Research of Polymer Planar Optical Waveguide Sensing Characteristics

In this paper, the theoretical model of transmission characteristic of microring resonators was established based on coupled-mode theory to get microring resonator resonance wavelength, free spectral range and other performance indicators. Working principle of optical waveguide microring biosensor was investigated. The article also researched the relationship between optical guide physical parameter and surface sensitivity and improved composite optical guide sensing components sensitivity calculation method and then established disappeared wave type sensing components sensitivity analysis method. Based on this, the article has developed sensitivity calculation software for high sensitivity optical guide sensing components and improved film refraction rate of calculation method for sensitivity calculation.


INTRODUCTION
Broadband communication can be achieved through the free space optics and waveguide optics.Free-space optics (FSO) refers to the modulation of visible light and infrared for broadband communications [1,2].This method can be used in the range of a few kilometers which is influenced by rain, snow, dust and fog relatively.Fiber is divided into optical fiber waveguide and planar waveguides mainly based on waveguide optics theory.Silica fibers are widely used in high-speed data transmission, but it is not conducive to the integration of high density.Planar light wave circuit devices can diversify its device integration.Planar integrated optics and waveguide not only for short distance optical networks, but also in all-optical networks.Recently, technology of dense wavelength division multiplexing for optical communication created a revolutionary progress.DWDM uses multiple wavelengths as carrier to allow the carrier channels simultaneously in the fiber-optic transmission [3].
Polymers have unique advantages in fabrication of optoelectronic devices.Preparation technology of polymer optical waveguide devices has more experienced and better compatibility where multiple types of substrate, lasers, modulators, detectors, sensors can be integrated into a single chip.Good flexibility of polymers can be used for vertical and level interconnection devices [4].While the gray-scale gradient of exposure and etching of polymer offers promising prospects for vertical integration and integrated stereo three-dimensional space and flexible polymer optical waveguide device.Polymers are very promising development and application prospect of the base material.At present, the polymers have been used production of arrayed waveguide grating Multiplexer, optical switches, amplifiers, modulators and micro-ring resonator.Photonics polymer devices has been involved in almost every field.Polymer materials have made a breakthrough in optical loss and optical amplification in recent years [5].
In the Photonics field of high-tech in the world today, manufactured by polymer planar waveguide technology sensors become the focus of research.Compared with the traditional use of sensors to detect electrical signals, polymer planar waveguide sensor uses optical signal for detection which has the advantages of light quality, antielectromagnetic interference ability, low power consumption, wide working frequency range, stable performance and so on.Compared with the fiber optic sensors, polymer planar waveguide sensor has the following advantages: (1) it has a wide choice of materials, flexible structural design and much higher sensitivity.(2) It can achieve multiple channels at the same time and system functions on a substrate integrated waveguide.(3) It can reduce the cost of product for the semiconductor technology for mass production.Based on the above advantages, polymer planar waveguide sensor is very significant and has market prospects and development potential [6][7][8].
Direction of optoelectronics development is the integration of functions and number of integration.Functional integration is different functional components integrated into a single chip which is miniaturized, high accuracy and high reliability.It can be combined with advantage properties of discrete devices and bring the overall integrated performance optimization.Number of integration is designed to include several single devices together in forming arrays of devices and it achieved a kind of discrete devices that cannot achieve functionality, device miniaturization and integration.components in one place.Mixed integration is the result of a mixture of different production processes after making some components, installation or other optical crystals in semiconductor substrate of assembly technology.
From the perspective of space, light integration can be divided into two-dimensional and three-dimensional integration.Two-dimensional integrated development of mature is a synthesized on planar optical waveguide devices.Three dimensional optical waveguide for integrated integration provides ample space and ideas not only in the fabrication of optical waveguide devices on a plane and on a different surface, different coupling modes where implement integrated optical waveguide devices.Compared to a twodimensional integration, three dimensional integration process is more complexity and difficulty of preparation.Three dimensional space achieved integration through two main methods which the first is a vertically coupled method of lithography and second is gradient etching.
With further development of optical technology, some problems were discovered in inorganic optical waveguide devices including cost, silicon-based optical switch driving power, wavelength tuning range of issues and so on.So people focus on the choice of materials in waveguide devices.In order to get highly-integrated optical components, polymer is concerned as an option [9,10].High performance polymer materials for integrated optical waveguide devices is very important, this is because the polymer is simple and it can improve the performance and reduce costs.For example polymer reduces optical loss of the device.In addition, we can allow devices with optical power zoom or improve the electro-optical properties of devices by doping the polymer devices.Due to polymer optical waveguide devices have more advantages, so the study of polymer optical waveguide devices is very important [11].

