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This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all‐pass ring resonator are extracted based on the transmission characteristics using finite‐difference time‐domain method. As compared to conventional graphene‐oxide‐semiconductor straight waveguide, graphene integrated on an all‐pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 μm radiation and ring radius of 3.75 μm with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro‐optic applications. [ABSTRACT FROM AUTHOR]

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red‐shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source. [ABSTRACT FROM AUTHOR]

Silicon-on-insulator photonic microring resonators are ideal components for applications that require a high degree of multiplexing because of their small size. However, when very high numbers of microrings are used in parallel, grating couplers and waveguide routing quickly take up more chip space than the actual rings. Therefore, we suggest to combine microring resonators with local weak gratings to read out light directly from the microring while still maintaining high-quality factors of 19 000. We demonstrate simulation results and an experimental analysis of different grating parameters. The resonance spectrum is recovered from the vertical emission of the microring grating, without using a traditional output waveguide. [ABSTRACT FROM PUBLISHER]

High frequency large scanning angle electrostatically actuated microelectromechanical systems (MEMS) mirrors are used in a variety of applications involving fast optical scanning. A 1-D parametrically resonant torsional micromirror for use in biomedical imaging is analyzed here with respect to operation by duty-cycled square waves. Duty-cycled square wave excitation can have significant advantages for practical mirror regulation and/or control. The mirror's nonlinear dynamics under such excitation is analyzed in a Hill's equation form. This form is used to predict stability regions (the voltage-frequency relationship) of parametric resonance behavior over large scanning angles using iterative approximations for nonlinear capacitance behavior of the mirror. Numerical simulations are also performed to obtain the mirror's frequency response over several voltages for various duty cycles. Frequency sweeps, stability results, and duty cycle trends from both analytical and simulation methods are compared with experimental results. Both analytical models and simulations show good agreement with experimental results over the range of duty cycled excitations tested. This paper discusses the implications of changing amplitude and phase with duty cycle for robust open-loop operation and future closed-loop operating strategies. [ABSTRACT FROM AUTHOR]

We present an integrated beam steering system with a microlens scanner and a vertical cavity surface-emitting laser (VCSEL) source. The scanner and the VCSEL are assembled with an alignment sphere process and with an accuracy of 121 ± 7μm defined by precision microspheres. The microlens scanner employs an electrostatic comb-drive actuator with prebent springs to extend the maximum displacement to 83 μm; 60% larger than that with standard folded springs. This translates to an angular scan range of ±9.6° with the double sided comb-drive scanner. The mechanical resonance with lens is measured to be 236 Hz. [ABSTRACT FROM AUTHOR]

A tunable slow-light hollow-core photonic crystal fiber (HPCF), applicable to miniaturized microstructure spectroscopic gas sensors is proposed. In the proposed structure, we have taken the advantage of the microfluidic infiltration technique to tune the slow-light regime so as to match the reference absorption line of the target gas sample, which is required for designing miniaturized gas sensors with reconfigurable detection sensitivity. The main feature of this structure is that the enhanced electrical field is strongly localized in the hollow-core of a photonic crystal fiber for any gas samples due to tunability of slow-light modes. We discuss the potential of slow light in HPCF for realizing compact and tunable gas sensor devices with low and high loss material. In particular, we present numerical results showing how this optofluidic microstructure can be used for detecting CO, CO2, H2S, CH4, SO2, and N2O gases. [ABSTRACT FROM AUTHOR]

Continuously tunable slow and fast light generation using a silicon-on-insulator microring resonator (MRR) incorporating a multimode interference (MMI) coupler is proposed and experimentally demonstrated. The MMI coupler is optimized for the transverse-magnetic mode. By changing the input polarization state, the self-coupling coefficient and the loss factor of the MRR are changed. The depth and the bandwidth of the MRR are tunable by tuning the self-coupling coefficient and the loss factor; thus, a tunable phase shift can be achieved at the resonance wavelength, which leads to the generation of a tunable slow and fast light. The proposed scheme is experimentally evaluated. A tunable slow light with a maximum time delay of 35 ps and a slow-to-fast light with a continuously tunable range of 102 ps are achieved for a 13.5-GHz Gaussian optical pulse by using a double-MMI coupler MRR and a single-MMI coupler MRR, respectively. [ABSTRACT FROM PUBLISHER]

In this letter, the microfluidic optical fiber devices composed of microchannel are modeled and thoroughly analyzed. The microchannel intersecting the fiber core allows direct infusion of surrounding substances for detection. The simulation results suggest that the dimension of the microchannel can significantly affect the detection sensitivity of the device. In addition, the off-center position of the microchannel also plays an important role in shaping the device performance. The optimized microfluidic device can be used for sensitive refractive index sensing and biosensing applications. [ABSTRACT FROM PUBLISHER]

