FP cavity electro-optical modulator array applicable to multi-wavelength-channel transmitter

Abstract

Disclosed in the present invention is a Fabry-Pérot (FP) cavity electro-optical modulator array applicable to a multi-wavelength-channel transmitter. The modulator array is mainly formed by sequentially connecting N modulator units, and each modulator unit comprises a 2×2 FP cavity structure, a substrate, and a pair of modulation electrodes, wherein the 2×2 FP cavity structure and the modulation electrodes are all arranged on the upper surface of the substrate, the two modulation electrodes are symmetrically distributed on two sides of the 2×2 FP cavity structure, a multiplexing end of a first mode demultiplexer is connected to an input end of one antisymmetric multimode waveguide grating, two antisymmetric multimode waveguide gratings are connected to each other by means of an intermediate waveguide, and an output end of the other antisymmetric multimode waveguide grating is connected to a multiplexing end of the second mode demultiplexer. The present invention has a compact structure, has modulator units having excellent electro-optical modulation performance, large modulation bandwidth and a flexible cascading mode, is applicable to a multi-wavelength-channel transmitter, and is suitable for being applied to scenarios such as high-capacity optical communication and optical computing.

Description

A FP cavity electro-optic modulator array for multi-wavelength channel transmitter Technical Field

[0001] The present invention belongs to the field of optical communication technology and relates to a modulator array, in particular to an FP cavity electro-optical modulator array that can be used for a multi-wavelength channel transmitter, achieving low energy consumption, large bandwidth, compact structure, and multi-wavelength channel transmission. Background Art

[0002] In recent years, with the rapid development of 5G communications, the Internet of Things, and data centers, society's demand for communication capacity has grown exponentially. Optical communication technology, with its advantages of interference immunity, low loss, high bandwidth, and low crosstalk, has become the mainstream technology for current communications. Optoelectronic devices, as key components, have gradually become a bottleneck in the development of ultra-high-capacity optical communications. Based on various materials and principles, solutions such as silicon-based modulators, indium phosphide modulators, electro-optic polymer modulators, and thin-film lithium niobate modulators have been widely researched, resulting in the emergence of a series of high-performance devices. Thin-film lithium niobate modulators, based on the linear electro-optic effect, offer linear response, low optical loss, and high stability, making them one of the most promising solutions. However, the electro-optic coefficient of lithium niobate is relatively low. In X-cut thin-film lithium niobate, the electro-optic coefficient is highest when light propagates along the ordinary optical axis of the crystal and the external electric field is along the extraordinary optical axis, reaching approximately 31 pm / V at a wavelength of approximately 1550 nm. Mach-Zehnder intensity modulators typically require phase-shifting arms on the order of millimeters to centimeters to accumulate sufficient phase change and reduce the half-wave voltage. Traveling-wave electrodes must also be incorporated. Microring cavity modulators typically require a larger waveguide radius to avoid mode hybridization in X-cut curved waveguides. Consequently, both structures have relatively large device dimensions.

[0003] In addition, lithium niobate modulators face the mutual constraints between modulation bandwidth and modulation efficiency. Specifically, in Mach-Zehnder traveling-wave electrode modulators, the modulation bandwidth decreases with increasing phase-shift arm length due to microwave loss and refractive index mismatch. In resonant modulators, high-quality microcavities offer higher modulation efficiency, but the longer photon lifetime within the cavity reduces the modulation bandwidth.

[0004] The data transmission rate of a single modulator has an upper limit. To meet the demand for transmission capacity in commercial optical communication systems, utilizing multidimensional multiplexing technology to increase the total transmission capacity by increasing the number of channels is a direct and reliable solution. Wavelength division multiplexing technology has been widely researched and adopted in optical fiber communication systems. In such large-scale array scenarios, high-performance lithium niobate modulators with small size and compact structure are particularly important. The existing technology lacks a compact electro-optical modulator array on a thin-film lithium niobate platform that can be used for multi-wavelength channel high-speed transmitters.

[0005] Summary of the Invention

[0006] To address the problems presented in the prior art, the present invention proposes an FP cavity (Fabry-Perot cavity) electro-optical modulator array for multi-wavelength channel transmitters. This modulator array, composed of a cascade of N 2×2 Fabry-Perot cavity electro-optical modulator units operating at different wavelengths, achieves higher communication capacity, more compact dimensions, and lower energy consumption. Furthermore, a subsequent overlay coating can compensate for errors in the resonant peak wavelength caused by manufacturing errors. The array offers advantages such as simple design and processability, along with scalability, making it crucial for on-chip integrated optical communication systems.

