Collimator Lens Research Articles

Compound parabolic concentrator for LED-based underwater optical communication transmitter

Laser sources have been used at the transmitter unit of underwater wireless optical communication (UWOC) systems since their invention. In recent years, light-emitting diodes (LEDs) have begun to be used as UWOC transmitters due to their low cost, long lifespan, and high energy efficiency. However, data transmission distances in UWOC systems using bare LEDs and LED arrays with collimating lens are limited due to LED’s large divergence angles and insufficient gains provided by the low cost lens designs. In this paper, we propose to use a compound parabolic concentrator (CPC), whose transmission efficiency curve is very close to the ideal concentrator, as a collimator that narrows the divergence angle of LEDs to design low-cost UWOC transmitter with long communication distance. Using the Bouguer–Beer–Lambert channel model, we derived the received optical power expression at the receiver side for the LED-based UWOC system with CPC at the transmitter. Furthermore, unlike existing studies in the literature, the full spectrum of the LED has been taken into account when deriving the power expression. The results show that using the CPC collimator instead of a typical collimation lens in an LED-based UWOC system can narrow the divergence angle by approximately 10 times, resulting in a 70 dB increase in signal-to-noise ratio (SNR) at the receiver and up to a 20 times increase in the communication distance.

Design and experimental validation of an aspheric multi-lenticular plano-convex lens for VCSEL beam collimation

In this work, we propose a design method of an aspheric lens that achieves collimation for a VCSEL laser beam. The designed lens features a planar front surface and an aspheric back surface of which the profile is mathematically characterized and precisely determined based on the proposed method. The method is derived from a basic geometric-optics analysis and construction approach. The collimating effect of the lens was first analyzed in simulation and then validated in experimental measurement. The experimental results show that the collimator lens transforms the input VCSEL laser beam divergence angle from 25° (436.33 mrad) to an output angle of 3.6906 mrad.

Low-cost visible spectrophotometer for detecting absorption and emission in metallic blends of colorful samples solution

The innovative, affordable assembled visible spectrophotometer employed in this study aims to analyze the absorption and emission of colorful metallic blends of colorful samples solution. It features a tungsten white light bulb source, an ammeter as a detection element, a digital voltmeter, a diffraction grating for light dispersion, a converging lens for light collimation, and filters of various wavelengths (blue, red, yellow, and yellow-green). The light bulb source was powered by a standard supply set at 6 V. Using metallic solutions of chromium chloride (CrCl3) and copper sulphate (CuSO4) with different filter wavelengths, the performance was assessed. The transmittance and absorbance of these metallic solution samples exhibit a linear relationship with approximately 3 % deviation compared to results from a commercial UV–VIS spectrophotometer (DR-6000). Similar investigations were conducted with equivalent quantities of CuSO4, CrCl3, and nickel chloride (NiCl2) solutions, showing a discrepancy ranging from 2 % to 8 % when compared with the commercial UV–VIS spectrophotometer. Therefore, in low-income countries like Ethiopia, colorful metallic solution samples can be effectively analyzed using the newly designed low-cost spectrophotometer.

Use of planar retarding field to improve energy resolution of projection-type electron spectroscopy collimator analyzer

A method to improve the energy resolution of the recently proposed projection-type electron spectroscopy collimator analyzer (PESCATORA) is presented. PESCATORA is a simple, highly compact two-dimensional electron analyzer with a wide acceptance angle of up to ±60°. The use of a combined planar retarding field and parallel-hole collimator (PRF–PHC) as a band-pass filter is analytically and numerically studied. In PESCATORA, a parallel-hole collimator placed behind a specially designed electrostatic collimator lens is used as a band-pass filter to obtain energy-resolved angular distributions of emitted or diffracted electrons (or charged particles) from sample surfaces. The PRF–PHC system can be introduced in PESCATORA by simply adding a planar grid in front of the collimator plate. This allows the transmittance and energy resolution to be effectively controlled by only changing the retarding voltage of PRF, consequently improving PESCATORA. Moreover, an improved PESCATORA instrument with the highest possible specifications is presented.

