Micro-Optomechatronics ppt

Chapter 2 Technological Outline of Micro-Optomechatronics 151 Precision and Information Devices Created by 2 Essence of Micro-Optomechatronics Technology 17 3 Control of Optical Beam Int

Hiroshi Hosaka

Graduate School of Frontier Sciences

The University of Tokyo Tokyo, Japan

Graduate School of Frontier Sciences

The University of Tokyo Tokyo, Japan

Kiyoshi Itao

Graduate School of Management of Science & Technology

Tokyo University of Science

Tokyo, Japan

translation from a portion of a Japanese publication issued by Kyoritsu Shuppan(1999).

Although great care has been taken to provide accurate and current information,neither the author(s) nor the publisher, nor anyone else associated with thispublication, shall be liable for any loss, damage, or liability directly or indirectlycaused or alleged to be caused by this book The material contained herein is notintended to provide specific advice or recommendations for any specific situation.Trademark notice: Product or corporate names may be trademarks or registeredtrademarks and are used only for identification and explanation without intent toinfringe

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Micro-optomechatronics is a technology that fuses optics, electronics, andmechanics by the MEMS technology This technology is used primarilyfor information and telecommunications equipment This book explainsthe basis and the application of micro-optomechatronics In informationoperation, mechanical movements are not required Use of movement inspace, however, often simplifies systems structure and increases the signal-to-noise ratio of transducers remarkably over a system constructed onlywith solid-state components There are many examples of informationinstruments that use optics, such as optical memories, optical communi-cation devices, and optical measurement instruments Moreover, controlsystems made of mechanical components and electronic circuits arenecessary for precise space movement Here, the fusion of optics,electronics, and mechanics is generated Generally, speed and precision ofmotion are improved by the miniaturization of movable parts In addition,the load is small, and the range of movement is narrow in informationdevices Thus, the application of MEMS technology needs to be studiedextensively

This book systematically discusses many micro-optomechatronicsdevices First, all devices are classified into groups depending on the controlmethods of power and the position of the laser beam Next, the devices areexplained in detail according to the classification of control methods.Finally, optics and dynamics, which are the theoretical background ofcontrol methods, are discussed

This book is aimed chiefly for university students, graduate students,and research engineers in the mechanical and electronics industries Itpresumes that readers will have knowledge in dynamics and electromag-netism taught in general education courses in universities In this book, laser

oscillation, Maxwell’s equation, the mechanics of materials, fluid dynamics,and machine dynamics are explained.

A major portion of this book is an English translation of a Japanesebook issued by Kyoritsu Shuppan in 1999 and the authors kindlyacknowledge the Kyoritsu Advanced Optoelectronic Series for use of thismaterial This book also discusses the next generation of optical memory,

in a section written originally for this book, because the progress of opticalmemory is fastest in this field and new technologies have been generated

in these last four years This book, first, explains examples of optomechatronics devices in information and communication systems Thenthe basis of optics and dynamics are explained as it is necessary tounderstand the theoretical background of these devices

micro-Chapter 1(K Itao) deals with the world of micro-optomechatronics.History, applications, and component technologies are explained

Chapter 2 (H Hosaka, K Itao, and Y Katagiri) presents atechnological outline of micro-optomechatronics An outline of powercontrol and position control of a laser beam, which is the performancedecision factor of micro-optomechatronics, is also described The method

of both controls is classified Details of each method are explained in thefollowing chapters with application devices

Chapter 3 (Y Katagiri) outlines intermittent positioning inmicro-optomechatronics This chapter details devices used in informationand communication systems In this chapter, devices that use intermittentpositioning for laser beam control are also explained The laser withtunable cavity, the pulse source laser, and an optical filter are discussed

in detail

Chapter 4 (Y Katagiri) deals with constant velocity positioning

in micro-optomechatronics The optical filter as used for optical nication systems is explained

commu-Chapter 5 (H Hosaka and Y Katagiri) concerns follow-up tioning in micro-optomechatronics Optical disk drives and their focusingand tracking servomechanisms, sampled servo systems, flying heads, and alaser sensor with a composite cavity are discussed

posi-In Chapter 6 (Y Katagiri) we deal with the fundamental optics ofmicro-optomechatronics In this chapter and the next, basics opticsand dynamics, which are useful for understanding the theoreticalbackground of micro-optomechatronics, are described The Maxwellequation, the wave propagation equation, and the laser oscillation arealso discussed here

Chapter 7(H Hosaka) discusses the fundamental dynamics of optomechatronics The dynamics of elastic beams, fluids, and microsizedobjects are also explained

micro-Chapter 8 (T Hirota and K Itao) concerns a novel technologicalstream toward nano-optomechatronics Nanotechnology and a near fieldoptical memory are discussed and explained in detail.

Hiroshi HosakaYoshitada KatagiriTerunao HirotaKiyoshi Itao

Chapter 2 Technological Outline of Micro-Optomechatronics 15

1 Precision and Information Devices Created by

2 Essence of Micro-Optomechatronics Technology 17

3 Control of Optical Beam Intensity 20

4 Control of Optical Beam Position 30

Chapter 3 Intermittent Positioning in Micro-Optomechatronics 43

1 Moving Micromirrors and Their Application 45

2 Micromechanical Control of Cavities Based onSlide Tuning Mechanism and its Applications 85

Chapter 4 Constant Velocity Positioning in Micro-Optomechatronics 99

1 Phase-Locked Loop for Constant Velocity

2 Linear Wavelength Scanning 108

3 Practical Examples of Linear Wavelength Scanning 111

Chapter 5 Follow-Up Positioning in Micro-Optomechatronics 127

1 Follow-Up Positioning in Conventional Optical Disk 127

2 Follow-Up Positioning of Optical Disk HeadMounted on Flying Head 138

3 Displacement Sensors Based on Coupled Cavity

Chapter 6 Fundamental Optics of Micro-Optomechatronics 161

2 Optical Resonators and Their Applications 182

3 Optics of Dielectric Thin Films 197

4 Extraordinary Electromagnetic Waves in CondensedMatter with Free Electrons 208

Chapter 7 Fundamental Dynamics of Micro-Optomechatronics 225

1 Dynamics of Microsized Objects 225

2 Equation of Motion of the Beam 226

3 Fluid Dynamics around Microsized Objects 243

4 Movement of the Beam with Air Resistance 249

5 Stick–Slip Caused by Friction Force 257

Chapter 8 Novel Technological Stream Toward

1 The Coming of Nanotechnology 265

2 Nano-Optomechatronics for Optical Storage 268

of any information to anyone was enabled by means of language Theinvention of writing supported circulation of information for practical use

