An optical delay line with optical switch assisted by an adjustable reflection ring

Abstract

The present invention proposes an optical delay line switched by an optical switch assisted by an adjustable reflection ring, which belongs to the field of optical communication and microwave photonic technology. The present invention includes a symmetrical Mach-Zehnder interferometer optical switch, an adjustable reflection ring and an optical circulator. By switching the port for light transmission and the port for reflection by the reflection ring through the optical switch, light is transmitted in delay waveguides of different lengths, and finally optical signals of different delay states are output. Among them, the optical path switching part changes the phase difference between the two arms of the interferometer through a phase shifter, thereby realizing the function of path selection. The present invention is suitable for optical cache, optical true delay network, optically controlled phased array technology, etc., and has the advantages of large delay adjustment range, compact size, simple structure, etc.

Description

Technical Field

[0001] The invention relates to an adjustable delay line, in particular to an optical switch-type optical delay line based on an adjustable reflection ring auxiliary, and belongs to the technical field of optical communication and microwave photon. Background Art

[0002] Adjustable optical delay lines are key units of microwave photonic systems such as optically controlled phased array radars. At present, adjustable optical delay lines are mainly divided into two categories: dispersive delay lines and routing delay lines. Dispersive delay lines usually use structures such as optical resonators, chirped gratings, and photonic crystals to change the waveguide dispersion. By changing the group refractive index of the device at the resonant wavelength, the delay is adjusted using the slow light effect. This solution often has large insertion loss and the delay is difficult to adjust significantly. Routing delay lines control the transmission path of the signal in the optical switch and switch the optical signal to propagate in waveguides of different lengths, thereby achieving adjustable optical signal delay, moderate insertion loss, and a large adjustable delay range.

[0003] The main drawback of routed delay lines is that the device area is large. In application scenarios that require multi-path delay, this drawback will become more obvious if the delay level is simply increased. Since it is a true optical delay line, the required delay amount determines the length of the delay waveguide. In application scenarios that require a wide range of adjustable delay amounts, a longer waveguide will affect the size, loss, and layout design of the device. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an adjustable optical delay line that can meet the requirements of wide range adjustable delay, compact size, high precision, etc.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] An optical switch switching optical delay line based on an adjustable reflection ring auxiliary includes an input port, two output ports, and N-level reflection delay units connected in sequence, N≥2, each level of reflection delay unit includes an optical switch, an adjustable reflection ring, a delay waveguide, and has two ports, the optical switch has four ports, and the adjustable reflection ring has two ports; in each level of reflection delay unit, the optical path sequentially passes through the first port of the reflection delay unit, the first port of the optical switch, the interior of the optical switch, the third port of the optical switch, the delay waveguide, the first port of the adjustable reflection ring, the interior of the adjustable reflection ring, the second end of the adjustable reflection ring port, the fourth port of the optical switch, the inside of the optical switch, the second port of the optical switch, and the second port of the reflection delay unit; the two ports of the odd-numbered reflection delay units are respectively connected to an optical circulator, and the two optical circulators form a group; the two ports of the even-numbered reflection delay units are respectively connected to the optical circulators of the corresponding ports of the previous odd-numbered reflection delay units, so that the two reflection delay units form a delay loop; each group of two optical circulators is also connected to the next group of two optical circulators in a one-to-one correspondence; one optical circulator in the first group is connected to the input port, and the two optical circulators in the last group are respectively connected to an output port.

[0007] Furthermore, the optical switch is a Mach-Zehnder optical switch structure, including a phase shifter and two couplers with a splitting ratio of 50:50, and the splitting ratio of the third port and the fourth port of the optical switch can be changed by adjusting the phase shifter.

[0008] Furthermore, the adjustable reflection ring is based on a Mach-Zehnder optical switch structure, and its third port and fourth port are connected by a waveguide; the reflectivity of light in the two ports of the adjustable reflection ring can be changed by adjusting the phase shifter.

[0009] Furthermore, the phase shifter is realized by using the thermo-optic effect, electro-optic effect or magneto-optic effect of the optical waveguide.

[0010] Furthermore, the two couplers with a splitting ratio of 50:50 are implemented by a directional coupler with a splitting ratio of 50:50, an adiabatic coupler with a splitting ratio of 50:50, or a multimode interference coupler with a splitting ratio of 50:50.