[0007] The technical solutions adopted in the present invention are as follows:

[0008] The modulator array is mainly formed by connecting N modulator units in sequence; for the nth modulator unit among the N modulator units, the nth modulator unit includes a 2×2 Fabry-Perot cavity structure, a substrate and a pair of modulation electrodes; the 2×2 Fabry-Perot cavity structure and the modulation electrodes are both arranged on the upper surface of the substrate, and the two modulation electrodes are symmetrically distributed on both sides of the 2×2 Fabry-Perot cavity structure.

[0009] The 2×2 Fabry-Perot cavity structure includes a first mode demultiplexer, a second mode demultiplexer, a first antisymmetric multimode waveguide grating, a second antisymmetric multimode waveguide grating and an intermediate waveguide;

[0010] The multiplexing end of the first mode demultiplexer is connected to the input end of the first antisymmetric multimode waveguide grating, the output end of the first antisymmetric multimode waveguide grating and the input end of the second antisymmetric multimode waveguide grating are connected through an intermediate waveguide, and the output end of the second antisymmetric multimode waveguide grating is connected to the multiplexing end of the second mode demultiplexer; the mode port 1 and the mode port 2 of the first mode demultiplexer serve as the input end and the reflection output end of the modulator unit respectively, and the mode port 1 and the mode port 2 of the second mode demultiplexer serve as the transmission output end and the upload end of the modulator unit respectively; the first antisymmetric multimode waveguide grating, the second antisymmetric multimode waveguide grating and the intermediate waveguide are all located between the two modulation electrodes.

[0011] The N modulator units are connected in sequence in a horizontal cascade or a vertical cascade manner;

[0012] When N modulator units are transversely cascaded, the N modulator units are transversely cascaded into a row, and the transmission output end of the n-1th stage modulator unit and the input end of the nth stage modulator unit are connected through a connecting waveguide;

[0013] When N modulator units are cascaded longitudinally, the N modulator units are cascaded longitudinally into a column, and the reflection output end of the n-1th stage modulator unit and the input end of the nth stage modulator unit are connected through a connecting waveguide.

[0014] In the nth modulator unit, the first antisymmetric multimode waveguide grating and the second antisymmetric multimode waveguide grating both reversely couple the TE0 mode of the signal to the TE1 mode or reversely couple the TE1 mode of the signal to the TE0 mode, and both modes satisfy the following phase matching conditions:

[0015] (n eff0 +n eff1 )Λ=λ bragg

[0016] Among them, n eff0 、n eff1 are the equivalent refractive indices of TE0 and TE1 modes, Λ is the grating tooth period of the antisymmetric multimode waveguide grating, and λ bragg is the center wavelength of the reflection band of the antisymmetric multimode waveguide grating.

[0017] The first antisymmetric multimode waveguide grating and the second antisymmetric multimode waveguide grating are both provided with tooth structures on both sides along the waveguide transmission direction, and the tooth structures on both sides are arranged with grating teeth and tooth grooves relatively symmetrically on both sides; the width of each grating tooth varies according to a specific function along the waveguide transmission direction.

[0018] The specific function is a Gaussian, sine or Hamming function.

[0019] The first mode demultiplexer and the second mode demultiplexer are mainly composed of a straight waveguide and a coupled waveguide; in the coupling working area, the straight waveguide and the coupled waveguide are both tapered.

[0020] The base is mainly composed of a substrate and a lower cladding stacked in sequence from bottom to top, the 2×2 Fabry-Perot cavity structure and the modulation electrode are both arranged on the upper surface of the lower cladding, and the upper surface of the intermediate waveguide in the 2×2 Fabry-Perot cavity structure is provided with an upper cladding modification layer.

[0021] The first mode demultiplexer, the second mode demultiplexer, the first antisymmetric multimode waveguide grating, the second antisymmetric multimode waveguide grating and the intermediate waveguide are all formed by etching an X-cut thin film lithium niobate material.

[0022] The present invention combines the wavelength selection characteristics of antisymmetric multimode waveguide gratings and Fabry-Perot cavities, cascades multiple 2×2 Fabry-Perot cavity electro-optical modulator units in different ways to construct multi-wavelength channels, significantly improving the total communication capacity of the transmitter. By covering the waveguide in the Fabry-Perot cavity with a modified layer, the resonance peak wavelength error caused by processing errors can also be compensated, and the channel spacing can be evened out. The present invention has a compact structure, excellent electro-optical modulation performance of the modulator unit, large modulation bandwidth, low energy consumption, low insertion loss, and avoids the use of circulators / isolators, with the potential for large-scale arraying; the modulator array based on this cascade has a simple architecture and flexible cascading methods, can be used for multi-wavelength channel transmitters, and is suitable for applications in scenarios such as large-capacity optical communications and optical computing.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention adopts 2×2 Fabry-Perot cavity electro-optic modulators as the basic structural unit, which are cascaded to form an array, with a compact structure, flexible architecture, simple design and convenient process.