by storing it Information storage was dramatically improved by the making invention of paper Modern printing technology, another invention,accomplished by Gutenberg, enabled worldwide circulation of hugeamounts of information

epoch-When modern times arrived, a traffic revolution broke out as a part ofthe Industrial Revolution, and the circulation of information was promoted.Another revolution in communication broke out with the invention ofMorse code This was the beginning of the telecommunication era Thistelegraph technology was eventually taken over by telephony, which wasfurther improved to digital communication technology using computers.Digital communication technology integrated telegraphy and telephony intodata communication technology based on the Internet Protocol Now westand at the multimedia age (Fig 1)

Important discoveries in the natural sciences show a concentrationfrom 1900 to 1960, but the principal industrial inventions were achieved inthe second half of the twentieth century Japan was acknowledged as aworldwide leader of industry in the last quarter of the 20th century asJapan achieved great success in various industries, including not only theautomobile, shipbuilding, and semiconductor industries but also precisionmachinery, providing products such as watches and cameras as well as

electronics-based products including home appliances and informationequipment Mechatronics has been also much advanced simultaneously withindustrial development Such a quarter-century is remembered as a GoldenAge in Japanese history [1].

Mechatronics technology is hierarchically classified, from the point ofview of function, into materials, parts of machines and electronics,equipment (devices), and systems These elements of mechatronics aresupported by fundamental technologies concerned with not only fabricationand measurement but also data processing including modern controlschemes [2].Table 1presents how mechatronics technology supports a widevariety of industries existing today Figure 2 is a tree-shaped diagram toshow the relationship between industry and corresponding technology Thisfigure is from the Mechatronics Education and Research Motion, promoted

by the Mechatronics Subcommittee with its chief examiner Professor SuguruArimoto, under the supervision of the Automatic Control ResearchCoordination Committee of the sixteenth Science Council of Japan [3].Figure 1 The history of communications

Information and communication industry Design, manufacturing, mass production techniques of semiconductors, liquid crystal, and

magnetic head Composition and mass production techniques of information input/output and storage devices Automation technique of communication lines construction work.

Wearable micromachine technology.

Consumer electronics industry Design, manufacturing, mass production, recycling, interface, and energy conservation

design techniques of AV products.

Heavy electricity industry High-efficiency power generation, electric power preservation, power control and

management techniques Industrial plant, atomic reactor maintenance techniques.

Radioactive waste treatment system with low environmental impact.

Industrial machinery industry High-speed, and high-precision machine tool techniques Technology for making NC an open

architecture Manufacturing system integration techniques Inverse manufacturing technique.

Business machinery industry Design and manufacturing techniques of fax, printer, and copy machine.

Digitalization, systemization, and miniaturization techniques.

Medical and welfare products industry Technology for cancer medical treatment apparatus and high-precision image processing

equipment SOR and electron beam diagnosis equipment technology Patient transfer system Home care medical equipment technology Wearable information systems for

physiological information monitoring.

Automobile and transportation industry Intelligent engine technology for ultralow pollution Recycle technology Car safety control

technology Car navigation and intelligent transportation system.

Aerospace industry Super high-speed engine integrated control technology Danger evasion system Active

vibration suppression technique Fault diagnosis technology Spatial robot remote manipulation technology.

Naval industry Welding and coating automation technology Simulation technology Attitude control and

obstacle detection technology Underwater robot technology.

Railways industry Technology for high-speed trains using vibration and inclination control Collision

simulation technology Railroad track state automatic measurement system.

Construction works industry Active and passive vibration control technology Building construction work automation.

Coating robot Vibration estimation simulation technology.

Environmental industry Environmental information sensing technology Waste treatment equipment technology.

Artificial environment design technology Recycle system technology.

The technical term mechatronics was born in Japanese industry [4] As

a word for a new technology, it came to be internationally used at thebeginning of the 1980s Mechatronics pushed Japan to the top as a leadingcountry in the supply of original high-tech products to the world At first theword merely expressed the miniaturization of products and the unificationFigure 2 Mechatronics-related technologies supporting each industry (FromRef 3.)

of electrical and mechanical appliances; in 1990 or thereabouts, tronics has been understood worldwide and recognized as a new current intechnology.

mecha-In the same period, a special international journal, Mechatronics,focusing on the subjects of interest in these areas, began to be published

by Pergamon Press in England with Professor R W Daniel of OxfordUniversity as a chief editor Four issues were published every year from 1991

to 1997, and eight have been published per year since 1998 Daniel stated inthe first issue that the word mechatronics best describes the remarkablecontribution of Japan to these interdisciplinary technologies by whichautomation and robotic conversion of the factory have been carriedout to supply advanced electrical and mechanical products such as cameras,camcorders, compact disks, and CD players Two major scientificorganizations in U.S., the Institute of Electrical and Electronics Engineers(IEEE) and the American Society for Mechanical Engineers (ASME),started a program of collaboration in publishing the IEEE/ASMETransactions on Mechatronics, whose first issue appeared in March of

1996 Two Japanese professors contributed to this program; the editorialpolicy was drafted by Fumio Harashima, and Masayoshi Tomizukadescribed in the first issue how important the magazine is to provide anopportunity for scientists and engineers belonging to the two completelydifferent scientific parties to exchange their ideas In the earlier issues of themagazine, mechatronics was temporarily defined as ‘‘the synergeticintegration of mechanical engineering with electronic and intelligentcomputer control in designing and manufacturing industrial products.’’The point was that when the robotic market was just approaching ten billionU.S dollars, the mechatronics market was estimated at ten times larger thanthe robotic market This was an underestimate; if the estimation was carriedout in Japan, it could be enormously enlarged by integrating the relatedmarkets concerned with automobiles and multimedia appliances

2 THE TREND OF INNOVATION

Looking back over the progress in physics, we realize that classical physicsbased on Newtonian mechanics had a great impact on the IndustrialRevolution, which started at the beginning of the second half of the 18thcentury, and which until today has been influential in subsequentlydeveloped technology and industry Newtonian mechanics shows the bestapplicability in the macroworld, in which objects of interest are visible tothe naked eye Invention was carried out based on mechanics, and novelmechanical products were launched; human power was substituted for by

mechanical power generated by steam engines large enough to driveautomobiles, ships, and other general machines In short, Newtonianmechanics has developed heavy industry However, we are now standing atthe turning point and reconsidering heavy industry, which has caused globalenvironmental destruction owing to its heavy consumption of naturalresources to meet great demand.