[0011] Furthermore, in the optical switch, light is input from the first port, and the phase shifter in the optical switch is adjusted. When the phase difference between the two arms is π, the light is completely output from the third port. When the phase difference between the two arms is 0, the light is completely output from the fourth port.

[0012] Furthermore, in the adjustable reflection ring, light is input from the first port, and the phase shifter in the adjustable reflection ring is adjusted. When the phase difference between the two arms is π / 2, the light is completely reflected from the first port, and when the phase difference between the two arms is 0, the light is completely reflected from the second port.

[0013] Furthermore, in the optical circulator, if the light is sent from the input port or the previous delay loop, it is output to the odd-numbered reflection delay unit of the current delay loop; if the light is sent from the odd-numbered reflection delay unit of the current delay loop, it is output to the even-numbered reflection delay unit of the current delay loop; if the light is sent from the even-numbered reflection delay unit of the current delay loop, it is output to the next delay loop.

[0014] Furthermore, the length of the delay waveguide in the Nth stage reflection delay unit is (3 N-1 )*ΔL, ΔL corresponds to the minimum delay Δt.

[0015] The beneficial effects of the present invention are:

[0016] 1. Compared with the traditional optical switch-type delay line, the present invention multiplexes each level of delay unit through the reflection ring, greatly increasing the utilization efficiency of the delay waveguide.

[0017] 2. For the same cascade number and the same total length of the delay waveguide, the present invention can obtain a wider range of adjustable delay amounts.

[0018] 3. The present invention is applicable to optical cache, optical true delay network, optically controlled phased array technology, etc., and has the advantages of large delay adjustment range, compact size, simple structure, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of an N-stage delay line according to an embodiment of the present invention.

[0020] Figure 2 Schematic diagram of the structure and function of the Mach-Zehnder optical switch according to an embodiment of the present invention.

[0021] Figure 3 It is a structural schematic diagram and a functional schematic diagram of an adjustable reflection ring according to an embodiment of the present invention.

[0022] Figure 4 Schematic diagram of the structure of a three-port optical circulator and a four-port optical circulator according to an embodiment of the present invention.

[0023] Figure 5 Schematic diagram of the structure of a two-stage delay line according to an embodiment of the present invention.

[0024] Figure 6 The structure and light field distribution of the waveguide used in the two-stage delay line embodiment of the present invention

[0025] Figure 7 The table of power applied to the phase shifter and delay state of the two-stage delay line according to the embodiment of the present invention.

[0026] Figure 8It is the time domain simulation output response of the two-stage delay line of the embodiment of the present invention.

[0027] Fig. 9 Schematic diagram of the secondary structure of the traditional cascade optical switch type optical delay line and the time domain simulation output response.

[0028] Fig.10 Schematic diagram of the N-stage delay line structure when N is an odd number.

[0029] In the figure, a, b, and c are the three ports of the three-port optical circulator, d, e, f, and g are the four ports of the four-port optical circulator; ①, ②, ③, and ④ are the four ports of the optical circulator 1, ⑤, ⑥, ⑦, and ⑧ are the four ports of the optical switch 1, ⑨ and ⑩ are the two ports of the adjustable reflection ring 1, They are the three ports of optical circulator 2. They are the four ports of optical switch 2. They are respectively two ports of the adjustable reflection ring 2. DETAILED DESCRIPTION

[0030] In order to deepen the understanding of the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and in combination with specific embodiments.

[0031] An optical delay line switching type based on an adjustable reflection ring has an N-level structure, including N 2×2 Mach-Zehnder optical switches, N adjustable reflection rings, N delay waveguides of different lengths and N optical circulators. The 2×2 Mach-Zehnder optical switch is composed of two 2×2 50:50 couplers, two-arm optical waveguides of equal length and a phase shifter, wherein the phase shifter can achieve a π phase shift; the adjustable reflection ring connects port 3 and port 4 of the 2×2 optical switch with a waveguide, wherein the phase shifter can achieve a π / 2 phase shift. The optical switch switches the port for light transmission and the port for reflection of the reflection ring, so that light is transmitted in delay waveguides of different lengths, and finally outputs optical signals of different delay states. The optical path switching part changes the phase difference between the two arms of the interferometer through the phase shifter, thereby realizing the function of path selection.