Inhomogeneous thermal analysis of microlayer mold for glass molding of fast-axis collimation lens array

Fast-axis collimation (FAC) lens arrays play a crucial role in laser systems, offering precise beam shaping and focusing for applications such as laser marking, and optical communication. Achieving high precision in these applications requires a FAC lens array with a long Rayleigh range. While precision glass molding with nickel-phosphorus (Ni-P) microlayer molds has revolutionized the mass production of FAC lens arrays, the extreme conditions during the molding process can lead to poor profile accuracy. To address this issue, we developed an optical collimation system to derive the final characteristic parameters and obtain the beam waist radius and Rayleigh range of the collimated laser. Additionally, we conducted a thorough analysis of the inhomogeneous thermal expansion process of the microlayer mold and established a mathematical solution for thermal compensation to modify the mold's shape. We validated the proposed method by fabricating an FAC lens array mold and measuring the profile error and waist radius of a molded FAC lens array. We also calculated the profile error of this method using a finite element (FE) model in ABAQUS. The results indicate that incorporating the inhomogeneous thermal expansion reduces the shape error of the FAC lens array from 0.577 μm to 0.135 μm. Moreover, using inhomogeneous thermal compensation significantly improves the Rayleigh range of the FAC lens array from 1.285 μm to 9.8 × 104 μm.

Newton ring interferometry application for 2D lens array alignment with micrometer accuracy.

The dense packing of two-dimensional (2D) lens arrays with high tilt and decentration accuracies is a technological challenge in coherent beam combining, as the collimator lens parameters and 2D lens array alignment must satisfy stringent requirements. A method for 2D lens array alignment based on Newton ring interferometry (NRI) is proposed. The analytical model and the algorithm presented in this study enabled the estimation of alignment sensitivity. An optical setup for alignment tests using NRI was developed and experimentally verified, and micrometer sensitivity was demonstrated. Analytical and experimental results showed that micrometer accuracy was achieved. Its limitations and prospects for improvement are also discussed.

Iterative assembly: a quick algorithm for generating aspherical collimating lenses in bidimensional optical systems

We present a proof of concept for a linear iterative technique that generates piecewise aspherical lenses suited for collimating any continuous monochromatic input of rays, in systems with translational symmetry along the perpendicular axis of a plane. A lens generated by our method was compared to a known analytical solution, yielding a maximum deviation of the order of 10−6 units for a hundred vertices. We exemplify its usage with a simulation where a lens corrects the spherical aberration of a mirror and also shifts its focal point at the user’s will. We also discuss the limitations of this technique and conjecture other applications, such as focalizing beams instead of collimating.

3D Printed Lenses for Vertical Beam Collimation of Optical Phased Arrays.

This article presents the design, fabrication, and characterization of edge-coupled 1D optical phased arrays (OPAs) combined with collimating lenses. Our concept was tested with two OPAs having different collimation ranges. Both OPA designs have 3-μm waveguide spacing and the maximum beam steering range is about 30° based on wavelength tuning around 1550 nm. The first generation had 37 channels with 108 μm of waveguide array width and the second generation had 512 channels with 1.5 mm array width. As the array outputs are edge coupled, suitable lenses are required to collimate the beam vertically. We report the comparison between a commercially available straight cylindrical lens and custom 3D printed curved cylindrical lenses. In the experiments, we demonstrate 1D beam steering of the light outcoupled from the waveguide facets and collimated by these lenses and analyzed parameters such as Rayleigh range and beam divergence. These parameters are estimated to be 9.9 mm and 7.0 mrad (0.4°), respectively, for the commercial lens, whereas 40.1 mm and 3.5 mrad (0.2°) for the dedicated 3D printed lens, showing a clear improvement.

