Transmission performance impairments in 3-span transmission using S-band lumped Raman amplifiers were analyzed experimentally and numerically, and a design guideline in view of chromatic dispersion of lumped Raman amplifiers was derived through systematic simulations.

We demonstrate 86.5-Tbps (801.5 Gbps × 108 channels) wavelength division multiplexing (WDM) transmission using the L- and U-bands over a 10.8-THz bandwidth across 70.4 km of field-deployed dispersion-shifted fiber (DSF). The key enabling technology is the wavelength-band conversion using periodically poled lithium niobate (PPLN) waveguides, which extends the usable bandwidth into the U-band where higher-chromatic dispersion reduces Kerr nonlinear impairments. Although U-band operation faces increased fiber loss, which is slightly exacerbated by bending, mechanical stress, and splicing in the field environment, these penalties are mitigated by the inter-channel stimulated Raman scattering (ISRS) gain derived from co-propagating L-band channels. The experimental results confirm the feasibility of bandwidth extension to the U-band and high-data-rate transmission over legacy DSF infrastructure.

Quantum state preparation (QSP) is a fundamental task in quantum computation to prepare a quantum state for a given classical description of the quantum state. The classical description of an n-qubit quantum state may have exp(O(n)) parameters in general, which are inherently inefficient to deal with in the worst case; however, in many practical cases, we may be able to employ suitable data structures to represent such large-scale data in a compressed way, e.g., by using a free binary decision diagram (FBDD), a rooted directed acyclic graph with two terminal nodes to concisely represent a Boolean function. We here construct a quantum algorithm for QSP when the classical description of a quantum state is given by an FBDD with weighted edges, and analyze the space, and time complexity of QSP in this setting. We provide a nontrivial example of an n-qubit state that can be represented by a weighted FBDD with N=O(poly(n)) nodes rather than exp(O(n)). We show that any quantum state represented by the weighted FBDD with N nodes can be prepared by an O(N)-sized quantum circuit using N ancillary qubits, exponentially improving the required circuit size for QSP compared to other BDD-based QSPs. We also provide another example of an n-qubit state that can be represented by a weighted FBDD with N=O(n^2) nodes, and O(n^2) ancillary qubits, but cannot be prepared efficiently by a QSP based on the amplitude amplification. These results provide techniques to employ FBDDs as a tool for broadening the possibility of efficient QSP.

We evaluate the optical and transmission characteristics of a step-index four-core fiber with a standard cladding diameter in the U-band. Transmission over 57 km is demonstrated by applying a bidirectional architecture to suppress the crosstalk.

We demonstrate a 38.4-Tbps (60 ch. × 640 Gbps) wavelength-division multiplexing (WDM) transmission across 5 × 80-km G.654.E single-mode fibers over 6 THz within L- and U-bands. The U-band (1625–1675 nm) is promising as a next transmission band for multiband networks because of its low transmission loss compared with E- and O-bands, but there are few demonstrations of coherent WDM transmission with the U-band. One reason is that promising optical components, especially for optical transceivers, are underdeveloped for the U-band. An optical parametric amplifier (OPA) using a periodically poled LiNbO3 (PPLN) waveguide has wide-gain bandwidth and wavelength conversion function, which allows the use of commercially available optical components for new bands. We achieve L- and U-band digital coherent WDM transmission within 1597.2–1649.9 nm (181.7–187.7 THz) using PPLN-based optical parametric inline amplification and wavelength-band conversion.

We present SRS-assisted reach extension of U-band WDM transmission in deployed fiber-optic cable. It is verified that U-band channels benefit from the reduction of span loss in 90-km transmission co-propagating with S+C+L-band WDM channels.

Allowing the accommodation of different types of optical signals across optical networks in single fiber core to relax constraints in the optical fiber infrastructure is assumed to eliminate bottlenecks of optical network in some cases. As an example of use-case for the coexistence of signals beyond the area of optical networks, we investigate the feasibility of a transmission of dense wavelength-division multiplexed (DWDM) signal typically used for long-haul transmission over a fiber that carries an optical signal for short-reach. We prepared a 176 channel DWDM signal across S+C+L-band to identify the impact of the interaction over a wider wavelength range and transmitted it through a 30-km field-deployed fiber propagating a 400GbE signal separated from the wavelength band occupied by the DWDM signal. Wavelength converters were used to evaluate S-band transmission channels by C-band transceiver. We demonstrate fiber sharing in long-haul and short-reach networks by evaluating signal quality deviation due to coexistence using 400-Gb/s real-time test channels in S-, C-, and L-band DWDM signals as well as the 400GbE signal.

