Large Optical Systems Research Articles

Space-time block code based MIMO encoding for large core step index plastic optical fiber transmission systems

The performance of Space-Time Block Codes combined with Discrete MultiTone modulation applied in a Large Core Step-Index POF link is examined theoretically. A comparative study is performed considering several schemes that employ multiple transmitters/receivers and a fiber span of 100 m. The performance enhancement of the higher diversity order configurations is revealed by application of a Margin Adaptive Bit Loading technique that employs Chow's algorithm. Simulations results of the above schemes, in terms of Bit Error Rate as a function of the received Signal to Noise Ratio, are provided. An improvement of more than 6 dB for the required electrical SNR is observed for a 3 × 1 configuration, in order to achieve a 10(-3) BER value, as compared to a conventional Single Input Single output scheme.

Design and optimization of broadband and polarization-insensitive dual-core photonic crystal fiber coupler

In this paper, we propose a novel (to our knowledge) broadband and polarization-insensitive dual-core photonic crystal fiber (PCF) coupler through the introduction of an elliptical-shaped central air hole to offset the slight birefringence arising from the dual core. With a full vectorial finite element method and anisotropic perfectly matched layers as the external boundaries, the impact of several fiber parameters on the coupling characteristics of dual-core PCF is investigated in detail. Through optimizing the main fiber parameters, including core diameter, size and ellipticity of the central air hole, and refractive index difference, broadband and polarization-insensitive characteristics are achieved in the wavelength range from 0.8 to 1.7 μm. The variation of the coupling ratio is stabilized at 50±1%, and the coupling ratio difference between x polarization and y polarization is less than 2% over the wavelength range. This dual-core PCF makes it easier to develop a 3 dB coupler over a wide wavelength for passive optical networks and large optical systems.

Ultra-Lightweight Design and Analysis of a 1.25m SiC Segmented Mirror

In order to explore the feasibility of large ultra-lightweight deployable optical systems, a 1.25m SiC segmented mirror is investigated. According to analysis and comparison, the mirror's material, ultra-lightweight structure pattern and support location are determined respectively. By FEM, an ultra-lightweight structure with areal density of 40kg/m2 is gotten. The results show that the self-weight deformation is 4.8nm RMS/22.6nm PV under supports, and the ultra-lightweight mirror has the enough strength to bear the stress at launch. The study may provide a technical scheme to develop the large ultra-lightweight deployable optical system.

共光路径向剪切干涉仪的设计

As conventional phase shifting interferometers can not test the wavefront aberration from a large diameter and long optical path system accuracely,a new commonpath shearing interferometer is designed to elimnate the system error introduced by the standard wavefront.The new design takes an agglutination prism consisting of a triangular prism and a rhombic prism as a shear device to produce interference by the wavefront under-test with its replication.A group of different relative aperture lens switching devices are used to control the shearing ratio of the shearing interferometer.Compared with the data from 4D dynamic interferometers under different temperature conditions,it shows that the repeatability of designed shearing interferometer is about λ/80 and the accuracy of root mean square is better than λ/80(λ=630 nm).The design of the commonpath shearing interferometer greatly reduces its dimension and weight and also improves the experiment efficiency for long optical path interference measurement.

“SSD scattering signal extraction in LSCT”

Sub-Surface Damage (SSD) in optical element had became a shackle of research and manufacture in energy, advanced technology and so on, for its severe influence to the laser-induced damage threshold, the long term stability of large optical system. So the evaluation of SSD was a hot topic in optical engineering. The scattering caused by optical component SSD links the optical non-destructive evaluation and SSD itself. Laser scanning confocal technology (LSCT) is an effective way for SSD assessment and it is also based on the back scattering of SSD. The scattering signal extraction is the key point in SSD measurement using LSCT. The difficulty of SSD signal extraction is introduced firstly. The signal composition accepted by LSCT detector is analysed in detail. The different component part is successively and independently analysed, and the elimination or reduction way of each part is given. Lastly, the high SNR SSD scattering signal of one element tested by LSCT equipment is displayed in 2D figure.

Dispersion compensation optical fiber modules for 40 Gbps WDM communication systems

Dispersion compensation was originally proposed to equalize pulse distortion. With the development of wavelength division multiplexing (WDM) techniques for large capacity optical communication systems, dispersion compensation technologies have been applied into the field. Fiber-based dispersion compensation is an attractive technology for upgrading WDM communication systems because of its dispersion characteristics and good compatibility with transmission optical fibers. Dispersion compensation fibers and the modules are promising technologies, so they have been receiving more and more attention in recent years.

