A microfluidic waveguide type variable optical attenuator

Abstract

A microfluidic waveguide type variable optical attenuator disclosed by the present invention belongs to the field of microfluidic photonics and relates to microfluidic optical waveguide functional devices and technologies. The microfluidic waveguide type variable optical attenuator proposed by the present invention is composed of 1 input waveguide (1), 1 output waveguide (2), 2 straight waveguides (3, 4) and 4 curved waveguides (5, 6, 7, 8), and the microfluidic channel is composed of 1 fluid input port (9), 1 output port (10), 2 microfluidic narrow channels (11, 12) and 1 microfluidic wide channel (13). After the optical signal is coupled into the input waveguide (1) through the tapered optical fiber, it travels forward along the straight waveguide (3), then enters the curved waveguides (8, 7, 6, 5) in sequence, then is combined in sequence and propagates along the straight waveguide (4), and finally is coupled to the tapered optical fiber through the output waveguide (2). Therefore, by changing the refractive index of the mixed liquid in the microfluidic channel, the optical loss in the curved waveguide is correspondingly changed, so as to realize the variable attenuation of the optical power output. The waveguide type variable optical attenuator provided by the present invention has the advantages of simple structure, easy fabrication, convenient regulation, low wavelength and polarization dependence, etc., and has broad application prospects in the field of microfluidic photonics.

Description

Technical Field

[0001] The present invention belongs to the technical field of microfluidic photonics, relates to optical functional devices, and particularly refers to a waveguide-type variable optical power attenuator based on microfluidic driving. Background Art

[0002] An optical attenuator is a functional device that effectively attenuates optical signals, and is mainly used to achieve power balance between channels in a system, or to achieve gain flattening of optical amplifiers in a system, or to protect photodetectors to prevent their gain saturation, etc., and has wide applications in optical communication and optical signal processing. At present, optical attenuators have various structural forms and different working principles. According to whether the attenuation method can be adjusted, they are divided into fixed optical attenuators and tunable optical attenuators. For a fixed optical attenuator, once its design and manufacture are completed, its optical attenuation amount is completely determined, which not only greatly limits its application fields, but also causes many new problems when integrated with other tunable photonic devices.

[0003] For tunable optical attenuators, driving technologies such as force, heat, light, and electricity are used to dynamically adjust their optical power attenuation, so this type of optical attenuator has received extensive attention and emphasis. At present, there are various implementation schemes for tunable optical attenuators. According to their working methods, they can be divided into micro-mechanical movement regulation type, attenuation sheet regulation type, thermo-optical regulation type, electro-optical regulation type, magneto-optical regulation type, photonic crystal regulation type, surface plasmon regulation type, etc. For these tunable optical attenuators, some have been actually applied in optical systems; some are in the basic or applied research stage and are still some distance from commercialization. However, these devices cannot be used in microfluidic photon systems, and usually have obvious deficiencies and defects in some aspects, such as the disadvantages of large structural size and large loss, or the disadvantages of small attenuation range and poor attenuation accuracy, or being very sensitive to device structure parameters, temperature, wavelength, and polarization state, or the disadvantages of difficult manufacturing, difficult regulation, and high cost, and they are often restricted in practical applications.

[0004] Microfluidic control technology is a new approach to obtaining tunable photonic devices. These novel devices achieve their tuning performance by regulating the refractive index of the fluid or changing the surface shape of the fluid. They have prominent advantages such as flexible design, large tuning range, simple tuning, and easy integration, and are widely used in the fields of optical signal processing, biosensing, chemical analysis, etc. So far, there have been relatively few research reports on microfluidic tunable optical attenuators. In 2005, L. Zhu et al. proposed a microfluidic waveguide-type tunable optical attenuator, where a partial region of the upper cladding serves as a microfluidic channel. By changing the refractive index of the fluid, the confinement ability of the guided light beam is regulated, thereby achieving optical attenuation. Although the device has a simple structure and is easy to integrate, the tuning linear range of this tunable optical attenuator is relatively small, and it has a large dependence on wavelength and polarization state. In 2008, H. Yu et al. used a pressure-driven method to change the thickness of the liquid in the light beam propagation region and change the light absorption of the liquid to achieve the regulation of optical attenuation. However, this scheme has low tuning accuracy and it is difficult to achieve a compact, easy-to-integrate, and easy-to-tune optical attenuator. In 2009, M. I. Lapsley et al. utilized the reflection and transmission characteristics of light at the liquid-solid interface. By changing the refractive index of the liquid, the reflection of the light beam at the interface is changed, thereby achieving the regulation of optical attenuation. But it has disadvantages such as poor stability, difficult optical path alignment and adjustment, and high optical loss, and cannot be used in an integrated microfluidic photonics system. In 2011, P. Muller et al. used electrowetting to drive the movement of the liquid to change the working liquid in the light beam propagation region, causing a change in its light absorption and achieving the regulation of optical attenuation. However, this attenuator has disadvantages such as high driving voltage, high wavelength dependence, large structural size, and inability to be integrated with waveguide devices. In 2016, J. Wan et al. used a micro-pressure pump to drive the movement of microfluid and air bubbles to change the reflection and transmission of the light beam, achieving adjustable optical attenuation of the light output. Its structure is simple and the tuning is easy, but it has disadvantages such as poor stability, low tuning accuracy, and difficulty in integration.

