Browsing by Author "Chang, Chi-Hsiang"

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Pulse compression irrespective of fiber dispersion using chirp of transistor lasers
(2019-04-15)
Tung, Chien-Ting
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Chang, Chi-Hsiang
;
Chang, Shu-Wei
;
Wu, Chao-Hsin
;
光電工程學系
The voltage modulation of transistor lasers (TLs) through Franze-Keldysh absorption can impose an unconventional chirp on optical signals. In this Letter, we model this chirp effect and demonstrate how the output Gaussian pulse is reshaped through optical fibers. It is shown that pre-chirped pulses of TLs may be compressed in fibers with both normal and anomalous dispersions. (C) 2019 Optical Society of America
The role of optoelectronic feedback on Franz-Keldysh voltage modulation of transistor lasers
(2016-01-01)
Chang, Chi-Hsiang
;
Chang, Shu-Wei
;
Wu, Chao-Hsin
;
光電工程學系
;
Department of Photonics
Possessing both the high-speed characteristics of heterojunction bipolar transistors (HBTs) and enhanced radiative recombination of quantum wells (QWs), the light-emitting transistor (LET) which operates in the regime of spontaneous emissions has achieved up to 4.3 GHz modulation bandwidth. A 40 Gbit/s transmission rate can be even achieved using transistor laser (TL). The transistor laser provides not only the current modulation but also direct voltage-controlled modulation scheme of optical signals via Franz-Keldysh (FK) photon-assisted tunneling effect. In this work, the effect of FK absorption on the voltage modulation of TLs is investigated. In order to analyze the dynamics and optical responses of voltage modulation in TLs, the conventional rate equations relevant to diode lasers (DLs) are first modified to include the FK effect intuitively. The theoretical results of direct-current (DC) and small-signal alternating-current (AC) characteristics of optical responses are both investigated. While the DC characteristics look physical, the intrinsic optical response of TLs under the FK voltage modulation shows an AC enhancement with a 20 dB peak, which however is not observed in experiment. A complete model composed of the intrinsic optical transfer function and an electrical transfer function fed back by optical responses is proposed to explain the behaviors of voltage modulation in TLs. The abnormal AC peak disappears through this optoelectronic feedback. With the electrical response along with FK-included photoncarrier rate equations taken into account, the complete voltage-controlled optical modulation response of TLs is demonstrated.
Theory for voltage modulation of transistor lasers using Franz-Keldysh absorption in the presence of optoelectronic feedback
(2016-10-31)
Chang, Chi-Hsiang
;
Chang, Shu-Wei
;
Wu, Chao-Hsin
;
光電工程學系
;
Department of Photonics
Compared with typical diode lasers (DLs), transistor lasers (TLs) support not only current-controlled but also voltage-controlled modulation. In this work, we theoretically investigate the small-signal voltage modulation of TLs based on the Franz-Keldysh (F-K) absorption and related optoelectronic feedback. In addition to the conventional rate equations relevant to DLs, our model physically includes various F-K effects. An optically induced current due to the F-K absorption may dramatically alter the voltage response of TLs. A model composed of the intrinsic optical response and an electrical transfer function which is fed back by this optical response is proposed to explain the true behaviors of voltage modulation in TLs. (C) 2016 Optical Society of America