• Journal of the Optical Society of Korea
• /
• v.13 no.1
• /
• pp.123-130
• /
• 2009

In this paper, we designed and fabricated an input-output coupler system using two or three volume gratings at 632.8nm wavelength. The additional third grating is added at the output coupler to enhance the overall efficiency. The experimental results show that the total system throughput reaches 63% with two-grating and 75% with three-grating input-output coupler. We also present a design method to obtain the desired output power ratio between the gratings.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.45 no.11
• /
• pp.29-34
• /
• 2008

The propagation characteristics of novel grating-assisted multimode interference (GA-MMI) coupler are explicitly and theoretically investigated by using longitudinal modal transmission-line theory (L-MTLT). The coupling efficiency of GA-MMI coupler is evaluated along the variation of grating thickness and duty cycle, and the spectrum is analyzed numerically. The numerical results reveal that the coupling length and the efficiency of $2{\times}2$ GA-MMI coupler along the variation of grating structure have low tolerance and the bandwidth varies dramatically along the output states.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.2
• /
• pp.221-227
• /
• 2015

The polarization characteristics of nano-scale grating-assisted polarization-insensitive coupler (GA-PIC) consisted of double sandwiched rib-type layers are evaluated in detail by using modal transmission-line theory (MTLT) based on equivalent network. To obtain the polarization-insensitive condition of GA-PIC, the coupling lengths as a function of the refractive index and thickness of sandwiched rib-type layer as well as the grating thickness and period are analyzed for quasi-TE and quasi-TM modes. The numerical results show that the GA-PIC with hundreds of nanometer scale is realized by properly choosing structural and material parameters of double sandwiched layers and grating.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.16 no.2
• /
• pp.241-246
• /
• 2021

In this paper, hydrogenated amorphous silicon(a-Si:H) grating coupler with distributed Bragg reflector(DBR) is proposed to achieve high-efficiency nanophotonic radiator for Light Detection and Ranging(LiDAR) application. The DBR reduces downward leakage of the optical field below the grating region. As a result, the far-field intensity shows about 1.4 times stronger, compared to the common grating coupler without the DBR.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.976-979
• /
• 2002

A focusing grating coupler (FGC) was not fabricated by the 'Continuous Path Control' writing strategy but by an electron-beam lithography system of more general exposure mode, which matches not only the address grid with the grating period but also an integer multiple of the address grid resolution (5 nm), To more simplify the fabrication, we are able to reduce a process step without large decrease of pattern quality by excluding a conducting material or layer such as metal (Al, Cr, Au), which are deposited on top or bottom of an e-beam resist to prevent charge build-up during e-beam exposure. A grating pitch period and an aperture feature size of the FGC designed and fabricated by e-beam lithography and reactive ion etching were ranged over 384.3 nm to 448.2 nm, and $0.5{\times}0.5mm^2$ area, respectively, This fabrication method presented will reduce processing time and improve the grating quality by means of a consideration of the address grid resolpution, grating direction, pitch size and shapes when exposing. Here our investigations concentrate on the design and efficient fabrication results of the FGC for coupling from slab waveguide to a spot in free space.

• Current Optics and Photonics
• /
• v.1 no.5
• /
• pp.514-524
• /
• 2017

We proposed an integrated wavelength-selective photodetector based on a grating-assisted contradirectional coupler and a graphene absorption layer for a coarse wavelength division multiplexing (CWDM) communication system. The center wavelength of the absorption spectrum of the proposed device can be tuned simply by changing the period of the grating, and the proposed device structure is suitable to forming a cascaded structure. Therefore, an array of the proposed device of different grating periods can be used for simultaneous wavelength demultiplexing and signal detection in a CWDM communication system. Our theoretical study showed that the designed device with a grating length of $500{\mu}m$ could have an absorption of 95.1%, an insertion loss of 0.2 dB, and a 3 dB bandwidth of 7.5 nm, resulting in a -14 dB crosstalk to adjacent CWDM channels. We believe that the proposed device array can provide a compact and economic solution to receiver implementation in the CWDM system by combining functions of wavelength demultiplexing and signal detection.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.5
• /
• pp.175-180
• /
• 2019

The optical characteristics and power transfers between guiding channels of blazed grating-assisted directional coupler (B-GADC) are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. To evaluate the coupling efficiency of B-GADC, the dispersion curves as a function of the grating period and wavelength are analyzed numerically for quasi-TE and quasi-TM modes. Furthermore, symmetric, sawtooth and asymmetric grating profiles are considered to know the effect of blazing characteristics on power transfer of GADC. The numerical results show that the grating period for minimum-gap condition to obtain maximum power transfer decreases gradually as the blazed structure changes from symmetric to asymmetric profile. On the other hand, the coupling length increases reversely.

• Proceedings of the IEEK Conference
• /
• 2000.11b
• /
• pp.313-316
• /
• 2000

Concentric-Circle-Grating (CCG) cavity is analyzed by coupled mode theory. In this case concentric grating is acting as both feedback element and output coupler. In our calculations radiation loss terms are included in guided coupled mode equations. The surface-emitted field distribution is obtained in self-consistent manner.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.11 s.116
• /
• pp.1172-1178
• /
• 2006

Measurement of blade strain with sensors directly installed on the blade has one critical issue, how to send the sensor signal to the ground. Strain-gauges have been dominantly used to directly measure stress of a blade and either a slip ring or a telemetry system has to be used to send measured signal to the ground. However, both systems have many inherent problems and sometimes very severe limitations to be practically used. In this paper, new on-line strain monitoring method using. FBG(Fiber Bragg Grating) sensors and a beam coupler is introduced. Measurement of rotor stress using FBG sensors is nothing new, but unlike other system which installs all necessary instruments on the rotor and use telemetry system to send data to the ground, this system makes use of light's unique characteristic - light travels through space. In this new approach, single optical fiber with many FBG sensors is installed on the blade and all other necessary instruments can be installed at ground thereby giving tremendous advantages over slip ring or telemetry system. A reference sensor is also introduced to compensate the beam coupler's transmission loss change due to rotation. The suggested system's good performance is demonstrated with experiments.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.1
• /
• pp.77-82
• /
• 2008

Strain-gauges have been dominantly used to measure strain at various points on a rotor, however, either a slip ring or telemetry has to be used to send sensor signals to data acquisition instruments at stationary side. Both slip ring and telemetry have numerous inherent problems which force severe limitations in real applications. This paper introduces a new rotor condition monitoring system using FBG(Fiber Bragg Grating) sensors and a rotary optical coupler. A single optical fiber with many FBG sensors is installed on the rotor and an optical dynamic interrogator is installed at stationary side. The sensor signal connection between rotating part and stationary part is made by the rotary optical coupling method which makes use of light's unique characteristic-light travels through space. Broad band light source from the interrogator travels to the optical fiber on the rotor and reflected FBG sensor signals travel back to the optical fiber on stationary side and are connected to the interrogator. Rotary optical coupler's insertion loss change due to rotation is compensated by using a reference sensor installed at the center of the rotor. The proposed system's performance has been successfully demonstrated by accurately measuring strains at 5 points on a blade rotating at high speed.