[0032] The delay path of each delay line is different. The lengths of the delay waveguides from the first to the Nth level are ΔL, 3ΔL, …, 3 N-1 ·ΔL, the corresponding delays are Δt, 3Δt, ..., 3 N-1 ·Δt, ΔL corresponds to the minimum delay Δt. The delay waveguide is connected to the 2×2 optical switch and the adjustable reflection ring, so that different transmission paths of the optical signal are selected by switching the optical switch, and the delay state is switched to achieve different delay amounts.

[0033] Figure 1 The figure is a schematic diagram of the structure of an N-stage delay line. It includes a schematic diagram of the overall structure of an N-stage delay line and a schematic diagram of an N-stage delay unit. Every two delay units share two optical circulators. Except for the three-port optical circulators at the non-input end of the two optical circulators in the first stage, the other optical circulators are all four-port optical circulators. The structure of each delay unit is similar, including an optical switch, a delay waveguide and an adjustable reflection ring. The length of the delay waveguide in each stage is different, and the rest of the structures are the same. The length of the delay waveguide in the N-stage delay unit is 3 N-1 ·ΔL, ΔL corresponds to a minimum delay of Δt. By switching the optical switch to select different waveguide transmission paths and reflection paths of the reflection ring, the delay state is switched to achieve different delay amounts.

[0034] Figure 2 The diagram is a schematic diagram of the structure and function of a Mach-Zehnder optical switch. The Mach-Zehnder optical switch structure includes port 1, port 2, port 3, port 4, two couplers with a splitting ratio of 50:50, and a phase shifter; if the phase shifter is implemented using the thermo-optic effect or electro-optic effect of the waveguide, the effective refractive index of the local waveguide can be changed by applying an external voltage, thereby changing the phase difference of the two-arm waveguide, thereby achieving the purpose of changing the splitting ratio of port 3 and port 4 of the optical switch; the optical switch device, when light is input from port 1, adjusts the phase shifter in the optical switch, and when the phase difference between the two arms is π, the light will be completely output from port 3, and when the phase difference between the two arms is 0, the light will be completely output from port 4. Figure 2 The relationship between the transmittance of port 3 and port 4 and the phase difference between the two arms is shown in FIG.

[0035] Figure 3 The diagram is a schematic diagram of the structure and function of an adjustable reflection ring. The adjustable reflection ring is based on an optical switch structure, and its port 3 and port 4 are connected by a waveguide; the reflectivity of the light in the adjustable reflection ring port A and port B can be changed by adjusting the phase shifter; the adjustable reflection ring device, when light is input from port A, adjust the phase shifter in the adjustable reflection ring, when the phase difference between the two arms is π / 2, the light will be completely reflected from port A, and when the phase difference between the two arms is 0, the light will be completely reflected from port B. Figure 3 The relationship between the reflectivity of port A and port B and the phase difference between the two arms is shown in FIG.

[0036] Figure 4 The diagram is a schematic diagram of the structure of a three-port optical circulator and a four-port optical circulator. When the optical circulator has three ports, if light is input from port a, it is output from port b, and if light is input from port b, it is output from port c; when the optical circulator has four ports, if light is input from port d, it is output from port e, if light is input from port e, it is output from port f, and if light is input from port f, it is output from port g.

[0037] Embodiment 1:

[0038] Taking the two-stage delay line structure as an example, Figure 5 Schematic diagram of a two-stage delay line structure. The two-stage delay line structure includes an input port, output port 1, output port 2, optical switch 1, optical switch 2, adjustable reflection ring 1, adjustable reflection ring 2, optical circulator 1, optical circulator 2, a delay waveguide with a length of ΔL and a delay waveguide with a length of 3ΔL. ΔL corresponds to a minimum delay of Δt.

[0039] The waveguide used in this example is a double-strip silicon nitride waveguide, and the waveguide cross-sectional structure is as follows: Figure 6 As shown, the waveguide width W is 1.2μm, the thickness H is 170nm, the vertical spacing Gap is 500nm, and SiO2 is filled in between. Finite element analysis is used and MODE tool is used for simulation. At a wavelength of 1.55um, the effective refractive index neff of the waveguide is 1.756 and the group refractive index ng is 2.212.

[0040] Using the formula Δt=(ng·ΔL) / c, where c is the speed of light, it is calculated that when the delay Δt is 10ps, the corresponding length of the delay waveguide ΔL is 1.356mm and 3ΔL is 4.068mm.

