Sie-Wook Jeon

Thermo-optic coefficient measurement of liquids based on simultaneous temperature and refractive index sensing capability of a two-mode fiber interferometric probe

A fiber-optic interferometric probe based on a two-mode fiber (TMF) is proposed and demonstrated for measuring the thermo-optic coefficients (TOCs) of liquid samples. The proposed probe can be simply fabricated by fusion-splicing a short piece of TMF to a lead single mode fiber (SMF) with small lateral offset, which makes interference between LP(01) and LP(02) modes. The sensing responses of the probe to temperature and surrounding refractive index (SRI) have been experimentally investigated to show the capability of simultaneous measurements; the phase change of the reflection spectrum was related to temperature variation and the intensity change was to SRI variation. The data analysis is made not only in the spectral domain but in the Fourier domain also to effectively quantify the measurements. The TOCs of several liquid samples including water, ethanol, and acetone have been obtained with the proposed method.

OSNR monitoring technique based on cascaded long-period fiber grating with optically tunable phase shifter

An optical signal-to-noise ratio (OSNR) monitoring technique using a cascaded long-period fiber grating with a tunable phase shifter is proposed for non return-to-zero on-off-keying (NRZ-OOK) and differential phase shift keying (DPSK) signals. This method is based on two key points: first, the cascaded long period fiber grating (CLPG) acts as an optical delay interferometer (ODI) by Mach-Zehnder configuration consisting of the core and cladding modes inside the CLPG. Secondly, an optically tunable phase shifter using an Yb3+ doped optical fiber (YDF) is inserted between the CLPG. The phase of the modulated signal propagating along the core mode of YDF is controlled by adjusting pumping power of 976-nm laser diode (LD). By combining the CLPG with the optically tunable phase shifter, the OSNR monitoring could be successfully executed.

Improvement of phosphor modeling based on the absorption of Stokes shifted light by a phosphor

We have found that the emission spectrum of phosphors measured in the powder state differs from that measured for a single phosphor. When the emission spectrum of the powder state is adopted in an optical simulation, the simulated optical properties e.g., the correlated color temperature, color rendering index, and chromaticity coordinates, show a remarkable discrepancy from those of the fabricated LED package. However, the discrepancy is significantly improved when the emission spectrum from a low concentration of phosphor in a silicone binder is employed. We suggest that the discrepancy originates from the absorption of Stokes shifted light by a phosphor.

A Wide Dynamics and Fast Scan Interrogating Method for a Fiber Bragg Grating Sensor Network Implemented Using Code Division Multiple Access

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 με and a low crosstalk of 950:1.

Long-reach transmission experiment of a wavelength division multiplexed-passive optical networks transmitter based on reflective semiconductor optical amplifiers

Sie-Wook JeonYoungbok KimChang-Soo ParkGwangju Institute of Science and TechnologySchool of Information and Communication261 Cheomdan-gwagiro, Oryong-dong500-712, Buk-gu, Gwangju, Republic of KoreaE-mail: pinemint@gist.ac.krAbstract. Wepropose and demonstrate a long-reach wavelength divisionmultiplexed-passive optical networks (WDM-PON) based on reflectivesemiconductor optical amplifiers (RSOAs) with easy maintenance ofthe optical source. Unlike previous studies the proposed WDM-PONuses two RSOAs: one for wavelength-selected light generation to providea constant seed light to the second RSOA, the other for active externalmodulation. This method is free from intensity-fluctuated power penaltiesinherent to directly modulated single-RSOA sources, making long-reachtransmission possible. Also, the wavelength of the modulated signalcan easily be changed for the same RSOA by replacing the external feed-back reflector, such as a fiber Bragg grating, or via thermal tuning. Theseed light has a high-side-mode suppression ratio (SMSR) of 45 dB,and the bit error rate (BER) curve reveals that the upstream 1.25-Gb∕snonreturn-to-zero (NRZ) signal with a pseudo-random binary sequence(PRBS) of length of 2

