Optical alignment algorithm using Hadamard transformation

We first studied the characteristics of alignment performances of two computer-aided alignment algorithms i.e. merit function regression (MFR) and differential wavefront sampling (DWS). The initial study shows i) that, utilizing damped least square algorithm, MFR offers accurate alignment estimation to the optical systems with non-linear wavefront sensitivity to changes in alignment parameters, but at the expense of neglecting the coupling effects among multiple optical components, and ii) that DWS can estimate the alignment state while taking the inter-element coupling effects into consideration, but at the expense of increased sensitivity to measurement error associated with experiment apparatus. Following the aforementioned study, we report a new improved alignment computation technique benefitted from modified MFR computation incorporating the concept of standard DWS method. The optical system used in this study is a three-mirror anastignmat (TMA) based optical design for the next generation geostationary ocean color instrument (GOCI-II). Using an aspheric primary mirror of 210 mm in diameter, the F/7.3 TMA design offers good imaging performance such as 80% in 4 um in GEE, MTF of 0.65 at 65.02 in Nyquist frequency. The optical system is designed to be packaged into a compact dimension of 0.25m × 0.55m × 1.050m. The trial simulation runs demonstrate that this integrated alignment method show much better alignment estimation accuracies than those of standard MFR and DWS methods, especially when in presence of measurement errors. The underlying concept, computational details and trial simulation results are presented together with implications to potential applications.

Optical wireless communication (OWC) can provide the last mile high data rate and broadband access to indoor users. Infrared-based communication (IRC) can also achieve high data rate OWC transmission using a directional and collimated line-of-sight (LOS) optical beam. However, a collimated optical beam with beam steering ability is required to provide the LOS communication channel to different mobile users. Different optical beam steering approaches have their limitations. Although the mechanical-based approach using fast steering mirror (FSM) usually has a large footprint and limited optical steering speed; it can provide a large field-of-view (FOV) and support a wide wavelength window with polarization, optical mode, and modulation format independence operations. These are crucial for the OWC systems as wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) are employed to boost the transmission capacity. In this work, we propose and reveal a proof-of-concept experimental demonstration of an adaptive fast steering mirror (FSM)-based optical beam tracking and alignment system. To enhance the FOV and the stability of the OWC transmission, high-precision adaptive optical tracking via a two-FSM system with a light spot approaching method is proposed and demonstrated. The operation mechanism of optical alignment using two FSMs to establish the reference optical axis path is discussed in detail. The first FSM is utilized to correct the beam displacement issue from the reference optical axis, while the second FSM is utilized to correct the incident beam angle issue from the reference optical axis. Experimental result shows that the FOV can be enhanced from 0.05° (i.e., using only a single fiber collimator) to 51.85° using the proposed FSM-based system. A high-speed and stable orthogonal frequency division multiplexing (OFDM) OWC transmission at 89.3 Gbit/s, 87.03 Gbit/s, and 84.47 Gbit/s after free space propagation distances of 3 m, 10 m, and 20 m, respectively, can be achieved, fulfilling the hard-decision forward-error-correction (HD-FEC) requirement (i.e., bit-error-rate, BER = 3.8 × 10-3).

As optical systems and packaging constraints become more complex, the demands on optical alignment become more severe. We describe a straightforward method of alignment that optimizes optical system performance.

In a point diffraction interferometer, the existence of alignment error between an objective convergent spot and a diffraction pinhole can lead to wavefront error and diffraction intensity reduction. Meanwhile, the contrast of the point diffraction interferograms probably decreases in this procedure. These changes will have significant influence on its inspection precision. A precise alignment system of an optical path for a point diffraction interferometer is proposed in this paper. First, diffraction theory is used to analyze the mathematical relationships of alignment error to diffraction wavefront error and numerical aperture and wavefront error to pinhole size. Then, according to the requirement, the scheme of an optical path alignment system is designed. In this stage, alignment images as well as intensities of a reflected and diffracted beam from the point diffraction plate will be acquired. In addition, an image processing algorithm for measuring alignment error is designed, and a mathematical model between quantities of measurement and control is constructed. Finally, implementation and experiment of this method are also introduced. Misalignment situations, including lateral translation, longitudinal defocus, and tilt error, are well eliminated, and the quality of interferograms is also improved. From the results, it can be concluded that the system is of desirable precision and efficiency.

The OAS is a camera and laser system that will be used as an end effector on the LDUA to properly align the arm with the entry riser. It is attached to the LDUA by means of a Tool Interface Plat (TIP) which provides a feed through for all electrical and pneumatic utilities needed by the end effector to operate.

