Surface-Emitting Active Photonic Lattices for Watt-Range Coherent Power

研究和使用了具有调制光增益的周期性介质结构，即有源光子晶格(APL)，以实现具有新颖设计的二阶光栅的二维水平腔器件的瓦级相干表面发射功率。与传统的APL形成鲜明对比的是，所提出的器件在低折射率晶格位置具有增益。通过低折射率晶格点之间的共振漏波耦合，行波的长程(相干)耦合成为可能。所提出的二维APL将反导锁相阵与二阶DFB/DBR光栅结构的表面发射相结合。与以前报道的所有二阶光栅DFB表面发射器不同，所提出的结构采用了约pi的中心光栅相移，从而在不影响器件效率的情况下确保了正交化的单瓣光束的发射。此外，除了确保单纵模工作外，该光栅结构还将作为单横向模式的高效选择器：同相阵列模式。因此，大口径(200 mm×1200 mm)相干源具有几乎均匀的二维导光场分布，将能够在稳定的单光束衍射限制下输出功率为瓦的连续波。首先，将建立一个Bloch函数模型来分析所提出的二维APL型器件。然后，将该模型应用于器件设计优化，通过金属-有机化学气相沉积制备器件结构，然后通过全息干涉测量和湿法化学刻蚀制作光栅。为了产生必要的光栅p相移，将使用双色调光致抗蚀剂。为了形成(横向)锁相阵列，将在顶面刻蚀窄的周期性沟槽，然后重新生长高折射率材料(GaAs)，以提供反导引阵列。在器件p侧沉积必要的金属化后，将在器件n侧金属化中创建条形窗口，以允许一阶衍射光在垂直于激光芯片表面的方向上发射。将在20元阵列上进行初步工作，以验证通过二阶衍射光栅进行横向阵列模式选择的概念，并证实由于仅在反导阵列芯中存在光栅，光束亮度得到了增强。然后将开发40个元素的阵列。为了有效地选择横向模式，将使用纵向锥形DBR反射器。为了分析这种模式间的区别，将采用光束传播法。器件将被制造(通过使用标准光刻和DBR-光栅(反射器)区域的湿化学刻蚀)。

What is proposed is the study and use of periodic dielectric structures with modulated optical gain, so called active photonic lattices (APLs), for the realization of watt-range coherent, surface-emitted powers from two-dimensional (2-D) horizontal-cavity devices with 2nd-order gratings of novel design. In sharp contrast to conventional APLs, the proposed devices have gain in the low-index lattice sites. In turn, long range (coherent) coupling via traveling waves will become possible via resonant leaky-wave coupling between the low-index lattice sites.The proposed 2-D APLs combine antiguided phase-locked arrays with surface emission from 2nd-order DFB/DBR grating structures. Unlike all previously reported 2nd-order grating DFB surface emitters, the proposed structures employ central grating phase shifts of around pi, which insure emission in an orthonormal, single-lobe beam at no penalty in device efficiency. In addition, the grating structure, besides insuring single-longitudinal-mode operation, will act as a highly effective selector of a single lateral mode: the in-phase array mode. As a consequence large-aperture (200mm x 1200mm) coherent sources of nearly uniform 2-D guided-field profiles will be capable to operate in a stable, single diffraction-limited beam to watt-range CW output powers.First, a Bloch-function model will be developed for analyzing the proposed 2-D APL-type device. Then, upon applying the model for device-design optimization, the device structure will be fabricated by metal-organic chemical vapor deposition, followed by grating fabrication via holographic interferometry and wet chemical etching. To create the necessary grating p phase shift, a dual-tone photoresist will be used. To create the phase-locked array (in the lateral direction), narrow periodic trenches will be etched into the top surface, and then high-index material (GaAs) will be regrown as to provide an antiguided array. After depositing the necessary metallization on the device p-side, a stripe window will be created in the device n-side metallization, to allow 1st-order diffracted light to be emitted in a direction normal to the laser-chip surface.Initial work will be done on 20-element arrays to prove the concept of lateral-array-mode selection via the 2nd-order diffraction grating as well as to confirm enhancement in beam brightness due to the grating existence only in the antiguided-array cores. 40-element arrays will then be developed. For effective lateral-mode selection, longitudinally tapered DBR reflectors will be used. For analysis of such intermodal discrimination the beam-propagation method will be employed. Devices will be fabricated (by using standard photolithrography and wet chemical etching in the DBR-grating (reflector) regions).