Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Nanodistance Measurement based on CD pick-up Head using Auto Offset Canceller AmplifierPezhman Sasanpour 1 , Mohammad Haghnegahdar 2 , Milad Taherian 2 and Bizhan Rashidian 1,2*1 Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran, Iran2 Department of Electrical and Electronics Engineering, Sharif University of Technology, Tehran, IranAbstract— We have designed and implemented system for detection of linear movement detection below 30 m. In linearregime focus error signal can be exploited as a criterion of displacement. In this regard optical pick-up head of CD drives andits quadrant photodiode and laser system can be used as a reliable system. In order to improve operation of system independentof environment light, we have added an additional system consisting amplifier + offset canceller after the module in order toomit background light noise and accordingly enhance the sensitivity and resolution of system.Precise displacement detection is one of important issuesin the nano science and nano technology. There are differentideas for detecting small scale movement with different levelsof accuracy. Among those, interferometery and capacitancesensors can be mentioned [1-3]. Using position sensitivephotodiodes and embedded quadrant photodiode system ofused in pickup head of optical disk drives, has found lots ofpotential applications [4-6]. Considering cost efficiency andeasily access, in addition to accuracy and sensitivity, we haveimplemented and improved a method of movement detectionbased on quadrant photodiode system used on optical pick-uphead of CD drives.The main idea in this method is exactly the same used inthe pickup head of CD/DVD for focus error detection andcorrection. In a usual pickup head light beam emitted from alaser diode after spreading over a grating is divided into 3separated light beam that are directed on the CD surface. Lightbeam reflected from CD surface will then be directed onto thecenter of quadrant photo diode. If position of CD is exactly onfocus plane of laser beam, reflected light beam on the quadphoto diode will have shape of circle. Otherwise reflection ofbeam on the surface of photo diode will not be a completecircle and it will be similar to ellipse. This elliptic figure willproduce different levels of power on each of photo diode.Focus error of CD in this system is defined (A+C)-(B+D).As it has been shown in figure 1, according to direction,focus error signal (FES) could be positive or negative. Byusing the FES in its linear regime, this system can be used as amethod for detection of displacement in linear direction.caADBC(A+C)(B+D)b(A+C)-(B+D)FE>0dADBC(A+C)(B+D)ADBC(A+C)(B+D)(A+C)-(B+D)FE=0(A+C)-(B+D)Figure1: (a) Microscopy image of quadrant photodiode (QPD)moduleused in optical pick-up head. (b) FES for Object in Focus plane.(c) FES for Object below focus plane. (d) FES for Object above focusplane.Figure 2 shows result of QPD signal obtained by movingobject. As it has been depicted linear region in this system is30 m.FE