OPTICAL WAVEGUIDE PRINCIPLE OF REFRACTION
Waveguides can make waves in transverse or longitudinal to be restricted to guide wave along a certain direction and inhibit dissipation of energy.Waveguides is divided into flat, rectangular, Ridge and the loading bar based on waveguide cross-sectional shapes.And it is divided into multimode interference (MMI), long/short periodic grating, arrayed waveguide grating (AWG), Mach-Zander Interferometer (MZI), coupling (DC) and the micro-ring resonator (MR) and many other types based on waveguide planar structures.Optical waveguide is a basic structure of many optoelectronic devices such as lasers, wavelength division multiplexers, modulators, amplifiers, attenuators, sensors, and so on.
Structure of planar optical waveguide devices and design of its scale is necessary to transmit optical waveguide analysis.Effective refractive index of optical waveguide determines the characteristics of light.We can solve various models of effective refractive index with Hay muesli equation and boundary conditions.The non-symmetrical three layer planar waveguide and guided modes of a rectangular waveguide structure equation is derived in this section.
The simplest structure consists of three-layer dielectric waveguide which in the middle of the dielectric layer known is the core called the cladding layer and both sides is the media.N1, N2, N3, respectively is the refractive index of the waveguide core, lower and upper cladding.Incidence and refraction of beam meet the Snell's law of refraction at the interface (Fig. 1).

Fig. (1).
Reflection and refraction of light. (1) There is total reflection for beams in the two boundaries at the same time.Refraction of light does not exist in the upper and lower layer.Light spreads along the z direction in a waveguide core layer called the guided mode (Fig. 2).

Fig. (2). Three layer planar waveguide cross section diagram.
There are two basic patterns in a slab waveguide.If we select electric field along the y direction which is parallel to the wave guide interface polarization and electric field perpendicular to the z direction is horizontal, the transverse electric mode is called transverse electric mode (TE-mode).If we select the direction of magnetic field which is parallel to the wave guide interface y polarization and magnetic field perpendicular to the z direction is horizontal, this model is called as transverse magnetic mode (TM-mode).
Combined with Hay muesli equations and boundary conditions we can obtained the characteristic equation of non-symmetrical three layer planar waveguide.
When S=0, it is for the TE mode.While s=1, it is for TM mode.

CHARACTERISTICS OF OPTICAL WAVEGUIDE SENSORS
In this type of sensors, sensitive reagent fixed on the surface of optical waveguide film affects with the object and changes waveguide propagation mode of light which is usually seen on the propagation of light on the loss or displacement.These factors change the output light intensity and output light intensity levels associated with the amount of detection output light intensity could be obtained by measuring the concentration of information.
Compared with other chemical sensors, optical waveguide sensors have the following characteristics: (1) Optical waveguide is very sensitive to ambient refractive index changes for waveguide layer.Optical chemical sensor sensitivity is good. ( We can achieve a high sensitivity through keeping the sensitive material and waveguide material and structure optimization design. (3) It has high mechanical strength and resistance to electromagnetic interference and small size and can work at room temperature. (4) We can achieve multiple channels at the same time and system miniaturization and multi-functional and reduce power consumption through single-chip integration.
(5) It can provide new sensing applications and integration potential by combining with micromachining and micro-electronics technology.(6) It can reduces costs through integrated process to achieve mass production.
Based on evanescent wave sensors of optical waveguide field strength enhancement mechanism, the current optical waveguide surface Plasmon resonance chemical sensors can be divided into surface Plasmon resonance (SPR) and flat glass optical waveguide sensors.

