CN104090331A - Efficient compact rectangular ring resonant cavity waveguide type optical filter - Google Patents

Abstract

The invention provides an efficient compact rectangular ring resonant cavity waveguide type optical filter, and belongs to the field of integrated optics. Each closed long rectangle is formed by single mode optical waveguides, and two parallel straight bar single mode optical waveguides penetrate through two long sides of each rectangular waveguide vertically and intersect with the rectangular waveguide; the portions, between an intersection, at the ends of each rectangular waveguide are phase shift arms; the portions, divided by each rectangular waveguide, between two straight bar waveguides are reference arms, and the portions, divided by every two parallel waveguides, of the long sides of each rectangle are connecting waveguides; the portion between the end of each straight bar waveguide and the corresponding intersection is an input waveguide, the portion between the other end of each straight bar waveguide and the adjacent intersection is an output waveguide I, and the portion between the end of the other straight bar waveguide adjacent to each input waveguide and the adjacent intersection is an output waveguide II. A rectangular ring resonant cavity is adopted to replace a traditional micro-ring resonant cavity, the limit to the radius of curvature due to poor refringence of a material of a micro-ring structure is overcome, and bending losses of a waveguide structure in a circular ring shape are further reduced.

Description

An Efficient and Compact Rectangular Ring Resonator Waveguide Optical Filter

technical field

The invention relates to an optical filter device, in particular to an efficient and compact rectangular ring resonator waveguide optical filter structure, which belongs to the field of integrated optics.

Background technique

Optical filter is an important device to realize wavelength division multiplexing technology, and is widely used in the field of optical communication and on-chip optical interconnection system. For example, it can be applied to the optical add-drop multiplexing node in the optical wavelength division multiplexing network, and its function is to selectively receive and send some wavelength channels locally up and down from the transmission optical path. The core device of the add-drop multiplexing node is an optical filter device, which selects the wavelength to be added/dropped to realize wavelength routing. The new type of optical filter is based on the optical waveguide structure, using semiconductor thin film manufacturing technology to obtain good optical domain performance and high integration characteristics. At present, chemical vapor deposition or molecular beam epitaxy and other methods are used on Si, GaAs, InP and other substrates, combined with etching technology to realize an integrated two-dimensional planar optical transmission system, so that the application of new optical filters in on-chip optical interconnection systems is also possible. become possible. At the same time, integrated optical filters also have broad application prospects in the fields of optical add-drop multiplexing, on-chip optical switching, and optical computing.

Common optical filters include filters based on interference principles, such as fused-cone fiber filters, Fabry Perot filters, multilayer dielectric film filters, Mach-Zehnder filters, etc.; and filters based on grating principles , such as volume grating filters, arrayed waveguide grating filters (AWG), fiber grating filters, etc. The size of the above-mentioned filters is relatively large, and they are often used in systems in the form of discrete devices, making it difficult to achieve large-scale integration. In addition, when applied to on-chip integrated systems for optical interconnection and optical computing, these bulk filters cannot meet the requirements of high integration. The waveguide optical filter came into being. Although the optical filter based on the microring resonator can solve the integration problem to a certain extent, there is a problem that the radius of curvature of the microring is limited by the difference in refractive index of the material and the bending loss of the waveguide. Temperature sensitivity and narrow bandwidth issues. Since the waveguide Mach-Zehnder filter uses conventional Y branches, directional couplers or multi-mode interference couplers in its structure, it also has the problem of occupying a large monolithic size or a long one-dimensional scale. It is not conducive to increasing the number of integration of discrete components in photonic integrated circuits. Therefore, it is technically necessary to realize a waveguide optical filter device that occupies a smaller area in the two-dimensional direction, has a more compact structure, and lower power consumption.

Contents of the invention

In view of the defects that the current integrated optical filter occupies a large single-chip size and cannot be integrated in two-dimensional directions, a new groove-based rectangular ring resonator waveguide optical filter structure is proposed, which can be highly integrated in two-dimensional directions. And obtain lower insertion loss and improve the quality factor.

