• ETRI Journal
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• 제45권2호
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• pp.193-202
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• 2023

We demonstrate the transmission of uncompressed 4K videos over the photonics-based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB-LD). For optical heterodyne mixing and data modulation, a DFB-LD was employed and directly modulated with a 5.94-Gb/s non-return-to-zero signal, which is related to a 6G-serial digital interface standard to support ultra-high-definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB-LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser-to-filter detuning for the adiabatic chirp management of the DFB-LD by the intentional discrepancy between the center wavelength of the optical band-pass filter and the output wavelength of the DFB-LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3-m wireless transmission distance without black frames induced by time synchronization error.

• Journal of the Optical Society of Korea
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• 제12권4호
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• pp.303-308
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• 2008

Directly modulated fiber-optic links generally suffer higher link loss and larger signal distortion than externally modulated links. These result from the electron-photon conversion loss and laser modulation dynamics. As a method to overcome the drawbacks, we have experimentally demonstrated the RF performance of directly modulated, ultra-strong injection-locked gain-lever distributed Bragg reflector (DBR) lasers. The free-running DBR lasers exhibit an improved amplitude modulation efficiency of 12.4 dB under gain-lever modulation at the expense of linearity. By combining gain-lever modulation with ultra-strong optical injection locking, we can gain the benefits of both improved modulation efficiency from the gain-lever effect, plus improved linearity from injection locking. Using an injection ratio of R=11 dB, a 23.4-dB improvement in amplitude response and an 18-dB improvement in spurious-free dynamic range have been achieved.

• Journal of information and communication convergence engineering
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• 제14권3호
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• pp.147-152
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• 2016

In radio-over-fiber (RoF) systems, nonlinear compensation is essential to improve performance. Among the several existing nonlinear compensation techniques, we investigate a predistortion technique for a directly modulated laser in an RoF system. First, we obtain the input-to-output response of a directly modulated laser at 160, 820, and 1,540 MHz. The results show that the laser response is dependent on the frequency band. Second, we design an optimal predistortion circuit to compensate for the nonlinear responses of three frequency bands. We design the predistortion circuit with two options: each predistortion circuit for each frequency band and one single predistortion circuit for all the three frequency bands. Finally, we present the simulation results of the predistortion system obtained using a commercial simulator. These results show that the third intermodulation distortion (IMD3) is improved by 0.6-9 dB for the three frequency bands with only a single predistortion circuit.

• ETRI Journal
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• 제38권2호
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• pp.227-234
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• 2016

Herein, we demonstrate clipping distortion suppression of directly modulated multi-IF-over-fiber links using a simple shunt diode predistorter. The dynamic range of a directly modulated analog fiber optic link is limited by nonlinear distortions caused by laser-diode clipping. We investigate the link performance in the context of carrie-to-noise and distortion ratio (CNDR) and error vector magnitude (EVM) requirements when supporting LTE-A services. We also design an analog predistorter with a shunt-diode structure, and demonstrate experimentally that the predistorter has the ability to suppress clipping-induced third-order intermodulation distortions of the link by at most 14 dB. It also improves the CNDR and EVM of the 4-IF-multiplexed LTE-A carriers by 7 dB and 2.9%, respectively.

• Journal of information and communication convergence engineering
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• 제7권4호
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• pp.556-560
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• 2009

We have investigated the spectral characteristics of semiconductor lasers locked to the external light injected from a modulated laser. study on FM sideband injection locking has shown that when SLs are locked to the target sidebands of the directly modulated ML, the presence of the unselected sidebands influences the resulting microwave signals. The unselected signals can produce the unwanted beat signals around the desired beat signal, which degrade the overall system performance. This analysis way to generate Giga HZ signal generation.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.478-480
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• 2009

This experiment implemented a laser projection system that used the 2D MEMS scanner as the driving method for the display device. The 2D MEMS scanner, which can scan the images horizontally and vertically, was applied to drive the projection system using the interlaced scanning method. The laser was directly modulated to implement the grayscale and the images were WVGA resolution quality.

• 한국광학회:학술대회논문집
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• 한국광학회 2006년도 하계학술발표회 논문집
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• pp.315-316
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• 2006

The modulation bandwidth, wavelength chirp of directly modulated coupled-ring reflector laser diode have been investigated using time-domain modeling. For a specific design, the modulation frequency could be 6 GHz and the frequency chirp could be in the range of $120^{\sim}200$ MHz/mA.

• 한국광학회:학술대회논문집
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• 한국광학회 1989년도 제4회 파동 및 레이저 학술발표회 4th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.214-217
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• 1989

The most attractive feature of semiconductor lasers as sources for coherent optical communication system is the ability to produce frequency modulation by modulation of the bias current. The frequency deviation of semiconductor lasers under direct modulation depends on the laser structure and modulation frequency. This paper describes a circuit modeling techniques for the directly frequency modulated CSP (Channeled Substrated Planner) semiconductor laser. Predictions from this model are compared with the other published results of sinusoidal frequency modulation below than 1 GHz.

• 한국레이저가공학회지
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• 제13권2호
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• pp.6-9
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• 2010

In printed electronics, printing rolls are used to transfer electronic ink onto a flexible substrate. Generally printing rolls are being made by the indirect laser method which is based on the etch process, thus not environment-friendly and not suitable for making a large printing roll. For the pursuit of making a large printing roll for mass printing of electronic devices, we have directly engraved micro-patterns into a Zn plated printing roll using a 30W pulse-modulated fiber laser. We have successfully engraved line patterns ranging from about 15-30${\mu}m$ in width.

• 한국전자통신학회논문지
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• 제18권6호
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• pp.1023-1030
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• 2023

본 논문은 눈, 비, 안개 등 열악한 운용환경에도 강건한 표적검출 특성을 가지는 FMCW LiDAR에 대해서 기술하고 있다. 특히 FMCW LiDAR의 거리 해상도, 가간섭거리 및 최대측정거리 성능에 직접적으로 영향을 미치는 주파수변조레이저의 성능개선에 대해 기술하고 있다. 불평형 Mach-Zehnder 레이저간섭계를 활용하여, 레이저의 발진주파수의 변화율을 실시간 측정하고, 주파수변조 오차를 보정하는 광학식 위상동기루프 기술을 이용한 주파수변조 방법에 대해 기술하였다. 가간섭거리가 긴 레이저 광원을 발진하기 위해 확장공진기형 레이저다이오드를 적용하였으며, 레이저에서 발진되는 주파수 측정을 위해 광집적회로 구조의 레이저간섭계를 적용하였다. 개발된 FMCW LiDAR의 대역폭과 거리해상도는 각각 10.045GHz와 0.84mm로 측정되었다.