Eigen-function division multiplexed coherent optical transmission in time domain by using higher-order Hermite-Gaussian pulses.

We describe a new multiplexing technique and its application to demultiplexing in the time domain by using higher-order Hermite-Gaussian (HG) pulses, which are solutions of the Schrödinger equation. We call this technique eigen-function division multiplexing (EDM). This method enables us to further increase the total transmission capacity by superimposing many different HG pulses in the same time slot. This technique is different from a conventional optical time domain multiplexing (OTDM) technique using interleaving, where one pulse exists only in one time slot. The transmitted EDM HG pulses can be demultiplexed by adopting the time-domain orthogonality of the HG pulses (eigen-function orthogonality). The information carried by the mth-order HG pulse (HGm pulse) can be coherently detected by a photo detector, where photo-mixing with a phase-locked HGm pulse generated by a local oscillator can realize demultiplexing. The overlap integral with a different HG pulse becomes zero due to the time domain orthogonality. First, we show numerically that such a new EDM transmission scheme in the time domain is possible. We then show experimentally that we could successfully carry out an EDM HG coherent pulse transmission with four different HG pulses (HG0, HG1, HG2, and HG3), where we report a 400∼480 Gbit/s (10 Gbaud x 4 eigen-functions x 2 pol-mux.) 32∼64 QAM EDM transmission over 300∼450 km.

Coherent Nyquist optical pulse transmission at nearly 1-Tb/s/λ over 1,600 km with a capacity of 21.5 Tb/s using PS-32 QAM signals.

We demonstrate the 1,600-km transmission at nearly 1-Tb/s/λ signals with a capacity of 21.5 Tb/s. Probabilistic shaping was newly applied to high-speed coherent optical Nyquist pulse transmission systems to maximize the transmission capacity. Employing a 160-GBd PS-32 QAM format, WDM signals at nearly 1-Tb/s/λ were successfully transmitted over 1,600 km with a capacity of 21.5 Tb/s.

Efficacy of all-inside devices in reducing gap and step-off in knee extension for ramp lesion repair: A cadaveric study.

PURPOSE: The aim of this study is to assess the dynamics of the tear site of meniscal ramp lesions, particularly considering knee flexion angles, and validate anchor fixation using an all-inside device. METHODS: Eight Thiel-embalmed paired cadaveric knees with their whole bodies were used in this study. The ramp lesions were created arthroscopically, and ramp lesion dynamics were evaluated by gradually extending the knee from 90° of knee flexion. Changes in the gap and step-off (0: no step-off; 1: cross-sectional overlap exists; and 2: tibial articular surface exposed) were evaluated at 90°, 60°, 30°, and 10° of knee flexion. After dynamic evaluation, all-inside repairs of the ramp lesions using all-inside devices were conducted. Dissection was performed to confirm the position of anchor fixation. RESULTS: As the knee was extended, the gap significantly decreased at all knee flexion angles. Similarly, the step-off grade decreased as the knee was extended, and the step-off completely disappeared in all cases when the knee was extended from 30° to 10°. The average knee flexion angle at which the gap and step-off completely disappeared was 22.5°. After suturing the ramp lesion, arthroscopic evaluation showed that the gap had disappeared and the step-off had been repaired in all cases. Anchor fixation locations were not found within the joint but were fixed to the semimembranosus tendon or its surrounding articular capsule. Overall, 31% (5/16) anchors were fixed to the attachment site of the semimembranosus tendon, whereas the remaining were fixed to the articular capsule, located peripherally to the semimembranosus tendon. CONCLUSION: Suturing with an all-inside device for ramp lesions is a good option, and the repair in knee extension was found to be reasonable, considering the dynamics of ramp lesions in this study. LEVEL OF EVIDENCE: Level IV.

Can Machine Learning Identify the Intravenous Contrast Dose and Injection Rate Needed for Optimal Enhancement on Dynamic Liver Computed Tomography?

