A photodetector system and method based on pixelated nanophotomechanical programmable gratings

Abstract

This invention discloses a photodetector system and method based on pixelated nano-opto-electro-mechanical programmable gratings. The detector includes an input waveguide, a pixelated nano-opto-electro-mechanical grating array optically coupled to the input waveguide, an output waveguide network, and at least one photodetector unit. The pixelated nano-opto-electro-mechanical grating array consists of multiple grating pixel units discretely arranged along the light propagation direction. Each grating pixel unit has an electrically drivable micro / nano-levitation structure and an electrode structure. By applying a driving voltage, electromechanical displacement is generated, thereby modulating the coupling strength and / or phase response between the pixel unit and the waveguide, thus achieving spectrally selective coupling, transmission suppression, splitting, or shaping of the incident light. The output waveguide network couples the spectrally shaped optical signal to the detector array to achieve multi-channel parallel detection. This scheme has the advantages of being ultra-compact, low-power, programmable, arrayable, and easy to integrate on-chip, making it suitable for applications such as communication monitoring and multispectral imaging.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronics and micro / nano-electromechanical systems (MEMS) technology, specifically to an on-chip spectroscopic detector and system based on a nano-suspended grating waveguide structure with capacitive out-of-plane displacement modulation. In particular, it relates to an on-chip integrated scheme that sets driving electrodes on the side of the waveguide and on the suspended grating, modulates the effective refractive index or local coupling characteristics of the waveguide through capacitive electromechanical effects, and combines a passive beam splitter structure with a branch waveguide array detector to achieve multi-channel spectral detection. Background Technology

[0002] With the development of integrated optoelectronic technology, on-chip spectrometers have attracted widespread attention in fields such as optical communication, environmental monitoring, biochemical detection, and spectral imaging due to their advantages such as small size, low power consumption, and large-scale integration. Existing on-chip spectrometer detection schemes typically rely on waveguide structures to separate, modulate, or weight optical signals of different wavelengths, and acquire spectral information through multiple photodetectors.

[0003] Existing on-chip spectrometers mainly include arrayed waveguide gratings (AWGs), Mach-Zehnder interferometer arrays (MZIarrays), and ring resonator arrays. These schemes typically rely on fixed geometries to achieve wavelength separation, and their main drawbacks include large device size and complex cascaded structures. Multi-stage interference or resonant structures usually require long optical path lengths or a large number of repeating units, making it difficult to achieve high-resolution or broadband spectral detection within a limited chip area. Furthermore, their spectral responses are fixed and their reconfigurability is limited. Once traditional structures are fabricated, the center wavelength and response function of their spectral channels are essentially fixed, making it difficult to flexibly adjust or reconfigure them during operation. Fixed structures are highly sensitive to process errors, temperature variations, and stress changes, often requiring additional thermal tuning or complex calibration methods.

[0004] To overcome the limitations of fixed spectral responses, several schemes combining micro-nano electromechanical systems (MEMS) with integrated optics have emerged in recent years. These schemes achieve tunable spectral responses by modulating optical structure parameters through mechanical displacement. The purpose of this invention is to overcome the shortcomings of existing on-chip spectrometers in terms of spectral reconfigurability, device compactness, array integration capability, and system stability. This invention provides a spectral detection scheme based on a suspended nanograting array waveguide using capacitive electromechanical effects. This scheme enables low-power, programmable modulation of the waveguide's optical properties and, when combined with a regularized detector array structure, constructs a compact and easily expandable on-chip spectrometer detection system. Summary of the Invention

[0005] To address the problems of large device size, fixed spectral response, high power consumption, and insufficient arraying and programmability in existing on-chip spectral detection technologies, this invention proposes an on-chip spectral reconfigurable photodetector system and method based on pixelated nano-opto-electro-mechanical programmable gratings.

[0006] As described in claim 1, the present invention provides an on-chip spectrally reconfigurable photodetector, comprising:

[0007] Input waveguide, used to input the optical signal to be measured;

[0008] A pixelated nano-opto-electro-mechanical programmable grating is optically coupled to the input waveguide within a predetermined coupling region;

[0009] A drive control circuit is used to apply voltage to the grating pixel unit to generate electromechanical displacement;

[0010] The output waveguide network and photodetector unit are used to receive the spectrally shaped optical signal and output the electrical signal.

