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We evaluate possibility of utilizing the mode-field matched center-launching (MCL) technique in the 850-nm band. For this purpose, we realize the MCL technique by fusion-splicing the HI-780 pigtail fiber of the transmitter to the OM2-type transmission multi-mode fiber (MMF). The results show that we can achieve the high coupling efficiency of >92% by optimizing the splicing conditions such as the arc-discharge duration and fiber-push distance. We confirm that, in the case of utilizing the MCL technique, the frequency-response characteristics of the MMF link becomes almost identical to that of the single-mode fiber (SMF) link. As a result, we could demonstrate the successful transmission of 112-Gb/s four-level pulse amplitude modulation (PAM4) signal operating at 852 nm over 1 km of the OM2-type MMF by utilizing the MCL technique. The performance of this link is measured to be very stable even in the presence of the mechanical perturbations such as fiber bending and fiber shaking.

We evaluate the effects of the external optical feedback on the on-off keying (OOK) and four-level pulse amplitude modulation (PAM4) signals in the single-mode fiber (SMF) link implemented by using a commercial 10G-class 1.55- $\mu \text{m}$ vertical-cavity surface-emitting laser (VCSEL). The results show that the PAM4 signal is much more sensitive to the external optical feedback than the OOK signal. For example, in the back-to-back condition, an error floor is observed at the bit-error rate (BER) of $\sim 8\times 10 ^{\mathbf {-3}}$ for the 10-Gbaud PAM4 signal when we set the optical feedback ratio to be −14 dB. In comparison, the 10-Gbaud OOK signal has a power penalty of only 0.4 dB (@BER $= 5\times 10 ^{-5}$ ) under the same conditions. The results also show that the PAM4 signal becomes more sensitive to the optical feedback after the SMF transmission due to the shallowed BER curve by the fiber dispersion. In addition, we confirm that the effects of the optical feedback are independent of the baud rate. From these results, we conclude that the error-free transmission of the high-speed PAM4 signal cannot be achieved if there is even one bad fiber connector having >2.5% reflection in the VCSEL-based SMF link.

We propose to implement a 2-channel optical-time-division-multiplexed (OTDM) system for short-reach optical interconnects by using a sinusoidally modulated light source instead of a complicated mode-locked laser as an input pulse source. In this system, the OTDM signal is obtained by bit-interleaving two optical return-to-zero (RZ) signals generated by using the sinusoidally modulated light. We operate these RZ signals in the orthogonal in-phase and quadrature domains to avoid the unwanted beat components. After the transmission, the OTDM signal is detected by using single photodetector, and then processed by a 2 × 2 multiple-input multiple-output equalizer. For a demonstration, we generate 150-Gb/s OTDM signal operating in the 8-level pulse-amplitude modulated (PAM-8) format by using commercial LiNbO3 Mach-Zehnder modulators and transmit this OTDM signal over 1.9 km of the standard single-mode fiber (SSMF). In addition, we fabricate the proposed OTDM transmitter in an integrated silicon-photonics chip and use it to demonstrate the transmission of the 64-Gb/s OTDM PAM-4 signal over 2.2 km of SSMF.

We propose to utilize the filtered Gaussian phase dither technique for the effective suppression of the multipath- interference (MPI) noises caused by multiple bad fiber connectors in the mobile fronthaul network (MFN) based on the radio-over- fiber (RoF) technology. We first evaluate the viable performances of the RoF-based MFN in the 5G wireless communication systems by using this technique and deduce the required bandwidth and phase modulation depth of the filtered Gaussian dither signal for the suppression of the MPI noises by numerical simulations. The results show that, by using the proposed technique, it is possible to suppress the MPI noises by ∼10 dB regardless of the number of bad fiber connectors. These simulation results are experimentally verified in the RoF link capable of transporting the 5G wireless signals (i.e., thirty-two 100-MHz orthogonal-frequency-division- multiplexed (OFDM) signals modulated in 64QAM or 256QAM format). We also evaluate the effectiveness of the proposed dither technique in a high-capacity RoF link implemented by using four wavelength-division-multiplexed channels and demonstrate the successful transmission of 128 100-MHz OFDM signals modulated in 256QAM format in the presence of multiple bad connectors.

We propose to utilize the digital optical phase conjugation (D-OPC) technique for the compensation of mode crosstalk in the mode-division-multiplexed (MDM) transmission system. To realize the D-OPC technique, we send the CW light from the receiver side, measure its wavefront at the transmitter side, and then, transmit the phase-conjugated signal to the receiver. By using this technique, we demonstrate the transmission of four LP modes, each carrying 10-Gb/s ON–OFF keying signals, over a 100-m long few-mode fiber link. These signals are detected by using direct-detection receivers with no electrical equalizer. The results show that, by applying the proposed D-OPC technique, we can achieve the bit-error rate of < 10−3 for all four modes.