Polarization-Insensitive Wideband OSNR Monitoring Using Thermally Expanded Core Fiber

We propose the in-band optical signal-to-noise-ratio (OSNR) monitoring method using a Mach-Zehnder interferometer. This interferometer is implemented by inserting a piece of Yb3+-doped optical fiber (YDF) between two strands of thermally expanded core (TEC) fibers: the former to give optical phase delay to one of the two arms (core and cladding modes of the YDF) and the latter to give two arm paths. By using TEC fibers to split the input signal and combine again, the fringe pattern necessary for OSNR monitoring shows polarization independence and wideband characteristics. The phase of the optical signal propagating along the core mode of YDF is changed by flowing a laser light of 976 nm to the core of YDF. Compared with the OSNR measured by optical spectrum analyzer (OSA), the errors are less than 0.5 dB over the OSNR range of 20 dB. Also, the dynamic range showed over 20 dB at the wavelength range of 1541-1566 nm.

UWB triplet pulse generation based on gain switching of RSOA

A simple and feasible techniques for ultra-wideband (UWB) triplet pulse generation based on gain switching of self-seeded reflective semiconductor optical amplifier (RSOA) is proposed and demonstrated. The proposed system consisted of RSOA, erbium doped fiber laser (EDFA), two fiber Bragg gratings (FBGs), and balanced photo detector (BPD). The short pulse train which has a low timing jitters and pulse width was generated based on gain switching of RSOA. The generated optical triplet Gaussian pulse was well match the Federal Communications Commission (FCC) mask in frequency domain. Generated UWB triplet pulse has a fractional bandwidth of about 146% and pulse width of 293ps, respectively.

Fiber Sensor Network for Vessel Monitoring based on Code Division Multiple Access

We propose a multiplexed fiber Bragg grating (FBG) sensor network for vessel monitoring to measure the variation of strain and temperature by environmental perturbation based on code division multiple access (CDMA). The center wavelength of FBG was linearly changed by environmental perturbation such as strain and temperature variation so that we could be monitoring the state of sensors. A RSOA was used as optical broadband source and which was modulated by using pseudo random binary sequence (PRBS) signal. The correlation peak of reflected signal from sensor networks was measured. In this paper, we used the sliding correlation techniques for high speed response and dynamic rage of sensors.

Accuracy-Enhancement of Optical Simulation for a White LED Based on Phosphors

There has been a critical issue in optical simulation of phosphors in LEDs due to their light-reabsorption properties. To improve the accuracy of optical modeling for a white LED package, we utilized the spectrum data of the phosphor-dispersed encapsulant film instead of the phosphor powder. By measuring white LED packages with green and red phosphors, the maximum difference between simulation and experimental results of a color temperature, a color rendition index number and a color coordinate corresponds to , and , respectively. Based on those results, the proposed method can well explain the change of emission spectra of white LEDs with more than two phosphors which introduce the complex optical phenomena such as absorption, reabsorption, light emission, reflection and scattering, etc.

Optical Properties of UV LEDs depending on Encapsulate Method using Silicone Encapsulants with Different Refractive Indices

Optical characteristics including the radiant flux and viewing angle of UV LEDs were investigated according to both silicone encapsulants with different refractive indexes and lens shapes. Lead frame was fabricated using the enhanced heat dissipation characteristics with a heat slug structure and the reflector based on EMC(Epoxy Mold Compound) material. Four types of lens shapes were designed and their optical characteristics depending on the refractive index of silicone encapsulants were evaluated. The maximum radiant flux can be achieved when the height of lens are 1.32mm and 1.08mm for silicone encapsulants with low and high refractive indexes, respectively. Depending on the encapsulating method, the viewing angle changes from to for low refractive index and from to for high refractive index. As a result, it is found that the optical characteristics of UV LEDs can be controled through both encapsulating method and the refractive index of encapsulants.