Tunable Optical Devices Research Articles

Tunable microfluidic optical devices with an integrated microlens array

Interest in dynamically tuning light has attracted great attention to the fabrication of tunable microlens arrays. Here we discuss the fabrication and characterization of a simple, robust, yet tunable microfluidic optical device with an integrated microlens array. The microfluidic device with a desired channel structure was micromachined on a polycarbonate plate with a resolution of up to 100 µm, followed by thermal bonding two plates above their glass transition temperature. The microlens arrays were replica molded on a glass slide, which was then attached to the polycarbonate plates. By simply actuating the liquids with variable refractive index into the fluidic channel to immerse the lens arrays without moving or deformation of microlenses, a large change of focal length of more than ten times (f = 0.74–8.53) was achieved. When a dye-containing liquid was pumped into the microfluidic channel to cover the lenses, the light transmission through the lenses was reduced from about 95% to 55% when the dye concentration was increased to 10 w/v%. The knowledge we gain from these studies will provide important insights to construct new, adaptive, micro-scale optical devices with multiple functionalities.

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.

Tunable Fano resonance in photonic crystal slabs

A three dimensional analysis of a special class of anisotropic materials is presented. We introduce an extension of the Scattering Matrix Method (SMM) to investigate the behavior of anisotropic Photonic Crystal Slabs (PhCS) subject to external radiation. We show how the Fano effect can play a fundamental role in the realization of tunable optical devices. Moreover, we show how to utilize electron injection, electric field and temperature as parameters to control the Fano resonance shift in both isotropic and anisotropic materials as Si and Potassium Titanium Oxide Phosphate (KTP). We will see that because Fano modes are sensitive and controllable, a broad range of applications can be considered.

Microlens arrays with integrated pores

Microlenses are important optical components that image, detect, and couple light. But most synthetic microlenses have fixed position and shape once they are fabricated, so their possible range of tunability and complexity is rather limited. By comparison, biology provides many varied, new paradigms for the development of adaptive optical networks. Here, we discuss inspirational examples of biological lenses and their synthetic analogs. We focus on the fabrication and characterization of biomimetic microlens arrays with integrated pores, whose appearance and function are similar to highly efficient optical elements formed by brittlestars. The complex design can be created by three-beam interference lithography. The synthetic lens has strong focusing ability for use as an adjustable lithographic mask and a tunable optical device coupled with the microfluidic system. Replacing rigid microlenses with soft hydrogels provides a way of changing the lens geometry and refractive index continuously in response to external stimuli, resulting in intelligent, multifunctional, tunable optics.

Design and analysis of a novel tunable optical filter

In this paper, an improved design of a tunable optical filter device which is driven by a piezoelectric actuator is proposed. The device can be used either as a tunable optical filter for discrete wavelength alignment or as a dynamic optical filter. The tunable filter is electrostatically driven and consists of three main parts: The electromechanical stage, the suspension and the thin film optical filter. The electromechanical stage and the suspension were designed using graph presentation methods, studied numerically using the finite element method (FEM). The thin film optical filter was designed by a thin film design software. The electromechanical stage was integrated with the suspension and tested as an angular driver of thin-film tilt interference filter for dense-wavelength division demultiplexing system applications.

Spectrum Tuning of Fiber Bragg Gratings by Strain Distributions and Its Applications

We report tunable optical devices based on fiber Bragg gratings (FBGs), whose filtering characteristics are controlled by strain distributions. These devices include a widely wavelength tunable filter, a tunable group-velocity dispersion (GVD) compensator, a tunable dispersion slope (DS) compensator, and a variable-bandwidth optical add/drop multiplexer (OADM), which will play important roles for next-generation reconfigurable optical networks.