A Fully Solid-State Beam Scanner for FMCW LiDAR Application

We demonstrate a fully solid-state beam scanner that incorporates a Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> photonic integrated switch array, a collimator lens, and a lithographically patterned diffraction grating. The off-chip components enable nearly circular output beams under the reduced system complexity. By manipulating the optical switch array and tuning the input wavelength, two-dimensional beam steering with 32 × 23 = 736 resolvable spots across a 14.3°×9.9° field of view (FOV) is realized. Furthermore, the coherent ranging within 18 m is demonstrated experimentally by utilizing the triangular frequency modulation. The tested results validate the feasibility of the proposed beam scanner, which might offer a flexible, scalable, and easily-implemented solution for the solid-state frequency modulated continuous-wave (FMCW) LiDAR.

Bidirectional transmission of a collimator with double-combined collimating lenses and thermally expanded core fibers.

The collimator is an essential part of the fiber optic rotary joint design. This study proposes the Large-Beam Fiber Collimator (LBFC) with a double collimating lens and a Thermally Expanded Core (TEC) fiber structure. The transmission model is constructed based on the defocusing telescope structure. The effects of TEC fiber's mode field diameter (MFD) on the coupling loss are investigated by deriving the loss function for the influence of collimator mismatch error and implementing it on a fiber Bragg grating temperature sensing system. The experimental results show that the coupling loss decreases with the increase of the MFD of TEC fiber, while the coupling loss is less than 1dB when the mode field diameter is greater than 14µm. TEC fibers can reduce the effect of angular deviation. Considering the coupling efficiency and deviation, the preferred mode field diameter for the collimator is 20µm. The proposed LBFC enables bidirectional transmission of optical signals for temperature measurement.

High resolution spatially extended 1D laser scattering diagnostics using volume Bragg grating notch filters.

Laser light scattering systems with volume Bragg grating (VBG) filters, which act as spectral/angular filters, have often been used as a point measurement technique, with spatial resolution as low as a few hundred μm, defined by the beam waist. In this work, we demonstrate how VBG filters can be leveraged for spatially resolved measurements with several μm resolution over a few millimeters along the beam propagation axis. The rejection ring, as determined by the angular acceptance criteria of the filter, is derived analytically, and the use of the ring for 1D laser line rejection is explained. For the example cases presented,i.e., for a focused probe beam waist with a diameter of ∼150 μm, the rejection ring can provide resolution up to several millimeter length along the beam propagation axis for a 1D measurement, which is also tunable. Additionally, methods to further extend the measurable region are proposed and demonstrated, using a collimation lens with a different focal length or using multiple VBG filters. The latter case can minimize the scattering signal loss, without the tradeoff of the solid angle. Such use of multiple VBGs is to extend the measurable region along the beam axis, which differs from the commonly known application of multiple filters, to improve the suppression of elastic interferences. 1D rotational Raman and Thomson scattering measurements are carried out on pulsed and DC discharges to verify this method. The system features compactness, simple implementation, high throughput, and flexibility, to accommodate various experimental conditions.

Research on the Influence Model of Collimating Lens Aberrations in Autocollimation System Based on the Ray-Tracing Method

An influence model of collimating lens aberrations in an autocollimation system based on the ray-tracing method is established. With the ray-tracing method, this model can accurately compute the direction and position of each light ray passing through the collimating lens in an autocollimation system, thereby obtaining the light-spot position of each light ray on the sensor and determining the systematic error caused by aberrations. Eventually, this model serves to compensate for the measurement error of autocollimators and improve the accuracy. Simulations and experiments demonstrate that the influence quantity of angular measurement value due to aberrations reaches 0.74 arcsec within the range of ±500 arcsec. Also, in a large-aberration situation, the measurement accuracy is promoted to 3.33 arcsec, approximately five times higher than that without compensation.

Wavefront measurement of a multilens optical system based on phase measuring deflectometry

Usually, a multilens optical system is composed of multiple undetectable sublenses. Wavefront of a multilens optical system cannot be measured when classical transmitted phase measuring deflectometry (PMD) is used. In this study, a wavefront measuring method for an optical system with multiple optics is presented based on PMD. A paraxial plane is used to represent the test multilens optical system. We introduce the calibration strategy and mathematical deduction of gradient equations. Systematic errors are suppressed with an N-rotation test. Simulations have been performed to demonstrate our method. The results showing the use of our method in multilens optical systems, such as the collimator and single-lens reflex camera lenses show that the measurement accuracy is comparable with those of interferometric tests.

