Design And Implementation Of Laser Diffraction Grating Test Instrument

DVD,VCD and CD player has been used more and more widely in our everyday life. Laser read-write head is the core part of these equipments, and diffraction grating is a very important component of laser read-write head. Diffraction gratings which are used in laser read-write head have two important parameters——ratio of the grade±1 and grade 0 light intensity and the grating's transmittance. And to test the two parameters of diffraction grating is an important means to judge whether it is qualified or unqualified.Design of laser diffraction grating test instrument based on ATmega16L MCU is discussed in the thesis. This instrument can test two parameters of diffraction grating, which are the ratio of the grade±1 and grade 0 light intensity and the grating's transmittance. Idea of design is that the light signal is converted to current and voltage, and then voltage signal is processed by MCU, and at last two parameters are displayed by LED.Hardware design and software design are discussed in detail in the thesis. Hardware design mainly includes constant-current driver circuit for laser-diode, photo-electric conversion, amplification and sampling micro signal circuit. Constant-current driver circuit consists of three parts: voltage stabilizing circuit, operational amplifilers circuit for voltage converting and voltage negative feedback circuit. Photo-electric conversion circuit consists of photoelectric detector, current sampling and voltage amplifier circuit. Relay is used in current sampling and voltage amplifier circuit, so two amplifier ranges are switched autoly within testing and test precision is improved.The software system adopts C as program language, ICC AVR as compile software and AVR Studio as simulation software. Software design mainly includes AD conversation, Zero, Alarm, LED dynamic scanning and key-press program design. Method of Zero by software is that during testing, the voltage converted by hybrid optical which is converted by laser and environmental light subtract the voltage converted by only environmental light. So, it can reject environmental light disturbance. Testing parameters and various special charaters are displayed by LED. And the whole systematic testing sequence depends on LED display hints and the four key-presses to cooperate the MCU to complete. Test error is less than 2% and mean-square deviation is less than 2.2×10-3. During the test, it can alarm automatically by displaying special characters if the diffraction grating is unqualified.