[0011] The pixelated nano-opto-electro-mechanical programmable grating array is composed of multiple grating pixel units discretely arranged along the light propagation direction. Each grating pixel unit forms a different spectral response under independent or addressable voltage control, thereby forming a spatially distributed programmable spectral mask as a whole.

[0012] Preferably, the input waveguide is disposed on an SOI (Silicon-On-Insulator) or SiN platform.

[0013] Preferably, the waveguide material is monocrystalline silicon, but it can also be replaced with polycrystalline silicon; in other embodiments, the waveguide can also be formed in a III–V material or a heterogeneous integration platform.

[0014] Preferably, the waveguide thickness is on the scale of 150 nm to 400 nm; the waveguide width is on the scale of 400 nm to 1.5 μm; to support single-mode or weak multimode propagation and adapt to different band applications.

[0015] Preferably, each grating pixel unit includes: a nanoscale suspended grating structure, a support beam structure, and a driving electrode and a reference electrode associated with the movable structure. The nanograting structure is preferably disposed above the input waveguide to form near-field coupling with the waveguide.

[0016] Preferably, the grating material is selected from monocrystalline silicon, polycrystalline silicon, silicon nitride (SiN), or a combination thereof;

[0017] Preferably, the grating period is 200 nm to 1 μm; the duty cycle of the grating tooth width to the period is 0.3 to 0.7; and the effective length of a single grating pixel unit is preferably 2 μm – 50 μm.

[0018] Preferably, the spacing between adjacent grating pixel units along the waveguide direction can be continuous or discrete to achieve different spatial sampling densities.

[0019] Preferably, the nanograting is suspended above the waveguide by a support beam, with an initial gap g0 between them, ranging from 50 nm to 500 nm.

[0020] Preferably, the driving electrode and the reference electrode can form a parallel plate capacitor structure; the electrode material is selected from indium tin oxide (ITO), graphene, doped zinc oxide or heavily doped semiconductor;

[0021] Preferably, in a further embodiment, displacement detection can also be achieved through capacitance changes, forming a closed-loop control and improving the stability of spectral modulation.

[0022] Preferably, the optical signal modulated by the pixelated grating array is coupled to the photodetector unit through the output optical path. The output waveguide network may include, but is not limited to, a beam splitter, a directional coupler, a multimode interferometer (MMI), an arrayed waveguide, or a combination thereof.

[0023] Preferably, the photodetector unit can be a silicon-based PIN, Ge-on-Si, InGaAs, avalanche photodiode, or two-dimensional material detector.

[0024] Preferably, different voltage configurations are applied to the grating pixel array through the voltage pattern generation module; the voltage pattern reconstruction can be selected from: orthogonal pattern, block code, and pseudo-random pattern.

[0025] Preferably, spectral reconstruction or classification is achieved by using compressed sensing, least squares, or machine learning algorithms based on the response matrix.

[0026] Through the above technical solutions, the present invention is significantly superior to the prior art in terms of device size, power consumption, programmability, array capability and system integration, and is especially suitable for applications such as on-chip spectral analysis, gas / biochemical sensing, communication monitoring and multispectral imaging. Attached Figure Description

[0027] Figure 1 Flowchart of a pixelated nano-opto-electro-mechanical programmable grating waveguide photodetector system

[0028] Figure 2 Pixelated nano-opto-electro-mechanical programmable grating waveguide detector structure diagram

[0029] Figure 3 Simulation diagram of polysilicon displacement at different voltages

[0030] Figure 4 A set of voltage code diagrams and spectral function diagrams

[0031] Figure 5 Optical field diagrams of 1550nm light in waveguides under different voltage codes

[0032] Figure 6 Cross-sectional view of the fabrication process of pixelated nano-opto-electro-mechanical programmable grating waveguide Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings:

[0037] Device structure and optimization design:

[0038] refer to Figure 1-5 This invention provides a waveguide photoelectric detection system with a pixelated nano-opto-electro-mechanical programmable grating, the system as follows: Figure 1These include: a pixelated nano-opto-electro-programmable grating waveguide 10, an output waveguide network 20, an array detector 30, a control and drive module and a readout module 40, and an input coupling terminal 50. In a specific implementation, the system is fabricated on a silicon-on-insulator (SOI) platform with a top silicon layer thickness of 220 nm.