Coupled resonator optical waveguides (CROWs) have shown theoretical promise as microoptical integrated gyroscopes with sensitivities exceeding comparably sized MEMS gyroscopes. Here, we analyze the effect of static disorder on the rotational sensitivity of a CROW gyroscope. Since CROWs consist of a one-dimensional array of evanescently coupled ring-shaped microresonators, disorder includes random variations of the resonator optical path length and couplings between them resulting from manufacturing errors. We show that the rotational sensitivity of the CROW gyro is relatively stable with respect to variations in the interresonator coupling. By contrast, even modest fluctuations in the resonators' roundtrip optical path length result in substantially lower rotational sensitives. Finally, it is shown that while most random configurations of defects reduce the maximum sensitivity, there are particular configurations for which the rotation sensitivity is significantly higher than that of a CROW without disorder. [ABSTRACT FROM PUBLISHER]

Microresonators with a high Kerr nonlinearity show great potential to generate optical frequency combs with ultrabroad spectra, high repetition rate, and high coherence between comb lines. The compact size and possibility of chip-level integration make the Kerr combs attractive for many applications, especially including photonic radiofrequency (RF) filters. In this paper we report the first demonstration of a programmable photonic RF filter based on the Kerr comb from a silicon nitride microring. A novel scheme enabled by the large frequency spacing of the Kerr comb is introduced in order to suppress unwanted RF passbands including the image and periodic passbands. As a result, a single passband is achieved. To the best of our knowledge, this is the first demonstration of a single-bandpass photonic RF filter employing a discrete-wavelength comb source. [ABSTRACT FROM PUBLISHER]

We demonstrate an integrated waveguide platform and optomechanical transduction circuit for chip-scale displacement sensing. The waveguide consists of a thin silicon nitride core layer, a thick silicon oxide bottom cladding, and a top air cladding with a large evanescent field at the waveguide surface. Although the structures feature subwavelength (<;λ/4ncore) vertical confinement, they are fabrication tolerant with micrometer-scale lateral features. We demonstrate via simulations and measurements that the waveguides exhibit a low confinement with a maximized evanescent field as well as an effective index only slightly larger than the SiO2 bottom cladding index. Despite the low confinement, the waveguide platform enables complex photonic circuits. As a demonstration of this technology, we fabricate and characterize an unbalanced Mach-Zehnder interferometer for chip-scale displacement sensing. A micrometer-scale fiber taper interacts with the waveguide's evanescent field and induces a phase shift proportional to displacement, thereby acting as an optomechanical transducer. We analyze the responsivity, displacement limit of detection, and strength of optomechanical coupling for high-resolution sensing. An outlook toward other applications is also given. [ABSTRACT FROM PUBLISHER]

We design and demonstrate for the first time an end-to-end binary phase-shift keying (BPSK) link based on silicon microring resonators, with an operational bit-rate at 10 Gb/s. The obtained bit-error-rate is below the forward error correction limit, validating the practical application of the demonstrated technique. Performance comparisons to conventional BPSK modulation and demodulation techniques are also made. The microring-based BPSK link promises a compact, energy efficient, and low-cost interconnect solution for high-capacity transceivers. [ABSTRACT FROM PUBLISHER]

In this paper, we numerically demonstrate the promise of silicon microdisks for Raman Stokes/anti-Stokes wavelength conversion. We design a silicon microdisk suitable for Raman wavelength conversion with “automatic” quasi-phase matching (QPM). By carefully designing the bus waveguide adjacent to the disk, we show that, for each wavelength involved in the nonlinear process, we can excite the proper light mode for which the “automatic” QPM concept is obtained in the microdisk, and find that with this design, we can achieve wavelength conversion efficiencies up to -2.4 dB at input pump powers as low as 3.4 mW. [ABSTRACT FROM PUBLISHER]

We propose a scheme to utilize a multimode microdisk resonator in silicon controlled through free-carrier injection for continuous fast-to-slow light tuning. Two nearby resonant modes are employed, i.e., undercoupling and overcoupling. The optical properties of a device are analytically investigated considering the resonance spacing, bandwidth, and density change of free carriers. Pulse propagation simulations are implemented, and the pulse delay/advance is studied for wavelengths between the two resonances. As the density of injected free carriers increases, a continuous transition from fast to slow light occurs for a range of wavelengths. Consequently, a microdisk resonator in silicon is experimentally realized with the desired two resonances, exhibiting electrooptical tuning with a fast response. The experimental results agree well with the simulation in power transmission, and the tunable time delay and advance are also predicted. [ABSTRACT FROM PUBLISHER]

