Browsing by Author "Chen, Lih-Ren"

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Anti-guiding and guiding effects in GaN-based vertical-cavity surface-emitting lasers
(2020-02-01)
Chen, Lih-Ren
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Chen, Bo-Yan
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Kuo, Shiou-Yi
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Hong, Kuo-Bin
;
Lu, Tien-Chang
We study the lateral optical confinement effect on the performance and lasing characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs). The anti-guiding and guiding structures are designed by calculating the effective refractive index difference of active and cladding regions. By varying the compensation layer configuration and thickness, the designed effective refractive index of the active region is 0.44% higher than peripheral for the guiding structure. The threshold current density of VCSEL with the guiding structure is 25.4 kA/cm(2), which is almost half of that with the anti-guiding structure showing 53.5 kA/cm(2). For the anti-guiding structure, the signals from both active and cladding regions are observed by the far-field angle-resolved spectrum at 1.4 x I-th driving current, which agrees well with our simulation. Throughout the study, we show the advantage of the guiding structure both theoretically and experimentally. Moreover, an effective guiding structure is obtained by a proper design and simple device process, which will be very promising for mass production.
Degradation mechanisms of bias stress on nitride-based near-ultraviolet light-emitting diodes in salt water vapor ambient
(2019-10-15)
Chen, Lih-Ren
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Huang, Shen-Che
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Chiu, Jo-Lun
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Lu, Chien-Cheng
;
Su, Wei-Ming
Degradation mechanisms of nitride-based near-ultraviolet (near-UV) light-emitting diodes (LEDs) were systematically analyzed by applying forward- and reverse-bias stresses to them in a salt water vapor ambient. The surface temperature of the forward-bias stress sample was higher than that of the reverse-bias stress sample. The high temperature of the forward-bias stress sample accelerated the chemical reaction of the device structure with salt water vapors and led to faster degradation. Composition analyses of the sample surface and cross-section were conducted to investigate the failure mechanism. The analyses results indicated that the erosion of the indium-tin-oxide layer enhanced the diffusion of the conducting metal into the LED crystal. The proposed method can effectively characterize the quality of near-UV LEDs in a short duration.
Effect of Passivation Layer on the Thin Film Perovskite Random Lasers
(2020-05-01)
Mallick, Subha Prakash
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Hong, Yu-Heng
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Chen, Lih-Ren
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Kao, Tsung Sheng
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Lu, Tien-Chang
Novel functionalities of disorder-induced scattering effect in random lasers, attributed to low spatial coherence, draw remarkable attention in high-contrast to superior quality speckle-free imaging applications. This paper demonstrates perovskite-polystyrene (PS)-based random lasing action with robust optical performance at room temperature. Optical characterizations are carried out upon perovskite thin films addition with polystyrene of different mixing concentrations (wt.%). A low threshold lasing operation is achieved with an increasing concentration of polystyrene, accompanying a wavy surface texture with high surface roughness. The rough surface dominating multiple scattering effects leads to enhanced feedback efficiency. Moreover, this study also elucidates efficient fabrication process steps for the development of high quality and durable PS-based random lasers. With the advantages of reduced coherent artifacts and low spatial coherence, speckle free projection images of the USAF (U. S. Air Force MIL-STD-150A standard of 1951) resolution test chart are shown for different PS-based random lasers.
Low threshold current photonic crystal surface emitting lasers with beam modulation capability
(2019-01-01)
Chen, Lih-Ren
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Chiu, Han-Lun
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Hong, Kuo-Bin
;
Lu, Tien-Chang
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We proposed a GaAs-based photonic crystal surface emitting laser with naturally formed periodic structures on the ITO top cladding layer. Low threshold current density and ability of beam modulation have been demonstrated. (C) 2019 The Author(s)
Photonic integrated multiwavelength laser arrays: Recent progress and perspectives
(2020-05-04)
Lee, San-Liang
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Lu, Tien-chang
;
Hung, Yung-, Jr.
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Chen, Lih-Ren
;
Huang, Zhen-Ting
With the significant technology advancement in photonic integration and the demands of compact light sources of multiple wavelengths, multiwavelength laser arrays (MWLAs) can play important roles in high-capacity optical signal transmission, photonic switching, and optical sensing. Manufacturing with semiconductor foundries and the integration with electronic integrated circuits bring not only advanced technologies but also new concepts for realizing MWLAs. This paper will first overview the existing technology development and then discuss the challenges and possible solutions for enabling photonic-integrated MWLAs. The overview will cover monolithically and hybrid-integrated MWLAs. The wavelength registration for both in-plane and vertical-cavity MWLAs will be discussed and compared.