Surface Plasmon Resonance
Surface Plasmon resonance was found in optical waveguide a physical optics phenomena.Due to special optical properties of metals, metal at the interface of surface Plasmon resonance waves can be transmitted.A beam of incident plane monochromatic when polarized light at an angle to the glass surface coated with a thin layer of gold film total internal reflection occurs.If the wave vector of the incident light and the surface electron oscillation frequency of occurrence within the gold film, caused resonant light is coupled into the gold film which is called as surface Plasmon resonance.Surface Plasmon resonance of metal near the surface of the refractive index change is extremely sensitive.The researchers used this nature to develop the waveguide surface Plasmon resonance chemical sensor.The sensor structure chart is as follows Fig. (3).
In science and technology height developed of modern social in the, human has entered changing of information era.People main relies on information resources of development and gets transmission and processing of sensor in research object and control system of interface location in engaged in industrial production and science experiment, activities.Detection information of window is perception and it provides system which for decision and processing by required of original data.Sensor is the human instrument and ascertain the nature of tentacles and its role is similar to the human senses.If the computer is equivalent to the human brain, the executor is equivalent to the human body and the sensor is equivalent to human facial features.If people's facial features is out of order, brains don't reach the right conclusion and behavior into blindness, this shows the importance of sensors.Sensors not only have senses that humans have a function, but also for human senses cannot perceive important information beyond human reach and unable to endure harsh environments which are important and indispensable component of modern information measurement and control system.
All scientific and production processes in particular obtain information on the automatic detection and control system.Sensor is required for easy transmission and processing of the signals.If there are no sensors for accurate and reliable measurements of the original parameters.If the sensor is not sensitive to feelings or measure, it cannot be converted to electrical signals which are measured accurately and other instruments and apparatus of precision high has no meaning (Fig. 3).

Flat Glass Optical Waveguide Sensors
We select some compound for sensitive material and film it fixed on the surface of the k + ion-exchanged glass waveguides.Prism coupling method is used to enter a laser beam into optical waveguide.When it enters angle to meet the special angle of incidence of the light, light is constrained to guided wave level of total internal reflection and transmission.Flat-glass optical waveguide sensors have high sensitivity and rapid response, simple fabrication process and so on.Sensitivity of Planar waveguides is related with waveguide refractive index, the thickness of the layer, the sensitive layer, sensitive layers of light absorption and scattering factors.Therefore we can obtain chemical sensor with high sensitivity and selectivity by choosing the guiding layer and sensitive with flexibility.
Principle of optical chemical sensor is based on evanescent waves.Evanescent waves are inherent characteristics of dielectric optical waveguide and it does not have any special requirements for the waveguide material.It has the advantages of high sensitivity and easy to implement and so on.
The total internal reflection of light occurred in guiding layer and formed the guided mode.Light waves are not all reflecting the guiding layer at the interface, but instead of through interfaces must penetrate the cladding and base plate height which displacement and returns the guiding layer.The light waves of penetrating the cladding and base plate was called evanescent wave and its electric field intensity decreased according to an exponential decay.

Temperature Sensors
Polymer planar waveguide temperature sensors are based on planar light wave circuit as the carrier and it can feel changes in temperature and converts the optical output signal a new generation of sensors.Compared to other types of temperature sensors, polymer planar waveguide temperature sensors have the advantages of anti-electromagnetic interference ability, wide working frequency range, singlechip multi-function, low cost and so on.Polymer waveguide of Bragg grating temperature sensor is a new type of waveguide based on temperature change of refractive index grating period changes and Bragg grating wavelength shift integrated optical temperature sensing elements.
The light entered into the device through wide spectrum of light output coupling and entered into the spectrometer through the device of light coupled.And it used computers, monitors, and cameras, microscopes, composed of display systems to aid in testing and used precision micro bench system for debugging (Table 1 and Fig. 4).

