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GaN-based vertical-cavity surface-emitting laser incorporating a TiO2 high-index-contrast grating
(2020-01-01)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Bengtsson, Jorgen
;
Gustavsson, Johan
;
Haglund, Asa
We demonstrate the first electrically injected GaN-based VCSEL with a TiO2 high-contrast grating (HCG) as the top mirror. The TiO2-HCG rested directly on the n-GaN without an airgap for mechanical stability. A VCSEL with an aperture diameter of 10 mu m had a threshold current of 25 mA under pulsed operation at room temperature. Multiple longitudinal modes coexist around 400 nm, each TM-polarized with a linewidth of 0.5 nm (spectral resolution limited). This first demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as post-growth setting of resonance wavelength.
Electrically Injected GaN-Based Vertical-Cavity Surface-Emitting Lasers with TiO2 High-Index-Contrast Grating Reflectors
(2020-04-15)
Chang, Tsu-Chi
;
Hashemi, Ehsan
;
Hong, Kuo-Bin
;
Bengtsson, Jorgen
;
Gustaysson, Johan
We demonstrate the first electrically injected GaNbased vertical-cavity surface-emitting lasers (VCSELs) with a TiO2 high-index-contrast grating (HCG) as the top mirror. Replacing the top distributed Bragg reflector (DBR) with an HCG offers substantial thickness reduction, polarization-pinning, and setting of the resonance wavelength by the grating parameters. Conventional HCGs are usually suspended in the low refractive index material, such as air, in order to create the largest refractive index contrast. However, the mechanical stability of such structures can be questioned and creating free-hanging GaN-membrane on top of GaN is problematic. We have therefore fabricated TiO2-HCGs resting directly on GaN without an air-gap. No DBR layers are used below the HCG to boost the reflectivity. A VCSEL with an aperture diameter of 10 mu m shows a threshold current of 25 mA under pulsed operation at room temperature. The lasing modes locate around 400 nm and are transversely electrically -polarized with a line width of 0.5 nm. The full-width half-maximum beam divergence is 10 degrees. This demonstration of a TiO2-HCG VCSEL offers a new route to achieve polarization pinning and could also allow additional benefits such as postgrowth setting of the resonance wavelength.
Design and Optimization of VCSELs for up to 40-Gb/s Error-Free Transmission Through Impurity-Induced Disordering
(2020-03-01)
Peng, Chun-Yen
;
Cheng, Hao-Tien
;
Kuo, Hao-Chung
;
Wu, Chao-Hsin
;
光電工程學系
This article describes an optimized design and process for the improvement of the electrical properties of vertical-cavity surface-emitting lasers (VCSELs) via the impurity-induced disordering (IID) technology. Through the IID process, the electrical current path can be tailored to detour around the defect centers introduced by the oxidation process, resulting in a noticeable improvement in the dc and the RF characteristics of the IID VCSEL. The threshold current was reduced from 0.341 to 0.225 mA due to better current injection efficiency in the IID VCSEL. The characteristic temperature of the IID VCSEL increased from 106 to 150 K, and the slope of the I-V characteristics under low-level-injection regime could be improved to a factor of exp. The RF characteristics also echoed the dc characteristics, which the optical bandwidth of the IID VCSEL enhanced from 18.95 to 23.49 GHz, and showed a prominent difference on the factor (similar to 0.26 to similar to 0.22 ns) and the D factor (similar to 7 to similar to 11 GHz/(mA)(1/2)). The IID VCSEL is then employed for a data transmission link, an eye diagram was characterized at up to 44 Gb/s and passed 40-Gb/s error-free testing under on-off-keying (OOK) modulation.
Design and Fabrication of the Reliable GaN Based Vertical-Cavity Surface-Emitting Laser via Tunnel Junction
(2019-04-01)
Shen, Chih-Chiang
;
Lu, Yun-Ting
;
Yeh, Yen-Wei
;
Chen, Cheng-Yuan
;
Chen, Yu-Tzu
In this study, we theoretically designed and experimentally fabricated an InGaN vertical-cavity surface-emitting laser (VCSEL) with a tunnel junction (TJ) structure. From numerical simulation results, the optical loss of the device can be reduced by a TJ structure. Additionally, the leakage current of the VCSEL with TJ structure was much smaller than that of the VCSEL with an Indium-Tin-Oxide (ITO) layer. We have been demonstrated that laser output performance is improved by using the TJ structure when compared to the typical VCSEL structure of the ITO layer. The output power obtained at 2.1 mW was enhanced by a factor of 3.5 by the successful reduction of threshold current density (J(th)) from 12 to 8.5 kA/cm(2), and the enlarged slope efficiency was due to less absorption in VCSEL with a TJ structure. Finally, the samples passed the high temperature (70 degrees C) and high operation current (1.5 x J(th)) test for over 500 h.