Interferometric monitoring of large optical systems for the UV region

This paper discusses the structure, the main modules, and the operating principle of an automatic interferometric system developed for monitoring large UV optical systems and its use for the assembly, adjustment, and monitoring of large UV objectives. Preliminary studies of the TA FHG-110 high-coherence laser have been carried out, based on two-stage frequency multiplication.

The Ultra-Precision Polishing of Large Aperture Reaction Bonded Silicon Carbide Mirror

Problem statement: Silicon Carbide (SiC) optical materials have becom e the first choice for mirrors in space optical systems and large grou nd-based optical systems due to their outstanding mechanical, physical and optical properties. Compar ed with traditional optical glasses, SiC optical materials are provided with the characteristics of high hardness and multiphase, which embarrass the high efficient fabrication of SiC mirrors with ultr a-smooth surfaces and high precision. Approach: We choose some typical polishing parameters and conduct a series of experiments, trying to find out the relationship between polishing parameters and resul ting surface roughness. The polishing parameters for Reaction Bonded Silicon Carbide (RB-SiC) are optimized from the analysis of these experiments. Then we can apply these parameters to the figuring process. Computer Controlled Optical Surfacing (CCOS) is a widely used deterministic polishing met hod and features in low-cost, high-precision and large flexibility. The basic theory and process of CCOS are given in detail. Then we employ CCOS in the ultra-precision machining of RB mirrors. Results: We polish a RB SiC sample with the optimized polishing parameters and a surface roughness better than 1nm (RMS) is obtained. A 475 mm diameter sphere RB-SiC mirror with a relative aperture of 1: 1 is polished by CCOS and the surface error reduces to 0.175 λ(PV)/0.009 λ(RMS) from 0.526 λ(PV)/0.080 λ(RMS). Both results represent a very smooth surface and a very precise figure. Conclusion: The result proves the feasibility of the polishing technology and CCOS method. These works also accumulate experience for the manufacturing of aspheric SiC mirror.

High-throughput fluorescence detection using an integrated zone-plate array

Microfluidic devices enable massive parallelization of sample manipulation and delivery, but a similarly parallelized and integrated optical detection system does not yet exist. Standard large numerical aperture wide field or scanning optical systems are not capable of the large field of view and detection sensitivity required to collect fluorescence from parallel arrays of microfluidic devices. Instead, we present a fluorescence measurement platform based on a microfabricated zone-plate array integrated into a parallelized microfluidic device. The zone-plate array is orientated so that a single high numerical aperture zone plate is aligned to read out the fluorescence from each of 64 output channels of a drop-making device. The parallelization of microfluidics and optics produces an integrated system capable of analysis of nearly 200,000 drops per second.

新型长波红外折衍混合消热差系统

To improve performance of a large area high resolution optical system,a novel infrared diffractive-refractive hybrid system in 8~12 μm with 16° FOV is designed based on the thermal properties of the diffractive lens and the theory of athermalization.The effective focal length and back working distance of the system are respectively 100 mm and 133 mm,while the F number is 1.9.The system is composed of three lenses,which used only two materials of Ge and ZnSe,including a conic surface and a diffractive surface.The results show that the hybrid system possesses better athermal performances and high image quality in-30 ℃~70 ℃.Additionally,the system has a compact structure,lightweight,which make the system can satisfy the necessary specifications of modern optical instruments.

Tunable coupled-ring-resonator of thermally actuated optical switch array

In this research, we design tunable micro-ring resonators and propose the employment of an integrated control circuit to compensate for the fabrication error, and tune as well as lock the wavelength in a thermal-actuated ring-type optical switch through an amplitude modulation scheme. Additional functionalities can also be added in this circuit by tailoring externally the roundtrip loss or coupling constants of the ring. The design concept can be easily scaled up for a large array optical switch system without much change to the terminal numbers thanks to the three-dimensional hierarchy of the high gray-scale control circuit design, which effectively reduces the terminal numbers to the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with free spectral range (FSR) equal to 1.5 nm at 1532 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for a thermal actuated ring type optical switch.