We experimentally verify wideband WDM transmission modeling in over 17-THz S+C+L+U quadrable-band transmission using PPLN-based wavelength converters. We confirmed within 3.3-dB errors between modeling after 80-km SSMF transmission of DP-16QAM and DP-QPSK signal.

We demonstrate a 5×80-km WDM transmission over 6 THz within 1597.19–1649.93 nm. PPLN-based optical parametric amplifiers provide sufficient gain for inline amplification of 60-channel 640-Gbps/λ signals allocated in L- and U-bands.

We propose a U-band transmission added to the C+L-band that can mitigate large loss at long wavelength by inter-channel SRS. The benefit is demonstrated in 80-km SSMF transmission of real-time 200-Gb/s DP-QPSK signal.

One of cost-effective ways to increase the transmission capacity of current standard wavelength division multiplexing (WDM) transmission systems is to use a wavelength band other than the C-band to transmit in multi-band. We proposed the concept of multi-band system using wavelength conversion, which can simultaneously process signals over a wide wavelength range. All-optical wavelength conversion could be used to convert C-band WDM signals into other bands in a highly nonlinear fiber (HNLF) by four-wave mixing and allow to simultaneously transmit multiple WDM signals including other than the C-band, with only C-band transceivers. Wavelength conversion has been reported for various nonlinear waveguide materials other than HNLF. In such nonlinear materials, we noticed the possibility of wideband transmission by dispersion-tailored silicon-on-insulator (SOI) waveguides. Based on the CMOS process has high accuracy, it is expected that the chromatic dispersion fluctuation could be reduced in mass production. As a first step in the investigation of the broadness of wavelength conversion using SOI-based waveguides, we designed and fabricated dispersion-tailored 12 strip waveguides provided with an edge coupler at both ends. Each of the 12 waveguides having different widths and lengths and is connected to fibers via lensed fibers or by lenses. In order to characterize each waveguide, the pump-probe experimental setup was constructed using a tunable light source as pump and an unmodulated 96-ch C-band WDM test signal. Using this setup, we evaluate insertion loss, input power dependence, conversion bandwidth and conversion efficiency. We confirmed C-band test signal was converted to the S-band and the L-band using the same silicon waveguide with 3 dB conversion bandwidth over 100-nm. Furthermore, an increased design tolerance of at least 90 nm was confirmed for C-to-S conversion by shortening the waveguide length. It is confirmed that the wavelength converters using the nonlinear waveguide has sufficiently wide conversion bandwidth to enhance the multi-band WDM transmission system.

Enabled by an autonomous calibration mechanism, crosstalk-free (−38.5 dB) fabrication-tolerant 32-ch DWDM demultiplexer on a standard Si PIC platform is demonstrated for the first time. On this platform, due to its nano-sized waveguide core dimensions, extremely precise fabrication control of waveguides has been required so far to suppress the crosstalk of demultiplexers for large-channel-count DWDM systems. This requirement made this platform impractical for such systems. To exclude this requirement, we have proposed a calibration mechanism which can be fully integrated into an assembly composed of an electric IC (EIC) and a standard Si PIC. The Si PIC has a structure of cascaded asymmetric Mach-Zehnder (AMZ) triplet consisting of AMZ interferometers designed to function as a demultiplexer. This structure enables monitoring the errors in the optical lengths of waveguides composing itself. Based on the monitored values, the controller implemented on the EIC determines the driving conditions of waveguide heaters to eliminate the errors. This feature excludes the necessity to strictly control the optical lengths in the fabrication process, making it possible to realize a crosstalk-free 32-ch DWDM demultiplexer on a standard Si PIC platform. Compatible with the vast component libraries of standard Si PIC platform, this device provides a path to ultrahigh-capacity integrated DWDM transceivers.