OBJECTIVES: This study aimed to investigate whether machine learning (ML) is useful for predicting the contrast material (CM) dose required to obtain a clinically optimal contrast enhancement in hepatic dynamic computed tomography (CT). METHODS: We trained and evaluated ensemble ML regressors to predict the CM doses needed for optimal enhancement in hepatic dynamic CT using 236 patients for a training data set and 94 patients for a test data set. After the ML training, we randomly divided using the ML-based (n = 100) and the body weight (BW)-based protocols (n = 100) by the prospective trial. The BW protocol was performed using routine protocol (600 mg/kg of iodine) by the prospective trial. The CT numbers of the abdominal aorta and hepatic parenchyma, CM dose, and injection rate were compared between each protocol using the paired t test. Equivalence tests were performed with equivalent margins of 100 and 20 Hounsfield units for the aorta and liver, respectively. RESULTS: The CM dose and injection rate for the ML and BW protocols were 112.3 mL and 3.7 mL/s, and 118.0 mL and 3.9 mL/s ( P < 0.05). There were no significant differences in the CT numbers of the abdominal aorta and hepatic parenchyma between the 2 protocols ( P = 0.20 and 0.45). The 95% confidence interval for the difference in the CT number of the abdominal aorta and hepatic parenchyma between 2 protocols was within the range of predetermined equivalence margins. CONCLUSIONS: Machine learning is useful for predicting the CM dose and injection rate required to obtain the optimal clinical contrast enhancement for hepatic dynamic CT without reducing the CT number of the abdominal aorta and hepatic parenchyma.

Broadband injection-locked homodyne receiver for digital coherent transmission using a low Q Fabry-Perot LD.

We describe the broadband injection-locking performance of a Fabry-Perot laser diode (FP-LD) for digital coherent transmission. The dynamic locking bandwidth of the FP-LD was as wide as 28.8 GHz, which makes it possible to achieve precise carrier-phase synchronization with extremely low phase noise over a wide frequency range. By applying the FP-LD as an LO in an injection-locked homodyne receiver for digital coherent quadrature amplitude modulation (QAM) transmission, we demonstrate, for the first time, the precise demodulation of 3, 10 and 20 Gbaud 256 QAM signals even when using a widely and randomly phase-modulated transmitter laser. This is attributed to the excellent wideband dynamic injection-locking characteristics of the FP-LD.

Spectrally efficient pilot tone-based compensation of inter-channel cross-phase modulation noise in a WDM coherent transmission using injection locking.

We propose the precise and wideband compensation of the nonlinear phase noise caused by cross-phase modulation (XPM) among WDM channels using a pilot tone (PT) and injection locking for short-reach, higher-order QAM transmission. A high spectral efficiency is maintained by sharing a single PT among multiple channels. We describe a 60 ch, 3 Gbaud PDM-256 QAM transmission over 160 km, where the bit error rate was improved from 6 × 10-3 to 2 × 10-3 by employing the proposed XPM compensation technique, with a spectral efficiency of 10.3 bit/s/Hz. We also analyze the influence of the group delay caused by fiber chromatic dispersion that determines the compensation range achievable with a single PT. We obtained good agreement with the experimental results.

Chromatic dispersion dependence of GAWBS phase noise compensation with pilot tone.

We describe experimental and numerical results regarding the influence of chromatic dispersion in optical fibers on guided acoustic-wave Brillouin scattering (GAWBS) phase noise compensation with a pilot tone (PT). We compared the compensation performance for GAWBS phase noise generated in an ultra-large-area fiber (ULAF) where DULAF = 21 ps/nm/km with that in a dispersion-shifted fiber (DSF) where DDSF = -1.3 ps/nm/km and found that the performance depends strongly on chromatic dispersion. The numerical analysis shows that the group delay between the signal and PT caused by chromatic dispersion reduces the GAWBS noise correlation between them, which degrades the compensation performance for GAWBS phase noise. It is clarified that a condition for effective GAWBS compensation is that the group delay between the signal and PT should be less than half the period of the GAWBS phase noise component.

GAWBS phase noise characteristics in multi-core fibers for digital coherent transmission.