[0041] The coupler used in the optical switch in this example is assumed to have an ideal 50:50 uniform splitting ratio in the simulation.

[0042] The phase shifter used in this example of optical switch is realized by the thermo-optical effect of waveguide. By applying voltage externally, the effective refractive index of the local waveguide is changed, thereby changing the phase difference between the two arm waveguides, and then changing the transmission path and reflection path of the light to obtain different combinations of delay states. In the simulation, it is assumed that the electric power P applied to achieve the π phase shift is π The applied power P is 100mW to achieve a π / 2 phase shift. π / 2 is 50mW.

[0043] In this example, Lumerical's INTERCONNECT tool is used to perform time domain simulation of the entire circuit. The input pulse is a hyperbolic secant pulse with a repetition frequency of 10 GHz and a time domain simulation accuracy of 10 fs. When different powers are applied to each phase shifter, the time domain pulse response of the output port at different delay states.

[0044] Figure 7 is the delay state table of the secondary delay line. π The electrical power to be applied to obtain a π phase shift, P π / 2 is the electric power to be applied to obtain a π / 2 phase shift. The two-stage delay line can achieve a total of 9 delay states of 0 to 80 ps (delay step 10 ps), and the external electric powers of the optical switch 1, optical switch 2, adjustable reflection ring 1 and adjustable reflection ring 2 corresponding to these 9 delay states are listed in the table.

[0045] When the light transmission path is When , the light is output at output port 2, and the delay state is S1, which is equivalent to not passing through the delay waveguide, and the corresponding delay amount is 0.

[0046] When the light transmission path is When , the light is output at output port 1, the delay state is S2, and the corresponding delay amount is Δt, which is 10ps.

[0047] When the light transmission path is When , the light is output at output port 2, the delay state is S3, and the corresponding delay amount is 2Δt, that is, 20ps.

[0048] When the light transmission path is When , the light is output at output port 1, the delay state is S4, and the corresponding delay amount is 3Δt, that is, 30ps.

[0049] When the light transmission path is When , the light is output at output port 2, the delay state is S5, and the corresponding delay amount is 4Δt, that is, 40ps.

[0050] When the light transmission path is When , the light is output at output port 1, the delay state is S6, and the corresponding delay amount is 5Δt, that is, 50ps.

[0051] When the light transmission path is When , the light is output at output port 2, the delay state is S7, and the corresponding delay amount is 6Δt, that is, 60ps.

[0052] When the light transmission path is When , the light is output at output port 1, the delay state is S8, and the corresponding delay amount is 7Δt, that is, 70ps.

[0053] When the light transmission path is When , the light is output at output port 2, the delay state is S9, and the corresponding delay amount is 8Δt, that is, 80ps.

[0054] As described above, through the control of the optical switch and the adjustable reflection ring, a total of 9 delay states S1 to S9 can be obtained in the two-stage delay line structure, and the total length of the required delay waveguide is 4ΔL.

[0055] Figure 8 The above analysis of the 9 delay states S1 to S9, including the four delay states of Δt, 3Δt, 5Δt, and 7Δt of output port 1 and the five delay states of 0, 2Δt, 4Δt, 6Δt, and 8Δt of output port 2, are all shown in Figure 8 middle.

[0056] Fig.10 Schematic diagram of the N-stage delay line structure when N is an odd number. In this case, the last stage is a combination of a reflection delay unit and two optical circulators, and the last stage optical circulator is a three-port optical circulator.

[0057] Fig. 9 The diagram is a schematic diagram of the secondary structure of the conventional cascade optical switch switching optical delay line and the time domain simulation output response, which is used for comparison with the secondary delay line of the present invention. The waveguide used in the simulation is also a double-strip silicon nitride waveguide, the length of the delay waveguide ΔL is 1.356mm, and the corresponding delay Δt is 10ps; assuming that the electrical power P applied by the phase shifter in each optical switch to achieve a π phase shift π The power is also 100mW; the coupler used is also assumed to be an ideal 50:50 uniform split ratio. The traditional two-stage cascade optical switch switching optical delay line can achieve a total of 4 delay states of 0 to 30ps (delay step 10ps) by switching the light transmission path through the optical switch.