On the other hand, quantum mechanics, being the core of modernphysics established in the first half of the twentieth century, is the drivingforce of the high-tech revolution in the twenty-first century and the secondhalf of the twentieth

Quantum mechanics was first developed to describe phenomena inthe supersmall world of atoms and atomic nuclei; then it was applied toexplaining the behaviors of electrons in semiconductors The high-techrevolution in the twentieth century in a wide variety of fields—includinginformation, electronics, biology, new materials, and micromachines—came from semiconductor technology (Table 2) [5] Figure 3 shows ascheme for the development of miniaturization For promoting miniatur-ization, further study must be carried out on integrated circuits, integratedmechanisms, and integrated intelligence The realization of new featureswith high-efficiency and high-level functionality becomes possible throughthe implementation of numerous microscopic artifacts by using thesetechniques Using these basic technologies and adopting the latestcomputer technologies such as image analysis and structure analysissoftware, mechatronics is improving toward new technologies that boostthe added value of artificial products expressed by the terms systemintegration and system synthesis

Today, Japan is seeing the rapid aging of the populace, and technology

is strongly required to serve the medical needs and the welfare of the aged.Although the situation is different in each country, the problems are similar.Developing countries are promoting rapid industrialization and will soonovertake developed countries If we continue consuming energy, the day isnot so far distant when environmental issues will become major globalproblems The provision of energy and food will become increasinglyimportant

In the twenty-first century, science and technology will be asked tocontribute to the care of the elderly, to the general welfare, and tothe terrestrial environment; thus a technology that saves resources andenergy will become more important Many companies will have tocollaborate on the industrialization of such technology Mechatronics isfundamental and will be useful for realizing the goals of technology asmentioned above Many Japanese companies have experienced theindustrialization of mechatronics and related technology for last quarter

Table 2 Progress of Sciences and Transformation of Industrial Structure

Newtonian mechanics (end of 17th century)Thermodynamics, electromagnetics,inorganic chemistry

Modern physicsQuantum mechanics (beginning of the 20thcentury)

Nuclear physics, organic chemistry,molecular biology

shipbuilding, automobile, chemical industry

at initial stage

Electronics, atomic energy, new materials,petrochemistry, biotechnology

Influence on earth environment Energy/resources consuming (severe) Energy/resources sparing (kind)

Impact on industrial history Supported the industrial revolution started in

the second half of the 18th century

Supported the high-tech revolution starting

in the second half of the 20th century andextending through the 21st century

of the twentieth century and hence will contribute to the collaboration withother countries.

Computers are devices for data processing, and they carry outcommunication between humans and machines All sorts of multimediaappliances are used to store, edit, and produce sound, images, and pictures.Nevertheless, it is important to be substantial in the real world wherehumans and machines perform versatile works for manufacturing infactories, and for medical treatment and rehabilitation in hospitals andrelated facilities, environmental activities, and various domestic duties Suchsubstantial activities are achieved by mechatronics Thereby mechatronicslinks the virtual (computer) world and the real world

In the twenty-first century, mechatronics will have to be extended to atechnology that unifies computer and human daily activity In other words,human-oriented mechatronics should positively contribute to manyproblems in medical care, human welfare, and elderly care Furthermore,through similar unification with the natural world, nature-orientedmechatronics will be accomplished It will contribute to improving theearthly environment and eliminating various problems in not only envi-ronmental conservation procedures but also sensor monitoring systemsinvestigating various natural phenomena including organic reactions in thehuman body A new technological evolution is now coming out for theconservation of natural resources and the saving of energy

Figure 3 Expansion of miniaturization technology

3 POSITIONING OF MICRO-OPTOMECHATRONICS [6]

It is said that the origin of machinery control technology corresponds to theinvention of a governor by James Watt, at the end of the eighteenth century.Moreover, there is the growth of the automobile, aircraft, and ship-building industries from the beginning of the twentieth century, and in

1957 an artificial satellite was launched, a milestone in the history ofmachine control Furthermore, at this time, Harrison of MIT realized ahigh-precision ruling engine using electric control, and basic research onnumerically controlled machine tools started

Given the history above, let us follow up with the germination of newtechnology related to mechatronics As shown in Table 3, at the beginning

of the 1960s, the process of automation started, and the second half of the1960s saw the period of mechanical automation using electric controltechnology Furthermore, entering the 1970s, the era of the combination

of electrical and mechanical elements using IC and LSI, namely themechatronics era, started, and in the second half of the 1970s, the use of themicroprocessor met the era of real mechatronics, combining mechanics,electronics, and information In this period, the laser diode was invented

in cc1962 and made a continuous oscillation at room temperature in 1970

Table 3 Period of New Technologies Germination

Period Progress of technology and signs of new period

1960– Process automation in chemical industry and heavy machinery industry1965– Period of mechanical automation by the introduction of electric control

technology

1970– Period of combination of mechanics and electronics by the introduction of

IC and LSI electronic technology (initial stage of mechatronics)1975– Period of combination of mechanics, electronics, and information by the

introduction of microprocessor (mechatronics)

1980– Period of combination of mechanics, electronics, information, and optics

by the introduction of laser diode (optical mechatronics)

1985– Period of combination of electronics, physics, mechanics, information, and

optics by the introduction of micromachining (micromechatronics)1990– Period of combination of optics, chemistry, physics, electronics, mechanics,

and information realizing the synthesis of information and energy(micro-optomechatronics)

1995– Period of synthesis of nanomachine, nanocontrol, and nanosensing

(nanomechatronics)

2000– Period of imitation of living organism (nanobiomechatronics)

Then at the beginning of 1980, optical mechatronics technology, combiningmechanics, electronics, information, and optics, put out its buds Buteven though these technologies were put together, true fusion was stillfar away.