Time response of a silicon photonic nanowire-waveguide microelectromechanical switch is studied by measuring optical output and analyzing mechanical and electrical dynamics. The switching mechanism is based on the gap variation of a directional waveguide coupler consisting of 400-nm-wide and 260-nm-thick waveguides. One of the coupler waveguides is moved by an ultrasmall comb actuator. A theoretical model is proposed by combining the mechanical motion and the electrical circuit response of the switch. By analyzing the model, an optimum condition for switching rise time is obtained to be ~10 μs, where the mechanical oscillation is suppressed by the driving electrical circuit with a large resistance. The rise time measured from the optical output intensity was 18 μs. [ABSTRACT FROM PUBLISHER]

We present a method for directly synthesizing coupled microring resonator filter networks of general 2-D coupling topologies. The method is based on the “energy coupling in time” formalism of systems of microring resonators and can be used to synthesize optical filter transfer functions in the s-domain. An example of a class of microring filters with equiripples in both the amplitude and group delay responses is also given to illustrate the application of the method to the design of complex microring filter architectures. [ABSTRACT FROM PUBLISHER]

Chip-embedded organic resonator is fabricated with 2,5-Bis(4-biphenylyl)thiophene (BP1T) crystals encapsulated with polydimethylsiloxane (PDMS). Whispering gallery mode lasing is demonstrated in these on-chip embedded crystalline microresonators, without decline in the spectral properties, and performance in comparison to the unencapsulated devices. The encapsulated lasers exhibit quality factor (Q) as high as 1066, and lasing threshold is about 120 nJ (1.5 mJ/cm2). Meanwhile, with protection of the PDMS, operation lifetime of the laser is increased from 2.1 × 106 to 4.6 × 106 pulses. [ABSTRACT FROM PUBLISHER]

We present a theoretical model to analyze all-optical switching by two-photon absorption induced free-carrier injection in silicon 2 × 2 add-drop microring resonators. The theoretical simulations are in good agreement with experimental results. The results have been used to design all-optical ultrafast (i) reconfigurable De-multiplexer/Multiplexer logic circuits using three microring resonator switches and (ii) universal, conservative and reversible Fredkin and Toffoli logic gates with only one and two microring resonator switches respectively. Switching has been optimized for low-power (25 mW) ultrafast (25 ps) operation with high modulation depth (85%) to enable logic operations at 40 Gb/s. The combined advantages of high Q-factor, tunability, compactness, cascadibility, reversibility and reconfigurability make the designs favorable for practical applications. The proposed designs provide a new paradigm for ultrafast CMOS-compatible all-optical reversible computing circuits in silicon. [ABSTRACT FROM PUBLISHER]

Microelectromechanical system (MEMS) technology, and surface micromachining in particular, have led to the development of miniaturized optical devices with a substantial impact in a large number of application areas. The reason is the unique MEMS characteristics that are advantageous in fabrication, systems integration, and operation of micro-optical systems. The precision mechanics of MEMS, microfabrication techniques, and optical functionality all make possible a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. In these systems, electrostatic, magnetic, thermal, and pneumatic actuators provide mechanical precision and control. The large number of electromagnetic modes that can be accommodated by beam-steering micromirrors and diffractive optical MEMS, combined with the precision of these types of elements, is utilized in fiber-optical switches and filters, including dispersion compensators. The potential to integrate optics with electronics and mechanics is a great advantage in biomedical instrumentation, where the integration of miniaturized optical detection systems with microfluidics enables smaller, faster, more-functional, and cheaper systems. The precise dimensions and alignment of MEMS devices, combined with the mechanical stability that comes with miniaturization, make optical MEMS sensors well suited to a variety of challenging measurements. Micro-optical systems also benefit from the addition of nanostructures to the MEMS toolbox. Photonic crystals and microcavities, which represent the ultimate in miniaturized optical components, enable further scaling of optical MEMS. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of different masking parameters onto the surface quality of the {111} sidewalls in order to generate specifically deep cavities by wet-anisotropic-etching of bulk silicon, for optical sensors using cavity sidewalls as reflectors. Mask alignment with crystal planes prior to wet-etching is found to be essential in order to avoid the appearance of additional planes during long etching. Mask deposition processes have been also evaluated. Among the different employed mask materials, Cr/Au gives the best results. It is then shown that cavities as deep as 1 mm with low roughness sidewalls can be simply produced with potassium hydroxide solution with periodic piranha cleaning. [ABSTRACT FROM AUTHOR]