Self-Alignment FSOC System With Miniaturized Structure for Small Mobile Platform

This paper presents a miniaturized equipment used in tracking and pointing, and provides a method for free space optical communication among small platform. This scheme uses simple scan mirror and receiver with single photo detector to achieve tracking function. Signal beacon is controlled to rotate around target receiver. Transmitter constantly adjusts emitting direction to track receiver according to received signal intensity, which is send back by reverse laser link. The prototype system is successfully established and its transmitting part consisted by directly modulated laser diode, mechanical collimation lens, and scan mirror is also proved. The receiving end is mainly composed of large area photo detector and short-focal lens. Field-programmable gate array chips set in both ends are used to implement tracking algorithm. This system can track target at speed of 40 mm/s within 2 m distance in an angle range of ±30°. For further application, the system has great potential for miniaturization because of elimination of motors, beacons and cameras in its scheme.

An Inertial Uni-Axial Interferometer-Based Accelerometer for Harsh Environments

For high-impact devices, subsequent vibrations have as much influence on the deterioration of the mechanical structure as the impact itself. To mitigate the consequences of both impacts and resulting vibrations, it is crucial to accurately understand the peak acceleration and vibration frequencies that originate in the structure. In this article, a radiation tolerant opto-mechanical sensor based on an absolute measurement inertial accelerometer is presented. This method of measurement is chosen due to the viability of placing the readout electronics far from the highly radioactive environment that the sensor may be installed in. The designed accelerometer consists of a fixed aluminum frame with a built-in membrane that acts as a leaf spring. In the same membrane, a retro-reflector is attached which acts as a seismic mass. The retro-reflector reflects the light beam coming from the collimator lens placed on the frame. To prove its viability, the device has been tested under different conditions. First, the device is calibrated and validated using a high-frequency exciter. Second, a high-acceleration testbench is used to compare its output signal with a commercial accelerometer and verify its proper operation as well as its expected lifetime. The experimental results showed an average sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${9} \times {10}^{-{4}}$ </tex-math></inline-formula> g/pm with reading measurements of up to 5000 g and a working bandwidth located between 50 and 800 Hz.

Study of the accuracy of the design method based on aberration theory for collimating lenses

The method was proposed choosing the initial construction and for the design of collimation and side-emitting lenses which includes the lens profile generating on the base of the conic curves using simple theoretical expressions from the third-order aberration theory. Compared to the other methods, this one gives the possibility to evaluate the necessary size and basic parameters of conic curves without any time-consuming procedures. In the paper, the accuracy of the solutions obtained on the basis of aberration theory has been analyzed from the viewpoint of lens efficiency and the forming surfaces’ shape both for different lens types and extended LED sources. The goal of the work was in researching how close to the more exact configuration the proposed solution was obtained using optimization technique. For different cases of lens size and lens dimensions, we have demonstrated that the deviation of the lens profile is comparable to the surface manufacturing accuracy. Thus, the method using aberration theory provides a basis for the fast automatic and visual tool for designing illumination lenses.

Performance enhanced terahertz imaging using a high-response thermomechanical microcantilever FPA

In this paper, we demonstrate a high-response thermomechanical microcantilever focal plane array (FPA) using a metamaterial absorber (MA) integrated thermomechanical microcantilever as a pixel for terahertz (THz) imaging at 2.52 THz. The response of the FPA was increased by thinning the silicon nitride (SiNx) thickness of the microcantilever leg but keeping the dielectric layer thickness of the MA unchanged to ensure enough absorption. A THz imaging system based on the high-response FPA was established using two parabolic mirrors to replace ordinary high-density polyethylene (HDPE) THz lenses for THz beam collimation and expansion, which can reduce the transmission loss of lens material to THz waves by more than 40%. THz images of hollow metal plate and different polymers as well as a THz video at a frame rate of 30 Hz were captured by the high-response FPA. The thermomechanical sensitivity was measured to 0.35 deg/K, which is increased by 1.34 times compared with the leg unthinned FPA. The noise equivalent power (NEP) was measured to be 18.0 nW/Hz1/2, which is about 44% of the leg unthinned FPA. The horizontal and vertical resolutions were 350 μm and 40 μm respectively.