[0039] Among them, pixelated nano-opto-electro-mechanical programmable grating waveguide 10, such as Figure 2 It includes: a transmission waveguide 101, a waveguide cladding 102, a grating support beam 103, a nanograting 104, a reference electrode 105, a driving electrode 106, a buried oxide layer 1022, and a substrate 1023. In a specific implementation, the thickness of the transmission waveguide is equivalent to the thickness of the top silicon layer, 220 nm, and the designed width is 450 nm.

[0040] One of the pixel units includes: a nanograting 104 and a driving electrode 106, in Figure 2 In this example, all pixel units share a common reference electrode 105 and a grating support beam 103. In a specific implementation, the nanograting has a length of 4 μm, a height of 100 nm, and a horizontal width of 400 nm. This design ensures that the beam's mechanical stiffness in the horizontal direction is significantly greater than its stiffness in the vertical direction, guaranteeing that vertical (Z-axis) displacement is primarily generated under electrostatic actuation.

[0041] A nanograting is suspended above the input waveguide, with an initial air gap (g0) of 80 nm between them. This gap is precisely controlled by the thickness of the sacrificial layer to balance the optical coupling strength and the driving voltage.

[0042] Spectral response function H m Calibration of (λ):

[0043] In this invention, an optical signal is introduced into the on-chip transmission waveguide 101 through an input coupling end 50 such as an optical fiber coupler or a grating coupler by a tunable laser, so that the optical signal propagates along the transmission waveguide direction in the form of a waveguide guided mode.

[0044] Simultaneously, the driving module 40 applies a voltage pattern V(m) to the nanograting 104. The voltage may include: applying voltages of different amplitudes or polarities to the driving electrodes 106 of different pixel units, or grouping and controlling the pixel units. For example... Figure 3 The nanograting has a length of 4 μm. In the first image, the electromechanical displacement at the end of the 104 nanograting is 23 nm when the voltage is 20 V, and in the second image, the electromechanical displacement at the end of the 104 nanograting is 62 nm when the voltage is 30 V. In specific implementation examples, such as... Figure 5A 20V driving voltage is applied to a subset of numbered nanogratings as a primary voltage code. The output current of the synchronous array detector 30 is normalized and divided by the laser's input power to obtain the spectral response function H under this voltage code. m (λ). The voltage code pattern is changed a total of m times (e.g., m=64), and the response matrix A is constructed, where the m-th row is the spectral response function H corresponding to the m-th voltage code pattern. m (λ).

[0045] In this invention, due to the variation in the gap between the nanograting 104 and the transmission waveguide 101, the coupling strength, phase response, or suppression characteristics of different grating pixel units for the light propagating in the waveguide change. In specific embodiments, such as... Figure 4 In the first image, the distance between the transmission waveguide 101 and the nanograting 104 is 80 nm. The normalized optical field intensity in the transmission waveguide is approximately 0 a.u. In the second image, a voltage is applied to the nanograting 104 with an even serial number, making its distance from the transmission waveguide 101 100 m and its horizontal period 800 nm. The normalized optical field intensity can reach 0.5 a u.

[0046] Actual spectral detection:

[0047] The unknown optical signal S(λ) to be measured is connected to the system. The driving module (40) rapidly applies m sets of calibrated voltage codes sequentially. The detector records the corresponding m intensity measurements, forming a measurement vector y. According to the physical model, this process satisfies the equation y = A*S + n. n is noise, and S(λ) represents the spectral power distribution of the optical signal to be measured, which contains the distribution information of the intensity of the input optical signal changing with wavelength S(λ). The least squares method is used to... Alternatively, other optimization algorithms can be used to solve the matrix equation to obtain the spectrum S to be measured, thereby reconstructing the spectral information of the incident light on the chip.

[0048] This invention provides a method for fabricating pixelated nano-opto-electro-mechanical programmable grating waveguides:

[0049] Step 1: In the practical example, the SOI platform is used, such as... Figure 6 The first image shows photoresist spin-coated onto the top intrinsic layer, followed by deep ultraviolet lithography and ICP-RIE etching to form the input waveguide 101 and necessary passive devices (MMI / coupler / beam splitter, etc.).

[0050] Step 2: A SiN or Al2O3 protective layer (10-20 nm) can be deposited. PECVD is used to deposit SiO2 as the waveguide cladding (e.g., 0.8–2 µm) to ensure low loss in the ordinary waveguide section. A window pattern is formed in the grating coupling region using photolithography. The upper SiO2 cladding layer is locally etched to thin it. A continuous SiO2 sacrificial layer (e.g., 80–200 nm) can be retained, located between the future suspended nanobeam and the waveguide. Figure 6 As shown in the first picture.