We discuss relevant design considerations for the fabrication of electromechanically tunable photonic crystal cavities based on double semiconductor slabs. A simple optical and electromechanical model of the device based on coupled-mode theory and electrostatics is discussed and used jointly with 3-D finite-element calculations of optical cavity modes to extract the tuning-range dependence on geometrical parameters. A design rule, which avoids the sticking of membranes due to capillary forces and keeps a large tunability, is defined. The details of the fabrication process and a summary of the experimental results on GaAs and InGaAsP/InP material systems are given. We also address the problem of nonsymmetric devices, where the thicknesses of the membranes are not exactly the same, resulting in an imbalanced power emission of coupled modes. [ABSTRACT FROM AUTHOR]

A novel out-of-plane MOEMS accelerometer based on near-field evanescent wave coupling by means of variable period subwavelength gratings has been proposed. First, the diffraction order number was calculated. Then, structure parameters were optimized by finite element analysis to achieve high sensitivity in an ideal vibration mode. Results show that the accelerometer has displacement sensitivity at 2033 nm/G with a measurement range of 0.12 G, corresponding to first diffraction beam optical sensitivity 0.46%/mG. Finally, we designed the fabrication method to form such MOEMS accelerometer and successfully fabricated the uniform and well-designed subwavelength gratings with the period of 1.0 μm by FIB/SEM dual beam system. The subwavelength gratings fabricated are very close to those designed within the experimental error to lay the foundation for the subsequent fabrication. These results provide a theoretical basis for design and fabrication of an out-of-plane MOEMS accelerometer with subwavelength gratings. [ABSTRACT FROM PUBLISHER]

We propose a direct and nondestructive self-referenced residual pressure measurement method for MEMS chip of fiber-optic pressure sensor. In the proposed method, two multimode fibers are placed at the center and the edge position of the sealed cavity. With scanning external pressure, two groups of cavity lengths data are obtained by using polarization low-coherence interference demodulator. The intersection point of their linear fitting curves indicates that the diaphragm is in flat condition and residual pressure is determined by the external pressure at this point. We successfully demonstrated the effectiveness of the residual pressure measurement method with measure error 0.049 kPa. [ABSTRACT FROM PUBLISHER]

A photonic integrated architecture realizing the concept of coupled-resonator dual-mode optical filters is presented. The proposed structure consists of a chain of directly coupled microring resonators with a partial reflector embedded in the last resonator. The contradirectional coupling induced by the reflector makes the effective order of the filter double with respect to the number of coupled resonators. Since the counterpropagating modes share the same physical cavity, the resonant frequencies are intrinsically aligned, sensitivity of the filter to fabrication tolerances is reduced, and control of the structure is eased with respect to coupled resonator filters of the same order. Second- and fourth-order dual-mode filters made of microring resonators loaded with a Bragg grating are experimentally demonstrated on a silicon-on-insulator photonic platform. [ABSTRACT FROM PUBLISHER]

The direct patterning of hybrid-polymer microring resonators with minimal residual layers by UV-assisted nanoimprint lithography is reported. The proposed stamp-and-repeat technology requires no post-processing. The imprint polymer was applied by spin-coating as a 130-150 nm thin initial film for an optimized processing. The importance of the initial film thickness is discussed in detail. Aspect ratios of more than 5:1 were realized with 2 μm high ridge-waveguides and sub-400 nm coupling gaps on maximal 130 nm thin residual layers. The achieved ratio of structure height to residual layer thickness of 15.4 (2 μm versus 130 nm) was much larger than the typical values in high-resolution imprinting and superseded the removal of the residual layer completely. The resonators are thought as biosensor transducers. High quality devices with Q-factors up to 13000 were produced with a minimal set of process steps. [ABSTRACT FROM PUBLISHER]

This study proposes a dense multichannel optical waveguide switch based on micro ring resonators (MRRs). The proposed design is achieved by cascading five MRRs of the same structure and the phase difference between two bus waveguides that are evanescently coupled to every two MRRs is purposely set at either 0 or π in order to minutely adjusting the positions of the corresponding resonant wavelengths of the MRRs. Our proposed structure is capable of controlling ON/OFF signals associated with four optical channels. Our study finds that the resonant channel spacing is less than twice the full-width-at-half-maximum of an individual optical signal. Furthermore, among 16 different combinations of output spectra obtained, the ON/OFF signal contrast of each optical channel could reach up to -29.68 dB. [ABSTRACT FROM PUBLISHER]

We study the properties of finite-length all-pass side-coupled microring delay lines optimized using a genetic algorithm. The average bandwidth-group delay product is found to follow a linear growth with the number of cascaded stages N. Both the magnitude and the slope of the figure of merit vary with the specific optimization criteria but, for all the cases addressed, they are below the unit slope linear dependence with N of a theoretical upper bound. [ABSTRACT FROM PUBLISHER]

