Hyoung-Jun Park

Low-cost 1×2 plastic optical beam splitter using a V-type angle polymer waveguide for the automotive network

The design, fabrication, and characteristic of the plastic optical fiber (POF), beam splitter, for the automotive network, has been demonstrated. The fabricated 1×2 POF beam splitter consisted of a poly(methylmethacrylate) (PMMA) core, which had a structure of circular waveguide and a diameter of 0.98 mm, UV curable epoxy (PC-414) clading of 0.02 mm thickness, and three POF pigtails with multimedia oriented system transport standard ferrules. A 1×2 PMMA waveguide, which was designed to have an optimal angle of 15.8 deg at the beam splitting point, was fabricated using the injection molding method for mass production. The total volume of the fabricated 1×2 POF beam splitter is 48×18×12 mm3 with 1.2 m length input and output POF pigtails. From the measurement results, we experimentally confirm that the fabricated 1×2 POF beam splitter has excellent properties such as a beam splitting ratio of 50:50 ± 10 % and excess loss of less than 3.52 dB and it works well up to 250 Mbps for the automotive network.

Awareness system for bowel motility estimation based on artificial neural network of bowel sounds

Awareness system of bowel motility estimation based on an artificial neural network (ANN) model of bowel sounds obtained by an auscultation was devised. Twelve healthy males and 6 patients with delayed bowel motility were examined. BS signals generated during the digestive process were recorded from 3 colonic segments (ascending, descending and sigmoid colon), and then, the acoustical features (jitter and shimmer) of the individual BS segment were obtained. Only 6 features (J1,3, J3,3, S1,2, S2,1, S2,2, S3,2) highly correlated to the conventional colon transit time (CTT) were used as the features. Through k-fold cross validation, the correlation coefficient and mean average error between the CTTs and the values estimated by our algorithm were 0.89 and 10.6 hours, respectively. The devised system showed good potential for the continuous monitoring and estimating the bowel motility, instead of conventional radiography, and thus, it could be used as an awareness tool for the non-invasive measurement of bowel motility.

Doppler Frequency Offset Estimation in OFDM systems

This paper presents frequency offset estimation algorithm in wireless OFDM cellular system such as 3G-LTE [1]. We first analyze the method of frequency offset estimation in general OFDM system. The analysis will show that the value of frequency offset estimation in cell boundary is inaccurate. Because doppler frequencies of signals transmitted from different base stations are different, the error of frequency offset estimation value is generated. We show how proposed algorithm can reduce the error of frequency offset estimation. Results of simulation show that the utilization of proposed algorithm can reduce the error of frequency offset estimation considerably. Proposed frequency offset estimation algorithm can increase overall system capacity because of performance improvement in cell boundary. Especially, 16-QAM or 64-QAM modulations for high data rate transmission is extremely sensitive to frequency offset, therefore proposed algorithm increases channel capacity for user in cell boundary.

1/10 Gb/s single transistor-outline-CAN bidirectional optical subassembly for a passive optical network

Abstract. We propose a novel, low-cost bidirectional optical subassembly (BOSA) that uses a single glass-sealed conventional transistor-outline (TO)-CAN package for passive optical network application. In this BOSA, optical transmitting and receiving functions are incorporated into a silicon optical bench and in a TO-CAN package, respectively. With these features, the optical and electrical crosstalk is efficiently suppressed. The single TO-CAN BOSA has an extinction ratio of 11.69 dB and output power of 2.93 dBm for 1.25  Gb/s operation. The penalty of optical dispersion is 1.2 dB after 20-km single-mode fiber transmission. The receiver sensitivity is less than −30  dBm at a bit error rate of 10−3 for 10.3  Gb/s operation and the signal crosstalk penalty of a single TO-CAN BOSA is 0.8 dB.

Enhanced optical coherence tomography imaging using a histogram-based denoising algorithm

Abstract. A histogram-based denoising algorithm was developed to effectively reduce ghost artifact noise and enhance the quality of an optical coherence tomography (OCT) imaging system used to guide surgical instruments. The noise signal is iteratively detected by comparing the histogram of the ensemble average of all A-scans, and the ghost artifacts included in the noisy signal are removed separately from the raw signals using the polynomial curve fitting method. The devised algorithm was simulated with various noisy OCT images, and >87% of the ghost artifact noise was removed despite different locations. Our results show the feasibility of selectively and effectively removing ghost artifact noise.