In the late 1980s, through the application of micromachiningtechnology for semiconductors to machine elements, research on microsizedsensors and actuators became vigorous, giving the possibility of realizingvarious sensors and microactuators Then the era of micromechatronicsarrived, which sought the miniaturization of mechatronics systems to theirlimits and synthesized all functions on a chip

Turning to the 1990s, the time was heading for the period of optomechatronics, which was born from micromechatronics technologywith light Furthermore, in the second half of the 1990s, we entered a period

micro-of nanomechatronics, where nanomachines micro-of molecular and atomic sizetook the main parts in cooperation with nanocontrol and nanosensing.Further, it will grow into imitation technology for living things and precisearrangements such as DNA’s helix structure and muscle mechanism, andthe nanobiomechatronics period will come along eventually

In addition to the progress of these advanced component technologies,image processing, control theory, and other computer application technol-ogies have started to integrate A system integration, a horizontaldevelopment, is next pursued, and, with new functional devices developed,new manufacturing technology is continuously being invented centered onthe industrial world

4 MI CRODYN AMICS AND OPTI CAL TECHNO LOGY

There are many artificial and organic systems implementing high-levelfunctions by using microscopic movement, such as insects’ movement, thelymph flow of animals’ semicircular canals, eyeball microscopic motion, themotion of the ink-jet printer’s ink particle, atomic force and scanningelectron microscopes, and very high density memory probe motion In short,using not only the solid-state elements of semiconductors but also micro-scopic movements, machine systems often and drastically increase theirperformance

In Fig 4, mechatronics technology used in information systems isclassified into three categories; microscopic energy, micromechanisms, andmicromovement measurement and control; and concrete technologicalthemes are illustrated

First of all, as for microscopic kinetic energy technology, (1)understanding of energy flow, (2) energy supply, and (3) energy

transformation are probably the main techniques Regarding (1), as toequipment size from centimeter to micrometer, it is necessary to explainenergy loss caused by airflow resistance, structural damping, and supportingpoint loss Furthermore, it is necessary to elucidate energy loss caused by theinterference of element cantilevers used in comb actuators that have severalhundred microactuators in them Regarding (2), it is necessary to investigatethe wireless driving method of microcantilevers by laser light andelectromagnetic waves and to investigate the microgeneration mechanismusing oscillators or rotors Finally, concerning (3), an efficient energyconversion method using resonant vibration is important.

Next, related to micromechanisms, the following research is necessary:(1) structural design, (2) the development of the actuator, and (3)microdynamics data accumulation Regarding (1), there are variousmechanisms based on the microcantilever: the V-groove sliding mechanism,the microrotation mechanism, the inchworm mechanism, and the micro-hinge mechanism Regarding (2), a great number of actuators formicroscopic movement using piezoelectric elements, electrostatics, electro-magnetism, or laser beams are promoted Considering (3), it will benecessary to accumulate experimental and theoretical data of tribology andstick-slip that appear in the positioning of microsized movement where theinertial force is negligible, such as in positioning of optical fibers and alsothe data of microtapping that appears in the AFM (atomic forcemicroscope) and the SNOM (scanning near field optical microscope).Figure 4 Main items of microscopic motion systems technology

Lastly, about micromovement measurement and control, varioustechniques such as (1) microscopic oscillation elucidation, (2) microsensordevelopment, (3) surface shape observation, (4) microbody recognitioncontrol, and (5) system evaluation are essential Regarding (1), researches onbiorhythm, microscopic oscillation, insects’ movement measurement, andtransient observation technique of microscopic force coming from staticfriction to kinetic friction in micromotion are important Considering (2),the development of sensor elements using microcantilevers and sensingsystems for miniature three-dimensional position measurement system due

to geomagnetism, gravity, acceleration, and Coriolis force are important.Considering (3), importance is put on the development of the three-dimensional surface shape measurement method using a three-dimensionalelectronic beam measuring instrument or a scanning electron microscope

As for (4), the tracking method of a microscopic object for recognition andimage processing is necessary Considering (5), the evaluation method ofmechanical characteristics of microscopic object is important

Figure 5 shows the classification of micromotion observed ininformation and precision systems: continuous, intermittent, and passivemovements If we take out the major phenomena dominating micromotionfrom there, the resonance phenomenon, the stick-slip phenomenon, thestatic friction and kinetic friction mixture phenomenon, and the tappingphenomenon (the microscopic collision phenomenon) appear

The microscopic vibration theory constitutes the basis of the abovemicrodynamics technologies In nature, we can see the microoscillation

Figure 5 Micromotion and dynamics

phenomenon in many places: the movement of celestial bodies, atomic andmolecular oscillations, pendulum movement, and tide flow In living things,microscopic vibration exists in birds’ twitter, hummingbirds’ hovering, theheartbeat, eardrum vibration, and the subtle oscillation of skin Edison andBell used microscopic vibration phenomena in the gramophone and thetelephone, and it became the roots of information home appliances.Finally, in recent years, information-sensing equipment and precisioninformation equipment that use microscopic vibration are developed in greatnumbers As an example of the former, there are the microscopic telephones,microphones, and microearphones in the acoustical vibration field, the piezoink-jet printer and the microscanner in the vision field, the odor sensor bycrystal oscillator in the smelling field, and the contact sensor by oscillatorand vibrator in the mobile telephone in the field of touching Also, asexamples of the latter, there are the SPM (scanning microscope), ultrasonicsensors, vibration transportation devices, and micropower generators [7] Inthis way, together with information systems’ miniaturization, machinerybecame organized on microvibrations, as if it were imitating living beings.When optical technology joined microdynamics technology, opticalmicromechatronics technology was born The following chapters willexplain the world of the unification of microdynamics and opticaltechnology in detail.