Although chloramphenicol is currently banned from use in livestock, other phenicols, such as florfenicol and thiamphenicol, have been used for the treatment of bacterial infections in domestic cattle in Korea. This study compares the characteristics of chloramphenicol-resistant Enterococcus faecalis isolated from the bulk tank milk of four major dairy companies in Korea. Although the distribution of multidrug resistance patterns showed no significant differences between the four companies, 85 chloramphenicol-resistant Enterococcus faecalis isolates showed a significantly high number of resistances against five or six antimicrobial classes (37.6%, respectively) (p < 0.05). When analyzing the distribution of phenicol resistance genes, 31 (36.5%) isolates only carried the catA gene, and two (6.3%) isolates from company A only carried the cfr gene. No isolates carried the catB or fexA genes. Regarding the distribution of other resistance genes, both the tetL and tetM (45.9%), ermB (82.4%), and both aac(6″)-Ie-aph(2″)-la and ant(6′)-Ia genes (30.6%) showed a high prevalence, and the optrA and poxtA genes were observed separately, each in only two (2.4%) isolates. Our results confirm that the dissemination of chloramphenicol-resistant Enterococcus faecalis and some antimicrobial resistance genes show significant differences between dairy companies. Therefore, our results support that each dairy company should undertake effective surveillance programs to better understand and minimize the emergence of resistance on a multidisciplinary level.

We proposed to implement a 2-channel OTDM system by using a sinusoidally modulated light source instead of a mode-locked laser. For a demonstration, we transmit 150-Gb/s OTDM-PAM8 signal over 1.9-km long SSMF by using the proposed system.

We demonstrate the transmission of the 84-Gb/s DMT signal over 5 km of SSMF by using an injection-locked 10G-class 1.55-µm VCSEL having a 3-dB bandwidth of only 7.4 GHz.

We demonstrate the transmission of 2×28-Gb/s MGDM OOK signals operating at 852.6 nm over 2.2-km long SSMF. Only two photodetectors are used for the detection of these two MGDM signals with the help of a multiple-input single-output equalizer.

We report on the practical multiplexing techniques applicable to the next-generation ultrahigh-speed data center networks. In particular, we evaluate the feasibility of doubling the transmission capacity of the short-haul direct-detection system cost-effectively by utilizing the optical-time-division-multiplexing (OTDM) and mode-group-division-multiplexing (MGDM) techniques.

We evaluate the performances of 25.78-Gb/s signals modulated in on–off keying and four-level pulse amplitude modulation (PAM4) formats in the 12.2-km long multi-mode fiber (MMF) transmission system implemented by using the mode-field matched center-launching technique, which is realized simply by fusion-splicing the single-mode fiber (SMF)-pigtailed transceivers to the transmission MMF. The results show a serious bit-error rate (BER) fluctuation as well as a large power penalty for the PAM4 signal after the 12.2-km long MMF transmission. We identify that the power penalty and BER fluctuations are caused by the signal-to-interference beat noise generated in the SMF-pigtailed receiver, resulting from the small portion of the signal (~5%) unwantedly carried by the high-order modes of MMF. However, we can suppress this beat noise by replacing the SMF-pigtailed receiver with the MMF-pigtailed one since all modes are orthogonal in MMF. For example, when we utilize this proposed method, the power penalty of the 25.78-Gb/s PAM4 signal measured after the transmission over 12.2 km of MMF is reduced from 3.9 to 0.9 dB (@ BER $= 5\times 10^{-5}$ ). We also demonstrate the transmission of the 56-Gb/s PAM4 signal over 2.3 km of MMF by using this method.

We report on the adaptive cancellation technique of the dispersion-induced composite second-order (CSO) distortions for use in radio-over-fiber (RoF) systems implemented by using directly modulated lasers (DMLs). The proposed technique utilizes the magnitude of the CSO distortions measured at outside the signal’s bandwidth as a cost function of the steepest descent algorithm. As a result, this technique can blindly cancel out the CSO distortions without the necessity of measuring any device and fiber parameters used in the RoF system. The effectiveness of the proposed technique is confirmed in the RoF link implemented by using a 1.55- $\mu \text{m}$ DML and is capable of transporting 24 100-MHz filtered-orthogonal-frequency-division-multiplexing signals in 64 quadrature amplitude modulation format.

