Masoud Kasraian

Metal‐grating‐outcoupled, surface‐emitting distributed‐feedback diode lasers

The theoretical analysis of antiphase, surface‐emitting, complex‐coupled, distributed feedback (SE‐CC‐DFB) lasers is presented. The specific configuration chosen for analysis is relatively simple: a metallic second order grating placed atop a diode‐laser structure. This type of SE‐CC‐DFB structure can be fabricated by a lift‐off and evaporation process; can operate in a single‐lobed, orthonormal beam with a rather uniform near‐field intensity pattern, and external differential quantum efficiency, ηd, values in excess of 30%. The dependence of the gain threshold on grating duty cycle for both the symmetric and antisymmetric (longitudinal) modes is presented and discussed. The external differential quantum efficiency for the symmetric mode is found to steadily increase with grating length at the expense of the degree of near‐field‐pattern uniformity.

Single‐lobed far‐field radiation pattern from surface‐emitting complex‐coupled distributed‐feedback diode lasers

Theoretical analysis of surface‐emitting complex‐coupled distributed‐feedback (SE‐CC‐DFB) lasers with a second‐order grating reveals that operation in a single‐lobed, orthonormal beam can be fundamentally favored. This happens when the modal‐gain difference between symmetric and antisymmetric modes due to the optical‐field (longitudinal) overlap with the gain/loss grating overcomes the modal‐gain difference based on radiation losses. The analysis is performed for a simple three‐layer structure with gain placed in the high‐index regions (i.e., in‐phase, second‐order CC‐DFB). Lasing at or near the Bragg frequency provides essentially uniform near‐field patterns, thus immunizing the device to gain spatial hole burning. The results and their implications are discussed.

Surface-emitting, distributed-feedback diode lasers with uniform near-field intensity profile

Theoretical analysis of second-order surface-emitting, complex-coupled distributed feedback diode lasers with first-order distributed Bragg reflectors (DBR) is presented. The DBR reflectors are shown to insure simultaneous operation in a virtually uniform near-field profile with high efficiency and adequate intermodal discrimination. Such devices display symmetric-mode (single-lobe) surface emission with relatively high external differential quantum efficiency (30%), low gain threshold (18 cm−1), and 100 mW of stable, single-mode cw power, significantly higher than it is possible with vertical-cavity surface-emitting lasers. It is also shown that the device studied here can be combined with a resonant optical waveguide array device to produce a 2D uniform near-field surface-emitting source capable of providing greater than 1 W cw power in a stable, single-lobed beam.

Uniform near-field, symmetric-mode surface emission from complex-coupled 2nd-order distributed-feedback lasers

Theoretical analysis of complex-coupled, surface-emitting distributed feedback (CC-SE-DFB) diode lasers with distributed Bragg reflectors (DBR) is presented. These devices are shown to produce symmetric-mode (single-lobe) surface emission with high efficiency (34%) and uniform near-field.

Antiphase complex-coupled surface-emitting distributed feedback diode lasers with absorptive gratings

Theoretical analysis of antiphase-type complex-coupled, surface-emitting distributed feedback (CC-SE-DFB) diode lasers with absorptive gratings is presented and discussed. Two different designs are studied: one utilizing a semiconductor-based second-order loss and index grating placed at the metal-semiconductor (p-side) interface, and the other employing a combination of metallic and semiconductor materials for the second-order loss and index grating. For certain design parameters, these two types of absorptive-grating structure are shown to select lasing in the symmetric mode (i.e., orthonormal emission in a single-lobe beam pattern). By comparison to metal-grating surface-emitting devices, the threshold gains for these structures are lower by factor of 3 to 4. For 500-/spl mu/m-long gratings, the symmetric-mode is favored to lase with threshold gain values as low as 18 cm/sup -1/ and differential quantum efficiency as high as 34%.

Thin film devices based on second order Bragg interaction

For an active dielectric film waveguide with different passive dielectrics for the cover and the substrate and with periodic corrugations on the upper surface, the characteristics of the second order Bragg interaction are investigated for the transverse electric mode with reference to such applications as frequency‐selective reflector, couplers, and distributed feedback laser. Four canonical equations that are valid for a distributed coupler with two guided waves and two free waves, incident and radiated, one each in the cover and the substrate, are deduced systematically. The coupling coefficients are shown to satisfy all the requirements imposed by symmetry, reciprocity, and power conservation. From the solution of the canonical equations with the appropriate terminal conditions, the characteristics of the devices are obtained. The design parameters leading to the optimum performance of these devices are determined. For the distributed feedback laser, the frequencies of oscillation, the corresponding ga...

Double‐grating thin‐film devices based on second‐order Bragg interaction

Four coupled‐mode equations describing the characteristics of the second‐order Bragg interaction are derived for the transverse electric mode of a dielectric film waveguide with periodic corrugations on both the film‐cover and the film‐substrate interfaces. The characteristics of the frequency‐selective filter, output coupler, input coupler, and distributed feedback laser are obtained. Proper choice of the design parameters leads to a frequency‐selective filter radiating neither in the cover nor in the substrate, a highly efficient output coupler radiating only in the cover, and an efficient input coupler exciting a guided wave only in one direction. Similarly, in the distributed feedback laser, a suitable choice of the parameters of the two gratings provides a mechanism for controlling the oscillation characteristics of the laser. The attractive feature of the double‐grating design is that the characteristics of the thin‐film devices are not very sensitive to small deviations of the grating parameters from their designed values.

Antiphase complex-coupled surface-emitting distributed-feedback diode lasers

Theoretical analysis of antiphase-type complex-coupled, surface-emitting distributed feedback (CC-SE-DFB) diode lasers with absorptive gratings is presented and discussed. Two different designs are studied: one utilizing a semiconductor-based second-order loss and index grating placed at the metal-semiconductor (p-side) interface, and the other employing a combination of metallic and semiconductor materials for the second-order loss and index grating. For certain design parameters, these two types of absorptive-grating structure are shown to select lasing in the symmetric mode (i.e., orthonormal emission in a single-lobe beam pattern). By comparison to metal-grating surface-emitting devices, the threshold gains for these structures are lower by factor of 3 to 4. For 500-/spl mu/m-long gratings, the symmetric-mode is favored to lase with threshold gain values as low as 18 cm/sup -1/ and differential quantum efficiency as high as 34%.

Single-lobe operation of surface-emitting complex-coupled second-order distributed-feedback diode lasers

We present the first theoretical analysis of surface-emitting, complex-coupled distributed feedback (SE-CC-DFB) lasers with a second-order grating. It is found that lasing operation in a single-lobed, orthonormal far-field radiation pattern as well as in a nearly uniform near-field intensity pattern is fundamentally favored.

Surface-emitting complex-coupled second-order distributed-feedback lasers for high-power applications

Theoretical analysis of complex-coupled, surface-emitting distributed feedback (CC-SE-DFB) diode lasers with distributed Bragg reflectors (DBR) is presented. These devices are shown to produce symmetric-mode (single-lobe) surface emission with high efficiency (30%) and uniform near-field in the longitudinal direction. High efficiency and uniform near-field are both necessary for achieving high powers in a single-lobed beam. It is also shown that the device studied here may be combined with a Resonant Optical Waveguide array device which has a uniform near-field in the lateral direction to achieve a two-dimensional surface-emitting device capable of providing greater than 1W CW power in a stable, single-lobed beam.