[0051] Step 3: Deposit a structural layer (Si / poly-Si / SiN, typically 100–300 nm thick) in the window region and form a nanograting 104 and grating support beam 103 by electron beam or deep ultraviolet lithography and dry etching. For example... Figure 3 As shown in the second picture.

[0052] Step 4: Photolithographically pattern the suspended beam, sputter ITO material and peel it off to form the driving electrode 106, while simultaneously depositing gold / titanium (Au / Ti) to form the metal pads for the reference electrode. A reference electrode 105 is formed in the adjacent region on the waveguide side. (Example...) Figure 6 As shown in the third picture.

[0053] Step 5: Isotropically etch sacrificial SiO2 using wet HF or vapor-phase HF to create a cavity beneath the grating beam, thus obtaining the gap (100-200 nm); Figure 6 As shown in the fourth picture.

[0054] Step 6: Integrate the detector array (Ge-on-Si / III-V / 2D, etc.) at the output waveguide branch and complete the metal interconnection, passivation and packaging.

[0055] The working principle of this invention is as follows:

[0056] This invention is based on the controllable modulation of light propagating in a waveguide using pixelated nano-opto-electro-mechanical programmable gratings. The optical signal under test is first coupled into the on-chip input waveguide through an input coupling structure and propagates along a predetermined propagation direction in the form of a waveguide guided mode. Multiple discretely arranged nano-opto-electro-mechanical grating pixel units are disposed along the propagation direction of the input waveguide.

[0057] The nanograting and waveguide are optically coupled via a near-field evanescent field. When a voltage is applied between the driving electrode and the reference electrode, an electric field is formed between them, generating an electrostatic force. This electrostatic force drives the nanograting structure to undergo electromechanical displacement, preferably an out-of-plane displacement perpendicular to the chip plane. This displacement changes the gap between the nanograting and the waveguide, thereby modulating the optical coupling conditions between them. As a high-refractive-index perturbation structure, the change in the distance between the nanograting and the waveguide alters the electromagnetic field distribution of the waveguide's guided mode, thus changing the effective refractive index of the guided mode. The gap change alters the scattering, coupling, or reflection intensity of the waveguide's guided mode by the grating, causing different wavelengths of light signals to be coupled, suppressed, or separated with different efficiencies. The equivalent phase modulation introduced by the nanograting changes with the displacement, thereby altering the coherent superposition conditions of light at a specific wavelength.

[0058] The optical signal, modulated by the pixelated nanograting waveguide, continues to propagate within the waveguide and enters the output optical path region. At the output end, the spectrally shaped optical signal is distributed to multiple output branches according to a predetermined ratio or structure; photodetector units are installed on or at the end of each output branch waveguide. Each photodetector unit converts the received optical signal into an electrical signal output, thereby obtaining a set of measurement values ​​corresponding to the current voltage pattern. The system control module rapidly and sequentially applies multiple sets of different preset voltage patterns to the grating array. Each set of patterns corresponds to a known system spectral response function, and the detector synchronously records the light intensity measurement value corresponding to each set of patterns. Based on these measurement values ​​and the pre-calibrated response matrix, spectral reconstruction algorithms, such as solving linear equations or compressed sensing algorithms, are used for inverse calculations to mathematically reconstruct the complete spectral information of the measured optical signal.

[0059] The advantages of this invention are:

[0060] Existing passive beam splitting technologies that rely on fixed optical path differences, such as cascaded AWG or MZI structures, often occupy millimeter- or even centimeter-scale chip areas, presenting significant challenges due to their large size and the need for high-power thermal tuning. Furthermore, traditional arrayed waveguide gratings (AWGs) or Mach-Zehnder interferometers (MZIs) typically utilize the phase difference generated by light propagating in waveguides of different lengths for interference beam splitting. This mechanism requires light to travel a sufficiently long distance to accumulate a significant phase difference.