Refractive Index Sensors
The refractive index is a basic parameter of liquid.In the daily life, liquid refractive index is required to obtain its parameters such as temperature, concentration and density.There is a requirements of real time detection of concentration and density in the area of food production, medical and health.So accurately detection of liquid refractive index is of great value in many fields of life and research.
The equation show that MZI waveguide output light intensity depends on the transmission phase difference of two branches of arms.We can carve eclipse on one of the support wave guide of package layer and make it as sensing arm and the other arm as reference arm.We make transmission light of died field energy as more of distribution in outside air in the dang to sensing arm drops plus liquid.Due to died field by this interference, transmission light of energy distribution will occurred change to led to sensing arm wave guide of guide die effective refraction rate changes.The two arm of transmission phase with of change caused output light strong changes (Figs. 5, 6).

CONCLUSION
At present, the world is a developing information age.Optical communications is an important technology building information society.Therefore, integrated optics has become the field that the international scholars focus on.Polymer planar optical waveguide is an important research field in the field of integrated optics.The polymer planar optical waveguide used as sensor is a new attempt which is very helpful to the future development of sensors.
Preparation of optical waveguide sensor surface sensitivity calculation on sensitive components in structural adjustment is very important.The optical properties of the electromagnetic theory of light and medium based on calculation method of relative sensitivity of the optical waveguide sensors was optimized.Results show that the relative sensitivity of optical waveguide sensors and surface film of refractive index and thickness as well as guided-wave optical wavelength.Results of the study on the preparation of sensors laser light source selection provides a theoretical foundation.Programming with VB.NET language sensitivity has been developed on the basis of this calculation and drawing software which is easily calculated for data analysis.Improved calculation of the refractive index method for sensitivities calculation provides a reliable parameter.
The thesis uses electronic communication and intelligent design of instrument automation to test hardware architecture.The exposure meter is connected to the computer with a data acquisition card and use VB.NET programming language.The supporting optical waveguide testing system has been developed for data collection and analysis software.Realizes detection system connects to your computer so as to solve the original of the original system which cannot detect data, processing and keeping of inconvenient and so on.The application software does not need any software support with friendly interface, easy operation and high operation stability.We can use the newly designed optical waveguide testing system based on optical waveguide with high sensitivity detection of sulfur dioxide and hydrogen sulfide gas sensor.We can use new design of optical waveguide testing system research team which has developed detection of acid gases and volatile organic compounds in chemical sensors of optical waveguide sensors with high sensitivity.We proved that the new design's detection systems is more powerful than the original analysis of the detection system.IT is accurate, sensitive and bringing great convenience to this kind of detection.
This thesis is about the fundamental research of the polymer MZI waveguide liquid refractive index sensor and the polymer waveguide Bragg grating temperature sensor, the main work are: (1) In the polymer MZI waveguide liquid refractive index sensor, the length of sensing window was optimized by means of the VC++ software programming.In the chosen measuring range, the monotonicity change of measurement curve can be realized, and the higher sensing sensitivity can be obtained.The device which has very good performances was fabricated taking advantage of microelectronics technology, and the stability of the test system is improved by the aluminum probe device fixed on the test platform, the refractive index sensing function is realized by testing the relationship between the output optical power and the measured liquid concentration.(2) In the polymer waveguide Bragg grating temperature sensor, according to the existing process conditions, the grating structure is reasonably designed, the grating characteristic parameters are analyzed by means of the MATLAB software programming, the Bragg waveguide grating filter which has good performances is prepared by using ultraviolet lithography and ICP etching, and the temperature sensing function is realized by the testing the drift of the resonance wavelength with the temperature change, the sensor sensitivity is -0.20686 nm/°C.