper surface of the silicon dioxide upper and lower cladding layers (14); and the heater (17) is connected to the control chip (2); The optical waveguide (10), the first beam splitter / combiner (110), the second beam splitter / combiner (111), the third beam splitter / combiner (112), the first microring resonator (12) and the second microring resonator (13) are arranged on the silicon waveguide device layer (15).

8. The silicon-based integrated external cavity tunable laser based on microring interferometry according to any one of claims 1 to 7, It is characterized in that The coupling point of the first microring resonator (12) along the two branch waveguides of the second beam splitter / combiner (111) is symmetrical to the line connecting the center point of the first microring resonator (12), and the coupling point of the second microring resonator (13) along the two branch waveguides of the third beam splitter / combiner (112) is symmetrical to the line connecting the center point of the second microring resonator (13).

9. The silicon-based integrated external cavity tunable laser based on microring interferometry according to any one of claims 1 to 7, It is characterized in that The first beam splitter / combiner (110) splits the optical signal into the second beam splitter / combiner (111) and the third beam splitter / combiner (112) in equal phases at a ratio of 1:

1.

10. The silicon-based integrated external cavity tunable laser based on microring interferometry according to any one of claims 1 to 7, It is characterized in that The optical waveguide (10) is in a zigzag shape or a spiral shape.

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