[0025] 2. The present invention is based on a thin-film lithium niobate platform, and its comprehensive performance in modulation linearity, device loss, and theoretical bandwidth limit is far superior to the electro-optic modulators based on other platforms mentioned in the background.

[0026] 3. In terms of the performance of the unit device, the unit device of the present invention adopts a lumped electrode, which has lower energy consumption than the traveling wave electrode modulator on thin film lithium niobate, and the bandwidth is only limited by the quality factor of the cavity and the RC bandwidth of the electrode, which can achieve a higher modulation bandwidth; the present invention can utilize the reflected output signal of the Fabry-Perot cavity, which has lower loss and higher modulation efficiency than the traditional transmission spectrum; the present invention has a 2×2 port, which can realize various forms of cascading.

[0027] 4. The advantages of the present invention's compact structure are even more pronounced in terms of device arraying and cascading. Furthermore, the present invention utilizes the wavelength-selective properties of antisymmetric waveguide gratings and Fabry-Perot cavities for direct cascading, eliminating the need for additional filters. The flexible architecture allows for achieving small or large channel wavelength spacing through various cascading methods. Furthermore, the invention can compensate for processing errors through an overlay coating, demonstrating excellent scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a schematic diagram of a structure in which N 2×2 Fabry-Perot electro-optical modulator units are arranged horizontally and cascaded with the input waveguide of the next stage through a transmission output waveguide to form a multi-wavelength channel transmitter;

[0029] FIG2 is a schematic diagram of a structure in which N 2×2 Fabry-Perot electro-optical modulator units are arranged vertically and cascaded with the input waveguide of the next stage through a reflective output waveguide to form a multi-wavelength channel transmitter;

[0030] FIG3 is a schematic diagram of the structure of a 2×2 Fabry-Perot electro-optical modulator unit used in the present invention;

[0031] FIG4 is a schematic structural diagram of an antisymmetric multimode waveguide grating used in the present invention;

[0032] FIG5 is a schematic structural diagram of a mode demultiplexer used in the present invention;

[0033] FIG6 is a schematic diagram of a waveguide cross section;

[0034] FIG7 is a schematic diagram showing how the transmission intensity of the reflection output end of a 2×2 Fabry-Perot electro-optical modulator unit varies with wavelength at different voltages in an example of the present invention;

[0035] FIG8 is a schematic diagram showing the variation of the output transmission intensity with wavelength of a multi-wavelength channel transmitter formed by cascading two 2×2 Fabry-Perot electro-optical modulator units arranged horizontally and connected to the input waveguide of the next stage through a transmission output waveguide in an example of the present invention;

[0036] FIG9 is a schematic diagram showing the variation of the transmission intensity at the output end of a multi-wavelength channel transmitter with wavelength, in which eight 2×2 Fabry-Perot electro-optical modulator units are arranged vertically and cascaded with the input waveguide of the next stage through a reflective output waveguide in an example of the present invention;

[0037] In the figure: 1-modulator unit (101, 102, ..., 10N), 2a-first mode demultiplexer, 2b-second mode demultiplexer, 3a-first antisymmetric multimode waveguide grating, 3b-second antisymmetric multimode waveguide grating, 4-intermediate waveguide, 5a-first modulation electrode, 5b-second modulation electrode, 201-straight-through waveguide, 202-coupled waveguide, 601-substrate, 602-lower cladding, 603-X-cut thin film lithium niobate material, 604-upper cladding modification layer. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and examples.

[0039] The transmitter is mainly formed by N modulator units 101, ..., 10n, ..., 10N connected in sequence; for the nth modulator unit among the N modulator units, the nth modulator unit includes a 2×2 Fabry-Perot cavity structure, a substrate and a pair of modulation electrodes 5a, 5b; the 2×2 Fabry-Perot cavity structure and the modulation electrodes 5a, 5b are both arranged on the upper surface of the substrate, and the two modulation electrodes 5a, 5b are symmetrically distributed on both sides of the 2×2 Fabry-Perot cavity structure along the waveguide transmission direction.

[0040] The modulator unit is specifically a 2×2 Fabry-Perot cavity electro-optical modulator unit, which includes a pair of mode demultiplexers 2a, 2b and a pair of antisymmetric multimode waveguide grating cavity mirrors 3a, 3b, which separate the input and output light to achieve 2×2 routing. The pair of modulation electrodes 5a, 5b includes a first modulation electrode 5a and a second modulation electrode 5b.

