Fiber-optic brain-machine interface device based on micro-lens array

Abstract

This invention provides a fiber optic brain-computer interface device based on a microsphere lens assembly. Its features include: a transmitting component formed by transmitting light sources 1-1 and 1-2 and a single-mode fiber wavelength division multiplexer 2; a microprism beam splitter / combiner 3; a fiber optic receiving cable 4; a brain-computer interface housing 5; fiber-end hemispherical transmitting / receiving microlenses 6; a beam-shaping coupling lens 7; and a single-photon detector receiver 8. This invention can be used to acquire diffuse reflection light information of blood oxygenation changes within brain tissue, enabling real-time monitoring of changes in blood oxygenation within the brain. It can be widely used in fields such as novel non-invasive optical brain-computer interface monitoring equipment.

Description

Technical Field

[0001] This invention relates to a fiber optic brain-computer interface device based on a microsphere lens combination. This invention can be used to acquire diffuse reflected light information of blood oxygenation changes in brain tissue, and to monitor changes in blood oxygenation in the brain in real time. It can be widely used in novel non-invasive optical brain-computer interface monitoring equipment and belongs to the field of fiber optic sensing technology. Background Technology

[0002] The biological brain relies on blood metabolism to provide the oxygen needed for neuronal activity. Oxygen consumption stimulates the dilation of local blood vessels in the brain, leading to an increase in local cerebral blood volume and flow, manifested as a rapid increase in cerebral blood oxygen levels. Therefore, when the brain engages in a cognitive activity, the local blood oxygen content in the active brain region will far exceed the required blood oxygen content in unstimulated areas. Oxygen is transported through hemoglobin in the blood; therefore, during cognitive activities, the concentration of oxyhemoglobin in the active brain region will significantly increase, while the concentration of deoxyhemoglobin will significantly decrease. Currently, many brain imaging techniques obtain brain activity signals related to brain function by detecting optical or magnetic changes caused by changes in local hemoglobin concentration during activity.

[0003] Currently, the most widely used mainstream brain imaging techniques include electroencephalography (EEG), magnetoencephalography (MEG), transcranial magnetic stimulation (TMS), electrocorticography (ECoG), local field potential array (LFP), positron emission tomography (PET), magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS) [Irani F, Platek SM, Bunce S, Ruocco AC, et al. Functional near infrared spectroscopy (fNIRS): an emerging neuroimaging technology with important applications for the study of brain disorders[J]. Clin Neuropsychol, 21(1):9-37, (2007).]. Invasive devices require craniotomy to implant sensors into brain tissue. This procedure is prone to triggering an immune response, posing a high risk, and the scab formed during wound healing can also affect signal transmission. In contrast, non-invasive devices do not require entry into the brain; signals can be detected simply by looking at the outer side of the skull. The experience, similar to wearing a hat, is more readily accepted, and they offer advantages such as ease of use, portability, and relatively lower cost. While non-invasive methods avoid the risks of surgery, the skull significantly attenuates reflected signals, causing the received signal to become scattered and blurred, affecting both signal strength and resolution. To delve deeper into brain function and elucidate the psychological processes and mechanisms of human cognition, early research into non-invasive neurofunctional detection technologies began. In 1831, London physician Richard Bright and others first applied this technology to clinical medicine, using candlelight to illuminate the back of the head, making the skull translucent.In 1977, Jobsis et al. first applied functional near-infrared spectroscopy (fNIRS) to observe changes in blood oxygen content in animal brains, and published their research results on the absorption characteristics of hemoglobin and cytochrome in the near-infrared spectral range in Science. Oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR) had two absorption peaks at 735 nm and 905 nm, respectively, and proposed that the changes in absorption spectra were directly related to the oxygen carrying capacity of hemoglobin. FF, Noninvasive. Infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters [J]. Science, 198(4323):1264-1267, (1977).].

