Browsing by Author "Ahmad, Zohauddin"

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BJT-Type Optical Phase Shifter With Small Power Consumption and Fast Response Time on a Silicon Photonics Foundry Platform
(2020-03-01)
Chao, Rui-Lin
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Ahmad, Zohauddin
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Chen, Jason
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Lai, Yinchieh
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Shi, Jin-Wei
We demonstrate a novel optical phase shifter with a bipolar junction transistor (BJT) type of device structure based on the silicon photonics foundry platform. By operating such a device in saturation mode, we obtain measured output I-EC-V-EC characteristics very similar to those of an ideal diode, which has a nearly zero turn-on voltage and an extremely small differential resistance. The huge amount of injected current under a small voltage swing (0.1 V) in the operation window makes it possible to obtain significant plasma induced change of the refractive index in the optical waveguide with an extremely small driving-voltage. The device has a small foot-print (500 mu m in length), but exhibits small static power consumption for the pi phase-shift (P-pi: 4.1 mW), reasonable propagation loss (0.02 dB/mu m), small driving-voltage (V-pi: 0.12 V), fast switching time (rise/fall <1.6/1 ns), a residue amplitude modulation (RAM) as small as 0.18 dB, and a very-low power consumption (0.45 mW) during dynamic operation.
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
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Chao, Rui-Lin
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Chang, Hsiang-Szu
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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.
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Chao, Rui-Lin
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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 Electro-Absorption Modulated Laser at 1.3 mu m Wavelength Based on Selective Area Growth Technique
(2019-01-01)
Ahmad, Zohauddin
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Chao, Rui-Lin
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Hung, Yung-Jr
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Chen, Jyehong
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Wei, Chia-Chien
We demonstrate InxAlyGa1-x-yAs based electro-absorption modulated DFB laser at 1.3 mu m wavelength based on selective area growth technique. The fabricated device exhibits 5 mW output power, wide E-O bandwidth (>40 GHz), 2V driving-voltage for 10 dB extinction ratio, and clear eye-opening at 32Gbit/sec.
PNP-Type Optical Phase-Shifter with Low Power Consumption and Fast Switching Time on Silicon Photonics Foundry Platform
(2019-01-01)
Chao, Rui-Lin
;
Ahmad, Zohauddin
;
Chen, Jyehong
;
Shi, Jin-Wei
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光電工程學系
We demonstrate a novel PNP bipolar junction transistor based optical phase-shifter on Si-photonic foundry platform. It exhibits a small static power consumption for pi phase-shift (P-pi: 3mW), small driving-voltages (V-pi:0.1 V), fast switching time (rise/fall <1.19/0.6ns), and very-low power consumption (0.7mW) during dynamic operations.
Three-Port Optical Phase-Shifters and Modulators With Ultra-High Modulation Efficiency, Positive RF-Linking Gain, and Low Residual Amplitude Modulation
(2020-01-01)
Chao, Rui Lin
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Ahmad, Zohauddin
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Chen, Jyehong
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Lai, Yinchieh
;
Shi, Jin-Wei
A three-port optical phase-shifter and Mach-Zehnder modulator (MZM) based on PNP-type bipolar junction transistor (BJT) is demonstrated. Significant plasma (injected carrier) induced changes of the refractive index for the optical waveguide become possible with an extremely small driving-voltage and a compact device size during operation of this BJT between the saturation and forward active modes. Devices with a standard MZM structure and a small foot-print (0.5 mm) exhibit a moderate optical insertion loss (2 dB), extremely small (0.18V) and (0.21mW), fast rise/fall time (& x007E; 1ns), and a residue-amplitude-modulation (RAM) as small as 0.18 dB. Furthermore, thanks to the ultra-high modulation efficiency characteristic of our device, a & x002B;4.0 dB net RF-linking gain can be obtained under dynamic operation. Compared to 2-port (base-collector) forward bias operation, under three-port operation, the extra bias current from the base-emitter junction provides a lower (0.18 vs. 0.22 V), a smaller RAM (0.18 vs. 0.6 dB), and a larger RF-linking gain (& x002B;4 vs. & x2212;3.2 dB). The superior performances of the three-port to two-port operations can be attributed to the additional forward bias B-E junction being able to provide more injected carriers to induce stronger plasma effects for optical phase-shifting.