High-power antiguided laser array fabricated without the need forovergrowth

The fabrication of conventional semiconductor antiguided laser array structures involves etching of the array profile followed by an overgrowth step. In this letter, we report the fabrication of an antiguided laser array using zinc diffusion induced intermixing of a superlattice to create the necessary index step. The technique was used to fabricate a five-element, 10-μm center, antiguided laser array operating at 0.860 μm. The device operated at 1.2× diffraction limit to 3-W pulsed (total, both facets) and 1.6-W quasi-continuous-wave (CW) (100-μs pulses; total, both facets)     

Proposal of a GaInAs/GaInAsP/InP antiguided filter laser arrayoperating in single longitudinal mode

The authors propose a type of in-phase lateral- and single-longitudinal-mode laser array, the so-called antiguided filter laser array (AFLA), in which an antiguided filter region is inserted between a positive-index-guided multiple-strip array region with a shallow corrugation grating and a high-reflectivity region with deep corrugation. Threshold current as low as 100 mA was obtained for a five-element laser array with active region length of 300 μm and total emitter width of 18 μm, using five-pairs of Ga_0.3In _0.7As (3 nm)/GaInAsP (10 nm) compressively strained quantum wells     

Modal properties of two-dimensional antiguided vertical-cavitysurface-emitting laser arrays

We present a detailed analysis on 2-D (4 × 4 square-lattice) antiguided vertical-cavity surface-emitting laser (VCSEL) arrays based on the effective-index model. The calculation shows that the array can operate under 2-D resonant coupling, provided that the resonance condition in both the horizontal and vertical directions is satisfied. Consequently, the resonant-mode edge radiation loss is inversely proportional to the number of array elements along one direction for a N × N array. Low-edge-loss out-of-phase and adjacent array modes are found to compete with the in-phase resonant mode. While the 3-D gain overlap is not a significant factor in modal discrimination, the introduction of inter-element loss allows the in-phase mode to exhibit the lowest threshold gain for a wide range of inter-element width, s (Δ₈ ≈ 0.5 μm for 980-nm wavelength devices). The 2-D antiguided array results from shifting the cavity resonance between the element and inter-element regions and is fabricated by selective chemical etching and two-step metalorganic chemical vapor deposition growth. Diffraction-limited in-phase and out-of-phase array mode operation is observed from top-emitting arrays, depending on the inter-element width. Substrate-emitting array structures are investigated as a means to lower heating and increase the coherent output power     

Antiguided laser array structure at 1.48 μm fabricated withoutovergrowth

The authors describe the fabrication of five-element antiguided laser arrays at 1.48 μm using a novel material design which removes the need for overgrowth. Adding undoped passive waveguiding layers to the standard laser design significantly alters the shape of the far field emission from the lasers, showing that the array elements are pulled in phase with each other     

Microstructured optical fibre with 16 linearly arrayed antiguided cores fabricated through stacking

A microstructured optical fibre with a linear-array of 16 antiguided cores was fabricated using the stacking technique. Coherent near-field guidance was observed in a 20 cm-long straight fibre. Proposals are made for achieving high-power laser output in this new type of antiguided multicore fibre on the basis of sensitivity to bending.     

10W near-diffraction-limited peak pulsed power from Al-free, 0.98μm-emitting phase-locked antiguided arrays

10 W peak-pulsed power emitted in a beam pattern 2×diffraction limit (DL) is obtained from a 40-element, 200 μm-aperture Al-free phase-locked antiguided array (λ=0.98 μm). 60% of the power resides in the central lobe, and the external differential quantum efficiency is 54%, for 1 mm-long optimised facet-coated devices     

Phase-locked antiguided multiple-core ribbon fiber

We report on the first experimental demonstration of a scalable fiber laser approach based on phase-locking multiple gain cores in an antiguided structure. A novel fabrication technology is used with soft glass components to construct the multiple core fiber used in our experiments. The waveguide region is rectangular in shape and comprised of a periodic sequence of gain and no-gain segments having nearly uniform refractive index. The rectangular waveguide is itself embedded in a lower refractive index cladding region. Experimental results confirm that our five-core Nd-doped glass prototype structure runs predominately in two spatial antiguided modes as predicted by our modeling.     