[0041] As shown in FIG3 , the 2×2 Fabry-Perot cavity structure includes a first mode demultiplexer 2 a , a second mode demultiplexer 2 b , a first antisymmetric multimode waveguide grating 3 a , a second antisymmetric multimode waveguide grating 3 b and an intermediate waveguide 4 ;

[0042] The multiplexing end of the first mode demultiplexer 2a is connected to the input end of the first antisymmetric multimode waveguide grating 3a, the output end of the first antisymmetric multimode waveguide grating 3a and the input end of the second antisymmetric multimode waveguide grating 3b are connected via a section of intermediate waveguide 4, and the output end of the second antisymmetric multimode waveguide grating 3b is connected to the multiplexing end of the second mode demultiplexer 2b; the mode port 1 and mode port 2 of the first mode demultiplexer 2a serve as the input end and reflection output end of the modulator unit 10n respectively, and the mode port 1 and mode port 2 of the second mode demultiplexer 2b serve as the transmission output end and upload end of the modulator unit 10n respectively; the first antisymmetric multimode waveguide grating 3a, the second antisymmetric multimode waveguide grating 3b and the intermediate waveguide 4 are all located between the two modulation electrodes 5a and 5b.

[0043] N modulator units are connected in sequence through horizontal cascade or vertical cascade;

[0044] When N modulator units are cascaded horizontally, they form a row. That is, the transmitter is primarily formed by N modulator units arranged horizontally and parallely at even intervals along the waveguide transmission direction. As shown in Figure 1, the transmission output end of the n-1th stage modulator unit 10(n-1) and the input end of the nth stage modulator unit 10n are connected via a connecting waveguide. The grating reflection bands of each stage modulator unit are different, ultimately achieving different resonant wavelengths for each modulator unit. Light of each wavelength is incident from the upstream end of each stage modulator unit, and the modulated output light is combined and output in the transmission output waveguide of the last stage modulator unit.

[0045] When N modulator units are cascaded vertically, they form a column. This means the transmitter is primarily composed of N modulator units arranged vertically and parallel to each other at even intervals perpendicular to the waveguide transmission direction. As shown in Figure 2, the reflective output end of the n-1th stage modulator unit 10(n-1) and the input end of the nth stage modulator unit 10n are connected via a connecting waveguide. Each stage of electro-optical modulator units has the same reflection band but a different equivalent cavity length, ultimately achieving different resonant wavelengths for each modulator unit. Light of all wavelengths is incident simultaneously from the input end of the first stage unit device, and the modulated output light is combined and output in the transmission output waveguide of the last stage modulator unit.

[0046] In the nth modulator unit, the first antisymmetric multimode waveguide grating 3a and the second antisymmetric multimode waveguide grating 3b both reversely couple the TE0 mode of the signal to the TE1 mode or reversely couple the TE1 mode of the signal to the TE0 mode, and both modes satisfy the following phase matching conditions:

[0047] (n eff0 +n eff1 )Λ=λ bragg

[0048] Among them, n eff0 、n eff1 are the equivalent refractive indices of TE0 and TE1 modes, Λ is the grating tooth period of the antisymmetric multimode waveguide gratings 3a and 3b, and λ bragg is the center wavelength of the reflection band of the antisymmetric multimode waveguide gratings 3a and 3b.

[0049] As shown in FIG4 , the first antisymmetric multimode waveguide grating 3 a and the second antisymmetric multimode waveguide grating 3 b are provided with tooth structures on both sides along the waveguide transmission direction, and the tooth structures on both sides are arranged with grating teeth and tooth grooves relatively symmetrically on both sides; the maximum width of the grating teeth is δ0, and the width of each grating tooth varies according to a specific function along the waveguide transmission direction, forming intensity toe-cutting.

[0050] The width of the grating tooth is specifically the length of the side of the grating tooth perpendicular to the waveguide transmission direction.

[0051] The specific function is a Gaussian, sine, or Hamming function.

[0052] As shown in Figure 5, the first mode demultiplexer 2a and the second mode demultiplexer 2b are dual-core waveguide structures. The first mode demultiplexer 2a and the second mode demultiplexer 2b are mainly composed of a straight waveguide 201 and a coupled waveguide 202. In the coupling working area of ​​the straight waveguide 201 and the coupled waveguide 202, the straight waveguide 201 and the coupled waveguide 202 are both tapered, and their widths gradually widen and narrow along the waveguide transmission direction, respectively.