We investigate the feasibility of implementing a mobile fronthaul network (MFN) based on the radio-over-fiber (RoF) technology for the fifth generation wireless communication systems cost effectively by using either directly modulated lasers (DMLs) or electroabsorption modulated lasers (EMLs) operating in the 1.55- μ m window. The results show that the performance of the RoF-based MFN implemented by using DMLs is primarily limited by the composite second-order (CSO) distortions arising from the interplay between the DML's adiabatic chirp and fiber's chromatic dispersion. Thus, when we implement the RoF-based MFN by using the currently available commercial DML, its reach could be limited to ∼5 km due to the CSO distortions. To increase this reach, we can utilize the DML having a very small adiabatic chirp (or the optical dispersion compensation or CSO cancelation technique). On the other hand, when we implement the RoF-based MFN by using EML, its performance is limited mostly by the relatively poor linearity and low output power of EML rather than the chirp. For example, if we increase the optical modulation index to compensate for the low output power of EML, the distortions caused by the EML's nonlinear transfer curve can also be increased. Thus, for the use in the RoF-based MFN, it would be highly desirable to increase the output power of EML as much as possible. For a demonstration, we successfully transmit 24 100-MHz-bandwidth filtered orthogonal-frequency-division-multiplexing signals over 20 km of the standard single-mode fiber by using an EML transmitter with 7-dBm output power.

This study aimed to compare the radiological and clinical outcomes of oblique lumbar interbody fusion (OLIF) and posterior lumbar interbody fusion (PLIF) surgeries and to confirm the effects of additional partial laminectomy on the surgical outcomes of OLIF.This retrospective study included 130 patients who underwent OLIF or PLIF for single-level fusion. Among them, 42 patients underwent PLIF and open pedicle screw fixation and 88 underwent OLIF and percutaneous pedicle screw fixation. In the OLIF group, 42 patients received additional neural decompression through partial laminectomy and discectomy (direct OLIF), whereas the remaining 46 patients did not (indirect OLIF). To measure the neurological deficits, the clinical outcomes were evaluated using a visual analog scale for back and leg pain and the Oswestry Disability Index. Radiologic outcomes were evaluated based on the disc and foraminal heights as well as the segmental lordotic and lumbar lordotic angles.The improvement in the clinical outcomes did not differ significantly among the 3 groups. Radiologically, the 2 OLIF groups showed statistically significant improvements in the disc and foraminal heights when compared with the PLIF group. The PLIF group showed a significant decrease in the disc height and segmental lordotic angle when compared with the OLIF group in the postoperative 1-year period.Both OLIF and PLIF showed similar clinical outcomes in the single-level lumbar fusion. However, OLIF grafts showed an advantage over PLIF with respect to the radiographic outcomes and complication rates. Additionally, partial laminectomy did not significantly affect the radiological results.

We propose to implement a simple 2-channel optical-time-division multiplexed (OTDM) system based on a phase-alternating pulse generator for a short-reach optical interconnects. The inserted pulse generator consisting of a phase modulator and an optical periodic filter can generate the optical pulse of which the repetition rate is double the frequency of the input electrical clock. The phase-alternating property of the pulse makes the OTDM signal robust to the chromatic dispersion. In the experiment, we optimize the optical pulse, use it for generating the 200-Gb/s OTDM signal operating in the 4-level pulse-amplitude modulated format, and transmit the signal over the 1.9-km standard single-mode fiber.

We experimentally demonstrate the transmission of 107-Gb/s PAM-4 signal over 25-km long standard single-mode fiber using a commercially available 1.31-μ m directly modulated laser. The limited bandwidth of laser is compensated bv using an electrical equalizer.

We demonstrate the transmission of 230-Gb/s DMT signal over 1.9 km of SSMF in the 1.5-μm IM/DD system by using a pre-chirp Mach-Zehnder modulator having a 3-dB bandwidth of only 22 GHz.

We propose a simple two-channel mode-group-division-multiplexing (MGDM) system operating in the 0.8 µm region over the standard single-mode fiber (SSMF). For the cost-effectiveness, we implement its receiver by using only two photodetectors (PDs) [instead of three PDs required for the detection of the L P 01 , L P 11 a , and L P 11 b modes]. We then detect the signal carried by the L P 01 mode by using a PD and a mode filter. On the other hand, the other signal carried by the L P 11 mode group is detected by using another PD and a multiple-input single-output equalizer (i.e., by subtracting the signal carried by the L P 01 mode from the multiplexed signal). For a demonstration, we transmit 2 × 28 G b / s MGDM on-off keying signal operating at 852.6 nm over 2.2 km of the SSMF by using the proposed technique. The results show that we can achieve the bit-error rate of < 3.8 × 10 − 3 for both the L P 01 and L P 11 modes.