Distributed-feedback grating used as a lateral-mode selector in phase-locked antiguided arrays

We show here, for the first time, that a distributed-feedback (DFB) grating can act as a lateral-mode discriminator if located below the active region of a phase-locked antiguided array. Spatial-mode selection from such a lower-DFB (LDFB) grating in a resonant antiguided structure (ROW-LDFB) relies on the fact that the optical field distribution below the active region is strongly array-mode dependent. In particular, it is shown that at and near resonance a ROW-LDFB structure strongly favors resonant-mode oscillation, while suppressing oscillation of high-order modes. ROW-LDFB devices thus accomplish both spatial- and frequency-mode selection in a single structure. Furthermore, for effective intermodal discrimination, there is no need for interelement loss or Talbot-type filters, thus eliminating all potential sources of self-pulsations.     

11.5 W pulsed operation of antiguided laser diode array

A 40-stripe array of antiguided laser diodes is operated to a pulsed output power of 11.5 W. At the output power of 11.5 W, the full width at half maximum of the central lobe of the in-phase far fields is 1 degrees .<>     

"Anti" up the aperture [antiguided VCSEL structures]

Coupled vertical cavity surface-emitting laser (VCSEL) arrays are an attractive means to increase the coherent output power of VCSELs. Single-mode VCSELs, with output powers greater than 10 mW, would be useful as telecommunication transmitters /spl lambda/=1.3-1.55 /spl mu/m) or sources for optical interconnects. Commercially available single-mode VCSELs, even at shorter wavelengths /spl lambda/=0.85 /spl mu/m), are generally limited to a few milliwatts of output power. The conventional VCSEL structure incorporates a built-in positive-index waveguide, designed to support a single fundamental mode. Promising results in the 3-5 mW range (/spl lambda/=0.85 /spl mu/m) have been obtained from wet-oxidized, positive-index-guided VCSELs with small emission apertures (less than 3.5 /spl mu/m-dia). The small aperture size leads to a high electrical resistance and high current density, which can impact device reliability. By contrast, antiguided VCSEL structures have shown promise for achieving larger aperture single-mode operation. To obtain high single-mode powers with a larger emitting aperture, the use of a negative-index guide (antiguide) is beneficial. This paper discusses antiguided structures and some of their advantages when incorporated in 2-D VCSEL array structures.     

Modal discrimination in leaky-mode (antiguided) arrays [diodelasers]

Presents on the fabrication of a ten-element antiguided (leaky-mode) diode laser array that operates in an in-phase mode with a diffraction-limited far-field pattern at drive currents up to 8.7 times the threshold current (pulsed) and an output power of 400 mW (both facets). This device evidences good discrimination against the out-of-phase leaky mode without the benefit of a `Talbot' spatial filter, relying instead on mode-sensitive interelement losses in an overlying GaAs layer. This device has been studied using two numerical models. Results from the more realistic of the two models predict in-phase-mode operation for certain restricted ranges of waveguide dielectric constant, in agreement with experiment. This behavior is shown to result from resonances between the waveguide modes and the modes of the active region. These results suggest that improved yields would result from a different type of leaky-mode array employing smaller, rectangularly shaped waveguides     

增益导引折射率反导引大模场光纤激光器特性分析

为了研究增益导引折射率反导引光纤激光器的功率分布及输出特性,根据此类光纤的结构原理和特点,建立了端面抽运的增益导引折射率反导引光纤激光器的基模光速率方程,推导了避免激发高阶模的增益阈值判决条件,并运用弦切法和Runge-Kutta法数值求解了该速率方程,分析了光纤长度、腔镜反射率等参量对基模输出功率的影响.采用芯径为1...     

Distributed-feedback grating used as an array-mode selector inresonant antiguided diode laser arrays: effects of the mirror facetposition with respect to the grating

In resonant and nearly resonant antiguided arrays (ROW arrays), if the grating is located below the active region, a distributed-feedback (DFB) grating can function as a selector for the in-phase array mode in addition to its role as a frequency discriminator. Threshold current densities are calculated for competing (lateral) spatial modes in AR/HR coated 10- and 20-element arrays incorporating lower gratings (ROW-LDFB arrays). Calculations include the effects of random facet locations relative to the grating phase. The threshold current density, J_th , of the in-phase mode and its discrimination, ΔJ_th , against other (array) spatial modes vary with facet location. For 20 (10) elements, J_th≈350-525 (400-550) A/cm² and ΔJ_th reaches a maximum of 55 (58) A/cm² for 0.01/0.95 AR/HR-coated 350 μm-long devices. For 10-element arrays, the probability of in-phase operation is approximately 50%; for 20-element arrays, the probability is 100%. Preliminary experimental results from 20-element nonresonant devices with uncoated facets are near diffraction-limited beams and nearly single-frequency operation to 250 mW     