A large displacement piston motion micromirror is designed, fabricated, and tested with device features tuned to applications requiring ultralow tilt. The fabricated MEMS mirror is based on electrothermal actuation and has a footprint of 1.9 mm × 1.9 mm with a mirror aperture of 1 mm. The application optimized device holds key features of ultralow maximum tilt of 0.25 ° and a strongly linear motion of 90 μm achievable at only 1.2 V. This device is further characterized in an interferometric system to determine the piston mode and the accurate piston displacement as a function of voltage, power, and frequency. [ABSTRACT FROM AUTHOR]

Speckle noise is a major obstacle for the application of laser light sources in projection displays and illumination. In this paper, a method for speckle reduction using a Micro-Electro-Mechanical Systems (MEMS) diffuser device is presented. The MEMS device consists of a random reflective pattern on the top surface of a moving mass that is vibrated in-plane by an electrostatic push-pull comb drive. The harmonic in-plane motion of the MEMS diffuser creates time-varying speckle patterns that are averaged by the camera or the eye, thus reducing speckle noise. The device is fabricated using Silicon-On-Insulator (SOI) technology. The measured device shows good agreement with analytical calculation and simulation. Using a red He-Ne laser, speckle contrast is measured both for free space geometry and for light pipe geometry. Speckle contrast reduction up to 43.08% for the free space geometry and 26.8% for the light pipe geometry is achieved. [ABSTRACT FROM AUTHOR]

We describe a microelectromechanical systems-based actuator for three-dimensional (3D) positioning of a polymer microlens implemented using silicon-on-glass technology. The actuator combines comb drives for lateral tracking with electrostatic parallel plates for out-of-plane focusing as well as tilting of a polymer microlens, yielding fully 3D actuation. The complete actuator is fabricated using wafer bonding of silicon and pyrex wafers; the lens is integrated using polymer dispensing techniques. The 3 DOF positioning of the lens for focusing, tracking, and tilting are experimentally characterized, furthermore, the layout and symmetry would allow 4 DOF movement, demonstrating how this actuation system combined with an integrated lens may be particularly useful for new generations of optical pickups. [ABSTRACT FROM AUTHOR]

An all-optical clock recovery (CR) scheme with wide locking range is demonstrated, based on a silicon microring resonator (MRR) and a semiconductor optical amplifier (SOA). The MRR with a free spectral range of 40 GHz works as a comb filter, which removes the modulation information, whereas the SOA operating in the saturation regime performs amplitude equalization to achieve a good optical clock signal. The design of the MRR is investigated according to the tolerance of the subsequent equalizer. Based on the fabricated MRR, single and dual channels CR from 40 Gb/s input data streams can be achieved successfully with root mean square time jitter of ~ 900 fs. Because of the moderate finesse of the MRR, the CR can be achieved with a wide range of several gigahertz. [ABSTRACT FROM PUBLISHER]

In this letter, we experimentally demonstrate, by integrating plasmonic nanoantennas, that membrane-based micromechanical resonators can become infrared (IR) active. The photo-thermomechanical effect induced by nanoantennas enables actuation of mechanical structures. Using this hybrid nanoantenna coupled mechanical device as a thermal IR detector, we achieved a current responsivity of 12 mA/W corresponding to a displacement responsivity of 98.7 μm/W and a thermal time constant of 5.7 ms at a wavelength of 6 μm. This approach can be extended to any mechanical resonator for new optomechanical sensing modalities. [ABSTRACT FROM PUBLISHER]

The presence of potentially harmful substances in milk is a concern for consumers. The discovery of recombinant DNA technology allowed the production of large quantities of recombinant bovine somatotropin (rbST), which is allowed to be used to increase milk and meat production in many countries. The use of rbST is controversial because of its potential effects on animal and human health. Use of the existing large instruments for the detection of rbST suffers disadvantages such as the need of large quantities of reagents, increased time of assays and most importantly, the high cost of equipment, etc. In this paper, a novel optical lab-on-a-chip (LOC) is proposed for the detection of a fluorophore-tagged rbST. The advantages of a silica-on-silicon platform for the optical waveguide and polydimethylsiloxane for microfluidics are exploited for the fabrication of a low-cost LOC. The tagging of rbST with two different types of fluorophores, such as FITC and Alexa-647, is carried out and used for detection in the proposed LOC. [ABSTRACT FROM PUBLISHER]

We investigate an optically resonant cavity which is created between a reflecting micro-cantilever and a diffraction grating etched into a silicon waveguide. Changes in cavity resonance, induced by small deflections of the micro-cantilever result in large changes in an optical signal transmitted through the waveguide. An analytical model can predict the cantilever position for maximum and minimum transmission and is confirmed by three-dimensional finite difference time domain (FDTD) simulations. This approach can be used to accurately determine the position of a micro-cantilever with a predicted optimal shot noise limited deflection noise density of 4.1 fm/ Hz. [ABSTRACT FROM PUBLISHER]