We design a heterogeneous 12-core 4-LP-mode fiber having two different types of cores and trench-assisted graded-index profiles. For the optimum design of the index profiles of these two heterogeneous cores, we first investigate the impacts of various geometric parameters on the effective refractive index of each LP mode, maximum differential modal delay (DMD), and bending losses of the guiding and higher order modes. We then design a heterogeneous 12-core 4-LP mode fiber having a cladding diameter of 242 μm. The numerical analyses based on the coupled-mode equation show that the inter-core crosstalk levels of the proposed fiber are lower than -55 dB/km, regardless of modes, as long as the fiber is not bent tightly with a bending radius of -3 μm-2 and 42.2, respectively.

We explore the possibility of utilizing 1.55- $\mu \text{m}$ directly modulated lasers (DMLs) for optical access networks operating at 28 Gb/s per wavelength. For this purpose, we attempt to maximize the power budgets of 28-Gb/s duobinary and four-level pulse amplitude modulation (PAM-4) signals generated from a DML without using optical amplifiers or optical dispersion compensation modules. For experimental investigation, we set the bias current of the DML far above the threshold current, optimize the extinction ratio of the signals, and utilize the electrical equalization at the receiver. The experimental results show that we can secure power margins of 9.6 and 10 dB after transmission over 40-km long standard single-mode fiber for the duobinary and PAM-4 signals, respectively.

We develop a space-efficient single-mode fiber (SMF) having a cladding diameter of only 82 μm. This SMF has the depressed-cladding index profile and its mode-field diameter, cutoff wavelength, and macro bending loss are designed to be similar to those of the conventional step-index SMF. We fabricate this reduced-cladding SMF and measure its optical and mechanical characteristics. The results show that this fiber satisfies major specifications of the ITU-T G.654 recommendations. We also fabricate a fiber ribbon by using twelve of these reduced-cladding SMFs. Compared to a commercial fiber ribbon made of twelve standard SMFs having 125-μm cladding diameter, this fiber ribbon can improve the spatial efficiency by ∼75%.

We demonstrate the mitigation of MPI noises in the RoF-based mobile fronthaul network by using high-frequency phase dither. By using this technique, we could transport thirty-two 97.2-MHz OFDM signals in 64 QAM even when the SIR was only 20 dB.

We demonstrate a 4-channel mode-division-multiplexed (MDM) system by compensating the mode crosstalk using the digital optical phase conjugation technique.

We evaluate the requirements of the chirp parameters of the directly modulated lasers, which are used for the cost-effective implementation of the RoF-based mobile fronthaul network of the 5G system.

We propose and demonstrate a common public radio interface (CPRI)-compliant 25.2923-Gb/s mobile fronthaul network for long term evolution-advanced (LTE-A) systems. In order to meet the CPRI specifications and the stringent latency requirement of the LTE-A fronthaul network cost-effectively, we use the synchronous time-division-multiplexing, forward-error correction, and electrical equalization techniques. To enhance the cost-effectiveness, we also use an electroabsorption-modulated laser and exploit the possibility of using simple modulation formats such as the ON–OFF keying, electrical duobinary, and four-level pulse amplitude modulation. The performance of the proposed network is evaluated experimentally in terms of the tolerances to fiber dispersion and optical reflection.

We propose a DSP-based nonlinearity compensation technique for RoF links which does not require any prior knowledge about the links. By using this technique, we successfully transport twelve 198-MHz-bandwidth 64-QAM f-OFDM signals over 20 km of SSMF.

We propose and demonstrate the compensation of mode coupling in MDM systems by using the digital optical phase conjugation technique. We achieve BERs better than 10-4 without electrical MIMO processing in a FMF link having large mode coupling.

We demonstrate the transmission of twelve 360-MHz filtered-OFDM signals in 64-QAM format over 20 km of SSMF by using a 1.55-µm directly modulated laser and a DSP-based composite second-order cancellation technique.

We examine the feasibility of utilizing RoF-based fronthaul network for the next-generation mobile communication systems. For this purpose, we evaluate the effects of the dispersion-induced RF power fading, CSO distortions induced by the interplay between the laser chirp and fiber dispersion, and MPI noises induced by optical reflections, etc.