We describe the guided acoustic-wave Brillouin scattering (GAWBS) phase noise characteristics in multi-core fibers (MCFs) used for a digital coherent optical fiber transmission both experimentally and analytically. We first describe the GAWBS phase noise in an uncoupled four-core fiber with a 125 µm cladding and compare the phase noise spectrum with that of a standard single-mode fiber (SSMF). We found that, unlike SSMF where the R0,m mode is dominant, off-center cores in MCF are affected by higher-order TRn,m modes. We then report measurement results for GAWBS phase noise in a 19-core fiber with a 240 µm cladding. The results indicate that the cores exhibit different spectral profiles depending on their distance from the center of the fiber, but the amount of phase noise generated in each core is almost identical. These results provide a useful insight into the space division multiplexing transmission impairments in digital coherent transmissions using MCF.

Precise measurements and their analysis of GAWBS-induced depolarization noise in various optical fibers for digital coherent transmission.

We undertake precise measurements of guided acoustic wave Brillouin scattering (GAWBS) depolarization noise caused by the TR2,m mode (torsional and radial mode) in various fibers and analyze the results. And we describe the influence of the noise on digital coherent transmission. We first show that the TR2,m mode is distributed over a wider bandwidth when the effective core area Aeff of the fiber is smaller. We then describe the strong mode-number dependence of the depolarization power generated from the profile of the refractive index change induced by the TR2,m mode. We also use two methods to measure the polarization crosstalk (XT) induced by the depolarization, namely, a direct detection method with a photodiode and a conventional power detection method with an optical spectrum analyzer. The results of the two methods agree well, and the XT increase is inversely proportional to the fiber Aeff and proportional to fiber length. Finally, we evaluate the influence of the GAWBS-induced XT on the BER characteristics in a coherent QAM transmission, where we find that the influence of the TR2,m mode is much weaker than that of the R0,m mode (radial mode). That is, the error-free transmission distance in standard single-mode fiber is extended to 8600 km for 256 QAM signal assuming hard-decision FEC with a 7% overhead. This distance is seven times longer than that obtained with the R0,m mode.

Injection-locked 256 QAM WDM coherent transmissions in the C- and L-bands.

We demonstrate WDM 256 QAM coherent transmissions with injection locking in the C- and L-bands and compare the transmission performance in the two bands. Although four-wave mixing (FWM) is more significant in an L-band EDFA than in a C-band EDFA, the FWM did not accumulate through the transmission and the FWM components were hidden by the ASE noise level. Since the FWM was weakened by the decorrelation of the WDM signals during the transmission, the transmission performance in the L-band was the same as that in the C-band. The injection locking circuit enabled precise carrier-phase synchronization between a data signal and a local oscillator regardless of the transmission band. By using this circuit, we successfully transmitted 58.2 and 57.6 Tbit/s 256 QAM WDM signals over 160 km with a spectral efficiency of 12 bit/s/Hz in the C- and L-bands, respectively.

Theoretical and experimental analyses of GAWBS phase noise in various optical fibers for digital coherent transmission.

We describe the fiber structural dependence of guided acoustic-wave Brillouin scattering (GAWBS) phase noise in a digital coherent optical fiber transmission. We present theoretical and experimental analyses of GAWBS phase noise spectra in three types of optical fibers and show that the GAWBS resonant modes are distributed over a wider bandwidth as the effective core area of the fiber becomes smaller. We also use a vector signal analysis to show phase fluctuations caused by GAWBS. On the basis of these analyses, we show that the GAWBS phase noise fluctuation has a Gaussian distribution, which is used to evaluate its influence on the BER characteristics in a coherent QAM transmission. As a result, we found that the error-free transmission distance in SSMF is limited to 4600, 1200, and 340 km with 64, 256, and 1024 QAM, respectively, assuming a hard-decision FEC with a 7% overhead. These results provide useful insights into the influence of GAWBS on digital coherent transmission.

Efficient synthesis of tert-butyl 3-cyano-3-cyclopropyl-2-oxopyrrolidine-4-carboxylates: Highly functionalized 2-pyrrolidinone enabling access to novel macrocyclic Tyk2 inhibitors.

