Microlens fabrication on single-mode fibres for efficient coupling from laser diodes

An analysis of the etching process for forming a truncated conical microlens on the end surface of a single-mode fibre (SMF) so as to improve its coupling efficiency with a laser diode (LD) has been carried out. This is followed by a simple geometric-optics and electromagnetic analysis to calculate this coupling efficiency, when the lens is formed on a SMF fabricated by the MCVD technique. The theory is supported by measurements which gave a maximum coupling efficiency of 57%.     

Efficiency and optical feedback of traveling-wave semiconductor laser amplifier to single-mode fiber coupling: Theory and experiment

This paper analyzes the coupling efficiency and optical feedback of the tapered fiber end with a high-index hemiellipsoidal microlens. Such a device has been used as a coupler of traveling-wave semiconductor laser amplifier (TW-SLA) to single mode fiber (SMF).

A theory of the calculation of coupling efficiency and optical feedback is presented including the effects of spherical aberration and Fresnel reflection of thick lens. In consideration of the large beam divergency of the TW-SLA chip, the finite transmission aperture is introduced.

The calculations are in agreement with experiment results and a group of optimum structure parameters of the coupler are given.     

Design, Fabrication, and Integration Technology of Large-Scale Microlens Array for Infrared Charge Coupled Device Application

Infrared charge coupled device (IRCCD) integration with microlens array is an effective method for improving the detecting sensitivity of IRCCD sensors. In this paper, we present the diffractive microlens array (MLA), which is manufactured by the submicron photolithography technology and magnetically enhanced reactive ion etching (MERIE) on infrared quartz substrate. The integration procedure between microlens array and PtSi Schottky-barrier IRCCD chip is introduced in detail. The optical response of IRCCD sensor with microlens array is tested and the average response increases 0.23 in the spectral range of 1.25.0 m. The measuring results show that the large-scale diffractive microlens array is able to improve the detecting sensitivity of IRCCD and that the integration technology mentioned is available.     

Sample-inverted reflow technique for fabrication of a revolved-hyperboloid microlens array in hybrid solgel glass

We propose a novel fabrication method, which is referred to as the sample-inverted reflow technique, to fabricate a refractive microlens array (MLA) with a revolved-hyperboloid profile in a solgel material. The fabricated solgel MLA demonstrates an excellent smooth profile with a fabrication error much less than the difference between the revolved hyperboloid and the spherical surface. In an application of coupling a laser diode (LD) to a single-mode fiber (SMF), we propose a two-MLA coupling scheme in which two revolved-hyperboloid MLAs are used between the LD and the SMF. In this configuration the coupling efficiency achieves 81.7% (-0.88 dB).     

1.3-μm InGaAsP planar buried heterostructure laser diodes with AlInAs electron stopper layer

This study reports on the realization of 1.3-μm InGaAsP buried-heterostructure (BH) laser diodes (LDs) via an Fe-doped semi-insulating InP layer and an AlInAs electron stopper layer (ESL). Experimentally, the as-cleaved BH LD with an AlInAs ESL exhibited improved characteristics in terms of threshold current, slope efficiency, and maximum light output power at 90 °C as compared to those of the normal BH LD without an AlInAs ESL. In addition, high internal quantum efficiency or reduced threshold current density was observed, indicating increased modal gain in BH LDs fabricated with an AlInAs epilayer on top of the active region. It was also found that the temperature sensitivity of the BH LDs with an AlInAs ESL is more stable than that of the normal BH LDs. These results could be attributed to the suppression of thermal carrier leakage out of strain-compensated multiple-quantum-well by a large conduction-band offset of the AlInAs/InGaAsP heterojunction. Otherwise, without consideration of damping factor or coupling loss, the 3-dB bandwidth of the proposed BH LDs reaches a high value of 15.3 GHz. Finally, this TO-can packaged BH LD shows an eye-opening feature with the extinction ratio of 7.49 dB while operating at 10 Gbit/s at 50 mA.     

Employing mutually injection-locked FP LDs scheme over full-duplex radio-on-fiber transport systems

A full-duplex radio-on-fiber (ROF) transport system based on mutually injection-locked Fabry-Perot laser diodes (FP LDs) as light source is proposed and demonstrated. Transmission performances over a 40-km standard single-mode fiber (SMF) for full-duplex transmission were investigated. Good performance of bit error rate (BER) was achieved in our proposed systems. We directly modulate the FP LDs in mutually injection-locked scheme instead of using expensive external modulator and sophisticated optical carrier suppression technique; it reveals an outstanding alternative with advantages in simplicity and cost.     