[0053] As shown in Figure 6, the base is mainly composed of a substrate 601 and a lower cladding layer 602 stacked in sequence from bottom to top. The Fabry-Perot cavity structure and the modulation electrodes 5a and 5b are all on the upper surface of the lower cladding layer 602. The upper surface of the intermediate waveguide 4 in the Fabry-Perot cavity structure is provided with an upper cladding modification layer 604, that is, the intermediate waveguide 4 is located between the buried oxide layer 602 and the upper cladding modification layer 604.

[0054] The lithium niobate-on-insulator (LNOI) thin film is composed of a substrate 601, a buried oxide layer 602, and a Fabry-Perot cavity structure stacked from bottom to top. The lower surface of the connecting waveguide also has a substrate and buried oxide layer. The substrate 601 and buried oxide layer 602 below the Fabry-Perot cavity structure are connected to the substrate and buried oxide layer below the connecting waveguide to form an integrated structure.

[0055] The first mode demultiplexer 2a, the second mode demultiplexer 2b, the first antisymmetric multimode waveguide grating 3a, the second antisymmetric multimode waveguide grating 3b, and the intermediate waveguide 4 are all formed by etching X-cut thin-film lithium niobate material 603. The structure made of X-cut thin-film lithium niobate material 603 forms an integrated thin-film lithium niobate ridge waveguide.

[0056] The Fabry-Perot cavity structure in the waveguide region is a partially etched ridge waveguide. Depending on the actual processing conditions, an upper cladding modification layer 604 of varying sizes can be added to the Fabry-Perot cavity of each modulator unit 10n to introduce additional phase shift and compensate for resonant wavelength errors caused by processing variations. The upper cladding modification layer 604 can be formed directly from an electron beam exposure resin or photoresist such as SU8, ZEP520A, or HSQ, or a cladding material such as silicon dioxide.

[0057] The working process and principle of the present invention are as follows:

[0058] The teeth and slots of the antisymmetric multimode waveguide gratings 3a and 3b in the Fabry-Perot cavity are arranged relatively symmetrically on both sides, satisfying the phase matching condition:

[0059] (n eff0 +n eff1 )Λ=λ bragg

[0060] Among them, n eff0 、n eff1 are the equivalent refractive indices of TE0 and TE1 modes, Λ is the period of the grating teeth of the antisymmetric multimode waveguide grating 3a and 3b, and λ bragg is the center wavelength of the reflection band of the antisymmetric multimode waveguide grating teeth 3a and 3b. Within the reflection band of the antisymmetric multimode waveguide gratings 3a and 3b, the gratings can partially reflect incident light in the TE0 mode as the TE1 mode, while transmitting part of it in the TE0 mode; or partially reflect incident light in the TE1 mode as the TE0 mode, while transmitting part of it in the TE1 mode.

[0061] The period and the center wavelength of the reflection band of the first antisymmetric multimode waveguide grating 3a and the second antisymmetric multimode waveguide grating 3b are the same.

[0062] When the resonance conditions of the Fabry-Perot cavity are met, a resonance peak forms at the modulator unit's transmission output, while a resonance dip forms at the reflection output. When light is incident from the modulator unit's input, the reflected light has a different mode than the incident light. Therefore, the reflected light is demultiplexed by the first mode demultiplexer 2a and output from the reflection output. The transmitted light, with the same mode as the incident light, is output from the transmission output. A similar situation occurs when light is incident from the upstream end: the reflected light passes through the second mode demultiplexer 2b and is output from the transmission output. The transmitted light signal is then output from the reflection output.

[0063] The Fabry-Perot cavity extends along the ordinary optical axis of the X-cut lithium niobate thin-film material 603, while the line connecting the modulation electrodes 5a and 5b is along the extraordinary optical axis of the X-cut lithium niobate thin-film material 603. Due to the electro-optical effect of lithium niobate, when a voltage U is applied to the modulation electrodes 5a and 5b, the refractive index along the extraordinary optical axis of the X-cut lithium niobate thin-film material 603 changes under the action of the electric field. The change Δn is:

[0064] Where n is the original refractive index of lithium niobate on the extraordinary optical axis, r 33 is the electro-optic coefficient corresponding to the case where light propagates along the ordinary optical axis of the lithium niobate crystal and the external electric field propagates along the extraordinary optical axis of the crystal, and d is the distance between the two modulation electrodes 5a and 5b. Due to the change in the refractive index of the X-cut thin-film lithium niobate material 603, the equivalent refractive index Δn corresponding to the TE0 and TE1 modes in the thin-film lithium niobate ridge waveguide eff0，1 Also change:

[0065] Δn eff0，1 =Γ 0，1 Δn

[0066] Among them, Γ 0，1 It is the coefficient of the change of the equivalent refractive index corresponding to the TE0 or TE1 mode with the refractive index of the electro-optical material, and is determined by the mode field distribution of the optical field and the electric field.