Origin and applications of magnetically tunable refractive indexof magnetic fluid films

When an external field was applied, the refractive index of the magnetic fluid film was observed to be modulated as the field exceeded a critical strength. We found that the stronger the magnetic field, the higher the refractive index. By taking both the formation of the columns and the variation in the concentration of the liquid phase in magnetic fluid films under external magnetic fields into account, the refractive index was calculated and compared with experimental data. When we did this, we noticed a consistency that implies that the phase separation leads to the variation in the refractive index of the magnetic fluid film as the magnetic field strength is changed. With such a property as a tunable refractive index, the feasibility of using a magnetic fluid in a tunable optical device is worthy of investigation.

Tunable optical fiber devices based on broadband long-period gratings and pumped microfluidics

This letter describes classes of tunable microfluidic fiber (μFF) devices that use specially designed long-period gratings in which the phase matching condition is satisfied over a wide spectral range. Dynamic tuning is achieved by electrowetting-based pumping of microfluidic plugs back and forth over the gratings. As specific examples, we demonstrate dynamically tunable broadband attenuators and filters with adjustable profiles by using fluids with different refractive indices. These devices have attractive features that include in-fiber design and polarization-independent behavior together with low-power, nonmechanical, fully reversible, and latchable tuning.

Digitally Tunable Microfluidic Optical Fiber Devices

This communication introduces a digital design for tunable microfluidic optical fiber devices. In these systems, multiple, independently controlled microfluidic plugs are pumped into or out of overlap with a fiber structure to modulate its transmission characteristics. The devices described here use eight plugs, eight electrowetting pumps and a corresponding set of molded planar recirculating microchannels to control the depth of the narrowband loss feature associated with a long period fiber grating. Optical measurements illustrate the digital and relatively fast operation of this type of microfluidic fiber device.

Analysis of heat flow in optical fiber devices that use microfabricated thin film heaters

This paper describes finite element analysis of heat flow in a new class of tunable optical fiber devices that uses thin film resistive heaters microfabricated on the surface of the fiber. The high rate of heat loss from these cylindrical microstructures and the relatively low thermal diffusivity of the glass yield thermal properties (e.g. short axial thermal diffusion lengths, small radial temperature gradients and good power efficiency) that can be exploited for tuning the optical properties of in-fiber gratings. The modeling captures important thermal characteristics of these devices and anticipates their suitability for dynamic dispersion compensation and other applications in high bit rate lightwave communication systems.

Optical Fock-state synthesizer

We suggest a tunable optical device to synthesize Fock states and their superpositions starting from a coherent source. The scheme involves an avalanche-triggering photodetector and a ring cavity coupled to a traveling wave through a cross-Kerr medium. Low quantum efficiency at the photodetector improves the synthesizing quality at the expense of reducing the synthesizing rate.

Optical characteristics of electrorheological and electromagnetorheological fluids

The optical character of electrorheological (ER) and electro- magnetorheological (EMR) fluids under the influence of an external field are investigated. It is found that the transmission of ER fluids could be adjusted through selecting the proper electric field and suspension con- centration. The IR spectral transmissions of ER fluids increase with an applied electric field. The maximum transmittance for low-concentration fluid changed from 4% to 23%. It is also observed that the window of transmission does not change with fluid consistency and external electric field. We find that the scattering patterns of ER fluids consist of the many bright and dark bands as a scattering grating. The widths of bright bands increase with increasing electric field. The scattering pattern of EMR fluids under electric and magnetic fields superimposed in the perpen- dicular is also observed. These phenomena provide new mechanics for the design of tunable optical devices and will have direct industrial ap- plication. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)01605-5)