[0058] It can be seen that the present invention can realize 9 delay states of 0 to 8 Δt (delay step Δt) for the same two-stage cascade structure, while the traditional two-stage structure can realize 4 delay states of 0 to 3 Δt (delay step Δt). If expanded to N stages, the N-stage delay line structure of the present invention requires [(3 N -1) / 2]*ΔL, when light enters the N-stage delay line from the input port, the optical switch and adjustable reflection ring of each stage are set to different states, which can achieve 0~(3 N -1)*Δt, the delay step is Δt for a total of 3 N The traditional cascade optical switch type optical delay line can achieve 2 N It can be seen that under the conditions of the same cascade number and the same delay accuracy, the present invention achieves a larger delay adjustment range.

Claims

1. An optical delay line with an optical switch assisted by an adjustable reflective ring, characterized in that: The invention comprises an input port, two output ports, and N-stage reflection delay units connected in sequence, N≥2, each stage of reflection delay unit comprises an optical switch, an adjustable reflection ring, a delay waveguide, and has two ports, the optical switch has four ports, and the adjustable reflection ring has two ports; in each stage of reflection delay unit, the optical path passes through the first port of the reflection delay unit, the first port of the optical switch, the interior of the optical switch, the third port of the optical switch, the delay waveguide, the first port of the adjustable reflection ring, the interior of the adjustable reflection ring, the second port of the adjustable reflection ring, the fourth port of the optical switch, the optical The inside of the switch, the second port of the optical switch, and the second port of the reflection delay unit; the two ports of the odd-numbered reflection delay unit are respectively connected to an optical circulator, and the two optical circulators form a group; the two ports of the even-numbered reflection delay unit are respectively connected to the optical circulators of the corresponding ports of the previous odd-numbered reflection delay unit, so that the two reflection delay units form a delay loop; each group of two optical circulators is also connected to the next group of two optical circulators in a one-to-one correspondence; one optical circulator in the first group is connected to the input port, and the two optical circulators in the last group are respectively connected to an output port; The optical switch is a Mach-Zehnder optical switch structure, including a phase shifter and two couplers with a splitting ratio of 50:

50. The splitting ratio of the third port and the fourth port of the optical switch can be changed by adjusting the phase shifter.

2. The optical delay line of optical switch type based on adjustable reflection ring assistance according to claim 1, characterized in that: The adjustable reflection ring is based on a Mach-Zehnder optical switch structure, and its third port and fourth port are connected by a waveguide; the reflectivity of light in the two ports of the adjustable reflection ring can be changed by adjusting the phase shifter.

3. The optical delay line of optical switch type based on adjustable reflection ring assistance according to claim 1, characterized in that: The phase shifter is realized by using the thermo-optic effect, electro-optic effect or magneto-optic effect of the optical waveguide.

4. The optical delay line with optical switch assisted by an adjustable reflective ring according to claim 1, characterized in that: The two couplers with a splitting ratio of 50:50 are implemented by a directional coupler with a splitting ratio of 50:50, an adiabatic coupler with a splitting ratio of 50:50, or a multimode interference coupler with a splitting ratio of 50:

50.

5. The optical delay line with optical switch assisted by an adjustable reflective ring according to claim 1, characterized in that: In the optical switch, light is input from the first port, and the phase shifter in the optical switch is adjusted. When the phase difference between the two arms is π, the light is completely output from the third port. When the phase difference between the two arms is 0, the light is completely output from the fourth port.

6. The optical delay line with optical switch assisted by an adjustable reflective ring according to claim 1, characterized in that: In the adjustable reflection ring, light is input from the first port, and the phase shifter in the adjustable reflection ring is adjusted. When the phase difference between the two arms is π / 2, the light is completely reflected from the first port, and when the phase difference between the two arms is 0, the light is completely reflected from the second port.

7. The optical delay line with optical switch assisted by an adjustable reflective ring according to claim 1, characterized in that: In the optical circulator, if the light is sent from the input port or the previous delay loop, it is output to the odd-numbered reflection delay unit of the current delay loop. If the light is sent from the odd-numbered reflection delay unit of the current delay loop, it is output to the even-numbered reflection delay unit of the current delay loop. If the light is sent from the even-numbered reflection delay unit of the current delay loop, it is output to the next delay loop.

8. The optical delay line with optical switch assisted by an adjustable reflective ring according to claim 1, characterized in that: The length of the delay waveguide in the Nth stage reflection delay unit is (3 N-1 )*ΔL, ΔL corresponds to the minimum delay Δt.

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