Multimode Optical Fiber Spectrometer Based On Interference Speckle Pattern

The spectrometer is an important part of the optical instrument.It is based on optical principle to measure and analyze,and is the basic equipment for analyzing the structure and composition of processed materials.It has the advantages of high accuracy,wide measuring range and fast speed.It is widely used in metallurgy,geology,petroleum,chemical,medical and health,environmental protection,and resources and hydrologic exploration.Modern spectroscopy technology began in the industrial application of the Second World War.Today,spectroscopy and related optical sensing technology have been developed into tens of billions of industries.The application of spectroscopy technology covers almost all the scientific fields.The classical spectrometer is an instrument based on the principle of spatial dispersion.According to the principle of dispersion,the prism spectrometer,the diffraction grating spectrometer and the interference spectrometer can be divided.Its core components include collimation element,dispersion element,focusing element,detector array,and so on.It has great weight.But the low resolution of the prism spectrometer;diffraction grating spectrometer needs by rotating grating scanning the entire spectrum,measuring speed is slow,some of the samples needed by pretreatment with specific,and should be put in the fixed sample chamber;Fourier transform spectrometer due to dynamic mirror interference,the online reliability limited,especially for the instrument the use of the environment where there are strict requirements,such as temperature,humidity,vibration,etc..There are technical bottlenecks in the ultraviolet band.The above spectrometer system is too large in volume and power,or the stability and repeatability of the instrument are not enough.In order to solve this series of problems,the researchers put forward a spectrometer with high resolution,light weight,easy to carry and use.It is very lightweight and can be used to choose between the resolution and spectral bandwidth of optical fibers with different geometric properties.Multimode fiber supports many different phase velocity transmission modes.From the point of view of geometry optics(for multimode fiber,it has a reasonable precision),different optical modes pass through the optical fiber axis at different angles.Because the transmission angle of the light is different,the transmission distance is also different.The result is that they will have different phase delays from the input of the fiber to the output face.A more accurate analysis of the distribution of the conductive magnetic field of light waves shows that there are many different possible modes of propagation,and these different modes have different phase velocities.No matter what kind of view is that a point for any optical output terminal,if the phase of these models have more than 2 pi delay,and light enough coherence,by the superposition of a large number of individual models,in the output light intensity distribution will see obvious interference phenomenon.Multimode fiber spectrometer is based on the interference speckle of the output side of multimode fiber,and the spectral information contained in the interference speckle pattern can be recovered according to the corresponding distribution relation of different speckle patterns of different spectra.The spatial intensity distribution of different wavelengths is stored in the matrix by the correspondence between the spectrum and the two-dimensional distribution of the interference speckle pattern space.The restoration algorithm can restore the unknown arbitrary input spectrum by using the stored spatial intensity distribution information.Compared with the conventional spectrometer,the multimode fiber interferometer is compact and light weight,and can be easily selected between the resolution and the spectrometer bandwidth.The core component is multi-mode optical fiber,and the price is low.Therefore,the multimode optical fiber spectrometer has a great advantage.In the experiment,the highest resolution of the spectrometer can reach 2 pm.