A timing synchronization design in OFDM systems

This paper presents time synchronization algorithm in OFDM system. We first analyze the impact of channel estimation performance when synchronization time drifts in general OFDM system. The analysis will show that channel estimation performance is degraded in transient region of time synchronization. When channel estimation process is initialized, channel estimation performance is degraded. This is because that channel estimation process should be initialized when synchronization time is changed. We then show how proposed algorithms can reduce the performance degradation of channel estimation. Results of simulation show that the utilization of proposed algorithms can reduce the performance degradation of channel estimation. Proposed algorithms can be utilized in both high speed and low speed OFDM system. Above all, the use of proposed algorithms prevents burst error that is harmful for general communication network system.

Fiber-optic current sensor using an internal trigger sampling technique

We present an advanced demodulation technique for a fiber-optics interferometric current transducer. A quadrature sampling method with internal triggers was adopted for structural simplification and cost-effective phase demodulation. The internal triggers for quadrature signal processing were generated at zero crossing points of an ac-coupled reference signal, which was distinguished from the current-induced interference signal by utilizing fiber Bragg grating. Phase variation was extracted from the arctangent demodulation process. The proposed technique demonstrated accurate and stable phase demodulations performance and better than that of the conventional lock-in amp demodulation.

Fully passive-alignment pluggable compact parallel optical interconnection modules based on a direct-butt-coupling structure for fiber-optic applications

Abstract. A low-cost packaging method utilizing a fully passive optical alignment and surface-mounting method is demonstrated for pluggable compact and slim multichannel optical interconnection modules using a VCSEL/PIN-PD chip array. The modules are based on a nonplanar bent right-angle electrical signal path on a silicon platform and direct-butt-optical coupling without a bulky and expensive microlens array. The measured optical direct-butt-coupling efficiencies of each channel without any bulky optics are as high as 33% and 95% for the transmitter and receiver, respectively. Excellent lateral optical alignment tolerance of larger than 60  μm for both the transmitter and receiver module significantly reduces the manufacturing and material costs as well as the packaging time. The clear eye diagrams, extinction ratios higher than 8 dB at 10.3 Gbps for the transmitter module, and receiver sensitivity of better than −13.1  dBm at 10.3 Gbps and a bit error rate of 10−12 for all channels are demonstrated. Considering that the optical output power of the transmitter is greater than 0 dBm, the module has a sufficient power margin of about 13 dB for 10.3 Gbps operations for all channels.

Real-time surface tracking system using common-path spectral domain optical coherence tomography

Abstract. An enhanced surface tracking system based on optical coherence tomography (OCT) modality has been developed and tested for use in a surgical guidance system. A surface detection algorithm based on a Savitzky-Golay filter of A-scan data and thresholding was applied to real-time depth tracking. The algorithm output controlled a motorized stage to adjust the probe position according to the sample’s topological variance in real-time. As a result, the root mean square error (RMSE: 4.2 μm) of our algorithm was relatively lower than the conventional method (RMSE: 16.6 μm). Also, OCT images obtained using the algorithm showed a significantly extended imaging range and active surface tracking in real time. Consequently, the devised method demonstrated potential for use in systems for guiding surgical robots and endoscopic OCT.

A hybrid fiber-optic sensor system for multi-stress monitoring of high-voltage power transformer

For condition monitoring of high-voltage power transformers, a fiber-optic multi-stress sensing system is suggested by combining fiber grating sensors and mandrel sensors embedded in a fiber-optic Sagnac interferometer. The gratings and the mandrel sensors measure the temperature and the vibrations at multi-locations in a power transformer. To separate and demodulate the sensor outputs, we used a wavelength-sweeping laser source and placed a fiber-optic attenuator in the Sagnac loop, which enabled to separate the Bragg wavelengths from the transmission spectrum. The temperature and vibrations of multi-locations could be measured at the same time by using optical circuit and single signal processing unit.