[0067] The change in the mode-equivalent refractive index changes the round-trip optical path in the Fabry-Perot cavity, shifting the resonant wavelength accordingly. At specific wavelengths near the resonant wavelength, the optical power changes, achieving electro-optical intensity modulation. Away from the resonant wavelength, the optical power remains essentially unchanged.

[0068] When the Fabry-Perot electro-optical modulator units are cascaded, the nth operating wavelength λ n Corresponding to the resonant wavelength λ of the nth-order Fabry-Perot electro-optic modulator unit res,nThe modulation voltage is applied to the n-th Fabry-Perot electro-optical modulator unit, and the n-th working wavelength λ n The optical power of the n-th order Fabry-Perot cavity changes, forming intensity modulation, while the power of other wavelengths is not affected because they are far away from the resonant wavelength of the n-th order Fabry-Perot cavity.

[0069] Due to process deviations during the manufacturing process and temperature changes in actual application scenarios, the resonant wavelength of the Fabry-Perot cavity may deviate from the designed value. The slight change in the resonant wavelength caused by the latter can be dynamically adjusted through DC bias, thermo-optical tuning, etc. The deviation caused by the former can be adjusted by introducing an upper coating modification layer 604. The additional phase shift that needs to be introduced by the upper coating modification layer 604 is The size should satisfy:

[0070] Where FSR is the free spectral range of a single Fabry-Perot cavity, and Δλ is the resonant wavelength deviation to be compensated. Specifically:

[0071] Among them, Δn' eff0 , Δn' eff1 are the changes in the equivalent refractive index of the TE0 and TE1 modes in the waveguide caused by the upper cladding modification layer 604, L is the length of the upper cladding modification layer 604, and λ res Therefore, by properly selecting the material, thickness, width, and length of the upper cladding modification layer 604, an additional phase shift of a specific magnitude can be introduced.

[0072] The specific embodiments of the present invention are as follows:

[0073] The following example is based on a ridge waveguide structure of a thin-film lithium niobate platform on an insulator. The cross-section is shown in Figure 6. The core layer is made of X-cut thin-film lithium niobate material 603, with a total thickness of 400nm, a ridge waveguide height of 200nm, and a plate height of 200nm. Typically, etching of lithium niobate produces a 30° tilt angle relative to the vertical direction. The lower cladding layer 602 is made of silicon dioxide with a thickness of 3μm, and no upper cladding layer is used. At a wavelength of around 1550nm, the refractive index n of the X-cut thin-film lithium niobate material 603 is o =2.211,n e =2.138, the refractive index of silicon dioxide is 1.444.

[0074] Example 1

[0075] The electro-optical modulator array, which can be used for multi-wavelength channel transmitters, consists of two 2×2 Fabry-Perot electro-optical modulator units arranged horizontally. The transmission output of the first-stage modulator unit is connected to the input of the second-stage modulator unit. Signal light with wavelengths λ1 and λ2 is input from the upstream terminals of the first and second-stage modulator units, respectively. Two microwave modulation signals are applied to the two modulator units through modulation electrodes, and the two modulated optical signals are combined and output from the transmission output of the second-stage modulator unit.

[0076] The modulation electrodes 5a and 5b are titanium-gold electrodes with thicknesses of 10 nm and 150 nm, respectively.

[0077] Figure 3 shows the specific form of the Fabry-Perot cavity in the 2×2 Fabry-Perot electro-optical modulator unit. The first and second antisymmetric multimode waveguide gratings 3a and 3b employ Gaussian line profiles for transverse amplitude apodization, with the grating teeth arranged in a completely antisymmetric pattern. The two antisymmetric multimode waveguide gratings 3a and 3b in the same stage are identical, but the grating periods of the first and second stages are different.

[0078] In this embodiment, a typical set of parameters for the Fabry-Perot cavity of the present invention is provided: the intermediate waveguide 4 has a length of 5 μm and a width of 2 μm; the spacing d between the two modulation electrodes 5a and 5b is 4.5 μm; the antisymmetric multimode waveguide gratings 3a and 3b have a base width of 2 μm, the tooth depth is a Gaussian line profile with a Gaussian coefficient of 8 for transverse amplitude apodization, the maximum width of the grating teeth is 0.55 μm, the grating tooth duty cycle is 0.5, the number of grating periods is 180, and the grating periods of the antisymmetric multimode waveguide gratings 3a and 3b in the first- and second-stage modulation units are 442 nm and 435 nm, respectively. The actual length of the Fabry-Perot cavity is approximately 160 μm, and the equivalent cavity length does not exceed 85 μm. Therefore, the modulation electrodes 5a and 5b only need to be 85 μm long, and the corresponding capacitance is only approximately 10 fF, which can significantly reduce energy consumption.