Cavity-induced antiguiding in a selectively oxidizedvertical-cavity surface-emitting laser

Cavity-induced antiguiding of a lasing mode is demonstrated in a vertical-cavity surface-emitting laser (VCSEL). Selective oxidation of a distributed Bragg reflector (DBR) layer is used to generate a spectrally red-shifted cavity region cladding the lasing mode, with a second selectively oxidized aperture used to form the current confinement to the antiguided mode. Near-field, far-field, and spectral measurements are used to characterize lasing in both the antiguided mode and the antiguiding region     

Hybrid Integration Between Long Focus Microlens Array and IR Detector Array

A special method, named step simulation method, is proposed for fabricating Si microlens array to improve the performance of infrared focal plane array (IR FPA). The focus length of rectangle-based multistep microlens array with element dimension of 40 µm×30 µm is 885.4 µm by the method, which is much longer than the focus length of microlens array fabricated by conventional Fresnel binary optics technique., The large-scale 256×256 element microlens array is hybridintegrated with the PtSi Schottky-barrier IR FPA by optical adhesive. The test results show that diffractive spot size of the microlens is 17 µm×15 µm and the average optical response of the IR FPA is increased by a factor of 2.4.     

Imaging Polarimeter Arrays for Near-Millimeter Waves

An integrated-circuit antenna array has been developed that images both polarization and intensity. The array consists of a row of antennas that lean alternately left and right, creating two interlaced sub-arrays that respond to different polarizations. The arrays and the bismuth bolometer detectors are made by a photoresist shadowing technique that requires only one photolithographic mask. The array has measured polarization at a wavelength of 800 µm with an absolute accuracy of 0.8° and a relative precision of 7 arc min. and has demonstrated nearly diffraction-Iimited resolutiort of a 20° step in polarization.     

Distributed-index planar microlens array prepared from deep electromigration

Monolithic fabrication of a new distributed index planar microlens array by means of a deep electromigration technique in a glass substrate is reported. The array consists of distributed index lenses of 1.2 mm in diameter with 6.8 mm focal length. The focused spot is as small as 16 ?m for ?=0.63 ?m. The coupling efficiency of 60% to a multimode VAD fibre has been obtained.     

Direction of Arrival Estimation using EM-ESPRIT with Nonuniform Arrays

This paper deals with the problem of the Direction Of Arrival (DOA) estimation with nonuniform linear arrays. The proposed method is based on the Expectation Maximization method where ESPRIT is used in the maximization step. The key idea is to iteratively interpolate the data to a virtual uniform linear array in order to apply ESPRIT to estimate the DOA. The iterative approach allows one to improve the interpolation using the previously estimated DOA. One of this method’s novelties lies in its capacity of dealing with any nonuniform array geometry. This technique manifests significant performance and computational advantages over previous algorithms such as Spectral MUSIC, EM-IQML and the method based on manifold separation technique. EM-ESPRIT is shown to be more robust to additive noise. Furthermore, EM-ESPRIT fully exploits the advantages of using a nonuniform array over a uniform array: simulations show that for the same aperture and with a smaller number of sensors, the nonuniform array presents almost identical performance as the equivalent uniform array.     

Constrained optimisation technique for general array patternsynthesis

A new technique for controlling the sidelobe level for general array pattern synthesis is presented. The basic idea is to introduce a weighting function to the performance index based on the integral of the power response over the sidelobe regions. This function more heavily weights the array power response further away from the mainlobe, so that in the minimisation of the integral of the weighted power response over the sidelobe regions, very low sidelobes can be achieved. The resulting beam pattern is highly directional. Numerical results show that the proposed technique is very effective for general array geometry sidelobe control design     

Leaky-guided channeled substrate planar (LCSP) laser with reducedsubstrate radiation and heating

A semiconductor laser design, the leaky-guided channeled substrate planar (LCSP) structure, is presented. The structure with a buffer layer in the region outside the channel provides a built-in negative effective index step. The transverse mode is well damped in the buffer layer, and the substrate radiation in the region outside the channel is virtually eliminated. As a result, the significant heating and facet degradation in the region outside the channel that is related to the substrate radiation in conventional CSP lasers is minimized. The calculated local temperature rise in the region outside the channel of the CSP laser is about 45°C for an output power level of 100 mW and is in reasonably good agreement with previously experimental results. Analysis using the complex domain effective index method shows that the LCSP structure provides better lateral mode discrimination than either gain-guided or positive index step structures. The LCSP structure with reduced heating and strong lateral coupling effect may be useful for high-power linear array lasers