REFERENCES

1 Itao, K Mechatronics of Electronics, Information and Communication; Institute

of Electronics, Information and Communication: Corona, 1992 in Japanese

2 Itao, K Technological portrait of opto-mechatronics Mechanical Design 1992,

36, 10 in Japanese

3 Takano, M.; Arimoto, S.; Futagawa, A.; Kosuge, K.; Itao, K.; Kurosaki, Y.Proposal to Mechatronics Education and Research.Automatic Control ResearchCoordination Committee Report, The Sixteenth Science Council of Japan, Alsopresented in Itao, K Mechatronics systems’ locus Journal of the Japan Societyfor Precision Engineering 1999, 65, 1 in Japanese

4 Mori, T Technical appearance of mechatronics Journal of the Japan Society forPrecision Engineering 1991, 57 (12), 2089 in Japanese

5 Mituhashi, T High-technology and Japanese Economy Iwanami: IwanamiShinsho, 1992; 24pp in Japanese

6 Itao, K The development of optical micromachine technology Opticalmicromachines Journal of Japan Society of Applied Physics 1998, 67 (6) inJapanese

7 Itao, K Information Microsystems—Microvibrations Theory Asakura, 1999; inJapanese

of waves and usually use propagating light In recent years, near field lightlocalized at dielectric surfaces has also come into use Propagating light

is characterized by traveling in straight lines, interference, diffraction,reflection, refraction, polarization, and resonance Many devices of micro-optomechatronics are realized based on such properties In the firstapplication field, there are communication devices The optical magnetismrelay [2] and the optical distortion relay [3] use the energy effect, and theoptical fiber switch [4], the waveguide switch [4], the optical MDF (maindistributing frame), the wavelength tunable laser, and the optical disk filteruse the information effect In the second application field, there areinformation memories Data recording is carried out on magneto-optical,phase-change, and rewritable compact disks by using the energy effects.Data reproduction, tracking, and focusing are carried out for all kinds ofdisks based on the information effect of light In the third application field,there is input/output equipment Digital micromirror devices (DMD) [3],laser printers, blurring-free VTRs, autofocus cameras, and scanners workbased on the information effect A photophone [5] uses the energy effect Inthe fourth application field, there are measurement apparatus They include

an optical fiber gyroscope [6], the optical tiltmeter [7], the CCL sensor, theSNOM (scanning near field optical microscope) [8], and the microencoder[3], all of which are based on the information effect The optical thermo-oscillator [4] use the energy effect In the fifth application field, there areprocessing, handling, and other power-oriented equipment These applica-tions include those for the microworld, such as optical tweezers, opticalgrippers, optical distortion actuators, laser processing machines, and theoptical molding machine; all of these use the energy effect.

Most devices that use the information effect are already ized Commercialized devices based on the energy effect include optical diskrecording, optical molding, and laser processing equipment Noncontactmotion drives are prosperous in the technology of the research level thatuses the energy effect Because the driving force by optical energy is verysmall, objects to be manipulated are limited to minute ones So it is appliedmostly to information devices, for example, the movement of relayelectrodes and the handling of optical parts The actual controllingtechnique of optical beams is explained in the following sections

commercial-Figure 1 Basic characteristics and application for micro-optomechatronics of light

2 ESSE NCE OF MICRO -OPTOM ECH ATRONI CS

2.1 Intensi ty Cont rol of Opt ical Beam

In optical micromechatronics, many functions are realized by controllingthe intensity of optical beams both temporally and spatially as shown inTable 1

In the time domain, it is most useful to control the optical strength byusing a small semiconductor laser Because the semiconductor laser emitsphotons by converting input electrical energy to optical energy, the outputpower can be controlled easily and quickly (at a maximal frequency ofseveral gigahertz) by modulating the input current So this method is widelyused for data coding in information and communication devices In micro-optomechatronics, this method is also used for driving optical-thermooscillator and photophones By using the property of coherent short opticalpulses, it is possible to achieve extremely high intensity Many light wavecomponents whose frequencies are precisely controlled can be concentrated

Table 1 Classification of Optical Beam Intensity Control

Method Control of pouring current of

semiconductor laser

Lens (positioning, forming)Mode synchronization Diffraction

Application Optical thermo-oscillator

(bending moment excitation)

Optical tweezers

Photophone (sound wave excitation) Hologram (exposure)Material processing by pulse

light source

in the time domain to generate a sharp beat waveform This method ofgenerating short pulses is called mode-locking Since most materials melt inhigh-intensity light, this method can be used for material processing andbasic experiments for nuclear fusion.

In the space domain, the intensity of an optical beam is controlled bymaking use of spatial nonuniformity of refractive index Beam convergence

by lens is a major example of it and is used for the generation of pits onoptical disks Optical tweezers that trap minute objects are achieved byusing the intensity gradient formed near the focal point of a lens Lightintensity control is also carried out through making a diffraction pattern.For example, a diffraction pattern can be designed to have the lens functionthat concentrates optical energy of the plane wave homogeneouslydistributed in space to a desired point A typical example of this diffractionpattern formation is holography, which is used for optical memories anddisplays

2.2 Position Control of an Optical Beam

The technology for optical beam position control is classified by accuracyand method as shown inTable 2 Accuracy of positioning is classified intothree categories by aspects of light In the first category, optical power isused; accuracy is defined by the size of the receiving and emitting elements(around 1 mm) In the second category, optical interference is used; requiredaccuracy is several tenths of a wavelength (around 0.1 mm) The focusingservomechanism of optical disks uses a wave property of light, but because

it does not use interference directly, the required accuracy is a little lowand is about the length of a wavelength (around 1 mm) In the thirdcategory, optical phase or near field light is used, or loss and accuracyare strictly specified; accuracy is requested to much less than 1/10 ofwavelength

There are three methods in positioning; intermittent, continuous,and follow-up In intermittent positioning, the object is positioned frompoint to point; it is used in tuning laser wavelengths and assembly processes