[0005] Currently, the research on microfluidic tunable optical attenuators is still in the basic exploration stage. There are relatively few relevant reports, and there are obvious disadvantages in terms of tuning performance, and there is still a large gap from practical applications. Therefore, actively constructing a new type of microfluidic tunable optical power attenuator has important application value for the development of the field of microfluidic photonics. Summary of the Invention

[0006] The object of the present invention is to provide a waveguide-type variable optical power attenuator based on microfluidic regulation. The attenuator is composed of curved waveguides with different radii and microfluidic channels. After the light beam is coupled into the waveguide input port, it propagates along the waveguide in the device, and its output optical power is closely related to the refractive index of the liquid in the microfluidic channel. Therefore, by changing the refractive index of the liquid, variable attenuation of the output optical power of the device can be achieved. The device has many advantages such as simple structure, easy fabrication, low wavelength and polarization dependence, and easy regulation.

[0007] The technical solution of the present invention is as follows:

[0008] A waveguide-type variable attenuator, as Figure 1 、 Figure 2 and Figure 3 shown, where Figure 1 is the top view of the overall structure of the device, and Figure 2 and Figure 3 are respectively the waveguide cross-sectional views at positions A1A2 and B1B2 in Figure 1 . The waveguide structure of the device is composed of an input waveguide 1, an output waveguide 2, straight waveguides 3, 4, and curved waveguides 5, 6, 7, 8 with different radii. The microfluidic channel of the device is composed of a fluid input port 9, an output port 10, microfluidic narrow channels 11, 12, and a microfluidic wide channel 13. The input waveguide 1 and the output waveguide 2 are ridge waveguide structures composed of a lower cladding material 14, a core material 15, and an upper cladding material 16, while the straight waveguides 3, 4 and the curved waveguides 5, 6, 7, 8 located in the regulation area are ridge waveguide structures composed of a lower cladding material 14, a core material 15, and an upper cladding material 17. The lower cladding material 14, the core material 15, and the upper cladding material 16 are different organic polymer materials, and their refractive indices are determined by the optical properties of the specific materials selected; while the upper cladding material 17 is a mixture liquid, and its refractive index is determined by the concentration of the mixture liquid. The input waveguide 1, the straight waveguide 3, the curved waveguide 5, the straight waveguide 4, and the output waveguide 2 are connected in sequence. The curved waveguide 5 is a semi-circular arc waveguide, so that the input waveguide 1 and the straight waveguide 3 are parallel to the straight waveguide 4 and the output waveguide 2. The curved waveguides 6, 7, 8 are respectively composed of 3, 5, 7 semi-circular waveguides connected in sequence, and the curved waveguides 6, 7, 8 are arranged side by side with the curved waveguide 5. The variable attenuation device is located between a lower substrate 18 and an upper substrate 19, and the lower substrate 18 and the upper substrate 19 are made of glass materials, which play a role in supporting and protecting the device.