We introduce and experimentally demonstrate an optofluidics-based refractometer structure arranged in a simple free-space Young interferometer design. Our key idea is based on the use of a very simple microfluidic chip structure that consists of one or two flow channels arranged in parallel. We then pass the optical beam through the flow channels of the microfluidic chip. Behind the flow channels, there are two small apertures where the incident optical beam is automatically divided into two optical beams. These two optical beams are propagating in free space for a desired distance before they interfere with each other at the observation plane. Key features include simplicity in design, ease of implementation, and robustness. In the experimental demonstration, we use a 655-nm wavelength laser diode; the free-space propagation distance is 57.5 cm. The two-channel microfluidic chip has a 900-μm channel spacing, a 100-μm channel width, and a 100-μm channel depth (i.e., d/L = 9). Results indicate a sensitivity of 1.34 × 10-4 RIU in measuring the refractive index of the sucrose solution which clearly agrees with the theoretical analysis. A higher sensitivity of 6.19 × 10-6 RIU is also accomplished when the single-channel microfluidic chip with a measured d/L ratio of 0.52 is combined with an optical mask having a 600- μm channel spacing. [ABSTRACT FROM PUBLISHER]

A novel method to fabricate microchannels into fused silica capillaries and hollow fibres by a high‐voltage high‐frequency corona discharge induced by a Tesla coil is demonstrated. Channels as narrow as 2.2 μm are successfully made in capillaries with 2 μm inner and 125 µm outer diameters. [ABSTRACT FROM AUTHOR]

We theoretically study the group-delay characteristics of a silicon microring resonator based on the coupled mode theory, and experimentally demonstrate error-free operations of an on-chip delay line using a silicon-on-insulator (SOI) microring resonator with a 20-mum radius. Four signals of different modulation formats are examined at 5 Gb/s, including return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ), return-to-zero duobinary (RZ-DB), and return-to-zero alternate-mark-inversion (RZ-AMI). Bit error rate (BER) measurements show that the maximal delay times with error-free operations are 80, 95, 110, and 65 ps, respectively, corresponding to a fractional group delay of ~0.4, ~0.5, ~0.55, and ~0.35. The differences in delay and signal degradations have been investigated based on the signal spectra and pattern dependences. Although the delays are demonstrated in a single ring resonator, the analysis is applicable in slow-light resonance structures such as all-pass filters (APF) and coupled resonator optical waveguides (CROW). [ABSTRACT FROM PUBLISHER]

All-pass, wavelength-selective, slowlight optical buffers using cascaded micro-ring resonator filters are theoretically and experimentally studied in the context of optical packet switching router architectures. Two optical buffers fabricated in high-index contrast silica technology are compared: an 8-ring buffer with narrow resonances for wavelength selective delay and a 32-ring buffer for distortion-free delay at 10 and 40 Gb/s. Accurate measurements and configurations of the transmission of the buffers allow for precise simulations that accurately predict pattern dependent distortions, signal integrity and performance extrapolation to higher data rates. Continuously tunable delays are demonstrated up to 8 bits with minimal distortion. [ABSTRACT FROM PUBLISHER]

In a metal film infrared microbolometer, the responsivity is improved by high bias current to compensate for its low-temperature coefficient of resistance (TCR). However, what are the upper limits of this current without damaging the microbolometer element is not well understood. To study the effects of large bias current, we performed the destructive I-V measurements on an element of a 16 times 16 Ti-microbolometer array developed at our laboratory and report here the experimental observations of its electrical and physical damages. In this study, we performed the I-V measurements repeatedly on a microbolometer element and increased the final bias current in steps of 50 muA in each repetition. The effect of the heating due to I2R power dissipation has been analyzed at each step by monitoring I-V characteristics, specific detectivity and physical health. We report a significant decrease in the detectivity when bias stress is increased beyond 450 muA, which corresponds to the element temperature of 370degC. Further, we found that the resistance started decreasing, when the power dissipated and the element had increased to about 2.5 mW, resulting in a peaked I-V characteristics. This corresponds to the bias stresses more than 650 muA. Using a new I-V model, we extracted the temperature to be about 750degC at these peaks. A further increase in bias stress has resulted in the complete physical damage of the element. [ABSTRACT FROM PUBLISHER]