A route between the target points is arbitrary In micro-optomechatronics,

in order to position a minute object with high accuracy, actuators withhigh resolution are needed Also in order to reduce a positioning time,movable parts should be as light as possible Moreover, compensatingfor the friction force is necessary, because this force becomes dominant

in minute objects In Chap 7, positioning under large friction force isexplained

Continuous positioning moves an object under the conditionproviding a moving position and/or speed that have been determined in

Table 2 Positioning Method and Accuracy at Micro-Optomechatronics

Positioning system

Positioning accuracy Usage of optical

power (>1 mm)

Optical tiltmeterWaveguide switchMagneto-optical actuatorOptical distortion actuatorUsage of optical

interference(>0.1 mm)

Usage of opticalphase (<0.1 mm)

Optical gyroscope, disk filter

advance Since inertial force and viscous resistance affects the motion,positioning becomes more difficult than with intermittent positioning.Typical examples are seeking control of optical disk heads and rotationcontrol of a disk-shaped optical filter The simplest continuous controlschemes refer to a constant velocity control The disk filter is a typicalexample: wavelength accuracy of around 0.01 nm is achieved by rotating adisk at a constant speed Since the rotating speed will be changed by friction

or external disturbance force, it is necessary to compensate for thesedisturbances to maintain a constant velocity Such high-performancecontrol is accomplished by measuring the transient rotation angle of thedisk using a sensor to generate a phase error signal from a clock signal as areference, and by controlling the motor torque so as to reduce the errorsignal to zero in a negative feedback loop

The follow-up positioning is a kind of continuous positioning andmakes the second object follow at a constant distance to the first object,which moves in an unknown manner Although the absolute position of thesecond object is needed to detect it in the usual continuous positioning,the relative position of the first and the second object is needed to detect inthe follow-up positioning A typical example is the tracking control ofoptical disks It is necessary to make a laser beam follow the pit with adiameter of about 1 mm and with a moving speed of about 10 m/s with anaccuracy of about 0.1 mm Section 4 explains the dynamic analysis ofcontinuous positioning and follow-up positioning

3 CON TROL OF OPT ICAL BEAM INTENSI TY

In this section a technology concerning light intensity control and itsapplications is described among the optical beam control technologies.3.1 Usage of Opt ical Radia tion Press ure

When light is applied to an object, a part (or all) of the momentum of thephoton is transferred to the object Consequently, the object receives forcefrom the photon according to the law of conservation of momentum Suchforce is called the radiation pressure Radiation pressure has been detected

by experiment since old times.Figure 2 shows the experimental system byStimmer in 1964 [10] The rotating moment was generated by irradiatingthe high-power laser beam to rotation mirrors hung by wire in a vacuumchamber The torque is obtained by detecting the angle of rotation of themirror by this moment from the angle of reflection of the laser

The radiation pressure is analyzed by the same method as that forsolid particles Let us study the case in which light with intensity I isvertically applied to a high-reflectivity mirror that is at a standstill, as shown

in Fig 2 The change in momentum becomes 2h
/c when a photon reflects

by colliding with the mirror Because the number of photons collidingwith the mirror at time intervals dt is I dt/h
, the impulse the mirrorreceives is

When the irradiation area of light on the surface of mirror is assumed to be

S, the radiation pressure P becomes

P ¼2I

Let us consider the case in which light 1 mm in wavelength, having anintensity of 10 mW, is applied to the area of 1 mm2 The optical beamcorresponds to a flow of photons of 5
1016per second Carrying out thecalculation according to the above equation, we estimate the radiationpressure as 60 N/m2, and we also estimate the force that acts on the entireirradiation area as 60 pN It is almost equal to gravity acting on an objectwith one side length of about 7 mm and a density of 2 g/cm2

The laser manipulation technology is a method to catch and dle small particles in a space by using the radiation pressure The fun-damental concept was proposed by Ashkin It is now being activelyused as optical tweezers in the fields of biology, chemistry, and physics toFigure 2 Measuring method of a photon (From Ref 10.)

han-perform trapping and transferring of the living body cell and themicrocapsule.

When the optical power is P ¼ 0.3 (W), the radiation pressure F isestimated as

Figure 3 explains the principle of how the radiation pressure acts on

a minute transparent object Radiation pressure is generated at every pointthe light is refracted The total force is obtained by integrating the pressures

at all the points (This is shown by an arrow in the figure.) The strength ofthe acting power shows strong dependence on the size and shape of theparticle, and the refractive index difference between the particle andthe surrounding material Hence optimizing the acting power according tothe particle of interest, we can freely manipulate the particle in a free space.For instance, the radiation pressure can float a particle made of transparentdielectric material in the air, eliminating the influence of the gravity [11] Inthe instrument suspending an object in the air as shown in Fig 4, theparticle diameter is 20 mm and the power of the Ar laser is 150 mW Thevertical position of the particle is measured and fed back to an electric

Figure 3 Principle of radiation pressure (From Ref 11.)

optical modulator, and the laser power is adjusted to generate an optimalpressure that balances with gravity Moreover, moving the object in water iseasily achieved because the radiation pressure can be remotely applied to

an object of interest whenever the medium is transparent Thereby theradiation pressure is used for the cell operation

It is also possible to rotate a small object using the spin momentum

of photons Photons in a pure circularly polarized state have the spinmomentum h/ p, whose signature depends on the direction of thepolarization Consider an absorbable object If the object acquires photons

in a circularly polarized state, it receives the momentum of photons by theangular momentum conservation theorem (see Fig 5a) This momentumtransfer is a driving force to rotate the object

Such rotary actuation is also available for some particular ent objects They are anisotropic optical media exhibiting dichroism Thesematerials exhibit two refractive indices according to the polarization of lightand hence give a phase difference between the two transmitted lights withdifferent polarization As the linearly polarized light consists of two cir-cularly polarized lights with different directions, the light transmittedthrough such an anisotropic object has a phase shift due to the dichroism.This phase shift is dependent on the transmission length Hence all kinds ofFigure 4 Floating of minute ball by radiation pressure

transpar-polarization states can be realized by changing the length In the particularcase that the length is adjusted to give a phase shift corresponding to a purecircularly polarized state (phase shift: d ¼ p/2), a linearly polarized light istransformed into a circularly polarized light while transmitted through theobject This means that the object receives the recoil angular momentumfrom the light by this polarization transformation (see Fig 5b) This angularmomentum is also a source of the driving force for rotary actuation Thismechanism is generally extended to the rotary actuation based on angularmomentum transformation.

