Intelligent Micro Near Infrared Optical Fiber Spectrometer Is Developed

This work is to develop a type of economic and practical near-infrared, fiber-optic spectrometer covering 900-2500nm, with high precision, speedy response and small size. The following is the summary of this paper:1)A study of the design theory of near-infrared spectrometer has been made by comparing the commonly-used optical system structures and their working principle. The fixed optical detector has been used in the miniature near-infrared spectrometer system as a framework to achieve a system suitable for small-scale integrated on-line analysis with speedy scanning, high accuracy in measurement and resolution, high signal to noise ratio and reliability. By the research of performances of two kinds of spectral plane grating, Ebert-Fastie horizontal system and Czerny-Turner system, a new model of near infrared spectrometer is designed with a plane diffraction grating, G9208 type of refrigeration temperature-control InGaAs detector and with SMA905 fiber optic interfaced with a variety of new devices based on asymmetric cross C-T optical platform, achieving the design requirements of miniaturization, image quality, optical resolution, stray light control and low cost. The key design parameters of the optical system, including grating, optical fiber, the entrance slit, collimating lens, imaging lens and InGaAs detector are obtained. The design and it’s mechanical structure is completed, taking into considerations of the key optical system parameters of the miniature near-infrared spectrometer.2)Altera’s low cost FPGA chip EP2C8T144C8 has been used as the key control elements to collect the hardware design parameters of the near-infrared spectrometer, covering the temperature G9208 type InGaAs driven design, the InGaAs semiconductor thermoelectric cooling control system based on the C8051F020 MCU, LTC1608CG type 16-bit A/D converter design, the signal acquisition and storage design, USB communication design, FPGA configuration circuit design and so on to improve the flexibility for system modification and upgrade. SOPC technology is used by embedding within the FPGA NiosII a 32-bit soft core CPU as a core processor, eliminating the need to use a micro-processor in the specific design. Both hardware and software programming can be changed simply by re-programming the internal hardware circuits and control procedures. All the circuitry is set in a single chip which lays the foundation of near-infrared spectrometer miniaturization to achieve an anti-interference ability and high integration. The design help reduce the complexity of hardware design and circuit board space which make it possible to produce a hardware physically.3)A study has been conducted of the software design principles of the miniature near-infrared spectrometer, including the underlying software design process, the PC application software development, the data processing and spectral wavelength calibration method, the implementation process block diagram of spectral acquisition, the processing and display.A comparison of the performances between the prototype and the Dutch Avantes AvaSpec-NIR256-2.5 type near-infrared spectrometer shows the new design is acceptable in terms of optical resolution, integration time and compactness. The results show that the prototype near-infrared spectrometer is advanced in optical resolution, measurement speed and compactness and it is a useful approach for commercialization in the future.