We propose a novel carrier phase estimation method for the high-speed coherent WDM PON based on the reflective semiconductor optical amplifier (RSOA). By using this method, we can utilize a cost-effective DFB laser as the seed light in such a network due to its fast trackability. We experimentally achieve an excellent receiver sensitivity of −30.8 dBm even when a DFB laser (linewidth: 3 MHz) is used as a seed light source in the 25.78-Gb/s upstream QPSK transmission over 20 km of SSMF.

Objective Recently, many studies have reported that cervical alignment is related to clinical outcomes. However, poor visibility of anatomical structures during X-ray (XR) imaging limits accurate measurements. In supine magnetic resonance (MR) imaging, the boundary of the anatomical structure is clear, but the correlation to XR images taken in a standing position is problematic. In this study, we evaluated the agreement of sagittal alignment parameters between MR and XR measurements. Methods We retrospectively reviewed 268 patients. Cervical sagittal parameters were measured using XR and MR images, and their relationships were evaluated using Pearson's correlation, paired t-tests, and 2-way random, single score intraclass correlation coefficient (ICCs) (2,1). Using simple linear regression analysis, MR results were converted to the expected value (MR-E). The subsequent comparison of MR-Es with XRs was used to examine whether MR-Es could replace XRs when the measurement difference was less than 2 mm or 2°. Results The correlation between the MR and XR measurements was high, but ICCs showed low reliability. All parameters were significantly different between XR and MR measurements in paired t-tests. Converting the MR values eliminated the t-test differences between MR-Es and XRs, but did not affect correlations and ICCs. The replacement ratio included the Cobb angle: 20.3%, T1: 27.1%, the sagittal vertical axis: 17.6%, C1–2: 29.7%, and C2: 16.0%. Conclusion These results indicate that supine MR measurements could not replace upright XR measurements.

We demonstrate the transmission of 56-Gb/s PAM-4 signal over 20-km long SSMF by using a 1.55-μm DML without optical dispersion compensation. Instead, a linear electric equalizer is used for the compensation of dispersion-induced waveform distortions.

We propose and demonstrate a simple composite second-order (CSO) cancellation technique based on the digital signal processing (DSP) for the radio-over-fiber (RoF) transmission system implemented by using directly modulated lasers (DMLs). When the RoF transmission system is implemented by using DMLs, its performance could be limited by the CSO distortions caused by the interplay between the DML's chirp and fiber's chromatic dispersion. We present the theoretical analysis of these nonlinear distortions and show that they can be suppressed at the receiver by using a simple DSP. To verify the effectiveness of the proposed technique, we demonstrate the transmission of twenty-four 100-MHz filtered orthogonal frequency-division multiplexing (f-OFDM) signals in 64 quadrature amplitude modulation (QAM) format over 20 km of the standard single-mode fiber (SSMF). The results show that, by using the proposed technique, we can suppress the CSO distortion components by > 10 dB and achieve the error-vector magnitude performance better than 6% even after the 20-km long SSMF transmission. (C) 2017 Optical Society of America

There have been substantial efforts to implement high-speed (> 10 Gb/s) upstream transmission using reflective semiconductor optical amplifiers (RSOAs) in a coherent wavelength-division-multiplexed (WDM) passive optical network (PON). In such a network, it is necessary to estimate the carrier phase of upstream optical signal to retrieve the phasemodulated information created by RSOA. However, due to the severe waveform distortions caused by the limited modulation bandwidth of RSOA (typically less than 3 GHz), previously reported carrier phase estimation (CPE) algorithms cannot accurately estimate the carrier phase of high-speed quadrature phase-shift keying (QPSK) signal generated from the RSOA seeded by a distributed-feedback (DFB) laser. We propose a novel CPE method capable of tracking the carrier phase rapidly by using a small number of symbols (e.g., 15 symbols) even when the waveforms are severely distorted by the limited modulation bandwidth of RSOA. The proposed CPE method utilizes the linear relationship between the intensity modulation and phase modulation indices inherent in the semiconductor opto-electronic device. By using the proposed method, we demonstrate the transmission of 25.78-Gb/s QPSK signal in a 20km long loopback fiber link. In this experiment, a commercial DFB laser (linewidth: 3 MHz) is used as the seed light instead of an expensive narrow-linewidth laser. Also shown through the experiment is that the proposed CPE method is highly unsusceptible to variations of parameters required in the proposed method, such as the number of test phases, the accuracy of linewidth enhancement factor, and the accuracy of the normalized amplitude of DC component. (C) 2017 Optical Society of America