{"id":{"repo_id":"vt","oai_identifier":"oai:vtechworks.lib.vt.edu:10919/23129"},"canonical_url":"https://search.dev.ndltd.org/etd/vt/oai:vtechworks.lib.vt.edu:10919/23129","repository":{"repo_id":"vt","name":"Virginia Tech","base_url":"https://vtechworks.lib.vt.edu/oai/request"},"display":{"title":"Theory of Modulation Response of Semiconductor Quantum Dot Lasers","abstract":"In this dissertation, a theory of modulation response of a semiconductor quantum dot (QD) laser is developed. The effect of the following factors on the modulation bandwidth of a QD laser is studied and the following results are obtained:
1) Carrier capture delay from the optical confinement layer into QDs
Closed-form analytical expressions are obtained for the modulation bandwidth omega_{-3 dB} of a QD laser in the limiting cases of fast and slow capture into QDs. omega_{-3 dB} is highest in the case of instantaneous capture into QDs, when the cross-section of carrier capture into a QD sigma_n = infinity. With reducing sigma_n, omega_{-3 dB} decreases and becomes zero at a certain non-vanishing sigma_n^{min}. This sigma_n^{min} presents the minimum tolerable capture cross-section for the lasing to occur at a given dc component j_0 of the injection current density. The higher is j_0, the smaller is sigma_n^{min} and hence the direct modulation of the output power is possible at a slower capture. The use of multiple layers with QDs is shown to considerably improve the modulation response of the laser -- the same omega_{-3 dB} is obtained in a multi-layer structure at a much lower j_0 than in a single-layer structure.
2) Internal optical loss in the optical confinement layer
The internal optical loss, which increases with free-carrier density in the waveguide region, considerably reduces the modulation bandwidth omega_{-3 dB} of a QD laser. With internal loss cross-section sigma_int increasing and approaching its maximum tolerable value, the modulation bandwidth decreases and becomes zero. There exists the optimum cavity length, at which omega_{-3 dB} is highest; the larger is sigma_int, the longer is the optimum cavity.
3) Excited states in QDs
Direct and indirect (excited-state-mediated) mechanisms of capture of carriers from the waveguide region into the lasing ground state in QDs are considered, and the modulation response of a laser is calculated. It is shown that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser -- at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.
","abstract_html":"In this dissertation, a theory of modulation response of a semiconductor quantum dot (QD) laser is developed. The effect of the following factors on the modulation bandwidth of a QD laser is studied and the following results are obtained:<br /><br />1) Carrier capture delay from the optical confinement layer into QDs<br /><br />Closed-form analytical expressions are obtained for the modulation bandwidth omega_{-3 dB} of a QD laser in the limiting cases of fast and slow capture into QDs. omega_{-3 dB} is highest in the case of instantaneous capture into QDs, when the cross-section of carrier capture into a QD sigma_n = infinity. With reducing sigma_n, omega_{-3 dB} decreases and becomes zero at a certain non-vanishing sigma_n^{min}. This sigma_n^{min} presents the minimum tolerable capture cross-section for the lasing to occur at a given dc component j_0 of the injection current density. The higher is j_0, the smaller is sigma_n^{min} and hence the direct modulation of the output power is possible at a slower capture. The use of multiple layers with QDs is shown to considerably improve the modulation response of the laser -- the same omega_{-3 dB} is obtained in a multi-layer structure at a much lower j_0 than in a single-layer structure.<br /><br />2) Internal optical loss in the optical confinement layer<br /><br />The internal optical loss, which increases with free-carrier density in the waveguide region, considerably reduces the modulation bandwidth omega_{-3 dB} of a QD laser. With internal loss cross-section sigma_int increasing and approaching its maximum tolerable value, the modulation bandwidth decreases and becomes zero. There exists the optimum cavity length, at which omega_{-3 dB} is highest; the larger is sigma_int, the longer is the optimum cavity.<br /> <br />3) Excited states in QDs<br /><br />Direct and indirect (excited-state-mediated) mechanisms of capture of carriers from the waveguide region into the lasing ground state in QDs are considered, and the modulation response of a laser is calculated. It is shown that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser -- at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.<br />","abstract_has_math":false,"creators":["Wu, Yuchang"],"institution":"Virginia Tech","degree_name":"Ph. D.","degree_level":"doctoral","degree_discipline":"Materials Science and Engineering","degree_department":"Materials Science and Engineering","school":null,"contributors":[],"advisors":[],"committee_chairs":["Asryan, Levon V."],"committee_members":["Pickrell, Gary R.","Orlowski, Mariusz Kriysztof","Guido, Louis J."],"year":2013,"date_issued":"2013-06-03","date_published":"2013-06-03","updated_at":"2026-07-22T22:20:11Z","subjects":["quantum dot lasers","semiconductor lasers"],"languages":[],"rights":["In Copyright"],"rights_urls":["http://rightsstatements.org/vocab/InC/1.0/"],"identifier_entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:522"],"render_values":[{"text":"vt_gsexam:522","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/10919/23129","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.committeechair","label":"Committee Chair","values":["Asryan, Levon V."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Pickrell, Gary R.","Orlowski, Mariusz Kriysztof","Guido, Louis J."]},{"key":"dc:contributor.department","label":"Department","values":["Materials Science and Engineering"]},{"key":"dc:creator","label":"Author","values":["Wu, Yuchang"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2013-06-04T08:00:23Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2013-06-04T08:00:23Z"]},{"key":"dc:date.issued","label":"Date","values":["2013-06-03"]},{"key":"dc:publisher","label":"Institution","values":["Virginia Tech"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science and Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph. D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Virginia Polytechnic Institute and State University"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["quantum dot lasers","semiconductor lasers"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:rights","label":"Dc Rights","values":["In Copyright"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://rightsstatements.org/vocab/InC/1.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.other","label":"Dc Identifier Other","values":["vt_gsexam:522"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/10919/23129"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In this dissertation, a theory of modulation response of a semiconductor quantum dot (QD) laser is developed. The effect of the following factors on the modulation bandwidth of a QD laser is studied and the following results are obtained:
1) Carrier capture delay from the optical confinement layer into QDs
Closed-form analytical expressions are obtained for the modulation bandwidth omega_{-3 dB} of a QD laser in the limiting cases of fast and slow capture into QDs. omega_{-3 dB} is highest in the case of instantaneous capture into QDs, when the cross-section of carrier capture into a QD sigma_n = infinity. With reducing sigma_n, omega_{-3 dB} decreases and becomes zero at a certain non-vanishing sigma_n^{min}. This sigma_n^{min} presents the minimum tolerable capture cross-section for the lasing to occur at a given dc component j_0 of the injection current density. The higher is j_0, the smaller is sigma_n^{min} and hence the direct modulation of the output power is possible at a slower capture. The use of multiple layers with QDs is shown to considerably improve the modulation response of the laser -- the same omega_{-3 dB} is obtained in a multi-layer structure at a much lower j_0 than in a single-layer structure.