[0079] The variation of the reflected output spectrum of the first-stage modulator unit with the modulation voltage is shown in Figure 7. The resonant wavelength drift with the electrostatic modulation efficiency is about 11pm / V. res / Δλ FWHM The quality factor Q of the Fabry-Perot cavity is calculated to be about 2800, where λ res is the resonant wavelength, Δλ FWHM is the full width at half maximum of the resonance peak. The theoretical 3dB modulation bandwidth f is limited by the photon lifetime in the cavity. 3dB :

[0080] f 3dB =f0 / Q

[0081] The 3dB modulation bandwidth is approximately 69GHz, where f0 is the frequency of light in vacuum.

[0082] The optical spectrum of the cascaded two-stage modulator unit is shown in Figure 8. The two curves in the figure represent the optical spectrum at the transmission output port of modulator unit 102, when inputs are from the upstream ports of modulator unit 101 and unit device 102, respectively. The output spectrum loss is less than 0.5dB, and the resonant wavelengths of the two modulator units are approximately 1570nm and 1550nm, respectively. As shown in Figure 8, when an optical signal with a wavelength near 1570nm is incident from the upstream port of modulator unit 101, the modulated reflected optical signal can be re-inputted into modulator unit 102 through the transmission output waveguide. Since the reflectivity of modulator unit 102 at 1570nm is less than -40dB, the optical signal can be transmitted and output almost losslessly.

[0083] As can be seen from this embodiment, the 2×2 Fabry-Perot electro-optical modulator unit described in the present invention has the advantages of compact structure, large bandwidth, low energy consumption, low loss, and simple process. The high-speed transmitter based on this modulator unit and cascaded in the manner described in this embodiment can directly utilize the wavelength selectivity, high side mode suppression ratio, and large free spectral range of the antisymmetric multimode waveguide grating. It is no longer limited by the free spectral range of the Fabry-Perot cavity, and the number of wavelength channels is highly scalable, which greatly improves the total communication capacity of the system.

[0084] Example 2

[0085] The electro-optical modulator array, which can be used for a multi-wavelength channel transmitter, consists of eight 2×2 Fabry-Perot electro-optical modulator units arranged vertically. The reflected output of the n-1th stage modulator unit is connected to the input of the nth stage modulator unit. Light with eight wavelengths, λ1, λ2, ..., λ8, is input from the input of the first stage modulator unit 101. Microwave modulation signals 1 to 8 are applied to each modulator unit via modulation electrodes 5a and 5b, respectively. The eight modulated optical signals are output from the reflected output of the eighth stage modulator unit 108.

[0086] The specific forms of the modulation electrodes 5a, 5b and the Fabry-Perot cavity are the same as those in Example 1 and will not be described in detail.

[0087] The eight modulator units use identical antisymmetric multimode waveguide gratings 3a and 3b. Specifically, the grating base width is 2.6 μm, the tooth depth uses a Gaussian line profile with a Gaussian coefficient of 6 for transverse amplitude apodization, the maximum grating tooth width is 1.6 μm, the grating tooth duty cycle is 0.5, the number of grating periods is 110, and the grating period is 430 nm. The spacing d between the two modulation electrodes 5a and 5b is 5.4 μm. The intermediate waveguide 4 has a width of 2.6 μm, and the lengths of the intermediate waveguide 4 for each stage of the modulator unit are 4.1 μm, 4.147 μm, 4.194 μm, ..., 4.382 μm, and 4.429 μm, respectively. When the intermediate waveguide 4 length increases in 47 nm steps as described above, the resonant wavelength spacing between two adjacent stages of the modulator unit is approximately 1.6 nm, or a frequency spacing of 200 GHz. The total output spectrum of the cascaded modulator array is shown in Figure 9. The total output spectrum loss is less than -1.8dB, the quality factor of each resonant cavity is approximately 3200, and the extinction ratio is greater than 18dB. Each wavelength is modulated by the microwave signal of the corresponding channel. By properly designing the quality factor of the Fabry-Perot cavity and controlling the linewidth, it is possible to achieve mutual non-interference between the channels.

[0088] It can be seen that the modulator array based on 2×2 Fabry-Perot electro-optical modulator units and cascaded in the manner described in this embodiment can achieve wavelength division multiplexing with smaller channel spacing, and has flexible and diverse methods for resonant wavelength calibration, strong scalability, and greatly improves the total communication capacity of the system.