In order to keep up with expected growth in data traffic, using multiple bands beyond the C band is an appealing solution as it can partly reuse deployed optical fibers. One way of handling multi-band data generation and reception is by using all-optical wavelength converters (AOWCs) to translate to or from the C band, where commercial equipment is easily available. In this work, we therefore designed and realized an AOWC targeting C-to-S band conversion. To respect the requirements of commercial applications, we aimed for a low-complexity high-bandwidth implementation with reasonably low power consumption, tolerance for typical process variations and potential for further integration. Thus we implemented the AOWC as a strip waveguide in a Silicon-on-insulator (SOI) technology. An optimization of the conversion bandwidth was conducted during design and initial characterizations confirmed a conversion efficiency of −32.8 dB and a high bandwidth of about 35 nm with grating couplers and likely beyond 50 nm for edge couplers. Using the fabricated converters, we were able to demonstrate a marginal 0.3 dB optical signal-to-noise ratio (OSNR) penalty for a back-to-back (b2b) transmission of a single-channel single-polarization 32 GBd quadrature-phase-shift keying (QPSK) signal converted from C to S band. Additionally, this converted signal was successfully transmitted over 100 km of standard single-mode fiber (SSMF). Finally, crosstalk issues arising in multi-channel conversion were investigated.

Using wavelength conversion of our fabricated SOI strip waveguide, we compared experimentally the polarization-insensitive configuration toward S-band real-time transmission. It is found that parallel configuration is 3dB superior in in-out conversion efficiency to loop configuration.

Multi -band WDM transmission beyond the C+L-band is a promising technology for achieving larger capacity transmission by a limited number of installed fibers. In addition to the C- and L -band, we can expect to use the S -band as the next band. Although the development of optical components for new bands, particularly transceivers, entails resource dispersion, which is one of the barriers to the realization of multi -band systems, wavelength conversion by transparent all -optical signal processing enables new wavelength band transmission using existing components. Therefore, we proposed a transmission system including a new wavelength band such as the S -band and made it possible to use a transceiver for the existing band by performing the whole -band wavelength conversion without using a transceiver for the new band. As a preliminary verification to demonstrate multi -band WDM transmission including S -band, we investigated the application of a novel wavelength converter between C -band and S -band, which consists of periodically poled lithium niobate waveguide, to the proposed system. We first characterized the conversion efficiency and noise figure of the wavelength converter and estimated the transmission performance of the system through the wavelength converter. Using the evaluated wavelength converters and test signals of 64 channels arranged in the C -band at 75-GHz intervals, we constructed an experimental setup for S -band transmission through an 80 -km standard single -mode fiber. We then demonstrated errorfree transmission of real-time 400-Gb/s DP-16QAM signals after forward error correction decoding. From the experimental results, it was clarified that the wavelength converter which realizes the uniform lossless conversion covering the whole C -band effectively achieves the S -band WDM transmission, and it was verified that the capacity improvement of the multi -band WDM system including the S -band can be expected by applying it in combination with the C+L-band WDM system.

We experimentally present a low-complexity dispersion-engineered all-optical wavelengthconverter using a photonic integrated-circuit based on SOI waveguide. We achieve a single-sided conversion bandwidth of ~35 nm from C- to S-band, and successfully transmit a converted 1-channel 32-GBd single-polarization QPSK S-band data over a 100-km SSMF link.

In view of application to wideband wavelength conversion, an SOI waveguide was fabricated and characterized. Conversion of C-band WDM test signals into S- and L- bands in a single waveguide is demonstrated.

We evaluated PPLN-based wavelength converters to achieve S-band transmission using commercial transceivers. The real-time 80-km SSMF transmission of 400-Gb/s signals in S-band was demonstrated by the conversion using them.

Enabled by a fully integrated autonomous calibration mechanism, crosstalk-free 32-ch WDM demultiplexer on standard Si PIC platform is demonstrated for the first time. Compatible with the vast component libraries of standard Si PIC platform, this device provides a path to ultrahigh-capacity integrated DWDM transceivers. © 2022 The Author(s)

We demonstrate fully automatic suppression of crosstalk, inevitable in WDM demultiplexers on Si nanowire PIC. This is realized with a low-cost CMOS ASIC dedicatedly designed for low-power control of our proposed CAT demultiplexer. It is shown to have zero OSNR penalty even under continuous control required to cancel dynamic environmental change.