The technical scheme adopted in the present invention is: a highly efficient and compact rectangular ring resonator waveguide optical filter, which is characterized in that: a closed long rectangle is formed by a single-mode optical waveguide, and two parallel straight single-mode optical waveguides pass through vertically. Cross the two long sides of the rectangular waveguide and cross the rectangular waveguide respectively; the part between the ends of the rectangular waveguide is the phase shift arm 4; the part between the two straight waveguides divided by the rectangular waveguide is the reference arm 5, and the rectangular waveguide is long The part where the side is divided by two parallel waveguides is the connecting waveguide 6; the part between the end of any straight waveguide and the intersection of the cross is the input waveguide 1, and it is between the other end of the same straight waveguide and the intersection of the adjacent cross The part is the output waveguide I8, the part between the end of another straight waveguide adjacent to the input waveguide and the intersection of the adjacent cross is the output waveguide II9; the other end of the straight waveguide where the output waveguide II9 is located and the intersection of the adjacent cross The part in between is the multiplexing waveguide 10 . On the outside of the right angle of the rectangular waveguide, the cut surface is etched at an angle of 45° along the propagation direction of the waveguide to form a total reflection mirror 7; at the intersection of the rectangular waveguide and the straight waveguide, micro-nano grooves are respectively etched along the direction parallel to the adjacent total reflection mirror 7 Slot 2.

The groove 2 is filled with a groove dielectric material 3, which includes air, polymethyl methacrylate (PMMA), SU-8 polymer, aluminum oxide, zirconium dioxide; for the same lining Filling different trench media with the bottom material results in different opening widths of the micro-nano trenches 2 when the power ratio is equal. Filling with a dielectric material with a larger refractive index, the wider the opening width of the trench 2, thereby reducing the difficulty of the device etching process; but the angle between the trench and each waveguide should be greater than the dielectric interface formed by the waveguide material and the trench filling material total reflection angle.

The waveguide input end is the coupling end face 1a of the input waveguide I1; the output end is the coupling end face 8a of the output waveguide I8 and the coupling end face 9a of the output waveguide II9 respectively. The input waveguide 1, the output waveguide I8, the output waveguide II9, and the multiplexing waveguide 10 are completely equivalent, and can be respectively used as input and output ports to realize cross-multiplexing.

The device is fabricated on a base material of silicon or silicon on insulator (Silicon on insulator, SOI) or GeSi/Si or GaAs or GaAs/AlGaAs and InP/InGaAsP semiconductor substrate materials.

The positive and progressive effects of the present invention are: 1. The present invention adopts the groove type micro-nano photon coupler based on the principle of frustrated total internal reflection to replace the light splitter/combiner in the traditional filter structure, such as the commonly used Y branch, directional coupling Couplers or multi-mode interference couplers, etc., break the limitation of the traditional coupler on the one-dimensional length of the device structure, make the device efficient and compact, and can meet the application requirements of device miniaturization, two-dimensional integration and multi-level cascading occupying a smaller area . 2. The rectangular ring resonant cavity is used to replace the traditional micro-ring resonant cavity, which overcomes the restriction of the curvature radius by the material refractive index difference of the micro-ring structure, and further reduces the bending loss of the circular ring waveguide structure.

Description of drawings

Fig. 1 is a schematic structural diagram of a highly efficient and compact rectangular ring resonator waveguide optical filter proposed by the present invention.

Fig. 2 is a schematic longitudinal sectional view along the A-A' direction shown in Fig. 1 .

FIG. 3 is a signal transmission model diagram of the structure shown in FIG. 1 .

Figure 4 shows the frequency response curve of the system when the spectral coefficient is used.

Figure 5 shows the frequency response curve of the system when the spectral coefficient is used.

Figure 6 shows the frequency response curve of the system when the spectral coefficient is used.

In the figure: 1 input waveguide, 1a input waveguide port, 2 micro-nano groove, 3 groove filled with dielectric material, 4 phase shift arm, 5 reference arm, 6 connecting waveguide, 7 total reflection mirror, 8 output waveguide I, 8a output Waveguide I port, 9 output waveguide II, 9a output waveguide II port, 10 multiplexing waveguide, 11 silicon-on-insulator (SOI) etched ridge waveguide, 12 ridge waveguide lower cladding silicon dioxide layer, 13 silicon substrate.

Detailed ways

The present invention will be further described in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention should not be limited thereby.