[0009] The mixture liquid is injected into the input port 9 via a fluid pump, and then successively flows through the microfluidic narrow channel 11, the microfluidic wide channel 13, and the microfluidic narrow channel 12, and finally exits from the output port 10. The concentration of the mixed liquid is closely related to its refractive index. Therefore, the refractive index can be regulated by changing the concentration ratio during liquid mixing. The optical signal is coupled into the input waveguide 1 through a tapered optical fiber and propagates forward along the straight waveguide 3. Then the optical signal is successively split and enters the curved waveguides 8, 7, 6, 5. Next, the optical signals are successively combined and continue to propagate along the straight waveguide 4, and finally are coupled to the tapered optical fiber through the output waveguide 2. The loss of the optical signal in the waveguide is closely related to the magnitude of the liquid refractive index. Therefore, effective attenuation of the optical power can be achieved by changing the liquid refractive index.

[0010] The waveguide-type variable optical attenuator based on microfluidic driving provided by the present invention is composed of an organic polymer material. The device structure consists of two units: curved waveguides with different radii and microfluidic channels. Its structure is simple and can be fabricated by optical lithography. The specific manufacturing process can refer to relevant literature and will not be elaborated here.

[0011] The working principle of the present invention is:

[0012] The waveguide cross-section of the waveguide-type variable optical attenuator proposed by the present invention is as Figure 2 shown in Figure 3 Let the refractive index of the lower cladding material 14 be n 1, the refractive index of the core layer material 15 be n 2, and the refractive index of the upper cladding material 16 be n 3. Both the cladding and core layer materials are organic polymer materials. The width, thickness, and ridge height of the core layer in the waveguide are respectively w , d , h . The mixture liquid in the microfluidic channel flows forward, and its refractive index is n 4, and its refractive index magnitude can be regulated by changing the concentration of the mixture liquid.

[0013] When the optical signal is coupled into the input waveguide 1, it propagates along the straight waveguide. At each branch, the optical power is split in the same proportion and successively enters the curved waveguides 8, 7, 6, 5 with different bending radii and continues to propagate. According to the optical waveguide transmission theory, there is usually radiation loss when the optical signal propagates in the curved waveguide. The loss magnitude is not only related to the bending radius but also to the magnitude of the refractive index of the mixture liquid in the upper cladding. When the refractive index of the mixture liquid is small (0 < n 4 < n a ), the radiation loss of the optical signal in the curved waveguides 8, 7, 6, 5 is zero, so the optical attenuation is zero at this time; when the refractive index of the mixture liquid is gradually increased ( n a <n 4 < n b ), where the bending waveguide 8 with a smaller bending radius cannot effectively confine the optical signal, resulting in radiation loss. The radiation loss increases with the increase of the refractive index of the mixture liquid until the optical signal in the bending waveguide 8 is completely lost; when the refractive index of the mixture liquid is within ( n b < n 4 < n c ), the radiation loss of the optical signal in the bending waveguide 7 begins to increase until it is completely lost; when the refractive index of the mixture liquid is within ( n c < n 4 < n d ), the radiation loss of the optical signal in the bending waveguide 6 begins to increase until it is completely lost; when the refractive index of the mixture liquid is within ( n d < n 4 < n e ), the radiation loss of the optical signal in the bending waveguide 5 begins to increase until it is completely lost. Here 0 < n a < n b < n c < n d < n e . It should be noted that the variable optical attenuator adopts a plurality of bending waveguides arranged in parallel with different bending radii, so as to regulate the optical attenuation in a large refractive index range of the mixture liquid, which is conducive to realizing the precise regulation of its optical attenuation.

[0014] The waveguide-type variable optical attenuator proposed by the present invention is a microfluidic-driven photon functional device. Its principle is to utilize the change of the refractive index of the liquid in the microfluidic channel to regulate the radiation loss of its bending waveguide, and the losses of the bending waveguides with different bending radii are different, so as to obtain a high-performance regulated optical attenuation. This is a microfluidic photon device with a new function, which has the advantages of easy regulation, simple structure, easy fabrication, low wavelength and polarization dependence, and has broad application prospects in the field of microfluidic photonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a top view of the microfluidic waveguide-type variable optical attenuator provided by the present invention.

[0016] Figure 2It is a schematic diagram of the waveguide cross-section at the position of the connection line A1A2 in the top view of the microfluidic waveguide type variable optical attenuator provided by the present invention.

[0017] Figure 3 It is a schematic diagram of the waveguide cross-section at the position of the connection line B1B2 in the top view of the microfluidic waveguide type variable optical attenuator provided by the present invention.

[0018] Figure 4 It is the relationship between the normalized optical power output of the microfluidic waveguide type variable optical attenuator provided by the present invention and the refractive index of the mixed liquid, where the solid line and the dashed line are the TE wave and the TM wave respectively.