Monolithically Integrated 8:1 SOA Gate Switch With Large Extinction Ratio and Wide Input Power Dynamic Range

A monolithic 8:1 SOA gate switch that integrates an 8-ch SOA gate array, an 8:1 optical coupler, and a 1-ch SOA gate was developed for use in a large scale optical packet switching system. A 250-mum-long compact field-flattened coupler (FFC) produces a very small channel-imbalance together with a compact total chip size of 3.0 times 1.0 mm. The device exhibited a large ON-state gain of >14.3 dB and a small total gain deviation of 3.0 dB. The optimized passive waveguide structure successfully suppressed the stray light, which resulted in a record-high ON-OFF extinction ratio of >70 dB. We used a thin tensile-strained multi-quantum well (MQW) active layer which can attain high-saturation output power, low noise, and polarization insensitivity for SOA gates. Due to the coexistence of a high saturation output power and a low noise figure, the device exhibited a very wide input power dynamic range of 20.5 dB for a 10-Gb/s NRZ signal.

Thermally actuated optoelectronic switch array for wavelength modulation/lock within <inline-formula><math display="inline" overflow="scroll"><mrow><mn>0.01</mn><mtext>-</mtext><mi>nm</mi></mrow></math></inline-formula> fluctuation

Thermal actuated optoelectronic ring switch provides the advantages of high accuracy, easy actuation, and reasonable switching speed. However, when scaled up, the thermal ring switch may encounter issues related to fabrication error, nonaccurate wavelength response, and large terminal numbers in the control circuit. We propose the employment of an integrated control circuit to compensate for the fabrication error and tune as well as lock the wavelength in a thermal-actuated ring-type optical switch through an amplitude modulation scheme. Additional functionalities can also be added in this circuit by externally tailoring the round-trip loss or coupling constants of the ring. The design concept can be easily scaled up for large array optical switch system without much change in the terminal numbers thanks to the three-dimensional hierarchy of high gray-scale control circuit design, which effectively reduces the terminal numbers into the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with free spectral range equal to 1.5 nm at 1534 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for the thermal actuated ring-type optical switch.

Dispersion-flattened Bragg photonic crystal fiber for large capacity optical communication system

A novelty dispersion ultra-flattened Bragg photonic crystal fiber (PCF) has been fabricated in this paper. The fiber is composed of compound cores and periodical claddings with 11 coaxial rings. It has flattened dispersion of 8.5±1.3 ps·(nm·km)−1 in the communication wavelength range of 1460–1625 nm. Its dispersion slope alters from −0.0428 to 0.0392 ps·nm−2·km−1. The low attenuation of 0.52 dB/km and low bending loss of 0.09 dB at 1550 nm of the fiber are also achieved. The Bragg PCF has enormously potential application in the fields of dense wavelength division multiplexing systems because of its superior dispersion properties and easy splicing performances.

Comparison of minimum-norm maximum likelihood and maximum a posteriori wavefront reconstructions for large adaptive optics systems

The performances of various estimators for wavefront sensing applications such as adaptive optics (AO) are compared. Analytical expressions for the bias and variance terms in the mean squared error (MSE) are derived for the minimum-norm maximum likelihood (MNML) and the maximum a posteriori (MAP) reconstructors. The MAP estimator is analytically demonstrated to yield an optimal trade-off that reduces the MSE, hence leading to a better Strehl ratio. The implications for AO applications are quantified thanks to simulations on 8-m- and 42-m-class telescopes. We show that the MAP estimator can achieve twice as low MSE as MNML methods do. Large AO systems can thus benefit from the high quality of MAP reconstruction in O(n) operations, thanks to the fast fractal iterative method (FrIM) algorithm (Thiébaut and Tallon, submitted to J. Opt. Soc. Am. A).

Integrated CMOS system and thermally actuated optical switch for wavelength modulation/lock in communication network

AbstractThe advancement of communication technology and growth of internet traffic have continuously driven the fast evolution of networks. Compared to the traditional optoelectronic switch, all-optical switch provides high throughput, rich routing functionalities, and excellent flexibility for rapid signal exchange in fiber optical network. Among various all-optical switches, thermal actuated ring switch provides the advantages of high accuracy, easy actuation, and reasonable switching speed. However, when scale up, thermal ring switch may encounter issues related to fabrication error, non-accurate wavelength response, and large terminal numbers in the control circuit. In this research, we propose the employment of an integrated CMOS control circuit to compensate the fabrication error and tune as well as lock the wavelength in a thermal-actuated ring-type optical switch through a frequency modulation scheme. Additional functionalities can also be added in this circuit by tailoring externally the roundtrip loss or coupling constants of the ring. The design concept can be easily scaled up for large array optical switch system without much change in the terminal numbers thanks to the three-dimensional hierarchy of control circuit design, which effectively reduces the terminal numbers into the cubic root of the total control unit numbers. The integrated circuit has been designed, simulated, as well as fabricated, and demonstrated a decent performance with free spectral range (FSR) equal to 1.5 nm at 1534 nm and very accurate wavelength modulation to 0.3 nm within 0.01 nm fluctuation for thermal actuated ring type optical switch.