Direct gauging of the poincaré group. III. Interactions with internal symmetries

The problem of gauging matter fields with a Poincaré invariant action functional that admits anr parameter, semisimple groupG(r) of internal symmetries is considered. A minimal replacement operator for the total groupP ₁₀×G(r) is obtained, together with the requisite compensating 1-forms for both the Poincaré and theG(r) sectors. A basis forP ₁₀×G(r)-invariant Lagrangian densities for the free fields is obtained. Restriction to Lagrangian densities that are at most quadratic in the associated curvature and torsion fields eliminates active coupling between theP ₁₀ free field Lagrangian and theG(r) free field Lagrangian, although there is passive coupling that arises through the requirement of tensorial covariance under general coordinate transformations generated by the local action of the translation group. A superposition principle, modulo passive coupling, thus holds for quadratic free field Lagrangian for the total group:L _TOT=L _P +L _G(r) . Field equations for the matter fields and the compensating fields of theG(r) sector are obtained. Both share the passive coupling toP ₁₀ that is required in order to achieve tensorial covariance, but only the matter fields couple directly to the Poincaré fields and only to the Lorentz sector. For weak Poincaré fields, the field equations for the matter fields and the compensating fields of the internal symmetries go over into the standard field equations of gauge theory for an internal symmetry group.     

The Optical Design of Relay Optics for Heterodyne Millimeter Wave Focal Plane Arrays

Since the use of focal plane arrays on millimeter and sub-millimeter telescopes has become more and more important during the last years, it has also become evident the need of optimized auxiliary optics that would efficiently couple the telescope to the receiver over large fields of view (i.e., 5-10 beams). In this work we systematically analyze several relay optics configurations for heterodyne focal plane arrays, all based on the Gaussian beam telescope concept. Because in examining the image performance of auxiliary optics design at millimeter wavelengths one cannot follow the usual image quality criteria, we analyze the designs using both the Strehl ratio and the coupling efficiency to evaluate the quality of the off-axis wave-fronts and the loss in the power coupling with the horn. Coupling efficiency and Strehl ratio cannot be included in the optimization procedures of commercial optical modelling packages and we thus describe how to optimize the design using a customized algorithm. We show that the minimization of the appropriate error function can reduce the anamorphism of the exit pupil and reduce the loss in the horn coupling.     

CW diode pumping and FM mode locking of a Nd: KGW laser

We have demonstrated cw diode end pumping of Nd: KGW, a novel solid-state gain medium, with up to 30% conversion efficiency into near-TEM₀₀ (M² < 1.05) output at = 1.067 µm for a pump level of 2.7 W. The slope efficiency was limited by intracavity reflections to 36%; however, direct comparison to a similar Nd:YAG laser indicates the same intrinsic slope efficiency of 60%. FM mode locking of this laser at 200 MHz has produced 12 ps pulses (compared to 16 ps for Nd: YAG), although an intracavity etalon was required. Considerable reduction in pulse width is possible (the line width limit is 0.5 ps) but different techniques may be necessary. Spatial hole burning was evident in both the 120 GHz free-running spectrum and the etalon-limited mode-locked spectrum.     

A microwave μSR spectrometer

A microwave-SR (WSR) spectrometer has been developed which operates in the frequency region of 1–2 GHz. The spectrometer geometry is that of longitudinal field (LF)SR and is typically used in time integral measurements. The high frequency of this instrument distinguishes it from the currently used RFSR spectrometers and allows high field measurements to be made for normal Mu type systems. This allows one to avoid low field broadening mechanisms that may be present, either from electronic spin-lattice relaxation or nuclear hyperfine interactions.Technical details of the tunable microwave cavity and the RF coupling scheme are presented. Experimental spectra of Mu lines in SiO₂ and GaAs are displayed.     

Semiconductor laser diode to single-mode fiber coupling using diffractive optical elements

An integrated mode converter consisting of two diffractive optical elements (DOEs) and a Silicon slab is presented for low-loss coupling between a semiconductor laser diode (LD) and a single-mode fiber (SMF). The phase structures of the DOEs are designed using iterative phase retrieval algorithm. We introduce a new far-field amplitude constraint into the iteration to provide very high mode conversion quality. Compared with previously published mode converters, the scheme is more universal because it’s applicable for any semiconductor LD. In simulation, coupling losses lower than 0.02 dB are predicted 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 0.9 μm. And the coupling loss is insensitive to tilt angle.     