A kind of highly efficient and compact rectangular ring resonator waveguide optical filter structure of the present invention can be made on silicon, silicon on insulator (Silicon on insulator, SOI), GeSi/Si, GaAs, GaAs/AlGaAs and InP/InGaAsP semiconductor substrate materials on a base material. As an example of specific implementation, the present invention takes as an example a filter composed of stripe-ridge waveguides prepared on an SOI substrate material. The optical signal enters the device from the input port 1a. Due to the Mach-Zehnder interference structure and the ring resonant cavity, the non-resonant frequency optical signal is output from the output port 8a, and the resonant frequency light is output from the output port 9a to realize the filtering function.

Referring to Fig. 1, a kind of highly efficient compact rectangular ring resonator waveguide optical filter structure of the present invention comprises input waveguide 1, micro-nano trench 2, trench filling dielectric material 3, phase shift arm 4, reference arm 5, connection waveguide 6 , total reflection mirror 7 , output waveguide I 8 , output waveguide II 9 , multiplexing waveguide 10 . The working principle of the etched micro-nano grooves is based on the frustrated total internal reflection of light waves, that is, when the light evanescent wave entering the groove from the input waveguide is compared with the width of the groove, a part of the evanescent wave passes through The groove reaches the opposite medium interface to form a penetrating light wave; another part of the evanescent wave passes through the Goos-Hanchen displacement phenomenon to form a reflected light wave. By changing the groove width or adjusting the refractive index of the groove filling dielectric material, the power ratio of the transmitted light wave and the reflected light wave can be adjusted, thereby adjusting the frequency response curve of the filter and improving the quality factor of the filter.

The optical signal enters the phase shift arm 4 and the reference arm 5 respectively after splitting through the groove 2, and combines light at the groove 2 to form a Mach-Zehnder interferometer structure. Through this structure, part of the optical signal is output from the output port I8a, and part of it enters the connection Waveguide 6-ring resonator. The reference arm 5 and the connecting waveguide 6 together form a rectangular ring resonant cavity. The non-resonant frequency optical signal re-enters the Mach-Zehnder structure formed by the phase shift arm 4 and the reference arm 5 through the splitting of the groove 2, and is output through the output port I8a. As a result, the transmission spectrum of the output port I is flatter except for the resonant frequency; and the optical signal at the resonant frequency is resonantly enhanced, and is output through the output port II9a, so that the output port I8a and the output port II9a are complementary. The reference arm 5 and the phase shift arm 4 at the other end of the resonant ring form another Mach-Zehnder structure, which enhances the signal resonance at the resonant center frequency of the ring resonant cavity, makes the transmission spectrum of the output port I sharper, and improves the quality factor of the filter.

Referring to Fig. 2, a schematic diagram of a longitudinal section in the direction of A-A' in Fig. 1, the present invention takes an SOI structure single-mode waveguide as an example, but the scope is not limited thereto. The single-mode SOI-based ridge optical waveguide 11 can be obtained by reactive ion etching in semiconductor device processing technology, and the lower cladding layer 12 of the ridge optical waveguide is made of silicon dioxide material and deposited on a silicon-based substrate 13 .

Referring to Figure 3, in order to illustrate the working effect of this highly efficient and compact rectangular ring resonator optical filter structure, based on the signal flow diagram of the structure in Figure 1, the transmission of optical signals in the filter structure in Figure 1 is shown. Considering that in the structure of the present invention, the length and refractive index of each segment of the waveguide are equal, and the optical paths passed by the optical signal through each waveguide are equal, the Z-transform signal processing method is adopted. The term represents the delay term, that is, the signal is delayed by a single waveguide signal, where n represents the refractive index of the waveguide, d represents the length of a single waveguide, and c represents the speed of light in vacuum. Due to the light-splitting characteristics of micro-nano grooves, the optical signal is divided into penetrating light waves and reflected light waves when passing through the grooves. Let the electric field amplitude coefficient of the penetrating light wave be t, and the electric field amplitude coefficient of the reflected light wave be r. Assuming that the amplitude coefficient of the electric field of the input light wave is 1, according to the principle of energy conservation,

In the device, due to the directionality of the signal, when the optical signal passes through the groove, the vector penetration coefficient τ is introduced, then. At the same time introduce the left reflection coefficient α and the right reflection coefficient β, then. As shown in FIG. 3 , the signal orientations in the four dotted circle boxes respectively indicate the light splitting conditions of the signals when they pass through each groove.

