Collimator Array Research Articles

An integrated reconfigurable optical add-drop multiplexer based on using an opto-VLSI processor and a 4-f imaging system

A novel integrated reconfigurable optical add-drop multiplexer (ROADM) structure is proposed and demonstrated experimentally. The ROADM employs an interface substrate that enables the integration of a fiber-lens collimator array and an Opto-VLSI processor to realise a 4-f imaging system through optical beam steering. Phase hologram optimization of the Opto-VLSI processor is investigated, for maximizing the number of wavelength channels while keeping adequate insertion loss and crosstalk levels. Experimental results are shown, which demonstrate a broadband operation and the principle of the ROADM with crosstalk of less than −30.5 dB and insertion loss of less than 6 dB for the drop and through operation modes.

Performance limitations of the pixelated ERD detector with respect to imaging using the rapid Tomographic Energy Dispersive Diffraction Imaging system

A prototype X-ray imaging system, using the principle of Tomographic Energy Dispersive Diffraction Imaging (TEDDI) has been developed at the University of Manchester's School of Materials. The non-destructive 3D imaging system makes use of a state of the art collimator array and a pixellated Si energy resolving detector. The new rapid TEDDI system is limited to thin, low density materials due to the low stopping power of Si at higher X-ray energies. In this paper the results of substituting Si for CdZnTe as the active detection element and limitations to the key parameters of energy resolution and count rate, for the detectors is presented. The findings have led to the design of a new ASIC which is discussed.

Adaptive Array of Phase-Locked Fiber Collimators: Analysis and Experimental Demonstration

We discuss development and integration of a coherent fiber array system composed of densely packed fiber collimators with built-in capabilities for adaptive wavefront phase piston and tilt control at each fiber collimator. In this system, multi-channel fiber-integrated phase shifters are used for phase locking of seven fiber collimators and the precompensation of laboratory-generated turbulence-induced phase aberrations. Controllable x and y displacements of the fiber tips in the fiber collimator array provide additional adaptive compensation of the tip and tilt phase aberration components. An additional control system is utilized for equalization of the intensity of each of the fiber collimator beams. All three control systems are based on the stochastic parallel gradient descent optimization technique. The paper presents the first experimental results of adaptive dynamic phase distortion compensation with an adaptive phase-locked fiber collimator array system.

Laser beam projection with adaptive array of fiber collimators II Analysis of atmospheric compensation efficiency

We analyze the potential efficiency of laser beam projection onto a remote object in atmosphere with incoherent and coherent phase-locked conformal-beam director systems composed of an adaptive array of fiber collimators. Adaptive optics compensation of turbulence-induced phase aberrations in these systems is performed at each fiber collimator. Our analysis is based on a derived expression for the atmospheric-averaged value of the mean square residual phase error as well as direct numerical simulations. Operation of both conformal-beam projection systems is compared for various adaptive system configurations characterized by the number of fiber collimators, the adaptive compensation resolution, and atmospheric turbulence conditions.

Laser beam projection with adaptive array of fiber collimators I Basic considerations for analysis

We present a mathematical model and provide an analysis of optical beam director systems composed of adaptive arrays of fiber collimators (subapertures), referred to here as conformal optical systems. Performances of the following two system architectures are compared: A conformal-beam director with mutually incoherent output laser beams transmitted through fiber collimators (beamlets), and a corresponding coherent system whose beamlets can be coherently combined (phase locked) at a remote target plane. The effect of the major characteristics of the conformal systems on the efficiency of laser beam projection is evaluated both analytically and through numerical simulations. The characteristics considered here are the number of fiber collimators and the subaperture and conformal aperture fill factors, as well as the accuracy of beamlet pointing.

Confinement degradation and transport of energetic ions due to Alfvén eigenmodes in JT-60U weak shear plasmas

The confinement degradation and transport of energetic ions due to Alfvén eigenmodes (AEs) destabilized by negative-ion-based neutral beam injection are quantitatively evaluated for the first time. AEs were observed in JT-60U weak shear plasmas with frequencies sweeping up to 30–50 kHz on a time scale of a few hundred milliseconds as the safety factor at the plasma centre, q(0), decreases from 1.75 to 1.5. Then as q(0) decreases from 1.5 to 1.25 in about 600 ms, the AE frequencies are saturated and the AEs are identified as the TAEs. The measured total neutron emission rate (Sn) in the presence of these AEs is compared with that predicted by classical theory. As a result, the confinement degradation of energetic ions is confirmed and the reduction rate in Sn is largest when AEs are destabilized and are located at the large fast ion pressure gradient region in the plasma core. In order to investigate the energetic ion transport due to these AEs, line-integrated neutron emission profiles measured with a large neutron collimator array are compared with the classical confinement calculations. It is found that energetic ions are transported from the plasma core region to the outer region due to these AEs. Furthermore, changes in the energy distribution of charge exchange energetic neutral particle fluxes suggest that the radial energetic ion transport is due to the resonance interaction between the energetic ions and the AEs.