[0004] This report has attracted widespread attention in the biomedical field. Since then, researchers from different fields have conducted more in-depth research on brain function activities in brain science through multidisciplinary collaboration and various non-invasive detection technologies. This has made fNIRS technology play a crucial role in promoting the development and application of cognitive neuroscience [Pinti P, Tachtsidis I, Hamilton A, et al. The present and future use of functional near-infrared spectroscopy (fNIRS) for cognitive neuroscience. Annals of the New York Academy of Sciences, 2020, 1464(1):5-29.]. Near-infrared brain functional imaging technology is a relatively novel non-invasive optical detection technology for brain function in recent years [Quaresima, V.; Ferrari, MA. Mini-Review on Functional Near-Infrared Spectroscopy (fNIRS): Where Do We Stand, and Where Should We Go?]. Photonics, 2019, 6(3):87.], has been fully affirmed in clinical medical applications in many fields. For example, fNIRS has been applied in the fields of mental illness, pediatrics, stroke rehabilitation, neurodegenerative diseases, anesthesia depth monitoring, and brain oxygen monitoring in neurosurgical patients. With the development of fNIRS technology, near-infrared brain imaging equipment has appeared more and more frequently in clinical applications [LI Mengqi, GONG Anmin, NAN Wenya, XU Bojun, DINGPeng, FU Yunfa. Neurofeedback technology based on functional near infrared spectroscopy imaging and its applications. Journal of Biomedical Engineering, 2022, 39(5):1041-1049.].

[0005] fNIRS technology generally consists of a light source, a light source detector, and a data acquisition unit. The light source emits near-infrared light into a specific area of ​​the brain through a light-emitting diode or fiber optic bundle. The light is scattered along a "banana-shaped" path, and the detector receives the light signals scattered back by the brain tissue. Currently, the effective monitoring distance of the light source and detector in near-infrared brain imaging equipment is generally within the range of 2-7 cm, and the monitoring depth is within 3 cm [Wigal SB, Polzonetti CM, Stehli AA. Phase synchronization of oxygenation waves in the frontal areas of children with attention-deficit hyperactivity disorder detected by optical diffusion spectroscopy correlates with medication[J]. Biomed Opt, 17(12):127002, (2012).]. Figure 2 As shown, effective detection signals from the brain tissue within the cerebral cortex must penetrate superficial tissues such as the skull and scalp to be received by the detector. Therefore, the received light signal comprises both superficial and deep cortical components. Existing techniques typically compensate for this by increasing the source-detector distance (SDS). As the distance between the light source and detector increases, the "banana-shaped" optical path also becomes longer, meaning the optical path becomes deeper, thus increasing the detection depth. However, according to diffusion theory, this method of compensating for detection depth by increasing SDS reduces the intensity of the received detection signal, and the signal intensity decreases exponentially with increasing SDS.

[0006] To facilitate subsequent signal processing, researchers hope to shorten the SDS to improve spatial resolution [Tamborini D, et al. Portable system for time-domain diffuse correlation spectroscopy[J]. Biomed. Eng. 66, 3014–3025, (2019).], while also reducing signal interference in the superficial brain and lowering measurement errors in blood flow and blood oxygenation. In 2005, Alessandro Torricelli et al. theoretically proposed a new method to improve the spatial resolution of fNIRS technology. This method can improve spatial resolution while reducing the distance between the light source and the detector. Compared with traditional methods, this method can better locate diffuse photons. Although at that time it was only derived from theoretical models and no feasible experimental scheme was found [Alessandro Torricelli, Antonio Pifferi, Lorenzo Spinelli, et al. Time-Resolved Reflectance at Null Source-Detector Separation: Improving Contrast and Resolution in Diffuse Optical Imaging[J]. Physical Review Letters, 95, 078101, (2005).]. To this end, invention patents with application numbers CN202310171813.6 and CN202310170049.0 proposed a solution based on a bidirectional functional device using multi-clad optical fiber and constructed a novel fiber diffuse time-resolved probe system for brain-computer interfaces.