Poled and unpoled chromophore-containing polymers offer some unique advantages in device functionality and fabrication. UV light and electron beam (e-beam) can bleach out the color of chromophores and reduce the index of refraction of the polymer. The photobleaching and e-beam bleaching methods form optical waveguides in a single step and do not involve solvents or wet chemicals, and can be applied to polymers that are not compatible with other waveguide fabrication techniques. A variety of microring resonator devices for fiber-optic telecommunication and sensors have been realized with chromophore-containing polymers. A novel broadband fiber-optic electric field sensor is presented as an example. The sensor uses a polymer with chromophores preferentially aligned after electric poling, and the microring resonator is directly coupled to the core of optical fiber. The feasibility of vertical integration of a poled electrooptic polymer waveguide device interfaced with silicon microelectronic circuits is also demonstrated. [ABSTRACT FROM PUBLISHER]

A diaphragm-type optical fiber pressure sensor, which has a sleeve for fiber insertion, is proposed, and its fundamental characteristics are demonstrated. The sleeve structure is fabricated by deep reactive ion etching (DRIE). The diaphragm with the sleeve is suitable for highly reliable and easy bonding between the sleeve and an optical fiber. The light intensity change by a Fabry-Perot interferometer according to pressure is increases by an improved DRIE method. The mesa attached to the diaphragm increased reflectance. The method of mass production for the developed diaphragm will be useful for realizing a low-cost pressure sensor. [ABSTRACT FROM PUBLISHER]

A novel 3-D hollow waveguide (HWG) is proposed and demonstrated to realize low propagation loss and polarization insensitivity for widely tunable and temperature insensitive photonic devices used in future dense wavelength division multiplexing networks. Low polarization dependence and low propagation loss, at the same time, are realizable by optimizing the shape of our 3-D structure. The modeling and experiment of the novel 3-D HWG is presented for low propagation loss and low polarization dependence. [ABSTRACT FROM PUBLISHER]

There has been extensive research into micro total analysis systems (micro-TAS) and lab-on-a-chip research due to the benefits of increased sample throughput, reduced sample consumption, and rapid analysis times. The integration of low-cost fluidic and optical components offers the possibility of complex systems with increased functionality on a single detection platform. For the development of an integrated optofluidic system for DNA hybridization, the key areas are optical/fluidic integration and the efficiency of surface chemistry integration within the system. The impact of fluidic parameters such as flow rate, channel height, and time on hybridization performance is to optimize detection performance over conventional assay (microtiter plate formats). The use of a passive waveguide device means DNA binding events can be monitored using fluorescence excitation or refractive index measurement. The integration of the three areas is enhanced by the robustness of the waveguide material (oxide, nitride), enabling chemical functionalization by initial silanization followed by addition of a linker molecule 1,4 phenylene diisothiocyanate (PDITC) for covalent immobilization of DNA probes together with the possibility to define microfluidics on the waveguide substrate using standard SU8 photolithography. The fluidic design requires 240 nl of analyte to fill the integrated optofluidic system. Here, we report the novel integration and optimization of a covalent surface chemistry with microfluidic channels for fluidic delivery, and a standard resonant mirror (RM) waveguide detection platform. The optofluidic detection platform was tested using fluorescence and refractive index to monitor binding events between target and probe DNA. We describe the detection system, using simulations to explain the response to changes in refractive index and outline a method for covalent attachment of DNA probes surface chemistry protocol to immobilize probe DNA on the sensor surface and the o- - ptimization of fluidic design, achieving pM detection limit. We highlight the benefit of optimizing the fluidic component and its benefit in hybridization efficiency an approach often overlooked in sensor design and performance. [ABSTRACT FROM PUBLISHER]

Due to the emergence of high-capacity wavelength-division multiplexing transmission systems, new optical cross-connect (OXC) architectures that make a large number of fiber/wavelength counts to switch the signal in the optical domain are needed. Optical microelectromechanical system (MEMS) switches are regarded as the most promising optical switch technology to achieve such functionalities. In this paper, we propose a novel integrated multistage two-dimensional (2-D) MEMS optical switch design with Spanke-Benes architecture and compare it with the conventional crossbar architecture, the L-switching architecture, and Shuffle-Benes architecture. Our proposed architecture is very suitable for building large-port-count 2-D MEMS switches and achieves much better performance in terms of beam divergence loss, longest optical path, mirror radius, substrate size, port-to-port repeatability, and power consumption than the other three architectures. Furthermore, compared with the 2-D conventional crossbar switch commercially available now, the proposed architecture can save 50% mirrors, shorten 87.5% longest optical path, minify 65% mirror radius, and shrink 90% substrate size. [ABSTRACT FROM PUBLISHER]

