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We report on technical challenges associated with the use of directly modulated lasers in the mobile fronthaul networks based on radio-over-fiber (RoF) technology. In particular, the effects of dispersion-induced RF power fading and multi-path interference are investigated through theoretical and experimental analyses for the RoF-based transmission system implemented by using directly modulated lasers.

We propose the generation of a high-speed four-level pulse amplitude modulated (PAM4) signal by combining two on-off keying (OOK) signals obtained by overdriving two Mach-Zehnder modulators (MZMs). By using this method, we can overcome the limited modulation bandwidth of the MZM and generate the high-speed PAM4 signal (faster than the PAM4 signal generated by modulating an MZM with a four-level electrical signal). For a demonstration, we generate the 95-Gb/s PAM4 signal by combining two OOK signals obtained from the bandwidth-limited MZM having a 3-dB bandwidth of only 10.5 GHz. In comparison, when we generate the PAM4 signal by using the conventional method, it is not possible to increase the bit rate to be faster than 60 Gb/s. We also successfully demonstrate the transmission of the 95-Gb/s PAM4 signal generated by the proposed method over 4 km of the standard single-mode fiber.

We demonstrate the transmission of 51.56-Gb/s OOK signals over 15 km of SSMF using a 1.55-μm DML. A receiver-side duobinary filter is used together with FFE for the compensation of the bandwidth limitation and fiber dispersion.

We demonstrate the transmission of 51.56-Gb/s on-off keying (OOK) signals generated by using a 1.55-mu m directly modulated laser (DML) over 15-km long standard single-mode fiber. In this experiment, a duobinary electrical equalizer based on a finite-impulse-response filter is used at the receiver to increase the dispersion-limited transmission distance. We evaluate the performances of the 51.56-Gb/s OOK signals with respect to the transmission distance by using the frequency response analysis of the proposed system. This result is used to explain why it is effective to utilize the duobinary equalization (instead of binary equalization) for increasing the transmission distance. (C) 2016 Optical Society of America

We design and fabricate a space-efficient single-mode fiber (SMF) having a diameter of only 82 µm. The results show that this fiber satisfies the optical and mechanical specifications of the ITU-T G.654 recommendation. In comparison to the conventional SMF having a diameter of 125 µm, this fiber can be used to double the spatial efficiency in the space-sensitive system.

We demonstrate a CPRI-based 25.2923-Gb/s optical link by using an electro-absorption modulated laser (EML) for the fronthaul network of LTE-A systems. We modulate the EML in OOK, electrical duobinary, and 4-PAM formats, and evaluate their performances for the fiber dispersion and optical reflections.

We analyze the inter-core crosstalk in homogeneous multi-core two-mode fibers (MC-TMFs) under bent condition by using the coupled-mode equations. In particular, we investigate the effects of the intra-core mode coupling on the inter-core crosstalk for two different types of MC-TMFs at various bending radii. The results show that the inter-core homo-mode crosstalk of LP(11) mode is dominant under the gentle fiber bending condition due to its large effective area. However, as the fiber bending becomes tight, the intra-core mode coupling is significantly enhanced and consequently makes all the inter-core crosstalk levels comparable to each other regardless of the mode. A similar tendency is observed at a reduced bending radius when the difference in the propagation constants between modes is large and core pitch is small.

In patients with tumors and spinal cord lesions, inflammation and tissue infection can result in mass effect detection on imaging. As a result, surgical biopsy procedures are often performed on the lesions. We report a rare case in which the thickening ligamentum flavum (LF) appeared to be a tumor in the epidural space of the cervical spine based on imaging findings. A 52-year-old man visited our outpatient clinic with severe shoulder pain and radicular pain in his right arm that had developed gradually after a traffic accident two months earlier. Magnetic resonance imaging of the cervical spine revealed an extradural mass at the cervicothoracic junction level. Suspecting a tumor, spinal decompression surgery was performed and a biopsy of the mass was obtained. At the time of surgery, the LF was thick and compressed the spinal cord. After successful removal of the LF, the spinal cord appeared normal. Histopathological examination confirmed the mass as the LF. The patient was discharged without pain or weakness two weeks postoperatively. This case demonstrated that when the LF of the cervicothoracic junction is thickened, it may be misdiagnosed as a cervical spine tumor compressing the spinal cord.

We analyze the inter-core crosstalk in a homogeneous multi-core two-mode fiber under bent condition by using coupled-mode equations. The effects of the intra-core mode coupling on the inter-core crosstalk are investigated for various bending radii.

함치성 낭종(dentigerous cyst)은 미맹출치의 치관(crown) 에서 발생하는 병변으로, 치관과 이를 둘러싸는 상피부 사이 에 체액이 축적된 결과로 치아 여포가 확장되어 발생하는 가 장 흔한 발육성 치성 낭종이다. 치성 낭종 중에 치근낭(radicular cyst) 다음으로 두 번째로 흔하며, 상악의 송곳니와 하악의 세 번째 대구치에서 흔히 발생한다. 미맹출치를 둘러싼 함치성 낭종은 흔히 미맹출치를 정상 위치에서 비정상적인 위치로 전 위시키는데, 특히 상악골에서 발생한 경우에는 미맹출치가 상 악동으로 전위되는 경우가 흔하다. 연관된 미맹출치와 함께 낭종을 완전히 제거하는 것이 표준 치료법으로, 상악동에서 발생한 함치성 낭종은 Caldwell-Luc 접근법을 통한 제거법이 현재까지 널리 사용되고 있다. 최근 에는 비강 내 접근법을 통한 내시경적 제거술로 치료한 증례 들이 외국 문헌에 소수 보고되었고, 국내에서도 중비도 상 악동 개방술(middle meatal antrostomy)을 통해 내시경적으 로 제거한 증례가 1예 보고되었다. 저자들은 비강 내 내시경을 이용한 하비도 상악동 개방술로 완전 절제한 상악동 내 함치성 낭종 증례를 경험하였고, 이에 대 한 장기 결과 보고와 더불어 내시경적 비강 내 제거술에 유용한 다양한 비강 내 접근법을 문헌고찰과 함께 보고하고자 한다.

Received October 28, 2010 Revised January 11, 2011 Accepted January 8, 2011 Address for correspondence Young-Jun Chung, MD Department of OtorhinolaryngologyHead & Neck Surgery, Dankook University College of Medicine, 359 Manghyang-ro, Dongnam-gu, Cheonan 330-715, Korea Tel +82-041-550-3974 Fax +82-041-556-1090 E-mail docjung@paran.com Background and ObjectivesZZThere have been some studies performed to evaluate subjective and objective changes after septoplasty and of their correlation, but have reported contradicting results. In this light, this study attempted to evaluate subjective and objective postoperative changes and investigate whether there is any correlation between them. Subjects and MethodZZThis study was performed prospectively in 48 patients who underwent septoplasty and outfracturing of both turbinates. The parameters of subjective nasal patency and acoustic rhinometry (AR) were measured before and after surgery. We evaluated these changes and determined if there exists a correlation between the changes of AR parameters and improvement of subjective nasal patency. ResultsZZMinimal cross-sectional area (MCA) and nasal volume in the convex side of nasal cavity were significantly improved after the surgery (p