CN202403893U - Active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging - Google Patents

Abstract

The utility model discloses an active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging, which uses a high numerical aperture microscopic objective lens to build a fluorescent imaging device, and the incident laser light is focused and irradiated to the active polymer through a high numerical aperture oil immersion microscopic objective lens. The source polymer film excites the active material doped in the film to make it emit fluorescence; the excited fluorescence can be coupled into a guided wave transmitted in the planar waveguide. During the propagation of the guided wave, part of the light energy will leak and radiate from the side of the waveguide to the far field along some specific angles, and will be collected and imaged by the same objective lens on the CCD image sensor. These specific angles and radiated fluorescence light field distribution are related to the propagation constant of the guided wave, and they are all reflected in the fluorescent image recorded by the CCD. Therefore, the propagation constants of various guided waves in the planar waveguide are deduced from the fluorescent image. The utility model has the advantages of simple and compact structure and high spatial resolution, and is suitable for real-time monitoring and rapid measurement of the propagation constant of the active polymer planar waveguide.

Description

A Measuring Instrument for Propagation Constant of Active Polymer Planar Waveguide Based on Fluorescence Imaging

technical field

The utility model relates to the technical field of measuring and calculating the intrinsic parameters of optical waveguide devices, in particular to an active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging.

Background technique

The integration and miniaturization of optical information processing systems have led to the rapid development of polymer planar waveguides relying on their advantages such as easy processing and low loss, and the propagation constant, one of the basic properties of optical waveguide devices, is not available in the design and research of optical devices in integrated optics. Or missing. Active substances (luminescent particles) doped in planar waveguides can effectively compensate waveguide transmission loss, and are also used to develop various active waveguide optical devices, such as waveguide lasers and waveguide amplifiers. Therefore, it is of great application value to study the measurement methods of various guided wave propagation constants in active material polymer waveguides. The existing relatively mature method of measuring the propagation constant of the planar waveguide is mainly based on the angular scanning method (M-line method) of the prism, and solving the transcendental equation to obtain the waveguide parameters. Its main problems are:

1. The process is cumbersome and the measurement speed is slow. The M-line method requires a specific prism coupling instrument (θ-2θ instrument) to measure the effective refractive index of the waveguide, and requires point-by-point scanning of the angle, which is slow and time-consuming, and cannot achieve real-time observation.

2. The spatial resolution is low. Its structure can only excite the resonant guided mode in one-dimensional direction, and there is no high numerical aperture objective lens focusing system, so the spatial resolution is low.

3. Limitations. This method is not easy to directly calculate the imaginary part of the propagation constant, that is, the propagation length of the guided wave.

Utility model content

The purpose of this utility model is to overcome the deficiencies of the prior art, and proposes an active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging, which has a simple and compact structure, high spatial resolution, no need for angle scanning, and real-time monitoring. Suitable for efficient and complete measurements of the propagation constant of planar waveguides.

The technical scheme that the utility model realizes above-mentioned purpose is as follows:

An active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging: it includes: laser light source, beam expander lens group, beam splitter, high numerical aperture oil immersion microscope objective lens, refractive index matching oil, planar waveguide, filter light sheet, convex lens and CCD image sensor; where,

The active polymer planar waveguide is a four-layer structure consisting of a glass substrate, a metal film, a polymer film doped with source material, and an upper air layer. The preparation process is: evaporation or sputtering on the glass substrate A metal thin film, and spin-coating a polymer solution doped with an active substance on the metal thin film to form an active substance polymer film, wherein the active substance is a fluorescent molecule;

The laser light emitted by the laser light source is expanded by a beam expander lens group and then passed through a reflector, a high numerical aperture oil-immersion microscope objective lens, and a refractive index matching oil to focus and irradiate the active polymer film with a wide angle range. The fluorescent molecules in the polymer film are stimulated to radiate fluorescence, and the fluorescence is coupled into a guided wave transmitted in the planar waveguide; at certain angles, part of the energy of the transmitted guided wave leaks out of the waveguide structure from the side of the glass substrate. Collected by the microscope objective lens, after passing through the beam splitter, filter and convex lens, bright rings of different radii will appear on the CCD image sensor. The real part of the propagation constant of various modes existing in the waveguide structure corresponds one by one, and the real part of the propagation constant of the guided mode is calculated by analyzing the radius of the bright ring in the fluorescence image and the known numerical aperture of the microscopic objective lens;

The imaginary part of the propagation constant is obtained by calculating the optical image of the reflected light field on the back focal plane. The fitting calculation steps are as follows: read the image, record the fluorescence intensity distribution curve along the diameter direction, and compare it with the Lorentzian curve Fitting, find the full width at half maximum of the fluorescence intensity distribution curve in the diameter direction, and calculate the propagation length; it corresponds to the imaginary part of the propagation constant of the guided mode.