We present a microoptical detection unit for both laser-induced fluorescence and absorbance analysis on fused silica capillaries, which can be used for chromatographic applications. The detection system is designed by means of nonsequential ray tracing simulations and prototyped by means of deep proton writing. In a proof-of-concept demonstration, the microoptical unit is used for the detection of various concentrations of coumarin dyes. The detection limit (SNR=3.3) achieved measures 0.6 nM for fluorescence analysis and 12 muM for absorbance measurements in capillaries with an inner diameter of 150 mum. [ABSTRACT FROM PUBLISHER]

This paper describes a free-space 1 timesP cyclically tunable optical multiplexer based on a stationary tunable blazed grating (TBG). An analytical model is used in deriving a closed- form expression for the transmission of the deformable grating, given an actuation scheme that requires only (P -1) control signals. A 1 times3 demultiplexer is implemented using a six-element TBG, and tuning over a free spectral range of 13.5 nm in C-band is demonstrated. [ABSTRACT FROM PUBLISHER]

A high-performance variable optical attenuator, which is based on an electrothermally actuated iris with a square pupil, is demonstrated. The device is fabricated from two separate dies that are formed by deep reactive ion etching of bonded silicon-on-insulator material. The iris die is inserted into an elastic clamp on a base-plate die carrying spring-mounted fiber alignment features, allowing the iris to be held in the optical path between two expanded core fibers. A novel aperture that dynamically reduces the clearances between the shutter blades is used to achieve an extinction of 25 dB and a wavelength dependent loss of plusmn1 dB at 1550-nm wavelength. Synchronous blade motion is achieved using thermally optimized folded electrothermal actuators with undercut hot arms, which reduce the operating power to 240 mW and allow a high mechanical resonant frequency. Optical analysis is carried out using a scalar model and diffraction theory. Thermomechanical analysis is performed using a 1-D model and finite element simulation (ANSYS). Good agreement is obtained between the models and by experimentation. [ABSTRACT FROM PUBLISHER]

Fabrication and optical characterization of single-mode polymeric embedded waveguides are performed. A specific material combination (SU-8 2005 as core and the modified SU-8 mr-L 6050XP as cladding) is chosen in order to obtain a small refractive index difference for single-mode propagation combined with the conventional fabrication method UV lithography to facilitate the integration of different types of optical detection methods on lab-on-a-chip systems. We analyze the behavior of the refractive index and carefully observe how the value of the refractive index can be tailored during processing. We show that we can fabricate waveguides with an index difference in the order of 10-3 , where both the core material and the cladding material are based on SU-8. The refractive index measurements are performed on thin polymeric films, while further optical characterizations are performed on waveguides with a height of 4.5 mum. We study the mode profiles of these waveguides and confirm that only the fundamental mode is excited. We also study the absorption spectra of the material in the wavelength range 800-1600 nm combined with cut-back measurements. We find that the waveguides have a propagation loss of 0.2-3 dB/cm in this wavelength range [ABSTRACT FROM PUBLISHER]

This paper reports the conceptual design and experimental demonstration of an optical switch that utilizes the thermo-optic effect (TOE) and total internal reflection (TIR) of a micromachined silicon prism. The key idea is to change the refractive index of the prism via TOE to switch the light from the transmission state to the TIR state. The structure is fabricated by microelectromechanical systems (MEMS) technology on a silicon-on-insulator wafer. It requires a temperature change of 69 K to switch from the transmission to the reflection states, which measure isolations of 15.6 and 40.1 dB, respectively. This design is advantageous over the other waveguide switches and photonic crystal devices in the aspects of the absence of beam splitting, tremendously enhanced sensitivity of switching to small change in refractive index, high compactness, and potentially fast and low power switching [ABSTRACT FROM PUBLISHER]

Micromirror arrays are promising components for generating reflective slit masks in future multiobject spectrographs. The micromirrors, 100 mum times200 mum in size, are etched in bulk single crystal silicon, whereas a hidden suspension is realized by surface micromachining. The micromirrors are actuated electrostatically by electrodes located on a second chip. The use of silicon on insulator (SOI) wafers for both mirror and electrode chip ensures thermal compatibility for cryogenic operation. A system of multiple landing beams has been developed, which latches the mirror at a well-defined tilt angle when actuated. Arrays of 5times5 micromirrors have been realized. The tilt angle obtained is 20deg at a pull-in voltage of 90 V. Measurements with an optical profiler showed that the tilt angle of the actuated and locked mirror is stable with a precision of 1 arcmin over a range of 15 V. This locking system makes the tilt angle independent from process variations across the wafer and, thus, provides uniform tilt angle over the whole array. The surface quality of the mirrors in actuated state is better than 10-nm peak to valley and the local roughness is about 1-nm root mean square [ABSTRACT FROM PUBLISHER]