Youngbok Kim

Q-switching of Yb3+-doped fiber laser using a novel micro-optical waveguide on microactuating platform light modulator.

We report a novel micro-optical waveguide (MOW) on microactuating platform (MAP) light modulator for Q-switched all-fiber laser applications. The light modulator employs a fused biconical taper (FBT) coupler, which acts as MOW, mounted on an electromechanical system, MAP, where an axial stress over the waist of FBT coupler is precisely controlled to result in modulation of output power. The modulator was implemented in a clad pumped Yb3+-doped fiber laser cavity as a Qswitching element. Q-switching was successfully achieved at the repetition rate of 18.6kHz and average pulse energy of 1.4microJ. The proposed structure can be readily applied in power scaling up of all-fiber Q-switching laser systems.

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

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.

Multiple fiber Bragg grating sensor network with a rapid response and wide spectral dynamic range using code division multiple access

Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was used. The proposed method improves the code interference and it also has advantages such as a large number of sensors, continuously measuring individual sensors, and decreasing the complexity of the sensor network.

A tunable photonic microwave notch filter using a self-injection locked reflective semiconductor optical amplifier

We propose a tunable photonic microwave notch filter using a self-injection locked reflective semiconductor optical amplifier (RSOA) and fiber Bragg gratings. Tunable filter characteristic is obtained by changing the center wavelength of one of the gratings. The achievable tuning range is determined by the gain profile of the RSOA and the tuning range of the grating.

Novel strain and temperature sensor network based on self-injection locked reflective semiconductor optical amplifier

We propose a serialized sensor network using a reflected SOA (RSOA) as a low-cost and wideband source. The RSOA is self-injection locked by the FBG sensors with different center wavelengths. By reading the wavelength shifts, the number of sensors up to 32 can be monitored with the side mode suppression ratio of >27 dB within 4 km.

Integrated all-fiber variable optical attenuator based on index-guiding holey fiber

We report an integrated all-fiber variable optical attenuator (VOA) for dynamic control of a device by achieving optimized taper and axial compression of an index-guiding holey fiber. We experimentally demonstrate a VOA device with dynamic ranges of 18 dB over the spectral range from 1450 to 1650 nm and a low insertion loss of 0.5 dB.

Hard polymer clad fiber (HPCF) optical components for high-speed short reach passive optical networks

We report a 4x4 HPCF coupler, HPCF pigtailed VCSEL and PIN PD with a low insertion loss and coupling loss, which can be readily applied in high speed short reach PON.