In order to solve the transfer function of the system in steady state, the state space representation is introduced. Let the output state of each delay item be ~, where k is a discrete time variable, and the state equation can be obtained from the signal transfer diagram,

Among them, the input state, the state equations of output port Ⅰ and output port Ⅱ are respectively,

Using matrix and vector methods, it is expressed as,

Among them, x(k+1), x(k), and y(k) are vectors of order 13 respectively. A is a matrix of order 13×13, B and D are matrices of order 13×1, and C is a matrix of order 1×13.

The transfer function can be expressed as

Bring in the corresponding coefficient matrix to get the transfer function of output port I and output port II as

Refer to Figure 4, Figure 5, and Figure 6, which illustrate the transmission characteristic curves of the filter under different splitting coefficients of the groove coupler. In practical applications, the groove width can be changed or the groove can be filled according to different requirements. The refractive index of the dielectric material can be used to obtain ideal filtering characteristics and quality factors.

Figure 4 is the transmission characteristic curve of the filter under the condition of . The center filtering amplitude reaches -64.7dB. It is a left-right symmetrical comb structure, and the filter curve quality factor is calculated as .

Figure 5 is the transmission characteristic curve of the filter under the condition of . The center filtering amplitude reaches ‐90dB, and the filtering figure of merit is calculated as .

Figure 6 is the transmission characteristic curve of the filter under the condition of . The central filtering amplitude reaches ‐74.3dB, and the filtering curve figure of merit is calculated as .

The invention of the device has a compact structure and is easy to be integrated and expanded in two-dimensional direction. At the same time, the preparation has a wide range of applications, and is a micro-nano structure waveguide optical filter device that can be prepared on different substrate materials.

Claims (4)

1. A highly efficient and compact rectangular ring resonator waveguide type optical filter is characterized in that: a closed long rectangle is formed by single-mode optical waveguides, and two straight single-mode optical waveguides parallel to each other vertically pass through the two long rectangular waveguides. The sides cross the rectangular waveguide respectively; the part between the ends of the rectangular waveguide at the intersection of the cross is the phase shift arm (4); the part divided by the rectangular waveguide in the middle of the two straight waveguides is the reference arm (5), and the long side of the rectangle is The part divided by two parallel waveguides is the connecting waveguide (6); the part between the end of any straight waveguide and the intersection of the cross is the input waveguide (1), and it is at the intersection of the other end of the same straight waveguide and the adjacent cross The part between them is the output waveguide I (8), the part between the end of another straight waveguide adjacent to the input waveguide and the intersection of the adjacent cross is the output waveguide II (9); the part where the output waveguide II (9) is located The part between the other end of the straight waveguide and the junction of the adjacent cross is a multiplexing waveguide (10). On the outside of the right angle of the rectangular waveguide, etch the cut surface along the waveguide propagation direction at an angle of 45° to form a total reflection mirror (7); at the intersection of the rectangular waveguide and the straight waveguide, respectively engrave along the direction parallel to the adjacent total reflection mirror (7). etched micro-nano trenches (2). 2. A kind of efficient and compact rectangular ring resonator waveguide optical filter according to claim (1), characterized in that: groove dielectric material (3) is filled in the groove (2), and the groove dielectric material (3) Including air, polymethyl methacrylate (PMMA), SU-8 polymer, aluminum oxide, zirconium dioxide; the angle between the groove and each waveguide is greater than that formed by the waveguide material and the groove filling material Total reflection angle at the medium interface. 3. A kind of efficient compact rectangular ring resonator waveguide optical filter according to claim 1, is characterized in that: described waveguide input end is the coupling end face (1a) of input waveguide (1); Output end is output respectively Coupling end face (8a) of waveguide I (8) and coupling end face (9a) of output waveguide II (9); input waveguide, output waveguide I (8), output waveguide II (9), multiplexing waveguide (10) etc. The price can be used as input and output ports respectively to realize cross-multiplexing. 4. according to claim 1,2,3 described efficient compact rectangular ring resonator waveguide optical filter, it is characterized in that: make on silicon or silicon on insulator (Silicon on insulator, SOI) or GeSi/Si or GaAs or On a base material of GaAs/AlGaAs and InP/InGaAsP semiconductor substrate materials.