Browsing by Author "Naseem"

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Enhancement in speed and responsivity of uni-traveling carrier photodiodes with GaAs0.5Sb0.5/In0.53Ga0.47As type-II hybrid absorbers
(2019-05-27)
Naseem
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Ahmad, Zohauddin
;
Chao, Rui-Lin
;
Chang, Hsiang-Szu
;
Ni, C-J
We demonstrate a top-illuminated high-speed uni-traveling carrier photodiode (UTC-PD) with a novel design in the p-type absorber, which call effectively shorten the photon absorption depth at telecommunication wavelengths (1.31 similar to 1.55 mu m) and further enhance the bandwidth-efficiency product of UTC-PD. In our proposed new UTC-PD structure, the p-type In0.53Ga0.47As absorption layer is replaced by the type-II GaAs0.5Sb0.5 (p)/In0.53Ga0.47As (i) hybrid absorber. Due to the narrowing of the bandgap and enhancement of the photo-absorption process at the type-II interface between the GaAs0.5Sb0.5 and In0.53Ga0.47As layers, our device shows an over 16.7% improvement in the responsivity compared with that of UTC-PD with the same thickness of pure In0.53Ga0.47As absorber (0.7 mu m) and a zero optical coupling loss. Our demonstrated device with a simple top-illuminated structure offers a large active mesa (25 mu m). a wide optical-to-electrical (O-E) bandwidth (33 GHz), a high responsivity (0.7 A/W), and a high saturation current (>5 mA) under 1.31 mu m optical wavelength. These promising results suggest that our proposed PD structure can fundamentally overcome the trade-off among bandwidth. efficiency. and device active diameter of high-speed PDs. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
High-Speed Avalanche Photodiodes With Wide Dynamic Range Performance
(2019-12-01)
Zhao, Hao-Yi
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Naseem
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Jones, Andrew H.
;
Chao, Rui-Lin
;
Ahmad, Zohauddin
In this work, we demonstrate a novel top-illuminated avalanche photodiode (APD) with high-speed and wide dynamic range performance for coherent lidar applications, which needs simultaneous processing of weak light reflections from the object and a strong optical local-oscillator (LO) signal at the receiving end. By taking advantage of a partially depleted p-type In0.53Ga0.47As absorbing layer and a thin In0.52Al0.48 As multiplication layer (88 nm), the demonstrated APDs exhibit a wide optical-to-electrical bandwidth (16 GHz) and high responsivity (2.5 A/W at 0.9 V-br) near the saturation output current which is as high as >8 mA. Furthermore, the measured low excess noise (k = 0.14) characteristics of this device ensure its wide dynamic range performance. In addition, it should be noted that the measured nonlinear behaviors of these APDs are quite different from those of typical fast p-i-n photodiodes (PDs), which always show serious degradation in their O-E bandwidths at their saturation output. On the other hand, the measured bias dependent 3-dB O-E bandwidth of the demonstrated APDs can be pinned at 16 GHz without any degradation at around the saturation current output. Such distinct nonlinear APD behaviors can be attributed to the space-charge-screening effect induced gain reduction under high-power operation.
High-Speed In0.52Al0.48As Based Avalanche Photodiode With Top-Illuminated Design for 100 Gb/s ER-4 System
(2018-12-01)
Wu, Song-Lin
;
Naseem
;
Wun, Jhih-Min
;
Chao, Rui-Lin
;
Huang, Jack Jia-Sheng
High-speed top-illuminated avalanche photodiodes (APDs) with large diameters (25 mu m) are demonstrated for the application of 4-channels 100 Gb/s data rate. They achieve a bandwidth of 17 GHz at low-gain (M-G = 6.2; 3.6 A/W) and large-gain bandwidth (responsivity bandwidth) product (410 GHz (237.8 GHz-A/W); 55% external efficiency at the unit gain) while maintaining invariant high speed (14 GHz) under high power (0.5 mW) and 0.9 V-b(r) operations. By packaging the demonstrated APD with a 25 Gb/s transimpedance amplifier in a 100 Gb/s ROSA package, a good sensitivity of around -20.6 dBm optical modulation amplitude (OMA) at the data rate of 25.78 Gb/s has been successfully demonstrated. The achieved sensitivity not only meets the required receiver sensitivity (-18.5 dBm OMA) in 100 GbE-ER-4 Lite (40 km) system, it is also comparable with that of the high-performance 1(N) Gb/s ROSA incorporated with the backside illuminated APD design. Overall, our novel APD structure can eliminate the costly flip-chip bonding package in the 100 Gb/s ROSA without sacrificing its sensitivity performance.