3.2 Usage of Photothermal Conversion

3.2.1 Vibration Excitation by Photothermal Stress

(Optical Oscillating Sensor)

When the thermal effect of optical energy (absorption) is used, opticalenergy can be converted to mechanical energy This type of generation ofmechanical energy is called photothermal drive This enables the noncontactdrive of a minute object

We explain the vibration excitation mechanism of the cantilever by thephotothermal effect When light is irradiated onto the side of a cantilever,

a thermal expansion is brought out in the irradiated part by temperature

Figure 5 Rotation of object using spin momentum of photons (a) Rotation ofobject by absorption of circularly polarized light (b) Rotation of object by change ofpolarization direction

increase, as shown in Fig 6 The bending moment is generated by thisthermal expansion, and the cantilever deflects When an optical irradiation

is stopped, the temperature of the irradiation part decreases rapidly bythermal diffusion and the moment disappears When the light is irradiated

in a row of pulses, moment is generated at every arrival of the pulse Asimilar effect as the mechanical forced vibration is achieved Figure 7 showsthe conversion process and the dissipation process from optical energy tothe vibration energy The essence of the bending moment generation isnonuniformity of the temperature distribution in the direction of thethickness of the oscillator, and such uniformity is generated by the opticalirradiation

Figure 6 Mechanism of bending moment generation in a beam by photothermalconversion

Figure 7 Energy flow in photothermal drive

3.2 2 Sound Wave Gene ration by Phot othermal

Expans ion (Ph otophone )

The photophone is an apparatus that converts optical signals (amplitudemodulation) into sound waves Figure 8 shows the outline of its structure.Thermal energy exists in the process that converts optical energy into soundenergy An optical signal is irradiated from the optical fiber to the medium

of the absorption cell The medium increases its temperature and heatssurrounding air after absorbing optical energy The heated air expands and

a resulting air-density wave propagates in the converter This wave is alongitudinal wave and so is recognized as sound The size of the converterwas r1¼0.4 mm, r2¼9 mm and 85 cm in length in Ashkin’s experimentalapparatus

When converting an optical signal to a sound signal, the sion efficiency was almost flat in the range from 300 to 3300 Hz Thisbandwidth includes almost all that of the human voice The researchwas started with a prototype photophone by Alexander Graham bell atthe end of 19th century and was further studied by Ashkin in theBell laboratory An optical speaker still being studied is based on the sameprinciple Carbon fibers are packed into a ventricle in the air, and the heatalternatively causes expansion and compression of the air in the ventricleaccording to the optical signal The sound impedance of the air in free space

conver-is matched with that of the horn Various experimental investigations

on such mechanisms have been carried out to find an optimal structure

of the horn and the heat absorption material Typical examples are shown

inFig 9

Figure 8 Structure of photophone (From Ref 5.)

3.2.3 Magnetic Circuit Control (Microrelay)

This section presents a micromagnetic actuator controlling magnetic force

by using the temperature-dependent magnetic phase transition phenomenon

of ferromagnetism The operation principle is that the equivalent gap length

is changed by heating a magnet around the gap with a laser; the magnetismdecreases with increasing the temperature and completely vanishes at atemperature higher than the Curie point as shown inFig 10

Its advantages over conventional electrostatic and electromagneticactuators are as follows (1) It is easy to provide the self-latching function.(2) In submillimeter size, it has larger power than that of electrostaticactuators (3) The structure is simpler than that of the electromagnetic type,and manufacturing is easier (4) The wireless operation control is possiblebecause it uses light On the other hand, its defects are as follows.(1) Displacement is mainly in binary motion, and multistep control isFigure 9 Example of experiment of photophone (From Ref 5.)

difficult (2) The moving frequency is several tens of Hz at most becauseheat is used.

A microsize relay (1.5 mm
200 mm) is developed as an application.Switch operation at 10 ms was realized by heating it with a 30 mW laserlight

3.2 4 Writing in Recor ding Film (Op tical Disk)

A typical structure of an optical disk is shown inFig 11 The disk has asandwich structure, a recording film lies between two transparent substrates.The inside of the disk has grooves to guide the optical beam The recordingfilm is protected and the reading error with dusts and other defects isprevented by the transparent substrates Because the laser beam converges

to a point on the recording layer with a lens, the optical beam diametercorresponds to about 1 mm at the disk surface The size of the dust is muchsmaller than the diameter, and its shadow is reduced greatly on therecording layer Then the probability of recording error caused by blocking

of laser light by the dusts or other defects becomes very small

For recording, the laser forms microscopic pits on the recording layeralong the guide grooves with a heating energy of approximately 1 nJ

Figure 12 describes typical data recording and reproducing methods forwrite-once and rewritable disks In the write-once type, the recordingprocess is as follows: the recording film is locally evaporated by laserheating, and uneven pits are generated In the reproducing process, a change

of power in reflected light is detected Also, there are methods that can makeflat pits with different reflectivity or transparency by thermally transformingthe recording material In the rewritable type, there is a magneto-opticalmethod of which the recording process is as follows: a laser beam isirradiated to the recoding layer, the layer temperature rises up to aboutFigure 10 Principle of thermomagnetization microrelay (From Ref 12.)