Proposed form for the atmospheric turbulence spatial spectrum at large scales

The performance of large optical systems can be strongly influenced by the behavior of large-scale atmospheric turbulence. Previous optical phase difference data diverged from theoretical predictions based on von Kármán's model. To establish a better model microthermal data over large spatial scales were collected at two sites with few terrain inhomogeneities, in unstable midday conditions. Spatial structure function and spectra are developed. A model spatial spectrum is fit to the data with parameters to set two power law dependencies and the transition rate between them. By working with spatial spectral data the assumption of frozen flow is avoided. The optimum spatial spectrum is Kolmogorov-like in the inertial range. Temporal spectral data compare favorably with the new model, which better describes the transition of turbulence scaling from small scales to large.

Differential schlieren-interferometry with a simple adjustable Wollaston-like prism

An adjustable Wollaston-like prism is characterized for use in shearing- and differential schlieren-interferometry with laser and white-light illumination. We demonstrate that a polycarbonate prism under mechanical loading behaves identically to Wollaston's classical birefringent beam splitter. A linear relationship is found between the pure bending moment applied to the polycarbonate prism and the resulting light-beam-divergence angle. The utility of this prism in shearing-interferometry is shown by using it in place of the knife-edge in small and large schlieren optical systems. It is inexpensive to fabricate, and it yields adjustable beam-divergence angles over a range of at least 0-24 arc min.

Fiber Pigtailed Multimode Laser Module Based on Passive Device Alignment on an LTCC Substrate

A concept that utilizes structured planar substrates based on low-temperature cofired ceramics (LTCC) as a precision platform for a miniature passive alignment multimode laser module is demonstrated. The three-dimensional shape of the laminated and fired ceramic substrate provides the necessary alignment structures including holes, grooves, and cavities for the laser-to-fiber coupling. The achieved passive alignment accuracy allows high coupling efficiency realizations of multimode fiber pigtailed laser modules. Thick-film printing and via punching can be incorporated in order to integrate electronic assemblies directly on the optomechanical platform. The platform is scalable, and it allows embedding of subsystems, such as silicon optical bench (SiOB), but it also provides the interface for larger optical systems. Temperature management of high-power laser diodes is achieved by realizing heat dissipation structures and a cooling channel into the LTCC substrate. The measured maximum laser metallization temperature was 70degC when a thermal power of 0.5 W was applied at the laser active area using a liquid cooling of 50 mL/min. The measured maximum temperature of the laser surface was about three times higher without liquid cooling. Optical coupling efficiency of the multimode laser systems was simulated using optical systems simulation software. The nominal coupling efficiency between 100times1 mum stripe laser and 62.5/125-mum graded index fiber (NA=0.275) was 0.37. The simulated coupling efficiency and alignment tolerances were verified by prototype realization and characterization. The measured alignment tolerance values between laser and fiber in AT prototype series were Deltax=7.7 mum, Deltay=7.6 mum, and Deltaz=10.8 mum (SD values). The corresponding values in A2 prototype series were Deltax=3.1 mum, Deltay=9.1 mum, and Deltaz=10.2 mum. The measured average coupling efficiency was 0.28 in AT series and 0.31 in A2 series. The coupling efficiencies of all operational prototypes varied from 0.05 to 0.43

Theory of Nonlinear Dispersive Waves and Selection of the Ground State

A theory of time-dependent nonlinear dispersive equations of the Schrödinger or Gross-Pitaevskii and Hartree type is developed. The short, intermediate and large time behavior is found, by deriving nonlinear master equations (NLME), governing the evolution of the mode powers, and by a novel multitime scale analysis of these equations. The scattering theory is developed and coherent resonance phenomena and associated lifetimes are derived. Applications include Bose-Einstein condensate large time dynamics and nonlinear optical systems. The theory reveals a nonlinear transition phenomenon, "selection of the ground state," and NLME predicts the decay of excited state, with half its energy transferred to the ground state and half to radiation modes. Our results predict the recent experimental observations of Mandelik et al. in nonlinear optical waveguides.