Analysis of the interchannel response in a MEMS 1 × N^2 wavelength-selective switch

A theoretical model based on Fourier optics and the power-coupling overlap integral is built to investigate the interchannel response in a micro-electro-mechanical systems 1xN(2) wavelength-selective switch. The simulation results demonstrate that the interchannel response depends significantly on the output port location and the radius of curvature of the micromirrors. For the output originally aligned with the input along the dispersion direction, it is possible to achieve interchannel-response suppression by rotating the two-dimensional (2D) collimator array by a slight angle, e.g., 20 degrees. Experimental results under different conditions are also shown.

Micro Diffraction Imaging of Bulk Polycrystalline Materials

X-ray diffraction imaging applies an array of parallel capillaries in front of a position sensitive detector. Conventional micro channel plates of a few millimetre thickness have successfully been used as collimator arrays but require short sample to detector distances to achieve high spatial resolution. Furthermore, their limited absorption restricts their applications to low energy X-rays of around 10 keV. Progress in the fabrication of long polycapillaries allows an increase in the sample to detector distance without decreasing resolution and the use of high X-ray energies enables bulk investigations in transmission geometry.

A high port-count wavelength-selective switch using a large scan-angle, high fill-factor, two-axis MEMS scanner array

We present a high-port-count (scalable to 1 times 32) wavelength-selective switch (WSS) using a large scan-angle, high fill-factor, two-axis analog micromirror array in conjunction with a densely packed two-dimensional array of fiber collimators. A partially populated (1 times 9) WSS exhibits a fiber-to-fiber insertion loss of 5.57 plusmn 1.4 dB and an extinction ratio of 51 plusmn 11 dB. The channel spacing is 100 GHz

The manufacture of a very high precision x-ray collimator array for rapid tomographic energy dispersive diffraction imaging (TEDDI)

A very high resolution x-ray collimator array has been constructed for use with tomographic energy dispersive diffraction imaging (TEDDI). The collimator consists of a 16 × 16 array of 50 µm diameter holes in a series of 0.1 mm tungsten plates aligned to a tolerance of ±2 µm. The minimum angular divergence of the transmitted x-ray beams through each transmission pathway in the collimator array has been designed to be 0.02°, which is equivalent to an energy dispersed resolution of 250 eV with an aspect ratio of 6000:1. The collimator array has been matched to the development of an energy sensitive x-ray detector array (Seller et al 1998 Proc. SPIE 3445 584–92) for TEDDI studies of materials. The very high tolerance of the aperture size and placement was achieved by utilizing high intensity femtosecond pulse duration laser machining from a diode pumped solid state laser (DPSS). Using a novel arrangement the laser acted as the principal alignment and cutting tool. The collimator transmission function has been tested using a uniform synchrotron radiation flood field. The transmission and spatial uniformity were found to be consistent with the design parameters for TEDDI applications and also as a diffracted beam collimator for monochromatic powder diffraction studies.

1/spl times/N/sup 2/ wavelength-selective switch with two cross-scanning one-axis analog micromirror arrays in a 4-f optical system

A new high-port-count wavelength-selective switch (WSS) has been realized using two cross-scanning one-axis analog micromirror arrays in a 4-f optical system. The number of output ports is increased from N to N/sup 2/, where N is the maximum linear port count limited by optical diffraction. Using surface-micromachined micromirrors with hidden vertical comb drives, large scan angles (>/spl plusmn/5/spl deg/ mechanical), low drive voltages (7 V), and high fill factors (> 96.25%) are achieved for both scanning mirrors. Experimental results for WSS are demonstrated using both two-dimensional (2-D) array of discrete collimators and monolithic 2-D collimator array. A fiber-to-fiber insertion loss ranging from 6 to 18 dB and a switching time of <700 /spl mu/s have been achieved.