TheN-body problem with spin-orbit or Coulomb interactions

A study is made of the resolventR() for a system ofn particles with spin-orbit coupling, an interaction which necessarily has a long range in momentum space. For short-range interactions, it has been known for several years thatR() satisfies a Fredholm equation whose kernel is in the Schmidt-class. The corresponding spin-orbit kernel is not in the Schmidt-class, but it is shown that it does belong to a certain class of compact operators which is larger than the Schmidt-class. A modified Fredholm theory is presented which applies to all operators in this larger class. This enablesR() to be found for all values of in the complex plane cut along the continuous spectrum of the Hamiltonian. It is shown that the modified Fredholm theory also holds for the Coulomb interaction.     

Magnetic Properties of Permalloy/Cu-Au Multilayers

The interlayer exchange coupling and GMR effect of (permalloy/Cu _x Au_1-x )30 (Py = Ni₈₃Fe₁₇; 0.29x0.75) sputtered multilayers (MLs) were investigated. The strength of the antiferromagnetic (AF) interlayer coupling J _AF was determined from M(H) and/or R(H) curves. GMR effect and AF coupling was found in entire investigated concentration range of Cu _x Au_1-x . For x<0.65 the J _AF values at the first maximum of AF coupling (1.3t _Cu-Au1.6 nm) were smaller than 3×10^-6 J/m² and for x>0.65 J _AF increased to a value characteristic of Py/Cu MLs (J _AF10^-5 J/m²). The second maximum of AF coupling (J _AF10^-7 J/m²) was only found for x0.75 at t _Cu-Au2.6 nm.     

Modeling,design, growth and characterization of red wavelength range microcavity emitters for plastic optic fiber applications

Resonant cavity light emitting diodes (RC-LEDs) and vertical cavity surface emitting lasers (VCSELs) for the red wavelength range are presented in the paper. A wide variety of simulation tools were employed in the device design and optimization and the good agreement between simulations and measurements enabled effective device development. Our red wavelength range RC-LEDs were mainly intended for short-haul communication systems based on polymethyl methacrylate plastic optical fiber and were optimized accordingly. They are achieving, under different structure and working regime variants, high output power (15 mW), high external efficiency (9.5%), record small-signal modulation bandwidth (f _-3dB up to 350 MHz), error-free back-to-back transmission rates beyond 622 Mbits/s, adjustable far-field pattern and good POF coupling efficiency with reasonably wide tolerances and without using auxiliary optics. In view of the possible use of graded-index POFs, free-space transmission and other high bandwidth or high spectral purity applications, VCSELs in the red wavelength range were also realized. They have achieved sub-milliamp room-temperature (RT) continuous-wave (CW) lasing for an 8 m diameter emission window and exhibited an external quantum efficiency of 6.65% for 10 m devices in RT CW operation. The VCSEL structures were far from optimal – not even incorporating all the RC-LED structure refinements – and significant improvement in performance characteristics are predicted for the optimized layer structure.     

基于ABCD矩阵的楔形柱面光纤微透镜的耦合技术分析

运用激光模式耦合理论分析了半导体激光器与楔形柱面光纤微透镜的连接损耗,设计并制作了楔形柱面光纤微透镜用来实现两者的模斑匹配。运用ABCD矩阵方法,对该组件的耦合效率进行了仿真计算和分析,得到了高耦合效率下楔形柱面光纤微透镜的结构参数。该方法可有效地用于楔形柱面光纤微透镜的优化设计。     

The temperature dependence of the methyl rotational potential in methyl iodide under pressure

Inelastic neutron scattering experiments have been performed on CH₃I under pressure. The tunnel splitting of the methyl librational groundstate decreases almost exponentially with increasing hydrostatic pressure: _t (p)=2.48 eV·exp (–0.138·p[kbar]), the librational energy increases asE ₀₁ (p)=13.2 meV (1+0.050p[kbar]). Both relations can be explained by a rotational potentialV which depends on the interatomic distancer asVr ^–9.6 . This large exponent shows the importance of valence forces. The shape of the rotational potential is almost unaffected by pressure. The coupling of the methyl group to phonons via a shaking and a breathing term which was observed at atmospheric pressure is also found at high pressure. The effect appears at higher temperature as expected for the stronger potential.     

Competing models for the relaxation of tunneling and paramagnetic defects

The phonon-assisted tunneling problem (which to a large degree is isomorphic to the phonon-assisted paramagnetic relaxation problem) is handled by means of unitary exponential transformations.In view of the hierarchical possibilities for the 3 Hamiltonian constituents (phonons, bare tunneling, coupling) there are 4 fundamental exponential transformations. These are discussed. Further, an exactly solvable model is studied. Finally, the underlying Fano problem is investigated by means of an exactly solvable model. It is found that a) the reduction of the tunneling frequency is modified by those lattice modes which lie below the bare tunneling splitting (there even may be an increase of); b) there may be more than a single relaxation path; c) there may be a relaxation process which approximately does not depend on at all; in this mechanism the tunneling behaviour is transferred to the phonon system.     