[0007] Based on the above-mentioned technology, this invention overcomes the technical difficulties in the implementation of prior art and proposes a new method that is simple and easy to prepare. This solution not only reduces the difficulty of technical implementation, but also makes it easy to mass-produce, which can greatly reduce costs.

[0008] This invention discloses a device for a fiber optic brain-computer interface, enabling near-infrared functional cerebral hemodynamic detection. It employs a microprism beam splitter / combiner and a hemispherical microlens device to connect and transmit the optical path of the system. The light source emitting component and detector convert and amplify the optical signal into an electrical signal for processing. Compared with prior art, the use of the microprism fiber optic beam splitter / combiner and the hemispherical microlens improves signal coupling efficiency, enhances the stability of emitted and received light, and further improves the integration of the device. Summary of the Invention

[0009] The purpose of this invention is to provide a fiber optic brain-computer interface device with a microsphere lens combination that has a simple and compact structure, high coupling efficiency, and can integrate multiple optical paths into a single channel.

[0010] The objective of this invention is achieved as follows:

[0011] A fiber optic brain-computer interface device based on a microsphere lens assembly comprises a transmitting component formed by transmitting light sources 1-1 and 1-2 and a single-mode fiber wavelength division multiplexer 2, a microprism beam splitter / combiner 3, a fiber optic receiving cable 4, a brain-computer interface housing 5, a fiber-to-the-edge hemispherical transmitting / receiving microlens 6, a beam-shaping coupling lens 7, and a single-photon detector (SPAD) receiver 8. In this system, two near-infrared wavelength light sources 1-1 and 1-2 emit light alternately. The optical signal passes through the wavelength division multiplexer 2, then through the microprism beam splitter / combiner 3, and via the fiber optic cable 4 to the 45° reflecting surface of the hemispherical transmitting microlens 6. After being focused by the hemispherical transmitting microlens 6, it passes through the beam-shaping coupling lens 7 and is injected into the cerebral cortex. The backscattered light signal from the cerebral cortex passes through the same beam-shaping coupling lens 7, and is sent back to the microprism beam splitter / combiner 3 via the fiber optic cable 4. After transmission through the microprism, it is received by the single-photon detector (SPAD) 8, converted, and amplified into an electrical signal for processing.

[0012] This fiber optic brain-computer interface device features bidirectional operation. Based on the microsphere lens combination, a small microprism fiber optic splitter / combiner is used to connect the light source, detector, and optical cable. In this way, regardless of the number of optical paths or the type of fiber structure in the optical cable, transmission connection between single and multiple optical paths can be achieved, improving the coupling efficiency between the input optical path, the receiving optical path, and the optical cable.

[0013] This fiber-optic hemispherical microlens consists of half a coated microsphere and a pigtail structure. The fiber-optic hemispherical microlens is fabricated according to the following steps: Step 1: Strip the coating from the spare fiber, cut and clean it; Step 2: Place the fiber end under a dual-electrode high-temperature plasma arc, rotating and sintering simultaneously until a microsphere structure is formed, then stop processing; Step 3: Place the fiber end with the microsphere on a fiber end polishing machine, adjust the angle with the fiber to 45°, and then polish and cut until only half a microsphere remains. A reflective film is then coated onto the beveled surface of the remaining half-microsphere; Step 4: Encapsulate and protect. The microsphere can be fabricated using large-diameter coreless optical fibers or smaller-diameter quartz rods. The microsphere and pigtail are welded together. The pigtail can be a single large-core optical fiber or multiple optical fibers of different structures, depending on the application requirements.