Further, the laser light source covers the entire entrance pupil of the high numerical aperture oil immersion microscope objective lens after beam expansion, and makes full use of the high numerical aperture of the objective lens to obtain a smaller focused spot, thereby improving the spatial resolution of the measurement , to achieve micro-area measurement; at the same time, the same objective lens is used to realize the collection and imaging of fluorescent signals, which simplifies the structure of the instrument.

The principle of the technical solution of the utility model is:

The excitation light is focused and irradiated on the active polymer planar waveguide through a high numerical aperture microscope, so that the active substance (fluorescent molecule) doped in it emits fluorescence, and the intensity distribution image of the fluorescence on the back focal plane of the objective lens is captured by the imaging method , by analyzing the light intensity distribution on the image, the propagation constants of various guided modes existing in this planar waveguide are deduced. The propagation constant of a guided mode includes a real part and an imaginary part, the real part corresponds to the effective refractive index of the guided mode, and the imaginary part corresponds to the propagation length of this mode in the waveguide structure. specific,

The laser light source, through the designed optical path, realizes strong focusing to irradiate the planar waveguide, excites the fluorescence in the micro area, and couples the fluorescence into a guided wave transmitted in the planar waveguide. Due to the existence of the high-refractive index glass substrate, at certain angles, during the transmission of these guided waves, part of the energy will leak from one end of the glass substrate and radiate to the far field, and then in the back focus of the oil-immersed microscope objective. Bright rings of various radii are produced on the surface. Calculate the radius of the bright ring (half of the peak value) and the radius of the field of view (r=f nsin θ is the radius of the bright ring, f is the focal length of the high numerical aperture oil immersion microscope objective, n is the refractive index of the matching oil, and θ is The excitation angle of the guided mode, R=f nsin θ _m is the radius of the field of view, the maximum viewing angle of θ _m corresponds to the ratio of the numerical aperture of the microscopic objective lens), calculates the excitation angle or wave number of different guided modes, that is, corresponds to the propagation The real part of the constant. Further, a Lorentzian curve fitting is performed on the intensity distribution of the radiated fluorescence along the diameter direction of the bright ring. By calculating the full width at half maximum of the curve W, the propagation distance (W ^-1 ) of the guided wave is obtained, which corresponds to the imaginary part of the propagation constant.

Compared with the traditional technology, the utility model has the following advantages:

1. The structure is simple: the microscopic objective lens is used in this device to focus the excitation light to excite various guided modes in the micro-area, and is also used to collect fluorescence for imaging. Through the CCD to image the back focal plane of the objective lens, the fluorescence image is used to directly measure and calculate the propagation constants of all guided modes, and its structure is simple and compact;

2. High efficiency: no need for angle scanning, directly measure by imaging method, the measurement time is short, easy to operate, high efficiency; at the same time, it can dynamically monitor the influence of external factors such as temperature and humidity on the effective refractive index of the guided mode in real time ;

3. High resolution: Utilizing the high numerical aperture characteristics of the oil immersion microscope objective lens, high spatial resolution measurement can be realized.

4. Convenient mode analysis: Use the CCD image sensor to observe the radius of the bright ring and its light intensity distribution in the fluorescence image, and calculate the propagation constants of various guided modes by fitting.

Description of drawings

Fig. 1 is a structural schematic diagram of an active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging of the present invention;

Figure 2 is a measurement flow chart;

Fig. 3 is the fluorescent image on the rear focal plane of the microscope objective lens;

Fig. 4 is the fluorescence intensity distribution curve of each point along the dotted line (along the diameter) shown in Fig. 3

Among them, 1. Laser light source; 2. Beam expander lens group; 3. Beam splitter; 4. High numerical aperture oil immersion microscope objective; 5. Refractive index matching oil; 6. Glass substrate; 7. Metal film; 8. Has Source polymer film; 9, optical filter; 10, convex lens; 11, CCD image sensor.

Detailed ways

The utility model will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the same reference numerals in the accompanying drawings always represent the same components.