[0019] Figure 5 It is the relationship between the normalized optical power output of the microfluidic waveguide type variable optical attenuator provided by the present invention and the working wavelength, where the solid line and the dashed line represent the TE wave and the TM wave respectively, and at this time the refractive index of the mixed liquid is 1.530. Detailed implementation manners

[0020] The present invention will be further described below with reference to the accompanying drawings. In the microfluidic photonics system, the working wavelength of its optical signal is usually the same as that of the optical communication system, generally in the C band. Therefore, it is assumed here that the working wavelength of the optical signal is 1.55 μm. As Figure 1 shown, the core layer material 15 of waveguides 1, 2, 3, 4, 5, 6, 7, and 8 is SU-8, and its refractive index is 1.575; the upper cladding material 16 is the polymer material PMMA, and its refractive index is 1.492; the lower cladding material 14 is the polymer material UV-15, and its refractive index is 1.500. The core layer thickness, ridge height, and width of the waveguide are 0.6 μm, 0.7 μm, and 6.0 μm respectively. The bending radii of waveguides 5, 6, 7, and 8 are 2000 μm, 660 μm, 400 μm, and 280 μm respectively. It is assumed here that the mixed liquid in the microfluidic channel is a mixture of carbon disulfide and chloroform, and its refractive index can be changed by adjusting its mixing ratio, and its change range is set to be 1.480 - 1.580.

[0021] The Beam Propagation Method (BPM) is a commonly used method for studying the transmission performance of optical waveguide devices. Here, this method is used to simulate and analyze the optical performance of the microfluidic waveguide type variable optical attenuator provided by the present invention. When the refractive index of the mixed liquid varies between 1.480 and 1.580, the normalized optical power output of its output waveguide 2 changes with the refractive index of the mixed liquid as Figure 4As shown. It can be seen from the figure that its optical power output decreases monotonically with the increase of refractive index until it is completely attenuated, and finally the output drops to zero. The solid line and the dashed line in the figure represent the TE wave and the TM wave respectively. It can be seen from the figure that for different polarized lights, the curves of their optical power output changes are approximately the same, indicating that the polarization dependence of this attenuator is small.

[0022] In addition, for an optical signal, it usually has a certain spectral width, about dozens of nanometers. For example, the optical communication C-band window is 1530nm to 1565nm. Therefore, the present invention further examines the dependence of this device on its operating wavelength. The simulation results are as Figure 5 shown. The solid line and the dashed line in the figure represent the TE wave and the TM wave respectively. It can be seen from the figure that its output optical power changes little with the operating wavelength. Therefore, the wavelength dependence of this device is low, which has important value in practical applications.

[0023] A microfluidic waveguide type variable optical attenuator proposed by the present invention has the advantages of simple structure, easy fabrication, large attenuation range, easy manipulation, low wavelength and polarization dependence, etc., and has broad application prospects in microfluidic photonics systems.

Claims

1. A microfluidic waveguide type variable optical attenuator, comprising a waveguide structure composed of an input waveguide (1), an output waveguide (2), two straight waveguides (3, 4), and four curved waveguides (5, 6, 7, 8) with different radii; a microfluidic channel structure composed of a fluid input port (9), an output port (10), two microfluidic narrow channels (11, 12), and a microfluidic wide channel (13); the input waveguide (1) and the first straight waveguide (3) are parallel to the output waveguide (2) and the second straight waveguide (4); the curved waveguides (5, 6, 7, 8) are all composed of an odd number of semi-circular arc waveguides with different radii; after the optical signal is coupled into the waveguide input port (1) through an optical fiber, the optical signal propagates in the optical waveguide. When it reaches the curved waveguide in the regulation area, the light will be attenuated, and the attenuation magnitude is jointly determined by the waveguide bending radius and the refractive index of the mixed liquid. By changing the liquid refractive index, variable optical attenuation is achieved.

2. The variable optical attenuator of the microfluidic waveguide type according to claim 1, characterized in that, The optical signal is input from the input port, then transmitted through different paths, and output from the output waveguide port. The waveguide lengths of these different paths are all equal.

3. The variable optical attenuator of the microfluidic waveguide type according to claim 1, characterized in that The appropriate range of the radius of the curved waveguide is: 250μm < r < 2500μm.

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