R. J. Simes

Electroabsorptive Fabry-Perot reflection modulators with asymmetric mirrors

A normally-on electroabsorptive surface-normal Fabry-Perot reflection modulator is reported with an on/off ratio of 22, insertion loss of 3.7 dB, and bandwidth of 3.4 nm for an operating voltage swing of 11 V. The asymmetric Fabry-Perot structure is made with asymmetric mirrors using a quarter-wavelength grating of 15 1/2-periods on the bottom and an air-semiconductor interface on the top. The active region is 1.4 mu m thick and composed of 100AA GaAs/100 A Al/sub 0.2/Ga/sub 0.8/As multiple quantum wells. The structure provides both high-efficiency and bandwidth for surface-normal modulators.<<ETX>>

Extremely low-voltage Fabry-Perot reflection modulators

A normally-on-electroabsorptive surface-normal Fabry-Perot reflection modulator with a reflection change of 47% for an operating voltage swing of only 2 V, i.e. 23%/V, is discussed. The structure has an active region of twenty-four 100-AA-GaAs/100-AA-Al/sub 0.2/Ga/sub 0.8/As multiple quantum wells, sandwiched between two quarter-wavelength grating mirrors with the bottom one more reflective. The wavelength range over which more than half of the maximum reflection change is observed is as wide as approximately 7 nm for 2 V.<<ETX>>

Electrically tunable Fabry-Perot mirror using multiple quantum well index modulation

We describe a novel surface normal Fabry–Perot multiple quantum well index reflection modulator which may be tuned electrically. The Fabry–Perot etalon, composed of two AlAs/Ga1−xAlxAs quarter‐wavelength grating mirrors separating a multiple quantum well GaAs/Ga1−xAlxAs active medium, is formed in a single growth by molecular beam epitaxy. Contrast ratios of up to 8:1 at 873 nm have been measured.

Transverse modulators with a record reflection change of >20%/V using asymmetric Fabry–Perot structures

An asymmetric Fabry–Perot structure with a multiple quantum well active region is demonstrated to provide a reflection change of >45% for an operating voltage swing of only ∼2 V, with a contrast ratio of more than 15. Photocurrent measurements show that the same devices also work as voltage‐tunable detectors. Such devices compete effectively with low‐voltage waveguide modulators, with further advantages of easy coupling and compact sizes, i.e., small capacitances.

Band gap modulation in two dimensions by MBE growth of tilted superlattices and applications to quantum confinement structures

Abstract The MBE growth of GaAs-AlAs “tilted superlattices” (TSLs) having interface planes tilted with respect to the substrate surface plane is reported. The TSLs are produced by depositing fractional monolayer superlattices (GaAs) m -(AlAs) n , with p = m + n ≈ 1, on vicinal (100) surfaces. The crystal growth parameters that are important to the TSL structural perfection are discussed. We demonstrate the growth of GaAs quantum wire arrays deposited directly by using the TSL deposition mode. Carrier confinement in 2 dimensions by the quantum wire structure is demonstrated by following the polarization dependence of the selectively excited photoluminescence from these structures.

Disordering of GaAs/AlGaAs multiple quantum well structures by thermal annealing for monolithic integration of laser and phase modulator

Conventional thermal annealing with various caps on the surface of the sample is used to selectively disorder one section of a multiple quantum well GaAs/AlGaAs structure. In the disordered section, the shift of the photoluminescence peak is in the range where the chirp parameter (ratio of real index change over absorption change) is large at the laser wavelength in the undisordered material. Moreover, photoconductivity measurements on samples under reverse bias, as well as laser testing, prove that the electric properties are preserved by the thermal treatment. Therefore, the investigated process should be highly suitable for the monolithic integration of a laser and phase modulator.

Wide‐bandwidth, high‐efficiency reflection modulators using an unbalanced Fabry–Perot structure

A normally‐on electroabsorptive multiple quantum well asymmetric Fabry–Perot reflection modulator with an on/off ratio of 22, insertion loss of 3.7 dB, and optical bandwidth of 3.4 nm for a voltage swing of 11 V has been measured. The trade‐off between low insertion loss and high contrast in such devices will be discussed in the present letter and is shown to be due to the relative placement in wavelength between the Fabry–Perot resonant mode and the heavy hole exciton position in the multiple quantum well active region.

Room‐temperature two‐dimension exciton exchange and blue shift of absorption edge in GaAs/AlGaAs superlattices under an electric field

The first room‐temperature two‐dimensional heavy hole exciton red shift, greater than 25 meV due to the exchange of Van Hove‐type M1 and quantum well excitons, was observed by photocurrent measurements in molecular beam epitaxy grown superlattices with periods of 30 A GaAs/25 A Ga0.5Al0.5As. At a photon energy of 1.66 eV, a 3000 cm−1 absorption change due to the blue shift of the superlattice absorption edge was also observed at room temperature in superlattices with periods of 20 A GaAs/20 A Ga0.5Al0.5As.

Optically addressed spatial light modulators by MBE-grown nipi MQW structures

Promising approaches for achieving optically addressed spatial light modulators (O-SLMs) are investigated based on combining nipi and multiple quantum well structures. Theoretical aspects of photooptic effects achievable in such structures are treated. Test structures are grown by molecular beam epitaxy using two material systems, (In,Ga)As/GaAs and (Al,Ga)As/GaAs. Experiments show large optically controlled modulation of the absorption coefficient in the quantum well layers ( approximately 10(4) cm(-1)), a log power dependence on the control signal, millisecond and shorter time response, and generally predictable behavior. The results are encouraging for several different O-SLM device structures proposed.

High-frequency electrooptic Fabry-Perot modulators

Electrooptic modulators built from GaAs/Al/sub x/Ga/sub 1-x/As Fabry-Perot cavities operating up to 6.5 GHz are reported. The measured frequency response agrees well with the one predicted using an equivalent circuit model derived from high-speed electrical measurements. The parasitic capacitances have been reduced to approximately 30 fF by fabricating the devices on semi-insulating GaAs substrates and integrating them with on-wafer bound pads which have dimensions compatible with microwave coplanar probes.<<ETX>>