A kind of active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging shown in Fig. 1, comprises: laser light source 1 (such as wavelength 532nm laser), beam expander lens group 2, beam splitter 3, high numerical aperture oil Immersion microscope objective lens 4 (hereinafter referred to as the microscope objective lens 4), refractive index matching oil 5, glass substrate 6, metal film 7, active polymer film 8 (in the embodiment, the active material is rhodamine B), Optical filter 9, convex lens 10, CCD image sensor 11. Among them, the specific measurement process is shown in Fig. 2 . The preparation method of the active polymer planar waveguide is to evaporate or sputter a layer of 45nm thick silver film on the glass substrate 6, and dissolve the rhodamine B powder (being the active substance) in polymethyl methacrylate ( PMMA) anisole solution, and then spin-coated on the glass substrate previously deposited 45nm silver film and dried, that is, the active polymer planar waveguide was prepared. The prepared waveguide is connected with the microscope objective lens 4 (such as 60X, N.A.=1.42) through the matching oil 5 with a refractive index of 1.516; the 532nm laser light emitted by the laser light source 1 makes the incident light beam expand to Can cover the entrance pupil surface of the whole microscopic objective lens 4, after being reflected by the beam splitter 3, the fluorescent molecules are converged to the waveguide structure by the microscopic objective lens 4 to emit fluorescence, collected by the microscopic objective lens 4, and passed through the optical filter 9 (such as center wavelength 580nm, bandwidth 10nm narrow-band filter), filter out the 532nm excitation light, only let the fluorescence pass through, and the fluorescence intensity distribution on the rear focal plane of the microscopic objective lens 4 is imaged on the photosensitive surface of the CCD image sensor 11 by the convex lens 10 , and then the fluorescence image of the back focal plane of the objective lens can be obtained.

As shown in Figure 3, the ratio of the first bright ring in the field of view formed based on the above conditions and parameters to the radius of the field of view is 0.9436, and it is known that the excitation angle of this mode is 61.83°, and the corresponding effective refractive index is Guided mode of 1.34. The ratio of the radius of the second bright ring to the radius of the field of view is 0.8232, and the excitation angle of this mode is 50.27°, corresponding to the guided mode with an effective refractive index of 1169. Similarly, the ratio of the radius of the innermost bright ring to the radius of the field of view is 0.7112, so the excitation angle of this mode is 41.64°, and its effective refractive index is 1.01.

Further, Lorenz curve fitting is performed on the intensity distribution of the bright ring, so that the full width at half maximum is calculated as 0.033K ₀ , 0.0182K ₀ , and 0.0143K ₀ . Corresponding to the above three modes, the propagation lengths are 2.80 μm, 5.07 μm and 6.46 μm, respectively.

The parts not elaborated in this utility model belong to the known technology in the art. The above examples are only used to illustrate the technical solutions of the present utility model and are not limited to the scope of the specific implementation. For those of ordinary skill in the art, as long as various changes are within the spirit of the utility model defined and determined by the claims Within the scope and range, these changes are obvious, and all inventions and creations utilizing the concept of the utility model are included in the protection list.

Claims (1)

1. An active polymer planar waveguide propagation constant measuring instrument based on fluorescence imaging, characterized in that: it includes: a laser light source (1), a beam expander lens group (2), a beam splitter (3), a high numerical aperture Oil immersion microscope objective lens (4), refractive index matching oil (5), active polymer planar waveguide, optical filter (9), convex lens (10) and CCD image sensor (11); among them, The active polymer planar waveguide is a four-layer structure composed of a glass substrate (6), a metal film (7), an active material polymer film (8) and an upper air layer. The preparation process is as follows: on the glass substrate (6) Evaporating or sputtering a metal film (7), and forming an active substance polymer film (8) on the metal film (7), wherein the active substance is a fluorescent molecule; The laser light emitted by the laser light source (1) is expanded by the beam expander lens group (2) and then passed through the beam splitter (3), the high numerical aperture oil-immersion microscope objective lens (4), and the refractive index matching oil (5). The angle range is focused and irradiated on the polymer film (8), the fluorescent molecules in the polymer film are stimulated to radiate fluorescence, and the fluorescence is coupled into guided waves transmitted in the planar waveguide; at certain specific angles, the transmitted guided waves Part of the energy leaks from the side of the glass substrate and radiates out of the waveguide structure, which is collected by the microscope (4), passes through the beam splitter (3), filter (9) and convex lens (10) and presents different images on the CCD image sensor (13). Radius-sized bright ring. the

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