Herein we report an efficient method for the synthesis of a highly functionalized 2-pyrrolidinone, tert-butyl 3-cyano-3-cyclopropyl-2-oxopyrrolidine-4-carboxylate, from readily available starting materials. Utility of this compound was demonstrated in the synthesis of a novel series of macrocyclic Tyk2 inhibitors, leading to the identification of a potent and selective macrocyclic Tyk2 inhibitor (26).

[Comparison of Contrast Enhancement between Bolus-tracking and Test-bolus Methods on Coronary CT Angiography].

PURPOSE: To compare the contrast enhancement between bolus-tracking (BT) and test-bolus (TB) methods in coronary computed tomography angiography (CCTA). METHOD: We enrolled 300 patients who underwent CCTA by BT (245 mg I/kg main bolus) or TB (77.4 mg I/kg test bolus with 245 mg I/kg main bolus) methods. In group BT (n=150), scanning was started automatically 5-second after contrast enhancement exceeded a predefined threshold of 150 Hounsfield units (HU). In group TB (n=150), TB peak attenuation plus 2-second was used as a delay. We recorded the CT number in the ascending aorta and determined whether the CT number was equivalent in two groups. For the equivalence test, we adopted 70 HU as the equivalence margin. The standard deviation (SD) in the CT number and the rate of patients with an acceptable CT number were compared. We also compared total iodine dose and total dose length product (DLP). RESULT: The CT number of the ascending aorta was 437.6±68.9 HU in group BT and 438.9±69.7 HU in group TB; the 95% confidence interval for the difference between the groups was from -11.6 to 20.2 HU and within the range of the equivalence margins. The SD of the CT number and the rate of patients with acceptable CT number did not differ significantly between the two groups (p=0.857 and p=0.614, respectively). Total iodine dose in group TB was significantly higher than in group BT (p<0.001), and total DLP was not statistically significant (p=0.197). CONCLUSION: The contrast enhancement between BT and TB methods in CCTA was equivalent, and the distribution was not significantly different between the two groups.

Suppression of large error floor in 1024 QAM digital coherent transmission by compensating for GAWBS phase noise.

There is a large error floor in an ultra multi-level digital coherent transmission signal of 1024 QAM or higher, and we have yet to determine its origin. In this paper, we show that this large error floor results from guided acoustic-wave Brillouin scattering (GAWBS) phase noise. We prove experimentally that such an error floor can be greatly reduced by compensating for the GAWBS noise with a phase modulation technique. We show that the BER of a 1024 QAM signal was reduced from 8.7 × 10-4 to 2.7 × 10-4 after a 160 km transmission with GAWBS noise compensation. Furthermore, we successfully extend the transmission distance from 160 to 240 km with a 7% overhead forward error correction.

Single-channel 15.3 Tbit/s, 64 QAM coherent Nyquist pulse transmission over 150†km with a spectral efficiency of 8.3 bit/s/Hz.

We report the first single-channel 15.3 Tbit/s, 1.28 Tbaud, 64 QAM transmission using 670 fs coherent Nyquist pulses. We newly constructed an optical gate to improve the signal-to-noise ratio (SNR) of the homodyne detection signal, a coherent spectral expansion technique, and an optical phase-locked loop (OPLL) circuit with a 0.6 deg. phase noise. We also constructed an active 70 fs timing stabilization circuit between the OTDM signal and Nyquist LO pulse to realize precise homodyne detection. With these new techniques, we successfully achieved a record speed of 15.3 Tbit/s in a single channel transmission over 150 km with a spectral efficiency of 8.3 bit/s/Hz.

Single-channel 10.2 Tbit/s (2.56 Tbaud) optical Nyquist pulse transmission over 300 km.

We describe a single-channel 10.2 Tbit/s online transmission using non-coherent ultrashort optical Nyquist pulses. A 10.2 Tbit/s signal was generated at a symbol rate of as fast as 2.56 Tbaud with a polarization-multiplexed DQPSK format. We developed a new ultrafast optical sampler for Nyquist OTDM demultiplexing with a nonlinear optical loop mirror, an RZ-CW conversion technique to improve the SNR, and an active stabilization technique providing stable long-term demultiplexing operation. With precise higher-order dispersion compensation up to fourth order, a 10.2 Tbit/s signal was transmitted over 300 km for the first time as a real-time demonstration with a spectral efficiency of 2.5 bit/s/Hz. We also report a 10.2 Tbit/s transmission over 225 km with a spectral efficiency of 3.7 bit/s/Hz, which we realized by reducing the roll-off factor to zero.