2) Internal optical loss in the optical confinement layer
The internal optical loss, which increases with free-carrier density in the waveguide region, considerably reduces the modulation bandwidth omega_{-3 dB} of a QD laser. With internal loss cross-section sigma_int increasing and approaching its maximum tolerable value, the modulation bandwidth decreases and becomes zero. There exists the optimum cavity length, at which omega_{-3 dB} is highest; the larger is sigma_int, the longer is the optimum cavity.
3) Excited states in QDs
Direct and indirect (excited-state-mediated) mechanisms of capture of carriers from the waveguide region into the lasing ground state in QDs are considered, and the modulation response of a laser is calculated. It is shown that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser -- at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.
"]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph. D."]},{"key":"dc:format.medium","label":"Dc Format Medium","values":["ETD"]},{"key":"dc:title","label":"Title","values":["Theory of Modulation Response of Semiconductor Quantum Dot Lasers"]}]}],"canonical_facts":{"dc:contributor.committeechair":["Asryan, Levon V."],"dc:contributor.committeemember":["Pickrell, Gary R.","Orlowski, Mariusz Kriysztof","Guido, Louis J."],"dc:contributor.department":["Materials Science and Engineering"],"dc:creator":["Wu, Yuchang"],"dc:date.accessioned":["2013-06-04T08:00:23Z"],"dc:date.available":["2013-06-04T08:00:23Z"],"dc:date.issued":["2013-06-03"],"dc:description.abstract":["In this dissertation, a theory of modulation response of a semiconductor quantum dot (QD) laser is developed. The effect of the following factors on the modulation bandwidth of a QD laser is studied and the following results are obtained:
1) Carrier capture delay from the optical confinement layer into QDs
Closed-form analytical expressions are obtained for the modulation bandwidth omega_{-3 dB} of a QD laser in the limiting cases of fast and slow capture into QDs. omega_{-3 dB} is highest in the case of instantaneous capture into QDs, when the cross-section of carrier capture into a QD sigma_n = infinity. With reducing sigma_n, omega_{-3 dB} decreases and becomes zero at a certain non-vanishing sigma_n^{min}. This sigma_n^{min} presents the minimum tolerable capture cross-section for the lasing to occur at a given dc component j_0 of the injection current density. The higher is j_0, the smaller is sigma_n^{min} and hence the direct modulation of the output power is possible at a slower capture. The use of multiple layers with QDs is shown to considerably improve the modulation response of the laser -- the same omega_{-3 dB} is obtained in a multi-layer structure at a much lower j_0 than in a single-layer structure.
2) Internal optical loss in the optical confinement layer
The internal optical loss, which increases with free-carrier density in the waveguide region, considerably reduces the modulation bandwidth omega_{-3 dB} of a QD laser. With internal loss cross-section sigma_int increasing and approaching its maximum tolerable value, the modulation bandwidth decreases and becomes zero. There exists the optimum cavity length, at which omega_{-3 dB} is highest; the larger is sigma_int, the longer is the optimum cavity.
3) Excited states in QDs
Direct and indirect (excited-state-mediated) mechanisms of capture of carriers from the waveguide region into the lasing ground state in QDs are considered, and the modulation response of a laser is calculated. It is shown that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser -- at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.
"],"dc:description.degree":["Ph. D."],"dc:format.medium":["ETD"],"dc:identifier.other":["vt_gsexam:522"],"dc:identifier.uri":["http://hdl.handle.net/10919/23129"],"dc:publisher":["Virginia Tech"],"dc:rights":["In Copyright"],"dc:rights.uri":["http://rightsstatements.org/vocab/InC/1.0/"],"dc:subject":["quantum dot lasers","semiconductor lasers"],"dc:title":["Theory of Modulation Response of Semiconductor Quantum Dot Lasers"],"dc:type":["Dissertation"],"thesis:degree_discipline":["Materials Science and Engineering"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Ph. D."],"thesis:institution_name":["Virginia Polytechnic Institute and State University"]},"updated_at":"2026-07-22T22:20:11Z"}