[0014] In the process of non-invasively detecting changes in brain blood flow using optical signals, the light needs to penetrate multiple layers of material, including the scalp and skull, to reach the target brain region. However, the signal transmitted to the detector after diffusion is very weak. To improve the efficiency of the optical signal, it is necessary to ensure good collimation of the emitted light, minimizing light diffusion as it passes through the scalp, skull, and multiple layers of meningeal tissue. Simultaneously, the receiving device for collecting diffused light signals must have a large area and a high signal-to-noise ratio to increase signal stability. Therefore, a beam-shaping lens is needed at the contact point between the interface device and the head before the light signal enters the brain tissue to achieve these objectives. Using a beam-shaping lens, the device can fulfill its bidirectional function. On one hand, it ensures that light diffusion is suppressed during injection as it passes through the scalp, skull, and multiple layers of meningeal tissue via a hemispherical microlens, increasing the penetration depth of the light source. On the other hand, it also expands the effective receiving area for collecting diffused light signals.

[0015] By comparing the light signals transmitted with and without a beam-shaping lens through simulation calculations, the divergence angle θ of the emitted light beam and the solid angle Ω of the diffused light received can be calculated to determine their necessity. Without the beam-shaping lens, the light from the source begins to diffuse after traveling approximately a few millimeters through the hemispherical microlens; however, the light signal transmitted through the beam-shaping lens maintains good directivity even at approximately 1 centimeter. This not only effectively suppresses severe beam diffusion of the hemispherical microlens output light in the cerebral cortex, skull layer, and superficial brain tissue, improving spatial resolution, but also enhances the penetration depth into brain tissue. Furthermore, when receiving diffused light signals, this self-focusing lens effectively expands the signal reception solid angle, improving the overall light-gathering efficiency and enabling the reception of more light signals. In this sense, it further enhances the detection capability of deep brain regions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a fiber optic brain-computer interface device based on a single microsphere lens combination.

[0017] Figure 2 This is a schematic diagram of a microprism beam splitter / combiner.

[0018] Figure 3 This is a schematic diagram of the connection between the fiber-end hemispherical transmitting / receiving microlens and the twin pigtails, one of which is a large-core fiber and the other is a double-clad fiber.

[0019] Figure 4 This is a schematic diagram of a fiber optic brain-computer interface device with a combination of dual microsphere lenses. Detailed Implementation

[0020] The present invention will be further illustrated below with reference to specific embodiments.

[0021] Example:

[0022] It is well known that the activity level of brain nerves is closely related to the degree of change in cerebral blood oxygen content. This allows us to infer the activity of brain nerves by measuring changes in local cerebral blood oxygen levels, thereby analyzing the neural activity of the brain and accurately locating specific brain regions of interest (e.g., the epileptogenic zone leading to epilepsy, the memory impairment zone corresponding to Alzheimer's disease, etc.). The fiber optic brain-computer interface device based on a microsphere lens combination disclosed in this invention features bidirectional operation. It constructs a high spatial and temporal resolution fiber optic brain-computer interface system by utilizing a microprism beam splitter / combiner, fiber-end hemispherical transmitting / receiving microlenses, and beam-shaping lenses. By acquiring diffuse reflected light information of blood oxygen changes within brain tissue, it enables real-time monitoring of changes in blood oxygen levels and blood flow within the brain, improving the spatial resolution of the detection. Through testing the dynamic changes of HbO2 and HbR in the brain region under test, it provides information reflecting changes in cerebral hemodynamics, and then determines the location of brain regions with abnormal blood flow changes, providing a basis for establishing a convenient correspondence between brain functional activity and anatomical location.