Long-Term Thermal Stability of Single-Mode VCSEL Under 96-Gbit/s OFDM Transmission
(2019-11-01)
Kao, Hsuan-Yun
;
Tsai, Cheng-Ting
;
Chi, Yu-Chieh
;
Peng, Chun-Yen
;
Leong, Shan-Fong
Thermal-dependent transmission performance and long-term stability of a single-transverse-mode (SM) vertical-cavity surface-emitting laser (VCSEL) with directly pre-leveled 16quadrature amplitude modulation orthogonal frequency-division multiplexing (16-QAM OFDM) data over 100 m 0M4 multi-mode-fiber (MMF) are demonstrated. Although narrowing the oxide-confined aperture to 3 mu m enables the SM VCSEL with low threshold current of 0.21 mA and high modulation bandwidth of 21.4 GHz, this technology also enlarges the insulating oxide area to accumulate the heat for raising core temperature. This induces a harsh environment as the core temperature persistently increases without dissipation even under the water-cooling control at 20 degrees C. As a result, the SM VCSEL can only guarantee a stable operation for 1.5 h under the encoding of QAM-OFDM data for transmission. After optimization, the SM VCSEL successfully supports a back-to-back transmission capacity as high as 96 Gbit/s. With the assistance of OFDM pre-leveling technique, the 96-Gbit/s QAM-OFDM data transmission is qualified over 100 m OM4 MMF with a receiving power penalty as low as 13 dB.
Low threshold current, low resistance 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE
(2007-01-01)
Yu, Hsin-Chieh
;
Wang, Jyh-Shyang
;
Su, Yan-Kuin
;
Chang, Shoou-Jinn
;
Kuo, Hao-Chung
The processing technology of 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE will be demonstrated. The threshold currents of the fabricated devices with 10 mu m oxide-confined aperture are 0.7mA, which correspond to 890A/cm(2) threshold current density. And the threshold voltage of the device is 1.03V and maximum output power is 33 M. The series resistance is 85 Omega which is 10 times lower then our preliminary work and 3 times lower then intracavity contacted InAs-InGaAs quantum-dot VCSEL. This relatively lower resistance can even comparable with the best result reported in InGaAs oxide-confined VCSELs with intracavity contact.
Bandwidth Enhancement Equalization Enabling a 40-Gbps PAM4 Transmission via a 9.5-GHz Photoreceiver
(2016)
Liu, Jun-Jie
;
Wei, Chia-Chien
;
Tzu, Ta-Ching
;
Chuang, Chun-Yen
;
Chi, Kai-Lun
We demonstrate a 40-Gbps PAM4 optical system by employing a photoreceiver with bandwidth of only 9.5 GHz. Following 100 m multimode fiber, the BER of l. 8 x 10(-4) and 1.2 x 10(-4) after FFE and DFE equalizations are successfully achieved
Modeling of slow light in vertical cavity surface emission lasers
(2007)
Chou, C. -S.
;
Lee, R. -K.
;
Peng, P. C.
;
Kuo, H. C.
;
Lin, G.
We develop a model for the slow light in the Vertical Cavity Surface Emission Lasers (VCSELs), with the combinations of cavity and the population pulsation effects. The dependences of pumping power, injection current and wavelength detuning for the group delays are demonstrated theoretically and experimentally. Up to 65 ps group delays and up to 10 GHz modulation frequency can be achieved in the room temperature at the wavelength of 1.3 mu m. Based on the experimental parameters of quantum dot VCSEL structures, we show that the resonance effect of laser cavity plays a significant role to enhance the group delays.
利用非極性/半極性氮化鎵基板製作氮化鎵垂直共振腔面射型雷射之研究
(2015)
盧廷昌
;
Lu Tien-chang
;
國立交通大學光電工程學系（所）
本計劃主旨在於使用非/半極性氮化鎵基板成長高品質發光層並將之搭配高反射率之分佈式布拉格反射鏡製作出垂直共振腔面射型雷射並進一步探討其中光與物質間的強耦合作用產生的微共振腔極化子之現象。透過半/非極性氮化鎵的特性可以將現有的c軸氮化鎵量子井發光層惱人的量子侷限史塔克效應給降低並去除，此外，半極性氮化鎵(20-2-1)具有窄線寬的特性，對於在氮化鎵微共振腔中觀察到極化子特性有極大的潛力。若是以氮化鎵做磊晶成長的基板，更可以大幅提高磊晶的品質以及降低成長時產生的缺陷製作出高內部量子效率的發光層。垂直共振腔面射型雷射的共振腔屬於微共振腔的一種，可以在其中觀察到極化子的現象，若能藉由適當的設計，更可以利用極化子為波色子的特性達成室溫下的玻色愛因斯坦凝聚態以及極低閾值的極化子雷射。磊晶層的製作將搭配程式模擬先行優化磊晶層參數再行製作。製作完成的元件將搭配一系列的電致發光實驗來驗證使用非/半極性氮化鎵基板成長並製作出的垂直共振腔面射型雷射的優點以及特性。接著利用膜層傳遞矩陣及激子的羅倫茲模型理論模擬，來分析實驗上是否有觀察到極化子的現象。
Control of optical loss in GaN-based planar cavities
(2015-12-01)
Ying, L. Y.
;
Hu, X. L.
;
Liu, W. J.
;
Zhang, J. Y.
;
Zhang, B. P.
Optical losses in GaN-based resonant planar cavity are discussed and experimentally examined in respects of indium tin oxide (ITO) inner-cavity current spreading layer, the defect-rich GaN layer, and multi-quantum well (MQW) active region. Devices with different structures are adopted to study the optical loss. It is demonstrated that a thin ITO layer and a coupled MQW active region are essential to achieve a low loss and high Q-value cavity. The results show that low-loss MQW design is particularly important in fabricating high-Q value GaN-based planar cavities. (C) 2015 Elsevier Ltd. All rights reserved.

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