Recent progress in tunable nonlinear optical devices for infrared spectroscopy

A laser source based on difference-frequency generation (DFG) in AgGaS 2 has been developed for high resolution IR kinetic spectroscopy (IRKS) of free radicals. Continuously tunable radiation has been generated between 4 and 9 μm (2500–1100 cm −1) by mixing two cw single-mode dye/Ti:Al 2O 3 lasers in a 90° type I phasematching configuration. Spectra of the free radicals HOCO, DOCO and HCCN were obtained by using this source. Concurrently, the suitability of III–V single-mode cw diode lasers for DFG of tunable IR radiation has been explored by mixing two laser diodes (808 and 690 nm) in AgGaS 2 (IR power generated ≈ 3 nW). Techniques to increase the IR DFG power level such as the use of high-power optical semiconductor amplifiers or an external build-up cavity for the nonlinear crystal have been investigated. As much as 50 μW of cw IR radiation, tunable near 4.3 μm have been generated by mixing a high-power tapered semiconductor amplifier at 858 nm and a Ti:Al 2O 3 laser in AgGaS 2. Recent progress in generating cw IR radiation near 3.2 μm by mixing an extended-cavity diode laser near 795 nm and a compact diode-pumped Nd:YAG laser in AgGaS 2 with an external enhancement cavity is also described.

Multiaccess in all-optical networks with wavelength and code concurrency

Abstract A major obstacle in realizing fast packet switching in all-optical networks is the large tuning delays of tunable optical devices. This article proposes a multiaccess scheme for all-optical local area networks that employs both wavelength and code concurrency. In this scheme, several users share a wavelength channel through code multiplexing. The delay performance of hybrid wavelength/code division multiaccess is obtained under a simple, suboptimal access protocol based on cyclic search. Due to the reduction in the number of wavelength channels without an associated reduction in transmission concurrency, hybrid multiaccess is robust against tuning delays. At a given network throughput, the hybrid scheme achieves considerably lower delays than that of Wavelength Division Multiple Access even with a small amount of code concurrency. Conversely, the hybrid network can support a higher load when there is a maximum allowable value for the average packet delay.

Switching Latency Impact on Star-Coupled WDM Photonic Network Pre-Allocation Protocol Performance

This paper evaluates the performance of two pre-allocation protocols when the switching latency of the wavelength tunable optical devices required for WDM networks is not negligible. The channels are pre-allocated to the nodes with the approach, where each node has a home channel that it uses either for all data packet transmissions or all data packet receptions. This approach reduces the resulting system complexity since both tunable transmitters and receivers are not required, and also has the advantage of being applicable to systems where there are many more nodes than wavelength channels. Switching latency is the time required by the tunable optical devices to tune to the required destination wavelength. The performance impact of switching latency on a generalized random access protocol is compared to an approach based on interleaved time multiplexing. Both protocols are designed to operate in a multiple-channel multiple-access environment and require each node to possess a tunable transmitter and a fixed (or slow tunable) receiver. Semi-markov analytic models are developed to investigate the performance of the two protocols. The analytic models are validated through extensive simulation. The performance is evaluated in terms of network throughput and packet delay with variations in the number of nodes, data channels, packet generation rate, and switching latency.

Absorptive bistability in a three-level system interacting with two fields

We have studied the case of purely absorptive bistability in a three-level system interacting with two coherent fields. The results show that in the limit where the neglect of propagation effects is justified, a tunable optical device (TOD) results. It is shown that varying the secondary field amplitude can alter the hysteresis curve of the two-level system dramatically. Under certain conditions, the secondary applied field can eliminate hysteresis and produce a tunable differential gain region. This type of adaptive behavior offers attractive possibilities for optically based analog-digital systems.

Systems criteria for thin film welding : J. L. Laub, Electronic Packaging and Production4, 20 (1964)

Nickel oxide (NiO) thin films were deposited onto glass substrates by sol-gel spin-coating technique. The coating solution was prepared by reacting nickel acetate tetrahydrate as precursor and absolute ethanol as solvent. The asdeposited films were annealed in air at 350oC. The color of the film can be changed from bleach color to be dark brownish after UV/ozone treatment. The change in optical density of more than 40% can be achieved after 5 min of treatment. The colored films can be readily recovered by thermal treatment at 150 °C within 30 min. Further increasing ozone exposure time leads to greater change in optical density. The presence of ozone-induced hydroxyl groups causes the color change of the films. The unique behavior of this chromic material can be applied as novel tunable neutral optical density filters and related devices by ozone-assisted method.