The optical system of the laser tracker utilizes plane mirrors to construct a reflective path, reducing its size and weight. However, maintaining the alignment of the laser with the ideal optical axis during its propagation in the optical system poses significant challenges in the design, fabrication, and assembly of the optical system. This paper explores the principle of error propagation during the assembly process of the optical system and improves the accuracy of the output laser through a numerical simulation and optimization methods. A general error model for the optical system is established to understand the principle of error propagation. A Monte Carlo numerical simulation and sensitivity analysis are used to study the influence of various errors on the accuracy of the output laser. The machining errors are optimized using a simulated annealing method to balance the manufacturing difficulty and system accuracy. The assembly process is also optimized to reduce the degrees of freedom and the number of optical parts required, and verified by experiments. The experimental results indicate that the average position error of the output laser is 15.743 µm, and the average angle error is 1.427′′. This study provides what we believe is a novel approach and methodology for the design and alignment of optical systems.

With the increasing demand for VBNS and VDSL, the development of the kernel parts of optical communication such as PLC(Planar Light Circuit), Coupler, and WDM elements has increased. The optical transmitter and the receiver module need precise and mechanical alignment within a few micrometers to couple the semiconductor device, optical fiber and waveguide. The alignment and the attachment technology are very important in the fabrication of an optical element. Presently, the alignment of the optical element is time consuming, and an effective alignment algorithm has not yet to be developed. In this paper, the optical element alignment of the multi-axis ultra precision stage is studied. Two alignment algorithms applied to the ultra precision multi-axis stage are used, the field search algorithm and the peak search algorithm. The automation program to improve the characteristics of the optical element alignment system is developed by Labview programming and is composed of three tabs, the field search tab, plotting tab and peak search tab. The developed program is applied to an actual system to determine the improvement in alignment performance.

A polarization analysis capability based upon polarization raytracing is described. The polarization ray trace can model the effects of various interface types including metallic reflectors and multilayer coatings. Idealized retarders and linear polarizers can also be incorporated into the model of an optical system. Information obtained during the polarization ray trace is used to compute image quality metrics such as the point-spread function and the modulation transfer function. In addition, the polarization state of the electric field at any point along a ray path can be found. The utility of the polarization raytracing approach is demonstrated by using the CODE V optical design program, which incorporates the modeling features described here, to perform an analysis of selected optical systems, including a corner-cube reflector, a folded beam expander, an imaging radiometer and a high numerical aperture objective. 1. INTRODUCTION The ability to accurately model the polarization effects in optical systems can be an important tool for assessing the performance of certain optical systems. From the standpoint of the optical designer who needs to determine whether or not a design meets specifications, the ideal tool for such an analysis task should provide information about how polarization effects can alter those performance metrics that he is familiar with, i.e. those that are typically used to specify design requirements for an optical system. Furthermore, such an analysis capability is most useful when it is integrated into the optical design/analysis software that he is using.This paper will describe a polarization analysis capability that enables the optical designer to model most of the effects that lead to polarization dependent behavior in conventional optical systems. The capability is primarily intended for analysis tasks rather than synthesis (i.e. design) tasks. At this time, though design techniques for reducing polarization effects do exist,1 they have not yet been fully integrated into optical design programs.

In this article, a record-high single-mode output power from a multi-junction vertical-cavity surface emitting laser (VCSEL) emitting at 905 nm is achieved. Single spectral mode emission of the VCSEL is realized by using an anti-phase mode filter, placed at the top surface of the device, that acts as a relief layer to suppress the higher order transverse modes. Placement of such anti-phase layer at the surface areas in which the higher order modes are expected to emit, leads to reduction in the effective mirror reflectivity at those areas, increased optical losses, and consequently, increased threshold gain for the higher order modes compared to the fundamental mode. The room-temperature light-current-voltage characteristics of a 6-junction 905 nm VCSEL with an oxide aperture size of ∼8 μm and mode filter size of 5 μm shows a single-mode optical power of 12.55 mW and maximum power conversion efficiency of 56.48%. Moreover, the emission spectrum of this device shows a stable side-mode suppression ration of >30 dB in the single-mode operation regime. The VCSEL remains reliably single-mode at higher temperatures, generating a maximum optical output power of 9.48 mW at 60 °C. Such remarkable single-mode performance can be mainly attributed to the multi-junction epitaxial structure of the device, in which the output optical power is expected to proportionally increase according to the number of bipolar cascade active regions.