[0089] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A FP cavity electro-optic modulator array that can be used for a multi-wavelength channel transmitter, characterized in that: The modulator array is mainly formed by connecting N modulator units (101, ..., 10n, ..., 10N) in sequence; for the nth modulator unit among the N modulator units, the nth modulator unit includes a 2×2 Fabry-Perot cavity structure, a substrate and a pair of modulation electrodes (5a, 5b); the 2×2 Fabry-Perot cavity structure and the modulation electrodes (5a, 5b) are both arranged on the upper surface of the substrate, and the two modulation electrodes (5a, 5b) are symmetrically distributed on both sides of the 2×2 Fabry-Perot cavity structure.

2. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 1, characterized in that: The 2×2 Fabry-Perot cavity structure comprises a first mode demultiplexer (2a), a second mode demultiplexer (2b), a first antisymmetric multimode waveguide grating (3a), a second antisymmetric multimode waveguide grating (3b) and an intermediate waveguide (4); The multiplexing end of the first mode demultiplexer (2a) is connected to the input end of the first antisymmetric multimode waveguide grating (3a), the output end of the first antisymmetric multimode waveguide grating (3a) is connected to the input end of the second antisymmetric multimode waveguide grating (3b) via an intermediate waveguide (4), and the output end of the second antisymmetric multimode waveguide grating (3b) is connected to the multiplexing end of the second mode demultiplexer (2b); the mode port 1 and the mode port 2 of the first mode demultiplexer (2a) are used as the input end and the reflection output end of the modulator unit (10n), respectively, and the mode port 1 and the mode port 2 of the second mode demultiplexer (2b) are used as the transmission output end and the upload end of the modulator unit (10n), respectively; the first antisymmetric multimode waveguide grating (3a), the second antisymmetric multimode waveguide grating (3b) and the intermediate waveguide (4) are all located between the two modulation electrodes (5a, 5b).

3. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: The N modulator units are connected in sequence in a horizontal cascade or a vertical cascade manner; When N modulator units are cascaded transversely, the N modulator units are cascaded transversely in a row, and the transmission output end of the n-1th modulator unit (10(n-1)) and the input end of the nth modulator unit (10n) are connected via a connecting waveguide; When N modulator units are cascaded longitudinally, the N modulator units are cascaded longitudinally into a column, and the reflection output end of the n-1th modulator unit (10(n-1)) and the input end of the nth modulator unit (10n) are connected through a connecting waveguide.

4. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: In the nth modulator unit, the first antisymmetric multimode waveguide grating (3a) and the second antisymmetric multimode waveguide grating (3b) both reversely couple the TE0 mode of the signal to the TE1 mode or reversely couple the TE1 mode of the signal to the TE0 mode, and both modes satisfy the following phase matching condition: (n eff0 +n eff1 )Λ=λ bragg Among them, n eff0 、n eff1 are the equivalent refractive indices of TE0 and TE1 modes, Λ is the grating tooth period of the antisymmetric multimode waveguide grating, and λ bragg is the center wavelength of the reflection band of the antisymmetric multimode waveguide grating.

5. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: The first antisymmetric multimode waveguide grating (3a) and the second antisymmetric multimode waveguide grating (3b) are both provided with tooth structures on both sides along the waveguide transmission direction, and the tooth structures on both sides are provided with grating teeth and tooth grooves arranged relatively symmetrically on both sides; the width of each grating tooth varies according to a specific function along the waveguide transmission direction.

6. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 5, characterized in that: The specific function is a Gaussian, sine or Hamming function.

7. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: The first mode demultiplexer (2a) and the second mode demultiplexer (2b) are both mainly composed of a straight waveguide (201) and a coupled waveguide (202); in the coupling working area, the straight waveguide (201) and the coupled waveguide (202) are both tapered.

8. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: The base is mainly composed of a substrate (601) and a lower cladding (602) stacked in sequence from bottom to top, a 2×2 Fabry-Perot cavity structure and modulation electrodes (5a, 5b) are both arranged on the upper surface of the lower cladding (602), and an upper cladding modification layer (604) is arranged on the upper surface of the intermediate waveguide (4) in the 2×2 Fabry-Perot cavity structure.

9. The FP cavity electro-optic modulator array applicable to a multi-wavelength channel transmitter according to claim 2, characterized in that: The first mode demultiplexer (2a), the second mode demultiplexer (2b), the first antisymmetric multimode waveguide grating (3a), the second antisymmetric multimode waveguide grating (3b) and the intermediate waveguide (4) are all formed by etching an X-cut thin film lithium niobate material (603).

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