Microfabrication of pre-aligned fiber bundle couplers using ultraviolet lithography of SU-8

This paper describes the design, microfabrication and testing of a pre-aligned array of fiber couplers using direct UV-lithography of SU-8. The fiber coupler array includes an out-of-plane refractive microlens array and two fiberport collimator arrays. With the optical axis of the pixels parallel to the substrate, each pixel of the microlens array can be pre-aligned with the corresponding pixels of the fiberport collimator array as defined by the lithography mask design. This out-of-plane polymer 3D microlens array is pre-aligned with the fiber collimator arrays with no additional adjustment and assembly required, therefore, it helps to dramatically reduce the running cost and improve the alignment quality and coupling efficiency. In addition, the experimental results for the fiber couplers are also presented and analyzed.

First results from the high-resolution mouseSPECT annular scintillation camera

High-resolution single-photon emission computed tomography (SPECT) imaging in small animals tends to use long imaging times and large injected doses due to the poor sensitivity of single pinhole gamma cameras. To increase sensitivity while maintaining spatial resolution, we designed and constructed a multipinhole collimator array to replace the parallel hole collimators of a Ceraspect human SPECT brain scanner. The Ceraspect scanner is composed of an annular NaI(TI) crystal within which the eight pinhole collimators (1-mm-diameter holes) rotate while projecting nonoverlapping images of the object onto the stationary annular crystal. In this manner, only one-eighth of a collimator rotation is required to acquire a full circle orbit tomographic data set. The imaging field of view (FOV) has a diameter of 25.6 mm in the transverse direction, which is sufficient to encompass a mouse in the transverse direction. The axial FOV is 25.6 mm at the center of the FOV and 13.9 mm at the edge of the transverse FOV. Data are currently acquired in step-and-shoot mode; however, the system is capable of list mode acquisition with the collimator continuously rotating. Images are reconstructed using a cone-beam ordered subsets expectation maximization method. The reconstructed spatial resolution of the system is 1.7 mm and the sensitivity at the center of the FOV is 13.8 cps/microCi. A whole-body bone scan of a mouse injected with [Tc-99 m]MDP clearly revealed skeletal structures such as the ribs and vertebral bodies. These preliminary results suggest that this approach is a good tradeoff between resolution and sensitivity and, with further refinement, may permit dynamic imaging in living animals.

X-ray diffraction imaging of bulk polycrystalline materials

X-ray diffraction imaging applies an array of parallel capillaries in front of a position sensitive detector. The use of conventional micro channel plates of few millimeter thickness as collimator array requires short sample to detector distances to achieve high spatial resolution. Progress in the fabrication of long polycapillaries allowed to increase the sample to detector distance without decreasing resolution. Furthermore these 300 mm long capillaries can be used with high X-ray energies enabling bulk investigations in transmission geometry.

Low-Insertion-Loss Optical Matrix Switch Using MEMS Micromirrors Assembled by Passive Alignment

A three-dimensional (3D)-type MEMS optical switch with low insertion loss and low assembly cost has been developed. The switch consists of two optical beam scanners placed facing each other. Each scanner consists of a collimator array and two mirror arrays. The scanner controls the direction of each optical beam by means of two single-axis mirrors. The mirror arrays are fabricated by MEMS technology and contain holes through which the beam traverses in each mirror array. The mirror arrays are stacked directly on the collimator array, which is passively aligned using pins and alignment holes. Based on this structure, a prototype 32-port (with three extra ports) optical switch was developed. Measured insertion loss of six arbitrary paths in the switch is in the range of 1.5- 1.9 dB. It is thus concluded that a 3D-type optical switch assembled by wholly passive alignment with lower insertion loss than 2 dB is feasible.

Highly scalable 2-D fiber collimator array based on an array of through-holes in silicon

A highly scalable 4×4 fiber collimator array with long collimation length has been fabricated by utilizing a two-dimensional array of precision-controlled through-holes in silicon. A fiber array and a lens array were prepared by precisely positioning corresponding fibers and lenses utilizing the holes in separate silicon substrates, and the two arrays were integrated to implement the collimator array. The achieved average angular pointing accuracy and positioning accuracy of the collimator array were about 0.1/spl deg/ and better than 2 μm, respectively. At a distance of 10 cm from the collimator, the measured collimated beam size was 400 μm with its full divergence angle of 0.18/spl deg/.