Core Selective Switch With Low Insertion Loss Over Ultra-Wide Wavelength Range for Spatial Channel Networks

The core selective switch (CSS) is an optical spatial switch that has been recently proposed as a key building block to achieve a scalable and low-insertion-loss spatial cross-connects for use in future spatial channel networks. In this paper, we report on a novel CSS design employing a two dimensionally arranged microlens-based multicore fiber (MCF) collimator array and a micro-electromechanical systems (MEMS) mirror array. The former enables precise alignment between MCFs and collimator lenses, and the latter yields polarization-independent high reflection over a wide wavelength range and a large tilt angle. Based on the design, a compact (∼50 mm) five-core <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1 \times 8$</tex-math></inline-formula> CSS prototype is fabricated. We experimentally show that the CSS prototype exhibits low insertion loss (1.2∼2.7 dB), low polarization dependent loss (< 0.25 dB), and low crosstalk (< <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ - 30$</tex-math></inline-formula> dB) characteristics over an ultra-wide wavelength range from 1500 nm to 1630 nm. Bit-error-rate measurements using optical signals in the C-band, S-band, and L-band show that the CSS prototype incurs no optical signal-to-noise ratio penalty in spatial channel routing over an ultra-wide wavelength band.

Radially Periodic Metasurface Lenses for Magnetic Field Collimation in Resonant Wireless Power Transfer Applications

In this paper, a new procedure and topology of magnetic metasurface lens are proposed for improving the performance of Resonant Wireless Power Transfer systems. Firstly, three subwave-length unit cells are optimized in order to get negative magnetic permeability in the same frequency, each one with a different refractive index, and they are experimentally characterized. Then, the Transformation Optics technique is applied in order to find the unit cell arrangements which lead to the magnetic field focusing in a given direction. For this purpose, two coordinate transformations are proposed, and the effective electric permittivity and permeability that generate these profiles are calculated. It is shown from simulations and measurements that the refractive index gradient produced by the radial disposition of the unit cells can lead to a magnetic field manipulation similar to the optical converging and diverging lenses. Both metamaterials lenses are built, and the calculation of the magnetic flux density as a function of the measured induced voltage in a probe coil verifies their effects on the magnetic field. Finally, their performance in a resonant wireless power transfer system is tested, and improvements in terms of efficiency and range are presented. The proposed design method and the lenses that were developed demonstrate that metasurface lenses can improve efficiency without reducing the range, once these lenses are positioned close to the transmitter coil. Besides that, this method can reduce the losses due to misalignment between coils once the field can be collimated in a specific direction.

Optical Coupling Efficiency of a Coupler with Double-Combined Collimating Lenses and Thermally Expanded Core Fibers.

Improving the coupling efficiency of two optical signals is a hot issue, where the efficiency of optical coupling has a significant effect on the signal transmission over the fiber link. To this end, the Large-Beam Fiber Coupler (LBFC) with a Double-combined Collimating Lens (DCL) and a single-mode TEC fiber structure are proposed in this study. Based on the propagation principle of Gaussian beams and the coupling requirements, the coupling mechanism of the fiber coupler and the coupling mismatch between the coupler is analytically modeled. The model and the optical path are optimized, then the ray tracing is used to calculate the coupling efficiency of inter-coupler signals for different SMF. The coupling efficiency is evaluated through experiments in terms of coupling efficiency and the radial, axial, and angular mismatches between the couplers. The results showed that with a large Mode Field Diameter (MFD), better coupling efficiency can be obtained, i.e., a large MFD of 28 m is tested with its maximal efficiency of 95.16%. Moreover, the angular mismatch has the most significant impact on the coupling efficiency, while the axial mismatch has the least. The use of large MFD can alleviate the angular mismatch and thus improve the optical coupling efficiency.