Space-variant (SV) digital image restoration methods attempt to restore images degraded by blurs that vary over the image field. One specific source of SV blurs is that of geometrical optical aberrations, which divert light rays as they pass through the optical system away from an ideal focal point. For simple optical system, aberrations can become significant even at moderate field angles. Restoration methods have been developed for some space- variant aberrations when they are individually dominant, but such dominance is not typically characteristic of conventional optical systems. In this paper, an iterative method of restoration that is applicable to generalized, known space-variant blurs is applied to simulations of images generated with a spherical lines. The method is based on the Gauss-Seidel method of solution to systems of linear equations. The method is applied to sub-images having off- axis displacements of up to 453 pixels, and found to be superior in restoration effectiveness to Fourier methods in that range of field angles.

Stimulated Brillouin scattering (SBS) is the major factor that limits the maximum optical fiber output power in narrow linewidth applications, which include important fields such as passive optical networks (PONs), high-power fiber amplifiers, and lasers. Great efforts have been dedicated to suppressing the SBS effect and increasing the maximum optical fiber output power. This paper focuses on key fiber-based techniques to suppress SBS. These techniques take advantages of the properties of optical fibers. We present how these properties (electric modes, acoustic modes, and material properties) could be utilized to suppress SBS. The fiber-based techniques are divided into transverse optical fiber design, longitudinal variant fiber design, and external perturbations (strain and temperature) on optical fibers. Transverse optical fiber design focuses on the mechanism electro-acoustic interaction. Large effective area fiber design and acoustic tailoring techniques have been discussed. Longitudinal variant fiber design considers the nonlinear SBS interaction along propagation distance, and various techniques related have been presented. External perturbations (strain and temperature) on optical fibers emphasize on how external static perturbations could modify the SBS effect.

Free space propagation and conventional optical systems such as lenses and mirrors all perform spatial unitary transforms. However, the subset of transforms available through these conventional systems is limited in scope. We present here a unitary programmable mode converter (UPMC) capable of performing any spatial unitary transform of the light field. It is based on a succession of reflections on programmable deformable mirrors and free space propagation. We first show theoretically that a UPMC without limitations on resources can perform perfectly any transform. We then build an experimental implementation of the UPMC and show that, even when limited to three reflections on an array of 12 pixels, the UPMC is capable of performing single mode tranforms with an efficiency greater than 80% for the first four modes of the transverse electromagnetic basis.

A new optical system with a resolution that is superior to the resolution of the usual optical systems with diffraction limit is presented. We introduce a newly generated narrow light beam that propagates for a long range while almost maintaining its beam width and show that the beam width is narrower than that of the diffraction limit of normal optics. Thus a super high resolution is achieved for a long range, e.g., a range of a few kilometers, by the use of a 10-cm-diameter telescope. The high resolution for long-range imaging can be obtained by a Galilean telescope with a negative eyepiece that has a spherical aberration. We demonstrate theoretically high-resolution imaging by using simple objects and assuming a telescope 10 cm in diameter and a visible wavelength. A comparison of simulation results by the conventional optical system and by the special optical system clearly shows the superiority of the new system.

The characteristics of high-power semiconductor lasers with an 800 μm emitting aperture based on tunnel-coupled InGaAs/AlGaAs/GaAs heterostructures with three optically uncoupled laser sections are studied. The maximum power achieved under pumping by current pulses with an amplitude of 47 A and a duration of 1 μs is 110 W with the maximum active region heating not exceeding 4.7 °C. At a pulse duration of 860 μs, the maximum optical power is 22.6 W, and the decrease in the optical power to the pulse end reaches 6.7 %. A decrease in the laser pulse duration to 85 μs leads to an increase in the peak laser power to 41.4 W at a pump current amplitude of 20 A.

In order to obtain a high resolution image required for ultra-precision measurement of microstructural object, a new approach is proposed for 3D microstructures. It uses the modulation transfer function with defocus aberration based on the ambiguity function and stable phase principle to achieve an optical phase filter, and utilizes generalized a spheric phase optical element to encode defocus images, and uses deconvolution technology to recover the images. In comparison with conventional optical system, the phase filter used in the optical system can make focal spot smaller when measure object defocusing, eliminates the effect of the defocus aberration, and improves the defocused property. Numerical results indicate the designed phase filter can improve lateral resolution of optical system, and the axial resolution of the optical system is not affect by the filter and defocus aberration. For different defocus plate, the phase filter can make character of modulation transfer function of lateral direction uniform approximation.