200C partially, and at the same time a magnetic field is externally applied.Then the magnetization direction of the heated area is reversed In themagneto-optical method, data codes are reproduced as follows: a laser beam

is applied to the recording layer, the polarization angle of the beam isFigure 11 Structure of the optical disk

Figure 12 Major recording methods

rotated by the magnetic Kerr effect, which is the interaction between lightand magnetism, a change of reflected light power is detected by a photo-diode, and the direction of the magnetization of the recording layer isdetected Another read/write method of a rewritable disk is the usage of thecrystal-amorphous reversible change of chalcogenide recording film When

a high-power laser is exposed to the recording layer for a short time, theexposed part is rapidly melted and cooled and then enters the amorphousstate When a low-power laser is exposed to the recoding layer for a longtime, the recording material is melted and cooled slowly and then returns tothe original crystal state Data are reproduced by detecting the difference

of reflectivity between crystal-amorphous states Reversible phase change

is possible more than 106 times by using a recording material made ofchalcogenide

4 CON TROL OF OPT ICAL BEAM POSITIO N

4.1 Cont inuous Positio ning Cont rol

In rotational movements of a disk filter, an optical disk, and the polygonmirror of a laser beam printer, the space information memorized in themedium is transformed to temporal signals Since the accuracy that changesspace information into time information depends on the accuracy of themedium movement, it is necessary to make a rotation speed into a fixedvalue strictly For this purpose, the angle of the rotating object is detectedand motor control is performed so that the difference of this angle and thereference signal created externally becomes zero The typical structure of

a constant-speed rotation system is shown in Fig 13 A direct-currentservomotor generates rotational movement Rotation of the motor ismeasured by the rotary encoder This signal and an external electric signalare compared, and synchronous rotation is realized by controlling therotation of the motor so that the signal difference becomes zero

A control block diagram is shown inFig 14 The rotation angle x of amoving object is measured, the difference between this angle signal and thereference signal r is calculated, and the driving force Cð _xx  _rrÞ þ Kðx  rÞof amotor is generated so that the angle deviation and the speed deviation,which is the differential of the angle, become zero If disturbance, such asfriction, is written as F, the movement equation is given by

M €xx ¼ F þ Kðr  xÞ þ Cð _rr  _xxÞ r ¼ vt ð4ÞThis equation is equal to that of the mechanism that the position x of mass

Mis controlled by the spring K and the dashpot C to the target position

r ¼ vt, which moves in proportion to time t (Fig 15) The dynamic model ofthe head seek control in the optical disk, where the object follows a variablespeed target, is also given by this model, although the relationship between

r and t is not so simple as a linear relation In the actual optomechatronics systems, characteristics of the motors and the controlcircuits are more complicated But the essential of positioning control isthe same

micro-4.2 Class ification of Foll ow-Up Position ing Cont rol

Many types of follow-up positioning control are used in mechatronics Its classification is shown inFig 16 The follow-up control isFigure 13 Constant-speed rotation mechanism

micro-opto-Figure 14 Block diagram of continuous positioning

divided into active and passive controls In active control, an object is driven

by an actuator such as a moving coil, the object position is measured by asensor, and the sensor signal is fed back to the actuator In passive control, anatural constraining force such as air bearing force is generated between thecontrolled object and the target object, and the object position is controlledwithout sensors Furthermore, there are out-of-plane (the direction ofdistance) and in-plane (the right and left direction) controls as movingdirections In active control, there are continuous and discrete controls asthe methods of data processing

4.3 Active Continuous Follow-Up Positioning

A typical example of the follow-up, out-of-plane positioning is the focusservo of the optical disk, which positions the focus of a laser beam in theFigure 15 Dynamic model of continuous positioning

Figure 16 Follow-up positioning in micro-optomicromechatronics

axial direction In an optical disk, it is necessary to position the focuspoint of the laser on the disk surface, which vibrates about 0.5 mm, and

a permissible error is about 1 m m For this purpose, a gap between thefocus point and the disk surface is detected from the reflected reproduc-tion beam, and the objective lens is driven so that the gap deviation becomeszero There are various methods in carrying out the focus error detection,and a typical method is the astigmatic method The electromagneticactuator shown in Fig 17 is built in an optical head and an objectivelens can be driven up and down If the current proportional to the gaplength is added to the coil, the focal point is always positioned on the disksurface

A typical example of the follow-up, in-plane positioning, whichpositions the focus of a laser beam in the vertical direction of the beam axis,

is track servo in an optical disk In the optical disk drive, it is necessary tomake a laser beam follow pits that vibrate about 70 mm in plane with anaccuracy of about 0.1 mm For this purpose, a position error is detected fromthe reflected recording/reproduction beam, and the objective lens is driven

so that the error becomes zero There are various methods for detectingin-plane focus position errors, and a typical method is the push–pullmethod Details of an astigmatic method and the push–pull method areexplained inChap 5

Figure 17 Focusing control mechanism (From Ref 13.)

We describe the dynamic model of active, continuous, follow-up tioning The model is common to in-plane and out-of-plane controls First,the position difference x  r and velocity difference d(x  r)/dt between atarget position and an object position are created by a sensor and a circuit.Next, with an amplifier, a difference signal of displacement is multiplied by Kand a velocity difference signal is multiplied by C, and the sum of them isapplied to an actuator Then the actuator force becomes larger as the positiondifference and the velocity difference become larger, and the position andvelocity of the controlled object become closer to those of the target object.

posi-To simplify the analysis, the actuator and the controlled object aremodeled by a rigid body of 1 degree of freedom In order to restrain theirmovement in other directions than the follow-up direction, some supportingmechanisms (e.g a parallel leaf spring) are necessary, and their springconstant is set to k Moreover, let M be the mass of the actuator and themoving object Then the block diagram of a control system becomes asshown in Fig 18 Moreover, if a displacement sensor (the push–pull method

or the astigmatic method) does not have an error and its gain is set to 1, theequation of motion is given by

M €xx þ kx ¼ Kðr  xÞ þ Cð _rr  _xxÞ ð5ÞThis equation is the same as that of 1-degree-of-freedom spring-mass-dashpot system as shown inFig 19 That is, displacement feedback becomesequivalent to a spring, and velocity feedback becomes equivalent to a dash-pot Moreover, if k is set to zero, this model becomes the same dynamicmodel as that of the continuous positioning system shown in the previoussection

4.4 Passi ve Continuou s Foll ow-Up Position ing

A method of positioning a laser beam in the axis direction without using asensor and an actuator is described A typical method is the use of a flyingFigure 18 Block diagram of active continuous follow-up positioning