Winston S. Fu

Near-infrared high-gain strained layer InGaAs heterojunction phototransistors : resonant periodic absorption

We report high‐gain phototransistors on GaAs substrates at wavelengths for which GaAs substrates are transparent, and hence, are promising for optoelectronic interconnect, optical‐logic device, neural network, and lightwave communication applications. Using a new technique called resonant periodic absorption we have achieved high‐optical gain at previously inaccessible wavelengths (≳925 nm). Resonant periodic absorption is achieved in an asymmetric microresonator consisting of a strained‐layer InGaAs/GaAs heterojunction phototransistor sandwiched between distributed Bragg reflectors. By aligning the optical intensity maxima with the InGaAs quantum wells in the collector region of the phototransistor, we dramatically enhance the optical absorption.

Hybrid integration of bipolar transistors and microlasers: Current‐controlled microlaser smart pixels

We describe the hybrid integration of GaAs/AlGaAs heterojunction bipolar transistors with GaAs/AlGaAs (850 nm operation) and InGaAs/AlGaAs (980 nm operation) vertical‐cavity microlasers to form ultra‐low‐drive‐current microlaser smart pixels. We achieved a single‐mode, low divergence, 1 mW output with a 70 μA base injection current and digital electronics matched input impedance. The integration technology is appropriate for the integration of optoelectronic integrated circuits to GaAs and Si microelectronics circuits.

Micro-optic and microelectronic integrated packaging of vertical-cavity lasers

The applications for optoelectronic integrated circuits demand high performance optoelectronic devices or smart pixels. The stringent requirements on these smart pixels require that packaging technology be developed concurrently to the development of the optoelectronic components. We discuss the packaging requirements of smart pixels based on vertical-cavity microlasers. We present a novel microlens/macrolens combination which allows high power densities to be focused to a diffraction-limited spot using present VCSEL technology. Finally, we discuss the applications for microlaser-based spatial light source arrays.

Commercial manufacturing of vertical-cavity surface-emitting laser arrays

Optoelectronic integrated circuits based on arrays of vertical- cavity surface emitting lasers (VCSELs) are evolving into functional chips enhancing the performance of fiber optic networks, optical data storage, laser printing and scanning, visual displays, and optoelectronic computing and other systems. This evolution involves the development of advanced manufacturing technology germane to packaged arrays of VCSELs comprising micro- optic lens arrays and interface electronics. In this paper we describe Photonics Researchs LASE-ARRAY commercial manufacturing efforts. Specifically we will discuss commercial manufacturing advancements in molecular beam epitaxial growth, full-wafer processing, interface electronics, microoptic lens arrays, packaging and implementation of statistical process control. Yield and reliability will also be discussed. Last we discuss emerging applications for the LASE-ARRAY technology.

Optical gain and ultrafast nonlinear response in GaAs/AlAs type‐II quantum wells

We describe the femtosecond optical gain nonlinearities for the unusual case of electrons which are distributed between the direct‐GaAs and indirect‐AlAs layers in a GaAs/AlAs type‐II multiple quantum‐well (MQW) structure. Due to the spatial separation of electrons from the holes, we observe a significant increase in the gain lifetime (≳150 ps) in type‐II MQWs, as compared to type ‐I MQWs (∼50 ps). In addition, we investigate the effect of a longitudinal electric field on Γ‐X energy splitting in type‐II structures. Finally, at early times we observe an ultrafast nonlinear optical response in the gain/absorption spectra which we attributed to electron‐hole scattering without carrier loss.

Nonlinear optical properties and ultrafast response of GaAs-AlAs type-II quantum wells

Femtosecond and CW optical nonlinearities associated with the spatial separation of electrons and holes in GaAs-AlAs type-II quantum wells are reported. Without applied electric field, the nonlinearities due to blue shift and bleaching of the heavy-hole exciton resonance are observed. An applied static longitudinal dielectric field changes these nonlinearities through the redistribution of electrons. Furthermore, optical nonlinearities and even gain for ultrahigh excitation conditions in type-II structures are reported and compared to those in similar type-I structures. The theoretical framework used for modeling the type-II system in the presence and absence of electrons is described. >

Femtosecond Nonlinear Optical Properties of GaAs/AlAs Type-II Superlattices

We present femtosecond nonlinear absorption spectra of highly-excited type-II GaAs/AlAs multiple quantum wells that reveal a pronounced optically-induced blue shift and bleaching of the heavy-hole exciton absorption peak. The optical nonlinearity arises from many-body effects associated with dense electron and hole plasmas that are separated in both coordinate and momentum spaces. The blue shift disappears as we approach the indirect-to-direct crossover region by application of an axial electric field, thus verifying our assertion that the blue shift arises from type-II behaviour.