[0061] This invention innovatively employs a pixelated nano-opto-electro-mechanical (NOEMS) suspended grating structure, directly modulating the optical coupling and phase response of the waveguide in the near field through electrostatically driven micro-nano displacement, achieving a paradigm shift from "hardware-fixed spectral dispersion" to "software-defined spectroscopy." Its core advantage lies in significantly overcoming size and power consumption limitations. Utilizing a monolithically integrated, ultra-compact micron-scale structure, the spectral response function can be flexibly reconstructed through voltage programming. Combined with computational reconstruction algorithms, it achieves low power consumption, high integration, and multifunctional parallel detection capabilities on a single device, effectively solving the challenge of simultaneously achieving miniaturization and spectral tunability in traditional photonic devices. This system can achieve efficient detection and reconstruction of light at different wavelengths, exhibiting extremely high flexibility and wide applicability, providing a new solution for future optoelectronic devices and integrated sensing platforms.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An on-chip spectral reconfigurable photoelectric detection system, characterized in that, include: An input waveguide is used to import the optical signal to be measured; a pixelated nano-opto-electro-programmable grating array is optically coupled to the input waveguide within a predetermined coupling region; the grating includes a plurality of grating pixel units discretely arranged along the optical propagation direction; each grating pixel unit includes at least one nanoscale grating structure, a support structure, and a driving electrode and a reference electrode associated with the grating; The driving control circuit is connected to the electrodes of each grating pixel unit and is used to apply voltage to each grating pixel unit to generate electromechanical displacement, thereby changing the coupling coefficient or phase response of the grating pixel unit to the light propagating in the input waveguide. An output optical path and a photodetector unit, wherein the output optical path includes at least one output waveguide or output waveguide network for carrying the optical signal after spectral shaping by the pixelated nano-opto-electro-mechanical programmable grating array, and the photodetector unit is optically coupled to the output optical path and outputs an electrical signal; Specifically, by applying voltage codes to the plurality of grating pixel units, the detector achieves a preset spectral response function, which is used for spectrally selective detection or spectral reconstruction of the light signal under test.

2. The detector according to claim 1, characterized in that, The electromechanical displacement includes electrodes forming a parallel plate capacitor, which changes the gap between the nanograting structure and the input waveguide through electrostatic drive, thereby modulating the effective refractive index or local coupling coefficient of the waveguide mode to achieve spectral selective response or pixel-level programmable spectral response.

3. The detector according to claim 1, characterized in that, The output waveguide network includes at least one of the following: a multimode interferometer, a directional coupler, a beam splitter tree network, an arrayed waveguide, or a multiport splitter structure, used to guide the spectrally shaped optical signal to the corresponding detector.

4. The detector according to claim 1, characterized in that, The nanograting structure of the grating pixel unit has a high aspect ratio cross-sectional characteristic, wherein the width (w) of the nanograting structure parallel to the chip surface and perpendicular to the light propagation direction is greater than its thickness (t) to enhance the lateral mechanical stiffness and suppress the lateral parasitic displacement caused by the lateral reference electrode.

5. The detector according to claim 1, characterized in that, The photoelectric detection unit includes any one or a combination of silicon-based PIN photodiodes, Ge-on-Si detectors, InGaAs detectors, avalanche photodiodes, and two-dimensional material photodetectors.

6. The detector according to claim 1, characterized in that, The driving electrode is made of a transparent conductive material, selected from one of indium tin oxide (ITO), graphene, doped zinc oxide, or heavily doped polycrystalline silicon.

7. A method for on-chip spectral detection using pixelated nano-opto-electro-programmable gratings, characterized in that, include: (1) Apply a first set of voltage codes to the pixelated nano-opto-electro-programmable grating to form a first spectral response function; The first measurement value is obtained by collecting the output of the photoelectric detection unit; (2) Apply at least one set of subsequent voltage codes in sequence to form the corresponding subsequent spectral response function; collect multiple sets of measurement values; (3). The response spectrum matrix is ​​calculated based on multiple sets of measurement data, which can be used to calculate the spectral information of the light signal to be measured, or to output the matching result or spectral decomposition of the target spectrum.

8. The method according to claim 7, characterized in that, The voltage code generation module generates codes including orthogonal codes, pseudo-random codes, sparse codes, or codes optimized for specific target spectra.

9. The method according to claim 7, characterized in that, Spectral information includes: optical power of at least one target band, optical power vectors of multiple discrete bands, reconstruction results of the continuous spectrum, or classification labels for spectral features.

10. The method according to claim 7, characterized in that, It can be used for any of the following applications: gas absorption spectroscopy detection, biochemical biomarker detection, communication link power monitoring, or multispectral imaging.

Images