Urbach-edge-assisted electro-absorption for enhanced free-space optical modulation

Hristovski, Ilija R.; Lesack, Nikolai I.; Herman, Luke A; Holzman, Jonathan F.

doi:10.1364/ol.388915

Cited by 7 publications

(5 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The challenges arise here because the ideal band gap neglects the continuum of Urbach tail states that can arise at the band edges. These states encroach into the band gap and yield field-induced changes in absorption that are especially strong (in comparison to those predicted in an ideal band gap) [8,11] and temperature dependent (as thermal energy transforms the characteristics of the Urbach tail) [12,13].…”

Section: Introductionmentioning

confidence: 93%

See 1 more Smart Citation

Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models

et al. 2022

Self Cite

View full text Add to dashboard Cite

The foundational Franz-Keldysh effect and Einstein model are applied in this work to characterize semiconductor band-edge absorption-and its departures from ideality. We unify the Franz-Keldysh and Einstein models to fully characterize the field-induced tunneling of photoexcited electrons from degenerate valence bands into the conduction band, with encroachment into the band gap arising as an Urbach tail. Our unified model is implemented for semi-insulating indium phosphide (SI-InP) with strong agreement seen between the theoretical and experimental results for varied photon energies and electric fields.

show abstract

Section: Introductionmentioning

confidence: 93%

“…This would give increased absorption at photon energies below the band-gap energy [3,4]. The Franz-Keldysh effect was later demonstrated and applied via electrorefraction, spanning the work of Seraphin and Bottka [5] to Pintus et al [6], or electroabsorption, spanning the work of Chester and Wendland [7] to ourselves [8].…”

Section: Introductionmentioning

confidence: 99%

Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models

et al. 2022

Self Cite

View full text Add to dashboard Cite

show abstract

“…Such an interaction allowed for energies below the bandgap to see increased absorption 3 . The demonstration and application of electroabsorption from the Franz-Keldysh effect was later seen through work spanning Chester and Wendland 4 to ourselves 5 . However, the relationship between photon energy, temperature, and electric field is complex and difficulties understanding and applying the Franz-Keldysh model exist 4 .…”

Section: Introductionmentioning

confidence: 99%

“…These difficulties are due to the continuum of Urbach tail states that are neglected by the ideal bandgap model. The Urbach tail states encroach into the bandgap and result in strong temperature dependent fieldinduced changes to absorption 5 . The degenerate valence band and Urbach tails at the band edges of the Franz-Keldysh model are unified with the temperature dependent tail states of the Einstein model.…”

Section: Introductionmentioning

confidence: 99%

Electroabsorption characteristics of semi-insulating indium phosphide as applied to optoelectronic modulation

MacGillivray

Lesack²,

Hristovski³

et al. 2023

Physics and Simulation of Optoelectronic Devices XXXI

View full text Add to dashboard Cite

In this work, we explore the band edge absorption characteristics of semiconductors as applied to optoelectronic modulation—with careful consideration to the departures from ideality in the semiconductors. To this end, we develop a rigorous model of electroabsorption in semiconductors that characterizes the electric-field-induced constriction/narrowing of the bandgap and the resulting increase in absorption of photons, whose energies are slightly below the bandgap energy. The model unifies the Franz-Keldysh effect, characterizing the electric-field-induced tunneling of photoexcited electrons from valence band states to conduction band states, and the Einstein model, quantifying the encroachment of valence and conduction band states into the bandgap. Careful consideration is given here to the nonidealities in the semiconductor, which arise within the valence band as degenerate states, due to light and heavy holes, and within the bandgap, as encroaching Urbach tail states. We apply the model in characterizing optoelectronic modulation of 980-nm photons with semi-insulating indium phosphide (SI-InP), and we see strong agreement between our theoretical and experimental results over a wide range of electric fields and photon energies. Ultimately, the findings show that optoelectronic modulation can be had with large modulation depths over short propagation lengths through the semiconductor. This opens the door to highly effective implementations of optoelectronic modulators in emerging free-space optical communication systems—given that such modulators do not allow for prolonged (guided-wave) propagation and have thus exhibited small modulation depths.

show abstract

“…However, effective retroreflection and modulation in these retro-modulators are required. Retroreflection can be applied for compatibility with planar modulators using corner cubes 5 , or omnidirectionality with spheres 6 . In light of the above devices, our work introduces a hemispherical retro-modulator as a hybrid structure, with directionality similar to the sphere and compatibility with planar modulators 7 .…”

Section: Introductionmentioning

confidence: 99%

Hemispherical retro-modulation technologies for passive free-space optical communication links

MacGillivray

Gorgani²,

Hristovski³

et al. 2023

Free-Space Laser Communications XXXV

View full text Add to dashboard Cite

In this work, we introduce the concept of a hemispherical retro-modulator for the realization of passive free-space optical communication links. The hemispherical retro-modulator is implemented with a high-refractive-index glass (S-LAH79) hemisphere on a semi-insulating-InP (SI-InP) layer, whose thickness dictates the effectiveness of both retroreflection and modulation. A voltage is applied across transparent indium tin oxide (ITO) and gold (Au) films on either side of the SI-InP layer to bring about the desired modulation. The overall device is designed to enable low divergence on the retroreflected beam, as defined by a small divergence angle, and deep modulation on the retroreflected beam, as a result of electroabsorption in the SI-InP layer. To this end, the device is analysed with a ray-based model for retroflection and a unified Franz-Keldysh/Einstein model for modulation in the SI-InP layer. The theoretical results show strong agreement with the experimental results from our prototype. Moreover, the results show effective retroflection and deep modulation-with an applied electric field of 2.167 kV/cm yielding modulation depths of 13%, 34%, and 50% for our 980-nm photons and SI-InP layer thicknesses of 200, 600, and 1,000 µm, respectively. From this, we deem the SI-InP layer thickness of 600 µm to be optimal given its combined capabilities for retroflection and modulation. Ultimately, the introduced hemispherical retro-modulator is shown to be an effective element for future realizations of passive freespace optical communication links.

show abstract

Urbach-edge-assisted electro-absorption for enhanced free-space optical modulation

Cited by 7 publications

References 25 publications

Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models

Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models

Electroabsorption characteristics of semi-insulating indium phosphide as applied to optoelectronic modulation

Hemispherical retro-modulation technologies for passive free-space optical communication links

Contact Info

Product

Resources

About