Designing a coupler for the intersatellite optical communication system

Coupling a single-mode laser diode with 200 mW to a single-mode fiber (SMF) through an orthonormal aspherical cylindrical lens and a GRIN lens for the intersatellite optical communication system is proposed and demonstrated. We experimentally studied how the coupling efficiency changes with the SMF's position displacement and axial angle variation, and obtained 80 mW output power at the end of the SMF, which shows that the coupling units have satisfied the designed request.     

A stationary apparent weight shift from a transient Machian mass fluctuation

A transient mass fluctuation, predicted by Lorentz-invariant theories of gravitation wherein inertia is gravitationally induced, can be combined with a synchronous thrust to produce a stationary change in the apparent weight of an object. A substantial effect of this sort—on the order of tenths of a gram or more—should be achievable in laboratory scale apparatus. A detailed derivation of the predicted transient mass fluctuation is given in an appendix.1. This does not mean, however, that it is impossible to directly detect the expected weight fluctuations at higher than low audio frequencies. In fact, in preliminary work toward the experiment described below, L. Shen, K. Wanser, and I have detected evidence of the effect at ultrasonic frequencies employing very unusual capacitors (high energy density ceramic multiplate chip capacitors with strongly suppressed first- and second-order electromechanical effects) mounted on an aluminum pedestal which acts as the spring in the system. The minute displacements produced are detected with a laser interferometer. This work will be described fully in a separate paper.2. Such a transformer can be made with, for example, an Amidon T 300A-26 powdered iron torus. Powdered iron is preferable to ferrite because of its superior flux saturation and energy loss characteristics at the frequencies in question.3. Einstein[7] was the first to point out (in 1912) that the simplest formalism for the gravitational field that incorporates Machian gravitational induction of inertia is that based on the analogy with the electromagnetic field, that is, a Lorentz-invariant four-vector potential theory. Many years later, Sciama[5] showed explicitly how such a theory could account for well-known inertial reaction effects, provided that the mean matter density of the universe were the right value (in fact, just cosmologically critical density). Later he showed that a general relativistic tensor formalism yielded the same conclusions[8]. And, as I have pointed out elsewhere[1–3], Nordtvedt's PPN formalism with GRT parameters chosen yields the same result when the effect of cosmic matter is included.4. Contributions from the Hubble flow tov and thusj are ignored here, since upon integration they vanish by symmetry. Hubble flow does, however, make _c a function ofr. 5. The advanced solutions of the wave equation required to account for inertia in the Lorentz gauge can be avoided if one chooses by using the Coulomb gauge with its action-at-a-distance characteristic. Asserting the equivalent of the Coulomb gauge to get instantaneous inertial reaction forces, as Trederet al.[9] point out, suggests an interesting generalization of GRT.6. This procedure for going from a particle to a continuous media representation is not in general valid, since in all frames, except the rest frame, will involve elements of the stress tensor. Those contributions, however, are of orderv ² /c ² and are here ignored.7. One may find this result troublesome, for one may think thatø is only fixed up to an additive constant. While this is true in linear theories, as discussed below, it is not true in nonlinear theories. Let me also point out here the similarity of Eq. (A12) and the field equations obtained by Trederet al.[9, pp. 70-73] in a higher-derivative manifestly Machian Einstein-Cartan theory of gravitation where the same potential-like coupling of gravity and matter occurs.8. Equation (A13) only applies in the instantaneous rest frame of the test particle. In all other frames of reference one obtains a term involving the time derivative of the acceleration. Terms of this sort, of course, are not normally allowed in dynamics. They are the signature of self-forces and radiation reaction effects. But this should come as no surprise, for the effect arises from the gravitational self-energy interaction when inertial reaction forces are stimulated.     

Design and Fabrication of Silcon Microlens with Low SAG for 528(H) × 528(V) Infrared Charge-Coupled Device Application

Microlens array is an important optical element to improve the photosensitivity of charge-coupled device (CCD). In this paper, a monolithic integration technology between microlens and 528 × 528 element PtSi Schottky-barrier infrared charge-coupled device (IRCCD) with a pixel size of 30m × 30m has been developed. The microlens array with low sag and long focal length is designed based on geometrical optics theory. It is directly formed on the back side of the substrate in IRCCD chip using successive photolithography and A⁺ ion beam etching (IBE) technology. The microlens array is characterized by both surface stylus and point spread function (PSF). The experiment results of integration device between IRCCD and microlens array indicate that the optical signal response is improved obviously and a responsivity increase by a factor of 1.8 in the operation band.