An integrated scheme is proposed for low-loss coupling between a semiconductor laser diode (LD) and a single-mode fiber (SMF) by using a diffractive optical element (DOE). The DOE is designed based on diffractive optics principle, which phase distribution is optimization result of iterative phase retrieval algorithm. A new far-field amplitude constraint is introduced into the iteration to provide very high mode conversion quality. The scheme is applicable to realize high efficient coupling to SMF for any semiconductor LD. Coupling losses lower than 0.02dB have been reached for all the discussed LDs with aspect ratios of the elliptical fields from 1 to 9. The requirements on axial displacement and rotation angle have been removed. The tolerance for 1-dB loss increment for lateral misalignment is 0.9μm. And the coupling loss is insensitive to tilt angle.
Very low-loss coupling between standard single-mode fibers (SMF) and high refractive-index waveguides is achieved using diffraction optical element (DOE) as mode converter. The DOE is a beam-shaping element designed based on diffraction optics theory. DOE shapes the mode field of SMF to that of the waveguide, or vice versa. The mode mismatch between them is eliminated. DOE is a pure phase element, which phase distribution optimized by G-S algorithm. The most attractive point of this mode converter is that the DOE can be designed to achieve any mode field distribution of any waveguide structure. This advantage makes DOE a strong and flexible mode converter. Though being a phase element, DOE has certain wavelength tolerance covering a sufficiently wide band, which makes it applicable in multi-wavelength integrated planar lightwave circuits (PLCs). DOE can be approximated by binary optical element (BOE), so that it can be fabricated using existing PLC fabrication step
A new type flat-field arrayed waveguide grating (AWG) has been designed. The focal points of all wavelengths of operation distribute on a straight line. With parallel output waveguides, it¡¯s convenient to connect with fiber-array directly. Flat-field AWG could function as a spectrometer when the output waveguides are thrown off. The work based on the developed aberration theory of AWG. In this theory, the restrains imposing on the conventional Rowland-type AWG have been removed. Various restrains will generate new type structures. In the flat-field AWG design, the restrains come from the concurrent imaging theory. Three aberration-free points restrain three dominant geometry parameters of AWG, geometry of star couplers, phased array ports distribution, and length increment between adjacent paths. A 16-channel flat-field AWG is designed. As stigmatic points introduced, the aberration of the device is much lower than that of the conventional Rowland-type AWG.
The beam propagation method (BPM) is one of the most popular approaches in modeling electromagnetic field propagation. The conventional BPM is established on scalar Helmholtz equation using paraxial approximation. There are limits in the analysis of the vector properties of electromagnetic field and wide-angle propagation. This paper presents the techniques of removing these limits. A full-vectorial BPM bases on finite-difference technique is described from vector wave equations, called finite-difference vectorial beam propagation method (FD-VBPM). The main disadvantage of FD-VBPM is the calculation inefficiency, especially in three dimensional modeling. To obtain two dimensional equivalent structures, a precise optimization approach is adopted. Propagation constant and field of fundamental mode best match those of the original waveguide. The method has very high accuracy. The decoupled
semi-vectorial BPM is also derived. The full-vectorial method is extended to wide-angle BPM removing paraxial limit. The method bases on Pade approximant. Simulations are made on rib waveguide.
Though DVD becomes more and more popular, there are still millions of CD-R disk in using. The ability of reading both DVD and CD-R disk is necessary in compatible disk drive. Traditional optical pickup consists of different bulk components, which result in high cost, high difficulty in assembly and low reliability. Integration is a way to overcome these troubles. Based on planar optics, an integrated digital versatile disk (DVD)/compact disk recordable (CD-R) compatible optical pickup has been developed. In this device, the beams of two wavelengths follow different zigzag optical paths inside a few-mm thick glass substrate, which is used as a light guide. It is demonstrated that a beam combiner, a polarized beam splitter, a Fresnel prism, and a beam separator were integrated around a glass substrate, and such a planar optical pickup exhibited an excellent performance with high efficiency. It confirms that planar optics is an effective way to realize compatibility of DVD/CD-R.
A radial finite-difference beam propagation method is proposed systematically with circular cylindrical coordinates, which is more accurate for simulation of some radiated waveguide structures. Theoretical design and simulation of low insertion loss arrayed waveguide gratings with couplers of tapered arrayed waveguides are presented using this full-vectorial beam propagation method.
A novel Newton recursive algorithm is proposed for an optimum design of arrayed waveguide gratings, which is different from the traditional complicated power-series expansion of the light-path function. The structure of an arrayed waveguide grating is represented by three constraint equations which may be chosen to meet some specific design demands. The new algorithm combines Newton algorithm with structure nonlinear constraint functions, which makes it more general and flexible for the optimum design of the device. From the initial value given, the arrayed-waveguide positions and matched waveguide lengths are determined from the numerical solutions for the roots of three constraint equations through a Newton recursive procedure in sequence. Anastigmatic mounts of arrayed waveguide gratings based on this algorithm are processed, and a three stigmatic-points one is designed. Further applications of this algorithm are also discussed, including the one that can not be designed with the theory of the power-series expansion of light-path function.
Beam-shaping plays a very important role in the field of laser processing. Laser quench needs a rectangular speckle, which has a flat top, steep sides, high efficiency and low sidelobes. Diffractive phase elements (DPEs) have many superexcellent characters, which conventional optical elements have difficulties to achieve. Designing of the phase plane comes down to phase retrieval problem. Geometrical transformation and multiform iterative algorithms, such as G-S algorithm, Input-Output algorithm, ST algorithm are adopted. Through comparison of the results from different methods, some evaluations about algorithms are made. ST algorithm is the most feasible method for the problem, the result of which can meet the requirements of practical process. Some simulation experiments and discussions about algorithms have been done. To be fabricated as a binary optical element (BOE), the result of design has been quantified to 16 steps.
Since micro robot has merits on small size and flexible movements, it could be used under many situations. A lot of novel designs of micro-robot have been developed recently. However, as miniaturizing the size of the micro-robot, the number of its sensor gets restricted. Then the information from the detectors becomes lack. This makes the micro robot difficult to acquire its status. A micro robot tracing a line has been designed in our lab. With the help of optoelectronic detection and logical algorithm, the micro robot could follow a black line printed on the white ground exactly. The micro robot's intelligence is realized through the program in its microprocessor. The technical details of the micro robot are as follows: dimensions: 30mm*25mm*35**; velocity: 60mm/s.
Optoelectric inspection may find applications in robotic system. In micro robotic system, smaller optoelectric inspection system is preferred. However, as miniaturizing the size of the robot, the number of the optoelectric detector becomes lack. And lack of the information makes the micro robot difficult to acquire its status. In our lab, a micro line trace robot has been designed, which autonomous acts based on its optoelectric detection. It has been programmed to follow a black line printed on the white colored ground. Besides the optoelectric inspection, logical algorithm in the microprocessor is also important. In this paper, we propose a simply logical algorithm to realize robot's intelligence. The robot's intelligence is based on a AT89C2051 microcontroller which controls its movement. The technical details of the micro robot are as follow: dimension: 30mm*25mm*35*mm; velocity: 60mm/s.
The basic principle and overall structure of a non-contact steel products dynamic on-line inspection instrument was described in the paper. During production of rolled steel, it performs auto-measurement of diameter and ellipticity of all kinds of wires, rods and steel pipes in red-hot and fast-moving situations, having high speed and high precision. Formulae of ellipticity error for rolled steel were derived and analyzed. The computer real-time data processing and control system were discussed in detail.