A novel assembling technique for fiber collimator arrays using UV-curable adhesives

Packaging and assembly covers almost 80% of the overall cost of any fiber-optic devices. It is thus a demanding issue to lower the cost of fiber-optic alignment and attachment process. This work summarizes the results for the development of automated alignment and attachment processes for the packaging of 1/spl times/8 collimator arrays, which are critical for many photonic devices. The emphasis of this work is on the comparison of the use of three different UV-curing adhesives (Adhesives A, B, and C). It is concluded that regardless of curing shrinkage, a proper adhesive joint design can alleviate the optical loss effect of the relative fiber-lens displacement induced during curing and the subsequent cooling processes.

A quality factor to compare the dosimetry of gamma knife radiosurgery and intensity-modulated radiation therapy quantitatively as a function of target volume and shape

✓The authors have developed a quality factor (QF) to compare gamma knife radiosurgery, linear accelerator radiosurgery, and intensity-modulated radiation therapy (IMRT) dosimetry. This QF relates the percentage of target covered (PTC) by the prescription radiation isodose, target volume (VT), and enclosed tissue volume, which receives greater than a particular dose (VX): QFX = PTC×VT/VX. The authors investigated target shape independent of volume in predicting radiosurgical complication rates. Plastic targets of a defined volume (0.2, 0.5, 1.5, and 10 cm3) and four increasingly complex shapes (spherical, ellipsoid, simulated arteriovenous malformation [AVM], and horseshoe) were created. Dosimetry was studied on the Leksell GammaPlan, Adac/Pinnacle, and Nomos Corvus workstations. The dosimetry of a new 4 mm × 10—mm IMRT collimator array (the Nomos Beak) not yet validated for use in our clinical practice was studied. Particularly for larger targets, the gamma knife and IMRT Beak plans show similar conformality (QF assuming 15-Gy volume [QF15]). Particularly for small and round targets the gamma knife plan quality is significantly higher (QF assuming 12-Gy volume [QF12]). As VT and complexity increase, the IMRT Beak QF12 approaches that of the gamma knife. The QF12 of gamma knife dosimetry has an inverse correlation with target shape complexity independent of VT. At a prescription dose of 15 Gy to the target margin, the QF15 is a conformality index. The 12-Gy volume (volume enclosed by 12-Gy surface/volume receiving at least 12 Gy) estimates the radiosurgical normal tissue complication rate for AVMs. When the target is well covered, the QF12 is inversely proportional to the complication risk and is a measure of the plan quality.

Gamma knife radiosurgery for low-grade astrocytomas: results of long-term follow up.

The purpose of this paper is to report the long-term results of gamma knife radiosurgery (GKS) for low-grade astrocytomas. Fifty-one patients with low-grade astrocytomas treated with GKS and followed for more than 24 months are reported. Of the 51 patients, 12 harbored Grade I astrocytomas in and around the visual pathways and hypothalamus. The remaining 39 harbored Grade II astrocytomas. The mean patient age at time of GKS was 9.8 years for patient with Grade I and 30.9 years for those with Grade II astrocytomas. The mean tumor diameter was 25.4 mm for Grade I and 23.7 mm for Grade II tumors. The mean margin dose was 12.5 Gy for Grade I and 15.7 Gy for Grade II tumors. In the mean follow-up period of 27.6 months, both Grade I and Grade II astrocytomas responded well to GKS. Grade I astrocytomas had a response rate of 50% and a control rate of 91.7%. Grade II astrocytomas had a 46.2% response rate and an 87.2% control rate. Statistical analyses concerning the efficacy and related factors showed a significantly better response for patients 10 years of age or older with Grade I and those with a follow-up period of more than 24 months. Complications included radiation-induced edema in 18 (35.3%) of 51 cases, cyst formation or enlargement in five (9.8%), and transient tumor enlargement in three (5.9%). Radiosurgery can play an important role in the treatment of low-grade astrocytomas, and complete cure of these tumors is expected in at least some of the cases.

Rotational aperture synthesis for x rays

Aperture synthesis for the x-ray region can be accomplished with an array of rotation modulation collimators. A Hermitianizing recipe extracts sine and cosine components from a pair of collimators for each fringe spacing, and Fourier synthesis then reconstructs the images. The point-spread function has low sidelobes and is applicable with extended sources. A Monte Carlo simulation is used to illustrate and evaluate the statistical effects of quantum noise. Even better images may be expected from positively constrained reconstruction. The effects of axial misalignment on the point-spread function are illustrated. The conclusion is a favorable appraisal of the array as an astronomical telescope for hard x rays.