Single-channel 200 Gbit/s, 10 Gsymbol/s-1024 QAM injection-locked coherent transmission over 160 km with a pilot-assisted adaptive equalizer.

We demonstrate a 10 Gsymbol/s, 1024 quadrature amplitude modulation (QAM) 160 km coherent transmission with an injection locking technique. Our newly developed, pilot-assisted adaptive equalizer has greatly improved the precision of waveform distortion compensation, and this has enabled us to increase the symbol rate to 10 Gsymbol/s in a 1024 QAM transmission. Thus, we could realize a 200 Gbit/s, 1024 QAM transmission over 160 km with a potential spectral efficiency of 12.6 bit/s/Hz.

Single-channel 7.68 Tbit/s, 64 QAM coherent Nyquist pulse transmission over 150 km with a spectral efficiency of 9.7 bit/s/Hz.

We achieved a record capacity of 7.68 Tbit/s in a single-channel OTDM transmission with a 9.7 bit/s/Hz spectral efficiency, where a polarization-multiplexed 640 Gbaud, 64 QAM coherent Nyquist pulse has been transmitted over 150 km. In this scheme, a 1.39 ps optical Nyquist pulse with an OSNR of 53 dB at a 0.1 nm resolution was generated by combining a mode-locked laser and a highly nonlinear fiber and used at both the transmitter and receiver. Phase synchronization was achieved between these pulse sources with an advanced optical phase-locked loop based on the higher harmonics of the mode-locked laser mode. In addition, we suppressed a nonlinear phase rotation at an EDFA in the transmitter by broadening the pulse width with second-order dispersion and recompressed it to the original pulse width before a 150 km transmission link. We succeeded in a bit error rate below 2 x 10-2 for all tributaries.

Experimental and numerical comparison of probabilistically shaped 4096 QAM and a uniformly shaped 1024 QAM in all-Raman amplified 160 km transmission.

We describe an experimental and numerical comparison of a probabilistically shaped (PS) 4096 QAM signal and a uniformly shaped 1024 QAM signal. Both modulation formats have the same transmission rate and a spectral efficiency of 15.3 bit/s/Hz. In the computational simulation, we compared the generalized mutual information (GMI) of both modulation formats with bit-wise soft decision decoding and bit-wise hard decision decoding. For bit-wise hard decision decoding with an overhead of 7%, a shaping gain of 1.8 dB was attained. Then we successfully transmitted a single-channel PS-4096 QAM signal for the first time in an all-Raman amplified 160-km link, in which the transmission performance was improved compared with a uniformly shaped 1024 QAM with the same transmission rate. Transmissions with a high QAM multiplicity were achieved by using an optical phase-locked loop (OPLL) and a frequency stabilized fiber laser locked to an acetylene absorption line. Thanks to a shaping gain based on a bit-wise hard decision decoder, the 1.9-dB power margin, which agreed with the simulation result to within 0.1 dB, was increased after transmission.

Observation of guided acoustic-wave Brillouin scattering noise and its compensation in digital coherent optical fiber transmission.

We describe the first observation of guided acoustic-wave Brillouin scattering (GAWBS) phase noise in a digital coherent optical fiber transmission. GAWBS noise, which is a forward lightwave generated by thermally excited vibration modes in a cylindrical fiber structure, occurs coherently not only in a signal at a single carrier frequency, but also in modulated wide-band optical signals. Since the signal-to-GAWBS-noise ratio is independent of signal power, it has caused problems in various fields including quantum optics. We point out that GAWBS noise exists even in a digital coherent transmission system such as quadrature amplitude modulation (QAM) and degrades the transmission performance since the phase noise is inevitably included within the bandwidth of the transmitted data. We propose two analogue and one digital method to compensate for the GAWBS noise and demonstrate improved performance in a QAM digital coherent transmission.