[0023] Figure 1 An embodiment of a fiber optic brain-computer interface (BCI) device based on a single microsphere lens assembly is presented. The system comprises a transmitting component formed by emitting light sources 1-1 and 1-2 and a single-mode fiber wavelength division multiplexer 2, a microprism beam splitter / combiner 3, a fiber optic receiving cable 4, a BCI housing 5, fiber-end hemispherical transmitting / receiving microlenses 6, a beam-shaping coupling lens 7, and a single-photon detector / receiver 8. In the fiber optic BCI device based on the single microsphere lens assembly, the two near-infrared wavelength light sources emit light at 735nm and 905nm respectively. The optical signal is transmitted to the optical cable via the wavelength division multiplexer and then by the microprism beam splitter / combiner. The optical cable contains two encapsulated optical fibers: one double-clad fiber for transmitting the optical signal and the other a large-diameter fiber for receiving the optical signal. The ends of the two fibers are twisted together and sintered at high temperature to form a microsphere structure, as shown below. Figure 3 As shown, the microspheres are then polished or cut at a 45° angle to the optical fiber, and a reflective film is coated onto the cut surfaces of the remaining hemispherical microspheres. The emitted light signal travels via optical cable to the 45° reflective surface of the hemispherical emitting microlens, is focused by the microlens, and then converged by a beam-shaping coupling lens before being injected into the cerebral cortex. The beam-shaping lens is essentially a self-focusing lens, satisfying a bidirectional optical path. It suppresses beam diffusion during injection, increases the penetration depth of the light source, and expands the effective receiving area for diffuse light signals.

[0024] Backscattered light signals from the cerebral cortex during detection are received by a beam-shaping coupling lens with a large detection area. After passing through the same lens, the light is sent back to the microprism beam splitter / combiner via an optical cable. After being transmitted through the microprism, the light is received by a single-photon detector (SPAD), converted, and amplified into an electrical signal for processing.

Claims

1. A fiber optic brain-computer interface device based on a microsphere lens assembly, characterized in that: It consists of a transmitting assembly formed by emitting light sources 1-1 and 1-2 and a single-mode fiber wavelength division multiplexer 2, a microprism beam splitter / combiner 3, an optical fiber receiving cable 4, a brain-computer interface housing 5, a fiber-to-the-edge hemispherical transmitting / receiving microlens 6, a beam-shaping coupling lens 7, and a single-photon detector / receiver 8. In this system, two near-infrared wavelength light sources 1-1 and 1-2 emit light alternately. The optical signal passes through the wavelength division multiplexer 2, then through the microprism beam splitter / combiner 3, and via the optical cable 4 to the 45° reflecting surface of the hemispherical transmitting microlens 6. After being focused by the hemispherical transmitting microlens 6, it passes through the beam-shaping coupling lens 7 and is injected into the cerebral cortex. The backscattered light signal scattered from the cerebral cortex passes through the same beam-shaping coupling lens 7, and is sent back to the microprism beam splitter / combiner 3 via the optical cable 4. After being transmitted through the microprism, it is received by the single-photon detector (SPAD) 8, converted, and amplified into an electrical signal for processing.

2. The fiber-to-the-end hemispherical microlens used in the fiber optic brain-computer interface device based on a microsphere lens assembly according to claim 1, characterized in that: The aforementioned fiber-optic hemispherical microlens consists of a half-coated microsphere and a pigtail structure. The hemispherical microlens can be manufactured by melting, rotating, and then cutting large-diameter coreless optical fibers; the pigtail can be a single large-core optical fiber or multiple different types of optical fibers.

3. The fiber optic brain-computer interface device based on a microsphere lens assembly according to claim 1, characterized in that: In a combined optical lens system consisting of a fiber-end hemispherical microlens and a beam-shaping lens, depending on the requirements, it can be divided into one where a single hemispherical microlens realizes the function of transmitting and receiving signals, or one where two hemispherical microlenses realize the function of transmitting or receiving signals independently.

4. The fiber optic brain-computer interface device based on a microsphere lens assembly according to claim 1, wherein the technical features of the fiber optic splitter / combiner based on the microprism are as follows: the single-mode fiber end and the two multimode fiber ends are respectively connected to the fiber end collimator, the three fiber ends are respectively placed on the three surfaces of the microprism splitter / combiner, the emitted light enters the microprism from the single-mode fiber and is reflected by the 45° reflecting surface to the multimode fiber, and then enters the optical cable 4; the received light enters the microprism through the optical cable 4 and is transmitted through the third multimode fiber, and is directly received by the single-photon detector (SPAD) 8.

Images